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  • 1. Asanou, I. P.
    et al.
    Bulusheva, L. G.
    Dubois, M.
    Yudanov, N. F.
    Alexeev, A. V.
    Makarova, Tatiana L.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Okotrub, A. V.
    Graphene nanochains and nanoislands in the layers of room-temperature fluorinated graphite2013Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 59, s. 518-529Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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 similar to 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 a conjugated system on the basal plane. It was shown that fluorine atoms form short chains, while non-fluorinated sp(2) 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 similar to 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.

  • 2.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Larsen, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Jia, Xueen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Palladium nanocrystals supported on photo-transformed C-60 nanorods: effect of crystal morphology and electron mobility on the electrocatalytic activity towards ethanol oxidation2014Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 73, s. 34-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the synthesis and decoration of high-aspect-ratio crystalline C-60 nanorods (NRs) by functionalized palladium nanoparticles with an average size of 4.78 +/- 0.66 nm. In their pristine form, C-60 NRs suffer from partial damage in the solution-based decoration process resulting in poor crystallinity. However, by modifying the NR surface via in situ photochemical transformation in the liquid state, we are able to prepare highly stable NRs that retain their crystalline structure during the decoration process. Our method thus opens up for the synthesis of highly crystalline nanocomposite hybrids comprising Pd nanoparticles and C-60 NRs. Bys measuring the electron mobility of different C-60 NRs, we relate both the effect of electron mobility and crystallinity to the final electrocatalytic performance of the synthesized hybrid structures. We show that the photo-transformed C-60 NRs exhibit highly advantageous properties for ethanol oxidation based on both a better crystallinity and a higher bulk conductivity. These findings give important information in the search for efficient catalyst support.

  • 3.
    Blank, Vladimir D.
    et al.
    Research Center for Superhard Materials, Centralnaya 7a, Troitsk, Moscow Region 142092, Russian Federation.
    Buga, Sergey G.
    Research Center for Superhard Materials, Centralnaya 7a, Troitsk, Moscow Region 142092, Russian Federation.
    Dubitsky, Gennadii A.
    Institute of Spectroscopy of the Russian Academy of Sciences, Troitsk, Moscow Region 142092, Russian Federation.
    Serebryanaya, Nadejda R.
    Research Center for Superhard Materials, Centralnaya 7a, Troitsk, Moscow Region 142092, Russian Federation.
    Popov, M. Yu.
    Research Center for Superhard Materials, Centralnaya 7a, Troitsk, Moscow Region 142092, Russian Federation.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    High-pressure polymerized phases of C601998Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 36, nr 4, s. 319-343Artikkel, forskningsoversikt (Annet vitenskapelig)
    Abstract [en]

    Data from recent experimental studies of C60 under high pressures are collected and analyzed, concentrating on the polymerized states where covalent intermolecular bonds have been formed through treatment of molecular C60 at high pressures and temperatures at or above room temperature. We give an overview of the observed phase transformations and the structures of metastable polymeric phases, both crystalline and disordered, as analyzed under ambient conditions, and we present and discuss a pressure-temperature diagram showing which synthesis conditions result in which final phases in the pressure range up to 20 GPa (200 kbar) and at temperatures up to 2300 K. The physical properties of the various phases are discussed whenever enough data are available. The pressure-temperature stability limits for C60 and the conditions for the transformation of C60 into graphite, diamond and chaoite-type carbon are derived.

  • 4. Cui, Wen
    et al.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sun, Shishuai
    Yao, Mingguang
    Liu, Bingbing
    High pressure and high temperature induced polymerization of doped C60 materials2016Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 109, s. 269-275Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several metastable doped C60 polymers are synthesized under high pressure and high temperature (1.5GPa, 573K and 2GPa, 700K, respectively), using C60/ferrocene (Fc, Fe(C5H5)2), C60/Ni(OEP) and C60/AgNO3 as starting materials. Raman and IR spectroscopy are used to study the polymerization of these samples after HPHT treatment. It is found that the polymerization degree is always lower than that of pure C60 treated at same conditions, which is attributed to the space limitation by the dopants. We also find that even at same conditions, the three doped materials form different polymeric phases of the doped materials. This is attributed to the unique initial lattice structures and the different degrees of spatial confinement provided by the dopants.

  • 5. Cui, Wen
    et al.
    Yao, Mingguang
    Yao, Zhen
    Ma, Fengxian
    Li, Quanjun
    Liu, Ran
    Liu, Bo
    Zou, Bo
    Cui, Tian
    Liu, Bingbing
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Reversible pressure-induced polymerization of Fe(C5H5)(2) doped C-702013Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 62, s. 447-454Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High pressure Raman, IR and X-ray diffraction (XRD) studies have been carried out on C-70(Fe(C5H5)(2))(2) (hereafter, "C-70(Fc)(2)") sheets. Theoretical calculation is further used to analyze the Electron Localization Function (ELF) and charge transfer in the crystal and thus to understand the transformation of C-70(Fc)(2) under pressure. Our results show that even at room temperature dimeric phase and one dimensional (1D) polymer phase of C-70 molecules can be formed at about 3 and 8 GPa, respectively. The polymerization is found to be reversible Upon decompression and the reversibility is related to the pressure-tuned charge transfer, as well as the overridden steric repulsion of counter ions. According to the layered structure of the intercalated ferrocene molecules formed in the crystal, we suggest that ferrocene acts as not only a spacer to restrict the polymerization of C-70 molecules within a layer, but also as charge reservoir to tune the polymerization process. This supplies a possible way for us to design the polymerization of fullerenes at suitable conditions.

