Preparation method of catalyst-loaded water inlet separation net with self-cleaning function

Abstract

The invention discloses a method for preparing a water inlet separation net loaded with copper oxide nanoparticles and having a self-cleaning function, and particularly relates to a method for preparing the water inlet separation net with the self-cleaning function by constructing a dopamine coating on a polypropylene separation net and then loading the copper oxide nanoparticles. The preparation method comprises the following steps: introducing a dopamine solution to the surface of a polypropylene separation net to form a polydopamine coating, chelating Cu by using surface functional groups of the polydopamine coating, then forming Cu (OH) in an alkaline environment, and further converting the Cu (OH) into CuO nano-particles to be deposited on the surface of the separation net; the finally prepared functional separation net is stable in structure, has self-cleaning capability, and can effectively slow down pollution in roll-type reverse osmosis and nanofiltration membrane elements.

Description

Technical Field

[0001] This invention relates to the field of feed water separators for spiral wound reverse osmosis / nanofiltration membrane elements, specifically to a method for preparing a self-cleaning feed water separator with a catalyst-loaded structure. Background Technology

[0002] Membrane separation technology is a highly efficient separation method centered on membrane materials with selective permeability, widely used in seawater desalination, municipal wastewater reuse, industrial wastewater treatment, and ultrapure water production. Reverse osmosis (RO) and nanofiltration (NF) systems, as representatives of membrane separation technology, separate solvents and solutes by applying pressure to drive water molecules through a semi-permeable membrane. In industrial applications, spiral-wound reverse osmosis / nanofiltration membrane elements have become the mainstream membrane element type due to their advantages such as high packing density, low unit cost, and compact structure. These membrane elements typically consist of a multi-layered structure, including a polyamide membrane sheet, a feed water separator, and a product water flow channel fabric, spirally wound around a central tube.

[0003] During long-term operation, membrane systems often face the problem of contaminant deposition. Source water often contains dissolved organic matter, colloids, bacteria, and their metabolic products, which easily form deposits on the influent channel and membrane surface, leading to decreased membrane flux, increased pressure differential, and reduced separation efficiency. The influent separator, being in direct contact with the raw water, becomes a critical site for preferential contaminant adhesion. Especially in spiral wound membrane elements, the contact area between the raised ribs of the separator and the membrane sheet easily traps organic matter and microorganisms, further inducing biofilm formation and exacerbating membrane fouling.

[0004] Currently, the mainstream materials for inlet membranes are mostly polypropylene (PP) or polyethylene (PE). Although they possess good mechanical strength and molding properties, their strong hydrophobicity makes them prone to adsorbing organic pollutants and bacteria from the water, making them one of the "starting points" for membrane fouling. Therefore, researchers have attempted to improve the antifouling performance of membranes through surface modification. Chinese patent document CN114874488A discloses a method of grafting thermosensitive hydrogels and fluoropolymer brushes onto the membrane surface, which can reduce the adhesion tendency of organic pollutants. Chinese patent document CN106365253A uses polyvinyl alcohol (PVA) aqueous solution treatment technology to improve the hydrophilicity of the membrane to reduce pollutant adsorption. Chinese patent document CN113041841A constructs a stable hydration layer on the membrane surface through a polyazo-containing heterocyclic polycarboxylic acid chemical fixation method, which to some extent enhances the membrane's ability to repel hydrophobic pollutants.

[0005] While the aforementioned modification strategies have improved the anti-adsorption capacity of the mesh surface for pollutants to some extent, they still have the following shortcomings: 1. The modification steps are complex and the process controllability is poor, making it difficult to promote on a large scale; 2. The resistance to biological contamination such as bacteria and extracellular polymers is limited, and biofilms are easily formed; 3. The material interface does not have a self-cleaning function, only having "adsorption" but lacking "removal". In addition, some methods rely on highly hydrophilic interfaces, but excessive hydrophilic modification can easily lead to an increase in the inlet and outlet water pressure difference, affecting the hydraulic stability of the system.

