Silica Nanoparticles In Matrix Research Articles

Effect of silica nanoparticles on the impregnation process, foaming dynamics and cell microstructure of styrene-methyl methacrylate copolymer/n-pentane foams

In the present study, two-step foaming procedure with a designed in-situ foaming observation apparatus was used to study the foaming dynamics of styrene-methyl methacrylate (St-MMA) copolymer/nanosilica composites. For this purpose, the St-MMA copolymer was synthesized using suspension copolymerization and its nanocomposites were prepared using solution method. The foaming dynamics was studied through temperature-induced (two-step batch foaming) method. Furthermore, the effects of content, size and surface chemistry of silica nanoparticles on the impregnation process, the foaming dynamics and the final morphology of prepared foams were investigated. The impregnation data showed that the presence of silica nanoparticles in matrix prolonged the impregnation and decreased diffusion coefficient. This effect would be clearer where nanoparticle contents are high and the temperature is quite above Tg. The foaming dynamics results illustrated that the nucleation and foaming rate were enhanced with the nanoparticle addition and its size reduction. At the St-MMA copolymer foaming system, the silica nanoparticles with hydrophilic surface chemistry are more efficient in comparison to hydrophobic nanoparticles where all foaming dynamics and the final microstructure parameters were improved.

Silica coating for enhanced Photoluminescence intensity in Zinc Sulfide nanoparticles

The study of discrete states in the energy band gap is greatly facilitated by the use of wide band gap II–VI semiconductors. ZnS is an efficient candidate for applications in photonic devices operating in the Visible to Near IR region. Silica coating enhances the quantum efficiency of the semiconductor nanoparticles without interfering their innate properties. Also, their optical transparency and mechanical strength are added advantages for usage in the device fabrication regime. In the present work, ZnS nanoparticles were synthesized by arrested precipitation using EDTA as capping agent. The as prepared ZnS nanoparticles were incorporated into silica matrix by sol-gel method in an aqueous base. Characterization studies of the coated and uncoated ZnS nanoparticles were conducted. X-Ray diffraction pattern of the ZnS nanoparticles was recorded and compared with the standard PDF values and it was found that the nanoparticles of present study were in the cubic phase. The grain size of the particles calculated using Debye-Scherrer equation was found to be approximately 3 nm. Structural and morphological studies of the silica coated ZnS were done by XRD and HRTEM. FTIR Spectrum confirmed the entrapment of ZnS nanoparticles in silica matrix. Optical characterization was done by UV Visible Absorption Spectroscopy and Photoluminescence studies at an excitation wavelength of 270 nm. The silica entrapment brought significant increase in the PL intensity compared to the uncoated ZnS.

MWCNTs and carbon onions grown by CVD method on nickel-cobalt alloy nanocomposites prepared via novel alcogel electrolysis technique and its oxygen evolution reaction application

Novel nanocatalyst designs to synthesize carbon based electrocatalyst are highly desirable for the production of sustainable energy technologies like hydrogen through electrochemical water splitting. Herein, we report alcogel electrolysis technique to prepare nickel cobalt alloy nanoparticles in silica matrix and then growth of carbon nanostructured material by chemical vapour deposition (CVD) method for its application towards electrochemical catalysis of oxygen evolution reaction. The growth conditions of carbon nanostructures specially multiwalled carbon nanotubes (MWCNTs) and carbon onions are tuned by controlling the temperature of CVD. It is found that MWCNTs at temperature of 650 °C are preferentially formed while carbon onions are formed predominantly at 750 °C. The onion like carbon formed on Ni-Co alloy nanostructures at temperature of 750 °C is attributed to over growth of NiCo alloy nanoparticles achievable at higher temperatures. The diameter of MWCNTs were found to be in the range of 5–25 nm while carbon onions in the range 50–100 nm as revealed by TEM studies after etching silica particles by HF. The oxygen evolution reaction activity of the sample synthesized at 750 °C was found to be inferior than exhibited by MWCNTs formed at 650 °C which was possibly due to the presence of bigger size carbon onions having a less surface area. The overpotential exhibited by NiCo-MWCNTs is 340 mV which is just 35 mV higher than bench mark Ir/C catalyst. The better OER performance exhibited by NiCo-MWCNTs is devoted to encapsulated nickel-cobalt alloy particles by well graphitized carbon layers, defective side walls of nanotubes and oxygenated functional groups (C=O, C–O) which are proven active sites for OER.

