Covalent-Organic Framework Materials and Methods of Making Thereof

Abstract

The present invention provides a covalent-organic framework (COF) body, populations of such bodies, a method for manufacturing a covalent-organic framework (COF) body, and (a) a gas storage system or a gas separation system comprising a gas storage vessel and a population of such COF bodies. The COF body comprises a plurality of primary COF particles, some or all of the primary COF particles being agglomerated as COF agglomerates. The average diameter of the primary COF particles is between nm and 120 nm, and the average diameter of the agglomerates is larger than the average diameter of the primary COF particles and between 15 nm and 250 nm. By careful control over particle size distribution during the formation of the COF material, it is possible (b) to form COF materials into high bulk density shapes and forms which are industrially useful and practical without losing sorbent performance.

Claims

1. A covalent-organic framework (COF) body comprising a plurality of primary COF particles, some or all of the primary COF particles being agglomerated as COF agglomerates, wherein: the average diameter of the primary COF particles is between 10 nm and 120 nm; the average diameter of the agglomerates is larger than the average diameter of the primary COF particles and between 15 nm and 250 nm.

2. (canceled)

3. The covalent-organic framework (COF) body according to claim 1 wherein not more than 10% of the agglomerates forming part of the covalent-organic framework (COF) body have a diameter greater than 800 nm.

4. The covalent-organic framework (COF) body according to claim 1 wherein the COF agglomerates and/or primary COF particles forming the body are formed from a single COF composition.

5. The covalent-organic framework (COF) body according to claim 1 wherein the COF agglomerates and/or primary COF particles forming the body are formed from two or more different COF compositions.

6. The covalent-organic framework (COF) body according to claim 1 wherein COF agglomerates and/or primary COF particles forming the body comprise an imine and/or a hydrazone linked COF composition.

7. The covalent-organic framework (COF) body according to claim 1 wherein the bulk density of the body is at least 80% of the calculated density of a COF single crystal of the same composition as the body.

8. The covalent-organic framework (COF) body according to claim 1 wherein the volume of the body is at least 0.5 mm.sup.3.

9. A method for manufacturing a covalent-organic framework (COF) body, comprising the steps of: providing a COF material comprising primary COF particles and agglomerates of primary COF particles, the primary COF particles having an average diameter of between 10 nm and 120 nm, the agglomerates having an average diameter of between 15 nm and 250 nm; centrifuging a liquid suspension comprising the COF material and one or more selected solvents to form a COF concentrate; and performing a temperature-controlled drying step to remove at least some of the solvent from the COF concentrate to thereby form the COF body.

10. The method according to claim 9 wherein the step of providing a COF material comprising primary COF particles and agglomerates of primary COF particles includes allowing the reaction of COF precursors in a reaction mix including one or more selected solvents to thereby form the particles and/or particle agglomerates of the COF material.

11. The method according to claim 10 wherein the reaction mix further comprises one or more catalysts selected from one or more of: a metal triflate; p-toluenesulfonic acid; acetic acid; benzoic acid; p-nitrobenzenesulfonic acid; benzenesulfonic acid; p-phenolsulfonic acid; trifluoroacetic acid; hydrochloroic acid; and/or sulphuric acid.

12. The method according to claim 9 wherein the one or more solvents are selected from one or more of mesitylene, 1,4-dioxane, acetonitrile, methanol, ethanol, isopropanol, n-butanol, 1,2-dichlorobenzene, 1-chlorobenzene, water, acetone, N,N-dimethylformamide, N-methyl-2-pyrrolidone, aniline, m-cresol, dimethylsulfoxide, tetrahydrofuran, toluene, chloroform, dichoromethane, xylene, tetrachloroethane, and/or trichloroethane.

13. The method according to claim 12 wherein the one or more solvents comprise acetonitrile (CH.sub.3CN) in combination with a 1:1 (v/v) mixture of mesitylene and 1,4-dioxane.

14. The method according to claim 12 wherein the one or more solvents comprise acetone in combination with 1,4-dioxane.

15. (canceled)

16. The method according to claim 9 wherein the density of the one or more solvents is selected to be less than the calculated density of a single crystal of the COF material.

17. The method according to claim 9 wherein the absolute density difference between the one or more solvents and the calculated density of a single crystal of the COF material is >0.2 g/l.

18. The method according to claim 9 wherein the temperature-controlled drying step is performed with a maximum temperature of not more than 60° C.

19. (canceled)

20. The method according to claim 9 wherein the method includes a step of activating the COF material by washing the COF material in a suitable solvent.

