Study On The Photocatalytic And Photoelectro-Catalytic Performance Of Bismuth Oxybromide

Photocatalytic technology is considered as a promising wastewater treatment,because of its handy device,moderate reaction condition and simple operation method.Recently,Bismuth oxybromide(BiOBr)has attracted extensive attention as new visible-light-driven photocatalyst with narrow band gap,which remedy the limitation of traditional titanium dioxide that cannot respond to visible light.However,the issue of low photocatalytic efficiency still restricts the development and application of narrow band gap semiconductor photocatalyst,and the most important reason is that the photo-generated electrons and holes are easy to recombine.Therefore,in order to promote the development of photocatalytic technology in wastewater treatment,it is necessary to improve the separation efficiency of photo-generated charge carriers in semiconductor photocatalyst.This paper starts from two aspects:microcosmic photocatalyst regulation and macroscopic electric field construction with preparing photocatalyst and photoanode based on BiOBr,which aimed at exploring efficient methods for improving the separation efficiency of photo-generated charge carriers.In the microcosmic aspect,pH adjustment was chosen as an efficient and convenient approach.The influence mechanism of hydrothermal pH value on the physicochemical property,charge carriers separation ability and photocatalytic activity was discussed.In the macroscopic aspect,two kinds of BiOBr-based photoanodes were prepared via powder loading method and in-situ synthesis method,which were further used to construct photocatalytic fuel cell(PFC).The properties of the above two PFCs were evaluated.Moreover,the photo-generated charge carrier separation ability and working mechanism of PFC were illustrated.The main conclusions are summarized as following:1.The influence of pH adjustment on the photocatalytic performance of BiOBr.The pH value influenced the morphology of BiOBr through chaning the exposed face and crystal formation by adjusting H+ concentration.The BiOBr obtained at pH 7(BOB-7)had flower-like structure assembled by small and thin nanosheets.Among all samples,BOB-7 had the optimal photocatalytic activity for the degradation of pollutants,and its degradation kinetics constants towards RhB and BPA were 3.16,1.91,1.31 times and 2.91,1.87,1.47 times as much as BOB-1,BOB-3 and BOB-5,respectively.It could be attributed to the beeter charge carriers separation due to the smaller nanosheets of BOB-7.According to the mechanism analysis,photo-generated holes were the main active substance in photocatalytic degradation reaction.2.The photoelectrocatalytic performance of PFC with BiOBr photoanode prepared via powder coating method.When the powder load ratio was 70%,the BiOBr/AlOOH/TNAs photoanode had the best photocatalytic activity.The crystallite structure,surface valence and photoabsorption properties of optical anode were basically consistent with BiOBr powders,but the morphology was affected by AlOOH.The degradation kinetics constant of BiOBr/AlOOH/TNAs-Pt PFC towards RhB was increased from 0.436 h-1 at open circuit to 0.562 h-1 at closed circuit.The PFC also had electricity generation capacity,which presented short-circuit current of 6.11 ?A/cm2 and a maximum output power density of 0.92 ?W/cm2.It was confirmed that photo-generated holes still played a main role in photocatalytic degradation of RhB.The photo-generated electrons were transferred to the cathode via external circuit and reacted with oxygen at cathode,which improved the photocatalytic efficiency.3.The photoelectrocatalytic performance of PFC with BiOBr photoanode prepared via a successive ionic layer adsorption and reaction(SILAR)method.The BiOBr/TNAs photoanode with 15 SILAR cycles showed the highest activity.The degradation kinetic constant of BiOBr/TNAs-Pt PFC was increased from 0.897 h-1 at open circuit to 1.271 h"1 at closed circuit.The PFC presented short-circuit current of 19.94 ?A/cm2 and a maximum output power density of 3.01 ?W/cm2.This PFC had superior photocatalytic degradation activity and electricity generation capacity,which were 2.26 and 3.27 times as BiOBr/AlOOH/TNAs-Pt PFC,respectively.It was because the BiOBr/TNAs photoanode had superior separation efficiency.The working mechanism of PFC showed that the photo-generated holes also played a main role in RhB degradation,and the electrons transferred to the cathode via the external circuit.The increacement of oxygen and RhB concentration could facilitate the comsumption of photo-generated electrons and holes,which improved the PFC performance.