Cellulose-like film composite nanofiltration membrane, preparation method and application of cellulose-like film composite nanofiltration membrane in treatment of nitrate-polluted underground water

Abstract

The invention provides a cellulose-like film composite nanofiltration membrane, a preparation method and application of the cellulose-like film composite nanofiltration membrane in treatment of nitrate-polluted underground water, the composite nanofiltration membrane comprises a supporting layer and a cellulose-like separation layer prepared on the surface of the supporting layer, and the cellulose-like separation layer is composed of a cellulose-like membrane containing D (+)-glucosamine and 1, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate. The preparation method comprises the following steps: carrying out double-crosslinking interfacial polymerization reaction (DPCL IP) on a water-phase reaction solution containing 1, 3-diamino-2-propanol and an organic-phase reaction solution containing 1, 3, 5-benzoyl chloride, thereby obtaining the 1, 3-diamino-2-propanol / 1, 3, 5-benzoyl chloride / 1, 3-diamino-2-propanol / 1, 3 The DPCL IP method is adopted, the synthesis method is mature and simple, the conditions are mild, in the preparation process, preferably under the alkaline condition, the by-product hydrogen chloride of the acylation reaction can be absorbed, the reaction equilibrium moves forward, the formation of the cellulose-like selection layer is promoted, the raw material cost is low, and the method is suitable for industrial production. The cellulose-like film composite nanofiltration membrane obtained through synthesis has high water flux and nitrate removal rate, and can be used for treating underground water polluted by nitrate.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and in particular relates to a cellulose-like thin film composite nanofiltration membrane, a preparation method and application thereof in treating nitrate-contaminated groundwater. Background Art

[0002] Traditional nitrate removal technologies such as reverse osmosis, ion exchange, and electrodialysis, while effective to some extent, have significant limitations. While reverse osmosis membranes can efficiently retain nitrates, they consume high operating energy and simultaneously remove beneficial minerals such as calcium and magnesium. Ion exchange resins require frequent regeneration, producing high-salt wastewater that can easily cause secondary pollution. Electrodialysis equipment is complex and expensive to maintain. While biological denitrification is environmentally friendly, it is significantly affected by water quality fluctuations and has a long reaction cycle, making it difficult to adapt to the stability requirements of groundwater treatment. Therefore, the development of nitrate removal technologies that combine high selectivity, low energy consumption, and sustainability is urgent.

[0003] Nanofiltration (NF) technology has become a research hotspot in the field of groundwater remediation due to its unique separation mechanism. The pore size of nanofiltration membrane is between that of reverse osmosis membrane and ultrafiltration membrane (1~2 nm). Through the synergistic effect of pore size screening and Donnan effect, it can selectively intercept divalent and higher ions (such as SO4 2- ), while for monovalent ions (such as NO3 - 、Cl - This characteristic makes the nitrate removal rate of traditional commercial nanofiltration membranes (such as NF270) generally less than 60%, and is easily affected by Cl - Competitive interference makes it difficult to meet the treatment needs of highly nitrate-contaminated water bodies. In recent years, research has focused on improving the nitrate selectivity of nanofiltration membranes by modifying membrane materials (such as introducing amino or quaternary ammonium groups) to control membrane surface charge characteristics or optimizing membrane pore structure to enhance nitrate-specific recognition. However, existing modification methods often face a "trade-off" effect between retention and permeate flux, and the membranes' insufficient anti-fouling properties hinder their practical engineering applications.

[0004] In summary, the inventors have developed a cellulose-like thin film composite nanofiltration membrane with high nitrate selectivity, high flux and long-term stability, which has important practical significance for solving the problem of nitrate pollution in groundwater. Summary of the Invention

[0005] In view of this, the present invention aims to propose a cellulose-like thin film composite nanofiltration membrane, a preparation method and its application in treating nitrate-contaminated groundwater, to obtain a cellulose-like thin film composite nanofiltration membrane with a high nitrate removal rate for treating nitrate-contaminated groundwater.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A cellulose-like thin film composite nanofiltration membrane comprises a support layer and a cellulose-like separation layer prepared on the surface of the support layer, wherein the cellulose-like separation layer is prepared by reacting an aqueous phase reaction solution containing D(+)-glucosamine and 1,3-diamino-2-propanol with an organic phase reaction solution containing 1,3,5-benzenetricarboxylic chloride through DPCL-IP reaction.

