Studies On The Preparation And Optical Properties Of ZnO Hollow Nanosphere-Based Photocatalysts

Since the beginning of the new century,the global crises of energy scarcity and water pollution are intensifying.Semiconductor photocatalysis technology uses abundant and clean solar energy as a power source to degrade pollutant molecules,and escorting the global sustainable development.ZnO is highly favored for its suitable energy band structure,abundant raw materials,clean and non-toxic and stable and efficient photoelectrochemical properties.However,ZnO has inherent defects such as narrow solar response range,low photoavailability and high photogenerated charge complexation rate,which limit its application in photocatalysis.Therefore,the research object of the thesis is to investigate the optimal conditions for the preparation of ZnO hollow nanospheres morphology,the construction of ZnO/ZnCo₂S₄ II-scheme heterojunction photocatalyst,the construction of ZnO/Bi Cl_0.8I_0.2 S-scheme heterojunction photocatalyst,and the study of its photocatalytic degradation performance,the specific experimental studies are as follows:（1）Firstly,the optimization of the conditions for the preparation of ZnO hollow nanospheres was explored.Carbon nanospheres synthesized by hydrothermal method using glucose as raw material were used as a sacrificial template for the preparation of ZnO hollow nanospheres.The precursors of ZnO hollow nanospheres were obtained by the adsorption treatment of Zn²⁺,and finally the structures of ZnO hollow nanospheres with different microstructures were obtained by adjusting the temperature rise rate of calcination.The experimental results show that the morphology of the ZnO hollow nanospheres prepared by calcination with a heating rate of 5°C/min is the best,exhibiting stronger light absorption,faster charge mobility and higher catalytic activity,and the best heat treatment conditions are determined.（2）A new binary composite photocatalyst consisting of ZnO hollow nanospheres and ZnCo₂S₄ nanoparticles was prepared by a two-step method.Using X-ray photoelectron spectroscopy（XPS）,ultraviolet-visible diffuse reflectance spectroscopy（UV-vis DRS）and Mott-Schottky curve measurements,the regulated band structure of the composite was determined,and then the type-II carrier transfer mechanism in the composite was identified.The effect of the mass ratio of ZnCo₂S₄ to ZnO on the photocatalytic performance of the composite was investigated.With the increase in the mass ratio of ZnCo₂S₄ to ZnO,the photocatalytic performance of the composite first increases and then decreases,and the composite sample with a mass ratio of 30%shows the best performance.Furthermore,the introduction of oxygen vacancy（V_O）defects into ZnO hollow nanospheres not only improves the photocatalytic performance of the composite but also greatly improves photocorrosion resistance.Therefore,the newly discovered ZnO/ZnCo₂S₄ composite photocatalyst has potential practical applications.（3）A binary composite consisting of ZnO hollow nanospheres and BiOCl_0.8I_0.2 nanosheets was successfully prepared by hydrothermal method based on ZnO hollow nanospheres prepared by the template method.The conduction band position was determined using Mott-Schottky test curves,and the energy band structures of the monomers in the composite were obtained by UV-vis DRS.Finally,the carrier transport mechanism of the composites was determined to be S-type by X-ray photoelectron spectroscopy（XPS）and radical scavenging experiments.The effect of different mass fractions of BiOCl_0.8I_0.2 and ZnO on the degradation efficiency of tetracycline（TC）was investigated.The test results show that the samples exhibit the best performance when the mass fraction of the composite is 20%.It is demonstrated that S-scheme transport mechanism could extend carrier lifetime and greatly improve the photocatalytic performance of the composite.The degradation rate of TC at a concentration of 30 mg/L is 85%at a photocatalytic time of 30 min,and the hydroxyl radical（·OH）playing a key role in the degradation process.