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

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.