Calcium Carbonate@silica Composite with Superhydrophobic Properties

In this paper, spherical calcium carbonate particles were prepared by using CaCl₂ aqueous solution + NH₃·H₂O + polyoxyethylene octyl phenol ether-10 (OP-10) + n-butyl alcohol + cyclohexane inverse micro emulsion system. Then, nanoscale spherical silica was deposited on the surface of micron calcium carbonate by Stöber method to form the composite material. Scanning electron microscope (SEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology and structure of the composite material. It is found that the surface of the composite material has a micro-nano complex structure similar to the surface of a “lotus leaf”, making the composite material show hydrophobicity. The contact angle of the cubic calcium carbonate, spherical calcium carbonate and CaCO₃@SiO₂ composite material were measured. They were 51.6°, 73.5°, and 76.8°, respectively. After modification with stearic acid, the contact angle of cubic and spherical CaCO₃ were 127.1° and 136.1°, respectively, while the contact angle of CaCO₃@SiO₂ composite was 151.3°. These results showed that CaCO₃@SiO₂ composite had good superhydrophobicity, and the influence of material roughness on its hydrophobicity was investigated using the Cassie model theory.     

A direct nitrogen-15 NMR study of cerium(III)-nitrate complexes in aqueous solvent mixtures

A study of the complex formation which occurs between cerium(III) and nitrate ions in aqueous solvent mixtures has been carried out by a direct, low-temperature, nitrogen-15 (¹⁵N) NMR technique. At temperatures in the range of –95 to –110°C, ligand exchange is slow enough to permit the observation of separate¹⁵N NMR signals for bulk nitrate, and this anion in the cerium(III) principal coordination shell. In water-acetone-Freon-12 mixtures, the spectra reveal the nitrato complexes do not form consecutively. Rather, signals are observed for Ce(NO₃)²⁺, Ce(NO₃) ₂ ¹⁺ , and only two other higher order complexes, even at very high NO ₃ ^– to Ce(III) mole ratios. Signal area evaluations were used to identify the possible higher order complexes. At comparable salt concentrations in aqueous-methanol mixtures, only Ce(NO₃)²⁺ and Ce(NO₃) ₂ ¹⁺ are formed, reflecting a decreased tendency for complexation in media of higher dielectric constant.     

A Direct Carbon-13 and Nitrogen-15 NMR Study of Cerium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures

A study of lanthanide complexation with isothiocyanate is underway using a multinuclear magnetic resonance technique. For isothiocyanate solutions in water–acetone–Freon mixtures at low temperature, –85––125°C, ligand exchange is slow enough to permit the observation of ¹³C and ¹⁵N NMR signals for coordinated and free anions. For the Ce³⁺–NCS^– system, four coordinated anion signals, displaced from the free anion signal by about +450 to +550 ppm for ¹⁵N and +50 to +80 ppm for ¹³C, are observed. The ¹³C and ¹⁵N spectral data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Ce(NCS)²⁺ through Ce(NCS)^1- ₄. In water–methanol, the extent of complexing is decreased, presumably because of the higher dielectric constant of this medium. In addition, the results of a competitive study of NCS^– and Cl^– ion binding, carried out using ³⁵Cl NMR, is presented.     

Separation of cerium and europium by extraction with tributyl phosphate and di(2-ethylhexyl)phosphoric acid in n-alkane from nitrate solutions

The following extraction systems have been studied: (Ce³⁺+Eu³⁺) (NO₃)-(EDTA, DCTA, DTPA)/TBP in n-alkane and (Ce³⁺+Eu³⁺)(NO₃)/DEHPA in n-alkane at concentration ratios as follows: [Ce³⁺]=trace –1 mol·dm^–3, [Eu³⁺]=trace –0.1 mol·dm^–3. [TBP]=(0.183–1.83) mol·dm^–3, [DEHPA]=(5·10^–3–0.1) mol·dm^–3, [(H, Na)NO₃]=(0.1–6) mol·dm^–3, [Eu³⁺]: [EDTA, DCTA, DTPA]=11–110. The initial concentration of Eu³⁺ in aqueous phase in the extraction system containing a mixture of Ce³⁺ and Eu³⁺ was trace, 1% and 10% compared with the Ce³⁺ concentration. The distribution of the elements between the phases was observed radiometrically using¹⁴¹Ce,¹⁵²Eu and¹⁵⁴Eu. The results are documented by the distribution ratios D_Ce, D_Eu and separation factor =D_Eu/D_Ce as functions of variable parameters of the systems.     

