A phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane and a preparation method and application thereof

Abstract

The application provides a ZIF-8 / NPBI mixed matrix membrane treated by phosphoric acid modification and a preparation method and application thereof. The ZIF-8 / NPBI mixed matrix membrane treated by phosphoric acid modification is prepared by immersing a ZIF-8 / NPBI mixed matrix membrane in an alcohol solution of phosphoric acid and then drying. The ZIF-8 / NPBI mixed matrix membrane is prepared by uniformly mixing a polar solvent solution of ZIF-8 and a polar solvent solution of NPBI, evaporating the membrane material, immersing the membrane material in a displacement solvent and then drying. After the ZIF-8 / NPBI mixed matrix membrane is immersed in the alcohol solution of phosphoric acid, the N on the NPBI main chain and the phosphoric acid interact to form hydrogen bonds, so that the NPBI chain segments are more closely connected, and the phosphoric acid etches the ZIF-8 to increase the pore size. In the ZIF-8 / NPBI mixed matrix membrane treated by phosphoric acid modification, the ZIF-8 is uniformly dispersed in the NPBI.

Description

Technical Field

[0001] This invention relates to a phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, its preparation method and application, belonging to the field of gas separation technology. Background Technology

[0002] Hydrogen, as a green energy source, is often used in fuel cells and hydrogen power generation. Currently, the main methods of hydrogen production in industry are methane reforming and water-gas conversion. However, these methods all produce carbon dioxide. To obtain high-purity hydrogen, the carbon dioxide must be removed for further application.

[0003] Membrane gas separation technology has attracted widespread attention due to its advantages such as low energy consumption, small footprint, and simple operation. Membrane materials used for separating H2 / CO2 should possess good thermal stability, high mechanical properties, and good chemical stability. Polymer membranes are widely used, but there is a trade-off between permeability and selectivity. In recent years, mixed matrix membranes (MMMs) have combined the advantages of both inorganic and polymer membranes, addressing the low gas permeability issue of polymer membranes while achieving better gas selectivity, thus gradually becoming a research hotspot in the field of membrane separation technology.

[0004] The most commonly used inorganic packing material for MMMs is the metal-organic framework (MOF). MOFs consist of metal nodes connected by organic bridging ligands, possessing a uniform pore structure, large surface area, chemical and thermal stability, and tunable properties. Zeolite imidazole frameworks (ZIFs) are a subset of MOFs, exhibiting ultra-micropore sizes and excellent chemical and hydrothermal stability, and have attracted widespread attention in gas membrane separation. Among the many ZIFs, ZIF-8 is one of the most widely used zeolite imidazole framework porous solids for H2 / CO2 separation research. Its high thermal stability (up to 400℃) and pore size of 3.4 Å, which falls between that of H2 and other large molecular gases, give it excellent sieving performance.

[0005] Tingxu Yang, et al. (Room-temperature synthesis of ZIF-90 nanocrystals and the derived nano-composite membranes for hydrogen separation. Journal of Materials Chemistry A, 2013: p. 10.1039. C3TA10928C.) introduces a novel synthesis method for relatively small ZIF-90 particles, which are then uniformly dispersed in PBI to prepare MMMs. The resulting 45% ZIF-90 / PBI membrane exhibited excellent gas separation performance in mixed gas tests at 180℃, with an H2 permeability of 226.9 Barrer and an H2 / CO2 separation coefficient of 13.3, exceeding the latest Robeson upper limit for H2 / CO2. It is evident that the introduction of MOF particles can improve gas permeability and exhibit excellent gas separation performance. However, with a high MOF loading, the particles may agglomerate in the polymer, resulting in uneven particle dispersion and a decrease in gas separation performance. Furthermore, a high loading can also cause the membrane to become brittle, thus reducing its mechanical properties.

[0006] Leiqing Hu, et al. (Facilely Cross-Linking Polybenzimidazole with Polycarboxylic Acids to Improve H2 / CO2 Separation Performance. ACS Appl. Mater. Interfaces 2021: p. 10.1021. acsami.0c23098.) introduces a method to improve H2 / CO2 selectivity by reducing free volume through cross-linking polybenzimidazole (PBI) with various acids. The separation performance of the cross-linked membranes was compared, and it was found that only the membrane cross-linked with H3PO4 showed increased H2 / CO2 selectivity with increasing test temperature. This is attributed to the relative stability of the hydrogen bonds formed between H3PO4 and the polymer at high temperatures. Therefore, it is evident that pure PBI polymer membranes can improve sieving performance after doping with phosphoric acid; however, the gas permeability of pure polymer membranes decreases after phosphoric acid cross-linking, making it difficult to meet industrial requirements.

[0007] Javier Sánchez-La´ nez., et al. (On the chemical filler–polymer interaction of nano and micro-sized ZIF-11 in PBI mixed matrix membranes and their application for H2 / CO2 separation. Journal of Materials Chemistry A, 2016: p. 10.1039. C6TA06438H.) introduces a mixed matrix membrane based on nano- and micro-sized ZIF-11 with high H2 and CO2 permeability. This work uses PBI as the polymer phase and nano- and micro-sized ZIF-11 as inorganic fillers to prepare mixed matrix membranes. Compared with pure polymers, both nano- and micro-sized MOFs improved the H2 permeability and selectivity of the PBI polymer phase in all cases when separating H2 / CO2 at 70–200 °C. Furthermore, MMMs prepared using microcrystalline ZIF-11 exhibited similar performance to similar nano-MOF membranes at low loading (up to 16 wt.%). Permeability increases at higher temperatures, with the best separation performance observed for 55 wt.% ZIF-11 / PBIMMM, exhibiting an H2 permeability of 495 Barrer and an H2 / CO2 selectivity of 7.0. Although the membrane shows a significant improvement in H2 and CO2 permeability, the excessively high MOF loading can lead to interfacial defects and reduce the membrane's mechanical properties. Furthermore, the slightly lower H2 / CO2 selectivity at high temperatures does not meet the requirements for industrial applications.

