François Reniers

This study focuses on producing in one single step nitrogen-doped TiO2 anatase (N-TiO2) coatings using a low-power dielectric barrier discharge reactor operating at atmospheric pressure. N-doping of TiO2 usually leads to amorphous coatings, and deposition of coatings using a DBD at atmospheric pressure usually require an additional annealing step. Thanks to an inductive integrated heating system, a solution has been found for the deposition of a crystalline coating at atmospheric pressure. To address the latter issue, this study varied the nitrogen precursor (N₂ or N₂O) and the deposition conditions, investigating the impact on film properties. This approach yielded a crystalline layer exhibiting crystal size ranging from 20 to 52 nm. The nitrogen dopant molecules introduced into the plasma gas mixture were found to improve crystal quality and reduce strain lattice, as determined by X-ray diffraction. The chemical composition of the films was analyzed using X-ray photoelectron spectroscopy and secondary ion mass spectrometry, revealing a significant amount of nitrogen (<10 at.%) in the bulk. The optical bandgaps for the different deposited films were estimated using ultraviolet diffuse reflectance spectroscopy and range from 2.9 to 2.2 eV for crystalline films. Finally, a relationship was established between the crystal size and the bandgap value.

Non-thermal plasmas offer a catalyst-free route for hydrogen (H2) production. Here, ethanol is decomposed in an atmospheric-pressure, vortex-stabilised non-self-sustained discharge, varying flow rate and plasma gas (Ar with N2 or CO2 admixtures). Gas chromatography identifies H2 as the main product, followed by CO and C2 unsaturated hydrocarbons. With 30 vol.% N2, ethanol conversion reaches 100%, H2 yield increases from 12% to 43%, and the H2 production rate rises to 14.6 g H2·mol-1EtOH·kWh-1 (2.75 times higher than Ar). In contrast, 30 vol.% CO2 reduces H2 yield to 4.7% and the production rate to 2.4 g H2·mol-1EtOH·kWh-1, with H2:CO decreasing to 0.05. CFD confirms a strong swirling vortex, and OES shows gas heating from ~2300 K (Ar) to ~3300 K (30% N2) and ~2850 K (30% CO2). Together, vortex-induced confinement and enhanced gas heating are identified as key factors governing ethanol conversion and product selectivity in this non-self-sustained plasma reactor.

Titanium dioxide in its anatase form is of significant interest nowadays due to numerous properties such as biocompatibility, photoactivity under ultraviolet irradiation, or corrosion resistance. In this paper, titanium dioxide (TiO2) films are synthesized with a controlled substrate temperature going up to 673 K. Crystalline anatase was synthesized in a low power atmospheric pressure dielectric barrier discharge in a single step process. The effect of deposition parameters (plasma gas, the voltage input, precursor flow, deposition time, and substrate temperature) on the crystal size, crystallinity, and coating morphology was studied. It shows that the crystal size can be tuned, that the layers can have a transition from hydrophilicity to hydrophobicity, and that the coating morphology can be modified by optimizing these parameters. Finally, it is found that crystalline anatase TiO2 can be grown at a substrate temperature as low as 523 K in an atmospheric pressure plasma enhanced chemical vapor deposition process.

The one-step deposition of spatially differentiated crystalline vanadium oxide coatings (V2O5) using an atmospheric pressure dielectric barrier discharge is reported. This feasibility study uses an original combination of immobilized filaments inside the plasma and an inductive heating device. Preliminary results show that thick crystalline deposits are achieved under the immobilized filaments, whether the interfilament spacing leads to much thinner deposits, with a different chemical composition. The gas flow inside the reactor, combined to the filament reactivity, leads to local depletions of reactants.

Cold atmospheric plasmas are a known source of reactive species enabling various treatments, from the healing of chronic wounds to the treatment of surface cancers. Therapeutic endoscopic procedures require developing specific flexible tools that can be used through or alongside endoscopes. Plasma devices for endoscopy have aroused significant research interest over the past few decades, but their electrical behaviour is not yet fully understood and predictable. There is thus a clear need for a robust model that provides a way to understand and optimize future devices. In this work, for the first time, an electrical equivalent model of a long plasma source (comprising plasma generation, transport and target interaction) was designed, implemented, and validated. System parameters were estimated based on the system geometry and independent measurements. The model reliably reproduces the double ignition (in the quartz chamber and at the treatment site) observed experimentally. Simulations globally agree with measurements taken for various gas gap distances and input voltages. Internal parameters that are difficult to measure, such as the electrical charge at the gas gaps, were inferred. The model can predict leakage current in the body and current at the target site. This work provides a new understanding of endoscopic plasma systems that could be used in the future to ensure patient and operator safety.

