photocatalytic decolorization of bismarck brown r

Ministry of Higher Education and Scientific Research

Babylon University – College of Science

Chemistry Department

Photocatalytic Decolorization

of

Bismarck Brown R

A thesis submitted to the council of the College of

Science, University of Babylon as a partial

fulfillment of the requirements for Master degree in

Chemistry

By Mohammed Obies Hamza AL Nafie

Supervisored by

Prof. Dr. Falah Hassan Hussein Ass. Prof. Dr. Abbas Abid Ali Drea

May 2011 Jamadee Alaulla 1432

4

بسم اهلل اؾرمحن اؾرحوم

اهلل ـُور اؾسمواِت واألرِض ؿثُل ـورِه ؽمشكوِة ػوها ؿصباٌح

يف زجاجِة اؾزجاجُة ؽأـها ؽوؽُب درُي يوؼُد ؿن ‘املصباح

شجرِة ؿبارؽِة زيتوـِة ال شرؼوِة وال غربوِة يكاُد زيتها يضيء وؾو

مل متسسُه ـاٌر ـوٌر على ـوِر يهدي اهلل ؾنورِه ؿن يشاُء ويضرُب

اهلل األؿثاَل ؾلنِاس واهلل بكِل شيِء علوٌم

يمـصدق اهلل اؾعظ

35

5

Abstract

This research consists of two parts. In the first part, photocatalytic

decolorization of an aqueous Bismarck brown R [(4-[5-C2, 4-diamino-5-

methylphenyl) diazenyl-2-methylphenyl] diazenyl-6-methlbenzene 1,3-

diamine dihydrochloride] solution in a suspension of different types of

catalyst including ZnO, TiO2 (Degussa P25), TiO2 (Hombikat UV100),

TiO2 (Millennium PC105), and TiO2 (Koronose 2073) was carried out by

using UV(A) as light source. The disappearance of original colored dye

concentration with irradiation time was monitored spectrophotometrically

by control with unexposed controls. The effect of various parameters,

such as mass of catalyst, type of catalyst, initial dye concentration, pH of

aqueous solution, light intensity and temperature was studied.

The results indicate that this photoreaction is a pseudo first order

reaction according to the Langmuir -Hinshelwood relationship.

The results of the study show that decolorization efficiency

increases with the increase of the catalyst concentration up to 3.75 g L-1

and 1.75g L-1

for ZnO and TiO2 respectively. If it is above that, the value

of the decolorization efficiency decreases. The results also show that the

decolorization efficiency is inversely directed with the initial dye

concentration. The increase of the pH of solution leads to increase of the

decolorization of Bismarck brown R until the zero point charge of

catalyst is achieved. Then, the increase in the pH of solution leads to the

decrease of dye decolorization. It has been observed that the increase of

light intensity leads to the increase of decolorization rate of dye. The

change in temperature was the factor that has less effect on rate of

photocatalytic decolorization. The decolorization of Bismarck brown R

increases slightly with temperature increase. The activation energy has

been calculated according to Arrhenius plot, and has been found equal to

24 ±1 kJ.mol-1

for ZnO and 14, 16, 21, 22 ±1 kJ.mol-1

for TiO2 (Degussa

6

P25), TiO2 (Hombikat UV100), TiO2 (Millennium PC105), and TiO2

(Koronose 2073) respectively.

The results of the total organic carbon (TOC) analysis indicate that

the rate of decolorization of dye is faster than the total mineralization.

Decolorization and mineralization of Bismarck brown R in the absence of

light and/or catalyst were performed to demonstrate that the presence of

light and catalyst is essential for the decolorization of this dye. The

results show that the activity of different types of catalyst used in this

study is of the sequence:

ZnO > TiO2 (Degussa P25) > TiO2 (Hombikat UV100) > TiO2

(Millennium PC105) > TiO2 (Koronose 2073).

In the second part of the thesis, the decolorization of Bismarck

brown R is studied theoretically. This part deals with the reaction of

Bismarck brown R in vacuum with reactive species in different

hypothetical ways. The reactive species such as hydroxyl radical and

superoxide anion have been produced from the heterogeneous

photocatalytic reaction.

Quantum methods such as semiempirical and ab initio calculation

that's loaded to hyperchem package program 7.5.

Chemical reactivity of hydroxyl radical and Bismarck brown R has

been calculated by 3-61G**

of ab initio method. The atom's charge, bond

length, electrostatic potential and surface potential energy have been

calculated to estimate the reactive sites in Bismarck brown R giving the

initial cleavage step.

The transition state has been studied by attaching the reactive

species in the reactive site in Bismarck brown R to give the first initial

step of photoreaction through activation energy, zero point energy, heat

of formation and imaginary frequency. They have been calculated by

7

PM3 method. The transition state of Bismarck brown R with hydroxyl

radical and catalyst has given the best probable of first cleavage step.

The activation energy that splits the hydrogen peroxide has give two

hydroxyl radicals equal to 189.610 kJ.mol-1

. The following bonds in

Bismarck brown R C7—N8, N8—N9, N9—C10, C12—N16, N16—N17,

and N17—C18 are the most probable ones to break down.

8

CHAPTER ONE

INTRODUCTION

9

INTRODUCTION

1-1 General Introduction

In 1972, Fujishima and Honda discovered that water could be split

into hydrogen and oxygen on the surface of TiO2 as electrode under UV

irradiation and in the presence of an anodic bias(1)

. The photochemistry

and photophysics process of semiconductors, especially TiO2, has

attracted much attention. Developing metal oxide semiconductor used as

photocatalyst for air and water purification needs great efforts(2)

.

Photodegradation of organic and inorganic pollutants on semiconductors

is currently the interest of research.

Numerous studies conducted so far on the treatment of colored

wastewater due to their low biodegradability and presence of toxic

materials. However, because of the complexity and variety of dyestuffs

employed in the dying processes, it has become rather difficult to find

one procedure to treat all types of dyes(3)

.

Particularly, biochemical oxidation suffers when treating the most

dyestuffs since commercially dyes are designed to resist aerobic

microbial degradation conversion to toxic or carcinogenic compound(4)

.

Physical methods such as reverse osmosis and adsorption on activated

charcoal are nondestructive, but they can transfer the pollutant to other

media, and, thus, cause secondary pollution(5)

.

More active technology depending on advanced oxidation process

(AOP) has studied extensively the treatment of the color for the broad

range of organic dyes which can be oxidized quickly and non-

selectively(6). As one of the novel AOP's, is the heterogeneous

photocatalytic oxidation process.

10

1-2 Heterogeneous Photocatalysis

The heterogeneous photocatalytic oxidation process using solar

light was developed in the 1970s for a special interest(7)

.

Band structure of photocatalyst particle is composed of low energy

valance band, filled with electrons, and high energy conduction band,

empty from electrons at zero Kelvin(8)

. Under illumination with photons,

if the energy is equal or greater than the band gap energy of

semiconductor, excitation will occur. The excitation requires UV-light (λ

< 390nm) to form reactive electron-hole pairs with an oxidation potential

of 2.9 V with normal hydrogen electrode (NHE). This potential is enough

to dissociate the molecule water adsorbed on the surface of

semiconductor to form hydroxyl radical(9-10)

. The hydroxyl radical is an

extremely and non-selective oxidant (Eo=3.06V) which leads to the

partial or complete mineralization of several organic compounds(11)

.

The photogenerated holes and electrons diffuse on the surface

where they promote the desorption of water from semiconductor surface

leaving behind free coordination positions for oxygen(12-13)

.

Infrared spectra (IR) prove the presence of hydroxyl groups and

chemisorbed water on TiO2 surfaces(14)

. The next step is the reaction of a

hole with a surface hydroxyl group or an adsorbed water molecule to

form reactive hydroxyl radicals. Subsequently, hydroperoxy radicals,

HO•-, may be formed

(15).

Heterogeneous photocatalysis involves irradiation using

semiconductor such as titanium dioxide TiO2, strontium titanium dioxide

SrTiO2, iron oxide Fe2O3, cadmium sulfide CdS, zinc sulfide ZnS, and

zinc oxide ZnO as a catalyst. This is due to specific characteristics of the

semiconductor which includes a favorable electronic structure, light

absorption properties, charge transport characteristic and excited state

lifetime(16)

.

11

The initial steps are given by following simplified equations:

CBVB ehhTiO 2 1-1

OHOHhVB 1-2

HOHOHhVB 2 1-3

22 OOeCB 1-4

OHCOteIntermediaROH 22 1-5

The radicals formed on the surface have enough potential to

oxidize many organic compounds adsorbed on the surface of

semiconductor and proposed that direct oxidation of adsorbed molecules

is also possible(17)

.

The disadvantage of advance oxidation processes is the loss of hole

electron pairs due to recombination, which occurs within a few

nanoseconds and as a result, the input energy is then dissipated as heat(18)

.

Figure 1-1 shows a reaction scheme for the TiO2 photocatalytic oxidation

of organic pollutants in the presence of oxygen(19)

.

Figure1-1: General mechanism of the photocatalysis on TiO2

particle(19)

.

12

1-3 Semiconductor

Semiconductors that have an electrical conductivity between

conductors and insulator a substance usually a solid chemical element or

compound. The electrical conductivity of semiconductor is generally in

the range 103 - 10

-8 S cm

-1. The conductivity of semiconductors depends

on the current, or voltage applied to the semiconductor or on intensity of

incident irradiation or temperature(20)

.

The gap between the valance band and the conduction band in

semiconductors is smaller than that of insulators. The conductivity

increases with the temperature increase because when temperature

increases, more electrons are thermally excited and jump the band gap

between the valance band and conduction band. The insulators are a

substance with very low electrical conductivity and the band gap is huge

between valance and conduction. Table 1-1 summarizes the classification

of solids according to the energy gap(21)

.

Table 1-1: Classification of solids according to their energy gap Eg

and carrier density (n) at room temperature.

Type of solid Eg (eV) n (cm-3

)

Metal No energy gap 1022

Semimetal Eg ≤ 0 1017

-1021

Semiconductor 0 > Eg > 4 > 1017

Insulator Eg ≥ 4 >> 1

13

There are two types of semiconductors, n-type semiconductor and

p-type semiconductor. The n-type semiconductor carries the current in the

form of negatively charge (electrons) similar to the conduction of current

in wire. The p-type semiconductor carries the current as electron

deficiencies (holes). A hole has an equal positive electric charge and

opposite to the charge on an electron. In semiconductor material flow of

hole occurs in opposite direction to the flow of electron(22)

. Figure 1-2

consists of two diagrams of the n-type and p-type semiconductor

according to the energy level(23)

.

Figure 1-2: Energy level diagram for n-type and p-type

semiconductor(23)

.

Fermi level which is defined as the highest occupied molecular

orbital in the valance band at 0.0K or can be defined as the energy at

which the probability of an energy level being occupied by an electron is

exactly 1/2. In semiconductor the Fermi level is located in the band gap.

In case of an intrinsic semiconductor, the Fermi level is approximately

the way between conduction band energy (EC) and valance band energy

14

(EV). For n-type doping the Fermi level shifts toward the conduction band

edge, while p-type doping shifts toward the valance band edge(24)

.

Several semiconductors are used for photocatalytic degradation

reaction such as TiO2, ZnO, WO3, Fe2O3, CdS and MoS2(25)

. Metal sulfide

is not stable enough in aqueous media due to photoanodic corrosion and

they are also toxic(26)

. Iron oxide undergoes photocathodic corrosion(27)

.

Zinc oxide is unstable in water and form Zn(OH)2 on the particle

surface(28)

. Table 1-2 summarizes the most common semiconductor used

in photocatalysis, their band gap and respective wavelength sensitivity(29)

.

Table 1-2: Energy band gap and wavelength sensitivity of different

semiconductors.

Semiconductor Eg (eV) λ (nm)

CdS 2.4 517

Fe2O3 2.3 539

MoS2 1.75 709

SrTiO3 3.2 388

TiO2 (rutile) 3.0 413

TiO2 (anatase) 3.2 388

WO3 2.8 443

ZnO 3.2 388

ZnS 3.6 344

A doped semiconductor has a vast difference in the concentration of

the two types of charge carriers. When the semiconductor is excited,

holes and electron are generated by light absorption. The sensitivity of a

semiconductor to the photon energy is indicated by the band gap energy.

15

When the wavelength incident light decreases below maximum

wavelength of band gap (λbg), the photo effect switches on. The

recombination is an important effect on the semiconductor. Direct

recombination may occur when the electron returns from the conduction

band edge to the hole at the valance band edge. Indirect recombination

occurs with an intermediate energy level. This mode of recombination

can be particularly effective because the intimidated energy level can

capture the hole and electron(30)

.

When the electron – hole pair is generated by the light absorption in

the depletion layer, the region's electrical filed directly separates the

created charge carriers pair. The electron moves towards the bulk of the

crystal and the hole moves towards the surface(31)

. The hole has strong

oxidizing power equivalent to the potential of valance band edge and

capable to oxidize a reduced molecule which has formal potential less

positive than the hole. In the wider band gap material e.g TiO2 the

electrolyte H2O is oxidizing by this catalyst to give hydrogen molecule

and oxygen atom. The electron in the conduction band flows via an

external circuit to another electrode where reduction takes place(32)

.

1-4 Properties of Zinc Oxide

1-4-1 General View

Zinc oxide is wide band gap semiconductor material with direct

band gap of 3.37eV at 300K and long exciton binding energy

(60meV)(33)

. Zinc oxide would be an insulator rather than a

semiconductor at room temperature. The concentration of free electrons

in the conduction band would in this case amount to only 4 m-3

compared

to 1014

-1025

m-3

in semiconductors and up to 8 x 1028

m-3

in metals(34)

.

16

Zinc oxide powder usually has n-type conductivity and increase n-

type conductivity by doping with Al, Ga or In. Among the p-type

dopants, nitrogen appears to be a promising acceptor for ZnO(35)

.

Much of the interest in ZnO is for its use in ultraviolet light

emitting and detecting devices as window material, transparent electrode

and active layer in different type of solar cell, UV emitters and UV

sensor. In addition zinc oxide has several properties such as low cost,

ready available, and high chemical stability, considerable stability,

decomposition the ZnO to zinc vapor and oxygen occur at around

2248K(36)

.

1-4-2 Structure and Crystal Morphology

Zinc oxide crystallizes in three forms. They are hexagonal

wurtizite, cubic zincblende and cubic rock salt. Each anion is surrounded

by four cations at the corners of tetrahedron. This tetrahedral coordination

is typical of sp3 covalent bonding, but these materials also have large

ionic character. The crystal structures of ZnO are shown in figure 1-3(37)

.

In hexagonal wurtzite structure, the crystal can be described as alternating

planes that are composed of tetrahedral coordinate O2-

and Zn2+

ion and

stacked along c-axis. The zincblende structure can be stabilized only by

growth on cubic substrates and the cubic rock salt may be obtained at

relatively high pressure(38-39)

.

17

Figure 1-3: ZnO crystals structure, the shaded gray and black

spheres denote Zn and O atoms, respectively(37)

.

1-5 Properties of Titanium Dioxide

1-5-1 General View

Titanium dioxide also known as titanium(ΙV) oxide, is the naturally

occurring by the oxide of titanium. When used as pigment it is called

titanium whit. Titanium dioxide was discovered in 1791 in England(40)

.

Titanium dioxide was first produced commercially in 1923 and

approximately counted 70% of the total volume of pigment production

while a small amount of titanium dioxide was used for non-pigment

purpose(41)

. In 2004, world-wide production of titanium dioxide was 4.4

million tones(42)

.

Since TiO2 is an inexpensive, stable, and non-toxic semiconductor

with a large band gap and strong oxidizing power, it can be activated

under UV light at wavelengths shorter than 388 nm. The limitation of

TiO2 is that it utilizes only about 4-6% of the solar energy reaching the

earth‘s surface in the UV region(43)

.

Rock salt (B1) Zinc blende (B3) Wurtzite (B4)

18

Titanium dioxide is obtained in the three crystalline forms: rutile,

anatase and brookite having three different density; 4.26 g.cm-3

, 3.84

g.cm-3

and 4.17 g.cm-3

respectively(44)

. The rutile phase is more

thermodynamically stable than anatase phase at low and high pH. The

anatase phase transfers to a rutile phase when the temperature gats above

873K(45)

.

To proceed the photocatalytic reactions, it is necessary to have light

at a sufficient intensity to possess energy that exceeds the TiO2 band gap

energy (Eg). For the two crystal structures of TiO2, Eg (anatase) = 3.2 eV,

and Eg (rutile) = 3.02 eV, the absorption of wavelength light 380 and

410 nm, respectively(46)

.

Among these crystal structures rutile and anatase are commonly

used in photocatalysis whereas brookite is not photoactive(47)

.

1-5-2 Structure and Crystal Morphology

The structure of rutile and anatase can be described in terms of

chains of TiO6 octahedra as illustrated in figure 1-4(48)

. Rutile and anatase

have both similar tetragonal crystal structure. The two crystal structures

differ by the distortion of each octahedron and the assembly pattern of the

octahedral chains. Each Ti4+

ion is surrounded by an octahedron of six O2-

ions. The octahedron in rutile is not regular because it shows a slight

orthorhombic distortion. The octahedron in anatase is significantly

distorted, so its symmetry is lower than orthorhombic(49)

.

19

Figure 1-4: Structure of anatase and rutile TiO2(48)

.

The Ti—Ti distance is 3.79 and 3.04 Aº in anatase and 3.57 and

2.96A° in rutile, whereas the Ti—O distance is shorter than in rutile (

they are 1.934 and 1.980Aº in anatase and 1.949 and 1.980A° in

rutile)(50)

.

The difference in lattice structure of anatase and rutile causes

different density and electronic band structure leading to different band

gaps. The absorption corresponds to 388 and 413nm wavelength for the

anatase and rutile respectively. The photocatalytic activity of two forms

of TiO2 anatase and rutile are different. Anatase is more photoactive than

rutile(51)

.

Studies indicate that the anatase form provides the highest OH·

formation rate(52)

. This is believed to be the band gap of anatase which is

wider than rutile about 0.2eV and higher degree of surface hydroxylation

in anatase(53)

. Other studies show that an optimum composition of

anatase-rutile gives better results in photodegradation of organic

pollutant(54)

.

There are many suppliers of titanium dioxide including

commercially available forms Degussa P25 and Hombikat UV100. There

20

are also manufacturing methods of titanium dioxide such as sol-gel

process(55)

and heat treatment(56)

.

The light required to activate the photocatalyst is near ultraviolet

radiation UV(A) making the use of solar light possible(57)

. TiO2 surface is

full of hydroxylated in water and these hydroxyl groups are the

precursors of the OH· radicals

(58).

1-6 Adsorption

Adsorption is an important factor which effects photocatalytic

oxidation reaction. According to Langmuir Hinshelwood relationship, the

rate of reaction is directly proportional with initial concentration of

reactant(59)

.

Adsorption is the adhesion of molecule of gas, liquid, or dissolved

solid to a surface. These processes produce a film of the adsorbate( the

molecule or atoms being accumulated) on the surface of the adsorbent.

The adsorption processes are generally classified into physisorption (

characteristic of weak van der Waals forces ) or chemisorption (

characteristic of covalent bonding )(60)

.

The chemisorption properties on catalyst surface have been

extensively studied(61)

. A Particular interest has been given to the

influence of defect sites on the chemisorption behavior of the surface.

These defect sites have also been found as the active site for

photocatalytic processes(62)

.

1-6-1 Water Adsorption

Water split on semiconductor surface into hydrogen and oxygen

takes place when interaction between them occurs depending on what

form of water (molecular or dissociated) exists on the surface and what

21

parameters are significant in controlling the adsorption behavior.

