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  • 1. Acharya, Shravan S.
    et al.
    Easton, Christopher D.
    McCoy, Thomas M.
    Spiccia, Leone
    Ohlin, C. André
    Umeå University, Faculty of Science and Technology, Department of Chemistry. School of Chemistry, Monash University, Clayton, Australia.
    Winther-Jensen, Bjorn
    Diverse composites of metal-complexes and PEDOT facilitated by metal-free vapour phase polymerization2017In: Reactive & functional polymers, ISSN 1381-5148, E-ISSN 1873-166X, Vol. 116, p. 101-106Article in journal (Refereed)
    Abstract [en]

    Abstract Oxidative polymerization for the manufacture of conducting polymers such as poly(3,4-ethylenedioxy-thiophene) has traditionally employed iron(III) salts. Demonstrated in this study is vapour phase polymerization of 3,4-ethylenedio- xythiophene using a metal-free oxidant, ammonium persulfate, leading to films with an estimated conductivity of 75 S/cm. Additionally, a route for embedding active transition metal complexes into these poly(3,4-ethylenedioxythiophene)/-poly(styrene-4-sulfonate) (PEDOT/PSS) films via vapour assisted complexation is outlined. Here, the vapour pressure of solid ligands around their melting temperatures was exploited to ensure complexation to metal ions added into the oxidant mixture prior to polymerization of PEDOT. Four composite systems are discussed, viz. PEDOT/PSS embedded with tris(8-hydroxyquinolinato)cobalt(III), tris(2,2-bipyridine)cobalt(II), tris(1,10- phenanthroline)cobalt(II) and tris(8-hyd-roxyquinolinato)aluminium(III). Using these composites, electrochemical reduction of nitrite to ammonia with a faradaic efficiency of 61% was reported.

  • 2.
    Aghbolagh, Mahdi Shahmohammadi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Meynaq, Mohammad Yaser Khani
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shimizu, Kenichi
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Aspects on mediated glucose oxidation at a supported cubic phase2017In: Bioelectrochemistry, ISSN 1567-5394, E-ISSN 1878-562X, Vol. 118, p. 8-13Article in journal (Refereed)
    Abstract [en]

    A supported liquid crystalline cubic phase housing glucose oxidase on an electrode surface has been suggested as bio-anode in a biofuel. The purpose of this investigation is to clarify some aspect on the mediated enzymatic oxidation of glucose in such a bio-anode where the mediator ferrocene-carboxylic acid and glucose were dissolved in the solution. The enzyme glucose oxidase was housed in the water channels of the mono-olein cubic phase. The system was investigated with cyclic voltammetry at different scan rates and the temperature was varied between 15 degrees C and 30 degrees C. The diffusion coefficient of the mediator and also the film resistance was estimated showing a large decrease in the mass-transport properties as the temperature was decreased. The current from mediated oxidation of glucose at the electrode surface increased with decreasing film thickness. The transport of the mediator in the cubic phase was the rate-limiting step in the overall reaction, where the oxidation of glucose took place at the outer surface of the cubic phase.

  • 3. Alhayali, Amani
    et al.
    Tavelin, Staffan
    Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Pharmacology.
    Velaga, Sitaram
    Dissolution and precipitation behavior of ternary solid dispersions of ezetimibe in biorelevant media2017In: Drug Development and Industrial Pharmacy, ISSN 0363-9045, E-ISSN 1520-5762, Vol. 43, no 1, p. 79-88Article in journal (Refereed)
    Abstract [en]

    The effects of different formulations and processes on inducing and maintaining the supersaturation of ternary solid dispersions of ezetimibe (EZ) in two biorelevant media fasted-state simulated intestinal fluid (FaSSIF) and fasted-state simulated gastric fluid (FaSSGF) at different temperatures (25 °C and 37 °C) were investigated in this work.

    Ternary solid dispersions of EZ were prepared by adding polymer PVP-K30 and surfactant poloxamer 188 using melt-quenching and spray-drying methods. The resulting solid dispersions were characterized using scanning electron microscopy, differential scanning calorimetry (DSC), modulated DSC, powder X-ray diffraction and Fourier transformation infrared spectroscopy. The dissolution of all the ternary solid dispersions was tested in vitro under non-sink conditions.

    All the prepared solid dispersions were amorphous in nature. In FaSSIF at 25 °C, the melt-quenched (MQ) solid dispersions of EZ were more soluble than the spray-dried (SD) solid dispersions and supersaturation was maintained. However, at 37 °C, rapid and variable precipitation behavior was observed for all the MQ and SD formulations. In FaSSGF, the melting method resulted in better solubility than the spray-drying method at both temperatures.

    Ternary solid dispersions show potential for improving solubility and supersaturation. However, powder dissolution experiments of these solid dispersions of EZ at 25 °C may not predict the supersaturation behavior at physiologically relevant temperatures.

  • 4.
    Annamalai, Alagappan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mühlbacher, Inge
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 19, p. 16467-16473Article in journal (Refereed)
    Abstract [en]

    To exploit the full potential of hematite (α-Fe2O3) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe2O3/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb5+) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb5+ states in Sb-doped Fe2O3 photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 1020 vs 1.3 × 1019 cm–3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb5+ can activate multiple Fe3+ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb5+- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

  • 5. Anugwom, Ikenna
    et al.
    Maki-Arvela, Paivi
    Virtanen, Pasi
    Willfor, Stefan
    Damlin, Pia
    Hedenström, Mattias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Treating birch wood with a switchable 1,8-diazabicyclo-[5.4.0]-undec-7-ene-glycerol carbonate ionic liquid2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 7, p. 809-815Article in journal (Refereed)
    Abstract [en]

    The suitability of a new switchable ionic liquid (SIL) has been investigated as a solvent for fractionation of lignocellulosic materials. SIL was prepared from inexpensive chemicals, e. g., glycerol, CO2, and 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU). Fresh Nordic birch wood (B. pendula) was treated with the SIL for a time period of 1-5 days at 100 degrees C and under atmospheric pressure. Upon SIL treatment, at best, 57 % of the hemicelluloses were dissolved and 50 % of lignins were dissolved from the native birch. The slightly fibrillated SIL treated chips contained about 55 % cellulose. Up to 76 % of the recovered species removed from the spent SIL liquor was originating from hemicelluloses, mainly from xylan. The spent SILs were reused for fresh wood dissolution in four consecutive cycles and each time the wood dissolution efficiency was similar. SILs could offer affordable (easy-to-synthesize) solvent systems for partial elimination of hemicelluloses and lignin from wood. SILs can also be prepared in-situ and on-site.

  • 6. Asres, Georgies Alene
    et al.
    Baldoví, José J.
    Dombovari, Aron
    Järvinen, Topias
    Lorite, Gabriela Simone
    Mohl, Melinda
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Pérez Paz, Alejandro
    Xian, Lede
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry & Reaction Engineering, Department of Chemical Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University, Åbo-Turku, Finland.
    Spetz, Anita Lloyd
    Jantunen, Heli
    Rubio, Ángel
    Kordás, Krisztian
    Ultrasensitive H2S gas sensors based on p-type WS2 hybrid materials2018In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 11, no 8, p. 4215-4224Article in journal (Refereed)
    Abstract [en]

    Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS2 nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity (0.043 ppm-1) as well as high selectivity towards H2S relative to CO, NH3, H2, and NO (with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 ppm-1, respectively). Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS2 alone are not sufficient to explain the observed high sensitivity towards H2S. A major role in this behavior is also played by O doping in the S sites of the WS2 lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety.

  • 7. Baburin, Igor A
    et al.
    Klechikov, Alexey
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mercier, Guillaume
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Seifert, Gotthard
    Hydrogen adsorption by perforated graphene2015In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 40, no 20, p. 6594-6599Article in journal (Refereed)
    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. 

