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  • 101.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    A study of the SiO2-aqueous electrolyte (NaCl, CsCl) interface by X-ray photoelectron spectroscopy2007In: Colloid Journal, ISSN 1061-933X (Print) 1608-3067 (Online), Vol. 69, no 4, p. 514-25Article in journal (Refereed)
    Abstract [en]

    The surface of amorphous silicon dioxide in NaCl and CsCl solutions with various values of ionic strength and pH is studied by X-ray photoelectron spectroscopy. Samples are prepared through the fast freezing of wet pastes prepared by the centrifugation of suspensions. It is shown that the X-ray photoelectron spectra of such samples provide experimental information on the composition of the SiO2-solution interface, the number of electrolyte ions near the solid phase surface, and its chemical modification. The sign of the charge of silicon dioxide particles can be judged from the dependence of a measured Na(Cs)/Cl atomic ratio; the controlled removal of water from the samples in the chamber of an electronic spectrometer makes it possible to directly estimate the surface potential and study the energy effects of counterion hydration using the shifts in the binding energies of the corresponding photoelectron levels. An analysis of the binding energies of Cs 3d5/2 and Cl 2p3/2 lines in the X-ray photoelectron spectra for the SiO2-CsCl solution interface yields additional information on the structure of the formed electrical double layer, thus making it possible to distinguish between the ions adsorbed at the surface and the counterions compensating for its charge.

  • 102.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Electrical double layer at the mineral-aqueous solution interface as probed by XPS with fast-frozen samples2010In: Journal of Electron Spectroscopy and Related Phenomena, Vol. 176, no 1-3, p. 13-7Article in journal (Refereed)
    Abstract [en]

    The electrical double layer (EDL) at the mineral-aqueous solution interface is a typical example of intrinsic charging effects. As a key feature of the interface, the EDL determines its chemical composition and electrical field. The ability of the XPS technique to probe this phenomenon on fast-frozen samples is presented. It allows the quantification of counter-ions and the direct observation of interface chemical processes, such as ion pairing, specific adsorption and ligand exchange reactions. It is also shown that binding energy shifts arising due to water removal provide an experimental possibility to estimate surface potentials and their distribution within the EDL. Future directions and perspectives of the technique are shortly discussed.

  • 103.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    XPS at solid-aqueous solution interface.2006In: Advances in Colloid Interface Science, ISSN 0001-8686, Vol. 122, no 1-3, p. 149-57Article in journal (Other academic)
    Abstract [en]

    Application of X-ray Photoelectron Spectroscopy (XPS) to study the solid-aqueous solution interface is reviewed. XPS provides complementary physicochemical information about electrical double layer from the perspective of the solid surface. Experimental techniques, such as differential pumping, controlled adsorption/co-adsorption, freeze-drying, and fast-freezing, are discussed for both electrochemical and dielectric solid-solution interfaces. The use of fast-freezing, as applied to wet pastes centrifuged from aqueous suspensions, makes it possible to approach a real solid-solution interface in UHV conditions. XPS data allow estimation of the surface density of counter-ions, surface point of zero charge, and in some cases the measurement of surface potential. Interfacial chemical reactions such as ion pair formation, specific adsorption and ligand exchange can be directly observed. The technique is easy to apply to any suspension including colloids and gels of inorganic or organic nature, and can be adapted for electrochemistry as complementary to traditional "emersed electrode" studies.

  • 104.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    XPS at solid-solution interface: experimental approaches2006In: Surface and Interface Analysis, Vol. 38, p. 682-5Article in journal (Refereed)
    Abstract [en]

    XPS is a very useful technique to study physicochemical phenomena at the solid-solution interface. It is essential that the interface remains unaltered during sample preparation and analysis.

    Experimental approaches dealing with this problem are reviewed and discussed. They include differential pumping, controlled adsorption/condensation from gas phase, fast freezing, and freeze-drying. A recently developed fast-freezing procedure of wet pastes that are obtained from powder suspensions by centrifuging is described. This method allows for estimating surface point-of-zero charge, thickness, and potential of electrical double layer from XPS data. New experimental findings on mineral-solution interfaces are presented. Copyright © 2006 John Wiley & Sons, Ltd.

  • 105.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    XPS study of the hematite-aqueous solution interface2008In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Surface and Interface Analysis, Vol. 40, no 3-4, p. 349-353Article in journal (Refereed)
    Abstract [en]

    The interaction between the surface of hematite colloidal platelets and Na+ and Cl- ions was investigated by XPS using the cryogenic technique. Pastes in ionic strengths of 0 and 10 mM NaCl contained about 10 at. % water and water/NaCl atomic ratios of 3 to 6. These results fall within the range of values obtained for a variety of minerals studied with this technique. Pastes in 100 mM NaCl background electrolyte, however, contained an unusually larger water content of 25 at. %, yielding a Na+: Cl-: H2O ratio of 1:1:2. This result is in strong contrast with other minerals at the same ionic strength, which typically reveal about 10 at. % water. Substituting Na+ for Cs+ in the hematite paste with 100 mM CsCl yielded, on the other hand, the same amount of water as in the pastes with 0 and 10 mM NaCl, and underpinned the role of Na+ ions in the large water content of the hematite paste. As surface concentrations of Na+ and Cl- exceeded those of hematite surface structural hydroxyl groups and Na 1s and Cl 2p spectra exhibited energy loss features, the electrolyte ions are proposed to be distributed in a three-dimensional array in the fast-frozen paste, possibly in a hydrohalite-like (NaCl·2H2O) phase. In addition, because the fast-frozen solution of 100 mM NaCl yields a water/NaCl ratio of about 70, hematite is proposed to play an important role in the stabilization of this three-dimensional distribution of Na+ and Cl- ions. The role of the neutrally charged {001} plane, a predominant feature in the hematite particles of this study, is notably discussed in the light of recent molecular models showing that this plane can stabilize several layers of hydrated ions up to 15 Å from the surface.

  • 106.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Chemistry.
    Felmy, Andrew R
    XPS of Fast-Frozen Hematite Colloids in NaCl Aqueous Solutions: I. Evidence for the Formation of Multiple Layers of Hydrated Sodium and Chloride Ions Induced by the {001} Basal Plane2007In: The Journal of Physical Chemistry C, Vol. 111, no 49, p. 18307-16Article in journal (Refereed)
    Abstract [en]

    The composition of fast-frozen wet pastes of hematite particles of different morphologies equilibrated in NaCl aqueous solutions was investigated by X-ray photoelectron spectroscopy. Two hematite preparations consisted of micrometer-sized platelets with 42% (HEM-1) and 82% (HEM-8) of the surface terminated by the {001} basal plane and a third of spheroids with no recognizable crystal plane (HEM-control). All hematite samples responded to changes in pH (4 and 9) and ionic strength (0, 10, 100 mM), showing that acid/base reactions of surface hydroxyl groups impact the composition of the paste. The HEM-1 and HEM-8 sample exhibited unusually large Na, Cl, and water contents at the highest ionic strength (100 mM) compared to HEM-control and all other minerals studied with this technique previously. The Na 1s and Cl 2p spectra occurred at binding energies typical of hydrated Na+ and Cl- ions and possessed energy-loss features, suggesting a three-dimensional distribution of these ions in the paste. An approximate stochiometric Na/Cl/H2O ratio of 1:1:2 was obtained in all samples in 100 mM NaCl as well as a strong correlation between the these compounds and the fraction of the {001} basal plane present in the hematite particles. The basal plane of hematite is proposed to induce the formation of a hydrated NaCl structure in the fast-frozen pastes, one that is compositionally reminiscent of hydrohalite (NaCl·2H2O), by stabilizing multiple layers of hydrated Na+ and Cl- ions prior to freezing.