21. The method according to claim 20 wherein the COF material is activated by washing the COF material in supercritical carbon dioxide.

22. The method according to claim 21 wherein the temperature-controlled drying step is performed after the step of washing the COF material in supercritical carbon dioxide, and wherein the temperature-controlled drying step is performed at a pressure release rate of from about 0.1 bar/h to about 20 bar/h.

23.-24. (canceled)

25. A gas storage system or a gas separation system comprising a gas storage vessel and a population of COF bodies according to claim 1, wherein the population of COF bodies is disposed within the gas storage vessel.

Description

SUMMARY OF THE FIGURES

[0083] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0084] FIG. 1 shows the structure of one TPB-DMTP-COF, a COF material suitable for use in the present invention.

[0085] FIG. 2 shows (a) an overlaid graph of PXRD data for COF powders produced using pure component solvents; and (b) an overlaid graph of PXRD data for COF powders produced using mixed component solvents.

[0086] FIG. 3 shows SEM images of TPB-DMTP-COF synthesized in (a) chloroform, (b) dichloromethane, (c) methanol, (d) a 1:1 (v/v) mixture of 1,3,5-trimethylbenzene and 1,4-dioxane, (e) a 1:1 (v/v) mixture of n-butanol and o-dichlorobenzene, and (f) a 1:1 (v/v) mixture of methanol and 1-chlorobenzene.

[0087] FIG. 4 shows a PXRD pattern of a COF body produced according to the invention, indicating major crystallographic peaks observed.

[0088] FIG. 5 shows various SEM images (a)-(d) of a COF body produced according to the invention taken at different magnifications.

[0089] FIG. 6 is a TEM image taken of a COF body produced according to the invention, including a graph indicating the size distribution of primary COF particles (inset).

[0090] FIG. 7 shows an overlaid graph comparing PXRD patterns for bodies produced according to the present invention. The patterns indicate no major differences in crystallinity when the reaction is scaled up by a factor of four.

[0091] FIGS. 8(a), (b) show SEM images of a COF body produced according to the invention at different magnifications after the reaction is scaled up by a factor of four.

[0092] FIG. 9 shows SEM images of various COF samples, showing solid state packing of TPB-DMTP-COF as a function of synthesis solvent.

[0093] FIG. 10 shows (a) BET area as a function of synthesis solvent; (b) intensity of the (100) crystallographic peak taken from the respective PXRD patterns as a function of synthesis solvent; (c) nonlocal density functional theory (NLDFT) pore size distribution of powders and open monoliths.

[0094] FIG. 11 shows overlaid isotherms of TPB-DMTP-COF bodies activated under different washing procedures.

[0095] FIG. 12 shows overlaid nonlocal density functional theory (NLDFT) pore size distributions of the same TPB-DMTP-COF bodies as FIG. 11.

[0096] FIG. 13 shows BET area as a function of synthesis solvent for scaled up and activated TPB-DMTP-COF bodies.

[0097] FIG. 14 shows (a) a plot comparing the experimental nitrogen isotherm measured at 77 K for a methanol activated 0.75 acetonitrile system, a supercritical carbon dioxide activated 1.00 acetonitrile system and a theoretical nitrogen isotherm derived from GCMC simulations performed on the theoretical structure exhibiting AA interlayer stacking; (b) a semi-logarithmic plot comparing the same data as in (a).

[0098] FIG. 15 shows theoretical isotherms in various units for commercial gases derived from GCMC simulations.

[0099] FIG. 16 shows BET area as a function of (a) catalyst concentration; (b) amine concentration; (c) time.

[0100] FIG. 17 shows overlaid graph comparing PXRD patterns of COF-300-OMe synthesized using different catalyst concentrations.

[0101] FIG. 18 shows an SEM image of COF-300-OMe synthesized in 1,4-dioxane using a catalyst concentration of 0.50 g L.sup.−1.

[0102] FIG. 19 shows an SEM image of COF-300-OMe synthesized in a 0.83 volume fraction 1,4-dioxane in acetone solvent system using a catalyst concentration of 0.50 g L.sup.−1.

[0103] FIG. 20 shows an SEM image of COF-300-OMe synthesized in a 0.83 volume fraction 1,4-dioxane in acetone solvent system using a catalyst concentration of 0.75 g L.sup.−1.

[0104] FIG. 21 shows an SEM image of COF-300-OMe synthesized in a 0.83 volume fraction 1,4-dioxane in acetone solvent system using a catalyst concentration of 0.63 g L.sup.−1.

