Preparation and application of GO-ZnO / PNIPAM temperature intelligent response nanofiltration membrane with self-cleaning capability

Abstract

The invention belongs to the field of membrane sewage treatment of graphene oxide-based nanofiltration membranes, and particularly relates to preparation and application of a GO-ZnO / PNIPAM temperature intelligent response nanofiltration membrane with self-cleaning capacity. By integrating the temperature response material PNIPAM and the photocatalytic material ZnO, the synergistic effect of dynamic adjustment and self-cleaning functions of the membrane layer spacing is achieved, the water flux of the membrane at the critical temperature of 32 DEG C is remarkably improved, the rejection rate of the membrane to various dyes and inorganic salts exceeds 90%, the maximum degradation recovery rate of pollutants under ultraviolet light reaches 98.88%, and the membrane has a good application prospect. The composite nanofiltration membrane has the characteristics of efficient separation, intelligent regulation and environmental protection, and is obviously superior to a traditional GO membrane in the aspects of interception performance, pollution resistance and applicability, and an efficient, intelligent and low-maintenance-cost solution is provided for industrial wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to the field of graphene oxide-based nanofiltration membrane wastewater treatment, and specifically relates to the preparation and application of a GO-ZnO / PNIPAM temperature-intelligent response nanofiltration membrane with self-cleaning ability. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Graphene oxide (GO) has attracted considerable attention in water purification research due to its two-dimensional nanosheet structure, high surface area, and rich chemical functional groups (epoxy, hydroxyl, carboxyl, and carbonyl groups). However, conventional GO-based nanofiltration membranes are limited in their application due to issues such as fixed interlayer spacing, easy surface fouling, and poor permeability and retention.

[0004] In the existing technology, single GO membranes lack the ability to dynamically adjust pore size, and the cleaning cost caused by membrane fouling is high. Although pollution can be alleviated through physical cleaning, chemical solvents, blending modification and surface modification, there are still defects such as high energy consumption and complex processes. Although photocatalytic technology is environmentally friendly, the integration effect of simple photocatalytic materials and membranes is limited, and it is impossible to achieve efficient retention and self-cleaning functions at the same time. In addition, the static hydrophilic and hydrophobic properties of traditional membrane materials limit their adaptability in different temperature environments. Therefore, there is an urgent need for a composite nanofiltration membrane with both intelligent response and self-cleaning capabilities. Summary of the Invention

[0005] To address these issues, the present invention aims to provide the preparation and application of a GO-ZnO / PNIPAM temperature-responsive nanofiltration membrane with self-cleaning capabilities. By incorporating the temperature-responsive polymer polyisopropylacrylamide (PNIPAM) and combining it with the photocatalytic and mechanically reinforcing properties of GO-ZnO, this novel ternary composite nanofiltration membrane achieves adjustable water flux, multiple antifouling mechanisms, and synergistic photocatalytic self-cleaning.

[0006] Specifically, the present invention provides the following technical solutions: In a first aspect of the present invention, a GO-ZnO / PNIPAM temperature-smart responsive nanofiltration membrane with self-cleaning capability is provided, wherein the GO-ZnO / PNIPAM temperature-smart responsive nanofiltration membrane comprises: A layered matrix composed of graphene oxide nanosheets; a graphene oxide-zinc oxide composite material uniformly embedded between the graphene oxide layers; a polyisopropylacrylamide temperature-responsive polymer distributed between the graphene oxide layers and on the surface; The graphene oxide-zinc oxide composite material is obtained by in-situ crystal growth of zinc oxide nanorods and graphene oxide; the mass ratio of zinc oxide to graphene oxide is 10:1 to 13:1; The volume ratio of the polyisopropylacrylamide to the graphene oxide-zinc oxide composite material is 1:3 to 3:1.

[0007] Preferably, the mass ratio of the zinc oxide nanorods to graphene oxide is 13:1, and the volume ratio of the polyisopropylacrylamide to the graphene oxide-zinc oxide composite is 2:1. A ratio that is too high (e.g., 1:4) results in an excess of PNIPAM, potentially blocking interlayer channels in the GO. A ratio that is too low (e.g., 5:1 or 4:1) results in insufficient PNIPAM, a weak temperature response, and a low level of photocatalytic components, impairing self-cleaning ability.