  • 8.
    Barzegar, Hamid Reza
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitrogen Doping Mechanism in Small Diameter Single-Walled Carbon Nanotubes: Impact on Electronic Properties and Growth Selectivity2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 48, p. 25805-25816Article in journal (Refereed)
    Abstract [en]

    Nitrogen doping in carbon nanostructures has attracted interest for more than a decade, and recent implementation of such structures in energy conversion systems has boosted the interest even more. Despite numerous studies, the structural conformation and stability of nitrogen functionalities in small diameter single-walled carbon nanotubes (SWNTs), and the impact of these functionalities on the electronic and mechanical properties of the SWNTs, are incomplete. Here we report a detailed study on nitrogen doping in SWNTs with diameters in the range of 0.8?1.0 nm, with well-defined chirality. We show that the introduction of nitrogen in the carbon framework significantly alters the stability of certain tubes, opening for the possibility to selectively grow nitrogen-doped SWNTs with certain chirality and diameter. At low nitrogen concentration, pyridinic functionalities are readily incorporated and the tubular structure is well pertained. At higher concentrations, pyrrolic functionalities are formed, which leads to significant structural deformation of the nanotubes and hence a stop in growth of crystalline SWNTs. Raman spectroscopy is an important tool to understand guest atom doping and electronic charge transfer in SWNTs. By correlating the influence of defined nitrogen functionalities on the electronic properties of SWNTs with different chirality, we make precise interpretation of experimental Raman data. We show that the previous interpretation of the double-resonance G?-peak in many aspects is wrong and instead can be well-correlated to the type of nitrogen doping of SWNTs originating from the p- or n-doping nature of the nitrogen incorporation. Our results are supported by experimental and theoretical data.

  • 9. Behravesh, Erfan
    et al.
    Kumar, Narendra
    Balme, Quentin
    Roine, Jorma
    Salonen, Jarno
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Process Chemistry Centre, Åbo Akademi University, FI-20500 Turku/Åbo, Finland.
    Peurla, Markus
    Aho, Atte
    Eränen, Kari
    Murzin, Dmitry Yu.
    Salmi, Tapio
    Synthesis and characterization of Au nano particles supported catalysts for partial oxidation of ethanol: Influence of solution pH, Au nanoparticle size, support structure and acidity2017In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 353, p. 223-238Article in journal (Refereed)
    Abstract [en]

    Partial oxidation of ethanol to acetaldehyde was carried out over gold catalysts supported on various oxides and zeolites by deposition precipitation. The special focus of this work was on the influence of H-Y zeolite surface charge on Au cluster size and loading linking it to activity and selectivity in ethanol oxidation and comparing with other studied catalysts. The catalysts were characterized by nitrogen physisorption, transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and zeta potential measurements. pH of the solution governed the Au NPs size within the range of 5.8–13.2 nm with less negatively charged surfaces leading to formation of smaller clusters. Au loading on H-Y zeolite with silica to alumina ratio of 80 was increased by raising the pH. In fact, H-Y-12 and H-Beta-25 were selective towards diethyl ether while acetaldehyde was the prevalent product on less acidic H-Y-80. The results demonstrated strong dependency of the catalytic activity on the Au cluster size. Namely turn over frequency (TOF) decreased with an increase in metal size from 6.3 to 9.3 nm on H-Y-80. Selectivity towards acetaldehyde and ethyl acetate did not change significantly on H-Y-80 within 6.3–9.3 nm Au particle size range. On Al2O3 support, however, selectivity towards acetaldehyde increased considerably upon diminishing Au average particle size from 3.7 to 2.1 nm.

  • 10. Biryulin, YF
    et al.
    Kurdybaylo, D
    Shamanin, V
    Aleksjuk, G
    Volkova, T
    Melenevskaya, E
    Saydashev, I
    Eidelman, E
    Makarova, Tatiana
    Ioffe Physico-Technical Institute RAS, Russia.
    Terukov, E
    Zaitseva, N
    Negrov, V
    Tkatchyov, A
    Strongly non-linear carbon nanofibre influence on electrical properties of polymer composites2008In: Fullerenes, nanotubes, and carbon nanostructures (Print), ISSN 1536-383X, E-ISSN 1536-4046, Vol. 16, no 5-6, p. 629-633Article in journal (Refereed)
    Abstract [en]

    Composites of carbon nanofibres (CNF) (30-50 nm diam., length up to 1 mu m) in two polymer matrices (polybutadiene-styrene and polypyrrhol) show strong non-linearities of conductivity vs. CNF concentration. We have studied their voltage-current dependencies, and observed correlation of their extrema and layer morphology. Multistability of conductivity is discovered, with apparent effect of magnetic field effect on it in polypyrrhol-based composites. In addition CNF spatial configuration influence on layers' conductivity is discussed.

  • 11.
    Boily, Jean-Francois
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Yesilbas, Merve
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Uddin, Munshi Md. Musleh
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Baiqing, Lu
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Trushkina, Yulia
    Salazar-Alvarez, German
    Thin Water Films at Multifaceted Hematite Particle Surfaces2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 48, p. 13127-13137Article in journal (Refereed)
    Abstract [en]

    Mineral surfaces exposed to moist air stabilize nanometer- to micrometer-thick water films. This study resolves the nature of thin water film formation at multifaceted hematite (alpha-Fe2O3) nanoparticle surfaces with crystallographic faces resolved by selected area electron diffraction. Dynamic vapor adsorption (DVA) in the 0-19 Torr range at 298 K showed that these particles stabilize water films consisting of up to 4-5 monolayers. Modeling of these data predicts water loadings in terms of an "adsorption regime" (up to 16 H2O/nm(2)) involving direct water binding to hematite surface sites, and of a "condensation regime" (up to 34 H2O/nm(2)) involving water binding to hematite-bound water nanodusters. Vibration spectroscopy identified the predominant hematite surface hydroxo groups (-OH, mu-OH, mu(3)-OH) through which first layer water molecules formed hydrogen bonds, as well as surface iron sites directly coordinating water molecules (i.e., as geminal eta-(OH2)(2) sites). Chemometric analyses of the vibration spectra also revealed a strong correspondence in the response of hematite surface hydroxo groups to DVA-derived water loadings. These findings point to a near-saturation of the hydrogen-bonding environment of surface hydroxo groups at a partial water vapor pressure of similar to 8 Torr (similar to 40% relative humidity). Classical molecular dynamics (MD) resolved the interfacial water structures and hydrogen bonding populations at five representative crystallographic faces expressed in these nanoparticles. Simulations of single oriented slabs underscored the individual roles of all (hydro)oxo groups in donating and accepting hydrogen bonds with first layer water in the "adsorption regime". These analyses pointed to the preponderance of hydrogen bond-donating -OH groups in the stabilization of thin water films. Contributions of mu-OH and mu(3)-OH groups are secondary, yet remain essential in the stabilization of thin water films. MD simulations also helped resolve crystallographic controls on water water interactions occurring in the "condensation regime". Water water hydrogen bond populations are greatest on the (001) face, and decrease in importance in the order (001) > (012) approximate to (110) > (014) >> (100). Simulations of a single (similar to 5 nm x similar to 6 nm x similar to 6 nm) nanometric hematite particle terminated by the (001), (110), (012), and (100) faces also highlighted the key roles that sites at particle edges play in interconnecting thin water films grown along contiguous crystallographic faces. Hydroxo water hydrogen bond populations showed that edges were the preferential loci of binding. These simulations also suggested that equilibration times for water binding at edges were slower than on crystallographic faces. In this regard, edges, and by extension roughened surfaces, are expected to play commanding roles in the stabilization of thin water films. Thus, in focusing on the properties of nanometric-thick water layers at hematite surfaces, this study revealed the nature of interactions between water and multifaced particle surfaces. Our results pave the way for furthering our understanding of mineral-thin water film interfacial structure and reactivity on a broader range of materials.

  • 12.
    Boulanger, Nicolas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Victor
    Hilke, Michael
    Toney, Michael F.
    Barbero, David R.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Graphene induced electrical percolation enables more efficient charge transport at a hybrid organic semiconductor/graphene interface2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 6, p. 4422-4428Article in journal (Refereed)
    Abstract [en]

    Self-assembly of semiconducting polymer chains during crystallization from a liquid or melt dictates to a large degree the electronic properties of the resulting solid film. However, it is still unclear how charge transport pathways are created during crystallization. Here, we performed complementary in situ electrical measurements and synchrotron grazing incidence X-ray diffraction (GIXD), during slow cooling from the melt of highly regio-regular poly(3-hexylthiophene) (P3HT) films deposited on both graphene and on silicon. Two different charge transport mechanisms were identified, and were correlated to the difference in crystallites' orientations and overall amount of crystallites in the films on each surface as molecular self-assembly proceeded. On silicon, a weak charge transport was enabled as soon as the first edge-on lamellae formed, and further increased with the higher amount of crystallites (predominantly edge-on and randomly oriented lamellae) during cooling. On graphene however, the current remained low until a minimum amount of crystallites was reached, at which point interconnection of conducting units (face-on, randomly oriented lamellae and tie-chains) formed percolated conducting pathways across the film. This lead to a sudden rapid increase in current by approximate to 10 fold, and strongly enhanced charge transport, despite a much lower amount of crystallites than on silicon.