[0008] Chinese patent application CN105879704A discloses a method for preparing a hybrid matrix membrane composed of a zeolite-like imidazole framework material ZIF-7 and polyimide Matrimid, and its application. The hybrid matrix membrane prepared using ZIF-7 nanoparticles and Matrimid has a dense structure and uniformly dispersed ZIF-7 particles. This hybrid matrix membrane combines the advantages of MOF membranes and organic membranes, exhibiting high separation and permeation performance. The H2 permeability of a 10% ZIF-7 / Matrimid hybrid matrix membrane is 211.7 Barrer, and the H2 / CO2 selectivity is 5.4, equivalent to a 36.7% increase in H2 permeability compared to a pure polymer membrane, and a 14.9% increase in the ideal separation coefficient. Although the permeability of H2 and CO2 in this mixed matrix membrane is significantly improved, the ability of the ZIF-7 / Matrimid mixed matrix membrane to permeate H2 increases with the increase of ZIF-7 content. The ideal separation coefficient of H2 / CO2 shows a trend of first increasing to the optimal value and then decreasing. Moreover, the H2 / CO2 selectivity of the membrane is slightly low, which cannot meet the needs of industrial applications.

[0009] Ling Xiang Zhu, et al. (Unprecedented size-sieving ability in polybenzimidazole doped with polyprotic acids for membrane H2 / CO2 separation. Energy Environ. Sci, 2018: p. 10.1039.C7EE02865B.) introduces a novel method for manipulating polymer structure through acid doping to achieve superior H2 / CO2 separation performance. This method involves immersing a polybenzimidazole (PBI) membrane in a phosphoric acid solution of a certain concentration for 20 hours until saturation. H3PO4 can form hydrogen bonds with the PBI chain through proton transfer from the acid to the imidazole ring of the PBI, resulting in strong interaction and crosslinking of the PBI chain. This reduces the free volume and d-interval, thereby improving the H2 / CO2 diffusion selectivity and enhancing the H2 / CO2 sieving ability of the material. 1.0 The membrane exhibits an H2 permeability of 1.5 Barrer and an H2 / CO2 selectivity of 140 at 150°C, far exceeding Robeson's 2008 upper limit. However, this method requires a high concentration of phosphoric acid and a long doping time, resulting in a lengthy experimental cycle. Although the H2 / CO2 selectivity is high, the permeability is extremely low, failing to meet the requirements for industrial applications.

[0010] Chinese patent application CN 112275146 A discloses a phosphoric acid-treated TrÖger's base polymer gas separation membrane, its preparation method, and its application. For TrÖger's base rigid polymers, phosphoric acid doping utilizes the interaction between nitrogen (N) and phosphoric acid on the polymer backbone. The polymer chains are linked by hydrogen bonds, making the membrane denser and reducing the permeability of large molecular gases. The stability of phosphoric acid crosslinking is maintained by adjusting the doping time, thereby improving the H2 / CO2 separation performance of the polymer membrane. Although this improves the H2 / CO2 separation selectivity of the gas separation membrane, the phosphoric acid doping time must be sufficiently long to ensure that the phosphoric acid absorption rate within the membrane reaches saturation and stability. Furthermore, the longer the doping time, the lower the gas permeability, resulting in a long experimental cycle and low gas permeability.

[0011] Therefore, providing a novel phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, its preparation method, and its application has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0012] To address the aforementioned shortcomings and deficiencies, one objective of this invention is to provide a ZIF-8 / NPBI hybrid matrix membrane modified with phosphoric acid.

[0013] Another object of the present invention is to provide a method for preparing the above-described phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane.

[0014] Another object of the present invention is to provide the above-described phosphoric acid-modified ZIF-8 / NPBI mixed matrix membrane as a gas separation membrane for separating a mixture of H2 and CO2. The phosphoric acid-modified ZIF-8 / NPBI mixed matrix membrane provided by the present invention solves the technical problems of low permeability and low separation selectivity of existing separation membranes when separating light gases such as hydrogen and carbon dioxide.

[0015] To achieve the above objectives, on the one hand, the present invention provides a phosphoric acid-modified ZIF-8 / NPBI mixed matrix membrane, wherein the phosphoric acid-modified ZIF-8 / NPBI mixed matrix membrane is obtained by first immersing the ZIF-8 / NPBI mixed matrix membrane in an alcoholic solution of phosphoric acid and then drying it; wherein the ZIF-8 / NPBI mixed matrix membrane is obtained by uniformly mixing a polar solvent solution of ZIF-8 and a polar solvent solution of NPBI, evaporating the mixture to obtain the membrane material, and then immersing the membrane material in a displacement solvent and drying it.

[0016] After immersing the ZIF-8 / NPBI hybrid matrix membrane in an alcoholic solution of phosphoric acid, the N on the NPBI main chain interacts with the phosphoric acid (crosslinking) to form hydrogen bonds, making the NPBI chain segments more tightly connected. Furthermore, the phosphoric acid etches ZIF-8 to increase its pore size. In the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, ZIF-8 is uniformly dispersed in NPBI.

[0017] As a specific embodiment of the phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane described above in this invention, the weight percentage of ZIF-8 in the phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane is 10 wt.%-40 wt.%, with the total weight of ZIF-8 and NPBI being 100%.

[0018] In a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above in this invention, the concentration of phosphoric acid in the phosphoric acid alcohol solution is 0.05 wt.%-0.2 wt.%, preferably 0.05 wt.%, based on the total weight of the phosphoric acid alcohol solution as 100%. In this invention, as the concentration of phosphoric acid in the phosphoric acid alcohol solution increases, the MOF particles may be decomposed to a greater extent, thus making its performance approach that of a pure membrane, and failing to increase the gas permeability.

[0019] As a specific embodiment of the ZIF-8 / NPBI hybrid matrix membrane modified with phosphoric acid as described above in this invention, the alcohol in the phosphoric acid alcohol solution can be, for example, a conventional alcohol solvent such as methanol.

[0020] In a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above, the ZIF-8 / NPBI hybrid matrix membrane is immersed in an alcoholic solution of phosphoric acid for 1-12 hours, preferably 1-9 hours, and more preferably 9 hours. As shown in the experimental data in Table 1 below, the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane obtained with an immersion time of 9 hours exhibits the best permeability and selectivity. If the immersion time is further extended, the MOF particles may decompose to a greater extent, thus approaching the performance of a pure membrane and failing to increase gas permeability.

