Assembling Colloidal Silica into Porous Hollow Microspheres (original) (raw)
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Materials Letters, 2011
Silicate (7 to 12 μm) microspheres with porous shell were prepared via modified double emulsion (water 1 /oil/water 2) method mediated with N 2 pressure filtration and calcination to completely remove the organic components. With the addition of sodium polymethacrylate (Na-PA) into the aqueous solution of water 1 /oil/water 2 emulsion system then calcined, led to the formation of stable hierarchical macroporous (surface area: 42.94 m 2 /g) from mesoporous (surface area: 259.2 m 2 /g) shell wall of silicate hollow microspheres.
Effect of Synthesis Time on Morphology of Hollow Porous Silica Microspheres
Materials …, 2012
Hollow porous silica microspheres may be applicable as containers for the controlled release in drug delivery systems (DDS), foods, cosmetics, agrochemical, textile industry, and in other technological encapsulation use. In order to control the surface morphological properties of the silica microspheres, the effect of synthesis time on their formation was studied by a method of water-in-oil (W/O) emulsion mediated sol-gel techniques. An aqueous phase of water, ammonium hydroxide and a surfactant Tween 20 was emulsified in an oil phase of 1-octanol with a stabilizer, hydroxypropyl cellulose (HPC), and a surfactant, sorbitan monooleate (Span 80) with low hydrophile-lipophile balance (HLB) value. Tetraethyl orthosilicate (TEOS) as a silica precursor was added to the emulsion. The resulting silica particles at different synthesis time 24, 48, and 72 hours were air-dried at room temperature and calcinated at 773 K for 3 hours. The morphology of the particles was characterized by scanning electron microscopy and the particle size distribution was measured by laser diffraction. The specific surface areas were studied by 1-point BET method, and pore sizes were measured by Image Tool Software. Both dense and porous silica microspheres were observed after all three syntheses. Hollow porous silica microspheres were formed at 24 and 48 hours synthesis time. Under base catalyzed solgel solution, the size of silica particles was in the range of 5.4 μm to 8.2 μm, and the particles had surface area of 111 m 2 /g -380 m 2 /g. The longer synthesis time produced denser silica spheres with decreased pore sizes.
Microporous and Mesoporous Materials, 2009
Spherical mesoporous silica particles with tunable pore size and tunable outer particle diameter in the nanometer range were successfully prepared in a water/oil phase using organic templates method. This method involves the simultaneous hydrolytic condensation of tetraorthosilicate to form silica and polymerization of styrene into polystyrene. An amino acid catalyst, octane hydrophobic-supporting reaction component, and cetyltrimethylammonium bromide surfactant were used in the preparation process. The final step in the method involved removal of the organic components by calcinations, yielding the mesoporous silica particles. Interestingly, unlike common mesoporous materials, the particle with controllable pore size (4-15 nm) and particle diameter (20-80 nm) were produced using the method described herein. The ability to control pore size was drastically altered by the styrene concentration. The outer diameter was mostly controlled by varying the concentration of the hydrophobic molecules. Relatively large organic molecules (i.e. Rhodamine B) were well-absorbed in the prepared sample. Furthermore, the prepared mesoporous silica particles may be used efficiently in various applications, including electronic devices, sensors, pharmaceuticals, and environmentally sensitive pursuits, due to its excellent adsorption properties.
Synthesis of Nanoscale Mesoporous Silica Spheres with Controlled Particle Size
Chemistry of Materials, 2002
A simple one-step procedure is described for the synthesis of spherical mesoporous silica, in which the size of the particles is controlled over a range of diameters from 65 to 740 nm by varying the initial silicate/surfactant concentration under dilute conditions. The particles were characterized using X-ray diffraction, transmission electron microscopy, and liquid nitrogen adsorption. Synthesis using a charged template, cetyltrimethylammonium bromide, under aqueous conditions yielded particles of irregular spherical shape with highly ordered mesoporous channels. Synthesis under ethanol/water cosolvent conditions yielded smooth spheres with a starburst mesopore structure extending from the center of the particle to the circumference. All materials were thermally stable and exhibited two steps in their liquid nitrogen isotherms corresponding to reversible channel filling and non-reversible adsorption between particles. Mesopore volumes varied from 0.64 to 0.93 cm 3 g -1 and surface areas varied from 917 to 1373 m 2 g -1 . From analysis of mesopore geometry and overall particle shape a three-stage mechanism for synthesis is proposed.
Facile synthesis of hollow silica microspheres
Journal of Materials Chemistry, 2001
Hollow silica microspheres were synthesised at room temperature from a vortexed mixture of water and droplets of tetraethoxysilane (TEOS) containing 10 mol% aminopropyltriethoxysilane: droplets stabilized with the surfactant cetyltrimethylammonium bromide produced silica shells, 30.6 mm in mean diameter, whereas replacing the Br 2 counterion with [Co(B 9 C 2 H 11 ) 2 ] 2 gave an approximately hundred-fold decrease in the size of the hollow spheres. Organo-functionalized hollow microspheres containing a covalently linked dye moiety were prepared by replacing 5 mol% of TEOS with dinitrophenylaminotriethoxysilane in the reaction mixture, and encapsulation of TEOS-soluble additives within the silica shells was demonstrated by incorporating porphyrin molecules and particles into the ethoxysilane droplets.
