Effective adsorptive removal of a cationic dye from aqueous solutions using a biosorbent derived from Sargassum sp

The present research evaluated the potential use of the macroalga Sargassum sp., which was modified with filamentous fungus Cunninghamella echinulata for the biosorption of methylene blue (MB) dye. The modified fungal biomass (FER_sarg) was obtained through solid-state fermentation of enzyme (alginate lyase). The FER_sarg showed a pH_PZC of 7.9, a low mass loss, material micro/ mesoporous, and the presence of hydroxyl, carboxylic, phenolic, and carbonyl functional groups. The influence of biomass dosage, solution pH, contact time, initial concentration, and temperature were evaluated for MB biosorption, and the best results were obtained at 2 g L^-1 and pH 6. The kinetic study revealed a better fit for the pseudo-second-order model, while the Sips model best described the equilibrium experimental data. The equilibrium was reached within 180 min and showed q_max yielding of 115.49 mg g^-1 at 323 K. The thermodynamic understanding of the present research revealed that the biosorbent exhibited spontaneous, exothermic, and physical nature for MB removal. The adsorptive mechanism shows that the process was controlled by electrostatic attraction. Also the feasibility of using residual fermented biomass as a potential adsorbent was applied and discussed, contributing to the concept of minimum waste generation, and supporting the concept of circular bioeconomy.