Role Of Mn Research Articles

Manganese(III) dominants the mobilization of phosphorus in reducing sediments: Evidence from Aha reservoir, Southwest China

Eutrophication has become one of the greatest threats to aquatic ecosystems. The release of phosphorus (P) from sediments exerts a critical role on eutrophication level. Both manganese (Mn) and iron (Fe), sensitive to redox conditions, own strong affinity for P. Numerous works have demonstrated that Fe was a key factor to drive P cycle in sediments. However, the role of Mn on P mobilization remains largely unexplored. Herein, the mechanism of P mobilization driven by Mn were investigated in a seasonal anoxic reservoir. Diffusive gradients in thin films (DGT) results, from both field investigations and laboratory incubations, showed P was synchronously distributed and significantly positive correlated (r2 ≥ 0.40, p < 0.01) with Mn, suggested that P cycle was associated with Mn. X-ray photoelectron spectroscopy (XPS) results showed that in the outer layers at the top 1 cm sediment pellet the contents of Mn and P occurred significantly synchronize changed, while that of Fe remains virtually unchanged when oxygen conditions changed. This demonstrated that Mn is likely to be the key factor affect P cycle. Most importantly, the relative content of Mn(III) changed the most (≈20 %) interpreted that Mn(III) is the key Mn species dominants the P mobilization. Furthermore, Dual-Beam scanning electron microscope (DB-SEM) maps clearly showed the co-enrichment of P and Mn in oxic sediments, confirmed P was mainly hosted by Mn minerals. In contrast, the random distributions and weak or negative correlations between P and Fe implied that P cycle was decouple with Fe, this resulted from that Fe was almost deposited as inert Fe fractions (>99.2 %) in reducing sediments. This study significantly expanded our knowledge on the geochemical behavior of P influenced by Mn in aquatic sediments.

Role of Mn in improving the corrosion resistance and cytocompatibility of antibacterial Mg-Ag-Mn alloy

To improve corrosion resistance and cytocompatibility of biodegradable Mg-Ag alloy, the non-toxic Mn was added to produce Mg-Ag-xMn (x=0, 0.5, 1, 2 and 3 wt%) alloys. It was revealed that Mg-Ag-2Mn alloy exhibits an optimized comprehensive property after post-casting heat treatment (PCHT). Microstructural factors for the improved performances are then determined. It is revealed that the addition of Mn promotes the precipitation of the Fe-containing α-Mn phase and alters the configuration of the corrosion product after PCHT, which enhances the corrosion resistance of the alloy and thus optimises the ionic release kinetics for improved biological performance.

Role of Mn in the Ni–Mn/SBA-15 Catalyst for Hydrogen Production by Biomass Steam Reforming at Relatively Low Temperature

Role of Mn in the Ni–Mn/SBA-15 Catalyst for Hydrogen Production by Biomass Steam Reforming at Relatively Low Temperature

Algal Extracellular Organic Matter Induced Photochemical Oxidation of Mn(II) to Solid Mn Oxide: Role of Mn(III)-EOM Complex and Its Ability to Remove 17α-Ethinylestradiol.

Photosensitizer-mediated abiotic oxidation of Mn(II) can yield soluble reactive Mn(III) and solid Mn oxides. In eutrophic water systems, the ubiquitous algal extracellular organic matter (EOM) is a potential photosensitizer and may have a substantial impact on the oxidation of Mn(II). Herein, we focused on investigating the photochemical oxidation process from Mn(II) to solid Mn oxide driven by EOM. The results of irradiation experiments demonstrated that the generation of Mn(III) intermediate was crucial for the successful photo oxidization of Mn(II) to solid Mn oxide mediated by EOM. EOM can serve as both a photosensitizer and a ligand, facilitating the formation of the Mn(III)-EOM complex. The complex exhibited excellent efficiency in removing 17α-ethinylestradiol. Furthermore, the complex underwent decomposition as a result of reactions with reactive intermediates, forming a solid Mn oxide. The presence of nitrate can enhance the photochemical oxidation process, facilitating the conversion of Mn(II) to Mn(III) and then to solid Mn oxide. This study deepens our grasp of Mn(II) geochemical processes in eutrophic water and its impact on organic micropollutant fate.

