Quercetin doped reverse osmosis composite membrane, preparation method thereof and water purification method

Abstract

This invention belongs to the field of membrane separation technology, specifically relating to a quercetin-doped reverse osmosis composite membrane, its preparation method, and a water purification method. The quercetin-doped reverse osmosis composite membrane comprises: a polysulfone microfiltration base membrane and a quercetin-doped polyamide selective layer; the quercetin-doped polyamide selective layer is attached to at least one side surface of the polysulfone microfiltration base membrane; the quercetin-doped polyamide selective layer includes quercetin and a polyamide backbone, with quercetin and the polyamide backbone linked by ester bonds and / or hydrogen bonds. The quercetin-doped reverse osmosis composite membrane satisfies at least one of the following conditions: surface roughness of 121 nm to 199 nm; water contact angle of 50° to 60°; and a water contact angle of 2000 mg·L⁻¹ under conditions of 20 bar and 25℃ ± 1℃. ‑1 The NaCl solution rejection rate is greater than or equal to 95%; the Zeta potential is -30mV to -60mV at pH=7; the quercetin sustained-release rate is 0.1μg·cm⁻¹. ‑2 ·d ‑1 ~10μg·cm ‑2 ·d ‑1 The kill rate of Escherichia coli is greater than or equal to 90%; the kill rate of Staphylococcus aureus is greater than or equal to 90%.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a quercetin-doped reverse osmosis composite membrane, its preparation method, and a water purification method. Background Technology

[0002] Reverse osmosis (RO) membranes are widely used in seawater desalination, wastewater treatment, and drinking water purification, but they still have many shortcomings during long-term operation: First, the membrane surface lacks sufficient hydrophilicity, which easily leads to the adhesion of pollutants, such as organic matter and bacteria, causing membrane fouling, reducing the membrane's operating flux and lifespan, and increasing operating costs. Second, the membrane surface has a single charge property, resulting in weak electrostatic repulsion against negatively charged bacteria, dissolved organic matter, and other pollutants, further exacerbating the fouling problem. Third, traditional membranes do not have antibacterial functions. During long-term operation, bacteria growing on the membrane surface can not only clog the membrane pores but may also produce toxic metabolites, affecting the quality of the effluent. Fourth, existing membrane materials lack responsive release functions and cannot achieve the controlled release of functional substances through external stimuli (such as the presence of enzymes), making it difficult to meet the dynamic antibacterial requirements in complex water treatment scenarios. Summary of the Invention

[0003] The purpose of this invention is to provide a quercetin-doped reverse osmosis composite membrane, its preparation method, and a water purification method. This invention introduces natural flavonoid polyphenol quercetin into the interfacial polymerization step, allowing it to be stably bound to the polyamide selective layer through various mechanisms such as ester bonds, hydrogen bonds, and van der Waals interactions. In biocontaminated environments, it can be gradually hydrolyzed by esterases in the membrane surface microenvironment, achieving on-demand and controllable slow-release antibacterial action. This invention also utilizes the polyhydroxy structure of quercetin to enhance the membrane surface's hydrophilicity, electrical properties, and interfacial energy, achieving a synergistic antifouling effect of "structural optimization + slow-release antibacterial action," thereby significantly improving the long-term antifouling capability of the reverse osmosis composite membrane in the treatment of seawater, brackish water, and high-salinity wastewater.

[0004] A first aspect of this invention is to provide a quercetin-doped reverse osmosis composite membrane, comprising: a polysulfone microfiltration base membrane and a quercetin-doped polyamide selective layer; the quercetin-doped polyamide selective layer is attached to at least one surface of the polysulfone microfiltration base membrane; the quercetin-doped polyamide selective layer comprises quercetin and a polyamide backbone, wherein the quercetin and the polyamide backbone are connected by ester bonds and / or hydrogen bonds. This reverse osmosis composite membrane, through the stable bonding of quercetin and the polyamide backbone, endows the membrane with antibacterial and hydrophilic properties while also retaining the separation function of the reverse osmosis composite membrane.

[0005] In some embodiments of the invention, the thickness of the quercetin-doped polyamide selective layer is 50 nm to 300 nm, preferably 80 nm to 150 nm. This selective layer thickness is suitable for reverse osmosis separation requirements, balancing high rejection rate and excellent water flux.

[0006] In some embodiments of the invention, the quercetin-doped polyamide selective layer is a cross-linked network formed by interfacial polymerization of m-phenylenediamine, 1,3,5-pyromellitic acid chloride, and quercetin. This cross-linked network structure enhances the compactness and stability of the selective layer, facilitating uniform dispersion of quercetin and preventing its loss.

[0007] In some embodiments of the invention, the quercetin-doped reverse osmosis composite membrane satisfies at least one of the following conditions: surface roughness of 121 nm to 199 nm; water contact angle of 50° to 60°; and a surface roughness of 20 bar and 25°C ± 1°C for 2000 mg·L⁻¹ water. -1 The NaCl solution rejection rate is greater than or equal to 95%; the Zeta potential is -30mV to -60mV at pH=7; the quercetin sustained-release rate is 0.1μg·cm⁻¹. -2 ·d -1 ~10μg·cm -2 ·d -1 The kill rate of Escherichia coli is greater than or equal to 90%; the kill rate of Staphylococcus aureus is greater than or equal to 90%. These conditions enable the reverse osmosis composite membrane to possess excellent antifouling properties (low roughness, moderate water contact angle), high separation performance (high rejection rate), strong electrostatic repulsion (suitable Zeta potential), and long-lasting antibacterial effect (specific slow release rate and high kill rate), meeting the purification needs of complex water bodies.

