CHAPTER-2
REVIEW OF LITERATURE
2.1 Nanotechnology:
Nanotechnology is a multidisciplinary field that includes a vast and diverse array of devices that derived from engineering, physics, chemistry, and biology leading to the development of structures, devices and systems that have novel functional properties by size ranging between 1 and 100 nm (Neethirajan and Jayas 2010; Borm et al, 2006; Ducan 2011). Nanotechnology involves the manipulation of materials at nanometer sizes leading to the fabrication of nanodevices to enhance their performance. In 1959, the seminal lecture, entitled “There’s Plenty of Room at the Bottom”, by Richard Feynman was widely acknowledged as a key event in the development of the field of nanotechnology (Kricka and Fortina
Historical evidences suggest that during 2500 BC Chinese used gold nanoparticles as drug. In traditional medicine system of India, called as Ayurveda, Red colloidal gold is still used under the name of “Swarna Bhasma and Makaradhwaja” (Bhattacharya and Mukherjee 2008). Nanoparticles of Gold-Silver alloy was also used for decoration purposes for example “Lycurgus Cup,” a vessel of Roman period (4th century AD) kept in British Museum, London (Freestone et al., 2007). Similarly, gold was used in colloidal state trapped within the matrix of glass for the making of aesthetically pleasant ruby coloured glasses of different hues and colours (due to the formation of nanoparticle of different sizes) in churches in Middle Age. In 16th Century an aqueous form of colloidal gold called “Aurum Potabile” (drinkable gold) was discovered in Europe which was thought to have curative properties for many diseases (Caseri 2000). In 1915, Wolfgang Ostwald, in his famous book “The World of Neglected Dimensions”, recognized colloidal particles as “so small that they cannot be recognized microscopically, but they are still too large to be called as molecules.” However Richard P. Feynman is the person to whom the credit is given for realizing the enormous potential of nanoparticles and its possible implications in different fields. In 1959, in his classical lecture, at California Institute of Technology (Caltech)
Nano sized metal oxides are prepared via hydrolysis of precursors, usually alcoxides in alcoholic solution which results in the formation of corresponding oxo-hydroxide. After that condensation of molecules is done by giving off water which leads to the formation of a network of the metal hydroxide wghich means the hydroxyl-species undergo polymerization by condensation reaction and dense porous gel is formed. It is further dried and this calcinations leads to the formation of ultrafine nano oxides of metals (Kobayashi et al., 2001).

2.3.3 Microemulsion technique. Microemusion or direct/inverse micelles is an excellent approach based on the formation of micro/nano-reaction vessels using a ternary mixture of water, a surfactant and oil. Precipitation as oxo-hydroxides occurs, because of metal precursor suspended in water, within the aqueous droplets, leading to monodispersed materials with size limited by the surfactant-hydroxide contact (Yoon and Wai 2005).

2.3.4 Solvothermal methods. In this method, decomposition of metal complexes takes place thermically either by boiling them in an inert atmosphere or by the application of an autoclave which utilizes the principle of pressure. A suitable surfactant agent is generally used in the reaction media. Its addition aims in controlling the particle size growth and to limit agglomeration (Han et al.,