Low Cation Concentrations Research Articles

Polystyrene nanoplastics are unlikely to aggregate in freshwater bodies.

The fate and toxicity of nanoplastics (NPs) in the environment is largely determined by their stability. We explored how water composition, nanoplastic size, and surface carboxyl group density influenced the aggregation of polystyrene (PS) NPs in fresh water. Unfunctionalized 200, 300, 500, and 1000nmPS NPs and 310nm carboxylated PS NPs with carboxyl group densities of 0.35 and 0.6mmolg-1 were used to simulate pristine and aged NPs. Natural water matrices tested in this study include synthetic surface water (SSW), water from the Schie canal (Netherlands) and tap water. Suwannee River Natural Organic Matter (SRNOM) was included to mimic organic matter concentrations. In CaCl2, we found PS NPs are more stable as their size increases with the increase of the critical coagulation concentration (CCC) from 44mM to 59mM and 77mM for NP sizes of 200nm, 300nm and 500nm. Conversely, 1000nmPS NPs remained stable even at 100mM CaCl2. Increasing the carboxyl group density decreased the stability of NPs as a result of the interaction between Ca2+ and the carboxyl group. These results were consistent with the mass of Ca2+ adsorbed per mass of NPs. The presence of SRNOM decreased the stability of PS NPs via particle bridging facilitated by SRNOM. However, in SSW, Schie water and tap water with low divalent cation concentrations, the hydrodynamic size of PS NPs did not change, even at prolonged durations up to one week. We concluded that PS NPs are unlikely to aggregate in water with low divalent cation concentrations, like natural freshwater bodies. Ecotoxicologists and water treatment engineers will have to consider treating PS NPs as colloidally stable particles as the lack of aggregation in fresh surface water bodies will affect their ecotoxicity and may pose challenges to their removal in water treatment.

Geochemical and GMS – Modeling Approach in Characterization of Anticipated Environmental Threats of Leachate from an Open Dumpsite, Niger Delta, Nigeria

Dumping of solid waste in open dumpsites is widespread in developing countries. A major disadvantage of this waste management system is the generation of leachate; this has been a primary concern to the environment because it can percolate into the groundwater and consequently contaminate it. In this work, leachate and groundwater samples were collected from a dumpsite in Asaba and its adjoining area to ascertain the conceivable effect of leachate percolation on groundwater quality. The results of physicochemical and heavy metals analyses of leachate confirmed that its characteristics were highly variable, with severe contamination by organics, salts, and heavy metals. The BOD5/COD ratio in leachate varied from 0.08 – 0.12 mg/l, suggesting a dumpsite yet to attain final maturation but is in its late stage of the methanogenic phase. The low BOD5/COD ratio value (0.08 mg/l) observed for leachate shows some microbial activity in the decomposing leachate yet to stabilize. The plume model showed leachate infiltrating beneath the dumpsite up to depths greater than 20 m after one year. The low concentrations of significant cations, anions, heavy metals, and COD in groundwater likely indicate that leachate did not significantly affect groundwater quality. However, specific parameters such as Fe exceeded the WHO limits; the source of Fe may be related to the geology of the area. The good protective capacity around the dumpsite and groundwater mounds was a barrier against inflow from contaminated leachate.

