Preparación y caracterización de sensores a base de óxidos metálicos y su aplicación para la detección de insecticidas organofosforados
Date
2019-09-04
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Pontificia Universidad Católica del Perú
Abstract
La presente tesis se centra en realizar la síntesis y caracterización de óxidos metálicos
dopados con metales de transición para mejorar su sensibilidad para detectar vapores de
dos pesticidas organofosforados, Clorpirifós y Malatión. Los óxidos estudiados son el óxido
de zinc (ZnO) dopado con Zr, ZnO dopado con Ag, y el óxido de estaño (SnO2) dopado con
Pt y Zr. La síntesis del ZnO se realiza mediante la aplicación de dos metodologías de
síntesis hidrotermal: (a) Precipitación asistida por microondas y (b) precipitación en
autoclave; mientras que el dopaje del ZnO se realiza agregando los precursores de los
dopantes (AgNO3 y ZrOCl2) a la mezcla de reacción. El SnO2 dopado con Zr y Pt se obtiene
a partir del óxido de estaño comercial (Merck) y se lleva a cabo en dos etapas: 1) Dopaje
del SnO2 con Zr por mezcla mecánica y 2) dopaje de SnO2 con Pt por reducción de este
con SnSO4. La caracterización de estos materiales se realiza mediante análisis por DRX,
FTIR, UV, SEM-EDS, TEM y sorción de N2. Además, se realiza la cuantificación de la
concentración de pesticidas en las muestras comerciales que se aplican en los ensayos de
sensado mediante HPLC.
Se obtienen las señales de respuesta con mayor estabilidad para largos tiempos de
sensado con los sensores de óxido de zinc dopado con Zr por síntesis en autoclave
(AT-Zr-ZnO). Su caracterización por XRD revela que el dopaje es sustitucional y no se
identifican fases adicionales.
Se lleva a cabo un estudio de las condiciones óptimas de temperatura
(entre 210°C y 220°C), concentración del dopante en el óxido de zinc y el óxido de estaño.
La temperatura tiene un efecto positivo en la sensibilidad de todos los sensores ensayados.
A la temperatura de ensayo de 220°C se logra maximizar la sensibilidad de los mejores
sensores (AT-Zr-2.0-ZnO y Pt-0.13-ZrO2-0.15-SnO2) por el Malatión. En el caso del
sensado del Clorpirifós, se obtienen mejores resultados con el sensor
Pt-0.13-ZrO2-0.15-SnO2, cuya señal se favorece a 210°C. Además, la sensibilidad del
Pt-0.13-ZrO2-0.15-SnO2 respecto al AT-Zr-2.0-ZnO a 220°C es mayor para el Clorpirifós,
pero menor para el Malatión.
El método de tratamiento estadístico PCA permite la evaluación de las señales de muestras
con diferentes concentraciones de pesticidas. Los mejores PCA, obtenidos con los datos
de las mediciones utilizando los sensores más sensibles, muestran una varianza total
explicada mayor al 90% y una mejor diferenciación entre muestras de aire contaminado
con pesticidas y muestras de aire sin contaminación.