The influence of Mn content on Fe2B properties and its impact at the [formula omitted] /Fe2B interface

Fe–B alloy is widely used in the field of wear resistance, and the collaborative performance of their precipitated phases and the matrix is of significant interest. This study utilizes first-principles calculations to investigate the influence of Mn on the thermodynamic and mechanical properties of the Fe2B precipitated phase within Fe–B alloys, as well as the role of Mn in regulating the interface between the matrix αz-Fe16C2 and the Fe2B precipitated phase. The computational results reveal that the formation enthalpy remains negative at varying Mn concentrations. The Poisson's ratio of Fe2B is measured at 0.2245. However, under Mn doping, the Poisson's ratio varies with Mn content, with Fe3Mn5B4 exhibiting the highest Poisson's ratio, reaching 0.3157, representing a remarkable 40.62% increase. Interface performance calculations indicate that the interface energy of αz-Fe16C2/Fe2B is 0.4172 eV/Å2, with an adhesive energy of −0.1984 eV/Å2. Upon Mn doping at the interface, the doped interface energy decreases to −3.5393 eV/Å2, and the doped adhesive energy increases to 1.6975 eV/Å2, significantly enhancing interface binding. In conclusion, Mn has the capacity to improve the ductility of Fe2B and enhance the interface binding between the matrix and the precipitates, consequently increasing the wear resistance of Fe–B alloys.

Manipulating the Curie point in γ-Fe filled carbon nano-onions: The role of Mn and Gd for enhanced magnetic functionalities

Recent works have proposed the stabilization of γ-Fe nanocrystals inside carbon nano-onions (CNOs) and nanotubes (CNTs) as active ferromagnetic phases for possible applications in hyperthermic dissipative systems. Stabilization of the γ-phase of iron is of particular interest due to the unit-cell dependent ferromagnetic properties and controllable Curie point. Here we investigate a modification of the chemical vapor synthesis (CVS) method for the in-situ manipulation of γ-Fe nanocrystals within CNOs, in presence of bis(isopropyl-cyclopentadienyl)manganese or tris(tetramethyl-cyclopentadienyl)gadolinium(III) as additional growth-precursors. In the presented experiments ferrocene, dichlorobenzene and sulfur mixtures were employed with a fixed ratio. Interestingly, when employing bis(isopropyl-cyclopentadienyl)manganese we demonstrate the stabilization of a modified FCC γ-Fe phase inside the CNOs, identifiable as a γ-Fe23C6 through X-ray diffraction and refinement of the structural model (obtained by employing the Rietveld method), with unit cell parameters a=b=c= 10.5569 Å and space group Fm-3m. The relative amount of Mn content was found to vary from 0.2% to 0.5%. Differently, comparative experiments performed in presence of great excess of tris(tetramethylcyclo-pentadienyl)gadolinium(III) reveal a significant variation of the sample’s morphology, with the nucleation of Gd nanoparticles around γ-Fe filled CNOs. Magnetic characterization with field-dependent zero field cooled (ZFC) and field cooled (FC) acquisitions revealed for the first batch of experiments (method 1) a ferromagnetic behavior comparable to that of γ-Fe, with a T1 Curie point located in proximity of T∼ 400 K and a T2 Curie point in proximity of T∼90 K. Differently, for method-2, an important interplay of ferromagnetic and paramagnetic components was found in the Gd-decorated γ-Fe filled CNOs, with a reduction of the Curie point down to T∼350 K. The presented findings highlight the important role of 1) the γ-Fe23C6 phase in enhancing the saturation magnetization Ms of the filled CNOs and 2) the crystallinity of the Gd-component in allowing for an enhancement of the paramagnetic response in the filled CNOs.

The influence of steroidal implants and manganese sulfate supplementation on growth performance, trace mineral status, hepatic gene expression, hepatic enzyme activity, and circulating metabolites in feedlot steers.

