Oxidation State Of Manganese Research Articles

Ferromagnetism in single-valent manganites

Structural and magnetization measurements have been performed on the La0.7Sr0.3Mn0.85Nb0.15-x5+Mgx2+O3 stoichiometric compounds. With rise of the Mg2+ content the formal oxidation state manganese increases from +3 (x=0) up to +3.55 (x=0.15). The compositions with 0⩽x≤0.08 undergo a structural transition from rhombohedral to orthorhombic symmetry below room temperature whereas x=0.1 and x=0.15 compounds are rhombohedral down to 2K. The structural parameters evidence that the orthorhombic phase is not long-range orbitally ordered and that the structural transition is associated with a steric effect. The Mg-free compound is ferromagnetic with the Curie point of around 150K and a magnetic moment of 3.1 μB/Mn. The substitution of Nb5+ with Mg2+ leads to a gradual weakening of the ferromagnetic component while in the x=0.15 compound A-type antiferromagnetic short-range order is stabilized in spite of macroscopic R3¯c symmetry. All the compositions show insulating behavior. It is suggested that ferromagnetism is originated from superexchange interactions via oxygen. Covalence enhances the positive part of the superexchange interactions whereas structural disorder induced by Nb5+ and Mg2+ ions leads to suppression of ferromagnetism.

Mn2+ Substitutional Doping of TiO2 Nanoribbons: A Three-Step Approach

An in situ doping approach was successfully employed for synthesis of Mn2+-doped sodium titanate nanoribbons, which were used as a precursor for preparation of TiO2 nanoribbons with homogeneous distribution of Mn2+ ions. The comprehensive structural characterization using powder X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) provided compelling evidence that the Mn2+ ion predominantly substitutes the Ti4+ ion at octahedral coordination sites in bulk. Measurements performed on individual nanoribbons using near edge X-ray absorption fine structure spectromicroscopy revealed that the strong alkaline environment required for the formation of sodium titanate nanoribbons did not affect the manganese oxidation state. In the next two steps, the ion exchange process in HCl(aq) solution followed by the thermal treatment in air, lead to the formation of Mn2+ doped TiO2 nanoribbons. Analysis of the manganese content by X-ray photoelectron spectroscopy of several TiO2 nanoribbon samples calcined in the temperature range from 400 to 700 °C as well as analysis performed at the Ti L2,3 and Mn L2,3 edges with electron energy loss spectroscopy (EELS) showed that calcination at elevated temperatures induced the diffusion of manganese ions toward the nanoribbons’ surface. However, transformation of anatase nanoribbons to rutile nanoparticles, this process started at around 580 °C, was also accompanied by the partial oxidation of Mn2+ to Mn3+ and Mn4+. Manganese atoms that diffused to the TiO2 surface preferentially formed MnOx clusters as observed from characteristic electron paramagnetic resonance spectra and EELS measurements. In addition, the presence of Mn2+ reduced the beginning of phase transformation from anatase to rutile to near 120 °C.

Study on the electrochemical behavior of nanostructure S-doping manganese oxide as a novel supercapacitor material.

A nanostructure S-doping manganese oxide (MnO(x)S(y)) amorphous powder was prepared by a homogeneous coprecipitation method for supercapacitor application. The structure and surface morphology of the as-prepared MnO(x)S(y) powder were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis and X-ray photoelectron spectroscopy (XPS). The as-prepared nanostructure S-doping manganese oxide powder was confirmed with a chemical composition of MnO1.26S0.23 by elemental analysis, in which the average oxidation state of manganese is about 3.1. The supercapacitive behavior of the as-prepared MnO1.26S0.23 was studied by means of cyclic voltammetry (CV) and constant current charge-discharge cycling (CD) experiments in 1 mol L(-1) Na2SO4 electrolyte. A maximum specific capacitance of 181 F g(-1) was obtained for MnO1.26S0.23. Furthermore, the specific capacitance remained 97.3% of the original value after 500 cycles. The superior capacitive behavior and better cycling stability indicate that the amorphous nanostructure MnO(x)S(y) maybe a promising electrode material for electrochemical capacitors.

