Selective ion exchange separation of uranium from concomitant impurities in uranium materials and subsequent determination of the impurities by ICP-OES

An ion exchange method has been developed for the separation of uranium from trace level metallic impurities prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES) in uranium materials. Selective separation of uranium from trace level metallic impurities consisting Cr, Co, Cu, Fe, Mn, Cd, Gd, Dy, Ni, and Ca was achieved on anion exchange resin Dowex 1 × 8 in sulphate medium. The resin (100–200 mesh, in chloride form) was packed in a small Teflon column (7.8 cm × 0.8 cm I.D.) and brought into sulphate form by passing 0.2 N ammonium sulphate solution. Optimum experimental conditions including pH and concentration of sulphate in the liquid phase were investigated for the effective uptake of uranium by the column. Uranium was selectively retained on the column as anionic complex with sulphate, while impurities were passed through the column. Post column solution was collected and analyzed by ICP-OES for the determination of metallic impurities. Up to 2,500 μg/mL of uranium was retained with >99% efficiency after passing 25 mL sample through the column at pH 3. Percentage recoveries obtained for most of the metallic impurities were >95% with relative standard deviations <5%. The method established was applied for the determination of gadolinium in urania–gadolinia (UO₂–Gd₂O₃) ceramic nuclear fuel and excellent results were achieved. Solvent extraction method using tributylphosphate (TBP) as extractant was also applied for the separation of uranium in urania–gadolinia nuclear fuel samples prior to the determination of gadolinium by ICP-OES. The results obtained with the present method were found very comparable with those of the solvent extraction method.     

Direct determination of bioavailable molybdenum in carbon nanotubes

Bioavailable residual metallic impurities within carbon nanotubes (CNTs) are responsible for the toxicity of CNTs. Herein we present a method for fast, sensitive determination of bioavailable molybdenum residual catalyst impurities within CNTs by using electrochemical oxidation in neutral pH buffers at low potentials. This method is unique because no other method can rapidly distinguish between bioavailable/mobilizable impurities from defects in CNTs and between the total amounts of impurities. This method will be indispensable for future toxicological studies of CNTs.     

Determination of U,Th and other impurities in molybdenum by radiochemical neutron activation analysis

A radiochemical separation method has been applied for determining uranium, thorium and other impurities in molybdenum metallic powder. The impurities of Na, K, Sm, Cr, Zr, Cs, Rb, Zn, Fe, Co and La were separated with a cation exchange resin, and uranium and thorium were, then, separated with an anion exchange resin. The content of impurities were determined by a single comparator method using two monitors, gold and cobalt.     

Inter-laboratory comparison of the chemical analysis of silicon nitride

Summary The results of a round robin for the determination of nitrogen, oxygen and carbon and the common metallic impurities like Al, Ca, Fe, Mg and Na in silicon nitride are reported. The following analytical methods have been tested: nitrogen by acid decomposition under pressure followed by Kjeldahl distillation; oxygen by carrier-gas hot extraction; carbon by combustion in oxygen and infrared detection; metallic impurities after acid decomposition under pressure and evaporation of silicon fluoride by AAS or ICP-OES.     

Impurities within carbon nanotubes govern the electrochemical oxidation of substituted hydrazines

Electrochemistry and electrocatalysis on carbon nanomaterials is at the forefront of research. The presence of carbonaceous and metallic impurities within carbon nanotubes (CNTs) is a persistent problem. Here we show that the electrochemistry of the entire group of hydrazine compounds is governed by impurities within single-walled, double-walled and few-walled CNTs. The oxidation of organic substituted hydrazines at CNTs is driven by nanographitic impurities, in contrast to unsubstituted hydrazine, for which the electrochemistry is driven by metallic impurities within CNTs. This finding is unexpected, as one would assume that a whole group of compounds would be susceptible to "electrocatalysis" by only one type of impurity. This discovery should be taken into account when predicting the susceptibility of whole groups of compounds to electrocatalysis by metallic or nanographitic impurities. Our findings have strong implications on the electrochemical sensing of hydrazines and on the use of hydrazines as fuels for nanomotors.     

Determination of metallic impurities in a silicon wafer by local etching and electrothermal atomic absorption spectrometry.

