We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

We present an overview of the main techniques for production and processing of graphene and related materials (GRMs), as well as the key characterization procedures. We adopt a ‘hands-on’ approach, providing practical details and procedures as derived from literature as well as from the authors’ experience, in order to enable the reader to reproduce the results. Section is devoted to ‘bottom up’ approaches, whereby individual constituents are pieced together into more complex structures. We consider graphene nanoribbons (GNRs) produced either by solution processing or by on-surface synthesis in ultra high vacuum (UHV), as well carbon nanomembranes (CNM). Production of a variety of GNRs with tailored band gaps and edge shapes is now possible. CNMs can be tuned in terms of porosity, crystallinity and electronic behaviour. Section covers ‘top down’ techniques. These rely on breaking down of a layered precursor, in the graphene case usually natural crystals like graphite or artificially synthesized materials, such as highly oriented pyrolythic graphite, monolayers or few layers (FL) flakes. The main focus of this section is on various exfoliation techniques in a liquid media, either intercalation or liquid phase exfoliation (LPE). The choice of precursor, exfoliation method, medium as well as the control of parameters such as time or temperature are crucial. A definite choice of parameters and conditions yields a particular material with specific properties that makes it more suitable for a targeted application. We cover protocols for the graphitic precursors to graphene oxide (GO). This is an important material for a range of applications in biomedicine, energy storage, nanocomposites, etc. Hummers’ and modified Hummers’ methods are used to make GO that subsequently can be reduced to obtain reduced graphene oxide (RGO) with a variety of strategies. GO flakes are also employed to prepare three-dimensional (3d) low density structures, such as sponges, foams, hydro- or aerogels. The assembly of flakes into 3d structures can provide improved mechanical properties. Aerogels with a highly open structure, with interconnected hierarchical pores, can enhance the accessibility to the whole surface area, as relevant for a number of applications, such as energy storage. The main recipes to yield graphite intercalation compounds (GICs) are also discussed. GICs are suitable precursors for covalent functionalization of graphene, but can also be used for the synthesis of uncharged graphene in solution. Degradation of the molecules intercalated in GICs can be triggered by high temperature treatment or microwave irradiation, creating a gas pressure surge in graphite and exfoliation. Electrochemical exfoliation by applying a voltage in an electrolyte to a graphite electrode can be tuned by varying precursors, electrolytes and potential. Graphite electrodes can be either negatively or positively intercalated to obtain GICs that are subsequently exfoliated. We also discuss the materials that can be amenable to exfoliation, by ...

In degassed water graphene re-aggregation is drastically slowed down due to the small intergraphene attractive dispersive forces (a consequence of graphene two-dimensional character) and the stabilizing electrostatic repulsion. As has been reported before for many hydrophobic objects, (i.e. hydrocarbon droplets 11 , 12 or air bubbles 13 ) graphene becomes electrically charged in water as a consequence of the spontaneous adsorption on its surface of OH -ions coming from graphenide oxidation and water dissociation. As two graphene flakes come together, they experience a repulsive force due to the overlap of their associated counterion clouds.Accordingly, graphene can be efficiently dispersed in water at a concentration of 0.16 g/L with a shelf life of a few months.The pH values after graphene transfer to water is very revealing. While the system resulting from the mixture with non-degassed water (left vial of Fig. 1b) has a pH close to 11, stable graphene suspensions have a pH close to neutrality (pH between 7 and 8; right vial of Fig. 1b). As the same amount of OH -is produced in both cases after graphenide oxidation, the remarkable difference in pH is attributed to the adsorption of OH -on the suspended graphene flakes. This hypothesis is supported by the electrophoretic mobility and zeta potential ζ of the graphene flakes. Negative ζ values (ζ = -45 ± 5) were observed at neutral pH conditions; on the contrary, charge reversal was observed in acidic pH environment (ζ = +4 ± 2 at pH 4). It could be argued that this ζ variation is due to the reduction of pH below the pK a of functional groups dissociated at basic pH. To discard this hypothesis, we measured ζ of water-dispersed graphene in presence of tetraphenylarsonium chloride, Ph 4 AsCl which contains a hydrophobic cation known to readily 3 adsorbs on hydrophobic surfaces 14 . As reported in Table 1, we observed a progressive increase in ζ with increasing concentration of the hydrophobic cation, with charge reversal at sufficiently large cation concentrations. Stability of SLG iw is determined by the interaction between the individual graphene plates. In regular laboratory conditions, gases dissolved in water (about 1 mM) adsorb on the graphene surface, inducing long-range attractive interaction between the dispersed objects and promoting aggregation (a, bottom left, gas bubbles and ions are not at scale). On the contrary, if water is degassed (removing dissolved gases) water-ions readily adsorb on the graphene surface, conferring a certain charge to the dispersed objects. The repulsive electrostatic interaction favors the stability of the dispersed material (b) Left vial: mixture of graphene in THF after addition to water which was not degassed. The aqueous dispersion is not stable and black aggregates visible to the eye begin to form a few minutes after mixing. Right vial: stable dispersion of graphene in degassed water after THF evaporation. No evidence of aggregation is observed after several months of storage at room temperature (c) UV-visible absorption...

The different exfoliation routes of graphite to produce graphene by sonication in solvent, chemical oxidation and electrochemical oxidation are compared. The exfoliation process and roughening of a flat graphite substrate is directly visualized at the nanoscale by scanning probe and electron microscopy. The etching damage in graphite and the properties of the exfoliated sheets are compared by Raman spectroscopy and X‐ray diffraction analysis. The results show the trade‐off between exfoliation speed and preservation of graphene quality. A key step to achieve efficient exfoliation is to couple gas production and mechanical exfoliation on a macroscale with non‐covalent exfoliation and preservation of graphene properties on a molecular scale.