CO and NO Detection by MN₄@SWCNT in Background Gases: Multiscale DFT, Microkinetic, Boltzmann Transport Study

Detecting hazardous gases like CO and NO at room temperature is vital for environmental and health monitoring. While single-walled carbon nanotubes (SWCNTs) are a potential material for a room-temperature sensor, their pristine forms exhibit very weak adsorption toward CO and NO gases. This study investigates the sensing performance of SWCNTs embedded with transition metal-nitrogen (MN₄) active sites (M = Mn, Fe Co, Ni, Cu). These active sites are known for their ability to properly bind small gases in various catalytic applications. By combining density functional calculations, microkinetic simulations, and Boltzmann conductivity calculations, we account for atmospheric background gases to provide a realistic evaluation of sensor selectivity and response. Our findings indicate that relative adsorption energies govern surface coverage, while changes in conductivity correlate with the density of states near the Fermi level. Our results show that the CuN₄@SWCNT system emerges as the optimal candidate for CO detection within the 1-10⁵ ppm working range. The NiN₄@SWCNT system is also viable for CO detection in this range, provided that interfering species such as NO and NO₂ are absent. For NO detection, the NiN₄@SWCNT system is identified as the best performer, operating effectively in the ultra-low concentration range (~0.01-100 ppb) with high selectivity. This work also elucidates the fundamental trade-off between adsorption strength and recovery time, offering a robust theoretical framework for designing highly selective and reversible gas sensors relevant to health risk monitoring and early warning applications.