Preparation Of Metal/ZnO Hierarchical Heterostructured Film Materials And Their Photocatalytic Performance

In recent years,energy shortage and environmental pollution have become the focus of the world.Semiconductor photocatalysis has attracted widespread attention as a promising technology for solving environmental and energy problems with the utilization of solar energy.Transition metal oxide semiconductors have broad application prospects in the fields of energy conversion and storage,environmental remedy,optoelectronics,and light emission.However,some key factors,such as high carrier recombination rate and limited light absorption range,limit their practical applications.In order to achieve higher photocatalytic efficiency,electron-hole pairs should be effectively separated,and the charge should be rapidly transferred through the surface/interface to inhibit recombination.To address these issues,the construction of metal and semiconductor heterojunctions has attracted much attention due to its ideal effect in improving photocatalytic activity.In this thesis,we focus on the preparation of metal/ZnO self-assembled,hierarchical,heterostructured materials based on the principle of galvanic replacement reactions.Through rationally screening the reaction systems and reasonably regulating the reaction conditions,a series of metal/ZnO heterostructured film materials with controllable crystal structure,morphology and size were prepared hydrothermally on Zn substrates.The synthesis mechanism was discussed in depth.The photocatalytic properties of the synthesized samples were investigated.The main research contents of the paper are summarized as follows:?1?A synthesis method based on“hydrothermal galvanic replacement reaction"was proposed to prepare heterostructured film materials on Zn substrate,and a Cu/ZnO heterostructured film was successfully synthesized.The synthesis method and mechanism of preparing Cu/ZnO heterostructured film are based on hydrothermal galvanic replacement reaction.That is,since ?Zn2+/Zn? is less than ?Cu2+/Cu?,a galvanic replacement reaction occurs at the interface between the Zn substrate and the CuCl2 aqueous solution.In the synthesis system of pine-like Cu/ZnO heterostructured film,the Zn substrate is used not only as a reducing agent to reduce Cu2+into Cu element,but also as a zinc source of forming ZnO.The pine-like Cu/ZnO heterostructured film exhibited excellent photocatalytic performance under the visible light irradiation.The catalytic degradation rate of methyl orange dye?Co=10 mg/mL?reached 91%using Cu/ZnO heterostructured film as the photocatalyst after 4.5 h catalytic reaction,while the bare ZnO nanorod film exhibited a much lower degradation rate of 59%under the same conditions.The catalytic degradation durability test showed that the Cu/ZnO heterostructured film catalyst displayed good stability with degradation rate decreased from 91%to 81%after five cycles.In addition,four kinds of hierarchical heterostructured films,including ball-like Sn/ZnO,flower-like Co/ZnO,brush-like Cd/ZnO and tube-like Cu/ZnO,were successfully synthesized by using the synthesis method based on"hydrothermal galvanic replacement reaction",through adjusting reaction temperature,reaction time,and concentration of different metal salts.These extended experiments show the universality of the synthesis strategy.Based on the experimental results,the synthesis mechanism of metal/ZnO heterostructured films is further summarized.That is,?Zn2+/Zn?<?Mn+/M?,weak hydrolysis of metal ions,and hydrothermal condition are three important prerequisites for the universal synthetic method.?2?A hierarchical flower-like Ag/ZnO heterostructured film self-assembled by ZnO nanorods loaded with Ag nanoparticles was successfully fabricated on Zn substrate by utilizing the synthesis method based on“hydrothermal galvanic replacement reaction".The catalytic properties of methyl orange solution and methylene blue solution each with an initial concentration of 10 mg/mL were studied under visible light irradiation by using flower-like Ag/ZnO heterostructured film as photocatalyst.The results showed that the catalytic degradation rate of methyl orange solution using the flower-like Ag/ZnO heterostructured film as the photcatalyst was 88%after 270 min,much higher than 59%using bare ZnO nanorod film.Compared with bare ZnO nanorod film?52%?,the catalytic degradation rate of methylene blue catalyzed by the flower-like Ag/ZnO heterostructure film reached 73%.?3?A Ni/ZnO microsphere composite was synthesized by sodium citrate assisted one-step hydrothermal method,which was a self-assembly of ZnO nanosheet loaded with Ni nanoparticles.The catalytic performance of photocatalytic degradation of rhodamine B solution?C0=5 mg/mL?under UV irradiation for 180 min was studied.The catalytic degradation rate of rhodamine B dye reached 93%using Ni/ZnO microsphere film as the photocatalyst,while the bare ZnO nanorod film exhibited a lower degradation rate of 72%under the same conditions.Density functional theory calculation reveals that the Ni cluster can tune the electronic structure of ZnO by forming mid-gap-like electronic states to enhance its optical absorption capability.