Optimizing low-temperature defect engineering in TiO2 nanosheets for enhanced photocatalytic water splitting

• Optimized low-temp reduction yields TiO 2 nanosheets rich in oxygen vacancies. • 50 mL/min Ar/H 2 for 1 h produces TiNSs with max Ti 3+ spin density (2.21 × 10 17 spins/mol). • H 2 evolution rate reaches 376.2 μL h −1 g −1 , ∼8 × higher than untreated TiNSs. • DFT shows saturation of mid-gap states beyond 10% oxygen vacancy concentration. Thermal treatment in H 2 -bearing atmospheres is widely used to introduce oxygen vacancies (O V ) both on the surface and within the bulk of TiO 2 . However, the influence of key processing parameters—particularly gas flow rate and exposure time—remains underexplored. In this work, we present a comprehensive study on the defect engineering of TiO 2 nanosheets (TiNSs) via controlled thermal reduction at 200 °C under varying Ar/H 2 flow rates (10–200 mL/min) and durations (0.5–4 h). Structural, electronic, chemical state, and photocatalytic characterizations—including BET, XRD, UV–Vis, EPR, XPS, and electrochemical measurements—reveal a strong correlation between treatment conditions, defect concentration, and photocatalytic performance. TiNSs treated at 50 mL/min Ar/H 2 for 1 h exhibited the highest Ti 3+ content, with an EPR-determined spin concentration of 2.21 × 10 17 spins/mole, significantly reducing charge transfer resistance. This optimized sample achieved an H 2 evolution rate of 376.2 µL h −1 g −1 , approximately 8 times higher than untreated TiNSs. DFT calculations indicate that the optimized sample most likely exhibits saturated mid-gap states. Together, these results shed new light on the critical role of reduction atmosphere dynamics in fine-tuning TiO 2 ′s defect landscape, paving the way toward the rational design of next-generation photocatalysts for green hydrogen production.