Sol–gel preparation of aminopropyl-silica-magnesia hybrid materials

A series of aminopropyl-silica-magnesia hybrid materials has been prepared by the sol–gel method from tetraethoxysilane (TEOS), magnesium chloride (MgCl₂) and aminopropyltriethoxysilane (APTES) under acid conditions. The APTES:TEOS ratio was varied between 0:1 and 1:0. The aminopropyl coverage concentrations for APTES-silica-Mg samples were in the range of 0.3–2.3 mmol g⁻¹. The hybrid materials were characterized by numerous techniques, including X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Fourier transform Raman spectroscopy (FT-Raman), solid-state ¹³C and ²⁹Si nuclear magnetic resonance (¹³C- and ²⁹Si-NMR), thermogravimetry (TGA), N₂ adsorption–desorption, small-angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). The increase of APTES content in the silica network resulted in the increase of six-membered siloxane rings. The hybrid systems were shown to be formed from fully-condensed, trifunctional APTES species. The porosity and morphology of the hybrid materials were influenced by the initial TEOS/APTES ratio. The radius of gyration of the primary particles, determined by SAXS, was between 1.1 and 2.9 nm.     

Tuning physical surface properties of tin dioxide nanopowders using zinc oxide as template

With a view to energetic and (opto)electronic applications, tin (IV) oxide (SnO₂) nanoparticles have been successfully prepared at the nanoscale by a templating approach based on the use of zinc (II) oxide (ZnO) as template. The procedure consisted in preparing a mixture of tin precursor and template, subsequently calcined at 650 °C under air to lead to the formation of a SnO₂/ZnO composite material. Finally, the material was washed with an alkali solution to remove the template. The template/tin precursor mass ratio was varied in order to tailor the tin (IV) oxide material, especially with a view to main particle size. The resulting SnO₂ nanomaterials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption and electron microscopy. The tin (IV) oxide nanomaterial exhibited enhanced textural and physical surface properties (particle size, surface area, pore size) correlated to an increasing template/tin precursor mass ratio. For instance, from optimized experimental conditions, the specific surface area and pore volume were heightened twofold, reaching values of 49 m²/g and 0.32 cm³/g, respectively.     

Synthesis and characterization of a new tin(IV) complex for fabrication of an organic light-emitting diode (OLED) and photoluminescence properties of the tin oxide core

A new tin(IV) complex, (C₁₃H₁₀NO)[SnCl₄(C₉H₆NO)]·2CH₃OH, was prepared in a facile process and characterized by ¹H, ¹³C, and ¹¹⁹Sn NMR, IR, and UV spectroscopy in addition to single-crystal X-ray diffraction analysis. Current–voltage (I–V) characteristics, photoluminescence (PL), and electroluminescence (EL) properties of the complex have been investigated and an application of the prepared complex in fabrication of an organic light-emitting diode has been demonstrated. The EL of the compound exhibits blue–green emission at 494?nm. Tin(IV) oxide core that resulted from direct thermal decomposition of the complex at 450?°C in air was characterized by X-ray powder diffraction and scanning electron microscopy; then, the PL property was investigated and compared with the PL of the complex. The tin(IV) oxide core showed a band gap of ～3.81?eV determined from the UV/visible absorption spectrum. The tin oxide core showed stable PL with one emission peak centered at 581?nm.     

A novel catalyst based on electrospun silver-doped silica fibers with ribbon morphology

Mesoporous silica nanofibers and Ag-doped composite nanoribbons were synthesized by a facile combination of an electrospinning technique and the sol–gel method. Tetraethyl orthosilicate, polyvinylpyrrolidone (PVP), triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), copolymer Pluronic P123, and silver nitrate (AgNO₃) were the components of sol for the production of Ag-doped hybrid silica ribbons. Heat removal of structure-directing agent P123 in the hybrid fibers at high temperatures resulted in a mesoporous morphology, and the degradation of PVP caused AgNO₃ to convert into silver in the form of nanoparticles. The size and content of the particles in the hybrid ribbons could be controlled by the concentration of AgNO₃ and thermal treatment conditions. Scanning electron microscopy, N₂ adsorption–desorption isotherm, transmission electron microscopy, X-ray diffraction, and UV–Vis spectroscopy were used to characterize the composite ribbons. The catalytic activity of the ribbons was evaluated by reduction of methylene blue dye and found to be better than in previous studies.     

