Research On Surface Hydrogenation And Morphology Design Of Graphitic Carbon Nitride And Its Photocatalytic Performance

The rapid development of society is closely related to energy supply.However,the traditional energy reserves on the earth are limited and the use of traditional energy will be accompanied by environmental pollution problems.Thus,we urgently need to find low-cost and environmentally friendly ways of generating energy.The technology of photocatalytic energy conversion driven by sunlight is expected to alleviate environmental and energy crises.Among many photocatalysts,graphitic carbon nitride（g-C₃N₄）has low cost and moderate energy band.It is a"star"material in the field of photocatalysis.However,the bulk g-C₃N₄ has poor carrier separation and low hydrophilicity,so it only exhibits low photocatalytic activity.Therefore,this work focuses on surface hydrogenation and morphology design to optimize g-C₃N₄,enhancing the photocatalytic performance of g-C₃N₄.The specific contents are as follows:（1）The surface-modified g-C₃N₄ nanosheets were prepared by plasma treatment of g-C₃N₄ in H₂,H₂-CH₄ and Ar atmosphere.Among them,the hydrogenated g-C₃N₄ was prepared by H₂plasma treatment of g-C₃N₄ at room temperature;the morphology of the hydrogenated g-C₃N₄ was stripped,and the hydrophilic group N-H and defect state were introduced during the hydrogenation process.The hydrogen-producing activity of hydrogenated g-C₃N₄ is significantly enhanced,and its rate exceeded that of pristine g-C₃N₄ by a factor of nearly ca.4.8.Photocatalytic activity improvement can be explained by the introduction of hydrophilic group N-H,defect states,and exfoliated nanosheet morphology.Theoretical calculations determined the possible locations of protons and calculated the changes in the adsorption energy of water molecules after hydrogenation,indicating that hydrogenated g-C₃N₄ possessed an enhanced adsorption capacity for water molecules.Optical emission spectroscopy supported the introduction of hydrogen species during H₂ plasma treatment of g-C₃N₄.The mechanism of enhanced photocatalytic H₂-production activity was further proposed using electron paramagnetic resonance,time-resolved fluorescence,and electrochemical characterization.（2）The hierarchical flower-like g-C₃N₄ assembled by nanosheets（CMN）was prepared through molecular self-assembly followed by ethanol molecule insertion strategies using cyanuric acid and melamine as the precursor.The synthesized CMN possessed high specific surface area and enhanced CO₂ adsorption capacity.In the absence of any sacrificial agent and cocatalyst,CMN exhibited improved CO₂photoreduction capability under visible light irradiation.The CO and CH₄ production rates of CMN reached 18.8 and 1.8μmol·h^-1·g^-1,which were 2.4 and 4.5 times higher than those of CN,respectively.The enhanced activity was mainly due to the enhanced adsorption capacity for CO₂,enabling the rapid electron capture of the reactants and reducing carrier recombination.The hierarchical porous flower-like structure facilitated the transport of reactant molecules.The increased specific surface area provided numerous active sites for the reaction.The characterizations of CO₂-temperature programmed desorption（CO₂-TPD）and transient fluorescence revealed the reason for the enhanced CMN activity.This research prepared a catalyst with a regular morphology through a convenient and simple method,providing a new idea for the design of the morphology and structure of the catalyst.