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  • 1.
    Abou-Hamad, Edy
    et al.
    Universite Montpellier II.
    Kim, Y
    University of Pennsylvania.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Goze-Bac, Christophe
    Universite Montpellier II.
    Luzzi, David
    University of Pennsylvania.
    Rubio, Angelo
    University of Basque Country.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Hydrogenation of C-60 in Peapods: Physical Chemistry in Nano Vessels2009Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 20, s. 8583-8587Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogenation of C-60 molecules inside SWNT was achieved by direct reaction with hydrogen gas at elevated pressure and temperature. Evidence for the C-60 hydrogenation in peapods is provided by isotopic engineering with specific enrichment of encapsulated species and high resolution C-13 and H-1 NMR spectroscopy with the observation of characteristic diamagnetic and paramagnetic shifts of the NMR lines and the appearance of sp(3) carbon resonances. We estimate that approximately 78% of the C-60 molecules inside SWNTs are hydrogenated to an average degree of 14 hydrogen atoms per C-60 molecule. As a consequence, the rotational dynamics of the encapsulated C60Hx molecules is clearly hindered. Our successful hydrogenation experiments open completely new roads to understand and control confined chemical reactions at the nano scale

  • 2. Ajuria, Jon
    et al.
    Arnaiz, Maria
    Botas, Cristina
    Carriazo, Daniel
    Mysyk, Roman
    Rojo, Teofilo
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Goikolea, Eider
    Graphene-based lithium ion capacitor with high gravimetric energy and power densities2017Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 363, s. 422-427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hybrid capacitor configurations are now of increasing interest to overcome the current energy limitations of supercapacitors. In this work, we report a lithium ion capacitor (LIC) entirely based on graphene. On the one hand, the negative-battery-type- electrode consists of a self-standing, binder-free 3D macroporous foam formed by reduced graphene oxide and decorated with tin oxide nanoparticles (SnO2-rGO). On the other hand, the positive-capacitor-type- electrode is based on a thermally expanded and physically activated reduced graphene oxide (a-TEGO). For comparison purposes, a symmetric electrical double layer capacitor (EDLC) using the same activated graphene in 1.5 M Et4NBE4/ACN electrolyte is also assembled. Built in 1 M LiPF6 EC:DMC, the graphene-based LIC shows an outstanding, 10-fold increase in energy density with respect to its EDLC counterpart at low discharge rates (up to 200 Wh kg(-1)). Furthermore, it is still capable to deliver double the energy in the high power region, within a discharge time of few seconds.

  • 3.
    Andersson, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Filinchuk, Yaroslav
    Dmitriev, Vladimir
    Quwar, Issam
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Phase coexistence and hysteresis effects in the pressure-temperature phase diagram of NH3BH32011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 2, s. 024115-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The potential hydrogen storage compound NH3BH3 has three known structural phases in the temperature and pressure ranges 110–300 K and 0–1.5 GPa, respectively. We report here the boundaries between, and the ranges of stability of, these phases. The phase boundaries were located by in situ measurements of the thermal conductivity, while the actual structures in selected areas were identified by in situ Raman spectroscopy and x-ray diffraction. Below 0.6 GPa, reversible transitions involving only small hysteresis effects occur between the room-temperature tetragonal plastic crystal I4mm phase and the low-temperature orthorhombic Pmn21 phase. Transformations of the I4mm phase into the high-pressure orthorhombic Cmc21 phase, occurring above 0.8 GPa, are associated with very large hysteresis effects, such that the reverse transition may occur at up to 0.5 GPa lower pressures. Below 230 K, a fraction of the Cmc21 phase is metastable to atmospheric pressure, suggesting the possibility that dense structural phases of NH3BH3, stable at room temperature, could possibly be created and stabilized by alloying or by other methods. Mixed orthorhombic Pmn21/Cmc21 phases were observed in an intermediate pressure-temperature range, but a fourth structural phase predicted by Filinchuk et al. [ Phys. Rev. B 79 214111 (2009)] was not observed in the pressure-temperature ranges of this experiment. The thermal conductivity of the plastic crystal I4mm phase is about 0.6 W m−1 K−1 and only weakly dependent on temperature, while the ordered orthorhombic phases have higher thermal conductivities limited by phonon-phonon scattering.

    Fulltekst (pdf)
    AnderssonPRB84_2011
  • 4. Anoshkin, Ilya
    et al.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nasibulin, Nasibulin
    Krasheninnikov, Arkady
    Jiang, Hua
    Nieminen, Risto
    Kauppinen, Esko
    Coronene Encapsulation in Single-Walled Carbon Nanotubes: Stacked Columns, Peapods, and Nanoribbons2014Inngår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, nr 8, s. 1660-1665Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Encapsulation of coronene inside single-walled carbon nanotubes (SWNTs) was studied under various conditions. Under high vacuum, two main types of molecular encapsulation were observed by using transmission electron microscopy: coronene dimers and molecular stacking columns perpendicular or tilted (45-608) with regard to the axis of the SWNTs. A relatively small number of short nanoribbons or polymerized coronene molecular chains were observed. However, experiments performed under an argon atmosphere (0.17 MPa) revealed reactions between the coronene molecules and the formation of hydrogen-terminated graphene nanoribbons. It was also observed that the morphology of the encapsulated products depend on the diameter of the SWNTs. The experimental results are explained by using density functional theory calculations through the energies of the coronene molecules inside the SWNTs, which depend on the orientation of the molecules and the diameter of the tubes.

  • 5. Araújo, C. Moysés
    et al.
    Ahuja, Rajeev
    Talyzin, Alexandr V
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Pressure-induced structural phase transition in NaBH42005Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 5, s. 054125-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a combined experimental and theoretical study of the technologically important NaBH4 compound under high pressure. Using Raman spectroscopy at room temperature, we have found that NaBH4 undergoes a structural phase transformation starting at 10.0 GPa with the pure high-pressure phase being established above 15.0 GPa. In order to compare the Raman data recorded under high pressure with the low-temperature tetragonal phase of NaBH4, we have also performed a cooling experiment. The known order-disorder transition from the fcc to the tetragonal structure was then observed. However, the new high pressure phase does not correspond to this low-temperature structure. Using first-principle calculations based on the density functional theory, we show that the high-pressure phase corresponds to the alpha-LiAlH4–type structure. We have found a good agreement between the measured and calculated transition pressures. Additionally, we present the electronic structure of both the fcc and the high-pressure phases.

