Common Impurities Research Articles

Selective scandium ion capture through coordination templating in a covalent organic framework.

The use of coordination complexes within covalent organic frameworks can significantly diversify the structures and properties of this class of materials. Here we combined coordination chemistry and reticular chemistry by preparing frameworks that consist of a ditopic (p-phenylenediamine) and mixed tritopic moieties-an organic ligand and a scandium coordination complex of similar sizes and geometries, both bearing terminal phenylamine groups. Changing the ratio of organic ligand to scandium complex enabled the preparation of a series of crystalline covalent organic frameworks with tunable levels of scandium incorporation. Removal of scandium from the material with the highest metal content subsequently resulted in a 'metal-imprinted' covalent organic framework that exhibits a high affinity and capacity for Sc3+ ions in acidic environments and in the presence of competing metal ions. In particular, the selectivity of this framework for Sc3+ over common impurity ions such as La3+ and Fe3+ surpasses that of existing scandium adsorbents.

Evaluating orthogonality between ion-pair reversed phase, anion exchange, and hydrophilic interaction liquid chromatography for the separation of synthetic oligonucleotides

The orthogonality of separation between ion-pair reversed phase (IP-RP), anion exchange (AEX), and hydrophilic interaction liquid chromatography (HILIC) was evaluated for oligonucleotides. A polythymidine standard ladder was first used to evaluate the three methods and showed zero orthogonality, where retention and selectivity were based on oligonucleotide charge/size under all three conditions. Next, a model 23-mer synthetic oligonucleotide containing 4 phosphorothioate bonds with 2′ fluoro and 2′-O-methyl ribose modifications typical of small interfering RNA was used for evaluating orthogonality. The resolution and orthogonality were evaluated between the three modes of chromatography in terms of selectivity differences for nine common impurities, including truncations (n-1, n-2), addition (n + 1), oxidation, and de-fluorination. We first evaluated different ion-pairing reagents that provided the best separation of the key impurities while suppressing diastereomer separation due to phosphorothioate linkages. Although different ion-pairing reagents affected resolution, very little orthogonality was observed. We then compared the retention times between IP-RP, HILIC, and AEX for each impurity of the model oligonucleotide and observed various selectivity changes. The results suggest that coupling HILIC with either AEX or IP-RP provide the highest degree of orthogonality due to the differences in retention for hydrophilic nucleobases and modifications under HILIC conditions. IP-RP provided the highest overall resolution for the impurity mixture, whereas more co-elution was observed with HILIC and AEX. The unique selectivity patterns offered by HILIC provides an interesting alternative to IP-RP or AEX, in addition to the potential for coupling with multidimensional separations. Future work should explore orthogonality for oligonucleotides with subtle sequence differences such as nucleobase modifications and base flip isomers, longer strands such as guide RNA and messenger RNA, and other biotherapeutic modalities such as peptides, antibodies, and antibody-drug-conjugates.

Analysis of the influence of impurity gas on the hydrogen storage performance of Ti/2C-BN

Ti-modified carbon-doped hexagonal boron nitride (Ti/2C-BN) at a concentration of 25 at% exhibits excellent hydrogen storage performance at room temperature. However, the presence of impurities in large-scale hydrogen production processes such as fossil fuel reforming and biomass gasification may contaminate the surface of hydrogen storage materials. Therefore, it is necessary to study the influence of common impurity gases in hydrogen sources, including O2, CO2, H2S, N2, CO, H2O, CH4, Ar, and He, on the adsorption capacity of H2 after pre-adsorption on the Ti/2C-BN surface, as well as their mechanism of influence. The VASP program package based on density functional theory (DFT) is employed to perform relevant simulation calculations. The results show that the hydrogen storage performance on Ti/2C-BN is not affected by CH4, Ar and He. Although O2, CO2 and CO will occupy the active site of the material, the adsorption energy of H2 is between physical adsorption and chemical adsorption, and its influence can be neglected. The adsorption energy of H2 is increased by H2O. The material is poisoned by H2S and N2, causing its adsorption energy to fall below −0.1 eV.

