Scientific Papers in SCI

Within these studies, the effect of surface topography for hydrophobic coatings was studied both numerically and experimentally. Chemically modified polyurethane coating was patterned by application of a laser beam. A set of patterns with variously distant linear peaks and grooves was obtained. The cross section of the pattern showed that the edges of the peaks and grooves were not sharp, instead forming a rounded, rectangle-like shape. For such surfaces, experimental studies were performed, and in particular the static contact angle (SCA), contact angle hysteresis (CAH), and roll-off angle (ROA) were measured. Profilometry was used to create a numerical representation of the surface. Finite volume method was then applied to simulate the behavior of the water droplets. The model developed herewith enabled us to reproduce the experimental results with good accuracy. Based on the verified model, the calculation was extended to study the behavior of the water droplet on the simulated patterns, both spiked and rectangular. These two cases, despite a similar SCA of the water droplet, have shown extremely different ROA. Thus, more detailed studies were dedicated to other geometrical features of such topography, such as the size and distance of the surface elements. Based on the results obtained herewith, the future design of superhydrophobic and/or icephobic topography is discussed.

This study examined the effects of the cationic ratio of Bi3+/Fe3+ via X-ray photoelectron spectroscopy (XPS) on the magnetic and multiferroic properties of BiFeO3 nanoparticles synthesized using a sonochemical-assisted method. X-ray diffraction revealed the successful synthesis of single-phase BiFeO3 powder after annealing the sonicated material at 723 K. The powder was composed of agglomerates of rounded particles with a mean particle size of 35 nm. XPS was performed to determine the Bi3+/Fe3+ ratio as a function of the heat treatment process and its relationship with secondary phases, which can modulate the magnetic properties of the nano powders. The cationic ratio obtained by XPS confirmed that the powders obtained at 623 and 923 K have excess Bi3+ and Fe3+, respectively, which induces the formation of Bi24Fe2O39 and Bi2Fe4O9 as the majority phases. Powder annealing at 723 K revealed a ferromagnetic order with specific magnetization of 1.8 Am-2/kg. This ferromagnetic behavior was preserved after applying spark plasma sintering (SPS) at 923 K. By contrast, conventional sintering at 1023 K promotes antiferromagnetic order. In addition, the dielectric properties of the ceramic material of the sintered powders showed a behavior related to a typical ferroelectric material.

Different Zn-Bi-O composites were synthesized following the starting chemical molar composition of ZnBi2O4 spinels by a sol–gel method, (ZnBiO)-SG, and its subsequent hydrothermal treatment, (ZnBiO)-HT. The acquired X-ray diffractograms after sequential thermal treatments at a programmed rate indicate that both precursors evolved, after calcination at 500 °C, to materials (ZnBiO) with different stoichiometry. The use of different characterization techniques (both FT-IR and TEM), allowed us to establish that, with the sol–gel process a mixed ZnO/Bi2O3 oxide is generated, while after hydrothermal process a ternary Zn-Bi-O oxide is formed, with small amounts of residual ZnO. The photocatalytic properties of the synthesized samples were evaluated using Caffeic acid, Rhodamine B and Methyl Orange as model substrates. It can be concluded that both catalysts showed excellent photocatalytic activity for the degradation of trans-caffeic acid under both UV and visible illumination. The leaching process (in particular of zinc), which is produced with the illumination time (in particular under UV illumination) in the presence of oxygen, raises the hypothesis of a foreseeable formation of complexes (photochemically stable or unstable) of caffeic acid with Zn2+ and Bi3+ ions. The plausible donor/acceptor interactions between the toxic molecules studied and the Zn2+ and Bi3+ ions, could condition the degradation processes, by means of a photoassisted process that would take place both, in the heterogeneous (photocatalytic) and homogeneous (photoassisted) phases. For the degradation processes of Rhodamine B and Methyl Orange, additional experimental conditions are studied that significantly improved their photocatalytic degradation.

The use of zirconium in chemical industries generates a potential risk of Zr contamination in the environment, with particular concern for the decommissioning of uranium-graphite reactors. Among the natural adsorbents employed for the treatment of nuclear waste, clay minerals showed a very high affinity adsorption for radionuclides, but the influence of the chemical composition, pressure, temperature and time reaction have not yet been analysed on deep. Thus, the objective of this research is to explore several experimental conditions for an actual prediction of the behaviour of zirconium immobilization by clay minerals. The results have shown that factors such as zirconium cation nature (Zr4+ or ZrO2+), temperature, time and pH influence the extent of zirconium immobilization by clay minerals and the zirconium phases generated. At moderate conditions, zirconium tectosilicates are formed and evolve to zircon at high temperature and a longer time reaction.