Metal Impurities Research Articles

A method for the preparation of graphene from spent graphite of retired lithium-ion batteries

Recycling spent graphite is significant for the sustainable development of the lithium-ion industry. In this study, due to the damaged structure of spent graphite, a modified Hummers' method combined with thermal reduction is proposed to achieve the preparation of graphene and the simultaneous removal of impurities from the spent graphite. In the preparation of graphene oxide, the results show that the optimum mass ratio of spent graphite to oxidizing agent (KMnO4) is 1:3, under which the C/O and ID/IG values of graphene oxide are 1.99 and 1.52, respectively. The residual contents of various metal impurities in graphene oxide are lower than 100 ppm, and the impurities removal efficiency is better than that by acid leaching with the same acid dosage. After thermal reduction, reduced graphene oxide with a disordered few-layer structure is successfully prepared. It shows that spent graphite as a raw material for the preparation of graphene is superior to commercial graphite in terms of cost, and processing one ton of spent graphite yields a profit of $52,651.4. Our research can realize the diversified and efficient utilization of spent graphite and has a broad industrial application prospect.

Nickel-embedded zeolite subcrystal catalyst: rapid enhancement of activity and metal impurity resistance in the hydrodesulfurization of 4,6-dimethyldibenzothiophene

Ni nanoparticles embedded in an Al-containing MFI zeolite subcrystal (<7 nm) lead to superior hydrodesulfurization activity and exceptional resistance to Ni/V metal impurities.

ICP-MS: a tool for detection and quantitation of fosfomycin residues in cleaning samples of finished product by estimation of phosphorous load

The ICP-MS technique is creatively utilized to quantify trace levels of fosfomycin, a non chromophoric and non-mass friendly molecule for cleaning validation samples.

Dynamics and impurity spectral characteristics of coaxial gun discharge plasma

<sec>The coaxial gun discharge can produce plasma jet with high velocity, high density and high energy density, and has extensive applications, such as in plasma space propulsion, simulation of the interaction between edge local mode and wall materials in ITER, fuel injection in magnetic confinement fusion devices, and laboratory astrophysics. In the pre-filled discharge mode or snowplow mode, the plasma current sheet is formed near the insulating layer surface and moves toward the end of the coaxial gun under Lorentz force. Plasma velocity, density and purity characteristics are very important research contents for the actual applications of coaxial gun. Emission spectrometry as a non-interference method can be used to diagnose a variety of plasma physical properties.</sec><sec>In this experiment, the effects of different discharge currents and gas pressures on the plasma dynamics, electron density and impurity emission spectra of coaxial gun discharge plasma are studied through the measurement of plasma photocurrent, emission spectra and the shooting of discharge images. The experimental results show that the acceleration time of the plasma in the gun decreases with current increasing in a range of 30–70 kA when the gas pressure is 10 Pa, the spectral intensity of anode and cathode impurities in plasma increase with current amplitude increasing. When the discharge current is 40 kA and the gas pressure is in a range of 10–70 Pa, the acceleration time of plasma increases with gas pressure rising, and the spectral intensity of the cathode impurity in the plasma decreases with the pressure increasing, while the spectral intensity of the anode impurity increases gradually, but its growth rate decreases continuously. The analysis indicates that the presence of metallic impurities originating from the electrode material limits the jet velocity of the plasma and is the main cause of the deviation from theoretical value. The plasma pinch effect at the nozzle of coaxial gun and the acceleration time of high-density arc in the gun are important factors affecting anode ablation. The impurity of cathode material is produced by ion bombardment sputtering, which mainly depends on the energy carried by ions. Therefore, a reasonable choice for discharge parameters is the key factor to obtain optimal plasma characteristics during the discharge of the coaxial gun.</sec>

Assessing the potential of TOPCon solar cells architecture using industrial n-type cast-mono silicon material

