Description:FORM 2
THE PATENTS ACT 1970
[39 OF 1970]
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[see section 10 and rule13]

“Porous Covalent Organic Framework (COF) Coated Zeolite Composites and Methods Thereof”

Name and Address of the Applicants:

Tata Steel limited
Jamshedpur, Jharkhand India 831001
Nationality: Indian

Indian Institute of Science Education and Research (IISER) Kolkata
Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, Mohanpur, West Bengal, India 741246
Nationality: Indian

The following specification particularly describes the invention and the manner in which it is to be performed.


TECHNICAL FIELD
The present disclosure relates to the field of zeolites, Covalent Organic Framework(s) (COF(s)) and composites thereof. Particularly, the present disclosure relates to a composite material comprising Covalent Organic Framework(s) (COF(s)) and zeolite(s), wherein the zeolite(s) is coated by the COF(s), methods of synthesis of said composite material and applications thereof.

BACKGROUND OF THE DISCLOSURE
The emission of greenhouse gases which includes CO2 is a matter of serious concern for centuries. The largest source of this gas is human activities like burning fossil fuels for electricity, heat, and transportation. Apart from that, industrial uses of fossil fuels for generating energy are another major source for the emission of CO2. Thus, it is very difficult to restrict the emission of CO2 without hampering human lifestyle. To tackle and alleviate this problem, the scientists have proposed an effective strategy called carbon capture and sequestration (CCS). The goal of this strategy is to develop new materials with high performance which can capture CO2 in a low-cost, efficient, and durable manner. For these purposes, the role of porous materials is found to be highly promising. Zeolites are a promising example of such porous material with a high chemical and thermal stability as well as high CO2 capacity and selectivity. However, the instability of zeolites in acidic and water environment is the major drawback of zeolites. The same issue is faced by the next-generation porous materials - Metal-Organic Frameworks (MOFs). Though they are compact with all the requirements- high selectivity, high CO2 capture capacity, good recyclability, uniform pore size distribution, low cost for the regeneration, easy to post modification, etc.; their instability in water due to strong binding with H2O than CO2 prevents their use in real-world CO2 capture applications. Covalent Organic Frameworks (COFs), a newly emerging class of porous crystalline materials, have been proposed as an excellent candidate for CO2 capture because they possess almost all the merits of MOFs as well as structural and chemical tenability. Some COFs can be used successively and repeatedly and maintain their good CO2 capture performance. Although the COFs are porous material, still the CO2 uptake capacity of COFs itself is not as much as free zeolite.

Zeolites are crystalline microporous aluminosilicates with a framework structure of three-dimensional tetrahedral units generating a network of pores and cavities having molecular dimensions. They are built by SiO4 and AlO4 tetrahedra (or by other tetrahedra such as PO4, GaO4, etc.), which are linked by oxygen atoms. A defining feature of zeolites is that their frameworks are made up of 4-coordinated atoms forming tetrahedra. These tetrahedra are linked together by their corners and make a rich variety of beautiful structures. The framework structure may contain linked cages, cavities, or channels, which are big enough to allow small molecules to enter. The system of large voids explains the consistent low specific density of these compounds. In zeolites, the voids are interconnected and form long wide channels of various sizes depending on the compound. These channels allow the easy drift of the resident ions and molecules into and out of the structure. The aluminosilicate framework is negatively charged and attracts the positive cations that reside in cages to compensate negative charge of the framework. Due to specific pore sizes and large surface areas, they offer a potential for a variety of industrial uses including molecular sieves, ion-exchangers, adsorbents, catalysts, detergent builders, the removal of cations from acid mine drainage and industrial wastewater. Zeolites are generally a good material for CO2 capture except for the drawback that when this material is used for the CO2 capture, the presence of acidic environment reduces the performance.

COFs are porous covalent organic structures whose pillar is composed entirely of light elements (B, C, N, O, Si). COFs are made of a combination of organic building units covalently linked into extended structures to make crystalline materials. The attainment of crystals is done by several techniques in which a balance is struck between the thermodynamic reversibility of the linking reactions and their kinetics. This success has led to the expansion of COF materials to include organic units linked by these strong covalent bonds: B-O, C-N, B-N, and B-O-Si. On a fundamental level, the directionality of covalent bonds provides a means of controlling how building units come together into predesigned structures. These advantages, combined with the strength of the linkages, lead to robust materials, which could be exploited in various applications, including gas storage and separation, catalysis, and electronics. The challenge in assembling materials in this way is to overcome the “crystallization problem”: the linking of molecular building blocks by strong covalent bonds often yields amorphous or poorly defined materials. This problem has been addressed fruitfully in making COFs through the formation of B-O, C-N, B-N, and B-O-Si linkages. For a porous framework to achieve the high CO2 uptake, it must satisfy the following requirements: significant adsorption capacity, efficient charge/discharge rate, high hydrophobicity, moderate adsorption enthalpy, and high heat capacity. Although the scientific community is focusing on the COF materials for quite some time, yet most of the reported COFs are 2D in nature and there are very few reports which deal with the synthesis, structure, and property of 3D COFs. Thus, a further development of 3D COFs is necessary which might present many opportunities in the functional material chemistry owing to their unique porous structure and potential applications. To synthesize the 3D COFs, at least one organic linker must be three-dimensional in nature which could connect with the other building block in all three-dimensional ways to form a covalently linked three-dimensional framework structure. As the framework expands three-dimensionally, the structure of 3D COFs could be of different topology and thereby generating a 3D pore channel which could be responsible for a very high value of the surface area in these materials.

Although zeolites and COFs are porous materials that can be employed for capturing greenhouse gases, there is a need for a zeolite and/or COF-based materials that are chemically and thermally stable and at the same time are stable in acidic and water environment. The present disclosure attempts to address this need.

STATEMENT OF THE DISCLOSURE
The present disclosure provides a composite material comprising a Covalent Organic Framework (COF) in an amount of about 2-10 % w/w and a zeolite in an amount of about 90-98 % w/w, wherein the zeolite(s) is coated by the COF(s).

