Imprinted photonic hydrogel pillar for self-reporting water treatment of heavy metal ions

We demonstrate here a general protocol to prepare a self-reporting water treatment to remove heavy metal ions via an imprinted photonic hydrogel. The interconnected porous photonic layer with a photonic crystal structure on the surface of the hydrogel pillars can self-indicate the variation of the treatment's adsorbing capacity by changing colour and increase the adsorption efficiency of the hydrogel pillars. Ion-imprinting technology was applied to improve the adsorption capacity of the hydrogel pillars. The Pb(II) ion was chosen as the preliminary case to verify the properties of the imprinted photonic hydrogel pillars. Studies were then performed utilizing Cu(II) and Zn(II) ions to corroborate the initial findings. The Ag(I) ion was a special sample of an oxidizing metal ion which can be reduced by the hydrogel. To investigate the universality of the adsorbent, we conducted similar experiments on Ni(II), Mn(II), Co(II), and Sn(II) ions. Furthermore, the used hydrogel pillars were proved to be recovered by eluting the ions. This protocol provides a promising contaminated water treatment with properties of self-reporting and high efficiency for the removal of heavy metal ions.