Cast-mono silicon material is interesting for its lower carbon footprint compared to Czochralski (Cz) monocrystalline silicon. However, solar cells fabricated using cast-mono (CM) silicon show lower performances. In this work, two routes to make cast-mono silicon advantageous over Cz silicon are considered. The first route is to further reduce carbon footprint of cast-mono silicon, by using Upgraded Metallurgical Grade silicon (UMG-Si) feedstock instead of Solar Grade silicon (SoG-Si) feedstock. TOPCon solar cells are fabricated using both feedstocks, and cast-mono growth technology, using industrial-type furnaces. Laboratory studies show that UMG-Si can result in efficiencies higher than solar cells made of SoG-Si when feeding the material to a CM crystallization process. But when compared to Cz, CM-UMG-Si TOPCon solar cells conversion efficiency values are still 0.5%abs lower. The second route is to take advantage of the TOPCon passivation layer (e.g., poly-Si) ability to getter metallic impurities, and thus improve the quality of cast-mono material. Several TOPCon sequences are tested and their effect on the carrier recombination properties of the device are studied. In the end, solar cells are fabricated and again, UMG-Si solar cells show better results than SoG-Si solar cells, with efficiency up to 22.65%, independently confirmed.

A stable Copper-Modified silica microsphere catalyst for the synthesis of N-substituted carbazoles and organosilanes

Carbenes are key precursors for various transformations and are applied broadly in the synthesis of complex molecules and drug. Typically, such transformations require expensive metal and complex ligands, leading to a vigorous reaction system and trace metal residues. Herein, we report copper-modified silica microspheres (SM-b) as heterogeneous catalyst in the insertion reaction of diazo compounds with carbazole and silanes. Under this strategy, the optimal SM-b catalyst can prevent the reaction from being too vigorous and can be reused in continuous reactions. Furthermore, gram-scale and catalyst recycling reactions have been proven as the potential industrial applications of the SM-b catalysts. Inductively coupled plasma analysis revealed a residual copper content of only 6.25 ppm in the reaction solution and no detectable copper in the final product, indicating that the residual metal content of the product is far below the FDA-imposed limit of metal impurities.

Effective separation of metal impurities from gypsum nanosludge: synergism of mechanical force and metal species regulation

A novel and sustainable method combining mechanical force and species regulation enables a two-step dehydration–rehydration process, achieving full extraction of impurities like P, or heavy metals like Cr, As, Sr, Cd, and Hg from gypsum waste.

Freon-CO2-assisted purification of single-walled carbon nanotubes.

With the rapidly growing applications, efficient purification of single-walled carbon nanotubes (SWCNTs) has become one of the key problems. This paper proposes Freon-CO2-assisted purification of SWCNTs, where CO2 can oxidize the graphitized carbon layer to expose iron (Fe) impurities, while the chlorine from Freon can react with the Fe impurities to form low-boiling-point metal chlorides that can be eliminated in a gas stream. After an acid washing with a very small amount of hydrochloric acid, the last remaining metal impurities are removed and highly pure SWCNTs are produced. Compared with traditional strong-acid-oxidation purification or high-temperature-vacuum purification, this method can maintain the structure and length of the SWCNTs. Raman spectra show that an I G/I D ratio of more than 100 can be obtained. This purification method can maintain the microstructure and excellent properties of SWCNTs and provide a solution for the preparation of high-quality SWCNTs to exert their properties.

Fractional precipitation of Ni and Co double salts from lithium-ion battery leachates

The isolation of Ni/Co double salts can be recovered by fractional precipitation with ammonium sulfate. The elemental analysis of these isolated double salts shows a total metal composition of >99% of Ni, Co, and Mn with negligible impurity metals.

