Low Metal Concentrations Research Articles

Three-Dimensional Printing of Metallic Parts by Means of Fused Filament Fabrication (FFF)

Obtaining metallic parts via Additive Manufacturing can yield several advantages over using other traditional manufacturing methods such as machining. Material extrusion (MEX) can handle complex shapes with porous structures and, at the present time, much low-end and desktop equipment is available. In the present work, different industrial and medical applications of metallic Fused Filament Fabrication (FFF) parts are presented. First, an overview of the process, equipment, and of the metal-filled filaments currently available is provided. Then, the properties of parts and different applications are shown. For example, metal-filled filaments with a low metal content that can be used to obtain plastic parts with metallic appearance (with either steel, copper, or bronze), and filaments with a high metallic content allow obtaining metallic parts with high mechanical strength after a sintering operation. The present contribution aims to be an up-to-date panorama for current industrial and medical results and lessons learnt from the application of FFF to obtain metallic parts.

Optimizing reverse water gas shift catalysis: Minimizing metal loading and enhancing performance with Pt/ZrO2 catalysts through Rh incorporation

In this study, the optimization of catalysts for the reverse water gas shift reaction by minimizing metal loading and enhancing the performance of supported Pt catalysts through Rh incorporation was done. The catalysts were synthesized by the wet impregnation method, in which the metal noble load in bimetallic samples decreased by approximately one-third compared to the reference platinum catalyst, with varying Rh-Pt ratios. In all materials, m-ZrO2, obtained by the hydrothermal method, was used as support. In the catalytic tests in a continuous packed-bed flow reactor at atmospheric pressure, all samples were active to catalyze CO2 reduction between 200 and 300 °C. Bimetallic samples, particularly those with an Rh-Pt atomic ratio of 20–80, exhibited superior performance in the RWGS reaction despite their lower metal content. Based on the results of H2-TPR, FTIR in situ, and XPS, we propose that the enhanced CO production in bimetallic samples compared to Pt/ZrO2 catalysts can be attributed to Rh increasing the reduction extent of supported Pt. This enhancement facilitates the hydrogenation of bicarbonate species into formate species, which subsequently evolve into Pt0-CO and ultimately into CO. Additionally, Rh incorporation enables an alternative pathway for CO generation, where Pt0-carbonyls, known for their CO-producing capability, are formed via CO2 dissociation on the Pt0 surface. However, higher Rh concentrations favor the CO2 methanation rather than the RWGS reaction.

Novel application of Ru-based catalysts on MgAl oxides alkaline adsorbents for cyclic CO2 methanation

This study explores the performances of Ru-based catalysts with a low metal content (2 wt%) supported on MgO and Mg-Al Oxides (MgAl) for cyclic CO2 adsorption and methanation at atmospheric pressure. Adsorption and desorption tests demonstrated that MgAl-based catalysts are more promising for CO2 capture due to their larger surface area and better distribution of active sites (Mg2+–O2-). Moreover, doping the MgAl support with K2CO3 further improves surface alkalinity and, consequently, capture performance. During cyclic operations, all the catalysts proved effective and selective for methane production. To simulate realistic conditions, both dry and wet CO2 adsorptions were conducted before the methanation stage. The presence of moisture positively influenced gas carbonation for all catalysts, increasing the overall amount of CO2 captured. Specifically, Ru/MgAl exhibited the best performance in terms of adsorption and conversion to methane (approximately 85 % after dry adsorption and 79 % after wet adsorption), with a maximum methane production of 183 and 220 μmolCH4 g−1, respectively. The reaction yield was further enhanced with Ru-K/MgAl, achieving 327 μmolCH4 g−1 after dry adsorption and 333 μmolCH4 g−1 after wet adsorption. However, this catalyst displays different conversion kinetics, attributed to slowed carbonate migration, low Ru dispersion, limited specific surface area, and excessive carbonation strength. Operando FTIR tests revealed differences in reaction intermediates between Ru/MgAl and Ru-K/MgAl, by going deeper into the kinetic differences observed. The study concludes that Ru/MgAl materials are highly promising catalysts for CO2 adsorption and methane production, supporting the development of technologies for CO2 abatement and renewable energy utilisation.