Determination of growth kinetics and size dependent structural, morphological, optical characteristics of sol-gel derived silica nanoparticles in silica matrix

Abstract Nanocomposite silica thin films made using the sol-gel method were studied. The nano-silica films were prepared using a mixture of tetraethyl orthosilicate (TEOS), deionized water, ethanol, and ammonia solution. To control the growth of the particles inside the film, the nanocomposite silica film was prepared using a mixture of the nano-silica sol and the silica sol. The change in the particle size with the heat treatment temperature ranging from 450 °C to 1100 °C was investigated. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), NKD (refractive index-N, extinction coefficient-K, and thickness-D) and ultraviolet-visible (UV-Vis) spectrophotometry were used for characterization purposes. The XRD studies showed that the nano-silica thin films were amorphous at all annealing temperatures except for 1100 °C. The_-cristobalite crystal structure formed at the annealing temperature of 1100 °C. Optical parameters, such as refractive indices and extinction coefficients, were obtained using the NKD analyzer with respect to the annealing temperature of the films. The activation energy and enthalpy of the nanocomposite silica film were evaluated as 22.3 kJ/mol and 14.7 kJ/mol, respectively. The cut-off wavelength values were calculated by means of extrapolation of the absorbance spectra estimated using the UV-Vis spectroscopy measurements. A red shift in the absorption threshold of the nanocomposite silica films indicated that the size of the silica nanoparticles increased with an increase of the annealing temperatures from 450 °C to 900 °C, and this confirms the quantum confinement effect in the nanoparticles.

Post-synthesis annealing of coprecipitated CoFe2O4 nanoparticles in silica matrix

Cobalt ferrite nanoparticles (d ∼ 11 nm, σd = 0.5) produced by coprecipitation at room temperature are heat treated up to 1000 °C after a preliminary dispersion in a sol-gel silica matrix to avoid aggregation and coarsening. This protected annealing allows for a significant increase of the crystallinity of the particles, as demonstrated by combined x-ray diffraction and transmission electron microscopy experiments. A large increase in the coercive field value is reported, from 1.0 to 1.6 Tesla after annealing at 600 °C. This enhanced coercivity can be explained by the cumulative effect of an increased magnetic anisotropy and of a decreased saturation magnetization (Ms). Mössbauer spectroscopy experiments show that these evolutions of the Ms and anisotropy constant (K) values originate from a small increase in canting angles and in inversion degree, i.e. a displacement of Co2+ ions from tetrahedral to octahedral sites of the spinel lattice. This study emphasizes the little impact of an improved crystallinity on saturation magnetization and canting angle values in coprecipitated CoFe2O4 nanoparticles and highlights that the main source of magnetic disorder is associated with the distribution of Co and Fe within the cationic sites.

Chemical synthesis of low-coercivity, silica/Co composites for high-frequency magnetic components

The paper reports correlation between processing, structural and magnetic properties of cobalt nanoparticles dispersed in an insulating oxide matrix. High-temperature, chemical decomposition approach was utilized to achieve highly-dispersed, ultra-fine cobalt nanoparticles in silica matrix. Synthesis parameters such as precursor to passivating agent ratio were designed to control the metal-to-oxide ratio so as to promote magnetic interactions between the metal particles while keeping the cobalt particle size in sub-nanometer. High-resolution TEM and XRD studies were carried out to demonstrate face-centered phase of single-crystal cobalt particles of size ∼8–10 nm monodispersed in thin silica matrix. The particle size variation as a function of precursor to passivating agent ratio was also studied to yield process conditions for ultra-fine nanoparticles. Composites with sub-10 nm metal particles showed superior soft magnetic properties with a lowest coercivity of 10 Oe. The reduction in coercivity with such fine particles is attributed to the transition to superparamagnetic regime. Larger particles showed higher saturation magnetization and higher coercivity of 100 Oe. The coercivity decreased with further increase in particle size from ∼50 nm to 80 nm because of the transition from single domain to multi-domain structures.

