Determination of chemical affinity of graphene oxide nanosheets with radionuclides investigated by macroscopic, spectroscopic and modeling techniques

The chemical affinity of graphene oxide (GO) nanosheets with radionuclides (Eu( iii ) and U( vi )) was determined by macroscopic, spectroscopic and modeling techniques. The macroscopic results showed that the adsorption of Eu( iii ) and U( vi ) on GO nanosheets was independent of ionic strength, indicating that inner-sphere surface complexation predominated their adsorption. The maximum adsorption capacities calculated from a Langmuir model at pH 4.0 and T = 303 K were 208.33 mg U( vi ) and 28.70 mg Eu( iii ) per gram of GO nanosheets, respectively. No hysteresis was observed for both Eu( iii ) and U( vi ) on GO nanosheets when desorption was initiated by lowering solution pH. While desorption was induced by replacing the radionuclide supernatant liquid with radionuclide-free electrolyte solution, the adsorption-desorption hysteresis was observed for U( vi ) but not for Eu( iii ), indicating that the chemical affinity of GO nanosheets with U( vi ) was stronger than that of GO nanosheets with Eu( iii ). The adsorption behaviors of Eu( iii ) and U( vi ) on GO nanosheets can be fitted by a double diffuse layer surface complexation model with the mononuclear monodentate >SOM ( n −1)+ and >SOMOH ( n −2)+ complexes, and larger log K values of U( vi ) was observed as compared to those of Eu( iii ). According to the spectroscopic analysis, the irreversible adsorption of U( vi ) on GO nanosheets at variable radionuclide concentrations was attributed to the oxygen-containing functional groups. The chemical affinity of graphene oxide nanosheets with radionuclides (Eu( iii ) and U( vi )) was determined by macroscopic, spectroscopic and modeling techniques.