  • 13.
    Calderon, Blanca
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Univ Alicante, Dept Chem Engn, San Vicente del Raspeig Rd S-N, Alicante 03690, Spain.
    Lundin, Lisa
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Aracil, Ignacio
    Fullana, Andres
    Study of the presence of PCDDs/PCDFs on zero-valent iron nanoparticles2017In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 169, p. 361-368Article in journal (Refereed)
    Abstract [en]

    Studies show that nanoscale zero-valent iron (nZVI) particles enhance the formation of chlorinated compounds such as polychlorinated dioxins and furans (PCDD/Fs) during thermal processes. However, it is unclear whether nZVI acts as a catalyst for the formation of these compounds or contains impurities, such as PCDD/Fs, within its structure. We analyzed the presence of PCDD/Fs in nZVI particles synthesized through various production methods to elucidate this uncertainty. None of the 2,3,7,8-substituted congeners were found in the commercially-produced nZVI, but they were present in the laboratory synthesized nZVI produced through the borohydride method, particularly in particles synthesized from iron (III) chloride rather than from iron sulfate. Total PCDD/F WHO-TEQ concentrations of up to 35 pg/g were observed in nZVI particles, with hepta-and octa-chlorinated congeners being the most abundant. The reagents used in the borohydride method were also analyzed, and our findings suggest that FeCl3 effectively contains PCDD/Fs at concentrations that could explain the concentrations observed in the nZVI product. Both FeCl3 and nZVI showed a similar PCDD/F patterns with slight differences. These results suggest that PCDD/Fs might transfer from FeCl3 to nZVI during the production method, and thus, care should be taken when employing certain nZVI for environmental remediation.

  • 14. Cano, A.
    et al.
    Rodríguez-Hernández, J.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Reguera, E.
    Intercalation of pyrazine in layered copper nitroprusside: synthesis, crystal structure and XPS study2019In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 273, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Hybrid inorganic–organic solids form an interesting family of functional materials, where their functionalities are determined by both, the inorganic and organic building blocks. This study reports the intercalation of pyrazine in 2D copper nitroprusside, the crystal structure of the resulting hybrid solid and explores the scope of cryogenic X-ray photoelectron spectroscopy (XPS) to shed light on its electronic structure. In this material, the pyrazine molecule appears coordinated to Cu atoms from neighboring layers, to form the columns in the resulting 3D porous framework. Its crystal structure was solved and refined from the corresponding XRD powder pattern. XPS data, recorded under cryogenic conditions, provided fine details on the electronic structure of this hybrid solid. The binding energy values for the ligand atoms and the involved metals show a definite correlation with the structural data and FT-IR spectra. When XPS spectra were recorded at room temperature, a significant sample decomposition was observed. Three possible mechanisms for the sample damage during the XPS experiment are considered. The hybrid material under study is representative of a wide series of nanoporous solids obtained by intercalation of organic pillars between 2D inorganic solids.

  • 15. Chilkoor, Govinda
    et al.
    Karanam, Sushma Priyanka
    Star, Shane
    Shrestha, Namita
    Sani, Rajesh K.
    Upadhyayula, Venkata K. K.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ghoshal, Debjit
    Koratkar, Nikhil A.
    Meyyappan, M.
    Gadhamshetty, Venkataramana
    Hexagonal Boron Nitride: The Thinnest Insulating Barrier to Microbial Corrosion2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 3, p. 2242-2252Article in journal (Refereed)
    Abstract [en]

    We report the use of a single layer of two-dimensional hexagonal boron nitride (SL-hBN) as the thinnest insulating barrier to microbial corrosion induced by the sulfate-reducing bacteria Desulfovibrio alaskensis G20. We used electrochemical methods to assess the corrosion resistance of SL-hBN on copper against the effects of both the planktonic and sessile forms of the sulfate-reducing bacteria. Cyclic voltammetry results show that SL-hBN-Cu is effective in suppressing corrosion effects of the planktonic cells at potentials as high as 0.2 V (vs Ag/AgCl). The peak anodic current for the SL-hBN coatings is ∼36 times lower than that of bare Cu. Linear polarization resistance tests confirm that the SL-hBN coatings serve as a barrier against corrosive effects of the G20 biofilm when compared to bare Cu. The SL-hBN serves as an impermeable barrier to aggressive metabolites and offers ∼91% corrosion inhibition efficiency, which is comparable to much thicker commercial coatings such as polyaniline. In addition to impermeability, the insulating nature of SL-hBN suppresses galvanic effects and improves its ability to combat microbial corrosion.

  • 16. 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 University, Faculty of Science and Technology, Department of Physics.
    Reversible pressure-induced polymerization of Fe(C5H5)(2) doped C-702013In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 62, p. 447-454Article in journal (Refereed)
    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.

  • 17. Durgadevi, Ganesan
    et al.
    Samikannu, Ajaikumar
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Chandran, Muthaiah
    Kuppusamy, Muniyan Ramasamy
    Dinakaran, Kannaiyan
    Synthesis and characterization of CdS nanoparticle anchored Silica-Titania mixed Oxide mesoporous particles: Efficient photocatalyst for discoloration of textile effluent2019In: International Journal of Nano Dimension, ISSN 2008-8868, E-ISSN 2228-5059, Vol. 10, no 3, p. 272-280Article in journal (Refereed)
    Abstract [en]

    An efficient photocatalyst consisting of CdS nanoparticle dispersed mesoporous silica-titania was prepared using amphiphilic triblock copolymer P123 as template and silica-titania sol-gel precursors. The CdS nanoparticle was incorporated into silica-titania mesoporous nanosturctures by post impregnation method. The synthesized catalyst has been characterized by FTIR, TEM, SEM, and EDAX analysis. The CdS nanoparticles incorporated silica-titania mesoporous particles exhibited an enhanced light harvesting, large surface area and excellent photocatalytic activity. Photocatalytic degradation experiments on methyleneblue solution at different pH of the medium revealed that, the catalyst ST0.5CdS0.2 is more effective in basic medium with a degradation efficiency of 98%. In addition, the catalyst is also tested for dye degradation against a raw textile dye effluent containing multiple dye molecules, and their results indicated that the raw effluent can be decolorized within 90min using ST0.5CdS0.2 catalyst.

  • 18. Dyson, P J
    et al.
    Laurenczy, G
    Ohlin, C A
    Vallance, J
    Welton, T
    Determination of hydrogen concentration in ionic liquids and the effect (or lack of) on rates of hydrogenation2003In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 19, p. 2418-2419Article in journal (Refereed)
    Abstract [en]

    The solubility of hydrogen and the corresponding Henry coefficients for 11 ionic liquids have been determined in situ at 100 atm H(2) pressure and are much lower than expected; attempts to correlate the solubility of hydrogen in the ionic liquids with the rate of reaction for the hydrogenation of benzene to cyclohexane in these solvents have been made.

