A method for preparing an amphoteric Janus nanofiltration membrane

Abstract

This invention discloses a method for preparing an amphoteric Janus nanofiltration membrane. First, dopamine hydrochloride is dissolved in a mixed solution of tert-butyl hydroperoxide and Tris buffer solution. Then, a nylon-based membrane is immersed in the dopamine solution to modify its surface. Next, a dual-nozzle electrospinning device is used to electrospray tert-butyl hydroperoxide in ethanol solvent and 1,3,5-benzenetricarbonyl trichloride in 2-methyltetrahydrofuran onto one side of the dopamine-modified membrane, forming a positively charged active layer. The spraying solutions are then changed to tetraethylenepentamine in ethanol solvent and 1,3,5-benzenetricarbonyl trichloride in 2-methyltetrahydrofuran, and the same spraying parameters are used to electrospray the other side of the dopamine-modified membrane to form a negatively charged active filtration layer. The resulting membrane is then vacuum-dried and thermosetting to obtain the amphoteric Janus nanofiltration membrane. The prepared amphoteric Janus nanofiltration membrane has positive and negative charges on both sides, respectively. When different sides are used, it has a good filtration effect on anionic or cationic dyes in wastewater and has a high water flux.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane preparation and membrane separation technology, specifically relating to a method for preparing an amphoteric Janus nanofiltration membrane. Background Technology

[0002] Nanofiltration membranes operate within the range between ultrafiltration and reverse osmosis. Compared to reverse osmosis membranes, they offer lower pressure drive and higher water flux, making them highly valuable for research. In recent years, Janus membranes have shown significant potential in many applications due to their superior performance compared to traditional membrane materials, enabling functions that traditional membranes cannot achieve. By modifying the two surfaces of nanofiltration membranes differently, ordinary nanofiltration membranes can possess various properties, resulting in high separation and removal efficiency for different pollutants in wastewater while achieving high water flux. Amphoteric Janus nanofiltration membranes provide technical support for the widespread application of membrane technology in water treatment.

[0003] Currently, there is limited research on hermaphroditic Janus nanofiltration membranes.

[0004] Chinese patent application CN202210996574.3, entitled "A Charged Janus Nanofiltration Membrane and Its Preparation Method," discloses a method for preparing a charged Janus nanofiltration membrane, belonging to the field of nanofiltration membranes. This patent uses positively charged diamine and piperazine as aqueous monomers, which undergo interfacial polymerization with the oil-phase monomer trimesoyl chloride on the surface of an electronegative ultrafiltration membrane to obtain a charged Janus nanofiltration membrane. However, this method uses traditional interfacial polymerization, which may suffer from problems such as uneven reaction and low reaction degree.

[0005] Chinese patent application CN201810535863.7, entitled "A Method for Preparing a Positively / Negatively Charged Janus Nanofiltration Membrane," discloses a method for preparing a positively / negatively charged Janus nanofiltration membrane, which also belongs to the field of nanofiltration membranes. This patent employs a method involving uniformly coating a sodium polyacrylate / polyvinyl alcohol solution onto one side of a porous base membrane, cross-linking with a cross-linking agent, and coating the other side of the membrane with a dopamine and polyethyleneimine solution, thereby obtaining a positively / negatively charged Janus nanofiltration membrane. This method utilizes a significant amount of charged pre-prepared polymers; the adhesion between the polymer and the base membrane needs improvement, and the long-term stability of the membrane requires further verification. Furthermore, the thickness of the polymer-based active layer needs careful control, and the utilization rate of the charged polymer needs to be improved.