  • 6. Baburin, Igor A
    et al.
    Klechikov, Alexey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mercier, Guillaume
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Seifert, Gotthard
    Hydrogen adsorption by perforated graphene2015Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 40, nr 20, s. 6594-6599Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We performed a combined theoretical and experimental study of hydrogen adsorption in graphene systems with defect-induced additional porosity. It is demonstrated that perforation of graphene sheets results in increase of theoretically possible surface areas beyond the limits of ideal defect-free graphene (∼2700 m2/g) with the values approaching ∼5000 m2/g. This in turn implies promising hydrogen storage capacities up to 6.5 wt% at 77 K, estimated from classical Grand canonical Monte Carlo simulations. Hydrogen sorption was studied for the samples of defected graphene with surface area of ∼2900 m2/g prepared using exfoliation of graphite oxide followed by KOH activation. The BET surface area of studied samples thus exceeded the value of single-layered graphene. Hydrogen uptake measured at 77 K and 296 K amounts to 5.5 wt% (30 bar) and to 0.89 wt% (120 bar), respectively. 

    Fulltekst (pdf)
    fulltext
  • 7.
    Boulanger, Nicolas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kuzenkova, Anastasiia S.
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation.
    Iakunkov, Artem
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nordenström, Andreas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Romanchuk, Anna Yu.
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation.
    Trigub, Alexander L.
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation; National Research Centre “Kurchatov Institute”, Moscow, Russian Federation.
    Zasimov, Pavel V.
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation.
    Prodana, Mariana
    Center for Surface Science and Nanotechnology, University Politehnica of Bucharest, Splaiul Independentei 313, Bucharest, Romania.
    Enachescu, Marius
    Center for Surface Science and Nanotechnology, University Politehnica of Bucharest, Splaiul Independentei 313, Bucharest, Romania; Academy of Romanian Scientists, Splaiul Independentei 54, Bucharest, Romania.
    Bauters, Stephen
    Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, Dresden, Germany; The Rossendorf Beamline at ESRF, The European Synchrotron, CS40220, Grenoble Cedex 9, France.
    Amidani, Lucia
    Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, Dresden, Germany; The Rossendorf Beamline at ESRF, The European Synchrotron, CS40220, Grenoble Cedex 9, France.
    Kvashnina, Kristina O.
    Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, Dresden, Germany; The Rossendorf Beamline at ESRF, The European Synchrotron, CS40220, Grenoble Cedex 9, France.
    Kalmykov, Stepan N.
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    High Surface Area "3D Graphene Oxide" for Enhanced Sorption of Radionuclides2022Inngår i: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 9, nr 18, artikkel-id 2200510Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Here preparation of high surface area activated reduced graphene oxide (arGO) oxidized into a 3D analogue of defect-rich GO (dGO) is reported. Surface oxidation of arGO results in carbon to oxygen ratio C/O = 3.3, similar to the oxidation state of graphene oxide while preserving high BET surface area of about 880 m2 g−1. Analysis of surface oxidized arGO shows high abundance of oxygen functional groups which converts hydrophobic precursor into hydrophilic material. High surface area carbons provide the whole surface for oxidation without the need of intercalation and lattice expansion. Therefore, surface oxidation methods are sufficient to convert the materials into 3D architectures with chemical properties similar to graphene oxide. The "3D graphene oxide" shows high sorption capacity for U(VI) removal in an extraordinary broad interval of pH. Notably, the surface oxidized carbon material has a rigid 3D structure with micropores accessible for penetration of radionuclide ions. Therefore, the bulk "3D GO" can be used as a sorbent directly without dispersing, the step required for GO to make its surface area accessible for pollutants.

    Fulltekst (pdf)
    fulltext
  • 8.
    Boulanger, Nicolas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kuzenkova, Anastasiia S.
    Iakunkov, Artem
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Romanchuk, Anna Yu
    Trigub, Alexander L.
    Egorov, Alexander, V
    Bauters, Stephen
    Amidani, Lucia
    Retegan, Marius
    Kvashnina, Kristina O.
    Kalmykov, Stepan N.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Enhanced Sorption of Radionuclides by Defect-Rich Graphene Oxide2020Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 12, nr 40, s. 45122-45135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Extremely defect graphene oxide (dGO) is proposed as an advanced sorbent for treatment of radioactive waste and contaminated natural waters. dGO prepared using a modified Hummers oxidation procedure, starting from reduced graphene oxide (rGO) as a precursor, shows significantly higher sorption of U(VI), Am(III), and Eu(III) than standard graphene oxides (GOs). Earlier studies revealed the mechanism of radionuclide sorption related to defects in GO sheets. Therefore, explosive thermal exfoliation of graphite oxide was used to prepare rGO with a large number of defects and holes. Defects and holes are additionally introduced by Hummers oxidation of rGO, thus providing an extremely defect-rich material. Analysis of characterization by XPS, TGA, and FTIR shows that dGO oxygen functionalization is predominantly related to defects, such as flake edges and edge atoms of holes, whereas standard GO exhibits oxygen functional groups mostly on the planar surface. The high abundance of defects in dGO results in a 15-fold increase in sorption capacity of U(VI) compared to that in standard Hummers GO. The improved sorption capacity of dGO is related to abundant carboxylic group attached hole edge atoms of GO flakes as revealed by synchrotron-based extended X-ray absorption fine structure (EXAFS) and high-energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy.

    Fulltekst (pdf)
    fulltext
  • 9.
    Boulanger, Nicolas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Li, Gui
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bakhiia, Tamuna
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation.
    Maslakov, Konstantin I.
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation.
    Romanchuk, Anna Yu.
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation.
    Kalmykov, Stepan N.
    Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Super-oxidized “activated graphene” as 3D analogue of defect graphene oxide: oxidation degree vs U(VI) sorption2023Inngår i: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 457, artikkel-id 131817Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Porous carbons are not favorable for sorption of heavy metals and radionuclides due to absence of suitable binding sites. In this study we explored the limits for surface oxidation of “activated graphene” (AG), porous carbon material with the specific surface area of ∼2700 m2/g produced by activation of reduced graphene oxide (GO). Set of “Super-Oxidized Activated Graphene” (SOAG) materials with high abundance of carboxylic groups on the surface were produced using “soft” oxidation. High degree of oxidation comparable to standard GO (C/O=2.3) was achieved while keeping 3D porous structure with specific surface area of ∼700–800 m2/. The decrease in surface area is related to the oxidation-driven collapse of mesopores while micropores showed higher stability. The increase in the oxidation degree of SOAG is found to result in progressively higher sorption of U(VI), mostly related to the increase in abundance of carboxylic groups. The SOAG demonstrated extraordinarily high sorption of U(VI) with the maximal capacity up to 5400 μmol/g, that is 8.4 – fold increase compared to non-oxidized precursor AG, ∼50 –fold increase compared to standard graphene oxide and twice higher than extremely defect-rich graphene oxide. The trends revealed here show a way to further increase sorption if similar oxidation degree is achieved with smaller sacrifice of surface area.