Nano-MnOx on activated carbon prepared by hydrothermal process for fast and highly efficient degradation of azo dyes

Azo dyes are recalcitrant and refractory pollutants that pose a threat to environmental safety. Therefore, it is of significance to develop fast, cheap and highly effective materials for removal of azo dyes in water. Herein, fast oxidative removal of azo dyes by highly active nano-MnOx on activated carbon prepared via hydrothermal process was explored. Active manganese oxide was supported on coconut shell activated carbon (CSAC) via hydrothermal method and was characterized. The hydrothermal treatment changed the morphology of the MnOx@CSAC and led to the in situ synthesis of nano-MnOx onto CSAC surfaces with the incorporation of the multi-valence oxidation states (Mn4+ and Mn3+) of manganese. The decolorization reactions by MnOx@CSAC were fast and the dye removal was most pronounced at pH 3 (99.1%). Through GC-MS analyses, the most detectable degradation products were identified and possible degradation pathway was proposed. Additionally, the MnOx@CSAC also could effectively degrade other anionic dyes. The oxidative degradation of C. I. Acid Red 73 was still strong after 20 usage cycles, with a maximum removal rate of 99.1% and a minimum removal rate of 89.7% from the same sample. Overall, these results indicate that highly active nano-MnOx@CSAC prepared via a hydrothermal method is very attractive, implying that this material has potential practical applications for treating azo dyeing effluent.

On the Oxidation State of Manganese in Li-Ion Cells: A New Perspective

It has been long recognized that dissolution of transition metals, particularly Mn, at the positive electrode is the starting point for a major performance degradation mechanism in Li-ion batteries (LIBs).1-4 We present recent X-ray absorption spectroscopy data on components from LixMn2O4 spinel – graphite (LMO-GR) cells with 1M LiPF6in an ethylene carbonate : diethyl carbonate (1:2 v/v) electrolyte, after 20 days of cycling at 50 °C with 100% depth of discharge and C/5 rate.Results from the Mn K edge (6539 eV) XANES analysis indicate average oxidation states near +3 for Mn cations in the graphite electrodes and separators from cells that were subjected to a 48 hour stand (in either discharged or charged state) subsequent to the high-temperature galvanostatic cycling, see Fig. 1. This suggests that Mn metal or in oxidation state +2 can only be minor fractions of the Mn existing outside the positive electrode of a Li-ion battery. Our results run counter to the prevailing view that Mn2+ cations arising from a disproportionation reaction of two Mn3+cations at the positive electrode, followed by dissolution into and migration through the electrolyte, and ending with deposition at the negative electrode, are widely responsible for the performance degradation observed in graphite-LMO LIBs. We will discuss the possible sources of discrepancy between our results and previously published data, as well as the implications of our results for measures to mitigate the Mn dissolution related LIB performance degradation mechanism, see Fig. 2.

Microporous assembly of MnO2 nanosheets for malachite green degradation

Porous assembly of MnO2 nanosheets has been prepared via a simple redox co-precipitation method using Mn(OAc)2 and KMnO4. The material has been characterized by XRD, XPS, FESEM, TEM, FTIR, and N2-adsorption–desorption analyses. The as-prepared MnO2 nanomaterial is microporous (average pore diameter: 0.8nm; surface area: 162m2/g) and poorly crystalline. The TEM and SEM images reveal the formation of spherical assembly of fine nanosheets. The oxidation state of manganese is determined by XPS analysis. The porous nature and the oxidizing property of the nano MnO2 has been exploited for MG degradation in aqueous media under ambient condition. The effects of various parameters (such as pH, MnO2 dose, initial MG concentration, air/O2, and organic acids) on MG degradation are evaluated. The mineralization of MG is monitored through TOC analyses. About 99% decolorization and ∼44% mineralization of MG (conc.: 50mg/L) is achieved in 120min with MnO2 (dose: 0.5g/L). The decolorization follows first order kinetics. During the oxidative degradation, slight leaching of Mn2+ is observed. The reusability of the material has been shown for three consecutive cycles with good performance.

Scalable synthesis and electrochemical investigations of fluorine-doped lithium manganese spinel oxide

A scalable synthesis route for the preparation of fluorine-doped lithium manganese spinel was developed. The effect of 2.5% fluorine doping on the properties of aluminum-doped lithium manganese spinel was investigated by examining the electrochemical performance and structural changes. The electrochemical study indicates that the initial discharge capacity increases by about 5% while other properties, like the capacity retention and rate performance, remain almost unchanged. The structural studies indicate that no impurity phase was formed, along with only little morphological changes and a slight increase in the lattice parameter. The Mn K-edge absorption spectra clearly show that the average manganese oxidation state decreases as a result of fluorine doping and Mn LII,III -edge spectra indicate that the electronic structure of the fluorine-doped spinel changes significantly, which may alleviate the intrinsic structural instability of this material.

