Transmission Electron Microscopy-energy Dispersive Spectroscopy Research Articles

Unveiling the chromate stress response in the marine bacterium Bacillus enclensis AGM_Cr8: a multifaceted investigation.

In this study, we introduce Bacillus enclensis AGM_Cr8, a gram-positive marine bacterium isolated from the chronically polluted Versova Creek in Mumbai, India. AGM_Cr8 exhibits robust tolerance to chromate stress, thriving in marine agar media containing up to 3200mg/l of hexavalent chromium [Cr(VI)], with the Minimum Inhibitory Concentration (MIC) established at 5000mg/l. Notably, AGM_Cr8 also displays tolerance to other heavy metals, including Lead [Pb (II)] (1200mg/l), Arsenic [As (III)] (400mg/l), Cadmium [Cd(II)] (100mg/l), and Nickel [Ni(II)] (100mg/l). Scanning Electron Microscopy (SEM) reveals the presence of Cr(VI) on the bacterial surface, accompanied by the secretion of extracellular polymeric substances (EPSs) facilitating Cr(VI) sequestration. This observation is validated through Energy Dispersive Spectroscopy (EDS). Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy-Energy Dispersive Spectroscopy (STEM-EDS) confirm internal bioaccumulation of Cr(VI). X-ray photoelectron spectroscopy (XPS) identifies distinct peaks around 579 and 576eV, indicating the coexistence of Cr(VI) and Cr(III), implying a bioreduction mechanism. De novo genome sequencing identifies twenty-two chromate-responsive genes, including putative chromate transporters (srpC1 and srpC2), suggesting an efflux mechanism. Other identified genes encode NAD(P)H-dependent FMN-containing oxidoreductase, NADH quinone reductase, ornithine aminotransferase, transporter genes (natA, natB, ytrB), and genes related to DNA replication and repair (recF), DNA mismatch repair (mutH), and superoxide dismutase. We therefore, propose a chromate detoxification pathway that involves an interplay of chromate transporters, enzymatic reduction of Cr(VI) to Cr(III), DNA repair and role of antioxidants in response to chromate stress. We have highlighted the potential of AGM_Cr8 for bioremediation in chromium-contaminated environments, given its robust tolerance and elucidated molecular mechanisms for detoxification.

Nanomineralogy of thorite in the supergiant Huayangchuan uranium ore deposit: Revealing a new geochemical behavior of actinide in environment

Thorium (Th) is a naturally occurring radioactive element found in the environment, and recent advancements have been made in identifying and characterizing Th-bearing nanoparticles (NPs). However, the main focus is still on synthesized Th-bearing NPs and knowledge about natural Th-bearing NPs remains limited. Here, high-resolution transmission electron microscopy (HRTEM) observations of thorite from the Huayangchuan uranium ore deposit in Shaanxi Province, Central China, have revealed the nanoscale mineral characteristics of thorite. In this study, thorite NPs ranging from 5–10 nm in size were identified within the uranium ore. A combination of transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) elemental mapping and corresponding HRTEM images alongside Selected Area Electron Diffraction (SAED) and Fast Fourier Transform (FFT) patterns revealed a complex nanoscale structure in the thorite NPs, consisting of both amorphous and crystalline nanodomains with abundant defects. These nanostructures are associated with a metamictization mechanism in micrometer-sized thorite. Our findings indicate that the metamictization process can generate numerous thorite nanoparticles. Given the high penetrability and mobility of these NPs, the metamictization of thorite poses new challenges for the long-term stability of radioactive substances and the storage containers for radioactive waste. Furthermore, considering the likelihood of environmental release and the chemical toxicity, radioactivity, and nanotoxicity of natural Th-bearing NPs, increased attention should be given to the presence of natural thorite NPs in the ore deposit.

Structural, morphological, and chemical composition of ternary ZrHfN thin films deposited by reactive co-magnetron sputtering

This study focuses on a deposited ternary zirconium hafnium nitride (ZrHfN) thin film prepared using the reactive co-magnetron sputtering technique. The effect of the nitrogen (N2) flow rate on the films' structural, morphological, and chemical composition was investigated. The gracing-incidence X-ray diffraction (GIXRD) showed that all ZrHfN thin films exhibited a crystalline face-centered cubic structure with a strong (111) orientation. With increasing the N2 flow rate, the film's crystallography changed based on thermodynamic theory. The films demonstrated uniformity and homogeneity in their ternary nitride composition, as confirmed by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) mapping and electron probe microanalyzer (EPMA). Chemical state analysis using X-ray photoelectron spectroscopy (XPS) indicated the presence of both nitride and oxynitride species in all samples. Notably, the atomic concentration of the main elements (Zr, Hf, and N) remained relatively stable over the controlled N2 flow rate range. However, the N2 flow rate played a crucial role in forming hafnium nitride and oxynitride chemical states, whereas it did not significantly influence the Zr phases, dominated by Zr oxides. Additionally, the hardness of the ternary ZrHfN thin films exhibited enhancement comparable to typical ternary nitrides.