Determination of rare earth element in carbonate using laser-ablation inductively-coupled plasma mass spectrometry: an examination of the influence of the matrix on laser-ablation inductively-coupled plasma mass spectrometry analysis

In this study, we examined the influence of the matrix on rare earth element (REE) analyses of carbonate with laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) using carbonate and NIST glass standards. A UV 213 nm Nd:YAG laser system was coupled to an ICP-MS. Laser-ablation was carried out in both He and Ar atmospheres to investigate the influence of ablation gas on the analytical results. A small amount of N₂ gas was added to the carrier gas to enhance the signal intensities. Synthetic CaCO₃ standards, doped with REEs, as well as NIST glasses (NIST SRM 610 and 612) were used as calibration standards. Carbonatite, which is composed of pure calcite, was analyzed as carbonate samples. The degree of the influence of the matrix on the results was evaluated by comparing the results, which were calibrated by the synthetic CaCO₃ and NIST glass standards. With laser-ablation in a He atmosphere, the differences between the results calibrated by the synthetic CaCO₃ and NIST glass standards were less than 10% across the REE series, except for those of La which were 25%. In contrast, for the measurements made in an Ar atmosphere, the results calibrated by the synthetic CaCO₃ and NIST glass standards differed by 25-40%. It was demonstrated that the LA-ICP-MS system can provide quantitative analysis of REE concentrations in carbonate samples using non matrix-matched standards of NIST glasses.     

Coordination and spectral-luminescence characteristics of Ce3+ in nonaqueous solutions

By means of luminescence spectroscopy, through the characteristics of interconfiguration transitions 4f^n–1 5d 4fⁿ, a study has been made of the composition and structure of the coordination sphere of Ce³⁺ in anhydrous alcohols in the presence of the inorganic anions ClO^– ₄, Cl^–, Br^–, and SCN^–. For solutions of CeCl₃ - or CeBr₃ or Ce(SCN)₃ ^–, it has been shown that the inner-sphere complexes Ce(R - OH)_8–XA_X ^{3 -x} dominate (where R 0B is a solvent molecule; A is an anion) in the concentration interval from 10^–4 to 10^–2 M, x = l. In solutions of Ce· (ClO )₄ in addition to the inner-sphere complex' an anion-freer form Ce(R³⁺ OH)_{6 3+} has been found. In the solutions that were investigated, dynamic equilibrium constants were determined, and also the absorption and luminescence characteristics of the individual species.A. N. Sevchenko Scientific-Research Institute of Applied Physics Problems, Belorussian University, Minsk. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. l, pp. 114–119, January–February, 1991. Original article submitted May 3, 1990.     

Separation of cerium from other lanthanides by leaching with nitric acid rare earth(III) hydroxide-cerium(IV) oxide mixtures

A simple operational method for separating cerium from other lanthanides in natural mixtures of cerium dioxide with lanthanide(III) hydroxides, obtained from Vietnamese parisite and Mongolian bastnasite, has been developed. The method is based on drying crude Ln(OH)₃×H₂O material in air at about 200°C within 6h, followed by leaching Ln(III) with concentrated nitric acid added carefully with stirring to the dried material/water 11.5 slurry. Under optimum conditions cerium (and Th, if present) virtually does not pass into solution while the yield of leaching and the sum of REE oxides (REO) concentration in the after-leach solution reach the maximum values of 97% (mass) and 0.18 kg·dm^–3, respectively. Besides an expected decrease of the leaching yield, roasting the starting material at 600°C results in over 7% Ce content in the Ln leached.     

Direct 1H, 13C, and 15N NMR Study of Lanthanum(III), Thulium(III), and Ytterbium(III) Complex Formation with Nitrate and Isothiocyanate

An ¹H, ¹³C, and ¹⁵N NMR study has been completed for the complexes of La(III), Tm(III), and Yb(III) with nitrate and isothiocyanate in aqueous solvent mixtures. Signals for four complexes are observed for both the Tm³⁺–NO₃ ^– and Yb³⁺–NO₃ ^– solutions, with the species identified as the mono-, di-, tetra-, and either the penta - or hexanitrato. These results are consistent with those determined for the nitrate complexes of the Ce(III)–Eu(III) metal ions. The chemical shifts for the Tm(III) and Yb(III) nitrate complexes indicate a pseudocontact binding mechanism prevails. The complexes of diamagnetic La(III) with NO₃ ^– produce three signals in the ¹⁵NO₃ ^– spectra, with assignments paralleling those observed with the paramagnetic lanthanides. Three complexes are formed in the La³⁺–NCS^– solutions, with signals assigned to the mono-, di-, and triisothiocyanato species.     

