Mohammad Choucair

University of Sydney, Sydney, New South Wales, Australia

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Publications (18)64.29 Total impact

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    ABSTRACT: The conjugated aromatic system of graphene was used to trap the reactive, boron-rich 1,2-carborane cluster. Functionalization of the graphene surface was confirmed by solid-state MAS (11)B NMR spectroscopy and quantified by X-ray photoelectron spectroscopy. This work represents the first confirmed example of direct functionalization of a graphene lattice with carboranes.
    Chemical Communications 08/2014; · 6.38 Impact Factor
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    Bálint Náfrádi, Mohammad Choucair, László Forró
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    ABSTRACT: A chemically synthesized graphitic material where the structural coherence between the layers is missing approximates very well the assembly of graphene sheets. Our multi-frequency (9.4–420 GHz) electron spin resonance (ESR) study clearly identifies itinerant and localized electrons below 50 K. The metallic signal ascribed to the conduction electrons in graphene is characterized by a remarkably long spin lifetime of 65 ns. Above this temperature incoherent in-plane and inter-plane scattering give a motionally narrowed single line at g = 2.0044.
    Carbon 08/2014; 74:346–351. · 6.16 Impact Factor
  • Mohammad Choucair, Bin Gong, John Arron Stride
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    ABSTRACT: The inability to readily upscale nanofabrication of carbon nanomaterials often restricts their application, despite outstanding performances reported in both the research laboratory and prototype stages. Here we report the direct chemical synthesis of graphene nanoribbons by a bottom-up approach based on the common laboratory reagents sodium and propanol; these are solvothermally reacted to give an intermediate precursor that is then rapidly pyrolized yielding single- and few-layer graphene nanoribbons. Our results show that confinement of the lateral dimensions of graphene can be achieved simply by varying the alcohol feedstock. The ability to produce bulk quantities of graphene nanoribbons by a low cost and scalable approach is anticipated to enable a wider range of affordable real-world graphene applications.
    Materials Letters. 01/2014; 119:75–78.
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    ABSTRACT: The hydrogen absorption of sodium intercalated fullerenes (NaxC60) was determined and compared to pure fullerenes (C60). Up to 3.5 mass% hydrogen can reversibly be absorbed in NaxC60 at 200 °C and a hydrogen pressure of 200 bar. The absorbed amount of hydrogen is significantly higher than for the case when only the sodium would be hydrogenated (1 mass% for x = 10). At 200 bar the onset of hydrogen absorption is observed at 150 °C. At a pressure of 1 bar hydrogen the major desorption starts at 250 °C and is completed at 300 °C (heating rate 1 °C min−1). This absorption and desorption temperatures are significantly reduced compared to pure C60, either due to a catalytic reaction of hydrogen on sodium or due to the negatively charged C60. The hydrogen ab/desorption is accompanied by a partial de/reintercalation of sodium. A minor part of the hydrogen is ionically bonded in NaH and the major part is covalently bonded in C60Hx. The sample can be fully dehydrogenated and no NaH is left after desorption. In contrast to C60, where the fullerene cages for high hydrogen loadings are destroyed during the sorption process, the NaxC60 sample stays intact. The samples were investigated by X-ray, in-situ neutron powder diffraction and infrared spectroscopy. NaxC60 was synthesized by reacting sodium azide (NaN3) with C60 (molar ratio of Na:C60 is 10:1).
    International Journal of Hydrogen Energy 10/2012; 37(19):14307. · 3.55 Impact Factor
  • Mohammad Choucair, John Arron Stride
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    ABSTRACT: The combustion of naphthalene has been found to yield gram-scale quantities of carbon onions that are free of impurities and furthermore without the use of catalysts. X-ray diffraction (XRD) indicates that the interlayer spacing between concentric shells of the carbon onions is not uniform across the particle; rather it decreases from a graphite-like 0.34nm and approaches a diamond-like 0.29nm interlayer spacing towards the inner layers. The dispersion in the interlayer spacing is believed to result from differing external pressures exerted on the individual nanometer-sized graphitic membranes during formation of the onions. Electron microscopy techniques such as high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy demonstrate the extensive formation of carbon onions. The HRTEM indicates that the onions consist of 50–54 shells, found to be in good agreement with the XRD data.
