Green Synthesis of CuO Nanoparticles—Structural, Morphological, and Dielectric Characterization

Abstract

This study investigates the structural, chemical, and morphological properties of CuO nanoparticles synthesized via a green synthesis route using <i>Opuntia ficus</i>-<i>indica</i> cladode extract, with a focus on the effects of stepwise versus direct calcination. Raman spectroscopy revealed the presence of CuO, Na₂CO₃, and Na₂SO₃, with the latter two being associated with elements inherited from the cactus extracts. XRD patterns confirmed the presence of crystalline CuO and Na₂CO₃ phases, with the low content of Na₂SO₃ inferred to be amorphous. Rietveld refinement estimated a CuO content of approximately 77% in the stepwise-calcined sample and 75% in the directly calcined sample, with lattice parameters closely aligning with reference values. SEM micrographs revealed a tendency for CuO nanoparticles to aggregate, likely due to high surface energy and interaction with the viscous plant extract used in the green synthesis. Crystallite size estimates, along with morphological observations, suggest that stepwise calcination enhances crystallinity and particle definition without altering the fundamental nanoparticle morphology. These findings highlight the influence of calcination method and natural extracts on the composition and morphology of green-synthesized CuO nanoparticles, offering insights into potential applications, namely in microelectronics, due to their promising dielectric properties.