Hongpeng Jia

Solvothermal syntheses of Bi and Zn co-doped TiO2 with enhanced electron-hole separation and efficient photodegradation of gaseous toluene under visible-light

This study investigated the effects of Bi doped and Bi-Zn co-doped TiO2 on photodegradation of gaseous toluene. The doped TiO2 with various concentration of metal was prepared using the solvothermal route and characterized by SEM, XRD, Raman, BET, DRS, XPS, PL and EPR. Their photocatalytic activities under visible-light irradiation were drastically influenced by the dopant content. The results showed that moderate metal doping levels were obviously beneficial for the toluene degradation, while high doping levels suppressed the photocatalytic activity. The photocatalytic degradation of toluene over TiBi1.9%O2 and TiBi1.9%Zn1%O2 can reach to 51% and 93%, respectively, which are much higher than 25% of TiO2. Bi doping into TiO2 lattice generates new intermediate energy level of Bi below the CB edge of TiO2. The electron excitation from the VB to Bi orbitals results in the decreased band gap, extended absorption of visible-light and thus enhances its photocatalytic efficiency. Zn doping not only further enhances the absorption in this visible-light region, but also Zn dopant exists as the form of ZnO crystallites located on the interfaces of TiO2 agglomerates and acts as a mediator of interfacial charge transfer to suppress the electron-hole recombination. These synergistic effects are responsible for the enhanced photocatalytic performance.

Efficient promotion of charge transfer and separation in hydrogenated TiO2/WO3 with rich surface-oxygen-vacancies for photodecomposition of gaseous toluene

Oxygen-deficient TiO2/WO3 constructed via the controllable temperature of hydrogen annealing is designed in view of combining the broad visible spectrum absorption with the prominent coupled semiconductor properties. Surface lattice disorder of TiO2/WO3 arises at hydrogen annealing temperature of 200 and 300°C, while critical phase transition from TiO2/WO3 to TiO2/WO2.9 occurs at 400°C, both of which can introduce oxygen vacancies. The hydrogenated TiO2/WO3 with rich surface-oxygen-vacancies exhibits much higher photocatalytic activity for decomposition of gaseous toluene than pristine TiO2/WO3 under visible-light illumination (λ>420nm). The photoelectrochemical analysis shows that the improved electronic properties of oxygen-deficient TiO2/WO3 enable dramatically efficient promotion of photoinduced charge transfer and separation, which is the key factor for the improved photocatalytic activity. It is hoped that the present work could boost ongoing interest for preparing various hydrogenated coupled semiconductors with enhanced activity for diverse photocatalytic applications.

A Novel Redox Precipitation to Synthesize Au-Doped α-MnO2 with High Dispersion toward Low-Temperature Oxidation of Formaldehyde

A novel method of redox precipitation was applied for the first time to synthesize a Au-doped α-MnO2 catalyst with high dispersion of the Au species. Au nanoparticles (NPs) can be downsized into approximate single atoms by this method, thereby realizing highly efficient utilization of Au element as well as satisfying low-temperature oxidation of formaldehyde (HCHO). Under catalysis of the optimal 0.25% Au/α-MnO2 catalyst, a polluted stream containing 500 ppm HCHO can be completely cleaned at 75 °C with the condition of a weight hourly space velocity (WHSV) of 60000 mL/(g h). Meanwhile, the catalyst retains good activity for removal of low-concentration HCHO (about 1 ppm) at ambient temperature with a high WHSV, and exhibits a high tolerance to water and long-term stability. Our characterization of Au/α-MnO2 and catalytic performance tests clearly demonstrate that the proper amount of Au doping facilitates formation of surface vacancy oxygen, lattice oxygen, and charged Au species as an active site, which are all beneficial to catalytic oxidation of HCHO. The oxidation of HCHO over Au-doped α-MnO2 catalyst obeys the Mars-van Krevelen mechanism as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy.