Preparation Of Copper Bismuth Oxide-based Photocatalysts And Their Performance For Tetracycline Degradation In Aqueous Environment

Antibiotics can be used to treat human and animal diseases and act as hormones to accelerate the biological growth.In recent years,antibiotics have been widely used in medical treatment,animal husbandry and agriculture,resulting in the abuse of antibiotics.The spread,accumulation and residue of antibiotics in the environment will eventually enter the human body through biological circulation,causing irreversible damage to human organs,carcinogenic and even teratogenic mutagenesis.Meanwhile,antibiotics will re-enter the aquatic environment through the ecological cycle,seriously threatening the ecological balance.Therefore,it is urgent to develop efficient and stable technologies to remove antibiotics from water environment.As one of the advanced oxidation treatment technologies,photocatalysis has the advantages of high efficiency,cost-effectivness,no secondary pollution and simple operation,which has been favored by many researchers and applied to the removal of antibiotics.Photocatalysis technology is very promising for the degradation and removal of pollutants in the environment.The poor visible light response and fast electron-hole pairs recombination of photocatalysts are major problems that restrict the development and application of photocatalysis technology.The photocatalytic performance of the semiconductor can be improved by coupling with another semiconductor with appropriate band postions.CuBi₂O₄,as a non-toxic and stable narrow band gap（1.8 e V）p-type semiconductor,is a typical visible-light-driven photocatalyst,and its conduction band position is relatively negative,enables its strong reduction ability.CuBi₂O₄ is mainly used in CO₂ reduction and hydrogen generation as photocathode material.Recently,by combining with other semiconductors,CuBi₂O₄ has been gradually applied in the field of organic compound destruction.However,because of its narrow band gap,the charge carriers’recombination rate is pretty high,the oxidation ability of holes in its valence band is very weak.Therefore,to modify the property of CuBi₂O₄,four different heterogeneous junction CuBi₂O₄-based composite photocatalytic materials were designed by combining with wide-band-gap semiconductor,such as CuBi₂O₄/WO₃Z-Scheme heterojunction,spherical-like CuBi₂O₄/Bi₂WO₃ heterojunction,p-n type CuBi₂O₄/Sr_0.5Na Ta O₃ heterojunction,ternary Z-Scheme CuBi₂O₄/Ag/KTa₂O₆ heterojunction.In order to analyze the morphology,crystal phase,element composition,surface functional group,valence state,photoelectric property,impedance,light absorption performance and other characteristics of the prepared composites,a variety of characterization techniques such as SEM+EDS,TEM,XRD,FT-IR,XPS,PL,IT,EIS and UV-vis.etc.were systematically conducted.The catalytic performance of the material was investigated through photocatalytic degradation experiment.The typical broad-spectrum tetracycline（TC）in antibiotic wastewater was selected as the target compound.The Xenon lamp was used as the excitation light source,and different wavelength ranges were controlled through the filter.Based on the capture experiment and the above experimental results,the specific mechanism in the photocatalytic reaction process was analyzed,and the electron migration path was discussed in detail.This study provides theoretical support for the future research of novel CuBi₂O₄-based composites construction.The main contents of this paper are as follows:（1）CuBi₂O₄/WO₃composites were prepared by the hydrothermal method.The photocatalytic performance of the CuBi₂O₄/WO₃composites was significantly higher than that of the pure CuBi₂O₄ and WO₃.Under simulated solar light irridation,90%TC was degraded in 2hours over 60 wt%CuBi₂O₄/WO₃composite,and the apprent rate constant was 8 and 4.5 times higher than that of the pure CuBi₂O₄ and WO₃,respectively.The superior photocatalytic performance of CuBi₂O₄/WO₃composite materials was mainly attributed to the Z-scheme heterojunction formed at the interface,which retained the strong redox ability of each semiconductor.The photocurrent density of the composite was increased,the impedance became smaller,the lifetime of the electron is extended,and the separation efficiency of the charge carriers was greatly improved.（2）Heterogeneous CuBi₂O₄/Bi₂WO₃complexes with different mass ratios were prepared by hydrothermal method.Under visible light irradiation,93%TC could be degraded within 1 h over60 wt%CuBi₂O₄/Bi₂WO₃,and its first-order rate constant was about 7 times higher than that of pure CuBi₂O₄and Bi₂WO₃.The capture experiment and the ESR experiment proved that·OH and·O₂^-were the main reactive species in the reaction.DFT results indicated that for CuBi₂O₄/Bi₂WO₃composites,photogenerated electrons migrated from the W 5d orbital of Bi₂WO₃to the O 2p+Bi 6s hybrid orbitals of CuBi₂O₄.The holes in the O 2p orbital of Bi₂WO₃ valence band and electrons in the Cu 3d orbital of CuBi₂O₄ conduction band play importan roles in the photocatalytic reaction.（3）p-type CuBi₂O₄ and n-type Sr_0.5Na Ta O₃was combined together by hydrothermal method.Firstly,perovskite Na Ta O₃was modified by Sr doping strategy to tune its electronic band structure.Under simulated sunlight irridation,TC degradation efficiency could reach up to 86%within 90mins.DFT calculations revealed that after Sr doping,the valence band maximum of Na Ta O₃moved upward for 0.036 V,the conduction band minimum moved downward for 0.62 V.The bandgap energy decreased from 3.86 e V to 2.82 e V.The Ta-O-Ta bonds were distorted and became more linear,which was more conducive to the migration of electron holes.Under visible light irradiation,the degradation rate of TC over 40 wt%CuBi₂O₄/Sr_0.5Na Ta O₃ could reach 92%within 2 h,while the degradation efficiency of TC over Sr_0.5Na Ta O₃in 2 h was only 59%under visible light irradiation.The improved photocatalytic performance of the composite was mainly attributed to the p-n heterojunction at the interface.The electric field on the interface promoted the lower carrier recombination rate and the higher carrier mobility as well.（4）Ternary Z-scheme CuBi₂O₄/Ag/KTa₂O₆heterojunction was prepared by hydrothermal method and photoreduction deposition method.Photocatalytic degradation experiment results under visible light showed that 94%TC could be degraded over ternary CuBi₂O₄/Ag/KTa₂O₆wtihin 2 hour.The trapping experiments results showed that·OH,h⁺and·O₂^-all played important roles in the TC degradation process.The reaction rate constant(k=0.0227 min^-1)of CuBi₂O₄/Ag/KTa₂O₆ was 7.6 times higher than that of pure KTa₂O₆(k=0.003 min^-1)and 5.7 times higher than that of pure CuBi₂O₄(k=0.0041 min^-1).The plasmon resonance effect of noble metal Ag inbetween the interface of CuBi₂O₄ and KTa₂O₆ had greatly enhance the visible-light-harvesting ability.The superior photocatalytic performance of CuBi₂O₄/Ag/KTa₂O₆ composite could be attributed to the Z heterojunction,and media effect of the noble metal,which resulted in the low carrier recombination rate and efficient carrier mobility.