Presence Of Mn3 Research Articles

Genesis of the Longfengchang polymetallic sulfide deposit in the southwest Fujian depression, southeast China, with a comparative study of the “Makeng-Type” iron deposit

The Southwest Fujian Depression Belt is a prominent metallogenic zone for skarn-type iron polymetallic deposits in China, with the Longfengchang (LFC) sulfur polymetallic deposit representing a medium-scale, sulfide-dominated deposit in this region. This study conducted a detailed analysis of the LFC deposit, focusing on its mineralogy, mineral composition, and in-situ sulfur isotopes, alongside a comparative study with the “Makeng-type” deposit. The study aims to elucidate the genesis of the LFC deposit, its relationship with the “Makeng-type” deposit, and the factors underlying differences in dominant economic minerals and resource scale. The LFC deposit is hosted within the skarn above the fault contact zone between the Lindi Formation sandstone and the Chuanshan–Qixia Formation carbonate, with mineralization stages classified as skarn-magnetite, quartz-sulfide, and carbonate. LFC garnets are primarily composed of CaO, TFeO, and SiO2, with minor Al2O3 and trace amounts of MgO and MnO, classifying them as distal exoskarn andradite. The presence of Mn3+ substituting for Fe3+ in garnet suggests that the ore-forming fluid during the garnet skarn stage was likely oxidizing and weakly acidic. LFC pyrites exhibit Co/Ni ratios primarily ranging from 1 to 10, decreasing from Py1 to Py3. In-situ sulfur isotope δ34S values range from −1.48 to 3.51 ‰, centering around 0 ‰, and increase from Py1 to Py3, suggesting a magmatic-hydrothermal origin and a cooling metallogenic process. Thus, the LFC deposit is classified as a magmatic-hydrothermal skarn-type deposit, consistent with the genesis of “Makeng-type” deposits. The absence of the Jinshe Formation, and mantle-derived magma contribution, and less developed “Si-Ca” interface may explain the smaller scale and different mineralization type in the LFC deposit compared to the “Makeng-type” deposit. The key prospecting area for large iron-sulfur polymetallic deposits in the Southwest Fujian Depression Belt should feature a nappe structural window, well-preserved Jinshe Formation, developed “Si-Ca” interface, Yanshanian high-K calc-alkaline to shoshonitic intrusions, and coeval mantle-derived magma.

Optical and EPR spectroscopy of manganese doped LiNaGe4O9 single crystals

The paper presents data on the study of optical absorption, photoluminescence and EPR of lithium-sodium tetragermanate crystals (LiNaGe4O9) doped with Mn ions. Optical spectra were measured in the range 11000–45000 cm−1 and temperatures 77–300 K. They are attributed to manganese in the +4 charge state. From the analysis of optical spectra, the crystal field strength Dq = 2175.2 cm−1 and Racah parameters A = 4065 cm−1, B = 813 cm−1, C = 3239 cm−1 were determined for the Mn4+ ions. The value of the Huang-Rhys factor SFHR = 17.56 indicates a strong electron-phonon interaction of the Mn4+ ion. The presence of Mn4+ ions was further confirmed by measurement of EPR spectra at microwave frequencies 8.9 and 320 GHz. EPR data show that Mn4+ ions occupy two structurally nonequivalent lattice sites with the formation of two Mn4+ centers: Mn1 and Mn2. From the angular dependences of the EPR spectra, the components of the g factor and the hyperfine interaction tensor A, the parameters of the axial D and rhombic E crystal field were determined for both centers. The axial constant D is large for both centers: 0.644 and 0.560 cm−1, respectively. Analysis of optical and EPR spectroscopic data testifies that Mn4+ ions replace the Ge4+ ions in oxygen octahedrons within the host. Structurally nonequivalent centers are attributed to manganese ions located in undistorted lattice sites (Mn1) and in sites perturbed by the LiNa antisite defect (Mn2).

