High-flux pollution-resistant composite reverse osmosis membrane and preparation method thereof

Abstract

The invention discloses a high-flux pollution-resistant polyamide composite reverse osmosis membrane prepared by surface modification and a preparation method, the preparation method of the high-flux pollution-resistant polyamide composite reverse osmosis membrane prepared by surface modification comprises the following steps: firstly, introducing multistage amine small molecules to the surface of a polyamide layer of a composite membrane; small molecule groups with positive charges are introduced to the surface of the polyamide composite membrane through layer-by-layer interfacial polymerization, small molecules can be coupled with carboxylic acid groups with negative charges on the surface of the polyamide membrane, and a zwitterionic surface is formed by balancing surface charges, so that the polyamide composite membrane with high water flux and certain antifouling capacity is obtained. Then a quaternary ammonium salt type cationic surfactant with active groups is introduced to the surface of the modified polyamide layer, one end of a molecule of the quaternary ammonium salt type cationic surfactant is quaternary ammonium salt, the other end of the molecule of the quaternary ammonium salt type cationic surfactant is an epoxy group with very high reaction activity, and the antifouling stability of the composite membrane is further improved. The membrane prepared by the invention has the advantages of simple preparation method, ultra-thin desalting layer, high flux and high stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of reverse osmosis composite membranes, and particularly relates to a high-flux fouling-resistant composite reverse osmosis membrane and a preparation method thereof. Background Art

[0002] In the application process of reverse osmosis membrane water treatment technology, how to improve the water flux and anti-fouling stability of the membrane under fixed pressure conditions is of great significance for cost and energy consumption savings. The level of water flux during the operation of the membrane is mainly affected by the "effective thickness" of the desalination layer of the membrane. Reducing the thickness of the desalination layer of the membrane can effectively improve the membrane flux. Early studies found that a reverse osmosis membrane with a cross-linked polyamide as the active separation layer obtained by interfacial polymerization using a polysulfone ultrafiltration membrane as the substrate, an aqueous solution of m-phenylenediamine as the aqueous phase, and trimellitic acid chloride monomer as the organic phase has a relatively high water flux.

[0003] Currently, among the means of improving the water flux and anti-fouling performance of reverse osmosis membranes, surface modification of the polyamide layer and introduction of interfacial polymerization additives can effectively regulate the interfacial polymerization process, with the advantages of low cost, simple process, and remarkable effects. During the interfacial polymerization process, the diffusion rate of monomers is affected by introducing additives to regulate the interfacial polymerization process and the separation performance of the composite membrane. Although this method has a simple process and low cost, when the membrane permeation flux is increased, the membrane rejection rate decreases significantly, and the long-term operation performance of the membrane also decreases significantly. The existing methods for improving the water flux of polyamide composite membranes mainly include: (1) Modifying the surface active layer of the polyamide composite membrane, mainly including two methods: surface modification and doping of inorganic nanomaterials in the active layer. (2) Doping various additives in the aqueous solution of polyamine and the oil phase solution of polyacyl chloride. (3) Designing and developing new polyamine and polyacyl chloride monomers for the preparation of high-flux polyamide composite membranes. The prior art also mentions that introducing materials containing hydrophilic groups can effectively improve the hydrophilicity of the membrane surface and thus increase the water flux of the membrane.

[0004] Chinese Patent Application Publication No. CN 112316752A discloses a preparation method of a sulfonamide small molecule surface-modified polyamide composite membrane. A modified membrane is obtained by grafting small molecule monomers with amino and sulfonamide functional groups onto the surface of the polyamide composite membrane through secondary interfacial polymerization. The hydrophilicity of the membrane surface is improved by utilizing the hydrophilicity of the sulfonamide group. However, the degree of flux improvement by this method cannot meet the actual industrial requirements.

