Confinement boosted heterogeneous advanced oxidation processes

Confined catalysts with large surface areas and adjustable pore and channel sizes have been recently used in advanced oxidation processes (AOPs) for water and wastewater treatment. Typically, a confinement scale depends on the geometric structure of a catalyst. In confinement environment for AOPs, hydrogen bond number, ionic hydration and diffusion of water molecules, adsorption energy and chemical bond length of oxidants as well as local concentrations and migration distances of active species can be strikingly affected, in turn influencing catalytic degradation efficiency. Confined catalysis will generally enhance the interaction between oxidants and pollutants, increasing reaction kinetics and improving contaminant removal compared with traditional non-confined catalysis. In this review, we firstly summarized the contaminant degradation behaviors in different confined catalytic systems. Then we elaborated on the entire AOPs from oxidant activation, active species generation and function with confined catalysis, focusing on the changes in water molecular structure and behavior and elucidating the mechanism of oxidant activation and contaminant degradation at the molecular level with confined catalysis. At last, we presented suggestions and perspectives for confined catalysis for AOPs. This review was believed to shed new light on the design of confined catalysts, contributing to contaminants removal efficiently and selectively in advanced oxidation systems.