An etching technique for the determination of the metallic impurities distribution in silicon wafers has been developed. An area of 10 mmphi and 10 microm depth was etched by 100 microL of an etching solution with a HF and HNO3 mixture. The acid matrix was evaporated on the wafer surface by IR lamp illumination and vacuum exhaust. Metallic impurities remaining on the wafer surface were redissolved into the collection solution, which was measured by electrothermal atomic absorption spectrometry (ET-AAS). The recovery invested by local etching/ET-AAS was within 95 - 112% for Fe, Cu and Ni. The detection limit (3sigma) for Fe, Cu and Ni in silicon was 1 x 10(13) atoms/cm3. To confirm the applicability, local etching was applied to evaluate the effects of metallic impurities in a gettering study and the electronic properties of semiconductor devices. It was found that local etching is a useful sample preparation technique for the analysis of metallic impurities in a specific area on a silicon wafer.     

Enhanced adsorption performance of the graphene oxide with metallic ion impurities by elution

The graphene oxides (GOs) with various content of metallic ions impurities were prepared, and the adsorption performance of the GO before and after elution was evaluated. The prepared GOs were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma and atomic force microscopy. The results indicated that the metallic ion impurities hardly affected the interlayer distance, microstructure and thickness of the prepared GOs. The adsorption isotherm and adsorption kinetic results showed that the metallic ions adsorbed on the GO surface had a negative influence on both the adsorption capacity and rate. After eluted by HNO₃ or HCl, most of the metallic ions adsorbed on the GO‐91 surface were ion‐exchanged by the protons of the acid eluents, and the purified GO showed enhanced equilibrium capacities and improved adsorption rate. The elution efficiency of HCl was better than that of HNO₃, and the adsorption capacity and rate of the GO eluted by HCl approximately reached to those of the GO prepared from the graphite with high purity. It indicated that HCl could efficiently remove the metallic ions adsorbed on the GO surface. Copyright © 2017 John Wiley & Sons, Ltd.     

Metal-based impurities in graphenes: application for electroanalysis

We show here that metallic impurities presented in graphenes prepared from graphite can be usefully employed for electroanalysis. We demonstrate that cumene hydroperoxide electrochemical reduction on graphene containing iron-based impurities provides significantly larger voltammetric currents than the same experiment using iron oxide nanoparticles. This opens doors for turning metallic impurities into potentially useful components of graphene based electrochemical systems.     

SWNTs as catalyst and/or support in the catalytic decomposition of hydrocarbons

Various SWNT samples as either catalyst or catalytic support were used in the chemical vapor deposition (CVD) method for the growth of MWNTs. Catalysts were prepared by the impregnation of SWNT soot with different transition metals. Decomposition of acetylene was investigated at different temperatures (650–720 °C). The quality of both original SWNTs and the newly formed carbon nanostructures was assessed by TEM. A significant difference was found between selectivities of original (known as metallic impurities in SWNT soot) and the posteriorly deposited metallic particles. In the presence of active catalyst SWNT ropes tend to disappear, absorbed into carbon fibers or MWNTs.     

Metallic impurities in graphenes prepared from graphite can dramatically influence their properties

All at C? Graphenes prepared by the top-down exfoliation of graphite are shown to contain metallic impurities (see scheme, metal impurities shown as black dots). These impurities may dominate their properties and can have a negative influence on their potential applications.     

Carbocatalysis: The State of “Metal‐Free” Catalysis

The rise in global demand for crucial chemical compounds has driven immense research in the fundamental science of catalysis. Graphene and its derivatives (chemically modified graphene, CMGs) have recently emerged as a new class of heterogeneous catalyst that promises economically viable and greener routes to these compounds. Although CMGs possess unique catalytic properties, the actual active sites are often points of discussion. Current minimal understanding on the possible effects of metallic impurities on the electrocatalytic performances of these CMGs calls forth the need to raise awareness on possible metallic impurities misrepresenting the actual chemical catalytic performances of the CMGs. This Minireview highlights the latest advances in the application of CMGs as catalysts, with an emphasis on the possible effects of metallic impurities on CMG catalysis.     

Determination of trace impurities in zircaloy-2 and tellurium by spark source mass spectrometry

Determination of trace impurities in zircaloy-2 and tellurium by Spark Source Mass Spectrometry (SSMS) is reported. The advantage of SSMS lies in the fact that along with metallic trace constituents even the nonmetallic impurities and gases including hydrogen can also be determined.     

