Tunable Luminescence in Monodisperse Zirconia Spheres

In this article, monodisperse spherical zirconia (ZrO2) particles with a narrow size distribution were prepared by the controlled hydrolysis of zirconium butoxide in ethanol, followed by heat treatment in air at low temperature from 300 to 500 degrees C. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric and differential thermal analysis (TG/DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra, kinetic decay, and electron paramagnetic resonance were used to characterize the samples. The experimental results indicate that the annealed ZrO2 samples exhibit broad, intense visible photoluminescence. The annealing temperature is indispensable for the luminescence of the obtained ZrO2 particles. The emission colors of the ZrO2 samples can be tuned from blue to nearly white to dark orange by varying the annealing temperature.

Magnetic Mesoporous Silica Spheres for Drug Targeting and Controlled Release

Magnetically functionalized mesoporous silica spheres with different size (average diameter, A.D.) from 150 nm to 2 mu m and pore size distribution were synthesized by generating magnetic FexOy nanoparticles onto the mesoporous silica hosts using the sol-gel method. The X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), N-2 adsorption/desorption results show that these composites conserved regular sphere morphology and ordered mesoporous structure after the formation of FexOy nanoparticles. XRD and X-ray photoelectron spectroscopy (XPS) analysis confirmed that the FexOy generated in these mesoporous silica hosts is mainly composed of gamma-Fe2O3. Magnetic measurements reveal that these composites with different gamma-Fe2O3 loading amounts possess super-paramagnetic properties at 300 K, and the saturation magnetization increases with increasing Fe ratio loaded.

Growth of highly crystalline CaMoO4 : Tb3+ phosphor layers on spherical SiO2 particles via sol-gel process: Structural characterization and luminescent properties

Highly crystalline CaMoO4:Tb3+ phosphor layers were grown on monodisperse SiO2 particles through a simple sol-gel method, resulting in formation of core-shell structured SiO2@CaMoO4:Tb3+ submicrospheres. The resulting SiO2@CaMoO4: Tb3+ core-shell particles were fully characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), and kinetic decays. The XRD results demonstrate that the CaMoO4:Tb3+ layers begin to crystallize on the SiO2 spheres after annealing at 400 degrees C and the crystallinity increases with raising the annealing temperature. SEM and TEM analysis indicates that the obtained submicrospheres have a uniform size distribution and obvious core-shell structure. SiO2@CaMoO4:Tb3+ submicrospheres show strong green emission under short ultraviolet (260 nm) and low-voltage electron beam (1-3 kV) excitation, and the emission spectra are dominated by a D-5(4) -F-7(5) transition of Tb3+(544 nm, green) from the CaMoO4:Tb3+ shells.

Design of polymeric stabilizers for size-controlled synthesis of monodisperse gold nanoparticles in water

A new methodology is described for the one-step aqueous preparation of highly monodisperse gold nanoparticles with diameters below 5 nm using thioether- and thiol-functionalized polymer ligands. The particle size and size distribution was controlled by subtle variation of the polymer structure. It was shown that poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) were the most effective stabilizing polymers in the group studied and that relatively low molar mass ligands (similar to 2500 g/mol) gave rise to the narrowest particle size distributions. Particle uniformity and colloidal stability to changes in ionic strength and pH were strongly affected by the hydrophobicity of the ligand end group. "Multidentate" thiol-terminated ligands were produced by employing dithiols and tetrathiols as chain-transfer agents, and these ligands gave rise to particles with unprecedented control over particle size and enhanced colloidal stability. It was found throughout that dynamic light scattering (DLS) is a very useful corroboratory technique for characterization of these gold nanoparticles in addition to optical spectroscopy and TEM.

