Aerobic oxidation of monoterpenic alcohols catalyzed by ruthenium hydroxide supported on silica-coated magnetic nanoparticles

Ruthenium hydroxide supported on silica-coated magnetic nanoparticles was shown to be an efficient heterogeneous catalyst for the liquid-phase oxidation of a wide range of alcohols using molecular oxygen as a sole oxidant in the absence of co-catalysts or additives. The material was prepared through the loading of the amino modified support with ruthenium(III) ions from an aqueous solution of ruthenium(III) chloride followed by treatment with sodium hydroxide to form ruthenium hydroxide species. Characterizations suggest that ruthenium hydroxide is highly dispersed on the support surface, with no ruthenium containing crystalline phases being detected. Various carbonylic monoterpenoids important for fragrance and pharmaceutical industries can be obtained in good to excellent yields starting from biomass-based monoterpenic alcohols, such as isobomeol, perillyl alcohol, carveol, and citronellol. The catalyst undergoes no metal leaching and can be easily recovered by the application of an external magnet and re-used. (C) 2011 Elsevier Inc. All rights reserved.

Synthesis of silica-coated ZnO nanocomposite : the resonance structure of polyvinyl pyrrolidone (PVP) as a coupling agent

Abstract The preparation of silica-coated ZnO nanocomposite using polyvinyl pyrrolidone (PVP) as a coupling agent was investigated. Transmission electron microscopy analysis revealed that silica has been deposited on the surface of PVP-capped ZnO nanoparticles as a continuous thin layer. Two-dimensional correlation analysis based on the time-dependent UV–vis spectra was introduced to study the interaction governing the deposition of silica on to PVP-capped ZnO. Strong hydrogen bonds formed between the amphiphilic PVP molecules and silica in the silicacoated PVP-capped ZnO composites. The reduced photocatalytic activity of silica-coated ZnO nanoparticles will enhance their performance as durable, safe, and nonreactive UV blockers in plastics, paints, and coating for outdoor textile and timber products.

Reducing photoyellowing of wool fabrics with silica coated ZnO nanoparticles

Though ZnO nanoparticles (NPs) are an excellent UV absorber, their photocatalytic activity greatly limits the application areas of these particles. Under sunlight exposure, ZnO NPs used as a UV absorber can accelerate the wool yellowing process by generating free radicals. To reduce this photocatalysis effect, a physical barrier has been fabricated by coating the ZnO NPs with a silica layer (ZnO@SiO2), hence providing good UV-shielding with low photocatalytic activity. The structure and optical properties of ZnO and ZnO@SiO2 NPs were characterized by transmission electron microscope (TEM) and UV–Vis spectrum. The photocatalytic activity of ZnO and ZnO@SiO2 NPs was evaluated by photo-degradation of Rhodamine B. The ZnO and ZnO@SiO2 NPs were applied to knitted wool fabrics using the dip coating method. The treated wool fabrics were characterized by a scanning electron microscope (SEM) and the photoyellowing level of treated fabrics after exposure under simulated sunlight was evaluated by a Datacolor Spectraflash spectrophotometer. The ZnO@SiO2 NPs demonstrated excellent protection of wool against photoyellowing.

Microtensile bond strength of a resin cement to silica-coated and silanized in-ceram zirconia before and after aging

Purpose: This study compared the microtensile bond strength of resin-based cement (Panavia F) to silica-coated, silanized, glass-infiltrated high-alumina zirconia (In-Ceram Zirconia) ceramic in dry conditions and after various aging regimens. Materials and Methods: The specimens were placed in 1 of 4 groups: group 1: dry conditions (immediate testing without aging); group 2: water storage at 37°C for 150 days; group 3: 150 days of water storage followed by thermocycling (× 12,000, 5°C to 55°C); group 4: water storage for 300 days; group 5: water storage for 300 days followed by thermocycling. Results: Group 1 showed a significantly higher microtensile bond strength value (26.2 ± 1 MPa) than the other aging regimens (6.5 ± 1, 6.2 ± 2, 4.5 ± 1, 4.3 ± 1 MPa for groups 2, 3, 4, and 5, respectively) (P < .01). Conclusion: Satisfactory results were seen in dry conditions, but water storage and thermocycling resulted in significantly weaker bonds between the resin cement and the zirconia.

Luminescence Enhancement of Carboxyl-Coated CdTe Quantum Dots by Silver Nanoparticles

Metallic nanoparticles (NPs) have been used to improve the sensibility of biosensors and bioassays either by enhancing radiative emission or inducing quenching process on fluorescent probes. The aim of this research was to study the interaction of silver and silver-pectin NPs with water-dispersed carboxyl-coated cadmium telluride (CdTe) quantum dots (QDs). Metallic NPs were observed to change the emission of these fluorophores through local field effects. In a solution-base platform, an increase of 82 % was observed for the CdTe emission due to the interaction of QDs and silver-pectin NPs. QDs interaction with silver NPs without pectin was also investigated and a smaller emission enhancement of 20 % was detected. We observed that the NPs' nature and QDs' surface charge and concentration are important parameters for NPs-QDs interaction. Moreover, the presence of the pectin polymer shows to be a key component to the observed fluorescence enhancement. © 2013 Springer Science+Business Media New York.

