Field of Invention

The current invention relates to covalent organic frameworks with bioinspired building blocks for gas separation and methods of using these covalent organic frameworks in gas separation processes.

Background

The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials connected by dynamic covalent bonds with symmetric organic subunits based on reticular chemistry. The modular nature and reticular structure of COFs provide a unique platform to incorporate various molecular building blocks and are beneficial in developing next-generation porous materials with tailor-made properties. COFs have attracted tremendous attention in multiple applications, such as adsorption and separation (Wang, Z. et al, Chem. Soc. Rev. 2020, 49, 708; Zeng, Y. et al., Adv. Mater., 2016, 28, 2855; Guan, X. et al., J. Am. Chem. Soc., 2018, 140, 4494), catalysis (Lu, M. et al., J. Am. Chem. Soc., 2022, 144, 1861 ; Zhong, H. et al., J. Am. Chem. Soc., 2021 , 143, 19992; Yue, Y. et al., J. Am. Chem. Soc., 2021 , 143, 18052), and other fields because of their permanent porosity, designable skeletons, and tunable pore chemistry (Gui., B., Acc. Chem. Res., 2020, 53, 2225; Jhulki, S. et al., J. Am. Chem. Soc., 2020, 142, 783; Jiang, L. et al., J. Am. Chem. Soc., 2018, 140, 15724; Xing, G. et al., J. Am. Chem. Soc., 2022, 144, 5042; Yuan, C. et al., J. Am. Chem. Soc., 2022, 144, 891 ; Duan, H. et al., J. Am. Chem. Soc., 2021 , 143, 19446; Yuan, S. et al., Chem. Soc. Rev., 2019, 48, 2665; Dong, J. et al., J. Am. Chem. Soc., 2018, 140, 4035; Zhao, Y. et al., Angew. Chem., Int. Ed., 2020, 59, 4354). Nevertheless, from the diversity viewpoint, the field of COFs is still in its infancy, especially compared with the impressive success of metal-organic frameworks (MOFs) (Diercks, C. & Yaghi, O. M., Science, 2017, 35, No. eaal1585; Guan, X. et al., Chem. Soc. Rev., 2020, 49, 1357; Nguyen, H. et al., J. Am. Chem. Soc., 2020, 142, 2218; Geng, K. et al., Chem. Rev. 2020, 120, 8814). The direct introduction of novel building blocks for the construction of COFs is the most straightforward approach to augment the diversity of COF structures. Various COFs with different structures and topologies have been fabricated using different building blocks such as boronic acid, amino, and aldehyde groups. Several COFs such as covalent-triazine frameworks (CTF-PO71), 3D-IL-COF-1 , and MCOF-1 have been reported for CO2 capture, C2H2/C2H4 separation, and other hydrocarbon separations, but their sorption performances are moderate (Diercks, C. & Yaghi, O. M., Science, 2017, 35, No. eaal1585; Ding, S. Y. et al., Chem. Soc. Rev., 2013, 42, 548; Geng, K. et al., Chem. Rev. 2020, 120, 8814; Wang, Z. et al., Chem. Soc. Rev., 2020, 49, 708; Zeng, Y. et al., Adv. Mater., 2016, 28, 2855; Zhang, S. et al., Chem. Eur. J., 2020, 26, 3205). The building blocks for COFs derived from the current petrochemical approaches are however still minimal and expensive due to the complex synthesis routes. Thus, the exploration of newfangled organic monomers with low cost is urgently needed to broaden the COF family.

Inspired by natural pharmaceutical chemistry, we notice that low-cost bioderived molecules are abundant and functionalized by various groups, such as phenolic hydroxyl groups. Such a brilliant feature is highly desirable in reticular chemistry. In particular, polyphenols are widely available and have served as precursors in life science and pharmaceutical chemistry. However, they are rarely investigated for the construction of porous materials, including MOFs.

In this invention, we proposed the unique strategy to construct novel COFs and broaden the varieties of COFs by using the bioderived materials as building blocks, which are cheap, easily available, and abundant in nature. The bioderived raw materials are usually functionalized with phenolic hydroxyl, aldehyde and amino groups. The resultant bioinspired COFs with high porosity and stability were synthesized via one-step condensation reaction. Benefitting from the functional groups on the bioderived molecules, the pore channels would be decorated with lots of oxygen and nitrogen atoms, which can be used as recognition sites for CO2 and hydrocarbon molecules, thus leading to high adsorption and separation performance.

The present invention will open new avenues towards development of novel COFs and energy efficient techniques for CO2 and hydrocarbon separations. The uniqueness in the present invention are listed as follow:

• bioinspired COFs constructed by the condensation of ellagic acid (EA) and the planar C3-symmetric building units, 1 ,3,5-benzenetriboronic acid (BTBA) or 1 ,3,5- benzenetris(4-phenylboronic acid) (BTPA), showing AB stacking mode with numerous oxygen atoms in the pore channels; • bioinspired COFs fabricated via the condensation of 2,5-diformylfuran (DFF) with the planar C3-symmetric building units, 2,4,6-triaminopyrimidine (TAPy) or 2,4,6-triamino- 5-nitrosopyrimidine (TANPy) or tris(4-aminophenyl)amine (TAPhA) or 2,4,6-tris(4- aminophenyl)-1 ,3,5-triazine (TAPhTr) or melem (Me) or 1 ,3,5-tris(4- aminophenyl)benzene (TAPhB), showing AA stacking mode with pore channels decorated with N atoms;

• bioinspired COFs synthesized by the condensation of 2,4,6-trihydroxy-1 ,3,5- benzenetricarbaldehyde (TFP) and 2,4,6-triaminopyrimidine (TAPy) or 2,4,6-triamino- 5-nitrosopyrimidine (TANPy) or 6-CI-2,4-diaminopyriimdine (CIDAPy) or 4,6- diaminopyrimidine (46DAPy), 2,6-diaminopurine (DAPu) or 1 ,3,5-triazine-2,4-diamine (TAD) or 2,4-diaminopyrimidine (24DAPy) exhibit the AA stacking mode with pore surface functionalized by N atoms; and

• the fabricated bioinspired COFs are used for CO2 capture and hydrocarbon separation as the bioinspired COFs exhibit high porosity and high acetylene (C2H2) capacity and good C2H2/CO2 separation performance.