    Fulltekst (pdf)
    fulltext
  • 10.
    Boulanger, Nicolas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Skrypnychuk, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nordenström, Andreas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Moreno-Fernández, Gelines
    Centre for Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA) Alava Technology Park, Vitoria-Gasteiz, Spain.
    Granados-Moreno, Miguel
    Centre for Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA) Alava Technology Park, Vitoria-Gasteiz, Spain.
    Carriazo, Daniel
    Centre for Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA) Alava Technology Park, Vitoria-Gasteiz, Spain.
    Mysyk, Roman
    Centre for Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA) Alava Technology Park, Vitoria-Gasteiz, Spain.
    Bracciale, Gaetan
    Thales Research & Technology, Palaiseau, France.
    Bondavalli, Paolo
    Thales Research & Technology, Palaiseau, France.
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Spray deposition of supercapacitor electrodes using environmentally friendly aqueous activated graphene and activated carbon dispersions for industrial implementation2021Inngår i: ChemElectroChem, E-ISSN 2196-0216, Vol. 8, nr 7, s. 1349-1361Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A spray gun machine was used to deposit high‐surface‐area supercapacitor electrodes using green non‐toxic aqueous dispersions based on different kinds of high specific surface area nanostructured carbon materials: activated graphene (a‐rGO) and activated carbon (AC). Tuning the spray conditions and dispersion formulation allowed us to achieve good adhesion to stainless‐steel current collectors in combination with high surface area and a satisfactory mechanical stability of the electrodes. The specific surface area of approximately 2000 m2/g was measured directly on a‐rGO and AC electrodes showing only around a 20 % decrease compared to the precursor powder materials. The performance of the electrodes deposited on stainless‐steel and aluminum current collectors was tested in supercapacitor devices using three electrolytes. The electrodes were tested in an “as‐deposited” state and after post‐deposition annealing at 200 °C. The spray deposition method and post‐deposition annealing are completely compatible with roll‐to‐roll industrial production methods. The a‐rGO demonstrated superior performance compared to AC in supercapacitor electrodes with gravimetric capacitance, energy, and power density parameters, which exceed commercially available analogues. The formulation of the dispersions used in this study is environmentally friendly, as it is based on only on water as a solvent and commercially available non‐toxic additives (graphene oxide, fumed silica, and carbon nanotubes).

    Fulltekst (pdf)
    fulltext
  • 11.
    Boulanger, Nicolas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Xiong, Shaojun
    Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Hultberg, Malin
    Department of Biosystems and Technology, Swedish University of Agricultural Sciences, Alnarp, Sweden.
    Grimm, Alejandro
    Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    High surface area activated carbon prepared from wood-based spent mushroom substrate for supercapacitors and water treatment2024Inngår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 680, artikkel-id 132684Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Edible white-rot fungi are commonly cultivated on wood-based substrates and selectively degrade lignin to a larger extent during their growth. Spent mushroom substrate (SMS) is produced in huge amounts by the mushroom industry and today there is a lack of proven methods to valorize this kind of biomass waste, which in most cases is landfilled or used as fuel. This study demonstrates that birch wood-based SMS from the cultivation of oyster mushrooms can be converted into high-quality activated carbon (AC) with an extremely high surface area of about 3000 m2/g. These activated carbons showed good performance when used in electrodes for supercapacitors, with energy storage parameters nearly identical to AC produced from high-quality virgin birch wood. Moreover, AC produced from SMS showed high potential as an adsorbent for cleaning reactive orange-16 azo dye from aqueous solutions as well as contaminants from synthetic effluents and from real sewage water. The kinetics of adsorption were well represented by the Avrami fractional order model and isotherms of adsorption by the Liu model. The theoretical maximum reactive orange-16 adsorption capacities were approximately 519 mg/g (SMS-based carbon) and 553 mg/g (virgin birch-based carbon). The removal of contaminants from synthetic effluents made of different dyes and inorganic compounds was around 95% and 83% depending on the effluent composition. The removal of contaminants from raw sewage water was around 84%, and from treated sewage water was around 68%. Overall, the results showed that activated carbon prepared from waste generated during cultivation of white-rot fungi is as good as activated carbon prepared from high-quality virgin wood.

    Fulltekst (pdf)
    fulltext
  • 12. Chernov, Alexander I
    et al.
    Fedotov, Pavel V
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Suarez Lopez, Inma
    Anoshkin, Ilya V
    Nasibulin, Albert G
    Kauppinen, Esko I
    Obraztsova, Elena D
    Optical properties of graphene nanoribbons encapsulated in single-walled carbon nanotubes2013Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 7, nr 7, s. 6346-6353Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the photoluminescence (PL) from graphene nanoribbons (GNRs) encapsulated in single-walled carbon nanotubes (SWCNTs). New PL spectral features originating from GNRs have been detected in the visible spectral range. PL peaks from GNRs have resonant character, and their positions depend on the ribbon geometrical structure in accordance with the theoretical predictions. GNRs were synthesized using confined polymerization and fusion of coronene molecules. GNR@SWCNTs material demonstrates a bright photoluminescence both in infrared (IR) and visible regions. The photoluminescence excitation mapping in the near-IR spectral range has revealed the geometry-dependent shifts of the SWCNT peaks (up to 11 meV in excitation and emission) after the process of polymerization of coronene molecules inside the nanotubes. This behavior has been attributed to the strain of SWCNTs induced by insertion of the coronene molecules.

