First successful synthesis of an Al-rich mesoporous aluminosilicate for fast radioactive strontium capture.

Al-rich zeolites such as NaA (Si/Al = 1.00) have been widely applied to remove radioactive Sr because of their high surface charge density enabling efficient ion-exchange of multivalent cations. However, due to the small micropore diameters of zeolites and large molecular size of strongly hydrated Sr, Sr-exchange with zeolites suffers from very slow kinetics. In principle, mesoporous aluminosilicates with low Si/Al ratios close to unity and tetrahedrally coordinated Al sites can exhibit both high capacity and fast kinetics in Sr-exchange. Nonetheless, the synthesis of such materials has not been realized yet. In this study, we demonstrate the first successful synthesis of an Al-rich mesoporous silicate (ARMS) using a cationic organosilane surfactant as an efficient mesoporogen. The material exhibited a wormhole-like mesoporous structure with a high surface area (851 m g) and pore volume (0.77 cm g), and an Al-rich framework (Si/Al = 1.08) with most Al sites tetrahedrally coordinated. Compared to commercially applied NaA, ARMS exhibited a dramatically improved Sr-exchange kinetics (>33-fold larger rate constant) in batch adsorption while showing similarly high Sr capture capacity and selectivity. Due to the fast Sr-exchange kinetics, the material also exhibited 3.3-fold larger breakthrough volume than NaA in fixed-bed continuous adsorption.