Hydrothermal stability of some manganese oxides

Hydrothermal phase reaction studies in the systemsβ-MnO₂-H₂O,γ-Mn₂O₃H₂O andγ-MnO₂-H₂O have been carried out. Based on the experimental data and the reported phase diagrams in Mn₂O₃-H₂O and MnO-H₂O systems, hydrothermal stability temperature of some of the manganese oxide minerals has been defined.     

Measuring the redox activity of individual catalytic nanoparticles in cerium-based oxides

We have followed the dynamic redox process taking place in individual ceria zirconia nanoparticles with changes in the oxygen chemical potential using an in situ environmental transmission electron microscopy (ETEM). We observe considerable variability in the redox activity and have been able to correlate these differences with nanoscale structural and compositional measurements. We find that the more active structure has predominantly disordered cations and shows no evidence for oxygen vacancy ordering during reduction.     

Control of nonstoichiometric defects in manganese oxides by self-propagating high-temperature synthesis

Nonstoichiometric compounds of Mn_1−δO were self-propagating high-temperature synthesized by ignition of thoroughly mixed powders of Mn, NaClO₄, and MnO without additional external heating. The mixing ratio was systematically varied to control δ. Single phase Mn_1−δO products containing nonstoichiometric defects were obtained for 0 < δ ≤ 0.025. With increase in δ, Mn₃O₄ content of the products is increased. Double phases of Mn_1−δO and Mn₃O₄ were obtained at 0.025 < δ ≤ 0.150. The lattice parameter, a, of the single phase Mn_1−δO was well explained by the linear equation: a = −0.0667δ + 4.448.     

Microcolumn studies of dye adsorption onto manganese oxides modified diatomite

The method described here cannot fully replace the analysis of large columns by small test columns (microcolumns). The procedure, however, is suitable for speeding up the determination of adsorption parameters of dye onto the adsorbent and for speeding up the initial screening of a large adsorbent collection that can be tedious if a several adsorbents and adsorption conditions must be tested. The performance of methylene blue (MB), a basic dye, Cibacron reactive black (RB) and Cibacron reactive yellow (RY) was predicted in this way and the influence of initial dye concentration and other adsorption conditions on the adsorption behaviour were demonstrated. On the basis of the experimental results, it can be concluded that the adsorption of RY onto manganese oxides modified diatomite (MOMD) exhibited a characteristic "S" shape and can be simulated effectively by the Thomas model. It is shown that the adsorption capacity increased as the initial dye concentration increased. The increase in the dye uptake capacity with the increase of the adsorbent mass in the column was due to the increase in the surface area of adsorbent, which provided more binding sites for the adsorption. It is shown that the use of high flow rates reduced the time that RY in the solution is in contact with the MOMD, thus allowing less time for adsorption to occur, leading to an early breakthrough of RY. A rapid decrease in the column adsorption capacity with an increase in particle size with an average 56% reduction in capacity resulting from an increase in the particle size from 106-250 microm to 250-500 microm. The experimental data correlated well with calculated data using the Thomas equation and the bed depth-service time (BDST) equation. Therefore, it might be concluded that the Thomas equation and the BDST equations can produce accurate predication for variation of dye concentration, mass of the adsorbent, flow rate and particle size. In general, the values of adsorption isotherm capacity obtained in a batch system show the maximum values and are considerably higher than those obtained in a fixed-bed.     

镍铬复合掺杂尖晶石锰酸锂的合成与性能研究

采用高温固相合成法制备了LiMn2O4、Ni和Cr以及Ni-Cr复合掺杂的锂离子电池用锰酸锂正极材料.采用扫描电子显微镜、X射线粉末衍射和充放电性能测试等手段研究了材料的形貌、物相和电化学行为.结果表明:掺杂改善了材料的形貌,稳定了材料的结构.样品LiMn1.85Ni0.075Cr0.075O4的表面光滑,粒度分布范围小,为单一的尖晶石结构的物相.其首次放电容量为81.2mAh/g,300次循环后容量保持率为首次的91%,表现出优异的循环性能.     

Mixed manganese spinel oxides: optical properties in the infrared range

Spinel oxides in manganite family are studied in terms of optical properties in the infrared range (3–12 μm). The reflectivity is measured on sintered pellets. The complex refractive index is estimated by fitting hemispherical directional reflectance in both polarizations, perpendicular and parallel. The influence of different metallic cations (Ni, Co, Fe, Cu) is compared. In particular, in the case of manganese nickel copper oxides, the impact of variations in copper and nickel contents is evaluated. Cationic distribution is determined and correlated to the optical characteristics. These materials, usually used for NTC thermistor applications, are investigated for IR charges in coating.     

