Levels Of Metal Impurities Research Articles

The challenge to produce magnetic nanoparticles from waste containing heavy metals aiming at biomedical application: New horizons of chemical recycling

Silica-coated magnetite nanoparticles (SMNPs) were prepared by a green approach based on waste pickling acid. A set of techniques (PXRD, ATR, VSM, SEM, TEM, DLS and XPS) was used for their characterization, and for monitoring the levels of heavy metal impurities. The SMNPs presented an expected profile, similar to that reported for nanoparticles produced from fresh chemicals. The crystallinity and magnetic saturation confirmed the formation of the Fe3O4 phase, silanol and siloxane absorption bands, as well as TEM images confirmed the coating SiO2. The SMNPs chosen for the biomedical tests did not present a significant level of contaminants, and the non-toxic silica coat produced by the sol-gel method ensured a preliminary study on its biocompatibility with reproductive cells in vitro. SMNPs presented a high ability to immobilize spermatozoon cells, suggesting that a fine control of their surface charge must be carried out for specific biomedical purposes. The agglomeration of the solid NPs was evidenced by SEM and by DLS measurements. Its aggregation was tuned by sonication, and a 5-min long ultrasound treatment was capable of halving the agglomerate size, allowing a one-to-one interaction (one SMNPs agglomerate to each cell). The CASA system used to monitor the semen quality showed that vigor, motility and velocity parameters were kept at levels very close to the control group. Finally, a waste-based input submitted to a meticulous purification process could be used as a source for magnetic materials synthesis and evaluated in the biomedical field as long as all precautions are taken into account.

Wide range hydrogen sensing behavior of a silver delafossite: Performance towards long term stability, repeatability and selectivity

Wide range H2 sensing behavior and the long term performance of thick films of AgInO2 delafossite, composed of hexagonal nanoplates, is presented. The material responds from 1 ppm to 10,000 ppm of H2 at the operating temperature of 360 °C at different humidity levels. The material exhibits a high degree of selectivity and repeatability without any significant drift in the baseline. AgInO2 exhibits oxygen non-stoichiometry. Both chemisorbed and lattice oxygen of AgInO2 participate in gas sensing. Presence of trace levels of metallic (Ag) or oxide (In2O3) impurities degrades its sensitivity and selectivity towards hydrogen.

An EXAFS and XANES Study of V, Ni, and Fe Speciation in Cokes for Anodes Used in Aluminum Production

Lower-quality petroleum coke with higher levels of sulfur and metal impurities will have to be used for the manufacturing of anodes for aluminum production in the future. The sulfur and metallic impurities affect the anode properties in the aluminum production process, but the chemical identity of the metal species in the coke is not known. In this study, industrial petroleum cokes with high sulfur levels were analyzed by X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS) in order to determine the identity of the V, Ni, and Fe impurities. The XANES spectra were compared with pure-phase standards. EXAFS was used to compare the impurity metal structures with known crystal structures. It was found that V is present mainly as hexagonal V3S4. Ni is present mainly as hexagonal NiS, and Fe is present as hexagonal FeS. This knowledge of the chemical states of the metal elements in coke, which are known to affect anode performance, is the first step in understanding the mechanism of the action of these elements on anode reactivity.

Direct determination of impurities in high purity chemicals by electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES)

An ELCAD-AES method was reported for direct determination of metallic impurities in different high purity chemicals such as ammonium hydroxide, hydrogen peroxide and sulphuric acid. Direct analysis of these chemicals for their impurities was found to be feasible by ELCAD-AES without going for chemical processing/treatment like dilution or evaporation of matrix. 100% solutions of NH4OH and H2O2 chemicals produced stable ELCAD plasma, whereas 0.5% solution produced stable plasma for H2SO4. As standard addition calibration method to quantify impurities in these chemicals could not be useful, an alternative aqueous calibration method was examined and found to be suitable for their quantification by ELCAD-AES. As the certified reference materials for these chemicals were not available, the ELCAD-AES results were validated with the corresponding graphite furnace atomic absorption spectrometer (GF-AAS) results for NH4OH and H2O2 whereas for sulphuric acid they were validated with inductively coupled plasma optical emission spectrometer (ICP-OES) and supplier's results. ELCAD-AES method was free from matrix related problems and did not demand for the dilution of NH4OH and H2O2. The method was found to be useful for direct determination of trace and ultra trace metallic impurities in NH4OH and H2O2 pure chemicals and also for trace impurities in H2SO4 chemicals. Repeatability and accuracy of this method were found to be <10% and between 10 and 20% respectively. Thus ELCAD-AES could be an alternative analytical, rapid and direct analysis technique to check levels of metallic impurities (i.e. metal salts) and quality of these high purity chemicals for various industries.

