Solvothermal Synthesis of Non-Oxide Nanomaterials

Inorganic non-oxide materials, such as III-V and II-VI group semiconductors, carbides, nitrides, phosphides, and borides, are traditionally prepared by solid state or gas-phase reactions. They have also been prepared via the pyrolysis of organo-metallic precursors but the products may be amorphous or poorly crystalline and a crystallization treatment at higher temperature is necessary. This treatment, however, may result in the crystalline size being beyond the nanometer scale. Exploration of milder techniques for preparing non-oxide nanomaterials with controlled shapes and sizes is very important for material science. 

Hydrothermal synthesis is one of the important methods for producing fine powders of oxides. A hydrothermal system is usually maintained at a temperature beyond 100 °C and the autogenous pressure of water exceeds the ambient pressure, which is favorable for the crystallization of products. Recent research indicates that the hydrothermal method is also a practical means for preparing chal-cogenide and phosphide nanomaterials, and hydrothermal treatment is an effective method for passivating porous silicons. Similar to hydrothermal synthesis, in a solvothermal process, a non-aqueous solvent, which is sealed in an autoclave and maintained in its superheated state, is the reaction medium, where the reactants and products are prevented effectively from oxidation and volatilization and the reaction and crystallization can be realized simultaneously. Furthermore, organic solvents may be favorable for the dispersion of non-oxide nanocrystallites and may stabilize some metastable phases. 

In this chapter, we briefly review our recent progress in the solvothermal preparation of non-oxide nanomaterials, y-ray irradiation and room temperature synthesis of chalcogenide nanocrystallites are also briefly described but first we present some progress in hydrothermal synthesis. 

In different hydrothermal conditions, Ti02 nanocrystallites (anatase and rutile) with nine kinds of morphologies have been prepared [1, 2]. CdW04 nanorods [3], which showed very strong photoluminescence at 486 nm (Aex = 253 nm) at room temperature, were prepared by a hydrothermal method at 130 °C. Lead tungstate 

The Chemistry of Nanomaterials Synthesis, Properties and Applications, Volume 1. Edited by C. N. R. Rao, A. Muller, A. K. Cheetham 

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Solvothermal method has been used in synthesis of a series of non-oxide nanomaterials, such as semiconductors [1,2], ceramic materials [3], and in fabricating special nanostructures [4]. It will be an exciting, promising field for designing and preparing advanced materials in the future. This paper focuses on some aspects of recent progress in solvothermal synthesis of non-oxides nanomaterials. 

Solvothermal process is now becoming a powerful technique for preparing nanomaterials. It is analogous to hydrothermal synthesis, except that non-aqueous solvents replace water as reaction medium. From the chemical reaction point of view, solvents in supercritical conditions play a significant role in reaction and crystallization. New materials, especially those having metastable phases and special nanostructures, can be obtained under mild conditions. By sealing the reaction system in an autoclave, the reactants and products prevent effectively from oxidation, hydrolysis and volatilization, and the reaction and crystallization can be realized synchronously. 

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