A GO composite membrane for highly selective separation of low molecular weight cationic dyes, preparation method and application thereof

Abstract

The present invention discloses a GO composite membrane for highly selectively separating low-molecular-weight cationic dyes, a preparation method, and its application. The composite membrane is constructed by coating polydopamine on a polymer ultrafiltration base membrane and alternately depositing composite graphene oxide and partially reduced graphene oxide. The composite graphene oxide is prepared by cross-linking crown ether amine with partially reduced graphene oxide. The cavity structure within the crown ether amine molecule can electrostatically interact with the cationic dye, thereby improving the composite membrane's selective retention of the cationic dye. By controlling parameters such as the crown ether amine structure, the degree of graphene oxide reduction, and the loading ratio of composite graphene oxide to graphene oxide, the performance of the composite membrane can be optimized to achieve efficient separation of dyes of different molecular weights and charge types. The GO composite membrane has high selectivity for low-molecular-weight cationic dyes and is suitable for industrial printing and dyeing wastewater treatment, efficient dye separation and recovery, and environmental pollution control.

Description

Technical Field

[0001] The present invention belongs to the field of functional composite membrane technology, and relates to graphene oxide (GO) membrane separation materials and modification technologies thereof. More specifically, it relates to a GO composite membrane for highly selectively separating low-molecular-weight cationic dyes, a preparation method, and its application, which is used for the efficient separation of cationic dyes and anionic dyes in industrial printing and dyeing wastewater treatment and for improving the stability and selectivity of membrane materials. Background Art

[0002] Printing and dyeing wastewater is complex, containing large amounts of organic dyes and other pollutants, posing significant risks to the environment and human health. Cationic dye molecules are a relatively important class of organic dye molecules. However, during the production and dyeing process, cationic dyes utilize a variety of chemicals that are harmful to the human body and the environment. These chemicals can irritate the skin and eyes, cause skin allergies, and even be carcinogenic. Therefore, prior to discharge, cationic dyes must be efficiently separated and removed through pre-treatment.

[0003] Traditional dye wastewater treatment methods mainly include physical, chemical and biological methods. Physical methods mainly include adsorption, flocculation and membrane separation. Their treatment efficiency is greatly affected by factors such as dye type, concentration and water quality, and there are problems such as adsorbent saturation and flocculant residue. Chemical methods mainly include oxidation, reduction and photocatalytic degradation. Their treatment costs are high and may cause secondary pollution. Biological methods mainly include activated sludge and anaerobic biological treatment. Their treatment efficiency is greatly affected by the biodegradability of the dye, and the treatment cycle is long. In addition, these methods usually lack the ability to selectively separate cationic and anionic dyes, making it difficult to achieve efficient and accurate separation.

[0004] Compared with traditional separation methods, membrane separation technology offers advantages such as energy conservation and environmental protection, small footprint, and continuous operation. In recent years, it has demonstrated tremendous potential for application in wastewater treatment. Ideal membrane separation materials can achieve high permeability, selectivity, and stability by regulating the size, distribution, and shape of the pore structure in the membrane material. However, research on membrane materials with higher selectivity for cationic dyes is still immature. Most existing membrane materials lack significant selectivity for both anionic and cationic dyes, making it difficult to achieve efficient and selective separation of specific target dyes.

[0005] In recent years, the rise of the synthesis and processing of two-dimensional nanomaterials such as graphene oxide (GO) has provided a platform for the development of ideal membrane materials with high selective separation performance due to its unique layered structure, rich oxygen-containing functional groups and excellent mechanical properties. By regulating the gaps between GO layers, GO membranes can be used as nanofiltration membranes to achieve dye separation. However, the rich oxygen-containing functional groups on the surface of GO make it easy to swell and peel in aqueous solution, reducing the stability of GO in water, resulting in the deterioration of the structure and stability of the assembled GO membrane. Existing technologies mostly use methods such as coating dopamine on the surface of the base membrane to increase the adhesion to GO and embedding intercalation molecules between GO layers to enhance the stability of GO membranes. However, how to design and synthesize intercalation molecules with specific functions and how to accurately control the embedded amount and distribution of intercalation molecules are still immature.

