Composite exopolysaccharide-based hydrogels extracted from Nostoc commune V. as scavengers of soluble methylene blue

The industrial water contamination with synthetic dyes is currently a cause for concern. This paper introduces composite hydrogels as alternative scavengers of soluble dyes. This research used kinetic models and adsorption isotherms to test composite exopolysaccharide hydrogels extracted from Nostoc commune V., pectin, and starch for their ability to remove methylene blue from water. The exopolysaccharides demonstrated a rather low extraction yield and a crystallinity percentage of 38.21%. However, the crystallinity increased in the composite hydrogels (48.95%) with heterogeneous surface. The pseudo-second-order kinetic model served to explain the adsorption mechanism at pH 8 and pH 11, while the Elovich model explained the adsorption mechanism at pH 5. When in acid fluid, the hydrogels had a heterogeneous surface, whereas alkaline fluid resulted in a homogeneous surface. The Temkin adsorption model showed a good fit in the treatments. At a basic pH value, composite exopolysaccharide-based hydrogels showed good results as scavengers of low-concentration methylene blue.