PES composite ultrafiltration membrane loaded with POMs, preparation method and application thereof

Abstract

The present invention discloses a PES composite ultrafiltration membrane loaded with POMs, a preparation method, and an application thereof, belonging to the field of ultrafiltration membrane preparation and application. The preparation method of the composite membrane comprises: dissolving PES, PEG, and phosphomolybdic acid in an organic solvent, DMF, to prepare a casting solution; then, using a one-step non-solvent induced phase separation method, the PES composite ultrafiltration membrane loaded with POMs is prepared. By varying the amount of phosphomolybdic acid added to the casting solution, the separation performance of the composite membrane can be regulated. The preparation process is simple, and the process flow is simple and efficient. The present invention solves the inherent defects of the PES ultrafiltration membrane, which has poor filtration and anti-pollution capabilities. The prepared composite membrane has higher water permeability, better separation performance, and stronger resistance to organic and biological pollution, and can significantly improve water treatment efficiency.

Description

Technical Field

[0001] The invention belongs to the field of ultrafiltration membrane preparation and application, and particularly relates to a PES composite ultrafiltration membrane loaded with POMs, a preparation method and application thereof. Background Art

[0002] With rapid economic development and a growing population, global water shortages are becoming increasingly serious. Currently, membrane separation technology, with its advantages of low energy consumption, low pollution, and excellent permeability and selectivity, has been widely used in fields such as industrial wastewater reuse and seawater desalination. Although membrane separation technology has achieved considerable development, the trade-off between membrane permeability and selectivity makes it difficult to balance treatment efficiency and operating costs while ensuring effluent quality.

[0003] Among various organic synthetic materials for ultrafiltration membranes, PES (polyethersulfone) has become one of the most popular ultrafiltration membrane preparation materials due to its excellent thermal stability, chemical stability, and strong compressive resistance under high temperature and humid conditions. It plays an important role in the field of membrane separation. However, the inherent hydrophobicity of polymers such as PES makes ultrafiltration membranes extremely susceptible to organic and biological fouling, resulting in a decrease in separation performance. Therefore, to maintain the separation performance of the membrane during long-term use, the contaminated membrane needs to be physically or chemically cleaned. However, frequent cleaning will shorten the service life of the membrane and increase operating costs. Therefore, the problem of membrane fouling has become one of the most challenging technical problems in the current membrane separation field.

[0004] To address the shortcomings of organic membranes in practical applications, co-modification is a simple and effective method that can improve membrane pore structure and enhance anti-fouling properties. Currently, hydrophilic polymers, particularly PEG (polyethylene glycol), PEI (polyethyleneimine), and PVP (polyvinylpyrrolidone), are commonly used as modifiers. These polymers not only improve the hydrophilicity of the membrane surface but also act as pore-forming agents to control pore size and porosity. However, the preparation of composite membranes using only these polymers as additives has significant drawbacks: it is difficult to achieve enhanced anti-fouling properties. In recent years, the introduction of nanomaterials into the membrane selective layer has become a promising membrane modification method. Researchers have successfully designed and developed quantum dots, nanotubes / wires, nanosheets, and nanocubes / spheres, and incorporated them into the membrane matrix. Studies have shown that the introduction of specialized nanomaterials into membranes can significantly improve the hydrophilicity, electronegativity, internal free volume, and selective layer thickness of the membrane, thereby enhancing membrane separation performance. However, the interaction between these inorganic nanomaterials and the membrane matrix is ​​weak and their compatibility is poor, so there is a risk of nanomaterial loss. The loss of nanomaterials will not only cause macroscopic defects in the membrane structure, but also lead to secondary pollution to the environment. Although emerging organic nanomaterials such as MOFs (metal organic frameworks), COFs (covalent organic frameworks), POPs (porous organic polymers) and ILs (ionic liquids) have better compatibility with membranes, there are still many problems with the dispersion of such materials in the membrane and their stability in water. In addition, the contaminated composite membrane needs to be chemically cleaned in acidic, alkaline and strongly oxidizing environments, and most nanomaterials have poor chemical stability. Therefore, the development of more suitable membrane modification materials remains an important research topic.

