Carotenoids Particle Formation by Supercritical Fluid Technologies

Based on the solubility in supercritical CO2,two strategies in which CO2 plays different roles are used to make quercetine and astaxanthin particles by supercritical fluid technologies.The experimental results showed that micronized quercetine particles with mean particle size of 1.0-1.5 μm can be made via solution enhanced dispersion by supercritical fluids(SEDS) process,in which CO2 worked as turbulent anti-solvent;while for astaxanthin,micronized particles with mean particle size of 0.3-0.8 μm were also made successfully by rapid expansion supercritical solution(RESS) process.

Effect of Fe_2O_3/SiO_2 ratio on maghemite-silica particulate nanocomposites

Abstract： Maghemite-silica particulate nanocomposites were prepared by modified 2-step sol-gel process. Superparamagnetic maghemite nanoparticles were successfully produced using Massart＇s procedure. Nanocomposites consisting of synthesized maghemite nanoparticles and silica were produced by dispersing the as-synthesized maghemite nanoparticles into the silica particulate form. The system was then heated at 140 ℃for 3 d. A variety of mass ratios of Fe2O3/SiO2 was investigated. Moreover, no surfactant or other unnecessary precursor was involved. The nanocomposites were characterized using XRD, BET and AGM. The XRD diffraction patterns show the reflection corresponding to maghemite nanoparticles and a visible wide band at 20 from 20° to 35° which are the characteristics of the amorphous phase of the silica gel. The patterns also exhibit the presence of only maghemite and SiO2 amorphous phase, which indicates that there is no chemical reaction between the silica particulate gel and maghemite nanoparticles to form other compounds. The calculated crystallite size for encapsulated maghemite nanoparticles is smaller than the as-synthesized maghemite nanoparticles indicating the dissolution of the nanoparticles. Very high surface area is attained for the produced nanocomposites （360-390 m^2/g）. This enhances the sensitivity and the reactivity of the nanocomposites. The shapes of the magnetization curves for nanocomposites are very similar to the as-synthesized maghemite nanoparticles. Superparamagnetic behaviour is exhibited by all samples, indicating that the size of the maghemite nanoparticles is always within the nanometre range. The increase in iron content gives rise to a small particle growth.

High-temperature creep properties of uranium dioxide pellet

High-temperature creep properties of sintered uranium dioxide pellets with two grain sizes （9.0 μm and 23.8μm） were studied. The results indicate that the creep rate becomes a little faster with the reduction of the uranium dioxide grain size at the same temperature and the same load. At the same temperature, the logarithmic value of the steady creep rate vs stress has linear relation, and with increasing load, the steady creep rate of the sintered uranium dioxide pellet increases. Under the same load, the steady creep rate of the sintered uranium dioxide pellet increases with increasing temperature; and the creep rates of sintered uranium dioxide pellet with the grain size of 9.0 μm and 23.8 μm under 10 MPa are almost the same. The creep process is controlled both by Nabarro--Herring creep and Hamper-Dorn creep for uranium dioxide pellet with grain size of 9.0 μm, while Hamper---Dora creep is the dominantmechanism for uranium dioxide with grain size of 23.8 μm.

Grinding Characteristics Of Directionally Aligned SiC Whisker Wheel - Comparison With A12O3 Fiber Wheel

A unique SiC whisker wheel was invented,in which the whiskers were aligned normally to the grinding wheel surface.In this paper,grindabilities of the SiC whisker wheel are investigated and compared with those of other wheels of SiC grains,Al2O3 grains,as well as Al2O3 long and short fibres which were also aligned normally to the grinding wheel surface,respectively.The main research contents concern grinding characteristics of a directionally aligned SiC whisker wheel such as material-removal volume,wheel-wear rates,integrity of the ground surfaces,grinding ratios and grinding efficiency.Furthermore,grinding wheels of whiskers and fibres have a common disadvantage:they tend to load easily.The authors have proposed a simple method of loading-free grinding to overcome this propensity and investigate some related grinding characteristics under loading-free grinding conditions.

Decomposition of formaldehyde based on gold-coated TiO2 nanoparticles

The synthesis of gold nanoparticles caped with visible light-responsible TiO2 nanoparticles. was prepared by using electrochemical Oxidation-Reduction Cycles （ORC） in 0.1 M HCI aqueous solution containing 60 mM visible light-responsible TiO2 nanoparticles. Firstly, an Au substrate was cycled in a deoxygenated aqueous solution containing 0.1 M HCI and 60 mM anatase TiO2 nanoparticles from -0.28 to ＋1.22 V vs Ag/AgCI at 500 mV/s with 25 scans. The durations at the cathodic and anodic vertexes are 10 and 5 s, respectively. After this process, Au-and TiO2-containing complexes were left in the solution. Then a Pt electrode immediately replaced the Au working electrode, and a cathodic overpotential of 0.6 V from the Open Circuit Potential （OCP） was applied under sonification to synthesize Au nanoparticles. Encouragingly, the prepared Au nanoparticles caped with visible light-responsible TiO2 nanoparticles are more active for the decomposition of formaldehyde than pure visible light-responsible TiO2 nanoparticles are in the same condition. After 5 days testing, the formaldehyde was decomposed ca. 35% in containing Au nanoparticles caped with visible light-responsible TiO2 nanoparticles, but the formaldehyde was decomposed only ca. 25% in containing pure visible light-responsible TiO2 nanoparticles.

Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.

Synthesis of Ag@Cu_2O core-shell metal-semiconductor nanoparticles and conversion to Ag@Cu core-shell bimetallic nanoparticles

Ag@Cu2O core-shell metal-semiconductor nanoparticles(NPs) were prepared by using solution phase strategy. It was found that Ag@Cu2O core-shell NPs were easily converted to Ag@Cu bimetallic core-shell NPs with the help of surfactant PVP and excessive reducer ascorbic acid in air at room temperature, which is a unique phenomenon. Varying volumes of Ag colloidal solutions were added into the reaction mixtures containing fixed initial concentrations of Cu2+ and PVP, Ag@Cu2O and Ag@Cu core-shell NPs with fixed core size but varying outer shell thicknesses could be obtained. The composites, structures, morphologies and extinction properties of Ag@Cu2O and Ag@Cu core-shell NPs were systematically characterized by XRD, TEM and extinction spectra. Both of these NPs show wide tunable optical properties. The extinction peaks could be shifted from 421 nm to 700 nm. FTIR results reveal that Cu+ ions on the surface of Cu2 O nanocrystalline coordinate with N and O atoms in PVP and further are reduced to metallic Cu by excessive ascorbic acid and then form a nucleation site on the surface of Cu2 O nanocrystalline. PVP binds onto a different site to proceed with the reduction until all the Cu sources in Cu2 O NPs are completely assumed. And the shell of Cu2 O is converted to Cu shell. The synthesis approach in this paper is simple and also a promising reference for synthesizing other core-shell NPs. Ag@Cu2O NPs can be easily converted to Ag@Cu NPs in air at room temperature, which is promising to be used in electronic devices.

Preparation of carbon-coated iron oxide nanoparticles dispersed on graphene sheets and applications as advanced anode materials for lithium-ion batteries

We report a novel chemical vapor deposition （CVD） based strategy to synthesize carbon-coated Fe203 nanoparticles dispersed on graphene sheets （Fe2Og@C@G）. Graphene sheets with high surface area and aspect ratio are chosen as space restrictor to prevent the sintering and aggregation of nanoparticles during high temperature treatments （800 ℃）. In the resulting nanocomposite, each individual Fe2O3 nanoparticle （5 to 20 nm in diameter） is uniformly coated with a continuous and thin （two to five layers） graphitic carbon shell. Further, the core-shell nanoparticles are evenly distributed on graphene sheets. When used as anode materials for lithium ion batteries, the conductive-additive-free Fe2OB@C@G electrode shows outstanding Li＋ storage properties with large reversible specific capacity （864 mAh/g after 100 cycles）, excellent cyclic stability （120% retention after 100 cycles at 100 mA/g）, high Coulombic efficiency （-99%）, and good rate capability.

Controllable hydrothermal synthesis of nanocrystal TiO_2 particles and their use in dye-sensitized solar cells

A simple method for the controllable hydrothermal synthesis of nanocrystalline anatase TiO2(nc-TiO2) particles involving the selection of suitable organic alkali peptizing agents is reported.A dye-sensitized solar cell(DSSC) with square-like nc-TiO2 particles with side lengths about 8-13 nm-prepared using tetraethylammonium hydroxide(TEAOH)-in the photoelectrode showed higher photovoltaic performance than two other DSSCs with square-like nc-TiO2 particles with side lengths about 7-10 nm-prepared using tetrabutylammonium hydroxide-or elongated nc-TiO2 particles with lengths about 18-35 nm and width about 10 18 nm-prepared using tetramethylammonium hydroxide(TMAOH)-in the photoelectrodes.When a scattering layer prepared from sub-micron size spheres or cone-like nc-TiO2 particles-synthesized using a higher concentration of TMAOH-was added on top of the photoelectrode fabricated from nc-TiO2 synthesized with TEAOH,the energy conversion efficiency of the DSSC was markedly increased from 6.77% to 8.18%.

Metal-induced oxygen vacancies on Bi_(2)WO_(6)for efficient CO_(2) photoreduction

Semiconductor-based photocatalysis for efficient solar energy conversion is an ideal strategy to tackle the growing global energy and environmental crisis.However,the development of photocatalysis is still limited by problems such as low utilization of visible light,low efficiency of charge transfer and separation,and insufficient reactive sites.Herein,Au nanoparticles(NPs)were deposited on the surface of Bi_(2)WO_(6)by a one-step reduction method,which simultaneously induced the formation of oxygen vacancies(OVs)on the surface of Bi_(2)WO_(6).The OVs concentration is found to be increased with the increase of Au loading.Au NPs and OVs improve the light absorption and facilitate the separation and transport of the photogenerated carriers.In addition,OVs act synergistically with the nearby metal active sites to optimize the adsorption energy of reactants on the catalyst surface,changing the adsorption form of CO_(2)molecules on the catalyst surface.The as-synthesized photocatalyst achieved a photocatalytic performance of up to 34.8μmol g^(−1)h^(−1)of CO_(2)reduction to CO without sacrificial agent in a gas-solid system,which is 9.4 times higher than that of the pristine Bi_(2)WO_(6).This work may further deepen our understanding on the relationship between metal NPs and OVs,and their combined role in photocatalysis.