The present disclosure also provides a method of preparing the composite material described herein, the method comprising: a) adding the zeolite in a solvent to obtain a zeolite solution; b) adding an aromatic diamine to the zeolite solution and sonicating to obtain a homogenous solution; c) adding trifluoroacetic acid to the homogeneous solution; d) adding a trialdehyde solution to the homogenous solution to obtain a reaction mixture; e) maintaining the reaction mixture at about 30-40? in a closed reaction vessel for about 2-4 hours; and f) subjecting the reaction mixture of step (e) to about 60-80? for about 12-24 hours to obtain the composite material.

The present disclosure also relates to a method for capturing greenhouse gases from a source, comprising contacting the source with the composite material described herein.

The present disclosure further provides a device for capturing greenhouse gases comprising the composite material described herein as a sorbent.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure where:

Figure 1 shows the structure of Zeolite A (a) and Zeolite X (b).
Figure 2 shows a schematic representation of the TpAzo COF/zeolite composite formation and selective CO2 gas separation.
Figure 3 depicts the synthetic scheme of formation of TpAzo COF (COF@TpAzo).
Figure 4 depicts the synthesis of solution-processable COF@TpAzo nanospheres in DCM.
Figure 5 shows the comparison of FT-IR spectra between synthesized COF@TpAzo and the starting materials (Tp and Azo).
Figure 6 shows synthesis of COF@TpAzo coated Zeolite nanospheres coated zeolite in DCM.
Figure 7 shows photograph of the 5A Zeolite @TpAzo COF (left) and 13X Zeolite @TpAzo COF (right) after the synthesis.
Figure 8 shows SEM images of (a,b) 5 A zeolite and (c,d) 5A zeolite@ TPAzo composites (scale of a, b are 1mm and c, d are 100 nm and 0.5 mm respectively).
Figure 9 shows comparative TGA spectra of TpAzo COF, 5A Zeolite, and the TpAzo COF coated 5A Zeolite composites.
Figure 10 shows comparison of FT-IR spectra between synthesized 13X Zeolite @TpAzo COF, 13X Zeolite, and TpAzo COF.
Figure 11 shows comparison of FT-IR spectra between synthesized 5A Zeolite @TpAzo COF, 5A Zeolite, and TpAzo COF.
Figure 12 shows the PXRD Analysis of 5A@TpAzo composite.
Figure 13 shows comparison of N2 uptake of 5A zeolite and 5A zeolite@TpAzo at 1 bar, 273K.
Figure 14 shows comparison of N2 uptake of 13X zeolite and 13X zeolite@TpAzo at 1 bar, 273K.
Figure 15 shows the pictorial representation and CO2 uptake of TpAzo COF at 1 bar, 293K.
Figure 16 shows the pictorial representation and CO2 uptake of 13X zeolite@TpAzo at 1 bar, 273K.
Figure 17 shows the pictorial representation and CO2 uptake of 5A zeolite@TpAzo at 1 bar, 273K.
Figure 18 shows comparison of CO2 uptake capacity for all 5A Zeolite@TpAzo and 5A@0.5xTpAzo materials at 1 bar and 0°C.
Figure 19 shows the CO2 uptake capacity of 5A Zeolite@0.5xTpAzo at high pressures (10 bar, 20 bar and 50 bar) and 10°C.
Figure 20 shows the CO2 adsorption data of Zeolite 5A at different pressures following Sips model.
Figure 21 shows the pictorial representation of the modification of Zeolite@TpAzo COF with EDA.
Figure 22 shows the possible binding motif of the EDA inside zeolite@COF materials.
Figure 23 shows the CO2 uptake of 5A-zeolite@TpAzo, 5A-zeolite@TpAzo@EDA, and 5A-zeolite@TpAzo@3(N)HCl.
Figure 24 depicts the structures of TpTTA COF and its starting materials Tp and TTA.
Figure 25 shows the comparison of TGA data for TpTTA COF, 5A Zeolite, 5A@TpTTA (96wt% 5A) and 5A@0.5xTpTTA (98wt% 5A) materials.
Figure 26 shows the comparison of CO2 uptake capacity for 5A Zeolite, 5A@TpTTA (96wt% 5A) and 5A@0.5xTpTTA (98wt% 5A) materials at 1 bar and 0°C.

DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Reference throughout this specification to “some embodiments”, “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in some embodiments”, “in one embodiment” or “in an embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

As used herein, the term ‘composite material’ or ‘composite’ refers to the product of the present disclosure comprising Covalent Organic Framework(s) (COF(s)) and zeolite(s), wherein the COF coats the zeolite.

As used herein, the term ‘covalent organic framework’ or ‘COF’ refers to a class of materials that form two- or three- dimensional crystalline organic polymeric structures through reactions between organic precursors resulting in strong, covalent bonds to afford porous, stable, and crystalline materials.

As used herein, the term ‘coated’ or ‘coating’ or ‘coats’ or other obvious variants thereof refer to the structural feature of the composite material of the present disclosure wherein the zeolite(s) is protected by the COF by virtue of the zeolite being coated by the COF or enclosed within the COF.

Sometimes, the present disclosure refers to the composite in the form ‘zeolite@COF’.

As used throughout the present disclosure, the term ‘Tp’ has been used as an abbreviation for 1,3,5-triformylphloroglucinol.

The term “about” as used herein encompasses variations of +/-10% and more preferably +/-5%, as such variations are appropriate for practicing the present invention.