  • 13. Chumakova, Natalia A.
    et al.
    Rebrikova, Anastasya T.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Paramonov, Nikita A.
    Vorobiev, Andrey Kh
    Korobov, Mikhail, V
    Properties of Graphite Oxide Powders and Membranes as Revealed by Electron Paramagnetic Resonance Spectroscopy2018Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 39, s. 22750-22759Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 14. Dmitriev, Vladimir
    et al.
    Filinchuk, Yaroslav
    Chernyshov, Dmitry
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Dzwilewski, Andrzej
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Andersson, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kurnosov, Alexander
    Pressure-temperature phase diagram of LiBH4: Synchrotron x-ray diffraction experiments and theoretical analysis2008Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, nr 17, artikkel-id 174112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An in situ combined high-temperature high-pressure synchrotron radiation diffraction study has been carried out on LiBH4. The phase diagram of LiBH4 is mapped to 10 GPa and 500 K, and four phases are identified. The corresponding structural distortions are analyzed in terms of symmetry-breaking atomic position shifts and anion ordering. Group-theoretical and crystal-chemical considerations reveal a nontrivial layered structure of LiBH4. The layers and their deformations define the structural stability of the observed phases.

  • 15.
    Dzwilewski, Andrzej
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Experimental Physics.
    Bromiley, G.
    Dub, S.
    Dubrovinsky, Leonid
    Characterization of phases synthesized close to the boundary of C60 collapse at high temperature high pressure conditions2007Inngår i: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 16, nr 8, s. 1550-1556Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Two sets of samples were synthesized at high pressure high temperature conditions in the P-T region where C-60 molecules collapse into a nearly amorphous graphite-like hard carbon phase. For the first set, heating temperature was varied at fixed pressure and preparation time. For the second set, synthesis time was varied at fixed pressure and fixed temperature. Detailed structural characterization of samples was performed using Raman spectroscopy and powder XRD. Mechanical properties of the samples have been studied by nanoindentation method. It has been found that duration of heat treatment under high pressure is an important parameter which influences the temperature of fullerene cage collapse. Both tetragonal and rhombohedral polymeric phases transform into hard carbon phase over a rather narrow temperature interval, but the tetragonal phase shows somewhat increased stability against C-60 collapse. Viscoelastic mechanical behavior during nanoindentation was observed for fullerene polymers but not for graphite-like hard carbon phase. Possible mechanism for nucleation of the hard carbon phase in polymeric C-60 networks is discussed.

  • 16. Fedotov, Pavel V.
    et al.
    Chernov, Alexander I.
    Talyzin, Alexander V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Anoshkin, Ilya V.
    Nasibulin, Albert G.
    Kauppinen, Esko I.
    Obraztsova, Elena D.
    Optical Study of Nanotube and Coronene Composites2013Inngår i: Journal of Nanoelectronics and Optoelectronics, ISSN 1555-130X, E-ISSN 1555-1318, Vol. 8, nr 1, s. 16-22Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    A novel nanomaterial, graphene nanoribbons encapsulated inside single-walled carbon nanotubes (GNR@SWNT), was studied by combined optical methods. This nanomaterial was found to have a bright photoluminescence both in IR and UV-Vis spectral ranges. Its spectral features have a complicated resonant structure different from the features of initial components: coronene molecules and SWNTs. The encapsulation ability appears to correlate strongly with the geometry of SWNTs. A weak interaction between nanotube walls and encapsulated species has been discovered: no evidence of charge or energy transfer has been registered.

  • 17. 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.

  • 18. Filinchuk, Yaroslav
    et al.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Chernyshov, D.
    Dmitriev, V.
    High-pressure phase of NaBH4: Crystal structure from synchrotron powder diffraction data2007Inngår i: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 76, nr 9, s. 092104-Artikkel i tidsskrift (Fagfellevurdert)
  • 19. Filinchuk, Yaroslav
    et al.
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hagemann, Hans
    Dmitriev, Vladimir
    Chernyshov, Dmitry
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Cation Size and Anion Anisotropy in Structural Chemistry of Metal Borohydrides. The Peculiar Pressure Evolution of RbBH42010Inngår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 49, nr 11, s. 5285-5292Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The pressure evolution of RbBH4 has been characterized by synchrotron powder X-ray diffraction and Raman spectroscopy up to 23 GPa. Diffraction experiments at ambient temperature reveal three phase transitions, at 3.0, 10.4, and 18 GPa (at 2.6, 7.8, and 20 GPa from Raman data), at which the space group symmetry changes in the order Fm-3m(Z=4) → P4/nmm(2) → C222(2) → I-42m(4). Crystal structures and equations of state are reported for all four phases. The three high-pressure structure types are new in the crystal chemistry of borohydrides. RbBH4 polymorphs reveal high coordination numbers (CNs) for cation and anion sites, increasing with pressure from 6 to 8, via an intermediate 4 + 4 coordination. Different arrangements of the tetrahedral BH4 group in the Rb environment define the crystal symmetries of the RbBH4 polymorphs. The structural evolution in the MBH4 series is determined by the cation’s size, as it differs drastically for M = Li (CNs = 4, 6), Na (CN = 6), and Rb. The only structure common to the whole MBH4 family is the cubic one. Its bulk modulus linearly decreases as the ionic radius of M increases, indicating that the compressibility of the material is mainly determined by the repulsive BH4···BH4 interactions.

  • 20. 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.

  • 21.
    Gurzęda, Bartosz
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Jørgensen, Mads R.V.
    Department of Chemistry and INANO, Aarhus University, Langelandsgade 140, Aarhus C, Denmark; MAX IV Laboratory, Lund University, Fotongatan 2, Lund, Sweden.
    Kantor, Innokenty
    MAX IV Laboratory, Lund University, Fotongatan 2, Lund, Sweden.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Graphite oxide by “chlorate route” oxidation without HNO3: Does acid matter?2024Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 221, artikkel-id 118899Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Very strong difference in many properties is well documented for graphite oxides (GtO) synthesized by Brodie (BGO) and Hummers (HGO) methods. The difference is typically assigned to the type of oxidant (chlorates or KMnO4, respectively). However, not only oxidants but also acids used in these methods are different. It is still unclear which of the different properties of GtO are dependent on the oxidant or acid used in the synthesis. Here we synthesized a new type of graphite oxide using an oxidation agent typical for the Brodie method (KClO3) in combination with acids so far used only in modified Hummers' method (H2SO4+H3PO4). The GtO synthesized by this method (MGO) demonstrates some properties similar to BGO (higher temperature of exfoliation and less defected structure) but also similarity to some other properties of HGO (absence of sharp swelling transitions). Comparing MGO, BGO, and HGO allows us to distinguish the effects of acids and oxidants on the properties of graphite oxides. The new procedure proposed in this study allows preparation of GtO nearly free from hole/vacancy defects (similarly to BGO) but avoids dangerous HNO3. MGO is suggested as a favorable precursor for the preparation of graphene films by thermal or chemical reduction methods.

