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Westin, Gunnar, ProfessorORCID iD iconorcid.org/0000-0001-6180-5513
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Publications (10 of 65) Show all publications
Marin, R., Oussta, F., Katea, S. N., Prabhudev, S., Botton, G. A., Westin, G. & Hemmer, E. (2019). Europium-doped ZnO nanosponges: controlling optical properties and photocatalytic activity. Journal of Materials Chemistry C, 7(13), 3909-3919
Open this publication in new window or tab >>Europium-doped ZnO nanosponges: controlling optical properties and photocatalytic activity
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2019 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 7, no 13, p. 3909-3919Article in journal (Refereed) Published
Abstract [en]

The optical features and photocatalytic activity of porous undoped and Eu3+-doped zinc oxide (ZnO) sponge-like structures, annealed at various temperatures, were assessed to establish the relationship between structure, morphology and photophysical properties. Upon monitoring the degradation of organic dye rhodamine B, undoped ZnO nanosponges annealed at 800 °C showed the highest photocatalytic activity, being among the best performing ZnO-based photocatalysts reported so far. The observed red- and blue-shift of the characteristic broad-band ZnO emission spectra as a function of the annealing temperature was ascribed to the nature of defects induced into the ZnO structure related to deficiency or excess of oxygen at lower (200 to 400 °C) and higher (500 to 1000 °C) annealing temperatures. These temperature-induced defects - along with the morphological sample characteristics - governed the photocatalytic performance. Doping-induced enhancement of the photocatalytic activity was noticed in specific samples and was found to markedly depend on the intrinsic properties of the undoped material. Overall, annealing temperature and europium doping concentration synergistically contributed to the defect structure, morphology and crystallinity, ultimately determining optical properties and therewith correlated photocatalytic activity.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-382862 (URN)10.1039/c9tc00215d (DOI)000464314700022 ()
Available from: 2019-05-03 Created: 2019-05-03 Last updated: 2019-05-03Bibliographically approved
Rautiainen, S., Di Francesco, D., Katea, S. N., Westin, G., Tungasmita, D. N. & Samec, J. S. M. (2019). Lignin Valorization by Cobalt-Catalyzed Fractionation of Lignocellulose to Yield Monophenolic Compounds. ChemSusChem, 12(2), 404-408
Open this publication in new window or tab >>Lignin Valorization by Cobalt-Catalyzed Fractionation of Lignocellulose to Yield Monophenolic Compounds
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2019 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 12, no 2, p. 404-408Article in journal (Refereed) Published
Abstract [en]

Herein, a catalytic reductive fractionation of lignocellulose is presented using a heterogeneous cobalt catalyst and formic acid or formate as a hydrogen donor. The catalytic reductive fractionation of untreated birch wood yields monophenolic compounds in up to 34 wt % yield of total lignin, which corresponds to 76% of the theoretical maximum yield. Model compound studies revealed that the main role of the cobalt catalyst is to stabilize the reactive intermediates formed during the organosolv pulping by transfer hydrogenation and hydrogenolysis reactions. Additionally, the cobalt catalyst is responsible for depolymerization reactions of lignin fragments through transfer hydrogenolysis reactions, which target the beta-O-4' bond. The catalyst could be recycled three times with only negligible decrease in efficiency, showing the robustness of the system.

Keywords
biomass fractionation, birch wood, cobalt, heterogeneous catalysis, lignin
National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-379235 (URN)10.1002/cssc.201802497 (DOI)000459737500005 ()30485687 (PubMedID)
Funder
Swedish Energy Agency
Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-03-19Bibliographically approved
Katea, S. N., Hajduk, S., Orel, Z. C. & Westin, G. (2017). Low Cost, Fast Solution Synthesis of 3D Framework ZnONanosponges. Inorganic Chemistry, 56(24), 15150-15158
Open this publication in new window or tab >>Low Cost, Fast Solution Synthesis of 3D Framework ZnONanosponges
2017 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 24, p. 15150-15158Article in journal (Refereed) Published
Abstract [en]

