A Smart Adsorbent with Ability of Environmentally Friendly Regeneration for p-Nitrophenol Removal in Aqueous Solution

Abstract

Every year, a large amount of waste water containing phenol derivatives is produced in industrial production, which causes serious pollution problem. In the present work, a dually photo- and thermo-responsive adsorbent was developed to remove p-nitrophenol in aqueous solution. N-isopropyl acrylamide was polymerized to build up the thermo-sensitive network of the adsorbent; and cyclodextrin/azobenzene supramolecular complex was grafted on the backbone to act as the photo-responsive adsorbing unit. Under low temperature and 365 nm irradiation, the adsorbent was found in swelling state. In this state, p-nitrophenol was easily caught and removed from aqueous solution by cyclodextrin cavities and azobenzene moieties grafted on the polymer chains. Most interesting, when irradiated at 430 nm, the inclusion of cyclodextrin cavities with azobenzene moieties let freedom of the p-nitrophenol molecules adsorbed previously; at this time if increasing the temperature up to 40 °C, the free p-nitrophenol molecules were forced out owing to the shrinkage of the poly(N-isopropylacrylamide) network. So, without any organic solvent, the adsorbent can be regenerated directly in water. It avoids the secondary pollution caused by traditional regenerating process of adsorbents with organic solvent, which is an important advantage for its practical application of the adsorbent.