Catalytic mechanism of Co-containing layered double hydroxide (Co-LDH) as a precursor in carbon nanotube (CNT) synthesis

The synthesis of carbon nanotubes (CNTs) by water-assisted chemical vapor deposition using Co-containing layered double hydroxides (Co-LDH) as catalyst precursors and the catalytic mechanism of Co-LDH catalyst precursors during CNT synthesis were investigated. Co-Al and Co-Mg-Al LDH were prepared by the hydrothermal or homogeneous precipitation method using urea. XPS analysis indicated an increase in Co0 content after a reduction process during CNT synthesis, and the TEM images show that metallic Co nanoparticles were formed while maintaining the LDH platelet-like crystal form. Consequently, these metal particles were found to act as the catalyst for the formation of CNTs. Finally, through control of the flow rate of C2H4 gas during CNT synthesis, the formation of single-walled CNTs with diameters of 4 nm or less was demonstrated.