Flat membrane assembly having Anti-contamination function, membrane filtration device, and water purification system

Abstract

The present invention relates to a flat membrane assembly having an anti-contamination function, a membrane filtration device, and a water purification system. The flat membrane assembly comprises a plurality of membrane bags that are stacked and connected, and each membrane bag comprises a plurality of layers of flat membranes. Each flat membrane comprises a flat membrane layer and a hydrophilic anti-contamination layer on the surface thereof. The hydrophilic anti-contamination layer is a mixture of sodium titanium 2,3-dihydroxyterephthalate and polyethyleneimine, and the sodium titanium 2,3-dihydroxyterephthalate is prepared by reacting titanium dioxide with 2,3-dihydroxyterephthalic acid. In a same membrane bag, a space between adjacent flat membranes is filled with a mixture of graphite-phase carbon nitride-iron-based metal-organic framework composite and graphitized biochar. The sodium titanium 2,3-dihydroxyterephthalate provided by the present invention can effectively prevent contaminants from adhering to the flat membranes, the graphite-phase carbon nitride-iron-based metal-organic framework composite can degrade organic contaminants on the flat membranes, and the graphitized biochar can adsorb contaminants and catalytically degrade residual small-molecule organic compounds.

Description

Flat sheet membrane modules, membrane filtration devices and water purification systems with antifouling function Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to flat sheet membrane modules, membrane filtration devices, and water purification systems with antifouling functions. Background Technology

[0002] Microfiltration / ultrafiltration membranes can be classified into tubular membranes, spiral wound membranes, hollow fiber membranes, and flat sheet membranes based on their shape. Tubular membranes have a simple structure and low pressure loss, making them suitable for treating high-viscosity and high-concentration liquids, but they have a small specific surface area. Spiral wound membranes have a large membrane area and good turbulence, but they require high-precision manufacturing and assembly, are inconvenient to clean and maintain, and cannot treat liquids with high suspension concentrations. Hollow fiber membranes have compact components and a large membrane area per unit volume, but the small inner diameter of the hollow fibers makes them prone to clogging, and contaminants are difficult to remove, thus requiring high-precision feed treatment. Flat sheet membranes have advantages such as good mechanical properties, high filtration flux, strong resistance to shock loads, simple equipment, and convenient membrane replacement, therefore they are commonly used in drinking water and advanced wastewater treatment.

[0003] However, flat-sheet microfiltration / ultrafiltration membranes can also experience a decrease in flux and an increase in water treatment costs due to fouling. The main cause of flat-sheet membrane fouling is the physicochemical and mechanical interactions between particulate matter, colloidal particles, and large solute molecules in the water being treated and the flat-sheet membrane. These substances are adsorbed and deposited on the surface of the membrane or within the membrane pores, causing the membrane pore size to decrease or become blocked, resulting in increased membrane resistance and a decrease in membrane flux.

[0004] In existing technologies, the methods for reducing fouling of flat sheet membranes include the following two:

[0005] The first approach is to mitigate pollution in the raw water by adding pretreatment processes, such as coagulation pretreatment, adsorption pretreatment, and oxidation pretreatment. However, this method significantly increases the complexity and cost of the water treatment process.

[0006] The second method involves modifying the membrane material or membrane to give it antifouling properties. However, the antifouling function of this modified membrane is not stable enough. After a period of use, pollutants will still affect the membrane's performance, causing fouling and failing to effectively reduce fouling of flat sheet membranes.

[0007] Therefore, there is a need to provide a flat sheet membrane module that can effectively reduce fouling. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] In view of the above-mentioned technical problems, the present invention provides a flat sheet membrane module, a membrane filtration device and a water purification system with anti-fouling function, which can effectively reduce the fouling of flat sheet membrane modules.

[0010] (II) Technical Solution

[0011] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0012] In a first aspect, the present invention provides a flat sheet membrane assembly with anti-fouling function, comprising a plurality of stacked and connected membrane bags; the membrane bags comprising multilayer flat sheet membranes;

[0013] The flat sheet membrane includes a flat sheet membrane layer and a hydrophilic antifouling layer coated on the surface of the flat sheet membrane layer; the hydrophilic antifouling layer is a mixture of sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine, wherein the sodium titanium-2,3-dihydroxyterephthalate is prepared by reacting titanium dioxide with 2,3-dihydroxyterephthalic acid.