Boosting the sonodynamic performance of CoBiMn-layered double hydroxide nanoparticles via tumor microenvironment regulation for ultrasound imaging-guided sonodynamic therapy

Sonodynamic therapy (SDT), a promising strategy for cancer treatment with the ability for deep tissue penetration, has received widespread attention in recent years. Sonosensitizers with intrinsic characteristics for tumor-specific curative effects, tumor microenvironment (TME) regulation and tumor diagnosis are in high demand. Herein, amorphous CoBiMn-layered double hydroxide (a-CoBiMn-LDH) nanoparticles are presented as multifunctional sonosensitizers to trigger reactive oxygen species (ROS) generation for ultrasound (US) imaging-guided SDT. Hydrothermal-synthesized CoBiMn-LDH nanoparticles are etched via a simple acid treatment to obtain a-CoBiMn-LDH nanoparticles with abundant defects. The a-CoBiMn-LDH nanoparticles give greater ROS generation upon US irradiation, reaching levels ~ 3.3 times and ~ 8.2 times those of the crystalline CoBiMn-LDH nanoparticles and commercial TiO2 sonosensitizer, respectively. This excellent US-triggered ROS generation performance can be attributed to the defect-induced narrow band gap and promoted electrons and holes (e−/h+) separation. More importantly, the presence of Mn4+ enables the a-CoBiMn-LDH nanoparticles to regulate the TME by decomposing H2O2 into O2 for hypoxia relief and US imaging, and consuming glutathione (GSH) for protection against ROS clearance. Biological mechanism analysis shows that a-CoBiMn-LDH nanoparticles modified with polyethylene glycol can serve as a multifunctional sonosensitizer to effectively kill cancer cells in vitro and eliminate tumors in vivo under US irradiation by activating p53, apoptosis, and oxidative phosphorylation-related signaling pathways.

Surface tailoring on bifunctional CuOx/MnO2 catalyst to promote the selective catalytic reduction of NO with NH3 and oxidation of CO with O2

NO and CO are two primary pollutants in the sintering flue gas emission, posing significant challenges for the treatment. Under oxygen-enriched conditions, CO was easily oxidized to CO2 before participating in CO-SCR reaction as a reducing agent. Consequently, NH3-SCR technology coupled with CO oxidation reaction is a promising approach for simultaneous NO and CO removal. In this study, a series of bifunctional CuOx/MnO2 catalysts were synthesized using a combine of hydrothermal and wet impregnation methods, and their catalytic performance for simultaneous removal of NO and CO was assessed. CuOx/α-MnO2 catalyst displayed outstanding catalytic activity for both NO and CO, achieving over 80 % NO removal efficiency and 96 % CO conversion rate at 150 °C, while CuOx/β-MnO2 catalyst exhibited poor catalytic activity in the entire temperature range. Moreover, the interplay between the NH3-SCR and CO catalytic oxidation reactions was also explored. XPS results revealed that the concentration of Mn4+ and Cu+ species significantly influenced the catalytic activity of the catalysts for the simultaneous removal of NO and CO. Particularly, the presence of Mn4+ species promoted “fast SCR” reaction, whereas Cu+ species demonstrated higher reactivity for both NO reduction and CO oxidation. In situ DRIFTS analysis of transient reactions revealed that the L-H mechanism was followed over CuOx/α-MnO2 catalyst in the NH3-SCR reaction, while both the M-K and L-H mechanisms were observed in CO catalytic oxidation reaction.

Synergy of radical and nonradical degradations triggered by self-floating MnO2/cotton hydrogels with photothermal effect and oxygen vacancy

