Adsorption of a cationic dye, methylene blue, on to chitosan hydrogel beads generated by anionic surfactant gelation.

Chitosan hydrogel beads (CSB) formed by sodium dodecyl sulphate (SDS) gelation were used for the removal of a cationic dye, methylene blue (MB), from aqueous solutions. The adsorption capacity of chitosan beads (CB) formed by alkali gelation was low because of charge repulsions between the chitosan (CS) and the MB. The adsorption capacity of CSB (4 g/L SDS gelation) for MB (100 mg/L) was 129.44 mg/g, and it decreased significantly with increasing SDS concentration during gelation. This decrease was a result of increased density of the CSB membrane materials. The CSB membrane materials formed with the 4 g/L SDS gelation showed the highest volumetric adsorption capacity. The MB adsorption on to CB and CSB increased with increasing values for the initial pH of solution. Data from both CB and CSB showed good fit to Sips isotherm models, and the maximum adsorption capacity of CSB (226.24 mg/g) was higher than that of CB (99.01 mg/g).