Sedimentation and phase transitions of colloidal gibbsite platelets

We study the competition between sedimentation, gelation, and liquid crystal formation in suspensions of colloidal gibbsite platelets of five different sizes at three ionic strengths. For large particles (with diameters of 350, 420, and 570 nm) sedimentation is initially the most important factor determining the macroscopic behavior. Only after the main part of the sample has sedimented in an amorphous phase, phase separation takes place. For the smallest particles (diameter 210 and 270 nm), it is the other way around: fast (within one week) phase separation or gelation takes place, after which sedimentation determines the final macroscopic appearance. We distinguish six different scenarios within this two-fold scheme and interpret these on the basis of the previously obtained phase diagram of colloidal gibbsite platelets (van der Beek, D.; Lekkerkerker, H. N. W. Langmuir 2004, 20, 8582).     

Seeded growth of monodisperse gibbsite platelets to adjustable sizes

Nanosized hexagonal gibbsite seeds are grown from a mixture of dissolved alumina alkoxides at 85 degrees C. Centrifugation reduces the polydispersity by 30%. The seeds can be grown further by adding them to a fresh alkoxide mixture and heating it. This procedure was repeated several times to obtain particles of 570 nm +/- 11% diameter and a thickness of 47 +/- 23%. No indications of a size limit were observed. The thus obtained particles may form easily a columnar phase. Individual gibbsite particles in solution can be seen by confocal microscope.     

Synthesis and characterization of the water-soluble silica-coated ZnS:Mn nanoparticles as fluorescent sensor for Cu ions

Silica-coated ZnS:Mn nanoparticles were synthesized by coating hydrophobic ZnS:Mn nanoparticles with silica shell through microemulsion. The core–shell structural nanoparticles were confirmed by X-ray diffraction (XRD) patterns, high-resolution transmission electron microscope (HRTEM) images and energy dispersive spectroscopy (EDS) measurements. Results show that each core–shell nanoparticle contains single ZnS:Mn nanoparticle within monodisperse silica nanospheres (40 nm). Photoluminescence (PL) spectroscopy and UV–vis spectrum were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnS:Mn nanoparticles, the silica-coated ZnS:Mn nanoparticles have the improved PL intensity as well as good photostability. The obtained silica-coated ZnS:Mn nanoparticles are water-soluble and have fluorescence sensitivity to Cu²⁺ ions. Quenching of fluorescence intensity of the silica-coated nanoparticles allows the detection of Cu²⁺ concentrations as low as 7.3 × 10⁻⁹ mol L⁻¹, thus affording a very sensitive detection system for this chemical species. The possible quenching mechanism is discussed.     

Synthesis and characterization of (Mo72Fe30)-coated large hexagonal gibbsite gamma-Al(OH)3 platelets

The polyoxometalates or POMs (clusters comprising at least two metal and many oxygen atoms) have recently gained significant interest owing to their versatile architecture and especially their catalytic activities. Due to their high catalytic activity but low surface area, there is always a demand for making high surface area POMs. This work demonstrates the attachment of the anionic (Mo72Fe30) POMs to gibbsite nanoplatelets with a residual positive charge to form large surface area composites. The resulting composite reported here has been characterized using cryo-TEM imaging, EDX/STEM (elemental) analysis, ATR-IR spectroscopy, SAXS, electrophoretic mobility determination and XRD. The composite reported here could find application in catalysis.     

Synthesis and magnetic properties of silica-coated FePt nanocrystals

Colloidal FePt nanocrystals, 6 nm in diameter, were synthesized and then coated with silica (SiO2) shells. The silica shell thickness could be varied from 10 to 25 nm. As-made FePt@SiO2 nanocrystals have low magnetocrystalline anisotropy due to a compositionally disordered FePt core. When films of FePt@SiO2 particles are annealed under hydrogen at 650 degrees C or above, the FePt core transforms to the compositionally ordered L1(0) phase, and superparamagnetic blocking temperatures exceeding room temperature are obtained. The SiO2 shell prevents FePt coalescence at annealing temperatures up to approximately 850 degrees C. Annealing under air or nitrogen does not induce the FePt phase transition. The silica shell limits magnetic dipole coupling between the FePt nanocrystals; however, low temperature (5 K) and room temperature magnetization scans show slightly constricted hysteresis loops with coercivities that decrease systematically with decreased shell thickness, possibly resulting from differences in magnetic dipole coupling between particles.     