Chemistry - A European Journal, 2015
A new dual soft-template system comprising the asymmetric triblock copolymer poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is used to synthesize hollow mesoporous silica (HMS) nanoparticles with a center void of around 17 nm. The stable PS-b-P2VP-b-PEO polymeric micelle serves as a template to form the hollow interior, while the CTAB surfactant serves as a template to form mesopores in the shells. The P2VP blocks on the polymeric micelles can interact with positively charged CTA + ions via negatively charged hydrolyzed silica species. Thus, dual soft-templates clearly have different roles for the preparation of the HMS nanoparticles. Interestingly, the thicknesses of the mesoporous shell are tunable by varying the amounts of TEOS and CTAB. This study provides new insight on the preparation of mesoporous materials based on colloidal chemistry.
Synthesis of monodispersed mesoporous spheres of submicron size amorphous silica
Glass Physics and Chemistry, 2011
A technique has been developed for synthesis of submicron monodispersed mesoporous spheres of amorphous silica from an alcohol-water-ammonia mixture by means of tetraethoxysilane hydrolysis in the presence of hexadecyltrimethylammonium bromide. The mechanism of sphere formation from aggre gates of close packed surfactant cylindrical micelles coated by silica has been proposed. The specific surface area in the synthesized spheres is higher than 800 m 2 /g, whereas the pore volume and average diameter are equal to 0.63 cm 3 /g and 3 nm, respectively. The average size of particles is shown to decrease twice after the tem perature of the synthesis is increased twice. According to the data of atomic force spectroscopy and dynamic light scattering, the average diameter of mesoporous spheres can be controllably varied in the range 300-1500 nm with a root mean square deviation of no more than 6%.
Size-controlled synthesis of monodispersed mesoporous silica nano-spheres under a neutral condition
Microporous and Mesoporous Materials, 2009
Under a neutral condition, monodispersed mesoporous silica nano-spheres (MSNs) with controllable size were synthesized. The effects of temperature, structure-directing agent (SDA), co-surfactant/co-solvent propanetriol (PT) and multistep addition modes on particle size and the dispersivity of MSNs were studied. The results showed that MSNs became bigger and more uniform in size with the increase of the temperature. Compared with single surfactant, the use of cationic-nonionic composite surfactants of CTAB and Brij-56 as SDA resulted in the improved dispersivity and regularity of spherical shape, and the decreased particle size of MSNs. PT as additive effectively improved the monodispersivity of MSNs. With the gradual increase of the PT concentration, PT played a role of co-surfactant at first and then of co-solvent, resulting in an unusual dependence of the particle size of MSNs on the PT concentration. Multistep addition modes further contributed to the uniformity and bigger size of MSNs.
Budded, Mesoporous Silica Hollow Spheres: Hierarchical Structure Controlled by Kinetic Self-Assembly
Advanced Materials, 2006
Dedicated to Professor Hexuan Li on the occasion of his 80th birthday Recently, mesoporous materials with hierarchical structures and well-defined morphologies have attracted much attention. [1] Besides possible practical applications, studies of mesoporous materials may also shed light on fundamental mechanisms of biomineralization. [2] Among the many types of mesoporous materials, hollow spheres are of significance because of their potential uses in encapsulation, drug-delivery, and controlled-release applications. Although many articles have been published describing the interior templating of mesoporous hollow particles using hard templates, [3] vesicles, [4] or emulsions, [5] the fabrication of hierarchical structures on the shell has rarely been reported. [6] In this Communication, we report a novel, single-step, emulsion-templating method to fabricate a unique, hierarchical morphology. Our products consist of budded, mesoporous silica hollow spheres. What distinguishes these structures from the traditional ones is that they combine two separate, distinct mesophases with different-sized mesovoids in a single hollow sphere. Specifically, the shell of the sphere is based on wormholelike mesoporous structures, while the protruding buds are formed from lamellar (vesicular) mesostructures. Our process utilizes the sodium salt of the anionic surfactant N-lauroylsarcosine (Sar-Na), which is commonly used in cosmetic and pharmaceutical industries due to its biodegradability and low toxicity. Instead of employing the usual emulsion-templating methods with nonpolar fluids such as trimethylbenzene, we employ a novel process in which the emulsion is generated by the acidification of a Sar-Na solution. As shown in Scheme 1, the addition of acid converts a portion of the Sar anions to Sar-H, which is an amphiphilic polar oil [7] that behaves as droplets. The condensation of the added silica precursors (3aminopropyltrimethoxysilane (APMS) and tetraethylorthosil