The coalescence and reconstruction of closed-shell graphitic carbon: from a nanosized polyhedron to a micron-sized dish stacked structure by KOH activation

Abstract

The coalescence and structural transformation of closed-shell graphitic carbon (CGC) induced by KOH activation were investigated by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy. It was found that with graphitization at 2800 °C, CGC retains a nanosized polyhedral structure with a diameter of ca. 25 nm. These thermally stable CGC nanoparticles could be coalesced and reconstructed to form a micron-sized dish stacked structure when treated by low temperature KOH activation at 400 °C. Each of the obtained carbon dishes retained a high crystallinity and possessed few layer graphene-like structure with closed loop edges. During activation, defects, disordered carbon atoms and dangling bonds were introduced into the CGC, which provide active positions for the coalescence and reconstruction of these nanoparticles. With the destruction of the closed-shell structure and the structural transformation, the inner-stress of these polyhedral nanoparticles was released. Accordingly, a possible formation mechanism was suggested.