Exchangeable fraction of elements in alluvial sediments under waste disposal site (Zagreb, Croatia)

Concentrations of Ag, Ba, Cd, Ce, Cs, Co, Cr, Eu, Fe, Rb, Sc, Sr, Th, and Zn exchangeable fractions were determined in alluvial sediments at waste disposal site area in the vicinity of water-well field. Samples have been leached with 0.5M NH₄Cl at a sample/solution ratio of 120 during 24 hours without shaking. INAA of dry NH₄Cl residues show that the concentrations of exchangeable elements determined in the most of the sediments below the wastes have natural levels. Ag, Ba and Sr are readily exchangeable; Rb, Cs and Zn have lower exchangeability, while Cd, Ce, Th, Sc, Eu, Cr, Fe and Co are rather immobile. Extremely high total and exchangeable silver concentration was found at 6.5–6.8 meters below waste in the aerated layer occasionally under the water table. Exchangeable concentrations in deeper water-bearing sediment layers are not elevated. Due to this, one can presume that the upper sediment layers act as chemical filter generally preventing the infiltration from overlying wastes into water-bearing layers.     

Extraktions-Flammenabsorptionsbestimmung von Spurenverunreinigungen in Salzen

Zusammenfassung Spurenverunreinigungen von Fe, Cu, Pb, Ni, Co, Cd, Zn wurden in KH₂PO₄, KNa-Tartrat, BaCl₂, CaCl₂, Citronensäure, Li₂CO₃, Na₂CO₃, K₂CO₃, BaCO₃ und CaCO₃ durch Flammenatomabsorption nach Extraktionsanreicherung mit Diethylammonium-N,N-diethyldithiocarbamat/MIBK bestimmt. Der Einfluß der Salz-matrix auf die Extraktion und Bestimmung der Elementspuren wurde untersucht. Die Methode erlaubt die Bestimmung von 5 · 10^–6–5 · 10^–7% der Elemente mit guter Präzision und Richtigkeit (rel. Standardabweichung 2–7%).

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Extraction flame atomic-absorption determination of microtraces in salts

Summary The trace content of Fe, Cu, Pb, Ni, Co, Cd, Zn in KH₂PO₄, KNa-tartrate, BaCl₂, CaCl₂, citric acid, Li₂CO₃, Na₂CO₃, K₂CO₃, BaCO₃ and CaCO₃ is determined by flame atomic-absorption spectrometry after preceding preconcentration of the traces using the extraction system diethylammonium-N,N-diethyldithiocarbamate/ MIBK. The influence of the salt matrix on the extraction and determination of the traces was investigated. The method permits the determination of 5·10^–6–5·10^–7% of the elements with good precision and accuracy (relative standard deviation 2–7%).

     

Isolation of Rare-Earth Elements from Mixtures of Calcium and Lanthanide Oxalates

The temperature regions for separate crystallization of rare-earth element (REE) oxides of the cerium group in the presence of CaCO₃ have been determined using X-ray diffraction, differential thermogravimetric analysis, inductively coupled plasma mass spectroscopy, and X-ray fluorescence. The possibility to separate REE oxides from CaCO₃ in H₂SO₄ solutions after heat treatment (450–600°C) has been studied. The solid phase of the precipitate is represented by slightly soluble calcium sulfate, whereas the REE oxides pass into the liquid phase in the form of highly soluble sulfates. After heat treatment of the test mixture of REE oxalates and calcium oxalate at a temperature higher than 750°C, calcium compounds pass into 1–2% HNO₃ liquid phase in the form of nitrates, whereas lanthanide oxides remain in the insoluble phase of REE oxide solid solution having CeO₂ structure.     

