Preparation Of Oxygen-Doped Porous Carbon Nitride And Its Photocatalytic Performance For Hydrogen Production

The increasingly severe energy crisis and environmental pollution problems make it urgent to use photocatalytic technology to convert clean solar energy into storable chemical energy.Among a series of photocatalysts,carbon nitride has attracted intense attention due to its innocuousness,low cost,and easy regulation of its energy band structure and optoelectronic properties by organic chemical methods.However,the pristine bulk carbon nitride has a small specific surface area,low electron-hole separation efficiency,and weak visible light response,resulting in its limited photocatalytic efficiency.In our work,the photocatalytic hydrogen production activity of carbon nitride has been enhanced by O doping and morphology tuning.The O doping can change the electronic state and energy band structure of carbon nitride,thereby enhancing the separation efficiency of photogenerated carriers and the absorption of visible light.The morphology tuning can effectively increase the specific surface area of the catalyst to expose more active sites and improve the separation efficiency of photogenerated carriers.The specific research contents are as follows:(1)Oxygen-doped porous carbon nitride(ABCN)was synthesized by thermal polymerization in air by using melamine,cyanuric acid,and barbituric acid as precursors.The obtained catalysts were characterized by SEM,XPS,BET,UV-Vis DRS,and PL tests,and their changes in optoelectronic properties and microstructures were analyzed,which confirmed the formation of porous structure in the catalyst and the incorporation of O into carbon nitride by substituting N between adjacent heptazine rings.The doping of O significantly enhanced the visible light utilization of the catalyst and promoted its photogenerated carrier separation ability.The porous structure enabled the catalyst to have a high specific surface area and expose more catalytically active sites.In addition,the photocatalytic performance of the catalyst was evaluated by photocatalytic hydrogen production.Under visible light irradiation,the photocatalytic hydrogen production rate of ABCN reached 3875 μmol g-1 h-1,which was 6.5 times that of ordinary bulk carbon nitride(g-C3N4)obtained under air.(2)A unique rod-like carbon nitride supramolecular precursor(FCMx)was synthesized by hydrothermal reaction of melamine and formic acid at 180℃,and then the FCMx was calcined under Ar at 550℃ to obtain oxygen-doped carbon nitrides nanorods(FCNx).More importantly,with the prolongation of hydrothermal time,the O content in the obtained FCNx gradually increased,and the FCNx transformed from a smooth columnar structure to a porous columnar structure with a rough surface.The incorporation of O into carbon nitride by substituting sp2 N in the heptazine ring was proved by XPS,FT-IR,and elemental analysis.The doping of O significantly promoted the electron-hole separation efficiency of the catalyst.The n-π*transition caused by the increase of its lone pair electrons also promoted its absorption of visible light.The porous rod-like structure endowed the catalyst with more active sites and significantly improved photogenerated carrier separation ability.The hydrogen production rate of FCNx reached 12766 μmol g-1 h-1,which was 18.3 times than that of ordinary bulk carbon nitride(CN)obtained under Ar.