Composite materials for carbon dioxide capture

Abstract

The invention provides a composite material comprising a hydrophobic polymer and a metal organic framework of formula I: Al1-xMx(HCO2)3 where M represents Fe, Cr, or Mn, and, x is from 0 to 0.9999, wherein the metal organic framework is provided in the form of a plurality of crystals, each having a surface, and the hydrophobic polymer is coated onto the surface of the metal organic framework crystals. The invention also provides a method of adsorbing CO2 and / or O2 from a gas, comprising subjecting the composite material to a flow of a gas comprising one or both of CO2 and O2. In addition, the invention also provides a method of releasing CO2 and / or O2 from the composite material.

Description

[0001] COMPOSITE MATERIALS FOR CARBON DIOXIDE CAPTURE

[0002] FIELD OF INVENTION

[0003] The present invention provides metal organic frameworks and more particularly, composite materials comprising a hydrophobic polymer and a metal organic framework.

[0004] BACKGROUND

[0005] 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 common general knowledge.

[0006] Efficient technologies for capturing and storing CO2 can significantly alleviate the environmental impact of fossil fuel use. Despite the substantial capacity demonstrated by conventional chemical sorbents, which typically utilize aqueous amine solutions for postcombustion CO2 capture, they are plagued by drawbacks such as oxidative reactions, corrosion, and thermal degradation, and involve energy-intensive regeneration processes. Solid sorbents (zeolites, silicas, carbons, resins, etc.) represent a transformative technology in carbon capture and have been successfully demonstrated at smaller scales. In many instances, chemisorptive materials show higher capacity and selectivity in CO2 capture. However, the enhancement of CO2 binding often results in a proportional increase in the energy required for sorbent regeneration and sometimes may intensify the binding of competing gases. When evaluating practical CO2 uptake, the pivotal factor is the working capacity under operational cycling conditions for regenerating solid sorbents. While selectivity over N2 is commonly reported, there is a lack of information on CO2 sorption in the presence of moisture, especially for physisorptive capture systems. Specifically, aluminosilicate zeolites exhibit insufficient CO2 uptake capacity in humid gas streams, and porous polymers and carbonaceous materials display low CO2adsorption capacities and inadequate CO2 / N2selectivities. A physisorptive solid for CO2capture can significantly reduce regeneration costs, but it must exhibit sufficient working capacity and selectivity for CO2in gas streams where molecules with stronger intermolecular attractive forces than CO2are present (unless mitigation steps are taken). Moisture significantly impacts CO2capture efficiency by interacting with adsorbent materials, potentially reducing their capacity and longevity. To address this issue, current efforts include adding an extra drying step before CO2capture, though this approach increases the overall process cost. Furthermore, for practical application in process productivity, the kinetics of sorption and release are as pivotal as the capacity itself. Metal-organic frameworks (MOFs) offer promising features as next-generation solid adsorbent materials for CO2capture due to their tunable pore sizes, high surface areas, structural diversity, and surface functionality. However, they often have inherent limitations, such as sensitivity to moisture, poor chemical stability, and limitations in scalability. To enhance humidity resistance, one can focus on incorporating hydrophobic ligands, especially fluorinated ligands, or metal nodes with lower susceptibility to water interactions, such as Zr- oxo nodes. However, these intricate fluorinated ligand precursors and metal Zr-oxo nodes are too expensive to be used in large-scale applications. Certain MOFs possess open metal or Lewis base sites, ultramicropores (<6 A), and additional polar functionalities, such as hydroxyl, amino, pyridyl, and thiol, indicating considerable CO2adsorption capacities. Although MOFs have been demonstrated in large-scale pilot studies due to high stability and facile regeneration, it is still imperative to keep reducing costs (both materials cost and regeneration cost) and maintaining CO2capture performance in the presence of moisture.

[0007] Aluminum formate [AI-(HCOO)3], known as ALF, has been shown to offer some distinct advantages over many existing MOFs. Most importantly, its affordability and scalability are striking, as its preparation is straightforward and requires only two simple precursors, aluminum hydroxide (AI(OH)a) and formic acid (HCOOH). ALF exhibits outstanding CO2uptake properties and high selectivity for CO2 / N2 and CO2 / hydrocarbon separations. In addition, it has great potential for noncryogenic air separation and hydrogen storage. However, when ALF is exposed to moisture at room temperature, it gradually undergoes decomposition. Nevertheless, the cost of ALF is arguably sufficiently low that a drying step before CO2 capture may become a viable option. Alternatively, it should be possible to develop moisture-stable ALF composites that preserve pore size without compromising selectivity. In this regard, designing a moisture-stable ALF by incorporating low-cost polymers is an attractive strategy.

[0008] Thus, there is a need for alternative and / or improved composite materials for efficient CO2capture.

[0009] SUMMARY

[0010] Aspects and embodiments of the current invention will now be described by reference to the following numbered clauses.

[0011] 1. A composite material comprising: a hydrophobic polymer; and a metal organic framework of formula I:

[0012] AII.XMX(HCO2)3where:

[0013] M represents Fe, Cr, or Mn; and x is from 0 to 0.9999, wherein the metal organic framework is provided in the form of a plurality of crystals, each having a surface, and the hydrophobic polymer is coated onto the surface of the metal organic framework crystals.

[0014] 2. The composite material according to Clause 1 , wherein x is from 0 to 0.85.

[0015] 3. The composite material according to Clause 2, wherein x is from 0.2 to 0.8, such as from 0.27 to 0.76, such as from 0.5 to 0.54.

[0016] 4. The composite material according to any one of the preceding clauses wherein the metal organic framework of formula I is selected from:

[0017] (a) Alo.46M0 54(HC02)3;

[0018] (b) Alo.5M0 5(HC02)3;

[0019] (c) Alo.73Mo27(HC02)3;

[0020] (d) AI(HCO2)3; or

[0021] (e) Alo 24Mo 76(HC02)3.

[0022] 5. The composite material according to Clause 4, wherein the metal organic framework of formula I is selected from:

[0023] (a) Alo 46Mo 54(HC02)3;

[0024] (b) Alo.5M05(HC02)3;

[0025] (c) Alo.73M0 27(HC02)3; or

[0026] (d) AI(HCO2)3, such as:

[0027] (i) Alo 46Mo 54(HC02)3;

[0028] (ii) Alo.5Mo 5(HC02)3; or

[0029] (iii) AI073M027(HCO2)3.

[0030] 6. The composite material according to Clause 5, wherein the metal organic framework of formula I is AI046M0.54(HCO2)3. 7. The composite material according to any one of the preceding clauses wherein the metal organic framework of formula I is selected from:

[0031] (a) Alo45Feo54(HC02)3;

[0032] (b) Alo.5Fe0.5(HC02)3;

[0033] (c) Alo73Feo27(HC02)3;

[0034] (d) AI(HCO2)3; or

[0035] (e) Alo24Fe076(HC02)3.

[0036] 8. The composite material according to Clause 7, wherein the metal organic framework of formula I is selected from:

[0037] (a) Al0.46Feo.54(HC02)3;

[0038] (b) Alo5Fe05(HC02)3;

[0039] (c) Alo.7sFeo.27(HC02)3; or

[0040] (d) AI(HCO2)3, such as:

[0041] (i) Alo46Feo54(HC02)3;

[0042] (ii) Alo.5Feo.5(HC02)3; or

[0043] (iii) Alo.73Feo.27(HC02)3.

[0044] 9. The composite material according to Clause 8, wherein the metal organic framework of formula I is Alo.46Feo.54(HC02)3.

[0045] 10. The composite material according to any one of the preceding clauses wherein the hydrophobic polymer is one that has a water contact angle of >90s, such as from 100eto 130s, such as from 1 15® to 125®, such as about 120®.

[0046] 11. The composite material according to any one of the preceding clauses wherein the hydrophobic polymer is selected from one or more of the group consisting of perfluoropolyether (PFPE), poly(vinylidene fluoride-co-hexafluoropropylene), poly(2,2,2- trifluoroethyl methacrylate-co- 3-methacryloxypropyltrimethoxysilane) and polyvinylidene fluoride (PVDF).

[0047] 12. The composite material according to Clause 1 1 , wherein the hydrophobic polymer is PVDF. 13. The composite material according to any one of the preceding clauses wherein the hydrophobic polymer is present in an amount of from 0.5 to 10 wt% of the entire weight of the composite material.

[0048] 14. The composite material according to Clause 13, wherein the hydrophobic polymer is present in an amount of from 5 to 7 wt%, such as about 6.7 wt% of the entire weight of the composite material.

[0049] 15. The composite material according to any one of the preceding clauses wherein: the hydrophobic polymer is PVDF and is present in an amount of about 6.7 wt% of the entire weight of the composite material; and the metal organic framework of formula I is Alo.46Fe054(HC02)3.

[0050] 16. The composite material according to any one of the preceding clauses wherein the composite material is provided in the form of a powder.

[0051] 17. The composite material according to any one of the preceding clauses wherein the composite material has a water contact angle of greater than 100s, such as from 105sto 130s, such as from 115sto 125s, such as about 120s, such as from 110sto 1 15s, such as from 1 12sto 114s.

[0052] 18. The composite material according to any one of the preceding clauses wherein the composite material displays a CO2adsorption value of from 3 to 6 (e.g. from about 4 to about 5, such as about 4.6 mmol / g) at 298 K and under 1 bar of CO2.

[0053] 19. The composite material according to any one of the preceding clauses, wherein the composite material displays a CO2adsorption value of from 2 to 3 (e.g. about 2.3) mmol / g and from 300 to 400 (e.g. from 350 to 390, such as about 387) selectivity over N2at 298 K and under 1 bar of total pressure provided by a gas stream of CO2and N2(15:85).

[0054] 20. A method of adsorbing CO2and / or O2from a gas, comprising subjecting a composite material according to any one of Clauses 1 to 19 to a flow of a gas comprising one or both of CO2and O2.

[0055] 21 . The method according to Clause 20, wherein the gas further comprises nitrogen and water vapour. 22. The method according to Clause 20 or Clause 21 , wherein the gas has a relative humidity of from less than or equal to 25% to 100%.