The present disclosure provides a composite material comprising a COF in an amount of about 2-10 % w/w and a zeolite in an amount of about 90-98 % w/w, wherein the zeolite is coated by the COF. In some embodiments, the composite comprises about 2-8% w/w COF and about 92-98% w/w zeolite, about 2-6% w/w COF and about 94-98% w/w zeolite, about 2-5% w/w COF and about 95-98% w/w zeolite, about 4-10% w/w COF and about 90-96% w/w zeolite, about 4-8% w/w COF and about 92-96% w/w zeolite, about 4-6% w/w COF and about 94-96% w/w zeolite, about 5-10% w/w COF and about 90-95% w/w zeolite, about 5-8% w/w COF and about 92-95% w/w zeolite, about 6-10% w/w COF and about 90-94% w/w zeolite, about 6-8% w/w COF and about 92-94% w/w zeolite or about 8-10% w/w COF and 90-92% w/w zeolite, including values and ranges thereof.

In some embodiments, the composite material comprises COF in an amount of about 2%, about 2.5%, about 3%, about 3.5%, about 4%, about 4.5%, about 5%, about 5.5%, about 6%, about 6.5%, about 7%, about 7.5%, about 8%, about 8.5%, about 9%, about 9.5% or about 10% w/w.

In some embodiments, the composite material comprises zeolite in an amount of about 90%, about 90.5%, about 91%, about 91.5%, about 92%, about 92.5%, about 93%, about 93.5%, about 94%, about 94.5%, about 95%, about 95.5%, about 96%, about 96.5%, about 97%, about 97.5% or about 98% w/w.

Zeolites are less expensive than the COF materials. As the composites of the present disclosure comprise lower amounts of COF (2-10 wt%) and higher amounts of zeolite (90-98 wt%), the cost for synthesizing the present composites is far less than the composites where COF is used in higher amounts. Further, the thermal profile (TGA) shows that the composite material composed of 90 wt% or more zeolites is stable up to 9000?. As the amount of COF employed in preparing the composite is low, a method comprising mechanochemical grinding cannot be employed to prepare the composite as it will lead to the loss of crystallinity in the composite structure. In the present invention, the COF coated zeolite composite material is synthesized using a solvothermal process.

In some embodiments, the zeolite(s) is selected from a group comprising zeolite A, zeolite X, zeolite Y, mordenite, zeolite L, zeolite beta, ZSM-5, zeolite 5A, zeolite 13X, or any combination thereof.

In some preferred embodiments, the zeolite(s) is selected from zeolite 5A and zeolite 13X or a combination thereof. Zeolites 5A and 13X have been interchangeably referred to as ‘5A’ and ‘13X’, respectively.

In some embodiments, the COF(s) is selected from a group comprising Tp-Azo, TpOMe-Azo, Tp-BD, Tp-BDMe2, Tp-Azo-BDMe2, TPTTA or any combination thereof.

In some preferred embodiments, the COF(s) is Tp-Azo or TPTTA. For purposes of clarity, reference to ‘Tp-Azo’ or ‘TpAzo’ or ‘ Tp Azo’ alone or ahead of ‘COF’ for e.g. ‘TpAzo COF’ in the present disclosure implies reference to the COF formed from 1,3,5-triformylphloroglucinol (Tp) and 4,4’-Azodianiline (Azo). Reference to TPTTA alone or ahead of ‘COF’ for e.g., ‘TpTTA COF’ in the present disclosure implies reference to the COF formed from 1,3,5-triformylphloroglucinol (Tp) and 4,4',4''-(1,3,5-Triazine-2,4,6-triyl) trianiline (TTA). Said references are intended to provide clarity as to the specific COF employed.

In some exemplary embodiments of the composites, the zeolite is selected from zeolite 5A, zeolite 13X or both and the COF is Tp-Azo.

In some exemplary embodiments of the composites, the zeolite is selected from zeolite 5A, zeolite 13X or both and the COF is TpTTA.

Industrially, zeolites are used for removing carbon dioxide (CO2) from high-pressure fuel gas streams using Pressure swing adsorption (PSA) and temperature swing adsorption (TSA) techniques. In order to facilitate efficient separation of gases such as CO2 it is desirable for zeolites to have high surface area. Depending upon the abundance of silica in zeolites they are classified into three categories, namely, “Low-silica" or aluminum-rich zeolites A and X, "Intermediate silica" zeolites: zeolite Y, mordenite, zeolite L, natural zeolites, and "High silica" zeolites: zeolite beta, ZSM-5, etc. Figure 1 provides the structure of Zeolite A (a) and Zeolite X (b). Importantly, among all, zeolite 5A and zeolite 13X are vastly used in industries for the separation of CO2/CH4 and they are among the most researched zeolites to date. Concern over climate warming and the need for sequestration of carbon dioxide has resulted in many studies of the adsorption of carbon dioxide on 5A and 13X zeolite.

Although both the zeolite and COF are highly porous in nature, COF has comparatively higher porosity and hence surface area. While zeolite has more thermal stability and CO2 adsorption capacity, the COF has more chemical stability and hydrophobicity. Zeolite is easy to prepare and is a naturally occurring material, but COF is a synthetic material. Protecting zeolite with COF as per the present disclosure confers improved porosity (hence surface area), chemical stability, and water resistance to the zeolite to facilitate efficient CO2 capture and sequestration at standard temperature and pressure as well as high pressure conditions. Further, as the COF coating protects the zeolite from acidic environment, it increases its chemical stability without compromising the CO2 uptake capacity of the zeolite itself. Therefore, the inventors have found that the COF-coated zeolite composite material of the present disclosure enhances the activity of the zeolite in terms of protection from acid up to a certain concentration and the improvement of surface area. While pristine zeolite powder shows far below 1000 m2/g surface area, the composite of the present disclosure boosts it to 1500-2000 m2/g depending upon the percentage of zeolite used. The schematic representation of the TpAzo COF/zeolite composite formation and selective CO2 gas separation is shown in Figure 2.

In some embodiments, the composite material has about 32% to about 48% higher surface area than pristine zeolite.

In non-limiting embodiments, the composite material has about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47% or about 48% higher surface area than pristine zeolite.

In some embodiments, the composite material has a surface area ranging from about 1500m2/g to about 2000m2/g.

