Preparation And Photocatalytic Performance Of KCa₂Nb₃O₁₀ Nanosheets Based Heterojunction Photocatalysts

China is in a period of rapid development.With the increasing energy consumption,especially the large consumption of traditional fossil fuels has brought severe energy and environmental problems.Therefore,environmental governance,energy conservation and emission reduction to achieve sustainable social development will become the focus of urgent issues in the world for a long time.Semiconductor photocatalysis technology is one of the most potential green energy technologies,which takes photocatalyst as the main body,through the redox reaction between photo-generated carriers formed by photoexcitation with other substances in the environment to achieve the purpose of degradation of pollutants or energy conversion.Potassium calcium niobate(KCa₂Nb₃O₁₀)photocatalyst is a typical Dion-Jacobson phase layered perovskite structural material with unique crystal structure,and it is easy to form two-dimensional structure.Therefore,through a specific synthesis strategy,the layered KCa₂Nb₃O₁₀0 can be successfully exfoliated into KCa₂Nb₃O₁₀0 nanosheets with more active sites.More active sites mean faster surface reaction,so it has higher photocatalytic activity.However,due to the inherent wide band gap,KCa₂Nb₃O₁₀0 nanosheets can only respond to ultraviolet light,and it also has the disadvantage of high electron-hole recombination rate,which seriously limit its practical application.Aiming at the above problems of KCa₂Nb₃O₁₀nanosheets,in this paper,we constructed different types of nanoheterostructures with different photocatalytic materials,such as sulfides and bismuth materials.In order to study the micro-morphology,crystal phase and light absorption property of the prepared heterojunction photocatalyst,various characterization techniques were used.Its properties and mechanism of photocatalytic degradation and photocatalytic reduction of CO₂ were also systematically studied.The specific research content are as follows:1.CdS/KCa₂Nb₃O₁₀?abbreviated as CdS/KCNO?nanoheterojunction composite photocatalyst was successfully prepared by electrostatic self-assembly method.XRD,XPS,TEM and other characterization results show that CdS particles are uniformly supported on KCa₂Nb₃O₁₀0 nanosheets.Taking tetracycline hydrochloride?TC,35mg/L?as the degradation substrate,photocatalytic degradation experiments were carried out under simulated sunlight irradiation conditions.The results indicate that the photocatalytic activity of CdS/KCNO sample is significantly improved compared with pure CdS and KCa₂Nb₃O₁₀.The degradation efficiency of TC exceeded 90%after 60 min illumination,and the prepared composite photocatalyst had good cycle stability.Further,through active species trapping experiments,·O₂^-and·OH are found to be the main active species in the photocatalytic reaction.The improved degradation performance of the prepared CdS/KCNO composite photocatalyst is mainly attributed to the heterojunction formed between the two semiconductor materials,which effectively enhances the separation efficiency of photo-generated charges.2.BiOCl/KCa₂Nb₃O₁₀?abbreviated as BK?nanoheterojunction photocatalyst was successfully prepared by a simple hydrothermal process.TEM,HRTEM,XPS,XRD,BET and AFM were adopted to study the crystal phase,microstructure,elemental composition and specific surface area of the prepared samples.Photocatalytic degradation experiments show that the prepared BK heterojunction composite photocatalyst has significantly improved photodegradation activity and cycle stability of tetracycline hydrochloride?TC,35 mg/L?.Among them,the BK-40sample has the best photocatalytic activity.HPLC-MS was used to analyze the intermediate products produced in the process of photocatalytic degradation of TC,and the possible mechanism of BK photodegradation of TC was proposed.Active species trapping experiments show that·O₂^-is the main active species for photocatalytic TC degradation over composite photocatalyst.The improvement of the degradation performance of the prepared composite photocatalyst is mainly attributed to the"Z-type"heterojunction formed between the two semiconductor materials,which improves the redox capability of the photocatalyst and promotes the separation of photo-generated carriers.3.ZnIn₂S₄ nanosheets were grown on KCa₂Nb₃O₁₀0 nanosheets in situ by a simple low-temperature hydrothermal method,and ZnIn₂S₄/KCa₂Nb₃O₁₀?abbreviated as ZnIn₂S₄/KCNO?two-dimensional nanosheet heterojunction composite photocatalyst was successfully prepared.XRD,XPS,BET and TEM were used to analyze its morphology and structure.The results show that ZnIn₂S₄ nanosheets are well dispersed on KCa₂Nb₃O₁₀0 nanosheets and formed a two-dimensional heterostructure with tight interfacial contact.The results of photocatalytic reduction of CO₂ show that the constructed ZnIn₂S₄/KCNO two-dimensional nanosheet composite photocatalysts have significantly improved photocatalytic activity compared to pure KCa₂Nb₃O₁₀.When ZnIn₂S₄ loading content reach 20%,the CO-production rate of as-prepared ZnIn₂S₄/KCNO(4.69?mol·h^-1·g^-1)is up to 1.95-fold and 12.31-fold as high as that of pure KCa₂Nb₃O₁₀0 and ZnIn₂S₄.From the relevant characterization results,it can be seen that the close contact between ZnIn₂S₄ and KCa₂Nb₃O₁₀0 greatly promotes the separation of photo-generated charges,and the introduction of ZnIn₂S₄effectively extends the photo-response range of KCa₂Nb₃O₁₀.