  • 107.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gälman, Veronika
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rydberg, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Speciation of iron and sulphur in seasonal layers of varved lake sediment: an XPS study2008In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 40, no 3-4, p. 354-357Article in journal (Refereed)
    Abstract [en]

    Under specific conditions, annually-laminated (varved) sediments are formed in lakes. Such lake sediments are rare, but of great interest to studies of past environmental conditions since they provide annual or even seasonal time resolution, and can be used to follow environmental changes over hundreds or thousands of years. The chemical composition of the varves and speciation of chemical elements reveal information on past conditions. The colour of sediment varves can vary between light brown to almost black, and it was hypothesised that black layers were deposited in seasons with oxygen deficit in the hypolimnion (summer and winter) and light layers were formed at spring and autumn over-turn periods when oxygen-rich water flow occurred near the lake bottom. We have tested this hypothesis by analyses of seasonal layers of varves formed in 1968 and 2005 using X-ray photoelectron spectroscopy with fast-frozen samples. We found that the organic (C, N, O, S) and inorganic (Al, Si, Ca, Fe, S) elemental composition was similar for all samples studied, but the chemical states of iron and sulphur differed remarkably depending on the season. The black colour of the summer layer was caused by the precipitation of inorganic FeS, while in the light layers only organic thiol (SH) and sulphate SO42- together with Fe(III) hydroxides were found.

  • 108.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Malekzadeh, Behnosh Öhrnell
    Ransjö, Maria
    Tengvall, Pentti
    Westerlund, Anna
    Surface characterization of insulin-coated Ti6Al4V medical implants conditioned in cell culture medium: an XPS study2017In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 216, p. 33-38Article in journal (Refereed)
    Abstract [en]

    Surface characterization of insulin-coated Ti6Al4V medical implants, after incubation in α-minimum essential medium (α-MEM), was done by X-ray photoelectron spectroscopy (XPS), in order to analyze the insulin behavior at the implant – α-MEM interface. In the absence of serum proteins in cell culture medium, the coated insulin layer remained intact, but experienced a time-dependent structural transformation exposing hydrophobic parts of the protein toward the solution. The presence of fetal bovine serum (FBS) in the medium resulted in partial substitution of insulin by serum proteins. In spite of some insulin release, the remaining coated layer demonstrated a direct surface effect by stabilizing the structure of protein competitors, and by supporting the accumulation of calcium and phosphate ions at the interface. A structurally stable protein layer with incorporated calcium and phosphate ions at the implant–tissue interface could be an important prerequisite for enhanced bone formation.

  • 109.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Mattsson, R
    Ödberg, L
    XPS imaging of surface diffusion of alkylketene dimer on paper surfaces2003In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol. 219, no 1-3, p. 35-43Article in journal (Refereed)
    Abstract [en]

    The alkylketene dimer (AKD) wax dispersion is introduced in the wet-end of a paper machine, and during drying it spreads and anchors to the fiber surface. Direct observation of the surface diffusion of the AKD wax at paper surfaces was obtained using X-ray photoelectron spectroscopy imaging technique. An AKD diffusion of approximately 400 μm was observed at a paper surface that was stored for 3 h at 80 °C. This gives a diffusion coefficient of approximately 10−11 m2 s−1. Storage for 1 week at room temperature also showed a remarkable spreading of AKD.

  • 110.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mladenovic, Zivko
    Umeå University, Faculty of Medicine, Department of Odontology, Ortodontics.
    Ransjö, Maria
    Umeå University, Faculty of Medicine, Department of Odontology, Ortodontics.
    Surface characterization of bone graft substitute materials conditioned in cell culture medium. 2. Protein adsorption2012In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 44, no 8, p. 919-923Article in journal (Refereed)
    Abstract [en]

    Three bone graft substitute materials (Bioglass 45S5, Bio-Oss (R) and Algipore (R)) were conditioned in a-minimum essential medium (alpha-MEM), with the addition of 10% fetal bovine serum (FBS), for 1 and 7?days. The chemistry of their solid-solution interface was monitored by X-ray photoelectron spectroscopy, using fast-frozen sample technique, and compared to that reported for original alpha-MEM. FBS added to the biological medium causes significant changes in the interface after only 1day of conditioning. Interfacial chemical composition and N 1s spectra show immediate adsorption of proteins at the surface of all three biomaterials, independent of their surface charge and chemical composition. However, the atomic ratio C/N and the C 1s spectra indicate a different orientation of adsorbed serum proteins, which is dependent on the particle's surface charge. Moreover, the adsorption of serum proteins at the surface of Bio-Oss causes a charge reversal at the interface, as evidenced by the change in the atomic ratio of Na/Cl. In addition to the particle's surface charge, the formation of the protein interfacial layer at the surface of the biomaterial seems to be the second major phenomenon important for subsequent cell recognition and the initiation of biomineralization. Copyright (c) 2012 John Wiley & Sons, Ltd.

  • 111.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cryo-XPS: probing intact interfaces in nature and life2017In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 49, no 4, p. 349-356Article in journal (Refereed)
    Abstract [en]

    Experimental studies of solid–aqueous solution interfaces are of great importance for reaching a better chemical understanding ofinterfacial phenomena at the molecular level. This perspective article presents a recently developed approach for investigation ofintact interfaces, based on fast freezing of centrifuged wet pastes followed by traditional XPS measurements at liquid nitrogentemperatures. Sample preparation and handling protocols, applicable to any suspension or gel, are discussed in detail. For mineralsuspensions, cryogenic XPS is an important complement to traditional analyses of supernatant solutions and dry solids that iscapable of revealing novel insights of the electrical double layer in terms of structure and composition. It can be used to studychanges in the biochemistry of bacterial cell walls as influenced by external stimuli, and interfacial features related tobiocompatibility of implant materials. Herein we review how the technique has been applied to minerals in electrolyte solutions,intact bacterial surfaces, and biomaterial interfaces in biologically relevant media, and highlight some future requirements fordevelopment of interface analysis methodologies.

  • 112.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ransjö, Maria
    Umeå University, Faculty of Medicine, Department of Odontology.
    Mladenović, Živko
    Umeå University, Faculty of Medicine, Department of Odontology.
    To build or not to build: the interface of bone graft substitute materials in biological media from the view point of the cells2011In: Biomaterials science and engineering / [ed] Rosario Pignatello, Published by InTech , 2011, p. 287-308Chapter in book (Refereed)
    Abstract [en]

    These contribution books collect reviews and original articles from eminent experts working in the interdisciplinary arena of biomaterial development and use. From their direct and recent experience, the readers can achieve a wide vision on the new and ongoing potentials of different synthetic and engineered biomaterials. Contributions were not selected based on a direct market or clinical interest, than on results coming from very fundamental studies which have been mainly gathered for this book. This fact will also allow to gain a more general view of what and how the various biomaterials can do and work for, along with the methodologies necessary to design, develop and characterize them, without the restrictions necessarily imposed by industrial or profit concerns. The book collects 22 chapters related to recent researches on new materials, particularly dealing with their potential and different applications in biomedicine and clinics: from tissue engineering to polymeric scaffolds, from bone mimetic products to prostheses, up to strategies to manage their interaction with living cells.

  • 113.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Rosenqvist, J
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    XPS study of the silica–water interface2004In: Journal of Electron Spectroscopy and Related Phenomena, Vol. 137-140, p. 171-6Article in journal (Refereed)
    Abstract [en]

    XPS was applied to study the silica–water interface formed in NaCl solution at variable pH (2–9) and ionic strength (10–600 mM).

