Synthesis of hollow spherical silica with MCM-41 mesoporous structure

Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm^–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N₂ gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N₂ adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased     

Synthesis and Efficiency of a Spherical Macroporous Epoxy-Polyamide Chelating Resin for Preconcentrating and Separating Trace Noble Metal Ions

A new spherical macroporous epoxy-polyamide chelating resin was synthesized from epoxy resin by simple and rapid means and used for the preconcentration and separation of trace noble metal ions from solution samples. The acidity, flow rate, reusability, capacity and interference with the adsorption of ions on the resin as well as the conditions of desorption of these ions from the resin are discussed. The results show that the relative standard deviations for the determination of 50ng mL^–1 Au(III), Pt(IV) and Pd(IV) by inductively coupled plasma atomic emission spectrometry are in the range of 0.5–3.6%. The procedure was applied to determine metal smelter samples with satisfactory results.     

The behaviour of plutonium in aqueous basic media

Behaviour of Pu(IV) and Pu(VI) in basic media has been investigated by studying their stabilities and quantitative determination by spectrophotometry. Beer's law was found to be obeyed in the range of 1·10^–3 to 5·10^–3 M Pu(IV) at 485 nm peak with a molar absorption coefficient of 95M^–1· cm^–1 in sodium carbonate medium. In case of Pu(VI), in the same medium Beer's law was obeyed in the concentration range of 2·10^–3 to 1·10^–2M at 550 nm with a molar absorption coefficient of 50M^–1·cm^–1. Distribution ratios of Pu(IV) and Pu(VI) for their sorption on Al₂O₃ and Amberlyst A-26 (MP) resin from bicarbonate and carbonate media have been determined. High distribution ratios obtained indicate the feasibility of decreasing the plutonium content of basic carbonate streams in reprocessing. 10% breakthrough capacities for Pu(IV) and Pu(VI) with these exchangers during column operations have also been determined.     

Titrimetric determination of octacyanotungstate(IV) ions with N-bromosuccinimide

Summary N-Bromosuccinimide has been successfully applied in the determination of 1–50 mg of W(CN)₈ ^4–in approximately 6 M hydrochloric acid using Naphthol Blue Black indicator. The average error is ±0.42% and the average standard deviation is ±0.06 mg. The method is not applicable to the determination of Mo(CN) ₈ ^4– ions. Tetrakis-(N-hydro-2-carbocyclic acid-pyridinium)octacyanotungstate(IV) and -molybdate(IV) were used as primary standards for the preparation of standard Mo(IV) and W(IV) solutions. The composition of the latter compounds was verified by analysis and single crystal X-ray data were obtained.

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Titrimetrische Bestimmung von Octacyanowolframat(IV)-ionen mit N-Bromsuccinimid

Zusammenfassung N-Bromsuccinimid wurde mit Erfolg zur Bestimmung von 1–50 mg W(CN)₈ ^4–-Ionen in ungefähr 6 M Salzsäure mit Naphthol-Blau-Schwarz als Indicator verwendet. Der mittlere Fehler beträgt ±0,42 %, die mittlere Abweichung ±0,06 mg. Die Methode ist nicht brauchbar für die Bestimmung von Mo(CN)₈ ^4–-Ionen. Tetrakis(N-hydro-2-carbonylsäure-pyridinium) octacyanowolframat(IV) und -molybdat(IV) wurden als Primärstandards für die Herstellung von Standard-Mo(IV)- und -W(IV)-Lösungen benutzt. Die Zusammensetzung dieser Verbindungen wurde durch Analyse kontrolliert und die Einkristall-Röntgen-Daten wurden festgestellt.

