Redox-responsive membrane, method for preparing the same, and use thereof

Abstract

The application discloses a kind of oxidation-reduction response films and preparation method and application thereof, it is related to membrane separation technical field.The method includes that Fc is dissolved in organic solvent, GO is added, and mixed solution A is obtained;GO and CD are added in water, and mixed solution B is obtained;After mixed solution A and mixed solution B are ultrasonic dispersion treatment, respectively under heating condition reaction, then by dialysis purification, freeze-drying treatment, respectively obtain GO-Fc and GO-CD;GO-Fc and GO-CD are dissolved in water, and they are mixed uniformly by ultrasonic dispersion, and the GO-Fc / GO-CD film, i.e. oxidation-reduction response film is prepared by vacuum assisted self-assembly method on substrate membrane and is extracted and is prepared.GO sheet layer nanometer channel size can be adjusted by changing the oxidation-reduction state of GO-Fc / GO-CD film, to realize the reversible regulation of membrane water permeability and molecular separation performance.In addition, the prepared GO-Fc / GO-CD film has excellent cycle response performance and stability, and shows wide application prospect in intelligent response gate and pollution removal separation.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a redox-responsive membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation technology plays a crucial role in numerous fields, including water purification, resource recovery, and energy extraction. However, the pore size and surface properties of traditional membranes are typically constant. When subjected to unavoidable membrane fouling, their performance deteriorates due to contaminants deposited on the pore surface and hindering membrane-solute interactions. Furthermore, the immutable pore size and surface characteristics limit the application of traditional membranes in broader fields. Therefore, for complex separation systems, smart-response membranes with tunable pore size and surface properties are more efficient and energy-saving, and hold promise for further expanding their application areas.

[0003] Compared to traditional separation membranes, smart responsive membranes possess controllable and tunable membrane permeability and selectivity due to their stimulus-responsive pore structure and surface properties. To date, a wide range of biomimetic smart responsive membranes have been developed by introducing stimulus-responsive agents into porous membrane substrates, enabling responses to various environmental stimuli, including pH, ionic strength, light, temperature, and current. When receiving stimulus signals from the external environment, these stimulus-responsive agents can alter their structure, thereby causing changes in the membrane's pore size or surface properties. The molecular chain or aggregate structure in traditional polymer membranes is advantageous for the structural design and introduction of stimulus-responsive agents. However, stimulus-responsive membranes based on traditional polymer substrates are still affected by heterogeneous pore structures and complex modification methods, resulting in lower response performance and limited application prospects.

[0004] Two-dimensional layered membranes, represented by graphene oxide (GO) membranes, have recently attracted much interest from researchers due to their unique water transport properties. Unlike the random finger-like pore structure in traditional polymer membranes, layered GO membranes possess unobstructed and uniform two-dimensional nanochannels, enabling ultra-fast, frictionless water transport and precise molecular sieving.

[0005] The abundant oxygen-containing groups on the GO surface are beneficial for the surface modification of specific functionalized polymers, which can not only effectively improve the stability of GO films but also endow them with the desired stimulus-response capabilities. Inspired by redox reactions ubiquitous in living systems and the natural environment, redox-responsive systems based on supramolecular host-guest interactions have attracted widespread attention in recent years. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a redox-responsive membrane, its preparation method, and its applications.

[0007] The specific technical solution adopted in this invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a redox-responsive membrane, specifically comprising the following steps:

[0009] S1: Dissolve the metal dicerocene compound (Fc) in an organic solvent, add graphene oxide (GO), and obtain mixture A;

[0010] S2: Add graphene oxide (GO) and cyclodextrin (CD) to water to obtain mixture B;

[0011] S3: The mixture A and mixture B are ultrasonically dispersed and then reacted under heating conditions. After dialysis purification and freeze-drying, metallolithocene-modified graphene oxide GO-Fc and cyclodextrin-modified graphene oxide GO-CD are obtained respectively.

