A steam-stable three-dimensional (3D) zinc-adeninate metal organic framework with a high selectivity for industrial co 2 capture

Abstract

The present disclosure relates to metal organic frameworks (MOFs). Specifically, the present disclosure relates to a Three-Dimensional (3D) Zinc-Adeninate MOF with a high selectivity industrial CO2 capture, and with weak interactions with water and a method of synthesizing the same. Further, the disclosure relates to a method for industrial CO2 capture using said 3D zinc-adeninate MOF.

Description

A STEAM-STABLE THREE-DIMENSIONAL (3D) ZINC-ADENINATE METAL ORGANIC FRAMEWORK WITH A HIGH SELECTIVITY FOR INDUSTRIAL CO2CAPTUREFIELD OF THE INVENTION

[0001] The present disclosure relates to metal organic frameworks (MOFs). Specifically, the present disclosure relates to a Three-Dimensional (3D) Zinc-Adeninate MOF (IISERP- MOF33) with a high selectivity industrial CO2 capture, and with weak interactions with water and a method of synthesizing the same. Further, the disclosure relates to a method for industrial CO2 capture using said 3D zinc-adeninate MOF.BACKGROUND OF THE INVENTION

[0002] Background description includes information that may be useful in understanding the present disclosure. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Carbon dioxide (CO2), a greenhouse gas, is often targeted for removal from natural gas and other industrial gas streams. Conventional methods for removing carbon dioxide is often a costly and multi-stage process since such gas streams must be dehydrated first before CO2capture. The reason for the same is because water vapor interacts strongly with porous materials that exhibit physiosorption towards CO2.

[0004] Many MOFs have been investigated for CO2capture. Only in a few cases needs withstanding humid conditions have been examined. The leading MOF in this regard is the CALF -20, recently published in Science (2021) by Shimizu and co-workers, patented and licensed. Other noteworthy MOFs include its predecessor Zinc-aminotriazolato-oxalate MOF also published in Science (2010) by Vaidhyanathan et al. An Aluminum formate (ALF) MOF has recently been reported in Science Advances (2022) for selective CO2 capture, reported by Cheetham and co-workers. However, this does not carry sufficient hydrolytic stability (water and steam). More relevant to this patent is the combination of the metal with adenine and terephthalic acid, aka 1,4-benzene dicarboxy lie acid, the closest ligand combination to the one presented here. Only two MOFs are known with this combination, copper / zinc-adenine- terephthalate (IISERP-MOF26(Cu) and IISERP-MOF27(Zn) (Maity et al., Chem. Asian J. 2019,14,3736 -3741). Our group reported both. We investigated these for CO2 removal from CO2 / N2 mixtures. However, their CO2 capacity and humidity stabilities were nowhere nearwhat is exhibited by CALF -20.

[0005] While many MOFs and other porous materials show selective CO2 capture properties, they do not meet all the demands of a CO2 sorbent. Key performance indicators are CO2 capacity and selectivity over the competing gas, which in this case is N2. Ability to withstand steam and hot water exposure, solvents, NOx, and SOx without losing crystallinity and porosity, cyclability, scalability and oxygen stability. Of all the MOFs, CALF-20, Zinc- triazole-oxalate, is the only one which has managed to meet most of these demands. However, if the low-pressure uptake of CALF -20 and the saturation CO2 capacity can be enhanced, it would make the sorbent suit for removing CO2 from some important CO2 / N2 composition (4%- 10%) beyond classical flue gas. However, making a material with such high performance is extremely difficult.

[0006] Therefore, there is an imminent need to design a MOF that has a superior Industrial CO2 capture.

[0007] The present disclosure satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.OBJECTS OF THE INVENTION

[0008] Objects of the present disclosure relate to provide a MOF that has a superior Industrial CO2 capture.

[0009] An object of the present disclosure is to provide a 3D Zinc-Adeninate MOF with a high selectivity for CO2 from humid atmosphere.

[0010] Another object of the present disclosure is to provide a method of synthesizing 3D Zinc-Adeninate MOF with a high selectivity for CO2 from humid atmosphere.

