Synthesis of ultra-small hollow silica nanoparticles using the prepared amorphous calcium carbonate in one-pot process

The ultra-small hollow silica nanoparticles were synthesized using the prepared amorphous calcium carbonate (ACC) particles as a template. The ACC particles were firstly prepared by carbonation method, which procedure was conducted in the methanol solvent to form the Ca(OCH₃)₂ layers on the ACC particles. An effect of methanol concentration on the morphology of ACC particles was also investigated. The prepared ACC particles were directly coated by silica through adding tetraethoxysilane (TEOS) into the methanol solvent. Hence, the ACC-silica core-shell particles were obtained since the ACC particles have a positive charge and interact with hydrolyzed TEOS. The ACC particles could be stabilized through the reaction between methanol and calcium ions when the methanol concentration was increased over than 40?vol%.     

Synthesis of Fe x O y nanoparticles during iron oxidation by supercritical water

It is established that iron is oxidized by supercritical water (SCW) with the formation of H₂ and nanoparticles of iron oxides (Fe₃O₄, FeO, and γ-Fe₂O₃). The kinetics of H₂ production and iron oxidation has been studied by SCW injection at T = 673, 723, 773, 823, and 873 K into a reactor with iron particles. Data of X-ray diffraction and transmission electron microscopy show that the phase composition and morphology of synthesized oxide nanoparticles depend on the SCW temperature.     

Doxorubicin loaded PVA coated iron oxide nanoparticles for targeted drug delivery

Magnetic drug targeting is a drug delivery system that can be used in locoregional cancer treatment. Coated magnetic particles, called carriers, are very useful for delivering chemotherapeutic drugs. Magnetic carriers were synthesized by coprecipitation of iron oxide followed by coating with polyvinyl alcohol (PVA). Characterization was carried out using X-ray diffraction, TEM, TGA, FTIR and VSM techniques. The magnetic core of the carriers was magnetite (Fe₃O₄), with average size of 10 nm. The room temperature VSM measurements showed that magnetic particles were superparamagnetic. The amount of PVA bound to the iron oxide nanoparticles were estimated by thermogravimetric analysis (TGA) and the attachment of PVA to the iron oxide nanoparticles was confirmed by FTIR analysis. Doxorubicin (DOX) drug loading and release profiles of PVA coated iron oxide nanoparticles showed that up to 45% of adsorbed drug was released in 80 h, the drug release followed the Fickian diffusion-controlled process. The binding of DOX to the PVA was confirmed by FTIR analysis. The present findings show that DOX loaded PVA coated iron oxide nanoparticles are promising for magnetically targeted drug delivery.     

Catalytic oxidation of carbon monoxide over radiolytically prepared Pt nanoparticles supported on glass

Platinum nanoparticles have been prepared by radiolytic and chemical methods in the presence of stabilizer gelatin and SiO₂ nanoparticles. The formation of Pt nanoparticles was confirmed using UV-vis absorption spectroscopy and transmission electron microscopy (TEM). The prepared particles were coated on the inner walls of the tubular pyrex reactor and tested for their catalytic activity for oxidation of CO. It was observed that Pt nanoparticles prepared in the presence of a stabilizer (gelatin) showed a higher tendency to adhere to the inner walls of the pyrex reactor as compared to that prepared in the presence of silica nanoparticles. The catalyst was found to be active at ≥150 °C giving CO₂. Chemically reduced Pt nanoparticles stabilized on silica nanoparticles gave ∼7% CO conversion per hour. However, radiolytically prepared Pt nanoparticles stabilized by gelatin gave ∼10% conversion per hour. Catalytic activity of radiolytically prepared platinum catalyst, coated on the inner walls of the reactor, was evaluated as a function of CO concentration and reaction temperature. The rate of reaction increased with increase in reaction temperature and the activation energy for the reaction was found to be ∼108.8 kJ mol⁻¹. The rate of CO₂ formation was almost constant (∼1.5 × 10⁻⁴ mol dm⁻³ h⁻¹) at constant O₂ concentration (6.5 × 10⁻³ mol dm⁻³) with increase in CO concentration from 2 × 10⁻⁴ mol dm⁻³ to 3.25 × 10⁻³ mol dm⁻³. The data indicate that catalytic oxidation of CO takes place by Eley-Rideal mechanism.     

