An acid-resistant poly-sulfonamide-metal organic framework nanofiltration membrane, a preparation method and application thereof

Abstract

The present application relates to the technical field of environmental functional materials, and provides a polysulfamide-metal organic framework acid-resistant nanofiltration membrane as well as a preparation method and application thereof. The present application utilizes the metal organic framework MIL-101(Cr) to regulate the interfacial polymerization process of the polysulfamide selective layer, so that the polysulfamide-metal organic framework acid-resistant nanofiltration membrane with high permeability and good acid resistance is obtained. The polysulfamide-metal organic framework acid-resistant nanofiltration membrane prepared by the present application has good stability in a strong acid solution, can continuously work in acidic wastewater, has a relatively high permeation flux, can significantly improve the separation efficiency, can efficiently recover heavy metal ions in industrial acidic wastewater, and has a good application prospect in water treatment processes. Meanwhile, the preparation method provided by the present application is simple in process, controllable in cost, and suitable for large-scale production and application.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials technology, and in particular to a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Wastewater resource recovery can reduce wastewater discharge, lower environmental pollution, and promote resource reuse. Membrane technology holds a significant advantage in wastewater resource recovery due to its safety, reliability, economy, and low energy consumption. However, nanofiltration membrane ion separation processes may require acidic environments. The pore structure of traditional nanofiltration membranes collapses under strongly acidic conditions, losing its ability to retain ions. For example, a considerable portion of industrial wastewater containing heavy metal ions is strongly acidic. Traditional nanofiltration membranes use a polyamide (PA) structure as the selective layer. Under acidic conditions, the carbonyl groups undergo protonation and are hydrolyzed by nucleophilic attacks from water molecules, significantly shortening their lifespan. Therefore, measures must be taken to address the stability issues of nanofiltration membranes under acidic conditions.

[0003] Furthermore, the permeation flux of nanofiltration membranes directly affects separation efficiency, and the low permeation flux resulting from the dense selective layer on the surface of nanofiltration membranes hinders their further application. Therefore, providing a nanofiltration membrane with high permeation flux and good acid resistance, and applying it to the efficient recovery of metal ions from acidic wastewater, has significant scientific and practical value. Summary of the Invention

[0004] In view of this, the present invention provides a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane, its preparation method, and its application. The polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane provided by the present invention exhibits good stability in strong acid solutions and has high permeation flux, which can significantly improve separation efficiency.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for preparing a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane includes the following steps:

[0007] A polysulfonamide-metal-organic framework selective layer was prepared on the upper surface of a substrate membrane using a surfactant solution, an aqueous phase, and an organic phase as raw materials, thereby obtaining the polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane.

[0008] The aqueous phase is an aqueous solution of polyethyleneimine; the components of the organic phase include 1,3-benzenedisulfonyl chloride, metal-organic framework MIL-101(Cr) and organic solvent; the base membrane is a polyethersulfone ultrafiltration membrane.

[0009] Preferably, the preparation method of the metal-organic framework MIL-101(Cr) includes: mixing chromium nitrate, terephthalic acid, an alkaline reagent and water to carry out a hydrothermal reaction to obtain the metal-organic framework MIL-101(Cr); the hydrothermal reaction temperature is 220-260℃ and the time is 6-12h.

[0010] Preferably, the molar ratio of chromium nitrate to terephthalic acid is 1:0.8 to 1.5; the alkaline reagent includes one or more of sodium hydroxide, ammonium hydroxide, and potassium hydroxide; and the molar ratio of the alkaline reagent to chromium nitrate is 1:0.8 to 1.5.

[0011] Preferably, the surfactant includes one or more of cationic and anionic surfactants; the concentration of the surfactant solution is 0.01% (w / v) to 0.1% (w / v).

[0012] Preferably, the concentration of the polyethyleneimine aqueous solution is 0.5% (w / v) to 2% (w / v);

[0013] The concentration of 1,3-benzenedisulfonyl chloride in the organic phase is 0.05% (w / v) to 0.2% (w / v), and the concentration of the metal-organic framework MIL-101(Cr) is 0.005% (w / v) to 0.02% (w / v); the organic solvent includes one or more of n-hexane, toluene, dichloromethane, and ethyl acetate.