[0014] In the same membrane bag, a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biocarbon is filled between adjacent flat membranes.

[0015] In the flat sheet membrane assembly described above, preferably, the thickness of the membrane bag is 1.0-3.0 mm, and sodium titanium-2,3-dihydroxyterephthalate accounts for 5-15 wt% of polyethyleneimine.

[0016] Preferably, in the flat sheet membrane assembly described above, the flat sheet membrane layer is a polyethylene flat sheet membrane, a polypropylene flat sheet membrane, a polyethersulfone flat sheet membrane, a polysulfone flat sheet membrane, a polyacrylonitrile flat sheet membrane, or a polyvinylidene fluoride flat sheet membrane.

[0017] In the flat sheet membrane module described above, preferably, the mass of the graphite phase carbon nitride-iron-based metal-organic framework composite material is 5-30 times the mass of the graphitized biocarbon.

[0018] Preferably, in the flat sheet membrane assembly described above, the preparation method of the sodium titanium-2,3-dihydroxyterephthalate includes the following steps:

[0019] S1: Add titanium dioxide and 2,3-dihydroxyterephthalic acid to acetonitrile and stir until homogeneous; the molar ratio of titanium dioxide to 2,3-dihydroxyterephthalic acid is 1:2-1:5;

[0020] S2: Add sodium bicarbonate to the mixture obtained in S1 and react for 1-3 hours; the molar ratio of sodium bicarbonate to titanium dioxide in step S1 is 2:1-3:1.

[0021] S3: Wash the system after the reaction to obtain sodium titanium-2,3-dihydroxyterephthalate.

[0022] Preferably, the preparation method of the graphite-phase carbon nitride-iron-based metal-organic framework composite material for the flat sheet membrane module described above includes the following steps:

[0023] A1: Melamine is calcined at 500-550℃ for 4-6 hours to obtain graphite phase carbon nitride, and then the graphite phase carbon nitride is ground to obtain grinding particles.

[0024] A2: Mix the grinding particles with the precursor for the preparation of iron-based metal-organic framework materials, and then hydrothermally react the mixture at 120-150℃ for 12-18h to obtain graphite phase carbon nitride-iron-based metal-organic framework composite material.

[0025] Preferably, in the flat sheet membrane module described above, the method for preparing the graphitized biocarbon includes the following steps:

[0026] B1: Dopamine hydrochloride was added to an aqueous solution of ammonia ethanol to react and prepare polydopamine microspheres;

[0027] B2: Graphitized biocarbon was prepared by calcining polydopamine microspheres at 600-800℃ for 2-4 hours in an inert atmosphere.

[0028] In the flat sheet membrane assembly described above, preferably, in step A2, the iron-based metal-organic framework material is MIL100;

[0029] The precursors for preparing MIL100 include an iron source and an organic ligand.

[0030] In a second aspect, the present invention provides a membrane filtration device, including the above-described flat sheet membrane assembly.

[0031] Thirdly, the present invention also provides a water purification system, including the membrane filtration device described above.

[0032] (III) Beneficial Effects

[0033] First, this invention provides a hydrophilic antifouling layer on the surface of the flat sheet membrane. The material of this layer includes sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine. Sodium titanium-2,3-dihydroxyterephthalate reduces the surface energy of the flat sheet membrane, effectively preventing contaminants from adhering to it. The amino groups in polyethyleneimine further enhance the antifouling performance of the membrane by increasing its hydrophilicity. Furthermore, the sodium titanium-2,3-dihydroxyterephthalate complex has good compatibility with polyethyleneimine, preventing the loss of the hydrophilic antifouling layer material during use.

