surfacemodificationofdamodnco2

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Adv. in Tech. of Mat. and Mat. Proc. J. (ATM, ISSN 1440-0731), Vol. 11 [2] 57-62 (2009) 57

SURFACE MODIFICATION OF DIAMOND POWDER THROUGH DISSOLUTION OF CO IN

WATER2

Heidy VISBAL*, Chanel ISHIZAKI** and Kozo ISHIZAKI

Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan

*Permanent address: KRI, Inc., Kyoto Research Park, 134, Chudoji Minami Machi, Shimogyo-ku, Kyoto, 600-8813, Japan

**Permanent address:Nano-TEM Co., Ltd., Shimogejo 1-485, Nagaoka, Niigata, 940-0012, Japan

E-mail: [email protected]

Surface modification of diamond powder (5-12 m) was achieved using a CO2 disssolution. The effects of the

reaction temperature were studied. The diamond surface was characterized by diffuse reflectance infrared

Fourier transform (DRIFT) spectroscopy. Four chemical structures; epoxy ( ), aliphatic ether (-C-O-C-) as

well as methyl (-CH3) and methyne (-CH) bands were identified in the diamond surface after the treatment. The

total intensity of the bands increases proportionally by augmenting the treatment temperature. An activation

energy of 51.2 kJ mol-1 was obtained, that is in the range of a chemisorption reaction energy. From the results it

is concluded that methyl formate (HCOOCH3) was chemisorbed on the diamond surface to a carbon with two

unsaturated valences. (KEY WORDS:Diamond Powder, Surface Modification, Chemisorption, CO2 dissolution,Diffuse Reflectance Infrared Fourier Transform (DRIFT) Spectroscopy)

INTRODUCTION

Several studies have been focused on diamond

powder surface modification. They can be classified

into two main groups: modifications in vapor phase

[1-7] and in liquid phase [8-14]. Modifications in the

liquid phase of diamond surface are more suitable forindustrial applications, because the commontechnology of chemical engineering can be used.

Another advantage is that organic substances with

organic functional groups can be chemisorbed on a

diamond surface and new organic-inorganic

functional materials can be developed. Silane

coupling reagents [10], carboxylic acids [9] have

been reported as precursors for modifying diamond

surface. In the previous paper it was shown that

formaldehyde solution [14] could modify diamond

surface. By this treatment, methyl formate is

chemisorbed to diamond surface. However, even

these chemical methods require solvents or expensivechemicals to activate the reaction. By far, the most

common acid maker is simple carbon dioxide (CO2).

When this dissolves, it makes carbonic acid (H2CO3).

It is well known that carbon dioxide is soluble in pure

water and its value of solubility is less than 0.039 mol

l-1 at 40. Once it has dissolved, a small proportion

of the CO2 reacts with water to form carbonic acid.

Disolved carbon dioxide consists mostly of the

hydrated oxide CO2 (aq) together with a small

amount of carbonic acid. Carbon dioxide is an

extremely abundant and inexpensive resource

because it is a waste product of many industries, such

as in the production of limestone and cement,fermentation of carbohydrates, and on a vast scale in

fossil-burning power plants. It may be also produced

by concentrated solar energy, by calcinations of

limestone at 800-900. Therefore if carbon dioxide

alone can be use to modify surfaces instead of

expensive reactives, it will be a promising source for

industrial applications. According to our knowledge

nobody has reported about modifying the diamondsurface using a carbonate water solution and its

mechanism. In this paper, the feasibility of

modifying the surface of diamond powder by

dissolution of CO2 in water is reported. The diamond

surface after treatment was characterized by diffuse

reflectance infrared Fourier transform (DRIFT)

spectroscopy. The reaction between the species

formed in the dissolution of CO2 in water and the

diamond powder is also discussed. The treatment

was studied at several reaction temperatures.

EXPERIMENTAL

Commercial available synthesized diamond powder

of 5-12 m grain size from Matsumoto Yushi-seiyaku Co., Ltd. was used in this study. First, 27 ml

of distilled water was saturated with carbon dioxide

(99.9% purity). Then, an amount of 0.06 grams of

diamond powder was put inside the flask containing

the saturated dissolution of CO2. To study the effects

of the temperature, the solution was heated in an oil

bath with reflux at 60, 80 and 100C for 3 h with

continuous stirring. The temperature of the liquid

inside the flask was monitored each 20 minand waskept constant. After the treatment, the solution was

Submitted: 24 August 2009, Accepted: 4 November 2009
mailto:[email protected]:[email protected]


