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)/H2O2 system reached 96.5% within 180 min and was nearly 14 times higher than that in the Fe(III)/H2O2 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 O2·− were the mainly species for CIP degradation, and O2·− was responsible for 81.9% •OH generation. In addition, H2O2 utilization kinetic modeling was also investigated. The optimum parameters of the 100 μM Fe(III)–GLDA complex and 15 mM H2O2 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)/H2O2 system performed better than common chelating agents at the same condition, manifesting good potential for environmental concerns.