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.
Keywords: Adsorption; Ciprofloxacin; Crystal facet; Goethite; Mechanisms; Two-dimensional correlation analysis (2D-COS).