Adsorption of Cr(III) and Pb(II) by graphene oxide/alginate hydrogel membrane: Characterization, adsorption kinetics, isotherm and thermodynamics studies

Graphene oxide/alginate hydrogel membranes (GAHMs) were prepared by cross-linking a casting solution (blending graphene oxide, sodium alginate and urea) with a calcium chloride solution. The adsorption performance and mechanism for the removel of Cr(III) and Pb(II) were investigated. The GAHMs, before and after adsorption, were characterized by FT-IR, SEM, EDX and XPS, and their hydrophilicity was determined. The kinetics, isotherm and thermodynamics models were introduced. Results indicated that the optimal pH for the membranes removing Cr(III) and Pb(II) was 6.0 and 5.0 respectively. The adsorption capacity for both metal ions was positively correlated with the initial concentration and contact time and their adsorption was consistent with the pseudo-second-order kinetic model. The Langmuir isotherm better described the adsorption equilibrium. Moreover, the Langmuir model showed that the maximum adsorption capacity for Pb(II) was better than that for Cr(III) (327.9 and 118.6 mg/g, respectively). Thermodynamics analysis showed that the adsorption for Cr(III) by GAHMs was endothermic, whereas that of Pb(II) was exothermic. After five adsorption-desorption cycles, a high adsorption efficiency for both metal ions was maintained. This novel membrane material (GAHMs) is potentially an effective membrane adsorbent for the removal of Cr(III) and Pb(II) ions in practical applications. (C) 2019 Elsevier B.V. All rights reserved.