[0056] 23. The method according to Clause 22, wherein the gas has a relative humidity of from 50 to 100%, such as from 70 to 95%, such as about 80%.

[0057] 24. A method of releasing CO2 and / or O2 from a composite material according to any one of Clauses 1 to 19 to which CO2 and / or O2 has been adsorbed, the process comprising:

[0058] (a) providing a composite material to which CO2 and / or O2 has been adsorbed; and

[0059] (b) activating it by subjecting it to:

[0060] (i) a temperature of from 90 to 160 °C (e.g. from 100 to 150 °C, such as 120 °C) under reduced pressure for a period of time (e.g. from hour to 2 days, such as about 24 hours); or

[0061] (ii) a temperature of from 170 to 250 °C (e.g. from 175 to 185 °C, such as about 180 °C) under 1 atmosphere pressure for a period of time (e.g. from hour to 2 days, such as about 24 hours).

[0062] 25. A method of obtaining a composite material according to any one of Clauses 1 to 19, the method comprising the steps of:

[0063] (a) providing an unactivated composite material; and

[0064] (b) activating it by subjecting it to:

[0065] (i) a temperature of from 90 to 160 °C (e.g. from 100 to 150 °C, such as 120 °C) under reduced pressure for a period of time (e.g. from 1 hour to 2 days, such as about 24 hours); or

[0066] (ii) a temperature of from 170 to 250 °C (e.g. from 175 to 185 °C, such as about 180 °C) under 1 atmosphere pressure for a period of time (e.g. from 1 hour to 2 days, such as about 24 hours).

[0067] BRIEF DESCRIPTION OF DRAWINGS

[0068] FIG. 1 depicts the synthesis scheme of M(lll) formates, M = Al and Fe. The as-made samples were activated at 150 °C under vacuum for 12 h, and the structures of activated samples are depicted in the scheme. Note that CO2molecules are shown in the structure of Fe-formate, as CO2removal via activation causes degradation. In contrast, ALF and Fe-ALF can be easily activated at 150 °C under vacuum, forming stable, porous frameworks for CO2sorption. FIG. 2 depicts (a) Crystal structure of ALF along c-axis. (b) Crystal structure of Alo.4sFeo.54-ALF along c-axis. (c) Representations of all cavities present in Fe-ALF, where SC = smaller cavity, LC = larger cavity. For both (a) and (b), the circles denote smaller cavity to larger cavity channels, and the squares denote smaller cavity to smaller cavity channels.

[0069] FIG. 3 depicts (a) Pawley refinement fit of activated Alo.46Feo.54-ALF-PVDF. (b) Thermogravimetric analysis of (i) Alo46Feo54-ALF and (ii) Alo46Feo54-ALF-PVDF. FE-SEM images of (c) ALF, (d) Fe-ALF, and (e, f) Alo.46Feo 54-ALF-PVDF. Water contact angle tests of (g) ALF, (h) Alo46Feo.54-ALF, and (i) Alo.46Feo54-ALF-PVDF.

[0070] FIG. 4 depicts (a) CO2adsorption isotherms of Alo.46Feo.54-ALF-PVDF at various temperatures, (b) Comparison of the CO2and N2adsorption isotherms at 298 K of Alo 46Feo54-ALF-PVDF. The inset shows the CO2 / N2 sorption selectivity based on ideal adsorbed solution theory (IAST) for a 15 / 85 mixture of CO2 / N2 at 298 K. (c) Comparison of CO2 / N2 selectivity for some chosen MOFs at 298 K and 1 bar. (d) Comparison of the H2O vapor sorption isotherms of (i) Alo46Feo54-ALF and (ii) Alo46Feo54-ALF-PVDF at 298 K. (e) Breakthrough curves of a 15 / 85 CO2 / N2 dry mixed gas experiment with Alo.46Feo54-ALF-PVDF at 298 K. (f) Breakthrough curves of a 15 / 85 CO2 / N2 humidified mixed gas (RH = 85%) for Alo.46Feo54-ALF-PVDF at 298 K.

[0071] FIG. 5 depicts the adsorption energies from first-principles calculations. The following cavities are computed for the P23 Alo5Feo.5-ALF structure: LC1 : corner, LC2: body center, SC1 : face center, SC2: edge center. Comparisons to AI(HCOO)3 and Fe(HCOO)3 in I m3 are also shown.

[0072] FIG. 6 depicts a scheme of the breakthrough setup used in this study.

[0073] FIG. 7 depicts a scheme illustrating the synthesis of ALF, Fe-ALF, and Fe-ALF-PVDF.

[0074] FIG. 8 depicts a schematic representation of the ALF and its hydrolysis to form AI(OH)(HCOO)2, by soaking ALF in water for 2 h at 298 K. (b) PXRD patterns of as-made and activated ALF at 150°C under vacuum for 12 h. (c) PXRD patterns of simulated AI(OH)(HCOO)2and the ALF sample after soaking it in water for 2 h.

[0075] FIG. 9 depicts the PXRD patterns of (i) as-synthesized Fe-formate, (ii) simulated Fe2O3, and (iii) activated Fe-formate. FIG. 10 depicts the FTIR spectra of (i) as-synthesized Fe-formate, (ii) activated Fe-formate.

[0076] FIG. 11 depicts the FTIR spectra of pristine ALF and ALF after soaking it in water for 2h. Note: The disappearance of the carbonyl (C=O) stretch and the appearance of a new O-H bend in the water-soaked ALF confirms that the formate group was replaced by hydroxyl (-OH) group after soaking ALF in water for 2h.

[0077] FIG. 12 is a1H NMR spectrum of liquid aliquots of hydrolysed ALF filtrate.

[0078] FIG. 13 depicts the PXRD patterns of as-synthesized ALF-PVF composite and the ALF-PVF composite after soaking it in water for 2h.

[0079] FIG. 14 depicts the TGA curves of ALF and ALF-PVDF composite.

[0080] FIG. 15 depicts the water contact angles of ALF and ALF-PVDF composite.

[0081] FIG. 16 depicts the CO2 and N2adsorption isotherm of ALF-PVDF composite at 298 K.

[0082] FIG. 17 depicts the representations of all cavities present in Fe-ALF, where SC = smaller cavity, LC = larger cavity.

[0083] FIG. 18 depicts the PXRD patterns of (i) simulated Alo.46Feo.54-ALF and (ii) activated Alo45Feo54- ALF.

[0084] FIG. 19 depicts the FT-IR spectra of ALF and FexAli.x-ALFs.

[0085] FIG. 20 depicts the EDS mapping for ALF (upper row), Alo46Fe054-ALF (middle row), and Alo45Feo54-ALF-PVDF (bottom row).

[0086] FIG. 21 depicts the CO2 adsorption isotherms for (i) Alo.46Feo.54-ALF, (ii) Alo73Feo27-ALF, (iii) ALF and (iv) Alo24Feo.76-ALF at 298 K.

[0087] FIG. 22 depicts the PXRD patterns of the AI0.46Fe0.54-ALF after water treatment for 2h at 25°C. FIG. 23 depicts the FTIR spectra of PVDF, Alo4eFeo.54-ALF and Alo.46Feo54-ALF-PVDF. The characteristic C-F peaks of PVDF at 1182 cm-1and 1210 cm-1appears in the composite.

[0088] FIG. 24 depicts the PXRD patterns of as-synthesized Alo.46Feo.54-ALF-PVDF and recovered Alo.46Feo.54-ALF-PVDF after water and humidity treatment at room temperature.

[0089] FIG. 25 depicts the CO2 sorption isotherms of Alo.46Feo 54-ALF-PVDF at various temperatures.

[0090] FIG. 26 depicts the comparison of CO2 and hydrocarbon adsorption isotherms at 298K of Alo.46Feo.54-ALF-PVDF.

[0091] FIG. 27 depicts the fit of CO2adsorption data of Alo,46Feo54-ALF to the Langmuir-Freundlich equation. The solid line corresponds to the Langmuir-Freundlich model fit for CO2 adsorption at 273K.

[0092] FIG. 28 depicts the fit of CO2 adsorption data of Alo.46Feo54-ALF to the Langmuir-Freundlich equation. The solid line corresponds to the Langmuir-Freundlich model fit for CO2 adsorption at 298K.

[0093] FIG. 29 depicts the fit of CO2 adsorption data of Alo.46Feo54-ALF-PVDF to the Langmuir- Freundlich equation. The solid line corresponds to the Langmuir-Freundlich model fit for CO2 adsorption at 273K.

[0094] FIG. 30 depicts the fit of CO2 adsorption data of Alo46Feo54-ALF-PVDF to the Langmuir- Freundlich equation. The solid line corresponds to the Langmuir-Freundlich model fit for CO2 adsorption at 298K.

[0095] FIG. 31 depicts the isosteric heat of adsorption (Qst) for CO2with AI046Fe0.54-ALF. These values were estimated by applying the Clausius-Clapeyron expression using the CO2- desorption isotherms. Note: The isosteric enthalpy adsorption in the main text (FIG. 5, Table 2) was reported with a negative sign.

[0096] FIG. 32 depicts the isosteric heat of adsorption (Qst) for CO2with Alo^Feo 54-ALF-PVDF. These values were estimated by applying the Clausius-Clapeyron expression using the CO2- desorption isotherms. Note: The isosteric enthalpy adsorption in the main text (FIG. 5, Table 2) was reported with a negative sign. FIG. 33 depicts the differential scanning calorimetry (DSC) plot for (i) Alo.46Feo54-ALF-PVDF and (ii) Alo.46Feo54-ALF-PVDF exposed to 100% RH at 298K for 12h. Note: The enthalpy change observed at around 110°C in the DSC plot corresponds to the loss of adsorbed water molecules in Alo.46Feo 54-ALF-PVDF exposed to 100% RH.

[0097] FIG. 34 depicts the breakthrough adsorption-desorption curves of CO2 for Alo.46Feo54-ALF- PVDF at 85% RH and 298K.

[0098] FIG. 35 depicts the breakthrough curves of a 15 / 85 CO2 / N2 wet gas mixture with Alo.4eFeo54- ALF-PVDF at 91 % RH and 298K.

[0099] FIG. 36 depicts the breakthrough curves of a 15 / 85 CO2 / N2 dry gas mixture with Alo.4eFeo.54- ALF at 0% RH and 298K.

