Construction Of Bi_xMo_yO_z-Based Photocatalytic Materials And Study On Their Degradation Of Typical Antibiotics In Water

In recent years,antibiotics have been widely used in industrial and agricultural fields,animal husbandry,and modern clinical medicine,and the water pollution caused by their residues has gradually gained attention from people.As an advanced oxidation technology,semiconductor photocatalysis is considered to be the greenest way to control antibiotic pollution in water environment.One of the core issues facing the application of this technology is to find photocatalysts with excellent performance.Bismuth-based semiconductor materials exhibit excellent application potential for photocatalytic degradation of organic pollutants due to their low toxicity,high stability,and resistance to the water chemical corrosion.Among them,bismuth molybdates（BixMoyOz）have attracted much attention in the field of photocatalytic environmental remediation due to their unique layered structure,suitable band gap,and tunable redox performance.However,single BixMoyOz phase still has some shortcomings when using sunlight to treat pollutants in water,such as:（i）narrow response range of visible light;（ii）high recombination rate of electron-hole pairs;（iii）easy to form highly toxic intermediate products.In view of the above problems,this thesis mainly uses strategies such as defect engineering and semiconductor heterojunction to modify BixMoyOz to prepare novel BixMoyOz-based photocatalysts,and systematically explore the effects of these strategies on the performance,mechanism,and ecotoxicity of BixMoyOz-based semiconductors used in photocatalytic/photo-Fenton degradation of typical antibiotics in water.（1）A simple molten salt-assisted synthesis method was developed for controlling the phase and morphology of BixMoyOz semiconductor photocatalysts.One-dimensional（1D）Bi₆Mo₂O₁₅ sub-microwires,two-dimensional（2D）Bi₂MoO₆ nanosheets,and threedimensional（3D）B₁₄MoO₉ and Bi₁₄MoO₂₄ irregular bulk photocatalytic materials were successfully prepared.By simply adjusting the molten salt synthesis times,BixMoyOz could be controlled to gradually change from Aurivillius type to Fluorite type.With the construction of different Fluorite-type bismuth molybdate phases,the samples exhibited an obvious red-shift of absorption band with the increase of Bi/Mo molar ratio,indicating the decreased band-gap energies.The photocatalytic performance tests indicated that the catalytic activity of the Fluorite-type 3D Bi₁₄MoO₂₄ sample for TC removal was higher than that of 1D Bi₆Mo₂O₁₅ sub-microwires,2D Bi₂MoO₆ nanosheets,and Bi₄MoO₉ bulk samples under visible light irradiation.In addition,the phase transition mechanisms and energy band structures of two different types of BixMoyOz were discussed.This study provides a new strategy for controllable synthesis of BixMoyOz with different sizes and structures.（2）A 0D Bi metal nanodot-decorated Bi₆Mo₂O₁₅ sub-microwire（B-BMO）heterojunctions with rich oxygen vacancies（OVs）was constructed.The wide bandgap value and high charge recombination rate of Bi₆Mo₂O₁₅ hinder its development and application in the field of photocatalysis.To address these issues,a simple chemical reduction method was used to treat the Bi₆Mo₂O₁₅ photocatalyst,aiming to introduce OD Bi nanoparticles and OVs.The optimized B-BMO heterojunction exhibited an optimal degradation efficiency of 98%in the photocatalytic degradation of tetracycline（TC）,significantly higher than the degradation efficiency of the original B₁₆Mo₂O₁₅（13%）.The significantly enhanced photocatalytic performance was mainly attributed to the synergistic effect of surface plasmon resonance（SPR）of Bi and the formation of OVs.（3）A novel Ce₄O₇ modified Bi₄MoO₉（C-BMO）photo-Fenton heterojunction catalyst with dual redox centers(Ce⁴⁺/Ce³⁺and Mo⁶⁺/Mo⁵⁺)was constructed.Ce₄O₇ nanodots were successfully loaded on the surface of Bi₄MoO₉ to form the C-BMO heterojunctions by a simple molten salt-assisted synthesis route.The optimized C-BMO heterojunction exhibited an optimal degradation rate of 2.16032 h^-1 in the photo-Fenton degradation of tetracycline（TC）,being nearly 12.27 and 7.69 times higher than that of pure Bi₄MoO₉ and Ce₄O₇.Such remarkably enhanced photo-Fenton performance was mainly ascribed to the formation of intimate contacted interface favoring the highly effective transfer and spatial separation of photoexcited carriers,and the Ce⁴⁺/Ce³⁺ and Mo⁶⁺/Mo⁵⁺cycling redox couples accelerating the activation of H2O2 to generate massive reaction radicals.Additionally,the possible photo-Fenton degradation pathways of TC were proposed and the toxicity changes during TC degradation were detailed investigated in this study.This study further broadens the application of Bi-based photocatalysts in the environmental field.（4）A novel cerium-rich CeO_2-x modified Bi₂MoO₆（CEO/BIM）self-cycling photoFenton heterojunction catalyst with Ce⁴⁺/Ce³⁺cycling redox couple was constructed.In view of the slow cycle of Ce³⁺/Ce⁴⁺redox,as well as the low activation efficiency of H₂O₂ and the leaching of a large number of metals in the Fenton-lik stoichiometric CeO₂ cocatalyst,a cerium-rich non-stoichiometric CeO_2-x cocatalyst was developed to accelerate the circulation of Ce³⁺/Ce⁴⁺.The cerium-rich CeO^2-x nanodots were perfectly anchored onto Bi₂MoO₆ nanosheets to fabricate a self-circulating CEO/BIM photoFenton system by a simple molten salt-assisted synthesis method.The optimized CEO/BIM-3 sample manifested the highest photo-Fenton degradation rate(0.02634 min^-1)of ofloxacin（OX）only under 5 W white LED irradiation,which was 7.90 and 5.79 times that of individual Bi₂MoO₆ and CeO^2-x,respectively.This study demonstrates the great potential of the self-circulating photo-Fenton system in degrading antibiotic pollutants.（5）A Fe-polyoxometalate（Fe-POM）-modified {010} facet Bi₂MoO₆（FePOM/BMO）heterojunction with a wide pH operating range was designed.Traditional Fe-based photo-Fenton catalysts have a narrow pH range and are prone to produce Fecontaining sludge.To address this issue,Fe-POM nanodots were supported on the surface of {010} facet Bi₂MoO₆ nanosheets to synthesize Fe-POM/BMO heterojunctions for the degradation of typical antibiotics through a simple in situ self-assembly process.Benefiting from the synergistic effect of the OVs defect and the Fe³⁺/Fe²⁺ redox couple,the Fe-POM/BMO heterojunctions exhibited remarkable photo-Fenton degradation performance at a wide pH range of 3.0-11.0.Based on the density functional theory（DFT）calculations and high performance liquid chromatography-tandem mass spectrometry（HPLC-MS/MS）analysis,the probable degradation pathways of TC were unraveled.In addition,the quantitative structure-activity relationship（QSAR）prediction and the Microtox test（Photobacterium phoshoreum T3 spp.as the luminescent bacteria）proved that the degradation process of tetracycline could effectively alleviate the ecotoxicity.According to the findings,the application of Fe-POM/BMO in the photo-Fenton degradation process of antibiotics is eco-friendly and exhibits high application potential in environmental remediation.