  • 19.
    Elhaj, Ahmed
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Porous Polymeric Monoliths by Less Common Pathways: Preparation and Characterization2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on my endeavors to prepare new porous polymeric monoliths that are viable to use as supports in flow-through processes. Polymer monoliths of various porous properties and different chemical properties have been prepared utilizing the thermally induced phase separation (TIPS) phenomenon and step-growth polymerization reactions. The aim has been to find appropriate synthesis routes to produce separation supports with fully controlled chemical, physical and surface properties. This thesis includes preparation of porous monolithic materials from several non-cross-linked commodity polymers and engineering plastics by dissolution/precipitation process (i.e. TIPS). Elevated temperatures, above the upper critical solution temperature (UCST), were used to dissolve the polymers in appropriate solvents that only dissolve the polymers above this critical temperature. After dissolution, the homogeneous and clear polymer-solvent solution is thermally quenched by cooling. A porous material, of three dimensional structure, is then obtained as the temperature crosses the UCST. More than 20 organic solvents were tested to find the most compatible one that can dissolve the polymer above the UCST and precipitate it back when the temperature is lowered. The effect of using a mixture of two solvents or additives (co-porogenic polymer or surfactant) in the polymer dissolution/precipitation process have been studied more in depth for poly(vinylidine difluoride) (PVDF) polymers of two different molecular weight grades. Monolithic materials showing different pore characteristics could be obtained by varying the composition of the PVDF-solvent mixture during the dissolute­ion/precipitation process. Step-growth polymerization (often called polycondensat­ion reaction) combined with sol-gel process with the aid of porogenic polymer and block copolymer surfactant have also been used as a new route of synthesis for production of porous melamine-formaldehyde (MF) monoliths. In general, the meso- and macro-porous support materials, for which the synthesis/preparation is discussed in this thesis, are useful to a wide variety of applications in separation science and heterogeneous reactions (catalysis).

  • 20. Feicht, Patrick
    et al.
    Siegel, Renee
    Thurn, Herbert
    Neubauer, Jens W.
    Seuss, Maximilian
    Szabo, Tamas
    Talyzin, Alexandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    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 modulus2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 114, p. 700-705Article in journal (Refereed)
    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.

  • 21. Gao, Sanshuang
    et al.
    Liu, Jing
    Luo, Jun
    Mamat, Xamxikamar
    Sambasivam, Sangaraju
    Li, Yongtao
    Hu, Xun
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi, China.
    Selective voltammetric determination of Cd(II) by using N,S-codoped porous carbon nanofibers2018In: Microchimica Acta, ISSN 0026-3672, E-ISSN 1436-5073, Vol. 185, article id 282Article in journal (Refereed)
    Abstract [en]

    Porous carbon nanofibers codoped with nitrogen and sulfur (NFs) were prepared by pyrolysis of trithiocyanuric acid, silica nanospheres and polyacrylonitrile (PAN) followed by electrospinning. The NFs were used to modify a glassy carbon electrode (GCE) which then displayed highly sensitive response to traces of Cd(II). Compared to a bare GCE and a Nafion modified GCE, the GCE modified with codoped NFs shows improved sensitivity for Cd(II) in differential pulse anodic sweep voltammetry. The stripping peak current (typically measured at 0.81 V vs. Ag/AgCl) increases linearly in the 2.0–500 μg·L−1 Cd(II) concentration range. This is attributed to the large surface area (109 m2·g−1), porous structure, and high fraction of heteroatoms (19 at.% of N and 0.75 at.% of S). The method was applied to the determination of Cd(II) in (spiked) tap water where it gave recoveries that ranged between 96% and 103%.

  • 22. Gao, Sanshuang
    et al.
    Xu, Chuyang
    Yalikun, Nuerbiya
    Mamat, Xamxikamar
    Li, Yongtao
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Xun
    Liu, Jing
    Luo, Jun
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Science, Urumqi 830011, People's Republic of China.
    Sensitive and Selective Differential Pulse Voltammetry Detection of Cd(II) and Pb(II) Using Nitrogen-Doped Porous Carbon Nanofiber Film Electrode2017In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 164, no 13, p. H967-H974Article in journal (Refereed)
    Abstract [en]

    Carbon matrix materials are regarded as one of the most important electrode materials for heavy metal detection. But even so, optimization procedures of carbon nanofibers (CNFs) for tracing Cd(II) and Pb(II) remains challenging. Here, zeolitic imidazolate framework (ZIF-8)/polyacrylonitrile (PAN)-derived nitrogen-doped porous carbon nanofibers (N-PCNFs) were investigated as a new electrode material for determining the concentration of Cd(II) and Pb(II). By optimizing electrochemical conditions such as deposition potential, deposition time, pH of buffer solution, and quantity of N-PCNFs loaded on a glassy carbon electrode (GCE), the linear response curves of Cd(II) and Pb(II) could be obtained. Due to the unique structural feature and N content, the N-PCNFs possess excellent detection limits of 0.8 mu g L-1 for Cd(II) and 0.3 mu g L-1 for Pb(II) (S/N = 3). To manifest the practical use of the sensor platform the concentration of Cd(II) and Pb(II) in normal tap and waste water were monitored. According to the ICP-MS results, the calculated recovery (97.0-107%) indicates that N-PCNFs have potential as a candidate material to monitor the concentration of Cd(II) and Pb(II) in practical samples.

  • 23. Gemo, Nicola
    et al.
    Sterchele, Stefano
    Biasi, Pierdomenico
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemical Engineering, Åbo Akademi University, Biskopsgatan 8, Åbo-Turku, Finland .
    Centomo, Paolo
    Canu, Paolo
    Zecca, Marco
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kordas, Krisztian
    Salmi, Tapio Olavi
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemical Engineering, Åbo Akademi University, Biskopsgatan 8, Åbo-Turku, Finland .
    The influence of catalyst amount and Pd loading on the H2O2 synthesis from hydrogen and oxygen2015In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 5, no 7, p. 3545-3555Article in journal (Refereed)
    Abstract [en]

    Palladium catalysts with an active metal content from 0.3 to 5.0 wt.% and supported on a strongly acidic, macroporous resin were prepared by ion-exchange/reduction method. H2O2 direct synthesis was carried out in the absence of promoters (acids and halides). The total Pd amount in the reacting environment was varied by changing A) the catalyst concentration in the slurry and B) the Pd content of the catalyst. In both cases, smaller amounts of the active metal enhance the selectivity towards H2O2, at any H-2 conversion, with option B) better than A). In case A), the Pd(II)/Pd(0) molar ratio (XPS) in the spent catalysts was found to decrease at lower catalyst Pd content. With these catalysts and this experimental set-up the dynamic H-2(1)/Pd molar ratio, the metal loading and the metal particle size were the key factors controlling the selectivity, which reached 57% at 60% H-2 conversion, and 80% at lower conversion.

  • 24. Golyakov, A. M.
    et al.
    Shchukarev, Andrey V.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ardasheva, L. P.
    Borisov, A. N.
    Electrochemical and spectral properties of the polymer form of Cu(II) complex with N,N '-bis(salicylidene)-1,3-propylenediamine2013In: Russian journal of general chemistry, ISSN 1070-3632, E-ISSN 1608-3350, Vol. 83, no 3, p. 423-429Article in journal (Refereed)
    Abstract [en]

    A conductive polymer based on the Cu(II) complex with N,N'-bis(salicylidene)-1,3-propylenediamine was obtained electrochemically. The optimal mode of the synthesis of the polymer under potentiostatic conditions was found. We determined the charge diffusion coefficient and activation barrier and elucidated the nature of the limiting step of the charge transfer in the polymer bulk in the electrolyte medium. The azomethine base, Cu(II) complex, and its polymer form in the oxidized and reduced states were characterized by X-ray photoelectron spectroscopy and electron absorption spectroscopy.

  • 25. Gorkina, Alexandra L
    et al.
    Tsapenko, Alexey P
    Gilshteyn, Evgenia P
    Koltsova, Tatiana S
    Larionova, Tatiana V
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Anisimov, Anton S
    Anoshkin, Ilya V
    Kauppinen, Esko I
    Tolochko, Oleg V
    Nasibulin, Albert G
    Transparent and conductive hybrid graphene/carbon nanotube films2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 100, p. 501-507Article in journal (Refereed)
    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.

  • 26. Han, Xin-Bao
    et al.
    Tang, Xing-Yan
    Lin, Yue
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Liu, San-Gui
    Liang, Hai-Wei
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China.
    Zhao, Xin-Jing
    Liao, Hong-Gang
    Tan, Yuan-Zhi
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Xie, Su-Yuan
    Zheng, Lan-Sun
    Ultrasmall Abundant Metal-Based Clusters as Oxygen-Evolving Catalysts2019In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 1, p. 232-239Article in journal (Refereed)
    Abstract [en]

    The oxygen evolution reaction is a crucial step in water electrolysis to develop clean and renewable energy. Although noble metal-based catalysts have demonstrated high activity for the oxygen evolution reaction, their application is limited by their high cost and low availability. Here we report the use of a molecule-to-cluster strategy for preparing ultrasmall trimetallic clusters by using the polyoxometalate molecule as a precursor. Ultrafine (0.8 nm) transition-metal clusters with controllable chemical composition are obtained. The transition-metal clusters enable highly efficient oxygen evolution through water electrolysis in alkaline media, manifested by an overpotential of 192 mV at 10 mA cm–2, a low Tafel slope of 36 mV dec–1, and long-term stability for 30 h of electrolysis. We note, however, that besides the excellent performance as an oxygen evolution catalyst, our molecule-to-cluster strategy provides a means to achieve well-defined transition-metal clusters in the subnanometer regime, which potentially can have an impact on several other applications.

