Modification method of reverse osmosis / nanofiltration membrane for strengthening interception of neutral small-molecular organic matters

Abstract

The invention relates to a modification method of a reverse osmosis / nanofiltration membrane for strengthening neutral small-molecular organic matters, which comprises the following steps: by taking a reverse osmosis / nanofiltration membrane as a modification object and an organic solvent as an activating solvent, enabling the organic solvent to permeate into the reverse osmosis / nanofiltration membrane when the organic solvent is activated and swelled by utilizing a molecular plug which can be dissolved in the organic solvent; and a large-volume free cavity is filled. Further, after modification, two-step surface defect end capping treatment of a high-molecular polymer and a dialdehyde compound is introduced, surface defects are repaired, molecular plug seepage is prevented, convective mass transfer of small-molecular organic matter through membrane defects is reduced, and interception of the small-molecular organic matter is further enhanced. The reverse osmosis / nanofiltration membrane prepared by a synergistic strategy of'introducing the molecular plug inside and packaging the surface defects' has uniform free volume distribution, the molecular plug forms a hydrophobic environment inside, interception of neutral small-molecular organic matters is enhanced through affinity interaction, and the surface defect packaging can reduce defects and improve the stability of the molecular plug.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and membrane separation technology, and particularly relates to a modification method for reverse osmosis / nanofiltration membranes to enhance the retention of neutral small molecule organic matter. Background Technology

[0002] As the proportion of reclaimed water utilization continues to increase, users are demanding stricter water quality standards. However, reclaimed water often contains various organic pollutants, especially neutral small-molecule organic compounds, such as drug metabolites and industrial residual chemicals, which are difficult to effectively retain by nanofiltration (NF) / reverse osmosis (RO) dense membranes. Current mainstream commercial dense membrane designs focus on desalination and do not incorporate specific functional groups or pore size control mechanisms for the retention of neutral small-molecule organic compounds. Therefore, their removal efficiency for neutral small-molecule organic compounds is not ideal. For example, commercial RO membranes (such as Film Tec™ BW30) have a retention rate of only 20–50% for phenol (molecular weight 94 Da), and NF-200 membranes have a rejection rate of 35% to 70% for neutral compounds. This limitation makes it difficult for membrane-reclaimed water to fully meet water quality standards in demanding application scenarios, thus restricting its wider application. With the increasing demand for reclaimed water and increasingly stringent water quality standards, especially the ever-improving requirements for controlling trace organic pollutants, commercial membranes must possess higher retention capabilities for small-molecule organic matter to ensure that the effluent meets the stringent standards for domestic or industrial water use. Therefore, improving the retention efficiency of neutral small-molecule organic matter is a pressing challenge in the field of membrane separation technology.

