A positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials, preparation method and application

Abstract

The present invention discloses a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials, a preparation method and an application. Para-phenylenediamine and isoamyl nitrite are added to the two-dimensional nanomaterial dispersion liquid, and the reaction is carried out by heating in a water bath. After the reaction is completed, the reaction solution is cooled to room temperature, and the functionalized modified two-dimensional nanomaterials are obtained through separation and drying. By grafting NH2 onto the two-dimensional nanomaterials, the surface of the membrane becomes positively charged. The positively charged nanofiltration membrane of amino-grafted two-dimensional nanomaterials prepared by the present invention has good hydrophilicity and provides an additional channel for filtration. For the prepared nanofiltration membrane, on the one hand, the water flux can be increased. On the other hand, since the surface of the membrane becomes positively charged due to the grafting of NH2 onto the two-dimensional nanomaterials, Ca 2+ and Mg 2+ ions can be removed due to the Donnan effect. At the same time, the membrane fouling problem is improved, the service life of the membrane is prolonged, the cost is reduced, and a better prospect is provided for the application of two-dimensional nanomaterials in the field of sewage treatment.

Description

Technical Field

[0001] The present invention relates to a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials, a preparation method and an application, belonging to the technical field of separation membrane materials. Background Art

[0002] Nanofiltration technology has the advantages of low cost and high efficiency, and is an effective method for solving water purification problems. Generally speaking, it has the advantages of low cost, easy operation and relatively simple preparation process. Most of the existing nanofiltration membranes are negatively charged or electrically neutral, and can effectively separate single and multivalent anions in water bodies, but the separation effect on single and multivalent cations in water bodies is poor. However, recent studies have found that positively charged nanofiltration membranes not only have good acid and alkali resistance, corrosion resistance and hydrophilicity, but also can, through the Donnan electrostatic repulsion and size exclusion effects, show excellent repellency to cations of different valence states such as Ca 2+ , Na + etc., so as to solve problems such as amino acid and protein separation, treatment of cathode electrophoresis paint waste liquid, and treatment of positively charged dye wastewater. Therefore, the development and application of positively charged nanofiltration membranes have gradually become a research hotspot in the field of water treatment. However, compared with negatively charged separation membranes, there are relatively few commercial positively charged nanofiltration membrane products. Currently, most researchers expect to obtain positively charged NF membranes with excellent performance in all aspects by innovating membrane-making materials and preparation processes.

[0003] Currently, common excellent positively charged nanofiltration membrane-forming materials include chitosan-based materials, polyethyleneimine-based materials, quaternary ammonium salt-based materials, and the research on preparation processes mainly focuses on IP method, layer-by-layer assembly method, grafting method, crosslinking method, etc. The method of grafting N, N-dimethylaminoethyl methacrylate (DMAEMA) onto a PSF substrate membrane by ultraviolet induction and then quaternizing with p-dichlorobenzyl to prepare a positively charged NF membrane on the surface. It is found that the hydrophilicity of the modified membrane is significantly enhanced. Under optimal conditions, the membrane flux is 6.03L.m -2 .h -1 .bar -1 , and the retention of MgCl2 solution reaches 93.2% (Liang Yu. Journal of Hazardous Materials. 2015); Qi Yawei used a polysulfone ultrafiltration membrane as the substrate membrane, and through the interfacial polymerization method, with piperazine and diaminodipropylamine as the aqueous phase monomers and trimesoyl chloride as the oil phase monomer, prepared a pristine nanofiltration membrane, and then used 2-chloro-1-methyl iodopyridine and sodium hydroxide as activators to prepare a positively charged nanofiltration membrane by grafting polyethyleneimine on the surface of the nanofiltration membrane (Qi Yawei, master's degree thesis, Zhejiang University of Technology, 2019). The above methods have obvious advantages respectively, but all have problems such as still relatively low water flux and high requirements for preparation processes.

[0004] Meanwhile, in recent years, new two-dimensional materials have emerged continuously. From the successful exfoliation of graphene to the design and synthesis of framework materials, their functional properties have also received extensive attention. Two-dimensional materials have a large aspect ratio, which is conducive to the assembly of ordered interlayer and in-plane channel structures. This characteristic provides the possibility for the preparation of high-performance nanofiltration membranes.

