Nano-sized SiO2 Research Articles

Investigation of nano-SiO2 impact on mechanical and biocompatibility properties of cyanoacryalate based nanocomposites for dental application

Although cyanoacrylate glues are widely used in medicine, cyanoacrylate-based nanocomposites have been recently suggested for dental restorative/filling applications. In the present research, SiO2 nanoparticles were used as filler for development of a novel dental nanocomposite base on alkoxy-ethyl-cyanoacrylate. The mechanical properties of nanocomposite samples filled with different levels of nano-sized SiO2 (wt%) were evaluated and comparisons were made with the neat cyanoacrylate. The hardness and wear behavior of the samples were measured using Vickers hardness and pin-on-disk tester, respectively. The wear mechanism of the samples was also evaluated using scanning electron microscopy (SEM). Furthermore, cell biocompatibility of the samples using MTT and LDH assays as well as inflammatory cytokine expression interleukin-6 (IL-6) from L929 cells was investigated. The results showed that an increase in nano-sized SiO2 content improves hardness and wear resistance of the cyanoacrylate-based nanocomposites and changes the wear mechanism from adhesive to abrasive. The results of cytotoxicity analysis showed a significant reduction in cell viability and IL-6 produced from the samples-exposed L929 cells compared with untreated control cells. Moreover, increasing the nano SiO2 powder content caused a decrease in the released formaldehyde.

Influence of micro- and nano-sized SiO2 excess support on the metathesis of ethylene and trans-2-butene to propylene over silica-supported tungsten catalysts

Silica-supported tungsten catalysts with various tungsten oxide loadings were physically mixed with micro- or nano-sized SiO2 excess supports and investigated in the metathesis of ethylene and trans-2-butene to propylene. Adding nano-sized SiO2 excess support led to higher trans-2-butene conversion and propylene yield than those of micro-one and also removed the induction period. It was indicated from FT-Raman spectra and in situ UV–vis spectra that silica-supported tungsten catalysts mixed with nano-sized SiO2 excess support had the higher ratio of isolated surface tetrahedral tungsten oxide species to WO3 crystal and could be well-dispersed than micro-one. The characterization results of the separated nano-sized SiO2 excess support from the spent catalyst by in situ Raman spectroscopy clearly exhibited the presence of isolated surface tetrahedral tungsten oxide species, the active site precursor of metathesis reaction, on the separated nano-sized SiO2 excess support, confirming the thermal spreading of tungsten from the original catalysts to the nano-sized SiO2 and creating more isolated surface tetrahedral tungsten oxide species.

A new coating system modified with nano-sized particles for archaeological bronze protection

A new coating system for archeological bronze protection that consists of a primer coating and a top coating was prepared in this study. The primer coating was prepared by mixing water-based acrylic emulsion with 1,2,3-benzotriazole, and the ultraviolet (UV) light-resistant top coating was prepared by mixing water-based acrylic emulsion with nano-sized TiO2 and SiO2 particles. UV light resistance and visible light transmission, contact angle, corrosion resistance, and mechanical properties of the new coating system were investigated and the results showed that UV resistance, hydrophobicity, oleophobicity, glossiness, and corrosion resistance all were improved. Application of the new system on real archaeological bronzes showed that the coating film was colorless, odorless, transparent, soft low-lustre, removable, and the original appearance of the archaeological bronze was well maintained.

Fabrication of composite particles by attaching surface-modified nanoparticles to core particles by wet processing in organic solvents