[0005] Due to their redox ability, thermal stability, and chemical stability, POMs (oxygen-containing metal clusters) are a research hotspot in the fields of photocatalysis, electrocatalysis, energy conversion, and storage. POMs are composed of oxide anions of early transition metal crystals (primarily Mo, W, and V). Their inherent oxygen-containing clusters give them excellent hydrophilicity and strong electronegativity. Simultaneously, relevant research in the biomedical field has shown that POMs are highly promising bactericidal and antiviral drugs. Furthermore, the excellent coordination ability of POMs also gives them the potential to be assembled into membrane structures through stable coordination. In summary, POMs are expected to become a modifier for improving the filtration performance and anti-fouling properties of ultrafiltration membranes. Patent CN114715977A discloses a POMs-modified membrane for water treatment, its preparation method, and application. In-situ immersion is used to prepare a polyacrylonitrile membrane loaded with POMs, which solves the poor pollution resistance of traditional polymers. However, the amount of POMs used is large, and POMs cannot be effectively utilized. In addition, there is limited improvement in membrane porosity, membrane pore size, pore density, and selective layer thickness. Summary of the Invention

[0006] The purpose of the present invention is to address the inherent defects of PES ultrafiltration membranes, such as poor filtration and anti-pollution capabilities, and propose a method for preparing a PES composite ultrafiltration membrane loaded with POMs, and secondly, to improve the wastewater treatment efficiency during actual use through this composite ultrafiltration membrane.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a PES composite ultrafiltration membrane loaded with POMs comprises the following steps:

[0009] Step 1: Prepare the casting solution: dissolve PES and PEG in DMF, place the solution in a 70°C oil bath, and stir to make PES and PEG dissolve evenly to obtain the basement membrane solution; 12 ) was dissolved in DMF to prepare PMo 12 -DMF solution; PMo 12 -DMF solution was added to the base film solution and stirred in a 70℃ oil bath; the mixture was allowed to stand and degas overnight to obtain the blended PMo 12 The casting solution;

[0010] Step 2: Preparation of a PES composite ultrafiltration membrane loaded with POMs: At room temperature, pour the casting liquid obtained in step 1 onto a glass plate, spread it, let it stand, and then immerse it in deionized water at room temperature. The casting liquid is phase-separated and solidified, and then the membrane is separated from the glass plate to obtain a PES composite ultrafiltration membrane; after taking out the PES composite ultrafiltration membrane, soak it in deionized water to remove residual solvents and additives, thereby obtaining a PES composite ultrafiltration membrane loaded with POMs.

[0011] Furthermore, the molecular weight of PEG in step 1 is 20,000.

[0012] Furthermore, the PMo in step 1 12 -PMo in DMF solution 12 The mass fraction is: 0.45%~1.35%.

[0013] Furthermore, in the basement membrane solution in step 1, the mass fractions of PES and PEG are 20% and 8%, respectively.

[0014] The PES composite ultrafiltration membrane loaded with POMs is prepared by the above method.

[0015] Application of PES composite ultrafiltration membrane loaded with POMs in water treatment.

[0016] The present invention adopts a one-step non-solvent induced phase separation method, wherein POMs and PEG are blended into a PES casting solution as additives. This method not only modifies the membrane matrix through coordination to optimize the membrane surface properties, but also promotes the transfer of PEG from the casting solution to the phase separation solution through the hydrogen bonding between POMs and PEG during the phase separation process, thereby achieving regulation of the membrane phase separation process and ultimately achieving optimization of key membrane performance parameters such as porosity, pore size, pore density and selective layer thickness. The prepared PES composite ultrafiltration membrane loaded with POMs can significantly improve the water flux and BSA retention rate, thereby improving wastewater treatment efficiency.

[0017] Compared with the prior art, the present invention has the following significant advantages:

[0018] (1) The present invention comprises PES, PEG and PMo 12 The PES composite ultrafiltration membrane loaded with POMs was prepared by dissolving in organic solvent DMF to prepare the casting solution through a one-step non-solvent induced phase separation method. 12 The addition amount can realize the regulation of the separation performance of the composite membrane. The preparation process is simple, the process flow is simple and efficient, and the obtained composite membrane is environmentally friendly and has the potential for large-scale manufacturing.

[0019] (2) The composite ultrafiltration membrane of the present invention can achieve a water flux of 572.67±21.73LMH, which is 238% higher than that of the blank PES membrane. One of the reasons is that the addition of PMo 12 , effectively promoting the formation of membrane pores and the increase of membrane pore diameter, reducing the mass transfer resistance of water molecules, and at the same time, the uncoordinated PMo 12 The hydrogen bonding between the membrane and PEG accelerates the release of PEG, further increasing the pore size, pore density and porosity. The retention rate of the organic pollutant bovine serum albumin (BSA) is as high as 99.31±0.22%, which is 0.7% higher than that of the PES blank membrane. 12 This enhances the hydrophilicity and electronegativity of the membrane surface, reducing the deposition of hydrophobic and negatively charged organic pollutants on the membrane surface. The increase in water flux and BSA retention will help improve the membrane's wastewater treatment efficiency during actual use.

