Cobalt oxide, a multifunctional, anti-ferromagnetic p-type semiconductor with an optical bandgap of ~2.00 eV, exhibits remarkable catalytic, chemical, optical, magnetic, and electrical properties. In our study, cobalt oxide nanoparticles (Co₃O₄ NPs) were prepared by the green synthesis method using dried fruit extracts of Hyphaene thebaica (doum palm) as a cost-effective reducing and stabilizing agent. Scanning electron microscopy (SEM) depicts stable hollow spherical entities which, consist of interconnected Co₃O₄ NPs, while energy-dispersive X-ray spectroscopy (EDS) indicates the presence of Co and O. The obtained product was identified by X-ray diffraction (XRD) that showed a sharp peak at (220), (311), (222), (400), (511) indicating the high crystallinity of the product. The Raman peaks indicate the Co₃O₄ spinel structure with an average shift of Δν~9 cm⁻¹ (191~470~510~608~675 cm⁻¹). In the Fourier transform infrared spectroscopy (FT-IR) spectrum, the major bands at 3128 cm⁻¹, 1624 cm⁻¹, 1399 cm⁻¹, 667 cm⁻¹, and 577 cm⁻¹ can be attributed to the carbonyl functional groups, amides, and Co₃O₄ NPs, respectively. The photocatalytic activity of the synthesized NPs was evaluated by degrading methylene blue dye under visible light. Approximately 93% degradation was accomplished in the reaction time of 175 min at a catalyst loading of 1 g/L under neutral pH. This study has shown that Co₃O₄ is a promising material for photocatalytic degradation.

In this study holmium oxide nanoparticles (Ho ₂ O ₃ NPs) are fabricated using Hyphaene thebaica extracts as a bioreductant.