A porous graphene-based acid-resistant composite film and a preparation method thereof

Abstract

The application discloses a kind of porous graphene-based acid-resistant composite membrane and preparation method thereof, the preparation method of the porous graphene-based acid-resistant composite membrane includes the following steps: step 1, functionalized graphene quantum dots are dispersed in aqueous solution containing surfactant to prepare aqueous solution, the concentration of the functionalized graphene quantum dots in the aqueous solution is 0.1~20g·L ‑1 ; Step 2, the base film is immersed in the aqueous solution, and the base film is taken out after soaking for a certain time, and the excess liquid is removed, preferably, the excess liquid is removed using a rubber roller; Step 3, the base film treated in step 2 is immersed in an organic phase solution with a concentration of 0.1~20g·L ‑1 Diisocyanate, interface polymerization reaction is carried out; Step 4, the film obtained after step 3 is treated is subjected to heat treatment to obtain a porous graphene-based acid-resistant composite membrane. It has the characteristics of acid resistance, oxidation resistance, solvent resistance, pollution resistance, etc., is suitable for various separation scenarios, and has broad industrial application prospects.

Description

TECHNICAL FIELD

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

[0002] With the expansion of the chemical industry, acid wastewater is posing a serious threat to the environment and human health. Nanofiltration is a membrane separation technology with excellent separation performance, and has a wide range of applications in water softening, drinking water purification, wastewater recovery, etc. However, some of these applications involve acidic environments, and these strong acids often degrade the membrane components by changing their morphology and physicochemical properties, leading to a decrease in membrane performance.

[0003] The interfacial polymerization method is one of the methods for preparing nanofiltration membranes with high selectivity and high flux. Common water-phase monomers include piperazine and its derivatives, polyethyleneimine, m-phenylenediamine, and polyols, etc., and oil-phase monomers mostly include trimesoyl chloride, terephthaloyl chloride, and isophthaloyl chloride, etc. Although polyamide membranes prepared from traditional monomers are currently commonly used nanofiltration membranes, these membranes are unstable under extreme conditions, such as extremely low pH values and high temperatures. The amide bonds present in the membranes are prone to hydrolysis under harsh conditions, thereby leading to a serious decrease in membrane performance. The introduction of functionalized graphene and its derivatives into the water phase is expected to solve this problem.

[0004] Graphene is a two-dimensional crystal composed of sp2 hybridized carbon atoms. By means of covalent bonding modification, non-covalent bonding modification, and element doping, atoms or functional groups such as nitrogen, boron, phosphorus, oxygen, sulfur, and halogens are introduced into graphene, changing its elemental composition and forming functionalized materials, such as graphene oxide (GO) and amino-functionalized graphene (AG), etc. By utilizing quantum confinement effects and quantum size effects to regulate the micro-morphology of graphene, zero-dimensional graphene quantum dots can also be obtained, which have the advantages of smaller size, larger specific surface area, and stronger hydrophilicity compared with two-dimensional graphene, and have more excellent dispersion performance in aqueous or organic phase solvents. In addition, graphene quantum dots (GOQDs) also have the advantages of wide raw material sources, easy preparation, good biocompatibility, low toxicity, and environmental protection. The introduction of GOQDs into the separation layer through interfacial polymerization can not only improve the hydrophilicity of the membrane, but also reduce the filtration resistance of the membrane. At the same time, the GOQD nanoclusters in the separation layer can also effectively shorten the water molecule path by constructing unique water channels, further improving the membrane flux. SUMMARY

[0005] The present application aims to solve the technical defects of polyamide membranes in the prior art, which are prone to hydrolysis under acidic conditions, and provides a porous graphene-based acid-resistant composite membrane and a preparation method thereof.

[0006] The technical scheme adopted to achieve the object of the present application is:

[0007] A preparation method of a porous graphene-based acid-resistant composite membrane, comprising the following steps:

[0008] Step 1, functionalized graphene quantum dots are dispersed in an aqueous solution to prepare an aqueous phase solution, wherein the concentration of the functionalized graphene quantum dots in the aqueous phase solution is 0.1-20 g·L -1 ;

[0009] Step 2, the base membrane is immersed in the aqueous phase solution, and the base membrane is taken out after soaking for a fixed time, and the excess liquid is removed, preferably, a rubber roller is used to remove the excess liquid;

[0010] Step 3, the base membrane treated in step 2 is immersed in an organic phase solution of diisocyanate with a concentration of 0.1-20 g·L -1 , and an interfacial polymerization reaction is performed;

[0011] Step 4, the membrane obtained after step 3 is treated by heat treatment to obtain a porous graphene-based acid-resistant composite membrane.

