A cellular level biocompatibility and biosafety evaluation of mesoporous SiO<Subscript>2</Subscript>-based nanocomposite with lanthanum species

The risk assessment of SiO₂ nanoparticles has attracted extensive attention due to their great potential for various commercial purposes. However, the toxicity of mesoporous SiO₂-based nanocomposite is still unclear. Herein SiO₂-based hexagonal mesoporous nanosphere doping La³⁺ ions with diameter of 40–50 nm (SLa-HMS) and micronsized SiO₂-based hexagonal mesoporous solid inlaid with nanowires, 80–250 nm in length and 4–5 nm in diameter, of La species (WLa-HMS) were synthesized via self-assembly method. The specimens were characterized by small angle XRD, TEM, EDS, FT-IR, and N₂ ad–desorption. HeLa, fibroblast, and HBMSC cells were exposed to 0.1–100 μg/mL of SLa-HMS and WLa-HMS colloids for 12, 24, 48, and 72 h. Our data demonstrated that exposure of SLa-HMS in the dose range tested had no hazardous effect on all three cell lines, which was greatly different from previous reports. However, the WLa-HMS with average particle size of 10–19 μm was proven to be very toxic to the growth of all three cell lines. These interesting findings strongly suggest that doping heteroatom could be a way to improve the cytotoxicity of nanomaterials, as well as to oncotherapy on the basis of the hazardous effect of nanomaterials.     

Prepolymerized organic–inorganic hybrid nanoparticles as fillers for light-cured methacrylate monomers

Poly(hydroxyethyl methacrylate)/silica (PHEMA/SiO₂) hybrid organic–inorganic nanocomposites were prepared through the simultaneous polymerization of 2-hydroxyethyl methacrylate and tetraethoxysilane. PHEMA/SiO₂ materials were obtained as monolithic and transparent films consisting of silica nanoparticles (diameter below 100 nm) surrounded by the PHEMA matrix. The films were crushed into fine powder and the PHEMA/SiO₂ particles were used as filler of methacrylate monomers. The polymeric methacrylate present in the PHEMA/SiO₂ hybrid particles improves the compatibility of the filler with the methacrylate monomer to be photopolymerized, resulting in enhanced wetting capabilities. The composites prepared from PHEMA/SiO₂-prepolymerized particles offer the possibility of reduced polymerization shrinkage without severe reductions in flow characteristics of the precured polymers. The monomer conversions of composites prepared with either 30 or 60 wt% PHEMA/SiO₂ particles were similar. This indicates that the penetration of visible radiation into the sample is not reduced significantly by the presence of the filler.     

Polyacrylamide and poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid)-silica composite nanogels through in situ microemulsion polymerisation

Nanosize monodisperse composite particles of polyacrylamide (PAM) and poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid)-silica [Poly(AM-co-AMPSA)-SiO₂] were prepared by water-in-oil in situ microemulsion polymerisation without surface treatment of silica. The synthesised composite particles were produced with controllable sizes ranging from 44 to 77 nm in diameter. Presence of silica filler in the nanoreactors facilitates the formation of well-defined discrete particles. The prepared nanocomposites were characterised by dynamic light scattering, transmission electron microscope, Fourier transform infrared spectrophotometer, thermogravimetric analyzer, differential scanning calorimeter, scanning electron microscope and X-ray diffraction. The spectroscopic result shows strong interactions of silica nanoparticles with sulphonic groups of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA). The onset degradation temperature is increased from 227 to 262 °C in copolymer–silica composite as compared to polyacrylamide–silica (PAM–SiO₂) which indicates improved thermal stability. The shifting of glass transition temperature from 194 to 203 °C in copolymeric composite nanogels further confirms the existence of strong interactions of silica filler with poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid) [Poly(AM-co-AMPSA)] chains. Also the chemical composition of polymeric chains and the affinity of polymer chains and silica influenced the morphology of nanogels.     

