Abstract
H2S gas is a toxic and hazardous byproduct of the oil and gas industries. It paralyzes the olfactory nerves, with concentrations above 100 ppm, resulting in loss of smell; prolonged inhalation may even cause death. One of the most important semiconducting metal oxides for the detection of H2S is CuxO (x = 1, 2), which is converted to CuxS upon exposure to H2S, leading to a remarkable modulation in the resistance and appearance of an electrical sensing signal. In this review, various morphologies of CuxO in the pristine form, composites of CuxO with other materials, and decoration/doping of noble metals on CuxO nanostructures for the reliable detection of H2S gas are thoroughly discussed. With an emphasis to the detection mechanism of CuxO-based gas sensors, this review presents findings that are of considerable value as a reference.
Highlights
Several types of gas sensors, including chemoresistive gas sensors made of semiconducting metal oxides, electrochemical sensors, optical sensors, and piezoelectric sensors, have been utilized for H2 S gas detection [23,24,25]
CuO is a low-cost semiconducting metal oxide and has a monoclinic crystal structure [31]. It can directly react with H2 S to form a Cux S layer with high conductivity
The oxygen molecules from air are adsorbed onto the sensor surface to form a hole accumulation layer (HAL); thereafter, the sensor resistance decreases relative to vacuum because of the adsorption of electrons as follows [37]: O2 → O2, O2 + e− → O2 −
Summary
H2 S, which has a disagreeable odor, is a colorless, highly toxic, corrosive, flammable, and explosive gas [1,2]. States Occupational Safety and Health Administration (US-OSHA, Washington, DC, USA), the concentration limit for exposure to H2 S within 8 h is approximately 20 ppm [11]. H2 S exposure at concentrations of 1000 ppm and above would result in Chemosensors 2021, 9, 127. The H2 S concentration (~100–500 ppb) in the breath of patients with halitosis is greater than that in healthy individuals. This is primarily due to local oral diseases and certain systemic diseases, such as digestive issues [22]. Detection of H2 S gas is important from the perspectives of safety, industry, and medicine
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