Preparation And Visible-light Catalytic Performance Of Direct Z-scheme Mpg-C₃N₄/Ag₆Si₂O₇ Composites

The treatment of water pollution is an important task which arouses the attention of the world.Compared to the traditional treatment of pollutants,photocatalytic technology has lots of distinctive advantages.However,the existing photocatalyst is still weak because of low stability,low utilization rate to visible light.and easy recombination of photogenerated electron-hole.Seeking stable and efficient photocatalyst has become a major concern.Ag₆Si₂O₇ is an efficient photocatalyst,but it is instable.On the contrary,mesoporous graphitic carbon nitride?mpg-C3N4?is stable,but it is inefficient.Based on the energy level matching features of Ag₆Si₂O₇ and mpg-C₃N₄,this research uses the ultrasonic assisted precipitation to prepare different mass percentage of mpg-C₃N₄ and Ag₆Si₂O₇ composite materials.The preparation is successful which is proved by using XRD,FT-IR,FE-SEM,UV-Vis DRS,XPS and BET to analyze phase,light absorption property,morphology and surface chemical elements of the composite photocatalyst.This composite photocatalyst contains C-N,C=N and triazine ring.In the composite samples,the Ag element exists in the form of Ag⁺and the Si element exists in the form of Si⁴⁺.Mpg-C₃N₄ is mesoporous structure,and Ag₆Si₂O₇ is irregular granular.The absorptive edge of mpg-C₃N₄ and Ag₆Si₂O₇ composite materials in different mass percentage presents red shift.And the absorption of visible light improves.By degrading methylene blue,it is found that 4%mpg-C₃N₄/Ag₆Si₂O₇ composite photocatalyst has best photocatalytic properties in different mass percentage of composite materials.It degrades 98.4%of methylene blue after visible light irradiation for 60min.Its performance is higher than the degradation efficiency of sole Ag₆Si₂O₇?90.9%?and is far higher than that of sole mpg-C₃N₄?11.1%?in the same condition.The apparent rate constant is 2.21 times as that of sole Ag₆Si₂O₇ and 64times as that of sole mpg-C₃N₄.4%mpg-C₃N₄/Ag₆Si₂O₇ composite photocatalystrespectively degrades 78.6%and 72.4%of methylene blue in the second time and third time cyclic repeated experiment.It proves that it has good stability.Moreover,it degrades 81.3%of methyl orange and 87.7%of rodenning B.The degradation experiment of colorless 2,4-dichlorophenol shows that dye sensitization is not the main factor in photocatalytic degradation.The result of degrading methylene blue by different photocatalysts which have same mass percentage of visible light active component indicates that 4%mpg-C₃N₄/Ag₆Si₂O₇ is significantly better than the simple mixture of mpg-C₃N₄ and Ag₆Si₂O₇.The result of PL shows that 4%mpg-C₃N₄/Ag₆Si₂O₇ composite photocatalyst delays the recombination between photogenerated electrons and holes.The active species capture experiments shows that·OH and h⁺are the main active species in photocatalytic reactions,and·O₂^-also participates in the reaction.It is found that silver is not involved in photocatalytic reaction by XPS.Combined with the above results,heterojunction mechanism couldn't explain that the photocatalytic performance of 4%mpg-C₃N₄/Ag₆Si₂O₇ composite photocatalyst improves.According to the further analysis,the mechanism of improvement is explained by Z-scheme mechanism.In summary,mpg-C₃N₄/Ag₆Si₂O₇ composite photocatalyst is a highly effective and stable visible-light photocatalyst,which has great potential for the visible-light photocatalytic degradation of organic pollutants.