Metal Oxide-Based Sensors for Ecological Monitoring: Progress and Perspectives

This paper aims to provide a large coverage of recent developments regarding environmental monitoring using metal oxide-based sensors. Particular attention is given to the detection of gases such as H2, COx, SOx, NOx, and CH4. The developments and analyses of the design of sensors and types of metal oxide sensing materials are emphasized. The sensing mechanisms and peculiarities of metal oxides used in chemoresistive sensors are provided. The main parameters that affect the sensitivity and selectivity of metal oxide sensors are indicated and their significance to the sensor signal is analyzed. Modern data processing algorithms, employed to optimize the measurement process and processing of the sensor signal, are considered. The existing sensor arrays/e-nose systems for environmental monitoring are summarized, and future prospects and challenges encountered with metal oxide-based sensor arrays are highlighted

Gas sensing properties of Ceo2 nanostructures

>Magister Scientiae - MScThe industrial safety requirements and environmental pollution have created a high demand to develop gas sensors to monitor combustible and toxic gases. As per specifications of World Health Organization (WHO) and Occupational Safety and Health Administration (OSHA), lengthy exposure to these gases lead to death which can be avoided with early detection. Semiconductor metal oxide (SMO) has been utilized as sensor for several decades. In recent years, there have been extensive investigations of nanoscale semiconductor gas sensor

Utilización de una Nariz Electrónica elaborada a partir de MOS para la evaluación y diferenciación de la calidad del pisco peruano

El objetivo de la presente tesis es realizar la diferenciación de las variedades de Pisco (Italia y Quebranta) que cumplan con la Denominación de Origen, así como la diferenciación del Pisco Quebranta con mezclas adulteradas con aguardiente de caña en diferentes proporciones. Para esta investigación se utilizó una nariz electrónica conformada por un arreglo de sensores basados en óxidos metálicos (SnO2 y TiO2) y composites a base de mezcla de óxidos en diferentes proporciones: (SnO2/TiO2) 1:4, (SnO2/TiO2) 1:2 y (SnO2/TiO2) 4:1. Estos materiales fueron dopados con Pt y/o Pd y adicionalmente fueron recubiertos con zeolita-Y. Este material funciona como un tamiz molecular que discrimina moléculas por su tamaño y forma. Para la preparación de los óxidos metálicos se utilizó el método sol-gel, y para el dopaje se utilizó el método por impregnación húmeda. La caracterización de los materiales se realizó mediante las siguientes técnicas: DRX, SEMEDS y FRX, con las que se lograron determinar las estructuras cristalinas y se pudo confirmar la presencia de los dopantes. Asimismo, por espectroscopía Raman se confirmó la presencia de vacancia de oxígenos superficiales, lo cual fue asociado con el incremento en la respuesta del sensor. La información de las respuestas obtenidas del análisis de sensado fue procesada utilizando la técnica de Análisis de Componentes Principales (PCA), esta técnica es un método estadístico multivariado que produce nuevas variables, denominadas componentes principales, a partir de transformaciones lineales de las variables originales, de modo tal que estas nuevas variables maximicen la Varianza Total que indica el nivel de confianza de los resultados. El PCA permite visualizar la diferenciación entre las variedades de pisco, así como la diferenciación frente a un pisco adulterado. Los sensores que mostraron una buena diferenciación de las muestras de Pisco según las variedades Italia y Quebranta son: (SnO2-TiO2)1:4, (SnO2/TiO2)1:2, (SnO2/TiO2) 4:1, 0.05% Pt (SnO2/TiO2) 4:1, 0.1% Pt (SnO2/TiO2)4:1, 0.05% -0.05% Pt-Pd(SnO2/TiO2) 4:1, 0.05% - 0.1% Pt-Pd(SnO2/TiO2) 4:1, 0.1% Pt/SnO2 y 0.05% -0.1% Pt/SnO2. El sensor (TiO2/SnO2) 4:1 es el que muestra una mayor sensibilidad y mayor capacidad para diferenciar las mezclas de Pisco con aguardiente de caña (AC), especialmente en las mezclas con menor concentración de AC. Asimismo, la capacidad de diferenciación mejora con el recubrimiento de zeolita-Y en los siguientes sensores: 0.1% Pt/SnO2 y 0.05%-0.1% Pt-Pd/SnO2.The aim of this thesis is to differentiate the varieties of Pisco (Italia and Quebranta) that act in accordance with the Denomination of Origin, as well as the differentiation of Pisco Quebranta with mixtures adulterated with cane liquor in different proportions. For this research, an electronic nose was used, constituted by an array of sensors based on metal oxides (SnO2 and TiO2) and composites based on oxides mixtures in different proportions: (SnO2/TiO2) 1:4, (SnO2/TiO2) 1:2 and (SnO2/TiO2) 4:1. These materials were doped with Pt and/or Pd and additionally they were coated with zeolite-Y. This material works as a molecular sieve that discriminates molecules by their size and shape. For the preparation of metal oxides, the sol-gel method was used. And for doping, the wet impregnation method was used. The characterization of the materials was performed using the following techniques: XRD, SEM-ED and XRF, with these techniques was possible the determination of the crystalline structures and the presence of dopants was confirmed. Raman spectroscopy confirmed the presence of surface oxygen vacancies, it was associated with the increase of the sensor response. The information obtained from the sensing analysis was processed using the Principal Component Analysis (PCA) technique. This technique is a multivariate statistical method that produces new variables, called principal components from linear transformations of the original variables, in such a way that these new variables maximize the Total Variance that indicates the confidence level of the results. The PCA allows to visualize the differentiation between the varieties of Pisco, as well as the differentiation against an adulterated Pisco. The sensors that showed a good differentiation of the Pisco samples according to the Italia and Quebranta varieties are: (SnO2/TiO2)1:4, (SnO2/TiO2)1:2, (SnO2/TiO2) 4:1, 0.05% Pt (SnO2/TiO2) 4:1, 0.1% Pt (SnO2/TiO2)4:1, 0.05% -0.05% Pt-Pd(SnO2/TiO2) 4:1, 0.05% -0.1% Pt-Pd(SnO2/TiO2) 4:1, 0.1% Pt/SnO2 and 0.05% -0.1% Pt/SnO2. The (SnO2/TiO2) 4:1 sensor is the one that shows greater sensitivity and greater capacity to differentiate the mixtures of Pisco with cane liquor (CA), especially in the mixtures with lower concentration of CA. Besides, the differentiation capacity improves with the zeolite-Y coating in the following sensors: 0.1% Pt/SnO2 and 0.05%-0.1% Pt-Pd/SnO2

Effects of Chemical State of the Pd Species on H2 Sensing Characteristics of PdOx/SnO2 Based Chemiresistive Sensors

In this paper, the PdOx nanoparticles modified SnO2 are prepared using sputtering and wet chemical methods. The SnO2 nanoparticles are separately added to a concentration of 0.75% to 10% PdCl2 to obtain a PdCl2/SnO2 composite material, which is calcined for 1 to 2 h at the temperatures of 120 °C, 250 °C, 450 °C and 600 °C. The PdOx/SnO2 nanocomposite was characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Microstructural observations revealed PdOx with different chemical states attached to the surface of SnO2. Hydrogen response change tests were performed on the obtained PdOx/SnO2 gas sensing materials. The results show that the high gas sensing performance may be attributed to the contribution of the PdOx-loaded SnO2. In hydrogen, the best sensitivity response was attained at 80 °C, which is 60 times that of pristine SnO2. It clarifies the role of PdOx in the gas sensing mechanisms