[0008] Furthermore, the support layer is a hydrophilic ultrafiltration membrane, and the support layer includes a flat plate type or a hollow fiber type.

[0009] D(+)-glucosamine, also known as DGA, is a naturally occurring, highly water-soluble, non-toxic compound. Its structural formula has secondary hydroxyl groups at the C-2 and C-3 positions, a primary hydroxyl group at the C-6 position, and an amino group at the C-5 position. The presence of multiple hydroxyl groups gives it excellent hydrophilicity; the coexistence of multiple hydroxyl groups and amino groups gives it multiple reaction sites.

[0010] 1,3-Diamino-2-propanol (DAP) not only contains an amino group that can participate in the cross-linking reaction, but also has a hydroxyl group at the C-2 position. This hydroxyl group can form a hydrogen bond with the hydroxyl group in DGA that does not participate in the reaction, thereby producing a unique cross-linking effect based on hydrogen bonds.

[0011] 1,3,5-Benzenetricarboxylic acid chloride, or TMC, has acyl chloride groups at the C-1, C-3, and C-5 positions in its structural formula. Multiple reaction sites can be cross-linked with a mixed solution of DGA and aqueous crosslinking agent DAP to form a cellulose-like separation layer.

[0012] A method for preparing a cellulose-like thin film composite nanofiltration membrane comprises the following steps:

[0013] S1. Dissolving a mixture of D(+)-glucosamine and 1,3-diamino-2-propanol in deionized water and adjusting the pH to obtain an aqueous phase reaction solution; dissolving 1,3,5-benzenetricarboxylic acid chloride in a non-polar organic solvent to obtain an organic phase reaction solution;

[0014] S2, soaking the surface of the support layer with the aqueous reaction solution, and removing residual droplets on the surface of the support layer;

[0015] S3, contacting the organic phase reaction solution with the surface of the support layer dipped in the aqueous phase reaction solution treated in S2 to perform a DPCL IP reaction;

[0016] S4. After terminating the reaction, drying is performed to obtain the cellulose-like thin film composite nanofiltration membrane.

[0017] Furthermore, in S1, the concentration of D(+)-glucosamine in the aqueous reaction solution is 1-4 w / v%, preferably 2.5 w / v%; and the concentration of 1,3-diamino-2-propanol is 0.005-0.02 w / v%, preferably 0.005 w / v%.

[0018] Furthermore, in S1, the concentration of 1,3,5-benzenetricarboxylic acid chloride in the organic phase reaction solution is 0.05-0.2 w / v%, preferably 0.15 w / v%.

[0019] Furthermore, in S1, the non-polar organic solvent is an isoparaffin solvent. The isoparaffin solvent is generally composed of C10-C16 isoparaffins; the isoparaffin solvent is preferably one of Isopar G, Isopar H, Isopar L, and Isopar M, and is preferably Isopar G.

[0020] Furthermore, in S1, the pH is adjusted by adding an inorganic base. The inorganic base includes sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, preferably sodium hydroxide. Furthermore, in S3, the DPCL IP reaction time is 20 to 120 seconds, preferably 30 seconds; the reaction temperature is 25 ± 2°C, and the relative humidity is 40 ± 5%.

[0021] Furthermore, in the S2, the support layer is pretreated before the reaction. The pretreatment is to first soak it in a 1-2 v / v% anhydrous ethanol solution for 10-30 min, then ultrasonically clean it for 1-2 min. This process is repeated twice to ensure that the chemical agents used in the preparation and storage of the support layer are removed; finally, the support layer is placed in deionized water and stored in a refrigerator at 4°C for use.

[0022] Furthermore, in S2, the aqueous reaction solution is allowed to soak the surface of the hydrophilic ultrafiltration membrane for 5 to 10 minutes, preferably 5 minutes.

[0023] Furthermore, in S4, the termination reaction is performed by directly discarding excess organic phase reaction solution on the surface of the support layer; the drying conditions are: heat treatment in an oven at 55-65°C for 3-5 minutes, preferably heat treatment at 60°C for 3 minutes.

[0024] Application of the cellulose-like thin film composite nanofiltration membrane of the present invention in nitrate-contaminated groundwater.

