Thermodynamics of binary gas adsorption in nanopores

Abstract

MCM-41 nanoporous silicas show a very high selectivity for monoalcohols over aprotic molecules during adsorption of a binary mixture in the gas phase. We present here an original use of gravimetric vapour sorption isotherms to characterize the role played by the alcohol hydrogen-bonding network in the adsorption process. Beyond simple selectivity, vapour sorption isotherms measured for various compositions help to completely unravel at the molecular level the step by step adsorption mechanism of the binary system in the nanoporous solid, from the first monolayers to the complete liquid condensation.

Microphase separation of a miscible binary liquid mixture under confinement at the nanoscale

“…Figure 2 shows that the predicted adsorption isotherms are in fair agreement with those obtained from experiments. 31 Interestingly, Fig. 2 exhibits that the capillary condensation pressure is qualitatively reproduced for both TOL and TBA components.…”

“…Whereas these effects have been largely investigated in the case of confined single components [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and immiscible binary mixtures, [28][29][30] less works have been devoted to the confinement of miscible liquid mixtures. 15,[31][32][33] Recently, Muthulakshmi et al 34 reported an experimental evidence of a partial phase separation of an ethanol-water mixture confined in mesoporous silica using positron annihilation lifetime spectroscopy. They showed that a small fraction of the ethanol molecules seemed to be anchored at the silica surface.…”

“…37,38 A consistent picture, showing the highly selective segregation of polar molecules at the pore surface, was deduced from binary gas adsorption experiments. 31 Although these experiments revealed the presence of a microphase separation, the local organization and microscopic processes controlling the CS structure has to be clarified. In a recent numerical work, Essafri et al 39 showed that the nanoconfinement of TBA/TOL mixture in a silica nanopore only induced strong heterogeneity.…”

“…The current study paves the way to a thorough understanding of the phenomenon from carefully designed simulations. 15,31,37,38 Using atomistic simulations, we aim to capture the CS structure and to clarify the microscopic driving force ruling it. To do so, the solid-liquid interactions were refined to qualitatively reproduce the experimental adsorption isotherm of pure TBA and TOL components confined through the silica nanopore.…”

“…To do so, the solid-liquid interactions were refined to qualitatively reproduce the experimental adsorption isotherm of pure TBA and TOL components confined through the silica nanopore. 31 An illustration of three TBA, TOL, and silica framework is provided in Fig. 1a.…”