Critical review on mechanochemical fabrication of full-carbon graphyne material

Graphyne, a novel regularly sp-/sp²-hybridized carbon allotrope, has attracted significant interest in synthetic chemistry and various applications. As a promising approach for material synthesis, mechanochemistry has first been successfully applied to fabricate γ-graphyne (γ-GY) which exhibits highest structural stability among graphyne family and possesses fascinating properties like a direct bandgap and unique nanoporosity. The γ-GY skeleton forms via an alkyne nucleophilic cross-coupling reaction induced by intense mechanical energy using hexahalobenzene and calcium carbide as precursors. This mechanochemical strategy is simple, high-yielding, scalable, and commercially viable. This review aims to offer a comprehensive and critical understanding of mechanochemical synthesis of γ-GY. Firstly, the basic concept, physicochemical properties and potential applications of graphyne, especially γ-GY, are introduced. Subsequently, the review summarizes several state-of-the-art synthetic strategies for γ-GY and corresponding representative characterizations. Furthermore, the feasibility of mechanosynthesis for γ-GY is elucidated through the discussion of its origin which involves mechanochemical dehalogenation, and its subsequent development for the synthesis of alkynyl cross-linked carbon derivatives. The reaction mechanism, and controversial factors (including solvent issue, side reaction, and carbonaceous impurities) of the mechanochemical route are adequately outlined and analyzed. Evidence confirms the existence of γ-GY in the as-prepared sample and inevitable generation of by-products such as carbonaceous impurities. Finally, the challenges and future research directions of mechanochemical synthesizing high-quality γ-GY and derivatives (analogues) are proposed.