Synthesis,Modification And Photocatalytic Hydrogen Evolution Of G-C₃N₄ Nanostructures

Photocatalytic technology is considered as one of the most direct and effective technologies for solving environmental and energy problems.And g-C₃N₄ as a new type of metal-free photocatalyst has been widely used in various fields of photocatalysis.In this paper,we helight an available pathway to prepare g-C₃N₄ nanosheets by thermal polycondensation combined with gaseous stripping.And the carbon-rich g-C₃N₄nanosheets were prepared by two and one step gaseous stripping method respectively with the introduction of ethanol.Carbon-rich g-C₃N₄ nanosheets perform well in photocatalytic hydrogen evolution,and the photocatalytic mechanism were preliminary explored as well.?1?Ultrafine g-C₃N₄ nanosheets were obtained by gaseous stripping method with vapor atmosphere.As comparison,g-C₃N₄ treated in air and N₂ atmospheres are also prepared.The obtained products were characterized by XRD,TEM,FTIR and XPS,respectively.Well dispersed g-C₃N₄ nanosheets can be obtained by this gaseous stripping process in vapor atmosphere,which possess much higher specific surface area?211.20 m²/g?than that of bulk g-C₃N₄?15.30 m²/g?.For photodegradation of RhB solution,the g-C₃N₄?w-N₂?nanosheets can degrade 20 mg/L RhB completely within12 min under visible light illumination,while 50 min needed of bulk g-C₃N₄.Also the g-C₃N₄?w-N₂?nanosheets possess the highest photocatalytic hydrogen evolution rate of 1113.48?mol h^-1 g^-1 under visible light illumination,which is 6 times that of bulk g-C₃N₄.?2?In order to decrease the recombination ratio of photogenerated electron-hole pairs during the photocatalytic process of g-C₃N₄ nanosheets,carbon-rich g-C₃N₄nanosheets were prepared with two-step gaseous stripping.Carbon-rich g-C₃N₄nanosheets with different carbon content were obtained by controlling the access time of C₂H₅OH,and the performance of visible light photocatalytic hydrogen evolution were also discussed.High optical absorption in visible light region and low recombination ratio of photogenerated electron-hole result in high efficiency of photocatalytic hydrogen evolution.Especialy when C₂H₅OH was inlet for 5 min,g-C₃N₄?5 min?nanosheets possess the highest hydrogen production efficiency of 2092.22?mol g^-1 h^-1,which is 11.3 and 1.9 times that of bulk g-C₃N₄ and g-C₃N₄?0 min?respectively.?3?For further improving the gaseous stripping efficiency,carbon-rich g-C₃N₄nanosheets with different carbon contents were obtained in wet N₂ atmospheres containing C₂H₅OH with different concentrations in one-step gaseous stripping process.And the performance of visible light photocatalytic hydrogen evolution were also discussed.The results show that g-C₃N₄ nanosheets possess the highest photocatalytic hydrogen production efficiency while the concentration of C₂H₅OH is 5%.The hydrogen evolution efficiency of g-C₃N₄?5%?is 2569.27?mol g^-1 h^-1 for 5 h under continuous visible light illumination,which was 13.9 and 2.3 times to that of bulk g-C₃N₄ and g-C₃N₄?0%?respectively.For the same time,g-C₃N₄?5%?nanosheets also show high hydrogen evolution ability under continuous visible light illumination for 25h,indicating high catalytic stability of g-C₃N₄?5%?nanosheets.