Structural characterization and in silico toxicity prediction of degradation impurities of roxadustat

Roxadustat is the first drug approved for anemia due to chronic kidney disease. Drug degradation profile is very crucial for assessing the quality and safety of the drug substances and their formulations. Forced degradation studies are conducted for quick prediction of drug degradation products. Forced degradation of roxadustat was carried out as per ICH guidelines, and nine degradation products (DPs) were observed. These DPs (DP-1 to DP-9) were separated using the reverse phase HPLC gradient method with an XBridge column (250 mm × 4.6 mm, 5 µm). The mobile phase consisted of 0.1% formic acid (solvent A) and acetonitrile (solvent B) at a flow rate of 1.0 ml/min. The chemical structures of all the DPs were proposed by using LC-Q-TOF/MS. DP-4 and DP-5, the two major degradation impurities, were isolated, and NMR was used to confirm their chemical structures. Based on our experiments, the roxadustat was found stable to thermal degradation in solid state and oxidative conditions. However, it was unstable in acidic, basic, and photolytic conditions. A very remarkable observation was made about DP-4 impurity. DP-4 was generated as a common degradation impurity in alkaline hydrolysis, neutral hydrolysis as well as photolysis conditions. DP-4 has a similar molecular mass to roxadustat but is structurally different. DP-4 is chemically, (1a-methyl-6-oxo-3-phenoxy-1,1a,6,6a-tetrahydroindeno [1,2-b] aziridine-6a-carbonyl) glycine. In silico toxicity study was conducted using Dereck software to gain the best knowledge of the drug and its degradation products towards carcinogenicity, mutagenicity, teratogenicity, and skin sensitivity. A further study using molecular docking confirmed the potential interaction of DPs with proteins responsible for toxicity. DP-4 shows a toxicity alert due to the presence of aziridine moiety.

Distribution of relaxation times analysis of electrochemical hydrogen pump impedance spectra

Polybenzimidazole-based electrochemical hydrogen pumps (EHPs) allow hydrogen separation from gas mixtures at low cell overpotential. An operating temperature of up to 180 °C provides robustness towards catalyst poisoning by common impurities in steam reformate, like CO or sulfur compounds. Electrochemical impedance spectroscopy (EIS) coupled with the distribution of relaxation times (DRT) analysis is performed on single-cell EHPs supplied by H2 contaminated with N2, CO2, and CO to investigate and quantify the underlying physicochemical processes. By systematically varying the operating parameters, five different processes were identified in the DRT spectrum: the proton transport in the electrode, the hydrogen evolution reaction (HER), the hydrogen oxidation reaction (HOR), the mass transport (MT) in the anode gas diffusion electrode, and the movement of phosphoric acid anions from the cathode to the anode at high current densities. At high contaminant concentrations, the HOR and the MT resistances increase. The HOR inhibition is dominant for CO, while for N2 and CO2, the MT resistance increase is more pronounced. At 180 °C cell temperature, the performance with 50% CO2 in the gas feed was worse than with 1% CO, highlighting the possibility of operating an EHP with a CO-contaminated gas feed at elevated operating temperature.

Size-selective downstream processing of virus particles and non-enveloped virus-like particles.

Non-enveloped virus-like particles (VLPs) are versatile protein nanoparticles with great potential for biopharmaceutical applications. However, conventional protein downstream processing (DSP) and platform processes are often not easily applicable due to the large size of VLPs and virus particles (VPs) in general. The application of size-selective separation techniques offers to exploit the size difference between VPs and common host-cell impurities. Moreover, size-selective separation techniques offer the potential for wide applicability across different VPs. In this work, basic principles and applications of size-selective separation techniques are reviewed to highlight their potential in DSP of VPs. Finally, specific DSP steps for non-enveloped VLPs and their subunits are reviewed as well as the potential applications and benefits of size-selective separation techniques are shown.