The influence of impurities on the crystal structure and mechanical properties of additive manufactured U–14 at.% Nb

Uranium-niobium alloys can exist with significantly different microstructures and mechanical properties, heavily influenced by thermomechanical processing history and impurities. Here, the influence of Ti and other impurities is studied on uranium-14at.% niobium additively manufactured using laser powder bed fusion. Two different metallic impurity levels were investigated and a Nb equivalent (Nbeq) composition is defined to represent the impurities. In-situ neutron diffraction during compression loading shows that increased Nbeq promotes the formation of γ°-tetragonal phase at the expense of α″-monoclinic phase, resulting in 2× higher yield strength than water quenched α″ and a strain induced transformation to α″ with superelastic strains to 4.5%.

Conversion of Bulk Metallurgical Silicon into Photocatalytic Nanoparticles by Copper-Assisted Chemical Etching

Low-grade metallurgical silicon (MG-Si, purity ∼98%–99%, $1/kg) with annual production over six million tons is an attractive feedstock to produce active photocatalysts. However, MG-Si is known as an electronically dead material due to serious charge recombination associated with high metal impurity levels. Upgrading MG-Si close to solar grade is essential to achieve desired performance; nevertheless, the traditional silicon refinement process is cost ineffective, has high energy consumption, and causes environmental pollution. Here, we address this critical issue by employing a room-temperature one-step Cu-assisted chemical etching (CuACE) process, which successfully purifies MG-Si into active photocatalysts. We discover that the use of reducing agent (H3PO3) instead of commonly employed oxidant (H2O2) in the etchant system induces a novel phenomenon called “chemical cracking effect”. This effect significantly decreases the granularity of bulk MG-Si particles and simultaneously exposes fresh surfaces car...

Simultaneous determination of seven anticoagulant rodenticides in agricultural products by gel permeation chromatography and liquid chromatography–tandem mass spectrometry

ABSTRACTA sensitive and reliable method for the simultaneous determination of hydroxycoumarin-type (brodifacoum, bromadiolone, coumatetralyl, and warfarin) and indandione-type (chlorophacinone, diphacinone, and pindone) rodenticides in agricultural products by gel permeation chromatography (GPC) and liquid chromatography–tandem mass spectrometry (LC–MS/MS) was developed. The procedure involved extraction of the rodenticides from samples with acetone, followed by liquid–liquid partitioning with hexane/ethyl acetate (1:1, v/v) and 10% sodium chloride aqueous solution, then cleanup using GPC, and finally, analysis using LC–MS/MS. High recoveries from the GPC column were obtained for all rodenticides tested using a mobile phase of acetone/cyclohexane/triethylamine (400:1600:1, v/v/v). An ODS column, which contains low levels of metal impurities, gave satisfactory peak shapes for both hydroxycoumarin- and indandione-type rodenticides in the LC–MS/MS separation. The average recoveries of rodenticides from eight agricultural foods (apple, eggplant, cabbage, orange, potato, tomato, brown rice, and soybean) fortified at 0.0005–0.001 mg/kg ranged from 76 to 116%, except for bromadiolone in orange (53%) and diphacinone in soybean (54%), and the relative standard deviations ranged from 1 to 16%. The proposed method effectively removed interfering components, such as pigments and lipids, and showed high selectivity. In addition, the matrix effects were negligible for most of the rodenticide/food combinations. The results suggest that the proposed method is reliable and suitable for determining hydroxycoumarin- and indandione-type rodenticides in agricultural products.

Iterative reactions of transient boronic acids enable sequential C-C bond formation.

