Preparation And Photoelectrocatalytic Organics Degradation Performance Of Bi₂MoO₆-based Hybrid Electrode

Photoelectrocatalysis（PEC）,as a coupling process of photocatalysis and electrocatalysis,has drawn great attention in the fields of new energy development and environmental pollution treatment and shown unique prospects in the application development of water organics degradation.In this study,Bi₂MoO₆,a bismuth-based visible light-responsive photocatalyst,was modified,made into composite electrodes and used in the PEC process to improve the degradation performance of organic in water.And the effects of modification and reaction conditions have been studied through characterization and testing.Firstly,Carbon quantum dots（CQDs）were used to modify the Bi₂MoO₆photoelectrode.Bi₂MoO₆ electrode was prepared by solvothermal and calcination process,and CQDs were loaded on its surface through a dynamic adsorption method.The introduction of CQDs accelerated the migration of photogenerated carriers on the electrode surface and enhanced the absorption capacity of visible light through its unique up-conversion fluorescence effect.Combined with the improvement of the carrier separation efficiency by external bias in PEC process,the CQDs/Bi₂MoO₆hybrid electrode showed 82.7%degradation rate toward methylene blue in 2 hours under visible light.An explanation of the PEC degradation mechanism was proposed based on the results of various characterization techniques.In order to further improve the transfer efficiency of photogenerated charges on the surface and interface of the Bi₂MoO₆ composite photoelectrode,surface oxygen vacancies（OVs）modification and semiconductor heterojunction construction were carried out.The WO₃ electrode substrate was prepared by hydrothermal and calcination process,and then OVs Bi₂MoO₆ was loaded in situ by solvothermal method.The combination of two semiconductors adjusted the band structure of the composite material,which led to enhanced visible light absorption.Furthermore,under the joint influences of the built-in electric field of heterojunction,the electron trapping effect of OVs and the electrons driving effect of PEC external bias,the mobility of carriers was greatly enhanced.And due to its suitable energy band position,the hybrid electrode was able to produce h⁺,·OH and·O₂^-radicals.Therefore,the OVs Bi₂MoO₆/WO₃ electrode possessed a higher PEC degradation performance than original monomer material and its degradation efficiency of rhodamine B reached 80.1%within 4 hours under visible light.Besides,a suitable composite ratio of OVs Bi₂MoO₆ and WO₃ was helpful to improve the cycle stability of photoelectrode.Combining the characterization and performance testing of the composite catalyst,the synergistic effect mechanism of heterojunction,surface OVs modification and PEC process was proposed.In addition,a water splitting threshold bias voltage was found in the PEC degradation.A bias voltage below but close to this threshold had the best PEC reaction efficiency.But a bias voltage higher than this threshold would cause oxygen evolution on the electrode,leading to a higher degradation ability but lower energy efficiency.According to different conditions,a corresponding control strategy can be specified,which will provide ideas for the PEC degradation of water organic pollution in practical application.