## 1 Introduction  
The extraordinary combination of distinctive physical and chemical properties of carbon nanotubes (CNTs)--including high thermal and electrical conductivity, large surface area per unit mass, robust mechanical properties, a wide range of electronic properties, and promising potential for practical applications--has clearly captured the imagination of the research community [1, 2, 3, 4]. Specifically, CNTs promise to emerge as fundamental components for advanced high-strength composites [5, 6], sensitive components in gas sensors [7], and key elements in lithium-ion batteries [8]. At the same time, the need for effective materials to facilitate the cathodic oxygen reduction reaction (ORR), cold electron emitters, and chemical capacitor electrodes has increased the demand for nitrogen-doped carbon nanotubes (N-CNTs) [9, 10, 11, 12, 13]. This requirement is supported by the incorporation of nitrogen in various chemical configurations, intricately integrated into the graphene wallsof the nanotubes. This procedure, in turn, exerts a profound influence on the physicochemical properties of these nanotubes. Specifically, this influence induces an increase in the concentration of n-type charge carriers, an increase in the surface energy, and a decrease in the work function. These configurations are based on three different nitrogen defect arrangements in graphene, illustrated in Figure 1: the pyridinic, pyrrolic, and graphitic (or quaternary) forms [14; 15; 16]. In the pyridinic configuration, two nitrogen electrons actively participate in \(\sigma\) bonds with adjacent carbon atoms, one electron contributes to the \(\pi\) system of the CNT, and the remaining two electrons form a lone pair localized near the nitrogen atom. On the other hand, within the pyrrolic configuration, three nitrogen electrons form \(\sigma\) bonds with carbon atoms and the two remaining electrons participate in \(\pi\)-bonding [10; 13; 14]. In addition, graphitic (quaternary) nitrogen refers to a nitrogen atom that replaces carbon atoms in benzene rings without creating vacancies [10; 13; 14]. In this context, the presence of one extra electron on the nitrogen atom makes an additional contribution to the \(\pi\) subsystem of CNTs. Such an increase in electron density can have a significant impact on the density of electronic states near the Fermi level, thereby playing a crucial role in the desired change and improvement in the physicochemical properties of nanotubes [17; 18; 19]. The inclusion of nitrogen into CNTs, known as nitrogen doping, can be achieved through two primary approaches: during CNT synthesis (in situ) or post-treatment (ex situ) methods [18; 19; 20; 21]. In situ doping involves directly incorporating nitrogen heteroatoms into the carbon matrix during the synthesis process and is commonly employed to produce nitrogen-doped CNTs (N-CNTs). Among the various in situ methods, chemical vapor deposition (CVD) and pyrolysis are widely used due to their ability to effectively incorporate nitrogen atoms into the carbon nanotubes [23; 24]. These methods use a wide range of carbon sources (acetylene, ethylene, benzene, methane, toluene, etc.) and nitrogen sources (acetonitrile, ethylenediamine, dimethylformamide, benzylamine, etc.) [25; 26; 27; 28; 29; 30; 31; 32]. Despite their advantages, including the high product yield, relatively low production costs, and flexibility to manipulate synthesis parameters (such as pyrolysis temperature, gas flow rate, and synthesis duration), these methods suffer from limitations. Notably, their lack of precise reproducibility arises from the significant influence of various factors (precursor concentration, gas flow rate, catalyst distribution, substrate type, temperature gradient in the CVD reactor, residual impurities, etc.) on the resulting morphology and structure of N-CNTs, as well as the nitrogen content and its distribution in nanotubes.