Осаждение металлов в пористую структуру оксида алюминия

Introduction. Nanostructured porous anodic aluminum oxide is used as a matrix, where it is often necessary to introduce impurities of various metals into its structure. In this case, an effective solution is the electrochemical deposition of metals into the pores of anodic aluminum oxide. However, metals can be deposited on the cathode from aqueous solutions of salts in which the electrode potential is electronegative and less than the potential for hydrogen evolution in solutions. Materials and methods. The anodizing process takes place in two stages: preliminary anodizing and anodizing itself. Before preliminary anodization, experimental samples were coated with a chemically resistant varnish for separation between the electrolyte and air. Then the samples prepared in this way were dried for 4–6 hours, after which the second stage of anodization was carried out. Results. It has been revealed that substrate inhomogeneities can be reduced by slowing down the oxide growth process or by using pore blanks. Using similar methods, a highly ordered structure can be achieved. A more dense arrangement of pores can be achieved through the use of strong acids, forming a barrier layer of thinner thickness with more penetration paths. It is worth noting that when using such acids, the number of inhomogeneities becomes not such an important parameter. Discussion. Films were obtained with greater chemical strength and a thickness of 84-100 microns, a pore diameter of 0.15-0.3 microns. By carrying out additional etching, the pore diameter was increased to 0.6 µm. Etching of PHA can be carried out in an alkali solution in an anhydrous solution of ethyl alcohol. Also, pores can be dissolved by reanodizing in a solution of phosphoric acid. The barrier layer grows to 100 A, removal is carried out with dilute hydrofluoric acid. The resulting PHAs have a fairly porous, homogeneous structure with an average effective pore size of 0.45-0.65 μm. Conclusion. Conditions have been developed for the joint deposition of two metals from aqueous solutions at close values of their electrode potentials, such as iron and cobalt. The conditions for the deposition of copper from copper sulfate into the pores of porous aluminum oxide have been established at 25 – 70 t/l of sulfate and 7÷12% sulfuric acid. Resume. The research results can be useful in obtaining films of porous anodic aluminum oxide, which can be used as substrates for creating solar-electric energy converters based on materials with a perovskite structure. This is especially true for the Republic of North Ossetia-Alania and for the mountainous territories of the North Caucasus. The use of solar energy converters will make it possible to more efficiently electrify populated areas in mountainous areas.

In Ukrainian

The review material reveals the question of the influence of impurities on the physical properties of alloys, as well as the influence of gases on processes in alloys. It has been established that the presence of hydrogen affects diffusion in alloys, and gases have a significant effect on the thermoelectromotive force of metals. The paper describes the addition of a third element to binary systems, which can expand or narrow the domain of existence of an ordered phase. The above examples of adding an impurity of vanadium or molybdenum to an alloy of iron and chromium increase the ordering temperature. It has been established that gases can have a significant effect on the thermoelectromotive force of metals and increase the hardness and reduce the ductility of metals, as well as cause their brittleness and delamination. It has been established that hydrogen (H2) in alloys (for example, Fe-Ni and Au-Cu) affects diffusion and atomic ordering processes. Also, a small concentration of hydrogen, as an impurity, can change the electrical resistance of alloys (for example, in a Pd-Au alloy). It has been established that the addition of a third element to binary systems can change the state diagram, which must be taken into account when solving problems for the production of heat treatment modes for alloys, determining the conditions for phase equilibrium, etc. The paper considers the dependence of hydrogen solubility on temperature in metals (Cu, Fe and Al) and establishes the dependence of hydrogen solubility in a metal on the concentration of impurity metals. The temperature dependence of hydrogen solubility in Fe-V alloys is also shown. The shift of the density of state is studied for different distributions of impurity atoms in the alloy in the order-disorder system, and the dependence of the density of states of disordered and ordered solid solutions is studied. The dependence of the relative solubility of atoms introduced into the pores of alloys with an fcc structure (of the Cu3Au type) is indicated, taking into account the solubility, on the parameter χ, which is proportional to the degree of long-range order in the octahedral and tetrahedral pores of the alloys. The dependence of the relative solubility of intercalated atoms in octahedral pores of alloys with a bcc structure (such as CuZn and Fe3Al) is considered. A plot of the dependence of the concentration of dissolved impurity atoms on the degree of order is shown for substitutional alloys with a bcc lattice, where the M2 coefficient is introduced, which does not depend on the degree of order. The effect of pressure as a measure of long-range order is also studied, where its step decreases or increases, or decreases and then increases and vice versa (order-disorder phase transition). An equally important result is the graphic dependence of solubility (c) on pressure (P) in disordered and ordered alloys.

