Hierarchically porous titania networks with tunable anatase:Rutile ratios and their enhanced photocatalytic activities

Mixed-phase hierarchically porous titania networks (PTNs) with 3D interconnected porous frameworks and tunable rutile contents have been synthesized via a facile sol-gel templating and calcination process. The products were characterized using scanning electron microscopy, powder X-ray diffraction, and nitrogen gas sorption analysis, and their photocatalytic activities were evaluated by measuring the photocatalytic degradation of methylene blue, a typical effluent from the textile industry, under UV light illumination. The hierarchically macro-/mesoporous titania structure formed after templating followed by calcination in air. The reduced interfaces between titania nanocrystals in these PTN materials can significantly decrease interface nucleation of the rutile phase and effectively retard the anatase to rutile phase transformation, therefore giving rise to porous titania photocatalysts featuring tunable rutile ratios (from 0 to 100 wt %), reduced crystal sizes, hierarchically porous structure, and relatively high specific surface areas (up to 71.0 m2 g-1). The photocatalytic performance of the materials was correlated to the anatase:rutile ratio and specific surface area of the materials, with the mixed-phase (rutile content of 15.4%) nanocrystalline titania calcined at 600 °C for 6 h showing the highest photocatalytic activity. This study demonstrates that a substantial improvement in photocatalytic activity of the titania can be achieved by controlling morphology and carefully tuning phase composition via a feasible solid-state phase transformation at a relatively low temperature (600 °C). This concept for the rational design and development of high-performance photocatalysts using an industrially simple process would be capable of mass production.