Goberna-Ferrón Sara, Asta Maria P, Zareeipolgardani Bahareh, Bureau Sarah, Findling Nathaniel, Simonelli Laura, Greneche Jean-Marc, Charlet Laurent, Fernández-Martínez Alejandro
University of Grenoble Alpes, University of Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France.
Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, 1015 Lausanne, Switzerland.
Environ Sci Technol. 2021 Mar 2;55(5):3021-3031. doi: 10.1021/acs.est.0c08146. Epub 2021 Feb 19.
The reactivity of iron(II/III) oxide surfaces may be influenced by their interaction with silica, which is ubiquitous in aquatic systems. Understanding the structure-reactivity relationships of Si-coated mineral surfaces is necessary to describe the complex surface behavior of nanoscale iron oxides. Here, we use Si-adsorption isotherms and Fourier transform infrared spectroscopy to analyze the sorption and polymerization of silica on slightly oxidized magnetite nanoparticles (15% maghemite and 85% magnetite, i.e., ∼2 maghemite surface layers), showing that Si adsorption follows a Langmuir isotherm up to 2 mM dissolved Si, where surface polymerization occurs. Furthermore, the effects of silica surface coatings on the redox-catalytic ability of magnetite are analyzed using selenium as a molecular probe. The results show that for partially oxidized nanoparticles and even under different Si surface coverages, electron transfer is still occurring. The results indicate anion exchange between silicate and the sorbed Se and Se. X-ray absorption near-edge structure analyses of the reacted Se indicate the formation of a mixed selenite/Se surface phase. We conclude that neither partial oxidation nor silica surface coatings block the sorption and redox-catalytic properties of magnetite nanoparticles, a result with important implications to assess the reactivity of mixed-valence phases in environmental settings.
氧化铁（II/III）表面的反应性可能会受到其与二氧化硅相互作用的影响，二氧化硅在水生系统中普遍存在。了解硅包覆矿物表面的结构-反应性关系对于描述纳米级氧化铁复杂的表面行为至关重要。在此，我们使用硅吸附等温线和傅里叶变换红外光谱来分析二氧化硅在轻度氧化的磁铁矿纳米颗粒（15%磁赤铁矿和85%磁铁矿，即约2个磁赤铁矿表面层）上的吸附和聚合情况，结果表明，在溶解硅浓度高达2 mM时，硅的吸附遵循朗缪尔等温线，此时会发生表面聚合。此外，以硒作为分子探针，分析了二氧化硅表面涂层对磁铁矿氧化还原催化能力的影响。结果表明，对于部分氧化的纳米颗粒，即使在不同的硅表面覆盖度下，电子转移仍在发生。结果表明，硅酸盐与吸附的硒和硒之间发生了阴离子交换。对反应后的硒进行的X射线吸收近边结构分析表明形成了亚硒酸盐/硒混合表面相。我们得出结论，部分氧化和二氧化硅表面涂层均不会阻碍磁铁矿纳米颗粒的吸附和氧化还原催化性能，这一结果对于评估环境中混合价态相的反应性具有重要意义。
