A pH-responsive graphene oxide composite film and a preparation method and application thereof

Abstract

The application relates to a pH-responsive graphene oxide composite film and a preparation method and application thereof, and belongs to the field of film materials. The preparation method of the composite film comprises the following steps: S1, dopamine is added into a solvent of a zwitterionic monomer to perform a self-polymerization reaction, and zwitterionic polydopamine soft nanospheres are obtained; S2, graphene oxide is added into a solvent A to obtain a graphene oxide dispersion liquid; S3, the zwitterionic polydopamine soft nanospheres are added into a solvent B to obtain a zwitterionic polydopamine dispersion liquid; and S4, the graphene oxide dispersion liquid and the zwitterionic polydopamine dispersion liquid are circularly spin-coated on a support from bottom to top layer by layer to form a film layer, and the composite film is obtained. The composite film obtained by the above preparation method has good stability in an acidic or alkaline environment, and high permeability and selectivity to response pH stimulation of a monovalent / divalent ion and a salt / molecular system.

Description

Technical Field

[0001] This invention belongs to the field of thin film materials, specifically relating to a pH-responsive graphene oxide composite film, its preparation method, and its application. Background Technology

[0002] Ion and small molecule transport dependent on external pH environment plays a crucial role in many biological activities and chemical separation processes. Inspired by the glomerular filtration barrier as an adaptive semipermeable membrane, it is of great significance to construct pH-responsive smart membranes based on novel membrane materials to achieve rapid permeation and selective transport of ions and small molecules under different acidic and alkaline environments.

[0003] Research has found that two-dimensional materials, represented by graphene oxide, possess atomic-level thickness and flexibly tunable physicochemical properties. Through ordered assembly, they can be stacked to form regular interlayer two-dimensional nanochannels for ion and small molecule transport, showing broad application prospects in many fields such as environment, resources, and energy. However, the nanofluidic channel structure between graphene oxide membrane layers is unstable in acidic or alkaline solutions. For example, low pH values ​​favor carboxyl group deprotonation, leading to a weakening of electrostatic repulsion between adjacent graphene oxide nanosheets and a narrowing of the interlayer spacing, resulting in greater osmotic resistance, hindering the transmembrane transport of ions and small molecules, and reducing membrane separation efficiency. Conversely, high pH values ​​promote carboxyl group deprotonation, exacerbating the swelling tendency of graphene oxide membranes and severely damaging their structural stability and ion and small molecule sieving properties.

[0004] Therefore, there is a need to develop an effective method to precisely control the physical size and charge properties of graphene oxide membrane nanofluidic channels, so that the membrane has good stability in acidic or alkaline environments, high permeability and selectivity in response to pH stimulation, and excellent separation performance in monovalent / divalent ion and salt / molecule systems. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a graphene oxide composite membrane with good stability in acidic or alkaline environments and high permeability and selectivity in response to pH stimulation of monovalent / divalent ions and salt / molecular systems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a pH-responsive graphene oxide composite film, comprising the following steps:

[0008] S1. Add dopamine to the solvent of zwitterionic monomer, mix evenly, and carry out self-polymerization reaction to obtain zwitterionic polydopamine soft nanospheres.

[0009] S2. Add graphene oxide to solvent A and disperse it evenly to obtain a graphene oxide dispersion; add the zwitterionic polydopamine soft nanospheres described in step S1 to solvent B and disperse them evenly to obtain a zwitterionic polydopamine dispersion.

[0010] S3. The graphene oxide dispersion and the zwitterionic polydopamine dispersion described in step S2 are cyclically spin-coated onto the support layer by layer from bottom to top to form a film layer, and then dried to obtain the pH-responsive graphene oxide composite film.

[0011] In step S1, the active functional groups of the zwitterionic monomer include amino and sulfonic acid groups.

[0012] The inventors of this invention have discovered that the polydopamine soft nanospheres described in this invention maintain the structural stability of the two-dimensional nanofluidic channels of graphene oxide in solvent environments through multiple interactions such as π-π, electrostatics, and hydrogen bonding. Further modification with zwitterionic monomers containing active functional groups of amine and sulfonic acid groups, as described in this invention, not only provides the polydopamine soft nanospheres with variable positive and negative charges, endowing the membrane with responsiveness to external pH stimuli, but also allows the amine groups to copolymerize with dopamine, and the sulfonic acid groups to impart better hydrophilicity to polydopamine, thereby improving membrane permeability. Simultaneously, using the layer-by-layer spin-coating method described in this invention, graphene oxide and zwitterionic polydopamine soft nanospheres are self-assembled layer by layer. Compared with traditional graphene oxide membranes, this invention achieves precise control of the physical size and charge characteristics of the two-dimensional nanofluidic channels between graphene oxide layers through the tight or loose polymerization of zwitterionic polydopamine soft nanospheres under external pH regulation, selectively improving the resistance to Cl. - SO4 2- or K + / Mg 2+ The selective properties of the zwitterionic polydopamine soft nanosphere / graphene oxide composite membrane described in this invention exhibit good stability in acidic or alkaline environments, as well as high permeability and selectivity in response to pH stimulation, demonstrating excellent separation performance in monovalent / divalent ion and salt / molecule systems.

