An ultra-thin PE-based multi-layer composite forward osmosis membrane and its preparation method and application

Abstract

The present invention discloses an ultra-thin PE-based multi-layer composite forward osmosis membrane and its preparation method and application. The ultra-thin PE-based multi-layer composite forward osmosis membrane includes an ultra-thin PE porous support layer, a charged corrugated transition layer and a polyamide layer stacked in sequence in the thickness direction thereof. The charged corrugated transition layer includes a hydrophilic polymer formed by polymerization of a hydrophilic charged monomer, and the hydrophilic polymer is constructed to form a corrugated structure and provide nano-water channels. The present invention provides a composite forward osmosis membrane with a large flux and a high retention rate by synergizing the high porosity and low structural parameters of the ultra-thin PE porous support membrane, the nano-water channels of the charged corrugated transition layer, and the high cross-linking degree and large specific surface area of ​​the polyamide layer. The polyamide layer formed by interfacial polymerization is uniform and defect-free, ensuring the retention rate of the membrane for solutes such as inorganic salts and dyes. The composite membrane is used in the forward osmosis process to realize the fields of seawater desalination and sewage purification.

Description

Technical Field

[0001] The present invention relates to a forward osmosis membrane, in particular to an ultra-thin PE-based multi-layer composite forward osmosis membrane and a preparation method thereof, as well as application of the composite forward osmosis membrane in the field of water treatment, belonging to the field of membrane separation technology. Background Art

[0002] Forward osmosis refers to the process in which water is transferred from one end of a low-concentration solution to another end of a high-concentration solution through a selective semipermeable membrane, while solutes or ions are retained. Forward osmosis is an osmotic pressure difference driven process that does not require the addition of external driving force and can screen out harmful substances such as inorganic salts, heavy metals and microorganisms in water.

[0003] Currently, the most common forward osmosis membrane is an asymmetric composite membrane, generally consisting of a support membrane composed of polyester non-woven fabric and polysulfone porous membrane, and a polyamide layer prepared by interfacial polymerization. The lower support membrane provides mechanical strength to the composite membrane, while the upper cortex directly determines the separation performance of the forward osmosis membrane. Traditional support membranes are polysulfone and polyethersulfone ultrafiltration membranes prepared by non-solvent (water) induced phase separation. The membrane surface is smooth and dense, with a small specific surface area, low porosity, and a wide pore size distribution. The water contact angle is often greater than 80°, which is not conducive to the diffusion of aqueous phase monomers on the membrane surface during interfacial polymerization and can easily lead to an uneven polyamide layer with many defects. Such support membranes often result in low flux of composite forward osmosis membranes, and the slow diffusion rate of the drawn liquid leads to severe concentration polarization. Summary of the Invention

[0004] The main purpose of the present invention is to provide an ultra-thin PE-based multi-layer composite forward osmosis membrane to overcome the deficiencies in the prior art.

[0005] Another object of the present invention is to provide a method for preparing a corresponding ultra-thin PE-based multi-layer composite forward osmosis membrane.

[0006] Another object of the present invention is to provide an application of the ultra-thin PE-based multi-layer composite forward osmosis membrane.

[0007] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0008] An embodiment of the present invention provides an ultra-thin PE-based multi-layer composite forward osmosis membrane, comprising an ultra-thin PE porous support layer, a charged corrugated transition layer and a polyamide layer stacked in sequence in the thickness direction thereof, wherein the charged corrugated transition layer comprises a hydrophilic polymer formed by a polymerization reaction of a hydrophilic charged monomer, and the hydrophilic polymer constructs a corrugated structure and provides nano-water channels.

[0009] The present invention also provides a method for preparing an ultra-thin PE-based composite forward osmosis membrane, which comprises:

[0010] The zeolite imidazole framework material is modified on the surface of the PE porous membrane to obtain the zeolite imidazole framework material / PE porous membrane;

[0011] Plasma treatment is performed on the zeolite imidazole skeleton material / PE porous membrane, thereby inducing polymerization of hydrophilic charged monomers and grafting them onto the surface of the zeolite imidazole skeleton material / PE porous membrane to obtain a hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane; and,

[0012] The surface of the hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane is first fully contacted with an aqueous solution containing an amine monomer, and then fully contacted with an oil phase solution containing an acyl chloride monomer after drying. The amine monomer and the acyl chloride monomer are subjected to an interfacial polymerization reaction on the surface of the hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane and heat-treated to generate a polyamide layer. The zeolite imidazole skeleton material is then removed to obtain an ultra-thin PE-based multi-layer composite forward osmosis membrane.

[0013] In some embodiments, the preparation method specifically comprises:

[0014] A mixed system containing tannic acid, a zinc source and a solvent is brought into contact with a PE porous membrane and reacted at 20-90° C. for 0.5-24 hours. After being taken out, the mixed system is quickly immersed in a methanol solution of 2-methylimidazole with a mass concentration of 5-50%, and reacted at room temperature for 1-48 hours to obtain a zeolite imidazole skeleton material / PE porous membrane.

[0015] In some embodiments, the hydrophilic charged monomer includes any one or a combination of two or more of methacrylamide, methacryloxyethyltrimethylammonium chloride, acrylic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, 3-sulfopropyl methacrylate potassium salt, 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt, methacrylethyl sulfobetaine, 2-(methacryloyloxy)ethyl-2-(trimethylamino)ethyl phosphate, etc., but is not limited thereto.