[0008] Preferably, the zinc oxide nanorods have a length of 50 to 200 nm and a diameter of 10 to 30 nm, and are uniformly dispersed between graphene oxide layers by physical intercalation.

[0009] Preferably, the surface roughness of the graphene oxide composite nanofiltration membrane is Ra≤42, and the quadratic mean square average value of the profile height is Rq≤51.6.

[0010] Preferably, at a temperature lower than the critical solution temperature of polyisopropylacrylamide (PIA) of 32°C, the water contact angle of the graphene oxide composite nanofiltration membrane is 34.13-64.35, and the water flux is 20.87-24.47. ; When the temperature is higher than 32°C, the water contact angle is 40.28~82.43°, and the water flux is 48.61~55.18 .

[0011] Preferably, the graphene oxide composite nanofiltration membrane has a retention rate of ≥81% for rhodamine B, Congo red, methylene blue, and Evans blue, and a retention rate of 74.69% to 77.82% for sodium nitrite.

[0012] Preferably, after the graphene oxide composite nanofiltration membrane is treated with ultraviolet light catalytic self-cleaning, the maximum water flux recovery rate is 56.17% to 98.88%.

[0013] A second aspect of the present invention provides a method for preparing the above-mentioned GO-ZnO / PNIPAM temperature-smart responsive nanofiltration membrane with self-cleaning ability, comprising the following steps: S1, mixing a zinc chloride solution and an ultrasonically exfoliated graphene oxide solution, adding a sodium hydroxide solution dropwise thereto after ultrasonic treatment, and allowing the mixture to react, filtering, washing, and drying to obtain a graphene oxide-zinc oxide (GO-ZnO) composite material; S2, mixing N-isopropylacrylamide monomer, azobisisobutyronitrile initiator and benzene solution, and conducting reflux reaction in a water bath. After removing benzene from the reflux product, the product is dissolved in acetone, and then dropped into n-hexane to precipitate the polymer, thereby obtaining polyisopropylacrylamide temperature-responsive polymer (PNIPAM); S3. Dispersing the graphene oxide-zinc oxide composite material in the graphene oxide solution, ultrasonically treating the solution and then keeping it warm to obtain a physically intercalated GO-ZnO solution, which is then mixed with a polyisopropylacrylamide temperature-responsive polymer solution, ultrasonically forming a composite membrane precursor solution, and finally filtering and drying the solution to form a membrane.

[0014] Preferably, in step S1, the concentration of the graphene oxide solution after ultrasonic exfoliation is 0.2-0.3 mg / mL, the concentration of the zinc chloride solution is 0.035-0.045 M, and the concentration of the sodium hydroxide is 0.02-0.03 M.

[0015] Further preferably, the concentration of the graphene oxide solution after ultrasonic exfoliation is 0.25 mg / mL, the concentration of the zinc chloride solution is 0.04 M, and the concentration of the sodium hydroxide is 0.0267 M.

[0016] Preferably, in step S1, the ultrasonic treatment time is 20-40 min; the static reaction temperature is 60-90° C., and the time is 5-10 h.

[0017] Preferably, in step S2, the usage ratio of the N-isopropylacrylamide monomer, azobisisobutyronitrile initiator and benzene solution is (3-4) g:(0.05-0.06) g:(15-25) mL, preferably 4 g:0.058 g:20 mL.

[0018] Preferably, in step S2, the temperature of the water bath reflux is 60-70° C., and the time is 8-12 hours.

[0019] Preferably, in step S3, the concentration of the graphene oxide solution is 0.2-0.3 mg / mL, preferably 0.25 mg / mL; the ultrasonic treatment time is 2.5-3.5 h, and the insulation temperature is 60-70° C. for 1-2 h.

[0020] Preferably, in step S3, the concentration of the polyisopropylacrylamide temperature-responsive polymer solution is 0.2-0.3 mg / mL, preferably 0.25 mg / mL.

[0021] Preferably, in step S3, the composite membrane precursor solution is loaded onto a cellulose acetate base membrane with a pore size of 0.2-0.25 μm by vacuum filtration, and then naturally dried to form a membrane.

