ZnO Nanoparticles and CeO ₂ /Ce ₃ Zn ₂₂ /ZnO Nanocomposites Fabricated From <i>Kigelia pinnata</i> Fruit Extract: Their Antibacterial Potential and Humidity Sensing Properties

ABSTRACT Nanomaterials and nanoparticles represent a rapidly expanding technological domain with applications across biomedical, environmental, and industrial sectors. In the present study, zinc oxide nanoparticles (KpZnO NPs) and cerium mixed ZnO nanocomposites were synthesized via a green route using the aqueous fruit extract of Kigelia pinnata . Two nanocomposite formulations were prepared, consisting of 5 mol % cerium with 95 mol % zinc salt (KpCe@ZnO‐5) and 10 mol % cerium with 90 mol % zinc salt (KpCe@ZnO‐10). The phytochemicals of the aqueous extract of fruit played important role in formation and stabilization of nanoparticles. The synthesized nanomaterials were subjected to comparative structural, morphological, and properties analyses, including antibacterial activity evaluation against the pathogenic strains Staphylococcus aureus and Pseudomonas aeruginosa . Comprehensive characterization was performed using UV–visible spectroscopy, FTIR, XRD, SEM, EDS, HRTEM, BET, 1 H NMR, and XPS. Structural analyses using Match software, the Crystallography Open Database (COD), and Chemcraft confirmed the composition and lattice structures (hexagonal, triclinic, and tetragonal) of the synthesized materials. The antibacterial efficacy of KpZnO, KpCe@ZnO‐5, and KpCe@ZnO‐10 was assessed through well diffusion, time‐kill, and biofilm inhibition assays. In addition, the humidity sensing performance of the nanocomposites was evaluated. The results demonstrated that pure KpZnO exhibited superior antibacterial activity compared to the cerium mixed nanocomposites, whereas KpCe@ZnO‐10 showed enhanced humidity sensing performance. Overall, the synthesized nanomaterials offer a cost‐effective and environmentally benign approach for multifunctional applications.