[0013] Furthermore, the method for preparing the pH-responsive graphene oxide composite membrane described in this invention is simple and easy to implement, and the prepared pH-responsive graphene oxide composite membrane has good application prospects in related fields such as ion / molecule separation and ion gating.

[0014] In a preferred embodiment of the preparation method of the present invention, in step S1, the zwitterionic monomer is N-aminoethylpiperazine propyl sulfonate.

[0015] The inventors of this invention have discovered that using N-aminoethylpiperazine propyl sulfonate as a zwitterionic monomer to modify dopamine allows for more precise control of the channel size in the graphene oxide composite membrane, thus addressing the problem of difficulty in separating ions due to smaller differences in the size of the objects being separated. Furthermore, amphoteric polydopamine soft nanospheres prepared using the specific zwitterionic monomer described in this invention, when simultaneously spin-coated layer-by-layer with graphene oxide, can further enhance the response of the graphene oxide composite membrane to external pH stimuli and its ion separation performance through differences in charge interaction and the forces within the confined channels.

[0016] In a preferred embodiment of the preparation method described in this invention, the D50 of the zwitterionic polydopamine soft nanospheres is (1-5) nm.

[0017] The inventors of this invention have discovered that using zwitterionic polydopamine soft nanospheres within the particle size range described above can further improve the ion sieving performance of graphene oxide composite membranes, thereby enhancing their high permeability and ion selectivity in response to pH stimulation in acidic or alkaline environments. In alkaline environments, the zwitterionic polydopamine soft nanospheres of this invention, due to their high degree of polymerization, can expand the interlayer spacing of the graphene oxide composite membrane, increasing the permeability of the composite membrane. Furthermore, because they carry a negative charge, they enhance the repulsion of divalent anions, thereby improving the composite membrane's ability to retain Cl- ions. - SO4 2- Selectivity; Under acidic conditions, the zwitterionic polydopamine soft nanospheres of this invention exhibit low polymerization degree, resulting in a smaller interlayer spacing in the expanded graphene oxide composite film. Due to their specific D50, the composite film's permeability is satisfied, and because they carry a positive charge, their repulsion of divalent cations is enhanced, thereby improving the composite film's resistance to K+. + / Mg 2+ Selectivity. The size of the zwitterionic polydopamine soft nanospheres, whether large or small, reduces the ion-sieving performance of the graphene oxide composite film, thus affecting its ability to filter K+ ions. + / Mg 2+ Selective or relative to Cl - SO4 2- Selectivity is reduced to varying degrees.

[0018] In a preferred embodiment of the preparation method described in this invention, the mass ratio of the zwitterionic monomer to dopamine is zwitterionic monomer: dopamine = 2:1 to 8:1.

[0019] In a preferred embodiment of the preparation method of the present invention, the self-polymerization reaction in step S1 takes 3 to 7 hours.

[0020] The inventors of this invention have discovered that by controlling the mass ratio of zwitterionic monomer to dopamine within the above-mentioned range, and simultaneously controlling the self-polymerization reaction time of dopamine within the above-mentioned range, it is possible to prepare zwitterionic polydopamine soft nanospheres with moderate diameter and charge density. This is more conducive to precisely controlling the physical structure and charge characteristics of the two-dimensional nanofluidic channels between graphene oxide layers.

[0021] In a preferred embodiment of the preparation method of the present invention, in step S2, the graphene oxide is monodisperse graphene oxide nanosheets; the lateral dimension of the monodisperse graphene oxide nanosheets is 20-30 μm, the monolayer ratio of the monodisperse graphene oxide nanosheets is ≥99%, and the oxygen content of the monodisperse graphene oxide nanosheets is 30-40%.

[0022] Through extensive experimental research on graphene oxide, the inventors discovered that the monodisperse graphene oxide nanosheets described in this invention, due to their high surface-to-volume ratio, can be orderly stacked to form a regular two-dimensional layered film structure with solvent assistance. Furthermore, the specific graphene oxide described in this application exhibits better dispersibility in solvents, reducing the likelihood of localized agglomeration, which is beneficial for the assembly and preparation of graphene oxide films.

