Effect of crystal phase composition on the reductive and oxidative abilities of TiO2 nanotubes under UV and visible light

• Published in: Applied catalysis. B, Environmental Environmental, 2010-06, Vol.97 (3-4), p.354-360
• Main Authors: Schulte, Kevin L., DeSario, Paul A., Gray, Kimberly A.
• Format: Article
• Language: English
• Subjects: Acetaldehyde oxidation; Carbon dioxide reduction; Catalysis; Chemistry; Colloidal state and disperse state; Electrochemistry; Exact sciences and technology; General and physical chemistry; Nanotubes; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Porous materials; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Titanium dioxide
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2010.04.017

Titania nanotube arrays synthesized by the electrochemical oxidation of titanium foils have generated considerable interest as photocatalysts for their ordered nature and large surface area. Mixed-phase materials combining the anatase and rutile crystal phases of TiO2, however, have been much more widely studied due to their enhanced reactivity in comparison to pure phase materials. In this study, we seek to integrate these two lines of research and investigate the reductive and oxidative reactivity of TiO2 nanotube arrays (anatase phase) supported on TiO2 films of varying crystal phase composition. A series of TiO2 nanotubes 1.2μm in length was synthesized, annealed at varying temperatures to control their crystallinity, and characterized by various physical techniques (e.g. XRD, diffuse reflectance, SEM). Photocatalytic CO2 reduction and acetaldehyde oxidation reactions were performed in the gas phase under UV and visible wavelengths. For CO2 reduction, reaction rates decreased with increasing rutile phase under UV. Rates increased with rutile phase ratio under visible and near visible light. For oxidation, the mixed-phase samples showed enhanced reactivity, with a maximum acetaldehyde destruction rate achieved at a 79:21 ratio of anatase to rutile. The samples were substantially less active under visible light, except for the 620°C composite (77% rutile) which showed a slight rate increase. Nanotubes annealed at 680°C collapsed to a random porous structure, but showed comparable reductive ability to the non-collapsed samples despite the loss of surface area. This is attributed to the creation of additional anatase–rutile crystallite interfacial area leading to the formation of unique active sites. Control of crystal phase composition through anneal temperature is found to be a simple way to tune the reactivity of these materials and enhance their ability to absorb visible light.