Search

Pr(OH)(3) one-dimensional nanostructures are a less studied member of lanthanide hydroxide nanostructures, which recently demonstrated an excellent adsorption capacity for organic pollutant removal from wastewater. In this study, Pr1-xEux(OH)(3) (x = 0, 0.01, 0.03, and 0.05) defective nanostructures were synthesized by a facile and scalable microwave-assisted hydrothermal method using KOH as an alkaline metal precursor. The phase and surface composition, morphology, vibrational, electronic and optical properties of the as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP-OES), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Raman, infrared (IR), photoluminescence (PL), and diffuse reflectance spectroscopy (DRS). It was deduced that the incorporation of Eu3+ ions promoted the formation of oxygen vacancies in the already defective Pr(OH)(3), subsequently changing the Pr(OH)(3) nanorod morphology. The presence of KNO3 phase was registered in the Eu-doped samples. The oxygendeficient Eu-doped Pr(OH)(3) nanostructures displayed an improved photocatalytic activity in the removal of reactive orange (RO16) dye under UV-vis light irradiation. An enhanced photocatalytic activity of the Eu-doped Pr(OH)(3) nanostructures was caused by the synergetic effect of oxygen vacancies and Eu3+ (NO3-) ions present on the Pr(OH)(3) surface, the charge separation efficiency and the formation of the reactive radicals. In addition, the 3% Eu-doped sample exhibited very good adsorptive properties due to different morphology and higher electrostatic attraction with the anionic dye. Pr1-xEux(OH)(3) nanostructures with the possibility of tuning their adsorption/photocatalytic properties present a great potential for wastewater treatment. more...

Plasmon-longitudinal-optical (LO) phonon interaction in pure and Nd-doped CeO2-y nanocrystals was investigated by measuring far-infrared reflectivity spectra in the 100-700 cm(-1) spectral range at room temperature. Analysis of the obtained results revealed that the presence of free charge carriers becomes significant with the particle size decrease to nanometer range and increase of lattice defects. The free charge carriers were found to be responsible for a plasmon mode which coupled strongly with two LO phonon modes of ceria. The presence of more pronounced low-frequency Drude tail and the screening of the phonon modes in Nd-doped CeO2-y nanocrystals implied that the Plasmon-LO phonon interaction increased with doping. Factorized and additive dielectric function models were applied to deduce about the coupled and decoupled LO phonon frequencies and the structure of the decoupled plasmon mode in pure and Nd-doped CeO2-y nanocrystals. These models were combined with Bruggeman effective medium approximation in order to properly describe the influence of porosity on the infrared reflectivity spectra. With increasing dopant content, the decoupled plasmon mode exhibited redshift and damping decrease implying that doping induced semiconductor-to-metalic state transition took place. more...

In this paper, we have investigated one-step preparation of vanadium doped TiO2 coatings formed by plasma electrolytic oxidation (PEO) of titanium in electrolyte containing 10 g/L Na3PO4 center dot 12H(2)O + 0.5 g/L NH4VO3. The morphology, phase structure, and elemental composition of the formed coatings were characterized by atomic force microscopy (AFM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) techniques. Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) was employed to evaluate the band gap energy of obtained coatings. Vanadium doped TiO2 coatings are partly crystallized and mainly composed of anatase phase TiO2, with up to about 2 wt% of vanadium present in the surface layer of the oxide. The valence band photoelectron spectra and UV-Vis DRS showed that vanadium doped TiO2 coatings exhibit notable red shift with respect to the pure TiO2 coatings. The photocatalytic activity was evaluated by monitoring the degradation of methyl orange under simulated sunlight conditions. Photocatalytic activity of vanadium doped TiO2 coatings increases with PEO time. Prolonged PEO times result in higher roughness of obtained coatings, thus increasing surface area available for methyl orange degradation. Vanadium doped TiO2 coatings obtained after 180 s of PEO time exhibit the best photocatalytic activity and about 67% of methyl orange is degraded after 12 h of irradiation under simulated sunlight. more...