[0006] Therefore, it is essential to obtain an amphoteric Janus nanofiltration membrane with high preparation efficiency and good water purification effect. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, this invention provides a method for preparing an amphoteric Janus nanofiltration membrane that is simple to prepare, has good stability, high reaction efficiency, high utilization rate, good rejection rate, high water flux, and high removal effect on different types of dyes.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing an amphoteric Janus nanofiltration membrane includes the following steps: First, tert-butyl hydroperoxide and a Tris buffer solution are added to a reactor. The amount of tert-butyl hydroperoxide added is 0.5-0.8%, the pH of the Tris buffer solution is 7-9, and the total volume of the mixed solvent is fixed at 200 mL. Dopamine hydrochloride is dissolved in the mixed solvent at a concentration of 0.2-0.4%. After thorough stirring and mixing, a dopamine solution is obtained. Then, a nylon-based membrane is immersed in the dopamine solution and reacted at room temperature for 20-30 h. The membrane is then immersed in deionized water for 24 h to remove unreacted dopamine, resulting in a dopamine-modified base membrane. Finally, a dual-nozzle electrospinning device is used to spin 0.2-0.3% (w / v) tert-butyl hydroperoxide and 0.08-0.15% (w / v) 2-methyl-tetrahydrofuran from an ethanol solvent. 1,3,5-Benzenetricarbonyltrichloride was electrosprayed onto one side of the dopamine-modified base membrane to form a positively charged active layer. The nozzle movement speed was 20–30 mm / min, the flow rate was 3–5 mL / h, and the number of scans was twice. The spray solution was changed to 0.1–0.15% (w / v) tetraethylenepentamine in ethanol and 0.08–0.15% (w / v) 1,3,5-Benzenetricarbonyltrichloride in 2-methyl-tetrahydrofuran. The other side of the dopamine-modified base membrane was electrosprayed using the same spray parameters to form a negatively charged active layer. The obtained membrane was dried and thermocured in a vacuum oven at 55–65 °C for 10–15 min to obtain the amphoteric Janus nanofiltration membrane. The prepared amphoteric Janus nanofiltration membrane has positive and negative charges on both sides, respectively. When different sides are used, it has a good filtration effect on anionic or cationic dyes in wastewater and has a high water flux.

[0010] Specifically, the following steps are included:

[0011] 1) Add tert-butyl hydrogen peroxide and Tris buffer solution to the reactor. The amount of tert-butyl hydrogen peroxide added is 0.5~0.8%, the pH of the Tris buffer solution is 7~9, and the total volume of the mixed solvent is fixed at 200mL. Dissolve dopamine hydrochloride in the mixed solvent and the dopamine concentration is 0.2~0.4%. After stirring and mixing thoroughly, a dopamine solution is obtained.

[0012] 2) Then, the nylon base membrane is immersed in a dopamine solution and reacted at room temperature for 20-30 hours; then the membrane is immersed in deionized water for 24 hours to wash away the unreacted dopamine, thus obtaining the dopamine-modified base membrane.

[0013] 3) Using a dual-nozzle electrospinning device, 0.2-0.3% (w / v) tert-butyl hydroperoxide in ethanol solvent and 0.08-0.15% (w / v) 1,3,5-benzenetricarbonyl trichloride in 2-methyltetrahydrofuran are electrospun onto one side of the dopamine-modified base film to form a positively charged active layer. The nozzle moving speed is 20-30 mm / min, the flow rate is 3-5 mL / h, and the number of scans is twice.

[0014] 4) Replace the spray solution with 0.1~0.15% (w / v) tetraethylenepentamine in ethanol and 0.08~0.15% (w / v) 1,3,5-benzenetricarbonyltrichloride in 2-methyltetrahydrofuran, and use the same spray parameters to electrospray the other side of the dopamine-modified base membrane to form a negatively charged active layer. Dry the obtained membrane in a vacuum oven at 55~65℃ and heat-cur it for 10~15 min to obtain the amphoteric Janus nanofiltration membrane.

[0015] Specifically: In step 1), the optimal concentration of tert-butyl hydrogen peroxide is 0.5-0.8%. Too little will prevent dopamine from forming polydopamine, while a small amount can promote the reaction. Excessive addition does not produce more polymers and is not economically viable. The optimal pH range for the Tris buffer solution is 7-9. At too low a pH, only a small amount of dopamine polymerizes, but too high a pH makes the polydopamine unstable. The optimal dopamine concentration is 0.2-0.4%. Too little dopamine will not achieve uniform surface modification of the nylon membrane, while too much may increase the membrane thickness and is uneconomical.

[0016] The reaction is carried out at room temperature for 20-30 hours as described in step 2). When the reaction time is less than 20 hours, the dopamine polymerization is incomplete; when the reaction time is too long, the preparation efficiency decreases, and the performance of the nanofiltration membrane is not significantly improved.

