Effect of CO₂ and H₂O on the synthesis of single-walled CNTs

Two different floating catalyst synthesis methods were used to investigate the effect of CO₂ and H₂O vapor on the growth of single‐walled carbon nanotubes (CNTs). As a carbon source and catalyst material, carbon monoxide and iron nanoparticles were used. The catalyst particles were prepared by evaporation from a resistively heated iron wire (hot wire generator) and by thermal decomposition of ferrocene vapor. The essential role of CO₂ and H₂O in the CNT formation was demonstrated. The 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 of the CNT synthesis from 890 °C to below 600 °C.