Fabrication of Ag nanoparticles-coated macroporous SiO2 structure by using polystyrene spheres

Ag nanoparticles-coated macroporous SiO₂ structure was fabricated by a novel approach in which at first Ag nanoparticles were coated onto polystyrene (PS) spheres without a surfactant, then these Ag nanoparticles-coated PS beads (Ag/PS) were self-assembled by sedimentation-aggregation with tetraethyl orthosilicate (TEOS), and finally Ag nanoparticles-coated macroporous silica (Ag/SiO₂) was obtained after removal of the PS cores. The heat-treatment temperature and the gelation time were investigated to optimize the microstructural morphology, thermal decomposition of organic materials, matrix wall thickness and densification behavior. The three dimensionally assembled Ag/SiO₂ had 200 nm uniform macropores and a high specific surface area of 142 m² g⁻¹. The XRD, FE-SEM, EDX, BET and optical absorbance analysis indicated that the exactly three-dimensional structure of the template had been imprinted in the final samples and the walls of the macroporous SiO₂ were coated uniformly with Ag nanoparticles.     

Sintering behavior of spherical aggregated nanoparticles prepared by spraying colloidal precursor in a heated flow

The sintering behavior of spherical aggregated nanoparticles prepared by spraying colloidal precursor into a heated flow was investigated both experimentally and theoretically. Spherical micrometer-sized particles consisting of compactly aggregated nanoparticles were formed, due to solvent evaporation and the drying process of the colloidal precursor. The degree of sintering of aggregated nanoparticles depended on the furnace temperature profile, residence time and primary particle size of the aggregated nanoparticles. Spherical monodispersed colloidal silica, in sizes ranging from 22 to 100 nm was selected as the primary particles. The sintering rate increased with temperature and residence time, and decreased with increasing primary particle size. The aggregated nanoparticles sintered completely, resulting in particles with smooth surfaces that were synthesized at 1400 °C, residence time 31.7 s that was obtained by using a carrier gas flow rate of 1.5 L/min and 0.1 M colloidal silica nanoparticles 100 nm in size. An appropriate model of sintering in the system was proposed to explain the shrinkage and the neck growth of the aggregated nanoparticles. The sintering analysis suggested that solid-state volume diffusion suitably described the sintering mechanism of spherical aggregated silica nanoparticles in a heated flow.     

Thermal stability of silica-coated magnetite nanoparticles prepared by an electrochemical method

Magnetite nanoparticles have been prepared by electrooxidation of iron in water. Surface modifications have been conducted by coating the nanoparticles with silica by a one-step synthesis in dilute sodium silicate solution. The mean size of particles was approximately 10–30 nm for the uncoated particles and 9–12 nm for the coated particles. The results obtained from thermal gravimetric/differential thermal analysis (TG/DTA) revealed that the silica layer formed by the electrochemical method was stable and could serve as a protective layer. Annealing the nanoparticles at 550 °C for 30 min converts magnetite into maghemite for the silica-coated particles, and it further converts the uncoated particles into hematite. The conversions cause the saturation magnetization to decrease for all samples.     

Growth of carbon nanofibers catalyzed by silica-coated copper nanoparticles

Silica-coated copper nanoparticles were synthesized by coating copper nanoparticles with a silica shell through microemulsion. The copper nanoparticles are 30–40 nm in diameter and the silica coating is 10 nm in thickness. After coating, copper nanoparticles were encapsulated in a silica matrix. These particles were used as a catalyst for the growth of carbon nanofibers in a tubular furnace. It is found that carbon nanofibers are mirror-symmetric growth and 100 nm in diameter. During growth, the copper nanoparticles moved out of the silica. As the experiment progressed, the interplanar spacing of copper (2 2 0) increased from 0.1288 nm to 0.1306 nm indicating that (2 2 0) plane exhibited high catalytic activity. The out-of-sync growth of different faces provides new evidence for the research of growth mode in carbon nanofibers.     