[0016] In some embodiments, the preparation method specifically comprises:

[0017] The hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane is immersed in an aqueous solution containing an amine monomer for 1 to 30 minutes and then taken out. After drying, it is immersed in an oil phase solution containing an acyl chloride monomer, and an interfacial polymerization reaction is carried out for 0.5 to 10 minutes. Then, it is taken out and heat-treated at 30 to 90° C. for 1 to 30 minutes to generate a polyamide layer. It is then immersed in an acidic aqueous solution to remove the zeolite imidazole skeleton material, thereby obtaining an ultra-thin PE-based multi-layer composite forward osmosis membrane.

[0018] The embodiment of the present invention also provides an ultra-thin PE-based multi-layer composite forward osmosis membrane prepared by the above method.

[0019] The embodiment of the present invention also provides the application of the aforementioned ultra-thin PE-based multi-layer composite forward osmosis membrane in the field of water treatment.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) The present invention provides a composite membrane with high flux and high rejection rate, which is achieved by synergizing the high porosity and low structural parameters of the ultra-thin PE porous support membrane, the nano-water channels of the charged corrugated transition layer, and the high cross-linking degree and large specific surface area of ​​the polyamide layer. The composite membrane is used in the forward osmosis process to achieve applications in seawater desalination, sewage purification, and other fields.

[0022] 2) The ultra-thin PE-based multi-layer composite forward osmosis membrane provided by the present invention uses an ultra-thin PE porous membrane with a thickness of 7 microns as a support membrane. It has high porosity and low structural parameters, which can reduce concentration polarization and membrane resistance, thereby increasing the water flux of the forward osmosis membrane and reducing the reverse salt flux;

[0023] 3) The ultra-thin PE-based multi-layer composite forward osmosis membrane provided by the present invention is combined with the zeolite imidazole framework material ZIF-8 and plasma treatment to construct a hydrophilic charged transition layer with a pleated structure. On the one hand, the rejection rate of inorganic salt ions is improved based on the Donnan effect; on the other hand, the pleated structure formed by the hydrophilic polymer provides nano-water channels, thereby improving the water flux of the forward osmosis membrane;

[0024] 4) During the preparation of the ultra-thin PE-based multi-layer composite forward osmosis membrane provided by the present invention, the aqueous phase solution is easily spread on the surface of the hydrophilic transition layer during the interfacial polymerization process, and the polyamide layer formed by the interfacial polymerization reaction is uniform and defect-free, ensuring the membrane's retention rate for solutes such as inorganic salts and dyes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 2 is a schematic structural diagram of an ultra-thin PE-based multi-layer composite forward osmosis membrane in a typical embodiment of the present invention;

[0027] Figure 2 is a partially enlarged scanning electron microscope image of the upper surface of a PE porous membrane in a typical embodiment of the present invention;

[0028] Figure 3This is a partially enlarged scanning electron microscope image of the upper surface of the ultra-thin PE-based multi-layer composite forward osmosis membrane prepared in Example 5 of the present invention. DETAILED DESCRIPTION

[0029] In light of the aforementioned problems with the prior art, after extensive research and extensive experimentation, the inventors of this case discovered that by synergizing the high porosity and low structural parameters of an ultra-thin PE porous support membrane, the nano-water channels of a transitionally hydrophilic, charged, corrugated polymer layer, and the high crosslinking and large specific surface area of ​​a polyamide layer, a high-flux, high-retention forward osmosis membrane can be achieved. Based on this discovery, the inventors of this case proposed an ultra-thin PE-based multilayer composite forward osmosis membrane comprising, from bottom to top, a three-layer structure: an ultra-thin PE porous support layer, a charged, corrugated transition layer, and a polyamide layer, as well as its preparation method and application.

[0030] The technical solution, its implementation process and principles are further explained below.

[0031] As one aspect of the technical solution of the present invention, it involves an ultra-thin PE-based multi-layer composite forward osmosis membrane, which includes an ultra-thin PE porous support layer, a charged corrugated transition layer and a polyamide layer stacked in sequence in the thickness direction, wherein the charged corrugated transition layer includes a hydrophilic polymer formed by a polymerization reaction of a hydrophilic charged monomer, and the hydrophilic polymer constructs a corrugated structure and provides nano water channels.

[0032] In some embodiments, the hydrophilic charged monomer includes any one or a combination of two or more of methacrylamide, methacryloxyethyltrimethylammonium chloride, acrylic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, 3-sulfopropyl methacrylate potassium salt, 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt, methacrylethyl sulfobetaine, 2-(methacryloyloxy)ethyl-2-(trimethylamino)ethyl phosphate, etc., but is not limited thereto.

[0033] In some embodiments, see Figure 1 As shown, the ultra-thin PE-based multi-layer composite forward osmosis membrane comprises three layers from bottom to top: an ultra-thin PE porous support layer 1, a charged corrugated transition layer 2, and a polyamide layer 3. In the present invention, the high porosity and low structural parameters of the ultra-thin PE porous support membrane, the nano-water channels of the transitionally charged corrugated polymer layer, and the high cross-linking degree and large specific surface area of ​​the polyamide layer are synergistically utilized to produce a high-flux, high-retention composite membrane. This membrane is then used in the forward osmosis process to achieve seawater desalination / wastewater purification.