Photocatalytic Activity of Fibrous Ti/Ce Oxides Obtained by Hydrothermal Impregnation of Short Flax Fibers

Fibrous Ti/Ce oxide photocatalysts were prepared for the first time by a biomimetic solution process using short flax fibers (flax straw processing waste) as a biotemplate. Titanium polyhydroxy complex solutions with 3% and 5% cerium were used as precursors. Flax fibers were impregnated in an autoclave under hydrothermal conditions. Ti/Ce oxides were obtained from the biotemplate by annealing at 600 °C. The photocatalytic activity of the Ti/Ce oxides was studied by the adsorption and decomposition of the dye rhodamine B under UV irradiation. The photocatalytic decomposition of the dye was 50% and 75% faster for Ti/Ce oxides with 3% and 5% Ce, respectively, than for the analogous undoped fibrous TiO₂. The morphologies, textures, and structures of the photocatalysts were studied by scanning electron microscopy, low temperature N₂ adsorption/desorption, UV-Vis spectroscopy, and X-ray and XPS analytical methods. It was shown that the introduction of Ce into the precursor solution increased the surface irregularity of the Ti/Ce oxide crystallites compared to pure TiO₂. This effect scaled with the Ce concentration. Ce improved the UV light absorption of the material. The Ti/Ce oxides contained Ce⁴⁺/Ce³⁺ pairs that played an important role in redox processes and intensified the photocatalytic activity.     

On the characteristics and mechanism of the radiation-induced chain reaction between sulfur dioxide and molecular oxygen in acid solutions

Characteristics of the -induced chain reaction between sulfur dioxide and molecular oxygen in perchloric and sulfuric acid media in the presence of Ce(III) ions have been studied. The concentration effects of dissolved oxygen (0.2·10^–3–9.4·10^–3 mol/dm³, sulfur dioxide (0.3·10^–1–2.0·10^–1 mol/dm³ and Ce(III) (0.2·10^–3–4.8·10^–3 mol/dm³) and dose rate (0.26·10¹⁹–1.0·10¹⁹ eV/dm³·s) on the radiation — chemical yield of oxygen consumption G(–O₂) and accumulation of sulfate G(HSO ₄ ^– ), have been investigated. The reaction proceeds with G(–O₂) reaching 10²–10³ molecule/100eV in a catalytic regime. The reaction rate in perchloric acid medium is 3–4 times lower than that in the sulfuric acid medium and depends on the SO₂, O₂ and Ce(III) concentrations, the reaction order varying from 1.0 to 0 and/or in the reverse direction. The mechanism of the process involves chain propagation with 3 stages and 3 intermediates: SO₃H, HSO₅ and Ce(IV). The catalytic effect is caused by the interaction of HSO₄ with Ce(IV) ions followed by their reduction when interacting with SO₂, yielding SO₃H radicals. Chain termination may be due to one or two of the three intermediates or due to all three particles, the kinetics depending on this. Kinetic equations describing the experimental data have been obtained.     

Effect of the Electrode Material on the Reduction of La<Superscript>3+</Superscript> and Ce<Superscript>3+</Superscript> in Fluoride-Conducting Solid Electrolytes

The reduction of immobile cations La³⁺ and Ce³⁺ in fluoride-conducting solid electrolytes (FSE) LaF₃ (Eu²⁺ 0.8 mol %), LaF₃ (Sr²⁺ 5 mol %), and CeF₃ (Sr²⁺ 5 mol %) in contact with Ag, Bi, Si, La, Ce, and Sm working electrodes is studied by chronoamperometry and voltammetry with linear potential scan. Discovered is linear dependence of initial segments of potentiostatic transients of cathodic current on t ^1/2 at FSE interfaces with Ag, Bi, La, Ce, and Sm. The dependence is due to diffusion-controlled instantaneous nucleation of Ln and Ce. The La³⁺ and Ce³⁺ reduction at the FSE/Ag interface is reversible in a narrow region. The reduction and oxidation of La³⁺ and Ce³⁺ (cations of the FSE rigid lattice) at the FSE/Me (Me = La, Ce and Sm, Bi, Si) interface is irreversible and involves a chemical reaction.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 662–672.Original Russian Text Copyright © 2005 by Turaeva, Kot, Urchukova, Murin.     