Hydroxyl group was detected on surface after H2O adsorption at 300K(63)

.

The amount of dissociative water at 300K as one monolayer and

coverage of hydroxyl group has been found independent on the coverage

of surface oxygen vacancy defect sites(64)

.

The adsorbed H2O molecule reacts with a bridging oxygen atom to

form two hydroxyl groups(65)

:

OHOOH L 22 1-6

Where O(L) is a lattice oxygen atom and OH hydroxyl group,

respectively. Oxygen vacancy on the TiO2 surface is nature strongly

adsorbed water.

It has also been found that the molecular water adsorbed below

160K and hydroxyl group produced by water dissociation when heating

the phyisorbed layer approaches to above 200K(66)

.

The H2O molecule or OH- group adsorbed on the surface catalyst

reacts with the holes in the valance band forming illumination to give

hydroxyl radical, but the electrons react with lattice oxygen and not with

adsorbed oxygen(67)

.

HOHTiOOHTiO adsadsh .2.2)(2 1-7

OHTiOOHTiO adsh 2.)(2 1-8

The existence of water vapor on the catalyst surface inhibits the

reaction rate because the presence of water vapor competes with

pollutants for adsorption sites on the photocatalyst, thus reducing the

pollutant removal rate. This is called ‗‗competitive adsorption‘‘ between

water vapor and pollutant(68)

.

22

1-6-2 Oxygen Adsorption

The presence of oxygen is essential for the photoreaction to occur.

The pollutant decomposition rate increases if oxygen concentration

increases because it acts as scavenger to electrons in conduction band of

semiconductor although the competitive adsorption effect between

oxygen and pollutants seems not strong(69)

. Oxygen is first chemisorbed

on electron rich sites and dissociated into oxygen atom(70)

.

Molecular oxygen after adsorption on the surface of the

photocatalyst can instantly trap the interfacial electron of the

photocatalyst so as to prevent the hole-electron recombination by the

presence of residual oxygen in the reaction system(71)

.

Several different surface oxygen species were adsorbed in active

site of surface catalyst such as weakly bound O2-

, O- and O2

·-.These

species were detected by using electronic spin resonance(ESR)

spectroscopy(72-73)

.

When adsorbed oxygen accepts a single electron from conduction

band of catalyst, it will be converted into the superoxide anion O2·-(74)

.

.)(2)(2 adsgas OO 1-9

.)(2.)(2 adsads OeO 1-10

.)().(.)(2 adsadsads OOO 1-11

Superoxide anion radical O2·- is one of the strongest reactive species

among the free radicals. Superoxide anion changes to other reactive

oxygen species and free radicals such as hydrogen peroxide H2O2 and

hydroxyl radical OH·(75)

.

22.)(2 HOOHOHO ads 1-12

22222 OOHHO 1-13

23

The two superoxide anions reduce the two hydrogen cations to form H2O2

and O2 as follows:

22222 2 OHOHOO 1-14

The proposed mechanism for the production OH· is the reduction of

H2O2 by O2·- is referred to by Haber Weiss reaction

(76).

OHOHOOOH 2222 1-15

The rate constant for the direct interaction of H2O2 and O2·- is low

compared to competing like the spontaneous dismutation of O2·-(77)

.

The photo holes are trapped at the surface absorbed group (organic

molecule) and electrons are trapped by molecular oxygen as follows:

HRRHh 1-16

.)(2.)(2 adsads OOe 1-17

The oxygen anion can form more free organic molecule or

hydrocarbon radicals(78)

:

OHRRHO 1-18

Anpo et al.(79)

studied the influence of water and oxygen on the

photocatalytic activity of TiO2. They found that the adsorption of water

on the TiO2 surface caused decrease in the upward band bending as

shown in figure 1-5(80)

. This leads to an increase in the efficiency of

recombination of photogenerated electron and hole. Which happens

24

because the barrier height and width are smaller for return of surface

trapped electron into bulk conduction band region. On the other hand,

addition of O2 leads to an increase in the upward band bending and,

therefore, suppresses the electron-hole recombination process which leads

to more efficient photoactivity. As a result, the adsorbed water can be

regarded as an effective electron-hole recombination center while the

adsorbed oxygen can be considered as an effective electron scavenger to

prevent recombination process.

Figure 1-5: Schematic description of the surface band bending

changes: Effect of H2O and O2 adsorption(80)

.

1-7 Dyes

Dyes are organic molecules that selectively absorb wavelength of

light within the visible range of the electromagnetic spectrum (400-

800nm). Dyes contain chromophores, delocalized electron systems with

conjugated double bonds, and auxochromes, electron-donating

substituent's that cause or intensify the color of the chromophore by

altering the overall energy of the electron system. Chromophores are

Usually CC , NC , NN and 2NO . Auxochromes are NH2,

COOH, SO3H and OH group. Large amounts of dyes (about 50% of the

worldwide dye production) are widely used in different types of

industries, such as textile dye, food, cosmetic, paper printing, and

pharmaceutical. The textile industry is the largest consumer of dyes(81-82)

.

25

Azo dyes constitute the largest and the most important class of

commercial dyes, forming about 60-70% of all dye and pigment. These

compounds are characterized by aromatic linkage together with azo group

( ). Azo dyes can be divided into monoazo, diazo, and triazo

classes according to the presence of one or more azo bonds (–N=N–) and

are found in various categories such as acid, basic, direct, disperse, azoic

and pigments(83)

. Azo dyes have the following basic structure:

Figure 1-6: General structure of azo compounds.

As with any double bond, the planner bond shows

geometrical isomerism:

Trans isomerism Cis isomerism

Figure 1-7: Trans and cis isomers of azo compounds.

This change from trans to cis isomerism can be effected by exposure to

UV radiation (84)

.

It seems that the name of Bismarck brown R dyes is derived from

the name of the person who prepared it ( Bismarck ) followed by the

color of the dye (brown) . Bismarck brown was listed in the Dictionary of

26

the Coal Tar Colors edited in London at 1896 by Hurst(85)

. In 1907 a team

from the George Washington University studied the effect of coloring

matters on some of the digestive enzymes and they observed that

Bismarck brown R diminished the enzymic activity of fibrin and

casein(86)

. The market report conscribed in 1920 classified Bismarck

brown to R and Y types. However in 1921 the classification was changed

to R and G(87-88)

.

Bismarck brown R is an azo dye which has the molecular formula

C21H24N8.2HCl and the molar mass 461.39 g mol-1

. The IUPAC name of

the Bismarck brown R is 4-[5-(2,4-Diamino-5-methylphenyl) diazenyl-2-

methylphenyl]diazenyl-6-methylbenzol-1,3-diamin. It is a dark brown

solid which is suitable for any fiber. Its solubility in water is at 25oC 11g

L-1

and in ethanol is 9.8g L-1

. Bismarck brown dyes are used by fishermen

to color bait and recent epidemiological evidence has suggested that this

may explain why those fishermen are at an increased risk of urothelial

cancer. In recent years Bismark brown dyes have been used as

chrysoidine substitutes(89)

. They are available in shades with deep color

applicable to dye cotton, paper, silk, weed, bamboo, straw and leather(90)

.

Bismarck brown dyes have two types; Bismarck brown R and

Bismarck brown G described in the following structure(89)

:

Bismarck brown G Bismarck brown R

Figure 1-8: Types of Bismarck brown compounds.

27

The incomplete fixation of azo dyes to fabrics contaminates the

effluents of wastewater. Azo dyes affect photosynthetic activity in aquatic

systems by reducing light penetration(91-92)

. Moreover, the reduction of

aromatic azo compounds gives aromatic amines. Aromatic amines are

carcinogenic (cancer causing) agent to human and toxic(93-94)

.

1-8 Phocatalytic Degradation of Azo Dye

Azo dyes are resistant to aerobic bacterial degradation and

anaerobic condition. They produce potentially carcinogenic aromatic

amines(95-96)

.

The semiconductor surface causing the degradation of dyes can be

expressed as follows(97)

:

)()( 22

VBCB heTiOUVhTiO 1-19

OHHTiOOHhTiO VB 222 )( 1-20

OHTiOOHhTiO VB 22 )( 1-21

2222 )( OTiOOeTiO CB 1-22

22 HOHO 1-23

productsnDegredatioOHDye 1-24

productsOxidationhDye VB 1-25

productsductioneDye CB Re 1-26

The mechanism of photosensitized oxidation by visible radiation

(λ>420 nm) is different from the pathway that occurs under UV light

illumination. In this pathway, the mechanism suggests that the excitation

of the adsorbed dye takes place by visible light to appropriate singlet or

triplet states. It is subsequently followed by electron injection from the

excited dye molecule into the conduction band of the semiconductor

28

particles, whereas the dye is converted to the cationic dye radicals (Dye•+

)

that undergoes degradation to yield products as those in the

followings(98)

:

DyevishDye .)( 1-27

)( .22

BCeTiODyeTiODye 1-28

222.2 )( TiOOOeTiO BC 1-29

productsnDegredatioDye 1-30

The cationic dye radicals react with hydroxyl ions or interact

effectively with O2•−

, HO2• or HO

•− species to generate intermediates that

ultimately lead to CO2 formation:

HODyeOHDye 1-31

productsOxidationOHHODye

22 1-32

22 HOHO 1-33

222.22 )( TiOOHeTiOHHO BC 1-34

2.222 )( TiOHOHOeTiOOH BC 1-35

productsnDegredatioODyeODye

22 1-36

productsDegredaionorHOHODye )(2 1-37

Chlorine ions are released easily in the solution during the

photocatalytic degradation of chlorinated dye molecules(99)

.

Photocatalysis associated with a biological treatment is generally not

efficient for chlorinated compounds. Nitrogen is mineralized into NH4+,

NO3− and N2. These species depend on the initial oxidation degree of

nitrogen, the substrate structure and irradiation time(100)

. By comparing

29

the initial rates, NH4+ appears to be the primary product respected to

NO3− in the case of amine compounds. The nitrogen atoms in the amino-

groups of the dyes can lead to NH4+ ions by the attacks with hydrogen

species:

32 NHRHNHR 1-38

43 NHHNH 1-39

Puzenat et al.(101)

found that the total amount of nitrogen-containing

ions present in the solution at the end of the experiments lower than that

expected from molecule structure. The authors(101)

explained this

reduction in total amount of nitrogen due to the adsorption of N-

containing species on the catalyst surface in addition to that significant

quantities of N2 and/or NH3 had been produced and transferred to the gas-

phase.

The formation of N2 in azo dyes can be accounted for by the same

processes responsible for NH4+ formation. Consider the following:

HRNNRHRNNR 1-40

NNRNNR 1-41

In pyrazoline ring and amino groups NH4+ cations evolved spontaneously

before being subsequently and slowly oxidized into nitrate. In the azo

bonds, each nitrogen atom evolves as nitrogen gas(102)

.

The sites near azo bond are the attacked area when TiO2 used for

photodegradation of azo dyes(103)

. The azo dyes distraction occurs through

the distraction of C–N= bond and –N–N– bonds(103)

.

30

Aromatic intermediates include aromatic amine or phenolic

compounds were identified for most dyes(104)

. The formation of

aminobenzenesulfonate suggests the reductive cleavage of the azo group

prior to the opening of the aromatic ring(105)

. On the other hand, the

phenolic compounds as intermediates is commonly observed forming in

the photocatalytic degradation of other aromatic compounds(106)

.

Aliphatic acids were found as intermediates(107)

. Konstantinou and

Albanis reported that the photocatalytic degradation of azo dyes in

aqueous solution of TiO2 produce several organic acids as aliphatic

intermediates, while the main products were formic and acetic acids(108)

.

The decarboxylation of carboxylic acids lead to the liberation of carbon

dioxide gas according to ―photo-Kolbe‖ reaction(109)

.

2CORhCOOR 1-42

The possibility of generating molecular fragments during the

photocatalyzed degradation can be more toxic than the parent

compound(110)

.

31

1-9 Computational Chemistry

During the development of computer's technology in the last

century, computational calculation science has become an important

branch of chemistry.

Computational chemistry is a branch of chemistry that uses

principles of computer science to assist solving chemical problems. It

uses the results of theoretical chemistry incorporated with efficient

computer program to calculate atomic, molecular properties and

reaction's path for chemical reactions and their mechanism.

Computational chemistry is used to find a starting point for synthesis

compound or to assist in experimental data such as the position of

spectroscopic peak(111)

.

The first semi-empirical atomic orbital calculation were carried out

in the early 1950s and last decade and ab initio Hartree-Fock calculations

on diatomic molecules were carried out by using bases set of Slater

orbital(112)

. The minimum basis set was used to study diatomic orbital and

the first calculation with a larger basis set was published in 1960(113)

. The

first polyatomic calculations were studied in the late 1950 by using

Gaussian orbital.

Computational chemistry has been employed to solve the non-

relativistic Schrödinger equation with relativistic correction added.

Although some progress used to solve the fully relativistic Dirac

equation(114)

, there cause possibility to solve the Schrödinger equation in

either time-dependent form and time-independent form is an appropriate

way for the problem in hand. This in practice is not excepted for very

small systems(115)

.

Computational chemistry could calculate the properties of molecule

contains up to about 40 electrons with efficient accuracy. The error of

calculated energy is less than a few kJ.mol-1

and for geometries, bond

32

length changes with a few Pico meters and bond angle with 0.5 degree.

The treatment of large molecule by approximate methods such as semi-

empirical method, and the larger molecule treated with classical

mechanism in method is called molecular mechanics(116)

.

1-10 Hartree-Fock Method

Hartree-Fock (HF) method is a method used for determination of

the ground state wave function and ground state energy for many

systems. It is typical in the solution of the Schrödinger equation of atoms

and molecules. The Hartree-Fock method is called the self-consistent

field method (SCF). It is the central starting point for most ab initio

quantum chemistry method(117)

.

Much of the difficulty of solving the Schrödinger equation is

represented by the determination of the energy of each electron in the

presence of all other electrons. The energy of each electron is calculated

in the field of initial electron configuration. The difference between

Hartree-Fock energy and the energy of the full Schrödinger equation is

called the correlation energy. Hartree-Fock calculations are widely used

to provide accurate solution for many problems. The ab initio method is

used in Hartree-Fock involving approximation to obtain absolute

energy(118)

.

Hartree-Fock method uses two forms of wave function restricted

Hartree-Fock (RHF) and unrestricted Hartree-Fock (UHF). Restricted

Hartree-Fock theory assumes that each pair (α , β) of spin orbital has the

same spatial orbital associated with it. Unrestricted Hartree-Fock allows

the spatial part of spin orbital to be different from the α spin and β spin

type. RHF does not correctly describe the fact that molecule dissociate

while UHF is given more accurate description. Restricted Hartree-Fock

33

uses equal orbital for different spin at all internuclear separations. This

does not allow the orbital to localize on the individual atoms(119)

.

1-11 Ab initio Calculation

The program uses various quantum chemical methods to solve the

Schrödinger equation associated with the molecular Hamiltonian by

function's basis Set. The term ab initio was first used in quantum

chemistry to refer to the first principle by Robert and Coworkers(120)

. In

the current time, ab initio means "from first principle of quantum

mechanics"(121)

.

The ab initio method depends on a few laws of quantum mechanics,

namely, the mass, charge of electron, atomic nuclei and the value of

fundamental physical constant such as the speed of light and Planck

constant.

Ab initio molecular orbital calculation is specified by chemical

modulation. Chemical modulation includes selected methods of suitable

basis Set to determine general structure, electronic state and electronic

spin treatment(122)

.

The simplest type of ab initio electronic structure calculation is the

Hartree-Fock (HF) scheme in which the columbic electron – electron

repulsion is not taken into account, but only its average (mean field) is

included in the calculation. The size of basis set which increases the

energy tends to limit this state which is called Hartree-Fock limited.

Many types of calculation that are called post Hartree-Fock methods

being with Hartree-Fock calculation and correct electron – electron

repulsion refer to electronic correlation(123)

.

Hyperchem package program performs ab initio (SCF) calculation

generally, post Hartree-Fock procedure and add to total SCF energy. Ab

initio method is the most accurate of semi-empirical calculations. The ab

34

initio method doesn't include any empirical or semi-empirical parameters.

Ab initio calculations are best for a small system (ten of atoms),

electronic transition, system without experimental data and system that

requires high accuracy. Ab initio calculation computational cost is often

enormous amount of computer time and disk space(124)

.

Electronic structure method particularly ab initio calculation is

capable of consistent prediction with high accuracy ±20 kJ.mol-1

over

wide rang of system(125)

.

1-12 Semi-empirical Calculation

Semi-empirical calculations have been used to solve the

Schrödinger equation based on Hartree-Fock formalism with some

parameters from empirical data to describe the properties of electrons in

atom or molecule. They are very important in computational chemistry

for treating large molecule(126)

.

The semi-empirical method has short time in calculation because of

using approximate technique by limiting choice of molecular orbital,

considering only valance electron or by neglecting many smaller integral

to reduce the time of calculation. Semi-empirical calculations used all

parameters derivation from the experimental results to correct the error in

calculation(127)

.

Several semi-empirical methods are commercially available as

computational chemistry software package such as GAMESS, Gaussian,

Hyperchem, and Chem3D(128-129)

.

Semi-empirical method calculations are carried out to study

structure and electronic properties including total energy, heat of

formation, and electrostatic potential. They deal with the effect of many

substituted biological systems by using AM1 and PM3 method(130)

.

35

Semi-empirical calculations that include AM1 level of calculation

have been used to study the physical properties of phenol compound and

some derivations. Their theoretical results have a good agreement with

experimental values(131)

.

The structure of methylene blue molecule has been studied by

molecular mechanics calculations. Which optimized the conformation

that has the low energy by semi-empirical AM1 and PM6 molecular

orbital calculation. Bond's length and angles of the structure of minimum

energy were then compared to the experimental X-ray crystallographic

data. The methylene blue modeled by the PM6 method is in a good

agreement with the x-ray crystallographic data(132)

.

The following are several methods of semi-empirical calculation:

1-12-1 Zero-Differential Overlap (ZDO)

This method is a principle of semi-empirical assuming the

interaction between pair of electrons in different orbital equal zero(133)

.

1-12-2 Complete Neglect of Differential Overlap (CNDO)

This method is used to calculate the properties of electron in ground

state in the open shell system such as bond length and total energy(134)

.

1-12-3 Intermediate Neglect of Differential Overlap (INDO)

This method is the development to the CNDO method containing

repulsion electron- electron in the same atom (valance electron). This

method is used to calculate properties of electron in ground state for the

open shell system, close shell system and calculate the geometry and total

energy(135)

.

36

1-12-4 Modified Intermediate Neglect of Differential

Overlap (MINDO3)

This method is used to calculate electronic properties for large

organic molecule. It is a development to the INDO method(136)

.

1-12-5 Modified Neglect of Diatomic Overlap (MNDO)

This method is used for organic molecule containing elements from

the first raw and second raw of periodic table, but it is not transition

element. It calculates electronic properties and heat of formation(137)

.

1-12-6 Austin Model 1 (AM1)

This method is the development of the MNDO method. It is more

accurate than MNDO for compounds containing phosphorus – oxygen

bond, nitro compounds and peroxide bond.

1-12-7 Parameterization Model, version 3 (PM3)

This method is the development to the AM1 method adding several

numbers of experimental value. It is used to calculate the electronic

properties for organic and inorganic molecule(138)

.

1-13 Geometry Optimization

The idea of geometry optimization of molecule is the concept of

molecular structure. The molecule is not only a collection of atoms but

also a collection of atoms in the particular set of location in space.

Determining the molecular structure is very important in chemistry to

calculate the properties of molecule. In the area of computational

chemistry, structure is determination through a geometry optimization.