[0105] FIG. 22 shows an SEM image of COF-300-OMe synthesized in a 0.83 volume fraction 1,4-dioxane in acetone solvent system using a catalyst concentration of 0.50 g L.sup.−1, with an extended reaction time of 60 minutes.

DETAILED DESCRIPTION OF THE INVENTION

[0106] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0107] In particular, in the current work, the solution-phase shaping and densification of COFs into centimetre scale monolithic pellets (bodies) is demonstrated. Pellets thus formed are mechanically robust and exhibit high internal surface areas (e.g. around 900 m.sup.2g.sup.−1 or greater, up to around 1300 m.sup.2 g.sup.−1 or in some instances 2500 m.sup.2 g.sup.−1). It is shown that the solid-state packing of these bodies can be controlled e.g. by choice of synthesis solvent to control COF primary particle and agglomerate size to thereby produce hierarchically porous structures enabling fast diffusion of gases into and out of COF pore spaces. Grand canonical Monte Carlo (GCMC) simulations indicate that these materials may be capable of delivering among the highest adsorption capacities for carbon dioxide capture in the presence of humidity.

[0108] In selecting an initial system capable of affording high degrees of crystallinity and control over particle size, Lewis Acid catalytic methods were adapted and employed. See, work by Matsumoto, M., et al..sup.[2].

[0109] These systems make use of efficient and water-tolerant metal triflate catalysts to prepare COF powders within minutes at room temperature with crystallinities, in some cases, approaching that of the theoretical maximum. As these methods are broadly applicable to the synthesis of imine-linked COFs, findings made in the present work can be subsequently generalized to other such COFs in the exploration of materials for a desired application. With its superior crystallinity, chemical stability, and amenability to pre- and post-polymerization modifications, TPB-DMTP-COF was selected as a trial system from which colloidal processing and monolith formation could be explored. While this material bears close structural similarity to TAPB-PDA-COF, from which colloidal particles 200-600 nm in diameter had been previously demonstrated, no prior synthetic procedure using Lewis Acid catalytic methods had been reported, necessitating a broad screen of synthetic conditions.

[0110] FIG. 1 shows the structure of TPB-DMTP-COF (indicating monomers and pore structure).

[0111] Investigation of Suitable Solvents for Production of a TPB-DMTP-COF COF Body

[0112] Using stoichiometric quantities of amine (1,3,5-tris(4-aminophenyl)benzene) and aldehyde (2,5-dimethoxybenzene-1,4-dicarboxaldehyde) and a catalyst at a given concentration, six single component and six multicomponent solvent systems were prepared as follows and then characterised:

[0113] To a 15 mL centrifuge tube were added 1,3,5-tris(4-aminophenyl)benzene (35.15 mg, 100 μmol) and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (29.13 mg, 150 μmol). Solvent (4 mL) was then added and the mixture was sonicated briefly to a homogenous suspension. Scandium(III)trifluoromethanesulfonate (3 mg, 6 μmol) was added, the tube was sealed, and the mixture was sonicated again for ca. 20 seconds. The mixture was then left to react for 30 minutes undisturbed. The sample powder was collected by centrifugation, washed with three portions of solvent (12 mL each) and an additional portion of methanol (12 mL), and was solvent exchanged in methanol (12 mL) for 24 hours. The powder was dried overnight at 120° C. under vacuum.

[0114] These solvent systems included one that had been reported for the synthesis of TPB-DMTP-COF under solvothermal conditions, a 1:1 (v/v) mixture of n-butanol and o-dichlorobenzene.sup.[1], and one that had been reported for the synthesis of TAPB-PDA-COF under Lewis Acid catalyzed conditions, a 1:4 (v/v) mixture of 1,3,5-trimethylbenzene and 1,4-dioxane.sup.[2]. While low dielectric constant solvents have been shown to be preferred for imine exchange reactions.sup.[3], some moderate to high dielectric constant solvents were also included.

[0115] Powder X-ray diffraction on finished COF powders gave crystalline patterns for several solvent systems as indicated in FIG. 2, which shows (a) an overlaid graph of PXRD data for COF powders produced using pure component solvents; and (b) an overlaid graph of PXRD data for COF powders produced using mixed component solvents. Among the single component solvents, chloroform and dichloromethane performed the best, with the 1:1 (v/v) mixture of 1,3,5-trimethylbenzene (also known as mesitylene) and 1,4-dioxane giving best results among multicomponent systems.

