Properties of Graphite Oxide Powders and Membranes as Revealed by Electron Paramagnetic Resonance Spectroscopy

Abstract

The spin probe technique was used to study graphite oxide (GO) powders swelled in polar liquids (CH3CN, CH3OH, and H2O) and liquid-free GO membranes (GOM). The nitroxide radicals TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) readily penetrated into the interplane space of GO from the solution. Electron paramagnetic resonance (EPR) spectra of these radical probes were sensitive to molecular mobility and orientation ordering within the internal space of GO. The radicals embedded in swelled GO were in two states with different rotational mobilities. The small fraction of radicals located in the interplane space of GO and detected in the broad range of temperatures was in the state of fast rotation, similar to the same radicals dissolved in bulk liquids, thus providing experimental evidence of formation of a liquid-like media within the interplane space of GO. Such mobile media may be responsible for the unusual permeation properties of GOM, which is reported in the literature. Second, less-mobile fraction of radicals was found to be immobilized at the internal surface of GO and was sensitive to phase transformations in the swelled GO structures. The transformations were detected as anomalies at temperature dependences of rotational mobility of radicals. The detected dependence of EPR spectra of probe radicals on orientation of GOM, relative to the direction of magnetic field in the EPR spectrometer, was used for quantitative characterization of orientation alignment of GO planes within the membranes. Such an approach may serve as an elegant method to estimate the relative quality of membranes and other GO-layered structures.

Liquid-like and solid-like acetonitrile intercalated into graphite oxide as studied by the spin probe technique

“…The main values of g - and hyperfine splitting (hfs-) tensors for TEMPO in the “B-GO–acetonitrile” system were determined in ref. 25. The intensities of I +1 and I −1 lines were measured directly from the spectrum in Fig.…”

Swelling properties of graphite oxides and graphene oxide multilayered materials

“…Independently on discussion about the exact size of permeation channels there is no doubt that the permeation properties of GO membranes are strongly related to the inter-layer distance provided by swelling and mobility of solvents inside the interlayers. 23,236,[243][244][245] As cited above, one needs to be careful in interpreting diffraction studies which provide only the value of the inter-layer distance averaged over many layers and averaged over the whole (but strongly inhomogeneous on the nm level) GO sheets. 152 The values reported for the averaged interlayer distances of GO multilayered structures in various solvents are summarized in Table 4.…”

pH of Water Intercalated into Graphite Oxide as Determined by EPR Spectroscopy

“…The GO powder was washed repeatedly with acetonitrile to remove residual oxidants. The procedure of washing is described in detail in [37]. HPLC grade acetonitrile was used for washing of the material and for introducing of the nitroxide radicals into the inter-plane space of GO.…”

“…Recently, it was shown by Chumakova and coauthors [37], [38], [39] that nitroxide radicals can be introduced into the inter-plane space of graphite oxide with various polar liquids. However, pH-sensitive spin probes have never been used for investigation of the swelled GO.…”