Cu-btc / cellulose composite-based mof membrane and preparation method thereof

Abstract

The application belongs to the technical field of MOF membrane and specifically relates to a Cu-BTC / cellulose composite-based MOF membrane and a preparation method thereof. After Cu-BTC / cellulose composite material is prepared by coating microcrystalline cellulose with Cu-BTC, the Cu-BTC / cellulose composite material is mixed with a membrane preparation mother liquor, a pore preparation agent and a homogeneous membrane material to form a homogeneous casting solution, and then the Cu-BTC / cellulose composite-based MOF membrane is prepared after coating, winding, solidification and drying. The Cu-BTC / cellulose composite material prepared by the application has a sub-micron rough surface and an elongated fibrous structure, and the MOF membrane prepared therefrom has more abundant pore and channel structures, which is beneficial to increasing the accessibility of active sites and greatly improving the gas permeability and gas separation performance of the membrane.

Description

Technical Field

[0001] This invention belongs to the field of MOF membrane technology, and particularly relates to a MOF membrane based on Cu-BTC / cellulose composite material and its preparation method. Background Technology

[0002] Membrane technology, as a highly efficient separation technology, has been increasingly widely developed in various fields such as wastewater treatment, water purification, and the food and pharmaceutical industries. Compared with traditional biochemical technologies, membrane separation technology has significant advantages such as selectivity, strong adaptability, high flexibility, and low pollution. In particular, polyvinylidene fluoride (PVDF) membranes have excellent chemical stability, excellent mechanical properties, and high chemical stability, and are widely used in gas separation. However, most membranes are limited by certain factors and cannot simultaneously meet the requirements of high selectivity and high permeability.

[0003] MOFs (Metal-Organic Facility-Containing Cells) are assembled from metal cations or clusters bridged by organic ligands, exhibiting high crystallinity and a network topology. The diverse combinations of metal nodes and organic groups provide MOFs with a wealth of structural and functional diversity. MOFs possess high specific surface area, high porosity, and abundant active sites, making them ideal materials for preparing separation membranes. However, MOFs are often present in powder form, characterized by poor stability and limited mechanical durability, especially when placed in strongly acidic environments. Therefore, shaping MOF nanocrystals into various useful structures remains a long-term challenge. Summary of the Invention

[0004] This invention addresses the problems of uneven distribution and defects in Cu-BTC membranes due to particle aggregation. It proposes adding a Cu-BTC / cellulose composite material made of Cu-BTC and microcrystalline cellulose to the matrix membrane to improve the membrane's gas permeability and gas separation capabilities.

[0005] This invention provides a MOF membrane based on Cu-BTC / cellulose composite material, and the specific preparation steps are as follows:

[0006] (1)Cu 2+ Preparation of the metal precursor solution: Zinc oxide was ultrasonically dispersed in deionized water, then methanol and copper nitrate trihydrate were added sequentially, and the mixture was stirred until homogeneous to obtain Cu. 2+ Metal precursor solution.

[0007] Furthermore, the Cu 2+ The specific steps for preparing the metal precursor solution are as follows:

[0008] Under normal temperature conditions, zinc oxide was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 5-8 mg / mL. Methanol and copper nitrate trihydrate were then added sequentially, and the mixture was stirred until homogeneous to obtain Cu.2+ Metal precursor solution; the Cu 2+ The concentration of copper nitrate trihydrate in the metal precursor solution is 10-45 mg / mL, and the volume ratio of deionized water to methanol is 1:(1-2).

[0009] (2) Preparation of Cu-BTC / cellulose composite material: Microcrystalline cellulose was ultrasonically dispersed in Cu 2+ After the metal precursor solution is evenly dispersed, the surfactant solution and the mixed solution are added dropwise. Then, the mixture is transferred to a heat-collecting constant temperature magnetic stirrer for stirring. After heating and stirring for a set time, the reaction product is centrifuged, washed, and then transferred to a vacuum drying oven for drying to obtain Cu-BTC / cellulose composite material.