A comparative study between graphene oxide and diamond nanoparticles as water-based lubricating additives

The tribological properties of graphene oxide(GO) nanosheets and modified diamond(MD) nanoparticles with excellent water-solubility were investigated.GO nanosheets were synthesized using carbon fibers with a regular and uniform size,the lateral size being around 30 nm and the thickness being 2 or 3 nm,while MD nanoparticles were about 30 nm in the three dimensions.The friction properties of ceramics were improved by GO nanosheets or MD nanoparticles used as additives in water-based lubrication,though the effects of two nanoparticles were quite different.For GO nanosheets,the friction coefficient at the beginning decreased sharply from 0.6 to 0.1,as compared with the dionized water lubrication.At the same time,the running-in period was shortened from 2000 s to 250 s.A steady state characterized by ultralow friction(friction coefficient=0.01) was obtained after the running-in period.In the case of MD nanoparticles,the friction coefficient stayed at 0.1 without further decrease during the whole experiment.Based on the observation of wear scar and characterization of remains on the wear track,the positive effect of GO nanosheets was attributed to their lamellar structure and geometric size.MD nanoparticles reduced friction by forming the regularly grained surface on the mating surfaces,and prevented further reduction in steady-state friction coefficient owing to their larger size and hardness.In conclusion,GO nanosheets exhibited favorable potential as an effective additive for water-based lubrication.

Formation of copper oxide nanowires and nanoparticles via electrospinning

Copper oxide nanowires and nanoparticles were fabricated through electrospinning followed by calcinations in different heating conditions.It was found that the solution viscosity and environment humidity had great impact on the morphologies of precursor nanowires,and the parameters of heat treatment,including final temperature and heating rate,significantly affected the product morphologies.

A Comparative Study of TiO_2 Nanoparticles Synthesized in Premixed and Diffusion Flames

Previous studies have been shown that synthesis of titania （TiO2） crystalline phase purity could be effectively controlled by the oxygen concentration through titanium tetra-isopropoxide （TTIP） via premixed flame from a Bunsen burner. In this study, a modified Hencken burner was used to synthesize smaller TiO2 nanoparticles via short diffusion flames. The frequency of collisions among particles would decrease and reduce TiO2 nanoparticle size in a short diffusion flame height. The crystalline structure of the synthesized nanoparticles was characterized by X-ray diffraction （XRD）, transmission electron microscope （TEM）, Barrett-Joyner- Halenda （BJH） and Brnnauer-Emmett-Teller （BET） measurements. The characteristic properties of TiO2 nanoparticles synthesized from a modified Hencken burner were compared with the results from a Bunsen burner and commercial TiO2 （Degussa P25）. The results showed that the average particle size of 6.63 nm from BET method was produced by a modified Hencken burner which was smaller than the TiO2 in a Bunsen burner and commercial TiO2. Moreover, the ruffle content of TiO2 nanoparticles increased as the particle collecting height increased. Also, the size of TiO2 nanoparticles was highly dependent on the TTIP loading and the collecting height in the flame.

Enhanced antibacterial activity of silica nanorattles with ZnO combination nanoparticles against methicillin-resistant Staphylococcus aureus

Silica nanorattles(SNs) with zinc oxide(ZnO) combination nanoparticles are reported to inhibit methicillin-resistant Staphylococcus aureus(MRSA) for the first time. SNs loaded with ZnO nanoparticles,which can produce free radicals, can cause severe damage to bacteria. ZnO nanoparticles not only provide free radicals in the combined nanostructures, which can inhibit the growth of bacteria, but also form nanorough surfaces with an irregular distribution of spikes on the SNs, which can enhance their adhesion to bacteria. Nanorough silica shell surfaces maintain the high activity and stability of small-sized ZnO nanoparticles and gather ZnO nanoparticles together to enhance production, which improves the efficiency of free radicals against the cytomembranes of bacterial cells. The enhanced adhesion of ZnO@SN nanoparticles to MRSA cells shortens the effective touching distance between free radicals and MRSA, which also improves antibacterial activity. As we expected, the ZnO@SN nanoparticles exhibit a better antibacterial effect than free ZnO nanoparticles against MRSA in vitro and in vivo. We also demonstrate that SNs loaded with ZnO nanoparticles can accelerate wound healing in MRSA skin inflammation models. This method of multilevel functionalization will be potentially applicable to the antibacterial field.