Photoluminescent and Photocatalytic Properties of Eu3+-Doped MgAl Oxide Coatings Formed by Plasma Electrolytic Oxidation of AZ31 Magnesium Alloy

The synthesis of Eu3+-doped MgAl oxide coatings containing MgO and MgAl2O4 was accomplished through plasma electrolytic oxidation of AZ31 magnesium alloy in aluminate electrolyte with the addition of Eu2O3 particles in various concentrations. Their morphological, structural, and above all, photoluminescent (PL) and photocatalytic activity (PA) were thoroughly investigated. PL emission spectra of MgAl oxide coatings feature characteristic emission peaks, which are ascribed to f–f transitions of Eu3+ ions from excited level 5D0 to lower levels 7FJ. The charge transfer state of Eu3+ or direct excitation of the Eu3+ ground state 7F0 into higher levels of the 4f-manifold are both attributed to the PL peaks that appear in the excitation PL spectra of the obtained coatings. The fact that the transition 5D0 → 7F2 (electrical dipole transition) in Eu3+-doped MgAl oxide coatings is considerably stronger than the transition 5D0 → 7F1 (magnetic dipole transition) indicates that Eu3+ ions occupied sites with non-inversion symmetry. Because of oxygen vacancy formation, the Eu3+-doped MgAl oxide coatings had a higher PA in the degradation of methyl orange than the pure MgAl oxide coating. The highest PA was found in Eu3+-doped MgAl oxide coating formed in an aluminate electrolyte with 4 g/L of Eu2O3 particles. The PA, morphology, and phase of Eu3+-doped MgAl oxide coatings did not change after several consecutive runs, indicating outstanding stability of these photocatalysts

ZnO Particles Modified MgAl Coatings with Improved Photocatalytic Activity Formed by Plasma Electrolytic Oxidation of AZ31 Magnesium Alloy in Aluminate Electrolyte

MgAl and MgAl/ZnO coatings were prepared by plasma electrolytic oxidation (PEO) of AZ31 magnesium alloy in aluminate electrolyte (5 g/L NaAlO2) without and with addition of ZnO particles in various concentrations. The MgAl coating was partially crystallized and contained MgO and MgAl2O4 phases. The addition of ZnO particles to aluminate electrolyte had no significant effect on the surface morphology of formed coatings, while the Zn content increased with ZnO particle concentrations. X-ray diffraction confirmed the incorporation of ZnO particles in the coatings. The photodegradation of methyl orange (10 cm3 of 8 mg/L) was used to measure the photocatalytic activity (PA) of MgAl and MgAl/ZnO coatings. The PA of MgAl coating after 8 h of irradiation was around 58%, while the PA of MgAl/ZnO coatings formed in aluminate electrolyte with the addition of ZnO particles in concentrations of 4 g/L, 8 g/L, and 12 g/L were around 69%, 86%, and 97%, respectively

Effect of Eu3+ - dopant concentration on structural and luminescence properties of SrY2O4 nanocrystalline phosphor and potential application in dye-sensitized solar cells

SrY2O4 phosphors were doped with different concentrations of Eu3+ (0.5, 1, 2, 4, 8 and 10 at %) in order to investigate the maximal doping concentration of Eu3+ and its implementation in solar cell devices. Samples were synthesized by a combustion method using citric acid and glycine as a fuel. The X-ray diffraction (XRD) patterns confirmed pure phase of SrY2O4. FE-SEM micrographs showed agglomerate phenomenon with spherical-like shape particles and diameter of about 50 nm. Upon excitation with 280 nm, emission spectra were recorded in the range from 450-750 nm and in all samples the same energy transitions were observed D-5(0 )-> F-7(J) (J = 1, 2, 3 and 4) with maximal intensity for sample with 8 at % of Eu3+. That sample was further examined for the purpose of application in solar cell devices and showed high value of efficiency at low light intensities

Application of Micro-Arc Discharges during Anodization of Tantalum for Synthesis of Photocatalytic Active Ta2O5 Coatings