[0008] A second aspect of the present invention provides a method for preparing a quercetin-doped reverse osmosis composite membrane, comprising the following steps: immersing a pretreated polysulfone microfiltration membrane in an aqueous quercetin solution, removing it to obtain an aqueous-loaded polysulfone microfiltration membrane; based on the total mass of the aqueous quercetin solution, the aqueous quercetin solution comprises 0.01wt%~0.10wt% quercetin, 0.04wt% sodium hydroxide, 2wt% m-phenylenediamine, 0.15wt% sodium dodecyl sulfate, and 0.05wt% 4-dimethylaminopyridine; the remaining components are made up to the total mass with deionized water, and stirred evenly; immersing the aqueous-loaded polysulfone microfiltration membrane in a 1,3,5-pyromellitic trimethylol chloride / n-hexane solution to perform an interfacial polymerization reaction to form a quercetin-doped polyamide selective layer; and post-treatment to obtain a quercetin-doped reverse osmosis composite membrane. This preparation method achieves stable loading of quercetin and in-situ formation of a polyamide selective layer. The process is controllable and easy to industrialize, and can produce composite films with excellent performance.

[0009] In some embodiments of the invention, the quercetin mass fraction in the aqueous quercetin solution is 0.02% to 0.06%. This range of quercetin mass fraction in the aqueous quercetin solution satisfies the quercetin doping ratio, which can further optimize the hydrophilicity, antibacterial properties, and separation performance of the reverse osmosis composite membrane, mitigating the problems of ineffectiveness due to excessively low concentrations or agglomeration due to excessively high concentrations.

[0010] In some embodiments of the invention, the preparation method of the aqueous quercetin solution includes: adding quercetin to a sodium hydroxide solution and dispersing it to obtain an activated quercetin solution; then sequentially adding m-phenylenediamine, sodium dodecyl sulfate, and 4-dimethylaminopyridine to the activated quercetin solution to obtain the aqueous quercetin solution. This method of preparing the aqueous quercetin solution facilitates the full activation of quercetin and the uniform dispersion of all components, improves the stability of the aqueous solution, and is beneficial for subsequent interfacial polymerization reactions.

[0011] In some embodiments of the invention, the mass fraction of 1,3,5-trimethylammonium chloride in the 1,3,5-trimethylammonium chloride / n-hexane solution is 0.12 wt% to 0.18 wt%. A suitable TMC concentration can regulate the interfacial polymerization rate, which is beneficial for forming a dense and uniform polyamide selective layer, balancing separation performance and structural stability.

[0012] In some embodiments of the invention, the interfacial polymerization reaction is controlled to be carried out at 5°C to 10°C; and / or the post-treatment conditions are: drying in hexane or air for 0.5 min to 5 min, and curing at 40°C to 80°C for 3 min to 10 min. Low-temperature interfacial polymerization can reduce side reactions and is beneficial to the formation of a uniform polyamide selective layer; post-treatment can improve the density and bonding strength of the selective layer and enhance the long-term operational stability of the membrane.

[0013] A third aspect of this invention is to provide a water purification method, which uses a quercetin-doped reverse osmosis composite membrane provided in the first aspect or a quercetin-doped reverse osmosis composite membrane prepared using the preparation method of the quercetin-doped reverse osmosis composite membrane provided in the second aspect for water purification. This water purification method can efficiently purify pollutants such as salts and bacteria in water, and the reverse osmosis composite membrane used has long-lasting anti-fouling and antibacterial capabilities, which can improve water purification efficiency and the stability of effluent water quality.

[0014] The beneficial effects of the present invention include at least one of the following:

[0015] Compared with existing technologies, this invention introduces a large number of phenolic hydroxyl groups onto the surface of the reverse osmosis composite membrane by chemically doping quercetin into the polyamide selective layer network. This effectively reduces the water contact angle of the membrane, enhances hydrophilicity, and reduces the adhesion of hydrophobic pollutants. It significantly improves the electrostatic repulsion between the reverse osmosis composite membrane and pollutants such as negatively charged bacteria and dissolved organic matter. At the same time, the surface morphology of the reverse osmosis composite membrane (fine and smooth wrinkles, reduced roughness) further reduces the attachment sites of pollutants, greatly improving the antifouling performance and long-term operational stability of the reverse osmosis composite membrane, with a high flux recovery rate after cleaning. Because quercetin is chemically bound to the polyamide selective layer network through ester bonds and is not easily lost, it exhibits slow-release characteristics under esterase-free conditions. In a polluted environment where esterases are present, the ester bonds are catalytically broken, and the release rate of quercetin is significantly increased, achieving precise and dynamic inhibition of bacteria, effectively reducing bacterial adhesion and growth, improving the quality of effluent, and quercetin is natural, environmentally friendly, and biocompatible, avoiding secondary pollution of the environment by chemical antibacterial agents.

[0016] This invention achieves in-situ chemical doping of quercetin through interfacial polymerization. The preparation steps are simple, the reaction conditions are mild, and it is easy to scale up for industrial production. Moreover, the raw materials used are widely available and the cost is controllable, which shows good prospects for industrial application. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings:

[0018] Figure 1 A schematic diagram illustrating the anti-biofouling properties of the quercetin-doped reverse osmosis composite membrane provided by this invention;

[0019] Figure 2 This is a schematic diagram illustrating the mechanism of interfacial polymerization reaction of the quercetin-doped reverse osmosis composite membrane provided by the present invention.

[0020] Figure 3 Scanning electron microscope (SEM) images of the surface and cross-section of the quercetin-doped reverse osmosis composite membrane provided for this invention;

[0021] Figure 4 A three-dimensional morphology image of the surface of the quercetin-doped reverse osmosis composite membrane provided by the present invention using atomic force microscopy (AFM).

[0022] Figure 5 The water contact angle test results of the quercetin-doped reverse osmosis composite membrane provided by the present invention are shown in the figure.

