单壁碳纳米管上毒性苯气体净化的分子模拟(英文)

Molecular Simulations of the Purification of Toxic Benzene Gas on Single-Walled Carbon Nanotubes

采用巨正则系综蒙特卡罗(GCMC)方法研究了空气中微量苯组分在单臂碳纳米管(SWNTs)上的吸附净化.模拟表明,具有较大孔径的(20,20)纳米管比较适合吸附纯苯蒸汽,而对于移除空气中的毒性苯物质,苯的吸附选择性分别在(12,12)纳米管及4.0 MPa时和(18,18)纳米管及0.1 MPa时出现最小值和最大值.为了解释这一异常行为,我们进一步分析了N2-O2-C6H6混合物的局部密度分布、吸附分子构型和概率密度分布,发现(18,18)纳米管内外完全被苯分子占据,而对于(12,12)纳米管,由于存在更强的吸附质-吸附剂相互作用,空气分子更倾向于吸附在管与管之间的间隙.此外,吸附分子的空间有序参数表明大多数苯分子采取"平躺"在纳米管表面的定位,而线性的N2和O2分子则多数平行于孔轴方向.最后研究了温度和苯分子主体相浓度对分离效果的影响.我们发现较大孔中的选择性随着温度的增加比小孔下降更加明显.与此对比,主体相苯浓度对小孔中的选择性起到更加重要的作用.

Grand canonical ensemble Monte Carlo （GCMC） simulations were performed to investigate the purification of benzene from air by single-walled carbon nanotubes （SWNTs）. It was found that （20,20） SWNT with a large diameter is suitable to adsorb pure benzene. For the removal of benzene in air, the minimum and maximum selectivities were observed for the （12,12） SWNT at 4.0 MPa and the （18,18） SWNT at 0.1 MPa, respectively. To obtain deep insight into the unusual behavior, we analyzed the local density profiles, snapshots, and probability profiles of N2-O2-C6H6 mixtures. The results showed that the （18,18） SWNT was entirely occupied by benzene molecules, while, for the （12,12） SWNT, N2 and O2 were prone to appear in the interstices between tubes, instead of inside tubes, because of stronger adsorbate-adsorbent interactions. Additionally, we calculated the orientation order parameters of the adsorbates. The results suggested that benzene molecules prefer lying nearly flat on the pore surface, while N2 and O2 molecules orient parallel to the pore axis. Finally, the effects of temperature and concentration on the selectivity of benzene were investigated. We found that with increasing temperature the selectivity in large pores decreased more evidently than that in small pores. By contrast, the concentration plays a more important role in affecting the selectivity in small pores.