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Nanostructured Metal Oxides group (NanOxide)

Group members:

Jan-Henrik Smått, Docent (Adjunct Professor) in Nanomaterials, Academy Research Fellow (Academy of Finland)

Motolani Sakeye, PhD student (Nanostructured metal oxides, Academy of Finland)
Björn Törngren, PhD student (Photovoltaic applications, Academy of Finland)
Dennis Kronlund, PhD student (Functional coatings, industrial partner)
Qian Xu, PhD student (Functional coatings, Magnus Ehrnrooth Foundation)
Emil Rosqvist, MSc student (Functional coatings, industrial partner)

Former group members:

Olga Vechter, MSc student, intern (University of Ulm, Germany), 2013
Jiaqi Guo, project researcher, 2012
Richard Fogde, project researcher, 2012 & 2013
Stefan Rommel, MSc student, intern (University of Ulm, Germany), 2011

Research areas

The Nanostructured Metal Oxide (NanOxide) group is focusing on synthesizing novel metal oxide materials (monoliths, microspheres, core-shell structures, and thin films) for the usage in various bio- and energy-related technologies (including phosphopeptide enrichment, chromatography, sensing and solar cells). More specific examples are given below.

Figure 1. A general overview of the research activities of the NanOxide group.

1. Hierarchically porous metal oxide materials

Hierarchically porous carbon and metal oxide materials offer great benefits in the above-mentioned applications, as such structures allow for better vapor diffusion and improved light scattering compared to conventional materials. The materials of interest are mainly prepared using the versatile nanocasting approach, which allows for a precise control of the material morphology, pore structure and chemical composition. In the nanocasting approach, a sacrificial hard silica template is first manufactured using a sol-gel approach. By careful control of the sol composition, macro/mesoporous monoliths with a structure independently tunable at four different length scales can be prepared (Fig. 2). The mesopores of these silica monoliths are then filled with a polymerizable organic monomer or a metal salt, which can be converted to carbon or the desired metal oxide, respectively. In the final step, the silica scaffold is removed by etching in HF or hydroxide solutions.

Figure 2. Hierarchically structured SiO2 monoliths with a controllable structure on four different length scales, which can be used as templates in the nanocasting approach [1].

Several of these metal oxide materials are studied in a number of high-end applications related to bioseparation and sensors through collaborating groups. For instance porous TiO2 and SnO2 spheres have been developed for phosphopeptide enrichment [2], while several types of metal oxide spheres have been used for microcolumn liquid chromatography and phospholipid coatings [3,4]. Another interesting application area of these materials is the use of nanocast SnO2 spheres and monoliths for sensor applications [5].

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2. Advanced materials for photovoltaic applications

Another area of interest is the development of new advanced materials for various photovoltaic applications. The objective here is to apply nanostructured semiconductor metal oxides, like TiO2, SnO2 and ZnO, as light harvesters in dye sensitized solar cells (DSSCs) or photocatalytic water splitting applications. The nanocasting approach described above is one of the cornerstones in the development of these novel materials. In addition to controlling the morphology, pore structure and chemical composition, nanocasting also allows for the control of physical properties like grain boundaries, crystal structure and doping.

Together with the Laboratory of Physics (ÅAU) and RCAST (University of Tokyo, Japan) plasmonic core-shell nanoparticles (Au@SiO2) are also being developed to improve the performance of DSSCs and organic hybrid solar cells. By adjusting the shape and size of the Au nanoparticles, it is possible to tailor the plasmon resonance to a specific wavelength. Thus, by integrating plasmonic nanoparticles into the solar cell structure, we have the possibility to enhance the absorption of light in the cell over a wide wavelength range or we can tune it to a desired wavelength of choice depending on the type of nanoparticle structure used (Fig. 3).

Figure 3. Incorporating core-shell Au@SiO2 nanoparticles into the TiO2 photoanode can readily improve the overall efficiency of DSSCs [6].

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3. Thin films and functional coatings

By applying a thin functional coating on a certain substrate, a wide range of properties of the substrate can be tuned (including stability towards weathering, electrical conductivity, photocatalytic and wettability properties). One area of interest of the NanOxide group is to produce nanostructured metal oxide thin films with tunable band gap energies, e.g. nanopatterned ZnO-TiO2 thin films [7].

Furthermore, we are also developing functional coatings which can both protect and actively clean natural stone surfaces. These coatings can efficiently prolong the lifetime of sensitive stone materials like marble.

Figure 4. A hydrophobized stone surface protecting the water from entering the porous stone.

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Collaborators (e.g.):

Selected recent publications:

1) “Formation of Hierarchically Porous Metal Oxide and Metal Monoliths by Nanocasting into Silica Monoliths”, J.H. Smått, F.M. Sayler, A.J. Grano, M.G. Bakker, Advanced Engineering Materials, 2012, 14, 1059-1073.

2) “Probing the Phosphoproteome of HeLa Cells Using Nanocast Metal Oxide Microspheres for Phosphopeptide Enrichment”, A. Leitner, M. Sturm, O. Hudecz, M. Mazanek, J.H. Smått, M. Lindén, W. Lindner, K. Mechtler, Analytical Chemistry, 2010, 82, 2726-2733.

3) “Polyethylenimine-Modified Metal Oxides as Packing Material for Capillary Electrochromatography and Capillary Liquid Chromatography”, S.K. Wiedmer, G. D’Orazio, D. Bourdin, C. Baños-Pérez, M. Kivilompolo, M. Kopperi, J. Ruiz-Jiménez, J.H. Smått, M. Sakeye, S. Fanali, M.L. Riekkola, Journal of Chromatography A, 2011, 1218, 5020-5029.

4) “Comparison of Different Amino-Functionalization Procedures on a Selection of Metal Oxide Microparticles: Degree of Modification and Hydrolytic Stability”, M. Sakeye, J.H. Smått, Langmuir, 2012, 28, 16941-16950.

5) “Micrometer-Sized Nanoporous Tin Dioxide Spheres for Gas Sensing”, J.H. Smått, M. Lindén, T. Wagner, C.D. Kohl, M. Tiemann, Sensors and Actuators B: Chemical, 2011, 155, 483-488.

6) “Investigation of Plasmonic Gold-Silica Core-Shell Nanoparticle Stability in Dye-Sensitized Solar Cell Applications”, B. Törngren, K. Akitsu, A. Ylinen, S. Sandén, H. Jiang, J. Ruokolainen M. Komatsu, T. Hamamura, J. Nakazaki, T. Kubo, H. Segawa, R Österbacka, J.H. Smått, Journal of Colloid and Interface Science, 2014, in press, DOI: 10.1016/j.jcis.2013.11.085.

7) “Nanopatterned Zinc Titanate Thin Films Prepared by the Evaporation-Induced Self-Assembly Process”, Q. Xu, M. Järn, M. Lindén, J.H. Smått, Thin Solid Films, 2013, 531, 222-227.

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