[0011] Yet another object of the present disclosure is to provide a method for industrial CO2 capture using said 3D zinc-adeninate MOF.SUMMARY OF THE INVENTION

[0012] This summary is provided to introduce a selection of concepts in a simplified form that is further described below in the detailed description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0013] The present disclosure relates to metal organic frameworks (MOFs). Specifically, the present disclosure relates to a Three-Dimensional (3D) amine-rich MOF with a high selectivity industrial CO2 capture, and a method of synthesizing the same. Further, thedisclosure relates to a method for industrial CO2 capture using said 3D zinc-adeninate MOF.

[0014] In a preferred aspect, the present disclosure relates to a IISERP-MOF33 showing more than 3mmol / g of CO2 uptake at RT with a CO2 / N2 selectivity of -350, which remains the same for the entire loading (zero to > 3mmol of CO2).

[0015] In a preferred aspect, the present disclosure relates to a IISERP-MOF33 shows > a two-step water uptake with the first inflexion at < 10% relative humidity (RH) reaching an uptake of 2mmol / g and then the second inflexion occurs at -25% RH reaching a saturation uptake of 1 Immol / g at ambient conditions (298K and 100% RH).

[0016] In an aspect, the present invention provides a three-dimensional (3D) hydrophobic zinc-adenine-dicarboxylate MOF having a formula Zn3(Ade)2(PDC)2. (solvent) for selective CO2 capture, wherein Ade is adeninate, PDC is 2,5 -pyridinedicarboxylate, and the solvent is selected from the group consisting of water, methanol, and tetrahydrofuran (THF), wherein the zinc-adenine-dicarboxylate MOF comprises zinc trimmers connected by adenine and pillared by dicarboxylate ligands, and wherein the zinc-adenine-dicarboxylate MOF does not have any strongly polar oxygen in the framework.

[0017] In an aspect of the present invention, the zinc-adenine-dicarboxylate MOF has slit-shaped ultra micropores of size -4.5 A.

[0018] In an aspect of the present invention, the zinc-adenine-dicarboxylate MOF exhibits CO2 capture efficiency of 90-99.9%.

[0019] In an aspect of the present invention, the zinc-adenine-dicarboxylate MOF exhibits stability to SOx and NOx at 500ppm levels.

[0020] In an aspect of the present invention, the zinc-adenine-dicarboxylate MOF exhibits stability to oxygen and air at 120 °C, and chemical conditions having pH 2-14.

[0021] In an aspect of the present invention, the zinc-adenine-dicarboxylate MOF remains crystalline and porous for over 20 months.

[0022] In another aspect, the present invention provides a method of synthesizing zincadenine-dicarboxylate MOF as claimed in claim 1, said method comprising the steps of: a solvothermal reaction between zinc acetate dihydrate, adenine, and 2,5 pyridine dicarboxylic acid in a solution containing water and methanol, THF and acetic acid, followed by cooling to room temperature to obtain reaction product; filtering reaction product to obtain rod-shaped colorless crystals of zinc-adenine- dicarboxylate MOF;washing the crystals of zinc-adenine-dicarboxylate MOF with methanol, followed by grinding to obtain powder form of zinc-adenine-dicarboxylate MOF; and activating the powder form of zinc-adenine-dicarboxylate MOF

[0023] In an aspect of the present invention, the ratio of zinc acetate dehydrate and adenine employed in the method is 0.1: 1 to 1:0.1 mmol, respectively.

[0024] In an aspect of the present invention, the solvothermal reaction in the method is effected at 100 °C to 200 °C for 48 hrs to 96 hrs.

[0025] In an aspect of the present invention, the yield of zinc-adenine-dicarboxylate MOF obtained in the method is 65-75%.

[0026] In an aspect of the present invention, the activation in the method is effected by heating at 150°C for 12 hrs under vacuum.

[0027] In yet another aspect, the present invention provides a method for capturing or sorbing CO2 form humid atmospheres comprising the steps of: providing zinc-adenine-dicarboxylate MOF as disclosed herein; contacting the zinc-adenine-dicarboxylate MOF with a fluid or gas stream including H2O, CO2, CH4, N2, H2, and the like, wherein CO2is sorbed on the zinc-adenine-dicarboxylate MOF; and optionally regenerating the zinc-adenine-dicarboxylate MOF.

