Reversible electro-mediated cesium ion removal using a zeolitic imidazolate framework derived zinc hexacyanoferrate composite

Cesium (137Cs) is one of the representative radionuclides which must be eliminated from nuclear waste. Here, we designed a zinc hexacyanoferrate (ZnHCF) composite using ZIF-8 derived carbon (ZDC) and utilized it as an electrode to selectively remove cesium ions. Specifically, we focused on how the ZIF-8 pyrolysis temperature affected the composite formation and non-radioactive cesium removal performance. With an optimized temperature of 700 °C, a highly conductive and uniform composite with well-distributed ZnHCF was produced, and it exhibited a large cesium uptake capacity (204.9 mg g−1). The composite electrode also retained high selectivity in Na-rich environments (molar Na/Cs = 1330, Kd (mL g−1) = 1.04 × 105), K-rich environments (molar K/Cs = 133, Kd (mL g−1) = 7.20 × 104), and groundwater conditions (95 % removal, C0 = 0.007 mM Cs+). Moreover, the reversible uptake and release of cesium over 5 cycles were feasible in our system without any chemical additives, which can be reached 100 % regeneration at the fourth cycle. Using in-depth characterizations including XRD and XPS, we investigated the faradaic behavior, phase transition, and structural stability of the ZnHCF-ZDC composite over 5 cycles. This study formed a composite electrosorbent with a ZIF-derived carbon support and applied it to cesium removal for the first time. This electro-mediated cesium removal process is expected to serve as a green technology for the future nuclear industry and environmental remediation.