[0012] In the above technical scheme, in step 1, the functionalized graphene quantum dots are graphene quantum dots containing reactive functional groups, the particle size is 0.5-10 nm, and it has typical zero-dimensional and two-dimensional characteristics, preferably, the reactive functional groups are amino, hydroxyl, sulfonic acid group, epoxy group, carbonyl or carboxylic acid group.

[0013] In the above technical scheme, in step 1, the aqueous phase solution also contains a surfactant, the surfactant is at least one of sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether sodium sulfate, sodium secondary alkyl sulfonate, sodium dodecyl sulfonate or fatty acid methyl ester sulfonate, and the concentration of the surfactant in the aqueous phase solution is 0.001-0.2 g·L -1 .

[0014] In the above technical scheme, in step 2, the base membrane is at least one of polysulfone, polyether sulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, nylon or polytetrafluoroethylene ultra / microfiltration membrane.

[0015] In the above technical scheme, in step 2, the soaking time is 5-15 min.

[0016] In the above technical scheme, in step 3, the diisocyanate is at least one of p-phenylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,4-phenylene diisocyanate or lysine diisocyanate.

[0017] In the above technical solution, in the step 3, the solvent of the organic phase solution is at least one of n-hexane, cyclohexane, n-heptane or isomeric alkanes.

[0018] In the above technical solution, in the step 3, the time of the interfacial polymerization reaction is 10-300s.

[0019] In the above technical solution, in the step 4, the heat treatment temperature is 40-50 DEG C, and the treatment time is 5-15 min.

[0020] Another aspect of the present application also includes a porous graphene-based acid-resistant composite film obtained based on the preparation method.

[0021] In the above technical solution, the porous graphene-based acid-resistant composite film includes a base film and a porous graphene film combined on the base film, the porous graphene film is assembled on the surface of the base film by interfacial polymerization of functionalized graphene quantum dots, the functional groups on the edge of the functionalized graphene quantum dots are connected with isocyanate through polyurethane and polyurea structure, and the thickness of the porous graphene film is less than 50 nm.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. The present application selects zero-dimensional nanomaterial functionalized graphene quantum dots as the only water phase monomer, diisocyanate as the oil phase monomer, and prepares an ultrathin porous graphene-based composite film through a traditional interfacial polymerization method. By adjusting the micro size and functional group characteristics of the nanomaterial, an ultrathin high-permeability acid-resistant nanocomposite film can be prepared. The functionalized graphene quantum dots have the advantages of large specific surface area, good water solubility and biocompatibility, rich reaction sites and easy modification, etc. This endows the nanofiltration composite film with high permeation flux and high retention rate at low pressure.

[0024] 2. The quantum dots have a smooth surface similar to graphene inside, and through functionalization, hydrophilic reactive groups are introduced, and a porous graphene film (separation layer) with an approximately vertical pore structure is assembled through an interfacial polymerization method. Combined with the low-friction smooth surface inside the graphene quantum dots, the permeation flux of the composite film can be greatly improved. This uniform high-density porous structure is different from the layer-by-layer stacked pore structure of the graphene layered film, which sharply reduces the length of the horizontal channel while increasing the density of the vertical nanochannel, greatly shortens the flow path length of the material penetrating the membrane, and thus significantly reduces the filtration resistance of the membrane and improves the separation efficiency.

[0025] 3. The present application adds a surfactant to the water phase system during interfacial polymerization to reduce surface tension, thereby further improving the rejection rate. Specifically, the water phase monomer is arranged and aggregated at the interface, reducing direct contact between the isocyanate with a large number of unsaturated bonds and the water phase system, reducing the probability of side reactions during interfacial polymerization, and facilitating the formation of a complete and defect-free ultra-thin film, thereby ensuring a higher permeation flux while improving the rejection rate. In addition, the addition of a surfactant can further reduce the thickness of the separation layer.

[0026] 4. The porous graphene-based composite membrane prepared by the method of the present application has a polyurethane and polyurea structure connecting between the functional groups of the quantum dot edges in the separation layer and the isocyanate. This functional group structure has natural acid resistance, so that the porous graphene-based composite membrane prepared has excellent acid stability without affecting the rejection rate and flux, and is suitable for separation and purification of high-acid material systems.