Protection of silica-coated ZnO nanoparticles on pre-dyed polyester fabrics against photofading

This work was designed to investigate the ability of silica-coated ZnO (ZnO&SiO2) nanoparticles (NPs) as ultraviolet (UV) absorbers for protecting pre-dyed polyester fabrics against photofading. Despite that ZnO NPs are excellent UV absorbers, their strong photocatalytic activity limits the application in UV protection. In this study, a silica layer was coated onto ZnO NPs to form a physical barrier between the ZnO and a polyester substrate, which allowed effective UV shielding while minimising the harmful effects of photocatalytic activity on the substrate. The structure and optical proprieties of ZnO&SiO2 NPs were observed. The bare ZnO and ZnO&SiO2 NPs were, respectively, applied to polyester fabrics coloured with three kinds of dyes by a dip coating method. The photofading level of treated fabrics after exposure under simulated sunlight was evaluated. The ZnO&SiO2 NPs exhibited excellent protection on pre-dyed polyester fabrics against photofading.

Gold/platinum hybrid nanoparticles supported on multiwalled carbon nanotube/silica coaxial nanocables: Preparation and application as electrocatalysts for oxygen reduction

A simple approach combining sonication and sol-gel chemistry was employed to synthesize silica coated carbon nanotube (CNTs) coaxial nanocables. It was found that a homogeneous silica layer can be coated on the surface of the CNTs. This method is simple, rapid, and reproducible. Furthermore, gold nanoparticle supported coaxial nanocables were facilely obtained using amino-functionalized silica as the interlinker. Furthermore, to reduce the cost of Pt in fuel cells, designing a Pt shell on the surface of a noble metal such as gold or silver is necessary. High-density gold/platinum hybrid nanoparticles were located on the surface of I-D coaxial nanocables with high surface-to-volume ratios. It was found that this hybrid nanomaterial exhibits a high electrocatalytic activity for enhancing oxygen reduction (low overpotential associated with the oxygen reduction reaction and almost four-electron electroreduction of dioxygen to water).

Carbon Nanotube/Silica Coaxial Nanocable as a Three-Dimensional Support for Loading Diverse Ultra-High-Density Metal Nanostructures: Facile Preparation and Use as Enhanced Materials for Electrochemical Devices and SERS

In this paper, we have reported a very simple strategy (combined sonication with sol-gel techniques) for synthesizing well-defined silica-coated carbon nanotube (CNT) coaxial nanocable without prior CNT functionalization. After functionalization with NH2 group, the CNT/silica coaxial nanocable has been employed as a three-dimensional support for loading ultra-high-density metal or hybrid nanoparticles (NPs) such as gold NPs, Au/Pt hybrid NPs, Pt hollow NPs, and Au/Ag core/shell NPs. Most importantly, it is found that the ultra-high-density Au/Pt NPs supported on coaxial nanocables (UASCN) could be used as enhanced materials for constructing electrochemical devices with high performance. Four model probe molecules (O-2, CH3OH, H2O2, and NH2NH2) have been investigated on UASCN-modified glassy carbon electrode (GCE). It was observed that the present UASCN exhibited high electrocatalytic activity toward diverse molecules and was a promising electrocatalyst for constructing electrochemical devices with high performance. For instance, the detection limit for H2O2 with a signal-to-noise ratio of 3 was found to be 0.3 mu M, which was lower than certain enzyme-based biosensors.

Silica-encapsulated nanomagnetic particle as a new recoverable biocatalyst carrier

Enzymes are versatile biocatalysts with major advantages of ultrahigh reaction selectivity and specificity under mild conditions, which currently find increasing applications. However, their applications are often hampered by difficulties in recovery and recycling. As a result, we carried out detailed investigations on the synthesis and characterization of silica-encapsulated iron oxide magnetic nanoparticles of controlled dimension as an enzyme carrier. It is shown that the relatively smaller sized silica-coated magnetic nanoparticle prepared by the microemlusion technique can a carry bulky enzyme, beta-lactamase, via chemical linkages on the silica overlayer without severely blocking the enzymatic active center ( which is commonly encountered in conventional solid supports). An activity study by Michalis-Menten kinetics reflects that this new type of immobilization allows enzyme isolation with accessibility as good as free enzyme. The recovery and reusability of the nanoparticle-supported enzyme upon application of magnetic separation are also demonstrated.