     

Interference of humic substances on the speciation analysis of inorganic selenium in waters and soils by DPCSV

A speciation scheme allowing the study of selenium speciation in environmental samples has been developed in order to study the transfer mechanism in the system water/soil/plant/animal. This scheme is based on a set of sample treatment procedures followed by Se(IV) determination by Differential Pulse Cathodic Stripping Voltammetry (DPCSV). Se(IV) may be determined with a detection limit close to 25 ng l^–1 and a linear response in the range 25–4000 ng l^–1. However, humic substances, present in some natural waters and soils, which are adsorbed at the mercury drop electrode (HMDE) surface may alter the signal. This may be caused by a competition between adsorption of organic matter and mercury(II) selenide formation at the electrode surface. As a consequence the detection limit has been increased to ca. 250 ng l^–1 in the presence of 1 mg l^–1 fulvic acids; the linear response range is then shifted to 250–10000 ng l^–1. After an extensive study of these interferences and using standard additions procedures, the Se(IV) content of various waters and soil extracts has been determined by DPCSV with a good reproducibility (RSD about 1%). Accuracy is satisfactory comparing the results obtained by DPCSV to those obtained by Hydride Generation/Quartz Furnace Absorption Atomic Spectrometry (HG/QFAAS).     

Adsorptive stripping voltammetric measurements of trace amounts of platinum(II) and ruthenium(III) in the presence of 1-(2-pyridylazo)-2-naphthol

An extremely sensitive stripping voltammetric procedure for low level measurements of platinum (II, IV) or ruthenium (III, IV) is reported. The method is based on the interfacial accumulation of the platinum (II) or ruthenium (III)-1-(2-pyridylazo)-2-naphthol complex on the surface of a hanging mercury drop electrode, followed by the reduction of the adsorbed complex during the cathodic scan. The peak potential was found to be –0.8 V vs. Ag/AgCl electrode and the reduction current of the adsorbed complex ions of platinum (II) or ruthenium (III) was measured by differential pulse cathodic stripping voltammetry. The optimum experimental conditions were: 1.5×10^–7 mol/l of 1-(2-pyridylazo)-2-naphthol solution of pH 9.3, preconcentration potential of –0.2 V, accumulation time of 3 min and pulse amplitude of 50 mV with 4 mV s^–1 scan rate in the presence of ethanol-water (30% v/v) — sodium sulphate (0.5 mol/l). Linear response up to 6.4 × 10^–8 and 5.1 × 10^–8 mol/l and a relative standard deviation (at 1.2×10^–8 mol/l) of 2.4 and 1.6% (n=5) for platinum (II) and ruthenium (III) respectively were obtained. The detection limits of platinum and ruthenium were 3.2×10^–10 and 4.1×10^–10 mol/l, respectively. The electronic spectra of the Pt(II) — PAN and Ru(III) — PAN complexes were measured at pH 9.3 and the stoichiometric ratios of the complexes formed were obtained by the molar ratio method. The effects of some interfering ions on the proposed procedure were critically investigated. The method was found suitable for the sub-microdetermination of ruthenium (IV) and platinum (IV) after their reduction to ruthenium (III) and platinum (II) with sulphur dioxide in acid media. The applicability of the method for the analysis of binary mixtures of ruthenium (III) and (IV) or platinum (II) and (IV) has also been carried out successfully. The method is simple, rapid, precise, and promising for the determination of the tested metal ions at micro-molar concentration level.     

Spectrophotometric determination of vanadium(IV) in the presence of vanadium(V) using Br-PADAP

In the present paper, a simple and sensitive method is proposed for vanadium(IV) determination in the presence of vanadium(V). This is based on the oxidation of vanadium(IV) present in the sample to vanadium(V) by addition of iron(III) cation, followed by a complexation reaction of iron(II) with the spectrophotometric reagent 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). The iron(II) reacts with Br-PADAP immediately, forming a stable complex with a large molar absorptivity. The vanadium(IV) determination is possible, with a calibration sensitivity of 0.549 g ml^–1, for an analytical curve of 18.8 ng ml^–1 to 2.40 g ml^–1, molar absorptivity of 2.80 × 10⁴ 1 mole^–1 cm^–1 and a detection limit of 5.5 ng ml^–1. Selectivity was increased with the use of EDTA as a masking agent. The proposed method was applied for the vanadium(IV) determination in the presence of several amounts of vanadium(V). The results revealed that 200 g of vanadium(V) do not interfere with determination of 5.00 g of vanadium(IV). The precision and the accuracy obtained were satisfactory (R. S. D.<2%).     

