Solvent-controlled synthesis of three-dimensional TiO2 nanostructuresvia a one-step solvothermal route

Abstract

Three-dimensional (3D) TiO₂ nanostructures with various microstructures have been successfully synthesized by altering the solventvia a surfactant-free and single-step solvothermal route. The effects of the solvent on the microstructures of 3D TiO₂ nanostructures were investigated. 3D dandelion-like TiO₂ structures self-assembled of nanorods were synthesized in non-polar solvent based on water–non-polar solvent interface. For the product derived from the solvent of n-hexane, the 3D microspheres have a homogeneous size distribution in diameter of about 2 μm and a uniform morphology of radially packed nanorods of 15 nm in diameter along a [001] preference growth direction. A three-step growth model is proposed to illustrate the growth mechanism of TiO₂ nanorods self-assembled into 3D dandelion-like structures. Microspheres composed of nanoparticles are obtained using low polar or polar solvent such as n-butyl alcohol and ethanol, which are also amphiphilic solvents. The amphiphile bilayer capped outside the particle serves as the microreactor and soft temple for crystal growth. Only bulky aggregated TiO₂ nanoparticles were obtained when pure water is used as the solvent due to the fast hydrolysis of titanium precursor. Mechanisms of the self-assembly of 3D TiO₂ structures in different solvents were proposed.