[0025] Compared with the prior art, the cellulose-like thin film composite nanofiltration membrane, preparation method, and application thereof in treating nitrate-contaminated groundwater of the present invention have the following advantages:

[0026] (1) The present invention adopts the DPCL IP preparation method, using DAP as a water phase crosslinking agent to synergize with TMC in the organic phase, effectively promoting the crosslinking reaction with DGA and enhancing the crosslinking degree of the system.

[0027] (2) The preparation process of the present invention is preferably carried out under alkaline conditions, which can absorb the by-product of the acylation reaction, hydrogen chloride, and move the reaction equilibrium toward the positive direction, thereby promoting the formation of the cellulose-like selective layer.

[0028] (3) The preparation method of the present invention is mature and simple, with mild conditions and low raw material cost. The prepared cellulose-like thin film composite nanofiltration membrane has high water flux and nitrate removal rate, and can be used to treat nitrate-contaminated groundwater.

[0029] (4) The cellulose-like thin film composite nanofiltration membrane prepared in the present invention synergistically integrates the advantages of traditional CA membrane and PA TFC membrane. Based on the unique cross-linking structure of covalent bonds (ester / amide bonds) and hydrogen bond networks, as well as the presence of a large number of residual hydroxyl groups, the composite nanofiltration membrane has excellent anti-fouling ability and chlorine resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram of the cross-linked structure of the cellulose-like thin film composite nanofiltration membrane prepared in Example 1.

[0031] Figure 2 Scanning electron microscope images of the polyethersulfone ultrafiltration membrane, the cellulose-like film composite nanofiltration membrane prepared in Example 1, and the commercial nanofiltration membranes of Comparative Examples 4 and 5.

[0032] Figure 3 This is the infrared spectrum of the cellulose-like thin film composite nanofiltration membrane prepared in Example 1.

[0033] Figure 4 This is a diagram of the hydrogen bond quantity of the cellulose-like thin film composite nanofiltration membrane prepared in Example 1 and the commercial nanofiltration membranes of Comparative Examples 4 and 5.

[0034] Figure 5 This is a comparison chart of the anti-pollution ability and chlorine resistance of the cellulose-like thin film composite nanofiltration membrane prepared in Example 1 and the commercial nanofiltration membranes of Comparative Examples 4 and 5. DETAILED DESCRIPTION

[0035] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0036] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0037] D(+)-glucosamine is DGA; 1,3-diamino-2-propanol is DAP; 1,3,5-benzenetricarboxylic acid chloride is TMC.

[0038] An embodiment of the present invention provides a cellulose-like thin film composite nanofiltration membrane comprising a support layer and a cellulose-like separation layer formed on the surface of the support layer. The cellulose-like separation layer is prepared by a DPCL-IP reaction between an aqueous reaction solution containing D(+)-glucosamine and 1,3-diamino-2-propanol and an organic reaction solution containing 1,3,5-benzenetricarboxylic chloride. The support layer is a hydrophilic ultrafiltration membrane, and the support layer can be either flat-plate or hollow-fiber. Thus, a flat-plate or hollow-fiber cellulose-like thin film composite nanofiltration membrane with a high nitrate removal rate can be obtained.

[0039] The main aqueous phase monomer is selected from D(+)-glucosamine (DGA), the chemical structure of which is shown below, and comprises an oxygen-containing six-membered ring, four alcoholic hydroxyl groups and an amino group.

[0040]

[0041] DGA is a naturally occurring, highly water-soluble compound extracted from natural chitin. It exists in large quantities in nature, is inexpensive, and is non-toxic and harmless to the environment and the human body. Because it has a similar structure to cellulose, it has high mechanical strength and stable organic chemical properties, and can be used in the field of membrane separation. Under alkaline conditions, when DGA reacts with TMC, the amino group is more active than the hydroxyl group, so the amino group reacts first with the acyl chloride group to form an amide bond. DGA has only one amino group, while TMC has three acyl chloride groups. In comparison, there are fewer reaction sites, so the reaction rate is lower. The separation layer structure formed is looser than that of traditional polyamide materials, which helps to improve the permeation flux of the composite membrane. In addition, DGA contains more hydroxyl groups, some of which undergo esterification reaction with the acyl chloride groups in TMC. The remaining unreacted hydroxyl groups can increase the hydrophilicity of the separation layer, while enhancing the electronegativity of the composite membrane and strengthening its desalination capacity.

