Mixed-metal strategy for rapid synthesis of metal-organic frameworks under environmental conditions

Abstract

To provide an improved material and a method capable of producing USTA-16 in a shorter time by a milder reaction while holding good CO2 capturing capacity.SOLUTION: A metal-organic framework (MOF) having a UTSA-16 structure, the composition comprising: 0-80 mol% of the total metals in the MOF is a first metal selected from one or more of the group consisting of Cr, Mn, Fe, Ni, Cu and Co; and 20-100 mol% of the total metals in the MOF is a second metal selected from one or more of the group consisting of Cd, Mn and Zn.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metal-organic framework (MOF) having the UTSA-16 structure. In particular, the present invention relates to a MOF with good CO capture performance and a method for producing the MOF at a significantly higher rate under milder reaction conditions. [Background technology]

[0002] The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is general general knowledge.

[0003] Metal-organic frameworks (MOFs) are porous crystalline materials with modular synthetic chemistry. Their easy tunability of composition allows for precise material design and they exhibit excellent performance in many commercially interesting applications. For example, certain MOFs exhibit large CO2 absorption capacity, high CO2 selectivity, and long-term stability, making them excellent CO2 capture adsorbents. The development of scalable and sustainable protocols is essential for the practical application of MOFs. This is because most intended MOF applications involve a large footprint (e.g., ~3000 tons of adsorbent for a capture unit integrated with a 500 MW coal-based power plant). Therefore, environmental impact and production costs significantly affect the overall economics of the process.

[0004] UTSA-16 is a highly promising MOF material for CO2 capture by adsorption due to its isotherm characteristics, adsorption mechanism, and stability. Almost all reported syntheses of this material are based on the protocol in Journal of the American Chemical Society 2005, 127(47), 16352-16353, where only the vessel and solvent volume are adjusted to fit the required synthesis scale. The reported protocol involves mixing precursor materials in a 50% / 50% ethanol-water mixture and isothermally heating at 120 °C for a certain period of time, corresponding to an autogenous pressure of 4-6 bar. Such solvothermal synthesis methods require specialized reactors, increasing the capital cost required for production and precluding the use of typical glass equipment with a pressure rating of 2 bar or less. Attempts to scale up this material are hindered by the inability to lower the synthesis temperature below the boiling point of the solvent. Furthermore, typical protocols require long crystallization times (up to 2 days). The reaction efficiency, estimated in terms of space-time yield, is 25 kg (m 3 ·day) -1 This would require an increase of approximately 10 times to be commercially viable. Ternary phase equilibria of the deprotonated ligand salts in solution (i.e., tripotassium citrate + ethanol + water) are accompanied by liquid-liquid phase separation. In the presence of cobalt salts, viscous gelation occurs. It is understood that mixing is adversely affected by high viscosity.

[0005] Moving from closed solvothermal conditions to open reflux synthesis using safe and inexpensive solvents is an important step toward a scalable protocol. Reflux synthesis of MOFs utilizes proven manufacturing process technology and has been demonstrated in ton-scale production of aluminum fumarate MOFs. Replacing solvothermal methods with reflux synthesis potentially reduces capital investment costs, safety compliance costs, and energy costs.

[0006] MOF reaction optimization is highly system-specific. Most reported reflux synthesis protocols for low- and high-valent MOFs involve binary systems with a single metal precursor and a single organic linker. These protocols do not address the synthesis of materials with more complex structures. UTSA-16 possesses unique chemical features, in that metal species within different structural motifs exhibit different coordination geometries. Generally accepted crystal field theory predicts that one of these coordination geometries is significantly favored in terms of stability. This is because, under conditions unfavorable to the formation of the less stable motif, the kinetics are significantly reduced, resulting in reduced yield and efficiency of product formation.

[0007] Therefore, there is a need for improved materials and methods that can produce USTA-16 with milder reactions and in shorter times while retaining good CO2 capture performance. Summary of the Invention

[0008] "Surprisingly, we found that incorporating a secondary metal component leads to UTSA-16 analogs with improved CO2 capture capacity that can be formed under significantly milder conditions and in shorter times. This allows the use of conventional laboratory equipment and open reflux synthesis. The optimized protocol is more suitable for industrial production, paving the way for the mass production of these promising materials."

[0009] Aspects and embodiments of the present invention are described in the following numbered sections. 1. A metal-organic framework (MOF) having the UTSA-16 structure, the composition being: 0-80 mol% of the total metals in the MOF are a first metal selected from one or more of the group consisting of Cr, Mn, Fe, Ni, Cu, and Co; and 20-100 mol% of the total metals in the MOF is a second metal selected from one or more of the group consisting of Cd, Mn, and Zn. A metal organic framework (MOF) comprising: 2. The MOF according to item 1, wherein the second metal is Zn. 3. The MOF according to item 1 or 2, wherein the second metal is present in an amount of 25 to 100 mol % of all metals present in the MOF. 4. The MOF according to item 3, wherein the second metal is present in an amount of 50 to 75 mol % of all metals present in the MOF. 5. The MOF according to any one of items 1 to 4, wherein the first metal is selected from Fe and Co. 6. The MOF according to item 5, wherein the first metal is Co. 7. The MOF according to any one of items 1 to 6, wherein the first metal is present in an amount of 25 to 50 mol % of all metals present in the MOF. 8. The MOF according to any one of items 1 to 7, characterized in that the second metal preferentially occupies tetrahedral metal sites within the MOF. 9. The MOF according to any one of paragraphs 1 to 8, characterized in that the majority of the first metal, if present, occupies octahedral metal sites within the MOF. 10. The MOF according to any one of paragraphs 1 to 9, characterized in that, when present, the first metal and the second metal preferentially occupy octahedral metal sites and tetrahedral metal sites, respectively, within the MOF. 11. The MOF according to any one of paragraphs 1 to 10, characterized in that the MOF has a saturated CO2 uptake of up to 5.0 mmol / g, optionally the MOF may have a saturated CO2 uptake of 2.5 to 4.5 mmol / g, such as 3.39 to 3.50 mmol / g. 12. The MOF according to any one of items 1 to 11, characterized in that the MOF has a breakthrough CO2 working capacity of up to 2.2 mmol / g, such as 1.0 to 1.8 mmol / g, such as 1.65 to 1.70 mmol / g. 13. A method for forming the MOF according to any one of items 1 to 12, comprising a step of aging a mixture containing a first metal precursor, a second metal precursor, a base, citric acid, a first solvent, and a second solvent at a temperature of 15 to 200°C for a certain period of time, the method comprising: the first metal precursor is selected from one or more of the group consisting of Cr, Mn, Fe, Ni, Cu and Co; the second metal precursor is selected from one or more of the group consisting of Cd, Mn, and Zn; and the metal in the first metal precursor is present in an amount of 0 to 80 mol % of the total amount of metal in the mixture; and The metal in the second metal precursor is present in an amount of 20-100 mol % of the total amount of metal in the mixture. A method characterized by: 14. The method according to item 13, characterized in that the temperature is 20 to 150°C. 15. The method according to item 14, characterized in that the temperature is 40 to 120°C, such as a temperature of 60 to 80°C. 16. The process according to item 15, characterized in that the temperature used results in refluxing one or both solvents. 17. (a) the first solvent is water and the second solvent is an alkyl alcohol (e.g., the alkyl alcohol is methanol, propanol, or more particularly ethanol); and / or (b) the base is a metal hydroxide (e.g., the base is KOH); and / or (c) performing the method under ambient atmospheric conditions (e.g., standard pressure); Item 17. The method according to any one of Items 13 to 16, 18. The method of any one of paragraphs 13 to 17, wherein the first and second metal precursors are metal salts in which the metal is in cationic form and balanced by one or more counterions selected from halides (e.g., chlorides), nitrates, sulfates, hydroxides, oxides, acetate anions, and hydrates thereof. 19. (a) the second metal precursor is Zn(OAc)2 or a hydrate thereof (e.g., Zn(OAc)2·2H2O); and / or (b) The method according to any one of items 13 to 18, characterized in that the metal in the second metal precursor is present in an amount of 25 to 100 mol %, such as 50 to 75 mol % of all metals present in the mixture. 20. (a) the first metal precursor is Fe(OAc)2, Co(OAc)2, or a hydrate thereof (e.g., Co(OAc)2·4H2O); and / or (b) The method according to any one of items 13 to 19, characterized in that the metal in the first metal precursor is present in an amount of 25 to 50 mol %, such as 50 to 75 mol %, such as 25 to 50 mol % of all metals present in the mixture. 21. A method for capturing CO2, comprising the step of exposing a material comprising the MOF according to any one of items 1 to 12 to an environment containing CO2. [Brief explanation of the drawings]

