Study The Molecules Dynamics In The Photocatalytic On The Surface Of TiO₂ By Molecules Dynamics Simulation

To improve the photocatalytic efficiency of TiO₂ is a hot research issues in recent years. We have received a lot of results after generations of scientific hard works. But the photocatalytic efficiency of semiconductor materials that we could get is not satisfactory. The existing methods to improve the photocatalytic efficiency are based on two principles. The one is to make the materials to absorb light in the visible range. The other one is to curb the carries counterbalance in the photoconductor. But the most of the methods have keep a watchful eye on improved the properties of photocatalytic materials, pay less attention to the environment variable. In this paper,we have studied the movement of Hg²⁺ in the progress photocatalytic reduction on the surface of nano-titanium dioxide by molecular dynamics simulations and have studied the movement of water in the progress of photocatalytic.Because a lot of water molecules get together in the result would interfere watch the observation. We have established droplets water model,included little water,to study the impact of water in photocatalytic. With energy minimization principle,we have identified the electron density model of the surface of TiO₂ . We have found that water on the surface had formed ice-structure. The ice-like structure have bound the internal molecules, and hindered the movement of the molecular out of it. It has limited the movement of materials on the surface of TiO₂. It also has restrained the spread of the reactant and product of photocatalytic, so the ice-like structure could reduce efficiency of photocatalytic. The photogenerated electrons,which gathered on the surface of Titanium dioxide,have accelerated the speed of formation of ice-like structure.In the base of droplets water model on the surface of TiO₂, we have established the model of Hg²⁺ photocatalytic reduce in droplets model water. We have found that the ice-structure hinder Hg²⁺ close to the surface. The trajectories of Hg²⁺ reflected the impediment of ice-like structure,and given us a method to study the ice-structure. In order to improve the photocatalytic efficiency,we have restricted the formation of ice-structure by surface doping. From the simulation result we conclude that: the doped Fe³⁺ on the surface of titanium dioxide had reduced the size of ice-like structure. It can promote the photocatalytic efficiency.In the base of water droplets model on the surface of TiO₂,we have established water layer model on the surface of TiO₂,included lot of water,to study the impact of water in photocatalytic. We have found that ice-structure was formed by redistributed of the structure of water under surface force. We also have found the higher the electron concentration,the larger the size of the space occupied by the ice-structure. In the ice-like structure, the energies to destroy each monolayer are different. The higher the monolayer takes, the less energy it cost to destroy it.Finally,we have made similar simulation with graphene instead of TiO₂ as the base. We have found that water molecules extended range,speed on the graphene surface must be greater than that on the surface of TiO₂ in the same level of electron density. The side effect of ice-structure on the surface of graphene is smaller than it of TiO₂. It explains that graphene/TiO₂ composite has more highlights catalytic efficiency than TiO₂.