The development of new adsorbents for gas separation-related applications is of prime importance, especially for those that are using high energy-demanding process such as cryogenic separation. Specially, acetylene (C2H2), one of the most critical raw chemicals, is widely used as precursor for fine chemicals and electronic gas. C2H2 is produced via partial combustion of methane or steam cracking of hydrocarbons, but CO2 would coexist as a primary impurity (Mukherjee, S. et al., Chem. Commun., 2020, 56, 10419). Isolation of C2H2 from CO2 via physiadsorbents is an energy-efficient and environmentally friendly technology for C2H2 purification; however, it is highly challenging due to their close similarities in physicalchemical properties (Mukherjee, S. et al., Chem. Commun., 2020, 56, 10419). Novel porous materials are highly needed.

A lot of MOFs have been reported for CO2 capture and C2H2/CO2 separation with high efficiency, yet the stability and cost of MOFs are still the main issues limiting the industrial scale-up and applications (Mukherjee, S. et al., Chem. Commun., 2020, 56, 10419). Strategic design of the porous bioinspired COFs is more predictable compared to MOFs and zeolites because of the easy control over the condensation reaction. Although some bioMOFs have been fabricated using bio-derived molecules, their application in CO2 capture and hydrocarbon separations is rarely investigated (Cai, H. et al., Chem. Rev., 2019, 378, 207). The bio-derived raw materials with low cost are easily available in nature. For separation using COFs or bioinspired COFs, even the bio-derived MOFs, C2H2/CO2 separation has not been reported yet, and their CO2 capture performance is also underexplored.

To our knowledge, this current invention is the first to report the fabrication of novel bioinspired COFs using bio-derived molecules in nature as a building unit under mild synthesis conditions, which undoubtedly enriches the varieties of COF chemistry. This invention provides not only a new perspective on the design of COFs with novel structures using the cheap and abundant raw materials, but also novel opportunities to broaden the COF family and for the exploration of bioinspired COFs in new areas.

Our proposed technology has two key characteristics: 1) easily available bioderived chemicals as building blocks for COFs would broaden COF family and greatly reduce the cost, which would speed up the commercialization of COFs in industry; and 2) the fabricated COFs exhibit high C2H2 uptake and C2H2/CO2 separation selectivity, which can be used for efficient C2H2/CO2 separation, exhibiting environmental friendliness and competitive advantages over traditional separation technologies.

Summary of Invention

1. A covalent organic framework having a repeating unit according to Formula I: where the wiggly lines represent the points of attachment to the rest of the covalent organic framework and A represents:

where the wiggly lines denoted with a represent the point of attachment to the rest of the repeating unit of Formula I and the wiggle lines denoted with b represent the points of attachment to the rest of the covalent organic framework.

2. A covalent organic framework having a repeating unit according to Formula Ila: m represents 2; n represents 2;

X represents: where the wiggly lines represent the point of attachment to a Y group;

Y represents:

where the wiggly lines denoted with a’ represent the point of attachment to the repeating unit of Formula I and the wiggle line(s) denoted with b’ represent the points of attachment to the rest of the covalent organic framework; and Ri represents H, OH, NO or Ci to Ce alkyl. 3. The covalent organic framework according to Clause 2, wherein Ri represents H, OH, NO or CH ₃ .

4. A covalent organic framework having a repeating unit according to Formula lib: where: m’ represents 1 ; n’ represents 3;

X’ represents: where the wiggly lines represent the point of attachment to a Y group;

Y’ represents:

where the wiggly lines denoted with a’ represent the point of attachment to the repeating unit of Formula I and the wiggle line(s) denoted with b’ represent the points of attachment to the rest of the covalent organic framework; R2 represents H, OH, halo or Ci to Ce alkyl; and

R3 represents H, NO or Ci to Ce alkyl.

5. The covalent organic framework according to Clause 4, wherein:

R2 represents H, OH, Cl or CH3; and

R3 represents H, NO or CH3.

6. A covalent organic framework having a repeating unit according to Formula He: where: m” represents 2; n” represents 3;

X” represents: where the wiggly lines represent the point of attachment to a Y group;

Y represents: where the wiggly lines denoted with a’ represent the point of attachment to the repeating unit of Formula I and the wiggle line(s) denoted with b’ represent the points of attachment to the rest of the covalent organic framework; and

Ri represents H, OH, NO or Ci to Ce alkyl (e.g. Ri represents H, OH, NO or CH3).

7. A method of using a covalent organic framework as described in any one of Clauses 1 to 6 in a process of separating a first gas from a second gas, the method comprising the steps of:

(a) providing a vessel packed with an activated covalent organic framework as described in any one of Clauses 1 to 6;

(b) passing a first gaseous mixture comprising a first proportion of a first gas and a first proportion of a second gas through the column packed with the activated covalent organic framework adsorb at least part of the first gas and to provide a second gaseous mixture that comprises a second proportion of the first gas and a second proportion of the second gas, where the second proportion of the first gas is less than the first proportion of the first gas and the second proportion of the second gas is greater than the first proportion of the second gas; and

(c) recovering the first gas adsorbed by the covalent organic framework by vacuum stripping the covalent organic framework and/or purging the covalent organic framework with the first gas, wherein: the first gas is C2H2; and the second gas is CO2 and/or C2H4.

8. The method according to Clause 7, wherein the vessel is a column or a fixed bed vessel. Drawings

FIG. 1 depicts (a) the schematic illustration of the construction and proposed structures of NLIS-71 and NLIS-72 using ellagic acid as the building block; (b, c) the refined structures and (d, e) the experimental (dot) and refined (line) powder x-ray diffraction (PXRD) patterns for (b, d) NUS-71 and (c, e) NUS-72.

FIG. 2 depicts the high resolution transmission electron microscopy (HRTEM) image of (a) NUS-71 and (b) NUS-72.

FIG. 3 depicts the PXRD patterns of NUS-71 collected after treatment under different conditions.

FIG. 4 depicts the thermogravimetric analyses (TGA) curves of NUS-71 (dotted line) and NUS- 72 (solid line) collected with a heating rate of 10 °C min ^-1 and a N ₂ flow rate of 50 mL min ^-1 .