[0027] 5. The porous graphene-based acid-resistant composite membrane prepared by the method of the present application has a hydrogen bond formed between the remaining unreacted functional groups in the graphene quantum dots and the oxygen-containing groups on the base film, making the porous graphene layer and the base film with excellent properties such as acid resistance, oxidation resistance, and solvent resistance more closely combined, which is beneficial for the application of membrane separation under complex environmental conditions. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The transmission electron microscope image of the graphene oxide quantum dots prepared in step 1 of Example 1, with an average size of 3.2 nm;

[0029] Figure 2 The transmission electron microscope image of the amino-functionalized graphene quantum dots prepared in step 2 of Example 1, with an average size of 3.4 nm;

[0030] Figure 3 The surface electron microscope image of the porous graphene-based acid-resistant composite membrane prepared in Example 4;

[0031] Figure 4 The cross-sectional electron microscope image of the porous graphene-based acid-resistant composite membrane prepared in Example 4. DETAILED DESCRIPTION

[0032] The present 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 present application and are not intended to limit the present application.

[0033] Example 1

[0034] In this embodiment, the functionalized graphene quantum dots are graphene oxide quantum dots and amino-functionalized graphene quantum dots, with a mass ratio of 1:2.

[0035] A method for preparing a porous graphene-based acid-resistant composite film, comprising the following steps:

[0036] Step 1, synthesis of graphene oxide quantum dots: 0.2 g of graphene oxide is dispersed in 100 mL of distilled water, then 100 mL of hydrogen peroxide is added to the graphene oxide aqueous dispersion, and after thorough mixing, it is reacted under ultrasonic environment for 3 h to ensure that the hydrogen peroxide can fully cut the graphene oxide. Subsequently, the mixture dispersion is filtered with a sand core filter equipped with a 0.22 μm polytetrafluoroethylene microfiltration membrane to remove larger graphene oxide sheets. After filtration, a light brown graphene oxide quantum dot solution is obtained. Its transmission electron microscope image is shown in Figure 1 The particle size distribution of the graphene oxide quantum dots is in the range of 2-5 nm, the particle size distribution range is relatively narrow, and the average particle size is about 3.2 nm.

[0037] Step 2, synthesis of aminated graphene quantum dots: 45 mg of graphene oxide is dispersed in 45 mL of distilled water, then 15 mL of ammonia is added to the graphene oxide aqueous dispersion, and thoroughly dispersed and mixed under ultrasonic environment. After mixing evenly, the dispersion is transferred to a reaction kettle, sealed and placed in a 120℃ muffle furnace 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, and after freeze-drying, aminated graphene quantum dot powder is obtained. Its transmission electron microscope image is shown in Figure 2 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 3.4 nm.

[0038] Step 3, preparation of a porous graphene-based acid-resistant composite film: the graphene oxide quantum dots and aminated graphene quantum dots prepared by the hydrothermal method are respectively made into aqueous solutions with a concentration of 1.0 g·L -1 -1. The two solutions are mixed in a ratio of 1:2, and an amphiphilic surfactant sodium dodecyl sulfate with a concentration of 0.01 g·L -1 is added to obtain a mixed aqueous solution. Subsequently, the polyether sulfone-based film is immersed in the mixed aqueous solution for 5 min, the excess liquid is removed with a rubber roller, and then it is immersed in an organic solution of p-phenylene diisocyanate with a concentration of 1.0 g·L -1 , and an interfacial polymerization reaction is carried out for 3 min. After the reaction is completed, the obtained film is placed in a 45℃ oven for heat treatment for 10 min, and finally a porous graphene-based acid-resistant composite film is obtained.

[0039] The embodiment adopts a top-down method to obtain amino-functionalized graphene quantum dots by chemically cutting graphene oxide with ammonia water, to obtain graphene oxide quantum dots by cutting graphene oxide with hydrogen peroxide, to use the graphene oxide quantum dots as a water-phase monomer, to use diisocyanate as an organic-phase monomer, to regulate interface polymerization reaction conditions, and to adopt a traditional interface polymerization method to prepare a porous graphene-based acid-resistant composite film containing polyurethane and polyurea structures.

[0040] The prepared porous graphene-based acid-resistant composite film in the embodiment has a rejection rate of 97.38% and a permeation flux of 223.71 L·m -2 ·h -1 ·bar -1 when performing interception testing on a 1.0 g·L -1 Congo red solution under a pressure of 0.2 MPa.

[0041] Example 2

[0042] In the embodiment, the functionalized graphene quantum dots are graphene oxide quantum dots.

[0043] A method for preparing a porous graphene-based acid-resistant composite film includes the following steps:

[0044] Step 1 is the same as step 1 in Example 1.

