Department of Storage and Transportation Engineering, China University of Petroleum, Qingdao 266555, China.
J Colloid Interface Sci. 2010 Feb 15;342(2):485-92. doi: 10.1016/j.jcis.2009.10.018. Epub 2009 Nov 14.
In this paper, the effects of surface mediation on the adsorption isotherm and isosteric heat of adsorption on a graphite surface were investigated, as the surface mediation is known to affect the intermolecular interaction of adsorbed molecules close to the surface. Kim and Steele (Phys. Rev. B 45 (11) (1992) 6226-6233) and others have assumed that the surface mediation is confined only to the first layer. This will be tested in this paper with a combined experimental and Grand Canonical Monte Carlo (GCMC) simulation of adsorption of argon on graphitized thermal carbon black (GTCB) over a range of temperatures (77-95.25K). By matching the simulation results against the experimental data, we have found that the surface mediation is extended up to the fourth layer, rather than only the first as suggested by Kim and Steele, and the extent of this mediation is reduced with distance from the surface. This reinforces the important role of surface on the intermolecular interaction. With regard to the heat of adsorption, we found that the isosteric heats obtained directly from the simulation agree fairly well with the heats calculated from the application of the Clausius-Clapeyron equation on experimental isotherms of 77 and 87.3K. The temperature dependence of the isosteric heat was investigated with the GCMC simulation results. One interesting observation is the existence of a heat spike at 77K and its absence at higher temperatures, a phenomenon which is common to both simulation results and experimental data. This lends good support to the molecular model with surface mediation as a proper one to describe adsorption of noble gases on GTCB.
本文研究了表面介导对石墨表面吸附等温线和等焓吸附的影响，因为表面介导已知会影响靠近表面的吸附分子的分子间相互作用。Kim 和 Steele（Phys. Rev. B 45（11）（1992）6226-6233）和其他人假设表面介导仅局限于第一层。本文通过对氩气在石墨化热炭黑（GTCB）上的吸附进行实验和大正则蒙特卡罗（GCMC）模拟，在一系列温度（77-95.25K）下，测试了这一假设。通过将模拟结果与实验数据进行匹配，我们发现表面介导扩展到第四层，而不是 Kim 和 Steele 所建议的仅第一层，并且这种介导的程度随着离表面的距离而减小。这进一步证明了表面在分子间相互作用中的重要作用。关于吸附热，我们发现直接从模拟中获得的等焓热与从实验等压线在 77 和 87.3K 下应用克劳修斯-克拉佩龙方程计算得到的热量相当吻合。用 GCMC 模拟结果研究了等焓热的温度依赖性。一个有趣的观察是在 77K 时存在热峰值，而在较高温度时不存在，这种现象在模拟结果和实验数据中都很常见。这为表面介导的分子模型提供了很好的支持，该模型可以很好地描述稀有气体在 GTCB 上的吸附。
