Electrochemical reactivity of Li–Mn–O and Li–Fe–Mn–O spinels

Electrochemical reductive dissolution of Li–Mn–O and Li–Fe–Mn–O spinels and Li⁺ extraction/insertion in these oxides were performed using voltammetry of microparticles. Both electrochemical reactions are sensitive to the Fe/(Fe+Mn) ratio, specific surface area, Li content in tetrahedral positions, and Mn valence, and can be used for electrochemical analysis of the homogeneity of the elemental and phase composition of synthetic samples. The peak potential (E _P) of the reductive dissolution of the Li–Mn–O spinel is directly proportional to the logarithm of the specific surface area. E _P of Li–Fe–Mn–O spinels is mainly controlled by the Fe/(Fe+Mn) ratio. Li⁺ insertion/extraction can be performed with Mn-rich Li–Fe–Mn–O spinels in aqueous solution under an ambient atmosphere and it is sensitive to the regularity of the spinel structure, in particularly to the amount of Li in tetrahedral positions and the Mn valence. Electronic Publication     

Calorimetric study of spinodal decomposition in β-Cu–Al–Mn

Journal of Thermal Analysis and Calorimetry - We report data obtained from the spinodal decomposition in samples of two compositions of intermetallic Cu–Al–Mn shape memory alloys....     

Phase diagram of the Pr–Mn–O system in composition–temperature–oxygen pressure coordinates

The phase relations in the Pr–Mn–O system were studied by the static method at lowered oxygen pressure in combination with thermal analysis and high-temperature X-ray diffraction. The equilibrium oxygen pressure in dissociation of PrMn₂O₅ and PrMnO₃ was measured, and the thermodynamic characteristics of formation of these compounds from elements were calculated. The Р–Т–х phase diagram of the Pr–Mn–O system was constructed in the “composition–oxygen pressure–temperature” coordinates.     

Phase transformations in an annealed Cu–9Al–10Mn–3Gd alloy

The phase transformations in the Cu–9Al–10Mn–3Gd alloy were studied using differential scanning calorimetry, X-ray diffraction patterns, scanning electron microscopy, energy dispersion X-ray spectroscopy and magnetic moment change with applied field and temperature. The results showed that the effects produced by the Mn atoms are dominant on those attributed to the Gd atoms in the annealed Cu–9Al–10Mn–3Gd alloy. For quaternary alloy the results also indicated that the Gd stabilizes a fraction of the paramagnetic β₃ phase at lower temperatures and suppresses its paramagnetic–ferromagnetic ordering; in addition, it increases the Curie temperature of the Cu–9Al–10Mn alloy.     

Phase equilibria involving solid solutions in the Li–Mn–O system

Phase equilibria involving LiMn₂O_4-, Li₂MnO_3-, LiMnO_2-, Mn₃O_4-, and MnO-base solid solutions were studied with varied temperature and partial oxygen pressure. The \({P_{{o_2}}}\)–T and x–y projections of the P–T–x–y phase diagram of the Li–Mn?O system were constructed, as well as the key x–y isotherms of the Li₂O–MnO–MnO₂ quasi-ternary system. In some experiments, the authors’ hydride lithiation method was employed to prepare lithium-rich homogeneous three-component nonstoichiometric phases.     

A new organic–inorganic hybrid based on Mn–salen and decavanadate

An organic–inorganic hybrid based on Mn-salen and decavanadate, [NH₄]₂[Mn(salen)(H₂O)₂]₄[V₁₀O₂₈]?·?6H₂O (1) (salen?=?N,N′-ethylene-bis(salicylideneiminate)), has been synthesized by the strategy of secondary building units in mixed methanol–water solution and was structurally characterized by single-crystal X-ray diffraction, elemental analyses, IR, and UV-Vis. The [Mn(salen)(H₂O)₂]⁺ cations and water molecules are located in the interspaces among the polyoxoanions [V₁₀O₂₈]^6? forming a POM-based supramolecule. Compound 1 is the first example of metal-Schiff-base polyoxovanadates. The photocatalytic analysis, cyclic voltammetry, and electrocatalytic analysis of 1 have been investigated.     

