Growth of ordered silver nanoparticles in silica film mesostructured with a triblock copolymer PEO-PPO-PEO

Elaboration of mesostructured silica films with a triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide, (PEO-PPO-PEO) and controlled growth of silver nanoparticles in the mesostructure are described. The films are characterized using UV-visible optical absorption spectroscopy, TEM, AFM, SEM, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Organized arrays of spherical silver nanoparticles with diameter between 5 and 8 nm have been obtained by NaBH₄ reduction. The size and the repartition of silver nanoparticles are controlled by the film mesostructure. The localization of silver nanoparticles exclusively in the upper-side part of the silica-block copolymer film is evidenced by RBS experiment. On the other hand, by using a thermal method, 40 nm long silver sticks can be obtained, by diffusion and coalescence of spherical particles in the silica-block copolymer layer. In this case, migration of silver particles toward the glass substrate-film interface is shown by the RBS experiment.     

Influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles

The experimental results on the influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles were reported. The spherical silica nanoparticles have been synthesized using polyethylene glycol (PEG) as the surfactant and oil shale ash (OSA) as a new silica source. In order to identify the optimal condition for producing the best quality silica nanoparticles with the good dispersion and uniformity, the effects of surfactant surface coverage and aging time were investigated. It was found that the particle size and distribution of silica nanoparticles depend on the concentration of PEG in dispersion. At relatively low concentration, 0–2 wt.%, the existing PEG is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the PEG concentration increases to 3 wt.%, self-assembled PEG layer on the surface stabilizes the initially formed silica nanoparticles and the silica particles with average diameter of 10 nm are uniformly distributed. With further increasing the concentration of PEG, the number of PEG aggregates increases and silica nanoparticles are mainly formed inside the entangled PEG chains, resulting in an observation of clusters of silica nanoparticles. Moreover, it was found that as the aging time increased, the shape of silica nanoparticles becomes regular and the particle size distribution becomes narrow.     

Thioether moiety functionalization of mesoporous silica films for the encapsulation of highly dispersed gold nanoparticles

Highly dispersed gold nanoparticles within mesoporous thin films (MTFs) have been synthesized through a newly developed controllable strategy, in which (1,4)-bis(triethoxysilyl)propane tetrasufide (BPTS) organosiloxane coupling agent was co-assembled with tetraethyl orthosilicate (TEOS) to form organic groups functionalized mesoporous composite films followed with oxidization, ion-exchange with Au(en)₂Cl₃ (en: 1,2-ethanediamine) compound and calcination under hydrogen/nitrogen mixing atmosphere. Small-angle X-ray diffraction (XRD) characterization indicated that up to 10 mol% of BPTS could be incorporated into mesoporous hybrid films, and that would not breakup the structural integrity and long-range periodicity. The loaded gold nanoparticles were uniformly distributed due to the molecular level homogenous mixing of the BPTS precursor with TEOS, and its concentration could be controlled via the original ratio of BPTS to TEOS. The nanoparticles had a narrow size distribution with diameters in the size range of 3-7 nm through transmission electron microscopy (TEM) observation and underwent a slight size increase with the higher gold load level. An overall increase in the absorption intensity, a red shift of absorption peak, together with a comparatively narrower bandwidth could be observed at higher gold concentration within composite films from UV-vis spectra. Wide-angle XRD, TEM, X-ray photoelectron spectroscopy (XPS) and UV-vis spectra characterizations all agreed on the fact that the gold loading level could be controlled by the amount of BPTS in the starting sol for preparing MTFs.     

Characterization of anticancer hypocrellin A encapsulated with silica nanoparticles

Hypocrellins, natural photosensitizers including hypocrellin A (HA) and hypocrellin B (HB), have been used as a traditional Chinese herbal medicine to cure various skin diseases. Hypocrellins have excellent antiviral activity, which can inhibit the growth of human immunodeficiency virus. They also exhibit significant light-induced antitumor property. In this article, thermal analysis technologies (e.g., differential scanning calorimetry and thermogravimetry) are employed to characterize whether the photosensitive hypocrellin A could be encapsulated with silica nanoparticle (SN) material or not, and evaluate the stability of inclusion complex. The results show that the inclusion complex exhibits improved performance in both stability and hydrophilicity than natural hypocrellin A. Fluorescence spectrophotometry studies have also been performed to verify the thermal analysis results. The results suggest that the thermal analysis technology could be used as an effective and rapid tool to characterize the encapsulation properties of the novel anticancer HA–SN complex.     

