Navegando por Palavras-chave "TiW alloy"

Agora exibindo 1 - 1 de 1
  • Imagem de Miniatura
    Item
    Acesso aberto (Open Access)
    Óxidos nanoestruturados crescidos sobre Ti e ligas TiW: preparação, caracterização e aplicação na remoção de estradióis da água
    (Universidade Federal de São Paulo, 2017-05-05) Kaminagakura, Verena Mandorino [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Among the sustainable alternatives for the treatment of water and effluents contaminated with endocrine disrupters such as estrone (E1) and 17α-ethynyl estradiol (EE2), the Advanced Oxidative Processes (POA) stand out. Among the POAs, the heterogeneous photocatalysis involves the formation of the hydroxyl radical (• OH) from the UV irradiation in a photocatalyst, usually a TiO2 type semiconductor. However, the use of sunlight by TiO2 is low due to its band gap energy (Ebg) of 3.2 eV, in the anatase phase. In the search for more efficient and active photocatalysts in visible light, this study studied the effect of tungsten composition on the manufacture of nanostructured oxide on Ti2.5%W and Ti5.0%W alloys. The oxide layer was obtained by anodic polarization in a solution of 0.2 mol L-1 of HF in ethylene glycol, varying the applied voltages from 100 to 140 V, the anodizing time from 10 to 60 min and the percentage of water in the electrolyte taking the values of 0%, 5%, 10%, 15% and 20% (v/v). In order to eliminate a compact and irregular layer on the nanotubes, known as nanograss, a treatment was made, after the anodizing process, with a bath in ethanol for 24 hours. Well-defined nanotubular oxide structures were obtained under 120 V after 40 min for Ti2.5% W and Ti5.0% W alloys. Under these conditions the internal diameter values were around 80 nm for the alloy with 2.5% W and 71 nm for the alloy with 5% W. The lengths remained around 6 μm for all alloys. As the W concentration increased, a gradual increase in the heat treatment temperature and a delay in the appearance of the rutile phase were observed. XPS analyzes showed the presence of W in oxidized and metallic form in oxide layer. Photo-current studies have shown that the best thermal treatment is 550ºC for Ti2.5W and Ti5.0W, with current density values around 2.6 mA cm-2 and 3.4 mA cm-2. UV-Vis-NIR spectrometry spectroscopy with diffuse reflectance and and photoluminescence showed that the increase of W decreases the intensity in the spectra and the recombination rate of the e- / h + pairs. The degradation performance of E1 and EE2 was evaluated using the electrodes of NT/TiW and NT/TiO2 in the processes of photolysis, photocatalysis and electrocatalysed photocatalysis. Analysis of HPLC showed a decrease of the initial concentration before 2 minutes for all processes. A maximum degradation of 90% for E1 and 96% for EE2 was achieved with the use of the NT / Ti5.0W electrode in photoelectrocatalysis processes.