Application of phytic acid-nitrogen doped carbon quantum dot composite as an aqueous monomer in the preparation of polyamide nanofiltration membranes

Abstract

The present invention discloses the application of a phytic acid-nitrogen-doped carbon quantum dot composite as an aqueous monomer in the preparation of a polyamide nanofiltration membrane. The preparation method of the phytic acid-nitrogen-doped carbon quantum dot composite includes: preparing nitrogen-doped carbon quantum dots by a hydrothermal reaction method, and then preparing a phytic acid-nitrogen-doped carbon quantum dot composite from the nitrogen-doped carbon quantum dots and phytic acid as raw materials by a solution synthesis method. By adding the phytic acid-doped carbon quantum dot composite to the aqueous monomer, a phytic acid-doped carbon quantum dot composite-doped polyamide nanofiltration membrane is prepared by interfacial polymerization. Under the test conditions of room temperature and 0.6 MPa, it has a high rejection rate (above 98%) for a 0.2 wt% magnesium sulfate solution, and the pure water flux is 65-75 LHM.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membranes, and in particular relates to the application of a phytic acid-nitrogen-doped carbon quantum dot complex as an aqueous phase monomer in the preparation of a polyamide nanofiltration membrane. Background Art

[0002] Nanofiltration membrane is a new type of pressure-driven membrane with a pore size between ultrafiltration and reverse osmosis, which can be used to separate divalent salts from monovalent salts. Nanofiltration membrane has the characteristics of low operating pressure, high flux and energy saving. Therefore, nanofiltration membrane is widely used in bioengineering, medicine, metallurgy, water treatment, electronics and other fields. The commonly used nanofiltration membrane in industry is organic nanofiltration membrane, which has many advantages such as high air permeability, low density, good film forming property, low cost and good flexibility. However, organic nanofiltration membrane has the disadvantages of low flux and poor anti-pollution ability in industrial applications. Therefore, it is necessary to modify the organic nanofiltration membrane to improve the flux and anti-pollution property of the membrane layer. In addition, as the thickness of the organic nanofiltration membrane increases, the flux of the membrane layer decreases. Therefore, the preparation of defect-free and ultra-thin organic nanofiltration membrane has become a research hotspot. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide the use of a phytic acid-nitrogen-doped carbon quantum dot complex as an aqueous phase monomer in the preparation of a polyamide nanofiltration membrane.

[0004] Another object of the present invention is to provide a polyamide nanofiltration membrane.

[0005] The technical solution of the present invention is as follows:

[0006] The invention discloses an application of a phytic acid-nitrogen-doped carbon quantum dot complex as an aqueous phase monomer in the preparation of a polyamide nanofiltration membrane. The preparation method of the phytic acid-nitrogen-doped carbon quantum dot complex comprises: preparing nitrogen-doped carbon quantum dots by a hydrothermal reaction method, and then preparing the phytic acid-nitrogen-doped carbon quantum dot complex by a solution synthesis method using the nitrogen-doped carbon quantum dots and phytic acid as raw materials.

[0007] In a preferred embodiment of the present invention, the method for preparing the phytic acid-nitrogen-doped carbon quantum dot composite comprises:

[0008] (1) Dissolving urea and citric acid in deionized water, performing a hydrothermal reaction at 175-185° C. for 2.5-3.5 h, and then dialysis for 6-8 days and freeze-drying to obtain a powder of nitrogen-doped carbon quantum dots, wherein the ratio of urea, citric acid and deionized water is 0.8-1.2 g: 1.5-2.4 g: 20-30 mL;

[0009] (2) After the phytic acid and the aqueous solution of the nitrogen-doped carbon quantum dots are uniformly mixed, the mixture is heated to reflux at 60-90° C. for 0.8-1.2 h to obtain a solution of the phytic acid-nitrogen-doped carbon quantum dots composite.

[0010] In a preferred embodiment of the present invention, the mass ratio of phytic acid to nitrogen-doped carbon quantum dots in the phytic acid-nitrogen-doped carbon quantum dot composite is 1-5:1.

[0011] More preferably, the mass ratio of phytic acid to nitrogen-doped carbon quantum dots in the phytic acid-nitrogen-doped carbon quantum dot composite is 1-2:1.

