阅读说明：本技术 金属有机骨架的生产和用途 (Production and use of metal-organic frameworks ) 是由 J·M·福尔科夫斯基 P·科图诺夫 Y·V·乔希 G·J·马亚诺 于 2020-04-01 设计创作，主要内容包括：一种生产具有柔性结构并包含铝和铁阳离子的双金属对苯二甲酸酯金属有机骨架(MOF)的方法包含使水溶性铝盐、螯合铁化合物和1,4-苯二甲酸或其盐与水和极性有机溶剂的无氟混合物在小于200℃的反应温度下接触以产生包含MOF的固体反应产物。(A method of producing a bimetallic terephthalate metal-organic framework (MOF) having a flexible structure and comprising aluminum and iron cations comprises contacting a water soluble aluminum salt, a chelated iron compound, and 1, 4-phthalic acid or a salt thereof with a fluorine-free mixture of water and a polar organic solvent at a reaction temperature of less than 200 ℃ to produce a solid reaction product comprising the MOF.)

1. A method of producing a bimetallic terephthalate metal-organic framework (MOF) having a flexible structure and comprising aluminum and iron cations, the method comprising:

(a) providing a fluorine-free mixture of water and a polar organic solvent;

(b) contacting a water soluble aluminum salt, a chelated iron compound, and 1, 4-phthalic acid or derivative or salt thereof with the mixture at a reaction temperature of less than 200 ℃ to produce a solid reaction product comprising MOF; and

(c) recovering the MOF from the mixture,

wherein the recovered MOF product is at N₂Exhibits a pattern comprising at least the characteristic lines listed in table 1 when subjected to X-ray diffraction analysis at 200 ℃ under a flowing atmosphere:

TABLE 1

2. The method of claim 1, wherein the polar solvent comprises at least one of dimethyl sulfoxide, dimethylacetamide, dimethylformamide, and ethylene glycol.

3. The method of claim 1, wherein the chelated iron compound comprises an iron diketonate compound.

4. The method of claim 1, wherein the chelated iron compound comprises at least one of iron acetylacetonate, tris (2, 6-dimethyl-3, 5-heptanedione) iron, and/or tris (2,2,6, 6-tetramethyl-3, 5-heptanedione) iron.

5. The method of claim 1, wherein the chelated iron compound is formed in situ during the contacting step (b).

6. The method of claim 1, wherein the chelated iron compound is preformed and added to the contacting step (b).

7. The process of claim 1, wherein the reaction temperature is from 25 ℃ to 150 ℃.

8. The method of claim 1, wherein said contacting is for at least 6 hours.

9. The method of claim 1, wherein the MOF recovered in (c) contains at least 10 mole% aluminum based on the total metal content of the MOF as determined by energy dispersive X-ray spectroscopy (EDX).

10. The method of claim 1, wherein the MOF recovered in (c) contains up to 90 mole% aluminum based on the total metal content of the MOF as determined by energy dispersive X-ray spectroscopy (EDX).

11. A method of producing a bimetallic terephthalate metal-organic framework (MOF) having a flexible structure and comprising aluminum and iron cations, the method comprising:

(a) providing a fluorine-free mixture of water and a polar organic solvent;

(b) contacting a water soluble aluminum salt, a chelated iron compound, and 1, 4-phthalic acid or derivative or salt thereof with the mixture at a reaction temperature of less than 200 ℃ to produce a solid reaction product comprising MOF; and

(c) recovering the MOF from the mixture,

wherein the recovered MOF product, when subjected to a methane adsorption measurement at 30 ℃, is at an inflection point in the methane adsorption isotherm at a pressure below 8 bar.

12. The method of claim 11, wherein the MOF product exhibits an adsorption capacity at 20 bar of methane of greater than 2mmol/g when subjected to a methane adsorption measurement at 30 ℃.

13. The method of claim 11, wherein the polar solvent comprises at least one of dimethyl sulfoxide, dimethylacetamide, dimethylformamide, and ethylene glycol.

