Low-temperature electrostatic self-assembly of noble metals on TiO2 nanostructured films with enhanced photocatalytic activity

Abstract

Photoactive TiO2 nanostructured films (i.e., nanoflowers and nanowires) have been directly synthesized on Ti sheets using an alkali-hydrothermal route. Ultrafine noble metals (i.e., Au, Pt, Pd) nanoparticles (NPs) were homogenously dispersed onto the TiO2 nanostructures using a facile low temperature electrostatic self-assembly approach. The resulting noble-metal/TiO2-nanostructured films supported on Ti sheets had an all-in-one structure with all of the virtues of a porous framework and enhanced photocatalytic activity. Ultra highresolution field-emission scanning electron microscopy (FESEM) revealed that the noble metal NPs were uniformly dispersed on the TiO2 surface with good physical separation properties. The average sizes of the loaded Au, Pt, and Pd NPs were approximately 4.0, 2.0, and 10.0 nm, respectively. Noble metal NPs were deposited not only on the film surface but also in the interior framework of the TiO2 films with a depth of more than 580 nm, as revealed by Auger electron spectroscopic (AES) in-depth profiling analysis. X-ray photoelectron spectroscopy (XPS) analysis revealed that the Pt and Pd NPs had been partially oxidized to PtOabs andimmobicompletely oxidized to PdO, respectively, whereas the Au NPs remained in a metallic state after being annealed in air at 300 °C. During the electrostatic self-assembly process, the loading of the noble metal can be adjusted by controlling the assembly time and the colloidal pH value. The degradation of aqueous methyl orange showed that the Au/TiO2 (or Pt/TiO2)-nanostructured films possessed remarkably enhanced photocatalytic activity compared with pure TiO2 films, and revealed that the metal NPs played a positive role in separating photogenerated hole-electron pairs. However, the deposited PdO species had no discernible impact on the activity of the TiO2 nanostructures. © Editorial office of Acta Physico-Chimica Sinica.