A method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane

Abstract

A method for preparing a polyamide nanofiltration membrane loaded with modified hydroxyl iron is disclosed, belonging to the field of nanofiltration membrane technology. The method solves the problems of low water flux, low interception rate, and easy shedding of the selective layer in existing nanofiltration membranes. Method: preparing hydroxyl iron functionalized with a silane coupling agent; preparing polyethyleneimine-modified hydroxyl iron; preparing a modified hydroxyl iron base membrane; and preparing a modified FeOOH nanofiltration membrane. The nanofiltration membrane of the present invention has higher water flux and retention rate because the introduced modified hydroxyl iron is loaded on the base membrane to form a scaffold, effectively preventing the polyamide layer from entering the base membrane and blocking the base membrane pores. The modified hydroxyl iron has a large number of hydrophilic groups, which can adsorb more aqueous phase monomers and facilitate subsequent interfacial polymerization reactions. At the same time, the grafted polyethyleneimine has a large number of amino groups that can react with acyl chloride groups, thereby increasing stability, preventing the selective layer from shedding, and increasing the crosslinking degree of the polyamide layer, forming a thinner and denser polyamide layer.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membranes, and particularly relates to a method for preparing a modified ferric oxyhydroxide-loaded polyamide nanofiltration membrane. Background Art

[0002] The main drivers of the world's growing demand for water are the growth of the world's population, improvements in living standards, changes in consumption patterns, and the expansion of agricultural irrigation. Currently, global freshwater resources can meet this growing demand, but water resources vary significantly in their distribution over time and space, leading to water shortages in some regions at specific times. Nanofiltration membrane technology utilizes external pressure or chemical potential differences to force a solvent through a semipermeable membrane, achieving separation between solute and solvent. It boasts simple processes, high integration, low costs, and automated operation. It has been widely used in many fields, including drinking water treatment, sewage treatment, seawater desalination, and wastewater reuse, providing technical support for ensuring water quality safety, treating water pollution, improving the water environment, and alleviating water resource crises.

[0003] Currently, the most common method for preparing nanofiltration membranes is to use a microfiltration membrane or ultrafiltration membrane as the base membrane, and then form a polyamide nanofiltration membrane through the interfacial polymerization reaction of piperazine and tricarboxylic acid chloride. The performance optimization methods of nanofiltration membranes mainly include water channel design, roughness optimization, hydrophilicity optimization, and thickness optimization. For example, micron-sized nanomaterials can be used as an intermediate layer to regulate the performance of nanofiltration membranes. Iron oxyhydroxide materials have the advantages of low cost, simple preparation, stable structure, and environmental protection. In addition, iron oxyhydroxide has an elongated morphology and can serve as a support between the base layer and the selective layer, which can effectively reduce the blockage of the base membrane by the polyamide layer. However, as the iron oxyhydroxide content increases, the force between the selective layer and the base membrane decreases, resulting in the problem of the selective layer being easily detached. Summary of the Invention

[0004] The present invention aims to solve the problems of low water flux, low interception rate and easy shedding of the selective layer in existing nanofiltration membranes, and to provide a method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane.

[0005] A method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane comprises the following steps:

[0006] 1. Preparation of silane coupling agent functionalized iron oxyhydroxide:

[0007] 0.5 g of ferric oxyhydroxide was added to 50 ml of an ethanol aqueous solution, ultrasonically dispersed, and then magnetically stirred. 1 mL of a silane coupling agent was then added and reacted at 40°C for 2 h. After centrifugation, washing, and drying, silane coupling agent-functionalized ferric oxyhydroxide was obtained.

[0008] 2. Preparation of polyethyleneimine-modified iron oxyhydroxide:

[0009] 0.2 g of the silane coupling agent-functionalized iron oxyhydroxide was added to 50 mL of anhydrous methanol, ultrasonically dispersed, and magnetically stirred. 2 g of polyethyleneimine was then added, and the mixture was heated to 90°C, refluxed for 6 h, and naturally cooled to room temperature. After centrifugation, washing, and drying, polyethyleneimine-modified iron oxyhydroxide was obtained, which was designated as FeOOH / PEI.