[0003] Currently, the main methods for improving the retention performance of reverse osmosis / nanofiltration membranes for neutral small-molecule organic compounds fall into two categories: one is membrane surface modification, which involves coating or grafting functional materials onto the surface of the polyamide selective layer to regulate the chemical composition and microenvironment of the membrane surface, reducing its affinity for neutral organic compounds, thereby effectively inhibiting the adsorption and permeation of solutes on the membrane surface; the other is interfacial polymerization process control strategies, which involve introducing additives (such as small organic molecules, nanomaterials, or phase transfer catalysts) during the interfacial polymerization process to optimize the microstructure of the polyamide layer by adjusting the monomer diffusion rate, reactivity, and degree of crosslinking, forming a denser selective layer with a narrower pore size distribution, thereby enhancing the size exclusion effect on small-molecule organic compounds. While surface modification can improve the rejection rate to some extent, it often leads to a significant decrease in water flux due to the thickening of the functional layer or pore blockage; while structural densification achieved by increasing the crosslinking density helps to enhance the size sieving capacity, it inevitably and significantly reduces the membrane's permeability. Therefore, while existing technologies can achieve efficient retention of neutral small molecule organic matter, they often sacrifice water flux, making it difficult to balance separation efficiency and operating energy consumption. This limits their long-term stability, sustainability, and economic feasibility in practical water treatment applications. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for modifying reverse osmosis / nanofiltration membranes to enhance the retention of neutral small molecule organic compounds, comprising the following steps: Step 1: Immerse the commercial reverse osmosis / nanofiltration membrane in deionized water to fully wet the microporous structure of the membrane surface and the polyamide selective layer, remove residual solvent and surface impurities, and then take out the membrane and place it in a clean and ventilated environment to dry it with an air gun until there are no free water droplets on the surface. Step 2: Dissolve the molecular plug in an organic solvent, and sonicate the mixed solvent in an ultrasonic oscillator; then transfer the solvent to a sealed, light-proof container for storage to obtain an organic solvent for functionalization modification; Step 3: Place the reverse osmosis / nanofiltration membrane treated in Step 1 into the dead end filtration device and place it in a constant temperature and humidity environment to ensure that the operating environment is dust-free and stable. Step 4: Evenly cover the surface of the membrane fixed in Step 3 with the organic solvent obtained in Step 2, ensuring that the solution completely immerses the effective membrane area, and pour out the excess solution after reacting under pressure for a certain period of time. Step 5: Immerse the membrane treated in Step 4 in deionized water to disperse the functional molecules that have not entered the membrane structure and detach them from the membrane surface. Then replace with fresh deionized water and continue immersion. Step 6: Dissolve the polymer in deionized water, and sonicate the mixture in an ultrasonic oscillator. Then transfer the solution to a sealed, light-proof container for storage, obtaining a modified solution for encapsulation. Step 7: Dilute the dialdehyde compound in deionized water, then add phosphate buffer to adjust the pH to obtain a crosslinking solution; Step 8: Air dry the membrane treated in step 5 in a clean environment, then immerse it in the encapsulation solution prepared in step 6, and then remove it; Step 9: Without drying or rinsing, immediately immerse the membrane from Step 8 into the crosslinking solution from Step 7 to achieve encapsulation and stabilization of the functionalized layer. Step 10: Take out the membrane after encapsulation in step 9 and rinse it to obtain a reverse osmosis / nanofiltration membrane for enhancing the retention of neutral small molecule organic matter.

[0005] Compared with the prior art, the present invention has the following beneficial effects: 1. The reverse osmosis membrane prepared by this invention has excellent free volume distribution and more uniform internal structure, smooth surface and good stability. The preparation process is simple and does not require further modification or reprocessing of organic solvents and molecular plugs.

[0006] 2. This invention uses a solvent-induced method to improve the retention efficiency of neutral small molecule organic matter, while realizing polymer structure rearrangement and uniform free volume distribution, thereby improving the permeability of water molecules.

[0007] 3. This invention employs a synergistic strategy of "internal introduction of molecular plugs + surface defect encapsulation," which repairs surface defects while simultaneously achieving polymer structure rearrangement and uniform free volume distribution. This improves the retention of neutral small molecule organic compounds. Attached Figure Description

[0008] Figure 1 Scanning electron microscope (SEM) images of TFC, TFC-0, and TFC-F.

[0009] Figure 2 X-ray photoelectron spectra of TFC, TFC-0, and TFC-F.

[0010] Figure 3 Fourier transform infrared spectra of TFC, TFC-0, and TFC-F.

[0011] Figure 4 This is a comparison chart showing the effects of pure water permeability and phenol rejection rate of TFC, TFC-0, and TFC-F. Detailed Implementation

[0012] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings: A method for modifying reverse osmosis / nanofiltration membranes to enhance the retention of neutral small molecule organic matter, characterized by comprising the following steps: Step 1: Immerse the commercial reverse osmosis / nanofiltration membrane in deionized water to fully wet the microporous structure of the membrane surface and the polyamide selective layer, remove residual solvent and surface impurities, and then take out the membrane and place it in a clean and ventilated environment to dry it with an air gun until there are no free water droplets on the surface.

[0013] Preferably, the soaking temperature is 25-30°C and the soaking time is 6-24 hours. The air-drying process is carried out in a clean environment with a temperature of 25-30°C and a relative humidity of 60%-80% RH, with the air-drying time controlled at 5-10 minutes and the airflow speed not exceeding 0.5 m / s.

