Thermal-responsive ion-imprinted polymer based on magnetic mesoporous silica SBA-15 for selective removal of Sr(II) from aqueous solution

Highly thermal-responsive magnetic Sr(II)-imprinted polymer (Sr(II)-TMIIP) was successfully synthesized as a potential effective adsorbent for selective removal of Sr(II) in aquatic environments. First, magnetic polyethyleneimine-loaded mesoporous SBA-15 (Fe3O4@PEI-SBA-15) was prepared via a simple polymer-mediated self-assembly method. Then, the surface of Fe3O4@PEI-SBA-15 was endowed with reactive vinyl groups through modification with 3-(methacryloyloxy)propyl trimethoxysilane (MPS). With the aid of vinyl groups, free radical polymerization of N-isopropylacrylamide (NIPAM), methacrylic acid (MAA), and N,N'-methylenebisacrylamide (BIS) in the presence of Sr(II) was performed with 2,2'-azobisisobutyronitrile (AIBN) as initiator, which provided a desired imprinted layer coating onto Fe3O4@PEI-SBA-15. The as-prepared Sr(II)-TMIIP was characterized by Fourier transmission infrared spectra (FT-IR), X-ray diffractometer (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM), UV, and N-2 adsorption-desorption techniques. The results showed that the Sr(II)-TMIIP exhibited thermal stability, temperature and magnetic sensitivity (M (s) = 10.34 emu/g), and ordered mesoporous structure. Batch mode adsorption studies were conducted to investigate the specific binding kinetics, adsorption equilibrium, and selective recognition ability of Sr(II)-TMIIP. Adsorption equilibrium experiments showed that the adsorption amount strongly depended on temperature and reached a maximum around the lower critical solution temperature (LCST). Regeneration experiments indicated that repeated adsorption and desorption by temperature swings were possible. Compared with the nonimprinted polymer (NIP), the Sr(II)-TMIIP had good temperature response and excellent selectivity and reusability, making it possible in applying for Sr(II) separation and controlled release.