[0010] Furthermore, the mass ratio of the microcrystalline cellulose to copper nitrate trihydrate is 1:2-18.

[0011] Furthermore, the surfactant solution concentration is 5-20 mg / mL, the solvent is ethanol, and the surfactant solute is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, polyethylene glycol 200, and polyvinylpyrrolidone.

[0012] Furthermore, the solute of the mixed solution is composed of pyromellitic acid and 2-aminoterephthalic acid mixed in a mass ratio of 1:0-2, the solvent is ethanol, and the concentration of the mixed solution is 10-50 mg / mL.

[0013] Furthermore, the stirring and heating temperature described in this invention is 20-40℃, the heating time is 8-12h, the rotation speed is 2000-2500rpm, the washing solution is methanol, and the process is repeated 3-4 times.

[0014] (3) Preparation of MOF membrane: The homogeneous membrane material is ultrasonically dispersed in the membrane preparation masterbatch, transferred to a heat-collecting constant temperature magnetic stirrer, and then the pore-forming agent and Cu-BTC / cellulose composite material are added in sequence. The mixture is heated and stirred until a homogeneous solution is formed. After degassing with a vacuum pump, a homogeneous casting liquid is formed. The casting liquid is cast onto an automatic coating machine for coating. After forming, the membrane is wound and placed in distilled water for curing for 3 days, and then dried to obtain the MOF membrane.

[0015] Furthermore, the specific steps for preparing the MOF membrane described in this invention are as follows:

[0016] The homogeneous membrane material was ultrasonically dispersed in the membrane preparation masterbatch and transferred to a 50-60℃ constant temperature magnetic stirrer. The pore-forming agent and Cu-BTC / cellulose were added sequentially, and the mixture was heated and stirred until a homogeneous solution was formed. After degassing with a vacuum pump, a homogeneous casting solution was formed. The casting solution was cast onto an automatic coating machine for coating. After forming, the membrane was wound and placed in distilled water for curing for 3 days, and then dried to obtain the MOF membrane.

[0017] Furthermore, the mass ratio of the homogeneous membrane material to the membrane-forming masterbatch is 1:2-5.5.

[0018] Furthermore, the mass ratio of the pore-forming agent to the homogenized membrane material is 1:3.5-10.

[0019] Furthermore, the mass ratio of the Cu-BTC / cellulose composite material to the homogeneous membrane material is 1:75-750.

[0020] Furthermore, the film-forming masterbatch is any one or a mixture of tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide.

[0021] Furthermore, the pore-forming agent is one of polyvinylpyrrolidone, isopropanol, or polyethylene glycol.

[0022] Furthermore, the homogenized membrane material is one of polyvinylidene fluoride, polyvinyl chloride, polystyrene, polyamide, polyethersulfone, polyacrylonitrile, polyetherimide, polyethylene terephthalate, cyclohexanediol, alumina, zirconium oxide, titanium dioxide, or silicon dioxide.

[0023] Furthermore, the specific steps for casting the film-forming liquid onto an automatic coating machine to form a film, as described in this invention, are as follows: A glass plate is slowly placed in the center of the coating machine, and a wire rod is placed vertically on the glass plate to ensure it is level. The casting liquid is poured evenly along the wire rod. Once the casting liquid is uniform, the coating machine is started by pressing the Start button. The casting liquid is extruded from the wire rod. After all the casting liquid is extruded and formed, it is wound and placed in a coagulation bath to solidify for 3 days, and then dried to obtain an MOF film. The coagulation solution in the coagulation bath is distilled water.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention utilizes the steric hindrance effect of surfactants to control the particle size of Cu-BTC to the submicron level. Then, through condensation and cross-linking reactions, the carboxyl groups in Cu-BTC and the hydroxyl groups in microcrystalline cellulose undergo covalent bonding, causing Cu-BTC to coat the surface of the microcrystalline cellulose. This forms a Cu-BTC / cellulose composite material with a submicron-level rough surface. On the one hand, this reduces the decline in membrane separation performance caused by Cu-BTC agglomeration and improves the utilization rate of Cu-BTC. On the other hand, the rough surface and slender fibrous structure of the Cu-BTC / cellulose composite material enhance its compatibility with the membrane matrix while forming a richer pore and channel structure, increasing the accessibility of active sites and significantly improving the gas permeability and gas separation performance of the membrane. Furthermore, the addition of the Cu-BTC / cellulose composite material can also improve the membrane's hydrophilicity, increase the critical flux, and enhance its antifouling ability. Attached image description:

