Magnetic Laponite/poly(AA-AM) composite hydrogels for efficient removal of heavy metals

Abstract

Heavy metal wastewater contamination has become one of the greatest global environmental problems. In this study, magnetic Laponite/poly(AA-AM) composite hydrogels (mLap/(AA-AM)) with multi-level three-dimensional networks were for the first time synthesized by radical copolymerization based on poly(acrylamide-co-acrylic acid), Laponite and PEI-magnetic nanoparticles. mLap/(AA-AM) with porous and uneven structure has the target structure and composition confirmed by FTIR, FESEM, EDX and XRD results. FTIR and XRD results show that mLap/(AA-AM) has been successfully prepared without destroying high crystallinity of magnetic Fe3O4 and Laponite is dispersed in the polymer matrix with amorphous structure. mLap/(AA-AM) have high adsorption capacities of Cu(II) (238mg/g), Cd(II) (259mg/g) and Pb(II)(466mg/g). The endothermic, entropy increasing and spontaneous nature of heavy metal ion adsorption is revealed from thermodynamic study. Heavy metal ions adsorption isotherms and kinetics are in agreement with the Langmuir model and pseudo-second-order kinetic model, respectively. In addition, mLap/(AA-AM) has good magnetic response and magnetic solid-liquid separation property, high gel strength and reusability, which can solve the disadvantage of insufficient gel strength and complicated recovery process of conventional hydrogels and has thus huge potential in removing heavy metal ions from the contaminated wastewater.