[0005] The Chinese invention patent with the publication number CN 114618313A discloses a preparation method of a high-flux anti-pollution reverse osmosis composite membrane. By constructing a hydrophilic skeleton layer with a two-dimensional or three-dimensional pore structure between the anti-pollution coating and the reverse osmosis substrate membrane, a water molecule transport channel is formed, thereby achieving the improvement of the membrane anti-pollution property while reducing the loss of the membrane water flux. After long-term operation, the water flux of the membrane prepared by this method decreases significantly. Summary of the Invention

[0006] In order to solve the above problems, the present invention aims to provide a method for preparing a high-flux anti-pollution polyamide composite reverse osmosis membrane by surface modification.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A high-flux anti-pollution polyamide composite reverse osmosis membrane prepared by surface modification, including a polyamide layer modified by a positively charged small molecule and a quaternary ammonium salt type cationic surfactant, and the polyamide layer covers the surface of the porous substrate membrane;

[0008] The polyamide layer modified by the positively charged small molecule and the quaternary ammonium salt type cationic surfactant first adopts an acylation reaction between the highly active amino group of the multi-stage amine small molecule and the excess acyl chloride group on the surface of the polyamide membrane. Through secondary interfacial polymerization, a small molecule with a positively charged group is introduced onto the polyamide membrane to obtain an amphoteric ion surface, and then a quaternary ammonium salt type cationic surfactant with an active group is introduced onto its surface; the positively charged small molecule is coupled with the negatively charged carboxylic acid group on the surface of the polyamide membrane to form an amphoteric ion surface by balancing its surface charge. One end of the quaternary ammonium salt type cationic surfactant is a quaternary ammonium salt, and the other end is an epoxy group with high reactivity; the purpose of the secondary surface modification is to introduce the functional group quaternary ammonium salt into the polymer molecular chain on the membrane surface, thereby further improving the anti-fouling stability performance of the composite membrane.

[0009] Preferably, the positively charged small molecule is at least one of N,N-dimethylethylenediamine and triethylenediamine.

[0010] Preferably, the average pore diameter of the porous substrate membrane is 8 - 10 nm.

[0011] Preferably, the thickness of the polyamide layer is 90 - 130 nm.

[0012] A method for preparing a surface-modified high-flux anti-pollution polyamide composite reverse osmosis membrane mainly includes the following steps:

[0013] Step 1: Treat the porous substrate membrane. Immerse the porous substrate membrane in an alkaline aqueous solution containing polyamine, make full contact, take out the porous substrate membrane and remove the excess water droplets on its surface;

[0014] Step 2: Prepare the polyamide desalination layer. Immerse the porous substrate membrane treated in Step 1 into the oil-phase solution containing polyacyl chloride, make full contact, conduct interfacial polymerization reaction to form the polyamide desalination layer, and pour out the residual acyl chloride oil-phase solution from above the membrane. Then place it in an oven at 50 °C for thermal crosslinking for 5 min;

[0015] Step 3: Add the modified reagent solution to the surface of the polyamide desalination layer membrane in Step 2 and keep it for 1 - 3 min;

[0016] Step 4: Obtain the surface-modified polyamide composite membrane. Wash the membrane obtained in Step 3 with an aqueous solution containing organic acid to remove the residual substances on the surface. Then place it in an oven at 70 °C for thermal crosslinking for 10 min to obtain the surface-modified high-flux fouling-resistant polyamide composite reverse osmosis membrane;

[0017] Step 5: Fix the modified polyamide composite membrane in a polytetrafluoroethylene frame, repeatedly rinse the membrane surface with pure water, then pour the glycidyltrimethylammonium chloride solution into the frame, wrap and seal the frame with plastic wrap, and place it in a constant temperature and humidity chamber for light-shielded reaction;

[0018] Step 6: Repeatedly rinse the surface of the membrane after the reaction with pure water and immerse it in deionized water for storage for later use.

[0019] Preferably, in Step 1, the contact time of the porous substrate membrane with the aqueous solution is 1 - 3 min, and the polyamine aqueous solution monomer is one of m-phenylenediamine or piperazine; preferably, the polyamine aqueous solution monomer is m-phenylenediamine, and the mass concentration of m-phenylenediamine is 1.0 - 8.0 wt%.

[0020] Preferably, in Step 2, the contact time of the porous substrate membrane immersed in the acyl chloride oil-phase solution is 1 - 2 min, and the polyacyl chloride is one of oxalyl chloride or trimesoyl chloride; preferably, it is trimesoyl chloride, and the mass concentration of trimesoyl chloride is 0.05 - 0.5 wt%, and the balance is an organic solvent.

