Evaluating iron-based nanoparticles for ciprofloxacin removal: Date seed extract as a biostabilizing and a bioreducing agent

Abstract

Iron-based nanoparticles (FeNPs) are promising materials for the removal of pharmaceutical pollutants. In this study, the following FeNPs were evaluated for ciprofloxacin (CIP) removal: (a) nanoscale zerovalent iron (nZVI) prepared using chemical reduction method (b) nZVI coated with extracts from Phoenix dactylifera/date palm seeds (ds-coated-nZVI) (c) iron-sulfide nanoparticles prepared using date seed extract in a green synthesis approach (ds-FeS). The successful use of date seed extract as a biostabilizer and as a bioreductant was evaluated through multiple characterization techniques to determine nanoparticle morphologies, sizes, and surface chemistry. Batch experiments were used to assess CIP removal capacities and rates by nZVI, ds-coated-nZVI and ds-FeS. Among the three isotherm models investigated (i.e., Langmuir, Freundlich and Hill), the Hill model provided the best fit with maximum removal capacities (qm) of 196 mg g−1 for nZVI, 92 mg g−1 for ds-coated-nZVI and 100 mg g−1 for ds-FeS. The CIP removal kinetics was better represented by the pseudo-second-order model compared to pseudo-first-order and showed concentration dependent enhancements and decreases depending on the FeNP. While nZVI outperformed ds-coated-nZVI and ds-FeS particles in terms of removal rates and extents at higher CIP concentrations (>10 mg/L), the removal performance was similar for the three FeNPs at lower CIP concentrations. Liquid chromatography mass spectrometry and total organic carbon measurements indicated the involvement of both sorption and degradative transformation of CIP. Overall, results from this study suggest the strong capability of FeNPs for CIP removal and also indicate the potential of employing comparatively eco-friendly FeNP alternatives at lower environmentally relevant CIP concentrations.