Unveiling the role of mixing enhancement in oxygen vacancy concentration and particle size during high-throughput synthesis of ZnO photocatalyst in a microreactor

Abstract

Oxygen vacancy (O_v) concentration and particle size (d) are critical to the performance of metal oxide photocatalysts. Here, taking advantage of strong chaotic mixing performance in a four-stage oscillating feedback microreactor (FOFM), the ZnO with small d and high O_v concentration were controllably prepared. First, dye-tracer experiments and Villermaux-Dushman reactions were used to investigate the macroscopic and micromixing performance within FOFM. Then, ZnO was prepared using FOFM at different flow rates, and the role of mixing enhancement in d and O_v concentration of ZnO was unveiled. The results indicate that increasing flow rates would enhance chaos intensity of fluids, thereby obtaining products with smaller d and higher O_v concentration. Photocatalytic tests indicate that ZnO prepared with small d has excellent photocatalytic performance for methyl orange degradation. DFT calculations prove that O_v can reduce adsorption energy of ZnO-*O₂ and enhance bonding strength between Zn and *O, thereby promoting adsorption of O₂.