[0021] As a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above in this invention, the ZIF-8 / NPBI hybrid matrix membrane, after being immersed in an alcoholic solution of phosphoric acid, is dried in a vacuum oven at 120-160°C for 4-12 h.

[0022] In a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above in this invention, the polar solvent solution of ZIF-8 and the polar solvent solution of NPBI use the same polar solvent.

[0023] As a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above in this invention, the polar solvent includes N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide.

[0024] In a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above in this invention, the evaporation temperature is 60-80°C.

[0025] As a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above in this invention, the membrane material is immersed in the displacement solvent for 12-24 hours.

[0026] As a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above in this invention, the membrane material after being immersed in the displacement solvent is dried in a vacuum oven at 120-160°C for 12-16 h.

[0027] As a specific embodiment of the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane described above in this invention, the displacement solvent includes methanol, ethanol, or water.

[0028] The displacement solvent used in this invention is mainly used to displace the solvent used in the preparation of the membrane material.

[0029] On the other hand, the present invention also provides a method for preparing the above-described phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, wherein the preparation method includes:

[0030] (1) Mix the polar solvent solution of ZIF-8 and the polar solvent solution of NPBI evenly;

[0031] (2) Evaporate the mixture obtained in step (1) to obtain a membrane material, then soak the membrane material in a displacement solvent and dry it to obtain a ZIF-8 / NPBI mixed matrix membrane;

[0032] (3) The ZIF-8 / NPBI mixed matrix membrane is immersed in an alcoholic solution of phosphoric acid and then dried to obtain the phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane.

[0033] As a specific embodiment of the preparation method described above in this invention, the preparation method includes the following specific steps:

[0034] 1) Take a certain amount of ZIF-8 and add it to a polar solvent. Stir for 1-3 h, sonicate for 10-15 min, and then stir at 80°C for 30-60 min to obtain zinc salt solution A.

[0035] 2) Take a certain amount of NPBI polymer, add it to a polar solvent and stir at 80℃ for 3-4 h until the polymer is completely dissolved to obtain polymer solution B;

[0036] 3) Add polymer solution B to zinc salt solution A in three portions and continue stirring for 1-3 hours. Before and after adding polymer solution B, sonicate for 10-15 minutes to obtain mixed solution C.

[0037] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60-80℃. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12-24 h to remove the solvent. Finally, it was dried in a vacuum oven at 120℃ for 12-16 h to obtain the ZIF-8 / NPBI mixed matrix membrane.

[0038] 5) Based on the 1:1 crosslinking of phosphoric acid and NPBI polymer, the ZIF-8 / NPBI mixed matrix membrane was immersed in a certain concentration of phosphoric acid methanol solution at room temperature. The solution was stirred at 50-80 rpm at room temperature for 1-9 hours. After soaking, the membrane was removed from the phosphoric acid methanol solution, the solution on the membrane surface was wiped dry, and then dried in a vacuum oven at 120-160°C for 4-12 hours to obtain the phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane.

[0039] Furthermore, this invention also provides the application of the phosphoric acid-modified ZIF-8 / NPBI mixed matrix membrane as a gas separation membrane in separating a mixture of H2 and CO2. Additionally, the gas permeation performance of the I mixed matrix membrane provided by this invention for a single gas or a mixture of gases can be tested, wherein the single gas is hydrogen or carbon dioxide, and the mixed gas is a mixture of H2 and CO2.

[0040] In this invention, the operating conditions for the application process or gas permeability testing process are: temperature 35-150℃ and pressure 0.4 MPa.

[0041] Compared with the prior art, the beneficial technical effects achieved by the present invention include:

[0042] The present invention first prepares a mixed matrix membrane by blending ZIF-8 with NPBI, a rigid polymer with good thermal stability, and then treats the mixed matrix membrane with phosphoric acid to obtain a phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane. ZIF-8 has a porous metal-organic framework structure with a pore size between that of hydrogen and macromolecular gases, thus increasing the gas transport channels. Since NPBI contains both naphthyl and biphenyl groups, its free volume is larger than that of PBI, resulting in a higher H2 permeability for the pure membrane compared to PBI. After phosphoric acid treatment, the N atoms on the NPBI polymer backbone interact with phosphoric acid to form hydrogen bonds, making the polymer segments more tightly connected. Furthermore, phosphoric acid etches ZIF-8, increasing gas permeability (H3PO4 can both etch ZIF-8 and interact with NPBI via hydrogen bonds or proton transfer, thus crosslinking NPBI), improving H2 / CO2 selectivity. Therefore, the phosphoric acid-modified ZIF-8 / NPBI mixed matrix membrane provided by this invention possesses both high gas permeability and high H2 / CO2 selectivity, solving the technical problems of low permeability and low separation selectivity in existing separation membranes when separating light gases such as hydrogen from carbon dioxide. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a comparison chart showing the gas separation performance of the membrane materials prepared in the embodiments and comparative examples of the present invention with the gas separation performance data recorded in the prior art literature.

[0045] Figure 2 For 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-1h (NPBI-1h), 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-3h (NPBI-3h), 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-6h (NPBI-6h), 10 XRD patterns of wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-9h (NPBI-9h) and NPBI.

[0046] Figure 3 XRD patterns for 20 wt.%ZIF-7 / NPBI-0.05 wt.%H3PO4-6h (20% ZIF-7 / NPBI-6h) and 20 wt.%ZIF-7 / NPBI (20% ZIF-7 / NPBI). Detailed Implementation

[0047] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0048] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0049] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0050] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0051] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the appendices and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0053] Example 1

[0054] This embodiment provides a phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0055] (1) Preparation of ZIF-8:

[0056] 70 mL of a methanol solution containing 3.3 g (40 mmol) of dimethylimidazole was added to 70 mL of a methanol solution containing 1.5 g (5 mmol) of Zn(NO3)2·6H2O. The resulting mixture was stirred at room temperature for 24 h, centrifuged at 8000 rpm for 15 min, and the product was washed three times in 50 mL of methanol. Finally, the obtained solid was dried in a vacuum oven at 80 °C for 12 h to obtain ZIF-8 white powder.