Exploring the Impact of Excess Cations in Acidic CO2 Reduction Reaction

To anticipate high performance in the electrocatalytic reactions, a comprehensive understanding of the electric double layer (EDL) is essential. Experimental, spectroscopic, and computational studies of the EDL have been reported for understanding the performance in electrocatalytic reactions such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO2 reduction reaction (CO2RR). Notably, in the CO2RR, previous studies have revealed the accumulation of cations near the outer Helmholtz plane (OHP) significantly has an impact on the reaction performance, product selectivity, and partial current density. The presence of these cations induces various effects, such as creating a strong electric field, altering local pH levels, stabilizing the intermediates, and specific adsorption. However, unraveling the sole cation effect remains challenging due to the system's complexity and hierarchical characteristics. Moreover, experiments predominantly conducted under favorable conditions for understanding the electric field and stabilization effects have left the specific adsorption effect relatively unexplored. Specific adsorption involves direct coordination with the electrode at the inner Helmholtz plane (IHP), with the degree determined by catalyst type and electrolyte conditions. Previous studies have highlighted the significant impact of specific adsorption on current density and intermediate stabilization, with potassium (K+) and cesium (Cs+) cation exhibiting the most pronounced effect owing to their minimal hydration degree compared to the lithium (Li+) and sodium (Na+).Acidic CO2RR has recently garnered attention for its high carbon efficiency (CE) and energy efficiency (EE). However, the abundance of hydronium ions can lead to a favorable occurrence of HER over CO2RR due to its facile protonation. To mitigate this challenge, excess cations have been employed to suppress the hydronium ion migration and enhance the performance of the CO2RR, which means accumulated cation layer at the OHP can suppress the HER and stabilize the intermediates of the CO2RR simultaneously. Meanwhile, in the excess cation condition, adsorbed cations can be dominant on the electrode originated from the excess cations, which is not investigated intensively. For the better performance of the electrocatalytic reactions in the acidic condition, we need to elucidate the EDL formed in the presence of the excess cations.In here, we investigated the electrode-electrolyte interface in the different cation species during the acidic CO2RR through the attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS), which can give the local information such as the adsorbed species on the metal and free species near the electrode. We confirmed the different product distribution and interface depending on the cation species, especially in the excess cations (1 M M+, M = Li, K, Cs). Specific adsorption in the presence of the excess cations can alter the product distribution, and it differs from the low cation concentration (0.1 M M+, M = Li, K, Cs). In final, to clarify the effect originated from the excess cations, we confirmed the interface on the copper and silver, which major products are C2+ and C1, respectively.

CHARACTERIZATION AND CLASSIFICATION OF SOILS DEVELOPED ON COASTAL PLAIN SOILS FOR CROP PRODUCTION IN ORON LGA, SOUTH- SOUTH, NIGERIA

Soils are characterized and classified based on its unique properties. Detailed characterization of four representative areas of Oron coastal plain soils in South –South, Nigeria was carried out. Soil samples were collected from pedogenic horizons of soils in four sampling sites. Routine analysis of soil properties was carried out in the laboratory with standard laboratory procedures. Soil data was subjected to descriptive statistics using statistical analytical system. The soils have a deep well drafted profile of about deep 200 cm. The soil texture varied in areas ranging from loamy sand to sandy loam, sandy and sandy clay loam while bulk density increased down the natural horizons. The pH varied between moderately acidic to strongly acidic in the soils of the study area. The morphology of soils ranged in various colour matrix of hues (10-7.5) and Chroma values (1-8) in all horizons. The soils were characterized by Dark Brown (10YR3/3), Dark Greyish Brown (10YR4/2) and Yellowish Brown (10YR 5/4) to Grey (7.5YR6/2). The soils had low concentrations of exchangeable cations (Ca, Mg, Na and K). The Coefficient of variation (CV%) values ranged from 0.74 to 91.6 in Ca, Mg, Na and K. All the parameters in the soils of the study area showed low and medium mean values except soils of Esin Ufot1 and 2 which showed high mean values of Na with Esin Ufot 2 having the highest mean value of sodium to be 0.18 Cmol/kg. Suborder soils were classified as Grossarenic Kandiaqualfs (CEC > 16 Cmol/kg) for Esin Ufot1.Esin Ufot2, Esuk Oron1 while Esuk Oron 2 were classified as Typic Kandaquults (CEC < 16 Cmol/kg). A great importance in providing adequate data to enable right decision taking in the choice of site for developmental projects and crop production.

Electrochemical CO2 Reduction in Acidic Electrolytes: Spectroscopic Evidence for Local pH Gradients.

