Two-dimensional monolayer ionic COF and its application in osmotic energy conversion

Abstract

The present invention discloses a two-dimensional monolayer ionic COF and its application in osmotic energy conversion. The two-dimensional monolayer ionic COF membrane is obtained by polymerizing 5,10,15,20-tetrakis (4-formaldehyde benzene)-21H, 23H-porphyrin and ethidium bromide to form an imine covalent bond through Schiff base reaction; the thickness is 0.9-1.1nm and the pore size is 1.6-1.8nm. The two-dimensional s-iCOF material of the present invention is formed by covalently linking 5,10,15,20-tetrakis (4-formaldehyde benzene)-21H, 23H-porphyrin and ethidium bromide, with larger porosity, good integrity, regular pore arrangement and positive charge. In osmotic energy conversion, larger porosity and regular pore arrangement ensure considerable ion flux, good integrity and the properties of the monolayer ensure its high energy conversion rate, and the positive charge surface indicates that ions can be selectively transmitted in order to seek a larger output potential. In summary, extremely excellent output power can be achieved by osmotic energy conversion using two-dimensional s-iCOF.

Description

Technical Field

[0001] The present invention relates to a two-dimensional single-layer ionic COF and application thereof in osmotic energy conversion, belonging to the technical field of osmotic energy conversion. Background Art

[0002] The osmotic energy between solutions of different salt concentrations is considered to be a renewable clean energy source. Using reverse electrodialysis technology to convert osmotic energy into electrical energy will greatly alleviate people's dependence on non-renewable energy. In recent years, selective permeable membranes based on graphene oxide, molybdenum disulfide, metal-organic frameworks, etc. have been widely used in the field of osmotic energy conversion due to their ability to selectively transport ions. However, they still face the problem of not being able to achieve both high permeability and high ion selectivity, which limits the improvement of their osmotic energy conversion efficiency. Therefore, the development of new porous membranes to achieve a trade-off between ion selectivity and permeability remains one of the huge challenges in the field of osmotic energy conversion. Summary of the Invention

[0003] The purpose of the present invention is to provide a two-dimensional single-layer ionic covalent-organic framework (s-iCOF) and its application in osmotic energy conversion. Using s-iCOF as an energy conversion membrane can significantly increase the output power of osmotic energy conversion and, to a certain extent, solve technical problems in the field of osmotic energy conversion.

[0004] The two-dimensional single-layer ionic COF membrane provided by the present invention is obtained by polymerization of 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin (TFPP) and ethidium bromide (EB) through Schiff base reaction to form imine covalent bonds.

[0005] The thickness of the two-dimensional single-layer ionic COF membrane is 0.9 to 1.1 nm, preferably 1 nm, and the pore size is 1.6 to 1.8 nm, preferably 1.7 nm.

[0006] The two-dimensional single-layer ionic COF membrane of the present invention possesses continuously and neatly arranged nanochannels, a high surface charge density, and extremely low thickness. These excellent properties further enhance the selectivity and permeability for anions and cations. The exposed positive charges on the surface of the two-dimensional single-layer ionic COF membrane enhance anion selectivity. The single-layer thickness and high porosity ensure minimal internal resistance and high ion flux during ion transport. Measurements of the two-dimensional Young's modulus also demonstrate the reliability of the monolayer membrane. Therefore, using the two-dimensional single-layer ionic COF membrane of the present invention as an osmotic energy conversion membrane can significantly increase osmotic energy output.

[0007] In a preferred embodiment, the two-dimensional single-layer ionic COF membrane has a positive charge and a charge density of 4.4 mC / m 2 , combined with extremely low thickness and pore size, the two-dimensional single-layer ionic COF membrane can be used as an osmotic power generation membrane to effectively increase the output power to the kilowatt level.

[0008] In a preferred embodiment, when the sodium chloride concentration is 0.5M and 0.01M, respectively, the two-dimensional single-layer ionic COF film of the present invention can output a power of 1062W·m -2 .

