Synthesis and Photocatalysis Property of Ultra-small TiO2 Nanoclusters in Aqueous Media

Abstract

Atomic clusters are of significant interest in catalysis. Ultra-small TiO2 nanoclusters, a stable Ti-O cluster with diameters of a few nanometers or less, can exhibit fascinating reactive, optical and electronic properties. In this work, ~2 nm TiO2 ultra-small nanoclusters were obtained by peptizing hydrolysate of tetrabutyl titanate (TPT) at 80℃. HRTEM and XRD were used to characterize microstructure of the ultra-small TiO2 nanoclusters, which was verified to have crystalline phase anatase. XPS demonstrated that the valence state of Ti atom was Ti4+ and no oxygen vacancy existed. Optical absorption properties were determined by UV-Vis spectroscopy and demonstrated that the ultra-small TiO2 nanoclusters had extraordinary strong absorption in the light wavelength range from 235 nm to 340 nm. According to the transmission spectrum, the optical band gap was calculated to be 3.56 eV, indicating an appreciable size-base quantum effect. The specific surface area was analyzed to be 269.28 m2/g for Langmuir surface area and 186.90 m2/g for multi-point BET surface area, respectively. Photocatalytic reduction of Cr6+ to Cr3+ in ultra-small TiO2 aqueous sol was investigated to estimate the photocatalytic activity. It demonstrated that the reduction rate of Cr6+ to Cr3+ by ultra-small TiO2 nanoclusters was four times faster than that by widely used nano-crystals one. And owing to extraordinary strong ultraviolet absorption of the former, Cr6+ was completely reduced to Cr3+ under sunlight illumination.