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The high theoretical capacity of sodium birnessite cathode materials for sodium-ion batteries (SIBs) has been restricted due to drastic volume variation and fast capacity fading. The underlying rea...

Ceria doped with manganese in various amounts was prepared via hydrothermal synthesis. XRD revealed that beside ceria, monoclinic birnessite (Na0.55Mn2O4 × 1.5H2O) appears in the samples. The occurrence of birnessite was achieved using different synthesis conditions and precursors. SEM imaging revealed birnessite layered formations surrounded with ceria nanoparticles, while EDS confirmed the presence of both phases. Weight percentage, lattice constants and crystallite size of ceria, as well as birnessite, were obtained through whole powder pattern decomposition. Pure and Mn doped ceria samples with crystallite sizes between 3.1 and 3.4 nm, and specific surface area values between 183 and 212 m2 g−1 were obtained. It was established that the amount of Mn entering the ceria lattice or forming birnessite varies with nominal composition. Introduction of Mn in ceria is evident from the decrease of ceria lattice constant (from 5.4185 A to 5.4002 A). The entrance of manganese in the ceria crystal lattice was confirmed via EDS spectroscopy. Thermally induced changes were monitored via DTA/TGA, XRD and FTIR. Birnessite decomposes below 200 °C, while thermal treatment at 500 °C for 2 h yields Na2Mn5O10. Weight percentage of birnessite was confirmed through calculations based on the loss of interlayer water during TGA analysis. HRTEM revealed nanorod morphology of Na2Mn5O10, while EELS gave insight into the composition of this phase.

Defect engineering is an effective strategy to enhance the activity of catalysts for various applications. Herein, it was demonstrated that in addition to enhancing surface properties via doping, the influence of dopants on the surface-intermediate interaction is a critical parameter that impacts the catalytic activity of doped catalysts for low-temperature formaldehyde (HCHO) oxidation. The incorporation of Co into the lattice structure of δ-MnO2 led to the generation of oxygen vacancies, which promoted the formation of surface active oxygen species, reduced activation energy, and enhanced catalytic activity for low-temperature oxidation of HCHO. On the contrary, Cu doping led to a drastic suppression of the catalytic activity of δ-MnO2, despite its enhanced redox properties and slight increase in the surface concentration of active oxygen species, compared to pristine δ-MnO2. Diffuse reflectance infrared Fourier transform analysis revealed that in the presence of Cu, carbonate intermediate species accumulate on the surface of the catalysts, leading to partial blockage of active sites and suppression of catalytic activity.

Widespread antibiotic resistance genes (ARGs) have caused critical threats to public health on a global scale. Soil, composed mainly of minerals, acts as a source of resistance determinants, playing a considerable role in the development and dissemination of ARGs. The great abundance of ARGs in the soil environment raises concern about the effect of minerals on the spread of ARGs. Herein, the horizontal transfer of a model plasmid pMP2463 containing ARGs from Escherichia coli S17‐1 to Pseudomonas putida KT2440 was monitored following exposure to four common soil minerals, namely, kaolinite, montmorillonite, goethite and birnessite. Birnessite resulted in concentration‐dependent increases in conjugative transfer of plasmid pMP2463 by 1.3–4.3 fold, compared with that in the control group. However, no obvious laws were found in the change of conjugative transfer rate at different concentrations of kaolinite and montmorillonite. As for goethite, the conjugative transfer rate increased firstly and then decreased as the concentration increased. The possible mechanisms underlying birnessite‐induced conjugative transfer of plasmid were explored; birnessite is capable of initiating intracellular reactive oxygen species (ROS) formation, inducing the oxidative stress response. Additionally, birnessite notably facilitated the mRNA expression of the outer membrane protein genes, which contributed to cellular membrane pore formation and horizontal gene transfer, and altered the mRNA expression of conjugative‐related genes that are responsible for conjugative transfer of mobile genetic elements between bacteria. This study triggers questions regarding the potential role of soil minerals in the global dissemination of antimicrobial resistance and provides insights into the interactions between bacteria and minerals in the natural soil environment. HIGHLIGHTS: The effect of soil minerals on conjugative transfer of ARGs was explored. Birnessite induced the concentration‐dependent increase of conjugative transfer. Mechanisms underlying ROS formation, membrane permeability increase, gene expression alteration were revealed. Our results provide evidence for the effect of birnessite on antibiotic resistance dissemination.

