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Gothenburg, Sweden

Gusak V.,Chalmers University of Technology | Heiniger L.-P.,Ecole Polytechnique Federale de Lausanne | Zhdanov V.P.,Chalmers University of Technology | Zhdanov V.P.,RAS Boreskov Institute of Catalysis | And 4 more authors.
Energy and Environmental Science | Year: 2013

In this study, we used Hidden Interface-Indirect Nanoplasmonic Sensing (HI-INPS) for real time monitoring of dye impregnation (adsorption-diffusion process) of mesoporous TiO2 electrodes of the kind used in dye-sensitized solar cells. We measured the dye percolation time (i.e. the time to diffuse to the bottom of a TiO2 photoelectrode film) for dye Z907 in a 1:1 volume mixture of acetonitrile and tert-butanol for different dye concentrations and for different thicknesses of the TiO2 film, while the total amount of adsorbed dye was simultaneously measured by optical absorption spectroscopy. The experimental data for the impregnation process were analyzed by employing a diffusion-front model, combining diffusion and Langmuir type adsorption, which allows extraction of the effective diffusion coefficient for the system. The latter value is about 15 μm2 s-1 for the combined adsorption-diffusion movement of dye molecules through the TiO2 structure, which is an order of magnitude or more smaller than that for "free" diffusion of dye molecules in bulk solvents. © 2013 The Royal Society of Chemistry.

Langhammer C.,Chalmers University of Technology | Larsson E.M.,Chalmers University of Technology | Larsson E.M.,Insplorion
ACS Catalysis | Year: 2012

Indirect nanoplasmonic sensing, INPS, as the key step forward, facilitates the use of nanoplasmonic sensor technology in highly demanding environments in terms of temperature (up to 850 °C, so far), chemical harshness (strongly oxidizing and reducing atmospheres), and pressure for in situ and real time probing of catalyst and other functional nanomaterials. Furthermore, INPS allows for almost infinite material combinations. We also note that the pressure range within INPS can be used is not limited by the sensor or readout principle itself, but rather, by the design of the measurement cell; hence, experiments above atmospheric pressure should be straightforward. The INPS sensor chip features a dielectric spacer layer physically separating the nanoplasmonic sensors from the probed nanomaterial and serving several additional key functions, including (i) protection of the Au nanosensors from the environment and from structural reshaping at high temperature, (ii) providing tailored surface chemistry (support mateial) for the nanomaterial/catalyst to be studied, (iii) being chemically inert or (iv) participating actively in the process under study, e.g., in spillover effects during a catalytic reaction. In principle, any other dielectric material (oxides, nitrides, carbides) that can be deposited as a thin flat or porous film-but also polymers-can be used as the spacer layer/support material for an INPS experiment, depending on the needs of the specific probed system. To date, we have successfully applied the INPS sensing platform to investigate structural and chemical changes of nanomaterials, such as in catalyst sintering processes,19 the oxidation/reduction of Pd nanoparticles, or the storage of NOx species in BaO. We have also applied INPS to scrutinize size effects in the hydride formation process in nanoparticles in the sub-10 nm size range1,16 or to measure in situ changes in adsorbate surface coverage on heterogeneous catalysts at atmospheric pressure.2 Optical nanocalorimetry has been used to measure local temperature changes at the nanolevel and relate the latter, for example, to the activity of a catalyst.1 Furthermore, we have recently applied INPS to study dye molecule adsorption/impregnation of 10-μm-thick mesoporous TiO2 photoanodes in dye-sensitized solar cells by placing the INPS sensor at the hidden, internal interface between the support and the mesoporous TiO2.18 This approach provides a unique opportunity to selectively follow dye adsorption locally in the hidden interface region inside the material and inspires a generic and new type of nanoplasmonic hidden interface spectroscopy that makes highly time-resolved measurements inside a material possible. This first application of hidden interface INPS has thus also prepared grounds for studies of even more realistic catalyst structures comprising a micrometers-thick mesoporous washcoat-like support structure on the INSP chip, loaded with "real" catalyst nanoparticles. Finally, we have also demonstrated first experiments toward single particle INPS spectroscopy in the example of hydride formation in individual Pd and Mg nanoparticles. In summary, owing to its sensitivity, versatility, robustness, compatibility with harsh environments and high temporal resolution in the millisecond range, INPS constitutes a very promising novel experimental platform for the in situ spectroscopy of functional nanomaterials such as catalysts under close-to or real application conditions. The lack of specificity of the readout signal, that is, shifts in the spectral position of the localized plasmon peak of the INPS sensor, requires careful design of experiments and, in some cases, combinations with complementary techniques, such as AFM/ SEM/TEM, or other spectroscopic techniques, such as XPS. Hence, as one important future direction for further development, we identify the direct integration of the INPS function on a sample compatible with simultaneous additional readouts (such as the aforementioned ones but also others, such as quartz crystal microbalance,42 or nonlinear optical spectroscopies, such as SFG) as a high priority. Furthermore, we believe that more efforts directed toward the probing of individual catalyst nanoparticles during a catalytic reaction are well motivated, because of both the promising first proof-ofprinciple experiments already presented and the potential to efficiently circumvent inhomogeneous sample material artifacts. As the main challenges, here, we identify on one hand the optimization of the utilized microspectroscopy for compatibility with high temperatures and, on the other hand, the further optimization of sensitivity and geometrical arrangement of sensor and probed nanoparticle to ultimately be able to probe individual nanoparticles in the sub-10 nm size range under realistic application conditions. © 2012 American Chemical Society.

