Construction Of Novel S-scheme G-C₃N₄ Based Heterojunction And Study On Photocatalytic Performance

Energy shortage and environmental pollution,as the two most intractable problems at present,seriously threaten the sustainable development of human society.Semiconductor photocatalysis technology is widely concerned in environmental remediation,energy development,antibacterial and other fields due to its high efficiency,low energy consumption and no secondary pollution properties.Among them,the application of solar energy in photocatalytic hydrogen production and pollutant degradation is the best way to solve the current energy and environmental problems.In this study,g-C₃N₄,a kind of visible light response catalyst,was taken as the main research object to construct Bi₂S₃/g-C₃N₄ and Bi OBr/g-C₃N₄ heterojunctions for the photocatalytic activity improvement of pure g-C₃N₄.The main research contents and results are as follows（1）First,C₃N₄ was prepared by calcination of melamine via thermal polycondensation method,and then the g-C₃N₄ nanosheet was obtained by secondary calcination.Bi₂S₃/g-C₃N₄composites with different mass ratios were synthesized by solvothermal reaction with thioacetamide（TAA）and Bi（NO₃）₃·5H₂O.Many characterization analyses（XRD,SEM,TEM,XPS,UV-Vis,BET and PL）were used to analyze the morphology,structure and photoelectric properties of the sample.The results show that the rod-like Bi₂S₃ grows uniformly on the surface of g-C₃N₄ nanosheets,forming an intimated 1D/2D contact interface between them,with an increased specific surface area increases,enhanced visible light absorption ability.improved charge carrier density,reduced interfacial migration impedance,and decreased recombination rate of the electron-hole pair.H₂ evolution experiment exhibit that the Bi₂S₃/g-C₃N₄ sample has enhanced activity,and the highest H₂ production rate of 0.6%Bi₂S₃/g-C₃N₄ is3394.1μmol·g^-1·h^-1,which is 2.6 times higher than that of pure g-C₃N₄(1298.4μmol·g^-1·h^-1).The carrier transfer of Bi₂S₃/g-C₃N₄ is in line with the S-scheme mechanism.Under the synergistic action of Coulomb force,built-in electric field and band bending,the relatively useless electrons in Bi₂S₃ conduction band and the relatively useless holes in g-C₃N₄ valence band recombine rapidly,leaving the electrons with strong reducing ability in g-C₃N₄ conduction band and the holes with strong oxidation ability in Bi₂S₃ valence band to participate in the photocatalytic reaction.（2）2D/2D BiOBr/g-C₃N₄ heterojunctions with different mass ratios were synthesized by g-C₃N₄,KBr and Bi（NO₃）₃·5H₂O via in situ growth method.Many characterization analyses（XRD,SEM,TEM,XPS,UV-Vis,BET and PL）were used to analyze the morphology,structure and photoelectric properties of the sample.The results show that Bi OBr uniformly distributes on the surface of g-C₃N₄ nanosheets with an intimated 2D/2D contact interface,leading to a bigger specific surface area,higher charge carrier density,stronger migration ability and smaller interfacial migration impedance.Rh B(10 mg·L^-1,100 m L)can be completely degraded by 1.5-Bi OBr/g-C₃N₄ in 30 min,and the degradation rate constant(0.01274 min^-1)is 48.2 times higher than that of g-C₃N₄(0.00026 min^-1).In addition,the composites also show enhanced photocatalytic H₂ evolution activity.Due to the Fermi energy level difference between the reductive semiconductor g-C₃N₄ and the oxidative semiconductor Bi OBr,electrons are transferred from g-C₃N₄ with high Fermi energy level to Bi OBr with low level,and a strong built-in electric field is generated at the interface.Under the synergistic action of the internal electric field,band-edge bending and Coulomb force,the Bi OBr/g-C₃N₄ heterojunction with S-scheme charge transfer was formed,which can realize the efficient separation of photogenerated charge carriers in space,and obtaine strong reducing power electrons and strong oxidizing power holes,leading to an improved catalytic activity of the system.