Porous graphene polyurea-based alkali-resistant composite membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of alkali-resistant composite nanofiltration membranes, and discloses a porous graphene polyurea-based alkali-resistant composite membrane and a preparation method and application thereof.The preparation method comprises the following steps that 1, aminated graphene quantum dots are dispersed in an alkaline aqueous solution with the pH being 10-14, a water-phase solution is prepared, diisocyanate is dissolved in a solvent, and the water-phase solution is prepared; preparing an oil phase solution; step 2, flatly laying the base membrane in a reaction device, sequentially adding a water phase solution and an oil phase solution into the reaction device, and carrying out interfacial polymerization, so that the aminated graphene quantum dots and isocyanate are pre-assembled to form a two-dimensional net structure; and step 3, adding an aqueous solution of diamine into the aqueous phase solution, enabling the diamine to react with the-NCO group in the two-dimensional network structure and the residual diisocyanate in the oil phase to form a separation layer, removing the aqueous phase solution and the oil phase solution, enabling the separation layer to be loaded on the surface of the base membrane, and performing heat treatment to obtain the porous graphene polyurea-based alkali-resistant composite membrane. The obtained composite membrane is high in alkali resistance and good in permeation separation performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of alkali-resistant composite nanofiltration membranes, in particular to a porous graphene polyurea-based alkali-resistant composite membrane and a preparation method and application thereof. BACKGROUND

[0002] Since graphene was separated from graphite in 2004, it has been widely applied in the fields of batteries, supercapacitors, energy storage, etc. due to its large specific surface area, good mechanical properties, high thermal conductivity, large electron mobility and low resistivity. By further reducing the size of graphene-based materials to the nanometer level through a top-down or bottom-up method, the surface effect, quantum size effect and macroscopic quantum tunneling effect of nanomaterials are combined with the advantages of graphene, so that graphene quantum dots applicable to the field of membrane preparation are obtained.

[0003] As a new type of carbon nanomaterial, graphene quantum dots are rich in hydroxyl and carboxyl hydrophilic chemical groups at the edges, which provide rich reaction sites for functional modification of the material. The functionalization mainly adopts a mode of introducing macromolecules or some small molecule substances through chemical bonding at the edges of graphene sheets, and embedding functional units between carbon-carbon skeletons through chemical reactions. Commonly used functionalization reagents mostly contain one or more elements such as fluorine, boron, nitrogen, sulfur and selenium. The introduction of these atoms or molecules can control the electronic structure and surface properties of graphene quantum dots, thereby endowing them with more rich physical and chemical properties such as fluorescence performance, catalytic activity and biocompatibility.

[0004] In common membrane preparation processes, functionalized graphene quantum dots with excellent performance often exist in the form of additives, which cannot fully exert their own advantages. At present, graphene oxide quantum dots (GOQDs) are applied to the preparation of nanofiltration membranes as the only water phase monomer. The introduction of GOQDs into the active layer not only improves the hydrophilicity of the membrane, but also reduces the filtration resistance of the membrane. The urethane groups generated by the reaction of GOQDs with isocyanate also have excellent acid resistance. However, in industrial production, nanofiltration membranes also need to face extremely alkaline water treatment environment. The application of aminated graphene quantum dots (AGQDs) to the preparation of nanofiltration membranes generates urea bonds with isocyanate, which not only exerts the stability of polyurea groups in extreme water environment, but also adds the excellent performance of graphene quantum dots to nanofiltration membranes. In addition to improving the alkali resistance and rejection rate, the unique water channels constructed by nanometer aggregates further improve the water flux, thereby expanding the application of nanofiltration membranes in different water environments. SUMMARY

[0005] The application aims at the technical defects in the prior art, and provides a porous graphene polyurea-based alkali-resistant composite membrane, a preparation method and application thereof.