[0010] 3. Preparation of modified iron oxyhydroxide-based membrane:

[0011] 3.0 mg of the above FeOOH / PEI was added to 100 mL of deionized water and ultrasonically dispersed for 10 min to obtain a modified FeOOH suspension. The suspension was then filtered from 0 mL to 10 mL through a PES bottom membrane with a diameter of 4.0 cm. After drying and washing, a modified FeOOH base membrane was obtained.

[0012] 4. Preparation of modified FeOOH nanofiltration membrane:

[0013] In a fume hood, the modified FeOOH-based membrane is horizontally spread on a smooth glass plate, and then a membrane frame is placed directly in the center of the modified FeOOH-based membrane and fixed on all four sides with iron clips. A piperazine (PIP) aqueous solution is poured into the membrane frame, and after 90 seconds, the remaining solution in the membrane frame is poured out and drained. After drying for 10 to 20 minutes, a trimesoyl chloride (TMC)-n-hexane solution is poured in, and the remaining solution in the membrane frame is poured out after 40 seconds. Then, 5 mL of n-hexane solution is poured in and shaken for 30 seconds. The glass plate is then vertically dried until the membrane surface is completely dry. The iron clip is removed and the membrane frame is taken down. The membrane is removed from the glass plate with tweezers and marked. The membrane is then placed in a forced air drying oven and thermally crosslinked at 60°C for 30 minutes to obtain a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane, thereby completing the preparation method.

[0014] Furthermore, the synthesis of iron oxyhydroxide described in step 1: 2.16 g of FeCl3·6H2O and 20 mL of ethylenediamine were added to 40 ml of deionized water, stirred for 20 minutes, transferred and sealed in a high-temperature reactor, kept at 85°C for 12 hours, then cooled to room temperature, centrifuged and washed, and then vacuum dried at 80°C to obtain iron oxyhydroxide.

[0015] Furthermore, the ethanol aqueous solution in step 1 is prepared by mixing 45 mL of deionized water and 5 mL of anhydrous ethanol.

[0016] Furthermore, the magnetic stirring after ultrasonic dispersion in step 1 is: ultrasonic dispersion for 30 minutes and then magnetic stirring for 30 minutes.

[0017] Furthermore, the silane coupling agent in step 1 is: KH560.

[0018] Furthermore, the centrifugation, washing and drying in step 1 are performed by centrifugation at a speed of 4000 r / min for 5 minutes, followed by washing with anhydrous ethanol 2 to 3 times, and then vacuum drying at 40° C. for 24 hours.

[0019] Furthermore, the ultrasonic dispersion in step 2 is followed by magnetic stirring: ultrasonic dispersion for 10 minutes and magnetic stirring for 30 minutes.

[0020] Furthermore, the centrifugation, washing and drying in step 2 are performed: centrifugation at a speed of 4000 r / min for 5 minutes, followed by washing with deionized water and anhydrous methanol for 2 to 3 times, and then drying at 60° C. for 24 hours.

[0021] Furthermore, the drying and washing in step 3 are as follows: drying in an oven at 60° C. for 3 minutes, and then rinsing with deionized water 2 to 3 times.

[0022] Furthermore, the amount of the piperazine aqueous solution in step 4 is 5 mL, and the concentration is 0.5% / wv.

[0023] Furthermore, the amount of the trimesoyl chloride-n-hexane solution in step 4 is 5 mL, and the concentration is 0.1% / wv.

[0024] The modified ferric hydroxide loaded polyamide nanofiltration membrane prepared in the present invention has higher water flux and retention rate than general polyamide nanofiltration membranes. This is because the introduced modified ferric hydroxide is loaded on the base membrane to form a scaffold, which can effectively prevent the polyamide layer generated by interfacial polymerization from entering the base membrane and blocking the base membrane pores. In addition, the modified ferric hydroxide has a large number of hydrophilic groups, which can adsorb more aqueous phase monomers and facilitate subsequent interfacial polymerization reactions. At the same time, the grafted polyethyleneimine has a large number of amino groups, which can react with acyl chloride groups, increase stability, and prevent the selective layer from falling off. In addition, the amino groups can consume the acyl chloride groups on the surface more quickly, increase the cross-linking degree of the polyamide layer, and form a thinner and denser polyamide layer.