The Role of Sulfur in the S‐PtRe/Al2O3 Catalysts: The Endogenous Deposition Effect on the Metal/acid Micro‐environment

AbstractAlumina is widely used as support in the industrial catalytic process. As a common impurity, the sulfur species, which are often considered a harmful component, play a positive role in some petrochemical reactions. Herein, the S‐modified catalysts were fabricated using the exogenous/endogenous deposition method to study the effect of the sulfur induced by introduction approaches. Series characterizations reveal that the exogenous sulfur from the sulfidation treatment affects the active metals by poisoning the low‐coordinated sites, leading to the active metal sites decrease. As for the endogenous deposition method, besides the poison effect, the removal of the endogenous sulfur from the S‐contain alumina support can produce oxygen vacancies, which can not only act as acid sites but work as an electron acceptor that optimizes the catalyst electronic structure. Benefits from the effect of endogenous sulfur, the catalyst with a suitable catalytic metal/acid micro‐environment exhibit the best dehydrocyclization performance.

CBD hydroxyquinone photo-isomerises to a highly reactive intermediate

The legalisation of hemp has led to wide commercial availability of cannabidiol (CBD)-containing products. Here we show that the CBD-hydroxyquinone (HU-331), a readily formed oxidation product and common impurity in CBD isolates, undergoes a previously unknown photo-isomerisation to produce a highly reactive intermediate in solution. Studies supported by calculations indicate that this intermediate rapidly reacts with oxygen to form a multitude of cannabinoid products. The purple colour observed in light-aged CBD-containing solutions is largely due to the anions of these by-products and is not significantly due to the HU-331 anion. Our findings suggest that these uncharacterized cannabinoid derivatives can be present in CBD-containing e-liquids and solutions that have been stored under ambient light conditions, calling for quality control processes that manage HU-331 contamination.

Microstructure Analysis of Progressive Secondary AlSi7Mg0.6 Alloy with Higher Fe Content Using Electron Metallography Techniques

This article investigates the effect of the higher Fe content on the formation of brittle Fe-rich needle-like phases in heat-treated secondary AlSi7Mg0.6 cast alloy. These secondary-recycled alloys contain an increased amount of impurities due to remelting of scrap. The common unwanted impurity found in these alloys is Fe. Its higher content negatively affects the structure and mechanical properties. Fe has low solubility in Al-alloys thus forming unwanted intermetallic phases such as β-Al5FeSi. Fe cannot be removed in the foundry conditions, so its content is reduced to an acceptable limit. One of the possibilities to eliminate the negative effect of high Fe content on the structure and mechanical properties is heat treatment. Heat treatment influences the size and morphology of structural components, which leads to a finer structure and thus better mechanical properties. Therefore, this study is focused on the changes in structure depending on the Fe content influenced by heat treatment applied to the secondary AlSi7Mg0.6 alloy with higher Fe content and evaluation using a scanning electron microscope, including methods of EDX analysis, and methods of deep etching.

Impurity-Resistant CO2 Reduction Using Reactive Carbon Solutions

Electrolyzers that electrochemically convert aqueous (bi)carbonate solutions (solutions containing captured CO2, or “reactive carbon solutions”) into commodity chemicals couple CO2 capture with CO2 conversion. Industrial exhaust streams contain nitrogen oxides (NOx) and sulfur oxides (SOx) that form redox-active anions in reactive carbon solutions that can interfere with downstream CO2 reduction. We therefore designed experiments to test how impurities produced from the dissolution of NOx (NO2– and NO3–) and SOx (SO32– and SO42–) impact the electrochemical conversion of (bi)carbonate to CO. We found that CO production was unaffected by SOx compounds in a 3.0 M KHCO3 feedstock, but 2000 ppm of NOx impurities decreased CO selectivity from ∼60% to <5%. This decrease was caused by the preferential reduction of NO2– and NO3– over CO2. Our study establishes tolerance limits for common flue gas impurities in reactive carbon solutions and provides strategies to mitigate toxification effects.

