Recognizing adsorption of Cd(Ⅱ) by a novel core-shell mesoporous ion-imprinted polymer: Characterization, binding mechanism and practical application

A novel monodispersed Cd(II) ion-imprinted polymer (IIP) was synthesized inside core-shell mesoporous silica (C-SMS) particles to improve the diffusion kinetics of the polymer. The synthesized IIP@C-SMS was characterized and subsequently used in solid-phase extraction (SPE) for the selective adsorption of Cd(II) in aquatic samples. The results indicated that IIP had been successfully assembled inside the C-SMS particles with a high specific surface area (546.3 m 2  g −1 ) and uniform mesoporous size (2.07 nm). The obtained IIP@C-SMS takes only 15 min to reach the adsorption equilibrium due to the highly developed mesoporous structure. IIP@C-SMS also presented a maximal adsorption capacity (201.9 μmol g −1 ) for Cd(II), which was much higher than that of NIP@C-SMS (80.3 μmol g −1 ). The relative selectivity coefficient of IIP@C-SMS for Cd(II)/M(II) (M = Cu(II), Pb(II), Cr(II), and Ni(II)) were 7.15, 8.70, 7.18, and 7.36, respectively, further confirming the satisfactory selectivity of IIP@C-SMS. The adsorption isotherms of IIP@C-SMS toward Cd(II) could be described by Langmuir model; whereas the adsorption kinetics could be fitted by the pseudo-second-order model, indicating chemisorption was the rate-limiting step. The FT-IR, ITC and XPS analysis further confirmed that the Cd(II)-induced cavities during the ion-imprinting process and the coordination between Cd(II) and –SH groups were the main adsorption mechanism. Furthermore, in real samples, IIP@C-SMS-SPE adsorbed approximately 93–104% of Cd(II). This work provides new insights for the design of novel macroporous sorbents for Cd(II).