Preparation And Photocatalytic Properties Of Metal Element Doped Bismuth Oxychloride Photocatalyst

With the continuous improvement of modern industrialization level,the problem of environmental pollution is becoming more and more serious.Photocatalytic technology has been widely used in solving environmental pollution,treating sewage and reducing carbon emissions.The research of photocatalytic materials with high catalytic activity has been widely concerned by researchers at home and abroad.Bismuth oxychloride（BiOCl）is a kind of bismuth-based photocatalyst.Compared with other photocatalysts,its unique layered structure has enough space to separate and migrate photogenerated carriers.The internal charge distribution is not uniform,so that the corresponding atomic/atomic orbitals produce an internal electric field under the polarization of charge,which promotes the efficient separation and migration of photogenerated carriers.BiOCl also has the advantages of low preparation cost,easy structure regulation and low toxicity,which is an important material in the field of photocatalysis.However,BiOCl still has shortcomings:low utilization of visible light,weak absorption of visible light,and thus the photocatalytic efficiency is greatly affected;the high recombination rate of photogenerated electron-hole leads to a decrease in the number of electrons and holes that can diffuse to the surface of the material to participate in the reaction,and the catalytic efficiency is further limited.Therefore,it is imperative to modify BiOCl.The structure of BiOCl is easy to control,and its shortcomings such as small light response range and easy recombination of carriers can be modified by element doping.In this paper,BiOCl photocatalyst was modified by metal element doping.The influence of metal element doping on BiOCl system was systematically studied by first-principles calculation method.Compared with the experimental results,the metal element doped BiOCl photocatalyst was studied by combining theory with practice.The specific research contents are as follows:（1）First-principles simulation calculations of modified BiOCl.The models of BiOCl,BiOCl doped with transition metal elements and BiOCl doped with rare earth metal elements were constructed by Materials Studio software.The models were calculated by PBE functional of generalized gradient approximation（GGA）,and the changes of electronic structure and optical properties of BiOCl system before and after doping were analyzed.The results show that in the BiOCl system doped with six transition metal elements（Co,Ni,Fe,Mn,W,Zr）,the doping has little effect on the band gap of BiOCl,and the photocatalytic performance mainly depends on the influence of the introduction of impurity energy levels on the system.The band structure of Co,Ni,Fe,Mn and Zr is theoretically more conducive to the improvement of photocatalytic performance.In terms of optical properties,the absorption band edge of Co,Ni and Fe doped system expands to the visible light region and improves the charge transfer efficiency,showing good optical properties.Therefore,it is theoretically predicted that the doping of Co,Ni and Fe elements can realize the response of BiOCl in the visible light region and improve its photocatalytic activity.In the four rare earth metal elements（Eu,Er,Sm,Nd）doped BiOCl materials,the band gap also did not change significantly.In terms of band structure,the doping of Eu and Er elements are theoretically more conducive to the improvement of photocatalytic performance;in terms of optical properties,only the absorption band edge of the Eu doped system extends to the visible light region and exhibits good optical properties.Therefore,it is theoretically predicted that the doping of Eu element can make BiOCl obtain response in the visible light region and improve its photocatalytic performance.（2）Study on the modification of BiOCl doped with transition metal elements.Six transition metal elements（Co,Ni,Fe,Mn,W,Zr）doped BiOCl were prepared by solvothermal method.Five different doping ratios were set for each element.The photocatalytic performance was evaluated by comparing the degradation efficiency of Rhodamine B（Rh B）solution under visible light irradiation.The results show that the Co-doped BiOCl photocatalyst（Co-BiOCl）has the best photocatalytic performance when the doping ratio of Co²⁺and Bi³⁺is 1:5,which is 6.35 times of the degradation efficiency of undoped BiOCl.The experimental results are consistent with the theoretical calculations.The Co-BiOCl materials were characterized and tested by SEM,XRD,XPS,BET,DRS and electrochemical tests.The composition,morphology,light absorption performance and catalyst stability of Co-BiOCl were analyzed.The experimental results show that the Co-doped BiOCl photocatalyst successfully improves the light absorption ability in the visible region and the migration efficiency of photogenerated carriers inside the material while retaining the unique structure of BiOCl.Combined with the calculation results,the main reason for the improvement of photocatalytic performance is that the Co 3d state changes the band structure of BiOCl,and introduces a strong local energy level in the band gap,which is beneficial to the separation and migration of photogenerated carriers,thus improving its photocatalytic performance.（3）Modification of rare earth metal elements doped BiOCl.BiOCl doped with rare earth metal elements（Eu,Er,Sm,Nd）was prepared by solvothermal method.Five different doping ratios were set for each element.The photocatalytic performance was evaluated by comparing the degradation efficiency of Rh B solution under visible light irradiation.The Eu-doped BiOCl photocatalyst（Eu-BiOCl）has the best photocatalytic performance when the doping ratio of Eu³⁺to Bi³⁺is 1:10,which is 4.37 times that of undoped BiOCl.Eu-BiOCl materials were characterized and tested by SEM,XRD,XPS,BET,DRS and electrochemical tests.The morphology,element distribution and light absorption properties of Eu-BiOCl were analyzed.The results show that the Eu-BiOCl photocatalyst successfully improves the light absorption intensity in the visible light region and promotes the migration efficiency of photogenerated carriers in the material while retaining the unique structure of BiOCl.Combined with the calculation results,the main reason for the improvement of its photocatalytic performance is the change of the energy band structure of BiOCl by Eu 4f state.The impurity energy level is introduced at the top of the valence band,which reduces the energy required for the photogenerated electron transition,thereby improving its photocatalytic performance and realizing the purpose of BiOCl modification.