Methods for removal of oxy-anions of iodine from liquids using zirconium-based metal-organic frameworks and regeneration of same

Abstract

The present invention is directed to methods for remove iodine species from a liquid or liquid stream. In particular, the present invention is directed to adsorbing iodine species from a liquid or liquid stream using a metal-organic framework (MOF), such as a zirconium-based MOF such as MOF-808. The iodine species in the liquid or liquid stream may be a radioisotopes of iodine such as 129I and 131I, which may exist in the liquid or liquid stream as iodide, I- or an oxy-anion of iodine, such as iodate, IO3-. The liquid or liquid stream containing iodine species, may include a coolant stream at a nuclear power plant. The present invention is also directed to methods for regenerating the adsorbent, such as the MOF, including a zirconium -based MOF such as MOF-808, using an acid wash, such as an aqueous solution of hydrochloric acid, to remove the adsorbed iodine species.

Description

METHODS FOR REMOVAL OF OXY- ANIONS OF IODINE FROM LIQUIDS USING ZIRCONIUM-BASED METAL-ORGANIC FRAMEWORKS AND REGENERATION OF SAMEBACKGROUND OF THE INVENTIONField of the Invention

[0001] The invention, including its various embodiments, relates to the removal of a given chemical species from a liquid. In particular, the present invention and its embodiments relate to the use of a metal-organic framework (MOF), such as MOF-808, having particular properties suitable for removal of iodine species, such as oxy-anions of iodine, including iodate, from a liquid or liquid stream.Description of Related Art

[0002] Radioisotopes of iodine such as129I and131I are produced as fission products in the generation of nuclear power and can enter water-based coolant and ultimately the environment, for example, if nuclear fuel cladding is breached during fuel use in operating nuclear power plants or during storage of spent nuclear fuel.129I is a particular concern, because it is extremely long-lived with a half-life of 15.7 million years. Radioisotopes of iodine exist in aqueous environments as iodide, I“, and its oxyanion, iodate, IO3-. Both species are readily soluble in water and can easily enter the human body through the ingestion of contaminated water or crops, as well as via inhalation. Exposure to radioisotopes of iodine can lead to thyroid pathologies, including issues with hormone production and cancer.

[0003] Many studies regarding the removal of iodine species from water are focused on removal of I“. Further, current materials for ICE- removal are often limited by slow kinetics or low uptake capacities, resulting in large amounts of sorbent being required for sufficient uptake. Further still, studies regarding the use of metal-organic frameworks (MOFs) as sorption platforms for iodine has been heavily focused on adsorption of gaseous 12.

[0004] Even in the absence of competitive anion impurities in water streams, the ability of typical ion exchange resins to reduce effluent concentrations of iodate, for example, down to desired, ultra-low levels is thermodynamically limited by dynamic re-release of captured anionic species of iodine back into otherwise purified effluent water. Such phenomena are termed “equilibrium sloughage.” Such sloughage makes use of typical resin-based, separations media essentially impossible for achieving, for example, Iodate removal to levels below roughly 10 ppb within the aqueous effluent.

[0005] Therefore, a novel technology is needed that effectively and efficiently removes these iodine species from water and other liquid streams, such as liquid streams used or produced in the generation of nuclear power and other industrial water-based streams, or from a quantity of liquid held in storage. There is a need for such technology to remove these impurities in the presence of other competing species, or species that may compete for removal thereby effectively reducing the removal efficiency of the species targeted for removal. There is also a need for such technology to remove these impurities in a manner that specifically targets capture of that impurity and minimizes any reversibility or release from capture, thereby holding it with a much higher binding energy. In particular, a different type of structural media is required to specifically address removal of low levels of particular species, such as species of iodine, with high enough binding energy to maintain near irreversible uptake as analyte concentrations are lowered while competitor concentrations are simultaneously raised.BRIEF SUMMARY OF THE INVENTION

[0006] In general, the present invention is directed to methods for remove iodine species from a liquid or liquid stream. In particular, the present invention is directed to adsorbing iodine species from a liquid or liquid stream using a metal-organic framework (MOF), such as a zirconium -based MOF such as MOF-808. MOF-808 has been found to have exceptionally high uptake capacity for iodate, on the order of 233 mg / g, equivalent to 1.63 iodate anions per Zre-metal node of the MOF.

[0007] In some embodiments, the iodine species in the liquid or liquid stream may be a radioisotopes of iodine such as129I and131I, which may exist in the liquid or liquid stream as iodide, I“, or an oxy-anion of iodine, such as iodate, IO3-. In some embodiments, the MOF-808 adsorbs oxy-anions of iodine, such as iodate, IO3-, and in some embodiments, an ammonium form of MOF-808 adsorbs iodide, I“. In some embodiments, the liquid or liquid stream containing iodine species, may include a coolant stream or other liquid stream at a nuclear power plant or liquid in contact with spent nuclear fuel.

[0008] The present invention is also directed to methods for regenerating the adsorbent, such as the MOF, including a zirconium -based MOF such as MOF-808. In some embodiments, the regeneration of the MOF includes using an acid wash to remove the adsorbed iodine species. In some embodiments, the acid wash may be an aqueous solution ofhydrochloric acid, including solutions having up to approximately 10% hydrochloric acid. In some embodiments, up to three washes may be used, resulting in a regenerated MOF having little to no affect on subsequent adsorption performance.

[0009] The present invention provides the ability to remove various iodine species from a liquid or liquid stream using a MOF. The present invention provides a significant advantage over other technologies with respect to removing iodine species, in particular iodate, from liquids or liquid streams, in particular those associated with nuclear power plants.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0010] Figures 1 A-C illustrate a zirconium-based MOF, namely MOF-808 according to one embodiment of the present invention;

[0011] Figure 2A illustrates powder X-ray diffraction patterns for the as-synthesized MOF-808 compared to a simulated pattern according to one embodiment of the present invention;

[0012] Figure 2B illustrates ’H NMR spectroscopy of MOF-808 showing the disappearance of the formate proton according to one embodiment of the present invention;

[0013] Figure 2C illustrates the nitrogen adsorption-desorption isotherm for as- synthesized MOF-808 and pore size distribution according to one embodiment of the present invention;

[0014] Figure 2D shows scanning electron microscopy (SEM) images of as- synthesized MOF-808 crystallites according to one embodiment of the present invention;

[0015] Figure 3A illustrates the kinetics for iodate adsorption using MOF-808 according to one embodiment of the invention;

[0016] Figure 3B illustrates a Langmuir plot of the adsorption of iodate in MOF-808 according to one embodiment of the present invention;

[0017] Figure 4A illustrates a density functional theory (DFT) optimized model of the MOF-808 node with bridging iodate ions according to one embodiment of the invention;

[0018] Figure 4B illustrates a simulated differential pair distribution function (dPDF) of the DFT model of Figure 4A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to one embodiment of the present invention;

[0019] Figure 4C illustrates diffuse reflectance infrared Fourier transform spectroscopy data of bare and iodate-loaded MOF-808 according to one embodiment of the present invention;

[0020] Figure 5A illustrates a DFT optimized model of the MOF-808 node with bridging iodate ions according to one embodiment of the invention;

[0021] Figure 5B illustrates a simulated dPDF of the DFT model of Figure 5 A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to one embodiment of the present invention;

[0022] Figure 6A illustrates a DFT optimized model of the MOF-808 node with bridging iodate ions according to another embodiment of the invention;

[0023] Figure 6B illustrates a simulated dPDF of the DFT model of Figure 6A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to another embodiment of the present invention;

[0024] Figure 7A illustrates a DFT optimized model of the MOF-808 node with bridging iodate ions according to another embodiment of the invention;

[0025] Figure 7B illustrates a simulated dPDF of the DFT model of Figure 7A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to another embodiment of the present invention;

[0026] Figure 8A illustrates a DFT optimized model of the MOF-808 node with bridging iodate ions according to another embodiment of the invention;

[0027] Figure 8B illustrates a simulated dPDF of the DFT model of Figure 8 A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to another embodiment of the present invention;

[0028] Figure 9A illustrates powder X-ray diffraction patterns for MOF-808 according to one embodiment of the present invention;

[0029] Figure 9B illustrates isotherms for various forms of MOF-808 according to one embodiment of the present invention;

[0030] Figures 10A-10D show SEM images for iodine, zirconium, and MOF-808 crystallite and an SEM-EDS line scan analysis according to one embodiment of the present invention; and

[0031] Figures 11 A-D illustrate adsorption and desorption cycles for iodate in MOF- 808 according to one embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention is more fully described below with reference to the accompanying drawings. While the present invention will be described in conjunction with various embodiments, such should be viewed as examples and should not be viewed aslimiting or as setting forth the only embodiments of the invention. Rather, the present invention includes various embodiments or forms, various related aspects or features, and various uses, as well as alternatives, modifications, and equivalents to the foregoing, all of which are included within the spirit and scope of the invention and the claims, whether or not expressly described herein. Further, the use of the terms “invention,” “present invention,” “embodiment,” and similar terms throughout this description are used broadly and are not intended to mean that the invention requires, or is limited to, any particular embodiment or aspect being described or that such description is the only manner in which the invention may be made or used.