Fabrication of superparamagnetic hydroxyapatite with highly ordered three-dimensional pores

Hydroxyapatite (HA) with highly ordered three-dimensional pores, whose size is about 300 nm, was prepared by colloidal template method. The effect of the surface modification of silica spheres on the order degree of porous structure was investigated by field emission scanning electron microscopy (FESEM). Then, superparamagnetic Fe₃O₄ nanoparticles were fabricated via redox reaction, followed by coating with silica via a sol–gel process, in which a certain amount of TEOS was used in order to control the thickness of the silica shell. X-ray diffraction (XRD), transmission electron microscopy (TEM), and magnetometry were applied to characterize the properties. Finally, Fe₃O₄ magnetic nanoparticles coated with silica were adsorbed in the mesopores of HA with highly ordered three-dimensional pores by capillarity. The influence of dispersing agent on the adsorption results has been studied. Magnetometry was applied to characterize the magnetic properties of superparamagnetic HA. The quantities of adsorbed SiO₂/Fe₃O₄ nanoparticles with core–shell have been compared by variation of saturation magnetization before and after adsorption.     

Ultra-long SiO<Subscript>2</Subscript> and SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> tubes embedded with Pt nanoparticles using magnus green salt as templating structures

For the first time, magnus green salt (MGS, [Pt(NH₃)₄][PtCl₄]) fibers precipitated by solvent modification have been employed as a structure-directing modifier to synthesize single silica and silica/titania microtubes via a sol–gel process. In the case of titania tubes, tetraethylorthosilicate must be used as a capping agent to hinder the aggregation of primary MGS fibers and to serve as a protective layer against thermal stress during the metal salt fiber reduction. This implies that SiO₂/TiO₂ tubes result. The synthesized tubular materials were imaged by scanning and transmission electron microscopy, while their composition was determined by energy dispersive X-ray analysis and thermogravimetric analysis. Crystallinity and thermal stability of the tube walls were studied using X-ray diffraction analysis. The obtained oxide tubes possess high aspect ratios (80–200) because they are up to 60 μm in length, but only 300–700 nm in thickness. The key aspects of the synthesis approach are that the templating MGS fibers control the internal diameter of the oxide tubes, while the synthesis conditions control their wall thickness. The suggested method is a simple approach which produces, at low temperatures, very long oxide tubes with a very high amount of Pt (48–51 wt%) directly incorporated inside the tubes. To the best of our knowledge, filling of SiO₂ or SiO₂/TiO₂ nanotubes with such a dense population of Pt metal nanoparticles has not been demonstrated so far; our own experiments with [Pt(NH₃)₄](HCO₃)₂ as templating salt formed only tubes containing about 40 wt% Pt and were only about 20 μm long. The now formed more Pt-rich tubes are expected to have vivid applications in (photo)catalysis and in fabricating novel devices, such as nano- or sub-microcables.     

Luminescence properties of Eu3+ or Dy3+/Au co-doped SiO2 nanoparticles

Silica nanoparticles, prepared by the Stober method, have been doped with Eu³⁺, Dy³⁺, or processed to result in Au nanoparticles on the silica surface. The luminescence of the rare earth (RE)-doped SiO₂ particles has been studied as a function of the nature of the RE, their concentration and also of the presence of Au nanoparticles at the surface of the SiO₂ nanoparticles. We have shown that the Eu³⁺ emission is observable over the experimental conditions examined, whereas it was not possible to observe any emission for Dy³⁺ doped materials. No enhancement of the Eu³⁺ emission was observed following the adsorption of gold nanoparticles at the surface of the SiO₂ nanoparticle, however an excitation at 250 nm leads to both the emission of the matrix and Eu³⁺ showing an energy transfer from the SiO₂ matrix to Eu³⁺ ions.     

