Band Structure Regulation And Photocatalytic Activity Of Bismuth Oxhalides

Environmental pollutant is serious threat human healthy and development of suitable society.Therefore,it is urgent to search highly efficient technology.Recently,semiconductor photocatalyst has been attracted intensive attention because of their superior photocatalytic activity for pollutant degradation.Bismuth oxhalides?BiOX,X=Cl,Br,and I?has been attracted widely attention due to self-built electric field of layered structure,it is found that the oxygen vacancies?OVs?and band gap are induced by solid solution.However,the problems are still existed in catalysts,for example:1)the catalysts exhibit low photocatalytic activity for azo compounds and aromatic compounds degradation;2)strategies are still less to enhance the photocatalytic actively of BiOX only including:solid solution,heterojunction and defect engineering et al;3)the synthesis of OVs is more severe.In our work,the Bi?NO?₃·5H₂O,KCl,KI,NaBr and NaH₂PO₄ are employed as raw material to situ synthesis of Z-scheme BiPO₄/BiOCl_0.9I_0.1 heterostructure.Moreover,BiOBr is synthesized via alter reaction temperature and different mixing EG and water solvent ratio.The photocatalytic activities of photocatalyst are tested by RhB,MO,p-Nitrophenol?p-NP?and phenol degradation.The structure,morphology,photoelectrochemical properties,optical properties and band structure of the synthesized catalyst are investigated.In addition,the band structure,density of states,population analysis and optical properties of BiOBr are performed through CASTEP of the Materials Studio software package.The obtained conclusions are as follow:?1?In situ synthesis of Z-scheme BiPO₄/BiOCl_0.9I_0.1 heterostructure exhibits superior photocatalytic activity for RhB and phenol degradation.9%BiPO₄/BiOCl_0.9I_0.1 could degrade96.4%RhB in 6 min.Moreover,30%BiPO₄/BiOCl_0.9I_0.1 heterostructure degrades 88%phenol within 10 min.The enhanced photoactivity of BiPO₄/BiOCl_0.9I_0.1 heterostructure could be attributed to multiple defects such as:Bi⁵⁺,Bi^?3-x?+,IO₃^-,I₃^-and oxygen vacancy.Multiple defects as electron transfer channels could effectivity promote the separation of electron-hole pairs and prolonging the lifetime of charges.Moreover,Z-scheme heterostructure promotes the separation rates of electrons and holes and retains strong redox capacity.?2?BiOBr is synthesized by alter temperature of hydrothermal reaction.When reaction temperatures are 120?,the obtained BiOBr sample shows excellent photoactivity for RhB and p-Nitrophenol?p-NP?degradation.BiOBr?120?almost degrades 100%RhB in 10 min.Meanwhile,BiOBr?120?could degrade 93%p-NP in 12 min.The BiOBr?120?exhibits the highest photoactively.Moreover,ethylene glycol can control the crystal plane growth of BiOBr.As the ethylene glycol content increases,the intensity of the?102?crystal plane peak gradually decreases and the?110?crystal plane becomes the main peak.The BiOBr?3:7?catalyst displays the best photocatalytic activity for pollutants degradation.The reaction rate constant K of BiOBr?3:7?is 16 times larger than that of BiOBr?0:10??3?BiOBr with OV_S shows the superior photocatalytic activity,which is ascribed to generate of OVs.The introduction of OVs could decrease the band gap to border the region of light adsorption.OVs as sub-band excitation could effectively inhibit the recombination of electron-hole pairs.Moreover,multiple defects such as:Bi⁵⁺,Bi^?3-x?+,IO₃^-,I₃^-and oxygen vacancy as electron transfer channels could effectivity promote the separation of electron-hole pairs and prolonging the lifetime of charges.Additionally,the direct Z-scheme heterostructure keep the stronger reduction and oxidizing ability of CB and VB.?4?BiOBr structure model with OVs is optimized and calculated based on density functional theory.The calculation results show that BiOBr with oxygen vacancy still maintain the indirect electronic transition mode.The calculated results of band structure and density distribution demonstrate that the OVs as sub-band excitation near the Fermi.Moreover,the state density calculation proves that the impurity level is mainly contributed by the Bi-6p and O-2p orbitals.The existence of impurity level of BiOBr decreases the band gap compared with the pure BiOBr.The calculated UV-vis DRS spectra shows that the existence of OVs leads to the red shift of adsoption,which are consistant with the experimental result.The calculated result further proves the reasonable guess.