oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Ultrasensitive Detection of Glyphosate Using CdTe Quantum Dots in Sol-Gel-Derived Silica Spheres Coated with Calix[6]arene as Fluorescent Probes  [PDF]
Tao Li, Yunyou Zhou, Junyong Sun, Kai Wu
American Journal of Analytical Chemistry (AJAC) , 2012, DOI: 10.4236/ajac.2012.31003
Abstract: We have developed a simple method for the preparation of highly fluorescent and stable, water-soluble CdTe quantum dots in sol-gel-derived composite silica spheres which were coated with calix[6]arene. The resulting nanoparticles (NPs) were characterized in terms of UV, fluorescence and FT-IR spectroscopy and TEM. The results show that the new NPs display more intense fluorescence intensity and are more stable than its precursors of the type SiO2/CdTe. Under the optimum, the novel NPs exhibit a higher selectivity and ultrasensitive fluorescence probes for the determination of gly-phosate over other pesticides, the fluorescence intensity increase with the concentration of glyphosate in the range from 1.0 to 25.0 nmol/L and the detection limit is low to 0.0725 nmol/L. A mechanism is suggested to explain the inclusion process by a Langmuir binding isotherm.
Characterization and Modification of Mesoporous Silica Nanoparticles Prepared by Sol-Gel  [PDF]
Meysam Keshavarz,Norhayati Ahmad
Journal of Nanoparticles , 2013, DOI: 10.1155/2013/102823
Abstract: Mesoporous silica nanoparticles (MSNs) were synthesized by sol-gel reaction at normal pressure by using TEOS as a silica source and CTAB as a directing agent in ammonia solution at 323?K subsequently calcined at 823?K. Then inorganic pores were modified with metal-supported MSN with attention to the acidity, surface area, pore size, and ability of ion exchange. Crystalline size was shown to decrease up to 20 molar ratios of Si/Al followed by increasing while further adding nanoparticles-aluminium. Moreover, the XRD patterns revealed the mesostructured material for all with 2D hexagonal structure. The obtained results from the XRD patterns were confirmed by using BET and EDX. The BET surface areas revealed the spherical shape for all samples with a decrease in the pore volume and surface area for various AlMSNs which emphasized that the loading of Al and was compatible with XRD results. MSN was prepared by sol-gel methods followed by loading of Al in order to prepare AlMSN which possess strong Lewis acidic sites. This modification occurred by using various molar ratios of 0, 5, 10, 20, 50, and 100 Si/Al, respectively. The XRD patterns of various ratios of Si/Al were interpreted in terms of strain, nanocrystalline size, and distribution of the particle size by deriving Wiliamson Hall equation. 1. Introduction More than 10 years passed since the discovery of the so-called M41S mesoporous silica materials, and the synthesis of the mesoporous materials with different characterizes has been gaining increasing attention. This study attempts to reveal the dependence effect of various ratios of Si/Al additive on nanocrystalline size, residual stress and physicochemical property of mesostructure siliceous nanoparticles (MSN) which can give a better insight of its application on petroleum refinery and petrochemical industries. Moreover, the nobility of this research might be the utilization of XRD pattern to find out nanocrystalline size, residual stress, and microstructure. The surfactant-templating method has been extended to the synthesis of nonsilica oxide mesoporous materials [1–3]. Potential application of mesoporous transition metal oxides has been found in the fields of electromagnetic, photoelectronics, catalysis, and separation [4]. By using cationic surfactants with quaternary ammonium derivatives and then nonionic alkoxysilanes, a series of ordered mesoporous silicas had been synthesized [5–7] and the various alkaline or acidic [8–10] conditions were used. These experiments have shown better condensation of the silanol groups in mesoporous silica
Synthesis of Silica Nanoparticles by Sol-Gel: Size-Dependent Properties, Surface Modification, and Applications in Silica-Polymer Nanocomposites—A Review
Ismail Ab Rahman,Vejayakumaran Padavettan
Journal of Nanomaterials , 2012, DOI: 10.1155/2012/132424
Abstract: Application of silica nanoparticles as fillers in the preparation of nanocomposite of polymers has drawn much attention, due to the increased demand for new materials with improved thermal, mechanical, physical, and chemical properties. Recent developments in the synthesis of monodispersed, narrow-size distribution of nanoparticles by sol-gel method provide significant boost to development of silica-polymer nanocomposites. This paper is written by emphasizing on the synthesis of silica nanoparticles, characterization on size-dependent properties, and surface modification for the preparation of homogeneous nanocomposites, generally by sol-gel technique. The effect of nanosilica on the properties of various types of silica-polymer composites is also summarized.
