Abstract
The influence of the compensating cation (Na+, Li+, Mg2+) nature on the water adsorption properties of LTA and FAU-type zeolites was investigated. Cation exchanges were performed at 80 °C for 2 h using 1 M aqueous solutions of lithium chloride (LiCl) or magnesium chloride (MgCl2). XRF and ICP-OES analyses indicate that the cation exchange yields reach values between 59 to 89% depending on the number of exchange cycles and the nature of the zeolite and cation, while both zeolites structures are preserved during the process, as shown by XRD and solid state NMR analyses. Nitrogen adsorption-desorption experiments indicate a higher available microporous volume when sodium cations are replaced by smaller monovalent lithium cations or by divalent magnesium cations because twice less cations are needed compared to monovalent cations. Up to 15% of gain in the available microporous volume is obtained for FAU-type zeolites exchanged with magnesium cation. This improvement facilitates the adsorption of water with an increase in the water uptake up to 30% for the LTA and FAU type zeolites exchanged with magnesium. These exchanged zeolites are promising for uses in water decontamination because a smaller amount is needed to trap the same amount of water compared to their sodium counterparts.
Highlights
The adsorption of water by porous solids is important for many applications which require capture and release of water such as electric dehumidifier, adsorption heat pumps (AHPs), alcohol/organic solvent dehydration, etc
O,homogeneous cations) is homogeneous in allleading the crystal leading the same properties. These results show that modifying the charge compensating cations of LTA-type and FAU-type. These results show that modifying the charge compensating cations of LTA-type and FAU-type zeolites change the water adsorption behavior
The characterization of LTA-type and FAU-type zeolites exchanged with lithium and magnesium cations were performed
Summary
The adsorption of water by porous solids is important for many applications which require capture and release of water such as electric dehumidifier, adsorption heat pumps (AHPs), alcohol/organic solvent dehydration, etc. Each alumina tetrahedron requires a +1 charge from an extra-framework cation in the structure to maintain electrical neutrality [18]. These cations are usually sodium ions that are present when the zeolite is synthesized [20]. The aluminosilicate framework of zeolite A (LTA-type) can be described in terms of two types of polyhedra, one being a simple cubic arrangement of eight polyhedra (double 4-rings); the other being a truncated octahedron of 24 tetrahedra named a β-cage. LTA and FAU-type zeolites show attractive adsorption uptake and high water affinity, their global performances regarding water adsorption are still not optimal, mostly due to the nature, size and affinity to water molecules of the compensating cations. The prepared samples were fully characterized and their adsorption performances were systematically evaluated by comparing their nitrogen and water adsorption isotherms
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