In non-limiting embodiments, surface area of the composite material is about 1500m2/g, about 1600m2/g, about 1700m2/g, about 1800m2/g, about 1900m2/g or about 2000m2/g.

In some embodiments, the composite material comprises an amine selected from ethylenediamine, mono-ethyl amine, ethanolamine or a combination thereof. The presence of amine increases the CO2 uptake capacity of the composite.

In some preferred embodiments, the amine is ethylenediamine.

In some exemplary embodiments, the composite material comprises zeolite selected from zeolite 5A, zeolite 13X or both, Tp-Azo and ethylenediamine.

In some exemplary embodiments, the composite material comprises zeolite selected from zeolite 5A, zeolite 13X or both, TpTTA and ethylenediamine.

The present disclosure further provides a method of preparing the composite material, wherein said method comprises: a. adding the zeolite in a solvent to obtain a zeolite solution; b. adding an aromatic diamine or triamine to the zeolite solution and sonicating to obtain a homogenous solution; c. adding trifluoroacetic acid to the homogeneous solution; d. adding a trialdehyde solution to the homogenous solution to obtain a reaction mixture; e. maintaining the reaction mixture at about 30-40? in a closed reaction vessel for about 2-4 hours; and f. subjecting the reaction mixture of step (e) to about 60-80? for about 12-24 hours to obtain the composite material.

In non-limiting embodiments, in step (e) of the method, the reaction mixture is maintained in a closed reaction vessel at about 30?, about 31?, about 32?, about 33?, about 34?, about 35?, about 36?, about 37?, about 38?, about 39? or about 40?.

In non-limiting embodiments, in step (f) of the method, the reaction mixture is subjected to about 60-80? including values and ranges thereof, such as about 60-75?, about 60-70?, about 70-80?, about 60?, about 62?, about 64?, about 66?, about 68?, about 70?, about 72?, about 74?, about 76?, about 78? or about 80? for about 24 hours.

In some embodiments, the zeolite(s) is selected from zeolite A, zeolite X, zeolite Y, mordenite, zeolite L, zeolite beta, ZSM-5, zeolite 5A, zeolite 13X, or a combination thereof.

In some embodiments, the solvent to which the zeolite is added to prepare the zeolite solution is selected from dichloromethane (DCM), dimethylformamide (DMF), acetonitrile, or a combination thereof.

In some embodiments, the aromatic diamine is selected from 4,4’-Azodianiline (Azo), Benzidine (BD), 3,3’-dimethylbenzidine (BDMe2), 3,3’-dinitrobenzidine (BD(NO2)2), 3,3’-dihydroxylbenzidine (BD(OH)2), 3,3’-dimethoxybenzidine (BD(OMe)2), Azo-BD, or a combination thereof. In some embodiments, the aromatic triamine is 4,4',4''-(1,3,5-Triazine-2,4,6-triyl) trianiline (TTA), 1,3,5- Tris(4-aminophenyl)benzene (TAPB), or a combination thereof.

In some embodiments, the trialdehyde is triformylphloroglucinol (Tp).
In some embodiments, the trialdehyde solution is prepared by adding the trialdehyde to dichloromethane.

In some embodiments, the method described herein comprises adding an amine to the composite material.

In some embodiments, the amine is selected from ethylenediamine (EDA), mono-ethyl amine, ethanolamine or a combination thereof.

In preferred non-limiting embodiments, the amine is ethylenediamine (EDA).

In some embodiments, after the composite is prepared, the method described herein comprises: a. washing the composite material; and b. drying the washed composite material.

In some embodiments, the washing is performed with a solvent selected from a group comprising dichloromethane, N, N-dimethylacetamide, water, ethanol, acetone and hexane or a combination thereof; and the drying is performed at a temperature of about 120?.

In some embodiments, the washing is performed sequentially with dichloromethane, N, N-dimethylacetamide, water, ethanol, acetone and hexane.

Accordingly, in some embodiments, the method of preparing the composite material comprises-
adding the zeolite in a solvent to obtain a zeolite solution;
adding an aromatic diamine or triamine to the zeolite solution and sonicating to obtain a homogenous solution;
adding trifluoroacetic acid to the homogeneous solution;
adding a trialdehyde solution to the homogenous solution to obtain a reaction mixture;
maintaining the reaction mixture at about 30-40? in a closed reaction vessel for about 2-4 hours;
subjecting the reaction mixture of step (e) to about 60-80? for about 12-24 hours to obtain the composite material;
washing the composite material; and
drying the washed composite material.

In some other embodiments, the method of preparing the composite material comprises-
adding the zeolite in a solvent to obtain a zeolite solution;
adding an aromatic diamine or triamine to the zeolite solution and sonicating to obtain a homogenous solution;
adding trifluoroacetic acid to the homogeneous solution;
adding a trialdehyde solution to the homogenous solution to obtain a reaction mixture;
maintaining the reaction mixture at about 30-40? in a closed reaction vessel for about 2-4 hours;
subjecting the reaction mixture of step (e) to about 60-80? for about 12-24 hours to obtain the composite material;
adding a diamine to the composite material;
washing the composite material; and
drying the washed composite material.

The present disclosure further provides a method for capturing greenhouse gases from a source, comprising contacting the source with the composite material described herein.

In some embodiments, the greenhouse gas is selected from carbon dioxide, carbon monoxide, hydrogen, methane, oxygen, nitrogen or a combination thereof.

In exemplary embodiments, the composite material is 5A zeolite@ TpAzo, 13X zeolite@ TpAzo, 5A zeolite@ TpAzo_EDA, 13X zeolite@ TpAzo_EDA, 5A zeolite@ TpTTA, 13X zeolite@ TpTTA, 5A zeolite@ TpTTA_EDA or 13X zeolite@ TpTTA_EDA, having varying amounts of the zeolite and/or the COF as herein described.

The present disclosure further provides a device for capturing greenhouse gases comprising the composite material described herein as a sorbent.

