Efficient adsorption of methylene blue on novel triple-nanocomposites of potassium Kappa-carrageenan, calcium alginate and nanohydroxyapatite obtained from sea scallop shells

Abstract

In this work, four nano-solid adsorbents were synthesized namely: nanohydroxyapatite based on sea scallop shells (NHAP), potassium kappa-carrageenan (KG), potassium kappa-carrageenan/nanohydroxyapatite (KPC), and potassium kappa-carrageenan/calcium alginate/nanohydroxyapatite as triple biocomposite (TBC) beads. These fabricated materials were used as solid adsorbents for methylene blue removal from wastewater under different conditions. Based on our experimental results, TBC particles were characterized by higher specific surface area (722.62 m2/g), mesoporosity (pore radius, 3.77 nm), smaller particle size (TEM particle size, 26 nm), the presence of abundant chemical functional groups, thermal stability, and lower swelling ratio (0.3%). TBC exhibited the maximum adsorption capacity (529.1 mg/g) towards methylene blue (MB) with endothermic, spontaneous, favorable, and physical adsorption process as reported by thermodynamic studies. Adsorption of MB fits well Freundlich, Langmuir, Dubinin-Radushkevich, and Temkin adsorption models with correlation coefficients reached about 0.9999. MB adsorption onto all the solid adsorbents shows the good suitability of Elovich and pseudo-second order kinetic models. Desorption investigation proves that hydrochloric acid (1 mol/L) is the most suitable desorbing agent with desorption efficiency that reached about 86%.