Preparation, characterization and electrochemical behaviors of Bi2O3 nanoparticles dispersed in silica matrix

Nanostructured bismuth oxide was prepared in silica media by a modified sol-gel method using of tetraethylorthosilicate and hydrated bismuth nitrate. The calcination temperature was determined by thermal gravimetric analysis. The morphology, crystal and electronic structure of composites were characterized by powder X-ray diffraction, XRD, scaning electron microscopy, SEM, transmission electron microscopy,TEM, UV-vis diffuse reflectance spectroscopy and Mott-Schottky analysis. Cyclic voltammetry and galvanostatic charge and discharge curves were used to study the electrochemical and capacitive behaviors of dispersed Bi2O3 nanoparticles in silica matrix in 1.0M NaOH. Our studies showed that by decreasing in the amount of Bi2O3 in nanocompsite, the normalized capacitance of bismuth oxide increases.

Optimization of mechanical properties of epoxy-based hybrid nanocomposite: Effect of using nano silica and high-impact polystyrene by mixture design approach

Epoxy resins have tight three-dimensional molecular network structures; because of this reason, these materials are brittle in nature and have pore resistance in front of crack propagation. In the present study, to overcome this issue, the optimized mixture proportions of epoxy-based hybrid nanocomposite with different composition of nano silica as nano reinforcement, high-impact polystyrene as thermoplastic phase and hardener were determined by applying the simplex-centroid mixture design method to achieve the ultimate tensile, flexural, compression and impact strength. Results revealed that the best mixture occurs in 2.67wt.% of HIPS, 4.01wt.% of nano SiO2 and 28phr of hardener. Experimental results indicate that new ternary nanocomposite improved ultimate tensile, compression and impact strength up to 59.5%, 45% and 414% compared to those of the neat epoxy resin respectively, although they did not show enhanced flexural strength. The tensile and flexural elongations at break were improved up to 71% and 83% larger than those of neat epoxy, respectively, but compression strain did not change considerably. Correlation between the morphology of the nanocomposite and its mechanical properties was noted when using the SEM technique. EDX analysis used to indicate homogeneous combination of Silica nano particles in matrix and show solvent evaporated completely under vacuum situation.

Multifunctional iron and iron oxide nanoparticles in silica

Iron and iron oxide nanoparticles in silica layers deposited by sol–gel techniques on Si wafers were formed and studied. It was shown that multifunctional nanoparticles of different iron oxides possessing various physical properties can be fabricated by means of post-growth annealing of (SiO 2:Fe)/SiO 2/Si samples in various atmospheres. The hematite, maghemite, and iron nanoparticles were found to be dominant upon annealing the samples in air, argon, and hydrogen atmosphere, respectively. The physical properties of produced hybrid structures were studied by Raman and FT-IR spectroscopy, spectroscopic ellipsometry, AFM, and magnetic measurements. The sol–gel technique with subsequent annealing procedure is demonstrated to be an effective method for the formation of multifunctional hybrid structures composed of iron or iron oxide nanoparticles in silica matrix.

Characterization of transverse tensile, interlaminar shear and interlaminate fracture in CF/EP laminates with 10 wt% and 20 wt% silica nanoparticles in matrix resins

The transverse tensile properties, interlaminar shear strength (ILSS) and mode I and mode II interlaminar fracture toughness of carbon fibre/epoxy (CF/EP) laminates with 10 wt% and 20 wt% silica nanoparticles in matrix were investigated, and the influences of silica nanoparticle on those properties of CF/EP laminates were characterized. The transverse tensile properties and mode I interlaminar fracture toughness ( G IC) increased with an increase in nanosilica concentration in the matrix resins. However, ILSS and the mode II interlaminar fracture toughness ( G IIC) decreased with increasing nanosilica concentration, especially for the higher nanosilica concentration (20 wt%). The reduced G IIC value is attributed to two main competing mechanisms; one is the formation of zipper-like pattern associated with matrix microcracks aligned 45° ahead of the crack tip, while the other is the shear failure of matrix. The ratio of G IIC/ G IC decreased with the concentration of silica nanoparticles, comparable with similar CF/EP laminates with dispersed CNTs in matrix. Fractographic studies showed that interfacial failure between carbon fibre and epoxy resin occurred in the neat epoxy laminate, whereas a combination of interfacial failure and matrix failure occurred in the nanosilica-modified epoxy laminates, especially those with a higher nanosilica concentration (20 wt%).

