Non-thermal plasma

Electrical discharges forming non-thermal plasma will be generated by different types of high voltage power supplies (DC, AC, or pulsed), depending on the specific application. Our lab is equipped with many power supplies (DC; AC; pulsed).

We investigate several configurations of electric discharges in contact with materials of different shapes, composition and catalytic properties (e.g. TiO₂, ZrO₂, BaTiO₃, Pt) and their plasma chemical effects. Namely: 1) Discharges in capillary tubes to mimic automotive catalysts with a similar geometric structure. 2) Discharges in pellets for the elementary studies of plasma-catalyst interaction and chemical processes in plasma catalysis. Besides the laboratory scale plasma-catalytic systems for exhaust air cleaning, we will also test larger devices for indoor cleaning where plasma will be combined with TiO₂ photocatalysis, ozonation and UV irradiation.

Diagnostics of plasma discharges

Electrical discharge characteristics will be measured by the high voltage probes and current monitors. The measured signals will be recorded by digital oscilloscopes. These measurements are needed for the calculation of the power input and energy efficiency of the plasma cleaning processes.

Optical emission spectroscopy, both time-integrated and nanosecond time-resolved will be used to investigate the physical characteristics of the studied discharges, both with and without water. We will attempt to determine the temperature of electrons, electron density or the reduced electric field strength. Intermediate reactive species will be identified.

Analysis of gases

We use several diagnostic methods for monitoring the concentrations of gaseous products. UV-Visible absorption spectroscopy will be used for the detection of NO, NO₂, O₃, and HNO₂. Infrared absorption spectroscopy, which is more versatile than UV-Visible spectroscopy, allows us to analyse the plasma treated gases, e.g. HNO₃, N₂O, CO, CO₂ and almost all volatile hydrocarbons can be detected. A Fourier transform infrared (FT-IR) spectrophotometer is be used. High sensitivity can be used when using 5 and 8 m long multi-pass absorption gas cells. To complement the gas analysis, gas chromatography equipped with FID and TCD detectors is used. This gas chromatograph is couples to a new mass spectrometer (MS). Using a combined GC-MS device, precise identification of many unidentified gaseous products is possible.

Analysis of liquids

One of the most efficient ways to activate water with plasma-generated reactive particles is making aerosol microdroplets, either by ultrasonic or mechanical nebulizers or by using high voltage nozzle that generates electrospray. We use several types of fast cameras that enable recording videos with a high frame rate, to visualize the nebulized and electrosprayed water microdroplets and to measure their size. We also employ an optical particle sizer for this need, which allows counting microdroplets and particles with sub-micron sizes and obtain their size distributions.

Plasma-activated water and water solutions are typically acidified and contain various reactive oxygen and nitrogen species delivered from the plasma discharge. We monitor the pH of PAW by calibrated pH meters its conductivity, total dissolved solids and oxidation-reduction potential. The concentrations of nitrites (NO₂^-), nitrates (NO₃^-) and hydrogen peroxide (H₂O₂) and ozone (O₃) in PAW are detected by the colorimetric methods (UV/VIS absorption spectrophotometer and microplate-reader ). Fluorescence spectrometry is used for hydroxyl radicals (OH), peroxynitrites (ONOO^-) and O₃ detection.. We plan to apply calibration-free laser induced breakdown spectroscopy (LIBS) for the analysis of polluted water contaminants, either by drying the sample on pure Si substrate, or by using the droplet levitation technique. We are acquiring new infrastructure for detailed and even more precise and more reliable liquid diagnostics including the organic components and ions, such as high precision liquid chromatography (HPLC) and ion chromatography (IC).

Seeds and plants treatment

One of the key objectives of the project is to achieve improvement in the cultivation of agricultural seeds and enhance the growth on plants by using PAW. PAW is a source of nitrogen exploitable by plants in the form of nitrates, and also contains many reactive oxygen species stimulating various physiological processes, such as e.g. seed germination. We perform seed germination and early seedling growth in controlled laboratory conditions in pots, in hydroponic and aeroponic systems, as well as under outdoor conditions that simulate the field farming. We will monitor the water intake of PAW by the seeds and their imbibition rate. We will determine selected growth parameters (length of roots and shoots, number and quality of leaves, fresh and dry weight of seedlings and plants, key vitality indexes, photosynthesis parameters, antioxidant enzymes and growth factors, etc., in some cases in outdoor conditions even fruit and seed production) to determine an optimal dose and application of PAW. Lignification of the root tissues will be observed by optical and fluorescence microscopy on the lignin deposition on the free hand sections of the roots. The scientific aim is to understand the correlation between the seed germination induction and the quality of plant growth parameters.

Investigating water decontamination effects

Micropollutant water pollution represents a challenge for conventional wastewater treatment technologies. Micropollutants are typically of organic nature, include low concentration pharmaceutical contaminants (e.g. various drugs, hormones, antibiotics), trace pesticides from agriculture, microplastics, as well as associated microbes. Plasma effects on microorganisms in model wastewater on in bio-aerosols or on seed/seedling germination/early growth is tested on model bacteria and yeast. . For microbiological cultivation we will use a sterile box equipped with laboratory glass, balances, pipettes, vortex, autoclave and a thermostat for a controlled microbial growth. Antimicrobial effects are examined by cultivation methods by comparing with fluorescence microscopy visualization and various fluorescence staining methodsin reference and treated water. Chemical low concentration contaminants, their degradation and by-products will be thoroughly analyzed by various sensors, UV-vis absorption spectroscopy, HPLC, and ion chromatography.