Low-temperature synthesis and characterization of the Mn–Zn ferrite

Nanocrystalline ferrite with the composition: Mn_0.6Zn_0.4Fe₂O₄ was synthesized by two-stage route: the precipitation of Zn, Mn and Fe hydroxides from sulphates solution and the synthesis of a precursor by the sol–gel auto-combustion method. The ferrite powder obtained from the gel by ashing was sintered under air at a temperature of 720, 1150 and 1300 °C. The composition and morphology of the as-obtained phases were examined by ICP-AES, TG/DTA, XRD, FTIR, SEM and low-temperature nitrogen adsorption (BET). It was found that the spinel phase forms after gel combustion. The nanometric ferrite powder obtained as a result of the combustion is soft-agglomerated. The zinc content in the ferrite during ashing and auto-combustion is lower by about 21 mol% than the assumed one and the final product turn out to be Mn_0.68Zn_0.32Fe₂O₄.     

Synthesis and electrochemical performance of LiNi0.475Mn0.475Al0.05O2 as cathode material for lithium-ion battery from Ni–Mn–Al–O precursor

LiNi_0.475Mn_0.475Al_0.05O₂ cathode material was prepared by solid-state reaction using Ni–Mn–Al–O solid solution as precursor. The solid solution is of spinel structure, in which nickel, manganese, and aluminum are sufficiently mixed at atomic level. Rietveld refinement of X-ray diffraction data revealed that Al doping in LiNi_0.5Mn_0.5O₂ was significantly effective to decrease the degree of Li/Ni cation mixing. XPS analysis showed that the valence states of nickel and manganese were mainly +2 and +4, respectively. LiNi_0.475Mn_0.475Al_0.05O₂ delivered a stable capacity of about 206 mAh g⁻¹ with high reversibility. High-rate capability test was also performed.     

Catalytic oxidation of NO over Mn–Co–Ce–Ox catalysts: effect of reaction conditions

Manganese–cobalt–cerium oxide (Mn–Co–Ce–Ox) catalysts were synthesized by the co-precipitation method and tested for activity in low-temperature catalytic oxidation of NO in the presence of excess O₂. With the best Mn–Co–Ce mixed-oxide catalyst, approximately 80 % NO conversion was achieved at 150 °C and a space velocity of 35,000 h^?1. The effect of reaction conditions (reaction temperature, volume fractions of NO and O₂, gas hourly space velocity (GHSV), and catalyst stability) was investigated. The optimum reaction temperature was 150 °C. Increasing the O₂ content above 3 % results in almost no improvement of NO oxidation. This catalyst enables highly effective removal of NO within a wide range of GHSV. Furthermore, the stability of the Me–Co–Ce–Ox catalyst was excellent; no noticeable decrease of NO conversion was observed in 40 h.     

Phase Transformations in the Mn–Ga–O System Depending on the Preparation Conditions

Manganese-gallium samples with cation ratios Mn:Ga = 1:2, 1.5:1.5, and 2:1 are synthesized by coprecipitation with subsequent annealing in air in a temperature range 600–1200 °C. Powder XRD, TEM, and BET methods are used to study the physicochemical characteristics of the samples. It is found that in the air at the annealing temperature of 600 °C finely dispersed low-temperature Mn_3–xGa_xO₄ spinels primarily form in all series, but in the whole temperature range (600–1200 °C) the system is multiphase. Annealing at 800–1200 °C leads to an increase in the concentration of simple oxides (β-Mn₃O₄ and β-Ga₂O₃). Only simple α-Mn₂O₃ and β-Ga₂O₃ oxides exist in a Mn:Ga = 2:1 series at 800 °C. In the sample with a cation ratio Mn:Ga = 1.5:1.5 annealed in air at 1000 °C, the formation of a superstructure based on the spinel structure is found.     