Volumetric determination of uranium in a mixture of uranium and plutonium employing Fe(III) as titrant

Summary A method for the determination of U in the presence of Pu based on the reduction of U to U(IV) and Pu to Pu(III) by zinc amalgam followed by oxidimetry of U(IV) has been developed. Fe(III) perchlorate was chosen as the most suitable titrant for the selective oxidation of U(IV) as conventional oxidising titrants fail in the presence of Pu(III). The potentiometric titration of U(IV) with Fe(III) is known to be slow. This problem, however, has been overcome by selecting a suitable buffer medium and complexing agent to alter the potentials of the Fe(III)/Fe(II) and U(VI)/U(IV) systems in the favourable direction. Results of the titration of U(IV) with Fe(III) at pH 2 in the presence of ferrozine as complexing agent for Fe(II) are summarized. R.S.D. obtained for twenty determinations of 3–5 mg of U was 0.3 % in the presence of 1–4 mg of Pu.

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Volumetrische Bestimmung von Uran in einem U/Pu-Gemisch mit Hilfe von Fe(III)

Zusammenfassung Das Verfahren beruht auf der Reduktion von U zu U(IV) und Pu zu Pu(III) mit Hilfe von Zinkamalgam und anschließender Titration mit Fe(III)-perchlorat. Dieses Reagens hat sich für die selektive Oxidation des U(IV) am besten bewährt, da andere Oxidationsmittel in Gegenwart von Pu(III) versagen. Die Endpunktsindikation erfolgt potentiometrisch, wobei die an sich langsame Einstellung des Endpunktes dadurch beschleunigt wird, daß durch Zusatz eines geeigneten Puffers und eines Komplexierungsmittels (Ferrozin) für Fe(II) die Redoxpotentiale von Fe(III)/Fe(II) und U(VI)/U(IV) entsprechend verschoben werden. Die relative Standardabweichung für die Bestimmung von 3–5 mg U in Gegenwart von 1–4 mg Pu liegt bei 0,3%.

     

A novel salicylate-selective electrode based on a Sn(IV) complex of salicylal-imino acid Schiff base

A novel poly(vinyl chloride) membrane electrode with high selectivity toward salicylate (Sal^–), based on the use of the salicylal-imino acid Schiff base dibenyl complex of Sn(IV) [Sn(IV)-SIADBen] as ionophore is described. The influence of lipophilic charged additives on the performance of the electrode was studied. The results suggested that Sn(IV)-SIADBen according to a positively-charged carrier mechanism. The influence of several other variables was investigated in order to optimize the potentiometric response and selectivity of the electrode. The electrode based on Sn(IV)-SIADBen, with 30.44 wt% PVC, 64.55 wt% plasticizer [dioctyl phthalate (DOP)], 3.81 wt% ionophore, and 1.2 wt% anionic additive exhibited a linear response for the Sal^– ion over the concentration range 1.0×10^–1 to 2.5×10^–6 mol l^–1, and displayed an anti-Hofmeister selectivity sequence as follows: salicylate perchlorate > thiocyanate > benzoate > iodide > nitrate > chloride > nitrite acetate > citrate > sulfate. UV-Visible absorption spectra were used to examine the specific interaction of salicylate with the ionophore. The electrode was applied to clinical medical analysis, and the results obtained were consistent with those obtained by conventional methods.     

Determination of fluoride by spectrophotometry of Arsenazo(III) complex of the back-extracted Th(IV)

A method based on the back-extraction of Th(IV) from its TTA complex in benzene by aqueous F^– followed by spectrophotometric measurement of Th(IV), for the determination of fluoride has been developed. The coefficients of variation obtained are 2.4% and 1.4% in 11 determinations at F^– concentration levels of 1.0 g ml^–1, respectively.     

Separation of mixtures of permanent gases and light hydrocarbons on spherical carbon molecular sieves by gas-solid chromatography

Summary Experimental results are presented on the application of Carbosieve S (Supelco) and Spherocarb (Analabs) spherical carbon molecular sieves for the gas chromatographic separation of mixtures of permanent gases and C₁–C₃ hydrocarbons using a single column or two columns in series. At a programmed temperature of 35–300°C, good separation of the sample components was obtained when using helium as the carrier gas. When hydrogen was used as the carrier gas and the analysis was carried out under isothermal conditions the elution sequence of oxygen and nitrogen reversed as the temperature was increased. This behaviour was observed within a temperature range of 35–225°C for Carbosieve S, and within a temperature range of 35–300°C for Spherocarb.     

