Edge‐Selectively Functionalized Graphene Nanoplatelets

Abstract

Graphene, as a single layer of graphite, is currently the focal point of research into condensed matter owing to its promising properties, such as exceptional mechanical strength, high thermal conductivity, large specific surface area, and ultrahigh electron-transport properties. Therefore, various physical and chemical synthetic procedures to prepare graphene and/or graphene nanoplatelets have been rapidly developed. Specifically, the synthesis of edge-selectively functionalized graphene (EFG) has been recently reported by using simple and scalable approaches, such as "direct" Friedel-Crafts acylation reactions in a mild acidic medium and a mechanochemical ball-milling process. In these approaches, chemical functionalization predominantly take place at the edges of the graphitic layers via the covalent attachment of targeted organic "molecular wedges". In addition, the distortion of the crystalline structures in the basal plane, which is beneficial for preserving the unique properties of the graphitic framework, can be minimized. In addition, the efficient exfoliation of graphene can be achieved, owing to the strong repulsive forces from the covalently linked wedges and strong shear forces during the reaction. Furthermore, EFG shows promising potential in many useful applications, such as highly conductive large-area films, metal-free electrocatalysts for the oxygen-reduction reaction (ORR), and as additives in composite materials with enhanced properties. Herein, we summarize the recent progress and general aspects of EFG, including synthesis, reaction mechanism, properties, and applications.

Facile production of ultrathin graphitic carbon nitride nanoplatelets for efficient visible-light water splitting

“…Meanwhile, the strong (002) peak at 27.5°, corresponding to the interlayer stacking of conjugated aromatic systems [35] in pristine bulk GCN, broadens and diminishes in the XRD spectrum of the UGCNPs, signifying that a high degree of exfoliation [27,28] occurred without lattice expansion during ball milling. As size reduction could generally provide entropic gains for good dispersion [30], the UGCNPs can be homogenously dispersed in various Nano Res. common solvents such as isopropanol, acetone, dimethylformamide, and water at concentrations of up to 0.1 mg·mL -1 , without precipitation even after storage for 1 month under ambient conditions (Fig.…”

“…Samples of bulk GCN were first prepared by using melamine as the precursors, and UGCNPs were synthesized by a facile ball-milling process. Ball milling can effectively induce the cleavage of C-C bonds, while simultaneously causing doping and exfoliation in graphene [29][30][31][32]. Hence it is reasonable to infer that ball milling can be employed to cut and exfoliate GCN, which has a similar 2D layered structure, except that the neighboring layers are held by hydrogen bonding rather than the weak van der Waals force [24,33,34].…”

Graphite Nanosheet Exfoliation From Graphite Flakes Through Functionalization Using Phthalic Acid

“…Functionalization mechanism of graphite using phthalic acid After functionalization, the phthalic acid-functionalized layers repel each other, opening a gap between them locally. Then, the viscous PPA infiltrates these gaps and causes strong shearing, thereby interrupting the restacking of the graphite nanosheets [29]. This shearing causes the gap to open up further.…”

“…Subsequently, P 2 O 5 dehydrates phthalic acid causing generation of carbonium ions (C=O + ) from the phthalic acid. In these reactions, defect sites (mostly C(sp 2 )-H/C=H), which are inherently present at the edges of graphite, host the electrophilic substitution reactions with the generated carbonium ions [29]. The homogenous grafting of phthalic acid onto the graphite edges across the basal plane without any damage to the crystalline structure is obtained through the mechanism of Friedel-Crafts acylation in the PPA/P 2 O 5 medium.…”

“…This shearing causes the gap to open up further. Additionally, PPA induces protonation of the surface of graphite nanosheets [29]. Subsequently, strong ionic interactions occur between the graphite surfaces.…”