Preparation Of TiO_{2（Anatase）}/WO₃/TiO_{2（Rutile）} Double-heterojunction By Solvothermal Sintering Method And Photocatalytic Activity

With the rapid development of industrialization,a large number of organic pollutants have been released and environmental pollution has become more and more serious.Photocatalysis is a green technology that uses catalysts to convert light energy into chemical energy.Because photocatalyst can be recycled without secondary pollution,it quickly becomes one of the research hotspots.As an excellent semiconductor material,TiO₂can be compounded with WO₃to form WO₃/TiO₂heterojunction.The synergistic effect between anatase and rutile of TiO₂can further reduce the band gap and improve the photocatalytic performance.In this work,TiO₂,WO₃,Cu（NO₃）₂and trethylamine are selected as raw materials.TiO_{2（Anatase）}/WO₃/TiO_{2（Rutile）}double-heterojunction is synthesized by the crystal shape regulation of TiO₂under solvothermal sintering condition.The aim is to solve the problems of TiO₂with large band gap,easy electron hole composite and low photocatalytic activity of visible light.First of all,in order to demonstrate that the solvothermic sintering method can successfully synthesize WO₃/TiO₂heterojunction and shorten the band gap,promote the separation of photogenerated electron holes and reduce their recombination probability,thus promoting the improvement of photocatalytic activity.WO₃/TiO₂heterojunctions are prepared by solvothermal-sintering,hydrothermal-sintering and sintering method,respectively,and characterized by XRD,SEM,TEM,XPS,ICP-MS,XPS,UV-vis,EIS,i-t,ESR and photocatalytic degradation under visible light.The results indicate that there are fuzzy lattice fringes on the contact interface and the lattice spacing is different from WO₃and TiO₂.It is proved that WO₃/TiO₂heterojunction can be successfully prepared by solvothermal sintering method.Needle-like TiO₂grow uniformly on the bulk WO₃in the WO₃/TiO₂heterojunction,which have large contact area and particle size of about 120 nm.The reduction of band gap,large specific surface area and presence of mesopore provide more active sites for light capture,oxygen absorption and catalytic redox reactions.Strong light electrical response and low charge transfer resistance promote charge transfer between two semiconductor interfaces.After visible light irradiation for 80 min,the degradation rates of RB,MB and MO of WO₃/TiO₂heterojunction is 95.31%,97.80%and 84.46%,respectively,which are significantly higher than that of TiO₂.After three photocatalytic cycles,the WO₃/TiO₂heterojunction still shows good photocatalytic activity and chemical stability.In order to regulate the crystal structure of TiO₂,the TiO_{2（Anatase）}/WO₃/TiO_{2（Rutile）}double-heterojunctions with different Cu doping amounts are prepared by solvothermal sintering method with Cu（NO₃）₂added into the WO₃/TiO₂heterojunction.They are characterized by XRD,SEM,TEM,XPS,ICP-MS,XPS,UV-vis,EIS,i-t,ESR and photocatalytic degradation under visible light.The results indicate that Cu leads to lattice defects of TiO₂through atomic substitution and promotes the formation of anatase at high temperature.Cu doping has a positive effect on the interfacial interaction between WO₃and TiO₂,which not only increases contact area,but also significantly changes the morphology structure of TiO₂.The coexistence of anatase and rutile confirm the successful synthesis of TiO_{2（Anatase）}/WO₃/TiO_{2（Rutile）}double-heterojunction.Its large specific surface area increases the contact area with pollutants,and the existence of oxygen vacancies and defects can serve as reactive sites to promote the transition of electron-holes.The synergistic effect of bi-phase TiO₂is crucial to enhance the photocatalytic activity.The good photoelectric response and low charge transfer resistance indicate that the synergy of TiO_{2（Anatase）}/WO₃/TiO_{2（Rutile）}double-heterojunction and the lattice defects are favorable for charge transfer,thus improving the photocatalytic activity.The degradation efficiency of Rh B,MB and MO by16%Cu-WO₃/TiO₂is 2.95,2.90 and 6.04 times that of P25,and the degradation speed is9.62,17.7 and 8.28 times that of P25,respectively.Moreover,the photocatalytic activity and chemical stability of the catalyst remained good after three photocatalytic cycles.