[0021] Preferably, the organic solvent is one or more of chlorobenzene, dichloromethane, ethylcyclohexane, toluene, m-xylene, mesitylene, cyclohexane, n-heptane, isopar E, isopar G, isopar H, isopar M.

[0022] Preferably, the modified reagent solution in Step 3 is a solution of positively charged small molecules.

[0023] Preferably, the organic acid in Step 4 is at least one of acetic acid, malic acid, citric acid, camphorsulfonic acid, oxalic acid, tartaric acid, benzoic acid, salicylic acid, the mass concentration of the organic acid solution is 10 - 13%, the washing time is 5 - 10 min, and the temperature is 50 - 55 °C.

[0024] Preferably, in step 5, the mass fraction of the glycidyltrimethylammonium chloride solution is 5-10 wt%, the temperature of the thermostatic and humidified climate chamber is 30-35 °C, and the light-shielded reaction time is 5-10 h.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) For a surface-modified high-flux anti-fouling polyamide composite reverse osmosis membrane of the present invention, the hydrophilicity of the membrane surface is increased through functional amino groups, greatly improving the mass transfer rate of water molecules, significantly enhancing the water flux of the membrane, while the rejection rate of the membrane changes little.

[0027] (2) For a surface-modified high-flux anti-fouling polyamide composite reverse osmosis membrane of the present invention, positively charged multi-stage amine small molecule groups are introduced onto the surface of the polyamide membrane through secondary interfacial polymerization to consume the negative charges on the newly formed polyamide membrane, balancing its surface charges to form an amphoteric ion surface, thereby enhancing the anti-fouling stability performance of the composite membrane.

[0028] (3) For a surface-modified high-flux anti-fouling polyamide composite reverse osmosis membrane of the present invention, after being modified with positively charged multi-stage amine small molecules, a quaternary ammonium salt type cationic surfactant is further introduced onto the membrane surface. One end of its molecule is a quaternary ammonium salt, and the other end is an epoxy group with high reactivity. Through the reaction of the epoxy group with the highly active amino group, the quaternary ammonium salt is introduced into the molecular chain on the membrane surface, further endowing the reverse osmosis membrane with excellent anti-fouling stability performance.

[0029] (4) For a surface-modified high-flux anti-fouling polyamide composite reverse osmosis membrane of the present invention, positively charged small molecules and a quaternary ammonium salt type cationic surfactant are introduced onto the surface of the polyamide membrane through layer-by-layer interfacial polymerization. First, they are coupled with negatively charged carboxylic acid groups to form an amphoteric ion surface, significantly enhancing the performance of the membrane. Then, the anti-fouling stability performance of the composite membrane is enhanced without significantly reducing the water flux. While maintaining a high water flux, it has good removal ability for various inorganic salt ions, and the preparation method is simple. Specific embodiments

[0030] The present invention will be further described below according to specific embodiments, but it should not be understood that the scope of the subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, all modifications, substitutions, and changes made according to ordinary technical knowledge and conventional means in the art are included in the scope of the present invention.

[0031] Example 1: A method for preparing a surface-modified high-flux anti-fouling polyamide composite reverse osmosis membrane and the membrane prepared thereby. The composite membrane comprises a porous substrate membrane and a polyamide layer modified with small molecules. The polyamide layer covers the surface of the porous substrate membrane.

[0032] The positively charged small molecule is N,N-dimethylethylenediamine.

[0033] The method for preparing a surface-modified high-flux anti-fouling polyamide composite reverse osmosis membrane comprises the following steps:

[0034] Step 1: Immerse a porous substrate membrane with an average pore size of 10 nm into an aqueous solution containing 6.0 wt% of m-phenylenediamine, and keep in full contact for 2 min. Take out the substrate membrane and remove the excess water droplets on its surface.

[0035] Step 2: Immerse the membrane obtained in Step 1 into an organic solution containing 0.3 wt% of trimesoyl chloride, and keep in full contact for 1 min to carry out an interfacial polymerization reaction to form a polyamide desalination layer. Pour out the residual acyl chloride organic solution from above the membrane, and then put it into an oven at 50 °C for thermal crosslinking for 5 min.

[0036] Step 3: Wash the membrane obtained in Step 2 thoroughly with deionized water, then gently add a 0.5 wt% N,N-dimethylethylenediamine modification reagent solution to the surface of the membrane obtained in Step 2, keep for 2 min, and then take out.

