eco-friendly methods for preparation of metal metal oxide nanoparticles
Post on 15-Jul-2015
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Nano
technologyhigh reactivity
high surface area to volume
ratio
specific physicochemical characteristics
The nanosize: 1-100 nm in at
least one dimension
Nanoparticlesagriculture
textiles
health care cosmetics
electronics
optics
Nanoparticles can be synthesized by a variety of methods using gas, liquid
or solid phase processes. These include
1. gas phase processes of flame pyrolysis, high temperature evaporation,
plasma synthesis, microwave irradiation, physical and chemical vapor
deposition synthesis;
2. colloidal or liquid phase methods in which chemical reactions in
solvents lead to the formation of colloids, molecular self-assembly,
3. and mechanical processes of size reduction including grinding, milling
and alloying.
Once the NPs are produced and purified to a satisfactory level it
is often necessary to introduce surface modifications. The surface
modifications can be for the purposes of:
(a) Passivating a very reactive nanoparticle,
(b) Stabilizing a very aggregative nanoparticle in a medium
where the NPs are to be dispersed,
(c) Functionalizing the nanoparticle for applications, or
(d) Promoting the assembly of NPs.
Different approaches to surface modifications(a) Surface treatment. The treatment could be the charging of the surface or coating with ligands,
(b) Surface adsorption of a surfactant or a block copolymer to provide interparticle electrostatic and/or
steric repulsions, and
(c) Surface modification to make the nanoparticle functional in one of many ways including
hydrophobic or hydrophilic, the ability to bind to specific molecular recognition elements, DNA,
enzymes, bridge to other NPs, etc.
Assembling NPs for applications
(a) Nanoparticles with stabilizing polymer molecules around them in a random three dimensional
arrangement to create a porous nanoparticle system for catalytic or adsorption applications,
(b) Nanoparticles assembled on a polyelectrolyte or a DNA molecule to serve as a nanoelectrical wire,
and
(c) Nanoparticles assembled on a block copolymer patterned surface with NPs located at the domain
boundaries for a sensor application.
For most practical applications, the NPs have to be assembled in
one, two or three dimensions, similar to how atoms and molecules
are assembled into matter. It will be necessary to place the NPs in
specified locations on a substrate so that addressing and connecting
them to the macroscopic outside world will be possible
A new branch of nanotechnology is nanobiotechnology.
Nanobiotechnology combines biological principles with physical
and chemical procedures to generate nano-sized particles with
specific functions. Nanobiotechnology represents an economic
alternative for chemical and physical methods of NPs formation.
Nanobiotechnology describes an application of biological systems
for the production of new functional material such as NPs.
Biosynthetic methods can be employed either by microorganism
cells, plant extract or biodegradable polymers for NPs
production.
Nanotechnology has found limited applications in textiles such as
chemical and biological filters, nanofiber-based biological
scaffolds, NPs-coated repellant textiles and nanofiber filters,
which are relatively few compared to those in electronics and
healthcare. Defense, healthcare and environmental sectors use
nano-textiles and nanotechnology related textile products for
improved functionality and performance. More importantly,
nanofibers, due to their enhanced surface area and lightweight,
can be used as effective filter and barrier media in chemical and
biological defense clothing, face masks and filtration equipment.
Nano
technology
Antibacterial
Textiles
Smart Textiles
Conductive Textiles
Solar Textiles
Repellent Textiles
1. Chemical Synthesis of Nanoparticles
2. Biosynthesis (plant extracts, biodegradable
polymers, and enzymes/bacteria) of metal
and metal oxide NPs,
3. Photoinduced reduction of metal ions to
metal NPs, and
4. Textile application of metal and metal
oxide NPs.
Nanoparticle Synthesis
Chemical
BiologicalPhysical
chemical
DMF
Polyols
Sodium borohydride
Thiosulfate
Hydrazine
Cts (chitosan), Cts/gelatin and gelatin suspension were used as
the stabilizers for reducing AgNO3 using NaBH4 as strong reducing
agent. As a result, AgNO3 was successfully reduced by NaBH4 in the
presence of Cts/gelatin or either one, resulting in the formation of
AgNPs according to the following equations (1–3):
“green” product + environment friendly process
”green” reducing and
stabilizing agent
“green” solvent
precursor
5
Mechanical processes of size reduction including grinding,
milling and alloying.
physical
Microwave
Ultrasonic
UV-radiation
Shear
-radiation
Plasma
Synthesis of metal NPs has been demonstrated by many physical
and chemical means. Because most of these methods are capital
intensive, toxic, non eco-friendly and have low productivity, it is
a need of today’s nanotechnology to adopt a variety of green routes
for synthesis of NPs. Amongst these are those concerned with plant
extract, bacteria, fungi, enzymes, algae and biodegradable
polymers. Due to their amenability to biological functionalization,
the biosynthesized NPs are finding important applications in the
field of medicine, in particular that related to the antimicrobial
activity.