[0025] The invention is suitable for the preparation of a modified ferric oxyhydroxide-loaded polyamide nanofiltration membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the SEM image of FeOOH / PEI in Example 1;

[0027] Figure 2 The infrared spectra of FeOOH / KH560, FeOOH / PEI and existing FeOOH in Example 1 are shown;

[0028] Figure 3IR spectra of the PES base membrane, the FeOOH / PEI polyamide nanofiltration membrane in Example 1, and the unmodified polyamide nanofiltration membrane in the comparative example;

[0029] Figure 4 Surface, cross-sectional SEM and AFM images of the PES base membrane, the modified FeOOH base membrane in Example 1, the FeOOH / PEI polyamide nanofiltration membrane and the unmodified polyamide nanofiltration membrane in the comparative example; wherein Figure a and Figure b are surface SEM images of the PES base membrane and the modified FeOOH base membrane, respectively; Figure c and Figure d are surface SEM images of the unmodified polyamide nanofiltration membrane and the FeOOH / PEI polyamide nanofiltration membrane, respectively; Figure e and Figure f are cross-sectional SEM images of the unmodified polyamide nanofiltration membrane and the FeOOH / PEI polyamide nanofiltration membrane; Figure g and Figure h are AFM images of the unmodified polyamide nanofiltration membrane and the FeOOH / PEI polyamide nanofiltration membrane;

[0030] Figure 5 The first figure is the water contact angle diagram of the unmodified polyamide membrane surface; the second figure is the water contact angle diagram of the polyamide membrane after adding FeOOH / PEI;

[0031] Figure 6 The molecular weight cut-off diagram of FeOOH / PEI polyamide nanofiltration membrane and unmodified polyamide nanofiltration membrane;

[0032] Figure 7 The water flux and rejection rate of FeOOH / PEI polyamide nanofiltration membrane with different loading amounts;

[0033] Figure 8 This is the effect of different material concentrations on the performance of FeOOH / PEI polyamide nanofiltration membrane;

[0034] Figure 9 This is the long-term operation diagram of FeOOH / PEI polyamide nanofiltration membrane;

[0035] Figure 10 This figure shows the effect of acid-resistant treatment on FeOOH / PEI polyamide nanofiltration membrane. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0037] Specific embodiment 1: This embodiment provides a method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane, which is carried out according to the following steps:

[0038] 1. Preparation of silane coupling agent functionalized iron oxyhydroxide:

[0039] 0.5 g of ferric oxyhydroxide was added to 50 ml of an ethanol aqueous solution, ultrasonically dispersed, and then magnetically stirred. 1 mL of a silane coupling agent was then added and reacted at 40°C for 2 h. After centrifugation, washing, and drying, silane coupling agent-functionalized ferric oxyhydroxide was obtained.

[0040] 2. Preparation of polyethyleneimine-modified iron oxyhydroxide:

[0041] 0.2 g of the silane coupling agent-functionalized iron oxyhydroxide was added to 50 mL of anhydrous methanol, ultrasonically dispersed, and magnetically stirred. 2 g of polyethyleneimine was then added, and the mixture was heated to 90°C, refluxed for 6 h, and naturally cooled to room temperature. After centrifugation, washing, and drying, polyethyleneimine-modified iron oxyhydroxide was obtained, which was designated as FeOOH / PEI.

[0042] 3. Preparation of modified iron oxyhydroxide-based membrane:

[0043] 3.0 mg of the above FeOOH / PEI was added to 100 mL of deionized water and ultrasonically dispersed for 10 min to obtain a modified FeOOH suspension. The suspension was then filtered from 0 mL to 10 mL through a PES bottom membrane with a diameter of 4.0 cm. After drying and washing, a modified FeOOH base membrane was obtained.

[0044] 4. Preparation of modified FeOOH nanofiltration membrane:

[0045] In a fume hood, the modified FeOOH-based membrane is horizontally spread on a smooth glass plate, and then a membrane frame is placed directly in the center of the modified FeOOH-based membrane and fixed on all four sides with iron clips. A piperazine (PIP) aqueous solution is poured into the membrane frame, and after 90 seconds, the remaining solution in the membrane frame is poured out and drained. After drying for 10 to 20 minutes, a trimesoyl chloride (TMC)-n-hexane solution is poured in, and the remaining solution in the membrane frame is poured out after 40 seconds. Then, 5 mL of n-hexane solution is poured in and shaken for 30 seconds. The glass plate is then vertically dried until the membrane surface is completely dry. The iron clip is removed and the membrane frame is taken down. The membrane is removed from the glass plate with tweezers and marked. The membrane is then placed in a forced air drying oven and thermally crosslinked at 60°C for 30 minutes to obtain a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane, thereby completing the preparation method.

