Preparation Of Zinc Oxide-based Heterojunctions And Photocatalytic Applications

With the arrival of the new century,due to the massive growth of population,the demand for energy will also increase,and environmental pollution problems will become more and more serious.According to scientists,energy consumption will nearly double by 2050.However,most of the energy we use today comes from non-recyclable fossil fuels.In the industrial process,many toxic or non-biodegradable organic wastes are produced.If these organic wastes are not treated effectively,they will cause serious water pollution problems,which will affect our health.Under the irradiation of sunlight,semiconductor materials can convert solar energy into chemical energy,degrade organic dyes,hydrogen and oxygen can also be produced under certain experimental conditions.Therefore,degrade organic dyes,and produce hydrogen and oxygen,photocatalysis technology is considered not only to solve the energy crisis but also to deal with the problem of non-degradable organic dyes in water.The energy used by photocatalytic technology is the most abundant,cheapest and cleanest energy-solar energy.And photocatalytic degradation of organic matter will not introduce new harmful substances,and will not produce secondary pollutants.However,a large number of studies have shown that photocatalysis still cannot meet the requirements of practical applications,which is mainly attributed to the low light absorption efficiency and hole separation of photogenerated electrons of a single component photocatalyst.The emergence of multiple composite photocatalyst has effectively improved the above problems.Therefore,multiple composite photocatalyst has become a research hotspot at present.ZnO is used as an effective photocatalyst due to its low price,high electron mobility,stability and high quantum yield.It has been reported that the following strategies are often used to modify ZnO,for example,metal doping,non-metal doping and semiconductor coupling can improve the photocatalytic activity of ZnO.In this topic,based on ZnO as the base material,the following work has been done in order to avoid electron-holes pairs in ZnO and broaden the absorption of visible light.Thesis will be divided into two parts:（1）The ZnO/NiO p-n junction is derived from the bimetallic MOF,and the framework of the original bimetallic MOF is retained to increase the active site in the photocatalytic reaction.By adjusting the content of NiO in the p-n junction,the optimal ratio of composites in photocatalytic applications was explored.The materials were tested and analyzed,such as crystal morphology characterization,photoelectric characterization,etc,The results were mutually verified with the photocatalytic experimental results,which improved the photocatalytic performance of pure ZnO and explained the photocatalytic enhancement mechanism.（2）ZnO nanorods and C₃N₄nanosheets were prepared by thermal decomposition,and Ag NPs were deposited on ZnO/CN heterojunctions by glucose deposition.The response of the prepared ternary composite increases in the visible light range,and the catalytic performance of the photocatalyst is obviously better than that of pure ZnO,under the same experimental conditions,the degradation rate is about three times that of pure ZnO.At the same time,the material is used in the production of H₂O₂,which further verifies the improvement of the photocatalytic performance of the ternary composite.This is because ternary complexes have multiple electron transfer pathways,which enhance charge separation and extend the lifetime of electron holes.The reusability experiment verifies that the material has good recyclability and reusability,and the corresponding photocatalytic mechanism is explored.