[0017] The optimal concentration range for tert-butyl hydroperoxide (0.2–0.3% w / v) and 1,3,5-benzenetricarbonyl trichloride (0.08–0.15% w / v) mentioned in step 3) is as follows: concentrations below this range may result in incomplete reaction and poor cation modification; concentrations above this range may increase membrane thickness, thereby reducing membrane flux. The nozzle's moving speed and flow rate both affect membrane thickness and the separation efficiency of the ion-active layer. Too slow a moving speed and too fast a flow rate will increase membrane thickness, affecting water flux during filtration; conversely, too fast a moving speed and too slow a flow rate will result in insufficient membrane thickness, failing to achieve nanofiltration separation.

[0018] The optimal concentration range for tetraethylenepentamine (0.1–0.15% w / v) and 1,3,5-benzenetricarbonyltrichloride (0.08–0.15% w / v) mentioned in step 4) is as follows: concentrations below this range may result in incomplete reaction and poor anionic modification; concentrations above this range may increase membrane thickness, thereby reducing membrane flux. When the curing temperature is below 55°C, good curing is not achieved, leading to reduced membrane stability; while temperatures above 65°C may damage the molecular structure of the membrane surface, affecting the nanofiltration performance.

[0019] Compared with existing technologies, the present invention has the following advantages:

[0020] 1. The preparation method of the present invention is simple to operate, easy to control, has low energy consumption, high reaction degree, and high economic feasibility.

[0021] 2. The preparation method of the present invention involves hydrophilically modifying the nanofiltration membrane and using sequential electrospray polymerization to prepare an amphoteric nanofiltration membrane, which can obtain an amphoteric Janus nanofiltration membrane with cationic and anionic forms on both sides.

[0022] 3. The amphoteric Janus nanofiltration membrane prepared by this invention has a uniform surface structure and a stable structure. This amphoteric Janus nanofiltration membrane has high water flux and nanofiltration separation performance, and has a good removal effect on cationic dyes and anionic dyes in wastewater. Detailed Implementation Example 1:

[0023] Amphoteric nanofiltration membranes were prepared using the following method:

[0024] 1) Add tert-butyl hydrogen peroxide and Tris buffer solution to the reactor. The amount of tert-butyl hydrogen peroxide added is 0.5%, the pH of the Tris buffer solution is 7, and the total volume of the mixed solvent is fixed at 200 mL. Dissolve dopamine hydrochloride in the mixed solvent and the dopamine concentration is 0.2%. After stirring and mixing thoroughly, a dopamine solution is obtained.

[0025] 2) Then, the nylon base membrane is immersed in a dopamine solution and reacted at room temperature for 20 hours; then the membrane is immersed in deionized water for 24 hours to wash away the unreacted dopamine, thus obtaining the dopamine-modified base membrane.

[0026] 3) Using a dual-nozzle electrospinning device, 0.2% (w / v) tert-butyl hydroperoxide in ethanol solvent and 0.08% (w / v) 1,3,5-benzenetricarbonyl trichloride in 2-methyl-tetrahydrofuran were electrospun onto one side of the dopamine-modified base film to form a positively charged active layer. The nozzle moving speed was 20 mm / min, the flow rate was 3 mL / h, and the number of scans was twice.

[0027] 4) The spray solutions were changed to 0.1% (w / v) tetraethylenepentamine in ethanol and 0.08% (w / v) 1,3,5-benzenetricarbonyltrichloride in 2-methyltetrahydrofuran, and the other side of the dopamine-modified base membrane was electrosprayed using the same spray parameters to form a negatively charged active layer. The obtained membrane was dried and heat-cured in a vacuum oven at 55°C for 10 min to obtain the amphoteric Janus nanofiltration membrane. Example 2:

[0028] Amphoteric nanofiltration membranes were prepared using the following method:

[0029] 1) Add tert-butyl hydrogen peroxide and Tris buffer solution to the reactor. The amount of tert-butyl hydrogen peroxide added is 0.8%, the pH of the Tris buffer solution is 9, and the total volume of the mixed solvent is fixed at 200 mL. Dissolve dopamine hydrochloride in the mixed solvent and the dopamine concentration is 0.4%. After stirring and mixing thoroughly, a dopamine solution is obtained.

[0030] 2) Then, the nylon base membrane is immersed in a dopamine solution and reacted at room temperature for 30 hours; then the membrane is immersed in deionized water for 24 hours to wash away the unreacted dopamine, thus obtaining the dopamine-modified base membrane.

