Metal extraction using novel polyoxometalate materials

Abstract

Provided is a polyoxometalate (POM) composition comprising a polyoxometalate cluster [e.g., polyoxoniobate (PONb)] forming a network, and methods and use thereof. A first metal (e.g., Mg2+) can be isolated from a source containing a first metal and a second metal (e.g., K+, Li+, or Na+) at varied ratios by contacting the source with the POM composition. According to the methods provided herein, the first metal can be sequestered with the POM composition from the second metal within a short time (e.g., one minute or less) with high selectivity (e.g., selectivity the second metal over the first metal remaining in the source of 200 or more) and high yield (e.g., at least 95% of the first metal is removed from the source). The POM composition can be regenerated by separating the bound first metal from the POM composition. A method of generating the POM composition is also provided.

Description

Docket No. 2024-076-02 | L102142 1640WOMETAL EXTRACTION USING NOVEL POLYOXOMETALATE MATERIALSInventors: Chaochao Dun. Linfeng Chen, and Jeffrey J. UrbanCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 751,418, filed on January 30, 2025, the content of which is incorporated herein by reference in its entirety.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in this invention.TECHNICAL FIELD

[0003] This disclosure relates generally to selective ion removal or metal extraction from various recourses.BACKGROUND

[0004] Lithium (Li) and magnesium (Mg) are recognized as critical mineral materials (CMM) due to their essential roles in modem technologies, particularly in energy storage and electric vehicle industries. Rising global demand has driven Li prices nearly tenfold from 2020 to 2022, with demand projected to rise sevenfold by 2030. However, efficient Li+isolation from brine is critically hindered by the presence of Mg2+, a physiochemically similar ion that is often abundant in Li-sources.

[0005] While brines account for -60% of identified Li reserves, their exploitation is limited by inefficient extraction methods. The conventional lime-soda process is slow, energy-intensive, and presents pollution challenges while offering only modest (<40%) recovery. Li extraction from brines requires purification steps to eliminate more abundant ions (Na+, Ca2+, Mg2+) before isolating the relatively dilute Li+. Na+is commonly removed via selective evaporation, while Ca2+is typically precipitated as CaCCL.

[0006] The core challenge remains the selective separation of Li+from Mg2+, which have similar hydrated radii and often coexist at high concentrations in natural brines. Conventional methods require repeated precipitation and concentration steps, causing Li+loss and generating hazardous waste. Although direct lithium extraction (DLE) technologies — including adsorption, electrochemical, and membrane processes — have emerged as potential improvements, they are often constrained by dependency on relatively low Mg-to-Li ratios and operate at low flux under highly controlled1WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOconditions, limiting scalability across diverse brine compositions. Meanwhile, Mg2+itself is a critical material for automotive and aerospace industries, making its co-recovery desirable.BRIEF SUMMARY

[0007] Provided herein is a novel polyoxometalate (POM)-based system designed for the selective removal and recovery’ of metals (e.g., critical metals), specifically lithium (Li+) and magnesium (Mg2+), from nontraditional brine sources. Traditional ion-removal methods such as precipitation, ion exchange, and reverse osmosis often lack specificity and are energy-intensive, making them less suitable for the selective extraction of these critical metals. The POM-based system addresses this issue by exhibiting remarkable selectivity for Li+and Mg2+, with a selectivity ratio of over 1000, allowing for targeted separation and recovery of these valuable metals. The versatility of POM structures, their tunable solubility profiles, and bespoke ion binding capabilities make them exceptional extraction agents. POM synthesis can be tailored to create specific binding site ("keyhole") sizes, shapes, and bonding energies that selectively interact with target ions, enhancing the efficiency and specificity of the ion removal process. The present disclosure not only enables the efficient recovery of critical metals but also contributes to the purification of brines, further enhancing the environmental and economic benefits of the technology.

[0008] In one aspect, the present disclosure provides a polyoxometalate (POM) composition comprising a polyoxometalate cluster bound to a metal and forming a network.

[0009] In some embodiments, the polyoxometalate comprises a polyoxoniobate (PONb). In some embodiments, the PONb comprises [Nb6O19]8−. In some embodiments, the metal is bound to the polyoxometalate cluster via a terminal oxygen (Ot), a bridging oxygen (Ob), or a hydrogen bonding (H-bond). In some embodiments, the metal is K+, Mg2+, Li+, or Na+. In some embodiments, the polyoxometalate composition comprises K8[Nb6O19], Li8[Nb6O19], H2Na6[Nb6O19], or Mg4[Nb6O19]. In some embodiments, the polyoxometalate composition is a hydrate.

[0010] In another aspect, the present disclosure provides a method of generating a first polyoxometalate (POM) composition comprising a polyoxometalate cluster bound to a first metal, the method comprising: mixing a metal oxide, a metal hydroxide, and water to provide a mixture; heating die mixture; cooling the mixture; adding methanol to precipitate the polyoxometalate composition, wherein the polyoxometalate cluster is derived from the metal oxide and the first metal is derived from the metal hydroxide; and isolating the precipitated polyoxometalate composition, thereby generating a polyoxometalate composition.

[0011] In some embodiments, the metal oxide comprises Nb20s. and the polyoxometalate comprises a polyoxoniobate (PONb). In some embodiments, the first metal is K, or the first polyoxometalate composition comprises K8[Nb6O19] and H2O.2WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0012] In some embodiments, the method further comprises: contacting the first polyoxometalate composition with a metal salt; and obtaining a second polyoxometalate composition comprising the POM bound to a second metal derived from the metal salt.

[0013] In some embodiments, the second metal is Li, Na, or Mg, or the second polyoxometalate composition comprises Li8[Nb6O19], H2Na6[Nb6O19], or Mg4[Nb6O19]. and H2O.

[0014] In yet another aspect, the present disclosure provides a method of isolating a first metal from a source containing a first metal and a second metal, the method comprising:

[0015] contacting the source with a polyoxometalate (POM) composition comprising a polyoxometalate cluster, thereby binding the first metal to the polyoxometalate cluster;

[0016] separating the polyoxometalate cluster bound to the first metal from the source, thereby isolating the first metal from the source and from the second metal.

[0017] In some embodiments, the polyoxometalate comprises a polyoxoniobate (PONb). In some embodiments, the first metal or the second metal comprises a critical mineral material. In some embodiments, the first metal comprises Mg2+and the second metal comprises Li+.

[0018] In some embodiments, the source is brine or wastewater.

[0019] In some embodiments, the selectivity of the second metal over the first metal remaining in the source after separating the polyoxometalate bound to the first metal from the source is about 200 or more, about 400 or more, or about 1000 or more. In some embodiments, at least 95%. 96%, 97%, 98%, or 99% of the first metal and at least 95%, 96%, 97%, 98%, or 99% of the second metal are recovered from the source. In some embodiments, binding of the first metal to the polyoxometalate cluster occurs within 1 minute after contacting the source with the polyoxometalate composition.

[0020] In some embodiments, the method further comprises regenerating the polyoxometalate composition by: after binding the first metal to the polyoxometalate cluster, treating the polyoxometalate cluster bound to the first metal with KOH at elevated temperature; and collecting the first metal as a hydroxide precipitate. In some embodiments, the polyoxometalate composition maintains polyoxometalate recovery efficiency of at least 98% over 5 regeneration cycles.

[0021] Details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary’ fee.3WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0023] FIGs. 1A and IB depict a comparison between the industrial lime-soda process and the PONb-based selective sequestration process. FIG. 1A depicts a schematic illustration of the conventional lime-soda evaporation method for Li+recovery from mixed Li+ / Mg2+brines. The process involves multiple sequential precipitation steps (typically 5-10 cycles), where Ca(OH)2 and Na2CO3are alternately added to remove Mg2+and Ca2+ions via the formation of (Mg(OH)2)n and (CaCO3)n precipitates. However, this process suffers from significant lithium loss at each stage due to coprecipitation and inefficient separation, lacks a regeneration mechanism, and produces large volumes of solid waste. FIG. IB depicts the PONb-based selective sequestration process that enables rapid and nearly complete separation of Mg2+and Li+from brine in a single step. Upon addition of PONb, Mg2+ions are selectively captured to form a Mg-PONb sponge, leaving Li+and K+in the supernatant. After filtration, Mg2+can be recovered as crystalline Mg(OH)2 (-99% yield), and the Li+-rich filtrate can be further processed with Na2CO3 to yield Li2CO3following literature -reported procedures. Importantly, the PONb material can be regenerated with -99% efficiency, enabling multiple-use cycles and significantly reducing waste generation.

[0024] FIGs. 2A-2C depict the PONb-based selective sequestration process and resulting structure.FIG. 2A depicts time-lapse photographs showing the rapid self-assembly process of the Mg-PONb sponge in brine solutions (left to right). Upon the addition of K8{Nb6O19}•9H2O (also referred to herein as 'native- PONb'') (0.1 M, 1 ml) to an aqueous simulated brine containing MgCL / LiCl (0.1 M / 0.02 M, 5 ml), the solution transitions from transparent to the formation of visible sponge-like aggregates, indicating the successful sequestration of Mg2+ions. This process occurs within 1 second and can be visually monitored, demonstrating the efficient and fast separation of Mg2+from Li+in brine. FIG. 2B depicts a schematic of the PONb-based selective sequestration process. Upon addition of PONb, Mg2+ions are selectively captured from brine, forming a regenerable Mg-PONb sponge. This rapid and selective sequestration process leads to the formation of a visible solid, enabling nearly complete separation of Mg2+from Li+. The Mg-PONb sponge can then be isolated by simple filtration and further treated to recover Mg(OH)2 with -99% yield. The PONb material demonstrates excellent reusability, with -99% regeneration efficiency over repeated cycles. FIG. 2C depicts the crystalline framework of the resulting Mg-PONb sponge material. Water omitted for clarity. Color code: Nb polyhedral (green). O atoms (red), Mg atoms (yellow).

[0025] FIG. 3 depicts a ball-and-stick representation of native-PONb that highlights bond connections. Water omitted for clarity. Color code: Nb (green), O (red), K (purple), H (grey), H-bond (dash line).

[0026] FIG. 4 depicts native-PONb network with polyhedral representation in ac-plane. Water omitted for clarity. Color code: Nb polyhedral (green), O (red), K (purple), H (grey), H-bond (dash line).4WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0027] FIG. 5 depicts native-PONb network with polyhedral representation in bc-plane. Water omitted for clarity. Color code: Nb polyhedral (green). O (red), K (purple), H (grey), H-bond (dash line).

[0028] FIG. 6 depicts the specific conditions for single crystal growth, where successful formations of Li-PONb (blue). Na-PONb (green). Mg-PONb (yellow) are highlighted, while the purple markers indicate failed attempts to grow Mg-PONb crystals.

[0029] FIGs. 7A-7D depict powder X-ray diffraction patterns measured using an oil-assisted method to preserve lattice water. FIG. 7A depicts Native-PONb, FIG. 7B depicts Li-PONb, FIG. 7C depicts Na-PONb, and FIG. 7D depicts Mg-PONb. Simulated patterns based on single-crystal data are shown at the bottom of each panel for comparison. The data demonstrate that all bulk samples retain structures consistent with their corresponding single crystals.

[0030] FIG. 8 depicts a ball-and-stick representation of Mg-PONb that highlights bond connections. Water omitted for clarity. Color code: Nb atom (green), O (red), Mg (yellow).

[0031] FIG. 9 depicts Mg-PONb network with polyhedral representation in ac-plane. Water omitted for clarity. Color code: Nb polyhedral (green), O (red), Mg (yellow).

[0032] FIG. 10 depicts a ball-and-stick representation of Li-PONb that highlights bond connections. Water omitted for clarity. Color code: Nb atom (green). O (red). Li (blue), H (grey), H-bond (dash line).

[0033] FIG. 11 depicts Li-PONb network with polyhedral representation in ac-plane. Water omitted for clarity’. Color code: Nb polyhedral (green), O (red), Li (blue), H (grey), H-bond (dash line).

[0034] FIG. 12 depicts Li-PONb network with polyhedral representation in ab-plane. Water omitted for clarity. Color code: Nb polyhedral (green). O (red). Li (blue), H (grey), H-bond (dash line).

[0035] FIG. 13 depicts a ball-and-stick representation of Na-PONb that highlights bond connections. Water omitted for clarity. Color code: Nb atom (green), O (red), Na (light blue), H (grey), H-bond (dash line).

[0036] FIG. 14 depicts Na-PONb network with polyhedral representation in ab-plane. Water omitted for clarity. Color code: Nb polyhedral (green). O (red). Na (light blue), H (grey), H-bond (dash line).

[0037] FIG. 15 depicts Na-PONb network with polyhedral representation in bc-plane. Water omitted for clarity. Color code: Nb polyhedral (green), O (red), Na (light blue), H (grey). H-bond (dash line).5WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0038] FIGs. 16A-16F depict structural and spectroscopic analysis of M-PONb materials. FIG. 16A depicts a ball-and-stick representation of different bond connections with PONb: Nb-Ot-M (left), Nb-Ob-M (middle) and Nb-O-H bond (right). Water omitted for clarity. Color code: Nb (green), terminal O atoms (pink), rest of O atoms (red), Mg (orange), K (purple), Li (blue). FIG. 16B depicts O Is (left) and Nb 3d (right) XPS of M-PONb. FIG. 16C depicts O K-edge TFY of M-PONb. FIG.16D depicts Raman spectra of M-PONb. FIG. 16E depicts N2adsorption isotherm plot of M-PONb.FIG. 16F depicts1H solid-state NMR spectra and the corresponding devolution of1H line shapes of M-PONb. (M=K+, Li+, Na+, Mg2+). Here, site A is associated with interactions between H2O and the POM cluster, while site B is associated with interactions between H2O and M. The observed 1H chemical shift of water in M-PONb is indicated for each spectrum.

[0039] FIGs. 17A-17G depict global brine analysis and ICP-OES results. FIG. 17A depicts a word map illustrating the Mg-to-Li ratio (MLR) in brines globally. FIGs. 17B-17G depict results from ICP-OES analysis of synthetic Li / Mg brine, designed to replicate the MLR of major brine sources worldwide.

[0040] FIGs. 18A-18E depict ICP-OES results for Li+ / Mg2+separation performance of laboratory-prepared simulated brines mimicking major salt lakes with different MLR. FIG. 18A depicts MLR 0.02, FIG. 18B depicts MLR 2.68, FIG. 18C depicts MLR 24.60, FIG. 18D depicts MLR 54.39, and FIG. 18E depicts MLR 116.82. Yellow curve represents the variation in Mg2+concentration, while the blue curve represents the variation in Li+concentration. The salt concentration of the binary salt mixture is less than 1000 ppm.

