Manganese Oxide Phases Research Articles

Oxygen vacancies lead to loss of domain order, particle fracture, and rapid capacity fade in lithium manganospinel (LiMn₂O₄) batteries.

Spinel-structured lithium manganese oxide (LiMn2O4) has attracted much attention because of its high energy density, low cost, and environmental impact. In this article, structural analysis methods such as powder neutron diffraction (PND), X-ray diffraction (XRD), and high-resolution transmission and scanning electron microscopies (TEM & SEM) reveal the capacity fading mechanism of LiMn2O4 as it relates to the mechanical degradation of the material. Micro-fractures form after the first charge (to 4.45 V vs. Li(+/0)) of a commercial lithium manganese oxide phase, best represented by the formula LiMn2O3.88. Diffraction methods show that the grain size decreases and multiple phases form after 850 electrochemical cycles at 0.2 C current. The microfractures are directly observed through microscopy studies as particle cracks propagate along the (1 1 1) planes, with clear lattice twisting observed along this direction. Long-term galvanostatic cycling results in increased charge-transfer resistance and capacity loss. Upon preparing samples with controlled oxygen contents, LiMn2O4.03 and LiMn2O3.87, the mechanical failure of the lithium manganese oxide can be correlated to the oxygen vacancies in the materials, providing guidance for better synthesis methods.

Cementicious Materials Reinforcement UsingAngustifolia kunthBamboo Fiber Covered with Nanostructured Manganese Oxide

In this work, to improve the interface interaction between natural fibers and a cementitious matrix, several Colombian Angustifolia kunth bamboo fibers were modified using different pretreatment methods before being covered with an inorganic phase of manganese oxide. The coating was performed by placing the fiber in contact with a manganese salt solution at low concentration, followed by drying of the fibers before performing physicochemical characterization. The fibers were characterized by atomic absorption, X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The coated fibers were added to a cementitious matrix, and the mechanical properties of the resulting composites were measured to determine the optimal treatment for reinforcing the cementitious matrix. The manganese content in the modified natural fibers obtained by atomic absorption was between 0.7 and 1.23 wt %, and the manganese oxide was deposited in a uniform manner onto the surface of the fiber, as indicated by the SEM images. The XRD patterns indicate some variation of the crystalline structure of cellulose, the TGA analysis indicates that the raw fiber lost more weight than did the covered fibers, and the FTIR revealed the vibrational bands associated with manganese oxide vibration. The mechanical properties measured by monitoring the flexural strength indicate the interplay between the physicochemical characterizations and the mechanical performance. Various samples of the composite material were prepared by varying the length, and the percentage of the addition of the fiber, and the flexural strength, toughness, energy index, and total energy of the samples were measured in all fibrocement materials; the measurement results indicate an improvement in the flexural strength of the materials occurred for the composite material synthesized with the addition of 2% fibers of 2.5 cm length.

Manganese-containing cellulose nanocomposites: The restrain effect of cellulose treated with NaOH/urea aqueous solutions

In this article, the manganese-containing cellulose nanocomposites were obtained using microcrystalline cellulose and Mn(CH3COO)2·4H2O in the NaOH/urea aqueous solutions by a efficient microwave-assisted method. The effects of the heating time and Mn(CH3COO)2·4H2O concentration on the cellulose nanocomposites were investigated. It was found that the microcrystalline cellulose pretreated with NaOH/urea aqueous solutions played an important role in the phase, shape, and thermal stability of manganese-containing cellulose nanocomposites. Well-crystalline phases of manganese oxides were not observed in the manganese-containing cellulose nanocomposites. Furthermore, well-crystalline phases of manganese oxides were not also observed by thermal treatment of the manganese-containing cellulose nanocomposites at 600°C for 3h. These results could be attributed to the restrain effect of cellulose treated with NaOH/urea aqueous solutions. It was supposed the possible mechanism during the phase transformation of cellulose nanocomposites.

Kinetic asymmetry in the growth of two-dimensional Mn oxide nanostripes

Nanostripes with very high (g20) aspect ratios of a two-dimensional manganese oxide phase are grown on the Ag(100) surface using a physical vapor deposition method and thoroughly characterized via low-energy electron diffraction and scanning tunneling microscopy. Despite the square pattern of the substrate, symmetry breaking is produced by the structural anisotropy of the kinetically stabilized, metastable Mn surface oxide phase. As rationalized by a first-principles analysis, the resulting asymmetry in edge diffusion and attachment energies and the difference in adsorption energetics between Mn and Ag adatoms leads to the kinetic formation of such strikingly anisotropic structural domains: they feature nanoscale width (\ensuremath{\approx}5--20 nm), mesoscopic length (up to \ensuremath{\approx}1 \ensuremath{\mu}), very low defect density, and grow along the high-symmetry directions of the Ag(100) substrate.