Effects of strain, pH and oxygen-deficient on catalytic performance of Ruddlesden-Popper oxide Srn+1RunO3n+1 (n=1, 2) for hydrogen evolution reaction

Due to low content of precious metals and good stability, Ruddlesden-Popper (R–P) structure oxides are considered as promising hydrogen evolution reaction (HER) catalysts. However, related research is scarce, hindering its further improvement. In this paper, effects of strain, pH, oxygen-deficient and layer numbers on HER catalytic performance of R–P structure oxides Sr2RuO4, Sr3Ru2O7 and Sr3Ru2O6 were comprehensively calculated for the first time. Our results confirm that oxygen-deficient R–P Sr3Ru2O6 is beneficial for its catalytic performance in alkaline environments. Ranking of catalytic performance in acidic environments: Sr2RuO4>Sr3Ru2O6>Sr3Ru2O7, relatively in alkaline environments: Sr3Ru2O6>Sr3Ru2O7>Sr2RuO4, which means pH actually affects the performance of R–P structure catalysts. In other words, acidic environments are conducive to the catalytic activity of Sr2RuO4, while alkaline environments are beneficial for Sr3Ru2O6 and Sr3Ru2O7. We also calculated the effects of tensile and compressive strains and found that 1% and 3% tensile strain can further enhance the HER catalytic performance of Sr3Ru2O6. Taking into account various practical factors, our work investigated the HER catalytic mechanism of R–P oxides, providing theoretical guidance for the development of R–P structure catalysts.

Precipitation–Flotation Process for Molybdenum and Uranium Separation from Wastewater

The mining of molybdenum and uranium ores inevitably results in the generation of large volumes of wastewater containing low concentrations of metals, which poses significant threats to the environment. This study presents a novel precipitation–flotation process for the simultaneous separation of molybdenum and uranium from wastewater. A systematic investigation was conducted on the impacts of the type of precipitant, flotation reagent type, and flotation parameters on the experimental results. Ferric salt served better as a precipitant than aluminum salt and humic acid did, and sodium dodecyl sulfate (SDS) was more suitable than sodium dodecyl benzene sulfonate for acting as a surfactant and foaming agent. Under specific conditions, including a pH of 6.6, an Fe3+ dosage of 0.6 mmol·L−1, an SDS dosage of 40 mg·L−1, an air flow rate of 25 mL·min−1, and a flotation time of 10 min, the removal efficiencies of molybdenum and uranium reached 96.6% and 93.6%, respectively. After flotation, the molybdenum concentration, uranium concentration, chemical oxygen demand, and turbidity of the treated water all meet the emission standards. Furthermore, the metal removal mechanisms, including the particle size distribution, functional group structure, surface element composition, microstructure, and element distribution, were elucidated on the basis of characterization of the precipitation–flotation products.

Changes in exposure to environmental contaminants in the aftermath of Hurricane Maria among pregnant women in northern Puerto Rico

Experiencing a hurricane during pregnancy is associated with increased risk of adverse birth outcomes and poor mental health. Pregnant people from marginalized communities are more susceptible to adverse effects, as they have fewer resources to overcome hardships at a time when shelter and nutrition are essential. When Hurricane Maria (HM) devastated Puerto Rico in September 2017, the archipelago was already burdened with high poverty, health disparities, environmental contamination, and fragile utility infrastructure. We aimed to compare biomarkers of environmental exposures among pregnant participants in the PROTECT cohort before and after HM and to identify hurricane-related sources of exposure. Metals, PAHs, phthalate metabolites, and phenols were measured in urine samples collected from participants at three prenatal visits (2011–2019). Samples were categorized as before, <3 months, 3–6 months, and >6 months after HM. Using linear mixed effects models, we found that in the 6 months after HM, participants had higher Co, Ni, and DEHPTP concentrations, indicating increased exposure, and lower concentrations of PAHs, several metals, and phthalates, suggesting decreased exposure, compared to pre-HM levels. Biomarkers were not associated with potential exposure sources assessed through questionnaire or previously measured tap water contaminants. This study provides insight into how extreme weather events may alter environmental exposures among pregnant people in Puerto Rico. As climate change has increased the frequency and magnitude of such events, additional research is needed to clarify the implications for maternal and child health and to identify sources of related environmental exposures within this vulnerable population.