[0034] In some embodiments, the ultra-thin PE porous support layer has a porosity of 40-60%, contains pores with a pore size of 0.02-0.1 μm, and has a thickness of 7 μm. The present invention utilizes an ultra-thin PE porous membrane with a thickness of 7 μm as the support membrane. Its high porosity and low structural parameters reduce concentration polarization and membrane resistance, thereby increasing water flux through the forward osmosis membrane and reducing reverse salt flux.

[0035] Furthermore, the thickness of the charged corrugated transition layer is 100 to 1000 nm. Compared with a smooth surface, the corrugated structure in the charged corrugated transition layer has a higher specific surface area, which can increase water flux.

[0036] Furthermore, the thickness of the polyamide layer is 10 to 500 nm. The crosslinking degree of the polyamide layer is 50 to 95%, and the specific surface area is 220 to 3000 m 2 / g.

[0037] Furthermore, the total thickness of the ultra-thin PE-based multi-layer composite forward osmosis membrane is 7.11 to 8.5 μm.

[0038] Furthermore, the pure water flux of the ultra-thin PE-based multi-layer composite forward osmosis membrane is 54 to 121 Lm -2 h -1 , reverse salt flux is 2~38gm -2 h -1 The retention rate of inorganic salts is 63-99%, and the retention rate of dyes is 72-99.9%.

[0039] Furthermore, the inorganic salt includes sodium chloride, but is not limited thereto.

[0040] Furthermore, the dye includes rhodamine B, but is not limited thereto.

[0041] As another aspect of the technical solution of the present invention, it also relates to a method for preparing an ultra-thin PE-based multi-layer composite forward osmosis membrane, which comprises:

[0042] The zeolite imidazole framework material is modified on the surface of the PE porous membrane to obtain the zeolite imidazole framework material / PE porous membrane;

[0043] Plasma treatment is performed on the zeolite imidazole skeleton material / PE porous membrane, thereby inducing the hydrophilic charged monomers in the reaction chamber to decompose, polymerize, and deposit on the surface of the zeolite imidazole skeleton material / PE porous membrane to obtain a hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane; and,

[0044] The surface of the hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane is first fully contacted with an aqueous solution containing an amine monomer, and then fully contacted with an oil phase solution containing an acyl chloride monomer after drying. The amine monomer and the acyl chloride monomer are subjected to an interfacial polymerization reaction on the surface of the hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane and heat-treated to generate a polyamide layer. The zeolite imidazole skeleton material is then removed to obtain an ultra-thin PE-based composite forward osmosis membrane.

[0045] In some embodiments, the preparation method specifically comprises:

[0046] A mixed system containing tannic acid, a zinc source and a solvent is brought into contact with a PE porous membrane and reacted at 20-90° C. for 0.5-24 hours. After being taken out, the mixed system is quickly immersed in a methanol solution of 2-methylimidazole with a mass concentration of 5-50%, and reacted at room temperature for 1-48 hours to obtain a zeolite imidazole skeleton material / PE porous membrane.

[0047] Furthermore, the mass ratio of the tannic acid to the zinc source is 0.5-5:2-10.

[0048] Furthermore, the zinc source includes zinc nitrate, but is not limited thereto.

[0049] Furthermore, the solvent includes a combination of water and methanol.

[0050] In some embodiments, the preparation method specifically includes: placing the zeolite imidazole skeleton material / PE porous membrane in a plasma generator containing hydrophilic charged monomers, introducing an inert gas, and turning on the glow discharge switch, thereby inducing the hydrophilic charged monomers in the reaction chamber to decompose, polymerize, and deposit on the surface of the zeolite imidazole skeleton material / PE porous membrane to obtain a hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane.

[0051] In some embodiments, the hydrophilic charged monomer includes any one or a combination of two or more of methacrylamide, methacryloxyethyltrimethylammonium chloride, acrylic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, 3-sulfopropyl methacrylate potassium salt, 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt, methacrylethyl sulfobetaine, 2-(methacryloyloxy)ethyl-2-(trimethylamino)ethyl phosphate, etc., but is not limited thereto.

[0052] In some embodiments, the preparation method specifically comprises:

[0053] The hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane is immersed in an aqueous solution containing an amine monomer for 1 to 30 minutes and then taken out. After drying, it is immersed in an oil phase solution containing an acyl chloride monomer, and an interfacial polymerization reaction is carried out for 0.5 to 10 minutes. Then, it is taken out and heat-treated at 30 to 90° C. for 1 to 30 minutes to generate a polyamide layer. It is then immersed in an acidic aqueous solution to remove the zeolite imidazole skeleton material, thereby obtaining an ultra-thin PE-based multi-layer composite forward osmosis membrane.

[0054] In some embodiments, the preparation method includes: dissolving an amine monomer (hereinafter also referred to as an aqueous phase monomer) in water to prepare the aqueous phase solution containing the amine monomer.

[0055] Furthermore, the concentration of the amine monomer in the aqueous solution containing the amine monomer is 1 to 100 g / L.

[0056] In some embodiments, the amine monomer includes any one or a combination of two or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, and piperazine, but is not limited thereto, and the solvent is water.

[0057] In some embodiments, the preparation method includes: dissolving an acyl chloride monomer (hereinafter also referred to as an oil phase monomer) in an organic solvent immiscible with water to prepare the oil phase solution containing the acyl chloride monomer.