[0037] Step 4: Wash the modified membrane obtained in Step 3 with an organic acid solution with a mass concentration of 12% and a temperature of 50 °C for 10 min to remove the residual substances on the surface, and then put it into an oven at 70 °C for thermal crosslinking for 10 min.

[0038] Example 2: A method for preparing a surface-modified high-flux anti-fouling polyamide composite reverse osmosis membrane and the membrane prepared thereby. The composite membrane comprises a porous substrate membrane and a polyamide layer modified with polyamine small molecules and a quaternary ammonium salt-type cationic surfactant. The polyamide layer covers the surface of the porous substrate membrane.

[0039] The positively charged small molecule is N,N-dimethylethylenediamine.

[0040] The method for preparing a surface-modified high-flux anti-fouling polyamide composite reverse osmosis membrane comprises the following steps:

[0041] Step 1: Immerse a porous substrate membrane with an average pore size of 10 nm into an aqueous solution containing 6.0 wt% of m-phenylenediamine, and keep in full contact for 2 min. Take out the substrate membrane and remove the excess water droplets on its surface.

[0042] Step 2: Immerse the diaphragm in Step 1 into an oil-phase solution containing 0.3 wt% of trimesoyl chloride, make full contact for 1 min, conduct interfacial polymerization reaction to form a polyamide desalination layer, pour out the residual acyl chloride oil-phase solution from above the membrane, and then place it in an oven at 50 °C for thermal crosslinking for 5 min.

[0043] Step 3: After thoroughly washing the membrane in Step 2 with deionized water, gently add a 0.5 wt% N,N-dimethylethylenediamine modification reagent solution to the surface of the membrane in Step 2, keep it for 2 min, and take it out.

[0044] Step 4: Wash the membrane modified in Step 3 with an organic acid solution with a mass concentration of 12% and a temperature of 50 °C for 10 min to remove the residual substances on the surface. Then place it in an oven at 70 °C for thermal crosslinking for 10 min.

[0045] Step 5: Fix the polyamide composite membrane modified in Step 4 in a polytetrafluoroethylene frame, repeatedly rinse the membrane surface with pure water, then pour a 10 wt% glycidyltrimethylammonium chloride solution into the frame, wrap and seal the frame with plastic wrap, and place it in a constant temperature and humidity chamber at 30 °C for light-shielded reaction for 8 h.

[0046] Step 6: Repeatedly rinse the surface of the reacted membrane with pure water, and immerse it in deionized water for storage for later use.

[0047] Example 3: A method for preparing a high-flux fouling-resistant polyamide composite reverse osmosis membrane by surface modification, the composite membrane includes a porous substrate membrane and a polyamide layer modified by small molecules, and the polyamide layer covers the surface of the porous substrate membrane;

[0048] The positive charge small molecule is triethylenediamine.

[0049] The method for preparing a surface-modified high-flux fouling-resistant polyamide composite reverse osmosis membrane includes the following steps:

[0050] Step 1: Immerse a porous substrate membrane with an average pore size of 10 nm into a mixed aqueous solution containing 6.0 wt% of m-phenylenediamine, make full contact for 2 min, take out the substrate membrane and remove the excess water droplets on its surface.

[0051] Step 2: Immerse the diaphragm in Step 1 into an oil-phase solution containing 0.3 wt% of trimesoyl chloride, make full contact for 1 min, conduct interfacial polymerization reaction to form a polyamide desalination layer, pour out the residual acyl chloride oil-phase solution from above the membrane, and then place it in an oven at 50 °C for thermal crosslinking for 5 min.

[0052] Step 3: After thoroughly washing the membrane obtained in Step 2 with deionized water, gently add a 0.5 wt% triethylenediamine modification reagent solution to the surface of the membrane in Step 2, keep it for 2 min, and take it out.

[0053] Step 4: Wash the membrane modified in Step 3 with an organic acid solution having a mass concentration of 12% and a temperature of 50°C for 10 min to remove residual substances on the surface. Then, place it in an oven at 70°C for thermal crosslinking for 10 min.

