Síntese via método dos precursores poliméricos e caracterização multifuncional de nanopartículas de SnO2 modificadas com zinco-nióbio e cobalto-nióbio
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Data
2017-08-24
Autores
Lustosa, Glauco Meireles Mascarenhas Morandi [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O objetivo deste projeto foi sintetizar dois sistemas à base de dióxido de estanho (SnO2), sendo um dopado com zinco e nióbio e outro dopado com cobalto e nióbio, respectivamente (Zn,Nb)-SnO2 e (Co,Nb)-SnO2, e realizar as devidas caracterizações a fim de verificar o potencial destes sistemas para aplicações como varistor, sensor de gás e fotocatalisador. Para síntese dos sistemas dopados foi usado o método dos precursores poliméricos (MPP) a partir da mistura estequiométrica dos reagentes, seguida por complexação, polimerização e calcinação e posterior submissão a etapa de moagem para promover a desaglomeração e redução do tamanho das partículas. As nanopartículas foram depositadas em substrato de Si (100)/SiO2 (10000 A°)/Ti (200 A°)/Pt (1500 A°) para estudo da propriedade varistora, em substrato de alumina com eletrodos interdigitais para análise da propriedade sensora de gás quando na presença de monóxido de carbono (CO). A obtenção dos filmes ocorreu através da técnica de deposição por eletroforese (EPD), com as seguintes condições: 20 mg do pó suspenso em 20 mL de isopropanol, a qual foi aplicada tensão de 2 kV, por diferentes tempos. Para o estudo fotocatalítico o pó foi disperso na solução objeto de estudo, e manteve-se agitação, aeração e irradiação com luz ultravioleta (9 W e 11 W) para promover a excitação eletrônica e a geração dos sítios ativos de oxirredução (par elétron-buraco, e-/h+). O tempo máximo de reação foi de 120 minutos. Para o estudo da atividade como sensor de gás os filmes de (Zn,Nb)-SnO2 foram tratados termicamente a 600 °C por 10 minutos e os filmes de (Co,Nb)-SNO2 a 500 °C por 10 minutos. Esta etapa visou dar resistência mecânica aos filmes sem o crescimento de grãos, mantendo a presença dos poros para aumento da área superficial para adsorção do gás. Os filmes avaliados quanto as propriedades varistoras foram sinterizados a 1000 °C por 40 minutos e 900°C por 30 minutos, para as composições, (Zn,Nb)-SnO2 e (Co,Nb)-SNO2 respectivamente. Após a sinterização os filmes para avaliação da propriedade varistora foram modificados através da deposição de ions Cr3+ por eletroforese, seguido de tratamento térmico de 15 minutos na mesma temperatura em que foram sinterizados. Os ions Cr+3 atuam diretamente na região do contorno de grão influenciando a formação da barreira de potencial. A introdução dos íons cromo, após a sinterização, visa controlar sua difusão por tratamento térmico, com o intuito de promover o aumento do coeficiente de não-linearidade (α) e a resistividade do contorno de grão, características necessárias a um varistor. Ambos os sistemas à base de SnO2 apresentaram respostas para as propriedades de interesse, sendo que o melhor resultado de atividade fotocatalítica, na descoloração da solução aquosa de rodamina B, de aproximadamente 80% de eficiência foi para (Zn,Nb)-SnO2 em 90 minutos de análise. Por sua vez, o sistema (Co,Nb)-SnO2 apresentou melhor resposta sensora e varistora, sendo que para sensor de gás o filme apresentou resposta de 2,6 no sistema self-heating e para a propriedade varistor o filme sinterizado com atmosfera rica em O2 apresentou melhores resultados com coeficiente de não-linearidade (α) entre 11,4 e 15,1; tensão de ruptura (220 V < VR < 242 V) e corrente de fuga (IF ~10-8 A/cm²), valores estes que indicam um potencial para aplicação como varistor de baixa tensão utilizado em dispositivos eletrônicos.
