Synthesis and characterization of lambda-Carrageenan/PAA/Alginate polymeric composite adsorbent for enhanced removal of toxic metals from aqueous environments

The development of sustainable and efficient adsorbents is required due to the contamination of aqueous environments by toxic heavy metals. A novel alginate/polyacrylic acid/λ-carrageenan (poly-AG/PAA/λ-CAR) ternary composite was synthesized and characterized in this study to improve the removal of Cr(IV), Co(II), and Cd(II) from aqueous solutions. Comprehensive characterizations, including FT-IR spectroscopy, swelling behavior analysis, and SEM morphological examination, were conducted to evaluate the structural and physicochemical properties of the synthesized polymeric system and their influence on its heavy metal adsorption capacity. The composite exhibited exceptional adsorption performance, with maximum Langmuir capacities of 105.15, 117.10, and 100.70 mg g⁻¹ for Cr(IV), Co(II), and Cd(II), respectively. Adsorption followed pseudo-second-order kinetics (R² > 0.99), confirming chemisorption as the predominant mechanism. Equilibrium was achieved within 60 minutes, with optimal removal at pH 3--7. The process was well-described by the Freundlich isotherm (R² = 0.92--0.99), indicating multilayer adsorption, while Temkin model analysis revealed strong adsorbate-adsorbent interactions (binding energy = 33.79-42.51 kJ mol⁻¹). A Freundlich isotherm fitting demonstrated multilayer adsorption behavior (R2 = 0.92–0.99). The results emphasize the collaborative efforts of the carboxyl functions of alginate, the sulfate groups of λ-carrageenan, and the mechanical resilience of PAA in establishing this composite as a viable alternative for the treatment of industrial effluent.