37

Geometry optimization is used to calculate the equilibrium structure

of molecule that has the lowest potential energy surface. The energy of

molecule is reduced by adjusting atomic coordinate in the best

combination of bond length, angle and dihedral(139)

.

The program of hyperchem can be used to calculate geometry

optimization with molecular mechanics or quantum mechanics method. It

starts with a set of Cartesian coordinate for a molecule to find a new set

of coordinates with minimum potential energy(140)

.

Application of molecular orbital theory through the semi empirical

AM1 method is used to determine the main geometry and characteristic

structure parameters of the cyclo phosphozenes. Dipole momentum, bond

distance and bond angles are quite reasonable when they are compared

with available experimental data, standard values and other theoretical

calculations(141)

.

The 3-azido-3-deoxythymide compound(142)

can be applied as an

anti-HIV agent and its derivative. The geometry optimization and

electronic properties were studied in gas phase by semi-empirical

molecular orbital theory. The program used is hyperchem 7.5 running on

windows XP workstation in Pentium IV PC. The calculations performed

with the AM1 level are in qualitative agreement to those obtained from

B3LYP/6-311G** and MP2/6-311+(3df,2p) // B3LYP/6-311G** level of

theory.

The semi-empirical methods including AM1 levels of calculation

are curried out to describe the geometry of phenol, the results indicated

having a close agreement with the experimental bond length and

angles(143)

.

The crystal and molecular structures of azo compound (2-methy-4-

(4-methoxyphenylazo)phenol) have been studied by X-ray single crystal

38

diffraction technique and compared with theoretical results of geometry

optimization using PM3 semi-empirical quantum mechanics(144)

.

Molecular mechanics, different method AM1,PM3,CNDO,ZINDO,

and ab initio quantum mechanics were used to study the equilibrium

molecular geometry, wavelength of maximum absorption, photo stability

and photodegradation mechanism of some organic pigments and

comparison predicated bond angle, bond length, hydrogen bond distance

and torsion angle to X-ray data(145)

.

Ab initio HF/STO-3G calculation generally provides prediction of

bond distance and bond angle. The increased basis set size through a

series of basis sets ( STO-3G, 3-21G, and 6-31G* ) improves the bond

length accuracy(146)

.

1-14 Transition State

Transition state of chemical reaction is a particular configuration

along high energy of the reaction coordinate. At this point, perfectly

irreversible reaction collides reactant molecule to form product. In classic

mechanism, the atoms or molecule collide with enough energy to form

transition structure. Transition state can be determined by searching for

first order saddle point on the potential energy surface. The reaction

passes over the lowest energy saddle point on the potential energy

surface. A saddle point with one negative Eigenvalue corresponds to

transition state for chemical reaction change isomeric form(147)

.

For bimolecular, transition state is performed when two molecules

old bond are broken and a new bond is formed. The energy difference

between the reactant and the potential energy maximum is referred to as

the activation energy.

39

At high temperature, the vibration energy higher than transition

energy to collision molecule leads to a farther predicted transition

state(148)

.

Obtained equilibrium geometry for reactant and product is

necessary to calculate the transition state. Calculated transition structure

may be very sensitive to the level of theory employed (147)

.

All quantum chemical methods can be used to find transition state.

Hyperchem program calculates transition structure with either semi-

empirical quantum mechanics method or the ab initio quantum mechanics

method.

There are many different methods of searching for transition state

and different quantum chemicals programs package. Hyperchem program

supplies two different type for transition state to search eigenvector and

synchronous transit(149)

.

The synchronous transit developed by H.B Schlegel and Coworkers

uses liner synchronous transit or quadratic transit approach to get closer

to the quadratic region around the transition state and then uses quasi-

Newton to complete the optimization(150)

.

In the liner synchronous transit (LST) approach the path is liner

between reactant and product. The quadratic synchronous transit (QST)

method uses curved path through reactant and product(151-152)

.

Estimation of activation energy for the hydrogen abstraction

reaction is between hydrocarbon radical and hydrocarbon compound on

the basis set of the MNDO-PM3 calculation. MNDO-PM3 method having

average errors ±20kJ.mol-1

is a very good liner correlation experimental

and calculated value(153)

.

The energy barrier of azo dye formation results from rotating the

NN phenyl bond calculated by semi-empirical PM3 method based

40

on the AMPAC 6.5 PC software. The best form has low energy barrier

equal to 10.79 kJ.mol-1

and another form has 21.84 kJ.mol-1

(154)

.

Semi-empirical and ab initio calculations have been used to

investigate the potential energy barrier to attach the hydroxyl ion on the

carbonyl group. The PM3 semi-empirical calculates the activation energy

equal to 56.90kJ.mol-1

. These result are very close to the experimental

value of 69.87kJ.mol-1 (155)

MM+, AM1, PM3 of semi-empirical calculation have been curried

out to study the transition state of syn and anti conformation of the some

nitrosulfamide compound. The anti conformation is more stable than syn

conformation because it has high energy of transition state(156)

.

Theoretical kinetic of elimination reaction of ethyl chloride by

AM1, PM3 and MNDO studies and calculates the rate constant for the

compute Arrhenius parameters which adequately simulates with

experimental values(157)

.

1-15 Electrostatic Potential

Electrostatic potential describes the classical nonbonded

electrostatic interaction of charge distribution. In the molecular

mechanics, electrostatic terms refer to simple charge interaction

particularly dipole-dipole interaction. The potential indicates what a

reactant molecule sees as approach molecule. The electrostatic energy

varies inversely with the distance between the atoms.

Electrostatic potential correlates with dipole moment,

electronegativity and partial charge to provide method to understand the

relative polarity of molecule. Quantum mechanical calculations generate

values for partial charge for the atoms in molecule related to electron

densities around various atom from bonding and lone pair of electrons.

Negative electrostatic potential corresponds to the attraction of the proton

41

by the concentrated electron density in molecule. Positive electrostatic

potential correspond to the repulsion of the proton by the atom's nuclei in

region where low electrons densities exist and nuclear charge is

incompletely shielded.

Molecular electrostatic potential is calculated within the MNDO,

AM1 or PM3 semi-empirical approximation to obtained atomic charge

from dipole moments and exact semi-empirical values. The result for

wide range of neutral molecule and ions shows excellent agreement

between the dipole moment and exact semi-empirical dipole moments

and the maximum error is D04.0(158)

.

The electrostatic potential for the eleven nitroimidazolyl and

nitrohetrocyclic compound has been computed using the CNDO/2

quantum chemical method. The location of the large nucleopilic reactivity

for each molecule is predicted to be mostly near or on the nitro group(159)

.

1-16 Basis Set

Basis set is a series of numbers used by computational chemistry

software to describe the electrons in the atomic orbital or describe the

electrons which are approximate to the nuclei, to each other or to

calculated wavefunction. Choice basis set for computational calculation is

important. There are two formula of basis set, the first is Slater type

orbital (STO) and the second is Gaussian type orbital (GTO)(160)

.

The basis set that uses the smallest of them is called minimal basis

set using minimum numbers of basis function required to represented all

the electrons on the each atom. A minimum basis set is one on each atom

in molecule, a single basis function is used for each orbital in Hartree-

Fock calculation on the free atom. The most common basis set is STO-

NG where N is an integer. The example for minimal basis set are STO-

3G and STO-6G(161)

.

42

The other type of basis set is the extended basis set which has the

most types of basis set, split – valance basis set and polarized basis set.

Split – valance basis set taken into account the valance electrons that are

involved in the bonding and chemical reaction as opposed to the core

electrons which are typically not involved in reaction. Split – valance

basis set includes 3-21G and 6-31G.

The number of functions assigned to valance orbital characterizes

split basis set Double Zeta (DZ) calculation. This calculates each of

electron in the valance orbital twice, Triple Zeta (TZ) and Quadruple

Zeta (QZ)(162)

.

Polarized basis set takes into account the overlap between the

orbital and necessarily has the characteristics of only one or the other. In

this case (s), the orbital has a little of (p) orbital that begins to have the

(d) flavor. The polarized basis set is indicated by (*) or by orbital name

such as 3-21G* basis set or 3-21G(d) basis set.

43

1-17 The Aim of the Present Work

The work is composed of two main parts. The first one reports an

investigation of the photocatalytic decolorization of Bismarck brown R

using different types of catalyst ZnO, TiO2 (Degussa P25), TiO2

(Hombikat UV100), TiO2 (Millennium PC105), TiO2 (Koronose 2073).

The effect of different parameters was studied to estimate the best

condition for decolorization of Bismarck brown R:

1. Amount of catalyst.

2. Dye concentration.

3. pH of solution.

4. Light intensity.

5. Current gas.

6. Temperature.

The second part includes theoretical calculation to estimate the

photocatalytic decolorization of Bismarck brown R using different

methods of quantum calculation, in order to investigate the most probable

pathway for the first cleavage step of Bismarck brown R through the

transition state studied.

44

CHAPTER TWO

EXPERIMENTAL

45

EXPERIMENTAL

2-1 Chemicals

The chemicals used in this work are listed in table 2-1. All

chemicals are standard and were used without further purification.

Table 2-1: Applied reagents

No. Chemicals

Company supplied

1

Titanium dioxide (DegussaP25)

Degussa AG, D-6000

2

Titanium dioxide (Hombikat UV100)

Sachtleben Chemie

GmbH

3

Titanium dioxide (Millennium PC105)

BP34-F 68801 Thann

4

Titanium dioxide (Koronose 2073)

Leverkusen, Germany

5

Zinc oxide (ZnO)

E. Merck

6

Bismarck brown R

Sigma – Aldrich

7

Sodium hydroxide (NaOH)

BDH

8

Hydrochloric acid (HCl)

BDH

46

2-2 Instruments

Different instruments were used in this study. Types of instruments

and the supplied companies are listed in table 2-2.

Table 2-2: Applied instruments

No.

Instrument Company

1

Mercury lamp UV(A)

Philips - Germany

2

UV-Visible spectrophotometer

Cary 100Bio, shimadzu

(Varian)- Germany

3

TOC analyzer

Shimadzu – Japan

5

B.E.T surface area

Micrometrics Automate 23 –

Germany

6

pH meter

691 pH meter Metrohm –

Germany

7

Electrical magnetic stirrer

IKAMAG RET – Germany

8

Centrifuge

Heraeus – Germany

9

Sensitive balance

Denver instrument –

Germany

10

UV-Meter BASIC

Germany

47

2-3 Apparatus

A photograph and schematic of the apparatus and the reaction

vessel are shown in figure 2-1. Irradiation with UV(A) light at an

intensity 2.93mW.cm-2

using a Philips (CLEO), Poland, mercury lamps

(containing 6 lamps with 15W for each one), and a mean wavelength of

λ=350nm. In all experimental, the required amount of the catalyst was

suspended in 100cm3 of aqueous solution of Bismarck brown R using

magnetic stirrer. At predetermined times; 2cm3 of the reaction mixture

was collected and centrifuged for 15minutes. The supernatant was

carefully removed by a syringe with a long pliable needle and centrifuged

again at same speed and the same period time. The second centrifuge was

found necessary to remove fine particle of the catalyst. After the second

centrifuge, the absorbance at the maximum wavelength of the Bismarck

brown R was measured with UV-visible spectrophotometer.

A B

Figure 2-1: A- The photograph of the outlook of experimental

apparatus . B- Schematic representation of reaction cell.

48

2-4 Calibration Curve

The calibration curve was obtained by using standard Bismarck

brown R aqueous solutions. The absorbance of each concentration was

measured at 459nm. Typical calibration value are given in table 2-3 and

plot in figure 2-2.

Figure 2-2: UV-Visible spectra of different concentration of

Bismarck brown R.

Table 2-3: Concentration with absorbance.

Conc.x10-4

M Absorbance

0.00 0.00

0.1 0.174

0.2 0.362

0.3 0.534

0.4 0.698

0.5 0.863

0.6 1.042

0.7 1.203

0.8 1.374

0.9 1.558

1 1.745

49

R2 = 0.9997

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Conc. x 10-4M

Ab

s.

Figure 2-3: Calibration curve at different concentration of Bismarck

brown R.

2-5 Light Intensity Measurement

The photon flux has been determined by a chemical ferrioxalate

actinometer(163-164)

. Briefly, freshly prepared 40mL iron (III) sulfate

aqueous solution (0.15M) and 50mL potassium oxalate aqueous solution

(0.45M) have been mixed in the reactor used for the photocatalyst

decolorization of Bismarck brown R in the dark. Afterwards, 10mL

H2SO4 aqueous solution (0.05M) has been adjusted to 100mL, the same

as that used for the photocatalyst decolorization of Bismarck brown R

tests. Under these conditions, the green color of ferrioxalate complex is

formed.

The rector has been irradiated from outside using mercury lamp

UV(A). This lamp incident light to the wavelengths between 320-390nm

has been employed during the photo flux measurements. The ferrioxalate

complex absorbs all photons of the incident light in this range and is

reduced to iron (II) complex according to the following equations:

50

2

2

42

2

242

3

342 2)(][2])([2 COOCOCFeOCFe h 2-1

The rate of iron (II) ions formation has been calculated by

determining the amount of iron (II) ions after different illumination times

using spectrophotometric method employed 1,10-phenanthroline reagent

at 510nm. The light intensity has been calculated by following equation:

1

2

31 sEinsteinIVtQ

VAV

2.02.160010463.0

100100491.10 3

I

Where :-

I0 : Light intensity.

A : Absorbent at 510nm.

V1 : Volume of solution irradiated (100cm3).

V3 : Total volume (100cm3).

Σ : Molar absorbent coefficient (slope value).

t : Irradiation time.

Q : Quantum yield (1.2).

V2 : Volume of irradiation solution (0.2cm3).

.1038.4 16

0

sEnstineI

51

2-6 Background Experiments

These experiments were made to determine the conditions

necessary for photocatalytic decolorization of Bismarck brown R. They

were carried out to evaluate the effect of catalyst and/or the UV light on

photocatalytic decolorization reaction.

2-6-1 Dark Reaction

In this part, a series of experimental has been done as blank

experimental. In each one 100cm3 of Bismarck brown R solution in

concentration 10-4

M at temperature (298.15 K) was stirred to 50 min in

presence the catalyst and absence the irradiation.

2-6-2 Photoreaction

In this part, a series of experiments were performed. In each one

100cm3 of Bismarck brown R solution in concentration 10

-4 M was

irradiation with ultraviolet UV(A) with the absence of catalyst, and

continuous stirring for 60 min at 298.15K.

2-7 Analysis

2-7-1 UV-Visible spectrophotometry

Absorption spectra of Bismarck brown R solution at different times

of irradiation was recorded with Cary 100Bio UV-visible

spectrophotometer shimadzu (Varian).

2-7-2 Total Organic Carbon (TOC) analysis

The total organic carbon (TOC) measurements was determined by

combustion method and the resultant CO2 was analyzed in the

combustion gases. The equipment used was shimadzu 5000A. The system

52

contain combustion tube filled with platinum catalyst, through which an

oxygen (99.999% purity) flow of 200cm3.min

-1 passed. The temperature

of the reaction zone was maintained at 680°C. The 20µL of samples were

introduced into combustion chamber by automatic sampler after which

combustion occurred (total oxidation to CO2 and H2O). Samples were

acidified with phosphoric acid (38%) to remove inorganic carbon. The

gases flux went out of the reactor pass condenser and gas/liquid separator

to eliminate almost all the water. The remaining droplet of water was

removed from the gas stream by the dehumidfactor, which operated at

temperature almost (0-10)°C. The dry gas that contained CO2 passed a

scrubber that separate halogens and finally reached an infrared detector

for determining the exact amount of total carbon which was in this case

the same as the total organic carbon. A two point calibration curve was

prepared to analyze the samples.

Calibration curve of total organic carbon was done by dissolve

accurately measured 2.125g of reagent grade potassium hydrogen

phthalate in water and completed to 1L. This solution contained 1000ppm

carbon. This solution was used as standard stock solution. The results are

shown in table 2-4 and plotted figure 2-4.

53

Table 2-4: Concentration with peak area for calibration curve of

total organic carbon.

Conc. / ppm Area

0.0 0.00

3.0 523

6.0 1038

12 2310

24 4248

48 8516

R2 = 0.9994

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 5 10 15 20 25 30 35 40 45 50

Conc. ppm

Area

Figure 2-4: Calibration curve of total organic carbon.

54

Calibration curve of inorganic carbon dissolve precisely measured

3.50 g of reagent grade sodium hydrogen carbonate and 4.41 g of sodium

carbonate (which heated for 30 minutes at 500 oC and cooled in sulfate

desicator) in water in 1L. This solution which contained 1000ppm of

inorganic carbon was used as standard stock solution. The results are

shown in table 2-5 and plotted in figure 2-5.

Table 2-5: Concentration with area for calibration curve of inorganic

carbon.

Conc. ppm Area

0 0

3 678

6 1245

12 2546

24 5178

48 9973

R2 = 0.9995

0

2000

4000

6000

8000

10000

12000

0 5 10 15 20 25 30 35 40 45 50

Conc. ppm

Are

a

Figure 2-5: Calibration curve of inorganic carbon.

55

2-7-3 Measurements of Surface Area

The measurements of specific surface area Brunaure-Emmett-

Teller (B.E.T) of ZnO, TiO2(DegussaP25), TiO2(HombikatUV100),

TiO2(MillenniumPC105) and TiO2(Koronose2073) were curried out

employing a micrometrics automate 23 instrument. The gas mixture used

in all experiments was 70% helium and 30% nitrogen gas. Samples were

heated to 150 oC for 1 hour to clean the surface from adsorbed organic

compound and water. The nitrogen gas adsorption and desorption

isotherms at 77K were measured using a Quantachure Autosorb 3B after

the sample were vacuum dried at 200 oC

over night.

2-8 Apparatus Used in Theoretical Calculation

The computer used in this study has the following characteristics:

Types Pentium IV computer.

Processor 2.8 x 4 GB.

Hard disk 0.5 tera.

RAM 11.8 GB.

UBS 3 Hour.

2-9 Program Used in Calculation

HyperChem program has been used in the calculation. This program

puts more molecular modeling tools than other programs. The version

7.52 was used in this study. This version has some properties with more

powerful, computation chemistry tools, new incorporate models,

additional basis set, and new drawing capabilities.

56

2-10 Routes of Calculation

2-10-1 Building and Display Molecules

HyperChem tools have been used to build and display molecule.

By using the drawing tool, a two dimension (2D) representation of

molecule was drawn, and the model builder to generation a three

dimensional (3D) structure was used. The model builder adds implicit

hydrogen atoms to the molecule at our request. Also, the manipulated

individual bond, bond geometry, angles, torsion, atomic charge and

atomic number were calculated during model building.

2-10-2 Geometry Optimization of Molecule

To calculate the properties of molecule a well defined structure

must be generated. A reliable calculation often requires a structure that

represents a minimum on a potential energy surface. Hyperchem contains

a several methods to calculate the geometry optimization of molecule.

Calculation of the geometry optimization of Bismarck brown R had been

carried out using the semi-empirical PM3 method .

2-10-3 Viewing Orbital and Electrostatic Potential

Orbital wave function has been plotted by using results of

semiempirical calculation. It was used to view the properties of molecule.

Also plotting the electrostatic potential and total charge density was

determined during the semi-empirical calculations.

2-10-4 Potential Energy of Bond

Energy calculation was required to break the bond by the elongation

to maximum scale by selecting the distance between two bonded atoms.

57

A distance exceeding a theoretical bond length may refer to bond

breaking through the reaction.

2-10-5 Transition State Calculated

Reaction pathway by synchronous transit method was calculated

from a compute menu to match reactants and products. Then log file was

started before running synchronous transition state. Then the log saving

the file. Activation energy has been examined theoretically the difference

between the total energy of transition state and reactant was stopped.