    To prevent alteration of the interface, the wet silica pastes were precooled with liquid nitrogen. After measurements under liquid nitrogen, XPS spectra were collected the next day at room temperature to follow changes at the silica surface caused by water loss.

    XPS data show that, at low ionic strength (<20 mM), Cl− ions could not be detected at the surface even at the lowest pH. Changes of the Na/Si atomic ratio with pH are in close agreement with the adsorption curve of OH− ions. At higher ionic strength (>100 mM), the silica surface’s point of zero charge can be determined from the Na/Cl atomic ratio. At pH 9 the amount of “free” Na+ at the surface is independent of NaCl concentration reflecting the formation of SiO---Na bonds, confirmed by O 1s spectra.

    Removing water from the sample surface allows determination of a “built-in” potential at the interface. Si 2p and O 1s spectra of the matrix shift to lower BE values whereas Na 1s and Cl 2p lines of the counter-ions shift to higher BE. At higher ionic strength and pH<2, shifts of Si 2p and O 1s spectra change sign, reflecting the formation of positively charged silica surfaces. The absolute value of the photoelectron line shifts for the matrix elements does not exceed 0.25 eV at any pH, whereas the shifts for counter-ions can reach 0.6 eV. The shifts decrease with increasing ionic strength, implying the formation of a more compact interface.

  • 114.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    XPS with fast-frozen samples: A renewed approach to study the real mineral/solution interface2005In: SURFACE SCIENCE, ISSN 0039-6028, Vol. 584, no 1, p. 106-12Article in journal (Refereed)
    Abstract [en]

    The procedure for XPS study of quick-frozen solutions developed at the end of 1970s [K, Burger. E. Fluck. Inorg. Nuel. Chem. Lett. 10 (1974) 171] was modified and applied to investigate the mineral/solution interrace formed at the surface of silica, gibbsite, goethite and manganite in aqueous sodium chloride solution at variable pH and ionic strength.

    The Na/Cl atomic ratio (frozen samples) allows determination of the pH range where the mineral surface charge is close to zero. This ratio can be used also to prove an ion pair formation at the surface. From the intensity of the O1s component corresponding to water, an interface thickness of 0.5 nm was estimated, A "built-in" potential at the interface, evincing as matrix elements photoelectron lines shifts after water loss, was found. This potential arises due to the spatial separation of the charged mineral surface and counter-ions in the electrical double layer (EDL), Its value does not exceed 250 mV and the sign depends on the charge of the mineral surface, (c) 2005 Elsevier B.V. All rights reserved.

  • 115.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sundberg, Björn
    Mellerowicz, Ewa
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    XPS study of living tree: Per Persson2002In: Surface and Interface Analysis, Vol. 34, no 1, p. 284-8Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) was used to study the distribution of elements and main wood components (cellulose and lignin) within the wood and at the bark/wood interface of a living hybrid aspen stem. The hybrid aspen was grown upright in a greenhouse and then tilted at 45° to induce tension wood formation and upright bending of the stem. The wood between the pith and the bark on the upper side of the tilted stem was analysed. Changes in the middle lamella/S1 layer chemical composition, which corresponded to the transition from normal wood produced during upright stem growth to tension wood produced upon stem tilting, were observed. Such changes were related to the lower lignin and higher cellulose/hemicellulose contents in the tension wood. A non-uniform radial distribution of nitrogen (amino acids, proteins) within the stem was also noted. At the bark/wood interface the presence of inorganic elements (Ca, K and P) and a significant increase in nitrogen were found. The opposite wood side of the tree was enriched in lignin and fatty acids. It was shown that application of XPS imaging to a very rough surface of wood split allows the inhomogeneous lateral lignin distribution to be visualized. Copyright © 2002 John Wiley & Sons, Ltd.

  • 116.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, UK.
    Driver, Gordon W.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lucas, Marie
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sparrman, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bifluoride ([HF2](-)) formation at the fluoridated aluminium hydroxide/water interface2016In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, no 22, p. 9045-9050Article in journal (Refereed)
    Abstract [en]

    This study uncovers bifluoride-type (difluorohydrogenate(I); [HF2](-)) species formed at mineral/water interfaces. Bifluoride forms at equivalent to Al-F surface sites resulting from the partial fluoridation of gibbsite (gamma-Al(OH3)) and bayerite (alpha-Al(OH3)) particles exposed to aqueous solutions of 50 mM NaF. Fluoride removal from these solutions is proton-promoted and results in a strongly self-buffered suspensions at circumneutral pH, proceeds at a F : H consumption ratio of 2 : 1, and with recorded losses of up to 17 mM fluoride (58 F nm(-2)). These loadings exceed crystallographic site densities by a factor of 3-4, yet the reactions have no resolvable impact on particle size, shape and mineralogy. X-ray photoelectron spectroscopy (XPS) of frozen (-155 degrees C) wet mineral pastes revealed coexisting surface F- and HF0 species. Electron energy loss features pointed to multilayer distribution of these species at the mineral/water interface. XPS also uncovered a distinct form of Na+ involved in binding fluoride-bearing species. XPS and solid state magic angle spinning F-19 nuclear magnetic resonance measurements showed that these fluoride species were highly comparable to a sodium-bifluoride (NaHF2) reference. First layer surface species are represented as =Al-F-H-F-Al= and =Al-F-Na-F-Al=, and may form multi-layered species into the mineral/water interface. These results consequently point to a potentially overlooked inorganic fluorine species in a technologically relevant mineral/water interfacial systems.

  • 117.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    X-ray photoelectron spectroscopy of fast-frozen hematite colloids in aqueous solutions: 3. stabilization of ammonium species by surface (hydr)oxo groups2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 14, p. 6796-6801Article in journal (Refereed)
    Abstract [en]

    The speciation of ammonium at the hematite/water interface was probed by cryogenic X-ray photoelectron spectroscopy. Wet pastes of colloidal hematite spheroids equilibrated in aqueous solutions of 50 mM NH4Cl exhibit distinctive pH-sensitive N 1s peaks for both NH4+ (401.7 eV) and NH3 (400.1 eV), yet total N/Fe ratios remain relatively invariant (0.029 ± 0.006) throughout the pH 2.2−10.5 range. Both NH4+ and NH3 species coexist throughout most of the tested pH range. NH4+ is most likely stabilized at the interface by hydrogen bonding with surface (hydr)oxo groups. A cationic sorption edge for NH3 is driven by proton abstraction of NH4+ by (hydr)oxo groups, forming surface complexes of the type ≡Fe−OH···NH3. These interactions shift the NH4+/NH3 equilibrium from pKa = 9.3 in water to 8.4 at the interface. Removal of excess water by vacuum dehydration induces, on the other hand, formation of NH2 directly bound to surface Fe atoms. These results underscore distinct ammonium species in contact with mineral surfaces and should be considered in understanding environmental and catalytic reactions in this medium.