[0054] Example 4: A method for preparing a high-flux and fouling-resistant polyamide composite reverse osmosis membrane by surface modification, the composite membrane comprising a porous substrate membrane and a polyamide layer modified with polyamine small molecules and a quaternary ammonium salt-type cationic surfactant, the polyamide layer covering the surface of the porous substrate membrane;

[0055] The positively charged small molecule is triethylenediamine.

[0056] The method for preparing a surface-modified high-flux and fouling-resistant polyamide composite reverse osmosis membrane comprises the following steps:

[0057] Step 1: Immerse a porous substrate membrane with an average pore size of 10 nm in an aqueous solution containing 6.0 wt% of m-phenylenediamine for 2 min to allow sufficient contact, take out the substrate membrane and remove the excess water droplets on its surface.

[0058] Step 2: Immerse the membrane obtained in Step 1 in an oil-phase solution containing 0.3 wt% of trimesoyl chloride for 1 min to allow sufficient contact, carry out an interfacial polymerization reaction to form a polyamide desalination layer, pour the residual acyl chloride oil-phase solution from above the membrane, and then place it in an oven at 60°C for thermal crosslinking for 5 min.

[0059] Step 3: After thoroughly washing the membrane obtained in Step 2 with deionized water, gently add a 0.5 wt% triethylenediamine modification reagent solution to the surface of the membrane obtained in Step 2, keep it for 2 min, and then take it out.

[0060] Step 4: Wash the membrane obtained in Step 3 with an organic acid solution having a mass concentration of 12% and a temperature of 50°C for 10 min to remove residual substances on the surface. Then, place it in an oven at 70°C for thermal crosslinking for 10 min.

[0061] Step 6: Fix the polyamide composite membrane obtained in Step 5 in a polytetrafluoroethylene frame, repeatedly rinse the membrane surface with pure water, then pour a 10 wt% solution of glycidyltrimethylammonium chloride into the frame, wrap the frame with a plastic wrap and seal it, and place it in a constant temperature and humidity chamber at 30°C for light-free reaction for 8 h.

[0062] Step 7: Repeatedly rinse the surface of the membrane after the reaction with pure water, and immerse it in deionized water for storage for later use.

[0063] Comparative Example:

[0064] A method for preparing a high-flux and fouling-resistant polyamide composite reverse osmosis membrane by surface modification comprises the following steps:

[0065] Step 1: Immerse the porous substrate membrane with an average pore size of 10 nm into an aqueous solution containing 6.0 wt% of m-phenylenediamine, and let them contact fully for 2 min. Then take out the substrate membrane and remove the excess water droplets on its surface.

[0066] Step 2: Immerse the membrane sheet obtained in Step 1 into an oil-phase solution containing 0.3 wt% of trimesoyl chloride, and let them contact fully for 1 min to carry out an interfacial polymerization reaction to form a polyamide desalination layer. Then pour out the residual acyl chloride oil-phase solution from above the membrane.

[0067] Step 3: Heat cross-link the membrane obtained in Step 2 in an oven at 50 °C for 5 min to obtain the comparative polyamide composite reverse osmosis membrane.

[0068] (1) Ion removal performance test:

[0069] The polyamide composite reverse osmosis membrane is prone to being contaminated by various pollutants during operation. In the present invention, the anti-fouling stability performance of the reverse osmosis membrane is characterized by the change in the long-term continuous operation performance of the membrane sheet.

[0070] Perform separation performance detection on Examples 1 to 4 and the comparative example. Membrane sheet performance detection 1: Use an aqueous solution of sodium chloride at 200 ppm to test the water flux and salt rejection rate of the membrane sheet under the conditions of an operating pressure of 60 psi and a temperature of 25 °C. The results are shown in Table 1.

[0071] Table 1

[0072]

[0073] (2) Membrane sheet performance detection:

[0074] Perform membrane sheet performance detection on Examples 1 to 4 and the comparative example. Use a water efficiency solution to test the water flux and salt rejection rate of the membrane sheet under the conditions of an operating pressure of 100 psi and a temperature of 25 °C; the preparation of the water efficiency solution is as follows: Add 3.33 g of NaCl, 7.88 g of CaCl2, 11.43 g of NaHCO3, and 8.88 g of MgSO4·7H2O to 42 L of pure water respectively, and then add 2.5 ml of the diluted sodium hypochlorite solution. The sodium hypochlorite solution is diluted according to the ratio of dissolving 2 - 3 ml of sodium hypochlorite solution containing 10% available chlorine in 17 ml of pure water. The results are shown in Table 2.

