Green synthesis and calcination effects of Ocimum lamifolium leaf-derived CuO microstructure for efficient methylene blue degradation

The increasing discharge of synthetic dyes into water bodies has become a major environmental concern due to their persistence, toxicity, and resistance to conventional wastewater treatment processes. Therefore, the development of efficient and environmentally sustainable photocatalysts for the degradation of dye pollutants is highly desirable. CuO microstructure were prepared through an environmentally friendly and economical green synthesis approach utilizing Ocimum lamiifolium leaf extract as both a reducing and capping agent. Phytochemical analysis revealed the presence of various bioactive constituents, which played a significant role in the formation and stabilization of the nanoparticles. Characterization of CuO structures was performed using XRD, UV-Vis, FTIR, and SEM. XRD results confirmed a monoclinic crystalline phase with an average crystallite size of 21.5 nm, a specific surface area of 44.3 m 2 g −1 , and a crystallinity of 83.4%. The UV-Vis spectrum displayed an absorption edge around 380 nm, corresponding to direct band gap energy in the range of 1.9–3.8 eV. FTIR analysis identified characteristic Cu–O stretching vibrations near 580 cm −1 . SEM micrographs showed particles with irregular morphology. The photocatalytic performance of the CuO NPs was assessed by monitoring the degradation of methylene blue under visible light exposure. The sample calcined at 300 °C demonstrated the highest removal efficiency of 85.4% after 120 min of irradiation. The degradation process followed pseudo-first-order reaction kinetics with a rate constant of 0.0165 min −1 . Additionally, the catalyst maintained good reusability, showing only a 3.5% reduction in efficiency after four consecutive cycles, highlighting its suitability for wastewater remediation applications.