[0014] Step 2: Dissolve the molecular plug in an organic solvent, and place the mixed solvent in an ultrasonic oscillator for ultrasonic treatment; then transfer the solvent to a sealed, light-proof container for storage to obtain an organic solvent for functional modification.

[0015] Preferably, the organic solvent can be ethanol or isopropanol; the molecular plug can be trifluoromethyldiaminobiphenyl, tetrafluorobiphenyl-4-phenol, or pentafluorobiphenyl; the molecular plug mass concentration is 0.1-3.0 wt%, the dissolution temperature is 25-30℃, and the ultrasonic vibration time is 30-60 min.

[0016] Step 3: Place the reverse osmosis / nanofiltration membrane treated in Step 1 into a dead-end filtration device and place it in a constant temperature and humidity environment to ensure that the operating environment is dust-free and stable.

[0017] Preferably, the ambient temperature is maintained at 25–30°C and the relative humidity is controlled at 60%–80% RH.

[0018] Step 4: Evenly cover the surface of the membrane fixed in Step 3 with the organic solvent obtained in Step 2, ensuring that the solution completely immerses the effective membrane area. After reacting under pressure for a certain period of time, pour out the excess solution.

[0019] Preferably, the reaction temperature is 25–30°C, the pressurization time is 5–10 minutes, the pressure range is 1–2 bar, and the pressurization is stopped immediately when liquid flows out of the filter end, and the excess solution is poured out.

[0020] Step 5: Immerse the membrane treated in Step 4 in deionized water to disperse the functional molecules that have not entered the membrane structure and detach them from the membrane surface. Then replace with fresh deionized water and continue immersion.

[0021] Preferably, the deionized water soaking temperature is 25–30°C, and the single soaking time is 30–60 minutes; a two-step cleaning method is adopted: after the first soaking, the wastewater is poured off, and fresh deionized water is replaced before soaking for another 10–30 minutes.

[0022] Step 6: Dissolve the polymer in deionized water, and sonicate the mixture in an ultrasonic oscillator. Then transfer the solution to a sealed, light-proof container for storage to obtain a modified solution for encapsulation.

[0023] Preferably, the polymer can be low molecular weight (cyclodextrin, crown ether, <2000 Da) or medium molecular weight (chitosan, polyethylene glycol, ...). <10000 Da), high molecular weight (polyvinyl alcohol, > 10000 Da); mass concentration of 0.05–0.5 wt%; dissolution temperature of 25–30°C; ultrasonic vibration time of 5–20 minutes.

[0024] Step 7: Dilute the dialdehyde compound in deionized water, then add phosphate buffer to adjust the pH to obtain a crosslinking solution.

[0025] Preferably, the dialdehyde compound can be glutaraldehyde, succinaldehyde, or adipaldehyde; the mass concentration is 0.01–0.1 wt%; the pH of the crosslinking solution is adjusted to 6.0–8.0; the concentration of the phosphate buffer is 0.005–0.02 M; the reaction temperature is 25–30°C; and the reaction time is 5–20 minutes.

[0026] Step 8: Air dry the membrane after the treatment in step 5 in a clean environment, then immerse it in the encapsulation solution prepared in step 6, and then take it out.

[0027] Preferably, the membrane is immersed in the encapsulation solution for 5–15 minutes, the ambient temperature is maintained at 25–30°C, and the relative humidity is controlled at 60%–80% RH.

[0028] Step 9: Without drying or rinsing, immediately immerse the membrane from Step 8 into the crosslinking solution from Step 7 to achieve encapsulation and stabilization of the functionalized layer.

[0029] Preferably, the surface cross-linking encapsulation is achieved by immediately immersing the device in the prepared cross-linking solution within 30 seconds and reacting it at 25–30°C for 5–15 minutes.

[0030] Step 10: Take out the membrane after encapsulation in step 9 and rinse it to obtain a reverse osmosis / nanofiltration membrane for enhancing the retention of neutral small molecule organic matter.