Synthesis of silver-integrated silica nanostructures using rice hulls and their electrochemical performance for supercapacitor application

We report the synthesis of silver-integrated silica nanostructures using rice hulls and silver chloride through a facile thermal combustion process. The formation of mesoporous silica nanomatrix embedded with silver nanoparticles (SiO₂:Ag 5 wt% and SiO₂:Ag 10 wt%) was confirmed by XRD, FTIR, EDX, BET, and TEM analysis. Also, the obtained results from the above studies revealed that the concentration of silver ions significantly increases the particle size and number of silver nanoparticles formed in the silica matrix. The electrochemical performance was studied using silver-integrated silica nanostructures as a working electrode in KOH electrolyte. The maximum specific capacitance of SiO₂:Ag 5 wt%- and SiO₂:Ag 10 wt%-coated electrode was found to be 517 and 580 F/g at current density of 1 A/g. It was also found that SiO₂:Ag 10 wt% electrode exhibit an excellent stability with the capacitance retention of 94% than SiO₂:Ag 5 wt% (capacitance retention of 85%) after 1000 cycles at a current density of 1 A/g. These results may be attributed to the inherent characteristic of more silver nanoparticles present in the silica nanomatrix in SiO₂:Ag 10 wt%. The intrinsic characteristic of rice hull-derived silica nanostructures such as high surface area and mesoporous structure along with the advantage of silver nanoparticles (conductivity) can facilitate the Faradic redox processes at electrode surface which are responsible for the supercapacitive behavior of the prepared silver-integrated silica nanostructures.

     

Characterization of silica-coated Ag nanoparticles synthesized using a water-soluble nanoparticle micelle

This article describes the synthesis of silica-coated Ag nanoparticles using a water-soluble nanoparticle micelle under basic conditions. Monodispersed Ag nanoparticles with a mean particle size of 7 nm were synthesized using AgNO₃ in the presence of ascorbic acid as a reducing agent. The Ag nanoparticles were easily re-dispersed into an aqueous solution by surface adsorption of surfactant molecules, indicating formation of water-soluble nanoparticle micelles. Silica-coated Ag nanoparticles ranging in size from 50 to 100 nm were obtained by controlling the surfactant, Ag nanoparticle and tetraethylortho silicate (TEOS) concentrations. Adsorbed surfactant monolayers on Ag nanoparticles were used as a template for the silica shell because of the hydrophobicity of TEOS. In all cases, the size of the resulting particles increased linearly as these concentrations increased. Based on transmission electron microscopy, all the Ag nanoparticles were completely covered with a silica shell. In most samples, however, Ag nanoparticle size increased from 7 to 50 nm due to evaporation of hexane by heating. Although mean particle size of silica-coated Ag nanoparticles was drastically altered, characteristic absorption peaks were observed at approximately 410 nm.     

Hydrophobic properties and color effects of hybrid silica spin-coatings on cellulose matrix

A novel sol–gel derived organic–inorganic hybrid silica sol consisting of organic direct red dye 4BS and inorganic silica (SiO₂) is successfully synthesized by adding coupling agent γ-chloropropyltriethoxysilane (CPTS). Hybrid silica coatings are deposited on cellulose matrix surface via spin-coating approach to introduce effective hydrophobic and color properties. Compared to the dye hybrid silica sol (DHSS), the particle size of CPTS/dye hybrid silica sol (CDHSS) increases from 64.51 to 129.70 nm, while the surface tension reduces from 34.27 × 10⁻³ N m⁻¹ to 31.22 × 10⁻³ N m⁻¹. The hydrostatic pressure of the cellulose matrix coating with CDHSS is 4530.5 Pa, the contact angle is 131.48°, and the wetting time is ~150 min, which attributes to the alkyl chloride aliphatic chain and sharp micro-surface roughness of the hybrid coatings validated directly by AFM and SEM images. The K/S value (5.15) of the cellulose matrix coated with CPTS/dye hybrid silica (CMCCDHS) is 12.44% higher than that of the cellulose matrix coated with dye hybrid silica (CMCDHS), and increased by 30.38% relative to the control coated sample. The maximum absorption wavelengths of the matrixes treated with different processes are the same as the maximum absorption wavelength of the silica sols (510 nm).     