[0034] Secondly, this invention further incorporates a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biochar between adjacent flat sheet membranes. In the graphitic carbon nitride-iron-based metal-organic framework composite material, the iron-based metal-organic framework contains photosensitive Fe-O clusters and unsaturated iron sites, which can fully absorb visible light. Its nanoporous structure also provides mass transfer channels for catalytic reactions. The narrow and controllable band gap of graphitic carbon nitride allows for the formation of heterojunctions at its interface with the iron-based metal-organic framework, enabling efficient utilization of visible light and separation of charge carriers, thus enhancing photocatalytic performance and degrading organic pollutants on the flat sheet membrane, further preventing membrane fouling. Graphitized biochar is an adsorbent material with good thermal stability and chemical properties, possessing a uniformly sized microporous structure, effectively adsorbing pollutants in water and small-molecule organic matter remaining after catalytic degradation by the graphitic carbon nitride-iron-based metal-organic framework composite material.

[0035] Compared with existing technologies, the flat sheet membrane module of the present invention has stronger anti-fouling function and higher anti-fouling stability, and can effectively reduce the clogging of flat sheet membranes. Detailed Implementation

[0036] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0037] This invention provides a flat sheet membrane module with antifouling function, comprising multiple stacked membrane bags, each membrane bag comprising a multilayer flat sheet membrane. In this invention, the flat sheet membrane includes a flat sheet membrane layer and a hydrophilic antifouling layer coated on the surface of the flat sheet membrane layer. The hydrophilic antifouling layer is a mixture of sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine, wherein sodium titanium-2,3-dihydroxyterephthalate is prepared by reacting titanium dioxide with 2,3-dihydroxyterephthalic acid. Within the same membrane bag, a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biocarbon is also filled between adjacent flat sheet membranes.

[0038] This invention provides a hydrophilic antifouling layer on the surface of a flat sheet membrane. The layer comprises sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine. Sodium titanium-2,3-dihydroxyterephthalate reduces the surface energy of the membrane, effectively preventing contaminants from adhering to it. The amino groups in polyethyleneimine further enhance the membrane's antifouling performance by increasing its hydrophilicity. Furthermore, the sodium titanium-2,3-dihydroxyterephthalate complex exhibits good compatibility with polyethyleneimine, preventing the loss of the hydrophilic antifouling layer material during use. Therefore, this invention reduces fouling problems in flat sheet membrane modules through the hydrophilic antifouling layer.

[0039] In addition to coating the surface of the flat sheet membrane with a hydrophilic antifouling layer, this invention also fills the spaces between adjacent flat sheet membranes with a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biochar. In the graphitic carbon nitride-iron-based metal-organic framework composite material, the iron-based metal-organic framework material contains photosensitive Fe-O clusters and unsaturated iron sites, which can fully absorb visible light. Its nanoporous structure can also provide mass transfer channels for catalytic reactions. The narrow and controllable band gap of graphitic carbon nitride allows for the formation of heterojunctions at its interface with the iron-based metal-organic framework material. This enables efficient utilization of visible light and separation of charge carriers, improving photocatalytic performance and degrading organic pollutants on the flat sheet membrane, thereby reducing membrane fouling.

[0040] Graphitized biocarbon is an adsorbent material with good thermal stability and chemical properties. It has a uniform microporous structure and can effectively adsorb pollutants in water as well as small molecule organic matter remaining after the catalytic degradation of graphitic carbon nitride-iron-based metal-organic framework composite materials, thereby reducing the fouling of flat sheet membranes.

[0041] Preferably, the thickness of the film bag in this invention is 1.0-3.0 mm, and more preferably 0.2 mm.

[0042] Preferably, the above-mentioned flat sheet membrane layer can be one or more of polyethylene flat sheet membrane, polypropylene flat sheet membrane, polyethersulfone flat sheet membrane, polysulfone flat sheet membrane, polyacrylonitrile flat sheet membrane, and polyvinylidene fluoride flat sheet membrane.

[0043] In this invention, the mass of the graphite phase carbon nitride-iron-based metal-organic framework composite material can be 5-30 times the mass of graphitized biocarbon.