[0010] [Figure 1] (a) Inorganic building blocks in UTSA-16 and their respective formation trends when different metal precursors are used. (b) Monometallic and mixed-metallic approaches to the synthesis of UTSA-16 with different formation kinetics. [Figure 2](a) PXRD patterns of mixed-metal UTSA-16-type MOFs with various Zn loadings (x represents the Zn molar fraction in the Zn / Co mixed precursor). (b) Reported Co–O bond lengths for the tetrahedral and octahedral Co motifs of UTSA-16. (c) Fourier transform of k3-weighted EXAFS data collected on the Co K-edge. (d) Fourier transform of k3-weighted EXAFS data collected on the Zn K-edge. (e) Position of the first peak maximum in the FT-EXAFS data as a function of Zn loading, x. Upward triangles: Co K-edge data. Downward triangles: Zn K-loading data. (f) Fraction of metal species occupying the tetrahedral sites, YCo,tet and YZn,tet, as a function of Zn loading, x. Note that YCo,tet (x = 0) and YZn,tet (x = 1) are 0.33 based on the SCXRD data. [Figure 3] (a) PXRD patterns of UTSA-16-Zn-0 obtained after 24 hours of incubation at various temperatures. (b) PXRD patterns of UTSA-16-Zn-0.50 obtained after 24 hours of incubation at various temperatures. (c) Growth kinetics of UTSA-16-Zn-x based on ex-situ experiments. A sigmoidal fit (solid line) is shown for line of sight. [Figure 4] (a) CO2 isotherm of UTSA-16-Zn-x at 298 K. (b) Wet CO2 (relative humidity 85%) breakthrough curve of UTSA-16-Zn-x at 298 K. (c) Equivalent heat of CO2 adsorption of UTSA-16-Zn-x. (d) IAST selectivity of UTSA-16-Zn-x for a 10:90 CO2 / N2 gas mixture at 298 K under various feed pressures. [Figure 5] Optical micrographs of UTSA-16-Zn-0.25 (a, b, scale bar: 50 μm) and UTSA-16(Co) (c, d, scale bar: 200 μm). The droplets are a relatively viscous liquid / gel. [Figure 6] FTIR spectra of UTSA-16-Zn-x: 400-4000 cm-1 (left) and 1000-1800 cm-1 (right). [Figure 7] DSLF fitting of CO2 isotherms at 273K and 298K for UTSA-16-Zn-x materials. [Figure 8] Comparison of TGA thermograms of UTSA-16-Zn-x materials (recorded in air, from 150 to 800 °C, with a heating rate of 5 °C / min). [Figure 9] UTSA-16-Zn-x photographs on A4 white paper: (left to right) x = 0 (pure Co), 0.25, 0.50, 0.75, 1.00 (pure Zn). [Figure 10] XANES spectra of the Co K-edge and Zn K-edge of the bimetallic UTSA-16-Zn-x material. [Figure 11] EXAFS fitting results. Experimental data are shown as white circles, and fitting curves are shown as solid lines. [Figure 12] Schematic diagram of the innovative homemade device used in this study. [Figure 13] Uncalibrated breakthrough curves for UTSA-16-Zn-x material under different conditions. Open symbols are N2 and filled symbols are CO2. DETAILED DESCRIPTION OF THE INVENTION

[0011] Surprisingly, the incorporation of a second metal as described herein yields mixed-metal UTSA-16 analogs that can be prepared under milder conditions than single-metal UTSA-16. These compounds have asymmetric site distributions of the first and second metals and can benefit from expanded reaction space and faster reaction kinetics. Furthermore, the materials disclosed herein can have improved gas separation properties while maintaining the basic structure of UTSA-16.

[0012] Thus, in a first aspect of the present invention, there is provided a metal-organic framework (MOF) having a UTSA-16 structure, wherein the composition comprises: 0-80 mol % of the total metals in the MOF is a first metal selected from one or more of the group consisting of Cr, Mn, Fe, Ni, Cu, and Co; and 20-100 mol % of the total metals in the MOF is a second metal selected from one or more of the group consisting of Cd, Mn, and Zn.

[0013] In the embodiments herein, "comprising" can be interpreted as requiring the recited features, but not limiting the presence of other features. Alternatively, "comprising" can also relate to situations where only the recited components / features are intended to be present (e.g., "comprising" may be replaced with the phrase "consisting of" or "consisting essentially of"). It is expressly intended that both broader and narrower interpretations may apply to all aspects and embodiments of the present invention. In other words, "comprising" and its equivalents may be replaced with "consisting of" or "consisting essentially of" or its equivalents, and vice versa.