Y-doped HfO2 nanopowders, produced by metathesis synthesis, exhibit ferromagnetism at room temperature. The X-ray diffraction and Raman measurements have shown that HfO2 nanopowders undergo phase transformation from monoclinic to tetragonal and cubic phase with increasing of Y content. The X-ray photoelectron spectroscopy and Raman analysis gave evidence that Y-doped HfO2 nanopowders are oxygen deficient. The ferromagnetic properties of Y-doped HfO2 nanocrystals are dependent on crystal structure changes. The structural transformation from monoclinic to tetragonal phase with Y doping is followed by increased ferromagnetic ordering because of the increased concentration of oxygen vacancies (V-O) in different charge states. Higher Y content favors the formation of cubic phase and the ferromagnetism significantly weakens. In cubic hafnia phase, yttrium can form (V-O-Y-Hf) defect complexes in different charge states. The appearance of these complexes can be responsible for the degradation of ferromagnetic ordering. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved. more...

Among potential replacements for chromates, cerium-based conversion coatings (CeCCs) have been identified as leading candidates, showing a good promise as environmentally compliant corrosion inhibitors on Al alloys. In this work, CeCCs were synthesized on M6060 by electrolytic deposition (ELD), a well-suited method for the fabrication of films with controllable properties, at low processing temperature and cost. The CeCCs were deposited at room temperature from Ce(NO3)(3) solution, applying different cathodic potentials (-1.1, -1.4 and -1.6 V vs. SCE) for different deposition times between 5 and 20 min. Structural, morphological and compositional properties of the films were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy coupled with energy dispersive spectroscopy. Ceria films were nanostructured, exhibiting a cubic fluorite structure. From corrosion perspective, the quality of CeCCs was evaluated in 0.5 M NaCI solution via electrochemical impedance spectroscopy and linear sweep voltammetry. As shown, the coating corrosion quality is the interplay between deposition potential and deposition time. The highest potential led to highly cracked films of poor adherence, even at the shortest deposition time, which disqualified them from any corrosion protection application. The lowest potential (-1.1 V) produced crack-free coatings, but longer times (>= 10 min) were needed to provide the protective layer formation. The best corrosion protection offered CeCCs prepared at -1.4 V. The highest R-p (582 k Omega cm(2)) and the smallest CPE (12.6 . 10(-6) s(n) Omega(-1) cm) were obtained at 20 min deposition time. However, from economical point of view, 10 min deposition is a promising choice. These CeCCs also improved pitting corrosion resistance owing to homogeneous microstructure and sufficient thickness. more...

Among potential replacements for chromates, cerium-based conversion coatings (CeCCs) have been identified as leading candidates, showing a good promise as environmentally compliant corrosion inhibitors on Al alloys. In this work, CeCCs were synthesized on M6060 by electrolytic deposition (ELD), a well-suited method for the fabrication of films with controllable properties, at low processing temperature and cost. The CeCCs were deposited at room temperature from Ce(NO3)(3) solution, applying different cathodic potentials (-1.1, -1.4 and -1.6 V vs. SCE) for different deposition times between 5 and 20 min. Structural, morphological and compositional properties of the films were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy coupled with energy dispersive spectroscopy. Ceria films were nanostructured, exhibiting a cubic fluorite structure. From corrosion perspective, the quality of CeCCs was evaluated in 0.5 M NaCI solution via electrochemical impedance spectroscopy and linear sweep voltammetry. As shown, the coating corrosion quality is the interplay between deposition potential and deposition time. The highest potential led to highly cracked films of poor adherence, even at the shortest deposition time, which disqualified them from any corrosion protection application. The lowest potential (-1.1 V) produced crack-free coatings, but longer times ( GT = 10 min) were needed to provide the protective layer formation. The best corrosion protection offered CeCCs prepared at -1.4 V. The highest R-p (582 k Omega cm(2)) and the smallest CPE (12.6 . 10(-6) s(n) Omega(-1) cm) were obtained at 20 min deposition time. However, from economical point of view, 10 min deposition is a promising choice. These CeCCs also improved pitting corrosion resistance owing to homogeneous microstructure and sufficient thickness. (C) 2013 Elsevier B.V. All rights reserved. more...

