锐钛矿型TiO2羟基化表面与H2O相互作用的分子动力学研究

Interaction of Hydroxylated Anatase TiO2 Surfaces and H2O by Molecular Dynamics Simulation

利用经典分子动力学对锐钛矿型TiO2(101)/(001)羟基化表面与水分子的相互作用进行模拟计算,分析得到表面羟基对TiO2鄄H2O界面性质的影响.首先,通过TiO2表面钛、氧原子与水中氧、氢原子间的径向分布函数及键长验证得到,所建羟基化TiO2(101)/(001)模型和力场能够很好地模拟TiO2鄄水体系的结构和相关特性.由分子动力学快照图可知,TiO2表面的O2c吸附位在羟基化前后不发生改变,而完整表面原有的Ti5c吸附位被表面羟基中的氢原子取代.羟基化表面的水分子以氢键作用吸附于TiO2表面引起界面电荷转移,根据水分子密度分布可知TiO2鄄H2O界面形成内亥姆霍兹层、外亥姆霍兹层和体相3个分层结构.与完整表面比较,羟基使TiO2(101)表面内、外亥姆霍兹层均变窄,而TiO2(001)表面仅内亥姆霍兹层变窄.对水分子的扩散性质和平均速度分布进行分析,相对于TiO2(101)羟基表面,TiO2(001)羟基表面结构更有利于水分子沿表面法线方向移动.最后,由水的电荷密度分布函数得到,表面羟基使得TiO2(101)和(001)表面的电荷波动加剧,正、负电荷密度分布极值的绝对值明显增加.

In this work,the interaction between hydroxylated anatase TiO2(101)/(001)surfaces and H2O was studied by molecular dynamics simulations and the effects of hydroxyl groups on the properties of TiO2-H2O interface were obtained.By analyzing the radial distribution functions and bond lengths of Ti5c-Ow and O2c-Hw,it is confirmed that the hydroxylated TiO2(101)/(001)model and the force field can well simulate the structures and properties of the TiO2-H2O system.With the molecular dynamics snapshots,the O2c adsorption sites on TiO2 surface had nearly no change before and after hydroxylation,while the Ti5c adsorption sites on perfect surfaces were replaced by the hydrogen atoms of hydroxyl groups.Further research on the hydrogen bonds between H2O and TiO2 was shown,which caused charge transfer on the interface,and the density distribution of H2O presents hierarchical structures made up of inner Helmholtz layer(IHL),outer Helmholtz layer(OHL)and bulk.Compared with perfect surfaces,hydroxyl groups made the IHL/OHL on TiO2(101)surface narrowed,while the IHL of TiO2(001)surface got narrowed.By analyzing the diffusion properties and average velocity distribution of H2O molecules,we found the surface structure of hydroxylated TiO2(001)is conducive to the movement of H2O along the surface relative to hydroxylated TiO2(101).Based on the charge density distribution of H2O,it is shown that the hydroxyl group do increase the charge fluctuation on the surface of TiO2(101)and(001),and the extreme value of the charge density is obviously improved.