Synthesis of helical carbon nanotubes, worm-like carbon nanotubes and nanocoils at 450 °C and their magnetic properties

High purity (99.21 wt.%) helical carbon nanotubes (HCNTs) were synthesized in large quantity over Fe nanoparticles (fabricated using a coprecipitation/hydrogen reduction method) by acetylene decomposition at 450 °C. Field-emission and transmission electron microscope images reveal that the selectivity to HCNTs (with two or three coiled nanotubes connected to a catalyst nanoparticle) is up to ca. 93%. The yield of HCNTs (as defined by the equation: yield=mtotal-mcatalystmcatalyst×100%) is ca. 7474% in a run of 6 h, higher than any of those reported in the literature. If hydrogen was introduced during acetylene decomposition for ca. 30 min, the HCNTs mainly consisted of two coiled tubes connected to a catalyst nanoparticle, and carbon nanocoils (CNCs) of different structures were generated. If hydrogen was present throughout acetylene decomposition, worm-like carbon nanotubes (CNTs) as well as CNCs were produced in large quantities. Because the HCNTs and worm-like CNTs are attached to Fe nanoparticles, the nanomaterials are high in magnetization.