Angus-cross steers (n = 144; 359 kg ± 13.4) were used to assess the effect of dietary Mn and steroidal implants on performance, trace minerals (TM) status, hepatic enzyme activity, hepatic gene expression, and serum metabolites. Steers (n = 6/pen) were stratified by BW in a 3 × 2 factorial. GrowSafe bunks recorded individual feed intake (experimental unit = steer; n = 24/treatment). Dietary treatments included (MANG; 8 pens/treatment; Mn as MnSO4): (1) no supplemental Mn (analyzed 14mg Mn/kg DM; Mn0); (2) 20mg supplemental Mn/kg DM (Mn20); (3) 50mg supplemental Mn/kg DM (Mn50). Within MANG, steers received a steroidal implant treatment (IMP) on day 0: (1) no implant; NO; or (2) combination implant (Revalor-200; REV). Liver biopsies for TM analysis and qPCR, and blood for serum glucose, insulin, non-esterified fatty acids, and urea-N (SUN) analysis were collected on days 0, 20, 40, and 77. Data were analyzed as a randomized complete block with a factorial arrangement of treatments including fixed effects of Mn treatment (MANG) and implant (IMP) using PROC MIXED of SAS 9.4 using initial BW as a covariate. Liver TM, serum metabolite, enzyme activity, and gene expression data were analyzed as repeated measures. No MANG × IMP effects were noted (P ≥ 0.12) for growth performance or carcass characteristic measures. Dietary Mn did not influence final body weight, overall ADG, or overall G:F (P ≥ 0.14). Liver Mn concentration increased with supplemental Mn concentration (MANG; P = 0.01). An IMP × DAY effect was noted for liver Mn (P = 0.01) where NO and REV were similar on day 0 but NO cattle increased liver Mn from days 0 to 20 while REV liver Mn decreased. Relative expression of MnSOD in the liver was greater in REV (P = 0.02) compared to NO and within a MANG × IMP effect (P = 0.01) REV increased liver MnSOD activity. These data indicate current NASEM Mn recommendations are adequate to meet the demands of finishing beef cattle given a steroidal implant. Despite the roles of Mn in metabolic pathways and antioxidant defense, a basal diet containing 14mg Mn/kg DM was sufficient for the normal growth of finishing steers. This study also provided novel insight into how implants and supplemental Mn influence genes related to arginine metabolism, urea synthesis, antioxidant capacity, and TM homeostasis as well as arginase and MnSOD activity in hepatic tissue of beef steers.

The role of Mn in widening the potential window of solid solution derived electrodes for aqueous supercapacitors

The role of Mn in widening the potential window and MnOx chemical stability in different electrolytes.

Uticaj varijacija u sadržaju Mn na mehaničke i korozione karakteristike Cu-Al-Mn legura sa memorijom oblika

In this work, the role of Mn on the shape memory effect and mechanical and corrosion behavior of Cu-Al-Mn shape memory alloys was studied. The composition of Al was fixed to 10 wt% while that of Mn was varied from 2 to 10 wt%. The strain recovery by SME was evaluated using the bend test, while the yield and ultimate tensile strength were obtained using the tension test. The corrosion behavior was studied using three different solutions: freshwater, substitute ocean water, and Hank's solution. The yield and ultimate tensile strength of Cu-Al-Mn alloys increased with Mn content up to 6%, which was attributed to grain refinement and precipitation hardening, while the fracture analysis showed mixed mode failure for all alloys. The corrosion behavior of Cu-Al-Mn alloys was modified due to the addition of Mn. With the increase in Mn content, the alloys displayed better corrosion resistance and lower corrosion rates. The corroded surface analysis tested in freshwater showed pitting corrosion, while Cu-Al-Mn alloy with low Mn content was tested in substitute ocean water. Hank's solution showed surface damage with an unstable surface layer.