[0020] (3) The composite ultrafiltration membrane of the present invention has significantly improved anti-pollution capabilities. The composite ultrafiltration membrane has a bactericidal activity against Escherichia coli of up to 96.9±1.2%. Furthermore, the composite ultrafiltration membrane exhibits excellent anti-pollution effects in both static and dynamic contamination processes with the organic pollutants BSA and humic acid (HA). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The different PMo in the present invention 12 Comparison images of casting solutions with different concentrations.

[0022] Figure 2 The different PMo in the present invention 12 Viscosity comparison chart of casting solutions with different concentrations.

[0023] Figure 3 1 and 2 are scanning electron microscopy (SEM) images of the surface (ad) and bottom (eh) of the blank PES membrane and the composite membrane of the present invention.

[0024] Figure 4 Graph showing the surface pore density and overall porosity test results of the blank PES membrane and the composite membrane of the present invention.

[0025] Figure 5 The different PMo in the present invention 12 Graph showing the absorbance change during the phase separation process of the casting solution with different concentrations.

[0026] Figure 6 It is the atomic force microscope (AFM) image of the PES blank membrane and the composite membrane in the present invention.

[0027] Figure 7 1 is the cross-sectional SEM image of the blank PES membrane and the composite membrane of the present invention, and the inset is the corresponding high-magnification image.

[0028] Figure 8 This is a comparison chart of the thickness of the selective layer of the PES blank membrane and the composite membrane in the present invention.

[0029] Figure 9 PMo in the present invention 12 , infrared spectra (IR) of PES blank membrane and composite membrane.

[0030] Figure 10 PMo in the present invention 12 , thermal decomposition process diagram of PES blank membrane and composite membrane.

[0031] Figure 11 PMo in the present invention 12 , X-ray photoelectron spectroscopy (XPS) of PES blank film and composite film.

[0032] Figure 12 The different PMo in the present invention 12 The PMo content in the composite membrane prepared by the casting solution with a concentration of 12 Content comparison chart.

[0033] Figure 13 Graphs showing water contact angles (WCA) of the blank PES membrane and the composite membrane of the present invention.

[0034] Figure 14 PMo in the present invention 12 Zeta potential diagram.

[0035] Figure 15 1 is the zeta potential diagram of the PES blank membrane and the composite membrane in the present invention.

[0036] Figure 16 1 is the molecular weight cut-off diagram (MWCOs) of the PES blank membrane and the composite membrane in the present invention.

[0037] Figure 17 This is a comparison chart of the effective pore size distribution and average pore size of the PES blank membrane and the composite membrane in the present invention.

[0038] Figure 18 1 is a graph showing the separation performance test results of the PES blank membrane and the composite membrane in the present invention.

[0039] Figure 19 It is the PMo in the PES-P2 composite membrane of the present invention. 12 Figure 2. Results of leaching risk testing in circulating solution.

[0040] Figure 20 This is a graph showing the static anti-organic pollution performance test results of the PES blank membrane and the PES-P2 composite membrane in the present invention.

[0041] Figure 21 This is a graph showing the dynamic anti-organic pollution performance test results of the PES blank membrane and the PES-P2 composite membrane in BSA in the present invention.

[0042] Figure 22 This is a graph showing the dynamic anti-organic pollution performance test results of the PES blank membrane and the PES-P2 composite membrane in HA in the present invention.

[0043] Figure 23 It is a comparison chart of the calculated results of membrane water flux decline value (Fd), flux recovery value (Fr) and irrecoverable flux value (Fir) of the PES blank membrane and the PES-P2 composite membrane in the dynamic fouling process in the present invention.

[0044] Figure 24 1 is a graph showing the anti-biological fouling performance test results of the PES blank membrane and the PES-P2 composite membrane of the present invention. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention.

