Brookite-phase TiO₂ synthesized by Spinacia oleracea: structure, photocatalytic activity and light-enhanced antimicrobial efficacy

Brookite-phase TiO₂ nanoparticles were synthesized via a green route using Spinacia oleracea leaf extract and TiOSO₄ as the precursor, and characterized by XRD, FESEM-EDX, FTIR, and UV-Vis/DRS analyses. The nanoparticles displayed a spherical morphology with sizes of 5-12 nm. Photocatalytic tests showed that approximately 50% of methylene blue was degraded within 3 h under UV light and 5 h under visible light. Antibacterial assays revealed minimum inhibitory concentrations (MICs) of 1 mg/mL for Escherichia coli (E. coli) and 2 mg/mL for Staphylococcus aureus (S. aureus) in dark conditions, pointing to higher susceptibility of Gram-negative bacteria. Under blue light irradiation, the MIC values decreased to 0.5 and 1 mg/mL, respectively, while bactericidal effects were observed at 0.5 and 2 mg/mL for the same strains. SEM observations confirmed severe bacterial membrane damage, highlighting the role of photocatalytic reactive oxygen species in bacterial inactivation.