Redox reaction of p-aminophenol at carbon nanotube electrodes is accelerated by carbonaceous impurities

We show here that the enhanced electrochemical behaviour of carbon nanotubes towards the redox reactions of p-aminophenol does not stem from the innate properties of carbon nanotubes. Investigating the isolated effect of each component present within carbon nanotubes samples, which are the carbon nanotube, the graphitic and amorphous carbonaceous impurities and the metallic impurities, we have elucidated that solely the carbonaceous impurities, both graphitic and amorphous, significantly accelerate the electron transfer reaction of p-aminophenol at carbon nanotube surfaces.     

Versuche zur Anreicherung von Edelmetallspuren in Reinstquecksilber durch partielles Lösen der Matrix

Trace impurities of gold and palladium in metallic mercury can be enriched in a simple way by partially dissolving the sample in nitric acid. Practically the whole trace content of the sample will be collected in the residue. Up to at least 100 g Hg the quantity of the mercury sample has no influence on the trace enrichment. After the partial dissolution of the metal the enriched gold was determined photometrically with Rhodamine B as a reagent, Pd was determined as [PdJ₄]^2? complex. For the analysis of metallic mercury containing 0.5 ppm of Au and 2 ppm of Pd the relative standard deviation is 0.046, respectively 0.037. The limit of detection was found to be at 0.2 ppm for both the elements. Using this method, the enrichment of traces of silver in mercury is not possible.     

Effect of impurity on electronic properties of carbon nanotubes

We have studied the effect of impurity on electronic properties of single-walled carbon nanotubes using Density Functional Theory. Electronic band structures and density of states of (4, 4) and (7, 0) carbon nanotubes in the presence of different amount of B and N impurities were calculated. It was found that these impurities have significant effect on the conductivity of carbon nanotubes. The metallic (4, 4) nanotube remains to be metallic after doping with B and N. The electronic properties of small gap semiconducting (7, 0) tube can extensively change in the presence of impurity. Our results indicate that B-doped and N-doped (7, 0) carbon nanotubes can be p-type and n-type semiconductors, respectively.     

X射线荧光光谱测定石墨烯粉体中的杂质元素

石墨烯粉体是我国已具备规模化生产能力的主要石墨烯材料,针对其关键物理化学特性建立准确可靠的测量方法极为重要.开发了一种利用X射线荧光光谱（XRF）技术对石墨烯粉体中杂质进行快速、无损分析的检测方法,可实现对石墨烯粉体产品质量的便捷初判.研究了石墨烯粉体样品的不同测试形态,并通过将XRF测量结果与电感耦合等离子体-原子发射光谱（ICP-OES）、电感耦合等离子体-质谱（ICP-MS）和X射线能谱（EDX）等检测技术的测量结果进行对比,结果表明XRF可对石墨烯粉体样品中的非金属杂质S、Cl、Si、P及金属杂质Na、Mg、Ca、Fe、Cu、Ti、W、Cr等可靠检出,可实现对石墨烯粉体中杂质元素的快速、简便、无损低成本的定量测量.     

Determination of Traces of Copper,Lead, and Cadmium in Cobalt by Derivative Pulse Polarography

Abstract

A derivative pulse polarographic method is described for determining traces of copper, lead and cadmium in cobalt and its compounds without separation. In hydrochloric acid medium the detection limits are respectively about 0.02, 0.04 and 0.1 ppm in metallic cobalt when analysing 2 M cobalt solutions. The procedure was applied to the analyses of synthetic and commercially available cobalt samples and showed a satisfactory sensitivity and precision at various concentrations levels of the three impurities.     

Metallic Impurities within Residual Catalyst Metallic Nanoparticles Are in Some Cases Responsible for “Electrocatalytic” Effect of Carbon Nanotubes

It′s what′s on the inside that counts : In some cases, the metallic impurities within residual catalyst metallic nanoparticle impurities, which remain in carbon nanotubes even after their purification, are responsible for the “electrocatalytic” properties of carbon nanotubes. This is demonstrated by using double‐walled carbon nanotubes (DWCNTs) containing cobalt residual catalyst nanoparticle impurities, which themselves contain iron‐based impurities.

     

Bestimmung und abtrennung von sauerstoffverunreinigungen in reinst-selenThe determination and separation of oxygen impurities in high-purity selenium

(The determination and separation of oxygen impurities in high-purity selenium)By distillation in high vacuum, high-purity selenium is almost completely freed from impurities caused by metallic elements, oxides and water. If bulk vitreous selenium has a suitable thermal history, the oxygen content may be determined from the intensity of the oxide absorption band at 932 cm^?1 in the i.r. spectrum of the glass. In distilled selenium this content is < 1 × 10^?4 wt.< %.