A facile method to synthesize novel monodisperse core–shell structure of spherical silica at nanocrystalline copper

A kind of monodisperse core–shell structure of spherical silica at nanocrystalline copper has been successfully synthesized by a two-step synthesis method. A uniform spherical particle of silica was firstly fabricated according to the Stöber method. The obtained silica sample was coated by nanocrystalline copper through oxidation–reduction process. The effects of the volume of water added in the reaction system on particle size of silica were investigated. The particle size of the as-synthesized silica changed from about 170 ± 2 to 160 ± 2 nm with the volume of the added water change from 2.3 to 20 ml. When the volume of the added water was changed to 40 ml, the diameter of the obtained silica particle was about 210 ± 5 nm. The thickness of the coated copper can be controlled by using different sizes of silica particle. The formation mechanism was also discussed.     

Influence of processing method on the properties of hydroxyapatite nanoparticles in the presence of different citrate ion concentrations

The objective of this study was to investigate the effect of processing methods on the formation of ultra fine hydroxyapatite (HAp) nanoparticles in the presence of citrate ions and analyze their various physical properties. The addition of the citrate ions was found to reduce the size and prevent the agglomeration of HAp particles dramatically in the high gravity (HG) method compared to precipitation method. In precipitation method, the particle size reduced from 300 ± 70 nm to 90 ± 20 nm with the addition of citrate ions. In high gravity method, the particle size decreased more significantly from 80 ± 10 nm to 13 ± 5 nm with the addition of citrate ions. Furthermore, more uniform size distribution of nanoparticles was achieved in high gravity method. X-ray diffraction of nanoparticles prepared in both method exhibited slight shift of peaks to the higher angle with the addition of citric acid, indicating the incorporation of carbonate (CO₃) content in the HAp nanoparticles irrespective of the particle size. The mechanical properties of HWMPE matrix composite reinforced with nanoparticles was examined and this nanocomposite with nanoparticles prepared in high gravity method with the addition of citrate ions showed increased mechanical strength due to the considerable reduction in the particle size and higher uniformity of the particles. In vitro cellular analyses of the nanoparticle prepared in high gravity with the addition of citrate ions also displayed the most pronounced spreading of cell growth.     

Structural and magnetic properties of pristine and Fe-doped NiO nanoparticles synthesized by the co-precipitation method

Ni_1?xFe_xO (x = 0 and 0.03) nanoparticles are synthesized by a chemical route. XRD and TEM measurements confirm phase purity and crystallinity of the nanoparticles. Fe substitution in NiO reduces considerably the average particle size of the nanoparticles. The pristine NiO sample with size 14 nm and Fe-substituted sample having size 7 nm show room temperature ferromagnetism. The pristine NiO having 31 nm size and Fe-substituted sample with size 25 nm are found to be antiferromagnetic. The M–H and M–T behavior of the pristine and Fe-doped samples are explained with a core–shell model with an antiferromagnetic core and a ferromagnetic shell. The disordered spins at the shell give rise to a spin-glass like frozen state below 10 K. The obtained room temperature ferromagnetism in the pristine and Fe-doped NiO has been attributed to particle size effect.     

Blending effect of sucrose and surfactant templating agents on silica mesostructure

We report the blending effect of surfactant and sucrose as a nonsurfactant templating agent on the silica mesostructure. The CTAB/sucrose-templated mesoporous silica (SCS) was compared with CTAB-templated MCM-41. The MCM-41 showed spherical morphology with a particle diameter of 1.1–1.5 μm, and gave a bimodal size distribution, centered at 2.1 nm and 8.9 nm, which is assigned to hexagonally-arrayed cylindrical pores and interparticle-pores between small MCM-41 clusters, respectively. SCS gave unique and extraordinary morphology in which two different mesostructures have grown with both of them facing each other. The ordered MCM-41 pore structure clung to silica nanosphere-framed wormlike mesostructure, resulting in a bimodal pore size distribution centered at 2.1 nm and 7.0 nm. It was revealed that both of CTAB and sucrose act independently as a surfactant and a nonsurfactant template.     

