A composite reverse osmosis membrane capable of automatically desorbing pollutants and a preparation method thereof

Abstract

The application belongs to the technical field of reverse osmosis membranes, and relates to a composite reverse osmosis membrane capable of automatically desorbing pollutants and a preparation method thereof. The application comprises the following steps: performing ultraviolet / ozone synergistic pretreatment on polysulfone particles; preparing microcrystalline trisodium citrate as a pore structure regulator; preparing a grafting stock solution of a temperature-sensitive monomer and a pH-sensitive monomer; preparing a base film rich in active sites through a phase inversion method; in-situ grafting of an intelligent polymer on the inner surface of the pore channel of the base film by using an oxidation-reduction initiation system; and finally, cyclically stabilizing the structure of the grafted layer through zonal heat treatment. The obtained composite reverse osmosis membrane can actively undergo a segment conformational transition, and through micro-mechanical force generated by swelling and shrinkage, the adsorbed pollutants can be automatically and dynamically desorbed, so that the self-cleaning and in-situ flux regeneration of the membrane are realized. The application overcomes the defects of traditional reverse osmosis membranes, such as dependence on external chemical cleaning and easy falling off of the anti-pollution functional layer, and significantly improves the long-term operation stability and anti-pollution durability of the membrane.

Description

Technical Field

[0001] This invention belongs to the field of reverse osmosis membrane technology, and relates to a composite reverse osmosis membrane that automatically desorbs pollutants and its preparation method. Background Technology

[0002] Reverse osmosis membrane technology has important applications in water treatment, seawater desalination, and industrial pure water production. Traditional composite reverse osmosis membranes typically consist of porous support layers such as polysulfone and polyethersulfone, and functional separation layers such as polyamide. Their separation mechanism mainly relies on size exclusion and dissolution-diffusion. Although these membranes exhibit excellent desalination rates and fluxes, their surfaces and pores easily adsorb contaminants such as organic matter, microorganisms, and colloids, leading to severe membrane fouling problems. This manifests as decreased flux, increased operating pressure, increased cleaning frequency, and shortened membrane life. Existing composite reverse osmosis membranes and their preparation methods mainly suffer from the following drawbacks:

[0003] 1) Antifouling ability depends on surface hydrophilicity and is a static protection. Existing technologies often improve the hydrophilicity of the membrane surface by grafting hydrophilic polymers onto the surface or introducing hydrophilic additives (such as PEG and PVP) to form a hydration layer to delay pollutant adsorption. However, this protection is passive and static. Once pollutants break through the hydration layer and adsorb onto the membrane surface, the hydrophilic layer cannot actively remove them. Pollutants gradually accumulate to form a filter cake layer, leading to irreversible fouling.

[0004] 2) Cleaning methods rely on external chemical cleaning, which damages the membrane structure. After membrane fouling, frequent chemical cleaning (such as acid, alkali, and oxidant cleaning) is required. This is not only complex to operate and results in long downtime, but strong chemical reagents can also easily damage the cross-linked structure of the polyamide layer, leading to membrane performance degradation and shortened lifespan. Repeated cleaning may also cause the surface layer to peel off, resulting in poor functional durability.

[0005] 3) The surface modification layer is not stable enough and is prone to falling off and failing. Existing grafting modification mostly adopts physical adsorption, coating or weak chemical bonding methods. The modified layer is prone to peeling, dissolution or structural damage during long-term operation and cleaning, resulting in poor functional durability and difficulty in achieving long-term anti-pollution.

[0006] 4) Lack of intelligent response mechanisms, unable to adapt to changes in operating conditions. Most existing membrane materials lack environmental responsiveness and cannot actively adjust their surface state according to pollutant type or microenvironmental changes (such as pH and temperature) to achieve real-time desorption of pollutants. Even when some studies introduce temperature-sensitive or pH-sensitive materials, they are often difficult to apply in practice due to problems such as uneven grafting, low response sensitivity, and poor mechanical strength.

