Cryptomelane-type manganese oxide octahedral molecular (OMS) sieve three-dimensional (3D) nanostructures were synthesized via facile temple-free low-temperature hydrothermal reactions. Morphologies of the cryptomelane-type OMS-2 nanoparticles with tunnel dimension of 4.6 x 4.6 A can be tuned by varying reaction temperatures. At low temperature (120 degrees C), OMS-2 dendritic nanoclusters composed of uniform single-crystal nanotetragonal prisms with square cross-sections were formed. At high temperature (180 degrees C), the morphologies of OMS-2 became spherical dandelion-like microspheres composed of uniform single-crystal OMS-2 nanoneedles. Slow oxidation of Mn(2+) by Cr(2)O(7)(-) under hydrothermal conditions is critical for the formation of the hierarchically ordered OMS-2 3D nanostructures.

Novel three‐dimensional (3D) hierarchical nanoarchitectures of ϵ‐MnO2 have been synthesized by a simple chemical route without the addition of any surfactants or organic templates. The self‐organized crystals consist of a major ϵ‐MnO2 dipyramidal single crystal axis and six secondary branches, which are arrays of single‐crystal ϵ‐MnO2 nanobelts. The growth directions of the nanobelts are perpendicular to the central dipyramidal axis, which shows sixfold symmetry. The shape of the ϵ‐MnO2 assembly can be controlled by the reaction temperature. The morphology of ϵ‐MnO2 changes from a six‐branched star‐like shape to a hexagonal dipyramidal morphology when the temperature is increased from 160 to 180 °C. A possible growth mechanism is proposed. The synthesized ϵ‐MnO2 shows both semiconducting and magnetic properties. These materials exhibit ferromagnetic behavior below 25 K and paramagnetic behavior above 25 K. The ϵ‐MnO2 system may have potential applications in areas such as fabrication of nanoscale spintronic materials, catalysis, and sensors.

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A new soft-step chemistry method has been developed to prepare pure cryptomelane-type manganese oxide materials (OMS-2) with the smallest particle sizes ever reported. The synthetic procedure is based on the reduction of KMnO4 by H2O2 under acidic conditions followed by reflux. An acetate-containing buffer solution and HNO3 are used to control the pH of the reaction mixture. The formation process, particle size, crystallite size, crystal structure, and properties of these nanomaterials have been investigated by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), potentiometric titration, thermogravimetric analysis, and N2 sorption analyses. Both the concentration of H2O2 and the nature of the acid used affect the crystalline phase formation, microstructure, thermal stability, and the composition of the final product. HRTEM images reveal that the OMS-2 nanofibers are not oriented preferentially and present significant twinning, along with discontinuity in the growth of the tunnel. Catalytic studies of these OMS-2 nanomaterials for oxidation of benzyl alcohol and fluorene have been performed. These nanomaterials show a low performance for the oxidation of benzyl alcohol and a unique catalytic activity for the oxidation of fluorene compared to OMS-2 materials prepared by conventional methods.

As the ethanol slowly evaporates, an iridescent film is formed on top of the glass slide. A sample can be made over 7±10 days, and the photonic crystal (PC) films are used as grown without any annealing. The three-dimensional structures of the samples and the microgrooves on the PC films were characterized using scanning electron microscopy (Hitachi, S-4200) and atomic force microscopy (AutoProbe CP Research System), respectively. Optical reflectance measurements were performed with a spectrophotometer (Ocean Optics, Inc., S2000). A pair of PC-coated ITO glass substrates were stacked and sealed to fabricate a vacant cell with a spacer. The cell gap was 7.0 lm and the y-directions of each substrate were set parallel to each other. Nematic liquid crystals (LCs) (ZLI2293, Merck) were introduced into the prepared cells using capillary action at the temperature of isotropic phase of the LCs. LC textures were observed using a polarizing microscope. The electro-optic measurements were made using He±Ne laser light (632.8 nm) with crossed polarizers at room temperature. Next, another nematic LC (PA1109) [17] was used in polarized reflectance measurements of a LC-filled Fabry±Perot cavity with PC films as a function of the amplitude of the applied rectangular voltage (f = 1 kHz). [1±7] Formation of ordered macroscopic, mesoscopic, and microscopic materials such as inorganic thin films and membranes has been an important goal, especially when specific physical properties such as porosity, permeability, and conductivity are of interest. These structures have potential applications as sensors, catalysts, and energy-storage devices, and in photoelectronics and separation processes.[8±10] Here we report the fabrication of ordered porous manganese oxide paper-like free-standing membranes (FSMs) by simply heating ªpulpº-like homogeneous suspensions at low temperatures. These free-standing membranes are robust and flexible, and can be formed on a patterned substrate in order to make micropatterns. Tangled manganese oxide nanowires in suspension aggregate and align systematically to form such membranes. The paper-like membrane is composed of single-crystal cryptomelane-type manganese oxide (OMS-2) fibers. The membrane has a metallic luster and can be folded or cut into various shapes. Manganese oxide structures can form mixed-valent octahedral molecular sieves with one-dimensional tunnel structures. Cryptomelane-type manganese oxide materials are an important group of octahedral molecular sieves. OMS-2 with a 2 2 tunnel structure has been synthesized via different methods including reflux, sol±gel, and solid-state chemical reactions, as well as by hydrothermal treatments, [11±13] to produce nanofibers, nanorods, and nanoneedles. Stoichiometric mixtures of potassium sulfate, potassium persulfate, and manganese sulfate monohydrate were hydrothermally treated at 250 C to produce cylindrical rigid solids.