[NEWS] Our review is one of the hotest articles in august!

at the Journal of Materials Chemistry A: http://blogs.rsc.org/jm/2013/08/07/hot-articles-for-august/

Functional hybrids based on biogenic nanofibrils and inorganic nanomaterials

Bernd Wicklein and German Salazar-Alvarez
J. Mater. Chem. A, 2013,1, 5469-5478 
DOI: 10.1039/C3TA01690K, Feature Article

[OPEN ACCESS] Anomalous Magnetic Properties of Nanoparticles Arising from Defect Structures: Topotaxial Oxidation of Fe1-xO|Fe3-δO4 Core|Shell Nanocubes to Single-Phase Particles

ACS Nano, 2013

DOI: 10.1021/nn402487q

Erik Wetterskog , Cheuk-Wai Tai , Jekabs Grins , Lennart Bergström, and German Salazar-Alvarez

Abstract:

Here we demonstrate that the anomalous magnetic properties of iron oxide nanoparticles are correlated with defects in their interior. We studied the evolution of microstructure and magnetic properties of biphasic core|shell Fe1-xO|Fe3-δO4 nanoparticles synthesized by thermal decomposition during their topotaxial oxidation to single-phase nanoparticles. Geometric phase analysis of high-resolution electron microscopy images reveals a large interfacial strain at the core|shell interface and the development of anti-phase boundaries. Dark-field transmission electron microscopy and powder x-ray diffraction concur that, as the oxidation proceeds, the interfacial strain is released as the Fe1-xO core is removed, but that the anti-phase boundaries remain. The anti-phase boundaries result in anomalous magnetic behavior, i.e., a reduced saturation magnetization and exchange bias effects in single-phase nanoparticles. Our results indicate that internal defects play an important role in dictating the magnetic properties of iron oxide nanoparticles.

[REVIEW][OPEN ACCESS] Dispersion and surface functionalization of oxide nanoparticles for transparent photocatalytic and UV-protecting coatings and sunscreens

Sci. Technol. Adv. Mater. 14 (2013) 023001
doi:10.1088/1468-6996/14/2/023001

Bertrand Faure, German Salazar-Alvarez, Anwar Ahniyaz, Irune Villaluenga, Gemma Berriozabal, Yolanda R De Miguel and Lennart Bergström

Abstract

This review describes recent efforts on the synthesis, dispersion and surface functionalization of the three dominating oxide nanoparticles used for photocatalytic, UV-blocking and sunscreen applications: titania, zinc oxide, and ceria. The gas phase and liquid phase synthesis is described briefly and examples are given of how weakly aggregated photocatalytic or UV-absorbing oxide nanoparticles with different composition, morphology and size can be generated. The principles of deagglomeration are reviewed and the specific challenges for nanoparticles highlighted. The stabilization of oxide nanoparticles in both aqueous and non-aqueous media requires a good understanding of the magnitude of the interparticle forces and the surface chemistry of the materials. Quantitative estimates of the Hamaker constants in various media and measurements of the isoelectric points for the different oxide nanoparticles are presented together with an overview of different additives used to prepare stable dispersions. The structural and chemical requirements and the various routes to produce transparent photocatalytic and nanoparticle-based UV-protecting coatings, and UV-blocking sunscreens are described and discussed.

Correlating material-specific layers and magnetic distributions within onion-like Fe3O4/MnO/γ-Mn2O3 core/shell nanoparticles

J. Appl. Phys. 113, 17B531 (2013)

K. L. Krycka; J. A. Borchers; M. Laver; G. Salazar-Alvarez; A. López-Ortega; M. Estrader; S. Suriñach; M. D. Baró; J. Sort; J. Nogués

DOI: 10.1063/1.4801423

Abstract
The magnetic responses of two nanoparticle systems comprised of Fe₃O₄/γ-Mn₂O₃ (soft ferrimagnetic, FM/hard FM) and Fe₃O₄/MnO/γ-Mn₂O₃ (soft FM/antiferromagnetic, AFM/hard FM) are compared, where the MnO serves to physically decouple the FM layers. Variation in the temperature and applied field allows for Small Angle Neutron Scattering (SANS) measurements of the magnetic moments both parallel and perpendicular to an applied field. Data for the bilayer particle indicate that the graded ferrimagnetic layers are coupled and respond to the field as a single unit. For the trilayer nanoparticles, magnetometry suggests a Curie temperature (T_C) ≈ 40 K for the outer γ-Mn₂O₃component, yet SANS reveals an increase in the magnetization associated with outer layer that is perpendicular to the applied field above T_C during magnetic reversal. This result suggests that the γ-Mn₂O₃ magnetically reorients relative to the applied field as the temperature is increased above 40 K.

