New hydrothermal process for hierarchical TiO2nanostructures

Abstract

Hydrothermolysis of inorganic Ti(IV) compounds (peroxo or sulfate) yields hierarchical titania nanocrystals of controlled morphologies on either a glass or resin surface.Semiconductors of metal chalcogenides have attracted much attention because of their stability and potential applications. Amongst all semiconductors, the nanocrystals of TiO2 have been investigated for a wide range of applications in solar cells, electronics, sensors, batteries and as photoelectrochromic, electroluminescent materials.1,2 These varied applications are dependent especially on the size, morphology, phase and crystallinity of the particles. The shape and size of nanosized materials depend on the crystallographic planes present in the nanocrystals. The physical, chemical and electronic properties of atoms in different crystallographic planes are different. Hence, the shape or size-controlled synthesis of anisotropic nanocrystals is becoming an important area in nanoscience and nanotechnology. Now, the problem is how to control these parameters of the nanocrystals with accomplished synthetic approaches which is a challenging job. Several techniques have been used for the growth of nanostructured TiO2viz., sol-gel processing, hydrolysis, thermal evaporation and metal–organic chemical vapor deposition.2 Templating method is one of the approaches to attain these confined structures on the sub-nanometer scale. It is also an effective way of obtaining nanostructures to increase the surface area. Titania powders or thin films in the form of tubes, rods, whiskers, wires, needles, and sheets have been synthesized in the nanoregime through various physical, chemical or electrochemical approaches.3,4 One-dimensional (1D) nanostructures, such as rods, wires, belts or tubes exhibit a wide range of electrical, optical and chemical properties that also strongly depend on both the shape and size. When the diameter of the nanorod, nanowire or nanotube becomes small, the physico-chemical properties of the one-dimensional nanostructures are clearly different from those of crystalline solids or even two-dimensional systems. Moreover, fabrication of complex architectures with three dimensional (3D) or highly ordered nanostructures is very much desirable in current materials synthesis, holding the promise of advanced applications in electronics, optoelectronics and self cleaning property involving TiO2.5