Iron Zeolitic Imidazolate Framework (ZIF), production method thereof and nanocomposite derived from same

Abstract

An electrocatalyst, more specifically an electrocatalyst derived from metal-organic framework is provided. An iron zeolitic imidazolate framework, the process for producing it, a graphite carbon nanocomposite containing it and iron nanoparticles, as well as the process for obtaining said nanocomposite from the iron zeolitic imidazolate framework are disclosed herein. Use of the nanocomposite as a catalyst is also disclosed.

Claims

1. A zeolitic framework comprising the general structure A-B-A wherein A is iron, and B is a compound of formula I ##STR00002## wherein R.sub.1, R.sub.2 and R.sub.3 are independently hydrogen, C.sub.1-4 alkyl, halo, cyano, or nitro, wherein when R.sub.2 and R.sub.3 are C.sub.1-4 alkyl, R.sub.2 and R.sub.3 may be (are optionally) joined together to form a ring comprising 3 to 7 carbons.

2. The zeolitic framework according to claim 1, wherein the compound of formula I is imidazolate or 2-methylimidazolate.

3. (canceled)

4. The zeolitic framework according to claim 1, wherein said framework has a SOD zeolitic topology.

5. The zeolitic framework according to claim 1, wherein said framework has the crystallographic structure of the ZIF-8.

6. The zeolitic framework according to claim 1, wherein said zeolitic framework has a micropore volume greater than 0.15 cm.sup.3.Math.g.sup.1, greater than 0.3 cm.sup.3.Math.g.sup.1, or wherein said zeolitic framework has a BET area greater than 100 m.sup.2/g, or greater than 200 m.sup.2/g, or greater than 400 m.sup.2/g, calculated using adsorption assays.

7. (canceled)

8. A process for obtaining the zeolitic framework according to claim 1, comprising the following steps: a. mixing ferrocene and a compound of formula I, in the presence of a template ligand, b. heating the sealed mixture of step (a) to a temperature between 80 and 250 C., between 110 and 200 C. or between 140 and 160 C. for at least 12 hours, or between 2 and 6 days, between 3.5 and 4.5 days.

9. The process according to claim 8, wherein the compound of formula I is 2-methylimidazolate.

10. The process according to claim 8, wherein the template ligand is solid at 25 C.

11. The process according to claim 8, wherein the mixture of step (a) is prepared in the absence of a solvent.

12. The process according to claim 8, wherein the template ligand is an aromatic heterocycle, or an aromatic heterocycle, wherein the heteroatom is nitrogen, or a pyridine, a pyridine derivative, an imidazole, or an imidazole derivative, or a bipyridine or a bipyridine derivative or a benzimidazole or a benzimidazole derivative; or wherein the molar ratio of the template ligand: compound of formula I in step (a) mixture is less than 1:1.

13. (canceled)

14. (canceled)

15. (canceled)

16. (canceled)

17. (canceled)

18. (canceled)

19. (canceled)

20. (canceled)

21. (canceled)

22. A nanocomposite, comprising: a graphite carbon matrix and between 0.1 and 3% by weight of iron nanoparticles with respect to the total weight of the nanocomposite, wherein said iron nanoparticles have a diameter of between 1 and 60 nm, wherein said nanocomposite comprises between 70 and 95% by weight of carbon, between 3 and 20% by weight of oxygen, and between 0.2 and 5% by weight of nitrogen with respect to the total weight of the nanocomposite, and wherein said nanocomposite has a current density in the oxygen evolution reaction (OER) greater than 200 mA/cm.sup.2 in KOH 1M.

23. The nanocomposite according to claim 22, wherein the pore size is 0.5 to 15 nm, calculated by adsorption assays, or the pore size is 1 to 10 nm, calculated la adsorption assays, or the pore size is 3 to 5 nm calculated by adsorption assays; and/or wherein the pore volume is 0.1 to 2 cm.sup.3 g.sup.1, calculated by adsorption assays, or the pore volume is 0.5 to 1.5 cm.sup.3 g.sup.1, calculated by adsorption assays, or the pore volume is 0.9 to 1.1 cm.sup.3 g.sup.1, calculated by adsorption assays; and/or wherein the micropore volume is 0.01 to 1 cm.sup.3 g.sup.1, calculated by adsorption assays, or the micropore volume is 0.05 to 0.5 cm.sup.3 g.sup.1, calculated by adsorption assays, or the micropore volume is 0.09 to 0.11 cm.sup.3 g.sup.1, calculated by adsorption assays; and/or the BET area is greater than 100 m.sup.2/g, calculated by adsorption assays, or the BET area is greater than 200 m.sup.2/g, calculated by adsorption assays, or the BET area is greater than 400 m.sup.2/g, calculated by adsorption assays.