A simple wet processing route for the formation of composite particles via the adsorption of highly dispersible nanoparticles onto the core particles in organic solvents, without the formation of strong aggregates, was developed. The process involved a simple mixing procedure using core particles and surface-modified highly dispersible nanoparticles (shell nanoparticles) in organic solvents, assisted by ultrasonication. As a model study, submicron-sized (ca. 400nm) and nano-sized (ca. 30nm) SiO2 particles, prepared by Stöber process, were applied as the core and shell materials, respectively. The surface of the shell SiO2 nanoparticles was modified by a layer-by-layer process that involves the adsorption of cationic polyethyleneimine and an anionic surfactant comprising branched alkyl and polyethylene glycol chains for improving the stability in various organic solvents, as well as for controlling the interaction with the core material. The surface modified shell SiO2 nanoparticles were found to be effectively adsorbed onto the core SiO2 particles when mixed in toluene, while minimal adsorption was observed in ethanol. The obtained composite particles showed improved stability compared to raw core SiO2 particles in toluene. The adsorption mechanism of the shell SiO2 nanoparticles on the core particles in various organic solvents was proposed on the basis of surface-interaction measurements by atomic force microscopy colloidal probe methods. We believe that a long-range adhesive force between the shell SiO2 nanoparticles and the core particles played an important role in promoting effective adsorption, allowing the formation of composite particles.

Sulfuric acid decomposition on the Pt/n-SiC catalyst for SI cycle to produce hydrogen

The sulfuric acid decomposition should be performed in the wide temperature ranges from 550 °C to 950 °C to absorb the sensible heat of He in SI process. Therefore, the catalysts for the reaction should be stable even in the very corrosive reaction condition of 650 °C. Here, the Pt/n-SiC catalyst was prepared for the purpose and compared with the Pt/SiC catalyst. The both catalysts showed the high stability in the temperature ranges from 650 to 850 °C. The n-SiC with the surface area of 187.1 m2/g was prepared using nano-sized SiO2, which resulted in amorphous SiC phase. The SiC support with the surface area of 19.2 m2/g for the comparison showed the well crystalline structure. In spite of the large surface area differences between the n-SiC and SiC support, the Pt particle sizes of the Pt/n-SiC (average Pt size: 26.4 nm) catalyst were not so much different from those of the Pt/SiC (average Pt size: 26.1 nm) catalyst after the calcination at 1000 °C for 3 h. However, the catalytic activity of the Pt/n-SiC was much higher than that of the Pt/SiC. XRD analysis indicated that the Pt particles on the Pt/n-SiC was more stable than those of the Pt/SiC in the sulfuric acid decomposition and XPS analysis showed that the Pt valence state on the Pt/n-SiC was higher than that on the Pt/SiC. The surface analysis showed that the surface of the n-SiC particles was covered by SiO2 and Si4C4−xO4. These experimental results indicate that the Pt metal particles on n-SiC were stabilized on the oxidized Si surface. Therefore, it is suggested that the Pt particles stabilized on the oxidized Si surface can be a reason for the higher activity of the Pt/n-SiC catalyst as compared with the Pt/SiC catalyst.

In-situ catalytic conversion of tar using rice husk char-supported nickel-iron catalysts for biomass pyrolysis/gasification

This paper aims to propose an effective tar conversion approach during biomass pyrolysis via in-situ dry reforming over rice husk (RH) char and char-supported Ni-Fe catalysts. Utilizing high pyrolysis temperature, tar from biomass pyrolysis could be removed effectively in the gasifier by mixing with the char-supported catalysts, simplifying the follow-up tar removal process. Under the optimized conditions, the conversion efficiencies of condensable tar can reach about 92.3% and 93% using Ni-Fe char (without calcination) and Ni char (with calcination), respectively. It is noteworthy that the condensable tar could be catalytically transformed into the non-condensable tar or small molecule gases resulting in the heating value increase of gaseous products to benefit of the power generation systems. Compared with the other catalysts preparation methods, Ni–Fe char exhibited more advantages of convenient and energy-saving. In the presence of catalysts, the concentration of CO2 (vol.%) was reduced slightly, while the CO concentration (vol.%) increased greatly because of dry reforming. Due to carbon loss, parts of RH char-supported catalysts (C-SiO2 catalysts) could be converted into SiO2-based catalysts because of high-content amorphous nano-sized SiO2 in RH char. In addition, partial metal oxides or ions via carbon (i.e., biochar) and gas (i.e., H2, CO) in-situ reduction were transformed into metallic states contributing to the enhancement of tar conversion. Therefore, RH char plays two significant roles during the process of biomass pyrolysis. On one hand, it works as an intermediate reductant to reduce the metal oxides and CO2; on the other hand, it can be considered as an adsorptive-support to adsorb metal ions and tar. After that, the char-supported catalysts could be used for tar conversion. In particular, since the metal catalysts still remain in the solid residues, the pyrolysis char could be regenerated via thermal regeneration using waste heat or gasified into syngas directly.

