The potential of graphite nanofiber supported platinum catalysts as an electrode for fuel cell applications was investigated using the electrochemical oxidation of methanol at 40 °C as a probe reaction. Various types of graphite nanofibers were used and the behavior of supported platinum particles on these materials compared to that when the metal was dispersed on Vulcan carbon (XC-72). Catalysts consisting of 5 wt % platinum supported on “platelet” and “ribbon” type graphite nanofibers, which expose mainly edge sites to the reactants, were found to exhibit activities comparable to that displayed by about 25 wt % platinum on Vulcan carbon. Furthermore, the graphite nanofiber supported metal particles were observed to be significantly less susceptible to CO poisoning than the traditional catalyst systems. This improvement in performance is believed to be linked to the fact that the metal particles adopt specific crystallographic orientations when dispersed on the highly tailored graphite nanofiber structures.

Manganese oxide hollow nanospheres were prepared using a straightforward, template-free synthesis. The resulting material was mesoporous, crystalline, and of uniform diameter. The nanospheres were characterized by XRD, HR-SEM, and HR-TEM, and pore size distributions were calculated from nitrogen desorption. Unlike previous synthesis methods that use an inorganic template, this procedure requires no separation after synthesis to remove the template. The nanospheres are composed of hexagonal gamma-manganese oxide flakes and are approximately 400 nm in diameter. gamma-MnO2 is composed of a ramsdellite matrix (1 x 2 tunnels) with randomly distributed microdomains of pyrolusite (1 x 1 tunnels). These materials could have applications as cathodic battery materials, oxidation catalysts, catalyst supports, and adsorbents for pollutants.

Porous solids, such as zeolites and other molecular sieves, contain intracrystallite/framework cavities and channels that produce microporous (pore diameter, D < 2 nm), mesoporous (2 nm < D < 50 nm), and macroporous (D > 50 nm) structures, and have demonstrated excellent potential as materials for use in many separation and catalytic processes.[1] The pore sizes of these porous materials (especially the micropore sizes, which are close to molecular dimensions) may play a critical role in controlling separation and catalytic selectivity due to their shape and size selectivity. The production of materials with different microporosities has always been challenging. Natural and synthetic tunnel-structured manganese oxide octahedral molecular sieves (OMSs) make up a promising group of functional porous materials. They can exhibit various nanometer-scale tunnel sizes from 2.3 2.3 to 4.6 11.5 , which correspond to different micropore openings. As such, they constitute excellent model systems for studying the synthesis of materials with controlled microporosities. Moreover, the potential applications for synthetic manganese oxide OMS materials can be expanded by molecular modification or decoration of the tunnel structures.[2] There have been several attempts to synthesize manganese oxide OMSs with the same tunnel structures as those found in natural manganese oxides, or to create materials with new tunnel structures.[3±7]However, there has been very little work reported on the direct control of tunnel sizes. In this communication, we report the successful synthesis of manganese oxide OMS materials with controlled nanometer-scale tunnel sizes by controlling the pH of the hydrothermal transformation of layered manganese oxide precursors. Hydrothermal transformation of layered manganese oxide materials is one of the most effective methods of obtaining tunnel-structured manganese oxides. Due to the mixed-valent manganese framework, usually (+2, +3, and +4) or (+3 and +4), a small number of guest cations are usually required for charge balance in most layer-and tunnel-structured manganese oxides. These guest cations usually reside between the layers or inside the tunnels.[3±7] When layered manganese oxides are transformed into tunnel structures, the interlayer cations remain inside the tunnels. Therefore, the types and sizes of the guest cations in these layered manganese oxides might play critical roles as structure directors in templating different tunnel sizes during synthesis of tunnel structures. Since many cations are in hydrated form under aqueous/hydrothermal conditions, the template effect may actually result from the size of the hydrated cations rather than from that of the isolated cations. This is particularly intriguing since many cations can adopt different hydration states, and thus the sizes of the hydrated cations can be different. The corollary of this is that, if the sizes of hydrated cations can be controlled by varying the extent of hydration, it may be possible to synthesize materials with controlled tu...

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.