Grote Fredrik, Lyubartsev Alexander P
Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16 C, 106 91 Stockholm, Sweden.
Nanoscale. 2022 Nov 17;14(44):16536-16547. doi: 10.1039/d2nr02354g.
Water structure, dynamics and reactivity at the surface of a small TiO-nanoparticle fully immersed in water was investigated by an molecular dynamics simulation. Several modes of water binding were identified by assigning each atom to an atom type, representing a distinct chemical environment in the ensemble, and then computing radial distribution functions between the atom types. Surface reactivity was investigated by monitoring how populations of atom types change during the simulation. In order to acquire further insight, electron densities for a set of representative system snapshots were analyzed using an atoms-in-molecules approach. Our results reveal that water dissociation, where a water molecule splits at a bridging oxygen site to form a hydroxyl group and a protonated oxygen bridge, can occur by a mechanism involving transfer of a proton over several water molecules. The hydroxyl group and protonated oxygen bridge formed in the process persist (on a 10 ps time scale) and the hydroxyl group undergoes exchange using a mechanism similar to the one responsible for water dissociation. Rotational and translational dynamics of water molecules around the nanoparticle were analyzed in terms of reorientational time correlation functions and mean square displacement. While reorientation of water O-H vectors decreases quickly in the proximity of the nanoparticle surface, translational diffusion slows down more gradually. Our results give new insight into water structure, dynamics and reactivity on TiO-nanoparticle surfaces and suggest that water dissociation on curved TiO-nanoparticle surfaces can occur more complex mechanisms than those previously identified for flat defect-free surfaces.
通过分子动力学模拟研究了完全浸没在水中的小TiO纳米颗粒表面的水结构、动力学和反应活性。通过将每个原子分配到一种原子类型来识别几种水结合模式，该原子类型代表系综中不同的化学环境，然后计算原子类型之间的径向分布函数。通过监测模拟过程中原子类型的数量如何变化来研究表面反应活性。为了获得更深入的了解，使用分子中的原子方法分析了一组代表性系统快照的电子密度。我们的结果表明，水分子在桥连氧位点分裂形成羟基和质子化氧桥的水离解，可以通过涉及质子在几个水分子上转移的机制发生。在此过程中形成的羟基和质子化氧桥持续存在（在10 ps时间尺度上），并且羟基通过类似于导致水离解的机制进行交换。根据重新取向时间相关函数和均方位移分析了纳米颗粒周围水分子的旋转和平移动力学。虽然水O-H向量在纳米颗粒表面附近的重新取向迅速降低，但平动扩散的减慢更为逐渐。我们的结果为TiO纳米颗粒表面的水结构、动力学和反应活性提供了新的见解，并表明弯曲的TiO纳米颗粒表面上的水离解可能通过比先前为平坦无缺陷表面确定的机制更复杂的机制发生。
