Adsorption hysteresis in nanopores

Abstract

Capillary condensation hysteresis in nanopores is studied by Monte Carlo simulations and the nonlocal density functional theory. Comparing the theoretical results with the experimental data on low temperature sorption of nitrogen and argon in cylindrical channels of mesoporous siliceous molecular sieves of MCM-41 type, we have revealed four qualitatively different sorption regimes depending on the temperature and pore size. As the pore size increases at a given temperature, or as the temperature decreases at a given pore size, the following regimes are consequently observed: volume filling without phase separation, reversible stepwise capillary condensation, irreversible capillary condensation with developing hysteresis, and capillary condensation with developed hysteresis. We show that, in the regime of developed hysteresis (pores wider than 5 nm in the case of nitrogen sorption at 77 K), condensation occurs spontaneously at the vaporlike spinodal while desorption takes place at the equilibrium. A quantitative agreement is found between the modeling results and the experimental hysteresis loops formed by the adsorption-desorption isotherms. The results obtained provide a better understanding of the general behavior of confined fluids and the specifics of sorption and phase transitions in nanomaterials.

Influence of Ni/SiO2 catalyst preparation methods on hydrogen production from the pyrolysis/reforming of refuse derived fuel

“…The hysteresis loop is of the H1 type associated with porous materials consisting of agglomerates or compacts of uniform sphere arrays, also presenting a narrow distribution of pore size. Hysteresis loops of type H1 have been observed on mesporous silica with a regular array of cylindrical pores and predetermined diameters such as MCM-41 [30] and SBA-15 [31].…”

Pore size distributions in low‐k dielectric thin films from X‐ray porosimetry

“…By maintaining a fixed concentration of solvent, P, in the cell, it is possible to vary the saturation pressure P 0 by changing the temperature. From a thermodynamic point of view, there should be no difference whether P or P 0 is varied in eq 2 (as long as spinodal condensation and/or evaporation does not occur, 15 in which case the Kelvin equation would also be in serious error). We revisit this temperature-pressure equivalency question once the automated pressure control device is in place.…”

Determination of pore size distributions using the Dual Site-Bond Model: experimental evidence

“…However this is not the only effect contributing to the histheresis. Another important contribution, which can be better studied in ordered or taylored porous solids, comes from the thermodynamical behavior of the fluid in the pore and the occurrence of metastable states in the condensationevaporation process and has been intensively studied by other authors [22][23][24][25].…”