[0005] Two-dimensional separation membranes represented by graphene and its derivatives have attracted the attention of many researchers due to their unique physical and chemical properties brought by their size. The membrane properties composed of these nanomaterials are much higher than those of traditional membranes, and they exhibit a mass transfer and separation mechanism quite different from that of traditional membranes. Representative materials include graphene, molybdenum disulfide, tungsten disulfide, graphitic carbon nitride, Ti3C2T x etc., which are widely used in current nanofiltration research. The nanofiltration membranes prepared by these nanomaterials have high water flux, high rejection rate for small molecule pollutants, and good flexibility, effectively ensuring the water flux and rejection effect of the nanofiltration membranes.

[0006] Zhang Xian et al. synthesized monolayer titanium carbide (Ti3C2T x ) nanosheets by etching aluminum titanium carbide with lithium fluoride / dilute hydrochloric acid, and then prepared a Ti3C2T x -doped polyamide thin-film composite nanofiltration membrane by interfacial polymerization method. The pure water flux of the nanofiltration membrane was increased while the sodium sulfate interception rate remained at 98% (Zhang Xian, Wu Mingbang, Yang Xi, Yang Jing, Xu Zhikang. Journal of Membrane Science and Technology, 2020, (01): 8-15.); Zhao Rui studied the influence of doping MoS2 nanosheets in the aqueous phase interface polymerization on the physical and chemical properties and permeation / separation performance of TFC membranes. The results showed that as the concentration of MoS2 nanosheets doped in the aqueous phase increased to 0.01 wt%, the surface roughness, hydrophilicity and electronegativity of the constructed TFN membrane were all increased, and the interception rate of sodium sulfate was also increased (Zhao Rui, Doctoral Thesis, Harbin Institute of Technology, 2021.).

[0007] Although the interception rate and water flux can be improved through two-dimensional nanomaterial nanofiltration membranes, pure two-dimensional nanomaterials cannot meet the treatment of divalent cations. Since most of these nanomaterials themselves are negatively charged, the prepared composite nanofiltration membranes also exhibit a negatively charged property, resulting in good interception ability of the obtained nanofiltration membrane materials for divalent anions (SO4 2 -, CO3 2- ), while the interception ability for hardness ions such as Ca 2+ , Mg 2+ is poor. Therefore, developing charged nanofiltration membranes through the Donnan effect is an important direction for the application of two-dimensional nanomaterials in nanofiltration membranes. There is still no relevant report on the technology of positively charged nanofiltration membrane materials based on the addition of two-dimensional nanomaterials. Summary of the Invention

[0008] Object of the invention: Aiming at the limitations in the practical application of two-dimensional nanomaterials in the field of separation membranes, the present invention proposes a preparation method of a positively charged nanofiltration membrane of amino-grafted two-dimensional nanomaterials for removing calcium and magnesium ions. The nanofiltration membrane prepared by this method has a good divalent cation salt rejection rate. At the same time, the nanomaterials provide additional transport channels, improving the water flux of the nanofiltration membrane and reducing membrane fouling, providing a prospect for the application of two-dimensional nanomaterials in the field of positively charged nanofiltration membranes.

[0009] The present invention also provides a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials prepared by the above preparation method.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0011] A preparation method of a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials, comprising the following steps:

[0012] Step 1: Disperse 200 - 300 mg of two-dimensional nanomaterials in 80 - 100 mL of deionized water, and ultrasonicate for 1 - 2 h to obtain a dispersion solution; place the dispersion solution in a water bath at 60 - 65 °C, and add 1 - 2 g of p-phenylenediamine and 1 - 3 mL of isoamyl nitrite to the dispersion solution, and stir and react in the water bath for 10 - 12 h. After the reaction is completed, cool the reaction solution to room temperature;

[0013] Step 2: Centrifuge the cooled reaction solution until the pH of the supernatant is 7, place it in a freeze dryer and freeze dry for at least 48 h to obtain amino-grafted two-dimensional nanomaterials; prepare a dispersion of the amino-grafted two-dimensional nanomaterials with deionized water at a concentration of 1.2 - 1.5 g / L;