Measurement of particle size distribution of silica nanoparticles by interactive force apparatus under an electric field

This paper describes the measurement of particle size distribution of silica nanoparticles by interactive force apparatus (IFA) under an electric field in order to suggest the application of the apparatus to the measurement of particle size distribution. The results were compared with results obtained from size measurement by dynamic light scattering. D₅₀ measured by IFA was closer to the average particle size determined by TEM (5 nm). Also, when compared the results under three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur due to electric breakdown. The distribution measured by IFA (D₅₀ = 5–7 nm) was larger than the one measured by DLS (D₅₀ = 1 nm). The electric breakdown was explained by curve fitting of three different particle size distribution functions with particle size distribution obtained from IFA measurement.     

Rapid synthesis of ordered hexagonal mesoporous silica and their incorporation with Ag nanoparticles by solution plasma

Rapid synthesis of silica with ordered hexagonal mesopore arrangement was obtained using solution plasma process (SPP) by discharging the mixture of P123 triblock copolymer/TEOS in acid solution. SPP, moreover, was utilized for Ag nanoparticles (AgNPs) incorporation in silica framework as one-batch process using silver nitrate (AgNO₃) solution as precursor. The turbid silicate gel was clearly observed after discharge for 1 min and the white precipitate formed at 3 min. The mesopore with hexagonal arrangement and AgNPs were observed in mesoporous silica. Two regions of X-ray diffraction patterns (2θ < 2° and 2θ = 35–90°) corresponded to the mesoporous silica and Ag nanocrystal characteristics. Comparing with mesoporous silica prepared by a conventional sol–gel route, surface area and pore diameter of mesoporous silica prepared by solution plasma were observed to be larger. In addition, the increase in Ag loading resulted in the decrease in surface area with insignificant variation in the pore diameter of mesoporous silica. SPP could be successfully utilized not only to enhance gelation time but also to increase surface area and pore diameter of mesoporous silica.     

Synthesis,characterization and surface modification of ZnCrFeO4 nanoparticles

The aim of this research was to investigate zinc chromium ferrite (ZnCrFeO₄) nanoparticles, synthesized using the sol gel technique with nanoparticle size controlled through a two-stage annealing process. Stage one was a low temperature firing which produced low quality nanocrystals with an average size of 15 nm. This was followed by a second firing stage at high temperature which enhanced the crystal quality. The nanoparticles were then coated with a bio-compatible shell to form a stable suspension in the ferrofluid carrier. The resulting nanoparticles were found by electron microscopy, atomic force microscopy and X-ray diffraction studies to have excellent crystal quality. The average size was 8.5 nm. Preliminary cell culture studies indicated the ZnCrFeO₄ nanoparticles were non-toxic. The relatively high measured value of the relaxivity r₂ showed that the nanoparticle coating was effective in substantially reducing aggregation and enhancing the properties of the nanoparticles associated with contrast enhancement in MRI.     

Highly stable,protein capped gold nanoparticles as effective drug delivery vehicles for amino-glycosidic antibiotics

A method for the production of highly stable gold nanoparticles (Au NP) was optimized using sodium borohydride as reducing agent and bovine serum albumin as capping agent. The synthesized nanoparticles were characterized using UV–visible spectroscopy, transmission electron microscopy, X‐ray diffraction (XRD) and dynamic light scattering techniques. The formation of gold nanoparticles was confirmed from the appearance of pink colour and an absorption maximum at 532 nm. These protein capped nanoparticles exhibited excellent stability towards pH modification and electrolyte addition. The produced nanoparticles were found to be spherical in shape, nearly monodispersed and with an average particle size of 7.8 ± 1.7 nm. Crystalline nature of the nanoparticles in face centered cubic structure is confirmed from the selected‐area electron diffraction and XRD patterns. The nanoparticles were functionalized with various amino-glycosidic antibiotics for utilizing them as drug delivery vehicles. Using Fourier transform infrared spectroscopy, the possible functional groups of antibiotics bound to the nanoparticle surface have been examined. These drug loaded nanoparticle solutions were tested for their antibacterial activity against Gram-negative and Gram-positive bacterial strains, by well diffusion assay. The antibiotic conjugated Au NP exhibited enhanced antibacterial activity, compared to pure antibiotic at the same concentration. Being protein capped and highly stable, these gold nanoparticles can act as effective carriers for drugs and might have considerable applications in the field of infection prevention and therapeutics.     

