Spray deposition of large-area covalent organic frameworks

Abstract

Methods for spray deposition of large-area covalent organic frameworks may comprise spray depositing a first monomer solution from a first nozzle and a second monomer solution from a second nozzle onto a collection surface, the first monomer solution comprising a first monomer and a first solvent, and second monomer solution comprising a second monomer and a second solvent; wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, or the first monomer comprises a triamine and the second monomer comprises a dialdehyde; and reacting the first monomer with the second monomer and optionally a catalyst upon the collection surface to form a covalent organic framework.

Description

SPRAY DEPOSITION OF LARGE-AREA COVALENT ORGANIC FRAMEWORKSFIELD OF THE DISCLOSURE

[0001] The present disclosure relates generally to membrane materials and, more particularly, to covalent organic frameworks (COF)s formed by spray deposition.BACKGROUND OF THE DISCLOSURE

[0002] Membrane separation presents a potentially superior and sustainable alternative to traditional energy-intensive separation processes that may necessitate phase transitions. Nonetheless, the deployment of membranes at an industrial scale, especially for the purification of complex mixtures, remains restricted. This restriction is predominantly attributed to prohibitive costs, low throughput, and the limited selectivity of commercially available membranes. Moreover, there exists an apparent trade-off between membrane throughput and selectivity. Commercially utilized polymeric membrane materials may also exhibit compromised stability when exposed to some organic solvents, cleaning agents, or elevated temperatures.

[0003] Covalent organic frameworks (COFs) are an emerging class of materials that may be utilized for membrane separations. COFs are covalently-bonded, porous, crystalline organic structures. They commonly display enhanced chemical and thermal resistance, and may have a variable pore size depending on the monomers and reaction conditions used during their formation. Such attributes potentially address the prevalent challenges associated with conventional polymeric membranes. An example COF of this type includes TpPa COF, which results from a Schiff base condensation reaction between 1,3,5-triformylphloroglucinol (Tp) and p-phenylen ediamine (Pa) monomers. The product exists predominantly as a 0-ketoenamine tautomer, which is believed to result from stabilization through intramolecular hydrogen bonding.

[0004] Various methods for synthesizing COFs are known, such as interfacial polymerization, microwave-assisted synthesis, mechanochemical synthesis, and solvothermal synthesis. However, most techniques require rigorous reaction conditions, including elevated temperatures and use of harsh organic solvents. Moreover, the surface area of the resulting material is often limited by these techniques and the quality of the resulting thin films may be poor, thereby limiting the utility of these materials as high-volume membrane materials. For example, when producing COFs as a thin film by interfacial polymerization between two immiscible monomer solutions, complications may arise in transferring the thin film to adesired substrate and ensuring its adhesion thereto. Similarly, vacuum deposition of exfoliated COF powders on a substrate may result in weak bonding of the COF to the substrate, which may lead to subsequent swelling and / or delamination under fluid shear. Achieving a homogenous deposition of COF powders and films devoid of anomalies by all current techniques is still a considerable challenge and limits the effectiveness of COFs as potential membrane materials.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The following figures are included to illustrate certain aspects of the embodiments, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

[0006] FIG. 1 is a graph of the FTIR spectra for 1,3,5-triformylphloroglucinol (Tp), p- phenylenediamine (Pa), and electrosprayed TpPa COF films synthesized using p-toluene sulfonic acid (pTSA) or scandium triflate catalysts (Sc(0Tf)3).

[0007] FIG. 2 is a graph of the XPS survey spectra for electrosprayed TpPa COF films synthesized using pTSA or Sc(OTf)3 catalysts.

[0008] FIG. 3 is a graph of the XPS Cis spectra for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst.

[0009] FIG. 4 is a graph of the XPS Ols spectra for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst.

[0010] FIG. 5 is a graph of the XPS Nls spectra for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst.

[0011] FIG. 6 is a graph of the XPS S2p spectra for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst.

[0012] FIG. 7 is a graph of the XPS Cis spectra for an electrosprayed TpPa COF membrane synthesized using a SC(OT1)3 catalyst.

[0013] FIG. 8 is a graph of the XPS Ols spectra for an electrosprayed TpPa COF membrane synthesized using a SC(OT1)3 catalyst.

[0014] FIG. 9 is a graph of the XPS Nls spectra for an electrosprayed TpPa COF membrane synthesized using a SC(OT1)3 catalyst.

[0015] FIG. 10 is a graph of the X-ray diffraction pattern derived from EWAXS measurements for electrosprayed TpPa COF synthesized using a Sc(OTfh catalyst.

[0016] FIG. 11 is a graph of the X-ray diffraction pattern derived from EWAXS measurements for electrosprayed TpPa COF synthesized using a pTSA catalyst.