[0014] Step 3: Prepare a mixed solution of piperazine PIP and polyethyleneimine PEI with deionized water at mass percentages of 2.0 - 2.2% and 2.7 - 3.0% respectively. Measure the dispersion solution and add it to the mixed solution. The added volume of the dispersion solution is 9 - 20% of the volume of deionized water; ultrasonicate for 15 - 30 min to obtain an aqueous phase;

[0015] Step 4: Weigh 0.1 - 0.3 g of trimesoyl chloride TMC and pour it into a beaker, and place it in an oven to melt it into a liquid phase;

[0016] Step 5: Measure 100 - 150 mL of n-hexane and add it to the beaker containing trimesoyl chloride TMC, and ultrasonically disperse for 10 - 20 min to obtain an oil phase;

[0017] Step 6: Fix the polysulfone support membrane in the reaction tank, pour in the aqueous phase, soak for 4 - 6 min, then pour out the aqueous phase, and air dry;

[0018] Step 7: Pour in the oil phase, soak for 1 - 2 minutes, then pour out the oil phase and air dry.

[0019] Step 8: Take out the dried polysulfone support membrane from Step 7, place it in a petri dish, take it out after heat treatment in an oven, cool it to room temperature, pour in deionized water, cut and soak it to obtain a positively charged organic-inorganic hybrid nanofiltration membrane.

[0020] In Step 1, the two-dimensional nanomaterials are graphene, MoS2, WS2, graphitic carbon nitride g-C3N4, and titanium carbide Ti3C2Tx x any one or several of them.

[0021] In Step 4, the process of melting it into a liquid phase in an oven is: hot melt in an oven at 50 - 60 °C for 5 - 10 minutes.

[0022] In Step 8, the size of the petri dish is 250 mm × 250 mm, the heat treatment temperature in the oven is 60 - 65 °C, and the treatment time is 5 - 10 minutes.

[0023] A positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials obtained by the preparation method of the present invention.

[0024] A positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials. The water flux of the positively charged nanofiltration material under a pressure of 4 bar is 26.57 - 32.10 Lm -2 h -1 ; The rejection rates of Ca 2+ and Mg 2+ are 95.69 - 97.23%.

[0025] Application of a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials in sewage treatment.

[0026] The sewage contains calcium and magnesium ions.

[0027] A membrane module includes a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials of the present invention.

[0028] Design principle: Lamellar two-dimensional nanomaterials and amino groups have excellent structural characteristics, which can provide additional transport channels, enabling water molecules to pass through easily, and at the same time having hydrophilic functional groups to ensure water flux. At the same time, the amino-grafted two-dimensional nanomaterials make the membrane surface maintain a positive charge. Due to electrostatic interaction, Ca 2+ , Mg 2+ and other ions are blocked from entering the membrane. To maintain electrical neutrality, negative ions are also retained on the membrane surface. And due to the presence of hydrophilic groups such as amino groups, the membrane surface is covered with water, and pollutants are difficult to adsorb on the membrane surface. Therefore, the pollutants attached to the membrane surface can be removed by rinsing with deionized water.

[0029] Design concept: At present, positively charged nanofiltration membranes are used in water treatment projects such as high-salt wastewater due to their high rejection rate of positively charged ions. However, the serious membrane fouling and the contradiction between their water flux and salt rejection rate have become increasingly prominent. The present invention aims to effectively ensure its water flux while removing Ca 2+ , Mg 2+ , and reduce the attachment of pollutants. Design is carried out around the idea of effectively removing positively charged ions and reducing pollutant attachment. By introducing NH2-grafted two-dimensional nanomaterials, the membrane surface becomes positively charged, and by introducing PIP, etc., the roughness of the membrane surface is reduced, reducing pollutant attachment, that is, it has a high rejection rate for positively charged ions such as Ca 2+ , Mg 2+ and is pollution-resistant.

