Bi₂WO₆/BiPO₄ Photocatalysts And Their Photocatalytic Performance Study

The photocatalytic technology is a promising way for solving the water pollution problem.But the usage of single photocatalyst is restricted in practical application for the low carriers separation rate and migration rate.Constructing heterojunctions can effectively enhance the quantum efficiency,so as to improve the photocatalytic performance.In this study,an ultrasonic chemical method is used to synthesize the Bi₂WO₆/BiPO₄ Z-scheme photocatalysts and Bi₂WO₆/BiPO₄/C₃N₄ double Z-scheme photocatalysts.The formation process and photocatalytic mechanism of the heterojunction are studied.A sol-gel method is used to synthesize the Bi₂WO₆/BiPO₄ films.The impacts of the heterojunction on the photocatalysis properties is studied by the photoelectrochemical analysis.The results are shown as follows:?1?The Bi₂WO₆/BiPO₄ Z-scheme photocatalysts are synthesized by an ultrasonic chemical method.Two kinds of semiconductors with internal polar electric fields,Bi₂WO₆ and BiPO₄,are chose as raw materials.The positron centers PO₄ tetrahedrons on the surface of BiPO₄ attract the WO₄ layers of Bi₂WO₆ which are electronically enriched.The synclastic polar electric fields of Bi₂WO₆ and BiPO₄ induce an electric field and they further render the generation of Bi₂WO₆/Bi PO₄ interface.The P-O-W bonds are generated in the interface and the Z-scheme heterajunctions are formed.When exposed to the simulated solar light in 270 min,the removal rate of Bi₂WO₆/Bi PO₄ Z-scheme photocatalysts are over 95%.The photodegradation rate are 1.88 and 4.29 times higher than Bi₂WO₆ and Bi PO₄,respectively.The photocurrent are 1.9 and 10.3 times higher than Bi₂WO₆ and BiPO₄ in the same condiction.?2?The Bi₂WO₆/Bi PO₄/C₃N₄ double Z-scheme photocatalysts are prepared by the ultrasonic chemical method with Bi₂WO₆/BiPO₄ Z-scheme photocatalysts and g-C₃N₄.The flower-like Bi₂WO₆/Bi PO₄ are destroyed into nanopieces and anchored to the surface of C₃N₄,forming the Bi₂WO₆/BiPO₄/C₃N₄ heterojunction.The absorption rates of Bi₂WO₆/BiPO₄/C₃N₄ heterojunction are around20%³0%,a little bit lower than Bi₂WO₆/C₃N₄ heterojunction and Bi₂WO₆.Under the irradiation of simulated solar light,the removal rate of Bi₂WO₆/BiPO₄/C₃N₄ heterojunction in 60 min is 95%,still lower than Bi₂WO₆/BiPO₄/C₃N₄ heterojunction,which is resulted from the shading effect of C₃N₄ to Bi₂WO₆ and BiPO₄.Meanwhile,the carriers separation rate,migration rate and photocatalytic ability of Bi₂WO₆/Bi PO₄/C₃N₄ heterojunction are apparently higher than Bi₂WO₆,C₃N₄ and Bi₂WO₆/C₃N₄,confirming that Bi₂WO₆/BiPO₄/C₃N₄ heterojunctions are double Z-scheme photocatalysts.?3?The Bi₂WO₆/BiPO₄ films are prepared by sol-gel method.The Bi₂WO₆films are annealed layer by layer and form porous morphology.BiPO₄ island particles are anchored at the surfaces,forming Bi₂WO₆/BiPO₄ Z-scheme composite films.The effective building of the Bi₂WO₆/BiPO₄ interfaces facilitate the enhancement of the carrier separation and migration rate in the films.The transient current density of the composite films are 1.93 and 17.17 times higher than Bi₂WO₆ film and BiPO₄ film.The redox activity of the composite films are1.38 times higher than Bi₂WO₆ film.The front-side-irradiation photocurrent of the composite films are larger than the back-side-irradiation current,which indicates that Bi₂WO₆/BiPO₄ composite films are Z-scheme heterojunction films.Under the irradiation of simulated solar light,the removal rate of RhB over the composite films are 32%,1.3 times higher than Bi₂WO₆ film.