[0041] FIGs. 19A-19E depict ICP-OES results for Li7Mg2+separation performance of laboratory-prepared simulated brines mimicking major salt lakes with different MLR. FIG. 19A depicts MLR 0.27, FIG. 19B depicts MLR 3.22, FIG. 19C depicts MLR 33.89, FIG. 19D depicts MLR 115.31, and FIG. 19E depicts MLR 200.64. Yellow curve represents the variation in Mg2+concentration, while the blue curve represents the variation in Li+concentration. The salt concentration of the binary metal salt mixture is between -1000-3000 ppm.

[0042] FIGs. 20A-20F depict ICP-OES results for Li+ / Mg2+separation performance of laboratory-prepared simulated brines mimicking major salt lakes with different MLR. FIG. 20A depicts MLR 0.04, FIG. 20B depicts MLR 0.35, FIG. 20C depicts MLR 2.83, FIG.20D depicts MLR 48.86, FIG.20E depicts MLR 94.96, and FIG.20F depicts MLR 199.85. Yellow curve represents the variation in Mg2+concentration, while the blue curve represents the variation in Li+concentration. The salt concentration of the binary’ metal salt mixture is between -7000-30000 ppm.

[0043] FIGs.21A-21C depict ICP-OES results for Na+ / Mg2+separation performance of laboratory-prepared simulated brines mimicking major salt lakes with different Mg-Na-ratio. FIG.21A depicts Mg-Na-ratio 0.10, FIG.21B depicts Mg-Na-ratio 1.11, and FIG. 21 C depicts Mg-Na-ratio 10.59.6WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOYellow curve represents the variation in Mg2+concentration, while the green curve represents the variation in Na+concentration. The salt concentration of the binary salt mixture is less than 300 ppm. When Na+was introduced into the Mg2+solution, at least 81.7% of Mg2+was captured within one minute and over 99.8% Mg2+was captured at the end of test, although 2.3% of Na+was also captured over 24 hours. Despite this minor co-capture of Na+. native-PONb still demonstrated robust separation capabilities for Na+ / Mg2+.

[0044] FIGs. 22A-22D depict ICP-OES results for K+ / Mg2+separation performance of laboratory-prepared simulated brines mimicking major salt lakes with different Mg-K-ratio. FIG.22A depicts Mg-K-ratio 0.06, FIG.22B depicts Mg-K-ratio 0.62, FIG.22C depicts Mg-K-ratio 6.19, and FIG.22D depicts Mg-K-ratio 61.23. Yellow curve represents the variation in Mg2+concentration, while the purple curve represents the variation in K+concentration. Due to the presence of K+ions within the native-PONb material, the effective concentration of K+in the system is determined by subtracting the K+contribution from the native-PONb from the total measured K+concentration. The results demonstrated that native-PONb exhibits near-perfect separation efficiency for K+ / Mg2+. Within one minute, over 99.4% of Mg2+was captured, and 99.9% was captured within 10 minutes. After 24 hours, 99.9% of K+remained in the mixtures. These findings underscore the exceptional potential of native-PONb materials for selective separation of K+ / Mg2+.

[0045] FIGs. 23A-23J depict molecular dynamics simulations and spectroscopic analysis. FIG. 23A depicts representative simulation snapshots depicting the initial configuration of native-PONb molecules in aqueous mixtures prior to the addition of various metal cations. FIG. 23B depicts aggregate state analysis based on cluster formation, using a cutoff distance of 2.30 A. FIG. 23C depicts representative snapshots illustrating the system following the addition of pure Li+ions, FIG.23D depicts a mixture of Li+and Mg2+ions at a 10:1 ratio, FIG. 23E depicts a mixture of Li+and Mg2+ions at a 1:10 ratio, and FIG.23F depicts pure Mg2+ions. Color code: Nb (green), O (red), Mg (orange), K (purple), Li (blue). FIG. 23G depicts in-situ Raman spectroscopy results following the addition of Mg2+ions and FIG. 23H depicts Li+ions within 60 s. FIG. 23I depicts Dynamic Light Scattering (DLS) analysis comparing the effects of different amount of Li+and Mg2+ions and FIG.23J depicts DLS analysis comparing the effects of different amounts of Li+and Mg2+ions.

[0046] FIGs. 24A-24F depict photographs of native-PONb solution interactions with different metal chlorides. FIG. 24A depicts photographs of native-PONb (0.01M, 5ml) solution interactions with aqueous MgCL (0.01 M, 50 pl), FIG.24B depicts additional photographs of the same interaction, FIG. 24C depicts further photographs of the same interaction, FIG.24D depicts photographs of native-PONb solution interactions with LiCl (2M, 50 pl). FIG.24E depicts additional photographs of the LiCl interaction, and FIG. 24F depicts further photographs of the LiCl interaction.5 ml of 0.01 M native-PONb was placed in a glass vial, followed by the sequential addition of 50 pl of 2.0 M LiCl and 50 pl of 0.01 M MgCL. Upon the addition of MgCL, a significant amount of 7WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOprecipitate formed instantaneously, while the Li solution remained clear. This observation is consistent with the in-situ Raman spectroscopy results, providing robust evidence for the rapid and efficient separation mechanism.

[0047] FIGs. 25A-25E depict the regeneration process and cyclability analysis. FIG. 25A depicts a schematic of the regeneration process. After the selective sequestration of Mg2+by PONb to form a Mg-PONb sponge, treatment with KOH and heating releases Mg2+as Mg(OH)2. allowing recovery of active PONb. FIG. 25B depicts Mg2+rejection rate and Li flux rate over five separation-regeneration cycles, showing stable performance without degradation. A yellow box indicates Mg2+and a blue box indicates Li+to clearly distinguish the two in the plot. FIG.25C depicts Raman spectra of the PONb sponge after each cycle. FIG. 25D depicts XRD pattern of the solid collected during the regeneration step, matching the reference pattern for Mg(OH)2(PDF# 30-0794), confirming that Mg(OH)2is formed as a by-product during PONb regeneration. FIG. 25E depicts Nb recovery efficiency across five regeneration cycles, consistently achieving over 98%, highlighting the excellent recyclability of the sy stem. The dotted line represents the 98% reference level.

[0048] FIGs. 26A and 26B depict different configurations for metal ions to connect with PONb.FIG. 26A represents the metal ions connect with bridge oxygen of PONb. FIG.26B represents the metal ions connect with terminal oxygen of PONb.DETAILED DESCRIPTION

[0049] Reference will now be made in detail to some specific examples of the invention including the best modes contemplated by the inventors for carrying out the invention. Examples of these specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

[0050] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Particular example embodiments of the present invention may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

[0051] Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise.8WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0052] The terms “about” or “approximate” and the like are synonymous and are used to indicate that the value modified by the term has an understood range associated with it, where the range can be ± 20%, ± 15%, ± 10%, ± 5%, or ± 1%. The terms “substantially” and the like are used to indicate that a value is close to a targeted value, where close can mean, for example, the value is within 80% of the targeted value, within 85% of the targeted value, within 90% of the targeted value, within 95% of the targeted value, or within 99% of the targeted value.

[0053] The present disclosure provides the use of Poly oxometalates (POMs) for selective ion removal from nontraditional brines or other water recourses, for example for extracting critical materials and minerals like magnesium (Mg2+) and lithium (Li+). These ions are used in industries like battery production and automotive alloys but are challenging to extract due to their similar ionic sizes.

[0054] POMs, characterized by their molecular metal-oxide anions formed through self-assembly, stand out for their high selectivity towards Mg2+and Li+ions, achieving a selectivity ratio over 1000. This high selectivity is attributed to their ability to disrupt hydrogen bonding in aqueous solutions due to their chaotropic nature, which enables them to induce precipitation of various ions. By manipulating the solubility differences between various cation-POM pairs, efficient separation of cations is facilitated. This innovative approach overcomes the limitations of traditional ion removal methods like precipitation, ion exchange, and reverse osmosis, which lack specificity and costeffectiveness. The technology is remarkably versatile, capable of handling a broad range of concentrations, with Li+concentrations ranging from 7 to 7000 mg / L. and Mg2+concentrations spanning from 24 to 24000 mg / L. Despite these wide ranges, the system maintains exceptional performance, rejecting less than 1% of Li+while achieving a Mg2+rejection rate of 99%. The selectivity between Li+and Mg2+is outstanding, exceeding a ratio of 1000, highlighting the system's precision and efficiency in distinguishing and separating these ions. Provided herein is a collection of POMs tailored for selective extraction of these valuable ions from real-world wastewater. The engineered structures of POMs allow for targeted interaction with specific ions.

[0055] The present disclosure provides methods of metal extraction with the separation time of less than 1 minute. The benefit of rapid separation, achieved in less than 1 minute not only enhances the efficiency of the process but also reduces operational costs and energy consumption. This quick separation capability with high selectivity enables continuous and high-throughput processing, helpful for large-scale applications and industries requiring timely extraction of critical materials.

[0056] For example, provided herein is a composition comprising a polyoxoniobate (PONb) cluster framework that selectively sequesters Mg2+from Li+from sources (e.g., brines), which can be called a “Mg-PONb sponge.” By' leveraging the high surface basicity and tunable coordination chemistry of the PONb cluster, the system achieves >99.9% Mg2+removal with negligible Li+loss in less than one minute, delivering Li+ / Mg2+selectivity values exceeding 5000 across an exceptionally broad range of Mg-to-Li ratios (0.02 to 200.63).9WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0057] The PONb sponge is robustly reusable (also referred to as recyclable), maintaining >99% Mg2+rejection and Li+permeability over five regeneration cycles without structural or functional degradation. Over 98.92% of the PONb material can be consistently regenerated, while more than 98.86% of captured Mg2+is recovered as crystalline Mg(OH)2. Mechanistic investigations confinn that Mg2+selectivity arises from strong coordination to terminal oxygen sites in the PONb structure, driving rapid formation of stable, porous Mg-PONb frameworks. The methods provided herein not only significantly enhance Li+ / Mg2+separation efficiency but also enable recovery of Mg2+, which is typically discarded as waste.

[0058] FIG. 1 A illustrates the conventional lime-soda evaporation method currently employed in industrial Li+recover}’ from mixed Li+ / Mg2+brines. This traditional approach requires multiple sequential precipitation steps, typically involving 5-10 cycles wherein Ca(OH)2and Na2CO3 are alternately added to remove interfering Mg2+and Ca2+ions through formation of (Mg(OH)2)n and (CaCO3)n precipitates, respectively. The conventional process suffers from several critical deficiencies: (i) significant lithium loss at each processing stage due to co-precipitation and inefficient separation; (ii) absence of a regeneration mechanism for process chemicals; and (iii) production of large volumes of solid waste requiring disposal. These limitations result in poor overall Li+recovery efficiency, typically below 40%, and substantial environmental burden from waste generation.

[0059] In contrast to conventional methods, FIG. 1B demonstrates the PONb-based selective sequestration process of the present invention, which enables rapid and nearly complete separation of Mg2+and Li+from brine in a single processing step. Upon addition of PONb to the brine solution, Mg2+ions are selectively captured to form a Mg-PONb sponge structure, while Li+and K+ions remain in the supernatant solution. Following simple filtration, captured Mg2+can be recovered as crystalline Mg(OH)2with approximately 99% yield, and the Li+-rich filtrate can be further processed with Na2CO3 to yield Li2CO3 according to established procedures. Critically, the PONb material demonstrates regeneration efficiency of approximately 99%, enabling multiple-use cycles and significantly reducing waste generation compared to conventional approaches.

[0060] As shown in FIG. 2A, the Mg-PONb sponge exhibits remarkably rapid self-assembly in brine solutions. When native-PONb (0.1 M, 1 ml) is added to an aqueous simulated brine containing MgCl2 / LiCl (0.1 M / 0.02 M, 5 ml), the solution immediately transitions from transparent to forming visible sponge-like aggregates, indicating successful Mg2+ion sequestration. This transformation occurs within approximately 1 second and can be visually monitored, demonstrating efficient and rapid Mg2+ / Li+separation in brine solutions. The rapid kinetics eliminate extended processing times required by conventional precipitation methods.

[0061] As shown in FIG. 2B, the PONb-based selective sequestration process enables selective Mg2+capture from brine through formation of a regenerable Mg-PONb sponge structure. This rapid and selective sequestration creates a visible solid phase that enables nearly complete Mg2+ / Li+10WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOseparation. The Mg-PONb sponge can be isolated by simple filtration and subsequently treated to recover Mg(OH)2 with approximately 99% yield. The PONb material maintains approximately 99% regeneration efficiency over repeated processing cycles, providing a sustainable and economically viable approach to critical metal recovery from brine sources.

[0062] The present disclosure can be used, for example, by or for (1) battery manufacturers involved in battery production, for example for electric vehicles, for efficient extraction of lithium, a key component in lithium-ion batteries; (2) automotive and alloy industries that require magnesium for lightweight vehicle parts and alloys, for example for sourcing Mg more efficiently; (3) environmental and water treatment companies specializing in water purification to treat brine waters, making them suitable for various uses, including potentially converting them into drinking water; (4) research institutions and universities conducting research on sustainable material recovery, water treatment, and environmental preservation for example for academic and practical research purposes; and (5) government and policy -makers looking to secure domestic critical material supply chains and promote sustainable practices in mining and material extraction.

[0063] The compositions disclosed herein can be used in the integration of material (e.g., critical material) recovery with environmental sustainability practices. By efficiently extracting valuable ions like Li and Mg from brines, the present disclosure not only taps into an abundant resource for materials (e.g., critical materials) necessary for modem technologies but also contributes to addressing global water scarcity. This integration aligns with global efforts towards reducing carbon footprints, promoting resource efficiency, and securing supply chains for critical materials, making it a highly relevant and impactful innovation.

[0064] The compositions and methods provided herein can provide the following advantages:

[0065] (1) Selective Ion Removal Efficiency: The invention employs polyoxometalates (POMs) for the selective removal of specific ions like Li+and Mg2+from nontraditional brines. This selectivity is an advantage over traditional ion removal methods such as precipitation, ion exchange, and reverse osmosis, which often lack specificity and can result in lower purity of the desired ions and higher contamination levels in the recovered materials.

[0066] (2) Cost-Effectiveness: By enabling the targeted extraction of valuable ions from brines, the technology potentially reduces the operational and capital costs associated with the extraction and purification processes. Traditional methods often involve energy-intensive processes and expensive materials, whereas this invention promises to offer a more cost-efficient solution by reducing energy consumption and leveraging more affordable and accessible materials.

[0067] (3) Environmental Sustainability: The technology aligns with sustainable and environmentally friendly practices by contributing to water purification and the efficient use of nontraditional water sources such as brines.11WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0068] (4) High Purity and Recovery Rates: The invention's capability to provide high selectivity in ion removal translates into higher purity levels of the recovered critical materials (Li and Mg), which is highly beneficial for industries such as battery manufacturing and automotive, where material purity directly impacts product performance and lifespan.

