Applying nanostructured manganese oxides (nano-MnO_x) in contaminated agricultural lands offers the coupled benefits of oxidizing a range of environmental contaminants while simultaneously releasing micronutrients (i.e., dissolved Mn²⁺) that are vital for crop growth. However, little is known about how the key nanocrystal properties affect the oxidation capabilities of nano-MnO_x. Here, we show that an α-MnO₂ nanostructure with predominantly exposed {100} facets (referred to as α-MnO₂-100) exhibits greater oxidation capability for bisphenol A (BPA, a model pollutant commonly found in agricultural lands) than an α-MnO₂ nanostructure with predominantly exposed {310} facets (α-MnO₂-310), while consistently releasing a greater amount of Mn²⁺. Fitting the reaction kinetics data using a retarded rate model shows that α-MnO₂-100 possesses more reactive sites with higher reactivity. Density functional theory (DFT) calculations show that the {100} facet possesses a higher density of binding sites and the complexation of BPA molecules on the facet is thermodynamically more favorable, mainly due to its specific surface topography. Moreover, ligand-promoted Mn(III) release experiments and X-ray photoelectron spectroscopy analysis verify that α-MnO₂-100 contains a greater abundance of surface Mn(III), a more effective electron acceptor than Mn(IV). The findings suggest that facet engineering can be exploited to improve the performance of nano-MnO_x for sustainable agricultural applications.

中文翻译：

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纳米结构的锰氧化物表现出与面有关的氧化能力

在受污染的农业土地上使用纳米结构的锰氧化物（nano-MnO _x）具有氧化多种环境污染物，同时释放对作物生长至关重要的微量元素（即溶解的Mn ²⁺）的双重好处。然而，关于关键的纳米晶体性质如何影响纳米MnO _x的氧化能力的知之甚少。在这里，我们表明，α-MnO的₂纳米结构具有主要露出{100}面（被称为α-MnO的₂ -100）比表现出更大氧化能力为双酚A（BPA，在农田中常见的模型污染物） α-MnO的₂纳米结构具有主要露出{310}面（α-MnO的₂ -310），而一致地释放的Mn量更大²⁺。拟合使用延迟率模型表明，α-MnO的反应动力学数据₂ -100具有与较高反应性以上反应性部位。密度泛函理论（DFT）计算表明，{100}刻面具有较高的结合位点密度，并且BPA分子在刻面上的复合在热力学上更有利，这主要是由于其特定的表面形貌。此外，配位体促进的锰（III）释放实验和X射线光电子能谱分析验证α-MnO的₂ -100包含表面的Mn的较大的丰度（III），比Mn（IV）更有效的电子受体。研究结果表明，可以利用刻面工程技术来改善纳米MnO _x在可持续农业应用中的性能。