[0022] The third aspect of the present invention provides an application of the GO-ZnO / PNIPAM temperature-smart response nanofiltration membrane with self-cleaning ability described in the first aspect in the purification or treatment of industrial wastewater.

[0023] One or more embodiments of the present invention have at least the following beneficial effects: (1) The present invention introduces GO-ZnO and PNIPAM into the GO nanofiltration membrane for innovative design, realizing a design strategy of synergistic dual functions of nanofiltration membrane temperature response and self-cleaning, and providing an innovative solution for the development of efficient and energy-saving sustainable water treatment technology.

[0024] (2) The temperature-responsive self-cleaning nanofiltration membrane designed in the present invention solves the pain points of traditional membrane technology, such as high energy consumption, single selectivity, and frequent maintenance, through the three core advantages of physical component response (temperature drive), dynamic function switching (separation / cleaning mode), and significantly extended life (mechanical-chemical synergistic anti-fouling). It realizes the step-by-step separation of dye / salt and the dual cleaning of "physical stripping + chemical degradation" of a single membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0026] Figure 1 This is a scanning electron microscope (SEM) image of the graphene oxide-zinc oxide / polyisopropylacrylamide smart responsive nanofiltration membrane prepared in Example 1 of the present invention; Figure 2 This is an X-ray photoelectron spectroscopy (XPS) graph of the graphene oxide-zinc oxide / polyisopropylacrylamide smart responsive nanofiltration membrane prepared in an embodiment of the present invention; Figure 3 This is a water flux test diagram of sample membranes of different proportions prepared in an embodiment of the present invention at different temperatures; Figure 4 This is a dye retention test chart of sample membranes with different ratios prepared in an embodiment of the present invention; Figure 5 This is a test chart of inorganic salt rejection of sample membranes with different ratios prepared in accordance with an embodiment of the present invention; Figure 6 This is a self-cleaning water flux recovery test chart of sample membranes of different proportions prepared in an embodiment of the present invention at different temperatures. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0028] The protection scheme of the present invention is described below by specific examples. It should be noted that these examples are only used to facilitate the understanding of those skilled in the art and should not be regarded as limiting the scope of protection of the present invention. Unless otherwise stated, the reagents used in the examples can be obtained commercially.

[0029] Example 1 :This embodiment provides a graphene oxide-zinc oxide / polyisopropylacrylamide smart response nanofiltration membrane and its preparation method (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0030] (2) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the amount of monomer. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in a vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0031] (3) Preparation of GO-ZnO / PNIPAM temperature-responsive smart nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The mixture was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. A 0.25 mg / mL PNIPAM solution was prepared, and the GO-ZnO solution and PNIPAM solution were mixed in a volume ratio of 2:1 to obtain 6 mL of composite membrane precursor solution, which was ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0032] like Figure 1 Figure 2 shows a scanning electron microscope (SEM) image of the graphene oxide-zinc oxide / polyisopropylacrylamide smart responsive nanofiltration membrane prepared in this example. As can be seen from the image, the membrane surface is highly undulating and has numerous wrinkles, providing transmission channels for the rapid passage of water molecules.

[0033] like Figure 1 As shown in the figure, it is the X-ray photoelectron spectroscopy (XPS) of the graphene oxide-zinc oxide / polyisopropylacrylamide smart response nanofiltration membrane prepared in this embodiment, in which 、 and The peak positions and peak intensity ratios of the peaks can be used to determine the presence of zinc oxide. The O1s and C1s peaks indicate the presence of oxygen and carbon in the sample, confirming the presence of graphene oxide. The presence of the N1s peak indicates the presence of nitrogen. Nitrogen originates from PNIPAM (poly (N-isopropylacrylamide)). The image shows Zn-O, C-C, C-H, C-O, C=O, and N-C bonds, demonstrating the GO-ZnO / PNIPAM composite structure.

