Jan 27, 2009
Solvents and surfactants control nanoparticle shape and size
The three most important characteristics of catalysts are activity, selectivity and durability. The ability of a catalyst to select one of a number of possible products of a chemical reaction is more important in many applications than its overall activity. The control of catalyst selectivity is a matter of preparing the catalyst so that it has uniform active sites, each of which is selective towards the desired product. Modern methods of nanoparticle synthesis have made it possible to prepare metal nanoparticles with uniform size and shape and thus pave the way towards preparation of highly selective catalytic materials.
Nisha Shukla and her team at Carnegie Mellon University, US, have developed a number of simple synthesis procedures that lead yield metal and alloy nanoparticles with control of both particle size and shape. In a recent study published in Nanotechnology the authors describe the synthesis of FexPt1–x nanoparticles with a variety of shapes including spheres, nanocubes, high aspect ratio nanowires and hexagons. They are able to control the nanoparticle shape by using various solvents and surfactants in the reaction mixture.
In related work, the group has also synthesized FePt nanocubes that can be self-assembled in such a way that their crystallographic axes are aligned and oriented with respect to the substrate. Other achievements include nanoparticles that have platinum cores embedded in an iron shell, chiral gold nanoparticles, nickel nanorods coated in silica and highly crystalline silver nanowires (see image for examples).
Shukla's group is currently focusing on the development of sintered resistant multiphase, multicomponent-shaped nanoparticles for applications in catalysis. Other uses for the shape-controlled material includes magnetic data recording.
Nanoparticles with anisotropic shapes such as rods or hexagons and with aspect ratios greater than one, can maximize their packing density when self-assembled on surfaces and can allow easy alignment of the magnetic axes of the nanoparticles. Shapes such as cubes will self assemble with their crystallographic axes aligned in space.
About the author
Dr Nisha Shukla is a special faculty of the Institute for Complex Engineered System at Carnegie Mellon University (Pittsburgh, PA, USA). She is also an Institute Fellow of the National Energy Technology Laboratory, Institute for Advanced Energy Solutions (NETL-IAES). Her research involves nanoparticle synthesis, characterization and applications in the area of catalysis, magnetics, photovoltaics and chiral separations.