The synthesis of sponge-type nitrogen-doped multiwall carbon nanotubes using ball-milled natural red-leptosol as catalyst precursor: A cycle voltammetry study

Sponge-type nitrogen-doped multiwall carbon nanotubes (N-MWCNTs), synthesized via an aerosol-assisted catalytic chemical vapor deposition (AACCVD) method, were extensively studied. A ball-milled and oxidized red-leptosol (RL) was used as the catalyst precursor, and benzylamine worked as a carbon and nitrogen source. The ball-milled and oxidized RL increased their contact area and purity for the N-MWCNT synthesis. X-ray diffraction characterization revealed that raw RL contained kaolinite, quartz, graphite, hematite, and goethite. According to the electron microscopy analysis, the N-MWCNTs exhibited exotic morphologies and microstructures. The high-resolution X-ray photoelectron spectroscopy showed that the as-grown N-MWCNTs contained pyrrolic and pyridinic nitrogen species. The cyclic voltammetry studies demonstrated that the redox processes in the N-MWCNTs in 0.1 M H₂SO₄ were dominated by the carboxyl, pyridinic, and pyrrolic groups. Using the natural RL as a catalyst precursor in AACCVD led to a large yield of N-MWCNTs mixed with different minerals, causing the observed morphologies and influencing the electrochemical behavior, which is of interest in energy-storage and sensing applications.