New 3D in vitro models for assessing the toxicity of carbon nanotubes

Introduction. In recent years, there has been interest in 3D cellular models that more accurately reflect in vivo conditions and can become an alternative to animal experiments in assessing the toxicity of nanomaterials. There is a need to develop 3D models of the human respiratory tract that can bridge the gap between traditional in vitro cell cultures and laboratory animals.
 Material and methods. Mono- and co-culture 3D-models based on bronchial epithelial cells BEAS-2B and lung fibroblasts MRC5-SV40 have been developed. Pristine and purified from metal impurities TUBALL™ SWCNTs and Taunit-M MWCNTs were used as materials for the study. The range of concentrations studied included concentrations corresponding to actual occupational exposures (0.0006–100 µg/ml). To assess the cytotoxicity of CNTs in cell models, the level of lactate dehydrogenase (LDH) activity was determined after 72 hours of exposure.
 Results. The cytotoxic effects of CNTs in 2D and 3D cell models manifested themselves in different concentration ranges: a three-dimensional model of bronchial epithelial cells turned out to be more sensitive to the effects of CNTs compared to a monolayer one, while in a spheroid model of fibroblasts a higher cytotoxicity threshold was noted for multi-walled carbon nanotubes compared to traditional cell culture. In three-dimensional cell co-cultures, a significant increase in LDH was observed starting at higher concentrations compared to monocultures.
 Limitations. The present study was limited to the use of one type of cytotoxicity test when examining the effects of CNTs on cells of the respiratory system.
 Conclusion. A method has been developed for three-dimensional cultivation of cells of the human respiratory system to simulate the interaction of epithelial and stromal cells of the lower respiratory tract. Traditional 2D cell models may underestimate or overestimate the toxicity of materials. Improved 3D in vitro models, closer in their properties and morphology to native tissue, are more reliable in determining toxic doses and targets.

Removal of metal impurities from diamond wire saw silicon powder by vacuum electromagnetic directional solidification

The utilization of high-purity silicon (∼99.9999 %) is prevalent in the solar photovoltaic sector, and achieving a reduction in its cost has emerged as a pivotal engineering objective within the silicon solar industry. Recycling silicon from diamond wire saw silicon powder (DWSSP) is a promising solution to fulfill the continuously expanding of high purity silicon demand. Vacuum directional solidification technology using high-frequency electromagnetic induction heating was proposed to purify DWSSP for the first time efficiently. The silicon melt and gas interface reaction, as well as metal impurities’ microsegregation in silicon ingot were observed. The effects of vacuum level and electromagnetic force on the separation of silicon and metal impurities were investigated using thermodynamics and electromagnetic mechanics. Results indicate that the content of oxygen in the silicon reduced from 30.91 wt% to 5.08 wt%, and the actual sample composition including for uptake of residual gas contamination steadily declined as the vacuum level increased from 600 Pa to 10 Pa. Vacuum electromagnetic directional solidification reduced the content of metal impurities from 641 ppmw to 29.80 ppmw, increases the proportion of crystalline silicon area, and makes the silicon lattice arrangement more regular.

Mild purification of multiwalled carbon nanotubes with increased selectivity for carbon impurity and residual metal removal

Mild purification of multiwalled carbon nanotubes with increased selectivity for carbon impurity and residual metal removal

Industrial Czochralski n‐type Silicon Wafers: Gettering Effectiveness and Possible Bulk Limiting Defects

An assessment of the bulk material quality of industrial Czochralski (Cz) grown phosphorus‐doped n‐type silicon (Si) wafers along an ingot is reported. The minority charge carrier lifetimes of the Cz‐Si wafer bulk before and after phosphorous (POCl3) diffusion gettering are assessed, by applying room‐temperature superacid surface passivation to avoid any additional gettering or hydrogenation effect. A substantial increase in the bulk lifetime of all of the n‐type Cz‐Si wafers along the ingot is observed, indicating the effectiveness of a gettering step for such wafers and the presence of getterable metallic impurities in these wafers. By experimentally monitoring the lifetime changes upon a gettering anneal and simulating the gettering kinetics based on different metal diffusivities, iron is identified to be a limiting defect, at least for the wafers from the tail part of the ingot. A dissolved iron concentration of is estimated from the bulk lifetimes of the tail wafers. This lifetime kinetics approach is also a demonstration of a new method to identify iron, or other getterable metals with moderate diffusivities such as chromium, in n‐type silicon wafers.