[0057] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0058] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0059] (3) Preparation of ZIF-8 / NPBI hybrid matrix membrane modified with phosphoric acid:

[0060] 1) Take 0.011 g of ZIF-8 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0061] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0062] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0063] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-8 / NPBI mixed matrix membrane, which was denoted as 10 wt.% ZIF-8 / NPBI.

[0064] 5) Immerse 10 wt.% ZIF-8 / NPBI in a 0.05 wt.% phosphoric acid methanol solution at room temperature. Stir the solution at 60 rpm at room temperature and soak for 1 h. Remove the membrane from the phosphate methanol solution, wipe the solution off the membrane surface, and dry it in a vacuum oven at 160°C for 4 h to obtain a phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane, denoted as 10 wt.% ZIF-8 / NPBI-0.05 wt.% H3PO4-1h.

[0065] Example 2

[0066] This embodiment provides a phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0067] (1) Preparation of ZIF-8:

[0068] 70 mL of a methanol solution containing 3.3 g (40 mmol) of dimethylimidazole was added to 70 mL of a methanol solution containing 1.5 g (5 mmol) of Zn(NO3)2·6H2O. The resulting mixture was stirred at room temperature for 24 h, centrifuged at 8000 rpm for 15 min, and the product was washed three times in 50 mL of methanol. Finally, the obtained solid was dried in a vacuum oven at 80 °C for 12 h to obtain ZIF-8 white powder.

[0069] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0070] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0071] (3) Preparation of ZIF-8 / NPBI hybrid matrix membrane modified with phosphoric acid:

[0072] 1) Take 0.011 g of ZIF-8 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0073] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0074] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0075] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-8 / NPBI mixed matrix membrane, which was denoted as 10 wt.% ZIF-8 / NPBI.

[0076] 5) Immerse 10 wt.% ZIF-8 / NPBI in a 0.05 wt.% phosphoric acid methanol solution at room temperature. Stir the solution at 60 rpm at room temperature for 3 h. Remove the membrane from the phosphate methanol solution, wipe the solution off the membrane surface, and dry it in a vacuum oven at 160°C for 4 h to obtain a phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane, denoted as 10 wt.% ZIF-8 / NPBI-0.05wt.% H3PO4-3h.

[0077] Example 3

[0078] This embodiment provides a phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0079] (1) Preparation of ZIF-8:

[0080] 70 mL of a methanol solution containing 3.3 g (40 mmol) of dimethylimidazole was added to 70 mL of a methanol solution containing 1.5 g (5 mmol) of Zn(NO3)2·6H2O. The resulting mixture was stirred at room temperature for 24 h, centrifuged at 8000 rpm for 15 min, and the product was washed three times in 50 mL of methanol. Finally, the obtained solid was dried in a vacuum oven at 80 °C for 12 h to obtain ZIF-8 white powder.

[0081] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0082] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0083] (3) Preparation of ZIF-8 / NPBI hybrid matrix membrane modified with phosphoric acid:

[0084] 1) Take 0.011 g of ZIF-8 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0085] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0086] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0087] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-8 / NPBI mixed matrix membrane, which was denoted as 10 wt.% ZIF-8 / NPBI.

[0088] 5) Immerse 10 wt.% ZIF-8 / NPBI in a 0.05 wt.% phosphoric acid methanol solution at room temperature. Stir the solution at 60 rpm at room temperature for 6 hours. After soaking, remove the membrane from the phosphate methanol solution, wipe the solution off the membrane surface, and dry it in a vacuum oven at 160°C for 4 hours to obtain a phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane, denoted as 10 wt.% ZIF-8 / NPBI-0.05 wt.% H3PO4-6h.

[0089] Example 4

[0090] This embodiment provides a phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0091] (1) Preparation of ZIF-8:

[0092] 70 mL of a methanol solution containing 3.3 g (40 mmol) of dimethylimidazole was added to 70 mL of a methanol solution containing 1.5 g (5 mmol) of Zn(NO3)2·6H2O. The resulting mixture was stirred at room temperature for 24 h, centrifuged at 8000 rpm for 15 min, and the product was washed three times in 50 mL of methanol. Finally, the obtained solid was dried in a vacuum oven at 80 °C for 12 h to obtain ZIF-8 white powder.

[0093] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0094] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0095] (3) Preparation of ZIF-8 / NPBI hybrid matrix membrane modified with phosphoric acid:

[0096] 1) Take 0.011 g of ZIF-8 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0097] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0098] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0099] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-8 / NPBI mixed matrix membrane, which was denoted as 10 wt.% ZIF-8 / NPBI.

[0100] 5) Immerse 10 wt.% ZIF-8 / NPBI in a 0.05 wt.% phosphoric acid methanol solution at room temperature. Stir the solution at 60 rpm at room temperature for 9 h. Remove the membrane from the phosphate methanol solution, wipe the solution off the membrane surface, and dry it in a vacuum oven at 160°C for 4 h to obtain a phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane, denoted as 10 wt.% ZIF-8 / NPBI-0.05wt.% H3PO4-9h.

[0101] Example 5

[0102] This embodiment provides a phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0103] (1) Preparation of ZIF-8:

[0104] 70 mL of a methanol solution containing 3.3 g (40 mmol) of dimethylimidazole was added to 70 mL of a methanol solution containing 1.5 g (5 mmol) of Zn(NO3)2·6H2O. The resulting mixture was stirred at room temperature for 24 h, centrifuged at 8000 rpm for 15 min, and the product was washed three times in 50 mL of methanol. Finally, the obtained solid was dried in a vacuum oven at 80 °C for 12 h to obtain ZIF-8 white powder.

[0105] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0106] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0107] (3) Preparation of ZIF-8 / NPBI hybrid matrix membrane modified with phosphoric acid:

[0108] 1) Take 0.011 g of ZIF-8 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0109] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0110] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0111] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-8 / NPBI mixed matrix membrane, which was denoted as 10 wt.% ZIF-8 / NPBI.

[0112] 5) Immerse 10 wt.% ZIF-8 / NPBI in a 0.10 wt.% phosphoric acid methanol solution at room temperature. Stir the solution at 60 rpm at room temperature and soak for 6 h. Remove the membrane from the phosphoric acid methanol solution, wipe the solution off the membrane surface, and dry it in a vacuum oven at 160°C for 4 h to obtain a phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane, denoted as 10 wt.% ZIF-8 / NPBI-0.10 wt.% H3PO4-6h.