Nanosized Carbon‐Supported Manganese Oxide Phases as Lithium–Oxygen Battery Cathode Catalysts

AbstractThe poor discharge and recharge efficiency demonstrated by lithium–air batteries renders the search for highly active and inexpensive oxygen reduction and evolution catalysts crucial to the development of these energy‐storage and conversion devices. Previous works have shown that manganese oxides are promising lithium–oxygen cathode catalysts, which is in agreement with their remarkable activities for the reduction and evolution of oxygen in aqueous media. Motivated by these resembling catalytic behaviors, we prepared and characterized a number of manganese oxide modifications directly on carbon black and attempted to correlate their oxygen reduction and evolution activities in aprotic and aqueous electrolytes. Although our results cannot confirm this correlation, they provide valuable insight into the reaction mechanisms at play in each medium. More precisely, in 0.1 M potassium hydroxide, the reduction of oxygen is related to the reduction of a manganese(III) intermediate whereas the oxidation of hydrogen peroxide (which was regarded as a mimic of the lithium peroxide produced upon lithium–oxygen battery discharge) correlates with the transition between manganese(II) and manganese(III) phases. In the aprotic medium, manganese oxide cathodes prefilled with lithium peroxide showed a strong catalytic effect but were not active in the oxidation of lithium peroxide produced in the previous discharge. This discrepancy is thought to arise from the stark differences in the sizes and morphologies of the lithium peroxide involved in each test, which implies that the catalytic activity of a material for the oxidation of lithium peroxide prefilled on electrodes is not indicative of its behavior in the charging of a real lithium–oxygen cell.

Investigating hydrogen storage behavior of CuMnO2glass-ceramic material

SUMMARY Crednerite glass-ceramic material (CuMnO2) has been investigated for the first time as a hydrogen storage candidate. The average gravimetric capacity is about 16 g H2/kg and about 50 g H2/kg of CuMnO2 at 473 and 573 K respectively under a pressure up to 20 bars. The hydrogen adsorbed capacity (weight percent) of CuMnO2 increased with increasing temperature. The material doesn't release hydrogen during desorption cycle revealing storage of hydrogen in the prepared material. X-ray diffraction patterns reveal a structure corresponding to Cu2O, CuMnO2, and traces of CuO and SiO2 phases. X-ray diffraction patterns exhibit a reduction of copper ions to copper metal beside cristobalite and traces from manganese oxide phase after exposing to H2 at 80 and 573 K. This reduction of Cu ions into Cu metal may explain the irreversibility of hydrogen adsorption process. Thermal stability detected by differential scanning calorimetry and thermal gravimetric analysis shows decomposition temperature up to ~473 K followed by gain of weight till 1173 K then another decomposition till 1273 K. Copyright © 2013 John Wiley & Sons, Ltd.

Atomic Scale Dynamics of a Manganese Oxide Phase Change Observed with STEM

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

As(III) oxidation kinetics of biogenic manganese oxides formed by Acremonium strictum strain KR21-2

We investigated As(III) oxidation kinetics of biogenic manganese oxides (BMOs) harvested at various stages of formation by a manganese-oxidizing fungus, Acremonium strictum strain KR21-2. Immature BMOs harvested at an early stage of BMO formation were rich in lower-valence Mn(II) and Mn(III) and oxidized As(III) very slowly. As the BMOs matured, the Mn(IV) content in the BMOs increased and had higher As(III) oxidation rates. The slower As(III) oxidation rates of the immature BMOs may be due to site-blocking by larger amounts of sorbed Mn(II) and/or due to increased structural Mn(III), which is less reactive than Mn(IV). Freshly mature BMOs demonstrated varying As(III) oxidation kinetics depending on dissolved oxygen. In deaerated solutions, the As(III) oxidation rate was slower and Mn(II) was released as As(III) oxidation progressed, indicating surface passivation with reduction of the manganese oxide phase producing Mn(II) and possibly Mn(III). In contrast, in air-equilibrated solutions, As(III) oxidation followed pseudo-first-order rate kinetics throughout the reaction without apparent passivation or significant release of Mn(II). We hypothesize that the active Mn(II) oxidase present in BMOs reoxidized Mn(II) and Mn(III) as autoclaved BMOs exhibited surface passivation even under air-equilibrated conditions. This self-regeneration of BMO minimizes passivation and is hence an important pathway for continuous As(III) oxidation. The data presented provide new insights into the potential applicability of BMOs for As remediation as well as for the oxidative treatments of chemicals other than As(III).