Preparation and Characterization of Silica and Clay-Silica Core-Shell Nanoparticles Using Sol-Gel Method  [PDF]
Olfat M. Sadek, Safenaz M. Reda, Reem K. Al-Bilali
Advances in Nanoparticles (ANP) , 2013, DOI: 10.4236/anp.2013.22025
Abstract:

Silica and montmorillonite-supported silica nanoparticles were prepared via an acid one step sol-gel process. The synthesized solids were characterized using XRD, FTIR, TEM and N2 adsorption. The effect of preparing temperatures on the structure and properties of the silica nanoparticles were studied. The results show that the increase of annealing temperature from 25 to 200, don’t change amorphous state of silica. While for montmorillonite-supported silica the clay platelets are delaminated during the sol-gel process. TEM results showed that the average particle size of silica is increased by increasing temperature due to the particle sintering and the clay-silica nanoparticles possessed core–shell morphology with diameter of 29 nm. The surface area measurements showed that by increasing annealing temperature the surface area was decreased due to aggregation of particle. The clay-silica sample showed lower average pore width than that of the silica prepared at 200 indicating that it has a macropores structure. The adsorption efficiency of the prepared samples was tested by adsorption of protoporphyrin IX. The highest adsorption efficiency was found for SiO2 prepared at 200. Temkin model describe the equilibrium of adsorption of

Synthesis of silica nanoparticles from Vietnamese rice husk by sol--gel method
Van Hai Le, Chi Nhan Thuc and Huy Ha Thuc
Nanoscale Research Letters , 2013, DOI: 10.1186/1556-276X-8-58
Abstract: Silica powder at nanoscale was obtained by heat treatment of Vietnamese rice husk following the sol--gel method. The rice husk ash (RHA) is synthesized using rice husk which was thermally treated at optimal condition at 600[degree sign]C for 4 h. The silica from RHA was extracted using sodium hydroxide solution to produce a sodium silicate solution and then precipitated by adding H2SO4 at pH = 4 in the mixture of water/butanol with cationic presence. In order to identify the optimal condition for producing the homogenous silica nanoparticles, the effects of surfactant surface coverage, aging temperature, and aging time were investigated. By analysis of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the silica product obtained was amorphous and the uniformity of the nanosized sample was observed at an average size of 3 nm, and the BET result showed that the highest specific surface of the sample was about 340 m2/g. The results obtained in the mentioned method prove that the rice husk from agricultural wastes can be used for the production of silica nanoparticles.
Magneto-optic Faraday effect in maghemite nanoparticles/silica matrix nanocomposites prepared by the Sol-Gel method  [PDF]
M. Dominguez,D. Ortega,J. S. Garitaonandia,R. Litran,C. Barrera-Solano,E. Blanco,M. Ramirez-del-Solar
Physics , 2012, DOI: 10.1016/j.jmmm.2008.04.022
Abstract: Bulk monolithic samples of {\gamma}-Fe2O3/SiO2 composites with different iron oxide/silica ratios have been prepared by the sol-gel technique. Iron oxide nanoparticles are obtained in-situ during heat treatment of samples and silica matrix consolidation. Preparation method was previously optimized to minimize the percentage of antiferromagnetic {\alpha}-Fe2O3 and parallelepipeds of roughly 2x5x12 mm3, with good mechanical stability, are obtained. RT magnetization curves show a non-hysteretic behavior. Thus, magnetization measurements have been well fitted to an expression that combines the Langevin equation with an additional linear term, indicating that some of the nanoparticles are still superparamagnetic as confirmed by X-ray diffraction and electron microscopy measurements. Zero field cooled /field cooled experiments show curves with slightly different shapes, depending on the size and shape distribution of nanoparticles for a given composition. Magneto-optical Faraday effect measurements show that the Faraday rotation is proportional to magnetization of the samples, as expected. As a demonstration of their sensing possibilities, the relative intensity of polarized light, measured at 5{\deg} from the extinction angle, was plotted versus applied magnetic field.
