Purification of single-walled carbon nanotubes by HCl treatment and analysis of the field emission property

High-quality single-walled carbon nanotubes (SWCNTs) were synthesized by catalytic decomposition of C₂H₂ using Fe-Mo/MgO catalyst at 800°C The as-synthesized SWCNTs typically occurred in the form of a bundle with a diameter of 10-20 nm together with amorphous carbon and catalytic impurities, which were removed by a two-step purification process consisting of oxidation and an acid treatment. The oxidation step, using an O₂-Ar mixture at 380°C for 5 hr in a vertical-type furnace and aHNO₃ treatment at 100°C for one hour, was utilized to remove the amorphous carbon particles. Subsequently, metallic catalysts were removed in HCl at room temperature for 5 hr under magnetic stirring. The SWCNT suspension was prepared by dispersing the purified SWCNTs in an aqueous sodium dodecyl benzene sulfonate solution with horn-type sonication. This was then air-sprayed on glass to fabricate CNT field emitters. The samples had a turn-on field value of 4 V/μm and a current density of 0.67 mA/cm² at 9 V/μm. Increasing the HCl treatment time improved the field emission properties.