Multifunctional Polymer Sponge with Molecule Recognition: Facile Mechanic Induced Separation.

Polymer sponges with molecular recognition provide a facile approach to water purification and industrial separation with easy operation, but its fabrication is still challenging because some critical issues of selective adsorption, high mechanical strength, and easy collection/re-use are difficult to be achieved in one material. Here, inspired by natural sponges, novel multifunctional polymer sponges were developed which were fabricated by ice-templating with multifunctional amine polyethylenimine and diepoxide cross-linker poly(ethylene glycol) diglycidyl ether for highly efficient harvesting of dyes and simultaneous pure water recovery both in mechanic pressing and filtration processes. The as-prepared sponge (SP-1) was further modified by poly(caffeic acid) through a simple dipping-cross-linking process to obtain the hybrid polymer sponge (SP-2), which showed higher compressive strength than SP-1. These sponges possessed a cross-linked three-dimensional macroporous structure with quick water absorbing properties over ten times of their own weight within 20 s directed by capillary. The adsorption behavior of the obtained polymer sponges to 11 hydrophilic dyes was studied in detail by mechanic induced separation. All these polymer sponges exhibited a high selective adsorption to hydrophilic dyes in water. For example, SP-1 has high adsorption capacity over 150 μmol/g to erythrosin B, which is 20 times higher than that of calcein. With the modified poly(caffeic acid) layer, SP-2 exhibited different adsorption properties for methylene blue (180 μmol/g) to SP-1 (∼0 μmol/g), indicating that the tailorable structures of the sponge can regulate their selectivity to guest molecules. Based on the unique recognition to guest molecules, the methodology of dynamic separation of the dye's mixture in water was demonstrated by using these sponges through mechanical pressing or fast filtration, which provides a facile alternative with easy operation for water purification.