[0009] The present invention also provides a method for preparing the two-dimensional single-layer ionic COF membrane, comprising the following steps:

[0010] Ethidium bromide and a catalyst were added dropwise to a uniformly spread 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin monolayer, and a two-dimensional monolayer ionic COF membrane was obtained through a Schiff base reaction.

[0011] The molar ratio of the 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin to the ethidium bromide is 1:100 to 1:200, preferably 1:200. Increasing the amount of EB is conducive to the formation of a large-area single-layer ionic COF film.

[0012] The catalyst is trifluoroacetic acid or glacial acetic acid, which can catalyze the dehydration condensation of aldehyde groups and amino groups to form imine bonds;

[0013] The Schiff base reaction time is 24 hours.

[0014] Preferably, the 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin monolayer is prepared according to the following steps:

[0015] The solution of 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin is dripped into the pulling instrument through a microinjector, and then the solvent is evaporated and the sliding barrier is compressed in sequence to obtain the 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin monolayer;

[0016] The solvent evaporation time is 20 to 40 minutes, preferably 30 minutes;

[0017] After the sliding barrier compression, the surface tension of the 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin monolayer is made 9-11 mN / m, preferably 10 mN / m. Under this condition, the TFPP molecules can be evenly and flatly spread on the water surface in the form of single molecules, which is conducive to the occurrence of the next polymerization reaction.

[0018] The present invention utilizes the evenly distributed aldehyde groups of TFPP and the symmetrically distributed amino groups of EB, so that the two can form a large-area network structure through imine bonds; in addition, the EB molecule carries nitrogen cations and can selectively transport anions.

[0019] The two-dimensional s-iCOF material of the present invention is formed by covalently linking 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin and ethidium bromide, and has a large porosity, good integrity, regular pore arrangement, and positive charge. In osmotic energy conversion, the large porosity and regular pore arrangement ensure a considerable ion flux, the good integrity and monolayer properties ensure its high energy conversion rate, and the positively charged surface indicates that ions can be selectively transported for a greater output potential. In summary, osmotic energy conversion by two-dimensional s-iCOF can achieve extremely excellent output power. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a surface tension curve of the s-iCOF synthesized in Example 1 of the present invention;

[0021] Figure 2 Zeta potential diagram of s-iCOF and s-COF synthesized in Example 1 of the present invention;

[0022] Figure 3 This is a contact angle experimental diagram of the s-iCOF synthesized in Example 1 of the present invention;

[0023] Figure 4 This is a light microscopy image of the s-iCOF synthesized in Example 1 of the present invention;

[0024] Figure 5 This is a scanning electron micrograph of the s-iCOF synthesized in Example 1 of the present invention;

[0025] Figure 6 This is a transmission electron microscopy image of the s-iCOF synthesized in Example 1 of the present invention;

[0026] Figure 7 This is a high-resolution cryo-TEM image of the s-iCOF synthesized in Example 1 of the present invention;

[0027] Figure 8 This is an atomic force microscope image of the s-iCOF synthesized in Example 1 of the present invention;

[0028] Figure 9 This is an elemental composition imaging diagram of the s-iCOF synthesized in Example 1 of the present invention;

[0029] Figure 10 This is the X-ray photoelectron spectrum of the s-iCOF synthesized in Example 1 of the present invention;

[0030] Figure 11 This is the Raman spectrum of the s-iCOF synthesized in Example 1 of the present invention;

[0031] Figure 12 This is the UV spectrum of the s-iCOF synthesized in Example 1 of the present invention;

[0032] Figure 13 Ion selectivity test of s-iCOF synthesized in Example 1 of the present invention;

[0033] Figure 14 The osmotic energy power density test of the s-iCOF synthesized in Example 1 of the present invention;

[0034] Figure 15 This is a concentration IV test of the non-ionic two-dimensional single-layer COF membrane synthesized in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0036] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0037] By using TFPP and EB as monomers for the COF backbone, this invention effectively synthesizes ionic COFs through a Schiff base reaction. The presence of surface charge distorts the conformation of this thin film material, resulting in a 1.7 nm pore size. This facilitates double-layer overlap and has the potential to be used as an osmotic energy conversion membrane to further enhance power generation. Furthermore, due to the membrane's monoatomic thickness, it significantly enhances both selectivity and permeability for positive and negative ions in saline solutions, further increasing output power.