[0023] Figure 6 The zeta potential test diagram of the quercetin-doped reverse osmosis composite membrane provided by the present invention;

[0024] Figure 7 Fourier transform infrared (FTIR) spectrum of the quercetin-doped reverse osmosis composite membrane provided by the present invention;

[0025] Figure 8 X-ray photoelectron spectroscopy (XPS) spectrum of the quercetin-doped reverse osmosis composite membrane provided by the present invention;

[0026] Figure 9 The graph shows the water flux and NaCl rejection rate of the quercetin-doped reverse osmosis composite membrane provided by this invention.

[0027] Figure 10 A curve showing the sustained-release performance of quercetin in the quercetin-doped reverse osmosis composite membrane provided by the present invention.

[0028] Figure 11 The confocal laser scanning microscope (CLSM) image of bacterial adhesion of the quercetin-doped reverse osmosis composite membrane provided by this invention is shown in the attached figure.

[0029] Figure 12 Flow cytometry (FACS) image of bacterial viability / death detection of the quercetin-doped reverse osmosis composite membrane provided by this invention;

[0030] Figure 13 The dynamic antifouling performance curve of the quercetin-doped reverse osmosis composite membrane provided by the present invention in a simulated seawater environment. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0033] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0034] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] Reverse osmosis technology, as a highly efficient membrane separation technology, is widely used in seawater desalination, wastewater treatment, and drinking water purification. Its core lies in the separation performance and stability of the reverse osmosis composite membrane. Currently, commercially available reverse osmosis composite membranes mainly use polyamide (TFC) as the selective layer, prepared through interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). This type of membrane has high rejection rate and water flux, dominating the water treatment field. However, existing polyamide reverse osmosis composite membranes still have many shortcomings in practical applications.

[0036] Quercetin, a natural flavonoid compound, possesses abundant phenolic hydroxyl groups and aromatic structures, which not only enhance the hydrophilicity of materials but also exhibit excellent antibacterial properties, good biocompatibility, and environmental friendliness. To address the problems in existing technologies, this invention introduces quercetin into the polyamide selective layer, improving the hydrophilicity, antifouling properties, and antibacterial performance of the reverse osmosis composite membrane. This invention achieves a strong chemical bond between quercetin and the polyamide network, enabling the reverse osmosis composite membrane to possess esterase-responsive sustained-release antibacterial function and excellent separation performance, such as... Figure 1 As shown, this is of great significance for promoting the application of reverse osmosis technology in complex water treatment scenarios.

[0037] Unless otherwise specified, all the main materials and reagents used in this invention are commercially available.

[0038] The main materials and reagents include:

[0039] Reagents: Quercetin (analytical grade), m-phenylenediamine (MPD, analytical grade), sodium dodecyl sulfate (SDS, analytical grade), 4-dimethylaminopyridine (DMAP, analytical grade), trimesoyl chloride (TMC, analytical grade), n-hexane (analytical grade), sodium hydroxide (NaOH, analytical grade).

[0040] Base membrane material: Polysulfone microfiltration base membrane (PSF).

[0041] In a first aspect, the present invention provides a quercetin-doped reverse osmosis composite membrane, comprising: a polysulfone microfiltration base membrane and a quercetin-doped polyamide selective layer; the quercetin-doped polyamide selective layer is attached to at least one surface of the polysulfone microfiltration base membrane; the quercetin-doped polyamide selective layer comprises quercetin and a polyamide backbone, wherein the quercetin and the polyamide backbone are connected by ester bonds and / or hydrogen bonds. This reverse osmosis composite membrane, through the stable bonding of quercetin and the polyamide backbone, endows the membrane with antibacterial and hydrophilic properties while also retaining the separation function of the reverse osmosis composite membrane.

[0042] In some embodiments of the invention, the thickness of the quercetin-doped polyamide selective layer is 50 nm to 300 nm, preferably 80 nm to 150 nm. This selective layer thickness is suitable for reverse osmosis separation requirements, balancing high rejection rate and excellent water flux.

[0043] In some embodiments of the invention, the quercetin-doped polyamide selective layer is a cross-linked network formed by interfacial polymerization of m-phenylenediamine, 1,3,5-pyromellitic acid chloride, and quercetin. This cross-linked network structure enhances the compactness and stability of the selective layer, facilitating uniform dispersion of quercetin and preventing its loss.

[0044] In some embodiments of the invention, the quercetin-doped reverse osmosis composite membrane satisfies at least one of the following conditions: surface roughness of 121 nm to 199 nm; water contact angle of 50° to 60°; and a surface roughness of 20 bar and 25°C ± 1°C for 2000 mg·L⁻¹ water. -1 The NaCl solution rejection rate is greater than or equal to 95%; the Zeta potential is -30mV to -60mV at pH=7; the quercetin sustained-release rate is 0.1μg·cm⁻¹. -2 ·d -1 ~10μg·cm -2 ·d -1 The kill rate of Escherichia coli is greater than or equal to 90%; the kill rate of Staphylococcus aureus is greater than or equal to 90%. These conditions enable the reverse osmosis composite membrane to possess excellent antifouling properties (low roughness, moderate water contact angle), high separation performance (high rejection rate), strong electrostatic repulsion (suitable Zeta potential), and long-lasting antibacterial effect (specific slow release rate and high kill rate), meeting the purification needs of complex water bodies.

[0045] Secondly, the present invention provides a method for preparing a quercetin-doped reverse osmosis composite membrane, comprising the following steps:

[0046] (a) Solution preparation

[0047] Preparation of aqueous quercetin solution

[0048] Add 0.04g of sodium hydroxide to 100mL of deionized water, stir, dissolve, and prepare a sodium hydroxide solution with a mass fraction of 0.04%.

[0049] Add 0g~0.10g of quercetin to the above solutions respectively, and stir magnetically for 1.5h to fully dissolve or disperse the quercetin, to obtain an activated quercetin solution with a quercetin mass fraction of 0%~0.10%.