[0033] In general, the present invention is directed to methods for remove iodine species from a liquid or liquid stream. In particular, the present invention is directed to adsorbing iodine species from a liquid or liquid stream using a metal-organic framework (MOF), such as a zirconium -based MOF such as MOF-808. MOF-808 has been found to have exceptionally high uptake capacity for iodate, on the order of 233 mg / g, equivalent to 1.63 iodate anions per Zre-metal node of the MOF.

[0034] In some embodiments, the iodine species in the liquid or liquid stream may be a radioisotopes of iodine such as129I and131I, which may exist in the liquid or liquid stream as iodide, I“, or an oxy-anion of iodine, such as iodate, IO3-. In some embodiments, the MOF-808 adsorbs oxy-anions of iodine, such as iodate, IO3-, and in some embodiments, an ammonium form of MOF-808 adsorbs iodide, I“. In some embodiments, the liquid or liquid stream containing iodine species, may include a coolant stream or other liquid stream at a nuclear power plant or liquid in contact with spent nuclear fuel.

[0035] The present invention is also directed to methods for regenerating the adsorbent, such as the MOF, including a zirconium -based MOF such as MOF-808. In some embodiments, the regeneration of the MOF includes using an acid wash to remove the adsorbed iodine species. In some embodiments, the acid wash may be an aqueous solution of hydrochloric acid, including solutions having up to approximately 10% hydrochloric acid. In some embodiments, up to three washes may be used, resulting in a regenerated MOF having little to no affect on subsequent adsorption performance.

[0036] Following, various specific aspects of the invention are described, including the structure of MOFs for use in the present invention, including their synthesis and adsorptive capacity. In addition, methods for using the MOFs of the present invention to remove various iodine species are described, followed by a description of methods forregenerating the MOFs of the present invention. Further, other variations of these embodiments are also described.

[0037] Metal-organic frameworks (MOFs) are coordination polymers consisting of metal centers connected to one another by molecular organic ligands to form networks that often form via self-assembly into crystalline and highly porous materials. The metal nodes can be single metal ions, chains, or clusters, while the organic ligands, or linkers, can be di-, tri, or tetratopic. Due to the vast array of metal and organic linker combinations, and a multitude of accessible topologies, MOFs can be designed to have large surface area, permanent porosity, and high thermal and chemical stability. In particular, zirconium-based MOFs, constructed using a Zre octahedron cluster as the metal node, take advantage of the strong Zr(IV)-0 bond between the metal center and multitopic carboxylate linkers, resulting in robust materials that are stable in aqueous conditions. Additionally, they can possess accessible metal sites, capped by labile -OH and -OH2 ligands, that allow for the adsorption of a variety of guest molecules. In one embodiment, the zirconium-based MOF is MOF-8O8, which is a Zre-cluster-based MOF with 6-connected nodes bridged by the commercially available, tritopic, 1,3,5-benzenetricarboxylate linker.

[0038] Figures 1 A-C illustrate a zirconium-based MOF, namely MOF-8O8, according to one embodiment of the present invention. Figure 1 A illustrates the Zre-clusters; Figure IB illustrates 1,3,5-benzenetricarboxylate linker; Figure 1C illustrates the 6-connected MOF- 808. MOF-808 is well suited towards wastewater remediation due to its high thermal and chemical stability (stable in solutions with pH ranging from 1-10). Of the possible 12 metal node binding sites, only 6 are occupied by structural organic linkers in the spn topology of MOF-808, leaving 6 available to interact with adsorbate molecules, leading to the potential for high uptake capacity of guest molecules.

[0039] MOF-808, which may be used in the present invention, has a molecular formula of ZreO4(OH)4(BTC)2(HCOO)6, where BTC is 1,3,5-benzenetricarboxylate, before activation, and a molecular formula of Zr6(p3-O)4(p3-OH)4(BTC)2(OH)e(H2O)6, where BTC = 1,3,5-benzenetricarboxylate, after acid washing and activation. Activation usually involves heating and vacuum drying in order to remove solvents employed during synthesis from the resultant MOF surface structures.

[0040] Figures 2A-D illustrates analytical results regarding the synthesis of MOF-808 accordingly to one embodiment of the invention. MOF-808 can be synthesized and activated as follows: MOF-808 can be synthesized under solvothermal conditions using ZrOCi2*8H2O and 1,3,5-benzenetricarboxylic acid in DMF with formic acid modulator at 120 °C. In oneembodiment, MOF-808 was synthesized using a by combining 97 mg of ZrOCh’SEEO with 63 mg of EEBTC in 7.5 mL each of DMF and formic acid. The resulting mixture was sonicated until the components were dissolved and placed in an oven at 120 °C to react for 72 hours. The MOF was washed three times with fresh DMF (3 x 10 mL) and soaked in fresh DMF (10 mL) overnight, followed by three acetone washes (3 x 10 mL) and an overnight acetone (10 mL) soak. The powder was subsequently dried in a vacuum oven at 80 °C before soaking in 10 mL of 0.1 M HC1 overnight to remove the formate capping ligands from the MOF nodes. The MOF was centrifuged and the HC1 solution was removed followed by three water washes (3 x 10 mL), and three acetone washes (3 x 10 mL). (The acetone washes were performed to avoid framework stability issues related to capillary forces exerted by repeated adsorption and desorption tests.) The MOF was soaked in acetone (10 mL) overnight before drying in a vacuum oven at 80 °C for one hour, and then activated on a Micromeritics SmartVacPrep at 120 °C for 20 hours. 45.4 mg of sample was activated and used to collect the isotherm appearing in Figure 2C.

[0041] To ensure that the 6 nodal sites are accessible for oxyanion adsorption, the as- synthesized MOF is soaked in 0.1 M HC1 to remove the formate capping ligands leftover from synthesis. Powder X-ray diffraction (PXRD) confirms that the MOF is phase pure and crystalline after the removal of formate capping ligands (Figure 2A showing powder X-ray diffraction patterns for the as-synthesized MOF-808 compared to a simulated pattern), andTH NMR spectroscopy shows the disappearance of the formate proton at 7.92 ppm (Figure 2B). N2 gas adsorption analysis performed on MOF-808 shows the expected Type lb isotherm, with a Brunauer-Emmett-Teller (BET) area of 2020 m2 / g and pore diameters of 10 and 18 A (Figure 2C showing the nitrogen adsorption-desorption isotherm for as-synthesized MOF-808 at 77 K with the MOF-808 pore size distribution (inset)), consistent with previous reports. Scanning electron microscopy images show the expected morphology, with crystallite sizes of approximately 5 pm (Figure 2D showing SEM images of as-synthesized MOF-808 crystallites).

[0042] In one embodiment iodate was adsorbed using MOF-808. 2.5 mg of MOF- 808 was exposed to solutions of potassium iodate with concentrations equivalent to exposures of 2-7 iodate anions per metal node of MOF (41-287 ppm). The MOF was submerged in the solution for 72 hours, resulting in iodate uptake between 0.95 per node and 1.93 per node for exposures of 2 and 7 iodate equivalents, respectively, as shown in Table 1 below. This translates to between 134 and 286 mg of iodate per gram of MOF-808, indicating that the MOF has a high gravimetric capacity for iodate adsorption.

[0043] Table 1. Iodate Uptake by MOF-808

[0044] Figure 3A illustrates the kinetics for iodate adsorption using MOF-808 according to one embodiment of the invention. The kinetics of the adsorption process were determined by exposing 2.5 mg of MOF-808 to 10 mL solutions of 1, 1.5, 2, 2.5, and 3 iodate anions per node (41, 61.5, 82, 102.5, and 123 ppm, respectively). The amount (q) of iodate adsorbed in mg / g of MOF was determined using Equation 1 : q = (Ci - Cf) x V / m Eq. 1 where Ci is the initial concentration (ppm), Cf is the final concentration (ppm), V is the volume of the iodate solution (L), and m is the mass of MOF-808 (g). In all cases, steep uptake is observed within the first few minutes of exposure of MOF-808 to the iodate solution, with uptake continuing to increase until reaching a plateau between 48-72 hours.