Synthesis of fluorescent coumarin triazolylglycosides

A series of coumarin triazolylglycosides were synthesized in good yields using copper-mediated 1,3-dipolar cycloaddition reactions of carbohydrate azides and 4-alkynyl-substituted coumarins. Several of the products show strong luminescence in the 490-560 nm region and are compatible with surface imaging applications.     

Hydrothermal process of synthetic gibbsite and the characteristics of Na in gibbsite crystal

The presence of Na in synthetic gibbsite was studied by several modern testing methods such as X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and inductively coupled plasma. Results show that Na is located between gibbsite crystals and is not present as sodium aluminosilicate hydrate in synthetic gibbsite. Synthetic gibbsite crystal can be transformed into boehmite under the hydrothermal condition of 210 °C for 60 min. During the reaction process, synthetic gibbsite crystal particles break up into small fragments and form boehmite. During the process, impurities are released and the Na can be removed by washing. Over 90% of Na can be removed during the hydrothermal transformation process. This technology can be applied in the production process of high-purity alumina.     

Synthesis of N-aryl imidazoles catalyzed by copper nanoparticles on nanosized silica-coated maghemite

A magnetically recoverable catalyst consisting of copper nanoparticles (CuNPs) on nanosized silica-coated maghemite is presented. The catalyst has been prepared under mild conditions by mixing the magnetic support with a freshly prepared suspension of CuNPs obtained by fast reduction of anhydrous CuCl₂ with lithium sand and a catalytic amount of DTBB (4,4′-di-tert-butylbiphenyl) as electron carrier. This copper-based catalyst has shown to be very efficient in the N-(hetero)arylation of imidazole using (hetero)aryl bromides and iodides as arylating agents under ligand-free conditions. The catalyst is easily recovered by means of an external magnet and can be reutilized in three N-arylation cycles without apparent loss of catalytic activity.     

Synthesis,characterizations of silica-coated gold nanorods and its applications in electroanalysis of hemoglobin

Gold nanorods (GNRs) were synthesized by a seed–mediated growth approach followed by TEOS polymerization leading to the formation of silica layer surrounding the gold nanorod core. TEM images showed that the silica-coated gold nanorods (GNRs@SiO₂) were dispersed with an average aspect ratio of 3.1 for the GNRs cores and a uniform thickness of the silica shell. The core/shell nanocomposites were further used as efficient supports for the immobilization of hemoglobin (Hb) to fabricate a novel biosensor. The immobilized Hb showed an enhanced electron transfer for its heme Fe(III) to Fe(II) redox couple. This biosensor showed an excellent bioelectrocatalytic activity towards H₂O₂ with a linear range from 8.0 × 10⁻⁷ to 6.1 × 10⁻⁵ M, and the detection limit was 6.0 × 10⁻⁸ M at 3σ. The apparent Michaelis–Menten constant of the immobilized hemoglobin was calculated to be 0.13 mM.     

一种蓝色荧光材料的合成

本文设计和合成了一种带有吡唑啉侧链基因的低聚酰胺,可用作蓝色荧光材料。分子中特殊的氢键序列(AADADD)及芳酰胺链可与制着器件所用的高分子基材分子之间的形成较强的作用力,从而将发光基团“铆定”在功能膜中。     

Synthesis of coumarin based fluorescent compounds

The reaction of different 7,8-disubstituted coumarin 4-acetic acids with 7-diethylaminocoumarin-3-carbaldehyde in the presence of piperidine in methanol gives highly fluorescent (E)-1-(7-diethylaminocoumarin-3-yl)-2-(7,8-disubstituted coumarin-4-yl)ethenes in good yield. Only the (E) diastereomers of these are obtained. The compounds are new, orange to red in colour and show emission in yellow to red region. These compounds were further studied for their emission properties.     

Synthesis of fluorescent coumarin-labeled organic glass

Polymerization of methyl methacrylate in bulk in the presence of 4-ethynylcoumarin and 4-butadiynylcoumarin (AIBN, 60 °C) leads to the formation of fluorescent polymers. A hypsochromic shift of fluorescence band maxima of polymer solutions is observed in dichloromethane. It was suggested using the quantum chemical calculations that 4-ethynylcoumarin is attached to the macroradical via the terminal carbon atom of the ethynyl group. The samples of fluorescent organic glasses were prepared. It was established that the addition of coumarins do not influence the microhardness of organic glass.     