Preparation of nano-hydroxyapatite/poly(L-lactide) biocomposite microspheres

Nano-hydroxyapatite (HA)/poly(L-lactide) (PLLA) composite microspheres with relatively uniform size distribution were prepared by a solid-in-oil-in-water (s/o/w) emusion solvent evaporation method. The encapsulation of the HA nanopaticles in microshperes was significantly improved by grafting PLLA on the surface of the HA nanoparticles (p-HA) during emulsion process. This procedure gave a possibility to obtain p-HA/PLLA composite microspheres with uniform morphology and the encapsulated p-HA nanoparticle loading reached up to 40 wt% (33 wt% of pure HA) in the p-HA/PLLA composite microspheres. The microstructure of composite microspheres from core-shell to single phase changed with the variation of p-HA to PLLA ratios. p-HA/PLLA composite microspheres with the diameter range of 2-3 mu m were obtained. The entrapment efficiency of p-HA in microspheres could high up to 90 wt% and that of HA was only 13 wt%. Surface and bulk characterizations of the composite microspheres were performed by measurements such as wide angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), environmental scanning electron microscope (ESEM) and transmission electron microscopy (TEM).

Physical and electrochemical characterizations of PtRu/C catalysts by spray pyrolysis for electrocatalytic oxidation of methanol

In this paper, it was reported that the carbon-supported Pt-Ru(Pt-Ru/C) catalyst used as the anodic catalyst in the direct methanol fuel cell (DMFC) was synthesized with a two-step spray pyrolysis (SP) method using the Pt and Ru metal salt as the precursors and polyethylene glycol (PEG) with the different molecular weights (Mw= 200,600,and 1000 analytical reagent) as cosolvent. PEG as a cosolvent plays a crucial role in producing PtRu/C catalysts. It was found that the Mw of PEG could affect the electrocatalytic activity of Pt-Ru and the morphology of the Pt-Ru particles in the Pt-Ru/C catalysts prepared with this method. When the Mw of PEG is 600, the Pt-Ru particles in the Pt-Ru/C catalyst prepared with this method possess the small average size, narrow size distribution, uniform dispersion, and high electrochemically active specific surface area. The electrocatalytic activity of the Pt-Ru/C catalyst prepared with this method using the cosolvent PEG with Mw = 600 for the methanol oxidation is much higher than that of the commercial E-TEK Pt-Ru/C catalyst. Therefore, the two-step SP method is an excellent method for the preparation of the Pt-Ru/C catalyst used in DMFCs.

Syntheses of Ag, PbSe, and PbTe nanocrystals and their binary self-assembly exploration at low size-ratio

Nanocrystals of Ag, PbSe, and PbTe were prepared via a high-temperature organic solution approach, respectively. Using a size-selection technique, the size-distribution of each set of nanocrystals could be fine-tuned and finally monodisperse products were achieved. Superlattice structure of binary self-assemblies in low size-ratio were also explored and characterized by transmission electron microscopy. It is realized that a success of achieving binary self-assembly pattern is greatly dependent on several key factors including particle size-distributions, relative concentrations of both components, as well as the size-ratios between Ag and PbSe (or PbTe) nanocrystals.

Determination of Nb and Ta in Nb/Ta minerals by inductively coupled plasmas optical emission spectrometry using slurry sample introduction

The determination of Nb and Ta in Nb-Ta minerals was accomplished by slurry nebulization inductively coupled plasma optical emission spectrometry (ICP-OES), using a clog-free V-groove ceramic nebulizer. Samples were first wet-ground to appropriate particle sizes with narrow size distribution and 90% of the particles in the slurry were smaller than 2.32 mu m in diameter. Subsamples were then dispersed in pH 9 aqueous solutions, and agitated in an ultrasonic bath for 15 min prior to analysis. Due to the lack of slurry standards matching well with the samples, calibration was simply carried out using aqueous solution standards. Results were compared with those obtained from a conventional fusion decomposition procedure and acid digestion procedures and a good agreement between the measured and referred values was obtained. The technique provided a good alternative for the rapid determination of Nb and/or Ta in their corresponding minerals.

Nonisothermal crystallization and melting behavior of poly(3-hydroxybutyrate) and maleated poly(3-hydroxybutyrate)

Nonisothermal crystallization and melting behavior of poly(3-hydroxybutyrate) (PHB) and maleated PHB were investigated by differential scanning calorimetry using various cooling rates. The results show that the crystallization behavior of maleated PHB from the melt greatly depends on cooling rates and its degree of grafting. With the increase in cooling rate, the crystallization process for PHB and maleated PHB begins at lower temperature. For maleated PHB, the introduction of maleic anhydride group hinders its crystallization, causing crystallization and nucleation rates to decrease, and crystallite size distribution becomes wider. The Avrami analysis, modified by Jeziorny, was used to describe the nonisothermal crystallization of PHB and maleated PHB. Double melting peaks for maleated PHB were observed, which was caused by recrystallization during the heating process.

