Superior adsorptive removal of brilliant green and phenol red dyes mixture by CaO nanoparticles extracted from egg shells

Calcium oxide (CaO) is an up-and-coming adsorbent, effectively accessible and extractable from natural resources. In this paper, the extraction and characterization of CaO extracted from eggshells and its adsorption efficiency is compared to commercially available CaO. The extracted CaO from egg shells was characterized for average hydrodynamic size through DLS, surface area (BET) (92 m 2 g −1 ), X-Ray Diffractometer (XRD), surface morphological studies (SEM), High Resolution TEM (HRTEM), electro-kinetic factor (zeta potential) and adsorption studies. The lattice strain and crystallite size for annealed (900 °C) nanospheres were assessed by W–H analysis from powder XRD data and the outcomes were found to be in good agreement with TEM results (40–50 nm). The current work reports the capability of CaO nanospheres towards removal of cationic (Brilliant Green) and anionic (Phenol Red) dye individually and their binary mixture as compared to monetarily CaO. Adsorption studies in binary system displayed that the extracted CaO showed higher adsorption (98%) of Brilliant Green (BG) than Phenol Red (PR) which is 78%, where strong electrostatic interactions played a significant role. The adsorption performance was evaluated in terms of Chemical Oxygen Demand (COD) that exhibited reduction up to 90.6% and followed Langmuir adsorption isotherm. Further, the catalysts’ reusability study was taken in pellet form so that it can be separated effortlessly from the reaction mixture. Graphic abstract Calcium oxide (CaO) nanospheres (40–50 nm) extracted from waste egg shells exhibited a better surface structural and electro-kinetic properties and efficiently adsorbed cationic and anionic dye separately, and in their binary mixture than commercial CaO. This reaction system was found to be capable in reducing the concentration of COD upto 90.6% during brilliant green and phenol red dye removal through Langmuir type adsorption.