Spin-Coated Erbium-Doped Silica Sol-Gel Films on Silicon  [PDF]
Sufian Abedrabbo,Bashar Lahlouh,Sudhakar Shet,Anthony Fiory,Nuggehalli Ravindra
Physics , 2012,
Abstract: This work reports optical functionality contained in, as well as and produced by, thin film coatings. A sol-gel process, formulated with precursor active ingredients of erbium oxide and tetraethylorthosilicate (TEOS), was used for spin-coating thin (~130 nm) erbium-doped (~6 at. %) silica films on single-crystal silicon. Annealed films produce infrared emission in the 1.5-micron band from erbium ions in the film, as well as greatly enhancing (~100X) band-gap emission from the underlying silicon. The distinctly different mechanisms for the two modes of optical activities are interpreted in terms of optical emission theory and modeling; prospects for opto-electronic applications are discussed.
Fabrication of Magnetite/Silica/Titania Core-Shell Nanoparticles  [PDF]
Suh Cem Pang,Sze Yun Kho,Suk Fun Chin
Journal of Nanomaterials , 2012, DOI: 10.1155/2012/427310
Abstract: Fe3O4/SiO2/TiO2 core-shell nanoparticles were synthesized via a sol-gel method with the aid of sonication. Fe3O4 nanoparticles were being encapsulated within discrete silica nanospheres, and a layer of TiO2 shell was then coated directly onto each silica nanosphere. As-synthesized Fe3O4/SiO2/TiO2 core-shell nanoparticles showed enhanced photocatalytic properties as evidenced by the enhanced photodegradation of methylene blue under UV light irradiation. 1. Introduction Over the past decades, titanium dioxide (TiO2) nanoparticles have gained much attention as a photocatalyst and catalyst support [1, 2]. TiO2 nanoparticles have many advantages as compared to other photocatalysts, which include excellent high stability against chemical and photonic corrosion and high photocatalytic activity [3]. TiO2 nanoparticles of small mean particle sizes possess high surface area and photocatalytic activity. However, TiO2 nanoparticles of high surface area are thermally unstable and lose their surface area readily [3]. Therefore, much effort has been focused on coating of TiO2 on high surface area supports such as silica or alumina in order to stabilize TiO2 nanoparticles. TiO2 nanoparticles could be difficult to recover and lost readily upon being dispersed into wastewater. One of the ways to overcome this problem is to coat TiO2 onto magnetite (Fe3O4) cores and the resulting Fe3O4/TiO2 core-shell nanoparticles can be recovered easily through manipulation by external magnetic field. Li et al. synthesized Fe3O4/TiO2 nanocomposite photocatalyst using a sol-gel method [3]. However, it was difficult to achieve complete coating of Fe3O4 nanoparticles with TiO2 at nanometer scale using the sol-gel method. Besides, TiO2 would oxidize Fe3O4 nanoparticles and lead to a reduction of magnetic moment. Some researchers had attempted to coat a thin layer of SiO2 between Fe3O4 nanoparticles and TiO2 shell. The presence of a SiO2 layer between TiO2 shell and Fe3O4 nanoparticles could increase the lifetime of photogenerated holes which in turn, resulted in increased photoreactivity [3, 4]. This is attributed to the SiO2 layer which serves as an insulating layer between Fe3O4 nanoparticles (hole-electron trap center) and the TiO2 shell. However, there are currently very few literature which report on the synthesis of Fe3O4/SiO2/TiO2 core-shell nanoparticles and their photocatalytic properties. Besides, the reported synthesis methods for Fe3O4/SiO2 nanoparticles were generally complicated and time consuming. Besides, the coating of Fe3O4 with SiO2 using TEOS was a very slow process
Preparation of AgI/Silica/Poly(Ethylene Glycol) Nanoparticle Colloid Solution and X-Ray Imaging Using It  [PDF]
Yoshio Kobayashi,Tetsuya Ayame,Tomohiko Nakagawa,Yohsuke Kubota,Kohsuke Gonda,Noriaki Ohuchi
