Correlation between Microstructure and Chemical Composition of Zinc Oxide Gas Sensor Layers and Their Gas-Sensitive Properties in Chlorine Atmosphere

Abstract

In this article, we present results concerning the impact of structural and chemical properties of zinc oxide in various morphological forms and its gas-sensitive properties, tested in an atmosphere containing a very aggressive gas such as chlorine. The aim of this research was to understand the mechanism of chlorine detection using a resistive gas sensor with an active layer made of zinc oxide with a different structure and morphology. Two types of ZnO sensor layers obtained by two different technological methods were used in sensor construction. Their morphology, crystal structure, specific surface area, porosity, surface chemistry and structural defects were characterized, and then compared with gas-sensitive properties in a chlorine-containing atmosphere. To achieve this goal, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL) methods were used. The sensing properties of obtained active layers were tested by the temperature stimulated conductance method (TSC). We have noticed that their response in a chlorine atmosphere is not determined by the size of the specific surface or porosity. The obtained results showed that the structural defects of ZnO crystals play the most important role in chlorine detection. We demonstrated that Cl2 adsorption is a concurrent process to oxygen adsorption. Both of them occur on the same active species (oxygen vacancies). Their concentration is higher on the side planes of the zinc oxide crystal than the others. Additionally, ZnO sublimation process plays an important role in the chlorine detection mechanism.

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“…Among many nanomaterials, zinc oxide nanostructures are exceptionally attractive thanks to their unique functional properties and the diversity of their applications. They have been used in many fields as gas sensors [8], piezoelectric devices [9], solar cells [10], fillers in polymeric nanocomposites [11,12], coatings [13,14], antimicrobial agents [15], and in textiles [16].…”

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“…With the development of the economy and the substantial improvement at industrial level, there are a growing number of toxic and harmful gases in the air, which pollute the environment and also seriously endanger human health [1][2][3]. Toluene gas, for example, produced during indoor decoration, has been linked to vision impairment; asthma; nasopharyngeal cancer; and other diseases and health events, including pregnancy loss [4][5][6][7]. In addition, when people are exposed to high concentrations of toluene vapor (200 ppm-500 ppm), various symptoms, such as headache, nausea, muscle cramps, and dizziness, may occur.…”

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