Preparation Of BiVO₄-based Composite Photoanodes And Study On The Catalytic Degradation Performance

With the rapid development of urbanization and industrialization,environmental pollution caused by the continuous release of various toxic substances into water has become a major problem in the world.Therefore,it is urgent to develop an efficient,safe and no secondary pollution water treatment technology.In recent years,new advanced oxidation technologies that combine photoelectrocatalysis（PEC）with other technologies（such as UV/H₂O₂and Fenton reaction）have attracted the attention of researchers.The core of PEC combined degradation technology is to design an efficient,stable,low-cost and environmentally friendly photoanode.In a variety of semiconductor materials,BiVO₄has been widely used in the field of photoelectrocatalysis due to its suitable narrow band gap（2.4～2.5 e V）,favorable band edge position,non-toxicity and low-cost.However,BiVO₄has defects of short hole diffusion length and low carrier mobility,which result in severe charge recombination and make the photocurrent density of BiVO₄much lower than 7.5 m A cm^-2（theoretical value）.In order to solve the above problems,this study designed two BiVO₄based composite photoanodes with excellent performance by means of element doping,post-treatment and cocatalyst loading,and then applied them to H₂O₂assisted in situ PEC degradation technology and PEC-Fenton technology,respectively,which achieved rapid degradation of organic pollutants.The specific research contents are as follows:（1）Gd_（0.50）:BiVO₄/FeOOH photoanode was prepared by electrodeposition and solution impregnation method.The doping of Gd and loading of FeOOH introduced more active sites for water oxidation to produce H₂O₂,improved the conductivity of composite photoanode,reduced charge recombination and accelerated the kinetics of surface water oxidation.The prepared Gd_（0.50）:BiVO₄/FeOOH photoanode shows an excellent photocurrent density of8.76 m A cm^-2at 1.76 V vs.RHE,which is 2.8 times that of pure BiVO₄(3.11m A cm^-2).At the same time,the composite photoanode showed a significantly enhanced H₂O₂production rate within the applied bias range,reaching 0.267μmol min^-1cm^-2at 3.0 V vs.RHE.The constructed PEC system realized in situ degradation of TC and MB with the help of produced H₂O₂.In result,the degradation rates of TC and MB exceeded 91%（40 min）and 96%（80 min）,respectively.（2）S-BiVO₄/CoOOH photoanode was prepared by a simple two-step solution impregnation method.Na₂SO₃post-treatment and CoOOH loading introduced oxygen vacancy defects into the composite photoanode,increased carrier density,accelerated electron hole separation and transfer as well as provided Fenton reagent.Compared with pure BiVO₄(1.03 m A cm^-2)and S-BiVO₄(1.80 m A cm^-2),the S-BiVO₄/CoOOH photoanode(2.88 m A cm^-2)has excellent photocurrent density.Meanwhile,the PEC-Fenton degradation rate of TC by S-BiVO₄/CoOOH photoanode reached 77.7%（40 min）,which was 2.0 times and 10.8 times of PEC degradation（39.8%）and Fenton degradation（7.2%）,respectively.Furthermore,the general applicability of transition metal hydroxyl oxides for PEC-Fenton degradation was demonstrated by loading NiOOH and FeOOH cocatalysts on S-BiVO₄.