Design Of TiO₂-Pt-BiVO₄ Composite Photocatalysts And Their Photocatalytic Performance

The semiconductor photocatalysis for organic contaminates degradation is considered as one of the most promising pollution control technology. Among various photocatalysts, TiO2 is the most widely used due to its high chemical stability,easy acquisition, low toxicity, etc. However, the application of TiO2 is restricted by its poor visible light response and low quantum yield. BiVO4, a efficient visble light response catalyst, has attracted great attention. Unfortunately, the photocatalytic activity of pure BiVO4 is still limited by the high rapid recombination rate of photogenerated electron-hole pairs.In this study, the TiO2-Pt-BiVO4 ternary composite film was fabricated by liquid deposition, light reduction and metal-organic decomposition methods. The SEM,UV-vis DRS, XRD, XPS, TEM, ICP-AES were characterized respectively to investigate the optical properties, structure and morphology of TiO2-Pt-BiVO4 ternary composite film. The results showed that metal Pt and monoclinic BiVO4 were orderly and successfully deposited on anatase TiO2. The catalyst exhibited nanoparticulate morphologyes. Compared to pristine TiO2 film, the absorption wavelength of composite film redshifted to longer wavelengthes and appeared absorption in the visible light region, which would favor the enhancement of photocatalysis.The degradation of RhB, BPA and o-CP was studied to evaluate the photocatalytic activity of TiO2-Pt-BiVO4 composite film. The factors influencing the photocatalytic degradation: Pt loading amount, BiVO4 coating times and reaction conditions(pH value of system, initial pollutant concentration) were investigated to determine the optimum degradation conditions. The study showed that:(1) When the concentration chloroplatinic acid to photodeposition of Pt is 5 μM and BiVO4 coating time is one, TiO2-Pt-BiVO4 show the best photocatalytic activity to the three target pollutants.(2) The greater concentration of pollutants, the lower efficiency of photocatalytic degradation.(3) RhB and o-CP have better degradation efficiency under acidic conditions, while BPA has better degradation efficiency under weakly alkaline conditions.Active species trapping experiments were used to analyze the generation,migration pathways of electrons and holes and responsible active species for degradation of BPA. The results showed that: the hydroxyl radicals from superoxide radicals play a major role, and the hydroxyl radicals are mainly from theconduction band electrons of TiO2. Therefore, electron transfer reactions may be electrons of BiVO4 conduction band transferred to the Pt nanoparticles, and the electrons of TiO2 conduction band react with oxygen molecular to superoxide radicals and hydroxyl radicals. Meanwhile, the holes of TiO2 valence band can quickly migrate to the Pt particles to achieve the regeneration of Pt. The holes of BiVO4 valence band can lead to direct oxidation of pollutants and improve the efficiency of photocatalytic degradation.