Investigating nalidixic acid adsorption onto ferrihydrite and maghemite surfaces: molecular-level insights via continuous-flow ATR-FTIR spectroscopy

Abstract

Contaminants sequestration by iron oxides are of particular relevance in environmental chemistry and Fourier transform infrared (FTIR) spectroscopy in attenuated total reflectance (ATR) mode is used in this study to investigate the molecular-scale adsorption mechanism of the antibiotic nalidixic acid (NAL) onto ferrihydrite and maghemite surfaces. High-surface area ferrihydrite and nano-sized maghemite were prepared as model adsorbents. This work provides a complete band assignment for protonated and deprotonated NAL to better describe in situ adsorption processes. In situ ATR-FTIR spectroscopy suggests that NAL mainly adsorbs on both iron oxides by a bidentate mode. Results also suggest that two sorption sites coexist on Maghemite surfaces leading to two sorption modes through the carboxylate group: bidentate chelate and bidentate bridging. The obtained results can contribute significantly towards molecular level understanding of antibiotics binding modes on iron oxides, a valuable piece of information to develop environmental remediation strategies.