[0028] In an aspect of the present invention, the regeneration in the method is effected by thermal treatment in a vacuum and / or inert gas environment.

[0029] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.BRIEF DESCRIPTION OF THE DRAWINGS:

[0030] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.

[0031] FIG. 1 represents the single crystal X-ray structure of IISERP-MOF33

[0032] FIG. 2A represents PXRDs of the framework after soaking it in solutions of different pH and subjecting to water for prolonged time and repetitive cycles of adsorption and breakthrough experiments shows negligible loss in the crystallinity of the framework.

[0033] FIG. 2B shows the comparison of the experimental and simulated PXRD patternsof IISERP-MOF33 - Bulk purity

[0034] FIG. 2C represent (i) Top Left - Variable temperature PXRD of IISERP-MOF33 confirming thermal stability; (ii) Top Right: Pore-size of IISERP-MOF33 determined using NLDFT fit to the 273K CO2 adsorption isotherm; (iii) Bottom: BET and Langmuir Surface area fit of the IISERP-MOF33 from the 273K CO2 isotherm

[0035] FIG. 3A represents the CO2 adsorption isotherms of IISERP-MOF33 after treatment to harsh relevant conditions.

[0036] FIG. 3B (i) Left represents CO2 adsorption isotherms of IISERP-MOF33 at different temperatures and (ii) Right represents N2 adsorption isotherms of IISERP-MOF33 at different temperatures

[0037] FIG. 4A represents (i) the TGA cycling (LEFT) and (ii) Isocycling (RIGHT) plots of IISERP-MOF33 at 298K showing the cyclability of the MOF without any loss in capacity.

[0038] FIG. 4B represents the TGA plot of IISERP-MOF33 showing thermal stability up to 400 °C

[0039] FIG. 5 represents (i) Left: A selectivity plot of IISERP-MOF33 at 313K showing the exceptional selectivity towards CO2 over N2; (ii) Right: Water adsorption isotherm of IISERP-MOF33 at 298K from 2 different runs - stepped isotherm with reproducibility.

[0040] FIG. 6 represents the PXRD comparison of the steam-treated IISERP-MOF33 with the as-synthesized phase

[0041] FIG. 7 represents the Self-diffusion coefficient for IISERP-MOF33 determined from rate of adsorption measurementsDETAILED DESCRIPTION OF THE INVENTION

[0042] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

[0043] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0044] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0045] In some embodiments, numbers have been used for quantifying weight percentages, ratios, and so forth, to describe and claim certain embodiments of the invention and are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0046] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0047] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0048] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”

[0049] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specificationas if it were individually recited herein.

[0050] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0051] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified.

[0052] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.

[0053] It should also be appreciated that the present disclosure can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.

[0054] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0055] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements a, b, and c, and a second embodiment comprises elements b and d, then the inventive subject matter is also considered to include other remaining combinations of a, b, c, or d, even if not explicitly disclosed.

[0056] As used herein, the term “capturing” or “capture” refers to the act of removing one or more chemical species from a bulk fluid composition (e.g., gas / vapor, liquid, and / or solid). For example, “capturing” may include, but is not limited to, interacting, bonding,diffusing, adsorbing, absorbing, reacting, and sieving, whether chemically, electronically, electrostatically, physically, or kinetically driven.

[0057] As used herein, “carbon dioxide” and / or “CO2” may include solid, liquid, and / or gas / vapor phases.

[0058] Embodiments of the present disclosure relate to metal organic frameworks (MOFs). Specifically, the present disclosure relates to a Three-Dimensional (3D) hydrophobic MOF with a high selectivity industrial CO2 capture, and a method of synthesizing the same. Further, the disclosure relates to a method for industrial CO2 capture using said 3D zinc-adeninate MOF.

[0059] In an embodiment, the present disclosure provides a zinc-adenine-dicarboxylate 3D zinc-adeninate MOF (IISERP-MOF33) with a formula Zn3(Ade)2(PDC)2. (solvent) (IISERP-MOF33), wherein Ade = adeninate; PDC = 2,5-pyridinedicarboxylate; and a method of producing the same.