Spherical hybrid silica particles modified by methacrylate groups

Organic–inorganic hybrid materials have been used as fillers to reinforce dental resin composites, which require strengthening to improve their performance in large stress-bearing applications such as crowns and multiple-unit restorations. Homogeneous organic–inorganic hybrid materials with high performance were prepared by mixing 3-methacryloxypropyltrimethoxysilane (MPTS) and tetraethylorthosilicate (TEOS) synthesized by the sol–gel route. The matrix was prepared by hydrolyzing and condensing the TEOS and MPTS, using basic catalysis and excess water. The resulting xerogel was treated at 50, 100, 150, and 200 °C for 4 h, and the structure was analyzed by thermogravimetry (TG/DTA), photoluminescence (PL), nuclear magnetic resonance (NMR ²⁹Si and ¹³C), transmission electron microscopy (TEM), infrared spectroscopy (IR), and Raman spectroscopy. The PL spectra displayed the Eu³⁺ lines characteristic of ⁵D₀ → ⁷F_{J (J = 0, 1, 2, 3, 4)} ions, and the blue emission was ascribed to the silica matrix. TG, MNR and infrared spectroscopy analyses indicated the hybrid silica was stable, with the organic part present up to 150 °C. Increasing the temperature of the heat treatment was found to increase the degree of hydrolysis. The size and morphology of the silica particles were identified by TEM.     

Modification of a Pt surface by spontaneous Sn deposition for electrocatalytic applications

In the present communication we explored a simple dip-coating method for spontaneous (without applying an external current or additional reducing agents) modification of Pt surface by both tin oxy-species and tin metal based on hydrolysis of tin chloride complex and autocatalytic (electroless) deposition of tin for fabrication of the fuel cell catalysts with improved CO tolerance. It consisted of (i) Pt immersion into SnCl₂/HCl solution under open-circuit conditions; (ii) subsequent rinsing of the surface by pure water. The resulting Sn-modified Pt surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). Two types of tin species, namely, tin oxide/hydroxide species and metallic tin were identified at Pt surface. Tin oxide/hydroxide species were assumed to be derived as a result of Sn(II) chloride complex hydrolysis, while tin metal particles were most likely deposited spontaneously on Pt surface due to disproportionation of Sn(II) to Sn(IV) and metallic tin, competing with dissolution of the Sn deposit in strongly acidic medium. Modifying tin species show a satisfactory stability in 0.5-M H₂SO₄ solution at potentials relevant to low-temperature fuel cell operating conditions (below 0.6 V vs. a standard hydrogen electrode, SHE).     

Preparation and Characterization of the Hybrids Containing Silica Nanoparticles by Sol-Gel Crosslinking Process

The organic/inorganic hybrid nanomaterials containing silica nanoparticles are synthesized by sol-gel crosslinking process. The tetraethoxysilane (TEOS) and γ-aminopropyltriethoxylsilane as coupling agents are used as a precursor. The 2,4,6-tri [(2-epihydrin-3-bimethyl-ammonium)propyl]-1,3,5-triazine chloride (Tri-EBAC) as crosslinking agent is used to form covalent bonds among the inorganic nanoparticles. The chemical and morphological structures of the organic/inorganic hybrid are characterized with FTIR spectra, ²⁹Si-NMR, x-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and atomic force microscope (AFM). The results show that the organic/inorganic hybrid forms covalent bond between the inorganic nanoparticle and Tri-EBAC. The network organic/inorganic hybrid can form good film with even nanometer particles. The network organic/inorganic hybrids nanomaterial not only exhibits the thermal properties of inorganic compounds, but also exhibits the thermal properties of organic polymer.     

Colloidal nanocomposite hydrogel particles

Quaternary ammonium salt, (3-acrylamidopropyl)-trimethylammonium chloride was used to synthesize nanohydrogel and composite particles such as inorganic–organic hybrid composites and hydrogel nanoparticles with magnetic properties utilizing a water-in-oil microemulsion system. The positively charged cationic monomer was chosen to promote silica hydrolysis and condensation to prepare silica-hydrogel nanocomposite particles with interesting morphologies. It was shown that highly monodisperse, completely charged nanohydrogel can be used to encapsulate ferrite particles. Furthermore, it was also confirmed that cationic nanohydrogel particles with variant morphology can be prepared by employing suitable silica precursor. Morphology, structure, properties, and size of nanocomposite materials were explored utilizing transmission electron microscopy, atomic force microscopy, and vibrating sample magnetometer.     

以微凝胶模板合成P(AM-co-DMC)/SiO_2杂化粒子

以聚(丙烯酰胺-co-甲基丙烯酰氧乙基三甲基氯化铵)[P(AM-co-DMC)]微凝胶为模板,TMOS为硅前驱体,中性水环境下合成了一系列P(AM-co-DMC)/SiO2有机-无机杂化粒子.对杂化粒子的大小、形态及表面形貌等进行研究,发现微凝胶对杂化粒子的形态和大小起主导作用,SiO2在模板上沉积,即使经过灼烧依然保持模板的形态;TMOS的用量对杂化粒子的性质也有重要影响——用量少时,得到的杂化粒子表面粗糙,增加用量会使表面变得光滑.杂化粒子经过灼烧后,表面会变得更加粗糙.     