Synthesis and characterization of PEG-iron oxide core-shell composite nanoparticles for thermal therapy

In this study, core-shell nanoparticles were developed to achieve thermal therapy that can ablate cancer cells in a remotely controlled manner. The core-shell nanoparticles were prepared using atomic transfer radical polymerization (ATRP) to coat iron oxide (Fe₃O₄) nanoparticles with a poly(ethylene glycol) (PEG) based polymer shell. The iron oxide core allows for the remote heating of the particles in an alternating magnetic field (AMF). The coating of iron oxide with PEG was verified through Fourier transform infrared spectroscopy and thermal gravimetric analysis. A thermoablation (55 °C) study was performed on A549 lung carcinoma cells exposed to nanoparticles and over a 10 min AMF exposure. The successful thermoablation of A549 demonstrates the potential use of polymer coated particles for thermal therapy.     

Fabrication of nanocomposite particles with superparamagnetic and luminescent functionalities

A new kind of superparamagnetic luminescent nanocomposite particles has been synthesized using a modified Stöber method combined with an electrostatic assembly process. Fe₃O₄ superparamagnetic nanoparticles were coated with uniform silica shell, and then 3-aminopropyltrimethoxysilane was used to terminate the silica surface with amino groups. Finally, negatively charged CdSe quantum dots (QDs) were assembled onto the surface of the amino-terminated SiO₂/Fe₃O₄ nanoparticles through electrostatic interactions. X-ray diffraction (XRD), transmission electron microscopy (TEM), microelectrophoresis, UV-vis absorption and emission spectroscopy and magnetometry were applied to characterize the nanocomposite particles. Dense CdSe QDs were immobilized on the silica surface. The thickness of silica shell was about 35 nm and the particle size of the final products was about 100 nm. The particles exhibited favorable superparamagnetic and photoluminescent properties.     

Facile synthesis of ordered mesoporous silica with high γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> loading via sol-gel process

A series of ordered mesoporous silica loaded with iron oxide was synthesized by facile one-step sol-gel route using Pluronic P123 as the template, tetraethylorthosilicate as the silica source, and hydrated iron nitrite as the precursor under acid conditions. The as-synthesized materials with Fe/Si molar ratio ranging from 0.1 to 0.8 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and N₂ adsorption porosimetry. All samples possess ordered hexagonal mesoporous structure similar to SBA-15, with a high surface area, large pore volume, and uniform pore size. Although higher iron content causes a distortion of hexagonal ordering structure to some extent, the materials still maintain the ordered mesopore structure even with Fe/Si molar ratio as high as 0.8. Pore structure and TEM data suggest that iron oxide nanoparticles are buried within the silica wall, and increasing the iron oxide loading has little effects on the pore structure of the mesoporous silica. VSM results show as-synthesized samples exhibit superparamagnetic behavior.     

Novel Aerosol-Based Approach toward Mesoporous Silica Nanoparticles

This study introduces a novel gas-phase method for the synthesis of mesoporous silica nanoparticles (MSNs). The method is a two-step templating approach by first forming silicon-coated carbon structures in a hybrid microwave-plasma/hot-wall reactor followed by an annealing step to produce mesoporous silica with distinct nanostructure and porosity. Two different (sacrificial) carbonaceous templates have been prepared (plasma reactor) and coated (hot-wall reactor), 2D few-layer graphene (FLG) flakes and soot-like fractal aggregates. Results show that the wall thickness of the porous silica structures can be adjusted by changing the concentration of the silicon precursor (monosilane). High monosilane concentrations, however, result in solid silica particles after annealing. Using soot-like particle templates permitted to control of the shell thickness of the hollow porous particles, while the FLG template results in ultrathin silica sheets after heat treatment. The pore volume and specific surface area increase up to 263 m² g⁻¹ and 0.6 cm³ g⁻¹, respectively, by the formation of hollow porous particles. An adsorption study on carbamazepine reveals up to ≈86% removal. The gas-phase aerosol-based template method presented here offers scalability and versatility, and it is capable of producing MSNs with a controlled structure and porosity by modifying the carbonaceous templates.     