Cerium/Ascorbic Acid/Iodine Active Species for Redox Flow Energy Storage Battery

In this study, we developed a novel cerium/ascorbic acid/iodine active species to design a redox flow battery (RFB), in which the cerium nitrate hexahydrate [Ce(NO₃)₃·6H₂O] was used as a positive Ce³⁺/Ce⁴⁺ ion pair, and the potassium iodate (KIO₃) containing ascorbic acid was used as a negative I₂/I⁻ ion pair. In order to improve the electrochemical activity and to avoid cross-contamination of the redox pair ions, the electroless plating and sol–gel method were applied to modify the carbon paper electrode and the Nafion 117 membrane. The electrocatalytic and electrochemical properties of the composite electrode using methanesulfonic acid as a supporting electrolyte were assessed using the cyclic voltammetry (CV) test. The results showed that the Ce (III)/Ce (IV) active species presented a symmetric oxidation/reduction current ratio (1.09) on the C–TiO₂–PdO composite electrode. Adding a constant amount of ascorbic acid to the iodine solution led to a good reversible oxidation/reduction reaction. Therefore, a novel Ce/ascorbic acid/I RFB was developed with C–TiO₂–PdO composite electrodes and modified Nafion 117–SiO₂–SO₃H membrane using the staggered-type flow channel, of which the energy efficiency (EE%) can reach about 72%. The Ce/ascorbic acid/I active species can greatly reduce the electrolyte cost compared to the all-vanadium redox flow battery system, and it therefore has greater development potential.     

Kinetics of the radiation chemical reactions of tervalent and quadrivalent actinides and lanthanides in carbonate solutions

The reactions of the ions of tervalent and quadrivalent actinides and lanthanides with hydrated electrons e_aq ^– and CO₃ ^– radicals in concentrated carbonate solutions have been studied by microsecond pulse radiolysis, using spectrophotometric recording of short-lived particles. It is shown that the rate of the reactions of e_aq ^– with carbonato complexes of Ce(IV), Pu(IV), and Np(IV) is controlled by diffusion. The carbonato complex of Eu(III) reacts with e_aq ^–appreciably more slowly. A linear relationship is obtained between the logarithm of the rate constant for the reactions of CO₃ ^– with the carbonato complexes of Am(III), Ce(III), and Pu(III) and the redox potential of the complexes. The rate of the reaction of CO₃ ^– with Np(III) in carbonate solutions is controlled by diffusion.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 28–32, January, 1990.     

The concentration of rare earth elements in plants and in the adjacent soils

La, Ce, Nd, Sm, Eu, Tb, Yb and Lu were determined in needles of age class 5 from 6 individual Norway spruce trees and in their soils. Measurements were done by neutron activation analysis with a group separation of the REE. Concentrations in spruce needles are among the lowest values reported for plant leaves. Concentrations show small variations between the soils, but large variations between the trees. The mean ratio plant/soil is about 5·10^–3 forall REE except Ce. Needles have no Eu-anomaly and a strong negative Ce-anomaly with respect to the soil. In addition to the fractionation of the individual REE between trees and the soil, there is also a considerable fractionation between the trees.     

Synthesis,crystal structure and characterization of a novel cerium(III) coordination compound based on the Dawson cluster

A novel organic–inorganic complex, [Ce(NMP)₃(H₂O)₆][Ce(NMP)₃(H₂O)₅][P₂Mo₁₈O₆₂]·0.5 NMP·H₂O, (NMP = N-methyl-2-pyrrolidone) consisting of [Ce(NMP)₃(H₂O)₆]³⁺, [Ce(NMP)₃(H₂O)₅]³⁺ and [P₂Mo₁₈O₆₂]^6– entities, has been synthesized and characterized by element analysis, i.r. spectra, and single crystal X-ray structural analysis. The results of the single crystal X-ray diffraction analyses and i.r. spectra are agreement; both show that there is interaction between the metal cation units and the Dawson cluster. The low temperature e.s.r. spectrum indicates thermal electron delocalization occurs among the Mo atoms in the compound.     

Evaluation of a microwave-assisted extraction technique for determination of water-soluble inorganic species in urban airborne particulate matter

A simple and rapid microwave-assisted extraction (MAE) technique has been developed for the determination of water-soluble inorganic species (cations: Na⁺, NH₄⁺, K⁺, Ca²⁺ and Mg²⁺ and anions: F^–, Cl^–, NO₃^–, PO₄^3– and SO₄^2–) in airborne particulate matter. The analytes were extracted under different treatment conditions such as microwave power and extraction time. They were quantified using ion chromatography. The observed concentrations and recovery yields obtained under different conditions were compared. The results of a comparison between this MAE and sonication using NIST SRM 1648 are also given in this paper. The optimized MAE technique gave results in good agreement with the values obtained by the sonication. For some ions, for example Mg²⁺ and K⁺, recovery was low with both techniques. The results demonstrated that the optimized MAE is fast and efficient compared with conventional ultrasonic extraction. Urban airborne particles were collected and subjected to the MAE followed by the IC analysis to determine the relative proportions of different water-soluble inorganic species. These results are briefly discussed.