The objective of this project was to synthesize two tin dioxide (SnO2) systems, one doped with zinc and niobium and one doped with cobalt and niobium, respectively (Zn, Nb)-SnO2 and (Co, Nb)-SnO2, and conduce the appropriate characterizations to verify the potential use of these systems for applications such as varistor, gas sensor and photocatalyst. The polymer precursors (MPP) method was used for the synthesis SnO2-based systems, this method involves the stoichiometric mixture of the reactants, followed by complexation, polymerization and calcination and subsequent submission to the grinding stage to promote the deagglomeration and reduction of the particle size. The nanoparticles were deposited onto Si (100)/SiO2 (10000 A°)/Ti (200 A°)/Pt (1500 A°) substrate for the study of the varistor property and for analysis of the gas sensor property (when in the presence of carbon monoxide - CO) deposited in substrate of alumina with interdigital electrodes. The films were obtained by electrophoresis deposition technique (EPD), with the following conditions: 20 mg of the powder suspended in 20 mL of isopropanol, which was applied at 2 kV voltage, for different times. For the photocatalytic study, the powder was dispersed into the solution under study, and stirring, aeration and submitted to irradiation with ultraviolet light (9 W and 11 W) to promote the electronic excitation and the generation of active oxidation sites (electron- hole, e- / h+ ). The maximum reaction time was 120 minutes. For the study of the gas sensor activity the (Zn, Nb)-SnO2 films were heat treated at 600 °C for 10 minutes and the (Co, Nb)-SnO2 films at 500 °C for 10 minutes. This stage aimed to promote mechanical resistance to the films avoiding the grain growth, maintaining the presence of the pores to increase the surface area for adsorption of the gas. The films analyzed for the varistor properties were sintered at 1000 °C for 40 minutes and 900 °C for 30 minutes for the compositions, (Zn, Nb)-SnO2 and (Co, Nb)-SnO2 respectively. After sintering, the films for evaluation of varistor properties were modified by the deposition of Cr3+ ions by electrophoresis, followed by a 15 minute heat treatment at the same temperature at which they were sintered. The Cr+3 ions act directly in the region of the grain boundary influencing the formation of the potential barrier. The introduction of the chromium ions, after sintering, aims to control their diffusion by heat treatment, in order to promote the increase of the coefficient of nonlinearity (α) and resistivity of the grain boundary, characteristics necessary to a varistor. Both SnO2-based systems presented responses to the properties of interest, and the best result of photocatalytic activity, in the discoloration of the aqueous solution of rhodamine B, of approximately 80% efficiency was for (Zn, Nb)-SnO2 in 90 minutes of analysis. On the other hand, the system (Co, Nb)-SnO2 presented better sensor and varistor response, and for gas sensor the film presented a response of 2.6 in the self-heating system and for the varistor property the sintered film with rich atmosphere in O2 presented better results with coefficient of nonlinearity (α) between 11.4 and 15.1; (VR <242 V) and leakage current (IF ~ 10-8 A/cm²), which indicates a potential for application as low voltage varistor used in electronic devices.
The objective of this project was to synthesize two tin dioxide (SnO2) systems, one doped with zinc and niobium and one doped with cobalt and niobium, respectively (Zn, Nb)-SnO2 and (Co, Nb)-SnO2, and conduce the appropriate characterizations to verify the potential use of these systems for applications such as varistor, gas sensor and photocatalyst. The polymer precursors (MPP) method was used for the synthesis SnO2-based systems, this method involves the stoichiometric mixture of the reactants, followed by complexation, polymerization and calcination and subsequent submission to the grinding stage to promote the deagglomeration and reduction of the particle size. The nanoparticles were deposited onto Si (100)/SiO2 (10000 A°)/Ti (200 A°)/Pt (1500 A°) substrate for the study of the varistor property and for analysis of the gas sensor property (when in the presence of carbon monoxide - CO) deposited in substrate of alumina with interdigital electrodes. The films were obtained by electrophoresis deposition technique (EPD), with the following conditions: 20 mg of the powder suspended in 20 mL of isopropanol, which was applied at 2 kV voltage, for different times. For the photocatalytic study, the powder was dispersed into the solution under study, and stirring, aeration and submitted to irradiation with ultraviolet light (9 W and 11 W) to promote the electronic excitation and the generation of active oxidation sites (electron- hole, e- / h+ ). The maximum reaction time was 120 minutes. For the study of the gas sensor activity the (Zn, Nb)-SnO2 films were heat treated at 600 °C for 10 minutes and the (Co, Nb)-SnO2 films at 500 °C for 10 minutes. This stage aimed to promote mechanical resistance to the films avoiding the grain growth, maintaining the presence of the pores to increase the surface area for adsorption of the gas. The films analyzed for the varistor properties were sintered at 1000 °C for 40 minutes and 900 °C for 30 minutes for the compositions, (Zn, Nb)-SnO2 and (Co, Nb)-SnO2 respectively. After sintering, the films for evaluation of varistor properties were modified by the deposition of Cr3+ ions by electrophoresis, followed by a 15 minute heat treatment at the same temperature at which they were sintered. The Cr+3 ions act directly in the region of the grain boundary influencing the formation of the potential barrier. The introduction of the chromium ions, after sintering, aims to control their diffusion by heat treatment, in order to promote the increase of the coefficient of nonlinearity (α) and resistivity of the grain boundary, characteristics necessary to a varistor. Both SnO2-based systems presented responses to the properties of interest, and the best result of photocatalytic activity, in the discoloration of the aqueous solution of rhodamine B, of approximately 80% efficiency was for (Zn, Nb)-SnO2 in 90 minutes of analysis. On the other hand, the system (Co, Nb)-SnO2 presented better sensor and varistor response, and for gas sensor the film presented a response of 2.6 in the self-heating system and for the varistor property the sintered film with rich atmosphere in O2 presented better results with coefficient of nonlinearity (α) between 11.4 and 15.1; (VR <242 V) and leakage current (IF ~ 10-8 A/cm²), which indicates a potential for application as low voltage varistor used in electronic devices.
Descrição
Palavras-chave
Óxido de estanho, Fotocatálise, Filmes, Eletroforese, Forno microondas, Sensor de gás, Varistor, Difusão de cromo, Tin oxide, Photocatalysis, Films, Electrophoresis, Microwave oven, Gas sensor, Chromium diffusion