Ultrasensitive H₂S and CH₃SH Sensors Based on SnO₂ Porous Structures Utilizing Combination of Flame and Ultrasonic Spray Pyrolysis Methods

The National Institute for Occupational Safety and Health (NIOSH) has established exposure limits for sulfur-based volatile components, particularly hydrogen sulfide (H2S), at 20 ppm for an 8-h exposure and 50 ppm for durations under 10 min. Detecting such toxic gases at low levels necessitates innovative sensor fabrication. This study introduces a unique sensor design, involving the direct thermophoretic deposition of SnO2 aerosol streams on one side and densely compacted SnO2 thick films via ultrasonic spray pyrolysis (UPS) on the other side, acting as a heater. Analyzing flame-made SnO2 particles using Brunauer–Emmett–Teller (BET), XRD, and transmission electron microscopy (TEM) techniques revealed highly crystalline particles approximately 8 nm in size. Methyl mercaptan (CH3SH) and H2S were employed as analyte gases, ranging from 20 ppb to 25 ppm and from 20 ppb to 50 ppm, respectively. The results indicate that the flame-made SnO2 exhibits significant potential for developing gas sensors that are highly sensitive to CH3SH and H2S gases across a broad concentration range. The sensor demonstrates a linear increase in response at lower concentrations, saturating at concentrations exceeding 20 ppm. Consequently, highly sensitive gas sensors capable of detecting very low levels can be manufactured, suitable for machine learning applications in environmental monitoring, healthcare, and industrial safety.