Persulfate-based advanced oxidation process is a promising technology for the water purification. While the synergy of radical and nonradical degradations are still unfeasible during persulfate activation, which process consumes a large amount of external energy. The self-floating manganese dioxide (MnO2)/cotton hydrogels (MCH) was developed, which achieves solar energy capture and wastewater treatment. In this study, a meticulously designed MCH enables simultaneous interface heating and persulfate activation. The MCH exhibited an excellent photothermal conversion capability with an evaporation rate of 2.89 kg/(m2·h) under 1 sun. The MCH coupled with peroxydisulfate (PDS) achieved a tetracycline (TC) degradation efficiency of 74.53 % under a visible light irradiation in 120 min. Furthermore, the result of TC evaporation experiment showed that 99.43 % of TC can be removed from the evaporated water. Interestingly, it was found that the singlet oxygen (1O2) increased with the concentration of Vo in the MCH during PDS activation process. In contrast to the conventional view, the thermal effect increases the concentration of Vo thus promoting the conversion of superoxide radicals (O2−) to 1O2 in the presence of Mn4+. Additionally, the polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP) hydrogel with porous structure that provided the oxygen for MnO2, promoting the production of reactive oxygen species. This study provides a new model for simultaneous evaporation and degradation, which deepens the understanding of synergy of radical and nonradical degradations.

All-in-one supercapacitor devices based on nanosized Mn4+-doped WO3

In this study, nanosized Mn-doped WO3-based materials were used as electrode materials for high-performance supercapacitor devices. Various Mn concentrations (0.5, 1, and 1.5%) were used to change the defect structure of WO3, which improved the material’s electrical properties. A thorough morpho-structural and defect structure analysis of the undoped and doped WO3 was performed through various characterization techniques, among which EPR and PL spectroscopy gave insight into the effect that Mn-doping caused on the defect structure and optical properties of WO3. The presence of Mn4+ ions and a high concentration of oxygen vacancies was observed, strongly influencing the electrode material when used in symmetric supercapacitors, where the electrochemical performance was tested. The symmetric supercapacitors were designed without booster materials (like carbon black) and showed increased specific capacitance (115 F/g) and energy density (16 Wh/Kg) values.

Ultrahigh‐Capacity Rocksalt Cathodes Enabled by Cycling‐Activated Structural Changes

AbstractMn‐redox‐based oxides and oxyfluorides are considered the most promising earth‐abundant high‐energy cathode materials for next‐generation lithium‐ion batteries. While high capacities are obtained in high‐Mn content cathodes such as Li‐ and Mn‐rich layered and spinel‐type materials, local structure changes and structural distortions ( often lead to voltage fade, capacity decay, and impedance rise, resulting in unacceptable electrochemical performance upon cycling. In the present study, structural transformations that exploit the high capacity of Mn‐rich oxyfluorides while enabling stable cycling, in stark contrast to commonly observed structural changes that result in rapid performance degradation, are reported. It is shown that upon cycling of a cation‐disordered rocksalt (DRX) cathode (Li1.1Mn0.8Ti0.1O1.9F0.1, an ultrahigh capacity of ≈320 mAh g−1 (energy density of ≈900 Wh kg−1) can be obtained through dynamic structural rearrangements upon cycling , along with a unique voltage profile evolution and capacity rise. At high voltage, the presence of Mn4+ and Li+ vacancies promotes local cation ordering, leading to the formation of domains of a “δ phase” within the disordered framework. On deep discharge, Mn4+ reduction, along with Li+ insertion transform the structure to a partially ordered DRX phase with a β′‐LiFeO2‐type arrangement. At the nanoscale, domains of the in situ formed phases are randomly oriented, allowing highly reversible structural changes and stable electrochemical cycling. These new insights not only help explain the superior electrochemical performance of high‐Mn DRXbut also provide guidance for the future development of Mn‐based, high‐energy density oxide, and oxyfluoride cathode materials.

Surface Reduced Manganese States as a Source of Oxygen Reduction Activity in BaMnO3

AbstractIn relation to perovskites, tweaking the oxidation state of the B‐site cation is fundamental to controlling the catalytic activity of these materials, thus necessitating a complete characterization of surface oxidation states. Herein, using a combination of atomic‐scale imaging and spectroscopic techniques, structure‐property correlation in barium manganese oxide (BaMnO3) is established for the oxygen reduction reaction (ORR). Electron energy loss spectroscopy (EELS) on the synthesized BaMnO3 find the rods to contain an amorphous surface layer with reduced Mn3+ states compared to Mn4+ states in the bulk. Consequently, the BaMnO3 rods show electrocatalytic activity for the ORR, which originates from the presence of Mn3+ at the rod surface. Furthermore, heating of the samples in air at 300 and 800 °C results in a decrease in the number of Mn3+ states, and thus lowering of the ORR activity. This study represents a step‐stone study in understanding the mechanism of ORR activity and its association to the Mn3+ state at the perovskite's surface, opening up possibilities for further surface engineering and tuning catalytic properties.

