Ti³⁺ Self-Doped Black TiO₂ Nanotubes with Mesoporous Nanosheet Architecture as Efficient Solar-Driven Hydrogen Evolution Photocatalysts

Abstract

Ti3+ self-doped black TiO2 nanotubes (TDBTNs) with mesoporous nanosheet architecture have been successfully synthesized by solvothermal method combined with ethylenediamine encircling strategy to protect mesoporous frameworks, then calcined at 600 °C under hydrogen atmosphere. In this case, ethylenediamine molecules play important roles on maintaining the mesoporous networks and inhibiting the phase transformation from anatase-torutile effectively. The as-prepared TDBTNs with mesoporous nanosheet architecture possess a relatively high specific surface area of ∼95 m2 g–1 and an average pore size of ∼15.6 nm. The reduced bandgap of ∼2.87 eV extends the photoresponse from ultroviolet to visible light region due to the Ti3+ self-doping. The solar-driven photocatalytic hydrogen evolution rate for TDBTNs is approximately 3.95 mmol h–1 g–1, which is much better (about four times) than that of the pristine one (∼0.94 mmol h–1 g–1). This improvement is attributed to the reduced bandgap increasing the utilization ratio of solar energy, the formed Ti3+ enhancing separation efficiency of photogenerated charge carriers, and the special one-dimensional mesoporous architecture offering more surface active sites.