Fabrication and photocatalytic properties of SnO2 double-shelled and triple-shelled hollow spheres

SnO₂ double-shelled and triple-shelled hollow spheres were tailored by adjusting concentration of tin (IV) chloride solution during the process of the tin (IV) ions infused carbonaceous spheres. The structures of these SnO₂ multi-shelled hollow spheres were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and their possible formation mechanism were also discussed. In virtue of triple-shelled hollow porous structure and higher specific surface area, SnO₂ triple-shelled hollow spheres exhibited enhanced photocatalytic properties compared to SnO₂ double-shelled hollow spheres.     

Nonenzymatic H2O2 Electrochemical Sensor Based on SnO2‐NPs Coated Polyethylenimine Functionalized Graphene

This paper demonstrated using polyethylenimine (PEI)‐functionalized graphene (Gr) incorporating tin oxide (SnO₂) hybrid nanocomposite as a platform for nonenzymatic H₂O₂ electrochemical sensor. The results of UV‐vis spectroscopy and X‐ray diffraction (XRD) confirmed the simultaneous formation of tin oxide (SnO₂) nanocomposite and reduction of graphene oxide (GO). Transmission electron microscopy (TEM) images showed a uniform distribution of nanometer‐sized tin oxide nanoparticles on the grapheme sheets, which could be achieved using stannous chloride (SnCl₂) complex instead of tin oxide as precursor. The electrochemical measurements, including cyclic voltammetry (CV) and amperometric performance (I‐t), showed that the PEI‐functionalized Gr supported SnO₂ (SnO₂‐PEI‐Gr) exhibited an excellent electrocatalytic activity toward the H₂O₂. The corresponding calibration curve of the current response showed a linear detection range of 9×10⁻⁶∼1.64×10⁻³ mol L⁻¹, while the limit of detection was estimated to be 1×10⁻⁶ mol L⁻¹. Electrochemical studies indicated that SnO₂ and functionalized Gr worked synergistically for the detection of H₂O₂.     

Biomimetic synthesis of raspberry-like hybrid polymer–silica core–shell nanoparticles by templating colloidal particles with hairy polyamine shell

The nanoparticles composed of polystyrene core and poly[2-(diethylamino)ethyl methacrylate] (PDEA) hairy shell were used as colloidal templates for in situ silica mineralization, allowing the well-controlled synthesis of hybrid silica core–shell nanoparticles with raspberry-like morphology and hollow silica nanoparticles by subsequent calcination. Silica deposition was performed by simply stirring a mixture of the polymeric core–shell particles in isopropanol, tetramethyl orthosilicate (TMOS) and water at 25 °C for 2.5 h. No experimental evidence was found for nontemplated silica formation, which indicated that silica deposition occurred exclusively in the PDEA shell and formed PDEA–silica hybrid shell. The resulting hybrid silica core–shell particles were characterized by transmission electron microscopy (TEM), thermogravimetry, aqueous electrophoresis, and X-ray photoelectron spectroscopy. TEM studies indicated that the hybrid particles have well-defined core–shell structure with raspberry morphology after silica deposition. We found that the surface nanostructure of hybrid nanoparticles and the composition distribution of PDEA–silica hybrid shell could be well controlled by adjusting the silicification conditions. These new hybrid core–shell nanoparticles and hollow silica nanoparticles would have potential applications for high-performance coatings, encapsulation and delivery of active organic molecules.     

Label-Free Electrochemiluminescent Determination of DNA Using Luminol and Hemin Functionalized Nanoparticles