[0100] FIG. 37 depicts the breakthrough curves of a 15 / 85 CO2 / N2 wet gas mixture with Alo4eFeo 54- ALF at 85% RH and 298K.

[0101] FIG. 38 depicts the cyclic CO2 adsorption analysis for Alo.46Feo 54-ALF-PVDF. Note: For each measurement, the sample was exposed to 85% RH at 298 K for 12h before activation at 120°C, and subsequent CO2adsorption test was conducted at 298 K.

[0102] FIG. 39 depicts the in situ cyclic TGA tests of Alo.46Feo.54-ALF-PVDF under 85% RH humidity condition. Note: this graph shows 45 cycles, where degassing occurred at 353 K and CO2 adsorption took place on cooling to 313 K. Each cycle was ~5 minutes, and the total time was 3.8 hours.

[0103] DESCRIPTION

[0104] The composite material disclosed herein has been surprisingly found to provide a stable and affordable adsorbent material that can capture CO2 from a flue gas (e.g., a flue gas having water vapour in the range of from less than or equal to 25% to 90% relative humidity). Similarly, the composite material disclosed herein has been surprisingly found to provide a simple sorbent material for the selective adsorption of O2from air (e.g., relative to nitrogen). As demonstrated in the Examples section, the composite material showed an enhanced CO2uptake (e.g., ~4.6 mmol / g at 298 K and 1 bar CO2 pressure), which is higher than that of the corresponding pristine MOF, with a superior CO2 / N2 selectivity (e.g., 387). Notably, the composite materials are highly stable in liquid water (e.g., water contact angle: 1 12°) and water vapor (RH of 80%) conditions, ensuring their wide applications under practical situations.

[0105] Thus, in a first aspect of the invention, there is provided a composite material comprising: a hydrophobic polymer; and a metal organic framework of formula I:

[0106] AII.XMX(HCO2)3where:

[0107] M represents Fe, Cr, or Mn; and x is from 0 to 0.9999, wherein the metal organic framework is provided in the form of a plurality of crystals, each having a surface, and the hydrophobic polymer is coated onto the surface of the metal organic framework crystal.

[0108] In embodiments herein, the word “comprising” may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word “comprising” may also relate to the situation where only the components / features listed are intended to be present (e.g., the word “comprising” may be replaced by the phrases “consists of” or “consists essentially of”). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word “comprising” and synonyms thereof may be replaced by the phrase “consisting of’ or the phrase “consists essentially of’ or synonyms thereof and vice versa.

[0109] The phrase, “consists essentially of’ and its pseudonyms may be interpreted herein to refer to a material where minor impurities may be present. For example, the material may be greater than or equal to 90% pure, such as greater than 95% pure, such as greater than 97% pure, such as greater than 99% pure, such as greater than 99.9% pure, such as greater than 99.99% pure, such as greater than 99.999% pure, such as 100% pure.

[0110] As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, reference to “an oxygen carrier” includes mixtures of two or more such oxygen carriers, reference to “the catalyst” includes mixtures of two or more such catalysts, and the like. Metal organic frameworks are well known to a person skilled in the art, and are a class of compounds comprising metal ions coordinated to organic ligands. Metal organic frameworks are typically crystalline materials having a regular array of metal ions coordinated to organic ligands.

[0111] The metal organic framework of formula I:

[0112] AII.XMX(HCO2)3where, M represents Fe, Cr, or Mn, and x is from 0 to 0.9999, may be provided in an activated or unactivated for (or a mixture of both). The term “activated metal-organic framework” when used herein refers to a metal-organic framework where materials that block the MOF’s channels (e.g. , from formation and / or sorption) are removed. As noted this may be achieved through the application of heat alone or by the application of vacuum and heat for a suitable period of time. The exact conditions can be readily determined by a person skilled in the art considering the entire disclosure of the application as filed. As will be appreciated, the term “unactivated metal-organic framework” when used herein refers to a metal-organic framework where materials that block the MOF’s channels (e.g., from formation and / or sorption) are present.

[0113] At least some of the metal-organic frameworks disclosed herein may have the following unitcell parameters: a = b = c = from 1 1 .303 to 11 .894 A, a = p = y = 90°, Volume = from 1562 to 1600 A3, space group: I m-3. As will be appreciated, the crystal system or space group may change depending on ligand and metal combination.

[0114] The value of x may range from 0 to 0.9999. For example, x may be from 0 to 0.99, such as, from 0.25 to 0.85. In certain embodiments, x may be from 0 to 0.85. In certain additional embodiments, x may be from 0.2 to 0.8, such as from 0.27 to 0.76, such as from 0.5 to 0.54. Particular point values of x that may be mentioned herein include 0.25, 0.50, 0.75 and 0.85. As will be appreciated, this approach essentially results in X being doped by Y (or vice versa, depending on the relative amounts of X and Y). It is believed that such doped metal-organic frameworks may display enhanced adsorption for CO2, O2etc.

[0115] For the avoidance of doubt, it is explicitly contemplated that where several numerical ranges related to the same feature are cited herein, that the end points for each range are intended to be combined in any order to provide further contemplated (and implicitly disclosed) ranges. Thus, for the values of x mentioned herein, there is disclosed the following ranges for x: from 0 to 0.25, from 0 to 0.50, from 0 to 0.75, from 0 to 0.85, from 0 to 0.99, from 0 to 0.9999; from 0.25 to 0.50, from 0.25 to 0.75, from 0.25 to 0.85, from 0.25 to 0.99, from 0.25 to 0.9999; from 0.50 to 0.75, from 0.50 to 0.85, from 0.50 to 0.99, from 0.50 to 0.9999; from 0.75 to 0.85, from 0.75 to 0.99, from 0.75 to 0.9999; from 0.85 to 0.99, from 0.85 to 0.9999; and from 0.99 to 0.9999.

[0116] In certain embodiments, the metal organic framework of formula I may be selected from:

[0117] (a) Alo46Mo54(HC02)3;

[0118] (b) AI0.5M05(HCO2)3;

[0119] (c) Alo.73Mo27(HC02)3;

[0120] (d) AI(HCO2)3; or

[0121] (e) Alo 24MO 76(HC02)3. In certain additional embodiments, the metal organic framework of formula I may be selected from:

[0122] (a) Alo.45M054(HC02)3;

[0123] (b) AI0.5M0.5(HCO2)3;

[0124] (c) AIO.73MQ27(HC02)3; or

[0125] (d) AI(HCO2)3, such as:

[0126] (i) AI0.45M054(HCO2)3;

[0127] (ii) Alo.5Mo 5(HC02)3; or

[0128] (iii) AIO.73MO27(HC02)3. In certain exemplary embodiments, the metal organic framework of formula I may be Al046Mo.54(HC02)3.

[0129] In certain embodiments, the metal organic framework of formula I may be selected from:

[0130] (a) Alo46Feo54(HC02)3;

[0131] (b) AI0.5Fe0.5(HCO2)3;

[0132] (c) AI073Fe027(HCO2)3;

[0133] (d) AI(HCO2)3; or

[0134] (e) Alo24Feo.76(HC02)3. In certain additional embodiments, the metal organic framework of formula I may be selected from:

[0135] (a) Alo.46Feo.54(HC02)3;

[0136] (b) Alo5Feo5(HC02)3;

[0137] (c) Alo.73Feo.27(HC02)3; or

[0138] (d) AI(HCO2)3, such as:

[0139] (i) Alo.46Feo.54(HC02)3;

[0140] (ii) Al0.5Feo.5(HC02)3; or (iii) Alo.73Fe0.27(HC02)3. In certain exemplary embodiments, the metal organic framework of formula I may be Alo 46Feo.54(HC02)3.

[0141] Aluminium formate, AI(HCOO)3, an earth-abundant, inexpensive and highly porous metalorganic framework (MOF), can be obtained from a readily available precursor. AI(HCOO)s is thermally stable to around 250 °C. AI(HCOO)3 has excellent and highly selective adsorption capacity for carbon dioxide gas in the presence of nitrogen gas and water vapour, at and above room temperature. It can be applied in the removal of carbon dioxide from flue gases in industrial combustion processes. It could also be used for the selective adsorption of molecular oxygen from air. However, it has been noted that the presence of high amounts of water may limit the use of this sorbent material.

[0142] The MOFs according to formula I are very easy to make from readily available starting materials comprising an aqueous solution of aluminium oxide and formic acid (this also holds true for the materials disclosed herein that include Fe, Cr, or Mn). The MOFs according to formula I are very inexpensive compared to other metal-organic frameworks or solid sorbents that have been proposed for carbon dioxide capture.

[0143] As disclosed herein (e.g. see the examples below), the MOFs according to formula I can selectively adsorb carbon dioxide from a flue gas that also contains nitrogen and water vapour. It is highly selective for CO2compared with N2. It is also selective for the adsorption of oxygen from air. In contrast, sorbates for air separation (e.g., lithium-containing zeolites) are based upon the selective adsorption of N2rather than O2. This requires removing the largest component in air (N2: 80%; O219%). It is believed that these properties also apply to the other metal-organic frameworks of formula I disclosed herein.

[0144] The MOFs according to formula I can be used with water-containing flue gases above room temperature, e.g. at 50 °C, while maintaining high CO2uptake and sorption selectivity. As noted herein, this may be particularly the case when the relative humidity of the water vapour is less than or equal to 25% relative humidity. It is noted that many other metal-organic frameworks or solid sorbents are unstable in the presence of water vapour or lose significant CO2 uptake capacity above room temperature.

[0145] It has been surprisingly found that the coating of a hydrophobic polymer onto the surface of the MOFs according to formula I enables the resulting composite material to withstand an environment having a relative humidity of greater than 50%, such as from 50% to 100%, such as from 70 to 95%, such as about 80%. This stability may be demonstrated over prolonged periods of time. This period of time may be over a period of from 12 hours to 1 year, such as from 1 day to 30 days, such as 5 day to 10 days.

[0146] The MOFs used herein (e.g. AI(HCOO)s) have excellent stability against corrosive gases (e.g., SO2 and NO2), while maintaining high CO2 uptake and sorption selectivity. Details of this stability may be found in the examples section below.

