Capillary Condensation of Nitrogen in MCM-48 and SBA-16

Abstract

To examine the effects of connectivity among pores of almost the same size and of different size and geometry on adsorption hysteresis and pore criticality, we measured the temperature dependence of the adsorption−desorption isotherm of nitrogen onto MCM-48 and SBA-16 materials, respectively, with well-defined three-dimensional networks of cylindrical pores and cagelike pores, over a wide temperature range of T/T c = 0.43 to 0.90. The results for MCM-48 strongly suggest that interconnections among pores of almost the same size and geometry do not have a significant effect on the adsorption hysteresis and pore criticality. For SBA-16 with well-defined ink-bottle pores, capillary condensation in the hysteretic isotherms takes place near the equilibrium, whereas capillary evaporation from large cavities is delayed. The classical concept of pore blocking is not supported by the experimental isotherms for SBA-16, because the delayed desorption is not concerned with emptying of the small channels. The hysteresis shrinks with increasing temperature and eventually disappears well below the bulk critical temperature, in disagreement with the classical concept of pore blocking.

Melting and freezing of water in cylindrical silica nanopores

“…However, such a scenario cannot explain the observed systematic decrease of the hysteresis width, DT H , with decreasing pore size. This behaviour is reminiscent of related phenomena in the sorption of vapours in MCM-41 and related materials, 42,43 which are attributed to the proximity to criticality of the fluid in the pores (see below).…”

“…42 However, critical-point behaviour requires that the two phases belong to the same symmetry class, which is the case for liquid/gas, but not for solid/liquid phase coexistence. Presumably, the observed similarities in the behaviour of the present ice/water system with pore-critical phenomena of fluids in MCM-41 result from a combination of two effects: (i) increasing disorder of the ice phase as the pore size decreases; and (ii) increasing short-range order in liquid water as the temperature is lowered.…”

Aminolysis of epoxides catalyzed by three-dimensional, mesoporous titanosilicates, Ti-SBA-12 and Ti-SBA-16

“…SBA-16 and Ti-SBA-16 showed isotherms with a broad H 2 -hysteresis loop, which is characterized by a steep desorption branch and a smooth increasing adsorption branch. This has been corresponded to the existence of inkbottle-type pores [27][28][29][30][31], namely pores consisting of wide bodies fitted with narrow necks. At the heart of this mechanism lies the supposition that capillary condensation during adsorption in such pores is governed by the radius of curvature of the wide body of the pores, while capillary evaporation, during desorption, of the capillary condensate in the pores is obstructed by liquid remaining condensed in the nano necks (pore blocking).…”

Preparation of mesoporous silicas using food grade emulsifiers and its application for enzyme supports

“…Their lengths were almost coincided with those of the other MPS materials: they were evaluated to be as 44,18,22,10,15, and 14 μm in length for MCM-41, HMS, FSM-22, SBA-16, FSM-7, and MSU-F, respectively. Most of the materials had the particle lengths in the range 10-20 μm.…”

“…The hysteresis loop belongs to H1 type of IUPAC classification [43]. The shape of the hysteresis loop suggests the presence of the channel-like pore system with the regular pores, while the cage-like pore system exhibited a marked H2 hysteresis loop originated from an ink-bottle type pores [44]. The inset shows the corresponding BJH pore size distributions whose peaks are 9.2, 12, and 16 nm for TMPS-9, TMPS-12 and TMPS-16, respectively.…”