[0006] Therefore, developing a feedwater separator material with stable structure, excellent anti-fouling performance, and self-cleaning function is of great significance for improving the overall operating performance of spiral wound reverse osmosis / nanofiltration membrane elements, delaying fouling accumulation, and extending system life and economy. This material should not only possess good mechanical compatibility but also synergistically inhibit pollutant adhesion and promote degradation during operation, providing a new solution for the efficient and long-term operation of spiral wound reverse osmosis / nanofiltration membrane elements. Summary of the Invention

[0007] This invention proposes a self-cleaning antifouling screen for fabricating spiral-wound reverse osmosis / nanofiltration membrane elements, aiming to enhance the antifouling capability of the membrane elements, delay the deposition of contaminants in the feed water channel and on the membrane surface, and improve the operational stability and service life of the membrane system. This invention involves constructing a polydopamine (PDA) coating on the surface of the feed water screen and in-situ loading catalytically active copper oxide (CuO) nanoparticles, allowing them to be coated with low-concentration hydrogen peroxide (H2O)... 2） In the presence of catalytic oxidation, hydroxyl radicals and microbubbles are generated, achieving localized disturbance and degradation of organic pollutants within the membrane element, thereby effectively mitigating fouling within the membrane element. To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a self-cleaning inlet filter with a supported catalyst comprises the following steps: 1) Select a feed separator made of commercially available polypropylene (PP) with a diamond-shaped mesh structure; 2) Cut the mesh to the appropriate size, rinse it with deionized water, and ultrasonically clean it in 70% ethanol solution for 15 minutes to remove surface impurities and organic contaminants; 3) Rinse thoroughly with deionized water and dry for later use; 4) Prepare Tris-HCl buffer (10mM, pH=8.5), add dopamine hydrochloride to it, stir quickly to dissolve, and prepare a dopamine solution of a certain concentration; 5) Place the pretreated mesh in a dopamine solution and let it stand at room temperature with stirring for 12 hours to allow dopamine to undergo auto-oxidation under alkaline conditions and form a polydopamine coating on the surface. 6) After the reaction, remove the separator and rinse it three times with deionized water to remove any unreacted residue; then vacuum dry for later use. 7) Prepare a Cu(NO3)2 solution of a certain concentration as a precursor; 8) The PDA-modified mesh was placed in a metal salt solution and reacted at room temperature for 24 hours. During the reaction, the functional groups on the PDA surface chelated with the metal ions and formed Cu(OH)2 in an alkaline environment, which was then converted into CuO nanoparticles and deposited in situ on the surface of the mesh. 9) After the reaction is complete, rinse thoroughly with deionized water and dry to obtain the PDA@CuO functionalized feed screen.

[0008] Preferably, the thickness of the feed screen in step 1) is 30 mil to 35 mil, and the mesh angle is 60° to 90°; Preferably, the concentration of the dopamine solution in step 4) is 2 mg / mL to 4 mg / mL; Preferably, the concentration range of the Cu(NO3)2 solution in step 7) is 0.005M to 0.05M; Preferably, the reaction time in step 8) is 12h to 48h, and the particle size of the generated CuO nanoparticles is 20nm to 80nm.

[0009] The beneficial effects of this invention are: 1. By loading catalytically active CuO nanoparticles onto the surface of the inlet mesh, low concentrations of hydrogen peroxide (H2O) can be catalyzed. 2） The presence of hydroxyl radicals and microbubbles in situ enables continuous micro-disturbance and in-situ degradation of pollutants within the membrane module, thereby effectively delaying the deposition of organic matter and the formation of biofilm.

[0010] 2. Hydroxyl radicals can efficiently destroy the molecular structure of organic pollutants and inhibit bacterial growth, which helps to improve the overall antifouling ability and operational stability of membrane systems.

[0011] 3. The functionalized separator is easy to prepare, does not damage the membrane structure, has good material compatibility and structural adaptability, and is easy to replace and promote in existing reverse osmosis membrane modules.

[0012] 4. The modified materials used (such as polydopamine and copper oxide) are widely available, environmentally friendly, and inexpensive, and have good engineering scalability and long-term operational application prospects. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the water inlet screen, microbubble generation, and self-cleaning principle of the CuO nanoparticle-loaded structure described in Example 1. Detailed Implementation

[0014] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be considered as specific limitations thereof. Example

