Exceptional activity for photocatalytic mineralization of formaldehyde over amorphous titania nanofilms

Abstract

As alternative photocatalysts, titania semiconductors have been extensively investigated for energy and environmental applications. However, amorphous titania is often considered not to be photoreactive catalyst. Here we demonstrate an amorphous titania thin film deposited at room temperature for a photocatalytic removal of formaldehyde from air, which features abundant hydroxyl groups and large surface area. Amorphous titania exhibited surprisingly higher apparent quantum yield of 60.4% than crystalline titania (the most active anatase). This exceptional activity is attributed to greatly reduced recombination of electron-hole pairs and abundant adsorption sites towards formaldehyde. The reduced recombination should result from rapid electron transfer along conduction band (>TiIIIOH) that allocates abundant terminal hydroxyl groups, and minimized transfer length from bulk to surface in small particles. The abundant adsorption sites are related to surface hydroxyl groups and large surface area. With the exceptional activity, amorphous titania nanofilm achieved at room temperature substantively enables photocatalysis on heat-susceptible substrates, while it is nearly impossible for crystalline films calcined at high temperature.