[0014] As used herein, the phrase "consisting essentially of" and its alternative names may be interpreted to refer to a material in which trace amounts of impurities may be present. For example, the material may be 90% or more pure, such as 95% or more pure, such as 97% or more pure, such as 99% or more pure, such as 99.9% or more pure, such as 99.999% or more pure, such as 100% pure.

[0015] As used herein, USTA-16 structure is intended to mean that the MOFs disclosed herein share a similar structure to that disclosed in the microporous cobalt citrate framework USTA-16 (University of Texas at San Antonio-16). However, for the avoidance of doubt, the compounds disclosed herein utilize different building blocks.

[0016] As noted above, the first metal, if present, may be selected from one or more of the group consisting of Cr, Mn, Fe, Ni, Cu, and Co. For example, the first metal (if present) may be selected from one or both of Fe and Co, and more particularly, the first metal (if present) may be Co. As understood from the above, the first metal may or may not be present in the MOFs of the present invention. If present in the MOF, the first metal may represent up to 80 mol% of the total metals in the MOF. In certain embodiments of the present invention, if the first metal is present, it may represent 25-50 mol% of the total metals present in the MOF.

[0017] As referred to herein, the second metal may be selected from one or more of the group consisting of Cd, Mn, and Zn. In more particular embodiments that may be referred to herein, the second metal may be Zn.

[0018] As will be appreciated, the second metal may be the only metal present in the MOF (i.e., the first metal represents 0 mol % of all metals in the MOF and the second metal represents 100 mol % of all metals in the MOF), but more typically will be present in combination with the first metal. Thus, in embodiments of the present invention, the second metal may represent 20-80 mol %, such as 25-100 mol %, e.g., 50-75 mol % of all metals in the MOF.

[0019] Thus, in an embodiment of the invention, the MOF may comprise: (a) 0 mol% of the first metal and 100 mol% of the second metal; (b) 25 mol% of the first metal and 75 mol% of the second metal; (c) 50 mol% of the first metal and 50 mol% of the second metal; (d) 75 mol % of the first metal and 25 mol % of the second metal; and (e) 80 mol % of the first metal and 20 mol % of the second metal; Here, 100 mol % represents the total metals contained in the MOF.

[0020] In the microporous cobalt citrate framework USTA-16, tetrameric [Co4] clusters and monomeric [Co(O2CR)4] units are present, with Co(II) species adopting octahedral and tetrahedral coordination environments, respectively.

[0021] In embodiments of the present invention in which only a second metal is present, then, by analogy, the second metal will occupy both octahedral and tetrahedral coordination environments. However, if a first metal is also present, the second metal will preferentially occupy tetrahedral metal sites within the MOF. For example, a majority of the second metal may occupy tetrahedral metal sites within the MOF. As used herein, "a majority" can mean that 51 mol% of the second metal occupies tetrahedral metal sites, such as 55 mol%, 60 mol%, 70 mol%, 75 mol%, 80 mol%, 85 mol%, 90 mol%, 95 mol%, or 99 mol%.

[0022] Similarly, when the second metal is present in small amounts (e.g., 20 mol%), the first metal may occupy both octahedral and tetrahedral coordination environments. However, the first metal may exhibit preferential occupation of the octahedral metal sites. For example, a majority of the first metal, if present, may occupy the octahedral metal sites within the MOF. As used herein, "majority" may mean that 51 mol%, such as 55 mol%, 60 mol%, 70 mol%, 75 mol%, 80 mol%, 85 mol%, 90 mol%, 95 mol%, or 99 mol%, of the first metal occupies the octahedral metal sites.

[0023] Thus, in embodiments of the present invention, when both a first and a second metal are present, the first metal and the second metal preferentially occupy octahedral and tetrahedral metal sites, respectively, within the MOF.

[0024] For example, in a 50:50 mixture of Zn and Co as the second and first metals, respectively, 65 mol % of Zn may occupy the tetrahedral metal sites. Further, in a 25:75 mixture of Zn and Co as the second and first metals, respectively, 82 mol % of Zn may occupy the tetrahedral metal sites.

[0025] The MOFs disclosed herein have a molecular weight of 691 to 863 m 2 g -1 500~1000m like 2 g -1 Like, 300~1500m 2 g -1 The specific surface area may be

[0026] The MOFs disclosed herein can be useful for CO capture. Thus, the MOFs of the present invention may exhibit a saturation CO uptake of up to 5.0 mmol / g, and optionally, the MOFs may have a saturation CO uptake of 2.5 to 4.5 mmol / g, such as 3.39 to 3.50 mmol / g. Additionally or alternatively, the MOFs of the present invention may have a breakthrough CO working capacity of up to 2.2 mmol / g, such as 1.0 to 1.8 mmol / g, such as 1.65 to 1.70 mmol / g.

[0027] The MOFs disclosed herein may be conveniently prepared. As noted above, the MOFs disclosed herein may be formed under milder conditions (such as lower temperatures or pressures). Accordingly, in a second aspect of the present invention, there is provided a method of forming the MOFs described herein, the method comprising aging a mixture comprising a first metal precursor, a second metal precursor, a base, citric acid, a first solvent, and a second solvent at a temperature of 15 to 200° C. for a period of time, wherein: the first metal precursor is selected from one or more of the group consisting of Cr, Mn, Fe, Ni, Cu, and Co; the second metal precursor is selected from one or more of the group consisting of Cd, Mn, and Zn; and the metal in the first metal precursor is present in an amount of 0 to 80 mol % of the total amount of metal in the mixture; and The metal in the second metal precursor is present in an amount of 20 to 100 mol % of the total amount of metal in the mixture.

[0028] Any suitable temperature in the range of 15 to 200° C. may be used. For example, the temperature may be 20 to 150° C., such as 40 to 120° C., such as a temperature of 60 to 80° C. In another embodiment, the temperature may be room temperature (i.e., 20 to 30° C., such as a temperature of about 25° C.).

[0029] As mentioned above, the present method utilizes a first and a second solvent. Thus, the temperature used in the preparation may result in refluxing one or both solvents. The use of reflux synthesis compared to solvothermal methods may reduce equipment costs, safety compliance costs, and energy costs.

[0030] Any suitable solvents may be used as the first and second solvents, for example, the first solvent may be water and the second solvent may be an alkyl alcohol (e.g., the alkyl alcohol may be methanol, propanol, or more particularly, ethanol).