[0017] FIG. 12 is a graph of the thickness growth curves for electrosprayed TpPa COF membranes synthesized using pTSA or Sc(OTf)3 catalysts.

[0018] FIG. 13 is a graph of the dye rejection data and lognormal cumulative distribution function curve for an electrosprayed TpPa COF membrane synthesized using a Sc(OTfh catalyst.

[0019] FIG. 14 is a graph of the dye rejection data and lognormal cumulative distribution function curve for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst.

[0020] FIG. 15 is a graph of the pore size probability density function for an electrosprayed TpPa COF membrane synthesized using a Sc(OTf)3 catalyst.

[0021] FIG. 16 is a graph of the pore size probability density function for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst.

[0022] FIG. 17 is a diagram of an illustrative electrospraying apparatus suitable for forming COFs according to the present disclosure.DETAILED DESCRIPTION

[0023] The present disclosure relates generally to membrane materials and, more particularly, to covalent organic frameworks (COFs) formed by spray deposition.

[0024] As discussed above, current techniques for synthesizing COFs are problematic and may provide an insufficient surface area to support commercial membrane separations. In response to the foregoing, the present disclosure provides spray deposition techniques for forming COFs. Electrospray deposition may be a particularly advantageous spray deposition technique, as discussed in more detail below.

[0025] Spray deposition, such as electrospray, represents a cost- and energy-efficient alternative for nanostructure fabrication in the form of thin films. FIG. 17 is a diagram of an illustrative electrospraying apparatus suitable for forming COFs according to the present disclosure. Electrospray may facilitate formation of diverse micro- and nanostructures by judiciously manipulating the properties of the electrospraying solution(s), including concentration, viscosity, and conductivity, or by modulating physical parameters, such as applied voltage, the distance betw een the nozzle and collector, and the solution discharge rate. Further modification may be realized through choice of the monomers forming the COF and / or the catalysts used in conjunction with forming the COF. When a significant voltage is applied to the capillary nozzles of the syringes containing the monomer solutions, a fluidic instabilitymay be induced at the nozzles' tips, thereby forming a Taylor cone. Electrostatic repulsion within the uniformly charged particles of the droplets may facilitate their fission into finer droplets, which may subsequently settle on a collection surface to result in film formation. The fine droplets may ensure a balanced spread of the monomer solutions across a large surface area. The uniformity may be further enhanced by employing a rotating collector and / or a linearly translating pump mechanism.

[0026] Electrospray, by modulating the delivery of precursor monomers to the collection surface to promote polymerization into a COF, may obviate the need for immiscible monomer solutions, as commonly used in interfacial polymerization techniques. As used herein, the terms "miscible” and / or “miscibility” refer to the ability of at least two substances to dissolve in each other at a specified concentration range and at a specified temperature, thus forming a homogenous mixture ( / .<?., a solution). Two or more substances may be freely miscible with each other over all concentration ranges or miscible over a particular concentration range. Two substances may be considered miscible when there is no more than 5% of a second phase by volume.

[0027] Consequently, the use of electrospray may broaden the spectrum of viable solvents for COF fabrication, enabling the use of environmentally favorable “green” solvents. In contrast to conventional interfacial polymerization techniques requiring immiscible organic solvents in large volumes, electrospraying may demand significantly reduced solvent volumes for COF syntheses, potentially resulting in minimal waste. Ethanol (EtOH) may be a particularly desirable solvent. Additionally, control over the thickness of COF films may be achieved by altering the monomer concentration(s) and / or the electrospraying duration. Advantageously, spraying techniques, such as electrospray, are not limited to small deposition areas, and therefore may yield large-area COFs with few defects in a short timeframe.

[0028] Methods of the present disclosure may comprise: spray depositing, preferably by electrospray, a first monomer solution from a first nozzle and a second monomer solution from a second nozzle onto a collection surface, the first monomer solution comprising a first monomer and a first solvent, and the second monomer solution comprising a second monomer and a second solvent; and reacting the first monomer with the second monomer upon the collection surface to form a covalent organic framework (COF). If a single monomer undergoes self-condensation to form a COF, the second monomer and second spray nozzle may be omitted. Spraying of the first monomer solution and the second monomer solution may form a thin film upon the collection surface. Spraying of the first and second monomer solutions may occur concurrently or sequentially in any order. Further, in alternative embodiments, oneof the monomer solutions may be deposited upon the collection surface by a non-spray technique, such as roller coating or dip coating, followed by spraying of the other monomer solution.