[0069] (5) Regeneration and Reuse: The POMs used in this invention can be efficiently regenerated and reused for ion removal, which enhances the system's overall sustainability and cost-effectiveness. This contrasts with some traditional materials that may degrade over time or require expensive regeneration processes. By addressing the limitations of existing technologies and offering improved performance, lower costs, and greater reliability, this invention presents a compelling option for industries and organizations focused on critical material recovery, water treatment, and sustainable environmental practices.A. Polyoxometalate (POM) Composition

[0070] A polyoxometalate (POM) composition is provided. The POM composition contains a polyoxometalate cluster bound to a metal and forming a network. The POM compositions described herein exhibit unique structural characteristics and binding properties that enable highly selective metal separation and recovery applications. These compositions demonstrate exceptional performance in isolating critical metals from complex aqueous solutions, including brines and industrial wastewaters.

[0071] The polyoxometalate can comprise a polyoxoniobate (PONb). The polyoxoniobate framework provides a robust, negatively charged cluster structure that exhibits strong affinity for specific metal cations. For example, the PONb can be [Nb6O19]8−, which represents a Lindqvist-type hexaniobate cluster with eight negative charges distributed across the oxygen atoms. This highly charged cluster creates multiple binding sites with varying affinities for different metal cations, enabling selective metal coordination and separation.

[0072] The metal can be bound to the polyoxometalate cluster via a terminal oxygen (Ot), a bridging oxygen (Ob), or hydrogen bonding (H-bond). The binding mode significantly influences the selectivity and stability of the metal-POM interaction. Terminal oxygen binding typically provides stronger, more direct coordination, while bridging oxygen binding offers intermediate strength interactions. Hydrogen bonding represents the weakest interaction mode, often associated with highly solvated metal cations that maintain their hydration shells.

[0073] The metal can be K+, Mg2+, Li+, or Na+Each metal cation exhibits distinct binding preferences and coordination geometries with the polyoxoniobate cluster. The charge density, ionic radius, and solvation characteristics of these metals determine their relative affinities for the POM structure. Mg2+demonstrates the strongest binding affinity due to its high charge density and ability to12WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOcoordinate directly with terminal oxygen sites, while Li+shows minimal interaction due to its strong solvation shell and low charge-to-radius ratio.

[0074] The polyoxometalate composition can comprise K8[Nb6O19], Li8[Nb6O19], FLNac^NbeOig], or Mg4[Nb60i9]. These specific stoichiometries reflect the charge balance requirements and coordination preferences of each metal cation with the [Nb6O19]8−cluster. The native potassium form K8[Nb6O19] serves as a precursor for ion exchange reactions, while the magnesium form Mg4[Nb6O19] exhibits unique structural properties including enhanced porosity and rapid precipitation kinetics.

[0075] The polyoxometalate composition can be a hydrate. The hydrated forms typically contain varying amounts of coordinated and lattice water molecules that stabilize the cry sial structure and influence the material properties. For example, the compositions can comprise K8[Nb6O19]·9H2O, Li8[Nb6O19]·13H2O, H2Na6[Nb6O19]·15H2O, or Mg4[Nb6O19]·16H2O. The water content varies depending on the metal cation and its coordination environment, with the magnesium form containing the highest water content due to its enhanced porosity and surface area.

[0076] The polyoxometalate composition can exhibit distinct cry stallographic structures depending on the bound metal. The native K8[Nb6O19]·9H2O can crystallize in a monoclinic P21 / c unit cell, exhibiting high structural flexibility in the arrangement of K+ions and lattice water around the PONb core. The Li-PONb (HLi7[Nb6O19]·13H2O) can crystallize in a R3“ unit cell, while Na-PONb (H2Na6[Nb6O19]·15H2O) can adopt an orthorhombic Pnnm unit cell. The Mg-PONb (Mg4[Nb6O19]·16H2O) can crystallize in a triclinic P1̄ unit cell, representing a structurally distinct form with unique properties.

[0077] The Mg-containing polyoxometalate composition can exhibit four crystallographically distinct Mg2+sites. Mgl and Mg2 can be fully occupied, while Mg3 and Mg4 can exhibit 0.5 occupancy due to positional disorder. Mg2 and Mg4 can serve as bridging ions between adjacent ‘NbeOigl clusters, whereas Mgl and Mg3 can be terminally bound and decorate the cluster peripheries. This structural arrangement can result in a partially connected one-dimensional framework best described as a mixed configuration of chain-like and dimeric motifs.

[0078] The Li-containing polyoxometalate composition can exhibit four crystallographically distinct Li+sites with disorder models. Lil and Li4 can be disordered and mutually exclusive, each modeled at 0.5 occupancy, corresponding to alternative structural motifs. Li+ions can be solvated and bridged by water molecules with no direct bonding to the {Nb6O19}8−cluster, instead coordinating exclusively through hydrogen bonding interactions.

[0079] The polyoxometalate composition can exhibit metal-specific bonding modes that determine selectivity and binding strength. In Li-PONb, the metals can coordinate with the cluster exclusively through hydrogen bonds. In native K-PONb, the metals can primarily bond with bridging oxygen (Ob). Na-PONb can exhibit an even distribution of terminal oxygen, bridging oxygen, and hydrogen 13WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WObonding connection types, while in Mg-PONb, the metals can connect solely to terminal oxygen (Ot) sites.

[0080] The Mg-containing polyoxometalate composition can exhibit a unique porous sponge-like structure with significantly enhanced surface area compared to other metal forms. The Mg-PONb composition can demonstrate a BET surface area of at least 30 m2 / g, at least 35 m2 / g, or about 40 m2 / g, representing approximately a 400-fold increase compared to the essentially non-porous nature of the K+, Li+, and Na+forms (less than 0.1 m2 / g). This enhanced porosity can result from the strong Mg-Ot bonding that promotes formation of extended network structures and immediate precipitation of ultrafine crystals.

[0081] For example, the polyoxometalate composition can exhibit metal-specific binding energies and coordination geometries. Mg2+can form the strongest bonds with terminal oxygen atoms, with bond lengths of approximately 2.0 A and corresponding vibrational frequencies around 925 cm−1in Raman spectroscopy. In contrast, Li+can interact primarily through hydrogen bonding without direct coordination to the cluster oxygen atoms, while K+can coordinate preferentially with bridging oxygen sites at distances greater than 3.0 A.

[0082] The polyoxometalate composition can exhibit distinct water molecule distributions as revealed by solid-state NMR. All PONb variants can exhibit a primary water resonance at approximately 6 ppm, with Mg-PONb showing a distinct shift to 6.3 ppm. Spectral deconvolution can reveal two distinct proton environments: site A at 5.7 ppm assigned to H2O-PONb cluster interactions, and site B ranging from 6.1 to 7.4 ppm demonstrating different bonding interactions between water and cations. Mg-PONb can show about a 15-fold increase in site A content and up to three times the water content of native-PONb due to its large surface area and pore size.

[0083] The polyoxometalate composition can exhibit rapid and selective precipitation behavior. Upon adding native-PONb to a MgCL solution, immediate precipitation of white powder can be observed. Conversely, no changes can be observed with addition of native-PONb to LiCl solution. Even when MgCL concentration is diluted to a thousand times lower than LiCl, precipitation can still occur instantly, demonstrating the exceptional selectivity for Mg2+over Li

[0084] The polyoxometalate composition can exhibit metal-specific binding energies calculated through density’ functional theory. Mg2+ions can exhibit the strongest bonding strength with oxy gen atoms on PONb molecules, regardless of whether the oxygen is in terminal or bridge position. The binding energy’ hierarchy can follow' the order Mg2+> Na+> Kt > Li+, with the binding energies directly correlating with the observed selectivity and precipitation behavior.

[0085] The polyoxometalate composition can be regenerable through treatment with base solutions. The metal-bound POM can be contacted with KOH at elevated temperatures (e.g., 200°C) for about 24 hours to release the bound metal as a hydroxide precipitate while regenerating the original POM 14WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOstructure. The regeneration process can maintain POM recovery efficiency of at least 95%, 96%, 97%, 98%, or 99% of Mg2+consistently recovered as Mg(OH)2, demonstrating the robust nature and reusability of these materials for sustainable metal separation applications.B. Producing the Polyoxometalate (POM) Composition

[0086] A method of generating a polyoxometalate (POM) composition is provided. The method includes mixing a metal oxide, a metal hydroxide, and water to provide a mixture; heating the mixture; cooling the mixture; adding methanol to precipitate the polyoxometalate composition, wherein the polyoxometalate cluster is derived from the metal oxide and the first metal is derived from the metal hydroxide; and isolating the precipitated poly oxometalate composition, thereby generating a polyoxometalate composition. This hydrothermal synthesis approach provides a robust, one-step method for producing high-quality polyoxometalate materials with excellent yields and purity.

[0087] The metal oxide can comprise Nb2O5. and the poly oxometalate can comprise a polyoxoniobate (PONb). The use of niobium pentoxide as the metal oxide precursor enables formation of the Lindqvist-type [NbeOw]8-cluster through controlled hydrothermal conditions. For example, the first metal can be K. and the first polyoxometalate composition can comprise KgfNbeOig] and FLO. The potassium form serves as an ideal starting material due to its structural stability and ability to undergo subsequent ion exchange reactions with other metal cations.

[0088] The method can comprise combining Nb2O5(about 0.2 g, 0.75 mmol) and KOH pellets (about 2.24 g, 40 mmol) with deionized water (about 20.0 ml) in a Teflon-lined acid digestion vessel. The reaction mixture can be stirred for approximately 5 minutes at room temperature to facilitate dissolution of the reactants. The molar ratio of KOH to Nb2O5can be maintained at about 53:1 to ensure complete dissolution and proper cluster fonnation.

[0089] The heating step can comprise sealing the vessel in an autoclave reactor and heating to about 200°C for about 72 hours. The hydrothermal conditions promote the formation of the hexaniobate cluster while allowing for proper crystallization and structural organization. The extended reaction time ensures complete conversion of the niobium oxide precursor to the desired poly oxometalate structure.

[0090] The cooling step can include allowing the autoclave to cool naturally to room temperature. Upon cooling, the supernatant can be collected, representing a clear solution containing the dissolved poly oxometalate product. The cooling rate can influence the final crystal size and morphology of the product.

[0091] The precipitation step can comprise adding about 60 ml of methanol to the collected supernatant. The mixture can then be stirred for approximately 30 minutes to precipitate the15WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOpolyoxometalate product. The methanol addition reduces the solubility of the poly oxometalate in the aqueous solution, leading to the fonnation of a white crystalline precipitate.

[0092] The isolation step can comprise filtering the precipitated product and washing three times with cold 1:1 methanol / deionized water solution (about 10.0 ml each wash). The washing steps remove residual salts and impurities while preserving the polyoxometalate structure. The purified white crystals can then be collected by filtration and dried for about 3 hours to yield the final product.

[0093] The method can achieve high yields, typically about 95.8% based on niobium content. The resulting native-PONb can have the formula K8[Nb6O19]·9H2O with a molecular weight of 1337.21 g / mol. Elemental analysis can confirm the composition with experimental mass percentages of Nb 41.82%, K 23.37%, and H2O 12.05%, closely matching calculated values.

[0094] The method can further include contacting the first polyoxometalate composition with a metal salt and obtaining a second polyoxometalate composition comprising the POM bound to a second metal derived from the metal salt. This ion exchange process allows for the preparation of various metal-substituted polyoxometalate derivatives with distinct properties and applications.

[0095] The second metal can be Li, Na, or Mg, and the second polyoxometalate composition can comprise Li8[Nb6O19], H2Na6[Nb6O19], or Mg4[Nb6O19]. each optionally hydrated. The ion exchange reactions can be performed under ambient conditions with varying reaction kinetics depending on the target metal cation.

[0096] The synthesis of Li-PONb can include combining about 50.0 pl of 2.0 M LiCl aqueous solution with about 100.0 pl of 0.01 M K8[Nb6O19]·9H2O aqueous solution in a vial. The mixture can be stirred for about 10 seconds, resulting in a colorless solution. Colorless crystals can precipitate over a few hours and can be collected for analysis. The reaction can be scaled up as needed, with the crystals washed three times with methanol to eliminate chloride salt impurities.

[0097] The synthesis of Na-PONb can comprise combining about 20 pl of 2.0 M NaCl aqueous solution with about 100 pl of 0.01 M native-PONb solution. The mixture can be stirred for about 10 seconds, with colorless crystals precipitating within minutes. This rapid precipitation indicates the favorable thermodynamics of sodium ion exchange with the native potassium form.

[0098] The synthesis of Mg-PONb can be more challenging due to the immediate and extensive precipitation that occurs upon Mg2+addition. Even minimal addition of Mg2+can instantly produce substantial amounts of low-crystallinity powder. For controlled synthesis, highly diluted conditions can be employed, such as mixing about 15 pl of 0.000625 M MgCL with about 100 pl of 0.000625 M native-PONb solution, allowing colorless crystals to form over several days.

[0099] The ion exchange reactions can exhibit dramatically different kinetics and precipitation behaviors. Li+and Na+exchange can occur gradually with controlled crystal formation, while Mg2+exchange can result in immediate precipitation even at concentrations 1000 times lower than Li+. This 16WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOdifferential behavior reflects the varying binding affinities and coordination preferences of the different metal cations.

[0100] In specific embodiments, the polyoxometalate composition can be synthesized through a one-step hydrothermal approach. A mixture of Nb2Os and metal hydroxide (such as KOH) can be combined with water in a Teflon-lined vessel, heated to about 200°C for about 72 hours, then cooled and treated with methanol to precipitate the product. The synthesis can yield high purity materials with yields exceeding 95% based on niobium content, as confirmed by elemental analysis and singlecrystal X-ray diffraction.

[0101] The method can include regeneration and recovery steps. The metal-bound poly oxometalate can be treated with KOH at elevated temperatures to release the bound metal and regenerate the original PONb structure. For instance, Mg-PONb (about 500 mg) can be combined with KOH pellets (about 5.6 g) and water (about 50 ml) in a Teflon-lined vessel, heated to 200°C for 24 hours, then separated by centrifugation to yield crystalline Mg(OH)2 and regenerated PONb.

[0102] The regeneration process can maintain high efficiency over multiple cycles. The regenerated PONb can retain about 95%, 96%, 97%. 98%, 99%, or 100% niobium recovery efficiency, while over 95%, 96%, 97%, 98%, 99%, or 100% of Mg2+can be consistently recovered as Mg(OH)2. This demonstrates the sustainable and reusable nature of the poly oxometalate materials for industrial applications.

