The Preparation And Photocatalytic Performance Of Porphyrin Metal-organic Frameworks And Semiconductor Composites

Energy shortage and environmental pollution are the core issues affecting the development of human society.However,the rational use of clean energy such as semiconductor photocatalytic technology and solar energy is one of the most effective strategies to solve the above problems.Semiconductor materials as photocatalysts have many extremely important values of research in the fields of dye-sensitized solar cells,photocatalytic carbon dioxide reduction,pollutant degradation,and photocatalytic decomposition of aquatic hydrogen to produce hydrogen.Porphyrins,metalloporphyrin derivatives,and metalloporphyrin organic frameworks are widely used in photocatalytic research due to their unique advantages such as easy adjustment of structures,diversification of central coordination atoms,and excellent optoelectronic properties.Therefore,the development of composite materials with excellent photocatalytic performance under visible light has become a research focus on the field of photocatalysis.In this thesis,semiconductor photocatalyst is deployed as the main research line.Metal porphyrins or porphyrin metal organic frameworks and semiconductor composites are prepared by one-step solvothermal method.Metal porphyrins or porphyrins with highly conjugated macrocycles and polyfunctional groups are selected.The phosphine metal organic framework material has modified the semiconductor photocatalyst.By studying the photocatalytic performance of the composite material,the thesis hopes to find out a new composite of catalytic material with better performance in the ablility ofresponse to visible light,whose possible photocatalytic mechanism is analyzed and discussed with characterization methods.The specific research content is as follows:?1?Composite material PCN-224?Cu?/TiO₂ photocatalytic CO₂ reduction:cubic PCN-224?Cu?was combined with TiO₂ by a one-step solvothermal method to prepare a series of PCN-224?Cu?/TiO₂ with different mass percentages.The composite materials were characterized by a series of characterization methods,and the photocatalytic CO₂reduction performance of all the samples was tested.The results show that the composite material 15%P?Cu?/TiO₂ displays the highest photocatalytic activity,and it also has a good photocatalytic stability and a better acid-and-alkali resistance.The photocatalytic CO₂ reduction mechanism was discussed and analyzed based on all the characterization and test results of photocatalytic performance,and the most likely photocatalytic CO₂ reduction reaction mechanism was proposed.The cubic PCN-224?Cu?and TiO₂ were compounded to develop a composite catalyst being able tosignificantly improve the photocatalytic Z-Scheme reduction mechanism of CO₂ to CO in the absence of a sacrificial agent and cocatalyst The speed of CO production achieves37.21?mol/g/h,which is 10 times and 45.5 times that of pure PCN-224?Cu?and pure TiO₂,respectively,for the photocatalytic reduction of CO₂ to CO.The catalyst significantly enhances the ability to capture light and the ability to separate photo-generated electrons and holes,thereby improving the photocatalytic activity of the catalyst.?2?Composite material Fe^?-TCPPCl?UiO-66?referred to as FTU?photocatalytic synergistic Fenton-like degradation of organic pollutants Rhodamine B?RhB?:Fe^?-TCPPCl was implanted into UiO-66 by a one-step synthesis strategy to obtaine FTU composites from the catalyst,and a series of characterization methods were used to characterize the prepared catalyst.All samples were tested for the degradation performance of a series of organic pollutants RhB under different systems.The test results showed that there was no significant degradation under dark reaction conditions;only under visible light irradiation for 60 min,the degradation rate of RhB by TU samples was 27%,and the degradation rate of FTU samples under these conditions was51%.However,in the presence of H₂O₂ at the same time for 60 minutes under visible light irradiation,the degradation rate of RhB by the TU sample is 45%,and the degradation rate of the FTU sample by this condition is 100%.In comparison,the removal rate of COD in FTU samples under the presence of visible light and H₂O₂increased by 15.5%.In addition,the degradation conditions were optimized.It was found that the optimal pH was 3.5,the optimal catalyst dosage was 0.10 g/L,and the optimal H₂O₂ concentration was 2.5 mM.The ESR test results fully proved that·OH is the most active species,and·O₂^—and h⁺play an auxiliary role in the degradation of RhB.The photocatalytic mechanism of FTU catalyst was discussed and analyzed by combining the above performance test results and characterization analysis.?3?Photocatalytic degradation and hydrogen production of layered ZnIn₂S₄@PCN-224 composites:A series of ZnIn₂S₄@PCN-224 composites with different mass percentages were prepared by in-situ one-step solvothermal method.The prepared catalyst was analyzed by characterization.All the samples were tested for photocatalytic degradation of tetracycline hydrochloride?TCH?.As a result,the composite material ZIS@P20 exhibited the highest photocatalytic activity.The removal rate of TCH was about 99.9%under visible light for 60 minutes.The apparent rate constant of degradation is about 4.7 times that of pure ZnIn₂S₄.And has excellent photocatalytic performance and good photocatalytic stability.The common factors affecting photocatalytic degradation of TCH were also investigated.The optimal catalyst dosage was 0.20 g/L,the initial concentration of TCH was 20 mg/L,and the optimal pH was 6.5.Therefore,ZIS@P20 composite can be considered as a stable and effective photocatalyst.In addition,a series of ZnIn₂S₄@PCN-224 composites were tested for photocatalytic hydrogen production performance.Through the test results,we found that the ZIS@P20 composite still exhibited the highest photocatalytic hydrogen production activity,and its photocatalytic decomposition The rate of hydrogen production from water is 4.5 times that of pure ZnIn₂S₄.In addition,Pt loading has a significant effect on the photocatalytic hydrogen generation rate of ZIS@P20.When the optimal Pt loading of ZIS@P20 is about 8%,the hydrogen production rate is the highest,which is about 19 times the hydrogen production rate of ZIS@P20,and 8wt%Pt-ZIS@P20 exhibits excellent photocatalytic hydrogen production performance and good photocatalytic stability.In this chapter,the photocatalytic mechanism is discussed and analyzed in combination with all the characterization and test results of photocatalytic performance,and the most probable mechanism of photocatalytic degradation of TCH and photocatalytic degradation of hydrogen by water are proposed.The catalyst significantly enhances the ability to capture light and the ability to separate photo-generated electrons and holes,thereby improving the photocatalytic activity of the catalyst.