Microstructure and corrosion behavior of Ti nanoparticles reinforced Ni–Ti composite coatings by electrodeposition

A survey on electrochemical codeposition of Ti nanoparticles in Ni matrix coating is given. The influences of Ti nanoparticle loadings in electrolyte on the microstructure, microhardness and corrosion behavior of Ni–Ti coatings were investigated. The results showed that a pyramidal surface structure evolved into a spherical surface structure of the coatings with increasing Ti nanoparticle loading. The content of Ti in the Ni–Ti coatings first increased and reached the maximum value of 7.1 vol.% at the loading of 16 g/L, then decreased due to agglomeration of nanoparticles. The [2 0 0] preferred orientation gradually evolved to [1 1 1] orientation with increasing Ti nanoparticle loading. At Ti nanoparticle loading of 16 g/L, the minimum crystallite size (44 nm) and maximum microstrain (0.25%) were obtained. The microhardness of the Ni–Ti coatings was improved and obtained the maximum value at the loading of 16 g/L. The anti-corrosion behavior of the Ni–Ti coatings had increased trend with increasing Ti nanoparticle loading. The pitting corrosion and the selective dissolution of Ti nanoparticles happened in corrosion of Ni–Ti coating electrodeposited at the loading of 16 g/L in a 3.5 wt.% NaCl solution.     

Nanoparticles synthesis of tungsten disulfide via AOT-based microemulsions

The tungsten disulfide (WS₂) nanoparticles (most probably inorganic fullerene (IF)) with a narrow size distribution were synthesized by a reverse micelle technique for the first time. The particle size was controlled by varying water-to-surfactant molar ratio (W₀), aging time and reagent concentration. The synthesized WS₂ nanoparticles were characterized by zetasizer, UV–visible spectrophotometers and transmission electron microscopy (TEM). The WS₂ nanoparticles with particle diameter size of 7–12 nm were obtained via 24 h aging time. The particle size was controlled by changing the aging time and molar ratio of water/surfactant. Doubling W₀ increased the amount and particle size of WS₂ by 22 and 26%, respectively. The effect of aging time in the range of 6–24 h was investigated and the complete disappearance of yellowish color at 24 h resulted in an optically clear solution, which was the indication of WS₂ formation with 100% conversion of reactant ((NH₄)₂WS₄) in the batch reactor.     

The fabrication of SnSe/Ag nanoparticles on TiO2 nanotubes

SnSe and silver (Ag) nanoparticles were sequentially deposited on TiO₂ nanotube (NT) by pulsed electrochemical deposition and polyol chemistry process, respectively. The morphological observation under scanning electron microscope (SEM) showed that the average size of SnSe was about 30 nm and the Ag was about 5 nm. Transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) examination indicated that Ag nanoparticles exhibited a well-defined crystallinity. However, SnSe nanoparticles were amorphous and they turned to crystalline after being annealed at 300 °C in the atmosphere. The photocatalytic behavior of SnSe/Ag-TiO₂ NT was evaluated by UV–vis diffuse reflectance spectra (DRS). The results showed that the deposition of SnSe and Ag nanoparticles increased light absorption intensity in the wavelength range of visible light, which implied that the SnSe/Ag-TiO₂ NT is a promising ternary hybrid material in photocatalysis.     

A study of optothermal and cytotoxic properties of silica coated Au nanorods

Au nanorods have been successfully passivated by silica coating. Our protocol successfully produced a silica layer at a minimum subnanometer-thick precision, and a thicker (approximately 3 nm) coating was achieved as well. Interestingly, the silica-coated Au nanorods showed very low cell toxicity with a half maximal inhibitory concentration > 400 μg/ml, and the optothermal efficiency was quite comparable to that of bare Au rods. These novel properties of the silica-coated Au nanorods open the path to biomedical applications, such as in vivo multimode cellular imaging and nanomedicinal hybrids.     