Biological
Plant extract
Bacteria
Fungi
Enzymes
Algae
Biodegradable polymers
Plant extractGreen tea extract
Geranium leaf extract
Citrus limon extract
Lemon leaves extract
Garlic extract
Ficus benghalensis leaf
Banana peel extract
Citrus sinensis peel
Dodonaea viscosa extract
Terminalia arjuna bark extract
All parts of a plant bearing antioxidants or sugars, including leaves, fruits, roots,
seeds, and stems, can be used in the synthesis process, replacing potentially hazardous
chemicals like sodium borohydride (NaBH4). They Can act as reducing and stabilizing
agents in the synthesis of metal NPs
The fungi are extremely good candidates in the synthesis of metal NPs.
The reduction of silver ions by several strains has been attributed to a nitrate-
dependent reductase.
Active metal transformation processes require viable microbes which
enzymatically catalyze the alteration of the metal.
The microorganisms probably play a role in providing a multitude of nucleation
centers and establish conditions for obtaining highly disperse nanoparticle
systems.
Microorganisms slow down or entirely prevent aggregation by immobilizing the
particles, and providing a viscous medium.
It is reported that polysaccharides extracted from algae have a dual effect as they
act as reducing agents of silver ions and as stabilizing agents for the formed silver
NPs.
Green Synthesis + Biocompatibility
Polysaccharides serve as both a reducing and a capping agent. In a case of dual
polysaccharide function, silver nanoparticles were synthesized by the reduction of
Ag+ inside of nanoscopic starch templates.
The so-called “alcohol reduction process” is a very general process for the
production of metal nanoparticles, often stabilized by organic polymers. In
general, the alcohols which were useful reducing agents contained 𝛼-hydrogen and
were oxidized to the corresponding carbonyl compounds. The oxidation of
primary alcohols (R–CH2OH) by Ag+ is also well established; the reaction is slow
and requires heating to be accelerated as follows:
The heart of the photochemical approach is the generation of M0 in such conditions that
their precipitation is thwarted. M0 can be formed through direct photoreduction of a
silver source, silver salt or complex, or reduction of silver ions using photochemically
generated intermediates, such as radicals. The photoreduction is often promoted by dyes
dispersed or dissolved in the polymer or present in the chemical structure of the matrix.
In this one-step approach, a strategy was reported involving the photoinduced formation
of homogeneous silver NPs in an acrylate polymer stemming from a crosslinking
photopolymerization of an acrylate monomer.
1. Silver nanoparticles were synthesized by exposing a mixture of 0.1 M [Ag(NH3)2]+
and diluted aqueous garlic extract under bright sunlight for 15 min. The garlic
extract components served as both reducing and capping agents in the synthesis of
silver nanoparticles while the sunlight acted as catalyst in the synthesis process.
2. In a similar study, silver nanoparticles were rapidly synthesized photochemically by
treating silver ions with lemon (Citrus limon) extract utilizing solar radiation. The
authors have hereby developed an energy efficient bio-based synthesis process
which produces silver nanoparticles rapidly.
3. Bhaduri et al reported a simple ‘green’ method of AgNP synthesis of using an
anionic surfactant without use of any additional reducing agents. They observed the
synthesis of AgNPs at room temperature (using sodium dodecyl sulphate and
sunlight). The nanoparticles are water soluble and the nature of the process is
amenable to scaling up.
Ag NPs (antibacterial,)
Cu/CuO NPs (electro-
conductive, antibacterial,
ZnO NPs (UV absorbers, anti-reflection
coatings, photo-catalysis , antibacterial)
TiO2 NPs (photo-catalytic,
self-cleaning, UV protection, antibacterial,
antiviral)
Metal and metal oxide nanoparticles have created a new
interesting field in all sciences for the continuous investigations
due to their undeniably unique properties. Their applications have
already led to the development of new practical productions.
These new fields in textile industry have been increasingly
welcomed. However, designing new applicable and affordable
techniques for manufacturing scale-up production will not only
create a new field of study, but meet the expanding human
requirements.
Thankyou
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