Study On The Regulation Of Point Defect And Enhancement Mechanism Of Photo Catalytic Performance For Porous Graphitic Carbon Nitride（g-C₃N₄）

Graphitic carbon nitride(g-C3N4)has been considered as a promising photocatalyst due to the low price,high physical and chemical stability and visible-light response.Nonetheless,the bulk g-C3N4 is still suffered from low specific surface area,limited active site and the fast recombination of charge carriers,which limits the applications of g-C3N4 in the fileds of photocatalysis.Porous g-C3N4 nanosheet with controllable point defect can provide high specific surface area.abundant active site,high charge separation and transport efficiency and enhanced the photo-redox ability,which is beneficial to improving visible-light-driven photocatalytic activity.However,purposeful design and construction of the porous-defect modified g-C3N4 nanosheets is still a challenge.Herein,we intentionally designed and fabricated targeted porous-defect modified g-C3N4 nanosheets by the strategy of "organic molecule-reformed melamine" to improve visible-light-driven photocatalytic activity.(1)The O-doped porous g-C-3N4 nanosheets have been succseefully prepared by thermal polymerization of the new hydroxylated and carbonylated melamine precursors that were intentionally designed and constructed.Because of their high specific surface areas,abundant active sites,improved charge carrier behavior and strong reduction potential,the as-prepared O-doped porous g-C3N4 nanosheets displayed an about 18-fold higher hydrogen production activity than the bulk counterpart,and the quantum efficiency reached to 12.06%(λ=420 nm).(2)A series of porous g-C3N4 nanosheets with controllable nitrogen vacancies have been successfully prepared by thermal polymerization of organic dyes(including 4-nitrophenol,rhodamine B,rhodamine 6G,malachite green,methyl orange,crystal violet and methylene blue)-reformed melamine precursors that were designed and fabricated intentionally.Because of their high specific surface areas,abundant active sites,shortened diffusion paths of photo-induced charge carriers,high charge separation and transport efficiency and high oxidation potential,the as-prepared porous g-C3N4 nanosheets with controllable nitrogen vacancies presented the higher visible-light-driven photocatalytic degradation activities towards different organic dye solution(such as rhodamine B,rhodamine 6G,methyl orange,methylene blue,crystal violet and malachite green).