[0026] Figure 1 SEM image of the Cu-BTC / cellulose composite material prepared in Example 1;

[0027] Figure 2 SEM image of Cu-BTC prepared in Comparative Example 1;

[0028] Figure 3 SEM images of the MOF membrane prepared in Example 3 are shown, where a is a surface view of the membrane and b is a cross-sectional view.

[0029] Figure 4 The graph shows a comparison of the permeability and gas selectivity of the MOF membranes prepared in Examples 1-8 and Comparative Examples 1-7.

[0030] Figure 5 This is a diagram of a VOCs fine recycling platform device. Detailed Implementation

[0031] The present invention is illustrated below with some specific examples, but the present invention is not limited to the examples. Any changes, modifications, additions and substitutions made within the technical scope of the present invention are also within the protection scope of the present invention.

[0032] Example 1

[0033] (1) After mixing 0.074 g of zinc oxide with 10 mL of deionized water and sonicating to form a dispersion, 10 mL of methanol and 0.44 g of copper nitrate trihydrate were added sequentially and stirred for 30 min until homogeneous, yielding Cu. 2+ Metal precursor solution;

[0034] (2) Dissolve 0.21g of 1,3,5-pyromellitic acid in 10mL of ethanol to prepare a mixed solution, and dissolve 0.2g of polyvinylpyrrolidone in 10mL of ethanol to prepare a surfactant solution for later use. Disperse 0.1g of microcrystalline cellulose ultrasonically in Cu... 2+ The metal precursor solution was stirred evenly, and then the surfactant solution and the mixed solution were added dropwise. The mixture was transferred to a 30℃ heat-collecting constant temperature magnetic stirrer and heated and stirred for 12 hours. After centrifugation and washing three times, it was dried in a vacuum drying oven at 100℃ for 12 hours and then ground to obtain Cu-BTC / cellulose composite material.

[0035] (3) 7.5g of polyvinylidene fluoride was ultrasonically dispersed in 30g of N,N-dimethylformamide to prepare a mixed solution, and then transferred to a 60℃ heat-collecting constant temperature magnetic stirrer; 1g of polyvinylpyrrolidone, 0.01g of Cu-BTC / cellulose composite material and 10g of N,N-dimethylformamide were ultrasonically mixed evenly, and then added to the mixed solution while stirring. The mixture was stirred at 60℃ for 5h until a homogeneous solution was formed. The solution was degassed by a vacuum pump to form a homogeneous casting liquid. The casting liquid was cast onto an automatic coating machine and coated to form a film. The film was then wound and placed in distilled water to cure for 3 days, and then dried to obtain an MOF film (8.4mm).

[0036] The specific steps of the separation experiment using the prepared MOF membrane are as follows: A self-made VOCs fine recovery platform device integrating a gas mixing system, adsorption device, membrane separation device, and detection system was used. First, all devices were powered on. The MCGS operating environment of the computer in the detection system was turned on to ensure normal communication and to check the circuit continuity. The prepared MOF membrane was installed in the membrane separation device, and the experimental temperature was maintained at 25℃. Then, the corresponding gas cylinders (N2, CO2, CH4) were opened to conduct the experiment, allowing the experimental gas to pass through the MOF membrane under test, and the experimental data were recorded.

[0037] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 10.1519 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 202.2292 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 6.3919 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 19.9202, and the CO2 / CH4 selectivity was 31.6380.