Single particle model of SnO2 deposition on silver nanoparticles

Silver nanoparticles coated with almost uniform, thin shell of tin oxide are synthesized via a simple colloid chemistry technique, where the reduction of Ag⁴⁺ to Ag⁰ followed by the encapsulation of oxide takes place. The as prepared dispersions of tin oxide coated silver nanocomposite particles display a surface plasmon band, which is significantly red shifted with respect to that of bare Ag. Morphology of the composite nanoparticles was investigated by TEM. Presence of SnO₂ shell on the silver nanoparticles was also supported by XPS results. A theoretical single particle model has been proposed for the formation of tin oxide shell on the silver nanoparticles.     

Preparation of silica/polyacrylamide/polyethylene nanocomposite via in situ polymerization

SiO₂/polyacrylamide (PAM) composite was prepared via the polymerization of acrylamide in the presence of silica sol in water/hexane emulsion, and pure SiO₂ was also prepared without the use of acrylamide in the same way. Field emission scanning electron micrographs (FESEM) showed that PAM covered the silica nanoparticles to form SiO₂/PAM nanospheres, which loosely agglomerated to form SiO₂/PAM secondary particles, while SiO₂ secondary particles were made up of tightly agglomerated silica nanoparticles. Metallocene catalyst was then immobilized over SiO₂ and SiO₂/PAM respectively to prepare supported metallocene catalyst for ethylene polymerization. Transmission electron micrographs (TEM) showed that support particles broke up to smaller particles and even nanoparticles in polyethylene (PE) matrix when the support particles were the fragile SiO₂/PAM secondary particles, which shows a novel way to prepare silica/polyacrylamide/polyethylene nanocomposite.     

Synthesis of cubic type hollow silica particles

Cubic-type hollow silica particles were prepared from Fe₂O₃-SiO₂ core-shell composite particles by selectively leaching the iron oxide core materials using acidic solution. The cubic Fe₂O₃ core particles were obtained by the hydrolysis reaction of iron salts. The Fe₂O₃-SiO₂ core-shell type particles were prepared by the deposition of a SiO₂ layer onto the surface of Fe₂O₃ particles using a two-step coating process. The first step involved primary coating with sodium silicate solution followed by subsequent coating by controlled hydrolysis of tetraethoxysilicate (TEOS). The core Fe₂O₃ was removed by dissolution in an acidic solution which gave rise to the hollow type silica particles. Scanning electron microscopic observation clearly revealed that the morphology is closely related to those of core the Fe₂O₃ particles. The cross sectional view determined by transmission electron microscopy revealed a silica shell with a thickness of about 50 nm. The porous texture of the hollow type silica particles is further characterized by nitrogen adsorption-desorption isotherm measurements.     

Synthesis and properties of hollow silica nanoparticles

Hollow nanoparticles of silicon dioxide (SiO₂) have been obtained using Cu/SiO₂ core-shell nanoparticles as precursors. An original technique based on heating the precursor nanoparticles to T = 400°C followed by a nanochemical reaction of copper oxide separation from hollow silica particles has been proposed and implemented for the first time. The obtained hollow SiO₂ nanoparticles have been studied by transmission electron microscopy. Mechanisms involved in the formation of hollow silica nanoparticles are discussed.     

