Collagen-CMC xerogels for methylene blue adsorption: kinetic and thermodynamic parameters

Collagen-carboxymethylcellulose (CMC) xerogels were obtained by drying the corresponding hydrogels at an environmental temperature, which were synthesized through the microemulsion method. The mass percentage of carboxymethylcellulose to collagen was varied (X=0, 8.3, 16.6, and 33.3 % m). The physicochemical characterization demonstrated the crosslinking between collagen’s amine groups with the hydroxyl group of the carboxymethylcellulose (ATR-FTIR), which is confirmed by the presence of fibrillar structures embedded on flat surfaces (SEM), whose amorphous crystalline structure is incremented with the CMC amount (WAXS). The methylene blue (MB) adsorption experiments data are better adjusted to Natarajan and Khalaf equation which is indicative of adsorption kinetics of first order. In addition, the adsorption data was adjusted to the Langmuir isotherm, the RL parameter range from 0 to 1, which is indicative of a favorable adsorption. The Gibbs free energy was positive which is in line with an irreversible (ΔS>0) and endothermic process (ΔH>0). Interestingly, when the adsorption temperature is incremented (50º C) the RL parameter ranges from 0 to 1, a characteristic of an irreversible adsorption, which implies a chemisorption of methylene blue on the xerogel surface favored by temperature instead of a physisorption process when a low temperature (30ºC) is applied.