A method for improving the resistance of AEMs to biofouling by modifying them with Co NPs and chloramines

Abstract

The application discloses a method for improving the anti-biofouling performance of an anion exchange membrane by modifying Co NPs and chloramine, and the method is used for improving the anti-biofouling performance of the anion exchange membrane by modifying Co NPs and chloramine. A chargeable anion exchange membrane with anti-biofouling performance is prepared, and the anion exchange membrane has good anti-biofilm performance, antibacterial performance, separation performance and chargeability in the antibacterial process.

Description

Technical fields:

[0001] This invention relates to a method for preparing an anion exchange membrane with antibacterial adhesion and bactericidal properties. Technical background:

[0002] Water is the source of life, the key to production, and the foundation of the ecosystem. In recent years, sustainable development has become a priority, and water is a core element of sustainable development, crucial for socio-economic development, energy and food production, ecosystem health, and human survival. Water is also a key element in adapting to climate change and a crucial link between society and the environment. Therefore, it is necessary to explore resource recovery and wastewater treatment technologies. Membrane separation technology has the advantages of high efficiency, selectivity, energy saving, simple operation, and environmental friendliness.

[0003] This technology is commonly used to separate, purify, and concentrate biomolecules such as proteins and polysaccharides. Ion exchange membranes, as the core component of electrodialysis systems, avoid the high concentration gradients and high osmotic pressures of nanofiltration membranes and are widely used in various aquatic environments. However, biofouling of ion exchange membranes has become a real problem. Microbial-mediated biofouling accumulates on the membrane surface and forms biofilms, increasing energy consumption and reducing the separation efficiency and lifespan of ion exchange membranes. Furthermore, the irreversible consumption and unsustainability of antimicrobial substances have been bottlenecks restricting the antibiocompatibility of membranes. Therefore, a rechargeable, multifunctional antibiocompatibility system should be researched to improve the sustainable utilization of ion exchange membranes. Summary of the Invention:

[0004] The technical problem to be solved by the present invention is to provide a method for improving the anti-biofouling performance of anion exchange membrane by modifying it with Co NPs and chloramine, thereby obtaining an anion exchange membrane with rechargeable anti-biofouling performance.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for improving the biofouling resistance of anion exchange membranes by modifying them with Co NPs and chloramines includes the following steps:

[0007] Step 1: The commercial anion exchange membrane is soaked in sodium hydroxide aqueous solution and sodium chloride aqueous solution in sequence, and then soaked and rinsed with deionized water to prepare the original membrane;

[0008] Step 2: At room temperature, add reaction solution ① to the feed chamber containing the original membrane and make one side of the original membrane contact the reaction solution ①. The reaction solution ① is a tris(hydroxymethyl)aminomethane hydrochloride buffer solution with a pH between 8 and 9 containing 8-12 mM L-dopamine, 5-7 mM CuSO4 and 15-20 mM H2O2. The reaction is carried out at room temperature for 8-16 hours with stirring during the reaction. After the reaction is completed, pour out the reaction solution in the feed chamber and rinse thoroughly with deionized water. The resulting membrane is named Fuji-L membrane.

[0009] Step 3: At room temperature, add reaction solution ② to the feed chamber and bring the modified surface of the Fuji-L membrane into contact with the reaction solution ②. The reaction solution ② is an aqueous solution containing 15-20 mM cobalt sulfamate, 4-5 mM EDC-HCl and 6-7 mM NHS. The reaction is carried out at room temperature for 12-36 hours with stirring during the reaction. After the reaction is fully completed, the reaction solution is poured out and then rinsed thoroughly with deionized water to obtain the Fuji-L-CoS membrane.

[0010] Step 4: Add reaction solution ③ to the feed chamber and bring the modified surface of the Fuji-L-CoS membrane into contact with reaction solution ③. The reaction solution ③ is an 8-12mM NaBH4 aqueous solution. Control the temperature of reaction solution ③ between 2-8℃ and react for 30-90 seconds. NaBH4 reduces Co(II) on the surface of the Fuji-L-CoS membrane to Co NPs attached to the membrane surface. Stir during the reaction. After the reaction is complete, pour out the reaction solution and rinse thoroughly with deionized water to obtain the Fuji-L-CoS-Na membrane.

[0011] Step 5: Add reaction solution ④ to the feed chamber and bring the modified surface of the Fuji-L-CoS-Na membrane into contact with reaction solution ④. The reaction solution ④ is obtained by diluting a 5 wt% sodium hypochlorite aqueous solution with neutral PBS buffer to a sodium hypochlorite concentration of 0.3-0.8 wt%. Perform the chlorination reaction at room temperature for 8-20 minutes. Use sodium hypochlorite to convert the NH bonds on the Fuji-L-CoS-Na membrane into N-Cl bonds. Stir during the reaction. After the reaction is complete, pour out the reaction solution and rinse thoroughly with deionized water to obtain the Fuji-L-CoS-Na-Cl membrane.

