An essential role of CO₂ and H₂O during single-walled CNT synthesis from carbon monoxide

Single-walled carbon nanotubes (CNTs) were synthesized from carbon monoxide and iron catalyst nanoparticles by two different aerosol methods. The catalyst particles were produced by physical vapor nucleation using a resistively heated iron wire (hot wire generator) and by thermal decomposition of ferrocene vapor. The essential role of etching agents (CO₂ and H₂O) in the CNT formation process was demonstrated. An addition of small amounts of CO₂ and H₂O vapor in the reactor resulted in an increase in CNT length. Also, the CO₂ introduction was found to decrease the minimum temperature for CNT synthesis from 890 °C to below 600 °C.