Contrasting shell thickness-dependent magnetic behaviors of CoFe2O4@Fe3O4 and Fe3O4@CoFe2O4 core/shell nanoparticles

The magnetic properties of bi-magnetic core/shell nanoparticles (NPs) have been a subject of extensive investigation. Yet, the role of shell thickness in hard/soft and soft/hard core/shell NPs, corresponding to conventional and inverse structures, remains incompletely elucidated. In this study, we synthesized two sets of core/shell NPs, namely Fe3O4@CoFe2O4 (IF@CF) and CoFe2O4@Fe3O4 (CF@IF), featuring a fixed core diameter of approximately 11 nm and varying shell thicknesses up to 5 nm. These NPs were synthesized via a seed-mediated particle growth approach. The formation of the core/shell configuration of typical NPs in both sets was directly verified through scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) imaging. Notably, the saturation magnetization (MS) of IF@CF NPs exhibited a significant increase compared to that of the IF core across all shell thickness variations, whereas it remained largely unchanged for CF core and CF@IF NPs. Conversely, the coercivity (HC) showed an opposite trend in the two structures with increasing shell thickness. We observed the emergence of a transition from constricted to smooth hysteresis loops in the conventional structure when the shell thickness reached 5 nm. The systematic evolution of hysteresis loops with escalating shell thickness in both structures closely correlates with distinct magnetic reversal mechanisms, influenced significantly by interparticle interactions. Our study presents a pathway for modulating the magnetic properties of bi-magnetic core/shell NPs, thereby opening avenues for advanced applications in magnetic imaging, sensing, drug delivery, and magnetic hyperthermia.

Pt/C and PtRu/C Catalysts Prepared by Modified Sulfite Complex Routes for Fuel Cell Applications

In-house 30 wt.% Pt and 50 wt.% Pt1Ru1 catalysts supported on high-surface area carbon (Ketjenblack, abbreviated as KB) were synthesized by the sulfite complex route. Two different procedures involving either a direct mixing of Pt-sulfite and Ru-sulfite complexes or Pt-sulfite preparation and subsequent impregnation of Ru precursor were adopted for the bimetallic species. In both cases, an impregnation of the formed metal oxides onto KB was adopted to increase the electronic conductivity of the samples. Finally, a carbothermal treatment at 600°C in He atmosphere was carried out for the reduction of the metal oxides to metallic PtRu/C compounds. The Pt1Ru1 ratio was calculated and revealed by X-ray fluorescence (XRF) analysis whereas the carbon percentage was calculated by weight loss. 50 mg of sample was treated in air at 550°C for 2 h and, after cooling, the weight corresponded to 25 mg, confirming a carbonaceous matrix percentage of 50 wt.%. In a similar way, the 30 wt.% Pt/C was determined. X-ray diffraction (XRD) revealed that the samples showed face centered cubic (fcc) structure for Pt nanoparticles. It appears that two distinct crystallographic phases of Pt and Ru nanoparticles were encountered after the synthesis conducted by Ru impregnation. In contrast, only a single fcc phase is visible when the Pt and Ru sulfite precursors were mixed, confirming the formation of an alloy. Furthermore, Scanning Transmission Electron Microscopy-Energy dispersive X-ray spectroscopy (S/TEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the differences in morphology and surface characteristics of the catalysts.For the electrochemical measurements, rotating disc electrode (RDE) technique under acid and alkaline conditions was employed to investigate the half cell reactions. The catalysts were also deposited at the anode and cathode of fuel cells to evaluate the activity, performance, and short-term durability. Acknowledgement “This research was funded by the European Union – EIT Raw Materials in the framework of the following project: LYDIA- Recycling Critical Metals from Fuel Cells (G.A. 22019)”

Leveraging Ligand Steric Demand to Control Ligand Exchange and Domain Composition in Stratified Metal-Organic Frameworks.

