Ultra-Clean Isotope Engineered Double-Walled Carbon Nanotubes as Tailored Hosts to Trace the Growth of Carbyne

A unique scope of mechanical, optical, and electrical properties makes the 1-D allotrope of carbon, carbyne, one of the most promising materials for applications in various fields. Despite the important progress in the synthesis of carbyne confined to double-walled carbon nanotubes (DWCNTs), its formation and growth mechanisms remain elusive. Here, it is shown how a rational design of isotope-engineered ultra-clean DWCNTs with ¹³C-enriched inner walls—which act as precursors and as tailored hosts—can trace the growth mechanism of confined carbyne upon high-vacuum annealing at high temperatures. It is unambiguously proven that an exchange of C atoms between the inner and outer tubes takes place, and it is distinguished from the growth of confined carbyne. The latter only happens after the ultra-clean DWCNT hosts react by partial oxidation yielding encapsulated carbonaceous products, which are well-defined precursors for the carbyne synthesis with a record of ≈28.8% ¹³C enrichment. Tracing the synthesis of carbyne and disentangling it from concomitant high-temperature processes like healing, reorganization and regrowth of DWCNTs are a crucial step towards accessing the full application potential of confined carbyne hybrids by tailoring the isotopic fillers, as well as the inner and outer tubes of the DWCNT hosts.