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 (E₀^*) and the temperature-dependent average site energy, respectively. The E₀^* on the surface of goethite was about 17–19 kJ mol⁻¹, where E₀^* 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.

中文翻译：

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环丙沙星与铁矿物表面的不同结合特性：热力学证据和位点能量分布分析

土壤中的铁矿物质在控制氟喹诺酮类药物的迁移中起重要作用。在本研究中，进行了批量实验以研究在 pH 6.0 时环丙沙星 (CIP) 吸附针铁矿、赤铁矿和磁铁矿的相互作用。采用热力学和位点能量分布理论（SEDT）来阐明络合类型。使用吸附结果，定性地阐明了依赖于 pH 的相互作用。热力学数据揭示了吸附机制的差异。随着山梨酸盐负载量的增加，CIP对赤铁矿和磁铁矿的吸附是吸热的，焓变和熵变均减小；然而，针铁矿的 CIP 吸附表现出相反的特征。E ₀ ^* ) 和温度相关的平均站点能量，分别。针铁矿表面的E ₀ ^*约为17-19 kJ mol ^-1，其中赤铁矿和磁铁矿的E ₀ ^*值为20-26 kJ mol ^-1. 当温度从289.15 K升高到308.15 K时，三种铁矿的高能位密度和低能位密度分别改变了-32％至167％和-36％至223％。不同的热力学和 SEDT 结果表明 CIP 对针铁矿和赤铁矿/磁铁矿的吸附机制分别主要是外球和内球络合。这项研究的结果揭示了吸附机制，有助于评估抗生素在含有典型铁矿物质的土壤中的运输。