Menisci Interactions during Adsorption on Mesoporous Materials: Evaluation of Delayed and Advanced Adsorption

Abstract

Menisci interactions can strongly affect the development of adsorption processes in mesoporous materials. Phenomena such as delayed and advanced adsorption represent outright manifestations of these interactions then leading to deceptive determinations of the pore-size distribution. At present, a characterization study involving simulated porous networks with qualities similar to those owned by real materials and in which the above processes can occur is still lacking. A Monte Carlo procedure is used to evaluate the extent of delayed and advanced adsorption in porous structures of assorted morphologies. This treatment allows a clear detection of the types of mesoporous structures that can experience the incidence of delayed and advanced adsorption.

Controlling the Role of Nanopore Morphology in Capillary Condensation

“…The capillary condensation within the cavity remains identical to that observed from pSi4 (i.e., the isolated cavity; black circles and blue triangles in Figure 3b, respectively). This may arise from either of two situations: (1) capillary condensation within the cavity can either be nucleated at the cavity end by the meniscus (created either by condensation within an adjacent constriction 13 (pSi1, funnel) or by multilayer adsorption at the capped end 34 (pSi4, isolated cavity)) or (2) physical and/or chemical heterogeneities within the cavity itself nucleate the gas−liquid phase transition, as was suggested experimentally by Wallacher 23 and investigated recently by numerical simulations. 13,16−21 Capillary condensation within the cavities of the ink bottle (see above) and constrictions (see below) confirms the latter to be the case.…”

“…For an "ink-bottle" geometry in which a narrow pore ("constriction") constricts a wider pore ("cavity"), there is experimental evidence of cavitation 23,26 within singlecrystal porous Si and pore-blocking in various other nanoporous media. 15,24,27 For a "funnel" geometry (cavity above constriction), there is one experimental observation of advanced adsorption, 24 as predicted theoretically by Cordero et al 13,28 In this work, we use optical interferometry to investigate how a particular porous region is affected by the presence of a morphologically different one. Two morphologically different porous regions were combined to produce two complex structures (ink bottle and funnel) as well as two single structures (one composed solely of cavities and the other of constrictions).…”

“…Although this is well understood for the simplest cases (i.e., disconnected cylindrical pores 8−11 ), deviation from ideality drastically affects the quantitative correlation between pore morphology and sorption isotherms. 13,14 Although large size variations within the pores affect capillary condensation and evaporation, 15 recent simulations suggest that small perturbations 16−21 have a larger effect than previously considered. This uncertainty requires further investigation into the mechanisms behind capillary condensation and evaporation in real systems.…”

“…22 A clear example is the long-standing controversy regarding the correlation between the pore morphology and hysteresis shape in single-crystal porous silicon (Si). 14,18,22,23 Previous experimental 15,23−27 and theoretical 13,28,29 studies have shown that complex geometries create cooperative effects that alter capillary condensation and evaporation within a nanoporous medium. For an "ink-bottle" geometry in which a narrow pore ("constriction") constricts a wider pore ("cavity"), there is experimental evidence of cavitation 23,26 within singlecrystal porous Si and pore-blocking in various other nanoporous media.…”

Estudio de la adsorción de materiales mesoporosos simples y complejos mediante simulación molecular

“…Finalmente, estudiamos las estructuras que hacen el principal objetivo de este trabajo, basado en algunos trabajos publicados [15,86,87]. En aquellos trabajos ellos usan el modelo DSBM para crear estructuras porosas complejas y analizarlas.…”