Metal-free nanodiamond catalyst for alcohol–amine oxidative coupling to imine

Metal-free catalyst in imine synthesis was a great challenge due to the continuous rise in metal prices and unfriendly massive mining of metal. Herein, sp 2 /sp 3 hybridization nanodiamond–graphene (ND@G) was obtained by simple heat treatment of the commercially nanodiamonds (ND) under argon atmosphere, the as-prepared catalyst showed excellent activity and selectivity for directly imine synthesis. The physical structure changes of nanodiamond before and after heat treatment were well-characterization, and it was found that the nanodiamond surface layer changed from disordered sp 3 hybridized carbon to sp 2 /sp 3 core–shell structure. This study demonstrates the possibility of using metal-free catalysts for imine synthesis by nanodiamond.