Incorporating diverse components into metal-organic frameworks (MOFs) can expand their scope of properties and applications. Stratified MOFs (sMOFs) consist of compositionally unique concentric domains (strata), offering unprecedented complexity through partitioning of structural and functional components. However, the labile nature of metal-ligand coordination handicaps achieving compositionally distinct domains due to ligand exchange reactions occurring concurrently with secondary strata growth. To achieve complex sMOF compositions, characterizing and controlling the competing processes of new strata growth and ligand exchange are vital. This work systematically examines controlling ligand exchange in UiO-67 sMOFs by tuning ligand sterics. We present quantitative methods for assessing and visualizing the outcomes of strata growth and ligand exchange that rely on high-angle annular dark-field images and elemental mapping via scanning transmission electron microscopy-energy dispersive X-ray spectroscopy. In addition, we leverage ligand sterics to create 'blocking layers' that minimize ligand exchange between strata which are particularly susceptible to ligand exchange and inter-strata ligand mixing. Finally, we evaluate strata compositional integrity in various solvents and find that sMOFs can maintain their compositions for >12 months in some cases. Collectively, these studies and methods enhance understanding and control over ligand placement in multi-domain MOFs, factors that underscore careful tunning of properties and function.

Effect of proteins as constituents of island-nanomatrix structure on vulcanization of natural rubber

Effect of proteins, constituents of the island-nanomatrix structure, on dispersion of zinc to natural rubber was investigated by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) and focused ion beam-scanning electron microscopy-energy dispersive X-ray spectroscopy (FIB-SEM-EDX). Films of natural rubber and deproteinized natural rubber (DPNR) prepared with urea were embedded in a mixture of ZnO, vulcanization accelerator and sulfur, and they were heated at 150 °C for 5 h. Migration of Zn from surface to inside of the films was observed by FIB-SEM-EDX. The Zn migrated from the surface to 14 μm for natural rubber, but not for DPNR. The optimum vulcanization time for natural rubber was short, i.e., about 4 min, whereas it was long for DPNR, i.e., about 15 min. To confirm the effect of the proteins, a latex-mixed rubber compound was prepared by mixing the latex with sulfur, ZnO and vulcanization accelerator followed by drying with a hotplate at 150 °C for 45 s since the proteins are segregated on the surface of natural rubber particles in the latex stage. Vulcanization was accelerated for the latex-mixed natural rubber compared with mechanically mixed natural rubber compound that was prepared by mixing natural rubber with ZnO, vulcanization accelerator and sulfur with a two-roll mill. The resulting latex-mixed natural rubber vulcanizate was superior in mechanical properties to the mechanically mixed natural rubber vulcanizate. It was found by rubber-state NMR spectroscopy that the difference in mechanical properties was attributed to the difference in the cis-1,4-average sequence length of the vulcanizates, which came from the difference in the dispersion of Zn.

Leaching kinetics of ash impurities from aphanitic graphite by combining dual-ultrasound and hydrochloric acid–potassium hydrogen fluoride

The hydrochloric acid-fluoride salt is useful for purifying graphite. Ultrasonic-assisted technique can significantly reduce the leaching time and improve the leaching efficiency. Compared with single-frequency, dual-frequency ultrasound has the advantages of high energy efficiency and wide cavitation area. In this study, the combination of a dual-frequency ultrasound-assisted technique and hydrochloric acid–potassium hydrogen fluoride leaching agent was proposed for the leaching of aphanitic graphite to remove impurity minerals. First, the effects of probe-type ultrasonic power, tank-type ultrasonic power, temperature, HCl concentration, ultrasonication time, and KHF2 concentration on the purification efficiency of impurities from aphanitic graphite with the assistance of dual-frequency ultrasound were investigated. It was found that the combination of dual-frequency ultrasound and hydrochloric acid–potassium hydrogen fluoride can reduce the ash content of aphanitic graphite from 13.02 % to 1.02 % with an ash removal rate of 94.17 %. Second, volumetric reaction models and unreacted shrinkage nucleation models were used to fit the kinetics of impurities from aphanitic graphite with dual-frequency ultrasound-assisted HCl-KHF2 leaching. Kinetic analysis shows that the volumetric reaction model with chemical control was better to fit the leaching process. This is consistent with the calculation results of the activation energy of the reaction (Ea = 58.13 kJ/mol). Finally, laser particle size analyzer, X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) were used to analyze the fugacity of impurity minerals during the process of dual-frequency ultrasound-assisted HCl-KHF2 leaching. It was revealed that combining ultrasonic cavitation fragmentation with chloric acid–potassium fluoride generated SiF4 with high solubility, thereby removing silica-bearing impurities more efficiently. The challenges in further reducing ash content from 1.02 % in the leached concentrate of aphanitic graphite could be attributed to the existence of titanium-bearing mineral impurities on the surface of graphite particles and the presence of silica-bearing minerals between graphite carbon layers.

