A study on the photo-reductive precipitation rate of europium sulfate from rare earth mixture by addition of hydrogen peroxide

The influence of H₂O₂ on the photo-reductive precipitation of Eu³⁺ from a solution containing Sm³⁺, Eu³⁺ and Gd³⁺ was investigated. The solution contains isopropanol as a reduction agent, ammonium sulfate as a precipitation agent, and hydrogen peroxide as an acceleration agent of precipitation rate. A mercury lamp emitting a wavelength of 254 nm was used as a light source. Adding a small amount of H₂O₂ considerably increased the photo-reductive precipitation rate of Eu³⁺. OH radicals obtained from the photodecomposition of H₂O₂ oxidized isopropanol into the radical (CH₃)₂C’OH and the resulting radicals reduced Eu³⁺ rapidly. It was found that the organic radical has the ability to reduce only Eu³⁺ in the solution containing Sm³⁺, Eu³⁺ and Gd³⁺. The precipitation yields of Eu, Sm and Gd were about 99%, 10% and 4%, respectively. It was also found that the Sm and Gd were not photo-reduced and co-precipitated with Eu.     

Factors Affecting on the Sorption/Desorption of Eu (III) using Activated Carbon

Abstract

The sorption and desorption of Eu (III) on H‐APC activated carbon using a batch technique has been studied as a function of carbon type, shaking time, initial pH solution, temperature, particle size of carbon, and concentration of the adsorbent and the adsorbate. The influence of different anions and cations on adsorption has been examined. The experimental data have been analyzed by Langmuir, Freundlich, and Temkin sorption isotherm models and the adsorption data for Eu (III) onto activated carbon were better correlated to the Temkin isotherm and the maximum absorption capacities obtained was 46.5 mg g^?1. Anions of phosphate, carbonate, oxalate, and acetate were found to increase the adsorption of Eu (III), whereas nitrate, chloride and all studied cations, potassium, sodium, calcium, magnesium, and aluminum have a negative effect on the adsorption capacity. More than 99% europium adsorbed on H‐APC eluted with 0.5 M HCl solution. The activated carbon prepared from apricot stone using 70% H₃PO₄ could be considered as an adsorbent that has a commercial potential for Eu (III) treatment.     

Europium(II) in glasses of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>-MnO-Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Triply and doubly charged states of europium are revealed by ¹⁵¹Eu Mössbauer spectroscopy in the structure of glasses of the composition (mol %) 19.5Al₂O₃, 31.5SiO₂, 26.5MnO, and 22.5Eu₂O₃. The isomer shifts in the Mössbauer spectra of Eu³⁺ and Eu²⁺ ions in the structure of glasses differ from the isomer shifts in the spectra of the Eu₂O₃ and EuO compounds. This difference is explained by the fact that the electron density at ¹⁵¹Eu nuclei is affected by the manganese and aluminum atoms, which are not bound directly to the europium atoms. The broadening of the spectra of the Eu²⁺ ions in glasses is caused by the nonuniform isomer shift.     

Synthesis and Structural Probing of Eu3+ Doped BaYF5 Nano-Crystals in Transparent Oxyfluoride Glass-Ceramics

Transparent oxyfluoride glass-ceramics containing Eu: BaYF₅ nano-crystals in the newly developed SiO₂–K₂CO₃–BaF₂–YF₃–Sb₂O₃ glass system are synthesized by melt quenching method followed by optimized ceramization process. The X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy confirmed the precipitation of tetragonal BaYF₅ nano-crystals in glass matrix. The coexistence of Eu²⁺ and Eu³⁺ ions in both glass and glass-ceramics are ascertained from their emission and excitation spectra. The in situ formation of divalent europium (Eu²⁺) along with Eu³⁺ during high temperature synthesis under ambient atmosphere is explained through optical basicity model. The Eu³⁺ emission from upper excitation states (⁵D₃₋₁) and reduced asymmetry ratio (R = I_ED/I_MD) in glass-ceramics have established the dopant ion incorporation into fluoride nano-crystalline environment. The observed luminescence properties of Eu:BaYF₅ are compared with that of Eu:BaYF₅ nanocrystals containing transparent glass-ceramics and their marked differences are discussed.     