Synthesis, characterization and polymer battery fabrication of hot-pressed ion conducting nano-composite polymer electrolytes

Synthesis and characterization of hot-pressed ion conducting nano-composite polymer electrolytes or polymer–matrix composites (NCPEs/PMCs):(1−x)[80PEO:20KI]:xSiO2 where 0<x<14wt.%, are reported. NCPEs were cast using a recently developed hot-press method in place of traditional solution-cast/sol–gel technique. Two and half orders of conductivity enhancement were found in NCPEs after the dispersion of nano-sized SiO2 inert material in the polymeric host, from the room temperature conductivity measurement. The polymer–salt/nano-filler SiO2 complexation, surface analysis and thermal properties characterization were done with the help of XRD, SEM, DSC and TGA studies. The ionic conductivity (σ) enhancements were explained using various experimental results viz. ionic mobility (μ), mobile ion concentration (n) values and various theoretical models. The ionic transference number (tion) of optimum conducting composition of NCPE was also determined with the help of Transient Ionic Current (TIC) technique. To compute the activation energy (Ea) in NCPEs, the temperature dependent conductivity studies were done and Ea values were determined by using logσ–1/T Arrhenius plots. A solid state polymer battery was fabricated using the NCPE OCC as an electrolyte and cell-potential discharge characteristic studies were also reported with different load conditions at room temperature.

New polymerized ionic liquid (PIL) gel electrolyte membranes based on tetraalkylammonium cations for lithium ion batteries

New polymerized ionic liquids (PILs) based on tetraalkylammonium cations with N(CF3SO2)2− (TFSI−) anions are synthesized by homopolymerization and anion exchange reaction. Furthermore, a gel polymer electrolyte membrane based on the PILs as polymer host is prepared incorporating a tetraalkylammonium ionic liquid, LiTFSI salt and nano-size SiO2. The gel polymer electrolyte membranes show exceptional thermal and electrochemical properties. They are found to be thermally stable up to 336°C. With the increase of the IL, Tg of the PIL-based electrolyte samples decreases obviously. When the IL concentration is 25wt%, the ionic conductivity of the electrolytes reaches 4.9×10−4Scm−1 at 60°C. After 130 cycles, the Li/LiFePO4 battery with the gel polymer electrolyte membranes at 60°C has discharge capacity of 122mAhg−1 at 0.1 current rates.

Robustness of Ru/SiO2 as a Hydrogen-Evolution Catalyst in a Photocatalytic System Using an Organic Photocatalyst

Effects of various metal oxide supports (SiO2, SiO2–Al2O3, TiO2, CeO2, and MgO) on the catalytic reactivity of ruthenium nanoparticles (RuNPs) used as a hydrogen-evolution catalyst have been evaluated in photocatalytic hydrogen evolution using 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh+–NA) and dihydronicotinamide adenine dinucleotide (NADH) as a photocatalyst and an electron donor, respectively. The 3 wt % Ru/SiO2 catalyst freshly prepared by an impregnation method exhibited the highest catalytic reactivity among RuNPs supported on various metal oxides, which was nearly the same as that of commercially available Pt nanoparticles (PtNPs) with the same metal weight. However, the initial catalytic reactivity of 3 wt % Ru/SiO2 was lost after repetitive use, whereas the catalytic reactivity of PtNPs was maintained under the same experimental conditions. The recyclability of the 3 wt % Ru/SiO2 was significantly improved by employing the CVD method for preparation. The initial catalytic reactivity of 0.97 wt % Ru/SiO2 prepared by the CVD method was higher than that of 2 wt % Ru/SiO2 prepared by the impregnation method despite the smaller Ru content. The total amount of evolved hydrogen normalized by the weight of Ru in 0.97 wt % Ru/SiO2 was 1.7 mol gRu–1, which is now close to that normalized by the weight of Pt in PtNPs (2.0 mol gPt–1). Not only the preparation method but also the morphology of SiO2 supports affected significantly the catalytic activity of Ru/SiO2. The Ru/SiO2 catalyst using nanosized SiO2 with undefined shape exhibited higher catalytic activity than Ru/SiO2 catalysts using mesoporous SiO2 or spherical SiO2. The kinetic study and TEM observation of the Ru/SiO2 catalysts suggest that the microenvironment of RuNPs on SiO2 surfaces plays an important role to exhibit the high catalytic performance in the photocatalytic hydrogen production.