Synthesis and optical limiting studies of HA<Subscript>P</Subscript> and HA<Subscript>P</Subscript>@SiO<Subscript>2</Subscript> core–shell nanoparticles

We report the spectral and optical limiting properties of two kinds of HA_P nanoparticles (pure HA_P and HA_P@SiO₂ core–shell nanoparticles) that were wet-chemically prepared and coated with silica by means of Stober method. The size, framework substitution and silica coating formation of the resultant particles were confirmed by Transmission Electron Microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy and Thermogravimetric analysis. The nonlinear optical limiting properties of HA_P and HA_P@SiO₂ nanoparticles suspended in ethylene glycol is studied at 532 nm using 5 ns Nd:YAG laser pulses. Observations indicate that effective three-photon absorption is found to be responsible for strong optical limiting characteristics in these nanoparticles and it is seen that the optical nonlinearity is enhanced in core–shell structures as compared with single counterparts. The nonlinear optical parameters calculated from the data show that these materials are efficient optical limiters.     

Study of preparation and magnetic properties of silica-coated cobalt ferrite nanocomposites

The structure and the magnetic properties of silica-coated cobalt ferrite nanoparticles (80 wt% CoFe₂O₄), prepared by sol–gel method and submitted to thermal treatments in the range 800–1,000 °C, were investigated through XRD, FT-IR, TEM and VSM. The effects of thermal treatment temperatures on the structure and magnetic properties of nanoparticles were examined. A silica shell thickness of about 5 nm was synthesized on top of cobalt ferrite nanoparticles. The non-crystalline silica confines the growth of cobalt ferrite nanoparticles, i.e., the particle sizes are almost independent of the thermal treatment. Saturation magnetization (Ms) was decreased slightly and coercivity (Hc) was increased, when the non-crystalline silica was coated on the surface of cobalt ferrite nanoparticles.     

Synthesis and characterization of TiO<Subscript>2</Subscript>-incorporated silica foams

Titania-incorporated silica (TiO₂–SiO₂) porous materials have great applications in diverse areas. In this work, TiO₂–SiO₂ porous materials with tunable Si/Ti molar ratio (R) have been successfully prepared through a one-pot method under a near-neutral condition. With decreasing Si/Ti R, a phase transition from a macroporous foam-like structure to mesostructure is observed. The resultant TiO₂–SiO₂ porous materials possess large surface areas and high pore volumes. In addition, the titania species are homogenously dispersed in silica matrix when Si/Ti R ≥ 10. Our contribution provides a convenient method to synthesize TiO₂/SiO₂ porous materials with very large pore size, high pore volume, and relatively high titania content well dispersed in the silica wall framework.     

Cathodoluminescence properties of SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript>and ZnO·SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript> phosphor nanopowders

The successful incorporation of ZnO nanoparticles in Pr³⁺-doped SiO₂ using a sol–gel process is reported. SiO₂:Pr³⁺ gels, with or without ZnO nanoparticles, were dried at room temperature and annealed at 600 °C. On the basis of the X-ray Diffraction (XRD) results, the SiO₂ was amorphous regardless of the incorporation of Pr³⁺ and nanocrystalline ZnO or annealing at 600 °C. The particles were mostly spherical and agglomerated as confirmed by Field Emission Scanning Electron Microscopy. Thermogravimetric analysis of dried gels performed in an N₂ atmosphere indicated that stable phases were formed at ≥900 °C. Absorption bands ascribed to ³H₄-³P_{(J = 0,1,2)}, ¹I₆ and ¹D₂ in the UV–VIS region were observed from SiO₂:Pr³⁺ colloids. The red cathodoluminescent (CL) emission corresponding to the ³P₀ → ³H₆ transition of Pr³⁺ was observed at 614 nm from dried and annealed SiO₂:Pr³⁺ powder samples. This emission was increased considerably when ZnO nanoparticles were incorporated. The CL intensity was measured at an accelerating voltage of 1-5 keV and a fixed beam current of 8.5 μA. The effects of accelerating voltage on the CL intensity and the CL degradation of SiO₂:Pr³⁺ and ZnO·SiO₂:Pr³⁺ were also investigated using Auger electron spectroscopy coupled with an Ocean Optics S2000 spectrometer.     