Inspired by recent advances in electrochemical CO2 reduction (CO2R) under acidic conditions, herein we leverage in situ spectroscopy to inform the optimization of CO2R at low pH. Using attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and fluorescent confocal laser scanning microscopy, we investigate the role that alkali cations (M+) play on electrochemical CO2R. This study hence provides important information related to the local electrode surface pH under bulk acidic conditions for CO2R, both in the presence and absence of an organic film layer, at variable [M+]. We show that in an acidic electrolyte, an appropriate current density can enable CO2R in the absence of metal cations. In situ local pH measurements suggest the local [H+] must be sufficiently depleted to promote H2O reduction as the competing reaction with CO2R. Incrementally incorporating [K+] leads to increases in the local pH that promotes CO2R but only at proton consumption rates sufficient to drive the pH up dramatically. Stark tuning measurements and analysis of surface water structure reveal no change in the electric field with [M+] and a desorption of interfacial water, indicating that improved CO2R performance is driven by suppression of H+ mass transport and modification of the interfacial solvation structure. In situ pH measurements confirm increasing local pH, and therefore decreased local [CO2], with [M+], motivating alternate means of modulating proton transport. We show that an organic film formed via in situ electrodeposition of an organic additive provides a means to achieve selective CO2R (FECO2R ∼ 65%) over hydrogen evolution reaction in the presence of strong acid (pH 1) and low cation concentrations (≤0.1 M) at both low and high current densities.

Rainfall Impacts Dissolved Organic Matter and Cation Export From Permafrost Catchments and a Glacial River During Late Summer in Northeast Greenland

ABSTRACTOngoing and amplified climate change in the Arctic is leading to glacier retreat and to the exposure of an ever‐larger portion of non‐glaciated permafrost‐dominated landscapes. Warming will also cause more precipitation to fall as rain, further enhancing the thaw of previously frozen ground. Yet, the impact of those perturbations on the geochemistry of Arctic rivers remains a subject of debate. Here, we determined the geochemical composition of waters from various contrasting non‐glacial permafrost catchments and investigated their impact on a glacially dominated river, the Zackenberg River (Northeast Greenland), during late summer (August 2019). We also studied the effect of rainfall on the geochemistry of the Zackenberg River, its non‐glacial tributaries, and a nearby independent non‐glacial headwater stream Grænse. We analyzed water properties, quantified and characterized dissolved organic matter (DOM) using absorbance and fluorescence spectroscopy and radiocarbon isotopes, and set this alongside analyses of the major cations (Ca, Mg, Na, and K), dissolved silicon (Si), and germanium/silicon ratios (Ge/Si). The glacier‐fed Zackenberg River contained low concentrations of major cations, dissolved Si and dissolved organic carbon (DOC), and a Ge/Si ratio typical of bulk rock. Glacial DOM was enriched in protein‐like fluorescent DOM and displayed relatively depleted radiocarbon values (i.e., old DOM). Non‐glacial streams (i.e., tributaries and Grænse) had higher concentrations of major cations and DOC and DOM enriched in aromatic compounds. They showed a wide range of values for radiocarbon, Si and Ge/Si ratios associated with variable contributions of surface runoff relative to deep active layer leaching. Before the rain event, Zackenberg tributaries did not contribute notably to the solute export of the Zackenberg River, and supra‐permafrost ground waters governed the supply of solutes in Zackenberg tributaries and Grænse stream. After the rain event, surface runoff modified the composition of Grænse stream, and non‐glacial tributaries strongly increased their contribution to the Zackenberg River solute export. Our results show that summer rainfall events provide an additional source of DOM and Si‐rich waters from permafrost‐underlain catchments to the discharge of glacially dominated rivers. This suggests that the magnitude and composition of solute exports from Arctic rivers are modulated by permafrost thaw and summer rain events. This event‐driven solute supply will likely impact the carbon cycle in rivers, estuaries, and oceans and should be included into future predictions of carbon balance in these vulnerable Arctic systems.