[0007] 5) Insufficient control of membrane pore structure can easily lead to internal contamination. The support layer prepared by the traditional phase inversion method has a wide pore size distribution and tortuous pore channels, making it easy for pollutants to enter the pores and be adsorbed, causing internal blockage. Moreover, it is difficult to remove them by surface cleaning, resulting in low flux recovery rate. Summary of the Invention

[0008] To address the above problems, this invention provides a composite reverse osmosis membrane for automatic desorption of contaminants and a method for its preparation, specifically comprising the following steps:

[0009] Step 1: Place polysulfone (PSF) particles in an argon-oxygen mixed gas environment at a flow rate of 40-50 sccm for 5-10 min. Then, mix the PSF particles with 55-65% N-methylpyrrolidone (NMP) by mass. Under the condition of passing ozone-oxygen mixed gas, intermittently irradiate the mixed solution with a UV lamp with a wavelength of 250-260 nm for 2.5-3 min, keeping the temperature of the mixed solution at 23-27℃. Mix the irradiated solution with 35-45% NMP by mass at 80-85℃ within 4-6 min, stir at 800-1000 rpm for 10-20 min, and then cure at 50-60℃ for 19-21 h to obtain the pretreated membrane substrate.

[0010] Preferably, the mass ratio of PSF to NMP is 100:(400-500).

[0011] Preferably, the volume ratio of argon to oxygen is (9-10):(1-2).

[0012] Preferably, the flow rate of the ozone-oxygen mixture is 0.7-0.9 L / min, and the ozone concentration is 75-85 mg / m³. 3 .

[0013] Preferably, the intermittent irradiation consists of irradiation for 10 seconds followed by an interval of 20 seconds, which constitutes one cycle, and a total of 5-6 cycles are performed.

[0014] Step 2: Mix trisodium citrate with deionized water and stir at 200-300 rpm for 10-15 min. Then, while stirring at 500-600 rpm, add anhydrous ethanol dropwise at a rate of 4-5% of total volume / min. Let stand at 3.5-4.5℃ for 22-26 h to ensure sufficient crystallization. Filter with a 0.2-0.25 μm filter membrane to remove the filtrate. Wash the filter residue with acetone at 4-5℃, then dry at (-0.1)-(-0.08) MPa and 25-35℃ for 11-13 h. Grind the mixture through a 750-850 mesh sieve to obtain microcrystalline trisodium citrate.

[0015] Preferably, the ratio of trisodium citrate, deionized water and anhydrous ethanol is (1.3-1.4)g:1mL:(0.7-0.9)mL.

[0016] Preferably, the mass ratio of the filter residue to acetone is 1:(9-10).

[0017] Step 3: Mix N-isopropylacrylamide (NIPAM), dimethylaminoethyl methacrylate (DMAEMA), tert-butanol, and 18-crown-6-ether at a mass ratio of (80-90):(14-16):(240-260):(0.26-0.28), remove oxygen, and stir in an oil bath at 39-41℃ and 150-250rpm for 2-3 hours. Then add tert-butanol-water solution to adjust the total concentration of NIPAM and DMAEMA to 6-7wt% to obtain the grafting stock solution.

[0018] Preferably, the deoxygenation process involves introducing an inert gas into the mixed solution at a flow rate of 40-60 mL / min for 25-35 min. Most preferably, the inert gas is nitrogen.

[0019] Preferably, the volume ratio of tert-butanol to water in the tert-butanol-water solution is (2-3):(7-8).

[0020] Step 4: Mix the pretreated membrane substrate, pore-forming agent, and trisodium citrate microcrystalline at a mass ratio of (500-550):(12-13):(6-7), stir at 55-65℃ and 250-350rpm for 7.5-8.5h, and degas at (-0.1)-(-0.09)MPa for 23-25h. Then perform membrane scraping treatment, mix the nascent membrane with deionized water at 45-55℃ at a mass ratio of 1:(9-10), soak for 34-38h, and change the water every 12h to obtain the base membrane.

[0021] Preferably, the pore-forming agent is polyvinylpyrrolidone (PVP K30).

[0022] Preferably, the film scraping process involves scraping a film onto a clean glass plate using an adjustable scraper with a scraper gap of 150-250 μm, a temperature of 24-26°C, and a humidity of 50-60%. After scraping, the film is left to stand for 10-20 seconds (evaporation time) and then immersed in deionized water at 24-26°C for 50-70 minutes to obtain a nascent film.