[0046] Example 1

[0047] A PES composite ultrafiltration membrane loaded with POMs is prepared in the following steps:

[0048] Step 1: Prepare the casting solution: Place PES in a 100°C oven and dry for 10-12 hours, then dissolve PES and polyethylene glycol (PEG) in DMF, place the solution in a 70°C oil bath, and mechanically stir for 1 hour to dissolve PES and PEG evenly to obtain the basement membrane solution; 12 Dissolve in DMF to prepare PMo 12 -DMF solution; PMo with a mass fraction of 0.45% 12 -DMF solution was added to the base film solution, and mechanical stirring was continued in a 70 ° C oil bath for 4 hours; it was allowed to stand and degas overnight to obtain the blended PMo 12 The casting solution prepared in step 1 was poured onto a tempered glass plate at room temperature. The casting solution was spread on the glass plate using a glass rod and allowed to stand in clean air for 20 seconds. The casting solution was then immersed in room temperature deionized water. The casting solution solidified through phase separation. After 20 minutes, the membrane separated naturally from the glass plate, resulting in a PES composite ultrafiltration membrane. The PES composite ultrafiltration membrane was carefully removed and immersed in deionized water to remove any residual solvent and additives. The deionized water was replaced every 24 hours. The resulting membrane was designated PES-P1.

[0049] Example 2

[0050] Same as Example 1, except that 0.90% of PMo 12 -DMF solution was added to the base membrane solution. The prepared membrane was designated as PES-P2.

[0051] Example 3

[0052] Same as Example 1, except that the mass fraction of PMo is 1.35% 12 -DMF solution was added to the base membrane solution. The prepared membrane was designated as PES-P3.

[0053] Comparative Example 1

[0054] Same as Example 1, except that PMo was not added to the casting solution. 12 The prepared membrane was recorded as PES blank membrane and the experimental mark was PES.

[0055] The present invention is to measure the various evaluation indexes of PES blank film, PES-P1, PES-P2 and PES-P3 as follows:

[0056] (1) Surface pore density and overall porosity. The surface pore density was calculated using ImageJ software based on the corresponding SEM images. The overall porosity was calculated by wet film (m w ) and dry film (m d The weight loss between ) is calculated and measured, and the calculation formula is as follows:

[0057]

[0058] Where ρ is the water density, A is the effective area of ​​the membrane, and l is the thickness of the membrane.

[0059] The test results are as follows Figure 4 shown.

[0060] (2) The surface roughness was measured by AFM. The results are as follows Figure 6 shown.

[0061] (3) The thickness of the selected layer was measured by SEM images of the cross section of the film. Figure 7 、 Figure 8 shown.

[0062] (4) The water contact angle (WCA) of the membrane was measured by a water contact angle meter. A 3 μL water droplet was dropped onto the membrane surface and the angle formed between the water droplet and the membrane surface was measured for 20 seconds. The measurement results are as follows: Figure 13 shown.

[0063] (5) The effective pore size of the membrane is reflected by the molecular weight cutoff of the test membrane. The calculation method is as follows. When the retention rate is 90%, it is achieved by using a solution containing 1g / L of PEG with different molecular weights. The PEG concentration in the feed solution and the filtrate is measured by TOC analyzer, and the pore size distribution of the membrane (d p ), the calculation formula is as follows:

[0064]

[0065] r s =16.73×10 -12 ×M 0.557

[0066] Among them, μ p is the Stokes radius of PEG when R is 50% (r s ), the geometric standard deviation (σp) of the membrane is the ratio of the radius when R is 84.13% to 50%, and M is the molecular weight of PEG.

[0067] The test results are as follows Figure 17 shown.

[0068] (6) The separation performance of the membrane was tested using the following method. Deionized water was used to pre-press the membrane at a flow rate of 0.6 m / s for 30 minutes under a pressure of 1.1 bar. The water flux of the membrane was tested at a pressure of 1 bar (J, L·m -2 ·h -1). Using 1g / L bovine serum albumin (BSA) solution (pH=7) as the feed solution, under 1 bar pressure conditions, the membrane retention rate (R, %) was investigated and calculated using the following formula:

[0069]

[0070]

[0071] Where, V is the permeate volume (L), S is the effective filtration area (m 2 ), Δt is the filtration time (h), C p is the concentration of BSA in the filtrate (g / L, measured by UV-visible spectrophotometer at an absorbance of 280 nm), C f is the concentration of BSA in the feed solution (g / L, measured by UV-visible spectrophotometer at an absorbance of 280 nm).

[0072] The test results are as follows Figure 18 shown.