[0030] Advantages: By using NH2-grafted two-dimensional nanomaterials, the membrane surface becomes positively charged, showing excellent rejection effects for Ca 2+ , Mg 2+ , providing additional channels to improve water flux, and reducing the attachment of pollutants.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0032] The positively charged nanofiltration membrane grafted with amino groups prepared by the present invention has good hydrophilicity and provides additional channels for filtration. The prepared nanofiltration membrane can, on the one hand, improve water flux, and on the other hand, since the NH2-grafted two-dimensional nanomaterials make the membrane surface positively charged, Ca 2+ , Mg 2+ ions can be effectively removed due to the Donnan effect. At the same time, it improves the membrane fouling problem, extends the service life of the membrane, reduces costs, and provides a better prospect for the application of two-dimensional nanomaterials in the field of sewage treatment. Brief description of the drawings

[0033] Figure 1 is the contact angle test diagram of the Ti3C2T x nanofiltration membrane material obtained in Example 1 of the present invention. Detailed description of the specific implementation

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] The experimental methods described in the embodiments are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0036] Example 1

[0037] A preparation method of a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials, the steps are as follows:

[0038] 1) Disperse 200 mg of Ti3C2T x in 80 mL of deionized water and sonicate for 1 h;

[0039] 2) Place the solution obtained in step 1) in a water bath device, add 1 g of p-phenylenediamine and 1 mL of isoamyl nitrite to the solution, set the water bath temperature to 60 °C, and heat and stir for 10 h. After the reaction ends and the product cools to room temperature, centrifuge the solution until the pH of the supernatant is 7 (specific process: centrifuge the solution, discard the supernatant, then add deionized water to mix and continue centrifuging until the pH of the supernatant is 7), and place it in a freeze dryer for freeze drying for 48 h to obtain Ti3C2T x -NH2; Prepare a dispersion of Ti3C2T x -NH2 with a concentration of 1.2 g / L;

[0040] 3) Weigh 2.4 g of piperazine (PIP) and 3.0 g of polyethyleneimine (PEI) respectively, add 110 mL of deionized water, and sonicate for 15 min;

[0041] 4) Add 10 mL of the Ti3C2T x -NH2 dispersion to the solution obtained in step 3), mix and sonicate for 15 min to prepare the aqueous phase;

[0042] 5) Weigh 0.1 g of trimesoyl chloride (TMC) and pour it into a beaker, place it in an oven at 60 °C for 5 min to melt it into a liquid phase;

[0043] 6) Measure 100 mL of n-hexane and add it to the beaker containing trimesoyl chloride, and sonicate for 10 min to prepare the oil phase solution required for the experiment;

[0044] 7) Fix the polysulfone support membrane in the reaction tank, pour the aqueous phase solution prepared in step 5) into it, soak for 4 min, then pour out the solution, and air dry it;

[0045] 8) Pour in the oil phase solution, soak for 1 min, then pour out the solution and air dry it;

[0046] 9) Take out the air-dried membrane and place it in a petri dish with a size of 250 mm × 250 mm, heat-treat it in an oven at 60 °C for 5 min, then take it out, cool it to room temperature, pour it into deionized water, and cut it into a specific shape (the specific shape is the shape required by the measuring machine, and cut it according to the needs of the measuring instrument) and soak it, then the organic-inorganic hybrid positively charged nanofiltration membrane is prepared, denoted as M1.

[0047] Application of a positively charged nanofiltration material added with modified two-dimensional nanomaterials in sewage treatment, where the sewage contains calcium and magnesium ions.

[0048] A membrane module, including the positively charged nanofiltration material added with modified two-dimensional nanomaterials in this embodiment.

[0049] The taken-out sample M1 was analyzed and observed by scanning electron microscopy etc., and the sample M1 was used for the separation performance and water flux study of CaCl2.

[0050] According to Table 1, when the addition amount of Ti3C2T x -NH2 reaches 0.01%, the rejection rate and water flux for Ca 2+ are 96.58% and 32.10 Lm -2 h -1 (4 bar) respectively. Compared with the case without adding two-dimensional nanomaterials, after adding Ti3C2T x -NH2, the rejection rate increased somewhat, and the water flux of the membrane increased significantly.