[0113] Comparative Example 1

[0114] This comparative example provides a pure NPBI polymer film, which is prepared by a method including the following specific steps:

[0115] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0116] After drying the NPBI polymer at 120°C for 12 hours, 0.1 g of the NPBI polymer was added to 4 mL of N,N-dimethylacetamide solvent and stirred at 80°C for 5 hours until completely dissolved. The resulting mixture was then poured onto a preheated glass plate at 60°C. After the solvent had completely evaporated, the film was scraped off the glass plate and then immersed in methanol for 12 hours to remove the solvent. Finally, the film was dried in a vacuum oven at 120°C for 12 hours to obtain a pure NPBI polymer film, denoted as NPBI.

[0117] Comparative Example 2

[0118] This comparative example provides a phosphoric acid-modified NPBI membrane, which is prepared by a method including the following specific steps:

[0119] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0120] After drying the NPBI polymer at 120°C for 12 hours, 0.1 g of the NPBI polymer was added to 4 mL of N,N-dimethylacetamide solvent and stirred at 80°C for 5 hours until completely dissolved. The resulting mixture was then poured onto a preheated glass plate at 60°C. After the solvent had completely evaporated, the film was scraped off the glass plate and then immersed in methanol for 12 hours to remove the solvent. Finally, the film was dried in a vacuum oven at 120°C for 12 hours to obtain a pure NPBI polymer film, denoted as NPBI.

[0121] Pure NPBI polymer membrane was immersed in a 0.05 wt.% phosphate methanol solution at room temperature. The solution was stirred at 60 rpm at room temperature and soaked for 1 h. After soaking, the membrane was removed from the phosphate methanol solution, the solution on the membrane surface was wiped dry, and then dried in a vacuum oven at 160°C for 4 h to obtain a phosphate modified NPBI membrane, denoted as NPBI-0.05wt.%H3PO4-1h.

[0122] Comparative Example 3

[0123] This comparative example provides a phosphoric acid-modified NPBI membrane, which is prepared by a method including the following specific steps:

[0124] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0125] After drying the NPBI polymer at 120°C for 12 hours, 0.1 g of the NPBI polymer was added to 4 mL of N,N-dimethylacetamide solvent and stirred at 80°C for 5 hours until completely dissolved. The resulting mixture was then poured onto a preheated glass plate at 60°C. After the solvent had completely evaporated, the film was scraped off the glass plate and then immersed in methanol for 12 hours to remove the solvent. Finally, the film was dried in a vacuum oven at 120°C for 12 hours to obtain a pure NPBI polymer film, denoted as NPBI.

[0126] Pure NPBI polymer membrane was immersed in a 0.05 wt.% phosphate methanol solution at room temperature. The solution was stirred at 60 rpm at room temperature for 3 hours. After immersion, the membrane was removed from the phosphate methanol solution, the solution on the membrane surface was wiped dry, and then dried in a vacuum oven at 160°C for 4 hours to obtain a phosphate-modified NPBI membrane, denoted as NPBI-0.05wt.%H3PO4-3h.

[0127] Comparative Example 4

[0128] This comparative example provides a phosphoric acid-modified NPBI membrane, which is prepared by a method including the following specific steps:

[0129] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0130] After drying the NPBI polymer at 120°C for 12 hours, 0.1 g of the NPBI polymer was added to 4 mL of N,N-dimethylacetamide solvent and stirred at 80°C for 5 hours until completely dissolved. The resulting mixture was then poured onto a preheated glass plate at 60°C. After the solvent had completely evaporated, the film was scraped off the glass plate and then immersed in methanol for 12 hours to remove the solvent. Finally, the film was dried in a vacuum oven at 120°C for 12 hours to obtain a pure NPBI polymer film, denoted as NPBI.

[0131] Pure NPBI polymer membrane was immersed in a 0.05 wt.% phosphate methanol solution at room temperature. The solution was stirred at 60 rpm at room temperature and soaked for 6 hours. After soaking, the membrane was removed from the phosphate methanol solution, the solution on the membrane surface was wiped dry, and then dried in a vacuum oven at 160°C for 4 hours to obtain a phosphate-modified NPBI membrane, denoted as NPBI-0.05wt.%H3PO4-6h.

[0132] Comparative Example 5

[0133] This comparative example provides a ZIF-8 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0134] (1) Preparation of ZIF-8:

[0135] 70 mL of a methanol solution containing 3.3 g (40 mmol) of dimethylimidazole was added to 70 mL of a methanol solution containing 1.5 g (5 mmol) of Zn(NO3)2·6H2O. The resulting mixture was stirred at room temperature for 24 h, centrifuged at 8000 rpm for 15 min, and the product was washed three times in 50 mL of methanol. Finally, the obtained solid was dried in a vacuum oven at 80 °C for 12 h to obtain ZIF-8 white powder.

[0136] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0137] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0138] (3) Preparation of ZIF-8 / NPBI hybrid matrix membrane modified with phosphoric acid:

[0139] 1) Take 0.011 g of ZIF-8 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0140] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0141] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0142] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-8 / NPBI mixed matrix membrane, denoted as 10 wt.% ZIF-8 / NPBI.

[0143] Comparative Example 6

[0144] This comparative example provides a ZIF-8 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0145] (1) Preparation of ZIF-8:

[0146] 70 mL of a methanol solution containing 3.3 g (40 mmol) of dimethylimidazole was added to 70 mL of a methanol solution containing 1.5 g (5 mmol) of Zn(NO3)2·6H2O. The resulting mixture was stirred at room temperature for 24 h, centrifuged at 8000 rpm for 15 min, and the product was washed three times in 50 mL of methanol. Finally, the obtained solid was dried in a vacuum oven at 80 °C for 12 h to obtain ZIF-8 white powder.

[0147] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0148] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0149] (3) Preparation of ZIF-8 / NPBI hybrid matrix membrane:

[0150] 1) Take 0.025 g of ZIF-8 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0151] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0152] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0153] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-8 / NPBI mixed matrix membrane, denoted as 20 wt.% ZIF-8 / NPBI.

