Quantum and Experimental Studies on the Adsorption Efficiency of Oyster Shells Based CaO Nanoparticles (CaONPO) Toward the Removal of MethyleneBlue Dye (MBD) from Aqueous Solution

Abstract

The significance of nanoparticles in environmental remediation of water pollution is attributed to their exceptional properties such as thermal stability, particle size, porosity, surface area and other properties. In this study, oyster shells were used as a precursor to synthesized CaO nanoparticles due to their high CaCO3 content. Sol gel method was employed. The synthesized nanoparticles exhibited strong thermal stability beyond 900 °C and exhibited \({}_{max}\), BET surface area, BET volume and mesoporous pore dimension of 281 nm, 10.395 m2/g, 369.30 m3 and 2.88 nm respectively. The Langmuir maximum adsorption capacity was 3333.33 mg/g and the adsorption process showed strong dependence on the period of contact, temperature, pH, initial concentration of the dye and ionic strength. The adsorption of the dye best fitted pseudo second order kinetic with boundary layer diffusion being the rate-limiting step. Perfect fitness was also observed for the Langmuir adsorption isotherm while two and three-parameters isotherms such as Redlich Peterson and Sipps were also useful in describing the adsorption behaviour of the dye. Based on the evaluated free energy of adsorption and adsorption energies, the mechanism of physical adsorption was proposed. Theoretical parameters derived from quantum chemical calculations indicated strong agreement with experimental values. The adsorbent can be re-used after washing and recalcination.