Growth of silica nanoparticles in methylmethacrylate-based water-in-oil microemulsions

The mechanism of silica particle formation in monomer microemulsions is studied using dynamic light scattering (DLS), atomic force microscopy, small-angle X-ray scattering (SAXS), and conductivity measurements. The hydrolysis of tetraethylorthosilicate (TEOS) in methylmethacrylate (MMA) microemulsions (MMA = methylmethacrylate) is compared with the formation of SiO₂ particles in heptane microemulsions. Stable microemulsions without cosurfactant were found for MMA, the nonionic surfactant Marlophen NP10, and aqueous ammonia (0.75 wt%). In the one-phase region of the ternary phase diagram, the water/surfactant ratio (R _w) could be varied from 6 to 18. The DLS and SAXS measurements show that reverse micelles form in these water-in-oil (w/o) microemulsions. The minimum water-to-surfactant molar ratio required for micelle formation was determined. Particle formation is achieved from the base-catalyzed hydrolysis of TEOS. According to atomic force microscopy measurements of particles isolated from the emulsion, the particle size can be effectively tailored in between 20 and 60 nm by varying R _w from 2–6 in heptane w/o microemulsions. For MMA-based microemulsions, the particle diameter ranges from 25 to 50 nm, but the polydispersity is higher. Tailoring of the particle size is not achieved with R _w, but adjusting the particle growth period produces particles between 10 and 70 nm.     

Encapsulation of silica nanoparticles by redox-initiated graft polymerization from the surface of silica nanoparticles

This study describes a facile and versatile method for preparing polymer-encapsulated silica particles by ‘grafting from’ polymerization initiated by a redox system comprising ceric ion (Ce⁴⁺) as an oxidant and an organic reductant immobilized on the surface of silica nanoparticles. The silica nanoparticles were firstly modified by 3-aminopropyltriethoxysilane, then reacted with poly(ethylene glycol) acrylate through the Michael addition reaction, so that hydroxyl-terminated poly(ethylene glycol) (PEG) were covalently attached onto the nanoparticle surface and worked as the reductant. Poly(methyl methacrylate) (PMMA), a common hydrophobic polymer, and poly(N-isopropylacrylamide) (PNIPAAm), a thermosensitive polymer, were successfully grafted onto the surface of silica nanoparticles by ‘grafting from’ polymerization initiated by the redox reaction of Ce⁴⁺ with PEG on the silica surface in acid aqueous solutions. The polymer-encapsulated silica nanoparticles (referred to as silica@PMMA and silica@PNIPAAm, respectively) were characterized by infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. On the contrary, graft polymerization did not occur on bare silica nanoparticles. In addition, during polymerization, sediments were observed for PMMA and for PNIPAAm at a polymerization temperature above its low critical solution temperature (LCST). But the silica@PNIPAAm particles obtained at a polymerization temperature below the LCST can suspend stably in water throughout the polymerization process.     

Uniform silica nanoparticles encapsulating two-photon absorbing fluorescent dye

We have prepared uniform silica nanoparticles (NPs) doped with a two-photon absorbing zwitterionic hemicyanine dye by reverse microemulsion method. Obvious solvatochromism on the absorption spectra of dye-doped NPs indicates that solvents can partly penetrate into the silica matrix and then affect the ground and excited state of dye molecules. For dye-doped NP suspensions, both one-photon and two-photon excited fluorescence are much stronger and recorded at shorter wavelength compared to those of free dye solutions with comparative overall dye concentration. This behavior is possibly attributed to the restricted twisted intramolecular charge transfer (TICT), which reduces fluorescence quenching when dye molecules are trapped in the silica matrix. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells with low cytotoxicity.     

Cell penetrating silica nanoparticles doped with two-photon absorbing fluorophores

Organosilica nanoparticles, doped with two-photon absorbing distyrylbenzene derivatives, were prepared and studied as cell staining agents. Two dyes were used, bearing either two peripheral dimethylamino groups or one dimethylamino and one cyano group. Due to the internal charge transfer character of their excited state, the dyes employed show a red-shifted quenched emission in polar solvents. Once included in the particles, the properties of the two dyes undergo a substantial variation. Particles doped with the cyano substituted distyrylbenzene show a remarkable emission quantum yield in water, probably due to solvent exclusion from the nanoparticle core. To the contrary, the emission of the particles containing the dye substituted with two dimethylamino groups is substantially quenched. Fluorescence emission induced by two-photon absorption follows the same behaviour. The doped nanoparticles can be rapidly internalized by tumour cells with accumulation limited to the cytoplasm and show no cytotoxicity at low concentrations.     

