Mesoporous Silica Hollow Spheres with Ordered Radial Mesochannels by a Spontaneous Self-Transformation Approach

Abstract

We demonstrate a self-transformation approach for the synthesis of ordered mesoporous silica hollow spheres with radially oriented mesochannels. The method is simple and facile, in which mesostructured silica spheres synthesized in a Stober solution can spontaneously transform to hollow structure when they are incubated with water. The formation of the hollow structure does not require any sacrificial templates, emulsion droplets, or surface protective agents. The obtained mesoporous silica hollow spheres possess controllable diameter, tunable shell thickness, high specific surface area, and uniform mesopore. Transmission electron microscopy (TEM) observations show that the formation of the hollow spheres undergoes a selective etching process in the inner section. 29 Si NMR spectra and detailed reactions demonstrate that the solid-to-hollow transformation of the Stober silica spheres in water is attributed to the difference in the degree of condensation of silica between their outer layer and inner section. Cytotoxicity and histological assays confirm that the obtained mesoporous silica hollow spheres possess good biocompatibility. Besides, the capability of the hollow spheres as contrast agents for untrasound imaging is conducted in vitro. Moreover, yolk−shell microspheres with a Fe 3 O 4 @ nSiO 2 core and a mesoporous silica shell are successfully prepared based on the facile self-transformation strategy, which provides a general method to create various yolk−shell structured multifunctional composites for different applications.

Facile Synthesis of Yolk-Shell-Structured Triple-Hybridized Periodic Mesoporous Organosilica Nanoparticles for Biomedicine

“…The 29 Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectrum of the yolkshell-structured triple-hybridized PMO nanoparticles shows two large peaks at −67 and −58 ppm, corresponding to T 3 (C-Si (OSi) 3 ) and T 2 (C-Si (OSi) 2 (OX), X = H or Et) species (Figure 2 b), [ 35,44 ] clearly suggesting the organosilica frameworks. Simultaneously, two small signals at −109 and −101 ppm, corresponding to Q 4 ( Si (OSi) 4 ) and Q 3 ( Si (OSi) 3 (OX)) species, [ 17,24 ] are also observed in the NMR spectrum due to the introduction of TEOS. Nitrogen sorption isotherms of the triple-hybridized PMOs show a type IV curve with a large hysteresis loop in the relative pressure range ( p / p 0 ) of 0.5-1.0 (Figure 2 c), suggesting a typical mesopore structure.…”

Facile Synthesis of Yolk–Shell Structured Inorganic–Organic Hybrid Spheres with Ordered Radial Mesochannels

“…The result is consistent with our previous observations that the inner section of the Stöber silica spheres has a low condensation degree, and thus, it is readily dissolved in water. [ 43 ] With the addition of BTSE, the yolk-shell structure with a loose core inside hollow sphere is obtained (Figure 3 e), strongly suggesting that the BTSE is a critical factor for the formation of yolk-shell structure. With the further increasing the BTSE/ TEOS ratio, the core of the yolk-shell mesoporous hybrid spheres becomes even darker due to more BTSE condensed (Figure 3 f).…”

“…The morphology and mesostructure of the spheres are similar to that of pure mesoporous silica spheres prepared by using only TEOS as a silica source in ethanol aqueous solution. [ 43 ] Then, the spheres were incubated with water to form yolk-shell structure, and CTAB templates were extracted with acidic ethanol to form mesoporous structure, resulting in the yolk-shell mesoporous hybrid spheres. TEM observations clearly reveal the uniform yolk-shell structure, where a dark core is encapsulated in a gray layer (Figure 1 b,c).…”

“…[ 49,50 ] Owing to the gradual hydrolysis of TEOS and BTSE, Si-OC 2 H 5 groups should exist in the as-made mesostructured hybrid spheres. When the as-made hybrid spheres are mixed with water, the silicate-CTAB composites with low condensation degree are easily attacked by water molecules and dissolved, [ 43,51 ] resulting in defects in the interiors. The dissolved silicate-CTAB composites can reassemble into the outer shells, where have lower curvature and interfacial energy compared to the defect surfaces originated from silicate-CTAB dissolution.…”

Macroscopic and Mechanically Robust Hollow Carbon Spheres with Superior Oil Adsorption and Light‐to‐Heat Evaporation Properties

“…[1][2][3][4] Many types of hollow spheres such as silica, [5] metal oxide (Al 2 O 3 , ZnS, TiO 2 ), [6][7][8] polymer, and carbon [9,10] have been developed. Among these systems, hollow carbon spheres (HCSs) are very attractive owing to their special properties, including their high specific surface area, good electrical conductivity, outstanding thermal stability, and good resistance to hydrolytes, acids and alkali, and solvents, which make of effervescent salts inside the droplet, hollow structures with large voids and hierarchical polymer shells could be achieved.…”