Enhancement of Titania Photoanode Performance by Sandwiching Copper between Two Titania Layers

Vacancies in semiconductors can play a versatile role in boosting their photocatalytic activity. In this work, a novel TiO2/Cu/TiO2 sandwich structure is designed and constructed. Abundant vacancies were introduced in TiO2 lattice by Cu reduction under heat treatment. Meanwhile, Cu atom could diffuse into TiO2 to form Cu-doped TiO2. The synergistic effect between oxygen vacancies and Cu atoms achieved about 2.4 times improved photocurrent of TiO2/Cu/TiO2 sandwich structure compared to bare TiO2 thin film. The enhanced photoactivity may be attributed to regulated electron structure of TiO2 by oxygen vacancies and Cu dopant from experimental results and density functional theory calculations. Oxygen vacancies and Cu dopant in TiO2 formed through copper metal reduction can introduce impurity levels and narrow the band gap of TiO2, thus improve the visible light response. More importantly, the Cu2+ and oxygen vacancies in TiO2 lattice can dramatically increase the charge density around conduction band and promote separation of photo-induced charge carriers. Furthermore, the oxygen vacancies on the surface may serve as active site for sufficient chemical reaction. This work presents a novel method to prepare doped metal oxides catalysts with abundant vacancies for improving photocatalytic activity.

Effect of Synthesized Conditions of Cu-K-OMS-2 on Toluene Oxidation Performance

The objective of this study was to optimize synthesis conditions for the Cu-K-OMS-2 hydrothermal process. The effects of ageing temperature, ageing time and amount of copper (Cu) dopant were considered via using the Box-Behnken design (BBD) method to characterize the conditions for gaseous toluene degradation. In the models studied, the independent variables were ageing temperature (55-145ºC), ageing time (6-18 h) and amount of Cu dopant (2-6% mole). The quadratic model fitted very well with the experimental data (15 runs), which showed a higher value of R2 (0.98) and adjusted R2 (0.95), confirming that the model can explain the results successfully. Ageing temperature was found to be the only significant variable for the Cu-K-OMS-2 transformation phase, with CuO and the bixbyite phase appearing as the highest ageing temperature condition. Furthermore, the effects of ageing temperature, ageing time and amount of Cu dopant on the Cu3+/Cu2+ mole ratio were also investigated. Ageing temperature and amount of Cu dopant displayed a significant effect on both toluene removal and the Cu3+/Cu2+ mole ratio. On the other hand, ageing time was not significant for both responses. The high Cu3+/Cu2+ mole ratio led to enhancement of toluene removal. The optimized conditions for Cu-K-OMS-2 synthesis were determined as 120ºC of ageing temperature, 6 h of ageing time and 6% by mole of Cu on K-OMS-2, which removed 80% of toluene at a reaction temperature of 180ºC.