Preparation And Visible-Light Photocatalytic Performance Study Of Bi₂WO₆-Based Nanocomposites For The Degradation Of Some Antibiotics

Environmental pollution caused by the abuse of antibiotics has attracted more and more attention.Among these antibiotics,fluoroquinolones and tetracyclines are the most common in water.Now it is urgent to develop efficient methods to deal with such antibiotic contamination in water.Photocatalysis involving nanomaterials is considered to be a simple,safe and efficient technology for removing antibiotics from water with no secondary pollution,in which the development of nano photocatalyst with high performance and visible-light response is the core.Bi₂WO₆ is an n-type semiconductor material with a band gap of about 2.8 e V.It has the advantages of visible-light response and good photostability,and is the preferred material for visible-light catalytic degradation of pollutants.However,the photocatalytic performance of Bi₂WO₆ can be affected by the problem of narrow photo-response range and easy recombination of photogenerated electron-hole.The construction of Bi₂WO₆-based nanocomposite heterojunction as a photocatalyst can effectively establish carrier transport pathway and realize the effective separation of electrons and holes,which is considered as a feasible method to solve the above problems.In view of this,two kinds of heterojunction nano-catalytic materials,II-scheme Bi₂WO₆/Ag₃PO₄ and Z-scheme Bi₂WO₆/e-h-WS₂,were prepared with nanoflower-like Bi₂WO₆ as the core and characterized.The formation mechanism of the materials was explored.Then the performance and mechanism of Bi₂WO₆/Ag₃PO₄ and Bi₂WO₆/e-h-WS₂ for the photocatalytic degradation of fluoroquinolones and tetracyclines under visible-light irradiation were systematically studied,which provided a method reference and experimental exploration for the effective removal of antibiotic pollutants in water.The thesis includes the following four parts:1.Firstly,the source,classification,environmental ecological behavior and the treatment methods of antibiotics in water were introduced.Secondly,the development and characteristics of nano-photocatalytic technology,the mechanism of nano-photocatalytic reaction,as well as the types and application of nano-photocatalysts were summarized.After that,the structure,composition and properties of bismuth tungstate,synthesis and modification methods,and the application of bismuth tungstate-based photocatalysts are discussed.Finally,the purpose and significance of this paper were clarified.2.A series of II-scheme Bi₂WO₆/Ag₃PO₄ heterojunction nano-catalysts（BA-10,BA-20,BA-30,BA-40）were prepared by a chemical precipitation method and characterized by XRD,SEM,FI-IR,UV-vis DRS and PL spectra.The photocatalytic degradation performance of BAs for levofloxacin hydrochloride（OFX）was systematically studied.The effect of the amount of photocatalyst,the initial concentration of OFX solution and the p H value on the degradation rate were investigated.The results showed that under optimized conditions,the photocatalytic reactions conformed to the quasi-first-order kinetic equation.The maximum degradation rate and mineralization rate of OFX within 80 min under visible-light irradiation,which were obtained by using BA-20 as the photocatalyst,were 86.50%and 41.51%,respectively.Furthermore,BA-20 still showed a degradation rate of 77.06%for OFX after being recycled four times.The contribution of active species in the degradation process was h⁺>·O₂^–>·OH,which was investigated by free radical capture experiment.The possible photocatalytic reaction mechanism was finally proposed.3.Z-scheme Bi₂WO₆/e-h-WS₂heterojunction nano-catalysts（BW-8,BW-9,BW-10）were prepared by a hydrothermal method and characterized by XRD,SEM,TEM,HRTEM,BET,FI-IR,UV-vis DRS and PL spectra.The differences of photocatalytic degradation performance of BW-8 to different types of antibiotics were compared and analyzed.On this basis,doxycycline（DOX）was selected as the target,and the photocatalytic degradation performance of Bi₂WO₆/e-h-WS₂ on DOX was systematically studied.The results showed that the highest degradation rate of DOX could reach 84.22%within 120 min with the use of BW-8,and the total organic carbon removal rate was52.14%.In addition,BW-8 remained a degradation rate of 74.54%for DOX after being recycled four times.The contribution of active species was h⁺>·O₂^–>·OH.Especially,the degradation of DOX by BW-8 was visually displayed by a novel plant seed growth experiment.4.With oxytetracycline（OTC）as the target pollutant,the photocatalytic degradation performance of Bi₂WO₆/e-h-WS₂ nanocomposites were further studied.The results showed that BW-8 had a high photocatalytic performance on the OTC degradation within120 min,with the maximum degradation rate of 83.22%and the mineralization rate of47.67%,BW-8 remained a degradation rate of 73.86%for OTC after being recycled four times.The free radical capture experiment revealed that·O₂^–and h⁺were the main active species generated in the reaction.The possible pathway and products of the photocatalytic degradation reaction were explored via high-resolution mass spectrometry and the possible photocatalytic reaction mechanism was discussed in depth.