[0060] In an embodiment of the present disclosure, the solvent is selected from but not limited to Water, methanol and tetrahydrofuran (THF).

[0061] MOFs comprise a network of nodes and ligands, wherein a node has a connectivity capability at three or more functional sites, and a ligand has a connectivity capability at two functional sites each of which connect to a node. Nodes are typically metal ions or metal containing clusters, while ligands are organic ligands. The particular combination of metal nodes and organic ligands within a framework will dictate the framework topology and functionality.

[0062] The MOF consists of a framework comprising zinc adenine pillared by dicarboxylate ligands, and this combination of ligands with zinc makes the composition unprecedented.

[0063] In an embodiment, the present disclosure provides a IISERP-MOF33 with slitshaped ultramicropores and a rigid, robust framework constructed from the multiple chelating ligands. The extended connectivity of the zinc trimers by the adenine and the pillaring dicarboxylate units leads to a 3D framework with slit-shaped ultra micropores of size ~4.5 A.

[0064] In an embodiment of the present disclosure, the IISERP-MOF33 may exhibit one or more of a high removal efficiency and / or high uptake, even at low concentrations of CO2. For example, the IISERP-MOF33 may exhibit a removal efficiency of greater than about 50%, greater than about 75%, but not less than about 90%. In many embodiments, the IISERP-MOF33 exhibit a removal efficiency of greater than about 90%. For example, the IISERP-MOF33 may exhibit a removal efficiency of at least 91%, at least 92%, at least 93%,at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, and / or at least 99.9%.

[0065] In an embodiment of the present disclosure, the IISERP-MOF33 lacks any strongly polar oxygen in the framework, which makes the material have a negligible affinity to water- evidenced by TGA and water sorptions.

[0066] In an embodiment of the present disclosure, the IISERP-MOF33 contain unique slit-shaped pores that are responsible for high uptake of CO2.

[0067] In an embodiment of the present disclosure, the IISERP-MOF33 with adenine and pillaring dicarboxylate units is still showing good stability towards NOx and SOx at the application specific concentrations and more.

[0068] In an embodiment of the present disclosure, the IISERP-MOF33 is stable to SOx and NOx at 500ppm levels; it is stable to oxygen and air at 120 °C, and with stands harsh chemical conditions (pH 2-14). It remains crystalline and porous on the shelf for over 20 months. Such properties are rare for an amine-fimctionalized MOF.

[0069] In an embodiment of the present disclosure, the IISERP-MOF33 exhibits CO2 capacity of 3 to 4mmol / g at 1 bar and 25°C; about 5 to 20% CO2 at 0.15 bar and 25°C. NOx and SOx tolerance of 500 ppm (Fig. 3A); Stable to Steam at 100°C; Stable to Steam and oxygen at 150°C and thermally stable up to 400°C.

[0070] In another aspect, the present disclosure provides a method of synthesizing IISERP-MOF33, said method comprising the steps of: a solvothermal reaction between zinc acetate dihydrate, adenine, and 2,5 pyridine dicarboxylic acid in a solution containing water and methanol, THF and acetic acid, followed by cooling to room temperature to obtain reaction product; filtering reaction product to obtain rod-shaped colorless crystals of IISERP-MOF33; and washing with copious amounts of methanol to obtain IISERP-MOF33.

[0071] In an embodiment of the present disclosure, the ratio of zinc acetate dihydrate, adenine ranges from about 0.1: 1 to 1:0.1 mmol, respectively. Most preferably the ratio is 0.4:0.6

[0072] In an embodiment of the present disclosure, the solvothermal reaction is performed at 100 °C to 200 °C. More preferably 150 °C.

[0073] In an embodiment of the present disclosure, the solvothermal reaction is performed for 48 hrs to 96 hrs. More preferably 72 hrs.

[0074] In an embodiment of the present disclosure, the yield of the IISERP-MOF33 is greater than about 50%, greater than about 60%, but not less than about 70%. In manyembodiments, the yield greater than about 65%. For example, at least 65%, at least 66%, at least 67%, at least 68%, at least 69%, at least 70%, at least 72%, at least 73%, at least 74%, and / or at least 75%.

