Synergistically improved adsorption of anionic surfactant and crystal violet on chitosan hydrogel beads

While a plethora of gel beads have shown to exhibit excellent adsorbent properties, biogel beads are more attractive because of their diverse nature and biocompatibility. To this regard, chitosan hydrogel beads, where ‘synergistic effect’ plays a significant role in the efficiency of adsorption, have shown great promise. The normal adsorption rate of sodium dodecylsulfate (SDS) on chitosan hydrogel beads is greatly enhanced in presence of crystal violet (CV) dye. In such situations, simultaneously enhanced adsorption rate for both the adsorbates (viz., SDS and CV) are observed. This synergistic adsorption on a hydrogel, chitosan is being reported herein, to the best of our knowledge, for the first time. Underlying ionic interaction between the cationic part of the dye and the anionic head group of the surfactant molecule already embedded in the chitosan gel bead makes this synergism possible. The adsorption of SDS on chitosan hydrogel beads is studied in detail. The ionic interaction is manifested in the pseudo-second order kinetics of SDS removal by chitosan beads. In this article, we report our findings of quantitative analyses on SDS adsorption via the study of Langmuir adsorption isotherm (Qmax = 76.9 mg g−1). Desorption studies are performed on chitosan gel beads after simultaneous adsorption of CV and SDS. Interestingly, the gel beads desorb the CV up to ∼47% on long standing, leaving aside SDS in the beads. This authenticates selectivity in the desorption process. In an effort to develop eco-friendly processes implementing ‘zero waste’ management strategies, we find that the dye can be recovered quantitatively from the beads with acetone.

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► Chitosan gel beads are used as adsorbent for anionic surfactant (AS) removal from water.
► The AS removal follows pseudo-second-order kinetics, indicating ionic adsorption.
► Crystal violet adsorption on chitosan beads is more efficient in presence of AS.
► AS adsorption on chitosan beads is faster in presence of CV.