Construction Of Heterojunction Based On Semiconductor-covalent Framework And Study On Photocatalytic Performance

1·Increasing environmental pollution has seriously restricted the sustainable development of society.Photocatalysis,as an efficient green technology,has attracted a lot of attention from researchers at home and abroad.The development of photocatalytic materials with novel structure and excellent performance has become one of the important topics for environmental pollution treatment.Metal-organic frameworks（MOFs）,inorganic-organic porous materials containing metal-oxygen clusters and organic molecules,have been developed rapidly for their applications in catalysis and separation.Covalent organic frameworks（COFs）are an emerging class of crystalline porous materials formed by the covalent bonding of institutional building blocks,and are also emerging in the field of photocatalysis due to their tunable porosity,modifiable backbone and precise atomic structure.However,single MOFs and COFs as photocatalysts suffer from defects such as poor catalytic effect due to the easy compounding of photogenerated carriers.To address this problem,this thesis constructs heterojunctions by metal oxide semiconductors and MOFs（or COFs）to promote the separation of photogenerated carriers and further improve the photocatalytic performance by using their energy band matching.In this paper,three novel metal oxide/organic framework composites were synthesized,and their photocatalytic degradation of organic pollutants was investigated by constructing composites of metal oxides with MOFs and metal oxides with COFs according to their different structural properties,focusing on their photocatalytic mechanisms.The research results are divided into three main parts as follows.1.A novel LZU1@WO₃ heterojunction photocatalyst was prepared by hydrothermal synthesis.The structure and properties of the catalysts were characterized by IR,PXRD,XPS,DRS,EIS,etc.The photocatalytic results show that the photocatalytic activity of LZU1_0.44@WO₃ is the highest under the simulated sunlight condition,and the degradation rate of BBR can reach 97.7%in 90minutes.The hydrogen yield of LZU1_0.5@WO₃ can reach 6133.2μmol·h-1·g-1.The photocatalytic activity of the composite is improved mainly because the heterojunction formed between WO₃ and LZU1 can effectively promote the separation of electron-hole pairs in the photocatalytic reaction process.The study of photocatalytic mechanism shows that the band structure of WO₃ and LZU1 constitute a traditional double transfer channel for photogenerated carriers.In addition,LZU1_0.44@WO₃ has good stability and reusability.This work may provide new ideas for the production of novel photocatalysts using semiconductor materials and COF photocatalysts to solve environmental pollution and hydrogen shortage problems.2.Hollow WO₃ nanospheres were synthesized by template method,and Mn-ZIF-67 was assembled on the surface of WO₃/Mn-ZIF-67 composite photocatalyst.The structure and properties of the catalysts were characterized by IR,PXRD,XPS,DRS,EIS,etc.The doping of Mn improves the photoelectric performance of ZIF-67.The hollow structure increases the multiple refraction of light and improves the utilization rate of light.Hollow WO₃/Mn_0.5-ZIF-67 composite showed higher photocatalytic activity for degradation of p-chlorophenol than hollow WO₃ pellets and Mn-ZIF-67 under simulated sunlight.Among them,WO₃/Mn_0.5-ZIF-67 showed the highest catalytic activity,and the degradation of TC within 60min was 93.2%.The improved photocatalytic activity of the composite was mainly attributed to the formation of z-type heterojunction between hollow WO₃nanospheres and Mn-ZIF-67,which effectively separated and transferred the photogenerated charge.In this study,the catalytic performance of photocatalyst was improved by changing the morphology and metal doping of the catalyst,which provided a new method for the design of novel heterojunction.photoelectric performance of ZIF-67.The hollow structure increases the multiple refraction of light and improves the utilization rate of light.Hollow WO₃/Mn_0.5-ZIF-67 composites showed higher photocatalytic activity for degradation of p-chlorophenol than hollow WO₃ pellets and Mn-ZIF-67.WO₃/Mn-ZIF-67 showed the highest catalytic activity,with degradation of TC reaching 94.5%within 60min.The improved photocatalytic activity of the composite was mainly attributed to the formation of z-type heterojunction between hollow WO₃ nanospheres and Mn-ZIF-67,which effectively separated and transferred the photogenerated charge.In this study,the catalytic performance of photocatalyst was improved by changing the morphology and metal doping of the catalyst,which provided a new method for the design of novel heterojunction.3.A novel heterojunction photocatalyst Ce O₂/UIO-66 was prepared by hydrothermal synthesis.The structure and properties of the catalysts were characterized by IR,PXRD,XPS,DRS,EIS,etc.The photocatalytic results showed that the degradation rate of Ce O₂/UIO-66_0.5 composite reached 91.15%for TC and94.23%for p-chlorophenol within 60min under simulated sunlight.The study on the photocatalytic mechanism showed that the band structure of Ce O₂ and UIO-66constituted a z-type transfer channel for photogenerated carrier.This work provides a reliable method for the design of efficient heterojunction photocatalysts.