Effect of calcination atmosphere on TiO2 photocatalysis in hydrogen production from methanol/water solution

TiO2 photocatalysts were synthesized by a sol–gel process followed by calcination at 400 °C in Ar, air, N2, H2 (3% in N2) and vacuum (∼5×10−3 torr), respectively. Toward H2 production from a water/methanol (vol. ratio=1.4/1) solution, the catalysts exhibited activities in the order, according to calcination atmosphere, of Ar>air>N2>vacuum∼H2. The low activity resulting from either vacuum or H2 calcination was ascribed to a reduced coverage of surface hydroxyl and high bulk defect density, based on the X-ray photoelectron and UV-Vis spectroscopic analyses, while the high activity from Ar calcination is to enhanced visible-light excitation.