The Study Of The Synthesis And Photocatalytic Properties Of Porphyrin-based MOFs And Their Derivatives

At present,the demand for energy,especially fossil fuels,is gradually increasing.At the same time,it is accompanied by more and more serious environmental pollution problems（such as air pollutant NO_x）and energy shortage.The strategy of“end-of-pipe treatment”and“source control”can not only control the existing environmental pollution,but also reduce the consumption of fossil fuels and the generation of environmental pollutants.Therefore,it plays a very important role in solving the problems of environmental pollution and energy shortage.Photocatalytic technology,on the one hand,can use photocatalytic technology to degrade environmental pollutants such as NO_x;On the other hand,photocatalytic technology can be used to decompose water to realize the precipitation of hydrogen,which can be stored as available clean energy.For photocatalytic technology,the most important thing is the development and utilization of catalytic materials.Metal organic frameworks（MOFs）,a kind of ordered materials self-assembled by organic connectors and metal nodes,have become a research hotspot in the field of photocatalysis because of their large specific surface area,high porosity and diverse structure.In this research,several MOFs materials were synthesized with porphyrin（TCPP）with excellent visible light absorption capacity as organic linker,and the charge separation and transfer efficiency were regulated by introducing ligand central metal,screening metal clusters and modifying metal clusters,so as to improve the catalytic performance.1.Ti-based porphyrin MOFs were prepared by hydrothermal method,and their photocatalytic hydrogen evolution and NO removal properties were studied.The results showed that MOFs（TMPd）with metal Pd in the ligand center had good effects in both aspects,and its hydrogen evolution rate was 1.32 mmol·g^-1·h^-1,which realized the transformation from nothing to something compared with metal free MOFs（TMH）in the ligand center;The photocatalytic removal rate of NO by TMPd could reach 62%,which was 18%higher than that of TMH.Through systematic characterization and analysis,it was found that TMPd could realize rapid charge separation and transfer process under visible light irradiation,and can produce·O₂^-and·OH active species for NO oxidation,so it could have a good effect in photocatalytic hydrogen evolution and NO removal.The process of photocatalytic purification of NO by TMH and TMPd was monitored by in situ infrared（DRIFTS）spectroscopy.The results showed that TMPd could more effectively inhibit the production of intermediate toxic by-product NO₂,convert NO into end-product NO₃^-,and realized the efficient purification of NO.Combined with the DRIFTS spectrum,paramagnetic resonance（ESR）data and energy band structure analysis of TMPd,the possible reaction path was speculated.2.2D nanosheets of porphyrin MOFs with various transition-metal clusters as metal nodes were prepared via a simple solvothermal method to apply in the photocatalytic hydrogen evolution,in which the hydrogen production rate of the optimal Cu-based porphyrin MOFs material（NS-Cu）was as high as 15.39 mmol·g^-1·h^-1.A series of experimental technologies especially Cyclic Voltammetry（CV）and Mott-Schottky（M-S）had been adopted to investigate the charge-transfer property of photo-generated electron-hole pairs,it was found that the uniformly dispersed Cu-clusters nodes in the original 2D MOFs played a key role in the electron transfer process,that was,the photo-generated electron transferred from excited state eosin-Y（EY）to the Cu-clusters nodes for the efficient hydrogen evolution.The excellent photocatalytic performance could be attributed to the reversible oxidation-reduction process of Cu^II/Cu^I,which had excellent electron-receiving and electron-outputting capabilities.3.2D Cd-based MOFs（NS-Cd）were prepared by a simple hydrothermal method,and a small amount of Cd S was derived in-situ from the metal cluster（Cd O_xcluster）of NS-Cd with thioacetamide（TAA）as sulfur source,which improved the photocatalytic water hydrogen desorption performance of NS-Cd.NS-Cd with a small amount of Cd S derived in-situ（Cd S/NS-Cd-5）had good photocatalytic hydrogen evolution rate(1.5mmol·g^-1·h^-1)and high quantum efficiency（8.3%）,and had excellent cycle stability.Through the analysis of fluorescence photoluminescence（PL）,electrochemical impedance（EIS）and Bode data obtained from EIS,it could be found that the in-situ derivation of a small amount of Cd S on NS-Cd improved the charge separation and transfer efficiency.This positive effect might be due to the matched band structure and the very short transmission distance between 2D NS-Cd and Cd S,which enabled the rapid transfer of photogenerated electron hole pairs.