In some embodiments, the greenhouse gas captured by the present composites is selected from carbon dioxide, carbon monoxide, hydrogen, methane, oxygen, nitrogen or a combination thereof.

Overall, the process of the present disclosure provides a zeolite based composite material that while retaining the functionality and properties of zeolite has improved chemical stability and high surface area. Also provided herein is a simple method of preparing the composite. The product and the method of the present disclosure may have obvious variants such as but not limited to composites comprising obvious alternatives or functionally identical alternatives of the COF(s) and zeolite(s) defined herein, reliance on ratios and proportions marginally different from those described herein, leading to no significant difference in the performance of the final composite, employment of a different order of method steps, reliance on slightly differing physical parameters during the method leading to no significant difference in process efficiency and post processing steps for the obtained composite. Taken together, the method of the present disclosure provides multiple advantages such as but not limited to:
High chemical stability of the zeolite-based composite;
High water resistance of the zeolite-based composite;
High surface area of the zeolite-based composite;
Applicability of the zeolite-based composite in selective gas separation even in conditions generally unfavourable for zeolites per se.

It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES
Materials and methods
Zeolite 5A
This zeolite has unique selectivity, acid properties, and high thermal stability, uniform pore size, definite skeleton structure, and high porosity (556 m2/g at 273K). The chemical formula is Ca5Na3[(AlO2)12(SiO2)12]. xH2O and could be selective for CO2 adsorption due to the strong interactions of the quadruple moment of CO2 and the cation positioned in the zeolite structure. The size cage of calcium zeolite 5A has an internal volume of 776 Å, formed by a cubic lattice of sodalites. The free aperture of the pore is 4.2 Å, allowing for the passage of molecules with a kinetic diameter of <4.9 Å. The mechanism of CO2 Adsorption on zeolite 5A follows physical adsorption (physisorption) and chemical adsorption (chemisorption). In physisorption, the target molecules are attracted to the surface of pore walls within a high surface-area sorbent by van der Waals forces and have a low heat of adsorption that is only slightly greater than the heat of sublimation of the adsorbate. This type is suitable for the insoluble adsorption process in the adsorbent but only to the surface. Chemisorption is a process involving the exchange and transfer of valence electrons between the molecule adsorbent and atoms (molecules) on the surface of the adsorbent to form a covalent bond. This process will decrease the adsorbent capacity due to its strong covalent bind so that the process is not reversible. The bond is formed strongly which is a monolayer. In chemisorption, there are a fixed number of Al-O sites, each of which will bind to the carbon dioxide.

Zeolite 13X
Zeolite NaX or commonly known as zeolite 13X has found wide use in industry for the separation of carbon dioxide from air, methane-containing landfill gas, and flue gases. Due to its low energy consumption and ease of operation, the zeolite-13X molecular-sieve pressure swing adsorption process has become the method of choice for the recovery and capture of carbon dioxide from air and flue gas. It is a synthetic crystalline sodium aluminosilicate and in the dehydrated form, the framework unit cell has the chemical formula Nax(AlO2)x(SiO2)192-x where, 77 = x = 96. The primary building units (PBUs) are alternating SiO4 and AlO4 tetrahedra with silicon or aluminium atoms at their centres and oxygen atoms at the vertices. Each AlO2 group in the zeolite framework introduces a negative charge that is compensated by the presence of an extra-framework sodium (Na+) ion. The free aperture of the pore is 2.2 Å. The binding with the carbon dioxide is similar to that of the zeolite 5A. The zeolite shows a surface area of ~535 m2/g. The surface area gradually decreases with the increase of zeolite percentage in the TpAzo COF.

EXAMPLE 1: Synthesis of TpAzo COF
About 0.045mmol of 4,4’-Azodianiline (Azo) was added into 100 ml dry dichloromethane (DCM) at room temperature, which resulted in a transparent homogeneous solution (light yellow coloured transparent homogeneous solution for Azo amine). Trifluoroacetic acid (20 µl) was added directly to the solution as the catalyst for Schiff base reaction which turned the colour of the solution from dark yellow and light yellow to wine red and orange respectively. Finally, a solution of 0.03 mmol of the trialdehyde 1,3,5-triformylphloroglucinol (Tp) in 100 ml dry DCM was added slowly with stirring at room temperature. The reaction mixture was kept at 30-40°C in a closed vessel and after 2-4 hours the reaction mixture started becoming opaque. To produce solution-processable COF nanospheres with higher crystallinity and porosity, the reaction was performed under refluxing conditions (~60 – 80°C) using a 250 ml round bottom flask. After 12-15 hours, when all the starting materials were consumed, a stable well-dispersed solution of COF nanospheres was obtained with high crystallinity and porosity. The pore diameter of the COF was found to be 2.7 nm. The refluxing condition (60-90°C) produces more crystalline and porous COF nanospheres. A synthetic scheme of formation of TpAzo COF (COF@TpAzo) and the synthesis of solution-processable COF@TpAzo nanospheres in DCM are shown in Figures 3 and 4, respectively.

EXAMPLE 2: FTIR Characterization of TpAzo COF
The spectra were obtained using a Bruker Optics ALPHAE spectrometer with a universal Zn-Se ATR (attenuated total reflection) accessory. FTIR was used to demonstrate the successful formation of COF@TpAzo from the starting materials like Tp and Azo. The disappearance of the N-H stretching bands at 3338 and 3375 cm-1 coming from Azo, the C=O stretching band (1636 cm-1) of Tp (Figure 5) and simultaneously the appearance of (C=O, 1616 cm-1), (C=C, 1554cm-1), and (C-N, 1225 cm-1) indicate the formation of COF@TpAzo with ß-ketoenamine backbone. The FTIR spectroscopy of COF@TpAzo also matches well with that of the literature.