[0031] Any suitable base may be used in the methods disclosed herein. For example, the base may be a metal hydroxide (e.g., the base is KOH).

[0032] The above methods may be carried out under any suitable pressure. For example, the methods may be carried out under ambient atmospheric conditions (e.g., standard pressure). This may also reduce the costs associated with preparing MOFs.

[0033] Any suitable chemical can be used as the first and second metal precursors. As will be understood, the selected chemical must contain the first and / or second metal so that it can act as a precursor. In embodiments of the present invention that may be mentioned herein, the first and second metal precursors can be metal salts, where the metal is in the form of a cation balanced by one or more counterions selected from one or more of halides (e.g., chlorides), nitrates, sulfates, hydroxides, oxides, acetate anions, and hydrates thereof.

[0034] In certain embodiments that may be mentioned herein, the second metal precursor may be Zn(OAc) or a hydrate thereof (e.g., Zn(OAc)·2H0). Additionally or alternatively, the metal in the second metal precursor may be present in an amount of 25-100 mol %, such as 50-75 mol % of the total metals present in the mixture.

[0035] In certain embodiments that may be mentioned herein, the first metal precursor is Fe(OAc), Co(OAc), or a hydrate thereof (e.g., Co(OAc)·4H0). Additionally or alternatively, the metal in the first metal precursor may be present in an amount of 25-50 mol%, such as 50-75 mol%, such as 25-50 mol% of the total metals present in the mixture.

[0036] As noted above, the MOFs disclosed herein may be useful for capturing CO. Accordingly, in a third aspect of the present invention, there is provided a method of capturing CO, comprising exposing a material comprising a MOF as described herein to an environment containing CO.

[0037] Further aspects and embodiments of the present invention will now be described with reference to the following non-limiting examples. [Example]

[0038] Pristine UTSA-16(Co) has a structure in which a tetrameric [Co4] cluster and a monomeric [Co(O2CR)4] unit coexist. II The species have octahedral and tetrahedral coordination environments, respectively. These units then form nodes with octahedral and trihedral connectivity, resulting in an anatase net. According to crystal field theory, the presence of weak-field ligands, such as carboxylates and solvent molecules, can lead to the formation of an anatase net. II As a result, under typical reaction conditions, tetrahedral Co II The low thermodynamic stability of [Co(O2CR)4] may reduce the driving force for the formation of the corresponding [Co(O2CR)4] motif, thus kinetically limiting the formation process of this material (Figure 1a). Because ZnII is known to exhibit a tetrahedral geometry in some systems, we hypothesized that including ZnII as a secondary metal component could generate a structurally similar [Zn(O2CR)4] motif in the framework. In the mixed-metal format, a one-pot combination of two metal sources could favor the formation of [Co4] and [Zn(O2CR)4] due to their specific coordination preferences. Importantly, cation partitioning decouples the formation rates of the two motifs from the octahedral-tetrahedral equilibrium of the individual precursors, accelerating the formation rate of the MOF (Figure 1b). Thus, mixed-metal formulations were prepared and analyzed.

[0039] material and method All reagents were obtained commercially and used without further purification. + Ultrapure water supplied by a purification system (VWR) was used.

[0040] [Table 1]

[0041] Powder X-ray diffraction: For phase analysis, PXRD patterns were collected over the 2θ range of 5–40° using Cu Kα radiation (λ = 1.5418 Å) on a Bruker D8 Advance instrument. Data were collected at a scan rate of 2° / min. FWHM data derived for kinetic experiments were collected on a Rigaku Miniflex 600 diffractometer, also using Cu Kα radiation (λ = 1.5418 Å). Patterns were collected over the 2θ range of 5–15° at a scan rate of 2° / min.

[0042] ICP-OES: The metal composition of the mixed-metal UTSA-16 MOF was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES, Optima 7300DV, Perkin Elmer). UTSA-16 samples were digested with 5% HNO3 aqueous solution, which completely dissolved the MOF. The solution was transferred to low-density polyethylene tubes (Fisher Scientific) for further analysis.

[0043] FTIR-ATR spectroscopy: Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectra were recorded on a Bruker Vertex 70 spectrometer.

[0044] UV-Vis spectroscopy: Solid-state UV-Vis spectra were collected in the range of 400–800 nm using a Shimadzu UV-2450 spectrophotometer with BaSO4 as the standard.

[0045] XPS Analysis: Photoelectron spectra (XPS) were collected at 15 kV on a Kratos Axis Ultra XPS system (Kratos Analytical) using monochromated Al Kα radiation (hν = 1286.71 eV). Measured binding energies (BE) were referenced to the C 1s peak (BE set at 284.5 eV), corresponding to the C–C bond. Fitting of the Co high-resolution spectrum considered individual peaks for sites in octahedrally coordinated environments (Oh) and tetrahedrally coordinated environments (Td), with the remaining contributions collapsed into a single satellite signal. Fitting was performed simultaneously for the Co 2p3 / 2 and Co 2p1 / 2 orbitals after subtracting the Shirley background. The full width at half maximum (FWHM) of the peaks was equal for both orbitals, and the area ratio was confirmed to be 2:1 by spin-orbit splitting. A similar fit was performed for the Zn 2p region, but excluding the satellite contribution.

[0046] TGA Experiments: Thermogravimetric analysis (TGA) data were collected using a Shimadzu DTG-60AH under an air flow of 30 mL / min. Samples were heated to 900 °C at a heating rate of 10 °C / min.

[0047] EXAFS analysis: X-ray absorption fine structure (XAFS) spectra were collected in transmission mode at room temperature at the XAFCA beamline of Singapore Synchrotron Light Source Ltd. Co and Zn K-edge spectra were processed conventionally using the IFEFFIT package.

[0048] Synthesis and activation procedure General Procedure 1: Solvothermal synthesis of UTSA-16-Zn-x materials UTSA-16(Co) (or UTSA-16-Zn-O) was synthesized as reported in the Journal of the American Chemical Society 2005, 127(47), 16352–16353. Briefly, Co(OAc)2·4H2O (1 mmol), KOH (3 mmol), and citric acid (1 mmol) were mixed in HO (2.5 mL) to obtain a homogeneous aqueous solution. This solution was transferred to a Teflon-lined reaction vessel (15 mL). Next, absolute ethanol (2.5 mL) was introduced while the vessel contents were manually stirred. To prepare bimetallic UTSA-16-Zn-x materials, varying amounts of Co(OAc)2·2H2O were replaced with Zn(OAc)2·2H2O while maintaining the overall stoichiometry of metal precursor to ligand and KOH. The reaction mixture was introduced into a preheated oven (Memmert UF) at 120 °C and held at that temperature for 2 days, after which it was collected and cooled to room temperature. This protocol yielded large single crystals (UTSA-16-Co) or powder, which were collected by centrifugation at 5000 rpm and washed with copious amounts of anhydrous methanol.