[0075] In yet another embodiment, the present disclosure provides a method for capturing or sorbing CO2 form humid atmospheres comprising the steps of: contacting the IISERP-MOF33 with a fluid or gas stream including H2O, CO2. CH4, N2, H2, and the like, wherein CO2is sorbed on the IISERP-MOF33; and optionally regenerating IISERP-MOF33.

[0076] In one embodiment of the present disclosure, the CO2capturing comprises the step of contacting IISERP-MOF33 with a fluid or gas stream including H2O, CO2, CH4, N2, H2, and the like. In an embodiment, the contacting may include bringing the metal-organic framework and fluid composition into physical contact, or immediate or close proximity. Examples of the contacting may include, but are not limited to, one or more of feeding, flowing, passing, pumping, and introducing.

[0077] In an embodiment of the present disclosure, the CO2capturing further comprises optional step of regenerating the IISERP-MOF33. The regenerating may include thermal treatment in a vacuum and / or inert gas environment (e.g., under nitrogen).

[0078] In an embodiment of the present disclosure, the contacting may proceed under any suitable conditions (e.g., temperature, pressure, etc.). For example, the contacting may proceed to or at a temperature ranging from about 25° C to about 200° C. In many embodiments, the contacting may proceed at or to a temperature less than about 200° C. In preferred embodiments, the contacting may proceed at or to a temperature of about 25°-35° C. (e.g., about room temperature).

[0079] In an embodiment of the present disclosure, the concentration of CO2in the gas stream may range from about 0% to about 99.9 %. In many embodiments, the concentration of CO2in the fluid composition is less than about 10%. In preferred embodiments, the concentration of CO2in the fluid composition is in the range of about 3 to about 50%. The material is stable to 100% CO2stream as well.

[0080] In an embodiment of the present disclosure, the activated powder of IISERP- MOF33 remains intact in aqueous solutions with pH ranging from 3 to 12 for more than 24 hours, as determined by the PXRD and porosity measurements. It does not show any loss in the crystallinity on soaking in water for a week or on exposure to the atmosphere (RH > 65%) for 18 months. Thus, IISERP-MOF33 has excellent acid stability, humid stability, and shelf life (FIG. 2C).

[0081] In an embodiment of the present disclosure, the finely ground powder form of IISERP-MOF33 can be activated by heating at 150°C for 12 hrs under vacuum.

[0082] In an embodiment of the present disclosure, the IISERP-MOF33 has water / steam stability, chemical stability and is more economical.

[0083] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.EXAMPLES

[0084] The present disclosure is further explained in the form of following examples. However, it is to be understood that the foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.Material and Methods:All the chemicals were purchased from Sigma Aldrich and used without further purification.

[0085] Example 1: Synthesis of IISERP-MOF33 (IISERP-MOF33)A solvothermal reaction between zinc acetate dihydrate (2 mmol), adenine (3 mmol), and 2,5 pyridine dicarboxylic acid (1.6 mmol) in a solution containing 3 ml water, 5 ml methanol, 3 ml THF and 200 pl of acetic acid was carried out at 150°C for 72 hours. After cooling to room temperature, rod-shaped colorless crystals of IISERP-MOF33 were obtained by filtration. The product was washed thoroughly with methanol. The crystals and the bulk material are stable to water and steam. The crystals and the bulk material are finely ground for further use.The finely ground powder form of IISERP-MOF33 was activated by heating at 150°C for 12 hrs under vacuum.

[0086] Example 2: Characterization of IISERP-MOF33 from Example 1Single crystal structure determination: Single-crystal data (FIG. 1) were collected on a Bruker SMART APEX four-circle diffractometer equipped with a CMOS photon 100 detector (Bruker Systems Inc.) and with a Mo Ka radiation (0.71073 A). The incident X-ray beamwas focused and monochromated using Micro focus (IJLLS). Crystal of 1 was mounted on nylon Cryo loops with Paratone-N oil. Data was collected at 100 K. Data was integrated using Bruker SAINT Software and was corrected for absorption using SADABS. Structure was solved by Intrinsic Phasing module of the direct methods and refined using the SHELXTL 2014 software suite. All non-hydrogen atoms were located from iterative examination of difference F-maps following which the structure was refined using leastsquares method. Hydrogen atoms were placed geometrically in a riding model.