FIG. 5 depicts the Fourier transform infrared (FTIR) spectra of NUS-71 and NUS-72 within the range of 400 to 4000 cm ^-1 .

FIG. 6 depict the FTIR spectra of EA within the range of 400 to 4000 cm ^-1 .

FIG. 7 depicts the FTIR spectra of BTBA and BTPA within the range of 400 to 4000 cm' ¹ .

FIG. 8 depicts the ¹³ C nuclear magnetic resonance (NMR) spectra of NUS-71 and NUS-72.

FIG. 9 depicts the scanning electron microscopy (SEM) image of NUS-71 powders.

FIG. 10 depicts the SEM image of NUS-72 powders.

FIG. 11 depicts the transmission electron microscopy (TEM) image of NUS-71.

FIG. 12 depicts the TEM image of NUS-72.

FIG. 13 depicts the pore channels of NUS-71.

FIG. 14 depicts the pore channels of NLIS-72. FIG. 15 depicts (a) the N ₂ adsorption-desorption isotherms at 77 K; (b, c) the C ₂ H ₂ and CO ₂ adsorption isotherms on (b) NLIS-71 and (c) NLIS-72; and (d) dynamic breakthrough curves of C ₂ H ₂ /CO ₂ on N US-71 at 298 K.

FIG. 16 depicts the pore size distributions of (a) NUS-71 and (b) NUS-72 derived from N ₂ adsorption isotherms at 77 K. Please note that in (b), there are three peaks for the pore size distributions of NUS-72. Two of them at 1.8 and 2.9 nm are the main pore size, which are consistent with the values measured from the refined NUS-72 structure. The third peak at 4.6 nm may be resulted from the packing of NUS-72 powders.

FIG. 17 depicts the schematic illustration of synthesis and structures of DFF-based COFs.

FIG. 18 depicts the schematic illustration of synthesis, coordination, and structures of bioinspired COFs using amino-functionalized bioderived molecules.

FIG. 19 depicts the SEM images of (a) TFP-46DAPy and (b) TFP-CIDAPy.

FIG. 20 depicts (a) the C ₂ H ₂ /CO ₂ separation selectivities of NUS-71 and NUS-72 at 298 K determined from ideal adsorbed solution theory (IAST); and (b) the calculated C ₂ H ₂ uptakes based on IAST from equimolar C ₂ H ₂ /CO ₂ mixtures on the synthesized COFs.

FIG. 21 depicts the isosteric heats of adsorption, Q _s t, for C ₂ H ₂ and CO ₂ on two COFs.

FIG. 22 depicts the dynamic breakthrough curves of C ₂ H ₂ /CO ₂ on NUS-72 at 298 Kwith a flow rate of 2.0 mL min' ¹ .

FIG. 23 depicts the home-made breakthrough setup.

FIG. 24 depicts the cycling breakthrough curves of C ₂ H ₂ /CO ₂ (50/50) mixture on NUS-71 with a flow rate of 2.0 mL min' ¹ at 298 K. Please note that the samples were regenerated at 398 K with a He flow rate of 10 mL mim ¹ for 6 hours.

FIG. 25 depicts the cyclic sorption isotherms of C ₂ H ₂ on NUS-71 at 298 K.

FIG. 26 depicts the experimental in situ and refined PXRD patterns of NUS-71 loaded with (a) C ₂ H ₂ and (b) CO ₂ ; and the binding configurations of (c) C ₂ H ₂ and (d) CO ₂ in NUS-71. FIG. 27 depicts view of NLIS-71 structure along c direction. The distance between the interlayers of the two-dimensional framework is 3.23 A. However, due to the interlayer structure being staggered in the AB stacking framework, the distance between the upper and lower layers is 7.32 A, which can accommodate gas molecules.

FIG. 28 depicts view of NLIS-72 structure along c direction. The distance between the interlayers is 3.89 A. However, due to the interlayer structure being staggered in the AB stacking framework, the distance between the upper and lower layers is 8.44 A.

Description

The purpose of the current invention is to provide a covalent organic framework material from bio-based sources that can be used advantageously for the separation of gases from one another. In this context, the invention may make use of bio-derived ligands of three types to generate the desired COF. The bio-derived ligands may be described as three different types:

1. Ellagic acid (EA), which can coordinate with C3-symmetric ligands;

2. 2,5-Diformylfuran (DFF), which coordinates with C3-symmetric ligands that have three amino groups; and

3. bio-derived ligands with two amino groups that can coordinate with TFP, which has three aldehyde groups.

Thus, in a first aspect of the invention, there is provided a covalent organic framework having a repeating unit according to Formula I: where the wiggly lines represent the points of attachment to the rest of the covalent organic framework and A represents: where the wiggly lines denoted with a represent the point of attachment to the rest of the repeating unit of Formula I and the wiggle lines denoted with b represent the points of attachment to the rest of the covalent organic framework. As such, each ellagic acid in the framework of formula I is attached, via a boron atom to one “A” group. This “A” group is attached to the ellagic acid depicted in Formula I and to two more ellagic acids, which in turn are attached to one further “A” group and so on to generate the covalent organic framework.

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

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

As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, reference to “an oxygen carrier” includes mixtures of two or more such oxygen carriers, reference to “the catalyst” includes mixtures of two or more such catalysts, and the like.

In a second aspect of the invention, there is provided a covalent organic framework having a repeating unit according to Formula Ila: m represents 2; n represents 2;

X represents: where the wiggly lines represent the point of attachment to a Y group;

Y represents:

where the wiggly lines denoted with a’ represent the point of attachment to the repeating unit of Formula I and the wiggle line(s) denoted with b’ represent the points of attachment to the rest of the covalent organic framework; and Ri represents H, OH, NO or Ci to Ce alkyl.

As will be appreciated, each “X” (furan ring) is attached to two Y groups and these Y groups are attached to three X groups in total. As such, each Y group in Formula Ila is attached to two further X groups, which are in turn attached to a further Y group, and so on to provide the covalent organic framework. As such, a broader view of the structure is provided by formula A below.

Where X and Y take their meanings in Formula Ila above and the dotted lines represent the point of attachment of the outermost X group to a further Y group in the covalent organic framework.