[0075] Table 2

[0076]

[0077]

[0078] As can be seen from Table 1 and Table 2, in Examples 1 to 4, a high-flux anti-fouling composite reverse osmosis membrane incorporating a multi-stage amine small molecule and a quaternary ammonium salt-type cationic surfactant was introduced: When operating in an NaCl solution, compared with the initial performance of the comparative example, it had a higher water flux while maintaining a high rejection rate. The flux was increased by about 26% at most, and the desalination rate only decreased from 99.3% to 98.9%, and it could operate stably for a long time. When operating in a water efficiency solution, compared with the initial performance of the comparative example, the flux was greatly increased, by about 38% at most, and the desalination rate only decreased from 99.0% to 98.1%, and it could operate stably for a long time.

[0079] In Table 1 and Table 2, after the secondary modification with glycidyltrimethylammonium chloride in Examples 2 and 4, both the membrane permeation flux and the desalination rate decreased slightly, but the decrease was not significant. This may be because the membrane was soaked in a glycidyltrimethylammonium chloride solution for a long time, and the structure of the polyamide separation layer was slightly damaged. After continuous operation in an NaCl solution for 96 h, the water fluxes of Examples 1 to 4 decreased by 5.85%, 3.25%, 5.87% and 3.42% respectively compared with the initial water fluxes, while that of the comparative example decreased by 11.97%. After continuous operation in a water efficiency solution for 40 h, the water fluxes of Examples 1 to 4 decreased by 4.04%, 2.37%, 4.14% and 2.51% respectively, while that of the comparative example decreased by 13.51%. Compared with Examples 1 and 3 modified with multi-stage amine small molecules once, Examples 2 and 4 after the secondary modification with glycidyltrimethylammonium chloride showed slightly lower water fluxes and desalination rates, but exhibited more excellent anti-fouling stability performance.

[0080] The high-flux anti-fouling composite reverse osmosis membrane and its preparation method provided by the present invention have been introduced in detail above. Specific examples are used in this article to elaborate on the structure and working principle of the present invention. The description of the above examples is only used to help understand the method and core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a high-flux anti-fouling polyamide composite reverse osmosis membrane by surface modification, characterized in that: it includes a polyamide layer modified by a positively charged small molecule and a quaternary ammonium salt type cationic surfactant, and the polyamide layer covers the surface of a porous substrate membrane; for the polyamide layer modified by the positively charged small molecule, first, an acylation reaction occurs between the highly active amino group of the multi-stage amine small molecule and the excessive acyl chloride group on the surface of the polyamide membrane. Through secondary interfacial polymerization, a small molecule with a positively charged group is introduced onto the polyamide membrane to obtain a polyamide membrane modified by the positively charged small molecule. The positively charged small molecule can couple with the negatively charged carboxylic acid group on the surface of the polyamide membrane, and by balancing its surface charge, an amphoteric ion surface is formed; then, a quaternary ammonium salt type cationic surfactant with an active group is introduced onto the surface of the polyamide membrane, and the quaternary ammonium salt is introduced into the molecular chain on the membrane surface. An antibacterial structure with a multi-stage amine molecule as the polymer framework and a movable quaternary ammonium salt at the end of the polymer chain as the bactericidal functional group is constructed on the membrane surface, thereby further endowing the reverse osmosis membrane with excellent anti-fouling stability performance.

2. The method for preparing a high-flux anti-fouling polyamide composite reverse osmosis membrane by surface modification according to claim 1, characterized in that: the positively charged small molecule is at least one of N,N-dimethylethylenediamine and triethylenediamine.

3. The method for preparing a high-flux anti-fouling polyamide composite reverse osmosis membrane by surface modification according to claim 1, characterized in that: the quaternary ammonium salt type cationic surfactant is glycidyltrimethylammonium chloride.

4. The method for preparing a high-flux anti-fouling polyamide composite reverse osmosis membrane by surface modification according to claim 1, characterized in that: the thickness of the polyamide layer is 90 - 130 nm, and the average pore diameter of the porous substrate membrane is 8 - 10 nm.