[0014] Preferably, the interfacial polymerization method includes: sequentially immersing the upper surface of the substrate membrane with a surfactant solution, an aqueous phase, and an organic phase, heating the immersed substrate membrane to crosslink and cure it, thereby obtaining a polysulfonamide-metal-organic framework selective layer on the upper surface of the substrate membrane.

[0015] Preferably, the soaking time of the surfactant solution is 5-12 min, the soaking time of the aqueous phase is 8-15 min, and the soaking time of the organic phase is 5-10 min.

[0016] Preferably, the cross-linking curing temperature is 60–90°C and the time is 5–15 min.

[0017] The present invention also provides an acid-resistant nanofiltration membrane of polysulfonamide-metal-organic framework prepared by the preparation method described above, comprising a base membrane and a polysulfonamide-metal-organic framework selective layer disposed on the upper surface of the base membrane; the base membrane is a polyethersulfone ultrafiltration membrane; the polysulfonamide-metal-organic framework selective layer comprises a polysulfonamide layer and a metal-organic framework MIL-101(Cr) dispersed in the polysulfonamide layer.

[0018] The present invention also provides the application of the polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane described above in water treatment.

[0019] This invention provides a method for preparing a polysulfonamide-metal-organic framework (MOF) acid-resistant nanofiltration membrane, comprising the following steps: using a surfactant solution, an aqueous phase, and an organic phase as raw materials, a polysulfonamide-MOF selective layer is prepared on the upper surface of a substrate membrane via interfacial polymerization to obtain the polysulfonamide-MOF acid-resistant nanofiltration membrane; the aqueous phase is an aqueous solution of polyethyleneimine; the organic phase comprises 1,3-benzenedisulfonyl chloride, MOF MIL-101(Cr), and an organic solvent; the substrate membrane is a polyethersulfone ultrafiltration membrane. This invention uses polysulfonamide (PSA) as the selective layer. The PSA structure has greater steric hindrance and electron density, making it difficult to protonate and hydrolyze, thus exhibiting strong stability under acidic conditions. Furthermore, this invention uses a MOF to control the interfacial polymerization process of the polysulfonamide selective layer, significantly improving its permeation flux while maintaining its acid resistance. In summary, the polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane prepared by this invention exhibits good stability in strong acid solutions, can operate continuously in acidic wastewater, and has a high permeation flux, which can significantly improve separation efficiency and efficiently recover heavy metal ions from industrial acidic wastewater, showing promising application prospects in water treatment processes. Furthermore, the preparation method provided by this invention is simple, cost-controllable, and has low requirements for operating conditions, making it suitable for large-scale production and application. Attached Figure Description

[0020] Figure 1 A schematic diagram of the interfacial polymerization process of polyamide (PA), polysulfonamide (PSA), and polysulfonamide-metal-organic framework (PSA-MOF);

[0021] Figure 2 X-ray diffraction energy spectrum of metal-organic framework MIL-101(Cr);

[0022] Figure 3 Scanning electron microscope image of metal-organic framework MIL-101(Cr), scale bar 1 μm;

[0023] Figure 4 Scanning electron microscope image of metal-organic framework MIL-101(Cr), scale bar is 100 nm;

[0024] Figure 5 X-ray photoelectron spectroscopy (a) and Fourier transform infrared spectrum (b) of polyamide nanofiltration membrane, polysulfonamide nanofiltration membrane and polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane;

[0025] Figure 6Scanning electron microscope image of polyethersulfone ultrafiltration substrate membrane;

[0026] Figure 7 A scanning electron microscope image of a polyamide nanofiltration membrane;

[0027] Figure 8 Scanning electron microscope image of a polysulfonamide nanofiltration membrane;

[0028] Figure 9 Scanning electron microscope image of a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane;

[0029] Figure 10 Atomic force microscopy images of polyethersulfone ultrafiltration substrate membrane (a), polyamide nanofiltration membrane (b), polysulfonamide nanofiltration membrane (c), and polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane (d);

[0030] Figure 11 Images showing the water contact angles of a polyethersulfone ultrafiltration substrate membrane (a), a polyamide nanofiltration membrane (b), a polysulfonamide nanofiltration membrane (c), and a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane (d);

[0031] Figure 12 The pure water permeation flux of the membrane (0.2 MPa) is shown in (a), and the change in rejection rate after immersion in strong acid conditions is shown in (b). Detailed Implementation

[0032] This invention provides a method for preparing a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane, comprising the following steps:

[0033] A polysulfonamide-metal-organic framework selective layer was prepared on the upper surface of a substrate membrane using a surfactant solution, an aqueous phase, and an organic phase as raw materials, thereby obtaining the polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane.

