Environmental Engineering Reference
In-Depth Information
expensive energy source, sophisticated equipment source, the need for a skilful operator. solar energy is one of the carbon-free,
easily available, and nonpolluting energy sources. There have been very few reports on the application of solar energy for the
synthesis of nanoparticles.
In this context, luo reported the size-controlled preparation of dendrimer-protected gold (Au) nanoparticles by application
of sunlight [97]. subsequent to this work, luo reported one-step dendrimer-protected gold nanoparticles using sunlight [98].
Recently, chien et al. reported the synthesis of gold nanoparticles under normal sunlight for 5 h wherein the reaction tempera-
ture was 34°c [99]. They showed that the synthesis of gold nanoparticles takes place in the temperature range of 30-50°c.
18.9
concentrated solar enerGy
In these cases, researchers achieved success in the synthesis of nanoparticles using solar as a green and inexpensive energy
source, but the same protocol fails for the synthesis of various other metal and metal oxide nanoparticle as it requires high-
intensity energy and this is not possible from natural solar energy sources. To overcome this problem and fulfill the necessity
of a higher driving force for nanoparticle synthesis, Bhanage and coworkers introduced the concept of concentrated solar
energy. Using this protocol, the authors reported a temperature rise to up to 95°c by using a Fresnel lens as a solar concentrator.
This method helps in the faster synthesis of nanoparticles because of the combination of radiation and thermal effects; this dual-
energy effect overcomes the limitation of insufficient driving force for nanoparticle synthesis. This novel technique has proven
its application for metal and metal oxide nanoparticle synthesis.
This concept was used for the first time for the synthesis of palladium nanoparticles [100, 101]. The reaction mixture was
irradiated under concentrated solar energy for palladium nanoparticle synthesis. The nanoparticles in the size range of 30-45 nm
have been reported with mixed morphology. The obtained nanoparticles come in various shapes like, triangular, octahedral,
decahedral, and icosahedral.
In continuation with this work, the same author applied this concept for shape-selective nanoparticle synthesis, wherein 70%
decahedral nanoparticle selectivity was obtained. The synthesized recyclable catalyst was then used for catalysis [102].
subsequent to this work, Patil et al. used this technique for the synthesis of metal oxides such as zinc oxide nanoparticles.
After 6 h of irradiation of Zn(ch
3
coo)
2
and 1,4-butanediol mixture a milky white Zno nanocrystalline material was obtained
consisting of nanoparticles in the size range of 10-15 nm [103]. Recently, the same author reported Mgo nanoparticle synthesis
by concentrated solar energy. The obtained nanoparticles show excellent catalytic applications for the claisen-schmidt conden-
sation reaction [104].
18.10
conclusion
This chapter provides a comprehensive review of current research activities that are dedicated to green synthesis methods for
metal and metal oxide nanoparticle preparation. In this chapter, typical green methods that involve the use of nonconventional
energy sources like ultrasonication, microwaves, hydrothermal energy, supercritical co
2
, biosynthesis, and solar energy and
avoid toxic reagents are discussed. It also covers the various examples for the shape-selective synthesis of metal and metal oxide
nanoparticles using green methods. The nanostructured materials that can be synthesized by these techniques include nanopar-
ticles, nanowires, nanofibers, and nanocomposites. Additionally, special weightage has been given to the solar energy concept
for metal and metal oxide nanoparticle synthesis, which also covers the use of concentrated solar energy, which was recently
introduced in this field.
references
[1] schmid G. large clusters and colloids. Metals in the embryonic state. chem Rev 1992;92:1709-1727.
[2] daniel Mc, Astruc d. Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward
biology, catalysis, and nanotechnology. chem soc Rev 2004;104:293-346.
[3] Wong Ts, schwaneberg U. Protein engineering in bioelectrocatalysis. curr opin Biotechnol 2003;14:590-596.
[4] Ramanaviciusa A, Kausaite A, Kausaite A, Ramanaviciene A. Biofuel cell based on direct bioelectrocatalysis. Biosens Bioelec
2005;20:1962-1967.
[5] Narayanan KB, sakthivel N. Biological synthesis of metal nanoparticles by microbes. Adv colloid Interf 2010;156:1-13.