[0006] In summary, while existing membrane materials show some potential for the treatment of printing and dyeing wastewater, there is still considerable room for improvement in terms of selective separation of cationic and anionic dyes, enhanced membrane stability, and optimized preparation processes. Therefore, the development of nanofiltration membrane materials with high selectivity, stability, and flux, particularly GO composite membranes with high selectivity for low-molecular-weight cationic dyes, is crucial for the efficient treatment of printing and dyeing wastewater and the sustainable utilization of water resources. Summary of the Invention

[0007] (1) Purpose of the invention

[0008] The present invention mainly solves the technical problem of low selectivity of cationic dyes and anionic dyes in the dye separation process of current membrane materials, and at the same time strengthens the problem of GO membrane stability. To this end, the present invention provides a GO composite membrane for highly selectively separating low molecular weight cationic dyes, a preparation method and its application. By depositing a polydopamine layer on the surface of the polymer ultrafiltration base membrane to enhance the adhesion between the base membrane and GO, and using a self-designed synthetic crown ether amine intercalation molecule and partially reduced graphene oxide to cross-link and react, a stable composite GO solution is prepared, and a pressure-assisted filtration method is used to assemble the composite membrane in multiple layers, ultimately achieving a comprehensive improvement in the performance of the membrane material. While the GO composite membrane has structural stability, it utilizes the unique negatively charged cavity structure of the crown ether amine molecule to electrostatically screen cationic dye molecules, achieving high selectivity for low molecular weight cationic dyes. By regulating the mixing ratio of crown ether amine and GO and the assembly parameters of the membrane, not only is the cationic dye separation efficiency of the membrane greatly improved, but it also has a comprehensive retention capacity for macromolecular dyes, and has broad prospects for industrial application.

[0009] (2) Technical solution

[0010] In order to achieve the purpose of the invention and solve the technical problems, the present invention adopts the following technical solutions:

[0011] The first object of the present invention is to provide a method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes, which is used for efficient separation and dye interception of low molecular weight cationic dyes and anionic dyes in the treatment of printing and dyeing wastewater. The preparation method comprises at least the following steps when implemented:

[0012] SS1. Design and Synthesis of Crown Ether Amine Intercalation Molecules

[0013] Based on the separation requirements of the target dye molecules, a crown ether amine with a cavity structure was independently designed and synthesized as an intercalation molecule. The crown ether amine intercalation molecule has a specific cavity structure and negative charge characteristics, which can specifically interact with low-molecular-weight cationic dyes through electrostatic interactions, thereby achieving selective retention of cationic dyes. The crown ether amine intercalation molecule is selected from benzo-15-crown-5 ether amine, aza-18-crown-6 ether amine, 14-crown-4 ether amine, or their derivatives. Its structure contains a crown ether ring and an amino group. The synthesis process includes optimized reaction conditions and purification treatment to ensure its structural stability and functionality.

[0014] SS2. Polydopamine Modification of Polymer-Based Membrane Surfaces

[0015] Dopamine hydrochloride is dissolved in Tris-HCl buffer to form a polydopamine solution, a polymer ultrafiltration base membrane is immersed in the polydopamine solution, and a stirring and shaking reaction is carried out in a constant temperature oscillator to allow dopamine to undergo a self-polymerization reaction on the surface of the base membrane to form a uniform polydopamine coating, and the modified base membrane surface has enhanced adhesion and reduced pore size, the base membrane is removed and rinsed with deionized water and dried for later use, wherein the polymer ultrafiltration base membrane is selected from polyvinylidene fluoride membrane, nylon membrane or polysulfone membrane;

[0016] SS3. Preparation of partially reduced graphene oxide solution

[0017] Graphene oxide (GO) is dispersed in deionized water and ultrasonically treated to uniformly disperse it. An alkaline solution is then added to perform a partial reduction reaction at a certain temperature. The degree of reduction is controlled to achieve precise adjustment of the GO interlayer spacing. After the reaction is completed and cooled to room temperature, the pH value is adjusted to a weakly acidic state with an acid solution to obtain a partially reduced graphene oxide solution for later use. The alkaline solution is sodium hydroxide, potassium hydroxide, or ammonia solution, and the acid solution is hydrochloric acid or acetic acid solution.

[0018] SS4. Preparation of composite graphene oxide solution

[0019] adding the crown amine intercalation molecules prepared in step SS1 to the partially reduced graphene oxide solution prepared in step SS3, and performing a stirring reaction at a certain temperature to cause a cross-linking reaction between the crown amine and the partially reduced graphene oxide, thereby ensuring that the crown amine molecules are grafted onto the surface of the GO nanosheets through chemical cross-linking, and ultrasonically treating the mixed solution after the reaction to uniformly disperse the composite graphene oxide in water, thereby forming a uniformly dispersed composite graphene oxide solution;

[0020] SS5. Pressure-assisted assembly of multilayer composite GO membranes

[0021] The partially reduced graphene oxide solution prepared in step SS3 and the composite graphene oxide solution prepared in step SS4 are ultrasonically treated respectively, and then the partially reduced graphene oxide solution and the composite graphene oxide solution are alternately deposited onto the surface of the polydopamine-modified polymer ultrafiltration base membrane prepared in step SS2 by vacuum filtration or pressure-assisted deposition, to obtain a multilayer composite GO membrane structure having a layered stacking structure, wherein the loading ratio of the composite graphene oxide to the partially reduced graphene oxide is 10-90:90-10, and the number of alternately deposited layers is 2-10;

[0022] SS6. Post-treatment of multilayer composite GO membrane

[0023] The composite GO membrane assembled in step SS4 is dried to stabilize the membrane structure, and finally a GO composite membrane with high selectivity for separating low molecular weight cationic dyes is obtained.