Ion exchange selectivity for protons by sodium ion-form crystalline silicotitanate

ABSTRACT At the Fukushima Daiichi Nuclear Power Station site, crystalline silicotitanate (CST) ion exchangers containing sodium ions (Na+) as exchange ions are used as an adsorbent to remove radioactive cesium (Cs) and strontium (Sr) from groundwater and contaminated water. The ion exchange reactions to remove Cs+ and Sr2+ compete with the reactions with other cations in the water sources. Since the groundwater and contaminated water have low concentrations of metal cations, the influence of competitive ion exchange reactions with protons (H+) is relatively large in the removal of Cs+ and Sr2+ from the water. In this paper, the H+/Na+ ion exchange property of the aqueous solution-CST system was evaluated. Results of batch tests were used to draw the isotherm and Kielland plot for the H+/Na+ ion exchange. The thermodynamic equilibrium constant K and the standard Gibbs energy ΔG 0 of the H+/Na+ ion exchange reaction were evaluated from the Kielland plot. CST exhibited high H+ selectivity in the H+/Na+ ion exchange reaction. The values of K and ΔG 0 were determined to be 7.3 × 104 and − 28 kJ mol−1, respectively. The selectivity of CST for H+ decreased with increasing H+ concentration on the ion exchange sites in CST.

The role of cations in hydrogen evolution reaction on a platinum electrode in mildly acidic media

The role of cations in hydrogen evolution reaction on a platinum electrode in mildly acidic media

Influence of Zr-doping on the structure and transport properties of rare earth high-entropy oxides

Fluorite-type ceria-based ceramics are well established as oxygen ion conductors due to their high conductivity, superseding state-of-the-art electrolytes such as yttria-stabilized zirconia. However, at a specific temperature and oxygen partial pressure they occasionally exhibit electronic conduction attributed to polaron hopping via multivalent cations (e.g. Pr and Ce). (Ce, La, Pr, Sm, Y)O2−δ is a high-entropy oxide with a fluorite-type structure, featuring low concentrations of multivalent cations that could potentially mitigate polaron hopping. However, (Ce, La, Pr, Sm, Y)O2−δ undergoes a structural transition to the bixbyite-type structure above 1000 °C. In this study, we introduce Zr doping into (Ce, La, Pr, Sm, Y)O2−δ to hinder the structural transition at elevated temperatures. Indeed, the fluorite structure at elevated temperatures is stabilized at approximately 10 at.% Zr doping. The total conductivity initially increases with doping, peaking at 5 at.% Zr doping, and subsequently decreases with further doping. Interestingly, electronic conductivity in (Ce, La, Pr, Sm, Y)1−x Zr x O2−δ under oxidizing atmospheres is not significant and is lowest at 8 at.% Zr. These results suggest that ceria-based high-entropy oxides can serve as oxygen ion conductors with a significantly reduced electronic contribution. This work paves the way for new compositionally complex electrolytes as well as protective coatings for solid oxide fuel cells.

The impact of geochemical and life-cycle variables on carbon dioxide removal by enhanced rock weathering: Development and application of the Stella ERW model

The impact of geochemical and life-cycle variables on carbon dioxide removal by enhanced rock weathering: Development and application of the Stella ERW model

Cation Effects on Hydrogen Oxidation Reaction on Pt Single-Crystal Electrodes in Alkaline Media.

The exact mechanism behind the cation-assisted hydrogen oxidation reaction (HOR) on platinum electrodes in alkaline media remains disputed. We show that the cation effects at platinum display a remarkable structure sensitivity: not only the H adsorption but also the HOR activity on (111) terrace sites are independent of the nature of cation and cation concentration. On (110) step sites, at low cation concentration and mildly alkaline media, cations promote the HOR, whereas at more alkaline pH and consequently higher near-surface cation concentrations, the HOR is inhibition by the cations. Moreover, the role of the cation on terrace-OHad is different from that on step-OHad, as can also be observed from the inhibition of the HOR current by terrace-OHad at higher potentials. These results suggest that near the onset potential, HOR mainly takes place on steps, but under diffusion-limited conditions at higher overpotential, HOR mainly takes place on terraces.