[0023] Step 5: Soak the base membrane in a 0.8-1.2% potassium persulfate solution for 10-15 minutes, filter, then soak it in a 1-1.5% sodium bisulfite solution at 0-2℃ for 4-6 minutes, filter, and soak it in a grafting solution at 10-20℃ under inert gas protection for 6-8 hours. After washing with deionized water and a 0.1-0.2% sodium dodecyl sulfate solution, the activated base membrane is obtained.

[0024] Preferably, the mass ratio of the base film, potassium persulfate solution, sodium bisulfite solution, grafting solution, deionized water and sodium dodecyl sulfate solution is 1:(5-6):(5-6):(3-4):(9-10):(7-8).

[0025] Step 6: Immerse the activated base membrane sequentially in phosphate buffer solution with pH=8.2-8.8 and phosphate buffer solution with pH=3.5-4.5. Repeat this process 4-5 times to obtain a composite reverse osmosis membrane that automatically desorbs contaminants.

[0026] When using phosphate buffer with pH=8.2-8.8, the mass ratio of the activated base membrane to the phosphate buffer is 1:(3-4), and the temperature is increased to 45-50℃ at a heating rate of 1-2℃ / min and held for 70-80min.

[0027] When using phosphate buffer with pH=3.5-4.5, the mass ratio of the activated base membrane to the phosphate buffer is 1:(3-4), and the membrane is soaked at 8-12℃ for 80-90 minutes.

[0028] Preferably, the phosphate buffer comprises 550-580 mg / L disodium hydrogen phosphate and 700-750 mg / L sodium dihydrogen phosphate, adjusted to the desired pH with sodium bicarbonate and citric acid.

[0029] The working principle of each key step in this invention:

[0030] Step 1, PSF pretreatment: Active functional groups are precisely introduced into the PSF molecular chains through a stepwise, gradual oxidation and relaxation process. The PSF surface is treated with a mixed gas, reacting with introduced oxygen to initially introduce hydroxyl (-OH) and peroxy (-OO-) groups. Ozone and ultraviolet light work synergistically to generate highly oxidizing atomic oxygen and free radicals, attacking the PSF chains, especially the methyl groups adjacent to ether bonds, deeply oxidizing them to carboxyl (-COOH) and aldehyde (-CHO) groups. Intermittent irradiation avoids chain breakage caused by localized overheating and excessive oxidation. The stressed molecular chains are rearranged under the action of heat and a good solvent, with some active groups being embedded or migrated, forming a non-uniform but stable distribution. This ensures that during subsequent film formation, these active sites tend to accumulate on the surface where the film contacts the coagulation bath and at the pore wall interface.

[0031] Step two, crystallization pretreatment of trisodium citrate: By controlling the crystallization process, it is transformed from a common additive into particles with a specific morphology. Ethanol induces the precipitation of microcrystals, which are then uniformly dispersed in the casting solution. During the phase transformation, these microcrystals act as heterogeneous nucleation sites, guiding water molecules to penetrate more uniformly, forming a porous structure with narrower pore size distribution and more regular pores. Simultaneously, after membrane solidification, some carboxylate ions on the trisodium citrate molecules are exposed on the inner walls of the pores, which can form ionic or hydrogen bonds with active sites (such as -NH-) on the polysulfone chain or with subsequently grafted polymers, helping to stabilize the grafted layer.

[0032] Step 3, Pretreatment of NIPAM and DMAEMA: Utilizing the complexation effect of crown ethers on specific functional groups, the spatial relative orientation of the monomers is pre-regulated before polymerization. The cavity of the 18-crown-6-ether interacts weakly with the nitrogen on the NIPAM amide group or the lone pair electrons of the tertiary amine group in DMAEMA, enabling a degree of "pre-assembly" of the two monomer molecules. This leads to a more ideal random distribution of the two monomer units on the polymer chain during subsequent free radical copolymerization, rather than the formation of long homopolymer segments. This more regular chain structure is the molecular basis for obtaining a sharp, synergistic temperature / pH dual-responsiveness.

