An ion-imprinted polymer based on palygorskite as a sacrificial support for selective removal of strontium(II)

Surface ion-imprinting technique combined with a sacrificial-support process was established to synthesize Sr(II) ion imprinted polymer (S-IIP) palygorskite which acted as the sacrificial support. FT-IR, TEM, nitrogen gas adsorption and laser particle size measurements were employed for the characterization of S-IIP and non-imprinted polymer (NIP). Factors for the adsorption of Sr(II) ions were investigated. Under the optimum condition, adsorption and selective recognition of Sr(II) ions followed the order S-IIP > NIP. The adsorption equilibrium data were fitted by the Langmuir isotherm model and the monolayer adsorption capacity of S-IIP was 45.0 mg g− 1 at 298 K, 53.5 mg g− 1 at 308 K and 58.5 mg g− 1 at 318 K. Adsorption was described by the pseudo-second-order kinetics, and the thermodynamic parameters also indicated that the adsorption process was spontaneous but endothermic. S-IIP was a promising adsorbent for the selective removal of traces of Sr(II) ions. It could be reused four times with only about 5% loss for adsorption and 17% loss for desorption.

Graphical Abstract
► Attapulgite is a hydrated octahedral layered magnesium aluminum silicate mineral which have siloxane groups in the bulk and silanol groups on its surface. It is available to be a support in surface-imprinting technique because of its particular intensity, special structure, stable chemical property and abundant raw materials.
► Then a new approach was used to synthesize a novel ion-imprinted polymer (IIP) based on surface ion-imprinting technique with attapulgite as a sacrificial-support material and chitosan incorporated sol–gel process. During this process, attapulgite as a support material was coated with a pre-polymerization ion-imprinting mixture. In a following step, the attapulgite was dissolved and removed, resulting in hollow spherical beads (S-IIP) with greater surface area and pore volume. Subsequently, the adsorption behaviors of S-IIP and non-imprinted polymer (NIP) for Sr2+ (containing adsorption parameters, isotherms, kinetics, thermodynamics, and selective recognition) were investigated, the structural characteristics and imprinting mechanism of S-IIP were discussed in detail.
► A model for selective removal of target radioelements could be set up according to the results.