Enhancement in the electrical transport properties of CaMnO3via La/Dy co-doping for improved thermoelectric performance.

The untiring endeavour towards green energy is a trending research among the research community. Thermoelectric materials are of vital importance here owing to their emission-free operation. As a righteous candidate, calcium manganate materials are being explored to increase its figure of merit. In this study, the structural, microstructural, electrical transport, and high-temperature thermoelectric measurements of LaxDyxCa1-2xMnO3 {x = 0.025 (L25D25), 0.05 (L50D50), 0.075 (L75D75), and 0.1 (L100D100)} were systematically performed. The structural confirmation of the synthesised sample was validated using X-ray diffraction, which also revealed the orthorhombic (space group: Pnma) crystallisation of co-doped samples with no traces of secondary peaks. A significant increase in the unit cell volume was observed with rare earth substitutions. The morphological studies revealed that the prepared samples were highly dense and the grain size was reduced with rare earth concentration. The substitution of La and Dy enhanced the conductivity values of pristine CMO by two orders of magnitude due to the high concentration of charge carriers and the presence of Mn3+ ions due to rare earth doping. The conductivity increased with rare earth concentrations but diminished for x = 0.1 due to the localization of charges. The Seebeck coefficient values were negative for all the prepared samples, indicating electrons as the predominant carriers over the entire operating range. A minimum κ of 1.8 W m-1 K-1 was achieved for La0.1Dy0.1Ca0.8MnO3 and the maximum value zT obtained was 0.122 at 1070 K for La0.075Dy0.075Ca0.85MnO3.

Optimizing Li‐Excess Cation‐Disordered Rocksalt Cathode Design Through Partial Li Deficiency

AbstractLi‐excess disordered rocksalts (DRXs) are emerging as promising cathode materials for Li‐ion batteries due to their ability to use earth‐abundant transition metals. In this work, a new strategy based on partial Li deficiency engineering is introduced to optimize the overall electrochemical performance of DRX cathodes. Specifically, by using Mn‐based DRX as a proof‐of‐concept, it is demonstrated that the introduction of cation vacancies during synthesis (e.g., Li1.3‐xMn2+0.4‐xMn3+xNb0.3O1.6F0.4, x = 0, 0.2, and 0.4) improves both the discharge capacity and rate performance due to the more favored short‐range order in the presence of Mn3+. Density functional theory calculations and Monte Carlo simulations, in combination with spectroscopic tools, reveal that introducing 10% vacancies (Li1.1Mn2+0.2Mn3+0.2Nb0.3O1.6F0.4) enables both Mn2+/Mn3+ redox and excellent Li percolation. However, a more aggressive vacancy doping (e.g., 20% vacancies in Li0.9Mn3+0.4Nb0.3O1.6F0.4) impairs performance because it induces phase separation between an Mn‐rich and a Li‐rich phase.

Simultaneous oxidation of aromatic compounds using Sr‐doped lanthanum manganites as catalysts

Strontium-doped lanthanum manganites, La1-xSrxMnO3 (LSMO), are promising and affordable catalysts for oxidative degradation of volatile organic compounds. LSMO catalysts (x = 0, .1, .2, and .3) were prepared by the citrate-nitrate autocombustion (CNA) and coprecipitation synthesis. The phase composition was confirmed by X-ray diffraction and Rietveld refinement analysis, while the oxygen content was determined by Mohr's salt permanganate titration. Morphology and porosity of prepared catalysts was correlated to catalytic oxidation of benzene, toluene, ethylbenzene and o-xylene. It was observed that both synthesis methods yielded catalysts of similar average pore size diameter and specific surface area, but the pore size distribution differed: CNA-prepared catalysts had a multimodal pore size distribution, while the coprecipitated ones had a single maximum at 4 nm. Catalysts prepared by the CNA method have shown a higher catalytic activity in the temperature range 373–723 K, as the presence of Mn3+/Mn4+ mixed valences increased their reducibility.