Synthesis and characterization of mesoporous Mn–Ni oxides for supercapacitors

Mesoporous Mn–Ni oxides with the chemical compositions of Mn_1-x Ni _x O _δ (x = 0, 0.2, and 0.4) were prepared by a solid-state reaction route, using manganese sulfate, nickel chloride, and potassium hydroxide as starting materials. The obtained Mn–Ni oxides, mainly consisting of the phases of α- and γ-MnO₂, presented irregular mesoporous agglomerates built from ultra-fine particles. Specific surface area of Mn_1–x Ni _x O _δ was 42.8, 59.6, and 84.5 m² g⁻¹ for x = 0, 0.2, and 0.4, respectively. Electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge/discharge in 6 mol L⁻¹ KOH electrolyte. Specific capacitances of Mn_1-x Ni _x O _δ were 343, 528, and 411 F g⁻¹ at a scan rate of 2 mV s⁻¹ for x = 0, 0.2, and 0.4, respectively, and decreased to 157, 183, and 130 F g⁻¹ with increasing scan rate to 100 mV s⁻¹, respectively. After 500 cycles at a current density of 1.24 A g⁻¹, the symmetrical Mn_1–x Ni _x O _δ capacitors delivered specific capacitances of 160, 250, and 132 F g⁻¹ for x = 0, 0.2, and 0.4, respectively, retaining about 82%, 89%, and 75% of their respective initial capacitances. The Mn_0.8Ni_0.2O _δ material showed better supercapacitive performance, which was promising for supercapacitor applications.     

Study of Mechanisms of CO and NO2O xidation on Zn–CNT(6,0) and Zn–BNNT(6,0),Mn–B38N38 and Mn–C76

The abilities and performances of Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)to the oxidation of NO2 and CO are investigated.The oxidation reactions of NO2 and CO through the Langmuir-Hinshelwood(LH)and Eley-Rideal(ER)mechanisms by theoretical methods are examined.The most stable intermediates of oxidation reactions of NO2 and CO on Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)are obtained from thermodynamics view point.In the LH pathway,Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)catalysts are deactivated via the second NO2 and CO molecules.In the ER pathway,the second NO3 and CO2 molecules are separated.Finally,the Mn–C76,Mn–B38N38,Zn–CNT(6,0)and Zn–BNNT(6,0)are proposed to oxidize NO2 and CO molecules with high performances at room temperature.     

Heterogeneous Fenton degradation of azo dye 4BS over Co–Mn–Fe ternary hydrotalcites

This work described the application of Co–Mn–Fe hydrotalcites (Co–Mn–Fe LDHs) as heterogeneous catalysts for Fenton reaction process. The Co–Mn–Fe LDHs were synthesized by the co-precipitation method and were characterized by X-ray diffractometry (XRD), infrared spectroscopy (IR), zeta potential, and BET surface area measurement. The catalytic activity of different kinds of hydrotalcites was evaluated by the degradation of Direct Scarlet 4BS (4BS). The Co–Mn–Fe LDHs showed the best catalytic performance among four catalysts. The presence of the Mn²⁺/Mn³⁺ at surface of catalyst could accelerate the reduction of Co³⁺–Co²⁺, and then increased in the catalytic activity of the Co–Mn–Fe LDHs. The effect of initial pH, catalyst dosage, dye concentration, and reaction temperature on the degradation of 4BS had been investigated. Radical reaction mechanism was proposed by the addition of radical scavenger. The degradation kinetic followed pseudo-first-order model. The activation energy of Co–Mn–Fe LDHs was determined to be 37.3 kJ/mol. The catalytic activity of Co–Mn–Fe LDHs was maintained after four cycles of reaction, which proved the reusability of catalyst. Finally, the possible reaction mechanisms involved in the heterogeneous Fenton system were proposed.     

A Comparison of NO Reduction Over Mn–Cu/ZSM5 and Mn–Cu/MWCNTs Catalysts Assisted by Plasma at Ambient Temperature