[0058] Furthermore, the concentration of the acyl chloride monomer in the oil phase solution containing the acyl chloride monomer is 1 to 50 g / L.

[0059] In some embodiments, the acyl chloride monomer includes any one or a combination of two or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride, but is not limited thereto.

[0060] Furthermore, the organic solvent includes n-hexane, but is not limited thereto.

[0061] Among them, as one of the more specific embodiments, the preparation method of the ultra-thin PE-based composite forward osmosis membrane may include the following steps:

[0062] (1) 0.5-5 g of tannic acid and 2-10 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The membrane was reacted at 20-90° C. for 0.5-24 h, and then taken out. The membrane was quickly immersed in a methanol solution of 2-methylimidazole with a mass concentration of 5-50%, and then reacted at room temperature for 1-48 h. The membrane was taken out to obtain an ultra-thin PE porous membrane modified with a zeolite imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane.

[0063] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, an inert gas was introduced, and the glow discharge switch was turned on to induce the hydrophilic charged monomer in the reaction chamber to decompose, polymerize, and deposit on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named hydrophilic polymer / ZIF-8 / PE porous membrane;

[0064] (3) The polymer / ZIF-8 / PE porous membrane is immersed in an aqueous solution containing an aqueous monomer for 1 to 30 minutes, taken out, drained of the surface moisture, and immersed in an oily solution containing an oily monomer. After reacting for 0.5 to 10 minutes, the membrane is taken out and heat-treated at 30 to 90°C for 1 to 30 minutes to generate a polyamide (PA) layer. The membrane is immersed in an aqueous solution with a pH value of 1 to remove the ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, named PA / polymer / PE composite forward osmosis membrane, which is applied to the forward osmosis process to achieve seawater desalination / wastewater purification.

[0065] In the preparation method of the present invention, the zeolite imidazole framework material ZIF-8 and plasma are synergistically used to construct a hydrophilic charged transition layer with a wrinkled structure. On the one hand, the retention rate of inorganic salt ions is improved based on the Donan effect; on the other hand, the wrinkled structure formed by the hydrophilic polymer provides nano-water channels, thereby improving the water flux of the forward osmosis membrane.

[0066] Moreover, the aqueous solution easily spreads on the surface of the hydrophilic transition layer during the interfacial polymerization reaction, and the polyamide layer formed by the interfacial polymerization is uniform and defect-free, ensuring the membrane's retention rate for solutes such as inorganic salts and dyes.

[0067] As another aspect of the technical solution of the present invention, it also relates to an ultra-thin PE-based multi-layer composite forward osmosis membrane prepared by the aforementioned method, which includes an ultra-thin PE porous support layer, a charged corrugated transition layer and a polyamide layer stacked in sequence in the thickness direction, wherein the charged corrugated transition layer includes a hydrophilic polymer formed by a polymerization reaction of a hydrophilic charged monomer, and the hydrophilic polymer constructs a corrugated structure and provides nano water channels.

[0068] Furthermore, the total thickness of the ultra-thin PE-based composite forward osmosis membrane is 100 to 1000 nm.

[0069] Furthermore, the pure water flux of the ultra-thin PE-based composite forward osmosis membrane is 54 to 121 Lm -2 h -1 , reverse salt flux is 2~38gm -2 h -1 The retention rate of inorganic salts is 63-99%, and the retention rate of dyes is 72-99.9%.

[0070] Furthermore, the inorganic salt includes sodium chloride, but is not limited thereto.

[0071] Furthermore, the dye includes rhodamine B, but is not limited thereto.

[0072] Another aspect of the embodiments of the present invention further provides the application of the aforementioned ultra-thin PE-based multi-layer composite forward osmosis membrane in the field of water treatment.

[0073] Furthermore, the application includes: application of the ultra-thin PE-based multi-layer composite forward osmosis membrane in seawater desalination or sewage purification.

[0074] Through the above-mentioned technical solution, the present invention provides a composite forward osmosis membrane with high flux and high retention rate by synergizing the high porosity and low structural parameters of the ultra-thin PE porous support membrane, the nano-water channels of the charged corrugated transition layer, and the high cross-linking degree and large specific surface area of ​​the polyamide layer. The polyamide layer formed by interfacial polymerization is uniform and defect-free, ensuring the membrane's retention rate for solutes such as inorganic salts and dyes. The composite membrane is used in the forward osmosis process to realize the fields of seawater desalination, sewage purification, etc.

[0075] The following describes the technical solution of the present invention in more detail with reference to several preferred embodiments and accompanying drawings. The specific embodiments described below are intended only to further illustrate and explain the present invention and are not intended to limit the present invention. All variations that can be derived from or inferred from the present disclosure are considered to be within the scope of protection of the present invention.

[0076] Example 1

[0077] (1) 0.5 g of tannic acid and 2 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The membrane was reacted at 20°C for 0.5 h, removed, and quickly immersed in a 5% methanol solution of 2-methylimidazole. The membrane was reacted at room temperature for 1 h, and removed to obtain an ultrathin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane.

