Insights into the facet-dependent adsorption of antibiotic ciprofloxacin on goethite

Goethite is the most ubiquitous iron oxide mineral in soils, and adsorption of organic pollutants on goethite dominates the fate and transportation in the environment. In this study, the facet-dependent adsorption behavior of ciprofloxacin (CIP) on goethite was systematically investigated with in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra and two-dimensional correlation analysis (2D-COS). The experimental results indicated that the goethite samples with higher facet proportion of {021}/{110} exhibited the better adsorption capacity compared to goethite with lower facet proportion of {021}/{110}. The reason is the more existence of singly coordinated sites with higher reactivity on the {021} facet. Moreover, CIP was found to be adsorbed on {021} and {110} facets by forming a tridentate complex involving the bridge coordination of bidentate ligands, H-bonding, and a bidentate chelate complex.

Automated summary

Goethite is the most common iron oxide mineral in soils, and the adsorption of organic pollutants on goethite has a significant impact on their fate and transport in the environment. This study found that goethite samples with a higher proportion of {021}/{110} facets exhibited better adsorption capacity due to the presence of more reactive singly coordinated sites on the {021} facet. Additionally, the adsorption of CIP on {021} and {110} facets was shown to involve the formation of a tridentate complex through bridge coordination, H-bonding, and bidentate chelate complex formation.