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58 Surface Modification of Diamond Powder Through Dissolution of CO2 in Water

decanted and washed few times with distilled water

and finally, the powder was dried in an oven at 120C

for 20 h. The surface of the diamond was

characterized by DRIFT spectroscopy using a

Shimadzu FT-IR 8300 spectrometer equipped with a

Spectra-Tech diffuse reflectance accessory, a

triglycine sulfate (TGS) detector and data processingsoftware. Three samples were prepared for each

condition. DRIFT spectra of three different portions

of the samples in the range of 4000-400 cm-1 were

obtained in dry air atmosphere with no dilution. For

each spectrum, 256 scans were accumulated at aresolution of 4 cm-1. Spectral processing such as

baseline adjustment and smoothing were performed

using an OMNIC software package. The second

derivative spectra derived from the absorbance

spectra were deconvoluted and the peaks quantified

using a Jandel peak separation and analysis software

PeakFitTM 4.0 (AISN Software Inc., USA) in log

(1/R) units. Peak fitting was carried out until squaredcorrelation coefficients with r2 greater than 0.999 and

best F standard values were obtained.

RESULTS AND DISCUSSION

DRIFT Spectral Characteristics

Diffuse reflectance DRIFT spectra of diamond

modified by CO2 as a function of reaction

temperature is presented in fig. 1. This figure showsthe average spectra of raw diamond powder (RD),

and the diamond after treatment. The presented

spectra are averaged spectra. In pure natural

diamond, only two-phonon (or second order)

absorption process (the broad bands in the region

2300-2000 cm-1) are infrared-active, but the presence

of impurities or defects in the structure causes the

forbidden single phonon modes to become infrared

active [15-16]. Therefore two bands in the region

2300-2000 cm-1 can be observed in the spectrum of

the diamond powder. Other small bands can be

observed in the region 1400-1100 cm-1 due probably

to impurities or defects in the diamond [16]. Afterthe CO2 chemical treatment the main differences

observed in the spectra are the new bands that appear

in the ranges of 3000-2800 cm-1 and 1600-400 cm-1

(these are superimposed to the defect bands observed

in the raw diamond). The absorbance intensity of

these bands normalized by the intensity of the

diamond band from 2250-2100 cm-1 for different

reaction temperatures is shown in fig. 2. It can be

observed that the total intensity of the bands increases

by augmenting the reaction temperature. Since the

results show that the samples prepared at 100C

shows the highest intensity, to study the effects of

treatment time, the reaction temperature was set atthis temperature. Deconvolution of all the spectra

was performed and the identified peaks in both

regions for a sample treated at 100C for 3 h are

shown in fig.3. In fig. 3(a), correspondent to the C-

H region, 4 peaks clearly defined around 2962, 2924,

2893 and 2855 cm-1 are observed. In the CH

frequency region, the spectra are very complex due to

Fermi resonances between the CH fundamental andcombinations or overtones, and therefore these bands

can be assigned to -CH stretching vibration modes of

methyl and or methyne [17-19]. Additionally, these

bands have been reported on adsorption of methyl

formate on powders [20]. In the region 1600-400cm-1

four main peaks can be observed as seen in fig. 3 (b).

The broad band from 1200 to 950 cm-1 can be

assigned to ether stretching vibrations ( C-O-C)

according to the literatures [3, 7, 10, 16-19]. Two

other peaks located at 1260 and 810 cm-1are observed.

These two bands can be assigned to asymmetric and

symmetric vibration of epoxide ( ) [17-19, 21-

25]respectively. Normally the strong band is due toasymmetrical -C-O-C- stretching and the symmetrical

stretching band is usually weak. However the -C-O-

C- group in a ring like epoxide and as the ring

becomes smaller, the asymmetrical -C-O-C-

stretching vibration moves progressively to lower

wave numbers, whereas the symmetrical -C-O-C-

stretching vibration moves to higher wave numbers[21-22, 24]. Diamond has a very small lattice

constant, so oxygen bonded to it would also be highly

strained and could exhibit this kind of behavior [22].

This can explain why the peak at 810 cm-1 has ahigher intensity than the band located at 1260 cm-1.

An additional small peak appears on the spectrumaround 1400 cm-1. This peak can be assigned to

carbonate [26-27].

4000

Log(1/R)/a.u.

Wave number, /cm-1

10003000

0.2

2000

T=100T=80T=60

t= 3 h

RD

Figure 1. Common scale DRIFT spectra of raw and

chemically modified diamond powder with CO2

dissolution for 3 h at different temperatures.


