Scientific Papers in SCI

Zinc oxide-hydroxyapatite composites were prepared using wet impregnation method. Firstly, a natural phosphate ore rich in silica and calcium phosphate was sieved to separate silica phase from phosphate phase. Then, through a chemical precipitation method, a pure hydroxyapatite (HAP) was obtained, which was used as a support for ZnO immobilization and applied for the photodegradation of two toxic contaminants: a transparent molecule (caffeine) and dye molecule (rhodamine B). During the present work two weight ratio percentages of zinc oxide were used: 25 wt.% and 50 wt.% of ZnO relative to HAP. The samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), X-ray Fluorescence (XRF), BET surface area (SBET), Scanning Electron Microscopy (SEM-EDS) and by Transmission Electron Microscopy (TEM-STEM). The immobilization of ZnO on HAP surface followed by thermal treatment at 400 °C for 2 h to get a homogenous dispersion of ZnO on the hydroxyapatite support. At high ZnO impregnation percentage, photodegradation performances of ZnO-HAP under UV illumination were fast and superior than the ZnO photocatalyst alone. The results showed that due to the presence of HAP, the conversion of both molecules became faster and greater, since it promotes the synergic phenomena of adsorption and photocatalysis. The toxicity of the treated substrate solutions obtained in the corn kernels germination test indicated a low toxicity after the photodegradation processes, probably due to a high mineralization degree.

A WO3@PANI heterojunction photocatalyst with a various mass ratio of polyaniline to WO3 was obtained via the in situ oxidative deposition polymerization of aniline monomer in the presence of WO3 powder. The characterization of WO3@PANI composites was carried via X-ray diffraction (XRD), scanning electron microscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). The photocatalytic efficiency of WO3@PANI photocatalysts was assessed by following the decomposition of the Rhodamine B (RhB) dye under visible light irradiation (λ >420 nm). The results evidenced the high efficiency of the WO3@PANI (0.5 wt %) nanocomposite in the photocatalytic degradation of RhB (90% within 120 min) under visible light irradiation 3.6 times compared to pure WO3. The synergistic effect between PANI and WO3 is the reason for the increased photogenerated carrier separation. The superior photocatalytic performance of the WO3@PANI catalyst was ascribed to the increased visible light in the visible range and the efficient charge carrier separation. Furthermore, the Density Functional Theory study (DFT) of WO3@PANI was performed at the molecular level, to find its internal nature for the tuning of photocatalytic efficiency. The DFT results indicated that the chemical bonds connected the solid-solid contact interfaces between WO3 and PANI. Finally, a plausible photocatalytic mechanism of WO3@PANI (0.5 wt %) performance under visible light illumination is suggested to guide additional photocatalytic activity development.

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.

Little is known about the structure and molecular arrangement of alpha- and beta-amyrin, a class of triterpenoids found within the cuticle of higher plants. Blends of both amyrin isomers with different ratios have been studied taking into consideration a combined methodology of density functional theory (DFT) calculations with experimental data from scanning electron microscopy, differential scanning calorimetry and Raman vibrational spectroscopy. Results indicate that trigonal trimeric aggregations of isomer mixtures are more stable, especially in the 1 : 2 (alpha : beta) ratio. A combination of Raman spectroscopy and DFT calculations has allowed to develop an equation to determine the amount of beta-amyrin in a mixed sample.