Synthesis of a 3D chitosan/cellulose acetate hydrogel: comparative impact of drying techniques on morphology for sustainable wastewater treatment

Abstract

Abstract Towards achieving the sustainable development goals, this work contributes to long-term improvements in water and sanitation infrastructure by developing new adsorbents from two naturally based polymers. To address this issue, a novel 3D chitosan/cellulose acetate hydrogel (CCA-HG), crosslinked with minimal glutaraldehyde, was synthesized and dried using two drying techniques: freeze-drying (CCA-HG F ) and air-drying (CCA-HG A ). The impact of the two drying techniques affected the adsorptive efficiency of the two products towards hazardous anionic textile dye. Both hydrogels were comprehensively characterized by FTIR, SEM, XPS, XRD, BET, and swelling capacity, confirming successful crosslinking and distinct morphologies. However, CCA-HG F showed a softer, more porous texture with greater surface area and swelling capacity than CCA-HG A . Applying the batch method indicated that the freeze-drying method produced a better and more efficient adsorbent since CCA-HG F achieved an adsorption capacity of 149.30 mg/g and 99.53% efficiency within 75 min, whereas CCA-HG A demonstrated 20.50 mg/g, 98.44% in 90 min. Adsorption followed a pseudo-second-order model and reached equilibrium within 75–90 min. Isothermal and thermodynamic studies indicated a spontaneous, exothermic, hybrid physical-chemical process. Both hydrogels maintained excellent reusability over five adsorption-desorption cycles. Complementary computational calculations; DFT and molecular dynamics simulations revealed a reduced energy gap (4.055 to 2.476 eV), enhanced charge transfer, and strong non-covalent interactions (–24.544 to − 22.312 Kcal/mol), upon adsorption. To the best of our knowledge, this study establishes freeze-drying as a key strategy for fabricating highly porous, high-capacity biopolymer adsorbents, bridging a crucial gap between sustainable material synthesis and high-performance application.