Selective ·OH generation in Fenton-like reaction by dual sulfur coordination of iron organic frameworks

Abstract

Traditional Fenton-like reaction simultaneously generates hydroxyl radical (·OH) and superoxide radical (·O₂^-) through Fe(Ⅲ)/Fe(Ⅱ) cycle, while ·OH with higher oxidation capacity is commonly consumed by ·O₂^-. Therefore, selective generation of ·OH but not ·O₂^- in Fenton-like reaction is highly desirable, but still remains challenging since it is hard to bypass Fe cycle process. This work constructed dual S coordination of Fe organic frameworks, i.e. S-Fe-MOFs, using ligand with mercaptan groups (-SH), which achieving 93.89 % selectivity of ·OH generation in Fenton-like reaction, much higher than that of Fe-MOFs without S-Fe coordination (48.65 %). Benefiting from selectivity of ·OH generation, Fenton-like activity of S-Fe-MOFs up to 0.36 min^-1 using bisphenol A (BPA) as a probe, was 75 times than that of Fe-MOFs (0.0048 min^-1). Dual S coordination could give rise to a symmetrical “push-pull” effect on OO bond of H₂O₂ by changing adsorption configuration from “end-on” to “side on” type that two O atoms in H₂O₂ adsorbed together on Fe sites, and thus resulting in one H₂O₂ split directly two ·OH. Differ from traditional ·OH generation pathway, this process not only bypasses electron transfer between Fe(Ⅱ)/Fe(Ⅲ) cycle but also avoids the electron loss of catalyst, endowing S-Fe-MOFs excellent stability in Fenton-like reaction. S-Fe-MOFs on fix-bed reactor maintained high efficiency towards BPA degradation in 12 h continuous flow in real water environment. This work provides new insight into designing catalyst to overcome the limitation of traditional Fenton-like reaction.