The ancient interest in noble metals was based on their aesthetic properties. Gold and silver, for example, were employed in the composition of ornaments and jewelry. In the past century and especially in the past few decades, revolutionary developments occurred in the field of nanoscience. A lot was studied about their optical, catalytic, electronic and biomedical properties. These unique properties hold enormous potential for applications in several areas such as catalysis, energy conversion and biomedicine. Nanoparticles have unique properties that are significantly different from their bulk counterparts. When the dimension of a particle decreases below 100nm, it exhibits many intriguing properties. High surface-to-volume ratio alters the thermal, mechanical and chemical properties of materials. The properties of nanoparticles are strongly dependent on their size, shape, solid or hollow interiors and composition. By tuning and controlling the parameters of synthesis, one can alter and optimize the desired property for a target application. For instance, in the case of catalysis, surface area, size and shape strongly affect catalytic activities and selectivity. Various nanoparticle synthesis approaches are available, which can be broadly classified into top-down and bottom-up approaches. In the first category, nanoparticles can be obtained by techniques such as milling which generates small particles from corresponding bulk materials. In the second category, nanoparticles can be formed atom-by-atom, which are obtained from ions in a solution. In the liquid phase, nanoparticles are chemically synthesized in colloidal solution containing precursors, a reducing agent, surfactants and a solvent. Bottom-up approaches have the potential to produce large quantities of nanoparticles with good control of size, shape, morphology and composition at reasonably low cost.
|