[0029] In more specific examples, the first monomer may comprise a diamine and the second monomer may comprise a trialdehyde, or the first monomer may comprise a triamine and the second monomer may comprise a dialdehyde. COFs prepared by these methods may demonstrate similar chemistry, structure, and / or performance to those prepared by conventional interfacial polymerization and similar techniques, with the potential benefit of a larger fabrication surface area, less surface defects, reduced production time, increased environmental favorability, and / or reduced solvent waste.

[0030] The COFs may be deposited as a thin film, wherein the thin film is only limited in size by the corresponding size of the collection surface upon which it is formed. In nonlimiting examples, the collection surface may have a surface area of about 560 cm2or greater, such as about 750 cm2or greater, or about 1000 cm2or greater, or about 1500 cm2or greater, or about 2500 cm2or greater, or about 5000 cm2or greater, or about 10000 cm2or greater.

[0031] In non-limiting examples, the collection surface may be a rotating drum, which may have a surface area within the foregoing ranges.

[0032] Non-limiting example membrane compositions of the present disclosure may therefore comprise a COF deposited as a thin film having a surface area of at least about 560 cm2, preferably wherein the COF is a P-ketoenamine reaction product of a diamine and a trialdehyde or a similar COF that may be prepared by the methods described herein.

[0033] In non-limiting examples, the covalent organic framework is deposited as a film having a thickness ranging from about 5 nm to about 1 pm.

[0034] In non-limiting examples, the deposited covalent organic framework has pore size from about 1 nm to about 2 nm.

[0035] Some COFs of the present disclosure may be prepared by a Schiff base condensation of a diamine and a trialdehyde or a triamine and a dialdehyde, which may occur under acid catalysis (Lewis acid or protic acid). Preferably, the initially formed imine undergoes substantial tautomerization to form a -ketoenamine. Tautomerization to form the P-ketoenamine may be realized based on the structure of the polyaldehyde monomer, as discussed subsequently. The initial Schiff base formation may occur reversibly and lead to the formation of a crystalline framework, and the subsequent tautomerization may occur substantially irreversibly to enhance the chemical stability of the framew ork. Without beingbound by any particular theory, the substantially irreversible nature of the tautomerism may result from stabilization of the P-ketoenamine by intramolecular hydrogen bonding. Still without being bound by theory, the tautomerization is not believed to affect the crystallinity of the COF because the transformation may only involve a shifting of bonds while keeping the majority of the atomic positions about the same.

[0036] In alternative embodiments, polyaldehydes that are incapable of undergoing tautomerization to form a P-ketoenamine when forming a COF may also be used in the methods described herein. Examples of such alternative polyaldehydes are discussed further below.

[0037] Diamine monomers suitable for use in the compositions and methods of the present disclosure are not considered to be particularly limited, provided that the diamine is sufficiently nucleophilic to undergo the Schiff base condensation with the trialdehyde monomer (alternately a triamine monomer undergoing Schiff base condensation with a dialdehyde monomer). The diamine monomer may, for example, comprise 2.5-dimethyl-p- phenylenediamine, or, preferably, p-phenylenediamine (Pa). More generally, the diamine may be an optionally substituted phenylenediamine, more preferably an optionally substituted p- phenylenediamine. Other examples of suitable polyamines may include, but are not limited to, aliphatic alkylenediamines, aliphatic triamines, aliphatic tetramines, aliphatic pentamines, and aliphatic hexamines, any of which may be optionally substituted. Suitable aliphatic poly amines may be linear or branched. Aromatic polyamines may also be used, wherein the multiple amine groups may be on the same or different aromatic rings. Examples of additional suitable polyamines are provided in the appendix. The term “optionally substituted’' means that the aromatic ring or carbon chain may or may not be substituted. Optional substitutions may include hydrocarbyl groups (e.g, alkyl, cycloalkyl, or aryl groups), halogens, heterocyclic or heteroaryl groups, carbonyl groups (e.g., ketones, carboxylic acids, esters, amides, and the like), sulfonic acids, and the like.

[0038] Suitable trialdehydes may include 1,3,5-triformylphloroglucinol (Tp) and the like. Other examples of suitable polyaldehydes may include, but are not limited to, aliphatic alkylenedialdehydes, aliphatic trialdehydes, aliphatic tetraaldehydes, aliphatic pentaaldehydes, and aliphatic hexaaldehydes, any of which may be optionally substituted. Suitable aliphatic polyaldehydes may be linear or branched. Aromatic polyaldehydes may also be used, wherein the multiple aldehyde groups may be on the same or different aromatic rings. Examples of additional suitable polyaldehydes are provided in the appendix.

[0039] A polyaldehyde and a polyamine may undergo a reaction to produce a COF in the disclosure herein. In illustrative examples, a diamine monomer and a trialdehyde monomermay undergo a reaction to produce a COF in the disclosure herein. Alternately, a triamine monomer and a dialdehyde monomer may undergo a reaction to produce a COF in the disclosure herein. In some examples, the polyaldehyde and the polyamine may form P- ketoenamine COF.