An efficient, template-free solution-chemical route to nanostructured ZnO sponges is presented: A mixture of Zn(NO3)(2)center dot 6H(2)O, Zn(OAc)(2).2H(2)O, and triethanolamine in methanol was evaporated to a highly viscous liquid and rapidly heated to >200 degrees C for 1-3 min to achieve highly porous, nanocrystalline sponges of ZnO. The viscous precursor concentrate obtained on evaporation in air was characterized by TG, DSC, and IR spectroscopy, and the product ZnO sponges by XRD, SEM, TEM, and IR spectroscopy. The fast reaction forming ZnO started at 140 degrees C and finished within a few seconds. Scherrer analysis of the XRD peak broadening showed average crystallite sizes of 8 to 11 nm for ZnO prepared by annealing at 200-450 degrees C (3 min), while grain growth to 134 nm was observed from 500 to 900 degrees C (3 min). The ZnO powders obtained at 200-900 degrees C had cell dimensions of a = 3.25 angstrom and b = 5.21 angstrom, matching the ZnO literature data well. SEM and TEM analyses showed highly porous, bread-like 3D nanostructures built by ca. 30-70 nm thick walls of ZnO crystallites of the approximate average sizes given by the XRD Scherrer analysis. It seems that the crystal growth above 450 degrees C takes place within the ZnO 3D structure obtained at lower temperatures without much sintering of the larger porous structure.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-338123 (URN)10.1021/acs.inorgchem.7b02459 (DOI)000418629500048 ()29172508 (PubMedID)
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2018-02-15Bibliographically approved
Kronawitter, C. X., Zegkinoglou, I., Shen, S.-H. -., Liao, P., Cho, I. S., Zandi, O., . . . Vayssieres, L. (2014). Titanium incorporation into hematite photoelectrodes: theoretical considerations and experimental observations. Energy & Environmental Science, 7(10), 3100-3121
Open this publication in new window or tab >>Titanium incorporation into hematite photoelectrodes: theoretical considerations and experimental observations
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2014 (English)In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 7, no 10, p. 3100-3121Article in journal (Refereed) Published
Abstract [en]

A theoretical and experimental perspective on the role of titanium impurities in hematite (alpha-Fe2O3) nanostructured photoelectrodes for solar fuel synthesis devices is provided. Titanium incorporation is a known correlate to efficiency enhancement in alpha-Fe2O3 cc photoanodes for solar water oxidation; here the relevant literature and the latest advances are presented and various proposed mechanisms for enhancement are contrasted. Available experimental evidence suggests that Ti incorporation increases net electron carrier concentrations in electrodes, most likely to the extent that (synthesis-dependent) charge compensating cation vacancies are not present. However, electron conductivity increases alone cannot quantitatively account for the large associated photoelectrochemical performance enhancements. The magnitudes of the effects of Ti incorporation on electronic and magnetic properties appear to be highly synthesis-dependent, which has made difficult the development of consistent and general mechanisms explaining experimental and theoretical observations. In this context, we consider how the electronic structure correlates with Ti impurity incorporation in alpha-Fe2O3 a from the perspective of synchrotron-based soft X-ray absorption spectroscopy measurements. Measurements are performed on sets of electrodes fabricated by five relevant and unrelated chemical and physical techniques. The effects of titanium impurities are reflected in the electronic structure through several universally observed spectral characteristics, irrespective of the synthesis techniques. Absorption spectra at the oxygen K-edge show that Ti incorporation is associated with new oxygen 2p-hybridized states, overlapping with and distorting the known unoccupied Fe 3d-O 2xp band of alpha-Fe2O3. This is an indication of mixing of Ti s and d states in the conduction band of alpha-Fe2O3. cc A comparison of spectra obtained with electron and photon detection shows that the effects of Ti incorporation on the conduction band are more pronounced in the near-surface region. Titanium L-2,L-3-edge absorption spectra show that titanium is incorporated into alpha-Fe2O3 as Ti4+ by all fabrication methods, with no long-range titania order detected. Iron L-2,L-3-edge absorption spectra indicate that Ti incorporation is not associated with the formation, of any significant concentrations of Fe2+, an observation common to many prior studies on this material system.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-236047 (URN)10.1039/c4ee01066c (DOI)000342884300001 ()
Available from: 2014-11-18 Created: 2014-11-12 Last updated: 2017-12-05Bibliographically approved
Kritikos, M., Moustiakimov, M. & Westin, G. (2012). Synthesis, structure and properties of two unexpected square pyramidal pentanuclear oxo-isopropoxide molecules: Ce5O(OPri)13 and La5O(OPri)13(HOPri)2. Inorganica Chimica Acta, 384, 125-132
Open this publication in new window or tab >>Synthesis, structure and properties of two unexpected square pyramidal pentanuclear oxo-isopropoxide molecules: Ce5O(OPri)13 and La5O(OPri)13(HOPri)2
2012 (English)In: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 384, p. 125-132Article in journal (Refereed) Published
Abstract [en]