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)

30. (canceled)

31. (canceled)

32. (canceled)

33. (canceled)

34. (canceled)

35. The nanocomposite according claim 22, wherein said nanocomposite comprises between 80 and 94% by weight of carbon, between 5 and 15% by weight of oxygen, and between 0.5 and 3% by weight of nitrogen, and between 0.3 to 2% by weight of iron, with respect to the total weight of the nanocomposite, or said nanocomposite comprises between 90 and 92% by weight of carbon, between 7 and 9% by weight of oxygen, and between 0.8 and 1.2% by weight of nitrogen, and between 0.7 and 0.9% by weight of iron, with respect to the total weight of the nanocomposite.

36. (canceled)

37. The nanocomposite according to claim 22, wherein the iron nanoparticles have a diameter between 5 and 45 nm, or between 10 and 30 nm.

38. (canceled)

39. The nanocomposite according to claim 22, wherein said nanocomposite has a current density in the oxygen evolution reaction (OER) greater than 230 mA/cm.sup.2 in KOH 1M, or has a current density in the oxygen evolution reaction (OER) greater than 300 mA/cm.sup.2 in KOH 1M.

40. (canceled)

41. A process for obtaining a nanocomposite according to claim 22, comprising the following steps: a. obtaining a zeolitic framework comprising the general structure A-B-A wherein A is iron, and B is a compound of formula I ##STR00003## wherein R.sub.1, R.sub.2 and R.sub.3 are independently hydrogen, C.sub.1-4 alkyl, halo, cyano, or nitro, wherein when R.sub.2 and R.sub.3 are C.sub.1-4 alkyl, R.sub.2 and R.sub.3 may be (are optionally) joined together to form a ring comprising 3 to 7 carbons; according to the following process: mixing ferrocene and a compound of formula I in the presence of a template ligand; heating the sealed mixture of step (a) to a temperature between 80 and 250 C., between 110 and 200 C., or between 140 and 160 C., for at least 12 hours, or between 2 and 6 days, between 3.5 and 4.5 days, and b. heating the zeolitic framework obtained in step (a) at a temperature between 500 and 900 C. for at least 1 hour.

42. The process according to claim 41, wherein step (b) is carried out at a temperature between 600 and 800 C., or between 680 and 720 C.

43. (canceled)

44. The process according to claim 41, wherein step (b) has a duration of at least 2 hours, or at least 3 hours.

45. (canceled)

46. A nanocomposite obtained by the process according to claim 41.

47. (canceled)

48. A process for obtaining the zeolitic framework according to claim 1, comprising the following steps: a. mixing ferrocene and a compound of the formula I in the presence of a template ligand selected from imidazolate or 2-methylimidazolate, and b. heating the sealed mixture of step (a) to a temperature between 80 and 250 C., between 110 and 200 C., or between 140 and 160 C., for at least 12 hours, or between 2 and 6 days, between 3.5 and 4.5 days.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0051] The following figures form part of the present description and describe exemplary embodiments of the claimed invention. The skilled artisan will, in light of these figures and the description herein, be able to practice the invention without undue experimentation.

[0052] FIGS. 1A and 1B depict photographs made using an electronic scanning microscope of the iron zeolitic imidazolate framework crystals of the present invention. FIG. 1C depicts a photograph made with an optical microscope of the crystals of the iron zeolitic imidazolate framework of the present invention. The scale bar is 300 microns in FIG. 1A and 500 microns in FIG. 1B.

[0053] FIG. 2A depicts a tetrahedral coordination environment of the iron atoms (II) in the structure of the iron zeolitic imidazolate framework of this invention. FIG. 2B depicts a representation of a pore and channel belonging to the structure of the iron zeolitic imidazolate framework of the present invention wherein the iron atoms have been represented in the form of tetrahedra, the carbons and nitrogens are represented as points, and the sphere represents the empty cavity or pore of the material. FIG. 2C depicts a representation of the SOD-type zeolite structure. FIG. 2D depicts an X-ray diffractogram of the iron zeolitic imidazolate framework of the present invention (peak line) and difference [(I.sub.obsI.sub.cald)] (bottom line) of the Pawley refinement (range of 2: 4.0-40.0).