Influence of the size of ultrafine CaCO3 powder on PP crystallization

The effects of CaCO3 on the crystallization behavior of polypropylene (PP) were studied by means of DSC and WAXD. The average sizes of the CaCO3 powders used were 0.1 mum (UC) and 0.5 mum (GC), respectively. The PP/CaCO3 composites at compositions of 1 phr and 10 phr were investigated. The results showed that the addition of CaCO3 reduced the supercooling, the rate of nucleation and the overall rate of crystallization (except for the 10 phr UC/PP sample). The crystallinity of PP was increased and the size distribution of the crystallites of alpha -PP; was: broadened. On the other hand,the crystallization rate of 10 phr UC/PP is 1.5 times higher than that of neat PP. It has an overall rate of crystallization 2 times as much as that of the neat PP and has the maximum crystallinity. The sizes of crystallites and the unit cell parameters of alpha -PP were varied by the addition of CaCO3. beta -PP was formed by addition of Ge and was not detected by addition of UC. The differences of crystallization behaviors of PP might be attributed to the combined effects of the content and size of CaCO3 filled.

Synthesis and properties of cerium oxide nanometer powders by pyrolysis of amorphous citrate

CeO2 nanometer powders of different sizes were prepared at low temperature by pyrolysis of amorphous citrate. XRD patterns show that CeO2 is cubic in structure, space group O-h(5)-F-M3M. TEM indicates that the prepared CeO2 is spherical in shape, and the particle size distribution is in narrow range. It was found that calcination temperature is a more important factor affecting the crystallite size of CeO2 than calcining time, the smaller the particle, the bigger the crystal lattice distortion, the worse the crystal growth. Solubility test of CeO2 in nitric acid reveals that the surface activity of CeO2 decreases with the increasing particle sizes. IR spectra analysis shows that the absorption of Ce-O bond is shifted to higher energy with the decrease of CeO2 particle sizes.

Recent 2000-year geological records of mud in the inner shelf of the East China Sea and their climatic implications

AXIS(14)C dating and grain-size analysis for Core DD2, located at the north of the Yangtze River-derived mud off the Zhejiang-Fujian coasts in the inner shelf of the East China Sea, provide us a high-resolution grain-size distribution curve varying with depth and time. Data in the upper mud layer of Core DD2 indicate that there are at least 9 abrupt grain-size increasing in recent 2000 years, with each corresponding very well with the low-temperature events in Chinese history, which might result from the periodical strengthening of the East Asian Winter Monsoon (EAWM), including the first-revealed maximum temperature lowering event at around 990 a BP. At the same time, the finer grain size section in Core DD2 agrees well with the Sui-Tang Warming Period (600-1000 a AD) defined previously by Zhu Kezhen, during which the climate had a warm, cold and warm fluctuation, with a dominated cooling period of 750-850 a AD. The Little Ice Age (LIA) can also be identified in the core. It starts around 1450 a AD and was followed by a subsequent cooling events at 1510, 1670 and 1840 a AD. Timing of these cold events revealed here still needs to be further verified owing to some current uncertainty of dating we used in this study.

Resuspension and advection processes affecting suspended particulate matter concentrations in the central English Channel

Suspended particulate matter (SPM) measurements obtained along a cross-section in the central English Channel (Wight-Cotentin transect) indicate that the area may be differentiated into: (1) an English coastal zone, associated with the highest concentrations; (2) a French coastal zone, with intermediate concentrations; and (3) the offshore waters of the Channel, characterised by a very low suspended-sediment load. The SPM particle-size distribution was modal close to the English coast (main mode 10-12 mu m); the remainder of the area was characterised by flat SPM distributions. Examination of the diatom communities in the SPM suggest:; that material resuspended in the intertidal zone and the estuarine environments was advected towards the offshore waters of the English Channel. Considerable variations in SPM concentrations occurred during a tidal cycle: maximum concentrations were sometimes up to 3 times higher than the minimum concentrations, Empirical orthogonal function (EOF) analysis of the SPM concentration time series indicates that, although the bottom waters were more turbid than the surficial waters, this was not likely to be the result of in situ sediment resuspension. Instead, the observed variations appear to be controlled mainly by advective mechanisms. The limited resuspension was probably caused by: (1) the limited availability of fine-grained material within the bottom sediments, and (2) 'bed-armouring' processes which protect the finer-grained fractions of the seabed material from erosion and entrainment within the overlying flow during the less energetic stages of the tide.