[0045] Figure 3B illustrates a Langmuir plot of the adsorption of iodate in MOF-808 according to one embodiment of the present invention. The maximum adsorption capacity, Q, was calculated by fitting the data to the Langmuir adsorption model using Equation 2:Ce / qe= (l / Q)Ce+ 1 / KLQ Eq. 2

[0046] where Q is the equilibrium adsorption capacity (mg / g), Ceis the equilibrium concentration (ppm), qeis the equilibrium uptake (mg / g), and KL is the Langmuir adsorption constant. Q was determined to be 233 mg / g. This is the highest reported gravimetric iodate uptake to date (for example, for either MOFs or ion exchange polymeric resins), with other materials showing maximum adsorption capacities ranging from 0.01 - 170 mg / g as shown in Table 2:

[0047] Table 2. Various Maximum Adsorption Capacities Compared to MOF-808

[0048] Based on the foregoing, MOF-808 adsorbs iodate, which is an oxy-anion of iodine that is a particularly difficult to adsorb. Accordingly, MOF-808 may also adsorb other anionic forms (e.g., I') by modifying the MOF nodal or linker chemistries to incorporate typical anion exchange ligands (e.g., pendant ammonium cation molecules, which could serve an anion exchange function in aqueous solution. Hence, the MOF Zr-nodal clusters can physi-sorb iodate oxy-anion while the cavity inner surface of the very same MOF, for example, incorporating ammonium chemistry features could hold-up anionic iodine electrochemically.

[0049] Figure 4A illustrates a density functional theory (DFT) optimized model of the MOF-808 node with bridging iodate ions according to one embodiment of the invention. Figure 4B illustrates a simulated differential pair distribution function (dPDF) of the DFT model of Figure 4A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to one embodiment of the invention. Figure 4C illustrates diffuse reflectance infrared Fourier transform spectroscopy data of bare and iodate-loaded MOF-808. Specifically, Figure 4A shows a DFT optimized model of the MOF-808 node with bridging iodate ions, with hydrogen atoms omitted for clarity. Figure 4B shows the model-simulated dPDF of the DFT model of Figure 4A (as shown in the upper distinct line trace), which is for two iodate anions with r|2g2 binding. Figure 4B also shows the dPDF foriodate-loaded MOF-808 (from synchrotron X-ray total scattering measurements) (varying width trace shown under the upper distinct line trace for the DFT model) and the dPDF for bare iodate (lower distinct line trace).

[0050] As shown, a substantial decrease in the O-H stretch at 3674 cm'1after iodate loading confirms that -OH ligands are replaced by iodate (Figure 4C). Distances obtained via dPDF analysis are consistent with those determined by density functional theory (DFT) calculations for the optimized geometry of the Zre cluster of MOF-808 with a bridging iodate. Atom-pair distances of 1.9 and 3.7 A are observed after loading with iodate, corresponding to 1-0 and Zr-I, respectively. The signal is consistent with a binding mode where the iodate bridges two adjacent zirconium metal centers in the cluster or a r|2g2 binding mode. Peaks at larger distances are consistent with distances expected between iodine and successively further zirconium metal centers within the cluster. The DFT calculations suggest that hydrogen bonding with bound water has a directive effect on the iodate orientation - thus parts of the dPDF not clearly indexed by the model may plausibly occur due to distributed orientations, e.g. by interaction with further water layers.

[0051] Figure 5A illustrates a DFT optimized model of the MOF-808 node with bridging iodate ions according to another embodiment of the invention. Figure 5B illustrates a dPDF of the DFT model of Figure 5 A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to one embodiment of the present invention. Specifically, Figure 5A shows an optimized structural model of two bridging iodate anion binding to opposite sides of a MOF-808 Zre node. Figure 5B shows the model- simulated dPDF of the DFT model of Figure 5 A (as shown in the upper distinct line trace). Figure 5B also shows the dPDF for iodate-loaded MOF-808 (varying width trace shown under the upper distinct line trace for the DFT model) and the dPDF for bare iodate (lower distinct line trace).

[0052] Figure 6A illustrates a DFT optimized model of the MOF-808 node with bridging iodate ions according to another embodiment of the invention. Figure 6B illustrates a simulated dPDF of the DFT model of Figure 6A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to one embodiment of the present invention. Specifically, Figure 6A shows an optimized structural model of a bridging iodate anion binding to one Zre node of a 2-node MOF-808 system. Figure 6B shows the model-simulated dPDF of the DFT model of Figure 6A (as shown in the upper distinct line trace). Figure 6B also shows the dPDF for iodate-loaded MOF-808 (varying width traceshown under the upper distinct line trace for the DFT model) and the dPDF for bare iodate (lower distinct line trace).

[0053] Figure 7A illustrates a DFT optimized model of the MOF-808 node with bridging iodate ions according to another embodiment of the invention. Figure 7B illustrates a simulated dPDF of the DFT model of Figure 7A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to one embodiment of the present invention. Specifically, Figure 7A shows an optimized structural model of two bridging iodate anion binding to nearest adjacent sites on opposite Zre nodes of a 2-node MOF-808 system. Figure 7B shows the model-simulated dPDF of the DFT model of Figure 7A (as shown in the upper distinct line trace). Figure 7B also shows the dPDF for iodate- loaded MOF-808 (varying width trace shown under the upper distinct line trace for the DFT model) and the dPDF for bare iodate (lower distinct line trace).

[0054] Figure 8A illustrates a DFT optimized model of the MOF-808 node with bridging iodate ions according to another embodiment of the invention. Figure 8B illustrates a simulated dPDF of the DFT model of Figure 8 A, experimental dPDF data of iodate-loaded MOF-808, and a simulated dPDF of unbound iodate according to one embodiment of the present invention. Specifically, Figure 8A shows an optimized structural model of two bridging iodate anion binding to the second nearest adjacent sites on opposite Zre nodes of a 2-node MOF-808 system. Figure 8B shows the model-simulated dPDF of the DFT model of Figure 8A (as shown in the upper distinct line trace). Figure 8B also shows the dPDF for iodate-loaded MOF-808 (varying width trace shown under the upper distinct line trace for the DFT model) and the dPDF for bare iodate (lower distinct line trace).

[0055] It should be appreciated that “T|2” refers to the fact that two adjacent oxygen atoms in the iodate are the adsorbing atoms and that “pf’ refers to those sites comprising the adsorption sites on the MOF surface that are two adjacent Zr metal atoms. In the oxygen cases, “adjacent” refers to one oxygen on each side of the included iodine atom, and in the Zr cases, “adjacent” refers to two Zr atoms separated by sufficient space to bind those two adjacent oxygens. It should be appreciated that the space can be comprised of the organic constituents of the MOF nodal features, with those Zr atoms being held either within the same nodal structure or in two neighboring nodal structures at equilibrium within the range of distance needed to bond the iodate oxygens. In both options the un-excluded space allows for an unencumbered approach from the liquid water solution toward the adsorption site or the two Zr atoms on one node or the two Zr atoms positioned properly for picking up the iodate using two nodes (one Zr atom from each node). It should also be appreciated that thehexagonal symmetry of the macrocrystal affords six full nodal structures pendant to the unit cell that are available to adsorb the iodate (and other oxy-anions analogously) unencumbered by linker excluded volume.

[0056] Figure 9A illustrates powder X-ray diffraction patterns for various forms of MOF-808 according to one embodiment of the present invention. Specifically, the X-ray for the bottom pattern is for a simulated MOF-808, and the pattern immediately above that is for an iodate-loaded MOF-808 (CuKa, X = 1.54178 A). These data confirm that crystallinity of the MOF is maintained after iodate adsorption. It should also be appreciated that the X-ray patterns shown for various concentrations of HC1, illustrate that the crystallinity of the MOF is maintained even after three regenerative washing steps with 1, 3, 5, or 10% HC1. (Regeneration is discussed further below.)

