Fabrication of xanthate-modified chitosan/poly(N-isopropylacrylamide) composite hydrogel for the selective adsorption of Cu(II), Pb(II) and Ni(II) metal ions

A novel xanthate-modified chitosan/poly( N -isopropylacrylamide) (X-CS/NIPAAm) composite hydrogel was fabricated by a facile two-step method for the selective adsorption of Cu(II), Pb(II) and Ni(II) metal ions from aqueous solutions. The equilibrium adsorption data fitted well to the Langmuir model and the adsorption kinetic data followed the pseudo-second-order model. The maximum equilibrium adsorption capacities of composite hydrogel to Cu(II), Pb(II) and Ni(II) at 293   K were about 115.1, 172.0 and 66.9   mg   g −1 , respectively. The thermodynamics parameters showed that the adsorption processes to Cu(II), Pb(II) and Ni(II) were spontaneous and exothermic. The interactions between metal ions for multi-components systems were evaluated by the values of Q b /Q s and Q t /Q s . The adsorption mechanism was analyzed by XPS spectra and the Hard–Soft, Acids–Bases (HSAB) theory. The X-CS/NIPAAm composite hydrogel could be regenerated and repeatedly utilized at least five cycles without obvious adsorption capacity loss.