14. The method of claim 11, wherein the chelated iron compound comprises an iron diketonate compound.

15. The method of claim 11, wherein the chelated iron compound comprises at least one of iron acetylacetonate, tris (2, 6-dimethyl-3, 5-heptanedione) iron, and/or tris (2,2,6, 6-tetramethyl-3, 5-heptanedione) iron.

16. The method of claim 11, wherein the chelated iron compound is formed in situ during the contacting step (b).

17. The method of claim 11, wherein the chelated iron compound is preformed and added to the contacting step (b).

18. The process of claim 11, wherein the reaction temperature is from 25 ℃ to 150 ℃.

19. The method of claim 11, wherein said contacting is performed for at least 6 hours.

20. The method of claim 11, wherein the MOF recovered in (c) contains at least 10 mole% aluminum based on the total metal content of the MOF as determined by energy dispersive X-ray spectroscopy (EDX).

21. The method of claim 11, wherein the MOF recovered in (c) contains up to 90 mole% aluminum based on the total metal content of the MOF as determined by energy dispersive X-ray spectroscopy (EDX).

22. A Metal Organic Framework (MOF) having the structure of MIL-53 and comprising iron and aluminum cations made by the method of claim 1.

23. An adsorbent comprising at least one C_4-A method of a hydrocarbon gas, the method comprising contacting the gas with the MOF of claim 22.

24. A Metal Organic Framework (MOF) having the structure of MIL-53 and comprising iron and aluminum cations made by the method of claim 11.

25. An adsorbent comprising at least one C_4-A method of a hydrocarbon gas, the method comprising contacting the gas with the MOF of claim 24.

Technical Field

The present disclosure relates to the production and use of Metal Organic Frameworks (MOFs), in particular terephthalate MOFs with flexible structures, such as MIL-53 and MOFs similar to MIL-53.

Background

Metal Organic Frameworks (MOFs) are porous crystalline materials prepared by self-assembly of metal ions and organic ligands. MOFs may have large pore volumes and up to 8,000m²Apparent surface area in g (apparent surface area). MOFs combine structural and chemical diversity such that they are attractive for many potential applications, including gas storage, gas separation and purification, sensing, catalysis, and drug delivery. The most significant advantage of MOFs over more traditional porous materials is the possibility of modulating host/guest interactions by selecting appropriate building blocks, i.e. metal ions and organic ligands, for the formation of MOFs. Furthermore, MOFs can exhibit unique structural features compared to pure inorganic zeolites (zeottypes), a notable example of which is the great structural flexibility in which reversible expansion and contraction can occur in response to changes in temperature or the introduction and removal of guest molecules.

One MOF material of particular interest is MIL-53. The material has the general chemical composition M^III(BDC) (OH) and consists of one-dimensional (1-D) chains of trans-linked metal-oxide octahedra cross-linked to each other by 1, 4-Benzandicarboxylate (BDC) dianions. In the simplest form of this material, the metal is trivalent and coordinates to four oxygen atoms from 1, 4-benzenedicarboxylic acid ester (1, 4-benzanedicarboxylate) and two oxygen atoms from trans-bridging μ 2-hydroxyl group in an octahedral environment. The interconnectivity of the 1-D metal oxide chains with the BDC linkages results in 1-D rhombohedral channels running parallel to the hydroxide chains(1-D, diamond-shaped channel). These channels are typically occupied by solvent and/or unreacted 1, 4-benzenedicarboxylic acid and can be evacuated using elevated temperatures or reduced pressures. The flexibility of the MIL-53 structure is well documented: with the addition of temperature, pressure or guest molecules, the framework can undergo atomic shifts involving a few angstroms while maintaining the structural topologyIs rapidly expanded.

