Abstract
The use of polymer gels for the removal of toxic chemicalsfromwastewater is an important area in terms of both academic and industrialresearch. This work presents a simple approach to the fabricationof chemically cross-linked cationic hydrogel adsorbents using designedionic liquid-based cross-linkers and their successful use in the removalof organic dyes.
Two different ionic liquid cross-linkers, [VIm-4VBC][Cl](ILA)/[DMAEMA-4VBC][Cl] (ILB), are synthesized by the simple nucleophilicsubstitution reaction of 4-vinylbenzyl chloride (4VBC) separatelywith 1-vinylimidazole (VIm) and 2-(dimethylamino)ethyl methacrylate(DMAEMA). Cross-linked poly(acrylamide) (CPAam) and poly(2-hydroxyethylmethacrylate) (CPHEMA) hydrogels are then prepared from the correspondingmonomers and as-synthesized cross-linkers (ILA and ILB) by free radicalpolymerization in the presence of a redox initiator combining ammoniumpersulfate (APS) and N,N,N',N'-tetra-methyl-ethylene-diamine(TEMED).
The dried CPAam and CPHEMA xerogels exhibit macroporous morphologyand high thermal stability. The hydrogel samples exhibit high swellingbehavior, and the diffusion of water molecules into the hydrogelsfollows pseudo-Fickian kinetics.
The cationic cross-linking sitesin the hydrogel networks allow preferable binding with anionic dyes,and these dye uptake capacities are determined using different modelanionic dyes via UV-vis spectroscopy. The dye adsorption ontothese hydrogels follows a pseudo-second-order kinetic model.
The adsorptionmechanism is also analyzed by employing intraparticle diffusion and Boyd kinetic models. The relationship between the maximum equilibriumadsorption capacity (q(m)) of the hydrogelsfor eosin B (EB) dye and the equilibrium EB concentration can be betterdescribed by Langmuir and Freundlich isotherm models, and the estimated q(m) using the Langmuir isotherm can reach morethan 100 mg g(-1).
The cross-linked hydrogels canbe easily regenerated and have a recycling efficiency of >80% forup to three consecutive dye adsorption-desorption cycles, whichis promising for their use in wastewater treatment.