In embodiments of the second aspect of the invention, Ri, when present, may represent H, OH, NO or CH ₃ .

In a third aspect of the invention, there is provided a covalent organic framework having a repeating unit according to Formula lib: where: m’ represents 1 ; n’ represents 3;

X’ represents:

where the wiggly lines represent the point of attachment to a Y group;

5 Y’ represents:

where the wiggly lines denoted with a’ represent the point of attachment to the repeating unit of Formula I and the wiggle line(s) denoted with b’ represent the points of attachment to the rest of the covalent organic framework;

R ₂ represents H, OH, halo or Ci to Ce alkyl; and

R ₃ represents H, NO or Ci to Ce alkyl. As will be appreciated, a’ is attached to the X’ depicted in formula Ila, while each b’ is attached to a further X’ group. As will be appreciated, each X’ (a tri-phenol, tri-aldehyde) is attached to three Y’ groups and these Y’ groups are attached to two X’ groups in total. As such, each Y’ group in Formula II is attached to one further X’ group, which is in turn attached to two further Y’ groups, and so on to provide the covalent organic framework. As such, a broader view of the structure is provided by formula B below.

In embodiments of the second aspect of the invention, when present:

R2 may represent H, OH, Cl or CH3; and R3 may represent H, NO or CH3.

In a fourth aspect of the invention, there is disclosed a compound of formula lie: where: m” represents 2; n” represents 3;

X” represents:

where the wiggly lines represent the point of attachment to a Y group;

Y represents: where the wiggly lines denoted with a’ represent the point of attachment to the repeating unit of Formula I and the wiggle line(s) denoted with b’ represent the points of attachment to the rest of the covalent organic framework; and Ri represents H, OH, NO or Ci to C ₆ alkyl (e.g. Ri represents H, OH, NO or CH ₃ ).

As will be appreciated, each X” (a tri-phenol, tri-aldehyde) is attached to three Y” groups and these Y” groups are attached to three X” groups in total. As such, each Y” group in Formula He is attached to two further X” group, which is in turn attached to two further Y” groups, and so on to provide the covalent organic framework. Such as in formula C.

As will be appreciated, the covalent organic framework used herein may be used to selectively adsorb a gas in a gaseous mixture. As such, when used for this purpose, the covalent organic framework may initially capture all (or virtually all, e.g. >95%, such as >99%) of the gas that it selectively adsorbs, while allowing other gas(es) to pass through it without (or virtually without, e.g. less than 5%, such as less than 1 %) adsorption. As such, the output gas obtained at this stage will be different to the input gas, as the output gas will be virtually devoid of the gas to be adsorbed. As the covalent organic framework becomes more saturated through the adsorption of the desired gas, it will reach a breakout point where at least some of the desired gas is not adsorbed. At this point some of the desired gas will appear in the output gas, but the proportion of the desired gas in the output gas will be lower than that in the input gas. As time progresses, the covalent organic framework will become completed saturated with the desired gas to the point where it cannot adsorb any more of the gas. At this stage, the output gas mixture will essentially be the same as the input gas mixture.

Thus, in a further aspect of the invention, there is provided a method of using a covalent organic framework as described in any first to fourth aspect of invention and any technically sensible combination of their embodiments in a process of separating a first gas from a second gas, the method comprising the steps of:

(a) providing a vessel packed with an activated covalent organic framework as described in the first to third aspects of the invention and any technically sensible combination of their embodiments;

(b) passing a first gaseous mixture comprising a first proportion of a first gas and a first proportion of a second gas through the column packed with the activated covalent organic framework adsorb at least part of the first gas and to provide a second gaseous mixture that comprises a second proportion of the first gas and a second proportion of the second gas, where the second proportion of the first gas is less than the first proportion of the first gas and the second proportion of the second gas is greater than the first proportion of the second gas; and

(c) recovering the first gas adsorbed by the covalent organic framework by vacuum stripping the covalent organic framework and/or purging the covalent organic framework with the first gas, wherein: the first gas is C2H2; and the second gas is CO2 and/or C2H4.

In a further example, the vessel may be a column or a fixed bed vessel.

Aspects and embodiments of the invention will now be discussed by reference to the following non-limiting examples.

Examples

Materials

All reagents were purchased from commercial sources and used without further purification.

Example 1. Preparation of Ellagic Acid-based COFs NUS-71 and NUS-72

Ellagic acid (EA), an edible and biocompatible polyphenol molecule, widely exists in plants such as strawberries, grapes, raspberries, and vegetables (Grape, E. et al., J. Am. Chem. Soc., 2020, 142, 16795; Landete, J. M., Food Res. Int., 2011 , 44, 1150; Ceci, C, et al., Nutrients, 2018, 10, 1756; Gupta, A. et al., Adv. Nutr., 2021 , 72, 1211). It shows excellent antiproliferative and antioxidation properties and exhibits a centrosymmetric molecular structure with two neighbouring phenols on each side (FIG. 1a) (Landete, J. M., Food Res. Int., 2011 , 44, 1150; Ceci, C, et al., Nutrients, 2018, 70, 1756; Gupta, A. et al., Adv. Nutr, 2021 , 72, 1211), which can undergo dehydration reactions with one boric acid or chelate to metal cations, forming five-membered rings (Diercks, C. & Yaghi, O. M., Science, 2017, 35, No. eaal1585; Guan, X. et al., Chem. Soc. Rev., 2020, 49, 1357; Nguyen, H. et al., J. Am. Chem. Soc., 2020, 142, 2218; Geng, K. et al., Chem. Rev. 2020, 720, 8814; Ding, S. et al., Chem. Soc. Rev., 2013, 42, 548; Li, J. et al., Chem. Soc. Rev., 2020, 49, 3565). We hypothesized that the phenol groups in EA would present active functionalities for condensation, which is a typical route to synthesize COFs. The molecular structure suggests adequate rigidity of EA for extension into reticular networks. However, the use of EA and other readily available and cheap bioderived molecules or chemicals to construct novel COFs remains unexplored.

Herein we present the construction of two targeted COFs, assigned as NLIS-71 and NLIS-72, by condensation of EA and two planar C3-symmetric building units, namely,

1.3.5-benzenetriboronic acid (BTBA) and 1 ,3,5-benzenetris(4-phenylboronic acid) (BTPA) (FIG. 1a).

