Graphene oxides cross-linked with hyperbranched polyethylenimines: Preparation, characterization and their potential as recyclable and highly efficient adsorption materials for lead(II) ions

Three GO-HPEI gels were prepared by a cross-linking reaction of graphene oxide (GO) with hyper-branched polyethylenimines (HPEIs) with different molecular weight. The GO-HPEI gels are different from the most reported GO-based materials and have superior adsorption performance because that these gels have more adsorption sites over using the common cross-linking agent (especially double-functionality or tri-functionality monomer). The morphology and structure of the GO-HPEI gels were characterized by FTIR, XRD, SEM, TEM, BET, TGA and elemental analyses. The adsorption property of Pb(II) onto GO-HPEI gels and the factors that influence the adsorption, such as the Pb(II) concentration, contact time and pH value, were investigated. The GO-HPEI gel exhibited an adsorption capacity as high as 438.6 mg g(-1) for Pb(II) ions, and its insolubility in water makes the separation from wastewater easy. Adsorption experiments demonstrated that the amino groups and the cross-link density affect the adsorption capacity. In the Pb(II) adsorption process, the adsorption kinetic and equilibrium data were well simulated with the pseudo-second-order and Langmuir isotherm models. The adsorption capacity of the GO-HPEI gel for Pb2+ only exhibited a slight decrease after eight cycles of adsorption/desorption, indicating its good stability. Therefore, the GO-HPEI gels could serve as promising adsorbents for potential application in the removal of Pb(II) from wastewater. (C) 2015 Elsevier B.V. All rights reserved.