[0045] Step 2, preparation of a porous graphene-based acid-resistant composite film: graphene oxide quantum dots prepared by a hydrothermal method are made into an aqueous solution with a concentration of 2.0 g·L -1 , the polyethersulfone-based film is immersed in the aqueous solution for 8 min, the excess liquid is removed by a rubber roller, the film is immersed in a toluene diisocyanate organic solution with a concentration of 1.0 g·L -1 , an interface polymerization reaction is performed for 3 min, after the reaction is completed, the obtained film is placed in an oven at 45°C for heat treatment for 10 min, and finally a porous graphene-based acid-resistant composite film is obtained.

[0046] The prepared porous graphene-based acid-resistant composite film has a rejection rate of 96.15% and a permeation flux of 198.31 L·m -2 ·h -1 ·bar -1 when performing interception testing on a 1.0 g·L -1 Congo red solution under a pressure of 0.2 MPa.

[0047] Example 3

[0048] In the embodiment, the functionalized graphene quantum dots are amino-functionalized graphene quantum dots.

[0049] A method for preparing a porous graphene-based acid-resistant composite film includes the following steps:

[0050] Step 1 is the same as Step 2 of Example 1.

[0051] Step 2, preparation of the porous graphene-based acid-resistant composite film: the amino-functionalized graphene quantum dots prepared by the hydrothermal method were made into an aqueous solution with a concentration of 1.0 g·L -1 , and the amphiphilic surfactant sodium fatty alcohol polyoxyethylene sulfate with a concentration of 0.15 g·L -1 was added to obtain an aqueous solution. Subsequently, the polyether sulfone-based film was immersed in the aqueous solution for 10 min, and the excess liquid was removed by a rubber roller. Then, the film was immersed in an organic solution of p-hexamethylene diisocyanate with a concentration of 1.4 g·L -1 for 2 min to perform interfacial polymerization. After the reaction was completed, the obtained film was placed in an oven at 45°C for heat treatment for 10 min, and a porous graphene-based acid-resistant composite film was finally obtained.

[0052] The prepared porous graphene-based acid-resistant composite film was subjected to interception test on a 1.0 g·L -1 congo red solution under a pressure of 0.2 MPa, and the interception rate was 98.02%, and the permeation flux was 102.34 L·m -2 ·h -1 ·bar -1 .

[0053] Example 4

[0054] In this example, the functionalized graphene quantum dots were prepared by mixing graphene quantum dots and amino-functionalized graphene quantum dots at a mass ratio of 1:1.

[0055] A method for preparing a porous graphene-based acid-resistant composite film, comprising the following steps:

[0056] Step 1 and Step 2 are the same as Step 1 and Step 2 of Example 1.

[0057] Step 3, preparation of the porous graphene-based acid-resistant composite film: the graphene quantum dots and the amino-functionalized graphene quantum dots prepared by the hydrothermal method were made into aqueous solutions with a concentration of 1.0 g·L -1 , respectively. The two solutions were mixed at a ratio of 1:1, and the amphiphilic surfactant sodium dodecyl sulfate with a concentration of 0.01 g·L -1 was added to obtain a mixed aqueous solution. Subsequently, the polyether sulfone-based film was immersed in the mixed aqueous solution for 10 min, and the excess liquid was removed by a rubber roller. Then, the film was immersed in an organic solution of p-phenylene diisocyanate with a concentration of 1.4 g·L -1 for 3 min to perform interfacial polymerization. After the reaction was completed, the obtained film was placed in an oven at 45°C for heat treatment for 10 min, and a porous graphene-based acid-resistant composite film was finally obtained.

[0058] Figure 3SEM images of the surface of the porous graphene-based acid-resistant composite membrane are shown. It can be seen that the surface structure of the membrane is smooth and has no obvious wrinkles. The concave hole structure shown on the surface of the membrane is the pore morphology of the base membrane surface. These concave hole structures are not permeable, indicating that the surface separation layer formed is very thin and not enough to cover the original pore morphology of the base membrane surface. Figure 4 The cross-sectional TEM image of the porous graphene-based acid-resistant composite membrane is shown. It can be seen that it has an ultra-thin thickness of about 18 nm, further proving the ultra-thin characteristics of the separation layer. The ultra-thinning of the separation layer is beneficial to the improvement of the permeation performance.

[0059] The prepared porous graphene-based acid-resistant composite membrane was subjected to interception test on 0.1 g·L -1 of Congo red solution under 0.2 MPa pressure, and the interception rate reached 99.23%, and the permeation flux was 142.84 L·m -2 ·h -1 ·bar -1 , showing excellent separation performance. Subsequently, the membrane was immersed in 4% HCl and 10% HNO3 for 120 h, and the interception rate on the dye was measured to be more than 98%, showing excellent acid resistance.