[0049] General Procedure 2: Growth of UTSA-16-Zn-x Single Crystals UTSA-16-Zn-x single crystals can be grown at lower temperatures. To grow UTSA-16-Zn-1.00 single crystals, 500 μL of 0.8 M aqueous Zn(OAc)2·2H2O was mixed with 500 μL of 0.8 M aqueous tripotassium citrate to obtain a clear solution. 500 μL of 1% (volume) ethanol in water was then added. The homogeneous reaction mixture was transferred to a loosely capped scintillation vial and incubated in a preheated oven at 80 °C. Crystals visible by optical microscopy were collected after approximately 24 h and maintained in the mother liquor prior to SCXRD characterization.

[0050] To grow UTSA-16-Zn-0.25 single crystals, 375 μL of 0.8M Co(OAc)2·4H2O solution was mixed with 500 μL of 0.8M potassium citrate solution. Next, 125 μL of 0.8M Zn(OAc)2·2H2O solution and 500 μL of 1% ethanol in water were added sequentially. The same heating and storage protocol was used as for UTSA-16-Zn-1.00 (ICP results: 63.3% Co and 36.7% Zn).

[0051] Note that the single crystal recipe involves an open system where the solvent is lost through evaporation. Therefore, the measured Co / Zn composition may differ from the starting material and may vary under different synthesis conditions. However, in all cases, strong preferential site occupation was observed.

[0052] General Procedure 3: Activation of UTSA-16-Zn-x material The powder samples were exchanged with fresh methanol every day to dissolve excess ligand or metal precursor. The samples were dried under dynamic vacuum at room temperature for 24 hours to obtain dry solid products. All samples tested in adsorption measurements were activated (see Examples 6 and 7). For characterization, samples were pre-activated but may be exposed to the environment or solvents during characterization.

[0053] Example 1: Synthesis and Characterization of UTSA-16-Zn-x Materials The mixed-metal MOF samples containing Co and Zn, designated as UTSA-16-Zn-x, where x represents the molar fraction of Zn in the mixed Zn / Co precursor and x = 0, 0.25, 0.50, 0.75, or 1.00, were prepared by a one-pot synthesis method according to General Procedure 1.

[0054] Structural characterization Bulk phase characterization confirmed that all samples had the same phase. Powder X-ray diffraction (PXRD) measurements confirmed the same single crystalline phase as UTSA-16 (Figure 2a). Fourier transform infrared spectroscopy (FTIR) data also confirmed the successful synthesis of UTSA-16-type MOFs (Figure 6). Elemental distributions measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) against Co and Zn standards were in good agreement with the feed composition (Table 2).

[0055] The combined XPS and UV-Vis spectroscopy data, along with the color change of the samples (Figure 9), suggest that the distribution of octahedral-tetrahedral species is a function of the metal composition of the mixed-metal MOFs. · XPS analysis indicates that when the Zn loading is increased from 0 to 50%, the contribution of the Td spectrum decreases compared to Oh. The octahedral CO2+ band position occurs at approximately 540 nm (suggesting a reddish-pink color), while the tetrahedral CO2+ band position occurs near 650 nm. The F(R) for the monometallic Zn compound (x=1.00) is close to zero. The F(R) for the monometallic Co compound (x=0) incorporates contributions from both octahedral and tetrahedral Co, consistent with the crystal structure. For x=0.50, the contribution near λ=625 nm is significantly reduced. This is consistent with the replacement of Cotet with Zntet, resulting in a smaller spectral contribution from Zntet.

[0056] Room temperature extended X-ray absorption fine structure (EXAFS) spectra were measured at the K-edges of Co and Zn for mixed-metal samples with varying Zn loading (x = 0, 0.25, 0.50, 0.75, and 1.00) to assess site occupancy within the bulk mixed-metal MOF. X-ray absorption near-edge structure (XANES) spectra (Figure 10) showed that the valence states of the samples were similar.

[0057] The BET method was used to measure the specific surface area of ​​the UTSA-16-Zn-x materials. The adsorption data were collected at 77 K. The obtained specific surface areas are shown in Table 3.

[0058] [Table 2]

[0059] [Table 3]

[0060] Example 2: Asymmetric site distribution of Co and Zn in UTSA-16-Zn-x The asymmetric site distribution of Co and Zn in UTSA-16-Zn-x is evidenced using X-ray absorption spectroscopy. Fourier transform EXAFS data at the Co and Zn K-edges for all MOF samples are shown in Figure 2c, d. The overall similarity of the peak profiles in the R range of 0.8–3.2 Å suggests that Co and Zn adopt substantially similar coordination environments in the mixed-metal MOFs. However, the peak positions for the mixed-metal samples are significantly different across the Co and Zn K-edges (Figure 2e). The peak maxima are 1.53(6) Å and 1.55(4) Å for the respective monometallic MOFs, but fall within the ranges of 1.59–1.60 Å for the Co K-edge and 1.51–1.53 Å for the Zn K-edge. These deviations are statistically significant (delta R > 0.06 Å). Since the average bond lengths of the four- and six-coordinate cobalt atoms in UTSA-16 are significantly different (Fig. 2b), the coordinated displacement of the peak positions of either element in opposite directions while maintaining the crystal structure suggests that Co atoms are substituted at specific sites by doping with Zn.

[0061] Quantification of site distribution based on EXAFS data was performed by simultaneous fitting of the Co and Zn K-edges of the mixed-metal samples, following a previous treatment of metal site doping in oxide materials (Physical Review B 2002, 66(22), 224405). The path amplitude was parameterized using the fraction of either metal species occupying the tetrahedral sites, YCo,tet and YZn,tet. The amplitude parameters were referenced to monometallic Co and Zn samples for which site occupancies had been previously established by SCXRD (Journal of the American Chemical Society 2005, 127(47), 16352-16353). Other parameters were defined as described below. The results of the combined EXAFS fitting of eight independent data sets are shown in Figure 11, and the resulting fitting parameter values ​​are listed in Tables 4 and 5. The fitting results are in good agreement with the experimental data. The obtained YCo,tet indicates that in the mixed-metal samples, the majority of Co species are located in octahedral sites, while YZn,tet indicates a strong tetrahedral preference for Zn (Figure 2f). At x = 0.25, Zn occupies 60.3% of the tetrahedral sites. This value increases to 84.4% and 93.5% when x is increased to 0.50 and 0.75, respectively. This strongly suggests that the site distribution in the mixed-metal materials is asymmetric.