The ability to form multiple carbon-carbon bonds in a controlled sequence and thus rapidly build molecular complexity in an iterative fashion is an important goal in modern chemical synthesis. In recent times, transition-metal-catalysed coupling reactions have dominated in the development of C-C bond forming processes. A desire to reduce the reliance on precious metals and a need to obtain products with very low levels of metal impurities has brought a renewed focus on metal-free coupling processes. Here, we report the in situ preparation of reactive allylic and benzylic boronic acids, obtained by reacting flow-generated diazo compounds with boronic acids, and their application in controlled iterative C-C bond forming reactions is described. Thus far we have shown the formation of up to three C-C bonds in a sequence including the final trapping of a reactive boronic acid species with an aldehyde to generate a range of new chemical structures.

Trace Levels of Copper in Carbon Materials Show Significant Electrochemical CO2 Reduction Activity

Carbon materials are frequently used as supports for electrocatalysts because they are conductive and have high surface area. However, recent studies have shown that these materials can contain significant levels of metallic impurities that can dramatically alter their electrochemical properties. Here, the electrocatalytic activity of pure graphite (PG), graphene oxide (GO), and carbon nanotubes (CNT) dispersed on glassy carbon (GC) are investigated for the electrochemical CO2 reduction reaction (CO2RR) in aqueous solution. It was observed that GO and CNT dispersed on GC all exhibit significant electrochemical activity that can be ascribed to impurities of Ni, Fe, Mn, and Cu. The level of Cu in GO can be particularly high and is the cause for the appearance of methane in the products produced over this material when it is used for the CO2RR. Washing these supports in ultrapure nitric acid is effective in removing the metal impurities and results in a reduction in the electrochemical activity of these form...

Metal impurities in crystallographic voids of beta-rhombohedral boron lattice: Binding energies and electron levels

Applying quasi-classical approach, the binding energies and electron levels of metal impurities (Li, Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Hf, Ta, and Re) introduced into crystallographic voids of types A, D and E in the beta-rhombohedral boron lattice are calculated. Binding energies are estimated as ∼1 eV–60 eV per bond. The most of the obtained metal–boron bond lengths are very close to the mean radii of voids in the undoped crystal. Relatively light impurities (from Li to Cu) are found to form donor electron states directly inside the conduction band, i.e., they cause metallization of the material being introduced at sufficiently high concentrations. Heavy impurities (from Zr to Re) form shallow or deep donor levels inside the band gap or even valence band depending on dopants and voids of accommodation.

Effect of trimethylsilane pre-capping on monomeric C18 stationary phases made from high-purity type-B silica substrates: Efficiency, retention, and stability

Silica-based monomeric C18 stationary phases are the most widely used in reversed-phase liquid chromatography (RPLC), and methods to improve the efficiency and chemical stability of such phases are always being investigated. Previous work showed that stationary phases made by pre-treating the silica surface with small amounts of trimethylsilane (TMS) reagents prior to C18 silanization showed vast improvements in the chromatographic efficiencies of both polar and non-polar analytes. It was concluded that this "pre-capping" step improved efficiency by selectively neutralizing the most reactive highly acidic silanol sites, producing a more energetically homogenous surface prior to exhaustive derivatization that subsequently yielded a more evenly distributed alkyl bonding arrangement. These previous studies were performed on Type-A silica, an older variety of silica gel material that contains higher levels of metal impurities than the Type-B silica used today. The purpose of the work presented here is to investigate the effects of trimethylsilane pre-capping on monomeric C18 stationary phases made from high-purity Type-B silica substrates. The results show little or no efficiency improvements for non-polar compounds, but a more noticeable improvement was observed for some drug compounds and bases under buffered conditions, with the magnitude of the improved efficiencies correlating with metal impurity content and physical parameters of the silica substrate. The results lend supporting evidence that metal impurities are the primary source of highly acidic silanols, but they also suggest a means to improve efficiencies for compounds of interest. Pre-capping also resulted in a decreased retention due to a decrease in carbon loading. In addition, hydrolytic stability of the stationary phases was investigated at high pH and elevated temperature, with results indicating a slight decrease in hydrolytic stability with increased pre-capping.