[0031] Preferably, the rinsing is performed using flowing deionized water for 10–30 seconds to remove residual impurities on the surface and obtain the final modified film.

[0032] Example 1: A method for modifying a reverse osmosis / nanofiltration membrane to enhance the retention of neutral small molecule organic matter, comprising the following steps: (1) Dissolve 0.1g of trifluoromethyldiaminobiphenyl in ethanol (HPLC grade, ≥99.8%) solution, sonicate at 25℃ to disperse it completely and evenly, and then seal and store it in the dark.

[0033] (2) Take a commercial RO membrane and dry it in a ventilated place using an air gun with an airflow speed of 0.5 m / s until there are no free water droplets on the surface. Then put it into the dead end filter device.

[0034] (3) Take 10 ml of the ethanol solution obtained in step (1) and pour it into the dead-end filter device with the membrane already placed. React at 25°C and 0.5 bar for 5 min and pour out the excess solution.

[0035] (4) Soak the membrane obtained in step (3) in deionized water for 30 minutes to wash away the residual trifluoromethyldiaminobiphenyl on the membrane surface, and then soak it in fresh deionized water for 10 minutes.

[0036] (5) Take out the membrane soaked in step (4) and dry it in a ventilated place with an air gun with an airflow speed of 0.5 m / s until there are no free water droplets on the surface. Soak it in 0.5wt% cyclodextrin aqueous solution for 10 min. After taking it out, immediately soak it in 0.1wt% glutaraldehyde for 5 min. Then soak it in deionized water and wait for use. Name it TFC-0.

[0037] (6) After rinsing the membrane prepared in step (5) with deionized water, deionized water was introduced into the dead-end filtration device and pressurized for membrane pure water permeability testing. First, it was run at 10 bar for 30 minutes to stabilize it, and then the pressure was adjusted to 8 bar for testing. The results showed that its permeability was 2.62 L / m³. -2 h -1 bar -1 .

[0038] (7) After wetting the membrane prepared in step (6) with deionized water, a phenol solution of a certain concentration was introduced into the dead-end filtration device and pressurized for retention performance testing. First, it was run at 10 bar for 30 minutes to stabilize it, and then the pressure was adjusted to 8 bar for testing. The results showed that the phenol retention rate reached 83%.

[0039] Example 2: A method for modifying a reverse osmosis / nanofiltration membrane to enhance the retention of neutral small molecule organic matter, comprising the following steps: (1) Dissolve 0.8g of trifluoromethyldiaminobiphenyl in ethanol (HPLC grade, ≥99.8%) solution, sonicate at 25℃ for 1h to completely dissolve, and then seal and store in the dark.

[0040] (2) Take a commercial RO membrane and dry it in a ventilated place using an air gun with an airflow speed of 0.5 m / s until there are no free water droplets on the surface. Then put it into the dead end filter device.

[0041] (3) Take 10 ml of the trifluoromethyldiaminobiphenylethanol mixture obtained in step (1) and pour it into the dead-end filter device with the membrane already placed. React at 25°C and 0.5 bar for 5 min, and then pour out the excess solution.

[0042] (4) Soak the membrane obtained in step (3) in deionized water for 30 minutes to wash away the residual trifluoromethyldiaminobiphenyl on the membrane surface, and then soak it in fresh deionized water for 10 minutes.

[0043] (5) Take out the membrane soaked in step (4) and dry it in a ventilated place with an air gun with an airflow speed of 0.5 m / s until there are no free water droplets on the surface. Soak it in 0.1wt% cyclodextrin aqueous solution for 15 min. After taking it out, immediately soak it in 0.05wt% glutaraldehyde for 10 min, and then soak it in deionized water for use. Name it TFC-F.

[0044] (6) After rinsing the membrane prepared in step (5) with deionized water, deionized water was introduced into the dead-end filtration device and pressurized for membrane pure water permeability testing. First, it was run at 10 bar for 30 minutes to stabilize it, and then the pressure was adjusted to 8 bar for testing. The results showed that its permeability was 2.12 L / m³. -2 h -1 bar -1 .