[0024] The second object of the present invention is to provide a GO composite membrane, wherein the preparation of the GO composite membrane is based on the above-mentioned method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes of the present invention.

[0025] The third object of the present invention is to provide an application of the above-mentioned GO composite membrane as a printing and dyeing wastewater treatment membrane or a selective nanofiltration membrane in industrial wastewater treatment, dye separation and / or environmental pollution control.

[0026] (3) Technical effects

[0027] Compared with the prior art, the method for preparing a composite membrane for highly selectively separating low molecular weight cationic dyes and its application have the following beneficial and significant technical effects:

[0028] (1) The composite GO membrane provided by the present invention addresses the shortcomings of existing nanofiltration membranes, such as their limited selectivity for anionic / cationic dye separation and their inherently unstable bonding with the basement membrane. By coating the polymer ultrafiltration basement membrane with a dopamine layer, the surface is modified to form a uniform adhesion coating. This significantly enhances the bonding strength between the GO membrane and the basement membrane, thus avoiding the problem of membrane shedding or failure caused by insufficient adhesion during use of conventional GO membranes. The dopamine coating also effectively reduces the basement membrane pore size, further improving the membrane's overall separation performance.

[0029] (2) The present invention controls the degree of reduction of graphene oxide (GO) through a process of partially reducing GO, and regulates the interlayer spacing of GO by loading reduced GO on the surface, thereby achieving size screening of dye molecules of different molecular weights. For large molecular weight dyes, whether anions or cations, the composite membrane exhibits a high rejection rate. For example, the rejection rate for brilliant yellow, acid green, reactive red, and acid violet is close to or reaches 100%. This shows that the composite membrane not only has high selectivity for low molecular weight cationic dyes, but also has a universal high rejection rate for large molecular weight dyes.

[0030] (3) The present invention uses self-designed and synthesized crown ether amine intercalation molecules in the composite GO membrane. The cavity structure of the crown ether amine carries a negative charge. Through the electrostatic interaction between the crown ether amine cavity and the cationic dye, the selective separation of cationic dyes can be achieved. Compared with traditional nanofiltration membranes, the composite membrane has a significantly improved retention rate for cationic dyes. Experimental results show that the composite membrane has a retention rate of up to 95.15% for rhodamine 6G (a cationic dye) with a molecular weight of 478, while the retention rate for the anionic dye lissamine rhodamine B with a larger molecular weight is only 25.75%, demonstrating excellent separation selectivity.

[0031] (4) The present invention increases the adhesion stability of GO to the polymer base film by coating dopamine on the base film. A crown amine-composite GO mixture prepared by cross-linking GO with a self-designed and synthesized crown amine molecule is loaded onto the polymer base film to improve the stability of GO interlayers. By varying the crown amine structure concentration, dopamine coating concentration and temperature, graphene oxide reduction degree, crown amine to GO ratio, composite GO to GO loading ratio, and assembly times, controllable retention of small molecular weight cationic dyes and complete retention of large molecular weight dyes can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 FIG2 is a flow chart of a method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes provided by an embodiment of the present invention;

[0033] Figure 2 Shown is a synthetic route for crown ether amines in the present invention, taking benzo-15-crown-5 ether amine as an example;

[0034] Figure 3 Shown is the NMR spectrum of benzo-15-crown-5 ether amine in the present invention;

[0035] Figure 4 Shown is the infrared spectrum of benzo-15-crown-5 ether amine in the present invention;

[0036] Figure 5 Shown is a schematic diagram of the retention of dyes filtered by the composite GO membrane in the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the implementation of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the drawings in the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention, not all of the embodiments, and the described embodiments are exemplary and are intended to be used to explain the present invention, but should not be understood as limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] As a specific example, Figure 1 As shown, the method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes of the present invention is used for efficient separation and dye interception of low molecular weight cationic dyes and anionic dyes in the treatment of printing and dyeing wastewater. The method comprises the following steps when implemented:

[0040] SS1. Design and Synthesis of Crown Ether Amine Intercalation Molecules

[0041] Based on the separation requirements of the target dye molecules, a crown ether amine with a cavity structure was independently designed and synthesized as an intercalation molecule. This crown ether amine intercalation molecule possesses a specific cavity structure and negative charge, enabling specific electrostatic interactions with low-molecular-weight cationic dyes, thereby achieving selective retention of cationic dyes. The crown ether amine intercalation molecule is selected from benzo-15-crown-5 ether amine, aza-18-crown-6 ether amine, 14-crown-4 ether amine, or their derivatives, and its structure contains a crown ether ring and an amino group. The synthesis process includes optimized reaction conditions and purification to ensure its structural stability and functionality.