[0147] The metal-organic frameworks of formula I (e.g., AI(HCOO)s) may be a mechanically robust material that is not particularly sensitive to water. This contrasts with other metal-organic frameworks, which tend to have poor mechanical properties and are sensitive to humidity.

[0148] The metal organic framework of formula I is provided in the form of a plurality of crystals, each having a surface, and the hydrophobic polymer is coated onto the surface of the metal organic framework crystals. The coating may be partial coating or a full coating. The term partial may refer to a coating covering from 5 to 99% of the surface area of the MOF crystals, such as from 10 to 95%, such as from 90 to 99%, such as from 50 to 80%.

[0149] Without wishing to be bound by theory, it is believed that the hydrophobic polymer may be stabilized on the framework surface by hydrogen bonding.

[0150] The hydrophobic polymer may be any suitable hydrophobic polymeric material. In the present disclosure, the hydrophobic polymer may refer to one that has a water contact angle of >90°, such as from 100sto 130°, such as from 1 15sto 125s, such as about 120s. In certain embodiments, the hydrophobic polymer may be selected from one or more of the group consisting of perfluoropolyether (PFPE), poly(vinylidene fluoride-co-hexafluoropropylene), poly(2,2,2-trifluoroethyl methacrylate-co- 3-methacryloxypropyltrimethoxysilane) and polyvinylidene fluoride (PVDF). In certain exemplary embodiments, the hydrophobic polymer may be PVDF.

[0151] The composite material may be conveniently formed in situ by forming a mixture of formic acid, the hydrophobic polymer material and the percursor metal salts (e.g. aluminium hydroxide, and metal salts (Fe, Cr or Mn salts)) together and heated for a period of time to provide the MOF coated with the hydrophobic material. The excess formic acid may be removed by any suitable means (e.g. centrifugation and washing). The resulting composite material may be in an unactivated form and may then be activated through heating at a suitable temperature (e.g. from 90 to 200BC, such as about 150BC) for a suitable period of time (e.g. from 1 hour to 2 days, such as 24 hours) under reduced pressure (e.g. about 1 x 10“4mmHg). It is noted that the temperature selected should be one in which the polymeric material will survive and that the temperature and hence reduced pressure and time may be selected accordingly.

[0152] Suitable hydrophobic polymers that may be mentioned herein include, but are not limited to, perfluoropolyether (PFPE), poly(vinylidene fluoride-co-hexafluoropropylene) or the copolymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) and 3- methacryloxypropyltrimethoxysilane (MAPTMS) in the presence of NUS-MOF-3 will also suitable options due to their hydrophobic nature. These polymers can be stabilized on the surface of the MOF by hydrogen bonding. It demonstrated stability in both water and humid conditions, and its preparation via an in-situ method proved to be straightforward. Secondly, all polymers with a contact angle over 90° will not work because the polymer should coat the surface of the MOF uniformly; otherwise, the stability of the composite will not be intact.

[0153] The hydrophobic polymer may be present in any suitable amount. In certain embodiments, the hydrophobic polymer may be present in an amount of from 0.5 to 10 wt% of the entire weight of the composite material. In certain additional embodiments, the hydrophobic polymer may be present in an amount of from 5 to 7 wt%, such as about 6.7 wt% of the entire weight of the composite material.

[0154] In certain exemplary embodiments, the hydrophobic polymer may be PVDF and may be present in an amount of about 6.7 wt% of the entire weight of the composite material; and the metal organic framework of formula may be Al046Feo54(HC02)3.

[0155] The composite material as disclosed herein can be shaped into pellets, spheres, cylinders, or other architectures, and packed into adsorption beds for pressure or temperature swing adsorption. The composite material as disclosed herein can also be coated onto substrates such as polymers, ceramics, or metals for adsorption purposes. The activated metal-organic framework of formula I as disclosed herein can also be incorporated into polymer matrices for adsorption or membrane processes. The activated metal-organic framework of formula I as disclosed herein can also be synthesized directly on any substrate or surface. The metalorganic framework of formula I can be processed into different 3D shapes or architectures. In certain embodiments, the composite material may be provided in the form of a powder. As demonstrated in the Examples section below, the present composite material shows excellent CO2 uptake, superior CO2 / N2 selectivity and are highly stable in liquid water. As such, in certain embodiments, one or more of the following may apply:

[0156] (a) the composite material may display a CO2 adsorption value of from 3 to 6 (e.g. from about 4 to about 5, such as about 4.6 mmol / g) at 298 K and under 1 bar of CO2;

[0157] (b) the composite material may have a water contact angle of greater than 100s, such as from 105sto 130s, such as from 115sto 125s, such as about 120s, such as from 110sto 1 15s, such as from 1 12sto 1 14s; and

[0158] (c) the composite material may display a CO2 adsorption value of from 2 to 3 (e.g. about 2.3) mmol / g and from 300 to 400 (e.g. from 350 to 390, such as about 387) selectivity over N2at 298 K and under 1 bar of total pressure provided by a gas stream of CO2 and N2(15:85).

[0159] As will be appreciated, the above properties may be measured by conventional devices / methods known to the skilled person in the art and as provided in the Examples section below.

[0160] In a second aspect of the invention that may be mentioned herein, there is provided a method of adsorbing CO2 and / or O2 from a gas, comprising subjecting a metal-organic framework of formula I as described herein to a flow of a gas comprising one or both of CO2 and O2, optionally wherein the gas further comprises nitrogen and water vapour. In embodiments of the invention where water vapour is present, this may be present in an amount of from 25 % to 100% relative humidity such as from 50 to 99.9%, such as from 70 to 95%, such as about 80%.

[0161] As an example, composite materials disclosed herein containing adsorbed carbon dioxide can release the CO2 on mild heating, enabling the regeneration of the composite materials. In contrast, other metal-organic frameworks or solid sorbents are relatively unstable on heating, making their regeneration more difficult.

[0162] Therefore, in a third aspect of the invention, there is provided a method of releasing CO2 and / or O2 from a composite material as disclosed herein to which CO2 and / or O2 has been adsorbed, the process comprising:

[0163] (a) providing a composite material to which CO2and / or O2has been adsorbed; and

[0164] (b) activating it by subjecting it to: (i) a temperature of from 90 to 160 °C (e.g. from 100 to 150 °C, such as 120 °C) under reduced pressure for a period of time (e.g. from hour to 2 days, such as about 24 hours); or

[0165] (ii) a temperature of from 170 to 250 °C (e.g. from 175 to 185 °C, such as about 180 °C) under 1 atmosphere pressure for a period of time (e.g. from hour to 2 days, such as about 24 hours).

[0166] In a further aspect of the invention, there is provided a method of obtaining a composite material as disclosed herein, the method comprising the steps of:

[0167] (a) providing an unactivated composite material; and

[0168] (b) activating it by subjecting it to:

[0169] (i) a temperature of from 90 to 160 °C (e.g. from 100 to 150 °C, such as 120 °C) under reduced pressure for a period of time (e.g. from 1 hour to 2 days, such as about 24 hours); or

[0170] (ii) a temperature of from 170 to 250 °C (e.g. from 175 to 185 °C, such as about 180 °C) under 1 atmosphere pressure for a period of time (e.g. from 1 hour to 2 days, such as about 24 hours).

[0171] It will be appreciated that the method of providing a composite material of the current invention may also be used to recycle the material after being used in a method adsorption.

[0172] Further aspects and embodiments of the invention will now be discussed by reference to the following non-limiting examples.

[0173] EXAMPLES

[0174] Materials and chemicals

[0175] All reagents were purchased from commercial sources and used without further purification. Aluminium hydroxide (AI(OH)3, > 99%) and formic acid (> 98%) were obtained from Tokyo Chemical Industry (TCI) Co. Ltd. Iron hydroxide (Fe(OH)3, > 98%) was obtained from ACME Chemicals. Ethanol (> 99.5%) was obtained from Thermo Fisher Scientific Pte Ltd (Singapore). All studies utilized deionized water from Millipore-Q (Millipore, Billerica, MA, USA). Fe-formate MOF was synthesized following a previously reported method (Tian, Y. Q.; Zhao, Y. M.; Xu, H. J.; Chi, C. Y. CO2template synthesis of metal formates with a ReO3net. Inorg Chem 2007, 46 (5), 1612-1616). Physical measurements

[0176] The crystallinity of the samples was analyzed by powder XRD recorded on a Rigaku Miniflex 600 diffractometer using Cu K, radiation (A = 1 .540598 A; 40 kV, 15 mA) with a scan rate of 2.0 min1. Fourier-transform infrared (FT-IR) spectra were recorded on a Perkin Elmer FTIR spectrometer. Field emission scanning electron microscopy (FE-SEM) images and energy- dispersive X-ray spectroscopy (EDAX) patterns were recorded on the FEI Nova SEM-450 instrument. The metal contents of Al and Fe in the MOFs were determined by Agilent’s Inductively coupled plasma-optical emission spectrometry (ICP-OES). Thermogravimetric analyses (TGA) were performed on TA Instruments STD-600 at a heating rate of 10 K min-1up to 600°C with an air flow rate of 50 mL min1. The sample holders were alumina crucibles, and the amount of sample used in each measurement was -8mg. The data collected were analyzed using Universal Analysis software (version 4.4A) from TA Instruments. The1H nuclear magnetic resonance (NMR) spectra were recorded in DMSOd6 on a JEOL JNM-ECS- 400 spectrometer operating at 400 MHz.

[0177] Gas sorption and separation experiments

[0178] CO2 and N2sorption isotherms were collected at different temperatures on a Micromeritics ASAP 2020 instrument equipped with commercial software for data calculation and analysis. The test temperatures were controlled by soaking the sample cell in a circulating water bath (for 298 K) or an ice / ethanol mixture (for 273 K or 313 K). Before measurement, the sample (80 mg - 100 mg) was degassed at 150 °C for 24 h. The breakthrough experiments were performed in a stainless-steel fixed bed (4.6 mm inner diameter x 50 mm length) packed with powder samples. Before the breakthrough experiment, the fixed bed was heated at 150 °C under a helium flow for complete activation. The fixed bed was then cooled to room temperature, the gas mixtures (N2 / CO2) were introduced, and the outlet gas was monitored by mass spectrometry (Hidden QGA quantitative gas analysis system).