Ultrapurification of hydrogen peroxide solution from ionic metals impurities to semiconductor grade by reverse osmosis

The present research is centred upon the application of reverse osmosis to the ultrapurification of aqueous hydrogen peroxide (35%, w/w). Semiconductor Equipment and Materials International (SEMI) organization develops the globally most respected standards to establish the quality requirements for the chemicals used in this sector; one of these standards, SEMI C30 is proposed for hydrogen peroxide. Electronic grade hydrogen peroxide accounts for sub-ppm metallic impurity levels (sub-ppb concentrations are required for the most exigent grades), so various elements present as impurities in technical grade hydrogen peroxide exceed the fixed limits. A preliminary experimental study was carried out with a laboratory-scale facility (flat-sheet membrane unit) with 6 different commercial reverse osmosis membranes in order to choose the most appropriate one for hydrogen peroxide ultrapurification. BE membrane (manufactured by Woongjin Chemical) was selected for further viability study because of its higher permeate flux (1.95 × 10 −5 m 3/m 2 s at 40 bar) and metal rejections values (ranging from 0.825 for B to 0.961 for Cu). The Kedem–Katchalsky model resulted as the most representative for characterizing the selected membrane behaviour as it achieved a percentage of overall variation explained upper than 94%.

Plutonium metal standards exchange program for actinide measurement quality assurance (2001–2007)

Plutonium metal exchange programs operated by the Rocky Flats Plant were conducted from 1956–1989 to ensure quality and to compare measurements in a plutonium metal matrix. Los Alamos National Laboratory (LANL) re-established the program in 2001 to assess the quality of analytical chemistry capabilities that support special nuclear material characterization. It is the only program of its kind for the preparation and distribution of plutonium metal reference materials with a range of impurity contents to multiple laboratories for destructive measurements of elemental concentration, isotopic abundance, and both metallic and non-metallic impurity levels. This program provides independent verification of analytical measurement capabilities for each of the seven currently participating laboratories, and allows any technical problems with analytical measurements to be identified and corrected. This paper focuses on basic program elements and presents a summary of methods and results for plutonium, uranium, neptunium, and americium, measurements.

The steam reforming of phenol over natural calcite materials

Five natural calcite materials of different geographical origin were studied towards the steam reforming of phenol reaction and the activity results obtained were correlated with some of their physico-chemical properties. It was found that the specific catalytic activity (μmol/(m 2 s)) of the calcite material following calcination at 850 °C was not correlated with the BET area and the primary crystal size of calcium oxide (CaO). The metal impurity levels of the natural calcite materials investigated were found to be very low as evidenced by EDX and XPS measurements, leading to the conclusion that their effect on the catalytic chemistry of phenol steam reforming and surface adsorption properties of CaO was minor. These results suggest that the reaction at hand depends on the heterogeneity and site reactivity present in each CaO surface examined. On the other hand, based on diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) CO 2 chemisorption and TPD-CO 2 mass spectrometry studies, it was found that the catalytic activity can be correlated with the amount of CO 2 adsorbed at 25 °C in the unidentate form. The latter species was found to be significantly more thermally stable than the bicarbonate adsorbed species also populated on the CaO surface after CO 2 chemisorption (15 Torr) at 25 °C. The least concentration of unidentate carbonate species accumulated on the catalyst surface the higher the catalytic activity of CaO to be expected. It was found that the presence of hydrogen in the feed stream results in a significant decrease of steam reforming of phenol activity over CaO. This result was probed to be likely related to the reduction in the rate of water dissociation to form –OH species, as revealed by the significant decrease in the concentration of adsorbed bicarbonate and –OH species on the surface of CaO according to in situ DRIFTS-CO 2 adsorption experiments in the presence of water and of varying hydrogen concentration in the feed. The inhibiting role of H 2 during steam reforming of phenol over CaO is discussed.

Electrical passivation by hydrogen plasma treatment of transition metal impurities in germanium

Transition metal impurities in germanium introduce deep levels in the band gap, which may influence the lifetime of carriers and leakage currents of devices. In this work it is shown that Ti, Cr and Fe centres in germanium can be passivated using plasma hydrogenation. The metals have been implanted at 90 keV in n- and p-type wafers and in-diffused during a 5 min thermal anneal at 500 °C. Samples have been hydrogenated using a DC plasma for 4 h at 200 °C and Schottky diodes were made for measurement using DLTS. It is found that the levels of metal impurities are passivated by hydrogenation. Characteristic hole and electron traps are assigned to the irradiation damage induced by the direct plasma exposure. Metal-specific levels are tentatively assigned to transition metal–hydrogen-related centres. Two hole traps at 0.05 and 0.10 eV above the valence band are only present in the Cr-doped samples and are tentatively assigned to chromium–hydrogen complexes. A comparison is made with copper–hydrogen in germanium.