Development and characterization of lipid nanocapsules loaded with iron oxide nanoparticles for magnetic targeting to the blood–brain barrier

Brain drug delivery is severely hindered by the presence of the blood–brain barrier (BBB). Its functionality relies on the interactions of the brain endothelial cells with additional cellular constituents, including pericytes, astrocytes, neurons, or microglia. To boost brain drug delivery, nanomedicines have been designed to exploit distinct delivery strategies, including magnetically driven nanocarriers as a form of external physical targeting to the BBB. Herein, a lipid-based magnetic nanocarrier prepared by a low-energy method is first described. Magnetic nanocapsules with a hydrodynamic diameter of 256.7 ± 8.5 nm (polydispersity index: 0.089 ± 0.034) and a ξ-potential of -30.4 ± 0.3 mV were obtained. Transmission electron microscopy-energy dispersive X-ray spectroscopy analysis revealed efficient encapsulation of iron oxide nanoparticles within the oily core of the nanocapsules. Both thermogravimetric analysis and phenanthroline-based colorimetric assay showed that the iron oxide percentage in the final formulation was 12 wt.%, in agreement with vibrating sample magnetometry analysis, as the specific saturation magnetization of the magnetic nanocapsules was 12% that of the bare iron oxide nanoparticles. Magnetic nanocapsules were non-toxic in the range of 50–300 μg/mL over 72 h against both the human cerebral endothelial hCMEC/D3 and Human Brain Vascular Pericytes cell lines. Interestingly, higher uptake of magnetic nanocapsules in both cell types was evidenced in the presence of an external magnetic field than in the absence of it after 24 h. This increase in nanocapsules uptake was also evidenced in pericytes after only 3 h. Altogether, these results highlight the potential for magnetic targeting to the BBB of our formulation.Graphical

Aminosilane assisted deposition of gold nanoparticles on Zn(OH)2 nanosheets and their application in electrochemical sensor

A facile and efficient method for systematical deposition of gold nanoparticles (AuNPs) on Zn(OH)2 nanosheets (NS) with different Zn and Au ratios was established in the presence of N-[3-(trimethoxysilyl)propyl]diethylenetriamine (TPDT silane), without adding any external reducing agents, at room temperature. Here, TPDT silane behaves as both a stabilizing and reducing agent. UV–vis absorption spectroscopy, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to confirm the formation of AuNPs on Zn(OH)2 NS. As the concentration of AuNPs increased, a proportional increase in both the number and size of deposited AuNPs on Zn(OH)2 NS was observed. To understand how the variation in the number and size of AuNPs affects their catalytic activity, the electrocatalytic activity of different composition ratios of Zn(OH)2-Au NS toward nitrite ions was studied using cyclic voltammetry and amperometric technique. The TPDT-stabilized Zn(OH)2-Au NS showed high electrocatalytic activity, attributed to the effective electron transfer from Zn(OH)2 NS to AuNPs, creating a synergistic effect that enhances the overall activity. The optimal Zn(OH)2-Au NS modified electrode showed an amperometric sensitivity of 5.72 nA/µM and a limit of detection of 1.2 µM for nitrite ions in water sample well below the guideline value of WHO. This demonstrates the practical applicability of this method for real-world water analysis.

Comparative Study of Exsolved and Impregnated Ni Nanoparticles Supported on Nanoporous Perovskites for Low-Temperature CO Oxidation.

This study investigated the redox exsolution of Ni nanoparticles from a nanoporous La0.52Sr0.28Ti0.94Ni0.06O3 perovskite. The characteristics of exsolved Ni nanoparticles including their size, population, and surface concentration were deeply analyzed by environmental scanning electron microscopy (ESEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) mapping, and hydrogen temperature-programmed reduction (H2-TPR). Ni exsolution was triggered in hydrogen as early as 400 °C, with the highest catalytic activity for low-temperature CO oxidation achieved after a reduction step at 500 °C, despite only a 10% fraction of Ni exsolved. The activity and stability of exsolved nanoparticles were compared with their impregnated counterparts on a perovskite material with a similar chemical composition (La0.65Sr0.35TiO3) and a comparable specific surface area and Ni loading. After an aging step at 800 °C, the catalytic activity of exsolved Ni nanoparticles at 300 °C was found to be 10 times higher than that of impregnated ones, emphasizing the thermal stability of Ni nanoparticles prepared by redox exsolution.

Synthesis of silver-palladium Janus nanoparticles using co-sputtering of independent sources: experimental and theorical study.

