Development of quantitative theory of adsorption-induced deformation is important, e.g., for enhanced coalbed methane recovery by CO 2 injection. It is also promising for the interpretation of experimental measurements of elastic properties of porous solids. We study deformation of mesoporous silica by n-pentane adsorption. The shape of experimental strain isotherms for this system differs from the shape predicted by thermodynamic theory of adsorption-induced deformation. We show that this difference can be attributed to the difference of disjoining pressure isotherm, responsible for the solid−fluid interactions. We suggest the disjoining pressure isotherm suitable for n-pentane adsorption on silica and derive the parameters for this isotherm from experimental data of n-pentane adsorption on nonporous silica. We use this isotherm in the formalism of macroscopic theory of adsorption-induced deformation of mesoporous materials, thus extending this theory for the case of weak solid−fluid interactions. We employ the extended theory to calculate solvation pressure and strain isotherms for SBA-15 and MCM-41 silica and compare it with experimental data obtained from small-angle X-ray scattering. Theoretical predictions for MCM-41 are in good agreement with the experiment, but for SBA-15 they are only qualitative. This deviation suggests that the elastic modulus of SBA-15 may change during pore filling.
In this work the use of coffee endocarp as precursor for the production of activated carbons by steam and CO2 was studied. Activation by both methods produces activated carbons with small external areas and microporous structures having very similar mean pore widths. The activation produces mainly primary micropores and only a small volume of larger micropores. The CO2 activation leads to samples with higher BET surface areas and pore volumes when compared with samples produced by steam activation and with similar burn--off value. All the activated carbons produced have basic characteristics with point of zero charge between 10 and 12. By FTIR it was possible to identify the formation on the activated carbon's surface of several functional groups, namely ether, quinones, lactones, ketones, hydroxyls (free and phenol); pyrones and Si-H bonds.
Universal mechanisms of adsorption and capillary condensation of toluene and nitrogen on ordered MCM-41 and PHTS materials are studied by means of high-resolution experiments and Monte Carlo molecular simulations. A molecular simulation model of toluene adsorption in silica nanopores, which accounts for surface heterogeneity, and a hybrid molecular-macsroscopic method for pore size distribution (PSD) calculations have been developed. For a range of reference materials, the PSD results obtained from toluene isotherms are consistent with the results of nitrogen adsorption using the nonlocal density functional theory method.
Adsorption-desorption isotherms of aromatic (mesitylene and toluene) and aliphatic (methylcyclohexane, neopentane and n-pentane) hydrocarbons were measured on ordered mesoporous materials, including MCM-41, MCM-48, SBA-15, SBA-16 and MCF silicas, a periodic mesoporous organosilica and a CMK-3 carbon, in order to evaluate the effect of the adsorbent characteristics on the organic compounds adsorption behaviour. A clear separation between aliphatic and aromatic hydrocarbons is observed at low p/p o for the materials having pores accessible by narrow openings. The presence of narrow pore openings causes an increase in the volume adsorbed of mesitylene, toluene, methylcyclohexane and n-pentane prior to capillary condensation that does not occur for neopentane. The increase of the hydrophobicity and change of the surface structure, resulting from the incorporation of chloromethyl groups on the silica walls, causes the p/p o at which the aromatic hydrocarbons condense to increase while the introduction of aromatic rings into the pore walls has a less significant effect on the condensation pressures. However, at low p/p o , all the hydrocarbons have higher affinity for the periodic mesoporous organosilica surface than for the pure silica or silica with chloromethyl groups surfaces, while these lower the affinity of the aromatic hydrocarbons. Good estimates of pore size (D p ) are obtained using the classical Kelvin equation from the mesitylene, toluene and methylcyclohexane adsorption data, for spheroidal pores of at least B20 nm. With n-pentane this occurs for pores of B30 nm while neopentane underestimates D p values even for pores as large as these, although to a lesser extent than nitrogen.
This contribution compares experimental nitrogen adsorption isotherms with molecular simulation results on effective non-porous silica models. A Molecular Dynamic (MD) annealing temperature scheme was adopted for the formulation of three samples of the solid surface. By means of Grand Canonical Monte Carlo (GCMC) simulations, nitrogen adsorption isotherms were obtained for each sample, with charged and uncharged nitrogen molecules, and compared with relevant experimental data. Following comparison of the experimental and simulated nitrogen results, a tuning process over the energetic parameter of the oxygen atoms was performed for the final proposed model. Specifically, the results are presented in terms of adsorption isotherms with an emphasis on the annealing effect over relevant model parameters, such as the surface concentration and the distribution of non-bridging oxygen atoms.
The thermal decomposition of magnesium hydroxide to magnesium oxide has been studied under carefully controlled conditions. Analysis of nitrogen and neopentane adsorption isotherm measurements shows that the micropore structure of the decomposition products is very well defined and consists of slit-shaped pores of width 0.93 _+ 0.03 nm from 40% to 90% decomposition. The mean pore width increases, up to ca. 1.8 nm, at higher levels of decomposition. For larger pore sizes two stages of secondary micropore filling by nitrogen (surface coverage followed by enhanced adsorption in the body of the pore) are clearly discernible. The results also show very clearly how the mechanism of micropore filling, and hence the shape of the isotherm, is dependent on the ratio of pore width to molecular diameter (dlo), and not just on d .
The effect of thermal pretreatment on the diffusion of O 2 , N 2 , CO 2 , and CH 4 at 298 K in the commercial carbon molecular sieve Takeda 3A was studied. The results indicate that pore mouth barrier controls nitrogen transport. For oxygen and carbon dioxide, however, two mechanisms are present. Pore mouth barrier control determines the transport at lower temperature degassing, and micropore diffusion is present with a high temperature degassing. When the degassing temperature is increased, the adsorption as a function of contact time is almost constant for O 2 and CO 2 , is almost null for CH 4 , and increases significantly for N 2 between 373 and 653 K. The rates of diffusion also increase with increasing degassing temperature, but more appreciably for N 2 , which results in a significant decrease in selectivity for O 2 /N 2 and CO 2 /N 2 separations. These separations are therefore more efficient for Takeda 3A if it is only subjected to temperatures lower than 373 K. On the other hand, for CO 2 /CH 4 , the separation is more efficient if the Takeda 3A sample is first submitted to a degassing temperature around 673 K.
scite is a Brooklyn-based startup that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.