Synthesis and characterization of manganese tetroxide (Mn3O4) nanofibers by electrospinning technique

Manganese tetroxide (Mn3O4) nanofibers were prepared by electrospinning homogeneous viscous solution of 20 wt%, 28 wt% and 36 wt% manganese acetate in poly vinyl alcohol (PVA) and calcining the nanofibers at 1000 °C for 2 h. Electrospinning was carried out at 9 kV DC with tip to collector distance (TCD) of 7 cm. Thermo gravimetric analysis (TGA) of the fibers indicates the pure phase of manganese oxide above 500 °C. XRD analysis of calcined (at 1000 °C) nanofibers indicates the formation of phase-pure tetragonal Mn3O4. Scanning electron microscopy (SEM) studies show the fibers cylindrical with the diameters in the range of 100–600 nm and aspect ratio > 1000. In general, the average diameter of the green fibers decreases with the increase in manganese acetate concentration. The diameter of calcined nanofibers is reduced by 34%.

Photoassisted synthesis of manganese oxide nanostructures using visible light at room temperature

A green chemistry approach was successfully used in this work to synthesize manganese oxide nanoparticles with different shapes and crystalline phases. This approach is based on the visible light irradiation (445 nm) at room temperature of an aqueous solution of a manganese(II) salt in the presence of an alkaline hydroxide (NaOH, KOH or LiOH). Several experimental parameters, i.e., the nature of the precursor salt, hydroxide concentration, hydroxide type, irradiation time and the atmosphere, were tuned and their influence on the morphology and the structure of the nanoparticles was studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. A diversity of manganese oxide phases (λ-MnO2, γ-Mn3O4 and MnO(OH)) were obtained. It must be emphasized that these compounds were easily and fairly quickly synthesized at room temperature, without surfactants and, moreover, by using an environmentally friendly method. In addition, the successful control of the size and the shape of the nanoparticles allowed to obtain a variety of nanoparticles morphologies ranging from one-dimensional (1-D) to three-dimensional (3-D) nanostructures (i.e., spherical, nanorods, nanoflowers, nanocubes). This synthetic approach could be readily extended to other transition metal oxides.

Self-assembled manganese oxide structures through direct oxidation

The morphology and phase of self-assembled manganese oxides during different stages of thermal oxidation were studied. Very interesting morphological patterns of Mn oxide films were observed. At the initial oxidation stage, the surface was characterized by the formation of ring-shaped patterns. As the oxidation proceeded to the intermediate stage, concentric plates formed to relax the compressive stress. Our experimental results gave a clear picture of the evolution of the structures. We also examined the properties of the structures.

Effect of Mn doping on structural and magnetic susceptibility of C-type rare earth nano oxides Er2−xMnxO3

The manganese doped rare earth oxides Er2−xMnx O3 (0.0≤x≤0.20) were synthesized by a sol–gel process and analyzed by X-ray diffraction using Rietveld refinement methods. A single phase solid solution is formed up to x=0.15 while for x≥0.2 a manganese oxide phase appears in the diffraction pattern. Preferential cationic distribution between the non-equivalent sites 8b and 24d of space group Ia3¯ is found for all samples but to a different extent. The octahedral volume and average bond length of Er1O for 8b site decrease while both octahedral volume and bond length of Er2O for 24d site increase. Magnetization measurements were done in the temperature range 5–300K. The effective magnetic moment μeff is found to decrease with composition parameter x, except for sample x=0.05 where the magnetization is enhanced. The Curie-Weiss paramagnetic temperatures indicate antiferromagnetic interaction.