[0015] This example provides a method for preparing a self-cleaning water inlet screen loaded with CuO nanoparticles, specifically including the following steps: 1) Select a feed separator made of commercial polypropylene (PP) with a diamond mesh structure, a separator thickness of 30 mil, and a mesh angle of 75°; 2) Cut the mesh to the appropriate size, rinse it with deionized water, and ultrasonically clean it in 70% ethanol solution for 15 minutes to remove surface impurities and organic contaminants; 3) Rinse thoroughly with deionized water and dry for later use; 4) Prepare Tris-HCl buffer (10 mM, pH=8.5), add dopamine hydrochloride to it, stir quickly to dissolve, and prepare a dopamine solution with a concentration of 2 mg / mL; 5) Place the pretreated mesh in a dopamine solution and let it stand at room temperature with stirring for 12 hours to allow dopamine to undergo auto-oxidation under alkaline conditions and form a polydopamine coating on the surface. 6) After the reaction, remove the separator and rinse it three times with deionized water to remove any unreacted residue; then vacuum dry for later use. 7) Prepare a 0.01 M Cu(NO3)2 solution as a precursor; 8) The PDA-modified mesh was placed in a metal salt solution and reacted at room temperature for 24 hours. During the reaction, the functional groups on the PDA surface chelated with the metal ions and were hydrolyzed in an alkaline environment to form Cu(OH)2, which was then converted into CuO nanoparticles and deposited in situ on the surface of the mesh. 9) After the reaction is complete, rinse thoroughly with deionized water and dry to obtain the PDA@CuO functionalized feed screen; 10) The functionalized separator was paired with a commercial thin-film composite reverse osmosis (RO) membrane sheet to roll up the experimental spiral reverse osmosis membrane element (effective membrane area 0.35 m²). The performance was tested by cross-flow filtration at a pressure of 4.5 bar and a temperature of 25 °C. During the test, a constant speed injection pump was used to inject hydrogen peroxide solution into the feed water end to maintain the H2O2 concentration on the feed water side at 7 mM. Example

[0016] This embodiment provides a water inlet screen with self-cleaning function loaded with CuO nanoparticles. The difference between this embodiment and Example 1 is the concentration of dopamine hydrochloride in step 4. The difference in its preparation method compared to Example 1 is that the concentration of dopamine hydrochloride is changed to 3 mg / mL. Example

[0017] This embodiment provides a water inlet screen with self-cleaning function loaded with CuO nanoparticles. The difference between this embodiment and Example 1 is the concentration of dopamine hydrochloride in step 4. The difference in its preparation method compared to Example 1 is that the concentration of dopamine hydrochloride is changed to 4 mg / mL. Example

[0018] This embodiment provides a water inlet screen with self-cleaning function loaded with CuO nanoparticles. The difference between this embodiment and Embodiment 1 is the concentration of Cu(NO3)2 in step 6. The difference in its preparation method compared to Embodiment 1 is that the concentration of Cu(NO3)2 is changed to 0.03M. Example

[0019] This embodiment provides a water inlet screen with self-cleaning function loaded with CuO nanoparticles. The difference between this embodiment and Example 1 is the concentration of Cu(NO3)2 in step 6; the difference in its preparation method compared to Example 1 is that the concentration of Cu(NO3)2 is changed to 0.06M. Example

[0020] This embodiment provides an anti-pollution mesh, which differs from Embodiment 1 in the concentration of H2O2 in step 10; its preparation method differs from Embodiment 1 in that the concentration of H2O2 is changed to 10mM. Example

[0021] This embodiment provides a water inlet screen with self-cleaning function loaded with CuO nanoparticles. The difference between this embodiment and Embodiment 1 is the concentration of H2O2 in step 10; the difference in its preparation method compared to Embodiment 1 is that the concentration of H2O2 is changed to 15mM.

[0022] Comparative Example 1: This comparative example provides an inlet screen, wherein the anti-fouling screen is an untreated polypropylene screen.

[0023] Comparative Example 2: This comparative example provides an inlet screen, the preparation method of which differs from that of Example 1 in that step 8 is omitted; the final antifouling screen only has a PDA coating.

[0024] Performance metrics testing: By preparing simulated fouled feed solutions, the separation performance changes of membrane elements under typical fouled operating conditions were investigated to evaluate the antifouling effect of the functionalized feed separator. Normalized flux (...) J n） As the main indicator for measuring the degree of impact of membrane fouling; using the normalized desalination rate (… R n） As a reference indicator reflecting changes in separation selectivity after contamination; using normalized pressure drop ( P n） As a reflection of the drag reduction performance of the grid, the normalized flux is defined as follows: In the formula, J n Normalized flux; J p To reduce the flux of the membrane module after pollution operation; J 0 Flux under initial operating conditions (unit: L·m) -2 ·h -1） .

[0025] The normalized desalination rate is defined as: In the formula, R n Normalized desalination rate; R p The desalination rate of the membrane module after pollution operation; R 0 This represents the salt rejection rate of the membrane module in its initial state. R Calculate using the following formula: in, C p and C f These are the NaCl concentrations in the product water and the influent water, respectively, in mg / L.

[0026] The normalized voltage drop is defined as: in, P n Normalized voltage drop; P inp and P outp These are the inlet and outlet pressures of the membrane module after pollution operation. P in0 and P out0 These are the inlet and outlet pressures (unit: Pa) under initial operating conditions.