  • 118.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kozin, Philipp A
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    X-ray photoelectron spectroscopy of fast-frozen hematite colloids in aqueous solutions. 5. halide ion (F, Cl, Br, I) adsorption2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 8, p. 2623-2630Article in journal (Refereed)
    Abstract [en]

    Halide anion (F, Cl, Br, and I) adsorption and its impact on sodium adsorption at the hematite/water interface were studied by cryogenic X-ray photoelectron spectroscopy (XPS). Measurements were carried out on frozen, centrifuged wet hematite pastes that were previously equilibrated in 50 mM electrolytic solutions in the pH 2–11 range. XPS-derived halide ion surface loadings decreased in the order F > I ≈ Cl > Br, whereas sodium loadings were in the order Na(F) > Na(I) > Na(Br) > Na(Cl). The greater sodium loadings in NaF and in NaI resulted from larger anion loadings in these systems. Bromide ion had the lowest loading among all halide ions despite having a charge-to-size ratio that is intermediate between those of Cl and I. This unexpected result may have arisen from specific properties of the hematite/water interface, such as water structure and electric double layer thickness. Fluoride ion adsorption proceeded via the formation of hydrogen bonds with the surface hydroxo groups (e.g., ≡Fe–OH2···F or ≡Fe–OH···F). Surface-bound fluoride ions exert a greater charge-screening effect than the other halide anions, as demonstrated by considerably small zeta potential values. Fe–F bond formation was excluded as a possible interfacial process as the F 1s peak binding energy (684.2 eV) was more comparable to that of NaF (684.6 eV) than FeF3 (685.4 eV). Overall, these findings motivate further refinements of existing thermodynamic adsorption models for predicting the ionic composition of hematite particle surfaces contacted with sodium halide aqueous solutions.

  • 119.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kozin, Philipp A
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François Boily
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    X-ray photoelectron spectroscopy of fast-frozen hematite colloids in aqueous solutions. 4. Coexistence of alkali metal (Na+, K+, Rb+, Cs+) and chloride ions2012In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 606, no 13-14, p. 1005-1009Article in journal (Refereed)
    Abstract [en]

    Colloidal suspensions of hematite in contact with aqueous solutions of 50 mM alkali metal chloride electrolytes (NaCl, KCl, RbCl, CsCl) were investigated by cryogenic X-ray photoelectron spectroscopy (XPS) and electrophoretic mobility. Suspension pH values were varied from 2 to 11 in order to evaluate effects of positively- and negatively-charged hematite surfaces. XPS revealed coexisting cations and chloride ions both below and above the point of zero charge. Concentration profiles of adsorbed cations point to a Hofmeister series in the order of Na+ > K+ > Rb+ ≈ Cs+. Binding energies of photoelectrons emitted from electrolyte ions increased with pH at roughly 0.04 eV per pH unit. This shift was attributed to variations in the surface electric potential of hematite. This effect, compounded by rises in aliphatic carbon signals with pH, called for referencing of all spectra to the 530.0 eV oxide component of the hematite O1s spectrum. This departure from the traditional use of the external C 1s 285.0 eV peak is hereby proposed for cryogenic XPS studies of interfacial reactions involving hematite.

  • 120. Skvarla, Jiri
    et al.
    Kanuchova, Maria
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Brezani, Ivan
    Skvarla, Juraj
    Accumulation of counterions and coions evaluated by cryogenic XPS as a new tool for describing the structure of electric double layer at the silica/water interface2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 43, p. 29047-29052Article in journal (Refereed)
    Abstract [en]

    We introduce a new method of evaluating the structure of electric double layer (EDL) at the native solid/liquid interface using cryogenic X-ray photoelectron spectroscopy technique. This method is based on evaluating the atomic concentration ratio of counterions and co-ions of supporting electrolyte at the close-to-in situ state surface of colloid particles by the cryo-XPS and comparing it with analogous ratio predicted by EDL models. For silica colloids in aqueous KCl solutions at pH 6 to 8 it has been found that the latter ratio is higher than unity, as expected for the negatively charged surface of silica, but does not correspond with the prediction of the basic Gouy-Chapman EDL model for the ideal interface. However, it agrees with that deduced from experiments on electrolytic coagulation kinetics of analogous silica colloids by applying a simple EDL model of swellable ion-permeable (Donnanian) polyelectrolyte gel layer. It turns out that the traditional Stern layer-based concept of EDL at solid/liquid interfaces is not justified for metal oxides at least in KCl solutions.

  • 121.
    Soroka, Inna L.
    et al.
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Stockholm, Sweden.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jonsson, Mats
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Stockholm, Sweden.
    Tarakina, Nadezda V.
    The University of Würzburg, Würzburg, Germany.
    Korzhavyi, Pavel A.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Stockholm, Sweden.
    Cuprous hydroxide in a solid form: does it exist?2013In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 26, p. 9585-9594Article in journal (Refereed)
    Abstract [en]

    Experimental studies have been performed to obtain the unknown cuprous hydroxide compound, which has recently been predicted theoretically (P. A. Korzhavyi et. al., Proc. Natl. Acad. Sci. U. S. A., 2012, 109, 686-689) to be metastable in a solid form. The reduction of Cu2+ with ferrous ethylenediamine tetraacetate (EDTA) results in the formation of a yellow powder precipitate whose composition corresponds to CuOH x H2O as probed by Fourier Transform Infrared Spectroscopy (FTIR) and cryogenic X-ray Photoelectron Spectroscopy (XPS). A similar compound has been found on the surface of Cu-CuH powder stored in water, as detected by XPS. The reduction of Cu2+ to Cu+ with free radicals in aqueous solutions results in a Cu2O precipitate as the final product, while the formation of the yellow cuprous hydroxide colloids may be an intermediate step. Our studies reveal that cuprous hydroxide does exist in a solid form and most likely has a hydrated form, CuOH x H2O.

  • 122.
    Sterchele, Stefano
    et al.
    Padova, Italy; Åbo-Turku, Finland.
    Biasi, Pierdomenico
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Åbo-Turku, Finland.
    Centomo, Paolo
    Padova, Italy.
    Campestrini, Sandro
    Padova, Italy.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rautio, Anne-Riikka
    Oulu, Finland.
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Åbo-Turku, Finland;.
    Salmi, Tapio
    Åbo-Turku, Finland.
    Zecca, Marco
    Padova, Italy.
    The effect of the metal precursor-reduction with hydrogen on a library of bimetallic Pd-Au and Pd-Pt catalysts for the direct synthesis of H2O22015In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 248, p. 40-47Article in journal (Refereed)
    Abstract [en]

    Two sets of bimetallic Pd-Pt (Pd: 1.0; Pt: 0.25-1.0%, w/w) and Pd-Au (Pd: 1.0; Au: 0.25-1.0%, w/w) catalysts have been used, with no added promoter, in the catalytic direct synthesis (CDS) of hydrogen peroxide from its elements at 2 °C with a CO2/O2/H2 mixture (72/25.5/2.5%, respectively). The catalysts were supported on the commercial macroreticular ion-exchange resin Lewatit K2621 and were obtained from the reduction with H2 of ion-exchanged cationic precursors at 5 bar and at 60 °C. The addition of Pt or Au to Pd produced an increase of the initial overall catalytic activity in comparison with monometallic Pd with both the second metals, but with Pt the increase was much higher than with Au. Moreover, the addition of 0.25% (w/w) Pt, or more, invariably made all the Pd-Pt catalysts less selective with respect to Pd alone. In the case of Au, by contrast, the addition of 0.25% w/w produced an increase, albeit small, of the selectivity. As the result, the most active and productive Pd-Pt catalyst was 1Pd025PtK2621 with 1891 mol(H2) mo l(Pd + Pt) - 1 h- 1 initially consumed, 1875 mol(H2 O2) mo l(Pd + Pt) - 1 h- 1 initially produced, a 45% selectivity towards H2O2 at 50% conversion of H2. In the case of the Pd-Au bimetallic catalysts, 1Pd025AuK2621 was the best one, with 1184 mol(H2) mo l(Pd + Pt) - 1 h- 1 initially consumed, 739 mol(H2 O2) mo l(Pd + Pt) - 1 h- 1 initially produced, a 55% selectivity towards H2O2 at 50% conversion of H2. Although the characterization of the Pd-Pt and Pd-Au catalysts with TEM showed that the morphology of the nanostructured metal phases in the Pd-Pt and Pd-Au catalysts was very different from each family to the other, no clear correlation between the size of the nanoparticles and their distribution and the catalytic performance was apparent. These catalysts were also generally different, especially the Pd-Au ones, from previously reported related materials obtained from the same support and the same precursor, but with a different reducing agent (formaldehyde). © 2014 Elsevier B.V. All rights reserved.