58

CHAPTER THREE

RESULTS

59

RESULTS

3-1 Preliminary Experimental

3-1-1 Dark Reaction

These experiments were carried out in the absence of the ultraviolet

radiation on different types of catalyst. The results are shown in table 3-1

and plotted in figure 3-1. These results show that there is no reaction in

the absence of the ultraviolet radiation.

Table 3-1: The change of C/C0 with adsorption time in absence the

radiation.

Type of catalyst ZnO TiO2 (Degussa P25)

Adsorption time/min C/C0

0 1.000 1.000

5 0.991 0.983

10 0.988 0.982

15 0.987 0.983

20 0.987 0.981

25 0.987 0.981

30 0.987 0.981

60

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 5 10 15 20 25 30

Time / min

C/C

0 ZnO

TiO2 (Degussa P25)

Figure 3-1: Dark reaction at different types of catalyst.

3-1-2 Photoreaction

These experiments were carried out in the absence of the catalyst

and the existence of the UV(A) light. The results are shown in table 3-2

and plotted in figure 3-2. Table 3-2 and figure 3-2 show that the

photolysis of Bismarck brown R is under UV(A) light. The

decolorization percentage is equal to 5.3 after the 60min of irradiation.

These results show that the dye is not effected by the ultraviolet radiation.

61

Table 3-2: The change of C/C0 with time of photolysis of Bismarck

brown R.

Irradiation time / min C/C0

0 1.000

10 0.998

20 0.969

30 0.966

40 0.953

50 0.998

60 0.983

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

Figure 3-2: Photolysis of Bismarck brown R.

62

3-2 Effect of Different Parameters on Photocatalyst

Decolorization of Bismarck Brown R

3-2-1 Effect of Photocatalyst Concentration

3-2-1-1 Effect of Photocatalyst Concentration for ZnO

The effect of photocatalyst concentration on the photocatalytic

decolorization of Bismarck brown R was investigated under a

predetermined experimental condition with initial Bismarck brown R

concentration of 10-4

M, light intensity equal to 2.93mW.cm-2

,

temperature equal to 298.15K and solution pH equal to 4.54. The results

are listed in table 3-3 and plotted in figure 3-3. The best weight of ZnO

3.75 g.L-1

gives the maximum photodecolorization efficiency which is

equal to 97.9%. The results of the change in photodecolorization

efficiency (P.D.E) with catalyst concentration are shown in table 3-4 and

plotted in figure 3-4. Maximum P.D.E was obtained at 3.75 g.L-1

of ZnO.

The results illustrated in table 3-5 and plotted in figure 3-5 which

shows the pseudo first order reaction curve for various catalyst

concentration according to Langmuir Hinshelwood relationship. The

kinetic results are plotted in figure 3-6 which shows that the rate constant

of reaction generally increases with increase of photocatalyst

concentration.

63

Table 3-3: The change of C/C0 with irradiation time on different

masses of ZnO.

Catalyst

Conc. g.L-1

1.00

2.00

3.00

3.50

3.75

4.00

4.50

5.00

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

15 0.531 0.469 0.421 0.385 0.269 0.324 0.322 0.375

30 0.304 0.258 0.195 0.157 0.081 0.102 0.106 0.121

45 0.147 0.118 0.087 0.072 0.022 0.029 0.033 0.043

60 0.086 0.058 0.044 0.027 0.006 0.008 0.011 0.013

75 0.044 0.028 0.018 0.011 0.002 0.002 0.003 0.006

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70 80

Time / min

C/C

0

1.00 g

2.00 g

3.00 g

3.50 g

3.75 g

4.00 g

4.50 g

5.00 g

Figure 3-3: Effect the masses of ZnO on photodecolorization of

Bismarck brown R.

64

Table 3-4: The effect of ZnO concentration on the efficiency of

decolorization of Bismarck brown R.

Catalyst Conc. g.L-1

P.D.E

0.00 0.00

1.00 49.4

2.00 74.8

3.00 91.5

3.50 97.0

3.75 97.9

4.00 96.0

4.50 89.0

5.00 80.6

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

Mass of catalyst g/L

P.D

.E

Figure 3-4: Effect the masses of ZnO on photodecolorization

efficiency of Bismarck brown R.

65

Table 3-5: The change of lnC/C0 with irradiation time on different

masses of ZnO.

Catalyst

Conc. g.L-1

1.00

2.00

3.00

3.50

3.75

4.00

4.40

5.00

Irradiation

time/min

lnC/C0

0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

15 0.634 0.757 0.836 0.959 1.311 1.127 1.131 0.981

30 1.189 1.353 1.631 1.839 2.503 2.301 2.243 2.106

45 1.911 2.131 2.409 2.656 3.775 3.518 3.396 3.145

60 2.453 2.837 3.116 3.581 4.972 4.752 4.457 4.137

75 3.106 3.542 3.998 4.474 6.142 5.829 5.524 5.057

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80

Time / min

lnC

/C0

m=1.00 g

m=2.00 g

m=3.00 g

m=3.50 g

m=3.75 g

m=4.00 g

m=4.50 g

m=5.00 g

Linear

(m=2.00 g)Linear

(m=1.00 g)Linear

(m=3.00 g)Linear

(m=3.50 g)Linear

(m=5.00 g)Linear

(m=4.50 g)Linear

(m=4.00 g)Linear

(m=3.75 g)

Figure 3-5: The change of lnC/C0 with irradiation time at different

masses of ZnO.

66

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 0.5 1 1.5 2 2.5 3 3.5 4


k m

in-1

Figure 3-6: Effect of masses of ZnO on rate constant.

3-2-1-2 Effect of Photocatalyst Concentration for TiO2

The effect of photocatalyst concentration on the photocatalytic

decolorization of Bismarck brown R was investigated under a determined

experimental condition with initial Bismarck brown R concentration of

10-4

M, light intensity equal to 2.93mW.cm-2

, temperature equal to

298.15K and solution pH equal to 4.54. The results are listed in table 3-6

and plotted in figure 3-7. The best weight of TiO2 (Degussa P25) 1.75

g.L-1

gives the maximum photodecolorization efficiency equal to 68.2%.

The results of the change in photodecolorization efficiency (P.D.E) with

catalyst concentration are shown in table 3-7 and plotted in figure 3-8.

Maximum P.D.E was obtained at 1.75 g.L-1

of TiO2 (Degussa P25).

The results illustrated in table 3-8 and plotted in figure 3-9 show the

pseudo first order reaction curve for various catalyst concentration

according to Langmuir Hinshelwood relationship. The kinetic results

plotted in figure 3-10 show that the rate constant of reaction generally

increases with increase of photocatalyst concentration.

67

Table 3-6: The change of C/C0 with irradiation time at different

masses of TiO2 (Degussa P25).

Catalyst

Conc. g.L-1

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.50

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

15 0.966 0.945 0.922 0.906 0.878 0.818 0.836 0.849

30 0.931 0.894 0.865 0.821 0.778 0.695 0.703 0.726

45 0.902 0.851 0.802 0.731 0.672 0.575 0.599 0.621

60 0.868 0.803 0.741 0.659 0.599 0.479 0.512 0.538

75 0.838 0.765 0.692 0.596 0.518 0.402 0.433 0.463

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50 60 70 80

Time / min

C/C

0

0.50 g

0.75 g

1.00 g

1.25 g

1.50 g

1.75 g

2.00 g

2.50 g

Figure 3-7: Effect the masses of TiO2 (Degussa P25) on

photodecolorization of Bismarck brown R.

68

Table 3-7: Effect of TiO2 (Degussa P25) concentration on efficiency

of decolorization of Bismarck brown R.

Catalyst Conc. g.L-1

P.D.E

0.00 0.00

0.50 37.1

0.75 49.0

1.00 57.0

1.25 63.4

1.50 67.0

1.75 68.2

2.00 65.0

2.50 56.3

Table 3-8: The change of lnC/C0 with irradiation time on different

masses of TiO2 (Degussa P25).

Catalyst

Conc. g.L-1

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.50

Irradiation

time/min

lnC/C0

0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

15 0.034 0.056 0.081 0.097 0.129 0.188 0.178 0.163

30 0.071 0.112 0.146 0.198 0.251 0.363 0.351 0.321

45 0.103 0.161 0.221 0.314 0.395 0.537 0.511 0.476

60 0.141 0.219 0.301 0.416 0.512 0.714 0.668 0.619

75 0.176 0.268 0.367 0.516 0.657 0.884 0.836 0.769

69

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3


P.E

.D

Figure 3-8: Effect the masses of TiO2 (Degussa P25) on

photodecolorization efficiency of Bismarck brown R.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 20 40 60 80

Time / min

lnC

/C0

m=0.50 g

m=0.75 g

m=1.00 g

m=1.25 g

m=1.50 g

m=1.75 g

m=2.00 g

m=2.50 g

Linear

(m=0.50 g)Linear

(m=0.75 g)Linear

(m=1.00 g)Linear

(m=1.25 g)Linear

(m=1.50 g)Linear

(m=2.50 g)Linear

(m=2.00 g)Linear

(m=1.75 g)

Figure 3-9: The change of lnC/C0 with irradiation time at different

masses of TiO2(Degussa P25).

70

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2


K /

min

-1

Figure 3-10: Effect of masses of TiO2(Degussa P25) on rate constant.

3-2-2 Effect of Initial Dye Concentration

3-2-2-1 Effect of Initial Dye Concentration for ZnO

Under the experimental condition ZnO concentration 3.75 g.L-1

,

light intensity equal to 2.93 mW.cm-2

, solution pH equal to 4.54 and

temperature equal to 298.15 K, the effect of change initial dye

concentration on decolorization percentage was studied in the range (0.2-

1)x 10-4

M. The results are listed in table 3-9 and plotted in figure 3-11. It

has been observed that the percent decolorization gradually increased

with the decreasing of initial dye concentration.

The kinetic results show that the rate constant of reaction inversely

proportional with dye concentration. This is listed in table 3-10 and

plotted in figure 3-12.

71

Table 3-9: The change of C/C0 with irradiation time on different dye

concentrations by ZnO.

Dye concentration

x 10-4

M

1.0

0.8

0.6

0.4

0.2

Irradiation

Time/min

C/C0

0 1.000 1.000 1.000 1.000 1.00

15 0.793 0.708 0.576 0.529 0.433

30 0.591 0.469 0.344 0.271 0.196

45 0.436 0.327 0.201 0.139 0.083

60 0.325 0.231 0.125 0.072 0.038

75 0.226 0.153 0.075 0.041 0.019

Table 3-10: Concentration with rate constant by ZnO.

Type of catalyst ZnO

Con.x10-4

M k min-1

1 0.045

0.8 0.54

0.6 0.64

0.4 0.079

0.2 0.092

72

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70 80

Time / min

C/C

0

0.0001M

0.00008M

0.00006M

0.00004M

0.00002M

Figure 3-11: Effect of initial dye concentration on

photodecolorization efficiency by ZnO.

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Conc. x 10-4 M

K /

min

-1

Figure 3-12: Effect of initial dye concentration on rate constant by

ZnO.

73

3-2-2-2 Effect of Initial Dye Concentration for Different

Types of TiO2

The effect of changing initial dye concentration on the

photocatalytic decolorization of Bismarck brown R in the range (0.2-1)x

10-4

M was studied under the determined experimental condition TiO2

dosage equal to 1.75 g.L-1

, light intensity equal to 2.93 mW.cm-2

,

temperature equal to 298.15 K and solution pH equal to 4.54. The results

are listed in tables 3-11, 3-12, 3-13, 3-14 and plotted in figures 3-13, 3-

14, 3-15, 3-16 for TiO2 (DegussaP25), TiO2 (HombikatUV100), TiO2

(MillenniumPC105), TiO2 (Koronose2073) respectively. The results

indicate that a decrease in dye concentration decreases the time of

decolorization.

The kinetic results show that the rate constant of reaction inversely

proportional with dye concentration. This is shown in table 3-15 and

plotted in figure 3-17.


concentrations by TiO2 Degussa P25.

Dye concentration

x 10-4

M

1.0

0.8

0.6

0.4

0.2

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

10 0.652 0.592 0.535 0.485 0.394

20 0.453 0.381 0.305 0.221 0.169

30 0.307 0.221 0.151 0.106 0.081

40 0.203 0.136 0.085 0.056 0.032

50 0.138 0.081 0.051 0.028 0.012

60 0.094 0.049 0.025 0.015 0.0051

74


concentrations by TiO2 Hombikat UV100.

Dye concentration

x 10-4

M

1.0

0.8

0.6

0.4

0.2

Irradiation

Time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

10 0.837 0.729 0.635 0.577 0.512

20 0.704 0.501 0.412 0.356 0.298

30 0.589 0.369 0.271 0.191 0.151

40 0.489 0.274 0.174 0.118 0.087

50 0.411 0.193 0.109 0.061 0.044

60 0.336 0.136 0.067 0.034 0.024


concentrations by TiO2 millennium PC105.

Dye concentration

x 10-4

M

1.0

0.8

0.6

0.4

0.2

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

10 0.761 0.689 0.634 0.541 0.496

20 0.552 0.481 0.388 0.272 0.189

30 0.434 0.362 0.282 0.155 0.103

40 0.317 0.253 0.192 0.099 0.058

50 0.241 0.182 0.127 0.072 0.032

60 0.183 0.144 0.106 0.051 0.025

75


concentrations by TiO2 koronose 2073.

Dye concentration

x10-4

M

1.0

0.8

0.6

0.4

0.2

Irradiation

Time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

10 0.959 0.928 0.902 0.887 0.874

20 0.892 0.852 0.829 0.791 0.761

30 0.827 0.782 0.749 0.703 0.665

40 0.773 0.721 0.672 0.623 0.591

50 0.744 0.671 0.618 0.563 0.518

60 0.703 0.624 0.572 0.525 0.481

Table 3-15: Concentration with rate constant by different types of

TiO2.

Type of

catalyst

TiO2

Degussa

P25

TiO2

Hombikat

UV100

TiO2

Millennium

PC105

TiO2

Koronose

2073

Con.x10-4

M K min-1

1 0.039 0.028 0.018 0.006

0.8 0.049 0.037 0.029 0.007

0.6 0.066 0.044 0.038 0.009

0.4 0.072 0.055 0.049 0.011

0.2 0.085 0.061 0.063 0.012

76

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

0.0001M

0.00008M

0.00006M

0.00004M

0.00002M


photodecolorization efficiency by TiO2 Degussa P25.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

0.0001M

0.00008M

0.00006M

0.00004M

0.00002M


photodecolorization efficiency by TiO2 Hombikat UV100.

77

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

0.0001M

0.00008M

0.00006M

0.00004M

0.00002M


photodecolorization efficiency by TiO2 Millennium PC105.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

0.0001M

0.00008M

0.00006M

0.00004M

0.00002M


photodecolorization efficiency by TiO2 koronose 2073.

78

0

0.02

0.04

0.06

0.08

0.1

0 0.2 0.4 0.6 0.8 1 1.2

Conc. x 10-4M

K /

min

-1

TiO2 (Degussa P25) TiO2 (Hombikat UV100)

TiO2 (Millenium PC105) TiO2 (Koronose 2073)

Figure 3-17: Effect of initial dye concentration on rate constant by

different types of TiO2.

3-2-3 Effect of Solution pH

3-2-3-1 Effect of Solution pH for ZnO

Under the determined experimental condition with initial dye

concentration equal to 10-4

M, ZnO dosage 3.75 g.L-1

, light intensity equal

to 2.93 mW.cm-2

and temperature equal to 298.15 K, the effect of change

solution pH on decolorization percentage was studied in the range 2-12.

The results are listed in table 3-16 and plotted in figure 3-18. The

decolorization percent was found to be strongly dependent on pH of

solution because the reaction takes place on the surface of semiconductor.

The decolorization percentage of Bismarck brown R increases with the

increase of pH, exhibiting maximum decolorization at pH 9.

The kinetic results listed in table 3-17 and plotted in figure 3-19

show that the rate constant of reaction increases with the increase of the

solution pH up to the maximum level and then decreases.

79


values of pH by ZnO.

pH 2.1 4.5 6.7 9.0 12.0

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

15 0.976 0.295 0.265 0.189 0.224

30 0.916 0.177 0.137 0.056 0.089

45 0.892 0.161 0.108 0.032 0.061

60 0.857 0.142 0.089 0.021 0.045

Table 3-17: pH with rate constant by ZnO.


pH k / min-1

2.1 0.0026

4.5 0.0301

6.7 0.0482

9.0 0.0933

12.0 0.0501

80

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

pH=2.1

pH=4.5

pH=6.7

pH=9.0

pH=12

Figure 3-18: Effect of pH on photodecolorization of Bismarck brown

R by ZnO.

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 2 4 6 8 10 12 14

pH

k /

min

-1

Figure 3-19: Effect of initial pH of solution on rate constant by ZnO.

81

3-2-3-2 Effect of Solution pH by Different Types for TiO2



M, TiO2 dosage 1.75 g.L-1


to 2.93 mW.cm-2

and temperature equal to 298.15 K, the effect of change

solution pH on decolorization percentage was studied in the range 2-10.

The results are listed in tables 3-18, 3-19, 3-20, 3-21 and plotted in

figures 3-20, 3-21, 3-22, 3-23 for TiO2 (DegussaP25), TiO2

(HombikatUV100), TiO2 (MillenniumPC105), TiO2 (Koronose2073)

respectively. It was observed that the decolorization percentage strongly

depends on pH of solution because the reaction takes place on the surface

of semiconductor. The decolorization percentage of Bismarck brown R

increases with the increase of pH, exhibiting maximum decolorization at

pH that is equal to 6.61, 6.54, 6.75, 6.63 for TiO2 (DegussaP25), TiO2

(HombikatUV100), TiO2 (MillenniumPC105), TiO2 (Koronose2073)

respectively.

The kinetic results show that the rate constant of reaction increases

with increase of the solution pH up to a maximum level and then

decreases. This is listed in table 3-22 and plotted in figure 3-24.

82


values of pH by TiO2 Degussa P25.

pH 2.25 4.54 6.61 7.56 9.05

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

10 0.886 0.652 0.356 0.481 0.521

20 0.781 0.453 0.145 0.209 0.286

30 0.705 0.307 0.058 0.099 0.161

40 0.611 0.203 0.024 0.049 0.095

50 0.546 0.138 0.0093 0.021 0.046

60 0.486 0.094 0.0039 0.0099 0.028


values of pH by TiO2 Hombikat UV100.

pH 2.22 4.54 6.54 7.50 9.23

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

10 0.903 0.837 0.478 0.565 0.651

20 0.822 0.704 0.242 0.343 0.392

30 0.756 0.589 0.133 0.201 0.263

40 0.694 0.489 0.065 0.112 0.154

50 0.638 0.411 0.034 0.066 0.102

60 0.581 0.336 0.014 0.041 0.063

83

Table 3-20: The change of C/C0 with irradiation time at different pH

values by TiO2 millennium PC105.

pH 2.53 4.54 6.75 7.65 9.00

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

10 0.899 0.761 0.431 0.565 0.834

20 0.833 0.552 0.184 0.343 0.706

30 0.754 0.434 0.077 0.201 0.609

40 0.692 0.317 0.037 0.112 0.521

50 0.629 0.241 0.017 0.066 0.443

60 0.574 0.183 0.007 0.041 0.379

Table 3-21: The change of C/C0 with irradiation time at different pH

values by TiO2 koronose 2073.

pH 2.21 4.54 6.63 7.52 9.00

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000

10 0.961 0.911 0.847 0.978 0.995

20 0.911 0.842 0.744 0.957 0.974

30 0.897 0.797 0.682 0.936 0.958

40 0.872 0.773 0.633 0.913 0.935

50 0.859 0.754 0.612 0.901 0.921

60 0.842 0.743 0.583 0.893 0.915

84

Table 3-22: pH with rate constant by different types of TiO2.

