Enhanced the removal of norfloxacin by oxalated zero-valent iron with rich surface Fe(II) sites activating the chlorite.

Oxalic acid-modified ball-milled zero-valent iron (OA-ZVI) was employed to activate sodium chlorite (ClO) for the removal of norfloxacin (NOR). The complete removal of 20 mg/L NOR was achieved within 60 min by the OA-ZVI/ClO process. Compared with the ZVI/ClO process which was the ball-milled zero-valent iron (ZVI) activate sodium chlorite, the reaction activity of the OA-ZVI/ClO process was increased by 102.6 times. Through scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical testing, and density functional theory (DFT) calculations, which has been confirmed that the introduction of oxalic acid can significantly increase the surface Fe(II) content of OA-ZVI, and accelerate the electron transfer rate of iron nuclei, thereby improve the efficiency of ClO activation for the removal of NOR. The role of various active species in NOR removal, which were •O, O, Fe(IV), ClO, and •OH, was elucidated through free radical quenching experiments, electron paramagnetic resonance (EPR) spectroscopy, and quantitative detection of active species. These active species all participated in the reaction, while •O played a dominant role in the reaction because it could transform into other active species, such as (•OH, O). Inorganic anions and natural organic matter have no significant effect on the removal of NOR in the OA-ZVI/ClO process. The protonation of oxalic acid ensured its good pH applicability range (pH = 2-11), thus exhibiting excellent performance in NOR removal in real water bodies. This further demonstrates that OA-ZVI prepared by oxalic acid ball milling modification is an efficient ClO activator, offering promising prospects for antibiotic removal technology.