[0006] The technical scheme adopted to achieve the object of the application is: A preparation method of a porous graphene polyurea-based alkali-resistant composite membrane comprises the following steps: Step 1, amino-functionalized graphene quantum dots are dispersed in an alkaline aqueous solution with a pH of 10-14 to prepare an aqueous solution with a concentration of 0.01-2 w / v %, and then diisocyanate is dissolved in a solvent to prepare an oil phase solution with a concentration of 0.01-2 w / v %; Step 2, a base film is laid in a reaction device, and the aqueous solution and the oil phase solution prepared in step 1 are added into the reaction device in sequence to perform interfacial polymerization, so that the amino-functionalized graphene quantum dots are pre-assembled with isocyanate to form a two-dimensional network structure; Step 3, an aqueous solution in which diamine is dissolved is added into the aqueous solution, and the diamine reacts with the -NCO groups in the two-dimensional network structure and the residual diisocyanate in the oil phase (part of the diamine further reacts with the unreacted -NCO groups in the two-dimensional network structure formed in step 2, and the other part of the diamine reacts with the residual diisocyanate in the oil phase, and the two reactions are used to supplement the pre-assembled two-dimensional network structure on the interface), so as to form a dense and defect-free separation layer and improve the retention performance, after the reaction is completed, the excess aqueous solution and oil phase solution are removed, the separation layer is loaded on the surface of the base film, and after heat treatment, the porous graphene polyurea-based alkali-resistant composite membrane is prepared.

[0007] In the above technical scheme, in step 1, the amino-functionalized graphene quantum dots are prepared by at least one of a hydrothermal method, a microwave method, an electrochemical method, a solvothermal method and an ultrasonic method, and the particle size of the amino-functionalized graphene quantum dots is 0.5-10 nm.

[0008] In the above technical scheme, in step 1, the diisocyanate is at least one of p-phenylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, 4,4'-diphenyl methane diisocyanate, 1,3-phenylene diisocyanate and lysine diisocyanate.

[0009] In the above technical scheme, in step 1, the solvent is at least one of toluene, n-hexane, cyclohexane, n-heptane and isomeric alkanes.

[0010] In the above technical scheme, in step 2, the base film is at least one of a polysulfone, a polyether sulfone, a polyvinylidene fluoride, a nylon or a polytetrafluoroethylene ultrafiltration membrane or a microfiltration membrane.

[0011] In the above technical solution, in step 2, the interfacial polymerization reaction time is 10-300s, and in step 3, the secondary site-filling reaction time is 10-120s.

[0012] In the above technical solution, in step 3, the diamine is at least one of piperazine, m-phenylenediamine, p-phenylenediamine, diethyltoluene diamine, hexanediamine, and polyethyleneimine.

[0013] In the above technical solution, in step 3, the heat treatment temperature is 50-80℃, and the treatment time is 10-30min.

[0014] Another aspect of the present application also includes a porous graphene polyurea-based alkali-resistant composite membrane obtained by the preparation method.

[0015] Another aspect of the present application also includes the application of the porous graphene polyurea-based alkali-resistant composite membrane as a separation membrane in water treatment.

[0016] Compared with the prior art, the present application has the following beneficial effects: 1. The present application selects amino-functionalized graphene quantum dots as water-phase monomers. Due to the nanoscale size of the quantum dots, they can be embedded between polymer chains to form nanochannels with precise size and low tortuosity, thereby improving separation accuracy while reducing separation resistance. In addition, due to the presence of a large number of amino groups, more hydrogen bonds are formed in the water phase, which regulates the diffusion rate of the water-phase diamine monomers, forming a separation layer with more ideal cross-linking degree and fewer defects.

[0017] 2. The present application uses a secondary interfacial polymerization reaction of small molecule monomers to perform site-filling reaction on the pre-assembled network structure of large-size monomers amino-functionalized graphene quantum dots. The diamine further reacts with the residual and unreacted -NCO groups in the first step to cross-link the originally loose network structure more closely through the formation of new polyurea bonds, while ensuring the graphene skeleton structure, reducing the size of the separation channel, and forming a high-efficiency low-resistance graphene / polyurea hybrid separation layer with small pore size and large flux, thereby significantly improving the permeation and separation performance of the composite membrane.

[0018] 3. The present application uses a secondary interfacial polymerization reaction to prepare a composite nanofiltration membrane, which "welds" the nanomaterials together in the form of covalent bonds, greatly improving the long-term chemical and physical stability of the nanocomposite membrane, reducing the risk of peeling and creep of the functional layer in complex environments, and reducing the formation of interface defects.

[0019] 4. The porous graphene polyurea-based alkali-resistant composite membrane prepared by the method of the present application is not prone to hydrolysis in a very alkaline environment due to the presence of polyurea structure, thereby improving the service life of the composite nanofiltration membrane. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Surface electron microscope image of the porous graphene polyurea-based alkali-resistant composite membrane prepared in Example 1; Figure 2 Section electron microscope image of the porous graphene polyurea-based alkali-resistant composite membrane prepared in Example 1. DETAILED DESCRIPTION

[0021] The application will be further described in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are merely intended to explain the application and not to limit the application.