[0050] 2g of m-phenylenediamine, 0.15g of sodium dodecyl sulfate, and 0.05g of 4-dimethylaminopyridine were added sequentially to the activated quercetin solution. The mixture was stirred until the solution became clear and transparent, yielding an aqueous quercetin solution for use in interfacial polymerization.

[0051] It should be noted that, in some embodiments, the mass fraction of quercetin in the activated quercetin solution may be, for example, 0%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, or a range of any two of these values, or other values ​​selected from the above range.

[0052] Organic phase solution preparation

[0053] Weigh 0.15 g of 1,3,5-trimethylbenzene chloride, dissolve it in 100 mL of n-hexane, seal and store in the dark after complete dissolution to obtain a 0.15% (w / w) 1,3,5-trimethylbenzene chloride / n-hexane solution.

[0054] (II) Base film pretreatment

[0055] Cut the polysulfone microfiltration membrane to a size of 4cm×2cm, and soak the cut polysulfone microfiltration membrane in deionized water for no less than 1 hour to remove impurities on the membrane surface and completely wet the pores.

[0056] (III) Preparation of polyamide selective layer

[0057] Aqueous immersion

[0058] The pretreated polysulfone microfiltration membrane was laid flat in an aqueous quercetin solution and immersed for 2 minutes to allow m-phenylenediamine, quercetin, and surfactant to fully penetrate the microporous structure of the membrane surface. The membrane was then removed and placed on non-fiber degreased paper for 10 to 20 seconds to allow excess water to flow down naturally, leaving only a thin water film, thus obtaining an aqueous-loaded polysulfone microfiltration membrane.

[0059] Interface aggregation

[0060] The aqueous-supported polysulfone microfiltration membrane was rapidly transferred to a 1,3,5-pyromellitic chloride / n-hexane solution and immersed for 1 min. Interfacial polymerization was carried out at 5℃~10℃. At this time, the m-phenylenediamine in the aqueous phase and 1,3,5-pyromellitic chloride formed a polyamide selective layer. The activated quercetin was embedded into the network of the polyamide selective layer through esterification.

[0061] (iv) Curing and post-treatment

[0062] After the interfacial polymerization reaction is completed, the membrane is dried with hexane / air for 0.5 min to 5 min, then transferred to an oven at 40℃ to 80℃ and heated for 3 min to 10 min to further densify the polyamide selective layer; then it is taken out and cooled to room temperature to obtain a quercetin-doped reverse osmosis composite membrane, which is stored in deionized water for later use.

[0063] In a third aspect, the present invention provides a water purification method, which uses a quercetin-doped reverse osmosis composite membrane provided in the first aspect or a quercetin-doped reverse osmosis composite membrane prepared by the preparation method of the quercetin-doped reverse osmosis composite membrane provided in the second aspect for water purification. This water purification method can efficiently purify pollutants such as salts and bacteria in water, and the reverse osmosis composite membrane used has long-term anti-fouling and antibacterial capabilities, which can improve water purification efficiency and the stability of effluent water quality.

[0064] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or through existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are all conventional methods.

[0065] Example 1

[0066] (a) Solution preparation

[0067] Preparation of aqueous quercetin solution

[0068] Add 0.04g of sodium hydroxide to 100mL of deionized water, stir, dissolve, and prepare a sodium hydroxide solution with a mass fraction of 0.04%.

[0069] Add 0.02 g of quercetin to the above solution and stir magnetically for 1.5 h to fully dissolve or disperse the quercetin, obtaining an activated quercetin solution. The mass fraction of quercetin in the activated quercetin solution is 0.02%.

[0070] 2g of m-phenylenediamine, 0.15g of sodium dodecyl sulfate, and 0.05g of 4-dimethylaminopyridine were added sequentially to the activated quercetin solution. The mixture was stirred until the solution became clear and transparent, yielding an aqueous quercetin solution for use in interfacial polymerization.

[0071] Organic phase solution preparation

[0072] Weigh 0.15 g of 1,3,5-trimethylbenzene chloride, dissolve it in 100 mL of n-hexane, seal and store in the dark after complete dissolution to obtain a 0.15% (w / w) 1,3,5-trimethylbenzene chloride / n-hexane solution.

[0073] (II) Base film pretreatment

[0074] Cut the polysulfone microfiltration membrane to a size of 4cm×2cm, and soak the cut polysulfone microfiltration membrane in deionized water for no less than 1 hour to remove impurities on the membrane surface and completely wet the pores.

[0075] (III) Preparation of polyamide selective layer

[0076] Aqueous immersion

[0077] The pretreated polysulfone microfiltration membrane was laid flat in an aqueous quercetin solution and immersed for 2 minutes to allow m-phenylenediamine, quercetin, and surfactant to fully penetrate the microporous structure of the membrane surface. The membrane was then removed and placed on non-fiber degreased paper for 10 to 20 seconds to allow excess water to flow down naturally, leaving only a thin water film, thus obtaining an aqueous-loaded polysulfone microfiltration membrane.

[0078] Interface aggregation

[0079] The aqueous-supported polysulfone microfiltration membrane was rapidly transferred to a 1,3,5-pyromellitic chloride / n-hexane solution and immersed for 1 min. Interfacial polymerization was carried out at 5℃~10℃. At this time, the m-phenylenediamine in the aqueous phase and 1,3,5-pyromellitic chloride formed a polyamide selective layer. The activated quercetin was embedded into the network of the polyamide selective layer through esterification.

[0080] (iv) Curing and post-treatment

[0081] After the interfacial polymerization reaction was completed, the membrane was transferred to a 60°C oven and heated for 5 minutes to further densify the polyamide selective layer. Then it was taken out and cooled to room temperature to obtain a quercetin-doped reverse osmosis composite membrane, denoted as QE0.02 / TFC, which was stored in deionized water for later use.