Plasma-Catalytic Oxidation of Toluene on MnxOy at Atmospheric Pressure and Room Temperature

MnxOy/SBA-15 catalysts were prepared via the impregnation method and utilized for toluene removal in dielectric barrier discharge plasma at atmospheric pressure and room temperature. The catalysts were characterized by X-ray diffraction, N2 adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, and O2 temperature-programmed desorption methods. The characterization results indicated that manganese loading did not influence the 2D-hexagonal mesoporous structure of SBA-15. The catalyst had various oxidation states of manganese (Mn2+, Mn3+, and Mn4+), with Mn3+ being the dominant oxidation state. Toluene removal was investigated in the environment of pure N2 and 80 % N2 + 20 % O2 plasma, showing that the toluene removal efficiency and CO2 selectivity were noticeably increased by MnxOy/SBA-15, especially in the presence of 5 % Mn/SBA-15. This activity was closely related to the high dispersion of 5 % Mn on SBA-15 and the lowest reduction temperature exhibited by this catalyst. Mn loading increased the yield of CO2 in the N2 plasma and promoted the deep oxidation of toluene. During toluene oxidation, oxygen exchange might follow a pathway, wherein bulk oxygen was released from the MnxOy/SBA-15 surface; gas-phase O2 subsequently filled up the vacancies created on the oxide. Each of the manganese oxidation states played an important role; Mn2O3 was considered as a bridge for oxygen exchange between the gas phase and the catalyst, and Mn3O4 mediated transfer of oxygen between the catalyst and toluene.

Oxide Wizard: An EELS Application to Characterize the White Lines of Transition Metal Edges

Physicochemical properties of transition metal oxides are directly determined by the oxidation state of the metallic cations. To address the increasing need to accurately evaluate the oxidation states of transition metal oxide systems at the nanoscale, here we present "Oxide Wizard." This script for Digital Micrograph characterizes the energy-loss near-edge structure and the position of the transition metal edges in the electron energy-loss spectrum. These characteristics of the edges can be linked to the oxidation states of transition metals with high spatial resolution. The power of the script is demonstrated by mapping manganese oxidation states in Fe3O4/Mn3O4 core/shell nanoparticles with sub-nanometer resolution in real space.

Mn(II) Deposition on Anodes and Its Effect on Capacity Fade in Spinel LiMn2O4-Carbon System

Dissolution and migration of manganese from cathode lead to severe capacity fading of Li2MnO4-carbon cells. Overcoming this major problem requires better understanding of the mechanism of manganese dissolution, migration, and deposition. Here, we apply a variety of advanced analytical methods to the study of LiMn2O4 cathodes cycled with different anodes. We provide solid evidence, for the first time, that oxidation state of manganese deposited on the anodes is +2, which differs from the results reported earlier. The results also indicates that a metathesis reaction between Mn(II) and some species on the solid-electrolyte interphase takes place during the deposition of Mn(II) on the anodes, rather than a reduction reaction that leads to the formation of metallic Mn otherwise, as speculated in earlier studies. The concentration of Mn deposited on the anode increases gradually with cycles; this trend is well correlated with anode’s rising impedance and capacity fading of the cell.

Manganese Oxidation State as a Cause of Irritant Patch Test Reactions

Manganese chloride (MnCl2) 2.5% is included in the extended metals patch test series to evaluate patients for contact hypersensitivity to this metal salt. The objective of this study was to prospectively determine the rate of allergic and irritant patch test reactions to MnCl2 (Mn(II)), Mn2O3 (Mn(III)), and KMnO4 (Mn(VII)) in a cohort of patients undergoing patch testing. Fifty-eight patients were patch tested with MnCl2, Mn2O3, and KMnO4, each at 2.5% in petrolatum. Patch readings were taken at 48, and 72 or 96 hours, and scored using standard methods. Cultured monolayers of keratinocytes (KCs) were exposed to MnCl2, Mn2O3, and KMnO4 in aqueous culture medium, and cell survival and cytokine release were studied. MnCl2 caused irritant patch test reactions in 41% of the cohort, whereas Mn2O3 and KMnO4 caused a significantly lower rate of irritant reactions (both 3%). No allergic morphologies were observed. Similarly, in cultured KC monolayers, only MnCl2 was cytotoxic to KC and induced tumor necrosis factor α release.The oxidation state of manganese used for patch testing affects the irritancy of this metal salt, as Mn(II) caused an unacceptably high rate of irritant reactions in a cohort of patients. In vitro studies confirmed these clinical data, as only Mn(II) was cytotoxic to cultured monolayers of KC.

