Navegando por Palavras-chave "Semicondutor"

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    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.
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    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.
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    Detectores Semicondutores: Histórico e Aplicações
    (Universidade Federal de São Paulo, 2022-02-11) Coimbra, João Vitor Pereira [UNIFESP]; Barbosa, Renata de Faria [UNIFESP]; http://lattes.cnpq.br/3663691702527038; Universidade Federal de São Paulo (UNIFESP)
    Este trabalho tem como finalidade apresentar uma revisão da literatura a respeito dos detectores semicondutores, enfatizando o seu desenvolvimento ao longo do tempo e suas aplicações. Para realizar essa compilação de informações sobre esse tipo de detector foi empregada a metodologia de referência bibliográfica. Os dados científicos foram selecionados e coletados utilizando bases de dados nacionais e internacionais, disponíveis de forma online, Science Direct, Scielo (Scientific Eletronic Library Online), Portal da CAPES, Springer LINK, Google Acadêmico/Scholar. O critério de seleção do material científico compreende artigos, teses e textos dos periódicos, livros com conceitos básicos e consolidados claros com palavras chave como: semicondutores, detectores, Raios X, histórico e aplicação utilizando detectores semicondutores. O estudo apresenta a evolução dos detectores semicondutores, explicando como são formados a partir da junção np, os chamados diodos, apresentando o que são os fotodiodos e a importância de sua aplicação na indústria, na medicina e em técnicas que utilizam radiação, já que os detectores semicondutores têm baixo custo e eletrônica simples, em contraste com os detectores à gás. Outra vantagem, deste dispositivo, é a rapidez no tempo de resposta e a eficiência na detecção de ondas de baixa energia, por exemplo, os raios X. Seu desempenho é aplicado para detectar a radiação X característica dos átomos excitados por uma radiação eletromagnética, na técnica de Fluorescência de Raios X, permitindo a identificação da composição e concentração de elementos presentes em uma amostra de natureza diversas (ambiental, alimentícia, industrial, geológica, etc.).