Green synthesis of ZnO nanoparticles from Lepidium virginicum extract for anticorrosive applications and photocatalytic degradation of methylene blue

Objectives This study aimed to synthesise zinc oxide nanoparticles (ZnO NPs) using Lepidium virginicum leaf extract by using eco-friendly approach and to investigate their physicochemical characteristics, anticorrosion efficiency, photocatalytic degradation, and antioxidant potential. Methods ZnO NPs were synthesized by optimizing the ZnCl₂ concentration, extract-to-precursor ratio, pH, time and temperature. The ZnO NPs were characterized using Fourier-transform infrared spectroscopy (FTIR), UV–visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM–EDX), dynamic light scattering (DLS), high-resolution transmission electron microscopy (HRTEM), and zeta-potential. Their corrosion inhibition performance for mild steel in 0.5 M HCl was evaluated using electrochemical impedance spectroscopy, potentiodynamic polarization (PDP), and gravimetric measurements. Photocatalytic degradation of methylene blue (MB) under visible-light irradiation and antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays were also investigated. Results The optimized synthesis conditions were 0.3 M ZnCl₂, a 3:2 extract-to-precursor ratio, pH 7, 48 h, and 60 °C. XRD confirmed the formation of hexagonal wurtzite ZnO with an average crystallite size of 22.5 nm. HRTEM revealed quasi-spherical particles mainly within the 20–25 nm range, while the DLS Z-average diameter of 479.4 nm indicated partial aggregation. The ZnO NPs exhibited maximum corrosion inhibition efficiencies of 93.79% by EIS, 84.82% by PDP, and 69.80% by gravimetric measurement. MB degradation reached 78.2%, while DPPH and ABTS assays demonstrated concentration-dependent antioxidant activity. Conclusions Lepidium virginicum -mediated ZnO NPs demonstrate promising multifunctional properties for corrosion protection, photocatalytic dye degradation, and antioxidant applications. Further studies addressing stability, mineralization, surface chemistry, and safety are warranted for practical applications.