Enhanced Detection of Hydrogen Sulfide Gas Using TEMPO-Functionalized Single-Walled Carbon Nanotube Electrochemical Sensors

Hydrogen sulfide (H₂S) is a toxic gas characterized by its corrosive and flammable properties, commonly found in hot springs, volcanic regions, and certain food sources. It is distinguished by its distinctive rotten egg odor and is typically produced through the bacterial decomposition of organic matter in oxygen-deficient environments. This gas is generated in industrial settings such as sewage treatment plants and slaughterhouses, and is a byproduct in various industrial processes including gas treatment, wood pulp processing, elemental sulfur production, and wastewater treatment. Due to its higher density compared to air, H₂S can rapidly accumulate in confined spaces such as tunnels and mines, posing significant risks of explosion and asphyxiation. At low concentrations, H₂S causes irritation to the eyes and respiratory system. It can be detected by its rotten egg smell; however, at concentrations exceeding 100 ppm, it can lead to olfactory fatigue, increasing the risk of accidents. Higher concentrations (&gt;500 ppm) can cause severe lung damage and potentially fatal asphyxiation.<br/>In this work, we introduce an electrochemical sensor designed to detect H₂S gas in the concentration range of 0.01 ppm to 100 ppm. This sensor leverages single-walled carbon nanotubes (SWCNTs) functionalized with 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) to enhance sensitivity. SWCNTs, defined as one-dimensional materials with hexagonal carbon structures, exhibit high aspect ratios and conductivity, resulting in low power consumption, high elasticity, and thermal conductivity, which confer thermal and chemical stability. The porous structure of SWCNTs is particularly suitable for gas sensing applications. Specifically, the chemical resistance of gas sensing related to surface reactions benefits from the substantial surface area and the significant quantity of atoms present on the nanostructured material surfaces. This leads to pronounced changes in the electrical signal even at very low gas concentrations, thereby enhancing sensitivity. In nanostructured materials, a considerable proportion of surface atoms are unscreened, resulting in high surface energy and strong molecular forces. This facilitates the adsorption or chemical bonding with gas molecules more readily than bulk atoms, enabling room temperature gas detection using nanostructured materials.<br/>The fabrication process involves a simple method for forming the sensor surface, demonstrated through the deposition of SWCNTs using drop-coating techniques. The TEMPO-functionalized sensor exhibits a sensitivity improvement of 201.056% at 0.01 ppm compared to the pristine SWCNTs sensor. Gas sensing measurements were conducted using a Gas Probe Station, and the sensor's response was analyzed. The results indicate that the developed sensor holds promise for real-time, low-concentration detection of H₂S gas at room temperature.