Photosystems functioning, the content of chemical elements, flavonoids and brassinosteroids in leaves of chimera Cornus controversa

he formation of chimera is a well-known phenomenon in variegated ornamental and wild plants, but the biochemical peculiarities of this phenomenon are not well studied. The purpose of this work was to conduct a comparative study of the photosynthetic apparatus functioning, the content of macro-, microelements, flavonoids and brassinosteroids in the variegated and green leaves of the periclinal chimera Cornus controversa plant grown in the collection of M. M. Gryshko National Botanical Garden of the NAS of Ukraine. Sampling was made during the period from June to October 2022. The content of photosynthetic pigments and brassinosteroids was measured spectrophotometrically, autofluorescence of leaf tissues was studied using an inverted microscope with a multi-channel fluorescence imaging system, Normalized difference vegetation index (NDVI) – using GreenSeeker devices and fluorimeter, the level of macro- and microelements – using plasma emission spectrometer. Phenolic secondary metabolites were separated by HPTLC. To assess the protective capacity of flavonoids, a bioassay on the germination of radish seeds Raphanus in the presence of AlCl3 was used. It was shown that green leaves of C. controversa chimera, compared to variegated ones, had a twice as high NDVI index, maintained photosynthetic function longer in autumn, and had higher content of macronutrients (Mg, Ca and S) but lower concentration of toxic metals (Al, Cu, Fe, Zn, Ti). Instead, variegated leaves accumulated more brassinosteroids and phenolic metabolites, which were found not only to reduce the toxic effect of aluminum but also to have a growth-stimulating effect on the roots of radish seedlings. Such specialization of green and variegated leaves may contribute to better plant chimeras adaptation to environmental pollution. Keywords: brassinosteroids, Cornus controversa, macroelements, microelements, NDVI index, periclinal chimera, phenolic metabolites, photosynthetic pigments, tissue autofluorescence

Groundwater Contamination by Heavy Metals in Malaysia: Sources, Transport, and Remediation Strategies

Groundwater contamination by heavy metals is a pressing environmental concern, particularly in regions highly dependent on groundwater as a freshwater source. While Malaysia primarily relies on river water, certain states and islands depend on groundwater for their supply. Research on heavy metal contamination in Malaysia’s groundwater remains limited, making it crucial to study the distribution and mobility of contaminants to develop appropriate remediation strategies. In addition to natural sources, anthropogenic activities such as landfills, mining, and the use of fertilizers contribute significantly to heavy metal pollution in groundwater. Factors like rainfall, fluctuating groundwater levels, and low soil pH can exacerbate heavy metal leaching into aquifers. Various models and techniques, including 2D resistivity imaging and MODFLOW, are used to assess groundwater flow and contaminant transport. These models suggest that contaminant concentrations decrease with increased depth and radial distance from pollution sources such as landfills and mining areas. The health risks associated with heavy metal exposure through groundwater consumption are significant, necessitating effective remediation strategies. Phytoremediation is an economical solution for groundwater containing low concentrations of heavy metals, while permeable reactive barriers may be suitable for more complex cases, pending detailed site investigation. This review aims to examine the current state of knowledge on heavy metal contamination in Malaysia’s groundwater, focusing on sources, distribution patterns, and movement of pollutants. It also seeks to evaluate existing remediation methods, including phytoremediation and permeable reactive barriers, while identifying gaps in research, particularly concerning risk assessments and heavy metal speciation.

Arsenic and Heavy Metals in Soils and Plants near Sulfide Mines: Implications for Phytoremediation and Phytomanagement.