Coherence between solar activity and the East Asian winter monsoon variability in the past 8000 years from Yangtze River-derived mud in the East China Sea

AMS(14)C dating and grain-size analysis for Core PC-6, located in the middle of a mud area on the inner shelf of the East China Sea (ECS), were used to rebuild the Holocene history of the East Asian winter monsoon (EAWM). The 7.5-m core recorded the history of environmental changes during the postglacial transgression. The core's mud section (the upper 450 cm) has been formed mainly by suspended sediment delivered from the Yangtze River mouth by the ECS Winter Coastal Current (ECSWCC) since 7.6 kyr BP. Using a mathematical method called "grain size vs. standard deviatioW', we can divide the Core PC-6's grain-size distribution into two populations at about 28 mu m. The fine population (< 28 mu m) is considered to be transported by the ECSWCC as suspended loads. Content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation. Thus, variation of mean grain-size from the fine population would reflect the strength of ECSWCC, which is mainly controlled by the East Asian winter monsoon. Abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ECSWCC, which was caused by the strengthened EAWM. Thus, the high resolution mean grain-size variation might serve as a proxy for reconstruction of the EAWM. A good correlation between sunspot change and the mean grain-size of suspended fine population suggests that one of the primary controls on centennial- to decadal-scale changes of the EAWM in the past 8 ka is the variations of sun irradiance, i.e., the EAWM will increase in intensity when the number of sunspots decreases. Spectral analyses of the mean grain-size time series of Core PC-6 show statistically significant periodicities centering on 2463, 1368, 128, 106, 100, 88-91, 7678, and 70-72 years. The EAWM and the East Asian summer monsoon (EASM) agree with each other well on these cycles, and the East Asian Monsoon (EAM) and the Indian Monsoon also share in concurrent cycles in Holocene, which are in accord with the changes of the sun irradiance. (c) 2005 Elsevier B.V. All rights reserved.

古龙咀周围海区沉积物粒度特征及海底地形变化

对古龙咀周围浅海区沉积物的粒度进行了测试与分析，结合相关的地质水文资料，探讨了海岸形态对沉积物粒度的影响。研究区表层沉积物平均粒径在海湾浅海区呈带状由岸向海变细，中等水深和岬角处分布着细粒区，向外海粒径相对变粗；除险岛湾砂质区外，分选差；偏态多数为正偏或近正态；整体峰形极窄，峰型多样。底质类型以粘土质粉砂和砂质粉砂为主，由东北经古龙咀岬角向西南形成S形粘土质粉砂分布带，险岛湾地区沉积物呈带状由砂逐渐过渡到粉砂。潮汐和波浪是本区沉积物输运的主要水动力，岬角的存在影响了沉积物粒度的分布。粒度趋势分析表明沉积物整体有向岬角汇聚的输运趋势。 对收集到基于1954年、1969年、1982年测量绘成的地形图水深数据进行数字化，结合2005年测量的水深数据，分别建立各时期DEM图，在此基础上分析研究区的地形特征。四个时期海底DEM呈现出大体一致的趋势，在险岛湾及白沙口海湾内为浅水区，水深值在-1～-4 m之间，深水区主要分布在南黄岛南端至古龙咀连线以南区域，呈扇形展布，水深由南黄岛两侧向中间逐渐加深，水深值在-10～ -17 m之间。从整体上看，研究区海底地形呈NW-SE方向逐渐加深。 将数字化后的水深数据统一校正到1956黄海高程系，分别建立DEM，运用GIS的栅格计算分析得出冲淤变化图。相关结果表明：1954～1969年研究区整体近岸为冲（险岛湾除外），离岸海域为淤；1969～1982年研究区总体处于弱淤积状态；1982-2005研究区海域近岸为淤，外海以弱冲刷状态为主。