  • 123. Sterchele, Stefano
    et al.
    Biasi, Pierdomenico
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Abo Akad Univ, Johan Gadolin Proc Chem Ctr, Lab Ind Chem & React Engn, Dept Chem Engn, Biskopsgatan 8, FI-20500 Abo Turku, Finland.
    Centomo, Paolo
    Shchukarev, Andrey
    Kordás, Krisztian
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Univ Oulu, EMPART Res Grp Infotech Oulu, Microelect & Mat Phys Labs, Fac Technol, FI-90014 Oulu, Finland.
    Rautio, Anne-Riika
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Abo Akad Univ, Johan Gadolin Proc Chem Ctr, Lab Ind Chem & React Engn, Dept Chem Engn, Biskopsgatan 8, FI-20500 Abo Turku, Finland.
    Salmi, Tapio
    Canton, Patrizia
    Zecca, Marco
    Influence of Metal Precursors and Reduction Protocols on the Chloride-Free Preparation of Catalysts for the Direct Synthesis of Hydrogen Peroxide without Selectivity Enhancers2016In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 8, no 8, p. 1564-1574Article in journal (Refereed)
    Abstract [en]

    Different metal precursors and reducing agents were applied in the preparation of 1 wt % Pd catalysts supported on commercial ion-exchange resin (Lewatit K2621) and used in the direct synthesis of H2O2. The catalysts were characterized by using TEM and their performance was evaluated in the direct synthesis of H2O2 (in a batch and semi-batch reactor) to investigate the relationship between the catalyst preparation methods, morphology, and catalytic performance. As expected, both the choice of the Pd precursor and the reduction conditions had a strong influence on the size and size distribution of the resulting supported nanostructured metal nanoparticles and, consequently, on the catalytic performance. The best combination of metal precursor and reduction agent was [Pd(NH3)4]SO4 reduced with hydrogen. This catalyst had the largest average size of the Pd nanoparticles and the broadest size distribution.

  • 124. Taheri, Masoud
    et al.
    Ghiaci, Mehran
    Moheb, Ahmad
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Organic–inorganic hybrid of anchored dicationic ionic liquid on Al-MCM-41-phosphovanadomolybdate toward selective oxidation of benzene to phenol2019In: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 33, no 8, article id e5012Article in journal (Refereed)
    Abstract [en]

    A phosphovanadomolybdate hybridized with an anchored dicationic ionic liquid on Al-MCM-41 was prepared through the anion exchange and characterized by 1H and 13C NMR, FTIR, UV?Vis, XRD, XPS, TGA, TEM, FESEM, ICP-OES and BET techniques. The obtained data demonstrated that the composite is a porous material with the high surface area and also having a large pore volume which are 405 m2 g?1 and 0.616 cm3 g?1 respectively. The prepared composite has shown an acceptable catalytic activity for converting benzene selectively to phenol with hydrogen peroxide as eco-friendly oxidant. Under the optimized reaction conditions, the hybrid catalyst resulted in phenol yield of 14.8% with 100% selectivity and a TOF value of 20.0 h?1. The catalyst also revealed a desired recovery and reusability. The efficient performance of the composite is related to the textural and polyoxometalate properties.

  • 125. Taheri, Masoud
    et al.
    Ghiaci, Mehran
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cross-linked chitosan with a dicationic ionic liquid as a recyclable biopolymer-supported catalyst for cycloaddition of carbon dioxide with epoxides into cyclic carbonates2018In: New Journal of Chemistry, ISSN 1144-0546, E-ISSN 1369-9261, Vol. 42, no 1, p. 587-597Article in journal (Refereed)
    Abstract [en]

    Development of eco-friendly, desirable and reusable catalysts particularly for reactions in regard to carbon dioxide fixation is still attractive in academic and industrial sectors. In this study, a dicationic ionic liquid was anchored to a cheap biopolymer, i.e., chitosan and the prepared hybrid composite was used in the cycloaddition reaction of CO2 with various epoxides for preparing five-membered cyclic carbonates under solvent-free conditions in high yield and selectivity without the addition any metal co-catalyst. The catalyst was characterized by 1H and 13C NMR, FTIR, UV-vis, XPS, TG, FESEM, and BET techniques. The catalyst was recovered and recycled at least five times without losing its activity and selectivity. Moreover, it has been demonstrated that chitosan through hydrogen bonding, coordination of amine groups with CO2 and also loosely bonded bromide ion to imidazolium ion have synergistic effects on the yield and selectivity of cyclic carbonates under optimum conditions. On the basis of the obtained results, a feasible mechanism was proposed for the reaction.

  • 126.
    Taube, Fabian
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Pommer, Linda
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Larsson, Tom
    Umeå University, Faculty of Science and Technology, Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Soil Remediation – Mercury Speciation in Soil and Vapor Phase During Thermal Treatment2008In: Water, Air, & Soil Pollution, Vol. 193, no 1-4, p. 155-63Article in journal (Refereed)
    Abstract [en]

    Spectroscopic (XRD, XPS, ICP-MS and AAS) and microscopic (ESEM) techniques have been used in order to study the chemical effects with emphasis on mercury speciation, during thermal treatment of a mercury contaminated soil. In the untreated soil, mercury was found concentrated in spherical particles, which were successively broken down upon thermal treatment. Hg0 and inorganic mercury compounds (presumably HgO(s) and HgSO4(s)) could be detected. No (CH3)2Hg and only traces of CH3Hg+ could be found. The dependence on temperature and heating time indicated that the evaporation of mercury from the soil was partly controlled by diffusion mechanisms. Mercury volatilized in two separate stages during heating; initial elemental vaporization, and subsequent volatilization of the oxide or sulfate phase at higher temperatures (>230°C). By thermal treatment at 470°C and 20 min, a removal of >99% of the mercury could be achieved.

  • 127. Taube, Fabian
    et al.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Li, Jiebing
    Gellerstedt, Göran
    Agnemo, Roland
    Peroxomolybdate Catalysts in Pulp Hydrogen Peroxide Bleaching: Improvement Inhexeneuronic Acid Removal and Delignification2008In: Tappi Journal: March, p. 8-14Article in journal (Refereed)
    Abstract [en]

    We have studied the catalytic effects of peroxomolybdates, i.e., [MoO(O2)2(OH)(H2O)]-, on hydrogen peroxide bleaching on hardwood and softwood pulps in terms of kappa number reduction, hexeneuronic acid (HexA) removal, and delignification. We found that, in the case of hardwood pulp, the decrease of HexA in the peroxomolybdate bleaching stage corresponds to more than 60% of the kappa number reduction obtained in that stage. In the case of pine pulp, inclusion of molybdate in the peroxide stage lowered the kappa number by 4.1. This work also shows that hydrogen peroxide, in the absence of molybdate, did not react to any noticeable extent with neither the lignin model compounds or HexA, under otherwise similar conditions. In order to investigate the oxidation mechanism, lignin model compounds with different side chain structures were reacted with peroxomolybdate. 1H-NMR revealed that lignin model compounds with double bond structure in conjugation with the aromatic ring has an extreme fast speed to react with the peroxomolybdate catalysts systems, presumably through hydroxylation reactions. This mechanism was supported by XPS analysis of the pulp samples, in which the activated hydrogen peroxide was found to act in a similar fashion on surface lignin as well. In conclusion, molybdate activated hydrogen peroxide can be considered a very efficient and selective bleaching agent.