[0116] SEM imaging of samples (see FIG. 3, (a)-(f)) exhibiting the best crystallinity revealed strikingly different morphological outcomes. FIG. 3(a) is an SEM image of TPB-DMTP-COF synthesized in chloroform, FIG. 3(b) is an SEM image of TPB-DMTP-COF synthesized in dichloromethane, FIG. 3(c) is an SEM image of TPB-DMTP-COF synthesized in methanol, FIG. 3(d) is an SEM image of TPB-DMTP-COF synthesized in a 1:1 (v/v) mixture of 1,3,5-trimethylbenzene and 1,4-dioxane, FIG. 3(e) is an SEM image of TPB-DMTP-COF synthesized in a 1:1 (v/v) mixture of n-butanol and o-dichlorobenzene, and FIG. 3(f) is an SEM image of TPB-DMTP-COF synthesized in a 1:1 (v/v) mixture of methanol and 1-chlorobenzene.

[0117] In all cases, there was evidence to suggest that the powder microstructure exists as agglomerations of discrete, primary particles less than 100 nm in diameter that subsequently aggregate into larger secondary structures with diameters greater than 100 nm.

[0118] One Example of Production of Monolithic COFs

[0119] Further experiments were then performed using acetonitrile as a solvent.sup.[2], using the protocol as follows:

[0120] To a 15 mL centrifuge tube were added 1,3,5-tris(4-aminophenyl)benzene (35.15 mg, 100 μmol) and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (7.30 mg, 38 μmol). Solvent (4 mL) was then added and the mixture was sonicated briefly to a homogenous suspension. Scandium(III)trifluoromethanesulfonate (3 mg, 6 μmol) was added, the tube was sealed, and the mixture was sonicated again for ca. 20 seconds. The mixture was then left to react for 30 minutes undisturbed. The sample powder was collected by centrifugation, washed with three portions of solvent (12 mL each) and an additional portion of methanol (12 mL), and was solvent exchanged in methanol (12 mL) for 24 hours. The solvent was then decanted, washed with methanol (12 mL), and left to dry at 20° C. for a further 24 hours. The body was dried overnight at 120° C. under vacuum prior to characterization.

[0121] A glassy pellet resulted that exhibited remarkable mechanical strength.

[0122] FIG. 4 shows a PXRD pattern of the resultant COF body, indicating major crystallographic peaks observed.

[0123] Analysis of the ground pellet by SEM (see FIG. 5(a), (b), (c), (d)) revealed that particles exist as macroscopic glassy shards exhibiting smooth surfaces and showing evidence of clean conchoidal fracturing—a common characteristic of brittle materials (e.g. silica and flint) exhibiting no natural planes of separation. At higher magnifications, surfaces appeared as rough aggregations of much smaller, discrete particles. Further analysis by TEM (see FIG. 6) confirmed the presence of a nanostructure comprised of assemblies of primary COF particles 38±8 nm (n=30, n being the number of particles used in the calculation, i.e. the sample size) in diameter packed closely together to form agglomerates with little to no interstitial space. Collectively, these results confirmed the formation of crystalline monoliths.

[0124] These materials were successfully scaled up by a factor of four without major differences either in crystallinity or morphology using the following protocol:

[0125] To a 50 mL centrifuge tube were added 1,3,5-tris(4-aminophenyl)benzene (140.60 mg, 400 μmol) and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (29.13 mg, 150 μmol). Solvent (16 mL) was then added and the mixture was sonicated briefly to a homogenous suspension. Scandium(III)trifluoromethanesulfonate (12 mg, 24 μmol) was added, the tube was sealed, and the mixture was sonicated again for ca. 20 seconds. The mixture was then left to react for 30 minutes undisturbed. The sample powder was collected by centrifugation, washed with three portions of solvent (40 mL each) and an additional portion of methanol (40 mL), and was solvent exchanged in methanol (40 mL) for 24 hours. The solvent was then decanted, washed with methanol (40 mL), and left to dry at 20° C. for a further 24 hours. The body was dried overnight at 120° C. under vacuum prior to characterization.

[0126] The resulting characterisation of scaled up bodies is shown in FIG. 7 (showing an overlaid graph comparing PXRD patterns for initially produced and standard protocol bodies as compared with scaled up bodies). It can be seen that there is substantially no difference in the major crystallographic peaks identified, showing that there is no major difference in either crystallinity or morphology between bodies produced according to the ‘standard’ and ‘scaled up’ protocols. FIGS. 8(a) and (b) shows SEM images of a COF body produced according to this ‘scaled’ protocol at different magnifications.