Luminol and hemin dual-functionalized silica nanoparticles were synthesized using a typical reverse water-in-oil microemulsion protocol. The obtained nanoparticles were further characterized by transmission electron microscopy, scanning electron microscopy, atomic absorption spectrometry, chemiluminescence, and electrochemiluminescence. The results indicated that the luminol and hemin dual-functionalized silica nanoparticles exhibited significantly higher chemiluminescence and electrochemiluminescence intensities than those of luminol functionalized silica nanoparticles due to the catalytic effect of hemin on the chemiluminescence and electrochemiluminescence of luminol. Furthermore, a simple and sensitive label-free electrochemiluminescence DNA biosensor was developed based on the chitosan modified luminol and hemin dual-functionalized silica nanoparticles and a single-stranded DNA probe. The chitosan modified luminol and hemin dual-functionalized silica nanoparticles were immobilized on the surface of an indium-doped tin oxide electrode and the single-stranded DNA probe was immobilized on the surface of the nanoparticles through electrostatic interactions between single-stranded DNA and chitosan, which allowed hybridization with the target DNA sequences. The hybridization events were evaluated by electrochemiluminescence, and only the complementary sequence formed double-stranded DNA with the DNA probe to give strong electrochemiluminescence signals. Finally, the electrochemiluminescence intensity was found to be linearly related to the concentration of the complementary sequence at concentrations from 1.0?×?10^?12 to 1.0?×?10^?6?mol·L^?1 with a detection limit of 5.0?×?10^?13?mol·L^?1.     

High Refractive Index Films Prepared from Titanium Chloride and Methyl Methacrylate via a Non-Aqueous Sol–Gel Route

Poly(methylmethacrylate)/silica/titania films were prepared via a nonaqueous sol–gel route at ambient temperature, followed by spin-coating and multistep baking. The acrylic monomers used were methyl methacrylate (MMA) and 3-(trimethoxysilyl)propyl methacrylate (MSMA). Silicic acid and titanium(IV) chloride were used as the precursors of the inorganic component. FTIR results indicated the successful bonding between TiO₂ and SiO₂. TEM images suggested the silica/titania particles were well dispersed in the Poly(methyl methacrylate) (PMMA) matrix with the particles size smaller than 40 nm in our study. The refractive index and extinction coefficient were also studied. The refractive index of the hybrid increased with increasing the titania content, and the hybrid films showed high optical transparency in visible region.     

Ionic liquid-modified silica as a new stationary phase for chromatographic separation

A new stationary phase based on silica modified with 1-methyl-3-propylimidazolium chloride was synthesized and characterized in this paper. A derivative of 1-methyl-3-propylimidazolium chloride was used to chemically modify the surface of silica particles to act as the stationary phase for HPLC. The modified particles were characterized by Fourier Transform Infrared (FT-IR), ¹³C NMR spectroscopy and thermogravimetric analysis (TGA). The surface modification procedure rendered particles with a surface coverage of 0.89 μmol/m² of alkylimidazolium chloride. Columns packed with the modified silica and blank silica particles were tested under HPLC conditions. Preliminary evaluation of the stationary phase for HPLC was performed using aromatic compounds as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic and electrostatic interactions.     

Electrochemical deposition and characterization of polyppyrrole coatings doped with nickel cobalt oxide for environmental applications

Electrochemical depositions of hybrid polypyrrole/nickel cobalt oxide (PPy/NiCoO) coatings onto ferritic stainless steel surface were carried out with different electrochemical techniques from 0.1 M pyrrole (Py) in 0.2-M oxalic acid (OA) solution and less than 150-nanometer-sized NiCoO particles. The structural properties of the composite were investigated by using different methods such as transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometer (EDS) and Raman spectroscopy. The embedded NiCoO particles, uniformly distributed onto the surface of the PPy film, have similar oxide ratios corresponding to a mixed oxide structure. The electrochemical characterization was done using polarization curves and linear sweep voltammetry (LSV) related to oxygen reduction reaction (ORR) in alkaline solution and hydrogen peroxide as an oxygen source. Concerning the exchange current densities for ORR, the obtained values (between 1.06 and 1.45?×?10^?3 mA cm^?2 for a total amount of NiCoO of 0.1 mg cm^?2) are comparable with other polymer films with Pt.     

Mechanism for the formation of tin oxide nanoparticles and nanowires inside the mesopores of SBA-15

The formation of polycrystalline tin oxide nanoparticles (NP) and nanowires was investigated using nanocasting approach included solid-liquid strategy for insertion of SnCl₂ precursor and SBA-15 silica as a hard template. HR-TEM and XRD revealed that during the thermal treatment in air 5 nm tin oxide NP with well defined Cassiterite structure were formed inside the SBA-15 matrix mesopores at 250 °C. After air calcination at 700 °C the NP assembled inside the SBA-15 mesopores as polycrystalline nanorods with different orientation of atomic layers in jointed nanocrystals. It was found that the structure silanols of silica matrix play a vital role in creating the tin oxide NP at low temperature. The pure tin chloride heated in air at 250 °C did not react with oxygen to yield tin oxide. Tin oxide NP were also formed during the thermal treatment of the tin chloride loaded SBA-15 in helium atmosphere at 250 °C. Hence, it is well evident that silanols present in the silica matrix not only increase the wetting of tin chloride over the surface of SBA-15 favoring its penetration to the matrix pores, but also react with hydrated tin chloride according to the proposed scheme to give tin oxide inside the mesopores. It was confirmed by XRD, N₂-adsorption, TGA-DSC and FTIR spectra. This phenomenon was further corroborated by detecting the inhibition of SnO₂ NP formation at 250 °C after inserting the tin precursor to SBA-15 with reduced silanols concentration partially grafted with tin chloride.     

