A critical review on reliability of quenching experiment in advanced oxidation processes

Advanced oxidation processes (AOPs) are promising, efficient and eco-friendly technologies for treatment of various organic wastewater. However, it has found that the identification of reactive species (RS) (e.g., •OH, SO4-•, 1O2, O2–•, h+, Cl•) during investigating catalytic and degradation mechanism is confused, maybe misunderstand the truth of RS contribution for degradation. Therefore, do we really understand the RS production, transformation process and the corresponding influencing factors? This is the key to correctly perform quenching experiment of RS and reveal precise catalytic degradation mechanism. This review comprehensively presents on the state-of-the-art research progress of the formation of RS in various AOPs, quenching experiment, reaction kinetics of RS and typical influencing factors on RS formation. Further, the main problems in the whole process of RS formation, transformation, identification, and related methods are discussed in detail. Finally, based on overall understanding, challenges for deeply revealing catalytic degradation mechanism via correctly obtaining the quenching results of RS are proposed. This review may help researchers to deeply understand the quenching process of RS in AOPs and make clear the real catalytic degradation mechanism of different organic pollutants.