  • 27. He, Hanbing
    et al.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Engineering, Division of Energy Science, Luleå University of Technology, Luleå SE-971 87, Sweden.
    Öhman, Marcus
    Time-Dependent Layer Formation on K-Feldspar Bed Particles during Fluidized Bed Combustion of Woody Fuels2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 11, p. 12848-12856Article in journal (Refereed)
    Abstract [en]

    Despite frequent reports on layer characteristics on quartz bed particles, few studies have focused on the layer characteristics of K-feldspar bed particles. The layer characteristics of K-feldspar bed particles were therefore investigated by collecting bed material samples of different ages from fluidized bed combustion of woody fuels in large-scale bubbling and circulating fluidized bed facilities. Scanning electron microscopy/energy-dispersive spectroscopy was used to analyze the layer morphology and elemental composition. Bed particles aged 1 day displayed a thin layer rich in Si, Ca, and Al. Inner layers had a more homogeneous composition than the outer layers, which instead were more heterogeneous and sometimes contained discernible fuel ash particles. The outer layer was thinner for K-feldspar bed particles sampled from circulating fluidized bed, as compared to particles from bubbling fluidized bed. The concentration of Ca in the inner layer increases toward the bed particle surface, the molar ratio of Si/Al is maintained, and the molar ratio of K/Al decreases as compared to the K-feldspar. The inner layer thickness for quartz and K-feldspar bed particles collected at the same operation conditions was found to be similar. No crack layers, as have been observed in quartz particles, were found in the core of the K-feldspar bed particles. The results suggest that the diffusion and reaction of Ca2+ into/with the feldspar particle play an important role in the inner layer formation process.

  • 28.
    Holmgren, Tomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Patrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Haglund, Peter
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Measurement and modelling of organophosphates leaching from concrete to waterManuscript (preprint) (Other academic)
    Abstract [en]

    Organophosphate triesters used as additives in materials are leaching into the environment and have been found as pollutants in both water and sewage samples. Concrete is one of the most commonly used materials in the world and often contains tributyl phosphate (TBP) and triisobutyl phosphate (TiBP) as anti-foaming agents. In the present study, leaching of TBP and TiBP from concrete to water was measured over 16 weeks under laboratory conditions. The release was initially high (TBP 2900 ± 1060 10 μg/m2h; TiBP 8500 ± 800 μg/m2h), and then dropped to a low stable level over a six-week period. A generic model was developed to predict leaching of organic compounds to water. Three types of diffusion were modelled, dissolution from the surface, diffusion in cracks and pores, and diffusion in micro-pores in the concrete. The former type was assessed using the Nernst-Brunner dissolution and Fickian diffusion theory. The latter types required the use of three modules to model diffusion, solubilisation and 15 convective mass transfer processes separately. The boundary layer solubilisation was modelled using the Abraham solubility equation and solvation parameters taken from literature data. The results showed that the initial release of organophosphates from concrete to water can be significant (in some cases, >40% of the additive leaches out over the first few weeks) and that the long-term release of organophosphates from concrete constructions to the surrounding water can be accurately modelled. The model was applied to 20 estimate the release of TiBP to river water from the foundation of a bridge, resulting in a total loss of 2% of the additive over 8 years, with seasonal fluctuations in loss rate following changes in temperature and water flow. Due to the generic nature of the model, it can also be used to assess the leaching of other additives from concrete constructions to aquatic environments.

  • 29.
    Holmgren, Tomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Patrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Haglund, Peter
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Modeling and measurement of triphenyl phosphate emissions from flat screensManuscript (preprint) (Other academic)
  • 30.
    Iakunkov, Artem
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sun, Jinhua
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rebrikova, Anastasia
    Korobov, Mikhail
    Klechikov, Alexey
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Physics and Astronomy, Uppsala University, Uppsala, 751 20, Sweden.
    Vorobiev, Alexei
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Aleksandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Swelling of graphene oxide membranes in alcohols: effects of molecule size and air ageing.2019In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, p. 11331-11337Article in journal (Refereed)
    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.

  • 31.
    Iqbal, Javed
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Enevold, Jenny
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    An Arylene-Vinylene Based Donor-Acceptor-Donor Small Molecule for the DonorCompound in High-Voltage Organic Solar CellsArticle in journal (Other academic)
    Abstract [en]

    ne"> A donor-acceptor-donor (D-A-D) molecule has been designed and synthesized for use as the electron-donating material in solution-processed small-molecule organic solar cells (OSCs). The D-A-D molecule comprises a central electron-accepting (2Z,2´Z)-2,2´-(2,5-bis(octyloxy)- 1,4-phenylene)bis(3-(thiophen-2-yl)acrylonitrile) (ZOPTAN) core, which is chemically connected to two peripheral and electron-donating triphenylamine (TPA) units. The ZOPTAN-TPA molecule features a low HOMO level of5.2 eV and an optical energy gap of 2.1 eV. Champion OSCs based on a solution-processed and non-annealed active-material blend of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and ZOPTAN-TPA in a mass ratio of 2:1 exhibits a power conversion efficiency of 1.9 % and a high open-circuit voltage of 1.0 V.

  • 32. Jiang, Ruyuan
    et al.
    Liu, Niantao
    Su, Yuhong
    Gao, Sanshuang
    Mamat, Xamxikamar
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Li, Yongtao
    Hu, Xun
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Chinese Acad Sci, Xinjiang Tech Inst Phys & Chem, State Key Lab Basis Xinjiang Indigenous Med Plant, Key Lab Chem Plant Resources Arid Reg, Urumqi 830011, Peoples R China.
    Polysulfide/Graphene Nanocomposite Film for Simultaneous Electrochemical Determination of Cadmium and Lead Ions2018In: NANO, ISSN 1793-2920, Vol. 13, no 8, article id 1850090Article in journal (Refereed)
    Abstract [en]

    An integrative electroanalytical method was developed for detecting Cd2+ and Pb2+ ions in aqueous solutions. Polysulfide/graphene (RGO-S) nanocomposites were prepared and their performance as electrochemical sensors for Cd2+ and Pb2+ was evaluated. The RGO-S nanocomposite was carefully characterized by scanning electron microscopy with energy-dispersive X-ray spectrometry, transmission electron microscopy, and X-ray photoelectron spectroscopy. The as-prepared RGO-S was incorporated into a pyrolytic graphite electrode (RGO-S/PGE) and used for detecting trace amount of Cd2+ and Pb2+ by differential pulse anodic stripping voltammetry. Under optimal conditions, the stripping peak current of RGO-S/PGE varies linearly with heavy metal ion concentration in the ranges 2.0-300 mu g L-1 for Cd2+ and 1.0-300 mu g L-1 for Pb2+. The limits of detection for Cd2+ and Pb2+ were estimated to be about 0.67 mu g L-1 and 0.17 mu g L-1, respectively. The prepared electrochemical heavy-metal-detecting electrode provides good repeatability and reproducibility with high sensitivity, making it a suitable candidate for monitoring Cd2+ and Pb2+ concentrations in aqueous environmental samples.