EXAMPLE 3: Synthesis of the composite zeolite@ TpAzo COF
In the first step, the required zeolite (~ 500mg of either 5A or 13X) was taken in 30 ml dry DCM and sonicated for 10 minutes. Then into this solution of zeolite, the diamine (0.045 mmol) (Azo) was added respectively at room temperature, and sonicated for the next 10 minutes, which resulted in a transparent homogeneous solution (light yellow coloured homogeneous solution). Trifluoroacetic acid (20 µl) was added directly to the solution as the catalyst for Schiff base reaction which turned the colour of the solution from dark yellow and light yellow to wine red and orange respectively. Finally, a solution of 0.03 mmol of the trialdehyde 1,3,5-triformylphloroglucinol (Tp) in 100 ml dry DCM was added slowly with stirring at room temperature. The reaction mixture was kept at 30-40°C in a closed vessel and after 3-4 hours the reaction mixture started becoming opaque and then performed under refluxing condition (~60 – 80°C) for the next 24 hours using a 250 ml round bottom flask. Synthesis of COF@TpAzo coated Zeolite nanospheres coated zeolite in DCM is shown in Figure 6.

After the reaction was complete, the solution was filtered using Whatman filter paper grade 42. The solid obtained was washed by DCM, DMAc, H2O, EtOH, Acetone, and hexane respectively. Then, the solid was dried in an oven (120 °C) for the next 24 hours to remove all undesired solvent molecules. The yield obtained was approximately more than 90% which is very cost-effective and desirable. Figure 7 shows the photograph of the 5A Zeolite @TpAzo COF (left) and 13X Zeolite @TpAzo COF (right) after synthesis. Figure 8 shows the Scanning Electron Microscopy (SEM) images of the zeolite@ TPAzo composites. From the images, the successful coating of COF material on zeolite surface is clearly evidenced.

Example 4: Thermogravimetric Analysis (TGA)
The composite as prepared in Example 3, zeolite 5A and TpAzo COF of Example 1 alone were subjected to thermogravimetric analysis.

The TGA curves of the COF and the composites showed thermal stability up to 400 °C. However, there was a 2 to 8% weight loss before 200 °C in the case of the composites which was absent in the TpAzo COF itself (Figure 9). This is completely due to the removal of trapped H2O from the zeolite. Zeolites contain a large amount of water in them and hence, pristine zeolites lose water during heat and there is no other loss in the whole range of heating even up to 900 °C. However, such weight loss is much lesser for composite material due to the increased hydrophobicity. The weight percentages shown in Figure 9 (12-15 wt% COF and 85-88 wt% zeolite) are different from the weight percentages employed in the synthesis of the composite (2-10 wt% COF and 90-98 wt% zeolite) which is likely due to removal of moisture from the zeolites during TGA measurements.

Example 5: Fourier Transform Infrared (FTIR) Analysis
FTIR was performed for the composites of the present disclosure as well as their starting materials. Figures 10 and 11 demonstrate the successful formation of 13X Zeolite@TpAzo COF and 5A Zeolite@TpAzo COF respectively, from the starting materials like zeolite, Tp aldehyde, and Azo amine.

Example 6: Powder X-Ray Diffraction (PXRD) Analysis
The composite of Example 3 and pristine zeolite were subjected to PXRD analysis and the results are shown in Figure 12. COF coated zeolites showed the intense peak of 2? value at 3.2 ± 0.2? which indicates the diffraction from (100) plane of TpAzo COF. This peak became more intense when the amount of 5A Zeolite was changed from 500mg to 200mg for 5A@TpAzo composites. From the result, it was concluded that with the decreasing amount of zeolites for the COF coated materials, COF coating became more acute as the amount of COF is the same.

Example 7: Porosity Measurement (N2 Adsorption)
The screening was done with different amounts of both 5A and 13X zeolites (Figures 13 and 14, respectively). The surface area varied with the amounts of zeolite added to the COF during the synthesis. The higher amount of zeolite destroyed the crystallinity of COF structure by intruding inside the packing of lattices. The results are depicted below in Table 1. As shown, there was ~48% and ~32% increase in surface area of the zeolite after COF coating.

Table 1: Comparison of the increase in surface area of the 5A and 13X zeolite after COF coating

Example 8: CO2 Uptake Study
At low pressure
The CO2 uptake data for the TpAzo-COF was first measured. The SABET of this TpAzo COF was quite high at ~2800 m2/g while it also exhibited moderate CO2 adsorption of ~54 cc/g (Figure 15). Next, the CO2 uptake for the zeolite@TpAzoCOF was measured. The percentage of COFs in zeolite@TpAzoCOF was also varied and their impact on CO2 tested. As shown in Figures 16 and 17 as well as in Table 2 below, the composites of the present disclosure exhibit CO2 uptake value comparable to that of zeolite alone.

Table 1: Comparison of the CO2 uptake data of TpAzo COF and Zeolite@TpAzo COF at 273 K

With varying concentrations of zeolite and COF
Composites containing three different amounts of 5A Zeolites (500mg, 300mg and 200mg) were prepared. Composites were also prepared with half amount of COF. All the composites are shown in Table 3 below:
Zeolites Amount of Zeolites COFs Amount of COFs Materials
5A 500mg TpAzo 20mg 500 mg 5A@TpAzo
300mg TpAzo 20mg 300 mg 5A@TpAzo
200mg TpAzo 20mg 200 mg 5A@TpAzo

5A 500mg TpAzo 10mg 500 mg 5A@0.5xTpAzo
300mg TpAzo 10mg 300 mg 5A@0.5xTpAzo
200mg TpAzo 10mg 200 mg 5A@0.5xTpAzo
Table 3: Composite materials prepared with varying amounts of zeolite 5A and TpAzo
The CO2 uptake data of the prepared composites was tested and compared with 5A Zeolite and TpAzo COF at very low pressure of 1 bar and 0ºC temperature. While TpAzo COF showed CO2 adsorption of ~56 cc/g, 5A zeolite showed CO2 adsorption of 138 cc/g at 0ºC.

