Exploiting Freshwater Mollusk Shell-Based CaO Nanoparticles: Preparation, Characterization, Insecticidal Activity, Antioxidant Potential, and Germination Enhancement in Greengram

The present study utilizes a naturally available biomass waste of freshwater molluscan shells as a source for preparation of biocalcium oxide nanoparticles (CaO NPs) in the management of pulse beetle of Callosobruchus maculatus (C. maculatus) and growth enhancement of agro-morphological characters and antioxidant enzyme level in greengram seeds. The UV-DRS spectrum exhibited a pronounced absorption peak at 267 nm. The stability of the particles was evidenced by a zeta potential of −37.3 mV. FTIR exhibited peaks at 1412 and 868 cm–1 are characteristic of the connection between the oxygen atom of CO32–, Ca, and C–O bonding, which signifies the carbonation of the CaO NPs. The peaks appearing in the 359, 482, and 1089 cm–1 bands of Raman spectra are the presence of calcium oxide. The XRD pattern was obtained and confirmed the polycrystalline nature of the CaO NPs, by a sharp peak and narrow spectrum. The TGA showed a major weight loss (∼43%) of freshwater mollusks’ shell between 695 and ∼800 °C. TEM and FE-SEM micrographs of CaO NPs found a granular morphology with an average size of 54.42 nm, respectively. The insecticidal activity of CaO NPs showed the LD50 and LD90 values of 12.58 and 406.64 mg/100 g of seeds, respectively. The pattern of mortality revealed that CaO NPs at a dose of 400 mg/100 g of seeds expressed 100% mortality on the third day after release of C. maculatus. CaO NPs interacted with C. maculatus by adherence on the body surface of the insect and caused sequential physical toxicity, dehydration, desiccation, and death. The in silico molecular docking studies of CaO with detoxifying enzymes revealed greater affinity and binding energies of −1.4, −1.4, and −1.3 kcal/mol in acetylcholinesterase, cytochrome-c, and glutathione-S-transferase, respectively. Furthermore, CaO NP-treated seeds showed significant enhancement in seed germination, shoot length, root length, seedling length, subroot numbers, and vigor index over deltamethrin and control. Seeds treated with CaO NPs produced more ROS than hydro-primed control, indicating that ROS are crucial for improving seed germination. CaO NPs in the greengram seedlings were confirmed through AAS. Leveraging biomass waste can be used as a novel source for sustainable control of insects and promising tools to enhance greengram seed for higher crop yield and bolstering food security.