[0034] The aqueous phase is an aqueous solution of polyethyleneimine; the components of the organic phase include 1,3-benzenedisulfonyl chloride, metal-organic framework MIL-101(Cr) and organic solvent; the substrate membrane is a polyethersulfone ultrafiltration membrane; the molecular weight cutoff of the polyethersulfone ultrafiltration membrane is preferably 20-50 kDa, more preferably 30 kDa.

[0035] In this invention, the preferred method for preparing the metal-organic framework MIL-101(Cr) includes: mixing chromium nitrate, terephthalic acid, an alkaline reagent, and water for a hydrothermal reaction to obtain the metal-organic framework MIL-101(Cr); the hydrothermal reaction is carried out at a temperature of 220–260°C for 6–12 hours; the chromium nitrate is preferably chromium nitrate nonahydrate; the molar ratio of chromium nitrate to terephthalic acid is preferably 1:0.8–1.5, more preferably 1:1; the water is preferably deionized water; the alkaline reagent preferably includes one or more of sodium hydroxide, ammonium hydroxide, and potassium hydroxide, wherein the ammonium hydroxide is preferably used in the form of ammonia; the molar ratio of the alkaline reagent to chromium nitrate is preferably 1:0.8–1.5, more preferably 1:1; the alkaline reagent serves to provide an alkaline environment and act as a catalyst. In a specific embodiment of the present invention, chromium nitrate, terephthalic acid, alkaline reagent and water are preferably ultrasonically treated until they are mixed evenly, and then the mixture is transferred to the polytetrafluoroethylene lining of a high-pressure reactor and then placed in a muffle furnace for hydrothermal reaction.

[0036] After the hydrothermal reaction is completed, the present invention preferably further includes: centrifuging the obtained reaction solution and then sequentially washing it with N,N-dimethylformamide (DMF), washing it with ethanol, and drying it to obtain the metal-organic framework MIL-101(Cr); the DMF washing temperature is preferably 70-90℃, more preferably 80℃, the DMF washing is preferably performed twice, and the washing time for each wash is preferably 1 hour; the present invention can remove impurities and unreacted substances from the synthesized product by DMF washing, thereby improving the purity and structural integrity of the product; the ethanol washing temperature is preferably 50-70℃, more preferably 60℃, and the ethanol washing time is preferably 20 minutes; the present invention removes DMF from the product by ethanol washing; the drying is preferably vacuum drying, the drying temperature is preferably 120℃, and the drying time is preferably 2 hours.

[0037] In this invention, the metal-organic framework MIL-101(Cr) is composed of metal ions (Cr). 3+ The metal-organic framework MIL-101(Cr) and its surrounding organic ligands (terephthalic acid) form a highly ordered octahedral coordination crystal structure. These octahedra form a three-dimensional network structure by sharing carboxyl groups in the ligands, which allows MIL-101(Cr) to remain stable under strong acid conditions, thereby improving the acid resistance of the nanofiltration membrane. Furthermore, the metal-organic framework MIL-101(Cr) can also regulate the interfacial polymerization process, reduce the reaction rate, and automatically fill defects in the selective layer, resulting in a high degree of smoothness on the surface of the final nanofiltration membrane. In addition, the presence of MIL-101(Cr) can also form more water channels, reduce the roughness of the membrane surface, enhance the hydrophilicity of the membrane, and thus improve the permeation flux of the nanofiltration membrane.

[0038] In this invention, the surfactant comprises one or more of cationic and anionic surfactants; the cationic surfactant preferably comprises one or two of hexadecyltrimethylammonium bromide (CTAB) and octyltrimethylammonium chloride (OTAC); the anionic surfactant preferably comprises one or two of sodium dodecyl sulfate (SDS) and sodium hexadecyl sulfate (SLES); in a specific embodiment of this invention, the surfactant is most preferably sodium dodecyl sulfate; the concentration of the surfactant solution is preferably 0.01% (w / v) to 0.10% (w / v), more preferably 0.05% (w / v); the solvent of the surfactant solution is preferably deionized water. This invention uses surfactants to stabilize the dispersion state of polymer precursors, adjust interfacial tension, improve wettability, and control the morphology and surface properties of polymers.

