Insight into the PEG-linked bis-imidazolium bridged framework of mesoporous organosilicas as ion exchangers

Abstract

Development of novel periodic mesoporous organosilicas (PMOs) were carried out by designing precursor, PEG-linked bis-imidazolium chloride bridged silsesquioxanes (PIMAILS, an ionic liquid). The involvement of tetraethyl ortho silicate (TEOS) as a template in an acidic medium led to the formation of a silica hybrid material (PMO-T). Contrary, in the absence of TEOS, PIMAILS self-assembled in a basic environment over the cationic surfactant, cetyl trimethyl ammonium bromide (CTAB) to form the silica hybrid material (PMO-S). The availability of surface silanols and ionic liquid (IL) in both the PMOs were verified using FT-IR and 13C solid NMR. Further, they were quantified using 29Si solid state NMR technique. The results depicted 3 times better loading of the precursor in the framework of PMO-S than PMO-T. Larger surface areas and higher porosities were found in PMO-S than PMO-T while analyzed using BET-BJH technique. Thermogravimetric (TG) analysis revealed nearly 2.2 times higher weight losses (%) from PMO-S than PMO-T, which validate the results of silica solid state NMR. Powder XRD analysis showed well-defined hkl reflections (110) and (200) from PMO-S in contrast of PMO-T, describing the periodic arrangement of IL within PMO-S. Finally ion-exchange capacities of these materials were estimated by employing them for recovery of W(VI). The PMO-S, which has higher percentage of IL in the framework, achieved better separation of W(VI) than PMO-T.