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Two-Dimensional Chemistry towards New Graphene Derivatives

Periodic Reporting for period 1 - 2D-CHEM (Two-Dimensional Chemistry towards New Graphene Derivatives)

Reporting period: 2016-06-01 to 2017-11-30

List the specific objectives for the project as described in section 1.1 of the DoA and described the work carried out during the reporting period towards the achievement of each listed objective. Provide clear and measurable details.
The specific objectives of the projects are:
1. Design and preparation of new stable graphene derivatives with high dispersability in polar environments, controllable band gap and sustainable magnetic ordering from FG and fluorinated graphenes.
Within the framework of the project we prepared new stable graphene derivatives with a high dispersability in water media. By reaction of fluorographene with NaCN we synthetized cyanographene, which is thermally stable up to 120 °C and water dispersible. We achieved ~15% of graphene functionalization by CN groups and this degree of functionalization lead to band gap opening. The cyanographene synthesis and properties were described in ACS Nano, 11(3), 2982–2991, 2017. We hydrolyzed the as prepared cyanographene in acidic environment to graphene acid, which is graphene functionalized by highly hydrophilic COOH group. The degree of functionalization of the graphene acid reached to ~15%, the material provided stable water colloids and displayed acid-base properties (with pKa of 5.2) comparable with classical organic acids. Sodium salt was also prepared from the graphene acid crystalizing in spherulite crystals. Properties of graphene acid and its sodium salt were described in ACS Nano, 11(3), 2982–2991, 2017. We also showed that the graphene acid can be further conjugated using carboimine chemistry with various diamines, aminoalcohols and aminothioalcohols, which enabled grafting of various (-NH2, -OH, and –SH) functional groups onto graphene surface. Using Grignard chemistry we prepared allyl, pentyl and anisolyl graphenes. These graphene derivatives were homogenously covered by the functional groups and represented materials thermally stable up to ~120 °C and dispersible in nonpolar media. Synthesis and properties of these derivatives were described in literature Chem. Mater., 29(3), 926–930, 2017. Applying fluorographene chemistry we prepared several hydroxofluorographenes CxFy(OH)z by treatment of fluorographene with bases B(OH)x. These materials displayed magnetic ordering depending on their composition. One of them was room temperature antiferromagnet. Preparation and properties of these nonmetallic magnets were described in Nat. Commun., 8, 14525, 2017. Within framework of this project we also overviewed current knowledge about chemistry, properties and applications of fluorographene in the review published in Appl. Mater. Today, 9, 60-70, 2017.
2. Identification of the application potential of the as-prepared derivatives and hybrids in (electrochemical and photoluminescence) sensing, magnetic delivery and catalytic applications.
All prepared graphene derivatives were thoroughly characterized and their application potential was screened. Particularly we focused on magnetism of graphene derivatives, we prepared various hydroxofluorographene derivatives, which magnetism depended on their composition. One derivative, G(OH)F exhibited room temperature antiferromagnetic ordering, with Neel temperature equaling to 62 K. The low-temperature FM state was supported by G(OH)F isothermal magnetization curve, measured at 5 K: the curve exhibited hysteresis with a coercivity of ∼80 Oe. Moreover, the magnetization of G(OH)F saturated above a value of 1 emu/g, placing G(OH)F among the strong magnetic graphene-based systems including doped and functionalized graphenes and graphene derivatives. Theoretical calculations suggested that the magnetism is triggered by sp2 domains bearing a diradical character entrapped in sp3 lattice, which enabled interaction among the sp2 domains via superexchange interaction. Behavior of this system was described in Nat. Commun., 8, 14525, 2017. We further focused on magnetism of other graphene-based system in order
Within framework of WP1 we carried out many tests concerning reactivity of fluorographene with a rather broad portfolio of chemicals. Particularly reaction with nucleophiles (NaCN, B(OH)x and carbanions) were successful leading to new graphene derivatives (described in part 1.1). We are systematically screening reactions with numerous chemicals in order to understand chemistry of FG and to prepare new graphene derivatives. We paid particular attention also to reaction with various amines, because, we observed nontrivial behaviour leading to unexpected graphene derivatives. Currently we continue in this research in order to carefully characterize reaction products as well as underlying reaction mechanisms. We started preliminary experiments in order to synthetize 3D scaffolds but we are facing significant troubles to prove that we really prepared 3D materials.
