The Construction Of Inorganic-organic Z-scheme BiVO₄/PDIsa Photocatalyst And The Study Of Mechanism During Their Photocatalytic Degradation Of Tetracycline

Antibiotics are widely used in clinical care,aquaculture,and livestock farming due to their ability to challenge microbial populations.It is worth noting that antibiotics must also be considered as an important pollutant that affects the structure and activity of microbiota in the environment and allows the progressive production of multi-drug resistant"superbugs"when they are released into the natural environment.Therefore,it is particularly important to find a green and efficient method and technology to remove antibiotics from the environment.Semiconductor photocatalysis,as a technology with excellent solar energy capture and conversion capability under mild conditions,is favored in many fields such as organic pollutant degradation,water aplitting,hrdrogen/oxygen evolution,organic synthesis.In recent years,perylene diimide organic supermolecule（PDI）has attracted significant interest in the field of photocatalytic degradation,but it suffers from rapid electron-hole recombination and unsatisfactory degradation efficiency.To adequately solve the above problems,herein,PDI was combined with monoclinic bismuth vanadate（BiVO₄）,and its photocatalytic performance was thoroughly explored and analyzed.Subsequently,the degradation efficiency,reaction kinetics,cycling stability,photocatalytic degradation mechanism and pathway,and electron transfer mechanism of the above photocatalysts for broad-spectrum antibiotics represented by tetracycline（TC）in water were simulated and studied in the laboratory.Finally,the feasibility of utilizing the catalyst in the treatment of antibiotics in real water was confirmed,and the main influencing factors in the photodegradation process were analyzed.The detailed contents are as follows.（1）The inorganic-organic Z-scheme BiVO₄/PDIsa photocatalysts were successfully constructed by wrapping the soft organic material PDI on the surface of 3D BiVO₄ through an in situ electrostatic self-assembly method.The optimized sample with 20%BiVO₄ loading（BP-2）exhibited excellent photocatalytic activity towards TC removal,with the highest degradation efficiency of 81.75%within 30 min,which was 19.16%and 43.31%higher than that of monomeric self-assembled PDI（PDIsa）and BiVO₄,respectively.The degradation rate constant(K_t=0.0545 min^-1)of BP-2 was 1.69 and 3.61 times higher than that of PDIsa and BiVO₄,respectively.Cycling experiments,powder X-ray diffraction spectroscopy（PXRD）analysis and Fourier transform infrared（FTIR）characterization demonstrated the good stability of the as-prepared BP-2.The radical trapping experiments and electron spin response（ESR）technique revealed that ¹O₂,^·O₂^-and h⁺played a dominant role in the TC degradation process.In addition,the^·O₂^-quantification assay showed that the^·O₂^-production rate of BP-2(2.26μmol L^-1 mg^-1)was 1.19 and 1.37 times higher than that of monomeric PDIsa and BiVO₄,respectively.The total organic carbon（TOC）test revealed that the mineralization efficiency of BP-2 for TC was 24.95%,and four possible degradation pathways of TC were analyzed and speculated utilizing a liquid chromatography coupled with tandem mass spectrometry（LC-MS）system.（2）The reasons for the enhanced photocatalytic performance of BP-2 were analyzed by experimental studies,various characterization tools and density functional theory（DFT）calculations.The introduction of the narrow bandgap semiconductor PDIsa broadens the absorption range of visible light for BiVO₄,while the combination of two direct bandgap semiconductors enhances the utilization of visible light for the composite material.The separation and transfer of photogenerated charge carriers at the interface is greatly enhanced by the synergistic effect of the Z-scheme heterojunction and the built-in electric field（IEF）.More interestingly,the polar structure andπ-πstacking mode of PDIsa molecules and the formation of direct Z-scheme heterojunction prolong the lifetimes of photogenerated electrons and holes by constructing efficient carrier-directed separation channels.（3）In this study,the catalysts were also applied to the degradation of TC in actual water bodies.It was found that the degradation efficiency of TC in river water,lake water,tap water and industrial wastewater was 59.14%,62.60%,68.04%and 71.46%,respectively,which confirmed the feasibility of the catalysts for practical use.Furthermore,through studying the factors affecting the process of photocatalytic degradation,it was found that no significant decline in TC removal efficiency was observed when the pH of the solution was in the range of 4.01-6.99,while the order of the effects of coexisting anions in solution on TC photodegradation was:SO₄^2-<NO₃^-<Cl^-.In conclusion,an inorganic-organic Z-scheme photocatalyst has been successfully designed in this study,which has a high removal efficiency for TC in wastewater.This work will provide a theoretical basis for the study of the degradation mechanism and electron transfer mechanism of the photocatalyst,and also provide a practical reference value for the application of photocatalyst in the removal of refractory antibiotics in real water bodies.