Two‐Dimensional Superstructures of Silica Cages

Abstract

observed structure formation, we assembled mesoporous silica at an interface between two immiscible liquids. Careful variation of synthesis conditions allowed the formation of a number of different 2D cage-like silica superstructures with controlled number of layers.Base-catalyzed hydrolysis of alkoxysilane precursors in water produces primary silica clusters of about 2 nm diameter [10,15] that can further condense to form ultrasmall (<10 nm) silica nanoparticles. [16] In the presence of cationic surfactants such as cetyltrimethylammonium bromide (CTAB), negatively charged clusters self-assemble into micelle-templated mesoporous silica, [1] with sizes controllable down to single pore nanoparticles. [17] The addition of a pore expander increases micelle size, size dispersity, and deformability, [9,18] enabling cage-like mesoporous structures. Numerous studies have identified bulk mesoporous materials formed from such cages as basic building blocks, [3,8,19] including 5 12 , 5 12 6 2 , or 5 12 6 3 cages, where 5 x 6 y refers to a cage made of x pentagonal and y hexagonal faces. In contrast, details of the self-assembly processes involved in their formation, in particular the transition from a single cage to a 3D superstructure, often remains obscure. In this work, the controlled growth of 2D cage-based mesoporous silica enabled the direct real-space observation of structure evolution and the emergence of 3D order in those superstructures, one layer at a time. To the best of our knowledge, no such singlelayer mesoporous silica films have ever been reported. These superstructures constitute a hitherto unknown type of material bridging the field of mesoporous materials with that of 2D materials. For example, borrowing ideas from the field of 2D electronic materials, [20] results open scalable synthetic approaches to mesoporous silica heterostacks with property profiles inaccessible to date.In order to create large liquid−liquid interfacial area for the confined growth of 2D mesoporous superstructures, a relatively large amount of an oil phase, namely cyclohexane, was dispersed in an equivalent volume of water under vigorous stirring, forming large droplets stabilized by CTAB. Tetramethyl orthosilicate (TMOS) was combined with (3-aminopropyl) trimethoxy silane (APTMS) as silica sources. Under basic conditions, neutral aminopropyl groups of APTMS intercalate the surfactant layer due to their hydrophobicity, [21] serving as anchor points for primary silica clusters at the oil−surfactant−water interface. [15] This nucleates silica layer growth at the surface of the oil droplets as verified by Despite extensive studies on mesoporous silica since the early 1990s, the synthesis of two-dimensional (2D) silica nanostructures remains challenging. Here, mesoporous silica is synthesized at an interface between two immiscible solvents under conditions leading to the formation of 2D superstructures of silica cages, the thinnest mesoporous silica films synthesized to date. Orientational correlations between cage units increase with...

Streamlined Mesoporous Silica Nanoparticles with Tunable Curvature from Interfacial Dynamic-Migration Strategy for Nanomotors

“…Then, TEOS precursors dispersed in the oil-phase ( n -pentanol) are hydrolyzed at the oil–water interface to form silicate oligomers under the catalysis of alkaline NH 3 ·H 2 O in the water phase. The negatively charged silicate oligomers can migrate into the water phase and are absorbed in the water/oil interface under the attraction of positively charged surfactant molecules (Step 2). , Whereafter, the negatively charged silicate oligomers further cross-link and coassemble with the surfactant/silicate composite micelles in the water phase to form the mesoporous silica shell (Step 3, Figure S22a). The growth of the silica shells in the water phase could induce the extrusion and deformation of water droplets, further triggering the migration of the oil–water interface (Step 4).…”

Versatile template-directed synthesis of gold nanocages with a predefined number of windows

“…As it can be adapted to numerous systems (noble and non noble metals, metal oxide or chalcogenide), it may enable a variety of fundamental studies and technological important applications in various fields including biological medicine, sensing and detection, energy conversion and catalysis. [71][72][73] Experimental Synthetic procedures of Au nanocages…”

Resilient three-dimensional ordered architectures assembled from nanoparticles by DNA

“…Sol-gel methods were also used to silicate more complex objects, such as proteins or even mammalian cells ( 51 , 52 ), to tailor morphology and surface chemistry of shaped NPs ( 53 ), as well as to embed NP assemblies into a silica matrix ( 54 , 55 ). Recently, an existence of ultrasmall symmetric silica cages formed from micelles was reported ( 56 ) and such cages were used to form 2D lattices ( 57 ). Various methods of obtaining DNA-templated silicas, including the formation of hollow tubules and circular replicas ( 58 ), ordered nanochannel arrays, and porous DNA-silica xerogels ( 59 ), have been reported.…”