  • 33. Jilal, I
    et al.
    El-Barkany, S.
    Bahari, Z.
    Sundman, Ola
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    El-Idrissi, A.
    Abou-Salama, M.
    Loutou, M.
    Ablouh, E.
    Amhamdi, H.
    New benzyloxyethyl cellulose (BEC) crosslinked EDTA: synthesis, characterization and application for supramolecular self-assembling nanoencapsulation of Pb (II)2019In: Materials today: Proceedings, Elsevier, 2019, Vol. 13, p. 909-919Conference paper (Refereed)
    Abstract [en]

    Cellulosic derivatives-modification by Ethylenediaminetetraacetic acid dianhydride (EDTAD) leads to an advanced state of the crosslinking degree, which often limits the adsorbent-metal ion interactions at the superficial level. Moreover, the specific area decreases by increasing crosslinking degree, resulting in a degradation of the adsorptive properties of the materials. In the present work, a new synthesis strategy of crosslinkedcellulose derivative with Ethylenediaminetetraacetic acid (EDTA) was proposed. The preparation of the adsorbent was based on the hydrophobation of hydroxyethyl cellulose (HEC) by partial benzylation (DS similar to 1). This helped to obtain a new cellulose derivative (Benzyloxyethyl cellulose (BEC)) soluble in the majority of the usual solvents, and the EDTA grafting reaction was performed under homogeneous conditions to ensure homogenous distribution of the chelating sites. The resulting BEC-EDTA material was then characterized by FT-IR, SEM and TGA. Thus, the Pb (II)-adsorption behavior on the bio-adsorbent was studied at the supramolecular level and the study of changes in adsorbent morphology before and after modification was performed based on SEM images and EDX spectra. Effect of Pb (II) on BEC-EDTA morphology was investigated as well. However, a self-assembly of BEC-EDTA as nanometric rods in the presence of Pb (II) ions was a strong indication of the Pb (II) nano-encapsulation in a stable polymer network. (c) 2019 Elsevier Ltd. All rights reserved.

  • 34.
    Järvinen, Kristiina
    et al.
    Department of Pharmacy, University of Eastern Finland, Kuopio, Finland.
    Jokiniemi, Jorma
    Deaprtment of Environmental Science.
    Lammi, Mikko
    Institute of Biomedicine, University of Eastern Finland, Kuopio, Finland.
    Lappalainen, Reijo
    Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
    Närvänen, Ale
    Department of Pharmacy, University of Eastern Finland.
    Pakkanen, Tapani
    Department of Chemistry, University of Eastern Finland, Kuopio,Finland.
    Lehto, Vesa-Pekka
    Department ofApplied Physics, University of Eastern Finalnd, Kuopio, Finland.
    Nanoteknologia biomateriaalien ja lääkkeiden kantaja-aineiden pintojen räätälöinnissä [Nanoscale tailoring of the surface properties of biomaterials and drug carriers]2012In: Duodecim, ISSN 0012-7183, E-ISSN 2242-3281, Vol. 128, no 20, p. 2085-2092, article id 23167167Article, review/survey (Refereed)
    Abstract [en]

    Functionalities of biomaterials and drug delivery systems are improved by tailoring their surface properties using modern nanotechnology. Orthopedic implants and invasive electrodes are examples of implantable biomaterials. Biological interactions of orthopedic implants can be optimized by the synergetic effect of surface micro- and nanotexturing with a chemical composition of coating. Further, mechanical flexibility and electrochemical characteristics of invasive electrodes are improved by using micro- and nanotechnology. In nano-size drug delivery systems, surface properties of nanocarriers strongly affect their safety and efficacy. Mesoporous silicon nanoparticles are example of nanocarriers those properties can be tailored for drug delivery applications.

  • 35.
    Kanematsu, Masakazu
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Waychunas, Glenn A.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Silicate Binding and Precipitation on Iron Oxyhydroxides2018In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 52, no 4, p. 1827-1833Article in journal (Refereed)
    Abstract [en]

    Silica-bearing waters in nature often alter the reactivity of mineral surfaces via deposition of Si complexes and solids. In this work, Fourier transform infrared (FTIR) spectroscopy was used to identify hydroxo groups at goethite (alpha-FeOOH) and lepidocrocite (gamma-FeOOH) surfaces that are targeted by ligand exchange reactions with monomeric silicate species. Measurements of samples first reacted in aqueous solutions then dried under N-2(g) enabled resolution of the signature O-H stretching bands of singly (-OH), doubly (mu-OH), and triply coordinated (mu(3)-OH) groups. Samples reacted with Si for 3 and 30 d at pH 4 and 7 revealed that -OH groups were preferentially exchanged by silicate and that mu-OH and mu(3)-OH groups were not exchanged. Based on knowledge of the disposition of -OH groups on the major crystallographic faces of goethite and lepidocrocite, and the response of these groups to ligand exchange prior oligomerization, our work points to the predominance of rows of mononuclear monodentate silicate species, each separated by at least one -OH group. These species are the attachment sites from which oligomerization and polymerization reactions occur, starting at loadings exceeding similar to 1 Si/nm(2) and corresponding to soluble Si concentrations that can be as low as similar to 0.7 mM after 30 d reaction time. Only above such loadings can reaction products grow away from rows of -OH groups and form hydrogen bonds with nonexchangeable mu-OH and mu(3)-OH groups. These findings have important repercussions for our understanding of the fate of waterborne silicate ions exposed to minerals.

  • 36.
    Kawde, Anurag
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Annamalai, Alagappan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Amidani, Lucia
    European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Boniolo, Manuel
    Molecular Biomimetics, Department of Chemistry – Ångström Laboratory, Uppsala University, Sweden.
    Kwong, Wai Ling
    Molecular Biomimetics, Department of Chemistry – Ångström Laboratory, Uppsala University, Sweden.
    Sellstedt, Anita
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Glatzel, Pieter
    European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Molecular Biomimetics, Department of Chemistry – Ångström Laboratory, Uppsala University, Sweden.
    Photo-electrochemical hydrogen production from neutral phosphate buffer and seawater using micro-structured p-Si photo-electrodes functionalized by solution-based methods2018In: Sustainable Energy and Fuels, ISSN 2398-4902, Vol. 2, no 10, p. 2215-2223Article in journal (Refereed)
    Abstract [en]

    Solar fuels such as H2 generated from sunlight and seawater using earth-abundant materials are expected to be a crucial component of a next generation renewable energy mix. We herein report a systematic analysis of the photo-electrochemical performance of TiO2 coated, microstructured p-Si photoelectrodes (p-Si/TiO2) that were functionalized with CoOx and NiOx for H2 generation. These photocathodes were synthesized from commercial p-Si wafers employing wet chemical methods. In neutral phosphate buffer and standard 1 sun illumination, the p-Si/TiO2/NiOx photoelectrode showed a photocurrent density of 1.48 mA cm2 at zero bias (0 VRHE), which was three times and 15 times better than the photocurrent densities of p-Si/TiO2/CoOx and p-Si/TiO2, respectively. No decline in activity was observed over a five hour test period, yielding a Faradaic efficiency of 96% for H2 production. Based on the electrochemical characterizations and the high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) and emission spectroscopy measurements performed at the Ti Ka1 fluorescence line, the superior performance of the p-Si/TiO2/ NiOx photoelectrode was attributed to improved charge transfer properties induced by the NiOx coating on the protective TiO2 layer, in combination with a higher catalytic activity of NiOx for H2-evolution. Moreover, we report here an excellent photo-electrochemical performance of p-Si/TiO2/NiOx photoelectrode in corrosive artificial seawater (pH 8.4) with an unprecedented photocurrent density of 10 mA cm2 at an applied potential of 0.7 VRHE, and of 20 mA cm2 at 0.9 VRHE. The applied bias photon-to-current conversion efficiency (ABPE) at 0.7 VRHE and 10 mA cm2 was found to be 5.1%

  • 37.
    Kawde, Anurag
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Annamalai, Alagappan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boniolo, Manuel
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cavallari, Chaira
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Glatzel, Pieter
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Si L-edge X-ray Raman spectroscopy insight on Si/TiO2 interaction in photoelectrodesManuscript (preprint) (Other academic)
  • 38.
    Kawde, Anurag
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Annamalai, Alagappan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sellstedt, Anita
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Glatzel, Pieter
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Molecular Biomimetics, Department of Chemistry, Ångström Laboratory, Uppsala University, Sweden.
    A microstructured p-Si photocathode outcompetes Pt as a counter electrode to hematite in photoelectrochemical water-splitting2019In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 4, p. 1166-1170Article in journal (Refereed)
    Abstract [en]

    Herein, we communicate about an Earth-abundant semiconductor photocathode (p-Si/TiO2/NiOx) as an alternative for the rare and expensive Pt as a counter electrode for overall photoelectrochemical water splitting. The proposed photoelectrochemical (PEC) water-splitting device mimics the "Z"-scheme observed in natural photosynthesis by combining two photoelectrodes in a parallelillumination mode. A nearly 60% increase in the photocurrent density (Jph) for pristine α-Fe2Oand a 77% increase in the applied bias photocurrent efficiency (ABPE) were achieved by replacing the conventionally used Pt cathode with an efficient, cost effective p-Si/TiO2/NiOx photocathode under parallel illumination. The resulting photocurrent density of 1.26 mA cm−2 at 1.23VRHE represents a new record performance for hydrothermally grown pristine α-Fe2O3 nanorod photoanodes in combination with a photocathode, which opens the prospect for further improvement by doping α-Fe2O3 or by its decoration with co-catalysts. Electrochemical impedance spectroscopy measurements suggest that this significant performance increase is due to the enhancement of the space-charge field in α-Fe2O3. 

