Computational Study of the Effect of Functional Groups on Water Adsorption in Mesoporous Carbons: Implications for Gas Adsorption

Abstract

The adsorption and diffusion of water in realistic CMK-1, CMK-3, and CMK-5 carbon models at 300 K has been studied via grand canonical Monte Carlo and molecular dynamics simulations. The presence of −COOH and −OH functional groups has been found to be crucial to describe the adsorption process, while the models without functional groups are unable to capture the host−guest interactions. Functional groups were attached in cylindrical shells on the outer walls of CMK models in 2 and 4 cylindrical shells to study the effect of their concentration and location on water adsorption. The adsorption isotherm starts at a lower chemical potential, with water adsorbed near functional groups forming small clusters. On increasing chemical potential the water cluster grows and merges to form bigger clusters and completely fills the pores. We also analyzed the isosteric heat, radial distribution functions, hydrogen bond, and cluster size of water molecules. It indicates that the adsorption occurs due to the formation and growth of water clusters. For CMK-1, CMK-3, and CMK-5 models with functional groups, the pore filling happens at lower chemical potential, when compared to the models without functional groups, owing to the presence of active sites which favors the nucleation of water molecules. The effect of functional groups is also remarkable in the diffusion of water inside the pores of CMK-1, CMK-3, and CMK-5 models, lowering the mobility of the adsorbed molecules. The agreement between the results of the models with functional groups and the experimental observations makes the presence of these groups necessary to study the adsorption and diffusion of water in CMK-1, CMK-3, and CMK-5 carbon models.

Robust Anionic LnIII–Organic Frameworks: Chemical Fixation of CO2, Tunable Light Emission, and Fluorescence Recognition of Fe3+

“…Moreover, CO 2 , a huge greenhouse gas devoted to the consumption of fossil fuels, vehicle emissions, industrial discharge, and straw combustion, has gradually become a focus of global concern and could cause devastation with regard to global pestilence diseases and sea-level rise. − Thereby, the unconquered technology of reducing the amount of CO 2 through consumption poses a challenge to global scientific researchers. So far, tentative and purposeful operations, including selective adsorption and storage and chemical conversion, have been widely launched with the help of consensus graphene, zeolite sieves, inorganic metal oxide or clusters, activated MOFs, etc. − At this time, catalytic cycloaddition of CO 2 under wild conditions is the most economic and convenient treatment method by the transformation of epoxides into cyclic carbonates, which could be further economically applied in the industrial fields of nontoxic aprotic solvent, raw material of polymer, pharmaceutical and pesticide intermediates, battery electrolyte, etc. − Among all porous MOF materials, Ln-MOFs are one of the most efficient and sustainable heterogeneous catalysts because Ln 3+ cations own rich empty electronic orbitals and a strong affinity for large dipole-moment CO 2 molecules, − whereas, hitherto, most of the reported Ln-MOFs were usually self-assembled from mixed ligands and lack solvent-accessible voids and structural stability.…”

Separation of CF4/N2, C2F6/N2, and SF6/N2 Mixtures in Amorphous Activated Carbons Using Molecular Simulations

“…An indication of the correlations between different molecules can be estimated by the difference between the self-diffusivities and the corrected diffusivities. 23 Figure S4 shows the ratio between the diffusion selectivities calculated from the corrected diffusivities and from the self-diffusivities of the components in each mixture. This ratio is almost the unity for the CF 4 /N 2 mixture, which indicates that there are no strong correlations between CF 4 and N 2 molecules.…”

“…For the same reason as in the previous results, the mixture containing higher concentration of nitrogen shows lower values of the diffusion selectivities. An indication of the correlations between different molecules can be estimated by the difference between the self-diffusivities and the corrected diffusivities Figure S4 shows the ratio between the diffusion selectivities calculated from the corrected diffusivities and from the self-diffusivities of the components in each mixture.…”

“…It is widely known that the adsorption and transport properties of fluid (mainly polar) molecules are governed by the presence of functional groups (those containing oxygen), mainly at low pressure (and thus at low loadings). 23 The presence of functional groups enhances the adsorption and separation of carbon materials. These functional groups interact via multipole interaction with the gas molecules and hence enhance the binding of the gas to the adsorbent.…”

“…Therefore, in order to simulate the most realistic experimental conditions, , we have included explicit oxygen and hydrogen atoms in the carbon models by taking into account the different ratios among carbon, oxygen, and hydrogen atoms observed experimentally. It is widely known that the adsorption and transport properties of fluid (mainly polar) molecules are governed by the presence of functional groups (those containing oxygen), mainly at low pressure (and thus at low loadings) . The presence of functional groups enhances the adsorption and separation of carbon materials.…”