[0012] S4: Dissolve the GO-Fc and GO-CD in water, disperse them by ultrasonication to make them evenly mixed, and prepare the GO-Fc / GO-CD membrane, i.e., the redox-responsive membrane, by vacuum-assisted self-assembly on the base membrane.

[0013] Preferably, the metallocerocene compound is one of amino-derived ferrocerocene, amino-derived manganese cerocerocene, or amino-derived cobalt cerocerocene; and the organic solvent is one of tetrahydrofuran, dimethyl ether, ethanol, or acetone.

[0014] Preferably, the cyclodextrin is one of amino-modified α-cyclodextrin, amino-modified β-cyclodextrin, or amino-modified γ-cyclodextrin.

[0015] Preferably, the mass ratio of the metallocerocene compound to graphene oxide is 1:(5-2), the mass ratio of cyclodextrin to graphene oxide is (3-1):(1-2), the mass ratio of GO-Fc to GO-CD is (1-9):(9-1), and the total mass of GO-Fc and GO-CD is 0.1-5 mg.

[0016] Preferably, the pH of the mixture B is adjusted to a range of 9-13 by adding a strong alkali, which is potassium hydroxide or sodium hydroxide.

[0017] Preferably, the ultrasonic dispersion treatment has a power of 150-300W and a time of 10-60min; the dialysis purification process uses a dialysis bag with a capacity of 8000-16000Da and a time of 4-8d, during which the pure water is replaced every 1d; the freeze-drying treatment has a temperature of (-30℃)-(-60℃) and a time of 24-48h.

[0018] Preferably, the heating conditions refer to reacting in a water bath at a temperature of 40-80°C for 24-48 hours.

[0019] Preferably, in the vacuum-assisted self-assembly method, the base membrane is one of nylon membrane, polyvinylidene fluoride membrane, polyethersulfone membrane, polypropylene membrane, mixed cellulose membrane or polytetrafluoroethylene membrane, with a pore size of 0.1-0.5 μm.

[0020] In a second aspect, the present invention provides a redox-responsive membrane obtained according to any of the preparation methods described in the first aspect.

[0021] Thirdly, the present invention provides an application of the redox-responsive membrane described in the second aspect in separating molecules of different sizes in a liquid under different redox states.

[0022] In practical applications, the separation performance can be evaluated using a terminal filtration device equipped with a nitrogen cylinder, digital balance, ultrafiltration cup, and computer. Throughout the measurement process, the transmembrane pressure is maintained at 1.0 bar. The feed solution is stirred at 500 rpm to eliminate concentration polarization effects.

[0023] To regulate the redox state of the redox-responsive membrane, the oxidation or reduction state of the membrane in solution can be changed by introducing NaClO, which has oxidizing properties, and NaHSO3, which has reducing properties. The concentrations of NaClO solution and NaHSO3 solution are preferably 0.02-0.2M.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) The size of the nanochannels between GO sheets can be adjusted by changing the redox state of the GO-Fc / GO-CD membrane, thereby achieving reversible control of the membrane's water permeability and molecular separation performance.

[0026] (2) GO-Fc / GO-CD membranes also exhibit excellent cycle reversibility and excellent stability under harsh environments;

[0027] (3) Well-designed redox-responsive membranes based on supramolecular host-guest interactions have shown great application potential in controllable molecular separation and pollutant removal. Attached Figure Description

[0028] Figure 1 It is a photo of the GO-Fc / GO-CD film.

[0029] Figure 2 These are top-view scanning electron microscope images of GO, GO-CD, GO-Fc, and GO-Fc / GO-CD films.

[0030] Figure 3 This is a cross-sectional scanning electron microscope image of the GO-Fc / GO-CD film.

[0031] Figure 4 These are the FTIR spectra of GO, GO-CD, GO-Fc, and GO-Fc / GO-CD films.

[0032] Figure 5 It refers to the dispersion and aggregation behavior of GO-Fc / GO-CD dispersions in oxidized and reduced states.

[0033] Figure 6 These are the UV-vis spectra of the GO-Fc / GO-CD dispersion in oxidized and reduced states.