[0073] (7) The present invention tests the anti-pollution performance of the PES blank membrane and the PES-P2 composite membrane, and the test method is as follows:

[0074] The static anti-organic pollution performance is tested by the following method. 2 Place the membrane surface upward in a culture dish. Pour 10 mL of BSA (or HA) solution with a concentration of 10 mg / L onto the membrane surface and shake continuously at 25°C overnight. The amount of pollutants adsorbed by the membrane is calculated based on the difference in BSA (or HA) concentration in the solution before and after contact with the membrane surface. The concentrations of BSA and HA are measured at 280 nm and 260 nm, respectively, using a UV-visible spectrophotometer. The test results are as follows: Figure 20 shown.

[0075] The dynamic anti-organic pollution performance test was performed as follows: the membrane was pre-pressed with deionized water at 1 bar for 30 minutes, and the water flux of the membrane was tested every 10 minutes (J0, L·m -2 ·h -1 ). Then, 1g / L BSA solution and 1g / L HA solution were used as feed solution and filtered for 90 minutes. The water flux of the membrane was tested every 10 minutes (J f , L·m -2 ·h -1 Then the membrane was taken out and soaked in deionized water for 10 minutes. After washing, the water flux of the membrane was tested again with deionized water for 30 minutes (J w , L·m -2 ·h -1The above pollution cycle was repeated three times for each test. The calculation formulas for membrane water flux decline value (Fd), water flux recovery value (Fr) and irrecoverable flux value (Fir) are as follows:

[0076]

[0077]

[0078]

[0079] The test results are as follows Figure 21 、 Figure 22 、 Figure 23 shown.

[0080] (8) The membrane's anti-biological contamination performance was tested by the contact inactivation process between the membrane and Escherichia coli (E. coli). The specific test method is as follows. Experimental equipment including culture dishes, pipettes and LB agar medium were sterilized at 121°C for 30 minutes. A drop of initial bacterial solution was cultured in a nutrient solution at 37°C. After 5 hours, 0.1ml of bacterial solution, 10ml of physiological saline and the membrane were placed in the same test tube and cultured at 37°C for 2 hours. 0.5ml of the above solution was gradiently diluted 1000 times using physiological saline. Subsequently, 0.1ml of the dilution was evenly dispersed on the surface of the LB agar medium and cultured overnight at 37°C. The anti-biological contamination performance was reflected by the growth of bacterial colonies. The test results are as follows. Figure 24 shown.

[0081] Figure 1 The different PMo in the present invention 12 Comparative images of casting solutions with different concentrations. Figure 1 It can be seen that the four casting solutions are clear and uniform, without suspended matter or precipitation. 12 With the increase of concentration, the yellow color of the casting solution becomes obviously darker.

[0082] Figure 2 The different PMo in the present invention 12 The viscosity of the casting solution of the concentration. Figure 2 It can be seen that PMo 12 The higher the concentration, the greater the viscosity of the casting solution. The change in the viscosity of the casting solution will inevitably affect the phase inversion process, thereby further affecting the membrane formation process and the separation performance of the membrane.

[0083] Figure 3 Figure 1 is a scanning electron microscope (SEM) image of the surface (ad) and bottom (eh) of the PES blank membrane and composite membrane of the present invention. Figure 3In the figure, (a), (b), (c), and (d) are surface SEM images of the blank PES membrane, PES-P1, PES-P2, and PES-P3 composite membranes, respectively. (e), (f), (g), and (h) are bottom SEM images of the blank PES membrane, PES-P1, PES-P2, and PES-P3 composite membranes, respectively. The surface pore count of the membrane increases from PES to PES-P2, while it decreases for PES-P3. Figure 3 The illustrations of (ad) show the analysis results of the average pore size and pore size distribution of the membrane surface, which are Figure 3 As can be seen from the illustrations in (ad), as PMo 12 As the concentration increases, the percentage of small-diameter pores decreases and the percentage of large-diameter pores increases, that is, the average pore size increases. Figure 3 (eh) It can be seen that the number of pores on the bottom surface of the membrane also increases with the increase of PMo 12 The concentration of PMo increases, indicating that the addition of PMo 12 , which effectively promotes the formation of membrane pores and the increase of membrane pore diameter, and improves water flux from the perspective of increasing water transmission channels.