[0042] The aqueous crosslinking agent is selected from 1,3-diamino-2-propanol (DAP), the chemical structure of which is shown below, and contains one alcoholic hydroxyl group and two amino groups.

[0043]

[0044] DAP is a polar alcohol containing two amino groups and one hydroxyl group. The amino group is a nitrogen-containing basic group with strong nucleophilicity, while the hydroxyl group is an oxygen-containing group with strong electronegativity. Therefore, the molecule has both nucleophilicity and electron affinity, making it highly polar. The hydroxyl group at the C-2 position can produce a unique cross-linking effect based on hydrogen bonds with the unreacted hydroxyl groups in the DGA molecule; the two amino groups at the C-1 and C-3 positions can participate in more chemical reactions, thereby increasing reactivity. In summary, DAP can participate in regulating the interfacial polymerization reaction between DGA and TMC.

[0045] A method for preparing a cellulose-like thin film composite nanofiltration membrane comprises the following steps:

[0046] S1. Dissolving a mixture of D(+)-glucosamine and 1,3-diamino-2-propanol in deionized water and adjusting the pH to obtain an aqueous phase reaction solution; dissolving 1,3,5-benzenetricarboxylic acid chloride in a non-polar organic solvent to obtain an organic phase reaction solution;

[0047] S2, soaking the surface of the support layer with the aqueous reaction solution, and then removing the aqueous reaction solution with a rubber scraper or an air knife until no droplets are visible to the naked eye;

[0048] S3, contacting the organic phase reaction solution with the surface of the support layer dipped in the aqueous phase reaction solution treated in S2 to perform a DPCL IP reaction;

[0049] S4. After terminating the reaction, drying the obtained composite membrane to obtain the cellulose-like thin film composite nanofiltration membrane.

[0050] As an improvement to an embodiment of the present invention, the hydrophilic ultrafiltration membrane is pretreated before use by soaking it in a 1-2 v / v% anhydrous ethanol solution for 10-30 minutes, followed by ultrasonic cleaning for 1-2 minutes. This process is repeated twice to ensure removal of chemicals added during the preparation and storage of the hydrophilic ultrafiltration membrane. The pretreated hydrophilic ultrafiltration membrane is stored in deionized water until use. Preferably, a 1 v / v% anhydrous ethanol solution is used; preferably, the soaking time is 20 minutes; and preferably, the ultrasonic cleaning time is 1 minute.

[0051] Hydrophilic ultrafiltration membranes are pretreated before use. This is because unused hydrophilic membranes are coated with protective agents, such as humectants like glycerin or antibacterial agents. Therefore, removing these protective agents during pretreatment improves hydrophilicity, allowing the membrane to bond more tightly with the cellulose-like separation layer in subsequent reactions. Anhydrous ethanol is used as a solution because it is non-toxic, harmless, and non-contaminating. Furthermore, at a specific concentration, anhydrous ethanol effectively dissolves organic reagents without causing membrane swelling.

[0052] As an improvement to the embodiment of the present invention, in S1, the concentration of DGA in the aqueous reaction solution is 1-4 w / v%, that is, 1-4 g of DGA is added to every 100 mL of deionized water; more preferably, 1-3 w / v%, and even more preferably 2.5 w / v%. At low concentrations, the small amount of DGA reacting with TMC is insufficient to form a loose cellulose-like separation layer, resulting in poor desalination performance; however, when this concentration is exceeded, on the one hand, the severe hydrogen bonding interaction between DGA molecules slows down its diffusion into the organic phase, and on the other hand, the mismatch in the number of DGA molecules and TMC molecules inhibits the formation of a cross-linked structure, thereby generating a large number of defects in the separation layer and deteriorating the desalination performance.

[0053] As an improvement to the embodiment of the present invention, in S1, based on a DGA concentration of 2.5 w / v% in the aqueous reaction solution, the aqueous crosslinker DAP is added in an amount of 0.005-0.02 w / v%, i.e., 0.005-0.02 g of DAP is added per 100 mL of deionized water, preferably 0.005-0.01 w / v, and more preferably 0.005 w / v. Pure water flux and salt rejection tests show that the cellulose-like thin film composite nanofiltration membrane prepared by adding 0.005 w / v% DAP exhibits a high salt rejection without sacrificing permeability.