[0044] Preferably, the preparation method of sodium titanium-2,3-dihydroxyterephthalate specifically includes the following steps:

[0045] S1: Add titanium dioxide and 2,3-dihydroxyterephthalic acid to acetonitrile at room temperature and stir until homogeneous. The molar ratio of titanium dioxide to 2,3-dihydroxyterephthalic acid is 1:2-1:5, preferably 1:3.

[0046] S2: Add sodium bicarbonate to the mixture obtained in S1 and react for 1-3 hours, preferably 2 hours. In this step, the molar ratio of sodium bicarbonate to titanium dioxide in step S1 is 2:1-3:1.

[0047] S3: The system after the reaction is washed with a solvent, such as isopropyl ether, to remove impurities other than the product, and sodium titanium-2,3-dihydroxyterephthalate is obtained.

[0048] In the above preparation method, acetonitrile is used as a solvent, and sodium bicarbonate is used as a buffer solution to maintain the pH of the reaction system. At room temperature, the carboxyl group in 2,3-dihydroxyterephthalic acid reacts with both titanium dioxide and sodium bicarbonate to generate sodium titanium-2,3-dihydroxyterephthalate.

[0049] After preparing the sodium titanium-2,3-dihydroxyterephthalate complex, it can be mixed with polyethyleneimine, and then the mixture can be coated on the surface of a flat film to form a hydrophilic antifouling layer. Preferably, the sodium titanium-2,3-dihydroxyterephthalate complex accounts for 5-15 wt% of the polyethyleneimine.

[0050] Preferably, the preparation method of graphite phase carbon nitride-iron-based metal-organic framework composite material specifically includes the following steps:

[0051] A1: Melamine is calcined at 500-550℃ for 4-6 hours, preferably at 530℃ for 5 hours, to obtain graphitic carbon nitride. Then, the graphitic carbon nitride is ground to obtain grinding particles.

[0052] A2: The abrasive particles are mixed with the precursors for preparing iron-based metal-organic frameworks (MOFs), and then the mixture is hydrothermally reacted at 120-150℃ for 12-18 hours. After washing, filtering, and drying, a graphitic carbon nitride-iron-based metal-organic framework composite material is obtained. In this step, graphitic carbon nitride is first mixed with two precursors for preparing iron-based MOFs, and then, under hydrothermal conditions, the graphitic carbon nitride reacts with the two precursors to generate the graphitic carbon nitride-iron-based metal-organic framework composite material. The precursors referred to in this step include the inorganic metal center, i.e., the iron source, and the organic ligands.

[0053] Preferably, in step A2, the iron-based metal-organic framework material is MIL100 (i.e., MIL-100(Fe) formed by the combination of iron ions and organic ligands). The precursors for preparing MIL100 include an iron source and an organic ligand. The iron source can be ferric nitrate nonahydrate, and the organic ligand can be trimesic acid. Of course, the iron source and organic ligand in this invention are not limited to these two substances.

[0054] Preferably, the method for preparing graphitized biochar specifically includes the following steps:

[0055] B1: Dopamine hydrochloride was added to an aqueous solution of ammonia ethanol to prepare polydopamine microspheres.

[0056] B2: Graphitized biocarbon is prepared by calcining polydopamine microspheres at 600-800℃ for 2-4 hours in an inert atmosphere, preferably at 700℃ for 3 hours.

[0057] In step B1 above, the ammonia-ethanol aqueous solution refers to a mixture of ammonia, ethanol, and water.

[0058] In step B2 above, the inert gas can be nitrogen or the like.

[0059] The present invention also provides a membrane filtration device, including the above-mentioned flat sheet membrane module. Since the modified flat sheet membrane module has good antifouling performance and good degradation and adsorption performance for pollutants in water, using the modified flat sheet membrane module in a membrane filtration device can improve the antifouling performance of the membrane filtration device, increase the operating time of the membrane filtration device, and reduce the number of backwashing cycles.

[0060] In addition, the present invention also provides a water purification system including the above-described membrane filtration device. Similarly, the water purification system using the above-described membrane filtration device can maintain stable membrane flux, water output, and water quality during the water treatment process over a long period of time, and the entire water purification system can operate stably for a long period of time.

