Insights into the Nucleation and Structure of Lignin-Based Carbon Nanotubes Synthesized Using Iron via Floating Catalyst Chemical Vapor Deposition

Lignin is an abundant biomass resource that can be converted to carbon nanotubes (CNTs) via floating catalyst chemical vapor deposition (FCCVD). This study investigates how Fe catalyst properties impact the synthesis, structure, and properties of lignin-derived CNTs. During CNTs synthesis via FCCVD, increasing the ferrocene concentration yields more CNT products, but the catalyst efficiency declines, as evidenced by the appearance of shorter CNTs and more Fe residue in the product. Transmission electron microscopy reveals that the size and morphology of Fe nanoparticles strongly influence CNT structure, defects, and graphene layer alignment in the nanotube sidewalls during growth. High-temperature graphitization effectively removes residual catalysts from the CNTs and improves their crystallinity and conductivity. During graphitization from 1600 to 2800 °C, the graphene interlayer spacing decreases, while the Raman IG/ID ratio increases from 3.16 to 8.08, electrical conductivity increases from 4.05 × 104 to 5.92 × 104 S m–1, and thermal conductivity can be enhanced from 31.20 to 50.49 W m–1 K–1. Correlating catalyst characteristics with CNT structure evolution provides insights into the controlled synthesis of tailored biomass-derived CNTs with specific structures and properties.