[0023] In a preferred embodiment of the preparation method of the present invention, in step S2, the concentration of graphene oxide in the graphene oxide dispersion is 0.05-0.2 mg / mL.

[0024] The inventors of this invention have discovered that when the concentration of the graphene oxide dispersion described in this invention is within the aforementioned range, it is beneficial to improve the preparation efficiency of the pH-responsive graphene oxide composite film and also enhances the dispersibility of graphene oxide nanosheets in solvents. Conversely, excessively low concentrations of the graphene oxide dispersion lead to reduced preparation efficiency of the graphene oxide composite film, while excessively high concentrations negatively impact the dispersibility of graphene oxide nanosheets in solvents.

[0025] In a preferred embodiment of the preparation method of the present invention, in step S2, the graphene oxide is added to solvent A and mixed evenly by stirring and / or ultrasonic treatment.

[0026] In a more preferred embodiment of the preparation method of the present invention, in step S2, the stirring time is 10-60 min; the ultrasonic power is 100-700 W; and the ultrasonic time is 5-30 min.

[0027] The inventors of this invention conducted extensive experimental research on the process parameters of stirring and ultrasound and found that the above-mentioned stirring and ultrasound process helps to uniformly disperse graphene oxide in the solvent. However, excessive ultrasound power and ultrasound events can lead to excessively small size of graphene oxide, affecting the structure and performance of graphene oxide composite film.

[0028] In a preferred embodiment of the preparation method of the present invention, in step S3, the concentration of polydopamine in the zwitterionic polydopamine dispersion is 0.1-0.5 mg / mL.

[0029] In a preferred embodiment of the preparation method of the present invention, in step S2, solvent A includes water; in step S3, solvent B includes water and / or anhydrous ethanol.

[0030] In a preferred embodiment of the preparation method of the present invention, in step S3, the spin coating process parameters are: rotation speed of 800-2000 r / min, single spin coating time of each spin coating layer of 30-120 s, and each spin coating layer of 30 layers ...

[0031] The inventors of this invention have discovered that by using the aforementioned spin-coating process parameters, a continuous and defect-free graphene oxide composite film can be prepared. Furthermore, by spin-coating layer by layer, amphoteric polydopamine soft nanospheres can be uniformly distributed between each layer of the graphene oxide film. When the number of spin-coating cycles is low, the resulting graphene oxide composite film is incomplete, leading to a decrease in its pH-responsiveness and ion selectivity. Conversely, when the number of spin-coating cycles is high, the thickness of the graphene oxide composite film results in greater resistance in the two-dimensional nanofluid channels, hindering ion passage and thus degrading the performance of the graphene oxide composite film.

[0032] In a preferred embodiment of the preparation method of the present invention, in step S4, the support is a porous support; the average pore size of the porous support is 10 to 1000 nm.

[0033] In a preferred embodiment of the preparation method of the present invention, in step S4, the porous support has a sheet-like or plate-like structure.

[0034] The inventors of this invention have discovered that spin-coating the specific graphene oxide and amphoteric polydopamine described in this invention onto a porous support within the aforementioned pore size range, in sheet or plate form, yields better performance. Conversely, excessively small pore sizes in the porous support introduce additional mass transfer resistance, affecting the separation efficiency of the graphene oxide composite membrane; excessively large pore sizes cause nanosheets to become trapped inside the support's pores, preventing film formation.

[0035] As a more preferred embodiment of the preparation method of the present invention, in step S4, the porous support is made of at least one of polyacrylonitrile, polycarbonate, nylon, mixed cellulose ester and alumina.

[0036] Through extensive material testing on porous supports, the inventors of this invention have discovered that porous supports made of the aforementioned materials can provide sufficient mechanical strength for graphene oxide composite films.

[0037] In a preferred embodiment of the preparation method of the present invention, in step S4, the drying temperature is 25-60°C and the drying time is 12-36 hours.

[0038] The inventors of this invention have discovered that by employing the aforementioned drying process parameters, residual moisture inside the graphene oxide composite membrane can be effectively removed, improving the preparation efficiency of the graphene oxide composite membrane. This results in a graphene oxide composite membrane with better stability in acidic or alkaline environments, as well as better permeability and selectivity in response to pH stimuli. Conversely, excessively low drying temperatures lead to lower preparation efficiency of the graphene oxide composite membrane, while excessively high drying temperatures can cause partial reduction or removal of oxygen-containing groups within the graphene oxide, damaging the membrane structure.

[0039] Secondly, the present invention also provides a graphene oxide composite film prepared by the above preparation method.

[0040] The inventors of this invention have discovered that by using the preparation method described above, a graphene oxide composite membrane with good stability in acidic or alkaline environments and high permeability and selectivity in response to pH stimulation can be prepared.

