Nanoporous In2O3 nanocrystal clusters: One-step synthesis, thermal stability and optical property

Nanoporous In2O3 nanocrystal clusters with high surface areas have been synthesized by a one-step solvent-thermal method at a relatively low temperature. On the basis of our experimental data and nanomaterial growth mechanism, a template-assistant dehydration accompanied by aggregation mechanism was proposed to explain their formation. Besides, the influence of the high-temperature treatment on their porous structure and optical properties were studied and compared by various technologies.

Removal of Cr(III, VI) by quaternary ammonium and quaternary phosphonium ionic liquids functionalized silica materials

A series of silica-based organic–inorganic hybrid materials were prepared by the sol–gel process for Cr(III) and Cr(VI) adsorption. These silica materials generally had high surface areas, good physical–chemical stability and high thermal stability. Trialkylmethylammonium bis 2,4,4-trimethylpentylphosphinate ([A336][C272]) and trihexyl(tetradecyl)phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL 104) were explored as porogens to prepare porous silica and as extractants to extract chromium ions. Cyphos IL 104 and [A336][C272] functionalized silica sorbents (SG-2, SG-5) can be effectively used for the removal of Cr(III) and Cr(VI) from aqueous solutions by adjusting pH values, whereas trialkylmethylammonium chloride (Aliquat 336) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) functionalized silica sorbents (SG-3, SG-4) can only be used for the removal of the single chromium species, Cr(VI) or Cr(III).

Direct synthesis of ordered N-methylimidazolium functionalized mesoporous silica as highly efficient anion exchanger of Cr(VI)

Ordered N-methylimidazolium functionalized mesoporous silica (SBA-15) anion exchangers were directly synthesized by co-condensation of tetraethoxysilane with 1-methyl-3(triethoxysilylpropyl)imidazolium chloride. The prepared samples with rod-like morphology showed high surface areas (> 400 m(2) g(-1)), well-ordered pores (> 58 angstrom), and excellent thermal stability up to 387 degrees C. The adsorption behaviors of Cr(VI) from aqueous solution on the anion exchangers were studied using the batch method. The anion exchangers had high adsorption capacity ranging from 50.8 to 90.5 mg g(-1), over a wider pH range (1-8) than amino functionalized mesoporous silica. The adsorption rate was fast, and the maximum adsorption was obtained at pH 4.6. The adsorption data for the anion exchangers were consistent with the Langmuir isotherm equation. Most active sites of the anion exchangers were easily accessible. The mixed solution of 0.1 mol L-1 NH3 center dot H2O and 0.5 mol L-1 NH4Cl was effective desorption solution, and 95% of Cr(VI) could be desorbed.

Morphology-controllable synthesis and characterization of single-crystal molybdenum trioxide

Molybdenum trioxide nanobelts and prism-like particles with good crystallinity and high surface areas have been prepared by a facile hydrothermal method, and the morphology could be controlled by using different inorganic salts, such as KNO3, Ca(NO3)(2), La(NO3)(3), etc. The possible growth mechanism of molybdenum trioxide prism-like particles is discussed on the basis of the presence of HI and the modification of metal cations. The as-prepared nanomaterials are characterized by means of powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and ultraviolet and visible spectroscopy (UV-vis). TEM and HRTEM micrographs show that the molybdenum trioxide nanobelts and prism-like particles have a relatively high degree of crystallinity and uniformity. BET specific surface areas of the as-prepared molybdenum trioxide nanocrystals are 67-79 m(2)g(-1). XPS analysis indicates that the hexavalent molybdenum is predominant in the nanocrystals. UV-vis spectra reveal that the direct band gap energy of the annealed molybdenum trioxide prism-like particles shows a pronounced blue shift compared to that of bulk MoO3 powder.

Preparation of highly dispersed gold microparticles and their electrocatalytic activity for the oxidation of formaldehyde

The electrochemical preparation of highly dispersed Au microparticles on the surfaces of glassy carbon (GC) electrodes and their electrocatalytic activities for the oxidation of formaldehyde were studied. It was found that the reduction of Au3+ to Au is controlled by diffusion and the formation mechanism of Au microparticles on the GC surfaces corresponds to an instantaneous nucleation and diffusion-controlled three dimensional growth process. The particle size is about 80-90 nm in diameter after the electrochemical ageing treatment. These highly dispersed Au microparticles have high surface areas and exhibit better electrocatalytic activity than that of bulk-form Au toward the electrochemical oxidation of formaldehyde in alkaline media.