[0033] Step four, base membrane preparation stage: The phase transformation process not only forms the dense skin and porous support layer required for separation, but also spatially positions and structurally fixes the "active sites" created by the pretreatment. Upon immersion in the coagulation bath, solvent and non-solvent exchange occurs, and polysulfone precipitates and solidifies from the solution. The active functional groups (-COOH, -CHO, etc.) introduced and relaxed during pretreatment, due to their strong polarity, are thermodynamically enriched on the inner and outer surfaces of the hydrophilic pores during phase separation. Simultaneously, microcrystalline trisodium citrate guides the formation of well-connected pores. The resulting base membrane has its internal pore surfaces covered with chemically active sites that can serve as grafting initiation points. The three-dimensional porous structure of the entire membrane resembles a microscopic columnar reactor, providing a perfect environment for subsequent in-depth and uniform grafting.

[0034] Step 5, Polymerization Grafting Stage: Utilizing the high activity of the redox initiation system at low temperatures and the spatial confinement effect of the membrane pores, chemical grafting is achieved to grow "from the inside out" from the substrate surface. A solution containing potassium persulfate (oxidant) is immersed into the membrane pores, where it adsorbs at positively charged or hydrogen-rich sites. Subsequently, a sodium bisulfite solution (reducing agent) is immersed, and the two react instantaneously near the active sites to generate sulfate radical anions (SO42-). -• and hydroxyl radicals (HO·). These radicals preferentially abstract hydrogen atoms from the active sites of PSF or trisodium citrate, generating macromolecular radicals on the substrate surface. When immersed in the grafting solution, the monomers diffuse into the pores. The surface radicals initiate the polymerization of NIPAM and DMAEMA monomers. The reaction proceeds at low temperature, which greatly inhibits the homopolymerization reaction in the bulk solution, forcing the polymerization reaction to mainly occur on the inner wall surface of the activated membrane pores. Polymer chains "grow" from the membrane skeleton in the form of covalent bonds (CC bonds). Because the reaction occurs within the nano / micron-scale pores, the steric hindrance effect brings the grown polymer chains close together, facilitating chain transfer or coupling termination, which is conducive to the formation of a network grafted layer with moderate crosslinking density, rather than a single linear brush structure. This structure is more stable, and the mechanical forces generated by swelling / contraction are stronger.

[0035] Step 6, Partitioned heat treatment stabilization stage: Under conditions of pH=8.5 and above LCST (32-40°C), the polymer chains (especially NIPAM units) dehydrate and shrink, the entire graft layer collapses, exposing the unreacted sites or shorter chain segments below.

[0036] When rapidly introduced into an environment with pH=4 and low temperature (8-10℃), the DMAEMA units become protonated and positively charged (increasing electrostatic repulsion), while the NIPAM units become highly hydrophilic, causing the chain segments to swell dramatically. This drastic volume change generates enormous microscopic mechanical stress. This stress forces the exposed active sites to undergo secondary reactions with neighboring free radicals or chain segments, forming additional crosslinking sites and removing weak polymer segments that are only physically entangled or weakly bonded. After several such drastic shrinkage-swelling cycles, the final grafted layer is a stable, intelligent skin layer with a moderately crosslinked network, firmly connected by strong chemical bonds, and exhibiting excellent responsiveness.

[0037] The working principle of the composite reverse osmosis membrane:

[0038] Temperature response (mainly contributed by NIPAM): When the temperature is below its low critical solution temperature (LCST, 32-40°C), the polymer chains interact strongly with water molecules through hydrogen bonds, resulting in highly extended chains and hydrophilic swelling. When the temperature is above the LCST, the hydrogen bonds are broken, hydrophobic interactions dominate, the chains dehydrate and undergo drastic shrinkage and collapse, becoming hydrophobic.

[0039] pH response (mainly contributed by DMAEMA): When the ambient pH is below its protonation constant (pKa, approximately 7.5), the tertiary amine group (-N(CH3)2) on the DMAEMA chain segments accepts a proton and transforms into a positively charged quaternary ammonium cation (-N⁺H(CH3)2). The strong electrostatic repulsion between the chain segments leads to further stretching and swelling, increasing hydrophilicity. When the pH is above pKa, the amine group deprotonates and becomes neutral, the electrostatic repulsion disappears, and the chain segments relatively shrink.

