Phytogenic cobalt nanoparticles from Cyperus scariosus : a promising antibacterial and antioxidant nanotherapeutic platform and as a photocatalytic agent

This study investigates the green synthesis of cobalt nanoparticles (CoNPs) using Cyperus scariosus root extract and evaluates their photocatalytic, antibacterial, and antioxidant properties. CoNPs were synthesized by reacting cobalt nitrate with the plant extract and characterized using UV–Vis spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). UV–Vis analysis showed a surface plasmon resonance peak at 270 nm, confirming nanoparticle formation. XRD revealed a face-centered cubic (FCC) crystalline structure with an average crystallite size of 18.9 nm, while TEM confirmed spherical particles ranging from 3.21 ± 0.71 nm. The photocatalytic activity of CoNPs was assessed against methylene blue dye under UV light, achieving 98% degradation within 40 min. Kinetic analysis indicated a first-order reaction with a rate constant of 0.12 min−1. Antibacterial studies using the disk diffusion method showed inhibition zones of 32 mm against Listeria monocytogenes and 30.5 mm against Escherichia coli. MIC values were 64 ± 1.2 µg/mL for L. monocytogenes and 32 ± 1.0 µg/mL for Bordetella bronchiseptica. Antioxidant assays demonstrated strong activity, with a DPPH IC50 of 12.6 µg/mL and a FRAP value of 123.6 µmol Fe2+/g, highlighting the potential of CoNPs for environmental and biomedical applications.