Selective Dye Adsorption and Antimicrobial Performance of Cellulose–Chitosan Hydrogels and Aerogels: Role of Supramolecular Organization

Cellulose and chitosan are biopolymers widely used to prepare composites due to their complementary charges and intrinsic biocompatibility. While they are mainly of interest for medical applications, they are also suitable for water remediation. In their native states both biopolymers are non-porous; however, after dissolution and subsequent regeneration they can form porous structures that are better suited for such applications. In this work, cellulose pulp and chitosan were dissolved in an ionic liquid and regenerated in water at different mass ratios to produce hydrogels and their corresponding aerogels. The materials were structurally characterized and evaluated for dye adsorption and antimicrobial performance. Methylene blue and Congo red were selected as cationic and anionic dyes, respectively. The concentrations went from 5 to 80 mg/L in 24 h batch adsorption experiments. Chitosan-rich and intermediate cellulose–chitosan hydrogels preferentially removed Congo red, reaching 27 ± 1 mg/g and 24 ± 1 mg/g at 80 mg/L, respectively; the fully cellulose hydrogel maximized methylene blue uptake, achieving 23 ± 1 mg/g under the same conditions. SEM and XRD analyses revealed a hybrid architecture in which chitosan coats cellulose fibers and becomes more amorphous, while cellulose preserves crystalline domains that act as a rigid, highly porous backbone. Aerogels derived from freeze-dried hydrogels exhibited high porosity and water uptake, together with broad-spectrum antimicrobial activity, achieving bactericidal levels (≥99.9% inhibition) against Staphylococcus aureus for all compositions and against Escherichia coli for selected cellulose–chitosan ratios. These results demonstrate that cellulose–chitosan hydrogels and aerogels function as multifunctional bio-based materials whose supramolecular organization, surface charge distribution, and porosity can be tuned to balance adsorption selectivity and antimicrobial performance for advanced environmental applications.