Synthesis ofNUS-71 and NUS-72

Typically, grey crystalline N US-71 and NUS-72 powders were obtained via a solvothermal method through the dehydration reaction between EA and BTBA or BTPA, respectively, in a 1 :5 (v/v) solution of mesitylene/1 ,4-dioxane at 100 °C for 3 days (FIG. 1a).

1.3.5-Benzenetriboronic acid (BTBA, 40 mg, 0.192 mmol) and ellagic acid (EA, 40 mg, 0.132 mmol) were dissolved in 15 mL of a 1 :5 (v/v) solution of mesitylene/1 , 4-dioxane. The solution was flash-frozen with liquid N2 and then evacuated on a Schlenk line for several freeze-pump-thaw cycles. The solution was then sealed and heated at 100 °C for 3 days to afford a grey precipitate, which was isolated by centrifugation and washed with anhydrous acetone and tetrahydrofuran (THF) several times. Then, the product was immersed in anhydrous acetone for 12 hours, during which the activation solvent was decanted and freshly replenished three times. The solvent was removed under vacuum at room temperature to afford N US-71.

NUS-72 was obtained via the same method except BTBA replaced by 1 ,3,5-benzenetris(4- phenylboronic acid) (BTPA, 40 mg, 0.092 mmol).

Example 2. Characterisation of Targeted COFs NUS-71 and NUS-72

Powder X-Ray Diffraction Analyses

Powder X-ray diffraction (PXRD) patterns were collected using a Rigaku Miniflex 600 diffractometer (Cu Ka = 1.540598 A) with an operating power of 40 kV, 15 mA, and a scan rate of 2.0 ⁰ min' ¹ . The data were collected in a two-theta range of 2-30°. In situ PXRD patterns were collected using a capillary tube packed with the sample, which was first evacuated and then filled with C2H2 or CO2. TGA Measurements

Thermogravimetric analyses (TGA) were performed on a TA instruments STD-600 equipment at a heating rate of 10 °C min’ ¹ with a N2 flow rate of 50 mL min’ ¹ . The sample holders were alumina crucibles, and the amount of sample used in each measurement was 8 (± 2) mg. The data collected were analyzed using Universal Analysis software (version 4.4A) from TA Instruments.

Fourier Transform Infrared (FTIR) Spectroscopy

The Fourier transform infrared (FTIR) spectra were recorded using a FTIR spectrometer (Bruker VERTEX 70-FTIR). Before each experiment, the sample was pretreated under high vacuum conditions (< 4 pmHg) at 393 K for 6 hours, and then cooled to room temperature. All the spectra were recorded over accumulative 32 scans with a resolution of 4 cm ^-1 in the range of 4000-400 cm ^-1 .

Solid State Nuclear Magnetic Resonance (NMR)

Solid state NMR experiments were completed on a 14.1 T Bruker Advance III HD 600 MHz spectrometer with a Bruker 4 mm HX MAS probe operating at a magic angle spinning frequency of 10 KHz. The proton decoupling field was 80 kHz.

Scanning Electron Microscopy (SEM)

Samples for SEM observation were conducted on a JEOL JSM-6701 F Field Emission Scanning Electron Microscope and operated at 5 kV. The samples were coated on conducting resin by using a toothpick.

Transmission Electron Microscopic (TEM) Analyses

Samples for transmission electron microscopy observation were taken from the solution after the as-obtained COF sample was sonicated in hexane for 30 minutes. A droplet of the solution containing the COFs was transferred onto a carbon-coated copper grid. The observation was performed on a JEOL JEM2100 microscope and operated at 200 kV (Cs 1.0 mm, point resolution 0.23 nm). Images were recorded with a Gatan Orius 833 CCD camera (resolution 2048 x 2048 pixels, pixel size 7.4 pm). Electron diffraction patterns were recorded with a Timepix pixel detector QTPX-262k (512 x 512 pixels, pixel size 55 pm, Amsterdam Sci. Ins.). The high resolution transmission electron microscopy images (HRTEM) were obtained by the same method with zooming in. Results and Discussions

The resultant NLIS-71 showed high crystallinity and reasonably good chemical stability, as evidenced by the intact PXRD patterns and thermogravimetric analysis data (FIGs. 3-4).

Fourier transform infrared (FTIR) spectroscopy was used to confirm the chemical structure. The FTIR spectra include strongly attenuated bands from hydroxyl groups (FIGs. 4-6). For EA, the C=O band at 1692 cm ¹ shifted to 1725 cm ¹ ; the C-0 stretching vibration mode in aromatic rings at 1196 cm ¹ shifted to 1183 cm ¹ ; and the phenolic O-H stretching bands at 1303 cm ¹ vanished after the coordination (FIGs. 5-6) (Wang, L. et al., Chem. Eng. Technol., 2018, 41, 1188; Gopalakrishnan, L. et al., Carbohydr. Polym., 2014, 111, 215). The two COFs show similar B-0 stretching modes at 1335 cm ¹ , typical strong C-0 stretching bands at 1254 cm ^-1 , and B-C stretching bands at 1213 cm ¹ , which are different from those of the starting materials (FIGs. 5-7), but with distinctive signals and fingerprints for the expected boronated ester five-membered rings (Cote, A. et al., J. Am. Chem. Soc., 2007, 129, 12914; El-Kaderi, H. et al., Science, 2007, 316, 268; Cote, A. et al., Science, 2005, 310, 1166; Baldwin, L. et al., J. Am. Chem. Soc., 2016, 138, 15134).

Furthermore, the ¹³ C NMR spectra correlate well with the respective structures of NLIS-71 and NLIS-72 (FIG. 8). Complementary scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed that both COFs show uniform 2D morphologies (FIGs. 9-12), confirming the phase purity of the as-synthesized COFs.

Example 3. Proposed Structures of Targeted COFs NUS-71 and NUS-72

Refinement of PXRD Patterns with Theoretical Structural Simulations

The crystal structures of NUS-71 and NUS-72 were resolved by refining the PXRD patterns in conjunction with theoretical structural simulations. PXRD patterns were obtained by following the protocol described in Example 2.

