Air-water interface of microdroplet enhances photocatalytic oxidative species generation and utilization

Reactive oxygen species (ROS) generated from semiconductor photocatalysis play crucial role in environmental remediation and clean energy production. However, the efficiency is hindered by charge carrier recombination and slow reaction kinetics. In this study, we found photocatalytic micropollutants treatment, with various concentrations and in actual wastewaters, was improved with the use of water microdroplet reactors, particularly in smaller microdroplets with removal rate constant about 5-fold higher than that in bulk solution. Besides the enhanced electron-hole pairs separation by ultrastrong interfacial electric fields, in-situ Raman spectroscopy measurement and theoretical calculation collectively suggested the partial solvation at microdroplet periphery improved ·OH production by decreasing oxidation barriers of OH^-. Furthermore, the interfacial concentration enrichment of organics revealed by micro-Raman spectroscopy increased ROS utilization and thus accelerated photocatalytic oxidation. This work highlights the paramount significances of interface chemistry of microdroplets in photocatalytic oxidation and shows huge implications in atmospheric chemistry and chemical synthesis.