  • 6. Cui, Wen
    et al.
    Sun, Shishuai
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Wang, Shuangming
    Liu, Bingbing
    Pressure induced metastable polymerization in doped C60 materials2017Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 115, s. 740-745Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High pressure Raman studies have been carried out on C60/AgNO3 and C60/Ni(OEP) up to 30 GPa. In both these doped C60 materials, pressure-induced metastable ordered polymers can be observed after pressure release. The results show that both the quenched materials contain chainlike polymers and dimers. We also find that the degree of polymerization is higher in these doped C60 materials than in bulk C60 materials after similar high pressure treatment and that C60/AgNO3 contains a higher fraction of chainlike polymers than C60/Ni(OEP) after decompression from same pressure. The results can be understood by considering the different initial lattice structures of these materials and the confinement effects of the dopants.

  • 7. Danilchenko, Boris A.
    et al.
    Tripachko, N.A.
    Lev, S.
    Petrychuk, M.V.
    Sydoruk, V.A.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Vitusevich, S.A.
    1/f noise and mechanisms of the conductivity in carbon nanotube bundles2011Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, nr 15, s. 5201-5206Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experimental results are reported of the investigation of conductivity mechanisms in metallic single-wall carbon nanotube (SWCNT) bundles in a wide temperature range from 4.2 K to 300 K. The temperature dependence of the resistance and noise parameters – the logarithmic slope of the current dependence of noise as well as the normalized current noise – are compared. Remarkable changes in noise characteristics are registered at temperatures typical of the transition from hopping conductivity to Luttinger liquid conductivity and the transition from Luttinger liquid conductivity to diffusion conductivity. In the first transition region, the slope of the normalized noise level of the current changes significantly as a function of temperature. In the region of diffusion conductivity, a stronger variation of the normalized noise level is revealed. These changes in noise properties are correlated with changes in the transport characteristics of SWCNT bundles that allow us to adequately explain the mechanisms of conductivity in the system. 

  • 8.
    Ekspong, Joakim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Surface activation of graphene nanoribbons for oxygen reduction reaction by nitrogen doping and defect engineering: An ab initio study2018Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 137, s. 349-357Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Introducing heteroatoms and creating structural defects on graphene is a common and rather successful strategy to transform its inert basal plane into an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR). However, the intricate atomic configuration of defective graphenes difficult their optimization as ORR electrocatalysts, where not only a large density of active sites is desirable, but also excellent electrical conductivity is required. Therefore, we used density functional theory to investigate the current-voltage characteristics and the catalytic active sites towards ORR of nitrogen-doped and defective graphene by using 8 zig-zag graphene nanoribbons as model systems. Detailed ORR catalytic activity maps are created for ten different systems showing the distribution of catalytic hot spots generated by each defect. Subsequently, the use of both current-voltage characteristics and catalytic activity maps allow to exclude inefficient systems that exhibit either low electrical conductivity or have adsorption energies far from optimal. Our study highlights the importance of considering not only the interaction energy of reaction intermediates to design electrocatalysts, but also the electrical conductivity of such configurations. We believe that this work is important for future experimental studies by providing insights on the use of graphene as a catalyst towards the ORR reaction. 

  • 9. Feicht, Patrick
    et al.
    Siegel, Renee
    Thurn, Herbert
    Neubauer, Jens W.
    Seuss, Maximilian
    Szabo, Tamas
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Halbig, Christian E.
    Eigler, Siegfried
    Kunz, Daniel A.
    Fery, Andreas
    Papastavrou, Georg
    Senker, Jurgen
    Breu, Josef
    Systematic evaluation of different types of graphene oxide in respect to variations in their in-plane modulus2017Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 114, s. 700-705Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graphene oxide samples prepared in various laboratories following a diversity of synthesis protocols based on Brodie's (BGO) and Hummers/Offeman's (HGO) methods were compared in respect of their in plane moduli. A simple wrinkling method allowed for a spatial resolution <1.5 pm by converting the wrinkling frequency. Quite surprisingly, a drastic variation of the in-plane moduli was found spanning the range from 600 GPa for the best BGO types, which is in the region of chemically derived graphene, all the way down to less than 200 GPa for HGO types. This would suggest that there are no two equal GO samples and GO should not be regarded a compound but rather a class of materials with very variable physical properties. While large differences between Brodie's and Hummers/Offeman's types might have been expected, even within the group of Hummers/Offeman's types pronounced differences are observed that, based on C-13 solid-state NMR, were related to over-functionalization versus over-oxidation.

  • 10. Gorkina, Alexandra L
    et al.
    Tsapenko, Alexey P
    Gilshteyn, Evgenia P
    Koltsova, Tatiana S
    Larionova, Tatiana V
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Anisimov, Anton S
    Anoshkin, Ilya V
    Kauppinen, Esko I
    Tolochko, Oleg V
    Nasibulin, Albert G
    Transparent and conductive hybrid graphene/carbon nanotube films2016Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 100, s. 501-507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon nanomaterials (carbon nanotubes (CNTs) and graphene) are promising materials for optoelectronic applications, including flexible transparent and conductive films (TCFs) due to their extraordinary electrical, optical and mechanical properties. However, the performance of CNT- or graphene-only TCFs still needs to be improved. One way to enhance the optoelectrical properties of TCFs is to hybridize CNTs and graphene. This approach leads to creation of a novel material that exhibits better properties than its individual constituents. In this work, the novel hybrid CNT-graphene nanomaterial was fabricated by graphene oxide deposition on top of CNT films. The graphene oxide was then reduced by thermal annealing at ambient atmosphere or in H2 atmosphere. At the final step the CNT-graphene hybrids were chemically doped using gold(III) chloride. As a result, we show that the hybrids demonstrate excellent optoelectrical performance with the sheet resistance as low as 73 Ω/□ at 90% transmittance.