Type of catalyst

TiO2

Degussa P25

TiO2

Hombikat

UV100

TiO2

Millennium

PC105

TiO2

Koronose 2073

pH k/min-1

pH k/min-1

pH k/min-1

pH k/min-1

2.25 0.0120 2.22 0.0088 2.53 0.0091 2.2 0.0028

4.45 0.0391 4.54 0.0181 4.54 0.0282 4.5 0.0048

6.61 0.0912 6.54 0.0672 6.75 0.0810 6.6 0.0086

7.56 0.0770 7.50 0.0531 7.65 0.0533 7.5 0.0019

9.05 0.0593 9.23 0.0460 9.00 0.0154 9.00 0.0016

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

pH=2.25

pH=4.54

pH=6.61

pH=7.56

pH=9.05

Figure 3-20: Effect pH on photodecolorization of Bismarck brown R

by TiO2 Degussa P25.

85

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

pH=2.22

pH=4.54

pH=6.54

pH=7.50

pH=9.23

Figure 3-21: Effect of pH on decolorization of Bismarck brown R by

TiO2 Hombikat UV100.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

pH=2.53

pH=4.54

pH=6.75

pH=7.65

pH=9.00


R by TiO2 Millennium PC105.

86

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0pH=2.2

pH=4.5

pH=6.6

pH=7.5

pH=9


R by TiO2 Koronose 2073.

0

0.02

0.04

0.06

0.08

0.1

0 1 2 3 4 5 6 7 8 9 10

pH

k /

min

-1

TiO2 (Degussa P25) TiO2 (Hombikat UV100)TiO2 (Mellinium PC105) TiO2 (Koronose 2073)Series5

Figure 3-24: Effect of solution pH on rate constant by different types

of TiO2.

87

3-2-4 Effect of Light Intensity

3-2-4-1 Effect of Light Intensity for ZnO

The dependence of the photocatalyst decolorization of Bismarck

brown R on the light intensity of the incident radiation was studied under

the determined experimental condition with initial concentration of

Bismarck brown R equal to 10-4

M, ZnO dosage equal to 3.75g.L-1

,

temperature equal to 298.15 K and solution pH equal to 4.54. Table 3-23

and figure 3-25 illustrate the change in the concentration of Bismarck

brown R as a function of illumination time under six different light

intensities of incident radiation. The results indicate that the

photocatalytic decolorization of Bismarck brown R increases with the

increase in light intensity, attaining maximum value at 3.52mW.cm-2.

The results listed in table 3-24 and plotted in figure 3-26 show that

the rate constant of reaction increases with the increase of the light

intensity.


light intensities by ZnO.

Light intensity

mW/cm2

0.55

1.05

1.41

1.97

2.93

3.52

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000 1.000

10 0.526 0.452 0.363 0.324 0.283 0.235

20 0.292 0.177 0.131 0.108 0.089 0.048

30 0.141 0.086 0.057 0.041 0.023 0.015

40 0.083 0.045 0.019 0.011 0.0075 0.0045

50 0.048 0.018 0.007 0.0033 0.0026 0.0011

60 0.023 0.008 0.004 0.0008 0.0006 0.0002

88

Table 3-24: Light intensity with rate constant by ZnO.


Light intensity mW/cm2 k / min

-1

0.00 0.000

0.55 0.061

1.05 0.078

1.41 0.100

1.97 0.116

2.93 0.122

3.52 0.134

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

0.55 mW/cm2

1.05 mW/cm2

1.41 mW/cm2

1.97 mW/cm2

2.93 mW/cm2

3.52 mW/cm2

Figure 3-25: Effect of light intensity on photodecolorization efficiency

by ZnO.

89

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 0.5 1 1.5 2 2.5 3 3.5 4

Light intensity / mW.cm-2

k /

min

-1

Figure 3-26: Effect of initial light intensity on the rate constant by

ZnO.

3-2-4-2 Effect of Light Intensity by Different Types for TiO2

The dependence of the photocatalytic decolorization of Bismarck

brown R on the light intensity of the incident radiation was studied under

the determined experimental condition with initial concentration of

Bismarck brown R equal to 10-4

M, ZnO dosage equal to 3.75g.L-1

,

temperature equal to 298.15 K and solution pH equal to 4.54. Tables 3-

25, 3-26, 3-27, 3-28 and Figures 3-27, 3-28, 3-29, 3-30 for TiO2

(DegussaP25), TiO2 (HombikatUV100), TiO2 (MillenniumPC105), TiO2

(Koronose2073) respectively, illustrate the change in the concentration of

Bismarck brown R as a function of illumination time under six different

light intensities of incident radiation. The results indicate that the

photocatalytic decolorization of Bismarck brown R increase with the

increase in light intensity, attaining maximum value at 3.52mW.cm-2

.

The table 3-29 and figure 3-31 shows that the rate constant of reaction

increases with increase of the light intensity.

90


light intensities by TiO2 Degussa P25.

Light intensity

mW/cm2

0.55

1.05

1.41

1.93

2.97

3.52

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000 1.000

10 0.945 0.902 0.881 0.809 0.712 0.637

20 0.875 0.814 0.769 0.652 0.503 0.411

30 0.797 0.723 0.681 0.527 0.367 0.271

40 0.745 0.658 0.605 0.405 0.244 0.178

50 0.676 0.578 0.521 0.338 0.168 0.112

60 0.613 0.517 0.458 0.266 0.124 0.075


light intensities by TiO2 Hombikat UV100.

Light intensity

mW/cm2

0.55

1.05

1.41

1.97

2.93

3.52

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000 1.000

10 0.914 0.903 0.889 0.864 0.837 0.812

20 0.834 0.801 0.781 0.729 0.704 0.665

30 0.756 0.723 0.684 0.624 0.589 0.551

40 0.684 0.658 0.618 0.532 0.489 0.453

50 0.622 0.589 0.538 0.461 0.411 0.381

60 0.575 0.525 0.475 0.382 0.336 0.313

91


light intensities by TiO2 millennium PC 105.

Light intensity

mW/cm2

0.55

1.05

1.41

1.93

2.97

3.52

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000 1.000

10 0.976 0.922 0.887 0.836 0.781 0.708

20 0.942 0.843 0.801 0.696 0.612 0.535

30 0.904 0.795 0.715 0.582 0.474 0.403

40 0.881 0.761 0.671 0.514 0.397 0.303

50 0.847 0.714 0.635 0.465 0.311 0.213

60 0.811 0.691 0.602 0.403 0.243 0.156


light intensities by TiO2 Koronose 2073.

Light intensity

mW/cm2

0.55

1.05

1.41

1.93

2.97

3.52

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000 1.000 1.000

10 0.998 0.978 0.965 0.935 0.911 0.874

20 0.965 0.936 0.905 0.878 0.842 0.805

30 0.919 0.896 0.869 0.833 0.797 0.758

40 0.897 0.876 0.834 0.805 0.773 0.732

50 0.879 0.854 0.819 0.789 0.754 0.713

60 0.863 0.821 0.801 0.774 0.743 0.689

92

Table 3-29: Light intensity with rate constant by different types of

TiO2.

Type of

catalyst

TiO2

Degussa

P25

TiO2

Hombikat

UV100

TiO2

Millennium

PC105

TiO2

Koronose

2073

Light

intensity

mW/cm2

k min-1

0 0 0 0 0

0.55 0.008 0.007 0.004 0.002

1.05 0.015 0.011 0.009 0.0033

1.41 0.018 0.013 0.01 0.0038

1.97 0.028 0.019 0.015 0.0042

2.93 0.035 0.023 0.018 0.0048

3.52 0.038 0.025 0.019 0.0051

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

0.55 mW/cm2

1.05 mW/cm2

1.41 mW/cm2

1.93 mW/cm2

2.97 mW/cm2

3.52 mW/cm2


by TiO2 Degussa P25.

93

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

00.55 mW/cm2

1.05 mW/cm2

1.41 mW/cm2

1.97 mW/cm2

2.93 mW/cm2

3.52 mW/cm2


by TiO2 Hombikat UV100.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

0

0.55 mW/cm2

1.05 mW/cm2

1.41 mW/cm2

1.93 mW/cm2

2.97 mW/cm2

3.52 mW/cm2


by TiO2 Millennium PC 105.

94

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time / min

C/C

00.55 mW/cm2

1.05 mW/cm2

1.41 mW/cm2

1.93 mW/cm2

2.97 mW/cm2

3.52 mW/cm2


by TiO2 Koronose 2073.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0 0.5 1 1.5 2 2.5 3 3.5 4

Light intensity / mW.cm-2

k /

min

-1

TiO2 (Degussa P25) TiO2 (Hombikat UV100)

TiO2 (Millenium PC105) TiO2 (Koronose 2073)

Figure 3-31: Effect of initial light intensity on rate constant by

different types of TiO2.

95

3-2-5 Effect of Temperature

3-2-5-1 Effect of Temperature for ZnO





to 2.93 mW.cm-2

and solution pH equal to 4.54, the effect of temperature

on the photocatalytic activity of ZnO was studied in the range 285.15-

301.15 K. The results indicate that the decolorization efficiency of

Bismarck brown R increases with increase of temperature. The results are

listed in table 3-30 and plotted in figure 3-32. Arrhenius relationship is

plotted in figure 3-33 to calculate the activation energy of the reaction.

The activation energy of 24±1 kJ.mol-1

for photocatalytic decolorization

efficiency of Bismarck brown R was calculated.


temperatures of ZnO.

Temperature K 285.15 290.15 295.15 301.15

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000

5 0.819 0.797 0.775 0.684

10 0.656 0.601 0.564 0.488

15 0.537 0.456 0.392 0.332

30 0.271 0.195 0.158 0.122

45 0.143 0.086 0.063 0.044

96

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50

Time / min

C/C

0

T= 285.15K

T= 290.15K

T=295.15K

T=301.15 K

Figure 3-32: Effect of temperature on photodecolorization of

Bismarck brown R by using ZnO.

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

3.3 3.35 3.4 3.45 3.5 3.55

1000 K/T

lnk

Figure 3-33: Arrhenius plot by ZnO.

97

3-2-5-2 Effect of Temperature by Different Types for TiO2



M, TiO2 dosage 1.75 g.L-1


to 2.93 mW.cm-2

and solution pH equal to 4.54, the effect of temperature

on the photocatalytic activity of different types of TiO2 was studied in the

range 286.15-301.15 K. The results are listed in tables 3-31, 3-23, 3-33,

3-34 and plotted in figures 3-34, 3-35, 3-36, 3-37 for TiO2 (DegussaP25),

TiO2 (HombikatUV100), TiO2 (MillenniumPC105), TiO2 (Koronose2073)

respectively. The results indicate that the decolorization efficiency of

Bismarck brown R increases with the increase temperature. Arrhenius

relationship is plotted in figure 3-38 to calculate the activation energy of

the reaction by different types of TiO2. The activation energy was found

equal to 14 ±1, 16 ±1, 21 ±1, 22 ±1 kJ.mol-1

for TiO2 (Degussa P25),

TiO2 (Hombikat UV100), TiO2 (Millennium PC105), and TiO2 (Koronose

2073) respectively.


temperatures of TiO2 Degussa P25.

Temperature K 286.15 291.15 296.15 301.15

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000

10 0.694 0.664 0.642 0.621

15 0.583 0.557 0.533 0.482

30 0.357 0.329 0.287 0.234

45 0.206 0.181 0.153 0.122

98


temperatures of TiO2 Hombikat UV100.

Temperature K 286.15 291.15 296.15 301.15

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000

5 0.965 0.953 0.949 0.934

10 0.933 0.913 0.904 0.891

15 0.891 0.876 0.856 0.836

30 0.802 0.771 0.733 0.708

45 0.721 0.683 0.638 0.597


temperatures of TiO2 Millennium PC105.

Temperature K 286.15 291.15 296.15 301.15

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000

5 0.986 0.957 0.936 0.922

10 0.949 0.916 0.901 0.873

15 0.913 0.876 0.861 0.822

30 0.831 0.775 0.727 0.684

45 0.729 0.678 0.626 0.576

99


temperatures of TiO2 Koronose 2073.

Temperature K 286.15 291.15 296.15 301.15

Irradiation

time/min

C/C0

0 1.000 1.000 1.000 1.000

5 0.852 0.825 0.781 0.744

10 0.717 0.683 0.632 0.583

15 0.622 0.578 0.514 0.462

30 0.389 0.354 0.287 0.218

45 0.239 0.199 0.151 0.101

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50

Time / min

C/C

0

286.15 K

291.15 K

296.15 K

301.15 K


Bismarck brown R by using TiO2 Degussa P25.

100

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50

Time / min

C/C

0T=286.15K

T=291.15K

T=296.15K

T=301.15K


Bismarck brown R by using TiO2 Hombikat UV100.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50

Time / min

C/C

0

T= 286.15K

T=291.15K

T= 296.15K

T= 301.15K


Bismarck brown R by using TiO2 millennium PC105.

101

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50

Time / min

C/C

0286.15 K

291.15 K

296.15 K

301.15 K


Bismarck brown R by using TiO2 Koronose 2073.

-6

-5

-4

-3

-2

-1

0

3.3 3.35 3.4 3.45 3.5 3.551000K/T

lnk

TiO2 (Degussa P25) TiO2 (Hombikat UV100)TiO2 (Mellinium PC105) TiO2 (Koronose 2073)Series6 Linear (TiO2 (Degussa P25))Linear (TiO2 (Koronose 2073)) Linear (TiO2 (Hombikat UV100))Linear (TiO2 (Mellinium PC105))

Figure 3-38: Arrhenius plot by different types of TiO2.

102

3-2-6 Effect of Current Gas

3-2-6-1 Effect of Current Gas for ZnO

The effect of the type current gas, oxygen and nitrogen gas was

discussed under the experimental condition initial dye concentration

equal to 10-4


, light intensity equal to 2.93

mW.cm-2

and solution pH equal to 4.54. The results are listed in table 3-

35 and plotted in figure 3-39. The results indicate that the maximum

decolorization efficiency is equal to 97.9 and 11.7 when oxygen and

nitrogen gases are used respectively.

Table 3-35: Effect of type currant gas on photodecolorization of

Bismarck brown R by ZnO.

Type of gas ZnO / N2 ZnO / O2

Irradiation time/min C/C0

0 1.000 1.000

10 0.954 0.413

20 0.893 0.191

30 0.887 0.096

40 0.887 0.045

50 0.884 0.026

60 0.883 0.008

103

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time/min

C/C

0 ZnO/O2

ZnO/N2

Figure 3-39: Effect of type of gas on photodecolorization of Bismarck

brown R by ZnO.

3-2-6-1 Effect of Current Gas for TiO2

The effect of the type of the current gas, oxygen and nitrogen gas

was discussed under the experimental condition initial dye concentration

equal to 10-4

M, TiO2(Degussa P25) dosage 1.75 g.L-1

, light intensity

equal to 2.93 mW.cm-2

and solution pH equal to 4.54. The results are

listed in table 3-36 and plotted in figure 3-40. The results indicate that the

maximum decolorization efficiency is equal to 68.2 and 22.3 when

oxygen and nitrogen gases are used respectively.

104

Table 3-36: Effect of type currant gas on photodecolorization of

Bismarck brown R by TiO2 (Degussa P25).

Type of gas TiO2 / N2 TiO2 / O2

Irradiation time/min C/C0

0 1.000 1.000

10 0.931 0.652

20 0.851 0.453

30 0.791 0.307

40 0.783 0.203

50 0.778 0.138

60 0.777 0.094

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Time/min

C/C

0 TiO2/N2

TiO2/O2

Table 3-40: Effect of types currant gas on photodecolorization of

Bismarck brown R by TiO2 (Degussa P25).

105

3-3- Mineralization of Bismarck Brown R

3-3-1 Mineralization of Bismarck Brown R for ZnO

The TOC degradation% was calculated under the experimental

conditions, initial dye concentration is equal to 10-4

M, ZnO dosage 3.75

g.L-1

, light intensity is equal to 2.93 mW.cm-2

, solution pH is equal to

4.54 and temperature is equal to 298.15K. The results are listed in tables

3-37 and 3-38 and plotted in figures 3-41and 3-42. The results indicate

that photocatalytic decolorization of Bismarck brown R was faster than

the decrease of total organic carbon (TOC). These results also show that

the complete decolorazation was achieved after being exposed to less

than 60 minutes, while the decrease of total organic carbon was about

88% after the same period time of irradiation.

Table 3-37: TOC degradation% with irradiation time by ZnO


Irradiation time/min TOC degradation % ppm

0.0 0.00

10 33.29

20 54.56

30 74.65

40 85.07

50 86.73

60 87.74

106

Table 3-38: P.D.E with irradiation time for ZnO.

Type of catalyst Zinc oxide

Irradiation time/min P.D.E

0 0.00

10 35.87

20 73.10

30 82.43

40 88.54

50 97.80

60 99.40

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Time(min)

TO

C d

eg

rad

ati

on

%

Figure 3-41: Mineralization of Bismarck brown R by ZnO.

107

0

10

20

30

40

50

60

70

80

90

100

10 20 30 40 50 60

Time (min)

%

TOC degreadation % P.D.E

Figure 3-42: TOC degradation % and P.D.E for Bismarck brown R

by ZnO.

3-3-2 Mineralization of Bismarck Brown R by Different

Types for TiO2

The TOC degradation% was calculate under the experimental

conditions, initial dye concentration equal to 10-4

M, TiO2 dosage 1.75

g.L-1

, light intensity equal to 2.93 mW.cm-2

, solution pH equal to 4.54

and temperature equal to 298.15K. The results are listed in tables 3-39, 3-

40 and plotted in figures 3-43, 3-44, 3-45, 3-46, 3-47 for TiO2

(DegussaP25), TiO2 (HombikatUV100), TiO2 (MillenniumPC105), TiO2

(Koronose2073) respectively. The results indicate that photocatalytic

decolorization of Bismarck brown R was faster than the decrease of total

organic carbon (TOC). These results also show that the complete

decolorazation was achieved after less than 60 minutes of irradiation,

while the decrease of total organic carbon was about 72.79%, 62.74%,

50.01%, 47.05% for TiO2 (DegussaP25), TiO2 (HombikatUV100), TiO2

108

(MillenniumPC105), TiO2 (Koronose2073) respectively after the same

period time of irradiation.

Table 3-39: TOC degradation% with irradiation time at different

types of TiO2.

Type of

catalyst

Degussa

P25

Hombikat

UV100

Millennium

PC105

Koronose

2073

Irradiation

time/min

TOC degradation % ppm

0.0 0.00 0.00 0.00 0.00

10 30.05 26.72 21.81 20.02

20 52.23 43.52 35.87 31.54

30 63.64 50.11 40.91 38.12

40 66.25 54.91 45.45 41.58

50 69.28 59.73 48.43 45.09

60 72.79 62.74 50.01 47.05

Table 3-40: P.D.E with irradiation time of different types of TiO2.

Type of

catalyst

Degussa

P25

Hombikat

UV100

Millennium

PC105

Koronose

2073

Irradiation

time/min

P.D.E

0 0.00 0.00 0.00 0.00

10 34.80 28.91 24.32 24.10

20 54.70 44.82 39.66 38.85

30 69.31 56.67 43.11 41.31

40 79.73 68.32 51.13 42.72

50 86.20 75.96 58.90 49.64

60 90.62 81.70 66.40 59.70

109

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Time / min

TO

C d

eg

rad

ati

on

%

TiO2 Degussa P25

TiO2 Hombikat UV100

TiO2 Millinium PC105

TiO2 Koronose 2073

Figure 3-43: Mineralization of Bismarck brown R by different types

of TiO2.