锰氧化物的结构分析及其在能源与环境中的典型应用EI北大核心CSCD

锰氧化物作为最常见的过渡金属氧化物之一,是一种极具潜力的材料,可通过改变其晶型、形貌、比表面积和氧空位数量等调节催化活性、吸附能力、稳定性等性能。调控MnO_(X)的晶体结构及形貌以提高其性能,一直是国内外学者极为关注的问题。本文分析了不同晶型二氧化锰(α,β,γ,δ,λ)的结构特点及其与催化/吸附性能之间的构效关系,系统总结了不同形貌MnO_(X)(纳米棒、纳米片、纳米花、纳米球)的制备方法及结构特点,并介绍了锰氧化物近年来在能源(生物质催化转化、电化学)及环境治理(气体污染物分解、重金属吸附、有机污染物降解)中的典型应用。最后,对锰氧化物存在作用机制复杂、稳定性较差等问题进行了分析。尽管锰氧化物在研究过程中还存在问题,但其作为一种重要的金属氧化物,未来在环境、能源等领域中的应用前景十分广阔。     

层状锰酸锂正极材料的掺杂改性及性能

采用溶胶-凝胶法制备层状LiMnO2的正极材料，并对其进行不同比例的过渡元素钴镍镧铈掺杂改性。用XRD以及SEM对其进行物相和表面形貌的分析，同时用锂离子电池模具装配电池以及进行恒电流充放电、循环伏安等电化学测试，分析了掺杂元素对其电化学性能的影响。XRD分析结果表明所合成的锰酸锂材料呈斜方晶系，SEM形貌显示产物为明显的层状结构，循环充放电测试结果表明掺杂2％Ni2％Co6％Ce的层状锰酸锂正极材料的初次放电比容量为161．8mAh／g，循环稳定性较好：而掺杂了6％Co4％La的层状锰酸锂正极材料的初次放电容量为111．5mAh／g，表现了很好的电化学性能。     

Potentiodynamical deposition of nanosized manganese oxides as high capacitance electrochemical capacitors

Nanosized manganese oxides powders were potentiodynamically deposition onto the Pb substrates by anodic oxidation in 0.5 mol L⁻¹ MnSO₄ and 0.5 mol L⁻¹ H₂SO₄ mixed solution at 40 °C. The chemical composition of the sample was determined by complex titration with ethylene diamine tetraacetic acid and redox titration. X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and chronopotentiometry were employed to characterize the materials. The highest specific capacitance of the MnO_x composite electrode was up to 420 F g⁻¹ in 1.0 mol L⁻¹ Na₂SO₄ electrolyte at the scan rate 5 mV s⁻¹. The synthesized nanosized manganese oxide exhibited ideal capacitive behavior indicating a promising electrode material for electrochemical supercapacitors.     

A facile template-free preparation of porous manganese oxides by thermal decomposition method

Porous Manganese oxides with large surface area were prepared by a facile template-free method. Highly crystallized MnCO₃ precursors with micron size in high dispersivity were prepared in water first. Thermal treatment was carried out with the obtained composite at different temperatures to produce porous manganese oxides. Thermogravimetry and differential thermal analysis (TG-DTA), X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and N₂ adsorption-desorption measurements were applied to characterize the porous manganese oxides. Amorphous MnO₂ obtained at 400°C shows a mesoporous structure and has a large specific surface area of 135.1 m²/g. Well crystallized α-Mn₂O₃ crystal with surface area of 18.51 m²/g macroporous framework was obtained at 600°C.     

Simultaneous synthesis of high crystalline manganese oxides with layered and tunnel structures

High crystalline manganese oxides with birnessite-type (H-BirMO) and large 2 × 4 tunnel-type (Na-2 × 4) were synthesized simultaneously using a low crystalline Na-form birnessite (NaBir) as a precursor in a 2 M NaOH solution at low temperature (150 °C) and autogenous pressure. The weight ratio of the obtained Na-2 × 4 to H-BirMO was about 50. Elemental analyses indicated that Na-2 × 4 had a formula in one unit cell of Na₈Mn₂₇O₅₃·9H₂O, and the manganese average oxidation state was 3.63. H-BirMO had a formula of Na_0.31Mn_2.04O₄·0.66H₂O and the manganese average oxidation state of 3.77. H-BirMO contained a set of basal reflections with d values that correspond to a minimum periodicity along c equal to 7.06 Å. H-BirMO belonged to a monoclinic system, and the lattice parameters were a = 5.18 Å, b = 2.85 Å, c = 7.35 Å, and β = 103.3°, respectively. Na-2 × 4 showed that the first peak appeared at a d spacing of 12.07 Å in the [0 0 2] direction, and the second peak had a similar d spacing of 7.16 Å in the [2 0 0] direction with Na-birnessite in the [1 0 0] direction. FE-SEM image of H-BirMO showed a very large plate-like morphology, while SEM photograph of Na-2 × 4 consisted of nanofibers with a thickness of about 80 nm and lengths ranging between 6 and 10 μm.     

Effect of Co on the magnetism and phase stability of lithiated manganese oxides

We present first-principles calculations of the relative energies of various phases of lithiated manganese oxides with and without Co. We use the ultrasoft pseudopotential method as implemented in the Vienna ab initio simulation package (VASP). The calculations employ the local spin density approximation (LSDA) as well as the generalized gradient approximation (GGA). We consider monoclinic and rhombohedral structures in paramagnetic, ferromagnetic and antiferromagnetic (AF3) spin configurations. Spin-polarization significantly lowers the total energy in all cases. The effect of Co on the stability of these phases is discussed.     

A facile method to prepare layered manganese oxides with large interplanar spacing

Layered manganese oxides with basal spacings up to 38.1 Å have been synthesized by a facile novel method in which cationic surfactant CTAB directly reacts with MnSO₄·H₂O and NaOH. The as-synthesized samples have expanded birnessite-type layered structures characterized by powder XRD and TEM. Synthetic parameters that are important to the formation and the basal spacing of the layered mesostructures are investigated, including the surfactant concentration, OH⁻/Mn²⁺ ratio, CTAB/Mn²⁺ ratio and aging time. Mechanisms based on self-assembling are discussed.