[0054] FIG. 3A depicts a graphical product representation of the magnetic susceptibility for the temperature versus temperature. FIG. 3B depicts a graphical representation of the magnetisation versus the field at 2K. The dotted line shows the Brillouin function for an S=2 system without magnetic interactions.

[0055] FIG. 4 depicts an X-ray diffractogram of the nanocomposite of the present invention.

[0056] FIGS. 5A-5D depicts photographs taken by a high-resolution transmission electron microscope of the nanocomposite of this invention. The scale bar length is 20 nm, 2 nm, 10 nm, and 10 nm, respectively, in the photographs.

[0057] FIGS. 6A and 6B depict photographs of the nanocomposite of this invention made by a scanning electron microscope.

[0058] FIG. 7 depicts an X-ray spectroscopy spectrum (XPS) of the iron in the nanocomposite of this invention.

[0059] FIG. 8 depicts an XPS spectrum of the nitrogen in the nanocomposite of the present invention.

[0060] FIG. 9 depicts an XPS spectrum of the carbon in the nanocomposite of the present invention.

[0061] FIG. 10 depicts a N.sub.2 isotherm of the nanocomposite of the present invention.

[0062] FIG. 11 depicts a CO.sub.2 isotherm of the nanocomposite of the present invention.

[0063] FIG. 12 depicts a chart of the pore distribution of the nanocomposite of the present invention.

[0064] FIG. 13 depicts a chart of the oxygen evolution reaction (OER) of the nanocomposite of the present invention (black) and the nickel foam (grey) in KOH 0.1 M.

[0065] FIG. 14 depicts a chart of the OER of the nanocomposite of the present invention (black) and the nickel foam (grey) in KOH 1 M.

[0066] FIG. 15 depicts a chart of the hydrogen evolution reaction (HER) of the nanocomposite of the present invention (black) and the nickel foam (grey) in KOH 0.1 M.

[0067] FIG. 16 depicts a chart of the HER of the nanocomposite of the present invention (black) and the nickel foam (grey) in KOH 1 M.

[0068] FIG. 17 depicts a chart of the HER of the nanocomposite of the present invention (black) the carbon felt (grey) in H.sub.2SO0.5 M.

[0069] FIG. 18 depicts a chart of the HER of the nanocomposite of the present invention (black) and the carbon felt (grey) in H.sub.2SO.sub.4 1 M.

[0070] FIG. 19 depicts a chart of the Tafel slopes of the nanocomposite of the present invention in the two basic media.

[0071] FIG. 20 depicts a chart of the galvanostatic stability of the nanocomposite of the present invention in KOH 0.1 M.

[0072] FIG. 21 depicts a chart of the galvanostatic stability of the nanocomposite of the present invention in KOH 1 M.

[0073] FIG. 22 depicts a chart of the potentiostatic stability of the nanocomposite of the present invention in KOH 1 M.

[0074] FIG. 23 depicts a chart of the N.sub.2 adsorption isotherm of the zeolitic framework of this invention, measured at 77 K.

[0075] FIG. 24 depicts a chart of the CO.sub.2 adsorption isotherm of the zeolitic framework of this invention, measured at 298 K.

DETAILED DESCRIPTION OF THE INVENTION

[0076] The following examples illustrate the present invention and demonstrate the advantageous properties of the nanocomposites of the present invention, as well as the method of the present invention. In view of the above description and the examples below, one of ordinary skill in the art will be able to practice the invention as claimed without undue experimentation. The foregoing will be better understood with reference to the following examples that detail certain procedures for the preparation of embodiments of the present invention. All references made to these examples are for the purposes of illustration. The following examples should not be considered exhaustive, but merely illustrative of only a few of the many embodiments contemplated by the present invention.