[0054] As an improvement to the embodiment of the present invention, in S1, the concentration of TMC in the organic phase reaction solution is 0.05-0.2 w / v%; that is, 0.05-0.2 g of TMC is added to every 100 mL of non-polar organic solvent. It is further preferably 0.12-0.18 w / v%, and more preferably 0.15 w / v%. If the concentration of the polyacyl chloride compound in the organic phase reaction solution is too low, the reaction is insufficient, and a sufficiently dense cellulose-like separation layer cannot be formed, resulting in poor desalination effect. If the concentration is too high, the cellulose-like separation layer will continue to thicken, but the water flux and desalination rate will not be significantly improved, but raw materials will be wasted and costs will increase.

[0055] As an improvement to an embodiment of the present invention, in S1, the pH is adjusted by adding an inorganic base selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate. Five pH values, 4, 7, 11, 12, and 13, were selected for optimization. Based on testing and analysis of membrane pure water flux and salt rejection, a pH of 12 was preferred. Under these conditions, interfacial polymerization can occur, while hydrogen chloride, a byproduct of the acylation reaction, can be absorbed, shifting the reaction equilibrium in a positive direction and promoting the formation of a cellulose-like separation layer.

[0056] As an improvement to an embodiment of the present invention, in S1, the organic phase solvent is a non-polar solvent selected from an isoparaffin solvent; the isoparaffin solvent is generally composed of a combination of C10-C16 isoparaffins, preferably one of Isopar G, Isopar H, Isopar L, and Isopar M; and Isopar G is preferred.

[0057] As an improvement to the embodiment of the present invention, in S2, the aqueous reaction solution is soaked on the surface of the support layer for 5 to 10 minutes, preferably 5 minutes, so that the aqueous reaction solution fully soaks the surface of the support layer, and then a rubber scraper or an air knife is used to remove the aqueous reaction solution until no droplets are visible to the naked eye; when a flat-plate hydrophilic ultrafiltration membrane is used for preparation, a rubber scraper is used to remove the aqueous reaction solution until no droplets are visible to the naked eye; when a hollow fiber hydrophilic ultrafiltration membrane is used for preparation, an air knife is used to remove the aqueous reaction solution until no droplets are visible to the naked eye.

[0058] As an improvement to the embodiment of the present invention, in S3, the interfacial polymerization reaction time is 20-120 s, the reaction temperature is 20-30°C, and the relative humidity of the reaction environment is 35-45%. The interfacial polymerization reaction time is preferably 30 s because the interfacial polymerization reaction is self-limiting, meaning that further increase in reaction time will not result in further reaction. However, if the reaction time is too short, the reaction is insufficient, resulting in a loose separation layer and weak desalination capacity. Because temperature significantly affects the reaction rate and monomer diffusion behavior, and thus the formation of the separation layer, the reaction temperature is controlled at room temperature. Due to the active chemical properties of DAP and TMC, excessive humidity can cause their direct hydrolysis. If the humidity is too low, the small amount of aqueous reaction solution on the surface of the hydrophilic ultrafiltration membrane obtained in S2 will evaporate too quickly, also affecting the progress of the interfacial polymerization reaction.

[0059] As an improvement to the embodiment of the present invention, in S4, the reaction is terminated by directly pouring away the excess organic phase reaction solution on the surface of the support layer.

[0060] As an improvement to the present embodiment, in step S4, forced air drying is used to further enhance the polymerization reaction and strengthen the adhesion between the active layer and the support layer. Otherwise, the formed cellulose-like separation layer will easily fall off. The drying conditions are: heat treatment in an oven at 55-65°C with forced air for 3-5 minutes. Excessively high drying temperatures and prolonged drying times can cause the composite nanofiltration membrane to dehydrate and lose its water permeability.

[0061] Example 1

[0062] A method for preparing a cellulose-like thin film composite nanofiltration membrane, the specific steps are as follows:

[0063] 1) Pretreatment: A polyethersulfone ultrafiltration membrane was used as the support layer. The membrane was first soaked in 1 v / v% anhydrous ethanol for 20 min and ultrasonically cleaned for 1 min. This process was repeated twice and then stored in deionized water for later use.