[0034] Figure 7 These are the water flux and gating ratio of GO-Fc / GO-CD membranes with different mass ratios.

[0035] Figure 8 It refers to the water flux of GO, GO-CD, GO-Fc, and GO-Fc / GO-CD membranes in the oxidized and reduced states.

[0036] Figure 9 The effects of different amounts of GO-Fc and GO-CD on the water flux and gating ratio of the GO-Fc / GO-CD membrane are investigated.

[0037] Figure 10 These are the UV-Vis absorption spectra of two dye solutions (BBG(a) and EY(b)) before and after filtration through a GO-Fc / GO-CD membrane (oxidized and reduced states).

[0038] Figure 11 It is the reversibility of the redox response gating characteristics of GO-Fc / GO-CD membranes.

[0039] Figure 12 The stability of GO and GO-Fc / GO-CD membranes in deionized water (DI water), 0.1M NaClO solution and 0.1M NaHSO3 solution.

[0040] Figure 13 The diagram shows the preparation process (a) and separation application principle (b) of the GO-Fc / GO-CD membrane.

[0041] Figure 14 These are XRD patterns of the GO-Fc / GO-CD membrane under oxidized and reduced conditions. Detailed Implementation

[0042] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following content is merely illustrative and explanatory of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the inventive concept or exceed the scope defined by the claims, all of which should fall within the protection scope of the present invention.

[0043] like Figure 13 The diagram shows the preparation process (a) and separation application principle (b) of the GO-Fc / GO-CD membrane of this invention. The principle of separating molecules of different sizes in a liquid using the GO-Fc / GO-CD membrane under different redox states is as follows:

[0044] Liquids contain molecules of different sizes. By adjusting the redox state of the solution, the Fc / CD complex in the redox-responsive membrane structure can be reversibly deformed and restored during the solution filtration process. This changes the size of the nanochannels between the GO sheets, thereby reversibly adjusting the water permeability of the redox-responsive membrane and allowing or retaining molecules of different sizes, thus achieving separation.

[0045] For example, the redox-responsive membrane of the present invention can be applied to the separation of mixed liquids containing dyes of different molecular sizes (containing Brilliant Blue G (BBG) and Eosin Y (EY), each at a concentration of 5 ppm) and sodium chloride (at a concentration of 200 ppm). The specific separation method is as follows:

[0046] 1) By adding 0.02-0.2M NaClO to adjust the mixed solution, the oxidizing mixed solution passes through the redox-responsive membrane. The membrane in the oxidized state retains BBG while allowing eosin Y and sodium chloride molecules to pass through. 2) Subsequently, 0.02-0.2M NaHSO3 is added to adjust the filtered mixed solution to make it reducing. The membrane in the reduced state retains eosin Y while allowing sodium chloride molecules to pass through, ultimately achieving the sequential separation of BBG, EY, and sodium chloride.

[0047] Example 1

[0048] like Figure 13 As shown in (a), a redox-responsive membrane was prepared in this embodiment, and the specific preparation method is as follows:

[0049] (1) First, weigh 300 mg of aminoferrocene (Fc) and dissolve it in 500 mL of tetrahydrofuran (THF). Then add 1000 mg of GO to the solution to obtain mixture A.

[0050] (2) Weigh 1000 mg of GO and dissolve it in 500 mL of water. Then add 600 mg of KOH and 1800 mg of hexamethylenediamine-β-cyclodextrin (β-CD) to the solution to obtain mixture B. At this time, the pH of mixture B is 10.5.

[0051] (3) Mixture A and mixture B were ultrasonically dispersed at 200W for 30 min, and then placed in a water bath at 60℃ for 36 h. After the obtained solution was cooled to room temperature, it was dialyzed with a 12000Da dialysis bag for 7 days to remove unreacted Fc and β-CD. Then it was freeze-dried at -36℃ for 24 h to finally obtain aminoferrocene-modified graphene oxide (GO-Fc) and hexamethylenediamine-β-CD-modified graphene oxide (GO-CD).

