Reaction: Porous Organic Polymers for Uranium Capture

Abstract

Cafer T. Yavuz received his PhD from Rice University in 2008 with a Welch scholarship under the supervision of Vicki Colvin. He then worked as a postdoctoral scholar at the University of California, Santa Barbara, with Galen Stucky. He started his independent group in 2010 at KAIST, Korea. He is currently a professor of chemistry at the King Abdullah University of Science and Technology in Saudi Arabia. His research focuses on the design and synthesis of nanoscale and porous materials for applications in energy and the environment. He uses fine chemistry in confined spaces to enable rapid and targeted transformations of CO2, methane, and water. Cafer T. Yavuz received his PhD from Rice University in 2008 with a Welch scholarship under the supervision of Vicki Colvin. He then worked as a postdoctoral scholar at the University of California, Santa Barbara, with Galen Stucky. He started his independent group in 2010 at KAIST, Korea. He is currently a professor of chemistry at the King Abdullah University of Science and Technology in Saudi Arabia. His research focuses on the design and synthesis of nanoscale and porous materials for applications in energy and the environment. He uses fine chemistry in confined spaces to enable rapid and targeted transformations of CO2, methane, and water. As clearly stated by Kushwaha and Patel,1Kushwahaa S. Patel K. Uranium extraction from seawater: a paradigm shift in resource recovery.Chem. 2021; 7: 271-274Abstract Full Text Full Text PDF Scopus (4) Google Scholar uranium recovery from seawater is largely a game of economics and scale because of the elevated costs of sorbents and labor. For example, extracting 1 g of uranium requires that 300 tons of seawater be processed. Not to mention less than 1% of natural uranium is fissile, and therefore the theoretical energy potential is just equivalent to 15~20 kg of dirt-cheap coal. In fact, the process of treating large amounts of caustic ocean water is no small task and requires corrosion-resistant equipment and oxidation-proof adsorbents that can also withstand immense pressure from the pumped brine. These unforgiving conditions necessitate robust adsorbent materials. Among porous materials developed thus far, porous organic polymers (POPs) offer the best of both worlds: porosity and stability. This is why there has been a surge in studies of uranium capture by POPs,2Wang Z. Meng Q. Ma R. Wang Z. Yang Y. Sha H. Ma X. Ruan X. Zou X. Yuan Y. Zhu G. Constructing an ion pathway for uranium extraction from seawater.Chem. 2020; 6: 1683-1691Abstract Full Text Full Text PDF Scopus (29) Google Scholar,3Sihn Y. Byun J.H.A. Patel H.A. Lee W. Yavuz C.T. Rapid extraction of uranium ions from seawater using novel porous polymeric adsorbents.RSC Advances. 2016; 6: 45968-45976Crossref Google Scholar which reach capacities of 13.0 mg g−1 from natural seawater.1Kushwahaa S. Patel K. Uranium extraction from seawater: a paradigm shift in resource recovery.Chem. 2021; 7: 271-274Abstract Full Text Full Text PDF Scopus (4) Google Scholar,2Wang Z. Meng Q. Ma R. Wang Z. Yang Y. Sha H. Ma X. Ruan X. Zou X. Yuan Y. Zhu G. Constructing an ion pathway for uranium extraction from seawater.Chem. 2020; 6: 1683-1691Abstract Full Text Full Text PDF Scopus (29) Google Scholar The challenges in uranium capture, however, are not just limited to scale or stability; solving uranyl (UO22+) selectivity over vanadyl (VO2+) ions is quite difficult.1Kushwahaa S. Patel K. Uranium extraction from seawater: a paradigm shift in resource recovery.Chem. 2021; 7: 271-274Abstract Full Text Full Text PDF Scopus (4) Google Scholar It is no coincidence that only a few of the literature reports report uranyl/vanadyl selectivity. Another downplayed problem is pH. It turns out that amidoximes, the most popular functional group for uranyl binding,3Sihn Y. Byun J.H.A. Patel H.A. Lee W. Yavuz C.T. Rapid extraction of uranium ions from seawater using novel porous polymeric adsorbents.RSC Advances. 2016; 6: 45968-45976Crossref Google Scholar,4Xu X. Zhang H. Ao J. Xu L. Liu X. Guo X. Li J. Zhang L. Li Q. Zhao X. et al.3D hierarchical porous amidoxime fibers speed up uranium extraction from seawater.Energy Environ. Sci. 2019; 12: 1979Crossref Google Scholar capture uranium far better when solutions are strongly acidic (e.g., pH < 5). We attempted to address this issue by bubbling CO2 into ocean water to bring down the pH,3Sihn Y. Byun J.H.A. Patel H.A. Lee W. Yavuz C.T. Rapid extraction of uranium ions from seawater using novel porous polymeric adsorbents.RSC Advances. 