Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj Macromolecular Nanotechnology Magnetoresponsive polymer networks as adsorbents for the removal of U (VI) ions from aqueous media Rafaella Ilia a , Ioanna Liatsou b , Ioanna Savva a , Eugenia Vasile c , Ladislau Vekas d , Oana Marinica e , Fotios Mpekris a , Ioannis Pashalidis b, ⁎ , Theodora Krasia-Christoforou a, ⁎ a Department of Mechanical and Manufacturing Engineering, University of Cyprus, 75, Kallipoleos Avenue, P.O. Box 20537, 1678 Nicosia, Cyprus b Department of Chemistry, University of Cyprus, 75, Kallipoleos Avenue, P.O. Box 20537, 1678 Nicosia, Cyprus c Politehnica University of Bucharest, 313 Splaiul Independentei, Bucharest, Romania d Center for Fundamental and Advanced Technical Research, Romanian Academy, Timisoara Branch, Timisoara, Romania e Research Center for Engineering of Systems with Complex Fluids, Politehnica University of Timisoara, Timisoara, Romania ARTICLE INFO Keywords: U(VI) adsorption Magnetic polymer networks Fe 3 O 4 nanoparticles Polymer metal ion adsorbents Superparamagnetism ABSTRACT Magnetoresponsive, methacrylate-based 3D polymer networks containing hydrophilic/thermoresponsive, hy- drophilic/pH-responsive and hydrophobic/metal chelating functionalities and oleic acid-coated magnetite na- noparticles, have been synthesized by conventional crosslinking radical polymerization and further evaluated as adsorbents for the removal of U(VI) ions from aqueous media. The adsorption properties of the networks prior and after magnetization regarding U(VI) ion removal from aqueous solutions of varying acidity and initial U(VI) concentration have been investigated. The effect of pH on the interaction of the adsorbents with U(VI) ions was shown to differ dramatically depending on solid phase composition, due to the fact that in the magnetite-loaded network, the Fe 3 O 4 nanoparticles act as buffers by binding solution protons. Nevertheless, U(VI) adsorption on both types of adsorbents follows the Langmuir adsorption isotherm and the value of their maximum adsorption capacity is q max = ∼0.02 mol kg -1 showing no statistically significant differences. The magnetic properties of these materials make their removal and adsorbed uranium separation from the aqueous phase quite simple by using an external magnetic field. 1. Introduction Uranium (U) is a natural element that plays a key role in the nuclear industry and particularly as a fuel for electricity generation by nuclear power plants. U can be released into the environment through various industrial activities (e.g. mining, ore beneficiation, enrichment etc.) related to nuclear power generation. Under acidic conditions, U is stabilized in its hexavalent form (U(VI)) and at near neutral and weak alkaline solution it forms very soluble and mobile U(VI)-carbonato complexes (UO 2 (CO 3 ) n (2n-2)- ). Through these complexes, U becomes highly stable in aqueous solutions resulting in a widespread environ- mental contamination [1,2]. Removal of U(VI) from aqueous solutions is of particular interest because U is a (radio)toxic element and its concentration in drinking water should not exceed 30 mg L -1 [3]. Among the various methods used for the removal of (radio)toxic metal ions from aqueous solutions such as chemical precipitation, ion exchange, solvent extraction and adsorption, the latter is the most attractive, because adsorption-based technologies are of low cost, simple and effective with limited environmental impact [4]. In the last years, the synthesis of magnetoactive polymer networks capable of acting as effective adsorbents for toxic metal ions that are present in aqueous environments has attracted considerable attention [5–7]. The 3D structure of polymer networks, their swelling ability in aqueous media due to the presence of hydrophilic moieties within their structures and the incorporation of specific metal binding functional- ities including hydroxyl, amino- and carboxylic acid groups [8–16], promote metal ion binding/removal [17]. In addition, the possibility of imparting magnetic properties to the polymer network adsorbent via the inclusion of magnetic nanoparticles within the network’s structure enables the facile removal of such adsorbents from aqueous media upon completion of the adsorption process by means of an externally applied magnetic field [7]. All the above literature examples focus on the use of magnetoactive polymer networks (hydrogels) for the removal of heavy metal ions from aqueous environments including Cu(II), Co(II), Pb(II), Cd(II), Ni(II) and Cr(VI). To the best of our knowledge only two scientific reports exists so far http://dx.doi.org/10.1016/j.eurpolymj.2017.10.005 Received 25 July 2017; Received in revised form 28 September 2017; Accepted 6 October 2017 ⁎ Corresponding authors. E-mail addresses: pspash@ucy.ac.cy (I. Pashalidis), krasia@ucy.ac.cy (T. Krasia-Christoforou). European Polymer Journal 97 (2017) 138–146 Available online 07 October 2017 0014-3057/ © 2017 Elsevier Ltd. 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