Room-temperature generation and transformation of graphitic CQDs into mixed sp2–sp3 hybridized carbon allotropes from liquid oxygenates

Abstract

The synthesis of nanocrystalline sp²–sp³ hybrid structures holds immense promise for advancing materials science, but conventional synthetic methods, which rely on graphite as a precursor, are economically and energetically impractical. In this study, we report a room-temperature strategy for generating nanocrystalline sp²–sp³ hybridized carbon allotropes from liquid oxygenates via graphitic CQDs intermediates. A range of liquid oxygenates including acetic acid, formic acid, acetone, acetaldehyde, ethanol, glycolic acid, acrylic acid, glycine, and glucose were employed as carbon sources. Under controlled electrochemical conditions that are conducive to an abundance of excess electrons on negatively charged metal nanoparticles (NPs), C₂ radicals are generated from these liquid oxygenates. Experimental results provide evidence of the formation of linear acetylenic carbon intermediates and graphitic CQDs in the electrolyte and on the cathode, alongside the transformation of CQDs into nanocrystalline sp²–sp³ hybrid carbon on the electrode. Complementary DFT studies support a mechanism wherein C₂ radicals align and bond into linear acetylenic carbon chain through intermolecular interactions, rather than strong adsorption to the surface. Meanwhile, the sp²-to-sp³ transformation is facilitated by the negatively charged metal nanoparticles, with the degree of transformation being dependent on the crystallographic structure of the metal (e.g. Ag > Bi). This approach provides not only a simple and energy-efficient synthesis route, but also a platform with potential to revolutionize the fabrication of advanced carbon materials by optimizing each step of the formation process through the interaction between negatively charged metal nanoparticles and liquid oxygenates.