# Effect of Nitrogen Atoms in the CNT Structure on the Gas Sensing Properties of PANI/CNT Composite
###### Abstract  
Herein we report the gas-sensitive properties to ammonia (at 2-10 ppm) of individual nanostructures of a polyaniline/nitrogen-doped carbon nanotube composite with a nitrogen content of 0 at.% (uCNTs), 2 at.% (N-CNTs) and 4 at.% (N\({}^{+}\)-CNTs). Doping of nanotubes with nitrogen was carried out in order to both reduce the electron work function, to form a potential barrier at the \"PANI-CNTs\" interface, and reduce the contribution of nanotubes to the composite conductivity. An increase in the nitrogen content in CNTs leads to an increase in conductivity, a decrease in the work function, and the formation of defects in the outer walls of CNTs. It was found that the structural and chemical state of the polymer layer of all composites is the same. However, polymer morphology on nanotubes changes dramatically with increasing nitrogen content in CNTs: a thin smooth layer on uCNTs, a globular layer on N-CNTs, and a thick layer with a sheet-like structure on N\({}^{+}\)-CNTs. All composites showed the same response time (\(\sim\)20 s) and recovery time (\(\sim\)120 s). Ammonia sensitivity was 10.5 \(\pm\) 0.2, 15.3 \(\pm\) 0.5 and 2.2 \(\pm\) 0.1 ppm\({}^{-1}\) for PANI/uCNTs, PANI/N-CNTs and PANI/N\({}^{+}\)-CNTs, respectively. Based on the results obtained here, we came to the conclusion that the morphological features of the polymer layer on CNTs with different nitrogen content have a dominant effect on the gas reaction than the change in the electronic properties of the polymer at the interface \"PANI-CNT\". polyaniline; carbon nanotube; composite; nitrogen heteroatoms; gas sensing: XPS; NEXAFS 2022127169 20222147169 20222147169 2022147169 2022147169 2022147169 2022147169 2022147169 2022147169 2022147169 2022147169 2022147169 20222147169 20222147169 20222147169 2022214 July 202214 July 2022216 July 202216 July 2022216 July 2 presence of pyridine and quaternary nitrogen in the CNT walls increases the concentration of charge carriers and consequently electrical conductivity. At the same time, nitrogen doping of carbon nanotubes enhances the degree of structural defects and distortion of nanotube walls, which is due to the size of impurity atoms being different from the size of carbon atoms. Thus, by changing the characteristics of nanotubes by doping, it is possible to achieve the required morphological and electronic parameters of PANI/CNT composites for various applications. PANI and PANI-doped composites have excellent reversible response to ammonia [10; 11; 12; 13]. PANI-CNT structures have a large surface-to-volume ratio, which makes them an extremely interesting material for use as the active layer of gas sensors. In this case, the main contribution to the gas response is made by the polymer, while nanotubes act as the reinforcing element and conduction channels. CNTs are known to have poor sensitivity to ammonia. [14]. Moreover, nanotubes in composites are in indirect contact with ammonia gas, but they can shunt the useful signal due to high conductivity. This effect can be eliminated by reducing the contribution of CNTs to the conductivity of composites. One of the possible approaches to reducing the contribution of nanotubes to the conductivity of PANI/CNT composites can be the formation of a potential barrier, opposing the diffusion of charge carriers at the PANI-CNT interface, which is determined by the difference in the work functions of the contacting materials. The work function values for PANI and undoped CNTs are close and amount to 4.4-4.9 and -4.6 eV, respectively [15; 16; 17; 18; 19]. Doping of CNTs with nitrogen atoms decreases the work function value and, consequently, creates a potential barrier at the PANI-CNT interface [20; 21]. Thus, by changing the degree of nitrogen doping of nanotubes, one can change the value of this barrier. In this work, the above-described approach is used to improve the sensing characteristics of PANI/CNT composites by varying the nitrogen concentration in nanotubes. For this purpose, nanotubes with 0, 2 and 4 at.