Pursuing more efficient nitrogen fixation in the context of the current climate crisis is of prime importance. The Haber‐Bosch process (NH₃ production) accounts for at least 2% of the yearly released greenhouse gases. Alternatively, different atmospheric nonthermal discharges have proven their ability to convert nitrogen and oxygen from the air into nitrogen oxides (NO, NO₂, and HNO₃ hereafter referred as NO_x). Among them, dielectric barrier discharges (DBDs) in N₂/O₂ are very interesting as they are characterized by microdischarges (MDs) developing into filaments under specific conditions (gap length, voltage, frequency, nature of the dielectrics). In this work, we used a sinusoidal voltage at 4, 12, 17.5, and 30 kHz as a key parameter to manipulate the MDs behaviors in an N₂/O₂ DBD and tailor the chemistry of the discharge. We characterized the MDs distribution by high‐speed camera imaging. Two different nitrogen emission systems, that is, the second positive system (SPS) and the first negative system (FNS), were used to assess the filament temperature and what we define as the delayed‐glow temperature, respectively. The influence of the filament's distribution on the overall discharge temperature has also been evaluated, by using a novel approach allowing the generation of heat distribution maps directly on a thermosensitive paper exposed to the discharge. Finally, the effect of the filaments on ozone (O₃) and NO_x production has been monitored by in situ Fourier‐transform infrared (FTIR). The DBD can be tuned between homogenously distributed MDs at 4 and 12 kHz to highly localized filaments at 17.5 and 30 kHz. A high filament temperature combined with a cold delayed‐glow is observed at 17.5 kHz while both the filament and the delayed‐glow temperature are high at 30 kHz. Low frequencies lead to heat spreading into the whole discharge volume, while localization of heat along the filament's paths is observed at high frequencies. High‐temperature filaments in the 30 kHz discharge and in the globally heated discharge at low frequencies quickly remove O₃ from the discharge and consequently limit the overall NO_x production by removing important oxidation pathways. On the contrary, filaments surrounded by cold gas observed at 17.5 kHz allowed to maintain a high concentration of O₃ necessary for a faster oxidation of NO and thus increase the HNO₃ production, even after 250 s, by avoiding backward reactions.

A simultaneous oxidation and reduction of nitrogen is performed for nitrogen fixation with a DC plasma-electrolysis operated in N ₂ .

This experimental study characterized the effect of carrier gas flow on an endoscopic plasma jet. This system generates and transports helium plasma in a tube over several meters, along with a separate channel transporting oxygen to enhance plasma reactivity on site. The resulting plasma plume exiting the tube allows treatment of tissue surfaces in an endoscopic setting with a view to perform therapeutic operations in the gastrointestinal tract. In a closed cavity simulating the tract, the carrier gas flow was studied by a combined approach investigating plasma plume chemistry, fluid dynamics, and plasma effects on the surface of a hydrogel tissue model reporting oxidation. These three aspects are shown to be closely inter-related. Plasma plume length, intensity, and shape strongly depend on helium content, velocity, turbulence, and environment. Optical emission spectroscopy was used to show that the helium gas flow rate increases the amount of helium and reactive oxygen species (ROS) in the plume. Schlieren imaging was used to visualize the transition of the fluid from buoyant to laminar and finally turbulent depending on flow rate, with a backflow in a closed cavity. Finally, the frontal and radial treatment of the cavity was assessed by measuring ROS delivery to a KI-starch agarose gel model. Helium flow rate had a noticeable effect on the treatment distribution profile and treatment intensity, with different maxima for frontal and radial treatments. This combined approach, in an accurate simulation of the target configuration (i.e. a closed, cylindrical cavity), is necessary to optimize treatment, as its outcome depends on a balance between ROS production, transport, and distribution.