Boosting the uranium adsorption capacity of UiO-66 (Ce) by incorporation of amino groups: Experimental and theoretical perspective

In pursuit of clean energy, nuclear field is growing at a rapid pace. To obtain sustainable power production, a large amount of uranium is required which makes it imperative to recover uranium present from different aqueous streams. Thus, this manuscript focuses on the synthesis of UiO-66 (Ce)-NH₂ MOF at ambient conditions and the uranium adsorption studies from aqueous solution. The MOF was thoroughly characterized using different conventional techniques as described in the manuscript. The γ-radiation stability revealed it to be stable up to 1000 kGy of dose. The synthesized MOF exhibited high surface area of 677 m² g⁻¹ and displayed a remarkable uptake of uranium. The stability of synthesized MOF was evaluated under different pH conditions and solvents as mentioned in the manuscript. The adsorption characteristics were evaluated by varying the pH from 2 to 8, time of adsorption, initial concentration of uranium (25–400 mg/L) etc. pH 5 was observed to be ideal with equilibration time of 4 h and followed Pseduo Second Order model implying chemisorption as the main driving force. The Maximum adsorption capacity of ∼321 mg/g was observed using Langmuir isotherm model which is higher than many other reported adsorbents as described in the main text. Adsorption capacity was independent of ionic strength which suggests inner sphere complexation. Further, the reusability studies showed the potential of MOF to be utilized atleast 3 times without any much loss in the adsorption capacity. The selectivity studies towards U in presence of different metal ions like Ni, Cu, K, Co, Fe, La showed MOF to be fairly selective towards U under experimental conditions and plausible mechanism of adsorption are also reported. Additionally, some insights regarding selective adsorption among different metal ions through computational methodology are depicted. Finally, a plausible mechanism of adsorption was deciphered through use of different techniques such as XRD, FT-IR and XPS which elucidated that the adsorption was governed mainly through chelation of NH₂ groups. Thus, the state of art in the field of MOFs is growing exponentially which could use be used to develop more advanced materials with superior adsorption characteristics.