The accumulation of heavy metals (i.e., As, Cu, Ni, Pb, and Zn) in soils and native plant species near copper, nickel, and pyrite mines in Vietnam was assessed. The highest soil As, Cu, Ni, Pb, and Zn concentrations recorded in mine soils were 42.3, 1570, 9870, 128, and 462 mg/kg, and those in agricultural soils were 11.4, 453, 94.9, 34.4, and 147 mg/kg, respectively. Pollution index (PI) values indicated heavy pollution (PI = 3.99-13.0) for mine soils, and unpolluted to severely polluted (PI = 0.65-2.84) for agricultural soils. Soil enrichment factors had a wide range, from minimal to extreme enrichment of heavy metals (EF = 0.03-91.4). Arsenic minerals may be the main source of high As concentrations in sulfide mines. The As, Cu, Ni, Pb, and Zn concentrations of 20 native plant species near three mines were in the ranges of 0.05-1150, 3.17-123, 0.47-291, 0.08-6.34, and 6.87-168 mg/kg (dry weight, DW), respectively. Based on the recorded hyperaccumulation levels (1150 mg/kg, DW), bioaccumulation factors (BAF = 2.4-90.0), biomass, and rapid growth, Pteris vittata L. is considered a promising plant for phytoextraction of As in soils. Bidens pilosa L. has potential for phytostabilization of sulfide-bearing soils, given its low concentrations of heavy metals in plant shoots, BAF values of <1, high biomass, and wide distribution. Integrated phytoremediation and phytomanagement are applicable to metal-contaminated soils. Phytomining, energy crops, and vegetation cover should be investigated for the phytomanagement of metal-contaminated soils in mining areas.

Constraints of upper crust magmatic processes on the formation of Saindak porphyry Cu deposit: Insights from mineral geochemistry

Upper crustal magmatic processes play a crucial role in linking the magmatic and hydrothermal systems of porphyry deposits, ultimately controlling the generation of ore-forming fluids. Understanding these processes within a magma chamber is essential for deciphering the formation of porphyry deposits. The Saindak deposit, a large porphyry Cu system in the western Chagai belt, features coeval ore-forming and barren magma pulses, providing key insights into the characterization of porphyry systems. In this study, detailed petrographic observations and geochemical analyses of amphibole, plagioclase, and apatite were conducted to unravel the magmatic evolution at Saindak. Based on textural relationships and crystallization sequences, three distinct populations of amphibole in the ore-forming magma were identified. These amphiboles record the entire fractional crystallization process of magma that initially emplaced at a depth of ∼5 km to the connected magma system at ∼2 km. The study of amphibole and apatite reveals that the fertile magma underwent large-scale fluid exsolution in an open system. The simultaneous and rapid depletion of Cu, Cl, S, and H2O in the magma indicates that Cl and S were highly partitioned into the exsolved fluid phase. These elements formed complexes, which effectively concentrated metals in the fluid. Conversely, the barren magma was characterized by either low metal content or limited fluid exsolution within the magma chamber. Overall, we reconstruct the upper crustal magmatic processes at Saindak and conclude that efficient extraction of Cu through fluid exsolution is the key to porphyry deposit formation.

Effectiveness of constructed wetland technology-treated industrial wastewater on the spinach (Spinacia oleracea) health risks and biochar efficiency.

In peri-urban areas, use of industrial wastewater for irrigation is a common practice. Industrial wastewater contains cadmium, chromium, lead, nickel, and other elements that deteriorate food quality and affect human health. Biochar has been proven to remediate heavy metal contaminated soil by reducing their mobility and bioavailability. A pot experiment was conducted to evaluate the efficiency of different levels of biochar on spinach growth with low heavy metal concentration and to minimize associated health issues. The experiment lasted two months and the treatments: Control (tap water), untreated and treated industrial wastewater and both in combination with biochar (0.5% and 1%) were applied in completely randomized design. Findings suggested that treated industrial wastewater with 1% biochar resulted in maximum plant height, shoot weight, chlorophyll contents (SPAD value), photosynthetic and transpiration rate. Biochar significantly reduced heavy metal mobility in soil due to its porous structure, high pH, higher CEC, and variety of surface functional groups. The cumulative hazard index (HI), hazard quotient, cancer risk, and total cancer risk (TCR) were calculated using method provided by US-EPA for each metal. All treatments had HI values of < 1, however applying 1% biochar significantly reduced the HI values to 2.00E-01 and 2.88E-01 in adults and children, respectively. TCR for all treatments was < 1, while treated industrial wastewater and biochar (1%) has significantly reduced to 1.55E-02 and 1.91E-03 for adults and children, respectively. Thus, it was determined that irrigation with industrial effluents caused toxicity in vegetables, which had a negative impact on human health. Biochar effectively mitigated metal toxicity in both soil and spinach plants that resulted in reduced health/cancer risk.

Metal variability of the shrimp Palaemon elegans across coastal zones: anthropogenic and geological impacts.