Silica nanoparticles modified with a Schiff base ligand: An efficient adsorbent for Th(IV), U(VI) and Eu(III) ions

Modification of SiO₂ nanoparticles by salicylaldiminepropyl results in efficient adsorbents for removal of Th⁴⁺, UO ₂ ²⁺ and Eu³⁺ ions from aqueous solutions. The effect of parameters influencing the adsorption efficiency such as aqueous phase pH, contact time, initial metal ions concentration, adsorbent dosage and temperature dependency of the process was verified and discussed. Under optimal conditions (pH 5.5, adsorbent dosage 0.05 g, contact time 30 min. and 25 °C), thorium and uranyl ions (initial concentration 20 mg/l) were quantitatively removed from 20 ml of sample solution. Under such conditions 85% of europium ions was removed. Comparison of the adsorption efficiency of the studied modified nano-particles with those unmodified ones shows a shift for uptake of the metal ions vs. pH curves towards lower pH values by applying the modified adsorbents. In addition, a significant improvement of europium ions adsorption was observed by using the modified nanoparticles. Kinetics of the process was studied by considering a pseudo second-order model. This model predicts chemisorption for the adsorption mechanism. Freundlich, Langmuir and Temkin models were suitable for describing the equilibrium data of Th⁴⁺, UO₂ ²⁺ and Eu³⁺ adsorption process, respectively. Thermodynamic investigation reveals the adsorption process of the studied ions is entropy driven.     

Simulation of CO2/CH4 high pressure separation on microporous activated carbon

Abstract

Pure component adsorption equilibrium of CH₄ and CO₂ on activated carbon have been studied at three different temperatures, 298, 323, and 348?K within a pressure range of 10–2000?kPa. Binary adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO₂/CH₄ (40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800?kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO₂/CH₄, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800?kPa, extended Sips model underestimated significantly the CO₂ adsorbed amount and overestimated the CH₄ adsorbed amount.     

Mössbauer investigation of the europium state in fluoride glasses

The structure of glasses based on fluorides of alkaline-earth metals, aluminum, and europium, in which aluminum fluoride is partially replaced by aluminum nitride, is investigated by ¹⁵¹Eu Mössbauer spectroscopy. It is found that these glasses contain europium atoms in two oxidation states (+2 and +3). The isomer shifts of the Mössbauer spectra of Eu³⁺ and Eu²⁺ ions entering into the composition of the fluoride glasses are somewhat different from the isomer shifts of the Mössbauer spectra of EuF₃ and EuF₂ compounds. This difference is explained by the effect of the alkaline-earth metal and aluminum atoms (not bound directly to the europium atoms) on the electron density at the ¹⁵¹Eu nuclei. The broadening of the Mössbauer spectra of the Eu²⁺ ions in the fluoride glasses is explained by the nonuniform isomer shift.     

Combustion Synthesis of BaCO3 and its Application for Eu(III) Adsorption from Aqueous Solution

A combustion method using urea as fuel and barium nitrate as oxidant was applied for the synthesis of barium carbonate, which was characterized by XRD, IR, SEM, and BET. A batch technique was employed to study the Eu(III) adsorption from an aqueous solution using BaCO₃. It was found that the adsorption process attains equilibrium within 3 hours and depends upon the pH, europium concentration, and temperature. The kinetic data of the process could be fitted by means of the pseudo-second order and the intraparticle mass transfer diffusion models, whereas the isotherm by means of the Langmuir equation. Thermodynamic parameters indicate that the process is spontaneous and endothermic in nature. These results suggest that BaCO₃ is an effective material for Eu(III) adsorption from aqueous solutions. The findings of this study could be relevant for heterogeneous catalytic processes as well have an environmental impact.     

Local microstructure characterization of rare earth‐doped PMMA with low‐ion content by fluorescence EXAFS

Fluorescence‐extended X‐ray absorption fine structure (EXAFS), and emission spectrum and excitation spectrum (ESES) were used to characterize the local structure of rare earth‐doped poly(methyl methacrylate)s (Re‐PMMAs) with ion concentration of 600–1000 ppm. Fluorescence EXAFS shows that the chemical state of Sm in Sm‐PMMA is the same as that in Sm₂O₃ and samarium octanoate (SOA), while that of Eu in Eu‐PMMA is different from that in Eu₂O₃ and europium octanoate. ESES also proves the concomitance of Eu²⁺ with Eu³⁺ ions in Eu‐PMMA. And, the almost identical peak positions of Eu L₃ edge at ～6976.7 eV in fluorescence EXAFS of Eu‐PMMA with various Eu content suggests the proportions of Eu²⁺ to Eu³⁺ are the same in these samples. The simulation of fluorescence EXAFS shows that the first‐shell coordination number of Sm³⁺ in Sm‐PMMA is 9.12, and the average first‐shell distance around Sm³⁺ in Sm‐PMMA is 2.43 Å. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1294–1298, 2006     