Janus-type nanoparticles are important because of their ability to combine distinct properties and functionalities in a single particle, making them extremely versatile and valuable in various scientific, technological, and industrial applications. In this work, bimetallic silver-palladium Janus nanoparticles were obtained for the first time using the inert gas condensation technique. In order to achieve this, an original synthesis equipment built by Mantis Ltd. was modified by the inclusion of an additional magnetron in a second chamber, which allowed us to use two monometallic targets to sputter the two metals independently. With this arrangement, we could find appropriate settings at room temperature to promote the synthesis of bimetallic Janus nanoparticles. The structural properties of the resulting nanoparticles were investigated by transmission electron microscopy (TEM), and the chemical composition was analyzed by TEM energy dispersive spectroscopy (TEM-EDS), which, together with structural analysis, confirmed the presence of Janus-type nanostructures. Results of molecular dynamics and TEM simulations show that the differences between the crystalline structures of the Pd and Ag regions observed in the TEM micrographs can be explained by small mismatches in the orientations of the two regions of the particle. A density functional theory structural aims to understand the atomic arrangement at the interface of the Janus particle.

The Impact of Mesopores of SnO2 Catalyst Support on the Performance of Polymer Electrolyte Fuel Cells

Recently, the focus of future polymer electrolyte fuel cell (PEFC) application for automobiles has shifted from the class of passenger light-duty vehicles (LDVs) to that of heavy-duty vehicles (HDVs). The total operating time in the lifetime of HDVs is much longer than that of LDVs. Thus, durability is becoming more and more important for the cell components including the catalyst materials, and the compatibility between initial performance and durability at a high level is desired. Employing mesoporous carbons as catalyst supports is a promising option to enhance the initial performance [1]. In the catalyst layer of a PEFC with mesoporous carbon support, Pt-based catalyst nanoparticles deposited inside the mesopores are not directly covered by ionomer. As a result, a catalyst poisoning by sulfonic acid groups of the ionomer is hindered and a high catalytic activity is obtained. In addition, a high oxygen transport resistance thorough Pt/ionomer interfaces [2] can be mitigated by employing mesoporous carbon support. Nonetheless, from the viewpoint of thermodynamics, carbon support can oxidatively degrade during the long-term operation. Tin oxide (SnO2) is one of the promising candidates for substituting the carbon support because of its high electrochemical stability at high potentials [3]. However, to our best knowledge, the mitigation of the ionomer adsorption on the Pt surface by using mesoporous SnO2 support has not been studied in previous works. In this study, we synthesized mesoporous SnO2 supports and investigated the impact of the mesopore on the performance of the PEFC. Connected mesoporous Sb-doped SnO2 particles (CMSbTOs) were synthesized by using a mesoporous carbon as a template (Figure (a)). The size of the mesopore was successfully controlled in the range of 4 – 10 nm by adjusting the carbon template structure and calcination temperature (Figure (b)). The BET surface area and conductivity of the CMSbTOs were in the ranges of 90 – 210 m2 g-1 and ca. 10-2 S cm-1, respectively. Pt nanoparticles were deposited on the CMSbTOs via a colloidal method to obtain Pt/CMSbTO catalyst (Pt loading of 20 wt.%). It was confirmed that the Pt nanoparticles were located both on the outer surface and inside the mesopores of the CMSbTOs by scanning transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) analysis. A membrane electrode assembly (MEA) was fabricated by using a Pt/CMSbTO catalyst for the cathode catalyst layer and single cell tests were performed under dried (30%RH, 82 °C) and highly humidified (80%RH, 60 °C) conditions. In addition, a homemade Pt/Sb-SnO2 catalyst with solid-core SnO2 support and a commercial Pt/Vulcan catalyst (TEC10V30E, TKK) were also tested for comparison. Under the dried conditions, the Pt/CMSbTO catalyst showed a better I-V performance than the Pt/Sb-SnO2 (solid) catalyst and Pt/Vulcan catalyst (Figure (c)). The oxygen reduction reaction (ORR) activity of the Pt/CMSbTO catalyst at 0.84 V was higher than that of the Pt/Sb-SnO2 (solid) and Pt/Vulcan catalysts. This result suggests that catalyst poisoning by the ionomer is mitigated when the mesoporous SnO2 support is employed. Moreover, the local oxygen transport resistance (oxygen transport resistance that is independent of the total gas pressure) of the Pt/CMSbTO catalyst was lower than that of the Pt/Sb-SnO2 (solid) and Pt/Vulcan catalysts, probably because of a decrease in the oxygen transport resistance due to Pt/ionomer interfaces. In contrast, under the highly humidified conditions, the I-V performance of the Pt/CMSbTO catalyst was comparable to that of the Pt/Sb-SnO2 (solid) catalyst and slightly lower than that of the Pt/Vulcan catalyst (Figure (d)). This result can be ascribed to floodings inside the mesopores of the CMSbTO support. Accelerated stress tests (repeated potential steps between 1.0 – 1.5 V under 100%RH, 80 °C) were also performed to confirm the electrochemical stability of the Pt/CMSbTO catalyst at high potentials. The Pt/CMSbTO catalyst showed a much higher retention rate of the electrochemical Pt surface area (ECSA) than the Pt/Vulcan catalyst as expected. More details, including the effect of the pore size of the CMSbTO support on the initial performance, will be discussed in the presentation.