[0046] The polyethyleneimine in step 2 of this embodiment is: PEI, M=10000.

[0047] The film frame in step 4 of this embodiment is an organic solvent-resistant film frame.

[0048] The purpose of the 90s waiting time in step 4 of this embodiment is to allow the aqueous solution to infiltrate the surface of the modified FeOOH base film.

[0049] The 40 seconds mentioned in step 4 of this embodiment is to allow the PIP and TMC to fully react.

[0050] The purpose of pouring 5 mL of n-hexane solution in step 4 of this embodiment is to wash away the unreacted trimesoyl chloride monomer on the membrane surface and accelerate volatilization of the membrane surface.

[0051] The modified iron oxyhydroxide-loaded polyamide nanofiltration membrane obtained in step 4 of this embodiment is placed in a sealed bag and stored at room temperature for future use.

[0052] Specific Embodiment 2: This embodiment differs from Specific Embodiment 1 in that, in step 1, the synthesis of the iron oxyhydroxide is as follows: 2.16 g of FeCl3·6H2O and 20 mL of ethylenediamine are added to 40 mL of deionized water, stirred for 20 minutes, then transferred to a high-temperature reactor and sealed. The reaction mixture is incubated at 85°C for 12 hours, cooled to room temperature, centrifuged and washed, and then vacuum-dried at 80°C to obtain the iron oxyhydroxide. The other steps and parameters are the same as those in Specific Embodiment 1.

[0053] In this embodiment, the washing is performed by rinsing with deionized water 2 to 3 times in order to eliminate residual chloride ions.

[0054] Specific embodiment 3: This embodiment differs from specific embodiment 2 in that the ethanol aqueous solution in step 1 is prepared by mixing 45 mL of deionized water and 5 mL of anhydrous ethanol. The other steps and parameters are the same as those in specific embodiment 2.

[0055] Specific embodiment 4: This embodiment differs from specific embodiment 1 in that the magnetic stirring after ultrasonic dispersion in step 1 is performed for 30 minutes followed by ultrasonic dispersion and magnetic stirring for 30 minutes. Other steps and parameters are the same as those in specific embodiment 1.

[0056] Specific embodiment 5: This embodiment differs from specific embodiment 1 in that the silane coupling agent in step 1 is KH560. Other steps and parameters are the same as those in specific embodiment 1.

[0057] Specific embodiment 6: This embodiment differs from specific embodiment 1 in that the centrifugation, washing, and drying in step 1 are performed at 4000 rpm for 5 minutes, followed by washing 2-3 times with anhydrous ethanol, and then vacuum drying at 40°C for 24 hours. The other steps and parameters are the same as those in specific embodiment 1.

[0058] Specific embodiment 7: This embodiment differs from specific embodiment 1 in that the ultrasonic dispersion in step 2 is followed by magnetic stirring: ultrasonic dispersion for 10 minutes and magnetic stirring for 30 minutes. Other steps and parameters are the same as those in specific embodiment 1.

[0059] Specific embodiment 8: This embodiment differs from specific embodiment 1 in that the centrifugation, washing, and drying in step 2 are performed at 4000 rpm for 5 minutes, followed by washing with deionized water and anhydrous methanol 2-3 times each, and then drying at 60°C for 24 hours. The other steps and parameters are the same as those in specific embodiment 1.

[0060] Specific embodiment 9: This embodiment differs from specific embodiment 1 in that the drying and washing in step 3 are: drying in a 60°C oven for 3 minutes, and then rinsing with deionized water 2-3 times. Other steps and parameters are the same as those in specific embodiment 1.

[0061] Specific embodiment 10: This embodiment differs from specific embodiment 1 in that the amount of piperazine aqueous solution used in step 4 is 5 mL, and the concentration is 0.5% / wv. Other steps and parameters are the same as those in specific embodiment 1.

