Regulating Bimetallic Asymmetry of Mn2+–O–Fe3+ Domain in Layered Double Hydroxides for Lattice Oxygen Activation toward Enhanced Photocatalytic Toluene Oxidation

In photocatalytic toluene oxidation, traditional semiconductor catalysts still face the problem of insufficient generation of reactive oxygen species (ROS). Herein, we first regulate the bimetallic asymmetry in layered double hydroxide (LDH) photocatalysts via different metal electronegativities to activate lattice oxygen for ROS generation. The MnFe-LDH, MnAl-LDH, and ZnFe-LDH photocatalysts with various electronegativities (Mn: 1.55, Al: 1.61, Zn: 1.65, Fe: 1.83) were designed, and MnFe-LDH with the maximum electronegativity difference achieved the best toluene oxidation. Characterizations and calculations revealed that due to the enhanced bimetallic asymmetry of Mn2+–O–Fe3+ domain, the significant contraction and expansion of Mn–O and Fe–O bonds occurred, respectively, leading to enhanced lattice oxygen activation and oxygen vacancy generation, and an intensive built-in electric field caused by charge transfer from Mn to Fe in MnFe-LDH, both of which, under light irradiation, promoted O2 adsorption on in situ-formed oxygen vacancy along with photoelectrons, leading to ROS formation. Specifically, the hydroxyl groups linking bimetallic sites in MnFe-LDH were beneficial for methyl oxidation and the subsequent ring-opening of toluene. This study provides fresh insights into the design of LDH-based photocatalysts for toluene oxidation.