Amine-bridged periodic mesoporous organosilica nanomaterial for efficient removal of selenate

Contamination of selenate (Se(VI)), an important oxyanion, has been widely detected in numerous water sources because of its high water solubility and mobility. In this study, a family of amine-bridged periodic mesoporous organosilicas (PMOs) with tunable and high contents of amine functionality were prepared through a facile (co-) condensation approach for adsorptive removal of Se(VI). The composition, structure and properties of amine-bridged PMOs were extensively characterized using various techniques, such as scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, surface area and porosity measurement, thermo-gravimetric analysis, zeta potential measurement, and elemental analysis. The optimal amine-bridged PMO had a high amine loading of 4.04 mmol/g. The Se(VI) adsorption behaviors strongly depended on the amine content of the amine-bridged PMOs. The optimal amine-bridged PMO exhibited both fast Se(VI) adsorption kinetics and a high Se(VI) adsorption capacity of similar to 175 mg/g, because of the high amine content, uniformly distributed amine functional groups within the mesoporous skeleton, and large surface area. Furthermore, the optimal amine-bridged PMO showed robust performance for efficient removal of Se(VI) under a wide range of pH and in the presence of various common co-existing anions, and can be conveniently regenerated and reused for multiple cycles. Combined spectroscopic characterization and aqueous adsorption experiments suggested that the primary mechanism for Se(VI) removal may be attributed to the formation of outer-sphere surface complexes between Se(VI) and the surface of amine-bridged PMOs.