0

10

20

30

40

50

60

70

80

90

100

10 20 30 40 50 60

Time (min)

%



by TiO2 (Degussa P25).

110

0

10

20

30

40

50

60

70

80

90

100

10 20 30 40 50 60

Time (min)

%



by TiO2 (Hombikat UV100).

0

10

20

30

40

50

60

70

80

90

100

10 20 30 40 50 60

Time (min)

%



by TiO2 (Millennium PC105).

111

0

10

20

30

40

50

60

70

80

90

100

10 20 30 40 50 60

Time (min)

%



by TiO2 (Koronose 2073).

3-4 Surface Area Measuring

The surface area was measured according to B.E.T method

depending on the adsorption and de adsorption of the nitrogen gas on the

active site of surface catalyst. The results are listed in table 3-41. The

surface area was measured and supplied from a company for different

types of catalyst used in this study. The results show that the surface area

of TiO2 (Millennium), TiO2 (Hombikat UV100), TiO2 (Koronose 2073),

TiO2 (Degussa P25) and ZnO equal to 285.386, 249.187, 220.987, 48.342

and 4.932 respectively.

112

Table 3-41: Surface area measuring for different types of catalyst

used in this study .

Type of catalyst Surface area

measuring

Surface area

standard

TiO2 DegussaP25 48.342 50

TiO2 HombikateUV100 249.187 250

TiO2 MillenniumPC105 285.386 287

TiO2 Koronose2073 220.987 223

Zinc oxide 4.932 7.11

3-5 Simulation Study of Photocatalyst Decolorization of

Bismarck Brown R

3-5-1 The Physical Properties of Hydroxyl Radical

Physical properties of the hydrogen peroxide have been studied by

6-31G**

level of the theory and semiempirical method. Number of atoms,

charge of atoms, bond length and type of basis set are the physical

properties of the hydrogen peroxide. They are listed in figure 3-48.

A- Number of atoms. B- Atomic charge

113

C- Basis set D- Bond length

E- Bond type F- Ball and cylinder view

Figure 3-48: The physical properties of hydrogen peroxide calculated

by ab initio 6-31G**

.

The bond length of O—O bond in hydrogen peroxide is estimated

by PM3 of semiempirical method. The other methods are given a similar

values. These results are shown in table 3-42.

114

Table 3-42: Different methods used to calculate the bond length of

O—O bond in H2O2 molecule.

methods Bond length in A0(O—O)

PM3 1.482

AM1 1.309

6-31G

1.472

6-31G*

1.405

6-31G**

1.404

Figure 3-49 shows that the potential energy surface stability of O—

O bond in hydrogen peroxide is calculated at 6-31G**

. Potential energy

surface has been used to calculate the stability of O—O bond. They found

that -395861.503 kJ.mol-1

is the energy stability value of this bond.

Figure 3-49: Potential energy surface stability of O—O bond in

hydrogen peroxide calculated at 6-31G**

.

115

The physical properties of hydroxyl radical which is calculated at the

6-31G**

level of theory is listed in figure 3-50. These results show that

the electrostatic potential in two and three dimensions refers to the

reactivity of molecule, the red color refer to the region reach of the

electrons or the region for localized to the electrons whereas the green

region appears to be the poor of electrons. This means that the hydroxyl

radical is attached with Bismarck brown R from the oxygen atom(165)

.

A- Ball and cylinder view. F- Electrostatic potential in 2D.

G- Electrostatic potential in 3D.

Figure 3-50: Physical properties of hydroxyl radical calculation at 6-

31G**

level of the theory.

116

3-5-2 Optimizing Structure of Bismarck Brown R

To understand the active site of reaction in Bismarck brown R,

molecule must optimize real structure. The result is illustrated in table 3-

43. This result shows that the accuracy of the calculated results depends

on the type of calculations, since the methods depend on the number of

atoms per one molecule. Ab initio and semiempirical methods are used

for 12 and 36 atoms respectively(166)

. The result shows that the calculated

energy by 3-21G is equal to -565429 kJ.mol-1

. The other calculation

bending energy, electronic energy, CI energy, heat of formation and

nuclear repulsion energy appear to have the same effect on the structure

of Bismarck brown R. The heat of formation calculated by PM3 of

semiempirical method is given the minimum value equal to 317.599

kJ.mol-1

. The binding energy which also results from the separated

practical from the system shows that the minimum value given by PM3

method is equal to -24390 kJ.mol-1

.

Table 3-43: Energetic properties of Bismarck brown R calculated by

semiempirical and ab initio methods.

method Total

energy

kJ.mol-1

Binding

energy

kJ.mol-1

Electronic

energy

kJ.mol-1

CI

energy

kJ.mol-1

Heat of

formation

kJ.mol-1

MNDO -522827 -24293 -3869524 -9.853 414.216

AM1 -525770 -24317 -4048914 -7.694 389.848

PM3 -465049 -24390 -3961990 -5.727 317.599

STO-3G -4132847 ------- 5758293 ------- --------

3-21G -5654265 ------- 5646587 ------ -------

117

3-5-3 Chemical Properties of Bismarck Brown R

Chemical properties of Bismarck brown R calculated at 3-21G level

of theory are shown in figure 3-51. Estimation of the probable active site

for the photoreaction can be achieved according to the orientation of

atomic charge and electrostatic potential of Bismarck brown R molecule.

B- Number of atoms. A-Basis set.

D- Bond length. C- Charge of atoms.

118

F- Electrostatic potential in 2D. E- Ball and cylindrical view.

Figure 3-51: physical properties of Bismarck brown R calculated at

3-21G level of theory.

3-5-4 Chemical Reactivity of Bismarck Brown R

Table 3-44 shows the properties of main bond in Bismarck brown

R. The N8—N9 and N16—N17 bond are more stable than the other

bonds, according to calculations of bond length and bond order. This

means that low probability participates in the photoreaction. The bond

angles of the N8—N9—C10 and N16—N17—C18 are equal to 114.048o

and 114.652o respectively. This bond angle is lower than the angle

between the C7—N8—N9 and C12—N17—C18. This means the attack

of the hydroxyl is radical to the N8—N9—C10 while N16—N17—C18

are lower than the other bonds.

Potential energy surface and bond angle torsion are illustrated in

figures 3-52 which indicate the main bond in Bismarck brown R. From

the potential energy and bond torsion the N9—C10 bond and N16—N17

bond are more stable than C7—N8, C12—N16 and N17—C18 bond.

This bond breaks at the lowest energy value than the other bond.

119

Table 3-44: The properties of main bonds in Bismarck brown R

calculated at 3-21G level of theory.

Angle of

bond

Bond Length of

bond A

bond

order

Bond

117.802 C7—N8—N9 1.364 1 C7—N8

114.048 N8—N9—C10 1.355 2 N8—N9

117.911 C12—N16—N17 1.381 1 N9—C10

114.652 N16—N17—C18 1.379 1 C12—N16

1.342 2 N16—N17

1.375 1 N17—C18

B- N8—N9 bond. A- C7---N8 bond.

D- C12—C16 bond. C- N9---C10 bond.

F- N17---C18 bond. E-N16---N17 bond.

120

B- N8—N9—C10 bond. A- C7—N8—N9 bond.

D- N16—N17—C18 bond. C- C12—N16—N17 bond.

Figure 3-52: The potential energy and bond torsion of main bond in

Bismarck brown R calculate at PM3 semi-empirical method.

3-5-5 Types of Reactants and Products Molecules

Figure 3-53 represents the fifty one chemical structures that are

predicated in the simulation process of decolorization reaction. All

structures have been optimized through PM3 method to give the stable

sterio geometry structure according to the lowest value of potential

energy.

STR.1 STR.2 STR.3

121

STR.4 STR.5 STR.6

STR.7 STR.8 STR.9

STR.10 STR.11 STR.12


122




123





124





125


Figure 3-53: Geometry optimization of chemical structures for

photodecolorization reaction of Bismarck brown R calculated by

PM3 method.

3-5-6 Transition State

There are several possibilities for transition state formation to the

photoreaction of Bismarck brown R depending upon the effective side

towards the attachment chemical species. Several atoms in Bismarck

brown R have affinity to accept the negative charge. That is manifest pear

on the attached most chemical species like OH• or O2

•-. The first step to

cleavage depends on the transition state with high probability to give up

stable products with low energy barrier compared with other probable

transition states.

3-5-6-1 Examination of Transition State Without Catalyst

Hydroxyl radical is attached to the Bismarck brown R at active site

with different probable confirmation. Figures 3-54 stick view for fourteen

transition states of Bismarck brown R with hydroxyl radical without

catalyst calculated at PM3 method. All the transition state structures have

been studied through optimizing their geometry and calculating their

126

vibration spectra. Tables 3-45 show that the activation energy for the

forward reaction is less than the activation energy for the backward

reaction, this means the reaction tends to the products.

TS2 TS1

TS4 TS3

TS6 TS5

127

TS8 TS7

TS10 TS9

TS12 TS11

TS14 TS13

Figure 3-54: Stick view of transition state calculate at PM3 for the

reaction OH● with Bismarck brown R in vacuum.

128

Table 3-45: The energy of forward , backward reaction, zero point

energy (ZPE), frequency, and heat of formation (Hf) of transition

state of Bismarck brown R without catalyst.

TS Ea of

forward

reaction

kJ.mol-1

Ea of

backward

reaction

kJ.mol-1

ZPE

kJ.mol-1

Imaginary

frequency

Heat of

formation

kJ.mol-1

1 158758 159051 1177.24 - 652.2061

2 158792 158072 1194.95 - 686.6153

3 158654 158651 1176.867 - 548.5893

4 158631 158684 1178.926 - 524.9414

5 158655 158904 1183.382 - 549.422

6 158662 158667 272.9432 - 556.7691

7 158671 158672 1176.445 - 565.3295

8 158564 158548 1209.184 - 458.1229

9 158754 158771 1132.621 - 647.8255

10 158319 158925 1213.653 - 210.338

11 158772 158742 1067.757 - 666.0468

12 158718 158555 1166.88 - 612.797

13 158782 158782 1172.474 - 675.8708

14 158712 158713 1190.047 - 606.3453

129

3-5-6-2 Examination of Transition State With Catalyst

Bismarck brown R can react with hydroxyl radical in the presence

of (TiO2) catalyst only giving the transition state with activation energy

equal to 2539371 kJ.mol-1

for forward reaction and 2539637 kJ.mol-1

for

backward reaction. The results are shown in figures 3-55. These results

show that the activation energy for the reaction is very high. This means

that the occurrence of the reaction is very difficult.

Transition state forward reaction. Transition state backward reaction.

Figure 3-55: Transition state for Bismarck brown R with TiO2

calculated at PM3 level of theory.

3-5-6-3 Examination of Transition State With Catalyst and

Hydroxyl Radical

Bismarck brown R can react with hydroxyl radical in the presence

of TiO2 catalyst in different suggested transition states. Figures 3-56

show ten transition states calculated at PM3 method with their

frequencies. Tables 3-46 show that the energetic properties for suggested

transition states with hydroxyl are radical in presence TiO2 calculated at

PM3 method. Tables 3-56 show that the activation energy for the forward

reaction is less than the activation energy for backward reaction. This

130

means that the reaction tends to the products. The heat formation shows

that the TS1,TS2,TS3, and TS4 have positive value. This means that this

transition state releases the energy as heat to form it. The transition state

calculation shows that the TS5 and TS9 have the minimum activation

energy equal to -0.79496 and -196.276 kJ.mol-1

, respectively. This means

that this reaction occurs spontaneously. Zero point energy for the TS5

equal to 1220.326 kJ.mol-1

is higher than the other transition state. This

means the energy needs to be lowered to give the product.

TS2 TS1

TS4 TS3

TS6 TS5

131

TS8 TS7

TS10 TS9

Figure 3-56: Transition state of Bismarck brown R that’s produced

by hydroxyl radical and TiO2 calculated at PM3 method.

132

Table 3-46: Energetic properties for suggested transition state with

hydroxyl radical in presence TiO2 calculated at PM3 method.

TS Ea for

forward

reaction

kJ.mol-1

Ea for

backward

reaction

kJ.mol-1

ZPE

kJ.mol-1

Imaginary

frequency

Heat of

formation

Hf kJ.mol-1

1 179.025 646.695 981.876 - 238.4336

2 121.252 144.992 1037.113 - 191.941

3 528.079 633.993 1159.721 - 6.54796

4 612.725 1909.983 1173.721 - 91.19446

5 -0.794 255.416 1220.326 - -403.898

6 151.1721 165.452 843.5028 - -199.861

7 355.225 370.945 1181.352 - -88.228

8 466.859 487.795 1190.829 - -751.375

9 -196.276 375.836 1193.808 - -444.596

10 342.803 414.349 1194.754 - -788.174

3-5-6-4 Examination Transition State Using Superoxide

Anion and Catalyst

Figures 3-57 shows the stick view of the suggested transition state

of Bismarck brown R with super oxide anion and TiO2 calculated at PM3

method. All the transition state structures have been studied through

optimizing their geometry and calculating their frequencies. Table 3-57

shows that the activation energy for the forward reaction is less than the

activation energy for backward reaction. This means that the reaction

tends to the products. Heat formation shows that the TS4,TS5,TS9, and

TS10 have positive value. This means that this transition state needs

energy to form it, but the TS1, TS2, TS3, TS6, TS7, TS8, TS10 and TS12

have a negative value. These transition states release the energy as heat to

133

form the fundamental elements. According to transition state calculation,

the TS6 has the lowest activation energy value forming the highest value

of zero point energy to produce their products in a faster rate than the

other probable transition state.

TS1 TS2

TS3 TS4

134

TS5 TS6

TS7 TS8

TS9 TS10

135

TS11 TS12

Figure 3-57: Transition state of Bismarck brown R with superoxide

anion in presence TiO2 calculated at PM3 method.

Table 3-47: Energetic probabilities of transition state using super

oxide anion in presence of TiO2 calculated at PM3 method.

TS Ea for

forward

reaction

kJ.mol-1

Ea for

backward

reaction

kJ.mol-1

ZPE

kJ.mol-1

Imaginary

frequency

Heat of

formation

Hf kJ.mol-1

1 154.515 309.544 1011.227 - -167.557

2 183.426 194.639 711.7151 - -138.633

3 274.641 278.123 970.3324 - -47.4215

4 428.713 436.663 1056.77 - 106.6543

5 441.755 445.018 704.3513 - 119.6708

6 82.675 90.571 1026.967 - -239.375

7 136.063 141.260 1178.947 - -514.615

8 591.182 610.332 1165.512 - -59.5258

9 803.503 815.432 1140.349 - 152.8248

10 629.210 631.754 1172.599 - -21.4848

11 510.393 517.447 989.0976 - 92.90572

12 828.574 833.047 1174.411 - -264.63

136

Table 3-48 represents a comparison among the high probable

transition states for reaction of Bismarck brown R for different paths. The

results show that the TS5 represents the highest probable pathway to give

up the first cleavage step because the activation energy is the lowest

value. On the other hand, the zero point energy is of the highest value and

lowest enthalpy formation than the other states.

Table 3-48: Comparison between different types of reactions.

Transition

state

Activation

energy

kJ.mol-1

Zero point

energy

kJ. mol-1

Imaginary

frequency

Heat of

formation

kJ. mol-1

TS10 158319.518 1213.652 - 210.338

TS5 -0.794 1220.326 - -403.898

TS6 82.675 1026.966 - -239.375

Figures 3-58, 3-59, 3-60 show the reaction coordinate for Bismarck

brown R different transition states with energy activation in different

conditions, reaction in the presence of hydroxyl radical only, reaction in

the presence of hydroxyl radical and catalyst, and the reaction in the

presence of superoxide anion and catalyst.

137

37820

37840

37860

37880

37900

37920

37940

37960

0 2 4 6 8 10 12 14 16

TS

Acti

vati

on

en

erg

y k

J/m

ol

Figure 3-58: Reaction coordinate of Bismarck brown R with

hydroxyl radical calculated at PM3 method.

-100

-50

0

50

100

150

200

0 2 4 6 8 10 12

TSActi

vati

on

en

erg

y k

J/m

ol

Figure 3-59: Reaction coordinate of Bismarck brown R with

hydroxyl radical in presence catalyst calculated atPM3 method.

138

0

50

100

150

200

250

0 2 4 6 8 10 12 14

TS

Acti

vati

on

en

erg

y k

J/m

ol

Figure 3-60: Reaction coordinate of Bismarck brown R with super

oxide anion in presence catalyst calculated at PM3 method.

139

CHAPTER FOUR

DISCUSSION

140

DISCUSSION

4-1 Introductory Discussion

The photocatalytic decolorization of Bismarck brown on both ZnO

and TiO2 has been the focus of research at Babylon university

laboratory(167-169)

. It has been established that:

1. The simultaneous presence of semiconductor, oxygen and UV

radiation was essential for sustained photocatalytic reaction.

2. The activity of photodecolorization full in the sequence



3. The activation energy for photodecolorization of Bismarck brown

G on zinc oxide over the temperature range of 278.15-293.15 K

was equal to 32 ± 1 kJ mol-1(167)

, while the activation energy over

the temperature range 285.15-301.15 K was equal to 24 ±1 kJ.mol-1

for ZnO and 14, 16, 21, 22 ±1 kJ.mol-1

for TiO2 (Degussa P25),

TiO2 (Hombikat UV100), TiO2 (Millennium PC105), and TiO2

(Koronose 2073) respectively.

The net activation energy was therefore associated with the

solid state properties of ZnO or titanium dioxide rather than with

the photocatalyst reaction.

4-2 Preliminary Experiments

The results in section 3-1 show that the photodecolorization

efficiency requires the simultaneous presence of semiconductor, oxygen

and UV(A) radiation for decolorization to increase linearly with

irradiation time. However, when the reaction mixture was irradiated in

the presence of nitrogen atmosphere, decolorization was extremely slow

141

and ceased entirely after an hour of irradiation when the photocatalytic

decolorization was only 11.7% in the case of ZnO and 22.3% in the case

of TiO2 (Degussa P25). Since the suspension of titanium dioxide became

gray-blue in such experiments, it was believed that photooxidation

involved lattice oxygen in addition to chemisorbed oxygen with the

associated reduction of Ti4+

to Ti3+

(185)

.

Figure 3-1 shows that no dark reaction was observed in the presence

of either oxygen or nitrogen. It follows that decolorization on ZnO or

TiO2 is a photocatalytic reaction.

4-3 Effect of Different Parameters on Photocatalyst

Decolorization of Bismarck Brown R

4-3-1 Effect of Photocatalyst Concentration

The results listed in tables 3-3 to 3-8 and plotted in figures 3-3 to 3-

10 show that the photodecolorization efficiency increased with the

increase of the concentration of catalyst up to a maximum value and

remained constant and then decreased with the increase of catalyst

concentration. These results are in agreement with other previous

observations(168-169)

. This behavior can be explained on the basis that on

increasing catalyst concentration the active site on the catalyst surface

increases. The increase of the catalyst concentration above the maximum

level will increase the number of particle suspended in aqueous solution

of Bismarck brown R (increase the turbidity of the suspension) and as a

result there will be a decrease in the penetration of irradiation and, hence,

the photoactivated volume of suspension decreases(170-171)

.

Figures 3-6 and 3-10 show that the relationship between the rate

constant and catalyst concentration is not linear as it was expected due to

the fact that the number of photon absorbed and the number of dye

142

molecule adsorbed on the active site on the surface catalyst increase

linearity with the increase of the number of free particles. The deviation

from the linearity is due to aggregation the excess of particles leading to

screening effect(172)

.

