Sustainable Preparation of CaO–Carica papaya Seed Oil Nanocomposite from Agro-Wastes and Its Insecticidal Activity against Callosobruchus maculatus

Abstract

This study investigated the sustainable preparation of a calcium oxide–Carica papaya seed oil nanocomposite (CaONC) from chicken eggshell and pawpaw seed wastes and evaluated its insecticidal activity against Callosobruchus maculatus. Calcium oxide nanoparticles (CaONPs) were produced from eggshells by calcination, hydration and thermal dehydration, while C. papaya seed oil (CP) was extracted by Soxhlet extraction and incorporated onto CaONPs through solvent-assisted adsorption. GC–MS revealed fatty acids including myristic, palmitic, palmitoleic, linoleic, oleic and stearic acids, together with squalene. FTIR, XRD, SEM–EDX and TGA confirmed the crystalline CaO phase, aggregated morphology and successful incorporation of the organic oil fraction into CaONC. EDX showed 29.55 at.% carbon in CaONC compared with no detectable carbon in CaONPs, while TGA showed higher mass loss for CaONC (62.50%) than CaONPs (48.30%). Insecticidal assays demonstrated concentration- and time-dependent activity, with CaONC showing the highest efficacy. After 72 h, maximum mortality reached 87.00% for CaONC, compared with 63.33% for CP and 21.93% for CaONPs. CaONC also exhibited the lowest LC₅₀ (7.77 mg/mL) and LC₉₀ (17.41 mg/mL), indicating enhanced pesticidal performance and potential for sustainable stored-grain protection. These findings demonstrate a promising waste-valorization strategy that combines mineral and botanical components in a bio-based formulation for cowpea weevil management.