Enhancing Fenton-like process at neutral pH by Fe(III)-GLDA complexation for the oxidation removal of organic pollutants.

N,N-bis(carboxymethyl)glutamic acid (GLDA) was utilized in this study to significantly enhance the Fe(III) mediated Fenton-like oxidation removal of organic pollutants at neutral pH, in which ciprofloxacin (CIP) was used as the model pollutant. The CIP degradation rate in the GLDA/Fe(III)/HO system reached 96.5% within 180 min and was nearly 14 times higher than that in the Fe(III)/HO system. This enhancement was contributed to the acceleration of the cycle of Fe(III)/Fe(II) caused by GLDA, which was verified by UV-vis spectroscopy, cyclic voltammetry, and radical quenching experiments. The results proved that the GLDA could complex with Fe(III) and greatly modify the redox potential of Fe(III)/Fe(II). Moreover, radical quenching experiments confirmed that •OH and O were the mainly species for CIP degradation, and O was responsible for 81.9% •OH generation. In addition, HO utilization kinetic modeling was also investigated. The optimum parameters of the 100 μM Fe(III)-GLDA complex and 15 mM HO were attained by lot-size optimization experiments. Two possible CIP degradation pathways were proposed on the basis of the intermediates identified by MS/MS. The GLDA/Fe(III)/HO system performed better than common chelating agents at the same condition, manifesting good potential for environmental concerns.