Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, 35000 Rennes, France.
Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, 35000 Rennes, France.
Environ Pollut. 2020 Feb;257:113626. doi: 10.1016/j.envpol.2019.113626. Epub 2019 Nov 15.
The oxidation of magnetite into maghemite and its coating by natural organic constituents are common changes that affect the reactivity of iron oxide nanoparticles (IONP) in aqueous environments. Certain ubiquitous compounds such as humic acids (HA) and phosphatidylcholine (PC), displaying a high affinity for both copper (Cu) and IONP, could play a critical role in the interactions involved between both compounds. The adsorption of Cu onto four different IONP was studied: magnetite nanoparticles (magnNP), maghemite NP (maghNP), HA- and PC-coated magnetite NP (HA-magnNP and PC-magnNP, respectively). According to the results, the percentage of adsorbed Cu increases with increasing pH, irrespective of the IONP. Thus, protonation/deprotonation reactions are likely involved within Cu adsorption mechanism. Contrary to the other studied IONP, HA-magnNP favor Cu adsorption at most of the pH tested including acidic pH (pH = 3), suggesting that part of the active surface sites for Cu were not grabbed by protons. The Freundlich adsorption isotherm of HA-magnNP provides the highest sorption constant K (bonding energy) and n value which supports a heterogeneous sorption process. The heterogeneous adsorption between HA-magnNP and Cu can be explained by both the diversity of the binding sites HA procured and the formation of multidendate complexes between Cu and some of the HA functional groups. Such favorable adsorption process was neither observed on PC-coated-magnNP nor on maghNP, whose behaviors were comparable to that of magnNP. On another hand, HA and PC coatings considerably reduced iron (Fe) dissolution from magnNP as compared with magnNP. It was suggested that HA and PC coatings either provided efficient shield against Fe leaching or fostered dissolved Fe re-adsorption onto the functional groups at the coated magnNP surfaces. Thus, this study can help to better understand the complex interfacial reactions between cations-organic matter-colloidal surfaces which are relevant in environmental and agricultural contexts. This work showed that magnetite NP properties can be affected by surface modifications, which drive NP chemical stability and Cu adsorption, thereby affecting the global water chemistry.
磁铁矿氧化成磁赤铁矿及其被天然有机成分包覆是常见的变化，会影响水相环境中氧化铁纳米颗粒（IONP）的反应活性。某些普遍存在的化合物，如腐殖酸（HA）和磷脂酰胆碱（PC），对铜（Cu）和 IONP 都具有很高的亲和力，可能在这两种化合物之间的相互作用中发挥关键作用。研究了 Cu 在四种不同的 IONP 上的吸附：磁铁矿纳米颗粒（magnNP）、磁赤铁矿 NP（maghNP）、HA 和 PC 包覆的磁铁矿 NP（HA-magnNP 和 PC-magnNP）。结果表明，无论 IONP 如何，随着 pH 值的升高，吸附的 Cu 百分比增加。因此，Cu 吸附机制中可能涉及质子化/去质子化反应。与其他研究的 IONP 不同，HA-magnNP 有利于在大多数测试的 pH 值下（包括酸性 pH 值 pH=3）吸附 Cu，这表明部分用于 Cu 吸附的活性表面位点未被质子占据。HA-magnNP 的 Freundlich 吸附等温线提供了最高的吸附常数 K（结合能）和 n 值，支持非均相吸附过程。HA-magnNP 和 Cu 之间的非均相吸附可以通过 HA 获得的结合位点的多样性和 Cu 与某些 HA 官能团之间形成的多齿络合物来解释。在 PC 包覆的 magnNP 上或在 maghNP 上均未观察到这种有利的吸附过程，它们的行为与 magnNP 相似。另一方面，HA 和 PC 涂层大大减少了与 magnNP 相比，从 magnNP 中溶解的铁（Fe）。有人认为，HA 和 PC 涂层要么提供了有效的铁浸出屏蔽，要么促进了溶解的 Fe 在涂层 magnNP 表面的官能团上重新吸附。因此，这项研究可以帮助更好地理解阳离子-有机物-胶体表面之间的复杂界面反应，这在环境和农业背景下具有重要意义。这项工作表明，磁铁矿 NP 的性质可能会受到表面修饰的影响，这会影响 NP 的化学稳定性和 Cu 的吸附，从而影响全球水化学。