[0022] Example 1 A method for preparing a porous graphene polyurea-based alkali-resistant composite membrane, comprising the following steps: (1) Synthesis of aminated graphene quantum dots: 376.6 mg of graphene oxide was dispersed in 352 mL of distilled water under ultrasonic environment for 3 h, then 108.93 mL of ammonia water was added to the aqueous dispersion of graphene oxide, and after uniform mixing, the dispersion was transferred to a reaction kettle, sealed and placed in a muffle furnace at 150℃ for chemical cutting reaction, and the reaction lasted for 5 h. After the reaction was completed, it was cooled to room temperature and filtered using a polyether sulfone filter membrane with a pore size of 0.22 μm. Then, the filtrate was distilled under reduced pressure in a 85℃ water bath for 2 h, and then freeze-dried to obtain aminated graphene quantum dot powder. The particle size distribution of the aminated graphene quantum dots is in the range of 1-3 nm, the particle size distribution range is relatively narrow, and the average particle size is about 2.0 nm.

[0023] (2) Preparation of alkali-resistant composite nanofiltration membrane: the aminated graphene quantum dots prepared by the hydrothermal method were dissolved in deionized water, and sodium hydroxide was added to adjust the pH to 11.8 to obtain an aqueous solution with a concentration of 2 g·L -1 . The p-phenylene diisocyanate was dispersed in n-hexane solution to obtain an oil phase solution with a concentration of 1 g·L -1 . Then, 2 ml of each of the two was added to a sand core funnel with a polyether sulfone base film, and the interfacial polymerization reaction lasted for 5 min. Then, 0.2 g·L -1 of a piperazine aqueous solution was added to the water phase, and the interfacial product was subjected to a counterion reaction for 60 s. After the reaction was completed, the lower liquid was discharged, the functional layer was settled on the base film, and the upper oil phase was sucked out with a needle tube. Then, the membrane was vertically taken out, air-dried at room temperature for 1 min, and heat-treated in an oven at 55℃ for 20 min to obtain a composite nanofiltration membrane.

[0024] The surface electron microscope image of the prepared composite nanofiltration membrane is shown in Figure 1 , it can be seen that a dense layer structure is formed on the surface, completely covering the open hole structure of the base film, and there is no obvious through hole structure. The section electron microscope image is shown in Figure 2The separation layer is thin, less than 50 nm. The composite membrane is subjected to interception test on 1.0 g·L -1 of Congo red solution under a pressure of 0.6 MPa, with an interception rate of 98.76% and a permeation flux of 123.70 L·m -2 ·h -1 ·bar -1 . Subsequently, the membrane is soaked in 4% NaOH for 120 h, and the interception rate on the dye is measured to be above 97%, showing excellent alkali resistance.

[0025] Example 2 A method for preparing a porous graphene polyurea-based alkali-resistant composite membrane, comprising the following steps: (1) Synthesis of amino-functionalized graphene quantum dots: 376.6 mg of graphene oxide is dispersed in 352 mL of distilled water under ultrasonic environment for 3 h, then 108.93 mL of ammonia water is added to the graphene oxide aqueous dispersion, and after being mixed uniformly, the dispersion is transferred to a reaction kettle, sealed and placed in a muffle furnace at 140℃ for chemical cutting reaction, and the reaction lasts for 5 h. After the reaction is completed, it is cooled to room temperature and filtered using a polyether sulfone filter membrane with a pore size of 0.22 μm. Then, the filtrate is distilled under reduced pressure in a 85℃ water bath for 2 h, and then freeze-dried to obtain an amino-functionalized graphene quantum dot powder. The particle size distribution of the amino-functionalized graphene quantum dots is in the range of 1-3 nm, the particle size distribution range is relatively narrow, and the average particle size is about 2.6 nm.

[0026] (2) Preparation of alkali-resistant composite nanofiltration membrane: the amino-functionalized graphene quantum dots prepared by the hydrothermal method are dissolved in deionized water, and sodium hydroxide is added to adjust the pH to 11.8 to obtain an aqueous solution with a concentration of 1 g·L -1 . The p-phenylene diisocyanate is dispersed in n-hexane solution to obtain an oil phase solution with a concentration of 1 g·L -1 . Then, 2 ml of each of the two solutions is added to a sand core funnel in which a polyether sulfone-based membrane is placed, and an interfacial polymerization reaction is carried out for 3 min. Then, 0.2 g·L -1 of a piperazine aqueous solution is added to the aqueous phase, and a counterion reaction is carried out on the interfacial product for 60 s. After the reaction is completed, the lower liquid is discharged, the functional layer is settled on the base membrane, and the upper oil phase is sucked out with a needle tube. Then, the membrane is vertically taken out, naturally air-dried at room temperature for 1 min, and heat-treated in an oven at 55℃ for 20 min to obtain a composite nanofiltration membrane.