EXAMPLES

Example 1: Synthesis of the Iron ZIF

[0077] Ferrocene (30 mg, 0.16 mmol), 4.4-bipyridine (50 mg, 0.32 mmol) and 2-methylimidazole (20 mg, 0.24 mmol) are used for the iron ZIF synthesis. These three solids are mixed and sealed under vacuum in a tube. The mixture is heated to 150 C. for 4 days to obtain yellow crystals suitable for single-crystal X-ray diffraction (FIG. 1). The obtained product is allowed to cool, and the tube is opened. The crystals are cleaned by removing the reagents that have not reacted with the acetonitrile and benzene. The purity of the final solid is determined by X-ray powder diffraction. All the reagents are commercially available and have been used without further purification.

[0078] In an alternative synthesis process, ferrocene, 2-methylbenzimidazole (as a template ligand), and 2-methylimidazole are used, and essentially the same steps are followed.

Example 2: Iron ZIF Analysis by X-ray Powder Diffraction

[0079] The crystallographic studies at 120 K reveal that the yellow crystals are isostructural with the ZIF-8 (a=17.1794 ), with the spatial group 1-43 m. The metallic centres, Fe(II), are located in a tetrahedral coordination environment, connected by NCN bridges created by the ligands 2-methylimidazole, as shown in FIG. 2. The FeN distances are 2.032 , and the FeFe distances are 6.069 . The Pawley refinement of the X-ray powder diffractogram (XRPD) obtained shows a single crystalline phase since a WPR factor (weighted powder profile R-factor) of 0.01462 is obtained. This WPR indicates that the error in the diffractogram profile is very low (1.46%), which implies that there is only one phase: the iron ZIF. Furthermore, a GOF factor (the goodness of fit) is obtained close to 1: from 1.103. The intensity and width of the peaks can be seen in FIG. 2D, which denotes a high crystallinity. With the scanning electron microscope (SEM), the morphology of the crystals was studied, showing crystals with very well-defined faces, about 300 microns in size (FIG. 1).

[0080] The NCN bridges between the iron centres allow a magnetic exchange, and the Fe(II) tetrahedral environment that provides S=2 for each metallic centre enables the appearance of magnetic sorting. As we can see in FIG. 3, wherein the product of the magnetic susceptibility (m) with the temperature (T) versus temperature is represented, mT decreases as it cools down, indicating the presence of anti-ferromagnetic interactions between the FeFe centres through the imidazolate bridges. The anti-ferromagnetic nature of the compound is also observed in the magnetisation graph, wherein a saturation value much lower than expected can be seen for the Fe(II) paramagnetic centres.

Example 3: Synthesis of the Nanocomposite

[0081] For the synthesis of the nanocomposite, the iron ZIF was introduced into a vessel with acetonitrile to avoid contact with oxygen in the atmosphere. The inert atmosphere of nitrogen was created, and the ramp was made, in which it is heated to 700 C. for 3.5 h, with a ramp up and down of 2 C./min. Once heated, the nanocomposite obtained from the heating is washed with a solution of nitric acid 0.5 M for 6 h to eliminate the excess metal.

Example 4: Characterisation of the Nanocomposite

[0082] X-ray measurements (XRPD) confirm the presence of small traces of iron nanoparticles in the nanocomposite, showing the characteristic peaks of metallic iron and graphite carbon (FIG. 4).

[0083] On the other hand, the images of the high-resolution transmission electron microscope (HRTEM) show that the structure of the nanocomposite consists of a graphitised carbon matrix, with iron nanoparticles of approximately 10 to 30 nm in size, as can be seen in FIG. 5 A. Said nanoparticles found in the carbonate matrix are also surrounded by layers of graphene (FIG. 5 B). The formation of carbon nanostructures, such as nano-cells and graphene layers mentioned above, can also be clearly observed (FIGS. 5 C and D).

[0084] The scanning electron microscope (SEM) images of the nanocomposite show how, after heating, the nanocomposite loses the geometric structure observed in the ZIF. Furthermore, a structure can be seen with different layers of graphene and many dimples that correspond to the pores that provide the high specific area to the nanocomposite.

TABLE-US-00001 TABLE 1 Percentages of carbon, nitrogen, and oxygen of the composite obtained by X-ray spectroscopy (XRS), with respect to one another and excluding the content of iron. C (at. %) N (at. %) O (at. %) 90.71 1.10 8.19

[0085] The X-ray spectroscopy (XRS) measurements show that the nanocomposite has a percentage of 90.7, 8.2, and 1.1 percent of atomic carbon, oxygen, and nitrogen, respectively (Table 1), demonstrating that there is nitrogen doping. In said measurement, iron is not detected as it is a superficial measurement, and the nanoparticles are surrounded by several layers of carbon as can be seen in HRTEM images. With regard to nitrogen, we can see in FIG. 8 that the pyridinic and graphitic nitrogen predominate in the nitrogen doping (Table 2).

