Nanoscale observation of morphological transformation during ageing of silica and silica-alumina

Atomic force microscopy (AFM) was used for in-situ observation of nanoscale morphological transformations during the ageing step in sol-gel synthesis. Silica, alumina and silica-alumina samples with different Si/Al ratios were prepared from inorganic salt precursors and geled at low pH. Silica and silica-alumina samples formed branch-like gel network made of nanometer-sized clusters. During ageing at room temperature, the overall structure of the gel network remained unchanged but the clusters underwent phase transformation, coaslesence, coarsening, fragmentation, as well as dissolution resulting in the internal restructuring of the gel material. Morphological transformation associated with crystallization of pseudo-boehmite phase was observed for the alumina samples. These nanometer-scale processes are expected to play a key role in dictating the material properties of the final sol-gel product.     

Multi-Stimuli-Induced Mechanical Bending and Reversible Fluorescence Switching in a Single Organic Crystal

Fluorescent single crystals that respond to multiple external stimuli are of great interest in molecular machines, sensors, and displays. The integration of photo- or acid-induced fluorescence enhancement and bending in one organic crystal, however, has not been reported yet. Herein, we report the interesting plastic photomechanical bending and switching on of the fluorescence of an azine crystal in a single-crystal transformation, due to extended π-conjugation and molecular slippage. Moreover, the fluorescent plastic bending driven by multiple volatile acid vapors was firstly observed, and attributed to the synergistic effect of push–pull electronic structure and hydrogen bonding. The single crystal also shows high elasticity under external force. In addition, reversible fluorescence switching can be triggered by grinding and solvent fuming, as well as by the adsorption and desorption of HCl vapor. The integration of plastic, elastic bending and switch-on fluorescence into one single crystal provides a new strategy for next-generation smart materials.     

Torsional buckling of a double-walled carbon nanotube embedded in an elastic medium

The torsional buckling of a double-walled carbon nanotube embedded in an elastic medium is studied in this paper. The effects of surrounding elastic medium and van der Waals forces between the inner and outer nanotubes are taken into account. Using continuum mechanics, an elastic double-shell model is presented for the torsional buckling of a double-walled carbon nanotube. Based on the model, a condition is derived in terms of the buckling modes of the shell and the parameters describing the effect of van der Waals interaction and surrounding elastic medium. A simplified analysis is also carried out estimate the critical torque for torsional buckling of the double-walled carbon nanotube.     

粒状十二磷钼酸铵结晶的合成及对Cs^＋的交换性能研究

用焦磷酸根在酸性钼酸铵溶液中缓慢水解释放出磷酸根，控制磷钼酸铵（ＡＭＰ）的结晶速度，合成了适合于柱操作的ＡＭＰ粒状结晶。结晶结构分析和化学组成分析确认其为十二磷钼酸铵。在１ｍｏｌ／ＬＨＮＯ３中对Ｃｓ＋的静态交换容量为０．６３ｍｍｏｌ／ｇ，分配系数为３５０ｍｌ／ｇ。在模拟中国裂变废液中，动态交换容量为０．５５ｍｍｏｌ／ｇ。经２×１０６Ｇｙ剂量γ辐照后，交换容量未发生变化。     

Partial Oxidation of Ethane to Syngas over Supported Metal Catalysts

The reaction performance for C₂H₆-O₂ to syngas over different supported metal catalysts was investigated in a flow-reactor. The activated behavior of ethane is different from that of methane over the supported nickel catalysts. Although there may exist a gas phase reaction at high temperatures, over a Ni (or Rh)/-Al₂O₃ catalyst, the partial oxidation of ethane to syngas is a heterogeneous process, while over a Pt (or Pd)/-Al₂O₃ catalyst, it may be a homo-heterogeneous process. The Ni/-Al₂O₃ and Rh/-Al₂O₃ catalysts are suitable for partial oxidation of ethane to syngas at high temperatures.     

Influence of the Sol-Gel Method on a NiO/Al2O3 Catalyst for CH4/O2 to Syngas Reaction

NiO/-Al₂O₃ catalysts were prepared by the impregnation and the sol-gel method. The sintering and loss of nickel, carbon deposition and 80 h life-test for POM reaction over the catalyst were investigated by a flow-reactor and by XPS, TG, EXAFS and AAS analysis. The results indicated that the sol-gel method could enhance the ability to suppress carbon deposition and to resist nickel sintering and loss over nickel-based catalysts.     

Nests with the partial factorization property

It is proved that a nest on a separable complex Hilbert space has the left (resp. right) partial factorization property, which means that for every invertible operator from onto a Hilbert space there exists an isometry (resp. a coisometry) from into such that both and are in the associated nest algebra if and only if it is atomic (resp. countable).

     

Kinetics of Methane Partial Oxidation to Syngas over a LiLaNiO/γ -Al2O3 Catalyst

The kinetic behavior of partial oxidation of methane to syngas over a LiLaNiO/γ -Al₂O₃ catalyst was investigated under steady-state conditions. Under kinetic control, syngas, to a large extent, is formed via a direct partial oxidation (DPO) scheme. CO and CO₂ are formed in parallel by oxidation reaction over the catalyst. The active sites in the kinetically controlled regime are different from those in the non-kinetic regime, thus the CO selectivity in the former may not increase with temperature. This revised version was published online in June 2006 with corrections to the Cover Date.     

Preliminary Study on Hydrogen Permeation and Stability of BaCe0.90Y0.10O3-δ Membrane under Asymmetric Atm osphere

High-temperature proton conductors (HTPC) have been extensively studied since I wahara et al?1? reported protonic conduction in SrCeO3-based oxid es. Later, the BaCeO3-based oxides, such as BaCe0.90Yb0.10O3- d (BCYb10) and BaCe0.90Y0.10-O3-d (BCY10), we re fou nd to show higher conductivity?2?. High electronic and protonic conducti vity makes BCY10 a potential membrane for hydrogen separation?3?. Thin f ilms with high density, most probably made by sequential coating on porous subst rates, are imperative in order to promote hydrogen permeation flux?4?. T his makes it more necessary for such membranes to be kept stable and unspoilt un der asymmetric hydrogen-permeation atmosphere at elevated temperatures. In this paper, the stability and hydrogen permeation ability of BCY10 membrane are stud ied by XRD, SEM, energy dispersive X-ray (EDX) analysis, H2-TPR process and hydrogen permeation experiment. The results showed that hydrogen cannot permeate through the BCY10 membrane without surface modification, and its surface cannot keep a uniform perovskite structure in the asymmetric atmosphere.     

离子色谱固定相最新进展

介绍离子色谱固定相的最新研究进展。离子色谱固定相在多种类型、含多种功能基和高交换容量固定相,羟基选择性固定相,高效的涂覆型固定相,可变交换容量的固定相,静电离子和仿生离子固定相,整体式固定相。以及芯片式固定相等方面均有所发展。