  • 39.
    Kawde, Anurag
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Annamalai, Alagappan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sellstedt, Anita
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Glatzel, Pieter
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Valence to core X-ray spectroscopic insight on the performance enhancing TiO2 interlayer of functionalized Si photoelectrodes for bias-free solar water splittingManuscript (preprint) (Other academic)
  • 40.
    Kawde, Anurag Y.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. European Synchrotron Radiation Facility | ESRF - Division of Experiments, Grenoble, France .
    Advanced silicon photoelectrodes for water splitting devices: design, preparation and functional characterization by photo-electrochemistry and high-energy X-ray spectroscopy2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    For the last century, mankind has been hugely dependent on fossil fuels to meet its energy needs. Harnessing energy from fossil fuels led to the emission of greenhouse gases. Greenhouse gases such as CO2 are a major contributor to global warming. Since the last decade, the global annual average temperature has increased by almost 1 oC, while the annual average temperature of Europe has increased by almost 1.7 oC. It is high time to find an alternative source of energy. Such an energy source must be renewable, sustainable, robust and free of greenhouse gases. Our earth has a non-stop supply of solar energy and water in oceans, harvesting energies from such resources will not only be clean but also inexpensive. Solar fuels such as H2 generated from sunlight and seawater using earth-abundant materials are expected to be a crucial component of a next generation renewable energy mix.

    My PhD research was thus focused on the use of solar energy to split water into molecular hydrogen and oxygen, a process that is referred to as ‘artificial photosynthesis’. This can be achieved with the help of semiconductor photocatalysts. As most of the earth crust has a high abundance of silicon (Si), I prepared my semiconductor photoelectrodes using Si. However, Si tends to degrade in an aqueous environment. Thus, my PhD research comprises the synthesis of microstructured Si photoelectrodes and their protection with a TiO2 inter layer followed by functionalization with various earth abundant co-catalysts. The study on the synthesis, morphology and elemental characterization of the photoelectrodes was carried out under the supervision of Prof. Dr. Johannes Messinger at the Chemistry Department of Umeå University. Deep insight on the electronic and atomic structure of the functionalized Si photoelectrodes was obtained by careful experiments at the European Synchrotron Radiation Facility (ESRF) under the supervision of Dr. Pieter Glatzel. I investigated the electronic and geometric structural properties of my photocatalysts using inner shell electron spectroscopy, which is also referred to as ‘X-ray spectroscopy’. Thus, my PhD thesis falls under the broad title of “Artificial Photosynthesis and X-Ray Spectroscopy”.

     With the motivation of developing a bias free photoelectrochemical device for overall water splitting, I first developed cost effective earth abundant photocathodes. The experimental data and detailed analysis of the photocathodes are presented in Paper I. The best photocathode obtained in Paper I (p-Si/TiO2/NiOx) was then coupled with a well-studied FTO/α-Fe2O3 photoanode in parallel-illumination mode. The two most significant information obtained in Paper II were: 1) p-Si/TiO2/NiOx outcompetes Pt as a counter electrode and 2) a space charge region in the pristine hematite can be enhanced using p-Si/TiO2/NiOx as photocathode without bias or using any dopant. The proof of concept device studied in Paper II was further optimized in Paper III by replacing the FTO substrate with the n-Si MW to a obtain n-Si MW/TiO2/α-Fe2O3 photoanode. A record high photocurrent density of 5.6 mA/cm2 was achieved for the undoped hematite photoanode. I also found out that the TiO2 inter layer plays a crucial role in enhancing the overall device performance. The role of TiO2 was thus further studied using valence to core X-ray emission spectroscopy, which opened a new avenue for identifying and investigating the prime components in such devices. Paper I to III discuss the role of TiO2 and of the co-catalysts towards solar water splitting and thus the only material left to study was the Si substrate. For paper IV, a detailed analysis on Si substrate was performed. The electronic structural changes on Si LII, III edge was studied using X-ray Raman spectroscopy. The X-ray spectroscopic studies presented in papers I to III were performed at the ID-26 beamline at ESRF, while the X-ray Raman Spectroscopy presented in Paper IV was performed at the ID-20 beamline at ESRF. The data presented in Paper IV is preliminary and needs to be processed and analyzed further.

  • 41.
    Klechikov, Alexey G.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mercier, Guillaume
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Merino, Pilar
    Blanco, Santiago
    Merino, Cesar
    Talyzin, Alexandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hydrogen storage in bulk graphene-related materials2015In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 210, p. 46-51Article in journal (Refereed)
    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.

  • 42.
    Klechikov, Alexey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sun, Jinhua
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zheng, Mingbo
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Graphene decorated with metal nanoparticles: Hydrogen sorption and related artefacts2017In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 250, p. 27-34Article in journal (Refereed)
    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.

  • 43.
    Kozyatnyk, Ivan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Latham, Kenneth G.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Valorization of Humic Acids by Hydrothermal Conversion into Carbonaceous Materials: Physical and Functional Properties2019In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 7, no 2, p. 2585-2592Article in journal (Refereed)
    Abstract [en]

    Humic acids (HAs) represent an economic and environmental challenge in water treatment, as they have the propensity to foul membranes and create toxic byproducts when interacting with chlorine. To overcome this, HAs were submitted to hydrothermal carbonization to convert them into an easy to remove, valuable carbon material. The result was a carbonaceous material which was easy to filter/dewater compared to HAs with a char yield of 49 +/- 1.8 wt %, and with 46.6 1.4 wt % ending up in the water phase, 2.2 +/- 0.2 wt % in the tar, and the rest in the gaseous fraction. The molecular weight distribution of the organic matter in the water pre-and post-HTC indicated that the structure was broken into several different fragments with a lower molecular weight than that initially present. Physicochemical analysis of the material via elemental analysis, X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and solid-state nuclear magnetic resonance indicated that under hydrothermal carbonization, the aromatic structure of HAs condensed. Carboxylic acids groups were also lost from the surface of HAs, with ether and alcohols increasing because of their loss. The morphology of the obtained material had an amorphous macrostructure consisting of many smaller light lamellar carbon fragments. Finally, the hydrothermal treatment increased the surface area from 0.4 to 103.0 m(2) g(-1).The porosity is located in the mesoporous range of 10-80 nm with a maximum peak at 50 nm.

  • 44.
    Kwong, Wai Ling
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lee, Cheng Choo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemistry-Ångström Laboratory, Uppsala University, S-75120 Uppsala, Sweden.
    Scalable Two-Step Synthesis of Nickel Iron Phosphide Electrodes for Stable and Efficient Electrocatalytic Hydrogen Evolution2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 1, p. 284-292Article in journal (Refereed)
    Abstract [en]

    The development of efficient, durable, and inexpensive hydrogen evolution electrodes remains a key challenge for realizing a sustainable H-2 fuel production via electrocatalytic water splitting. Herein, nickel-iron phosphide porous films with precisely controlled metal content were synthesized on Ti foil using a simple and scalable two-step strategy of spray-pyrolysis deposition followed by low-temperature phosphidation. The nickel-iron phosphide of an optimized Ni:Fe ratio of 1:4 demonstrated excellent overall catalytic activity for hydrogen evolution reaction (HER) in 0.5 M H2SO4, achieving current densities of -10 and -30 mA cm(-2) at overpoteritials of 101 and 123 mV, respectively, with a Tafel slope of 43 mV dec(-1). Detailed analysis obtained by X-ray diffraction, electron microscopy, electrochemistry, and X-ray photoelectron spectroscopy revealed that the superior overall HER activity of nickel iron phosphide as compared to nickel phosphide and iron phosphide was a combined effect of differences in the morphology (real surface area) and the intrinsic catalytic properties (electronic structure). Together with a long-term stability and a near-100% Faradaic efficiency, the nickel-iron phosphide electrodes produced in this study provide blueprints for large-scale H-2 production.

