Synthesis And Visible Light Photocatalytic Performance Of Two Dimensional WO₃ Nanosheets Based Composite Photocatalysts

Since from the twentieth century,the development of modern industry has promoted the rapid enhancement of social economy.However,numerous environmental problems have also been caused due to the yearly increased emission of industrial“three wastes”.Therefore,it is urgently desirable to control and solve environmental pollution for the social sustainable development.Semiconductor photocatalytic technology can effectively degrade hazardous organic contaminants in wastewater by harvesting solar energy.This environmental friendly technology is expected to be one of the most effective strategy to control environmental pollution in the future.As one of the earliest studied visible light-responsive photocatalysts,Tungsten oxide?WO₃?has great potential in the field of photocatalytic degradation of organic pollutants due to its unique structure and excellent performance.In addition,controlling the morphology of WO₃ photocatalyst to be two-dimensional nanosheet,which can enlarge its specific surface area,increase its active site on the surface and further improve its photocatalytic activity.However,WO₃ nanosheets still have some disadvantages such as high electron-hole pair recombination rate and narrow optical absorption range,which seriously restricts their practical application.Based on the above research background,in this academic dissertation,two-dimensional WO₃nanosheets was coupled with other semiconductors to form hetero-nanostructures.Various characterizations were used to analyze crystal phase,morphology and photogenerated charge carriers separation efficiency.We also systematically studied its photocatalytic degradation properties and mechanism.Research content were listed as following:1.A series of WO₃/SnNb₂O₆ heterostructures?abbreviated as WO₃/SNO?were constructed by simple hydrothermal approach.The as-prepared samples were characterized by XRD?XPS?TEM?DRS and PL.The photocatalytic performances were examined by the photodegradation of Rhodamine B?Rh B,10 mg/L?under irradiation of visible light.The as-prepared 30%-WO₃/SNO heterojunctions showed the optimal performance and it could degrade approximately 93.4%of Rh B in 180min,the WO₃/SNO hetero-nanostructures also showed excellent reusability and stability.Radical capturing experiments and the spin-trapping ESR technique demonstrate that both·O₂^-and h⁺are the important active species responsible for the Rh B degradation process over the nanosheet heterojunctions.Such remarkable activities should be owned to the uniquely redox-mediator-free“Z-scheme”system.2.The ultrathin K⁺Ca₂Nb₃O^-₁₀ nanosheets were synthesized by calcination,protonation and exfoliation methods.Then 2D-2D WO₃/K⁺Ca₂Nb₃O^-₁₀ binary heterojunction photocatalyst?abbreviated as WO₃/KCNO?is successfully constructed through an easy hydrothermal method.XRD,XPS,AFM,Mapping and BET were used to obtain the information of crystal phase,elemental composition,morphology and specific surface area.WO₃/KCNO heterojunctions exhibits a significant enhancement in the efficiency for the photodegradation of antibiotic agent tetracycline hydrochloride?TC,35 mg/L?.Among them,20%-WO₃/KCNO exhibits the best performance with a degradation rate of 85.8%within 120 min.HPLC-MS analysis is introduced to analyse the direct reactive intermediates formed by the photodegradation of TC.·O₂^-and h⁺are the major reactive species responsible for the photodegradation process of TC over the WO₃/KCNO nanosheet heterojunctions.3.A high performance WO₃/Bi₂₄O₃₁Br₁₀ composite photocatalyst composed of WO₃ and Bi₂₄O₃₁Br₁₀ was successfully synthesized by simple hydrothermal methods.XPS,XRD,TEM,DRS and PL were introduced to obtain the information of chemical component,crystal phase,morphology,optical absorption properties and photogenerated charge carriers separation efficiency.The photodegradation activity of the as-prepared samples were systematically examined for the degradation of antibiotic agent tetracycline hydrochloride?TC,35 mg/L?as the probing target under visible light illumination,and improved photocatalytic activities are founded on all WO₃/Bi₂₄O₃₁Br₁₀ samples.Among them,10%-WO₃/Bi₂₄O₃₁Br₁₀ exhibited the highest degradation efficiency for TC with a rate of 80%within 60 min.Through the trapping and ESR experiments results,it has been proved that the holes?h⁺?is the main active species of WO₃/Bi₂₄O₃₁Br₁₀ heterojunctions for TC degradation.The enhanced photocatalyticactivitiesaremainlyduetoenergeticallymatching hetero-nanostructures and efficient separation of electron-hole pairs.