Phytochemical-Mediated Structural and Defect Engineering of TiO₂ 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.