[0082] Example 2

[0083] The only difference from Example 1 is that the activated quercetin solution used has a quercetin mass fraction of 0.04%.

[0084] Take 100 mL of deionized water and add 0.04 g of sodium hydroxide. Stir and dissolve to prepare a 0.04% sodium hydroxide solution. Add 0.04 g of quercetin to the solution and stir magnetically for 1.5 h to fully dissolve or disperse the quercetin, thus obtaining an activated quercetin solution.

[0085] In this embodiment, a quercetin-doped reverse osmosis composite membrane, denoted as QE0.04 / TFC, was obtained and stored in deionized water for later use.

[0086] Example 3

[0087] The only difference from Example 1 is that the activated quercetin solution used has a quercetin mass fraction of 0.08%.

[0088] In this embodiment, a quercetin-doped reverse osmosis composite membrane, denoted as QE0.08 / TFC, was obtained and stored in deionized water for later use.

[0089] Comparative Example 1

[0090] Compared with Example 1, the only difference is that quercetin is not used, and the resulting reverse osmosis composite membrane is designated as TFC and stored in deionized water for later use.

[0091] Performance of Quercetin-Doped Reverse Osmosis Composite Membranes

[0092] (I) Characterization of membrane surface and cross-sectional morphology

[0093] Testing instrument: Scanning electron microscope (SEM).

[0094] Test procedure: After drying the prepared quercetin-doped reverse osmosis composite membrane, it was sputter-coated with gold. Then, the surface and cross-sectional morphology of the quercetin-doped reverse osmosis composite membrane were observed under a scanning electron microscope. The effects of different quercetin doping amounts on the "ridge-valley" wrinkled structure and polyamide layer density of the quercetin-doped reverse osmosis composite membrane surface were analyzed, as well as whether it would lead to quercetin aggregation.

[0095] (II) Characterization of membrane surface roughness and morphology

[0096] Testing instrument: Atomic force microscope (AFM).

[0097] Test parameters: The surface of the quercetin-doped reverse osmosis composite membrane was scanned in a 5μm × 5μm range.

[0098] Test indicators: Obtain the three-dimensional morphology image of the quercetin-doped reverse osmosis composite membrane surface, analyze the roughness parameters (Ra: arithmetic mean roughness; Rq: root mean square roughness), and evaluate the influence of quercetin doping on the surface undulation of the quercetin-doped reverse osmosis composite membrane.

[0099] (III) Characterization of membrane surface wettability

[0100] Testing instrument: Contact angle measuring instrument.

[0101] Test conditions: At room temperature, 2 μL of deionized water was added to the surface of the quercetin-doped reverse osmosis composite membrane.

[0102] Test method: Five different locations were tested on each quercetin-doped reverse osmosis composite membrane, and the average value was taken as the water contact angle data of the quercetin-doped reverse osmosis composite membrane. The effect of quercetin doping amount on the surface hydrophilicity of quercetin-doped reverse osmosis composite membrane was analyzed.

[0103] (iv) Characterization of zeta potential on membrane surface

[0104] Test instrument: flow potentiometer.

[0105] Test conditions: The determination was carried out in a KCl buffer solution with a pH value of 3 to 7.

[0106] Test objective: To analyze the effect of quercetin doping on the surface charge properties (negativity) of quercetin-doped reverse osmosis composite membranes and to evaluate the potential for electrostatic repulsion between quercetin-doped reverse osmosis composite membranes and negatively charged bacteria and dissolved organic matter.

[0107] (v) Chemical structure characterization

[0108] Fourier Transform Infrared Spectroscopy (FTIR) Analysis

[0109] Test instrument: Attenuated total reflection Fourier transform infrared spectrometer (ATR-FTIR).

[0110] Test range: 4000 wavenumbers (cm) -1 ~500 wavenumbers (cm) -1 ).

[0111] Test objective: To detect changes in the functional groups on the surface of quercetin-doped reverse osmosis composite membranes, using the C=O vibration peak of the ester bond (approximately 1720 cm⁻¹). -1 –OH absorption peak (3300cm) -1 ~3500cm -1 ) and C–O–C vibration peak (1240 cm⁻¹) -1 ~1270cm -1 The changes in quercetin were verified to indicate that quercetin is fixed in the polyamide network via ester bonds.

[0112] X-ray photoelectron spectroscopy (XPS) analysis

[0113] Testing instrument: X-ray photoelectron spectrometer.

[0114] Test indicators: The C1s and O1s spectra of the surface of the quercetin-doped reverse osmosis composite membrane were analyzed to observe the peak areas of CO (approximately 286 eV) and OC=O (approximately 288.5 eV) and the changes in high binding energy components related to hydroxyl / ester bonds, further verifying the chemical bonding mode of quercetin and polyamide.

[0115] (vi) Reverse osmosis separation performance test

[0116] Test apparatus: Flat plate reverse osmosis test apparatus.

[0117] Test conditions: Quercetin-doped reverse osmosis composite membrane with an effective area of ​​approximately 28 cm². 2 , at 2000 mg·L -1 The NaCl solution was used as the influent, and the system was operated at 20 bar pressure and 25°C. Data was recorded after the system stabilized for 30 minutes.

[0118] Test indicators: water flux and sodium chloride rejection rate, to evaluate the effect of different quercetin doping amounts on the separation performance of quercetin-doped reverse osmosis composite membranes.

[0119] (vii) Quercetin sustained-release behavior and esterase response test

[0120] Test sample preparation: The quercetin-doped reverse osmosis composite membrane was cut into circular pieces with a diameter of 25 mm and placed in 20 mL of artificial high-salt solution (containing sodium chloride, magnesium chloride, calcium chloride, etc.) and soaked in a shaker at 25 °C and 100 rpm.

[0121] Test grouping: Two experimental groups were set up, one without esterase and the other with 1 U·mL⁻¹. -1 Esterase.

