Ultraporous Mesostructured Silica Nanoparticles

Abstract

M esoporous silica materials find use in many applications such as catalysis, separations, drug delivery, and gas adsorption wherein a large pore volume is desirable. 1−4 High pore volumes can be achieved by swelling traditional surfactant templates, 5−8 by employing larger templates such as block copolymers 9,10 or sacrificial nanoparticles, 11,12 or through interface-directed syntheses. 13−20 For example, Stucky and coworkers demonstrated structural control over silica materials at two size scales by utilizing phase boundaries at the micelle level and at a bulk oil−water interface. 13 Oil−water interfaces were also used in the biphasic stratification synthesis of dendritic mesoporous silicas. 19 Further, solid−liquid interfaces between 3DOM carbon materials and water resulted in uniform silica nanoparticles with large pores. 20 Despite novel structures and pore swelling strategies, pore volumes of mesoporous silica nanoparticles have seldom topped 2.0 cm 3 g −1 . 21−23 In addition, swollen or hollow structures can suffer from other disadvantages. Some literature describes small micro-or mesopores on the shell portion of a particle, 14,24 and many schemes result in thin silica walls, 25,26 all of which are prone to breakage and aggregation.Herein, we report the development of a new mesoporous silica nanoparticle structure with extremely high pore volume and an open pore structure. These nanoparticles, which are formed from combinations of surfactant swelling strategies, stirring, and sonication, demonstrate pore volumes of up to 4.5 cm 3 g −1 while maintaining the high surface areas of traditional mesoporous silica (>1000 m 2 g −1 ). In addition, these structures demonstrate thermal stability and mechanical sturdiness. We propose that this new structure is formed through micellar aggregation during silica condensation.These ultraporous mesostructured nanoparticles (UMN) were synthesized with cetyltrimethylammonium bromide (CTAB) as a surfactant, dimethylhexadecylamine (DMHA) as a cosurfactant, and decane as an oil phase (exact combinations are shown in Table 1). Prior to silica condensation from tetraethylorthosilicate (TEOS), CTAB, DMHA, and decane mixtures were stirred and then sonicated for 90 min. The prepared suspension was equilibrated at 50 °C. After TEOS condensation, the synthesized material was dialyzed and centrifuged at 66 000 × g multiple times for purification.The textural properties of UMN are shown in Figure 1, Table 1, and Supporting Information Table S1 and Figures S1−S3. The difference in transmission electron microscopy (TEM) mass contrast between the center and edges of each particle suggests either a hollow or lacy interior silica network (Figure 1a). Image analysis of UMN-3, the structure with the highest pore volume, revealed average particle diameters of 71.3 ± 13.4

Oxygen Sensing with Perfluorocarbon-Loaded Ultraporous Mesostructured Silica Nanoparticles

“…In our previous study with bare UMNs, scanning electron microscopy analysis revealed a spherical 3D–structure with raspberry-like surface textures. 39 …”

A Vesicle Supra‐Assembly Approach to Synthesize Amine‐Functionalized Hollow Dendritic Mesoporous Silica Nanospheres for Protein Delivery

“…From the TEM observation, the sizes of radial pores are smaller than that observed in the SEM images. Moreover, it is hard to unambiguously determine whether A‐HDMSN have a hollow cavity, or the shape of radial pores in the silica walls …”

“…Moreover, it is hard to unambiguously determine whether A-HDMSN have a hollow cavity, or the shape of radial pores in the silica walls. [ 35 ] Electron tomography (ET) [ 27,30,36,37 ] was applied to further explore the detailed structure of A-HDMSN. An ET slice cutting across the center of one A-HDMSN particle clearly shows a hollow central core with ≈170 nm in diameter (Figure 1 d).…”

“…It is evident that A-HDMSN has a unique architecture of a hollow core, a mesoporous shell packed by cone-type units with open pores, and amine-functionalized surface, which is distinct from the previously reported MSNs with core-cone (the core is not hollow), [ 27 ] center-radial, [ 42 ] radial wrinkle, [ 43 ] and dendrimer-like structures. [ 28,29,35 ] In order to understand the formation mechanism of A-HDMSN, the time-dependent structural evolution was monitored by TEM. The reaction time ( t ) was recorded after mixing water and oil phases.…”

Photocracking Silica: Tuning the Plasmonic Photothermal Degradation of Mesoporous Silica Encapsulating Gold Nanoparticles for Cargo Release

“…Among bioinorganic nanomaterials [5], mesoporous silica and organosilica nanoparticles (NPs) are promising hybrid nanomaterials for biomedical applications [6,7]. Silica particles have indeed many unique benefits such as tunable dissolution rates from under a day to months [1], high surface areas and pore volumes (e.g., 1000-1500 m 2 ·g −1 ; 1.0-4.5 cm 3 ·g −1 ) [8,9], and can be produced in kilogram quantities while maintaining a high control of particle monodispersity [10]. Silica can be hybridized using organic and inorganic doping strategies to mediate biodegradability through pH [11,12], enzymatic [12][13][14], redox [3,[15][16][17][18], and biochelation [19][20][21][22] mechanisms [1,2].…”