Single-walled carbon nanotubes filled with sulfur and phosphorus compounds for real-time detection of NO2 in air

Filling cavities in single-walled carbon nanotubes (SWCNTs) opens up additional opportunities for modifying their surface physicochemical properties. Here, we use a vaporization-condensation method to encapsulate individual phosphorus and sulfur and their mixtures and study the effect of filler composition on the gas sensor properties of SWCNTs with respect to nitrogen dioxide exposure. The introduction of a filler leads to significant improvement in the sensor's response to low concentrations of nitrogen dioxide in the air by enhancing charge transfer, reducing the number of adsorption sites inside the bundles/nanotubes, and lowering the adsorption energy. Sensors based on filled SWCNTs exhibit a calculated detection limit of 2–7 ppb NO₂ at a response time of less than 1 min, long-term stability of more than one year, and exceptional selectivity to NO₂.