[0087] Further characterizations reveal FIG. 2C Top Left - Variable temperature PXRD of IISERP-MOF33 confirming thermal stability; FIG. 2C Top Right: Pore-size of IISERP- MOF33 (3.6 A) determined using NLDFT fit to the 273K CO2 adsorption isotherm; FIG. 2C Bottom: BET (354 m2 / g) and Langmuir Surface (445 m2 / g) area fit of the IISERP-MOF33 from the 273K CO2 isotherm.Stability studies:

[0088] The activated powder of IISERP-MOF33 was soaked in solutions of different pH (3- 12) and water for more than 24 hours, and then the crystallinity was determined by the PXRD (FIG. 2A). FIG. 2B shows the comparison of the experimental and simulated PXRD patterns of IISERP-MOF33 - Bulk purity.

[0089] TGA cycling experiment carried out for 10 cycles of adsorption - desorption also did not show any loss in the gravimetric capacity (FIG. 4A). Further, FIG. 4B represents the TGA plot of IISERP-MOF33 showing thermal stability up to 400 °C.

[0090] In a separate experiment, the finely ground powder of IISERP-MOF33 was tested for its steam stability by placing it inside a highly controlled humidity chamber (ESPEC) for 24 hrs at 80 °C and 80% RH. The sample was stable to steam as evidenced by the PXRD and adsorption isotherms performed on the post-treated samples. IISERP-MOF33 does not show any loss in the crystallinity on soaking in water for a week or on exposure to atmosphere (RH > 65%) for a period of 18 months.

[0091] In a separate experiment, the finely ground powder of IISERP-MOF33 was exposed to NOx and SOx gas generated as follows.NO2 was generated by the reaction of concentrated nitric acid with copper metal.SO2 was generated by the reaction of concentrated nitric acid with copper metal.

[0092] Copper turnings (50 mg) were added to two different two neck round bottom flasks. And H2SO4 (2ml) and HN03 (2ml) was added to the respective flasks through a dropping fuel. On heating the flasks, SO2 and a brown coloured NO2 gas was generated which was fedto the MOF (taken in another round bottom flask). In order to dilute the toxic gases, a balloon of N2 was also attached to the system. The process was continued for 12 hours.

[0093] In an embodiment of the present disclosure, the IISERP-MOF33 is stable to SOx and NOx at 500ppm levels.

[0094] These results not only establish the recyclability of IISERP-MOF33 but also confirm the smooth desorption kinetics.Adsorption isotherm of IISERP-MOF33 from Example 1

[0095] Water adsorption isotherm of IISERP-MOF33 at 298K from 2 different runs - stepped isotherm with reproducibility (FIG. 5, Right).IAST Selectivity of IISERP-MOF33 from Example 1

[0096] CO2 adsorption shows that there is no falls in the CO2 uptake up to a pressure of 0. 15 bar (FIG. 3A). FIG. 3B Left represents CO2 adsorption isotherms of IISERP-MOF33 at different temperatures and FIG. 3B Left Right represents N2 adsorption isotherms of IISERP- MOF33 at different temperatures.

[0097] A selectivity plot of IISERP-MOF33 at 313K showing the exceptional selectivity towards CO2 over N2 (FIG. 5, Left).

[0098] Hence IISERP-MOF33 has excellent humid stability as well as shelf life. For the practical application, a sorbent should have a good recyclability and smooth kinetics in addition to good capacity and selectivity. In this regard, we performed iso-cycling experiment, in which 10 consecutive CO2 adsorption - desorption cycles were performed and no noticeable fall in the volumetric capacity was observed.