Growth and characterization of Fe3O4 nanoparticles in silica matrix

Nano-magnetic Fe3O4 particles coated with silica are synthesized. The study of structural and magnetic properties was carried out using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometer (VSM) techniques. The VSM results show that these kinds of composite particles exhibit superparamagnetic behavior with zero coercivity and remanence. The magnetic spheroid alumina carriers containing these magnetic composite particles were prepared by an internal gelation process. The SiO2 coatings prevent the reaction between Fe3O4 and Al2O3 during the sintering process and maintain the superparamagnetic behavior of the catalyst carriers.

Improved Energy Transfer between Ce3+and Tb3+Ions at the Interface between Y2Sn2O7:Ce3+,Tb3+Nanoparticles and Silica

Very small spherical nanoparticles (size in the range of 2−5 nm) of Y2Sn2O7 doped with both Ce3+ and Tb3+ were prepared by the urea hydrolysis of Y3+, Sn4+, Ce3+, and Tb3+ in ethylene glycol medium at 150 °C followed by heating at 700 °C. These nanoparticles exhibit very poor energy transfer between Ce3+ and Tb3+ ions and associated luminescence due to the combined effect of centrosymmetric D3d environment around the lanthanide ions and quenching of the lanthanide ion excited state due to the vibrations of surface hydroxyl groups present on the nanoparticles. However, the energy transfer and associated luminescence can be significantly improved after dispersing the nanoparticles in silica matrix. On the basis of the detailed steady-state and time-resolved luminescence studies, it has been established that a significant amount of Ce3+ and Tb3+ ions migrate from Y2Sn2O7 host to both the silica matrix and the interface region between silica and Y2Sn2O7 nanoparticles. Improved energy transfer from Ce3+ to Tb3...

Formation of Au−Ag Core−Shell Nanostructures in Silica Matrix by Sequential Ion Implantation

Formation of Au core-Ag shell bimetallic nanoparticles in silica matrix is demonstrated through sequential implantation of Ag and Au ions and subsequent thermal annealing. Formation of core-shell structures is verified through optical absorption spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, and simulated optical extinction spectra. A mechanism for the formation of such unusual structures in ion-implanted silica is proposed. By controlling the implantation energy of the two ions properly and keeping the implantation sequence Ag first and then Au, it is possible to create Au core-Ag shell nanoparticles in the silica matrix with homogeneous distribution.

A comparative studyof heat‐treated Ag:SiO2 nanocomposites synthesized by cosputtering and sol‐gel methods

AbstractIn this work, we compared formation and properties of heat‐treated Ag nanoparticles in silica matrix synthesized by RF‐reactive magnetron cosputtering and sol–gel methods separately. The sol–gel and sputtered films were annealed at different temperatures in air and in a reduced environment, respectively. The optical UV‐visible spectrophotometry have shown that the absorption peak appears at 456 and 400 nm wavelength indicating formation of silver nanoparticles in SiO2 matrix for both the sol–gel and sputtering methods at 100 and 800 °C, respectively. XPS measurements showed that the metallic Ag0 nanoparticles can be obtained from both the techniques at these temperatures. According to XPS and AFM analysis, by increasing annealing temperature, the concentration of the Ag nanoparticles on the surface decreased and the nanoparticles diffused into the substrate for the sol–gel films, while for the films deposited by cosputtering method, the Ag surface concentration increased by increasing the temperature. Based on AFM observations, the size of nanoparticles on the surface were obtained at about 25 and 55 nm for sputtered and sol–gel films, respectively, supporting our optical data analysis. In comparison, the sputtering technique can produce Ag metallic nanoparticles with a narrower particle size distribution relative to the sol–gel method. Copyright © 2008 John Wiley & Sons, Ltd.

Influence of embedded particles on microstructure, corrosion resistance and thermal conductivity of CuO/SiO 2 and NiO/SiO 2 nanocomposite coatings

Homogeneous CuO/SiO 2 and NiO/SiO 2 nanocomposite coatings containing CuO and NiO nanoparticles in silica matrix were successfully synthesized by sol–gel process on an aluminum alloy substrate, respectively. The evolution of phase and morphology of both nanocomposites was characterized by XRD, SEM, TEM and FTIR. The effect of incorporating various nanoparticles on the corrosion behavior and the thermal conductivity of nanocomposite coatings was investigated by potentiodynamic polarization curve and comparative exponential method. The thermal conductivity as well as the corrosion resistance of nanocomposite coatings was significantly improved by the introduction of metal oxide particles. In comparison with NiO/SiO 2 nanocomposite coatings, CuO/SiO 2 composite coatings displayed lower protective behavior as well as higher thermal conductivity. Experimental results revealed that those improvements can directly be related to the nanocomposite effect and the nature of added nanoparticles.

