Optimizing Synergies: Unraveling the Effect of ZnO Nanoparticle Calcination on in Vitro Antibacterial Potency and Photocatalytic Efficiency of Cephalexin A Study into Kinetics and Isotherms

This study reports the successful green synthesis of ZnO nanoparticles (NPs) utilizing an aqueous leaf extract of Olea europea L. The biogenic ZnO NPs were dreied at 100 °C and calcined at 450 °C. Their nanoscale dimensions were confirmed by UV-visible spectroscopy, scanning electron microscopy (SEM) revealing a size range of 40–60 nm, and X-ray diffraction (XRD) analysis confirming a hexagonal structure for both calcination processes. The ZnO particle size increased from 18.79 nm at 100 °C to 25.04 nm at 450 °C. The successful eco-friendly synthesis of ZnO NPs was further validated by FT-IR spectroscopy, which identified functional groups on the particle surface. Importantly, the ZnO NPs demonstrated remarkable efficiency in degrading Cephalexin, achieving a degradation rate of 95% for ZnO (100 °C) and 98% for ZnO (450 °C).The corresponding rate constants were determined to be 0.0334 min^− 1 and 0.0250 min^− 1, respectively. Treatment with ZnO NPs at varying temperatures (100ºC and 450 ºC) exhibited inhibitory effects on the growth and reproduction of E. coli and S. typhimurium cells. The observed antibacterial activity is attributed to ZnO NPs, with potential mechanisms involving damage to bacterial cell membranes, extrusion of cytoplasmic contents, and the release of antimicrobial ions (Zn²⁺) and reactive oxygen species (ROS). B. cereus and S. aureus cells treated with 200 µg/ml ZnO at different temperatures revealed varying growth patterns, indicating that ZnO non calcined (dried at 100 ºC) exhibited higher growth inhibition potential compared to ZnO (450 ºC).