Enhanced removal of sulfamethoxazole by Mn(II)/bisulfite in presence of nitrilotriacetic acid: Role of Mn(III)

Currently, the research on bisulfite (BS) activation by Mn(II) is very limited probably because of the low catalytic efficiency of Mn(II). Adding ligands to Mn(II)/BS system is likely to improve the BS activation, but the relative information is very rare. Therefore, the effect of nitrilotriacetic acid (NTA) on Mn(II)/BS system was investigated in this work using sulfamethoxazole (SMX) as the target contaminant. The results showed that the addition of NTA enhanced SMX removal in Mn(Ⅱ)/BS system through forming Mn(Ⅱ/III)-NTA complexes driving Mn(III)/Mn(II) cycle and stabilizing Mn(III). Alcohol scavenging experiments and competitive kinetic experiments indicated that sulfate radical (SO4•−) and hydroxyl radical (HO•) were not the main reactive species in Mn(II)/NTA/BS system. Mn(Ⅲ) was the primary oxidant for SMX elimination in this system and its existence was proved by UV-Vis absorption spectrum of reaction solution. Mn(Ⅱ)/NTA/BS system could greatly degrade SMX in near-neutral conditions, while nearly no SMX removal was observed at pH 3.0. The decrease of dissolved oxygen concentration significantly inhibited BS autocatalytic stage, thus suppressing the removal of SMX. Due to the competitive complexation of HCO3− and FA with NTA for Mn(II), their addition in Mn(Ⅱ)/NTA/BS system obviously inhibited SMX degradation. Four intermediates were detected during SMX degradation in Mn(Ⅱ)/NTA/BS system, and the possible SMX transformation pathways were speculated as N-S bond breaking, hydroxylation, amino oxidation and coupling reaction.

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

Metal (oxyhydr)oxides are key factors for the transformation and stabilization of organic carbon (OC) in soil. While sorptive interactions between Al and Fe (oxyhydr)oxides and dissolved organic matter (DOM) are well studied, the role of Mn(IV) oxides (manganates) in DOM sorption, fractionation, and oxidation has not been extensively investigated. Therefore, we examined sorptive interactions between manganates (δ-MnO2, birnessite, cryptomelane; 5 g L−1) and different DOM types (beech litter and Oa/Oe material under pine; ∼100 mg L−1 dissolved organic carbon, DOC) at pH 4 and 7 in different background electrolytes (BGE; no salt, 0.01 M NaCl or CaCl2) for up to 32 h. Changes of DOM solutions and mineral phases were assessed by solid, liquid, and gas analyses, and statistically evaluated for the effects of manganate, DOM type, pH, and BGE on DOC sorption, fractionation, and oxidative transformation. Manganates sorbed 0.2–8.7 mg OC g−1. Per unit mass, δ-MnO2 was least effective in DOC retention due to its high DOC oxidation capacity. Manganates sorbed more DOC at acidic pH and more aromatic pine than more aliphatic beech DOC, with Ca2+ generally facilitating DOC sorption. Up to 56 % of added DOC (average: 25 %) was oxidized to CO2, which is comparable to the extent of DOC respiration by soil microorganisms. DOC oxidation by δ-MnO2 and cryptomelane exceeded that of birnessite, which had the lowest specific surface area of all manganates. However, we found no difference in the efficiency of manganates to oxidize DOC, implying a similar redox activity of phyllo- and tectomanganates. More beech than pine DOM was oxidized to CO2 and an acidic pH facilitated DOC decomposition. While the presence of Na-BGE increased DOC oxidation to CO2 relative to no-salt treatments, Ca-BGE had the opposite effect, as Ca2+ apparently impeded the electron transfer from sorbed OC to structural Mn(III/IV). Contact of DOM with manganates also produced high concentrations of dissolved low-molecular-weight organic acids (mainly formate, acetate, and oxalate), accounting for up to 19 % of the initial DOC concentration. In addition, reduced specific ultraviolet absorbance of DOM solutions at 280 nm indicated preferential sorption of aromatic moieties, especially in Ca-BGE. However, in the absence of Ca2+ and at neutral pH, manganates increased the aromaticity of beech DOM, most likely due to polymerization reactions. No mineral transformations occurred after reaction of manganates with DOM, despite reductive manganate dissolution. Our results imply that soil manganates accumulate more OC in acidic soils and in presence of more aromatic DOM. However, manganates oxidatively destabilize DOC by generating CO2 and low-molecular-weight organic compounds, which is presumably more relevant in acidic soils with low concentrations of polyvalent cations and for more aliphatic DOM. The produced low-molecular-weight organic compounds may promote microbial activity and foster mineral weathering. Our results suggest a pivotal role of manganates in soil OC cycling, including the fate and bioavailability of nutrient elements associated with DOM, and in supporting ligand-promoted mineral weathering and soil formation.

