Interface Modification And Electron Transfer Mechanism Of Metal Oxide Semiconductor Photocatalysts

Due to the growing energy crisis and environmental pollution problems,renewable and clean energies are vital to be developed.Solar energy and hydrogen energy are recognized as two potential new energies.The conversion of solar energy to hydrogen energy by photocatalytic technology has attracted widespread attentions of researchers.Among them,the design and assembly of efficient and stable catalysts are the focus of research.Transition metal oxides possesses excellent properties,such as adjustable valence states,various structures,and low prices,which are considered to be the semiconductor photocatalysts with practical value.Based on the metal oxides with photocatalytic activity,through non-covalent interaction,metal oxide/porphyrin and metal oxide/MOFs nano-assemblies were fabricated.Furthermore,the assembly mechanisms,photocatalytic activity of hydrogen evolution,and photogenerated electron transfer mechanism were studied.The main contents are summarized as the followed:Semiconductor nanophotocatalysts with high performance for hydrogen generation require well-designed and optimized interfaces.This work aimed at the rational design and facile assembly of a highly efficient 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin/Cu2O(TSPP/Cu2O)heteroarchitectural nanocomposite photocatalyst.The assembly mechanism was explored in detail by spectroscopy and calculation.It was confirmed that the excellent photoactive conjugate molecule TSPP was strongly anchored onto the cubic Cu2O by facilely combined coordination with a hydrogen bond,which was profitable for inhibiting the oxidation of Cu2O and aggregation among TSPP molecules.Importantly,it was shown that the TSPP/Cu2O nanocomposite possessed higher activity.On the basis of the results of fluorescence spectroscopy,X-ray photoelectron spectroscopy,and electrochemical measurements,the increased optical structure and dual interfacial interaction between TSPP and Cu2O were beneficial to improving the transfer of charge carriers.Therefore,the performance was greatly improved.The purpose of this work is to facilely fabricate a novel and efficient Cu-linked ZnO nanorod/5,10,15,20-tetrakis(4-sulfophenyl)porphyrin composite photocatalyst(ZnO NR-Cu-TSPP).The result about the assembly mechanism showed that the TSPP was anchored onto the ZnO NR-Cu through dual interaction,hydrogen bond and coordination interaction.Importantly,the ZnO NR-Cu-TSPP nanocomposite exhibited high photocatalytic activity on account of extended light absorption and greatly enhanced charge separation at the hetero-interface.By studying the photocatalytic mechanism,it revealed that the Cu as the bridged linker not only strengthened the interaction between ZnO NR and TSPP,but also provided more active sites for photocatalytic H2 evolution.Furthermore,it was found that a certain amount of TSPP can significantly enhance the photocatalytic activity of the nanocomposite.Moreover,the composite showed a superior stability according to the cycling tests.Cu2O@TiO2 heterostructure were constructed through hydrolysis and sintering of tetrabutyl titanate on the surface of nano-cubic Cu2O.Furthermore,ZIF-8 was coated on its outer surface to construct a new MOFs nanocomposite based on Cu2O@TiO2 heterojunction(Cu2O@TiO2@ZIF-8).Under visible light irradiation,the nanocomposite showed excellent photocatalytic activity for hydrogen evolution and high catalytic stability.On the basis of the results of fluorescence spectra,photocurrent response,and electrochemical impedance spectroscopy measurements,the built-in electric field generated by Cu2O@TiO2@ZIF-8 nano-heterojunction can effectively suppress the electron-hole recombination.In addition,the enhanced absorption and synergistic effect between Cu2O@TiO2 and ZIF-8 in the nanocomposite system were also the main factors to significantly improve the photocatalytic activity for hydrogen evolution.The series of metal oxide-based assemblies above quickly constructed through non-covalent interaction are with novel structures,excellent photocatalytic performance,and stable catalytic performance,which will provide new ideas for designing and synthesizing other highly efficient photocatalysts,and also provides theoretical basis and experimental references for exploring the photo-generated electron transfer mechanism.