[0062] Specific embodiment 11: This embodiment differs from specific embodiment 1 in that the amount of trimesoyl chloride-n-hexane solution used in step 4 is 5 mL, and the concentration is 0.1% / wv. Other steps and parameters are the same as those in specific embodiment 1.

[0063] The beneficial effects of the present invention are verified by the following examples:

[0064] Example 1:

[0065] A method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane comprises the following steps:

[0066] 1. Preparation of silane coupling agent functionalized iron oxyhydroxide:

[0067] 0.5 g of iron oxyhydroxide was added to 50 ml of ethanol in water, ultrasonically dispersed, and then magnetically stirred. Then, 1 mL of KH560 was added and reacted at 40°C for 2 h. After centrifugation, washing, and drying, KH560-functionalized iron oxyhydroxide (FeOOH / KH560) was obtained.

[0068] 2. Preparation of polyethyleneimine-modified iron oxyhydroxide:

[0069] 0.2 g of the above FeOOH / KH560 was added to 50 mL of anhydrous methanol, ultrasonically dispersed and magnetically stirred, and then 2 g of polyethyleneimine was added. The temperature was raised to 90°C, refluxed for 6 h, and naturally cooled to room temperature. After centrifugation, washing, and drying, polyethyleneimine-modified iron oxyhydroxide was obtained, which was recorded as FeOOH / PEI.

[0070] 3. Preparation of modified iron oxyhydroxide-based membrane:

[0071] 3.0 mg of the above FeOOH / PEI was added to 100 mL of deionized water and ultrasonically dispersed for 10 min to obtain a modified FeOOH suspension. The suspension was then filtered from 0 mL to 10 mL through a PES bottom membrane with a diameter of 4.0 cm. After drying and washing, a modified FeOOH base membrane was obtained.

[0072] 4. Preparation of modified FeOOH nanofiltration membrane:

[0073] In a fume hood, the modified FeOOH-based membrane is horizontally spread on a glass plate with a smooth surface, and then a membrane frame is placed directly in the center of the modified FeOOH-based membrane and fixed on all four sides with iron clips; a piperazine (PIP) aqueous solution is poured into the membrane frame, and after 90 seconds, the remaining solution in the membrane frame is poured out and drained, and after drying for 10 to 20 minutes, a trimesoyl chloride (TMC)-n-hexane solution is poured in, and the remaining solution in the membrane frame is poured out after 40 seconds, and then 5 mL of n-hexane solution is poured in and shaken for 30 seconds, and then the glass plate is vertically dried until the membrane surface is completely dry, the iron clip is removed and the membrane frame is taken down, and the membrane is removed from the glass plate with tweezers and marked, and then placed in a blast drying oven and thermally cross-linked at 60° C. for 30 minutes to obtain a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane (denoted as FeOOH / PEI polyamide nanofiltration membrane), thereby completing the preparation method;

[0074] Synthesis of the iron oxyhydroxide described in step 1 of this example: 2.16 g of FeCl3·6H2O and 20 mL of ethylenediamine were added to 40 mL of deionized water, stirred for 20 min, transferred to a high-temperature reaction kettle, and sealed. The mixture was kept at 85°C for 12 h, then cooled to room temperature, centrifuged and washed, and then vacuum-dried at 80°C to obtain iron oxyhydroxide;

[0075] The ethanol aqueous solution described in step 1 is prepared by mixing 45 mL of deionized water and 5 mL of anhydrous ethanol;

[0076] The magnetic stirring after ultrasonic dispersion in step 1 is: ultrasonic dispersion for 30 minutes and then magnetic stirring for 30 minutes;

[0077] Centrifugation, washing and drying in step 1: centrifugation at 4000 rpm for 5 min, followed by washing three times with anhydrous ethanol, and vacuum drying at 40°C for 24 h;

[0078] Magnetic stirring after ultrasonic dispersion in step 2: ultrasonic dispersion for 10 minutes and magnetic stirring for 30 minutes;

[0079] Centrifugation, washing and drying in step 2: centrifugation at 4000 rpm for 5 min, followed by washing with deionized water and anhydrous methanol three times each, and then drying at 60°C for 24 h;

[0080] Drying and washing in step 3: drying in a 60°C oven for 3 minutes, then rinsing with deionized water 3 times;

[0081] The amount of the piperazine aqueous solution in step 4 is 5 mL, and the concentration is 0.5% / wv;

[0082] The amount of trimesoyl chloride-n-hexane solution used in step 4 is 5 mL, and the concentration is 0.1% / wv.

