Adsorption of carbon dioxide, sulfur dioxide and water vapour by MCM-41, a model mesoporous adsorbent

Branton, Peter; Hall, Peter G.; Tréguer, Mona; Sing, K. S. W.

doi:10.1039/ft9959102041

Cited by 85 publications

(67 citation statements)

References 8 publications

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“…glass, and -13.7 ± 3.0 for andesite glass. The value for dacite glass is close to the −26 kJ/mol reported for SO 2 adsorption on MCM-41, a mesoporous alumosilicate material, at high surface coverage (Branton et al 1995).…”

Section: A Multiple Regression Model Of So 2 Adsorptionsupporting

confidence: 63%

Adsorption of sulfur dioxide on volcanic ashes

Schmauss

Keppler

2014

American Mineralogist

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The adsorption of pure sulfur dioxide gas on volcanic ashes has been studied from 0.1 mbar to 1 bar and from -80 to +150 °C. Finely ground synthetic glasses of andesitic, dacitic, and rhyolitic composition served as proxies for fresh natural ash surfaces. Powders from two natural obsidian samples were also studied and yielded results broadly similar to the synthetic model systems. SO 2 adsorption on ash is partially irreversible; it appears that the first layer of SO 2 molecules absorbed on the surface cannot be removed. The pressure and temperature dependence of adsorption can be described by the equation lnc = A T -1 + B lnP + C, where c is the surface concentration of adsorbed SO 2 in mg/m 2 , T is temperature in Kelvin, and P is the partial pressure of SO 2 in mbar. A multiple regression analysis of the experimental data yielded A = 1645, B = 0.29, C = -7.43 for andesite, A = 2140, B = 0.29, C = -9.32 for dacite, and A = 910, B = 0.21, C = -4.48 for rhyolite. These data imply that adsorption strongly decreases with temperature, but only slowly decreases with decreasing partial pressure of SO 2 . Therefore, adsorption primarily occurs in the cool and diluted parts of the volcanic plume. Model calculations show that most of the SO 2 may be removed from the plume, if the initial SO 2 concentration in the volcanic gases is low and the surface area of the ash is high. For high initial SO 2 concentrations, the fraction of SO 2 that is lost by adsorption decreases, since the amount of SO 2 in the gas phase is proportional to the SO 2 partial pressure P, while adsorption is proportional only to P 0.2 -P 0.3 . Adsorption of SO 2 on ash particles may therefore be one reason why the climatic impact of explosive volcanic eruptions does not always scale with total sulfur yield.

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Section: A Multiple Regression Model Of So 2 Adsorptionsupporting

confidence: 63%

Adsorption of sulfur dioxide on volcanic ashes

Schmauss

Keppler

2014

American Mineralogist

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“…On average, the resulting values, N w = 31.1 AE 1 nm À3 , are about 7% smaller than the number density of bulk water (33.4 nm À3 at 20 1C), but no systematic dependence of the density on the pore width can be detected. In other studies 29,32 the density of water in the pores of MCM-41 was reported to be 11-12% smaller than that of bulk water.…”

Section: Water Sorption Isothermsmentioning

confidence: 84%

Melting and freezing of water in cylindrical silica nanopores

Jähnert

Chávez

Schaumann

et al. 2008

Phys. Chem. Chem. Phys.

328

394

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Freezing and melting of H 2 O and D 2 O in the cylindrical pores of well-characterized MCM-41 silica materials (pore diameters from 2.5 to 4.4 nm) was studied by differential scanning calorimetry (DSC) and 1 H NMR cryoporometry. Well-resolved DSC melting and freezing peaks were obtained for pore diameters down to 3.0 nm, but not in 2.5 nm pores. The pore size dependence of the melting point depression DT m can be represented by the Gibbs-Thomson equation when the existence of a layer of nonfreezing water at the pore walls is taken into account. The DSC measurements also show that the hysteresis connected with the phase transition, and the melting enthalpy of water in the pores, both vanish near a pore diameter D* E 2.8 nm. It is concluded that D* represents a lower limit for firstorder melting/freezing in the pores. The NMR spin echo measurements show that a transition from low to high mobility of water molecules takes place in all MCM-41 materials, including the one with 2.5 nm pores, but the transition revealed by NMR occurs at a higher temperature than indicated by the DSC melting peaks. The disagreement between the NMR and DSC transition temperatures becomes more pronounced as the pore size decreases. This is attributed to the fact that with decreasing pore size an increasing fraction of the water molecules is situated in the first and second molecular layers next to the pore wall, and these molecules have slower dynamics than the molecules in the core of the pore.

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“…16 This critical pore size is smaller for water than for any other adsorbate investigated so far, including N 2 , O 2 , Ar, or CO 2 . 16,37,39 In some of these studies, it has been suggested that the width of the hysteresis loop, or the critical pore diameter, is determined by the molecular size of the adsorbate. 37 The density of the liquid plug can be computed from the data in Fig.…”

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confidence: 99%

Water filling of hydrophilic nanopores

Llave

Molinero

Scherlis

2010

The Journal of Chemical Physics

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Phase diagram of supercooled water confined to hydrophilic nanopores J. Chem. Phys. 137, 044509 (2012) Molecular dynamics simulations of water in cylindrical hydrophilic pores with diameters of 1.5 and 3 nm were performed to explore the phase behavior and the nucleation dynamics of the confined fluid as a function of the percentage of volume filled f. The interactions of water with the pore wall were considered to be identical to the interactions between water molecules. At low water contents, all the water is adsorbed to the surface of the pore. A second phase consisting of a liquid plug appears at the onset filling for capillary condensation, f onset = 27% and 34% for the narrow and wide pores, respectively. In agreement with experimental results for silica pores, the liquid phase appears close to the equilibrium filling f eq in the 1.5 nm pore and under conditions of strong surface supersaturations for the 3 nm pore. After condensation, two phases, a liquid plug and a surface-adsorbed phase, coexist in equilibrium. Under conditions of phase coexistence, the water surface density ⌫ coex was found to be independent of the water content and the diameter of the pore. The value of ⌫ coex found in the simulations ͑ϳ3 nm −2 ͒ is in good agreement with experimental results for silica pores, suggesting that the interactions of water with silica and with itself are comparable. The surface-adsorbed phase at coexistence is a sparse monolayer with a structure dominated by small water clusters. We characterize the density and structure of the liquid and surface phases, the nucleation mechanism of the water plug, and the effect of surface hydrophilicity on the two-phase equilibrium and hysteresis. The results are discussed in light of experiments and previous simulations.

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Adsorption of carbon dioxide, sulfur dioxide and water vapour by MCM-41, a model mesoporous adsorbent

Cited by 85 publications

References 8 publications

Adsorption of sulfur dioxide on volcanic ashes

Adsorption of sulfur dioxide on volcanic ashes

Melting and freezing of water in cylindrical silica nanopores

Water filling of hydrophilic nanopores

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