[0034] Example 2 :This embodiment provides a graphene oxide-zinc oxide / polyisopropylacrylamide smart response nanofiltration membrane and its preparation method (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0035] (2) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the amount of monomer. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in a vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0036] (3) Preparation of GO-ZnO / PNIPAM temperature-responsive smart nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The membrane was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. A 0.25 mg / mL PNIPAM solution was prepared, and the GO-ZnO solution and PNIPAM solution were mixed in a volume ratio of 3:1 to obtain 6 mL of composite membrane precursor solution, which was ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0037] Example 3 :This embodiment provides a graphene oxide-zinc oxide / polyisopropylacrylamide smart response nanofiltration membrane and its preparation method (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0038] (2) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the amount of monomer. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in a vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0039] (3) Preparation of GO-ZnO / PNIPAM temperature-responsive smart nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The membrane was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. A 0.25 mg / mL PNIPAM solution was prepared, and the GO-ZnO solution and PNIPAM solution were mixed in a volume ratio of 1:1 to obtain 6 mL of composite membrane precursor solution, which was ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0040] Example 4 :This embodiment provides a graphene oxide-zinc oxide / polyisopropylacrylamide smart response nanofiltration membrane and its preparation method (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0041] (2) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the amount of monomer. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in a vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0042] (3) Preparation of GO-ZnO / PNIPAM temperature-responsive smart nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The mixture was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. A 0.25 mg / mL PNIPAM solution was prepared, and the GO-ZnO solution and PNIPAM solution were mixed in a volume ratio of 1:2 to obtain 6 mL of composite membrane precursor solution, which was ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0043] Example 5 :This embodiment provides a graphene oxide-zinc oxide / polyisopropylacrylamide smart response nanofiltration membrane and its preparation method (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0044] (2) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the amount of monomer. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in a vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0045] (3) Preparation of GO-ZnO / PNIPAM temperature-responsive smart nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The membrane was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. A 0.25 mg / mL PNIPAM solution was prepared, and the GO-ZnO solution and PNIPAM solution were mixed in a volume ratio of 1:3 to obtain 6 mL of composite membrane precursor solution, which was ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0046] Comparative Example 1 This comparative example provides a composite nanofiltration membrane and a preparation method thereof The difference between this comparative example and Example 1 is that this comparative example does not carry out the preparation of step (1), and only involves the preparation of a composite film of the temperature-responsive polymer PNIPAM and the graphene oxide solution. The specific preparation process is as follows: (1) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the monomer amount. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0047] (2) Preparation of GO-PNIPAM temperature-responsive nanofiltration membrane: A 0.25 mg / mL PNIPAM solution was prepared. The GO solution and PNIPAM solution were mixed in a ratio of 1:1 to obtain 6 mL of composite membrane precursor solution, which was then ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to form a membrane.

[0048] Comparative Example 2 This comparative example provides a composite nanofiltration membrane and a preparation method thereof The difference between this comparative example and Example 1 is that this comparative example does not carry out the preparation of step (2), but only involves the physical intercalation of graphene oxide into the photocatalytic composite material GO-ZnO, and then the preparation of the composite film. The specific preparation process is as follows: (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0049] (2) Preparation of GO-ZnO temperature-responsive nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The mixture was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. 6 mL of the physically intercalated GO-ZnO solution was used as a composite membrane precursor and ultrasonically treated for 1 h. The precursor was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0050] Comparative Example 3 : (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0051] (2) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the amount of monomer. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in a vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0052] (3) Preparation of GO-ZnO / PNIPAM temperature-responsive smart nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The mixture was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. A 0.25 mg / mL PNIPAM solution was prepared, and the GO-ZnO solution and PNIPAM solution were mixed at a volume ratio of 1:4 to obtain 6 mL of composite membrane precursor solution, which was ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0053] Comparative Example 4 : (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0054] (2) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the amount of monomer. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in a vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0055] (3) Preparation of GO-ZnO / PNIPAM temperature-responsive smart nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The membrane was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. A 0.25 mg / mL PNIPAM solution was prepared, and the GO-ZnO solution and PNIPAM solution were mixed in a volume ratio of 4:1 to obtain 6 mL of composite membrane precursor solution, which was ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0056] Comparative Example 5 : (1) Preparation of photocatalytic composite material GO-ZnO: 50 mg GO was dispersed in 200 mL pure water, 33.3 mL was taken and then ultrasonicated for 60 minutes to prepare a GO solution with a concentration of 0.25 mg / mL. Subsequently, 33.34 mL 0.04 M ZnCl2 was added dropwise to the GO solution and ultrasonicated continuously for 30 minutes to produce a uniform solution. 0.0267 M NaOH solution was added dropwise to the solution under vigorous stirring. The mixture was sealed in a glass bottle (60 mL), allowed to stand at 90 ° C for 6 h, and then naturally cooled to room temperature. Finally, the composite material was filtered, washed several times with distilled water and ethanol, and dried at 80 ° C for 24 hours.

