Understanding the charge separation and transfer in mesoporous carbonate doped phase-junction TiO2 nanotubes for photocatalytic hydrogen production

Novel mesoporous carbonate-doped phase-junction TiO2 nanotubes were fabricated for the first time by a general simple and cost-effective strategy, namely, olive oil-assisted electrospinning. The as-prepared mesoporous carbonate-doped phase junction TiO2 nanotubes show a high photocatalytic hydrogen evolution activity of 6108 mu mol h(-1) g(-1), which is nearly six times higher than that of the commercially available P25. This outstanding photocatalytic performance originates from the morphology, electronic, crystal and textural structures of the photocatalysts. The refined porous structure can increase the optical path by multiple reflection effect, thus enhancing light harvesting. Particularly, first-principles calculations suggest that doping TiO2 with carbonate can effectively reduce the bandgap of TiO2, thus the absorbance of TiO2 in visible light region can be highly enhanced. Moreover, anatase-rutile phase junctions were elaborately introduced into TiO2 nanotubes by changing the anneal temperature and the roles of phase junctions are studied by photoelectrochemical measurements, which reveal that appropriate phase junction interface can significantly enhance the charge separation and transfer, hence achieving about 2 and 18 times photocurrent density enhancement compared to pristine anatase and rutile phase samples, respectively. Our study not only demonstrates a facile and eco-friendly strategy to synthesize highly efficient porous TiO2-based nanotubes photocatalysts, but also provides a new strategy for rational design and synthesis of advanced photocatalysts by combining the strong synergistic effects of the morphology, electronic, crystal and textural structures.