[0045] (7) After wetting the membrane prepared in step (6) with deionized water, a phenol solution of a certain concentration was introduced into the dead-end filtration device and pressurized for retention performance testing. First, it was run at 10 bar for 30 minutes to stabilize it, and then the pressure was adjusted to 8 bar for testing. The results showed that the phenol retention rate reached 94%.

[0046] Example 3: A method for modifying a reverse osmosis / nanofiltration membrane to enhance the retention of neutral small molecule organic matter, comprising the following steps: (1) Dissolve 0.8g of trifluoromethyldiaminobiphenyl in ethanol (HPLC grade, ≥99.8%) solution, sonicate at 25℃ for 1h to completely dissolve, and then seal and store in the dark.

[0047] (2) Take a commercial RO membrane and dry it in a ventilated place using an air gun with an airflow speed of 0.5 m / s until there are no free water droplets on the surface. Then put it into the dead end filter device.

[0048] (3) Take 10 ml of the trifluoromethyldiaminobiphenylethanol mixture obtained in step (1) and pour it into the dead-end filter device with the membrane already placed. React at 25°C and 0.5 bar for 5 min, and then pour out the excess solution.

[0049] (4) Soak the membrane obtained in step (3) in deionized water for 30 minutes to wash away the residual trifluoromethyldiaminobiphenyl on the membrane surface, and then soak it in fresh deionized water for 10 minutes.

[0050] (5) Take out the membrane soaked in step (4) and blow it dry in a ventilated place with an air gun with an airflow speed of 0.5 m / s until there are no free water droplets on the surface. Soak it in 0.5wt% cyclodextrin aqueous solution for 10 min. After taking it out, immediately soak it in 0.1wt% glutaraldehyde for 5 min. Then soak it in deionized water and wait for use. Name it TFC-1.

[0051] (6) After rinsing the membrane prepared in step (5) with deionized water, deionized water was introduced into the dead-end filtration device and pressurized for membrane pure water permeability testing. First, it was run at 10 bar for 30 minutes to stabilize it, and then the pressure was adjusted to 8 bar for testing. The results showed that its permeability was 1.61 L / m³. -2 h -1 bar -1 .

[0052] (7) After wetting the membrane prepared in step (6) with deionized water, a phenol solution of a certain concentration was introduced into the dead-end filter device and pressurized for retention performance testing. First, it was run at 10 bar for 30 minutes to stabilize it, and then the pressure was adjusted to 8 bar for testing. The results showed that the phenol retention rate reached 90%.

[0053] Example 4: A method for modifying a reverse osmosis / nanofiltration membrane to enhance the retention of neutral small molecule organic matter, comprising the following steps: (1) Dissolve 2g of trifluoromethyldiaminobiphenyl in ethanol (HPLC grade, ≥99.8%) solution, sonicate at 25℃ for 1h to completely dissolve, and then seal and store in the dark.

[0054] (2) Take a commercial RO membrane and dry it in a ventilated place using an air gun with an airflow speed of 0.5 m / s until there are no free water droplets on the surface. Then put it into the dead end filter device.

[0055] (3) Take 10 ml of the trifluoromethyldiaminobiphenylethanol mixture obtained in step (1) and pour it into the dead-end filter device with the membrane already placed. React at 25°C and 0.5 bar for 5 min, and then pour out the excess solution.

[0056] (4) Soak the membrane obtained in step (3) in deionized water for 30 minutes to wash away the residual trifluoromethyldiaminobiphenyl on the membrane surface, and then soak it in fresh deionized water for 10 minutes.

[0057] (5) Take out the membrane soaked in step (4) and dry it in a ventilated place with an air gun with an airflow speed of 0.5 m / s until there are no free water droplets on the surface. Soak it in 0.1wt% cyclodextrin aqueous solution for 15 min. After taking it out, immediately soak it in 0.05wt% glutaraldehyde for 10 min, and then soak it in deionized water for use. Name it TFC-F.

[0058] (6) After rinsing the membrane prepared in step (5) with deionized water, deionized water was introduced into the dead-end filtration device and pressurized for membrane pure water permeability testing. First, it was run at 10 bar for 30 minutes to stabilize it, and then the pressure was adjusted to 8 bar for testing. The results showed that its permeability was 1.81 L / m³. -2 h-1 bar -1 .

