Water vapor adsorption on metal-exchanged hierarchical porous zeolite-Y

Abstract

The development of efficient zeolite-based adsorbents with high water uptake capacity is an essential requirement for water adsorption and moisture removal technologies. In the present study, zeolite-Y samples with interconnected hierarchical micro-mesoporous network were synthesized by employing a bifunctional cationic polymer (namely, polydiallydimethyl-ammonium chloride, PDDA), and ion-exchanged with several metal salts (such as Zn, Mg, Li) targeting high capacity water adsorption. We systematically investigated water adsorption behavior of hierarchically porous NaY (HP–NaY) samples and studied the influence of their distinct metal exchange analogues on water affinity and total adsorption capacity. The water affinity and water uptake increased for the HP-NaY samples compared to conventional NaY. HP-NaY samples demonstrating a high water adsorption capacity (17.32–17.98 mmol/g) at 303 K and 0.7 relative pressure (P/Po) when compared to commercial zeolite-Y (CBV-400, 14.83 mmol/g). A further improvement in water uptake was attained by introduction of distinct metal ions into the hierarchical porous zeolite-Y. HP-LiY exhibited the highest water adsorption capacity (19.08 mmol/g at 0.7 P/Po) amounting to 28% and 15% improvement when compared to CBV-400 and CBV-Li respectively. The observed improvements in water adsorption capacity are attributed to (i) the existence of interconnected micro-mesoporous channel network and higher total pore volume and (ii) the enhancement in accessibility of adsorption sites by H2O molecules. The adsorption data of the samples were also fitted using various adsorption models. Hierarchically porous zeolites displayed site heterogeneity, the latter being rendered by the existence of varying chemical environments between sites within the micropores and the mesopores and the nature of the host metals.