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  • 22.
    Han, Kyoo-Hyun
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Dzwilewski, Andrzej
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Makarova, Tatiana
    Höhne, Roland
    Esquinazi, Pablo
    Spemann, D.
    Dubrovinsky, Leonid S.
    Magnetic properties of carbon phases synthesized using high-pressure high-temperature treatment.2005Inngår i: Physical Review B, Vol. 72, s. 224424-Artikkel i tidsskrift (Fagfellevurdert)
  • 23.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nordenström, Andreas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Swelling Pressures of Graphite Oxide and Graphene Oxide Membranes in Water and Ethanol2021Inngår i: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 8, nr 14, artikkel-id 2100552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Swelling of graphene oxide (GO) membranes and bulk graphite oxide under confinement conditions is found to produce pressures up to ≈220 bar. Swelling pressure is important to take into account in many applications of GO membranes, but it has not been previously reported. Swelling pressures are typically measured only for bulk materials. However, it is demonstrated that even µm thick GO membranes develop pressures 3–25 bar due to the volume expansion caused by swelling in water. A rather strong difference in kinetics of pressure increase is found for both graphite oxide and GO membranes in water and ethanol despite similar lattice expansion due to swelling. This effect is attributed to slower penetration of ethanol into GO interlayers. Significantly faster saturation of swelling pressure is found for GO membranes (few hours) as compared to bulk graphite oxides (weeks) due to a higher degree of compaction. Swelling pressure is an important factor in applications, which require confinement, encapsulation of GO membranes or using external pressure to limit the lattice expansion. Finally, the swelling pressure can be used as an estimation for the suction pressure developed in pervaporation or vapor permeation applications, which is suggested as a driving force in rapid water permeation across GO membranes.

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  • 24.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Klechikov, Alexey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sun, Jinhua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Steenhaut, Timothy
    Hermans, Sophie
    Filinchuk, Yaroslav
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gravimetric tank method to evaluate material-enhanced hydrogen storage by physisorbing materials2018Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 44, s. 27983-27991Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The most common methods to evaluate hydrogen sorption (volumetric and gravimetric) require significant experience and expensive equipment for providing reproducible results. Both methods allow one to measure excess uptake values which are used to calculate the total amount of hydrogen stored inside of a tank as required for applications. Here we propose an easy to use and inexpensive alternative approach which allows one to evaluate directly the weight of hydrogen inside a material-filled test tank. The weight of the same tank filled with compressed hydrogen in the absence of loaded material is used as a reference. We argue that the only parameter which is of importance for hydrogen storage applications is by how much the material improves the total weight of hydrogen inside of the given volume compared to compressed gas. This parameter which we propose to name Gain includes both volumetric and gravimetric characterization of the material; it can be determined directly without knowing the skeletal volume of the material or excess sorption. The feasibility of the Gravimetric Tank (GT) method was tested using several common carbon and Metal Organic Framework (MOF) materials. The best Gain value of ∼12% was found for the Cu-BTC MOF which means that the tank completely filled with this material stores a 12% higher amount of hydrogen compared to H2 gas at the same PTconditions. The advantages of the GT method are its inexpensive design, extremely simple procedures and direct results in terms of tank capacity as required for industrial applications. The GT method could be proposed as a standard check for verification of the high hydrogen storage capacity of new materials. The GT method is expected to provide even better accuracy for evaluation of a material's performance for storage of denser gases like e.g. CO2 and CH4.

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  • 25.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Lienert, Ulrich
    DESY Photon Science, Hamburg, Germany.
    Sun, Jinhua
    Department of Industrial and Materials Science, Chalmers University of Technology, Göteborg, Sweden.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Swelling of Ti3C2Tx mxene in water and methanol at extreme pressure conditions2024Inngår i: Advanced Science, E-ISSN 2198-3844, Vol. 11, nr 9, artikkel-id 2307067Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pressure-induced swelling has been reported earlier for several hydrophilic layered materials. MXene Ti3C2Tx is also a hydrophilic layered material composed by 2D sheets but so far pressure-induced swelling is reported for this material only under conditions of shear stress at MPa pressures. Here, high-pressure experiments are performed with MXenes prepared by two methods known to provide “clay-like” materials. MXene synthesized by etching MAX phase with HCl+LiF demonstrates the effect of pressure-induced swelling at 0.2 GPa with the insertion of additional water layer. The transition is incomplete with two swollen phases (ambient with d(001) = 16.7Å and pressure-induced with d(001) = 19.2Å at 0.2 GPa) co-existing up to the pressure point of water solidification. Therefore, the swelling transition corresponds to change from two-layer water intercalation (2L-phase) to a never previously observed three-layer water intercalation (3L-phase) of MXene. Experiments with MXene prepared by LiCl+HF etching have not revealed pressure-induced swelling in liquid water. Both MXenes also show no anomalous compressibility in liquid methanol. The presence of pressure-induced swelling only in one of the MXenes indicates that the HCl+LiF synthesis method is likely to result in higher abundance of hydrophilic functional groups terminating 2D titanium carbide.