[0042] Preferably, the design and synthesis of crown ether amine intercalation molecules includes the following steps: using crown ethers and their derivatives as raw materials, introducing amino groups through an amination reaction, dissolving the crown ether in an anhydrous solvent under the protection of an inert gas, adding an amination reagent for reaction, and then purifying the reaction product by vacuum distillation or column chromatography to obtain the crown ether amine intercalation molecules; the reaction conditions include a reaction temperature of 50-80° C., a reaction time of 4-8 hours, and anhydrous ethanol or dichloromethane as the reaction solvent; and the synthesized crown ether amine intercalation molecules are characterized and confirmed by nuclear magnetic resonance (NMR) and / or infrared spectroscopy (IR) to ensure that they meet the design requirements.

[0043] SS2. Polydopamine Modification of Polymer-Based Membrane Surfaces

[0044] Dopamine hydrochloride is dissolved in Tris-HCl buffer to form a polydopamine solution, a polymer ultrafiltration base membrane is immersed in the polydopamine solution, and a stirring and oscillating reaction is carried out in a constant temperature oscillator to allow dopamine to undergo a self-polymerization reaction on the surface of the base membrane to form a uniform polydopamine coating, and the modified base membrane surface has enhanced adhesion and reduced pore size. The base membrane is removed, rinsed with deionized water, and dried for later use, wherein the polymer ultrafiltration base membrane is selected from polyvinylidene fluoride membrane, nylon membrane or polysulfone membrane.

[0045] Preferably, the specific process conditions for polydopamine modification include: soaking the polymer ultrafiltration base membrane in 0.01-0.03 mol / L Tris-HCl buffer with a pH value of 8.0-9.0, adding 0.5-3.0 g / L dopamine hydrochloride solution, and oscillating at a speed of 100-130 rpm in a constant temperature oscillator at 25-40°C for 4-8 hours to allow dopamine to undergo self-polymerization reaction on the surface of the base membrane to form a polydopamine coating with a thickness of 10-50 nm. After the oscillation is completed, the base membrane is removed and rinsed with deionized water, wherein the thickness of the polymer ultrafiltration base membrane is 100-200 μm, and the pore size range of the membrane is 50-200 nm, so as to ensure the stability and uniformity of the membrane material in the subsequent graphene oxide loading process.

[0046] Preferably, the functionality of the polydopamine coating is further enhanced by adding 0.1-0.5 g / L of an oxidant (such as potassium persulfate) during the reaction to promote the polymerization rate of dopamine, and by adjusting the polymerization time (4-8 hours) to control the thickness and density of the coating. The optimized polydopamine coating not only significantly enhances the adhesion between graphene oxide and the base film, but also further enhances the chemical stability and anti-fouling properties of the film through its surface active groups (such as amino and phenolic hydroxyl groups).

[0047] SS3. Preparation of partially reduced graphene oxide solution

[0048] Graphene oxide (GO) is dispersed in deionized water and ultrasonically treated to uniformly disperse it. An alkaline solution is then added to perform a partial reduction reaction at a certain temperature. The degree of reduction is controlled to achieve precise adjustment of the GO interlayer spacing. After the reaction is completed and cooled to room temperature, the pH value is adjusted to a weakly acidic state with an acid solution to obtain a partially reduced graphene oxide solution for later use. The alkaline solution is sodium hydroxide, potassium hydroxide, or ammonia solution, and the acid solution is hydrochloric acid or acetic acid solution.

[0049] Preferably, the preparation of the partially reduced graphene oxide solution includes the following conditions: after ultrasonic treatment of a 1-10 mg / L graphene oxide dispersion for 0.5-2 hours, 0.02-0.08 mol / L sodium hydroxide solution is added, and the reaction is stirred at 60-80° C. for 1-2 hours, partial reduction of GO is achieved by regulating the reaction time and temperature, and after cooling to room temperature, the pH value is adjusted to 5-7 with an acid solution, and the GO interlayer spacing is adjusted to 0.8-1.2 nm by controlling the degree of reduction to meet the needs of low molecular weight dye screening, and the degree of reduction of graphene oxide is characterized by X-ray photoelectron spectroscopy (XPS), and the C / O ratio is controlled between 2.5-3.0 to ensure that the GO interlayer spacing is suitable for the separation requirements of low molecular weight dyes while maintaining its dispersion stability in an aqueous environment.

[0050] SS4. Preparation of composite graphene oxide solution

[0051] The crown ether amine intercalation molecules prepared in step SS1 are added to the partially reduced graphene oxide solution prepared in step SS3, and the reaction is stirred at a certain temperature to cause a cross-linking reaction between the crown ether amine and the partially reduced graphene oxide, thereby ensuring that the crown ether amine molecules are grafted onto the surface of the GO nanosheets through chemical cross-linking. The mixed solution after the reaction is ultrasonically treated to uniformly disperse the composite graphene oxide in water, thereby forming a uniformly dispersed composite graphene oxide solution.

