Valorization of red crab shell waste into chitosan films for enhanced Reactive Black 5 adsorption

T his study explores the preparation and application of chitosan/glycerol films for the removal of Reactive Black 5 (RB5) textile dye from aqueous solutions. Chitosan, derived from red crab shells (Chaceon notialis) and exhibiting a high deacetylation degree (around 97%) and a molar mass of 125 kDa, was used to produce films via the casting method. These films demonstrated low solubility in distilled water (approximately 20% after 24 h) and tunable mechanical properties, with tensile strength ranging from 10.58 to 42.15 MPa (inversely proportional to plasticizer content) and elongation at break from 2.94 to 43.05% (directly proportional to chitosan concentration). Adsorption studies revealed a maximum adsorption capacity of 389.47 mg.g^-1, with the Langmuir isotherm (R² > 0.94; adj-R² > 0.88) best describing the equilibrium data. Kinetic analysis, specifically with the pseudo-first-order model (R² > 0.99), indicated that the film reaches 74.8% saturation after 2 h of adsorption. Furthermore, thermodynamic investigations demonstrated that the adsorption process is spontaneous and favorable across the studied temperature range (298 to 318 K), with Gibbs free energy (ΔG) values ranging from - 22.86 to - 23.97 kJ.mol^-1.