Table 1.

Comparison of various catalysts assisted growth of CNCs reported in the literature

No.	Catalysts	Preparation method	Puritya	Economyb	Thickness of carbon layer (μm)	Yield	Refs.
1	Ag/K	Thermal evaporation	Good	Fair	Several microns	–	[35]
2	Au/K	Thermal evaporation	Good	Fair	Several microns	–	[34]
3	Cu	ALD	Excellent	Fair	Few	–	[28]
4	BaSrTiO3/Sn	Mechanical mixing	Excellent	Fair	Few	–	[36]
5	Na/K	Solution method	Good	Good	–	1178%	[37]
6	Fe	Sol–Gel method	Excellent	Fair	Few	8078%	[23]
7	Fe/In/Sn	PVD	Good	Fair	–	–	[33]
8	Fe/Sn	Solution method	Good	Good	Tens of microns		[30]
9	Fe/Sn	PVD	Good	Fair	Tens of microns		[41]
10	Fe/Sn	Sol–Gel method	Good	Good	–	2510%	[29]
11	Fe/Sn	Solution method	Good	Good	Several of microns	–	[30]
12	Fe/Sn	PVD	Good	Fair	Several of microns	–	[42]
14	Fe	Sol–Gel method	Good	Good	–	7474%	[24]
15	Fe/Sn	Solvothermal method	Excellent	Good	Few	9098%	This work

^aExcellent: The products are basically carbon nanocoils, and there is no by-product carbon layer; Good: The products are composed of carbon nanocoils and carbon layer

^BGood: The equipment used is common, and the chemical reagents used are low cost. Fair: use of expensive equipment or chemical reagents containing noble metals