Phytochemical-Mediated Structural and Defect Engineering of TiO ₂ Nanoparticles for Light-Activated Photocatalysis

This study reports a phytochemical-driven green synthesis of TiO2 nanoparticles using aqueous extracts of Stryphnodendron adstringens and Origanum vulgare, establishing a sustainable route for engineering light-responsive functional nanomaterials. Distinct plant matrices actively governed nanoparticle nucleation, surface chemistry, crystallinity, and defect density, as evidenced by FTIR, Raman spectroscopy, XRD, and Williamson–Hall analysis. The synthesized nanoparticles exhibited a predominantly anatase phase, uniform spherical morphology, and crystallite sizes in the 40–60 nm range. Structural analyses revealed that extract composition and precursor concentration directly modulated lattice strain and dislocation density, enabling controlled defect engineering. Photocatalytic assays demonstrated efficient methylene blue degradation, with TiO2 synthesized using S. adstringens at lower precursor concentrations achieving the highest efficiency (53%), highlighting the role of phytochemical–oxide interactions in enhancing charge separation and ROS generation. Microbiological assays conducted in the absence of light showed no biocidal activity, confirming that TiO2 does not act as a passive antimicrobial agent. Instead, its functionality is intrinsically light-triggered, arising from photocatalytically generated reactive oxygen species. Overall, this work advances the current literature by demonstrating how medicinal plant phytochemistry can be harnessed to simultaneously control structure, defects, and stimulus-responsive functionality in green-synthesized TiO2 nanomaterials.