Study Of Preparation And Photocatalytic Performance Of ZnO Nanomaterial,Ag/ZnO And ZnO/Cu₂O Heterojunctions

ZnO has rich nanostructures.It is nanomaterials with different morphologies can be synthesized by controlling the ratio and composition of the raw materials required for the synthesis reaction.The properties of ZnO is affected by morphology,size,specific surface area,and defect distribution.ZnO is also a direct band-gap semiconductor with a band-gap energy of 3.37 e V.It can be effectively excited by ultraviolet light???368 nm?,which exhibits excellent photocatalytic activity.Based on these advantages,we designed and synthesized ZnO nanomaterials with unique structures.However,photogenerated carriers of a pure ZnO catalyst are easy to recombine quickly,which leads to the decrease in photocatalytic efficiency.For this reason,It is essential for ZnO to improve light quantum and charge separation afficiency.Therefore,on the basis of the prepared ZnO,a novel Ag/ZnO composite material and Z-scheme ZnO heterostructure were designed and synthesized.1.High reaction activity,strong oxidizing ability and large specific surface area help to improve the photocatalytic performance of the catalyst.We used N,N-dimethylformamide?DMF?and phthalic acid?BDCA?as a capping agent by a simple hydrothermal method to adjust the amount of DMF and BDCA to prepare various spherical ZnO nanostructures,which greatly expanded research on ZnO synthesis methods and microstructures.In order to stably synthesize strong oxidizing ability ZnO and nanosheet self-assembled sphere ZnO,the concentration of DMF added to the reaction solution can be controlled.The higher the concentration is,the stronger the oxidation capability of ZnO may be.DMF also controls the shape of ZnO from nanorods to nanosheets and then to spheres.As BDCA changes from 1,2-BDCA to 1,3-BDCA to 1,4-BDCA,particles on the surface of spherical ZnO is small.The particles number ranges from nothing to a small amount,to a large one,which indicates that the larger the distance between the two-COOH groups in a BDCA molecule is,the more nanoparticles appear on the surface of the ZnO spherical structure.However,the nanosheets self-assemble into spheres of ZnO,the photocatalytic performance is best when a small amount of nanoparticles was added,which indicates that the number of small ZnO nanoparticles is moderate and not too much.These nanosheets increase the specific surface area of ZnO and active sites on the ZnO surface,which is conducive to the improvement of photocatalytic degradation efficiency of pollutants.The results show that the photocurrent density of ZnO?J3?remains unchanged at about 9.35?A·cm^-2,which is about 21 and 338 times higher than that of pure ZnO?J2?and ZnO?J1?,respectively,indicating that the addition of 1,2-BDCA and DMF can inhibit the recombination of photogenerated electron-hole pairs,which is beneficial to the degradation of organic pollutants.The ZnO having a strong ability to remove pollutants due to the high concentration of holes in the n-type ZnO valence band.The degradation efficiency of ZnO?J3?samples for salicylic acid?SA?and tetracycline?TC?reached93.0%and 87.3%respectively.The best degradation rate constant K for SA and TC was0.0133 min^-1 and 0.0445 min^-1,respectively.The research provides a new ZnO material for the preparation of nanorods-and nanosheets-based spheres,and a possible photocatalytic mechanism was proposed.2.Novel structure and good contact interface are helpful to improve the photocatalytic performance of the catalyst.We used a novel combination of L-tartaric?L-TA?and Ethanolamine?EA?to form a unique and controllable well-organized ZnO hollow cage for the first time through intelligent assembly,which can produce a strong synergy in the hydrothermal synthesis process.Meanwhile,the conformation of L-TA and D-TA shows that these ZnO cages have special spatial assembly order.The photocatalytic activity of Ag/ZnO is remarkably larger than that of pristine ZnO?S2?under ultraviolet or simulated sunlight irradiation.The Congo red?CR?degradation rate of the Ag/ZnO composite was 83.7%under ultraviolet light illumination.Under simulated sunlight irradiation,S2-10%Ag/ZnO degraded 80%of Rhodamine B?Rh B?in 135 min.The photocurrent and EIS results indicate enhanced photocatalytic performance due to the interfacial formation between Ag and ZnO,which facilitates the separation and transfer of photoinduced carriers and enhances the photocatalytic activity of Ag/ZnO composites.This work provided a new way to design and construct well-organized ZnO hollow cages and their derived Ag/ZnO photocatalysts.3.The n-p heterojunction with high activity,strong redox capability,stable Z-scheme transfer and good photostability significantly contributes to excellent photocatalytic performance.We used novel 1,2-BDCA,1,3-BDCA and 1,4-BDCA as two-COOH groups distance tuning agent and charge transfer controlling agent to synthesize ZnO by hydrothermal method,and then constructed n-ZnO/p-Cu₂O Z-scheme heterojunctions by anchoring p-Cu₂O nanoparticles?NPs?.With shortening the distance of two-COOH groups in one BDCA molecule,their synergistic effect on the ZnO surface becomes stronger,which leads to the formation of excellent connected interface,and can control charge transfer along with the Z-scheme pathway.The S1-Cu₂O heterojunction prepared by 1,2-BDCA exhibits high charge separation efficiency,strong redox potentials,stable Z-scheme charge transfer for four different pollutants during degradation process,which results in the high activity and better photocatalytic performance than that of pure ZnO,Cu₂O and commercial TiO₂?P25?under the ultraviolet and visible?UV+Vis?light irradiation.In addition,the ZnO-Cu₂O heterojunction exhibits the excellent photostability.Therefore,this study reported a novel and controllable strategy to keep the Z-scheme charge transfer unchanged for the photocatalysis of different pollutants,and the as-prepared ZnO-Cu₂O photocatalysts have a prospect for environmental purification and remediation.