A clean process for liquid-phase synthesis of α-PbO based on the selective leaching of lead sulfate from spent lead paste

In the recycling process of waste lead-acid battery paste, the traditional hydrometallurgical process of recovering α-PbO as a product presents the issues of the high concentration of alkali and the waste alkaline solution cannot be recycled. This study seeks a clean process for the liquid-phase synthesis of α-PbO based on the selective leaching of lead sulfate from spent lead paste. The pre-treated spent lead paste was initially leached with a sodium acetate solution to obtain a lead acetate solution. The leaching rate of PbSO4 in the leaching process was 99.87%. Metal impurities such as Fe and Ba could be removed. Then the lead acetate solution was mixed with NaOH particles to synthesize α-PbO. The purity of α-PbO obtained could be reached above 99.99% when the molar ratio of M(nOH-/Pb2+) was 3:1, the reaction temperature was 85 ℃, and the reaction time was 40 min. Meanwhile, a reaction pathway was also proposed in which β-PbO could be converted to α-PbO rapidly at low alkali concentrations. Furthermore, the recirculation process of the waste alkaline solution did not result in the accumulation of metal impurities and did not affect the purity of the α-PbO. The non-recyclable waste alkaline solution could be used to prepare sodium acetate solutions and sodium sulfate by-products. This study provides a feasible method for green recycling of spent lead paste.

Performance evaluation of Gallium-68 radiopharmaceuticals production using liquid target PETtrace 800 cyclotron

Due to increased demand, cyclotron has an expanding role in producing Gallium-68 (68Ga) radiopharmaceuticals using solid and liquid targets. Though the liquid target produces lower end-of-bombardment activity compared to the solid target, our study presents the performance of 68Ga radiopharmaceuticals production using the liquid target by evaluating the end-of-bombardment activity and the end-of-purification activity of [68Ga]GaCl3. We also present the effect of increasing irradiation time, which significantly improves the end-of-synthesis yield. From the result obtained, the end-of-bombardment activity produced was 4.48 GBq, and the [68Ga]GaCl3 end-of-purification activity produced was 2.51 GBq with below-limit metallic impurities. Increasing the irradiation time showed a significant increase in the end-of-synthesis activity from 1.33 GBq to 1.95 GBq for [68Ga]Ga-PSMA-11 and from 1.13 GBq to 1.74 GBq for [68Ga]Ga-DOTA-TATE. Based on the improvements made, the liquid target production of 68Ga radiopharmaceuticals is feasible and reproducible to accommodate up to 5 patients per production. In addition, this work also discusses the issues encountered, together with the possible corrective and preventative measures.

Large hysteretic hydrogen adsorption in Double Wall Carbon Nanotubes bundles

We have observed isothermal large hysteretic hydrogen adsorption in samples made out of Double Wall Carbon Nanotubes (DWCNTs) bundles at 50 K, 77 K and 150 K and up to 1.3 MPa of pressure. In order to gain information about the microscopic mechanisms responsible for this remarkable phenomena we made a series of inelastic neutron scattering measurements at various temperatures and H2 loads. The elastic component of the signals (diffraction) observed at different loads are consistent with the uptake of the H2 molecules within the interstitials of the bundles. The quasielastic part, i.e., that centered around the null energy transfer, displays a dependence on momentum transfer which is reproduced by a 1D dimensional diffusion model as expected for interstitial confinement of the H2 fluid. Finally, the inelastic signals reveal rotational spectra that preclude the possibility of chemisorption onto the sample metallic impurities. To the best of our knowledge this is the first observation of supercritical H2 hysteretic adsorption in nanostructured carbons not ascribed to chemisorption onto metallic centers. Instead, the results point to the hierarchy of energy and entropic barriers associated with the adsorption into the bundle interstitials through the external grooves as the microscopic origin of the observed metastable adsorption.

