Exploring mechanisms of different active species formation in heterogeneous Fenton systems by regulating iron chemical environment

How chemical environment of iron influence active species formation in heterogeneous Fenton processes is poorly understood. Herein, a series of metal organic frameworks (MOFs) with various substituents (UiO-66-X) were prepared as templates for iron chemical environment regulation. The results show that bisphenol A (BPA) degraded in the system modified with electron-donating groups (X = NH2, OH, OCH3) was predominantly attributed to HO. While Fe(IV) was detected in systems modified with electron-withdrawing groups (X = Cl, F, NO2). The introduction of electron-donating groups on FeOx@UiO-66-X increases the length of Fe-O bond from 2.06 to 2.12 Å, and reduces the binding energy of H2O2 on FeOx, which were beneficial for HO generation. However, electron-withdrawing groups (X = Cl, F, NO2) reduces the Fe-O bond length to 1.99 Å, and generates transition product Fe(IV)O. Consequently, this research contributes to the first mechanistic insight into active species regulation during Fenton-like processes by manipulating substituents on MOFs ligand.