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60 80 100

1

2

3

4

5

6

7

8

3000-2800 cm-1

Norma

lizedAbsorbanceInt

ensity

Reaction temperature,T/oC

Experimental dataLinear fit R

2=0.99

t=3 h

(a)

60 80 10010

20

30

40

50

Reaction temperature,T/oC

Experimental data

Linear fit R2=0.99

t=3 h1300-750 cm-1

Normaliz

edAbsorbanceInten

sity

(b)

Figure 2. Normalized absorbance intensity of bands as a function of reaction temperature by region, a) 3000-

2800 cm-1, b) 1300-750 cm-1. The total intensity of the bands increases by augmenting the reaction temperature.


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1600 1400 1200 1000 800

0.02

Log(1/R)/a.u

Wave number, /cm-1

-C-O-C-

sym.

assy.

1260 cm-1

810 cm-1

3000 2950 2900 2850 2800

2855

2893

2924

2962

0.01

Log(1/R)/a.u

Wave number, /cm-1

(b)

(a)

Figure 3. Deconvolution of the spectrum obtained for a diamond sample treated at 100C for 3 h by region,

a) 3000-2800 cm-1 b) 1300-750 cm-1


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Modified Surface

Based on the four chemical units obtained from the

spectral results; epoxy ( ), aliphatic ether (-C-O-

C-), methyl (-CH3) and methyne (-CH), we proposed

that methyl formate: is attached to one

surface carbon with two unsaturated valences as

follows:

where Cs represents diamond surface carbons.

Reaction Mechanism and Activation Energy

When carbon dioxide gas (CO2) dissolves in water

(H2O), its molecules often cling to water molecules insuch a way that they form carbonic acid molecules

(H2CO3). Carbonic acid is a weak acid, an acid in

which most molecules are completely intact at any

given moment. But some of those molecules are

dissociated and exist as two dissolved fragments: a

negatively charged HCO3- ion and a positively

charged H+ ion. The H+ ions are responsible for

acidity--the higher their concentration in a solution,

the more acidic that solution is. For the water

dissociation reaction, it had been shown that the

value of the free-energy change, hence the

electrochemical potential, decreases as thetemperatures is raised. The following reaction has

been reported in photo catalysis of CO2

CO2(g)+2 H

2O HCOOH + O2 (1)

CO2(g)+ H

2O HCHO + O2 (2)

CO2(g)+ 2H

2O CH

3OH + 3/2O2 (3)

CO2(g)+ 2H

2O CH

4 + 2 O2 (4)

The electrochemical potentials of these reactions ofCO2 are affected by changes in temperature. The

formation of methanol (CH3OH) and formaldehyde

(HCHO) is enhanced by temperature. If

formaldehyde and methanol are formed in the system,

formaldehyde can be produced to methyl formate as

explain in previous paper [13]. Therefore methyl

formate could chemisorb to the diamond surface as

follows

The experimental results show that it is possible to

modify the surface of diamond powder using a CO

This mechanism is in agreement with the spectral

data.

Figure 4shows the ln of the absorbance intensity of

the 810 cm-1 epoxy band normalized by the diamond

peak area versus 1/T. The extent of the reaction is

temperature dependent. From Arrhenius equation we

can calculate the activation energy, as shown inEquation 1.

ln C= lnA -E/RT (1)

whereA is the pre exponential factor,Ethe activation

energy, T the absolute temperature, C the

concentration of the reaction product and R the gas

constant.

The activation energy of this process was calculated

from the slope of the graph shown in the fig. 4 in

accordance with equation (1). The calculated

activation energy is 51.2 kJ mol-1. This value is in

the range of activation energy reported in theliterature for chemisorption mechanisms [28-29].

2.7 2.8 2.9 3.0-0.4

0.0

0.4

0.8

1.2

y=-6676x + 7.8

R2=0.98

60100 80

Temperature,T/oC

1000/T, K-1

Ln[normalizedintensity]

Figure 4. Ln normalized intensity of the 810 cm-1

epoxy band vs. 1/T. The activation energy is

calculated from the slope of this graph.

CONCLUSIONS

2

dissolution. Four chemical structures that increase

proportionally with reaction temperature and time

could be identified as follows; epoxy ( ),

aliphatic ether (-C-O-C-), methyne (-CH) and methyl

(-CH3). From the spectral results and the obtainedvalue of activation energy for the reaction (51.2 kJ

mol-1), it is concluded that methyl formate

H

H O-C-O-CH3 (5)

O=C-O-CH3 + Cs-Cs- Cs-Cs-


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(HCOOCH3) chemisorbed to a diamond surface

carbon with two unsaturated valences.

ACKNOWLEDGMENTS

The authors are indebt to the Japanese government

for financial support to Heidy Visbal through the

Monbukagakusho scholarship as well as the partial

support to the research through the 21st century

Centers of Excellence (COE) program of the Ministry

of Education, Culture, Sports, Science and

Technology.

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