Effect of multiple firing and silica deposition on the zirconia-porcelain interfacial bond strength

Objectives. To test the hypothesis that multiple firing and silica deposition on the zirconia surface influence the bond strength to porcelain.Materials and methods. Specimens were cut from yttria-stabilized zirconia blocks and sintered. Half of the specimens (group S) were silica coated (physical vapor deposition (PVD)) via reactive magnetron sputtering before porcelain veneering. The remaining specimens (group N) had no treatment before veneering. The contact angle before and after silica deposition was measured. Porcelain was applied on all specimens and submitted to two (N2 and S2) or three firing cycles (N3 and S3). The resulting porcelain-zirconia blocks were sectioned to obtain bar-shaped specimens with 1 mm(2) of cross-sectional area. Specimens were attached to a universal testing machine and tested in tension until fracture. Fractured surfaces were examined using optical microscopy. Data were statistically analyzed using two-way ANOVA, Tukey's test (alpha = 0.05) and Weibull analysis.Results. Specimens submitted to three firing cycles (N3 and S3) showed higher mean bond strength values than specimens fired twice (N2 and S2). Mean contact angle was lower for specimens with silica layer, but it had no effect on bond strength. Most fractures initiated at porcelain-zirconia interface and propagated through the porcelain.Significance. The molecular deposition of silica on the zirconia surface had no influence on bond strength to porcelain, while the number of porcelain firing cycles significantly affected the bond strength of the ceramic system, partially accepting the study hypothesis. Yet, the Weibull modulus values of S groups were significantly greater than the m values of N groups. (C) 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effect of silica coating on flexural strength of fiber posts

Purpose: Fiber-reinforced composite (FRC) posts can be air-abraded to obtain good attachment to the resin cement. This study tested the effect of silica coating on the flexural strength of carbon, opaque, and translucent quartz FRC posts. Materials and Methods: Six experimental groups of FRC posts (n = 10 per group) were tested, either as received from the manufacturer or after chairside silica coating (30-μm CoJet-Sand). Results: There was no significant difference in the flexural strength of nonconditioned (504 to 525 MPa) and silica-coated (514 to 565 MPa) specimens (P > .05) (analysis of variance). The type of post did have a significant effect on flexural strength (P < .05). Conclusion: Chairside silica coating did not affect the flexural strength of both carbon and quartz FRC posts.

Avaliação de carbonilas na atmosfera interior e exterior de salas de aula de escolas públicas

Compostos carbonílicos representam uma das principais classes de poluentes atmosféricos e são frequentemente reportados em estudos de poluição atmosférica de interiores. São emitidos para a atmosfera a partir de uma variedade de fontes naturais e antropogênicas. Em projeto empreendido em 2011 pela Secretaria de Estado de Educação do Estado do Rio de Janeiro,foi implementada a climatização em todas as salas de aula de todas as escolas da rede pública estadual. A escala de exposição de ocupantes à climatização, em salas de aula, não apresenta precedentes em nosso estado e representa uma tendência de todo o país. Como é um projeto recente, não há dados a respeito da qualidade do ar interior nesses ambientes e, portanto, das consequências na saúde dos ocupantes. Os procedimentos foram baseados na metodologia TO-11A da U.S.EPA. A técnica de amostragem foi por via seca com reação química, empregando-se cartuchos de sílica revestidos de octadecil (SiO2-C18) impregnados com 2,4-dinitrofenilhidrazina. As carbonilas foram analisados através de Cromatografia Líquida de Alta Eficiência com detecção por UV. Foram encontradas concentrações de formaldeído na faixa de 3,59 a 26,62 μg m-3 (interior) e 0,74 a 23,47 μg m-3 (exterior), acetaldeído na faixa de 0,19 a 259,47 μg m-3 (interior) e 1,19 a 127,51 μg m-3 (exterior), acetona+acroleína na faixa de 0,00 a 48,45 μg m-3 (interior) e 0,00 a 37,00 μg m-3 (exterior). Os valores encontrados geralmente não ultrapassaram os limites determinados por organismos internacionais

Recoverable rhodium nanoparticles: Synthesis, characterization and catalytic performance in hydrogenation reactions

We here report the first magnetically recoverable Rh(0) nanoparticle-supported catalyst with extraordinary recovery and recycling properties. Magnetic separation has been suggested as a very promising technique to improve recovery of metal-based catalysts in liquid-phase batch reactions. The separation method is significantly simple, as it does not require filtration, decantation, centrifugation, or any other separation technique thereby, overcoming traditional time- and solvent-consuming procedures. Our new magnetically separable catalytic system, comprised of Rh nanoparticles immobilized on silica-coated magnetite nanoparticles, is highly active and could be reused for up to 20 times for hydrogenation of cyclohexene (180,000 mol/mol(Rh)) and benzene (11,550 mol/mol(Rh) under mild conditions. (c) 2007 Elsevier B. V. All fights reserved.

Preparation of supported Pt(0) nanoparticles as efficient recyclable catalysts for hydrogenation of alkenes and ketones

A magnetically recoverable Pt(0) catalyst was prepared by in situ H(2) reduction of Pt(2+) species bound to an amino modified silica-coated magnetic nanoparticles. Compared to ordinary silica (maximum uptake Pt 0.03 wt%), the amino-functionalized silica surfaces were loaded with 1.95 wt% of metal. The supported Pt(0) nanoparticles exhibit high catalytic activity in the hydrogenation of alkenes and ketones under solventless mild reaction conditions. Partially hydrogenated products could also be isolated. The magnetic property of the catalyst grants a fast and efficient product isolation compared to traditional methods used in heterogeneous systems that generally make use of time- and solvent-consuming procedures. (C) 2009 Elsevier B.V. All rights reserved.