Synthesis Of Hollow Silica Spheres Research Articles

Polyethylenimine-assisted synthesis of hollow silica spheres without shape deformation

A self-templating method has been employed to explore both the concentration and size of template silica particles suitable for synthesis of rigid hollow spheres. Herein, polyethylenimine (PEI) was used as a surface protecting layer for the silica particles whose interiors were selectively dissolved in water to form the hollow particle structure. The morphology of hollow silica particles formed by the silica dissolution strongly depended on total surface area of the PEI-modified particles in aqueous solution. Spherical hollow particles were obtained in the range of low total surface area. In the range of high total surface area, however, hollow particle structures were deformed during the synthetic processes including the silica dissolution, centrifugation, and drying processes. The deformation phenomenon of hollow particles was explained using relative dimension of shell thickness to particle diameter. According to the total surface area of template silica particles studied above, the concentration of silica-coated gold nanorod in water was adjusted to selectively dissolve the particle interior, succeeding in hollow spherical particles containing a gold nanorod.

Facile synthesis of hollow silica spheres with nanoholes

The synthesis of designed nanostructures is an ultimate target of nanomaterial science. Here, silica spheres with nanoholes have been selectively prepared. Coating the necklace-like structured and magnetic nanoparticles along carbon nanotubes, which is an essential step of the simple synthetic procedure of silica hollow spheres, led to the formation of silica hollow spheres with controllable sized nanoholes in their shell walls. The synthesized hollow spheres with nanoholes would be a good support for loading large molecules, e.g. drugs and proteins.

Synthesis of Hollow Silica Spheres with Hierarchical Shell Structure by the Dual Action of Liquid Indium Microbeads in Vapor–Liquid–Solid Growth

Geometry-based adhesion arising from hierarchical surface structure enables microspheres to adhere to cells strongly, which is essential for inorganic microcapsules that function as drug delivery or diagnostic imaging agents. However, constructing a hierarchical structure on the outer shell of the products via the current microcapsule synthesis method is difficult. This work presents a novel approach to fabricating hollow microspheres with a hierarchical shell structure through the vapor-liquid-solid (VLS) process in which liquid indium droplets act as both templates for the formation of silica capsules and catalysts for the growth of hierarchical shell structure. This hierarchical shell structure offers the hollow microsphere an enhanced geometry-based adhesion. The results provide a facile method for fabricating hollow spheres and enriching their function through tailoring the geometry of their outer shells.

Hydrothermal Synthesis of Hollow Silica Spheres under Acidic Conditions

It is well-known that silica can be etched in alkaline media or in a unique hydrofluoric acid (HF) solution, which is widely used to prepare various kinds of hollow nanostructures (including silica hollow structures) via silica-templating methods. In our experiments, we found that stöber silica spheres could be etched in generic acidic media in a well-controlled way under hydrothermal conditions, forming well-defined hollow/rattle-type silica spheres. Furthermore, some salts such as NaCl and Na(2)SO(4) were found to be favorable for the formation of hollow/rattle-type silica spheres.

C12mimBr Ionic Liquid/SDS Vesicle Formation and Use As Template for the Synthesis of Hollow Silica Spheres

The phase behavior of an aqueous catanionic surfactant system, composed of a long-chain imidazolium ionic liquid 1-dodecyl-3-methylimidazolium bromide (C(12)mimBr) and sodium dodecyl sulfate (SDS), is described. The phase diagram of the catanionic system was determined by electrical conductivity measurements and the formation of vesicles in a birefringent L(alpha) phase characterized by transmission electron microscopy (TEM) and freeze-fracture transmission electron microscopy (FF-TEM). Rheological measurements were used to characterize the macroscopic properties of the birefringent L(alpha) phase. Both electrostatic and hydrophobic interactions contribute to the vesicle formation in the catanionic system. Compared to the DTAB/SDS aqueous solution, differences between the imidazolium and trimethylammonium headgroups geometric packing and charge density induce the different phase behavior in each system. Silica hollow spheres, with diameters 30-60 nm and a wall thickness of 8-10 nm, were prepared by using the vesicles as the templates. The hollow silica spheres were characterized by TEM, scanning electron microscopy (SEM), and nitrogen adsorption-desorption. The results suggest additional application for ionic liquid based vesicles to be used as templates for the synthesis of hollow inorganic materials.

