Synthesis And Interfacial Regulation Of Pt@MOF Composites For Photocatalytic Hydrogen Production

With the development of society,fossil fuels are continuously explored and consumed,which makes the earth face an energy crisis and environmental pollution.Photocatalytic hydrogen production by using natural sunlight and converting it into hydrogen energy,has been regarded as one of the ways to solve the energy problem.However,the separation efficiency of photogenerated electrons and holes in the current photocatalytic hydrogen production process is very low,which is an urgent problem to be solved.As for heterogeneous photocatalysts,the interface electron transfer between photosensitizer and cocatalyst is quite complicated,and its internal mechanism is unclear as well.In particular,the effect of surfactants capped on the surface of co-catalysts（such as Pt NPs）on the separation of photogenerated carriers has been neglected in many cases.Metal-organic frameworks（MOFs）,constructed by metal ions/clusters and organic linkers via coordination bonds,are promising crystalline porous materials.MOFs feature the ultrahigh surface area,tunable pore size,well-defined and tailorable structures,have been widely applied in various fields,such as gas storage and separation,chemical sensors,drug delivery,proton conductivity,catalysis,et.al.Among these,based on the semiconductor-like behaviour,MOFs have been widely used in photocatalysis.Thanks to the pore structure,NPs can be well stabilized and dispersed in the channal of MOFs.Combined with the well-defined and tailorable structure,MOFs are suitable for the microenvironment regulation around the active site to study the electron transfer process and photocatalytic active in photocatalysis.This will be of great significance for a deep understanding of charge separation in photocatalysis.In this work,we choose a classic MOF,UiO-66-NH₂,to encapsulate Pt nanoparticles（NPs）with different surface microenvironments,PVP capped Pt NPs（denoted as Ptpvp）,Pt with partially removed PVP（PtrPVP）,and clean Pt without PVP（Pt）,affording Ptpvp@UiO-66-NH₂,PtrPVP@UiO-66-NH₂ and Pt@UiO-66-NH₂,respectively.The photo-electrochemical measurements suggest that the gradual removal of interfacial PVP gives rise to improved electrical conductivity and benefits electron transfer from MOF to Pt,supporting the photocatalytic H₂ production activity trend:UiO-66-NH₂<PtPVP@UiO-66-NH₂<Ptrpvp@UiO-66-NH₂<Pt@UiO-66-NH₂.Based on the above,introducing Fc as the electron mediator greatly improves electron transfer of Pt@UiO-66-NH₂,giving rise to the best photocatalytic activity of Pt-Fc@UiO-66-NH₂.Furthermore,the ESR in conjunction with time-resolved PL spectroscopy further uncovers the underlying charge transfer mechanism and well explains efficient charge separation in Pt@UiO-66-NH₂ and Pt-Fc@UiO-66-NH₂.