This study focused on 120 specimens of the shrimp Palaemon elegans collected in intertidal zones in eight selected areas. This study aimed to assess the suitability of P. elegans as a bioindicator of natural and anthropogenic marine pollution. Metal concentrations of aluminum (Al), cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), and zinc (Zn) were measured in shrimp collected from various sites in the Canary Islands, including areas affected by volcanic activity, industrial activity, and control zones. The determination of metal concentrations was conducted using inductively coupled plasma optical emission spectrophotometry (ICP-OES). The results showed significant differences in metal concentrations across the studied sites, with the highest levels of Al, Cu, Fe, Pb, and Zn observed in areas impacted by the Tajogaite volcanic eruption and harbor activity. Sites near old landfills and sewage pipes also exhibited elevated levels of Cd, Cu, and Pb, indicating strong anthropogenic influence. Al was found in the highest concentration in Harbour, reaching 25.7 ± 6.2mg/kg, while the lowest concentration was observed in Control Lp at 11.5 ± 0.69mg/kg. Conversely, lower metal concentrations were detected in control zones and areas with high dinoflagellate presence, suggesting a potential role of bioremediation by marine phytoplankton. The ability of P. elegans to accumulate metals in its tissues, particularly in areas of high pollution, highlights its potential as a bioindicator species. This study underscores the importance of P. elegans in monitoring marine pollution and provides insights into the environmental impact of both natural and human-induced contamination on coastal ecosystems.

First full-scale application of barium carbonate as an effective dispersed alkaline substrate for sulfate removal from acid mine drainage

A full-scale passive treatment plant using barium carbonate (BaCO3), the mineral witherite, as a Dispersed Alkaline Substrate (DAS) for strongly contaminated acid mine drainage was implemented for the first time globally at Mina Concepción, located in the Iberian Pyrite Belt (SW Spain). The plant was monitored over a 105-day period, covering the wettest months of the hydrological year and with a mean flow around 4 L s−1. The AMD treated in the plant exhibits a high strength, with an average sulfate concentration around 1500 mg L−1 and net acidity close to 1000 mg L−1 as CaCO₃ equivalent. According to the above, the loading rate for SO4 and Fe was around 400 and 80 kg day−1, respectively. The treatment process produced an alkaline effluent with low metal content. Nearly complete removal of most metal(loid)s was achieved, with significant sulfate decrease to below 500 mg L−1 in the alkaline outflow of the barium carbonate tank. Barium carbonate demonstrated superior performance compared to magnesia, particularly in enhancing alkalinity and lowering net acidity and concentrations of sulfate and manganese. The high efficiency attained by the plant after the barium carbonate treatment is evidenced by compliance with environmental water quality standards for most contaminants.

Convert food waste into easily biodegradable liquid substrate: New insights into wet oxidation as a pretreatment for anaerobic digestion

This study is the first comprehensive investigation into the industrial application of wet oxidation (WO) for food waste (FW) valorization. We analyzed the physicochemical properties of WO products and performed a material flow analysis. WO achieved a 25.7 % reduction in chemical oxygen demand and produced liquid and solid products suitable for high-value applications. The liquid product featured high biodegradability (B/C ratio of 0.65), significant BOD5 (33 ± 9 g/L), low total solids (3.5 % ± 0.4 %), and low metal concentrations, making it ideal for high-efficiency anaerobic digestion or as a carbon source in wastewater treatment. The solid product, with a total solids content of 63.9 % ± 1.4 %, is a potential organic fertilizer alternative. Life cycle assessment showed that WO-related scenarios offered superior greenhouse gas (GHG) reduction compared to conventional anaerobic digestion (11.30 kg CO2-eq/t FW slurry). The most effective scenario, combining WO with a carbon source and organic fertilizer alternative, achieved a GHG reduction of −21.80 kg CO2-eq/t FW slurry. Consequently, this study demonstrates that WO, as a pretreatment for food waste valorization, is both technically feasible and environmentally sound, offering valuable engineering references for the implementation of high-efficiency anaerobic digestion processes for food waste.

