Multiple Metal Elements Research Articles

Estimation of heavy metals using deep neural network with visible and infrared spectroscopy of soil

Heavy metal contamination in soil disturbs the chemical, biological, and physical soil conditions and adversely affects the health of living organisms. Visible and near-infrared spectroscopy (VNIRS) shows a potential feasibility for estimating heavy metal elements in soil. Moreover, deep learning models have been shown to successfully deal with complex multi-dimensional and multivariate nonlinear data. Thus, this study implemented a deep learning method on reflectance spectra of soil samples to estimate heavy metal concentrations. A convolutional neural network (CNN) was adopted to estimate arsenic (As), copper (Cu), and lead (Pb) concentrations using measured soil reflectance. In addition, a convolutional autoencoder was utilized as a joint method with the CNN for dimensionality reduction of the reflectance spectra. Furthermore, artificial neural network (ANN) and random forest regression (RFR) models were built for heavy metal estimation. Principal component analysis was utilized for dimensionality reduction of the ANN and RFR models. Among these models, the CNN model with convolutional autoencoder showed the highest accuracies for As, Cu, and Pb estimates, having R2 values of 0.86, 0.74, and 0.82, respectively. The convolutional autoencoder disentangled the relevant features of multiple heavy metal elements and delivered robust features to the CNN model, thereby generating relatively accurate estimates.

Aerosol Synthesis of High Entropy Alloy Nanoparticles.

Homogeneously mixing multiple metal elements within a single particle may offer new material property functionalities. High entropy alloys (HEAs), nominally defined as structures containing five or more well-mixed metal elements, are being explored at the nanoscale, but the scale-up to enable their industrial application is an extremely challenging problem. Here, we report an aerosol droplet-mediated technique toward scalable synthesis of HEA nanoparticles with atomic-level mixing of immiscible metal elements. An aqueous solution of metal salts is nebulized to generate ∼1 μm aerosol droplets, which when subjected to fast heating/quenching result in decomposition of the precursors and freezing-in of the zero-valent metal atoms. Atomic-level resolution scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis reveals that all metal elements in the nanoparticles are homogeneously mixed at the atomic level. We believe that this approach offers a facile and flexible aerosol droplet-mediated synthesis technique that will ultimately enable bulk processing starting from a particulate HEA.

Online, Continuous, and Interference-Free Monitoring of Trace Heavy Metals in Water Using Plasma Spectroscopy Driven by Actively Modulated Pulsed Power.

This work presents the development of an online continuous heavy metals monitoring system using optical emission spectroscopy of plasma in water. The plasmas were driven by actively modulated pulsed power (AMPP) to control the plasma and its emission behavior in solutions with a wide range of conductivity. The AMPP quantified in situ the solutions' conductivity and modulated in real time the pulse width based on the conductivity. We demonstrated the online monitoring of the metallic elements. The results show that multiple metallic elements, namely Pb and Zn, can be independently and simultaneously detected with less than a 10% variation in the corresponding optical emission lines in solutions with a wide range of conductivity. An alert system was integrated to demonstrate the capability of an instant warning via e-mail once metallic elements were detected. Finally, we demonstrated that this system was robust even with the existence of several interferences and able to perform online continuous monitoring for days. We believe the system using plasma spectroscopy with AMPP for online monitoring of metals in water will have a significant impact on the fields of environmental monitoring and protection.