  • 11. Han, K-H
    et al.
    Spemann, D
    Hohne, R
    Setzer , A
    Makarova, T
    Umeå universitet.
    Esquinazi, P
    Butz, T
    Observation of intrinsic magnetic domains in C60 polymer - Addendum2003Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 41, nr 12, s. 2425-2426Artikkel i tidsskrift (Fagfellevurdert)
  • 12. Han, K-H
    et al.
    Spemann, D
    Hohne, R
    Setzer, A
    Makarova , T
    Umeå universitet.
    Esquinazi, P
    Butz, T
    Observation of intrinsic magnetic domains in C-60 polymers2003Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 41, s. 785-Artikkel i tidsskrift (Fagfellevurdert)
  • 13. Jehova Gonzalez, Viviana
    et al.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Morelos-Gomez, Aaron
    Lopez-Urias, Florentino
    Terrones, Humberto
    Terrones, Mauricio
    Biotin molecules on nitrogen-doped carbon nanotubes enhance the uniform anchoring and formation of Ag nanoparticles2015Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 88, s. 51-59Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An efficient method for anchoring silver nanoparticles (Ag-NPs) on the surface of nitrogendoped multi-walled carbon nanotubes (CNx-MWCNTs) is reported. The process involves the attachment of biotin molecules on the surface of CNx-MWCNTs (both, pristine and acid treated) that act as a reducing agent for AgNO3, thus generating an efficient and homogeneous coating of Ag-NPs (similar to 3 nm in diameter). The reduction of AgNO3 on either pristine CNx-MWCNTs or acid treated CNx-MWCNTs (without biotin) results in Ag-NPs of large diameters and size distribution, in addition to a low anchoring efficiency. We confirmed that the use of biotin substantially improves the Ag-NPs anchoring efficiency, especially on acid treated CNx-MWCNTs. In order to elucidate the mechanism whereby Ag-NPs strongly bind to the surface of CNx-MWCNTs, density functional theory (DFT) calculations were carried out. These revealed the existence of covalent bonds established between one side of the biotin molecule and the CNx-MWCNT surface through oxygen atoms, leaving accessible the exposed sulfur atoms at the other end, which further provided an excellent interaction with the Ag-NPs via S Ag bonds. Finally, we demonstrate that these Ag-NPs coated CNx-MWCNTs could be used as efficient sensors of CS2. (c) 2015 Elsevier Ltd. All rights reserved.

  • 14.
    Klechikov, Alexey
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    You, Shujie
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Lackner, Lukas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sun, Jinhua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Iakunkov, Artem
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Rebrikova, Anastasia
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Chemistry, Moscow State University, Moscow, Russia.
    Korobov, Mikhail
    Baburin, Igor
    Seifert, Gotthard
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Graphite oxide swelling in molten sugar alcohols and their aqueous solutions2018Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 140, s. 157-163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graphite oxides (GO) are intercalated rapidly by one to several layers of solvent when immersed in liquid but the GO solvates are typically unstable on air due to solvent evaporation. Here we study swelling of GO in solvents (sugar alcohols) with melting temperature point above ambient. Using in situ synchrotron radiation XRD experiments we demonstrated GO swelling in molten xylitol and sorbitol. The expanded GO structure intercalated with one layer of xylitol or sorbitol is preserved upon solidification of melt and cooling back to ambient conditions. The structure of solid solvates of GO with xylitol and sorbitol is based on non-covalent interaction and pristine GO can be recovered by washing in water. Intercalation of xylitol and sorbitol into GO structure in aqueous solutions yields similar but less ordered structure of GO/sugar alcohol solid solvates. Very similar inter-layer distance was observed for GO intercalated by sugar alcohols in melt and for GO immersed in sugar solutions. This result shows that sugar alcohols penetrate into GO inter-layer space without hydration shell forming 2D layers with orientation parallel to graphene oxide sheets. Therefore, hydration diameter of molecules should not be considered as decisive factor for permeation through graphene oxide inter-layers in multilayered membranes.

  • 15. Korobov, Mikhail V.
    et al.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Rebrikova, Anastasiya T.
    Shilayeva, Elizaveta A.
    Avramenko, Natalya V.
    Gagarin, Alexander N.
    Ferapontov, Nikolay B.
    Sorption of polar organic solvents and water by graphite oxide: thermodynamic approach2016Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 102, s. 297-303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sorption of polar organic solvents CH3OH, C4H8O (THF), CH3CN, C3H7NO (DMF), C2H6OS (DMSO), C5H9NO (NMP) and water was quantitatively evaluated for Hummers (H-GO) and Brodie (B-GO) graphite oxides at T = 298K and at melting temperature (Tm) of the solvents. H-GO showed stronger sorption compared to B-GO for all studied solvents and the increase of sorption upon lowering temperature was observed for both H-GO and B-GO. Thermodynamic equations allowed to explain earlier reported "maximums" of swelling/sorption in the binary systems H-GO – solvent at Tm. The specific relation between the values of enthalpies of sorption and melting leads to the change of sign in enthalpies of sorption at Tm and causes maximal swelling/sorption. The same thermodynamic explanation was given for the "maximum" on the swelling vs. pressure dependence in B-GO and H-GO – H2O systems earlier reported at pressure of phase transition "liquid water-ice VI". Notably higher sorption of H2O was observed for H-GO compared to H-GO membrane (H-GOm) at high relative humidity (RH), RH > 0.75. Experimental sorption isotherm of H-GOm was used to simulate permeation rates of water through H-GOm and to estimate effective diffusion coefficient of water through the membrane.