Preparation of monodisperse ZnO/SiO2 composite particles using spray drying with an anionic surfactant template and their photoluminescence characteristics

The photoluminescence (PL) characteristics of ZnO/SiO₂ composite particles were investigated. ZnO/SiO₂ composite particles were synthesized utilizing the consecutive sol–gel spray drying method by incorporating sodium lauryl sulfate (SLS) as a particle morphology control agent. The effect of SLS concentration and ZnO ratio on precursors was studied further on the composite particle morphology and PL performance. Elevating the SLS concentration exhibited a reduction in the particle diameter and an increase in particle uniformity. The particle diameter without SLS was 6.18 µm and reduced to 2.6 µm with the addition of SLS at 3 critical micelle concentrations (CMC). The decrease in ZnO concentration also reduced the particle diameter of the ZnO/SiO₂ composite to 1.74 µm at a ZnO concentration of 25% mol. In addition, the increase in the excitation wavelength from 230 nm to 320 nm indicates a shift in the peak emission intensity at higher wavelengths from 467 nm to 645 nm. The excitation wavelength-dependent photoluminescence phenomenon was exhibited by incorporating silica into the ZnO precursor pre- and post-drying to deliver composite particles. The addition of silica to the composite particles can augment the PL emission intensity without causing a shift in the PL emission peaks when excited at the same wavelength. The 25% mol ZnO composite particles with the addition of SLS 3 CMC had the highest PL emission intensity. The amount of silica nanoparticles sufficient to trap the ZnO nanoparticles in the droplet is an important factor besides the size and uniformity of the particles, which causes the high intensity of PL emission.     

Structural verification and optical characterization of SiO2–Au–Cu2O nanoparticles

In this paper, SiO₂–Au–Cu₂O core/shell/shell nanoparticles were synthesized by reducing gold chloride on 3-amino-propyl-triethoxysilane molecules attached silica nanoparticle cores for several stages. Cu₂O nanoparticles were synthesized readily with the size of 4–5 nm using a simple route of sol–gel method Then, they were clung to the surface of Au seeds. The morphology of the resultant particles was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Transmission electron microscopy images demonstrate growth of monodispersed gold seeds and Cu₂O nanoparticles in narrow size up to 10 nm and 5 nm, respectively. The presence of gold and Cu₂O coating was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. Absorption spectroscopy shows considerably 40 nm blue shift in absorption edge for SiO₂–Au–Cu₂O nanostructure rather than SiO₂–Au core/shell nanoparticles.     

SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> fibers from titanium-modified polycarbosilane

We developed a process for preparing SiO₂/TiO₂ fibers by means of precursor transformation method. After mixing PCS and titanium alkoxide, continuous SiO₂/TiO₂ fibers were fabricated by the thermal decomposition of titanium-modified PCS (PTC) precursor. The tensile strength and diameter of SiO₂/TiO₂ fibers are 2.0 GPa, 13 μm, respectively. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) measurements, the microstructure of the SiO₂/TiO₂ fibers is described as anatase–TiO₂ nanocrystallites with the mean size of ~10 nm embedded in an amorphous silica continuous phase.     

Molecular orientation of nonlinear optical polymer nanosheets on silica nanoparticle monolayer studied by optical waveguide spectroscopy

The paper describes molecular orientation of nonlinear optical (NLO) polymer monolayer transferred onto a sphere-shaped silica nanoparticle monolayer using optical waveguide spectroscopy. Structurally well-defined hybrid polymer nanoassemblies were constructed through bottom-up approaches: Langmuir–Blodgett technique and immersion method. Silica nanoparticles (SiO₂ NPs, 40–50 nm diameter) were immobilized on a quartz waveguide using cationic polymer Langmuir–Blodgett films (nanosheets) as a template. The SiO₂ NPs took a uniformly distributed monolayer formation without any aggregates, which minimizes light scattering. This allows us to gain reproducible absorption spectra of dye molecules embedded in polymer nanosheet monolayer on the nanoscale rough surface using optical waveguide spectroscopy. The NLO polymer nanosheets containing disperse red 1 (DR) were transferred onto the SiO₂ NP monolayer. The polarized absorption spectra were obtained; the s-light absorption was larger than the p-light absorption, indicating that polymer nanosheets are wrapped around SiO₂ NPs so that DR moieties undergo molecular disorientation not to form H-aggregates. This method provides us with useful information on structure–property relationship between nanoshaped inorganic nanoparticle and organic functional molecules in hybrid nanoassemblies.     