[0064] 2) A mixed solution of 2.5 w / v% D(+)-glucosamine and 0.005 w / v% DAP was prepared using deionized water as a solvent, and sodium hydroxide was added to adjust the pH to 12 to obtain an aqueous reaction solution. Simultaneously, a 0.15 w / v% TMC organic reaction solution was prepared using Isopar G as a non-polar organic solvent.

[0065] 3) During the operation, the experimental temperature was maintained at 25 ± 2°C and the humidity was maintained at 40 ± 5%. The surface of the polyethersulfone ultrafiltration membrane described in step 1) was fully contacted with the mixed aqueous reaction solution of DGA and DAP in step 2) for 5 minutes to allow the aqueous reaction solution to fully infiltrate the surface of the polyethersulfone ultrafiltration membrane. The membrane surface was then cleared to ensure that there were no visible droplets.

[0066] 4) The organic phase reaction solution in step 2) is brought into contact with the surface of a polyethersulfone ultrafiltration membrane impregnated with an aqueous phase reaction solution of DGA and an aqueous phase crosslinking agent DAP and reacted for 30 seconds.

[0067] 5) The excess organic phase reaction solution on the surface of the polyethersulfone ultrafiltration membrane was poured into a waste liquid bucket to terminate the IP reaction. Finally, the obtained composite membrane was placed in an oven at 60°C with air blower for 3 minutes to obtain a composite nanofiltration membrane containing a cellulose-like separation layer, referred to as DGA / DAP-TMC.

[0068] Among them, the cross-linked structure of the cellulose-like thin film composite nanofiltration membrane is shown in the figure Figure 1 As shown in Figure 2, in addition to forming covalent bonds (amide / ester bonds) in the cellulose-like selective layer, hydrogen bonds are formed between the hydroxyl groups in the DAP molecules and the unreacted hydroxyl groups in the DGA molecules, creating a unique hydrogen-bonding crosslinking effect that further enhances the crosslinking degree of the system. Furthermore, the presence of hydrogen bonds can enhance the hydrophilicity and chlorine resistance of the membrane surface.

[0069] The scanning electron microscopy morphologies of polyethersulfone ultrafiltration membrane, newly prepared cellulose-like film composite nanofiltration membrane, NF270 and NF90 membranes are shown in Figure 2. Figure 2 As shown. Figure 2 a and Figure 2 b Compared with the above, it can be seen that a clear separation layer is formed on the polyethersulfone ultrafiltration membrane; in addition, Figure 2 b and Figure 2 c. Figure 2 d Compared with the cellulose film composite nanofiltration membrane prepared in Example 1, the surface is smoother, especially compared with Figure 2 Compared with the NF90 membrane of Example d, it shows that the cellulose-like thin film composite nanofiltration membrane prepared in Example 1 has stronger anti-pollution ability.

[0070] The infrared spectrum of the cellulose-like thin film composite nanofiltration membrane prepared in Example 1 is as follows: Figure 3 As shown, the ester bond (1727 cm -1 ), amide I bond (1650 cm -1 ) and amide II bonds (1583 cm -1 ) characteristic peaks indicate the formation of a cellulose-like separation layer. In addition, the hydroxyl group (3500-3100 cm -1 ) characteristic peaks, indicating that the cellulose-like thin film composite nanofiltration membrane prepared in Example 1 has good hydrophilicity, giving it excellent anti-pollution performance and permeability.

[0071] Example 2

[0072] Example 2 was prepared under the same conditions as Example 1, with the only difference being that the concentration of the aqueous crosslinking agent DAP was 0.01 w / v%.

[0073] Example 3

[0074] Example 3 was prepared under the same conditions as Example 1, except that the concentration of the aqueous crosslinking agent DAP was 0.02 w / v%.

[0075] Comparative Example 1

[0076] Comparative Example 1 was prepared under the same conditions as Example 1, except that the concentration of the aqueous crosslinking agent DAP was 0 w / v%.

[0077] Comparative Example 2

[0078] Comparative Example 2 was prepared under the same conditions as Example 1, except that the aqueous crosslinking agent was 1,3-propylenediamine (DMP).