[0127] Production of Further Monolithic COFs from TPB-DMTP-COF

[0128] Taking acetonitrile and the 1:1 (v/v) mixture of mesitylene and dioxane as extremes from which phase pure monoliths and powders could be respectively obtained in high crystallinity, solvent systems were prepared and the resulting COF materials analysed. The resulting systems produced monoliths in typical yields above 90% that upon characterization exhibited three distinct solid state packings characteristic of powders, permeable “open” monoliths and impermeable “closed” monoliths. FIG. 9 shows SEM images of various COF samples, showing solid state packing of TPB-DMTP-COF as a function of synthesis solvent—the amount of acetonitrile (MeCN) is indicated. The remaining proportion is 1:1 (v/v) mixture of mesitylene and dioxane. For example, for the samples indicated as 0.50 MeCN, the remaining solvent fraction is 0.50 1:1 (v/v) mixture of mesitylene and dioxane.

[0129] It can be seen that increasing the acetonitrile volume fraction increases the solid state packing density due to the reduction in agglomerate size, thereby leading to monolith formation. At acetonitrile fractions below 0.67 powdered systems were solely obtained. Crystallinity for these systems is almost completely preserved showing little evidence of anisotropic ordering and manifesting high nitrogen capacities. At acetonitrile fractions between 0.67 and 0.70, bodies were produced which exhibited Type IVc isotherms with BET areas just below 900 m.sup.2g.sup.−1—similar to those of powder systems (FIG. 10a). The nanostructure of these materials is characterized by a polydispersity of agglomerate sizes with an average diameter of approximately 150 nm. Primary COF particles forming these agglomerates have a size range of about 30 nm to 50 nm. The lower interstitial space, while not enough to result in loss of gas permeability, does reduce the intensity of the (100) peak to levels consistent with those of closed monoliths (FIG. 10b) suggesting that some mechanical disruption of crystallites may take place.

[0130] Analysis of the non-local density functional theory (NLDFT) pore size distributions (FIG. 10c) confirms that while crystalline COF pores (25 Å) are the dominant free volume elements, substantial mesoscale elements with average diameters of about 95 Å and about 130 Å in width exist that vary in relative prominence favouring the smaller value as the system becomes more monolithic.

[0131] Above acetonitrile fractions of 0.70, closed monoliths are obtained. The crystallinity for these remains comparable to that of open monoliths but nitrogen uptake drops off dramatically suggesting that the hierarchical porosity (or the interparticle mesopores) present in the open systems may play a role in permitting ingress and egress of gas within the monolithic body.

[0132] To assess the extent to which incomplete activation contributes to the low N.sub.2 uptake observed for various monolithic bodies, three additional 0.67 acetonitrile samples were prepared and washed using different methods. Activation, as described previously, involves the expulsion of undesired substances that remain in the pore structure immediately following synthesis (e.g. impurities, remaining COF precursor materials, trapped solvent molecules etc.). Through this expulsion or “activation”, the sorption capacity of the porous material can be improved.

[0133] Extending the wash time in methanol from the standard 1 day to 2 days gives a dramatic improvement in BET area from 867 m.sup.2 g.sup.−1 to 1,155 m.sup.2 g.sup.−1, as shown in FIG. 11, which displays overlaid isotherms of the TPB-DMTP-COF bodies produced from an 0.67 acetonitrile system. The solvent at the end of this period is pale brown, compared to the more characteristic clear solution obtained after one day, indicative of additional dissolved components. Exchanging the solvent after 24 hours yielded further enhancements in nitrogen uptake, with no visible discoloration of the exchanged solvent at the end of the 2-day period. Compared with methods of MOF washing and activation, which have been shown to be complete after a few minutes.sup.[6] these results indicate that the corresponding timescales for COF monoliths are substantially longer—consistent with existing literature procedures (e.g. Soxhlet extraction) for COF powder activation.sup.[1]. Best results were obtained after heating the sample to 50° C. during washing in methanol. BET areas up to 1,309 m.sup.2 g.sup.−1 were achieved with pronounced discoloration of the wash solvent suggesting that removal of unreacted components and low molecular weight phases is most complete under these conditions.

[0134] Analysis of the respective NLDFT pore size distributions (see FIG. 12 which shows overlaid NLDFT pore size distributions of the same TPB-DMTP-COF bodies as analysed in FIG. 10c) showed no detectable changes in the pore profiles across the various methods of activation employed.

[0135] Collectively, these results confirm that improvements in monolith performance can be obtained without any disruption to the hierarchical pore structure previously established by use of more rigorous washing and activation protocols. They also suggest that the lack of N.sub.2 uptake previously observed for closed monoliths was in part due to the presence of substantial quantities of impurities or otherwise pore-blocking substances.