[0012] Another technical solution of the present invention is as follows:

[0013] A polyamide nanofiltration membrane includes a polyethersulfone ultrafiltration support layer and an organic nanofiltration membrane layer formed on the polyethersulfone ultrafiltration support layer by interfacial polymerization. In this interfacial polymerization, the aqueous-phase monomer consists of a phytic acid-nitrogen-doped carbon quantum dot composite and piperazine, the acid acceptor is a polyamine, and the organic-phase monomer is trimesoyl chloride. The preparation method of the phytic acid-nitrogen-doped carbon quantum dot composite includes: preparing nitrogen-doped carbon quantum dots by a hydrothermal reaction method, and then preparing the phytic acid-nitrogen-doped carbon quantum dot composite from the nitrogen-doped carbon quantum dots and phytic acid as raw materials by a solution synthesis method.

[0014] In a preferred embodiment of the present invention, the preparation method of the phytic acid-nitrogen-doped carbon quantum dot composite includes:

[0015] (1) Dissolve urea and citric acid in deionized water, carry out a hydrothermal reaction at 175-185 °C for 2.5-3.5 h, then dialyze for 6-8 d and freeze-dry to obtain a powder of nitrogen-doped carbon quantum dots. The ratio of urea, citric acid, and deionized water is 0.8-1.2 g:1.5-2.4 g:20-30 mL;

[0016] (2) Mix the phytic acid and the aqueous solution of the above-mentioned nitrogen-doped carbon quantum dots evenly, and carry out a heating reflux reaction at 60-90 °C for 0.8-1.2 h to obtain a solution of the phytic acid-nitrogen-doped carbon quantum dot composite.

[0017] In a preferred embodiment of the present invention, the mass ratio of phytic acid to nitrogen-doped carbon quantum dots in the phytic acid-nitrogen-doped carbon quantum dot composite is 1-5:1.

[0018] More preferably, the mass ratio of phytic acid to nitrogen-doped carbon quantum dots in the phytic acid-nitrogen-doped carbon quantum dot composite is 1-2:1.

[0019] In a preferred embodiment of the present invention, the polyamine is diethylamine or triethylamine.

[0020] In a preferred embodiment of the present invention, the mass ratio of the phytic acid-nitrogen-doped carbon quantum dot composite to piperazine is 1-5:1.

[0021] The beneficial effects of the present invention are as follows: By adding a phytic acid-doped carbon quantum dot composite to an aqueous monomer, an ultrathin phytic acid-doped carbon quantum dot composite-doped polyamide nanofiltration membrane is prepared through interfacial polymerization. By reducing the thickness of the nanofiltration membrane layer, the flux and anti-pollution ability can be significantly improved. Under the test conditions of room temperature and 0.6 MPa, it has a high rejection rate (above 98%) for a 0.2 wt% magnesium sulfate solution, and the pure water flux is 65 - 75 LHM. Description of the Drawings

[0022] Figure 1 It is a scanning electron microscope photograph of the organic nanofiltration membrane layer of the phytic acid-polyamide nanofiltration membrane prepared in Comparative Example 2 of the present invention.

[0023] Figure 2 It is a scanning electron microscope photograph of the organic nanofiltration membrane layer of the phytic acid-nitrogen-doped carbon quantum dot-doped polyamide nanofiltration membrane prepared in Example 2 of the present invention. Detailed Embodiments

[0024] The technical solutions of the present invention will be further described and illustrated below through specific embodiments in conjunction with the drawings.

[0025] Comparative Example 1

[0026] (1) Dissolve 1 g of urea and 2 g of citric acid in 25 mL of deionized water, place it in a 25 mL hydrothermal reaction kettle, and react at 180 °C for 3 h. After taking it out, dialyze for 7 days and then freeze-dry to obtain nitrogen-doped carbon quantum dot powder;

[0027] (2) Stir evenly an aqueous solution of 0.1 g of the above nitrogen-doped carbon quantum dot powder and 100 mL of a 0.1 wt% piperazine aqueous solution (the mass ratio of the phytic acid-nitrogen-doped carbon quantum dot composite to piperazine is 1:1), add 1 wt% PEG1000 and 1 wt% diethylamine, and ultrasonicate for 30 min to prepare a uniform aqueous solution;