[0099] The activated MOF was also exposed to different relative humidities at 50°C for 24 hours each, and the recovered sample was characterized by the PXRD and CO2 sorption at 298K, and it showed that IISERP-MOF33 exhibits a very high degree of hydrolytic stability (Figures 3 A, 5 and 6). For practical application, a sorbent should have good recyclability, smooth kinetics, and good capacity and selectivity. In this regard, we performed the isocycling experiment in which 10 consecutive CO2 adsorption-desorption cycles were performed, and no fall in the volumetric capacity was observed. TGA cycling experiment carried out for 10 cycles of adsorption-desorption also did not show any loss in the gravimetric capacity. These results establish the recyclability of this Zn-MOF and confirm the smooth desorption kinetics. The CO2 self-diffusion coefficient was found to be 5.9e'9m2 / s which is quite comparable to other MOFs and is much higher than Zeolite- 13X used as the industrial standard (Figure 7).

Claims

We Claim:

1. A three-dimensional (3D) hydrophobic zinc-adenine-dicarboxylate MOF having a formula Zn3(Ade)2(PDC)2. (solvent) for selective CO2 capture, wherein Ade is adeninate, PDC is 2,5 -pyridinedicarboxylate, and the solvent is selected from the group consisting of water, methanol, and tetrahydrofuran (THF), wherein the zinc-adenine-dicarboxylate MOF comprises zinc trimmers connected by adenine and pillared by dicarboxylate ligands, and wherein the zinc-adenine-dicarboxylate MOF does not have any strongly polar oxygen in the framework.

2. The 3D hydrophobic zinc-adenine-dicarboxylate MOF as claimed in claim 1, wherein the zinc-adenine-dicarboxylate MOF has slit-shaped ultra micropores of size ~4.5 A.

3. The 3D hydrophobic zinc-adenine-dicarboxylate MOF as claimed in claim 1, wherein the zinc-adenine-dicarboxylate MOF exhibits CO2 capture efficiency of 90-99.9%.

4. The 3D hydrophobic zinc-adenine-dicarboxylate MOF as claimed in claim 1, wherein the zinc-adenine-dicarboxylate MOF exhibits stability to SOx and NOx at 500ppm levels.

5. The 3D hydrophobic zinc-adenine-dicarboxylate MOF as claimed in claim 1, wherein the zinc-adenine-dicarboxylate MOF exhibits stability to oxygen and air at 120 °C, and chemical conditions having pH 2-14.

6. The 3D hydrophobic zinc-adenine-dicarboxylate MOF as claimed in claim 1, wherein the zinc-adenine-dicarboxylate MOF remains crystalline and porous for over 20 months.

7. A method of synthesizing zinc-adenine-dicarboxylate MOF as claimed in claim 1, said method comprising the steps of: a solvothermal reaction between zinc acetate dihydrate, adenine, and 2,5 pyridine dicarboxylic acid in a solution containing water and methanol, THF and acetic acid, followed by cooling to room temperature to obtain reaction product; filtering reaction product to obtain rod-shaped colorless crystals of zinc- adenine-dicarboxylate MOF;washing the crystals of zinc-adenine-dicarboxylate MOF with methanol, followed by grinding to obtain powder form of zinc-adenine-dicarboxylate MOF; and activating the powder form of zinc-adenine-dicarboxylate MOF8. The method as claimed in claim 7, wherein the ratio of zinc acetate dehydrate and adenine is 0.1: 1 to 1:0.1 mmol, respectively.

9. The method as claimed in claim 7, wherein the solvothermal reaction is effected at 100 °C to 200 °C for 48 hrs to 96 hrs.

10. The method as claimed in claim 7, wherein the yield of zinc-adenine-dicarboxylate MOF is 65-75%.

11. The method as claimed in claim 7, wherein the activation is effected by heating at 150°C for 12 hrs under vacuum.

12. A method for capturing or sorbing CO2 form humid atmospheres comprising the steps of: providing zinc-adenine-dicarboxylate MOF as claimed in claim 1; contacting the zinc-adenine-dicarboxylate MOF with a fluid or gas stream including H2O, CO2, CH4, N2, H2, and the like, wherein CO2 is sorbed on the zinc-adenine-dicarboxylate MOF; and optionally regenerating the zinc-adenine-dicarboxylate MOF.

13. The method as claimed in claim 12, wherein the regeneration is effected by thermal treatment in a vacuum and / or inert gas environment.

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