4-3-2 Effect of Initial Dye Concentration

The results illustrated in tables 3-9 to 3-15 and plotted in figures 3-

11 to 3-17 show that when the dye concentration decreases, the

decolorization of dye increases. This behavior is due to the decrease of

the concentration OH- adsorbed on catalyst surface with the increase of

dye concentration. The competitions between OH- to adsorb on active site

of catalyst will be in the favor of dye ions when the dye concentration

increases. As a result, OH● formation rate decreases and then the rate

decolorization decreases.

Tables 3-10 and 3-15 and figures 3-12 and 3-17 show that the

inverse proportionality of rate constant of decolorization reaction with

dye concentration is due to the increase to reduction of light intensity

which reaches the catalyst surface and consequently photon absorption on

surface of catalyst is reduced with the increasing the dye

concentration(173)

. Also this behavior is explained according to the

Lambert-Beer law. When the dye concentration increases, the path length

of photon entering the solution is reduced and as a result, the rate of

decolorization of dye decreases. The increase of the dye concentration

leads to shield the entering photons in solution and as a result the rate of

decolorization decreases due to the reduction in hydroxyl radical

formation(174)

.

143

4-3-3 Effect of Solution pH

The pH of solution is a complex parameter because it is related to

the ionization state of the surface of catalyst as shown in the following

equations(175-176)

:

2TiOHHTiOH 4-1

OHTiOOHTiOH 2 4-2

2ZnOHHZnOH 4-3

OHZnOOHZnOH 2 4-4

The decolorization of Bismarck brown R was found to be strongly

dependent on the pH of solution because the reaction of heterogeneous

photocatalytic takes place on the surface of semiconductors. The

decolorization of dye increases with the increase of the pH of solution

until to 9.0, 6.61, 6.54, 6.75, and 6.63 for ZnO, TiO2 (Degussa P25), TiO2

(Hombikat UV100), TiO2 (Millennium PC105), and TiO2 (Koronose

2073), are listed in tables 3-16 to 3-22 and plotted in figures 3-18 to 3-24

respectively. This behavior could be explained on the basis of zero point

charge (ZPC)(177)

. The zero point charge is equal to 9.00 for ZnO and 6.25

for TiO2 (Degussa P25)(178)

. With the increase of the pH of solution the

surface of catalyst will be negatively charged by adsorbed hydroxyl ions.

The presence of large quantities of adsorbed OH- ions on the surface of

catalyst favor the formation of OH• radical, however, if pH is lower than

ZPC, the hydroxyl ions adsorbed on the surface will be decreased and,

therefore, increase the hydrogen ions adsorbed on the surface and the

surface will be positive charge. The two medium acidic and basic leave

an inverse impact on the photodecolorization efficiency because of the

144

decrease of the formation of the hydroxyl radical. The decolorization of

Bismarck brown R decreases dramatically at strong acid media (pH=2.1)

for ZnO. This could be explained due to photocorrosion of ZnO as shown

in the follow equations(179)

.

VBCB

h heZnO 4-5

2

2 2/12 OZnhZnO VB 4-6

The results in tables 3-17 and 3-22 indicate that the rate constant of

decolorization of Bismarck brown R increases with the increase of the pH

of solution until the same value of zero point charges of different types of

catalyst and then decreases.

4-3-4 Effect of Light Intensity

The results in section 3-2-4 show that the decolorization of

Bismarck brown R increases with the increase of the light intensity

reaching the maximum value at 3.52 mW/cm2. The increase of light

intensity lead to the increase of the number of electron – hole pairs and

increases the decolorization efficiency of Bismarck brown R.

The results also show that the effect of light intensity on rate

constant of photocatalyst decolorization of Bismarck brown R increase of

the light intensity leading to the increase of rate constant. These results

which are listed in tables 3-24 and 3-29 and plotted in figures 3-26 and 3-

31, are in a good agreement with the findings of Lim and Kim(180)

. The

authors reported that at light intensity more than one sun equivalent (1-2

mW.cm-2

), the increase of rate reaction is proportional with square root of

light intensity. However at light intensity less than one sun equivalent, the

increase of rate reaction is proportional directly with the light intensity.

This concludes that with the increase of light intensity, the recombination

rate of photogeneration electron-hole pairs increase, preventing the

145

generation rate of OH● radical to reach the expected linearly proportional

value. The rate constant is proportional to the generation of OH● radicals

on catalyst surface.

4-3-5 Effect of Temperature

The results listed in tables 3-30 to 3-34 and plotted in figures 3-32

to 3-38 show that the change of temperature indicates that the rate of

decolorization of Bismarck brown R increases with the increase of the

temperature. The rise of the temperature may lead to promote the

production of free radicals(181-182)

. The results indicate that the variation in

temperature within the range of 285.15 to 301.15K does not significantly

affect the photocatalyst decolorization of Bismarck brown R. These

results confirm those presented by previous authors(183)

. The effect of

temperature is explained as the variable with the smallest effect,

especially for a value near 323.15K where the limited stag is the

adsorption of the dye on the surface of catalyst. However, at a low

temperature the desorption of the products formed limits the reaction

because it is slower than the degradation on the surface and the

adsorption of the reactants on the surface of catalyst(184)

.

Figures 3-33 show the activation energy of decolorization on ZnO

similar to the other previous photocatalyst oxidation of different types of

alcohols on anatase and metalized anatase(185)

. The very small activation

energy in the photocatalytic reaction is the apparent activation energy Ea,

whereas the true activation energy Et is nil. The apparent activation

energy tends to the heat of adsorption of the product whereas desorption

of the final product from the surface of catalyst is the limiting step(186)

.

146

4-3-6 Effect of Current Gas

The results in section 3-2-6 show that the decolorization percentage

was extremely slow in the case of nitrogen gas. This results also indicate

that the TiO2 is more active than ZnO. The TiO2 (Degussa P25) which

becomes gray-blue in color may be attributed to the sharing of lattice

oxygen from the surface. This leads to the reduction of oxygen atoms at

the surface of catalyst which in turn leads to the reduction in the

efficiency of trapping of photoelectrons leading to the increase of the rate

of recombination reaction. The recombination of electron-hole pairs is

important in enhancing the performance of photocatalytic degradation.

Generally, oxygen is considered a common oxidizing agent which

plays an important role in the trapping of conduction band electrons and

increasing charge separation between electron and hole pair giving a high

activity for photocatalytic oxidation reaction.

4-4 Mineralization of Bismarck Brown R

The results listed in tables 3-37 to 3-40 and plotted in figures 3-41

to 3-47 show that the color degradation is faster than the decrease of total

organic carbon (TOC). These findings are in agreement with other

pervious ones(187-188)

. It is suggested that the low concentration of TOC in

the solution indicates that some byproducts are resistant to photocatalytic

degradation. The TOC in presence of different types of catalyst show that

the ZnO is more rapid than the other catalyst.

147

4-5 Comparison of the Reactivity of Catalysts

Table 4-1 show the comparison of the reactivity of different types

of catalyst.

Table 4-1: The change of P.D.E with irradiation time of different

types of catalyst.

Type of

catalyst

Zinc

oxide

Degussa

P25

Hombika

t UV100

Millenniu

m PC105

Koronos

e 2073

Irradiatio

n time/min

P.D.E

0 0.00 0.00 0.00 0.00 0.00

10 35.87 34.80 28.91 24.32 24.10

20 73.10 54.70 44.82 39.66 38.85

30 82.43 69.31 56.67 43.11 41.31

40 88.54 79.73 68.32 51.13 42.72

50 97.80 86.20 75.96 58.90 49.64

60 99.40 90.62 81.70 66.40 59.70

The photocatalytic decolorization of Bismarck brown R was

investigated in aqueous suspensions containing ZnO, TiO2 (DegussaP25),

TiO2 (HombikatUV100), TiO2 (MillenniumPC105), TiO2 (Koronose2073)

as a photocatalyst under different reaction condition. The results show

that the rate constant of decolorization of Bismarck brown R in the

presence of ZnO is more rapid than the other catalyst because of the small

band gap of ZnO. This means promoting the electrons from the valance

band to conduction band needs low energy.

TiO2 (Degussa P25) high photoreactivity is due to slow

recombination between electron and hole because the TiO2 (Degussa

148

P25) is composed of small nano-crystallites of rutile being dispersed with

anatase matrix (consist of 75% anatase and 25% rutile). The smaller band

gap of rutile catches the photons and leads to the generation of electron-

hole pairs. The electrons transfer from the rutile conduction band to

anatase conduction band. The recombination is inhibited leading to the

increase of the reactivity of catalyst(189-190)

.

TiO2 (Hombikat UV100) is more active than the other catalyst

(Millennium PC105 and Koronose 2073) due to the fact the specific

B.E.T surface area and the particle size 5nm compare to the Millennium

PC105 5-10nm(191)

.

The efficiency of these catalyst arrangement is as follows :



149

4-6 Simulation Study of Photocatalyst Decolorization of

Bismarck Brown R

Theoretical calculations have been carried out by ab initio and

semiempirical methods to investigate the initial step of photoreaction

using hydroxyl radical for Photocatalyst decolorization of Bismarck

brown R.

The chemical properties are very important to examine the reactive

sites in molecule and give the chemical reactivity of Bismarck brown R.

The reaction pathway depends on the type of intermediate formation

through the reaction, transition state and zero point energy giving the type

of product(192)

.

Hydroxyl radical and superoxide anion are reactive species formed

by an advance oxidation process in heterogeneous photocatalytic reaction

which is used as an initiator for sequences free radical reaction.

4-6-1 The physical Properties of Hydroxyl Radical

Hydroxyl radical has a single unpaired electron on oxygen atom. It

is produced by splitting the O—H bond in water molecule, or by the O—

O bond in the hydrogen peroxide.

The splitting of hydrogen peroxide molecule forms two hydroxyl

radicals OH●. This radical inters the photoreaction and leads to the

photodegradation of Bismarck brown R molecule.

The bond length has been studied by different methods because of

its importance in molecule. When the bond length is long, the required

energy for breaking this bond is low compared with short bonds. This

means it needs a larger energy(193)

. These results are shown in table 3-40.

150

The proposed reaction in gas phase of OH● producing from H2O2

molecule is as follows:

OHOH 222 4-7

The activation energy of this reaction equal to 189.610 kJ.mol-1

is

calculated at 6-31G**

level of theory according to the transition state

pathway. The value of energy equal to 465nm of UV-lamp is needed to

initiate this reaction. The physical properties of hydroxyl radical

calculated at the 6-31G**

level of theory are list in figure 3-71.

4-6-2 Optimizing Structure of Bismarck Brown R

Stable geometrical structure of molecule has a minimal total

energy(194)

. The AM1 provides heat of formation of molecule since it is

about 40% smaller than MNDO. The PM3 and AM1 are more accuracy

than MNDO(195)

.

151

4-6-3 Transition State

4-6-3-1 Examination of Transition State Without Catalyst

According to the results shown in table 3-45 and figure 3-54, the

transition state TS10 is the most probable state for initiating the step for

photodecolorization reaction(196)

.

Scheme 4-1 represents the first initiation step of

photodecolorization reaction through TS10.

Sch

eme 4

-1: su

gg

ested m

echa

nism

for first clea

va

ge step

Bism

arck

bro

wn

R w

ith O

H● w

itho

ut ca

taly

st in v

acu

um

.

152

4-6-3-2 Examination of Transition State with Catalyst and

Hydroxyl Radical

According to the results in table 3-46 and figures 3-56 the first

initiation step of decolorization of Bismarck brown R reacts with

hydroxyl radical in the presence of the catalyst passing from the TS5.

Scheme 4-2 represents the suggested mechanism.

Sch

eme 4

-2: S

ug

gest m

echa

nism

of th

e first cleava

ge step

of rea

ction

Bism

arck

bro

wn

R w

ith O

H● in

presen

ce the ca

taly

st.

153

4-6-3-3 Examination Transition State using Superoxide

Anion and Catalyst

The results shown in the above tables and figures show the first

initiation step of decolorization reaction of Bismarck brown R reaction

with superoxide anion in the presence of the catalyst passing through the

TS6 as shown in scheme 4-3.

Sch

eme 4

-3: su

gg

ested m

echa

nism

of th

e first cleav

ag

e step fo

r reactio

n th

e

Bism

arck

bro

wn

R w

ith su

pero

xid

e an

ion

in p

resence th

e cata

lyst.

154

CHAPTER FIFE

CONCLUSIONS

AND

RECOMMENDATIONS

155

CONCLUSIONS AND RECOMMENDATIONS

5-1 Conclusions

The enhancement of decolorization efficiency of Bismarck brown R

increasing masses of catalysts is attributed to the increase of the

availability of photocatalysts sites. Nevertheless, the decrease of catalytic

activity often the plateau region is related to a shielding effect of excess

partials occurred and resulted in a reduced performance.

The photocatalytic decolorization of Bismarck brown R using

different types of catalysts like photocatalyst strongly depends on the

amount of catalyst, dye concentration, pH of solution, light intensity and

type of current gas.

The photocatalytic process can be expressed by both, the pseudo

first order reaction kinetics and the Langmuir-Hinshelwood kinetic

model.

The phenomenon of increasing the photodecolorization efficiency

of Bismarck brown R with decreasing the concentration of solution is due

to the decrease of the concentration OH- adsorbed on catalyst surface.

The increasing of dye concentration increases the competitions between

OH- and dye to adsorb on active site of catalyst.

The photocatalyst decolorization efficiency of Bismarck brown R

increases with the increase of the pH of solution up to a maximum value

and then decreases. This behavior could be explained on the basis of zero

point charge (ZPC).

The decolorization of Bismarck brown R increases with the increase

of light intensity. Nevertheless, the increase of light intensity leads to the

increase of the number of electron–hole pair and, hence, increases the

decolorization efficiency of Bismarck brown R.

156

The temperature is the factor that has the smallest effect on the

photocatalytic decolorization of Bismarck brown R.

The controlled experimental indicates that the presence of UV light,

oxygen, and catalyst are essential for the effective destruction of

Bismarck brown R.

Photocatalytic decolorazation of Bismarck brown R is faster than

the decrease of total organic carbon (TOC).

The activation energy of hydrogen peroxide dissociation into two of

hydroxyl radicals is equal to 189.610 kJ.mol-1

. The activation energy for

react Bismarck brown R with catalyst is very high since it is equal to

2539371kJ.mol-1

. The reaction of Bismarck brown R with hydroxyl

radical in the presence of catalyst gives the initial cleavage step according

to activation energy, zero point energy and heat of formation.

157

5-2 Recommendations

1- The photodecolorization of Bismarck brown R by using different

types of catalyst from is a following pseudo-first order kinetic

according to Langmuir-Hinshelwood relationship. Calculations of

the rate of photocatalytic decolorization of Bismarck brown R and

the adsorption equilibrium constant (Kad) are very important.

2- Improve the Photoreactor design to join the output stream to

GC/MS measuring the intermediate concentration in each

irradiation time concomitantly.

3- The photocatalytic decolorization of Bismarck brown R was

studied by measuring the residual concentration of Bismarck

brown R and the total organic carbon concentration without

identification the intermediate. Study the suggested mechanism

required for detection and identification of intermediate.

4- The photocatalytic decolorization of Bismarck brown R depends

on the light intensity illustrating the importance of the inverse

effect of electron-hole pair recombination and radiation energy

loss. Improve the Photoreactor design to take that into account.

158

REFERENCES

1. A. Fujishima, and K. Honda, Nature, 1972, 37, 238.

2. J. Yu, J. C. Yu, M. K. Leung, W. Ho, and B. Cheng, J. Catal.

2003, 69, 217.

3. H. Zollinger, "Color Chemistry-Synthesis, Properties and

Application of Organic Dyes and Pigments". VCH publishers,

New York, 1987.

4. H. H. Locher, T. Leisinger and A. M. Cook, Biochemical

Journal, 1991, 274, 833.

5. C. Belver, R. Bellod. A. Fuerte, and M. Fernandez-Garcia., Appl.

Catal. B: environmental, 2006, 65, 301.

6. N. Daneshvar, H. Ashassi-Sorkhabi, and A. Tizpar, Sep. Purif.

Technol., 2003, 31, 153.

7. C. Hachem, F. Bocquillon, O. Zahraa, and M. Bouchy, Dyes

Pigments, 2001, 49, 117.

8. S. Malato, J. Blanco, J. Ca´eres, A.R. Ferna´ dez-Alba, A. Agu¨ ra,

and A. Rodrı´uez, Catal. Today, 2002, 76, 209.

9. Zhang Lide, and Mou Jimei, "Nanophase Material and

Nanostructure", Beijing Science Press, 2001, p140.

10. M. L. Saner and D. F. Ollis, J. Catal., 1996, 158, 570.

11. K. Hofstadler, R. Bauer, S. Novalie and G. Heisler, Environ. Sci.

Technol., 1994, 211, 670.

12. G. Marci, V. Augugliaro. M. J. Munoz, C. Martin, L. Palmisano,

V. Rives, M. Schiavello, R. J. Tilly, and A. M. Venezia, J. Phys.

Chem. B, 2001, 105, 1033.

13. L. A. Phillips and G. B. Raupp, J. Mol. Cat., 1992, 77, 297.

159

14. L. A. Dibble and G. B. Raupp, Environ. Sci Technol., 1992, 26,

492.

15. L. A. Dibble and G. B. Raupp, Catal. Lett., 1990, 4, 345.

16. J. Peral and D. F. Ollis, J. Catal., 1992, 136, 554.

17. M. R. Hoffmann, S. T. Martin, W. Choi and D. W. Bahnemarm,

Chem. Rev., 1995, 95, 69.

18. A. R. Khataee, H. Aleboyeh, and A. Aleboyeh, J. Experimental

Nanoscience, 2009, 4, 121.

19. H. LiX, L. Cheng, and H. Toug, Environ. Sci. Technol., 2003,

17, 3989.

20. Y. Peter and Y. Cardona, "Fundamentals of Semiconductors :

Physics and Materials Properties", Springer. ISBN 3-540-41323-5,

2004.

21. H. T. Grahn, "Introduction to Semiconductor Physics", world

scientific, Pub Co. 1999.

22. P. W. Atkins, "Physical Chemistry", 7th

Edition, Oxford

University presses Oxford 2002.

23. P. Nigam, I. M. Banat, D. Singh and R. Marchant, J.

Biochemistry, 1996, 31, 435.

24. S. Y. Huang, G. Schlichthorl, A. J. Nozik, M. Gratzel, and A. J.

Frank, J. Phys. Chem. B, 1997, 101, 2576.

25. L. B. Revtergardh, and M. Iangphasuk, Chemosphere, 1997, 35,

585.

26. C. Karunakan, and S. Senthivelon, Sol. Energy, 2005, 79, 505.

27. E. R. Carraway, A. J. Hoffman, and M. R. Hoffmann, Environ.

Sci. Technol., 1994, 28, 786.

28. A. Hagfeldt, and M. Gratzel, Chem. Rev., 1995, 95, 49.

29. M. A. Fox, and M. T. Dulay, Chem. Rev., 1993, 93, 341.

http://en.wikipedia.org/wiki/International_Standard_Book_Number

http://en.wikipedia.org/wiki/Special:BookSources/3-540-41323-5

160

30. M. W. Peterson, J. A. Turner, and A. J. Nozik, J. Phy. Chem.,

1991, 95, 665.

31. Y. Cho, and W. Choi, Environ. Sci. Technol., 2001, 35, 966.

32. W. Stum, "Chemistry of the Solid-Water Treatment Interface",

John Wiley and sons, New Yoke, USA, 1992.

33. H. O. Finklea, "Semiconductor Electrodes", ed. H.O. Finklea,

Elsevier, Amsterdam, 1988.