[0028] (3) Immerse a 20KD polyethersulfone that has been washed with ethanol and water in a 0.2 wt% TMC n-hexane solution, take it out after reacting at room temperature for 10 min, soak it in water and blow it dry with an air gun; then immerse it in the above aqueous solution, take it out after reacting at room temperature for 10 min, soak it in water and blow it dry with an air gun, repeat this step once, then place it in a cool place to dry and put it in an oven at 50 °C for heat treatment for 15 min, and then cool it with the furnace to prepare a nitrogen-doped carbon quantum dot polyamide nanofiltration membrane.

[0029] The nitrogen-doped carbon quantum dot-doped polyamide nanofiltration membrane prepared in this comparative example was tested under the pressure conditions of room temperature and 0.6 MPa. Its pure water flux was 56.8 LHM, and the rejection rate for a 0.2 wt% magnesium sulfate solution was 97.1%.

[0030] Comparative Example 2

[0031] (1) Stir 100 mg of phytic acid and 100 mL of 0.1 wt% piperazine aqueous solution evenly, add 1 wt% PEG1000 and 1 wt% diethylamine, and ultrasonicate for 30 min to prepare a uniform aqueous solution;

[0032] (4) Immerse the 20KD polyethersulfone support layer after being washed with ethanol and water in a n-hexane solution of 0.2 wt% trimesoyl chloride, react at room temperature for 10 min, then soak in water and blow dry with an air gun, and then immerse in the above aqueous solution, react at room temperature and then soak in water and blow dry with an air gun; Repeat this step once;

[0033] (5) After air-drying the material obtained in step (4) in a cool place, heat-treat it in an oven at 50 °C for 15 min, and then cool it in the furnace to obtain a phytic acid-polyamide nanofiltration membrane, and the thickness of its organic nanofiltration membrane layer is 112 nm, as Figure 1 .

[0034] Membrane tube performance test: The phytic acid-polyamide nanofiltration membrane prepared in this comparative example was tested at room temperature and a pressure of 0.6 MPa. Its pure water flux was 56 LHM, and the rejection rate for a 0.2 wt% magnesium sulfate solution was 98.5%.

[0035] Example 1

[0036] (1) Dissolve 1 g of urea and 2 g of citric acid in 25 mL of deionized water, place it in a 25 mL hydrothermal reaction kettle, and react at 180 °C for 3 h. After taking it out, dialyze for 7 days and then freeze-dry to obtain nitrogen-doped carbon quantum dot powder;

[0037] (2) Dissolve phytic acid and nitrogen-doped carbon quantum dot powder in a mass ratio of 5:1 in 100 mL of water. After mixing evenly, reflux at 60 - 90 °C for 1 h to obtain a 20 mg / mL phytic acid-nitrogen-doped carbon quantum dot composite solution;

[0038] (3) Stir and mix the above 20 mg / mL phytic acid-nitrogen-doped carbon quantum dot composite solution and 0.1 wt% piperazine aqueous solution (the mass ratio of phytic acid-nitrogen-doped carbon quantum dot composite to piperazine is 1:1) evenly, then add 1 wt% PEG1000 and 1 wt% diethylamine, and after ultrasonic treatment, obtain an aqueous solution;

[0039] (4) Immerse the 20KD polyethersulfone support layer after being washed with ethanol and water in a n-hexane solution of 0.2 wt% trimesoyl chloride, react at room temperature for 10 min, then soak in water and blow dry with an air gun, and then immerse in the above aqueous solution, react at room temperature and then soak in water and blow dry with an air gun; Repeat this step once;

[0040] (5) After air-drying the material obtained in step (5) in a cool place, heat-treat it in an oven at 50 °C for 15 min, and then cool it with the furnace to obtain the phytic acid-nitrogen-doped carbon quantum dot-doped polyamide nanofiltration membrane.

[0041] Membrane tube performance test: The phytic acid-nitrogen-doped carbon quantum dot-doped polyamide nanofiltration membrane prepared in this example was tested at room temperature and a pressure of 0.6 MPa. Its pure water flux was 70 LHM, and the rejection rate for a 0.2 wt% magnesium sulfate solution was 98.6%.