Ta2O5 coatings were created using micro-arc discharges (MDs) during anodization on a tantalum substrate in a sodium phosphate electrolyte (10 g/L Na3PO4·10H2O). During the process, the size of MDs increases while the number of MDs decreases. The elements and their ionization states present in MDs were identified using optical emission spectroscopy. The hydrogen Balmer line Hβ shape analysis revealed the presence of two types of MDs, with estimated electron number densities of around 1.1 × 1021 m−3 and 7.3 × 1021 m−3. The effect of MDs duration on surface morphology, phase and chemical composition, optical absorption, and photoluminescent, properties of Ta2O5 coatings, as well as their applications in photocatalytic degradation of methyl orange, were investigated. The created coatings were crystalline and were primarily composed of Ta2O5 orthorhombic phase. Since Ta2O5 coatings feature strong absorption in the ultraviolet light region below 320 nm, their photocatalytic activity is very high and increases with the time of the MDs process. This was associated with an increase of oxygen vacancy defects in coatings formed during the MDs, which was confirmed by photoluminescent measurements. The photocatalytic activity after 8 h of irradiation was around 69%, 74%, 80%, and 88% for Ta2O5 coatings created after 3 min, 5 min, 10 min, and 15 min, respectively

Morphology and fractal dimension of tio2 thin films

The influence of annealing temperature on the morphology and surface fractal dimension of titanium dioxide (TiO2) films prepared via the spray deposition process was investigated. Thin films with various morphologies were obtained at different temperatures and characterized by X-ray diffraction and atomic force microscopy (AFM). It was found that the crystalline structure of TiO2 films depends strongly on annealing temperature. At higher temperatures, the partial phase transformation of anatase-to-rutile was observed. The morphology and surface fractal dimensions were evaluated by image analysis methods based on AFM micrographs. The results indicate that the value of surface roughness (the standard deviation of the height values within the given area of AFM image) of TiO(2)films increases with increasing annealing temperature. Fractal analysis revealed that the value of the fractal dimension of the samples decreases slowly from 2.23 to 2.15 following the annealing process

A multidisciplinary study on magnesium

During plasma electrolytic oxidation of a magnesium alloy (96% Mg, 3% Al, 1% Zn) we obtained a luminescence spectrum in the wave number range between 19 950 and 20 400 cm-1. The broad peak with clearly pronounced structure was assigned to the v’-v” = 0 sequence of the B 1Σ+ → X 1Σ+ electronic transition of MgO. Quantum-mechanical perturbative approach was applied to extract the form of the potential energy curves for the electronic states involved in the observed spectrum, from the positions of spectral bands. These potential curves, combined with the results of quantum-chemical calculations of the electric transition moment, were employed in subsequent variational calculations to obtain the Franck-Condon factors and transition moments for the vibrational transitions observed. Comparing the results of these calculations with the measured intensity distribution within the spectrum we derived relative population of the upper electronic state vibration levels. This enabled us to estimate the plasma temperature. Additionally, the temperature was determined by analysis of the recorded A 2Σ+ (v’ = 0) - X 2П (v” = 0) emission spectrum of OH. The composition of plasma containing magnesium, oxygen, and hydrogen under assumption of local thermal equilibrium was calculated in the temperature range up to 12 000 K and for pressures of 105, 106, 107, and 108 Pa, in order to explain the appearance of the observed spectral features and to contribute to elucidation of processes taking place during the electrolytic oxidation of Mg. [Projekat Ministarstva nauke Republike Srbije, br. 172040

Synthesis and characterisation of ZnO synthesized by glycine-nitrate combustion process

One of the ways to get rid of toxic organic compounds that industries release into natural waters is photocatalysis of the decomposition of organic compounds on the surface of heterogenous photocatalysts such as zinc oxide. Zinc oxide is a semiconductor that interacts with UV and near-UV visible light by generating electron-hole pairs which decompose organic molecules. Therefore it is useful to explore different ways of synthesizing zinc oxide and to test quality and quantity of organic decomposition photocatalysis so as to enable the commercial use of the material. Zinc oxide is also a respectable material for use as a photoelectrocatalyst in water oxidation, for example, which can be useful for generating oxygen while using natural sunlight - a clean and abundant energy source. In this project nanocrystalline zinc oxide was synthesized by glycin-nitrate combustion process and the powder was annealed on temperatures of 400 °C and 500 °C. Obtained particles where characterized in detail using X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission scanning microscopy (FESEM), photoluminescence spectroscopy (PL) and diffuse reflectance spectroscopy (DRS). The results show that obtained samples are nanocrystalline wurtzite zinc oxide, with particle diameters of 33 nm (annealed at 400 °C) ad 48 nm (annealed at 500 °C). Both samples show significant amount of various crystal defects. Zinc oxide band gap of the samples are determined to be lower than the band gap of the bulk zinc oxide. Photoelectrocatalytic properties were investigated via electrochemical methods: linear voltammetry (LV), chronoamperometry (CA) and impedance spectroscopy (EIS). The results show that material is photostable and reactive to the light. Water oxidation is enhanced by exposing to sunlight. Finally, photocatalytic properties are tested with determining kinetic parameters of phenole and methyl blue decomposition. Zinc oxide nanoparticles are efficient photocatalysts, although sample annealed at 500 °C shows better properties than sample annealed at 400 °C