The synthesis, structure and properties of two pentanuclear oxo-alkoxides are described. A combination of metathesis of LnCl(3) and 3KOPr(i) and stoichiometric hydrolysis resulted in the solvated oxo-alkoxide La5O(OPri)(13)(HOPri)(2) (1) and the non-solvated Ce5O(OPri)(13) (3). 1 is rather stable at room-temperature, but desolvation into La5O(OPri)(13) (2), identified by spectroscopy, could be achieved by vacuum treatment. 1 and 3 were structurally characterised by single-crystal X-ray diffraction. In both 1 and 3 the metal atoms have a square pyramidal arrangement. In 1, each crystallographically independent La5O(OPri)(13) (HOPri)(2) molecule contains 3 six-coordinated and 2 seven-coordinated La atoms, while in 3 all Ce atoms are six-coordinated. 3 Is the first structurally characterized example of a purely Ce3+ isopropoxide. Characterisations of 1 and 3 were by IR- and Raman spectroscopy and differential scanning calorimetry, and for 1 also by H-1 and C-13 NMR spectroscopy. The great similarity of the IR spectra of the solid 1 and 3, respectively, to their corresponding solutions, showed that the molecular structure present in the solid state is close to retained in solution.

Keywords
Lanthanide, Alkoxides, Oxo-ligand, Cerium, Lanthanum, Metathesis
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-172026 (URN)10.1016/j.ica.2011.11.041 (DOI)000301179600017 ()
Available from: 2012-04-02 Created: 2012-04-01 Last updated: 2017-12-07Bibliographically approved
Mäkie, P., Westin, G., Persson, P. & Österlund, L. (2011). Adsorption of Trimethyl Phosphate on Maghemite, Hematite, and Goethite Nanoparticles. Journal of Physical Chemistry A, 115(32), 8948-8959
Open this publication in new window or tab >>Adsorption of Trimethyl Phosphate on Maghemite, Hematite, and Goethite Nanoparticles
2011 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, no 32, p. 8948-8959Article in journal (Refereed) Published
Abstract [en]

Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanopartides was studied by in situ DRIFT spectroscopy as a model system for adsorption of organophosphorous (OP) compounds on iron minerals. The iron minerals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area, and pore size distribution. The minerals were found to consist of stoichimetrically and morphologically well-defined maghemite, hematite, and goethite nanoparticles. Analysis of in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy shows that TMP bonds mainly to Lewis acid Fe sites through the O phosphoryl atom (-P=O-Fe) on hematite and maghemite. On goethite most TMP molecules bond to Bronstedt acid surface OH groups and form hydrogen bonded surface complexes. The vibrational mode analysis and uptake kinetics suggest two main reasons for the observed trend of reactivity toward TMP (hematite > maghemite > goethite): (i) larger number of accessible Lewis acid adsorption sites on hematite; (ii) stronger interaction between the Lewis acid Fe sites and the phosphoryl O atom on TAP for hematite and maghemite compared to goethite with concomitant formation of surface coordinated TMP and dimethyl phosphate intermediates. As a result, on the oxides a surface oxidation pathway dominates during the initial adsorption, which results in the formation of surface methoxy and formate. In contrast, on goethite a slower hydrolysis pathway is identified, which eventually yields phosphoric acid. The observed trends of the reactivity and analysis of the corresponding surface structure and particle morphology suggest an intimate relation between the surface chemistry of exposed crystal facets on the iron minerals. These results are important to understand OP surface chemistry on iron minerals.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-159252 (URN)10.1021/jp201065w (DOI)000293758500021 ()
Available from: 2011-09-26 Created: 2011-09-26 Last updated: 2020-02-18Bibliographically approved
Westin, G., Pohl, A., Ekstrand, Å. & Jansson, K. (2011). Scalable Solution Based Processes to Energy Materials. In: World Journal of Engineering, Issue Suppl (pp. 1437).
Open this publication in new window or tab >>Scalable Solution Based Processes to Energy Materials
2011 (English)In: World Journal of Engineering, Issue Suppl, 2011, p. 1437-Conference paper, Published paper (Refereed)
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-166787 (URN)
Available from: 2012-01-13 Created: 2012-01-13
Boström, T., Valizadeh, S., Lu, J., Jensen, J., Westin, G. & Wäckelgård, E. (2011). Structure and morphology of nickel-alumina/silica solar thermal selective absorbers. Journal of Non-Crystalline Solids, 357(5), 1370-1375
Open this publication in new window or tab >>Structure and morphology of nickel-alumina/silica solar thermal selective absorbers
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2011 (English)In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 357, no 5, p. 1370-1375Article in journal (Refereed) Published
Abstract [en]