Regulation of the Sulfur Environment in Clusters to Construct a Mn-Sn2S6 Framework for Mercury Bonding.

The remarkable chemical activity of metal-sulfur clusters lies in their unique spatial configuration associated with the abundant unsaturated-coordination nature of sulfur sites. Yet, the manipulation of sulfur sites normally requires direct contact with other metal atoms, which inevitably changes the state of the coordinated sulfur. Herein, we facilely construct a Mn-Sn2S6 framework by regulating the sulfur environment of the [Sn2S6]4- cluster with metal ions. Mn-Sn2S6 showed superior removal performance to gaseous elemental mercury (Hg0) at low temperatures (20-60 °C) and exhibited high resistance against SO2. Moreover, Mn-Sn2S6 can completely remove liquid Hg2+ ions with low or high concentrations from acid wastewater. In addition, the adsorption capacities of Mn-Sn2S6 toward Hg0 and Hg2+ reached 21.05 and 413.3 mg/g, respectively. The results of physico-chemical characterizations revealed that compared with Cu2+, Co2+, and Fe2+, the moderate regulation of Mn2+ led to the special porous spherical structure of Mn-Sn2S6 with uniform element distribution, due to the difference of electrode potentials [Eθ(Mn2+/Mn) < Eθ(S/S2-) < Eθ(Sn4+/Sn2+)]. The porous structure was beneficial to Hg0 and Hg2+ adsorption, and the presence of Mn4+/Mn3+ and S1- promoted the oxidation of Hg0, resulting in stable HgS species. The constructed Mn-Sn2S6, thus, is a promising sorbent for both Hg0 ang Hg2+ removal and provides guidelines for cluster-based materials design and tuning.

EPR Study of the Mn-Doped Magnesium Titanate Ceramics

Manganese-doped magnesium titanate ceramic samples obtained by a solid-state reaction via sintering in the air from a mixture of MgO and TiO2 powders of different molar ratios were analyzed by electron paramagnetic resonance (EPR) technique. The EPR signals of Mn2+ ions (S = 5/2, І = 5/2) in crystal phases of MgO, Mg2TiO4, and MgTiO3 were detected. We have obtained the following spin Hamiltonian parameters for Mn2+ ions: g = 2.0015, A ∼81.0 × 10−4 cm−1 (in MgO phase); g = 2.0029, A ∼73.8 × 10−4 cm−1 , b 2 0 = 35 × 10−4 cm−1 (in Mg2TiO4 phase); g = 2.0040, A ∼79.0 × 10−4 cm−1 , b 2 0 = 165 × 10−4 cm−1 (in MgTiO3 phase). Despite the presence of Mn4+ centers in both Mg2TiO4:Mn and MgTiO3:Mn ceramics confirmed by previous optical studies, no EPR signals related to Mn4+ ions (S = 3/2, І = 5/2) were found. The Mn2+ EPR signals are proposed as structural probes in manganese-doped magnesium titanate ceramics.

Understanding the Efficiency of Mn4+ Phosphors: Study of the Spinel Mg2Ti1–xMnxO4

We present a spectroscopic study of Mn-doped Mg2TiO4 as a function of pressure and temperature to check its viability as a red-emitting phosphor. The synthesis following a solid-state reaction route yields not only the formation of Mn4+ but also small traces of Mn3+. Although we show that Mn4+ photoluminescence is not appreciably affected by the presence of Mn3+, its local structure at the substituted Ti4+ host site causes a reduction of the Mn4+ pumping efficiency yielding a drastic quantum-yield reduction at room temperature. By combining Raman and time-resolved emission and excitation spectroscopies, we propose a model for explaining the puzzling nonradiative and inefficient pumping processes attained in this material. In addition, we unveil a structural phase transition above 14 GPa that worsens their photoluminescence capabilities. The decrease of emission intensity and lifetime with increasing temperature following different thermally activated de-excitation pathways is mostly related to relatively small activation energies and the electric–dipole transition mechanism associated with coupling to odd-parity vibrational modes. A thorough model based on the configurational energy level diagram to the A1g normal mode fairly accounts for the observed excitation and emission─the quantum yield─of this material.

