Influence of nitriding gases on the growth of boron nitride nanotubes

Boron nitride (BN) nanotubes of different sizes and tubular structures exhibit very different mechanical and chemical properties, as well as different applications. BN nanotubes of different sizes and nanostructures have been produced in different nitriding gases in a milling and annealing process, in which elemental boron powder was first milled in NH₃ for 150 h and subsequently annealed at 1,200 °C for 6 h. The influence of nitriding gases was investigated by using N₂, NH₃, N₂–H₂ mixture gases. A relatively slow nitriding reaction in NH₃ gas leaded to a 2D growth of BN (002) basal planes and the formation of thin BN nanotubes without the help of metal catalysts. Fast nitriding reactions occurred in N₂ or N₂–H₂ mixture gases, catalyzed by metal particles, resulted in 3D crystal growth and the formation of many large cylindrical and bamboo tubes.

Improvement of light harvesting and device performance of dye-sensitized solar cells using rod-like nanocrystal TiO2 overlay coating on TiO2 nanoparticle working electrode

Novel TiO2 single crystalline nanorods were synthesized by electrospinning and hydrothermal treatment. The role of the TiO2 nanorods on TiO2 nanoparticle electrode in improvement of light harvesting and photovoltaic properties of dye-sensitized solar cells (DSSCs) was examined. Although the TiO2 nanorods had lower dye loading than TiO2 nanoparticle, they showed higher light utilization behaviour. Electron transfer in TiO2 nanorods received less resistance than that in TiO2 nanoparticle aggregation. By just applying a thin layer of TiO2 nanorods on TiO2 nanoparticle working electrode, the DSSC device light harvesting ability and energy conversion efficiency were improved significantly. The thickness of the nanorod layer in the working electrode played an important role in determining the photovoltaic property of DSSCs. An energy conversion efficiency as high as 6.6% was found on a DSSC device with the working electrode consisting of a 12 μm think TiO2 nanoparticle layer covered with 3 μm thick TiO2 nanorods. The results obtained from this study may benefit further design of highly efficient DSSCs.

Mechanochemical synthesis of niobium pentoxide nanoparticles

Acicular α-FeOOH particles are formed through aging of ferric oxyhydroxide colloidal solution formed by the neutralization of FeCl₃ aqueous solution by NaOH. The effect of foreign ion addition to the colloidal solution on the formation and morphology of α-FeOOH particles has been investigated. The magnetic properties of Fe₃O₄ particles made from the obtained particles have also been investigated. The rate constant of the formation of α-FeOOH remarkably decreased, but the crystallite size of α-FeOOH particles increased with increasing the quantity of phosphate ion added even with small amounts. These results have been explained as follows: the phosphate ions are selectively adsorbed on the (a) plane of α-FeOOH, cover the (a) plane, and block the crystal growth of the (a) plane of the α-FeOOH. The quantities of the phosphate ion adsorbed on the b and c planes are relatively small. The complex ion of Fe(OH)₄^- is preferentially deposited on both (b) and (c) planes, and the crystal growth of (b) and (c) planes is greatly accelerated. The relationship between the morphology of the formed α-FeOOH particles and the quantity of phosphate ion added has been investigated. The asterisk type particles: α-FeOOH particles heterogeneously junctioned to α-Fe₂O₃ particles, were formed when a small amount of phosphate was added to the mother liquid. The α-FeOOH crystal epitaxially grew on the junction interface with the α-Fe₂O₃ crystal. In the case of the aging at the temperature as high as 80°C, the cross type junctioned particles were stably formed at pH below 12.0. The Fe₃O₄ particles with screw-like unique three-dimensional morphology were produced from the heterogeneously junctioned particles.

Plastic deformation in a partially crystallized Zr-based BMG under Vickers indenter

Vickers indentations were carried out on an anneal-introduced partially crystallized Zr₄₁Ti₁₄Cu_12.5 Ni₁₀Be_22.5 bulk metallic glass (BMG), and the evolution of the shear bands in this samplewas investigated and compared to the as-cast, aswell as the structurally relaxed counterparts. The results indicate that the plastic deformation in the partially crystallized BMG was accommodated by the semi-circular (primary) and radial (secondary) shear bands. A full crack or flake that was produced due to the spring back during the load removal was observed. The shear band density in the annealed alloy which was dispersed with crystalliteswas significantly lower than that of the as-cast alloy. The difference of the shear band features among the three kinds of alloy status, i.e., partially crystallized, structurally relaxed and as-cast alloys was discussed in terms of the free volume in the BMGs and the characteristics of nano-composites. It has been demonstrated that the plasticity for the three statuses of alloys queues in the descending order as the as-cast, annealed with partial crystallization, and annealed without crystallization.

New insight into non-isothermal crystallization of PVA-graphene composites

The melt crystallization of poly(vinyl alcohol) (PVA) and PVA composites has been a controversial subject due to inconclusive evidence and different opinions for its decomposition during crystallization. Using graphene as a model, the melt crystallization of PVA and PVA-graphene composites occurring during single-cycle and multiple-cycle non-isothermal annealing processes was systematically analyzed using different characterization techniques. The results obtained using single-cycle non-isothermal annealing indicated that the entire crystallization process took place through two main stages. The graphene in the PVA matrix regulates the nucleation and crystal growth manner of the PVA, yet resulting in retardation of the entire crystallization. The FTIR and Raman spectroscopic results particularly demonstrated that the annealing process not only improved the crystallinity but also led to clear decomposition in PVA and PVA-graphene composites, such as the elimination of hydroxyl groups and the production of C=C double bonds. The newly produced C=C double bonds were found to be responsible for the retardation of PVA macromolecule crystallization and the breaking of hydrogen bonds among the hydroxyl groups in the PVA chains. In addition, the morphological observation and multi-cycle non-isothermal crystallization further confirmed the existence of decomposition based on the surface damage as well as decreased crystallization enthalpy and crystallization peak temperature. Therefore, the non-isothermal crystallizations of the pure PVA and the PVA-graphene composites were in fact the combination of non-isothermal crystallization and non-isothermal degradation processes.

Testing the transferability of a coarse-grained model to intrinsically disordered proteins

The intermediate-resolution coarse-grained protein model PLUM [T. Bereau and M. Deserno, J. Chem. Phys., 2009, 130, 235106] is used to simulate small systems of intrinsically disordered proteins involved in biomineralisation. With minor adjustments to reduce bias toward stable secondary structure, the model generates conformational ensembles conforming to structural predictions from atomistic simulation. Without additional structural information as input, the model distinguishes regions of the chain by predicted degree of disorder, manifestation of structure, and involvement in chain dimerisation. The model is also able to distinguish dimerisation behaviour between one intrinsically disordered peptide and a closely related mutant. We contrast this against the poor ability of PLUM to model the S1 quartz-binding peptide.