On line speciation of Se(VI), Se(IV), and trimethylselenium by HPLC-microwave oven-hydride generation-atomic absorption spectrometry

An on-line system is proposed consisting of an anion-exchange chromatographic column, microwave-induced thermooxidation of trimethylselenium in the presence of persulphate, and microwave-induced thermoreduction of Se(VI) to Se(IV) in HCl medium, followed by hydride generation and atomic absorption for the determination of trimethylselenium (TMeSe), Se(IV) and Se(VI). Trimethylselenium is eluted in the dead volume of an anion-exchange column (Hamilton PRP-X-100), before elution of Se(IV) and Se(VI). Optimum chromatographic conditions have been obtained using 100 mmol L^–1 phosphate buffer (pH=6.8) H₂PO ₄ ^– /HPO ₄ ^2– as the mobile phase. Recoveries were around 100%, absolute detection limits were 1.1, 1.4 and 2.2 ng for TMeSe, Se(IV) and Se(VI), respectively. Precision was lower than 10% in all cases. The method has been applied to tap water.     

Synthesis of Spherical Titanium Dioxide Particles by Homogeneous Precipitation in Acetone Solution

Titania powders were synthesized by thermal hydrolysis of titanium tetrachloride in a mixed solvent was studied. The dielectric constant was tuned by regulating the acetone/water volume ratio (R/H ratio) and temperature of the solvent. Hydroxypropyl cellulose (HPC) was used as a steric dispersant. The synthesis were carried out at R/H ratios of 0–4, temperatures of 70–90°C, TiCl₄ concentrations of 0.05–0.2 M, HPC concentrations of 0–5 × 10^–3 g/cm³, and synthesis times of 15–60 min. The TiO₂ particles obtained at an R/H ratio of 0, i.e., pure water system, were fine and agglomerated. In contrast, the TiO₂ particles prepared at an R/H ratio of 3 were uniform and spherical. The TiO₂ particle size increased with increasing TiCl₄ concentration. The synthesis temperature did not influence the particle size, but greatly influenced the morphologyof the TiO₂. Adding HPC to the solution yielded more uniform and spherical particles. In addition, the synthesis time should be longer than 30 min to obtain the most uniform and spherical particles. The dielectric constant of the acetone-water mixed solvent at 28 gave the most uniform and spherical TiO₂ particles. The powders prepared at the condition of 0.1 M TiCl₄, R/H ratio of 3, HPC concentration of 0.001 g/cm³, temperature of 70°C, and synthesis time of 1 h exhibited the most uniform and spherical morphology. The as-synthesized powder was anatase and retained the phase below 400°C. It transformed to the rutile phase after calcination at 700°C.     

Sorption of Tc(IV) and Tc(VII) on Soils: Influence of Humic Substances

The technetium sorption behaviour in different samples of soils was studied under aerobic conditions. Tc(VII) was reduced to Tc(IV) by Sn²⁺ ions. About 99% of reduced technetium is absorbed by the soils under investigation. Sorption of TcO₄ ^– was studied in short-term (1-hour) and long-term (1-month) experiments. Sorption of TcO₄ ^– in presence of sodium humate (Aldrich) was generally lower than from pure water (from 99% to 12%) and depends on the depth of origin of the ground. Immobilisation of TcO₄ ^– after sorption on superficial sample of soils was studied by paper chromatography. Oxidation of Tc(IV) in presence of NO₃ ^– and NO₂ ^– (concentration range 10^–1–10^–5 mol·dm^–3) ions was studied as a function of time and concentration of NO₃ ^– and NO₂ ^– ions. The content of Tc(IV) in NO₃ ^– and NO₂ ^– solutions decreases with time (46 hours) relatively slowly.     