Effect of Mn3+ doping on crystal structure, point defects, and optical properties in green Ca3(VO4)2 single crystals

Calcium orthovanadate Ca3(VO4)2 (CVO) is an efficient media for laser applications. Czochralski-grown green CVO single crystals doped with over-stoichiometric 0.1 (CVO:0.1Mn) and 1.0 wt.%Mn (CVO:1.0Mn) were studied by X-ray diffraction and X-ray absorption spectroscopy for the first time. In the CVO:1.0Mn, an occurrence of Mn3+ in Ca3 (two-capped trigonal prism), Ca4 (distorted octahedron), and defective Ca5 and Ca5A (highly-distorted octahedron) sites and vacancies in V2 and V3 sites (distorted tetrahedra) were revealed. In the CVO:0.1Mn, a presence of Mn3+ in Ca3 and Ca5A sites and vacancies in V2 site were found. In the CVO, the Mn3+ form elongated octahedra (tetragonal bipyramid; coordination number, 4 + 2) typical for the Jahn-Teller ions. Models for the rearrangement of Ca3 and Ca4 polyhedra into a tetragonal bipyramid are proposed. Along with the Mn3+, the Mn2+ and Mn5+ ions were observed by optical spectroscopy in CVO:0.1Mn (predominantly Mn2+ ions) and CVO:1.0Mn (only Mn5+ ions).

(Invited) Exploring Sodium Layered Oxide Cathodes: Designing Tailored Materials

Interest in developing energy storage systems to meet a wide array of future challenges has driven research into a range of new battery technologies. Sodium-ion batteries (SIBs) have proven to be particularly popular due to their attractive properties and broad range of potential applications. However, before SIBs take their place in the pantheon of battery technologies, there still remain challenges to overcome - perhaps the most significant of which is the ongoing development of optimal cathode materials.Sodium Mn-rich layered oxides, i.e. NaxMn1-yMyO2 (y ≤ 0.33; M is one or more transition metals, such as Ni, Ti, Fe, etc.), have proven to be a promising family of SIB cathode materials with a low cost, highly tuneable, and environmentally friendly nature synergises well with the main advantages of SIBs.[1] Considerable research in this area, using a variety of conventional and specialised techniques, has led to an increased understanding of the nature and behaviour of these materials, and the key factors affecting their electrochemistry.[1-4]Performance of these materials is frequently governed by their structure, and in this work, we will highlight the importance of taking this into consideration. For example, while Manganese-rich layered oxides are particularly attractive due to their combination of low cost and low toxicity, their performances are often hindered by the effect of Jahn-Teller distortion (resulting from the presence of Mn3+).[5] We will not only discuss this in detail, but also highlight mitigation strategies – such as doping with electrochemically active (e.g. Fe) and inactive (e.g. Mg, Ti) elements, or synergetic P2/O3 combination effect.[5–8] This understanding has enabled the rapid investigation of not only suitable elements (selected with careful attention to electrochemical performance, cost, scarcity, etc.) but also appropriate degrees of doping and substitution.In this presentation, we will highlight some of the most significant Mn-rich materials and their properties, as well as examining and explaining the key parameters and factors which determine their performance. We will explain how this understanding has been used to develop a rational design approach, before summarising the trends in this area and areas of future exploitation.