In this paper, the reaction mechanism for the adsorption of Zn2+ by synthetic triclinic Na-birnessite was studied by reacting synthetic triclinic Na-birnessite with Zn2+ in solution, thereby provid...

Birnessite not only oxidizes arsenite into arsenate but also interacts with organic matter in various ways. However, effects of organic matter on interaction between As and birnessite remain unclear. This study investigated effects of citrate and EDTA (3.12 and 2.05 mM, respectively) on oxidation of As(III) (1.07 mM) and adsorption of As(V) (0.67 mM) on birnessite (5.19 mM as Mn) at near-neutral pH. We found that As(V) adsorption on birnessite was enhanced by citrate and EDTA, which resulted from the increase in active adsorption sites via dissolution of birnessite. In comparison with citrate batches, more As was adsorbed on birnessite in EDTA batches, where dissolved Mn was mainly presented as Mn(III)-EDTA complex. Citrate or EDTA-induced dissolution of birnessite did not decrease the As(III) oxidation rate in the initial stage where As(III) oxidation rate was rapid. Afterwards, As(III) oxidation was conspicuously suppressed in citrate-amended batches, which was mainly attributed to the decrease in adsorption sites by adsorption of citrate/Mn(II)-citrate complex. This suppression was enhanced by the increase in concentrations of dissolved Mn(II). Citrate inhibited As adsorption after As(III) oxidation due to the strong competitive adsorption of citrate/Mn(II)-citrate complex. However, the As(III) oxidation rate was increased in EDTA-amended batches in the late stage, which mainly derived from the increase in the active sites via birnessite dissolution. The strong complexation ability of EDTA led to formation of Mn(III)-EDTA complex. Arsenic adsorption was not affected due to the limited competitive adsorption of the complex on the solid. This work reveals the critical role of low molecular weight organic acids in geochemical behaviors of As and Mn in aqueous environment.

The mineral composition of ferromanganese crusts from Belyaevsky Volcano in the Central Basin of the Sea of Japan has been studied. The crusts have diverse structures and a complex polymineral composition. Along with the previously known todorokite, birnessite, manganite, pyrolusite, and vernadite, we determined rhodochrosite, quenselite, manganosite, hetaerolite, manganotantalite, and tungomelane for the first time. The group of accessory minerals includes magnetite, titanomagnetite, hematite, titanohematite, pyrite, pyrrhotite, galena, monazite, cerianite, and baddeleyite. Copper gold was recognized for the first time in manganese breccia. The origin of manganese minerals was caused by low-temperature hydrothermal fluids, which supplied metals and defined local conditions and intermittent growth of manganese crusts. Sapropel organic matter of siliceous–clayey carbonaceous sediments in the Cenozoic sequences of the deep basin could be a source of metals and the reason for the suboxidizing environments of crystallization of some manganese (manganite, todorokite, and birnessite) and accessory (intermetallics, sulfides, and native elements) minerals.

Various manganese oxides are considered as rather active ORR catalysts and/or supercapacitor materials for operation in alkaline medium. However all these oxides are thermodynamically unstable at high pH and undergo more or less slow transformations to non-stoichiometric oxides containing alkali metal cations M (MxMnO2*nH2O, known also as birnessite mineral). We report a possibility to deposit birnessite thin layers by means of permanganate cathodic reduction. We consider ORR activities and reversible recharging data for birnessite deposited at various potentials with account for XRD information on birnessite cell disordering and microscopic data on the morphology of the deposits. Deposition is complicated by formation of soluble Mn(V) and Mn(VI) species and their disproportionation. However fortunately these by-side reactions appear to be strongly inhibited by forming birnessite solid, and the resulting current efficiencies are high enough. We compare deposition efficiency and adhesion for Pt, Ni, and glassy carbon supports. The best adhesion is found for Ni support. Deposits morphology strongly depends on deposition potential. Thin deposits formed at low overvoltage demonstrate homogeneously distributed pores, and only starting from sub-mkm thickness branched flakes appear, which are typical for natural birnessite morphology. Contrary, at higher overvoltage the deposits start to branch from the very beginning, and consist from thin flakes exclusively. This morphology is unfavorable for electrode behavior because of too high material resistance. Deposition transients allow to monitor the morphology. For flakes formation, oscillatons at deposition transients are observed, which can be associated with layer-by-layer growth. The recharging of all birnessite materials is reversible, but the specific capacity strongly depends on deposition potential and deposit thickness. The best results (ca. 500 mkF/cm2 at scan rates up to 0.1 V/s) are found for thin deposits fabricated at low overvoltage. ORR mass activity is comparable with observed earlier for MnO2, which is believed to undergo slow transformation to birnessite in alkaline solutions. The important advantage of electrodeposited birnessite as compared to the majority of chemically synthesized manganese oxides is a possibility to operate in the absence of conducting binder.