[0040] The overall reaction of the diamine monomer and the trialdehyde monomer may produce an enamine-linked COF, for example, a P-ketoenamine COF (e.g., a TpPa COF). Formula 1 below shows a portion of a P-ketoenamine COF formed from p-phenylenediamine and 1,3,5 -triformy Iphlorogl ucinol .Formula 1

[0041] In still another example, a P-ketoaldehyde may be used to produce an enamine- linked COF. Examples of suitable P-ketoaldehydes are provided in the appendix.

[0042] In non-limiting examples, the COF may comprise linkages other than enamine linkages. For example, suitable COF linkages may include, but are not limited to, boroxines, boronic esters, imines, hydrazones, azines, imides, and the like. Examples are provided in Lohse, M.S.; et al., '‘Covalent Organic Frameworks: Structures, Synthesis, and Applications,”Advanced Functional Materials, 2018, 28 (33), 1705553. Additional example chemistries to produce such COFs are described in the appendix. Any of these alternative COFs may be produced using the methods described herein.

[0043] The reaction to form the COF may take place on a polymeric substrate, such as polyacrylonitrile (PAN), on which the monomers undergo polymerization. Other polymers including polyvinylidene fluonde (PVDF), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), poly ether sulfone (PES), polysulfone (PSf), cellulose acetate (CA), nitrocellulose, cellulose ester (CE), polyamide and polyimide, and the like may also be suitable in this regard. Each monomer, having been diluted in a solvent to form a monomer solution, may be individually spray deposited upon the polymeric substrate by nozzles mounted to a deposition head capable of moving freely in two dimensions. To achieve uniformity in the deposited COF, the polymeric substrate may be applied to a rotating drum collector and the monomer solutions applied thereto by the spray deposition process. The nozzles may, for example, be mounted at a distance from the rotating drum collector of about 1 cm to about 10 cm, or about 1 cm to about 5 cm, or about 5 cm to about 10 cm.

[0044] To further improve uniformity of the COF, electrospray may be employed as the spray deposition technique. As previously mentioned, the electric repulsion forces generated within the similarly charged particles produced from the monomer solutions by electrospray may promote fission of the monomer solution into fine droplets. Additionally, electrospray techniques may obviate the need for immiscible monomer solutions. Consequently, the solvents used in the monomer solutions may be miscible with each other. For example, both the first solvent and the second solvent in the first monomer solution and the second monomer solution, respectively, may comprise ethanol, water, or a combination thereof. The first solvent and second solvent may preferably be ethanol.

[0045] The monomer solutions’ discharge rates and the applied voltages across the nozzles may be varied to optimize the electrospraying cone-jet, eliminate solution sputtering and dripping, and prevent nozzle clogging. For example, the voltage applied across the nozzles may be about 1 kV to about 15 kV, or about 1 kV to about 10 kV, or about 1 kV to about 5 kV, or about 5 kV to about 15 kV, or about 5 kV to about 10 kV, or about 10 kV to about 15 kV. The nozzles’ discharge rate may vary individually, and may, for example, be about 1 mL / h to about 10 mL / h, or about 1 mL / h to about 5 mL / h, or about 5 mL / h to about 10 mL / h. Furthermore, the monomer solutions may, for example, be deposited onto the collection surface for a duration of about 1 hour to about 6 hours, or about 1 hour to about 4 hours, or about 1hour to about 2 hours, or about 2 hours to about 6 hours, or about 2 hours to about 4 hours, or about 4 hours to about 6 hours.

[0046] Embodiments disclosed herein include:

[0047] A. A method for spray deposition of large-area covalent organic frameworks including: spray depositing a first monomer solution from a first nozzle and a second monomer solution from a second nozzle onto a collection surface, the first monomer solution comprising a first monomer and a first solvent, and the second monomer solution comprising a second monomer and a second solvent; wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, or the first monomer comprises a triamine and the second monomer comprises a dialdehyde; and reacting the first monomer with the second monomer and optionally a catalyst upon the collection surface to form a covalent organic framework.

[0048] B. A membrane composition including: a covalent organic framework comprising a P-ketoenamine reaction product of a diamine and a trialdehyde having a surface area of at least 560 cm2.

[0049] C. A method for spray deposition of large-area covalent organic frameworks including: spray depositing a first monomer solution from a first nozzle and a second monomer solution from a second nozzle onto a collection surface, the first monomer solution comprising a first monomer and a first solvent, and the second monomer solution comprising a second monomer and a second solvent: and reacting the first monomer with the second monomer and optionally a catalyst upon the collection surface to form a covalent organic framework.