[0052] (4) Weigh 500 μg of GO-Fc and GO-CD (mass ratio of 5:5) and dissolve them in 20 mL of water. Disperse them under ultrasonication at 200 W for 20 min to make them evenly mixed. Then, use a nylon microfiltration membrane with a diameter of 4.5 cm and a pore size of 0.22 μm for vacuum filtration. Store the filtered GO-Fc / GO-CD membrane at room temperature.

[0053] like Figure 1 As shown, the GO-Fc / GO-CD membrane obtained in this embodiment exhibits a typical yellow-brown color, can be bent arbitrarily, and has good flexibility.

[0054] Comparative Example 1

[0055] As a comparison with Example 1, a pure GO membrane was prepared in this comparative example. The specific preparation method is as follows:

[0056] Weigh 1000 μg of GO and dissolve it in 20 mL of water. Disperse the GO under ultrasonication at 200 W for 20 min. Vacuum filter the GO using a nylon microfiltration membrane with a diameter of 0.22 μm. Store the filtered GO membrane at room temperature.

[0057] Comparative Example 2

[0058] In this comparative example, a GO-Fc membrane was prepared under the same conditions as in Example 1. The specific preparation method is as follows:

[0059] First, 300 mg of aminoferrocene (Fc) was weighed and dissolved in 500 mL of tetrahydrofuran (THF). Then, 1000 mg of GO was added to the solution to obtain mixture A. Mixture A was ultrasonically dispersed at 200 W for 30 min, and then placed in a water bath at 60 °C for 36 h. After the solution was cooled to room temperature, it was dialyzed using a 12000 Da dialysis bag for 7 days to remove unreacted Fc. Then, it was freeze-dried at -36 °C for 24 h to finally obtain aminoferrocene-modified graphene oxide (GO-Fc). 1000 μg of GO-Fc was weighed and dissolved in 20 mL of water. After ultrasonic dispersion at 200 W for 20 min to ensure uniform mixing, it was vacuum filtered through a nylon microfiltration membrane with a diameter of 0.22 μm. The obtained GO-Fc membrane was stored at room temperature.

[0060] Comparative Example 3

[0061] In this comparative example, a GO-CD membrane was prepared under the same conditions as in Example 1. The specific preparation method is as follows:

[0062] 1000 mg of GO was dissolved in 500 mL of water. Then, 600 mg of KOH and 1800 mg of hexamethylenediamine-β-cyclodextrin (β-CD) were added to the solution to obtain mixture B. At this time, the pH of mixture B was 10.5. Mixture B was ultrasonically dispersed at 200 W for 30 min, and then reacted in a water bath at 60 °C for 36 h. After the obtained solution was cooled to room temperature, it was dialyzed using a 12000 Da dialysis bag for 7 days to remove unreacted β-CD. Then, it was freeze-dried at -36 °C for 24 h to finally obtain hexamethylenediamine-β-CD modified graphene oxide (GO-CD). 1000 μg of GO-CD was dissolved in 20 mL of water and ultrasonically dispersed at 200 W for 20 min to ensure uniform mixing. The mixture was then vacuum filtered through a nylon microfiltration membrane with a diameter of 0.22 μm and stored at room temperature.

[0063] Top-view scanning electron microscope images of the GO, GO-CD, GO-Fc, and GO-Fc / GO-CD films obtained in Examples 1 and Comparative Examples 1-3, as shown below. Figure 2 As shown in the figure, the surface of the GO-Fc / GO-CD film is relatively smooth, with many wrinkles and ripples. These wrinkles and ripples are due to the curling and folding of the flexible GO nanosheets during the assembly process. Furthermore, no obvious cracks or pinholes were found on the surface of the GO-Fc / GO-CD film, indicating that the film structure is intact.

[0064] like Figure 3As shown in the cross-sectional scanning electron microscope image of the GO-Fc / GO-CD membrane, the membrane exhibits a typical layered structure due to the uniform stacking of GO nanosheets. Furthermore, the thickness of the GO-Fc / GO-CD membrane is much less than 100 nm, which is beneficial for achieving high water flux.

