<![CDATA[Textile wastewater containing synthetic dyes is a significant environmental concern due to its high color intensity, toxicity, chemical stability, and resistance to conventional treatment. This work prepared Ti3+ self-doped TiO2 photocatalysts using a simple sol-gel route combined with NaBH4-assisted calcination. The strategy was designed to generate intrinsic lattice defects, mainly Ti3+ centers and oxygen vacancies, in anatase TiO2 without the use of flammable reducing gases or complicated post-synthesis treatments. The influence of calcination temperature was examined by preparing samples at 200, 500, and 600 °C. XRD results showed that the selected samples maintained the anatase TiO2 phase, indicating that the reduction-calcination treatment did not produce detectable secondary crystalline phases. Higher calcination temperature increased the degree of crystallinity, with crystallinity values of 59.1%, 68.2%, and 69.6% for the samples of T-200, T-500, and T-600, respectively. Raman spectra confirmed the anatase framework and revealed features related to lattice disorder in the reduced samples, while EPR analysis directly confirmed Ti3+/oxygen-vacancy defect sites, with the strongest signal observed for T-600. UV-vis DRS demonstrated that the samples calcined at 500 and 600 °C absorbed more strongly in the visible region. The T-600 sample showed an effective band gap of 2.42 eV, evidencing that defect-related states contributed to broader light harvesting. Photocatalytic evaluation indicated that methylene blue degradation improved with increasing calcination temperature, and the best performance was obtained using T-600, with an apparent rate constant of 0.017 min-1. Reusability testing showed that T-600 retained activity for three cycles, although the rate constant decreased to 0.0116 and 0.0089 min-1 in the second and third cycles, respectively. The enhanced activity is attributed to the combined contribution of higher anatase crystallinity, improved visible-light response, and an appropriate concentration of Ti3+-oxygen vacancy sites that support charge separation and reactive oxygen species formation.]]>
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