The flexibility of the MIL-53 structure also depends on the nature of the metal and the organic linking anion. To date, attempts to alter the flexibility and adsorption properties of MIL-53 materials have focused primarily on modifying organic linkers with different functional groups. However, a simpler and more intuitive way to modify the MIL-53 behaviour is to synthesize bimetallic MIL-53 materials, in particular with metals that have antagonistic behaviour (antagonistic behavior) to the flexibility of the structure. For example, chromium and aluminum materials transform to a fully open or "LP" (macroporous) structure upon heating with a large increase in pore volume, while iron analogs undergo slight shrinkage of the structure. MIL-53(Fe) expands only slightly even upon further heating, especially maintaining the "NP" (narrow pore) structure.

Breeze, m.i.; clet, g.; campo, b.c.; vimont, a.; daturi, m.; greneche, J-M.; dent, a.j.; millange, F. and Walton, F.I. in an article entitled "Isophorphorus stabilization in a Flexible frame: Mixed-Metal, Mixed-valve MIL-53Type Materials", Inorg.chem.2013,52,8171-8172 describes a bimetallic method for modulating the adsorption properties of MIL-53. In this method, mixed iron-vanadium analogues of MIL-53 were synthesized by heating metal chlorides together with 1, 4-phthalic acid in a mixture of N, N' -dimethylformamide, water and hydrofluoric acid at temperatures ranging from 170 to 200 ℃ for up to 3 days. However, the ability to adjust the composition of MIL-53by this method is limited because the highest vanadium content that can be achieved is 50%. According to the authors, attempts to increase the vanadium content above this value led to "formation of the known V (III) phase MIL-68 (V)".

Nouar, f.; devic, t.; guillou, n.; gibson, e.; clet, g.; daturi, m.; vimont, a.; greneche J-M.; breeze, m.i.; walton, r.i.; llewellyn, p.l.; and Serre, C. in "Tuning the breaking leather of MIL-53by location", chem.Commun.2012,48, 10237-. This process involves heating a stoichiometric mixture of chromium nitrate, iron powder, hydrofluoric acid and terephthalic acid in water at 453K for 4 days. However, not only did the authors show the ability to precisely adjust the cation content and hence the adsorption properties by their synthetic techniques, such synthesis also required harsh mineralization conditions (high temperature, hydrofluoric acid) to incorporate iron into chromium-based materials.

Kim, m.; cahill, J.F; fei, H.; prather, k.a.; and Cohen, S.M. in an article entitled "Postsynthetic light and Cation Exchange in Robust Metal-Organic Frameworks", J.Am.chem.Soc.2012,134,18082-18088 describes an alternative process involving solid-solid Cation Exchange between, for example, MIL-53(Al) and MIL-53 (Fe). This mechanism, in addition to being indirect, produces materials with a large range of metal compositions. In their experiments, the authors observed that > 60% of the material remained unchanged (i.e. still containing 100% Fe or 100% Al). In addition, the authors do not specify the concentrations of iron and aluminium that they are able to obtain. But based on the results presented, it is expected that only an extremely wide distribution can be obtained.

There is therefore a need for new methods for producing MIL-53 and similar flexible MOFs in bimetallic form, which provide the ability to adjust the metal ratio to a wide extent and under fine control and still can be performed under mild conditions without the use of caustic/toxic solvents.

SUMMARY

In accordance with the present invention, it has now been found that Al/Fe-containing terephthalate MOFs (Al/Fe-conforming terephthalic MOFs) having a flexible structure conforming to MIL-53 can be produced from a fluorine-free mixed solvent system under relatively mild conditions. The method enables the adjustment of the Al to Fe ratio over a wide range and under fine control in order to obtain a unique and predictable adsorption phenomenon.