A practical organometallic decorated nano-size SiO2–Al2O3 mixed-oxides for methyl orange removal from aqueous solution

In this study, the application of a functional ferrocene (ferrocenecarboxaldehyde) firmly heterogenized over a modified nano-size SiO2–Al2O3 mixed-oxides was reported as a novel adsorbent for the removal of methyl orange from aqueous solution. SiO2–Al2O3 mixed-oxides was functionalized with 3-aminopropyl-triethoxysilane (3-APTES) group and ferrocenecarboxaldehyde covalently linked on this organo-functionalized SiO2–Al2O3 mixed-oxides support. The synthesized materials were characterized by FT-IR spectroscopy, UV–vis, CHN elemental analysis, BET, TGA, ICP-MS, TEM, and XPS. The contact time to obtain equilibrium for maximum adsorption was 50min. XPS of Fe ions evidenced that most of the active sites of the nano-adsorbent is in the form of Fe3+ ions at the surface. The heterogeneous Fe3+ ions were found to be effective adsorbent for the removal of dyes from solution. The adsorption of methyl orange ions has been studied in terms of pseudo-first-order and pseudo-second-order kinetics, and the Freundlich, Langmuir, and Langmuir–Freundlich isotherm models have also been applied to the equilibrium adsorption data. The adsorption process was spontaneous and endothermic in nature and followed pseudo-second-order kinetic model.

Creep in an electrodeposited nickel

This paper reports the experimental results on the creep behavior of electrodeposited ultrafine-grained nickel and its particle-reinforced nanocomposite. The objective of this research was to further improve the knowledge of the creep behavior of monolithic nickel and to explore the role of nano-sized SiO2 particles in the potential creep strengthening of electrodeposited Ni nanocomposite. The creep behavior and microstructure of the pure ultrafine-grained nickel and its nanocomposite reinforced by 2 vol% nano-sized SiO2 particles were studied at temperatures in the range from 293 to 573 K and at the applied tensile stresses between 100 and 800 MPa. The results indicate that the creep resistance of the nanocomposite may be noticeably improved compared to the monolithic nickel due to the interaction of the particles with dislocation motion. It was found that the applied stress interval can be divided into lower and higher stress intervals corresponding to dislocation (power-law) and exponential creep regions, respectively. Analysis of the creep data leads to the suggestion that the creep behavior of both electrodeposited nickel and its nanocomposite in power-law region may be grain boundary controlled. However, the mechanism responsible for the observed creep behavior at lower temperatures and the highest stresses is still not well established.

Morphological evolution of GaN nano-pyramids grown by using metal-organic chemical vapor deposition

High-density GaN nano-pyramids were grown on a nano-sized SiO2 pattern, and their morphological evolution was characterized. The effect of the growth temperature was studied with respect to pyramidal growth and was analyzed based on the growth rate anisotropy among crystal planes. At 750 °C, uniform nano-pyramids surrounded by \(\left( {1\bar 101} \right)\) facets were easily formed due to the large growth rate anisotropy of the planes while the pyramids showed smooth surfaces at 950°C. We observed that a low growth temperature was beneficial in suppressing the growths of giant pyramids formed by the coalescence of several smaller pyramids.