Rietveld structural refinements were performed on the obtained PXRD data using the Reflex Module in Materials Studio software. Due to a large number of atoms in the crystal unit cell, the ligand molecule and the gas molecule were both treated as rigid bodies during the Pawley refinements, with the molecule orientation and center of mass freely refined. Final refinement on the positions/orientations of the rigid bodies, thermal factors, occupancies, lattice parameters, background, and profiles converged with satisfactory R-factors. Results and Discussions

The simulated PXRD profiles were in excellent agreement with the experimental data with regard to the peak positions and relative intensities (FIG. 1d-e). The resultant structure models of the two materials exhibit a staggered AB stacking mode with a triclinic crystal system (FIG. 1b-c). The AB stacking structure showed that the abundant O atoms on the pore surfaces could provide potential recognition sites (FIGs. 13 and 14), which are favourable for the adsorption and separation of gas mixtures, especially C2H2/CO2 (Mukherjee, S. et al., Chem. Commun., 2020, 56, 10419; Ye, Y. et al., J. Am. Chem. Soc., 2022, 144, 1681).] Pawley refinement accordingly yielded the following unit cell parameters of NLIS-71 : a = 27.897 A, b = 28.589 A, c = 7.318 A, cr = 90.12°, /3 = 89.97°, y = 118.41 ° (P1/CI-1 space group) with good residual factors of R _wp = 1.72% and R _p = 0.94%. The final cell parameters of NLIS-72 were a = 8.447 A, b = 40.804 A, c = 41.205 A, a = Q7.75°, = 86.43°, y = 88.42° (P1/CI-1 space group) with acceptable low residual factors of R _wp = 1.08% and R _p = 0.51 % (FIG. 1 b-e).

The high crystallinity of the two COFs was confirmed by high resolution TEM (HRTEM) images (FIG. 2) by following protocol in Example 2. The clear lattice distance of 0.73 nm observed on NLIS-71 is comparable with the distance of the (001) crystallographic planes (FIG. 2a), and the clear lattice distance of 1.26 nm observed on NLIS-72 is comparable with the distance of the (003) crystallographic planes (FIG. 2b).

Example 4. Permanent Porosities of Targeted COFs NUS-71 and NUS-72

The permanent porosities of NUS-71 and NUS-72 were determined by N2 sorption measurements at 77 K (FIG. 15a).

N2 Sorption Measurement

N2 isotherms on targeted COFs were collected on a Micromeritics ASAP2020 instrument at 77 K. About 0.1 g of each sample was used for the measurement. The measurement temperatures was maintained at 77 K using liquid nitrogen.

Brunauer-Emmett-Teller (BET) Surface Area and Pore Size Distribution (PSD)

N2 adsorption and desorption isotherm at 77 K (liquid Nitrogen) was employed to determine pore textural properties including the specific Brunauer-Emmett-Teller (BET) surface area, micropore volume, and pore size distribution by using a Micromeritics ASAP 2020 adsorption porosimeter. The sample amount used for the test was 0.1 g. Results and Discussions

Both COFs showed type-1 isotherms with sharp uptakes at low pressures, a signature feature of the microporous structure. The calculated Brunauer-Emmett-Teller (BET) surface areas were 582 m ² g ¹ and 720 m ² g ¹ with pore volumes of 0.32 cm ³ g ¹ and 0.68 cm ³ g ¹ for NLIS-71 and N US-72, respectively. Pore size distribution (PSD) analyses revealed a major pore diameter of 14.5 A in NUS-71 (FIG. 16). In contrast, there are two main pore diameters of 18 A and 29 A in NUS-72.

Example 5. Preparation of 2,5-Diformylfuran-based COFs with AA Stacking Mode

2,5-diformylfuran (DFF), an important monomer due to its symmetrical and unsaturated structure, has been considered as a potential intermediate for fungicides, pharmaceuticals, heterocyclic ligands, and macrocyclic ligands (Zhou, C. et al., ACS Sustainable Chem. Eng., 2018, 7, 315). DFF is mainly obtained from 5-hydroxymethylfurfural (HMF), which is one of the abundantly available resources in biomass (Zhou, C. et al., ACS Sustainable Chem. Eng., 2018, 7, 315).

Synthesis of 2,5-Diformylfuran-based COFs

Herein, the condensation reactions between DFF and the planar C3-symmetric building units, 2,4,6-triaminopyrimidine (TAPy) or 2,4,6-triamino-5-nitrosopyrimidine (TANPy) or tris(4- aminophenyl)amine (TAPhA) or 2,4,6-tris(4-aminophenyl)-1 ,3,5-triazine (TAPhTr) or melem (Me) or 1 ,3,5-tris(4-aminophenyl)benzene (TAPhB), were completed in 10:1 (v/v) 1 ,4-dioxane and mesitylene mixture at 85 °C for 72 hours (FIG. 17).

Result and Discussion

The resultant COFs show AA stacking mode.

Example 6. Bioinspired COFs Using Amino-Functionalized Bioderived Molecules as Building Units

Synthesis of Bioinspired COFs

This kind of bioinspired COFs were synthesized by reacting 2,4,6-trihydroxy-benzene-1 ,3,5- tricarbaldehyde (TFP) with 2,4,6-triaminopyrimidine (TAPy) or 2,4,6-triamino-5- nitrosopyrimidine (TANPy) or 4,6-diaminopyrimidine (46DAPy) or 6-CI-2,4-diaminopyriimdine (CIDAPy) or 2,6-diaminopurine (DAPu) or 1 ,3,5-triazine-2,4-diamine (TAD) or 2,4- diaminopyrimidine (24DAPy) in 1 ,4-dioxane and mesitylene (v/v, 5:1) mixture at 80 °C for 72 hours (FIG. 18).

All the synthesized samples were characterized using techniques including powder X-ray diffraction (PXRD), Fourier transform infrared (IR) spectroscopy, Raman spectra, ultraviolet- visible (UV-vis) adsorption spectra, nuclear magnetic resonance (NMR), gas sorption, transmission electron microscope (TEM), scanning electron microscope (SEM) by following protocols described in Example 2 and 4, or as follow.

