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The sorption of methane, ethane, ethene and carbon dioxide in NaX, NaY and Na-mordenite zeolites (at 305-353 K and 0-200 kPa) and the thermodynamics of sorption have been investigated using a novel gravimetric sorption apparatus. The Dubinin-Polanyi equation fits the sorption of methane in all three zeolites, whereas the Langmuir model fits the sorption of carbon dioxide in all the zeolites. It was not possible to fit the sorption data for ethane and ethene in the different zeolites to a single isotherm equation. The isosteric heat of sorption and its variation with surface coverage of these gases are dependent on the sorbate and the zeolite sorbent. Except for ethene in NaM, the sorbed molecules are supermobile in the three zeolites, and their mobility is influenced by the surface coverage. Ethene sorbed in NaM exhibits an intermediate degree of freedom and the twodimensional (2D) translational motion of the sorbed molecules parallel to the zeolite surface itself is restricted.

Layered double hydroxide materials (Zn/Al, Mg/Al, Zn/Fe) with varying composition (M 2+ :M 3+ molar ratio, x ) 3, 2, 1, and 0.33) were synthesized and evaluated for their selenium adsorption characteristics in aqueous medium. Zn/Al and Mg/Al LDHs with x ) 3 and 2, exhibited very high selenite adsorption capacity. XRD patterns of the pristine LDHs, LDH after selenite adsorption, and chloride ion leaching studies revealed that adsorption of selenium on the LDHs occurred through both surface adsorption and ion-exchange mechanism. The adsorption data was fitted to Langmuir and Freundlich isotherm models. A pseudo second-order kinetic model was used to describe the adsorption kinetics of selenite on LDH materials. Desorption of selenite ions in water from the LDH-Se matrix was studied up to 5 h.

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The sorption of methane, ethane, ethylene, and carbon dioxide in ALPO-5 and SAPO-5 (temperature 305−353 K, and pressure 0−200 kPa) and the thermodynamics of sorption have been investigated under similar conditions using a gravimetric sorption apparatus. The Dubinin−Polanyi equation is found to fit the sorption of all the sorbates in both the sorbents except for carbon dioxide in ALPO-5. The Freundlich model fits the equilibrium data on the sorption of carbon dioxide in ALPO-5. The two sorbents differ widely in the isosteric heat of sorption and also in its variation with surface coverage of these sorbates. Entropy changes on the sorption have also been analyzed. The sorption of these gases in both the sorbents is found to be supermobile, the mobility being much higher in ALPO-5 than in SAPO-5.