[0041] Thirdly, the present invention also provides the application of the above-mentioned graphene oxide composite membrane in the preparation of ion-selective separation membranes.

[0042] The graphene oxide composite membrane prepared by this invention exhibits excellent separation performance in monovalent / divalent ion and salt / molecule systems, which is beneficial for its application in the preparation of ion-selective separation membranes.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) Using the spin-coating method described in this invention, graphene oxide and zwitterionic polydopamine soft nanospheres are self-assembled layer by layer. The zwitterionic polydopamine soft nanospheres undergo tight or loose polymerization under the regulation of external pH, thereby achieving precise control of the physical size and charge characteristics of the two-dimensional nanofluid channels between the graphene oxide film layers. It can also endow the film with the ability to respond to external pH stimulation, so that the zwitterionic polydopamine soft nanosphere / graphene oxide composite film described in this invention has good stability in acidic or alkaline environments and high permeability and selectivity in response to pH stimulation, and exhibits excellent separation performance in monovalent / divalent ion and salt / molecule systems.

[0045] (2) The method for preparing the pH-responsive graphene oxide composite membrane of the present invention is simple and easy to implement. The prepared pH-responsive graphene oxide composite membrane has good application prospects in related fields such as ion / molecule separation and ion gating. Attached Figure Description

[0046] Figure 1 This is a scanning electron microscope image of the surface of the graphene oxide composite film of Example 1 of the present invention;

[0047] Figure 2 This is a cross-sectional scanning electron microscope image of the graphene oxide composite film of Example 1 of the present invention;

[0048] Figure 3 This is the surface elemental energy spectrum scan of the graphene oxide composite film in Example 2 of the present invention. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the methods or operations used in the embodiments are conventional methods or operations in the art.

[0050] The permeation tests were conducted on the graphene oxide composite membranes of the following embodiments and comparative examples of the present invention. The specific testing methods are as follows:

[0051] The membrane under test was placed between the feed side and the permeate side of a commercially available two-chamber membrane permeation device, with the graphene oxide side facing the feed side. The effective area of ​​the membrane under test was 4.15 cm². 2100 mL of deionized water was added to the permeate side, and an equal volume of 0.5 mol / L test solution was added to the feed side. Both sides were stirred with rotors to eliminate concentration polarization. The ion concentration on the permeate side was measured every 10 minutes using a conductivity meter for a total of 2 hours. A linear fitting graph of the permeate concentration versus time was plotted, with the slope representing the ion permeation rate and selectivity. Using the above method, the test membrane was tested in potassium chloride, magnesium chloride, and potassium sulfate solutions, respectively, to obtain K0. + Permeation rate, Mg 2+ Permeation rate and SO4 2- Permeation rate. The formula for calculating the permeation rate is as follows:

[0052]

[0053] Among them, J s This is the ion permeation rate, in mol·m⁻¹. 2 ·h -1 Δc / Δt represents the change in ion concentration per unit time on the osmotic side, in mg·L·h. -1 V p A is the volume of solution on the osmotic side, in L; A is the effective area of ​​the membrane, in m². 2 M s To test the molecular weight of the solution.

[0054] The formula for selective calculation is as follows:

[0055]

[0056] Among them, J S1 and J S2 These represent the ion permeation rates.

[0057] In the following embodiments and comparative examples of the present invention, the solvents used for the zwitterionic monomers are all aqueous solutions containing zwitterionic monomers, and the amount of water added is 50 mL.

[0058] Example 1

[0059] An embodiment of the present invention is a pH-responsive graphene oxide composite membrane.

[0060] The method for preparing the pH-responsive graphene oxide composite membrane described in this embodiment includes the following steps:

[0061] S1. Add 0.2g of dopamine to an aqueous solution containing 0.8g of zwitterionic monomer N-aminoethylpiperazine propyl sulfonate, mix and dissolve evenly, and carry out a dopamine self-polymerization reaction for 5 hours to obtain zwitterionic polydopamine soft nanospheres.

[0062] S2. 20 mg of graphene oxide nanosheets (with a lateral size of 20 μm, a monolayer rate of 99%, and an oxygen content of 40%) were dispersed in 100 mL of water, stirred for 30 min, and then sonicated at 500 W for 5 min until the dispersion was uniform to obtain a graphene oxide dispersion.

[0063] S3. Dissolve 0.02g of zwitterionic polydopamine soft nanospheres in 100mL of 20% anhydrous ethanol aqueous solution, stir for 30min, and sonicate at 700W for 30min to obtain zwitterionic dopamine dispersion.

