Post-Synthetically Modified Metal Organic Framework Functionalized with a 1,2-Dihydroxybenzene Chelating Unit for Efficient Removal of Thorium and Uranyl Ions from Radioactive Waste

Abstract

Metal organic frameworks (MOF) are proven to be the efficient solid phase sorbents for uranium and thorium, the driver fuels for the present and future nuclear power program of India. In this article, a novel sorbent material (MOF-DHB) has been dove-tailed by a post-synthetic modification technique (here, 1,2-dihydroxybenzene functionalized on the surface of UiO66-NH₂), and sorption efficacy of the material for UO₂²⁺ and Th⁴⁺ from acidic solutions has been explored for the first time. It exhibits very high (>98%) removal efficiency for both actinides compared to the unfunctionalized MOF (with 52% and 65% for UO₂²⁺ and Th⁴⁺, respectively). The surface functionalization induced the enhancement in the saturation sorption capacity values of UO₂²⁺ and Th⁴⁺ (nearly 1.3-fold compared to parent MOF). Reusability has been demonstrated by quantitative back extraction of metal ions using suitable stripping agents and subsequent use of the sorbent for new extraction without any performance compromise. The synthesized MOF is stable up to 500 kGy dose and can be applied for more than five cycles of operation. FTIR analysis illustrates that major modes of coordination in MOFDHB and MOF are through phenolic −OH and −NH₂ groups.