[0103] The method can be adapted for different scales of production. Laboratory-scale synthesis can produce hundreds of milligrams of product, while the process can be scaled up for larger quantities by proportionally adjusting reagent amounts and vessel sizes. The hydrothermal approach is particularly amenable to scale-up due to its robust reaction conditions and high reproducibility.

[0104] The quality and purity of the products can be confirmed through various analytical techniques. Single -crystal X-ray diffraction can reveal the detailed crystal structures and unit cell parameters. Powder X-ray diffraction can confirm phase purity’ and crystallinity. Elemental analysis through ICP-OES can verify the metal content and stoichiometry, while thermogravimetric analysis can determine water content. These characterization methods ensure consistent product quality across different synthesis batches.C. Isolating Metal from Source Using the Polyoxometalate (POM) Composition

[0105] A method of isolating a first metal from a source containing a first metal and a second metal is provided. This selective separation method leverages the unique binding affinities and coordination preferences of different metal cations with polyoxometalate clusters to achieve efficient metal isolation and purification. The method includes contacting the source with a polyoxometalate (POM) composition comprising a polyoxometalate cluster, thereby binding the first metal to the polyoxometalate cluster. The binding process can occur through various mechanisms including direct 17WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOcoordination to tenninal oxygen atoms, bridging oxygen atoms, or through hydrogen bonding interactions. The selectivity of binding can be determined by the charge density, ionic radius, and solvation characteristics of the target metal cations.

[0106] The method further includes separating the polyoxometalate cluster bound to the first metal from the source, thereby isolating the first metal from the source and from the second metal. The separation can be achieved through precipitation, filtration, centrifugation, or other solid-liquid separation techniques. The bound metal-polyoxometalate complex can form distinct phases that can be readily separated from the remaining solution containing the unbound second metal.

[0107] In some embodiments, the poly oxometalate comprises a polyoxoniobate (PONb) having the formula [Nb6O19]8−. The hexaniobate cluster can provide multiple binding sites with vary ing affinities for different metal cations, enabling selective coordination and separation. The highly charged nature of the cluster can create strong electrostatic interactions with metal cations, particularly those with high charge densities.

[0108] The first metal or the second metal can include a critical mineral material. Critical minerals can include lithium, magnesium, cobalt, nickel, rare earth elements, and other metals essential for clean energy technologies, electronics, and advanced manufacturing. The selective isolation of these critical metals from complex mixtures can be crucial for resource recovery and sustainability.

[0109] In some embodiments, the first metal comprises Mg2+and the second metal comprises Li+. This combination has represented a particularly challenging separation due to the similar chemical properties of these alkali and alkaline earth metals. However, the poly oxometalate-based method provided herein can achieve exceptional selectivity for Mg2+over Li+, enabling efficient separation from brines and other complex aqueous systems.

[0110] In some embodiments, the source is brine or wastewater. Natural brines can include those from salt lakes, geothermal sources, oil field produced waters, and seawater. Industrial wastewaters can contain various metal contaminants that require selective removal and recovery. The polyoxometalate method can be applicable across a wide range of source compositions and concentrations.

[0111] The method can be effective across a broad range of metal-to-lithium ratios (MLR) found in natural brines. Laboratory studies can demonstrate successful separation across MLR values ranging from 0.02 to 200, representing over a 10,000-fold variation in relative metal concentrations. This broad operational window can make the method applicable to diverse brine compositions found globally.

[0112] In some embodiments, the selectivity of the second metal over the first metal remaining in the source after separating the polyoxometalate bound to the first metal from the source is about 200 or more, about 400 or more, about 1000 or more, or about 5000 or more. The selectivity can be 18WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOcalculated based on the relative concentrations of the metals before and after treatment, with higher values indicating more efficient separation. The exceptional selectivity can surpass that of conventional separation technologies by orders of magnitude.

[0113] In some embodiments, at least 95%, 96%, 97%, 98%. or 99% of the first metal and at least 95%, 96%. 97%. 98%, or 99% of the second metal are recovered from the source. The high recovery efficiency can ensure minimal loss of valuable metals during the separation process. The method can achieve near-quantitative removal of the target metal while preserving the desired metal in the remaining solution.

[0114] The separation efficiency can be maintained across different concentration ranges. At low concentrations (less than 1000 ppm total salts), an average of over about 99% of Li+can remain in solution w hile only less than about 0.1% of Mg2+can be detectable after treatment. At higher concentrations (7000-30000 ppm), less than about 1% of Li+can be lost while over about 99% of Mg2+can be completely removed.

[0115] In some embodiments, binding of the first metal to the polyoxometalate cluster occurs within 1 minute after contacting the source with the polyoxometalate composition. The rapid kinetics can be particularly advantageous for industrial applications where processing time is critical. The binding can occur within seconds for highly selective metal pairs, such as Mg2+with polyoxoniobate clusters.

[0116] The rapid binding can be demonstrated through in-situ spectroscopic monitoring. Raman spectroscopy can show spectral shifts from 889 cm to 925 cm−1within 5 seconds upon addition of Mg2+to native-PONb solutions, indicating complete structural transformation. Dynamic light scattering can reveal immediate aggregation and precipitation upon contact with selective metal cations.

[0117] The method can further include regenerating the polyoxometalate composition by treating the polyoxometalate cluster bound to the first metal with KOH at elevated temperature and collecting the first metal as a hydroxide precipitate. The regeneration process can enable multiple reuse cycles of the polyoxometalate material, enhancing the economic viability and sustainability of the separation process.

[0118] The regeneration can be performed under hydrothermal conditions, such as heating to about 200°C for about 24 hours in the presence of excess KOH. The treatment can release the bound metal as an insoluble hydroxide precipitate while regenerating the original poly oxometalate structure. The regenerated material can be recovered through precipitation with organic solvents such as methanol.

[0119] In some embodiments, the polyoxometalate composition maintains polyoxometalate recovery efficiency of at least 98%, about 99%, or about 100% over 5 or more regeneration cycles. The high recovery’ efficiency can demonstrate the structural stability and reusability’ of the19WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOpolyoxometalate materials. Simultaneously, over about 98% or 99% of the bound metal can be consistently recovered as a hydroxide precipitate, enabling efficient metal recovery.

[0120] The method can be adapted for different operational scales and conditions. The polyoxometalate dosage can be adjusted based on the metal concentration and desired separation efficiency. Lower concentrations may require about 4.0 mg of polyoxometalate per 1.0 ml of solution, while higher concentrations may require proportionally larger amounts to achieve complete metal removal.

[0121] The method can demonstrate superior performance compared to conventional separation technologies. Traditional methods such as precipitation, ion exchange, electrodialysis, and membranebased approaches can suffer from limited selectivity, high energy requirements, or operational complexity. The polyoxometalate method can outperform these technologies in terms of selectivity, speed, and operational simplicity while maintaining high metal recovery rates.

[0122] The following examples illustrate various aspects and embodiments of the present disclosure, but are not intended to limit the scope of the invention.EXAMPLESExample 1: Mg2+-Induced Formation of the Structurally Distinct Mg-PONb Sponge

[0123] A Lindqvist PONb was first prepared through a one-step hydrothermal approach. Singlecrystal X-ray diffraction (SC-XRD) revealed the structure of K8{Nb6O19}·9H2O (also referred to as native-PONb), which exhibits a monoclinic P21 / c unit cell containing {NbeOie} coordinating with eight K+(FIGs.3-5, Table 1). While this structure adopts a well-defined monoclinic P21 / c unit cell. K-PONb materials can exhibit high structural flexibility in the arrangement of K+ions and lattice water around the PONb core. Upon adding native-PONb to a MgCP solution, an immediate precipitation of the white powder was observed. Conversely, no changes were observed with the addition of native-PONb to the LiCl solution. Remarkably, even when the MgCL concentration was diluted to a thousand times lower than that of the LiCl, precipitation still occurred instantly; further investigation by diluting MgCf and native-PONb by a factor of 10.000 and mixing thoroughly resulted in the successful formation of single crystals after several days (FIGs. 6-7). SC-XRD analysis confirmed the structure of the compound as Mg4[Nb6O19]·16H2O (denoted as Mg-PONb), which crystallized in a triclinic Fl unit cell with {Nb6O19} cluster coordinated by four Mg2+ions (FIGs. 2C and 7-9, Table 1). In this structure, four crystallographically distinct Mg2+sites are observed. Among them, Mgl and Mg2 are fully occupied, while Mg3 and Mg4 exhibit 0.5 occupancy and are modeled using PART 1. The complementary positions are occupied by disordered water molecules represented by PART 2. Mg2 and Mg4 serve as bridging ions between adjacent {Nb6O19} clusters, whereas Mgl and Mg3 are terminally bound and decorate the cluster peripheries without 20WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOcontributing to intercluster linkages. Due to the partial occupancy and positional disorder of Mg3 and Mg4, the overall structure exhibits a partially connected one-dimensional framework that is best described as a mixed configuration of chain-like and dimeric motifs. As controls, single-crystal Li-PONb (HLi7{Nb6Oi9}*13H2O) and Na-PONb (^NaeJNbeOi }• I5H2O) crystals were also analyzed. The structure of Li-PONb crystallized in a R3 unit cell (FIGs. 7 and 10-12, Table 1) and Na-PONb crystallized in an orthorhombic Pnnm unit cell (FIGs. 7 and 13-15, Table 1). In Li-PONb, four crystallographically distinct Li+sites were identified. Lil and Li4 are disordered and mutually exclusive (each modeled at 0.5 occupancy), corresponding to two alternative structural motifs. Lil and 06 participate in the formation of a water-coordinated adamantane-like cluster, which is further connected to a chain composed of Li2 and Li3. Alternatively. Li4 and 05 form a more extended chain of octahedrally coordinated Li ions. In both disorder models, Li+ions are solvated and bridged by water molecules, with no direct bonding to the {NbeOig}8' cluster. This structural arrangement is consistent with previously reported lithium hexaniobate frameworks, and the current disorder model provides a good fit to the cr stallographic data. For Na-PONb, this Na-PONb structure represents only the third reported single-crystal Na-containing hexaniobate. Compared to previously reported Na analogues, it contains fewer Na+ions per [Nbi j8' unit and was obtained via post-synthetic ion exchange from native-PONb. Despite these differences, the Na+coordination geometry and linkage pattern are consistent with prior models.

[0124] Through the analysis of Mg-PONb, native-PONb, Na-PONb, and Li-PONb, three distinct types of bond connections were identified (FIG. 16A). The first type involves direct bonding to terminal oxy gen (Ot), the second type involves bonding to bridging oxygen (Ob), and the third type involves metal-cluster connection via hydrogen bonding (H-bond). The bonding modes of these four different crystals and their corresponding calculated binding energies were summarized (Table 2). In Li-PONb, the metals coordinate yvith the cluster exclusively through H-bonds. In native-PONb, the metals primarily bond with Ob. Na-PONb exhibits an even distribution of the three connection ty pes, while in Mg-PONb, the metals connect solely to Ot.

[0125] X-ray photoclcctron spectroscopy (XPS) was conducted to further analyze the bond coordination. The O Is and Nb 3d spectra of native-PONb, Li-PONb, Na-PONb and Mg-PONb are shown in FIG. 16B. The binding energies attributed to Nb-0 were measured at 529.0, 529.2529.5 and 530.2 eV, respectively. A similar peak shift order was observed in the Nb 3d spectra. native-PONb and Li-PONb retained their peaks at 205.80 and 205.94 eV, respectively, while Na-PONb and Mg-PONb shifted to 206.24 and 206.86 eV, respectively. This behavior is primarily attributed to the coordination environment of Ot in the different PONb structures. In Li-PONb and native-PONb, Li+and K+ions exhibit minimal coordination with Ot. allowing the Nb = Ot bonds to remain predominantly double bonds. This results in a relatively uniform electron cloud distribution over the bridging O atoms (FIG. 16A). However, in Na-PONb and Mg-PONb, the metal ions coordinate with 21WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOOt, causing the negative charge to be distributed across five single Nb-0 bonds. The bond to the central O site is significantly elongated and weak, effectively rendering it negligible and resulting in the anion site being localized on the Ot coordinated to the metal. Consequently, the overall O ls peak shifts to higher binding energies. A similar shift is observed in the Nb 3d spectra due to analogous coordination. These observations are consistent with the phenomena observed in the SCXRD analysis and bond classification in Table 2. Additionally, O K-edge X-ray Absorption Spectra (XAS) was also measured (FIG. 16C). A similar shift, with Mg-PONb showing a higher photon energy compared to native-PONb and Li-PONb, was also observed in the O K-edge Total Fluorescence Yield (TFY). This further confirms the presence of the unique and strong Nb-Ot-Mg bonds in Mg-PONb.

[0126] Raman spectroscopy can distinguish the vibrational bands of different oxygen atoms within PONb, providing a deeper understanding of their bond coordination. FIG. 1 D reveals the consistent highly symmetric octahedral {NbgOis} cluster coirfiguration, as indicated by similar vibrational bands for Nb-Oc-Nb and Nb-Ob-Nb in the 200-600 cm1regions. The sharp peaks in the >800 cm1region were assigned to vibrational bands of Nb-Ot, exhibiting notable differences among the four samples. Notably, intense peaks at 889 cm1in both native-PONb and Li-PONb are attributed to the Nb = Ot bond vibrational modes. For Na-PONb, two distinct peaks were observed around 900 cm'1: one at 899 cm1, associated with the Nb-Ot-Na vibrational mode, and another at 883 cm1, corresponding to the Nb = Ot vibrational mode. In addition to these high-frequency peaks, a prominent band near 825 cm'1is consistently observed in the spectra of Native-, Li-, and Na-PONb. This peak is assigned to the symmetric stretching of Nb = Ot bonds within the PONb. These observations are consistent with bond connections elucidated through crystal structure analysis (FIGs. 3, 8, 10, and 13). Crystallographic data indicate the presence of tw o Nb-Ot-Na bond in Na-PONb (2.45-2.47 A), which contrasts with the native-PONb structure, featuring only a K-Ot bond over 3.24 A (FIG. 3). and Li-PONb. which lacks a Li-Ot bond (FIG. 10). The significant spectral shifts were observed in Mg-PONb. with the intense peaks at 925 cm'1and 860 cm1, attributed to the Nb-Ot-Mg vibrational mode. This also aligns with crystallographic data (FIG. 8), which confirm that all Mg2+ions are coordinated to Ot and exhibit four robust Nb-Ot-Mg bonds, each approximately 2.0 A in length. The shift to higher frequencies indicates stronger interactions between cations and {NbeOig} cluster, with the Nb-Ot Raman shift directly correlated to the M-Ot bond distance (Table 2). Such frequency shifts are also evident in the {NblO} cluster. Another key difference is the broadening of Mg-PONb Raman peaks, likely indicating poor crystallinity, which is also consistent with the PXRD results for Mg-PONb (FIG. 7). This is inferred from the immediate precipitation, which prevents large crystal growth and results in ultrafine crystals.