[0038] Example 2

[0039] The difference between Example 2 and Example 1 is that the amount of Cu-BTC / cellulose composite material added in step (3) is 0.03g, while the rest is the same as in Example 1, resulting in an MOF membrane (8.4mm).

[0040] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 10.3561 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 213.9068 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 The CH4 permeability is 6.6586 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 20.6551, and the CO2 / CH4 selectivity was 32.1246.

[0041] Example 3

[0042] The difference between Example 3 and Example 1 is that the amount of Cu-BTC / cellulose composite material added in step (3) is 0.05g, while the rest is the same as in Example 1 to obtain MOF membrane (8.4mm).

[0043] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 11.1220 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 262.5867 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 7.3055 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 23.6096, and the CO2 / CH4 selectivity was 35.9433.

[0044] Example 4

[0045] The difference between Example 4 and Example 1 is that the amount of Cu-BTC / cellulose composite material added in step (3) is 0.1g, while the rest is the same as in Example 1, resulting in an MOF membrane (8.4mm).

[0046] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 11.8622 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 225.4461 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 6.8850 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 19.0054, and the CO2 / CH4 selectivity was 32.7441.

[0047] Example 5

[0048] The difference between Example 5 and Example 3 is that in step (2), "dissolving 0.21g of 1,3,5-pyromellitic acid in 10mL of ethanol to prepare a mixed solution" is changed to: dissolving 0.14g of 1,3,5-pyromellitic acid and 0.07g of 2-aminoterephthalic acid in 10mL of ethanol to prepare a mixed solution, and the rest is the same as in Example 1, to obtain an MOF membrane (8.4mm).

[0049] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 12.4673 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 320.2254 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 The CH4 permeability is 7.7353 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 25.6851, and the CO2 / CH4 selectivity was 41.3978.

[0050] Example 6

[0051] The difference between Example 6 and Example 5 is that the amount of 1,3,5-pyromellitic acid and 2-aminoterephthalic acid added in step (2) is 0.07 g and 0.14 g, respectively. The rest is the same as in Example 5, and an MOF membrane (8.4 mm) is obtained.

[0052] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 12.3428 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 357.3149 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 7.8030 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 28.9491, and the CO2 / CH4 selectivity was 45.7914.

[0053] Example 7

[0054] The difference between Example 7 and Example 1 is that step (3) is changed to: 8g of polyamide is ultrasonically dispersed in 30g of N,N-dimethylacetamide to prepare a mixed solution, and transferred to an 80°C heat-collecting constant temperature magnetic stirrer; 1g of polyvinylpyrrolidone, 0.01g of Cu-BTC / cellulose composite material and 10g of N,N-dimethylacetamide are mixed and ultrasonically homogenized, and then added to the mixed solution while stirring. The mixture is heated to 80°C and stirred for 5 hours to form a homogeneous solution. The solution is degassed by a vacuum pump to form a homogeneous casting liquid. The casting liquid is cast onto an automatic coating machine and coated to form a film. The film is then wound and placed in distilled water to cure for 3 days, and then dried to obtain an MOF film (8.5mm). The rest is the same as in Example 1.

[0055] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 9.1430 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 182.2486 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 7.3919 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1The CO2 / N2 selectivity was 19.9331, and the CO2 / CH4 selectivity was 24.6551.

[0056] Example 8

[0057] The difference between Example 8 and Example 1 is that step (3) is changed to: 8g of polyethersulfone is ultrasonically dispersed in 30g of dimethyl sulfoxide to prepare a mixed solution, which is then transferred to an 80℃ heat-collecting constant-temperature magnetic stirrer; 1g of polyvinylpyrrolidone, 0.01g of Cu-BTC / cellulose composite material and 10g of dimethyl sulfoxide are mixed and ultrasonically homogenized, and then added to the mixed solution while stirring. The mixture is heated to 80℃ and stirred for 5 hours to form a homogeneous solution. The solution is degassed using a vacuum pump to form a homogeneous casting solution. The casting solution is then cast onto an automatic coating machine, coated and shaped, and then wound and placed in distilled water to cure for 3 days, and then dried to obtain an MOF membrane (8.5mm).