[0154] Comparative Example 7

[0155] This comparative example provides a ZIF-8 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0156] (1) Preparation of ZIF-8:

[0157] 70 mL of a methanol solution containing 3.3 g (40 mmol) of dimethylimidazole was added to 70 mL of a methanol solution containing 1.5 g (5 mmol) of Zn(NO3)2·6H2O. The resulting mixture was stirred at room temperature for 24 h, centrifuged at 8000 rpm for 15 min, and the product was washed three times in 50 mL of methanol. Finally, the obtained solid was dried in a vacuum oven at 80 °C for 12 h to obtain ZIF-8 white powder.

[0158] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0159] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0160] (3) Preparation of ZIF-8 / NPBI hybrid matrix membrane:

[0161] 1) Take 0.043 g of ZIF-8 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0162] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0163] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0164] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-8 / NPBI mixed matrix membrane, denoted as 30 wt.% ZIF-8 / NPBI.

[0165] Comparative Example 8

[0166] This embodiment provides a phosphoric acid-modified ZIF-7 / NPBI hybrid matrix membrane, which is prepared by a method including the following specific steps:

[0167] (1) Preparation of ZIF-7:

[0168] ZIF-7 was prepared according to the method reported by Bassem A. Al-Maythalony, et al. (Tuning the Interplay between Selectivity and Permeability of ZIF-7 Mixed Matrix Membranes. ACS Appl MaterInterfaces, 2017: p. 10.1021 / acsami.6b15803.). Specifically, Zn(NO3)2·6H2O (1.25 g, 4.2 mmol) and benzimidazole (1.54 g, 13 mmol) were dissolved separately in 100 mL of DMF. After dissolution, the two solutions were mixed in a round-bottom flask and stirred continuously at 35 °C for 72 h. Then, the mixture was centrifuged at 6000 rpm for 20 min for separation. After separation, the mother liquor was discarded, and the resulting white powder was washed three times with methanol (50 mL). Finally, ZIF-7 was dried at 90 °C for 12 h.

[0169] (2) Preparation of NPBI, namely poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole]:

[0170] 36 g of P2O5 and 360 g of methanesulfonic acid were placed in a 500 mL flask and stirred at 50 °C until P2O5 was completely dissolved to obtain a mixed reagent. 25 g of the mixed reagent, 2.1427 g (10 mmol) of 3,3-diaminobenzidine, and 2.1619 g (10 mmol) of 1,4-naphthalenedicarboxylic acid were placed in a 100 mL three-necked flask (monomer concentration approximately 15 wt.%). The mixture was stirred under a nitrogen atmosphere and gradually heated to 140 °C for 8 h. The viscous mixture was then filtered and washed several times with 500 mL of deionized water, neutralized overnight in NaHCO3 solution, rinsed several times with water, and finally dried overnight in a vacuum oven at 120 °C to obtain the NPBI polymer.

[0171] (3) Preparation of ZIF-7 / NPBI hybrid matrix membrane modified with phosphoric acid:

[0172] 1) Take 0.025 g of ZIF-7 and add it to 1 mL of N,N-dimethylacetamide. Stir for 2 h, sonicate for 10 min, and then stir at 80°C for 30 min to obtain zinc salt solution A.

[0173] 2) Take 0.1 g of NPBI polymer, add it to 4 mL of N,N-dimethylacetamide and stir at 80℃ for 4 h until the polymer is completely dissolved to obtain polymer solution B;

[0174] 3) Add solution B to zinc salt solution A in three portions and continue stirring for 1 h. The polymer solution B is ultrasonically treated for 10 min before and after addition to obtain mixed solution C.

[0175] 4) The mixed solution C was then cast into an evaporating dish at a temperature of 60°C. After the solvent was completely evaporated, the membrane was peeled off and soaked in methanol for 12 h to remove the solvent. Finally, it was dried in a vacuum oven at 120°C for 12 h to obtain the ZIF-7 / NPBI mixed matrix membrane, denoted as 20 wt.% ZIF-7 / NPBI.

[0176] 5) Immerse 20 wt.% ZIF-7 / NPBI in a 0.05 wt.% phosphoric acid methanol solution at room temperature. Stir the solution at 60 rpm at room temperature for 6 hours. After soaking, remove the membrane from the phosphoric acid methanol solution, wipe the solution off the membrane surface, and dry it in a vacuum oven at 160°C for 4 hours to obtain a phosphoric acid modified ZIF-7 / NPBI mixed matrix membrane, denoted as 20 wt.% ZIF-7 / NPBI-0.05 wt.% H3PO4-6h.

[0177] Test Example 1

[0178] This test example demonstrates gas separation testing on the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membranes prepared in Examples 1-5 of this invention, as well as the membranes prepared in Comparative Examples 1-7. The gas separation test was conducted using a constant volume variable pressure device and included the following steps:

[0179] Before measurement, the corresponding membrane is sandwiched between aluminum foils and pasted in the middle of the gas permeation cell. The edges of the membrane are sealed with epoxy resin. The flange is assembled to form a flanged cell, i.e., a complete gas permeation cell. Then, the heating belt is wrapped with fiberglass insulation tape for heat preservation, and the test temperature is controlled by a temperature controller. The upstream and downstream of the gas permeation cell are emptied to ensure that the downstream pressure is less than 0.05 Torr. Then, the feed gas is introduced into the upstream permeation cell (high pressure) and allowed to permeate from the upstream permeation cell through the corresponding membrane to the downstream of the gas permeation cell (low pressure).

[0180] In this test example, a feed gas with an H2 / CO2 (volume ratio) of 1:1 was used for testing. The test temperatures were controlled at 35℃ and 150℃, and the pressure was controlled at 0.4 MPa. An Agilent 8860 gas chromatograph was used to detect the permeate gas components downstream of the gas permeation cell in order to calculate the permeability and selectivity of each component.

