Nanocarbon-Based Catalytic Ozonation for Aqueous Oxidation: Engineering Defects for Active Sites and Tunable Reaction Pathways

Catalytic ozonation relies on the direct oxidation by ozone (O3) and indirect oxidation by reactive oxygen species (ROS) produced from activated ozone molecules, and the technique has been recognized as one of the most promising remediation technologies in water decontamination. Functional nanocarbon materials have been extensively exploited as heterogeneous catalysts to drive catalytic ozonation because of the environmental-benign process, easy applicability, and high efficiency. Nevertheless, the bottlenecks in the processes are the economical production of high-performance and robust carbocatalysts and the debatable oxidation regimes. Different active sites have been suggested in engineered nanocarbons, and the corresponding mechanisms of the carbocatalytic ozonation are ambiguous including the evolution of various ROS, occurrence of radical and nonradical reaction pathways, selectivity toward organics, and tunable oxidation capacity. In this Review, we will showcase the roadmap of the development of reaction-oriented carbocatalysts and clarify the arguments in the mechanisms of the intrinsic active sites, identification of ROS, reaction intermediates, and oxidation pathways in carbocatalytic ozonation. We will provide critical comments and innovative strategies on the mechanistic investigations in carbon-based ozonation from the molecular level (electronic structures) to macroscale (kinetics), by deliberate radical screening/capture techniques, advanced characterizations and in situ analysis, and theoretical computations. More importantly, the critical issues and future directions will be proposed in the rational material/system design, mechanistic exploration, and the implementation of this powerful technology in catalytic oxidation and real wastewater treatment.