[0012] The commercial anion exchange membranes described in this invention refer to commercially available anion exchange membranes, especially unmodified anion exchange membranes.

[0013] Preferably, in step 1, the commercial anion exchange membrane is soaked in 0.2M sodium hydroxide solution and sodium chloride solution for 30 minutes each, then the membrane is taken out and rinsed with deionized water and soaked until the surface pH is neutral and the leaching solution cannot cause 0.1M AgNO3 to precipitate. The soaking time shall not be less than 24 hours.

[0014] Preferably, in step 2, the pH of the tris(hydroxymethyl)aminomethane hydrochloride buffer is controlled between 8.3 and 8.7, with the optimal condition being controlled at 8.5.

[0015] Preferably, in step 2, the reaction time is controlled at 12 hours.

[0016] Preferably, in step 2, the content of L-dopamine in the reaction solution ① is 9-11 mM, and most preferably 10.01 mM.

[0017] Preferably, in step 3, the cobalt aminosulfonate content in the reaction solution ② is 17-18 mM, and most preferably 17.5 mM.

[0018] Preferably, in step 3, the reaction time is controlled at 24 hours.

[0019] Preferably, in step 4, the NaBH4 content in the reaction solution ③ is between 9-11 mM, with 10 mM being optimal.

[0020] Preferably, in step 4, the reaction time is controlled between 35 and 90 seconds, with the optimal time controlled between 40 seconds; the reaction temperature is controlled between 2 and 7°C, with the optimal temperature controlled between 2°C.

[0021] Preferably, in step 5, the reaction solution ④ is obtained by diluting a 5 wt% sodium hypochlorite aqueous solution with neutral PBS buffer to a sodium hypochlorite concentration of 0.5 wt%.

[0022] Preferably, in step 5, the reaction time between sodium hypochlorite and the membrane is controlled at 10-20 minutes, with the optimal reaction time being 15 minutes.

[0023] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses Co NPs and chloramine modification to improve the anti-biofouling performance of anion exchange membrane, and prepares a rechargeable anion exchange membrane with good anti-biofouling performance. The anion exchange membrane has good anti-biofilm performance, antibacterial performance, separation performance and charge-discharge capability during the antibacterial process. Attached Figure Description

[0024] Figure 1 This diagram shows a schematic of the anion exchange membrane surface modification device used in this invention.

[0025] Figure 2 The anion exchange membrane surface modification processes of the present invention are shown in the following: (a) Fuji-L; (b) Fuji-L-CoS; (c) Fuji-L-CoS-Na and (d) Fuji-L-CoS-Na-Cl.

[0026] Figure 3 (a) is a photograph of these groups subjected to the crystal violet test; (b), (c), (d), and (e) show the anti-biofilm effects of the blank control group, Fuji, Fuji-L, Fuji-L-Cos-Na, and Fuji-L-Cos-Na-Cl groups on Staphylococcus aureus and Escherichia coli biofilms at (b) 12h, (c) 18h, (d) 24h, and (e) 36h, respectively. At each time point, the five columns are arranged from left to right as the blank control group, Fuji, Fuji-L, Fuji-L-Cos-Na, and Fuji-L-Cos-Na-Cl groups.

[0027] Figure 4 The changes in optical density of the blank group, Fuji, Fuji-L-Cos-Na and Fuji-L-Cos-Na-Cl membranes at 12 and 24 hours are shown. The four columns at each time point are arranged from left to right as the blank group, Fuji, Fuji-L-Cos-Na and Fuji-L-Cos-Na-Cl membranes.

[0028] Figure 5 The desalination performance of Fuji, Fuji-L-Cos, Fuji-L-Cos-Na, and Fuji-L-Cos-Na-Cl membranes at 60, 120, 180, and 240 minutes is shown. The four columns at each time point are arranged from left to right as Fuji, Fuji-L-Cos, Fuji-L-Cos-Na, and Fuji-L-Cos-Na-Cl membranes.

[0029] Figure 6 SEM images of Fuji and Fuji-L-Cos-Na-Cl membranes after immersion in bacterial solution for 28 days are shown. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited:

[0031] The cobalt aminosulfonate, levodopa, sodium borohydride, Tris, etc. used in the embodiments of this invention were all purchased from Aladdin Technology Co., Ltd.; the base membrane was a homogeneous Type-II commercial anion exchange membrane manufactured by Fuji Corporation. The strains used in this invention were E. coli (K88), Bacillus (CCTCC AB 90008), and S. aureus (ATCC25923).