[0039] In this invention, the concentration of the polyethyleneimine aqueous solution is preferably 0.5% (w / v) to 2% (w / v), more preferably 1.5% (w / v).

[0040] In this invention, the concentration of 1,3-benzenedisulfonyl chloride in the organic phase is preferably 0.05% (w / v) to 0.2% (w / v), more preferably 0.1% (w / v); the concentration of the metal-organic framework MIL-101(Cr) in the organic phase is preferably 0.005% (w / v) to 0.02% (w / v), more preferably 0.01% (w / v); and the organic solvent used in the organic phase preferably includes one or more of n-hexane, toluene, dichloromethane, and ethyl acetate, more preferably n-hexane.

[0041] In this invention, the interfacial polymerization method preferably includes: sequentially immersing the upper surface of the substrate membrane with a surfactant solution, an aqueous phase, and an organic phase; heating the immersed substrate membrane to crosslink and cure it, thereby obtaining a polysulfonamide-metal-organic framework selective layer on the upper surface of the substrate membrane; the upper surface of the filter membrane is specifically the front side of the filter membrane, i.e., the smooth surface; preferably, after washing the substrate membrane, the substrate membrane is placed in an interfacial polymerization reactor, exposing only the upper surface, and then the surfactant solution, aqueous phase, and organic phase are sequentially added to the interfacial polymerization reactor to immerse the upper surface of the substrate membrane; this invention does not have special requirements for the specific structure of the interfacial polymerization reactor, as long as it can expose the upper surface of the substrate membrane while the lower surface is not immersed.

[0042] In this invention, the soaking time of the surfactant solution is preferably 5 to 12 minutes, more preferably 10 minutes; the soaking time of the aqueous phase is preferably 8 to 15 minutes, more preferably 10 minutes; and the soaking time of the organic phase is preferably 5 to 10 minutes, more preferably 7 minutes.

[0043] In this invention, the crosslinking curing temperature is preferably 60–90°C, more preferably 80°C, and the crosslinking curing time is preferably 5–15 min, more preferably 10 min; the crosslinking curing is preferably carried out in an oven. After the crosslinking curing is completed, the resulting polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane is preferably cooled and then washed.

[0044] The present invention also provides an acid-resistant nanofiltration membrane of polysulfonamide-metal-organic framework prepared by the preparation method described above, comprising a base membrane and a polysulfonamide-metal-organic framework selective layer disposed on the upper surface of the base membrane; the base membrane is a polyethersulfone ultrafiltration membrane; the polysulfonamide-metal-organic framework selective layer comprises a polysulfonamide layer and a metal-organic framework MIL-101(Cr) dispersed in the polysulfonamide layer.

[0045] The present invention also provides the application of the polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane described above in water treatment; the water treatment specifically involves the recovery of heavy metal ions from strongly acidic wastewater; the pH value of the strongly acidic wastewater is preferably 1 to 2; the heavy metal ions preferably include one or more of copper ions, zinc ions, and lead ions.

[0046] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0047] Example 1

[0048] In this embodiment, the overall synthesis route is as follows: Figure 1 As shown, polyamide nanofiltration membranes (PA), polysulfonamide nanofiltration membranes (PSA), and polysulfonamide-metal-organic framework acid-resistant nanofiltration membranes (PSA-MOF) were prepared by interfacial polymerization. The preparation, elemental composition, and surface properties of the membranes are then described. The specific steps are as follows:

[0049] (1) Preparation of metal-organic framework MIL-101(Cr) using a solvothermal method. 4.0 g (0.01 mol) of chromium nitrate nonahydrate (Cr(NO3)3·9H2O), 0.4 g (0.01 mol) of sodium hydroxide (NaOH), and 1.66 g (0.01 mol) of terephthalic acid (PTA) were placed in a 100 mL beaker, along with 50 mL of deionized water. The mixture was sonicated repeatedly until homogeneous. The mixture was transferred to a polytetrafluoroethylene lining in a high-pressure reactor, which was then placed in a muffle furnace at 220 °C. After reacting under high temperature and pressure for 8 h, the reaction was completed, and the reaction system was cooled to room temperature. The product from the reactor was poured into centrifuge tubes and centrifuged at 4200 rpm for 20 min to separate the solid and liquid phases. Next, the supernatant was poured off, and 15 mL of N,N-dimethylformamide (DMF) was added to the reaction system. The temperature was raised to 80 °C, and the mixture was washed continuously for 1 h. This washing process was repeated twice. Then, 15 mL of ethanol was added to the system, and the temperature was raised to 60 °C. Finally, the washed reaction mixture was placed in a vacuum drying oven at 120 °C for 2 h to obtain the metal-organic framework MIL-101(Cr).

