Metal-free synthesis of carbon nanotubes filled with calcium silicate

A new metal-free catalyst CaSiO3 was developed to grow carbon nanotubes (CNTs) on a pyrolytic graphite paper tape by an ethanol catalytic chemical vapor deposition method at 1200–1400 °C. The prepared CNTs with a droplet tip had a multi-walled structure and were filled with amorphous CaSiO3. Temperature, determining the melting of CaSiO3, was critical for the growth of the CNTs. This new catalyst is suggested to follow the similar roles of transition metals in the growth of CNTs by a molten state to absorb carbon and form CNTs after reaching saturation.