[0052] Preferably, the cross-linking reaction conditions of the crown ether amine intercalation molecules and the partially reduced graphene oxide include: adding the crown ether amine intercalation molecules to the partially reduced graphene oxide solution so that the mass fraction of the crown ether amine is 0.05-0.2wt%, stirring the mixed solution at 20-40°C for 2-4 hours, and ultrasonically treating the mixed solution for 0.5-2 hours after the reaction to ensure that the crown ether amine molecules are evenly distributed between the GO sheets. The ratio of the crown ether amine intercalation molecules to the graphene oxide in the final composite graphene oxide solution is 1-99:99-1, thereby achieving precise control of the GO interlayer spacing and significantly improving the structural stability.

[0053] SS5. Pressure-assisted assembly of multilayer composite GO membranes

[0054] The partially reduced graphene oxide solution prepared in step SS3 and the composite graphene oxide solution prepared in step SS4 are ultrasonically treated respectively, and then the partially reduced graphene oxide solution and the composite graphene oxide solution are alternately deposited onto the surface of the polydopamine-modified polymer ultrafiltration base membrane prepared in step SS2 by vacuum filtration or pressure-assisted deposition, thereby obtaining a multilayer composite GO membrane structure having a layered stacking structure, wherein the loading ratio of the composite graphene oxide to the partially reduced graphene oxide is 10-90:90-10, and the number of alternately deposited layers is 2-10.

[0055] Preferably, the alternating deposition process of the partially reduced graphene oxide solution and the composite graphene oxide solution comprises: using a vacuum filtration device to filter the partially reduced graphene oxide solution and the composite graphene oxide solution at a rate of 50-100 mL / m 2 The amount of the dye is deposited onto the surface of the polymer base membrane modified with polydopamine; a drying treatment of 60-120 seconds is performed after each deposition to ensure the flatness and stability of the deposited layer; the total number of alternating deposition layers is controlled at 4-8 layers to achieve optimal separation performance for low molecular weight cationic dyes.

[0056] Preferably, the loading ratio of partially reduced graphene oxide and composite graphene oxide is 20-80:80-20, which is optimized by adjusting the solution concentration and filtration time of each deposition; wherein the loading amount of partially reduced graphene oxide is 50-100 mg / m 2 The loading amount of composite graphene oxide is 10-50 mg / m 2 The total loading of composite GO membrane is 50-150 mg / m 2 To ensure that the layered stacking structure of the membrane has both efficient separation performance and good mechanical strength and long-term stability.

[0057] SS6. Post-treatment of multilayer composite GO membrane

[0058] The composite GO membrane assembled in step SS4 is dried to stabilize the membrane structure, and finally a GO composite membrane with high selectivity for separating low molecular weight cationic dyes is obtained.

[0059] Preferably, the drying treatment of the multilayer composite GO membrane includes the following steps: placing the assembled composite GO membrane in an environment of 40-60°C for 12-24 hours and drying it in a low humidity environment to avoid deformation of the membrane structure due to humidity changes. The thickness of the dried membrane is controlled within the range of 100-200 μm, and the interlayer adhesion of the membrane is characterized by scanning electron microscopy (SEM) to verify the integrity of the membrane structure and the uniformity of the GO layer. In addition, the final performance of the GO composite membrane includes at least the following indicators: the retention rate of low molecular weight cationic dyes (such as rhodamine 6G, molecular weight 478) reaches more than 95%, the retention rate of anionic dyes with larger molecular weight (such as lissamine rhodamine B, molecular weight 580) does not exceed 30%, and the retention rate of large molecular weight dyes (such as acid green and reactive red) exceeds 97%; each performance index is obtained by dynamic filtration experiment under the conditions of pressure of 0.3 MPa and dye concentration of 20 mg / L, and the filtration flux is controlled at 20-50 L / m 2 Within the range of h.

[0060] The GO composite membrane prepared by the above steps achieves efficient separation by utilizing the electrostatic interaction between the negative charge of the crown ether amine cavity and the cationic dye. At the same time, by regulating the spacing between GO sheets and the ratio of intercalated molecules, the structural stability and separation selectivity of the membrane are significantly enhanced.

[0061] It should be noted that the present invention achieves selective interception of low-molecular-weight cationic and anionic dyes, as well as complete interception of dyes with larger molecular weights, by varying the crown amine molecular structure, concentration, dopamine hydrochloride depth, coating temperature and time, graphene oxide reduction temperature, crown amine and GO mixing ratio, composite GO and GO ratio, assembly times, and total GO loading. Because the unique cavity structure within the crown amine intercalation molecule in the present invention carries a negative charge, it exhibits high selectivity for intercepting cationic dyes. Furthermore, the interlamellar spacing of graphene oxide can be adjusted by varying the degree of graphene oxide reduction, while the crosslinking of crown amines can enhance the stability of GO interlamellar structures. The present invention is applicable to the modification of polymer-based membranes of various shapes, including flat membranes and hollow fiber membranes. It is also applicable to polymer-based membranes of various materials, including polyvinylidene fluoride membranes, nylon membranes, and polysulfone membranes. The structure of the crown amine can be 14-crown-4 etheramine, benzo-15-crown-5 etheramine, aza-18-crown-6 etheramine, and the like.