Roles of Mn and Co in the Air Synthesizability of Layered Oxide Cathodes for Lithium-Based Batteries

Roles of Mn and Co in the Air Synthesizability of Layered Oxide Cathodes for Lithium-Based Batteries

The role of Mn in Bi2-xMnxTe3 topological insulator: Structural, compositional, magnetic, and weak anti-localization property analysis

The role of Mn in Bi2-xMnxTe3 topological insulator: Structural, compositional, magnetic, and weak anti-localization property analysis

Metal-Chelating Self-Assembling Peptide Nanofiber Scaffolds for Modulation of Neuronal Cell Behavior.

Synthetic peptides are promising structural and functional components of bioactive and tissue-engineering scaffolds. Here, we demonstrate the design of self-assembling nanofiber scaffolds based on peptide amphiphile (PA) molecules containing multi-functional histidine residues with trace metal (TM) coordination ability. The self-assembly of PAs and characteristics of PA nanofiber scaffolds along with their interaction with Zn, Cu, and Mn essential microelements were studied. The effects of TM-activated PA scaffolds on mammalian cell behavior, reactive oxygen species (ROS), and glutathione levels were shown. The study reveals the ability of these scaffolds to modulate adhesion, proliferation, and morphological differentiation of neuronal PC-12 cells, suggesting a particular role of Mn(II) in cell-matrix interaction and neuritogenesis. The results provide a proof-of-concept for the development of histidine-functionalized peptide nanofiber scaffolds activated with ROS- and cell-modulating TMs to induce regenerative responses.

Mn-Doped Spinel for Removing Cr(VI) from Aqueous Solutions: Adsorption Characteristics and Mechanisms

In this study, the manganese (Mn) was doped in the MnFe2O4 crystal by the solid-phase synthesis method. Under the optimum conditions (pH = 3), the max removal rate and adsorption quantity of Cr(VI) on MnFe2O4 adsorbent obtain under pH = 3 were 92.54% and 5.813 mg/g, respectively. The DFT calculation results indicated that the adsorption energy (Eads) between HCrO4- and MnFe2O4 is -215.2 KJ/mol. The Cr(VI) is mainly adsorbed on the Mn atoms via chemical bonds in the form of HCrO4-. The adsorption of Mn on the MnFe2O4 surface belonged to chemisorption and conformed to the Pseudo-second-order equation. The mechanism investigation indicated that the Mn in MnFe2O4 has an excellent enhancement effect on the Cr(VI) removal process. The roles of Mn in the Cr(VI) removal process included two parts, providing adsorbing sites and being reductant. Firstly, the Cr(VI) is adsorbed onto the MnFe2O4 via chemisorption. The Mn in MnFe2O4 can form ionic bonds with the O atoms of HCrO4-/CrO42-, thus providing the firm adsorbing sites for the Cr(VI). Subsequently, the dissolved Mn(II) can reduce Cr(VI) to Cr(III). The disproportionation of oxidized Mn(III) produced Mn(II), causing Mn(II) to continue to participate in the Cr(VI) reduction. Finally, the reduced Cr(III) is deposited on the MnFe2O4 surface in the form of Cr(OH)3 colloids, which can be separated by magnetic separation.

Plasma Manganese Levels and Risk of Gestational Diabetes Mellitus: A Prospective Cohort Study.