[0051] Ti3C2T x The calculation method for the addition amount of -NH2 is: (1.2 g / L × 10 mL / 1000) / (110 mL + 10 mL) × 100% = 0.01%.

[0052] As Figure 1 shown, it is the contact angle test diagram of the Ti3C2T x nanofiltration membrane material obtained in this embodiment. It can be seen from the figure that the contact angle of this material is relatively large, indicating good hydrophilicity.

[0053] Example 2

[0054] A preparation method of a positively charged nanofiltration material added with modified two-dimensional nanomaterials, the steps are as follows:

[0055] 1) Disperse 200 mg of Ti3C2T x in 80 mL of deionized water and ultrasonicate for 1 h;

[0056] 2) Place the solution obtained in step 1) in a water bath device, add 1 g of p-phenylenediamine and 1 ml of isoamyl nitrite to the solution, set the water bath temperature to 60 °C, and heat and stir for 10 h. After the reaction ends and the product cools to room temperature, centrifuge the solution until the pH of the supernatant is 7, and place it in a freeze dryer for freeze drying for 48 h to obtain Ti3C2T x -NH2; Prepare a dispersion of Ti3C2T x -NH2 with a concentration of 1.2 g / L;

[0057] 3) Weigh 2.4 g of piperazine (PIP) and 3.0 g of polyethyleneimine (PEI) respectively. After adding 105 mL of deionized water, ultrasonicate for 15 min;

[0058] 4) Add 15 mL of Ti3C2T x -NH2 dispersion to the solution obtained in step 3), mix and ultrasonicate for 15 min to prepare the aqueous phase;

[0059] Ti3C2T x The calculation method for the addition amount of Ti3C2T

[0060] -NH2 is: (1.2 g / L × 15 mL / 1000) / (105 mL + 15 mL) × 100% = 0.015%;

[0061] 5) Weigh 0.1 g of trimesoyl chloride (TMC) and pour it into a beaker. Place it in an oven at 60 °C for 5 min to melt it into a liquid phase;

[0062] 6) Measure 100 mL of n-hexane and add it to the beaker containing trimesoyl chloride. Ultrasonically disperse for 10 min to prepare the oil-phase solution required for the experiment;

[0063] 7) Fix the polysulfone support membrane in the reaction tank, pour the aqueous phase solution prepared in step 5) into it, soak for 4 min, then pour out the solution, and let it dry in the air;

[0064] 8) Pour in the oil-phase solution, soak for 1 min, then pour out the solution and let it dry;

[0065] 9) Take out the dried membrane and place it in a petri dish with dimensions of 250 mm × 250 mm. Heat-treat it in an oven at 60 °C for 5 min, then take it out, cool it to room temperature, pour it into deionized water, and cut it into a specific shape and soak it to obtain an organo-inorganic hybrid positively charged nanofiltration membrane, denoted as M2.

[0066] Example 3

[0067] A preparation method of a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials is as follows:

[0068] 1) Disperse 200 mg of Ti3C2T x in 80 mL of deionized water and ultrasonicate for 1 h;

[0069] 2) Place the solution obtained in step 1) in a water bath device, add 1 g of p-phenylenediamine and 1 ml of isoamyl nitrite to the solution, set the water bath temperature to 60 °C, and heat and stir for 10 h. After the reaction is completed and the product is cooled to room temperature, centrifuge the solution until the pH of the supernatant is 7, and place it in a freeze dryer for freeze drying for 48 h to obtain Ti3C2T x -NH2; Prepare a dispersion of Ti3C2T x -NH2 with a concentration of 1.2 g / L;

[0070] 3) Weigh 2.4 g of piperazine (PIP) and 3.0 g of polyethyleneimine (PEI) respectively, add 100 mL of deionized water, and ultrasonicate for 15 min;

[0071] 4) Add 20 mL of the Ti3C2T x -NH2 dispersion to the solution obtained in step 3), mix and ultrasonicate for 15 min to prepare the aqueous phase;

[0072] Ti3C2T x The calculation method for the addition amount of Ti3C2T

[0073] -NH2 is: (1.2 g / L × 20 mL / 1000) / (100 mL + 20 mL) × 100% = 0.02%;