2016; 6: 45968-45976Crossref Google Scholar but the logistics and environmental impact of such processes are not attractive. And yet another, never truly addressed problem is the wettability of the adsorbents. Uranyl ions are dissolved in water, and the kinetics of adsorption will depend squarely on the efficient mass transport of seawater within a porous framework. Unfortunately, hydrophobicity is often used to make porous materials water resistant. Covalent frameworks of POPs, however, do not require such preventive measures and can be tuned with chemical grafting. In addition to the challenges above, practical seawater testing for uranium adsorbents often necessitates polymer fibers.4Xu X. Zhang H. Ao J. Xu L. Liu X. Guo X. Li J. Zhang L. Li Q. Zhao X. et al.3D hierarchical porous amidoxime fibers speed up uranium extraction from seawater.Energy Environ. Sci. 2019; 12: 1979Crossref Google Scholar This is for easy processing and deployment, because otherwise adsorbent powders would need enclosures such as “teabags.” Many porous materials are not easily made into fibers, and monolithic design efforts backfire with a heavy loss in porosity. A subset of POPs that can address all these requirements are called polymers of intrinsic microporosity (PIMs). PIMs are linear ladder polymers that feature covalently locked curvatures enabling permanent porosity while providing handling just like any other polymer fiber. We have previously shown an amidoxime-PIM-1 enhancing the kinetics of uranium capture.3Sihn Y. Byun J.H.A. Patel H.A. Lee W. Yavuz C.T. Rapid extraction of uranium ions from seawater using novel porous polymeric adsorbents.RSC Advances. 2016; 6: 45968-45976Crossref Google Scholar Our investigations continue in this direction because we believe an optimized PIM would check all the boxes for a commercial uranium-capture operation. There is still a lot of hope in pursuing the development of uranium-adsorbing POPs. One clear advantage of the exceptional stability of POPs, compared with other emerging porous materials, is that they can be cast in the ocean for months without any loss of activity and harvested periodically for sustained uranium production. And because they’re fully organic, regeneration and single use are both feasible given the budgets of the operator. Catalyst: Uranium Extraction from Seawater, a Paradigm Shift in Resource RecoveryKushwaha et al.ChemFebruary 11, 2021In BriefNuclear energy, a low-carbon route to lowering worldwide greenhouse gas emissions, could play a critical role in the transition to a clean energy future. However, low terrestrial supplies of uranium ore could limit the potential of nuclear power unless alternative extraction methods are employed. This Catalysis article highlights the development of methods for sustainable uranium extraction from seawater by discussing past progress and future goals for the discovery and implementation of seawater extraction methods. Full-Text PDF Reaction: Semiconducting MOFs Offer New Strategy for Uranium Extraction from SeawaterLi et al.ChemFebruary 11, 2021In BriefUranium extraction from seawater is one of the most important chemical separations for society given that oceanic uranium reserves could enable the expansion of low-carbon nuclear energy production. In this reaction piece, Li and Wang discuss the potential of metal-organic frameworks (MOFs) for efficient and sustainable uranium extraction from seawater. Full-Text PDF Reaction: Goal-Oriented PAF Design for Uranium Extraction from SeawaterGuangshan ZhuChemFebruary 11, 2021In BriefAlthough nuclear power is a promising technology for achieving a clean energy economy, the terrestrial availability of uranium limits implementation of nuclear power. In this reaction piece, Zhu discusses how porous aromatic frameworks, which are especially promising for adsorbent methods given their open framework architectures, chemically amenable fragments, and high surface areas, have advanced uranium extraction from seawater. Full-Text PDF Reaction: Engineer Biology for UraniumSun et al.ChemFebruary 11, 2021In BriefCost and scalability remain major hurdles facing existing technologies for the extraction of oceanic uranium, but repurposing existing biological systems could help overcome these obstacles. In this reaction piece, Sun and He discuss the progress in protein engineering of biological systems to sustainably mine uranium from seawater. 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