Formation of hollow and solid carbon spheres in thermally stressed jet fuel in the low temperature autoxidation regime

We report the formation of hollow and solid carbon spheres and spherical nanostructures by self-assembly through thermal stressing of jet fuel (Jet A-1) in the autoxidation temperature range. The characterization of Jet A-1 deposits was conducted by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS). Additionally, high resolution mass spectrometry with electro spray ionization source (ESI-MS) have been used to identify large molecular weight compounds in the mass range 350 Da to 1000 Da in the thermally stressed fuel. Fourier transform infrared (FTIR) spectroscopy analysis revealed oxygenated functional groups in the jet fuel treated by flask tests. Compositional analysis of deposit by TEM EDS and scanning transmission electron microscopy (STEM) and a high-angle annular dark field (HAADF) detector identified multiple trace metallic elements such as Cu, Fe, Zn, Sn, Mg, Al and heteroatoms S, N, O. Hollow carbon sphere formation was due to the catalytic activity of trace metals. Spherical particle growth in this method also appeared to follow Ostwald ripening mechanism. Simple flask static tests in the low temperature regime with jet fuel as hydrocarbon source without externally added catalysts thus is a novel method for hollow and solid carbon sphere synthesis and presented in this paper.

Plasma arc discharge synthesis of multicomponent Co-Cr-Cu-Fe-Ni nanoparticles

The controllable alloying multiple metallic elements into an individual nanoparticle offers the promise material properties. Here a series of spherical Co-Cr-Cu-Fe-Ni nanoparticles (NPs) with an average size of around 80–120 nm can be easily synthesized with a controllable microstructure and composition by modified plasma arc-discharge method. The crystal structure of the as-prepared NPs is largely composed of Cu-rich FCC phase with a small amount of BCC phase, and the content of BCC phase increases with the decrease of Cu content in the NPs. The differences in components between the raw materials and as-prepared NPs are ascribed to the evaporating pressure and the molar mass of raw materials, and by designing the target to CoaCrbCucFedNie, the atomic composition of CoaCr3bCu12cFe1.5dNie NPs can be obtained. Moreover, the as-prepared nanoparticles exhibit comparable soft magnetic features, and the asymmetric characteristic is probably due to the magnetic coupling of Cu-rich FCC phase with a relatively hard magnetic BCC crystalline phase. The case of Co-Cr-Cu-Fe-Ni NPs is a good example, which opens new ways to synthesize other multicomponent metal NPs with controllable structure and composition by controlling the molar mass of the raw material.

Metal‐organic Frameworks Incorporating Multiple Metal Elements

AbstractThe obtaining of materials incorporating multiple metal elements is of interest because the combination of various metal cations results in the achievement of new and enhanced properties. Metal‐organic frameworks (MOFs) offer a suitable platform to combine multiple metal elements due to their modular nature and highly controllable structure. The incorporation of various metal elements into MOFs might be accomplished by following different synthetic approaches, which in turn determine the way in which the various metal elements are arranged in the framework. In this contribution, we will overview the formation of multi‐metal MOFs by the introduction of new metal sites in the organic linkers, or in the inorganic secondary building units through cation exchange process, or one‐pot synthesis.

A second order numerical scheme for the annealing of metal–intermetallic laminate composite: A ternary reaction system

Metal–Intermetallic Laminate (MIL) composites are laminate structures that are fabricated by optimizing unique benefits of constituent components to have attractive physical and mechanical features, such as high strength, stiffness, and toughness. The synthesis of MIL composites involves annealing reaction of multiple metallic elements at high temperatures. In this work, we propose, analyze, and implement a second-order semi-implicit scheme for the annealing of a ternary metallic reaction system. The robustness of such a numerical scheme is demonstrated by various numerical experiments, as well as the expected accuracy tests. At the theoretical level, we provide a detailed convergence analysis, which confirms the second-order accuracy in both the temporal and spatial discretization. Moreover, this numerical scheme is used to study the annealing process of the Al–Fe–Ni ternary system. The computation reproduces the formation of the Al-rich and Ni-rich layers in the annealing process. We present the computational results as diffusion paths in a ternary phase diagram, with a nice agreement with that of experimental data. We also study the growth kinetics of the two layers by calculating the rate constant and kinetic exponent of the reaction. The morphology of interfaces between different layers is thoroughly investigated as well. The computational results indicate that the numerical scheme is an effective, useful tool for predicting the microstructure evolution in the annealing process of a ternary reaction system.

Water Quality in Surface Water: A Preliminary Assessment of Heavy Metal Contamination of the Mashavera River, Georgia.

