Study On Preparation And Mechanism Of Z-type Transfer Photocatalyst

The transfer mechanism of photogenerated carriers has been one of the photocataly sisresearch hotspots.In our recent studies,we found that the built-in internal electric field of a relative p-n junction formed by the different photocatalysts is the inner impetus of the photogenerated carriers migration in the heterojunctions.To verify the above conclusion,a series of g-C₃N₄/TiO₂ composites with different weight ratios were prepared andthe transfer mechanisms and natural law for the g-C₃N₄/TiO₂heterojunction photocatalysts were amply characterized by physical and chemical methods.The result showed that no matter whether the primary part of g-C₃N₄/TiO₂composites is TiO₂ or g-C₃N₄,the transfer of the photogenerated charge carriers adopts a Z-scheme system in the g-C₃N₄/TiO₂ heterojunctions.The accumulated photogenerated electrons in the CB of g-C₃N₄ with more negative potential can reduce O₂ to superoxide radical（·O₂^-）,and the photogenerated holes in the VB of TiO₂ with more positive potential may oxidize H₂O（or OH^-）into hydroxyl radical（·OH）.Thus,the photocatalytic activities of g-C₃N₄/TiO₂ aremuch higher than that of pure TiO₂ or g-C₃N₄.The Z-scheme mechanism is confirmed by the relative p-n heterojunction theory between g-C₃N₄ and TiO₂.Under the effect of the built-in electric field,the transfer directions of the photogenerated charge carriers in the heterojunctions are opposite to the migration directions of the photogenerated charge carriers in the conduction band（CB）and valence band（VB）of g-C₃N₄ and TiO₂.We also chose CdS and TiO₂ as the research objects.First,a series of CdS/TiO₂ composite materials with different weight ratios were prepared by solid-phase grinding.Through their activity changes,the photo-generated carrier transfer mechanism and the transfer mechanism of the composite photocatalyst were studied.Inner power.When the main body of the CdS/TiO₂ composite material is TiO₂,the photocatalytic performance decreases rapidly with the increase of a small amount of CdS.The reason may be that although it is a band transfer,the combination trend of electrons and holes in the composite catalyst is still greater than TiO₂ itself Trend of electron-hole combination.Then the photocatalytic activity of the sample increases with increasing CdS amount until70%CdS/TiO₂.The reason for the increase in catalyst activity may be that the transfer direction of electrons and holes in the relative pn junction is the same as the transfer direction of electrons and holes in the catalyst itself,which accelerates the separation of photogenerated electrons and holes,so the catalyst activity is improved.When the main body of the TiO₂ composite material is CdS,the migration direction of electrons and holes in the relative pn junction is opposite to the transfer direction of photogenerated electrons and holes in TiO₂ and CdS,so the photogenerated carrier The transfer mechanism uses a Z-type mechanism.The electrons accumulated in CB in CdS show high reducibility,thereby reducing O₂ to·O_2-,and the holes of VB in TiO₂ show high oxidizability to oxidize H₂O to·OH.The relative p-n junction mechanism is not only used to clarify the transfer mechanism of photogenerated carriers and the internal natural behavior of heterojunction photocatalysts,but also has a guiding significance for the design and construction of composite photocatalysts,and has theoretical and practical significance.