[0064] S4. The graphene oxide dispersion described in step S2 and the zwitterionic polydopamine dispersion described in step S3 are spin-coated at a speed of 2000 r / min for 30 s, and then cyclically spin-coated layer by layer from bottom to top onto an alumina sheet support. The alumina sheet support has an average pore size of 1000 nm, forming a film layer after 20 spin-coating cycles. The prepared film is placed in a vacuum drying oven and dried at 45°C for 18 h to obtain a graphene oxide composite film.

[0065] The preparation method of N-aminoethylpiperazine propylsulfonate (AEEPS) described in this embodiment is based on the literature: Qfa A, WdsA, Qiang ZA, et al. Study on a novel nanofiltration membrane prepared by interfacial polymerization with zwitterionic amine monomers[J]. Journal of Membrane Science, 2013, 431: 171-179. The synthetic equation is as follows: the ring-opening reaction between N-aminoethylpiperazine (AEP) and 1,3-propanesulfonate (1,3-PS) synthesizes the zwitterionic monomer N-aminoethylpiperazine propylsulfonate (AEPPS).

[0066]

[0067] The specific preparation method is as follows: 7.22 g of AEP and 65 mL of acetonitrile were placed in a round-bottom flask, and then a mixed solution of 5.9 g of 1,3-PS and 5 mL of acetonitrile was slowly added dropwise. The system temperature was maintained at 30 °C for 6 h, and the mixture was filtered to obtain a light yellow crude product, AEPPS. After being thoroughly washed with ethanol, the product was dried under vacuum at 50 °C for 24 h for later use.

[0068] Figure 1 This is a scanning electron microscope image of the surface of the graphene oxide composite film prepared in this embodiment. Figure 1As can be seen, the surface of the graphene oxide composite film in this embodiment is uniformly distributed with zwitterionic polydopamine soft nanospheres.

[0069] Figure 2 The image shows a cross-sectional scanning electron microscope (SEM) image of the graphene oxide composite film prepared in this embodiment. Figure 2 As can be seen, the graphene oxide composite film in this embodiment exhibits an orderly stacked two-dimensional layered film structure.

[0070] The graphene oxide composite membrane of this embodiment was subjected to a permeation test. The test results were as follows: under the test conditions of pH=10, K was obtained. + The permeation rate is 0.576 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.038 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.056 mol·m⁻¹ 2 ·h -1 When the test condition is pH=7, K can be obtained. + The permeation rate is 0.628 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.047 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.051 mol·m⁻¹ 2 ·h -1 When the test condition is pH=4, K can be obtained. + The permeation rate is 0.518 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate was 0.041 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.066 mol·m⁻¹ 2 ·h -1 .

[0071] Based on the selectivity calculation formula, when the test condition is pH=10, K can be obtained. + / Mg 2+ Selectivity is 15.2, Cl - SO4 2- The selectivity was 10.3; the test conditions were pH=7, and K was obtained. + / Mg 2+ Selectivity was 13.4, Cl - SO4 2-The selectivity is 12.3; the test condition is pH=4, and K can be obtained. + / Mg 2+ Selectivity is 12.6, Cl - SO4 2- The selectivity is 7.8.

[0072] Example 2

[0073] An embodiment of the present invention is a pH-responsive graphene oxide composite membrane.

[0074] The method for preparing the pH-responsive graphene oxide composite membrane described in this embodiment includes the following steps:

[0075] S1. Add 0.2g of dopamine to an aqueous solution containing 0.4g of zwitterionic monomer N-aminoethylpiperazine propyl sulfonate, mix and dissolve evenly, and carry out a dopamine self-polymerization reaction for 7 hours to obtain zwitterionic polydopamine soft nanospheres.

[0076] S2. Disperse 5 mg of graphene oxide nanosheets (with a lateral size of 20 μm, a monolayer rate of 99%, and an oxygen content of 40%) in 100 mL of water, stir for 60 min, and sonicate at 700 W for 5 min until the dispersion is uniform to obtain a graphene oxide dispersion.

[0077] S3. Dissolve 0.05g of zwitterionic polydopamine soft nanospheres in 100mL of 50% anhydrous ethanol aqueous solution, stir for 120min, and sonicate at 700W for 10min to obtain zwitterionic dopamine dispersion.

[0078] S4. The graphene oxide dispersion described in step S2 and the zwitterionic polydopamine dispersion described in step S3 are spin-coated at a speed of 1500 r / min for 60 s, and then cyclically spin-coated layer by layer from bottom to top onto a polyacrylonitrile flat plate support. The average pore size of the polyacrylonitrile flat plate support is 10 nm, forming a film layer after 25 spin-coating cycles. The prepared film is placed in a vacuum drying oven and dried at 50 °C for 15 h to obtain a graphene oxide composite film.

