石墨狭缝中甲烷吸附的分子动力学模拟

用分子动力学模拟研究石墨狭缝中甲烷的吸附,考察狭缝宽度和温度对甲烷吸附的影响.模拟发现甲烷在石墨狭缝中出现分层现象,吸附层中甲烷具有类液特征,第一吸附层内甲烷中总有两个氢原子的连线与另外两个氢原子的连线分别位于平行于狭缝壁的两个平面内,游离层中甲烷呈现气体的特征;碳原子间的平均作用势说明吸附层中甲烷分子间结合能力大于游离层,吸附态是甲烷在石墨狭缝中的主要赋存形式之一;伦敦力以及由吸附层净电荷产生的电场力是甲烷吸附和分层的主要原因;甲烷的吸附量随狭缝宽度增大或温度升高而减少,当狭缝宽度小于16.46Å时,甲烷仅以吸附形态存在.甲烷在第一吸附层中的扩散能力最弱、游离层中最强,甲烷扩散系数随狭缝宽度的增大或温度的升高而增大.

A Molecular Dynamics Simulation of Methane Adsorption in Graphite Slit-pores

Adsorption of methane in graphite slit-pores and effect of slit-pores width and temperature on methane adsorption were studied with molecular dynamics simulation. It indicates that methane molecules have layering phenomenon in graphite slit-pores. Structure of methane in adsorption layers shows similar characteristics of liquid while to those of gas in free layers. And in a methane molecule there always exist two hydrogen atoms in a plane that parallels to slit-pore wall and other two hydrogen atoms in another plane that also parallels to slit-pore wall in the first layer. Potential of mean force between carbon atoms shows that binding capacity of methane is stronger in adsorption layers than in free layers. Adsorption state is one of the main occurrence state of methane in graphite slit-pores. London force and electric field force generated by net charge in adsorption layers are dominating reasons of methane adsorption and layering. Adsorption capacity of methane in graphite slit-pores decreases with increasing pore width or temperature. Methane is persisted only in adsorption state in slit-pore with width of 16.46 Å. Diffusivity of methane is the weakest in the first layer and the strongest in a free layer. Diffusion coefficients of methane increase with increasing pore width or temperature.