Hierarchical nanofabrication of microporous crystals with ordered mesoporosity

Abstract

Shaped zeolite nanocrystals and larger zeolite particles with three-dimensionally ordered mesoporous (3DOm) features hold exciting technological implications for manufacturing thin, oriented molecular sieve films and realizing new selective, molecularly accessible and robust catalysts. A recognized means for controlled synthesis of such nanoparticulate and imprinted materials revolves around templating approaches, yet identification of an appropriately versatile template has remained elusive. Because of their highly interconnected pore space, ordered mesoporous carbon replicas serve as conceptually attractive materials for carrying out confined synthesis of zeolite crystals. Here, we demonstrate how a wide range of crystal morphologies can be realized through such confined growth within 3DOm carbon, synthesized by replication of colloidal crystals composed of size-tunable (about 10-40 nm) silica nanoparticles. Confined crystal growth within these templates leads to size-tunable, uniformly shaped silicalite-1 nanocrystals as well as 3DOm-imprinted single-crystal zeolite particles. In addition, novel crystal morphologies, consisting of faceted crystal outgrowths from primary crystalline particles have been discovered, providing new insight into constricted crystal growth mechanisms underlying confined synthesis.

A general approach to crystalline and monomodal pore size mesoporous materials

“…The mesopores are the intraconnecting voids formed in between randomly packed nanocrystals. Formation of microporosity and mesoporosity by aggregation of colloidal nanoparticles or using these materials for nanocasting has previously been observed 32 .…”

π–π interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets

“…Here, we rationally designed a series of bolaform amphiphilic molecules with bi-quaternary ammonium head groups and biphenyl groups (BC Ph-n-6-6 ), which could act as particular cationic dimers, to direct a new type of hierarchical SCZN with uniform mesopore size due to the presence of their hydrophobic parts (we denoted these samples as SCZN-2). Figure 2 shows the XRD patterns of the as-made SCZNs synthesized with BC Ph-n-6-6 (n ¼ 4, 6,8,10,12). All samples show ordered lamellar structures.…”

“…There are several methods to prepare hierarchical zeolites such as top-down desilication by alkali post-synthetic modification 5 , bottom-up directed assembly by self-assembly of various zeolite seeds 6 and by templates. Much attention has been focused on the synthesis of zeolites with desired pore structure using soft and hard templates, such as surfactants [7][8][9] , cationic polymer 10 , polystyrene beads 11 , mesoporous silica 12 and carbon materials [13][14][15] . Although much considerable progress has been made in developing strategies to direct the formation of porous zeolites, designing a templating strategy for obtaining ordered hierarchical pore structures with crystallographically ordered zeolite remains an unsolved challenge.…”

Well‐Organized Zeolite Nanocrystal Aggregates with Interconnected Hierarchically Micro–Meso–Macropore Systems Showing Enhanced Catalytic Performance

“…Recently, various successful attempts to synthesize mesoporous or macroporous zeolites with bimodal porosity and framework acidity have been reported. [4][5][6][7][8][9][10][11][12][13][14][15] These materials hold great promise, particularly in catalysis and separation processes in which optimization of the diffusion and confinement regimes is required. Whereas micro-and/or mesopores provide size and shape selectivity for the guest molecules, and thus enhance the host-guest interactions, the presence of macropores can considerably favor diffusion of the guest molecules and thus their access to the active sites.…”