[0065] FTIR spectroscopy analysis was performed on GO film, GO-CD film, GO-Fc film, and GO-Fc / GO-CD film. The results are as follows: Figure 4 As shown, compared with the GO film, the spectra of GO-Fc, GO-CD, and GO-Fc / GO-CD are at 1719 cm⁻¹. -1 The C=O stretching vibration at point 1567 cm⁻¹ almost completely disappeared, while at point 1567 cm⁻¹... -1 A new peak appears, which is attributed to the asymmetric stretching of the amide (NC=O), which originates from the formation of amide bonds between the carboxyl group in GO and the amino groups in aminoferrocene and hexamethylenediamine-β-CD.

[0066] Example 2

[0067] In this embodiment, the redox response characteristics of the GO-Fc / GO-CD membrane prepared in Example 1 were tested, as follows:

[0068] The principle is as follows: Fc / CD complexes based on host-guest interactions can be reversibly deformed and restored by adjusting the oxidation and reduction states of the solution.

[0069] like Figure 5 As shown, reversible dispersion and aggregation of GO-Fc / GO-CD were achieved by changing the redox state of the dispersion using NaClO and NaHSO3.

[0070] like Figure 14 The figure shows the XRD patterns of the GO-Fc / GO-CD film in the oxidized and reduced states. The calculation shows that the GO sheet spacing in the GO-Fc / GO-CD film is 1.13 nm in the oxidized state and 0.99 nm in the reduced state, indicating that the GO-Fc / GO-CD film on the surface has a redox response.

[0071] UV-Vis spectroscopy further verified the redox response behavior of GO-Fc / GO-CD, such as Figure 6 As shown, a new peak of approximately 293.1 nm can be observed in the oxidized state, while the spectrum in the reduced state is almost unchanged compared to the original GO-Fc / GO-CD complex. This may be due to the increased light absorption of Fc in the oxidized state, resulting in the dissociation of Fc from the β-CD cavity.

[0072] The above results indicate that the successful grafting of Fc and CD gives the GO-Fc / Go-Cd complex good redox response characteristics in an aqueous dispersion system.

[0073] Example 3

[0074] This embodiment investigates the effects of different mass ratios of GO-Fc / GO-CD on the water flux and gating ratio of the resulting GO-Fc / GO-CD membrane in the preparation method of the GO-Fc / GO-CD membrane, as detailed below:

[0075] (1) First, weigh 500 mg of aminoferrocene (Fc) and dissolve it in 500 mL of tetrahydrofuran (THF). Then, add 1500 mg of GO to the solution to obtain mixture A.

[0076] (2) Weigh 1800 mg of GO and dissolve it in 500 mL of water. Then add 800 mg of KOH and 3000 mg of hexamethylenediamine-β-cyclodextrin (β-CD) to the solution to obtain mixture B. At this time, the pH of mixture B is 11.8.

[0077] (3) Mixture A and mixture B were ultrasonically dispersed at 250W for 20 min, and then placed in a water bath at 70℃ for 36 h. After the obtained solution was cooled to room temperature, it was dialyzed with a 14000Da dialysis bag for 5 days to remove unreacted Fc and β-CD. Then it was freeze-dried at -40℃ for 36 h to finally obtain aminoferrocene-modified graphene oxide (GO-Fc) and hexamethylenediamine-β-CD-modified graphene oxide (GO-CD).

[0078] (4) Weigh 2000 μg of GO-Fc and GO-CD in mass ratios of 1:9, 3:7, 5:5, 7:3, and 9:1 and dissolve them in 20 mL of water. Disperse the mixture by ultrasonication at 300 W for 15 min until it is homogeneous. Then, vacuum filter the mixture using a nylon microfiltration membrane with a diameter of 4.5 cm and a pore size of 0.45 μm. Store the filtered GO-Fc / GO-CD membrane at room temperature.

[0079] In this embodiment, the redox state of the GO-Fc / GO-CD membrane was adjusted using 0.05M NaClO and NaHSO3 solutions.