As shown in Figure 18 and Table 4 below, in all conditions, the composites showed high CO2 uptake data. 500mg 5A@0.5xTpAzo showed highest CO2 uptake of 132 cc/g at 0ºC.
Materials CO2 uptake data
(cc/g)
5A Zeolite 138
TpAzo 56
500 mg 5A@TpAzo 128
300 mg 5A@TpAzo 97
200 mg 5A@TpAzo 106
500 mg 5A@0.5xTpAzo 132
300 mg 5A@0.5xTpAzo 116
200 mg 5A@0.5xTpAzo 119
Table 4: Comparative CO2 uptake data for all materials at 273K

At high pressures
For the high-pressure measurement, first the sample was regenerated at 100 degrees Celsius for 4-5 hours, weighed and filled into a 10cc reactor. At 10 degrees Celsius, the reactor was placed in a chiller, and gas was charged at the desired pressure (10 bar, 20 bar and 50 bar). A time period of 1 hour was allowed to examine the data from the data logger. After a constant value was obtained, it was immediately placed in a sand bath at 50 degrees Celsius for 1 hour, after which the temperature was increased to 70 degrees Celsius.
The CO2 uptake capacity of 5A Zeolite@0.5xTpAzo at high pressures (10 bar, 20 bar and 50 bar) and 10°C are shown in Figure 19 and Table 5 below.
Materials Pressure
(bar) millimoles of CO2 consumed (10ºC)
5A zeolite@0.5xTpAzo (24 hrs) 10 8.5
5A zeolite@0.5xTpAzo (24 hrs) 20 14
5A zeolite@0.5xTpAzo (24 hrs) 50 20

Table 5: CO2 uptake capacity of 5A Zeolite@0.5xTpAzo at high pressure (10 bar, 20 bar and 50 bar) and 10ºC

As can be seen from the above table, the composite of the present disclosure shows CO2 uptake even at very high pressures.

CO2 adsorption by 5A zeolite:
Veawab et al (Energy Procedia 114 (2017) 2450 – 2459) have developed a generic model to calculate the CO2 adsorption at different pressure and Sips model provides the best fit with the isotherm curves for zeolite 13X, zeolite 5A, zeolite 4A, and carbon molecular sieve (MSC-3R), which indicates that an adsorbed molecule can occupy more than one adsorption site during the adsorption process. The generic equation for the 5A zeolite adsorbent is given below:

q= q_max (P^1.64 ?[6.3783?exp?^(-0.005T)]?^1.64)/(1+?[6.3783?exp?^(-0.005T)]?^1.64 ) (1)

Where qmax is the maximum zeolite loading.

Figure 20 shows the CO2 adsorption data of Zeolite 5A at different pressures following Sips model. As can be observed from the figure, the adsorption capacity of zeolite 5A became saturated after 4 bar pressure and the same has also been validated by experimental results provided by Veawab et al. Now, qmax is the intrinsic property of a zeolite and can be calculated by the following equation (Adsorption (2013) 19:1149–1163),
For 5A zeolite, q_max= -34.291T_r+55.696, where 0.9=T_r=1.25
At 283 K, q_max=5.22 mmole and for 293K, q_max~ 4.5 mmole
This value is much lower compared to the value obtained for 5A zeolite@TP-Azo composite of the present disclosure as shown in Table 5 above.

Example 9: Modification of Zeolite@TpAzo COF with EDA
In a saturated solution of EDA, the zeolite@TpAzoCOF material as prepared in Example 3 was soaked overnight. The modified composite material was then washed with acetone and dried completely. Figure 21 shows the pictorial representation of the modification of Zeolite@TpAzo COF with EDA.

It is expected that the free amine group should bind with the oxygen atom of the Si-O-Al bond present in the zeolite moiety. Figure 22 shows the possible binding motif of the EDA inside zeolite@COF materials.

The CO2 uptake data of the EDA modified composite was tested and compared with the others. As shown in Figure 23, while 5A zeolite@TpAzo showed CO2 adsorption capacity of 100 cc/gm, in the presence of ethylenediamine, the CO2 uptake capacity increased to 127 cc/gm.

Example 10: Chemical Stability Check: Acid Treatment of Zeolite@TpAzo COF
To check the chemical stability of the composite material of the present disclosure (Zeolite@TpAzo COF), the composite material was treated with H2O and 3N HCl. Zeolite is completely soluble and hence loses its structural motif in presence of water and acids. However, as shown in Figure 23, the composite material of the present disclosure was able to keep its structural integrity and CO2 uptake ability even after treatment with 3N HCl overnight.
This shows that the hydrophobic COF material successfully protects the zeolite from acidic environment. Therefore, the Zeolite@TpAzo COF/composite material of the present disclosure can be used in industrial conditions to successfully adsorb CO2 for a longer time without losing its property.

Example 11: General Synthetic Procedure of TpTTA/ Zeolite composite
In the first step, the required zeolite (~ 500mg of either 5A or 13X) was taken in 30 ml dry DCM and sonicated for 10 minutes. Then into this solution of zeolite, the triamine, 4,4',4''-(1,3,5-Triazine-2,4,6-triyl) trianiline (0.03 mmol) (TTA) was added respectively at room temperature, and sonicated for the next 10 minutes, which resulted in a transparent homogeneous solution (light yellow coloured homogeneous solution). Trifluoroacetic acid (20 µl) was added directly to the solution as the catalyst for Schiff base reaction which turned the colour of the solution from dark yellow and light yellow to wine red and orange respectively. Finally, a solution of 0.03 mmol trialdehyde (Tp) in 100 ml dry DCM was added slowly with stirring at room temperature. The reaction mixture was kept at 30-40°C in a closed vessel and after 3-4 hours, the reaction mixture started becoming opaque and then performed under refluxing condition (~60 - 80°C) for the next 24 hours using a 250 ml round bottom flask. After the reaction was complete, the solution was filtered using Whatman filter paper grade 42. The solid obtained was washed using DCM, DMAc, H2O, EtOH, Acetone, and hexane respectively. Then, the solid was dried in an oven (120 °C) for the next 24 hours to remove all undesired solvent molecules. Figure 24 depicts the structures of TpTTA COF and its starting materials Tp and TTA.