[0062] Parameterization of fitting Reported and collected crystallographic data for UTSA-16(Co) and UTSA-16(Zn) were imported and the associated scattering paths were generated using the FEFF program. Paths with lengths less than 2.5 Å were considered for fitting. Four path parameters, S02, E0, delta R, and sigma 2, were considered for each path. Path degeneracy, N, was maintained as specified in the FEFF software.

[0063] A single global E0 was identified as the refineable parameter for each edge.

[0064] For monometallic samples, i.e., x = 0 and x = 1, S02 was parameterized as a single refinable parameter. The contributions of the Cotet-O and Cooct-O single scattering paths were weighted at 0.33 and 0.67, respectively, according to the stoichiometry within the resolved crystal structure. A similar weighting scheme was identified for UTSA-16-Zn-x (x = 1).

[0065] For the bimetallic samples, the distribution between the octahedral and tetrahedral sites in the structure was parameterized as YCo,tet(x=0.25), YZn,tet(x=0.25), etc., and introduced as weighting factors. These were then referenced to the S02 of the single-metallic samples. In other words, the S02 of the Cotet-O scatterer at x=0.25 is defined as (S02,x=0×YCo,tet(x=0.25)), while the S02 of the Cooct-O scatterer is defined as [S02,x=0×(1−YCo,tet(x=0.25))].

[0066] Delta R is parameterized as a single refineable parameter for each edge, weighted by the respective Reff for each path.

[0067] It is reasonably expected that the Debye-Waller coefficients for Cotet-O, ​​Cooct-O, Zntet-O, ​​and Znoct-O will be different, and a single refinable parameter was defined for each.

[0068] All parameters were allowed to vary freely during simultaneous fitting of eight data sets, and a global R-factor was calculated.

[0069] The fitted delta R and sigma 2 converge to physically reasonable values, which are summarized as follows: The amplitude reduction coefficient (S02) is slightly outside the typical range (0.7–1.1) for both edges.

[0070] [Table 4]

[0071] [Table 5]

[0072] Example 3: Synthesis and Characterization of UTSA-16-Zn-0.25 and UTSA-16-Zn-1.00 Materials The difference in the three-electron structure of Co and Zn incorporated into the sample provides additional possibilities for determining site occupancy by SCXRD. To prepare samples of suitable size for SCXRD data collection, we employed a modified protocol. Specifically, large single crystals of UTSA-16-Zn-1.00 and UTSA-16-Zn-0.25 were grown according to General Procedure 2.

[0073] Unrestricted refinement of the occupancy of the octahedral and tetrahedral sites showed that the tetrahedral sites are almost completely occupied by Zn, while the occupancy of the octahedral sites is approximately 20% for UTSA-16-Zn-0.25. This model is in good agreement with the diffraction data (see Table 6). This occupancy corresponds to a bulk composition of 68.3% Co and 31.7% Zn in the single crystal (ICP results: 63.3% Co and 36.7% Zn).

[0074] Single Crystal X-ray Diffraction (SCXRD) Single-crystal X-ray diffraction data for UTSA-16-Zn-1.00 and UTSA-16-Zn-0.25 were collected at 100 K on a Bruker D8 Venture diffractometer. Data integration and reduction were processed with SAINT software. Multiscan absorption corrections were applied to collected reflections. The structures were solved by direct methods using SHELXTL and refined on F2 by full-matrix least-squares using the SHELXL-2014 / 7 package within the WINGX program. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were located in successive difference Fourier maps and treated as power atoms using SHELXL's default parameters. The structures were examined using the Adsym subroutine in PLATON to confirm that no additional symmetries could be applied to the models.

[0075] [Table 6]

[0076] Example 4: Effect of Zn loading on temperature-dependent crystallization The temperature-dependent crystallization of UTSA-16(Co) (viz. UTSA-16-Zn-0) and UTSA-16-Zn-0.50 was compared.

[0077] Temperature-dependent crystallization Reaction mixtures (corresponding to UTSA-16-Zn-0 and UTSA-16-Zn-0.50) were prepared according to General Procedure 1, except that heating was carried out in a preheated oven at the specified temperatures (60, 80, or 100 °C) or at room temperature (25 °C) for 24 hours.

[0078] Samples were collected by centrifugation at 5000 rpm and washed with copious amounts of anhydrous MeOH before being dried in a vacuum oven for PXRD testing. Because the samples were rich in Co, they exhibited a high signal-to-noise ratio due to X-ray absorption when using a Cu Kα radiation source (Rigaku Miniflex). Therefore, the samples were subjected to background subtraction and filtering with the Savitsky-Golay function using the instrument's processing software (Rigaku PDXL). The same processing was performed for all samples in Figures 3a and 3b. The intensity metrics of samples with different compositions cannot be directly compared due to absorption phenomena.

[0079] result In the case of the monometallic parent MOF (UTSA-16-Zn-0), a sticky gel precipitated, from which purple prismatic crystals emerged. XRD patterns (Figure 3a) collected on the crystallized product after 24 h incubation at 25, 60, 80, and 100 °C show that the solid obtained at low temperatures (25 and 60 °C) is primarily amorphous. Increasing the temperature to 80 °C revealed peaks corresponding to UTSA-16 after 24 h. At 100 °C, large single crystals visible by optical microscopy began to form (Figure 5). For UTSA-16-Zn-0.50, characteristic PXRD peaks could be observed even after the reaction mixture was left at room temperature for 24 h (Figure 3b).

[0080] Example 5: Effect of Zn loading on induction time The effect of Zn loading on the formation rate was estimated by ex-situ PXRD experiments. The MOF formation rate was estimated by the inverse full width at half maximum (FWHM) of the dominant PXRD peak at approximately 7.5°, which was further normalized by a long-term average value to allow comparisons across different Zn loadings.

[0081] method To accurately estimate the induction time, the composition was optimized to obtain a homogeneous starting solution. Taking into account the salting-out effect, it is necessary to balance the solvent composition to suppress liquid-liquid phase separation. Here, a starting solution of MII(acetate)-K3(citrate) (0.4 M in 15% (v / v) EtOH aqueous solution) was used.