Water quality contamination by heavy metal pollution has severe effects on public health. In the Mashavera River Basin, an important agricultural area for the national food system in Georgia (e.g., vegetable, dairy and wine production), water contamination has multiple influences on the regional and country-wide health. With new industrial activities in the region, sediment extraction, and discharge of untreated wastewater into the river, its tributaries and irrigation canals, a comprehensive study of water quality was greatly needed. This study examined sediment and water samples from 17 sampling sites in the Mashavera River Basin during the high and low precipitation seasons. The results were characterized utilizing the Geo-accumulation Index (Igeo), Enrichment Factor (EF), Pollution Load index (PLI), Contamination Factor (CF) and Metal Index (MI). According to the CFs, Cu > Cd > Zn > Pb > Fe > Mn > Ni > Cr > Hg is the descending order for the content of all observed heavy metals in sediments collected in both seasons. Fe and As were additionally examined in water samples. Overall, As, Cd and Pb, all highly toxic elements, were found in high concentrations in downstream sample sites. According to these results, comprehensive monitoring with narrow intervals between sampling dates, more sample sites along all waterways, and proximate observation of multiple trace metal elements are highly recommended. Moreover, as the part of the water quality governance system, an immediate and sustainable collective action by all stakeholders to control the pollution level is highly recommended, as this issue is linked to the security of the national food system and poses a local public health risk.

Coupled physicochemical and bacterial reduction mechanisms for passive remediation of sulfate- and metal-rich acid mine drainage

Treatment of acid mine drainage (AMD) highly rich in sulfate and multiple metal elements has been investigated in a continuous flow column experiment using organic and inorganic reactive media. Treatment substrates that composed of spent mushroom compost (SMC), limestone, activated sludge and woodchips were incorporated into bacterial sulfate reduction (BSR) treatment for AMD. SMC greatly assisted the removals of sulfate and metals and acted as essential carbon source for sulfate-reducing bacteria (SRB). Alkalinity produced by dissolution of limestone and metabolism of SRB has provided acidity neutralization capacity for AMD where pH was maintained at neutral state, thus aiding the removal of sulfate. Fe, Pb, Cu, Zn and Al were effectively removed (87–100%); however, Mn was not successfully removed despite initial Mn reduction during early phase due to interference with Fe. The first half of the treatment was an essential phase for removal of most metals where contaminants were primarily removed by the BSR in addition to carbonate dissolution function. The importance of BSR in the presence of organic materials was also supported by metal fraction analysis that primary metal accumulation occurs mainly through metal adsorption onto the organic matter, e.g., as sulfides and onto Fe/Mn oxides surfaces.

Addressed realization of multication complex arrangements in metal-organic frameworks.

The preparation of materials with structures composed of multiple metal cations that occupy specific sites is challenging owing to the difficulty of simultaneously addressing the incorporation of different elements at desired precise positions. We report how it is possible to use a metal-organic framework (MOF) built with a rod-shaped inorganic secondary building unit (SBU) to combine multiple metal elements at specific positions in a manner that is controllable at atomic and mesoscopic scales. Through the combination of four different metal elements at judiciously selected molar ratios, 20 MOFs of different compositions and the same topology have been prepared and characterized. The use of diffraction techniques, supported by density functional theory calculations, has led us to determine various possible atomic arrangements of the metal cations within the SBUs. In addition, seven of the compounds combine multiple types of atomic arrangements, which are mesoscopically distributed along the crystals. Given the large diversity and importance of rod-based MOFs, we believe that these findings offer a new general strategy to produce complex materials with required compositions and controllable arrangements of the metal cations for desired applications.