[0038] The present invention provides a method for preparing a two-dimensional single-layer ionic COF:

[0039] First, a TFPP solution in chloroform is slowly dripped onto the flat surface of a Langmuir-Blodgett puller filled with secondary water using a microinjector in a symmetrical "W" pattern, and the solvent is allowed to evaporate. After the solvent evaporates and the surface tension reading stabilizes, a sliding barrier is slowly moved to compress the molecular layer until the surface tension reaches 10 mN / m. Once the barrier stops sliding, 2 mL of a 4.1 mmol / L EB solution is slowly dripped onto both sides of the reaction chamber. After 24 hours, a two-dimensional s-iCOF film is obtained. The COF layer is then transferred to a silicon nitride window substrate using a dipping method and rinsed with chloroform and secondary water. After evaporation of the water, the substrate is clamped in a holding chamber and sealed with UV-curable adhesive to prevent leakage. The corresponding IV curves are obtained by placing the silicon nitride substrate between two chambers, injecting 0.5 M and 0.01 M NaCl solutions, respectively, into the chamber, and then placing an Ag / AgCl salt bridge electrode within the chamber.

[0040] Comparative Example 1

[0041] The Langmuir-Blodgett puller was cleaned with ethanol and secondary water, and the trough was filled with secondary water until the water level was 1-2 mm above the trough surface. A platinum sheet was rinsed with ethanol, burned over an alcohol burner to remove any organic residue, and then placed on a hook, halfway submerged in the water. A 30 μL TFPP solution in chloroform was then slowly added to the water surface in a "W" pattern using a microinjector to spread the molecules as much as possible. Wait 30 minutes for the solvent to evaporate. Once the surface tension stabilized, a sliding barrier was slowly moved at a speed of 1 mm / min to continuously compress the TFPP molecules, tightly packing them on the water surface until the surface tension reached 10 mN / m. Finally, 1 mL of a 4.1 mM p-phenylenediamine solution was added dropwise to each side of the barrier. The reaction was allowed to proceed for 24 hours to obtain a two-dimensional monolayer COF film.

[0042] Example 1

[0043] The Langmuir-Blodgett puller was cleaned with ethanol and secondary water, and the trough was filled with secondary water until the water level was 1-2 mm above the trough surface. A platinum sheet was rinsed with ethanol, burned over an alcohol burner to remove any organic residue, and then placed on a hook, half submerged in the water. A 30 μL TFPP solution in chloroform was then slowly added dropwise to the water surface in a "W" pattern using a microinjector to spread the molecules as much as possible. Wait 30 minutes for the solvent to evaporate. Once the surface tension stabilized, a sliding barrier was slowly moved at a speed of 1 mm / min to continuously compress the TFPP molecules, tightly packing them on the water surface until the surface tension reached 10 mN / m. Finally, 1 mL of a 4.1 mM ethidium bromide solution was added dropwise to each side of the barrier. The reaction was allowed to proceed for 24 hours to obtain a two-dimensional monolayer COF film.

[0044] The properties of the two-dimensional single-layer ionic COF prepared in Example 1 and Comparative Example 1 were measured, and the specific steps were as follows:

[0045] Cryo-high-resolution transmission electron microscopy measurement: A two-dimensional monolayer ionic COF was placed on a copper grid, and its lattice fringes and pore size and their corresponding diffraction points were measured.

[0046] Atomic force microscopy: A two-dimensional monolayer ionic COF is placed on a silicon wafer and allowed to dry naturally. The material's edge is located under an optical microscope and its thickness is measured.

[0047] Determination of 2D Young's modulus: A 2D monolayer ionic COF was placed on a 1.8 μm diameter silicon window and allowed to dry naturally. The corresponding pores were located under a light microscope and the 2D Young's modulus was measured.

[0048] Surface potential measurement: A two-dimensional monolayer ionic COF was placed on a silicon wafer and immersed in a 0.01 M KCl solution to measure its surface potential.