  • 128. Taube, Fabian
    et al.
    Ylmén, R
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nietzsche, S
    Norén, J G
    Morphological and chemical characterization of tooth enamel exposed to alkaline agents2010In: Journal of dentistry, ISSN 1879-176X, Vol. 38, no 1, p. 72-81Article in journal (Refereed)
    Abstract [en]

    OBJECTIVES: In this study, morphological and chemical changes in teeth enamel exposed to alkaline agents, with or without surfactants, have been investigated. In addition, chemical effects of the organic surface layer, i.e. plaque and pellicle, were also investigated. METHODS: The present study was conducted using several techniques; Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). RESULTS: From XPS-measurements, it was found that exposure to alkaline solutions resulted in a massive removal of carbon from the tooth surface, and that the addition of surfactants increased the rate under present conditions. Based on the results from the FTIR-analysis, no substitution reactions between phosphate, carbonate and hydroxide ions in the enamel apatite could be detected. From a minor SEM-analysis, degradation and loss of substance of the enamel surface was found for the exposed samples. From XRD-analysis, no changes in crystalinity of the enamel apatite could be found between the samples. CONCLUSIONS: The findings in this study show that exposure to alkaline solutions results in a degradation of enamel surfaces very dissimilar from acidic erosion. No significant erosion or chemical substitution of the apatite crystals themselves could be discerned. However, significant loss of organic carbon at the enamel surface was found in all exposed samples. The degradation of the protective organic layer at the enamel surface may profoundly increase the risk for caries and dental erosion from acidic foods and beverages.

  • 129.
    Trubetskaya, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Hofmann Larsen, Flemming
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ståhl, Kenny
    Umeki, Kentaro
    Potassium and soot interaction in fast biomass pyrolysis at high temperatures2018In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 225, p. 89-94Article in journal (Refereed)
    Abstract [en]

    This study aims to investigate the interaction between potassium and carbonaceous matrix of soot produced from wood and herbaceous biomass pyrolysis at high heating rates at 1250°C in a drop tube reactor. The influence of soot carbon chemistry and potassium content in the original biomass on the CO2 reactivity was studied by thermogravimetric analysis. The XPS results showed that potassium incorporation with oxygen-containing surface groups in the soot matrix did not occur during high temperature pyrolysis. The potassium was mostly found as water-soluble salts such as KCl, KOH, KHCO3 and K2CO3 in herbaceous biomass soot. The low ash-containing pinewood soot was less reactive than the potassium rich herbaceous biomass soot, indicating a dominating role of potassium on the soot reactivity. However, the catalytic effect of potassium on the reactivity remained the same after a certain potassium amount was incorporated in the soot matrix during pyrolysis. Raman spectroscopy results showed that the carbon chemistry of biomass soot also affected the CO2 reactivity. The less reactive pinewood soot was more graphitic than herbaceous biomass soot samples with the disordered carbon structure.

  • 130. Viipsi, K.
    et al.
    Sjöberg, S.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tõnsuaadu, K.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cd2+ and Zn2+ sorption on apatite in the presence of EDTA and humic substance2013In: Proceedings of the 16th International Conference on Heavy Metals in the Environment / [ed] Pirrone, N, EDP Sciences, 2013, article id 01008Conference paper (Refereed)
    Abstract [en]

    The sorption of Cd2+ and Zn2+ on hydroxyapatite [HAP-Ca-10(PO4)(6)(OH)(2)] and fluorapatite [FAP-Ca-10(PO4)(6)(F)(2)] with different specific surface area and stoichiometry was investigated in batch experiments in the pH range 4 to 11 (25 degrees C; 0.1 M KNO3). The impact of different conditions was concerned: solution pH, the presence of complexing ligands (EDTA and humic substance) and competing metal ions, as well as reaction kinetic and equilibrium conditions. To evaluate the reversibility of Cd2+ sorption onto HAP, desorption characteristics in water, Ca, EDTA, and HUM-solutions were determined. Additionally to solution analysis the surface composition of solid phases was analysed by X-Ray Photoelectron Spectroscopy (XPS). The information from the chemical analyses was used to design an equilibration model that takes into account dissolution, surface potential, solution and surface complexation, as well as possible phase transformations. It was revealed that apatites effectively sorb Cd2+ and Zn2+ by ion exchange reactions on surface by formation of new surface phases. Using XPS the formation of a Me-enriched HAP surface was found, which was interpreted as the formation of a solid solution with the general formula: Ca8.4-xMex(HPO4)(1.6)(PO4)(4.4)(OH)(0.4). In a binary solution (Cd+ Zn) the competition of metals reduced individual sorbed amount compared with the single component solutions but the total adsorption maximum was approximately constant. The presence of EDTA reduces the metal sorption on apatite due to [CdEDTA](2)- and [ZnEDTA] 2-complexes and increases apatite solubility due to [CaEDTA](2)-complex formation. The dissolved humic substance was bound on apatite in suspensions but the amount of Cd2+ bound was not changed. The results showed that the solution pH and the presence of complexing ligands have a significant effect on heavy metal sorption on apatite and must be considered if apatites are used as remediation agent. The proposed model can be used to predict apatite dissolution and surface phase transformations in the presence of metal ions and EDTA.

  • 131. Viipsi, Karin
    et al.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tõnsuaadu, Kaia
    Surface phase transformations, surface complexation and solubilities of hydroxyapatite in the absence/presence of Cd(II) and EDTA2012In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 27, no 1, p. 15-21Article in journal (Refereed)
    Abstract [en]

    The removal of Cd from aqueous solutions by hydroxyapatite (HAP) was investigated with and without EDTA being present. Batch experiments were carried out using synthetic hydroxyapatite with Ca/P 1.57 and a specific surface area of 37.5 m2/g in the pH range 4–9 (25 °C; 0.1 M KNO3). The surface composition of the solid phases were analysed by X-ray Photoelectron Spectroscopy (XPS). The surface layer of HAP was found to undergo a phase transformation with a (Ca + Cd)/P atomic ratio of 1.4 and the involvement of an ion exchange process (Ca2+ ↔ Cd2+). The amount of Cd removed from the solution increased with increasing pH, reaching ≈100% at pH 9. In the presence of EDTA Cd removal was reduced due to the formation of [CdEDTA]2− in solution. The solubility of HAP increases in the presence of EDTA at pH values above 5, mainly due to the formation of [CaEDTA]2−. In contrast to this, the solubility was found to decrease in the presence of Cd2+ and CdEDTA2−. Using XPS the formation of a Cd-enriched HAP surface was found, which was interpreted as the formation of a solid solution of the general composition: Ca8.4-xCdx(HPO4)1.6(PO4)4.4(OH)0.4.

    The information from the chemical analyses and XPS data was used to design an equilibrium model that takes into account dissolution, solution and surface complexation, as well as possible phase transformations. The total concentration of Ca, phosphate, EDTA, and Cd in solution were used in the equilibrium analysis. In the calculations the computer code WinSGW, which is based on the SOLGASWATER algorithm, was used. The following equilibria and compositions of the solid solutions were found to give the best fit to experimental data: . The corresponding value for the composition Ca5.6Cd2.8(HPO4)1.6(PO4)4.4(OH)0.4(s) is −27.39 ± 0.06.