[0057] Figure 9B illustrates isotherms for various forms of MOF-808 according to one embodiment of the present invention. Specifically, the top two isotherms, which essentially trace on top of each other, are adsorption / desorption isotherms for bare MOF-808, whereas the bottom two lower isotherms, which similarly trace on top of each other, are adsorption / desorption isotherms for MOF-808 having adsorbed iodate or after loading with iodate. It should be appreciated that the isotherms are Type lb isotherms, with a reduction in BET area from 1860 m2 / g to 1270 m2 / g and a reduction in pore volume from 0.75 cm3 / g to 0.51 cm3 / g. These data confirm that the porosity of the MOF is retained after iodate adsorption. It should also be appreciated that the porosity of the MOF is retained even after regeneration as shown by the two middle isotherms. After regeneration the surface area returned to 1850 m2 / g, and the pore volume to 0.75 cm3 / g. (Regeneration is discussed further below.)

[0058] Figures 10A-10D show SEM images for iodine, zirconium, and MOF-808 crystallite and an SEM-EDS line scan analysis according to one embodiment of the present invention. Larger crystallites of MOF-808 were grown for easier visualization by electron microscopy. Scanning electron microscopy (SEM) images show that the MOF-808 expected morphology is maintained after loading with iodate. Furthermore, energy dispersive X-ray spectroscopy (EDS) elemental mapping and line scan analysis of iodate loaded MOF-808 crystallites show iodine distributed evenly throughout the MOF crystallite.

[0059] Depending on the application envisioned, the ability to reuse and recycle an adsorbent material may be an important factor, reducing the cost and amount of material required to remediate contaminated water. To assess the reusability of MOF-808, 10 mg of MOF-808 was loaded with iodate by exposing the MOF to a 1148 ppm solution of potassiumiodate overnight resulting in uptake of 1.36-1.61 iodate / node. The following day, the iodate- loaded MOF-808 in the iodate solution was placed on a membrane filter in a glass microfiltration apparatus and the solution was passed through the filter by applying vacuum to the flask. The MOF-808 powder was then washed three times with 10 mL of water. 10 mL of either 1%, 3%, 5%, or 10% HC1 was then passed through the MOF by controlled vacuum filtration over the course of 5 minutes. The MOF was then washed with water three times and placed in 10 mL of fresh 1148 ppm iodate solution overnight. When using the 1% HC1 solution for regeneration of MOF-808, a maximum of 0.40 iodate / node was removed from the MOF. The performance increased, however, with increasing acid strength.

[0060] Figures 11 A-D illustrate adsorption and desorption cycles for iodate in MOF- 808 according to one embodiment of the present invention. Washing the MOF with 3% HC1 (Figure 1 IB) was found to remove a maximum of 0.55 iodate / node with a further increase when using 5% HC1 (Figure 11C) to 1.15 iodate / node. Using 10% HC1 (Figure 11D), the highest removal was obtained, with a maximum of 1.43 node equivalents removed, representing up to 85% removal of adsorbed iodate from the MOF. In between each acid wash, MOF-808 was exposed to an 1148 ppm solution of potassium iodate, and in each case, the maximum iodate uptake was preserved over 2 subsequent adsorption-desorption cycles.

[0061] It should also be appreciated that modifications to the MOF, such as MOF- 808, can be made. Because there exists in the literature established chemistries for modifying the linker portion of a MOF, such as SALE (solvent assisted linker exchange) and SALI (solvent assisted ligand incorporation (see e.g., P. Deria, W. Bury, J.T. Hupp and O.K. Farha, “Versatile Functionalization of the NU-1000 Platform by Solvent- Assisted Ligand Incorporation,” Chem. Commun. 2014, 50, 1965-1068; and, P. Deria, J.E. Mondloch, O. Karagiardi, W. Bury, J.T. Hupp and O.K. Farha, “Beyond Post-Synthesis Modification: Evolution of Metal-Organic Frameworks via Building Block Replacement,” Chem. Soc. Rev., 2014, 43, 5896-5912), one of expertise in the art should be able to envision suitable algorithms for applying such chemistries to introduce into the MOF-808 cavity appropriate ligand functionalities that further attract anions such as chloride (O'), iodide (I"), and oxyanions such as selenate (SeOs2-), selenite (SeOs2-), antimonate (SbOs"), antimonite (SbO2‘), lead oxides (including Pb(OH)e2', Pb(OH)e4', PbOs2', and PbO22'), and sulfate (SO42') so as to enhance the overall binding capacity of the material for these analyte species and hence to improve engineering operations employing these media for water treatment functions. In the specific case of selenate or selenite, one linker chemistry expected by those expert in the art of theoretical bonding calculation is a functionalized urea chemistry, like a pyridyl-urea heldpendant on a carbon or ether oxygen linear chain of sufficient length (for example, six to twelve elemental carbon or oxygen atoms long) to allow the urea derived ligand to contact the selenium oxy-anions that permeate the MOF cavity, with an appropriate terminal group to attach said ligand onto the MOF cavity and aperture forming components.

[0062] In use and according to one embodiment of the present invention, the MOF of the present invention can be used to selectively remove particular species from a liquid stream. In particular, MOF-808 can be used to remove various iodine species, such as129I,131I, iodide (I-), and iodate, (IO3-), noting that the129I and131I will typically exist in the liquid as iodide (F) and iodate (IO3-). To accomplish removal of a given species from a liquid or liquid stream requires, in some embodiments, a certain amount of the MOF and a structure for holding the MOF or to which the MOF is attached and permitting contact between the liquid or liquid stream and the MOF.

[0063] In general, it should be appreciated that the amount of MOF required will depend upon several factors. For example, a Langmuir adsorption capacity (moles of ion per unit weight of MOF) can be obtained for a specific analyte to be removed (e.g., iodine containing iodate oxy-anion) to determine in conjunction with the stream to be treated or the influent stream concentration of the analyte, the amount of MOF required for contact with the liquid stream or influent stream, for example, in a demineralizer bed or on a powdered resinholding filter demineralizer membrane associated with a nuclear power plant, such as a coolant clean-up system. Other factors include the sufficiency of contact between the liquid stream and the MOF on the substrate, which would be dependent upon the geometry or design of the corresponding equipment being used for contact between the liquid stream and the MOF, and the loss of MOF during any loading or unloading of the substrate, such as loading or unloading of beads in a demineralizer or other equipment being used. In the case of a demineralizer, it should be appreciated that the demineralizer beads may be a mixture of beads or a mixed bed of beads containing beads for both cation removal (e.g., by ion exchange) and anion removal (by MOF). In this case, the amount of contact between the liquid stream and the MOF beads specifically will also need to be accounted for in determining the amount of MOF beads to be used.

[0064] Further, in the case of a filter demineralizer normally holding powdered, ion exchange resin on its membrane pleats (e.g., in a Reactor Water Cleanup System [RWCU] for Boiling Water Reactor [BWR] nuclear power plant aqueous reactor coolant), the MOF crystallites themselves may be placed onto these pleats either independently or in combination with powdered ion exchange resin (such as a sulfonic acid-functionalized cationexchange polystyrenedivinylbenzene [PS / DVB] polymeric network resin). In this case, hydrodynamic forces obtained by the water flowing through the membrane pleats would serve to embed the MOF media directly into the high-pressure side of the filter demineralizer. In this case, the MOF as described could serve the function of anion clean-up media as a companion to a powdered, cation exchange resin. The amount of contact between the liquid stream and the MOF crystallites themselves specifically will also need to be accounted for in determining the amount of MOF to be used.

[0065] The particular MOF can be attached to any structure or substrate that is used to facilitate contact between the liquid stream having the particular species to be removed and the MOF. It should be appreciated that the structure or substrate may be any substrate to which a given MOF may be attached and that is suitable for use in the environment or process in which it will be used to remove certain chemical species or compounds from a liquid or a liquid stream. In some embodiments, the substrate may be an inert substrate to avoid any chemical interaction with the liquid or liquid stream being treated. In some embodiments, the substrate has a physical shape that allows for its deployment and use in a given process or in a particular piece of processing equipment for removing certain chemical species from a given liquid stream.

[0066] For example, the MOF can be attached to precoatable filter / demineralizers (described above for nuclear power plant coolant clean-up applications) or independent packed columns, including such devices already in use at a given facility or plant (e.g., existing vessels used for ion exchange). For example, the MOF can be pre-coated onto a filter weave of an existing filter demineralizer or similar filter system. Thereafter, the structure can be appropriately mounted to allow contact between the liquid stream and the MOF on the structure. For example, using a MOF-coated demineralizer or similar filter, the liquid or water to be treated would flow through the filter weave, for example from outside of a cylindrical filter, through the filter fibers and into the lumen, to allow contact between the MOF and the water. Once in contact with the liquid stream, the particular species to be removed is adsorbed onto the MOF, thereby reducing the concentration of that species in the liquid stream.