[0079] Comparative Example 3

[0080] Comparative Example 3 was prepared under the same conditions as Example 1, except that the aqueous crosslinking agent was 1,2,3-propylenetriamine (PTA).

[0081] Comparative Example 4

[0082] The commercial nanofiltration membrane Dow NF270 was selected.

[0083] Comparative Example 5

[0084] The commercial nanofiltration membrane Dow NF90 was selected.

[0085] Performance Testing

[0086] Performance tests were performed on the composite nanofiltration membranes prepared in Examples 1-3, the composite nanofiltration membranes prepared in Comparative Examples 1-5, and commercial nanofiltration membranes.

[0087] The testing method involved using a cross-flow filtration membrane pool apparatus, pre-pressurized for 30 minutes at 6 bar operating pressure at 25°C. After the membrane performance stabilized, the membrane was tested for pure water flux and desalination performance at 5 bar pressure and a cross-flow velocity of 0.45 m / s. The feed solution NO⁻ concentration was always 100 ppm. The experimental results are shown in Table 1.

[0088] Table 1

[0089] Serial number <![CDATA[Pure water flux L / (m 2 ·h·bar)]]> <![CDATA[NO3 - (%)]]> Example 1 13.6 84.1 Example 2 7.4 86.9 Example 3 4.4 90.4 Comparative Example 1 14.9 76.7 Comparative Example 2 7.4 82.4 Comparative Example 3 9.5 79.8 Comparative Example 4 15.5 53.7 Comparative Example 5 9.0 76.5

[0090] It can be seen from Examples 1-3 that when the concentration of the aqueous crosslinking agent DAP is 0.005 w / v%, the prepared cellulose-like thin film composite nanofiltration membrane has high water permeability and salt rejection rate, and can get rid of the "trade-off effect".

[0091] It can be seen from Examples 1-3 and Comparative Example 1 that as the amount of aqueous crosslinking agent DAP increases, the pure water flux decreases linearly. - The retention rate increased linearly, indicating that DAP could effectively regulate the interfacial polymerization reaction between DGA and TMC and enhance the cross-linking degree of the system.

[0092] It can be seen from Example 1 and Comparative Examples 2-3 that the cellulose-like thin film composite nanofiltration membrane (DGA / DAP-TMC) prepared with DAP as the aqueous phase crosslinking agent not only has the highest pure water flux, but also has excellent desalination performance.

[0093] The number of hydrogen bonds between the cellulose-like film composite nanofiltration membrane prepared in Example 1 and the commercial nanofiltration membranes of Comparative Examples 4 and 5 is as follows: Figure 4As shown in Example 1 and Comparative Examples 4-5, it can be seen that the cellulose-like thin film composite nanofiltration membrane (DGA / DAP-TMC) prepared in Example 1 has excellent water permeability (13.6 L·m -2 ·h -1 bar -1 ) and nitrate removal rate (84.1%), which are better than the current commercial nanofiltration membranes NF270 (53.7%) and NF90 (76.5%), and can be used to treat nitrate-contaminated groundwater.

[0094] The anti-pollution ability and chlorine resistance of the cellulose-like film composite nanofiltration membrane prepared in Example 1 and the commercial nanofiltration membranes of Comparative Examples 4 and 5 are analyzed as follows: Figure 5 shown.

[0095] The membrane fouling process of DGA / DAP-TMC and NF270 / NF90 membranes was studied using 200 mg / L sodium alginate (SA) as a model pollutant. Figure 5 As shown in Figure a, during the first fouling cycle, the flux decay rate (FDR) of DGA / DAP-TMC was 20.56%, significantly lower than that of NF270 (27.53%) and NF90 (37.69%). After rinsing with deionized water, the flux recovery rate (FRR) of DGA / DAP-TMC was 98.90%, higher than that of NF270 (94.57%) and NF90 (88.20%). Lower FDRs and higher FRRs are associated with stronger antifouling capabilities. The difference in FDR between DGA / DAP-TMC and NF270 / NF90 gradually increased with increasing fouling cycles. This is primarily due to the fact that fouling deposited on the surfaces of NF270 and NF90 cannot be removed by hydraulic cleaning. At the end of the third fouling cycle, the FDRs of NF270 and NF90 reached 49.99% and 51.03%, respectively, while the FDR of DGA / DAP-TMC was only 25.03%. These data differences confirm that the cellulose thin film composite nanofiltration membrane prepared in Example 1 has excellent anti-fouling ability.