  • 45. Kwong, Wai Ling
    et al.
    Lee, Cheng Choo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemistry-Ångstro¨m Laboratory, Molecular Biomimetics, Uppsala University, 75120 Uppsala, Sweden.
    Cobalt- doped hematite thin films for electrocatalytic water oxidation in highly acidic media2019In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 55, no 34, p. 5017-5020Article in journal (Refereed)
    Abstract [en]

    Earth-abundant cobalt-doped hematite thin-film electrocatalysts were explored for acidic water oxidation. The strategically doped hematite produced a stable geometric current density of 10 mA cm(-2) for up to 50 h at pH 0.3, as a result of Co-enhanced intrinsic catalytic activity and charge transport properties across the film matrix.

  • 46.
    Lammi, Mikko
    et al.
    Institute of Biomedicine, University of Eastern Finland.
    Qu, Chengjuan
    Institute of Biomedicine, University of Eastern Finland.
    Prittinen, Juha
    Institute of Biomedicine, University of Eastern Finland.
    Kröger, Heikki
    Department of Orthopaedics and Traumatology, Kuopio University Hospital, Kuopio, Finland.
    Koistinen, Arto
    SIB-Labs, University of Eastern Finland, Kuopio, Finland.
    Myllymaa, Sami
    SIB-Labs, University of Eastern Finland, Kuopio, Finland.
    Lappalainen, Reijo
    Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
    Adhesion and spreading of different skeletal celltypes on variable surface coatings2012In: 5th International Conference on Biomedical Engineering and Informatics, IEEE Conference Publications , 2012, p. 582-587Conference paper (Refereed)
    Abstract [en]

    The adhesion and spreading of human bone marrow-derived mesenchymal stem cells (hMSCs), bovine primary chondrocytes and human osteoblastic osteosarcoma cell line (Saos-2) cultured on various coated surfaces were examined to determine whether different materials coated on the silicon wafer could affect the growth of the different cell types. The amorphous diamond (AD), titania (TiO2), alumina (Al2O3) or carbon nitride (C3N4) coating on the silicon wafer was obtained by using ultra short pulsed laser deposition. The differences in surface characteristics were characterized with atomic force microscope and contact angles and zeta potential measurements. Human MSCs, bovine primary chondrocytes and Saos-2 osteoblasts were cultured for 48 h in direct contact with AD-, TiO2-, Al2O3- and C3N4-coated surfaces. Cell proliferation was assayed with MTT assay. The morphology, adhesion and spreading of the cultured cells were examined with scanning electron microscope. Human MSCs had the highest cell number after 48-h-culture on all of the different coated surfaces, followed by Saos-2 osteoblasts, and then bovine primary chondrocytes. The morphological appearance of MSCs, chondrocytes and Saos-2 osteoblasts remained as original. No statistically significant differences on cell proliferation were found among the different coated surfaces. Ultra short pulsed laser deposited high quality AD-, TiO2-, Al2O3- and C3N4-coated surfaces, and provided a good environment for the adhesion and spreading of the hMSCs, primary chondrocytes and Saos-2 osteoblasts

  • 47.
    Lanz, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lindh, E. Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    On the asymmetric evolution of the optical properties of a conjugated polymer during electrochemical p- and n-type doping2017In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 5, no 19, p. 4706-4715Article in journal (Refereed)
    Abstract [en]

    We report on the in situ measured evolution of the spectral complex refractive index of a prototypical conjugated polymer, a phenyl-substituted poly (para-phenylenevinylene) copolymer (Ph-PPV, “Super Yellow”), during electrochemical p- and n-type doping. We find that the real part of the refractive index is lowered in a significant and continuous fashion over essentially the entire visible range with doping, as exemplified by a drop in the peak value at ∼480 nm from 2.1 for pristine Ph-PPV to 1.8 at a p-type doping concentration of 0.2 dopants per repeat unit and an n-type doping concentration of 0.6 dopants per repeat unit. The imaginary part features a concomitant distinct bleaching of the high-energy π–π* transition and the emergence of a low-energy polaron band. Interestingly, we observe that the optical response of Ph-PPV to p-type and n-type doping is highly asymmetric, with the former resulting in much stronger changes and a distinct blue-shift of all optical transitions. We tentatively attribute this difference in response to larger effective size of the p-type polaron compared to the n-type polaron. We anticipate that the presented results should be of value for the rational design of emerging optical devices that utilize the doping capacity of conjugated polymers.

  • 48.
    Latham, Kenneth G.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Discipline of Chemistry, University of Newcastle, Callaghan, Australia.
    Donne, Scott W.
    Nitrogen Doped Heat-Treated and Activated Hydrothermal Carbon: examination of Electrochemical Performance Using Step Potential Electrochemical Spectroscopy2018In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 165, no 11, p. A2840-A2848Article in journal (Refereed)
    Abstract [en]

    Step potential electrochemical spectroscopy (SPECS) has been applied to nitrogen-doped and non-doped hydrothermal carbons that have been activated or heat-treated at a range of temperatures. The highest surface area achieved was 422 m(2).g(-1) under heat-treatment at 600 degrees C, and 2275 m(2).g(-1) using H3PO4 chemical activation at 800 degrees C. The heat-treated series reported a maximum capacitance of 84 F.g(-1) at 10 mV.s(-1), whereas the activated series had a maximum capacitance of 306 F.g(-1) at 10 mV.s(-1) . SPECS analysis revealed that pseudo-capacitance for the hydrothermal carbon doped with nitrogen was interlinked with the degree of oxygen functionality, and that decreasing the oxygen content of the surface increased the pseudo-capacitance contribution from nitrogen. Pseudo-capacitance also increased with activation from the incorporation of phosphate groups; however, the nitrogen-doped hydrothermal carbons displayed minimal double-layer capacitance (60.6 F.g(-1) at 10 mV.s(-1)) despite having reasonable surface areas (1500-1600 m(2).g(-1)).

  • 49.
    Latham, Kenneth G.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. 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 temperatures2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 128, p. 179-190Article in journal (Refereed)
    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. 

  • 50.
    Latham, Kenneth G.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Discipline of Chemistry, University of Newcastle, Callaghan, NSW 2308, Australia.
    Ferguson, Adam
    Donne, Scott W.
    Influence of ammonium salts and temperature on the yield, morphology and chemical structure of hydrothermally carbonized saccharides2019In: SN Applied Sciences, ISSN 2523-3963, Vol. 1, no 1, article id 54Article in journal (Refereed)
    Abstract [en]

    In this work, the influence of (NH4)(2)SO4 and (NH4)(2)HPO4 as well as temperature is examined on the hydrothermal carbonization of glucose, fructose and sucrose. Increasing the temperature from 160 to 220 degrees C increased the yield of hydrothermal carbon for each saccharide for the (NH4)(2)SO4 solution, whereas (NH4)(2)HPO4 produced a yield that was independent of temperature. The addition of (NH4)(2)SO4 increased the yield obtained at 220 degrees C by 4.27, 7.03 and 2.01 wt% for glucose, fructose and sucrose over the baseline salt free solution, respectively. (NH4)(2)SO4 also increased the quantity of acid produced and the average size of the hydrothermal carbon spheres. Conversely, (NH4)(2)HPO4 produced carbon structures consisting of interlocked spherical shapes and produced almost no acidic products. XPS analysis revealed that (NH4)(2)SO4 incorporated nitrogen and sulfur into the hydrothermal structure, while (NH4)(2)HPO4 only allowed nitrogen to be incorporated. It was assessed that NH4(+) enhances the production of hydrothermal carbon, except in the presence of PO43-, which prevents the reaction from effectively forming hydrothermal carbon and organic acids. [GRAPHICS] .

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