Macroscopic and molecular study of the sorption and co-sorption of graphene oxide and Eu(III) onto layered double hydroxides

Abstract

In recent years, the fate and transport of graphene oxide (GO) has received considerable attention owing to its inevitable release into the natural ecosystem during production and applications, wherein mineral particles and radionuclides are generally co-presented. This paper aimed to clarify the sorption and co-sorption of Eu(III) and GO onto Mg/Al layered double hydroxides (LDH) using batch and extended X-ray absorption fine structure (EXAFS) studies. The results showed that Eu(III) and GO displayed interactively enhancement roles in their co-sorption on LDH. Eu(III) enhanced GO co-sorption on LDH which was mainly due to the formation of “LDH-Eu(III)-GO” ternary surface complexes (i.e., Eu(III)-bridging). While, GO increased Eu(III) co-sorption on LDH which was primarily due to the formation of “LDH-GO-Eu(III)” ternary surface complexes (i.e., GO-bridging). EXAFS fitting results exhibited that the presence of GO could suppress the formation of outer-sphere complexes of Eu(III) on LDH at low pH values, while inhibit the formation of surface precipitates of Eu(III) on LDH at high pH values. The enhanced co-sorption of Eu(III) and GO on LDH as they co-presented might decrease their mobility in the natural environment. These new findings are important to understand the environmental behavior and impact of GO in real ecosystem, and the natural purification of radionuclides in ecological environments.