Synthesizing new types of ultrathin 2D metal oxide nanosheets via half-successive ion layer adsorption and reaction

Two-dimensional (2D) metal oxide nanosheets have demonstrated their great potential in a broad range of applications. The existing synthesis strategies are mainly preparing 2D nanosheets from layered and specific transition metal oxides. How to prepare the other types of metal oxides as ultrathin 2D nanosheets remains unsolved, especially for metal oxides containing alkali, alkaline earth metal, and multiple metal elements. Herein, we developed a half-successive ion layer adsorption and reaction (SILAR) method, which could synthesize those types of metal oxides as ultrathin 2D nanosheets. The synthesized 2D metal oxides nanosheets are within 1 nm level thickness and 500 m2 · g−1 level surface area. This method allows us to develop many new types of ultrathin 2D metal oxides nanosheets that have never been prepared before.

Potential human health risk from consumption of metallic elements-contaminated benthic mollusks from Don Hoi Lot sandbar, Thailand

Environmental pollutants have raised more concerns for human health risk, especially via consumption of contaminated food. Terrestrial as well as aquatic animals are capable of bioaccumulation a variety of toxic substances including metallic elements. With increasing anthropogenic activities along the coastal areas, living organisms have more chances to be exposed to released contaminants. In this study, seven metallic elements (Cd, Cu, Fe, Mn, Ni, Pb and Zn) were determined in sediments and water from Don Hoi Lot sandbar, Samutsongkharm province, Thailand. Potential human health risks via the consumption of two benthic bivalves Solen corneus (Larmarck, 1818) and Meretrix meretrix (Linnaeus, 1758) were also estimated using the target hazard quotients (THQs). The variations of metallic element concentrations were apparent between wet and dry season. Fe was the predominate metallic element in the sediment and the remaining were Mn>Pb>Zn>Ni>Cu>Cd. Whereas metallic element concentrations in water were Pb>Ni>Fe>Zn>Cu>Mn>Cd. PCA analysis confirmed that the contaminations of these metallic elements were from Mae Klong river surface water. Most Pb THQ values in both S. corneus and M. meretrix were >1 indicating that human health risk is of concern. However, the sum of THQs of an individual metallic element should also be considered since multiple metallic elements exposure is so common.

In-vivo analysis of the uptake process of heavy metals through maize roots by using synchrotron X-ray fluorescence spectroscopy

The uptake of heavy metals by plants has been receiving much attention for crop contamination and phytoremediation. We employed synchrotron X-ray fluorescence (XRF) spectroscopy for an in-vivo analysis of heavy-metal uptake through a strand of maize root. A focused X-ray beam of 2.5 × 2.5 μm2 in physical dimensions was scanned along horizontal lines of the maize root at intervals of 3 μm at the 4B X-ray micro-diffraction beamline of the Pohang Accelerator Laboratory (PAL). Time-resolved mapping of the fluorescence intensities from multiple metallic elements in the root tissues provided information about the radial distributions of heavy-metal elements and their temporal variations. The concentrated core stream of heavy-metal elements spread radially up to roughly 500 μm, corresponding to 40 % of the root diameter. The absorption characteristics of three heavy metals, Cr, Mn and Ni, and their physiological features were analyzed. The absolute concentrations and the contents of the heavy-metal elements in the tested maize roots were quantitatively evaluated by using the calibration curve obtained from reference samples with preset concentrations. The uptake quantities of the tested heavy-metal elements are noticeably different, although their molecular weights are similar. This study should be helpful for understanding plant physiology related with heavy-metal uptake.

Dynamics of multiple metallic elements during foliar litter decomposition in an alpine forest river