[0060] Example 5

[0061] In this embodiment, the functionalized graphene quantum dots are graphene oxide quantum dots and aminated graphene quantum dots, and the mass ratio of the two is 2:1.

[0062] A method for preparing a porous graphene-based acid-resistant composite membrane, comprising the following steps:

[0063] Step 1 and step 2 are the same as step 1 and step 2 of example 1.

[0064] Step 3, preparation of the porous graphene-based acid-resistant composite membrane: the graphene oxide quantum dots and the aminated graphene quantum dots prepared by the hydrothermal method are respectively made into aqueous solutions with a concentration of 2.0 g·L -1 , the two solutions are mixed in a ratio of 2:1, and an amphiphilic surfactant sodium dodecyl sulfate with a concentration of 0.01 g·L -1 is added to obtain a mixed aqueous solution. Subsequently, the polyether sulfone-based membrane is immersed in the mixed aqueous solution for 10 min, the excess liquid is removed with a rubber roller, and then the membrane is immersed in an organic solution of p-phenylene diisocyanate with a concentration of 1.6 g·L -1 for 3 min to perform interfacial polymerization reaction. After the reaction is completed, the obtained membrane is placed in an oven at 45°C for heat treatment for 10 min, and finally a porous graphene-based acid-resistant composite membrane is obtained.

[0065] The prepared porous graphene-based acid-resistant composite membrane was subjected to interception test on 1.0 g·L -1The Congo red solution was tested for retention, with a retention rate of 99.13% and a permeation flux of 163.57 L·m -2 ·h -1 bar -1 .

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a porous graphene-based acid-resistant composite membrane, characterized in that: The following steps are involved: Step 1: Dispersing functionalized graphene quantum dots in an aqueous solution to prepare an aqueous solution, wherein the concentration of the functionalized graphene quantum dots in the aqueous solution is 0.1-20 g·L -1 ; The functionalized graphene quantum dots are graphene quantum dots containing reactive functional groups, and the reactive functional groups are amino, hydroxyl or carboxylic acid groups; Step 2, immersing the basement membrane in the aqueous solution, taking out the basement membrane after immersing for a fixed time, and removing excess liquid; Step 3: Immerse the basement membrane treated in step 2 in a solution with a concentration of 0.1-20 g·L -1 In the organic phase solution of diisocyanate, interfacial polymerization reaction is carried out; Step 4: heat-treating the membrane obtained after the treatment in step 3 to obtain a porous graphene-based acid-resistant composite membrane.

2. The preparation method according to claim 1, wherein In the step 1, the particle size of the functionalized graphene quantum dots is 0.5-10 nm.

3. The preparation method according to claim 1, wherein The aqueous solution in step 1 further contains a surfactant, which is at least one of sodium lauryl sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium secondary alkyl sulfonate, sodium lauryl sulfonate, or sodium fatty acid methyl ester sulfonate. The concentration of the surfactant in the aqueous solution is 0.001-0.2 g·L -1 .

4. The preparation method according to claim 1, wherein In step 2, excess liquid is removed using a rubber roller; In the step 2, the base membrane is at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, nylon or polytetrafluoroethylene ultrafiltration / microfiltration membrane, and the immersion time is 5-15 minutes.

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

6. The preparation method according to claim 1, wherein In step 3, the solvent of the organic phase solution is at least one of n-hexane, cyclohexane, n-heptane or isoparaffin.

7. The preparation method according to claim 1, wherein In step 3, the interfacial polymerization reaction time is 10 to 300 s.

8. The preparation method according to claim 1, wherein In step 4, the heat treatment temperature is 40-50° C., and the treatment time is 5-15 minutes.

9. A porous graphene-based acid-resistant composite membrane obtained by the preparation method according to any one of claims 1 to 8.

10. The porous graphene-based acid-resistant composite membrane according to claim 9, characterized in that: The invention comprises a base film and a porous graphene film composited on the base film, wherein the porous graphene film is assembled on the surface of the base film by functionalized graphene quantum dots through interfacial polymerization, wherein the functionalized graphene quantum dots are graphene quantum dots containing reactive functional groups, wherein the reactive functional groups are amino, hydroxyl or carboxylic acid groups, and the functional groups at the edges of the functionalized graphene quantum dots are connected to isocyanate through polyurethane and polyurea structures, and the thickness of the porous graphene film is less than 50 nm.

Images