[0080] like Figure 7As shown, the gating ratios of GO-Fc:GO-CD in the GO-Fc / GO-CD membrane are 1.2, 1.8, 5.6, 1.9, and 1.4, respectively, when the mass ratio of GO-Fc:GO-CD is 1:9, 3:7, 5:5, 7:3, and 9:1. The GO-Fc:GO-CD ratio in the GO-Fc / GO-CD membrane exhibits the highest gating ratio, indicating the highest content of the Fc / CD complex at this ratio.

[0081] Furthermore, the water flux of GO, GO-Fc, GO-CD, and GO-Fc / GO-CD membranes under different redox states was compared under the same conditions. Water flux J (L·m -2 ·h -1 ·bar -1 ) Calculated by the following formula:

[0082] J = V / (t * A * P)

[0083] In the formula, A is the effective membrane area (m²). 2 V is the volume of the filtered liquid (L), t is the filtration time (h), and P is the applied pressure (bar).

[0084] like Figure 8 As shown, for GO and GO-CD membranes, the water flux remained almost unchanged even under redox stimulation; while the water flux of the GO-Fc membrane showed only a small change under redox stimulation. The GO-Fc / GO-CD membrane exhibited the most significant redox response performance, with the water flux increasing from 5.7 L·m⁻¹ in the reduced state. -2 ·h -1 ·bar -1 Increased to 31.8 L·m to the oxidized state -2 ·h -1 ·bar -1 The gating ratio is 5.6.

[0085] Example 4

[0086] This embodiment investigates the effects of different amounts of GO-Fc and GO-CD on the water flux and gating ratio of the GO-Fc / GO-CD membrane in the preparation method of the GO-Fc / GO-CD membrane. Details are as follows:

[0087] (1) First, weigh 400 mg of aminoferrocene (Fc) and dissolve it in 500 mL of tetrahydrofuran (THF). Then add 1300 mg of GO to the solution to obtain mixture A.

[0088] (2) Weigh 1200 mg of GO and dissolve it in 500 mL of water. Then add 700 mg of KOH and 2500 mg of hexamethylenediamine-β-cyclodextrin (β-CD) to the solution to obtain mixture B. At this time, the pH of mixture B is 11.0.

[0089] (3) Mixture A and mixture B were ultrasonically dispersed at 200W for 40 min, and then placed in a water bath at 65℃ for 36 h. After the obtained solution was cooled to room temperature, it was dialyzed with a 10000Da dialysis bag for 8 days to remove unreacted Fc and β-CD. Then it was freeze-dried at -55℃ for 24 h to finally obtain aminoferrocene-modified graphene oxide (GO-Fc) and hexamethylenediamine-β-CD-modified graphene oxide (GO-CD).

[0090] (4) Weigh 100, 200, 500, 1000 and 2000 μg of GO-Fc and GO-CD in a mass ratio of 5:5 and dissolve them in 20 mL of water. After ultrasonic dispersion at 300 W for 30 min to make them evenly mixed, vacuum filter them with a nylon microfiltration membrane with a diameter of 4.5 cm and a pore size of 0.3 μm. Store the filtered GO-Fc / GO-CD membrane at room temperature.

[0091] In this embodiment, the redox state of the GO-Fc / GO-CD membrane was adjusted using 0.15M NaClO and NaHSO3 solutions.

[0092] like Figure 9 As shown, as the amount of GO-Fc and GO-CD (μg) increased from 50:50 to 1000:1000, the water flux of the GO-Fc / GO-CD membrane decreased under both oxidative and reducing conditions.

[0093] When the mass ratio of GO-Fc to GO-CD is 1000:1000, the gating ratio can reach a maximum of 13.3, but the hydraulic conductivity in the reduced state is only 1.2 L·m. -2 ·h -1 ·bar -1 It has poor practicality.

[0094] Therefore, a GO-FC / GO-CD membrane with a ratio of 500:500 was selected for redox response separation experiments.