[0032] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained through conventional technical means or commercially available.

[0033] Example 1

[0034] The base membrane was first soaked in deionized water for 2 hours and rinsed clean, then soaked in 0.2M sodium hydroxide solution for 30 minutes. Next, it was soaked in 0.2M sodium chloride solution for 30 minutes, then rinsed with clean water until the surface was neutral, and then soaked for 24 hours to obtain the Fuji membrane.

[0035] like Figure 1 As shown, reaction solution ① was added to the feed chamber equipped with the Fuji membrane, and one side of the Fuji membrane was brought into contact with reaction solution ①. The reaction solution ① (100 mL) was a Tris-HCl buffer solution (pH = 8.5 ± 0.1) containing 10.01 mM levonorgestrel, 5 mM CuSO4, and 19.6 mM H2O2. The membrane was modified on one side at 20 °C for 12 h, with stirring during the reaction. After the reaction was complete, the reaction solution in the feed chamber was poured out, and the membrane was rinsed multiple times with deionized water. The resulting membrane was named the Fuji-L membrane.

[0036] Based on the above-mentioned modification device, reaction solution ② is added to the feed chamber to bring the modified surface of the Fuji-L membrane into contact with the reaction solution ②. The reaction solution ② (100 mL) is an aqueous solution containing 17.5 mM cobalt sulfamate, 4.1 mM EDC-HCl, and 7 mM NHS. The reaction is carried out at 20°C for 24 h, allowing cobalt sulfamate to covalently bind to the surface of the Fuji-L membrane through a coupling reaction between EDC-HCl and NHS. The reaction is stirred during the process. After the reaction is complete, the reaction solution is poured out, and the membrane is thoroughly rinsed with deionized water to obtain the Fuji-L-CoS membrane.

[0037] Based on the above-mentioned modification device, reaction solution ③ is added to the feed chamber, and the modified surface of the Fuji-L-CoS membrane is brought into contact with reaction solution ③. The reaction solution ③ (100 mL) is a 10 mM NaBH4 aqueous solution. The temperature of reaction solution ③ is controlled at 2 °C, and the reaction time between NaBH4 and the membrane is controlled at 40 seconds. NaBH4 reduces Co(II) on the surface of the Fuji-L-CoS membrane to Co NPs attached to the membrane surface. Stirring is carried out during the reaction. After the reaction is complete, the reaction solution is poured out and thoroughly rinsed with deionized water to obtain the Fuji-L-CoS-Na membrane.

[0038] Based on the above modification device, reaction solution ④ (100 mL) was added to the feed chamber, and the modified surface of the Fuji-L-CoS-Na membrane was brought into contact with reaction solution ④. Reaction solution ④ was obtained by diluting a wt% sodium hypochlorite aqueous solution with neutral PBS buffer (the sodium hypochlorite PBS buffer solution was prepared by dissolving 2.3 g NaH2PO4 and 10.9 g Na2HPO4 in 700 mL of water) to a sodium hypochlorite concentration of 0.5 wt%. The chlorination reaction was carried out at 20°C for 15 minutes, using sodium hypochlorite to convert the NH bonds on the Fuji-L-CoS-Na membrane to N-Cl bonds. Stirring was performed during the reaction. After the reaction was complete, the reaction solution was poured out and thoroughly rinsed with deionized water to obtain the Fuji-L-CoS-Na-Cl membrane. The specific reaction formula is as follows: Figure 2 As shown.

[0039] Example 2

[0040] Crystal violet staining confirmed the anti-biofilm properties of the Fuji-L-CoS-Na-Cl membrane prepared in Example 1 against Staphylococcus aureus and Escherichia coli. Using Escherichia coli (OD = 0.100, diluted with LB solution) and Staphylococcus aureus (OD = 0.100, diluted with LB solution) as the research subjects, the membrane was placed in contact with bacterial solutions in 96-well plates for 12, 18, 24, and 36 hours, respectively. Biofilm formation was detected by crystal violet staining, and the OD (Synergy LX, BioTek, USA, 600nm UV) values ​​after contact were recorded. The specific operation included the following six steps: In the first stage, 100 μL of bacterial solution and the membrane (0.3 × 0.4 cm) were placed in a 96-well plate, and the OD of the diluted bacterial solution was 0.05; after shaking, the culture dish was removed and incubated at 37°C for X hours (X = 12, 18, 24, 36). In the second stage, at the end of the incubation, the bacterial solution was completely aspirated by pipette. In the third stage, 0.2 mL of methanol was added to each well to fix the bacteria for 20 min. It was important to ensure the pipette did not touch the membrane material when placing it. In the fourth stage, 200 μL of 0.1% crystal violet solution was added to each well for staining for 20 min. In the fifth stage, each well was slowly washed three times with 0.5 mL of PBS, and the crystal violet solution was aspirated (air-dried for 2 minutes). Finally, 200 μL of 95% ethanol solution was added to each well to dissolve the crystal violet stain. After shaking for 5 min, the absorbance of the biofilm was measured at 600 nm. The results are as follows: Figure 3 As shown, the synergistic antibacterial modified ion exchange membrane Fuji-L-CoS-Na-Cl exhibits good biofilm inhibition performance at 12, 18, 24, and 36 h.

