Contribution of complexed Fe(Ⅱ) oxygenation to norfloxacin humification and stabilization: Producing and trapping of more humified products

Organic pollutants polymerization in advanced oxidation processes or environmental matrices has attracted increasing attention, but little is known about stabilization of the polymerization products. The results in this work revealed the contribution of Fe(Ⅱ) oxygenation to stabilization of the products from norfloxacin (NOR) humification. It was found that upon oxygenation of Fe(Ⅱ) complexed by catechol (CT), NOR polymerized into the products with larger molecular weight through nucleophilic addition. Around 83.9-89.7 % organic carbon (OC) can be retained in the reaction solution and the precipitates at different Fe(II)/CT molar ratio. In this system with humification potential, the produced hydroxyl radical (HO•) dominantly modified, instead of decomposed, the structure of transformation products (TPs). TPs with diversified side chains were formed through hydroxylation and ring-opening, leading to the more humified products. In the subsequent Fe(Ⅱ) oxidative precipitation, Fe-TPs composites were formed as spherical particle clusters, which could steadily incorporate OC species with molecular fractionation. Specifically, lignin-like, tannins-like, condensed aromatic and high-molecular-weight TPs were preferentially preserved in the precipitates, while the recalcitrant aliphatic products mainly retained in the solution. These findings shed light on the role of Fe(Ⅱ) oxygenation in stabilizing the products from pollutants humification, which could strengthen both decontamination and organics sequestration.