Modification Of Graphite Carbon Nitride（g-C₃N₄）and Its Photocatalytic And Electrocatalytic Properties

Graphite carbon nitride（g-C₃N₄）is an excellent non-metallic semiconductor photocatalyst with wide application prospects.g-C₃N₄ has aroused wide interest of reserchers,due to its extensive sources,easy synthesis in laboratory,chemical stability in acid and alkali solutions and stable existence at 600℃.However,the specific surface area of carbon nitride sintered at high temperature is far lower than the theoretical value and the recombination efficiency of photogenerated electron hole pairs is high,which leads to low utilization of photogenerated charge,and the narrow absorption range of visible light leads to low utilization of lightPolymeric carbon nitride with frustrated-Lewis-pairs was constructed by intercalation of electron-deficient boron（B）into metal-free carbon nitride.NH₃-temperature programmed desorption（TPD）and pyridine-adsorption diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）results demonstrated that B heteroatoms（Lewis acid）and proximal amino groups（Lewis base）were more likely to form frustrated Lewis pairs,which would capture,activate and reduce N₂ to NH₃ through a“pull-push”effect.Molybdenum-based oxide was further employed as a co-catalyst to improve the charge separation efficiency of site-engineered photocatalysts.The synergistic effect between intercalated B and defective Mo O₂ resulted in an 8-fold increased photoactivity of carbon nitride for N₂ fixation.This work provides a new avenue for the rational design and engineering of frustrated Lewis pair sites on polymeric photocatalysts toward efficient N₂ fixation.The typical S-scheme photocatalyst can be obtained by a simple water heating method,in which pristine g-C₃N₄ has been treated with NaOH solution.After pretreatment,the homogenous hydrolyzed g-C₃N₄（h-CN）dispersity can be obtained and is beneficial to fabricate the novel S-scheme heterojunction.In addition,the mechanism and the electrons transporting route have been investigated detailedly by XPS and EPR measurements.The significantly improved H₂ production performance can be attributed to the formation of S-scheme heterojunction between h-CN and Cd S,which is beneficial to charge separation efficiency and transport.Compared with B-CN/Cd S,h-CN/Cd S exhibits remarkably photocatalytic activity.This work provides a facile pretreatment for g-C₃N₄ may have a significant impact on extending the application of bulk g-C₃N₄ with poor dispersed performance.N-doped carbon nanotubes derived from hydrolyzed graphitic carbon nitride（h-CN）wrapped Fe nanoparticles with core–shell nanostructures grafted on carbon nanotubes（Fe@h-CN/CNT）were obtained by a simple process.After the pretreatment,the introduced hydrophilic groups can improve the dispersibility of graphitic carbon nitride in water.Compared with its analogue prepared using untreated carbon nitride,Fe@h-CN/CNT exhibits a higher specific surface area and has more graphitic N for Fe–Nxcoordination and more pyridinic N facilitating the four-electron pathway.In addition,the CNT network structure increases the conductivity of the Fe@h-CN/CNT composite electrocatalyst.As a result,our composite electrocatalyst shows desirable ORR performances with outstanding limited current density,comparable to commercial Pt/C in alkaline electrolyte.This work reveals that the pretreatment of the carbon nitride may have a significant effect on the electrocatalytical performance and provide a facile method for developing non-noble metal ORR catalysts.