6 PhD positions in Physical, Inorganic, Materials and Environmental Chemistry

6 PhD positions in Physical, Inorganic, Materials and Environmental Chemistry at the Department of Materials and Environmental Chemistry. Reference number SU FV-1026-13 (project numbers – see below). Deadline for applications: May 2, 2013.

Application to the graduate research program (PhD studies) at MMK, April 2013
The Department of Materials and Environmental Chemistry (MMK), www.mmk.su.se, offers 6 new places for graduate students after an application procedure as described below.

General information
The extensive research activities of MMK, hosting the Berzelii Center EXSELENT for development of nanoporous materials for catalysis, span over Materials and Solid State Chemistry focusing on different classes of materials; e.g. ceramics and glasses, self-assembled and porous materials, and soft matter. The work often encompasses synthesis, characterisation by X-ray diffraction and electron microscopy, NMR studies, modelling with computer simulations of materials with a potential for various applications. Environmental aspects are an important part of the research activities, where refined natural or anthropogenic inorganic and organic chemicals and materials are studied in relation to their sole or combined impact on, and interaction with biological and non-biological systems in our global environment.

More information about available projects, requirements, and details about the application procedure at:

http://www.su.se/english/about/vacancies/phd-studies/6-phd-positions-in-physical-inorganic-materials-and-environmental-chemistry-1.129642

[OPEN ACCESS] Structural diversity in iron oxide nanoparticle assemblies as directed by particle morphology and orientation

Nanoscale, 2013, Just Accepted Manuscript

Sabrina Disch,  Erik Wetterskog,  Raphaël P. Hermann,  Denis Korolkov,  Peter Busch,  Peter Boesecke,  Olivier Lyon,  Ulla Vainio,  German Salazar-Alvarez,  Lennart Bergström and Thomas Brückel

DOI: 10.1039/C3NR33282A

Abstract:

The mesostructure of ordered arrays of anisotropic nanoparticles is controlled by a combination of packing constraints and interparticle interactions, two factors that are strongly dependent on the particle morphology. We have investigated how the degree of truncation of iron oxide nanocubes controls the mesostructure and particle orientation in drop cast mesocrystal arrays. The combination of grazing incidence small angle X-ray scattering and scanning electron microscopy shows that mesocrystals of highly truncated cubic nanoparticles assemble in an fcc-type mesostructure - similar to arrays formed by iron oxide nanospheres, but with a significantly reduced packing density and displaying two different growth orientations. Strong satellite reflections in the GISAXS pattern indicate a commensurate mesoscopic superstructure that is related to stacking faults in mesocrystals of the anisotropic nanocubes. Our results show how subtle variation in shape anisotropy can induce oriented arrangements of nanoparticles of different structures and also create mesoscopic superstructures of larger periodicity.

Preparation of dry ultra-porous cellulosic fibres: Characterization and possible initial uses

Carbohydrate Polymers, 92 (2013) 775–783

Anna Svensson, Per Tomas Larsson, German Salazar-Alvarez, Lars Wågberg

DOI: 10.1016/j.carbpol.2012.09.090

Abstract


Dry ultra-porous cellulose fibres were obtained using a liquid exchange procedure in which water was replaced in the following order: water, methanol, acetone, and finally pentane; thereafter, the fibres were dried with Ar(g). The dry samples (of TEMPO-oxidized dissolving pulp) had a specific surface area of 130 m2 g−1as measured using BET nitrogen gas adsorption. The open structure in the dry state was also revealed using field emission scanning electron microscopy.

