Adsorption of Eu(III) on sulfonated graphene oxide: Combined macroscopic and modeling techniques

The sulfonated graphene oxide (GO-OSO3H) was synthesized by the oxidation of GO under concentrated H2SO4 conditions. It is demonstrated based on characterization results that sulfonated groups was satisfactorily grafted on the surface of GO. Macroscopic investigation indicated that the adsorption of Eu(III) on GO-OSO3H can be better fitted by pseudo-second-order kinetic model with high correlation coefficient (R2 > 0.999) compared to pseudo-first-order kinetic model (R2 < 0.95). The adsorption of Eu(III) on GO-OSO3H was independent of ionic strength, revealing that inner-sphere surface complexation dominated the Eu(III) adsorption at pH from 2.0 to 11.0. The maximum adsorption capacity of GO-OSO3H for Eu(III) calculated from Langmuir model was 125.0 mg/g at pH 5.5 and T = 293 K conditions. The calculation of thermodynamic parameters showed that the adsorption of Eu(III) on GO-OSO3H was an exothermal and spontaneous processes. According to fitting of surface complexation modeling, the adsorption of Eu(III) on GO-OSO3H can be satisfactorily simulated by diffuse layer model with monodentate and mononuclear complexes (SOEu2 + species) and bidentate and mononuclear complexes ((SO)2Eu (OH)3− species) at pH 2.0-11.0 conditions.