Study On The Preparation And Photocatalytic Activity Of ZnO Nanotubes Composite Materials

ZnO is an important n-type semiconductor,which is abundant,non-toxic,and low cost.The band gap of ZnO is 3.14 ev,and ZnO can product photogenerated electron-hole pairs under the irradiation of ultraviolet light.The photogenerated electron-hole pairs can further transform to the high active groups such as ·OH and ·O2-with strong oxidization and reduction abilities,which can be used for the degradation of the organic pollutants such as dyes.Due to the rapid recombination of the photo-generated electron-hole,the photocatalytic activity of ZnO is low.Moreover,photo-chemical corrosion easily occurs during the photocatalytic process for ZnO catalyst,so it is not conductive to the actual large-scale industrialization.Therefore,it is a research focus to improve its photocatalytic activity and stability by design the composition and structure of ZnO.In this thesis,the photocatalytic performance of ZnO were carried out using 2-methyl-4-chlorophenoxy acetic acid and organic dye methyl orange as degradation target.The effects of the composition and structure on the photocatalytic properties of ZnO were stuided.The main research contents are as follows:ZnO nanotubes with a diameter of 400 nm,a wall thickness of 80 nm were prepared by electrochemical deposition.Well-aligned ZnO nanotube arrays loaded with WO3 nanoparticles are successfully synthesized by a chemical bath deposition technique in combination with a pyrolysis process.The photocatalytic activities of the ZnO-WO3 composite photocatalysts with different WO3 contents are systematically evaluated for the degradation of chlorinated phenoxyacetic acid herbicide under simulated sunlight irradiation.It is found that WO3 contents have great effect on the photocatalytic activities of ZnO-WO3 composites.ZnO-WO3(3%)shows the highest photocatalytic activity,and the degradation rate is 98.5%in 200 minutes with 20 mg photocatalyst,which is about 2 times higher than that of pristine ZnO nanotube arrays.The recombination of photogenerated electron-holes is depressed with the addition of WO3 to ZnO.High relative content of defects on the surface of ZnO-WO3 composite is beneficial to the photocatalytic activity for the degradation of chlorinated phenoxyacetic acid herbicide.Secondly,the effect of AgNO3 addition into MO solution on the photocatalytic activity of ZnO nanotubes was studied under the simulated solar irradiation..The experimental results show that the photocatalytic activity of ZnO nanotubes with the addition of 0.050 M AgNO3 solution is higher than that without AgNO3 solution,which is about 12.5 times.Meanwhile,the AgNO3 solution can improve the photocatalytic cycle performance.When the concentration of AgNO3 solution is kept at 0.050 M,the photocatalytic degradation rate remains above 83%after 5 cycles.In the process of photocatalysis,Ag+ serves as the electron acceptor forming nano-Ag which is deposited on the surface of ZnO nanotubes,which can inhibit the recombination of electron-hole and improving the photocatalytic performance.Sacrificial agent experiments show that·OH free radicals and holes played a major role in the degradation of MO.At last,nano-Ag was deposited on the surface of ZnO nanotubes by photoreduction forming ZnO-Ag nanotube arrays.The effects of different photoreduction time on the photocatalytic properties of ZnO-Ag nanotube arrays were studied under simulated solar irradiation with methyl orange(MO)as the degrading object.ZnO-Ag-5min sample presents the highest photocatalytic activity,and the methyl orange at 16 mg/L was completely degraded oin 200 min.The results of sacrificial agent showed that·OH free radicals and holes play a major role in degradation of MO..