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  • 26.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nordenström, Andreas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hennig, Christoph
    Institute of Resource Ecology, Helmholtz Zentrum Dresden Rossendorf, Dresden, Germany; The Rossendorf Beamline, European Synchrotron Radiation Facility, Grenoble, France.
    Baburin, Igor
    Theoretische Chemie, Technische Universität Dresden, Dresden, Germany.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Temperature-dependent swelling transitions in MXene Ti3C2Tx2022Inngår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 14, nr 30, s. 10940-10949Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Swelling is a property of hydrophilic layered materials, which enables the penetration of polar solvents into an interlayer space with expansion of the lattice. Here we report an irreversible swelling transition, which occurs in MXenes immersed in excess dimethyl sulfoxide (DMSO) upon heating at 362-370 K with an increase in the interlayer distance by 4.2 Å. The temperature dependence of MXene Ti3C2Tx swelling in several polar solvents was studied using synchrotron radiation X-ray diffraction. MXenes immersed in excess DMSO showed a step-like increase in the interlayer distance from 17.73 Å at 280 K to 22.34 Å above ∼362 K. The phase transformation corresponds to a transition from the MXene structure with one intercalated DMSO layer into a two-layer solvate phase. The transformation is irreversible and the expanded phase remains after cooling back to room temperature. A similar phase transformation was observed also for MXene immersed in a 2 : 1 H2O : DMSO solvent ratio but at a lower temperature. The structure of MXene in the mixed solvent below 328 K was affected by the interstratification of differently hydrated (H2O)/solvated (DMSO) layers. Above the temperature of the transformation, the water was expelled from MXene interlayers and the formation of a pure two-layer DMSO-MXene phase was found. No changes in the swelling state were observed for MXenes immersed in DMSO or methanol at temperatures below ambient down to 173 K. Notably, MXenes do not swell in 1-alcohols larger than ethanol at ambient temperature. Changing the interlayer distance of MXenes by simple temperature cycling can be useful in membrane applications, e.g. when a larger interlayer distance is required for the penetration of ions and molecules into membranes. Swelling is also very important in electrode materials since it allows penetration of the electrolyte ions into the interlayers of the MXene structure.

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  • 27.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nordenström, Andreas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Li, Gui
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hennig, Christoph
    Institute of Resource Ecology, Helmholtz Zentrum Dresden Rossendorf, Dresden, Germany; European Synchrotron Radiation Facility, The Rossendorf Beamline, Grenoble, France.
    Jørgensen, Mads Ry Vogel
    MAX IV Laboratory, Lund University, Lund, Sweden; Department of Chemistry and iNANO, Aarhus University, Aarhus C, Denmark; Department of Physics, The Technical University of Denmark, Kgs. Lyngby, Denmark.
    Kantor, Innokenty
    MAX IV Laboratory, Lund University, Lund, Sweden; Department of Chemistry and iNANO, Aarhus University, Aarhus C, Denmark; Department of Physics, The Technical University of Denmark, Kgs. Lyngby, Denmark.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Effect of chain length on swelling transitions of Brodie graphite oxide in liquid 1-alcohols2024Inngår i: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 11, nr 1, artikkel-id 2300554Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Swelling is the most fundamental property of graphite oxides (GO). Here, a structural study of Brodie graphite oxide (BGO) swelling in a set of long chain 1-alcohols (named C11 to C22 according to the number of carbons) performed using synchrotron radiation X-ray diffraction at elevated temperatures is reported. Even the longest of tested alcohols (C22) is found to intercalate BGO with enormous expansion of the interlayer distance from ≈6Å up to ≈63Å, the highest expansion of GO lattice ever reported. Swelling transitions from low temperature α-phase to high temperature β-phase are found for BGO in all alcohols in the C11–C22 set. The transitions correspond to decrease of inter-layer distance correlating with the length of alcohol molecules, and change in their orientation from perpendicular to GO planes to layered parallel to GO (Type II transitions). These transitions are very different compared to BGO swelling transitions (Type I) found in smaller alcohols and related to insertion/de-insertion of additional layer of alcohol parallel to GO. Analysis of general trends in the whole set of 1-alcohols (C1 to C22) shows that the 1-alcohol chain length defines the type of swelling transition with Type I found for alcohols with C<10 and Type II for C>10. 

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  • 28.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Skrypnychuk, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nordenström, Andreas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shilayeva, Elizaveta A.
    Korobov, Mikhail
    Prodana, Mariana
    Enachescu, Marius
    Larsson, Sylvia H.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Activated graphene as a material for supercapacitor electrodes: effects of surface area, pore size distribution and hydrophilicity2019Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 32, s. 17901-17912Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Activated reduced graphene oxide (a-rGO) is a material with a rigid 3D porous structure and high specific surface area (SSA). Using variation of activation parameters and post-synthesis mechanical treatment we prepared two sets of materials with a broad range of BET (N2) SSA ∼1000–3000 m2 g−1, and significant differences in pore size distribution and oxygen content. The performance of activated graphene as an electrode in a supercapacitor with KOH electrolyte was correlated with the structural parameters of the materials and water sorption properties. a-rGO is a hydrophobic material as evidenced by the negligibly small BET (H2O) SSA determined using analysis of water vapor sorption isotherms. However, the total pore volume determined using water vapor sorption and sorption of liquid water is almost the same as the one found by analysis of nitrogen sorption isotherms. Ball milling is found to provide an improved bulk density of activated graphene and collapse of all pores except the smallest ones (<2 nm). A decrease in the activation temperature from 850 °C to 550 °C is found to result in materials with a narrow micropore size distribution and increased oxygen content. Elimination of mesopores using ball milling or a lower activation temperature provided materials with better specific capacitance despite a significant decrease (by ∼30%) of the BET (N2) SSA. The best gravimetric and volumetric capacitances in KOH electrolyte were achieved not for samples with the highest value of the BET (N2) SSA but for materials with 80–90% of the total pore volume in micropores and an increased BET (H2O) SSA. Comparing the performance of electrodes prepared using rGO and a-rGO shows that a more hydrophilic surface is favorable for charge storage in supercapacitors with KOH electrolyte.

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  • 29.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sun, Jinhua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Rebrikova, Anastasia
    Korobov, Mikhail
    Klechikov, Alexey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Physics and Astronomy, Uppsala University, Uppsala, 751 20, Sweden.
    Vorobiev, Alexei
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Swelling of graphene oxide membranes in alcohols: effects of molecule size and air ageing2019Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, E-ISSN 2050-7496, Vol. 7, s. 11331-11337Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Swelling of Hummers graphene oxide (HGO) membranes in a set of progressively longer liquid alcohols (methanol to 1-nonanol) was studied using synchrotron radiation XRD after air ageing over prolonged periods of time. Both precursor graphite oxides and freshly prepared HGO membranes were found to swell in the whole set of nine liquid alcohols with an increase of interlayer spacing from ∼7 Å (solvent free) up to ∼26 Å (in 1-nonanol). A pronounced effect of ageing on swelling in alcohols was found for HGO membranes stored in air. The HGO membranes aged for 0.5–1.5 years show progressively slower swelling kinetics, a non-monotonic decrease of saturated swelling in some alcohols and complete disappearance of swelling for alcohol molecules larger than hexanol. Moreover, the HGO membranes stored under ambient conditions for 5 years showed a nearly complete absence of swelling in all alcohols but preserved swelling in water. In contrast, precursor graphite oxide powder showed unmodified swelling in alcohols even after 4 years of ageing. Since the swelling defines the size of permeation channels, the ageing effect is one of the important parameters which could explain the strong variation in reported filtration/separation properties of GO membranes. The time and conditions of air storage require standardization for better reproducibility of results related to performance of GO membranes in various applications. The ageing of GO membranes can be considered not only as a hindrance/degradation for certain applications, but also as a method to tune the swelling properties of HGO membranes for better selectivity in sorption of solvents and for achieving better selective permeability.

