Synthesis of crown-ether-embedded graphene by the solution plasma

Abstract

Crown ethers consisting of several ether linkages (R–O–R′) have been attracting attention in the fields of inorganic and organic chemistry, attributed to their cavity sizes and superior cation selectivity. However, they exhibit comparatively low selectivity and ion-binding affinities due to their structural flexibility. Recent studies have shown that crown ethers rigidly formed within 2D matrices, e.g., graphene, exhibit enhanced binding energy and selectivity. However, most of these studies were based on computational modeling and simulations. In this study, the synthesis of crown-ether-embedded graphene was attempted for the first time by the solution plasma process (SPP). Crown-ether-embedded graphene was successfully synthesized through C–H activation and polymerization reactions between as-produced intermediates (i.e., polycyclic aromatic hydrocarbons, including multiply fused benzene rings) and activated cation radicals. Structural and chemical analyses were conducted to verify the existence of the crown ether structure (cyclic ether, C–O–C) in the carbon matrix, and a 2D graphene structure with a cavity originating from the crown ether was observed by transmission electron microscopy analysis. Moreover, adsorption test confirmed successful synthesis of crown ether-embedded graphene with ordered cavity size. We believe that the proposed synthesis approach for crown ether-embedded graphene will be valuable for a wide range of applications, such as ion-selective membrane applications and waste cleanup.