| Metal organic frameworks?MOFs?represent a new class of crystalline organic-inorganic hybrid porous semiconductor-like materials,which are bridged by inorganic metal ions and organic ligands.These porous materials possess many attractive properties,such as high surface area,good crystalline nature,high porosity,easy functionalization,and abundant active sites.As such MOFs can serve as ideal photocatalysts.However,most MOFs are not suitable for photocatalytic H2 generation or the efficacy is low,restrained by ultraviolet-light absorption,inappropriate conduction band positions,surface reaction potential.In order to solve above problems,in this thesis we propose two strategies to promote MOFs for photocatalytic H2 production:dye sensitization and co-catalysts engineering.We have developed several dye-sensitized MOFs photocatalysts with enhanced photocatalytic activity.The contents of this research are as follows:First,Eosin Y?EY?as photosensitizer and Pt as cocatalyst,respectively,and successfully harness several Fe-MOFs for photocatalytic H2 production.We found that dye-sensitized Fe-MOFs can absorb visible light and their conduction band positions become more negative after EY-dye sensitization,suitable for the thermodynamic requirements of H2 production.At the same time,the introduction of catalyst Pt can significantly reduce their overpotentials for HER reaction,leading to improved H2 production efficiency.We studied the band structures of MOFs before and after dye-sensitization by the means of UV-visible diffuse reflectance spectra,Mott-Schottky plots,and so on.We took LSV curves to explore the change of surface overpotentials before and after the introduction of Pt on Fe-MOFs.By means of photocurrent,EIS Nyquist plots,PL emission spectra and fluorescence lifetimes,the working mechanism of these dye-sensitized Fe-MOFs was also revealed.We also investigated the H2 production efficiency of Fe-MOFs under different conditions,such as pH value of solution and dye concentration,further clarifying the optimal working condition of this dye-sensitization system.Second,we introduced Ni2+as a co-catalyst into Fe-MOFs by doping,and obtained a series of bimetallic Fe-Ni-MIL-88?B?materials with adjustable concentration of Ni2+.Then we successfully applied them to the dye-sensitized photocatalytic H2 generation system.This strategy of doping Ni2+in MOFs as cocatalyst has some advantages,such as monodispersity,abundant active sites,unoccupied MOFs channels,and favorable electron transfer,and so on.The morphologies of these Fe-Ni-MIL-88?B?particles were characterized by SEM,TEM,and element mapping.The structures and compositions of Fe-Ni-MIL-88?B?were analyzed by means of XRD patterns,Raman spectra and FTIR spectra.The overpotentials of Fe-Ni-MIL-88?B?before and after Ni2+doping for H2 evolution was studied by LSV method.The electron transfer means in the Fe-Ni-MIL-88?B?after dye-sensitization was investigated by XPS,PL emission spectra and fluorescence lifetimes.Through exploring the wavelength-dependent H2 production efficiency of dye-sensitized Fe-Ni-MIL-88?B?,we discovered the optimal condition of this system for photocatalytic H2 production,such as the best irradiation wavelength and the highest apparent quantum efficiency. |
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