Chiroptical properties of steroid 1,3-diaxial diols in the presence of [Mo2(OAc)4]

Summary Bidentate complexes of dimolybdenum tetraacetate with 1,3-diaxial diols show Cotton effects around 490–540 nm (CD band I), 400–440 nm (II), 350–380 nm (III), 320 nm (IV) and 280 nm (V). The sign of the Cotton effect II can be predicted by a proposed sector rule. It seems that from the Cotton effects for cyclic 1,3-diols the absolute configurations or conformations can be obtained.A part of this material was presented at III-rd International Conference on CD Spectroscopy [1]     

Fabrication and electrochemical properties of novel ternary Sb–Co–P alloy electrodes for lithium-ion batteries

A novel ternary Sb–Co–P alloy electrode was prepared by electroplating on copper current collector as a promising negative electrode material for lithium-ion batteries. The structural and morphological features of the Sb–Co–P alloy were characterized by powder X-ray diffraction (XRD) and scanning electron microscope (SEM). The as-prepared alloy electrode exhibits a high specific capacity and an excellent cycleability. The initial discharge and charge capacities of the Sb–Co–P alloy anode were measured 700 and 539 mA h g⁻¹, respectively. The results suggest that the Sb–Co–P alloy material obtained by the electrodeposition shows a good candidate anode material for lithium-ion batteries.     

The mean association number: Ultraviolet spectroscopic study of PbCl2−H2O−C2H5OH

The concept of mean asociation number (MAN) has been proposed to describe the association state of an electrolyte. Both the mean spherical approximation (MSA) and the generalized mean spherical approximation (GMSA) are used to calculate the MAN. The theoretical results obtained are compared to the experiment results from an ultraviolet spectroscopic study of PbCl₂–H₂O–C₂H₅OH solutions and also to the predictions of the Bjerrum theory as given by Friedman.     

The size of sodium dodecyl sulfate micelles in the presence ofn-alcohols as determined by fluorescence quenching measurements

The steady-state fluorescence quenching technique was used to investigate the effect of the presence of a series of alcohol homologues of mid-sized straight chain on the size of mixed micelles of sodium dodecyl sulfate (SDS). We used pyrene at concentration of ca. 10^–6M, where only its monomer exhibits any fluorescence, as fluorescent probe, and cetylpiridinium chloride at concentrations in the range (1–9)×10^–5 M as quencher. This technique allows one to determine the micellar aggregation number. The number of alcohol molecules per micelle was calculated from reported values for the micelle-water partition coefficient. On the assumption of spherical micelles, their hydrophobic radii was then calculated. The hypothesis that micelle size is determined by the available surface area per charged headgroup is discussed in the light of the results obtained.     

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.     

Extraction of U(VI), Th(IV), and La(III) from acidic streams and geological samples using AXAD-16–POPDE polymer

A new chromatographic extraction method has been developed using Amberlite XAD-16 (AXAD-16) resin chemically modified with (3-hydroxyphosphinoyl-2-oxo-propyl)phosphonic acid dibenzyl ester (POPDE). The chemically modified polymer was characterized by ¹³C CPMAS and ³¹P solid-state NMR, Fourier Transform–NIR–FIR–Raman spectroscopy, CHNPS elemental analysis, and thermogravimetric analysis. Extraction studies performed for U(VI), Th(IV), and La(III) showed good distribution ratio (D) values of approximately 10³, even under high acidities (1–4 M). Various physiochemical parameters that influence the quantitative metal ion extraction were optimized by static and dynamic methods. Data obtained from kinetic studies revealed that a time duration of 10 min was sufficient to achieve complete metal ion extraction. Maximum metal sorption capacity values under optimum pH conditions were found to be 1.38, 1.33, and 0.75 mmol g^–1 for U(VI), Th(IV), and La(III), respectively. Interference studies performed in the presence of concentrated diverse ions and electrolyte species showed quantitative analyte recovery with lower limits of analyte detection being 10 and 20 ng cm^–3 for U(VI) and both Th(IV) and La(III), respectively. Sample breakthrough studies performed on the extraction column showed an enrichment factor value of 330 for U(VI) and 270 for Th(IV) and La(III), respectively. Analyte desorption was effective using 15 cm³ of 1 M (NH₄)₂CO₃ with >99.8% analyte recovery. The analytical applicability of the developed resin was tested with synthetic mixtures mimicking nuclear spent fuels, seawater compositions and real water and geological samples. The rsd values of the data obtained were within 5.2%, thereby reflecting the reliability of the developed method.