Understanding the oxidation resistance of zirconium alloy at 1000°C based on the formation of a Zr-Sn intermetallic phase and co-precipitation of Sn and Nb

The oxidation behavior of zirconium alloy in high-temperature steam plays a dominant role in the operation of nuclear reactors under accident conditions. The present work investigated the effect of Sn on the oxidation behavior of zirconium alloys in high-temperature steam at 1000 °C. The results of scanning electron microscopy (SEM), metallographic microscopy and synchrotron X-ray diffraction (S-XRD) analyses show that there are three layers in the oxidized sample, including prior β-Zr, α-Zr(O) and ZrO2. High resolution analyses conducted in these layers by transmission electron microscopy (TEM) show that Sn atoms segregate around the oxide-metal (O-M interface and Zr-Sn intermetallic precipitates only present in the oxide film. Clear atomic arrangements of Zr5Sn3 were obtained by TEM, resulting in accurate identification of the Zr-Sn intermetallic phase. Also, TEM energy dispersive spectroscopy (EDS) maps show that Zr-Sn particles invariably accompany the segregation or precipitation of Nb. However, no clear precipitation sequence was observed, which suggests that a co-precipitation mechanism of Sn and Nb is in operation. As oxidation proceeds, nanovoids next to the Zr-Sn intermetallic particles were observed accompanied by local areas deficient in oxygen, identified as ZrO. Combining the interdiffusion trend obtained by Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, a mechanism for the transformation from the Zr-Sn intermetallic precipitates to nanovoids was proposed. This proposed mechanism may shed new light into the role of Sn in the oxidation resistance of zirconium alloy under LOCA conditions.

Water-dispersible colloids facilitate the release of potentially toxic elements from contaminated soil under simulated long-term acid rain

The release behaviors of potentially toxic elements (PTEs) associated with water-dispersible colloids (WDCs) in contaminated soils are of considerable public concern. However, little information is available on the size distribution and elemental composition of WDCs and their effects on the release of PTEs in contaminated soils under long-term acid rain. Here, a quantitative accelerated aging leaching test was conducted to evaluate the long-term release risks of PTEs from four contaminated agricultural soil types exposed to acid rain. Asymmetric flow field-flow fractionation (AF4), scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) and ultrafiltration were used to clarify the size distribution and elemental composition of WDCs containing PTEs. Solution dynamics of successive leaching indicate high release potential for As, Cd, and Pb depending on soil properties under long-term (∼65 years) acid rain. Both ultrafiltration and AF4 analysis show that As in leachate was mainly in the “truly dissolved” fraction, while Pb, Cu, Cd and Fe were predominantly in the colloidal fraction and their percentages increased with increasing extraction time by acid rain. AF4-UV-ICP-MS and STEM-EDS reveal that nanoparticles at 1–7 nm most likely composed of organic matter (OM)-Fe/Al(/Si) oxides composite were the main carriers of Pb, Cu, As and Cd. Lead was also verified in Fe-oxide colloids at 34–450 nm in the first extracts but disappeared in the tenth extracts. This indicates that WDC-bearing PTEs become smaller as leaching proceeds. The study indicates the quantitative description and size-resolved understanding of WDC- and nanoparticle-bound PTEs in leachates of contaminated soils subjected to long-term acid rain.