[0127] It is posited that the unique open network structure of Mg-PONb is driven by Mg-bonding at Ot sites which leads to formation of Mg-PONb sponge; these condensed structures lead to the immediate precipitation of ultrafine Mg-PONb crystals. Consistent with fonnation of these larger, mesoscopic open network structures, Mg-PONb exhibits significantly enhanced (~400-fold increase)22WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOporosity compared to native-PONb. Li-PONb. and Na-PONb which retain their cluster identity even after metal binding. The Brunauer-Emmett-Teller (BET) surface area was approximately less than 0.1 m2 / g for Na-PONb, Li-PONb, and native-PONb, confirming that these samples are almost non-porous (FIG. 16E). However, after the introduction of Mg2+. the BET surface area markedly increased to 39.25 m2 / g. This substantial increase corresponds with the porous sponge structure observed through SCXRD analysis and small crystals size from PXRD and Raman.

[0128] Quantitative *H spin-echo solid-state NMR (ssNMR) measurements under fast MAS conditions were further used to reveal detailed insights into the chemical structure and water molecule distribution within PONbs, especially the unique porosity of Mg-PONb. As can be seen in FIG. 16F, all four PONbs variants exhibited a primary water resonance at approximately 6 ppm, indicative of a highly charged niobate cluster environment, similar to Bronsted acid sites in zeolites. Notably, Mg-PONb showed a distinct shift in water resonance to 6.3 ppm, slightly higher than the others, suggesting a unique interaction within its structure. Furthermore, spectral deconvolution confirmed the presence of two distinct proton environments related to water molecules in these PONbs. The first site, A, maintains its chemical shift across all four PONbs at 5.7 ppm and was assigned to f LO-PONb cluster while the second site, B, was downfield to site A and found in a range of chemical shifts across PONbs (from 6.1 to 7.4 ppm). These variations in chemical shift demonstrate different bonding interactions between water and cations (Li+. Na+, K+and Mg2+). Table 3 reveals that native-PONb has a disproportionate distribution of water sites, with a ratio of 10.8: 1 in favor of site B, while the other three PONbs (Mg-PONb, Li- PONb, Na- PONb) exhibit a more balanced distribution near 1:1. This observation agrees with the crystal structures obtained from SCXRD (FIGs.3-5), where native-PONb has eight K+centers surrounding PONb that limit interactions between water molecules and the cluster. The limited presence of site A protons in native-PONb also aligns with its acidic Ob-H proton resonances, indicating fewer available PONb sites for water interaction due to occupied hydroxyl groups. In contrast, Mg-PONb shows the most significant increase in site A content. 17-fold, reflecting the reduction in acidic proton resonances. Overall, Mg-PONb displayed the most significant variation, with a marked increase in one type of proton environment, correlating with its increased porosity and water content — up to three times that of native-PONb. This enhanced water content in Mg-PONb is attributed to its large surface area and pore size, which facilitates more extensive water molecule adsorption, as supported by BET and SCXRD analyses.Table 1. Crystallographic parameters of coordination networksNative- {Nb. Oi } Mg-{Nb60i9} Li-{Nb60i9} Na-{Nb60i9} Empirical formula H1383K797 C25Mg3 HisLi? H26Na6NbeO3544 NbeOsgs NbeO46 Nb6O32 Formula w eight 1450.18 1292.42 1360.2 1233.60 (g / mol)23WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WONative- {NbeOis} Mg-{Nb60i9} Li-{Nb60i9} Na-{Nb60i9} Cry stal size (111 nr) 0.2 x 0.15 x 0.1 0.2 x 0.15 x 0.1 0.15 x 0.13 x 0.1 0.15 x 0.12 x 0.1 Crystal system monoclinic triclinic trigonal Orthorhombic Space group P2i. V Pl R3 Pnnm a (A) 8.9534(14) 11.003(2) 11.9894(9) 12.0538(10) b (A) 11.744(2) 11.1882(19) 11.9894(9) 12.6260(10) c (A) 17.927(3) 15.878(3) 23.798(2) 10.0226(7) « (°) 90 100.587(7) 90 90 fi (°) 97.973(6) 109.191(8) 90 90 Y (°) 90 90.392(7) 120 90 Volume (A’) 1866.8(5) 1809.9(6) 2962.6(5) 1525.2(2)Z 2 2 3 4 Pcalc (g / cm3) 2.580 2.372 2.287 2.686 p (mm-1) 2.776 2.010 1.813 2.377 Goodness-of-fit on 1.374 1.239 1.389 1.085 F2Reflections 79121 88574 34425 68641 collectedIndependent 3827 6386 1342 1656 reflectionsRi 0.0448 0.0528 0.0359 0.0171 wRz 0.0927 0.1224 0.1001 0.0463CSD # 2371924 2371923 2371921 2371922Table 2. Summary of bonding parameters for M-PONb (M=K+, Li+, Na+, Mg2+) and their corresponding calculated binding energiesM" -O / Mn-O / > Number of Exp. Theor. Binding Exp. Theor. Binding oyovH- Bond Bond Energy Bond Bond Energy’ bond Length Length (eV)’ Length Length (eV)fA] fA] [A] [A]Li+N / A 3.12 -0.068 N / A 2.812 -0.013 0 / 0 / 7 Na+2.465 2.781 -0.463 2.452 2.796 -0.449 2 / 2 / 2 K+3.244 3.388 -0.237 2.948 2.789 -0.432 1 / 5 / 2 Mg2+2.034 2.316 -0.615 N / A 2.324 -0.547 4 / 0 / 0Table 3. Relative ratios of water environments in PONbs

[0129] The first three columns show relative water content between PONbs normalized to nativc-PONb, while the last column shows relative ratios of the two sites within each PONb. Site A is associated with f LO-PONb interactions, and site B is associated with H2O-M interactions (M = K+,24WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOMg2+, Li+, Na+). Substitution of Mg, Li, or Na for K results in an increase in water content primarily due to an increase in site A content. Mg-PONb has the highest overall water content.Site A Integral Site B Integral Total water Site B: Site A content ratio Native-PONb 1.00 1.00 1.00 10.8:1 Mg-PONb 17.0 1.70 3.00 1.08:1 Li-PONb 8.58 1.44 2.04 1.80:1Na-PONb 13.5 1.08 2.14 0.86:1Example 2: Selective Li+ / Mg2+Separation over a Broad Mg-to-Li Ratio Window

[0130] Due to its unique structural features such as strong Nb-Ot-Mg bonds and significantly enhanced surface area, Mg-PONb rapidly precipitates, showing great promise for efficient Li and Mg separation. The performance of native-PONb materials in the selective separation of Li+ / Mg2+, Na+ / Mg2+. and K+ / Mg2+was evaluated using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Given the substantial global variability hi MLR of brines (FIG.17A) and the significant concentration differences even among brines with identical MLRs, 22 laboratory-prepared simulated binary salt mixture composed of MgCL and LiCl were developed to mimic the compositions of major salt lakes (Tables 4-6).

[0131] First, 11 different MLRs ranging from 0.02 to 200 of binary Li+ / Mg2+salt mixtures with a total salt concentration of less than 1000 ppm were tested (FIGs. 17B-17G and 18A-18E, Table 4).The obtained mixtures at different time intervals were compared with the initial simulated salt mixtures. The concentration of Li+remained in the supernatant almost constant within the 24-hour testing period, whereas the concentration of Mg2+in the supernatant significantly decreased within a short period, with almost no Mg2+detectable after 24 hours. Specifically, for these 11 different MLR simulated feed mixtures with relatively low concentrations, an average of 99.74% of Li+remained in mixtures after 24 hours, while an average of 0.07% of Mg2+was detectable. The average Li+ / Mg2+selectivity for these 11 reactions reached 3243, with the highest exceeding 5000, marking the most exceptional Li / Mg2selectivity reported to date. This material also represents the first to maintain such high selectivity across a wide range of MLRs (varying by over 10000-fold).

[0132] To further investigate the potential for Li+ / Mg2+separation under higher feed concentrations, closer to actual industrial conditions, total salt concentrations of -1000-3000 ppm and 7000-30000 ppm were also tested. For higher feed concentrations, 5 different mid-range concentration simulated feed mixtures (MLR = 0.27-200.63, FIGs. 19A-19E, Table 5) and 6 different high concentrations simulated feed mixtures (MLR = 0.036-199.85, FIGs.20A-20F, Table 6) were prepared. Similar to the low concentration scenario, in the mid-range concentration (-1000-3000 ppm), over 99.69% of Li+in the supernatant remained in mixtures after 24 hours, while less than 0.36% of Mg2+was detectable, achieving a selectivity of 1523. At high concentrations (7000-3000025WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOppm), even with the addition of higher concentrations of native-PONb material, less than 0.65% of Li+was lost, and over 99.91% of Mg2+was completely excluded. The average Li+ / Mg2+selectivity in this scenario also exceeded 1709. These ICP-OES results robustly confirm the superior Mg2+extraction capability of native-PONb materials and their high selectivity for Li+ / Mg2+, underscoring their potential for efficient Li+ / Mg2+separation in diverse brine compositions.

[0133] Native-PONb of the present disclosure exhibits the highest reported Li+ / Mg2+selectivity across a broad MLR range, along with high Li+purity and minimal Li+loss, outperforming previously reported separation technologies (such as precipitation using triammonium phosphate trihydrate, hydrotalcite, magnesium oxalate, TLPE, or MgAlCOs-LDHs; electrodialysis using or EID- MgNFLPCL, S-ED process, constant-voltage ED, or ED membranes; and membrane-based approaches using OSARIP, TBP / FeCL and PVC, PSS / PAH LBL, PSS / LBL NF, positively charged surfaces, and QEDTP). Native-PONb also demonstrates near-complete Mg2+removal from Na+- and K+-containing mixtures with minimal co-capturc, confinning its robust applicability for alkali-Mg2+separations (FIGs. 21A-21C and 22A-22D, Tables 7 and 8).Table 4. The rejection of Li+and Mg2+ and Li+ / Mg2+ selectivity as a function of MLR of feed solution

[0134] The salt concentration of the binary metal salt mixture is less than 1000 ppm. Sn / Mg represents Li+ / Mg2+selectivity.Feed (ppm) Receive (ppm) Li+Mg MLR2+Li+Mg2+Li+Mg2+rejection rejection Su / Mg 0.02 669.315 14.997 668.812 0.007 0.08% 99.95% 2050.09 0.82 4.754 3.885 4.732 0.001 0.48% 99.97% 3866.00 2.68 75.580 202.715 75.337 0.034 0.32% 99.98% 5872.21 3.47 6.954 24.141 6.921 0.004 0.47% 99.98% 5461.03 5.95 4.851 28.883 4.832 0.005 0.40% 99.98% 5753.36 17.17 5.096 87.517 5.078 0.056 0.37% 99.94% 1557.04 24.60 20.135 495.297 20.119 0.116 0.08% 99.98% 4267.04 35.84 4.620 165.591 4.619 0.037 0.02% 99.98% 4449.35 54.39 4.606 250.533 4.603 0.744 0.06% 99.70% 336.40 16.82 3.861 451.073 3.851 0.409 0.26% 99.91% 1101.2900.18 2.444 489.233 2.442 0.507 0.09% 99.90% 964.32Table 5. The rejection of Li+and Mg2+and Li+ / Mg2+selectivity as a function of MLR of feed solution

[0135] The salt concentration of the binary salt mixture is between '1000 3000 ppm. ST i / \i*> represents Li+ / Mg2+selectivity’.Feed( PPm) Receive (ppm)MLR Li+Mg2+rejection rejecti $Li / Mg Li+Mg2+Li+Mg2+on0.27 754.522 205.518 753.621 0.743 0.12% 99.64% 276.1926WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO3.22 727.011 2341.691 725.718 1.381 0.18% 99.94% 1692.63 33.89 69.184 2344.732 68.994 1.093 0.27% 99.95% 2139.33 115.31 20.382 2350.151 20.319 1.602 0.31% 99.93% 1462.48200.64 9.972 2000.748 9.941 0.976 0.31% 99.95% 2043.57Table 6. The rejection of Li+and Mg2+and Li+ / Mg2+selectivity as a function of MLR of feed solution

[0136] Tlie salt concentration of the biiiari salt mixture is betw een 7000 30000 ppm. Sui / Mg represents Li+ / Mg2+selectivity.Feed( PPm) Receive (ppm)MLR Li+Mg2+Li+Mg2+Li+Mg2+rejection rejection SLi / Mg 0.036 7016.104 249.719 6989.112 0.134 0.38% 99.95% 1856.41 0.35 7107.702 2479.011 7086.382 1.010 0.30% 99.96% 2447.10 2.83 7079.069 20037.910 7049.014 11.129 0.42% 99.94% 1792.87 48.86 206.190 10074.962 204.904 8.601 0.62% 99.91% 1164.07 94.96 211.179 20053.373 209.919 13.906 0.60% 99.93% 1433.46199.85 100.165 20018.179 99.510 12.710 0.65% 99.94% 1564.70Table 7. The rejection of Na+and Mg2+and Na+ / Mg2+selectivity as a function of Mg-Na ratios (MSR) of feed solution.

[0137] The salt concentration of the binary metal salt mixture is less than 300 ppm. xazvig represents Na+ / Mg2+selectivity.Feedi PPm) Receive (ppm) Na S1Mg M R2+Na+Mg2+Na+Mg2+rejection rejection SNa / Mg 0.10 240.540 24.224 234.996 0.038 2.30% 99.85% 630.42 1.11 23.593 26.088 23.246 0.025 1.47% 99.91% 1049.1310.59 23.179 245.453 22.765 0.468 1.79% 99.81% 514.89Table 8. The rejection of K+and Mg2+and K+ / Mg2+selectivity as a function of Mg-K ratios (MPR) of feed solution.