[0031] 3) Using a dual-nozzle electrospinning device, 0.3% (w / v) tert-butyl hydroperoxide in ethanol solvent and 0.15% (w / v) 1,3,5-benzenetricarbonyl trichloride in 2-methyltetrahydrofuran were electrospun onto one side of the dopamine-modified base film to form a positively charged active layer. The nozzle moving speed was 30 mm / min, the flow rate was 5 mL / h, and the number of scans was twice.

[0032] 4) The spray solutions were changed to 0.15% (w / v) tetraethylenepentamine in ethanol and 0.15% (w / v) 1,3,5-benzenetricarbonyltrichloride in 2-methyltetrahydrofuran, and the other side of the dopamine-modified base membrane was electrosprayed using the same spray parameters to form a negatively charged active layer. The obtained membrane was dried and heat-cured in a vacuum oven at 65°C for 15 min to obtain the amphoteric Janus nanofiltration membrane. Example 3:

[0033] Amphoteric nanofiltration membranes were prepared using the following method:

[0034] 1) Add tert-butyl hydrogen peroxide and Tris buffer solution to the reactor. The amount of tert-butyl hydrogen peroxide added is 0.7%, the pH of the Tris buffer solution is 8, and the total volume of the mixed solvent is fixed at 200 mL. Dissolve dopamine hydrochloride in the mixed solvent and the dopamine concentration is 0.3%. After stirring and mixing thoroughly, a dopamine solution is obtained.

[0035] 2) Then, the nylon base membrane is immersed in a dopamine solution and reacted at room temperature for 25 hours; then the membrane is immersed in deionized water for 24 hours to wash away the unreacted dopamine, thus obtaining the dopamine-modified base membrane.

[0036] 3) Using a dual-nozzle electrospinning device, 0.3% (w / v) tert-butyl hydroperoxide in ethanol solvent and 0.10% (w / v) 1,3,5-benzenetricarbonyl trichloride in 2-methyltetrahydrofuran were electrospun onto one side of the dopamine-modified base film to form a positively charged active layer. The nozzle moving speed was 25 mm / min, the flow rate was 4 mL / h, and the number of scans was twice.

[0037] 4) The spray solutions were changed to 0.12% (w / v) tetraethylenepentamine in ethanol and 0.10% (w / v) 1,3,5-benzenetricarbonyltrichloride in 2-methyltetrahydrofuran, and the other side of the dopamine-modified base membrane was electrosprayed using the same spray parameters to form a negatively charged active layer. The obtained membrane was dried and heat-cured in a vacuum oven at 60°C for 12 min to obtain the amphoteric Janus nanofiltration membrane. Example 4:

[0038] Amphoteric nanofiltration membranes were prepared using the following method:

[0039] 1) Add tert-butyl hydrogen peroxide and Tris buffer solution to the reactor. The amount of tert-butyl hydrogen peroxide added is 0.5%, the pH of the Tris buffer solution is 9, and the total volume of the mixed solvent is fixed at 200 mL. Dissolve dopamine hydrochloride in the mixed solvent and the dopamine concentration is 0.3%. After stirring and mixing thoroughly, a dopamine solution is obtained.

[0040] 2) Then, the nylon base membrane is immersed in a dopamine solution and reacted at room temperature for 30 hours; then the membrane is immersed in deionized water for 24 hours to wash away the unreacted dopamine, thus obtaining the dopamine-modified base membrane.

[0041] 3) Using a dual-nozzle electrospinning device, 0.2% (w / v) tert-butyl hydroperoxide in ethanol solvent and 0.08% (w / v) 1,3,5-benzenetricarbonyl trichloride in 2-methyl-tetrahydrofuran were electrospun onto one side of the dopamine-modified base film to form a positively charged active layer. The nozzle moving speed was 30 mm / min, the flow rate was 3 mL / h, and the number of scans was twice.

[0042] 4) The spray solutions were changed to 0.12% (w / v) tetraethylenepentamine in ethanol and 0.15% (w / v) 1,3,5-benzenetricarbonyltrichloride in 2-methyltetrahydrofuran. The other side of the dopamine-modified base membrane was electrosprayed using the same spray parameters to form a negatively charged active layer. The obtained membrane was dried and heat-cured in a vacuum oven at 65°C for 15 min to obtain the amphoteric Janus nanofiltration membrane. Example 5:

[0043] Amphoteric nanofiltration membranes were prepared using the following method:

[0044] 1) Add tert-butyl hydrogen peroxide and Tris buffer solution to the reactor. The amount of tert-butyl hydrogen peroxide added is 0.8%, the pH of the Tris buffer solution is 8, and the total volume of the mixed solvent is fixed at 200 mL. Dissolve dopamine hydrochloride in the mixed solvent and the dopamine concentration is 0.4%. After stirring and mixing thoroughly, a dopamine solution is obtained.