Accordingly, in one aspect, there is provided a method of producing a terephthalate Metal Organic Framework (MOF) having a flexible structure and comprising aluminum and iron cations, the method comprising:

(a) providing a fluorine-free mixture of water and a polar organic solvent;

(b) contacting a water soluble aluminum salt, a chelated iron compound, and 1, 4-phthalic acid or derivative or salt thereof with the mixture at a reaction temperature of less than 200 ℃ to produce a solid reaction product comprising MOF; and

(c) recovering the MOF from the mixture,

wherein the recovered MOF product is at N₂Exhibits a pattern comprising at least the characteristic lines listed in table 1 when subjected to X-ray diffraction analysis at 200 ℃ under a flowing atmosphere:

TABLE 1

In another aspect, there is provided a method of producing a terephthalate Metal Organic Framework (MOF) having a flexible structure and comprising aluminum and iron cations, the method comprising:

(a) providing a fluorine-free mixture of water and a polar organic solvent;

(b) contacting a water soluble aluminum salt, a chelated iron compound, and 1, 4-phthalic acid or derivative or salt thereof with the mixture at a reaction temperature of less than 200 ℃ to produce a solid reaction product comprising MOF; and

(c) recovering the MOF from the mixture,

wherein the recovered MOF product, when analyzed by methane adsorption, is at a pressure below 8 bar (the pressure of the inflection point in the adsorption isotherm for pure MIL-53 (Fe)).

In further aspects, the invention relates to Al/Fe-containing terephthalate MOFs with flexible structures made by the methods described herein and the use of the resulting MOFs in methane adsorption.

Brief Description of Drawings

Figure 1 shows the X-ray diffraction patterns of MOF products of examples 1 to 3 (containing different amounts of aluminum and iron) performed at 200 ℃ (top) and 30 ℃ (bottom), respectively.

Figure 2 compares the gravimetric methane adsorption isotherms performed at 30 ℃ on the MOF products of examples 1 to 3 for samples containing 100% aluminum and 100% iron.

Figure 3 shows the volumetric methane adsorption isotherms performed at 30 ℃ on the MOF product of example 1 (containing about 50 mole% Al based on total metal content as determined by EDX).

Detailed description of the embodiments

The present disclosure provides novel and advantageous methods for producing terephthalate Metal Organic Frameworks (MOFs) having flexible structures and comprising aluminum and iron cations. The method includes providing a fluorine-free mixture of water and a polar organic solvent, and then contacting the mixture with a water-soluble aluminum salt, a chelated iron compound, and 1, 4-phthalic acid or a salt thereof at a reaction temperature of less than 200 ℃ to produce a solid reaction product comprising Al/Fe-containing MOF having a flexible structure similar to MIL-53. The MOF can then be recovered from the mixture.

Polar organic solvents, including water-miscible solvents and water-immiscible solvents, can be combined with water in the absence of hydrofluoric acid to produce a fluorine-free mixture. Examples of suitable polar organic solvents include dimethyl sulfoxide, dimethylacetamide, dimethylformamide, and ethylene glycol. The volume ratio of solvent to water is not critical, but typically the water/solvent mixture comprises at least 50 volume percent, such as at least 60 volume percent, such as at least 70 volume percent, of water, with the balance being polar organic solvent.

Any water soluble aluminum salt may be used in the present process including, for example, aluminum chloride, aluminum bromide, aluminum iodide, aluminum fluoride, aluminum nitrate, aluminum acetate, aluminum formate, and aluminum sulfate. Aluminum nitrate is generally preferred.

Similarly, any known chelated iron compound, especially Fe, may be used in the present process³⁺A compound is provided. In particular, the use of chelated iron starting materials was found to be important for better control of iron incorporation into the framework of MOFs than conventional iron salts. Suitable iron chelates include iron diketonate compounds, such as iron acetylacetonate, iron tris (2, 6-dimethyl-3, 5-heptanedionate) or iron tris (2,2,6, 6-tetramethyl-3, 5-heptanedionate). These iron chelates can be added directly or generated in situ.

The relative amounts of aluminum salt and iron chelate in the reaction mixture used in the present process will depend on the desired composition of the final MIL-53 material, but the reaction mixture should typically contain at least 10 mole%, such as 18 to 90 mole%, of aluminum salt, based on the total metal content of the mixture.

