Surface Complexation Modeling of Eu(III) and U(VI) Interactions with Graphene Oxide

Area of Science:

• Environmental Science
• Materials Science
• Radiochemistry

Background:

• Graphene oxide (GO) shows promise for actinide removal due to high sorption capacity.
• The exact sorption mechanism on GO remains poorly understood, hindering its application.

Purpose of the Study:

• To elucidate the sorption mechanism of Eu(III) and U(VI) on graphene oxide.
• To identify and quantify reactive surface sites on GO responsible for actinide complexation.

Main Methods:

• Characterization of GO surface functional groups (carboxylate, sulfonate) using acid/base titrations and diffuse layer modeling.
• Elemental analysis and X-ray photoelectron spectroscopy confirmed sulfonate presence.
• Batch sorption experiments with Eu(III) and U(VI) across varying pH and concentrations.
• Surface complexation modeling (SCM) to analyze sorption data.

Main Results:

• Carboxylate functional groups are the primary sites for Eu(III) and U(VI) sorption on GO.
• Sulfonate functional groups also contribute to sorption, particularly at lower pH.
• Eu(III) shows stronger complexation with sulfonate sites than U(VI).
• High actinide concentrations induced GO aggregation, likely due to surface charge neutralization.

Conclusions:

• The study clarifies the dual-site sorption mechanism of actinides on GO, involving both carboxylate and sulfonate groups.
• Understanding these mechanisms is crucial for optimizing GO-based materials for radioactive waste remediation.
• GO aggregation under high actinide loading needs consideration for practical applications.