TiO2 coating on silica particles by deposition of sol-gel-derived nanoparticles

TiO₂ was coated on nonporous transparent silica particles of 3.2 μm diameter by deposition of sol-gel-derived TiO₂ nanoparticles. Effects of water concentration, feed rate of titanium tetraisopropoxide (TTIP) solution and amount of supplied TTIP solution on the amount of TiO₂ coated on the silica particles were examined. Scanning electron microscopy observation confirmed that TiO₂ was coated on the silica particles in the form of ‘nanoparticles’ by using this method. Because of that, even though the TiO₂ surface area decreased due to sintering after calcination at high temperature to change the crystalline phase of TiO₂ to the anatase phase, the final surface area was still much larger than that of the original silica particles. The results also showed that as the water concentration increased, the amount of coated TiO₂ decreased. On the other hand, when the amount of supplied TTIP solution increased, the amount of coated TiO₂ increased. It was also confirmed that the feed rate of TTIP solution had little effect on the amount of coated TiO₂. The photocatalytic activities of the resulting TiO₂-coated silica particles were also evaluated by the photocatalytic decomposition of 2,4-dinitrophenol as a model substance. The results showed that the photocatalytic activity of the particles is not a function of the total surface area, but of the surface area in which anatase phase TiO₂ is exposed to the reaction space. The sedimentation velocity of the TiO₂-coated silica particles becomes about 5 orders of magnitude faster than that of the primary particles of the TiO₂. This indicates that the handling of the TiO₂ was also improved considerably by coating on the silica particles.     

Synthesis and magnetic property of silica/iron oxides nanorods

To better understand the shape dependent property of binary nanostructure, magnetic silica/iron oxides (α-Fe₂O₃ and Fe₃O₄) nanocomposites in rodlike shape have been synthesized using β-FeOOH nanorods as the starting material. The silica layer was coated on the surface of β-FeOOH nanorods, which were prepared by hydrolyzing of FeCl₃ under hydrothermal conditions. Silica/α-Fe₂O₃ nanorods were prepared by calcining silica/β-FeOOH nanorods, and magnetic silica/Fe₃O₄ nanorods were obtained after the reduction of silica/α-Fe₂O₃ nanorods in an inert atmosphere. The role of the silica layer during the phase transformation process was discussed. The magnetic properties of silica/iron oxides (α-Fe₂O₃ and Fe₃O₄) nanorods were investigated and the results revealed that silica/iron oxides nanorods showed higher magnetic saturation value compared with the reported data.     

Titania-reduced graphene oxide nanocomposite as a promising visible light-active photocatalyst for continuous degradation of VVOC in air purification process

Titania-reduced graphene oxide nanocomposites have been prepared through facile hydrothermal method by a reaction between P25 as TiO₂ source and graphene oxide. Reduction of graphene oxide and its reaction with P25 nanoparticles were achieved simultaneously at high temperature and pressure during the hydrothermal process with the minimum organic solvents. Chemical bonds, crystalline structure, morphology, porosity and light absorption of composites along with their photocatalytic activity under UV and visible light irradiation were investigated. Transmission electron microscopy images showed that P25 nanoparticles, with diameters about 25 nm, were dispersed on the sheets of reduced graphene oxide (RGO) homogeneously. A stronger interaction between P25 and RGO provided a red shift about 20 nm in the absorption edge of the composites. To set up a continuous tubular reactor made from thin layer of the prepared material, composite films were coated on the external surface of a steel tube to make an annular reactor. The reactor was equipped with UV or visible light sources to investigate the photocatalytic activity of the prepared composites in a continuous air flow contaminated with specified amount of acetaldehyde as a VVOC (very volatile organic compound) model molecule. Degradation efficiency of P25–RGO with 0.5 wt% RGO was significantly high under visible light irradiation, and about 70% conversion was observed using an air flow at normal conditions with specific flow rate of 17 ml min^?1 and 500 ppm acetaldehyde, by 30 mg of the coated composite in the reactor. Composites with low amount of RGO would be an appropriate photosensitizer and electron acceptor to suppress the recombination of photogenerated electron–hole pairs to enhance the photocatalytic performance.     

