Theoretical study on the anisotropic photo-induced carrier mobilities in layered double hydroxide-based photocatalysts

Abstract

In order to suppress the unwanted photo-induced electron–hole recombination which restricts the quantum efficiency and reaction rate of photocatalysis reactions, the transportation routes of electrons and holes in photocatalysts should be different. In this work, layered double hydroxide (LDH)-based photocatalysts were investigated because of their flexible structural compositions. Deformation potential theory and Marcus theory were employed to calculate the carrier mobilities of electrons and holes in the orthogonal x, y and z directions of LDHs, respectively, revealing that the carrier mobilities of electrons and holes in the z direction (i.e., along the (110) facet) of LDHs are close to 0 cm² V⁻¹ s⁻¹, while those in the x and y directions (i.e., along the (003) facet) range from 0.01 to 1196.70 cm² V⁻¹ s⁻¹. Therefore, carriers can only move along the (003) facet in the x and y directions. Moreover, the polarities of LDHs in the x and y directions can be finely modified by changing the metal species in the LDH matrix so as to suppress the carrier recombination. Thus, two approaches for suppressing the carrier recombination in LDH-based photocatalysts are proposed: (1) decreasing the number of layers in the z direction of LDHs, and (2) adjusting the metal species in the LDH matrix to modify the polarities, which may be appropriate for other supramolecular photocatalysts with host–guest structures.