[0040] Anti-adsorption (prevention phase): Under normal operating conditions (e.g., 25°C, neutral pH), the grafted chains exhibit a moderately swollen, hydrophilic state, forming a highly hydrated "molecular brush" on the membrane surface. This hydrated layer effectively repels the approach and initial adsorption of hydrophobic organic matter, proteins, and microorganisms.

[0041] Dynamic shedding (washing and regeneration stage): Microenvironmental changes caused by contaminants. When certain contaminants (such as microbial metabolic acids and organic acids) accumulate locally on the membrane surface, the interfacial pH decreases. At this time, DMAEMA units protonate, and the grafted chains suddenly and violently extend and swell due to electrostatic repulsion. This rapid volume expansion generates a strong lateral pushing force on the contaminants already attached to it, destroying their adhesion points and loosening them.

[0042] Regular gentle cleaning: When using acidic hot cleaning (such as citric acid solution at pH=4 and 40°C), the temperature and pH responses produce a synergistic amplification effect.

[0043] Step 1 (Shrinkage): At 40°C above LCST, the NIPAM unit dominates chain thermal shrinkage, attempting to pull the chain segments and the dirt adhering to them toward the membrane surface.

[0044] The second step (intense swelling): At pH 4, which is much lower than pKa, the strong electrostatic repulsion generated by the protonation of DMAEMA units counteracts thermal contraction and leads to super-swelling of the dominant chain. This sudden, violent expansion in the opposite direction of contraction is like a spring being compressed and then suddenly released, generating extremely large, periodic micromechanical oscillations and shear forces.

[0045] Under the combined action of the aforementioned pushing, oscillation, and shearing forces, the physical / chemical forces (van der Waals forces, hydrophobic interactions, hydrogen bonds, etc.) between the contaminants and the membrane surface and polymer chains are disrupted. The contaminants are effectively peeled off or detached from the membrane interface and flow away with the cleaning solution, thereby dynamically and efficiently achieving self-cleaning and flux regeneration of the membrane surface.

[0046] The present invention has the following advantages:

[0047] (1) Intelligent response and self-cleaning mechanism to achieve dynamic anti-fouling: This invention grafts temperature / pH dual-responsive copolymers (NIPAM and DMAEMA) onto the membrane surface and within the pores, enabling the membrane to have sensing-response-desorption behavior. During operation, the membrane surface maintains a moderately hydrophilic state to resist pollutant adsorption; once local pollutant accumulation causes a decrease in the microenvironment pH, the grafted chains rapidly swell due to protonation, generating micro-mechanical forces to push the pollutants away from the surface, achieving in-situ, active, and dynamic pollutant desorption without the need for shutdown chemical cleaning, significantly reducing cleaning frequency and operation and maintenance costs.

[0048] (2) Dual-response synergistic amplification enhances cleaning efficiency and gentleness. Compared with traditional single-response membranes, this invention utilizes the synergistic effect of temperature and pH responses to achieve highly efficient cleaning under gentle cleaning conditions (such as 40°C and pH=4). The grafted chains first shrink and tighten the contaminants due to heat, and then generate a powerful mechanical oscillation and shearing action similar to spring release due to the violent swelling in the acidic environment, which completely destroys the adhesion of contaminants. The cleaning effect is significantly better than traditional chemical cleaning, and it avoids damage to the membrane material by strong acids, strong alkalis or oxidants, greatly extending the service life of the membrane. Detailed Implementation

[0049] The technical solutions in the embodiments of the invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Example 1

[0051] Step 1: The mass ratio of PSF to NMP is 100:450.

[0052] PSF particles were placed in an argon-oxygen (9:1 volume ratio) gas environment at a flow rate of 45 sccm for 8 min. Then, the PSF particles were mixed with 60% NMP by mass, followed by the introduction of ozone-oxygen mixture (flow rate 0.8 L / min, ozone concentration 80 mg / m³). 3 Under mixed gas conditions, the mixed solution was intermittently irradiated with a 254nm ultraviolet lamp for 10s followed by a 20s interval, which constituted one cycle. A total of 5 cycles were performed, with the temperature of the mixed solution maintained at 25℃. The irradiated solution was then mixed with 40% NMP at 82℃ within 5 minutes, stirred at 900rpm for 15 minutes, and then aged at 55℃ for 20 hours to obtain the pretreated membrane substrate.