[0138] The salt concentration of the binary salt mixture is less than 500 ppm. SK / MKrepresents K+ / Mg2+selectivity.Feedi PPm) Receive (ppm) K M R+Mg P2+K+Mg2+K+Mg2" rejection rejection SK / Mg 0.06 393.812 24.187 393.776 0.001 0.01% 99.99% 16231.48 0.62 39.800 24.706 39.791 0.008 0.02% 99.97% 2912.82 6.20 39.975 247.733 39.970 0.154 0.01% 99.94% 1608.4861.23 4.003 245.133 4.001 0.193 0.05% 99.92% 1267.08Example 3: Mechanistic Insights and Long-Term Regenerability27WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0139] To further elucidate the kinetic mechanism of Li-Mg extraction using PONb-based methods (FIGs. 23A-23F), molecular dynamics (MD) simulations were also employed. The computational results demonstrated a strong preference for PONb clustering in the presence of Mg2+ions, leading to almost complete adsorption of Mg2+and significant aggregation, while interactions with Li+ions were weak, resulting in minimal adsorption and no notable aggregation. These observations are consistent with prior MD studies by Bo et al., which reported that Li+interacts with [NbgOig]8’ via bridging oxygens without inducing aggregation. The computational results indicate that native-PONb exhibited remarkable selectivity and sensitivity for both Li+and Mg2+ions. These findings are consistent with those obtained from Dynamic Light Scattering (DLS), which also indicated that native-PONb showed significant selectivity and sensitivity for Li+, Na+and Mg2+ions: Mg2+ions caused significant aggregation of at least 1000 nm even at very small amount (8 pl, 0.0025 M) once injected, unlike the changes observed until thousands of times of Li+(40 pl, 0.5 M) and Na+(40 pl, 0.5 M) ions, suggesting lower solubility and higher reactivity of native-PONb with Mg2+ions (FIGs.231 and 23J). DLS measurements were also employed to investigate the effect of pH on the solubility behavior of Li+and Mg2+in native-PONb solutions. The results show that at lower pH values (7-9), the solubility of both ions increases, but Li+is more strongly affected than Mg2+, leading to improved Li / Mg selectivity. These findings suggest that native-PONb maintains robust Li+ / Mg2+selectivity across a broad pH range (7-14), highlighting its potential applicability under various brine conditions.

[0140] Reaction time is a factor in the efficiency of Li+and Mg2separation. Traditional methodologies typically require several minutes to hours for completion. This study found that over 99.9% Mg2+can be captured within one minute, with Li+concentrations remaining above 99.0%, even across a wide MLR range of 0.27-200.64 (FIGs. 2A-2C, 17B-17G, 18A-18E, 19A-19E, and 20A-20F). In cases of low MLR (< 0.05), Mg2+rejection rates reached approximately 90% within the first hour, escalating to 99.9% after 24 horns. This rapid separation is underscored by in-situ Raman spectroscopy, which detected a significant spectral shift from 889 cm-1 to 925 cm-1 within five seconds after adding MgCL, indicating a quick structural transition of native-PONb. The stability of the 889 cm-1 peak with the addition of LiCl confirms the absence of interaction with Li+(FIGs.23G, 23H and 24A-24F) These observations, coupled with molecular dynamics simulation results demonstrate that native-PONb enables fast and efficient Li+ / Mg2+separation, significantly reducing the required reaction time compared to existing methods.

[0141] To evaluate the regeneration capability of PONb after Mg2+sequestration, a cyclic regeneration-reuse test was conducted based on the conversion of Mg-PONb sponge back to its active form (FIG.25A). After the selective sequestration of Mg2+by PONb, forming a Mg-PONb sponge, the solid was treated with KOH under heating, allowing complete release of Mg2+as crystalline Mg(OH)2 with a conversion efficiency around 99%, and enabling recovery of the PONb precursor. Notably, the high purity and crystallinity of the resulting Mg(OH)2 facilitate its potential reuse in 28WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOdownstream applications. The regenerated PONb was then reused for Li+ / Mg2+separation. As shown in FIG.25B and Table 9, the regenerated PONb exhibits Mg2+rejection rates and Li+flux values both over 99%. demonstrating separation performance nearly identical to that of the native material across five cycles. Raman spectroscopy further confirmed the structural integrity of the regenerated PONb, with characteristic Nb = O vibrational peaks at 925 and 889 cm-1 retained throughout the regeneration cycles (FIG. 25C). XRD analysis of the solid by-product revealed crystalline Mg(OH)2 formed during regeneration (FIG. 25D, Table 10), while Nb recovery efficiency remained above 98.1% in all cases (FIG. 25E, Table 10). validating the high-fidelity regeneration and reusability of the PONb system. This excellent recyclability significantly mitigates concerns regarding the cost of Nb, as the PONb can be efficiently reused with minimal loss, supporting long-term viability for potential large-scale application.

[0142] In summary’, the Nb-based polyoxometalate material (also called Mg-PONb sponge) provided herein enables rapid and highly selective Li+ / Mg2+separation across a broad range of brine compositions. Spectroscopic, cry stallographic, and computational analyses reveal that strong Mg2+coordination to terminal oxygen sites in the PONb cluster drives the formation of a structurally distinct porous framework, enabling >99.9% Mg2+exclusion within seconds while achieving nearly 100% separation efficiency for both Li+and Mg2+. In contrast to conventional evaporation-based methods, the Mg-PONb sponge operates with exceptional speed, selectivity, and scalability. The material maintains consistent structural integrity and separation performance over at least five regeneration cycles, with Nb recovery efficiency remaining around 98.92% and over 98.86% of Mg2+consistently recovered as Mg(OH)2. These results demonstrate a robust, selective sequestration mechanism unique to PONb frameworks and establish their practical potential for sustainable ion separations in complex aqueous systems.Table 9. The rejection of Li+and Mg2+and Li+ / Mg2+selectivity as a function of MLR of feed solution for over five separation-regeneration cycles.

[0143] The salt concentration of the binary metal salt mixture is less than 1000 ppm. SIJ / MSrepresents Li+ / Mg2+selectivity.Feed( ppm) receive (ppm) Li+Mg MLR2+Li+Mg2+Li+Mg2+rejection rejection $Mg / Li 3.47 6.954 24.141 6.914 0.005 0.57% 99.98% 4800.57 23.81 6.954 165.591 6.901 0.028 0.76% 99.98% 5869.06 Recyclel116.82 3.861 451.073 3.830 0.319 0.81% 99.93% 1402.57 Average 0.71% 99.96% 4024.07 3.47 6.954 24.141 6.908 0.008 0.66% 99.97% 2997.75 23.81 6.954 165.591 6.921 0.026 0.47% 99.98% 6338.84 Recycle2116.82 3.861 451.073 3.853 0.141 0.21% 99.97% 3192.25 Average 0.45% 99.97% 4176.2829WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO3.47 6.954 24.141 6.933 0.007 0.30% 99.97% 3438.40 23.81 6.954 165.591 6.937 0.031 0.24% 99.98% 5328.74 Recycles116.82 3.861 451.073 3.846 0.224 0.40% 99.95% 2005.76 Average 0.31% 99.97% 3590.96 3.47 6.954 24.141 6.925 0.006 0.41% 99.98% 4006.84 23.81 6.954 165.591 6.918 0.033 0.51% 99.98% 4992.08 Recycle4116.82 3.861 451.073 3.844 0.194 0.45% 99.96% 2314.72 Average 0.46% 99.97% 3771.21 3.47 6.954 24.141 6.938 0.006 0.23% 99.98% 4014.36 23.81 6.954 165.591 6.920 0.042 0.49% 99.97% 3923.48 Recycles116.82 3.861 451.073 3.839 0.106 0.58% 99.98% 4230.86Average 0.43% 99.98% 4056.23Table 10. Quantitative analysis of Mg(OH)2and PONb recovery during five regeneration cycles.

[0144] The table lists the amount of Mg-PONb used in each cycle, the corresponding recovered Mg(OH)2. and regenerated PONb. Both Mg2+and PONb show consistently high recovery efficiencies across all cycles.Mg-PONb Mg(OH)2PONb mg mmol mg mmol RMS% mg mmol R>b% Recyclel 500.11 0.401 92.18 1.581 98.50% 534.25 0.400 99.59% Recycle! 420.94 0.338 78.29 1.342 99.39% 443.01 0.331 98.11% Recycles 320.85 0.257 59.23 1.016 98.65% 341.48 0.255 99.22% Recycle4 220.65 0.177 40.87 0.701 98.99% 233.65 0.175 98.72%Recycles 163.51 0.131 30.22 0.518 98.77% 173.59 0.130 98.97%Example 4: Experimental MethodsChemicals and basic characterization

[0145] Chemicals. Example chemical manufacturers and purities for the present disclosure are provided in Table 11. Ultrapure water was collected from a MilliQ Advantage A10 system. All chemicals were used without further purification.Table 11. Example Chemicals UsedChemical Purity Manufacturer Hydrochloric Acid (HC1), 36.5 wt% CMOS Grade J. T. Baker Lithium Chloride (LiCl) 99.9% Fisher Chemical Magnesium Chloride (MgCl2) 99.9% Sigma-Aldrich Methanol (MeOH) 99.90% Fisher ChemicalNiobium(V) Oxide (Nb2Os) 99.99% Sigma-Aldrich 30WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WONitric acid (HNO3), 70 wt% ACS reagent Sigma-Aldrich Potassium Chloride (KC1) 99.5% Sigma-Aldrich Potassium Hydroxide (KOH) 99.9% Sigma-Aldrich Methanol (MeOH) 99.90% Fisher ChemicalSodium Chloride (NaCl) >99% Sigma-AldrichFormula determination

[0146] Elemental analysis was conducted using inductively coupled plasma optical emission spectrometry (ICP-OES) on a Varian ICP-OES 720 Series to determine the total trace ions. The samples underwent digestion in 2 mL aqua regia solution, with sonication for 12 hours. Prior to ICP analysis, the samples were diluted with 2 wt% HNO3. Standard solutions of niobium, potassium, lithium, sodium, and magnesium (Sigma Aldrich) were prepared in concentrations ranging from 1 to 500 ppm to create diluted standard solutions for calibration. Thermogravimetric analysis (TGA) was executed utilizing a TA Instruments Q5500 TGA-MS under an inert argon atmosphere. The sample temperature was increased at a controlled rate of 5 °C / min. The water content percentage was quantitatively assessed based on the mass reduction observed from 30 °C to 600 °C, with the values subsequently rounded to the nearest 0.5% FEO for precision. Where appropriate, the experimental values are compared to literature values or to those calculated from the crystal structure.N adsorption isotherms and surface area measurements

[0147] Gas adsorption isotherms were obtained using an ASAP-2020 surface area analyzer. N? adsorption isotherms were recorded at 77 K within a liquid nitrogen bath. Prior to data acquisition, powder samples were degassed under vacuum at 120 °C for 12 horns.X-ray photoelectron spectroscopy (XPS)

[0148] XPS analysis was conducted using a Thermo Scientific™ K-AlphaPlus™ instrument, equipped with a monochromatic Al Ka radiation source emitting at 1486.7 eV. The measurement area was configured to an elliptical shape of 200 x 400 pm, and a flood gun was employed for charge compensation. For spectral acquisition, the pass energy settings were 200 eV for survey spectra and 50 eV for high-resolution spectra, with an energy resolution maintained at 0.1 eV. The analysis chamber maintained the pressure of approximately 1x10 mbar during data acquisition. Data processing was executed using the Thermo Scientific Avantage XPS software, with peak fitting performed through a combination of Gaussian / Lorentzian shapes and a Shirley background subtraction. Reference for all peak positions was established using the C Is peak from adventitious carbon at 284.4 eV. XPS spectra covered several binding energy regions, including Nb 3d, Mg Is, C Is, and O Is orbitals, ensuring comprehensive surface composition analysis.WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WORaman spectroscopy

[0149] Operando Raman spectroscopy was carried out on a confocal Raman spectrometer (HORIBA LabRAM HR Evolution) to elucidate the in-situ structural changes upon ion incorporation. The system employed a 532 mn laser with a power range of 1-3.2 mW. carefully chosen to optimize the signal-to-noise ratio while preserving the microstructure of the samples. Specifically, a 0.01 M native-PONb solution (100 pl) was placed on a grooved slide for initial Raman spectral acquisition. Subsequently, 20 pl of 0.10 M MgCL solution was sequentially added, with data collected at 5-second intervals for up to one minute. A distinct spectral shift from 889 cm'1to 925 cm'1was observed within 5 seconds, corresponding to the transition from v(Nb = Ot) to v(Nb-OrMg). The absence of the 889 cm-1peak indicates that the structural transition of native-PONb to Mg-PONb was completed within 5 seconds (FIG. 4G). Additionally, 20 pl of 1 M LiCl was similarly added to the 0.01 M native-PONb solution on the grooved slide. In-situ Raman spectroscopy revealed that the peak at 889 cm'1remained unchanged within one minute, confinning the absence of interaction with Li+within this timeframe (FIG.4H)Dynamic light scattering measurement (DLS)

[0150] Dynamic light scattering (DLS) measurements were conducted using a Malvern Analytical Zetasizer Nano-ZS instrument. All samples were analyzed in a plastic cuvette at room temperature with a 633 nm laser source. The scattering angle was set at 173 degrees. The refractive index of the solute was 2.3403, and the refractive index of the solvent (water) was 1.33. Data analysis was performed using Zetasizer software version 7.13.

[0151] Generally, a 0.01M aqueous solution of native-PONb (100 pl) was initially tested.Subsequently, different concentrations of LiCl, MgCL, andNaCl solutions (0.0025 M, 0.0125 M, 0.025 M, 0.10 M, 0.50M, 1.00 M) were added individually and measured (FIG.231). The initial relative diameter of native-PONb was approximately 59.95 nm, indicating no aggregation. Upon the addition of 0.10 M LiCl, the relative diameter exhibited no significant change, even with the addition of over 100 pL of LiCl. When the LiCl concentration was increased to 0.50 M, the relative diameter remained stable up to 30 pL of LiCl; however, with the addition of 40 pL. the relative diameter sharply increased to 1525 nm. This indicates that Li ions interact with native-PONb, forming large aggregates. This rapid increase in diameter suggests the formation of a precipitate, corresponding to the solubility limit of the PONb aggregates. In contrast, when MgCL was introduced, the addition of just 3 pL of 0.0025 M MgCL caused the relative diameter to reach 578 mn. With the addition of 8 pL, the diameter exceeded 1000 nm, indicating that even a small amount of Mg ions can induce significant aggregation with PONb clusters. Higher concentrations of MgCL were also tested: at 0.0125 M, the addition of 10 pL resulted in a relative diameter of 1852.83 nm, and at 0.025 M, the relative diameter dramatically increased to 2967.50 mn with the same volume addition. For comparison, similar concentrations of LiCl (0.0025 M, 0.0125 M, and 0.025 M) were tested, and in all 32WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOcases, the relative diameter remained between 60-80 mn, indicating no significant aggregation. Similar tests with NaCl yielded results comparable to those of LiCl, with significant aggregation observed when 40 pL of 0.5 M NaCl was added, resulting in an aggregate diameter of 2296.33 mn. These findings demonstrate that native-PONb has a significantly lower solubility in the presence of Mg2+ions compared to Li+and Na+ions. The high sensitivity of native-PONb to Mg2+, as evidenced by these experiments, aligns with the results obtained from ICP-OES.