Synthesis and magnetic properties of Ni–SiO2 nanocomposites

Nanocomposite Ni_(1 − x)/(SiO₂)_x soft magnetic materials were synthesized by a simple sol–gel combined hydrogen reduction method. The crystal structure of the particles was determined by X-ray diffraction (XRD). The shapes and sizes of the metal particles embedded in the SiO₂ matrix were determined by transmission electron microscopy (TEM), and magnetic properties were measured by the vibrating samples magnetometer (VSM). The obtained nanocomposite material is composed of nanoparticles coated with a thin SiO₂ layer, and with the content of the silicon increase, the thickness of the silica shells increase and the saturation magnetization decrease. The diameter of Ni particle in the sample is about 30–40 nm. The influence of the Ni content and preparation conditions on the microstructures and magnetic properties were discussed.     

Structural Characterization and Magnetic Properties of Iron Oxides Biological Polymers

Iron oxide nanoparticles (IONs) coated with different biological (dextran, sucrose) polymers have been synthesized by the coprecipitation method. Biological polymers coated iron oxide nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM). Zero field cooled and field cooled magnetizations measurements are also reported. We present a preliminary study of the influence of biological polymer on the interaction effects in powders. The temperature, T _max, of the maximum, increased from 25 K (dextran) to 52 K (sucrose). These values are due to the decrease of interparticle interactions, mainly as a result of the interparticle distance increase.     

Atomic layer deposition of iron(III) oxide on zirconia nanoparticles in a fluidized bed reactor using ferrocene and oxygen

Conformal films of amorphous iron(III) oxide and α-Fe₂O₃ have been coated on zirconia nanoparticles (26 nm) in a fluidized bed reactor by atomic layer deposition. Ferrocene and oxygen were alternately dosed into the reactor at temperatures between 367 °C and 534 °C. Self-limiting chemistry was observed via in situ mass spectrometry, and by means of induced coupled plasma-atomic emission spectroscopy analysis. Film conformality and uniformity were verified by high resolution transmission electron microscopy, and the growth rate was determined to be 0.15 Å per cycle. Energy dispersive spectroscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy were utilized as a means to determine film composition at each deposition temperature. Over all of the deposition temperatures investigated, films were deposited as amorphous iron(III) oxide. However, after heat treatment at 850 °C in air and N₂ atmospheres, α-Fe₂O₃ was the predominant species.     

Silica-coated iron nanoparticles: Shape-controlled synthesis,magnetism and microwave absorption properties

Body-centered cubic (bcc) phase iron nanocrystals with granular, rod-like and flaky shapes were prepared through a simple surfactant-controlled chemical reduction route. In view of extra stability and enhanced manipulative ability, thus-prepared iron nanoparticles were morphology-retained modified with a thin silica shell through a Stöber process. A serial of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS), thermogravimetry (TG), vibrating sample magnetometer (VSM) and scalar network analyzer (SNA) were used to characterize the iron particles before and after silica coating. Results showed that the surface silica coating could effectively improve the oxidation resistance and microwave absorption performance of iron particles, while slightly influenced their magnetic properties. Furthermore, the flaky Fe@SiO₂ nanocapsules particles exhibited better microwave absorption performance than that of the granular and rod-like counterparts, which could be ascribed to the shape effect.     

Growth of nano-particles of Al2O3, AlN and iron oxide with different crystalline phases in a thermal plasma reactor

The paper presents the experimental results showing that the crystalline phase of the nano-particles, synthesized in a DC transferred arc thermal plasma reactor, critically depend on the operating pressure in the reaction zone. The paper reports about the changes in crystalline phases of three different compounds namely: aluminium oxide (Al₂O₃), aluminium nitride (AlN) and iron oxide (Fe_xO_y) synthesized at 760 Torr and 500 Torr of operating pressures. The major outcome of the present work is that the phases having higher defect densities are more probable to form at the sub-atmospheric operating pressures. The variations in the crystalline structures are discussed on the basis of the change in the temperature during the nucleation process, prevailing at the boundary of the plasma, on account of the ambient pressures. The as-synthesized nano-particles were examined by X-ray diffraction analysis and transmission electron microscopy. In addition, the confirmatory analysis of the crystalline phases of iron oxides was carried out with the help of Mössbauer spectroscopy.