[0042] Example 2

[0043] (1) Dissolve 1 g of urea and 2 g of citric acid in 25 mL of deionized water, place it in a 25 mL hydrothermal reaction kettle, and react at 180 °C for 3 h. After taking it out, dialyze for 7 days and then freeze-dry to obtain nitrogen-doped carbon quantum dot powder;

[0044] (2) Dissolve phytic acid and nitrogen-doped carbon quantum dot powder in a mass ratio of 5:1 in 100 mL of water. After mixing evenly, reflux and react at 60-90 °C for 1 h to obtain a 20 mg / mL phytic acid-nitrogen-doped carbon quantum dot composite solution;

[0045] (3) Stir and mix the above 20 mg / mL phytic acid-nitrogen-doped carbon quantum dot composite solution and 0.1 wt% piperazine aqueous solution (the mass ratio of the phytic acid-nitrogen-doped carbon quantum dot composite to piperazine is 5:1) evenly, then add 1 wt% PEG1000 and 1 wt% diethylamine, and after ultrasonic treatment, obtain an aqueous solution;

[0046] (4) Immerse the 20KD polyethersulfone support layer after being washed with ethanol and water in a n-hexane solution of 0.2 wt% trimesoyl chloride at room temperature. After reacting for 10 min at room temperature, soak it in water and blow it dry with an air gun, then immerse it in the above aqueous solution, react at room temperature, and then soak it in water and blow it dry with an air gun; repeat this step once;

[0047] (5) After air-drying the material obtained in step (5) in a cool place, heat-treat it in an oven at 50 °C for 15 min, and then cool it with the furnace to obtain the phytic acid-nitrogen-doped carbon quantum dot-doped polyamide nanofiltration membrane, the thickness of its organic nanofiltration membrane layer is 45 nm, as Figure 2 shown.

[0048] Membrane tube performance test: The phytic acid-nitrogen-doped carbon quantum dot-doped polyamide nanofiltration membrane prepared in this example was tested at room temperature and a pressure of 0.6 MPa. Its pure water flux was 75 LHM, and the rejection rate for a 0.2 wt% magnesium sulfate solution was 98%.

[0049] Example 3

[0050] (1) Dissolve 1 g of urea and 2 g of citric acid in 25 mL of deionized water, place it in a 25 mL hydrothermal reactor, and react at 180 °C for 3 h. After taking it out, dialyze for 7 days and then freeze-dry to obtain nitrogen-doped carbon quantum dot powder;

[0051] (2) Dissolve phytic acid and nitrogen-doped carbon quantum dot powder in 100 mL of water at a mass ratio of 10:1. After mixing evenly, reflux and react at 60 - 90 °C for 1 h to obtain a 20 mg / mL phytic acid-nitrogen-doped carbon quantum dot composite solution;

[0052] (3) Stir and mix the above 20 mg / mL phytic acid-nitrogen-doped carbon quantum dot composite solution and 0.1 wt% piperazine aqueous solution (where the mass ratio of phytic acid-nitrogen-doped carbon quantum dot composite to piperazine is 1:1) evenly, then add 1 wt% PEG1000 and 1 wt% diethylamine. After ultrasonic treatment, obtain an aqueous solution;

[0053] (4) Immerse the 20KD polyethersulfone support layer after being washed with ethanol and water in a n-hexane solution of 0.2 wt% trimesoyl chloride at room temperature. After reacting for 10 min at room temperature, soak it in water and blow it dry with an air gun, then immerse it in the above aqueous solution and react at room temperature, and then soak it in water and blow it dry with an air gun; Repeat this step once;

[0054] (5) After air-drying the material obtained in step (5) in a cool place, heat-treat it in an oven at 50 °C for 15 min, and then cool it with the furnace to obtain a phytic acid-nitrogen-doped carbon quantum dot-doped polyamide nanofiltration membrane.

[0055] Membrane tube performance test: Test the phytic acid-nitrogen-doped carbon quantum dot-doped polyamide nanofiltration membrane prepared in this example at room temperature and a pressure of 0.6 MPa. Its pure water flux is 68 LHM, and the rejection rate for a 0.2 wt% magnesium sulfate solution is 99%.

