Narrow Results

By using a negative-magnetoresistivity scaling deduced from Mott's model, a specific scheme to quantitatively describe in detail the effects of the colossal magnetoresistivity (CMR) is proposed. The field-dependence of the magnetoresistance of the magnetic perovskite La_0.7Ca_0.3MnO₃ film is analyzed. The range of error for the value of the Curie temperature is reduced by our calculations. So, the Curie temperature can be determined more precisely. Through analyzing the variation of the field sensitivity (FS) with respect to some physics quantities, the main elements that influence the values of FS are revealed. Finally, the behaviors of the magnetically aligned clusters in the magnetic perovskite La_0.7Ca_0.3MnO₃ and Nd_0.52Sr_0.48MnO₃ film are investigated and analyzed.

Mn₂O₃/Mn₅O₈ and MnO/Mn nanoparticles were prepared by annealing manganese nanoparticles in air and hydrogen, respectively. The antiferromagnetic Mn₂O₃/Mn₅O₈ and MnO/Mn nanoparticles exhibit anomalous magnetic properties, such as large moments, and large coercivity of up to 169 kA/m and 105 kA/m, respectively. This ferromagnetic-like behavior is attributed to the finite size effect of antiferromagnetic nanoparticles and the presence of ferrimagnetic Mn₃O₄ phases.

Manganese oxide nanoparticles with narrow size distribution were prepared in large scale by arc sublimation of bulk MnO. Although MnO is antiferromagnetic, the as-prepared manganese oxide nanoparticles exhibit ferromagnetic behaviors with coercivity and exchange bias up to 417,065 A/m and 162,099 A/m at 5 K, respectively. We attribute these anomalous magnetic properties to the presence of ferrimagnetic Mn₃O₄, uncompensated surface spins and their coupling to the antiferromagnetic MnO.

A simple hydrothermal growth process was developed to deposit conformal manganese oxide nanospheres with a diameter of 10 to 20 nm on mesoporous carbon paper. The coating of nanospheres increased the cyclic-voltammogramic response of carbon paper by a factor of 5 with a slight dependence on the scan rate. For comparison, a related chemistry was also developed to fabricate a dense packing of manganese oxide nanorods with a diameter of 20 to 50 nm and a length of approximately 500 nm. The nanorods also increased the cyclic-voltammogramic response of carbon paper but only by a factor of approximately 3.

Herein, a modified interfacial synthetic route has been demonstrated by synthesizing uniform poly(3,4-ethylenedioxythiophene)/MnO₂ hierarchical mesoporous nanocomposite. The in-situ generated polymer has been proven to be effective in constraining the overgrowth of nuclei. Consequently, assembled nanosheets with a thickness less than 5 nm have been prepared. At a high rate of 10 A g^-1 charge/discharge process, the nanocomposite electrode retains 73.4% of the specific capacitance exhibited at 1 A g^-1. At a current density as large as 800 mA g^-1, the nanocomposite electrode attains reversible lithium storage specific capacities of 400 mAh g^-1 after 50 cycles and 300 mAh g^-1 after 100 cycles. The excellent high-rate performance of the nanocomposite electrode is highlighted in terms of its extremely large surface area, unique microstructure and mesoporous features.

The core-shell Mn₃O₄/birnessite-MnO₂ (Mn₃O₄/MnO₂) was successfully established by assembly of birnessite-type MnO₂ over Mn₃O₄ backbones. The product was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), as well as UV–vis absorption spectra (UV–vis) to assess its adsorption of methylene blue (MB) from neutral aqueous solutions. Compared to the individual Mn₃O₄, the prepared Mn₃O₄/MnO₂ shows enhanced adsorption capability towards MB. Such enhancement is due to the higher surface area and the unique nanosheet shells. The adsorption of MB on the surface of Mn₃O₄/MnO₂ was studied in terms of pseudo-first-order and the pseudo-second-order kinetic models, and the latter was found better. The present study indicates that hierarchically structured core-shell manganese oxides are promising adsorbents for wastewater treatment.

Exploring high-capacity and stable cathode materials for aqueous rechargeable Zn ion batteries (ZIBs) is highly attractive but challenging. Herein, we present a kind of Mn₃O₄@MnS heterostructured nanoparticle as a robust ZIB cathode. These Mn₃O₄@MnS nanoparticles are facilely synthesized by in-situ transformation of MnO₂ under sulfidation thermal treatment. Owing to the heterostructured architecture and improved electrical conductivity, the as-obtained Mn₃O₄@MnS nanoparticles afford a stable capacity of 128.3 mA h g${}^{-1}$ at 2 mA cm${}^{-2}$ and good stability of more than 65% capacity retention after 1000 cycles. Additionally, a remarkably energy density of 184.72 Wh kg${}^{-1}$ is also achieved by the assembled Zn//Mn₃O₄@MnS battery. This work paves the way for constructing Mn-based heterostructures as high-performance cathodes in aqueous ZIBs.

The yMnO_x/SBA-16 samples with high surface areas (504–835 m²/g) were prepared using via an incipient wetness impregnation route. Compared to the bulk MnO₂ sample, the yMnO_x/SBA-16 samples showed better catalytic activities for the oxidation of toluene. Among all of the samples, the yMnO_x/SBA-16 sample with a Mn surface density of 1.21 Mn atom/nm² performed the best, giving a toluene consumption rate of 204.5 mL/(g_MnO2h) at reaction temperature = 380°C and space velocity = 20,000 mL/(g h). It is concluded that the high-dispersion MnO_x species, high surface area, and good low-temperature reducibility were responsible for the good catalytic performance of yMnO_x/SBA-16.

The manganese oxide (MnO₂) sample was synthesized by the reduction of KMnO₄ by MnSO₄. Cu doped manganese oxide materials have been synthesized by incorporation method and traditional wet-impregnation method. The structure of the catalysts was characterized by X-ray diffraction and N₂ adsorption/desorption analyses and their catalytic activities were performed by catalytic oxidation of CO. The doping Cu to manganese oxide by traditional wet-impregnation method result in a significant drop of area, due to the aggregation of copper oxides particles. Loading Cu to manganese oxide by incorporation method caused a slight change in surface area of the obtained Cu/MnO₂-Q catalysts. The catalytic activities of Cu/MnO₂ samples strongly depended upon the used methods, among which 5Cu/MnO₂-Q catalyst, prepared by the incorporation method, was the most efficient catalyst towards the addressed reactions. The excellent performance of 5Cu/MnO₂-Q was mainly associated with the good low-temperature reducibility, richest surface oxygen and broadly dispersed copper oxides species.