Controlled Synthesis And Photocatalytic Properties Of Pt-coordinated Porphyrin-based MOFs

The rapid development of industrialization has promoted the prosperity of the global economy,while also consuming a large amount of fossil fuels,which has brought serious energy and environmental problems（such as the production of pollutants such as NO_x）.Global energy consumption and ecological and environmental issues make it particularly urgent to rationally develop and utilize existing resources,as well as to find new ways to obtain new resources and protect the environment.Solar energy is a huge and sustainable resource derived from nature and has the greatest potential to provide power for energy conversion reactions.Photocatalytic technology is considered to be an applicable and environmentally friendly technology for using solar energy.The use of photocatalytic technology can not only produce clean and non-toxic hydrogen energy to replace traditional fossil fuels,but also can degrade NOx and other pollutants through photocatalytic technology,thereby effectively protecting the environment.Photocatalyst is the core issue of photocatalytic technology.Therefore,it is very important to seek a photocatalyst with high efficiency,high stability and easy synthesis.Metal-organic frameworks（MOFs）are a new type of porous inorganic-organic hybrid supramolecular materials.Due to their flexible structure and functional tunability,they have recently developed into ideal photocatalysts.In MOFs,the light-induced electrons from the photosensitive organic linker migrate rapidly to the metal node serving as the reaction center,thereby effectively promoting the separation of charge carriers.Porphyrins,organic linkers with a wide range of light absorption wavelengths,are recognized as very suitable for use as light absorbers in MOFs.In this paper,the N atom in the porphyrin ring is used as the target site to effectively confine Pt ions to achieve maximum atom utilization and form a more effective electron transfer channel,thereby increasing the transfer rate and separation of photogenerated carriers Efficiency:The photocatalytic performance of Pt-coordinated porphyrin-based MOFs is improved through the selection of central metal clusters,defect control,and morphological structure control:1.Using the Pt-coordinated Pt Ⅱ tetrakis（4-carboxyphenyl）porphyrin（PtTCPP）with wide absorption rate as the linking group and Ti-oxo cluster as the metal node,a robust and efficient metal organic framework（Ti-MOFs-Pt）photocatalyst,and then carried out photocatalytic hydrogen evolution and NO removal research.It is worth noting that,compared with most reported MOFs-based photocatalysts,Ti-MOFs-Pt has extremely high hydrogen evolution activity(15456μmol·g^-1·h^-1)and NO removal rate（70.3%）.Spherical aberration corrected scanning transmission electron microscopy（AC-STEM）and synchrotron radiation-based X-ray absorption fine structure（XAFS）spectroscopy detected the presence of single-atom Pt.Through ultraviolet-visible light absorption spectroscopy（UV-Vis）,fluorescence spectroscopy（PL）,photocurrent and impedance test experiments,it is found that the extremely high atomic utilization efficiency of single-atom Pt and the rapid separation and transfer of photo-generated carriers lead to high efficiency The main reason for photocatalytic performance.The introduction of single-atom Pt into the center of the planar porphyrin skeleton can combine the wide light absorption capacity of the porphyrin unit with the extremely high atom utilization efficiency of the single-atom Pt,thereby greatly improving the photocatalytic performance,which provides us with a preparation A novel strategy for efficient MOFs photocatalysts.2.Connecting PtTCPP and Zn（COO）₄ clusters to synthesize a layered structured metal-organic framework Zn-TCPP-X with controlled structural defects（X represents the ratio of the amount of regulator pyrazine to PtTCPP）.The effect of structural defects on photocatalytic performance was systematically studied.With the increase of structural defects,the rate of photocatalytic hydrogen production showed a volcanic trend.Among them,Zn-TCPP-2 showed the highest activity(hydrogen production rate was 4806μmolg^-1h^-1).UV-Vis,PL,photocurrent,impedance and other test experiments revealed that Zn-TCPP-2 with moderate structural defects has the highest charge separation efficiency and therefore has the best photocatalytic activity,while too many defects will reduce the charge separation efficiency and then Reduce photocatalytic activity.By changing the equivalent of pyrazine,the defects of the Zn-TCPP metal-organic framework structure were successfully controlled,and the purpose of improving the photocatalytic performance was achieved.3.Using PtTCPP and ZrCl₄ as raw materials,adding formic acid or benzoic acid to the solvent respectively to prepare Zr-MOFs photocatalysts with different morphologies（nanorod,cube and block）.Under visible light irradiation,the nanorod-shaped Zr-MOFs-S showed excellent photocatalytic activity,achieving a H₂release rate of5212.6μmol·g^-1·h^-1.After three consecutive cycles of hydrogen production,it would not be significant Decrease catalytic activity.The Brunauer-Emmett-Teller（BET）test found that Zr-MOFs-S has the largest specific surface area,which promotes the exposure of more active sites and ultimately leads to the highest catalytic activity.This provides us with a method to increase the photocatalytic activity of MOF through morphology and structure regulation.