The uptake of europium by reduced graphene oxide-supported nanoscale zerovalent iron investigated by batch and modeling techniques

Abstract

The reduced graphene oxide-supported nanoscale zerovalent iron (NZVI@rGO) composites were synthesized towards the uptake of europium (Eu(III)) in environmental cleanup. In this study, the effect of environmental factors on the uptake of Eu(III) from aqueous solutions on NZVI@rGO composites was investigated under ambient conditions by batch techniques. The uptake kinetics indicated that the uptake of Eu(III) on NZVI@rGO composites can be satisfactorily fitted by pseudo-second order kinetic model. The uptake of Eu(III) on NZVI@rGO composites was independent of ionic strength at pH > 5.0, indicating that inner-sphere surface complexation dominated the uptake of Eu(III) on NZVI@rGO composites. It is demonstrated that the maximum uptake capacities of NZVI@rGO composites for Eu(III) calculated from Langmuir models was 96.675mg/g at pH 5.0 and T=293K. The thermodynamic parameters indicated that the uptake of Eu(III) on NZVI@rGO composites was an endothermic and spontaneous process. Based on surface complexation modeling, the diffuse layer model gave an excellent fits to the uptake of Eu(III) on NZVI@rGO composites with cation exchange complexes (X3Eu species) at pH<4.5, mononuclear and monodentate complexes (SOEu2+ species) at pH 5.0–7.0, and mononuclear and bidentate complexes ((SO)2Eu(OH)2− species) at pH>7.0, respectively. The results indicated that NZVI@rGO composites can be considered as a promising adsorbent for the uptake of trivalent radionuclides from wastewaters in environmental cleanup.