[0096] In order to understand the difference in chlorine resistance between DGA / DAP-TMC and NF270 / NF90 membranes, we placed them in 100 mg / L sodium hypochlorite (NaClO) solution and then performed comprehensive characterization on them. Figure 5As shown in Figure (b), the normalized flux of the DGA / DAP-TMC membrane remained essentially unchanged with increasing chlorine exposure, while the performance of the NF270 and NF90 membranes changed significantly. Notably, at a chlorine exposure intensity of 6000 ppm·h, the normalized water flux of the NF270 and NF90 membranes decreased significantly by approximately 39% and 16%, respectively, indicating poor chlorine resistance. This confirms that the cellulose thin film composite nanofiltration membrane prepared in Example 1 possesses strong chlorine resistance.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cellulose-like thin film composite nanofiltration membrane, characterized in that: The invention comprises a support layer and a cellulose-like separation layer prepared on the surface of the support layer. The cellulose-like separation layer is prepared by reacting an aqueous phase reaction solution containing D(+)-glucosamine and 1,3-diamino-2-propanol with an organic phase reaction solution containing 1,3,5-benzenetricarboxylic chloride through DPCL-IP reaction.

2. The cellulose-like thin film composite nanofiltration membrane according to claim 1, characterized in that: The support layer is a hydrophilic ultrafiltration membrane, and the support layer includes a flat plate type or a hollow fiber type.

3. A method for preparing a cellulose-like thin film composite nanofiltration membrane according to any one of claims 1 to 2, characterized in that: The steps include: S1. Dissolving a mixture of D(+)-glucosamine and 1,3-diamino-2-propanol in deionized water and adjusting the pH to obtain an aqueous phase reaction solution; dissolving 1,3,5-benzenetricarboxylic acid chloride in a non-polar organic solvent to obtain an organic phase reaction solution; S2, soaking the surface of the support layer with the aqueous reaction solution, and removing residual droplets on the surface of the support layer; S3, contacting the organic phase reaction solution with the surface of the support layer dipped in the aqueous phase reaction solution treated in S2 to perform a DPCL IP reaction; S4. After terminating the reaction, drying is performed to obtain the cellulose-like thin film composite nanofiltration membrane.

4. The method for preparing the cellulose-like thin film composite nanofiltration membrane according to claim 3, characterized in that: In S1, the concentration of D(+)-glucosamine in the aqueous reaction solution is 1-4 w / v%, and the concentration of 1,3-diamino-2-propanol is 0.005-0.02 w / v%.

5. The method for preparing the cellulose-like thin film composite nanofiltration membrane according to claim 3, characterized in that: In S1, the concentration of 1,3,5-benzenetricarboxylic acid chloride in the organic phase reaction solution is 0.05-0.2 w / v%.

6. The method for preparing the cellulose-like thin film composite nanofiltration membrane according to claim 3, characterized in that: In the above S1, the non-polar organic solvent is an isoparaffin solvent.

7. The method for preparing the cellulose-like thin film composite nanofiltration membrane according to claim 3, characterized in that: In the step S1, the pH is adjusted by adding an inorganic base.

8. The method for preparing the cellulose-like thin film composite nanofiltration membrane according to claim 3, characterized in that: In S3, the DPCL IP reaction time is 20-120 s, the reaction temperature is 25±2° C., and the relative humidity of the reaction environment is 40±5%.

9. The method for preparing the cellulose-like thin film composite nanofiltration membrane according to claim 3, characterized in that: In S2, the support layer is pretreated before the reaction by soaking in an anhydrous ethanol solution and then ultrasonic cleaning. This process is repeated to ensure that the chemical agents used in the preparation and storage of the ultrafiltration membrane are removed. Finally, the support layer is placed in deionized water and stored at low temperature.

10. Use of the cellulose-like thin film composite nanofiltration membrane according to any one of claims 1 to 2 or the cellulose-like thin film composite nanofiltration membrane prepared by the preparation method according to any one of claims 3 to 9 in treating nitrate-contaminated groundwater.

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