Synthesis of spherical NiO nanoparticles through a novel biosurfactant mediated emulsion technique

Spherical nickel oxide nanoparticles were synthesized by microemulsion technique using rhamnolipids as the surfactant along with n-heptane and water. Nickel hydroxide (Ni(OH)₂) particles were first formed which were then calcined to obtain nickel oxide (NiO) particles. Scanning Electron Microscopy (SEM) studies revealed that the synthesized nickel hydroxide particles were spherical in shape with stacked lamellar sheets. Nickel hydroxide was converted to nickel oxide by calcinations at 600 °C for 3 h and was confirmed by X-ray Diffraction (XRD) analysis. Transmission Electron Microscopy (TEM) showed that the nickel oxide particles were crystalline and of uniform size. The effect of pH on particle size was investigated and it was found that the particle size decreased from 86 ± 8 nm at pH 11.6 to 47 ± 5 nm at pH 12.5. A novel method using rhamnolipid biosurfactant for microemulsion synthesis has been demonstrated which offers an eco-friendly alternative to conventional microemulsion technique based on organic surfactants.     

Silanized polymeric nanoparticles for DNA isolation

The aim of this study is to prepare silanized polymeric nanoparticles for DNA isolation. Polymeric p(HEMA)-IMEO-PBA nanoparticles around 85.7 nm diameter, was obtained by surfactant free emulsion polymerization for DNA isolation. Synthesized nanoparticles for characterization studies were realized scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Zeta-size. Surface area, average particle size and size distribution were also performed. The surface area of synthesized silanized polymeric nanoparticles was 2460 m²/g. Synthesized polymeric nanoparticles were silanized with 3-(2-imidazoline-1-yl)propyl (triethoxysilane) (IMEO). After that, phenylboronic acid (PBA) which is DNA specific ligand were covalently binded to silanized polymeric nanoparticles. The amount of DNA adsorbed onto the p(HEMA)-IMEO-PBA nanoparticles first increased and then reached a saturation value at around 14.0 mg/mL of DNA concentration. The maximum adsorption was 672.41 mg/g silanized polymeric nanoparticles in the optimum adsorption medium. The maximum DNA adsorption was achieved at 4 °C. The overall recovery of DNA was calculated as 95%. In repetitive adsorption–desorption circles, it is observed not being important decrease in DNA adsorption capacities. The results were shown that silanized polymeric nanoparticles can be a good alternative for DNA isolation.     

Toughening performance of glass fibre composites with core–shell rubber and silica nanoparticle modified matrices

The fracture energies of glass fibre composites with an anhydride-cured epoxy matrix modified using core–shell rubber (CSR) particles and silica nanoparticles were investigated. The quasi-isotropic laminates with a central 0°/0° ply interface were produced using resin infusion. Mode I fracture tests were performed, and scanning electron microscopy of the fracture surfaces was used to identify the toughening mechanisms.The composite toughness at initiation increased approximately linearly with increasing particle concentration, from 328 J/m² for the control to 842 J/m² with 15 wt% of CSR particles. All of the CSR particles cavitated, giving increased toughness by plastic void growth and shear yielding. However, the toughness of the silica-modified epoxies is lower as the literature shows that only 14% of the silica nanoparticles undergo debonding and void growth. The size of CSR particles had no influence on the composite toughness. The propagation toughness was dominated by the fibre toughening mechanisms, but the composites achieved full toughness transfer from the bulk.     

Ultrasound-assisted synthesis of colloidal nanosilica from silica fume: Effect of sonication time on the properties of product

Current methods of colloidal nanosilica production are relatively energy-intensive and in some cases not environmentally friendly and therefore essential needs are felt to develop new low cost environmentally friendly methods. This study is devoted to the synthesis and characterization of colloidal silica nanoparticles prepared from silica fume using ultrasound. Colloidal nanosilica has been synthesized via dissolution-precipitation process followed by applying ultrasonic waves with the power and frequency of 30 W and 20 kHz, respectively. The produced colloidal nanosilica was characterized via dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and measurements of its zeta potential and specific surface area. DLS results show that minimum particle size, average diameter and maximum particle size of the produced colloidal nanosilica decrease sharply from 28.21, 54.92 and 164.20 nm to 18.17, 38.72 and 141.80 nm, respectively, during the first 15 s of sonication. No significant changes have been observed in applying continued sonication up to 60 min. Measurements of zeta potential confirmed a relatively good stability of the produced colloidal nanosilica.