Synthesis of various types of green biosorbents materials for removals of sulphates from contaminated water for better aquatic environments

Human and industrial activities pollute water resources with sulphur metal, endangering human health and ecosystems. Chemical precipitation and membrane filtration are expensive when treating large amounts of water, inefficient at low metal concentrations, and produce large amounts of toxic sludge and other products that must be disposed of waste water bio-sorption is eco-friendly and alternative. These methods are cheaper, more accessible, and reusable than conventional ones. This study investigates the bio-sorption of sulphur from contaminated water using neem leaf, custard apple leaf, mango tree leaf, orange peels, and banana peels biological waste materials. This work achieves 100 % removal efficiency. Biosorbents remove sulphates from contaminated water: custard leaves 100 % at 4gm, orange peels 40 % at 5gm, tea waste 50 % at 4gm, neem leaves 70 % at 5gm, and mango leaves 75 % at 5gm. The performances of biosorbents for removals of sulphates from water as follows: Custard leaves waste > Mango leaves > Neem leaves > Tea trash > Orange peels the sulphate reduction by biosorbents. The best biosorption occurred at basic pH 6.5, 3.7gm dosage, 90 min contact duration, 30 °C temperature, and 120 rpm agitation speed. The effects of contact time, agitation speed, adsorbent dosage, pH, and temperature are also examined. Before usage, biosorbents materials can be physically and chemically measured the changes. Regenerating and reusing bio-sorbent after sulphates removals makes the method cost-effective for removals of pollutants from water.

Subsurface Superoxide Spans the Baltic Sea

AbstractSuperoxide is a reactive oxygen species that is influential in the redox chemistry of a wide range of biological processes and environmental cycles. Using a novel in situ sensor we report the first water column profiles of superoxide in the Baltic Sea, at concentrations higher than previously observed in other oceans. Our data revealed consistent peaks of superoxide (2.0–15.1 nM) in dark waters just below the mixed layer. The oxic waters, low metal concentrations, and lack of sunlight imply that the peak is likely of biological origin. Several profiles displayed a concomitant dip in dissolved oxygen mirroring this superoxide peak, strongly suggesting a link between the two features. The magnitude and distribution of superoxide observed warrants re‐evaluation of the most relevant sources and controls of superoxide in seawater. Locally, these high concentrations of superoxide may create environments conducive to reactions with trace metals and organic matter and present an overlooked sink of oxygen in the Baltic Sea.

Comparative study of silica-based porous materials in the purification of radioactive wastewater

A significant challenge in the treatment of low-level radioactive wastewater is the effective purification of low-concentration radionuclides. Silica-based adsorbents are advantageous for the deep-purification of low-concentration metal ions. This study investigates three primary types of silica-based adsorbents: functionalized mesoporous silica, various modified zeolites, and mesoporous calcium silicate hydrate (C-S-H). These adsorbents were synthesized and their deep-purification effects on heavy metals and radionuclides were compared. The results indicated that mesoporous silica showed relatively poor adsorption for most metal ions. Zeolites outperformed mesoporous silica, with Zn framework-modified zeolites showing enhanced adsorption for several metal ions. Notably, C-S-H displayed superior adsorption performance, achieving high adsorption capacities for various metal ions and radionuclides. Specifically, at a dose of 0.5 g/L, the adsorption efficiency of C-S-H for numerous radionuclides in nuclear power plant wastewater exceeded 92–99 %, highlighting its potential for practical applications. An in-depth analysis of the physical and chemical structure and the adsorption mechanisms of C-S-H revealed its large mesoporous structure and electrostatic attraction to cations across a wide pH range. Multivalent cations were removed through exchange with Ca2+ in C-S-H, whereas monovalent cations were removed through exchange with Na+ in C-S-H. The cyclic structure of silica-oxygen tetrahedra in C-S-H, which promotes large pore formation and provides abundant ion exchange sites, underpins its excellent adsorption properties. This study offers valuable insights for the selection and application of silica-based materials in radioactive wastewater treatment.

