Novel mesoporous organosilicas containing size-selective micropores from covalently bound calixcrowns

Abstract

Novel mesoporous organosilicas containing size-selective micropores from covalently bound calix[4]arenecrown-6s (calixcrowns) have been synthesized. Microporous calixcrowns, which are selective for caesium ions, were bonded covalently to triethoxysilyl groups via hydrosilylation. Co-polymerization of the silylated calixcrown monomer with tetraethoxysilane in the presence of a structure-directing surfactant, cetyltrimethylammonium bromide (CTAB), resulted in the formation of organosilicas containing calixcrown-based size-selective micropores. Removal of the surfactants produced organosilicas containing both mesoporous matrix cavities and microporous calixcrown host cavities. The solid-state ¹³C and ²⁹Si spectra provided evidence for intact covalently attached calixcrown hosts. The mesoporosity of the surfactant-extracted calixcrown-containing organosilicas was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen porosimetry. Experiments on the extraction of caesium ions from water in the presence of high concentrations of sodium ions by the insoluble calixcrown-containing mesoporous organosilicas showed good uptake and high caesium selectivity by these novel materials. Simple filtration removes the material containing the extracted caesium ions.