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- ItemAcesso aberto (Open Access)Crescimento de óxidos nanoestruturados sobre liga de Ti7Nb para processos fotocatalíticos(Universidade Federal de São Paulo, 2018-10-05) Gomes, Mariany Ludgero Maia [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)This work presents the production of nanotubular photocatalytic oxides on Ti7Nb alloy, made in two ways: as-cast and material subjected to quenching starting at 1000°C and cooled in melting ice, both without going through the process of homegenization. Initially, a study of the alloy substrate was held by undergoing Vickers Microtoughness test, Optical Microscopy test, EDS, DRX and FRX. It was verified the presence of the following phases in both alloys: α, α`, β e ω. The latter was detected by means of Microtoughness tests, and was present in greater quantity in the alloy that was subjected to quenching. The nanotubular photocatalytic oxides were grown by the anodizing process using an aqueous solution containing Fions and a voltage difference of 20V, and were subjected to MEV-FEG and EDS analyses. It was obtained, for all samples, a continuous and regular oxide layer comprising of nanotubes with a mean length of 321 nm and mean internal diameter of 88 nm. EDS trials demonstrated a greater solubility of the Nb on the substrate that undergone to quenching, such that, in the as-cast alloy, regions rich in Nb appeared. Due to the amorphous characteristics of these nanoscale oxides, they were subjected to a thermal treatment to obtain a highly ordered crystalline phase. Heat treatment temperatures varying from 450°C to 650°C were investigated aiming to obtain crystalline nanotubular oxides with high photoactivity. The presence of Nb delayed the transition temperature from anatase to rutilo, and the best temperatures for the crystallization of samples of Ti7Nb in the as-cast form and quenched at 1000°C were 450°C and 550°C, respectively. Studies of the optical properties were performed using DRS techniques, and it was possible to verify that there was an increase in the photocatalytic efficiency of the oxide grown on the alloys in relation to the TiO2 due to a shift of the absorption into the visible region (alloy under quenching) and due to the reduction of the recombination rate of the photogenerated charges (as-cast alloy), confirmed by the RAMAN spectroscopy techinique. A study of the stability of the oxide layer grown on the Ti7Nb alloy prepared under quenching at 1000°C was carried out and no changing was observed. Photocurrent values of the oxide nanolayer grown on the Ti7Nb alloys were higher than that of the TiO2, both in the visible and in the UV-Vis light, with higher efficiency for the as-cast alloy. This efficiency was confirmed on the photocatalytic degradation of the Reactive Blue 4 (RB4) textile dye, where a reduction of 99.99% on the solution coloring and a reduction of 86.13% of the organic load was obtained after 180 min of photoelectrocatalytic treatment, under 1.2V and 80W UV radiation.
- ItemAcesso aberto (Open Access)Degradação de estrogênio presente em águas de abastecimento empregando eletrodo de óxido nanoestruturado crescido sobre liga de TiW(Universidade Federal de São Paulo, 2014-11-24) Oliveira, Marizilda Escudeiro de [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)The advanced oxidation process (AOP) has been a sustainable alternative for treatment of water supplies of urban centers, mainly for the degradation of endogenous hormones estrone (E1) and 17 α-ethinyl estradiol (EE2), called endocrine disrupting compounds (EDC). Among the AOP, the heterogeneous photocatalysis the most promising. It involves the formation hydroxyl radical (OH •) from the UV irradiation on a photocatalyst, usually a semiconductor-type TiO2. Aiming to increase the efficiency of photocatalytic processes this work studied the formation of nanotubulares structures on Ti-0.5W in function of concentration of HF in the electrolyte solution, varying from 0.1 to 0.2 mol L-1 HF in ethylene glycol; applied potential, from 80 to 130V, and anodization time, from 10 to 60 min. The use of nanostructured oxides grown on TiW alloy in photocatalytic processes is attractive because of the proximity of the valence bands and conduction of these metals which contributes to the reduction of recombination of photogenerated charges, increasing the efficiency of the process. The best condition for obtaining a well-defined, regular and homogeneous layer of nanostructured oxide on Ti-0.5W surface was: HF solution 0.2 mol L-1 at 120V during 30 minutes. In order to eliminate an irregular layer of oxide over the nanotubes, known as nanograss, it was made a treatment after the anodizing process using ethanol bath for 24h. Because of the amorphous characteristics of nanotubular oxides, different annealing temperatures were evaluated to obtain a highly ordered crystalline phase, mainly anatase. Photoactivity studies shown that the best temperature of heat treatment is 450 ° C, reaching current values around 1.8 mA cm-2 , about 50% higher than an nanotubular oxide layer grown on pure Ti using HF aqueous solution 0.3% (v/v) at 20V for 2 hours, followed by heat treatment at 450 °C. Then the performance of degradation of estrogens E1 and EE2 was evaluated via photolysis, photocatalysis and electroassisted photocatalysis employing as semiconductor oxide nanostructures grown on Ti alloy (Ti-0.5W) and pure Ti. CLAE analysis shown a decrease in initial concentration of E1 and EE2 in less than 2 minutes of treatment for all process investigated, regardless of the type of semiconductor used. While for E1 was observed 50% of degradation after 1 min in photoelectrocatalysis process using Ti0.5W. The subproducts generated from the degradation of these estrogens also shown a decrease in concentration until 120 minutes of treatment, due to subsequent degradations.
- ItemSomente MetadadadosMicrowave-assisted hydrothermal synthesis of ag-2(w1-xmox)o-4 heterostructures: nucleation of ag, morphology, and photoluminescence properties(Biomed Central Ltd, 2016) Silva, M. D. P.; Gonçalves, Rosana de Fátima [UNIFESP]; Nogueira, I. C.; Longo, V. M.; Mondoni, L.; Moron, M. G.; Santana, Y. V.; Longo, ElsonAg2W1-xMoxO4 (x = 0.0 and 0.50) powders were synthesized by the co-precipitation (drop-by-drop) method and processed using a microwave-assisted hydrothermal method. We report the real-time in situ formation and growth of Ag filaments on the Ag2W1-xMoxO4 crystals using an accelerated electron beam under high vacuum. Various techniques were used to evaluate the influence of the network-former substitution on the structural and optical properties, including photoluminescence (PL) emission, of these materials. X-ray diffraction results confirmed the phases obtained by the synthesis methods. Raman spectroscopy revealed significant changes in local order-disorder as a function of the network-former substitution. Field-emission scanning electron microscopy was used to determine the shape as well as dimensions of the Ag2W1-xMoxO4 heterostructures. The PL spectra showed that the PL-emission intensities of Ag2W1-xMoxO4 were greater than those of pure Ag2WO4, probably because of the increase of intermediary energy levels within the band gap of the Ag2W1-xMoxO4 heterostructures, as evidenced by the decrease in the band-gap values measured by ultraviolet-visible spectroscopy. (C) 2015 Elsevier B.V. All rights reserved.