Effect of nitrogen pressure on the fabrication of AlCrFeCoNiCu0.5 high entropy nitride thin films via cathodic arc deposition

In the past two decades, high entropy alloy (HEA) coatings have attracted great attention due to their superior mechanical properties, outstanding corrosion and oxidation resistance, and exceptionally high thermal stability. In comparison to HEA thin films, high entropy nitrides (HENs) exhibit higher mechanical strength and chemical inertness. In this work, AlCrFeCoNiCu0.5 HEA and HEN thin films were fabricated using a filtered cathodic arc. By regulating the deposition pressure from 0.0005 Pa (HEA thin film) to 0.05 Pa, the nitrogen concentration in each thin film was precisely controlled to tune the mechanical properties. Scanning transmission electron microscopy-energy dispersive spectroscopy revealed that the nitrogen concentration of the films was up to 21.2 at. % at the pressure of 0.05 Pa. The reduced effect of preferential sputtering increased aluminum concentration from 8.3 ± 1.5 to 12.9 ± 2.2 at. % as pressure increased up to 0.05 Pa. X-ray photoelectron spectroscopy further confirmed the formation of AlN and CrN at pressures of 0.01–0.05 Pa. The highest hardness and elastic modulus of the HEN film were 12.4 ± 0.6 and 347.3 ± 17.7 GPa, respectively, which were 84.8% and 131.4% higher than those of the HEA thin film.

Magnetic core/shell structures: A case study on the synthesis and phototoxicity/cytotoxicity tests of multilayer graphene encapsulated Fe/Fe3C nanoparticles

This study reports on a novel and optimized synthesis procedure of multilayer graphene (MLG) encapsulated Fe/Fe3C nanoparticles using a combined method of spray drying, chemical vapor deposition (CVD) and leaching from FeCl3.6 H2O based precursor, in addition to phototoxicity/cytotoxicity tests for their potential use in biomedical applications. CVD studies were employed at various temperature/time and gas flow rate values. Based on the X-ray diffractometry (XRD), Raman spectroscopy, vibrating sample magnetometry (VSM), transmission electron microscopy/energy-dispersive spectroscopy (TEM/EDS) and differential thermal analysis/thermogravimetry (DTA/TG), CVD parameters of 900 °C, 60 min, 50 mbar and CH4/H2:1/1 were determined as optimum conditions. MLG encapsulated (d-spacing: 0.34 nm) nanoparticles consisting BCC Fe, FCC (Fe, C) and orthorhombic Fe3C phases were obtained with average core diameter of ∼45 nm and average shell thickness of ∼6 nm (8–50 layers). MLG encapsulated Fe/Fe3C nanoparticles were achieved with soft ferromagnetic (Ms: ∼64 emu/g; Hc: ∼276 Oe) property. MLG coated Fe/Fe3C nanoparticles were suspended in an aqueous media using poly/acrylic acid as a post-synthetic treatment. They were found cytocompatible even at 200 µg/mL and 75 µg/mL after 24 and 48 h exposure, respectively. Dose dependent cytotoxicity was studied on both MCF7 and HeLa cells after 72 h incubation. Light-to-heat conversion efficiency of these nanoparticles at 795 nm irradiation in water was calculated as 37.60 %. After laser irradiation, with an increased concentration of nanoparticles (75–200 µg/mL), more than 80 % cell death was observed on both MCF7 and HeLa cells lines via late apoptotic cell death as a result of photothermal effect.

Alkaline Leaching: A Facile Strategy to Improve the Surface Activity of Air Electrodes for Solid Oxide Electrochemical Cells

Solid oxide electrochemical cells (SOCs) have been focused on as next-generation energy conversion devices. However, since SOCs are operated at high temperatures (>800 °C), several issues are present, such as limited material selection and high system cost. Therefore, lowering the operating temperature and developing suitable electrode materials which have high oxygen evolution/reduction reaction (OER/ORR) activity at relatively low temperatures are crucial.In this manner, surface modification methods have been researched, such as nanocatalyst decoration, surface coating, and acid etching. However, nanocatalyst decoration and surface coating require a long annealing time and complicated vacuum devices, respectively, and acid etching is not favorable for rational control on the surface of the electrode. Therefore, a cost- and time-efficient surface modification method while maintaining reasonable controllability can have a meaningful advantage.We suggest a facile method of surface modification for electrodes of SOCs: alkaline leaching. During the water splitting in a conventional 3-electrode system with an alkaline medium, cations in perovskite oxide lattice are selectively dissolved into the alkaline solution, which is called as leaching phenomenon. As a result of leaching, the composition of the perovskite oxide surface differs from the pristine condition (e.g. the transition metal-rich surface). We adopted this phenomenon as a strategy to improve the activity of air electrodes for SOCs.In this study, we chose PrBa0.8Ca0.2Co2O5+δ (PBCC) as the air electrode material for the first case-study. Recently, PBCC has gained a lot of attention due to its outstanding OER/ORR activity even at relatively low temperatures (<650 °C). We compared the reactivity of PBCC electrodes in different alkaline leaching conditions by electrochemical impedance spectroscopy. After the surface treatment, area-specific resistance of 0.018 Ω·cm2 (at 650 °C) was recorded, corresponding to the 5-fold and 53-fold enhanced ORR reactivity compared to the pristine PBCC air electrode and commercialized La0.6Sr0.4Co0.2Fe0.8O3 air electrode, respectively.To elucidate the enhanced surface activity, various analyses were carried out. Scanning electron microscopy images showed the porous structure of the PBCC electrode and the removal of Ba-containing secondary phases on the PBCC surface, which are known to degrade surface activity. Transmission electron microscopy-energy dispersive spectroscopy results demonstrated that the surface of the PBCC electrode becomes amorphous and Co-rich, which are both known to be advantageous for ORR activity. Inductively coupled plasma-mass spectrometry results of the alkaline medium in the 3-electrode system revealed that specific cation species (i.e. Ba and Ca) were selectively dissolved into the alkaline medium and were more leached out by the applied anodic bias, resulting in the Co-rich surface. X-ray photoelectron spectroscopy results suggest that surface Ba species were decreased and defective O species were increased, leading to improved ORR activity.In this case, we showcased alkaline leaching as a strategy to enhance the PBCC electrodes for SOCs, but with the sufficient current collection, our method can be further applied to various perovskite oxides in various structures. Taking the various advantages of perovskite-oxide-based materials, the alkaline leaching method will be a novel strategy to achieve a high-performance (electro)chemical catalyst.

