Research progress on detection methods of active species in the catalytic oxidation degradation of organic pollutants: A review

Catalytic oxidation processes have the significant advantage of fast and efficient removal of refractory organic matter, including radical and non-radical pathways, and the active species play a critical role in this process. Detecting these active species quickly and accurately is of utmost importance. Such detection not only aids in optimizing the catalytic oxidation process but also helps clarify the degradation mechanism of pollutants. However, detecting these active species has been a major difficulty. Existing detection technologies are primarily used for conventional free radicals, singlet oxygen, high-valent metals, and other active species. Most of these methods involve indirect detection, but they come with inevitable defects. Given the high activity and short lifespan of active species, detecting them directly, along with other unknown active species, poses significant challenges. This review systematically introduces the technical principles and application status of several main detection methods, analyzing the drawbacks and proposing solutions for each detection method. New methods such as EPR/ESR and XANES for the direct detection of active species and emerging organic free radicals are also mentioned. Finally, we propose the combination of different methods according to the specific requirements as the optimal approach for detecting active species in a catalytic oxidation system, enabling cross-confirmation of detection results.