In this contribution, based on the analyses of the discharge behavior as well as final properties of the deposited Ni-O films during reactive high power impulse magnetron sputtering discharge, we have demonstrated that monitoring the oxygen flow rate leads to 4 different regimes of discharge. Tuning the oxygen partial pressure allows deposition of a large range of chemical compositions from pure nickel to nickel-deficient NiOx (x > 1) in the poisoned mode. Investigation of the plasma dynamics by time-resolved optical emission spectroscopy suggests that the discharge behavior in the poisoned mode principally comes from the higher contribution of both oxygen and argon ions in the total ionic current, leading to a change in the ion induced secondary electron emission coefficient. Additionally, material characterizations have revealed that optoelectronic properties of NiOx films can be easily tuned by adjusting the O/Ni ratio, which is influenced by the change of the oxygen flow rate. Stoichiometric NiO films (O/Ni ratio ∼ 1) are transparent in the visible range with a transmittance ∼80% and insulating as expected with an electrical resistivity ∼106 Ω cm. On the other hand, increasing the O/Ni > 1 leads to the deposition of more conductive coating (ρ ∼ 10 Ω cm) films with a lower transmittance ∼ 50%. These optoelectronic evolutions are accompanied by a band-gap narrowing 3.65 to 3.37 eV originating from the introduction of acceptor states between the Fermi level and the valence band maximum. In addition, our analysis has demonstrated that nickel vacancies are homogeneously distributed over the film thickness, explaining the p-type of the films.
The current work presents new and versatile photocatalytic surfaces designed to remove contaminants of emerging concerns (CECs) from water. Photocatalytic thin films of titanium dioxide (TiO2) were deposited on a polyethylene terephthalate (PET) surface (PET-TiO2) and photosensitized by a natural and non-hazardous curcumin (turmeric). The nanocrystalline TiO2 thin film was deposited in a single stage and solvent-free process, without thermal post treatment, using the high power impulse magnetron sputtering (HiPIMS) technique. The photocatalytic film was characterized by different techniques (SEM/EDS, STEM, AFM, UV-Vis spectroscopy, and wettability via water droplet contact angle measurements). The photocatalytic activity was assessed by the degradation of two model CECs: the fungicide carbendazim (CBZ), used in different crops around the world (coffee, rice, fruits, etc.), and the anthropogenic pollution tracer caffeine (CAF). Removal of these model CECs of up to 39% were achieved under 2 combined UV and visible irradiation under 7 h photocatalytic treatments. The degradation process was further studied by organic carbon dissolved analysis, with 80% removal achieved, and acute ecotoxicity tests with Aliivibrio fischeri bacteria, indicating reduction of toxicity or non-change. The PET-TiO2 surfaces remained stable for 5 consecutive cycles of use, with similar kinetic rates. Finally, the species involved in photocatalytic reactions were investigated by use of h + , HO • and • O2trapping agents for the degradation reactions, both in the presence and absence of turmeric. The results were indicative of the fact that the addition of the turmeric led to an increase in photogenerated • O2radicals due to a synergistic effect between the photocatalyst and photosensitizer. The results demonstrate the potential of the PET-TiO2 surfaces as a straightforward solution for the removal of CECs in wastewater treatment plants (WWTP), using a flexible, scalable, reusable and environmental friendly photocatalytic material.
4941 (2020) Nb-doped TiO2 coatings developed by high power impulse magnetron sputtering-chemical vapor deposition hybrid deposition process.
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