Three-dimensional-printed hierarchical reduced graphene oxide/ ethylenediamine filter with super-high uranyl ions with recycling capacity and unique selectivity

Highly efficient and selective adsorption materials for the removal and recycling of U(VI) from radio-active wastewater or seawater are increasingly in demand due to the severe scarcity of strategic uranium sources for nuclear engineering. In this study, a three-dimensional (3D) hierarchical reduced graphene oxide/ethylenediamine scaffold (3D rGOE) was constructed using a direct-ink-writing-based 3D printing method. This technique contained orderly aligned microstructures, good hydrophilicity, mechanical robustness, and a high specific surface area. The optimized 3D rGOE structure obtained by multiscale and rational chemical modification exhibited a significantly higher U(VI) adsorption capacity (908 mg/g at pH = 5.8) compared to other previously reported amino/graphene-oxide-based composites. Additionally, the 3D rGOE mostly retained its high adsorption capacity (decay rate < 3.8%) after 11 cyclical adsorption processes. The adsorbed U(VI) could be eluted in acid through a protonation mechanism, allowing for further enrichment and recovery of U(VI). Characterization and simulations demonstrated that the U(VI) adsorption behaviors of 3D rGOE were due to the synergistic effects of electrostatic adsorption between uranyl ions and oxygen functional groups and the chelation between uranyl ions and amino functional groups. Thus, 3D rGOE shows promise for U(VI) recovery applications because of its high selectivity and adsorption capacity for uranyl ions due to its optimized microstructure and chemical composition. (C) 2021 Elsevier Ltd. All rights reserved.