Optimization and evaluation of networked single-wall carbon nanotubes as a NO2 gas sensing material

We have prepared conductometric NO2 gas sensors based on single-wall carbon nanotube (SWNT) networks. The SWNT properties are modified systematically by varying the annealing temperature between 350 to 550 °C under vacuum. Thermal annealing is not only necessary to remove dispersant used for nanotube dispersion but also plays an important role in optimizing the gas sensing abilities. In this paper, the sensing performance is evaluated through three crucial sensing characteristics: sensitivity to NO2, humidity interfering effect, and sensor stability over repeated use, all examined at room temperature. The sensor annealed at 400 °C shows the highest NO2 sensitivity because of the structural properties, i.e., high specific surface area and the molecular geometry of having all carbon atoms at the tube-surface. The sensor also shows negligible humidity interfering effect and high sensor stability, originating from the hydrophobicity and chemical stability of the material, respectively. In contrast, annealing temperatures higher than 400 °C lead to structural defects in SWNTs and thus lower the sensing performance. We experimentally confirm that these SWNT characteristics make SWNTs a suitable gas sensing material from a practical perspective.