We report a selective, room-temperature NH
3 gas-sensing platform with enhanced sensitivity, superfast response and recovery, and good stability, using Ag nanocrystal-functionalized multiwalled carbon nanotubes (Ag NC鈥揗WCNTs). Ag NCs were synthesized by a simple mini-arc plasma method and directly assembled on MWCNTs using an electrostatic force-directed assembly process. The nanotubes were assembled onto gold electrodes with both ends in Ohmic contact. The addition of Ag NCs on MWCNTs resulted in dramatically improved sensitivity toward NH
3. Upon exposure to 1% NH
3 at room temperature, Ag NC鈥揗WCNTs showed enhanced sensitivity (9%), very fast response (7 s), and full recovery within several minutes in air. Through density functional theory calculations, we found that the fully oxidized Ag surface plays a critical role in the sensor response. Ammonia molecules are adsorbed at Ag hollow sites on the AgO surface with H pointing toward Ag. A net charge transfer from NH
3 to the Ag NC鈥揗WCNTs hybrid leads to the conductance change in the hybrid.
Keywords:
ammonia gas sensor; nanohybrid; silver nanocrystal; carbon nanotube; high performance; room-temperature