1 Novel membrane-supported hydrogel for removal of heavy metals 2 Aleksandar Staj9 ci  c a Q1 , Aleksandra Nastasovi  c a , Jasna Staji  c-Troši  c a , Jelena Markovi  c b , 3 Antonije Onjia b , Filip Radovanovi  c a, * 4 a University of Belgrade, Institute for Chemistry, Technology and Metallurgy, Njegoševa 12, Belgrade, Serbia 5 b University of Belgrade, Vin9 ca Institute of Nuclear Sciences, P.O. Box 522, Serbia A R T I C L E I N F O Article history: Received 28 August 2014 Accepted 12 January 2015 Keywords: Membrane formation Photoirradiation Hydrogel Heavy metal removal A B S T R A C T Polyethersulfone membranes with integrated negatively-charged hydrogel of crosslinked poly (acrylamido-2-methylpropane sulfonic acid) were prepared by a combination of a liquid phase inversion process with photopolymerization and crosslinking of functional monomers included in the casting solution. A designed experiment was conducted to select the optimal composition for preparing membranes with a sufficient degree of swelling and ion exchange capacity. Scanning electron microscopy images revealed an ultrafine hybrid structure with an interconnected network of submicron particles embedded within the microporous polyethersulfone support. An intramembrane diffusion model was used to describe kinetics of heavy metal sorption by these hydrogels, and the calculated apparent diffusion coefficients were 2–3 times larger than in commercial ion-exchange resins. Equilibrium sorption of heavy metals was described using a semi-empirical Langmuir model. ã 2015 Published by Elsevier Ltd. 6 Introduction 7 Hydrogels are a very interesting class of polymeric materials 8 which are insoluble due to presence of chemical or physical 9 crosslinks, but which can swell to absorb large quantities of water. 10 Synthetic hydrogels could incorporate various functionalities and, 11 therefore, have a wide range of possible applications primarily in 12 life sciences including bioseparations, controlled release, wound 13 dressing, contact lenses, tissue engineering and sensing applica- 14 tions [1,2]. However, since they can incorporate a wide range of 15 functional groups, hydrogels were also investigated for pollution 16 control, especially for heavy metal removal. A monomer containing 17 sulfonic groups, such as AMPS (2-acrylamido-2-methylpropane 18 sulfonic acid) was often used as a building block in these hydrogels 19 [3,4]. Since sulfonic groups are strong acids, they are quite efficient 20 in capturing heavy metal cations by electrostatic forces, but such 21 gels have a limited selectivity for heavy metals in comparison to 22 alkali or alkaline earth metals, such as sodium or calcium, which 23 are often more prevalent in water. In order to improve heavy metal 24 selectivity, AMPS was combined with materials having other 25 functional groups, such as copolymerization with itaconic acid [5] 26 or acrylamide [6], copolymerization with N-vinyl pyrrolidone and 27 acrylic acid [7], or grafting on chitosan [8]. One of the drawbacks 28 restricting the use of such hydrogels is that they are mechanically 29 weak due to excessive swelling, so a focus of recent research 30 activities has been to reinforce them by preparing composites with 31 porous membranes. These composites are generally prepared by 32 pore filling or surface grafting, and the extensive review of these 33 materials has been published a couple of years ago [9]. 34 Microporous membranes are in most cases made by a variation 35 of a liquid phase inversion process [10] . In this process a 36 homogeneous solution of a polymer in a solvent is cast as a thin 37 film and immersed in a non-solvent bath, where it undergoes 38 phase separation into a polymer-rich and a polymer-lean phase 39 [11,12]. These phases are precursors for the membrane matrix and 40 membrane pores, respectively, which are formed after the 41 solidification of the polymer-rich phase. Photopolymerization 42 has been used in the past mainly for the modification of 43 polymeric membranes [13,14]. A comprehensive review of the 44 work in this field was recently presented by He et al. [15]. A novel 45 process to prepare asymmetric membranes with interpenetrating 46 proton-conducting morphology by a sequential combination of 47 photoirradiation and liquid phase inversion has been recently 48 disclosed [16] . 49 In this paper, sequential combination of photoirradiation and 50 liquid phase inversion used to prepare membrane-supported 51 hydrogels for heavy metal removal is presented. Swelling of 52 hydrogel in these materials is restricted by the glassy polymer shell 53 resulting in easier handling and presumably better mechanical 54 properties. Compared to the traditional pore-filling process of * Corresponding author. Tel.: +381 11 2628 587. E-mail address: filip@nanosys.ihtm.bg.ac.rs (F. Radovanovi c). http://dx.doi.org/10.1016/j.jece.2015.01.005 2213-3437/ ã 2015 Published by Elsevier Ltd. Journal of Environmental Chemical Engineering xxx (2015) xxx–xxx G Model JECE 541 1–9 Please cite this article in press as: A. Staj9 ci c, et al., Novel membrane-supported hydrogel for removal of heavy metals, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.01.005 Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.else vie r.com/locat e/jece