[0067] In some embodiments, the substrate may be a bead or plurality of beads. In some embodiments, the beads may be inert polypropylene polymer resin beads. In some embodiment, the substrate may be a macroscopic fabric, such as a mesh material or mesh filter. In some embodiment, the substrate may be a molecular fabric made from organic strands, essentially consisting of a two-dimensional copolymer framework or organic wovenmaterial. In some embodiments, the substrate may be a filter of pleated media constructed from metal or ceramic based materials to which the MOF adsorbs.

[0068] It should be understood that the following description of the methods for attaching a given MOF to a substrate, as well as the description of the methods for using the substrate with the attached MOF, refers to a MOF generically. However, it should be appreciated that in all of the embodiments described herein, the specific MOFs noted above, such as MOF-808, may be used. Accordingly, it should be appreciated that while some of the above specific MOFs are capable of removing, or configured to remove, specific liquid phase anionic species, other MOFs capable of removing other liquid phase species from a liquid or liquid stream may similarly be used and attached to a given substrate. In addition, while the following methods are described with reference to specific substrates, it should be appreciated that other substrates, including substrates having a difference chemical composition or having a different geometric shape, may be used in any combination with any suitable MOF.

[0069] In general, methods for attaching a given MOF particle to a substrate may depend upon the specific substrate used. Accordingly, the following describes methods for attaching a given MOF, including any applicable MOF and including NU-1000 and MOF- 808, to a bead, including a plurality of beads, a macroscopic fabric, such as a mesh fabric or mesh filter, and a molecular fabric made from organic strands, essentially consisting of a two- dimensional copolymer framework or organic woven material.

[0070] In some embodiments, a given MOF may be attached to a substrate that is a bead or a plurality of beads. In some embodiments, the bead may be an inert polypropylene polymer resin bead. In some embodiments, beads are used in the removal of anions, including oxy-anions of selenium, including selenite (SeOs2-) and selenate (SeO42-); oxyanions of antimony, including oxy-anions in either the Sb[III] (antimonite) or the Sb[V] (antimonate) redox state; oxy-anions of lead, including oxy-anions in either the Pb[II] or the Pb[IV] redox state, such as Pb(OH)e2', Pb(OH)e4', PbCh2', and PbCh2'; oxy-anions of sulfur such as sulfate (SC2'); and oxy-anions of iodine, such as ICh" (iodate).

[0071] In general, the method for attaching the MOF is performed using a buffer modifier that adheres the MOF to the surface of the bead. In some embodiments, the buffer modifier may be a buffer modifier typically used in capillary electrophoresis such as an osmotic flow modifier, including cetyl-trimtheylammonium bromide (CTAB) and betacyclodextrin (beta-CD). Both CTAB and beta-CD are compounds that bind well to MOFparticles at room temperature and cause the MOF to be chemisorbed onto the surface of the bead.

[0072] In one embodiment, CTAB may be used to attach the MOF to the bead surface. In this case, atomic layer deposition (ALD) is used to seed the beads with metal oxides that provide surface hydroxyl groups capable of forming chemical bonds with MOF particles via the CTAB. In some embodiments, the metal oxide chemisorbs onto the bead surface in water, thereby making hydroxyl groups available for attachment to the CTAB, via, for example, the cationic head groups of the CTAB. These metal oxides include, but are not limited to, aluminum oxide, titanium oxide, zinc oxide, and combinations thereof. Once exposed to water, the deposited metal oxides will appear similar to silicon dioxide / surface hydroxide in a capillary electrophoresis osmotic flow reversal application of CTAB. Accordingly, the MOF is then attached to the CTAB through hydrogen bonding, electrostatic interactions, and van der Waals induced dipole-dipole forces. Without being limited by theory, it is believed that the non-polar surfaces of the MOF, such as the organic linkers of the MOF, can attach to the trimethyl “arms” of the CTAB.

[0073] In one embodiment using CTAB, substrate (such as beads) may first be subjected to ALD to chemisorb the metal oxide to the surface of the beads. Separately, the CTAB and MOF may be combined at room temperature to attach the MOF to the CTAB and form a solution of the CTAB with the MOF attached. The beads with the metal oxide attached may then be contacted with the solution or combined with the CTAB having the attached MOF resulting in the CTAB attaching to the bead surface via the metal oxide, again, which can be done at room temperature in a water solution and in some embodiments in a basic water solution. Alternatively, the beads after being subjected to ALD to attach the metal oxide may be mixed in a water solution containing the MOF and, in some embodiments, a basic water solution containing the MOF. Subsequently, the CTAB may be added to the solution to attach to both the MOF and the metal oxide resulting in attachment of the MOF to the bead surface. Thereafter, the beads can be washed and dried. Accordingly, at this point, a MOF-adsorbed bead, such as a plurality of MOF-adsorbed polypropylene beads, has been produced and may constitute a commercial product that can be used as further described below.

[0074] In another embodiment, beta-CD may be used to attach the MOF to the bead surface. In this case, the substrate does not need to be subjected to ALD. Rather, the nonpolar region of the beta-CD will attach to a corresponding non-polar portion of the polypropylene beads via hydrogen bonding, electrostatic interactions, and van der Waalsinduced dipole-dipole forces. The MOF can then be attached to the beta-CD via interaction between one or more polar portions on the surface of the MOF with the negative charge on the beta-CD. In some embodiments, the MOF can be attached to the beads in a water solution containing beta-CD. In some embodiments, a less polar solvent, such as an alcohol, may be used. Thereafter, the beads can be washed and dried. Accordingly, at this point, a MOF-adsorbed bead, such as a plurality of MOF-adsorbed polypropylene beads, has been produced and may constitute a commercial product that can be used as further described below.

[0075] It should be appreciated that in some embodiments both beta-CD and CTAB may be used in combination. In this case, the substrate or beads would be subjected to ALD, after which a solution containing the MOF and both CTAB and beta-CD would be added.

[0076] It should also be appreciated that in some embodiments, the surface of the beads for functionalization of the CTAB and beta-CD may be silicon dioxide. In some cases, silane hydroxide chemistry may be used to functionalize the polymer bead to accept silicon adducts followed by hydroxide to provide the necessary chemistry for the attachment of the CTAB or beta-CD.

[0077] It should be appreciated that in some embodiments, the ion exchange resin beads are polystyrene divinylbenzene crosslinked (2-12%) copolymer beads functionalized in the pores by chemical attachment of exchange ligands to the pendant benzyl rings from the polymer backbone. In such cases, to achieve adequate water sluicing of the anion beads from the mixed bed with replacement by the MOF coated substrate beads, the latter beads need to be density-matched to the anion exchange resin beads. Further, there are several choices of polypropylenes, depending on the local stereochemistry of the propylene adduct in the free radical polymerization process.

[0078] Accordingly, in some embodiments, a process for preparing an appropriate plurality of beads for use, for example, in a plant demineralizer deep bed, would include determining the MOF specific weight capacity for the analyte / oxy-anion of interest; calculating the amount of MOF required to be associated with each bead, thereby allowing an assessment of the number concentration of MOF-coated beads in water that must be sluiced into the existing demineralizer deep bed pre-existing in the process stream; testing for density balancing with the existing anion exchange beads within the plant demineralizer deep bed and examining the likelihood of exchange between those beads and the MOF coated beads via typical plant sluicing methods; and adjusting the MOF-coated bead number concentration to account for lost beads in the preceding steps.

[0079] In another embodiment, the invention comprises a method for attaching the MOF to a macroscopic fabric for subsequent use. In some embodiments, the macroscopic fabric may be any fabric, including artificial fiber-based materials, to which a given MOF may be attached. In some embodiments, the macroscopic fabric is a mesh material or a mesh filter, including an inert polypropylene-based mesh material or filter. Accordingly, it should be appreciated that the fabric may have any dimensions, such as any area or surface area, as desired or dictated by the ultimate use of the fabric. MOF particles may be attached to the fibers of the fabric in the same manner described above for attachment to a bead. Accordingly, it should be appreciated that buffer modifiers such as beta-CD and CTAB may be used as described above to attach the MOF to the fabric in combination with ALD treatment of the fabric. After attachment of the MOF to the macroscopic fabric, a MOF- adsorbed macroscopic fabric has been produced and may constitute a commercial product that can be used as further described below. It should be appreciated that the term “macroscopic” is being used to distinguish this fabric as being one that is visible to the naked eye or that can be physically manipulated by hand, as opposed to a molecular fabric as described below.

