Effect of single and binary mixed surfactant impregnation on the adsorption capabilities of chitosan hydrogel beads toward rhodamine B

Abstract

The adsorption of cationic xanthene dye rhodamine B (RhB) on pure chitosan (CS), single surfactant (SDS, Brij30 and DTAB) and binary surfactant (SDS-Brij30 and DTAB-Brij30) modified chitosan beads has been investigated. While the adsorption capacity of CS/SDS and CS/Brij30 beads was enhanced at all concentrations of SDS (0–4 mM) and Brij30 (0–1 mM), the increase in the concentration of DTAB above 1 mM in CS/DTAB beads reduced the adsorption capacity of the beads significantly. Furthermore, the adsorption studies were carried out in the mixed surfactant impregnated CS beads. The adsorption capacity of CS/SDS-Brij30 beads increased with the increase in the mole fraction of SDS and in CS/DTAB-Brij30 the adsorption capacity increased up to a mole fraction of DTAB = 0.4, beyond which it decreased with a further increase in the DTAB mole fraction. The mixing of surfactants in CS beads had a synergistic effect on the adsorption capability of these beads which is important from an environmental point of view and cost effectiveness in the manufacture of such beads. The equilibrium adsorption data were analyzed using Langmuir, Freundlich, and Temkin adsorption isotherm models. The results showed better agreement with the Langmuir model and hence indicated a homogeneous adsorption process. The maximum Langmuir adsorption capacity of CS and surfactant modified CS follows the order CS < CS/DTAB < CS/DTAB-Brij30 < CS-Brij30 < CS/SDS-Brij30 < CS/SDS. In comparison with the various adsorbents reported in the literature, the SDS and SDS-Brij30 modified CS beads were found to exhibit significantly higher adsorption capacities (≈1000 mg g⁻¹) for the effective removal of Rh B.