Influence of Carrier Gas Flow Rate on the Synthesis of Long MWCNTs from Biorenewable Carbon Feedstock: α-Pinene.

chemistry Medicinal and pharmaceutical chemistry Nano- and molecular-scale electronics Nano-biomaterials and bioscience Nanomagnetics Nanomaterials, thin films and nanointerfaces Nanomedicine Nanometrology and nanomechanics Nano-optics Nanopatterning, self-assembly and nanofabrication Nanostructures for energy and sensing applications Natural products chemistry Organo main group chemistry Other nanotechnology (unclassified) Other organic chemistry (unclassified) Photochemistry and photovoltaics Physical organic chemistry Supramolecular chemistry This study investigates the efficient synthesis of millimeter-long multi-walled carbon nanotubes (MWCNTs) via the spray pyrolysis of a sustainable α-pinene/ferrocene precursor. The impact of carrier gas flow rate (2500, 5000, and 7500 sccm) on the morphology, purity, and structural integrity of the resulting nanotubes was systematically evaluated across different zones of a horizontal quartz reactor. Results indicate a clear trade-off between growth kinetics and crystalline quality. The maximum nanotube length of 1.416 mm was achieved at the lowest flow rate of 2500 sccm, with length decreasing to 0.584 mm as the flow rate tripled. Conversely, comprehensive characterization using Raman spectroscopy, X-ray diffraction (XRD), and Thermogravimetric Analysis (TGA) revealed that the 5000 sccm flow rate produced the most thermally stable and highly crystalline structures. Spatial analysis across the furnace showed high uniformity in the central isothermal zones, while the entrance and exit sections exhibited higher residual metal content (up to 27.5 wt.%) and reduced crystallinity due to thermal gradients. These findings demonstrate that while lower flow rates favor longitudinal growth, moderate flow rates optimize the graphitic perfection of MWCNTs, providing a tunable pathway for the large-scale production of high-quality nanotubes from bio-derived precursors.

Carbon nanotubes, α-pinene, length profile, spray pyrolysis, crystallinity When a peer-reviewed version of this preprint is available, this information will be updated in the information box above. If no peer-reviewed version is available, please cite this preprint using the following information: Pérez Gasquez y Marín, A.; López-Tinoco, J.; Lara-Romero, J.; Rangel-Segura, R.; Huirache-Acuña, R.; Stacchiola, D. Beilstein Arch. 2026, 202611. doi:10.3762/bxiv.2026.11.v1 Citation data can be downloaded as file using the "Download" button or used for copy/paste from the text window below. Citation data in RIS format can be imported by all major citation management software, including EndNote, ProCite, RefWorks, and Zotero. © 2026 Pérez Gasquez y Marín et al.; licensee Beilstein-Institut. This is an open access work licensed under the terms of the Beilstein-Institut Open Access License Agreement (https://www.beilstein-archives.org/xiv/terms), which is identical to the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0). The reuse of material under this license requires that the author(s), source and license are credited. Third-party material in this work could be subject to other licenses (typically indicated in the credit line), and in this case, users are required to obtain permission from the license holder to reuse the material.