    Carbon. 03/2012;
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    ABSTRACT: Here we explore the exceptional structural characteristics of a set of graphene-related materials prepared by a wet chemical approach. We present a comprehensive study of the effects of morphology, sonication, temperature, probe species, and stacking behaviour on the measurement of graphene surface area. Nitrogen gas was used in the solid state gas adsorption measurements and methylene blue dye for adsorption measurements on aqueous dispersions of graphene. The surface area values obtained are among the highest reported for synthetic graphenes: 1700 m2 g− 1 in aqueous dispersions and 612 m2 g− 1 in the solid state. Microscopy revealed the graphene used in the study was present in large part as free sheets and electron diffraction confirmed the successful synthesis of high quality graphene with a regular C–C bond length of 1.41 ± 0.02 Å.Highlights► Surface area measurements of graphene in the solid state and as aqueous dispersions. ► Surface area of graphene is tuneable based on post-synthesis preparation. ► Nitrogen adsorption was affected by the consolidation of the graphene layers. ► Kinetic effects influenced the outcome of methylene blue dye adsorption.
    Surface Science 01/2012; 606:34-39. · 1.87 Impact Factor
  • Mohammad Choucair, Bin Gong, John A. Stride
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    ABSTRACT: Large multi-walled carbon nanotubes (MWCNTs) have been synthesized by the reaction of polytetrafluoroethylene and ethanol with metallic lithium under solvothermal conditions. Production of the MWCNTs depends on a series of coupled reactions that utilize the liberation of chemical energy in the thermodynamically closed system. Various characterization studies show tubes with diameters of 50–150 nm and micrometer lengths. The interwall spacing was found to be 0.39 ± 0.04 nm. X-ray photoelectron spectroscopy reveals the tubes are functionalized with up to 2.2 %/wt. fluorine and 6.0 %/wt. oxygen.
    Journal of Nanoparticle Research 01/2012; 14(6). · 2.18 Impact Factor
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    ABSTRACT: Here, we present the first muon spectroscopy investigation of graphene, 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 CH(2)) 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.
    Nano Letters 11/2011; 11(11):4919-22. · 13.03 Impact Factor
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    ABSTRACT: Sulfur-graphene (S-GNS) composites have been synthesized by heating a mixture of graphene nanosheets and elemental sulfur. According to field emission electron microscopy, scanning electron microscopy with energy dispersive X-ray mapping, Raman spectroscopy, and thermogravimetric analysis, sulfur particles were uniformly coated onto the surface of the graphene nanosheets. The electrochemical results show that the sulfur-graphene nanosheet composite significantly improved the electrical conductivity, the capacity, and the cycle stability in a lithium cell compared with the bare sulfur electrode.
    Lancet. 01/2011; 196(16):7030-7034.
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    ABSTRACT: It has been shown that graphene doping is sufficient to lead to an improvement in the critical current density - field performance (Jc(B)), with little change in the transition temperature in MgB2. At 3.7 at% graphene doping of MgB2 an optimal enhancement in Jc(B) was reached by a factor of 30 at 5 K and 10 T, compared to the un-doped sample. The results suggested that effective carbon substitutions by grapheme, 2D nature of grapheme and the strain effect induced by difference thermal coefficient between single grapheme sheet and MgB2 superconductor may play an important role in flux pinning enhancement.
    Superconductor Science and Technology 01/2010; · 2.76 Impact Factor
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    ABSTRACT: Si/graphene composite was prepared by simply mixing of commercially available nanosize Si and graphene. Electrochemical tests show that the Si/graphene composite maintains a capacity of 1168 mAh g−1 and an average coulombic efficiency of 93% up to 30 cycles. EIS indicates that the Si/graphene composite electrode has less than 50% of the charge-transfer resistance compared with nanosize Si electrode, evidencing the enhanced ionic conductivity of Si/graphene composite. The enhanced cycling stability is attributed to the fact that the Si/graphene composite can accommodate large volume charge of Si and maintain good electronic contact.
    Electrochemistry Communications. 01/2010;
  • M. Choucair, M.R. Hill, J.A. Stride
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    ABSTRACT: Nested spheres of carbon with an outer shell diameter of approximately 50 nm have been synthesized in gram-scale quantities. The present study demonstrates the formation of a superhydrophobic surface using the inherent curvature of the graphitic shells on the nano-molecular level. The contact angle produced by a water droplet on a carbon onion coated glass slide was 156.0°±0.5° with a difference in advancing and receding angles of 11.0°±1.0°.