Octahedral layered birnessite (OL) was synthesized by redox method, and OL supported Ag catalysts (xAg/OL, x = 0.1wt%, 0.2wt%, 0.3wt%, 0.5wt%) were prepared by ion exchange method. Then catalysts were characterized by XRD, SEM, BET, H2-TPR, TG, O2-TPD and in-situ DRIFTS, while the catalytic activity of CO was evaluated. Among xAg/OL samples, the 0.3Ag/OL exhibited the best catalytic activity for CO oxidation (T50 = 105 oC and T90 = 135 oC). The results show that the chemical adsorption of oxygen, the low-temperature reducibility and the strong interaction between the Ag species and OL are related to the excellent catalytic activity of xAg/OL. The reaction mechanism was studied by in-situ DRIFTS. First, O2 was adsorbed and activated on the oxygen vacancies of xAg/OL, then formed oxygen free radical attacked the adsorbed CO and produced CO2, subsequently CO2 desorbed from the catalyst surface. Oxygen vacancies was supplemented by gas O2, thus circulating.

Enrichments of REY (rare earth + yttrium) and other trace metals (Co and Ni) in deep-sea ferromanganese (Fe Mn) micronodules have received increasing attention in both deep-sea research and mineral exploration. Due to the presence of multiple, easily-crushed and poorly-crystallized phases in micronodules, the genesis of micronodules and their adsorption of various trace elements are poorly understood. To address this gap, we examined the spatial distributions of elements in cross-sections of micronodules from the western tropical North Pacific Ocean using high-resolution (HR) LA-ICP-MS raster mapping coupled with laser Raman and X-ray photoelectron spectroscopy (XPS). The ferromanganese micronodules we studied are dominated by Fe and Mn oxides with minor carbonate minerals, such as siderite, rhodochrosite and calcite. LA-ICP-MS maps show that these micronodules consist of a Mn-rich core and a Fe-rich rim. The Fe-enriched rim is enriched in As and surrounds a Mg, Mn, Cu, Co and Ni concreted core. Laser Raman maps show that the micronodule core contains more birnessite, an important scavenger of trace metals in deep sea sediments, than the rim. The birnessite filled core of these micronodules does not have elevated REY. Indeed, birnessite line channels may feed metal-rich fluid containing REY to adjacent minerals, including well-crystallized bio-apatite and zeolite, as high Ce and Y levels are spatially correlated with these minerals. The observed element profiles and XPS observations showing the coexistence of multiple oxidation states of Mn (+2, +3 and +4), Fe (+2 and +3) and Ce (+3, +4) demonstrate that the Fe Mn phases of these micronodules are of a diagenetic origin and that they are sites of redox-driven metal enrichment in deep-sea sediment.

The layered manganese dioxide (δ-type MnO2) film electrodeposited on carbon cloth (CC) functioned as a cathode in aqueous zinc-ion batteries. Battery performance was notably improved by doping MnO2...

The polygenic mineral composition of Mn crusts from Belyaevskii Volcano of the Central Basin of the Sea of Japan is determined. The crusts are found for the first time to contain rhodochrosite, manganosite, quenselite, heterolith, manganotantalite, and tungomelane in addition to the previously described todorokite, birnessite, manganite, pyrolusite, and vernadite. Among ore minerals, the breccia crusts include magnetite, titanomagnetite, hematite, pyrite, pyrrhotine, galena, monazite, cerianite, baddeleyite, and pentlandite, while fragments of manganite have silver and numerous particles of copper gold. A significant role in the formation of the mineral composition of the crust was likely played by pore waters involved in the hydrothermal process and organic matter (OM) of the Miocene–Quaternary siliceous–argillaceous strata, which served as the source of many rare and noble metals and affected the redox conditions of mineral formation.

