Browsing by Author "Choucair, M"
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- ItemEngineering solvothermal reactions to produce multi-walled carbon nanotubes(Springer, 2012-06-01) Choucair, M; Gong, B; Stride, JALarge 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 thermo-dynamically 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. © 2012, Springer.
- ItemEnhanced reversible lithium storage in a nanosize silicon/graphene composite.(Elsevier, 2010-02) Chou, SL; Wang, JZ; Choucair, M; Liu, HK; Stride, JA; Dou, SXSi/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. © 2010, Elsevier Ltd.
- ItemGram-scale production of graphene based on solvothermal synthesis and sonication.(Nature Publishing Group, 2009-01) Choucair, M; Thordarson, P; Stride, JACarbon 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(1), and larger amounts of chemically modified graphene sheets have been produced by a number of approaches(2-7). 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 nongraphitic precursors with a scalable, low-cost approach should take us a step closer to real-world applications of graphene. © 2009, Nature Publishing Group
- ItemGraphene doping to enhance the flux pinning and supercurrent carrying ability of a magnesium diboride superconductor(Institute of Physics, 2010-08) Xu, X; Dou, SX; Wang, XL; Kim, JH; Stride, JA; Choucair, M; Yeoh, WK; Zheng, RK; Ringer, SPThe effect of graphene doping on the electromagnetic properties of MgB2 has been examined, in comparison with the case for undoped MgB2. It was found that graphene doping is more efficient than other forms of carbon doping for effecting improvement in the critical current density–field performance (Jc(B)), with little change in the transition temperature of MgB2. An optimal enhancement of Jc(B) was achieved for 3.7 at.% graphene doped MgB2, by a factor of 30 at 5 K and 10 T, as compared to undoped MgB2. It is found that spatial fluctuation in Tc is responsible for the flux pinning mechanism of graphene doped MgB2. © 2010, Institute of Physics
- ItemA low temperature reduction of CCl4 to solid and hollow carbon nanospheres using metallic sodium.(Elsevier, 2015-03-15) Choucair, M; Hill, MR; Stride, JACarbon nanospheres are obtained by reacting metallic sodium at 100 °C with tetrachloromethane under a flow of N2 gas at ambient pressure. The product consisted of both hollowed and solid carbon spheres, ranging between 20 and 300 nm in size and comprised of concentrically oriented, disordered graphitic fragments. The maximum surface area recorded for this nanostructured carbon is 830 m2 g−1. Morphological, structural, and chemical analysis of the product is carried out with HR-TEM, BET surface area, XPS, XRD, and Raman spectroscopy. The formation of the spherical shape of the carbon nanoparticles is discussed based on direct observations of the reaction at the interfacial phase boundary.Copyright © 2017 Elsevier B.V.
- ItemMuons probe strong hydrogen interactions with defective graphene(American Chemical Society, 2011-11-01) Riccò, M; Pontiroli, D; Mazzani, M; Choucair, M; Stride, JA; Yazyev, OVHere, 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. © 2011, American Chemical Society
- ItemTuning the defect density in chemically synthesized graphene(Institute of Electrical and Electronics Engineers (IEEE), 2010-01-22) Choucair, M; Stride, JAGram-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 π-π interactions between overlaid carbon sheets. The overall defect density was shown to decrease by simply varying the carbon precursor used in the chemical synthesis. © Copyright 2020 IEEE
- ItemVersatile and scalable synthesis of graphene nanoribbons(Elsevier, 2014-03-15) Choucair, M; Gong, B; Stride, JAThe 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. © 2014 Elsevier B.V.