TiO2 nanotubes modification by photodeposition with noble metals: Characterization, optimization, photocatalytic activity, and by-products analysis

Abstract

Self-organized TiO2 nanotubes (TNTs) with 4 µm length were obtained by anodization method and calcined to obtain anatase crystallite phase. The photocatalysts were further decorated with Au, Ag, Pt or Pd nanoparticles (NPs), varying the metal loads (0.50, 0.75, 1, 2 and 5 mol%) by photodeposition. The material characterization confirmed the presence of nanoparticles in the TNTs surface, signs of the localized surface plasmon resonance (LSPR) effect for some samples and a bandgap energy of 3.1–3.2 eV. Photoluminescence measurements also confirmed that most of the samples with metallic nanoparticles had the recombination of photogenerated carriers lowered due to the trapping effect of the deposited metal NPs. The photoactivity was evaluated by phenol degradation using UV-Vis or visible radiation. Under UV-Vis, the best samples (2 and 5 mol% of Au-TNTs and 0.75, 1, and 2 mol% of Pd-TNTs) led to 97% phenol removal in 60 min while pristine TNTs reached 92% removal. Under visible radiation, the pristine and the Au-TNTs led to about 3% removal, with the best sample being 2 mol% Pd-TNTs with 14% removal in 60 min. Similar results were obtained for 1 and 5 mol% Pd-TNTs (12% and 13% of phenol removal, respectively). The by-products analysis suggest different degradation mechanisms and it is observed different kinetic rates for different metal types, metal loads or types of radiation.