Fundamental characteristics study of anion-exchange PVDF–SiO2 membranes

A new type of poly(vinylidene fluoride)(PVDF)-SiO(2) hybrid anion-exchange membrane was prepared by blending method. The anion-exchange groups were introduced by the reaction of epoxy groups with trimethylamine (TMA). Contact angle between water and the membrane surface was measured to characterize the hydrophilicity change of the membrane surface. The effects of nano-sized SiO(2) particles in the membrane-forming materials on the membrane mechanical properties and conductivity were also investigated. The experimental results indicated that PVDF-SiO(2) anion-exchange membranes exhibited better water content, ion-exchange capacity, conductivity and mechanic properties, and so may find potential applications in alkaline membrane fuel cells and water treatment processes.

Study on the Synthesis of Polyester Type Waterborne Polyurethane and Modifying by Nano-Sized Particles

The waterborne polyurethane was prepared by reaction between polyester polyol and isophorone diisocyanat, different nanoparticles were filled into the system for modification. The effect of different ratio of materials, the kinds and mass of nanoparticles on the characters of waterborne polyurethane latex and film were investigated. The results showed that the stable polyurethane latex and polyurethane film with perfect characters could be prepared when the ratio of NNCO/NOH was 2.5~3.0, the DMPA with a mass fraction of 5%~6% was added into reaction as a macromolecule extender after adding small molecule chain extender BPO. Filling nanoparticles into the polyurethane latex could improve the water resistance and mechanical characters of the film. Nano-sized SiO2 was a better modifier than TiO2, and the appropriate mass fraction of SiO2 was 6% of polyurethane raw materials.

Polyethersulfone Composites Reinforced by Silica Nanoparticles

Three series of PES/SiO2 composites, containing 0.5-7 wt% nano-sized SiO2 with different specific surface area, were prepared by solution blending. The resulting composites exhibit the higher glass transition temperature (Tg) than that of pure PES. The Tg of composite showed a maximum increment of 24.0 °C by the addition of 7 wt% A300. The trade name of A300 is Aerosil 300. It is one of the fumed silica nanoparticles products of Degussa. The decomposition temperatures (Td) of composites were always higher than that of pure PES and showed a maximum increment of 37.0 °C by the addition of 3 wt% A300. The oxygen transmission rate of composites are always lower than that of pure PES and decreases with increasing SiO2 content to 1 wt% and then increases to 7 wt%. The composite with 1 wt% A300 exhibits a maximum decrement percentage of 46 %. The Tg, Td, and oxygen barrier property are as a function of the SiO2 content and size. The finer SiO2 are more effective in increasing the Tg, Td and oxygen barrier property.

Fumed silica concentration effect on structure and dielectric properties of a styrene-cross-linked unsaturated polyester resin

Concentration effects of a high-reactive-surface nanosized SiO2 filler on structure and dielectrical properties of a styrene-cross-linked polyester resin have been experimentally studied. Thermal desorption mass-spectroscopy, IR-spectroscopy, dielectric spectroscopy, and positron annihilation lifetime spectroscopy were used to determine an atomic content of thermal destruction products, IR-reflection spectra, complex dielectric permittivity, and a nature of positron traps as function of filler content in the polymer matrix. Interaction between active surface centers of SiO2-nanoparticles and atoms of polyester chains and styrene molecules gives the non-monotonous influence on the structure of polyester chains, macromolecule polarity, dielectric parameters and the number of positronium nanotraps.

Effects of the Multi-Layered Light Scattering Layers Dual-Coated by Al2O3 and SiO2 on Dye-Sensitized Solar Cells

Multi-layered light scattering layer has been designed to improve the energy conversion efficiency of dye-sensitized solar cells (DSSCs) by scattering of the incident light. To enhance the light scattering properties, the surface of light scattering TiO2 particle was dual-coated with nano-sized Al2O3 and SiO2 particles by using a modified sol-gel method. Four kinds of the TiO2 electrodes with different thicknesses were fabricated and their photovoltaic effects on DSSCs were investigated. By increasing the thickness of light scattering layer, the total reflectance of working electrodes increased to 37%, resulting in an increase in the energy conversion efficiency up to 6.76%.