  • 16. Kuzenkova, Anastasiia S.
    et al.
    Romanchuk, Anna Yu
    Trigub, Alexander L.
    Maslakov, Konstantin K.
    Egorov, Alexander V.
    Amidani, Lucia
    Kittrell, Carter
    Kvashnina, Kristina O.
    Tour, James M.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kalmykov, Stepan N.
    New insights into the mechanism of graphene oxide and radionuclideinteraction2020Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 158, s. 291-302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The sorption of U(VI), Am(III)/Eu(III) and Cs(I) radionuclides by graphene oxides (GOs) synthesized byHummers’s, Brodie’s and Tour’s methods was studied through a combination of batch experiments withcharacterization by microscopic and spectroscopic techniques such as X-ray photoelectron spectroscopy(XPS), attenuated total reflection fourier-transform infrared spectroscopy (ATR-FTIR), high-energy resolutionfluorescence detected X-Ray absorption spectroscopy (HERFD-XANES), extended X-ray absorptionfine structure (EXAFS) and high resolution transmission electron microscopy (HRTEM). Remarkablydifferent sorption capacity and affinity of radionuclides was found towards GOs synthesized by Hummers’sand Brodie’s methods reflecting different structure and oxidation state of these materials.Mechanism underlying GO e radionuclide interaction is determined using variety of experimentaltechniques. For the first time it is shown here that GO - radionuclides interaction takes place on the smallholes or vacancy defects in the GO sheets. Mechanism of GO’s interaction with radionuclides wasanalyzed and specific functional groups responsible for this interaction were identified. Therefore, a newstrategy to produce improved materials with high capacity for radionuclides suggests the use perforatedand highly defected GO with a larger proportion of carboxylic functional groups.

  • 17.
    Latham, Kenneth G.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Discipline of Chemistry, University of Newcastle, Callaghan, NSW 2308, Australia.
    Dose, Wesley M.
    Allen, Jessica A.
    Donne, Scott W.
    Nitrogen doped heat treated and activated hydrothermal carbon: NEXAFS examination of the carbon surface at different temperatures2018Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 128, s. 179-190Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrothermal carbons have been shown to have controllable surface functionalization through various post-treatment techniques, which indicates these materials may be tuned for specific applications. For this reason, Near Edge X-ray Absorption Fine Structure (NEXAFS) studies have been conducted on a series of nitrogen doped and non-doped heat treated and activated hydrothermal carbons to further understand the changes in surface functionality with treatment. The NEXAFS carbon K-edge spectrum of the non-doped samples displayed a loss of oxygen functionalities (C=O and C-OH) as well as the furan ring structure with increasing temperature, while C=C bonds from graphitic groups increased. This effect was amplified further upon the addition of phosphoric acid (H3PO4) during activation. The doped hydrothermal carbons displayed similar functionality to the non-doped, although the effect of both heat treatment and activation was diminished. The nitrogen K-edge displayed characteristic peaks for pyridine and imines/amides, with pyrroles located under the broad ionization step. This work represents the first time a series of heat treated and activated hydrothermal carbons have been examined via NEXAFS spectroscopy. Additionally, difference analysis has been applied to the NEXAFS spectra to obtain a deeper understanding in the changes in surface functionality, a previously unused technique for these materials. 

  • 18. Leino, Anne-Riikka
    et al.
    Mohl, Melinda
    Kukkola, Jarmo
    Mäki-Arvela, Päivi
    Kokkonen, Tommi
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Kordas, Krisztian
    Low-temperature catalytic oxidation of multi-walled carbon nanotubes2013Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 57, s. 99-107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When in a pure form, carbon nanotubes are known to be stable in air up to ∼800 K making them attractive for a large variety of applications. In this work, we report a significant decrease of ignition temperature (in some cases occurring at ∼500 K) and a reduction in the apparent activation energy for oxidation in air as a result of impregnation with nanoparticles (<2 nm) of metal (Pt, Pd, Ni and Co) acetylacetonates or by decoration with corresponding oxides. Surprisingly, defects introduced by partial oxidation of the carbon nanotubes do not in practice have any influence on the enhancement of further oxidation. Reduction temperatures of metal oxides with H2 were close to those of other carbon supported catalyst materials. However, the carbon nanotubes showed a tendency for low temperature gasification in the presence of hydrogenation catalyst metals (Pt, Pd).

  • 19.
    Lundin, Anders
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Soldatov, Alexander
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Strongin, R.M.
    Brard, L.
    Fischer, John E.
    Smith, III, A.B.
    Compressibility of C61D2 up to 1 GPa in the temperature range 175 - 345 K1996Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 34, nr 9, s. 1119-1121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have measured the bulk modulus K for C61D2 up to 1 GPa in the temperature range 175–343 K. For face-centered cubic C61D2 above 290 K, we find an anomalously low value for K below about 0.15 GPa, possibly indicating pressure-induced changes in the structure. The (extrapolated) zero-p bulk modulus K(0) decreases with increasing T from 6.7 GPa at 175 K to 5.2 GPa at 343 K. A comparison with hypothetical expanded f.c.c. C60 with the same lattice constant shows that K(0) values are similar, indicating that the main intermolecular interactions are still between molecular bellies, not the sidegroups.