Manganese (Mn) intake has been found to be linked with risk of type 2 diabetes. However, the role of Mn in the development of gestational diabetes mellitus (GDM) remains to be investigated. This prospective study included pregnant women from the Tongji Maternal and Child Health Cohort. A total of 2327 participants with plasma specimens before 20 weeks were included. Among the pregnant women, 9.7% (225/2327) were diagnosed with GDM. After adjustment, pregnant women with the third and highest quartile of plasma Mn levels had 1.31-fold (RR, 2.31 [1.48, 3.61]) and 2.35-fold (RR, 3.35 [2.17, 5.17]) increased risk of GDM compared with those with the lowest quartile. A 1 standard deviation increment of ln-transformed plasma Mn levels (0.53 μg/L) was related to elevated risks of GDM with RRs of 1.28 [1.17, 1.40]. The positive associations between Mn and GDM remained consistent in all the subgroups. The weighted quantile sum index was significantly related to GDM (RR, 1.60 [1.37, 1.86]). The contribution of Mn (58.69%) to the metal mixture index was the highest related to GDM. Higher plasma Mn levels were found to be linked with elevated fasting and 2 h post-load blood glucose. This study revealed relationships of higher plasma Mn levels in early pregnancy and increased risk of GDM, suggesting that though essential, excess Mn in the body might be a potential important risk factor for GDM.

Alleviating Anisotropic Volume Variation at Comparable Li Utilization during Cycling of Ni-Rich, Co-Free Layered Oxide Cathode Materials

Driven by demand for greater energy densities, Ni-rich cathode materials, such as lithium nickel cobalt manganese (NCM) and nickel cobalt aluminum (NCA) oxides, with compositions approaching the lithium nickel oxide (LiNiO2) end-member have been investigated intensively. While such compositions are targeted assuming the redox activity of nickel will lead to higher capacities, the role of even small amounts of Mn and Co in these systems is of great importance. To raise considerations about the role of Mn and Co, operando X-ray diffraction has been used to resolve the structure–electrochemistry relationships in a series of Ni-rich NMX (LiNi1–yMnyO2, y = 0.25, 0.17, 0.10, 0.05) cathode materials. To ensure a meaningful comparison, the upper cutoff potential was varied as a function of the Mn content in the material to ensure comparable states of delithiation and thereby provide a capacity-normalized comparison of the structural evolution. During the first cycle all materials deliver a specific charge capacity exceeding 230 mAh g–1, corresponding to a residual Li content of x(Li) ≈ 0.15, and exhibit a structural evolution free of any first-order phase transitions. Monitoring the structural parameters of the materials during cycling shows that Mn substitution substantially reduces the magnitude of expansion/contraction of lattice parameters even when comparable amounts of Li are removed from the structure and more significantly also reduces the anisotropy of the volume changes. Thus, these Co-free, Ni-rich materials hold promise as high-capacity cathodes with good structural and mechanical stability.

Mn uptake system affects the virulence of Streptococcus suis by mediating oxidative stress

Manganese (Mn) is an important micronutrient that is not readily available to pathogens during infection. Hosts resist the invasion of pathogens through nutritional immunity and oxidative stress. To overcome this nutrient restriction, bacteria utilize high affinity transporters to compete with nutrient-binding proteins (e.g., calprotectin). Little is known about the role of Mn in the pathophysiology of Streptococcus suis. Here, we revealed that the tolerance of S. suis to calprotectin and oxidative stress was associated with Mn. Inactivation of Mn uptake system, TroABCD, in S. suis decreased the tolerance to calprotectin and oxidative stress. Furthermore, Mn uptake system mutant strains reduced capacity for bacterial cellular survival, and attenuated virulence in a mouse model. To explore the regulatory mechanism, we determined the transcriptional start site of troABCD using capping rapid amplification of cDNA ends. Furthermore, we revealed that TroR was a transcriptional regulatory repressor of troABCD. In the absence of troR, transcription levels of troA, troB, troC, and troD were not inhibited by low or high Mn levels, and intracellular Mn contents of mutant strains were higher than that of the wild-type strain. Finally, we used electrophoretic mobility shift assay to demonstrate that TroR bound the promoter region of troABCD. Collectively, this study revealed that Mn acquisition was essential for pathogenesis of S. suis and Mn uptake systems should be targets for the development of new antimicrobials.