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  • 30.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Swelling properties of graphite oxides and graphene oxide multilayered materials2020Inngår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 12, nr 41, s. 21060-21093Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Graphite oxide (GtO) and graphene oxide (GO) multilayered laminates are hydrophilic materials easily intercalated by water and other polar solvents. By definition, an increase in the volume of a material connected to the uptake of a liquid or vapour is named swelling. Swelling is a property which defines graphite oxides and graphene oxides. Less oxidized materials not capable of swelling should be named oxidized graphene. The infinite swelling of graphite oxide yields graphene oxide in aqueous dispersions. Graphene oxide sheets dispersed in a polar solvent can be re-assembled into multilayered structures and named depending on applications as films, papers or membranes. The multilayered GO materials exhibit swelling properties which are mostly similar to those of graphite oxides but not identical and in some cases surprisingly different. Swelling is a key property of GO materials in all applications which involve the sorption of water/solvents from vapours, immersion of GO into liquid water/solvents and solution based chemical reactions. These applications include sensors, sorption/removal of pollutants from waste waters, separation of liquid and gas mixtures, nanofiltration, water desalination, water-permeable protective coatings, etc. Swelling defines the distance between graphene oxide sheets in solution-immersed GO materials and the possibility for penetration of ions and molecules inside of interlayers. A high sorption capacity of GO towards many molecules and cations is defined by swelling which makes the very high surface area of GO accessible. GtO and GO swelling is a surprisingly complex phenomenon which is manifested in a variety of different ways. Swelling is strongly different for materials produced using the most common Brodie and Hummers oxidation procedures; it depends on the degree of oxidation, ad temperature and pressure conditions. The value of the GO interlayer distance is especially important in membrane applications. Diffusion of solvent molecules and ions is defined by the size of "permeation channels" provided by the swelled GO structure. According to extensive studies performed over the last decade the exact value of the inter-layer distance in swelled GO depends on the nature of solvent, temperature and pressure conditions, and the pH and concentration of solutions and exhibits pronounced aging effects. This review provides insight into the fundamental swelling properties of multilayered GO and demonstrates links to advanced applications of these materials.

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  • 31. Khaliha, Sara
    et al.
    Marforio, Tainah D.
    Kovtun, Alessandro
    Mantovani, Sebastiano
    Bianchi, Antonio
    Navacchia, Maria Luisa
    Zambianchi, Massimo
    Bocchi, Letizia
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Iakunkov, Artem
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Calvaresi, Matteo
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Palermo, Vincenzo
    Melucci, Manuela
    Defective graphene nanosheets for drinking water purification: Adsorption mechanism, performance, and recovery2021Inngår i: FlatChem, ISSN 2452-2627, Vol. 29, artikkel-id 100283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Defect-rich graphene oxide (dGO) was used as sorbent for organic contaminants of emerging concern in tap water, including drugs and dyes, and the performance compared to those of lower-defects graphene types. The role of holes and carbonyl- carboxylic groups on graphene nanosheets surface on the adsorption mechanism and efficiency was investigated. dGO showed enhanced adsorption capacity toward two fluoroquinolone antibiotics (ofloxacin, OFLOX, and ciprofloxacin, CIPRO) in tap water with a maximum capacity of 650 mg/g, compared to 204 mg/g for Hummers derived commercial GO (hGO) and 125 mg/g for less defected Brodie derived GO (bGO) for OFLOX. The role of defects on the selective adsorption of OFLOX was also modelled by MD simulations, highlighting a mechanism mainly driven by the shape complementarity between the graphene holes and the molecules. Adsorption isotherms revealed different adsorption model for dGO, with a Langmuir fitting for dGO and BET fitting for all the other investigated samples. The maximum adsorption capacity of dGO for OFLOX was about six times higher than that of Granular Activated Carbon (95 mg/g), the industrial adsorption standard technology. Finally, it was also demonstrated that dGO can be recovered from treated water by ultrafiltration, this preventing secondary contamination risks and enabling safe use of graphene nanosheets for water purification.

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  • 32. Kim, Y
    et al.
    Abou-Hamad, E
    Rubio, A
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boesch, D
    Aloni, S
    Zettl, A
    Luzi, D E
    Goze-Bac, C
    Communications: nanomagnetic shielding: high-resolution NMR in carbon allotropes2010Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, nr 2, s. 021102-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The understanding and control of the magnetic properties of carbon-based materials is of fundamental relevance in applications in nano- and biosciences. Ring currents do play a basic role in those systems. In particular the inner cavities of nanotubes offer an ideal environment to investigate the magnetism of synthetic materials at the nanoscale. Here, by means of 13 C high resolution NMR of encapsulated molecules in peapod hybrid materials, we report the  largest diamagnetic shifts (down to -68.3 ppm) ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon doping. This diamagnetic shift can be externally controlled by in situ modifications such as doping or electrostatic charging. Moreover, defects such as C-vacancies, pentagons, and chemical functionalization of the outer nanotube quench this diamagnetic effect and restore NMR signatures to slightly paramagnetic shifts compared to nonencapsulated molecules. The magnetic interactions reported here are robust phenomena independent of temperature and proportional to the applied magnetic field. The magnitude, tunability, and stability of the magnetic effects make the peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronics and nanobiomedical engineering.

