Preparation and characterization of a clam shell powder/carrageenan composite for methylene blue adsorption

The valorization of biological by-products into sustainable adsorbents has gained significant attention as an effective approach for waste management and wastewater treatment. A carrageenan/clam shell powder (CSP@Car) composite was developed as a low-cost, environmentally friendly adsorbent with potential for dye removal from wastewater. The composite was successfully prepared and evaluated for its ability to adsorb methylene blue (MB) from aqueous solutions. FT-IR and PXRD analyses confirmed the physical combination of carrageenan (Car) and clam shell powder (CSP), while SEM observations indicated that CSP@Car-1 (CSP : Car = 0.05 : 1, w/w) exhibited the most porous microstructure. Compared to other composites, CSP@Car-1 demonstrated lower moisture content and water solubility, as well as the highest adsorption capacity. Batch adsorption experiments identified optimal conditions at room temperature, with an adsorption time of 2 hours, an adsorbent dosage of 10.0 g L^-1, an initial MB concentration of 80 mg L^-1, and pH approximately 7, resulting in a removal efficiency of 49.7% and an adsorption capacity of 401 mg g^-1. The adsorption process followed the pseudo-second-order kinetic model, and the equilibrium data were best described by the Langmuir isotherm model. Furthermore, CSP@Car-1 maintained adsorption activity after five adsorption-desorption cycles, although adsorption performance gradually decreased with repeated regeneration. These findings indicate that CSP@Car-1 is a promising low-cost and eco-friendly adsorbent for dye removal from wastewater, although further enhancement of its regeneration stability is necessary for practical applications.