Anomalous preparation,intense 5D0→7F4 emission and adjustable double center emission of Eu3+ and Eu2+ codoped Ca2Al2SiO7

A series of Eu³⁺/Eu²⁺ codoped Ca₂Al₂SiO₇ were synthesized by traditional solid-state synthesis in reducing atmosphere. In this work, XRD powder diffraction proved that the obtained sample was pure. Photoluminescence properties are characterized by excitation, emission spectra and decay curves. Double center emission is achieved by adjusting excitation wavelength and concentration. Under the 394 nm excitation, the emission spectra Ca₂Al₂SiO₇: Eu phosphors exhibit two bands situated at blue emission of 4f5d-4f transition from Eu²⁺ ion and red emission of 4f-4f transition coming from Eu³⁺ ion. The red and yellow light can be obtained when the concentration of doped europium ions is at 0.5% and 1%, respectively. When the excitation wavelength was 394, 280 and 584 nm, the emission color change from yellow to blue, respectively. The bond energy theory explains Eu²⁺ and Eu³⁺ ion occupy Ca1 site in the Ca₂Al₂SiO₇ lattices. In addition, the spectra show that the abnormal intensity peaks of europium ion at 701 nm can be found. Analysis of the related intensity ⁵D₀-⁷F₂(618 nm) transition peak is similar to that of ⁵D₀-⁷F₄(701 nm) transition peak in the emission spectra with the Judd-Ofelt theory.     

Electrochemical removal of boron from water: Adsorption and thermodynamic studies

The present work provides an electrochemical removal of boron from water and its kinetics, thermodynamics, isotherm using mild steel and stainless steel as anode and cathode respectively. The various operating parameters on the removal efficiency of boron were investigated, such as initial boron ion concentration, initial pH, current density and temperature. The results showed that the optimum removal efficiency of 93.2% was achieved at a current density of 0.2 A dm^?2 at pH of 7.0. First‐, second‐order rate equations, Elovich and Intraparticle models were applied to study adsorption kinetics. Adsorption isotherms of boron on Fe(OH)₃ were determined and correlated with isotherm equations such as Langmuir, Freundlich and D‐R models. Thermodynamic parameters, such as standard Gibb's free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°), were also evaluated by Van't Hoff equation. The adsorption process follows second‐order kinetics. The adsorption of boron preferably fits with Langmuir adsorption isotherm suggesting monolayer coverage of adsorbed molecules. The adsorption of boron onto Fe(OH)₃ was found to be spontaneous and endothermic. © 2011 Canadian Society for Chemical Engineering     

A Novel 3D Europium (III) Coordination Polymer Constructed from 3,5-Pyridinedicarboxylate Acid: Synthesis, Crystal Structure and Emission Spectrum

Abstract  A novel 3D coordination polymer Eu₂(PDC)₃(H₂O)₃ (1) has been synthesized by hydrothermal reaction of europium chloride with 3,5-pyridinedicarboxylate acid (H₂PDC) under acidic condition (pH 2–3). Complex 1 is a 3D coordination polymer via 1D infinite chains built by the pyridinium moieties of the PDC²⁻ anions. The thermal analyses and luminescent properties of 1 have also been investigated. Graphical Abstract   A novel 3D coordination polymer Eu₂(PDC)₃(H2O)₃ has been synthesized by hydrothermal reaction of europium chloride with 3,5-pyridinedicarboxylate acid under acidic conditions (pH 2–3). The formation of the title complex demonstrates that pH plays an important role during the synthesis.      

