Multilayered and Chemiresistive Thin and Thick Film Gas Sensors for Air Quality Monitoring

Abstract

Selective detection of gases such as nitrogen dioxide (NO 2 ), carbon monoxide (CO), carbon dioxide (CO 2 ), and various volatile organic components (VOCs) is necessary for air quality monitoring. Detection of hydrogen (H 2 ) is equally important as it is a flammable gas and poses serious threat of explosion when exposed to oxygen gas. We have studied the sensing characteristics of these gases using thin film deposited by chemical solution deposition as well as relatively thicker films deposited by atmospheric plasma spray (APS) process. The chapter starts with the sensing mechanism of chemiresistive sensors followed by the definition of gas sensing parameters. Subsequently, we have demonstrated selective NO 2 sensing characteristics of zinc oxide-graphene (ZnO-G) multilayered thin film followed by CO and H 2 sensing characteristics of ZnO thin film and SnO 2 thick film. Cross-sensitivity among CO and H 2 gases has been addressed through the analysis of conductance transients with the determination of activation energy, E a , and heat of adsorption, Q. The concepts of reversible and irreversible sensing have also been discussed in relation to CO and H 2 gases. CO 2 sensing characteristics of LaFe 0.8 Co 0.2 O 3 (LFCO)-ZnO thin film have been elucidated. Interference from CO has been addressed with principal component analyses and the ascertaining of E a and Q values. Additionally, the variation of response with temperature for each gas was simulated to determine distinct parameters for the individual gases. Further, VOC sensing characteristics of copper oxide (CuO) thin film and WO 3 -SnO 2 thick film were investigated. Principal component analysis was performed to discriminate the gases in CuO thin film. The interaction of WO 3 -SnO 2 thick film with various VOCs was found to obey the Freundlich adsorption isotherm based on which E a and Q values were determined.Keywords: air quality monitoring, gas sensing, thin film sensor, thick film sensor, Langmuir adsorption isotherm, Freundlich adsorption isotherm, reversible sensing, irreversible sensing Salient features of semiconducting oxide gas sensorSemiconducting metal oxide (SMO) sensors are attractive for lower cost, smaller size, simpler operation principle, durability, and ease of fabrication together with their low concentration of gas detection limit [9]. These sensors change their conductivity when exposed to test gases of different concentrations [9]. However, the sensor operating temperature ($300°C) needs to be lowered, and cross-sensitivity toward multiple gases needs to be minimized for its wide commercial adaptation. The operating principle and salient features of SMO-based chemiresistive sensors are briefly described as follows:3 Multilayered and Chemiresistive Thin and Thick Film Gas Sensors for Air Quality Monitoring DOI: http://dx.doi.org/10.5772/intechopen.89710

Metal-Oxide Based Nanomaterials: Synthesis, Characterization and Their Applications in Electrical and Electrochemical Sensors

“…To summarize, for p-type MOX, an increase in resistance if exposed to reducing gas, while a decrease in resistance if exposed to oxidizing gas were observed. This is exactly the opposite behavior with respect to n-type MOX sensing materials [ 54 , 58 , 59 ].…”

Carbon Dioxide Sensing—Biomedical Applications to Human Subjects

“…As stated earlier, our aim is not to produce a complete bibliographic review of each mentioned technique. We do so for the sake of conciseness, and because comprehensive reviews focusing on one or another of the techniques presented here are available in the literature [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. While the latter performs an in-depth coverage of their respective topic (e.g., nanomaterials-based sensors [ 18 , 22 ]), they never cover the full range of CO sensing possibilities.…”

“…Interestingly, while most works focused on the change in conductivity of metal oxide upon CO adsorption, other works were based on capacitive [ 171 , 175 , 190 ], work function [ 173 , 174 ] or optic properties [ 161 ] measurements. Thorough reviews on metal oxide-based sensors for gas sensing—although not focused on CO detection alone—are also available [ 23 , 191 ].…”

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“…Chemosensors 2021, 9, x FOR PEER REVIEW 2 of 11 the chemisorption interaction mostly takes place at the geometric surface and, to a limited extent, along grain boundaries. Meanwhile, for a thick-film sensor, the active surfaces are much larger, due to the porous nature of the film, and the gas interaction occurs throughout the bulk material [8]. Furthermore, thick-film gas sensors have other added advantages, including low-cost material deposition, simple construction, and good sensing properties, making them more favourable to some VOC applications [9].…”