Preparation And Photocatalytic Properties Of Metal Ion Doped Bi₄O₅Br₂ Materials

A new type of semiconductor material,oxygen-rich bismuth oxyhalide Bi_xO_yBr_z(X=Cl,Br,I),whose structure is similar to bismuth oxyhalide(Bi OX,X=Cl,Br.I),is composed of alternating layers of bismuth oxygen and halogen ions The graphene-like structure formed by the arrangement forms a built-in electric field inside,so that the photo-generated electron holes generated by the compound are effectively separated,so that this type of material exhibits good photocatalytic performance.Among these materials,such as Bi OBr,Bi₄O₅Br₂ and Bi₂₄O₃₁Br₁₀,show unique optical properties due to their suitable energy band structures.Compared with Bi OBr(the band gap value is 2.85 e V),Bi₄O₅Br₂ has a narrow band gap(2.4 e V)and a more negative conduction band position(-0.4 e V),which has attracted extensive attention of researchers.Pure Bi₄O₅Br₂ nanosheets still suffer from low quantum efficiency,which affects the ability of photocatalysts to degrade pollutants.In this paper,using Re(NO₃)₃·6H₂O(Re=Cu,Er,Cd)as the metal ion source,the photocatalysts with pure phase and metal ions singly and co-doped Bi₄O₅Br₂ nanostructures were prepared by microwave hydrothermal method.By changing the concentration of doped metal ions,nanostructured photocatalysts with flakes were prepared and their visible light photocatalytic performance was investigated.This paper mainly includes the following three aspects:(1)BiOBr and Bi₄O₅Br₂ photocatalysts were synthesized by one-step hydrothermal method and microwave hydrothermal method.The photocatalytic activities of the as-prepared Bi OBr and Bi₄O₅Br₂ photocatalysts were evaluated experimentally with SMZ as a pollution source under simulated sunlight irradiation conditions.The results show that Bi₄O₅Br₂ has a narrower bandgap structure,more reactive sites(OVs),and stronger photocatalytic activity than Bi OBr materials.By analyzing the optical properties and photocatalytic activity of Bi₄O₅Br₂,Bi₄O₅Br₂has a 20%increase in the degradation efficiency of broad-spectrum antibiotics compared with Bi OBr,which is mainly due to the role of O₂^-and OH^-are leading in the catalytic reaction..(2)Bi₄O₅Br₂ and metal mono-doped and co-doped Bi₄O₅Br₂ photocatalysts were prepared by microwave hydrothermal method,and the effect of photocatalytic removal of broad-spectrum antibiotic sulfamethoxazole was studied under simulated sunlight irradiation conditions.Compared with the intrinsic Bi₄O₅Br₂catalyst,the photocatalytic activity of the single-doped Bi₄O₅Br₂ catalyst was improved,but the photocatalytic activity of Er Cd-Bi₄O₅Br₂ and Cu Cd-Bi₄O₅Br₂ in the co-doped Bi₄O₅Br₂ photocatalyst was more significantly improved.The photodegradation rates of photocatalysts Bi₄O₅Br₂,Cu-Bi₄O₅Br₂,Er-Bi₄O₅Br₂,Cd-Bi₄O₅Br₂ and co-doped Er Cd-Bi₄O₅Br₂ and Cu Cd-Bi₄O₅Br₂ reached 20%,60%,55%,34%,100%and 95%,respectively.The reduction rate constants of SMZ induced by Cu-Bi₄O₅Br₂,Er-Bi₄O₅Br₂,Cd-Bi₄O₅Br₂,Er Cu-Bi₄O₅Br₂,Er Cd-Bi₄O₅Br₂ and Cu Cd-Bi₄O₅Br₂ were 4.12,3.8,2.26,2.07,12.12 and 15.96times higher than those of Bi₄O₅Br₂ respectively.The results show that the single-doped photocatalysts of Cu-Bi₄O₅Br₂,Er-Bi₄O₅Br₂ and Cd-Bi₄O₅Br₂ have the catalytic effect of single metal ions,and the co-doped photocatalysts of Er Cu-Bi₄O₅Br₂,Er Cd-Bi₄O₅Br₂ and Cu Cd-Bi₄O₅Br₂ have the synergistic effect of double ions catalytic effect.The improvement of the photocatalytic activity is mainly attributed to the generation of more kinds of radical functional groups to participate in the catalytic reaction after metal co-doping Bi₄O₅Br₂.(3)Bi₄O₅Br₂ materials are theoretically studied based on first principles.The optical and catalytic properties of metal-doped Bi₄O₅Br₂ catalysts were systematically analyzed.In the visible light range,samples with narrow band gaps can easily detect high photocatalytic performance.Therefore,the calculated results show that the band gaps of Bi₄O₅Br₂ and metal-doped Bi₄O₅Br₂ materials are:Bi₄O₅Br₂(2.77 e V),Cu-Bi₄O₅Br₂(2.70 e V),Er-Bi₄O₅Br₂(2.75 e V),Cd-Bi₄O₅Br₂(2.71 e V),Er Cd-Bi₄O₅Br₂(2.69 e V)and Cu Cd-Bi₄O₅Br₂(2.67 e V).The research results show that both metal single-doping and co-doping can reduce the band gap,but the band gap of metal co-doping is smaller than that of metal single-doping,and the effective spectral range is wider.catalytic activity.In order to further study the influence of Cu,Er and Cd ions on the electronic structure and photocatalytic activity of the doped system,Bi₄O₅Br₂,Cu-Bi₄O₅Br₂,Er-Bi₄O₅Br₂,Cd-Bi₄O₅Br₂,Er Cu-Bi₄O₅Br₂,Er Cd-Bi₄O₅Br₂ and Cu Cd-Bi₄O₅Br₂ were calculated in this paper.Total density of states(TDOS)and partial density of states(PDOS)of photocatalysts.The results show that the redox reactions that the separated electrons and holes participate in at the bottom and top of the CB reduce the efficiency of photogenerated electron and hole recombination and significantly improve the photocatalytic activity.In addition,the calculated catalyst charge density difference results showed that the doping of metal ions provided additional electrons and holes,which promoted the catalytic activity of the reactants,resulting in the generation of free radicals and the enhancement of pollutant degradation in Bi₄O₅Br₂ catalysts.In particular,Cu-Cd co-doping and Er-Cd co-doping ions can effectively improve the charge separation efficiency and inhibit the recombination of electron-hole pairs,thereby obtaining excellent photocatalytic performance..