[0041] Example 3

[0042] To evaluate the antimicrobial growth ability of the Fuji-L-CoS-Na-Cl membrane prepared in Example 1, the optical density (OD) after contact with the bacterial solution was tested. All test membranes were cut into squares with a side length of 1.5 cm. Furthermore, all samples were thoroughly sterilized and handled on a clean workbench to prevent interference from external bacteria. *Escherichia coli* and *Staphylococcus aureus* were used as test bacteria in this experiment, and their OD values ​​(Synergy LX, BioTek, USA, UV at 600 nm) were diluted to 0.1 with LB solution. After shaking, the supernatant was collected, and the OD value was measured. Each sample was immersed in a 12-well plate containing 1 mL of bacterial solution, and the OD value was measured at 12 h and 24 h, respectively. The results are as follows: Figure 4 As shown, the synergistic antibacterial modified ion exchange membrane Fuji-L-CoS-Na-Cl exhibits strong antibacterial properties at 12 and 24 hours.

[0043] Example 4

[0044] To measure the separation performance of the Fuji-L-CoS-Na-Cl membrane prepared in Example 1, ED desalination was performed on a laboratory-made apparatus. The laboratory-made apparatus and experimental methods have been described in previous studies; see reference [J.Liao, J.Zhu, S.Yang, N.Pan, X.Yu, C.Wang, J.Li, Jiangnan Shen. Long-side-chaintype imidazolium-functionalized fluoro-methyl poly(arylene ether ketone) anion exchange membranes with superior electrodialysis performance. Journal of Membrane Science. 574, 2019, 181-195.]. Before testing, 80 mL of 0.5 M NaCl solution was filled into both intermediate tanks, and 0.3 M Na2SO4 solution was pumped into the electrode chamber (maintaining circulation). The conductivity of the dilution and concentration chambers was measured every 10 minutes using a conductivity meter. The results are as follows: Figure 5 As shown, the synergistic antibacterial modified ion exchange membrane Fuji-L-CoS-Na-Cl showed almost no loss of separation performance at 60, 120, 180, and 240 minutes.

[0045] Example 5

[0046] Chloramine compounds can achieve sterilization and disinfection by releasing active chlorine in water, and the chlorination reaction is reversible (rechargeable). To demonstrate the charge-discharge properties of the Fuji-L-CoS-Na-Cl membrane prepared in Example 1 during the antibacterial process, the biofilm morphology on the surfaces of Fuji and Fuji-L-CoS-Na-Cl was monitored using scanning electron microscopy. *Escherichia coli*, *Bacillus*, and *Staphylococcus aureus* were used as research subjects. Fuji-II (*E. coli* and *Staphylococcus aureus*) and Fuji-L-CoS-Na-Cl (*E. coli* and *Bacillus*) in 12-well plates were immersed in bacterial solutions (OD value (Synergy LX, BioTek, USA, UV at 600 nm) = 0.1). The membrane samples were immersed for 7, 15, and 28 days, respectively. During the immersion process, the membrane was charged for 10 minutes every 72 hours with a 0.5 wt% sodium hypochlorite PBS buffer solution. Correspondingly, the LB solution and bacterial solution were replaced every 72 hours. After soaking, the membrane samples were rinsed three times with sterile water. Then, the membrane samples were soaked in glutaraldehyde (2.5%) buffer at 4°C for 3 hours and dried in a vacuum oven at 40°C for 24 hours. SEM results showed that the bacterial thickness increased significantly 28 days after bacterial contamination (Fuji substrate, Figure 6 (d)). Especially in Figure 6 In (d)Ⅰ, the biofilm is mature, and the bacteria are intact (as shown by the arrow). Moreover, this state of biofilm has the ability to protect the bacteria, making it difficult for most antibiotics to bind. Compared to the substrate membrane, Fuji-L-CoS-Na-Cl ( Figure 6 (e) can inhibit biofilm formation to some extent. This is due to the long-term effect of Co NPs and the oxidation of n-chloramine compounds. Furthermore, due to Co NPs and N-Cl bonds, bacteria appear shrunken and incomplete (as indicated by the arrows). This experiment effectively demonstrates the charging and discharging process of chloramine compounds in the ion exchange membrane during antibacterial activity.