Mapping radial abundance gradients with Gaia -ESO open clusters. Evidence of recent gas accretion in the Milky Way disk

Recent evidence from spectroscopic surveys points towards the presence of a metal-poor, young stellar population in the low-alpha , chemically thin disk. In this context, the investigation of the spatial distribution and time evolution of precise, unbiased abundances is fundamental to disentangle the scenarios of formation and evolution of the Galaxy. We study the evolution of abundance gradients in the Milky Way by taking advantage of a large sample of open star clusters, which are among the best tracers for this purpose. In particular, we used data from the last release of the Gaia -ESO survey. We performed a careful selection of open cluster member stars, excluding those members that may be affected by biases in spectral analysis. We compared the cleaned open cluster sample with detailed chemical evolution models for the Milky Way, using well-tested stellar yields and prescription for radial migration. We tested different scenarios of Galaxy evolution to explain the data, namely, the two-infall and the three-infall frameworks, which suggest the chemical thin disk is formed by one or two subsequent gas accretion episodes, respectively. With the performed selection in cluster member stars, we still find a metallicity decrease between intermediate-age ($1&lt;$ Age/Gyr $&lt;3$) and young (Age $&lt;1$ Gyr) open clusters. This decrease cannot be explained in the context of the two-infall scenario, even by accounting for the effect of migration and yield prescriptions. The three-infall framework, with its late gas accretion in the last 3 Gyr, is able to explain the low metallic content in young clusters. However, we have invoked a milder metal dilution for this gas infall episode relative to previous findings. To explain the observed low metallic content in young clusters, we propose that a late gas accretion episode triggering a metal dilution would have taken place, extending the framework of the three-infall model for the first time to the entire Galactic disk.

Fabrication of Gold and Silver Nanoparticles Supported on Zinc Imidazolate Metal-Organic Frameworks as Active Catalysts for Hydrogen Release from Ammonia Borane.

Well-dispersed Au and Ag nanoparticles (NPs) have been immobilized on a zinc imidazolate metal-organic framework, Zn(mim), using the "one-pot" method and tested as catalysts in ammonia borane hydrolysis. The AuNPs@Zn(mim) and AgNPs@Zn(mim) materials were characterized by FTIR, XRD, ICP-OES, TGA, BET, SEM, and TEM. The AgNPs@Zn(mim) catalyst showed a high yield (98.5%) and high hydrogen generation rate (3352.71 mL min-1 gAg -1) in NH3BH3 dehydrogenation. The determined activation energies (19.6 kJ mol-1 for AuNPs@Zn(mim) and 38.13 kJ mol-1 for AgNPs@Zn(mim)) are lower than those for most reported catalysts containing Au/Ag-MOF used in the hydrolysis of NH3BH3. Moreover, the catalysts tested here revealed good stability and reusability, preserving 71.42% (AuNPs@Zn(mim)) and 88.23% (AgNPs@Zn(mim)) of their initial catalytic activities after five consecutive cycles. In the case of AgNPs@Zn(mim), the combination of the simple and green synthesis method, low active metal content, relatively low cost, and moderate dehydrogenation conditions makes the material an excellent candidate to produce hydrogen from ammonia borane.

An overview of the constructions of conveyors for moving bulk materials, comparison and study of their parameters

The production of concrete mixes, along with their use in the production of building materials and structures, is one of the key processes in the construction industry during the construction, restoration and repair of buildings and structures. Because of this, the need to create modern concrete mixing plants that will meet the requirements of minimum energy consumption and maximum productivity of concrete mixture production is an urgent task. Not only the main operations, which include the dosing of the components of the mixture and their mixing, but also the maintenance operations, namely operations that ensure the timely movement of the components of the concrete mixture from warehouses to the main technological equipment, affect the set rhythm of the concrete mixture production. Conveyors of various types and designs are used to move bulk materials, such as crushed stone and sand. For the rational selection of such equipment in accordance with the characteristics of the cargo to be transported, knowledge of the types of conveyors, their structures and parameters, understanding of operation issues and methods of parameter calculation are required. In addition, it is worth paying attention to the following parameters: maximum cargo transportation productivity, low energy consumption per unit of moved products, low metal content of the structure. The work reviewed the most common designs of conveyors used to move bulk materials in concrete mixing plants, analyzed the disadvantages and advantages of conveyors, as well as technical parameters. As a result, the predominant directions for the use of belt and plate conveyors at construction enterprises were determined. The advantages of belt conveyors, which contribute to their widespread distribution, are high productivity, simplicity of design, reliability, quiet operation, low specific power consumption. When choosing a conveyor, it is recommended to choose the equipment with the highest productivity and the lowest power of the drive motors, however, the performance should be clearly related to other technological equipment.