Spectrochemistry

In our group we concentrate on development of spectroscopic techniques that allow us to gain insight into the interplay between electronic, optical, magnetic and chemical properties of matter. The current areas of expertise include, but are not limited to, table-top ambient pressure XPS for studying metallic and organic membranes exposed to hydrogen and other gasses, deep UV Raman spectroscopy for detection of trace-pollutants in liquid environment, air lasing as remote environmental sensor and magneto-optical Faraday and Kerr effect set-up for analysis of photo- and electrochemically induced electronic structures of water splitting catalysts. Moreover, we make use of our state-of-the-art facilities equipped with the commercially available Raman, IR, UV-Vis spectrometers and other analytical methods for bridging analytical problems to the existing methods, establishing collaborations and proving consulting for academia and industry. The element in focus is hydrogen as its analysis faces specific challenges. Here, we collaborate with a number of large research facilities (PSI-SINQ, RAL-ISIS, ORNL-SNS) providing neutrons as a selective probe for hydrogen in matter.

Ongoing projects

Chemical analysis of CO2 reduction

We utilize a variety of special analysis tools to characterize processes generating fuel from CO2 and hydrogen. For more information please see here. Recent highlights are the develop-ment and utilization of neutron imaging to observe the CO2 reduction in real-time in collabo-ration with the Laboratory for Neutron Scattering and Imaging at PSI. The movie below shows the diffusion of water into mm-sized zeolite beads. Further fascinating results are found in the recent publication in Journal Physical Chemistry. The video shows a H2O absorption experiments into mm-sized zeolite beads, visualized using neutron imaging. Image size is 4x5 mm2, time step is 1 min per image.

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LightCheC project in collaboration with the University of Zurich:

“Laser membrane photoemission and magneto-optical spectroscopy shining light on solar water splitting” (see also https://www.empa.ch/web/s502/catalytic-methanation) We are heading for a comprehensive understanding of the electronic structure and its dynamics of materials for solar water splitting. The work may be divided into two parts: the investigation of homo-geneous and heterogeneous solar water splitting by time resolved magneto-optical spectroscopy (trMOKE) and by laser-induces photoemission. For the latter, we are developing a pulsed laser-driven plasma UV source and membrane-based tabletop photoemission set-up. Thus, the method provides information on in-situ probing of the electronic changes in the catalyst over the course of the reaction and offers an alternative to the expensive and often inaccessible synchrotron sources. The magnetic properties of materials are very sensitive to the electronic properties and thus serve as a probe for the changes induced by light and adjacent chemical processes in photocatalytic reactions. Thus, we take advantage of the trMOKE approach for studying magnetic and optical properties of homogeneous and heterogeneous systems in transmission and reflection geometries. Apart from empirical investigations, we model the obtained data using the established models for anticipating the activity of catalytic sur-faces (e.g., the Norskov model). We are aiming at extending these models by the time dimension as needed in photo-catalysis.

 

BAFU-project: deepUV-Raman for water analysis

An alternative online technique to perform quantitative analysis and detection is missing. Raman spec-troscopy is one of the most promising spectroscopic techniques for such purpose, because it offers a chemically selective online analysis of most common organic pollutants. However, its maximum sensi-tivity is limited to 100 mg/l. Different factors restrict its limit of detection (LOD). The majors are the low Raman scattering cross section (intrinsic low efficiency of the Raman scattering process), the overlap of the weak Raman signal by strong fluorescence emission, and the absorption in liquid environments. Excitation and measurement of Raman spectra below 260 nm (deepUV) is not hindered by fluorescence and has markedly higher cross sections than common Raman spectrometer working in the visible. Within this joined project with rascope ag, which is financed by the BAFU, we develop a prototype of a deepUV-Raman spectrometer as cost-competitive water analysis device.

 

Air-lasing as remote environmental sensor

Air lasing refers to the remote optical pumping of the constituents of ambient air that results in a di-rectional laserlike emission from the pumped region. This concept has potential applications in remote sensing, because the lasing process is sensitive to gas composition on one hand, and on electric and/or magnetic fields at the lasing location on the other. In this project we want to utilize the de-pendence of the spin during the optical pumping and lasing to develop a remote magnetometer. As this concept is new, the project funded by the company Artha AG aims at demonstrating the proof of concept, i.e., the demonstration of the influence of a magnetic field on air lasing. An assessment of the measurement parameters will give an estimation of the sensitivity of a remote optical magnetometer based on this setup.

 

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References

Sambalova, O., Thorwarth, K., Heeb, N.V., Bleiner, D., Zhang, Y., Borgschulte, A., Kroll, A. Carboxylate Functional Groups Mediate Interaction with Silver Nanoparticles in Biofilm Matrix (2017) ACS Omega, 3 (1), pp. 724-733. DOI: 10.1021/acsomega.7b00982