The influence of La-doping in the range of 0.5-6.0 mol% on structural and morphological properties of TiO2 nanopowders synthesized by sol-gel routine has been investigated by XRPD, AFM, EDS and BET measurements, as well as Raman spectroscopy. The XRPD and Raman measurements have revealed the anatase phase as dominant in all nanopowders, with crystallite size decreasing from similar to 15 nm in pure TiO2 to similar to 12 nm in La-doped samples. The BET data suggest that all samples are fully mesoporous, with mean pore diameters in the range of similar to 6-8 nm. The specific surface area and the complexity of pore structure are greater in doped samples than in pure TiO2 sample. The spectroscopic ellipsometry has apparently shown that the band gap has been gradually increased with the increase of La content. The STM and STS techniques have been used successfully to evaluate the surface morphology and electronic properties of La-doped nanopowders. All investigated properties have been related to photocatalytic activity, tested in degradation of a metoprolol tartrate salt (0.05 mM), and induced by UV-radiation. All doped samples showed increased photocatalytic activity compared to pure TiO2, among which the 0.65 mol% La-doped sample appeared to be the most efficient. (C) 2013 Elsevier Inc. All rights reserved. more...

The structural and morphological properties of mesoporous anatase nanopowders, synthesized by sol-gel method, have been modified by varying the duration of calcination, in order to obtain more efficient photocatalyst than Degussa P25 in the degradation of relatively large pollutant molecules ( GT 1 nm in size). According to X-ray diffraction analysis, the crystallite size was increased from 13 to 17.5 nm with the increase of calcination time from 1 to 7 h. The analysis of nitrogen sorption experimental data revealed that all samples were mesoporous, with a mean pore diameters in the range of similar to 5-9 nm. The corrugated pore structure model was employed to evaluate pore structure tortuosity. Nanopowder properties have been related to the photocatalytic activity, tested in the degradation of metoprolol tartrate salt, selective beta(1)-blocker used in a variety of cardiovascular diseases, with molecular size of 0.610 nm x 1.347 nm. The study has demonstrated that samples calcined for 4 and 5 h have displayed higher photocatalytic performance than Degussa P25, whereas the sample calcined for 3 h has shown comparable activity. (C) 2013 Published by Elsevier Ltd. more...

Nanocrystalline powders of solid solution CeO2-Bi2O3 were synthesized by self-propagating room temperature reaction (SPRT) procedure with composition (Ce1-xBixO2-delta where the x = 0.1-0.5). X-ray diffraction analyses show that for x LT 0.50 a solid solution with fluorite structure is formed. Rietvelds structure refinement method was applied to characterize prepared powders and its microstructure (size strain). The lattice parameters increase according to Vegards rule with increasing of Bi concentration. The average crystallite size is about 2-3 nm. Spectroscopic ellipsometry and Raman scattering measurements were used to characterize the samples at room temperature. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas increase of Bi content provokes a small decrease of optical absorption edge in comparison with pure ceria. Specific surface area of obtained powders was measured by Brunauer-Emmet-Teller (BET) method. (C) 2011 Elsevier Ltd. All rights reserved. more...

Nanopowdered solid solution Ce(1-x)Cu(x)O(2-gamma) samples (0 LT = x LT = 0.15) were synthesized by self-propagating room temperature synthesis (SPRT). Raman spectroscopy and XRD at room temperature were used to study the vibration properties of these materials as well as the Cu solubility in ceria lattice. The solubility limit of Cu(2+) in CeO(2) lattice was found to be lower than published in the literature. Results show that obtained powders with low dopant concentration are solid solutions with a fluorite-type crystal structure. However, with Cu content higher than 7.5 mass%, the phase separation was observed and two oxide phases, CeO(2) and CuO, coexist. All powders were nanometric in size with high specific surface area. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. more...