TABLE-US-00002 TABLE 2 Percentages of the different types of N obtained using XRS. Pyridinic nitrogen Graphitic nitrogen 34.5 65.5

[0086] The nitrogen doping is very important in this type of composites, as it induces electronic interaction with nearby carbon/metal atoms to provide active catalytic areas and also produces structural defects in the carbon nanoforms to form oxygen adsorption sites. Finally, FIG. 9 shows the carbon signal, which can be deconvoluted into four different peaks, of which we obtain the proportions of the different types of carbon shown in Table 3.

TABLE-US-00003 TABLE 3 Percentages of the different types of carbon obtained using XRS. CC sp.sup.2 CC sp.sup.3 CO/CN CO/CN % 82.61 9.62 6.85 0.92

[0087] The inductively coupled plasma atomic emission spectroscopy (ICP-OES) analyses indicate that the nanocomposite contains 0.79% of iron by weight.

[0088] To estimate the surface area of the nanocomposite, the porous texture of the nanocomposite was characterised by nitrogen adsorption assays (N.sub.2) at 77 K and carbon dioxide adsorption assays (CO.sub.2) at 273 K (FIGS. 10 to 12). AUTOSORB-6 equipment was used for this purpose. The samples were degassed for 8 hours at 523 K and 5.10.sup.5 bar before being analysed. The surface areas were estimated according to the BET model, and the pore size dimensions were calculated using the solid density functional theory (QSDFT) for the adsorption branch assuming a cylindrical pore model. The micropore volumes were determined by applying t-plot and DR methods to the N.sub.2 and CO.sub.2 adsorption data.

TABLE-US-00004 TABLE 2 Porosity data obtained by adsorption measures, from the nitrogen and carbon dioxide isotherms. S.sub.BET.sup.a t-plot V.sub.t.sup.b V.sub.(<0.7 nm) .sup.c V.sub.DR.sup.d V.sub.meso.sup.e V.sub.meso (P/P0=0.7) .sup.f (m.sup.2g.sup.1) S.sub..sup.a (m.sup.2g.sup.1) S.sub.T.sup.a (m.sup.2g.sup.1) (cm.sup.3g.sup.1) (cm.sup.3g.sup.1) (cm.sup.3g.sup.1) (cm.sup.3g.sup.1) (cm.sup.3g.sup.1) 462.71 363.39 99.33 0.96 0.121 0.181 0.780 0.297 .sup.aData obtained from the N.sub.2 adsorption. Specific area calculated using the BET method. Area contributed by micropores S.sub. and external area S.sub.T using the t-plot method. .sup.bTotal Volume at P/P.sub.0 = 0.96. .sup.c Data obtained from the CO.sub.2 adsorption. The micropore volume (<0.7 nm) calculated according to the DR method. .sup.dMicropore volume calculated by N.sub.2 adsorption using the DR method. .sup.eCalculated mesopore volume according to: V.sub.meso = V.sub.Total V.sub.DR. .sup.f Mesopore volume (.sub.Vmeso (P/P0)) calculated from the difference between the total (V.sub.t) at P/P.sub.0 and the micropore volume (V.sub.micro).

[0089] The nitrogen isotherms show an IV type adsorption, whose values are illustrated in Table 4, showing a specific area of 463 m.sup.2g.sup.1. The pore volume of the nanocomposite is 0.96 cm.sup.3g.sup.1, indicating a distribution of micropores and mesopores of approximately 3 nm. For a better micropore study of less than 0.7 nm in size, CO.sub.2 adsorption measurements were made at 273 K. In this case, the measurements indicate a micropore volume of 0.12 cm.sup.3g.sup.1 (FIGS. 10 to 12).