An on-line electrodialyzer-ICP-MS analytical system for direct determination of trace metal impurities in KOH

We have developed an on-line electrodialysis system equipped with a cation-permeable membrane that, when coupled to an ICP mass spectrometer, provides a simple and sensitive hyphenated method for the determination of trace metal impurities in concentrated KOH. Because our proposed on-line electrodialysis method allows the quantitative removal of K+ and OH− ions, which may seriously interfere with and potentially damage the ICP-MS system, the safety risks and the analytical errors arising from the presence of extremely high alkalinity KOH are both low. To prevent loss of the analyte cations during the electrodialysis process, a selective chelating agent—ethylenediaminetetraacetic acid (EDTA)—was added to form anionic metal–EDTA complexes. To achieve maximum signal intensities, we optimized the sample flow rate and the amount of EDTA in terms of their effects on the retention and removal efficiencies of the analyte species and K+ ions. Based on the optimized operating conditions, near 100% of trace metal ions in 11.25% KOH solutions—added with 10 mg EDTA L−1 in advance—could pass through electrodialyzer and be delivered to the ICP-MS at a flow rate of 0.1 mL min−1. Because over 99.99% of 11.25% KOH was removed prior to ICP-MS measurement and low blank levels were achieved, this hyphenated method is sufficiently robust for the determination, with detection limits ranging from μg L−1 to sub-μg L−1, of trace Cu, Mn, Zn, Co, Ni, Cd, and Pb impurities in high-alkalinity samples. Because no certified values for the analyte content in KOH were available, the overall analytical method was validated for accuracy and precision by analyzing KOH solutions spiked with known amounts of analytic ions. Based on the analytical data, the analytical accuracy, expressed as spike recovery was found to be at 100 ± 10% for all the elements tested. This method is superior to the reported voltammetric methods for the determination of trace impurities in terms of detection limits, ability of simultaneous multi-elements analysis and speed of analysis. The validated method was successfully applied to determine trace levels of metal impurities in concentrated KOH solutions.

Nanosize Mn 3O 4 (Hausmannite) by microwave irradiation method

The present investigation reports, the novel synthesis of nanosize Mn 3O 4 powder with nanorods using microwaves and its physicochemical characterization. The nanosize Mn 3O 4 powder has been prepared using manganese nitrate as a precursor and effect of ethanolamine and ethylenediamine on particle morphology has been studied. The microwave irradiation has been carried out in the range 50–500 W and it was observed that formation of Mn 3O 4 takes place at 50 W. TEM analysis demonstrated nanosize Mn 3O 4 powder and nanorods with an average diameter of about 10 nm. The structural study by XRD indicates that these nano-powders have pure tetragonal phase. The phase pure samples were characterized using X-Ray Photoelectron Spectroscopy (XPS) for both Mn 2p and Mn 3s levels. The values of binding energies are consistent with the relative values reported in the literature. The metallic impurity levels have been characterized using Inductively Coupled Plasma-Optical Emission Spectrophotometer (ICP-OES).

Supported Chiral Mo‐Based Complexes as Efficient Catalysts for Enantioselective Olefin Metathesis.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Supported chiral Mo-based complexes as efficient catalysts for enantioselective olefin metathesis.

Syntheses and catalytic activities of seven new polymer-supported chiral Mo-based complexes are disclosed. Four of the complexes are polystyrene-based, and three involve polynorbornene supports. Studies concerning the ability of the polymer-bound chiral complexes to promote an assortment of asymmetric ring-closing (ARCM) and ring-opening (AROM) metathesis reactions are detailed. In many instances, levels of reactivity and enantioselectivity are competitive with those of the analogous homogeneous catalysts. The positive effect of lower cross-linking within the polymer backbone on reaction efficiency and asymmetric induction is detailed. The optically enriched products obtained through the use of the supported complexes, after simple filtration and removal of the supported Mo catalysts, contain significantly lower levels of metal impurities as compared to products synthesized with the corresponding homogeneous catalysts.

Looking at trace impurities on silicon wafers with synchrotron radiation.

Because even very low levels of metal impurities can seriously degrade silicon integrated circuits, extremely sensitive methods must be developed to improve wafer cleaning.