In situ assembly of ZSM-5 nanocrystals into micro-sized single-crystal-like aggregates via acid-catalyzed hydrolysis of tetraethylorthosilicate

ZSM-5 aggregates were synthesized with the silica source tetraethylorthosilicate (TEOS) being hydrolyzed at acidic conditions to produce siliceous precursors, followed by the addition of aluminum sulfate and tetrapropyl ammonium bromide (TPABr), and with the resulting gel mixture being hydrothermally crystallized at basic conditions. The obtained products were characterized by XRD, SEM, and N₂ adsorption. Well crystallized ZSM-5 can be successfully synthesized through the sulfuric acid-catalyzed hydrolysis of TEOS within a short crystallization time 35 h. The thus produced micro-sized single-crystal-like zeolite ZSM-5 aggregates (10 μm) are made of uniformly distributed nanocrystals with sizes of about 200 nm. Moreover, by adjusting the hydrothermal reaction parameters, such as increasing the crystallization temperature, the TPABr/SiO₂ ratio and the pH value of reaction solution, the crystallization is accelerated substantially. Also, the moderate H₂O/SiO₂ molar ratio of 20–60 in the synthesis mixture can lead to pure ZSM-5, and yet the optimal ratio is 40. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Corrosion behavior of Cu–SiO<Subscript>2</Subscript> nanocomposite coatings obtained by electrodeposition in the presence of cetyl trimethyl ammonium bromide

Copper silica composite coatings are an attractive alternative to chromium and nickel coatings in order to avoid environmental problems and for application in electrical devices. However, co-deposition of SiO₂ particles with metals occurs to a rather limited extent, generally under 1%, due to the hydrophilicity of SiO₂, which makes the incorporation of particles in a metallic matrix difficult. To overcome this drawback, the influence of cetyl trimethyl ammonium bromide (CTAB) on the deposition and corrosion behavior of Cu–SiO₂ coatings on steel has been studied. It was established that CTAB plays a beneficial role in SiO₂ suspension stabilization, promotes the co-deposition of nanoparticles in the copper matrix and improves the deposit morphology and structure. Consequently, a higher corrosion resistance of Cu–SiO₂ deposits obtained in the presence of CTAB was noticed. The most important effect was observed in the case when CTAB was used in concentration of 10⁻³ M in the electroplating bath.     

Amorphous Silica Nanoparticles Promote Monocyte Adhesion to Human Endothelial Cells: Size‐Dependent Effect

There is evidence that nanoparticles can induce endothelial dysfunction. Here, the effect of monodisperse amorphous silica nanoparticles (SiO₂‐NPs) of different diameters on endothelial cells function is examined. Human endothelial cell line (EA.hy926) or primary human pulmonary artery endothelial cells (hPAEC) are seeded in inserts introduced or not above triple cell co‐cultures (pneumocytes, macrophages, and mast cells). Endothelial cells are incubated with SiO₂‐NPs at non‐cytotoxic concentrations for 12 h. A significant increase (up to 2‐fold) in human monocytes adhesion to endothelial cells is observed for 18 and 54 nm particles. Exposure to SiO₂‐NPs induces protein expression of adhesion molecules (ICAM‐1 and VCAM‐1) as well as significant up‐regulation in mRNA expression of ICAM‐1 in both endothelial cell types. Experiments performed with fluorescent‐labelled monodisperse amorphous SiO₂‐NPs of similar size evidence nanoparticle uptake into the cytoplasm of endothelial cells. It is concluded that exposure of human endothelial cells to amorphous silica nanoparticles enhances their adhesive properties. This process is modified by the size of the nanoparticle and the presence of other co‐cultured cells.