Characterization of silica-coated tobacco mosaic virus

The deposition of silica on the surface of tobacco mosaic virus (TMV) is achieved at a higher pH (>7) as a means to enhance its usefulness as a template for the synthesis of nanostructures. Electron energy loss spectroscopy definitively shows the presence of a silica shell on the surface of the TMV while small angle X-ray scattering differentiates successfully between silica-coated TMV and silica particles in the presence of uncoated TMV. Importantly, coating reactions done in a 50% w/v methanol/water solution produce smaller silica nanostructures during the condensation of the hydrolysis intermediates, possibly aiding in obtaining uniform coating. Furthermore, TMV-templated silica coatings are found to enhance the stability of the virus particle in methanol at conditions that would ordinarily disrupt the assembled particle. Combined these findings demonstrate that TMV can function as an efficient template for the controlled deposition of silica at neutral pH.     

Synthesis and characterization of red-luminescent graphene oxide functionalized with silica-coated Eu3+ complex nanoparticles

Traditional dye-doped fluorescent graphene oxide (GO) reveals a low quantum yield and a short life expectancy. Herein, red-luminescent silica-coated Eu(3+) complex nanoparticles were synthesized and covalently coupled to GO nanosheets by means of a carbodiimide-mediated amidation process. SEM and TEM studies demonstrated successful attachment of the silica-coated Eu(3+) complex nanoparticles onto the GO surface. Spectroscopic studies showed that the GO-nanoparticle conjugates exhibit strong luminescence, long lifetimes, as well as good photostability, which suggests that this new type of luminescent nanomaterial has the potential for highly sensitive time-resolved fluorescence cyto- and histochemistry imaging.     

Template-directed synthesis of silica-coated J-aggregate nanotapes

Self-assembly of porphyrin nanotapes in the presence of alkoxysilane reaction solutions produces hybrid nanofilaments consisting of an optically responsive J-aggregate core encased within an ultrathin shell of amorphous silica.     

Kinetics and hydrothermal transformation of gibbsite

The transformation of gibbsite have been studied under hydrothermal influence. Results of the X-ray diffraction analysis of the samples heated at different temperatures from 170°C to 265°C are also discussed in detail. The percentage of the boehmite phase formed, due to the transformation of the gibbsite, have been determined by comparing the intensity of the most strongest reflection of the boehmite phase with a fully transformed sample. The activation energy value calculated form X-ray diffractograms is almost comparable with the value calculated from main DTA endotherm of gibbsite.Es wurde die Umwandlung von Gibbsit unter hydrothermalem Einfluß untersucht. Weiterhin werden auch Ergebnisse der Röntgendiffraktionsanalyse an den bei verschiedenen Temperaturen zwischen 170°C und 265°C erhitzten Proben besprochen. Durch Vergleich der Intensität der stärksten Reflexion der Böhmitphase mit einer vollständig umgewandelten Probe wurde der prozentuelle Anteil der während der Umwandlung von Gibbsit gebildeten Böhmitphase bestimmt. Der Wert für die Aktivierungsenergie, berechnet aus den Röntgendiffraktogrammen ist annähernd vergleichbar mit dem aus der DTA von Gibbsit berechneten Wert.

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RRL Contribution No. 2028.     

Synthesis and characterization of new fluorescent nanoparticles

A novel kind of fluorescent nanoparticles（FNPs）has been prepared using a precipitation polymerization method.Methacrylic acid,trimethylolpropane trimethacrylate and azobisisobutyronitrile were used as functional-monomer,cross-linker and initiator, respectively.Compared with other fluorescent nanoparticles,the FNPs have the characteristics including low dye leakage and good photostability.The fluorescence microscopy imaging indicates that the FNPs can be used as fluorescent labels in bioanalysis.     

Synthesis of biologically active fluorescent phorbol esters

Pure fluorescent derivatives of 12-O-tetradecanoyl phorbol-13-O-acetate (TPA), labeled in the tetradecanoyl chain, are synthesized by two ways: 1) from both enantiomers of β-N-dansylaminotetradecanoic acid which requires the resolution of the (±) β-aminoacid precursor; 2) from an achiral fluorescent chain derived from 3-azatetradecanoic acid. The new phorbol derivatives retain the main biological activity of TPA.