[0058] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 11.1522 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 173.2366 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 6.4716 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 15.5338, and the CO2 / CH4 selectivity was 26.7687.

[0059] Comparative Example 1

[0060] (1) After mixing 0.074 g of zinc oxide with 10 mL of deionized water and sonicating to form a slurry, 10 mL of methanol was added first, followed by 0.44 g of copper nitrate trihydrate. The mixture was stirred for 30 min until homogeneous, and then Cu was obtained. 2+ Metal precursor solution;

[0061] (2) Dissolve 0.21g of 1,3,5-pyromellitic acid in 10mL of ethanol to prepare a mixed solution, and dissolve 0.2g of polyvinylpyrrolidone in 10mL of ethanol to prepare a surfactant solution. Add the surfactant solution and the mixed solution dropwise to Cu. 2+ The metal precursor solution was stirred evenly, transferred to a 30℃ heat-collecting constant temperature magnetic stirrer, heated and stirred for 30 min, centrifuged and washed 3 times, dried in a vacuum drying oven at 100℃ for 12 h, and then ground to obtain Cu-BTC.

[0062] (3) 7.5g of polyvinylidene fluoride was ultrasonically dispersed in 30g of N,N-dimethylformamide to prepare a mixed solution. The solution was transferred to a 60℃ heat-collecting constant temperature magnetic stirrer. 1g of polyvinylpyrrolidone, 0.01g of Cu-BTC and 10g of N,N-dimethylformamide were ultrasonically mixed evenly and then added to the mixed solution while stirring. The solution was heated to 60℃ and stirred for 5 hours until a homogeneous solution was formed. After degassing with a vacuum pump, a homogeneous casting solution was formed. The casting solution was cast onto an automatic coating machine and coated to form a film. The film was then wound and placed in distilled water to cure for 3 days and then dried to obtain an MOF film (8.4mm).

[0063] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 19.6667 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 56.7449 × 10 -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 10.4150 × 10 -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 2.8853, and the CO2 / CH4 selectivity was 5.4483.

[0064] Comparative Example 2

[0065] The difference between Comparative Example 2 and Comparative Example 1 is that the amount of Cu-BTC added in step (3) is changed to 0.03g, while the rest is the same as Comparative Example 1, and a MOF film (8.4mm) is obtained.

[0066] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 19.4395 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 120.8738 × 10 -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 9.2054 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 6.2179, and the CO2 / CH4 selectivity was 13.1307.

[0067] Comparative Example 3

[0068] The difference between Comparative Example 3 and Comparative Example 1 is that the amount of Cu-BTC added in step (3) is changed to 0.05g, while the rest is the same as Comparative Example 1, and a MOF film (8.4mm) is obtained.

[0069] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 20.0258 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 140.4640 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 9.9127 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 7.0141, and the CO2 / CH4 selectivity was 14.1701.

[0070] Comparative Example 4

[0071] The difference between Comparative Example 4 and Comparative Example 1 is that the amount of Cu-BTC added in step (3) was changed to 0.1g, while the rest was the same as Comparative Example 1, and a MOF membrane (8.4mm) was obtained.

[0072] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 15.6929 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 80.0415 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 7.7172 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 5.1004, and the CO2 / CH4 selectivity was 10.3718.

[0073] Comparative Example 5

[0074] 7.5g of polyvinylidene fluoride was ultrasonically dispersed in 30g of N,N-dimethylformamide and transferred to a 60℃ thermostatic magnetic stirrer. 1g of polyvinylpyrrolidone, 0.1g of microcrystalline cellulose and 10g of N,N-dimethylformamide were ultrasonically mixed evenly, and the mixture was added while stirring. The mixture was heated and stirred until a homogeneous solution was formed. After degassing with a vacuum pump, a homogeneous casting solution was formed. The casting solution was cast onto an automatic coating machine and coated to form a film. The film was then wound and placed in distilled water to cure for 3 days, and then dried to obtain an MOF film (8.4mm).

