Intrinsically Porous Polyoxometalate-Based Frameworks for Critical Metal Recovery
Z. Peng, University of Missouri-Kansas City (Principal Investigator)
P. Thallapally, Pacific Northwest National Laboratory (Co-Investigator)
M. Momenitaheri, University of Missouri-Kansas City (Co-Investigator)
As the world transitions to renewable energy technologies, demands on critical metals are expected to surge, exacerbating the already dire critical metal shortage issue and threatening the US economy and national defense. With dwindling terrestrial ore mining and increasing environmental concerns, aqueous saline sources are increasingly being recognized as one of the major sources of critical metals. One critical technical challenge is how to selectively extract the desired critical metals, often in very low concentrations, from the saline sources and then effectively release them afterward for recovery.
This project hypothesizes that intrinsically porous polyoxometalate (POM) molecular clusters and POM-derived porous frameworks (POMFs) with precisely controlled pore sizes and chemical environments are potentially effective, selective, and electrically switchable adsorbents for critical metal ions from saline sources. This hypothesis is rooted in POMs’ unmatched structural and compositional tunability, ease of synthesis, and high thermal stability. More importantly, POMs are robust redox active materials that can undergo repeated reduction-oxidation cycles. The redox process does not alter the overall structure but can result in changes in the size and chemical environment of the pores, which in turn affects the binding affinity and selectivity toward different metal ions. Such a property may allow electrochemical switching of the adsorption and desorption of critical metal ions, addressing the challenging paradox of sorption-based recovery where a sorbent must have favored adsorption isotherm during capture but unfavored isotherm during release. To test this hypothesis and to accelerate materials discovery, a closed-loop approach that encompasses data science adaptation, computationally aided materials design, materials synthesis, and performance evaluation is adopted. The technical approach of the project includes 1) building comprehensive mega-databases of POMFs using an in-house developed Crystal Structure Producer for POM (CrySP4POM) software package and expanding our calculation programs to predict their properties. These databases and calculation programs can be the launch pad to initiate machine learning programs to design not only adsorbents for critical metal recovery but also POM-based materials for other applications such as catalysis and energy storage. (2) Materials design through modeling and simulation. Tungsten-based Preyssler anions have already been shown to possess remarkably high selectivity toward some lanthanoid and actinoid due to the narrow size selectivity, while the internal cavity of the super-lacunary cyclic heteropolyanion {P8W48} has been shown to be able to capture a wide variety of transition metal ions, lanthanoids, and other elements. To understand, predict and develop porous POMs with the right pore size and to establish structure-property relationships, we will perform high-throughput electronic structure calculations combined with molecular dynamic simulations to survey and predict selective metal adsorption capabilities of doughnut-shaped POMS (ds-POMs) with varied compositions. (3) Synthesis of predicted promising ds-POMs with varied chemical compositions and controlled pore sizes. (4) Preparation of POM-derived porous frameworks (POMFs) using the most promising ds-POMs as building blocks. The network formation can be carried out in the presence of polymers such as polyethylene glycol or polyethyleneimine to form intrinsically porous interpenetrating POM/polymer hybrids, which may be fabricated as membranes for convenient filtration applications. (5) Performance evaluation of ds-POMs and POMFs as selective critical metal adsorbents with or without electrochemical reduction. At the conclusion of the project, the hypothesis that POMs with precisely tuned pores and porous structures are electrochemically switchable critical metal ion-capturing materials from aqueous saline sources will be thoroughly tested.