[0059] (7) After wetting the membrane prepared in step (6) with deionized water, a phenol solution of a certain concentration was introduced into the dead-end filter device and pressurized for retention performance testing. First, it was run at 10 bar for 30 minutes to stabilize it, and then the pressure was adjusted to 8 bar for testing. The results showed that the phenol retention rate reached 86%.

[0060] To demonstrate the performance advantages of the membrane obtained by the modification method of this invention, comparative examples based on existing technology preparation processes will be provided. The table below lists Example 2 and Comparative Examples 1-3 for illustration:

[0061] Comparative Example 1: A highly cross-linked polyamide membrane was prepared via interfacial polymerization, with a trimethylbenzene chloride (TMC) concentration of 0.2 wt% and a m-phenylenediamine (MPD) concentration of 2.0 wt%, and the reaction time was extended to 60 seconds. The resulting membrane exhibited a phenol rejection rate of 68%, but a pure water flux of only 0.85 L m⁻² h⁻¹ bar⁻¹, demonstrating that traditional structural modulation methods struggle to balance permeability and selectivity.

[0062] Comparative Example 2: A commercial nanofiltration membrane was immersed in a 200 mg / L dopamine solution (pH = 8.5, Tris buffer), reacted for 1 hour, removed, thoroughly rinsed with deionized water, and air-dried. The resulting polydopamine (PDA) coated membrane exhibited a phenol rejection rate of 82%, but the pure water flux decreased to 0.71 L m⁻² h⁻¹ bar⁻¹, indicating that although the surface coating can improve rejection, severe flux loss occurs due to pore blockage.

[0063] Comparative Example 3: Nano-TiO2 particles were dispersed in the aqueous phase of MPD (concentration 0.1 wt%) and a composite membrane was prepared by conventional interfacial polymerization. The resulting membrane had a phenol rejection rate of 75% and a flux of 1.2 L m⁻² h⁻¹ bar⁻¹, indicating that the inorganic filler has limited effect on improving the rejection of small molecules.

[0064] As the comparative examples above demonstrate, commonly used methods in existing technologies such as surface coatings, high cross-linking, and nanofilling cannot effectively overcome the trade-off between high retention and low flux. However, this invention, through a synergistic mechanism of "internal molecular plug filling of free volume + surface defect encapsulation," achieves a phenol retention rate as high as 94% while maintaining an excellent water flux of 2.12 L m⁻²h⁻¹ bar⁻¹, significantly outperforming traditional modification strategies. The prepared product was analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, such as... Figure 2 , Figure 3 As shown.

[0065] Figure 1 The images show the scanning electron microscope (SEM) morphology of TFC, TFC-0, and TFC-F. Specifically, a is a surface SEM image of the original reverse osmosis membrane TFC; b is a surface SEM image of the reverse osmosis membrane TFC-0 modified with ethanol in Example 1; c is a surface SEM image of the reverse osmosis membrane TFC-F modified with trifluoromethyldiaminobiphenyl molecular plugs in Example 2; d is a cross-sectional SEM image of the original reverse osmosis membrane TFC; e is a cross-sectional SEM image of the reverse osmosis membrane TFC-0 modified with ethanol in Example 1; f is a cross-sectional SEM image of the reverse osmosis membrane TFC-F modified with trifluoromethyldiaminobiphenyl molecular plugs in Example 2; g is a schematic diagram of the surface roughness of the original reverse osmosis membrane TFC; h is a schematic diagram of the surface roughness of the reverse osmosis membrane TFC-0 modified with ethanol in Example 1; and i is a schematic diagram of the surface roughness of the reverse osmosis membrane TFC-F modified with trifluoromethyldiaminobiphenyl molecular plugs in Example 2. This shows that although the addition of molecular plugs significantly improves the membrane performance, the swelling and molecular plug insertion processes do not significantly change the surface morphology of the membrane. SEM cross-sections show that ethanol activation slightly increases the thickness of the active layer, which may be due to solvent-induced polymer chain rearrangement or slight swelling. The introduction of molecular plugs, on the other hand, makes the dense layer thinner, indicating that it penetrates into the network and causes local shrinkage or cross-linking densification.

