Comparative Study of Water Vapor Adsorption on Activated Carbons, Styrenic Polymers, and Metal Oxides: Elucidating the Roles of Hydrophilicity and Porosity

The presence of water vapor in industrial gas streams often necessitates energy-intensive dehydration and can hinder the adsorption of target compounds. While various adsorbents are available, a comparative understanding of how surface chemistry and porosity govern their water uptake across different humidity levels is limited and often conflated in existing literature. Unlike prior studies that focus on single material classes, this work establishes a unified framework investigating water vapor adsorption on seven diverse adsorbents. This study systematically investigates water vapor adsorption on seven diverse adsorbents, including activated carbons, styrenic polymers, and metal oxides, to elucidate the roles of hydrophilicity and porosity. Quantitative analysis of sorption isotherms revealed a clear dichotomy: hydrophilic metal oxides (silica gel and Al2O3) dominated adsorption at low relative humidity (RH < 40%) due to polar surface sites. In contrast, at high RH (>60%), textural properties became paramount. Remarkably, the hypercrosslinked polymer V493, despite its hydrophobic nature, achieved the highest capacity at 95% RH (50.35 wt.%), surpassing hydrophilic silica gel (38.06 wt.%). This is attributed to V493’s exceptional micropore volume (0.60 cm3/g), which facilitates capillary condensation. The results demonstrate that adsorbent selection is critically dependent on the operating humidity, with hydrophilicity controlling low-RH performance and microporosity dictating ultimate capacity, providing a vital framework for designing efficient separation and dehumidification processes.