Application of periwinkle shell for the synthesis of calcium oxide nanoparticles and in the remediation of Pb2+-contaminated water

Abstract

The recovery of CaCO3 from periwinkle shells as a precursor for the synthesis of CaO nanoparticles is validated in this work. The sol-gel synthesized CaO nanoparticles were characterized by XRD, FT-IR, UV visible spectrophotometer, SEM, BET and ICP instrumentation. Information obtained from the characterization showed that the material has a band gap of 4.12 eV, porosity in the mesoporous range (average pore size of 3.02 nm), crystalline size of 18 nm, BET surface area and pore volume of 220.11 m 2 /g and 8.43 cc/g respectively. The application of the nanoparticles for the separation of lead (II) from aqueous solution yielded results that indicated a strong dependency of the adsorption efficiency on decreasing temperature but increasing pH (up to 6.5), initial concentration of Pb 2+ , adsorbent dosage and period of contact.The interaction of concentration, time, temperature and adsorbent dosage indicated that optimum efficiency greater than 80% can be obtained at a temperature of 318 K, concentration of 250 ppm, an adsorbent dosage of 0.5 g and contact period of 75 minutes. Enhanced removal capacities (reaching almost 100% efficiency) were obtained under UV-activated adsorption experiments. The adsorbent showed an excellent ability to favourably adjust the pH, dissolved oxygen, alkalinity and conductivity of the contaminated water. It also displayed an appreciable tendency towards reusability and the total recovery of the adsorbed heavy metal ions from its surface. The pseudofirst-order kinetic, liquid film diffusion, Freundlich, Halsey and Elovich adsorption isotherms best fitted the adsorption process and confirmed the multimolecular adsorption layer with physical adsorption profile. Also, the adsorption of the heavy metal ions is limited by liquid film diffusion and supported surface heterogeneity and physical adsorption mechanism.