Preparation And Visible-light Catalytic Performance Of Dual Z-scheme Bi₂O₃/g-C₃N₄/Ag₆Si₂O₇ Composites

To construct a photocatalyst with satisfactory visible light response,excellent redox capacity,high electron-hole separation efficiency and stability,a new ternary composite photocatalyst Bi₂O₃/g-C₃N₄/Ag₆Si₂O₇ was prepared via in situ precipitation of Ag₆Si₂O₇ on Bi₂O₃/g-C₃N₄ surface by a facile ultrasonic-assisted wet-chemical method in this paper,and the phase composition,microstructure,light absorption characteristics and surface chemical states of the prepared catalysts were characterized by XRD,XPS,EDS,FESEM,TEM,HRTEM,UV-Vis DRS,FTIR.The results show that in the Bi₂O₃/g-C₃N₄/Ag₆Si₂O₇ ternary composite photocatalyst,g-C₃N₄ exhibited a layered plate structure,Bi₂O₃ particles were randomly anchored on the surface of g-C₃N₄,and Ag₆Si₂O₇ was randomly distributed randomly on the surface of Bi₂O₃/g-C₃N₄,Bi₂O₃ and Ag₆Si₂O₇ were tightly bound to g-C₃N₄,and there was an interaction between Bi₂O₃,Ag₆Si₂O₇ and g-C₃N₄.UV-Vis DRS test results show that the absorption edge of the ternary composite sample had a significant red shift compared with g-C₃N₄ and Bi₂O₃,and the absorption of visible light was significantly enhanced.Methylene blue?MB?was chosen as the target pollutant,and the effects of mass ratios of?Bi₂O₃+g-C₃N₄?/Ag₆Si₂O₇ on the visible light photocatalytic performance of the ternary composite catalyst was investigated.The results show that the ternary composite photocatalyst with a mass ratio of 1:25.5 had the highest visible light catalytic activity,the removal rate of MB could reach 99.2%after 20 min of illumination,and the apparent rate constant of photocatalysis reached 0.2278min^-1,which attained 61.57,49.52,1.87,27.78,1.44,1.84 and 2.2 times that by sole Bi₂O₃,g-C₃N₄,Ag₆Si₂O₇,binary composite catalyst Bi₂O₃/g-C₃N₄,g-C₃N₄/Ag₆Si₂O₇,Bi₂O₃/Ag₆Si₂O₇ and the mechanical mixture of Bi₂O₃/g-C₃N₄ and Ag₆Si₂O₇,respectively,indicating that the ternary composite photocatalyst had excellent visible light catalytic performance.The catalyst also showed excellent photocatalytic activity for rhodamine B?RhB?and tetracycline?TC?,and was significantly higher than the sole Ag₆Si₂O₇ and Bi₂O₃/g-C₃N₄,indicating that dye sensitization was not the main reason for promoting dye degradation.The removal rate of MB still reached 94.2%and remained stable after three recycling runs.The formation of metallic silver in the process of photocatalysis was beneficial to the effective separation of photogenerated electron-hole pairs.The mechanism of visible light catalytic activity of Bi₂O₃/g-C₃N₄/Ag₆Si₂O₇ternary composite photocatalyst was studied by PL,EIS,active species capture experiment and ESR test.The results show that the recombination rate of electron-hole pairs in the ternary composite catalyst was slowed down,and the active species worked together in the order of h⁺>·OH>·O₂^-.The excellent photocatalytic activity of the ternary composite photocatalyst and the separation process of photogenerated electrons and holes could be well explained by dual Z-scheme photocatalytic mechanism.