[0122] Test method: Samples were taken at preset time points, and the absorbance of the characteristic absorption peak of quercetin at 370 nm was measured using a UV-Vis spectrophotometer. The amount of quercetin released was calculated by combining the standard curve, and the effect of esterase on the release rate of quercetin was analyzed.

[0123] (viii) Bacterial adhesion and bactericidal performance test

[0124] Test strains: Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria).

[0125] Observation using a confocal laser scanning microscope (CLSM)

[0126] Test procedure: Place the quercetin-doped reverse osmosis composite membrane in a bacterial suspension (approximately 10 μL). 6 CFU·mL -1The bacteria were incubated in the culture medium for 12 hours. After staining with live / dead bacteria fluorescent staining reagent, the bacterial adhesion and distribution of live and dead bacteria on the surface of the quercetin-doped reverse osmosis composite membrane were observed using a confocal laser scanning microscope (green fluorescence indicates live bacteria, and red fluorescence indicates dead bacteria).

[0127] Flow cytometry (FACS) analysis

[0128] Test procedure: Take the bacterial suspension after incubation with quercetin-doped reverse osmosis composite membrane, stain with propidium iodide (PI), and use flow cytometry to detect the proportion of dead cells to evaluate the damage effect of quercetin-doped reverse osmosis composite membrane on bacterial cell membrane and bactericidal efficiency.

[0129] (ix) Dynamic anti-pollution performance test

[0130] Test apparatus: Cross-flow filtration device.

[0131] Test conditions: Artificial seawater was used as the influent, and a certain amount of organic matter and bacteria were added to simulate the actual seawater environment; the quercetin-doped reverse osmosis composite membrane was installed in the test tank and operated continuously for 48 hours at 15 bar.

[0132] Test indicators: Record the changes in water flux and transmembrane pressure during operation. After operation, perform physical flushing, test the flux recovery rate, and evaluate the antifouling ability of quercetin-doped reverse osmosis composite membrane under high salt and multiple pollutant conditions.

[0133] Combination Figures 2-13 Specifically, from Figure 2 As can be seen, in the interfacial polymerization reaction system provided by this invention, the aqueous phase components achieve efficient activation and uniform dispersion of quercetin through a specific ratio: the addition of sodium hydroxide activates the phenolic hydroxyl groups of quercetin, wherein 4-dimethylaminopyridine plays a catalytic role, and m-phenylenediamine and sodium dodecyl sulfate synergistically ensure the stability of the aqueous phase system, laying the foundation for subsequent interfacial polymerization; in the organic phase, 1,3,5-pyromellitic acid chloride dissolves in n-hexane to form a homogeneous solution, which, after contacting the aqueous phase-loaded base film, undergoes a rapid polymerization reaction at the interface between the two phases, ultimately forming a cross-linked network of quercetin and polyamide backbone covalently bonded together, clearly presenting the complete reaction path of "aqueous phase activation-loading-interfacial polymerization-chemical bonding", verifying the rationality and feasibility of the preparation process.

[0134] from Figure 3 (a)~ Figure 3 As can be seen in (d), the surface and cross-sectional morphology of the composite films with different quercetin doping amounts provided by the present invention exhibit significant regularity: traditional TFC films ( Figure 3 The surface of the (a) layer has large and unevenly distributed "ridge-like" wrinkles, while the quercetin-doped composite film ( Figure 3 (b) Figure 3 (c) Figure 3 The surface wrinkles in the middle (d) are finer and smoother, with no quercetin aggregation, indicating that the introduction of quercetin optimizes the interfacial tension and reaction rate during the polyamide polymerization process. Cross-sectional images show that the polyamide selective layer of all composite membranes is tightly bonded to the polysulfone microfiltration base membrane without peeling or voids. The selective layer thickness is within the designed range of 50nm to 300nm, with QE0.04 / TFC (…) showing the best results. Figure 3 The thickness of the selective layer in (c) is about 120 nm, which is within the preferred range of 80 nm to 150 nm. This ensures both the density required for separation performance and the efficient transport of water flux.

[0135] from Figure 4 (a)~ Figure 4 As can be seen in (d), the surface roughness of the quercetin-doped composite film provided by the present invention shows a significant decreasing trend with increasing doping amount: traditional TFC film ( Figure 4 The arithmetic mean roughness (Ra) of (a) is 156±20.9 nm, and the root mean square roughness (Rq) is 199.9±18.7 nm, indicating significant surface undulations; as the quercetin doping concentration increases from 0.02 wt% ( Figure 4 (b) increased to 0.08wt% Figure 4 In the middle (d) section, the Ra of the composite membrane decreased to 152±18.4nm, 150±11.1nm, and 94.4±7.2nm respectively, while the Rq decreased to 189.7±16.5nm, 189.2±13.1nm, and 121±10nm. The three-dimensional morphology of the surface became smoother, and the degree of protrusion and depression was significantly reduced, which effectively reduced the physical adsorption sites of pollutants and provided structural support for the antifouling performance of the composite membrane.

[0136] from Figure 5 As can be seen, the water contact angle of the quercetin-doped composite membrane provided by this invention is significantly lower than that of the traditional TFC membrane: the water contact angle of the traditional TFC membrane is 73°, indicating strong surface hydrophobicity; while the water contact angles of QE0.02 / TFC, QE0.04 / TFC, and QE0.08 / TFC are approximately 61°, 51°, and 57°, respectively, all within the design range of 50°~65°, and gradually decrease with increasing quercetin doping concentration. This result confirms that the polyhydroxy hydrophilic groups in the quercetin molecule are successfully exposed on the membrane surface, enhancing the interaction between the membrane and water molecules, improving surface wettability, effectively reducing the adhesion of hydrophobic contaminants, and avoiding the membrane structure swelling problem caused by excessive hydrophilicity, thus balancing antifouling properties and structural stability.

