Self-Assembly of Carbyne Nanocrystals by a Two-step Process Based on Laser Ablation in Liquids

We reported a general strategy for the self-assembly of carbyne nanocrystals by a two-step process based on laser ablation in liquids (LALs). First, a pulsed laser is used to ablate a graphite target in the ethanol liquid injected with nitrogen gas to synthesize hydrogen-capped polyynes, and cyano groups (–CN) are meanwhile generated in the synthesized solution. At the same time, a pulsed laser is used to ablate a gold target in pure water to synthesize the gold nanoparticle (AuNP) colloidal solution. Second, the synthesized solution containing hydrogen-capped polyynes and –CN and AuNP colloidal solution is mixed in a certain proportion and then stands at room temperature for 24 h to self-assemble carbyne nanocrystals. It was found that –CN plays a crucial role in the self-assembly of carbyne nanocrystals. Due to the presence of lone electron pairs, –CN can act as a hydrogen bond acceptor and form hydrogen bonds with the capped hydrogen of polyyne chains, thereby binding together with polyynes to form –CN@polyynes like tadpoles upon the first ablating process. Then, the complexation between –CN and gold causes a large number of –CN@polyyne chains to vertically align on the surface of AuNPs through –CN as an adhesive upon the second mixing step. The polyyne chains on the surface of AuNPs that are adjacent to each other spontaneously form chain bundles through van der Waals interactions between chains, and then nucleate and grow into small crystalline grains and finally grow into nanocrystals through the coalescence of small grains. This method can be expected to become a technique for the macroscopic and controllable synthesis of carbyne nanocrystals.