Fluorination-induced magnetism in boron nitride nanotubes from ab initio calculations

Ab initio calculations were conducted to investigate the electronic structures and magnetic properties of fluorinated boron nitride nanotube (F-BNNT). It was found that the chemisorption of F atoms on the B atoms of BNNT can induce spontaneous magnetization, whereas no magnetism can be produced when the B and N atoms are equally fluorinated. This provides a different approach to tune the magnetic properties of BNNTs as well as a synthetic route toward metal-free magnetic materials.<br /

Stabilization of mesoporous nanocrystalline zirconia with Laponite

The mesoporous nanocrystalline zircoina was synthesized via solid state reaction-structure directing method in the presence of Laponite. The introduction of Laponite renders the higher thermal stability and lamellar track to the zirconia. Laponite acts as inhibitor for crystal growth and also hard template for the mesostructure. The role of Laponite is attributed to the interaction between the zirconia precursors and the nano-platelets of Laponite via the bridge of hydrophilic segments of surfactant. It results in the formation of Zr-O-Mg-O-Si frameworks in the direction of Laponite layer with the condensation of frameworks during the calcination process, which contributes the higher stability and lamellar structure to the nano-sized zirconia samples

Mesoporous carbon fabricated with an alumina template

There has been much interest in porous carbon materials fabricated from both silica and zeolite templates. Typical procedures involve the synthesis of a silica template, impregnation of the template with a carbon precursor, polymerisation of the carbon and then removal of the template using hydrofluoric acid. Both the synthesis and removal of the silica template can be time consuming and expensive. Porous alumina can offer a cheaper and more facile template removal process using NaOH instead of hydrofluoric acid. The alumina template may also allow different pore structure than that of silica or zeolite template. Here we present initial results for mesoporous carbon templated from alumina. The carbon material had a dominant pore diameter of approximately 3.5 nm

Role of charge in destabilizing AlH4 and BH4 complex anions for hydrogen storage applications: Ab initio density functional calculations

NaAlH4 and LiBH4 are potential candidate materials for mobile hydrogen storage applications, yet they have the drawback of being highly stable and desorbing hydrogen only at elevated temperatures. In this letter, ab initio density functional theory calculations reveal how the stabilities of the AlH4 and BH4 complex anions will be affected by reducing net anionic charge. Tetrahedral AlH4 and BH4 complexes are found to be distorted with the decrease of negative charge. One H-H distance becomes smaller and the charge density will overlap between them at a small anion charge. The activation energies to release of H2 from AlH4 and BH4 complexes are thus greatly decreased. We demonstrate that point defects such as neutral Na vacancies or substitution of a Na atom with Ti on the NaAlH4(001) surface can potentially cause strong distortion of neighboring AlH4 complexes and even induce spontaneous dehydrogenation. Our results help to rationalize the conjecture that the suppression of charge transfer to AlH4 and BH4 anion as a consequence of surface defects should be very effective for improving the recycling performance of H2 in NaAlH4 and LiBH4. The understanding gained here will aid in the rational design and development of hydrogen storage materials based on these two systems

Nanomaterials for water splitting

This chapter starts with a brief introduction to the knowledge of water splitting on semiconductor nanocatalysts. Then it overviews the semiconductor nanocatalysts according to their light absorption property and element compositions. In the real photocatalytic water-splitting reactions, different aspects affecting the reaction dynamics such as stability of photocatalysts, overpotential, reaction media, and lifetime of photogenerated charges should be considered. To develop an “omnipotent” semiconductor photocatalyst, efforts in the following two aspects should be considered. First, the fundamental issue affecting the photocatalytic water-splitting process needs to be clearly illustrated at a microcosmic level. This could be realized with the development of advanced characterization techniques such as time-revolved infrared and fluorescence spectroscopy. Second, the novel band-gap engineering strategy and synthesis methods should be developed to fine-tune the crystal structure, electronic structure, surface state, and morphology of photocatalysts

The effect of photoanode thickness on the performance of dye-sensitized solar cells containing TiO2 nanosheets with exposed reactive {001} facets

Nanosized anatase TiO2 nanosheets with highly exposed reactive {001} facets (similar to 80%) were prepared via hydrothermal reaction with the addition of hydrofluoric acid and characterized by various techniques including transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller. High-quality TiO2 nanosheets films with different thicknesses (similar to 5-20 mu m) were fabricated by doctor blading, and the effect of film thickness on the performance of dye-sensitized solar cells (DSSCs) was investigated by I-V characterization and dark current potential scan. The results show that each parameter of DSSCs performance depends strongly on the thickness of the TiO2 nanosheets films. An optimized DSSCs performance of 8.39% was obtained by the TiO2 nanosheets film with a thickness of similar to 15 mu m

Controllable cathodic electrodeposition of cobalt films and their electrochemical behaviour

Cobalt thin films with tunable nanostructures were deposited onto flat substrates by a simply electrochemical deposition procedure. A number of experimental parameters including solution concentration, the addition of surfactant and deposition time were studied. XRD and TGA data indicated the formation of cobalt metal on substrates. SEM images revealed the morphological evolution of the materials by varying experimental conditions. The resulting cobalt films exhibited noticeably electrochemical oxidation-reduction behaviour upon cyclic voltammogram measurement, which might be used as electrodes for electrochemical application

Effect of nanofillers on phase separation behavior of diblock copolymer: a molecular dynamic study

Polymer nanocomposites are recognized as the next generation of polymer composites due to their exceptional properties. Understanding the molecular origin of the reinforcement mechanism is crucial to the development of such promising materials. This paper reports our recent molecular dynamic study on clay-based polyurethane nanocomposites. The effect of clay platelets on phase separation behavior of polyurethane, at the clay-polyurethane interface, is quantified in terms of molecular interactions, structure and dynamics. The results show that the nano-confinement of polyurethane chains in clay gallery impedes the development of phase separation commonly observed in bulk polyurethane. The absence of phase separation of intercalated polyurethane is believed to be related to the competitive interactions among clay platelet, polyurethane and surfactant