| Graphitic carbon nitride（g-C3N4）as a photocatalyst has been widely paid attention due to many excellent potential properties,such as renewable and pollution-free,high thermodynamic and chemical stability,visible light response,etc.However,the easily recombined photogenerated electron holes,lack of visible light absorption and low surface area is still limit its development.So far,there are many methods to promote the properties of the g-C3N4,including defects proven to adjust the electronic structure and enhance light absorption,effectively improve the g-C3N4 photocatalytic hydrogen production performance.In this paper,different defects introduction methods were used to prepare C defect inducedπelectron delocalization in g-C3N4,sulfur-doped g-C3N4 nanosheets with defects and facile steam activation route to synthesize S-doped g-C3N4 nanosheets,which improved the photocatalytic H2 generation to varying degrees.1.Carbon defects inducedπelectron delocalization in g-C3N4 for increased photocatalytic H2 generation.By autogenic ammonia gas route via in-situ urea decomposition to create C defects in g-C3N4 to generates high specific surface area of nanosheets,for realizing increased photocatalytic H2 generation under visible light irradiation.Illustrated by the density functional theory calculations,the C defects thus incorporated can not only reduce the band gap for increased light harvesting,but also delocalize theπelectrons in valence band and conduction band for efficient charge transfer.Such delocalization ofπelectrons facilitates the efficient separation of electrons in LUMO and holes in HOMO,then promoting the photocatalytic H2generation.The optimized g-C3N4(36.62μmol h-1)photocatalytic H2 production rate increased by 10 times,comparing with the condition without authigenic ammonia(3.63μmol h-1).2.S-doped g-C3N4 nanosheets with defects for increased photocatalytic H2 generation.In order to improve the photocatalytic H2 production,in-situ S-doped block g-C3N4 was treated in the atmosphere of autogenous ammonia gas to generate defects modified g-C3N4 nanosheets.Due to the easy disbonding of S groups,thiourea as precursor may help to form surface and structural defects and thus adjust the optical and electronic structure of g-C3N4.The bulk g-C3N4 exfoliated into nanosheets,which increased the specific surface area of the catalyst.The introduction of carbon defects not only broadened the range of visible light absorption,but also effectively inhibited the recombination of photogenerated electron-hole pairs.The results showed that the photocatalytic activity of g-C3N4 was significantly improved,and the hydrogen production rate of g-CN-SU0.8 reached 13.69μmol h-1,which was 7.5 times higher than that of g-CN-S without urea(1.81μmol h-1).3.Steam activation of S-doped g-C3N4 nanosheets with defects is used for photocatalytic hydrogen production.By treating the S-containing precursors at high temperature in the atmosphere of water vapor,the S-doped g-C3N4 nanosheets with rich defects were obtained,which improved the photocatalytic H2 production rate under visible light irradiation.The H2O molecules in the steam are highly active and can intercalate the interlayers to delaminate bulk g-C3N4 into ultrathin nanosheets,and the specific surface area of the catalyst can be increased.Since-SH is easy to disbond,the doping of S element is conducive to the introduction of defects and then adjust the electronic structure of g-C3N4.The results showed that the introduction of defects enhanced the visible light absorption,accelerated the separation of photogenerated electrons and hole pairs,and significantly improved the photocatalytic activity.Compared with the contrast sample,the hydrogen production efficiency of g-CN-MT1:1 photocatalyst reached44.3μmol h-1,which increased by 5 times. |
