Cavitation and Pore Blocking in Nanoporous Glasses

Abstract

In gas adsorption studies, porous glasses are frequently referred to as model materials for highly disordered mesopore systems. Numerous works suggest that an accurate interpretation of physisorption isotherms requires a complete understanding of network effects upon adsorption and desorption, respectively. The present article deals with nitrogen and argon adsorption at different temperatures (77 and 87 K) performed on a series of novel nanoporous glasses (NPG) with different mean pore widths. NPG samples contain smaller mesopores and significantly higher microporosity than porous Vycor glass or controlled pore glass. Since the mean pore width of NPG can be tuned sensitively, the evolution of adsorption characteristics with respect to a broadening pore network can be investigated starting from the narrowest nanopore width. With an increasing mean pore width, a H2-type hysteresis develops gradually which finally transforms into a H1-type. In this connection, a transition from a cavitation-induced desorption toward desorption controlled by pore blocking can be observed. Furthermore, we find concrete hints for a pore size dependence of the relative pressure of cavitation in highly disordered pore systems. By comparing nitrogen and argon adsorption, a comprehensive insight into adsorption mechanisms in novel disordered materials is provided.

Enhancement of CO2 Adsorption and CO2/N2 Selectivity on ZIF‐8 via Postsynthetic Modification

“…For the ZIF‐8 sample, the total pore volume is calculated to be 0.54 cm 3 /g, because part of the pores might be blocked. However, after the postsynthetic modification, the blocked pores were reopened, and at meanwhile, some new pores were formed . Thus, the total pore volume of the ED‐ZIF‐8 sample is greatly improved.…”

Phase transitions in disordered mesoporous solids

“…Interestingly and somewhat intriguingly, the patterns expected for disordered solids have also been observed with ordered MCM-41 and SBA-15 materials 26 , 27 . Similarly, disordered porous solids may also exhibit the transition patterns resembling that of ideal materials 28 .

Figure 1 Phase transition patterns in ideal and disordered pores.

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Porosity of Silica Monoliths with Tailored Mesopores of Ink-Bottle Shape Determined by Nitrogen Adsorption and Positron Annihilation Lifetime Spectroscopy

“…In many cases the larger pores (the main cavities) are connected via smaller one which act as a neck. In such complex pore system the mechanism of desorption may involve the pore blocking and cavitation effects which are widely presented in the literature of the subject [15][16][17]. The analysis adsorption branch of N 2 isotherm gives information concerning the main pore/cavity size distribution, whereas the distribution of neck sizes (smaller pores) can be obtained from an analysis of the desorption branch of N 2 isotherm [17].…”