DEVELOPMENT OF HIGH-EFFICIENCY REPLACEMENT FILTERS FOR PURIFICATION OF DRINKING WATER ON HOUSEHOLD FILTER PITCHERS

Water filter pitchers s are the simplest and most affordable devices for local purification of drinking water from centralized and decentralized water sources. The main filter element of such pitchers is a cartridge containing a mixture of sorption materials that are able to absorb certain impurities from the water. However, as previous studies demonstrated, the quality of water, purified with filter pitcher cartridges currently available on the market, does not usually reach the level sufficient to meet the standards for drinking water, which are specified in the document DSanPin 2.2.4-171 -10 "Hygienic requirements for drinking water intended for human consumption", while maintaining compliance with consumer needs. Therefore, the aim of this study is to develop a cartridge for filter pitchers, which would provide high efficiency of purification of tap water in Kyiv from the most common impurities: chlorine, organic compounds and hardness ions. In this work, 5 newly created cartridge samples with different ratios of sorption material content, drainage material density, cartridge filling density, presence or absence of inert material in the loading were studied to identify the impact of these factors on water purification efficiency and water filtration rate, as well as the connection between these parameters. According to the results of the study, a cartridge for a filter pitcher was proposed and determined its the optimal composition. It provides adjustment of tap water composition, namely: reduction by 60 % of the average concentration of chlorine (per 150 dm3 of water), by 15 % - permanganate oxidizability and by 20 % concentration of hardness ions to standard values at filtration rate not less than 0.15 dm3/min and a resource of 150 dm3. These results were achieved by selecting the optimal ratio of the components of the filter loading mixture and the density of the bottom drainage material.

Preparation of RE-containing magnesium alloys via molten-salt-mediated magnesiothermic reduction

Abstract RE-containing magnesium alloys were prepared via molten-salt-mediated magnesiothermic reduction by using RE2O3 (RE=Y, Nd and Gd) and Mg metal as raw materials. The thermomechanical analysis of the magnesiothermic reduction reactions in molten salt was investigated. Then the molten-salt-mediated magnesiothermic reduction process was studied from three different perspectives. After that, the RE-containing magnesium alloy was characterized by using chemical analysis, XRD analysis and SEM analysis. The magnesiothermic reduction was a liquid-liquid reaction with relatively weak driving force. During the melting process and the magnesiothermic reduction process, magnesium metal and the obtained alloy went up and down as a whole in molten salt, which improved the process safety without introducing chloride inclusions. Meanwhile, the hydrolysis of the RECl3-containing molten salt occurred at elevated temperature, which severely impeded the magnesiothermic reduction process. After the magnesiothermic reduction at 750 °C for 2.0 h, the content of RE and the common impurity elements in the obtained RE-containing alloy met the both requirements of the commercial WE43A and WE43B.

DiatomNet v1.0: A novel approach for automatic diatom testing for drowning diagnosis in forensically biomedical application

Background and ObjectiveDiatom testing is supportive for drowning diagnosis in forensic medicine. However, it is very time-consuming and labor-intensive for technicians to identify microscopically a handful of diatoms in sample smears, especially under complex observable backgrounds. Recently, we successfully developed a software, named DiatomNet v1.0 intended to automatically identify diatom frustules in a whole slide under a clear background. Here, we introduced this new software and performed a validation study to elucidate how DiatomNet v1.0 improved its performance with the influence of visible impurities. MethodsDiatomNet v1.0 has an intuitive, user-friendly and easy-to-learn graphical user interface (GUI) built in the Drupal and its core architecture for slide analysis including a convolutional neural network (CNN) is written in Python language. The build-in CNN model was evaluated for diatom identification under very complex observable backgrounds with mixtures of common impurities, including carbon pigments and sand sediments. Compared to the original model, the enhanced model following optimization with limited new datasets was evaluated systematically by independent testing and random control trials (RCTs). ResultsIn independent testing, the original DiatomNet v1.0 was moderately affected, especially when higher densities of impurities existed, and achieved a low recall of 0.817 and F1 score of 0.858 but good precision of 0.905. Following transfer learning with limited new datasets, the enhanced version had better results, with recall and F1 score values of 0.968. A comparative study on real slides showed that the upgraded DiatomNet v1.0 obtained F1 scores of 0.86 and 0.84 for carbon pigment and sand sediment, respectively, slightly worse than manual identification (carbon pigment: 0.91; sand sediment: 0.86), but much less time was needed. ConclusionsThe study verified that forensic diatom testing with aid of DiatomNet v1.0 is much more efficient than traditionally manual identification even under complex observable backgrounds. In terms of forensic diatom testing, we proposed a suggested standard on build-in model optimization and evaluation to strengthen the software's generalization in potentially complex conditions.