[0066] Figure 2 X-ray photoelectron spectra of the original reverse osmosis membrane TFC, the reverse osmosis membrane TFC-0 modified with ethanol in Example 1, and the reverse osmosis membrane TFC-F modified with trifluoromethyldiaminobiphenyl molecular plugs in Example 2 are shown. In the spectrum, a is the XPS C1s spectrum of TFC; b is the XPS C1s spectrum of TFC-0; c is the XPS C1s spectrum of TFC-F; d is the high-resolution F1s spectrum; e is the total XPS spectrum at 0 nm; and f is the total XPS spectrum at 80 nm. The presence of a CF bond at 292 eV in the C1s spectrum confirms the presence of the trifluoromethyldiaminobiphenyl molecular plug. The F1s peak is still visible in the full spectrum at an etching depth of 80 nm, indicating that the trifluoromethyldiaminobiphenyl molecular plug has been successfully introduced into the polymer.

[0067] Figure 3 Fourier transform infrared (FTIR) spectra of the original reverse osmosis membrane TFC, the reverse osmosis membrane TFC-0 modified with ethanol in Example 1, and the reverse osmosis membrane TFC-F modified with trifluoromethyldiaminobiphenyl molecular plugs in Example 2. (At 1049 cm⁻¹) -1 A characteristic peak appears nearby, defined as the characteristic vibration of the CF group. The appearance of this peak provides strong evidence for the successful insertion of the trifluoromethyldiaminobiphenyl molecular plug.

[0068] Figure 4 The graph compares the pure water permeability and phenol rejection rate of the original reverse osmosis membrane TFC, the reverse osmosis membrane TFC-0 modified with ethanol in Example 1, and the reverse osmosis membrane TFC-F modified with trifluoromethyldiaminobiphenyl molecular plugs in Example 2. It can be seen that the reverse osmosis membrane modified with ethanol has improved flux and rejection rate compared to the original membrane, but the rejection of pollutants did not meet the expected standard. The introduction of the molecular plug achieved efficient rejection of small molecule organic matter, while also increasing the water flux compared to the original membrane.

[0069] This invention provides a method for modifying reverse osmosis / nanofiltration membranes to enhance the retention of neutral small-molecule organic matter. Using commercial reverse osmosis / nanofiltration membranes as the modification target, an organic solvent is used as an activator. Molecular plugs soluble in the organic solvent are then utilized, allowing them to swell and penetrate into the reverse osmosis / nanofiltration membrane while being activated by the organic solvent. This results in a more uniform volume distribution and a more homogeneous, dense, and internally hydrophobic reverse osmosis / nanofiltration membrane structure. Furthermore, after introducing the molecular plugs, a two-step end-capping treatment using a polymer and a dialdehyde compound repairs surface defects. The reverse osmosis / nanofiltration membrane modified by this invention exhibits excellent free volume distribution and a more uniform internal structure, with no surface defects, and the membrane modification process is simple. The reverse osmosis / nanofiltration membrane prepared by this invention through the synergistic strategy of "internal introduction of molecular plugs + surface defect encapsulation" can be applied to the recycling of wastewater from chemical, dyeing, and pharmaceutical industries. The concentration of neutral small-molecule organic matter in the effluent is less than 1 mg / L, making it suitable for reuse in production.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for modifying reverse osmosis / nanofiltration membranes to enhance the retention of neutral small molecule organic matter, characterized in that... Includes the following steps: Step 1: Immerse the commercial reverse osmosis / nanofiltration membrane in deionized water to fully wet the microporous structure of the membrane surface and the polyamide selective layer, remove residual solvent and surface impurities, and then take out the membrane and place it in a clean and ventilated environment to dry it with an air gun until there are no free water droplets on the surface. Step 2: Dissolve the molecular plug in an organic solvent, and sonicate the mixed solvent in an ultrasonic oscillator; then transfer the solvent to a sealed, light-proof container for storage to obtain an organic solvent for functionalization modification; Step 3: Place the reverse osmosis / nanofiltration membrane treated in Step 1 into the dead end filtration device and place it in a constant temperature and humidity environment to ensure that the operating environment is dust-free and stable. Step 4: Evenly cover the surface of the membrane fixed in Step 3 with the organic solvent obtained in Step 2, ensuring that the solution completely immerses the effective membrane area, and pour out the excess solution after reacting under pressure for a certain period of time. Step 5: Immerse the membrane treated in Step 4 in deionized water to disperse the functional molecules that have not entered the membrane structure and detach them from the membrane surface. Then replace with fresh deionized water and continue immersion. Step 6: Dissolve the polymer in deionized water, and sonicate the mixture in an ultrasonic oscillator. Then transfer the solution to a sealed, light-proof container for storage, obtaining a modified solution for encapsulation. Step 7: Dilute the dialdehyde compound in deionized water, then add phosphate buffer to adjust the pH to obtain a crosslinking solution; Step 8: Air dry the membrane treated in step 5 in a clean environment, then immerse it in the encapsulation solution prepared in step 6, and then remove it; Step 9: Without drying or rinsing, immediately immerse the membrane from Step 8 into the crosslinking solution from Step 7 to achieve encapsulation and stabilization of the functionalized layer. Step 10: Take out the membrane after encapsulation in step 9 and rinse it to obtain a reverse osmosis / nanofiltration membrane for enhancing the retention of neutral small molecule organic matter.

