Construction and Properties of Micro-Mesoporous Composite Materials

(1.1) π-π Interaction of Aromatic Groups in Amphiphilic Molecules Directing for Single-Crystalline Mesostructured Zeolite Nanosheets

We designed and synthesized some novel templates with single quaternary ammonium head by grafting aromatic group into the carbon chain, as a result, single-crystalline mesostructured zeolite nanosheets (SCZN-1) was obtained. The presence of π-π stacking could effectively stabilize the micelles and the zeolitic framework. Owning to the geometrical match between aromatic groups and MFI zeolitic framework, the single-crystalline hierarchical structures were finally constructed. We also designed the bolaform templates with bi-quaternary ammonium head (BCPh-n-6-6, n≥4), and the corresponding products of zeolite synthesis were the single-crystalline MFI nanosheets with 90º rotational intergrowth structure (SCZN-2). Because the intergrowth on (010) faces is crystallographically correlative, when n equals to 6 and 8, the molecular size and space distance between two adjacent MFI sheets would well geometrically match and result in the successive rotational intergrowth. The HRTEM observation indicated that the connectivity at the joints could arise through the formation of a new set of Si-O-Si bonds and the lamellar structures did not completely collapse after calcination because of the framework connectivity. The readily apparent house-of-cards-like morphology could construct a new macroporous system (~100 nm) due to the mutual pillaring between ultrathin plates. Therefore, SCZN-2 possesses well-defined micro-meso-macroporous architecture. This work has been published in Nature Communications (2014, 5:4262 doi: 10.1038/ncomms5262).            

(1.2) Surfactants with Aromatic-Group Tail and Single Quaternary Ammonium Head for Directing Single-Crystalline Mesostructured Zeolite Nanosheets

We systematically studied the synthesis results of the templates with different number of benzene rings and carbon chain length, and discussed the formation mechanism of SCZN-1 by following the crystallization growth process. The results showed that the SCZN-1 could be obtained by the templates only with two benzene rings and a carbon chain larger than 4, otherwise, bulk zeolite MFI was the actual product. Through the characterization of products obtained at different crystallization time point, it indicated that one MFI layer was transformed in situ by two amorphous aluminosilicate layers. Based on the elemental analysis and HRTEM observation, the formation mechanism of SCZN-1 and the arrangement of templates during the whole crystallization process were discussed in detail; the well geometrical match between aromatic groups and MFI zeolitic framework resulted in the single-crystalline feature of MFI nanosheets. This work has been published in  Chemistry of Materials (2014, DOI: 10.1021/cm502027j).