Response of wheat (Triticum aestivum L.) and cowpea (Vigna unguiculata L.) to foliar wetting with low pH mine waters containing acid-generating metal cations

Response of wheat (Triticum aestivum L.) and cowpea (Vigna unguiculata L.) to foliar wetting with low pH mine waters containing acid-generating metal cations

Dilute but significant: low cation concentration affects field dependent properties of Eu2Ga11Sn35.

We investigate the temperature and magnetic field-dependent electrical and thermal properties of Eu2.2Ga11Sn35, revealing a change in electronic structure and an increase in magnetoresistance with increasing field, as well as the origin of magneto-suppressed thermal conductivity of this unconventional inorganic clathrate-I material with very low cation concentration.

Interactions of manganese oxides with natural dissolved organic matter: Implications for soil organic carbon cycling

Interactions of manganese oxides with natural dissolved organic matter: Implications for soil organic carbon cycling

The Effects of Aminium and Ammonium Cations on the Ice Nucleation Activity of K‐Feldspar

AbstractMineral dust is one of the most abundant types of ice nucleating particles in the atmosphere. During atmospheric transport, mineral dust particles can become coated with inorganic and organic solutes, which can impact their ice nucleation activity. Aminium cations formed from amines are one type of organic solute that can coat mineral dust particles in the atmosphere, but their effects on the ice nucleation activity of mineral dust have not been studied. We investigated the effects of primary, secondary, and tertiary aminium cations with methyl and ethyl groups, as well as ammonium cations, on the ice nucleation activity of K‐feldspar, an important type of mineral dust, in the immersion freezing mode at low cation concentrations (0.2–20 mM) using a droplet‐freezing apparatus. Ammonium cations substantially increased the ice nucleation activity of K‐feldspar, consistent with previous studies. In contrast, primary aminium cations significantly reduced K‐feldspar ice nucleation activity, and secondary and tertiary aminium cations had no significant effect (the effect was less than the uncertainty of our measurements). Our combined results are consistent with the following mechanisms: ammonium cations undergo ion exchange with K‐feldspar, providing exposed N–H groups for hydrogen bonding with ice; primary aminium cations undergo ion exchange with K‐feldspar, exposing a hydrophobic tail that is not effective at nucleating ice; secondary and tertiary aminium cations do not undergo ion exchange with K‐feldspar due to steric effects caused by the multiple hydrophobic groups on the cation.

Impact of Ion-Mixing Entropy on Orientational Preferences of DNA Helices: FRET Measurements and Computer Simulations.

Biological processes require DNA and RNA helices to pack together in specific interhelical orientations. While electrostatic repulsion between backbone charges is expected to be maximized when helices are in parallel alignment, such orientations are commonplace in nature. To better understand how the repulsion is overcome, we used experimental and computational approaches to investigate how the orientational preferences of DNA helices depend on the concentration and valence of mobile cations. We used Förster resonance energy transfer (FRET) to probe the relative orientations of two 24-bp helices held together via a freely rotating PEG linker. At low cation concentrations, the helices preferred more "cross"-like orientations over those closer to parallel, and this preference was reduced with increasing salt concentrations. The results were in good quantitative agreement with Poisson-Boltzmann (PB) calculations for monovalent salt (Na+). However, PB underestimated the ability of mixtures of monovalent and divalent ions (Mg2+) to reduce the conformational preference. As a complementary approach, we performed all-atom molecular dynamics (MD) simulations and found better agreement with the experimental results. While MD and PB predict similar electrostatic forces, MD predicts a greater accumulation of Mg2+ in the ion atmosphere surrounding the DNA. Mg2+ occupancy is predicted to be greater in conformations close to the parallel orientation than in conformations close to the crossed orientation, enabling a greater release of Na+ ions and providing an entropic gain (one bound ion for two released). MD predicts an entropy gain larger than that of PB because of the increased Mg2+ occupancy. The entropy changes have a negligible effect at low Mg2+ concentrations because the free energies are dominated by electrostatic repulsion. However, as the Mg2+ concentration increases, charge screening is more effective and the mixing entropy produces readily detectable changes in packing preferences. Our results underline the importance of mixing entropy of counterions in nucleic acid interactions and provide a new understanding on the impact of a mixed ion atmosphere on the packing of DNA helices.