5. A method for preparing the high-flux anti-fouling polyamide composite reverse osmosis membrane by surface modification according to any one of claims 1 to 4, characterized in that: it includes the following steps: Step 1: Treat the porous substrate membrane. Take the porous substrate membrane and immerse it in an alkaline aqueous solution containing polyamine, make full contact, take out the porous substrate membrane and remove the excess water droplets on its surface; Step 2: Prepare the polyamide desalination layer. Immerse the porous substrate membrane treated in Step 1 in an oily solution containing polyacyl chloride, make full contact, carry out an interfacial polymerization reaction to form a polyamide desalination layer, and pour the remaining acyl chloride oily solution from above the membrane. Subsequently, place the membrane in an oven at 35 - 60 °C for 1 - 5 min; Step 3: Prepare the modified polyamide desalination layer. After thoroughly washing the membrane obtained in Step 2 with deionized water, add the modified reagent solution to the surface of the polyamide membrane desalination layer and keep it for 1 - 3 min; Step 4: Obtain the surface-modified polyamide composite membrane. Wash the membrane modified in Step 3 with an aqueous solution containing organic acid to remove the residual substances on the surface. Then place it in an oven at 70 °C for thermal cross-linking for 1 - 10 min; Step 5: Obtain the polyamide composite membrane with secondary surface modification. Fix the modified polyamide composite membrane in Step 4 in a polytetrafluoroethylene frame, repeatedly rinse the membrane surface with deionized water, then pour the trimethylammonium chloride glycidyl solution into the frame, wrap and seal the frame with plastic wrap, and place it in a constant temperature and humidity chamber for light - avoiding reaction. Step 6: Repeatedly rinse the membrane surface of the reacted membrane with deionized water and soak it in deionized water for standby.

6. A preparation method for a surface - modified high - flux anti - fouling polyamide composite reverse osmosis membrane according to claim 5, characterized in that: In Step 1, the contact time between the porous substrate membrane and the aqueous solution is 1 - 5 min. The monomer of the polyamine aqueous solution is one of m - phenylenediamine, p - phenylenediamine or piperazine. The monomer of the polyamine aqueous solution is m - phenylenediamine, and the mass concentration of m - phenylenediamine is 1.0 - 8.0 wt%.

7. A preparation method for a surface - modified high - flux anti - fouling polyamide composite reverse osmosis membrane according to claim 5, characterized in that: In Step 2, the contact time when the porous substrate membrane is immersed in the polyacyl chloride organic phase solution is 1 - 3 min. The polyacyl chloride is one of oxalyl chloride, terephthaloyl chloride or trimesoyl chloride. The mass concentration of trimesoyl chloride is 0.05 - 0.5 wt%, and the balance is an organic solvent.

8. A preparation method for a surface - modified high - flux anti - fouling polyamide composite reverse osmosis membrane according to claim 5, characterized in that: The modified reagent solution in Step 3 is a solution of small positively - charged molecules.

9. A preparation method for a surface - modified high - flux anti - fouling polyamide composite reverse osmosis membrane according to claim 5, characterized in that: The organic acid in Step 4 is at least one of acetic acid, malic acid, citric acid, camphorsulfonic acid, oxalic acid, tartaric acid, benzoic acid, caffeic acid, salicylic acid. The mass concentration of the organic acid solution is 10 - 15%, the water - washing time is 1 - 10 min, and the temperature is 50 - 60 °C.

10. A preparation method for a surface - modified high - flux anti - fouling polyamide composite reverse osmosis membrane according to claim 5, characterized in that: In Step 5, the mass fraction of the trimethylammonium chloride glycidyl solution is 1 - 10 wt%, the temperature of the constant temperature and humidity chamber is 25 - 35 °C, and the reaction time is 1 - 10 h.

11. A preparation method for a surface - modified high - flux anti - fouling polyamide composite reverse osmosis membrane according to claim 7, characterized in that: The organic solvent is one or more of chlorobenzene, dichloromethane, propylene oxide, ethylcyclohexane, toluene, xylene, m - xylene, mesitylene, hexane, cyclohexane, n - heptane, isopar E, isopar G, isopar H, isopar L, isopar M.

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