Defect-engineered mixed-phase TiO₂ via aloe vera-assisted photothermal synthesis for enhanced solar photocatalytic degradation of Acid Red-18

A photon-assisted biogenic approach was employed to synthesize defect-engineered TiO₂ nanoparticles using Aloe vera extract as a transient structure-directing precursor. During photothermal treatment and subsequent calcination (700 °C), the organic constituents do not persist as intact phytochemicals but undergo transformation into oxygen-functionalized surface species and defect states within the TiO₂ lattice. X-ray diffraction confirms the formation of mixed-phase anatase–rutile TiO₂, which facilitates interfacial charge separation. UV–visible diffuse reflectance analysis reveals a reduced optical band gap of 2.86 ± 0.05 eV, attributed to defect-induced electronic states rather than quantum confinement. FTIR analysis indicates the presence of surface hydroxyl and oxygen-containing functional groups, while FESEM and BET results confirm nanoscale morphology (50–100 nm) with mesoporous architecture and a specific surface area of 57.37 m² g⁻¹ . The photocatalytic performance was evaluated through the degradation of Acid Red-18 under natural sunlight irradiation, achieving ∼96% removal within 60 min with an apparent rate constant of 0.220 min⁻¹ . Control experiments confirm that the degradation is dominated by photocatalysis rather than adsorption or photolysis. Total organic carbon (TOC) analysis demonstrates ∼95% mineralization, while scavenger studies verify the involvement of reactive oxygen species, including •OH, •O₂⁻, electrons, and holes. The enhanced photocatalytic activity arises from the synergistic effect of defect-induced band gap narrowing, mixed-phase heterojunctions, and improved charge carrier dynamics. This study establishes a structure–defect–performance relationship in Aloe vera-mediated TiO₂ and demonstrates a scalable, dopant-free strategy for efficient solar-driven wastewater remediation