Single Atom Active Sites@Photosensitizer Implanted In In-MOFs For Photocatalytic CO₂ Reduction

It is of great prospect to slove the energy shortage crisis and environmental pollution problem by using sunlight as driving power to photo-catalytically reducing CO₂ into fuel molecules.However,photocatalytic CO₂ reduction still have various problems,such as lacking of visible light response,relatively low selectivity,noble metal participation,et al.Therefore,developping efficient photocatalytic CO₂ reduction catalyst with reduced noble metal or noble metal free is able to fundamentally solve the environmental problems and achieve the goal of sustainable development.In recent years,indium-based metal organic frameworks(In-MOFs),a non-noble metal material,has been caused much attention in the area of photocatalytic CO₂ reduction due to the merits of specific structure information,adjustable ligand and metal nodes which can provid a multivariant platform to build photocatalyst.A potential method is to build an integral structure of photosensitizer and catalytic center by introducing visable light respons ligand and catalytically active metal center into MOFs,thus could possibly improve catalytic activity.According to the above merits,it is of great advantages and potential for constructing CO₂ reduction photocatalyst based on In-MOFs.In this thesis,we focus on building an integral structure by introducing visible light respons photosensitizer(porphyrin)and catalytically active metal center(Fe/Co)into In-MOFs.A series of Fe/Co doped indium-porphyrin frameworks are synthesized and applied to highly selective photoreduction of CO₂under visible light.The detail research contents and conclusions are as follows:A series of indium-porphyrin frameworks,In(H₂TCPP)_(1-n)[Fe(TCPP)(H₂O)]_(1-n)[DEA]_(1-n)(H₂TCPP=tetrakis(4-benzoic acid)porphyrine;DEA=diethylamine;In-Fe_nTCPP-MOF,n=0.75,1.91 and 3.56;n%represents the percentage of metal loading)and In-Co_1.71TCPP-MOF were designed and synthesized via solvent thermal method by changing the dosage of Fe³⁺and Co²⁺.Single crystal X-ray diffraction,powder X-ray diffraction and XPS analysis reveal the structural information of as-prapared In-In/Co_n/Fe_nTCPP-MOF are double interpenetrating flexible 3D structure with respect to+2 or+3 of the Co or Fe center.UV-vis spectra indicate In-Fe_1.91TCPP-MOF has strong visible light absorption.Steady state fluorescence spectra,transient fluorescence spectra and electrochemical experiment reveal In-Fe_1.91TCPP-MOF possesses efficient carrier separation efficiency,thus could enhance the photocatalytic activity.As a result,In-Fe_1.91TCPP-MOF shows highly selective photoreduction of CO₂ to CO,achieving a total CO yield of 3469?mol g^-1 with ca.99.5%CO selectivity in 24 h visible light irradiation.This value is superior to that of In-Co_1.71TCPP-MOF(930?mol g^-1,98%)and In-In TCPP-MOF(550?mol g^-1,97%).Systematic experimental and theoretical studies indicate that the porphyrin-supported iron centers in the MOF matrix serve as efficient active sites,which can accept electrons from photo-excited MOFs to mediate CO₂ reduction.