[0078] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 0.5 min to induce the cleavage-polymerization-deposition of methacrylamide placed in its reaction chamber on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named polyacrylamide / ZIF-8 / PE porous membrane;

[0079] (3) The polyacrylamide / ZIF-8 / PE porous membrane was immersed in an aqueous solution of m-phenylenediamine with a concentration of 1 g / L, taken out after soaking for 1 min, and the surface moisture was drained. The membrane was then immersed in an n-hexane solution of trimesoyl chloride with a concentration of 1 g / L, reacted for 0.5 min, taken out, and heat-treated at 30°C for 1 min to generate a polyamide (PA) layer. The membrane was immersed in an aqueous solution with a pH value of 1 to remove ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, which was named PA / polyacrylamide / PE composite forward osmosis membrane.

[0080] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 54Lm when 1mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 17gm -2 h -1 The retention rate of sodium chloride is 70%, and the retention rate of rhodamine B is 90.3%.

[0081] Example 2

[0082] (1) 5 g of tannic acid and 10 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The membrane was reacted at 90° C. for 24 h, removed, and quickly immersed in a methanol solution of 50% by mass of 2-methylimidazole. The membrane was reacted at room temperature for 48 h, and removed to obtain an ultrathin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane.

[0083] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 10 min to induce the cleavage-polymerization-deposition of methacrylamide placed in its reaction chamber on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named polymethacrylamide / ZIF-8 / PE porous membrane;

[0084] (3) The poly(methacrylamide) / ZIF-8 / PE porous membrane was immersed in an aqueous solution of o-phenylenediamine with a concentration of 100 g / L, taken out after soaking for 30 minutes, and the surface moisture was drained. The membrane was then immersed in an n-hexane solution of terephthaloyl chloride with a concentration of 50 g / L, reacted for 10 minutes, taken out, and heat-treated at 90°C for 30 minutes to generate a polyamide (PA) layer. The membrane was immersed in an aqueous solution with a pH value of 1 to remove ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, which was named PA / poly(methacrylamide) / PE composite forward osmosis membrane.

[0085] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 93Lm when 1mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 7gm -2 h-1 The retention rate of sodium chloride is 91%, and the retention rate of rhodamine B is 99.6%.

[0086] Example 3

[0087] (1) 3 g of tannic acid and 5 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The membrane was reacted at 40°C for 10 h, removed, and quickly immersed in a methanol solution of 25% by mass of 2-methylimidazole. The membrane was reacted at room temperature for 24 h, and removed to obtain an ultrathin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane.

[0088] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 5 minutes to induce the methacryloyloxyethyltrimethylammonium chloride placed in its reaction chamber to decompose, polymerize, and deposit on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named polymethacryloyloxyethyltrimethylammonium chloride / ZIF-8 / PE porous membrane;

[0089] (3) The poly(methacryloyloxyethyltrimethylammonium chloride) / ZIF-8 / PE porous membrane was immersed in an aqueous solution of p-phenylenediamine with a concentration of 10 g / L, taken out after soaking for 20 minutes, and the surface moisture was drained. The membrane was then immersed in an n-hexane solution of isophthaloyl chloride with a concentration of 20 g / L, reacted for 5 minutes, taken out, and heat-treated at 60°C for 5 minutes to generate a polyamide (PA) layer. The membrane was immersed in an aqueous solution with a pH value of 1 to remove ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, which was named PA / poly(methacryloyloxyethyltrimethylammonium chloride) / PE composite forward osmosis membrane.

[0090] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 74Lm when 1mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 5gm -2 h -1 The retention rate of sodium chloride is 63%, and the retention rate of rhodamine B is 72%.

[0091] Example 4

[0092] (1) 2 g of tannic acid and 4 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, added to a PE porous membrane, reacted at 40°C for 12 h, removed, and quickly immersed in a 30% 2-methylimidazole methanol solution, reacted at room temperature for 14 h, removed, and obtained an ultrathin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, named ZIF-8 / PE porous membrane;

[0093] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 5 minutes to induce the cracking, polymerization, and deposition of acrylic acid in the reaction chamber on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named polyacrylic acid / ZIF-8 / PE porous membrane;

[0094] (3) The polyacrylic acid / ZIF-8 / PE porous membrane was immersed in an aqueous solution with a concentration of 30 / L piperazine, taken out after soaking for 15 minutes, and the surface moisture was drained. It was then immersed in an n-hexane solution with a concentration of 5g / L phthaloyl chloride, reacted for 3 minutes, taken out, and heat-treated at 80°C for 10 minutes to generate a polyamide (PA) layer. The membrane was immersed in an aqueous solution with a pH value of 1 to remove ZIF-8, and an ultra-thin PE-based multilayer composite forward osmosis membrane was obtained, which was named PA / polyacrylic acid / PE composite forward osmosis membrane.

[0095] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 121Lm when 1mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 18gm -2 h -1 The retention rate of sodium chloride is 94%, and the retention rate of rhodamine B is 99.9%.

