Valorization of cactus cladode wastes and chitin nanowhiskers in biocomposite designed for sorption of new methylene blue

Unconventional adsorbents based on biodegradable matrices are affordable and promote a circular economy. These materials can remove colorings and color-fixing compounds in the textile industry, whose environmental impact is associated with other pollutants and the large volume of effluents produced. The new methylene blue is used in the pharmaceutical, cosmetics, and textile industries. It can also be a model molecule of organic contaminants due to its proven higher ecotoxicity than conventional methylene blue. The present study analyzed the adsorption capacity of new methylene blue utilizing the composite of cactus cladode wastes and chitin nanowhiskers. The ratio of biopolymers in the composite, dose, and pH of the adsorption media were significant factors in the dye removal. Based on swelling, pzc, pka distribution, adsorption capacity, and removal efficiency of composites, further work was carried out with the composite cactus and chitin (3:1), CNCh_50. This composite displayed hydrogel-like behavior (464% of swelling in new methylene blue solution (1 mM)) and polyanionic nature, producing affinity for the dye with adsorption capacities of 65–350 mg/g. The dose did not significantly affect the composites' swelling; only pH significantly influenced adsorption. The composites could remove more than 80% of the dye at neutral to alkaline conditions.