[0181] Furthermore, the comparison results of the gas separation performance of the membrane materials prepared in the embodiments and comparative examples of the present invention with the gas separation performance data recorded in the prior art literature are shown in the figure below. Figure 1 As shown, Figure 1 In this context, 10%-1h, 10%-3h, 10%-6h, and 10%-9h represent 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-1h, 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-3h, 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-6h, and 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-9h, respectively, as shown in Table 1. 10% represents 10 wt.%ZIF-8 / NPBI, as shown in Table 1. NPBI-1h, NPBI-3h, and NPBI-6h represent NPBI-0.05 wt.%H3PO4-1h, NPBI-0.05wt.%H3PO4-1h, and NPBI-0.05wt.%H3PO4-9h, respectively, as shown in Table 1. wt.%H3PO4-3h and NPBI-0.05wt.%H3PO4-6h;

[0182] Figure 1The straight lines at the lower left, middle, and upper right represent the Robeson upper bound at 35°C in 1991, 2008, and 2008, respectively. The sources are Lloyd M. Robeson, et al. Correlation of separation factor versus permeability for polymeric membranes. Journal of Membrane Science, 1991: p. 10.1016 / 0376-7388(91)80060-J, Lloyd M. Robeson, et al. The upper bound revisited. Journal of Membrane Science, 2008: p. 10.1016 / j.memsci.2008.04.030, and Brandon W. Rowe, et al. (Influence of temperature on the upper bound: Theoretical considerations and comparison with experimental results. Journal of Membrane Science, 2010: p. 10.1016 / j.memsci.2010.04.047.

[0183] Other, Figure 1 The meanings, sources, and corresponding data represented by numbers 1-7 are shown in Table 1 below.

[0184] Table 1

[0185]

[0186] Note: Refs [1]-[5] in Table 1 are shown below:

[0187] [1] ZHU L, SWIHART MT, LIN H. Unprecedented size-sieving ability inpolybenzimidazole doped with polyprotic acids for membrane H2 / CO2 separation[J]. Energy & Environmental Science, 2018, 11(1): 94-100.

[0188] [2] SáNCHEZ-LAíNEZ J, ZORNOZA B, FRIEBE S, et al. Influence of ZIF-8particle size in the performance of polybenzimidazole mixed matrix membranesfor pre-combustion CO2 capture and its validation through interlaboratorytest [J]. Journal of Membrane Science, 2016, 515: 45-53.

[0189] [3] HU L, BUI V, HUANG L, et al. Facilely Cross-LinkingPolybenzimidazole with Polycarboxylic Acids to Improve H2 / CO2 SeparationPerformance [J]. 2021.

[0190] [4] NADERI A, ASADI TASHVIGH A, CHUNG T-S, et al. Molecular design ofdouble crosslinked sulfonated polyphenylsulfone / polybenzimidazole blendmembranes for an efficient hydrogen purification [J]. Journal of MembraneScience, 2018, 563: 726-33.

[0191] [5] SUHAIMI H S M, LEO C P, AHMAD A L. Hydrogen separation usingpolybenzimidazole membrane with palladium nanoparticles stabilized bypolyvinylpyrrolidone [J]. International Journal of Energy Research, 2021, 45(10): 15171-81.

[0192] The comparison results of the H2 / CO2 gas permeation performance of the above membranes obtained in this test example are shown in Table 2 below.

[0193] Table 2

[0194]

[0195] Note: Test conditions were 35℃ and 150℃, pressure 0.4 MPa, and feed gas was a 1:1 H2 / CO2 mixture. 1 barrer = 10 -10 cm 3 (STP)cm / (cm 2 scmHg).

[0196] From Table 2 above and Figure 1 As can be seen, the gas permeability of pure NPBI polymer membrane is higher than that of PBI. This invention, by changing the ZIF-8 doping amount, crosslinking time (i.e., the immersion time of the corresponding membrane material in the phosphate methanol solution), and the phosphoric acid concentration in the phosphate methanol solution, found that 10 wt.% ZIF-8 / NPBI-0.05wt.%H3PO4-6h exhibited relatively high H2 permeability and H2 / CO2 selectivity at 150℃. 10 wt.% ZIF-8 / NPBI-0.05wt.%H3PO4-9h showed the highest H2 permeability, and its H2 / CO2 selectivity showed no significant loss compared to 10 wt.% ZIF-8 / NPBI-0.05wt.%H3PO4-6h. The H2 permeability was increased by 80% and the H2 / CO2 selectivity by 97% compared to 10 wt.% ZIF-8 / NPBI, and the H2 purity reached 91%, which was obtained from the peak area of ​​the chromatographic peaks.

[0197] Compared to most pure films, the gas permeability did not increase after doping with phosphoric acid. However, the hydrogen permeability data for NPBI-0.05wt.%H3PO4-1h (150℃) and NPBI-0.05 wt.%H3PO4-3h (150℃) were higher than that of NPBI (150℃). One possible reason is that the cross-linking time of phosphoric acid was shorter, resulting in less saturation and fewer hydrogen bonds formed. This increased chain flexibility at high temperatures led to higher gas permeability. Another possible reason is the change in interplanar spacing, i.e., d-interval. XRD characterization was performed on NPBI-0.05 wt.%H3PO4-3h and NPBI (XRD figures are shown below). Figure 2As shown in the figure, the d-spacing of NPBI-0.05 wt.%H3PO4-3h is calculated according to Bragg's formula to be greater than that of pure NPBI membrane, thus the gas permeability of NPBI-0.05 wt.%H3PO4-3h is greater than that of pure NPBI membrane. After doping the mixed matrix membrane with phosphoric acid, compared with the mixed matrix membrane (such as 10 wt.%ZIF-8 / NPBI), the H2 permeability decreases for mixed matrix membranes with shorter phosphoric acid doping times (such as 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-1h, 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-3h and 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-6h). However, for mixed matrix membranes with longer phosphoric acid doping times (such as 10 wt.%ZIF-8 / NPBI-0.05wt.%H3PO4-6h), the H2 permeability decreases. The H2 permeability of the phosphoric acid-doped mixed matrix membrane (e.g., 10 wt.% ZIF-8 / NPBI-0.05wt.% H3PO4-9h) is increased, even greater than that of the untreated mixed matrix membrane (e.g., 10 wt.% ZIF-8 / NPBI). At the same time, the H2 / CO2 selectivity of the phosphoric acid-doped mixed matrix membrane is improved compared to the mixed matrix membrane. The above results of H2 permeability and H2 / CO2 selectivity are caused by the combined effect of etching and crosslinking of H3PO4.