Adsorption properties of Pb2+ on thermal-activated serpentine

ABSTRACT

Adsorption properties of nature and thermal-activated serpentines to Pb²⁺ in aqueous solution were investigated. The results showed that Freundlich isotherm and pseudo-second-order kinetics model were suitable to describe the adsorption process of Pb²⁺ on serpentines. The thermodynamic parameters indicated that the adsorption process was endothermic and spontaneous. The serpentine activated at 700°C exhibited maximum adsorption capacity to Pb²⁺. Based on the XRD and XPS characterization, it could be found that the structure of serpentine did not change significantly during the adsorption process, and Pb²⁺ was adsorbed on the serpentine surface as the precipitation of Pb(OH)Cl and Pb(OH)₂.     

Sensitization of Eu3+ luminescence with titanium(IV) oxide in the composition of nanoparticles in porous glasses

A series of modified porous glasses with a fixed europium content Q(Eu³⁺) = 30 μmol/g and a variable titanium oxide content Q(TiO₂) = 15–375 μmol/g are synthesized. The luminescence properties of the prepared glasses are investigated as a function of the component ratio in the composition of oxide nanoparticles. The specific features of the luminescence quenching in a wet medium are analyzed. It is shown that titanium(IV) oxide substantially sensitizes the photoluminescence of Eu³⁺ ions and shields them against the water adsorption.     

Study of complexing reactions causing the depletion of gadolinium ions from the moderator of CANDU-PHW nuclear reactors

The addition of gadolinium nitrate solution in the moderator of Hydro-Québec's Gentilly 2 reactor led to an unexpected depletion of gadolinium (Gd) by precipitation. Analysis of moderator samples revealed that bicarbonate (HCO₃^?) was the main anionic impurity. A study of the complexing reactions of Gd in concentrated solutions (0.0509M) of Gd(NO₃)₃ showed that in the absence of HCO₃^? and at pH < 6, the species in equilibrium are distributed as follows: predominant: Gd³⁺, NO₃^? and [GdNO₃]²⁺; and traces: [GdOH]²⁺ and [Gd(NO₃)₂]⁺. An increase in pH over 6.4 led to the formation of the solid phase: Gd₂(OH)_5.1(NO₃)_0.9. In the presence of bicarbonate, the solid phase Gd₂(OH)_5.0(NO₃)_1.0 is visually detected at a pH as low as 5.8. In other respects, analysis of dilute solutions (0.00065M) of Gd(NO₃)₃ containing bicarbonate allows the solid phase precipitating between pH 5.5 and 6.6 to be ascribed to the formula Gd₂(OH)₄CO₃·3H₂O. In the absence of HCO₃^?, no precipitation occurred up to pH 6.8. Finally, the loss of Gd from the moderator was established as being due to the formation of a hydroxide carbonate salt.     

Adsorption of trivalent chromium from aqueous solutions onto activated carbon

The adsorption of chromium (III) onto activated carbon was investigated as a possible alternative method for its removal from aqueous solutions. The adsorption data were obtained in a batch adsorber and fitted the Langmuir adsorption isotherm well. The effect of pH on the adsorption isotherm was investigated at pH values of 2, 4, 5 and 6. It was found that at pH values below 2 the Cr(III) was not adsorbed and at pH values above 6.4 the Cr(III) was precipitated as Cr(OH)₃. Maximum adsorption occurred at pH 5. The pH plays a very important role in the adsorption of Cr(III) since Cr(III) can form different complexes in aqueous solutions. The adsorption capacity was increased by about 20% as the temperature was raised from 25 to 40°C. It was concluded that Cr(III) is adsorbed to an appreciable extent on activated carbon and that the adsorption is highly dependent upon pH.     

Anion-responsive luminescent Eu3+ complexes with ring-like rigid quinoline–amide ligands

Two novel ring-like rigid quinoline–amide ligands, 2-[2-(1,3-dioxolan-2-yl)quinolin-8-yloxy]-N-benzylacetamide (L^I) and 3-[2-(1,3-dioxolan-2-yl)quinolin-8-yloxy]-1,1-diphenylpropan-2-one (L^II), were designed to assemble the anion-responsive luminescent europium complexes. Crystallographic studies of the EuL^I(NO₃)₃ and EuL^II(NO₃)₃ revealed that the tetradentate ligands L^I and L^II cooperatively coordinated with Eu³⁺ ion and some available sites around central europium ions for guest anions were reserved in the complexes. The luminescent properties of the Eu(III) nitrate complexes in acetonitrile solutions were investigated. And the lowest triplet state energy levels of the ligands are well placed to allow energy transfer to the resonance level of Eu(III). At the same time, the luminescence titration experiments and the Job's plot analysis demonstrated the formation of 1:1 complexes in the solutions. The luminescence intensities at 616 nm were enhanced by addition of NO₃^? or Cl^? anion to the mixed acetonitrile solutions of Eu(CF₃SO₃)₃ and the ligands.     

