Charge-Transfer Induced Reactivity in sp Carbon Atomic Wires: Towards 0-D sp-sp2 Nanostructures

TL;DR

This study demonstrates electrochemical reduction of carbon atomic wires into stable amorphous sp-sp2 carbon nanoparticles with tunable sizes, preserving chain length and sp character, opening pathways for quantum-dot applications.

Contribution

It introduces a novel electrochemical synthesis method for stable, size-controlled amorphous sp-sp2 carbon nanoparticles from polyynes, with preserved chain length and sp character.

Findings

Formation of amorphous carbon nanoparticles with tunable diameters.

Nanoparticles retain over 60% sp character and show stability for over six months.

Size control influences disorder and chain length preservation.

Abstract

Carbon Atomic Wires (CAWs) are finite linear chains of sp-hybridized carbon atoms. Here the electrochemical reduction of CAWs in the form of polyynes (i.e. with alternated single-triple bonds) is reported. Upon applying a reducing potential to a solution containing polydispersed hydrogen-capped polyynes, the formation of a black precipitate was observed. Electronic absorption spectroscopy confirmed the irreversible reaction of the carbon chains while excluding degradation or side reactions. Subsequent analyses revealed that the precipitate consisted of amorphous carbon nanoparticles with tunable diameters. This control over particle size is attributed to the modulation of growth kinetics through restricted mass transport toward the solid-liquid interface. Raman spectroscopy showed that the resulting material exhibits an amorphous sp-sp2 character, with a retained sp fraction exceeding 60%. Smaller nanoparticles displayed reduced disorder within the sp2 domains and a broader distribution of sp-chain lengths preserved in the amorphous matrix. Additional experiments on size-selected polyynes suggest that this synthesis method allows to better preserve the starting chain length in the final structure. Unlike previously reported amorphous sp-sp2 carbon networks, the nanoparticles produced in this study show remarkable stability under ambient conditions, retaining their sp character for times in excess of six months. These findings pave the way for future applications, particularly as further diameter tuning may enable access to the quantum-dot regime.