[0050] Each of embodiments A, B, and C may have one or more of the following additional elements in any combination:

[0051] Element 1 : wherein spray depositing comprises electrospraying.

[0052] Element 2: wherein a voltage is applied across the first nozzle and the second nozzle, and the voltage ranges from about 1 kV to about 15 kV.

[0053] Element 3: wherein the collection surface comprises a rotating drum.

[0054] Element 4: wherein the rotating drum has a surface area of at least about 560 cm 2.

[0055] Element 5: wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, and the diamine comprises optionally substituted p- phenylenediamine.

[0056] Element 6: wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, and the trialdehyde comprises 1,3,5- triformylphloroglucinol.

[0057] Element 7: wherein the covalent organic framework comprises a [3- ketoenamine.

[0058] Element 8: wherein the first solvent and the second solvent are water-miscible and optionally the same.

[0059] Element 9: wherein the covalent organic framework is deposited as a film having a thickness ranging from about 5 nm to about 1000 nm.

[0060] Element 10: wherein the diamine comprises optionally substituted p- phenylenediamine.

[0061] Element 11: wherein the trialdehyde comprises 1.3.5-triformylphloroglucinol.

[0062] By way of non-limiting example, exemplary element combinations applicable to A, B, and C include but are not limited to: 1 and 2; 1 and 3; I and 5; 1 and 6; 1 and 7; 1 and8; 1 and 9; 2 and 3; 2 and 5; 2 and 6; 2 and 7; 2 and 8; 2 and 9; 3 and 4; 3 and 5; 3 and 6; 3 and7; 3 and 8; 3 and 9; 4 and 5; 4 and 6; 4 and 7; 4 and 8; 4 and 9; 5 and 6; 5 and 7; 5 and 8: 5 and9; 6 and 7; 6 and 8; 6 and 9; 7 and 8; 7 and 9: 8 and 9; 9 and 10; 9 and 11; 10 and 11; 1, 2. and3; 1, 3, and 5; 1, 5, and 6; 1, 6, and 7; 1, 7 and 8; and 1, 8, and 9.

[0063] The present disclosure is further directed to the following non-limiting clauses: Clause 1. A method comprising: spray depositing a first monomer solution from a first nozzle and a second monomer solution from a second nozzle onto a collection surface, the first monomer solution comprising a first monomer and a first solvent, and the second monomer solution comprising a second monomer and a second solvent; wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, or the first monomer comprises a triamine and the second monomer comprises a dialdehyde; and reacting the first monomer with the second monomer and optionally a catalyst upon the collection surface to form a covalent organic framework.Clause 2. The method of clause 1, wherein spray depositing comprises electrospraying.Clause 3. The method of clause 2, wherein a voltage is applied across the first nozzle and the second nozzle, and the voltage ranges from about 1 kV to about 15 kV.Clause 4. The method of any one of clauses 1-3, wherein the collection surface comprises a rotating drum.Clause 5. The method of clause 4. wherein the rotating drum has a surface area of at least about 560 cm2.Clause 6. The method of any one of clauses 1-5, wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, and the diamine comprises optionally substituted p-phenylenediamine.Clause 7. The method of any one of clauses 1-6, wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, and the trialdehyde comprises 1 ,3,5-triformylphloroglucinol.Clause 8. The method of any one of clauses 1-7, wherein the covalent organic framework comprises a P-ketoenamine.Clause 9. The method of any one of clauses 1 -8, wherein the first solvent and the second solvent are water-miscible and optionally the same.Clause 10. The method of any one of clauses 1 -9, wherein the covalent organic framework is deposited as a film having a thickness ranging from about 5 nm to about 1000 nm.Clause 11. A membrane composition comprising: a covalent organic framework comprises a -ketoenamine reaction product of a diamine and a trialdehyde having a surface area of at least about 560 cm2.Clause 12. The membrane composition of clause 11, wherein the diamine comprises optionally substituted p-phenylenediamine.Clause 13. The membrane composition of clause 11 or clause 12, wherein the trialdehyde comprises 1 ,3.5-triformylphloroglucinol.Clause 14. The membrane composition of any one of clauses 11-13, wherein the covalent organic framework comprises a film having a thickness ranging from about 5 nm to about 1000 nm.Clause 15. A method comprising: spray depositing a first monomer solution from a first nozzle and a second monomer solution from a second nozzle onto a collection surface, the first monomer solution comprising a first monomer and a first solvent, and the second monomer solution comprising a second monomer and a second solvent: and reacting the first monomer with the second monomer and optionally a catalyst upon the collection surface to form a covalent organic framework.

