Facile preparation of hierarchical TiO2 nano structures: growth mechanism and enhanced photocatalytic H2 production from water splitting using methanol as a sacrificial reagent.

Owing to unique features, hierarchical nanostructure of TiO2 has superior photocatalytic activity. In this work a facile hydrothermal route has been explored to prepare 3D hierarchical TiO2 (3D-HTiO2), 1D/3D hybrid hierarchical TiO2 composite (HHC), and 3D hierarchical protonated titanate microspheres H2Ti2O5·H2O (3DHPTMS) at the expense of free-standing titania nanotube membrane (TiO2-Memb). It proceeded through the formation of peroxotitanium complex, a water-soluble Ti complex as an intermediate. Mechanism of formation, role of membrane crystallinity, and reaction parameters giving fine control on tuning morphology and crystal structure have been investigated systematically. Photocatalytic activities were determined by measuring the amount hydrogen generated from water splitting under UV irradiation in the presence of methanol as a sacrificial reagent. Self-assembled hierarchical titania nanostructures exhibited much superior photocatalytic activity compared to that of starting material, i.e., TiO2-Memb. Enhanced photocatalytic activity is due to characteristic morphology, increased surface area, and enhanced production of photogenerated charge carriers.