Mixed Valence Of Manganese Research Articles

δ‐MnO2/KMnF3 Composite with Mixed Valence as Cathode for Potassium Ion Battery

AbstractPotassium ion batteries (PIBs) are regarded as potentially promising large‐scale energy storage systems. δ‐MnO2/KMnF3‐30 (mass percentage of KMnF3: 30%) with mixed valence of manganese is constructed by homogeneous precipitation method, as cathode for PIBs. As a buffer and chelating agent for the reaction, disodium ethylenediamine tetraacetate (EDTA‐2Na) is helpful to form composites with good mixing and uniform dispersion. δ‐MnO2 nanowires with different lengths can fully utilize the cross‐linking of long nanowires and short‐range filling of short nanowires, resulting in more stable network connectivity. Additionally, the uniform embedding of the KMnF3 nanoparticles among δ‐MnO2 nanowires can effectively accommodate the volume expansion associated with ion intercalation during cycling process. δ‐MnO2/KMnF3 combines the advantages of Mn‐based fluoride and Mn‐based oxide as cathode materials, and has high capacity, good cycle performance and rate performance. The capacity at a current density of 100 mA g−1 after 200 cycles can still be as high as 90 mAh g−1. Electrochemical impedance spectroscopy is used to study the reaction process of the δ‐MnO2/KMnF3 cathode at the electrode/electrolyte interface and to explain some electrochemical phenomena.

Preparation and performance of manganese-oxide-coated zeolite for the removal of manganese-contamination in groundwater

ABSTRACTA promising and easily prepared catalytic filler media, manganese-oxide-coated zeolite (MOCZ), for the removal of Mn (II) contamination in groundwater was studied. The optimal condition for MOCZ preparation was given as follows: acid activation of zeolite with 5% HCl mass percent for 12 h, then soaking of acid-activated zeolite with 7% KMnO4 mass percent for 8 h, and finally calcination at 300°C for 5 h. Acid activation significantly enlarged the specific surface area of the zeolite (>79 m2 g−1), subsequently enhancing the coating of manganese oxides onto the surface of the zeolite. This was further supported by the manganese-to-zeolite ratio (γMn) and Energy dispersive analysis-mapping. The γMn was over 12.26 mg Mn g−1 zeolite, representing more active sites for the adsorption and catalytic-oxidation of Mn (II). As such, great performance of Mn (II) removal by MOCZ was obtained in the filter experiment. An estimated 98–100% removal efficiency of Mn (II) was achieved in a greatly short startup time (only 2 h). During the filtration process, newborn flocculent manganese oxides with a mixed-valence of manganese (Mn (II) and Mn (IV)) were generated on the MOCZ surface, further facilitating the adsorption and catalytic-oxidation of Mn (II). The filter with MOCZ as adsorbent had a great performance on the Mn (II) removal in a wide range of hydraulic retention time (HRT) (4–40 min), particularly in a short HRT. Besides, the filter prolonged the filtration period (60 days), which would significantly reduce the frequency of backwash. Thus, it could be concluded that MOCZ prepared in this study showed a good performance in terms of Mn (II) removal in waterworks, especially small waterworks in the villages/towns.

A cost-effective catalytically adsorbent for in situ remediation of manganese contaminated groundwater

Abstract Manganese oxide coated scoria (MOCS) was prepared as a cost-effective catalytically adsorbent with high permeability to remediate manganese contaminated groundwater. Scanning electron microscope visual expressed that on the relatively smooth surface of raw scoria (RS) a large amount of micro pores and dense bulk-like structures after modification and filtration appeared. The data from Fourier transform infrared showed that the intrinsic scoria structure was unchanged during modification. The X-ray diffraction and X-ray photoelectron spectroscopy instrumental studies revealed that the newborn manganese oxide layer was a mixed-valence of manganese (Mn3+ and Mn4+) which could absorb the Mn2+ and catalytically facilitate oxidation with oxygen. Subsequently, the adsorption capacity of RS and MOCS was demonstrated in adsorption experiments. The kinetics of manganese adsorption by RS and MOCS followed pseudo-second-order with the correlation coefficients of 0.983 and 0.989, respectively. The experimental data were better fitted to Langmuir isotherm than Freundlich isotherm, indicating that the monolayer adsorption process for manganese was acting on the surface of RS and MOCS. The filtration experiment showed high Mn2+ removal efficiency by MOCS in a wide range of hydraulic retention time (15–40 min) in 40 days, which demonstrated that the MOCS is a good potential application prospect for manganese removal from groundwater.

