Buffer gas optimization in CO2 laser ablation for structure control of single-wall carbon nanohorn aggregates Original Research Article

We succeeded in morphology-selective preparation of single-wall carbon nanohorn (SWCNH) aggregates by changing the buffer gas (760 Torr) in CO2 laser ablation of graphite: He for seed type, N2, Ar and Ne for dahlia type, and Kr for petal dahlia type. In Xe, aggregates of thin graphene sheets were the major product. The degree of graphitization increased with the mass number of the buffer gas. We specifically compared the structure and properties of SWCNHs prepared in N2 with those prepared in Ar for possible costs reduction for production by substituting N2 for Ar buffer gas. As-grown SWCNH aggregates prepared with N2 had smaller specific surface area than those prepared in Ar, however, this discrepancy almost completely disappeared with heat treatment at 1200 °C. By additional oxidation treatments, the specific surface area of the former became larger than the latter, and this is the largest surface area ever reported. We inferred that as-grown SWCNH aggregates (N2) had less number of petal-like graphenes, therefore after the removal of non-SWCNH carbons by the heat treatment and/or oxidation, leading to the large surface area.