ISRN Nanomaterials , 2013, DOI: 10.1155/2013/670402
Abstract: This work performed X-ray imaging of mouse by using aqueous colloid solution of AgI nanoparticles coated with silica (AgI/SiO2) and then surface-modified with poly(ethylene glycol) (PEG) (AgI/SiO2/PEG). A colloid solution of AgI nanoparticles was prepared by mixing silver perchlorate and potassium iodide in water. The AgI nanoparticles were surface-modified with 3-mercaptopropyltrimethoxysilane and then were silica-coated by a sol-gel reaction between tetraethylorthosilicate and H2O catalyzed with NaOH in ethanol. The AgI/SiO2 particle surface was modified with PEG by using methoxy PEG silane . The AgI/SiO2/PEG colloid solution revealed a computed tomography value as high as 1343.6?HU at an iodine concentration of 0.1?M, which was higher than a commercial X-ray contrast agent with the same iodine concentration. Tissues of mouse could be imaged by injecting the concentrated colloid solution into them. 1. Introduction X-ray imaging is one of the quite useful techniques for medical diagnosis. Chemicals composed of iodine absorb strongly X-ray. This property has been utilized for making X-ray images clearer, or taking high contrast images. Various iodine compounds have been thus far proposed as X-ray contrast agents [1–5], and several iodine compounds are commercially available. The iodine compounds, however, cannot be used for patients, in which adverse events as allergic reactions may be provoked by the iodine compounds [6–8]. In iodine compound nanoparticles coated with shell of materials inert for living bodies, that is, core-shell particles composed of core of iodine compound nanoparticles and shell of materials inert for living bodies, the shell prevents the iodine compound particles from contacting with living bodies. As a result, toxicity of iodine compounds will decrease. Several researchers have extensively performed coating of nanoparticles with silica, which is inert for living bodies [9–15]. Their coating methods are based on a sol-gel process. Our research group has studied silica coating of various nanoparticles with the sol-gel process [16–26]. Our group has also proposed a method for silica coating of nanoparticles of silver iodide (AgI) that is one of the iodine compounds [27–35]. The present work performed synthesis of colloid solution of silica-coated AgI nanoparticles (AgI/SiO2) by our proposed method. Furthermore, the AgI/SiO2 nanoparticles were surface-modified with poly(ethylene glycol) (PEG) (PEGylation), which is expected to improve its imaging ability in living bodies. X-ray imaging ability of the colloid solution of the PEGylated
Effect of Solvent Content on the Properties of Nanostructure Silica Thin Film by Sol-Gel
Nanoscience and Nanotechnology , 2012, DOI: 10.5923/j.nn.20120201.05
Abstract: It is known that silica sol-gel coatings microstructure depend on the components of the sol. In order to develop different microstructures of the silica coatings and comparing their optical properties, a variety of silica sols were prepared which were consist of TEOS, water, catalyst and changing the solvent content, at room temperature. Prepared glass surfaces were coated with silica sol using a dipping technique, with constant withdrawing rate. Prepared coatings were investigated by field-emission scanning electron microscopy (FE-SEM) and UV–Vis. spectroscopy. Transmittance spectra showed that silica coatings featured a distinct increase of substrate transmittance at all wavelengths (400-1100 nm). The result indicated that by increasing the solvent content, the porosity of coating increased and the coating was more densified therefore the silica coating transmittance increased by 3-4% points. FE-SEM showed that the nanostructure silica coating grain size were estimated ~20-40 nm.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.