Altitudinal differences in the leaf fitness of juvenile and mature alpine spruce trees (Picea crassifolia)

In many plant species, leaf morphology varies with altitude, an effect that has been attributed to temperature. It remains uncertain whether such a trend applies equally to juvenile and mature trees across altitudinal gradients in semi-arid mountain regions. We examined altitude-related differences in a variety of needle characteristics of juvenile (2-m tall) and mature (5-m tall) alpine spruce (Picea crassifolia Kom.) trees growing at altitudes between 2501 and 3450 m in the Qilian Mountains of northwest China. We found that stable carbon isotope composition (delta C-13), area- and mass-based leaf nitrogen concentration (N-a, N-m), number of stomata per gram of nitrogen (St/N), number of stomata per unit leaf mass (St/LM), projected leaf area per 100 needles (LA) and leaf mass per unit area (LMA) varied nonlinearly with altitude for both juvenile and mature trees, with a relationship reversal point at about 3 100 m. Stomatal density (SD) of juvenile trees remained unchanged with altitude, whereas SD and stomatal number per unit length (SNL) of mature spruce initially increased with altitude, but subsequently decreased. Although several measured indices were generally found to be higher in mature trees than in juvenile trees, N-m, leaf carbon concentration (C.), leaf water concentration. (LWC), St/N, LA and St/LM showed inconsistent differences between trees of different ages along the altitudinal gradient. In both juvenile and mature trees, VC correlated significantly with LMA, N-m, N-a, SNL, St/LM and St/N. Stomatal density, LWC and LA were only significantly correlated with delta C-13 in mature trees. These findings suggest that there are distinct ecophysiological differences between the needles of juvenile and mature trees that determine their response to changes in altitude in semi-arid mountainous regions. Variations in the fitness of forests of different ages may have important implications for modeling forest responses to changes in environmental conditions, such as predicted future temperature increases in high attitude areas associated with climate change.

中国华北和美国加州地区地震层析成像研究

In recent years seismic tomography has become a powerful tool for studying the three-dimensional crust and mantle structure. In this study, we collected a large number of regional and teleseismic travel-time data and used seismic tomography method to study the relationship between earthquake occurrence and crustal heterogeneity for the 1992 Landers earthquake, heterogeneity and evolution of lithosphere under North China Craton and Southern California, and deep structure and origin of the Changbai intraplate volcano in Northeast China. Our results show a correlation between the seismic rupture zone and crustal heterogeneity. The distribution of the Landers aftershocks is cluster-like and separated or terminated in areas where low-velocity anomalies exist．Most of the large earthquakes with magnitudes >4.0 occurred in or around areas with high P-wave velocity．The possibility is that high-velocity areas are brittle and strong parts which can sustain seismogenic stress，and so can generate earthquakes. Our tomographic images show a very heterogeneous structure in the crust and upper mantle beneath Southern California. Three major anomalies in the upper mantle are revealed clearly beneath the southern Sierra Nevada, Transverse Ranges and Salton Trough. We consider that the high-velocity anomaly beneath the Transverse Ranges was formed through asymmetrical two-side convergence of subcrustal lithosphere and sinking to asthenosphere. Formation of the dense crust root and “drip structure” caused the high-velocity anomaly under the southern Sierra Nevada. The Salton Trough low is the response to the lithospheric extension when the Pacific plate was rifted away from the North American Plate. The tomograpic images beneath the North China Craton show that there exist different lithospheric structures under the different blocks. Complex, prominent low-velocity and high-velocity anomalies are imaged beneath the North China Basin, Trans-North China Orogen (TNCO), and Ordos Block which correspond to rifted, orogenic and cratonic lithospheres, respectively. The thickness of the three-type lithospheres is about 70, 90 and >250 km, respectively. Our results suggest that lithospheric thinning under the eastern part of North China Craton is due to long-term replacement and chemical and thermal erosion of the ancient lithosphere by the hot asthenosphere. The remains of ancient lithosphere exist either in the present upper mantle or have sunk into the mantle transition zone. Our tomographic result of the Changbai volcanic area suggests that the origin of the Changbai volcano is related to the deep dehydration of the subducted Pacific slab and corner flow in the big mantle wedge (BMW) above the stagnant Pacific slab.

