Overlooking the effect of alcohol quenchers can mislead mechanistic understanding in ferrate-based advanced oxidation processes

Alcohols serve as effective quenchers and are widely employed to assess the role of reactive species in advanced oxidation processes (AOPs). However, this study reveals that frequently used alcohol quenchers, including tert-butanol (TBA), methanol (MA), ethanol (EA), and furfuryl alcohol (FFA), can substantially affect the ferrate (Fe(VI)) system. Firstly, the presence of alcohols was found to influence the decomposition of Fe(VI). In the pH range of 7–11, various alcohols promoted Fe(VI) decomposition, especially at pH 7–8, namely, the pH conditions often used in Fe(VI)-based advanced oxidation studies. The magnitude of Fe(VI) decomposition influenced by the alcohols was ranked as FFA > EA > MA > TBA. Secondly, alcohols may alter the formation and conversion of high-valent iron active species. Using the phenylmethyl sulfoxide (PMSO) probe, we observed that MA and TBA inhibited the removal of PMSO by Fe(VI), while FFA and EA substantially enhanced it. These results indicate that alcohols may not only influence the decomposition of Fe(VI) itself, but also affect the degradation of pollutants mediated by high-valent iron active species. These phenomena may lead to misconceptions about the mechanisms and efficacy of Fe(VI)-based AOPs. Overall, this work underscores the importance of carefully selecting quenchers in complex oxidation systems involving Fe(VI) to avoid misleading interpretations of Fe(VI) decomposition and oxidation behavior.