[0179] Reflux synthesis of AI / Fe(HCOO)3

[0180] The AI / Fe(HCOO)3 were synthesized by following previously reported procedur (Evans, H. A.; Mullangi, D.; Deng, Z.; Wang, Y.; Peh, S. B.; Wei, F.; Wang, J.; Brown, C. M.; Zhao, D.; Canepa, P.; et al. Aluminum formate, AI(HCOO)3: An earth-abundant, scalable, and highly selective material for CO2capture. Sci Adv 2022, 8 (44), eade1473e). In a typical synthesis, formic acid (100 ml) and aluminum hydroxide or iron hydroxide (0.015 mol) were refluxed in a 250-ml three-neck round-bottom flask at 100°C for 48 hours. Upon completion of the reaction, excess formic acid was removed via centrifugation, and the resulting light brown solid was washed extensively with ethanol and separated using vacuum filtration. The air-dried sample gave a yield of » 95% solid product of AI / Fe-formates. The air-dried samples were heated at 150°C for 24 hours under high vacuum (1 x 10"4mmHg) yielding quantitative amounts of the guest-free activated samples.

[0181] Hydrolysis test of ALF

[0182] ALF (100 mg) was placed in a 30-mL glass vial, and 10 mL of water was added. The vial was then securely sealed and left undisturbed at room temperature for 2 hours. The resulting solid was separated by centrifugation, washed thoroughly with ethanol, and heated at 150°C for 24 hours under high vacuum conditions (1 x 10'4mmHg), yielding samples for further analyses.

[0183] Reflux synthesis of FexAli.x-ALF solid solutions

[0184] The synthesis of FexAli.x-ALF solid solutions followed a procedure similar to that of ALF synthesis, with variations in the molar ratio of aluminium and iron metal ions ensuring that the total moles of AI(OH)3and Fe(OH)3were fixed at 1 mmol. In a typical synthesis, formic acid (100 mL), AI(OH)3(X mmol) and Fe(OH)3(1-x mmol) were refluxed in a 250-millilitre three- neck round-bottom flask at 100°C for 48 hours. Upon completion of the reaction, excess formic acid was removed via centrifugation. The resulting light brown solid was washed extensively with ethanol and separated using vacuum filtration and air-dried to afford a light brown solid product of FexAli-x-ALF (yield: 96%). The air-dried sample gave a yield of 96% white solid product of FexAli-x-ALF. The air-dried samples were heated at 150°C for 24 hours under high vacuum (1 x 10“4mmHg), yielding quantitative amounts of the guest-free activated solid solutions.

[0185] Hydrothermal Synthesis of FexAli.x-ALF-PVDF composite

[0186] In a typical synthesis, formic acid (10 mL) and PVDF (20 mg) was thoroughly mixed for 30 minutes in a Teflon liner. Subsequently, AI(OH)3(x mmol) and Fe(OH)3(1-x mmol) were added to this solution, ensuring that the total moles of AI(OH)3and Fe(OH)3were fixed at 1 mmol. The contents were placed in a 23-mL Teflon-lined Parr stainless steel autoclave and heated at 130°C (403 K) for 3 days followed by slow cooling to room temperature. After the reaction was complete, excess formic acid was removed by centrifugation, and the resulting solid was extensively washed with ethanol and then separated via vacuum filtration. The air-dried solid product, denoted as as-made FexAli.x-ALF-PVDF, was further treated by heating at 150°C for 24 hours under high vacuum (1 x 10~4mmHg), resulting in quantitative yields of guest-free sample (yield: 92%).

[0187] Reflux synthesis of FexAli.x-ALF-PVDF composite In a 250-mil li liter three-neck round-bottom flask, a mixture of 100 mL of formic acid and PVDF (20 mg) was thoroughly mixed for 30 minutes. Subsequently, AI(OH)3(x mmol) and Fe(OH)3(1 -x mmol) were added to this solution, followed by refluxing at 100°C for 48 hours. After the reaction was complete, excess formic acid was removed by centrifugation, and the resulting solid was extensively washed with ethanol and then separated via vacuum filtration. The airdried solid product, denoted as as-made FexAli.x-ALF-PVDF, was further treated by heating at 150°C for 24 hours under high vacuum (1 x 10~4mmHg), resulting in quantitative yields of guest-free sample (yield: 89%).

[0188] Analysis of gas adsorption isotherms

[0189] Clausius-Clapeyron equation (eq. 1 ) was used to calculate the enthalpies of carbon dioxide adsorption and by using the Langmuir-Freundlich equation (Yang, R. T. Gas Separation By Adsorption Processes; World Scientific Publishing Company, 1997), an accurate fit was retrieved to get a precise prediction of CO2 adsorbed at saturation. A modification of the Clausius-Clapeyron equ where Pi and P2 = pressures for isotherm at 273 K and 298 K, respectively; T1 and T2= temperatures for isotherm at 273 K and 298 K, respectively; AHads = enthalpy of adsorption; R = universal gas constant = 8.314 J / K / mol. The pressure is a function of the amount of gas adsorbed which was determined by using the Langmuir-Freundlich fit. where Q = moles of gas adsorbed; Qm= moles of gas adsorbed at saturation; B and t = constants; P = Pressure.

[0190] By rearranging equation (ii) we get equation (3) Substituting equation (3) into equation (1 ) we get equation (4):

[0191] In equation (4), subscripts 1 and 2 represent data corresponding to 273 K and 298 K, respectively.

[0192] Breakthrough measurements

[0193] The breakthrough experiments were conducted using a homebuilt setup as illustrated in FIG.

[0194] 6. Gas cylinders containing argon (99.95%), a 15 / 85 mixture of CO2 and N2, nitrogen (99.95%), and helium (99.95%) were sourced from Air Liquide Singapore Pte Ltd. Powder samples were pelletized before loading into breakthrough columns. The stainless-steel columns used to hold the metal-organic framework (MOF) powders are 4 cm in length with an inner diameter of 0.3 cm. Metal mesh and cotton wool were placed at both ends of the column to prevent sample powders from contaminating the system. A glass fiber heating tape was employed to regulate the temperature for column activation, regeneration, and breakthrough experiments at temperatures above room temperature. The temperature of the heating tape (Omega DHT102040LD) was monitored by an Omega thermocouple (5SC-TT-K-30-36) and controlled by an Omron E5CC microcontroller. Gas composition at the column's exit was analyzed using a Hiden QGA quantitative gas analysis system. The flow rate for each gas component was determined using an internal argon flow reference with a fixed flow rate of 5 ± 0.05 standard cubic centimetres per minute (seem). Before conducting the breakthrough experiments, the adsorption columns were activated by purging a constant helium flow (5 ± 0.1 seem) through the column at a set temperature of 120°C for at least 12 hours, ensuring that no solvent or moisture signals were detected by the mass spectrometer. For the dry gas breakthrough experiments, a premixed flow of 15 / 85 CO2 / N2, with a total flow rate of 5 ± 0.05 seem, was stabilized for 40 minutes before being introduced into the column. For the wet gas breakthrough experiments, a helium flow (5 ± 0.05 seem) was passed through a water reservoir to create a relative humidity of 85% at 25°C (298 K), as determined by an Omega RH318 hygro-thermometer. This helium flow was used to saturate the adsorption columns before introducing the 15 / 85 CO2 / N2mixed gas (5 ± 0.05 seem) into the column.

[0195] Adsorption capacity and selectivity calculations based on breakthrough data.

[0196] Based on the mass balance of a specific gas component within the mixed gas throughout the entire packed column (inflow minus outflow equals accumulation), incorporating the dead volume of the setup (the volume inside the setup excluding the column), it can be deduced that where £ represents the bed porosity estimated based on the crystal density of the adsorbents, vQstands for the total interstitial gas velocity at the column inlet in meters per second, Co denotes the inlet gas concentration in moles per cubic meter, A represents the cross- sectional area of the column in square meters, tcsignifies the elution time in seconds, vLindicates the interstitial gas velocity at the exit of the column in meters per second, Ctrepresents the exit gas concentration in moles per cubic meter, Cedenotes the average gas concentration in the column in moles per cubic meter, Vd represents the dead volume of the setup in cubic meters, L signifies the column length in meters, and qeis the equilibrium concentration of adsorbate in the adsorbent in moles per cubic meter corresponding to the average column pressure Pe(calculated below). By dividing both sides of equation (5) by the gas molar flow rate of this component at the column inlet, equation (5) can be rearranged as

[0197] The gas concentration at the inlet of the column can be calculated by the following equation, where yo and Pmare the gas composition and pressure (kilopascals) at the inlet (upstream) of the column.

[0198] According to Darcy’s law, we assume a linear pressure profile in the bed. Therefore, the average column pressure (Pe) and average gas concentration (Ce) can be calculated as where ytand Pout are the gas composition and pressure (kilopascals) at the outlet

[0199] (downstream) of the column. Equation (6) can be further rearranged as

[0200] The dead volume item in the above equation can be obtained by performing the dead volume breakthrough experiments using the bypass of the setup and by performing the integration as where t’cis the elution time of the dead volume breakthrough experiments and 'feiank is the mean residence corresponding to the setup dead volume. Breakthrough selectivity was calculated using equation (f 2) where Ceiis the equilibrium concentration of component / ' in gas phase and qeiis the gas concentration of component / ' in the adsorbent.