[0137] from Figure 6As can be seen, the quercetin-doped composite membrane provided by this invention exhibits a strongly negative Zeta potential under neutral conditions of pH=7, which increases with optimized doping concentration: the Zeta potential of a conventional TFC membrane is approximately -30.11 mV, while the Zeta potentials of QE0.02 / TFC, QE0.04 / TFC, and QE0.08 / TFC are approximately -33.13 mV, -44.77 mV, and -38.94 mV, respectively, all within the design range of -30 mV to -60 mV. With increasing quercetin doping concentration, the negative charge density on the membrane surface gradually increases. This is due to the ionization of the phenolic hydroxyl groups in quercetin. The strong negative charge causes a strong electrostatic repulsion between the membrane surface and negatively charged bacteria, dissolved organic matter, and other pollutants, effectively preventing pollutants from migrating and adsorbing to the membrane surface. Combined with hydrophilicity and low roughness, this forms a multi-layered anti-fouling barrier.

[0138] from Figure 7 As can be seen from the FTIR spectrum, the quercetin-doped composite film provided by this invention exhibits significant changes in characteristic functional groups, confirming the chemical bonding between quercetin and the polyamide backbone: compared with traditional TFC films, the doped composite film shows significant changes in characteristic functional groups at 3300 cm⁻¹. -1 ~3500cm -1 The significantly enhanced intensity of the -OH absorption peak in the region indicates the successful introduction of the polyhydroxy structure of quercetin; at 1740 cm⁻¹ -1 The presence of a characteristic C=O vibrational peak of the ester bond nearby, with the peak intensity gradually increasing with increasing quercetin doping concentration, proves that quercetin is covalently bonded to the polyamide backbone via ester bonds; simultaneously, at 1240 cm⁻¹... -1 ~1270cm -1 The increased intensity of the C–O–C vibration peak in the region confirms the formation of the cross-linked network structure, while the absence of shift in the position of the amide bond characteristic peak indicates that the polyamide skeleton structure has not been destroyed, thus ensuring the basic separation performance of the composite membrane.

[0139] from Figure 8 (a)~ Figure 8 As shown in (b), the XPS spectra of the quercetin-doped composite film provided by this invention verify the chemical doping and binding mode of quercetin at the elemental chemical state level: In the C1s spectrum, the characteristic peak area ratio of the doped composite film at 286 eV (CO) and 288.5 eV (OC=O) is significantly higher than that of the traditional TFC film, and gradually increases with the increase of quercetin doping amount, confirming that the hydroxyl and ester groups of quercetin are successfully integrated into the polyamide network; In the O1s spectrum, the proportion of high binding energy components related to hydroxyl / ester bonds increases, further verifying the chemical binding morphology; The NC=O characteristic peak position in the N1s spectrum is stable, indicating that the polyamide skeleton structure is intact. The XPS test results and FTIR analysis corroborate each other, clarifying the stable chemical existence form of quercetin in the polyamide selective layer.

[0140] from Figure 9 As can be seen, the quercetin-doped composite membrane provided by this invention exhibits superior reverse osmosis separation performance compared to traditional TFC membranes, and meets the design requirements: under conditions of 20 bar and 25℃±1℃, with a concentration of 2000 mg·L⁻¹ -1 NaCl solution was used as the feed water. The traditional TFC membrane had a rejection rate of approximately 98.31% and a water flux of approximately 1.92 L·m⁻¹. -2 ·h -1 The rejection rates of QE0.02 / TFC, QE0.04 / TFC, and QE0.08 / TFC reached 98.51%, 98.91%, and 98.21%, respectively, all ≥98%, with water fluxes of 1.93 L·m⁻¹. -2 ·h -1 1.95 L·m -2 ·h -1 1.91 L·m -2 ·h -1 All of these performances are higher than those of traditional TFC membranes. Among them, QE0.04 / TFC exhibits the best overall separation performance, indicating that appropriate doping of quercetin (0.02wt%~0.06wt%) can achieve a synergistic improvement in retention rate and water flux by optimizing the compactness and hydrophilicity of the polyamide selective layer.

[0141] from Figure 10 (a)~ Figure 10 As can be seen in (b), the quercetin-doped composite membrane provided by the present invention exhibits esterase-responsive quercetin sustained-release properties, and the release rate meets the design requirements: under esterase-free conditions ( Figure 10 In (b), the sustained-release rates of quercetin for QE0.02 / TFC, QE0.04 / TFC, and QE0.08 / TFC were 0.3 μg·cm⁻¹, respectively. -2 ·d -1 0.8 μg·cm -2 ·d -1 2.1 μg·cm -2 ·d -1 All were at 0.1 μg·cm -2 ·d -1 ~10μg·cm -2 ·d -1 Within a certain range, it exhibits stable and slow release characteristics; with the addition of 0.25 U·mL -1 esterase in simulated polluted environments ( Figure 10 In (a), the release rate of the three composite membranes was significantly increased to 3.2 μg·cm⁻¹. -2 ·d -1 6.5 μg·cm -2 ·d -1 9.8 μg·cm -2 ·d -1It still did not exceed the design limit, and achieved intelligent regulation of "conventional slow release + pollution response accelerated release", which can inhibit bacterial growth as needed and avoid waste of functional substances.

[0142] from Figure 11 (a)~ Figure 11 As shown in (b), the quercetin-doped composite membrane provided by this invention exhibits excellent antibacterial adhesion and bactericidal properties: CLSM observation shows that a large number of green fluorescent live bacteria (Escherichia coli and Staphylococcus aureus) adhere to the surface of the traditional TFC membrane, with a dead bacteria ratio of less than 10%; while the amount of live bacteria adhering to the surface of the quercetin-doped composite membrane is significantly reduced, and the proportion of red fluorescent dead bacteria is greatly increased. Among them, QE0.04 / TFC and QE0.08 / TFC have a kill rate of ≥90% for both types of bacteria, meeting the design requirements; quantitative analysis further confirms that as the amount of quercetin doping increases, the amount of bacterial adhesion gradually decreases, and the bactericidal rate gradually increases, verifying the synergistic effect of "anti-adhesion + bactericidal", and showing good inhibitory effects on both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus).

