Tiling Silicalite‐1 Nanoslabs into 3D Mosaics

Abstract

Silica molecular sieves with controlled porosity crystallize from hydrogel in the presence of organic template molecules.[1] Patterned, mesoporous silica materials with amorphous walls are obtained using structure directing surfactants [2] or block polymers. [3] In diatoms and sponges the formation of macroporous silica structures is directed by biopolymers and proteins. [4] We report the discovery of crystalline silica materials with two levels of porosity and structural order. At the first level, building units are nanoslabs of uniform size with the Silicalite-1 zeolite framework generated by the tetrapropylammonium template. [5] At the second structural level, the nanoslabs are linked through their corners, edges, or faces following patterns imposed by interaction with surfactant or triblock copolymer molecules. After evacuation of the organic molecules, microporosity is obtained inside the nanoslabs, and a precise mesoporosity between the nanoslabs depending on the tiling pattern of the nanoslabs. Three different tiling patterns are directly imaged by electron microscopy. X-ray diffraction (XRD) and N 2 adsorption confirm the mosaic structures derived from electron microscopy. The generation of zeolite properties such as acidity and hydrothermal stability in mesostructured materials is a lively research field. The possibility to transform part of the amorphous walls of a mesoporous precursor into a zeolite framework has been demonstrated, [6] but segregation of a zeolite phase from the mesostructure as conversion proceeds seems difficult to avoid. [7,8] A more direct way to embed zeolite fragments in walls separating mesopores is by assembling the mesophase from suspensions containing zeolite crystallization nuclei.[9±12] The obtained materials typically have hexagonal symmetry and contain undefined zeolite fragments. We used as a silicon source the recently discovered uniform, nanometer-size zeolite slabs [5] and succeeded in linking them in various ways into materials with well-defined mesoporosity.Nanoslabs with the Silicalite-1 structure type [13] are prepared through hydrolysis of tetraethylorthosilicate (TEOS) in concentrated solution of tetrapropylammonium hydroxide (TPAOH).[5] Silicalite-1 nanoslab formation is directed by TPA cations. The nanoslab size, which can be monitored with low-angle X-ray scattering, dynamic light scattering, and electron microscopy, is controlled by the synthesis conditions.[5]Zeotile-1 preparation departs from a basic suspension of nanoslabs with dimensions of 1.3 nm 2.0 nm 4.0 nm. Aggregation of these nanoslabs into an open structure is achieved by addition of an aqueous solution of cetyltrimethylammonium bromide (CTMABr). In Zeotile-2 preparation, CTMABr is added in powder form. The organics are removed from the products obtained through leaching with ethanolic acetic acid solution followed by calcination. XRD and high-resolution electron microscopy (HREM) are used to characterize the obtained superstructures. In HREM, a low-intensity electron beam and medium magnificatio...

On the TEM and AFM Evidence of Zeosil Nanoslabs Present during the Synthesis of Silicalite‐1

“…[8,9] In ref. [8], the assynthesized suspension was used to make thin films on silicon wafers. Although fringes arising from silicon wafers were resolved, the silica-TPA film is featureless.…”

Design and Synthesis of Hierarchical Materials from Ordered Zeolitic Building Units

“…[31] A remarkably high mesostructural order is typical for these assemblies. After evacuation of the organics, microporosity inside the nanoslabs and an exceptionally open mesopore network between the nanoslabs, depending on the tiling pattern of the slabs, is obtained.…”

Synthesis and characterization of Pd/ZSM-5/MCM-48 biporous catalysts with superior activity for benzene oxidation

“…However, M41S materials generally exhibit weak acidity and low hydrothermal stability due to their amorphous frameworks. As a consequence, new synthesis strategies have been developed to obtain materials which com-bine the advantages of mesoporous materials and those of zeolites [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. For example, Corma et al [21] reported a post-synthesis dealumination process via steaming or acid leaching on full-grown zeolites.…”

“…Over the last couple of years, several simple and reliable approaches have been developed to form micro/mesoporous combined materials using zeolite nanoparticles or zeolite seeds as the silica source [31][32][33][34][35][36]. However, most of the published reports on composite catalysts have focused on one-dimensional materials (such as MCM-41 or SBA-15) as the mesostructured component, although three-dimensional materials, such as cubic MCM-48, are more interesting from the viewpoint of catalysis due to the interwoven pore system, which allows the sufficient diffusion of reactants within the pores, subsequently leading to a better catalytic performance [37].…”