2. The modification method according to claim 1, characterized in that... In step 1, the soaking temperature is 25-30°C and the soaking time is 6-24 hours; the air drying process is carried out in a clean environment with a temperature of 25-30°C and a relative humidity of 60%-80% RH, and the air drying time is controlled to be 5-10 minutes, with an airflow speed ≤0.5 m / s.

3. The modification method according to claim 1, characterized in that... In step 2, the organic solvent is ethanol or isopropanol; the molecular plug is at least one of trifluoromethyldiaminobiphenyl, tetrafluorobiphenyl-4-phenol, and pentafluorobiphenyl; the molecular plug mass concentration is 0.1-3.0 wt%, the dissolution temperature is 25-30℃, and the ultrasonic vibration time is 30-60 min.

4. The modification method according to claim 1, characterized in that... In step 3, the ambient temperature is maintained at 25–30°C and the relative humidity is controlled at 60%–80% RH.

5. The modification method according to claim 1, characterized in that... In step 4, the reaction temperature is 25–30°C, the pressurization time is 5–10 minutes, the pressure range is 1–2 bar, and the pressurization is stopped immediately when liquid flows out of the filter end, and the excess solution is poured out.

6. The modification method according to claim 1, characterized in that... In step 5, the deionized water soaking temperature is 25–30°C, and the single soaking time is 30–60 minutes; a two-step cleaning method is adopted: after the first soaking, the wastewater is poured off, and fresh deionized water is replaced before soaking for another 10–30 minutes.

7. The modification method according to claim 1, characterized in that... In step 7, the dialdehyde compound may be glutaraldehyde, succinaldehyde, or adipaldehyde; the mass concentration is 0.01–0.1 wt%; the pH of the crosslinking solution is adjusted to 6.0–8.0; the concentration of the phosphate buffer is 0.005–0.02 M; the reaction temperature is 25–30°C; and the reaction time is 5–20 minutes.

8. The modification method according to claim 1, characterized in that... In step 8, the membrane is immersed in the encapsulation solution for 5–15 minutes, the ambient temperature is maintained at 25–30°C, and the relative humidity is controlled at 60%–80% RH.

9. The modification method according to claim 1, characterized in that... In step 9, the sample is immediately immersed in the prepared crosslinking solution within 30 seconds and reacted at 25–30°C for 5–15 minutes to achieve surface crosslinking encapsulation.

10. The modification method according to claim 1, characterized in that... In step 10, rinsing is performed using flowing deionized water for 10–30 seconds to remove residual impurities on the surface and obtain the final modified film.

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