The reaction mixture used in the process contains, in addition to the aluminium salt and the iron chelate, 1, 4-benzenedicarboxylic acid or a substituted derivative thereof or a salt thereof. Suitable salts of 1, 4-phthalic acid include sodium, potassium and ammonium salts. Suitable 1, 4-benzenedicarboxylic acid derivatives include halogen substituted derivatives, such as chloro substituted derivatives. In some embodiments, the amount of 1, 4-benzenedicarboxylic acid component present in the reaction mixture varies between 50 and 300 mole%, such as between 150 and 250 mole%, based on the total amount of aluminum salt and iron chelate in the reaction mixture.

The reaction between aluminium salt, iron chelate and 1, 4-benzenedicarboxylic acid in the presence of mixed water and polar organic solvent can be carried out at a wide range of temperatures and times, lower temperatures requiring longer times to obtain high yields of MOFs. In embodiments, the reaction temperature is less than 200 ℃, such as from 25 ℃ to 150 ℃, for example from 50 ℃ to 150 ℃, such as from 75 ℃ to 125 ℃. The reaction time is typically at least 6 hours, such as 12 to 96 hours.

The product of the methods described herein is a terephthalate Metal Organic Framework (MOF) having a flexible structure similar or identical to MIL-53 and comprising iron and aluminum cations. When in N₂When subjected to X-ray diffraction analysis at 200 ℃ under a flowing atmosphere, the product exhibits a pattern comprising at least the characteristic lines listed in table 1:

TABLE 1

By having solid-state detectors provided with germaniumPanalytical X' Pert Pro diffraction system for xcellerator multichannel detector using copper K-alpha radiation and in N₂The X-ray diffraction data reported herein were collected on an Anton Paar HTK600 sample stage set to 200 ℃. Diffraction data was recorded by step scanning at 0.02 ° 2 θ, where θ is the bragg angle, and an effective count time of 2 seconds per step was used. The interplanar spacing d is calculated in angstroms and the relative intensity of the lines I/I_oIs the ratio of the peak intensity above background to the intensity of the strongest line. These intensities are uncorrected for Lorentz and polarization effects. The relative intensities are given in symbols: vs. very strong (75-100), s-strong (50-74), m-medium (25-49) and w-weak (0-24).

In particular, it was found that as the aluminum content of the final material increased, the X-ray powder diffraction pattern indicated that the presence of the macro-porous form of MIL-53 increased. This is particularly so as to be discussed in the following examples Andthe variation in intensity and position of the X-ray lines centered on the d-spacing value of (a) is apparent.

The product of the process described herein can be further characterized by methane adsorption as if the inflection point in the gravimetric methane adsorption isotherm is at a methane pressure below 8 bar (the pressure of the inflection point in the methane adsorption isotherm for pure MIL-53 (Fe)) and typically at a methane pressure of 6 bar or less. In some embodiments, the MOF product, when subjected to methane adsorption measurements at 30 ℃, exhibits an adsorption capacity at a methane pressure of 20 bar of greater than 2mmol/g MOF product. Gas sorption isotherm measurements were performed on a Hiden Isochema IGA gravimetric gas sorption analyzer at 30 ℃.

Aluminum and iron containing MIL-53 made by the present method can be used in a variety of applications, including as a catalyst or as a small hydrocarbon molecule (Technols)Other is C_4-Molecules, especially methane-containing mixtures, such as natural gas). It is well known that natural gas generally contains>85 mol% of methane,<10 mole% ethane and lesser amounts of propane and butane.