Amphiphilic silica nanoparticles as pseudostationary phase for capillary electrophoresis separation

Amphiphilic silica nanoparticles surface-functionalized by 3-aminopropyltriethoxysilane (APTES) and octyltriethoxylsilane (OTES) were successfully prepared and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FT-IR) and thermogravimetry (TG) techniques. The potential use of these bifunctionalized nanoparticles as pseudostationary phases (PSPs) in capillary electrophoresis (CE) for the separation of charged and neutral compounds was evaluated in terms of their suitability. As expected, fast separation of representative aromatic acids was fulfilled with high separation efficiency, because they migrate in the same direction with the electroosmotic flow (EOF) under optimum experimental conditions. Using a buffer solution of 30mmol/L phosphate (pH 3.0) in the presence of 0.5mg/mL of the synthesized bifunctionalized nanoparticles, the investigated basic compounds were baseline-resolved with symmetrical peaks. Due to the existence of amino groups on the surface of nanoparticles, "silanol effect" that occurs between positively charged basic analytes and the silanols on the inner surface of capillary was greatly suppressed. Furthermore, the separation systems also exhibited reversed-phase (RP) behavior when neutral analytes were tested.     

Sol-Gel processing of silica nanoparticles and their applications

Recently, silica nanoparticles (SNPs) have drawn widespread attention due to their applications in many emerging areas because of their tailorable morphology. During the last decade, remarkable efforts have been made on the investigations for novel processing methodologies to prepare SNPs, resulting in better control of the size, shape, porosity and significant improvements in the physio-chemical properties. A number of techniques available for preparing SNPs namely, flame spray pyrolysis, chemical vapour deposition, micro-emulsion, ball milling, sol-gel etc. have resulted, a number of publications. Among these, preparation by sol-gel has been the focus of research as the synthesis is straightforward, scalable and controllable. Therefore, this review focuses on the recent progress in the field of synthesis of SNPs exhibiting ordered mesoporous structure, their distribution pattern, morphological attributes and applications. The mesoporous silica nanoparticles (MSNPs) with good dispersion, varying morphology, narrow size distribution and homogeneous porous structure have been successfully prepared using organic and inorganic templates. The soft template assisted synthesis using surfactants for obtaining desirable shapes, pores, morphology and mechanisms proposed has been reviewed. Apart from single template, double and mixed surfactants, electrolytes, polymers etc. as templates have also been intensively discussed. The influence of reaction conditions such as temperature, pH, concentration of reagents, drying techniques, solvents, precursor, aging time etc. have also been deliberated. These MSNPs are suitable for a variety of applications viz., in the drug delivery systems, high performance liquid chromatography (HPLC), biosensors, cosmetics as well as construction materials. The applications of these SNPs have also been briefly summarized.     

Nanoclay synergy in flame retarded/glass fibre reinforced polyamide 6

Exfoliated clay nanocomposites of flame retarded/glass fibre reinforced polyamide 6 were prepared by twin-screw extrusion compounding. A flame retardant system based on phosphorus compounds and zinc borate was used at various levels in glass fibre reinforced PA6 and nanocomposites. Thermal stability and combustion behaviours were evaluated by TGA, LOI, UL94 and cone calorimetry. Substitution of a certain fraction of the flame retardant with nanoclays was found to significantly reduce the peak heat release rate and delay ignition in the cone calorimeter. Moreover, remarkable improvements were obtained in LOI along with maintained UL94 ratings. Residue characterization by FTIR, XRD and SEM ascribed the enhanced flame retardancy of nanocomposite formulations to the formation of a glassy boron/aluminium phosphate barrier reinforced by clay layers at the nanoscale. The physically strong and consolidated barriers formed from nanocomposites were much more effective in impeding heat and mass transfer compared to those from conventional formulations.     