[0074] 5) Weigh 0.1 g of trimesoyl chloride (TMC) and pour it into a beaker, place it in an oven at 60 °C for 5 min to melt it into a liquid phase;

[0075] 6) Measure 100 ml of n-hexane and add it to the beaker containing trimesoyl chloride, and ultrasonically disperse for 10 min to prepare the oil phase solution required for the experiment;

[0076] 7) Fix the polysulfone support membrane in the reaction tank, pour the aqueous phase solution prepared in step 5) into it, soak for 4 min, then pour out the solution, and let it dry in the air;

[0077] 8) Pour in the oil phase solution, soak for 1 min, then pour out the solution and let it dry;

[0078] 9) Take out the dried membrane and place it in a petri dish with a size of 250 mm × 250 mm, heat-treat it in an oven at 60 °C for 5 min, then take it out, cool it to room temperature, pour it into deionized water, and cut it into a specific shape and soak it to obtain an organic-inorganic hybrid positively charged nanofiltration membrane, denoted as M3;

[0079] Example 4

[0080] A preparation method of a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials, the steps are as follows:

[0081] 1) Disperse 200 mg of graphene (or MoS2, WS2, graphitic carbon nitride (g-C3N4)) in 80 mL of deionized water and ultrasonicate for 1 h;

[0082] 2) Place the solution obtained in step 1) in a water bath device, add 1 g of p-phenylenediamine and 1 mL of isoamyl nitrite to the solution, set the water bath temperature to 60 °C, and heat and stir for 10 h. After the reaction ends and the product cools to room temperature, centrifuge the solution until the pH of the supernatant is 7, place it in a freeze dryer and freeze-dry for 48 h, and prepare it into a dispersion of 1.2 g / L;

[0083] 3) Weigh 2.4 g of piperazine (PIP) and 3.0 g of polyethyleneimine (PEI) respectively, add 100 mL of deionized water, and ultrasonicate for 15 min;

[0084] 4) Add 20 mL of graphene-NH2 (or MoS2-NH2, WS2-NH2, g-C3N4-NH2) dispersion to the solution obtained in step 3), mix and ultrasonicate for 15 min to obtain an aqueous phase;

[0085] 5) Weigh 0.1 g of trimesoyl chloride (TMC) and pour it into a beaker, place it in an oven at 60 °C for 5 min to melt it into a liquid phase;

[0086] 6) Measure 100 mL of n-hexane and add it to the beaker containing trimesoyl chloride, and ultrasonically disperse for 10 min to obtain the oil-phase solution required for the experiment;

[0087] 7) Fix the polysulfone support membrane in the reaction tank, pour the aqueous phase solution prepared in step 5) into it, soak for 4 min, then pour out the solution, and air-dry it;

[0088] 8) Pour in the oil-phase solution, soak for 1 min, then pour out the solution and air-dry it;

[0089] 9) Take out the air-dried membrane and place it in a petri dish with a size of 250 mm × 250 mm, heat-treat it in an oven at 60 °C for 5 min, then take it out, cool it to room temperature, pour it into deionized water, and cut it into a specific shape and soak it to obtain an organic-inorganic hybrid positively charged nanofiltration membrane, denoted as M4;

[0090] Analyze and observe the taken-out sample M4 by scanning electron microscopy, etc., and use the sample M4 for the separation performance and water flux study of CaCl2 / MgCl2.

[0091] Example 5

[0092] A preparation method of a positively charged nanofiltration material based on the addition of modified two-dimensional nanomaterials is as follows:

[0093] 1) Disperse 300 mg of Ti3C2T x in 100 mL of deionized water and ultrasonicate for 2 h;

[0094] 2) Place the solution obtained in step 1) in a water bath device, add 2 g of p-phenylenediamine and 3 mL of isoamyl nitrite to the solution, set the water bath temperature to 65 °C, and heat and stir for 12 h. After the reaction ends and the product cools to room temperature, centrifuge the solution until the pH of the supernatant is 7, and place it in a freeze dryer for freeze drying for 60 h to obtain Ti3C2T x -NH2; Prepare a dispersion of Ti3C2T x -NH2 with a concentration of 1.5 g / L;