[0152] FIG. 23 J shows the relationship between aggregate size and the molar ratios of Li+, Mg2+, and PONb. This figure was generated by smoothly connecting data points from the 0.0025 M MgCL and 0.5 M LiCl curves in FIG. 231, which provided the corresponding volumes of MgCL and LiCl solutions needed to form aggregates of various sizes, from 0 mn to 2000 mn. The plot displays the molar amounts of Li+, Mg2+, and PONb associated with each aggregate size, reflecting changes in ion composition as aggregate size increases and revealing characteristics of the aggregation dynamics in these solutions.Solid-state nuclear magnetic resonance spectroscopy (ssNMR)

[0153] 1H ssNMR spectra were recorded at 9.4 T (400MHz for 'H) using a Bruker BioSpin spectrometer equipped with an Avancc IV NEO console and 1.3 mm double resonance HX magic angle spinning (MAS) probe. 'H chemical shift was referenced with respect to tetramethylsilane (TMS) using the Cl L resonance of adamantane as a secondary external reference at 5 iso ('ll) = 1.85 ppm.

[0154] PONb samples were first dried in an oven for 48 hours at 80°C. NMR samples were then packed in 1.3 mm zirconia rotors in air and closed with Vespel® SP1 drive caps. Packed sample masses for native-PONb, -Mg, -Li, and -Na were 5.0 mg. 3.1 mg. 5.2 mg, and 4.6 mg, respectively. Samples were spun at VR= 58-60 kHz at the magic angle using dry nitrogen to avoid moisture exposure. H ssNMR spectra were obtained using a rotor-synchronized Hahn echo sequence (90°-r-180°- T-AQ. where r is one rotor period and 2T is the echo duration) with a 90° pulse of 1.4 JJ. S. 64 scans were averaged using a repetition delay of 5 s (Mg-PONb and Li-PONb) or 10 s (native-PONb and Na-PONb) which was long enough to reach full relaxation of all 'H signals across all 4 samples.

[0155] T2 relaxation measurements were obtained by varying the 2r echo duration in rotor synchronized spin-echo experiment from 33.3 ps to 2.10 ms for the native-PONb (VR = 60 kHz) and 34.5 ps to 1.65 ms for the Mg-PONb. -Li. and -Na (VR= 58 kHz). For echo delay, signals were averaged out over 16 scans with a repetition time of 2 s. To ensure a constant initial steady condition prior to the recovery delay for each echo, a train of 50 evenly spaced (5 ms) 90° pulses (1.4 ps) were used. Peak area was fitted to the echo time with exponentials of the form MoeT2 + c using the SciPy package in Python. All solid-state NMR data were acquired and processed using Bruker TopSpin 33WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO4.4.0. Fitting of T2 relaxation data was performed in Python as described above, while spectral deconvolution was performed using the DMfit software.Solid-state nuclear magnetic resonance spectroscopy

[0156] Quantitative ’H spin-echo ssNMR measurements w ere performed under fast MAS (VR= 60 kHz). Na-PONb shows a weak and broad resonance around 2 ppm, which is associated with a basic hydroxyl (NbOH) site. native-PONb shows three low intensity resonances at 8.6, 9.9, and 13.4 ppm. Nyman et al.18has noted such acidic (downfield) 'H resonances are associated with hydrogen bonding between bridging oxygens (Oj) in niobate clusters. native-PONb and Mg-PONb show multiple weak but sharp signals between 1-4 ppm, indicative of highly mobile proton environments. These are associated with alcohol impurities18, 19from MeOH used during synthesis, and thus will not be discussed further. The water resonance provides the most information about the chemical structure of the PONbs. Its chemical shift (around 6 ppm in all four PONbs) is higher than that observed for physisorbed H2O in zeolites (ranging from 3.5 to 4.9 ppm)20. This shift is similar to that of H2O in Bronsted acid sites in zeolites, indicating the highly charged nature of the niobate cluster21. Notably, the water resonance in Mg-PONb was slightly downfield compared to the other three PONbs, at 6.3 ppm vs 5.9, 5.8, and 6.0 ppm in native-PONb, Li-PONb, and Na-PONb. respectively.

[0157] Quantification of water content in these four PONb materials is achieved by recording 'll ssNMR echo that are fully Ti relaxed with back-calculation of T2 losses during the echo delay (~34 ps) knowing T2 values of each sample. T2 values of 378 ps, 278 ps, 219 ps, and 274 ps for native-PONb, Mg-PONb. Li-PONb. and Na-PONb, respectively correspond to T2 losses of 8.4%, 11.7%, 14.6%, and 11.8%. The presence of multiple non-H2O proton sites requires spectral deconvolution for accurate quantification of water content. Additionally, the broadening of the water resonance caused by dipolar coupling interactions of 'H spins obscures the presence of multiple distinct water resonances. After normalization by number of scans, sample loading weight, anhydrous molecular weight, and T2 losses, the 'H line shape was deconvolved. verifying its limited resolution. In all four samples, a single site deconvolution of the broad water resonance led to a poor fit and at least two components were needed to obtain a satisfactory' deconvolution. One site. A, maintains its chemical shift across all four PONbs at 5.7 ppm. While in native-PONb and -Li, site B was observed at 6.1 ppm, in Mg-PONb and -Na. the site shifted to 7.4 ppm and 6.7 ppm. respectively. This matches the observation from Raman spectroscopy, which suggests the existence of an Nb-O-M (M = Mg2+, Na+) bridging bond for Mg-PONb and -Na only. For these reasons, site A was associated with interactions between H2O and the Nb metal center, while site B was associated with interactions between H2O and M (M = K+, Mg2+, Li+, Na+). These sites A and B are designated as H2O-Nb and H2O-M interactions.Structure determination34WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO

[0158] Single crystal X-ray diffraction studies for compounds 1-4 were performed using a Broker D8 Venture diffractometer equipped with Mo Karadiation (L= 0.71073 A). Crystals were mounted on a Cryoloop with Paratone oil. Data were collected in a nitrogen gas stream at 100(2) K using <|> and to scans. The data were integrated using the Broker SAINT software program and scaled using the SADABS software program. Solution by direct methods (SHELXT) produced a complete phasing model consistent with the proposed structure. All nonhydrogen atoms were refined anisotropically by full-matrix least-squares (SHELXL-2014).

[0159] In die cry stal structure of Na-PONb, hydrogen atoms on oxygen atoms were found in difference Fourier map and O-H bond distances were restrained to 0.85 A. For highly disordered solvent molecules, the PLATON routine SQUEEZE was used to account for die corresponding electrons as a diffuse contribution to the overall scatering without specific atom positions.

[0160] There is a disorder of Li and O atoms in Li-PONb structures, the ratio of two possible positions is 50:50. Atom 09 represents a disordered solvent, it is most probably MeOH or MeOH / water mixture, but it is not possible to properly model such solvent disorder.

[0161] In the case of nativc-PONb, K5 and one of the bonded O atoms is disordered in two positions with a ratio of occupancy approximately 9:1. Atom KI is disordered in two positions due to symmetry, the occupancy of KI and bonded atom 020 was refined freely. Hydrogen atoms on oxygen atoms were found in difference Fourier map and O-H bond distances were restrained to 0.85 A.

[0162] In Mg-PONb, part of the terminal O atoms bonded to Mg are disordered in two positions with occupancy fixed to 0.5. The crystal quality was lower in this case, we could see some of the hydrogen atoms on oxygen atoms in difference Fourier map, but not every position could be estimated. Therefore, we decided not to include hydrogen atoms in refinement.

[0163] In all cases, all atoms were refined based on the electron density and {NbeOis}8' structural chemistry, and referenced to ICP-OES elemental analysis results with any remaining negative charge compensated by protons.Separation efficiency evaluation: precipitation performances for a mono-component M^+solution

[0164] Approximately 3.87 mg of native-PONb material was individually introduced into conical tubes containing 5.0 mL of MgCL solutions with varying magnesium concentrations of 0.67, 1.18, 1.68, 2.50, 5.33, 10.29, 25.62, 53.09, 111.39, and 256.13 ppm. These concentrations were verified using ICP-OES. The mixtures were placed on a Cole-Parmer digital tube roller shaker to ensure continuous mixing at a speed of 1000 rpm with a 360° rotation for a duration of 1 minute and then left undisturbed for 24 hours. After the 24-hour period, the samples were subjected to centrifugation for 1 minute to achieve homogeneous suspensions. The supernatants were collected and analyzed for magnesium content using ICP-OES. The magnesium precipitation performance of native-PONb was calculated by deducting the residual magnesium concentration from the initial concentration in the 35WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOsolution. In the study of the experimental amount of Mg2+captured per efficient amount of {NbeOig j':shown as a function of Mg2+concentration, a rapid increase in the amount of Mg2+captured was observed up to a concentration of approximately 111 ppm, after which the captured amount levels off, indicating saturation.

[0165] The precipitation kinetics of Mg2+by native-PONb material over time were tested using a similar method. The same mass of native-PONb material (3.87 mg) was individually added to conical tubes containing 5.0 ml of MgCL solutions with magnesium concentrations of 53.09 ppm. The mixtures were placed on a Cole-Parmer digital tube roller shaker to ensure continuous mixing at a speed of 1000 rpm with a 360° rotation for a duration of 10 seconds and then left undisturbed. At 1, 10, 30, and 60 minutes, as well as 24 hours, the samples were subjected to centrifugation for 1 minute at 5000 rpm (with a 30-second centrifugation for the 1 -minute sample) to achieve homogeneous suspensions. The supernatants were collected and analyzed for magnesium content using ICP-OES. The magnesium precipitation performance of native-PONb material was calculated by deducting the residual magnesium concentration from the initial concentration in the solution. In the study of the precipitation kinetics of Mg2by native-PONb material over time, a rapid decrease in Mg2+concentration was observed within the first 1 minute, reaching near-zero levels, followed by a stable concentration over the remaining time up to 1440 minutes. This indicates that the native-PONb material has a rapid and strong capture capability for Mg2+.Separation performances of bimetal mimic brine solution

[0166] The separation performance of bimetallic mimic brine solutions by native-PONb material over time was tested using a similar method. Binary salt mixtures of MgCE / LiCl, MgCp / NaCl, and MgCh / KCl with various concentrations and mass ratios were used as feed solutions. The detailed concentrations and mass ratios are shown in Tables 4-8. Approximately 8.0 mg of native-PONb material was individually added to conical tubes containing 1.0 ml of bimetal solutions (Mg2+concentration was between 100-500 ppm). The mixtures were placed on a Cole-Panner digital tube roller shaker to ensure continuous mixing at a speed of 1000 rpm with 360° rotation for 10 seconds, then left undisturbed. At 1. 10, 30, and 60 minutes, as well as 24 hours, the samples were centrifuged for 1 minute at 5000 rpm (with a 30-second centrifugation for the 1-minute sample) to achieve homogeneous suspensions. The supernatants were collected and analyzed for magnesium content using ICP-OES.

[0167] When the Mg2+concentration was less than 100 ppm, approximately 4.0 mg of native-PONb material was added to conical tubes containing 1.0 ml of bimetal solutions. When the Mg2+concentration was between 1000-3000 ppm, approximately 8.0 mg of native-PONb material was added to conical tubes containing 0.2 ml of bimetal solutions. When the Mg2+concentration was over 7000 ppm, approximately 80.0 mg of native-PONb material was added to conical tubes containing 0.236WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOml of bimetal solutions. The magnesium precipitation performance of the native-PONb material was calculated by deducting the residual magnesium concentration from the initial concentration in the solution.

[0168] To evaluate the separation performances, some equations were employed:The salt rejection, R (%). is calculated according to Eq. (1):R=(l - x 100% (1)where Crand C / is used to denote receive and feed solution concentrations, respectively, which is determined by ICP-OES.

[0169] The Li7Mg2+selectivity, SLLM8, could be calculated through the rejection of Li+( Ru) and Mg2+(R ig):SLi; Mg^ (2)

[0170] This formula can also be extended to SNa / Mg and Sjc / Mg by replacing Ru in Formula 2 with R’.fiand RK, respectively.

[0171] As the purpose of the separation is to extract Li from a Li / Mg mixture in a simplified scenario with Li+and Mg2+cations, the purity, qu24, is defined as the mass fraction of cations in the received solution that are Li+:PL. =c(3)

[0172] The Li+ / Mg2+separation performance of native-PONb characterized by rapid separation within seconds, a broad operational range, and high efficiency, is driven by their unique structural and electrostatic properties. native-PONb exhibits a highest negative charge density on their surface oxygen atoms, which results from Nb's relatively low electronegativity. This weaker electronwithdrawing ability enhances the nucleophilicity of the oxygen atoms, making them more available for cation coordination. Additionally, the longer M-0 bond lengths and minimal Nb 7-orbital participation in native-PONb further increase accessibility to cations. Mg2+, with its higher charge density and small ionic radius, demonstrates stronger electrostatic interactions with the negatively charged PONb surface due to its high charge-to-radius ratio (z / r). This interaction is further strengthened by the formation of shorter Mg-0 bonds at the terminal oxygen sites, which are associated with lower binding energies. These shorter bonds not only stabilize the Mg2+coordination but also promote the self-assembly of Mg-PONb complexes into large porous structures with significantly higher surface areas. In contrast, Li+, with its lower charge density, is heavily solvated in solution, surrounded by a robust solvation shell that diminishes its direct interaction with the PONb surface, significantly reducing its affinity for coordination. This combination of strong Mg2+attraction 37WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOand limited Li+interaction underpins the exceptional efficiency and selectivity observed in the Li+ / Mg2+separation process using native PONb.Molecular Dynamics Simulations

[0173] Molecular dynamics (MD) simulations were conducted using the Large-scale Atomic / Molecular Massively Parallel Simulator (LAMMPS) to investigate the behavior of PONb in aqueous solution. The simulations utilized the Lennard-Jones (LJ) force field with long-range Coulombic interactions to efficiently model atomic interactions. The TIP3P model was employed to describe water molecules, providing a simplified yet effective approach for simulating their behavior across various environments. Lorentz-Berthelot rules (4) were used to calculate the LJ parameters for species i and j in the studied system.Eij = 7^’aiJ = (CTi+°j) / 2(4)

[0174] The simulation box dimensions were set to 160 A in each direction, containing 125.000 water molecules. The PONb molecules were randomly placed within the water box. Periodic boundary conditions were applied in all three dimensions to mimic an infinite system. The particleparticle particle-mesh (PPPM) method was used to efficiently handle long-range electrostatic interactions with a precision of 10"5. The system was equilibrated at 300 K using the NVT ensemble, followed by production rims in the NPT ensemble to ensure proper density and pressure conditions. The simulation timestep was set to 2 fs, and the optimization time was approximately 40 ns. After reaching equilibrium, Li+, Mg2. Na+, and CL ions were added to the simulation box. The concentrations of cations and anions were adjusted to ensure electrical neutrality of the solution. To ensure sufficient reaction and contact between PONb and metal ions, following simulations were performed at least 60 ns under NVT ensemble.