    The proposed model can be used to predict HAP dissolution and surface phase transformations in the presence of Cd and EDTA.

  • 132. Viipsi, Karin
    et al.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tõnsuaadu, Kaia
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hydroxy- and fluorapatite as sorbents in Cd(II) - Zn(II) multi-component solutions in the absence/presence of EDTA2013In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 252-253, p. 91-98Article in journal (Refereed)
    Abstract [en]

    Apatites are suitable sorbent materials for contaminated soil and water remediation because of their low solubility and ability to bind toxic metals into their structure. Whereas in soil/water systems different complexing ligands are present, it is important to examine how these ligands affect apatite metal sorption process. The removal of cadmium (Cd) and zinc (Zn) ions from aqueous solutions by hydroxyapatite (HAP) and fluorapatite (FAP) was investigated by batch experiments with and without EDTA being present in the pH range 4 to 11. The surface composition of the solid phases was analysed by X-ray photoelectron spectroscopy (XPS). The surface layer of apatites (AP), according to the (Ca + Cd + Zn):P atomic ratio, remained constant (1.4 ± 0.1) through an ion exchange. The amount of Cd2+ and Zn2+ removed increased with increasing pH. The removed amount of Zn2+ was higher than Cd2+. In the Cd-Zn binary system, competitive sorption reduced the individual removed amounts but the total maximum sorption was approximately constant. In the presence of EDTA, Cd2+ and Zn2+ removal was reduced because of the formation of [CdEDTA]2− and [ZnEDTA]2− in solution. XPS revealed an enrichment of AP surface by Cd2+ and Zn2+ and formation of new surface solid-solution phase with the general composition Ca8.4-xMex(HPO4)1.6(PO4)4.4(OH)0.4.

  • 133.
    Wahlqvist, Mattias
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    XPS spectra and electronic structure of Group IA sulfates2007In: Journal of Electron Spectroscopy and Related Phenomena, Vol. 156-158, p. 310-14Article in journal (Refereed)
    Abstract [en]

    The results of systematic XPS measurements of Group IA (H, Li, Na, K, Rb and Cs) sulfates together with NaHSO4, KHSO4 and (NH4)2SO4 are presented. The experiments on the alkali metal salts were preformed on ground powders at both liquid nitrogen and room temperatures; concentrated sulfuric acid was measured as a fast-frozen liquid drop. Spectra from grounded and floated samples were compared, and no significant difference relating to charging effects was observed. The influence of grinding on surface chemistry of the powders is described. Such a mechanical activation produces mainly monohydrates on the surface of all sulfates. In the case of Na2SO4, an additional NaHSO4 surface phase seems to form that is not stable in vacuum even at liquid nitrogen temperatures.

    It was found that the binding energies (O 1s and S 2p) of sulfate ion decrease down the group. The shifts are discussed and related to ionicity of the metal–sulfate bond.

    The structure of XPS valence band spectra is in good agreement with cluster calculations of SO42− and HSO4− [A.A. Audi, P.M.A. Sherwood, Surf. Interface Anal. 29 (2000) 265]. While the energies of bisulfate bands are not influenced by the cation (H+, Na+ or K+), the sulfate ones experience an increase in bond ionicity and demonstrate the same binding energy shifts as the core levels.

  • 134. Wan, Moli
    et al.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lohmayer, Regina
    Planer-Friedrich, Britta
    Peiffer, Stefan
    Occurrence of Surface Polysulfides during the Interaction between Ferric (Hydr)Oxides and Aqueous Sulfide2014In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 48, no 9, p. 5076-5084Article in journal (Refereed)
    Abstract [en]

    Polysulfides are often referred to as key reactants in the sulfur cycle, especially during the interaction of ferric (hydr)oxides and sulfide, forming ferrous-sulphide minerals. Despite their potential relevance, the extent of polysulfide formation and its relevance for product formation pathways remains enigmatic. We applied cryogenic X-ray Photoelectron Spectroscopy and wet chemical analysis to study sulfur oxidation products during the reaction of goethite and lepidocrocite with aqueous sulfide at different initial Fe/S molar ratios under anoxic conditions at neutral pH. The higher reactivity of lepidocrocite leads to faster and higher electron turnover compared to goethite. We were able to demonstrate for the first time the occurrence of surface-associated polysulfides being the main oxidation products in the presence of both minerals, with a predominance of disulfide (S22?(surf)), and elemental sulfur. Concentrations of aqueous polysulfide species were negligible (<1%). With prior sulfide fixation by zinc acetate, the surface-associated polysulfides could be precipitated as zerovalent sulfur (S°), which was extracted by methanol thereafter. Of the generated S°, 20?34% were associated with S22?(surf). Varying the Fe/S ratio revealed that surface polysulfide formation only becomes dominant when the remaining aqueous sulfide concentration is low (<0.03 mmol L?1). We hypothesize these novel surface sulfur species, particularly surface disulfide, to act as pyrite precursors. We further propose that these species play an overlooked role in the sulfur cycle.

  • 135. Wu, Ming-Chung
    et al.
    Hiltunen, Jussi Tapio
    Sápi, András
    Avila, Anna
    Larsson, William
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Liao, Hsueh-Chung
    Huuhtanen, Mika
    Tóth, Géza
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Laufer, Noémi
    Kukovecz, Akos
    Konya, Zoltan
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Keiski, Riitta
    Su, Wei-Fang
    Chen, Yang-Fang
    Jantunen, Heli
    Ajayan, Pulickel M
    Vajtai, Robert
    Kordás, Krisztián
    Nitrogen-doped anatase nanofibers decorated with noble metal nanoparticles for photocatalytic production of hydrogen2011In: ACS NANO, Vol. 5, no 6, p. 5025-5030Article in journal (Refereed)
    Abstract [en]

    We report the synthesis of N-doped TiO2 nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol-water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N-Ti bonds appear in the lattice resulting in slight lattice expansion as shown by XPS and HR-TEM analyses, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests the N-doped samples were clearly outperforming their un-doped counterparts showing remarkable efficiency not only under UV-B but also with UV-A illumination. Applying 100 mg catalyst (N-doped TiO2 nanofiber decorated with Pt nanoparticles) in 1 L water-ethanol mixture the H2 evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h (UV-B) corresponding to photo energy percentages of ~3.6% and ~12.3%, respectively.

  • 136. Wu, Ming-Chung
    et al.
    Liao, Hsueh-Chung
    Cho, Yu-Cheng
    Hsu, Che-Pu
    Lin, Ting-Han
    Su, Wei-Fang
    Sapi, Andras
    Kukovecz, Akos
    Konya, Zoltan
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sarkar, Anjana
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Larsson, William
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Åbo Akademi University, Åbo-Turku, Finland.
    Mohl, Melinda
    Toth, Geza
    Jantunen, Heli
    Valtanen, Anna
    Huuhtanen, Mika
    Keiski, Riitta L.
    Kordas, Krisztian
    Photocatalytic activity of nitrogen-doped TiO2-based nanowires: a photo-assisted Kelvin probe force microscopy study2013In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 16, no 1, p. Article Number: UNSP 2143-Article in journal (Refereed)
    Abstract [en]

    In this study, a set of nitrogen-doped TiO2-based nanomaterials demonstrating photocatalytic activity was developed by combining the efforts of lattice doping and metal nanoparticle decoration and tested for photo-degradation of methylene blue dye by applying solar simulator irradiation. The surface potential shifts of these TiO2-based photocatalytic nanomaterials measured by Kelvin probe force microscope have been used to study the degree of electron generation of the photocatalysts after irradiation and were well correlated with the photocatalytic activity. The nitrogen-doped TiO2 nanowires decorated with Pt nanoparticles can induce obvious electron accumulation and result in a large shift of surface potential. The analysis shows a clear correlation between the surface potential shift and the photodegradation activity. Furthermore, a thorough comparative photocatalytic activity study combined with X-ray photoelectron spectroscopy analysis of the materials-doped with nitrogen under various conditions-reveals that the photocatalytic efficiency of the catalysts is maintained even if the lattice doping is leached e.g., by thermal treatments after doping. By monitoring the surface potential shifts of various TiO2-based photocatalysts by photo-assisted Kelvin probe force microscopy, we obtain a useful tool for developing novel materials with high photocatalytic activity.