[0050] Figure 2 The X-ray diffraction pattern of the obtained metal-organic framework MIL-101(Cr) is shown. Figure 3 and Figure 4 Scanning electron microscope images of the metal-organic framework MIL-101(Cr) obtained at different magnifications. Figure 3 The scale bar is 1 μm. Figure 4 The scale bar is 100 nm. For example... Figure 2 X-ray diffraction pattern (XRD) and Figures 3-4 As shown in the scanning electron microscope (SEM) image, MIL-101(Cr) consists of metal ions (Cr). 3+ MIL-101(Cr) and its surrounding organic ligands (terephthalic acid) form a highly ordered octahedral coordination crystal structure. These octahedra form a three-dimensional network structure by sharing carboxyl groups in the ligands, which makes MIL-101(Cr) stable under strong acid conditions and has the potential to prepare acid-resistant filter membranes.

[0051] (2) Nanofiltration membranes PA / PES, PSA / PES and PSA-MOF / PES were synthesized by interfacial polymerization (IP) using polyethersulfone (PES) membrane as the base membrane.

[0052] The preparation process of the PA / PES membrane is as follows: 0.05 g of sodium dodecyl sulfate (SDS) and 1 g of piperazine (PIP) are each dissolved in 100 mL of deionized water to prepare 0.05% (w / v) SDS solution and 1.00% (w / v) PIP solution, respectively. At the same time, 0.1 g of 1,3,5-benzenetricarboxylic acid chloride (TMC) is dissolved in 100 mL of n-hexane to prepare 0.10% (w / v) TMC organic solution. The PES substrate membrane, washed with deionized water, was fixed in a custom-designed interfacial polymerization reactor, exposing only the upper surface. A 0.05% (w / v) surfactant SDS solution was poured into the reactor and allowed to stand for 10 min. The solution was then discarded, and a 1.00% (w / v) PIP solution was added and allowed to stand for 2 min. After discarding the solution, air bubbles and small droplets on the surface were removed with a rubber roller to prevent affecting the structural and functional integrity of the nanofiltration membrane's selective layer. Then, a 0.10% (w / v) TMC organic solution was slowly added, and the reaction time was 100 s. After the reaction was completed, the prepared membrane was placed in an oven at 80°C for 10 min to promote the cross-linking and curing of the polymer on the membrane surface. After the cross-linking and curing were completed, the nanofiltration membrane PA / PES was obtained.

[0053] The preparation process of nanofiltration membrane PSA / PES is similar to that of membrane PA / PES. During preparation, 0.05% (w / v) SDS solution, 1.50% (w / v) polyethyleneimine (PEI) solution, and 0.10% (w / v) 1,3-benzenedisulfonyl chloride (BDSC) solution are sequentially placed on the upper surface of the substrate membrane and allowed to stand. The standing time for SDS solution is 10 min, the standing time for PEI solution is 10 min, and the standing time for BDSC solution is 7 min. All other conditions are the same as those for the preparation process of PA / PES.

[0054] Preparation of nanofiltration membrane PSA-MOF / PES: Other conditions were the same as those for PSA / PES preparation, except that 0.01% (w / v) of the metal-organic framework MIL-101 (Cr) was added to the organic phase. The prepared membrane was cooled, washed multiple times, and then placed in deionized water for later use.