[0079] The preparation method of N-aminoethylpiperazine propyl sulfonate (AEEPS) in this embodiment is the same as that in Example 1.

[0080] The graphene oxide composite membrane of this embodiment was subjected to a permeation test. The test results were as follows: under the test conditions of pH=7, K was obtained. + The permeation rate is 0.458 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate was 0.041 mol·m⁻¹ 2 ·h-1 SO4 2- The permeation rate is 0.074 mol·m⁻¹ 2 ·h -1 .

[0081] Based on the selectivity calculation formula, when the test condition is pH=7, K can be obtained. + / Mg 2+ Selectivity is 11.2, Cl - SO4 2- The selectivity is 6.2.

[0082] Figure 3 This is a surface elemental energy dispersive spectroscopy (EDS) scan of the graphene oxide composite film in this embodiment. From... Figure 3 It can be seen that zwitterionic sites containing cationic amino groups (containing nitrogen) and anionic sulfonic acid groups (containing sulfur and oxygen) are uniformly modified on the graphene oxide composite film.

[0083] Example 3

[0084] An embodiment of the present invention is a pH-responsive graphene oxide composite membrane.

[0085] The method for preparing the pH-responsive graphene oxide composite membrane described in this embodiment includes the following steps:

[0086] S1. Add 0.2g of dopamine to an aqueous solution containing 1.6g of zwitterionic monomer N-aminoethylpiperazine propyl sulfonate, mix and dissolve evenly, and carry out a dopamine self-polymerization reaction for 3 hours to obtain zwitterionic polydopamine soft nanospheres.

[0087] S2. Disperse 1 mg of graphene oxide nanosheets (with a lateral size of 30 μm, a monolayer rate of 99%, and an oxygen content of 30%) in 100 mL of water, stir for 10 min, and sonicate at 100 W for 30 min until the dispersion is uniform to obtain a graphene oxide dispersion.

[0088] S3. Dissolve 0.01g of zwitterionic polydopamine soft nanospheres in 100mL of 30% anhydrous ethanol aqueous solution, stir for 60min, and sonicate at 300W for 20min to obtain zwitterionic dopamine dispersion.

[0089] S4. The graphene oxide dispersion described in step S2 and the zwitterionic polydopamine dispersion described in step S3 are spin-coated at a speed of 800 r / min for 120 s, and then cyclically spin-coated layer by layer from bottom to top onto a nylon flat plate support. The average pore size of the nylon flat plate support is 500 nm, forming a film layer after 10 spin-coating cycles. The prepared film is placed in a vacuum drying oven and dried at 25°C for 36 h to obtain a graphene oxide composite film.

[0090] The preparation method of N-aminoethylpiperazine propyl sulfonate (AEEPS) in this embodiment is the same as that in Example 1.

[0091] The graphene oxide composite membrane of this embodiment was subjected to a permeation test. The test results were as follows: under the test conditions of pH=4, K was obtained. + The permeation rate was 0.489 mol·m⁻¹. 2 ·h -1 Mg 2+ The permeation rate is 0.025 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.076 mol·m⁻¹ 2 ·h -1 .

[0092] Based on the selectivity calculation formula, when the test condition is pH=4, K can be obtained. + / Mg 2+ Selectivity was 19.6, Cl - SO4 2- The selectivity is 6.4.

[0093] Example 4

[0094] An embodiment of the present invention is a pH-responsive graphene oxide composite membrane.

[0095] The method for preparing the pH-responsive graphene oxide composite membrane described in this embodiment includes the following steps:

[0096] S1. Add 0.2g of dopamine to an aqueous solution containing 1.2g of zwitterionic monomer N-aminoethylpiperazine propyl sulfonate, mix and dissolve evenly, and carry out a dopamine self-polymerization reaction for 6 hours to obtain zwitterionic polydopamine soft nanospheres.

[0097] S2. Disperse 10 mg of graphene oxide nanosheets (with a lateral size of 25 μm, a monolayer rate of 99%, and an oxygen content of 30%) in 100 mL of water, stir for 20 min, and sonicate at 500 W for 15 min until the dispersion is uniform to obtain a graphene oxide dispersion.

[0098] S3. Dissolve 0.04g of zwitterionic polydopamine soft nanospheres in 100mL of water, stir for 30min, and sonicate at 100W for 30min to obtain zwitterionic dopamine dispersion.

[0099] S4. The graphene oxide dispersion described in step S2 and the zwitterionic polydopamine dispersion described in step S3 are spin-coated at a speed of 1200 r / min for 90 s, and then cyclically spin-coated layer by layer from bottom to top onto the mixed cellulose ester support. The average pore size of the nylon flat support is 200 nm, forming a film layer after 20 spin-coating cycles. The prepared film is placed in a vacuum drying oven and dried at 30°C for 24 h to obtain the graphene oxide composite film.

