Highly Efficient Response of Ammonia Gas Sensor Based on Surfactant-Free Sorted-Semiconducting Single-Walled Carbon Nanotubes at Room Temperature

A comparative analysis of sorted semiconducting (sc-) single-walled carbon nanotubes (SWCNTs) films, metallic (m-) SWCNTs films, pristine SWCNTs films, and graphene-based simple two-terminal sensors for the applications of ammonia gas sensing is presented. The comparison of the sensing response of different devices by separately measuring the SWCNTs film resistance and the contact resistance between SWCNTs and the electrodes reveals that the performance mainly relies on the modification of tube conductivity under exposure to gas. Moreover, the measurements show that the highest sensitivity of the devices is achieved by use of sc-SWCNTs as the conducting channels. Sensor coated with surfactant-free sc-SWCNTs shows a sensitivity of 0.78% ppm at 5–100 ppm ammonia (NH₃) concentrations that happened to be ≈28, ≈22, and ≈173 times more sensitive than pristine-SWCNTs, m-SWCNTs, and graphene-based sensors, respectively, at 50 ppm and ≈4.5 times the previously reported sc-SWCNTs-based sensor at 5 ppm. Notably, all the experiments values are achieved at room temperature without any extra heating treatment for the recovery process. These results show that surfactant-free sc-SWCNTs provide a promising way of creating sensors with improved selectivity and sensitivity, which predicts the auspicious prospects in the development of future applications.