[0201] Calculation of CO2 / N sorption selectivity

[0202] The gas adsorption selectivity of CO2and N2is defined by the following equation, where q^ and q2are the molar loading in the adsorbed phase in the mixture, mmol g1, yi and y2(=1 - y represent the mole fraction of CO2and N2in the feed gas. Density functional theory computations

[0203] First-principles density functional theory (DFT) calculations were performed using the Vienna ab initio Simulation Package (VASP). The projected augmented wave (PAW) potentials were used for DFT calculations where the following electrons were explicitly included: Al Ss^1, Fe 4s23c / 7, H 1 s1, C 2s22p2, N 2s22p3, and O 2s22p4. The exchange-correlation energy was computed at the generalized gradient approximation (GGA-PBE) level. The open shell Fe-3d orbitals were treated using a simplified DFT+U approach with the difference of effective onsite Coulomb (U) and exchange (J) parameters to be U-J = 4 eV. The geometry optimization started from the crystal structure as identified by Mullangi et al (Mullangi, D.; Evans, H. A.; Yildirim, T.; Wang, Y.; Deng, Z.; Zhang, Z.; Mai, T. T.; Wei, F.; Wang, J.; Hight Walker, A. R.; et al. Noncryogenic Air Separation Using Aluminum Formate AI(HCOO)s (ALF). J Am Chem Soo 2023, 145 (17), 9850-9856) and modified to an ordered Al-Fe configuration in a 50:50 composition. Then, it was fully relaxed until the interatomic forces were less than 0.01 eV / A. The adsorption energies were computed using equation (14),

[0204] Eads = (EALF+adsorbates—EALF—nEadsorbate) / n . (14) where Eads, EALF+adsorbates, EALF, Ea SOrbate and n are adsorption energy, DFT total energies of ALF with adsorbates, without adsorbates, and total number of adsorbates in cavities, respectively. EALF+adsorbates were computed by placing the adsorbate at the center of cavity and fully relaxed using the same criteria as described above, where Eadsorbate were computed by putting the adsorbate in a 10Ax10Ax10A empty box.

[0205] Example 1 : Synthesis of ALF derivatives and their behavior in water.

[0206] The ALF and Fe-formate MOFs were synthesized using a reflux method by following previously reported procedures (FIG. 1 , see details above) (Chakraborty, D.; Yurdusen, A.; Mouchaham, G.; Nouar, F.; Serre, C. Large-Scale Production of Metal-Organic Frameworks. Adv. Fund. Mater. 2023, 34 (43), No. 2309089; Tian, Y. Q.; Zhao, Y. M.; Xu, H. J.; Chi, C. Y. CO2template synthesis of metal formates with a ReO3net. Inorg. Chem. 2007, 46 (5), 1612-1616). Although manganese (Mn), indium (In), and gallium (Ga) formates with the ReO3structure are well-documented in the literature, In and Ga formates are significantly limited by their high costs, making them unsuitable for practical large-scale applications. In addition, it has not been demonstrated that they can be successfully activated. In the case of Mn-formate, it is only stable at low temperatures (4 °C). Therefore, Fe and Al metals were selected for MOF preparation due to their low cost and greater stability. The phase purity of the resulting bulk metal formates (Al / Fe) was confirmed by comparing the experimentally collected powder X- ray diffraction (PXRD) data with the simulated patterns of ALF (FIG. 8). Note that ALF refers to the activated material rather than the as-made aluminium formate, which has guest species in its cavities. However, Fe-formate collapsed upon activation due to the oxidation of formate linkers by Fe3+. PXRD analysis indicated its transformation into Fe2O3upon activation (FIG. 9), while the disappearance of all the Fourier-transform infrared (FTIR) peaks of Fe-formate confirmed the decomposition of the framework (FIG. 10).

[0207] The crystal structures of activated ALF materials are of the ReO3type and exhibit several distinct types of ultra-microporous cavities. ALF has two types of cavities: the small cavity (SC) and the large cavity (LC). The SCs constitute three-quarters of ALF total cavities, with the remaining quarter being LCs. The SCs distinguish themselves by having inward-facing hydrogens of the formate ligands. During CO2adsorption, these inward-facing hydrogens create a hydrogen bond “hand-in-glove” association with adsorbed CO2. The LCs have no inward-facing hydrogen. In terms of cavity arrangement, there are two kinds of interpenetrating channels. One channel is made up entirely of SCs (FIG. 2a), while the other has alternating SCs and LCs (FIG. 2a). This unique cavity confinement by hydrogen atoms makes ALF a promising candidate for selective CO2adsorption with good selectivity over N2and hydrocarbons. However, as noted above, ALF is unstable in high humidity conditions. When subjected to immersion in water under room temperature conditions (see above), ALF degrades, as observed by PXRD (FIG. 8). The experimental PXRD pattern corresponds closely to the simulated PXRD pattern of AI(HCOO)2(OH), indicating that hydrolysis of ALF occurs according to the reaction: [AI(HCOO)3+ H2O -»■ AI(HCOO)2(OH) + HCOOH] (FIG. 8). The absence of the carbonyl stretching frequency, along with the appearance of a new O-H bending frequency in the hydrolyzed ALF, confirms that the formate group has been replaced by a hydroxyl (-OH) group (FIG. 11 ). Additionally, formic acid was detected in the1H nuclear magnetic resonance (NMR) spectra of liquid aliquots of the ALF filtrate, again indicating that hydroxyl units have replaced some formate groups, resulting in the formation of linear bridging groups (FIG. 12). Furthermore, the water contact angle measurement revealed that ALF exhibited a contact angle of 39°, clearly indicating its hydrophilic nature (FIG. 3g). These experiments collectively confirm that ALF is unsuitable for carbon capture scenarios involving high humidity without a precapture drying step.

[0208] Example 2: Synthesis and Properties of ALF-Polymer Composites.

[0209] To address the water sensitivity issue, ALF-polymer composites were prepared using several hydrophobic polymers (poly(vinyl formal) (PVF), perfluoropolyether (PFPE), and polyvinylidene fluoride (PVDF)) during the synthesis of ALF (FIG. 1). The nonfluorinated ALF- PVF composite proved to be unstable in water over an extended period. After 24 h of soaking in water, peaks corresponding to AI(HCOO)2(OH) appeared, indicating material degradation (FIG. 13). Consequently, this polymer was excluded from further consideration. Subsequently, PFPE was found to be completely immiscible in formic acid, resulting in a nonuniform MOF- polymer composite. However, the ALF-PVDF composite appeared phase-pure with excellent crystallinity (FIG. 3a). The thermogravimetric analysis (TGA) analysis indicated the presence of 6.7 wt % PVDF in the ALF-PVDF composite, as well as enhanced thermal stability to almost 300 °C after activating the as-made ALF-PVDF (FIG. 14). Importantly, ALF-PVDF exhibits high hydrophobicity, as evidenced by a water contact angle of 114° (FIG. 15). Comparatively, the CO2 uptake of the ALF-PVDF composite decreased to 3.4 mmol / g (298 K, 1 bar), whereas pristine ALF showed a higher CO2 uptake of 3.9 mmol / g under identical conditions (FIG. 16). Therefore, further chemical modification of ALF to be moisture- and humidity-stable was attempted while preserving its CO2 uptake and CO2 / N2 selectivity properties.

[0210] Example 3: Synthesis and properties of Fe-ALFs and Fe-ALF-Polymer Composites.

[0211] To improve the CO2 uptake properties, iron was incorporated into the ALF network in a controlled manner by varying the Fe and Al atomic ratio during the synthesis, as outlined in FIG. 1. These materials are generally referred to as Fe-ALFs in the present disclosure; however, specific ratios will be denoted when pertinent. Notably, as the iron content increased from 0 to 50%, the symmetry of Fe-ALFs decreased from the space group Im to P23. The lower symmetry of certain Fe-ALFs compared to ALF was confirmed by the presence of extra Bragg reflections in the PXRD pattern, which can be attributed to the loss of the body-centering symmetry (FIG. 3a). The previous synchrotron X-ray powder analysis (Rayder, T. M.; Formalik, F.; Vornholt, S. ML; Frank, H.; Lee, S.; Alzayer, ML; Chen, Z.; Sengupta, D.; Islamoglu, T.; Paesani, F.; et al. Unveiling Unexpected Mlodulator-CO(2) Dynamics within aZirconium Metal- Organic Framework. J. Am. Chem. Soc. 2023, 145 (20), 1 1 195-1 1205) indicated that iron and aluminum are ordered for compositions near the 50 / 50 Al / Fe ratio, as opposed to forming a solid solution (FIG. 2b). Structurally, the specific Fe-ALF AI0.46Fe0.54-ALF comprises both smaller cavities (where formate hydrogens point more toward the center of the cavity) and larger cavities (where formate hydrogens do not point inward). Like ALF, in Alo.46Feo.54-ALF, the smaller cavities constitute three-quarters of the total cavities, with the remaining quarter being larger cavities (FIG. 2b). However, as Alo4sFeo 54-ALF has lower symmetry, there is a further distinction between the smaller and larger cavities. Crystallographically, there are two small and two large cavities, with the Wyckoff cavity centers being at 3d / 3c and 1 b / 1 a, respectively (FIG. 2c, FIG. 17). The root of this distortion of the cavities appears to be caused by the mismatch of the Al and Fe ionic radii. As such, the formate ligands are more angled, and the metal octahedra more tilted (FIG. 2b, FIG. 2c).

[0212] The phase purity of all bulk Fe-ALFs was confirmed by comparing the experimentally collected PXRD data with simulated patterns of Fe-ALFs (FIG. 18). Inductively coupled plasma-optical emission spectrometry (ICP-OES) data revealed that the synthetic compositions of Fe-ALFs with x = 0.25, 0.50, and 0.75 are in fact Alo.72Feo 28-ALF, Alo48Feo 52-ALF, and Alo23Feo.77-ALF, respectively. These results are very close to the ICP-OES data for Fe-ALF-PVDF with similar Fe / AI ratios: Alo 73Feo.27-ALF-PVDF, Alo46Feo.54-ALF-PVDF, and Alo.24Feo.76-ALF-PVDF, respectively.