The adsorption-oxidation of Sb on manganese oxide plays an important role in controlling Sb mobility and fate in soils and sediments. Widespread organic substances such as microbes may greatly affect this process, and deserve a careful investigation. This study examines the adsorption and oxidation of Sb(III, V) on birnessite, a typical manganese oxide, with and without Bacillus cereus cells. Adsorption isotherms were conducted to explore the adsorption capacity of Sb to the birnessite–bacteria composite. X-ray photoelectron spectroscopy (XPS) was applied to determine the valence state of Mn and the adsorbed Sb species. The SEM results show that birnessite adheres to the outer surface of bacterial cells, and the aggregation of minerals occurs to a lesser extent in the presence of cells. Batch adsorption results show a much larger Sb adsorption on individual birnessite than on bacteria, and the measured Sb adsorption to the birnessite–bacteria composite is larger than that predicted assuming additive, i.e., the sum of the end-member metal adsorptivities. On birnessite, Sb(III) is predominately oxidized to Sb(V) according to the XPS analysis, and the presence of bacteria hinders this oxidation reaction. We propose that microbe−birnessite association favors the immobilization of Sb on solid phases, but can inhibit the oxidation of Sb(III) to Sb(V), which is of great significance for evaluating the toxicity, bio-availability, and mobility of Sb in both natural and contaminated environments.

The development of efficient and noble-metal-free electrocatalysts for the challenging oxygen evolution reaction (OER) is crucial for sustainable energy solutions. In this work, a facile co-precipitation method, followed by thermal postsynthetic treatment in N2/air, was developed to synthesize molybdenum-doped α-Mn2O3 materials (Mn2O3:1.72%Mo, Mn2O3:2.64%Mo, Mn2O3:32.23%Mo, and Mn2O3:49.67%Mo) as low-cost water-oxidizing electrocatalysts. Powder X-ray diffraction (PXRD), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) investigations showed the presence of strong distortions in the molybdenum-doped α-Mn2O3 host lattice (Mn2O3:2.64%Mo) and an average oxidation state of Mn2.8+. Several test assays demonstrated that these structural features significantly promote the OER activity. Mn2O3:2.64%Mo was found to exhibit very good activity among the series in cerium ammonium nitrate (CAN)-assisted water oxidation with a maximum turnover frequency (TOF) of 585 μmol O2 m–2 h–1, which is a 15-fold improvement of the pure α-Mn2O3 activity and higher than the value of the previously reported benchmark Mn-based catalyst, birnessite. The optimized catalyst (Mn2O3:2.64%Mo) excelled through a low onset potential (300 mV) and a promising overpotential of 570 mV for OER at a current density of 10 mA cm–2, which is only 20 mV above that of the noble metal benchmark RuO2 electrode and competitive with that of the most active Mn-based OER catalysts reported to date. Electrochemical impedance spectroscopy (EIS) studies demonstrated that the catalytically active surface area of Mn2O3:2.64%Mo is much higher than that of α-Mn2O3 for the OER at the applied potential. In addition, stability during 30 h without degradation was achieved, which exceeds that of a wide range of current noble-metal-free electrocatalysts. Our study provides a facile and effective approach for the preparation of economical and high-performance manganese-based electrocatalysts for water oxidation.

Although δ-MnO2 with a layered structure is a promising electrode material for supercapacitors, its poor electronic conductivity and structural instability limit its electrochemical performance. In this work, structure reinforced birnessite with improved electron transfer is developed via Cr doping in δ-MnO2 using hydrothermal synthesis. The Cr-doped δ-MnO2 exhibits significantly improved specific capacitance and cycling stability in an extended potential window (0–1.2 V vs. Ag/AgCl) compared to pristine δ-MnO2. Specifically, the 2 mol% Cr-doped δ-MnO2 (0.02CrMO) electrode exhibits large specific capacitances of 250 F g−1 at 0.2 A g−1 and 150 F g−1 at 10 A g−1 (∼5 mg cm−2 mass loading) as well as an outstanding capacitance retention of 82.6% after 30 000 cycles. Both calculations and experimental results demonstrate that Cr doping in δ-MnO2 can narrow the band gap, enhance electron transfer, and strengthen the layered structure with suppressed Jahn–Teller distortion, resulting in reduced Mn dissolution and phase transition.

