Preparation of Carboxymethyl Cellulose-Based Hydrogels for Atmospheric Moisture Adsorption

Abstract

Hygroscopic hydrogels have emerged as promising adsorbents for atmospheric water harvesting owing to their tunable network structures and strong affinity for water. In this study, carboxymethyl cellulose (CMC) hydrogel beads were fabricated using a dual-crosslinking strategy in which covalent bonding with epichlorohydrin (ECH) and ionic interactions with Ca2+ ions in a CaCl2 coagulation bath occurred simultaneously. This approach enabled the in situ incorporation of hygroscopic calcium species, eliminating the need for an additional salt-loading step. The effects of CMC (1–6 wt %), ECH (1–10 wt %), and NaOH (1–6 wt %) concentrations on precursor viscosity, hydrogel yield, bead morphology, calcium distribution, and atmospheric moisture adsorption were systematically evaluated. Precursor viscosity increased with CMC concentration (53–26,114 cP) but decreased with NaOH concentration (11,263–2,344 cP). Atmospheric moisture adsorption increased with relative humidity (RH), reaching 3.0–4.9 g/g at 90% RH. The formulation containing 3 wt % CMC, 5 wt % ECH, and 1 wt % NaOH achieved the highest hydrogel yield and moisture adsorption capacity. Using a custom gravity-driven multi-nozzle bead-dropper, this formulation produced dry hydrogels at a rate of 0.983 kg/h, approximately 1,000 times that of the conventional syringe-pump system, while a lower-viscosity reference formulation further increased throughput to 1.350 kg/h. Collectively, these findings highlight the feasibility of scalable production of biomass-derived hygroscopic hydrogel beads for atmospheric moisture harvesting.