34. N. Greenwood, and A. Earnshaw, "Chemistry of the Elements",

Oxford, Pergamon, 1996.

35. M. Fujihira, Y. Satoh, and T. Osa, Bull. Chem. Soc. Jpn., 1982,

55, 666.

36. J. S. Kim, K. Itoh, and M. Murabayashi, Chemosphere, 1998, 36,

483.

37. N. Huang et al., J. Biomater. Appl., 1994, 8, 404.

38. B. Ohtani, Y. Ogawa, and S. Nishimoto, J. phys. Chem. B, 1997,

19, 3746.

39. S. Bakardjivea, J. Subart, V. Stengl, M. J. Dianez, and M.J. Saya,

Appl. Catal. B: Environ., 2005, 58, 193.

40. M. Zhou, J. Yu, B. Cheng, and H. Mater, J. Phys. Chem., 2005,

93, 159.

41. D. H. Kim, H. S. Park, S. H. Kim, and K. S. Lee, Catal. Lett.,

2006, 106, 29.

42. Z. Wang, U. Lwersson and P.O. Kall, Thin Solid Film, 2002, 50

405.

43. I. K. Konstantinon, and T. A. Albanis, Appl. Catal. B: Environ.,

2003, 42, 319.

44. U. Ozgur, I. Y. Alivov, C. Liu, A. Teke, M. A. Reshehikov, S.

Dogan, V. Aurutin, S. J. Cho, and H. A. Morkos, J. Appl. Phys.,

2005, 98, 41301.

161

45. H. W. Hirschwald, Acc. Chem. Rev., 1985, 18, 228.

46. M. Caglar, Y. Caglar, and S. Iican, Phys. Status Solid, 2007, 4,

1337.

47. S. D. Mo, and W. Y. Ching, Phys. Rev. B, 1995, 51, 13023.

48. A. L. Linsebigler, G. Lu, and J. T. Yates, Chem. Rev., 1995, 95,

735.

49. A. Tsukazaki et al., Nat. Mater, 2005, 4, 42.

50. D. Song, Appl. Surface Science, 2008, 254, 4171.

51. J. E. Jaffe, and A. C. Hess, Phys. Rev. B, 1993, 48, 7903.

52. S. Forberg, Ceramics, 1986, 20, 321.

53. J. Wang, B. Guo, X. Zhang, Z. Zhang, J. Han, and J. Wu,

Ultrason. Sonochem., 2005, 12, 331

54. D. Dvoranova, V. Brezova, M. Mazur, and M. A. Malati, Appl.

Catal. B, 2002, 37, 91.

55. J. K. Burdett, Inorg. Chem., 1985, 24, 2244.

56. X. Y. Deng, and Z. Gao, Appl. Catal. Environ. B, 2002, 39, 135.

57. G. A. Epling, and C. Lin, Chemosphere, 2002, 46, 561.

58. S. J. Pearton, D. P. Noton, Y. W. Heo, and T. Steiner, Progress in

Materials of Science, 2005, 50, 293.

59. J. M. Herrmann, Catalysis Today, 1999, 53, 129.

60. R. K. Brandt, M. R. Bounrget, K. Truszkows and R. G. Greenler,

Surface Science, 1993, 286, 15.

61. G. Lu, A. Linsebigler, J.T. Yates, J. Phys. Chem., 1995, 97, 754.

62. V. E. Henrich, M. Dresslhaus, and G. Zeiger, J. Sold State

Commun, 1977, 24, 623.

63. S. Sakka, "Application of Sol-Gel Technology", Kluwer

Academic Publishers, Massachusetts, USA 2005.

64. R. L. Kurtz, R. Stockbauer, T. E. Madey, E. Roman, and L.

Desegovia, J. Surf. Sci., 1989, 218, 178.

162

65. H. Al-Ekabi, and N. Serpone, J. Phys. Chem., 1988, 92, 5726.

66. T. N. Obee, and S. O. Hay, Environ. Sci. & Technol., 1997, 31,

2034.

67. C. P. Chang, J. N. Chen, and M. C. Lu, J. of Environ. Sci. and

Health Part A–Toxic/Hazardous Substances & Environ.

Engineering, 2003, 38, 1131.

68. S. G. Chen., R. T. Yang, F. Kapteijen, and J. A. Moulijn, Ind.

Eng. Chem. Res., 1993, 32, 2835.

69. M. Zhang, T. An, J. Fu, G. Sheng, X. Wang, X. Hu, and X. Ding,

Chemosphere, 2006, 64, 423.

70. C. Li, K. Domen, K. L. Maruya, and T. Onishi, J. Amer. Chem.

Soc., 1989, 111, 7683.

71. G. Munuera, A. Navio, and V. Rivel-Arnau., J.C.S. Faraday

Trans., 1981,77, 2747.

72. V. F. Freiako, N. G. Maksimov, and M. P. Komaror, Kinet. and

Catal., 1973, 34, 1532.

73. A. A. Davdov, M. P. Komaror, V. F. Freiako and N. G.

Maksimov, Kinet. and Catal., 1973, 14, 1342.

74. I. M. Goldstein, M. Cerqueira, S. Lind, and H. B. Kaptau, J. Clin.

Invest., 1977, 59, 249.

75. T. Muramoto, M. Higashiyama, and T. Kondo, Asia-Aust J.

Anim. Sci., 2004, 18, 420.

76. F. Haber, and J. Weiss, Proc. Roy. Soc. Ser. A., 1934, 147, 332.

77. A. Rigo, R. Stevanato, A. Finazzi-Agro, and G. Rotilio, Fed. Eur.

Biochem. Soc., Lett., 1977, 80, 130.

78. F. H. Hussein, and F. J. M. Al Imarah, J. of Arabic Industrui.,

2001, 14, 28.

79. M. Anpo et. al. Chem. Soc., 1991, 64, 543.

80. A. Stolz, Appl. Microbiol. Biotechnol., 2001, 56, 69.

163

81. F. P. Zee, and S. Villaverde, Water Research, 2005, 39, 1425.

82. C. M. So, M. Y. Cheng, J. C. Yu, and P. K. Wong,

Chemosphere, 2002, 46, 905.

83. C. Ràfols, and D. Barceló, J. Chromatogr. A, 1997, 177, 777.

84. A. Welham, J. Soc. Dyers. Colour, 2000, 116, 140.

85. B. Kahr and R. W. Gurney, Chem. Rev., 2001, 101, 893 and

references therein.

86. H. W. Houghton, J. Amer. Chem. Soc., 1907, 29, 1351.

87. Markt Report January, J. of Industried and Engineering Chem.,

1920, 12, 207.

88. Markt Report May, J. of Industried and Engineering Chem.,

1921, 13, 587.

89. G. M. Sole, and J. K. Chipman, Carcinogenesis, 1923, 7, 1921.

90. H. Zollonger, "Color Chemistry-Synthesis, Properties and

Applications of Organic Dyes and Pigments", (VCH), New York,

1987.

91. P. Pekakis, N. P. Xekoukoulotakis, and D. Mantzavinos, Water

Research, 2006, 40, 1276.

92. S. Sharma, S. Pathak, and K. P. Sharma, Bulletin of Environ.

Contamination and Toxicology, 2003, 70, 753.

93. M. Stylidi, D. I. Kondarides, and X. E. Verykios, Appl. Catal. B:

Environ., 2003, 40, 271.

94. E. J. Weber, Environ. Sci. Technol., 1996, 30, 716.

95. S. Sugie, T. Tanaka, and K. El-Bayoumy, J. Health Sci., 2000,

46, 422.

96. P. Brough, C. Klumpp, A. Bianco, S. Campidelli, and M. Prato, J.

Org. Chem., 2006, 71, 2014.

97. A. Houas, H. Lachheb, M. Ksibi, E. Elaloui, C. Guillard, and J.

M. Hermann, Appl. Catal. B: Environ., 2001, 31, 145.

164

98. N. Guettai, and A. H. Amar, Desalination, 2005, 185, 427.

99. G. Liu, T. Wu, J. Zhao, H. Hidaka, and N. Serpone, Environ. Sci.

Technol., 1999, 33, 2081.

100. S. Sakthivel, B. Neppolian, M. V. Shankar, B. Arabindoo, M.

Palanichamy, and V. Murugesan, Solar Energy Mater. Solar

Cells, 2003, 77, 65.

101. E. Puzenat, H. Lacheb, M. Karkmaz, A. Houas, C. Guillard, and

J. M. Hermann, Int. J. Photoenergy, 2003, 5, 51.

102. H. Lachheb, E. Puzenat, A. Houas, M. Ksibi, E. Elaoui, G.

Guillard, and J. M. Hermann, Appl. Catal. B: Environ., 2002, 39,

75.

103. K. Tanaka, K. Padermpole, and T. Hisanaga, Wat. Res., 2000,

34, 327.

104. F. Zhang, J. Zhao, T. Shen, H. Hidaka, E. Pelizzetti, and N.

Serpone, Appl. Catal. B: Environ., 1998, 15, 147.

105. C. Harmer and P. Bishop, Water Sci. Technol., 1992, 26, 627.

106. K. Tanaka, K. Padermpole, and T. Hisanaga, Water Research,

2000, 34, 327.

107. M. Vauthier, C. Guillard, and J. M. Hermann, J. Catal., 2001, 46

201.

108. I. K. Konstantinou, and T. A. Albanis, Appl. Catal. B:

Environ., 2004, 49, 1.

109. B. A. Donlon, E. Razo-Flores, M. Luijten, H. Swarts, G. Lettinga

and J. A. Field, Appl. Microbiology and Biotechnology, 1997,

47, 83

110. W. F. Jardim, S. G. Moraes, and M. M. Takiyama, Water

Research, 1997, 31, 1728.

111. S. J. Smith, and B. T. Sutcliffe, Rev. in Computational Chem.,

1997, 70, 271.

165

112. F. Schaefer Henry, "The Electronic Structure of Atomic and

Molecules", Reding, Massachusetss, Addison-Wesley Publishing

Co. 1996.

113. A. Dearing, J. Comuter-Aided Molecular Design, 1988, 2, 179.

114. P. A. M. Dirac, Proc. Roy. Soc., 1929, 123, 714.

115. T. A. Clark, "Hand Book of Computational Chemistry", Wiley,

New York, 1985.

116. J. Cramer Christopher, "Essential of Computational Chemistry",

Chichester , John Wily & Sons., Ltd, 2002.

117. H. L. Paige, R. J. Berry, R. F. Donald, and M. R. Nyden.

"Technical Working Conferernce", Albuquerque, New Maexico,

1996.

118. G. F. Gyorgy, A. R. Christopher, and W. R. Graham, J.

Computational Chem., 2004, 11, 159.

119. C. J. Cramer, "Essential of Computational Chemistry", John

Wiley & Sons., 2002.

120. R. J. Robert, and J. F. Coworkers, Rev. of Computational

Chem., 1994, 5, 678.

121. G. Parr Robert, D. P. Craig, and I. G. Ross, J. Chem. Phys.,

1950, 18, 1561.

122. T. C. Chen, J. Chem.. Phys., 1955, 23, 2200.

123. L. C. Peter, and E.G. Jill, Chem. Phys. Lett., 1994, 225, 11.

124. Z. Anqi, X. Shujuan, H. Dianmin, and L. Zuyu, Int. J. of

Radiation, 1989, 56, 893.

125. T. H. Dunning, and P. J. Hay, "Modern Theoretical Chemistry",

Plenum, New York, 1976.

126. W. J. Hehre, R. F. Stewart, and J. A. Pople, J. Chem. Phys.,

1969, 51, 2657.

166

127. I. N. Levine, "Quantum Chemistry", Boston: Allyn and Bacon,

Inc., 1983.

128. J. Cramer Christopher, "Essential of Computational Chemistry",

Chichester, John Wiley and Sons., Ltd, 2002.

129. Y. Akutsu, and S. Y. Tahara, J. Energetic Materials, 1991, 9,

161.

130. H. Dorsett and A. White, "Overview of Molecular Modelling

and Ab initio Molecular Orbital Methods Suitable for Use with

Energetic Materials", Aeronautical and Maritime Research

Laboratory, Australia 2000.

131. W. Thiel, Adv. Chem. Phys., 1996, 93, 703.

132. Y. Akutsu, and S.Y. Tahara, J. Energetic Materials, 1991, 9,

161.

133. J. D. Madura, and W. L. Jorgensen, J. Amer. Chem. Soc., 1986,

108, 2517.

134. J. C. Smith and M. Karplus, J. Amer. Chem. Soc., 1992, 114,

805.

135. A. J. Hameed, J. of Molecular Structure: THEOCHEM, 2005,

728, 43.

136. A. A. Ibrahim and A. E. Abdalrazaq, Amer. J. of Appl. Sci.,

2009, 6, 1385.

137. S. F. Timofei, UNV. Timisoara, 2008, 53, 1.

138. A. D. Bacon , and M. C. Zerner, Theor. Chim. Acta., 1979, 53,

21.

139. J. A. Popel and G. A. Segal , J. Chem. Phys., 1965, 43, 136.

140. J. A. Popel , D. L. Beveridge and P. A. Dobosh , J. Chem. Phys.

, 1967, 47,2026.

141. R. C. Bingham , M. J. S. Dewar and D. H. Lo , J. Amer. Chem.

Soc., 1975, 97, 1294.

167

142. M. J. S. Dewar and W. Thiel , J. Amer. Chem. Soc. , 1977, 99,

4899.

143. D. M. Hirst, "A Computational Approach to Chemistry", Blac.

Well Scientific Publication , Oxford, 1990.

144. R. Fletcher, "Practical Methods of Optimization", John Wily and

Sons., New York, 1980.

145. V. Mora and E. A. Castro, Chem. Rev., 2002, 4, 250.

146. C. C. J. Roothan, Rev. Mod. Phy., 1951, 23, 69.

147. M. J. S. Dewar, E. G. Zoebisch, E. F. Healy, and J. J. P. Stewart,

J. Amer. Chem. Soc., 1985, 107, 3902.

148. A. H. Essa and A. F. Jalbout, J. Iran. Chem. Soc., 2008, 5, 498.

149. S. Dewar, E. G. Zoebisch, E. F. Healy, and J. P. Stewart, J.

Amer. Chem. Soc., 1987, 107, 3902.

150. H. B. Schlegel, P. Coworker, J. Phy. Chem., 1993, 33, 449.

151. I. N. Levine, "Quantum Chemistry", 5th

Edition Prentice, Inc.,

New Jorsey, 2000.

152. F. Jensen, "Introduction to Computatational Chemistry", John

Wiley and Sons, Ltd, England, 1999.

153. W. W. Cleland, Method in Enzymology, 1995, 249, 341.

154. J. Baker, J. Comp. Chem., 1986, 7, 385.

155. P.Y. Peng, H. B. Ayala, and M. J. Frisch, J. Comp. Chem., 1996,

17, 49.

156. T. A. Halgren, and W. N. Lipscomb, Chem. Phys. Lett., 1977,

49, 225.

157. X. Ma, and H. Schobert, Prep. Div. Fuelchem. Acs., 1999, 56,

678.

158. P. Lipkowski, A. Koll, A. Karpform, and P. Wolschann, Chem.

Phys. Lett., 2003, 74, 370.

159. J. Frau, J. Donose, F. Munoz, and F. G. Blanco, J. Molecular

Structure Theochem., 1977, 390, 247.

168

160. I. Fleming, "Frontier Orbital And Organic Chemical Reaction",

Wiley And Sons, London, 1976.

161. K. Djameleddine, S. Soumeya, and M. Fatiha, Molecules, 2004,

9,883.

162. I. A. Adejoro, E-J. Chem., 2010, 7, 271.

163. C. G. Hatchard, and C. A. Parker, Proc. R. Soc. Ser. A., 1956,

235, 518.

164. A .D. Kirk, and C. Namasivayam, Ana. Chem., 1983, 55, 2428.

165. I. Fleming, "Frontier Orbital And Organic Chemical Reaction",

Wiley and Sons, London, 1976.

166. J. H. Jensen, and M. S. Gordon, J. Am. Chem. Soc., 1991, 113,

7917.

167. F. H. Hussein, A. F. Halbus, H. A K. Hassan and W. A K.

Hussein, E-J. of Chem., 2010, 7, 540.

168. F. H. Hussein, M. H. Obies and A. A-Ali Drea, Int. J. Chem.

Sci., 2010, 8, 2736.

169. F. H. Hussein, M. H. Obies and A. A-Ali Drea, Int. J. Chem.

Sci., 2010, 8, 2763.

170. F. H. Hussein and T.A. Abass, Int. J. Chem. Sci., 2010, 8, 1353.

171. F. H. Hussein and T.A. Abass, Int. J. Chem. Sci., 2010, 8, 1409.

172. N. Daneshvar, D. Salari, and A. R. Khataee, Photochem. J.

Photobiol. A. Chem., 2003, 157, 111.

173. S. K. Kansal, and S. Singh, Nanoscale Res. Lett., 2009, 4, 709.

174. T. Sauer, G. C. Neto, G. C. Jose, and G. C. Moreira, J.

Photochem. Photobiol. A., Chem., 2002, 149, 147.

175. S. K. Kavitha, and P. N. Palanisamy, Inter. J. of Civil and

Enviro. Engineering, 2011, 3, 1.

176. H. K. Singh, M. Muneer and D. Bahnemann, J. Photochem.

Photobiol. Sci., 2003, 2, 151.

169

177. M. Movahedi, A. R. Mahjoub and S. Janitabar-Darzi, J. Iran.

Chem. Soc., 2009, 6, 570.

178. Z. He, S. Song, H. Zhu, and H. Ying, J. Ultrasonics

Sonochemistry, 2007,14, 298.

179. S. Sakthivel, B. Neppolian, M. V. Shankar, B. Arabindoo, and M.

Palanichamy, V. Sol. Energy Mater Sol. Cells, 2003, 77, 65.

180. T. Won Kim and M. Lee, J. of Advanced Engineering and

Technology, 2010, 3, 193.

181. C. Chih-Yu, Water Air Soil Pollut., 2009, 202,335.

182. J. Hermann, Catal. Today, 1999, 53, 115.

183. F. Al-zahra Gassim, A. N. Al-khateeb, and F. H. Hussein,

Desalination, 2007, 209, 353.

184. F. H. Hussein, and R. Rudham, Chem. Farad. Trans., 1984, 1,

2817.

185. F. H. Hussein, and R. Rudham, Chem. Farad. Trans., 1987, 1,

1631.

186. F. H. Hussein, J. Abhath Alyarmouk, 2002, 11,327.

187. C. Chih-Yu, Water Air Soil Pollut., 2009, 202,335.

188. Z. He, S. Song, H. Zhou, H. Ying, and J. Chen, Ultrasonics

Sonochemistry, 2007, 14, 298.

189. S. T. Martin, H. Hermann, W. Choi, and R. Hoffmann, J. Chem.

Soc. Faraday Trans, 1994, 90, 3315.

190. R. Hoffman, J. Chem. Phys., 1963, 39, 1397.

191. M. Saqib, and M. Muneer, J. Environ. Sci. Health Part A, 2003,

8, 98.

192. J. J. P. Stewart, J. Computer-Aided Mol. Design, 1990, 4, 1.

193. E. Scrocco and J. Tomasi, "Topic in Current Chemistry",

Springer-Verlag, Berlin 1973.

194. S. J. Weiner et al., J. Comp. Chem., 1986, 7, 230.

170

195. D. M. Seeger, C. Korzeniewski, and W. Kowalchyk, J. Phys.

Chem., 1991, 95, 68.

196. A. H. Saeed, "Principle of Chemical Reaction Rates", Basrah

University, 1988.

photocatalytic decolorization of bismarck brown r

Documents