Synthesis of Ca2Mn3O8 films and their electrochemical studies for the oxygen evolution reaction (OER) of water

Based on the oxygen evolving μ-oxido-Mn4Ca cluster unit in photosynthesis II, Ca2Mn3O8 films prepared by dip-coating and screen-printing were tested as oxygen evolving catalysts. Structural analysis confirmed that smooth 100nm films can be grown from a Ca2MnO4 sol–gel solution showing a high orientation in (100) direction when deposited on F:SnO2/quartz and quartz substrates. The distance found by X-ray diffraction between the layers exactly fitted the monoclinic layer compound of composition Ca2Mn3O8. To compare the electrochemical behavior of this layer with the bulk Ca2Mn3O8 powder, a 6μm thick film was prepared by screen-printing. Differential electrochemical mass spectroscopy performed in 0.1M KH2PO4 at pH 7 and 1M Tris(hydroxymethyl)aminomethane at pH 7.8 revealed that both films were able to oxidize water as well as organic matter with a good correlation to the slope of the current density curves; however, the dip-coated films displayed lower current densities than the screen-printed Ca2Mn3O8 layers. A closer look into the cyclic voltammetry revealed that capacity values were similar indicating that not only the different surface areas played a role, but variations in the specific capacity values possibly due to the orientation of the films or the manganese mixed valence in the surface as determined by X-ray photoelectron spectroscopy (XPS) could be responsible for these effects.

Single Crystalline La0.7Sr0.3MnO3Molecular Sieve Nanowires with High Temperature Ferromagnetism

Porous mixed-valent manganese oxides are a group of multifunctional materials that can be used as molecular sieves, catalysts, battery materials, and gas sensors. However, material properties and thus activity can vary significantly with different synthesis methods or process conditions, such as temperature and time. Here, we report on a new synthesis route for MnO(2) and LaSr-doped molecular sieve single crystalline nanowires based on a solution chemistry methodology combined with the use of nanoporous polymer templates supported on top of single crystalline substrates. Because of the confined nucleation in high aspect ratio nanopores and of the high temperatures attained, new structures with novel physical properties have been produced. During the calcination process, the nucleation and crystallization of ε-MnO(2) nanoparticles with a new hexagonal structure is promoted. These nanoparticles generated up to 30 μm long and flexible hexagonal nanowires at mild growth temperatures (T(g) = 700 °C) as a consequence of the large crystallographic anisotropy of ε-MnO(2). The nanocrystallites of MnO(2) formed at low temperatures serve as seeds for the growth of La(0.7)Sr(0.3)MnO(3) nanowires at growth temperatures above 800 °C, through the diffusion of La and Sr into the empty 1D-channels of ε-MnO(2). Our particular growth method has allowed the synthesis of single crystalline molecular sieve (LaSr-2 × 4) monoclinic nanowires with composition La(0.7)Sr(0.3)MnO(3) and with ordered arrangement of La(3+) and Sr(2+) cations inside the 1D-channels. These nanowires exhibit ferromagnetic ordering with strongly enhanced Curie temperature (T(c) > 500 K) that probably results from the new crystallographic order and from the mixed valence of manganese.

Complex competition between ferromagnetism and antiferromagnetism in the CMR manganites Pr1−x Ca x MnO3

The systematic investigation of the magnetic susceptibility of the CMR manganites Pr1−x Ca x MnO3 versus temperature has been performed for 0.25 ≤ x ≤ 0.50. Due to the similar size of calcium and praseodymium, these results show the important role of the mixed valence of manganese upon the complex magnetic behaviour of these compounds. They demonstrate that the appearance of antiferromagnetism coincides with charge ordering, T N = T CO varying with x, from 250K for x = 0.50 to 225K for x = 0.35. A strong competition between ferromagnetism and antiferromagnetism is observed for 0.35 ≤ x 170 K) and going through canted antiferromagnetic or weak ferromagnetic states for intermediate temperatures (70 K < T < 170 K). For 0.25 ≤ x ≤ 0.30, a strong ferromagnetic state is observed for 95 K ≤ T ≤ 150 K, with a transition to a spin glass like state below 95–110 K.