[0027] The prepared composite nanofiltration membrane is subjected to interception test on 1.0 g·L -1 of Congo red solution under a pressure of 0.6 MPa, with an interception rate of 95.32% and a permeation flux of 182.44 L·m -2 ·h -1 ·bar -1 .

[0028] Example 3 A method for preparing a porous graphene polyurea-based alkali-resistant composite membrane, comprising the following steps: (1) Synthesis of aminated graphene quantum dots: 376.6 mg of graphene oxide was dispersed in 352 mL of distilled water under ultrasonic environment for 3 h, then 108.93 mL of ammonia water was added to the graphene oxide aqueous dispersion, and after being mixed uniformly, the dispersion was transferred to a reaction kettle, sealed and placed in a muffle furnace at 120°C for chemical cutting reaction, and the reaction lasted for 5 h. After the reaction was completed, it was cooled to room temperature and filtered using a polyether sulfone filter membrane with a pore size of 0.22 μm. Then, the filtrate was distilled under reduced pressure in a 85°C water bath for 2 h, and then freeze-dried to obtain aminated graphene quantum dot powder. The particle size distribution of the aminated graphene quantum dots is in the range of 2-4 nm, the particle size distribution range is relatively narrow, and the average particle size is about 3.6 nm.

[0029] (2) Preparation of alkali-resistant composite nanofiltration membrane: the aminated graphene quantum dots prepared by the hydrothermal method were dissolved in deionized water, and sodium hydroxide was added to adjust the pH to 12.5 to obtain an aqueous solution with a concentration of 2 g·L -1 -1. The p-phenylene diisocyanate was dispersed in n-hexane solution to obtain an oil phase solution with a concentration of 1 g·L -1 -1. Then 2 ml of each of the two was added to a sand core funnel with a polyether sulfone base film, and the interfacial polymerization reaction lasted for 3 min. Then 0.2 g·L -1 -1 of piperazine aqueous solution was added to the water phase, and the interfacial product was subjected to a counterion reaction for 30 s. After the reaction was completed, the lower layer liquid was discharged, the functional layer was settled on the base film, and the upper layer oil phase was sucked out with a needle tube. Then the membrane was taken out vertically, and air-dried at room temperature for 1 min, and then heat-treated in an oven at 55°C for 20 min to obtain a composite nanofiltration membrane.

[0030] The prepared composite nanofiltration membrane was subjected to rejection test under 0.6 MPa pressure for 1.0 g·L -1 -1 of Congo red solution, and the rejection rate was 94.02%, the permeation flux was 243.71 L·m -2 ·h -1 ·bar -1 .

[0031] Example 4 A method for preparing a porous graphene polyurea-based alkali-resistant composite membrane, comprising the following steps: (1) The same as step (1) of example 1 (2) Preparation of alkali-resistant composite nanofiltration membrane: the aminated graphene quantum dots prepared by the hydrothermal method were dissolved in deionized water, and sodium hydroxide was added to adjust the pH to 13.8 to obtain an aqueous solution with a concentration of 1 g·L -1An aqueous solution was prepared. Terephthalic diisocyanate was dispersed in a hexane solution to obtain a concentration of 1 g·L⁻¹. -1 The oil phase solution. Then, 2 ml of each was added to a sintered funnel containing a polyethersulfone-based film, and the interfacial polymerization reaction was carried out for 2 min. Then, 0.2 g·L⁻¹ of the solution was added. -1 A piperazine aqueous solution was added to the aqueous phase to allow the interfacial products to undergo a replacement reaction for 30 seconds. After the reaction was completed, the lower liquid was discharged, and the functional layer was deposited onto the base membrane. The upper oil phase was then aspirated with a syringe. The membrane was then vertically removed, allowed to air dry at room temperature for 1 minute, and then heat-treated in an oven at 55°C for 20 minutes to obtain the composite nanofiltration membrane.

[0032] The prepared composite nanofiltration membrane exhibits good performance at 0.6 MPa pressure for 1.0 g·L⁻¹ -1 Retention tests were performed on the Congo red solution, and the retention rate was 99.38%, with a permeation flux of 153.14 L·m⁻¹. -2 ·h -1 ·bar -1 It exhibits excellent separation performance. Subsequently, the membrane was immersed in 4% NaOH for 120 hours, and the dye rejection rate was found to be above 98%, demonstrating excellent alkali resistance.

