Influence of Biopolymer Composition on Swelling Behavior and Crystal Violet Adsorption of Xanthan Gum–Alginate Hydrogel Beads

Crystal violet (CV) is a persistent synthetic dye that must be effectively removed from contaminated water. This study investigated how biopolymer composition affects the swelling behavior and equilibrium CV adsorption of xanthan gum–alginate hydrogel beads containing either chitosan (XAC) or guar gum (XAG). The beads were prepared by Ca²⁺-mediated ionic gelation and characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and swelling analysis at different pH values. XAG demonstrated a higher degree of swelling at a pH of 2. Conversely, XAC exhibited a greater degree of swelling at pH 6.8 and 13. Equilibrium adsorption was evaluated using 30 milligrams of dried beads in 5 mL of CV solution at initial concentrations ranging from 10-1,000 mg/mL. This was followed by 2 h of shaking and 22 h of static equilibration at room temperature. XAC demonstrated more consistent adsorption behavior, with Langmuir Qmax values ranging from 0.87-1.0437 mg/g and R² > 0.99 across three replicates. In contrast, XAG exhibited highly variable Langmuir Qmax values (0.2436–99.97 mg/g), indicating unstable parameter estimation despite high R² values, while the Freundlich model provided more consistent fitting. These findings demonstrate that differences in ternary biopolymer composition substantially affect the swelling and adsorption behavior of xanthan gum–alginate hydrogel beads. The findings provide a comparative framework for understanding how polysaccharide composition influences the performance and consistency of simple hydrogel bead adsorbents for CV-contaminated water, while further studies are needed to establish their cost-effectiveness, scalability, and practical applicability.