  • 20.
    Makarova, Tatiana L
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Han, K.-H.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Esquinazi, P
    da Silva, R.R.
    Kopelevich, Yakov
    Zakharova, I.B.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Magnetism in photopolymerized fullerenes2003Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 41, nr 8, s. 1575-1584Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The phototransformation of bulk C-60 and laser- and electron-beam treatment of C-60 films in air changes their magnetic properties. Nonlinear magnetization is observed only for samples irradiated in the presence of oxygen, while, in the case of pressure-polymerized C-60, oxygen adversely affects the magnetic properties. The contrasting roles of oxygen in these processes are discussed. Magnetic force microscopy shows that laser- and electron-beam irradiation of fullerene films produces magnetic images which are highly correlated with the topographic images.

  • 21.
    Makarova, Tatiana L
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Scharff, Peter
    Gaevski, M.E.
    Olsson, Eva
    Davydov, V.A.
    Rakhmanina, A.V.
    Kashevarova, L.S.
    Electrical properties of two-dimensional fullerene matrices2001Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 39, nr 14, s. 2203-2209Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electrical properties of two-dimensionally polymerized C60 fullerenes were studied. Fullerene matrices consisting of randomly oriented domains are compared to the highly-oriented rhombohedral phase. The conductivity of the randomly oriented polymers obeys the Arrhenius law and can be described in a multiple trapping model. The oriented phase of polymeric C60 shows a distinct anisotropy in the electrical properties with a metallic-like in-plane conductivity at high temperatures.

  • 22.
    Nitze, Florian
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Abou-Hamad, Edy
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Carbon nanotubes and helical carbon nanofibers grown by chemical vapour deposition on C60 fullerene supported Pd nanoparticles2011Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, nr 4, s. 1101-1107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chemical vapour deposition (CVD) represents a cheap and versatile method to produce carbon nanostructures. Here we present how we by using a standard CVD setup together with Pd nano particles as a catalyst can produce helical fibers with very periodic pitch, helicity, and narrow diameter distribution. The C60 supported Pd catalyst particles are produced by a wet chemistry process and applied to silicon substrates. By raising the growth temperature from 550 °C to 800 °C we can tune the growth products from helical carbon fibers to straight hollow carbon fibers and finally to carbon nanotubes at the highest temperatures. In the intermediate temperature region of 650 °C a mixture of all three components appears. At 550 °C the efficiency of the process is optimized by the amount of water during the growth. Different from most previous studies we can detect most of the catalyst particles embedded in the grown structures. In all fibers the catalyst particles are situated exactly in the middle of the fibers suggesting a two-directional growth. From the shape of the catalyst particles and by adopting a simple model we conclude that the fibers coil due to blocked carbon diffusion pathways on or through the catalyst particles.

  • 23. Pei, Cuiying
    et al.
    Feng, Meina
    Yang, Zhenxing
    Yao, Mingguang
    Yuan, Ye
    Li, Xin
    Hu, Bingwen
    Shen, Ming
    Chen, Bin
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wang, Lin
    Quasi 3D polymerization in C60 bilayers in a fullerene solvate2017Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 124, s. 499-505Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The polymerization of fullerenes has been an interesting topic for almost three decades. A rich polymeric phase diagram of C60 has been drawn under a variety of pressure-temperature conditions. However, only linear or perpendicular linkages of C60 are found in the ordered phases. Here we used a unique bilayer structural solvate, C60∙1,1,2-trichloroethane (C60∙1TCAN), to generate a novel quasi-3D C60 polymer under high pressure and/or high temperature. Using Raman, IR spectroscopy and X-ray diffraction, we observe that the solvent molecules play a crucial role in confining the [2+2] cycloaddition bonds of C60s forming in the upper and lower layers alternately. The relatively long distance between the two bilayers restricts the covalent linkage extended in a single individual bilayer. Our studies not only enrich the phase diagram of polymeric C60, but also facilitate targeted design and synthesis of unique C60 polymers.

  • 24.
    Sharifi, Tiva
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Tai, Cheuk-Wai
    Mazurkiewicz, Marta
    Malolepszy, Artur
    Stobinski, Leszek
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitrogen doped multi walled carbon nanotubes produced by CVD-correlating XPS and Raman spectroscopy for the study of nitrogen inclusion2012Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 50, nr 10, s. 3535-3541Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High purity aligned nitrogen doped multi walled carbon nanotubes were synthesized by the catalytic chemical vapor deposition method using pyridine and Fe/Co (2:1 volume ratio) as the single C/N precursor and catalyst material. The average diameter of the synthesized tubes ranges between 29 nm and 57 nm and the nitrogen content of the tubes reaches a maximum of 9.2 (at.)% nitrogen. The effect of nitrogen doping on the Raman scattering of doped tubes and its correlation with X-ray photoelectron spectra (XPS) was investigated. The analysis is based on the investigation of the I-D/I-G (integrated area ratio), other nitrogen characteristic Raman modes and the type of nitrogen inclusion interpreted from the N 1s electron bonding energies in XPS. At doping levels higher than 5% the nitrogen inclusion takes place through another mechanism than at low nitrogen doping levels. Most significant is that pyridinic defects are relatively readily incorporated at low nitrogen doping levels while at nitrogen content higher than 5% the major incorporation mechanism is dominated by pyridinic and pyrrolic defects on an equal basis. Our study gives further insight into nitrogen doping effects and the relation between type of nitrogen inclusion and nitrogen doping levels. (C) 2012 Elsevier Ltd. All rights reserved.