Result and Discussion

The structure of the resultant bioinspired COFs (FIG. 18) exhibits AA stacking mode. Specially, the TFP-46DAPy exhibits the morphology of ultra-long nanoribbons (FIG. 19a), TFP-CIDAPy shows nanosheets morphology (FIG. 19b).

Example 7. Acetylene (C2H2) and CO2 Adsorption and Separation Performance

Acetylene (C2H2), a widely used precursor and electronic gas, is produced via partial combustion of methane or steam cracking of hydrocarbons but with the impurity of cogenerated CO2 (Zhang, S. et al., Chem. Eur. J., 2020, 26, 3205; Zhang, D. et al., Angew. Chem., Int. Ed., 2021 , 60, 17198; Mukherjee, S. et al., Chem. Commun., 2020, 56, 10419). Thus, C2H2/CO2 separation is essential for high purity C2H2 production but highly challenging because of the similarities in their physical and chemical properties. Adsorptive separation using porous materials has shown great promise in reducing the energy penalty compared with energy-intensive processes such as the cryogenic distillation (Mukherjee, S. et al., Chem. Commun., 2020, 56, 10419; Liao, P. et al., Science, 2017, 356, 1193; He, T. et al., Nat. Mater., 2022, 21, 689; Zhang, Z. et al., EnergyChem, 2021 , 3, 100057). However, COFs are still underexplored for separating C2H2/CO2 mixtures (Wang, Z. et al., Chem. Soc. Rev., 2020, 49, 708; Zhang, S. et al., Chem. Eur. J., 2020, 26, 3205). Promoted by the specific pore chemistry with abundant O atoms, the C2H2 and CO2 adsorption performances on N US-71 and N US-72 were investigated.

C2H2 and CO2 Gas Sorption Experiments

Gas sorption experiments of C2H2 and CO2 were performed on a Micromeritics ASAP 2020 instrument equipped with commercial software for data calculation and analysis. The test temperatures were controlled by soaking the sample cell into a circulating water bath (298 K) or an ice water bath (273 K). Before each measurement, the sample (50-70 mg) was degassed at 373 K for 24 hours. The gas isotherms were obtained under a pressure range of 0-1.06 bar.

Ideal Adsorbed Solution Theory (I AST) Selectivity Calculations

The pylAST package (Qazvini, O. T. et al., Nat. Commun., 2021 , 12, 197) was used to perform the IAST calculations and predict the sorption performance of porous material for binary mixed gas. The isotherm data for CO2 and C2H2 were first fitted with a dual-site Langmuir-Freundlich isotherm model (Eq. 1 and Table 1) (Walton, K. S. & Scholl, D. S., AIChEJ., 2015, 61, 2757; Myers, A. L. et al., AIChEJ., 1965, 11, 121):

Table 1. Dual-site Langmuir-Freundlich parameter fits for CC>2 and C2H2 isotherms on NLIS-71 and N US-72 at 298 K.

The adsorption selectivity for C2H/2CO2 separation is defined by: where qi and <72 are the molar loadings in the adsorbed phase in the mixture, mmol g ^-1 ; yi and y ₂ (y ₂ = 1 . y ₇ ) represent the mole fractions of CO2 and C2H2 in the feed gas. Isosteric Heat of Adsorption Calculations

A virial-type expression comprising the temperature-independent parameters a, and bj was employed to calculate the heat of adsorption for different gases (at different temperatures). In each case, the data were fitted using Eq. 3 (Chen, K. J. et al., Chem, 2016, 1, 753; Zhang, Z. et al., Angew. Chem., Int. Ed., 2020, 59, 18927):

Here, P is the pressure expressed in Pa, N is the amount adsorbed in mmol g- ¹ , T is the temperature in K, a, and bj are virial coefficients, m and n represent the number of coefficients required to describe the isotherms adequately.

The values of the virial coefficients ao to a _m were then used to calculate the isosteric heat of adsorption using the following expression (Eq. 4):

Qst is the coverage-dependent isosteric heat of adsorption, and R is the universal gas constant.

Results and Discussions

Impressively, the C2H2 uptakes can reach 42.4 and 48.0 cm ³ g ¹ on NLIS-71 and NLIS-72, respectively, at 298 K and 1.0 bar. By comparison, the CO2 uptakes are only 10.3 and 11.2 cm ³ g ¹ on NLIS-71 and NLIS-72, respectively (FIG. 15b-c). Notably, the C2H2/CO2 uptake ratio of ca. 4 on the two COFs is much higher than that on other COFs, such as ZJUT-2 (1 .7) (Gong, C. et al., Angew. Chem., Int. Ed., 2022, 61, No. e202204899) and NKCOF-12 (1.4) (Zhang, P. et al., Sci. China Chem., 2022, 65, 1173), and most MOFs, such as MLIF-17 (1.2) (Qazvini, O. et al., Chem. Mater., 2019, 31, 4919) and MAF-2 (3.7) (Zhang, J. et al., J. Am. Chem. Soc., 2009, 131, 5516).

The separation selectivities of C2H2/CO2 on NLIS-71 and NLIS-72 were calculated via the ideal adsorbed solution theory (IAST) and estimated to be 16 and 6.7, respectively (FIG. 20), which are much higher than those of COFs like ZJUT-3 (3.2) (Gong, C. et al., Angew. Chem., Int. Ed., 2022, 61, No. e202204899) and 2D sql COF (4.8) (Chen, L. et al., J. Am. Chem. Soc., 2021 , 143, 10243) but still lower than the benchmark MOFs for C2H2/CO2 separation (Mukherjee, S. et al., Chem. Commun., 2020, 56, 10419), such as CPL-1-NH2 (119) (Yang, L. et al., Angew. Chem., Int. Ed., 2021 , 60, 4570) and MIL-160 (10) (Ye, Y. et al., J. Am. Chem. Soc., 2022, 144, 1681).

The heats of adsorption (Q _s t) for C2H2 were further calculated to be 32.7 and 30.1 kJ mol ¹ on NLIS-71 and NLIS-72, respectively, which are higher than those for CO2 (20.6 and 20.8 kJ mol’ ¹ , respectively; FIG. 21), thus indicative of the preferential sorption of C2H2 over CO2 on the two COFs.

