Efeito de agentes mineralizadores na síntese de cristais de óxido de cério visando detecção de monóxido de carbono
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Data
2021-02-26
Autores
Garcia, Gabriel [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O presente trabalho propõe uma rota alternativa de síntese de cristais de óxido de cério (CeO2) dissolvendo os precursores em soluções alcalinas de NaOH e KOH com concentrações de 2M e 4M pelo método hidrotermal assistido por micro-ondas (HAM). O material obtido foi caracterizado por Difratometria de Raios X (DRX), Espectroscopia Raman (Raman), Infravermelho com transformada de Fourier (FT-IR), Ultravioleta-visível (UV-Vis) e Espectroscopia de Fotoluminescência (PL). Os difratogramas das amostras sintetizadas apresentaram picos referentes à estrutura tipo fluorita do CeO2, e nota-se por espalhamento Raman melhoras nas propriedades referentes a mobilidade de oxigênio nas amostras preparadas com KOH. Dados de espectroscopia no infravermelho com transformada de Fourier não demonstram quaisquer contaminantes ou impurezas durante a síntese, com modos comumente observados para este tipo de material. O band gap das amostras tende a diminuir para as soluções básicas mais concentradas. A alta área superficial específica para compostos obtidos a partir do KOH pode ser explicada por sua baixa perda dielétrica, devido à conversão mais lenta de microondas em energia térmica e, portanto, a nucleação no material ocorre em uma taxa mais baixa. Observa-se uma melhor distribuição de tamanho de partículas para as amostras de KOH, com formas esféricas, romboidais e cúbicas, com predominância de octaedros. As amostras obtidas a partir do NaOH possuem áreas de superfícies menores com distribuição de tamanho de partícula mais disperso. Também é possível concluir pela PL que as amostras preparadas com soluções de 4M para ambos os mineralizadores exibem mais defeitos superficiais em comparação as demais. Os filmes depositados apresentam resposta bastante seletiva e rápida a exposição de CO, com tempos de resposta de 0,77 s para a amostra obtida a partir do KOH e 11,53 s para o NaOH. Os valores obtidos comprovam a eficácia do método HAM, com a utilização do KOH apresentando propriedades e morfologia mais adequadas à aplicação final como sensores para detecção de CO.
In this work, the influence of an alternative synthesis route of cerium oxide (CeO2) crystals, utilizing alkali solutions of NaOH and KOH for the precursors preparing for the microwave-assististed hydrothermal synthesis method were studied. The obtained material was characterized by X-ray Diffraction (XRD), Raman Spectroscopy (Raman), Infrared (IR-FT), Ultraviolet-Visible (UV-Vis) and Photoluminescence Spectroscopy (PL). The diffractograms of the samples showed peaks related to the fluorite-like structure of CeO2, and improvements in the properties related to oxygen mobility were observed in samples prepared with KOH by Raman spectroscopy. Fourier transform infrared spectroscopy reveal no traces of any contaminants or impurities during synthesis, with bands commonly observed for this type of material. The samples band gap tends to decrease in energy value for the more concentrated alkali solutions. The high specific surface area for KOH can be explained by its low dielectric loss, due to the slower conversion of microwave to thermal energy and, therefore, nucleation in the material occurs at a lower rate. Better particle size distribution is observed for the KOH samples, with spherical, rhomboid, and cubic shapes, with a predominance of octahedrons. The NaOH samples have lower specific surface area and disperse particle size distribution. The PL also concludes that samples at 4M shows more superficial defects if compared to the others. All deposited films show great and selective response when exposed to CO, with response times of 0,77 s for the KOH sample and 11,53 s for the NaOH sample. The obtained values affirm the efficacy of the MAH method, as the KOH shows adequate properties and morphology to the final application as CO detection sensors.
In this work, the influence of an alternative synthesis route of cerium oxide (CeO2) crystals, utilizing alkali solutions of NaOH and KOH for the precursors preparing for the microwave-assististed hydrothermal synthesis method were studied. The obtained material was characterized by X-ray Diffraction (XRD), Raman Spectroscopy (Raman), Infrared (IR-FT), Ultraviolet-Visible (UV-Vis) and Photoluminescence Spectroscopy (PL). The diffractograms of the samples showed peaks related to the fluorite-like structure of CeO2, and improvements in the properties related to oxygen mobility were observed in samples prepared with KOH by Raman spectroscopy. Fourier transform infrared spectroscopy reveal no traces of any contaminants or impurities during synthesis, with bands commonly observed for this type of material. The samples band gap tends to decrease in energy value for the more concentrated alkali solutions. The high specific surface area for KOH can be explained by its low dielectric loss, due to the slower conversion of microwave to thermal energy and, therefore, nucleation in the material occurs at a lower rate. Better particle size distribution is observed for the KOH samples, with spherical, rhomboid, and cubic shapes, with a predominance of octahedrons. The NaOH samples have lower specific surface area and disperse particle size distribution. The PL also concludes that samples at 4M shows more superficial defects if compared to the others. All deposited films show great and selective response when exposed to CO, with response times of 0,77 s for the KOH sample and 11,53 s for the NaOH sample. The obtained values affirm the efficacy of the MAH method, as the KOH shows adequate properties and morphology to the final application as CO detection sensors.
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Palavras-chave
Nanopartículas, Monóxido de carbono, Material cerâmico, Gas sensors, Carbon monoxide