[0083] Comparative Example:

[0084] In this example, the modified FeOOH-based membrane was replaced with an unmodified PES-based membrane, and then the method of step 4 of Example 1 was used for preparation to obtain an unmodified polyamide nanofiltration membrane.

[0085] result:

[0086] Figure 1 This is the SEM image of FeOOH / PEI obtained in step 2 of Example 1. Figure 1 As shown, FeOOH / PEI is a nanorod with a length of 440 nm and a width of 63 nm, which can be used as a scaffold.

[0087] Figure 2 The infrared spectra of FeOOH / KH560 obtained in step 1 of Example 1, FeOOH / PEI obtained in step 2, and existing FeOOH are shown in FIG. Figure 2 As shown, the peaks at 899 cm-1 and 801 cm-1 are due to the Fe-OH bending vibration in FeOOH, while the peak at 620 cm-1 corresponds to the Fe-O stretching vibration, confirming the successful synthesis of FeOOH. After reaction with KH560, new peaks at 2925 cm-1 and 2854 cm-1 correspond to the CH stretching vibrations of the methyl and methylene groups, respectively, and the peak at 1112 cm-1 corresponds to the Si-O stretching vibration, demonstrating the successful grafting of KH560 onto the FeOOH surface. After the introduction of PEI, peaks at 1658 cm-1, 1476 cm-1, and 1115 cm-1 correspond to the -NH2 stretching vibration, CH bending vibration, and CN stretching vibration, respectively, indicating the successful grafting of PEI onto the FeOOH surface.

[0088] Figure 3 The infrared spectra of the PES base membrane, the FeOOH / PEI polyamide nanofiltration membrane in Example 1 and the unmodified polyamide nanofiltration membrane in the comparative example are shown in FIG. Figure 3 As shown in the figure, compared with the PES-based membrane, the FeOOH / PEI polyamide nanofiltration membrane and the unmodified polyamide nanofiltration membrane have a wavelength of 1647 cm -1There is an extra peak at 920 cm in the spectrum of FeOOH / PEI polyamide nanofiltration membrane, which is caused by the C=O of polyamide generated during interfacial polymerization, indicating that the polyamide layer was successfully synthesized on the modified FeOOH base membrane. -1 The peak of 899 cm-1 does not appear in the spectra of unmodified polyamide nanofiltration membrane and modified FeOOH-based membrane. This peak is caused by the Fe-OH bending vibration in FeOOH. It may be due to the interaction between FeOOH / PEI and modified FeOOH-based membrane, which shifts the peak from 899 cm-1 to 920 cm-1. -1 .

[0089] Figure 4 The surface and cross-sectional SEM and AFM images of the PES base membrane, the modified FeOOH base membrane in Example 1, the FeOOH / PEI polyamide nanofiltration membrane and the unmodified polyamide nanofiltration membrane in the comparative example are shown in FIG. Figure 4 As shown, Figure a and Figure b are surface SEM images of PES-based membrane and modified FeOOH-based membrane, respectively. It can be seen that the surface pores of the modified FeOOH-based membrane are clearly visible, and the FeOOH / PEI on the surface of the FeOOH / PEI polyamide nanofiltration membrane is evenly dispersed without aggregation; Figure c and Figure d are surface SEM images of the unmodified polyamide nanofiltration membrane and the FeOOH / PEI polyamide nanofiltration membrane, respectively. It can be seen from Figure c that the surface of the unmodified polyamide nanofiltration membrane is a standard nodular structure. After adding FeOOH / PEI, the surface nodular structure disappears, and a network-like structure appears on the surface, which increases many cavities and is conducive to water permeability. It contributes to the increase in water flux. Figure e and Figure f are cross-sectional SEM images of unmodified polyamide nanofiltration membrane and FeOOH / PEI polyamide nanofiltration membrane. It can be seen that with the addition of FeOOH / PEI, the thickness of the polyamide layer decreases from 403nm to 296nm, which contributes to the increase in water flux. Figure g and Figure h are AFM images of unmodified polyamide nanofiltration membrane and FeOOH / PEI polyamide nanofiltration membrane. With the addition of FeOOH / PEI, the surface roughness of the unmodified polyamide nanofiltration membrane increases from 7.16nm to 26nm. The increase in surface roughness can add more water channels, which contributes to the increase in water flux.