湖北恩施表生高硒环境中有机结合态硒的形态研究

硒是人体和动物必需的微量元素，摄入过高或过低均可导致不同的健康效应。已有的研究表明，硒的生物有效性不仅与地质环境中的总硒有关，更取决于硒的形态分布。不同形态的硒具有显著差异的地球化学特性，影响着环境中硒的迁移、循环、生物有效性和毒性。渔塘坝是中国唯一发生过人群硒中毒爆发性流行的地区，该地区风化富硒碳质岩和高硒土壤中有机结合态硒可达到总硒的60%以上，而有机结合态硒的进一步研究有助于深入了解硒的分布和生物可利用性，阐明富硒碳质岩风化及其成土过程中硒的生物地球化学次生富集过程与循环机制。本论文利用改进的7步连续化学浸提技术和优化的有机结合态硒提取方案，使用氢化物发生－原子荧光光谱法，研究了恩施表生高硒环境中有机结合态硒的形态分布，得出了以下几点结论： 1. 在硒七步连续提取方案的基础上，对影响硒提取的因素如液固比、提取剂浓度等进行了优化、并对不同结合态（相态）硒提取中的若干问题进行了讨论。研究结果表明，硒的连续化学提取过程中，液固比为20:1到50:1时能够满足不同结合态硒提取的要求；在水浴加热条件下，NaOH浓度0.1M～0.5M时能有效提取有机结合态硒；1M Na2SO3溶液是元素硒的较好提取剂；而对于硫化物/硒化物结合态硒，合适配比的NaOH＋H2O2混合液有利于H2Se的完全吸收，500～600mL/min的载气气流能保证其被CrCl2+HCl混合液还原所产生H2Se气体的完全吸收。 2. 利用优化的连续化学浸提方案提取风化富硒碳质岩石和高硒土壤样品的有机结合态硒，进而分离出富里酸硒和胡敏酸硒，并用高压密闭消化－氢化物原子荧光光谱法测定了硒的含量。该方案的回收率为84.4～104.2%，平均回收率为96.1%；有机结合态硒与胡敏酸富里酸硒加和值之间有良好的一致性，线性相关系数为0.999（n＝14），斜率为1.0026。而后使用自制的氢化物反应发生和吸收装置进一步分离了与富里酸（胡敏酸）吸附的Se(IV)和强结合的硒，其中分离富里酸硒的回收率为86.3%～107.6%，平均值为97.1%；分离胡敏酸硒的回收率为85.5%～105.9%，平均值为97.9%。表明本论文所采用的实验方案是切实可行的。 3. 风化富硒碳质岩石样品中胡敏酸硒比例较高，所占比例为36.3%～75.8%，平均值为58.1%，但胡敏酸硒并不是占有绝对的优势，且各个样品之间存在较大差异。高硒土壤样品中富里酸硒占有机结合态比例在25.4%～85.0%，除个别样品外，多数样品的富里酸硒所占比例均在70%～80%，表明富里酸硒是渔塘坝土壤有机结合态硒的一种主要存在形式，在适当的条件下（如环境的pH-Eh变化），能够被转化从而被植物吸收利用。并且这种岩石中胡敏酸硒含量高、土壤中富里酸硒含量高的分布特征指示了硒在风化过程中可能的迁移和转化规律。 4. 富里酸硒和胡敏酸硒的形态分析表明，不同岩石样品中各有机结合态硒的形态分布差异较大，分布规律不明显，这可能与岩石样品的风化程度有关；而对于土壤样品，不论是在富里酸还是胡敏酸中，吸附Se(IV)的含量都大于强结合硒，尤其是富里酸中的吸附Se(IV)，平均值为83.4%，最高达95.4%。这部分吸附的Se(IV)相对于强结合的富里酸硒更容易被释放，而这也进一步佐证了富里酸硒易于受环境变化（pH-Eh）和倍半氧化物等的影响而转变为生物可利用态硒。 5. 无论是胡敏酸强结合硒（HA-Se）还是富里酸强结合硒（FA-Se）均在有机结合态硒中以一定的比例存在，对这部分硒的研究还仅局限于定量，而其究竟是以何种形态、以何种方式与腐殖质结合尚不清楚。因此，有必要对这部分硒进行进一步研究。

