Adsorptive removal of cationic methylene blue dye by kappa-carrageenan/poly(glycidyl methacrylate) hydrogel beads: Preparation and characterization

Abstract

Kappa-carrageenan hydrogel containing numerous functional groups used as an environmental-friendly adsorbent shows limitations due to its high water solubility, low gel strength and low regeneration ability. In this work, a new biopolymeric-based hydrogel of κ-carrageenan/poly(glycidyl methacrylate) (CG/PG) was prepared for adsorptive removal of cationic methylene blue (MB) as a toxic dye model. The physicochemical properties and morphology of the hydrogel beads were characterized by swelling test, FT-IR, TGA and SEM. Parameters affecting the adsorption of MB from aqueous solution such as CG/PG ratios, initial dye concentration, solution pH, time, adsorbent dosage and solution temperature were investigated in a batch system. Incorporation of PG with reactive function groups into the CG matrix was proven to enhance the adsorption capacity and stability of the hydrogel required for the application of adsorbent as compared to the pristine CG biopolymer. The experimental adsorption followed pseudo-second order model and well fitted with Langmuir isotherm, with maximum MB adsorption of 166.62 mg g−1. Thermodynamic parameters indicated that the process was spontaneous and exothermic. The beads could be easily regenerated after washing with ethanol and reused for at least five adsorption-desorption cycles with high efficiency. The fabrication of CG/PG hydrogel beads provided a feasible strategy for the design and modification of bio-based polymers in the field of wastewater treatment.