[0057] (2) Preparation of temperature-responsive polymer PNIPAM: 4 g of N-isopropylacrylamide monomer was weighed and placed in a 100 mL three-necked flask. 0.058 g of azobisisobutyronitrile (AIBN) and 20 mL of benzene were added, equivalent to 1% of the amount of monomer. The mixture was refluxed in a constant temperature water bath at 65°C for 10 h under nitrogen protection. The refluxed product was evaporated in a constant temperature water bath at 90°C to remove benzene and dissolved in 50 mL of acetone. The product was then added dropwise to n-hexane. After the reaction was completed, it was filtered and dried in a vacuum at 30°C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid.

[0058] (3) Preparation of GO-ZnO / PNIPAM temperature-responsive smart nanofiltration membrane: 25 mg of the prepared GO-ZnO was weighed and dispersed in 100 mL of 0.25 mg / mL GO solution and ultrasonically treated for 3 h. The solution was then placed in a 65°C incubator for 1.5 h to obtain a physically intercalated GO-ZnO solution. A 0.25 mg / mL PNIPAM solution was prepared, and the GO-ZnO solution and PNIPAM solution were mixed in a volume ratio of 5:1 to obtain 6 mL of composite membrane precursor solution, which was ultrasonically treated for 1 h. The precursor solution was filtered onto a cellulose acetate base membrane with a pore size of 0.22 μm using a vacuum filtration device at a pressure of 1 bar. After filtration, the membrane was naturally dried to obtain the membrane.

[0059] Comparative Example 6 : Disperse 50 mg of GO in 200 mL of pure water and sonicate for 60 minutes to prepare a 0.25 mg / mL GO solution. Sonicate 6 mL of the solution for 1 hour. Use a vacuum filtration device at 1 bar to filter the precursor solution onto a cellulose acetate base membrane with a pore size of 0.22 μm. Allow the membrane to dry naturally after filtration.

[0060] Experimental Example 1 :This experimental example measured the contact angle of the composite nanofiltration membrane prepared by graphene oxide, Examples 1 to 5 and Comparative Examples 1 to 6 The contact angle test shows that the composite nanofiltration membrane prepared in the embodiment of the present invention exhibits a more hydrophilic property when the critical solution temperature of polyisopropylacrylamide is below 32°C; when the critical solution temperature of polyisopropylacrylamide is above 32°C, the surface wettability of the nanofiltration membrane changes to a hydrophobic direction. The specific values are shown in Table 1: Table 1

[0061] Analysis of the data in Table 1 shows that the filtration membrane prepared in Example 1 of the present application exhibits the most superior hydrophilic properties, achieving temperature responsiveness, thereby achieving changes in surface contact angle and, consequently, water flux. While Examples 2-5 exhibited changes in contact angle, their performance was inferior. Comparative Examples 1-6 showed no change in contact angle.

[0062] Test Example 1 :This test example tests the water flux of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Examples 1 to 6 The water flux of the membrane was tested by filtering deionized water under a vacuum of 1 bar. ) is determined by the formula J=V / (A×t×P).

[0063] The results are as follows Figure 3 As shown in the water flux test pictures of nanofiltration membranes with different ratios at different temperatures, it can be seen that as the temperature increases, the water flux of the nanofiltration membrane increases. This is because the molecular chain of the temperature-responsive material polyisopropylacrylamide shrinks as the temperature increases, resulting in larger gaps. The specific values are shown in Table 2: Table 2

[0064] Analysis of the data in Table 2 shows that the water flux performance of the filtration membrane prepared in Example 1 of the present application is the most superior. Although Examples 2 to 5 show a trend of water flux changing with temperature, the water flux performance is relatively poor. This is because when the volume ratio of GO-ZnO solution to PNIPAM solution is 2:1 in Example 1, the synergistic effect of PNIPAM molecular chain contraction and GO interlayer spacing is optimal, achieving efficient dynamic flux regulation. The water flux performance of Comparative Example 1 is poor, and there is no obvious water flux increase caused by temperature response. This may be because the PNIPAM molecules are firmly fixed and the molecular chain changes under temperature response cannot be achieved, thus unable to achieve changes in water flux; the water flux of Comparative Example 2 is equivalent to that of Comparative Example 1, and there is no temperature response function; the water flux performance of Comparative Example 6 is poor, and there is no temperature response change.