  • 25.
    Sharifi, Tiva
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Materials Science and Nanoengineering, Rice University, Houston, 77005, USA.
    Xie, Yu
    Zhang, Xiang
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Physics, University of California, Berkeley, 94720-1234, USA.
    Lei, Jincheng
    Coulter, Gabriel
    Sun, Shiyun
    Tiwary, Chandrasekhar
    Zettl, Alex
    Yakobson, Boris
    Ajayan, Pulickel M.
    Graphene as an electrochemical transfer layer2019Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 141, s. 266-273Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The capability of graphene to adopt a property from an adjacent material is investigated by measuring the electrochemical performance of a monolayer graphene placed on top of thin cobalt oxide (Co3O4) nanosheets. In this assembly, monolayer graphene works as an interfacial layer which inhibits the direct contact of the actual electroactive material and electrolyte during electrochemical reaction. The results show that while graphene is electrochemically inert, it behaves as an active material to catalyze oxygen evolution reaction (OER) once placed on top of Co3O4 nanosheets. The graphene-covered Co3O4 model system shows electrochemical performance similar to Co3O4 indicating complete transference of the electrochemical property of the metal oxide to the graphene. Based on density functional theory (DFT) calculations, charge transfer from graphene to Co3O4 is the key factor for turning the electrochemically inactive graphene to an apparent active material. 

  • 26.
    Sun, Jinhua
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Morales-Lara, Francisco
    Klechikov, Alexey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Baburin, Igor A.
    Seifert, Gotthard
    Cardano, Francesca
    Baldrighi, Michele
    Frasconi, Marco
    Giordani, Silvia
    Porous graphite oxide pillared with tetrapod-shaped molecules2017Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 120, s. 145-156Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Porous pillared graphene oxide (GO) materials were prepared using solvothermal reaction of Hummers GO with solution of Tetrakis(4-aminophenyl)methane (TKAm) in methanol. The intercalation of TKAm molecules between individual GO sheets, performed under swelling condition, results in expansion of inter-layer distance of GO from ∼7.5 Å to 13-14 Å. Pillaring GO with bulky, rigid 3D shaped TKAm molecules could be an advantage for the preparation of stable pillared structures compared to e.g. aliphatic or aromatic diamines. Insertion of TKAm molecules into inter-layer space of GO results in formation of interconnected network of sub-nanometer slit pores. The expanded GO structure prepared with optimized GO/TKAm composition shows Specific Surface Area (SSA) up to 660 m2/g which is among the highest reported for GO materials pillared using organic spacers. Modelling of GO structures pillared with TKAm molecules shows that maximal SSA of about 2300 m2/g is theoretically possible for realistic concentration of pillaring molecules in GO interlayers. Hydrogen sorption by pillared GO/TKAm is found to follow standard correlation with SSA both at ambient and liquid nitrogen temperatures with highest uptakes of 1.66 wt% achieved at 77 K and 0.25 wt% at 295 K. Our theoretical simulations show that pillared GO structures do not provide improvement of hydrogen storage beyond well-established physisorption trends even for idealized materials with subnanometer pores and SSA of 2300–3700 m2/g.

  • 27.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Jilin Univ, State Key Lab Superhard Mat, Changchun 130012, Jilin, Peoples R China.
    Intermolecular bonding in C70 at high pressure and temperature2017Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 125, s. 258-268Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Near-infrared (NIR) Raman spectroscopy has been used to analyze intermolecular bonding in solid C70, treated for two hours under pressures in the range 0.8 to 2 GPa at temperatures between 350 and 600 K. The spectra obtained are analyzed in detail with the aim of finding spectral lines characteristic for the monomer C70, the dimer C140, and possibly for higher oligomers. In agreement with earlier studies, several new modes are observed in the NIR Raman spectra, in sharp contrast to what is found in Raman studies using visible light excitation. From the relative intensities of the characteristic dimer stretch line at 88 cm-1 and a mode at 457 cm-1, characteristic for the monomer, a semi-quantitative estimate for the dimer fraction in the material can be found as a function of pressure and temperature. From these results a reaction map, similar to that recently derived for C60, can be drawn. The data obtained indicate that C70 is almost completely polymerized into large, random oligomers (or polymers) after long-time treatment at elevated temperatures (> 500 K) and pressures (>1.2 GPa). The phase diagram of C70 is updated and briefly discussed in the light of this and other recent high pressure studies.

  • 28. Szabó, Tamás
    et al.
    Péter, Zsolt
    Illés, Erzsébet
    Janovák, László
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stability and dye inclusion of graphene oxide/polyelectrolyte layer-by-layer self-assembled films in saline, acidic and basic aqueous solutions2017Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 111, s. 350-357Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate that a simple spectrophotometric method can be efficiently applied for the characterization of structural and chemical stability and adsorption properties of composite graphene oxide (GO) films in various solutions. The immersion stability of GO layer-by-layer (LbL) self-assembled with a polycation into ultrathin multilayered films was studied in water and in concentrated salty, acidic and basic solutions by UV-visible spectroscopy. These films were found to retain both their chemical stability and physical integrity in water, salt and HCl solutions with a slight rearrangement of the nanoscale structure as shown by the change in their visible spectrum. However, immersion into NaOH solutions above molar concentration led to the deconstruction of the multilayer structure by base-induced deoxygenation of GO. The adsorption of methylene blue on polymer/GO LbL films of various thicknesses revealed that the multilayers are largely impermeable towards this cationic dye.