Methods to Improve the Stability of Nucleic Acid-Based Nanomaterials.

Nucleic acid strands can be synthesized into various nucleic acid-based nanomaterials (NANs) through strict base pairing. The self-assembled NANs are programmable, intelligent, biocompatible, non-immunogenic, and noncytotoxic. With the rapid development of nanotechnology, the application of NANs in the biomedical fields, such as drug delivery and biological sensing, has attracted wide attention. However, the stability of NANs is often affected by the cation concentrations, enzymatic degradation, and organic solvents. This susceptibility to degradation is one of the most important factors that have restricted the application of NANs. NANs can be denatured or degraded under conditions of low cation concentrations, enzymatic presence, and organic solvents. To deal with this issue, a lot of methods have been attempted to improve the stability of NANs, including artificial nucleic acids, modification with specific groups, encapsulation with protective structures, etc. In this review, we summarized the relevant methods to have a deeper understanding of the stability of NANs.

Structural and thermal properties of Eu2Ga11Sn35

Clathrates have been reported to form in a variety of different structure types; however, inorganic clathrate-I materials with a low-cation concentration have yet to be investigated. Furthermore, tin-based compositions have been much less investigated as compared to silicon or germanium analogs. We report the temperature-dependent structural and thermal properties of single-crystal Eu2Ga11Sn35 revealing the effect of structure and composition on the thermal properties of this low-cation clathrate-I material. Specifically, low-temperature heat capacity, thermal conductivity, and synchrotron single-crystal x-ray diffraction reveal a departure from Debye-like behavior, a glass-like phonon mean-free path for this crystalline material, and a relatively large Grüneisen parameter due to the dominance of low-frequency Einstein modes. Our analyses indicate thermal properties that are a direct result of the structure and composition of this clathrate-I material.

Effects of soil grain size and solution chemistry on the transport of biochar nanoparticles

Biochar nanoparticles (BC-NP) have attracted significant attention because of their unique environmental behavior, some of which could potentially limit large-scale field application of biochar. Accurate prediction of the fate and transportability of BC-NP in soil matrix is the key to evaluating their environmental influence. This study investigated the effects of soil grain size and environmentally relevant solution chemistry, such as ionic strength (cation concentration, 0.1 mM–50 mM; cation type, Na+, and Ca2+), and humic acid (HA; 0–10 mg/L), on the transport behavior of BC-NP via systematic column experiments. The transportability of BC-NP in the soil-packed column decreased with decreasing soil grain size and was inversely proportional to soil clay content. At low cation concentrations (0.1–1.0 mM), a considerable proportion of BC-NP (15.95%–67.17%) penetrated the soil columns. Compared with Na+, Ca2+ inhibited the transportability of BC-NP in the soil through a charge shielding effect. With increasing HA concentration, the transportability of BC-NP increased, likely due to an enhanced repulsion force between BC-NP and soil particles. However, at a high HA concentration (10 mg/L), Ca2+ bridging reduced the transportability of BC-NP in the soil. Breakthrough curves of BC-NP were explained by the two-site kinetic retention model. The antagonistic effects of ionic strength and HA indicated that the transport behavior of BC-NP in the soil was governed by competitive effects of some environmental factors, including soil grain size, environmental solution chemistry, and natural organic matter content.

Revealing uncommon transport in the previously unascertained very low cation clathrate-I Eu2Ga11Sn35

We report on the structure and electrical transport of single-crystal Eu2Ga11Sn35, the sole example of a very low cation concentration clathrate-I composition with atypical transport directly attributable to the structure and stoichiometry.