Claims

1. A method for improving the biofouling resistance of anion exchange membranes by modifying them with Co NPs and chloramine, characterized in that: The method includes the following steps: Step 1: The commercial anion exchange membrane is soaked in sodium hydroxide aqueous solution and sodium chloride aqueous solution in sequence, and then soaked and rinsed with deionized water to prepare the original membrane; Step 2: At room temperature, add reaction solution ① to the feed chamber containing the original membrane and make one side of the original membrane contact the reaction solution ①. The reaction solution ① is a tris(hydroxymethyl)aminomethane hydrochloride buffer solution with a pH between 8 and 9 containing 8-12 mM L-dopamine, 5-7 mM CuSO4 and 15-20 mM H2O2. The reaction is carried out at room temperature for 8-16 hours with stirring during the reaction. After the reaction is completed, pour out the reaction solution in the feed chamber and rinse thoroughly with deionized water. The resulting membrane is named Fuji-L membrane. Step 3: At room temperature, add reaction solution ② to the feed chamber and bring the modified surface of the Fuji-L membrane into contact with the reaction solution ②. The reaction solution ② is an aqueous solution containing 15-20 mM cobalt sulfamate, 4-5 mM EDC-HCl and 6-7 mM NHS. The reaction is carried out at room temperature for 12-36 hours with stirring during the reaction. After the reaction is fully completed, the reaction solution is poured out and then rinsed thoroughly with deionized water to obtain the Fuji-L-CoS membrane. Step 4: Add reaction solution ③ to the feed chamber and bring the modified surface of the Fuji-L-CoS membrane into contact with reaction solution ③. The reaction solution ③ is an 8-12mM NaBH4 aqueous solution. Control the temperature of reaction solution ③ between 2-8℃ and react for 30-90 seconds. NaBH4 reduces Co(II) on the surface of the Fuji-L-CoS membrane to Co NPs attached to the membrane surface. Stir during the reaction. After the reaction is complete, pour out the reaction solution and rinse thoroughly with deionized water to obtain the Fuji-L-CoS-Na membrane. Step 5: Add reaction solution ④ to the feed chamber and bring the modified surface of the Fuji-L-CoS-Na membrane into contact with reaction solution ④. The reaction solution ④ is obtained by diluting a 5 wt% sodium hypochlorite aqueous solution with neutral PBS buffer to a sodium hypochlorite concentration of 0.3-0.8 wt%. Perform the chlorination reaction at room temperature for 8-20 minutes. Use sodium hypochlorite to convert the NH bonds on the Fuji-L-CoS-Na membrane into N-Cl bonds. Stir during the reaction. After the reaction is complete, pour out the reaction solution and rinse thoroughly with deionized water to obtain the Fuji-L-CoS-Na-Cl membrane.

2. The method as described in claim 1, characterized in that: In step 2, the pH of the tris(hydroxymethyl)aminomethane hydrochloride buffer solution is controlled between 8.3 and 8.

7.

3. The method as described in claim 1, characterized in that: In step 2, the reaction time is controlled at 12 hours.

4. The method as described in claim 1, characterized in that: In step 2, the content of levodopamine in the reaction solution ① is 9-11 mM.

5. The method as described in claim 1, characterized in that: In step 3, the cobalt aminosulfonate content in the reaction solution ② is 17-18 mM.

6. The method as described in claim 1, characterized in that: In step 3, the reaction time is controlled at 24 hours.

7. The method as described in claim 1, characterized in that: In step 4, the NaBH4 content in the reaction solution ③ is between 9-11 mM.

8. The method as described in claim 1, characterized in that: In step 4, the reaction time is controlled between 35 and 90 seconds; the reaction temperature is controlled between 2 and 7°C.

9. The method as described in claim 1, characterized in that: In step 5, the reaction solution ④ is obtained by diluting a 5 wt% sodium hypochlorite aqueous solution with neutral PBS buffer to a sodium hypochlorite concentration of 0.5 wt%.

10. The method as described in claim 1, characterized in that: In step 5, the reaction time between sodium hypochlorite and the membrane is controlled at 10-20 minutes.

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