Electronic Structure-Tuning And Photocatalytic Hydrogen Production Of Graphitic Carbon Nitride

Nowadays,the increasing forms of global environmental pollution and the depletion of energy have seriously affected the survival of human beings and the development of civilization.Therefore,human beings have invested huge efforts to develop new energy sources.Among new energy sources,solar energy is considered to be one of the most promising natural energy sources because of its inexhaustible and sustainable characteristics.Among the solar energy application technologies,the conversion of photocatalytic solar energy into chemical energy,especially the development of photocatalytic water splitting for H₂ production,is considered to have great potential to solve the above-mentioned crisis.The discovery of the polymer semiconductor graphitic carbon nitride as a metal-free two-dimensional conjugated semiconductor,compared to traditional inorganic semiconductor catalysts（such as TiO₂,MoS₂,etc.）,stimulates the sustainable development of conjugated polymers for water splitting.The research of photocatalysts has been shifted from inorganic semiconductors to more abundant organic polymers by this in-depth study of photocatalysis.However,pristine graphitic carbon nitride has low quantum efficiency due to weak light absorption ability and high photo-generated electron-hole recombination rate.The methods of electronic structure modulation mainly include copolymerization and doping.Therefore,the main research content of this paper is to modulate the electronic structure of graphitic carbon nitride.The details are as follows:（1）We developed a facile method to produce okra-like g-C₃N₄ tube catalysts(TCN_MCA-PImM)by thermal polymerization of poly-（imidazolium-methylene）chloride（PImM）modified melamine-cyanuric acid supramolecular precursor,under nitrogen conditions,which was synthesized by hydrothermal self-assembly of melamine with appropriate amount of PImM.Due to the incorporation of PImM and its strongπ-πinteractions,and van der Waals force,the thermal polymerization process of g-C₃N₄ were affected,so that the molecular framework of this catalyst contains more graphitic N and the morphology is similar to okra,which endows it with the markedly promoted charge carrier mobility,the improved light absorption capacity and enlarged reduction potential.The hydrogen evolution rate（HER）of the photocatalyst(TCN_MCA-PImM)obtained with the optimal amount of PImM modified carbon nitride reaches1902μmol g^-1 h^-1,which is 25.7 times higher than that of bulk g-C₃N₄（BCN）.The apparent quantum yield（AQY）of light is increased to 4%at a wavelength of 420 nm.（2）We developed a microwave solvothermal method to successfully anchor Mo₁S₂ at Cu₁N₃ site to form Mo₁S₂/Cu₁N₃ gemini entities decorated CN.Here,super hot spot was formed on Cu by microwave.The formed super hot spot can promote the interaction between Mosalt and precipitant,so that Mowas anchored around Cu to form Cu₁N₃/Mo₁S₂gemini entities to modify CN.Through the experimental results and theoretical calculation,it is found that the electronic structure of semiconductor photocatalyst is affected by the synergistic effect of Mo₁S₂ and Cu₁N₃.Thus,the photocatalytic hydrogen evolution ability of CN is enhanced by reducing the reduction potential of the catalyst,reducing the band gap and inhibiting carrier recombination.Finally,the HER of the as-prepared Cu₁N₃/Mo₁S₂/CN photocatalyst reaches6213μmol g^-1 h^-1,which is 84 times that of BCN,and the AQY is increased to 7.6%at 420 nm.