[0082] The final composition of a 10 mL solution contains 1.5 mL of EtOH, 8.5 mL of HO, 4 mmol of MII (acetate), and 4 mmol of citric acid (neutralized with 12 mmol of KOH). The 4 mmol of MII (acetate) is further distributed between the two metals, keeping all other reagent amounts constant. For example, a 50 / 50 solution (x = 0.5) can be prepared using 2 mmol of Co(OAc)2·4HO and 2 mmol of Zn(OAc)2·2HO in 5 mL of HO as solvent and 4 mmol of citric acid neutralized with 12 mmol of KOH. Then, 1.5 mL of EtOH + 3.5 mL of HO solution is added to begin the experiment. By varying the relative ratio of MII (acetate) without changing the total molar amount, different relative amounts of Co / Zn can be prepared. For example, 25 / 75 (x = 0.75) and 75 / 25 (x = 0.25) mixtures can be prepared using 1 mmol of Co(OAc)2·4H2O and 3 mmol of Zn(OAc)2·2H2O or 3 mmol of Co(OAc)2·4H2O and 1 mmol of Zn(OAc)2·2H2O, respectively. The concentration of EtOH correlates well with the precipitation of solids; to prevent immediate solid formation, EtOH is added as a dilute solution (<30%) in water. Samples were incubated in a preheated oven at 65°C and periodically removed and quenched on ice. The products were centrifuged (8,000 rpm, 3 min), dried under vacuum at room temperature, and subjected to PXRD analysis. Product recovery times were minimized and kept constant among samples with different Zn loadings. Samples in which no solids separated after centrifugation are reported as having a FWHM of 0.

[0083] result Figure 3c shows that the induction time, defined as the time at which the product exhibits significant crystallinity, decreases significantly as the Zn content in the system increases. Even with a low Zn loading (x = 0.25), the induction time was significantly reduced to approximately 70 minutes. This result demonstrates that mixed-metal UTSA-16 materials can be obtained at ambient pressure in reasonable synthesis times (<48 hours).

[0084] In Figure 3c, the experiment was performed at T = 65 °C. The product crystallized in less than an hour. This temperature is below the boiling point of the solvent, allowing the reaction to be carried out at ambient pressure using a simple reflux setup. As is evident from Figure 3c, the reaction time can be manipulated by adjusting the structural composition. This property can be used to manipulate other parameters besides reaction time, such as temperature, by making appropriate process tradeoffs.

[0085] Example 6: Carbon Capture Performance of UTSA-16-Zn-x Gas sorption experiments Gas isotherms were measured up to 1 bar using a Micromeritics ASAP2020 surface area and pore size analyzer. Prior to the measurements, samples were degassed under reduced pressure (<10-2 Pa) at 150 °C until the outgassing rate was 5 μm Hg / min or less. UHP-grade N2 and CO2 were used for gas adsorption measurements. An oil-free vacuum pump and oil-free pressure regulator were used to prevent sample contamination during the degassing process and isothermal measurements. Temperatures of 77, 273, and 298 K were maintained in a liquid nitrogen bath, an ice-water bath, and at room temperature, respectively.

[0086] CO2 isotherm fitting The measured CO2 isotherms were calculated using the Dual Site Langmuir-Freundlich (DSLF) isotherm model:

[0087]

number

[0088] The model takes into account site heterogeneity by defining two adsorption sites, A and B, with different saturation capacities and affinity parameters. where q is the amount of adsorbed gas, q sat is the amount of gas adsorbed at saturation (mmol g -1 ), b is the Langmuir-Freundlich affinity parameter (kPa -1 ), where alpha is a dimensionless exponent.

[0089] Simultaneous fitting at 298 K and 273 K was performed using the Solver function in Microsoft Excel, and the temperature dependence is described in a separate b section.

[0090] [Table 7]

[0091] N2 isotherm fitting The measured N2 isotherms were modeled using the single-site Langmuir (SSL) isotherm model.

[0092]

number

[0093] Due to the low curvature of the isotherm, independent fittings to samples with different Zn loadings resulted in large variations in the obtained parameters. To reduce the number of free parameters, the q of individual UTSA-16-Zn-x samples was sat The values ​​are constrained to a common value scaled by N2 uptake at 100 kPa. This constraint is supported by the substantial agreement of the isotherms for CO2, the isostructural nature, and the very similar adsorption behavior.

[0094] [Table 8]

[0095] Research results Single-component CO and N isotherms were collected for UTSA-16-Zn-x at 273 K and 298 K. The shapes of the CO isotherms and total uptake at 1 bar were virtually identical to those of the parent Co. Furthermore, several other parameters obtained by isotherm analysis, such as the isothermal heat of CO adsorption (Qst) and CO / N selectivity calculated by ideal adsorption solution theory (IAST), were also identical (Figure 4; Figure 7; and Table 9), suggesting similar CO capture performance between UTSA-16-Zn-x and UTSA-16(Co).

[0096] [Table 9]

[0097] Example 7: Competitive adsorption of UTSA-16-Zn-x under dynamic conditions Breakthrough experiments using simulated exhaust gas (15 / 85 CO2 / N2 feed) were also carried out to analyze competitive adsorption under dynamic conditions.

[0098] Groundbreaking experiment Breakthrough experiments were carried out using a homemade setup as shown in Figure 12. The MOF sample (700–900 mg) was packed into a stainless steel column (L = 7 cm, D = 0.46 cm) and fixed with quartz wool and steel mesh.

[0099] The feed flow rate during the experiment was controlled using a mass flow controller (with an error of 0.1 sccm). The total flow rate through the column was set to 3 sccm. These were stabilized using a bypass line, which was then switched to the flow through the adsorption column immediately before the experiment.

[0100] The gas composition at the column outlet was measured with a mass spectrometer (Hiden QGA). To accurately determine the flow rate, Ar was introduced into the outlet gas at a fixed flow rate of 3 sccm as an internal standard for mass flow calibration. The upstream and downstream pressures were recorded. The original breakthrough plot was obtained as relative composition versus elapsed time and then converted to mole fraction normalized to the inlet versus elapsed time plot.

[0101] The performance evaluation was based on three experiments:

[0102] Dry feedstock (relative humidity (RH) = 0%) The column was activated by purging the column with a steady helium flow of 10 sccm at 120 °C for 24 h. The feed gas was a (15 ± 1) / (85 ± 1) CO2 / N2 mixture prepared by mixing dry gases upstream of the column. Wet feedstock (relative humidity (RH) = 85%) The column was activated by purging the column with a steady 10 sccm helium flow at 120 °C for 24 h. The feed gas was a (15 ± 1) / (85 ± 1) CO / N mixture with a relative humidity of approximately 85%. Moisture was introduced by passing a stream of N through a room-temperature water bubbler prior to mixing.

