Insights into the effect of inner polarization and multiple Ag-O units on high-efficient Ag-based photocatalyst

- Compared with Ag2O and Ag3PO4, the advantageous transfer of carriers in Ag6Si2O7 is found responsible for its high photocatalytic activity.
- The multiple Ag-O units in Ag6Si2O7 result in the separated distribution of holes and electrons.
- Built-in electric field promotes the transfer of electrons and holes in different regions then reduces the recombination of carriers.
- The most stable (100) surface of Ag6Si2O7 with holes trapped at surface layers is also beneficial to the photo-oxidation reaction.

Ag-based materials are one kind of important photocatalysts. In the present work, the electronic structure and related properties of Ag6Si2O7, Ag2O and Ag3PO4 are systematically investigated by first principle calculations. The origin of the high photocatalytic activity of Ag6Si2O7 is analyzed. Our results indicate that compared with Ag2O and Ag3PO4, the multiple Ag-O units in Ag6Si2O7 result in the separate distribution of holes and electrons, which are driven by the built-in electric field to transfer in different regions, contributing to the high photocatalytic activity by reducing the recombination of carriers. The intrinsic transfer of carriers tends to along [010] direction, leading to the best photocatalytic activity of the polar (010) surface though the high cleavage energy limits its exposure to some extent. In addition, the most possible exposed (100) surface corresponding to the lowest surface energy, with holes trapped at surface layers and electrons flowing into bulk region, is also advantageous to the photo-oxidation reaction. Therefore compared with other Ag-based photocatalytic materials, Ag6Si2O7 shows the main advantages in the transfer and separation of carriers, and its high photocatalytic activity can be understood well. We expect this work can be helpful to guide the exploration of new photocatalysts with higher photocatalytic activity.

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