Porous Manganese Oxide Research Articles

Spontaneous Formation of Inorganic Helical Fibers and Rings

Helical fibers of porous manganese oxide have been prepared from colloidal solutions. Such fibers have diameters ranging from several mm to the micrometer range. These helices are formed, starting from a well-mixed colloidal precursor and applying no external forcing other than its confinement in a capillary or beaker and heating for a period of time. Structural changes occur during gelation, leading from an amorphous to a layered structure. The layered structure can be ion-exchanged with hard cation template ions and then heated to form tunnel structure materials that retain the helical morphology. The helices are semiconductors and permeable. As the concentration of the colloidal precursor is lowered, helices are no longer formed, but instead, two-dimensional rings are produced. The formation process of these helices is related to contraction of the gel during heating with capillary pressure until solvent is removed followed by expansion of the helix.

Primary Alkaline Battery Cathodes A Three‐Scale Model

A mathematical model for the galvanostatic discharge and recovery of porous, electrolytic manganese dioxide cathodes, similar to those found within primary alkaline batteries is presented. The phenomena associated with discharge are modeled over three distinct size scales, a cathodic (or macroscopic) scale, a porous manganese oxide particle (or microscopic) scale, and a manganese oxide crystal (or submicroscopic) scale. The physical and chemical coupling between these size scales is included in the model. In addition, the model explicitly accounts for the graphite phase within the cathode. The effects that manganese oxide particle size and proton diffusion have on cathodic discharge and the effects of intraparticle voids and microporous electrode structure are predicted using the model. © 2000 The Electrochemical Society. All rights reserved.

Spontaneous formation of inorganic helices

Attempts to generate films, wires, helices, rings and regular patterns out of inorganic materials1,2,3,4,5,6,7,8,9,10 have been going on for the past 100 years. We show here that stable helices of porous manganese oxide materials can be formed spontaneously from uniform sols and that they are excellent semiconductors. These inorganic helices contain micropores, can be converted into other structures, and their composition can be varied.

Manganese oxide porous crystals

This article reviews the structure, synthesis, host-guest reaction in aqueous phase, and ion-sieve and molecular-sieve properties of porous manganese oxide crystals. Tunnel and layered manganese oxides constitute a large family of porous materials having pore size from ultramicropores to mesopores. The manganese oxide crystals consist of MnO 6 octahedral units shared by corners and/or edges. They can be prepared by using various metal ions or organic surfactants as templates. The templates are extracted/inserted topotactically from/into the tunnels or interlayer spaces of the manganese oxides by two different mechanisms: redox-type and ion-exchange-type. These manganese oxides show excellent ion-sieve and molecular-sieve properties for the adsorptions of cations or organic molecules. The adsorptive selectivities are dependent on their structures.

A Review of Porous Manganese Oxide Materials

This review concerns the synthesis, characterization, and applications of porous manganese oxides during the last two years. The synthesis of porous tunnel structures, layered structures, and related materials is discussed. Both microporous and mesoporous systems materials are covered here. Characterization discussed here focuses around structural studies. The focus of the application sections include electrochemical and catalytic studies.

Standard Nitrogen Adsorption Data for Manganese Oxide and like (CBET = 40–60) Surfaces

Calcination to 1170 K of materials obtained by mild and intensive reduction of KMnO4 and HMnO4 solutions was found to produce manganese oxides assuming the crystalline bulk structure of α-Mn2O3 Nitrogen adsorption isotherms at 77 K revealed that they also assume non-porous surfaces of low specific area (4 ± 1 m2/g) with CBET equal to 40–60; t- and αs-curves derived therefrom were found to coincide with those determined reportedly on non-porous surfaces of 11 < CBET < ∞, irrespective of the surface chemical similarity. The experimental and reported standard adsorption data were used to analyze a type-IV nitrogen adsorption isotherm determined at 77 K on a porous manganese oxide (δ-MnO2) which was obtained by sol–gel processing of a KMnO4 solution, and found to similarly reveal a mesoporous surface of SBET = 73 m2/g and CBET = 125. The close agreement between the surface area values (St and Sα) derived for the test material (δ-MnO2) from the t- and αs-plots thus obtained and its CBET value (73 m2/g) was the basis on which reference materials with 11 < CBET < ∞ were found to be appropriate. Since most of the appropriate reference materials were dissimilar chemically to the test material, the results of the present investigation may imply that the surface chemical similarity demanded by the αs-method is better manifested in terms of the surface activity (heat of adsorption monitored by the CBET value) than the chemical composition.

Microporous manganese oxides

Several types of new materials including tunnel and layer structures of porous manganese oxides have recently been reported. New developments in the characterization and application of such materials are also of current interest. Manganese doped oxide systems are sometimes useful models for these microporous materials.

Decomposition of Pinacyanol Chloride Dye Using Several Manganese Oxide Catalysts

The decomposition of the cyanine dye, pinacyanol chloride, has been studied using hydrogen peroxide and several mixed valent manganese oxide catalysts in aqueous, alkaline solution at room temperature. These catalysts belong to a class of porous manganese oxides known as octahedral molecular sieves (OMS). The most active catalysts were those of Fe3+-, Cr3+-, and Co2+-doped OMS-2. Rates of reaction were found to be first-order with respect to the dye. The highest reaction rates were observed when no H2O2 was present. Reactions were studied at pH = 6−11, which caused variations in the catalytic activity. The decomposition of the dye was examined using varying amounts of the catalysts, which showed the dye decomposing activity to be proportional to the amount of catalyst. X-ray diffraction studies showed that no changes in the catalyst structure occurred, implying that these reactions are surface controlled.