Example 12: Thermogravimetric Analysis (TGA)
The composite prepared in Example 11, composite with half amount of TpTTA COF, zeolite 5A and TpTTA COF alone were subjected to thermogravimetric analysis.

The TGA curves of the COF, 5A@TpTTA and 5A@0.5xTpTTA composites as shown in Figure 25 demonstrated thermal stability up to 400 °C. However, there was a 2 to 8% weight loss before 200 °C in the case of the composites which was absent in the TpTTA COF itself. This is completely due to the removal of trapped H2O from the zeolite. Zeolites contain a large amount of water in them and hence, the pristine zeolites lose water during heat and there is no other loss in the whole range of heating even up to 900°C.

Example 13: CO2 Uptake Study
The CO2 uptake capacity for 5A Zeolite, 5A@TpTTA (96wt% 5A) and 5A@0.5xTpTTA (98wt% 5A) materials at 1 bar and 0ºC was studied and compared. As shown in Figure 26, the composites of the present disclosure exhibit CO2 uptake value comparable to that of zeolite alone.
, Claims:We claim:
1. A composite material comprising a Covalent Organic Framework (COF) in an amount of about 2-10 % w/w and a zeolite in an amount of about 90-98 % w/w, wherein the zeolite(s) is coated by the COF(s).
2. The composite material as claimed in claim 1, wherein the zeolite is selected from a group comprising zeolite A, zeolite X, zeolite Y, mordenite, zeolite L, zeolite beta, ZSM-5, zeolite 5A, zeolite 13X, or any combination thereof.
3. The composite material as claimed in claim 1 or 2, wherein the COF is selected from a group comprising Tp-Azo, TpOMe-Azo, Tp-BD, Tp-BDMe2, Tp-Azo-BDMe2, TpTTA or any combination thereof.
4. The composite material as claimed in any one of claims 1-3, wherein the composite material has about 32% to about 48% higher surface area than pristine zeolite.
5. The composite material as claimed in any one of claims 1-4, wherein the composite material has a surface area ranging from about 1500m2/g to about 2000m2/g.
6. The composite material as claimed in any one of claims 1-4, wherein the composite material comprises an amine selected from ethylenediamine, mono-ethyl amine, ethanolamine or a combination thereof.
7. A method of preparing the composite material as claimed in claim 1, the method comprising:
a. adding the zeolite in a solvent to obtain a zeolite solution;
b. adding an aromatic diamine or triamine to the zeolite solution and sonicating to obtain a homogenous solution;
c. adding trifluoroacetic acid to the homogeneous solution;
d. adding a trialdehyde solution to the homogenous solution to obtain a reaction mixture;
e. maintaining the reaction mixture at about 30-40? in a closed reaction vessel for about 2-4 hours; and
f. subjecting the reaction mixture of step (e) to about 60-80? for about 12-24 hours to obtain the composite material.
8. The method as claimed in claim 7, wherein the zeolite(s) is selected from zeolite A, zeolite X, zeolite Y, mordenite, zeolite L, zeolite beta, ZSM-5, zeolite 5A, zeolite 13X, or a combination thereof.
9. The method as claimed in claim 7 or 8, wherein the solvent to which the zeolite is added to prepare the zeolite solution is selected from dichloromethane (DCM), dimethylformamide (DMF), acetonitrile, or a combination thereof.
10. The method as claimed in any one of claims 7-9, wherein the aromatic diamine is selected from 4,4’-Azodianiline (Azo), Benzidine (BD), 3,3’-dimethylbenzidine (BDMe2), 3,3’-dinitrobenzidine (BD(NO2)2), 3,3’-dihydroxylbenzidine (BD(OH)2), 3,3’-dimethoxybenzidine (BD(OMe)2), Azo-BD, or a combination thereof and wherein the aromatic triamine is 4,4',4''-(1,3,5-Triazine-2,4,6-triyl) trianiline (TTA), 1,3,5- Tris(4-aminophenyl)benzene (TAPB), or a combination thereof.
11. The method as claimed in any one of claims 7-10, wherein the trialdehyde is triformylphloroglucinol (Tp).
12. The method as claimed in any one of claims 7-10, wherein the trialdehyde solution is prepared by adding the trialdehyde to dichloromethane.
13. The method as claimed in any one of claims 7-12, comprising adding an amine to the composite material.
14. The method as claimed in claim 13, wherein the amine is selected from ethylenediamine, mono-ethyl amine, ethanolamine or a combination thereof.
15. The method as claimed in any one of claims 7-14, comprising:
a. washing the composite material; and
b. drying the washed composite material.
16. The method as claimed in claim 15, wherein the washing is performed with a solvent selected from a group comprising dichloromethane, N, N-dimethylacetamide, water, ethanol, acetone and hexane or a combination thereof; and wherein the drying is performed at a temperature of about 120?.
17. The method as claimed in claim 15 or 16, wherein the washing is performed sequentially with dichloromethane, N, N-dimethylacetamide, water, ethanol, acetone and hexane.
18. A method for capturing greenhouse gases from a source, comprising contacting the source with the composite material as claimed in any one of claims 1-6.
19. The method as claimed in claim 18, wherein the greenhouse gas is selected from carbon dioxide, carbon monoxide, hydrogen, methane, oxygen, nitrogen or a combination thereof.
20. A device for capturing greenhouse gases comprising the composite material as claimed in any one of claims 1-6 as a sorbent.

21. The device as claimed in claim 20, wherein the greenhouse gas is selected from carbon dioxide, carbon monoxide, hydrogen, methane, oxygen, nitrogen or a combination thereof.