[0103] Water-saturated adsorbent layer (saturated column) The column was activated by purging with a constant 10 sccm He flow at 120 °C for 24 h. For presaturation, a wet purge flow was prepared by passing a stream of N2 through a water bubbler at room temperature before mixing. This purge flow was passed through the column for 72 h until a stable water signal was detected by mass spectrometry. The column was then briefly activated under a constant 10 sccm He flow at room temperature. Under these conditions, desorption of N2 / CO2 was nearly complete, but desorption of adsorbed H2O was barely observed. Next, experiments were performed using "wet feed" conditions. Under these conditions, the MOF-packed column showed negligible uptake of either component.

[0104] The average residence time in the adsorption column was obtained by performing a mass balance using the molar flow rates of the inlet and outlet gases, i.e.:

[0105]

number

[0106] The resulting residence times were corrected for the residence times of control experiments performed using blank tubes under the same pressure drop and feed conditions. The validity of this calibration depends on the linear additive relationship between the residence time and band broadening characteristics of the experiment. The uncalibrated breakthrough curve (Figure 13) and the residence times obtained after calibration are shown in Table 10.

[0107] result The saturated CO2 uptake of UTSA-16-Zn-x is 1.65–1.70 mmol g -1 , which showed considerable resistance to moisture (Fig. 4). This is in contrast to the parent Co MOF (1.82 mmol g -1 ) and is similar to the static CO2 uptake results.

[0108] The maximum CO2 productivity (qmax) was 1.8 mmol g for single component static uptake (x = 0.5 and 1, respectively). -1 and 1.94 mmol g -1 ) in good agreement. In general, there was a slight capacity decrease (-2.3%) when going from dry to RH = 85% feed due to competitive adsorption by H2O.

[0109] [Table 10]

[0110] summary In summary, we show that replacing the rate-limiting tetrahedral Co species in UTSA-16 with Zn dramatically accelerates the formation rate of these MOFs and provides mild synthetic conditions suitable for the mass production of these materials. The new UTSA-16-type MOFs exhibit CO2 capture performance similar to their parent Co counterparts and are also highly moisture tolerant.

[0111] The present invention generates mixed-metal complexes from known binary (single-metal / single-linker) MOFs with appropriate structures, offering improved synthetic robustness compared to single-metal materials. Optimized protocols derived from this strategy are compatible with scale-up production and will facilitate the process development of these materials for various commercial applications.

Claims

1. A metal-organic framework (MOF) having a UTSA-16 structure, MOF is: 0-80 mol% of the total metals in the MOF is a first metal that is one or more selected from the group consisting of Cr, Fe, Ni, Cu, and Co; and 20-100 mol % of the total metals in the MOF is a second metal, which is one or more selected from the group consisting of Cd, Mn, and Zn. This includes: A metal organic framework (MOF), wherein the MOF comprises tetrahedral metal sites and a majority (or 51 mol % or more) of the second metal occupies the tetrahedral metal sites in the MOF.

2. 2. The MOF of claim 1, characterized in that the second metal is Zn.

3. 3. The MOF according to claim 1 or 2, characterized in that the second metal is present in an amount of 25 to 100 mol % of the total metals present in the MOF.

4. 4. The MOF of claim 3, wherein the second metal is present in an amount of 50 to 75 mol % of the total metals present in the MOF.

5. 5. The MOF according to any one of claims 1 to 4, characterized in that the first metal is selected from Fe and Co.

6. 6. The MOF of claim 5, characterized in that the first metal is Co.

7. 7. The MOF according to any one of claims 1 to 6, characterized in that the first metal is present in an amount of 25 to 50 mol % of the total metals present in the MOF.

8. 8. The MOF according to any one of claims 1 to 7, characterized in that a majority (or 51 mol % or more) of the first metal, if present, occupies octahedral metal sites within the MOF.

9. MOF up to 5.0 mmol / g saturated CO ２ 9. MOF according to any one of claims 1 to 8, characterized in that it has an incorporation.

10. MOF achieves breakthrough CO2 production of up to 2.2 mmol / g ２ Work capacity (breakthrough CO ２ 10. The MOF according to claim 1, characterized in that it has a high working capacity.

11. 11. A method of forming a MOF according to any one of claims 1 to 10, comprising aging a mixture comprising a first metal precursor, a second metal precursor, a base, citric acid, a first solvent and a second solvent at a temperature of 15 to 200°C for a period of time, comprising: the first metal precursor comprises one or more selected from the group consisting of Cr, Fe, Ni, Cu, and Co; The second metal precursor comprises one or more selected from the group consisting of Cd, Mn, and Zn; and The metal in the first metal precursor is present in an amount of 0 to 80 mol % of the total amount of metal in the mixture; and The metal in the second metal precursor is present in an amount of 20-100 mol % of the total amount of metal in the mixture. A method characterized by:

12. 12. The method according to claim 11, characterized in that the temperature is between 20 and 150°C.

13. 13. The method according to claim 12, characterized in that the temperature is between 40 and 120°C.

14. 14. A process according to claim 13, characterized in that the temperature used results in refluxing one or both solvents.

15. (a) the first solvent is water and the second solvent is an alkyl alcohol (e.g., the alkyl alcohol is methanol, propanol, or, more particularly, ethanol); and / or (b) the base is a metal hydroxide (e.g., the base is KOH); and / or (c) conducting the method under ambient atmospheric conditions (e.g., standard pressure); The method according to any one of claims 11 to 14, characterized in that

16. 16. A method according to any one of claims 11 to 15, characterized in that the first and second metal precursors are metal salts in which the metal is in cationic form, balanced by one or more counterions selected from one or more halides (e.g. chloride), nitrates, sulfates, hydroxides, oxides, acetate anions, and hydrates thereof.

17. (a) The second metal precursor is Zn(OAc) ２ or its hydrate (e.g., Zn(OAc) ２ ・2H ２ O); and / or 17. The method of any one of claims 11 to 16, wherein the metal in (b) the second metal precursor is present in an amount of 25 to 100 mol % of all metals present in the mixture.

18. (a) The first metal precursor is Fe(OAc) ２ , Co(OAc) ２ or their hydrates (e.g., Co(OAc) ２ ・4H ２ O); and / or 18. The method of any one of claims 11 to 17, wherein (b) the metal in the first metal precursor is present in an amount of 25 to 50 mol % of all metals present in the mixture.

19. The material comprising the MOF according to any one of claims 1 to 10 is subjected to CO ２ Exposing the mixture to an environment containing CO ２ How to capture.

20. 2. The MOF of claim 1, wherein 51 mol % or more of the second metal occupies tetrahedral metal sites in the MOF.

21. 2. The MOF of claim 1, wherein 60 mol % or more of the second metal occupies tetrahedral metal sites in the MOF.

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