[0055] (3) Characterization of nanofiltration membranes

[0056] The chemical elements on the membrane surface were characterized by X-ray photoelectron spectroscopy. Figure 5 In the diagram, 'a' represents the X-ray photoelectron spectroscopy (XPS) spectrum of polyamide nanofiltration membrane, polysulfonamide nanofiltration membrane, and polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane. (Example:) Figure 5As shown in Figure a, PA / PES exhibits peaks at 283.88 eV, 398.78 eV, and 531.08 eV, corresponding to C1s, N1s, and O1s, respectively, indicating the presence of amide bonds on the PA / PES surface. In contrast, both PSA / PES and PSA-MOF / PES show an S2p peak at 167.48 eV, indicating the presence of sulfonamide bonds on their surfaces. Compared to PSA / PES, which also contains sulfonamide bonds, PSA-MOF / PES shows a smaller Cr2p peak at 575.38 eV, demonstrating the successful introduction of the metal-organic framework MIL-101(Cr) into the selective layer formed by interfacial polymerization.

[0057] The functional groups on the membrane surface were characterized by Fourier transform infrared spectroscopy (FTIR). Figure 5 In the image, 'b' represents the Fourier transform infrared spectrum of the polyamide nanofiltration membrane, the polysulfonamide nanofiltration membrane, and the polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane; for example... Figure 5 As shown in Figure b, PA / PES at 853 cm⁻¹ -1 and 1630cm -1 The presence of infrared absorption peaks at 1670 cm⁻¹, representing carbon-chlorine single bonds (C-Cl) and carbon-oxygen double bonds (C=O), indicates the formation of polyamide (PA) structures on the PA / PES membrane surface. Both PSA / PES and PSA-MOF / PES membranes show absorption peaks at 1670 cm⁻¹. -1 The appearance of an infrared absorption peak belonging to a sulfur-oxygen double bond (S=O) indicates the formation of a sulfonamide structure (PSA) on the surface. This is consistent with the XPS spectrum, indicating that the IP reaction was successfully carried out on the film surface and that MIL-101(Cr) is present in the selective layer of the PSA.

[0058] (4) Surface morphology observation

[0059] PA / PES is prepared by interfacial polymerization (IP) of piperazine (PIP) in the aqueous phase and 1,3,5-benzenetricarboxyl chloride (TMC) in the organic phase on the polyethersulfone surface. PSA / PES is prepared by interfacial polymerization of polyethyleneimine (PEI) in the aqueous phase and 1,3-benzenedisulfonyl chloride (BDSC) in the organic phase on the polyethersulfone surface. PSA-MOF / PES is further prepared by adding MIL-101 (Cr) to the organic phase. The metal-organic framework regulates the interfacial polymerization process and participates in the construction of the selective layer.

[0060] The surface morphology of the film was observed using a scanning electron microscope (SEM). Figures 6-9 The images are scanning electron microscope (SEM) images of a polyethersulfone ultrafiltration substrate membrane, a polyamide nanofiltration membrane, a polysulfonamide nanofiltration membrane, and a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane, respectively. The scale bar is 100 nm for each membrane. Figures 6-9 As shown, the PES substrate membrane exhibits a large and relatively uniform pore size, indicating that the ultrafiltration-grade substrate membrane has good flatness. In contrast, a very dense selective layer forms on the PA / PES surface, but the selective layer is uneven with many irregular protrusions, indicating that the interfacial polymerization process of PIP and TMC on the substrate membrane surface is very vigorous and the reaction rate is very fast. PSA / PES forms an even denser selective layer on its surface, and the selective layer surface is smoother, indicating that the interfacial polymerization process of PEI and BDSC is more moderate and the reaction rate is relatively slow, which corresponds to the set reaction time (100s for polyamide and 7min for polysulfonamide). PSA-MOF / PES forms a similarly dense and smooth selective layer on its surface, and the complete structure of MIL-101(Cr) can be observed, indicating that the dispersed metal-organic framework in the organic phase participates in the interfacial polymerization process.

[0061] (5) Surface roughness test

[0062] The surface roughness of nanofiltration membranes was characterized using atomic force microscopy (AFM). Figure 10 Atomic force microscopy images of a polyethersulfone ultrafiltration substrate membrane (a), a polyamide nanofiltration membrane (b), a polysulfonamide nanofiltration membrane (c), and a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane (d). Figure 10 As shown, the roughness Ra of PES is 1.64 nm, indicating a relatively smooth substrate film. In contrast, PA / PES has an Ra of 13.9 nm, with significant surface undulations and a roughness much greater than the substrate film, likely due to a faster interfacial polymerization rate. PSA / PES has an Ra of 1.25 nm, indicating smooth interfacial polymerization and a very uniform polymer distribution in the selective layer. PSA-MOF / PES has an Ra of 0.986 nm, which may be because MOF modulates the interfacial polymerization process, further reducing the reaction rate and automatically filling defects in the selective layer, resulting in PSA-MOF / PES exhibiting the highest smoothness.

