Surface Complex and Nonradical Pathways Contributing to High-Efficiency Degradation of Perfluorooctanoic Acid on Oxygen-Deficient In2O3 Derived from an In-Based Metal Organic Framework

The mediating role of surface structure of In2O3 on the adsorption and photocatalytic degradation of perfluorooctanoic acid (PFOA) is important but still unclear. Herein, In2O3 with various oxygen vacancy concentrations are designed by pyrolyzing a metal organic framework (MIL-68(In)-NH2) for PFOA degradation. The results demonstrate that the In2O3-400 obtained at a lower pyrolysis temperature of 400 °C possesses the highest oxygen vacancy concentration, thus exhibiting remarkably boosted adsorption capacity and degradation performance for PFOA. Adsorption kinetics, isotherm adsorption model, and Fourier transform infrared spectroscopy (FTIR) results show that PFOA is chemically adsorbed on the In2O3-400 surface in the form of monodentate mode. Notably, there is a linear correlation between the adsorption capacity and the degradation kinetic rate constant of In2O3-400 for PFOA, indicating that surface adsorption is a prerequisite for the PFOA degradation. Furthermore, density functional theory (DFT) results indicate that oxygen vacancies, as the structural characteristic for PFOA chemisorption, can promote the nonradical oxidation process of PFOA. This study provides a new perspective to explain the role of the surface structure of In2O3 in relation to its adsorption and photocatalytic performance for PFOA, which is helpful for the development of more effective PFOA adsorption coupled degradation technology.