[0095] Example 5

[0096] This embodiment, based on the GO-Fc / GO-CD membrane obtained in Example 1, investigated its molecular retention and separation performance. Specifically, the membrane's response retention performance was evaluated using a mixed liquid containing dyes of different molecular sizes (including Brilliant Blue G (BBG) and Eosin Y (EY), each at a concentration of 5 ppm) and sodium chloride (concentration of 200 ppm). Details are as follows:

[0097] The separation performance was evaluated using a dead-end filtration system equipped with a nitrogen cylinder, digital balance, ultrafiltration cup, and computer. The transmembrane pressure was maintained at 1.0 bar throughout the measurement process. The feed solution was magnetically stirred at 500 rpm to eliminate concentration polarization.

[0098] The retention rate is calculated using the following formula:

[0099] R = (C0 - C1) / C0 * 100%

[0100] Where R is the rejection rate, and C0 and C1 are the dye and sodium chloride concentrations before and after filtration, respectively.

[0101] use and Using molecules as probes, solutions of 5 ppm BBG and EY were prepared to test the rejection rate of GO-Fc / GO-CD membranes under different redox states; solutions containing 5 ppm BBG, 5 ppm EY, and 200 ppm sodium chloride were also prepared. A mixed solution was used to test the separation effect of the GO-Fc / GO-CD membrane on molecules of different sizes under different redox states. The concentration of dye in the solution before and after filtration was determined by UV-Vis spectrophotometry, and the concentration of sodium chloride was determined by ion chromatography.

[0102] In this embodiment, the redox state of the GO-Fc / GO-CD membrane was adjusted using 0.1M NaClO and NaHSO3 solutions.

[0103] like Figure 10 As shown in (a), the GO-Fc / GO-CD membrane retains 99.3% of BBG in both oxidized and reduced states. This result is attributed to the large molecular size of BBG, which prevents it from passing through the channels of the GO-Fc / GO-CD membrane even when the channel size is increased in the oxidized state.

[0104] For EY, such as Figure 10 As shown in (b), the intermediate molecular size, close to the pore size of the GO-Fc / GO-CD membrane, gives the separation process a distinct redox response. Therefore, the rejection rate in the reduced state (90.1%) is much higher than that in the oxidized state (37.2%).

[0105] By adding 0.1M NaClO to a mixed solution containing BBG, EY, and sodium chloride, the solution was made oxidizing. When the mixed solution passed through a redox-responsive membrane, the oxidized membrane showed retention rates of 99.3% for BBG, 37.2% for EY, and 0.2% for sodium chloride. The filtrate was collected, and 0.1M NaHSO3 was added to make the solution reducing. When the mixed solution passed through the redox-responsive membrane, the reduced membrane showed retention rates of 90.1% for EY and 0.3% for sodium chloride. Thus, by controlling the redox state of the membrane, the three mixtures can be separated sequentially using the same membrane.

[0106] Example 6

[0107] This embodiment, based on the GO-Fc / GO-CD membrane obtained in Example 1, investigated the reversibility of water flux after five cycles under alternating redox reactions (adjusted by 0.1M NaClO and NaHSO3). The specific results are as follows:

[0108] like Figure 11 As shown, the oxidized water flux of the GO-Fc / GO-CD membrane is 31.0–32.3 L·m⁻¹. -2 ·h -1 ·bar -1 The reduced state has a concentration of 5.6–6.1 L·m⁻². -2 ·h -1 ·bar -1 .

[0109] After 5 cycles, the water flux response performance between the two states remained almost unchanged, indicating that the GO-Fc / GO-CD membrane has stable and reversible redox response characteristics.

