Síntese, caracterização e fabricação de dispositivos sensores de gás com base em materiais calcogenóides de estanho
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Data
2022-12-15
Autores
Melquiades, Miécio de Oliveira
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Nesse trabalho, dispositivos sensores de gás foram fabricados e testados. Dicalcogenóides de estanho foram usados como camada ativa dos sensores, nas composições SnS2, Sn(S0.5Se0.5)2 e SnSe2, sintetizados por moagem mecânica de alta energia. A análise estrutural revelou nanoestruturas anisotrópicas politípicas 2H com alta densidade de defeitos e índices de textura (orientação preferencial). Uma significante redução da microtensão foi observado em função da substituição, no sítio 2d, por calcogenóides mais pesados (selênio). Nanocristalitos com alta microtensão alargaram e deslocaram para a esquerda (redshifts) os picos associados aos modos Raman A1g e Eg da estrutura cristalina. O efeito redshift também ocorre quando os parâmetros de rede são aumentados via dopagem. As medidas de DSC apresentaram uma linha de base com perfil exotérmico e uma modificação sutil acima de 450 ºC associada a nucleação de SnO2. Medidas de UV-Vis, analisadas pelo método de Tauc, estimaram o band gap das amostras que foram 3,4, 3,0 e 2,3 eV para SnS2, Sn(S0.5Se0.5)2 e SnSe2, respectivamente, e demonstraram sub-bands provenientes de uma microestrutura de multicamadas. Como sensor, os materiais apresentaram altos sinais de resposta, com valores variando entre 102 a 106 em função da concentração de NO¬2 (2 a 100 ppm) e temperatura de operação (30 a 300 °C). Os materiais não foram sensíveis ao CO, enquanto a detecção de H2 só foi observada acima de 200 °C, implicando em alta seletividade ao NO2. Adicionalmente, foi investigado a influência da diluição das amostras em água e isopropanol no tamanho e morfologia dos grãos. Observou-se que o isopropanol cristaliza a fase amorfa de selênio dispersa no sistema Sn-Se e aumenta a aglomeração no sistema Sn(S0.5Se0.5)2. Micropartículas deformadas e defeituosas foram observadas independentemente da metodologia de preparação. Essa morfologia única pode aumentar a reatividade superficial para detecção seletiva de NO2 por fisissorção, devido a uma alta taxa de adsorção a temperatura ambiente.
In this work, gas sensing devices were manufactured and tested. Tin dichalcogenoids were used as the active layer of the sensors, in the compositions SnS2, Sn(S0.5Se0.5)2 and SnSe2, synthesized by high energy mechanical milling. Structural analysis revealed 2H polytypic anisotropic nanostructures with high defect density and texture indices (preferred orientation). A large reduction in microstrain was observed due to the replacement, at the 2d site, by heavier chalcogen (selenium). Nanocrystallites with high microstrain broadened and shifted to the left (redshifts) the peaks associated with the Raman modes A1g and Eg of the crystalline structure. The redshift effect also occurs when the lattice parameters are increased via doping. DSC measurements showed a baseline with an exothermic profile and a subtle change above 450 ºC associated with SnO2 nucleation. UV-Vis measurements, analyzed by the Tauc method, estimated the band gap of the samples that were 3.4, 3.0 and 2.3 eV for SnS2, Sn(S0.5Se0.5)2 and SnSe2, respectively, and demonstrated sub-bands arising from a multilayer microstructure. The materials showed high response signals as a gas sensor, with values ranging from 102 to 106 as a function of NO2 concentration (2 to 100 ppm) and operating temperature (30 to 300 °C). The materials were not sensitive to CO, while detection of H2 was only observed above 200 °C, implying high selectivity to NO2. Additionally, the influence of sample dilution in water and isopropanol on grain size and morphology was investigated. It was observed that isopropanol crystallizes the amorphous selenium phase dispersed in the Sn-Se system and increases agglomeration in the Sn(S0.5Se0.5)2 system. Deformed and defective microparticles were observed regardless of preparation methodology. This unique morphology can increase surface reactivity for selective NO2 detection by physisorption due to a high adsorption rate at room temperature.
In this work, gas sensing devices were manufactured and tested. Tin dichalcogenoids were used as the active layer of the sensors, in the compositions SnS2, Sn(S0.5Se0.5)2 and SnSe2, synthesized by high energy mechanical milling. Structural analysis revealed 2H polytypic anisotropic nanostructures with high defect density and texture indices (preferred orientation). A large reduction in microstrain was observed due to the replacement, at the 2d site, by heavier chalcogen (selenium). Nanocrystallites with high microstrain broadened and shifted to the left (redshifts) the peaks associated with the Raman modes A1g and Eg of the crystalline structure. The redshift effect also occurs when the lattice parameters are increased via doping. DSC measurements showed a baseline with an exothermic profile and a subtle change above 450 ºC associated with SnO2 nucleation. UV-Vis measurements, analyzed by the Tauc method, estimated the band gap of the samples that were 3.4, 3.0 and 2.3 eV for SnS2, Sn(S0.5Se0.5)2 and SnSe2, respectively, and demonstrated sub-bands arising from a multilayer microstructure. The materials showed high response signals as a gas sensor, with values ranging from 102 to 106 as a function of NO2 concentration (2 to 100 ppm) and operating temperature (30 to 300 °C). The materials were not sensitive to CO, while detection of H2 was only observed above 200 °C, implying high selectivity to NO2. Additionally, the influence of sample dilution in water and isopropanol on grain size and morphology was investigated. It was observed that isopropanol crystallizes the amorphous selenium phase dispersed in the Sn-Se system and increases agglomeration in the Sn(S0.5Se0.5)2 system. Deformed and defective microparticles were observed regardless of preparation methodology. This unique morphology can increase surface reactivity for selective NO2 detection by physisorption due to a high adsorption rate at room temperature.
Descrição
Palavras-chave
Sensor de gás, Dicalcogenóides de estanho, Moagem mecânica de alta energia, Gas sensor, Tin-dichalcogenides, High energy ball milling physisorption