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

Thermal treatment in H₂-bearing atmospheres is widely used to introduce oxygen vacancies (O_V) both on the surface and within the bulk of TiO₂. 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 TiO₂ nanosheets (TiNSs) via controlled thermal reduction at 200 °C under varying Ar/H₂ 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/H₂ for 1 h exhibited the highest Ti³⁺ content, with an EPR-determined spin concentration of 2.21 × 10¹⁷ spins/mole, significantly reducing charge transfer resistance. This optimized sample achieved an H₂ 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 TiO₂′s defect landscape, paving the way toward the rational design of next-generation photocatalysts for green hydrogen production.