Biogenic CuO nanoparticles from Azadirachta indica and Kalanchoe pinnata: Synthesis, characterization, and antibacterial activity

This paper is on the preparation of copper oxide nanoparticles (CuONPs) by the use of Azadirachta indica and Kalanchoe pinnata extract. UV-Vis spectroscopy revealed the formation of the nanoparticles due to a typical absorbance at 230–360 nm, and with a bandgap constituting 5.35 eV, indicating a nanoscale impact and phytochemical stability. FTIR analysis identified CuO stretching bands and hydroxyl, carbonyl and aromatic signals of the plant metabolites which helped in the stabilization of the nanoparticles and ensured that they did not clump together. FESEM and TEM revealed morphology of porous, agglomerated and heterogeneous structures with a particle size of 5–40 nm being the most common. EDX established that the composition is dominated by copper and oxygen and some bio-organic remnants are insignificant. The distribution of the particle size showed that it was polydisperse although the majority of the particles are in the nanoscale. XRD revealed that the material is crystalline-amorphous composite, which is observed in the sharp diffraction peaks on a broad background. The thermal analysis (TGA/DSC) revealed that the biogenic CuONPs had a multi-step weight loss of approximately 42 amongst dehydration and organic residues, which suggests the moderate thermal stability of the biogenic CuONPs. The synthesized nanoparticles were tested based on their antibacterial activity on Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) bacteria. The CuONPs inhibited both strains with inhibition rates of 99.99 and this is quite impressive and indicates that they are active against most bacteria. The enhanced antibacterial efficacy is explained by the reduced size of the nanoparticles and rapid release of ion as well as strong binding to a bacterial DNA and enzymes. This can easily be attributed to plant-based functional groups which include polyphenols and carboxylic acids. In the study, plant synthesis is highlighted as helping to create a sustainable method of synthesizing CuONPs with beneficial structural, biological, and antibacterial characteristics. The findings show that CuONPs can be used as antibacterial agents within medicine and environment.