Highly Stable and Hierarchical Porous Ce-Based MOF for Efficient Uranium Extraction from Seawater

Owing to rapidly growing world population and swift industrialization, there is an escalating global demand for a sustainable and environmentally friendly energy resource, triggering the exploration of uranium source for nuclear energy. Seawater with a vast and untapped uranium reservoir (4.5 billion tons) is a promising source and holds an immense potential for uranium mining over an extended period. However, efficient, and selective uranium extraction from seawater (UES) is profoundly challenging due to ultralow concentration of dissolved uranium in seawater (about 3.3 ppb), complex chemical matrix, harsh and corrosive marine environments as well as economic viability.<br/>To overcome these challenges, various approaches have been explored so far including ion exchange, precipitation, membranes, and electrochemical methods. However, these methods often suffer due to high cost, low selectivity, inefficient uranium extraction, susceptibility to degradation, and environmental concerns. Among the various methods utilized for UES, application of metal organic frameworks (MOFs) has grabs significant attention due to their high surface area and selective reactivity, tunable pore structure, tailored functionality, and optimal structural stability in ocean water.<br/>This study aims to boost the uranium extraction efficiency as well as chemical and structural stability in marine environment by fabricating a hierarchically mesoporous Ce-based MOF (CeHMMOF). Leveraging efficient coordination between Ce and the ligand (2-amino terephthalic acid) incorporated with soft template (Pluronic, F127), a superstructure CeHMMOF (particle size; 1.5 - 2 µm) was successfully synthesized via one pot solvothermal approach. The synthesized MOF was systematically characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) to ascertain its structural, chemical, and morphological attributes.<br/>The stability test conducted in simulated seawater conditions (Na⁺ = 23,000 mg/L, Cl^- = 35,500 mg/L, C₀ = 100 µg/L , pH = 8.0) revealed promising chemical stability and structural resilience of CeHMMOF during prolonged exposure to simulated seawater up to 21 days, signifying its potential for practical deployment of UES at a larger scale. In terms of affinity for uranium and extraction efficiency in simulated seawater conditions, CeHMMOF displayed robust uranium removal efficiency (&gt;50% of 100 µg/L initial U concentration in 12 minutes), surpassing reported materials concerning the extraction efficiency, and thus affirming the outstanding capability and considerable scope of synthesized Ce-based MOF sorbent for UES application.<br/>In this work, we have developed a highly stable hierarchically mesoporous Ce-based MOFs with an efficient uranium extraction performance in harsh seawater conditions and proposed as an emerging candidate material for a high-throughput and sustainable UES, aligning well with ongoing global efforts to develop a clean and renewable energy resource.<br/>To ensure the practical utilization of CeHMMOF on commercial scale, our research is ongoing and in the subsequent phases of this study, firstly, we will comprehensively evaluate the irradiation stability of synthesized MOF to assure its material stability and structural integrity under induced irradiation for long term onshore UES applications. Thereafter, uranium removal mechanism will be investigated in conjunction with other parameters impacting UES performance, including regeneration rate and selectivity of fabricated MOF for uranium extraction in natural seawater.