[0136] To determine the effect of improved activation on the BET area of COF monoliths over the range of reaction solvent systems examined, the reaction was scaled up by a factor of four and was subjected to an activation procedure consisting of heating the sample to 50° C. during washing in methanol. After 24 hours, the methanol was additionally exchanged to ensure complete activation was achieved under the scaled up conditions. FIG. 13 shows BET area as a function of synthesis solvent for the set of scaled up COF body samples on which this improved activation procedure has been performed. The new series shows the characteristic maximum behaviour as was previously established. However, the increase in scale does result in a shift in the position of the maximum in BET area to an acetonitrile fraction of around 0.75. In both instances, the maximum BET area obtained with improved activation methods is around 1,300 m.sup.2 g.sup.−1. It can be seen that in both cases BET areas above 500 m.sup.2 g.sup.−1 are achieved at acetonitrile fractions between about 0.55 and about 0.85.

[0137] Additionally, it can be seen from FIG. 13 that trends with BET area remain consistent with those predicted from theory until the maximum is reached. The inventors hypothesize that the subsequent decrease in BET area that takes place above an acetonitrile fraction of 0.75 occurs as a result of mechanical damage to individual COF particles. These particles are likely damaged as a result of the increased capillary forces exerted during drying for the monolithic bodies formed from smaller particles and that consequently possess smaller inter-particle voids. 2D COFs including TPB-DMTP-COF are known to be unstable to in-plane shear forces, suggesting that the capillary forces generated during drying may be sufficient to cause mechanical disruption of the COF pore structure.

[0138] To test whether BET areas could be further improved by use of a lower surface tension solvent, following the initial activation procedure consisting of heating the sample to 50° C. during washing in methanol, a further activation step was performed, wherein the samples were washed and dried using supercritical carbon dioxide. As capillary forces are known to be proportional to the surface tension of the in-pore fluid, the use of supercritical carbon dioxide as an ultra-low surface tension solvent was expected to result in substantially less mechanical damage to individual crystallites. FIG. 13 shows that by drying at a slow rate of 3 bar h.sup.−1, BET areas can be increased to over 2,500 m.sup.2 g.sup.−1.

[0139] Comparison of the experimental nitrogen isotherm for the best performing scaled up monoliths (1.00 acetonitrile and 0.75 acetonitrile) with the isotherm predicted from GCMC simulations reveals excellent consistency (FIG. 14). Specifically, FIG. 14(a) shows a plot comparing the experimental nitrogen isotherm measured at 77 K for the methanol activated 0.75 acetonitrile system, the supercritical carbon dioxide activated 1.00 acetonitrile system and the theoretical nitrogen isotherm derived from GCMC simulations performed on the theoretical structure exhibiting AA interlayer stacking; FIG. 14(b) shows a semi-logarithmic plot of the same.

[0140] To investigate the effect of synthetic parameters such as catalyst concentration, starting material concentration and reaction time on monolith formation, further tests were carried out using the 0.75 (v/v) scaled up acetonitrile system (FIG. 16(a)-(c)).

[0141] With increases in catalyst concentration, a characteristic maximum was observed where monolithic bodies exhibited increasing BET areas until an upper limit, at which point BET area decreased. The inventors hypothesize that this decrease occurs as a result of a shift in the reaction equilibrium at higher concentrations of scandium ions in solution consistent with findings from previous reports.sup.[2] [3] (FIG. 16(a)).

[0142] With increases in the concentration of amine, BET area was found to increase until a maximum, at which point performance plateaued and no subsequent improvements in BET area could be obtained (FIG. 16(b)).

[0143] With reaction time, BET area was found to be largely time invariant suggesting that the timescales for ordering are relatively low i.e. below 15 minutes. These results are comparable to those previously described.sup.[2] [4] and suggest that it may be possible to generate the particles and agglomerates needed to form monolithic bodies in as little as 15 minutes (FIG. 16(c)).

[0144] Trends with BET area as a function of aldehyde concentration were not investigated as a result of the relatively low solubility of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde in the solvent systems tested—around 1.82 g L.sup.−1.

[0145] To identify analytes suitable for high pressure storage in the TPB-DMTP-COF bodies produced in these works, GCMC simulations were carried out for a variety of commercial gases of interest including methane, ethane, ethylene, carbon dioxide, oxygen and hydrogen (FIG. 15(a)-(c)).