[0080] In another embodiment, the invention comprises a method for attaching the MOF to a molecular fabric for subsequent use. In some embodiments, the molecular fabric is made from organic strands, essentially forming a two-dimensional copolymer framework or organic woven material, to which a given MOF may be attached. MOF particles may be attached to the strands of the fabric in the same manner described above for attachment to a bead. Accordingly, it should be appreciated that buffer modifiers such as beta-CD and CTAB may be used as described above to attach the MOF to the fabric in combination with ALD treatment of the fabric. After attachment of the MOF to the molecular fabric, a MOF- adsorbed molecular fabric has been produced and may constitute a commercial product that can be used as further described below. It should be appreciated that the molecular fabric is a fabric formed at the molecular level and is, therefore, much smaller in size than, for example, the macroscopic fabric described above.

[0081] Once attached and as described above, the substrate with the attached MOF, such as MOF-808, can be used to remove certain chemical species, as described above, from a liquid or liquid stream, such as industrial liquid streams (e.g., power plant coolant streams such as nuclear power plant streams) or waste streams. Generally, the substrate with the attached MOF would be positioned to allow contact between the liquid containing one or more liquid species to be removed from the liquid with the MOF. Upon contact, the liquidspecies to be removed would attach to the MOF and, therefore, be removed from the liquid. In this regard, the manner in which the substrate with the attached MOF would be used depends the particular MOF attached and the liquid phase species that it can remove and upon the physical configuration of the inert substrate used (e.g., beads or fabric). It should be appreciated, however, that any method or equipment that provides for or allows contact between the MOF and the liquid could be used.

[0082] In the case of beads, such could be used in the same manner as traditional resin beads to remove certain chemical species from a liquid, for example, by placing the beads in a resin bed in a given vessel through which the liquid being treated would pass. It should be appreciated that existing equipment designed to manage resin beads may be adapted, if necessary, to manage the use of beads coated with MOF particles. In one embodiment, a cylindrical vessel containing a bed of beads coated with MOF particles could be used. In this case, the bed of beads would be stationary within the vessel and a liquid stream would pass through the vessel, thereby passing through the bed of beads and providing contact between the liquid containing a liquid species to be removed and the MOF particles. Upon contact, the liquid species to be removed would attach to the MOF and, thereby, be removed from the liquid passing through the vessel.

[0083] It should be appreciated that in some embodiments in which the vessel contains resin beads that are used to remove certain liquid phase species, such resin beads can be replaced with beads coated with a given MOF according to the present invention. In one embodiment, when the resin beads are in need of replacement, such can be easily replaced with beads coated with a given MOF according to the present invention within the same equipment. Alternatively, the resin beads could be replaced with inert polypropylene beads and attachment of the selected MOF can be performed in-situ. In this case, the beads could be pre-treated with ALD to attach a given metal oxide and then disposed within the vessel or such treatment with ALD to attach a metal oxide could also be performed in-situ. In the latter case, the beads would be disposed within the vessel and then treated using ALD to attach a metal oxide. Thereafter, a solution containing CTAB and the selected MOF could be added to the vessel to attach the CTAB and the MOF to the beads, or a solution of CTAB could be added to the vessel followed by a solution of the selected MOF. The result would be the replacement of the original resin beads with beads coated with a selected MOF without having to alter or change any of the existing equipment used for the original resin beads.

[0084] Alternatively, the beads would be disposed within the vessel and thereafter, a solution containing beta-CD and the selected MOF could be added to the vessel to attach thebeta-CD and the MOF to the beads, or a solution of beta-CD could be added to the vessel followed by a solution of the selected MOF. The result would be the replacement of the original resin beads with beads coated with a selected MOF without having to alter or change any of the existing equipment used for the original resin beads.

[0085] In the case of a macroscopic fabric coated with a select MOF, such fabric could be positioned or placed such that a liquid stream would pass through the fabric, thereby providing contact between the liquid containing a liquid species to be removed and the MOF particles attached to the fibers of the fabric. Upon contact, the liquid species to be removed would attach to the MOF and, thereby, be removed from the liquid passing through the fabric. It should be appreciated that the fabric may be placed within a vessel or pipe or any piece of equipment such that the liquid would pass through the fabric.

[0086] In one embodiment, a demineralizer through which a liquid stream passes may be used. In this case, the macroscopic fabric may be a mesh filter that can be wound into a spiral, thereby creating a lumen in the center. Liquid may pass into the demineralizer and around the outside of the wound mesh filter. The liquid would then pass through the wound mesh filter and into the lumen or center of the demineralizer and out through the center of the demineralizer. It should be appreciated that in some embodiments, an existing mesh filter may be coated with a select MOF. In this case, the MOF can be attached to the existing mesh filter in-situ in the same manner as described above for in-situ coating of beads in an existing vessel.

[0087] It should also be appreciated that a MOF-coated fabric may be used in many different situations. In one embodiment, the MOF-coated fabric may be used on top of a resin bed to facilitate removal of liquid phase species, either providing removal of other liquid phase species relative to those removed by the resin bed or additional removal of the same or similar species. Additionally, it should be appreciated that in the embodiment in which a bed of beads are coated with a select MOF in-situ, the use of a macroscopic fabric on top of the bed may also be coated with a select MOF in-situ and concurrently with the coating of the bed of beads. Accordingly, it should also be appreciated that the MOF used for the beads and the fabric may be the same or different, noting that if different, either the beads or the fabric may need to be coated prior to disposing both within a given vessel.

[0088] In the case of a molecular fabric coated with a select MOF, such fabric could be positioned or placed such that a liquid stream would pass through the fabric, thereby providing contact between the liquid containing a liquid species to be removed and the MOF particles attached to the fibers of the fabric. Upon contact, the liquid species to be removedwould attach to the MOF and, thereby, be removed from the liquid passing through the fabric. It should be appreciated that the fabric may be placed within a vessel or pipe or any piece of equipment such that the liquid would pass through the fabric. It should also be appreciated that the molecular fabric could be generated in-situ and the select MOF particles attached thereafter. In some embodiments, the molecular fabric could be constructed such that it is located on at the outlet of a vessel, such as a vessel containing resin beads in a bed or a demineralizer.

[0089] While the MOF of the present invention may be usable in such liquid flow applications in its native structure, it is possible that the amount of pressure required to permeate packed beds of such small particles (typical size ranging from 75 to 1200 nanometers with 5 micron crystallites forming from the MOF particles) may exceed available fluid driving equipment, meaning that the MOF particles may need to be ported upon some other larger particle carrier (more of the order of a resin particle, typically 50 to 850 microns diameter in powder or bead form) such that fluid may permeate conglomerates of carrier particles more easily. Any methodology can be used for contacting the MOF particles with a suitable carrier particle such that the hydraulic permeability of a conglomerate of such carrier particles, either in a columnar flow through a bed of such carrier particles or a flow through a filter providing a porous surface onto which such carrier particles are coated, to afford the required fluid volumetric throughput. As such, the adsorptive properties of the MOF will still manifest since the MOF itself will be exposed to the analyte in the water stream as it flows about the carrier particles onto which the MOF media are attached.

[0090] Regardless of the substrate used, however, it should be appreciated that for a given liquid stream and concentration of various liquid phase components to be removed, the capacity of a selected MOF to remove those liquid phase components will generally be much greater, such that saturation of the MOF is not a limitation. Accordingly, rather than using, for example, a bed full of MOF particles, the use of a substrate coated with MOF particles will still provide the requisite surface area required to obtain the desired removal of a given liquid phase species.

[0091] Once removal of the desired species from the given liquid or liquid stream is performed, regeneration of the MOF may be optionally performed. Generally, regeneration of a given MOF can be performed to remove the adsorbed species from the MOF to thereby allow the MOF to be re-used. One of skill in the art will appreciate that the MOF may be in need of regeneration or spent depending upon the performance of the MOF over time or a change in the removal of the adsorbed species from the liquid. Testing to determine a chancein the removal rate or testing of a sample of the MOF to determine the saturation level of the adsorbed species on the MOF can be done to determine whether regeneration is appropriate.

[0092] Regeneration of the MOF can be done using a chemical wash or rinse. For example, for removal of adsorbed anion, such may be done via acid treatment, such as, but not limited to, hydrochloric, sulfuric or nitric acid washes. Subjecting the MOF to such treatment results in the adsorbed species being collected in the solution used to regenerate the MOF, which can be further processed as necessary. The MOF at this point would be ready for re-use.