[0100] The preparation method of N-aminoethylpiperazine propyl sulfonate (AEEPS) in this embodiment is the same as that in Example 1.

[0101] The graphene oxide composite membrane of this embodiment was subjected to a permeation test. The test results were as follows: under the test conditions of pH=10, K was obtained. + The permeation rate was 0.569 mol·m⁻¹. 2 ·h -1 Mg 2+ The permeation rate is 0.038 m0l·m 2 ·h -1 SO4 2- The permeation rate is 0.053 mol·m⁻¹ 2 ·h -1 .

[0102] Based on the selectivity calculation formula, when the test condition is pH=4, K can be obtained. + / Mg 2+ Selectivity was 15.0, Cl - SO4 2- The selectivity is 10.7.

[0103] Example 5

[0104] An embodiment of the present invention is a pH-responsive graphene oxide composite membrane.

[0105] The preparation method of the pH-responsive graphene oxide composite membrane described in this embodiment differs from that in Example 1 only in step S1: the amount of the zwitterionic monomer N-aminoethylpiperazine propylsulfonate added is 1.6 g. All other steps in the preparation method of the pH-responsive graphene oxide composite membrane described in this embodiment are the same as in Example 1.

[0106] The preparation method of N-aminoethylpiperazine propyl sulfonate (AEEPS) in this embodiment is the same as that in Example 1.

[0107] The graphene oxide composite membrane of this embodiment was subjected to a permeation test. The test results were as follows: under the test conditions of pH=10, K was obtained. + The permeation rate is 0.677 mol·m⁻¹ 2 ·h -1Mg 2+ The permeation rate is 0.040 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate was 0.059 mol·m⁻¹. 2 ·h -1 When the test condition is pH=7, K can be obtained. + The permeation rate is 0.605 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.045 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.054 mol·m⁻¹ 2 ·h -1 When the test condition is pH=4, K can be obtained. + The permeation rate is 0.532 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.051 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.078 mol·m⁻¹ 2 ·h -1 .

[0108] Based on the selectivity calculation formula, when the test condition is pH=10, K can be obtained. + / Mg 2+ Selectivity was 16.9, Cl - SO4 2- The selectivity was 11.5; the test condition was pH=7, at which point K was obtained. + / Mg 2+ Selectivity was 13.4, Cl - SO4 2- The selectivity was 11.2; the test condition was pH=4, at which point K was obtained. + / Mg 2+ Selectivity is 10.4, Cl - SO4 2- The selectivity is 6.8.

[0109] Comparative Example 1

[0110] This invention provides a comparative example of a pH-responsive graphene oxide composite membrane.

[0111] The preparation method of the pH-responsive graphene oxide composite film described in this comparative example includes the following steps:

[0112] S1. Disperse 20 mg of graphene oxide nanosheets in 100 mL of water, stir for 30 min, and sonicate at 500 W for 5 min until the dispersion is uniform to obtain graphene oxide dispersion.

[0113] S2. The graphene oxide dispersion described in step S1 is spin-coated at a speed of 2000 r / min for 30 s, sequentially spin-coated from bottom to top onto an alumina sheet support. The alumina sheet support has an average pore size of 1000 nm, forming a film layer after 20 spin-coating cycles. The prepared film is placed in a vacuum drying oven and dried at 45°C for 18 h to obtain a graphene oxide composite film.

[0114] The graphene oxide composite membrane of this comparative example was subjected to a permeation test. The test results were as follows: under the test conditions of pH=10, K was obtained. + The permeation rate is 0.288 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.043 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.052 mol·m⁻¹ 2 ·h -1 When the test condition is pH=7, K can be obtained. + The permeation rate is 0.274 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.037 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.057 mol·m⁻¹ 2 ·h -1 When the test condition is pH=4, K can be obtained. + The permeation rate is 0.259 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.034 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.068 mol·m⁻¹ 2 ·h -1 .

[0115] Based on the selectivity calculation formula, when the test condition is pH=10, K can be obtained. + / Mg 2+ Selectivity is 6.7, Cl - SO4 2- The selectivity is 5.5; the test condition is pH=7, and K can be obtained.+ / Mg 2+ Selectivity is 7.4, Cl - SO4 2- The selectivity is 4.8; the test condition is pH=4, and K can be obtained. + / Mg 2+ Selectivity is 7.6, Cl - SO4 2- The selectivity is 3.8.

