No abstract

Emerging pollutants are an essential class of recalcitrant contaminants that are not eliminated from water after conventional treatment. Here, a photocatalytic microporous membrane based on polyvinylidene difluoride-co-trifluoroethylene (PVDF−TrFE) with immobilised TiO2 nanoparticles, prepared by solvent casting, was tested against representative emerging pollutants. The structure and composition of these polymeric membranes were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, porosimetry, and contact angle goniometry. The nanocomposites exhibited a porous structure with a uniform distribution of TiO2 nanoparticles. The addition of TiO2 did not change the structure of the polymeric matrix; however, it increased the wettability of the nanocomposite. The nanocomposites degraded 99% of methylene blue (MB), 95% of ciprofloxacin (CIP), and 48% of ibuprofen (IBP). The microporous nanocomposite exhibited no photocatalytic efficiency loss after four use cycles, corresponding to 20 h of UV irradiation. The reusability of this system confirms the promising nature of polymer nanocomposites as the basis for cost-effective and scalable treatments of emerging pollutants.

Transparent n-type niobium-doped titanium dioxide thin films (TiO 2 :1.5 at.%Nb) with pronounced thermoelectric properties were produced from a composite Ti:Nb target by reactive magnetron sputtering. The thin films were comprehensively characterized by X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, electrical conductivity, and thermoelectric measurement techniques. The local structure of the thin films was investigated in detail by X-ray absorption spectroscopy at the Ti and Nb Kedges. A set of radial distribution functions were extracted from the simultaneous analysis of EXAFS data at two absorption edges using the reverse Monte Carlo method. It was found that Nb dopant atoms modify the local environment of the films, but their average structure remains close to that of the anatase phase. This conclusion is also supported by the ab initio simulations of XANES. A very high absolute Seebeck coefficient (S=155 µV/K) for n-type TiO 2 was achieved with Nb doping, yielding a maximum power factor and thermoelectric figure of merit of 0.5 mW•m -1 •K -2 and 0.18 at a temperature of 300 K, respectively, for a 150 nm thick film. From frequencydomain thermoreflectance experiments, a thermal conductivity value of 1.3 W•m -1 •K -1 was obtained for the optimized TiO 2 :Nb film.

Rutherford backscattering spectrometry, X-ray photoelectron and X-ray energy dispersive spectroscopies were employed to analyse Bi incorporation into ZnO:Al and ZnO:Ga transparent and electrically conductive thin films deposited by d.c. magnetron sputtering, with thickness in the range of 300-400 nm. Sputtering was performed in an argon atmosphere from two targets in confocal geometry being one composed of either ZnO:Al 2 O 3 or ZnO:Ga 2 O 3 composites and the other a Bi metal target. The content of bismuth dopant in the ZnO matrix was controlled by the respective target current density (J Bi) in order to attain a high optical transparency (> 80%) in the visible region. For ZnO:Al,Bi films Bi content varied from 0.1 to a maximum of 1.5 at.% when varying J Bi from 0.06 to 0.26 mA cm −2. However, for ZnO:Ga,Bi films, deposited in similar conditions, Bi reached a maximum overall layer content of 2.4 at.%, with a surface enrichment content that varied from 1.3 to 8.8 at.%. It was also observed that the Bi content in the topmost layers of the films is slightly depleted due to thermal evaporation upon thermal annealing in vacuum at 350°C. It is envisaged applications for these films as transparent photoelectrodes and thermoelectric materials.

Dendritic growth of bismuth oxide nanostructured films was accomplished by reactive magnetron sputtering. The deposition of the Bi 2 O 3 template layers was adapted to abide a vapour-liquid-solid mechanism in order to develop a 3D growth morphology with high surface area templates for photocatalytic applications. TiO 2 photocatalytic thin films were deposited at a later stage onto Bi 2 O 3 layers. The obtained heterostructured films were characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy. Additionally, the photocatalytic efficiency was assessed by conducting an assay using methylene blue dye as testing pollutant under a UV-A illumination. The photocatalytic tests revealed that the Bi 2 O 3 layers functionalized with TiO 2 thin films are more efficient at degrading the pollutant, by a factor of 6, when compared with the individual layered films.