Extraordinary U(vi) sorption capacity of high surface area super-oxidized carbons

Abstract

Porous carbons based on activated reduced graphene oxide (rGO) have been demonstrated as excellent sorbents for U(VI), with their sorption capacity correlating with the degree of their oxidation. Herein, we demonstrate an extraordinarily high U(VI) sorption of ∼7050 μmol g⁻¹ for super-oxidized porous carbon (SOPC) with a specific surface area (SSA) of ∼970 m² g⁻¹ and an extremely high degree of oxidation (C/O = 2.1), similar to graphene oxide. The SOPC materials were prepared using an oxidation treatment applied to activated carbon produced from spruce cones. The extremely high SSA of the precursor activated carbon (∼3400 m² g⁻¹) as well as its microporous structure and mild oxidation treatment allowed for the preservation of a significant part of the surface area, providing materials with rather narrow pore size distribution (∼7.5 Å). The SOPC prepared from spruce cone biochar is similar to defective graphene oxide but with a significantly higher surface area, resulting in superior U(VI) sorption. Analysis of EXAFS and XPS data shows that U(VI) likely binds to carboxylic groups on the opposite sides of the micropores. The small size of the micropores and irregular pore wall structure are the main factors affecting pore sorption. The spruce-cone biochar has a strong advantage compared with earlier used rGO as a precursor for the preparation of SOPC.