[0056] The above is only a preferred embodiment of the present invention, and thus the scope of implementation of the present invention cannot be limited thereby. That is, equivalent changes and modifications made according to the scope of the present invention patent and the content of the specification should still fall within the scope covered by the present invention.

Claims

1. Application of phytic acid-nitrogen doped carbon quantum dot composite as aqueous monomer in preparation of polyamide nanofiltration membrane, characterized in that: The preparation method of the phytic acid-nitrogen doped carbon quantum dot composite includes: preparing nitrogen doped carbon quantum dots by a hydrothermal reaction method, and then preparing the phytic acid-nitrogen doped carbon quantum dot composite by a solution synthesis method using the nitrogen doped carbon quantum dots and phytic acid as raw materials; The preparation method of the above phytic acid-nitrogen doped carbon quantum dot composite includes: (1) Dissolve urea and citric acid in deionized water, carry out a hydrothermal reaction at 175 - 185 °C for 2.5 - 3.5 h, then dialyze for 6 - 8 d and freeze-dry to obtain a powder of nitrogen doped carbon quantum dots. The ratio of urea, citric acid and deionized water is 0.8 - 1.2 g: 1.5 - 2.4 g: 20 - 30 mL; (2) Mix the phytic acid and the aqueous solution of the above nitrogen doped carbon quantum dots evenly, and carry out a heating reflux reaction at 60 - 90 °C for 0.8 - 1.2 h to obtain a solution of the phytic acid-nitrogen doped carbon quantum dot composite.

2. The application according to claim 1, characterized in that: The mass ratio of phytic acid to nitrogen doped carbon quantum dots in the phytic acid-nitrogen doped carbon quantum dot composite is 1 - 5:

1.

3. The application according to claim 2, characterized in that: The mass ratio of phytic acid to nitrogen doped carbon quantum dots in the phytic acid-nitrogen doped carbon quantum dot composite is 1 - 2:

1.

4. A polyamide nanofiltration membrane, characterized in that: It includes a polyethersulfone ultrafiltration support layer and an organic nanofiltration membrane layer formed on the polyethersulfone ultrafiltration support layer by interfacial polymerization. In this interfacial polymerization, the aqueous phase monomer consists of a phytic acid-nitrogen doped carbon quantum dot composite and piperazine, the acid acceptor is a polyamine, and the organic phase monomer is trimesoyl chloride. The preparation method of the phytic acid-nitrogen doped carbon quantum dot composite includes: preparing nitrogen doped carbon quantum dots by a hydrothermal reaction method, and then preparing the phytic acid-nitrogen doped carbon quantum dot composite by a solution synthesis method using the nitrogen doped carbon quantum dots and phytic acid as raw materials; The preparation method of the above phytic acid-nitrogen doped carbon quantum dot composite includes: (1) Dissolve urea and citric acid in deionized water, carry out a hydrothermal reaction at 175 - 185 °C for 2.5 - 3.5 h, then dialyze for 6 - 8 d and freeze-dry to obtain a powder of nitrogen doped carbon quantum dots. The ratio of urea, citric acid and deionized water is 0.8 - 1.2 g: 1.5 - 2.4 g: 20 - 30 mL; (2) Mix the phytic acid and the aqueous solution of the above nitrogen doped carbon quantum dots evenly, and carry out a heating reflux reaction at 60 - 90 °C for 0.8 - 1.2 h to obtain a solution of the phytic acid-nitrogen doped carbon quantum dot composite.

5. A polyamide nanofiltration membrane according to claim 4, characterized in that: The mass ratio of phytic acid to nitrogen doped carbon quantum dots in the phytic acid-nitrogen doped carbon quantum dot composite is 1 - 5:

1.

6. The polyamide nanofiltration membrane according to claim 5, wherein: The mass ratio of phytic acid to nitrogen doped carbon quantum dots in the phytic acid-nitrogen doped carbon quantum dot composite is 1 - 2:

1.

7. The polyamide nanofiltration membrane according to claim 4, characterized in that: The polyamine is diethylamine or triethylamine.

8. The polyamide nanofiltration membrane according to claim 4, wherein: The mass ratio of the phytic acid-nitrogen doped carbon quantum dot composite to piperazine is 1 - 5:1.

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