[0064] To facilitate a better understanding of the embodiments of the present disclosure, the following examples of preferred or representative embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention.Examples

[0065] For fabrication of enamine-linked TpPa COF-based membranes, 2.4 mg p- phenylenediamine (Pa) monomer and 0.44 mg scandium triflate (Sc(OTf)3) were dissolved in 15 mL pure ethanol to prepare the diamine monomer solution. 3.16 mg 1,3,5- triformylphloroglucinol (Tp) was dissolved in 12 mL ethanol to prepare the trialdehyde monomer solution. An alternate diamine monomer solution was prepared with pTSA as the acid catalyst by dissolving 2.4 mg Pa and 21.3 mg pTSA in 15 mL ethanol. All solutions were sonicated for 15 minutes to obtain a homogeneous solution. The composition of the aldehyde solution remained the same for the two TpPa COF membranes synthesized with different catalysts.

[0066] Electrospraying was performed using a custom-built system with dual channel syringe pump (NEW ERA, NE 1000) mounted to a linearly translating stage (VELMEX) with programmable control. During electrospraying, monomer solutions were simultaneously discharged at 4 mL / h from two parallel syringes placed 4 cm from a grounded metallic rotating drum collector with surface area of 560 cm2. A voltage of 12 kV was applied to the needles from a high voltage source. Monomer solution discharge rates and applied voltages were varied to optimize the electrospraying cone-jet, eliminate solution sputtering and dripping, and prevent nozzle clogging. The speed of the rotating collector and linearly translating pump stage were varied to achieve uniform monomer distribution on the substrate.

[0067] The chemistry of synthesized TpPa COF membranes was verified using Fourier Transform Infrared (FTIR) spectroscopy. Ultrathin COF film thicknesses were measured by surface profilometry with a measurement force of 0.1 mg and stylus speed of 0.1 mm / s. Scanning Electron Microscopy was performed using a ZEISS LEO 1525 with an FEG gun.

[0068] COF membrane selectivity was characterized by molecular weight cut-off, which was determined from dye rejection tests with solutions of primulin, nitroanaline, safranine o, Congo red, methyl blue, and reactive black dyes in anhydrous ethanol to minimize dye dissociation and any associated Donnan exclusion effects. Thus, dye rejection measurements investigate only steric exclusion of solutes by the two COF membranes. Dye solutions with concentration of 50 mg / L were measured by calibration to UV absorbance at a characteristic wavelength. Solvent permeance and dye rejection experiments were performed for both TpPa electrosprayed membranes in AMICON® plastic stirred dead end filtration cells with effective membrane diameter of 25 mm. The dead end filtration experiments were performed at room temperature (21 °C), and the feed solution in the cell was continuouslystirred using a magnetic stir bar. The dead end cells were pressurized at 1-2 bars with compressed nitrogen gas.

[0069] Solvent permeance (L / m2h bar) was calculated according to Equation 1, in which AV (L) is the volume of solvent permeating through the membrane, At (h) is the duration over which the permeate volume was collected. Aeff (m2) is the membrane's effective area, and AP (bar) is the transmembrane pressure.ARPermeance = - - - - —At x Aeffx APEquation 1

[0070] Dye concentrations in the permeate were measured by UV-Vis absorbance, which was calibrated to dye concentration. Rejection values were calculated according to Equation 2, where Cpis concentration of dye in the permeate and Cr is the concentration of dye in the feed solution.Rejection (Equation 2

[0071] FIG. 1 is a graph of the FTIR spectra for 1, 3, 5-triformylphloroglucinol (Tp), p-phenylenediamine (Pa), and electrosprayed TpPa COF films synthesized using p-toluene sulfonic acid (pTS A) or scandium triflate catalysts (Sc(OTf)3). Comparison of the FTIR spectra shows complete conversion of the starting monomers to the COF materials. The disappearance of the N-H bonds (3183 cm1. 3293 cm1, and 3367 cm1) in the diamine (Pa) monomer and the C=O bonds (1639 cm-1) in the aldehyde (Tp) monomer, and the appearance of signature C=C bonds (1582 cm'1) and C-N bonds (1257 cm'1) in the COF membranes indicates essentially complete conversion of the monomers and significant tautomerization to the enamine form of the TpPa COFs.