[0061] To further clarify the present invention and its technological advancements, the following description is provided in conjunction with specific embodiments and technical effects.

[0062] Example 1

[0063] This embodiment provides a membrane filtration device, which includes a flat sheet membrane assembly. The flat sheet membrane assembly includes multiple stacked membrane bags, each membrane bag comprising multiple layers of flat sheet membranes, with a thickness of 2.0 mm. The flat sheet membrane includes a flat sheet membrane layer and a hydrophilic antifouling layer coated on the surface of the flat sheet membrane layer. The flat sheet membrane layer is a polypropylene flat sheet membrane. The hydrophilic antifouling layer is a mixture of sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine, with sodium titanium-2,3-dihydroxyterephthalate accounting for 10 wt% of polyethyleneimine. Within the same membrane bag, a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biochar is filled between adjacent flat sheet membranes. The mass of the graphitic carbon nitride-iron-based metal-organic framework composite material is 20 times the mass of the graphitized biochar.

[0064] In this embodiment, the preparation method of sodium titanium-2,3-dihydroxyterephthalate includes the following steps:

[0065] S1: Add titanium dioxide and 2,3-dihydroxyterephthalic acid to acetonitrile and stir until homogeneous. The molar ratio of titanium dioxide to 2,3-dihydroxyterephthalic acid is 1:3.

[0066] S2: Add sodium bicarbonate to the mixture obtained in step S1 and react for 2 hours. The molar ratio of sodium bicarbonate to titanium dioxide in step S1 is 3:1.

[0067] S3: Wash the reaction system with isopropyl ether to obtain sodium titanium-2,3-dihydroxyterephthalate.

[0068] In this embodiment, the preparation method of the graphite phase carbon nitride-iron-based metal-organic framework composite material includes the following steps:

[0069] A1: Melamine was calcined at 530℃ for 5 hours to obtain graphitic carbon nitride, which was then ground to obtain grinding particles.

[0070] A2: The grinding particles were mixed with ferric nitrate nonahydrate and trimesic acid. The mixture was hydrothermally reacted at 140°C for 15 hours. After washing, filtering and drying, a graphite-phase carbon nitride-iron-based metal-organic framework composite material was obtained.

[0071] In this embodiment, the method for preparing graphitized biocarbon includes the following steps:

[0072] B1: Dopamine hydrochloride was added to an aqueous solution of ammonia ethanol to prepare polydopamine microspheres.

[0073] B2: Graphitized biocarbon was prepared by calcining polydopamine microspheres at 700°C for 3 hours under a nitrogen atmosphere.

[0074] The raw water with a turbidity of 100 NTU was provided. After being processed by the membrane filtration device of this embodiment, the turbidity of the resulting product water was 0.5 NTU. No fouling occurred during the entire product water production process, the membrane flux did not change significantly, and the product water flow rate remained stable.

[0075] Example 2

[0076] This embodiment provides a membrane filtration device, which includes a flat sheet membrane assembly. The flat sheet membrane assembly includes multiple stacked membrane bags, each membrane bag comprising multiple layers of flat sheet membranes, with a thickness of 1.0 mm. The flat sheet membrane includes a flat sheet membrane layer and a hydrophilic antifouling layer coated on the surface of the flat sheet membrane layer. The flat sheet membrane layer is a polyethylene flat sheet membrane. The hydrophilic antifouling layer is a mixture of sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine, with sodium titanium-2,3-dihydroxyterephthalate accounting for 5 wt% of polyethyleneimine. In the same membrane bag, a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biochar is filled between adjacent flat sheet membranes. The mass of the graphitic carbon nitride-iron-based metal-organic framework composite material is 5 times the mass of the graphitized biochar.

[0077] In this embodiment, the preparation method of sodium titanium-2,3-dihydroxyterephthalate includes the following steps:

[0078] S1: Add titanium dioxide and 2,3-dihydroxyterephthalic acid to acetonitrile and stir until homogeneous. The molar ratio of titanium dioxide to 2,3-dihydroxyterephthalic acid is 1:2.