[0062] Example 2

[0063] On the basis of the above Example 1, in order to more clearly demonstrate the preparation method and performance of the GO composite membrane for the highly selective separation of low molecular weight cationic dyes of the present invention, this Example 2 uses benzo-15-crown-5 ether amine intercalation molecules as an example to elaborate on the preparation process of the composite membrane and the dye retention test results.

[0064] 1. Design and synthesis of benzo-15-crown-5 ether amine intercalation molecules

[0065] First, we designed and synthesized the benzo-15-crown-5 ether amine intercalation molecule. The synthesis route is shown in Figure 2 , dried and set aside. The specific synthesis steps are carried out according to the method described in SS1 of Example 1, and the target product benzo-15-crown-5 etheramine is finally obtained. The structure of the product is confirmed by nuclear magnetic resonance (NMR, Figure 3 ) and infrared spectroscopy (IR, Figure 4 ) characterization to confirm that its structure and functionality meet the design requirements. Figure 3 The characteristic peaks in the NMR spectrum are consistent with the theoretical structure of benzo-15-crown-5 ether amine. Figure 4 The IR spectrum also clearly showed the characteristic absorption peak of amino group, proving the successful synthesis of the target compound.

[0066] 2. Deposit a polydopamine adhesion layer on the surface of the polymer base film

[0067] First, prepare a 0.01 mol / L Tris-HCl (pH = 8.5) buffer solution: Use an analytical balance to accurately weigh 1.2114 g of Tris (tris(hydroxymethylaminomethane)), dissolve it, and dilute to 1 L. Add 4.8 mol / L hydrochloric acid solution and 0.48 mol / L dilute hydrochloric acid to adjust the pH to 8.5. Pour a certain amount of Tris-HCl buffer solution into a beaker and weigh 2 g / L of dopamine hydrochloride and add it to the buffer solution. Place the basement membrane in the above solution and oscillate in a constant temperature oscillator with the temperature set at 35°C and the speed adjusted to 115 rpm for 6 hours. After the oscillation is complete, remove the basement membrane, rinse it clean, and soak it in deionized water for later use.

[0068] 3. Partial reduction of graphene oxide

[0069] A 5 mg / L graphene oxide solution was prepared and sonicated for 1 hour. Sodium hydroxide was added to a concentration of 0.05 mol / L. The mixture was placed on a magnetic stirring heater, maintained at 70°C for one hour, and then cooled to room temperature. After the reaction, the pH was adjusted to approximately 5.89 with 4.8 mol / L concentrated hydrochloric acid to completely neutralize the excess sodium hydroxide. The prepared partially reduced GO solution was characterized by X-ray photoelectron spectroscopy (XPS), and the C / O ratio was controlled between 2.5 and 3.0 to ensure the stability of the sheet structure and suitability for subsequent use.

[0070] 4. Cross-linking reaction between benzo-15-crown-5 ether amine intercalation molecules and GO

[0071] Take an appropriate amount of the partially reduced GO solution and add benzo-1,5-crown-5-etheramine to a 0.1 wt% concentration of crown etheramine. The mixture is stirred magnetically at 30°C for 3 hours to ensure the crown etheramine is grafted onto the GO nanosheets. The resulting mixture is then ultrasonicated for 1 hour to ensure uniform dispersion of the composite graphene oxide in the water. This creates a composite graphene oxide solution, which is then set aside.

[0072] 5. Pressure-assisted assembly of composite graphene oxide membranes

[0073] The partially reduced graphene solution was deposited on the polydopamine-coated base film using a suction filtration device, with a loading of 80 mg / m 2 The composite graphene oxide solution was then filtered using the same method, with a loading of 20 mg / m 2 After the composite graphene oxide solution is filtered, it forms a layered stacking structure under pressure. Alternate deposition is performed 4 times (a total of 8 layers) to form a multilayer composite GO membrane with a gradient distribution structure. After each layer is deposited, it is dried for 60 seconds to enhance the interlayer bonding strength. After filtration, the composite GO membrane is placed at 40°C and dried for 16 hours. This completes the preparation process.