This dry open structure was used as a scaffold for in situ polymerization. Both poly(methyl methacrylate) and poly(butylacrylate) were successfully used as matrix polymers for the composite material (fibre/polymer), comprising approximately 20 wt% fibres. Atomic force microscopy phase imaging indicated a nanoscale mixing of the matrix polymer and the cellulose fibril aggregates and this was also supported by mechanical testing of the prepared composite where the open fibre structure produced superior composites. The fibre/polymer composite had a significantly reduced water absorption capacity also indicating an efficient filling of the fibre structure with the matrix polymer.

[REVIEW] [OPEN ACCESS] Functional hybrids based on biogenic nanofibrils and inorganic nanomaterials

Bernd Wicklein and German Salazar-Alvarez

J. Mater. Chem. A, 2013, Accepted Manuscript

DOI: 10.1039/C3TA01690K

Abstract:

This feature article reviews some of the recent work on the fabrication of functional hybrids based on biogenic nanofibers and inorganic nanomaterials with an emphasis on the functional properties and suggested potential applications. We also discuss some of the work oriented towards the formation of ordered materials in the pursuit of achieving a hierarchical construction. Besides the academic interest in biogenic nanomaterials, it is anticipated that the use of natural, abundant nanomaterials, e.g., cellulose, chitin, collagen, and silk, could provide affordable functional nanomaterials in developing countries.

Resolving Material-Specific Structures within Fe3O4|γ-Mn2O3 Core|Shell Nanoparticles Using Anomalous Small-Angle X-ray Scattering

ACS Nano 2013, 7, 921-931.

Kathryn L. Krycka, Julie A. Borchers, German Salazar-Alvarez, Alberto López-Ortega , Marta Estrader, Sonia Estradé, Elin Winkler, Roberto Daniel Zysler, Jordi Sort, Francesca Peiró, Maria Dolors Baró, Chi-Chang Kao and Josep Nogués

DOI: 10.1021/nn303600e

http://pubs.acs.org/doi/abs/10.1021/nn303600e

Abstract:

The material specific structure of monodispersed Fe3O4|γ-Mn2O3 core|shell nanoparticles is determined using multiple energy, anomalous, small-angle x-ray scattering (ASAXS). The contribution of each component to the total scattering profile is identified with unprecedented clarity. We show that Fe3O4|γ-Mn2O3 core|shell nanoparticles with a diameter of 8.2 nm ± 0.2 nm consist of a core with a composition near Fe3O4 surrounded by a (MnXFe1−X)3O4 shell with a graded composition, i.e., ranging from X ≈ 0.40 at the inner shell toward X ≈ 0.46 at the surface. Evaluation of the scattering contribution arising from the interference between material-specific layers additionally reveals the presence of Fe3O4cores without a coating shell. Importantly, the present analysis enhances the sensitivity of the method with regard to the chemical boundaries and internal nanoparticle morphology compared with traditional approaches. Finally, it is found that the material-specific scattering profile shapes and chemical compositions extracted by this method are independent of the original input chemical compositions used in the analysis, revealing multi-energy ASAXS as a powerful tool for determining internal nanostructured morphology even if the exact composition of the individual layers is not known a priori.

[OPEN ACCESS] 2D to 3D crossover of the magnetic properties in ordered arrays of iron oxide nanocrystals - Nanoscale (RSC Publishing)

Nanoscale 5 (2013) 953-960.

Bertrand Faure , Erik Wetterskog , Klas Gunnarsson , Elisabeth Josten , Raphaël P. Hermann , Thomas Brückel , Jens Wenzel Andreasen , Florian Meneau , Mathias Meyer , Alexander P Lyubartsev , Lennart Bergström , German Salazar-Alvarez and Peter Svedlindh

DOI: 10.1039/C2NR33013JD

http://pubs.rsc.org/en/Content/ArticleLanding/2013/NR/c2nr33013j

Abstract:

The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain γ-Fe2O3 spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC) simulations. Using structural information of the arrays obtained from grazing incidence small-angle X-ray scattering and scanning electron microscopy together with experimentally determined values for the saturation magnetization and magnetic anisotropy of the nanoparticles, we show that MC simulations can reproduce the thickness-dependent magnetic behavior. The magnetic dipolar particle interactions induce a ferromagnetic coupling that increases in strength with decreasing thickness of the array. The 2D to 3D transition in the magnetic properties is mainly driven by a change in the orientation of the magnetic vortex states with increasing thickness, becoming more isotropic as the thickness of the array increases. Magnetic anisotropy prevents long-range ferromagnetic order from being established at low temperature and the nanoparticle magnetic moments instead freeze along directions defined by the distribution of easy magnetization directions.