[0053] Step 2: The ratio of trisodium citrate, deionized water, and anhydrous ethanol is 1.35g:1mL:0.8mL.

[0054] Trisodium citrate was mixed with deionized water and stirred at 250 rpm for 13 min. Then, anhydrous ethanol was added dropwise at a rate of 5% total volume / min while stirring at 550 rpm. The mixture was allowed to stand at 4 °C for 24 h, filtered through a 0.22 μm filter membrane, and the filtrate was removed. The filter residue was washed with acetone at 4 °C, with a mass ratio of 1:9 between the filter residue and acetone. The mixture was then dried at -0.09 MPa and 30 °C for 12 h and ground through an 800-mesh sieve to obtain microcrystalline trisodium citrate.

[0055] Step 3: Mix NIPAM, DMAEMA, tert-butanol and 18-crown-6-ether at a mass ratio of 85:15:250:0.27, purge with nitrogen at a flow rate of 50 mL / min for 30 min, stir in an oil bath at 40 °C and 200 rpm for 2.5 h, then add tert-butanol-water solution (tert-butanol to water volume ratio of 3:7) to adjust the total concentration of NIPAM and DMAEMA to 6.5 wt% to obtain the grafting stock solution.

[0056] Step 4: Mix the pretreated membrane substrate, PVP K30, and trisodium citrate microcrystalline at a mass ratio of 525:12.5:6.5, stir at 60℃ and 300rpm for 8 hours, and degas at -0.095MPa for 24 hours. Then, use an adjustable doctor blade to scrape the membrane onto a clean glass plate with a doctor blade gap of 200μm, a temperature of 25℃, and a humidity of 55%. After scraping, let it stand for 10-20 seconds, and then immerse it in deionized water at 25℃ for 60 minutes to obtain the nascent membrane. Mix the nascent membrane with deionized water at 50℃ at a mass ratio of 1:10 and soak for 36 hours, changing the water every 12 hours to obtain the base membrane.

[0057] Step 5: The mass ratio of the base film, potassium persulfate solution, sodium bisulfite solution, grafting solution, deionized water and sodium dodecyl sulfate solution is 1:5:5:4:9:7.

[0058] The base membrane was mixed with a 1% potassium persulfate solution and soaked for 13 minutes, filtered, and then mixed with a 1.25% sodium bisulfite solution at 1°C and soaked for 5 minutes, filtered, and then mixed with a 15°C grafting solution and soaked for 7 hours under nitrogen protection. After washing with deionized water and a 0.15% sodium dodecyl sulfate solution, the activated base membrane was obtained.

[0059] Step six, the phosphate buffer solution comprises 560 mg / L disodium hydrogen phosphate and 725 mg / L sodium dihydrogen phosphate, and is adjusted to the desired pH using sodium bicarbonate and citric acid.

[0060] The activated base membrane was soaked in phosphate buffer solution with pH=8.5±0.05 and phosphate buffer solution with pH=4±0.05 in sequence. This process was repeated 4-5 times to obtain a composite reverse osmosis membrane that automatically desorbs contaminants.

[0061] When using phosphate buffer with pH=8.5±0.05, the mass ratio of the activated base membrane to the phosphate buffer is 1:3. The temperature is increased to 48℃ at a rate of 1℃ / min and held for 75min.

[0062] When using phosphate buffer with pH=4±0.05, the mass ratio of the activated base membrane to the phosphate buffer is 1:4, and the membrane is soaked at 10℃ for 85 min.

[0063] Experimental Example 1

[0064] 1. Membrane sample

[0065] Experimental group: The self-desorbing composite reverse osmosis membrane (hereinafter referred to as "smart membrane") prepared according to the method of Example 1.

[0066] Control group: Polyamide composite reverse osmosis membrane (PA-RO, no response function) purchased from Suzhou Tangrun Environmental Protection Technology Co., Ltd.