[0090] Figure 5 The surface water contact angle diagram of FeOOH / PEI polyamide nanofiltration membrane and unmodified polyamide nanofiltration membrane is shown in Figure 2. Figure 5As shown in the first figure, the water contact angle of the unmodified polyamide membrane surface decreases from 61.1 degrees to 44 degrees after the addition of FeOOH / PEI. As shown in the second figure, the surface is more hydrophilic. This is because the nodular structure on the surface of the polyamide membrane without the addition of FeOOH / PEI hinders the diffusion of water to the surrounding areas. After the addition of FeOOH / PEI, a uniform network structure is formed on the membrane surface with a large number of pores, which is more conducive to the diffusion of water droplets. In addition, the FeOOH / PEI polyamide nanofiltration membrane has a higher degree of cross-linking and the PA layer formed is thinner, which may also be a reason for the decrease in water contact angle.

[0091] Figure 6 The molecular weight cut-off diagram of FeOOH / PEI polyamide nanofiltration membrane and unmodified polyamide nanofiltration membrane is shown in Figure 2. Figure 6 As shown in the figure, the size of the membrane pore size is expressed by the molecular weight cut-off. The retention rates of the two membranes for PEG of different molecular weights are shown in the figure. When the nanofiltration membrane's PEG retention rate reaches 90%, it is the molecular weight cut-off of the membrane. Figure 6 It can be seen that the retention rate of unmodified polyamide nanofiltration membrane for PEG is lower than that of FeOOH / PEI polyamide nanofiltration membrane. Therefore, FeOOH / PEI polyamide nanofiltration membrane has a smaller pore structure. The results show that the retention molecular weight of FeOOH / PEI polyamide nanofiltration membrane is 517Da, which is lower than 580Da of unmodified polyamide nanofiltration membrane, further proving that FeOOH / PEI polyamide nanofiltration membrane has a denser PA layer.

[0092] Figure 7 The water flux and rejection rate of FeOOH / PEI polyamide nanofiltration membrane with different loading amounts are shown in Figure 2. Figure 7 As shown in the figure, after adding FeOOH / PEI, the water flux of the nanofiltration membrane increased to varying degrees, with the largest increase at 7.5ml. With the addition of FeOOH / PEI, the cross-linking degree of the polyamide layer on the surface of the nanofiltration membrane continued to increase, forming a denser polyamide layer. Therefore, the subsequent water flux will decrease slightly, and the salt retention rate will increase slightly with the increase of FeOOH / PEI because a defect-free polyamide layer is formed on the surface. In general, the addition of FeOOH / PEI increases the water flux of the nanofiltration membrane from 13.58L / m 2 ·h increased to 19.89 L / m 2 h, the retention rate increased from 90.78% to 94.3%.

[0093] Figure 8 The figure shows the effect of different material concentrations on the performance of FeOOH / PEI polyamide nanofiltration membrane. Figure 8 As shown in the figure, with the increase of Na2SO4 solution concentration, the water flux of FeOOH / PEI polyamide nanofiltration membrane gradually decreases, and the rejection rate remains stable.

[0094] Figure 9 This is the long-term operation diagram of FeOOH / PEI polyamide nanofiltration membrane, such as Figure 9 As shown in the figure, the FeOOH / PEI polyamide nanofiltration membrane still maintains high water flux and retention rate after 24 hours of long-term operation, indicating that the FeOOH / PEI polyamide nanofiltration membrane has high stability and is not easy to fall off.