Thermodynamics of manganese oxides: Effects of particle size and hydration on oxidation-reduction equilibria among hausmannite, bixbyite, and pyrolusite

The surface enthalpies of manganese oxide phases, hausmannite (Mn3O4), bixbyite (Mn2O3), and pyrolusite (MnO2), were determined using high-temperature oxide melt solution calorimetry in conjunction with water adsorption calorimetry. The energy for the hydrous surface of Mn3O4 is 0.96 ± 0.08 J/m2, of Mn2O3 is 1.29 ± 0.10 J/m2, and of MnO2 is 1.64 ± 0.10 J/m2. The energy for the anhydrous surface of Mn3O4 is 1.62 ± 0.08 J/m2, of Mn2O3 is 1.77 ± 0.10 J/m2, and of MnO2 is 2.05 ± 0.10 J/m2. Supporting preliminary findings (Navrotsky et al. 2010), the spinel phase (hausmannite) has a lower surface energy than bixbyite, whereas the latter has a smaller surface energy than pyrolusite. Oxidation-reduction phase equilibria at the nanoscale are shifted to favor the phases of lower surface energy—Mn3O4 relative to Mn2O3 and Mn2O3 relative to MnO2. We also report rapidly reversible structural and phase changes associated with water adsorption/desorption for the nanophase manganese oxide assemblages.

Road Dust Lead (Pb) in Two Neighborhoods of Urban Atlanta, (GA, USA)

Road dust continues to be a major potential reservoir of Pb in the urban environment, and an important potential component of child Pb exposure. This study presents ICP-AES analyses of metals in 72 samples of road dust (<250 µm) collected in the urban core of Atlanta, Georgia. In the Downtown area, median Pb concentrations are ~63 mg/kg Pb, with high values of 278 mg/kg. For comparison, median Pb values in a nearby residential neighborhood (also in the urban core) were ~93 mg/kg, with a high of 972 mg/kg. Geospatial variability is high, with significant variation observed over tens to hundreds of meters. Spearman Rank Correlation tests suggest that Pb and other metals (Cu, Ni, V, Zn) are associated with iron and manganese oxide phases in the residential area, as reported in other cities. However, Pb in the Downtown area is not correlated with the others, suggesting a difference in source or transport history. Given these complexities and the expected differences between road dust and soil Pb, future efforts to assess exposure risk should therefore be based on spatially distributed sampling at very high spatial resolution.

Electrodeposited MnOx Films from Ionic Liquid for Electrocatalytic Water Oxidation

AbstractA novel method for the electrodeposition of highly active water oxidation catalysts is described. The manganese oxide (MnOx) films are electrodeposited on fluorine tin oxide (FTO) glass substrate at high temperature (120 °C) from an ionic liquid electrolyte (ethylammonium nitrate). A range of analytical techniques, including X‐ray absorption spectroscopy (XAS), X‐ray diffraction (XRD), and energy‐dispersive X‐ray analyzer (EDX), indicate that the valence state of manganese in the deposited films can be controlled by changing the electrolyte composition. Along with the different phase compositions, a number of different morphologies including nanowires, nanoparticles, nanofibers as well as highly open and dense structures are obtained by varying the acidity of the electrolyte. The effect of morphology and chemical composition on the catalytic activity towards water oxidation is investigated. The film composed of Mn3O4 shows low catalytic activities, while the films composed of birnessite‐like manganese oxide phase and Mn2O3 exhibit high catalytic activities for water oxidation. The catalytic activities are also affected by the surface morphology, i.e., a higher surface area and more open structure shows a higher catalytic activity. High rates of oxygen production are observed from MnOx films prepared in a neutral electrolyte.

The choice of precipitant and precursor in the co-precipitation synthesis of copper manganese oxide for maximizing carbon monoxide oxidation

Copper manganese oxides (CMOs) were synthesized using a co-precipitation method with different precursors and precipitants for carbon monoxide oxidation. The as-synthesized catalysts were characterized by powder X-ray diffraction (XRD), low temperature N2 sorption, Fourier transform-infrared spectroscopy (FT-IR), H2-temperature programmed reduction (H2-TPR), and thermal gravimetric analysis (TGA). Their catalytic activities for CO oxidation were tested by temperature programmed reaction. The results showed that the activity of CO oxidation strongly depended on the combination of precipitant and precursor anions, ranking in the order (Ac−+CO32−)>(NO3−+CO32−)>(Ac−+OH−)>(NO3−+OH−). The crystalline phase of copper manganese oxides obtained using strong electrolyte (OH−) as the precipitant were mainly spinel Cu1.5Mn1.5O4, while the catalysts prepared with weak electrolyte (CO32−) as the precipitant mostly comprised of MnCO3, Mn2O3 and CuO, and showed a much higher CO oxidation activity than that of the Cu1.5Mn1.5O4. Keeping the same precipitant while changing the precursor caused a change in the H2 consumption which influenced the CO oxidation activity. A suitable combination of precipitant and precursor resulted in the most efficient CO oxidation catalyst.

