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

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.