[0095] Figure 10 The effect of acid-resistant treatment on FeOOH / PEI polyamide nanofiltration membrane is shown in Figure 2. Figure 10 As shown in the figure, after the FeOOH / PEI polyamide nanofiltration membrane was treated with acid, the water flux increased slightly and the retention rate decreased slightly, indicating that the FeOOH / PEI polyamide nanofiltration membrane has good acid resistance.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, 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 method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane, characterized in that It proceeds as follows:

1. Preparation of silane coupling agent functionalized iron oxyhydroxide: 0.5 g of ferric oxyhydroxide was added to 50 ml of an ethanol aqueous solution, ultrasonically dispersed, and then magnetically stirred. 1 mL of a silane coupling agent was then added and reacted at 40°C for 2 h. After centrifugation, washing, and drying, silane coupling agent-functionalized ferric oxyhydroxide was obtained.

2. Preparation of polyethyleneimine-modified iron oxyhydroxide: 0.2 g of the silane coupling agent-functionalized iron oxyhydroxide was added to 50 mL of anhydrous methanol, ultrasonically dispersed, and magnetically stirred. 2 g of polyethyleneimine was then added, and the mixture was heated to 90°C, refluxed for 6 h, and naturally cooled to room temperature. After centrifugation, washing, and drying, polyethyleneimine-modified iron oxyhydroxide was obtained, which was designated as FeOOH / PEI.

3. Preparation of modified iron oxyhydroxide-based membrane: 3.0 mg of the above FeOOH / PEI was added to 100 mL of deionized water and ultrasonically dispersed for 10 min to obtain a modified FeOOH suspension. The suspension was then filtered from 0 mL to 10 mL through a PES bottom membrane with a diameter of 4.0 cm. After drying and washing, a modified FeOOH base membrane was obtained.

4. Preparation of modified FeOOH nanofiltration membrane: In a fume hood, the modified FeOOH-based membrane is horizontally spread on a smooth glass plate, and then a membrane frame is placed directly in the center of the modified FeOOH-based membrane and fixed on all four sides with iron clips. A piperazine aqueous solution is poured into the membrane frame, and after 90 seconds, the remaining solution in the membrane frame is poured out and drained. After drying for 10 to 20 minutes, a trimesoyl chloride-n-hexane solution is poured in, and the remaining solution in the membrane frame is poured out after 40 seconds. Then, 5 mL of n-hexane solution is poured in and shaken for 30 seconds. The glass plate is then vertically dried until the membrane surface is completely dry. The iron clip is removed and the membrane frame is taken down. The membrane is removed from the glass plate with tweezers and marked, and then placed in a forced air drying oven and thermally crosslinked at 60°C for 30 minutes to obtain a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane, thereby completing the preparation method.

2. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that Synthesis of iron oxyhydroxide in step 1: Add 2.16 g of FeCl3·6H2O and 20 mL of ethylenediamine to 40 mL of deionized water, stir for 20 minutes, transfer and seal the mixture in a high-temperature reactor, keep it at 85°C for 12 hours, then cool to room temperature, centrifuge and wash, and then vacuum dry at 80°C to obtain iron oxyhydroxide.

3. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that The magnetic stirring after ultrasonic dispersion in step 1 is: ultrasonic dispersion for 30 minutes and then magnetic stirring for 30 minutes.

4. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that Silane coupling agent described in step 1: KH560.

5. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that Centrifugation, washing and drying in step 1: centrifugation at a speed of 4000 r / min for 5 minutes, then washing with anhydrous ethanol 2 to 3 times, and then vacuum drying at 40°C for 24 hours.

6. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that Magnetic stirring after ultrasonic dispersion in step 2: ultrasonic dispersion for 10 minutes and magnetic stirring for 30 minutes.

7. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that The centrifugation, washing and drying in step 2 are as follows: centrifugation at a speed of 4000 r / min for 5 minutes, followed by washing with deionized water and anhydrous methanol for 2 to 3 times, and then drying at 60° C. for 24 hours.

8. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that Drying and washing in step 3: Dry in a 60°C oven for 3 minutes, then rinse with deionized water 2 to 3 times.

9. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that The amount of the piperazine aqueous solution in step 4 is 5 mL, and the concentration is 0.5% / wv.

10. The method for preparing a modified iron oxyhydroxide-loaded polyamide nanofiltration membrane according to claim 1, characterized in that The amount of trimesoyl chloride-n-hexane solution used in step 4 is 5 mL, and the concentration is 0.1% / wv.

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