Robust microporous hydrogen−bonded organic framework for highly selective purification of methane from natural gas

Methane (CH4) purification using energy-efficient separation technology is important for the economic and safety of natural gas refining. Meanwhile, the common impurity acetylene (C2H2) was also served as raw material to produce various organic products, therefore the highly efficient purification of CH4 and C2H2 are very important and challenging. Herein, we demonstrate the separation ability of HOF-16 for C2H2/CH4 and CO2/CH4 mixtures in detail. HOF-16 has a potential affinity for C2H2 capture, resulting from the exposed free –COOH sites in the suitable pore channel. Gas sorption isotherms reveal that HOF-16a creates a high C2H2/CH4 uptake ratio of 7.9 at 298 K and 1 bar, resulting in a C2H2/CH4 separation selectivity of 107 (50/50, v/v) under ambient conditions, which is a record value among HOFs and even exceeds many MOFs. Theoretical calculations confirm that the free –COOH sites in the HOF-16a channel provide additional interactions for the C2H2 molecules. Dynamic breakthrough experiments indicate that C2H2 could be highly selective removed from C2H2/CH4 (1/99, v/v) mixture. Combined with the low isosteric heat of adsorption (Qst), HOF-16a can efficiently extract C2H2 from the adsorption bed and purify CH4 into high purity (>99.9%) with low energy consumption.

Manganese-doped hydroxyapatite as an effective adsorbent for the removal of Pb(II) and Cd(II)

The water polluted by lead(Pb(II)) and cadmium(Cd(II)) seriously endangers ecological safety and needs to be solved urgently. Because of the relatively low adsorption rate of pure hydroxyapatite for heavy metals, a series of manganese-doped hydroxyapatites (MnHAPs) were prepared by using manganese, a common impurity in hydroxyapatite, as a doping element to improve the adsorption performance. The structural and functional groups of the materials with different Mn/(Ca +Mn) molar ratios (0%, 5%, 10%, 20%, and 30%) were investigated by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), X-Ray diffraction (XRD), Raman spectrometer and Fourier transform infrared spectroscopy (FTIR) characterization. The presence of manganese influenced the formation and growth of hydroxyapatite crystals, resulting in lattice distortion and a large number of lattice defects in materials. Among them, manganese-doped hydroxyapatite with a Mn/(Ca +Mn) molar ratio of 10% (MnHAP-10) could most effectively remove Pb(II) and Cd(II), with the adsorption capacity of 1806.09 mg g−1 for Pb(II) at pH = 5 and 176.88 mg g−1 for Cd(II) at pH = 5.5. Then the adsorption behavior and mechanism were further researched systemically. It was concluded that the immobilization of Pb(II) by MnHAP-10 was mainly through dissolution precipitation and ion exchange, while Cd(II) was adsorbed by ion exchange and electrostatic interaction. In conclusion, MnHAP-10 has the potential to be applied as an effective adsorbent for the removal of Pb(II) and Cd(II) pollution.

Experimental study of impurity effects on convective mixing in Hele-Shaw cell with application to CO2 geological sequestration

Density-driven convective mixing, i.e., convective fingering, has been identified to enhance CO2 dissolution trapping in deep saline aquifers. In this study, a series of experiments in Hele-Shaw cells were conducted, and the effects of common impurities (N2, O2, and/or Ar) on the occurrence and development of the convective mixing process were compared and analyzed. It is demonstrated that the existence of these impurities, whether single or their mixture, delayed the onset of convection. However, the subsequent fingering development, including the mixing length and fingering footprint, exhibited different patterns and trends depending on the species and compositions of the impurities. The development and growth of the convective fingers displayed non-monotonic characteristics as a function of the concentration of single impurity Ar. Furthermore, the multiple impurities containing Ar had the potential to enhance the fingering development, especially during the advanced stage. Other than these cases involving Ar, the inclusion of other impurities (N2, and/or O2) was found to weaken the fingering development compared with the pure CO2 case. Nevertheless, the results of dissolved CO2 inventory suggested that the effects of different impurities at the same content, both single and multiple, might be similar to each other in the long term, except for the three-impurity case involving Ar. The laboratory experiments in the present study can help establishing a better understanding of the effects of multiple impurities in the application of impure CO2 geological sequestration.

