Design Of Bi₂WO₆-TiO₂-Pt Heterojunction Photocatalysts And Their Photocatalytic Performance

Photocatalytic degradation of orangnic pollutants provides a green technique for environmental purification, which displayed well application prospect in pollution management of air, water and soil. TiO2is an intensively studied material due to its non-toxic, physicochemical properties and fascinatinating economic advantages. However, its practical application suffers from the low light utilization and poor quantum efficiency. These years, Bi2WO6with the visble-light response has attracted great interest. Unfortunately, the photocatalytic activity of pure Bi2WO6is low owing to its high rapid recombination rate of photogenerated electron-hole pairs. Therefore, development of wide photo-respond and high quantum efficiency catalysts is becoming the key point of the research of photocatalyst.In this dissertation, based on the photocatalytic chemical theory, for the sake of achieving photocatalysts with wide photo-respond and high quantum efficiency, TiO2and Pt were used to modify Bi2WO6to synthesize a new type of heterostructure photocatalyst. The inductively coupled plasma atomic emission spectrometer (ICP-AES), X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectrum (UV-vis DRS) were characterized respectively to investigate the morphology, structure and optical properties of Bi2WO6-TiO2-Pt nanojuction catalyst. The results showed that both TiO2and Pt in the nanojunction system, and the crystalline structure of russellite is orthorhombic. The catalyst exhibited aggregated sheet-like morphologyes and the TiO2and Pt nanoparticles were assembled on the surface of Bi2WO6support. The absorption edge of Bi2WO6-TiO2-Pt composite has somewhat redshift, which widen the photo-respond region.In this paper, the photocatalytic activity of the Bi2WO6-TiO2-Pt has been investigated by degradation of Rhodamine B (RhB), Bisphenol A (BPA) and o-chlorophenol (2-CP) under the simulated sunlight irradiation. The factors influencing the pollutants degradation, such as TiO2loading amount, Pt loading amount, initial pollutant concentration and pH value of system were investigated to determine the optimum degradation conditions. In addition, the recycling property of catalyst were tasted. The results were shown as following.(1) The optimal condition for the degradation of RhB:the loading amount of TiO2is30%, the loading amount of Pt is1.95%, the initial pollutant concentration of RhB is20mg/L, the pH value is6. The degradation of RhB reached98.9%after120min irradiation, the kinetic constant of photocatalytic degradation3.11times as great as that using pristine Bi2WO6and the degradation rate of RhB still achieved89.5%after five recycling.(2) The optimal condition for the degradation of BPA:the loading amount of TiO2is30%, the loading amount of Pt is1.95%, the initial pollutant concentration of BPA:is20mg/L, the pH value is8. The degradation of BPA:reached100%after20 min irradiation, the kinetic constant of photocatalytic degradation13.76times as great as that using pristine Bi2WO6and the mineralization efficiency attained59.2%after12h irradiation. The degradation rate of BPA:still achieved89.5%after five recycling.(3) The optimal condition for the degradation of2-cp:the loading amount of TiO2is30%, the loading amount of Pt is1.95%, the initial pollutant concentration of2-CP is10mg/L, the pH value is6. The degradation of2-CP reached100%after60min irradiation, the kinetic constant of photocatalytic degradation17.77times as great as that using pristine Bi2WO6and the degradation rate of2-CP still achieved92.1%after five recycling.Using active species trapping experiments to analyzed the photocatalytic mechanisms and discovered the·O2radical was responsible active species for degradation of BPA under the simulated sunlight irradiation. The enhanced photocatalytic performance was ascribed to the synergistic effect between Bi2WO6, TiO2, and Pt. Herein, both narrow band gap semiconductor Bi2WO6and wide band gap semiconductor TiO2can excited by simulated sunlight, achieving full spectrum respond increased light harvesting efficiency, and the heterojunction between Bi2WO6and TiO2and the schottky junction between TiO2and Pt, obtaining enhanced quantum efficiency. This work could promot the practical application of photocatalytic technology and the management of environmental organic pollutants.