Smart responsive microcapsules capable of recognizing heavy metal ions

Smart responsive microcapsules capable of recognizing heavy metal ions are successfully prepared with oil-in-water-in-oil double emulsions as templates for polymerization in this study. The microcapsules are featured with thin poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (P(NIPAM-co-BCAm)) membranes, and they can selectively recognize special heavy metal ions such as barium(II) or lead(II) ions very well due to the “host–guest” complexation between the BCAm receptors and barium(II) or lead(II) ions. The stable BCAm/Ba2+ or BCAm/Pb2+ complexes in the P(NIPAM-co-BCAm) membrane cause a positive shift of the volume phase transition temperature of the crosslinked P(NIPAM-co-BCAm) hydrogel to a higher temperature, and the repulsion among the charged BCAm/Ba2+ or BCAm/Pb2+ complexes and the osmotic pressure within the P(NIPAM-co-BCAm) membranes result in the swelling of microcapsules. Induced by recognizing barium(II) or lead(II) ions, the prepared microcapsules with P(NIPAM-co-BCAm) membranes exhibit isothermal and significant swelling not only in outer and inner diameters but also in the membrane thickness. The proposed microcapsules in this study are highly attractive for developing smart sensors and/or carriers for detection and/or elimination of heavy metal ions.

A novel smart responsive microcapsule has been developed for sensing heavy metal ions. The microcapsule exhibits an isothermal and significant swelling by recognizing special heavy metal ions.Figure optionsDownload high-quality image (61 K)Download as PowerPoint slideResearch highlights
► Smart responsive microcapsules are fabricated with poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) membranes.
► Microcapsules can selectively recognize heavy metal ions such as Pb2+ or Ba2+ by forming host-guest complexes.
► Microcapsules exhibit isothermal and significant swelling by recognizing Pb2+ or Ba2+.