[0110] Example 7

[0111] This embodiment, based on the GO-Fc / GO-CD membrane obtained in Example 1, investigated the stability of the GO-Fc / GO-CD membrane. Specifically, the GO-Fc / GO-CD membrane was immersed in deionized water, 0.1M NaClO solution, and 0.1M NaHSO3 solution for 7 days, respectively, to evaluate its stability. The results are as follows:

[0112] like Figure 12As shown, due to the swelling behavior caused by the electrostatic repulsion between GO nanosheets, the pure GO membrane dissociates in deionized water and alkaline NaClO solutions. In acidic NaHSO3 solution, the structure of the pure GO membrane is preserved due to the reduced electrostatic repulsion. The GO-Fc / GO-CD membrane did not exhibit significant pyrolysis in any of the three solutions, indicating its good stability. Therefore, the GO-Fc / GO-CD membrane demonstrates high stability, a characteristic that enables it to maintain stable response performance during multiple redox transitions, which is of great significance for its practical applications.

[0113] In summary, the size of the nanochannels between GO sheets can be adjusted by changing the redox state of the GO-Fc / GO-CD membrane, thereby achieving reversible control over the membrane's water permeability and molecular separation performance. Furthermore, the prepared GO-Fc / GO-CD membrane exhibits excellent cycling response performance and stability, showing broad application prospects in intelligent response gating and contaminant removal and separation.

[0114] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. An application of a redox-responsive membrane in separating molecules of different sizes in a liquid under different redox states, characterized in that, The preparation method of the redox-responsive membrane specifically includes the following steps: S1: Dissolve the metal dicerocene compound in an organic solvent, add graphene oxide, and obtain mixture A; S2: Add graphene oxide and cyclodextrin to water to obtain mixture B; S3: The mixture A and mixture B are ultrasonically dispersed and then reacted under heating conditions. After dialysis purification and freeze-drying, metallolithocene-modified graphene oxide GO-Fc and cyclodextrin-modified graphene oxide GO-CD are obtained respectively. S4: Dissolve the GO-Fc and GO-CD in water, disperse them by ultrasonication to make them evenly mixed, and prepare a redox-responsive membrane by vacuum-assisted self-assembly on a base membrane; The metallocerocene compound is one of amino-derived ferrocerocene, amino-derived manganese cerocerocene, or amino-derived cobalt cerocerocene; the cyclodextrin is one of amino-modified α-cyclodextrin, amino-modified β-cyclodextrin, or amino-modified γ-cyclodextrin; the pH range of the mixture B is adjusted to 9-13 by adding a strong alkali.

2. The application of the redox-responsive membrane according to claim 1 in separating molecules of different sizes in a liquid under different redox states, characterized in that, The organic solvent is one of tetrahydrofuran, dimethyl ether, ethanol, or acetone.

3. The application of the redox-responsive membrane according to claim 1 in separating molecules of different sizes in a liquid under different redox states, characterized in that, The mass ratio of the metallocerocene compound to graphene oxide is 1:(5-2), the mass ratio of cyclodextrin to graphene oxide is (3-1):(1-2); the mass ratio of GO-Fc to GO-CD is (1-9):(9-1), and the total mass of GO-Fc and GO-CD is 0.1-5 mg.

4. The application of the redox-responsive membrane according to claim 1 in separating molecules of different sizes in a liquid under different redox states, characterized in that, The strong base is potassium hydroxide or sodium hydroxide.

5. The application of the redox-responsive membrane according to claim 1 in separating molecules of different sizes in a liquid under different redox states, characterized in that, The ultrasonic dispersion process uses a power of 150-300 W for 10-60 min; the dialysis purification process uses a dialysis bag with a capacity of 8000-16000 Da for 4-8 days, with the pure water replaced every day; the freeze-drying process uses a temperature of -30 ℃ to -60 ℃ for 24-48 h.

6. The application of the redox-responsive membrane according to claim 1 in separating molecules of different sizes in a liquid under different redox states, characterized in that, The heating conditions refer to reacting in a water bath at a temperature of 40-80 ℃ for 24-48 h.

7. The application of the redox-responsive membrane according to claim 1 in separating molecules of different sizes in a liquid under different redox states, characterized in that, In the vacuum-assisted self-assembly method, the base membrane is one of nylon membrane, polyvinylidene fluoride membrane, polyethersulfone membrane, polypropylene membrane, mixed cellulose membrane or polytetrafluoroethylene membrane, with a pore size of 0.1-0.5 μm.

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