Precipitation of arsenic-bearing solids as a secondary control on arsenic speciation in groundwater: Evidence from field study and geochemical analysis

Among the mechanisms controlling elevated arsenic (As) speciation in groundwater, dissolution-precipitation of As-bearing solids, possibly as colloids, has not been systematically evaluated even though reported groundwater saturation states often indicate super- or near-saturation with respect to multiple solids. In this contribution, a detailed geochemical analysis was performed on well-constrained groundwater quality data collected through (a) sustained sampling (n = 84) over 2.5 y at a newly-identified site in the middle Gangetic plain of India; and (b) metadata analysis on studies conducted worldwide (n = 414). Groundwater saturation indices, speciation (EH-pH), and mineral solubilities (logC-pH) were calculated, consistent with a carefully-selected and updated thermodynamic database. Results suggest that under oxidizing conditions, secondary precipitation of solids similar to scorodite [FeAsO4·2H2O(s)] and pharmacolite [CaHAsO4·2H2O(s)] influences the As(V) concentrations in groundwater. In addition, groundwater at the investigated site was saturated with calcite [CaCO3(s)] and rhodochrosite [MnCO3(s)]. Evidence of colloidal forms of As-containing and As-free solids was found from SEM-EDS characterization of solids collected on 0.2 μm filter membranes used to sample groundwater. XPS analysis showed that the relative As(V) and As(III) signatures in these solids were consistent with the prevalence of dissolved As(V) and As(III) in groundwater, independently quantified using IC-ICP-MS. HR-TEM-SAED characterization of these solids indicated the possible presence of poorly crystalline scorodite- and pharmacolite-like phases along with calcite and lepidocrocite [γ–FeOOH(s)] in a predominantly amorphous matrix. Also, a possible role of Mn in inducing As immobilization in calcite was suggested with the identification of ∼ 1:1 Mn:As atomic ratios in these solids, consistent with significant (p < 0.05) correlation of dissolved total As and total Mn. These findings imply that solubility-driven secondary processes may exert additional controls on the eventual fate and transport of arsenic in mixed-redox state shallow groundwaters, apart from the known primary mobilization mechanisms. To the best of our knowledge, this is the first study that has characterized colloidal arsenic in groundwater and related it to prevailing mechanisms.

Magnetic Frustration Effect on the Rate Performance of LiNi0.6Co0.4−xMnxO2 Cathodes for Lithium‐Ion Batteries

AbstractCobalt‐free LiNixMn1−xO2 (NM, x ≥ 0.5) layered oxides are considered to be promising cathode materials for next‐generation lithium‐ion batteries because of exceptionally high capacity and low cost, yet the fundamental role of manganese ions in the NM layered structure and rate performance has not been fully addressed to date. Herein, a series of Ni‐fixed LiNi0.6Co0.4−xMnxO2 (x = 0, 0.1, 0.2, 0.3, and 0.4) systems are employed as cathode materials to investigate the functionality of Mn ions on their structures and electrochemical properties. It is found that contrary to prior reports, the change in the c‐axis lattice parameter is not in close connection with the rate performance of NM cathodes. In particular, superconducting quantum interference device (SQUID) measurements are performed to verify the fact that Mn3+ and Mn4+ ions with high spin states cause severe magnetic frustration in the structures of cathode materials, which profoundly aggravates the Li/Ni ionic disorder and blocks Li+ migration, contributing to inferior rate performance. In addition, Li+ migration hindered by Li/Ni disorder, is theoretically demonstrated by ab initio calculation. This work not only provides fresh insight into the role of Mn in NM layered oxide cathodes but also proposes an effective strategy to resolve their inferior rate performance.