Birnessite-type manganese oxides and their magnetic composites with iron oxides are known due to their effective properties in water oxidation catalysis (WOC). The present work demonstrates how transition metal ion doping influences the WOC performances of magnetic and non-magnetic MnOx catalysts in a comparative manner. Transition metal cation (TM = Cr3+, Co2+, Ni2+, Cu2+, Zn2+) doped layered birnessite and birnessite-manganese ferrite composite nanocatalysts were synthesized and characterized. Core-shell type, magnetic composite catalyst particles of similar to 150 nm diameter were obtained by in situ deposition of birnessite shells onto 50-60 nm sized manganese ferrite spheres by reducing MnO4- ions with propionic acid in the presence of the TM ions. The resulting TM-doped catalyst materials were analyzed by XRD, SEM, TEM, IR, TGA and AAS to verify their compositions, structures and morphologies. WOC activities and stabilities were comparatively examined in both chemical (using Ce4+ as sacrificial oxidant at pH similar to 1-2) and electrochemical (pH 7, screen-printed particles on FTO) test setups. In both types of experiments, the highest catalytic activity was observed for catalysts doped with Co2+ ions, followed by Ni2+-doped samples. In comparison to the K-birnessite reference material, the Co2+- and Ni2+-doped analogs were additionally found to be more stable and more active in the chemical and long-term electrocatalysis measurements, demonstrating the potential of TM-doping to improve the performance of magnetic-MnOx-based WOC materials. In addition, the formation of a magnetic core-shell structure converts the micron-sized amorphous MnO2 particles to spherical at the nanoscale and thus facilitates the mass-energy transfer throughout the entire catalyst surface.

In the past few years, intensive attention has been focused on birnessite based electrodes for supercapacitors. Much progress has been achieved in developing birnessite based nanostructures with high electrochemical performance. However, challenges still remain in taking full advantage of birnessite and building smart structures to overcome the gap between the obtained capacitance and its theoretical capacitance. In this review, the basic information on birnessite and its preparation strategies are summarized and the current challenges are put forward. Finally, some new strategies for preparing high electrochemical performance birnessite based nanostructures are highlighted.

Anaerobic oxidation of methane (AOM) is a major biological process that reduces global methane emission to the atmosphere. Anaerobic methanotrophic archaea (ANME) mediate this process through the coupling of methane oxidation to different electron acceptors, or in concert with a syntrophic bacterial partner. Recently, ANME belonging to the archaeal family Methanoperedenaceae (formerly known as ANME-2d) were shown to be capable of AOM coupled to nitrate and iron reduction. Here, a freshwater sediment bioreactor fed with methane and Mn(IV) oxides (birnessite) resulted in a microbial community dominated by two novel members of the Methanoperedenaceae, with biochemical profiling of the system demonstrating Mn(IV)-dependent AOM. Genomic and transcriptomic analyses revealed the expression of key genes involved in methane oxidation and several shared multiheme c-type cytochromes (MHCs) that were differentially expressed, indicating the likely use of different extracellular electron transfer pathways. We propose the names “Candidatus Methanoperedens manganicus” and “Candidatus Methanoperedens manganireducens” for the two newly described Methanoperedenaceae species. This study demonstrates the ability of members of the Methanoperedenaceae to couple AOM to the reduction of Mn(IV) oxides, which suggests their potential role in linking methane and manganese cycling in the environment.

Manganese oxides (MnO2) are a class of promising electrode materials for high-performance supercapacitors. Among various possible crystal phases of MnO2, the two-dimensional layered birnessite (δ-MnO2) is considered to facilitate cation intercalation/deintercalation with little structural rearrangement during the charging and discharging process. Here, we report a facile strategy for synthesis of δ-MnO2 with significantly enhanced electrochemical capacitive energy storage performance via phase transformation of orthorhombic MnO2. The resultant δ-MnO2 delivers a specific capacitance of 251.4 F g−1 at a current density of 1 A g−1, which is almost three times higher than that of the original orthorhombic phase. The solid-state flexible asymmetric supercapacitor based on birnessite MnO2 as the positive electrode possesses an operating potential window as high as 2.0 V as well as high energy density and power density. This work demonstrates the post crystal engineering of MnO2 is an effective way to optimize their electrochemical properties.