[0067] Contaminant simulation solutions: Bovine serum albumin (BSA) solution: 1 g / L, simulating protein contamination; Humic acid (HA) solution: 0.5 g / L, simulating organic contamination; Silica suspension (SiO2, particle size 0.2 μm): 0.1 g / L, simulating colloidal contamination.

[0068] Experimental setup: Laboratory-scale flat sheet membrane testing system (effective membrane area 20 cm²) 2 ); constant temperature circulating water bath (temperature control range: 10-60℃); pH automatic adjustment and monitoring system; electronic balance (accuracy 0.1mg); ultraviolet-visible spectrophotometer (for pollutant concentration determination).

[0069] Cleaning conditions: Smart membrane triggered cleaning: pH=4.0, temperature 40℃, circulation for 30 min; Traditional chemical cleaning: 0.1% NaOH solution + 0.1% EDTA solution, circulation for 30 min.

[0070] 2. Experimental Procedure

[0071] Step 1: Initial flux determination

[0072] The membrane sample was placed in the test cell and pre-pressurized with deionized water for 30 min at 25℃ and 0.5 MPa until the flux stabilized. The pure water flux (J0, L·m⁻¹) after stabilization was recorded. -2 ·h -1 ).

[0073] Step Two: Contamination Experiment

[0074] BSA, HA, and SiO2 contaminated solutions were used respectively, and the mixtures were circulated and filtered for 2 hours at 25℃ and 0.5MPa. Flux (J) was recorded every 30 minutes, and the flux reduction rate (FRR) was calculated. atter =J / J0×100%).

[0075] Step 3: Triggered automatic cleaning (smart membrane only)

[0076] After contamination, without disassembling the membrane, the cleaning solution (pH=4.0, 40℃) was circulated directly into the system for 30 minutes. After cleaning, the system was switched back to deionized water, and the flux (J) was measured again under the initial conditions. re ), calculate flux recovery rate (FRR=J re / J0×100%).

[0077] Step 4: Traditional chemical cleaning (control group)

[0078] After contamination, the membrane was disassembled and circulated in a cleaning solution (0.1% NaOH solution + 0.1% EDTA solution) for 30 minutes. After rinsing with deionized water, it was reinstalled, and the flux recovery rate was measured.

[0079] Step 5: Stability test of multiple contamination-cleaning cycles

[0080] The smart membrane was subjected to three consecutive "contamination-triggered cleaning" cycles, and the flux recovery rate was recorded after each cycle.

[0081] Table 1 Experimental Results Data Table

[0082]

[0083] As shown in Table 1, the flux decline rate of the smart membrane under various pollutants is significantly lower than that of commercial membranes, indicating its excellent antifouling capability. High-efficiency flux recovery (>96%) can be achieved simply through mild pH / temperature triggering, without disassembly or chemical cleaning, demonstrating its "automatic desorption" function. After multiple fouling-cleaning cycles, the smart membrane maintains a high recovery rate, indicating the stability of its response layer structure and good long-term use potential. Compared with traditional membranes that rely on chemical cleaning, the smart membrane has significant advantages in terms of cleaning gentleness, ease of operation, and membrane lifespan.