[0045] 2) Then, the nylon base membrane is immersed in a dopamine solution and reacted at room temperature for 30 hours; then the membrane is immersed in deionized water for 24 hours to wash away the unreacted dopamine, thus obtaining the dopamine-modified base membrane.

[0046] 3) Using a dual-nozzle electrospinning device, 0.2% (w / v) tert-butyl hydroperoxide in ethanol solvent and 0.12% (w / v) 1,3,5-benzenetricarbonyl trichloride in 2-methyltetrahydrofuran were electrospun onto one side of the dopamine-modified base film to form a positively charged active layer. The nozzle moving speed was 20 mm / min, the flow rate was 3 mL / h, and the number of scans was twice.

[0047] 4) The spray solutions were changed to 0.12% (w / v) tetraethylenepentamine in ethanol and 0.15% (w / v) 1,3,5-benzenetricarbonyltrichloride in 2-methyltetrahydrofuran. The other side of the dopamine-modified base membrane was electrosprayed using the same spray parameters to form a negatively charged active layer. The obtained membrane was dried and heat-cured in a vacuum oven at 55°C for 10 min to obtain the amphoteric Janus nanofiltration membrane.

[0048] The rejection rates of the anionic facet and water flux of the amphoteric Janus nanofiltration membranes prepared in Examples 1-5 were measured respectively, and the results are shown in Table 1.

[0049] Table 1 Nanofiltration performance of the amphoteric Janus nanofiltration membrane

[0050] product Congo Red Retention Rate (%) Methylene blue rejection rate (%) <![CDATA[Water flux (L / (m 2 ·h 2 ))]]> Example 1 97.94 96.88 55.47 Example 2 98.57 97.56 49.41 Example 3 98.40 97.22 50.22 Example 4 100 100 45.54 Example 5 100 100 44.45

[0051] As can be seen from Table 1 above, the amphoteric Janus nanofiltration membrane prepared by this invention has a high rejection rate for Congo red and methylene blue dyes and a high water flux.

[0052] The above embodiments of the present invention are merely illustrative examples and are not intended to limit the implementation of the invention. Those skilled in the art can make various changes and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious changes or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing an amphoteric Janus nanofiltration membrane, comprising: firstly, adding tert-butyl hydroperoxide and a Tris buffer solution to a reactor, wherein the pH of the Tris buffer solution is 7-9, and the total volume of the mixed solvent is fixed at 200 mL; dissolving dopamine hydrochloride in the mixed solvent at a concentration of 0.2-0.4%, and stirring and mixing thoroughly to obtain a dopamine solution; then immersing a nylon-based membrane in the dopamine solution and reacting at room temperature for 20-30 h; then immersing the membrane in deionized water for 24 h, and washing away any unreacted dopamine to obtain a dopamine-modified base membrane; and using a dual-nozzle electrospinning device to spin 0.2-0.3% (w / v) tert-butyl hydroperoxide and 0.08-0.15% (w / v) 2-methyl-tetrahydrofuran in an ethanol solvent. 1,3,5-Benzenetricarbonyltrichloride was electrosprayed onto one side of the dopamine-modified base membrane to form a positively charged active layer. The spraying solution was changed to 0.1-0.15% (w / v) tetraethylenepentamine in ethanol and 0.08-0.15% (w / v) 1,3,5-Benzenetricarbonyltrichloride in 2-methyltetrahydrofuran. The other side of the dopamine-modified base membrane was electrosprayed using the same spraying parameters to form a negatively charged active layer. The obtained membrane was dried in a vacuum oven at 55-65°C and heat-cured for 10-15 min to obtain the amphoteric Janus nanofiltration membrane.

2. The method for preparing the amphoteric Janus nanofiltration membrane according to claim 1, characterized in that... The amount of tert-butyl hydroperoxide added is 0.5~0.8%.

3. The method for preparing the amphoteric Janus nanofiltration membrane according to claim 1, characterized in that... During the electrospray operation, the nozzle moving speed is 20~30 mm / min, the flow rate is 3~5 mL / h, and the number of scans is twice.