[0079] S2: Add sodium bicarbonate to the mixture obtained in step S1 and react for 1 hour. The molar ratio of sodium bicarbonate to titanium dioxide in step S1 is 2:1.

[0080] S3: Wash the reaction system with isopropyl ether to obtain sodium titanium-2,3-dihydroxyterephthalate.

[0081] In this embodiment, the preparation method of the graphite phase carbon nitride-iron-based metal-organic framework composite material includes the following steps:

[0082] A1: Melamine was calcined at 500℃ for 4 hours to obtain graphitic carbon nitride, which was then ground to obtain grinding particles.

[0083] A2: The grinding particles were mixed with ferric nitrate nonahydrate and trimesic acid. The mixture was hydrothermally reacted at 120°C for 18 hours. After washing, filtering and drying, a graphite-phase carbon nitride-iron-based metal-organic framework composite material was obtained.

[0084] In this embodiment, the method for preparing graphitized biocarbon includes the following steps:

[0085] B1: Dopamine hydrochloride was added to an aqueous solution of ammonia ethanol to prepare polydopamine microspheres.

[0086] B2: Graphitized biocarbon was prepared by calcining polydopamine microspheres at 600°C for 4 hours under a nitrogen atmosphere.

[0087] The raw water with a turbidity of 50 NTU was provided. After being processed by the membrane filtration device of this embodiment, the turbidity of the resulting product water was 0.3 NTU. No fouling occurred during the entire product water production process, the membrane flux did not change significantly, and the product water flow rate remained stable.

[0088] Example 3

[0089] This embodiment provides a membrane filtration device, which includes a flat sheet membrane assembly. The flat sheet membrane assembly includes multiple stacked membrane bags, each membrane bag comprising a multilayer flat sheet membrane with a thickness of 3.0 mm. The flat sheet membrane includes a flat sheet membrane layer and a hydrophilic antifouling layer coated on the surface of the flat sheet membrane layer. The flat sheet membrane layer is a polyethersulfone flat sheet membrane. The hydrophilic antifouling layer is a mixture of sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine, wherein sodium titanium-2,3-dihydroxyterephthalate accounts for 15 wt% of polyethyleneimine. In the same membrane bag, a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biochar is filled between adjacent flat sheet membranes. The mass of the graphitic carbon nitride-iron-based metal-organic framework composite material is 30 times the mass of the graphitized biochar.

[0090] In this embodiment, the preparation method of sodium titanium-2,3-dihydroxyterephthalate includes the following steps:

[0091] S1: Add titanium dioxide and 2,3-dihydroxyterephthalic acid to acetonitrile and stir until homogeneous. The molar ratio of titanium dioxide to 2,3-dihydroxyterephthalic acid is 1:5.

[0092] S2: Add sodium bicarbonate to the mixture obtained in step S1 and react for 3 hours. The molar ratio of sodium bicarbonate to titanium dioxide in step S1 is 2.5:1.

[0093] S3: Wash the reaction system with isopropyl ether to obtain sodium titanium-2,3-dihydroxyterephthalate.

[0094] In this embodiment, the preparation method of the graphite phase carbon nitride-iron-based metal-organic framework composite material includes the following steps:

[0095] A1: Melamine was calcined at 550℃ for 6 hours to obtain graphitic carbon nitride, which was then ground to obtain grinding particles.

[0096] A2: The grinding particles were mixed with ferric nitrate nonahydrate and trimesic acid. The mixture was hydrothermally reacted at 150°C for 12 hours. After washing, filtering and drying, a graphite-phase carbon nitride-iron-based metal-organic framework composite material was obtained.

[0097] In this embodiment, the method for preparing graphitized biocarbon includes the following steps:

[0098] B1: Dopamine hydrochloride was added to an aqueous solution of ammonia ethanol to prepare polydopamine microspheres.

[0099] B2: Graphitized biocarbon was prepared by calcining polydopamine microspheres at 800℃ for 2 hours under a nitrogen atmosphere.