[0049] Contact angle measurement: A two-dimensional monolayer ionic COF is placed on a silicon wafer and the entire structure is placed on the instrument platform. A water droplet is slowly dripped into the surface and the corresponding contact angle is measured.

[0050] UV spectrum measurement: A two-dimensional monolayer ionic COF was placed on a quartz substrate, placed in a groove, and its UV spectrum was measured.

[0051] Raman spectroscopy measurement: A two-dimensional monolayer ionic COF was placed on a gold-coated silicon wafer, and its Raman spectrum was measured using a 532nm wavelength light source.

[0052] Measurement of X-ray photoelectron spectroscopy: A two-dimensional monolayer ion COF was placed on a silicon wafer, and the X-ray photoelectron spectrum of the two-dimensional monolayer ion COF was measured.

[0053] Ion selectivity was determined by etching a 100 nm diameter hole in a silicon nitride window using a focused ion beam system and depositing a two-dimensional monolayer ionic COF on top. After the material dried naturally, it was placed in potassium chloride solutions of varying concentrations, and the permeation voltage and current were measured using a scanning IV curve using an Ag / AgCl salt bridge electrode.

[0054] Osmotic power generation: A 1μm diameter hole was etched in a silicon nitride window using a focused ion beam system, and a two-dimensional monolayer ionic COF was placed on top. After the material dried naturally, it was placed between 0.5M and 0.01M sodium chloride solutions, with a resistor connected inside and outside the circuit. By varying the resistance value, an Ag / AgCl salt bridge electrode was used to scan the IV curve to measure the osmotic voltage and current, and the corresponding output power and maximum power were calculated.

[0055] For this system, the following formula P=IOS 2 R / A calculates its power generation. OS The penetration current can be obtained from the source meter data, R is the external resistance which can be read from the corresponding value, and A is the aperture area which is given by the focused ion beam drilling setting area.

[0056] The results of the determination of the properties of the two-dimensional single-layer ionic COF prepared in Example 1 are as follows: Figures 1-11 shown.

[0057] Figure 1 This is the surface tension curve of the two-dimensional monolayer ionic COF. It can be seen that the TFPP molecules are densely arranged at 10mN / m.

[0058] Figure 2 The surface zeta potential of the two-dimensional monolayer COF in different pH solutions is shown in Figure 2. It can be seen that the zeta potential corresponds to a charge density of 4.4 mC / m at pH = 6. 2 , providing the necessary conditions for the selective transport of chloride ions, while the non-ionic COF is -2.2mC / m 2 , which can be selective for sodium ions.

[0059] The charge density of the two-dimensional single-layer ionic COF in Comparative Example 1 is -2.2 mC / m 2 , that is, the charge density is too small and cations are preferred to pass through. In this way, in the NaCl salt difference system, the selection of cations to pass through will reduce the osmotic voltage and osmotic potential, which is not conducive to the conversion and output of osmotic energy.

[0060] Figure 3 is the contact angle of the two-dimensional monolayer ionic COF. By comparing it with the monolayer COF without surface positive charge, it can be seen that its contact angle becomes smaller, indicating that it is more hydrophilic and is conducive to high ion flux.

[0061] Figure 4 、 Figure 5 and Figure 6 The optical, scanning electron microscopy and transmission electron microscopy characterizations of the two-dimensional single-layer ionic COF are shown. It can be seen that this film can be prepared on a large area, is smooth and dense, has no residual nanoparticles and can exist stably.

[0062] Figure 7 This is the cryo-high-resolution transmission electron microscopy characterization of the two-dimensional single-layer ionic COF. It can be seen that the pore size and corresponding diffraction fringes are 1.7 nm, which can prove the existence of the corresponding nanopores.

[0063] Figure 8 Atomic force microscopy characterization of the two-dimensional single-layer ionic COF. It can be seen that its thickness is 1nm.

[0064] Figure 9This is the elemental imaging of the two-dimensional single-layer ionic COF. It can be seen that it includes carbon atoms and nitrogen atoms.