    Nanoscience and Nanotechnology (ICONN), 2010 International Conference on; 01/2010
  • M. Choucair, J.A. Stride
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    ABSTRACT: Gram-scale quantities of graphene sheets can be synthesized in a bottom-up chemical approach and we have sought to address the extent of the defect density using various characterization techniques which include X-ray diffraction, high resolution transmission electron microscopy, single area electron diffraction, Raman spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. It was found that the chemically synthesized graphene sheets have a tendency to stack without inter-planar coherence such as that found in graphite. The driving force behind this stacking is believed to be due to ¿-¿ interactions between overlaid carbon sheets. The overall defect density was shown to decrease by simply varying the carbon precursor used in the chemical synthesis.
    Nanotechnology, 2009. IEEE-NANO 2009. 9th IEEE Conference on; 08/2009
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    Mohammad Choucair, Pall Thordarson, John A Stride
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    ABSTRACT: Carbon nanostructures have emerged as likely candidates for a wide range of applications, driving research into novel synthetic techniques to produce nanotubes, graphene and other carbon-based materials. Single sheets of pristine graphene have been isolated from bulk graphite in small amounts by micromechanical cleavage, and larger amounts of chemically modified graphene sheets have been produced by a number of approaches. Both of these techniques make use of highly oriented pyrolitic graphite as a starting material and involve labour-intensive preparations. Here, we report the direct chemical synthesis of carbon nanosheets in gram-scale quantities in a bottom-up approach based on the common laboratory reagents ethanol and sodium, which are reacted to give an intermediate solid that is then pyrolized, yielding a fused array of graphene sheets that are dispersed by mild sonication. The ability to produce bulk graphene samples from non-graphitic precursors with a scalable, low-cost approach should take us a step closer to real-world applications of graphene.
    Nature Nanotechnology 02/2009; 4(1):30-3. · 31.17 Impact Factor
  • Mohammad Choucair, John A. Stride
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    ABSTRACT: Numerous techniques for the purification of chemically synthesized graphene have been investigated, exploiting the relative aqueous solubilities of the impurities and carbon sheets. This demonstrates that simple aqueous washing provides a reliable platform for the purification of graphene, without the need for harsh chemical treatments. The presence of cavities or pores in the as-obtained graphene structure are believed to inhibit small particles, that are interspersed throughout the material, from undergoing hydrolysis reactions.
    01/2008;
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    ABSTRACT: Si/graphene composite was prepared by simply mixing of commercially available nanosize Si and graphene. Electrochemical tests show that the Si/graphene composite maintains a capacity of 1168 mAh g(-1) and an average coulombic efficiency of 93% up to 30 cycles. EIS indicates that the Si/graphene composite electrode has less than 50% of the charge-transfer resistance compared with nanosize Si electrode, evidencing the enhanced ionic conductivity of Si/graphene composite. The enhanced cycling stability is attributed to the fact that the Si/graphene composite can accommodate large volume charge of Si and maintain good electronic contact. (C) 2009 Elsevier B.V. All rights reserved.
    Electrochemistry Communications. 12(2):303-306.
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    ABSTRACT: Post-synthetic modification of H3[(Cu4Cl)3(BTTri)8] or CuBTTri, where H3BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene, with piperazine (pip) has yielded the grafted framework H3[(Cu4Cl)3(BTTri)8(pip)12], pip-CuBTTri, which exhibits an improved CO2 uptake at pressures pertinent to postcombustion flue gas capture compared with the non-grafted material. In particular, the volumetric capacity of pip-CuBTTri was 2.5 times higher than that of CuBTTri at ca. 0.15 bar and 293 K. A chemisorption mechanism for CO2 adsorption was proposed on the basis of diffuse reflectance infrared spectra (DRIFTS) and the high initial isosteric heat of adsorption (−Qst, ≈96.5 kJ/mol). Application of the Ideal Adsorbed Solution Theory (IAST) to a simulated mixture of 0.15 bar CO2/0.75 bar N2 revealed a selectivity factor of 130. Both pressure and temperature swing processes were found to be suitable for facile regeneration of the material over multiple adsorption–desorption cycles.
    Microporous and Mesoporous Materials 174:74–80. · 3.37 Impact Factor