XRD and XPS studies on the ultra-uniform Raney-Ni catalyst prepared from the melt-quenching alloy

We present a novel method for preparing an ultra-uniform Raney-Ni catalyst, which includes melt-quenching, hydrogen treatment and leaching in an alkali solution. The resultant catalyst shows superior activity in the reaction of cyclohexanone hydrogenation. X-ray diffraction (XRD) and XPS have been employed to characterize the catalysts. As demonstrated, the pretreatment with hydrogen caused a distinct phase transfer of the Ni-Al alloys, forming more of the Ni2Al3 component. In the subsequent leaching process, the Ni2Al3 component shows high activity and the resultant catalyst exhibits high surface areas and small pores. Moreover, metallic Al in the hydrogen-pretreated alloy appeared to be leached more easily and thus the aluminium species remaining on the catalyst surface is aluminium oxide predominantly, which serves as a matrix to stabilize active Ni species on the surface. Copyright (C) 2001 John Wiley & Sons, Ltd.

Distribution, feeding and body condition of four small fish species in the near-shore and central areas of Liangzi Lake, China

Small fish abundance is usually high in heavily vegetated habitats in Yangtze lakes, China. Visual and swimming barriers created by dense macrophytes beds could reduce feeding efficiency and growth of small fishes. We tested the hypothesis that small fishes in habitats with dense macrophytes would show decreased feeding efficiency and reduced growth rates by comparing feeding efficiency (measured as the relative weight of fore-gut contents), total length, and condition factor of four small young-of-the-year fishes collected in the near-shore (heavily vegetated) and central (less vegetated) areas of Liangzi Lake. Feeding efficiency, total length, or condition factor were each significantly reduced in the near-shore area compared with the central area for Ctenogobius giurinus, Pseudorasbora parva and Carassius auratus auratus. This supports our hypothesis that vegetation abundance may mediate feeding efficiency and growth of small fishes. Although Hypseleotris swinhonis did not show significant decreases in feeding efficiency or growth in the near-shore area, there was not any reversed tendency, i.e. increased feeding rate or growth in the near-shore area compared to the central area.

High energy ion implantation enhanced intermixed quantum well structures and their absorption characteristics in passive optical waveguides

We have shown that high energy ion implantation enhanced intermixing (HE-IIEI) technology for quantum well (QW) structures is a powerful technique which can be used to blue shift the band gap energy of a QW structure and therefore decrease its band gap absorption. Room temperature (RT) photoluminescence (PL) and guided-wave transmission measurements have been employed to investigate the amount of blue shift of the band gap energy of an intermixed QW structure and the reduction of band gap absorption, Record large blue shifts in PL peaks of 132 nm for a 4-QW InGaAs/InGaAsP/InP structure have been demonstrated in the intermixed regions of the QW wafers, on whose non-intermixed regions, a shift as small as 5 nm is observed. This feature makes this technology very attractive for selective intermixing in selected areas of an MQW structure. The dramatical reduction in band gap absorption for the InP based MQW structure has been investigated experimentally. It is found that the intensity attenuation for the blue shifted structure is decreased by 242.8 dB/cm for the TE mode and 119 dB/cm for the TM mode with respect to the control samples. Electro-absorption characteristics have also been clearly observed in the intermixed structure. Current-Voltage characteristics were employed to investigate the degradation of the p-n junction in the intermixed region. We have achieved a successful fabrication and operation of Y-junction optical switches (JOS) based on MQW semiconductor optical amplifiers using HE-IIEI technology to fabricate the low loss passive waveguide. (C) 1997 Published by Elsevier Science B.V.