The Preparation of Monodisperse Cationic Polystyrene and its Application to the Synthesis of Hollow Silica Spheres

The fabrication of hollow spheres with well defined size and morphology has been attracting much attention due to their unique structures and related physicochemical properties. Among the synthetic methods, the template-directed method is particularly interesting and extensively employed to fabricate hollow spheres due to templates available of essentially any size, shape, and chemistry. As a result, a new monodispersed cationic polystyrene (PS) template in this paper was fabricated by using 2-(methacryloyloxy) ethyltrimethylammonium chloride as co-monomer via emulsifier-free polymerization. The template not only can easily be tuned to the size, but can combine the advantages of hard-templating and soft-templating methods. Subsequently, we used cationic PS particles as templates to prepare hollow silica spheres – the results indicated that cationic templates can attract the assembly of tetraethylorthosilicate hydrolyzate on their surface and that the dissolution of templates can be done in the system of silica encapsulation by modification of the reaction conditions.

Polyelectrolyte Controlled Large-Scale Synthesis of Hollow Silica Spheres with Tunable Sizes and Wall Thicknesses

High-yield synthesis of hollow silica spheres with controllable sizes and wall thicknesses can be realized by a modified Stöber method under the control of poly(acrylic acid) (PAA). This synthetic route is involved in the formation of spherical colloid aggregates in ethanol solution, hydrolysis of TEOS under control of ammonia, and the following removal of polyelectrolyte by washing. Hollow silica spheres with controllable diameters between 25 and 400 nm and wall thicknesses of several tens of nanometers can be controlled. This method can be scaled up for large-scale synthesis of hollow silica spheres and the synthesis of other inorganic materials with core−shell or hollow structures, as well as encapsulation of other materials.

Synthesis of mesoporous silica hollow spheres in supercritical CO2/water systems

The synthesis of hollow silica spheres with mesopore wall structures via CO2-in-water emulsion templating in the presence of non-ionic PEO-PPO-PEO block copolymer surfactants as mesostructure-directing templates has been investigated under various conditions. The successful synthesis of hollow spheres strongly depends on the pressure and density of CO2. The mesoporosity (pore size) and morphology of the silica hollow spheres can be controlled by varying the operating CO2 pressure. Other types of surfactants, such as long chain alkylammonium ions, may also be used to template the porosity of the shells.

Synthesis of Hollow Silica Spheres with Mesostructured Shell Using Cationic−Anionic-Neutral Block Copolymer Ternary Surfactants

Hollow silica spheres with mesostructured shells (HSSMS) were prepared with a vesicle template of cetyltrimethylammonium bromide-sodium dodecyl sulfate-Pluronic P123 (C(16)TMAB-SDS-EO(20)PO(70)EO(20)) at a SDS/C(16)TMAB ratio of 0.6-0.8 following a fast silicification in dilute silicate solution at pH approximately 5.0. The mesostructure of the shell is disordered, and the mesopore size is about 5.5-7.5 nm. Moreover, the direction and length of the nanochannels of the shell change with the SDS/C(16)TMAB ratios. A bi-template model, in which the C(16)TMA(+)-DS(-) form the stable bilayer vesicle structure and the P123 copolymers anchored on C(16)TMA(+)-DS(-) vesicle act as the template for the mesoporous silica, was proposed to explain the formation of the HSSMS. This bi-template model can be applied extensively to prepare the HSSMS with different diameters and pore sizes by using other C(n)TMAX-SDS-EO(n)PO(m))EO(n) ternary-surfactant mixtures.