Oxidation state of cross-over manganese species on the graphite electrode of lithium-ion cells

It is well known that Li-ion cells containing manganese oxide-based positive electrodes and graphite-based negative electrodes suffer accelerated capacity fade, which has been attributed to the deposition of dissolved manganese on the graphite electrodes during electrochemical cell cycling. However, the reasons for the accelerated capacity fade are still unclear. This stems, in part, from conflicting reports of the oxidation state of the manganese species in the negative electrode. In this communication, the oxidation state of manganese deposited on graphite electrodes has been probed by X-ray absorption near edge spectroscopy (XANES). The XANES features confirm, unequivocally, the presence of fully reduced manganese (Mn(0)) on the surface of graphite particles. The deposition of Mn(0) on the graphite negative electrode acts as a starting point to understand the consequent electrochemical behavior of these electrodes; possible reasons for the degradation of cell performance are proposed and discussed.

Water oxidation by manganese oxides formed from tetranuclear precursor complexes: the influence of phosphate on structure and activity

Two types of manganese oxides have been prepared by hydrolysis of tetranuclear Mn(iii) complexes in the presence or absence of phosphate ions. The oxides have been characterized structurally using X-ray absorption spectroscopy and functionally by O2 evolution measurements. The structures of the oxides prepared in the absence of phosphate are dominated by di-μ-oxo bridged manganese ions that form layers with limited long-range order, consisting of edge-sharing MnO6 octahedra. The average manganese oxidation state is +3.5. The structure of these oxides is closely related to other manganese oxides reported as water oxidation catalysts. They show high oxygen evolution activity in a light-driven system containing [Ru(bpy)3](2+) and S2O8(2-) at pH 7. In contrast, the oxides formed by hydrolysis in the presence of phosphate ions contain almost no di-μ-oxo bridged manganese ions. Instead the phosphate groups are acting as bridges between the manganese ions. The average oxidation state of manganese ions is +3. This type of oxide has much lower water oxidation activity in the light-driven system. Correlations between different structural motifs and the function as a water oxidation catalyst are discussed and the lower activity in the phosphate containing oxide is linked to the absence of protonable di-μ-oxo bridges.

Chemical vs. electrochemical extraction of lithium from the Li-excess Li1.10Mn1.90O4 spinel followed by NMR and DRX techniques

Lithium extraction from the Li-excess Li1.10Mn1.90O4 spinel has been performed by chemical and electrochemical methods in aqueous and in organic media, respectively. De-lithiated samples have been investigated by XRD, SEM, TG, (7)Li and (1)H MAS-NMR techniques. The comparative study has allowed demonstrating that the intermediate de-intercalated samples prepared during the chemical extraction by acid titration are similar to those prepared by the electrochemical way in a non-aqueous electrolyte. LiMn2O4 based spinel with a tailored de-lithiation degree can be prepared as a single phase by controlling the pH used in chemical extraction. (7)Li MAS-NMR spectroscopy has been used to follow the influence of the manganese oxidation state on tetra and octahedral Li-signals detected in Li-extracted samples. The oxidation of Mn(III) ions goes parallel to the partial dissolution of the spinel, following Hunter's mechanism. Based on this mechanism, a generalized chemical reaction has been proposed to explain the formation of intermediate Li(+) de-intercalated samples during acid treatment in aqueous media. By the (1)H MAS NMR study, no evidence of Li-H topotactic exchange in the bulk of the acid treated material was found.

Manganese: Its Speciation, Pollution and Microbial Mitigation

Manganese is known to be one of the essential trace elements and has plenty of applications. Inspite of its essential nature, concerns are arising due to its toxic nature at higher concentration. Several methods of removing manganese from environment have been proposed during the last few decades. However, the most favourable option based on cost-effectiveness, performance, and simplicity is still under investigation. The current review summarizes updated information on various technical aspects on manganese, including chemical nature, speciation, toxicity and remediation strategies. The review starts with covering the major sources of manganese, its interaction with biological biomolecules causing toxicity. This is followed by its speciation in environment, describing both biotic and abiotic processes. The biotic processes describe the role of microorganisms in the oxidation/ reduction of various oxidation states of manganese. Whereas, abiotic processes mainly describes the role of pH and oxygen taking thermodynamical aspects. The main part of this review focuses on recent developments on using microbial systems for manganese bioremediation. The updated works on different strategies adopted for the remediation of manganese from the environment have also been summarized.DOI: http://dx.doi.org/10.3126/ijasbt.v1i4.9164 Int J Appl Sci Biotechnol, Vol. 1(4): 162-170

