Synthesis And Investigation On The Photocatalytic Properties Of Strontium Niobate Nanosheets Composites

Photocatalytic technology has been extensively investigated as a potential application for the solution of environmental and clean energy problems.Usually,the photocatalysys are semiconductors which should meet the requirements of visible light active radiation,chemically stable,low cost and nontoxic.Variety of metial oxide photocatalyst materials,including first generation?TiO₂,ZnO and SnO₂?ultraviolet radiation photocatalysts,and second generation?WO₃,Fe₂O₃ and Cu₂O?visible-light-driven photocatalysts,have been widely explored,however,their pervasive application is restricted by their wide bandgap and low quantum yiels efficiency.Therefore,the third generation with more effective visible-light photocatalysts,such as perovskite and perovskite-related materials are being developed to meet the requirements of future environmental and energy technologies driven by solar energy.Layered perovskite compounds have a unique layered structure,which can be esily exfoliated into ultra-thin two-dimensional nanosheets and constructing heterojunction structure to gain proper range bandgap for potential visible-light-driven photocatalytic application.In this thesis,the perovskite compounds,KSr₂Nb₃O₁₀ were exfoliated into ultra-thin two-dimensional nanosheets and modified by heterogeneous coupling to broaden the light response range,hence improving the visible-light-driven photocatalytic activity.To understand the fundamental photocatalytic mechanism of the photocatalytic materials,several structural measurements?XRD,SEM,TEM,XPS,DRS,EIS?were carried out to build up the relationship with their photoelectrochemical properties.The main research contents in this thesis are shown as below:1.KSr₂Nb₃O₁₀ was synthesized by solid state method.The ultrathin two-dimensional nanosheets HSr₂Nb₃O₁₀ nanosheets?HSNO-ns?were obtained by protonating and exfoliating reaction via microwave assistance.Nanosized WO₃nanosheets were obtained through hydrothermal methos.The Z-scheme heterojunctions were formed by ball milling WO₃ nanosheets with HSNO-ns nanosheets.This structural heterojunction between the HSNO-ns and WO₃ nanosheets enlarges the optical response of HSNO-ns nanosheets,and enhances the redox abilitu of semiconductors.In addition,this unique structure also improves the separation and migration rate of photogenerated carriers.According to the photoelectrochemical results,7wt.%ratio of WO₃ nanosheets constructures onto HSNO-ns nanosheetd leads to the highest photocatalytic activity,where the methyl orange degradation rate reached 99.7%within 20 minutes under simulated solar irradiation.2.CdSe quantum dots modified HSNO-ns nanosheets were synthesized by green aqueous method.With the modification of CdSe quantum dots,the absorption edge of HSNO-ns shifted from 400 nm to 780 nm,which greatly enhanced the utilization rate of light energy.In the meantime,the separation and migration of photogenerated carriers of the samples effectively promoted,hence the photocatalytic activity is improved.For the pure CdSe photocatalyst,the methyl orange degradation rate was65.3%in 6 min under visible light irradiation,while the pure HSNO-ns nanosheets shows no degradation ability for methyl orange under visible light.However,as a50wt.%CdSe loading with HSNO-ns,the photocatalytic degradation rate was 95%within 5 mimutes.3.CdS-HSNO-ns nanosheet composite was synthesized by hydrothermal method.The optical absorption edge of HSNO-ns shifted from 400 nm to 570 nm by CdS loading.Under visible light irradiation,the photocatalytic activity of the composite sample is better than that of pure phase CdS and HSNO-ns,the sample HSNO-ns/CS3 showed a photocatalytic activity of 330.85 umol·g^-1·h^-1 hydrogen wvolution rate in 20vol.%triethanolamine solution under visible light irradiation at298 K.