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

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.