Compared with previously reported data, we found that plant litter decomposes faster in river ecosystem than on forest floor in a comparable period, but the dynamics of metallic elements during litter decomposition in river are likely to share common patterns with the corresponding ones in decomposing litter on forest floor. Litter decomposition in terrestrial lotic ecosystem is one of the most important pathways for metallic elements cycling, while little information is currently available about the dynamics of metallic elements in the decomposing litter of lotic ecosystems. The concentrations and release rates of potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and aluminium (Al) were investigated in the decomposing foliar litter of four dominant species in an alpine forest river. Over a 1-year period of decomposition, K, Ca, and Mg were released from virtually all types of litter, whereas Na, Fe, Mn, Zn, Cu, and Al were released from willow litter but accumulated in azalea, cypress, and larch litters during litter decomposition. Litter species, decomposition period, and river water characteristics (e.g., temperature, pH, flow velocity, and nutrient availability) were significantly related to the dynamics of these metallic elements in decomposing litter. Our results suggested that the similarity between the dynamics of metallic elements in the decomposing litter of lotic ecosystems reported here and previously for forest floors indicates a general pattern for the cycling of metallic element across different ecosystem types, and the net accumulation patterns for elements such as Zn, Cu, and Al during litter decomposition suggested that some litter species may act as efficient “cleaner” for metal purification in future ecological engineering.

Both Phosphorus Fertilizers and Indigenous Bacteria Enhance Arsenic Release into Groundwater in Arsenic-Contaminated Aquifers.

Arsenic (As) is a human carcinogen, and arsenic contamination in groundwater is a worldwide public health concern. Arsenic-affected areas are found in many places but are reported mostly in agricultural farmlands, yet the interaction of fertilizers, microorganisms, and arsenic mobilization in arsenic-contaminated aquifers remains uncharacterized. This study investigates the effects of fertilizers and bacteria on the mobilization of arsenic in two arsenic-contaminated aquifers. We performed microcosm experiments using arsenic-contaminated sediments and amended with inorganic nitrogenous or phosphorus fertilizers for 1 and 4 months under aerobic and anaerobic conditions. The results show that microcosms amended with 100 mg/L phosphorus fertilizers (dipotassium phosphate), but not nitrogenous fertilizers (ammonium sulfate), significantly increase aqueous As(III) release in arsenic-contaminated sediments under anaerobic condition. We also show that concentrations of iron, manganese, potassium, sodium, calcium, and magnesium are increased in the aqueous phase and that the addition of dipotassium phosphate causes a further increase in aqueous iron, potassium, and sodium, suggesting that multiple metal elements may take part in the arsenic release process. Furthermore, microbial analysis indicates that the dominant microbial phylum is shifted from α-proteobacteria to β- and γ-proteobacteria when the As(III) is increased and phosphate is added in the aquifer. Our results provide evidence that both phosphorus fertilizers and microorganisms can mediate the release of arsenic to groundwater in arsenic-contaminated sediments under anaerobic condition. Our study suggests that agricultural activity such as the use of fertilizers and monitoring phosphate concentration in groundwater should be taken into consideration for the management of arsenic in groundwater.

MicroRNA399 is involved in multiple nutrient starvation responses in rice.

The increasing evidences have revealed that microRNAs (miRNAs) play significant role in nutrient stress response. Previously, miR399 was documented to be induced by phosphorus (P) starvation and involved in regulating P starvation responses. To further investigate the function of miR399 in rice (Oryza sativa L.), we performed GeneChip analysis with OsmiR399 over-expressing plants. Interestingly, our results showed that, besides P starvation responsive genes, the expression of a number of genes involved in iron (Fe), potassium (K), sodium (Na), and calcium (Ca) absorption was dramatically up-regulated in OsmiR399 over-expressing plants. Consistently, the concentrations of Fe, K, Na, and Ca were also increased in OsmiR399 over-expressing plants. The expression of OsmiR399 was also up-regulated by these nutrient starvations, respectively. Moreover, the loss-of-function of LTN1, the down-stream target of OsmiR399, also resulted in the increase of multiple metal elements and the up-regulation of the absorption related genes. These results indicated that OsmiR399 participates in the regulation of multiple nutrient starvation responses, which also gives new view on understanding the interaction among different nutrients mediated by miR399.