Synthesis of elongated Au nanoparticles in silica matrix by ion irradiation

The present work reports the synthesis of elongated Au nanoparticles (NPs) parallel to each other, embedded in silica matrix. Au NPs in silica, prepared using rf magnetron sputtering, were irradiated by 120MeV Au ions at different fluences to induce elongation. Optical absorption study of irradiated film showed a clear splitting of surface plasmon bands corresponding to transverse and longitudinal modes. Transmission electron microscopy investigations of pristine and irradiated samples revealed an elongation (aspect ratio of ∼3.5) in Au NPs occurred as a result of irradiation. The results are discussed in the framework of thermal spike model.

SnO 2:Eu nanoparticles dispersed in silica: A low-temperature synthesis and photoluminescence study

SnO 2:Eu and SnO 2:Eu nanoparticles dispersed in silica matrix were prepared at a relatively low temperature of 185 °C in ethylene glycol medium. For as-prepared SnO 2:Eu nanoparticles there exists a weak energy transfer from the SnO 2 host to the Eu 3+ ions. However, the energy transfer can be significantly improved by dispersing the Eu 3+-doped SnO 2 nanoparticles in silica matrix. Effective shielding of surface Eu 3+ ions in SnO 2:Eu nanoparticles from the stabilizing ligand by silica matrix is the reason for the improved extent of energy transfer. Increase in asymmetric ratio of luminescence (ratio of the intensity of the electric dipole allowed transition, 5D 0→ 7F 2, to magnetic dipole allowed transition, 5D 0→ 7F 1) for SnO 2:Eu nanoparticles dispersed in silica compared to that of SnO 2:Eu nanoparticles, has been attributed to the distorted environment around surface Eu 3+ ions brought about by the presence of both tin and silicon structural units. 119Sn and 29Si MAS NMR studies on this sample confirmed that there is no interaction between the tin and silicon structural units even after heating the samples at 900 °C.

Swift heavy ion-induced dissolution of gold nanoparticles in silica matrix

Gold nanoparticles embedded in silica matrix were prepared by co-evaporation. After deposition, the samples were annealed at different temperatures in inert environment for 30 min. No signature of nanoparticle formation was found in case of as-deposited samples, while the annealed samples showed a clear signature of a surface plasmon resonance absorption peak around 520 nm, which indicated the formation of Au nanoparticles. The samples annealed at 900 °C were irradiated with 100 MeV Ag ions at fluences 2.5×1012 and 1×1013 ions/cm2. UV-visible absorption measurements of pristine and irradiated films showed a clear signature of dissolution of Au nanoparticles with ion beam fluence. X-ray diffraction studies of pristine and irradiated samples also supported the dissolution of Au nanoparticles with ion beam fluence. Rutherford backscattering spectrometry was used for quantification of gold.

Synthesis and characterization of Ag nanoparticles in silica matrix by atom beam sputtering

Silver nanoparticles (Ag NPs) embedded in silica were prepared by a novel process of atom beam sputtering (ABS). Optical and structural properties of Ag NPs were studied by using ultraviolet–visible absorption, transmission electron microscopy and X-ray diffraction. The processes involving nucleation and growth of Ag NPs are discussed. The superiority of the ABS over ion implantation and ion beam mixing is discussed. These Ag NPs are found to be glucose sensitive, indicating their possible application in medical diagnostics.

The effect of surface modification on the morphology and magnetic properties of NiFe 2O 4 nanoparticles

Three NiFe 2O 4/SiO 2 nanocomposites have been obtained by dropping different silica source into ferrite sol in this study. X-ray fluorescence spectroscopy and X-ray diffractometer are, respectively, used to detect the content of nickel ferrite and crystalline phase in the formed nanocomposites. Transmission electron microscopy characterization shows a more-ordered array of NiFe 2O 4 nanoparticles in silica matrix after the particles are modified by a coupling agent, APS, before TEOS and sodium silicate. Magnetic measurements indicate that the lower dipole–dipole interactions between NiFe 2O 4 nanoparticles have been obtained after surface modification.