Detailed description of the preferred embodiments

Embodiment 1. a method of producing a bimetallic terephthalate Metal Organic Framework (MOF) having a flexible structure and comprising aluminum and iron cations, the method comprising:

(a) providing a fluorine-free mixture of water and a polar organic solvent;

(b) contacting a water soluble aluminum salt, a chelated iron compound, and 1, 4-phthalic acid or derivative or salt thereof with the mixture at a reaction temperature of less than 200 ℃ to produce a solid reaction product comprising MOF; and

(c) recovering the MOF from the mixture,

wherein the recovered MOF product is at N₂Exhibits a pattern comprising at least the characteristic lines listed in table 1 when subjected to X-ray diffraction analysis at 200 ℃ under a flowing atmosphere:

TABLE 1

Embodiment 2. a method of producing a bimetallic terephthalate metal-organic framework (MOF) having a flexible structure and comprising aluminum and iron cations, the method comprising:

(a) providing a fluorine-free mixture of water and a polar organic solvent;

(b) contacting a water soluble aluminum salt, a chelated iron compound, and 1, 4-phthalic acid or derivative or salt thereof with the mixture at a reaction temperature of less than 200 ℃ to produce a solid reaction product comprising MOF; and

(c) recovering the MOF from the mixture,

wherein the recovered MOF product, when subjected to methane adsorption measurements at 30 ℃, is at an inflection point in the adsorption isotherm at a pressure below 8 bar.

Embodiment 3. the method of embodiment 2, wherein the MOF product, when subjected to methane adsorption measurement at 30 ℃, exhibits an adsorption capacity at 20 bar of methane of greater than 2 mmol/g.

Embodiment 4 the method of any one of embodiments 1 to 3, wherein the polar solvent comprises at least one of dimethyl sulfoxide, dimethylacetamide, dimethylformamide, and ethylene glycol.

Embodiment 5 the method of any one of embodiments 1 to 4, wherein the chelated iron compound comprises an iron diketonate (iron dionate) compound.

Embodiment 6 the method of any one of embodiments 1 to 5, wherein the chelated iron compound comprises at least one of iron acetylacetonate, iron tris (2, 6-dimethyl-3, 5-heptanedionate) and/or iron tris (2,2,6, 6-tetramethyl-3, 5-heptanedionate).

Embodiment 7 the method of any one of embodiments 1 to 6, wherein the chelated iron compound is formed in situ during the contacting step (b).

Embodiment 8 the method of any one of embodiments 1 to 6, wherein the chelated iron compound is preformed and added to the contacting step (b).

Embodiment 9 the process of any one of embodiments 1 to 8 wherein the reaction temperature is from 25 ℃ to 150 ℃.

Embodiment 10 the method of any one of embodiments 1 to 9, wherein said contacting is carried out for at least 6 hours.

Embodiment 11 the method of any of embodiments 1 to 10, wherein the MOFs recovered in (c) contain at least 10 mole% aluminum based on the total metal content of the MOFs as determined by energy dispersive X-ray spectroscopy (EDX).

Embodiment 12 the method of any one of embodiments 1 to 11, wherein the MOFs recovered in (c) contain up to 90 mole% aluminum based on the total metal content of the MOFs as determined by energy dispersive X-ray spectroscopy (EDX).

Embodiment 13. a Metal Organic Framework (MOF) having the structure of MIL-53 and comprising iron and aluminum cations made by the method of any one of embodiments 1 to 12.

Embodiment 14. an adsorption comprises at least one C_4-A method of a hydrocarbon gas, the method comprising contacting the gas with the MOF of embodiment 13.

The invention will now be described more particularly with reference to the following non-limiting examples and the accompanying drawings.

Example 1:synthesis of MIL-53(Fe54/Al46)

82 mg of terephthalic acid, 244 mg of iron (III) acetylacetonate and 112 mg of aluminum nitrate nonahydrate were dissolved in 10ml of 20% (v/v) aqueous dimethyl sulfoxide. This solution was heated at 120 ℃ for 3 days under magnetic stirring. After cooling to room temperature, the solid was separated by centrifugation. These solids were washed with water (10mL x 2) followed by dimethylformamide (10mL x 1). The solid was then suspended in dimethylformamide at 100 ℃ overnight to remove any soluble impurities. The solid was then collected and washed with methanol (10mL x 3) and dried at 70 ℃. The product obtained is in N₂The X-ray diffraction pattern at 200 ℃ under flowing atmosphere is shown in table 2 below and indicates that the product is a mixture of large and narrow pore phases of MIL-53(Al), some of the line shifts being likely due to the presence of iron.

