PEG-linked bis-imidazolium and polyhedral oligomeric based silsesquioxanes as ion exchangers

Abstract

There is a growing demand for functional silica-based porous materials in the market. In this regard, PEG-linked bis-imidazolium chloride silsesquioxane (PIMAILS, an ionic liquid) was functionalized on polyhedral oligomeric silsesquioxanes (POSS). The materials were characterized with FT-IR, 1H and 13C NMR. The structural morphology of the adsorbent was analyzed with BET, TEM and FE-SEM techniques. The NMR results imply that during the PIMAILS loading over the POSS framework, the O–CH3 bond was cleaved out and the ionic liquid bridge was attached to the Si vertices of the POSS cage. The BET surface area of 853 m2 g−1 indicates higher porosity of the material. The ion exchanger has smooth and round-shaped morphology with continuous porous structures and an average particle size of 20–40 nm. The porous framework contains imidazolium binding sites, which have ion-exchange capability and was used to separate Cr(VI) ion from wastewater. With neat POSS and POSS-IL, comparative adsorption of Cr(VI) was carried out at different contact times, wastewater pH and initial concentrations. Maximum removal of 92% of Cr(VI) from an aqueous solution was achieved with POSS-IL at pH 2. The results showed that the adsorption adequately fit the linear Langmuir model and second-order kinetics. After adsorption, the adsorbents and treated solutions were further analyzed with XPS and ion chromatography instruments, indicating ion exchange mediated adsorption for the POSS-IL.