Synthesis of novel graphite/graphene systems
Work Package Leader NIIC (A. V. Okotrub)
Involved Partners NIIC, LUT, UmU, UNIPR, UNSW
M 1.1 Technology for the synthesis of semifluorinated graphene
We have synthesized layered inclusion (intercalation) compounds with the general formula (C2F xBr0.01 · yG) n , where (C2F x Br0.01) n is a host component, G stands for ethyl acetate (guest component), 0.5 < x < 1.0, y 1 = 0.109–0.162 (stage 1), and y 2 = 0.052–0.074 (stage 2). Using IR spectroscopy, we studied the behavior of the functional groups in the guest and host subsystems. The influence of the composition (structure) of the polymer host (C2F x Br0.01) n on the properties of the synthesized compounds was studied using physicochemical characterization techniques (differential thermal analysis and X-ray diffraction).
We were able to produce graphene nanochains and nanoislands in the layers of room-temperature fluorinated graphite Intercalated compound of graphite fluoride with n-heptane has been synthesized at room temperature using a multi-stage process including fluorination by a gaseous BrF3 and a set of intercalant exchange reactions. It was found that composition of the compound is CF0.40(C7H16)0.04 and the guest molecules interact with the graphite fluoride layers through the van der Waals forces. Since the distance between the filled layers is 1.04 nm and the unfilled layers are separated by ~0.60 nm, the obtained compound can be considered as a stack of the fluorinated graphenes. These fluorinated graphenes are large in area making it possible to study local destruction of the pi- conjugated system on the basal plane. It was shown that fluorine atoms form short chains, while non-fluorinated sp2 carbon atoms are organized in very narrow ribbons and aromatic areas with a size smaller than 3 nm. These pi- electron nanochains and nanoislands preserved after the fluorination process are likely responsible for the value of the energy gap of the compound of ~2.5 eV. Variation in the size and the shape of pi-electron regions within the fluorinated graphene layers could be a way for tuning the electronic and optical characteristics of the graphene-based materials.
M 1.2 Elaboration of the novel semiflourinated graphite/graphene systems with controlled structure and stoichiometry
We have synthesized C2Fx intercalation compounds with C2Fx) as a host and G (dichloromethane, chloroform, carbon tetrachloride, and dichloroethane) as a guest. The behavior of the functional groups in the guest and host subsystems has been studied by IR spectroscopy. We have examined the influence of the degree of fluorination of the polymer host (0.5 < x < 1.0) and the nature of the guest on the vibrational frequencies of the C-F and C-Cl bonds.
M 1.3 Elaboration and characterization of the systems consisting of С2F with different intercalated molecules
Inclusion compounds (intercalates) of fluorinated graphite matrix with butanone were prepared by guest substitution from acetonitrile to butanone, chlorinated derivatives of methane and ethane. The kinetics of the thermal decomposition (the 1st stage of filling -> the 2nd stage of filling) was studied under isothermal conditions at 294-313 K. The relationship of the host matrices structure with inclusion compounds’ thermal properties and kinetic parameters is established.
M 1.4 Full set of protocols for the synthesis of graphene with established defects concentration
The first muon spectroscopy investigation of graphene has been focused on chemically produced, gram-scale samples, appropriate to the large muon penetration depth. We have observed an evident muon spin precession, usually the fingerprint of magnetic order, but here demonstrated to originate from muon–hydrogen nuclear dipolar interactions. This is attributed to the formation of CHMu (analogous to CH2) groups, stable up to 1250 K where the signal still persists. The relatively large signal amplitude demonstrates an extraordinary hydrogen capture cross section of CH units. These results also rule out the formation of ferromagnetic or antiferromagnetic order in chemically synthesized graphene samples.
Perforation of graphite is carried out by treating the graphite oxide with a boiling mineral acid H2SO4 or H3PO4. High-resolution transmission electron microscopy shows formation of a large number of vacancy defects (holes) in the graphene sheets, which are caused more likely by the CO2 liberation during the reduction process. The characteristic size of the holes is about 2 nm. The obtained materials are comparatively examined by X-ray diffraction, Raman and IR-absorption spectroscopy, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. It is found that the products obtained using a strong acid H2SO4 and a weak acid H3PO4 are different in the concentration and electronic state of oxygen and the mean distance between defects.
Bulk defective graphene produced by thermal exfoliation of graphite oxide was treated under H2 and investigated with X-ray photoemission spectroscopy, neutron spectroscopy, and solid state nuclear magnetic resonance. Graphene defects appear effective in dissociating H2 molecule and in promoting H covalent absorption on the carbon backbone. Measured generalized phonon density of states shows the presence of localized peaks ascribed to C–H bending modes already in pristine graphene, whose intensities enhance when samples are treated under H2 at 1273 K. However, 1H NMR evidences a thermally activated dynamics with a correlation time of a few microseconds assigned to a part of H atoms bound onto the graphene plane. These findings point toward a diffusive dynamics of the hydrogen chemically bound to graphene sheets, already active at room temperature.