  • 29.
    Talyzin, Alexandr
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Luzan, Serhiy
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Temperature dependent structural breathing of hydrated graphite oxide in H2O2011Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, nr 6, s. 1894-1899Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydration of graphite oxide by excess of water was studied in the temperature interval 295–230 K. A structural breathing effect is found for fully hydrated graphite oxide near the water solidification/melting point. Expansion of hydrated graphite oxide structure due to insertion of additional water occurs upon cooling down from ambient temperature to the point of water media freezing. Cooling down below the point of water medium solidification results in stepwise contraction of graphite oxide interlayer distance by ∼25% due to partial withdrawal of water from the hydrated structure. Heating back from 230 K to ambient temperature results in graphite oxide structure expansion due absorption of water from medium, thus making a reversible cycle. The effect of structure breathing is important for any chemical treatments performed with graphite oxide in solution, e.g. graphite oxide functionalizationand conversion into graphene-related materials.

  • 30.
    Talyzin, Alexandr
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mercier, Guillaume
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Klechikov, Alexey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hedenström, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Johnels, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wei, Di
    Cotton, Darryl
    Opitz, Andreas
    Moons, Ellen
    Brodie vs Hummers graphite oxides for preparation of multi-layered materials2017Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 115, s. 430-440Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graphite oxides synthesized by one and two step Brodie oxidation (BGO) and Hummers (HGO) methods were analyzed by a variety of characterization methods in order to evaluate the reasons behind the difference in their properties. It is found that the Brodie method results in a higher relative amount of hydroxyl groups and a more homogeneous overall distribution of functional groups over the planar surface of the graphene oxide flakes. The higher number of carbonyl and carboxyl groups in HGO, detected by several methods, including XPS, NMR and FTIR, unavoidably results in defects of the graphene "skeleton", holes and overall disruption of the carbon-carbon bond network, stronger deviation from planar flake shape and poor ordering of the graphene oxide layers. It is also suggested that functional groups in HGO are less homogeneously distributed over the flake surface, forming some nanometer-sized graphene areas. The presence of differently oxidized areas on the GO surface results in inhomogeneous solvation and hydration of HGO and effects of inter- and intra-stratification. The proposed interpretation of the data explains the higher mechanical strength of multi-layered BGO membranes/papers, which are also less affected by humidity changes, thus providing an example of a membrane property superior to that of HGO.

  • 31.
    Wu, Jufang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Claesson, Ola
    Fängmark, Ingrid
    Hammarström, Lars-Gunnar
    A systematic investigation of the overall rate coefficient in the Wheeler-Jonas equation for adsorption on dry activated carbons2005Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 43, nr 3, s. 481-490Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Modelling of the adsorption rate coefficient, kv of the Wheeler-Jonas equation for estimating the service life of packed carbon beds, is addressed. Current methods for extracting kv from experimental breakthrough data include approaches that introduce easily propagated errors. The weaknesses of these approaches are analyzed, and a calculation based on multiple points on the breakthrough curve is suggested. Experimental breakthrough data for a representative set of volatile organic compounds (VOCs) has been measured. A systematic investigation of factors influencing kv, including adsorbate and carbon properties, adsorbate inlet concentration and flow velocity is performed. It is found that flow velocity and carbon particle size have the largest influence, followed by adsorbate properties related to the adsorption capacity. A simple linear empirical model for kv, including air flow velocity, carbon particle size, and dielectric constant of the adsorbate, is presented. The model is based on the breakthrough range up to 20% of the inlet concentration, for which kv is shown to be almost constant. The range of the model covers breathing rates valid for a respirator at different work loads. The model can be used to estimate the adsorption rate coefficient for specific carbon particle sizes and various VOCs present in workplace environments.

  • 32. Yang, Zhenxing
    et al.
    Hu, Kuo
    Meng, Xianwei
    Tao, Qiang
    Dong, Jiajun
    Liu, Bo
    Lu, Qian
    Zhang, Hua
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. State Key Laboratory of Superhard Materials, College of Physics, Jilin University, People's Republic of China.
    Zhu, Pinwen
    Yao, Mingguang
    Liu, Bing bing
    Tuning the band gap and the nitrogen content in carbon nitride materials by high temperature treatment at high pressure2018Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 130, s. 170-177Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon nitride (C-N) materials have been attracting great interest because of their extraordinary performance in photocatalysis and energy conversion. However, developing an effective strategy for achieving band-gap engineering of C-N materials to satisfy practical applications remains highly desired. Here we report an efficient way to tune the band gap and control the nitrogen stoichiometry in carbon nitride compounds by using high pressure and high temperature (HPHT) treatment. It is found that treating a g-C3N4 precursor at relatively low temperature (630oC and below) under pressure can efficiently narrow the band gap even down to the red light region (~600 nm), increase the crystallinity, and significantly improve the charge carrier separation efficiency (by two orders of magnitude), almost without changing their stoichiometry. When increasing the treatment temperature under pressure, nitrogen-doped graphene/graphite materials with weak ferromagnetism were obtained. We thus obtained C-N materials with tunable band gaps, ranging from semiconducting to metallic states. XPS measurements show that pyridinic nitrogen is preferentially eliminated under such HPHT conditions while graphitic nitrogen is preserved in the C-N network. Our results thus provide an efficient strategy for tuning the structure and physical properties of C-N materials for applications.