[0065] Figure 10 、 Figure 11 and Figure 12 They are X-ray photoelectron spectroscopy, ultraviolet spectroscopy and Raman spectroscopy. The X-ray photoelectron spectroscopy shows that compared with monomers and uncharged COFs, charged COFs have obvious nitrogen positive peaks, indicating that the material was successfully synthesized; the red shift of the ultraviolet spectrum shows that the material has formed a large-area conjugated structure, proving that the material was successfully synthesized; the formation of imine bonds and the elimination of aldehyde peaks in the Raman spectrum reflect the occurrence of chemical reactions and the successful synthesis of two-dimensional COF.

[0066] Figure 13 To test its ion selectivity using potassium chloride solutions of different concentrations, it can be seen that this positive ion membrane selects chloride ions to pass through.

[0067] Figure 14 To test the output power using sodium chloride solutions of different concentrations, it can be seen that its maximum power density can reach 1062W / m 2 , beyond existing materials.

[0068] Figure 15 The IV curve of the uncharged two-dimensional single-layer COF (COF membrane prepared in Comparative Example 1) was tested using 0.5M / 0.01M NaCl solution. It can be seen that the osmotic potential is very small, which is not conducive to the conversion and utilization of osmotic energy.

[0069] The pore size of the single-layer two-dimensional ionic COF prepared in Example 1 of the present invention is 1.7 nm.

[0070] Using tetraaminophenylporphyrin and 1,1'-bis(4-formylphenyl)-4,4'-bipyridyl dichloride would increase the pore size and reduce the surface charge, thereby reducing the selectivity of the COF membrane and hindering the conversion of osmotic energy. Therefore, choosing a two-dimensional monolayer ionic COF constructed with tetraaldehydephenylporphyrin and ethidium bromide as an osmotic energy conversion membrane can improve the osmotic energy output.

Claims

1. A two-dimensional monolayer ionic COF membrane, obtained by polymerization of 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin and ethidium bromide via a Schiff base reaction to form an imine covalent bond; The method for preparing the two-dimensional single-layer ionic COF membrane comprises the following steps: Ethidium bromide and a catalyst were added dropwise to a uniformly spread monolayer of 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin, and a two-dimensional monolayer ionic COF membrane was obtained through a Schiff base reaction. The 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin monolayer was prepared according to the following steps: The solution of 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin is dripped into the pulling instrument through a microinjector, and then the solvent is evaporated and the sliding barrier is compressed in sequence to obtain the 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin monolayer.

2. The two-dimensional single-layer ionic COF membrane according to claim 1, characterized in that: The thickness of the two-dimensional single-layer ionic COF membrane is 0.9-1.1 nm, and the pore size is 1.6-1.8 nm.

3. The method for preparing the two-dimensional single-layer ionic COF membrane according to claim 1 or 2, comprising the following steps: Ethidium bromide and a catalyst were added dropwise to a uniformly spread monolayer of 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin, and a two-dimensional monolayer ionic COF membrane was obtained through a Schiff base reaction. The 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin monolayer was prepared according to the following steps: The solution of 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin is dripped into the pulling instrument through a microinjector, and then the solvent is evaporated and the sliding barrier is compressed in sequence to obtain the 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin monolayer.

4. The preparation method according to claim 3, wherein: The molar ratio of the 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin to the ethidium bromide is 1:100 to 1:200; The catalyst is trifluoroacetic acid or glacial acetic acid; The Schiff base reaction time is 24 h.

5. The preparation method according to claim 3, wherein: The solvent evaporation time is 20 to 40 minutes; After the sliding barrier compression, the surface tension of the 5,10,15,20-tetrakis(4-formaldehydephenyl)-21H,23H-porphyrin monolayer is adjusted to 9-11 mN / m.

6. Use of the two-dimensional single-layer ionic COF membrane according to claim 1 or 2 in osmotic energy conversion or as an osmotic energy conversion membrane.

7. Use of the two-dimensional single-layer ionic COF membrane according to claim 1 or 2 in salinity gradient energy generation.

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