Preparation and mechanical properties of bacterial cellulose nanocomposites loaded with silica nanoparticles

Bacterial cellulose (BC), which is produced by Gluconacetobacter xylinus (Ga. xylinus) in culture, is made up of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. In the current studies, we used two processes to prepare nanocomposites of BC filled with silica particles. In Process I, Ga. xylinus was incubated in medium containing silica sol Snowtex 0 (ST 0, pH 2–4) or Snowtex 20 (ST 20, pH 9.5–10.0). The elastic modulus at 20 °C was improved by keeping the amount of silica in the nanocomposites below 4% when ST 20 was used and below 8.7% when ST 0 was used. This process allowed incorporation of 50% silica in BC. Inclusion of higher amounts of silica reduced the modulus at 20 °C and the strength of the nanocomposites below that of BC. X-ray diffraction measurements revealed that the silica particles disturb the formation of ribbon-shaped fibrils and affect the preferential orientation of the ( ) plane. We also produced BC-silica nanocomposites by Process II, wherein the BC hydrogel was immersed in different concentrations of silica sols, allowing silica particles to diffuse into the BC hydrogel and lodge in the spaces between the ribbon-shaped fibrils. This method increased the modulus at 20°C and the strength compared to the BC matrix, but it was difficult to load the BC with more than 10% silica in this way.     

Characterization of gold nanoparticles electrochemically deposited on amine-functioned mesoporous silica films and electrocatalytic oxidation of glucose

This study reports the preparation and characterization of gold nanoparticles deposited on amine-functioned hexagonal mesoporous silica (NH₂–HSM) films and the electrocatalytic oxidation of glucose. Gold nanoparticles are fabricated by electrochemically reducing chloroauric acid on the surface of NH₂–HSM film, using potential step technology. The gold nanoparticles deposited have an average diameter of 80 nm and show high electroactivity. Prussian blue film can form easily on them while cycling the potential between −0.2 and 0.6 V (vs saturated calomel electrode) in single ferricyanide solution. The gold nanoparticles loading NH₂–HSM-film-coated glassy carbon electrode (Au–NH₂–HSM/GCE) shows strong catalysis to the oxidation of glucose, and according to the cathodic oxidation peak at about 0.16 V, the catalytic current is about 2.5 μA mM⁻¹. Under optimized conditions, the peak current of the cathodic oxidation peak is linear to the concentration of glucose in the range of 0.2 to 70 mM. The detection limit is estimated to be 0.1 mM. In addition, some electrochemical parameters about glucose oxidation are estimated.     

Preparation of ultrathin coating layers using surface modified silica nanoparticles

Silica nanoparticles are used in various applications including catalysts, paints and coatings. To reach an optimal performance via stability and functionality, in most cases, the surface properties of the particles are altered using complex procedures. Here we describe a simple method for surface modification of silica nanoparticles (SNP) using sequential adsorption of oppositely charged components. First, the SNPs were made cationic by adsorption of a cationic polyelectrolyte. Poly(allylamine hydrochloride) (PAH) and polyethyleneimine (PEI) were chosen as polycations to investigate the difference between a linear and a branched polyelectrolyte. Next, the dispersion of cationic SNPs was combined with an anionic alkyl ketene dimer (AKD) emulsion. Using this approach cationic, hydrophobic silica particle dispersions were produced. Dynamic light scattering, contact angle measurements and atomic force microscopy (AFM) were used for analyzing the particle and coating layer properties. The chosen polyelectrolyte affected the structure of the dispersion. The layer build-up was studied in detail using a quartz crystal microbalance with dissipation monitoring (QCM-D). The adsorption and layer properties of the cationic polyelectrolytes adsorbed on silica as well as the affinity of AKD to this layer were explored. The application possibilities of the modified particle dispersions were demonstrated by preparing paper and silica surfaces with tailored properties, such as elevated surface hydrophobicity, using an ultrathin coating layer.     

Diamino moiety functionalized silica nanoparticles as pseudostationary phase in capillary electrochromatography separation of plant auxins

A novel and simple method for the preparation of silica nanoparticles having surface-functionalized diamino moiety (dASNPs) was reported in our paper and characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrometry, and thermogravimetry techniques. To test this method practically, in this contribution we describe the enhanced separation of four plant auxins - indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), 2,4-dichlorophenoxyacetic acid (dCPAA), and 2-(1-naphthyl) acetic acid (NAA) - by capillary electrochromatography using diamino moiety functionalized silica nanoparticles as pseudostationary phase (PSP) in the running buffer. The effect of pH, buffer concentration, and diamino moiety functionalized silica nanoparticles concentration on the selectivity of separation was investigated. A combination of the nanoparticles and running buffer reversed the electroosmotic direction making possible the rapid and efficient separation of the auxins from the auxins migrated in the same direction with the EOF under optimum experimental conditions. A good resolution of four auxins was obtained within 5.5 min under optimum experimental conditions. The precision (RSD, n = 5) was in the range of 0.72-0.91% and 1.89-2.23% for migration time and peak area response, respectively. The detection limits were 0.48, 0.44, 0.46, and 0.42 μM for NAA, IBA, IAA, and dCPAA, respectively. Furthermore, the method was successfully tested for the determination of IAA in the grapes.     