[0063] (6) Hydrophilicity test

[0064] The hydrophilicity or hydrophobicity of nanofiltration membranes is characterized by water contact angle (WCA). Figure 11 Images showing the water contact angles of a polyethersulfone ultrafiltration substrate membrane (a), a polyamide nanofiltration membrane (b), a polysulfonamide nanofiltration membrane (c), and a polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane (d). Figure 11As shown, the water contact angles of PES, PA / PES, PSA / PES, and PSA-MOF / PES are 39.3°, 50.0°, 66.3°, and 43.0°, respectively. Compared with the base membrane PES, PA / PES exhibits poorer hydrophilicity, which may be due to the larger roughness of PA / PES (13.9 nm vs. 1.64 nm), reducing the contact area between the membrane surface and water. PSA / PES, despite having a smaller roughness, exhibits even worse hydrophilicity, possibly because both PEI and BDSC, which participate in interfacial polymerization, have non-polar structures. The PSA-MOF / PES with added metal-organic framework exhibits strong hydrophilicity. This is due to the fact that PSA-MOF / PES has the smallest roughness (0.986 nm), and MIL-101(Cr) contains polar functional groups; the combined effect results in the strong hydrophilicity of PSA-MOF / PES.

[0065] Example 2

[0066] The permeability and acid resistance of the polyamide nanofiltration membrane (PA), polysulfonamide nanofiltration membrane (PSA), and polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane (PSA-MOF) prepared in Example 1 were characterized.

[0067] Permeation flux test: Cut the membrane to a length of 4.9 cm. 2 The circular sample was placed in the dead-end filter and pre-pressurized at 0.25 MPa for 10 minutes. Then, the osmotic pressure was set to 0.2 MPa, and the stable flux after 30 minutes was taken as the pure water osmotic flux value.

[0068] Figure 12 In the figure, 'a' represents the test result of the pure water permeation flux of the nanofiltration membrane. After the metal-organic framework participates in the interfacial polymerization of polysulfonamide, it modulates the degree of polymerization of the selective layer of the nanofiltration membrane. For example... Figure 12 As shown in a, the pure water permeation flux of PSA-MOF / PES is 19.08 L·m. -2 ·h -1 The pure water permeation flux of PSA / PES is 12.39 L·m -2 ·h -1 Compared to PSA / PES, PSA-MOF / PES showed a 54% increase in pure water permeation flux. This is likely due to the presence of MIL-101(Cr) altering the polymerization rate of the polysulfonamide selective layer. Furthermore, MIL-101(Cr) creates more water channels, reduces membrane surface roughness (Ra value decreased from 1.25 nm to 0.986 nm), enhances membrane hydrophilicity (water contact angle WCA decreased from 66.3° to 43°), and improves the generally low flux of PSA-type nanofiltration membranes.

[0069] Acid resistance test: A CuSO4 solution with a concentration of 1000 ppm was prepared and filtered using a nanofiltration membrane under the pressure conditions specified in the permeation flux test. The conductivity before and after filtration (proportional to ion concentration) was measured, and the copper ion rejection rate was calculated. The nanofiltration membrane was immersed in HNO3 solution at pH 1 and temperature of 50℃ for 12 h, 24 h, 36 h, 48 h, 60 h, and 72 h, respectively. The copper ion rejection rate was then tested using the method described above to characterize the acid resistance of the nanofiltration membrane.

[0070] Figure 12 In the figure, b represents the change in the rejection rate of the nanofiltration membrane after immersion in strong acid conditions, such as... Figure 12 As shown in b, PA / PES exhibits a high rejection rate of 93.9% for CuSO4 solution at a concentration of 1000 ppm. After soaking in HNO3 solution at pH 1 and 50℃ for 12 h, the rejection rate decreases to 88.5%, to 78.3% after 24 h, to 60.1% after 36 h, and to 0% after 48 h. At this point, the polyamide selective layer of PA / PES undergoes protonation and loses its ion-retention capacity. In contrast, PSA / PES shows a rejection rate of 91.5% for CuSO4 solution. After soaking in strong acid for 72 h, the rejection rate for divalent ions decreases slightly (89.1%), demonstrating the excellent acid resistance of the polysulfonamide selective layer. The PSA-MOF / PES with added MIL-101(Cr) exhibited a divalent ion rejection rate of 86.7%, slightly lower than that of PSA / PES (91.5%). This may be due to the lower Zeta potential of PSA-MOF / PES under strongly acidic conditions, resulting in weaker electrostatic repulsion between PSA-MOF / PES and ions, thus reducing ion rejection capacity. After soaking in strongly acidic conditions for 72 hours, the rejection rate of PSA-MOF / PES still reached 85.0%, indicating its good acid tolerance.