Phosphorus Amendment of a Lead-Spiked Soil with Low Phosphorus Availability: Roles of Phosphorus on Soil and Plant Lead

Phosphorus (P) is both a macronutrient for plants and an effective amendment to reduce lead (Pb) toxicity in soil. Thus, in Pb-polluted soil with low P availability, P will act as a nutrient as well as a Pb-immobilizing agent. However, this has not been fully investigated. A soil with 2.50 mg kg−1 Olsen P was spiked with soluble Pb and then amended with superphosphate to examine the effect of P on soil Pb availability and ryegrass (Lolium perenne L. cv. Aubisque) growth. It was found that P/Pb = 2 increased ryegrass yield by 804% and decreased root Pb concentration and soil diethylenetriaminepentaacetic acid (DTPA)–extractable Pb concentration by 25.6% and 1.0%, respectively. As P amendment increased to P/Pb = 4, both plant yield and root Pb concentration declined compared with P/Pb = 2. Results of the sequential extraction indicated that the proportion of carbonate phase Pb decreased, while that of the manganese oxide phase increased as P was added. The proportion of residual Pb was little affected by the amendment. The results suggest that in soils with low P availability and high Pb availability, availability of soil Pb and root concentration of Pb are less affected, whereas the toxicity of Pb is greatly depressed by the P amendment; P/Pb = 2 is high enough to alleviate the stresses of low P availability.

Size and Morphology Controlled Lithium Manganese Oxide on Silica Sphere with Core–Shell Structure

Core-shell structures were prepared from synthesized SiO2-LiMn2O4 with manganese oxide as shell on the silica core by a precipitation method, which allowed control of core structure in terms of thickness and particle size. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), field emission-transmission electron microscopy (FE-TEM), and energy dispersive spectroscopy (EDS) were used to characterize the SiO2-LiMn2O4. According to FE-SEM images, particle growth was controlled by controlling the amount of manganese precursor and the temperature. The synthesized core-shell structure was composed of silica, lithium silicate, Mn2O3, and the spinel phase of lithium manganese oxide. Electrochemical measurements show that the synthesized core-shell structure has poorer electrochemical performance than that of LiMn2O4.

Evaluation of GO/MnO2 composites as supercapacitors in neutral electrolytes: role of graphite oxide oxidation level

Manganese oxide/graphite oxide (GO) composites containing GO of two different oxidation levels are investigated as supercapacitors in neutral electrolytes, Na2SO4 and Li2SO4. Addition of only 10 wt% of GO with a low oxidation level results in an 18 times improvement in the capacitance in lithium sulfate and in a 60 times improvement of the capacitance in sodium sulfate as compared to that measured on manganese oxide. Even though the performance of the composites is similar in both electrolytes, in Na2SO4 the electrodes are more stable and the capacitance retention ratio is higher. The charge storage in sodium sulfate is linked to the double layer capacitance in the small pores of the composites and to the pseudocapacitance of the manganese oxide phase. In lithium sulfate the insertion of the lithium cation into the structure of the manganese oxide phase enhances the performance. Addition of GO with a high oxidation level is not favorable owing to the defects in the graphene layers limiting the conductivity and charge propagation for Faradaic reactions.

Catalytic activity of Pt catalysts promoted by MnOx for n-hexane oxidation

The deep oxidation of n-hexane was studied over Pt catalysts with small and large Pt crystallites, promoted by MnOx. The Mn was deposited on the Pt/Al2O3 by deposition-precipitation method using two alkalis, ammonia and dimethylamine. The strength of the base influenced morphology and performances of Mn-Pt catalysts. Ammonia formed mostly spherical structure of manganese oxide, while dimethylamine created fibrous needle-like shape of MnOx, typical for cryptomelane phase of manganese oxide. This was confirmed by XPS results that show an oxidation state of Mn close to that for cryptomelane. The Pt-Mn catalysts were more active than catalysts containing Pt only. Promoting effect of MnOx is more pronounced for larger Pt crystallites. Among Pt-Mn samples, catalysts synthesized with dimethylamine exhibited the highest activities. Mobility and reactivity of oxygen from Pt–O–Mn sites associated with cryptomelane phase may be responsible for increased activity.