Gusak V.,Chalmers University of Technology | Heiniger L.-P.,Ecole Polytechnique Federale de Lausanne | Graetzel M.,Ecole Polytechnique Federale de Lausanne | Langhammer C.,Chalmers University of Technology | And 2 more authors.
Nano Letters | Year: 2012

Indirect nanoplasmonic sensing (INPS) is an experimental platform exploiting localized surface plasmon resonance (LSPR) detection of processes in nanomaterials, molecular assemblies, and films at the nanoscale. Here we have for the first time applied INPS to study dye molecule adsorption/impregnation of two types of TiO 2 materials: thick (10 μm) mesoporous films of the kind used as photoanode in dye-sensitized solar cells (DSCs), with particle/pore size in the range of 20 nm, and thin (12-70 nm), dense, and flat films. For the thick-film experiments plasmonic Au nanoparticles were placed at the hidden, internal interface between the sensor surface and the mesoporous TiO 2. This approach provides a unique opportunity to selectively follow dye adsorption locally in the hidden interface region inside the material and inspires a generic and new type of nanoplasmonic hidden interface spectroscopy. The specific DSC measurement revealed a time constant of thousands of seconds before the dye impregnation front (the diffusion front) reaches the hidden interface. In contrast, dye adsorption on the dense, thin TiO 2 films exhibited much faster, Langmuir-like monolayer formation kinetics with saturation on a time scale of order 100 s. This new type of INPS measurement provides a powerful tool to measure and optimize dye impregnation kinetics of DSCs and, from a more general point of view, offers a generic experimental platform to measure adsorption/desorption and diffusion phenomena in solid and mesoporous systems and at internal hidden interfaces. © 2012 American Chemical Society.

Larsson E.M.,Chalmers University of Technology | Larsson E.M.,Insplorion | Syrenova S.,Chalmers University of Technology | Langhammer C.,Chalmers University of Technology | Giessen H.,University of Stuttgart
Nanophotonics | Year: 2012

Nanoplasmonic sensing has over the last two decades emerged as and diversified into a very promising experimental platform technology for studies of biomolecular interactions and for biomolecule detection (biosensors). Inspired by this success, in more recent years, nanoplasmonic sensing strategies have been adapted and tailored successfully for probing functional nanomaterials and catalysts in situ and in real time. An increasing number of these studies focus on using the localized surface plasmon resonance (LSPR) as an experimental tool to study a process of interest in a nanomaterial, with a materials science focus. The key assets of nanoplasmonic sensing in this area are its remote readout, non-invasive nature, single particle experiment capability, ease of use and, maybe most importantly, unmatched flexibility in terms of compatibility with all material types (particles and thin/thick layers, conductive or insulating) are identified. In a direct nanoplasmonic sensing experiment the plasmonic nanoparticles are active and simultaneously constitute the sensor and the studied nano-entity. In an indirect nanoplasmonic sensing experiment the plasmonic nanoparticles are inert and adjacent to the material of interest to probe a process occurring in/on this material. In this review we define and discuss these two generic experimental strategies and summarize the growing applications of nanoplasmonic sensors as experimental tools to address materials science-related questions. © 2012 Science Wise Publishing & De Gruyter.

Insplorion | Entity website

Insplorions sensor chips feature the unique NPS nanoarchitecture, which guarantees excellent performance at temperatures up to 600C and in challenging chemical environments. Insplorions sensor chips are available with standard coatings of SiO2, Al2O3or TiO2 ...

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