[0143] from Figure 12 (a)~ Figure 12 As shown in (c), the bactericidal performance of the quercetin-doped composite membrane provided by this invention was quantitatively verified by flow cytometry: For *Escherichia coli*, the mortality rate of the traditional TFC membrane was only 15.03%, while the mortality rates of QE0.02 / TFC, QE0.04 / TFC, and QE0.08 / TFC increased to 15.66%, 25.2%, and 29.41%, respectively; for *Staphylococcus aureus*, the mortality rate of the traditional TFC membrane was 6.5%, while the mortality rates of the doped composite membrane increased to 8.21%, 21.01%, and 25.38%, respectively. The significant increase in the mortality rate confirms that the sustained release of quercetin can effectively damage bacterial cell membranes, leading to bacterial death, and the bactericidal efficiency is positively correlated with the quercetin doping amount, consistent with the CLSM observation results, providing quantitative data support for the antibacterial performance of the composite membrane.

[0144] from Figure 13 As can be seen, the quercetin-doped composite membrane provided by this invention exhibits significantly better dynamic antifouling performance than the traditional TFC membrane in a simulated seawater environment: after 48 hours of continuous operation, the water flux of the traditional TFC membrane is only 60% of the initial value, and the flux recovery rate after physical flushing is only 86%; while the water flux of QE0.08 / TFC retains 78.96% of the initial value, with a flux recovery rate of 89%. This confirms that the improved hydrophilicity, reduced roughness, enhanced electrostatic repulsion, and intelligent slow-release antibacterial function brought about by quercetin doping can effectively inhibit pollutant adhesion and bacterial growth, significantly improving the long-term operational stability of the composite membrane in complex aquatic environments.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A quercetin-doped reverse osmosis composite membrane, characterized in that, include: Polysulfone microfiltration membrane and quercetin-doped polyamide selective layer; The quercetin-doped polyamide selective layer is attached to at least one side surface of the polysulfone microfiltration membrane; The quercetin-doped polyamide selective layer comprises quercetin and a polyamide backbone, wherein the quercetin is connected to the polyamide backbone by ester bonds and / or hydrogen bonds. The quercetin-doped polyamide selective layer is a cross-linked network formed by interfacial polymerization of m-phenylenediamine, 1,3,5-pyromellitic acid chloride and quercetin; the thickness of the quercetin-doped polyamide selective layer is 80 nm to 150 nm. The quercetin-doped reverse osmosis composite membrane exhibits a quercetin slow-release rate of 0.1 μg·cm⁻¹. -2 ·d -1 ~10μg·cm -2 ·d -1 .

2. The quercetin-doped reverse osmosis composite membrane according to claim 1, characterized in that, The quercetin-doped reverse osmosis composite membrane must meet at least one of the following conditions: The surface roughness is 121 nm to 199 nm; The water contact angle is 50°~60°; At 20 bar and 25℃±1℃, for 2000 mg·L -1 The rejection rate of the NaCl solution is greater than or equal to 95%; The zeta potential is -30mV to -60mV at pH=7; The kill rate of E. coli is greater than or equal to 90%; The kill rate of Staphylococcus aureus is greater than or equal to 90%.

3. A method for preparing a quercetin-doped reverse osmosis composite membrane as described in any one of claims 1 to 2, characterized in that, Includes the following steps: The pretreated polysulfone microfiltration membrane was immersed in an aqueous quercetin solution and then removed to obtain an aqueous-loaded polysulfone microfiltration membrane. Based on the total mass of the aqueous quercetin solution, the aqueous quercetin solution included 0.01wt%~0.10wt% quercetin, 0.04wt% sodium hydroxide, 2wt% m-phenylenediamine, 0.15wt% sodium dodecyl sulfate, and 0.05wt% 4-dimethylaminopyridine. The aqueous-supported polysulfone microfiltration membrane was immersed in a 1,3,5-pyromellitic trimethylol chloride / n-hexane solution to carry out an interfacial polymerization reaction, forming a quercetin-doped polyamide selective layer. Post-processing yields the quercetin-doped reverse osmosis composite membrane.

4. The preparation method according to claim 3, characterized in that, The quercetin mass fraction in the aqueous quercetin solution is 0.02%~0.06%.

5. The preparation method according to claim 3, characterized in that, The method for preparing the aqueous quercetin solution includes: adding quercetin to a sodium hydroxide solution and dispersing it to obtain an activated quercetin solution; and sequentially adding m-phenylenediamine, sodium dodecyl sulfate, and 4-dimethylaminopyridine to the activated quercetin solution to obtain an aqueous quercetin solution.

6. The preparation method according to claim 3, characterized in that, The mass fraction of 1,3,5-pyromellitic chloride in the 1,3,5-pyromellitic chloride / n-hexane solution is 0.12wt%~0.18wt%.

7. The preparation method according to claim 3, characterized in that, The interfacial polymerization reaction is controlled to be carried out at 5°C to 10°C; and / or The post-treatment conditions are: drying in hexane or air for 0.5 min to 5 min, and curing at 40℃ to 80℃ for 3 min to 10 min.

8. A water purification method, characterized in that, Water purification is performed using the quercetin-doped reverse osmosis composite membrane according to any one of claims 1 to 2 or the quercetin-doped reverse osmosis composite membrane prepared by the preparation method of the quercetin-doped reverse osmosis composite membrane according to any one of claims 3 to 7.

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