[0093] Depending upon the structure to which the MOF is attached or the media to which it is attached, the equipment used for regeneration may vary. Industrial uses, including nuclear power plant reactor coolant kidney clean-up loops, may employ regeneration procedures on attached MOF, meaning to include the substrate to which it is ported in the process equipment. Detached MOF crystallites may be regenerated themselves according to the procedure described above for acid regeneration and remaining adsorption capacity and porosity following regeneration with various concentrations of aqueous HC1, which may be as high as approximately 10% Once regenerated, the MOF can then be re-deployed for use. Accordingly, it should be appreciated that depending upon the substrate used to support the MOF, the MOF may be regenerated in-situ or removed from a given process, regenerated, and return to use in the process.

[0094] As described above, in one embodiment, MOF-808 can be regenerated using hydrochloric acid wash. With reference to Figures 11 A-D, varying concentrations of HC1 provide for varying amounts of removal to the adsorbed species, in this case, iodate. One of skill in the art can determine the concentration of any acid wash so as to provide the desired removal of the adsorbed species from the MOF.

[0095] In the specific application of reactor coolant clean-up media, MOFs for iodate removal may in fact afford continued, safe operation of a nuclear power plant for which a fuel cladding leak has been detected during normal power operation. Typical polymer resinbased anion exchange resins are not capable of removing radioactive iodates from water at low concentrations; in particular, they slough the iodate back into the effluent of the clean-up loop from the resin media due to equilibrium constraints on concentration at the filtration effluent. MOFs, like MOF-808, on the other hand, hold iodate more strongly such that effluent concentration below roughly 10 ppb may be possible.

[0096] In the case of boiling water reactors (BWRs), fuel cladding defects can afford release of iodine gas from within the fuel rod. This radio-iodine is produced within thenuclear fuel during operation, by nuclear activation of xenon within the normally pressurized fuel rod. Once released into the coolant water, under radiolytically produced oxidative conditions, this iodine is oxidized to iodate and must be removed from the reactor coolant water in order to continue operation. Hence, using the MOF to take up these low concentrations of radio-iodate may afford continued safe operation of a BWR nuclear core because in BWRs it is possible to use control blade maneuvers together with off-gas gamma scanning to isolate the assembly region from which the fuel cladding leak is occurring. While the ultimate cause of the cladding defect can be varied (like debris impact, hydrogen embrittlement and crack initiation, thermal transients, or other reasons such as grid-to-rod fretting), the solution to afford continued operation in the instance of a suitable small defect is to first be able to isolate and suppress the fission reaction in the leaking assemblies (using independent control blade positioning in BWR cores) and second to be able to continuously clean-up the radio-iodate being added to the coolant by the leaking rods. If these two conditions are met (the latter with MOF use according to the present invention) then the plant could continue operation until the planned end of the power cycle when the core is going to be rebuilt with subsets of assemblies replaced by new fuel anyway In that instance, the leaking assemblies would be removed as well during the refueling outage, before the BWR was allowed to re-start. This is much more economical than being forced to shut the reactor down prior to a planned refueling outage in order to find and remove the slightly leaking assemblies, causing a mid-cycle re-build of the core before the plant would be allowed to restart. Hence, MOF use in clean-up according to the present invention would be essential for affording this type of continued full cycle operation in BWRs. Further, BWR RWCU systems employ filter demineralizers to which the MOF crystallites might be deployed directly, without need for an extra substrate on which to port them.

[0097] In pressurized water reactors (PWRs), similar fuel leakers can occur, though PWRs have less capability to find and isolate them neutronicly given that their control rod designs do not afford partial, independent insertion like BWR designs do. Hence, once a leak is detected, the PWR typically must undertake a mid-cycle outage to find the offending fuel assemblies (by sipping them in the spent fuel pool) and remove them. As with BWRs, the degree to which radio-iodates might be controlled in the reactor water clean-up loop will be beneficial to personnel dose once the refueling actions are underway during the mid-cycle outage. Nevertheless, the degree as well to which the released iodine gas is oxidized to iodate can vary with the shutdown operations of the PWR reactor coolant. It may end up mostly as off-gas or it may end up as aqueous iodate to which a bead-supported MOFaccording to the present invention could apply for clean-up purposes. The determining factors include the method and rate at which hydrogen is removed during shut down transients when the plant is going into the mid-cycle outage, as well as the degree of peroxidation of the coolant during those transients for the PWR mid-cycle planned at each PWR. Generally, individual plants are constrained by their technical specifications as to the freedom they might have in a PWR to re-start with elevated concentrations of radio-iodate or fuel leakers within their primary reactor coolant circuit.EXPERIMENTAL METHODS

[0098] Maximum Iodate Uptake per Node. 2.5 mg of activated MOF-808 was placed in a 15 mL centrifuge tube with 10 mL of either 41, 82, 123, 164, 205, 246, or 287 ppm solution of potassium iodate, corresponding to an exposure of 2, 3, 4, 5, 6, and 7 iodate anions per metal node of MOF. After 72 hours, the solutions were centrifuged to settle the MOF. 50 pL aliquots were taken and diluted to 5 mL with 0.5% ammonium hydroxide. The iodine concentration in each sample was determined by ICP-MS and compared to that of the corresponding stock solution to determine the iodate uptake by the MOF. A basic matrix for iodate samples is required to prevent the formation of volatile b, which can permeate polypropylene, causing memory effects and incorrect concentration measurements.

[0099] Iodate Uptake Kinetics. 2.5 mg of activated MOF-808 was placed in a 15 mL centrifuge tube with 10 mL of either 41, 61.5, 82, 102.5, or 123 ppm solution of potassium iodate, corresponding to exposure of 1, 1.5, 2, 2.5, and 3 iodate molecules per node of MOF. The solution was centrifuged for 3 minutes for the MOF to settle, before aliquots of the supernatant were taken at 4, 6, 8, 10, 20, 40, 60, 120, and 180 minutes, as well as 24, 48, and 72 hours after initial exposure. The concentration of iodine was measured by ICP-MS, where the samples were diluted 100-fold with a 0.5% ammonium hydroxide solution by adding 50 pL aliquots to 5 mL.

[0100] The adsorption (q) in mg / g was determined for each exposure concentration performed using equation 1. The maximum equilibrium adsorption capacity (Q) was determined by fitting the data to the Langmuir adsorption model. The Langmuir equation (Equation 2) was used to determine the Q for iodate uptake in MOF-808, where Ceis the equilibrium adsorption concentration (ppm) taken as the average of the concentrations at 48, 72 and 96 hours, and qeis the equilibrium uptake (mg / g), taken as the average of the calculated q values at 48, 72, and 96 hours.

[0101] Powder X-ray Diffraction (PXRD). Powder X-ray diffraction (PXRD) patterns were collected on a Bruker D8 Advance diffractometer (measurement made over a range of 3° < 29 < 40° in 0.02° step with a 0.200 s scanning speed) equipped with a LYNXEYE linear position sensitive detector (Bruker AXS, Madison, WI). Neat samples were smeared directly onto the silicon wafer of a proprietary low-background sample holder. Data was collected using a continuous coupled 9 / 29 scan with Ni-filtered CuKa (X = 1.54178 A radiation operating at 40 kV and 40 mA).

[0100] 1H-NMR Spectra.XH-NMR spectra were collected with a 300 MHz Bruker spectrometer. Chemical shifts were referenced to the residual solvent peaks. Approximately 2 mg of MOF-808 was digested in 8 drops of D2SO4 before dilution in 0.6 mL DMSO-de.

[0102] Diffuse Reflectance Infrared Spectra. Diffuse reflectance infrared spectra were collected using a Thermo Scientific Nicolet 6700 FT-IR equipped with a liquid nitrogen cooled MCT detector with a resolution of 1 cm'1.

[0103] SEM and X-ray Spectroscopy. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy data were collected on a Phenom ProX desktop SEM.

[0104] MOF Activation. MOF samples were activated using a Micromeritics SmartVacPrep instrument equipped with a hybrid turbo vacuum pump.

[0105] BET Surface Area. BET surface areas are calculated using isotherm points between 0.0005 and 0.1 P / Po that satisfy all BET criteria.

[0106] Nitrogen Adsorption-Desorption Isotherms. Nitrogen adsorption-desorption isotherms were measured at 77 K on a Micromeritics TriStar II Plus instrument.

[0107] ICP-MS. Inductively coupled plasma - mass spectrometry (ICP-MS) data was measured on an Agilent 7500 Series. Standards were prepared at concentrations of 0.05, 0.1, 0.2, 0.5, and 1 ppm I' by serial dilution in a 0.5% (v / v) solution of ammonium hydroxide.

