Objective The residual catalyst during the preparation of helical carbon nanofibers(HCNFs) can affect its intrinsic properties. Acid washing is often used to remove the catalyst in helical carbon nanofibers, but it can destroy the structure of the fiber and increase the cost of use. Helical carbon nanofibers were prepared by using water-soluble salt as catalyst, and the catalyst was removed by washing to obtain high-purity helical carbon nanofibers.

Methods Helical carbon nanofibers were prepared by chemical vapor deposition using potassium carbonate as catalyst and acetylene as carbon source. The potassium carbonate catalyst was removed by simple water washing, and the effect of preparation temperature on the morphology of helical carbon nanofibers was investigated. The microstructure and elemental composition of the helical carbon nanofibers were characterized by field emission scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The crystal structure and surface functional groups of the helical carbon nanofibers were characterized by X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy.

Results The helical carbon nanofibers prepared at 700 ℃ have a diameter of about 60 nm, a helical structure and a uniform morphology. The carbon atoms of HCNFs are arranged in a short-range order, mainly composed of C-H and C=C functional groups. The potassium carbonate catalyst has a rhombic symmetrical structure in the fiber, resulting in a chiral symmetrical growth of the fiber on both sides of the catalyst.

Conclusions Helical carbon nanofibers with uniform morphology were prepared by chemical vapor deposition. High purity helical carbon nanofibers can be obtained by washing off the surface catalyst.