[0198] Test Example 2

[0199] In this test example, the gas separation test was performed on 20 wt.% ZIF-7 / NPBI and 20 wt.% ZIF-7 / NPBI-0.05wt.% H3PO4-6h prepared in Comparative Example 8 using the test method in Test Example 1. The experimental data are shown in Table 3 below.

[0200] Table 3

[0201]

[0202] Note: Test conditions were 35℃ and 150℃, pressure 0.4 MPa, and feed gas was a 1:1 H2 / CO2 mixture. 1 barrer = 10 -10 cm 3 (STP)cm / (cm 2 scmHg).

[0203] As shown in Table 3 above, by preparing MMMs by doping ZIF-7 and then performing phosphoric acid doping on the mixed matrix membrane, it was found that the H2 / CO2 selectivity of the mixed matrix membrane obtained after phosphoric acid doping increased. This is because phosphoric acid forms hydrogen bonds with the polymer, thereby improving gas selectivity. However, Table 3 also shows that at a temperature of 35℃, the hydrogen permeability of 20 wt.% ZIF-7 / NPBI-0.05 wt.% H3PO4-6h (35℃) is close to that of 20 wt.% ZIF-7 / NPBI (35℃), indicating that the ZIF-7 in the 20 wt.% ZIF-7 / NPBI-0.05 wt.% H3PO4-6h material is decomposed by acid, and there is almost no ZIF-7 present in the membrane. Furthermore, the phosphoric acid crosslinks NPBI, and the etching and crosslinking work simultaneously, resulting in no significant change in permeability. At the same time, its XRD pattern (as shown in Table 3) also shows this. Figure 3 As shown in the figure, the characteristic peaks of ZIF-7 disappear, further proving that ZIF-7 is decomposed by acid. At a temperature of 150°C, the increase in temperature causes the hydrogen bonds formed by cross-linking to become free. The flexibility of the polymer chain segments at high temperatures amplifies the defects formed by etching. Moreover, high temperature reduces the solubility of carbon dioxide, thereby increasing the permeability of hydrogen.

[0204] In summary, doping pure NPBI polymer membranes with phosphoric acid improves their H2 / CO2 selectivity but reduces their gas permeability. For MMMs, however, phosphoric acid doping not only improves their H2 / CO2 selectivity but also increases their gas permeability. The former is due to the hydrogen bonding between nitrogen and phosphoric acid in the NPBI backbone, resulting in tighter chain connections (phosphoric acid crosslinking), while the latter is due to the etching of the MOF by phosphoric acid. Because the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane provided in this embodiment exhibits both phosphoric acid etching and crosslinking effects, it achieves both high gas permeability and high gas selectivity.

[0205] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, characterized in that, The phosphoric acid modified ZIF-8 / NPBI hybrid matrix membrane is prepared by first immersing the ZIF-8 / NPBI hybrid matrix membrane in an alcoholic solution of phosphoric acid and then drying it. The ZIF-8 / NPBI hybrid matrix membrane is obtained by mixing a polar solvent solution of ZIF-8 and a polar solvent solution of NPBI evenly, evaporating the mixture to obtain the membrane material, and then immersing the membrane material in a displacement solvent and drying it. After immersing the ZIF-8 / NPBI hybrid matrix membrane in an alcoholic solution of phosphoric acid, hydrogen bonds are formed between the N on the NPBI main chain and the phosphoric acid, making the NPBI chain segments more tightly connected. Furthermore, the phosphoric acid etches ZIF-8 to increase its pore size. In the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane, ZIF-8 is uniformly dispersed in NPBI. Specifically, based on the total weight of ZIF-8 and NPBI as 100%, the weight percentage of ZIF-8 in the phosphoric acid-modified ZIF-8 / NPBI mixed matrix membrane is 10 wt.%-40 wt.%. Based on the total weight of the alcoholic solution of phosphoric acid as 100%, the concentration of phosphoric acid in the alcoholic solution of phosphoric acid is 0.05 wt.%-0.2 wt.%. The ZIF-8 / NPBI hybrid matrix membrane was immersed in an alcoholic solution of phosphoric acid for 1-12 hours. Among them, NPBI is poly[2,2'-(1,4-naphthalene)-5,5'-bisbenzimidazole].

2. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to claim 1, characterized in that, The ZIF-8 / NPBI hybrid matrix membrane was immersed in an alcoholic solution of phosphoric acid for 1-9 hours.

3. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to claim 2, characterized in that, The ZIF-8 / NPBI hybrid matrix membrane was immersed in an alcoholic solution of phosphoric acid for 9 hours.

4. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to any one of claims 1-3, characterized in that, The ZIF-8 / NPBI hybrid matrix membrane, after being soaked in an alcoholic solution of phosphoric acid, was dried in a vacuum oven at 120-160℃ for 4-12 h.

5. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to any one of claims 1-3, characterized in that, The polar solvent solution of ZIF-8 uses the same polar solvent as the polar solvent solution of NPBI.

6. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to claim 5, characterized in that, The polar solvent includes N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide.

7. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to any one of claims 1-3, characterized in that, The evaporation temperature is 60-80℃.

8. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to any one of claims 1-3, characterized in that, The membrane material is immersed in the replacement solvent for 12-24 hours.

9. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to any one of claims 1-3, characterized in that, The membrane material soaked in the displacement solvent was dried in a vacuum oven at 120-160℃ for 12-16 h.

10. The phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to any one of claims 1-3, characterized in that, The replacement solvent includes methanol, ethanol, or water.

11. The method for preparing the phosphoric acid-modified ZIF-8 / NPBI hybrid matrix membrane according to any one of claims 1-10, characterized in that, The preparation method includes: (1) Mix the polar solvent solution of ZIF-8 and the polar solvent solution of NPBI evenly; (2) Evaporate the mixture obtained in step (1) to obtain a membrane material, then soak the membrane material in a displacement solvent and dry it to obtain a ZIF-8 / NPBI mixed matrix membrane; (3) The ZIF-8 / NPBI mixed matrix membrane is immersed in an alcoholic solution of phosphoric acid and then dried to obtain the phosphoric acid modified ZIF-8 / NPBI mixed matrix membrane.

12. The application of the phosphoric acid-modified ZIF-8 / NPBI mixed matrix membrane according to any one of claims 1-10 as a gas separation membrane in the separation of a mixture of H2 and CO2.

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