Development of xanthan gum-based solid desiccants for the extraction of water vapors from humid air†

Abstract

This research paper reports the synthesis of a super-porous hydrogel of xanthan gum with acrylamide (i.e., XG-SPH) with highly dense interconnected capillary channels and its application as a desiccant material to capture water vapors from humid air. For the generation of the porous structure with interconnected capillary channels, the polymer desiccant was synthesized via gas blowing, foaming and polymerization. The presence of interconnected capillary channels was observed in the scanning electron microscopy (SEM) images. The synthesized desiccant exhibited 0.27 g g⁻¹ adsorption capacity at 50% relative humidity and 25 °C which drastically increased to 1.38 g g⁻¹ at 25 °C and 90% relative humidity which suggested that the hydrophilic nature or the desiccant performance of the synthesized polymer desiccant increased with increasing relative humidity. The main driving force behind this high-water vapor adsorption capacity was the capillary condensation process which facilitated the adsorption or accommodation of more incoming water molecules at higher pressures. The adsorption of water molecules by the capillary condensation mechanism was further supported by the applicability of the type-III adsorption isotherm and the experimental data fitted well with the GAB adsorption isotherm. Moreover, the experimental kinetics data correlated well with the driving force model and indicated that water diffusion within the polymer structure followed a type II diffusion mechanism. The desorption kinetics indicated that the desorption occurred rapidly in the initial desorption stages, and most of the captured water was released within the first hour. Moreover, regenerating XG-SPH was energy efficient as it could be successfully regenerated at 50 °C and used for twenty adsorption–desorption cycles. The desiccant was able to retain almost 70% of its original adsorption capacity in the twentieth adsorption cycle. This suggests that gum polysaccharide-based super-porous hydrogels can extract or capture a considerable amount of water from the atmosphere without using any hygroscopic salt.