Plasmon-induced transparency by detuned magnetic atoms in trirod metamaterials

We demonstrate theoretically an analog of electromagnetically induced transparency (EIT) in the plasmonic metamaterial with the unit cell consisting of three parallel metallic rods. The electromagnetic mechanism for the EIT-like transmission is discussed based on our investigation of the localized surface plasmon resonances in three trirod configurations. We find that the transmission minima surrounding the transparency window on both sides correspond to two detuned magnetic resonances, which arise respectively from the antiphase plasmon couplings between a long rod and a short rod and between two short rods. A decrease of more than 10 times in the group velocity can be achieved for the trirod structure at the transparency window in the optical regime, and the EIT-like response can be well described by the theoretical model of two harmonic oscillators. This work not only reveals the EIT-like transmission in plasmonic metamaterial consisting of detuned magnetic "atoms," but also provides further insight into the plasmons' interactions, especially for metallic nanostructures comprising multiple metallic elements.

Scanning X‐ray fluorescence microspectroscopy of metallic impurities in solar‐grade silicon

AbstractA rapid scanning synchrotron‐based X‐ray fluorescence microprobe technique is applied to relatively impure crystalline silicon feedstock for solar cells. The results reveal the distributions of metallic impurities in the material over regions several millimetres in size, allowing scans across several grains. Relatively high concentrations of Fe, Cu and Zn were observed, with traces of Mn and Ni. The metals were mostly present as discrete particles up to 60 µm in size, while Cu was more uniformly distributed. More than 50% of the detected Fe was present as large particles at the grain boundaries, probably due to diffusion and precipitation during cooling. In contrast, less than 5% of the Cu resided in such large particles. The particles contained multiple metallic elements, with strongly varying proportions of their metal constituents.

First measurement using three-in-one cell: a new design of the fixed-point cell for the calibration of thermometers

A new design of the fixed-point cell that contains multiple metal elements in a single crucible has been introduced for fixed-point calibration of secondary thermometers such as thermocouples. A multicell with aluminium, silver and copper was fabricated and used for the calibration of a Pt/Pd thermocouple. The expanded uncertainties (k = 2) of the realization of the multicell were 0.07 °C, 0.12 °C and 0.24 °C, plus an additional term from the inhomogeneity of the thermocouple, for aluminium, silver and copper, respectively. These uncertainties are considerably smaller than those obtained from the method of calibration by comparison in similar temperature ranges. This proves the suitability of the metal multicells for the calibration of secondary thermometers.

Investigation of the Microcharacteristics of PM2.5 in Residual Oil Fly Ash by Analytical Transmission Electron Microscopy

Atmospheric emissions from combustion of residual oils often consist of carbonaceous material and metal compounds, both of which are of concern for health and environmental issues. In this study, particulate matter fractions with aerodynamic diameters nominally less than 2.5 microm (PM2.5) in two residual oil fly ash (ROFA) samples generated from combustion experiments were investigated by analytical transmission electron microscopy (TEM) techniques, including energy-dispersive X-ray spectroscopy, selected area electron diffraction (SAED), high-resolution TEM, and electron energy loss spectroscopy (EELS). Carbonaceous particles, which dominate both samples, exist in two distinctive forms: as soot aggregates with spherical primary particles of size 10-80 nm that exhibit a concentric arrangement of graphitic layers around the particle center and as larger spherical or irregular-shaped porous residual char particles of size 1-20 microm that usually have anisotropic microtextures and contain organic sulfur species. Such carbon-rich particles were often observed to be coated with inorganic species, notably transition metals (V, Ni, Fe, Zn) in the form of sulfates, oxides, vanadates, and phosphates. In this respect, they therefore differ from similar carbonaceous particles generated in combustion of diesel fuels that lack significant inorganic species. Crystalline phases of vanadium, nickel, and iron oxides and multi-element oxides were identified by the SAED technique. The valence state of V in some V-rich oxide particles probed by EELS was found to vary from +2 to +5. Individual transition metal sulfate, oxide, and phosphate particles are typically compositionally complex, containing multiple metallic elements. These microcharacteristics of individual PM2.5 particles revealed by electron microscopy techniques should be important parameters to include in future toxicological investigations of ROFA PM.