25 Positions as Postdoctoral Research Fellow - Stockholm University

25 Positions as Postdoctoral Research Fellow - Stockholm University

25 Positions as Postdoctoral Research Fellow in subject areas within the Faculties of Science, Humanities, Law, and Social Sciences of Stockholm University. 

Ref. No. SU 619-2974-12. 
Deadline for applications: December 17, 2012.

More information on how to apply here.

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If you are interested in applying with a project related to our topics (click here for a description of the activities and list of related publications) and have a strong CV, please contact me directly at german@mmk.su.se.

4 Open PhD positions at MMK - Stockholm University

The Department of Materials and Environmental Chemistry offers 4 new places for graduate students

Application to the graduate research program (PhD 

studies) at MMK, November 2012

The Department of Materials and Environmental Chemistry (MMK,http://www.mmk.su.se/), offers 4 new places for graduate students after an application procedure as described below.

General information:

The extensive research activities of MMK, hosting the Berzelii Center EXSELENT for development of nanoporous materials for catalysis, span over Materials and Solid State Chemistry focusing on different classes of materials; e.g. ceramics and glasses, self-assembled and porous materials, and soft matter. The work often encompasses synthesis, characterisation by x-ray diffraction and electron microscopy, NMR studies, modelling with computer simulations of materials with a potential for various applications. Environmental aspects are an important part of the research activities, where refined natural or anthropogenic inorganic and organic chemicals and materials are studied in relation to their sole or combined impact on, and interaction with biological and non-biological systems in our global environment.

More information on the positions and application procedure here.

The deadline is November 20, 2012

For more information on the project HT12-3: Fabrication of biopolymer–nanoparticle hybrids contact directly the project leader Germán Salazar-Álvarez at german@mmk.su.se .

Stora anslag från Knut och Alice Wallenbergs stiftelse till forskning inom naturvetenskap - Stockholms universitet

Från http://www.wallenberg.com/docs/kaw/pressrelease-2012-10-05.pdf

Drygt 700 miljoner kronor till forskning från Knut och Alice Wallenbergs Stiftelse

 

25 forskningsprojekt som har potential att leda till nya vetenskapliga genombrott beviljas drygt 700 miljoner kronor av Knut och Alice Wallenbergs Stiftelse i årets ansökningsomgång.

 

– Det är mycket glädjande att få bevilja anslag till så många projekt som har bedömts ligga i den internationella forskningsfronten. Att spännvidden på ämnena dessutom sträcker sig från jordens uppkomst till nanomaterial visar att svensk forskning fortfarande håller hög kvalitet på bred front, säger Peter Wallenberg Jr, vice ordförande i Knut och Alice Wallenbergs Stiftelse.

Genom programmet ger Knut och Alice Wallenbergs Stiftelse Sveriges främsta forskare resurser och villkor så att de kan angripa komplexa och svåra forskningsproblem.

I huvudsak stödjer Stiftelsen grundforskning inom medicin, teknik och naturvetenskap.

– Starka grundforskningsmiljöer är fundamentet för framgångsrik tillämpad forskning. Det är ett gott betyg att de internationella bedömargrupperna som utvärderat ansökningarna funnit att så många håller hög klass. För att nå banbrytande rön behövs en långsiktig trygghet som också tillåter misslyckanden, vi hoppas att denna anslagsform medger detta säger Göran Sandberg, verkställande ledamot, Knut och Alice Wallenbergs Stiftelse.

Anslagen delas ut inom tre huvudområden: Teknik/fysik/matematik, övrig naturvetenskap samt medicin.

Mer info finns på www.su.se webbsidan:

Stora anslag från Knut och Alice Wallenbergs stiftelse till forskning inom naturvetenskap - Stockholms universitet