Photochemical Modification of Graphene

Graphene, a two-dimensional (2D) atomic crystal composed of single-layer hexagonal mesh of carbon atoms, is one of the most exciting materials being investigated today. Graphene chemistry, the covalent functionalization of graphene as a giant molecule, provides a promising approach to controllably engineer graphene's band structure, create novel graphene derivatives and tailor the interfacial characteristics. One of the great challenges for graphene functionalization originates from its strong chemical stability, thus highly reactive chemical species are needed as the reactants. In recent years, we have been working on the photo-induced free radicals-based photochemistry of graphene, targeting the efficient graphene functionalizalion for its band structure engineering. Various photochemical modification methods have been developed, such as photochemical chlorination, photochemical methylation, photocatalytic oxidation and bifacially asymmetric functionalization of graphene. The homogeneous and nondestructive photochlorination of graphene could remove the conducting pi-bands and open up a band gap in graphene. TiO2-based photocatalytic oxidation of graphene could realize photochemical tailoring of graphene, including ribbon cutting, arbitrary patterning on any substrate, layer-by-layer thinning, and localized graphene to graphene oxidation conversion. Using photochemical reaction of graphene as a probe, we have investigated the dimension effects on graphene chemistry, including the thickness, stacking order, single-and double-side, and edge dependent reactivity in graphene. After two-step functionalization of graphene, we have fabricated the thinnest Janus disc named Janus graphene, which comprises two kinds of decorations separated by the one-atom-thick carbon layer. It is found that chemical decorations on one side are capable of affecting both chemical reactivity and wettability of the opposite side, indicative of communication between the two grafted decorations separated by a single-layer graphene. In this review, we select several typical examples to demonstrate such kinds of photochemical graphene engineering and its intrinsic 2D reaction characteristics, together with a brief discussion on the future directions, challenges and opportunities in this research area.