[0071] In summary, this invention regulates the interfacial polymerization process of polysulfonamides through an easily synthesized metal-organic framework. The resulting polysulfonamide-metal-organic framework acid-resistant nanofiltration membrane exhibits excellent acid resistance and high permeation flux, solving the problem of low permeation flux in traditional polysulfonamide nanofiltration membranes, which cannot efficiently recover heavy metal ions from acidic wastewater. It has broad application prospects in the field of water treatment.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a poly-sulfonamide-metal organic framework acid-resistant nanofiltration membrane, characterized in that, The method comprises the following steps: The poly-sulfonamide-metal organic framework acid-resistant nanofiltration membrane is prepared by interfacial polymerization on the surface of a substrate film using a surfactant solution, an aqueous phase and an organic phase as raw materials; the aqueous phase is a polyethyleneimine aqueous solution; components of the organic phase include 1,3-benzenedisulfonyl chloride, metal organic framework MIL-101Cr and an organic solvent; the substrate film is a polyether sulfone ultrafiltration membrane; the concentration of 1,3-benzenedisulfonyl chloride in the organic phase is 0.05% (w / v) to 0.2% (w / v), and the concentration of metal organic framework MIL-101Cr is 0.005% (w / v) to 0.02% (w / v).

2. The production method according to claim 1, characterized by, The preparation method of the metal organic framework MIL-101Cr comprises: mixing chromium nitrate, terephthalic acid, an alkaline reagent and water to perform a hydrothermal reaction, so as to obtain the metal organic framework MIL-101Cr; the temperature of the hydrothermal reaction is 220-260 ℃, and the time is 6-12 h.

3. The production method according to claim 2, characterized by, The molar ratio of the chromium nitrate and the terephthalic acid is 1:0.8-1.5; the alkaline reagent includes one or more of sodium hydroxide, ammonium hydroxide and potassium hydroxide; the molar ratio of the alkaline reagent and the chromium nitrate is 1:0.8-1.

5.

4. The preparation method according to claim 1, characterized in that, The surfactant includes one or more of a cationic surfactant and an anionic surfactant; the concentration of the surfactant solution is 0.01% (w / v) to 0.1% (w / v).

5. The preparation method according to claim 1, characterized in that, The concentration of the polyethyleneimine aqueous solution is 0.5% (w / v) to 2% (w / v); the organic solvent includes one or more of n-hexane, toluene, dichloromethane and ethyl acetate.

6. The method of claim 1, wherein, The interfacial polymerization method comprises: sequentially immersing the upper surface of the substrate film with the surfactant solution, the aqueous phase and the organic phase, heating the immersed substrate film to perform cross-linking and solidification, and obtaining the poly-sulfonamide-metal organic framework selective layer on the upper surface of the substrate film.

7. The production method according to claim 6, characterized by, The immersion time of the surfactant solution is 5-12 min, the immersion time of the aqueous phase is 8-15 min, and the immersion time of the organic phase is 5-10 min.

8. The preparation method according to claim 6, characterized in that, The temperature of the cross-linking and solidification is 60-90 ℃, and the time is 5-15 min.

9. The poly-sulfonamide-metal organic framework acid-resistant nanofiltration membrane prepared by the preparation method of any one of claims 1-8, comprising a substrate film and a poly-sulfonamide-metal organic framework selective layer arranged on the upper surface of the substrate film; the substrate film is a polyether sulfone ultrafiltration membrane; and the poly-sulfonamide-metal organic framework selective layer comprises a poly-sulfonamide layer and metal organic framework MIL-101Cr dispersed in the poly-sulfonamide layer.

10. Application of the poly-sulfonamide-metal organic framework acid-resistant nanofiltration membrane of claim 9 in water treatment.

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