Biogenic manganese oxides (BMOs) have attractive environmental applications owing to their metal sequestration and oxidizing abilities. Although Co readily accumulates into Mn oxide phases in natural environments, the Co2+ sequestration process that accompanies the enzymatic Mn(II) oxidation of exogenous Mn2+ remains unknown. Therefore, we prepared newly formed BMOs in a liquid culture of Acremonium strictum KR21-2 and conducted repeated sequestration experiments in a Mn2+/Co2+ binary solution at pH 7.0. The sequestration of Co2+ by newly formed BMOs (~1 mM Mn) readily progressed in parallel with the oxidation of exogenous Mn2+, with higher efficiencies than that in single Co2+ solutions when the initial Co2+ concentrations (0.16–0.8 mM) were comparable to or lower than the exogenous Mn2+ concentration (~0.8 mM). This demonstrates a synergetic effect on Co sequestration. Powder X-ray diffraction showed a typical pattern for asbolane only when newly formed BMOs were treated in Mn2+/Co2+ binary systems, implying that the enzymatic Mn(II) oxidation by newly formed BMOs favored asbolane formation. Cobalt K-edge X-ray absorption near-edge structure measurements showed that both Co(II) and Co(III) participated in the formation of the asbolane phase in the binary solutions, whereas most of the primary Co2+ was sequestered as Co(III) in the single Co2+ solutions, which partly explains the synergetic effects on Co sequestration efficiency in the binary solutions. The results presented here provide new insights into the mechanism of Co interaction with Mn oxide phases through asbolane formation by enzymatic Mn(II) oxidation under circumneutral pH conditions.

International audience; Our understanding of the up to seven orders of magnitude partitioning of thallium (Tl) between seawater and ferromanganese (FeMn) deposits rests upon two foundations: (1) being able to quantify the Tl(I)/Tl(III) ratio that reflects the extent of the oxidative scavenging of Tl by vernadite (δ-MnO2), the principle manganate mineral in oxic and suboxic environments, and (2) being able to determine the sorption sites and bonding environments of the Tl(I) and Tl(III) complexes on vernadite. We investigated these foundations by determining the oxidation state and chemical form of Tl in FeMn crusts and nodules from the global oceans at a Tl concentration ranging from several hundreds ppm (mg/kg) down to the low ppm level. Seventeen hydrogenetic crusts and eleven nodules from the Pacific, Atlantic, and Indian oceans and Baltic Sea were characterized by chemical analysis, X-ray diffraction, Raman spectroscopy, Mn K-edge X-ray absorption near-edge structure (XANES) spectroscopy, and Tl L3-edge high energy-resolution XANES (HR-XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The Tl concentration increases linearly from 1.5 to 319 ppm with the Mn/Fe ratio in Fe-vernadite from hydrogenetic crusts, whereas the percentage of Tl(III) to total Tl varies between 62% and 100% independent of both the Mn/Fe and Mn(III)/Mn(IV) 2 ratios. The data, complemented by molecular modeling of the Tl(III) coordination and by XANES calculations, suggest that the enrichment of Tl in Fe-vernadite is driven by (1) the oxidative uptake of octahedrally coordinated Tl(III) above the vacant Mn(IV) sites and on the layer edges of the vernadite layers, and (2) the sorption of Tl(I) on the crystallographic site of Ba at the surface of the vernadite layers, which is analog to the surface site of K. Thus, Tl has a high affinity for vernadite regardless of its oxidation state, and the lack of correlation between Tl(III) and the Mn/Fe ratio in FeMn crusts is explained by the affinity of Tl(I) for the Ba site. The Tl concentration varies between 2 and 112 ppm in surface and buried nodules independent of the Mn/Fe ratio, and the percentage of Tl(III) varies between 0% and 100%. Nodules subjected to sediment diagenesis with replacement of layered vernadite by tunneled todorokite are depleted in Tl and have more reduced thallium. Knowledge of the complex interplay of mineralogy, surface chemical processes, and crystallographic siting are required to understand the variability of Tl concentrations, redox state, and acquisition processes by marine FeMn deposits.