[0065] Comparative Example 3 had the worst water flux performance and could not achieve efficient nanofiltration. This was because when GO-ZnO was excessive, zinc oxide nanorods (50-200 nm) over-accumulated between GO layers, forming a dense and rigid skeleton. This resulted in: PNIPAM molecules being difficult to fully embed between layers, unable to dynamically adjust the channel size through chain segment contraction / extension, and nanorods occupying the transport path of water molecules, increasing mass transfer resistance; Although Comparative Examples 4 and 5 have a certain temperature response effect, the water flux data is poor. This is because when PNIPAM is excessive, the polymer molecular chains are over-filled between the GO layers and on the surface, resulting in the interlayer channels being blocked by the polymer, and the polymers are entangled with each other, resulting in the inability to effectively expand the pore size during high-temperature shrinkage, affecting the water flux.

[0066] Test Example 2 :This test example tests the membrane retention performance of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Examples 1 to 6 (1) The membrane retention performance was tested using a 20 ppm organic dye solution. According to the Beer-Lambert law, the concentration of the dye solution is proportional to its UV-visible absorbance. The permeate was collected and analyzed using UV-vis absorption spectroscopy (PerkinElmer, Lambda 750 S, USA) to calculate the retention performance. The retention rate (R) was calculated by the formula R = (1-C P / C f )×100% confirmed.

[0067] (2) To verify the inorganic salt retention capacity of the GO-ZnO-PNIPAM nanofiltration membrane, a 0.75 mg / mL sodium nitrite solution was used for retention performance testing. According to the Beer-Lambert law, the concentration of the dye solution is proportional to its UV-visible absorbance. The permeate was collected and analyzed using UV-vis absorption spectroscopy (PerkinElmer, Lambda 750 S, USA) to calculate the retention performance. The retention rate (R) was determined by the formula R = (1-CP / Cf) × 100%.

[0068] The specific test data are shown in Table 3: Table 3

[0069] The results are shown in Table 3 and Figure 4 As shown in the figure, the dye retention test pictures of nanofiltration membranes with different ratios show that when the ratio is 2:1, the dye retention performance of the nanofiltration membrane is greatly improved. The retention rates of the four dyes RB, CR, MB, and EB are all over 90%, and the retention rate of MO is 4.5 times higher than that of GO membrane.

[0070] The dye retention performance of Comparative Examples 1 and 2 is relatively poor, and the dye cannot be effectively retained; the retention rate of Comparative Example 6 is poor, and only some dyes can meet the nanofiltration standard; The dye retention of Comparative Example 3 was poor. It had a certain dye retention capacity but could not meet the nanofiltration membrane standard. This was because the GO-ZnO was excessive but not effectively dispersed by PNIPAM, resulting in the agglomeration of ZnO nanorods, thereby reducing the effective catalytic sites and affecting the photocatalytic efficiency. The dye retention performance of Comparative Examples 4 and 5 is very poor and cannot meet the nanofiltration membrane standard. This is because the excessive PNIPAM covers the active adsorption sites of GO-ZnO (such as oxygen-containing functional groups and ZnO catalytic sites), which leads to a sharp drop in the dye retention rate. In addition, polymer blockage causes uneven distribution of membrane pores and loss of molecular sieving selectivity.

[0071] Therefore, Comparative Examples 1, 2, 3, 4, and 5 can neither achieve the temperature response function nor achieve effective retention of dye molecules.