[0096] Example 5

[0097] (1) 4 g of tannic acid and 4 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The membrane was reacted at 40°C for 15 h, and then taken out. The membrane was quickly immersed in a 10% 2-methylimidazole methanol solution, and the reaction was continued at room temperature for 20 h. The membrane was taken out to obtain an ultra-thin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane. The upper surface of the PE porous membrane can be seen in the enlarged scanning electron microscope image. Figure 2 As shown;

[0098] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 1 min to induce the 2-acrylamido-2-methyl-1-propane sulfonic acid placed in its reaction chamber to decompose, polymerize, and deposit on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named poly(2-acrylamido-2-methyl-1-propane sulfonic acid) / ZIF-8 / PE porous membrane;

[0099] (3) The poly(2-acrylamido-2-methyl-1-propanesulfonic acid) / ZIF-8 / PE porous membrane was immersed in an aqueous solution of m-phenylenediamine at a concentration of 50 g / L for 30 min, removed, and the surface water was drained. The membrane was then immersed in an n-hexane solution of trimesoyl chloride at a concentration of 10 g / L, reacted for 10 min, removed, and heat-treated at 75°C for 6 min to form a polyamide (PA) layer. The membrane was immersed in an aqueous solution of pH 1 to remove the ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, named PA / poly(2-acrylamido-2-methyl-1-propanesulfonic acid) / PE composite forward osmosis membrane. A partial magnified scanning electron micrograph of its upper surface is shown in FIG. Figure 3 .

[0100] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 106 Lm when 1 mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 6gm -2 h -1 The retention rate of sodium chloride is 98%, and the retention rate of rhodamine B is 99.9%.

[0101] Example 6

[0102] (1) 2.5 g of tannic acid and 7.5 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The mixture was reacted at 40°C for 8 h, and then the membrane was taken out and quickly immersed in a methanol solution of 2-methylimidazole with a mass concentration of 12%. The membrane was reacted at room temperature for 9 h and then taken out to obtain an ultrathin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane.

[0103] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 6 minutes to induce the decomposition, polymerization, and deposition of 3-sulfonate propyl methacrylate potassium salt placed in the reaction chamber on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named poly (3-sulfonate propyl methacrylate potassium salt) / ZIF-8 / PE porous membrane;

[0104] (3) The poly (3-sulfonated propyl methacrylate potassium salt) / ZIF-8 / PE porous membrane was immersed in an aqueous solution with a concentration of 50 g / L m-phenylenediamine, taken out after soaking for 30 minutes, and the surface moisture was drained. Then, the membrane was immersed in an n-hexane solution with a concentration of 10 g / L trimesoyl chloride, reacted for 10 minutes, taken out, and heat-treated at 75°C for 6 minutes to generate a polyamide (PA) layer. The membrane was immersed in an aqueous solution with a pH value of 1 to remove ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, which was named PA / poly (3-sulfonated propyl methacrylate potassium salt) / PE composite forward osmosis membrane.

[0105] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 69Lm when 1mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 32gm -2 h -1 The retention rate of sodium chloride is 87%, and the retention rate of rhodamine B is 92.1%.

[0106] Example 7

[0107] (1) 3 g of tannic acid and 9 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The membrane was reacted at 40°C for 5 h, removed, and quickly immersed in a 5% methanol solution of 2-methylimidazole. The membrane was reacted at room temperature for 16 h, and removed to obtain an ultrathin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane.

[0108] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 3 minutes to induce the decomposition, polymerization, and deposition of 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt placed in the reaction chamber on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named poly(3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt) / ZIF-8 / PE porous membrane;

[0109] (3) The poly(3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt) / ZIF-8 / PE porous membrane was immersed in an aqueous solution with a concentration of 50 g / L m-phenylenediamine, taken out after soaking for 30 minutes, and the surface moisture was drained. The membrane was then immersed in an n-hexane solution with a concentration of 10 g / L trimesoyl chloride, reacted for 10 minutes, taken out, and heat-treated at 75°C for 6 minutes to generate a polyamide (PA) layer. The membrane was immersed in an aqueous solution with a pH of 1 to remove ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, which was named PA / poly(3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt) / PE composite forward osmosis membrane.

[0110] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 73Lm when 1mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 38gm -2 h -1 The retention rate of sodium chloride is 82%, and the retention rate of rhodamine B is 89.3%.

[0111] Example 8

[0112] (1) 3 g of tannic acid and 5 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The membrane was reacted at 40°C for 4 h, removed, and quickly immersed in a methanol solution of 2-methylimidazole with a mass concentration of 11%, reacted at room temperature for 15 h, and removed to obtain an ultrathin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane.

[0113] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 8 minutes to induce the decomposition, polymerization, and deposition of methacryloylethyl sulfobetaine on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named polymethacryloylethyl sulfobetaine / ZIF-8 / PE porous membrane;

[0114] (3) The poly(methacryloylethyl)sulfobetaine / ZIF-8 / PE) porous membrane was immersed in an aqueous solution of m-phenylenediamine at a concentration of 80 g / L for 10 min, taken out, and the surface moisture was drained. The membrane was then immersed in an n-hexane solution of trimesoyl chloride at a concentration of 20 g / L, reacted for 2 min, taken out, and heat-treated at 45 °C for 8 min to generate a polyamide (PA) layer. The membrane was immersed in an aqueous solution with a pH value of 1 to remove ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, which was named PA / poly(methacryloylethyl)sulfobetaine / PE composite forward osmosis membrane.

[0115] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 104Lm when 1mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 2gm -2 h -1 The retention rate of sodium chloride is 99%, and the retention rate of rhodamine B is 99.8%.

[0116] Example 9

[0117] (1) 3.5 g of tannic acid and 6 g of zinc nitrate hexahydrate were dissolved in a mixed solvent consisting of 50 mL of water and 50 mL of methanol, and a PE porous membrane was added. The membrane was reacted at 40°C for 21 h, removed, and quickly immersed in a methanol solution of 46% 2-methylimidazole. The membrane was reacted at room temperature for 32 h, and removed to obtain an ultrathin PE porous membrane modified with a zeolitic imidazole framework material ZIF-8, which was named ZIF-8 / PE porous membrane.