[0074] 6. Perform dye retention test on the membrane to determine the selectivity for anionic / cationic dyes

[0075] The dye concentration was selected as 20 mg / L, and the filtration pressure was 0.3 MPa. The rejection rate for the cationic dye Rhodamine 6G with a molecular weight of 478 was 95.15%, while the rejection rate for the anionic dye Lissamine Rhodamine B with a molecular weight of 580, which is basically similar to it, was only 25.75%. This data fully demonstrates that the introduction of crown ether amine intercalation molecules has given the composite GO membrane an extremely high selectivity for cationic dyes. In addition, for dyes with larger molecular weights, the rejection rate for anionic dyes has also been significantly improved due to the screening effect of the GO membrane layer. The rejection rate for brilliant yellow can reach 97.74%, the rejection rate for acid green is 99.56%, the rejection rate for reactive red is 100%, and the rejection rate for acid violet is 100%. For details, see Figure 5 .

[0076] Experiments have shown that the introduction of crown ether amine intercalation molecules significantly improves the selectivity of the GO composite membrane for cationic dyes. Furthermore, the sieving effect of the GO membrane's layered structure enhances the retention of large molecular weight dyes. The superior performance of the membrane further validates the scientific and innovative nature of the present invention's technical solution.

[0077] The above embodiments fully and effectively achieve the objectives of the present invention. Those skilled in the art will appreciate that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the above specific embodiments. Although the present invention has been described with reference to the embodiments currently considered to be the most practical and preferred, it should be understood that the present invention is not limited to the disclosed embodiments, and any modifications that do not deviate from the functional and structural principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes, characterized in that: The preparation method comprises at least the following steps when implemented: SS1. Based on the separation requirements of the target dye molecule, a crown ether amine with a cavity structure was independently designed and synthesized as an intercalation molecule. The crown ether amine intercalation molecule was selected from benzo-15-crown-5 ether amine, aza-18-crown-6 ether amine, 14-crown-4 ether amine, or their derivatives, and its structure contained a crown ether ring and an amino group. The synthesis process included optimized reaction conditions and purification to ensure its structural stability and functionality. SS2. Dopamine hydrochloride is dissolved in Tris-HCl buffer to form a polydopamine solution, a polymer ultrafiltration base membrane is immersed in the polydopamine solution, and the reaction is stirred and shaken in a constant temperature oscillator to cause dopamine to self-polymerize on the base membrane surface to form a uniform polydopamine coating. The modified base membrane surface has enhanced adhesion and reduced pore size. The base membrane is removed, rinsed with deionized water, and dried for later use. The polymer ultrafiltration base membrane is selected from polyvinylidene fluoride membrane, nylon membrane, or polysulfone membrane; SS3. Graphene oxide (GO) is dispersed in deionized water and ultrasonically treated to achieve uniform dispersion. An alkaline solution is then added and a partial reduction reaction is performed at a specific temperature. The degree of reduction is controlled to precisely adjust the spacing between GO interlayers. After the reaction is completed and cooled to room temperature, the pH is adjusted to a weakly acidic pH using an acid solution, thereby obtaining a partially reduced graphene oxide solution for later use. The alkaline solution is sodium hydroxide, potassium hydroxide, or ammonia solution, and the acid solution is hydrochloric acid or acetic acid solution. SS4. The crown amine intercalation molecules prepared in step SS1 are added to the partially reduced graphene oxide solution prepared in step SS3, and the reaction is stirred at a certain temperature to cause the crown amine to cross-link with the partially reduced graphene oxide, ensuring that the crown amine molecules are grafted onto the surface of the GO nanosheets by chemical cross-linking. The mixture after the reaction is ultrasonically treated to uniformly disperse the composite graphene oxide in water to form a uniformly dispersed composite graphene oxide solution; SS5. The partially reduced graphene oxide solution prepared in step SS3 and the composite graphene oxide solution prepared in step SS4 are separately subjected to ultrasonic treatment, and then the partially reduced graphene oxide solution and the composite graphene oxide solution are alternately deposited onto the surface of the polydopamine-modified polymer ultrafiltration base membrane prepared in step SS2 by vacuum filtration or pressure-assisted deposition to obtain a multilayer composite GO membrane structure having a layered stacking structure, wherein the loading ratio of the composite graphene oxide to the partially reduced graphene oxide is 10-90:90-10, and the number of alternately deposited layers is 2-10; SS6. The composite GO membrane assembled in step SS4 is dried to stabilize the membrane structure, and finally a GO composite membrane with high selectivity for separating low molecular weight cationic dyes is obtained.

2. The method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes according to claim 1, characterized in that: In step SS1, the design and synthesis of crown ether amine intercalation molecules include the following steps: using crown ethers and their derivatives as raw materials, introducing amino groups through an amination reaction, dissolving the crown ether in an anhydrous solvent under the protection of an inert gas, adding an amination reagent for reaction, and then purifying the reaction product by vacuum distillation or column chromatography to obtain the crown ether amine intercalation molecules; the reaction conditions include a reaction temperature of 50-80°C, a reaction time of 4-8 hours, and a reaction solvent of anhydrous ethanol or dichloromethane; the synthesized crown ether amine intercalation molecules are structurally characterized and confirmed by nuclear magnetic resonance (NMR) and / or infrared spectroscopy (IR) to ensure that they meet the design requirements.

