Malachite Green Dye Decoloration over Au/TiO2-Nanotubes Photocatalyst under Simulate Visible-Light Irradiation

Abstract

Au nanoparticles were supported on TiO2 nanotubes by a novel vapor phase impregnation approach (VPI) using gold dimethyl-acetylacetonate as a precursor. This study aimed to evaluate the capacity of these materials in the photodecoloration of malachite green dye, with the vision to correlate the chemical, structural, morphological, and optical properties with its photocatalytic performance. The photocatalysts were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectronic spectroscopy (XPS), electronic microscopy (HAADF-STEM and HRTEM), and UV–vis spectroscopy. The techniques mentioned above made it possible to detect the presence of small gold nanoparticles (around 3.1 nm), with a high apparent dispersion even at high metal loading for all analyzed systems. According to the XPS results, the Au nanoparticles remain reduced (Au°), and they have a high electronic interaction with TiO2, which eventually originates an electronic exchange between them and consequently a decrease in the band gap energy. In addition, the surface plasmonic resonance observed through UV–vis spectroscopy of the Au nanoparticles are factors that can be related to the high decoloration observed in these photocatalysts, specifically in the 15 wt% Au material, which achieves maximum photodecoloration of malachite green dye at 93%.

Synthesis and Characterization of Titania Nanotubes with Au Nanoparticles

“…After the deposition of Au species by the DPU method, a new signal at 147 cm -1 appeared. This signal was attributed previously to anatase in nanotubular form [30]. Its appearance indicates that after the DPU treatment, titania-like domains were formed in the TNT support.…”

“…The electrodeposited films have a high mechanical and chemical stability [23][24][25]. Other methods used for the preparation of materials modified with metal Au nanoparticles are supercritical CO 2 and wet impregnation [26], thermal atomic layer deposition [27], physical adsorption, cyclic voltammetry and chronoamperometry [28], electrophoresis deposition [29], vapor phase impregnation [30], etc.…”