  • 33.
    Yao, Mingguang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Andersson, Britt M
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Stenmark, Patrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Liu, Bingbing
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Synthesis and growth mechanism of differently shaped C60 nano/microcrystals produced by evaporation of various aromatic C60 solutions2009Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 47, nr 4, s. 1181-1188Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a detailed study of the synthesis of C60 nano- and microrods as well as crystals with normal shapes by the evaporation of C60 solutions based on different aromatic solvents. C60 nano- and microrods are grown with high yield by vaporizing C60 solutions in meta-isomers of aromatic solvents on different substrates while para-isomers give a different type of growth leading to highly crystalline two- and three-dimensional nano- and microcrystals with fcc structure. The role of solvent properties was investigated by using positional isomers containing different halogen radicals. The as-grown crystal rods formhexagonal structures but transform into fcc structure on annealing in vacuum. IR and EDX analysis indicate that solvents remain in the hexagonal nano- and microrods, while it is hard to detect any trace of solvents in the two- or three-dimensional nano- and microcrystals. Furthermore, we present direct proof of the nucleation-growth mechanism for C60 rods. By the vaporization method, the solubility of C60 in the studied halogen aromatic solvents is found to correlate with the diameter distribution of the C60 rods and we suggest that the chemical affinity of the aromatic solvent molecules to C60 may determine its ability to force C60 to form rod-shaped crystals.

  • 34. Yao, Mingguang
    et al.
    Fan, Xianhong
    Liu, Dedi
    Liu, Bingbing
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Synthesis of differently shaped C(70) nano/microcrystals by using various aromatic solvents and their crystallinity-dependent photoluminescence2012Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 50, nr 1, s. 209-215Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a simple synthesis of Cm microcrystals by a fast solvent-assisted evaporation method by selectively using aromatic solvents with halogen radicals as a controller. In a detailed analysis we show that depending on solvent, C(70) concentration in the solution, and synthesis temperature both C(70) microrods and microcubes can be produced. The samples were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. From meta-type solvents microrods or microcrystal cubes grow with a single orthorhombic or a monoclinic structure or a mixture of both. These crystals show traces of solvents in the structure. From para-type solvents cubic (or rectangular) crystals grow with a hexagonal structure and with no trace of solvents. Room temperature photoluminescence (PL) of the C(70) crystal samples reveals that the PL efficiency of the crystals increases with crystalline order and that the best crystalline Cm cube crystals show 10 times higher PL efficiency than that of pristine C(70) polycrystalline samples. (C) 2011 Elsevier Ltd. All rights reserved.

  • 35.
    Yao, Mingguang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stenmark, Patrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Abou-Hamad, Edy
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Qin, Jian
    Royal Institute of Technology, SE-16440 Stockholm, Sweden.
    Goze-Bac, Christophe
    Centre National de la Recherche Scientifique, Université Montpellier 2, F-34079 Montpellier, France.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Confined adamantane molecules assembled to one dimension in carbon nanotubes2011Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, nr 4, s. 1159-1166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have encapsulated adamantane (C10H16) in single- and multi-walled carbon nanotubes. Adamantane is a high symmetry cage like molecule with point group symmetry Td and can be considered as a hydrogen-terminated diamond fragment. We confirmed and identified the successful filling by high resolution transmission electron microscopy, 13C nuclear magnetic resonance, infrared and Raman spectroscopy. 13C nuclear magnetic resonance of the adamantane filled nanotubes reveals that the adamantane molecules stop rotating after encapsulation. A blue-shift of the Raman active radial breathing modes of the carbon nanotubes supports this and suggests a significant interaction between encapsulated adamantane molecules and the single wall nanotubes. The encapsulated adamantane molecules exhibit red shifted infrared C–H vibration modes which we assign to a slight elongation of the C–H bonds. We observe both a nanotube diameter dependence of the adamantane filling ratio and a release rate of adamantane from the CNTs that depends on the CNT diameters.

  • 36.
    You, Shujie
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Luzan, Serhiy
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Szabo, Tamas
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Effect of synthesis method on solvation and exfoliation of graphite oxide2013Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 52, s. 171-180Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graphite oxides (GOs) synthesized by Brodie’s and Hummers’ methods are significantly different with respect to hydration, solvation and exfoliation properties. Hummers GO is more easily intercalated by liquid water and alcohols, exhibiting osmotic type of swelling. In contrast, Brodie GO shows crystalline swelling in alcohol solvents with step-like insertion of methanol or ethanol monolayers. However, the stronger hydration and easier dispersion in water observed for Hummers GO do not correlate with better dispersion of graphene powder obtained by thermal exfoliation. Higher surface area graphene powder was obtained by exfoliation of Brodie GO, while the temperature of its exfoliation is about 75 C higher than that for the studied sample of Hummers GO. It is suggested that higher exfoliation temperature and better crystallinity of GO are important factors for preparation of graphene powder using thermal exfoliation.

  • 37.
    Yu, Junchun
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Tonpheng, Bounphanh
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gröbner, Gerhard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Andersson, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal properties and transition studies of multi-wall carbon nanotube/nylon-6 composites2011Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, nr 14, s. 4858-4866Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transition behavior and thermal properties of a multi-wall carbon nanotube (MWCNT)/nylon-6 composite (P-composite) made by in situ polymerization and subsequently structurally modified by high-pressure–high-temperature treatment have been established. The thermal conductivity (κ) of nylon-6 improved 27% by the addition of 2.1 wt.% MWCNT filler simultaneously as the heat capacity per unit volume decreased 22% compared with that of nylon-6 at 1 atm and 298 K. Moreover, the MWCNT filler raises the glass transition temperature (Tg) of nylon-6, but the pressure dependence of Tg remains unchanged. A model for κ indicates that the interfacial thermal resistance between the MWCNT filler and the nylon-6 matrix decreases 20% up to 1 GPa and most significantly above 0.8 GPa. P-composite was structurally modified by a sluggish cold-crystallization transition at 1.0 GPa, 530 K, which further increased κ by as much as 37% as the crystallinity of nylon-6 improved from 31% to 58% with a preferred crystal orientation and increased crystal size.

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