  • 33.
    Kim, Y
    et al.
    Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania.
    Abou-Hamad, Edy
    CNRS Université Montpellier 2, France .
    Rubio, Angelo
    European Theoretical Spectroscopy Facility (ETSF), Universidad del País Vasco UPV/EHU, Spain .
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boesch, D
    Department of Physics, University of California, Berkeley, California 94720 USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA .
    Aloni, S
    Department of Physics, University of California, Berkeley, California 94720 USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA .
    Zettl, Alex
    Department of Physics, University of California, Berkeley, California 94720 USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA .
    Luzzi, David E.
    Department of Materials Science and Engineering, University of Pennsylvania, USA .
    Goze-Bac, Christophe
    CNRS Université Montpellier 2, France .
    Nanomagnetic shielding: High-resolution NMR in carbon allotropes2010Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, s. 021102-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theunderstanding and control of the magnetic properties of carbon-based materialsis of fundamental relevance in applications in nano- and biosciences.Ring currents do play a basic role in those systems.In particular the inner cavities of nanotubes offer an idealenvironment to investigate the magnetism of synthetic materials at thenanoscale. Here, by means of 13C high resolution NMR ofencapsulated molecules in peapod hybrid materials, we report the largestdiamagnetic shifts (down to −68.3 ppm) ever observed in carbonallotropes, which is connected to the enhancement of the aromaticityof the nanotube envelope upon doping. This diamagnetic shift canbe externally controlled by in situ modifications such as dopingor electrostatic charging. Moreover, defects such as C-vacancies, pentagons, andchemical functionalization of the outer nanotube quench this diamagnetic effectand restore NMR signatures to slightly paramagnetic shifts compared tononencapsulated molecules. The magnetic interactions reported here are robust phenomenaindependent of temperature and proportional to the applied magnetic field.The magnitude, tunability, and stability of the magnetic effects makethe peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronicsand nanobiomedical engineering

  • 34.
    Klechikov, Alexey G.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mercier, Guillaume
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Merino, Pilar
    Blanco, Santiago
    Merino, Cesar
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hydrogen storage in bulk graphene-related materials2015Inngår i: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 210, s. 46-51Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogen sorption properties of graphene-related materials were studied by gravimetric and volumetric methods at 2931< and 77K. Rapid thermal exfoliation of different types of graphite oxide (GO) precursors yielded samples with maximal surface areas up to 850 m(2)/g, whereas surface areas up to 2300 m(2)/g were achieved by post-exfoliation activation treatments. Therefore, hydrogen storage parameters of graphene materials could be evaluated in a broad range of surface areas. The H-2 uptake vs surface area trend revealed in this study shows that hydrogen storage by graphene materials do not exceed 1 Wt% at 120 Bar H-2 at ambient temperatures. Linear increase of hydrogen adsorption vs surface area was observed at 77 K with maximal observed value of similar to 5 Wt% for 2300 m(2)/g sample. It can be concluded that bulk graphene samples obtained using graphite oxide exfoliation and activation follow standard for other nanostructured carbons hydrogen uptake trends and do not demonstrate superior hydrogen storage parameters reported in several earlier studies. Nevertheless, graphene remains to be one of the best materials for physisorption of hydrogen, especially at low temperatures.

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  • 35.
    Klechikov, Alexey
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mercier, Guillaume
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Baburin, Igor A.
    Technische Universität Dresden, Theoretische Chemie, Bergstraße 66b, 01062 Dresden, Germany .
    Seifert, Gotthard
    Technische Universität Dresden, Theoretische Chemie, Bergstraße 66b, 01062 Dresden, Germany .
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hydrogen storage in high surface area graphene scaffolds2015Inngår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 51, nr 83, s. 15280-15283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using an optimized KOH activation procedure we prepared highly porous graphene scaffold materials with SSA values up to 3400 m2 g−1 and a pore volume up to 2.2 cm3 g−1, which are among the highest for carbon materials. Hydrogen uptake of activated graphene samples was evaluated in a broad temperature interval (77–296 K). After additional activation by hydrogen annealing the maximal excess H2 uptake of 7.5 wt% was obtained at 77 K. A hydrogen storage value as high as 4 wt% was observed already at 193 K (120 bar H2), a temperature of solid CO2, which can be easily maintained using common industrial refrigeration methods.

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  • 36.
    Klechikov, Alexey
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sun, Jinhua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Baburin, Igor A.
    Seifert, Gotthard
    Rebrikova, Anastasiia T.
    Avramenko, Natalya V.
    Korobov, Mikhail V.
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Multilayered intercalation of 1-octanol into Brodie graphite oxide2017Inngår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, nr 20, s. 6929-6936Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multilayered intercalation of 1-octanol into the structure of Brodie graphite oxide (B-GO) was studied as a function of temperature and pressure. Reversible phase transition with the addition/removal of one layer of 1-octanol was found at 265 K by means of X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The same transition was observed at ambient temperature upon a pressure increase above 0.6 GPa. This transition was interpreted as an incongruent melting of the low temperature/high pressure B-GO intercalated structure with five layers of 1-octanol parallel to GO sheets (L-solvate), resulting in the formation of a four-layered structure that is stable under ambient conditions (A-solvate). Vacuum heating allows the removal of 1-octanol from the A-solvate layer by layer, while distinct sets of (00 l) reflections are observed for three-, two-, and one-layered solvate phases. Step by step removal of the 1-octanol layers results in changes of distance between graphene oxide planes by similar to 4.5 angstrom. This experiment proved that both L- and A-solvates are structures with layers of 1-octanol parallel to GO planes. Unusual intercalation with up to five distinct layers of 1-octanol is remarkably different from the behaviour of small alcohol molecules (methanol and ethanol), which intercalate B-GO structure with only one layer under ambient conditions and a maximum of two layers at lower temperatures or higher pressures. The data presented in this study make it possible to rule out a change in the orientation of alcohol molecules from parallel to perpendicular to the GO planes, as suggested in the 1960s to explain larger expansion of the GO lattice due to swelling with larger alcohols.

  • 37.
    Klechikov, Alexey
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sun, Jinhua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zheng, Mingbo
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Graphene decorated with metal nanoparticles: Hydrogen sorption and related artefacts2017Inngår i: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 250, s. 27-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogen sorption by reduced graphene oxides (r-GO) is not found to increase after decoration with Pd and Pt nanoparticles. Treatments of metal decorated samples using annealing under hydrogen or air were tested as a method to create additional pores by effects of r-GO etching around nanoparticles. Increase of Specific Surface Area (SSA) was observed for some air annealed r-GO samples. However, the same treatments applied to activated r-GO samples with microporous nature and higher surface area result in breakup of structure and dramatic decrease of SSA. Our experiments have not revealed effects which could be attributed to spillover in hydrogen sorption on Pd or Pt decorated graphene. However, we report irreversible chemisorption of hydrogen for some samples which can be mistakenly assigned to spillover if the experiments are incomplete.