[0095] 3) Weigh 2.2 g of piperazine (PIP) and 3.3 g of polyethyleneimine (PEI) respectively, add 110 mL of deionized water, and ultrasonicate for 30 min;

[0096] 4) Add 10 mL of the Ti3C2T x -NH2 dispersion to the solution obtained in step 3), mix and ultrasonicate for 30 min to prepare the aqueous phase;

[0097] Ti3C2T x The calculation method for the addition amount of -NH2 is: (1.5 g / L × 10 mL / 1000) / (110 mL + 10 mL) × 100% = 0.0125%;

[0098] 5) Weigh 0.3 g of trimesoyl chloride (TMC) and pour it into a beaker, place it in an oven at 50 °C for 10 min to melt it into a liquid phase;

[0099] 6) Measure 150 mL of n-hexane and add it to the beaker containing trimesoyl chloride, and ultrasonically disperse for 20 min to prepare the oil phase solution required for the experiment;

[0100] 7) Fix the polysulfone support membrane in the reaction tank, pour the aqueous phase solution prepared in step 5) into it, soak for 6 min, then pour out the solution, and air dry it;

[0101] 8) Pour in the oil phase solution, soak for 2 min, then pour out the solution and air dry it;

[0102] 9) Take out the air-dried membrane and place it in a petri dish with a size of 250 mm × 250 mm, heat-treat it in an oven at 65 °C for 10 min, then take it out, cool it to room temperature, pour it into deionized water, cut it, and soak it to obtain an organic-inorganic hybrid positively charged nanofiltration membrane.

[0103] Comparative Example 1

[0104] A preparation method of a nanofilter membrane without adding nanomaterials, and the preparation steps are as follows:

[0105] 1) Weigh 2.4 g of piperazine (PIP) and 3.0 g of polyethyleneimine (PEI) respectively. After adding 120 mL of deionized water, ultrasonicate for 15 min to obtain the aqueous solution required for the experiment;

[0106] 2) Weigh 0.1 g of trimesoyl chloride (TMC) and pour it into a beaker. Place it in an oven at 60 °C for 5 min to melt it into a liquid phase;

[0107] 3) Measure 100 mL of n - hexane and add it to the beaker containing trimesoyl chloride. Ultrasonically disperse for 10 min to obtain the oil - phase solution required for the experiment;

[0108] 4) Fix the polysulfone support membrane in the reaction tank. Pour the aqueous solution prepared in step 1) into it, soak for 4 min, then pour out the solution, and leave it to dry in the air;

[0109] 5) Pour in the oil - phase solution, soak for 1 min, then pour out the solution and dry it;

[0110] 6) Take out the dried membrane and place it in a petri dish with a size of 250 mm×250 mm. Heat - treat it in an oven at 60 °C for 5 min, then take it out, cool it to room temperature, pour it into deionized water, cut it into a specific shape and soak it, and then an organic - inorganic hybrid positively charged nanofilter membrane is obtained, denoted as M0;

[0111] Comparative Example 2

[0112] A preparation method of a nanofilter membrane with added nanomaterials, and the preparation steps are as follows:

[0113] 1) Weigh 2.4 g of piperazine (PIP) and 3.0 g of polyethyleneimine (PEI) respectively. After adding 110 mL of deionized water, ultrasonicate for 15 min.

[0114] 2) Add 10 mL of nano - TiO₂ to the ultrasonically treated solution to obtain the aqueous solution required for the experiment;

[0115] 3) Weigh 0.1 g of trimesoyl chloride (TMC) and pour it into a beaker. Place it in an oven at 60 °C for 5 min to melt it into a liquid phase;

[0116] 4) Measure 100 mL of n - hexane and add it to the beaker containing trimesoyl chloride. Ultrasonically disperse for 10 min to obtain the oil - phase solution required for the experiment;

[0117] 5) Fix the polysulfone support membrane in the reaction tank. Pour the aqueous solution prepared in step 2) into it, soak for 4 min, then pour out the solution, and leave it to dry in the air;

[0118] 6) Pour in the oil-phase solution, soak for 1 min, then pour out the solution and air dry.

