Design Of Hierarchical Heterostructure Based On Bismuth Oxycarbonate And Study On The Mechanism Of Photocatalytic Tetracycline Hydrochloride Degradation

With the improving of health awareness and the growing production of pharmaceutical,antibiotics are widely applied in the field of healthcare,animal husbandry and aquaculture.However,most antibiotics with stable structure cannot be completely metabolized by human or animal body and so that they are constantly discharged into water in various forms,which pose a threat to the ecological environment.Therefore,it is necessary to develop an economical,efficient and environmentally friendly method to treat antibiotics in the environment,while solar photocatalysis technology has huge application potential in this regard.As a member of the Aurivillius-related oxide family,Bi₂O₂CO₃（BOC）characterized by the alternating Bi₂O₂²⁺and CO₃^2–layers has attracted the attention of researchers.However,the large band gap（about 3.3 e V）renders pristine BOC semiconductor only to absorb ultraviolet light and greatly limits its practical photocatalytic applications.In order to enhance adsorption of visible light,a feasible approach is coupling BOC with other narrow-band-gap semiconductors,g-C₃N₄（CN）is considered as an excellent candidate due to its adjustable band gap and energy band matching.However,most of the reported Bi₂O₂CO₃/g-C₃N₄-based composites lack precise control of their morphology,which leads to the reduction of surface area and active sites as well as the accelerated recombination of photo-generated electron-hole pairs,thereby inhibiting the interface reaction.Inspired by previous studies,in this study,we successfully fabricated 1D sulfur doped g-C₃N₄（SCN）hollow tubes through molecular self-assembly,and then prompted BOC nanoflakes to parallel grow in situ on the surface of the tube to construct 2D/1D interfacial phase via surfactant-assisted hydrothermal method.The formation of 2D/1D heterojunctions could maximize the synergistic and multi-dimensional effects of 2D and 1D materials,and expanded their photocatalytic applications.Through various characterization techniques and tetracycline hydrochloride（TCH）degradation experiments,the morphology,crystal and chemical structure,photoelectrochemical properties,reaction influencing factors and the degradation mechanism of the as-prepared photocatalysts were explored.Results showed that:（1）S doping adjusted the energy band structure of CN and thus expanded the visible-light absorption range.The 1D length-to-diameter ratio had a direct and fast charge transfer channel,and the hollow structure strengthened the visible-light capture ability due to the multiple reflections of incident light.In addition,the coupling of SCN and BOC retained the original crystal structure,the intensive contact between semiconductors promoted the transfer of interface charges,and the increased specific surface area enhanced the adsorption of TCH molecules.（2）Compared with BOC and SCN,BOC/SCN-3 composite possessed superior visible light response,photo-generated electron-hole pairs separation efficiency and lower charge transfer resistance.BOC/SCN-3 showed the optimal TCH degradation efficiency of 82.6%under 30 min visible-light irradiation,which was 2.2 and 3.5 times of the pristine BOC（38.2%）and CN（23.9%）,and its reaction apparent rate constant k was 9.7 and 3.0 times of BOC and SCN,the TOC mineralization efficiency was 2.2 and 1.6 times of BOC and SCN,respectively.Furthermore,BOC/SCN-3 also exhibited excellent stability and light corrosion resistance.In addition,by simulating the influence of various factors in wastewater（initial TCH concentration,inorganic anions,reaction p H）,it was found that in this research system,the conditions of low TCH concentration,CO₃^2-,weak acid or weak base were more suitable for the photocatalytic TCH degradation.（3）Through active radicals trapping tests and ESR signal analysis,h⁺and·O₂^-generated during the photocatalytic reaction were together participated in the degradation of pollutants,of which h⁺played a major role,and·O₂^-played an auxiliary role.Due to the well-matched band structure and electronic interaction between BOC and SCN,a built-in electric field was formed at the heterojunction interface,which promoted the transfer of photo-generated electrons from single phase to composite phase,forming a Z-scheme electron transfer pathway.This work pointed out a new route to develop Z-scheme heterojunction photocatalyst with hierarchical structure for efficient tetracycline hydrochloride degradation,and provided a theoretical basis for the removal of antibiotic in actual wastewater.