Ice–Water Quenching Induced Ti3+ Self-doped TiO2 with Surface Lattice Distortion and the Increased Photocatalytic Activity

5 years ago

Ice–Water Quenching Induced Ti3+ Self-doped TiO2 with Surface Lattice Distortion and the Increased Photocatalytic Activity

Baoshun Liu, Kazuya Nakata, Akira Fujishima, Huogen Yu, Shengchao Nie, Xiujian Zhao, Kai Cheng, Jiaguo Yu

The present research reported a facile strategy to prepare Ti³⁺ self-doped TiO₂ with increased photocatalytic activity. The TiO₂ subjected to high temperature preannealing was directly thrown into ice–water for rapid quenching. It is interesting to see that the quenched samples show pale blue color due to the absorption in visible and near-IR region. The comprehensive analyses of X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, field-emission scanning electron microscope, and Brunauer–Emmett–Teller (BET) show that the crystallinity, the morphologies, and the specific surface area are almost unchanged after the ice–water quenching. The spectroscopic analyses of UV–vis diffusion reflectance spectra, photoluminescence spectra, and X-ray photoelectron spectra clearly show the change of electronic structure of TiO₂ due to presence of Ti³⁺ ions induced by the ice–water quenching, which is further confirmed by the electron paramagnetic resonance analysis. No Ti³⁺ ions are generated if the preannealing temperature is below 800 °C. The energy band structure model involving the Ti³⁺ ions and the associated oxygen defects was proposed to explain the change of UV–vis diffusion absorption. It is considered that the high concentration of oxygen defects at high preannealing temperatures can be partially frozen by the ice–water quenching, which then can denote the high concentration of excess electrons. Some excess electrons can be localized at Ti lattice sites, resulting in the presence of Ti³⁺ ions. More interestingly, it is also seen that the rapid ice–water quenching causes the distortion of surface lattice due to the interaction between hot TiO₂ and water, which tends to be poly crystalline and disordered for high preannealing temperature. The surface lattice distortion is considered to be correlated with the generation of oxygen defects during the ice–water quenching. The quenched samples show obviously increased photocatalytic activity for both methylene blue degradation and hydrogen evolution under UV light illumination. Although they do not have visible activity, loading amorphous Cu(OH)_x nanoclusters can greatly increase their ability to degrade methylene blue under visible light illumination. It is also shown that the photocatalytic activity of ZnO can also be increased to some extent by the ice–water quenching. Therefore, the ice–water quenching could be a general method for increasing the photocatalytic activity of many materials.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b06274

DOI: 10.1021/acs.jpcc.7b06274