[0100] The raw water with a turbidity of 20 NTU was provided. After being processed by the membrane filtration device of this embodiment, the turbidity of the resulting product water was 0.1 NTU. No fouling occurred during the entire product water production process, the membrane flux did not change significantly, and the product water flow rate remained stable.

[0101] Example 4

[0102] This embodiment provides a membrane filtration device, which includes a flat sheet membrane assembly. The flat sheet membrane assembly includes multiple stacked membrane bags, each membrane bag comprising multiple layers of flat sheet membranes, with a thickness of 1.50 mm. The flat sheet membrane includes a flat sheet membrane layer and a hydrophilic antifouling layer coated on the surface of the flat sheet membrane layer. The flat sheet membrane layer is a polysulfone flat sheet membrane. The hydrophilic antifouling layer is a mixture of sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine, with sodium titanium-2,3-dihydroxyterephthalate accounting for 8 wt% of polyethyleneimine. Within the same membrane bag, a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biochar is filled between adjacent flat sheet membranes. The mass of the graphitic carbon nitride-iron-based metal-organic framework composite material is 15 times the mass of the graphitized biochar.

[0103] In this embodiment, the preparation method of sodium titanium-2,3-dihydroxyterephthalate includes the following steps:

[0104] S1: Add titanium dioxide and 2,3-dihydroxyterephthalic acid to acetonitrile and stir until homogeneous. The molar ratio of titanium dioxide to 2,3-dihydroxyterephthalic acid is 1:4.

[0105] S2: Add sodium bicarbonate to the mixture obtained in step S1 and react for 2.5 h. The molar ratio of sodium bicarbonate to titanium dioxide in step S1 is 2:1.

[0106] S3: Wash the reaction system with isopropyl ether to obtain sodium titanium-2,3-dihydroxyterephthalate.

[0107] In this embodiment, the preparation method of the graphite phase carbon nitride-iron-based metal-organic framework composite material includes the following steps:

[0108] A1: Melamine was calcined at 520℃ for 4.5h to obtain graphitic carbon nitride, and then the graphitic carbon nitride was ground to obtain grinding particles.

[0109] A2: The grinding particles were mixed with ferric nitrate nonahydrate and trimesic acid. The mixture was hydrothermally reacted at 130°C for 16 hours. After washing, filtering and drying, a graphite-phase carbon nitride-iron-based metal-organic framework composite material was obtained.

[0110] In this embodiment, the method for preparing graphitized biocarbon includes the following steps:

[0111] B1: Dopamine hydrochloride was added to an aqueous solution of ammonia ethanol to prepare polydopamine microspheres.

[0112] B2: Graphitized biocarbon was prepared by calcining polydopamine microspheres at 650°C for 2.5 h under a nitrogen atmosphere.

[0113] The raw water with a turbidity of 5 NTU was provided. After being processed by the membrane filtration device of this embodiment, the turbidity of the resulting product water was 0.05 NTU. No fouling occurred during the entire product water production process, the membrane flux did not change significantly, and the product water flow rate remained stable.

[0114] Comparative Example 1

[0115] This comparative example provides a membrane filtration device, which differs from Example 1 in that the flat sheet membrane is not coated with a hydrophilic antifouling layer, and the mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biocarbon is not filled between adjacent flat sheet membranes.

[0116] Comparative Example 2

[0117] This comparative example provides a membrane filtration device, which differs from Example 1 in that the flat sheet membrane layer is not coated with a hydrophilic antifouling layer.

[0118] Comparative Example 3

[0119] This comparative example provides a membrane filtration device, which differs from Example 1 in that the mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biocarbon is not filled between adjacent flat sheet membranes.

[0120] Raw water with a turbidity of 50 NTU was provided and treated by the membrane filtration devices of Comparative Examples 1 to 3, resulting in product water with turbidities of 1 NTU, 0.8 NTU, and 0.6 NTU, respectively.

