Ball Mill–assisted Preparation of Nano-CaCO3 as a Novel and Green Catalyst–based Eggshell Waste

Ball mill–assisted preparation of nano-bio Calcite (CaCO3) based on avian shell and its application as a novel, biodegradable, and heterogeneous catalyst with high catalytic activity and reusability in the green and high efficient synthesis of pyrano[4,3- b]pyrans via a condensation reaction of different aromatic aldehydes, malononitrile, and 4-hydroxy-6-methyl-2 H-pyran-2-one at 120°C under solvent-free conditions is reported. The reaction proceeds to completion within 5–30 min in 90–98% yield. The nanocatalyst was characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscope (SEM), elemental analysis, and laser particle sizer.