Friction and Wear of Epoxy Composites Containing Silica Nanoparticles Grafted by Hyperbranched Aromatic Polyamide

Nano-sized SiO2 particles grafted with hyperbranched aromatic polyamide were employed as fillers for fabricating epoxy based composites. The hyperbranched aromatic polyamide was selected because its terminal amine groups could take part in the curing reaction of epoxy resin and covalently connect silica nanoparticles with the matrix. The experimental results proved the occurrence of this reaction, and indicated that the presence of the grafted SiO2 in epoxy does not change the overall curing mechanism of epoxy. In comparison to the composites filled with untreated nano-SiO2 particles, the composites with the grafted nano-SiO2 exhibited significantly improved sliding wear resistance and reduced frictional coefficient owing to the strong filler/matrix interfacial bonding. Moreover, hyperbranched aromatic polyamide grafted nano-SiO2 was more effective to enhance tribological properties of epoxy than linear polymers grafted versions.

Improved performance of dye-sensitized solar cells: An TiO2–nano-SiO2 hybrid photoanode with post-treatment of TiCl4 aqueous solution

A TiO2–nano-SiO2 hybrid film was prepared on a conductive F-doped tin oxide (FTO) substrate by depositing a mixture paste of TiO2 (P25) and nano-sized SiO2 particles. The hybrid film was further treated by a titanium tetrachloride (TiCl4) aqueous solution with different concentrations before it was assembled as a photoanode in dye sensitized solar cells (DSSCs). We studied the performance of DSSCs by using the dye molecule of cis-bis(isothiocy-anato)-bis-(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) bis-tetrabutylammonium (N719) as sensitizer. Results suggested that the post-treatment using TiCl4 could enhance the dye adsorption. The thin TiO2 layer hydrolyzed from TiCl4 could fill gaps between nanoparticles in the composite film, leading to a better electron transport than non-treated films, and improve the light harvesting efficiency. The optimal concentration was found to be 75mM for the post-treatment of TiO2–SiO2 hybrid film by TiCl4 solution. A photoelectron conversion efficiency of 6.39% was achieved in the back-side illuminated dye-sensitized solar cells, which is ∼105% higher than the basic efficiency of the bare TiO2 sensitized sample. TiO2–nano-SiO2 hybrid photoanode was prepared by incorporation of nano-sized SiO2 in the TiO2 film. The introduced SiO2 as a wide band-gap material gives a significant improvement of the performance of corresponding DSSCs in terms of photocurrent densities and energy conversion efficiency.

Significant influence of nano-SiO2 on the performance of dye-sensitized solar cells based on P25

The present paper describes a new type of composite photo-anode of SiO2/TiO2 that was prepared by adding nano-sized SiO2 into the TiO2 (P25) paste during the fabrication of dye-sensitized solar cells (DSSCs). The effects of the added SiO2 on the performance of DSSCs were investigated and the preparative procedures of DSSCs were optimized. It was found that certain amount of SiO2 added in the P25 powder was crucial to reduce the agglomeration and enhance the dispersion of P25 powders, which helps to achieve a better connection and thus higher electron transfer efficiency not only between the TiO2 particles but also between the TiO2 particles and the FTO substrate. Under the same standard air mass 1.5 illumination (100mWcm−2), the DSSCs constructed by SiO2/P25 composite photo-anodes show higher solar energy-to-electricity conversion efficiency (e.g., η=8.4%) compared to those by bare P25 electrodes (typically η=5.8%). The higher η mainly results from its higher short-circuit photocurrent density (Jsc=18.7mAcm−2) while the open-circuit voltage (Voc) remains unchanged and was found to be ∼780mV. The fill factor (FF) was 0.57. The great enhancement in Jsc of DSSCs is ascribed to the SiO2 energy barrier layer which increases the separation of injected electrons and oxidized dyes/redox couple as well as retards the recombination reactions in the resulting DSSCs.