The Effects of Pt Doping on the Structure and Visible Light Photoactivity of Titania Nanotubes

Abstract

Platinum-doped titania nanotubes were prepared by a hydrothermal technique to produce visible light activated catalysts. Pt loading, however, also affected the morphology of the titania nanotubes. Scanning electron microscopy and scanning transmission electron microscopy (STEM) results reveal that up to 1 mol % loading Pt-doped titania retains its nanotubular structure, but at 2 and 4 mol % Pt the nanotubes collapse to a nanopowder. High-angle annular dark field STEM images show that the Pt nanoparticles have diameters of !2-5 nm and are uniformly distributed on the nanotube surface. Pt doping enhances the photoactivity of titania nanotubes in visible light for the photooxidation of acetaldehyde. Titania nanotubes doped with 0.5 mol % Pt show the maximum visible light photoactivity with a decay rate constant nearly 7 order of magnitude (0.0034 min -1 )g reater than commercially available P25 titania (0.0005 min -1 ). Electron paramagnetic resonance (EPR) spectroscopy was used to probe the mechanism by which Pt-doping alters the structure and function of the titania nanotubes. EPR spectra revealed that undercoordinated sites and oxygen deficiency on the surface of the titania nanotube are created in synthesis (calcination in hydrogen atmosphere). These surface features interact with the Pt centers to alter the optical, electronic, and chemical behavior of the titania nanotube. These results also suggest the potential for practical applications such as incorporating Pt-doped titania nanotubes with commercially available light sources for indoor air purification.