Functional Capsules Encapsulating Molecular-Recognizable Nanogels for Facile Removal of Organic Micro-Pollutants from Water

A novel method has been successfully developed for the facile and efficient removal of organic micro-pollutants (OMP) from water based on novel functional capsules encapsulating molecular-recognizable nanogels. The functional capsules are composed of ultrathin calcium alginate (Ca-Alg) hydrogel shells as semipermeable membranes and encapsulated poly(N-isopropylacrylamide-co-acrylic acid-g-mono-(6-ethanediamine-6-deoxy)-β-cyclodextrin) (PNCD) nanogels with β-cyclodextrin (CD) moieties as OMP capturers. The semipermeable membranes of the capsules enable the free transfer of OMP and water molecules across the capsule shells, but confine the encapsulated PNCD nanogels within the capsules. Bisphenol A (BPA), an endocrine-disrupting chemical that is released from many plastic water containers, was chosen as a model OMP molecule in this study. Based on the host–guest recognition complexation, the CD moieties in the PNCD nanogels can efficiently capture BPA molecules. Thus, the facile and efficient removal of BPA from water can be achieved by immersing the proposed functional capsules into BPA-containing aqueous solutions and then simply removing them, which is easily done due to the capsules’ characteristically large size of up to several millimeters. The kinetics of adsorption of BPA molecules by the capsules is well described by a pseudo-second-order kinetic model, and the isothermal adsorption thermodynamics align well with the Freundlich and Langmuir isothermal adsorption models. The regeneration of capsules can be achieved simply by washing them with water at temperatures above the volume phase transition temperature of the PNCD nanogels. Thus, the proposed functional capsules encapsulating molecular-recognizable nanogels provide a novel strategy for the facile and efficient removal of OMP from water