3. The method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes according to claim 1, wherein: In step SS2, the specific process conditions for polydopamine modification include: soaking the polymer ultrafiltration base membrane in 0.01-0.03 mol / L Tris-HCl buffer with a pH value of 8.0-9.0, adding 0.5-3.0 g / L dopamine hydrochloride solution, and oscillating at a speed of 100-130 rpm in a constant temperature oscillator at 25-40 ° C for 4-8 hours to allow dopamine to self-polymerize on the surface of the base membrane to form a polydopamine coating with a thickness of 10-50 nm. After the oscillation is completed, the base membrane is removed and rinsed with deionized water, wherein the thickness of the polymer ultrafiltration base membrane is 100-200 μm, and the pore size range of the membrane is 50-200 nm, to ensure the stability and uniformity of the membrane material in the subsequent graphene oxide loading process.

4. The method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes according to claim 1, characterized in that: In step SS3, the preparation of a partially reduced graphene oxide solution includes the following conditions: after ultrasonic treatment of a 1-10 mg / L graphene oxide dispersion for 0.5-2 hours, 0.02-0.08 mol / L sodium hydroxide solution is added, and the reaction is stirred at 60-80°C for 1-2 hours, partial reduction of GO is achieved by regulating the reaction time and temperature. After cooling to room temperature, the pH value is adjusted to 5-7 using an acid solution, and the GO interlayer spacing is adjusted to 0.8-1.2 nm by controlling the degree of reduction to meet the needs of low molecular weight dye screening, and the degree of reduction of graphene oxide is characterized by X-ray photoelectron spectroscopy (XPS), and the C / O ratio is controlled between 2.5 and 3.

0.

5. The method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes according to claim 1, wherein: In step SS4, the cross-linking reaction conditions of the crown ether amine intercalation molecules and the partially reduced graphene oxide include: adding the crown ether amine intercalation molecules to the partially reduced graphene oxide solution so that the mass fraction of the crown ether amine is 0.05-0.2wt%, stirring the mixed solution at 20-40°C for 2-4 hours, and then ultrasonically treating the mixed solution for 0.5-2 hours after the reaction to ensure that the crown ether amine molecules are evenly distributed between the GO sheets. The ratio of the crown ether amine intercalation molecules to the graphene oxide in the final composite graphene oxide solution is 1-99:99-1.

6. The method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes according to claim 1, characterized in that: In step SS5, the alternating deposition process of the partially reduced graphene oxide solution and the composite graphene oxide solution comprises: using a vacuum filtration device to filter the partially reduced graphene oxide solution and the composite graphene oxide solution at a rate of 50-100 mL / m 2 The amount of partially reduced graphene oxide was deposited on the surface of the polymer base film modified with polydopamine, and a drying treatment was performed for 60-120 seconds after each deposition. The total number of layers of alternating deposition was controlled at 4-8 layers; the loading ratio of partially reduced graphene oxide and composite graphene oxide was 20-80:80-20, which was optimized by adjusting the solution concentration and filtration time of each deposition; the loading amount of partially reduced graphene oxide was 50-100 mg / m 2 The loading amount of composite graphene oxide is 10-50 mg / m 2 The total loading of composite GO membrane is 50-150 mg / m 2 .

7. The method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes according to claim 1, characterized in that: In step SS6, the drying treatment of the multilayer composite GO membrane includes the following steps: the assembled composite GO membrane is placed in an environment of 40-60°C for 12-24 hours and is completed in a low humidity environment to avoid deformation of the membrane structure due to humidity changes. The thickness of the dried membrane is controlled in the range of 100-200μm, and the interlayer adhesion of the membrane is characterized by scanning electron microscopy (SEM) to verify the integrity of the membrane structure and the uniformity of the GO layer.

8. The method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes according to claim 1, characterized in that: In step SS6, the final performance of the GO composite membrane includes at least the following indicators: a retention rate of more than 95% for low molecular weight cationic dyes, a retention rate of no more than 30% for larger molecular weight anionic dyes, and a retention rate of more than 97% for large molecular weight dyes; The performance indicators were obtained through dynamic filtration experiments under the conditions of 0.3MPa pressure and 20mg / L dye concentration, and the filtration flux was controlled at 20-50L / m 2 Within the range of h.

9. A GO composite membrane, characterized in that The preparation of the GO composite membrane is based on the method for preparing a GO composite membrane for highly selectively separating low molecular weight cationic dyes according to any one of claims 1 to 8.

10. Use of the GO composite membrane according to claim 9 as a printing and dyeing wastewater treatment membrane or a selective nanofiltration membrane in industrial wastewater treatment, dye separation and / or environmental pollution control.

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