Molecular Precursor Chemistry Shapes Early-Stage Reaction Pathways in Nitrogen-Doped Carbon Nanotube Synthesis

Abstract

The structural characteristics of carbon nanotubes are usually discussed in terms of processes occurring during nanotube nucleation and subsequent growth from an already formed catalyst nanoparticle. Here, we show that their structural trajectory can begin much earlier, within the first nanoseconds of precursor decomposition and catalyst formation. We combine experiment and reactive molecular dynamics to compare nitrogen-free CNT synthesis with two closely related aromatic nitrogen precursors, pyridine and pyrazine, containing one and two nitrogen atoms per molecule, respectively. Experimentally, both nitrogen-containing precursors promote bamboo-like CNT formation and produce substantially more structurally disordered CNTs than the nitrogen-free reference. Notably, nitrogen incorporation does not scale simply with the amount of nitrogen supplied, demonstrating a strong contribution from precursor chemistry. Reactive molecular dynamics reveals that nitrogen-containing precursors significantly modify local Fe-carbon and Fe-SiO2 interactions during catalyst evolution, while pyridine and pyrazine exhibit distinct decomposition pathways, with pyrazine showing significantly greater decomposition within the simulated timescale. These results demonstrate that precursor chemistry influences the local chemical environment and early catalyst evolution, highlighting its potential role in the initial stages of CNT growth.