Environmental Engineering Reference
In-Depth Information
Nano
devices
Optics and
electronics
Bioengineering
Nano-
biotechnology
Industrial
Nanotechnology
Medical and
pharmaceutical
Energy
Catalysis
fiGure 18.1
Applications of nanoscale particles in various fields.
and nanotechnology. In addition to the green techniques mentioned earlier, some of the techniques utilize the vast and easily avail-
able solar energy for the synthesis of metal nanoparticles. In recent investigations Bhanage and coworkers developed the concept of
concentrated solar energy for the synthesis of metal and metal oxide nanoparticle and proved their applicability in catalysis.
18.2
Biosynthesis Methods
Though biological processes are associated with a variety of problems like lengthy time periods (due to culturing of microbes),
size distribution and crystallinity, difficulty in shape control synthesis, slow reduction rate, these methods are safe, inexpensive,
sustainable, and environmentally friendly. The related limitations are overcome by apt strain selection, incubation temperature,
and time, concentration of metal ions, optimal ph conditions, and the quantity of biological material that produce them on a
large scale and for commercial applications. Microbial synthesis of nanoparticles is a green chemistry approach that combines
microbial biotechnology and nanotechnology. Till date biosynthesis of various nanoparticles, such as gold, silver, gold-silver,
alloy, selenium, tellurium, platinum, palladium, silica, titania, zirconia, quantum dots, magnetite and uraninite (Uo) nanopar-
ticles, by bacteria, actinomycetes, fungi, and yeasts has been reported [5].
18.2.1
nanoparticles by Bacteria
Bacteria produce inorganic materials in nanoscale dimensions with attractive morphology either by extra- or by intracellular
mechanism. Microbial systems can detoxify the metal ions by reduction and/or precipitation from soluble toxic inorganic ions
to insoluble nontoxic metal nanoclusters. This detoxification can be made by intracellular bioaccumulation or extracellular
biosorption, biomineralization, complexation, or precipitation. In intracellular production, the accumulated particles are of
particular dimension and with less polydispersity; therefore, metal nanoparticles produced extracellularly have more commercial
applications in various fields.
18.2.1.1 Bacteria-Assisted Intracellular Nanoparticle Synthesis
The various classes of bacteria used for intracellular
synthesis of metal and metal oxide nanoparticles such as
Bacillus subtilis
168 are used to reduce water-soluble Au ions to
metallic Au having octahedral morphology inside the cell walls in the range of 5-25 nm [6, 7]. however, in recent investiga-
tions
Escherichia coli
dh5α-mediated bioreduction process has been reported for Au(0) nanoparticles production from chlo-
roauric acid; the collected particles on the cell surface were mostly spherical with some having quasi-hexagonal and triangular
morphology [8].
In case of silver nanoparticle synthesis, an airborne
Bacillus
sp. isolated from the atmosphere has been reported recently to
reduce Ag ions to metallic Ag in the size range of 5-15 nm [9]. Metal ion-reducing bacteria,
Shewanella algae
, was incubated
anaerobically at room temperature and neutral ph in an aqueous solution of h
2
Ptcl
4
, to reduce ionic platinum in the existence