[0116] Comparing Example 1 with Comparative Example 1, it can be seen that the graphene oxide composite membrane of Example 1 significantly improved the permeability of monovalent ions and the selectivity of monovalent / divalent ions under different pH values. Therefore, the graphene oxide composite membrane prepared by the present invention has high permeability and selectivity in response to pH stimulation in acidic or alkaline environments.

[0117] Comparative Example 2

[0118] This invention provides a comparative example of a pH-responsive graphene oxide composite membrane.

[0119] The preparation method of the pH-responsive graphene oxide composite film described in this comparative example differs from that in Example 1 only in step S1: the amount of zwitterionic monomer N-aminoethylpiperazine propyl sulfonate added is 0.2 g.

[0120] The preparation method of N-aminoethylpiperazine propyl sulfonate (AEEPS) in this comparative example is the same as that in Example 1.

[0121] The graphene oxide composite membrane of this comparative example was subjected to a permeation test. The test results were as follows: under the test conditions of pH=10, K was obtained. + The permeation rate is 0.338 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.047 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.066 mol·m⁻¹ 2 ·h -1 When the test condition is pH=7, K can be obtained. + The permeation rate is 0.312 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.047 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate is 0.058 mol·m⁻¹ 2 ·h -1 When the test condition is pH=4, K can be obtained.+ The permeation rate is 0.269 mol·m⁻¹ 2 ·h -1 Mg 2+ The permeation rate is 0.048 mol·m⁻¹ 2 ·h -1 SO4 2- The permeation rate was 0.071 mol·m⁻¹ 2 ·h -1 .

[0122] Based on the selectivity calculation formula, when the test condition is pH=10, K can be obtained. + / Mg 2+ Selectivity is 7.2, Cl - SO4 2- The selectivity is 5.1; the test condition is pH=7, and K can be obtained. + / Mg 2+ Selectivity is 6.6, Cl - SO4 2- The selectivity is 5.4; the test condition is pH=4, and K can be obtained. + / Mg 2+ Selectivity is 5.6, Cl - SO4 2- The selectivity is 3.8.

[0123] Comparing Example 1 and Comparative Example 2, it can be seen that the mass ratio of zwitterionic monomer to dopamine is within the protection scope of this invention, which enables the ionized polydopamine soft nanospheres to have a more suitable diameter and charge density. This is beneficial for precisely controlling the physical structure and charge characteristics of the two-dimensional nanofluid channels between graphene layers, thereby improving the ion permeability and ion selectivity of the prepared graphene oxide composite film under different pH responses.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a pH-responsive graphene oxide composite membrane, characterized by, The preparation method comprises the following steps: S1, adding dopamine into a solvent of a zwitterionic monomer, mixing uniformly, and performing a self-polymerization reaction to obtain zwitterionic polydopamine soft nanospheres; S2, adding graphene oxide into a solvent A and uniformly dispersing to obtain a graphene oxide dispersion; S3, adding the zwitterionic polydopamine soft nanospheres in step S1 into a solvent B and uniformly dispersing to obtain a zwitterionic polydopamine dispersion; S4, sequentially and circularly spin-coating the graphene oxide dispersion in step S2 and the zwitterionic polydopamine dispersion in step S3 on a support from bottom to top to form a film layer, and drying to obtain the graphene oxide composite film with pH responsiveness; In the step S1, the active functional groups of the zwitterionic monomer include amino groups and sulfonic acid groups. In the step S2, the solvent A includes water; and in the step S3, the solvent B includes water and / or anhydrous ethanol.

2. The production method according to claim 1, wherein In the step S1, the zwitterionic monomer is N-aminoethylpiperazine propyl sulfonate.

3. The production method according to claim 1, wherein In the step S1, the D50 of the zwitterionic polydopamine soft nanospheres is 1-5 nm.

4. The production method according to claim 1, wherein In the step S1, the mass ratio of the zwitterionic monomer to dopamine is zwitterionic monomer:dopamine=2:1-8:

1.

5. The production method according to claim 1, wherein In the step S2, the concentration of graphene oxide in the graphene oxide dispersion is 0.05-0.2 mg / mL.

6. The production method according to claim 1, wherein In the step S4, the process parameters of the spin-coating are as follows: the rotation speed is 800-2000 r / min, the single spin-coating time of each spin-coating layer is 30-120 s, and water is used for cleaning after spin-coating of each spin-coating layer; and the cycle number of the spin-coating is 5-30.

7. The production method according to claim 1, wherein In the step S4, the support is a porous support; and the average pore size of the porous support is 10-1000 nm.

8. The graphene oxide composite film prepared by the preparation method in any one of claims 1-7.

9. The use of the graphene oxide composite film in claim 8 in the preparation of an ion-selective separation membrane.

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