Example 8. Dynamic Breakthrough Experiments

Dynamic breakthrough experiments were conducted to illustrate the actual separation performance of NLIS-71 and NLIS-72 for C2H2/CO2 mixtures (FIGs. 15d and 22).

Breakthrough experiments

The breakthrough experiments were performed using a home-built dynamic gas breakthrough setup (FIG. 23). The experiment was conducted using a stainless-steel column (4.6 mm inner diameter * 100 mm length). Before the breakthrough experiment, the column packed with NLIS-71 or NLIS-72 (0.47 and 0.51 g, respectively) was firstly activated with a He flow (10 mL min’ ¹ ) at 413 K for 24 hours. After activation, the gas mixture (C2H2/CO2, 50/50) with a flow rate of 2.0 mL min’ ¹ was introduced, and outlet gas from the column was monitored by a mass spectrometer (Hidden QGA quantitative gas analysis system). After the breakthrough experiment, the sample was regenerated with a He flow (10 mL min’ ¹ ) at 393 K.

Results and Discussions

The results indicated that C2H2 and CO2 could be separated clearly. CO2 first eluted from the columns with a short time, and then C2H2 broke through with a much longer retention time, indicating that the two COFs have excellent C2H2/CO2 separation performance and good affinity for C2H2 over CO2. The C2H2 capture amounts were calculated to be 1.4 and 1.6 mmol g ¹ on NUS-71 and NUS-72, respectively, consistent with the amounts on the collected isotherms (FIG. 15). Recycling breakthrough measurements and sorption isotherms (FIGs. 24-25) demonstrated good stability of NUS-71 for C2H2/CO2 separation. The above results clearly represent the exceptional separation potential of NUS-71 and NUS-72 for C2H2/CO2 mixtures. Example 9. Insights of The Preferential C2H2 Trapping Mechanism

Grand Canonical Monte Carlo (GCMC) Simulations

GCMC simulations were performed in Sorption package (Materials Studio software, Accelrys Software Inc.). The frameworks were treated rigid with atoms frozen at their crystallographic positions during simulations. C2H2 and CO2 atoms were rigid model with Lennard-Jones 12-6 parameters. The charges for atoms of N US-71 were derived from QEq method and QEq_charged1.1 parameter. The simulations were conducted in the locate task, Metropolis method in sorption module and the universal force field (UFF) was used to describe the Lennard-Jones interactions. The charge of C2H2 and CO2 was derived from the QEq method. The interaction energy between the adsorbed molecules and the framework were computed through the Coulomb and Lennard-Jones 6-12 (LJ) potentials. The cutoff radius was chosen 15.5 A for LJ potential and the long-range electrostatic interactions were handled using the Ewald summation method. For each state point considered, GCMC simulation consists of 1 X 10 ⁷ Monte Carlo steps to guarantee equilibration followed by an additional 1 x10 ⁷ steps to sample the desired thermodynamic properties.

Density Functional Theory (DFT) Calculations

First-principles density functional theory (DFT) calculations were performed in Castep software (BIOVIA Materials Studio) (Zhang, Z. et al. , Angew. Chem., Int. Ed., 2017, 56, 16282). A semi-empirical addition of dispersive forces to conventional DFT was included in the calculation to account for van der Waals interactions. Vanderbilt- type ultra-soft pseudopotentials and generalized gradient approximation with Perdew-Burke-Ernzerhof exchange correlation were used. A cutoff energy of 590 eV and a 1 x 1 x 2 -point mesh (generated using the Monkhorst-Pack scheme) were found to be enough for the total energy to converge within 0.01 meV atom' ¹ . The structures of the synthesized materials were firstly optimized, then using GCMC method to load the guest gas molecules to the optimal positions of the pore channels, followed by a full structural relaxation. To obtain the gas binding energy, an isolated gas molecule placed in a supercell (with the same cell dimensions as the material crystal) was also relaxed as a reference. The static binding energy (at T = 0 K) was then calculated using Eq. 5.

EB = E(MOF) + E(gas) - E(MOF + gas) Eq. 5

To gain deep insights into the preferential C2H2 trapping mechanism, in situ PXRD measurements were carried out on C2H2- and CO2-loaded COFs by following the protocol described in Example 2. Results and Discussions

The resolved structure of NLIS-71 loaded with C2H2 (FIG. 26a-d) shows that due to the stagged interlayers, C2H2 is preferentially trapped between two parallel EA units coming from the upper and lower layers, forming multiple sandwich-like host-guest interactions, including H-bonding between H of C2H2 and O on EA and TT -TT interactions between C = C and six-ring members of EA (FIG. 26c). Such a unique binding configuration of C2H2 with this sandwich structure occurs mainly because of the staggered interlayer structure with suitable distance, which can well-accommodate C2H2. In contrast, CO2 locates only between interlayers with multiple O -C=O interactions (FIG. 26d). Additionally, after C2H2 loading, the full width at halfmaximum (FWHM) of the (002) plane decreased from 0.43 to 0.42 A, accompanied by a decrease in the d-spacing distance from 4.08 to 3.96 A (FIG. 26a), indicating strong attractions between C2H2 and the frameworks. However, no changes were observed in the PXRD pattern of CO ₂ -loaded NUS-71 (FIG. 26b).

The DFT-calculated binding energy of NUS-71 for C2H2 was 33.2 kJ mol ¹ , which is higher than that for CO2 (24.6 kJ mol ¹ ), indicating the stronger host-guest interactions of NUS-71 for C2H2. The results are consistent with the adsorption isotherms and breakthrough curves showing that NUS-71 exhibits highly preferential adsorption of C2H2 over CO2.

In conclusion, the bioinspired COFs using bioderived molecules show good crystallinity and high porosity with pore channels decorated with abundant O atoms. Benefitting from this, these bioinspired COFs show excellent C2H2/CO2 separation performance at ambient conditions, which was verified by gas adsorption isotherms and dynamic breakthrough experiments. C2H2 is trapped in the pore channels of COFs via multiple host - guest interactions, forming a unique sandwich structure, which was proved by in situ PXRD refinement and molecular simulations.

This invention not only provides new perspectives for the construction of COFs using biocompatible building blocks but also expands the diversity of COFs for diverse various applications.