Oxalic Acid Adsorption on Rutile: Molecular Dynamics and ab Initio Calculations
Oxalic Acid Adsorption on Rutile: Molecular Dynamics and ab Initio Calculations
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DOI：
10.1021/acs.langmuir.8b03984
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发表时间：
2019-06-18
期刊：
影响因子：
3.9
通讯作者：
Predota, Milan
中科院分区：
文献类型：
--
作者：
Biriukov, Denys;Kroutil, Ondrej;Predota, Milan
采用分子动力学方法，结合自由能计算和从头计算，对草酸根离子（草酸根和草酸氢根）在金红石（110）表面的吸附进行了详细的分析。预测的吸附在完美的非羟基化和羟基化的表面与表面电荷密度从中性到+0.208 C/m（2）对应的pH值约为6和3.7，分别与实验吸附数据和电荷分布多位离子络合模型的预测一致，使用我们的模拟中确定的最有利的表面络合物。我们发现，外层复合物是最有利的，由于草酸离子与表面羟基和物理吸附水的强氢键。单齿配合物，最稳定的内球配合物，是约15 kJ/mol的能量高，但分开了一个大的能量障碍。其他的内球复合物，包括一些以前在文献中提出的可能的吸附结构，如双齿和螯合物，被发现是不稳定的经典和从头算建模。表面和（氢）草酸根离子建模使用的电荷缩放到标称值的75%，雅阁与电子连续理论和我们早期的参数化（氢）草酸根离子，这表明标称电荷夸大离子-水的相互作用。
Detailed analysis of the adsorption of oxalic acid ions, that is, oxalate and hydrogenoxalate, on the rutile (110) surface was carried out using molecular dynamics augmented by free energy calculations and supported by ab initio calculations. The predicted adsorption on perfect nonhydroxylated and hydroxylated surfaces with surface charge density from neutral to +0.208 C/m(2) corresponding to pH values of about 6 and 3.7, respectively, agrees with experimental adsorption data and charge-distribution multisite ion complexation model predictions obtained using the most favorable surface complexes identified in our simulations. We found that outer-sphere complexes are the most favorable, owing to strong hydrogen binding of oxalic acid ions with surface hydroxyls and physisorbed water. The monodentate complex, the most stable among inner-sphere complexes, was about 15 kJ/mol higher in energy, but separated by a large energy barrier. Other inner-sphere complexes, including some previously suggested in the literature as likely adsorption structures such as bidentate and chelate complexes, were found to be unstable both by classical and by ab initio modeling. Both the surfaces and (hydrogen)oxalate ions were modeled using charges scaled to 75% of the nominal values in accord with the electronic continuum theory and our earlier parameterization of (hydrogen)oxalate ions, which showed that nominal charges exaggerate ion-water interactions.