[0033] Example 5 A method for preparing a porous graphene-polyurea-based alkali-resistant composite membrane includes the following steps: (1) Same as step (1) in Example 3 (2) Preparation of alkali-resistant composite nanofiltration membrane: Aminographene quantum dots prepared by hydrothermal method were dissolved in deionized water, and sodium hydroxide was added to adjust the pH to 13.8, resulting in a concentration of 2 g·L⁻¹. -1 An aqueous solution was prepared. Terephthalic diisocyanate was dispersed in a hexane solution to obtain a concentration of 1 g·L⁻¹. -1 The oil phase solution. Then, 2 ml of each was added to a sintered funnel containing a polyethersulfone-based film, and the interfacial polymerization reaction was carried out for 5 min. Then, 0.2 g·L⁻¹ of the solution was added. -1 A piperazine aqueous solution was added to the aqueous phase to allow the interfacial products to undergo a replacement reaction for 60 seconds. After the reaction was completed, the lower liquid was discharged, and the functional layer was deposited onto the base membrane. The upper oil phase was then aspirated with a syringe. The membrane was then vertically removed, allowed to air dry at room temperature for 1 minute, and then heat-treated in an oven at 55°C for 20 minutes to obtain the composite nanofiltration membrane.

[0034] The prepared composite nanofiltration membrane exhibits good performance at 0.6 MPa pressure for 1.0 g·L⁻¹ -1 Retention tests were performed on the Congo red solution, and the retention rate was 99.64%, with a permeation flux of 98.93 L·m⁻². -2 ·h -1 ·bar -1 .

[0035] The above merely describes the preferred embodiments of the present application, and it should be pointed out that for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the scope of the present application.

Claims

1. A method for preparing a porous graphene polyurea-based alkali-resistant composite membrane, characterized in that, The method comprises the following steps: Step 1, dispersing amino-functionalized graphene quantum dots in an alkaline aqueous solution with a pH of 10-14 to prepare an aqueous solution with a concentration of 0.01-2 w / v%, and then dissolving diisocyanate in a solvent to prepare an oil phase solution with a concentration of 0.01-2 w / v%; Step 2, laying a base film in a reaction device, and then adding the aqueous solution and the oil phase solution prepared in step 1 to the reaction device in sequence, and performing interfacial polymerization to make the amino-functionalized graphene quantum dots pre-assembled with isocyanate to form a two-dimensional network structure; Step 3, adding a water solution in which diamine is dissolved to the aqueous solution, and then allowing the diamine to react with the -NCO groups in the two-dimensional network structure and the residual diisocyanate in the oil phase, respectively, after the reaction is completed, removing the excess aqueous solution and oil phase solution, allowing the separation layer to be loaded on the surface of the base film, and then performing heat treatment to prepare a porous graphene polyurea-based alkali-resistant composite film.

2. The production method according to claim 1, wherein In step 1, the amino-functionalized graphene quantum dots are prepared by at least one of a hydrothermal method, a microwave method, an electrochemical method, a solvothermal method, and an ultrasonic method, and the particle size of the amino-functionalized graphene quantum dots is 0.5-10 nm.

3. The production method according to claim 1, wherein In step 1, the diisocyanate is at least one of p-phenylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, and lysine diisocyanate.

4. The production method according to claim 1, wherein In step 1, the solvent is at least one of toluene, n-hexane, cyclohexane, n-heptane, and isomeric alkanes.

5. The production method according to claim 1, wherein In step 2, the base film is at least one of a polysulfone, a polyether sulfone, a polyvinylidene fluoride, a nylon, or a polytetrafluoroethylene ultrafiltration membrane or microfiltration membrane.

6. The production method according to claim 1, wherein In step 2, the time of the interfacial polymerization reaction is 10-300 s, and in step 3, the time of the secondary substitution reaction is 10-120 s.

7. The production method according to claim 1, wherein In step 3, the diamine is at least one of piperazine, m-phenylenediamine, p-phenylenediamine, diethyltoluene diamine, hexanediamine, and polyethyleneimine.

8. The production method according to claim 1, wherein In step 3, the heat treatment temperature is 50-80℃, and the treatment time is 10-30 min.

9. A porous graphene polyurea-based alkali-resistant composite film prepared by the method of any one of claims 1-8.

10. Application of the porous graphene polyurea-based alkali-resistant composite film of claim 9 as a separation membrane in water treatment.

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