TABLE 2

Assessment of the metal content of the resulting MOF materials was performed by energy dispersive X-ray spectroscopy (EDX) on a Hitachi 4800HR-SEM using a ThermoFisher Scientific UltraDry EDS detector. This experiment shows that the iron and aluminum content of the MOF product fit those of the reaction mixture (i.e., Fe/Al molar ratio of about 50: 50), although the EDX measurement is inherently semi-quantitative and the resulting values may have a margin of error of ± 20%.

Example 2:synthesis of MIL-53(Fe30/Al70)

The procedure of example 1 was repeated, but the amounts of iron (III) acetylacetonate and aluminum nitrate nonahydrate were adjusted to 104mg and 262mg, respectively. The product obtained is in N₂Under a flowing atmosphere at 200 DEG CThe lower X-ray diffraction pattern is shown in table 3 below and again indicates that the product is a mixture of MIL-53(Al) macroporous/narrow pore phases, some of the line shifts may be due to the presence of iron.

TABLE 3

EDX measurements again showed that the Fe/Al molar ratio of the MOF product corresponded to that of the starting mixture.

Example 3:synthesis of MIL-53(Fe83/Al17)

The procedure of example 1 was repeated, but the amounts of iron (III) acetylacetonate and aluminum nitrate nonahydrate were adjusted to 174mg and 186mg, respectively. The product obtained is in N₂The X-ray diffraction pattern at 200 ℃ under flowing atmosphere is shown in table 4 below and again shows that the product is a macro-/narrow-pore mixture of MIL-53(Al), some line shifts and intensity variations, possibly due to the presence of iron.

TABLE 4

EDX measurements again showed that the Fe/Al molar ratio of the MOF product corresponded to that of the starting mixture.

FIG. 1 shows the results of the temperature-variable X-ray diffraction analysis of the products of examples 1 to 3, the patterns being taken at 30 ℃ and 200 ℃. It can be seen that as more aluminum is present in the final material, the powder diffraction pattern begins to exhibit more "macroporous" characteristics. This is manifested by a decrease in the relative intensities of the peak centered at 13.5 ° 2 θ and the peak centered at 17.5 ° 2 θ. In addition, figure 1 shows that the "narrow-hole" feature disappears when these materials are heated to 200 ℃. This is particularly evident by observing the relative intensities of the peak centered at 9 ° 2 θ and the peak centered at 17.5 ° 2 θ. This data indicates that one-dimensional structural features of MIL-53 are intact in the products from all three synthesis conditions.

FIG. 2 compares the gravimetric methane adsorption isotherms performed at 30 ℃ on the products of examples 1 to 3 for MIL-53 samples containing 100% aluminum and 100% iron. It can be seen that the 100% aluminum and 100% iron MIL-53 materials exhibit classical type I and type V isotherms, respectively. Isotherms of the mixed metal materials of examples 1 to 3 demonstrate that the pressure at which the material "opens" into the macroporous form can be displaced by varying the Al/Fe ratio. In addition, the material produced by the present process has the desired properties of opening into a "macroporous" phase rather than some mesophase.

Figure 3 shows the volumetric methane adsorption isotherm of the product of example 1 at 30 ℃. It can be seen that this MOF specific composition undergoes a two-step pore opening process (between 0-5 bar and between 10-40 bar). Each phase change is endothermic. The endothermic phase change compensates for the heat of adsorption, an important attribute for methane storage applications.

While the invention has been described and illustrated with reference to specific embodiments, those of ordinary skill in the art will recognize that variations of the invention may be made which are not necessarily described herein. Accordingly, the true scope of the invention should be determined only by reference to the claims that follow.