[0146] The grand canonical Monte Carlo (GCMC) simulations were performed using the code RASPA.sup.[5] to obtain nitrogen isotherms at 77 K, as well as ethane, ethylene, methane, carbon dioxide, oxygen and hydrogen isotherms at 298 K. The simulations were based on a model that included Lennard-Jones (LJ) interactions for the guest-guest and guest-host interactions. The LJ potential parameters for the framework atoms were taken from the Universal Force Field (UFF). The interactions involving nitrogen, ethane, ethylene, methane, carbon dioxide, oxygen and hydrogen were described by the TraPPE force field. Adsorbate-adsorbate and adsorbate-adsorbent van der Waals interactions were taken into account by Lorentz-Berthelot mixing rules. An atomistic representation was used for the COF, starting from CoRE COF database entry 260 (TPB-DMTPCOF). The structure was treated as rigid. The simulation cell consisted of 8 (1×1×8) unit cells with a LJ cut-off radius of 12.8 Å and no tail corrections. Coulombic interactions were calculated using Hirshfeld partial charges on the framework atoms. For carbon dioxide, oxygen and hydrogen, the long-range electrostatic interactions were handled by the Ewald summation technique. Periodic boundary conditions were applied in all three dimensions. For each state point, GCMC simulations consisted of 20,000 Monte Carlo cycles to guarantee equilibration, followed by 20,000 production cycles to calculate the ensemble averages. All simulations included insertion/deletion, translation and rotation moves with equal probabilities.

[0147] From the theoretical isotherms generated, volumetric and gravimetric storage capacities were observed to be highest for C.sub.2 hydrocarbons and for carbon dioxide. While for pure component carbon dioxide capture at 1 bar and 298 K, with a storage capacity of 2.2 wt. %, TPB-DMTP-COF performs below leading materials such as Mg-MOF-74 (>35 wt. %), its stability to moisture, acid and base may place it among the best performing adsorbents for carbon capture under humid conditions. As TPB-DMTPCOF is one example of a wide range of COF materials having similar chemistry, it is theorised that other COF materials would provide similar or even superior performance. Indeed, it has previously been shown in literature that COFs are among the best performing materials for storage of H.sub.2, CH.sub.4 and CO.sub.2.sup.[9].

[0148] Extension of Monolithic Processing to 3D COFs

[0149] To demonstrate the generalizability of our approach to the preparation of monolithic bodies from 3D COFs in addition to 2D COFs, the inventors applied similar principles to those described in the preceding section to demonstrate control over COF crystallinity and particle size in arriving at monolithic bodies from a representative 3D COF: COF-300-OMe (a methoxylated variant of COF-300). Based on the observation that the formation of monolithic COF bodies is most sensitive to the choice of reaction solvent and the catalyst concentration, a screening procedure similar to that described in the preceding section was performed.

[0150] COF-300 is known to form readily in 1,4-dioxane (also referred to as dioxane) under solvothermal conditions.sup.[10]. Using this as a starting point, molar ratios of monomers were selected such that complete solubility in dioxane was ensured. Five samples employing different catalyst concentrations between 0.25 gL.sup.−1 and 1.25 gL.sup.−1 were then prepared and processed in a similar manner to that used to prepare TPB-DMTP-COF monoliths. A typical procedure is as follows:

[0151] To a 15 mL centrifuge tube were added tetrakis(4-aminophenyl)methane (33.31 mg, 87 μmol) and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (7.30 mg, 38 μmol). Solvent (4 mL) was then added and the mixture was sonicated briefly to a homogenous suspension. Scandium(III)trifluoromethanesulfonate (3 mg, 6 umol) was added, the tube was sealed, and the mixture was sonicated again for ca. 20 seconds. The mixture was then left to react for 30 minutes undisturbed. The sample powder was collected by centrifugation, washed with three portions of solvent (12 mL each) and an additional portion of methanol (12 mL), and was solvent exchanged in methanol (12 mL) for 24 hours. The solvent was then decanted, washed with methanol (12 mL), and left to dry at 20° C. for a further 24 hours. The monolith was dried overnight at 120° C. under vacuum prior to characterization.

[0152] Characterization of the dried powders by PXRD revealed a maximum trend with crystallinity as previously observed, with catalyst concentrations of 0.50 g L−1 producing the most intense patterns (FIG. 17).

[0153] Characterization of the powder by SEM revealed, as before, a nanostructure comprising of primary particles that aggregate into larger secondary particles suggesting that similar solvent-based strategies could be used to control the degree of particle agglomeration en route to monolith body formation (FIG. 18).

[0154] A pure and mixed component solvent screen was then carried out in order to identify solvents that could be used to control the size of agglomerates.

