A systematic method of synthesizing composite superabsorbent hydrogels from crosslink copolymer for removal of textile dyes from water Ruma Bhattacharyya a , Samit Kumar Ray a, *, Bidyadhar Mandal b a Department of Polymer Science and Technology, University of Calcutta, 92, A.P.C. Road, Kolkata 700 009, India b Department of Chemistry, Bijoy Krishna Girls’ College, Howrah, India 1. Introduction Superabsorbent polymers (SAPS) are crosslink hydrogel which can absorb much more water than general absorbing materials and the absorbed water can hardly be removed from the gel even under pressure [1]. The presence of crosslink network prevents this highly hydrophilic polymer from dissolution in water. These polymers generally contain functional groups, such as NH 2 , CONH 2 , COOH, OH etc., in its structures. In water the long polymer chain of the SAPs extends due to electrostatic repulsion of these ionized groups resulting in extensive swelling of the crosslink network of these polymers. SAPs are generally synthesized by free radical polymerization of various vinyl monomers and their salts by solution polymerization [2–5], inverse suspension or emulsion polymerization [6–10] or by radiation polymerization [11–13]. These SAPs are extensively used as absorbent in agriculture, horticulture, personal care products, dye removal from aqueous waste, drug delivery, etc. [14–17]. In recent years various composite SAPS are also being used for the above applications because of its reduced cost, higher water absorbency and increased gel strength. These organic–inorganic composite SAPs are synthe- sized by incorporation of various clays, such as montmorillonite, kaolin, mica, attapulgite, sericite, zeolyte, in acrylic polymers [18– 20]. Various vinyl monomers, such as acrylamide, acrylic acid, are not very expensive and may be easily converted to a superabsor- bent hydrogel by free radical polymerization in water [10]. Unﬁlled and ﬁlled composite SAPs based on various acrylic polymers and inorganic/organic ﬁllers have been widely used for removal of industrial dye or heavy metal ions from water. The performance of SAPs based on acrylic copolymer is inﬂuenced markedly by various reaction parameters, such as comonomer ratios, total monomer concentration in water, concentration of initiator and comonomer crosslinker (e.g. NMBA) in reaction medium. Similarly, synthesis of a composite or ﬁlled hydrogel from a hydrogel based on acrylic copolymer depends on type, concentration and mode of addition of ﬁller. A systematic approach of optimizing various operating parameters for selecting the right membrane for nanoﬁltration [21] or pervaporation [22] has already been reported. However, there is no systematic study about synthesis of an unﬁlled or ﬁlled hydrogel showing optimum adsorption or removal% of dye or metal ion from water depending on speciﬁc reaction parameters and selecting optimum concentration of ﬁller. Thus, the objective of the present work was to synthesize three acrylic copolymer hydrogels from AM and HEMA at varied comonomer ratio and evaluating its swelling characteristic at varied initiator, crosslinker and total monomer concentration in water. The hydrogel showing the optimum swelling characteristic was then ﬁlled with three different concentrations of hydrophilic ﬁllers, i.e. sodium alumi- nosilicate by in situ mixing of the ﬁller during polymerization to produce three ﬁlled or composite hydrogels. This aluminosilicate ﬁller was reported to increase hydrophilicity of polyvinyl alcohol membranes [23]. The ﬁlled or composite gel showing the optimum swelling characteristic was then used for removal of varied concentrations of two industrial dyes, i.e. rhodamine B and methyl Journal of Industrial and Engineering Chemistry 19 (2013) 1191–1203 A R T I C L E I N F O Article history: Received 1 August 2012 Accepted 11 December 2012 Available online 20 December 2012 Keywords: Composite hydrogel Network parameter Dye removal Adsorption kinetics and isotherm Thermodynamic parameters A B S T R A C T A systematic method was employed to synthesize several hydrogels by crosslink copolymerization of acrylamide (AM), hydroxyl ethylmethacrylate (HEMA) and N,N’-methylenebisacrylamide (NMBA) at varied operating conditions. Composite hydrogels were also prepared by in situ incorporation of varied amounts of sodium aluminosilicate ﬁller to the monomer mixtures at optimum operating conditions. These hydrogels were used for removal of rhodamine B and methyl violet dye from water at low (0.5– 3 mg/L) and high concentration (50–500 mg/L) ranges. The composite hydrogels showed much higher dye adsorption than the unﬁlled hydrogels. Kinetic, adsorption and thermodynamic parameters for dye adsorption were also evaluated. ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. * Corresponding author. Fax: +91 33 23508386. E-mail address: samitcu2@yahoo.co.in (S.K. Ray). Contents lists available at SciVerse ScienceDirect Journal of Industrial and Engineering Chemistry jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jiec 1226-086X/$ – see front matter ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2012.12.017