[0072] The results are shown in Table 3 and Figure 5 As shown in the figure, the inorganic salt retention test pictures of nanofiltration membranes with different proportions show that compared with traditional graphene oxide nanofiltration membranes, the GO-ZnO / PNIPAM temperature intelligent response nanofiltration membrane has greatly improved the retention performance of inorganic salts. Example 1 has good inorganic salt retention performance and can achieve the treatment capacity of industrial inorganic salt wastewater. Comparative Examples 1 and 2 have the worst inorganic salt retention performance and cannot effectively retain inorganic salts. The inorganic salt retention of Comparative Examples 3 and 6 is poor and cannot meet the nanofiltration membrane standard. The retention capacity of Comparative Examples 4 and 5 is very poor, which is due to the polymer covering the catalytic sites. The photocatalysis cannot be triggered, and the retention of inorganic salts cannot be achieved, and the industrial wastewater treatment effect cannot be achieved.

[0073] Test Example 3 :This test example tests the self-cleaning performance of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Examples 1 to 6 The water flux was tested after vacuum filtration of 20 ppm of RB, CR, MB, EB, and MO dyes at 1 bar pressure for 30 minutes. The nanofiltration membrane was then placed under a UV lamp with a wavelength of 385 nm for 1 hour to test the water flux. The self-cleaning performance of the membrane was analyzed by the recovery rate of the water flux. The recovery rate is calculated by the formula FRR=J C / J O ×100% confirmed, the specific test data are shown in Tables 4 to 6 (Tables 4 to 6 were tested under 25, 32, and 35°C conditions respectively): Table 4

[0074] Table 5

[0075] Table 6

[0076] The results are shown in Tables 4 to 6 and Figure 6 As shown in the figure, the self-cleaning water flux recovery test images of nanofiltration membranes with different ratios at different temperatures show the highest water flux recovery rates of 91.06%, 89.34%, 98.88%, 74.61%, and 56.17%. All recovery rates show an upward trend with increasing ambient temperature and the ratio of the photocatalytic component GO-ZnO.

[0077] The nanofiltration membrane prepared in Example 1 had the best self-cleaning performance, and Examples 2 to 5 had relatively good self-cleaning performance. Comparative Examples 1 and 2 had the worst self-cleaning performance, failing to degrade pollutants and extending the membrane's service life. Comparative Example 1 lacked the GO-ZnO composite material, and the membrane lacked photocatalytic active sites (ZnO). Consequently, it could not generate reactive oxygen free radicals under UV irradiation, preventing pollutant degradation. While Comparative Example 2 had photocatalytic activity provided by GO-ZnO, it lacked the physical exfoliation synergy of PNIPAM, resulting in the inability of attached pollutants to detach from the catalytic sites through chain contraction. The self-cleaning performance of Comparative Example 3 is poor, and it is judged that the self-cleaning ability is poor. Its insufficient PNIPAM content leads to discontinuous molecular chain network, which cannot drive the dynamic change of interlayer spacing. In addition, excessive ZnO nanorods will accumulate excessively between GO layers, resulting in ZnO nanorods blocking the mass transfer path and ZnO agglomeration, reducing the effective catalytic area. The self-cleaning performance of Comparative Examples 4 and 5 is slightly reduced, which is due to the excessive PNIPAM wrapping of ZnO nanorods, which hinders the penetration of ultraviolet light and the contact of pollutants with catalytic sites, resulting in the lowest self-cleaning recovery rate.

[0078] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A GO-ZnO / PNIPAM temperature-sensitive nanofiltration membrane with self-cleaning capability, characterized in that: The GO-ZnO / PNIPAM temperature intelligent response nanofiltration membrane includes: A layered matrix composed of graphene oxide nanosheets; a graphene oxide-zinc oxide composite material uniformly embedded between the graphene oxide layers; a polyisopropylacrylamide temperature-responsive polymer distributed between the graphene oxide layers and on the surface; The graphene oxide-zinc oxide composite material is obtained by in-situ crystal growth of zinc oxide nanorods and graphene oxide; the mass ratio of the zinc oxide nanorods to the graphene oxide is 10:1 to 13:1; The volume ratio of the polyisopropylacrylamide to the graphene oxide-zinc oxide composite material is 1:3 to 3:

1.