Translocation of TiO2 nanoparticles enhances phosphorus uptake by wetland plants: Evidence from Pistia stratiotes and Alisma plantago-aquatica

Titanium dioxide nanoparticles (nTiO2) and phosphorus (P) are widely present in sewages. To verify the hypothesis and the associated mechanisms that root-to-shoot translocation of nTiO2 can enhance plant P uptake thus P removal during sewage treatment, two wetland plants (Pistia stratiotes and Alisma plantago-aquatica) with different lateral root structures were used to examine the effect of nTiO2 (89.7% anatase and 10.3% rutile) on plant growth and P uptake in a hydroponic system. Inductively coupled plasma-optical emission spectroscopy and transmission electron microscopy-energy dispersive spectroscopy showed that P. stratiotes with well-developed lateral roots translocated 1.4–16 fold higher nTiO2 than A. plantago-aquatica with poorly developed roots, indicating P. stratiotes is efficient in nTiO2 uptake. In addition, nTiO2 root-to-shoot translocation in P. stratiotes increased with increasing nTiO2 concentration, while the opposite occurred in A. plantago-aquatica. Corresponding to the stronger nTiO2 translocation in P. stratiotes, its P uptake efficiency (Imax) and P accumulation were greater than that in A. plantago-aquatica, with Imax being increased by 35.8% and −16.4% and shoot P concentrations being increased by 16.2–64.6% and 11.4%, respectively. The strong positive correlation between Ti and P concentrations in plant tissues (r = 0.72–0.89, P < 0.01) indicated that nTiO2 translocation enhanced P uptake. Moreover, nTiO2-enhanced P uptake promoted plant growth and photosynthetic pigment synthesis. Therefore, wetland plants with well-developed lateral roots like P. stratiotes have potential to be used in P removal from nTiO2-enriched sewages.

Mobilization of Colloid- and Nanoparticle-Bound Arsenic in Contaminated Paddy Soils during Reduction and Reoxidation.

The association of arsenic (As) with colloidal particles could facilitate its transport to adjacent water systems or alter its availability in soil-rice systems. However, little is known about the size distribution and composition of particle-bound As in paddy soils, particularly under changing redox conditions. Here, we incubated four As-contaminated paddy soils with distinctive geochemical properties to study the mobilization of particle-bound As during soil reduction and subsequent reoxidation. Using transmission electron microscopy-energy dispersive spectroscopy and asymmetric flow field-flow fractionation, we identified organic matter (OM)-stabilized colloidal Fe, most likely in the form of (oxy)hydroxide-clay composite, as the main arsenic carriers. Specifically, colloidal As was mainly associated with two size fractions of 0.3-40 and >130 kDa. Soil reduction facilitated the release of As from both fractions, whereas reoxidation caused their rapid sedimentation, coinciding with solution Fe variations. Further quantitative analysis demonstrated that As concentrations positively correlated with both Fe and OM concentrations at nanometric scales (0.3-40 kDa) in all studied soils during reduction and reoxidation, yet the correlations are pH-dependent. This study provides a quantitative and size-resolved understanding of particle-bound As in paddy soils, highlighting the importance of nanometric Fe-OM-As interactions in paddy As geochemical cycling.