To sum up all recent achievements we follow the schedule of WP1. In future we plan to focus the future research on the basis on the experience gained during the project realization. Nonetheless, we do not expect any significant changes in the planned schedule. Concerning the specific goals we already achieved the specific goal i) of WP1, nonetheless, we plan to prepare more graphene derivatives.
Within framework of WP2 we focused on magnetic properties of new graphene derivatives (as described in 1.1.2). We also subjected the N-doped graphenes to muons, in order to provide proof of inherent magnetism of the studied materials without necessity to placing them into external field. The collected results are promising and are under extensive evaluation and analysis. We also analysed redox properties and capacitance of the newly prepared graphene derivatives and we realized that some of them exhibit properties, which can be exploited in materials for supercapacitors. Currently we systematically screen charging/discharging properties of new graphene derivatives in order to design new graphene derivatives with high-energy storage capacity. Currently we prepare manuscript describing capacitance of graphene derivative prepared via Bingel reaction on fluorographene. We also grafted divalent metal cation to G-CN and we tested the as prepared material as heterogenous catalyst. We achieved very encouraging results both concerning the catalytic activity and selectivity. Currently, we prepare draft of manuscript describing these results.
We follow the suggested schedule and we are significantly contributed to the specific goal ii) of WP2.
As mentioned before we carried out extensive study combining experimental methods (EPR and NMR) with theoretical calculations at DFT level in order to understand the reactivity of fluorographene. Using these experimental methods we analysed behaviour of fluorographene in DMF and compared it with behaviour of fluorographene in benzene. We concluded that defects present in the fluorographene structure trigger the unexpected reactivity of this perfluorinated hydrocarbon. The theoretical calculations elucidated the potential reaction mechanism and role of DMF in triggering the defluorination. Manuscript describing our achievements is now under consideration in peer-reviewed journal. We plan to continue this research in order to fully understand of all aspects of fluorographene chemistry with the aim to control it. In order to understand chemical processes taking place at surfaces of 2D materials we analysed oxidation of individual graphene flake during ultraviolet/ozone treatment through in situ atomic force microscopy based on dynamic force mapping. The results showed that graphene oxidation started at edges and expanded from the graphene edges to the entire graphene surface. The interaction force mapping results correlated well with X-ray photoelectron spectroscopy data quantifying the degree of chemical oxidation. Density functional theory calculations confirmed the specific interaction forces measured between a silicon tip and graphene oxide. The
In future we plan to focus the future research on the basis on the experience gained during the project realization. Nonetheless, we do not expect any significant changes in the planned schedule. Concerning the specific goals we already achieved the specific goal i) of WP1, nonetheless, we plan to prepare more graphene derivatives. Within framework of this project we plan to analyze electrochemical properties of new graphene derivatives. It was speculated that the electrochemical properties of vdW materials can also be related to their surface properties. In order to test this hypothesis we employed iGC and characterized surface properties of various MoS2 samples. We have to use this TMD as a prototype system, because inverse gas chromatography experiments require at least a few tens of milligrams of the prepared powder materials and employing fluorographene chemistry we are currently able to synthetize maximally ~ten milligrams of graphene derivatives. However, we plan up-scaling of our synthetic approaches in order to prepare at least one order of magnitude high amount of graphene derivatives. We analyzed surface properties of various bulk as well as single layer MoS2 samples using inverse gas chromatography. All samples displayed significant variations in surface energies and their heterogeneities. The surface energy ranged from 50 to 120 mJ m−2 depending on the sample and surface coverage. We correlated the surface properties and previously reported structural features of MoS2 with their electrochemical activities. We concluded that the observed differences in electrochemistry are caused by the surface properties. This is an important finding with an enormous impact on the whole field of electrocatalysis of layered materials. This work was published in Nanoscale, 9, 19236-19244, 2017.