Layered double hydroxides (LDHs) have been intensively studied for phosphate (Pi) removal but suffer from poor stability and low sorption affinity under ambient conditions. In this paper, well crystallized MnIIFeIIFeIII-Cl, MnIIFeIII-CO3 and novel MnIVFeIII-CO3 LDHs were synthesized. The LDHs show fast Pi sorption with 90 % uptake within 20 min, and high Pi sorption capacity of 11 mg P/g at low solution Pi concenrations of 0.1 mg P/L, corresponding to a very high Pi sorption affinity (Kd 1.1 × 105 L/kg). Fast MnII dissolution from the MnIIFeIIFeIII-Cl LDHs and formation of MnFe2O4 at pH 7 were observed in aqueous suspensions of non-oxidized material where up to 70% of total Mn was released within 2 h. However, when interlayer Cl- was exchanged with CO32−, much lower Mn dissolution (5.4%) was observed. Furthermore, after oxidation of MnII to MnIV, the obtained MnIVFeIII-CO3 LDH maintained the layered structure of LDH and the particles were surrounded by birnessite nanorods. The MnIVFeIII-CO3 LDH showed excellent stability but lower Pi sorption capacity. However, a high sorption affinity was maintained which is attributed to more positively charged Fe-centered sorption sites. XPS and ATR-FTIR data together with DFT calculations demonstrated that Pi was mainly sorbed via the formation of mononuclear mono- and bidentate Pi surface complexes on planar LDH particle surfaces.

A very low concentration of manganese (Mn) in water is a critical issue for municipal and industrial water supply systems. Mn removal technology is based on the use of manganese oxides (MnOx), especially manganese dioxide (MnO2) polymorphs, under different conditions of pH and ionic strength (water salinity). The statistical significance of the impact of polymorph type (akhtenskite ε-MnO2, birnessite δ-MnO2, cryptomelane α-MnO2 and pyrolusite β-MnO2), pH (2–9) and ionic strength (1–50 mmol/L) of solution on the adsorption level of Mn was investigated. The analysis of variance and the non-parametric Kruskal–Wallis H test were applied. Before and after Mn adsorption, the tested polymorphs were characterized using X-ray diffraction, scanning electron microscope techniques and gas porosimetry analysis. Here we demonstrated the significant differences in adsorption level between MnO2 polymorphs’ type and pH; however, the statistical analysis proves that the type of MnO2 has a four times stronger influence. There was no statistical significance for the ionic strength parameter. We showed that the high adsorption of Mn on the poorly crystalline polymorphs leads to the blockage of micropores in akhtenskite and, contrary, causes the development of the surface structure of birnessite. At the same time, no changes in the surfaces of cryptomelane and pyrolusite, the highly crystalline polymorphs, were found due to the very small loading by the adsorbate.

Investigating the interfaces between electrolytes and electrocatalysts during electrochemical water oxidation is of great importance for an understanding of the factors influencing catalytic activity and stability. Here, the interaction of a well-established, nanocrystalline and mesoporous Ca-birnessite catalyst material (initial composition K0.2Ca0.21MnO2.21·1.4H2O, initial Mn-oxidation state ∼+3.8) with an aqueous potassium phosphate buffer electrolyte at pH 7 was studied mainly by using various electron microscopy and X-ray spectroscopy techniques. In comparison to electrolyte solutions not containing phosphate, the investigated Ca-birnessite electrodes show especially high and stable oxygen evolution activity in phosphate buffer. During electrolysis, partial ion substitutions of Ca2+ by K+ and OH−/O2− by HnPO4(3−n)− were observed, leading to the formation of a stable, partially disordered Ca–K–Mn–HnPO4–H2O layer on the outer and the pore surfaces of the active electrocatalyst material. In this surface layer, Mn3+ ions are stabilized, which are often assumed to be of key importance for oxygen evolution catalysis. Furthermore, evidence for the formation of [Ca/PO4/H2O]− complexes located between the [MnO6] layers of the birnessite was found using the soft Ca 2p and Ca L-edge X-ray spectroscopy. A possible way to interpret the observed, obviously very favorable “special relationship” between (hydrogen)phosphates and Ca-birnessites in electrocatalytic water oxidation would be that HnPO4(3−n)− anions are incorporated into the catalyst material where they act as stabilizing units for Mn3+ highly active centers and also as “internal bases” for the protons released during the water-oxidation reaction.

