Sensitive and Reversible Ammonia Gas Sensor Based on Single-Walled Carbon Nanotubes

The present study reports on the fabrication and performance of ammonia sensors based on single-walled carbon nanotubes (SWCNTs) coated with gold nanoparticles (AuNPs). The AuNPs were incorporated onto the SWCNTs using two different methods: sputtering and chemical deposition. The sensors were exposed to controlled concentrations of ammonia at two temperatures, namely, 25 degrees C and 140 degrees C, and their response was monitored through successive cycles of ammonia exposure (0.5 ppm and 1.0 ppm) and nitrogen purging. The results demonstrate that the sputtering-based deposition of the AuNPs on SWCNTs led to the best sensor performance, characterized by a rapid increase in resistance values (t(resp) = 12 s) upon exposure to ammonia and an efficient recovery at 140 degrees C (t(rec) = 52 s). By contrast, the sensor with chemically impregnated AuNPs exhibited a slower response time (t(resp) = 25 s) and the same recovery time (t(rec) = 52 s). Additionally, a novel device was developed that combined MoS2-AuNPs (sputtering)-SWCNTs. This sensor was obtained by impregnating nanosheets of MoS2 onto AuNPs (sputtering)-SWCNTs showing improved sensor performance compared to the devices with only AuNPs. In this case, the sensor exhibited a better behavior with a faster recovery of resistance values, even at room temperature. Overall, the study provides valuable insights into the fabrication and optimization of SWCNT-based ammonia sensors for various applications, particularly in detecting and quantifying small amounts of ammonia (concentrations below 1 ppm).