[0175] FIG. 23A shows the equilibrium configuration of PONb molecules in aqueous solution, that is, the initial configuration before the addition of different metal cations. At this stage. PONbs were relatively isolated and remained relatively stable, with no obvious aggregation tendency. Thereafter, several different ion sets were added to the simulation box to study the interactions between PONbs and different metal ions, as well as the aggregation state between PONb molecules. Here, four configurations were studied: the first configuration is Li+ions, the second is a mixture of Li+and Mg2+ions with a ratio of 10:1, the third is a one-to-ten mixture of LL and Mg2+ions, and the last is pure Mg2+ions. FIGs. 23C-23F show the MD snapshots after 60 ns of the addition of different metal ions.FIG. 23C shows the snapshot after the addition of Li+ions. The aggregation state of PONb was basically the same as the initial configuration (FIG. 23A) with no PONb clusters. Some Li+ions were adsorbed on PONB, but most Li+ions were still scattered in the aqueous solution. The MD snapshots after adding a mixture of Mg2+and Li+ions were shown in FIGs.23D and 23E. The PONb molecules were clustered together and adsorbed almost all Mg2+ions independent of the concentration.38WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOHowever, the interaction between PONb and Li ions was relatively weak, which was manifested by less than 5% Li+ion adsorption and more than 95% of free Li+ions even in a Li+-rich environment FIG. 23F shows the results of adding Mg2+ions where the PONb molecules in the simulation box aggregated together. Almost all Mg2+ions were adsorbed onto PONb clusters, and it was difficult to find free Mg2+ions in aqueous solution.

[0176] Based on distance-based neighboring criterion, the PONbs could be divided into separate groups as clusters to analyze the aggregate state. Particles are considered connected when they fall within a specified cutoff range. Due to the stable skeleton of PONb molecular, the Nb and O atoms in PONb were considered during analysis process. Since the metal ions effect will change the molecule distance, the neighbor cutoff distance was treated as 2.30 A to represent the PONb’s aggregate state. As shown in FIG.23B, when the only added ion was Li", this possibility remained low during the whole simulation period. In the case of Mg2+ions, despite the concentration of Mg2+and other ion effects, the PONbs would cluster together in a short period of time when they met with the Mg2+ions, which indicated the interaction was strong and active. In short, it can be concluded that PONb molecules exhibit a strong preferred attraction to Mg2+ions, and the Mg2+ions would lead the cluster of PONbs.Binding Energy Calculations

[0177] Binding energy calculations were performed using the Vienna Ab initio Simulation Package (VASP). Density functional theory (DFT) with the generalized gradient approximation (GGA) was employed to calculate the electronic structure and total energies of the systems. The projector augmented-wave (PAW) method was used to describe the core-electron interactions. During the computation process, the cut-off energy for the employed plane-wave was adjusted to 520 eV.Brillouin zone integrations were carried out using only the T-point. The supercell used has dimensions of (31 A x 31 A x 31 A) to eliminate the periodic interaction. The water environment was defined using the VASPsol package, which incorporates solvation effects. Considering the complex interactions in this solution, geometrical optimization was conducted until all the forces acting on each atom were less than 0.05eV A1.

[0178] The binding energy of the PONb in the water solution was determined by calculating the total energy of the isolated PONb, the isolated metal cations, and the combined system. The structure of PONb was converted from the experimental observations, while the full optimization in aqueous solvent was performed. The metal cations were placed at corresponding positions to connect to bridge or terminal oxygen atoms of PONb to form the PONb-cations system (as shown in FIG.26). The binding energy was then obtained using tire following equation:E binding — EPOM-M (EPOM + EM) (5)WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOwhere EP0M-Mis the total energy of the PONb-cations system, EP0Mis the total energy of the isolated PONb, and EMis the total energy of the metal cations in aqueous solution.

[0179] DFT calculations corroborate this preference, aligning with the binding energy hierarchy. Among these four metal ions, the Mg2+ions exhibit the strongest bonding strength with the oxygen atoms on PONb molecules, regardless of whether the oxygen is in a terminal or bridge position. The binding energy of K+ions to bridge oxygen is lower than that to terminal oxygen, consistent with experimental observations on much higher ratio of bridge site bonding. In the case of Na+ions, the binding energies to bridge and terminal oxygen are similar, indicating no significant preference for either connection site.Synthesis

[0180] Synthesis of native-PONb, K>: / Nb. Oi «9H: O, A mixture consisting of NbzOs (0.2 g, 0.75 mmol) and KOH pellets (2.24 g, 40 mmol) was combined with 20.0 ml of deionized water (DI water) in a 43 ml Teflon-lined acid digestion vessel. This reaction mixture was stirred for approximately 5 mins at room temperature to facilitate dissolution. Subsequently, the vessel was scaled in an autoclave reactor and heated to 200 °C for 72 h. Upon cooling to room temperature, the supernatant was collected, and 60 ml of methanol (MeOH) was added. The mixture was then stirred for 30 mins to precipitate out the product. The resultant white precipitate was isolated via filtration and washed three times with 10.0 ml of cold 1:1 MeOH / DI water solution. The purified white crystals were finally collected by filtration, followed by drying for 3 hours. Formula: KsINb. Oi'fyOFFO. 1337.21 g / mol. Yield: 320.1 mg, 0.239 mmol, 95.8% based on Nb. Experimental (calculated) % mass: Nb 41.82 (41.69), K 23.37 (23.39), H2O 12.05 (12.11).

[0181] Synthesis of the Li-PONb, HLi / NbeOigJ’ / H O. A 50.0 pl aliquot of 2.0 M LiCl aqueous solution was combined with 100.0 pl of a 0.01 M I<dNbf, Oi9|«9H:O aqueous solution in a 2-ml vial. The mixture was stirred for 10 seconds, resulting in a colorless solution. Over a few hours, few colorless cry stals precipitated and were subsequently collected for Single crystal X-ray diffraction. The reaction was scaled up to obtain enough powder for subsequent characterization. To purify the crystals for the further characterizations, they were washed three times with 10 ml of MeOH to eliminate chloride salt impurities. Formula: Lis / NbeOig / ’ / SH^, 1144.00 g / mol. Experimental (calculated) % mass: Nb 48.81 (48.73), Lr 4.23 (4.25), H2O 20.44 (20.45).

[0182] Synthesis of the Na-PONb, H; Na.! / Nb. i') / , / 5H20, A 20 pl aliquot of 2.0 M NaCl aqueous solution was combined with 100 pl of a 0.01 M K8[NbeOi9]«9H2O aqueous solution in a 2-ml vial. The mixture was stirred for 10 seconds, resulting in a colorless solution. Over a few minutes, colorless crystals precipitated and were subsequently collected for Single crystal X-ray diffraction. The reaction was scaled up to obtain enough powder for subsequent characterization. To purify the crystals for the further characterizations, they were washed three times with 10 ml of MeOH to eliminate chloride salt 40WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOimpurities. Formula: H2Na6[Nb6O19]•15H2O, 1269.36 g / mol. Experimental (calculated) %mass: Nb 43.79 (43.91), Na 10.92 (10.87), H2O 21.33 (21.27).

[0183] Synthesis of the Mg-PONb, Mg4[Nb6O19]•16H2O, The synthesis of single-crystal Mg-PONb is more challenging compared to Li-PONb and Na-PONb. Even a minimal addition of Mg2+can instantly produce a substantial amount of low-crystallinity powder. For instance, when 20 pl of a 0.10 M MgCl2solution was added to 100 pl of a 0.01 M native-PONb solution, a massive precipitation of powder occurred, almost completely filling the vial. To reduce the reaction rate and minimize powder formation, thereby allowing an assessment of the limited solubility of Mg2+in the native-PONb solution, lower concentrations and smaller volumes of MgCl2were used. Despite this, the addition of even 5 pl of a 0.005 M MgCl2solution still resulted in immediate turbidity. For further analysis of the product formed by adding Mg2+to the native-PONb solution, a 15 pl aliquot of 0.000625 M MgCl2aqueous solution was mixed with 100 pl of a 0.000625 M native-PONb aqueous solution in a 2 ml vial. The mixture was stirred for 60 seconds, resulting in a clear solution. Colorless cry stals precipitated after several days and were collected for SC-XRD analysis. Due to the minimal amount of Mg2+added during the preparation of Mg-PONb single cry stals, the structure of Mg-PONb exhibits two Mg atoms with partial occupancy. This is attributed to the input ratio of Mg2+ / PONb being significantly lower than the expected ratio for the Mg-PONb structure. Consequently, the chemical fomrula of Mg-PONb is more reliably determined from the powder samples obtained at a normal scale. Powder X-ray diffraction patterns of Mg-PONb synthesized at standard dosages (amounts used for other characterizations) are presented at FIG. 7 to indicates that the Mg-PONb single crystals obtained under highly diluted conditions exhibit a consistent structure with the powder fonn of Mg-PONb synthesized at standard dosages. To purify the samples for the further characterizations, they were washed three times with 10 ml of MeOH to eliminate chloride salt impurities. Fomrula:Mg4[Nb6O19]•16H2O, 1246.64 g / mol. Experimental (calculated) % mass: Nb 44.74 (44.72), Mg 7.79 (7.80), H2O 22.99 (23.10).

[0184] Regeneration of Native-PONb and Recovery of Mg(OH)2. A mixture consisting of Mg- PONb (500.11mg, 0.40 mmol) and KOH pellets (5.60 g, 100 mmol) was combined with 50.0 ml of deionized water (DI water) in a 100 ml Teflon-lined acid digestion vessel. When smaller amounts of Mg-PONb were used, the quantities of KOH and water were proportionally reduced. This reaction mixture was stirred for approximately 5 mins at room temperature to facilitate dissolution.Subsequently, the vessel was sealed in an autoclave reactor and heated to 200 °C for 24 h. After naturally cooling to room temperature, the reaction suspension was separated by centrifugation. The resulting solid and supernatant were collected separately. The solid was washed with deionized water and dried under vacuum for 3 hours to yield crystalline Mg(OH)2. The supernatant was subsequently treated with 200 mL of MeOH to induce precipitation. The resulting solid was washed three times41WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WOwith 20.0 mL of cold 1:1 MeOH / DI water solution and then dried under vacuum for 3 hours to yield the regenerated PONb as a white powder.

[0185] Other objects, features and advantages of the disclosure will become apparent from the foregoing figures, detailed description, and examples. It is contemplated that changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from the detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

[0186] The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described in any way.WBD (US) 4924-1634-1883vl

Claims

1. Docket No. 2024-076-02 | L102142 1640WOCLAIMSWhat is claimed is:

1. A poly oxometalate (POM) composition comprising a poly oxometalate cluster bound to a metal and forming a network.

2. The polyoxometalate composition of claim 1, wherein the poly oxometalate comprises a polyoxoniobate (PONb).

3. The polyoxometalate composition of claim 2, wherein the PONb comprises [Nb6O19]8-", 4. The polyoxometalate composition of any one of claims 1-3, wherein the metal is bound to the polyoxometalate cluster via a terminal oxygen (Ot), a bridging oxygen (Ob). or a hydrogen bonding (H-bond).

5. The polyoxometalate composition of any one of claims 1-4, wherein the metal is K+, Mg2+, Li+, or Na+.

6. The polyoxometalate composition of claim 5, wherein the poly oxometalate composition comprises K8[Nb6O19], Li8[Nb6O19], H2Na6[Nb6O19], or Mg4[Nb6O19],7. The polyoxometalate composition of any one of claims 1-6, wherein the poly oxometalate composition is a hydrate.

8. A method of generating a first polyoxometalate (POM) composition comprising a polyoxometalate cluster bound to a first metal, the method comprising:mixing a metal oxide, a metal hydroxide, and water to provide a mixture;heating the mixture;cooling the mixture;adding methanol to precipitate the polyoxometalate composition, wherein the polyoxometalate cluster is derived from the metal oxide and the first metal is derived from the metal hydroxide; andisolating the precipitated polyoxometalate composition, thereby generating a polyoxometalate composition.

9. The method of claim 8, wherein the metal oxide comprises NbjOs, and the polyoxometalate comprises a polyoxoniobate (PONb).43WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO10. The method of claim 8 or 9, wherein the first metal is K, or the first poly oxometalate composition comprises K8[Nb6O19] and H2O.

11. The method of any one of claims 8-11, further comprising:contacting the first polyoxometalate composition with a metal salt; andobtaining a second polyoxometalate composition comprising the POM bound to a second metal derived from the metal salt.

12. The method of claim 11, wherein the second metal is Li, Na, or Mg, or the second polyoxometalate composition comprises Li8[Nb6O19], H2Na6[Nb6O19], or Mg4[Nb6O19], and H2O.

13. A method of isolating a first metal from a source containing a first metal and a second metal, the method comprising:contacting the source with a polyoxometalate (POM) composition comprising a polyoxometalate cluster, thereby binding the first metal to the polyoxometalate cluster;separating the polyoxometalate cluster bound to the first metal from the source, thereby isolating the first metal from the source and from the second metal.

14. The method of claim 13, wherein the polyoxometalate comprises a polyoxoniobate (PONb).

15. The method of claim 13 or 14, wherein the first metal or the second metal comprises a critical mineral material.

16. The method of any one of claims 13-15, wherein the first metal comprises Mg2+and the second metal comprises Li+.

17. The method of any one of claims 13-16, wherein the source is brine or wastewater.

18. The method of any one of claims 13-17. wherein the selectivity of the second metal over the first metal remaining in the source after separating the polyoxometalate bound to the first metal from the source is about 200 or more, about 400 or more, or about 1000 or more.

19. The method of any one of claims 13-18, wherein at least 95%, 96%. 97%, 98%, or 99% of the first metal and at least 95%, 96%. 97%, 98%, or 99% of the second metal are recovered from the source.

20. The method of any one of claims 13-19. wherein binding of the first metal to the polyoxometalate cluster occurs within 1 minute after contacting the source with the polyoxometalate composition.44WBD (US) 4924-1634-1883vlDocket No. 2024-076-02 | L102142 1640WO21. The method of any one of claims 13-20. further comprising regenerating the polyoxometalate composition by:after binding the first metal to the polyoxometalate cluster, treating the polyoxometalate cluster bound to the first metal with KOH at elevated temperature; andcollecting the first metal as a hydroxide precipitate.

22. The method of claim 21, wherein the polyoxometalate composition maintains polyoxometalate recovery efficiency of at least 98% over 5 regeneration cycles.WBD (US) 4924-1634-1883vl

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