Soft chemical approaches to inorganic nanostructures

Abstract

Chemical approaches have emerged as the preferred means to synthesize nanostructures of various inorganic materials due to superior control over size, shape, and surface functionality. This article provides an overview of the contributions made in the authors' laboratory toward the synthesis of nanocrystals, nanowires, nanotubes, nanowalls, and other nanostructures of several inorganic materials. Thus, thiolized monodisperse metal nanocrystals have been obtained by a ligand exchange process and the stability of their 2D assemblies studied. Nanocrystals of pure CoO and ReO₃ have been synthesized, for the first time, employing a one-pot solvothermal technique. The solvothermal method has also been used to obtain organic soluble nanocrystals of semiconducting materials such as CdS, CdSe, and GaN. Inorganic nanowires and nanotubes have been prepared by several soft chemical routes, including surfactant-assisted synthesis and hydrogel templating. A simple reaction between elemental Se and Te with NaBH₄ in water has been utilized to obtain nanowires of Se and Te. We also describe the nebulized spray pyrolysis (NSP) technique to synthesize carbon nanotubes and nanowires of metals and III-V nitride semiconductors with improved yields. An important new technique for preparing nanocrystalline films of materials is by the reaction of the metal precursors in the organic layer at the interface of two immiscible liquids, with appropriate reagents. Nanocrystalline films of metals, alloys, and semiconductors and ultra-thin single-crystalline films of metal chalcogenides and oxides have been obtained by this technique. Apart from these, we discuss single precursor routes to iron sulfide, GeSe₂, and III-V nitride nanostructures as well as the first synthesis of GaS and GaSe nanowalls and nanotubes obtained through exfoliation by laser irradiation and thermal treatment.