Manganese oxides occur in a wide range of environmental settings either as coatings on rocks, sediment, and soil particles, or as discrete grains. Although the production of biologically mediated Mn oxides is well established, relatively little is known about microbial-specific strategies for utilizing Mn in the environment and how these affect the morphology, structure, and chemistry of associated mineralizations. Defining such strategies and characterizing the associated mineral properties would contribute to a better understanding of their impact on the local environment and possibly facilitate evaluation of biogenicity in recent and past Mn accumulations. Here, we supplement field data from a Mn rock wall deposit in the Ytterby mine, Sweden, with data retrieved from culturing Mn oxidizers isolated from this site. Microscopic and spectroscopic techniques are used to characterize field site products and Mn precipitates generated by four isolated bacteria (Hydrogenophaga sp., Pedobacter sp., Rhizobium sp., and Nevskia sp.) and one fungal-bacterial co-culture (Cladosporium sp.—Hydrogenophaga sp. Rhizobium sp.—Nevskia sp.). Two of the isolates (Pedobacter sp. and Nevskia sp.) are previously unknown Mn oxidizers. At the field site, the onset of Mn oxide mineralization typically occurs in areas associated with globular wad-like particles and microbial traces. The particles serve as building blocks in the majority of the microstructures, either forming the base for further growth into laminated dendrites-botryoids or added as components to an existing structure. The most common nanoscale structures are networks of Mn oxide sheets structurally related to birnessite. The sheets are typically constructed of very few layers and elongated along the octahedral chains. In places, the sheets bend and curl under to give a scroll-like appearance. Culturing experiments show that growth conditions (biofilm or planktonic) affect the ability to oxidize Mn and that taxonomic affiliation influences crystallite size, structure, and average oxidation state as well as the onset location of Mn precipitation.

The layered birnessite derivatives as intercalation cathode materials for rechargeable batteries and supercapacitors receive great attention due to the abundant, low-cost, highly safe, and environmentally friendly manganese element. However, the practical application of chemically synthesized birnessite in energy storage has been restricted by low specific capacity and poor cyclability because of the limited interlayer metal ions intercalation and inferior structural stability during cycling. In this focused review, we discuss the origin of unsatisfying charge storage performance of the chemically synthesized birnessite and disclose the reinforced birnessite structures derived from spinel Mn3O4 by in-situ electrochemical conversion. With enhanced structural stability and large interlayer distance, the electrochemically converted birnessite shows promising electrochemical performance in various batteries and supercapacitors. Finally, critical perspectives on the future development of layered birnessite from spinel Mn3O4 are provided, which may guide advanced electrode design for high-performance sustainable batteries.

Biogenic Mn oxides (BMOs) have become captivating with regard to elemental sequestration, especially at circumneutral pH conditions. The interaction of BMOs with oxyanions, such as vanadate (V), molybdate (VI), and tungstate (VI), remains uncertain. This study examined the sequestration of V(V), Mo(VI), and W(VI) (up to ~1 mM) by BMOs formed by the Mn(II)-oxidizing fungus, Acremonium strictum KR21-2. When A. strictum KR21-2 was incubated in liquid cultures containing either Mo(VI) or W(VI) with soluble Mn2+, the oxyanions were sequestered in parallel with enzymatic Mn(II) oxidation with the maximum capacities of 8.8 mol% and 28.8 mol% (relative to solid Mn), respectively. More than 200 μM V(V) showed an inhibitory effect on growth and Mn(II) oxidizing ability. Sequestration experiments using preformed primary BMOs that maintained the enzymatic Mn(II) oxidizing activity, with and without exogenous Mn2+, demonstrated the ongoing BMO deposition in the presence of absorbent oxyanions provided a higher sequestration capacity than the preformed BMOs. X-ray diffraction displayed a larger decline of the peak arising from (001) basal reflection of turbostratic birnessite with increasing sequestration capacity. The results presented herein increase our understanding of the role of ongoing BMO formation in sequestration processes for oxyanion species at circumneutral pH conditions.