Study On Photoelectric Pollutant Degradation On BiPO₄ Films And Their Enhanced Degradation Performance Through In Situ H₂O₂ Production

Photoelectrocatalytic pollutant degradation has attracted more and more attention due to its advantages of high efficiency,energy-saving and non-toxic.The external electric field that derives from the bias can facilitate the separation of photogenerated electrons and holes,and thus sufficiently accelerate the degradation.Up to now,many photoelectrodes have been developed,such as TiO₂,BiVO₄,WO₃,et al.However,their photoelectrocatalytic activity is limited by inappropriate band structure and low carrier separation efficiency.Moreover,the wide band gap of some catalysts also leads to the insufficient utilization of sunlight.Therefore,photoelectrodes with high photoelectrocatalytic degradation activity still need to be explored.It was reported that the photocatalytic activity of BiPO₄ for MB degradation was twice that of TiO₂.On the one hand,the high activity is due to the deep valence band of BiPO₄,which promotes the oxidation of OH^-to produce strong oxidizing·OH.On the other hand,it is due to the higher electron-hole pair separation efficiency of BiPO₄.However,there are also some disadvantages for the application of BiPO₄,such as the limitation of wide band gap,the rapid recombination of electrons and holes,and the separation of powder from the system after reaction.In this paper,Au/BiPO₄ film and AgI/BiPO₄ film with high photoelectrocatalytic activity and visible light response were synthesized using monoclinic BiPO₄ film as the raw material for modification.The effects of electrolyte HF concentration on the crystal phase,morphology and performance of BiPO₄ film was investigated,the catalytic activity of the photoelectrochemical H₂O₂ production and photoelectric pollutant degradation on series BiPO₄films was evaluated,and the mechanism of in-situ H₂O₂ production enhancing degradation activity was revealed.The main research contents and conclusions are as follows:（1）The monoclinic BiPO₄ nanorod film with excelent photoelectrocatalytic activity was synthesized by anodization.The crystal phase and morphology were characterized by XRD and SEM,and the composition and pore size distribution were investigated by XPS and mercury intrusion measurement.The photoelectrocatalytic experimental results show that the optimal BiPO₄ film can degrade MB to less than 10%within 30 min.The excellent photoelectrocatalytic activity originate from suitable crystal phase and nanorod diameters and the high carrier separation efficiency.（2）Au/BiPO₄ film photocathode with visible light response and enhanced UV light activity was prepared by loading Au nanoparticles on BiPO₄ film via photoelectric deposition.The plasma resonance effect of Au broadens the spectral absorption range of BiPO₄ film.Moreover,the activity of photoelectrocatalytic H₂O₂ production on Au/BiPO₄ film under UV irradiation was 1.8 times that of BiPO₄ films,which was due to the improved separation efficiency of photogenerated carriers by electron transfer from BiPO₄ to Au.MB was degraded to less than10%on Au/BiPO₄ photocathode within 15 minutes under UV light,which is greatly improved compared with the BiPO₄ photoanode.Active species capture experiments revealed that·OH was the main active species during the degradation process,which was produced by the oxidation of H₂O at the anode or the decomposition of H₂O₂ produced at the cathode.（3）AgI/BiPO₄ heterojunction film was fabricated by darkroom deposition-precipitation,and the catalytic activities for photoelectrochemical（PEC）H₂O₂ production and the degradation of typical organic pollutant MB under UV and visible light were investigated.The results show that the activity of H₂O₂ production on AgI/BiPO₄ film photoanode is twice that of BiPO₄ photoanode,and the enhanced activity is due to the increased carrier separation efficiency caused by heterojunction.The production of H₂O₂ was detected during the PEC degradation process,which enhanced the degradation performance.The loading of AgI nanoparticles expands the light absorption range of BiPO₄ film to 450 nm,which endows BiPO₄film with visible light activity and improves the utilization of sunlight.