Biuret toxicity induces accumulation of nitrogen-rich compounds in rice plants

AimsExcess biuret, a common impurity in urea fertilizers, is toxic to plants. Little is known about the mechanisms of biuret toxicity in plants. This study aimed to investigate the accumulation of biuret and the changes in metabolites in rice (Oryza sativa) plants under biuret toxicity.MethodsA previous study had shown that transgenic rice plants overexpressing bacterial biuret hydrolase had improved biuret tolerance. Here, we grew wild-type and bacterial biuret hydrolase-overexpressing rice plants in hydroponics at different biuret levels. Concentrations of biuret and allantoin, a nitrogenous intermediate in the purine degradation pathway, in the plants were determined. The expression levels of genes related to purine degradation and ureide metabolisms were analyzed using wild-type plants. Additionally, we performed a metabolome analysis using rice suspension cells.ResultsThe biuret hydrolase-overexpressing plants did not contain biuret, whereas wild-type plants accumulated biuret in shoots in the order of mmol L−1 tissue water. The concentration of allantoin in shoots of wild-type plants under biuret toxicity was higher than those in control conditions. Inhibition of allantoinase activity by biuret was not detected, and allantoin accumulation appeared to be associated with changes in the expression of allantoinase, allantoate amidohydrolase and putative allantoin transporter genes. Furthermore, another nitrogenous compound citrulline, which is a non-protein amino acid, accumulated in rice suspension cells under biuret toxicity.ConclusionThe accumulation of these compounds suggests that rice plants subjected to biuret toxicity need to reduce the concentration of surplus ammonium ions via synthesizing nitrogen-rich compounds.

The impact of common impurities present in gypsum deposits on in situ dissolution kinetics

The impact of common impurities present in gypsum deposits on in situ dissolution kinetics

Development of a Novel, Impurity-Scavenging, Corrosion-Resistant Coating for Ni-Based Superalloy CMSX-4

Sulfur, a common impurity arising from atmospheric and environmental contamination, is highly corrosive and detrimental to the lifespan of nickel superalloys in jet engines. However, sulfur-scavenging coatings have yet to be explored. Our study presents the successful development of a stable, uniform, impurity-scavenging Ni-Mn coating on Ni-based superalloy CMSX-4, through electroplating. The coating was characterised via combined scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. An optimal coating thickness of > 600 nm was deposited. The coated alloy was exposed to corrosive salt mixture 98% Na2SO4–2% NaCl at 550 °C for 100 h, mimicking engine exposure conditions, thereby proving that the coating successfully trapped sulfur and prevented its diffusion into an underlying alloy. This work presents a promising development for the prevention of sulfur-induced corrosion in industrial setting such as gas turbine engine, where the effects of sulfur diffusion into the bulk alloy could lead to premature failure.Graphical

Identification of carbon location in p-type GaN: Synchrotron x-ray absorption spectroscopy and theory

Identifying atomic configurations of impurities in semiconductors is of fundamental interest and practical importance in designing electronic and optoelectronic devices. C impurity acting as one of the most common impurities in GaN, it is believed for a long time that it substitutes at Ga site forming CGa with +1 charge-state in p-type GaN, while it substitutes at N site forming CN with -1 charge-state in n-type GaN. However, by combining x-ray absorption spectroscopy and first-principles simulations, we observed that C is mainly occupying the N site rather than the Ga one in p-GaN. We further reveal that this is due to an H-induced EF-tuning effect. During growth, the existing H can passivate Mg dopants and upshifts the EF to the upper region of bandgap, leading to the CN formation. After the p-type activation by annealing out H, although the EF is pushed back close to the valence band maximum, whereas the extremely large kinetic barrier can prevent the migration of C from the metastable CN site to ground-state CGa site, hence stabilizing the CN configuration. Additionally, the CN with neutral charge-state (CN0) in the p-GaN is further observed. Therefore, the real C-related hole-killer in p-type GaN could be CN rather than the commonly expected CGa. Our work not only offers the unambiguous evidence for the C defect formation in p-GaN but also contributes significantly to an in-depth understanding of the C-related hole-killers and their critical role on electrical and optoelectrical properties of p-GaN and even p-AlGaN.