Unrecognized role of humic acid as a reductant in accelerating fluoroquinolones oxidation by aqueous permanganate

A great concern has been raised regarding the issue of fluoroquinolones (FQs) in the environment. In this work, the transformation of FQs by commonly used oxidant permanganate (Mn(VII)) in the absence and presence of humic acid (HA), ubiquitously existing in aquatic environments, was systematically investigated. Here, the catalytic role of in situ formed MnO2 on Mn(VII) oxidation of FQs depending on solution pH and co-existing substrates was firstly reported. It was interestingly found that HA could appreciably accelerate FQs degradation by Mn(VII) at environmentally relevant pH. HA as a reductant in accelerating FQs by Mn(VII) oxidation was distinctly elucidated for the first time, where MnO2 in situ formed from the reduction of Mn(VII) by HA served as a catalyst. Similar products were observed in the presence versus absence of HA. Considering that the accelerating role of HA was related to its reducing ability, an activation method based on Mn(VII) and reductant (i.e., Fe(II), Mn(II) and (bi)sulfite) was proposed, which exhibited considerable potential for application in the treatment of FQs contaminated water. (C) 2021 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.

Automated summary

This study systematically investigated the transformation of fluoroquinolones (FQs) by the oxidant permanganate (Mn(VII)) in the presence or absence of humic acid (HA) in aquatic environments. It was found that HA could accelerate the degradation of FQs by Mn(VII) oxidation, with the in situ formed MnO2 acting as a catalyst. The study also proposed an activation method based on Mn(VII) and reductants for the treatment of FQs contaminated water.