[0108] X-ray Total Scattering. X-ray total scattering measurements were conducted using beamline P02.1 of Petra III at the Deutsches El ektronen- Synchrotron (DESY), in Hamburg, Germany. Data were collected in a rapid acquisition mode using a 2D VAREX XRD4343CT detector (2880 x 2880 pixels, 150 x 150 / m2each) mounted orthogonal to the beam path. The samples were packed in 1 mm diameter glass capillaries and measured with a sample-to-detector distance of 499.0 mm. The incident energy of the X-ray beam was 59.58 keV (2 = 0.20729 A). LaB6was used to calibrate the detector position. The damping of data in real space due to the instrumental resolution in reciprocal space was characterizedby fitting the structure of the calibration standard in the program PDFgui:14Qdamp =0.0170 A-1.

[0109] Data Reduction. Calibration of the detector geometry and image integration were performed using the azimuthal integration software pyFAI. The raw data images were summed and corrected for polarization effects, then masked and azimuthally integrated to produce ID powder diffraction patterns. Further normalization and transformation to the real space PDF was performed using PDFgetX3 within xPDF suite. The total scattering structure function S(O) is obtained from the coherent scattering intensities c(O), after removal of the self-scattering by,Q is the magnitude of the scattering momentum transfer (Q = 4zr sin(6*) / 2 for elastic scattering, where A is the wavelength, and 26* is the scattering angle). f(Q) is the atomic form factor for atom z, and averaging denoted byis performed stoichiometrically over all atoms (N) in the sample. The reduced total structure function is defined asF Q) = Q[S Q) - 1] and the experimental PDF, G(r), is obtained via truncated Fourier transformation,which corresponds to the real space density distribution byG(r) = 4?tr [p(r) - poyo] where po is the average atomic number density and p(r) is the local atomic pair density, which is the average density of neighboring atoms at a distance r from an atom at the origin. yo is the characteristic function of the diffracting domains which equals 1 for bulk crystals but has an r-dependence for nanosized domains. The PDFs were determined with values of Qmax = 20.7 A-1. Simulated PDFs were determined from cluster models using the Debye function calculator in the Diffpy-CMI software,16using a Qrange = 0.5-20.0 A-1and BiS0= 0.5 A2.

[0110] For the difference PDF analysis, a modification function M(O)19was multiplied by F(Q) prior to the Fourier transformation (Qmax= 20.7 A ’) to minimize the presence of termination effects in the real-space signal. In order to assess the systematicerrors introduced by the difference PDF (dPDF) extraction method used, the dPDF was extracted using four different subtraction methods:1. Direct subtraction of empty MOF from loaded MOF intensities in reciprocal space;2. Subtraction in real space by optimizing the scale of empty and loaded MOF PDFs over a range of 1.5-6 A;3. Subtraction in real space by fitting the empty to loaded MOF PDF : empty MOF PDF was modified by a spherical domain damping function, and a damped sine wave was added and refined to adjust for atomic density differences; and4. Same as above: the empty MOF PDF was additionally modified by an expansion coefficient to allow the signal to expand / contract to best fit the loaded MOF PDF signal.

[0111] Systematic uncertainties in the experimental dPDFs were then estimated as the standard deviations between the four different extraction methods. The model dPDFs were simulated from the clusters considering atom-pairs between I atoms and O atoms of the IO3 motif (not bound to the cluster) with each other and with the rest of the atoms. The Debye function calculator in Diffpy-CMI software,7was used with a Qrange = 1.0-20.0 A1and Biso = 1.0 A2.

[0112] Additional Diffraction Measurements. For verification of the sample structures, additional measurements were performed on the samples using a STOE Stadi-P diffractometer with CuKa radiation (z = 1.540596 A, a Ge(l 11) Johann monochromator, and a single Mythen detector scanned over a range of 0.0-115.0° 26 over a timespan of approximately 3.7 hours. The samples were loaded into 0.7 mm diameter borosilicate capillaries, and the samples were spun during the measurement for optimal orientational sampling of the powdered crystallites.

[0113] Pawley and Rietveld Refinements. Pawley and Rietveld refinements were performed using TOPAS v5 / v6.22In either case, refinements were performed considering the cubic Fd 3m symmetry along with Gaussian and Lorentzian contributions to the peak profile broadening, and the Stephens model for strain (3 parameters). Further corrections included a zero-offset correction, sample length parameter in the full axial model for peak asymmetry, and the Lorentz-Polarisation factor for the given radiation and monochromator. The complicated backgrounds were described using combinations of Chebychev polynomials and broad Gaussian peaks or using a second hkl phase with a fixed peak broadening set to 1 nm.Additional pseudoatoms with atomic displacement parameters fixed to a larger value were included to account for pore water content and bound water or IO3.

[0114] Regeneration. To test the reusability of MOF-8O8 in multiple adsorption cycles, 10 mg of MOF-8O8 was exposed to 10 mL of a 1148 ppm solution (7 iodate anions / node) of potassium iodate overnight. The MOF powder and iodate solution was then placed on a membrane filter in a glass microfiltration apparatus attached to a vacuum pump. The iodate solution was drawn through the membrane, the filtrate collected, and the MOF on the membrane was washed with 3 x 10 mL of water. 10 mL of 1%, 3%, 5%, or 10% HC1 was then drawn through the MOF sample over the course of 5 minutes by vacuum control.Aliquots (100 pL) of the acid filtrate were taken immediately after filtration and diluted 2000x by serial dilution with 0.5% ammonium hydroxide. The iodine concentration was measured via ICP-MS to determine the amount of iodate removed from the MOF by the acid wash. After washing with acid, the MOF on the membrane was again washed with 3 x 10 mL of water. The powder was then placed in a fresh solution of 1148 ppm potassium iodate to soak overnight and begin the next adsorption cycle. Three adsorption-desorption cycles were performed.

[0115] To assess the porosity after recycling, 5 batches of 10 mg MOF-808 were loaded with iodate and regenerated with 10% HC1 as described above. After the 3rdcycle, the MOF samples were combined and washed 3x with 20 mL of water, and 3x with 20 mL of acetone and left to soak in acetone overnight before activation and BET measurement.

[0116] To assess the porosity of MOF-808 after adsorption, 50 mg of MOF-808 was exposed to 50 mL of a 1148 ppm (7 iodate anions / node) solution of potassium iodate overnight. Iodate loaded samples were then washed 3x with 20 mL of water, and 3x with 20 mL of acetone and left to soak in acetone overnight before activation and BET measurement.

[0117] For the nitrogen adsorption-desorption isotherms appearing in Figure 9B, 234.0 mg, 20.1 mg, and 33.2 mg of MOF was used for analysis of MOF-808, MOF-808 + iodate, and HC1 regenerated MOF-808, respectively.

[0118] Various embodiments of the invention have been described above. However, it should be appreciated that alternative embodiments are possible and that the invention is not limited to the specific embodiments described above. For example, the present invention is not necessarily limited to treating liquid or liquid streams associated with nuclear power plants. Other industrial streams or liquids comprising iodine species, such as those discussed above, may be removed using the methods and MOFs described herein. Similarly, themethods described herein for regeneration a MOF may be used to regenerate MOFs used in other industrial processes as well.

Claims

CLAIMSWhat is claimed is:

1. A method for removing an iodine species from a liquid, comprising: contacting MOF-808 with a liquid comprising an iodine species; adsorbing the iodine compound onto the MOF-808.

2. The method of claim 1, wherein the iodine species is 1“ or IO3-.

3. The method of claim 1, wherein the iodine species comprises an iodine oxy-anion.

4. The method of claim 3, wherein the iodine oxy-anion comprises iodate.

5. The method of claim 1, further comprising: regenerating the MOF-808 after said adsorbing to remove the iodine species from the MOF-808.

6. The method of claim 5, wherein said regenerating comprises: contacting the MOF-808 with an acid wash.

7. The method of claim 6, wherein said acid wash comprises HC1.

8. The method of claim 5, further comprising: adsorbing an additional iodine species after said regenerating.

9. A method for regenerating an adsorbent used for removing an iodine species from a liquid, comprising: contacting a MOF-808 comprising an adsorbed iodine species with an acid wash.

10. The method of claim 9, wherein said acid wash comprises HC1.

11. The method of claim 9, wherein the iodine species is iodine species is L or IO3-.

12. The method of claim 9, wherein the iodine species comprises an iodine oxy-anion.

13. The method of claim 12, wherein the iodine oxy-anion comprises iodate.

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