[0090] The electrocatalytic behaviour of the nanocomposite of the present invention was characterised by different electrochemical measurements in a typical 3-electrode cell. Different electrolytes with different concentrations (i.e. media with different pH) were used for said measurements, always using a stainless-steel sheet and an Ag/AgCl electrode as a counter-electrode and reference electrode respectively. Each working electrode used the different nanocomposites, embedded in nickel foam for the basic media and in carbon felt for the acid media, (to prevent the reaction between nickel foam and the acid) of an area of 0.2 cm.sup.2. The deposition of the nanocomposites was carried out by preparing a suspension of the material to be analysed with polyvinylidene difluoride (PVDF) and carbon black (ratio 80:10:10) in ethanol. Once it was deposited in the nickel foam or carbon felt, it was allowed to dry for two hat 80 C. Basic media (1 M and 0.1 M KOH), acid media (0.5 M H.sub.2SO.sub.4), and a neutral medium (phosphate buffer of pH 7) were used to study the electrocatalytic activity of the nanocomposite.

[0091] To measure their behaviour as an oxygen catalyst (OER), it was tested in two basic media (KOH 0.1 and 1 M). Linear voltammetry measurements were performed, showing the beginning of catalysis at 1.542 V and 1.588 V (vs RHE) for the 0.1 M and 1 M KOH media, respectively. As can be seen in FIGS. 13 and 14, we see that the values obtained with the nanocomposite with respect to their respective targets are much higher, showing that the nanocomposite of the present invention has a high electrocatalytic behaviour.

TABLE-US-00005 TABLE 5 Voltage values for the beginning of oxygen catalysis of the material in different media. OER KOH 1M KOH 0.1M V (vs RHE) 1.588 1.542

[0092] For a better characterisation of its catalytic behaviour other parameters were calculated, such as the overvoltage () obtained at different current densities (10 and 15 mA.Math.cm.sup.2); the current density (j) at an overvoltage of =300 and 400 mV; and the Tafel slopes in the different media. In FIG. 19, we can see the Tafel slopes in the two basic media, obtaining very low values of 48 and 37 mV per decade for 0.1 M and 1 M KOH respectively.

[0093] The stability and durability of the nanocomposite of this invention were tested by means of a galvanostatic test applying continuous current densities of j=10 and 15 mA.Math.cm.sup.2, and by potentiometric tests applying an overvoltage of =300 and 400 mV, for 1000 seconds in both cases. As can be seen in FIGS. 20 to 22, very good stability is observed in both media, obtaining practically constant values of current density and overvoltage.

[0094] Finally, the behaviour of the nanocomposite of the present invention was measured as a hydrogen catalyst (HER), tested in basic media (KOH 0.1 and 1 M), acid media (H.sub.2SO.sub.4 1 and 0.5 M), and in neutral medium (pH 7 phosphate buffer). Linear voltammetry measurements were performed, showing the initiation of catalysis always above the corresponding target measurement in that medium, as shown in FIGS. 15 to 18. The beginning values of hydrogen catalysis in the different media can be seen in Table 6.

TABLE-US-00006 TABLE 3 Beginning voltage values of hydrogen catalyst of the material in different media. KOH KOH H.sub.2SO.sub.4 H.sub.2SO.sub.4 Buffer HER 1M 0.1M 1M 0.5M pH 7 V (vs RHE) 0.398 0.319 0.514 0.659 0.762

Example 5: Characterisation of Iron ZIF

[0095] The zeolitic framework of the present invention is porous, as can be seen in FIG. 2b. To estimate the surface area of the iron ZIF, the porous texture of the iron ZIF was characterised by nitrogen adsorption assays (N.sub.2) at 77 K and carbon dioxide adsorption assays (CO.sub.2) at 273 K (FIGS. 23 and 24). AUTOSORB-6 equipment was used for this purpose. The samples were degassed for 8 hours at 523 K and 5.10.sup.5 bar before being analysed. The surface areas were estimated according to the BET model, and the pore size dimensions were calculated using the solid density functional theory (QSDFT) for the adsorption branch assuming a cylindrical pore model. The micropore volumes were determined by applying t-plot and DR methods to the N.sub.2 and CO.sub.2 adsorption data.

[0096] The ZIF of the present invention presents BET area values always greater than 400 m.sup.2/g and up to 1,200 m.sup.2/g after cleaning the pore by activation of the material.

[0097] The ZIF of the present invention presents micropore volume values between 0.3 and 0.6 cm.sup.3.Math.g.sup.1.

[0098] The above is a detailed description of particular embodiments of the invention. It will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims. All of the embodiments disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure.