Selective synthesis of single walled carbon nanotubes on metal (iron, nickel or cobalt) sulfate-based catalysts

Selective synthesis of single-walled carbon nanotubes (SWCNTs) is highly desirable for various applications. Among the strategies proposed for achieving this, the method involving sulfur-containing compounds is a promising approach showing the conversion of common cobalt/silica catalysts (Co/SiO₂) into chirality selective catalysts. However, the possible influence of sulfur-containing compounds in promoting the selectivity of non-cobalt-based metal/silica catalysts has not been studied. Here three metal sulfate based catalysts (MSO₄/SiO₂, M=Fe, Ni, or Co) were prepared for SWCNT synthesis under the same growth condition. Detailed SWCNT and catalyst characterizations show that well-dispersed Fe oxides and silicates are formed on Fe₂(SO₄)₃/SiO₂, favoring the formation of small diameter (6,5) nanotubes. NiSO₄/SiO₂ contains a portion of NiSO₄ together with Ni silicate and relatively large NiO particles, leading to a wider diameter distribution centered around (8,7) nanotubes. CoSO₄/SiO₂ consists of dominantly well-dispersed CoSO₄ and a small amount of Co silicates, showing the good selectivity toward the relatively larger diameter (9,8) nanotubes with an abundance of 40.6% among the semiconducting nanotubes. Sulfur retained on the catalysts influences the selectivity toward relatively larger diameter SWCNTs. Current work highlights the potential of using metal sulfates with varied decomposition temperatures to achieve the selective growth of SWCNTs.