[0118] (2) The ZIF-8 / PE porous membrane was placed in a plasma generator, inert gas was introduced, and the glow discharge switch was turned on for 2 minutes to induce the cleavage, polymerization, and deposition of 2-(methacryloyloxy)ethyl-2-(trimethylamino)ethyl phosphate in the reaction chamber on the surface of the ZIF-8 modified ultrathin PE porous membrane, which was named poly(2-(methacryloyloxy)ethyl-2-(trimethylamino)ethyl phosphate) / ZIF-8 / PE porous membrane;

[0119] (3) The poly(2-(methacryloyloxy)ethyl-2-(trimethylamino)ethyl phosphate) / ZIF-8 / PE porous membrane was immersed in an aqueous solution with a concentration of 75 / L m-phenylenediamine, taken out after soaking for 5 minutes, and the surface moisture was drained. The membrane was then immersed in an n-hexane solution with a concentration of 40 g / L trimesoyl chloride, reacted for 10 minutes, taken out, and heat-treated at 55°C for 15 minutes to generate a polyamide (PA) layer. The membrane was immersed in an aqueous solution with a pH value of 1 to remove ZIF-8, thereby obtaining an ultra-thin PE-based multilayer composite forward osmosis membrane, which was named PA / poly(2-(methacryloyloxy)ethyl-2-(trimethylamino)ethyl phosphate) / PE composite forward osmosis membrane.

[0120] The test showed that the pure water flux of the forward osmosis membrane prepared in this embodiment was 83Lm when 1mol / L sodium chloride solution was used as the draw liquid. -2 h -1 , reverse salt flux is 27gm -2 h -1 The retention rate of sodium chloride is 84%, and the retention rate of rhodamine B is 96.1%.

[0121] Comparative Example 1: This comparative example is basically the same as Example 5, except that the PE porous membrane is not modified with the zeolite imidazole framework material ZIF-8. The forward osmosis membrane obtained in this comparative example uses 1 mol / L sodium chloride solution as the draw solution, and the pure water flux is 1.3 L m -2 h -1 , reverse salt flux is 42gm -2 h -1 The retention rate of sodium chloride is 14%, and the retention rate of rhodamine B is 54%.

[0122] Comparative Example 2: This comparative example is basically the same as Example 5, except that no hydrophilic charged polymer transition layer is introduced. The forward osmosis membrane obtained in this comparative example uses 1 mol / L sodium chloride solution as the draw solution, and the pure water flux is 4.5 L m -2 h -1 , reverse salt flux is 51gm -2 h -1 The retention rate of sodium chloride is 5%, and the retention rate of rhodamine B is 29%.

[0123] Comparative Example 3: This comparative example is basically the same as Example 5, except that the zeolite imidazole framework material ZIF-8 is not removed. The forward osmosis membrane obtained in this comparative example uses 1 mol / L sodium chloride solution as the draw solution, and the pure water flux is 29 L m -2 h -1 , reverse salt flux is 11gm -2 h -1 The retention rate of sodium chloride is 27%, and the retention rate of rhodamine B is 75%.

[0124] Comparative Example 4: This comparative example is basically the same as Example 5, except that the intermediate hydrophilic polymer layer does not have a pleated structure. The forward osmosis membrane obtained in this comparative example uses 1 mol / L sodium chloride solution as the draw solution, and the pure water flux is 5 L m -2 h -1 , reverse salt flux is 24gm -2 h -1 The retention rate of sodium chloride is 3%, and the retention rate of rhodamine B is 10%.

[0125] In addition, the inventors of this case also conducted experiments with other raw materials and conditions listed in this specification, referring to the methods of Examples 1 to 9, and also produced a composite forward osmosis membrane with high flux, low salt flux and high salt retention rate.

[0126] Although the present invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions, and / or additions may be made and that substantial equivalents may be substituted for the elements of the embodiments without departing from the spirit and scope of the present invention. Additionally, many modifications may be made to adapt specific circumstances or materials to the teachings of the present invention without departing from the scope of the present invention. Therefore, it is not intended herein to limit the present invention to the disclosed specific embodiments for carrying out the present invention, but rather to include all embodiments within the scope of the appended claims. Furthermore, unless specifically stated, any use of the terms first, second, etc. does not indicate any order or importance, but rather uses the terms first, second, etc. to distinguish one element from another.

Claims

1. A method for preparing an ultra-thin PE-based multi-layer composite forward osmosis membrane, characterized in that include: The zeolite imidazole framework material is modified on the surface of the PE porous membrane to obtain the zeolite imidazole framework material / PE porous membrane; Plasma treatment is performed on the zeolite imidazole framework material / PE porous membrane, thereby inducing hydrophilic charged monomers to decompose, polymerize, and deposit on the surface of the zeolite imidazole framework material / PE porous membrane to obtain a hydrophilic polymer / zeolite imidazole framework material / PE porous membrane; as well as, The surface of the hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane is first fully contacted with an aqueous solution containing an amine monomer, and then fully contacted with an oil phase solution containing an acyl chloride monomer after drying. The amine monomer and the acyl chloride monomer are subjected to an interfacial polymerization reaction on the surface of the hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane and heat-treated to generate a polyamide layer. The zeolite imidazole skeleton material is then removed to obtain an ultra-thin PE-based multi-layer composite forward osmosis membrane.