[0084] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a composite reverse osmosis membrane that automatically desorbs a contaminant, characterized by, Includes the following steps: Step 1: PSF particles are treated in an argon-oxygen mixed gas environment. Then, the PSF particles are mixed with 55-65% NMP by total mass. Under the condition of passing ozone-oxygen mixed gas, the mixed solution is intermittently irradiated with ultraviolet lamp at a temperature of 23-27℃. The irradiated solution is then mixed with NMP at 80-85℃ and 35-45% NMP by total mass, stirred, and matured to obtain the pretreated film substrate. The mass ratio of PSF to NMP is 100:(400-500); Step 2: Mix trisodium citrate with deionized water and stir. Then, under stirring conditions, add anhydrous ethanol, let stand, filter with a 0.2-0.25μm filter membrane, remove the filtrate, wash the filter residue with acetone at 4-5℃, dry, grind and sieve to obtain microcrystalline trisodium citrate. The ratio of trisodium citrate, deionized water, and anhydrous ethanol is (1.3-1.4) g: 1 mL: (0.7-0.9) mL; Step 3: Mix NIPAM, DMAEMA, tert-butanol and 18-crown-6-ether at a mass ratio of (80-90):(14-16):(240-260):(0.26-0.28), remove oxygen, stir in an oil bath, and then add tert-butanol-water solution to adjust the total concentration of NIPAM and DMAEMA to 6-7 wt% to obtain the grafting stock solution; Step 4: Mix the pretreated membrane substrate, pore-forming agent and trisodium citrate in a mass ratio of (500-550):(12-13):(6-7), stir under vacuum degassing, perform membrane scraping treatment, and soak the nascent membrane in deionized water at 45-55℃ in a mass ratio of 1:(9-10) to obtain the base membrane. Step 5: The base membrane is successively immersed in a potassium persulfate solution with a mass fraction of 0.8-1.2%, a sodium bisulfite solution with a mass fraction of 1-1.5% and a temperature of 0-2℃, and a grafting solution with a temperature of 10-20℃. Then, it is washed with deionized water and a sodium dodecyl sulfate solution with a mass fraction of 0.1-0.2% to obtain an activated base membrane. The mass ratio of the base film, potassium persulfate solution, sodium bisulfite solution, grafting solution, deionized water and sodium dodecyl sulfate solution is 1:(5-6):(5-6):(3-4):(9-10):(7-8); Step 6: Soak the activated base membrane in phosphate buffer solution with pH=8.2-8.8 and phosphate buffer solution with pH=3.5-4.5 in sequence. Repeat this process 4-5 times to obtain a composite reverse osmosis membrane that automatically desorbs contaminants.

2. The method for preparing a composite reverse osmosis membrane for automatic desorption of pollutants according to claim 1, characterized in that, The volume ratio of argon and oxygen in step one is (9-10):(1-2), the flow rate of the ozone-oxygen mixed gas is 0.7-0.9 L / min, and the ozone concentration is 75-85 mg / m 3 .

3. The method for preparing a composite reverse osmosis membrane for automatic desorption of pollutants according to claim 1, characterized in that, The intermittent irradiation described in step one is irradiation for 10 seconds followed by an interval of 20 seconds, which constitutes one cycle. A total of 5-6 cycles are performed.

4. The method of claim 1, wherein the method further comprises: The mass ratio of filter residue to acetone in step two is 1:(9-10).

5. The method for preparing a composite reverse osmosis membrane for automatic desorption of pollutants according to claim 1, characterized in that, The specific operation for deoxygenation in step three is to introduce an inert gas into the mixed solution at a flow rate of 40-60 mL / min for 25-35 min.

6. The method for preparing a composite reverse osmosis membrane for automatic desorption of pollutants according to claim 1, characterized in that, In step three, the volume ratio of tert-butanol to water in the tert-butanol-water solution is (2-3):(7-8).

7. The method of claim 1, wherein the method further comprises: The film scraping process described in step four involves using an adjustable scraper to scrape a film onto a clean glass plate with a scraper gap of 150-250 μm, a temperature of 24-26℃, and a humidity of 50-60%. After scraping, the film is left to stand for 10-20 seconds, and then immersed in deionized water at 24-26℃ for 50-70 minutes to obtain the nascent film.

8. The method for preparing a composite reverse osmosis membrane for automatic desorption of pollutants according to claim 1, characterized in that, In step six, when using phosphate buffer with pH=8.2-8.8, the mass ratio of the activated base membrane to the phosphate buffer is 1:(3-4), and the temperature is increased to 45-50℃ at a heating rate of 1-2℃ / min and held for 70-80min. When using phosphate buffer with pH=3.5-4.5, the mass ratio of the activated base membrane to the phosphate buffer is 1:(3-4), and the membrane is soaked at 8-12℃ for 80-90 minutes.

9. The method of claim 1, wherein the method further comprises: The phosphate buffer solution described in step six comprises 550-580 mg / L of disodium hydrogen phosphate and 700-750 mg / L of sodium dihydrogen phosphate, adjusted to the desired pH using sodium bicarbonate and citric acid.

10. A composite reverse osmosis membrane for automatic desorption of contaminants prepared by the method of any one of claims 1-9.

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