Different binding characteristics of ciprofloxacin to iron mineral surfaces: Thermodynamic evidence and site energy distribution analysis

Abstract

Iron minerals in soil play an important role in controlling the migration of fluoroquinolones. In this study, batch experiments were carried out to investigate interactions in ciprofloxacin (CIP) adsorption to goethite, hematite, and magnetite at pH 6.0. Thermodynamics and the site energy distribution theory (SEDT) were adopted to clarify the complexation types. Using the adsorption results, pH-dependent interactions were qualitatively elucidated. The thermodynamic data revealed the difference in adsorption mechanisms. With increasing sorbate loading, CIP adsorption to hematite and magnetite was endothermic, and both enthalpy change and entropy change decreased; however, CIP sorption to goethite showed opposite characteristics. The higher adsorption capacity and affinity of CIP to hematite and magnetite than those to goethite were caused by their higher site energy of the highest occurring frequency (E 0 * ) and the temperature-dependent average site energy, respectively.The E 0 * on the surface of goethite was about 17-19 kJ mol −1 , where E 0 * values of hematite and magnetite were 20-26 kJ mol −1 . When temperature increased from 289.15 to 308.15 K, the high-and low-energy site densities for three iron minerals changed by −32 to 167% and by −36 to 223%, respectively. The different thermodynamic and SEDT results indicated that CIP adsorption mechanisms to goethite and hematite/magnetite were mainly outer-and inner-sphere complexation, respectively. The findings of this study reveal the adsorption mechanisms and are helpful in evaluating the transport of antibiotics in soils containing typical iron minerals.

Predicting the speciation of ionizable antibiotic ciprofloxacin by biochars with varying carbonization degrees

“…Moreover, the right side of E * 0 in the energy distribution was dened as the high-energy area and the le side was the lowenergy area. 50 Therefore, CIP sorption was concentrated on low-energy and middle-energy site areas according to Fig. 6d-f.…”

Predicting the effect of dissolved humic acid on sorption of benzotriazole to biochar

“…The peak of site energy distribution curves was indicated as F(E 0 *), meanwhile, the site energy (E 0 *) at the peak position showed the highest occurring frequency. The two parameters can provide valuable information in describing solute-sorbent interactions (Li et al 2021;Shen et al 2015). The energy distribution curve of BTA sorption with DHA addition showed lower E 0 * (3.41-10.4 versus 13.1-20.1 kJ mol −1 ) and higher F(E 0 *) (4.09-16.1 versus 2.35-2.88 mol mg kJ −1 g −1 ) than those without DHA addition (Fig.…”

“…The effect of DOM on sorption of BTA to biochar would come from that on both partition and adsorption, which may be quite different due to the diverse roles of DOM. Furthermore, site energy distribution analysis was often used to describe sorption on heterogeneous surfaces (Li et al 2021;Shen et al 2015). Estimation of site energy distribution of sorbent for target organic compounds as affected by DOM might be helpful for the analysis of sorption mechanism from the standpoint of energy.…”

Predicting the speciation of ionizable antibiotic ciprofloxacin by biochars with varying carbonization degrees

“…Furthermore, WC600 exhibited a higher F(E*) value compared with WC200 and WC400, suggesting there were more energy sites for CIP sorption to WC600. Moreover, the right side of E0 * in the energy distribution was defined as the highenergy area and the left side was the low-energy area (Li et al 2021). Therefore, CIP sorption was concentrated on low-energy and middle-energy site areas according to Fig.…”