Hematite (Fe₂O₃) nanoparticles are omnipresent in nature and of great importance in controlling the environmental fate of arsenic (As). Fe₂O₃ facets exhibit a significant effect on the surface reactivity; however, the underlying chemical driving force that controls Fe₂O₃ facet reactivity towards As(III/V) adsorption remains poorly defined. Here, As(III/V) adsorption on the Fe₂O₃ {001}, {110}, and {214} facets was explored to understand the facet-dependent binding mechanisms. Multidisciplinary spectroscopic characterization and density functional theory (DFT) calculations revealed monodentate mononuclear As(III/V) complexes on the {001} facet, and bidentate binuclear surface complexes on the {110} and {214} facets. Different adsorption configurations were ascribed to the chemical diversity in surface active sites, where the under-coordinated Fe atoms served as Lewis acid sites. The strength of Lewis acid sites determined the facet-dependent reactivity towards As(III/V) adsorption. Partial density of states (PDOS) and crystal orbital Hamilton population (COHP) analysis suggested that the surface bonding was attributed to the interactions between the Fe(3d and 4s) and O(2p) orbitals. The experimental and theoretical results indicate that the intrinsic nature of facet-dependent mechanism lies in the surface site coordination and its bonding strengths. The mechanistic insights into the bonding chemistry on facets improve our ability in predicting the behavior of environmental contaminants at the solid/liquid interface.

中文翻译：

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赤铁矿面上砷的吸附：光谱学和DFT研究

赤铁矿（Fe ₂ O ₃）纳米粒子在自然界中无处不在，在控制砷（As）的环境命运方面具有重要意义。Fe ₂ O ₃晶面对表面反应性具有显着影响。但是，控制Fe ₂ O ₃面对As（III / V）吸附的反应性的基本化学驱动力仍然定义不清。在这里，As（III / V）在Fe ₂ O ₃上的吸附探索了{001}，{110}和{214}方面，以了解方面相关的绑定机制。多学科光谱表征和密度泛函理论（DFT）计算显示，{001}面上的单齿单核As（III / V）络合物，{110}和{214}面上的双齿双核表面络合物。表面活性部位的化学多样性归因于不同的吸附构型，其中配位不足的Fe原子充当路易斯酸部位。Lewis酸位的强度决定了其对As（III / V）吸附。状态的部分密度（PDOS）和汉密尔顿晶体轨道人口（COHP）分析表明，表面键合归因于Fe（3d和4s）与O（2p）轨道之间的相互作用。实验和理论结果表明，面依赖​​机制的内在本质在于表面位点配位及其结合强度。机械学上对小平面上的键合化学的见解提高了我们预测固/液界面处环境污染物行为的能力。