[0155] Blends of acetone and 1,4-dioxane were found to produce monolithic bodies with the desired crystallinity. A series of samples were produced using different 1, 4-dioxane/acetone solvent systems, at a range of different catalyst concentrations. These were then characterized by SEM imaging. SEM characterization of a sample prepared in a 0.83 solution of dioxane to acetone (v/v) at a catalyst concentration of 0.50 g L.sup.−1 indicates a complete disappearance of larger secondary aggregations and the emergence of a characteristic dense monolithic nanostructure comprised of primary particles and smaller secondary aggregations (FIG. 19).

[0156] Similar results were also seen for COF-300-OMe synthesized in a 0.75 volume fraction 1,4-dioxane in acetone solvent system using a catalyst concentration of 0.50 g L.sup.−1, as well as for COF-300-OMe synthesized in a 0.83 volume fraction 1,4-dioxane in acetone solvent system using catalyst concentrations of 0.75 g L.sup.−1 and 0.63 g L.sup.−1 (FIG. 20 and FIG. 21, respectively).

[0157] Finally, the effect of reaction time on COF-300-OMe morphology was also investigated by applying an extended reaction time of 60 minutes (in comparison to the 30 minutes reaction time of other samples) for COF-300-OMe synthesized in a 0.83 volume fraction 1,4-dioxane in acetone solvent system using a catalyst concentration of 0.50 g L.sup.−1. FIG. 22.

[0158] In each of FIGS. 19 to 22, the diameters of the monolithic primary particles fall between 10 nm and 120 nm, and the dimeters of monolithic secondary particles fall between 15 nm and 250 nm. Collectively, these results indicate that similar principles used to arrive at monolithic 2D COF bodies can be easily extended to prepare monolithic 3D COF bodies.

[0159] Materials

[0160] Scandium(III)trifluoromethanesulfonate (98%) was purchased from Alfa Aesar, 1,3,5-tris(4-aminophenyl)benzene (93%) was purchased from TCI, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (97%) and tetrakis(4-aminophenyl)methane (>90%) were purchased from Sigma-Aldrich, 1-butanol (99%) and perfluorohexanes (98%) were purchased from Alfa Aesar, tetrahydrofuran (HPLC), dimethyl sulfoxide (HPLC), dimethylformamide (HPLC) and ethanol (HPLC) were purchased from Fisher Scientific, and acetone (99%), acetonitrile (99%), methanol (99%), dichloromethane (99%), 1,3,5-trimethylbenzene (99%), 1,4-dioxane (99%), chloroform (99%), 1,2-dichlorobenzene (99%), isopropanol (99%) and 1-chlorobenzene (99%) were purchased from Acros Organics. All chemicals were used as received without further purification.

[0161] General Characterisation Protocols

[0162] Powder X-ray diffraction (PXRD) patterns were recorded with a Bruker D8 diffractometer using CuKα1 (λ=1.5405 Å) radiation in Bragg Brentano parafocusing geometry with a step of 0.03° at a scan speed of 1.5 s per step. Predicted patterns were generated in Materials Studio using optimized structures obtained from the CoRE COF database.

[0163] Scanning electron microscope (SEM) images were acquired using an FEI XL30 FEGSEM with an accelerating voltage of 5 kV. Samples were sputter coated with gold.

[0164] Transmission electron microscopy (TEM) was carried out using a FEI Tecnai F20 STEM operated at 200 kV in scanning mode.

[0165] Particle size distributions were obtained using ImageJ processing software.

[0166] Nitrogen adsorption isotherms were collected at 77 K on a Micromeritics Tristar II Plus gas sorption analyzer.

[0167] BET areas were calculated using software provided by Micromeritics using Rouquerol criteria 1 & 2.

[0168] NLDFT pore-size distributions were calculated using a Micromeritics carbon slit model with a regularization parameter of 0.2.

[0169] All samples for nitrogen adsorption were degassed under vacuum at 120° C. overnight prior to analysis.

[0170] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0171] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0172] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0173] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0174] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0175] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example +/−10%.

REFERENCES

[0176] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

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[0182] [6] Ma, J., et al. “Rapid Guest Exchange and Ultra-Low Surface Tension Solvents Optimize Metal—Organic Framework Activation.” Angewandte Chemie International Edition 56.46 (2017): 14618-14621.

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[0185] [9] Furukawa, H., et al. “Storage of Hydrogen, Methane, and Carbon Dioxide in Highly Porous Covalent Organic Frameworks for Clean Energy Applications” Journal of the American Chemical Society 131.25 (2009): 8875-8883.

[0186] [10] Uribe-Romo, F. J., et al. “A Crystalline Imine-Linked 3-D Porous Covalent Organic Framework” Journal of the American Chemical Society 131.13 (2009): 4570-4571.