Understanding the Effects of Transition Metal Impurities on Nickel (oxy) Hydroxide Electrocatalysts in Alkaline Media

Nickel-based materials are widely used as critical components of electrochemical energy devices, including alkaline electrolyzers, capacitors, and alkaline batteries. These materials are often preferred because of their availability and low cost compared to precious metals, which makes them excellent candidates for accomplishing the decarbonization goals and electrifying our society. However, several studies have demonstrated that the incorporation of trace impurities from commercial alkaline electrolytes induces significant changes in the intrinsic activity, pseudocapacitance, and stability of Ni-based materials, resulting in erroneous descriptions of their performance. Thus, having a better understanding of the effects of these impurities will lead to practical ways to prevent or control their impact on electrochemical energy devices.In this work, we study the incorporation of transition metals (i.e., Fe, Co, Cu) that form insoluble hydroxides in alkaline media over nickel (oxy) hydroxide electrocatalysts. We systematically examine how these trace impurities modify the OER activity, stability, and the pseudocapacitive properties of NiOOH. As depicted in Figure 1, KOH electrolytes containing trace impurities of Fe and Co induce significant changes in the OER onset potential of Ni(OH)2/NiOOH electrocatalysts, according to the irreversible charge increase measured through coulovoltammetry (QV) curves. Moreover, distinct redox peaks can be seen for each scenario. After aging in purified KOH electrolyte (Fig. 1a), the cyclic voltammogram (CV) of Ni(OH)2/NiOOH exhibits four oxidation peaks that can be ascribed to a mixture of both α and β structural phases (Fig. 1b) while aging in Fe-unpurified KOH promotes the α phase and shifts the redox peak anodically (Fig. 1c). Aging in Co-unpurified KOH promotes a more ordered β structural phase without changing the OER activity significantly (Fig. 1d), which is desirable for pseudocapacitive materials. Additional experiments examining the OER activity, stability, and capacitance provide valuable insights into these impurities, and specific strategies to prevent and minimize their effects will be discussed. Overall, this work illustrates the importance of tracking trace metal impurities in alkaline electrolytes to minimize undesirable effects in electrochemical energy devices. Figure 1

Effects of two mild amino acids on benzotriazole residue desorption during cobalt post-chemical mechanical polishing cleaning: Experimental and theoretical studies

During the polishing process of the cobalt (Co) interconnect layer, the corrosion inhibitor in the polishing solution will leave an organic residue on the polished cobalt surface, which needs to be removed by the post-chemical mechanical polishing (CMP) cleaning process. However, given the active chemical properties of cobalt, the potent and corrosive complexing agents in traditional cleaning solutions have the drawback of generating new corrosion defects on the cobalt surface. In this study, an eco-friendly cleaning solution is developed utilizing tetraethyl ammonium hydroxide (TEAH), deionized water, and either sarcosine or serine, thereby ensuring the absence of any additional introduction of metal impurities. The removal effect of the cleaning solution on BTA was tested using atomic force microscopy (AFM) and X-ray photoelectron spectrometer (XPS). The results demonstrate that post-CMP cleaning with either sarcosine or serine yielded a cobalt surface with reduced roughness (2.78 nm and 2.63 nm), diminished Co-BTA content (10.6% and 9.5%), and a lowered contact angle (44.3° and 37.9°). To elucidate the mechanism of post-CMP cleaning, electrochemical measurements and molecular dynamics were employed. Initially, in the cleaning solution with a pH of 10.4, the adsorption of BTA and cobalt is minimized. Subsequently, as serine permeates through the BTA residue layer, the desorption of BTA is expedited through competitive adsorption. These findings contribute valuable insights into the mechanism of residue removal in post-CMP cleaning processes.