[0027] Performance testing conditions: Using bovine serum albumin (BSA) as a typical contaminant, the membrane system was initially run using a 500 mg / L NaCl solution as the feed solution. After the water flux stabilized, BSA was added to the feed solution to bring the contaminant concentration in the mixture to 50 mg / L. Simultaneously, the pH of the feed solution was adjusted to 7.0 ± 0.2 using a 0.1 mol / L hydrochloric acid or sodium hydroxide solution to simulate the contamination environment of the membrane system during normal operation. After the system stabilized following a period of operation, the water flux and pressure drop of the reverse osmosis membrane elements were tested.

[0028] The test results are summarized in Table 1.

[0029] Table 1 In the tests of PDA concentration variation (Examples 1–3), appropriately increasing the dopamine concentration significantly enhanced the functional group density of the mesh surface and the compactness of the PDA coating. Example 2 (3 mg / mL) showed the best performance. J n 、R n and P n The values ​​were 0.981, 0.988, and 0.980, respectively. It is speculated that the PDA coating was formed more uniformly at this time, providing more sites for chelation with Cu²⁺, which is beneficial to the stable loading of CuO nanocatalyst, thereby enhancing the ability to catalyze the degradation of pollutants.

[0030] Despite the increasing concentration of Cu(NO3)2 (Examples 4–5), the functionalized mesh still exhibited good performance. J n and P n The concentration decreased slightly (approximately 0.965–0.972), but remained significantly higher than the control. This indicates that increasing the metal salt concentration can promote CuO deposition, but excessively high concentrations can induce nanoparticle aggregation, thereby affecting flux and pressure drop. Therefore, a suitable loading rate is required.

[0031] Examples 6-7 primarily investigated the effect of H2O2 concentration on membrane performance. The results showed that 7 mM was a relatively ideal injection concentration; above this value (e.g., 10 mM, 15 mM), system performance gradually decreased. In Example 7... J n It dropped to 0.918. P n The value also dropped significantly to 0.910, suggesting that excessive H2O2 concentration may cause side reactions on the membrane surface, indicating that excessive oxidant will weaken the long-term stability of the separator.

[0032] In contrast, Comparative Example 1 (untreated) and Comparative Example 2 (PDA coated only) were significantly lower than the functionalized group on all metrics, especially in normalized flux ( Jn <0.84) and normalized pressure drop ( P n The <0.88) indicates that although the PDA layer has a certain degree of hydrophilicity, it lacks the synergistic effect of CuO nanocatalysts, and its ability to degrade pollutants is limited. This suggests that CuO loading is a key factor in achieving anti-pollution and drag reduction effects.

[0033] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions conceived without inventive effort should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a self-cleaning inlet filter with a supported catalyst, characterized in that, Includes the following steps: 1) Select a feed separator made of commercially available polypropylene with a diamond-shaped mesh structure; 2) Cut the mesh to the appropriate size, rinse it with deionized water, and ultrasonically clean it in 70% ethanol solution for 15 minutes to remove surface impurities and organic contaminants; 3) Rinse thoroughly with deionized water and dry for later use; 4) Prepare Tris-HCl buffer solution by adding dopamine hydrochloride, stirring rapidly to dissolve, and preparing a dopamine solution of a certain concentration. 5) Place the pretreated mesh in a dopamine solution and let it stand at room temperature with stirring for 12 hours to allow dopamine to undergo auto-oxidation under alkaline conditions and form a polydopamine coating on the surface. 6) After the reaction, remove the separator, rinse it three times with deionized water to remove unreacted residues, and vacuum dry it for later use; 7) Prepare a Cu(NO3)2 solution of a certain concentration as a precursor; 8) The PDA-modified mesh was placed in a metal salt solution and reacted at room temperature for a certain time. During this process, the functional groups on the PDA surface chelated with the metal ions and formed Cu(OH)2 in an alkaline environment, which was then converted into CuO nanoparticles and deposited in situ on the surface of the mesh. 9) After the reaction is complete, rinse thoroughly with deionized water and dry to obtain the PDA@CuO functionalized feed screen.

2. The method for preparing a self-cleaning inlet screen with a supported catalyst according to claim 1, characterized in that: In step 1), the thickness of the feed screen is 30mil to 35mil, and the mesh angle is 60° to 90°.

3. The method for preparing a self-cleaning inlet screen with a supported catalyst according to claim 1, characterized in that: In step 4), the concentration of the dopamine solution is 2 mg / mL to 4 mg / mL.

4. The method for preparing a self-cleaning inlet screen with a supported catalyst according to claim 1, characterized in that: In step 7), the concentration range of the Cu(NO3)2 solution is 0.005M to 0.05M.

5. The method for preparing a self-cleaning inlet screen with a supported catalyst according to claim 1, characterized in that: In step 8), the reaction time is 12h to 48h, and the generated CuO nanoparticles have a particle size of 20nm to 80nm.

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