[0121] Furthermore, after verification, under the same conditions of raw water turbidity, raw water inlet temperature, raw water inlet flow rate, and inlet pressure, after the membrane filtration device of Comparative Example 1 became fouled, the membrane filtration device of Comparative Example 2 was still able to continue to operate stably for 7 days, the membrane filtration device of Comparative Example 3 was able to continue to operate stably for 15 days, and the membrane filtration devices of Examples 1-4 were all able to continue to operate stably for more than 40 days. During the period when the membrane filtration devices of Examples 1-4 continued to operate stably, no fouling occurred during the entire water production process, the membrane flux did not change significantly, and the water production flow rate remained stable.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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.

Claims

1. A flat sheet membrane module with anti-fouling function, characterized in that, It includes multiple stacked and connected membrane bags; the membrane bags include multilayer flat films; The flat sheet membrane includes a flat sheet membrane layer and a hydrophilic antifouling layer coated on the surface of the flat sheet membrane layer; the hydrophilic antifouling layer is a mixture of sodium titanium-2,3-dihydroxyterephthalate and polyethyleneimine, wherein the sodium titanium-2,3-dihydroxyterephthalate is prepared by reacting titanium dioxide with 2,3-dihydroxyterephthalic acid. In the same membrane bag, a mixture of graphitic carbon nitride-iron-based metal-organic framework composite material and graphitized biocarbon is filled between adjacent flat membranes.

2. The flat sheet membrane module according to claim 1, characterized in that, The thickness of the membrane bag is 1.0-3.0 mm, and sodium titanium-2,3-dihydroxyterephthalate accounts for 5-15 wt% of polyethyleneimine.

3. The flat sheet membrane module according to claim 1, characterized in that, The flat sheet membrane is a polyethylene flat sheet membrane, a polypropylene flat sheet membrane, a polyethersulfone flat sheet membrane, a polysulfone flat sheet membrane, a polyacrylonitrile flat sheet membrane, or a polyvinylidene fluoride flat sheet membrane.

4. The flat sheet membrane module according to claim 1, characterized in that, The mass of graphitic carbon nitride-iron-based metal-organic framework composites is 5-30 times that of graphitized biocarbon.

5. The flat sheet membrane module according to claim 1, characterized in that, The preparation method of the sodium titanium-2,3-dihydroxyterephthalate includes the following steps: S1: Add titanium dioxide and 2,3-dihydroxyterephthalic acid to acetonitrile and stir until homogeneous; the molar ratio of titanium dioxide to 2,3-dihydroxyterephthalic acid is 1:2-1:5; S2: Add sodium bicarbonate to the mixture obtained in S1 and react for 1-3 hours; the molar ratio of sodium bicarbonate to titanium dioxide in step S1 is 2:1-3:

1. S3: Wash the system after the reaction to obtain sodium titanium-2,3-dihydroxyterephthalate.

6. The flat sheet membrane module according to claim 1, characterized in that, The preparation method of the graphite phase carbon nitride-iron-based metal-organic framework composite material includes the following steps: A1: Melamine is calcined at 500-550℃ for 4-6 hours to obtain graphite phase carbon nitride, and then the graphite phase carbon nitride is ground to obtain grinding particles. A2: The grinding particles are mixed with the precursor for the preparation of iron-based metal-organic framework materials, and then the mixture is hydrothermally reacted at 120-150℃ for 12-18h to obtain graphite phase carbon nitride-iron-based metal-organic framework composite material.

7. The flat sheet membrane module according to claim 1, characterized in that, The method for preparing the graphitized biochar includes the following steps: B1: Dopamine hydrochloride was added to an aqueous solution of ammonia ethanol to react and prepare polydopamine microspheres; B2: Graphitized biocarbon was prepared by calcining polydopamine microspheres at 600-800℃ for 2-4 hours in an inert atmosphere.

8. The flat sheet membrane module according to claim 6, characterized in that, In step A2, the iron-based metal-organic framework material is MIL100; The precursors for preparing MIL100 include an iron source and an organic ligand.

9. A membrane filtration device, characterized in that, Includes the flat sheet membrane assembly according to any one of claims 1-8.

10. A water purification system, characterized in that, Includes the membrane filtration device as described in claim 9.