This thesis focuses on the synthesis and characterization of metal oxides doped with transition metals to improve their sensitivity to detect vapors of two organophosphorus pesticides, Chlorpyrifos and Malathion. The oxides studied are Zr doped zinc oxide (ZnO), Ag doped ZnO, and tin oxide (SnO2) doped with Pt and Zr. The synthesis of ZnO is carried out through the application of two hydrothermal synthesis methodologies: (a) Microwave assisted precipitation and (b) autoclave precipitation; while ZnO doping is conducted by adding the dopant precursor (AgNO3 or ZrOCl2) to the reaction mixture. SnO2 doped with Zr and Pt is prepared from commercial tin oxide (Merck). The doping process was carried out in two stages: 1) Zr doped SnO2 is obtained by mechanical mixing and 2) Pt doped SnO2 is prepared by reduction with SnSO4. The characterization of these materials is carried out by employing DRX, FTIR, UV, SEM-EDS, TEM and sorption of N2 analysis. In addition, the quantification of pesticide concentration in commercial samples, that are used in the sensing essays, is performed with HPLC. Response signals are obtained with greater stability for long sensing times with zinc oxide sensors doped with Zr by autoclave synthesis (AT-Zr-ZnO). Its characterization by XRD reveals that doping is substitutional and no additional phases are identified. A study of the optimum temperature conditions (between 210°C and 220°C), concentration of the dopant in zinc oxide and tin oxide is carried out. The temperature has a positive effect on the sensitivity of all the sensors tested. At the test temperature of 220°C, the sensitivity of the best sensors (AT-Zr-2.0-ZnO and Pt-0.13-ZrO2-0.15-SnO2) for Malathion can be maximized. In the case of Chlorpyrifos, better results are obtained for the Pt-0.13-ZrO2-0.15-SnO2 sensor, whose signal is favored at 210°C. In addition, the sensitivity of Pt-0.13-ZrO2-0.15-SnO2 with respect to AT-Zr-2.0-ZnO at 220°C is higher for Chlorpyrifos, but lower for Malathion. The statistical treatment method PCA allows the evaluation of the signals of samples with different concentrations of pesticides. The best PCA, obtained with the data of the measurements using the most sensitive sensors, show a total explained variance greater than 90% and a better differentiation between air samples contaminated with pesticides and air samples without contamination.
This thesis focuses on the synthesis and characterization of metal oxides doped with transition metals to improve their sensitivity to detect vapors of two organophosphorus pesticides, Chlorpyrifos and Malathion. The oxides studied are Zr doped zinc oxide (ZnO), Ag doped ZnO, and tin oxide (SnO2) doped with Pt and Zr. The synthesis of ZnO is carried out through the application of two hydrothermal synthesis methodologies: (a) Microwave assisted precipitation and (b) autoclave precipitation; while ZnO doping is conducted by adding the dopant precursor (AgNO3 or ZrOCl2) to the reaction mixture. SnO2 doped with Zr and Pt is prepared from commercial tin oxide (Merck). The doping process was carried out in two stages: 1) Zr doped SnO2 is obtained by mechanical mixing and 2) Pt doped SnO2 is prepared by reduction with SnSO4. The characterization of these materials is carried out by employing DRX, FTIR, UV, SEM-EDS, TEM and sorption of N2 analysis. In addition, the quantification of pesticide concentration in commercial samples, that are used in the sensing essays, is performed with HPLC. Response signals are obtained with greater stability for long sensing times with zinc oxide sensors doped with Zr by autoclave synthesis (AT-Zr-ZnO). Its characterization by XRD reveals that doping is substitutional and no additional phases are identified. A study of the optimum temperature conditions (between 210°C and 220°C), concentration of the dopant in zinc oxide and tin oxide is carried out. The temperature has a positive effect on the sensitivity of all the sensors tested. At the test temperature of 220°C, the sensitivity of the best sensors (AT-Zr-2.0-ZnO and Pt-0.13-ZrO2-0.15-SnO2) for Malathion can be maximized. In the case of Chlorpyrifos, better results are obtained for the Pt-0.13-ZrO2-0.15-SnO2 sensor, whose signal is favored at 210°C. In addition, the sensitivity of Pt-0.13-ZrO2-0.15-SnO2 with respect to AT-Zr-2.0-ZnO at 220°C is higher for Chlorpyrifos, but lower for Malathion. The statistical treatment method PCA allows the evaluation of the signals of samples with different concentrations of pesticides. The best PCA, obtained with the data of the measurements using the most sensitive sensors, show a total explained variance greater than 90% and a better differentiation between air samples contaminated with pesticides and air samples without contamination.
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Keywords
Óxidos, Estaño, Zinc, Semiconductores--Materiales, Detectores--Pesticidas
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