The fabrication of photosensitive self-assembly Au nanoparticles embedded in silica nanofibers by electrospinning

In this study, we demonstrated a simple, efficient, and low-cost method to fabricate large-area self-assembly Au nanoparticles (AuNPs) encapsulated within silica nanofibers (Au/SiO₂). The method is based on electrospinning and thermal decomposition of hybrid nanofibers prepared from the solution of tetraethylorthosilicate (TEOS), polyvinylpyrrolidone (PVP) and AuNPs. This study employed the electrospinning technique for the first time as a successful method for preparing a self-organized AuNP peapod chain in a silica nanofiber matrix, under mild conditions. It has the advantage of easily controlling the diameters of the silica nanofibers as well as the concentration of the AuNPs in the spinning solution. The Au/SiO₂ hybrid nanofibers fabricated by this method exhibited an obvious photoelectric response under the illumination wavelength around the Au/SiO₂ nanofibers surface plasmon resonance (SPR) absorption band, whereas no photoelectric response was observed for the pure silica fibers. The excellent characteristics of photoelectric response suggest that the electrospinning technique has a great potential for large-scale fabrication of functional nanofiber devices. The ability of coupling light responses into the nanosystems dependent on metallic nanoparticle SPR opens up new prospects for the construction of nanoscale waveguiding devices, sensors and optoelectronics.     

Polypyrrole/silica/magnetite nanoparticles as a sorbent for the extraction of sulfonamides from water samples

A magnetic solid‐phase extraction sorbent of polypyrrole/silica/magnetite nanoparticles was successfully synthesized and applied for the extraction and preconcentration of sulfonamides in water samples. The magnetite nanoparticles provided a simple and fast separation method for the analytes in water samples. The silica coating increased the surface area that helped to increase the polypyrrole layer. The polypyrrole‐coated silica provided a high extraction efficiency due to the π–π and hydrophobic interactions between the polypyrrole and sulfonamides. Several parameters that affected the extraction efficiencies, i.e. the amount of sorbent, pH of the sample, extraction time, extraction temperature, ionic strength, and desorption conditions were investigated. Under the optimal conditions, the method was linear over the range of 0.30–200 μg/L for sulfadiazine and sulfamerazine, and 1.0–200 μg/L for sulfamethazine and sulfamonomethoxine. The limit of detection was 0.30 μg/L for sulfadiazine and sulfamerazine and 1.0 μg/L for sulfamethazine and sulfamonomethoxine. This simple and rapid method was successfully applied to efficiently extract sulfonamides from water samples. It showed a high extraction efficiency for all tested sulfonamides, and the recoveries were in the range of 86.7–99.7% with relative standard deviations of < 6%.     

Dynamics of water sorbed in reverse osmosis polyamide membrane

Dynamical motion of water sorbed in reverse osmosis polyamide membrane (ROPM) material is reported as studied by quasielastic neutron scattering (QENS) technique. The ROPM studied here has pore size of 4.4 Å as determined by positron annihilation lifetime spectroscopy. Analysis of the QENS data showed that diffusion behavior of the water within the membrane is describable by random jump diffusion model. A much longer residence time is found as compared to bulk water. Positive shift of the freezing point as observed in differential scanning calorimetry indicates presence of strong attractive interaction corroborating the slower diffusivity as observed in QENS.     

Enhanced separation of seven quinolones by capillary electrophoresis with silica nanoparticles as additive

This paper describes the enhanced separation of lomefloxacin, sparfloxacin, fleroxacin, norfloxacin, ofloxacin, gatifloxacin and pazufloxacin by capillary zone electrophoresis (CZE) using silica nanoparticles (SiNPs) as running buffer additive. The impact of SiNPs concentration on the resolution and selectivity of separation was investigated and a given value of SiNPs was finally chosen under the optimum conditions. The addition of the SiNPs to the running buffer enabled electroosmotic flow (EOF) decrease and permitted full interaction between SiNPs and analytes. The influence of separation voltage, pH and buffer concentration on the separation in the presence of SiNPs was examined. Interactions between drugs and nanoparticles during the separation are discussed; the determination of interaction constants is also achieved. A good resolution of seven quinolones was obtained within 15 min in a 50 cm effective length fused-silica capillary at a separation voltage of +10 kV in a 12 mM disodium tetraborate-phosphate buffer (pH 9.08) containing 5.2 μg mL⁻¹ SiNPs.