Abstract

As semiconductor materials, metal oxides with specific physical and chemical characters are widely used as catalysts, co-catalysts and carriers. Hollow spheres with specific structure and morphology has attracted increasingly interest because of its unique properties such as well monodispersity and stability, high specific area and low density. In addition, particles of hollow spheres itself can be seen as a nano-reactor, which can improve the metal oxide performance by varying the internal micro reaction environment. Recently, various chemical and physicochemical methods, including templates, selfassembly techniques, chemical induction, ultrasonic and solvent thermal growth methods have been developed for the preparation of hollow metal oxide spheres. Among these techniques, hard template methods using carbon spheres from monosaccharide hydrothermal carbonization exhibited great promising.

Hydrothermal carbonization is proved apt to generate monodispersed carbonaceous spheres. Carbon spheres obtained via hydrothermal carbonization is a promising hard template for the preparation of hollow metal oxide spheres with following advantages: (1) the HTC reaction facilities are simplicity and carbon raw materials are usually monosaccharide, cellulose, lignocelluloses and such biomass that are environmental friendly; (2) reaction proceeds in a mild condition (T=100-300) and the templates can be facile removal by calcinations; (3) the carbon spheres are rich in oxygen-containing hydrophilic functional groups such as hydroxyl groups, carboxyl groups and carbonyl groups which are benefit for binding with metal; (4) the size, structure and properties of the templates can be controlled produced through change the reaction conditions, in turn determine the properties of hollow metal oxide spheres.