2. The GO-ZnO / PNIPAM temperature-smart responsive nanofiltration membrane according to claim 1, characterized in that: The mass ratio of zinc oxide nanorods to graphene oxide is 13:1; the volume ratio of polyisopropylacrylamide to graphene oxide-zinc oxide composite material is 2:1; Preferably, the zinc oxide nanorods have a length of 50 to 200 nm and a diameter of 10 to 30 nm, and are uniformly dispersed between graphene oxide layers by physical intercalation.

3. The GO-ZnO / PNIPAM temperature-smart responsive nanofiltration membrane according to claim 1, characterized in that: The surface roughness of the graphene oxide composite nanofiltration membrane is Ra≤42, and the quadratic mean square average value of the profile height is Rq≤51.

6.

4. The GO-ZnO / PNIPAM temperature-smart responsive nanofiltration membrane according to claim 1, characterized in that: When the critical solution temperature of polyisopropylacrylamide is 32°C, the water contact angle of the graphene oxide composite nanofiltration membrane is 34.13~64.35, and the water flux is 20.87~24.47 ; When the temperature is higher than 32°C, the water contact angle is 40.28~82.43°, and the water flux is 48.61~55.18 ; Preferably, the graphene oxide composite nanofiltration membrane has a retention rate of ≥81% for rhodamine B, Congo red, methylene blue, and Evans blue, and a retention rate of 74.69% to 77.82% for sodium nitrite; Preferably, after the graphene oxide composite nanofiltration membrane is treated with ultraviolet light catalytic self-cleaning, the maximum water flux recovery rate is 56.17% to 98.88%.

5. A method for preparing the GO-ZnO / PNIPAM temperature-smart responsive nanofiltration membrane with self-cleaning ability according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, mixing a zinc chloride solution and an ultrasonically exfoliated graphene oxide solution, adding a sodium hydroxide solution dropwise thereto after ultrasonic treatment, allowing the mixture to react, filtering, washing, and drying to obtain a graphene oxide-zinc oxide composite material; S2, mixing N-isopropylacrylamide monomer, azobisisobutyronitrile initiator and benzene solution, performing reflux reaction in a water bath, evaporating the reflux product to remove benzene, dissolving it in acetone, and then dropping it into n-hexane to precipitate a polymer, thereby obtaining a polyisopropylacrylamide temperature-responsive polymer; S3. Dispersing the graphene oxide-zinc oxide composite material in the graphene oxide solution, ultrasonically treating the solution and then keeping it warm to obtain a physically intercalated GO-ZnO solution, which is then mixed with a polyisopropylacrylamide temperature-responsive polymer solution, ultrasonically forming a composite membrane precursor solution, and finally filtering and drying the solution to form a membrane.

6. The preparation method according to claim 5, wherein In step S1, the concentration of the graphene oxide solution after ultrasonic stripping is 0.2-0.3 mg / mL, the concentration of the zinc chloride solution is 0.035-0.045 M, and the concentration of the sodium hydroxide is 0.02-0.03 M; Preferably, the ultrasonic treatment time is 20-40 min; the static reaction temperature is 60-90° C., and the time is 5-10 h.

7. The preparation method according to claim 5, wherein In step S2, the amount ratio of the N-isopropylacrylamide monomer, azobisisobutyronitrile initiator and benzene solution is (3-4) g: (0.05-0.06) g: (15-25) mL, preferably 4 g: 0.058 g: 20 mL; Preferably, the water bath reflux temperature is 60-70° C., and the time is 8-12 hours.

8. The preparation method according to claim 5, wherein The concentration of the graphene oxide solution is 0.2-0.3 mg / mL, preferably 0.25 mg / mL; the ultrasonic treatment time is 2.5-3.5 h, and the insulation temperature is 60-70° C. for 1-2 h.

9. The preparation method according to claim 5, wherein In step S3, the concentration of the polyisopropylacrylamide temperature-responsive polymer solution is 0.2-0.3 mg / mL, preferably 0.25 mg / mL; Preferably, the composite membrane precursor solution is loaded onto a cellulose acetate base membrane with a pore size of 0.2-0.25 μm by vacuum filtration, and then naturally dried to form a membrane.

10. Use of the GO-ZnO / PNIPAM temperature-smart responsive nanofiltration membrane with self-cleaning ability according to any one of claims 1 to 4 in the purification or treatment of industrial wastewater.

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