In this work, the mesoporous-assembled TiO2 nanocrystal photocatalysts were successfully synthesized by a sol-gel process with the aid of urea-glycerol mixtures used as mixed mesopore-controlling agents. The photocatalytic activity of the synthesized mesoporous-assembled TiO2 nanocrystal photocatalysts was investigated for hydrogen production from the water splitting reaction using methanol as a hole scavenger under UV light irradiation. The synthesized TiO2 nanocrystal photocatalysts were systematically characterized by TG-DTA, N-2 adsorption-desorption, SEM, high resolution TEM, and XRD analyses. The characterization results showed that the well-controlled contents of urea and glycerol in a urea-glycerol mixture at 75 mol% urea and 25 mol% glycerol resulted in not only the most highly porous network (i.e. the highest specific surface area and total pore volume, and the smallest mean mesopore diameter), but also the smallest crystallite size of the synthesized TiO2 nanocrystal photocatalyst. The photocatalytic reaction results, hence, revealed a much superior photocatalytic hydrogen production activity of the mesoporous-assembled TiO2 nanocrystal synthesized with 75 mol% urea and 25 mol% glycerol to the other synthesized TiO2 nanocrystals, also being much higher than those of the commercially available P-25 TiO2 and ST-01 TiO2 powders. (C) 2012 Elsevier Ltd. All rights reserved.