Phytic Acid-Functionalized Rgo/Sns2 Electrode Composed of 2d/2d Sandwich Lamellas with Multiple Sites (P, O, S) for Efficient Long-Term Cyclic Capture of U(Vi)

Abstract

Electrosorption is a fascinating method for U(VI) capture due to its energy-efficiency, eco-friendliness and recyclability. However, the high demand of rapid electron/ion transfer, the inaccessibility of active sites, and the deterioration of electrochemical and structural stability of electrode vastly hamper its long-term cyclic U(VI) capture. Here, we rationally designed a 3D tough interconnected phytic acid/reduced graphene oxide/selenium sulfide (PA/rGO/SnS2, PGS) electrode composed of 2D/2D sandwich-like lamellas for U(VI) cyclic capture. By virtue of the synergistic effect between in-situ growth of SnS2 lamella on both sides of graphene and post-functionalization of PA, the PGS electrode possesses enlarged interlayer spacing, improved electroconductivity, abundant P, O, and S sites, as well as enhanced electrochemical and structural stability, which drive UO22+ ions first to be electro-adsorbed and intercalated into PGS layers, then electrostatically attracted and coordinated by negatively charged P, O, and S-containing active sites, and eventually chemically/electrocatalytically reduced by S2- species. Consequently, the maximum U(VI) removal rate of PGS electrode within 60 min was 99.2%, and it could still reach above 90.0% after 15 cycles, with a cumulative adsorption capacity of 1351.6 mg g-1. The long-term cyclic capture mechanism of U(VI) and its reaction path were also systematically explored for the first time.

Keywords: Electrosorption, Selenium sulfide, Cyclic U(VI) capture, Chemical reduction, Coordination