Nickel hydroxide has received increased attention especially due to its electrochemical properties and potential applications in rechargeable Ni-base alkaline batteries, e.g., Ni/Cd, Ni/Zn, and Ni/MH. Ni(OH)2 has a hexagonal layered structure with two polymorphs, α- and β-Ni(OH)2. α-Ni(OH)2 shows superior electrochemical properties compared to those of the β-form. Nanosized flowerlike α-nickel hydroxide materials with an interlayer spacing of 7.0 Å have been prepared by a microwave-assisted hydrothermal method. The experimental results from XRD and FT-IR showed that the Ni(OH)2 sample prepared by this method had the typical α-phase. FE-SEM images showed many uniform flowerlike architectures with diameters of 700 nm−1µm which consisted of the aggregated flakes. TEM results showed the flakes were built up from many nanocrystals with 2–3 nm diameters. TGA and TPD were employed to investigate thermal stability and gas evolution during the heating process. α-Nickel hydroxide was transferred to NiO with a cubic crystalline structure after being calcined at 450 °C; the NiO still kept the morphology of α-Ni(OH)2. Cyclic voltammetry was used to determine the electrochemical properties of the Ni(OH)2 electrode in 1 M KOH. α-Ni(OH)2 prepared by MW-HT had the best electrochemical activity for the electrochemical reduction of O2 compared with α-Ni(OH)2 synthesized by conventional HT methods and β-Ni(OH)2. The effects of nickel sources and precipitators on the phase and morphology of the products were studied. Conventional hydrothermal methods were used to study the role of microwave irradiation. The possible growth mechanism is discussed here. The CV experiments showed that H2O2 can be reduced to OH− on the α-Ni(OH)2 electrode. The Levich equation was used to calculate the number of electrons transferred during the O2 redox reaction.

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...

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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