Nanoscaled Amorphous TiO 2 Hollow Spheres: TiCl 4 Liquid Droplet-Based Hydrolysis Fabrication and Strong Hollow Structure-Enhanced Surface-Enhanced Raman Scattering Effects.

A very simple route is developed for fast fabrication of nanosized amorphous titanium dioxide (TiO ₂ ) hollow spheres (THPs) just via dropping the pure four titanium chloride (TiCl ₄ ) liquid droplets into deionized water at around room temperature. The THPs, at around 80 nm in mean diameter, can be formed within a few seconds after dropping TiCl ₄ droplets into water. The shell layers of the obtained THPs are amorphous and porous in structure with a porosity of 58-80% and show a linear increase in thickness with the size of THPs. Further experiments have revealed that the reaction temperature, initial pH value, and size of the TiCl ₄ droplet are crucial to the formation, size, productivity, and microstructure of the THPs. A model is proposed on the basis of the fragmentation of liquid droplets, hydrolysis-induced formation, and inward growth of TiO ₂ shell layers, which can well describe the formation of the THPs. Importantly, such amorphous nanoscaled THPs have exhibited some strong hollow structure-enhanced performances. Typically, the THP-built film shows the highest reflectivity in the visible region compared to the other structured TiO ₂ films. Especially, if it supports the film of the Au nanoparticle, the surface-enhanced Raman scattering effect is significantly enhanced by more than 1 order of magnitude. This work provides not only a simple and quick fabrication method for the THPs but also a new member for their family.