Synergistic effect between MnO and CeO2 in the physical mixture: Electronic interaction and NO oxidation activity

MnO and CeO2 powders were mechanically mixed by a spatula and by milling to obtain loose-contact and tight-contact mixed oxides, respectively. The monoxides and their physical mixtures were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), Raman, O2 temperature-programmed desorption (O2-TPD), H2 temperature-programmed reduction (H2-TPR) and NO temperature-programmed oxidation (NO-TPO). The MnOx-CeO2 solid solutions did not form without any calcination process. The oxidation state of manganese tended to increase while the ionic valence of cerium decreased in the mixed oxides, accompanied with the formation of oxygen vacancies. This long-ranged electronic interaction occured more significantly in the tight-contact mixture of MnO and CeO2. The formation of more Mn4+ and oxygen vacancies promoted the catalytic oxidation of NO in an oxygen-rich atmosphere.

Determination of the oxidation states of metals and metalloids: An analytical review

The hazard of many heavy metals/metalloids in the soil depends on their oxidation state. The problem of determining the oxidation state has been solved due to the use of synchrotron radiation methods with the analysis of the X-ray absorption near-edge structure (XANES). The determination of the oxidation state is of special importance for some hazardous heavy elements (arsenic, antimony, selenium, chromium, uranium, and vanadium). The mobility and hazard of each of these elements depend on its oxidation state. The mobilities are higher at lower oxidation states of As, Cr, V, and Se and at higher oxidation states of Sb and U. The determination of the oxidation state of arsenic has allowed revealing its fixation features in the rhizosphere of hydrophytes. The known oxidation states of chromium and uranium are used for the retention of these elements on geochemical barriers. Different oxidation states have been established for vanadium displacing iron in goethite. The determination of the oxidation state of manganese in the rhizosphere and the photosynthetic apparatus of plants is of special importance for agricultural chemists.

Enzymatic Aerobic Alkene Cleavage Catalyzed by a Mn3+‐Dependent Proteinase A Homologue

New clothes for Mn3+: Aerobic alkene cleavage of styrene-type substrates by Trametes hirsuta is attributed to an enzyme that is dependent on manganese in oxidation state three. The enzyme has a proteinase backbone and binds Mn3+ exclusively via oxygen atoms, in contrast to all known Mn3+ enzymes.

Design of Desintering in Tin Dioxide Nanoparticles

Controlling sintering is a critical aspect for the processing of dense parts and to improve stability of nanoparticles. Dopants are typically used for this purpose, but the extension of the role of dopants in the phenomena is still not completely understood. In this work we demonstrate the possibility of inducing desintering in a ceramic system by programming a dopant redistribution during heat treatment. Tin dioxide doped with manganese was sintered up to intermediate densities and density was decreased afterward by exposing the sample to a lower temperature. A change in the oxidation state and ionic radius of manganese caused it to segregate at high temperatures and to partially redissolve in the crystal at a lower one. This interfacial chemistry change caused a decrease of the dihedral angle at lower temperature, creating a driving force for porosity volume increase (dedensification) by mass flow against curvature potential. The result is predictable from extrapolations of pore stability theories but n...

Mn(II) deposition on anodes and its effects on capacity fade in spinel lithium manganate–carbon systems

Dissolution and migration of manganese from cathode lead to severe capacity fading of lithium manganate-carbon cells. Overcoming this major problem requires a better understanding of the mechanisms of manganese dissolution, migration and deposition. Here we apply a variety of advanced analytical methods to study lithium manganate cathodes that are cycled with different anodes. We show that the oxidation state of manganese deposited on the anodes is +2, which differs from the results reported earlier. Our results also indicate that a metathesis reaction between Mn(II) and some species on the solid-electrolyte interphase takes place during the deposition of Mn(II) on the anodes, rather than a reduction reaction that leads to the formation of metallic Mn, as speculated in earlier studies. The concentration of Mn deposited on the anode gradually increases with cycles; this trend is well correlated with the anodes rising impedance and capacity fading of the cell.