Analytical Prediction of Gas Permeation through Graphene Nanopores of Varying Sizes: Understanding Transitions across Multiple Transport Regimes
Analytical Prediction of Gas Permeation through Graphene Nanopores of Varying Sizes: Understanding Transitions across Multiple Transport Regimes
复制标题
DOI：
10.1021/acsnano.9b05779
复制
发表时间：
2019-10-01
期刊：
影响因子：
17.1
通讯作者：
Blankschtein, Daniel
中科院分区：
文献类型：
--
作者：
Yuan, Zhe;Misra, Rahul Prasanna;Blankschtein, Daniel
纳米多孔石墨烯由于其原子厚度和低的跨膜传输阻力，是一种很有前途的气体分离膜的候选材料。在文献中已经报道了在大孔径和小孔径限制下气体渗透通过石墨烯纳米孔的机制。然而，仍然缺乏对从小孔径极限到大孔径极限的交叉的机械见解。在这项研究中，我们开发了一个全面的理论框架来预测气体渗透通过石墨烯纳米孔具有广泛的直径范围内使用分析方程。我们制定的运输动力学与直接冲击从散装和表面扩散从石墨烯上的吸附层，然后联合收割机预测使用反应网络模型的整体气体渗透速率。我们还利用分子动力学模拟来验证和校准我们的理论模型。我们表明，直接撞击和表面扩散途径的速率需要使用不同的乘法因子进行校正，这些乘法因子是温度，气体动力学直径和孔径的函数。此外，我们发现一个次要的溢出途径，源于表面吸附层，但不包括在我们的理论模型。最后，我们利用修正后的模型来预测通过石墨烯纳米孔的CO2，CH 4和Ar的渗透率。我们表明，随着孔径的增加，通过石墨烯纳米孔的气体传输可以从以易位为主（孔径< 0.7 nm）转变为以表面途径为主（孔径1-2 nm），最后转变为以直接途径为主（孔径> 4 nm）。在这项研究中概述的各种气体渗透机制将是特别有用的，用于气体分离应用的二维材料，如石墨烯制成的膜的合理设计。
Nanoporous graphene is a promising candidate material for gas separation membranes, due to its atomic thickness and low cross- membrane transport resistance. The mechanisms of gas permeation through graphene nanopores, in both the large and small pore size limits, have been reported in the literature. However, mechanistic insights into the crossover from the small pore size limit to the large pore size limit are still lacking. In this study, we develop a comprehensive theoretical framework to predict gas permeance through graphene nanopores having a wide range of diameters using analytical equations. We formulate the transport kinetics associated with the direct impingement from the bulk and with the surface diffusion from the adsorption layer on graphene and then combine them to predict the overall gas permeation rate using a reaction network model. We also utilize molecular dynamics simulations to validate and calibrate our theoretical model. We show that the rates of both the direct impingement and the surface diffusion pathways need to be corrected using different multiplicative factors, which are functions of temperature, gas kinetic diameter, and pore diameter. Further, we find a minor spillover pathway that originates from the surface adsorption layer, but is not included in our theoretical model. Finally, we utilize the corrected model to predict the permeances of CO2, CH4, and Ar through graphene nanopores. We show that as the pore diameter increases, gas transport through graphene nanopores can transition from being translocation dominated (pore diameter < 0.7 nm), to surface pathway dominated (pore diameter 1-2 nm), and finally to direct pathway dominated (pore diameter > 4 nm). The various gas permeation mechanisms outlined in this study will be particularly useful for the rational design of membranes made out of two-dimensional materials such as graphene for gas separation applications.