Novel sol–gel method for low temperature synthesis of nanostructured Mn3O4: Structure, cation valence states, optical and electrical properties

Novel low temperature sol–gel route for the synthesis nanostructured Hausmannite, Mn3O4with very small crystallite size (9 ± 1 nm) and phase purity is reported. Reaction temperature of 0–5 °C and drying temperature of 40 °C is the lowest reported so far. Average particle size (8 ± 1 nm) measured from Transmission Electron Microscopy is in good agreement with the crystallite size indicating monodispersed nature. Raman analysis indicates the presence of +4 valence states for Mn over and above +2 and +3 and the presence of an Mn2O3 like surface layer. XPS analysis confirms the phase purity as well as the presence of Mn4+ions. Presence of +4 valence state for Mn is attributed to the presence of cation vacancies that lead to disproportionate reactions. UV–visible absorption spectra is quite broad with charge transitions associated with Mn2+, Mn3+ and Mn4+ states and d-d crystal field transitions. DC electrical conductivity is about two orders of magnitude higher than that of single crystalline Mn3O4 and the conduction mechanism is defect dependent.

Metal-organic frameworks as template for synthesis of Mn3+/Mn4+ mixed valence manganese cobaltites electrocatalysts for oxygen evolution reaction

Cobalt-based oxides are among the most promising electrocatalysts for oxygen evolution reactions (OER). In this context, this work reports the synthesis of manganese-doped cobaltites using the Zeolitic-Imidazolate Frameworks 67 (ZIF-67) as template. The incorporation of manganese ions into ZIF-67 structure was evaluated in ethanol and methanol, in order to obtain the best synthetic route. Non-doped (ZIF-67C) and Mn-doped cobaltites (Mn/ZIF-67C(E) and Mn/ZIF-67C(M)) were obtained after thermal treatment at 350 °C. Structural and morphological properties were investigated and presence of Mn3+ and Mn4+ was confirmed by X-ray photoelectron spectroscopy (XPS) data and magnetization curves. The electrocatalytic activity in OER was investigated in alkaline medium for manganese cobaltites, and compared to the ZIF-67C. Overpotentials to generate a current of 10 mA cm−2 were 338 mV and 356 mV for Mn/ZIF-67C(E) and Mn/ZIF-67C(M), respectively. These results are superior to those found for similar materials in the literature. The material obtained in methanol (Mn/ZIF-67C(M)) presents lower overpotential, however, shows superior electrocatalytic performance for current density above 100 mA cm−2, therefore being an efficient electrode for commercial electrolysers.

Mössbauer and Magnetic Study of Lanthanum Manganite La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20): Nonstoichiometric and Stoichiometric Composition

Mossbauer and magnetic study of calcium-doped lanthanum manganites La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20) of nonstoichiometric (LCM–NS) and stoichiometric (LCM–S) compositions have been carried out in a wide temperature range. Phase structural separation is observed in the samples of stoichiometric composition (δ = 0). With a decrease in temperature all investigated lanthanum manganite samples exhibit superparamagnetic behavior, caused by the formation of small magnetic clusters in the structure. An expansion of the concentration range toward lower dopant concentrations in the LCM–S samples allowed us to establish the competing processes occurring at a low Ca content, including the Jahn‒Teller effects (orbital order) and the presence of Mn4+ ions (violation of orbital order), and study the dynamics of the structure and magnetic properties as functions of the Ca content.

Optical and electrical properties of manganese doped-alkali metaphosphate glasses

Phosphate glasses are of large interest for a variety of technological applications due to their several unique properties. In this work we investigate structural, optical and electrical properties of some alkali metaphosphate glasses doped with manganese oxide inside the system (50-x/2) K2O-xMnO2-(50-x/2) P2O5 with (0 ≤ x ≤ 30%mol). The glassy samples have been prepared using a melt-quench process. The obtained glasses are colored and the valence of manganese is composition dependence. The local structure of Mn2+ in the glasses is evaluated by EPR spectroscopy. The optical absorption spectra have been used to evaluate the values of the optical band gap (Eg) and Urbach energy (ΔE). The variation of these optical parameters as a function of composition is investigated. The presence of Mn3+ in the glasses is established by the optical absorption and this ion is associated with the absorption band at 520–530 nm. dc conductivity of the glasses is studied and it is found that it is thermally activated and followed an Arrhenius behavior.