Pristine and Postsynthetically Modified UiO-66-NH2 (Ce) MOF for Efficient Capture of Uranium from Aqueous Solutions

Nuclear power is increasingly viewed as a solution to growing global energy demand and challenges posed by climate change. Large-scale extraction of uranium from seawater is considered crucial for sustainable nuclear power generation. This paper presents the room temperature synthesis of UiO-66-NH2 (Ce) MOF and its subsequent postsynthetic modification to phosphorus-functionalized UiO-66-NHPOPh2 (Ce) MOF as efficient materials for uranium capture. The MOFs were thoroughly characterized by FT-IR spectroscopy, pXRD, TGA, SEM, and BET surface area analysis. The influence of pH and contact time on uranium uptake was systematically investigated. pH-dependent adsorption studies revealed over 95 and 99% sorption for UiO-66-NH2 (Ce) and UiO-66-NHPOPh2 (Ce), respectively, in the pH range of 3–9, with maximum adsorption observed at pH 5, mirroring the pH range of most naturally occurring water bodies. Interestingly, phosphinic-amide-functionalized MOF exhibited a higher uranium sorption capacity across a wide pH range compared to amine functionalized MOF. Uranium sorption kinetics suggests significant uptake of uranium (more than 95%) by these MOFs within 1 min of interaction. Moreover, the sorption capacity of UiO-66-NHPOPh2 (Ce) MOF, estimated at 95 mg of U/g of sorbent using the Langmuir isotherm model, surpassed that of many other reported sorbents. Adsorption studies conducted with tap water, drinking water, and seawater demonstrated uranium sorption from real samples. Importantly, these MOFs were observed to be selective in the presence of most of the common competing ions. Desorption studies with various reagents indicated the material’s potential for reuse. Additionally, EXAFS studies on the uranium-sorbed samples suggest that both the MOFs lead to efficient coordination of the uranyl(VI) ions, thereby providing the mechanism for their capture.