[0213] Additionally, FTIR spectra of Fe-ALFs exhibited two distinct characteristic peaks for carbonyl at 1597 and 1553 cm-1, while ALF showed a single peak at 1603 cm-1, supporting the alternating presence of Fe and Al (FIG. 19). Moreover, thermogravimetric analysis showed that Fe-ALF was stable up to 180 °C (FIG. 3b). Field emission scanning electron microscopy (FE-SEM) analysis revealed that the Fe-ALF compounds maintained their cubic morphology like ALF (FIG. 3c, FIG. 3d), and energy dispersive X-ray spectroscopy (EDS) supported the presence of all the constitution elements Al, Fe, C, and O in the Fe-ALF (FIG. 20). In addition, the weight percentages of various elements are well-matched with the ICP-OES results (Table 1). The CO2 sorption tests found that Alo.46Feo54-ALF exhibited a higher CO2 uptake of 5.1 mmol / g (298 K, 1 bar) compared to other Fe-ALFs, as well as the pristine ALF (FIG. 21). This could be attributed to channels in the material having less pronounced formate hydrogen gating between cavities (FIG. 2). As the iron content in ALF increases from zero to 50%, the symmetry decreases from the space group Im3 lo P2.3, as discussed above. These structural changes enhance the CO2 uptake of the framework. Additionally, the higher atomic number of Fe compared to Al strengthens host-guest nonbonding interactions, further improving adsorption performance. Based on the previous work on O2 / N2 separation, iron doping was demonstrated to significantly enhance adsorption kinetics compared to ALF alone (Mullangi, D.; Evans, H. A.; Yildirim, T.; Wang, Y.; Deng, Z.; Zhang, Z.; Mai, T. T.; Wei, F.; Wang, J.; Flight Walker, A. R.; et al. Noncryogenic Air Separation Using Aluminum Formate AI(HCOO)3 (ALF). J. Am. Chem. Soc. 2023, 145 (17), 9850-9856). This improvement arises from an increase in aperture size due to the substitution of Al with the larger Fe ion. Furthermore, Al / Fe ordering at the 50:50 composition in this study induces a symmetry change, further opening the framework windows and enhancing gas adsorption properties. Although Alo.46Feo.54-ALF demonstrates significant potential for CO2adsorption, it is still prone to instability under humid and moist conditions, much like ALF itself. It shows a water contact angle of 36°, clearly indicating its hydrophilic nature (FIG. 3h). Additionally, PXRD analysis of water-soaked Fe- ALFs at room temperature revealed that the Fe-ALFs are relatively unstable in water, transforming into AI(OH)(HCOO)2upon water soaking (FIG. 22).

[0214] Table 1. EDS weight percentages of elements in various Fe-ALF samples

[0215] A Fe-ALF-PVDF composite was synthesized to render it hydrophobic and improve its stability in humid and moist conditions. The PXRD analysis of the synthesized bulk Alo.46Feo 54-ALF- PVDF confirmed retention of crystallinity after passivation with PVDF polymer (FIG. 3a). Further, FTIR spectra exhibited the characteristic peaks for the C-F bonds of PVDF at 1 182 and 1210 cm-1, supporting the presence of PVDF in the composite material (FIG. 23). Moreover, thermogravimetric analysis confirmed that 5.8 wt % of PVDF was incorporated in the framework. The composite material remained stable up to 220 °C, after which decomposition began (FIG. 3b). A second weight loss near 325 °C, corresponding to the decomposition of PVDF, matches the known decomposition temperature of PVDF (316 °C). Under an air atmosphere, both the composite and Fe-ALF decomposed further into metal oxide. After 500 °C, the residue consisted entirely of metal oxide. Interestingly, the residual weight loss aligns well with the polymer content (5.7 and 5.8 wt %), confirming the presence of 5.8 wt % PVDF in the composite material. Notably, the incorporation of iron reduces the lattice energy due to the larger size of Fe3+compared with Al3+. This renders the iron-doped materials slightly less stable than ALF itself. Note, too, that the pure Fe analog of as-made Fe(HCOO)3 cannot be activated due to the redox behavior of Fe. FE-SEM analysis revealed that Fe-ALFPVDF samples maintained their cubic particle morphology (FIG. 3e, FIG. 3f). The PVDF composite resulted in a polymer coating visible on the Fe-ALF crystal surfaces (FIG. 3f), and the cubic crystals appear less monodispersed in the composite (FIG. 3e). EDS supported the presence of all the constitution elements Al, Fe, C, O, and F in the composite (FIG. 20). The water stability of the composite was studied by soaking Fe-ALF-PVDF in water for 1 week. The PXRD of water-soaked material was well matched with activated Alo.46Feo54- ALF-PVDF (albeit with a slight loss of crystallinity), revealing the improved water stability of the stabilized framework (FIG. 24). The water contact angle measurement showed a contact angle of 112°, confirming enhanced hydrophobicity (FIG. 3i). The humidity stability of the composite was tested at 80% RH. It demonstrated good stability at room temperature under these humid conditions (FIG. 24), indicating that the composite is well-suited for CO2 capture in humid environments.

[0216] Example 4: Gas Sorption Behavior of Fe-ALF-PVDF Composites.

[0217] The analysis of CO2 adsorption revealed that the Alo.46Feo.54-ALF-PVDF composite exhibited a CO2 uptake of 4.6 mmol / g at 298 K and 1 bar, surpassing the uptake observed at 273 K and 1 bar (3.8 mmol / g, FIG. 4a, FIG. 25) due to improved gas diffusion kinetics at higher temperatures. Furthermore, at 313 K and 1 bar, the CO2 uptake remained notably high at 4.58 mmol / g, which is very close to the CO2 uptake observed at 298 K and 1 bar (FIG. 4a, FIG. 25). This consistency underscores the stability and reliability of the composite’s CO2 adsorption capabilities across a range of temperatures. ALF and its Fe-doped analogues are examples of sorbents with “Critical Gating Temperatures” (CGT) for CO2 adsorption. CGT refers to the temperature at which a material undergoes a transition in its adsorption behavior, often linked to structural flexibility or gate-opening mechanisms. While rigid microporous MOFs generally show continuous adsorption, materials with framework dynamics can exhibit temperaturedependent structural changes. Below the CGT, the framework remains “closed”, restricting CO2 access. However, as the temperature rises, thermal energy triggers a structural transition, opening the pores for adsorption. This interesting behavior is crucial for optimizing gas adsorption in temperature-sensitive applications.

[0218] Of significant note is the selective adsorption behaviour observed when comparing CO2 and N2adsorption at 298 K (FIG. 4b). The composite exhibits a distinct preference for CO2 over N2, as evidenced by its ideal adsorbed solution theory (IAST) selectivity of 387 (298 K and 1 bar, FIG. 4b insert), which is even slightly higher than that of pristine ALF (368) under the same conditions (FIG. 4c). This selectivity highlights the potential of the composite for efficient CO2 capture applications compared with Fe-ALF and other benchmark materials such as CALF-20, UTSA-16, and Mg-MOF-74 (FIG. 4c). Notably, AI046Fe0.54-ALF-PVDF demonstrates selective CO2adsorption not only over N2but also over hydrocarbons such as CH4, C2H4, and C2H5, highlighting its potential for applications like biogas upgrading (FIG. 26).

[0219] Furthermore, the CO2 adsorption isotherms were analyzed using the Freundlich-Langmuir eq (FIG. 27 - FIG. 30). The resulting values of heat of adsorption (Qst), determined using the Clausius-Clapeyron equation, were found to be 42.8 and 39.6 kJ mol-1for Alo.46Feo.54-ALF and AI046Fe0.54-ALF-PVDF, respectively (FIG. 31 , FIG. 32). This indicates a significant affinity of the composite for CO2molecules. The reduced affinity of the AI0.46Fe0.54-ALF-PVDF composite for water vapor, as observed in the adsorption isotherm (FIG. 4d) , can be attributed to the hydrophobic nature of the PVDF coating. This characteristic was further confirmed through differential scanning calorimetry (DSC) measurements, which quantified the binding energy for water adsorption. The measured binding energy of 5.5 kJ / mol substantiates the hydrophobic behavior of the composite (FIG. 33). By limiting water interactions with the MOF surface, the hydrophobic PVDF layer serves as a protective barrier, enhancing the resistance of the composite to moisture-induced degradation. This improved stability not only preserves the gas adsorption capacity but also optimizes water vapor uptake. As a result, the Alo.46Feo.54- ALF-PVDF composite demonstrates significant potential for practical applications in gas separation and air dehumidification. The water affinity of the composite was found to be lower than that of well-known MOFs such as MOF-74-Ni and UiO-66-(OH)2.

[0220] Density functional theory calculations have also been performed to estimate the heat of adsorption of CO2 and several other small molecules into the P23 structure of Alo.46Feo.54-ALF (Table 2, FIG. 5). The details of computational methodologies can be found above. The heats of adsorption in both the larger and smaller cavities are predicted to be very similar to those in ALF (Table 2). In addition, the calculated heats of adsorption in the two small cavities (48.3 and 48.4 kJ / mol) are in reasonable agreement with the experimental heat of adsorption at low loadings, which is 42.8 kJ / mol (FIG. 31). Experiments were conducted to evaluate the practical utility of the Alo46Feo.54-ALF-PVDF composite. Recognizing that moisture is a common challenge in most carbon capture processes, the Alo46Feo 54-ALF-PVDF composite was first activated by purging it with helium at 423 K overnight to remove any adsorbed water. Under these circumstances, Alo46Feo.54-ALF-PVDF demonstrated notable efficacy, as evidenced by the dynamic column breakthrough experiments conducted at 298 K using a simulated feed comprising a 15 / 85 mixture of CO2 and N2. Notably, the progression of the CO2 concentration fronts experienced considerable delay compared to that of N2due to the selective adsorption facilitated by the composite within the column (FIG. 4e; detailed experimental procedures are provided above).

[0221] Table 2. Adsorption energies from first-principles calculations (in kilojoules per mole). The following cavities are computed for the P23 Alo 5Feo 5-ALF structure: LC1 : corner, LC2: body center, SC1 : face center, SC2: edge center. Comparisons to AI(HCOO)s and Fe(HCOO)s in / m”3 are also shown.

[0222] The calculated dry C02coadsorption capacity amounted to 3.6 mmol g-1, contrasting sharply with the minimal N2coadsorption capacity, which was less than 0.1 mmol g-1, affording a CO2 / N2 selectivity of 308. To evaluate the performance of AI0.46Fe054-ALF-PVDF in the presence of high humidity, a breakthrough experiment was conducted under 85% RH conditions. The Alo 46Feo.54-ALF-PVDF was presaturated at 85% RH to assess the impact of moisture on CO2adsorption through a multicomponent dynamic column breakthrough experiment. Interestingly, even with the saturated humidity, Alo.46Feo54-ALF-PVDF could still effectively separate CO2 / N2, with a CO2coadsorption capacity of 2.7 mmol g-1at 298 K (FIG. 4f). This increased water resilience was attributed to the hydrophobicity of Alo.46Feo54-ALF- PVDF. Although water impacted total adsorption, selectivity performance remained robust (284). Further, to validate the CO2adsorption in the moisture-saturated Alo.46Feo 54-ALF-PVDF column, the CO2desorption curve was measured at 85% RH. After correcting for the dead volume, the CO2yield was 2.6 mmol g-1, which closely matched the dynamic adsorption values (2.7 mmol g~1, FIG. 34).