[0072] FIG. 2 is a graph of the XPS survey spectra for electrosprayed TpPa COF films synthesized using pTSA or Set OT )?, catalysts. As shown in FIG. 2, the spectra show peaks representing carbon, nitrogen, and oxygen. FIG. 3 is a graph of the XPS Cis spectra for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst. Analysis of the Cis spectra in FIG. 3 shows characteristic peaks associated with C=C. C-N, and C=O as expected of the enamine form of the TpPa COF. A shoulder also appears in the C-0 range (290.2 eV) which could indicate that a portion of the membrane surface may exist in the imine form. FIG. 4 is a graph of the XPS Ols spectra for an electrospray ed TpPa COF membrane synthesized using a pTSA catalyst. The Ols spectra in FIG. 4 confirm the presence of both C=O and C-OH. FIG. 5 is a graph of the XPS Nls spectra for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst. The Nls spectra in FIG. 5 show enamine nitrogen C=C- NH and a shoulder indicating the possible presence of C-NH-C nitrogen. The spectra also show a small peak attributed to sulfur, which may indicate a residual catalyst species. FIG. 6 is a graph of the XPS S2p spectra for an electrosprayed TpPa COF membrane synthesized using a pTSA catalyst. Indeed, the S2p spectra in FIG. 6 show peaks attributed to SO3H, which may indicate the presence of residual pTSA. FIGS. 7-9 are graphs of the XPS Cis, Ols, and Nls spectra, respectively, for an electrosprayed TpPa COF membrane synthesized using a Sc(0Tf)3 catalyst. The high-resolution Cis, Ols, and Nls spectra in FIGS. 7-9, respectively, show characteristic peaks for the P-ketoenamine form in addition to shoulders indicating that some of the COF may remain in the imine form.

[0073] As a comparative example, FIG. 10 is a graph of the X-ray diffraction pattern derived from extended wide angle x-ray scattering (EWAXS) measurements for a TpPa COF powder synthesized by electrospray deposition using a Sc(0Tf)3 catalyst. The diffraction pattern from EWAXS measurements shows three peaks at 20 values of 4.7° (corresponding to reflection from the 100 plane), 8.2° and 26.4°. The peak at about 26.4° corresponds to reflection from the 001 plane and may be used for the estimation of the 7t-7i stacking distance between COF layers (approximately 3.3 A for TpPa COF).

[0074] FIG. 11 is a graph of the X-ray diffraction pattern derived from EWAXS measurements for a TpPa COF powder synthesized by electrospray deposition using pTSA catalyst. The diffraction pattern from EWAXS measurements shows multiple peaks, including characteristic peaks at 20 values of 4.7° (corresponding to reflection from the 100 plane), 8° and 26.4°. The peak at about 26.4° corresponds to reflection from the 001 plane and may be used for the estimation of the 7t-7t stacking distance betw een COF layers (approximately 3.3 A for TpPa COF). The diffraction pattern for TpPa COF synthesized using pTSA as a catalyst shows additional peaks at 20 values of 12.3° and 18° which may be the characteristic peaks for the staggered stacking of the COF.

[0075] Top-view SEM images of the polyacrylonitrile (PAN) 400,000 MWCO support and electrosprayed TpPa COFs synthesized using Sc(OTf 3 or pTSA as catalysts showed full coverage of the support with defect-free and continuous COF films. FIG. 12 is a graph of the thickness growth curves for electrosprayed TpPa COF membranes synthesized using pTSA or Sc(OTf)3 catalysts. The strong linear correlation for thickness as a function of electrospraying duration, as evaluated by an R2of 0.98 and 0.93 for pTSA and Sc(OTf catalysts, respectively,indicates that predictable and controlled thickness may be achieved for COF films using electrospray-based techniques.

[0076] FIGS. 13 and 14 are graphs of the dye rejection data and lognormal cumulative distribution function curves for electrosprayed TpPa COF membranes synthesized using Sc(OTf)3 or pTSA catalysts, respectively. Solute rejections are plotted versus the minimal projection diameters of the dye molecules. FIGS. 15 and 16 are graphs of the pore size probability density functions for electrosprayed TpPa COF membranes synthesized using Sc(OTf)3 or pTSA catalysts, respectively. As estimated from FIGS. 15 and 16, the COF membrane synthesized using pTSA had a larger average pore size than the COF membrane synthesized using Sc(OTf)3, but had a narrower pore size distribution and a smaller standard deviation. The estimated average pore diameter for the Sc(OTf)3 COF membrane (1.4 nm) is consistent with the pore diameter of similar enamine-linked COFs fabricated by an interfacial polymerization technique. However, the larger surface areas achievable through electrospray deposition techniques are a significant distinction over the latter.Table 1 summarizes the various COF linkage chemistries and how they may be prepared.Table 1Boronic acids may undergo self-condensation to produce boroxine COFs. Examples of boronic acids that may be suitable include, but are not limited to, the following, wherein any combination of boronic acids may undergo self-condensation to produce a COF:Boronic acids and catechols may undergo condensation to produce boronate ester COFs. Examples of boronic acids and catechols that may be suitable include, but are not limited to, the following:Polyamines and polyaldehydes may undergo condensation to produce imine COFs. Examples of polyamines and polyaldehydes that may be suitable include, but are not limited to, the following, wherein any polyamine(s) and any polyaldehyde(s) may undergo condensation with one another to produce a COF :Polyhydrazides and polyaldehydes may undergo condensation to produce hydrazone COFs (e.g., acyl hydrazone COFs). Examples of polyhydrazides and polyaldehydes that may be suitable include, but are not limited to, the following, wherein any polyhydrazide(s) and any polyaldehyde(s) may undergo condensation with one another to produce a COF:Hydrazine and polyaldehydes may undergo condensation to produce azine COFs. Examples of polyaldehydes that may be suitably condensed with hydrazine include, but are not limited to. the following:Polyamines and certain polyaldehydes (e g.,, 1,3,5-triformylphloroglucinol) may undergo condensation to produce p-keto enamine COFs. Examples of poly amines that may be suitable include, but are not limited to:In another example, polyamines and P-keto polyaldehydes may undergo condensation to produce P-keto enamine COFs. Examples of polyamines and P-keto polyaldehydes that may be suitable include, but are not limited to. wherein any polyamine(s) may be condensed with any P-keto polyaldehyde(s):Polyamines and polyanhydrides may undergo condensation to produce imide COFs.Examples of polyamines and polyanhydrides that may be suitable include, but are not limitedto, the following, wherein any polyamine(s) and any polyanhydride(s) may undergo condensation with one another to produce a COF:

[0077] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, for example, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “contains.” “containing,” “includes.” “including.” “comprises,” and / or “comprising,” and variations thereof, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0078] Terms of orientation used herein are merely for purposes of convention and referencing and are not to be construed as limiting. However, it is recognized that these terms could be used with reference to an operator or user. Accordingly, no limitations are implied orto be inferred. In addition, the use of ordinal numbers (e.g., first, second, third, etc.) is for distinction and not counting. For example, the use of '‘third” does not imply there must be a corresponding “first” or “second.” Also, if used herein, the terms “coupled” or “coupled to” or “connected” or “connected to” or “attached” or “attached to” may indicate establishing either a direct or indirect connection, and are not limited to either unless expressly referenced as such.

[0079] While the disclosure has described several exemplary embodiments, it will be understood by those skilled in the art that various changes can be made, and equivalents can be substituted for elements thereof, without departing from the spirit and scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation, or material to embodiments of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, or to the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.

[0080] While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.

[0081] All documents described herein are incorporated by reference herein for purposes of all jurisdictions where such practice is allowed, including any priori ty documents and / or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element, or groupof elements is preceded with the transitional phrase ‘"comprising / ’ it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is” preceding the recitation of the composition, element, or elements and vice versa.

[0082] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary7, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by one or more embodiments described herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Claims

CLAIMSThe invention claimed is:

1. A method comprising: spray depositing a first monomer solution from a first nozzle and a second monomer solution from a second nozzle onto a collection surface, the first monomer solution comprising a first monomer and a first solvent, and the second monomer solution comprising a second monomer and a second solvent; and, reacting the first monomer with the second monomer and optionally a catalyst upon the collection surface to form a covalent organic framework.

2. The method of claim 1, wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, or the first monomer comprises a triamine and the second monomer comprises a dialdehyde;3. The method of claim 1. wherein spray depositing comprises electrospraying.

4. The method of claim 3, wherein a voltage is applied across the first nozzle and the second nozzle, and the voltage ranges from about 1 kV to about 15 kV.

5. The method of claim 1, wherein the collection surface comprises a rotating drum.

6. The method of claim 5, wherein the rotating drum has a surface area of at least about 560 cm .

7. The method of any one of claims 1-6, wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, and the diamine comprises optionally substituted p- phenylenediamine.

8. The method of any one of claims 1-6, wherein the first monomer comprises a diamine and the second monomer comprises a trialdehyde, and the trialdehyde comprises 1,3,5- triformylphloroglucinol.

9. The method of any one of claims 1-6, wherein the covalent organic framework comprises a P-ketoenamine.

10. The method of any one of claims 1-6 wherein the first solvent and the second solvent are water-miscible and optionally the same.

11. The method of any one of claims 1, 2. or 5. wherein the covalent organic framework is deposited as a film having a thickness ranging from about 5 nm to about 1000 nm.

12. A membrane composition comprising: a covalent organic framework comprising a P-ketoenamine reaction product of a diamine and a trialdehyde having a surface area of at least about 560 cm2.

13. The membrane composition of claim 12, wherein (i) the diamine comprises optionally substituted p-phenylenediamine. (ii) the trialdehyde comprises 1,3,5-triformylphloroglucinol; or (iii) the covalent organic framework comprises a film having a thickness ranging from about 5 nm to about 1000 nm; or (iv) all of (i), (ii), and (iii).

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