Pore architecture affects photocatalytic activity of periodic mesoporous nanocrystalline anatase thin films

Abstract

We report the photocatalytic activity of periodic mesoporous nanocrystalline anatase thin films (denoted meso-nc-TiO₂) using Methylene Blue (denoted MB) as a probe of pore architecture effects on reactivity. Specifically, 2D hexagonal and 3D cubic mesoporous nanocrystalline anatase thin films (denoted h-meso-nc-TiO₂ and c-meso-nc-TiO₂ respectively) annealed at different temperatures were investigated to reveal the effects of different pore architectures on the photocatalytic activity. The adsorption behavior of MB on the films annealed at the same temperature signaled that c-meso-nc-TiO₂ has a larger accessible surface area but a lower adsorption surface affinity, compared to h-meso-nc-TiO₂. In the case of the solid-state photodegradation of MB, the most efficacious photocatalyst was found to be c-meso-nc-TiO₂ annealed at 450 °C. For MB in solution, a 400 °C annealed c-meso-nc-TiO₂ was established to have the optimum photocatalytic activity among the samples investigated. The observed superior photocatalytic activity of c-meso-nc-TiO₂ relative to both h-meso-nc-TiO₂ and nc-TiO₂ is believed to originate from the higher photoactivity of anatase nanocrystallites comprising the more open cubic framework. as well as geometrical advantages, such as a larger surface area and less obstructed 3D diffusion paths of guest molecules. It is concluded that the photocatalytic efficiency of periodic mesoporous nanocrystalline anatase thin films depends on the pore architecture.