Manganese–copper bimetal oxide catalysts supported on ZSM5 and acid-treated multi-walled carbon nanotubes (MWCNTs) were produced by incipient wetness impregnation for selective catalytic reduction of NO with dielectric barrier discharge plasma. Plasma can activate molecules even at ambient temperature, generating active oxygen species such as O, O₃, and HO₂ radicals, which can oxidize NO to NO₂ effectively. The SCR activity of Mn–Cu/MWCNTs was studied and compared to that of the Mn–Cu/ZSM5. The obtained samples were characterized by XRD, SEM, TEM, ICP, H₂-TPR, Raman spectroscopy, and XPS. The results show that Mn–Cu/MWCNTs catalyst possesses NO removal activity superior to that of the Mn–Cu/ZSM5 catalyst. MWCNTs-based catalyst attains NO removal efficiency of 88% at 480 J/L, while the ZSM5-supported catalyst achieves NO removal efficiency of 82% at the same energy density. The oxygen content increased from 3.33 to 19.07% on the nanotube surface after introducing Mn and Cu, which almost remained unchanged on ZSM5. The oxygen-containing functionalities are important for NO_x adsorption and removal. Moreover, the characterization revealed that CuO is the main phase of copper oxide, but copper dispersion decreases on Mn–Cu/ZSM5 surface because of the formation of copper dimer species. The manganese is well-dispersed on the catalysts, MnO₂ and Mn₂O₃ contents of Mn–Cu/MWCNTs are larger than that of Mn–Cu/ZSM5, MnO₂ is the predominant phase of manganese oxide.     

Ligand-free C–N bond formation in aqueous medium using a reusable Cu–Mn bimetallic catalyst

A general ligand-free protocol has been described for the recyclable and reusable Cu–Mn catalyzed C–N bond forming cross coupling reaction of arylboronic acids with various amines to form N-arylated amine products in aqueous medium affording excellent yields under ambient conditions, in 3–4 h.     

Effects of vanadium and cadmium on transformation temperatures of Cu–Al–Mn shape memory alloy

Cu-based quaternary shape memory alloys were extensively investigated alloy in last decade. In this study, Cu–Al–Mn, Cu–Al–Mn–V and Cu–Al–Mn–Cd shape memory alloys were produced by arc melting. We have investigated the effects of the alloying elements on the characteristic transformation temperatures, variations in structure and microstructure. The characterization of the transformation temperatures was studied by the differential scanning calorimetry. It was observed that the addition of the vanadium and cadmium decreases the characteristic transformation temperatures. The structural changes of the samples were studied by X-ray diffraction measurements and optical microscope observations. The crystal structure of the martensite Cu–Al–Mn, Cu–Al–Mn–V and Cu–Al–Mn–Cd shape memory alloys were identified as M18 at room temperature. The crystallite sizes of the alloys were determined. The microstructure of the alloy was studied with the help of optical microscope and V-type martensites with different orientations were detected. Microhardness value of the alloys were found between 194 and 211 Hv.     

Influence of Mn on the solidification of Fe–Si–Al alloy for non-oriented electrical steel

Differential scanning calorimetry, thermodynamic calculations, and metallographic analyses were used for a determination of the solidification sequence in a Fe–2.42 %Si–0.5 %Al–0.94 %Mn alloy. For the prediction of the solidification process of the Fe–Si–Al–Mn alloy also a modified Scheil–Gulliver solidification model was used. According to the thermodynamic calculations the two-phase region in the selected Fe–Si–Al–Mn alloy is stable between 1,303 and 913 °C. The highest mass-fraction of the γ-phase is reached at 1,150 °C. With decreasing temperature the austenite retransforms into ferrite. In the temperature range where the thermodynamic calculations predict the existence of the two-phase region in the DSC curves, weak thermal events were observed. A post-exposure metallographic analysis revealed that the substructures in the ferrite microstructure indicate the γ → α phase transformation. This suggests consistency between the differential scanning calorimetry, the thermodynamic calculations, and the metallographic analyses.     

Simple preparation of Mn–N-codoped titania photocatalyst with visible light response

Mn–N-codoped TiO₂ nanocrystal photocatalysts responsive to visible light were synthesized for the first time by a simple hydrothermal synthesis method. X-ray powder diffraction (XRD) measurement indicated that all the photocatalysts have an anatase crystallite structure, and that increase of the doping concentration had little effect on the structure and particle size. Compared to N-doped TiO₂, a shift of the absorption edge of Mn–N-codoped TiO₂ to a lower energy and a stronger absorption in the visible light region were observed. The Mn–N-codoped TiO₂ showed higher photocatalytic reactivity than undoped TiO₂ or N-doped TiO₂ for the photodegradation of rhodamine B (RhB) under visible light irradiation. The highest photocatalytic activity was achieved on 0.4 mol% Mn–N–TiO₂ calcined at 673 K.