[0119] 7) Take out the air-dried membrane and place it in a petri dish with dimensions of 250 mm × 250 mm. Heat-treat it in an oven at 60 °C for 5 min, then take it out and cool it to room temperature. Pour in deionized water, cut it into a specific shape and soak it, thus obtaining a positively charged organic-inorganic hybrid nanofiltration membrane, denoted as M01.

[0120] The nano-TiO₂ in this comparative example is an ordinary nano-material, not a two-dimensional nano-material.

[0121] Separation performance experiment:

[0122] Table 1 shows the water flux (4 bar) and rejection rate of the positively charged nanofiltration membrane material of the amino-grafted two-dimensional nano-material obtained under the experimental parameters. It can be seen that by adding the amino-grafted two-dimensional nano-material, the rejection rate and water flux of the nanofiltration membrane can be effectively improved while ensuring a relatively high rejection rate. In the present invention, in the CaCl₂ / MgCl₂ solution, the concentrations of CaCl₂ and MgCl₂ are both 2000 mg / L.

[0123] Table 1 Water flux and rejection rate table

[0124]

[0125] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. Application of a positively charged nanofiltration material added with modified two-dimensional nanomaterials in sewage treatment, characterized in that, The sewage contains calcium and magnesium ions; Among them, a preparation method of a positively charged nanofiltration material based on the addition of a modified two-dimensional nanomaterial includes the following steps: Step 1: Disperse 200-300 mg of two-dimensional nanomaterial in 80-100 mL of deionized water, and ultrasonicate for 1-2 h to obtain a dispersion solution; place the dispersion solution in a water bath at 60-65 °C, and add 1-2 g of p-phenylenediamine and 1-3 mL of isoamyl nitrite to the dispersion solution, and stir and react in the water bath for 10-12 h. After the reaction is completed, cool the reaction solution to room temperature; Step 2: Centrifuge the cooled reaction solution until the pH of the supernatant is 7, and place it in a freeze dryer for freeze drying for at least 48 h to obtain an amino-grafted two-dimensional nanomaterial; prepare the amino-grafted two-dimensional nanomaterial into a dispersion with a concentration of 1.2-1.5 g / L with deionized water; Step 3: Prepare a mixed solution of piperazine PIP and polyethyleneimine PEI with deionized water with mass percentages of 2.0-2.2% and 2.7-3.0% respectively. Measure the dispersion solution and add it to the mixed solution. The added volume of the dispersion solution is 9-20% of the volume of deionized water; ultrasonicate for 15-30 min to obtain an aqueous phase; Step 4: Weigh 0.1-0.3 g of trimesoyl chloride TMC and pour it into a beaker, and place it in an oven to melt it into a liquid phase; Step 5: Measure 100-150 mL of n-hexane and add it to the beaker containing trimesoyl chloride TMC, and ultrasonically disperse for 10-20 min to obtain an oil phase; Step 6: Fix the polysulfone support membrane in the reaction tank, pour in the aqueous phase and soak for 4-6 min, then pour out the aqueous phase and air dry it; Step 7: Pour in the oil phase and soak for 1-2 min, then pour out the oil phase and air dry it; Step 8: Take out the polysulfone support membrane air-dried in Step 7 and place it in a petri dish. After heat treatment in the oven, take it out and cool it to room temperature, then pour it into deionized water, cut and soak it to obtain an organic-inorganic hybrid positively charged nanofiltration membrane; Among them, the two-dimensional nanomaterial is two-dimensional titanium carbide Ti3C2T x .

2. The application according to claim 1, wherein: In Step 4, the process of melting it into a liquid phase in the oven is: hot melt in an oven at 50-60 °C for 5-10 min.

3. The application according to claim 1, characterized in that: In Step 8, the size of the petri dish is 250 mm × 250 mm, the heat treatment temperature in the oven is 60-65 °C, and the treatment time is 5-10 min.

4. The application according to claim 1, wherein: The water flux of the positively charged nanofiltration membrane material under a pressure of 4 bar is 26.57~32.10 Lm -2 h -1 ; The rejection rates of Ca 2+ and Mg 2+ are 95.69~97.23%.

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