Structural, morphological and optical characteristics of ZnO particles synthesized in the presence of surfactants CTAB and Pluronic F-127

Due to its optical and electrical properties, low toxicity, chemical and physical stability, as well as inexpensiveness, zinc oxide (ZnO) based materials have a great potential to be used as photoelectrode in photo(electro)catalysis. Photo(electro)catalytic activity of ZnO materials can be improved by modification of particles morphology and surface topology. In this work, the influence of two different surfactants: cetyltrimethylammonium bromide (CTAB) and Pluronic F-127, on the crystal structure, morphology, optical and photo(electro)catalytic properties of ZnO particles, were examined. ZnO powders were synthesized by microwave processing of a precipitate which was previously prepared by "drop by drop" method in the presence of the surfactants. The crystal structure and phase purity of the ZnO particles were determined by X-ray diffraction and Raman spectroscopy. The effects of the surfactants on ZnO particles morphology were examined by the field emission scanning electron microscopy (FE-SEM). The optical properties were studied using UV-Vis diffuse reflectance and photoluminescence spectroscopy. Photocatalytic activity was examined via decolorization of methylene blue under direct sunlight irradiation. It was found that synthesized ZnO powders have a significant photocatalytic activity. Electrochemical properties were studied using linear sweep voltammetry and impedance spectroscopy in Na2SO4 electrolyte. ZnO powder synthesized in the presence of CTAB (ZnO/CTAB) showed the most significant reduction of potential and the fastest kinetic of oxygen evolution

Synergy of Nd:YAG Picosecond Pulsed Laser Irradiation and Electrochemical Anodization in the Formation of TiO2 Nanostructures for the Photocatalytic Degradation of Pesticide Carbofuran

This study proposes a simple and controlled method for producing TiO2 with phase junction, oxygen vacancies, and Ti3+ by combining picosecond pulsed laser irradiation and electrochemical anodization. Ti mesh was pretreated by irradiating with a picosecond pulsed laser technique using an Nd:YAG laser (1064 nm) at two fluencies, 15 J/cm2 and 30 J/cm2 . The samples were then subjected to electrochemical anodization to form TiO2 nanotube arrays on the previously laser-treated surface. This study will investigate the possibility of forming TiO2 nanotube arrays on a pre-laser-treated Ti substrate and determine their physicochemical and photocatalytic properties. The samples were characterized by FESEM, XRD, Raman, XPS, and UV-Vis DRS. UV-Vis spectroscopy was used to observe the progress of photocatalytic degradation for all samples, and degradation products were determined using GC-MS. With the synergistic effects of phase junction, oxygen vacancies, and Ti3+, the laser-treated TiO2 with 30 J/cm2 showed a higher photocatalytic degradation rate (85.1%) of the pesticide carbofuran compared to non-laser-treated TiO2 (54.8%), remaining stable during successive degradation cycles, which has promising practical applications

Synthesis of calcium doped phosphate tungsten bronze

A study is presented of phase transitions of acid CaHPW12O40∙6H2O salt of 12-tungstophosphoric acid and characterized in the temperature range from room temperature to 1093 K. The structure and its phase transformations were characterized by thermal analysis (TGA and DSC), X-ray powder diffraction (XRPD) and Fourier-transform infrared spectra (FTIR). Dehydration processes are finished at about 770 K. Keggin’s anions are transformed by solid-solid recrystallization at about 873 K in calcium doped phosphate tungsten bronze