Preparation And Photocatalytic Performance Of Bi₂O₂CO₃ Based Heterojunction Photocatalysts

Semiconductor photocatalysis technology is highly efficient and environmentally friendly and has been applied to antibiotic mineralization.However,the performance of most semiconductor photocatalysts is not very satisfactory.It is still a big challenge to prepare semiconductor photocatalysts with wide spectral response,good cyclic stability and high redox capacity.Bi2O2CO3 is one of the most promising semiconductor photocatalysts,but its practical application was limited by its narrow optical absorption range,low photogenerated carrier separation rate and weak photocatalytic performance when used alone.In this thesis,oxygen vacancy is constructed in Bi2O2CO3,Bi/OV-Bi2O2CO3,RGO-Bi/OV-Bi2O2CO3 and Z-scheme OV-CuBi2O4/Bi2O2CO3 heterojunctions are prepared.The broad spectral response,cycle stability and redox ability of photocatalysts are studied,and the enhancement mechanism of catalytic performance are discussed by DFT calculation.The main conclusions are as follows:(1)Bi/OV-Bi2O2CO3 photocatalyst was prepared by solvothermal method and NaBH4 reduction method.C6H5O7Na3 complexes with Bi3+to form C6H5BiO7,and OV-Bi2O2CO3 is formed by solvothermal process.OV-Bi2O2CO3 is hydrolyzed to generate OV-Bi2O2CO3·BiO+,which is then reduced by NaBH4 to form Bi/OV-Bi2O2CO3.Bi and oxygen vacancies synergistically facilitate carrier separation and transfer and broaden light absorbance to the full spectral range.Under visible/near-infrared light,the removal rate of TC by Bi-OV-Bi2O2CO3 is 78%/75%,and the degradation rate is 2.9/3.5 times that of Bi2O2CO3.Due to the migration of Bi’s free electrons to Bi2O2CO3,and the oxygen vacancy of Bi2O2CO3 store the electrons,TC was mineralized into small molecule organic products with m/z of 114 and 102 after 30 min of dark reaction.Bi/OV-Bi2O2CO3 realizes the full-spectrum degradation of TC and has a certain dark degradation ability.(2)RGO-Bi/OV-Bi2O2CO3 heterojunction photocatalysts were prepared by UV irradiation.Bi/OV-Bi2O2CO3 is adsorbed on the surface of GO and the chemical bond is formed.Under the effect of photoelectrons,GO is reduced to RGO,OV-Bi2O2CO3 absorbs photoelectrons to increase the oxygen vacancy concentration,and the charges are transferred from Bi/OV-Bi2O2CO3 to RGO,storing electrons on RGO.After 30 min of dark reaction,TC is degraded into intermediate products with m/z of 100,83,74 and 60,indicating that RGO enhance the dark catalytic ability of Bi/OV-Bi2O2CO3.Under visible/near-infrared light,the degradation rate of RGO-Bi/OV-Bi2O2CO3 to TC is 87%/80%,the removal rate of TOC is 58%/50%,the degradation rate is 2.7/4.2 times that of Bi2O2CO3,and the degradation stability remains good after five runs.The synergistic effect of oxygen vacancy,the LSPR effect of Bi and the TE of RGO achieve the dark and full spectrum stable and efficient mineralization of TC.(3)Z-scheme OV-CuBi2O4/Bi2O2CO3,heterojunctions are prepared by hydrothermal and self-assembly methods.Bi2O2CO3 is added to the methanol solution of CuBi2O4,and a uniform and stable solution is obtained under electrostatic repulsion.CuBi2O4 microspheres and Bi2O2CO3 flower-like microspheres self-assemble into heterojunction under gravity when methanol is volatilized.The electron concentration differences between CuBi2O4 and Bi2O2CO3 lead to electron transfer from CuBi2O4 to Bi2O2CO3,which is accompanied by the decrease of Bi5+ in OV-CuBi2O4/Bi2O2CO3.Thus,the built-in electric field pointing from CuBi2O4 to Bi2O2CO3 is formed.81%/80%of TC,53%/52%of TOC can be reduced by the heterojunction under vis/NIR light,and the degradation efficiencies are 16/9.8 and 3.8/4.1 times that of CuBi2O4 and Bi2O2CO3,respectively.The enhanced photocatalytic performance of OVCuBi2O4/Bi2O2CO3 can be attributed to the following reasons:the presence of built-in electric field and the construction of Z-scheme heterojunction promote the redox capacity;the LSPR effect of OVs raises the absorbance and molecular oxygen activation efficiency;the photoexcitation cycle of Bi3+/Bi5+ boosts the photocatalytic activity under NIR light;the superior light absorption characteristics of CuBi2O4 with a narrow band gap broaden the light response range of heterojunction.