  • 137.
    Yanamandra, Kiran
    et al.
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
    Alexeyev, Oleg
    Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
    Zamotin, Vladimir
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
    Srivastava, Vaibhav
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Brorsson, Ann-Christin
    Department of Chemistry, University of Cambridge, Cambridge, United Kingdom.
    Tartaglia, Gian Gaetano
    Department of Chemistry, University of Cambridge, Cambridge, United Kingdom.
    Vogl, Thomas
    Institute of Immunology, University of Münster, Münster, Germany.
    Kayed, Rakez
    Department of Neurology, University of Texas Medical Branch, Galveston, Texas, United States of America.
    Wingsle, Gunnar
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Olsson, Jan
    Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
    Dobson, Christopher M
    Department of Chemistry, University of Cambridge, Cambridge, United Kingdom.
    Bergh, Anders
    Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
    Elgh, Fredrik
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Morozova-Roche, Ludmilla A
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
    Amyloid formation by the pro-inflammatory S100A8/A9 proteins in the ageing prostate2009In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 4, no 5, p. e5562-Article in journal (Refereed)
    Abstract [en]

    Background The conversion of soluble peptides and proteins into polymeric amyloid structures is a hallmark of many age-related degenerative disorders, including Alzheimer's disease, type II diabetes and a variety of systemic amyloidoses. We report here that amyloid formation is linked to another major age-related phenomenon - prostate tissue remodelling in middle-aged and elderly men.

    Methodology/Principal Findings By using multidisciplinary analysis of corpora amylacea inclusions in prostate glands of patients diagnosed with prostate cancer we have revealed that their major components are the amyloid forms of S100A8 and S100A9 proteins associated with numerous inflammatory conditions and types of cancer. In prostate protease rich environment the amyloids are stabilized by dystrophic calcification and lateral thickening. We have demonstrated that material closely resembling CA can be produced from S100A8/A9 in vitro under native and acidic conditions and shows the characters of amyloids. This process is facilitated by calcium or zinc, both of which are abundant in ex vivo inclusions. These observations were supported by computational analysis of the S100A8/A9 calcium-dependent aggregation propensity profiles. We found DNA and proteins from Escherichia coli in CA bodies, suggesting that their formation is likely to be associated with bacterial infection. CA inclusions were also accompanied by the activation of macrophages and by an increase in the concentration of S100A8/A9 in the surrounding tissues, indicating inflammatory reactions.

    Conclusions/Significance These findings, taken together, suggest a link between bacterial infection, inflammation and amyloid deposition of pro-inflammatory proteins S100A8/A9 in the prostate gland, such that a self-perpetuating cycle can be triggered and may increase the risk of malignancy in the ageing prostate. The results provide strong support for the prediction that the generic ability of polypeptide chains to convert into amyloids could lead to their involvement in an increasing number of otherwise apparently unrelated diseases, particularly those associated with ageing.

  • 138. Yu, Changxun
    et al.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Drake, Henrik
    Song, Zhaoliang
    Hogmalm, K. Johan
    Åström, Mats E.
    A cryogenic XPS study of Ce fixation on nanosized manganite and vernadite: Interfacial reactions and effects of fulvic acid complexation2018In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 483, p. 304-311Article in journal (Refereed)
    Abstract [en]

    This study investigated interfacial reactions between aqueous Ce(III) and two synthetic nanosized Mn (hydr-)oxides (manganite: γ-MnOOH, and vernadite: δ-MnO2) in the absence and presence of Nordic Lake fulvic acid (NLFA) at circumneutral pH by batch experiments and cryogenic X-ray photoelectron spectroscopy (XPS). The surfaces of manganite and vernadite were negatively charged (XPS-derived loadings of (Na + K)/Cl > 1) and loaded with 0.42–4.33 Ce ions nm−2. Manganite stabilized Ce-oxidation states almost identical to those for vernadite (approximately 75% Ce(IV) and 25% Ce(III)), providing the first experimental evidence that also a Mn(III) phase (manganite) can act as an important scavenger for Ce(IV) and thus, contribute to the decoupling of Ce from its neighboring rare earth elements and the development of Ce anomaly. In contrast, when exposed to Ce(III)-NLFA complexes, the oxidation of Ce by these two Mn (hydr-)oxides was strongly suppressed, suggesting that the formation of Ce(III) complexes with fulvic acid can stabilize Ce(III) even in the presence of oxidative Mn-oxide surfaces. The experiments also showed that Ce(III) complexed with excess NLFA was nearly completely removed, pointing to a strong preferential sorption of Ce(III)-complexed NLFA over free NLFA. This finding suggests that the Ce(III)-NLFA complexes were most likely sorbed by their cation side, i.e. Ce(III) bridging between oxide groups on the Mn (hydr-)oxides and negatively-charged functional groups in NLFA. Hence, Ce(III) was in direct contact with the oxidative manganite and vernadite but despite that not oxidized. An implication is that in organic-rich environments there may be an absence of Ce(IV) and Ce anomaly despite otherwise favorable conditions for Ce(III) oxidation.

  • 139.
    Öberg, Kjell
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Edlund, Ulf
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Seshadri, Kannan
    Allara, David
    Spectroscopic Characterization of the Bonding, Orientation, and Coverage of Copper Tetraazaphthalocyanine Monolayer Films on SiO2 Surfaces2000In: The Journal of Physical Chemistry B, Vol. 104, no 45, p. 10627-34Article in journal (Refereed)
    Abstract [en]

    Self-assembled monolayer films of a metallotetraazaphthalocyanine were prepared using two different reaction conditions. The films were characterized by ellipsometry, AFM, electronic absorption spectroscopy, semiempirical MO calculations, core-level XPS, and projection of a calculated structure of the chromophore onto a surface to obtain its silhouette area for comparison with surface concentration from absorption spectroscopy. A denser packing of the chromophores is found in the SAM film prepared with bromonaphthalene at 250 C as compared with the film from the more polar solvent DMF at 120 C. Data is consistent with an almost vertical orientation of the chromophores in the former film. A different number of bonds connecting the chromophore with the coupling molecule is suggested as an explanation to differences in the absorption bands for the two films.

  • 140.
    Öberg, Kjell
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Chemistry.
    Comparison of monolayer films of stearic acid and methyl stearate on an Al2O3 surface2001In: Thin Solid Films, Vol. 397, no 1-2, p. 102-8Article in journal (Refereed)
    Abstract [en]

    Both stearic acid and methyl stearate chemisorbs onto an oxide surface of aluminum with an asymmetric coordination of the carboxylate group as concluded from infrared (IR) spectroscopy data. Similarities in the IR spectra of the films from the two compounds suggest that the ester is bonded in the same way as the acid, and that the ester therefore undergoes hydrolysis during the surface reaction. X-Ray photoelectron spectroscopy (XPS) and IR data are interpreted in terms of self-assembled monolayer formation and a more dense film from the carboxylic acid in comparison with that from the ester.

123 101 - 140 of 140
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