[0075] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 23.0216 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 28.3885 × 10 -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 10.6347 × 10 -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 1.2331, and the CO2 / CH4 selectivity was 2.6694.

[0076] Comparative Example 6

[0077] (1) Dissolve 1.05g of copper nitrate trihydrate in 15mL of a mixed solvent of ethanol and deionized water with a volume ratio of 1:1 and sonicate for 10min.

[0078] (2) Dissolve 0.5g of 1,3,5-pyromellitic acid in 15mL of a 1:1 mixture of ethanol and deionized water and sonicate for 10min.

[0079] (3) After mixing the solution in step (1) and the solution in step (2) and sonicating for 10 min, add 0.1 g of microcrystalline cellulose and sonicate for 20 min. Then transfer to a 120℃ heat-collecting constant temperature magnetic stirrer and stir for 12 h. After centrifugation and washing 3 times, dry in a vacuum drying oven at 100℃ for 12 h. After grinding, obtain Cu-BTC / cellulose composite material.

[0080] (3) 7.5g of polyvinylidene fluoride was ultrasonically dispersed in 30g of N,N-dimethylformamide and transferred to a 60℃ heat-collecting constant temperature magnetic stirrer. 1g of polyvinylpyrrolidone, 0.05g of Cu-BTC / cellulose and 10g of N,N-dimethylformamide were ultrasonically mixed evenly and then added to the mixed solution while stirring. After heating and stirring to remove bubbles, a homogeneous casting solution was formed. The casting solution was cast onto an automatic coating machine for coating. After forming, it was wound and placed in distilled water to cure for 3 days and then dried to obtain an MOF membrane (8.4mm).

[0081] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 18.2863 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 164.6721 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CH4 permeability is 8.2173 × 10⁻⁶ -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 9.0052, and the CO2 / CH4 selectivity was 20.0396.

[0082] Comparative Example 7

[0083] The difference between Comparative Example 7 and Comparative Example 3 is that in step (3), 0.05g Cu-BTC was replaced with 0.04g Cu-BTC and 0.01g cellulose, while the rest was the same as in Comparative Example 3, and an MOF membrane (8.4mm) was obtained.

[0084] The separation results of the prepared MOF membrane are shown in Table 1. The N2 permeability is 18.6778 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 CO2 permeability is 166.4579 × 10 -3 ·mol·m -2 ·s -1 ·Pa -1 The CH4 permeability is 9.4113 × 10⁻⁶. -3 ·mol·m -2 ·s -1 ·Pa -1 The CO2 / N2 selectivity was 8.9120, and the CO2 / CH4 selectivity was 17.6870.

[0085] Table 1. Permeability and Selectivity of Different Gases

[0086]

[0087] Figure 1 This is a SEM image of the Cu-BTC / cellulose composite material. Figure 2 This is a SEM image of a MOF membrane based on Cu-BTC / cellulose composite material. Figure 3 This is a comparison chart of the permeability and selectivity of different gases. Figure 1 Cellulose was successfully grafted onto the Cu-BTC surface; Figure 2 It can be observed that pores are uniformly distributed on the membrane surface. The Cu-BTC / cellulose composite material is doped into the polymer, and gas can permeate and separate through the membrane channels; as shown in Table 1 and Figure 3 It is known that the addition of Cu-BTC / cellulose composite material simultaneously improves the gas permeability and gas separation performance of the membrane. Examples show that as the amount of Cu-BTC / cellulose composite material in the MOF membrane increases, its gas permeability and gas selectivity increase. However, when the composite material content increases to a certain level, the permeability does not increase but decreases, possibly because the composite material blocks the pores, leading to a decrease in permeability. Figure 3 It is evident that the permeability and gas selectivity of the prepared examples are higher than those of the comparative examples. Specifically, the permeability and gas selectivity of the Cu-BTC / cellulose composite membrane are significantly higher than those of membranes prepared from Cu-BTC and cellulose separately. This invention improves both membrane permeability and gas selectivity. Examples 5 and 6 demonstrate that adding modified amino groups to Cu-BTC / cellulose can also greatly improve the CO2 permeability of the MOF membrane and enhance gas separation performance. The introduction of amino groups can provide active sites that promote CO2 reaction, and both gas permeability and gas separation performance increase with increasing amino content.

