Acidity of the Aqueous Rutile TiO2(110) Surface from Density Functional Theory Based Molecular Dynamics
Acidity of the Aqueous Rutile TiO2(110) Surface from Density Functional Theory Based Molecular Dynamics
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DOI：
10.1021/ct100013q
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发表时间：
2010-03-01
影响因子：
5.5
通讯作者：
Sprik, Michiel
中科院分区：
文献类型：
--
作者：
Cheng, Jun;Sprik, Michiel
采用基于密度泛函理论的分子动力学方法（DFTMD）和自由能微扰方法研究了金红石型TiO 2（110）-水界面质子化和去质子化的热力学.酸度常数计算从自由能伴侣辅助插入/去除质子在完全原子周期性模型系统处理的固体和溶剂在相同的理论水平。我们发现TiO 2（110）上的两个活性表面羟基、桥OH（Ti 2 OH+）和吸附在5倍Ti位点（TiOH 2）上的末端H2O的pK（a）值分别为-1和9，导致零质子电荷点为4，完全在实验值（4.5-5.5）的计算误差范围（2 pK（a）单位）内。计算的固有表面酸度也被用来估计解离的吸附水的自由能给出0.6 eV，这表明水的解离是不可能在一个完美的水性TiO 2（110）表面。为了进一步的分析，我们比较的预测的MultiSlte络合（MUSIC）和溶剂化，键强度和静电（SBE）模型。关于MUSIC模型的结论是，虽然吸附的水分子的酸度有很好的一致性，但在DFTMD计算中获得的桥氧的质子亲和力明显低于MUSIC模型值（超过5 pKa单位）。结构分析表明，有显着的差异，氢键，特别是桥氧，这是假定为更强的MUSIC模型相比，我们发现使用DFTMD。然而，使用DFTMD配位数作为MUSIC模型的输入，导致pK（a）预测与从DFTMD自由能计算获得的估计不一致。
The thermodynamics of protonation and deprotonation of the rutile TiO2(110) water interface is studied using a combination of density functional theory based molecular dynamics (DFTMD) and free energy perturbation methods. Acidity constants are computed from the free energy for chaperone assisted insertion/removal of protons in fully atomistic periodic model systems treating the solid and solvent at the same level of theory. The pK(a) values we find for the two active surface hydroxyl groups on TiO2(110), the bridge OH (Ti2OH+), and terminal H2O adsorbed on a 5-fold Ti site (TiOH2) are -1 and 9, leading to a point of zero proton charge of 4, well within the computational error margin (2 pK(a) units) from the experimental value (4.5-5.5). The computed intrinsic surface acidities have also been used to estimate the dissociation free energy of adsorbed water giving 0.6 eV, suggesting that water dissociation is unlikely on a perfect aqueous TiO2(110) surface. For further analysis, we compare to the predictions of the MultiSlte Complexation (MUSIC) and Solvation, Bond strength, and Electrostatic (SBE) models. The conclusion regarding the MUSIC model is that, while there is good agreement for the acidity of an adsorbed water molecule, the proton affinity of the bridging oxygen obtained in the DFTMD calculation is significantly lower (more than 5 pKa units) than the MUSIC model value. Structural analysis shows that there are significant differences in hydrogen bonding, in particular to a bridging oxygen which is assumed to be stronger in the MUSIC model compared to what we find using DFTMD. Using DFTMD coordination numbers as input for the MUSIC model, however, led to a pK(a) prediction which is inconsistent with the estimates obtained from the DFTMD free energy calculation.