Adsorption Hysteresis in Open Slit-like Micropores

Abstract

Adsorption hysteresis in the low-pressure range is only rarely described in the literature. To optimise, for example, heat storage technologies, a deeper understanding of the low-pressure hysteresis (LPH) process is necessary. Here, two thermodynamically based approaches are further developed for analysing the LPH within the framework of thermodynamically irreversible processes and fractal geometry. With both methods developed, it is possible to obtain the description of the adsorption and desorption branches with high accuracy. Within the framework of the two thermodynamic models of the hysteresis loop, generalised equations are obtained with the control parameter in the form of the degree of irreversibility. This is done by taking the adsorption of water on alumina as an example. It is shown that the fractal dimension of the adsorption process is larger than the fractal dimension of the desorption branch, meaning that the phase state of the adsorbate is more symmetric during the adsorption step than in the desorption process.

Facile modification of cobalt ferrite by SiO 2 and H‐ZSM‐5 support for hydrogen and filamentous carbon production from methane decomposition

“…Figure 2A,B shows the nitrogen adsorption/desorption isotherms and the pore size distribution curves of CoFe 2 O 4 /SiO 2 and CoFe 2 O 4 /H‐ZSM‐5 catalysts at temperature of 77.4 K. As seen in Figure 2A, the CoFe 2 O 4 /SiO 2 catalyst exhibit type III isotherm with H3 hysteresis loop, characterize aggregates of plate like particles forming slit‐like pores, and indicating strong adsorbate‐adsorbate (multilayers) interaction 39,44,45 . Meanwhile, CoFe 2 O 4 /H‐ZSM‐5 catalyst reveals type V isotherm with H2 characteristics hysteresis loop, implying relatively uniform channel‐like pores.…”

Customized Nanostructured Ceramics via Microphase Separation 3D Printing

“…[ 43 ] At low relative pressures ( P / P 0 ), the desorption and adsorption branches did not overlap with each other, resulting in the open type isotherm previously observed for some nanoporous PIMS materials [ 26b ] and materials with open slit‐like pores (Figure 5A). [ 44 ] Such sorption behavior can be attributed to partial dissolution of nitrogen within the ceramic walls due to the high Laplace pressure and the capillary condensation within the micro‐ and mesopores. [ 45 ] The ceramic materials prepared using PLAc‐CTAs with X n = 69, 103, and 137 displayed a comparable isotherm shape similar to type IV with H2‐type hysteresis at P / P 0 of 0.4 to ≈0.85, [ 43 ] typically observed for disordered PIMS mesoporous materials (Figure 5B–D, Supporting Information).…”

Multi-Compound H2, CH4, and N2 Adsorption Analysis

“…A solution of this set of equations was obtained by the Newton-Raphson method. Once ϕ i is known, the adsorbed-phase mole fractions are calculated for the Raoult's law (Equation ( 19)), the total adsorbed concentration is calculated from Equation ( 14), and the adsorbed-component concentration is obtained from Equation (15).…”

“…The major objective is to describe any multi-component adsorption equilibrium based on the results of pure-component adsorption isotherms, as obtained in a previous work [11]. Different models have been used to correlate pure/single-component adsorption data and to subsequently predict the multi-component equilibrium; some of them consider an ideal behaviour of the system without taking into account the possible sources of non-ideal behaviour, such as the adsorbate-adsorbate interactions in the adsorbed phase, the heterogeneity of the adsorbent surface, the differences in the molecular size of the adsorbates, or the loss of symmetry [12][13][14][15].…”