[0088] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a MOF membrane based on Cu-BTC / cellulose composite material, characterized in that, The MOF membrane is doped with a Cu-BTC / cellulose composite material; the Cu-BTC / cellulose composite material is prepared by coating Cu-BTC onto the surface of microcrystalline cellulose; the method for preparing the MOF membrane based on the Cu-BTC / cellulose composite material includes the following steps: (1) Under normal temperature conditions, zinc oxide was ultrasonically dispersed in deionized water to form a dispersion, and then methanol and copper nitrate trihydrate were added sequentially and stirred evenly to prepare Cu. 2+ Metal precursor solution; (2) Ultrasonic dispersion of microcrystalline cellulose in Cu 2+ After the metal precursor solution is evenly dispersed, the surfactant solution and the mixed solution are added dropwise. Then, the mixture is transferred to a heat-collecting constant temperature magnetic stirrer for heating and stirring. The reaction product is then centrifuged, washed, and dried to obtain Cu-BTC / cellulose composite material. (3) After the homogeneous membrane material and the membrane preparation masterbatch are ultrasonically mixed evenly, they are transferred to a heat-collecting constant temperature magnetic stirrer, and the pore-forming agent and Cu-BTC / cellulose composite material are added in sequence. The mixture is heated to 50-60℃ and stirred for 6 h. Then, the casting liquid is degassed by a vacuum pump to form a casting liquid. The casting liquid is cast onto an automatic coating machine to form a shape, and then wound into distilled water for curing and drying to obtain a MOF membrane.

2. The method for preparing MOF membrane based on Cu-BTC / cellulose composite material according to claim 1, characterized in that, The concentration of the dispersion in step (1) is 5-8 mg / mL; The Cu 2+ The concentration of copper nitrate trihydrate in the metal precursor solution is 10-45 mg / mL; The volume ratio of deionized water to methanol is 1:(1-2).

3. The method for preparing MOF membrane based on Cu-BTC / cellulose composite material according to claim 1, characterized in that, The mass ratio of microcrystalline cellulose to copper nitrate trihydrate is 1:2-18; The solute of the surfactant solution is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, polyethylene glycol 200 and polyvinylpyrrolidone, and the solvent is ethanol with a concentration of 5-20 mg / mL. The solute in the mixed solution is composed of pyromellitic acid and 2-aminoterephthalic acid in a mass ratio of 1:0-2, and the solvent is ethanol with a concentration of 10-50 mg / mL.

4. The method for preparing MOF membrane based on Cu-BTC / cellulose composite material according to claim 1, characterized in that, The heating and stirring time in step (2) is 8-12 h, the rotation speed is 2000-2500 rpm, and the temperature is 20-40℃.

5. The method for preparing a MOF membrane based on Cu-BTC / cellulose composite material according to claim 1, characterized in that, The mass ratio of the homogeneous membrane material and the membrane preparation masterbatch mentioned in step (3) is 1:2-5.5; The mass ratio of the pore-forming agent to the homogenized film material is 1:3.5-10; The mass ratio of the Cu-BTC / cellulose composite material to the homogeneous membrane material is 1:75-750.

6. The method for preparing a MOF membrane based on Cu-BTC / cellulose composite material according to claim 1, characterized in that, The homogenized membrane material mentioned in step (3) is one or a mixture of polyvinylidene fluoride, polyvinyl chloride, polystyrene, polyamide, polyethersulfone, polyacrylonitrile, polyetherimide, and polyethylene terephthalate; The film-forming masterbatch is any one or a mixture of tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide; The pore-forming agent is one or more of polyvinylpyrrolidone, isopropanol, or polyethylene glycol.

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