Biogenic Synthesis of Titanium Dioxide Nanoparticles Using Plant Extracts: Mechanistic Insights and Photocatalytic Therapeutic Applications

Titanium dioxide (TiO₂) nanoparticles have emerged as the most photocatalytically active metal oxide in nanomedicine, yet their biogenic synthesis via plant extracts remains significantly under-studied compared to zinc oxide nanoparticles. This review presents a mechanistic analysis of TiO₂ green synthesis, focusing on how phytochemical composition governs particle nucleation, phase selection between anatase and rutile polymorphs, and ultimate bioactivity. The central argument is that TiO₂’s photodynamic therapy (PDT) potential is unmatched among metal oxide nanoparticles: its band gap of 3.0–3.2 eV enables the generation of singlet oxygen (¹O₂), hydroxyl radicals (•OH), and superoxide anions (O₂•⁻) under UV and visible light, enabling targeted destruction of cancer cells and pathogens. We systematically review antimicrobial, anticancer, anti-inflammatory, and wound healing applications of biogenic TiO₂, compare the synthesis challenges inherent to TiO₂ relative to ZnO, critically evaluate the current toxicity profile and limitations for clinical translation, and introduce new perspectives on doping strategies, combination therapies, environmental remediation, and regulatory pathways..