Ultrasmall carbon nanotube-like network in ZSM-5 by optimized methane CVD

Achieving high filling of sub-nanometer carbon structures in zeolite channels remains challenging because premature carbon deposition can hinder precursor diffusion and internal growth. Here, we report an optimized methane chemical vapor deposition route for growing an ultrasmall carbon nanotube-like network in ZSM-5 zeolite with intersecting 5.1–5.6 Å channels. By introducing methane only after the reactor reaches the target temperature under high vacuum, carbon deposition during heating is suppressed and pore filling is markedly improved. The resulting carbon loading reaches 29.1 wt%, corresponding to a model-dependent estimated pore-filling factor of about 0.98. Raman spectra reveal characteristic features of strongly confined ultrasmall one-dimensional carbon structures, while thermogravimetric analysis indicates high thermal stability. Four-probe transport measurements show metallic-like behavior, further supported by density functional theory calculations. This work shows that process design governs precursor transport, pore filling, confined structure formation, and final properties, and thereby provides a practical route to densely filled ultrasmall carbon networks in zeolite hosts.