Novel luminescent europium(III) complexes covalently bonded to bis(phosphino)amine oxide functionalized MCM-41

A novel organo-functionalized mesoporous MCM-41 type of hybrid materials MCM–Si–DPBB was synthesized by co-condensation of bidentate Si(OR)₃ substituted N,N-2-diphenyloxyphosphine-4-bromomethyl-benzenamine (Si–DPBB) and tetraethoxysilane (TEOS) in the presence of the cetyltrimethylammonium bromide (CTAB) surfactant as template. Its ternary europium complex covalently bonded to the silica-based network MCM–Si–DPBB–Eu was also prepared by introduction the Eu(DBM)₃(H₂O)₂ into the hybrid materials. The hybrid material MCM–Si–DPBB–Eu has strong luminescence, and when excited by the ligands absorption wavelength (386 nm), it displays the emission of the Eu^{3+ 5}D₀-⁷F_J (J = 0, 1, 2, 3 and 4) transition lines due to the efficient energy transfer from the ligands to Eu³⁺.     

Adsorption of BSA on DEAE-Dextran: Equilibria

Abstract

Equilibrium isotherms for adsorption of BSA on DEAE-dextran have been determined experimentally. They were little affected by the initial concentration of BSA but were considerably affected by pH. They were correlated by the Langmuir equation when pH ≥ 5.05 and by the Freundlich equation at pH 4.8 (≈ pI). The maximum amounts of inorganic anion exchanged for BSA were 1 and 0.4% of the exchange capacity of the ion exchanger at pH 6.9 and 4.8, respectively. When NaCl coexisted in the solution, the shape of the isotherm was similar to the Langmuir isotherm but was shifted to the right. When the concentration of NaCl was 200 mol/m³, BSA was not adsorbed on the resin. When BSA was dissolved in pure water, the saturation capacity of BSA on HPO₄ ^2? -form resin was about 3.5 times larger than that with buffer (pH 6.9). The amount of BSA adsorbed on univalent-form resin decreased when the liquid-phase equilibrium concentration of BSA was increased.     

Synthesis of Eu-doped hydroxyapatite whiskers and fabrication of phosphor layer via electrophoretic deposition process

Highly biocompatible and efficiently luminescent whiskers of the hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) doped with various concentrations (0-5 at.%) of europium were prepared by hydrothermal synthesis and the Eu-doped Hap-coating layers onto the surface of titanium substrate were fabricated by the electrophoretic deposition (EPD) process for fluorescent probe application. The maximum doping concentration of Eu accommodating into the host lattice of HAp was detected as ~1.5 at.% and all the hydrothermally synthesized Eu-doped HAp whiskers were found to have high crystallinity and orientation growth along the c-axis by X-ray diffraction (XRD) identification. The valence of the doped Eu was identified as trivalent and divalent coexistence at a concentration percentage of Eu³⁺: Eu²⁺ = 78%: 22% by X-ray photoelectron spectroscopy (XPS) spectra. The replacement site of the doped Eu ions in the crystal structure of HAp host was clarified by Rietveld refinement. The whisker morphology of the hydrothermally synthesized particle was demonstrated by field-emission scanning electron microscopy (FE-SEM) observation and their component elements were analyzed by energy dispersive X-ray (EDX) mapping. The photoluminescence (PL) emissions of the Eu-doped HAp whiskers and fabricated their coating layers were both revealed mainly at ~615 nm (⁵D₀ → ⁷F₂) and ~697 nm (⁵D₀ → ⁷F₄), which is a wavelength that easily transmitting through living system for biological imaging. The PL emission are falling in the region of reddish orange and belonging to color temperature below 1500 K. Decay time and internal and external quantum efficiencies (QEs) were also measured to reveal them depending on the doping concentration of Eu. The hydrothermally prepared Eu-doped HAp whiskers would be aimed at biomedical application, due to their promising fluorescent function of probe for in vivo imaging in medical diagnose by utilizing the superior biocompatibility of the HAp host and highly efficient luminescent property of the Eu activator.