[0223] Recognizing the importance of evaluating the material’s performance with wet gas, additional breakthrough experiments were performed by using a 15 / 85 mixture of CO2and N2at 91 % RH. The results demonstrated that the Fe-ALF-PVDF material effectively maintained CO2 / N2separation, achieving a CO2coadsorption capacity of 2.9 mmol g’1at 298 K (FIG. 35). Additionally, recyclability is essential for industrial applications, so four cycles of breakthrough experiments at 85% RH (FIG. 4f) were conducted. The results showed that Alo.46Feo 54-ALF- PVDF exhibited excellent recyclability even after multiple breakthrough tests in the presence of moisture (FIG. 4f). This indicates that Alo46Feo54-ALF-PVDF not only withstands repeated use but also remains effective in capturing CO2under humid conditions, which is critical for practical applications in carbon capture processes. Breakthrough experiments for a 15 / 85 CO2 / N2gas mixture were conducted under both dry and wet conditions to assess the performance of Fe-ALF. Under wet conditions, Fe-ALF exhibited a significant reduction in CO2capture capacity (from 2.5 to 0.8 mmol g’1) due to framework decomposition (FIG. 36 and FIG. 37). In contrast, the polymer coating in Fe-ALF-PVDF significantly improved stability and CO2selectivity in the presence of humidity, as evidenced by the retention of CO2capture capacity under wet conditions (FIG. 4f). These results highlight the effectiveness of PVDF in mitigating moisture-induced degradation, enhancing the material’s practical applicability. Two types of recycling experiments were also conducted under highly humid conditions. The first experiment included exposing the sample to 85% RH at 298 K for 12 h before activation at 120 °C and subsequent CO2 adsorption at 298 K. This experiment showed that the Alo.4eFeo54- ALF-PVDF material maintained its ability to adsorb CO2 during 10 cycles over a period of 30 days (FIG. 38). Additionally, in situ GA cycling studies of Alo.46Feo.54-ALF-PVDF under a wet CO2 atmosphere were conducted (FIG. 39). The graph illustrates 45 adsorption / desorption cycles under humid CO2 with temperature swings between 313 and 353 K. For those 5 min cycles, the Alo.46Feo54-ALF-PVDF showed sustained adsorption without a significant decrease in capacity (<5%). Combined with the breakthrough experiments under humid CO2 conditions, these findings highlight the excellent water resistance and sustained CO2capture capability of Fe-ALF-PVDF in humid conditions.

[0224] Conclusion

[0225] In summary, this work showcases improving adsorptive CO2 capture by using advanced framework sorbents engineered for high selectivity, stability, and ease of regeneration. Ultra- microporous MOFs, specifically Fe-ALFs, were synthesized to achieve this goal, with their moisture and humidity stability enhanced by passivating with polyvinylidene fluoride (Fe-ALF- PVDF). Gas adsorption tests on Alo.46Feo54-ALF-PVDF revealed the composite’s exceptional CO2adsorption capacities (4.6 mmol / g at 298 K and 1 bar) and remarkable CO2 / N2 selectivity (387). Compared to similar-performing MOFs, ALF-like MOFs are expected to offer significant cost advantages due to their simplicity, low cost, and streamlined manufacturing characteristics. Overall, this design strategy has created a superior adsorbent material for CO2 capture from humid post-combustion flue gas streams, as well as other gas streams containing CO2, surpassing ALF itself and boosting its potential for utility in carbon capture technologies under practical conditions. Further work examining optimum humidity envelope conditions for sustained performance is needed to verify long-term stability.

Claims

CLAIMS1 . A composite material comprising: a hydrophobic polymer; and a metal organic framework of formula I:AII-XMX(HCO2)3where:M represents Fe, Cr, or Mn; and x is from 0 to 0.9999, wherein the metal organic framework is provided in the form of a plurality of crystals, each having a surface, and the hydrophobic polymer is coated onto the surface of the metal organic framework crystals.

2. The composite material according to Claim 1 , wherein x is from 0 to 0.85.

3. The composite material according to Claim 2, wherein x is from 0.2 to 0.8, such as from 0.27 to 0.76, such as from 0.5 to 0.54.

4. The composite material according to any one of the preceding claims wherein the metal organic framework of formula I is selected from:(a) Alo.46Mo54(HC02)3l(b) AI0.5M0.5(HCO2)3;(c) Alo.7sMo27(HC02)3;(d) AI(HCO2)3; or(e) AIO.24MQ 76(HC02)3.

5. The composite material according to Claim 4, wherein the metal organic framework of formula I is selected from:(a) Alo.4sMo54(HC02)3;(b) AI0.5M05(HCO2)3;(c) AI073M027(HCO2)3; or(d) AI(HCO2)3, such as:(i) AIO.46MQ 54(HC02)3;(ii) AI05M05(HCO2)3; or(iii) AIO.73MQ27(HC02)3.

6. The composite material according to Claim 5, wherein the metal organic framework of formula I is AI046M0.54(HCO2)3.

7. The composite material according to any one of the preceding claims wherein the metal organic framework of formula I is selected from:(a) Alo.46Fe0.54(HC02)3;(b) Al05Feo5(HC02)3;(c) Alo.73Feo.27(HC02)3;(d) AI(HCO2)3; or(e) Alo.24Feo.76(HC02)s.

8. The composite material according to Claim 7, wherein the metal organic framework of formula I is selected from:(a) Alo45Feo54(HC02)3;(b) AI0.5Fe0.5(HCO2)3;(c) Alo73Fe027(HC02)3; or(d) AI(HCO2)3, such as:(i) Alo.4sFeo.54(HC02)3;(ii) Al0.5Feo.5(HC02)3; or(iii) Alo73Feo27(HC02)3.

9. The composite material according to Claim 8, wherein the metal organic framework of formula I is Al046Feo.54(HC02)3.

10. The composite material according to any one of the preceding claims wherein the hydrophobic polymer is one that has a water contact angle of >90B, such as from 100Bto 130s, such as from 115sto 125s, such as about 120s.11 . The composite material according to any one of the preceding claims wherein the hydrophobic polymer is selected from one or more of the group consisting of perfluoropolyether (PFPE), poly(vinylidene fluoride-co-hexafluoropropylene), poly(2,2,2- trifluoroethyl methacrylate-co- 3-methacryloxypropyltrimethoxysilane) and polyvinylidene fluoride (PVDF).

12. The composite material according to Claim 11 , wherein the hydrophobic polymer is PVDF.

13. The composite material according to any one of the preceding claims wherein the hydrophobic polymer is present in an amount of from 0.5 to 10 wt% of the entire weight of the composite material.

14. The composite material according to Claim 13, wherein the hydrophobic polymer is present in an amount of from 5 to 7 wt%, such as about 6.7 wt% of the entire weight of the composite material.

15. The composite material according to any one of the preceding claims wherein: the hydrophobic polymer is PVDF and is present in an amount of about 6.7 wt% of the entire weight of the composite material; and the metal organic framework of formula I is Alo,46Feo.54(HC02)3.

16. The composite material according to any one of the preceding claims wherein the composite material is provided in the form of a powder.

17. The composite material according to any one of the preceding claims wherein the composite material has a water contact angle of greater than 100B, such as from 105“ to 130s, such as from 115sto 125s, such as about 120s, such as from 1 10“ to 115s, such as from 1 12sto 114s.

18. The composite material according to any one of the preceding claims wherein the composite material displays a CO2 adsorption value of from 3 to 6 (e.g. from about 4 to about 5, such as about 4.6 mmol / g) at 298 K and under 1 bar of CO2.

19. The composite material according to any one of the preceding claims, wherein the composite material displays a CO2adsorption value of from 2 to 3 (e.g. about 2.3) mmol / g and from 300 to 400 (e.g. from 350 to 390, such as about 387) selectivity over N2at 298 K and under 1 bar of total pressure provided by a gas stream of CO2 and N2(15:85).

20. A method of adsorbing CO2 and / or O2 from a gas, comprising subjecting a composite material according to any one of Clauses 1 to 19 to a flow of a gas comprising one or both of CO2 and O2.21 . The method according to Claim 20, wherein the gas further comprises nitrogen and water vapour.

22. The method according to Claim 20 or Claim 21 , wherein the gas has a relative humidity of from less than or equal to 25% to 100%.

23. The method according to Claim 22, wherein the gas has a relative humidity of from 50 to 100%, such as from 70 to 95%, such as about 80%.

24. A method of releasing CO2 and / or O2 from a composite material according to any one of Claims 1 to 19 to which CO2and / or O2has been adsorbed, the process comprising:(a) providing a composite material to which CO2and / or O2has been adsorbed; and(b) activating it by subjecting it to:(i) a temperature of from 90 to 160 °C (e.g. from 100 to 150 °C, such as 120 °C) under reduced pressure for a period of time (e.g. from hour to 2 days, such as about 24 hours); or(ii) a temperature of from 170 to 250 °C (e.g. from 175 to 185 °C, such as about 180 °C) under 1 atmosphere pressure for a period of time (e.g. from hour to 2 days, such as about 24 hours).

25. A method of obtaining a composite material according to any one of Claims 1 to 19, the method comprising the steps of:(a) providing an unactivated composite material; and(b) activating it by subjecting it to:(i) a temperature of from 90 to 160 °C (e.g. from 100 to 150 °C, such as 120 °C) under reduced pressure for a period of time (e.g. from 1 hour to 2 days, such as about 24 hours); or(ii) a temperature of from 170 to 250 °C (e.g. from 175 to 185 °C, such as about 180 °C) under 1 atmosphere pressure for a period of time (e.g. from 1 hour to 2 days, such as about 24 hours).

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