Size-controlled synthesis of SnO2 nanoparticles using reverse microemulsion method

Tin oxide nanoparticles were prepared using an ionic surfactant (sodium dodecyl sulfate) and tin (IV) chloride as an inorganic precursor via the reverse microemulsion method. The size of the nanoparticles is controlled by variation of water-to-surfactant ratio. Eliminating of surfactant in prepared nanoparticles was confirmed by the infrared spectroscopy after sequential calcinations. Transmission electron microscopy, surface area, pore volume, average pore diameter, pore size distribution and X-ray diffraction results were used for evaluation of size distribution, shape and structure of prepared SnO₂ nanoparticles. Transmission electron micrographs confirmed that the obtained materials are spherical nanoparticles. The X-ray diffraction results show the crystalline phases of all samples are SnO₂ with tetragonal structured crystal. In addition, the X-ray diffraction and transmission electron microscopy data showed that the size of SnO₂ nanoparticles decreased with decreasing the water-to-surfactant ratio.     

Direct formation of thermally stabilized amorphous mesoporous Fe2O3/SiO2 nanocomposites by hydrolysis of aqueous iron III nitrate in sols of spherical silica particles

Nanocomposite materials containing 10% and 20% iron oxide/silica, Fe2O3/SiO2 (w/w), were prepared by direct hydrolysis of aqueous iron III nitrate solution in sols of freshly prepared spherical silica particles (St?ber particles) present in their mother liquors. This was followed by aging, drying, calcination up to 600 degrees C through two different ramp rates, and then isothermal calcinations at 600 degrees C for 3 h. The calcined and the uncalcined (dried at 120 degrees C) composites were characterized by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), N2 adsorption/desorption techniques, and scanning electron microscopy as required. XRD patterns of the calcined composites showed no line broadening at any d-spacing positions of iron oxide phases, thereby reflecting the amorphous nature of Fe2O3 in the composite. The calcined composites showed nitrogen adsorption isotherms characterizing type IV isotherms with high surface area. Moreover, surface area increased with the increasing of the iron oxide ratio and lowering of the calcination ramp rate. Results indicated that iron oxide particles were dispersed on the exterior of silica particles as isolated and/or aggregated nanoparticles. The formation of the title composite was discussed in terms of the hydrolysis and condensation mechanisms of the inorganic FeIII precursor in the silica sols. Thereby, fast nucleation and limited growth of hydrous iron oxide led to the formation of nanoparticles that spread interactively on the hydroxylated surface of spherical silica particles. Therefore, a nanostructured composite of amorphous nanoparticles of iron oxide (as a shell) spreading on the surface of silica particles (as a core) was formed. This morphology limited the aggregation of Fe2O3 nanoparticles, prevented silica particle coalescence at high temperatures, and enhanced thermal stability.     

Synthesis of raspberry‐like organic–inorganic hybrid nanocapsules via pickering miniemulsion polymerization: Colloidal stability and morphology

Raspberry‐like hybrid nanocapsules with a hydrophobic liquid core were successfully prepared via the copolymerization of styrene, divinylbenzene (DVB), and 4‐vinyl pyridine (4‐VP) in Pickering‐stabilized miniemulsions by using silica particles as the sole emulsifier and hexadecane (HD) as liquid template. When compared with conventional Pickering miniemulsions and Pickering suspensions, the colloidal stability of the current systems is much more sensitive to the variation of reaction parameters such as pH, size, amount of silica particles, and content of 4‐VP. The systems without coagulum were only obtained in a narrow pH range at around 9.5 and by using 12 nm silica particles as emulsifier. The formation of well‐defined raspberry‐like capsules was confirmed by transmission electron microscopy (TEM) and high‐resolution scanning electron microscopy (HRSEM). The stable attachment of silica particles on the surface of hybrid particles was verified by centrifugation and subsequent characterizations, such as Fourier transform infrared spectroscopy, TEM, and HRSEM. The influence of pH and weight content of HD, DVB, and 4‐VP on the particle morphology was extensively investigated. Interestingly, the particle morphology strongly depends on the particle size. When compared with the organic surface‐active surfactant, the formation of capsule morphology could be promoted by the application of silica particles taking advantage of their surface inactivity. The formation mechanisms of capsules/solid particles are discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011