2. The preparation method according to claim 1, wherein Specifically include: A mixed system comprising tannic acid, a zinc source, and a solvent is brought into contact with a PE porous membrane and reacted at 20 to 90° C. for 0.5 to 24 hours. The membrane is then quickly immersed in a methanol solution of 5 to 50% 2-methylimidazole by mass and reacted at room temperature for 1 to 48 hours to obtain a zeolite imidazole framework material / PE porous membrane. The mass ratio of the tannic acid to the zinc source is 0.5-5:2-10, the zinc source includes zinc nitrate, and the solvent includes a combination of water and methanol.

3. The preparation method according to claim 1, wherein Specifically include: The zeolite imidazole skeleton material / PE porous membrane is placed in a plasma generator containing hydrophilic charged monomers, an inert gas is introduced, a glow discharge switch is turned on, and plasma treatment is performed for 0.5 to 10 minutes, thereby inducing the hydrophilic charged monomers in the reaction chamber to decompose, polymerize, and deposit on the surface of the zeolite imidazole skeleton material / PE porous membrane to obtain a hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane.

4. The preparation method according to claim 3, wherein: The hydrophilic charged monomer includes any one or a combination of two or more of methacrylamide, methacryloxyethyltrimethylammonium chloride, acrylic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, 3-sulfopropyl methacrylate potassium salt, 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt, methacrylethyl sulfobetaine, and 2-(methacryloyloxy)ethyl-2-(trimethylamino)ethyl phosphate.

5. The preparation method according to claim 1, characterized in that Specifically include: The hydrophilic polymer / zeolite imidazole skeleton material / PE porous membrane is immersed in an aqueous solution containing an amine monomer for 1 to 30 minutes and then taken out. After drying, it is immersed in an oil phase solution containing an acyl chloride monomer, and an interfacial polymerization reaction is carried out for 0.5 to 10 minutes. Then, it is taken out and heat-treated at 30 to 90° C. for 1 to 30 minutes to generate a polyamide layer. It is then immersed in an acidic aqueous solution to remove the zeolite imidazole skeleton material, thereby obtaining an ultra-thin PE-based multi-layer composite forward osmosis membrane.

6. The preparation method according to claim 5, characterized in that include: The amine monomer is dissolved in water to prepare the aqueous phase solution containing the amine monomer.

7. The preparation method according to claim 6, characterized in that: The concentration of the amine monomer in the aqueous solution containing the amine monomer is 1 to 100 g / L.

8. The preparation method according to claim 6, characterized in that: The amine monomer includes any one or a combination of two or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine and piperazine.

9. The preparation method according to claim 5, characterized in that include: The acyl chloride monomer is dissolved in an organic solvent that is immiscible with water to prepare the oil phase solution containing the acyl chloride monomer.

10. The preparation method according to claim 9, characterized in that The concentration of the acyl chloride monomer in the oil phase solution containing the acyl chloride monomer is 1 to 50 g / L.

11. The preparation method according to claim 9, characterized in that The acyl chloride monomer includes any one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and phthaloyl chloride, or a combination of two or more thereof; and the organic solvent includes n-hexane.

12. An ultra-thin PE-based multi-layer composite forward osmosis membrane prepared by the preparation method according to any one of claims 1 to 11, wherein the ultra-thin PE-based multi-layer composite forward osmosis membrane comprises an ultra-thin PE porous support layer, a charged corrugated transition layer and a polyamide layer stacked in sequence in the thickness direction, wherein the charged corrugated transition layer comprises a hydrophilic polymer formed by polymerization of a hydrophilic charged monomer, and the hydrophilic polymer forms a corrugated structure and provides nano-water channels.

13. The ultra-thin PE-based multi-layer composite forward osmosis membrane according to claim 12, characterized in that: The porosity of the ultra-thin PE porous support layer is 40-60%, the diameter of the contained pores is 0.02-0.1 μm, and the thickness of the ultra-thin PE porous support layer is 7 μm.

14. The ultra-thin PE-based multi-layer composite forward osmosis membrane according to claim 12, characterized in that: The thickness of the charged wrinkled transition layer is 100 to 1000 nm.

15. The ultra-thin PE-based multi-layer composite forward osmosis membrane according to claim 12, characterized in that: The thickness of the polyamide layer is 10 to 500 nm, the cross-linking degree of the polyamide layer is 50 to 95%, and the specific surface area is 220 to 3000 m 2 / g.

16. The ultra-thin PE-based multi-layer composite forward osmosis membrane according to claim 12, characterized in that: The total thickness of the ultra-thin PE-based multi-layer composite forward osmosis membrane is 7.11-8.5 μm.

17. The ultra-thin PE-based multi-layer composite forward osmosis membrane according to claim 12, characterized in that: The pure water flux of the ultra-thin PE-based multi-layer composite forward osmosis membrane is 54 to 121 Lm -2 h -1 , reverse salt flux is 2~38gm -2 h -1 The retention rate of inorganic salts is 63-99%, and the retention rate of dyes is 72-99.9%. The inorganic salts include sodium chloride, and the dyes include rhodamine B.

18. Use of the ultra-thin PE-based multi-layer composite forward osmosis membrane according to any one of claims 12 to 17 in the field of seawater desalination or sewage purification.

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