Nickel-alumina/silica thin film materials for the use in solar thermal absorbers have been investigated using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Elastic Recoil Detection Analysis (ERDA). The TEM images revealed that all layers have a very small thickness variation and that the layers are completely homogenous. High resolution images showed 5-10 nm (poly) crystalline nickel nano-particles. ERDA showed that both the silica and alumina compositions contain more oxygen than 2:1 and 3:2 respectively. SEM showed the surface morphology and characteristics of the top silica anti-reflection layer. Hybrid-silica has showed to generate a smoother surface with less cracking compared to pure silica. The final curing temperature revealed to be of importance for the formation of cracks and the surface morphology.

Keywords
Solar, Absorber, SEM, TEM, ERDA
National Category
Engineering and Technology Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-151660 (URN)10.1016/j.jnoncrysol.2010.09.023 (DOI)000288726700004 ()
Available from: 2011-04-15 Created: 2011-04-15 Last updated: 2017-12-11Bibliographically approved
Knut, R., Wikberg, J. M., Lashgari, K., Coleman, V. A., Westin, G., Svedlindh, P. & Karis, O. (2010). Magnetic and electronic characterization of highly Co-doped ZnO: An annealing study at the solubility limit. Physical Review B. Condensed Matter and Materials Physics, 82(9), 094438
Open this publication in new window or tab >>Magnetic and electronic characterization of highly Co-doped ZnO: An annealing study at the solubility limit
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 9, p. 094438-Article in journal (Refereed) Published
Abstract [en]

We report on investigations of the electronic structure and magnetic properties of ZnO doped with 15 at. % Co and postgrowth annealed at temperatures ranging between 250 and 800°C. In particular, we demonstrate how the presence of Co3+, indicative of secondary phases, is manifested in spectroscopy. Through resonant photoemmision spectroscopy we have found that x-ray diffraction in some cases underestimates or does not reveal the presence of secondary phases, possibly due to unrelaxed structures or structural arrangements with sizes below the detection limit. The magnetic properties are in most cases understood by assuming small antiferromagnetic clusters but can also show a behavior indicative of ferromagnetic interactions.

National Category
Physical Sciences Engineering and Technology Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-133314 (URN)10.1103/PhysRevB.82.094438 (DOI)000282097200003 ()
Available from: 2010-11-06 Created: 2010-11-06 Last updated: 2017-12-12
Berger, E. & Westin, G. (2010). Structure of a hepta-nuclear termetallic oxo-alkoxide: Eu3K3TiO2(OBut)11(OMe/OH)(HOBut). Journal of Sol-Gel Science and Technology, 53(3), 681-688
Open this publication in new window or tab >>Structure of a hepta-nuclear termetallic oxo-alkoxide: Eu3K3TiO2(OBut)11(OMe/OH)(HOBut)
2010 (English)In: Journal of Sol-Gel Science and Technology, ISSN 0928-0707, E-ISSN 1573-4846, Vol. 53, no 3, p. 681-688Article in journal (Refereed) Published
Abstract [en]

The novel termetallic oxo-methoxo-tert-butoxide Eu3K3TiO2(OBut)11(OMe/OH)(HOBut) (1) has been synthesised and structurally and spectroscopically characterised. Its unusual structure features an Eu3K3O fac-octahedron, capped by a distorted K3TiO tetrahedron on the K3 face. The compound, crystallising in space group P21/n with cell parameters a = 14.44 Å, b = 23.58 Å, c = 21.27 Å and β = 96.18°, is the result of incomplete metathesis between EuCl3 and potassium and titanium tert-butoxides in combination with deliberate hydrolysis and decomposition. It provides one of few examples of termetallic lanthanide alkoxides, as well as of an alkoxide tert-butyl group decomposing into a methyl group.

Keywords
Precursor chemistry, Oxo-alkoxide, Crystal structure, Alkoxide, Sol-gel precursor, Europium, Termetallic alkoxide, Structure
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-121631 (URN)10.1007/s10971-010-2150-8 (DOI)000275161100027 ()
Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2017-12-12Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-6180-5513

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