Electrospinning provides a simple approach to fabricating nanofibers and assemblies with controllable hierarchical structures. In this communication, we demonstrate that electrospinning can be combined with calcination to further maneuver the morphology and phase structure of nanofibers. More specifically, single-crystal V2O5 nanorods could be grown on rutile nanofibers by carefully calcining composite nanofibers consisting of amorphous V2O5, amorphous TiO2, and poly(vinylpyrrolidone). The size of the resulting V2O5 nanorods could be conveniently controlled by varying the composition of the nanofibers and/or the calcination temperature. In addition to the nanorod-on-nanofiber hierarchical structure, we believe this approach can also be extended to fabricate other more complex architectures.

Herein, we report the synthesis and photocatalytic properties of novel Bi2O3 nanomaterials. Cubic mesoporous films were produced by coassembly of hydrated bismuth nitrate with a poly(ethylene-co-butylene)-block-poly(ethylene oxide) diblock copolymer, referred to as KLE, while nanofiber mats were produced via electrospinning. We establish that all materials employed in this work are highly crystalline after thermal treatment and that the nanoscale order of the self-assembled samples is further retained. KLE-templated films can readily produce phase-pure β-Bi2O3 with an optical band gap of about 3.4 eV. Calcination of nanofibers, by contrast, leads to the formation of a composite consisting of β-Bi2O3 and trace amounts of the thermodynamically stable α-Bi2O3 phase. We further show the benefits of a mesoporous morphology in heterogeneous semiconductor photocatalysis. KLE-templated β-Bi2O3 films exhibit much greater photocatalytic activity than nanofiber mats and nontemplated Bi2O3 films (prepared under otherwise identical conditions) as well as than KLE-templated anatase TiO2 films on a mass normalized basis. We associate this exceptional activity with (1) the comparatively high BET surface area, which provides for a large number of adsorption sites, and (2) the high phase purity of the more catalytically active β-Bi2O3.

No abstract

The new dinuclear nickel-ruthenium complexes [Ni(xbsms)RuCp(L)][PF(6)] (H(2)xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene; Cp(-) = cyclopentadienyl; L = DMSO, CO, PPh(3), and PCy(3)) are reported and are bioinspired mimics of NiFe hydrogenases. These compounds were characterized by X-ray diffraction techniques and display novel structural motifs. Interestingly, [Ni(xbsms)RuCpCO][PF(6)] is stereochemically nonrigid in solution and an isomerization mechanism was derived with the help of density functional theory (DFT) calculations. Because of an increased electron density on the metal centers [Eur. J. Inorg. Chem. 2007, 18, 2613-2626] with respect to the previously described [Ni(xbsms)Ru(CO)(2)Cl(2)] and [Ni(xbsms)Ru(p-cymene)Cl](+) complexes, [Ni(xbsms)RuCp(dmso)][PF(6)] catalyzes hydrogen evolution from Et(3)NH(+) in DMF with an overpotential reduced by 180 mV and thus represents the most efficient NiFe hydrogenase functional mimic. DFT calculations were carried out with several methods to investigate the catalytic cycle and, coupled with electrochemical measurements, allowed a mechanism to be proposed. A terminal or bridging hydride derivative was identified as the active intermediate, with the structure of the bridging form similar to that of the Ni-C active state of NiFe hydrogenases.

No abstract

The study demonstrates that mesoporous anatase nanofibers can be prepared via electrospinning of preformed TiO 2 nanoparticles in an adequate solvent mixture without the use of any surfactant. A systematic study of several parameters influencing the fiber formation, that is, solvent composition, molecular weight of the polymer, TiO 2 source, and humidity, was conducted to investigate the underlying physicochemical principles that determine the formation of the porous structure. The porosity of the fibers was characterized by nitrogen physisorption and SEM investigations with consistent results. It is proposed that the microphase separation of nanoparticles from the polymer produces a mesoscopic hybrid, resulting in pronounced mesoporosity after calcination. We believe that our study thus presents a general methodology to generate nonwovens of metal oxides with intrinsic mesoporosity based on electrospinning of preformed nanoparticles.

Electrospinning of a polyelectrolyte and vapor deposition polymerization were combined to fabricate nanotubes of oxidatively stabilized poly(acrylonitrile) (PANDelta) with an outer diameter of 100 nm, a wall thickness of 14 nm, and centimeter-scale length. Poly(styrene sulfonate) sodium (PSSNa) nanofibers serves as sacrificial cores while vapor deposition polymerization was used to form smooth PAN sheaths of even thickness. After the PAN sheaths had been oxidatively stabilized, the PSSNa cores were etched away with water to form nanotubes of PANDelta. High-temperature carbonization of these nanotubes at 900 degrees C under Ar flow yielded carbon nanotubes with an outer diameter of 80 nm and wall thickness of 10 nm. Raman spectroscopy confirms that the carbon nanotubes were composed of highly disordered graphene sheets, consistent with the carbonization of PAN under similar conditions. These carbon nanotubes have many promising applications as catalyst supports, gas absorbents, and as encapsulants for controlled release of active compounds.

Long‐term stability is a major issue in heterogeneous catalysis and is often related to structural instabilities, which are difficult to assess in the early stage of catalyst screening. However, studies of morphological transformations in catalytic systems can greatly benefit from a well‐defined starting morphology and microstructure of the catalyst to be analysed. The present study suggests the use of catalysts in the form of 1 D nanofibres (NFs) as a conceptual methodology to assess catalyst stability, which is exemplified for the HCl oxidation reaction. These nanostructured model catalysts are synthesised by electrospinning, a versatile method to produce metal oxide NFs. We have studied the stability of RuO2‐ and CeO2‐based materials in the harsh HCl oxidation reaction (Deacon process). At 573 K pure RuO2 NFs have shown to be morphologically unstable, whereas mixed RuO2‐TiO2 NFs are stable. The stability of CeO2‐based NFs in the HCl oxidation was studied at 703 K. Under HCl lean conditions CeO2 NFs are stable, whereas under HCl rich conditions pure CeO2 NFs disintegrate by recrystallisation, forming (hydrated) Ce‐chloride. If CeO2 is doped with 20 % of Zr, the resulting mixed oxide Zr0.20Ce0.80O2 NFs have shown to be stable even under HCl rich reaction conditions and are similarly active as pure CeO2. These are the first activity experiments of mixed oxide ZrxCe1−xO2 in the Deacon process. The versatility of electrospun NFs as model catalysts has been demonstrated for testing catalyst stability in terms of morphology changes, thus serving as a proof‐of‐principle study.