[0084] Figure 4 is the surface pore density and overall porosity of the PES blank membrane and composite membrane in the present invention. Figure 4 It can be seen that the pore density of the membrane surface increases from 1.25×10 14 / m 2 Increased to 4.55×10 14 / m 2 , while the pore density of PES-P3 composite membrane decreased to 2.78×10 14 / m 2 At the same time, the internal porosity of the membranes increased from 66.35 ± 3.07% for the PES blank membrane to 87.62 ± 1.76% for the PES-P2 composite membrane, while it decreased to 80.99 ± 2.53% for the PES-P3 composite membrane. The increase in pore size, pore density, and porosity is likely due to the uncoordinated PMo 12 Causes accelerated release of PEG. 12 When the concentration is 1.35 wt%, the phase separation rate slows down due to the high viscosity, and the membrane pore formation is hindered, thereby reducing the pore density and porosity of the membrane.

[0085] Figure 5 The different PMo in the present invention 12 The absorbance change process of the casting solution with different concentrations during the phase separation process. Figure 5 It can be seen that during the phase separation process, the release of the casting solution leads to a sharp increase in absorbance. 12 Strong hydrogen bonds are formed between the oxygen-containing groups and the hydroxyl groups of PEG.12 Afterwards, some PMo 12 The coordination is assembled into the microstructure of PES, while the other part of the hydrophilic free PMo 12 During the phase inversion process, PEG molecules are transferred from the casting solution to the coagulation bath, which increases the absorbance, indicating an increase in the phase conversion rate and an accelerated phase separation rate, thereby increasing the pore size, pore density and porosity.

[0086] Figure 6 It is the atomic force microscope (AFM) picture of the PES blank membrane and the composite membrane in the present invention. Figure 6 In the figure, (a), (b), (c), and (d) are AFM images of PES blank membrane, PES-P1, PES-P2, and PES-P3 composite membranes, respectively. Figure 6 It can be seen that the surface roughness of the membrane gradually decreases from 5.57±2.17nm of the PES blank membrane to 2.62±0.45nm of the PES-P3 composite membrane, indicating that the blended PMo 12 The problem of organic pollution can be alleviated by reducing the surface roughness of the membrane and reducing the adhesion of organic pollutants to the membrane surface.

[0087] Figure 7 The cross-sectional morphology SEM images of the blank PES membrane and the composite membrane of the present invention are shown in the figure, and the inset is the corresponding high-magnification image. Figure 7 In the figure, (a), (b), (c), and (d) are PES blank membrane, PES-P1, PES-P2, and PES-P3 composite membranes, respectively. Figure 7 It can be seen that the membrane mainly includes a selective layer composed of a dense surface layer and sponge pores and a finger-like pore support layer. Figure 7 The inset is a high-magnification image of the membrane, obtained by Figure 7 As can be seen from the illustration, the thickness of the selection layer is related to the PMo 12 The concentration is positively correlated.

[0088] Figure 8 Is the thickness of the selected layer of the PES blank film and composite film in the present invention. Figure 7 The thickness of the selected layer was measured in the SEM images of the cross section of the PES blank film and the composite film. Figure 8 It can be seen that the thickness of the selective layer increases from 3.0±0.7μm of the PES blank membrane to 8.7±0.9μm of the PES-P3 composite membrane. 12 The film thickness is more than doubled. Figure 2 It can be seen that PMo 12 The higher the concentration, the greater the viscosity of the casting solution. The increased viscosity of the casting solution slows down the phase separation rate, increases the thickness of the selective layer, and far exceeds PMo 12The promotion of phase inversion plays a dominant role in affecting the thickness of the selective layer of the membrane.

[0089] Figure 9 PMo in the present invention 12 , PES blank membrane and composite membrane infrared spectra (IR). Figure 9 It can be seen that PMo 12 The IR curve of the composite membrane is obviously different from the IR curve of the membrane, and the characteristic peaks of the membrane are basically the same. Compared with the PES blank membrane, the characteristic peak of the composite membrane is at 950cm -1 A red shift appears near 1071cm -1 At the same time, PMo 12 At 957(υ(Mo=O)) and 1057(PO))cm -1 There is a strong absorption peak, from which it can be inferred that the blended PMo 12 This caused the shift of the two characteristic peaks mentioned above, indicating that PMo 12 Present in composite membranes.

[0090] Figure 10 PMo in the present invention 12 Thermal decomposition process of PES blank membrane and composite membrane. Figure 10 It can be seen that with the increase of temperature, the thermal decomposition curves of all samples show a downward trend. At 700℃, the residual mass percentage of the PES blank membrane is the lowest, and the residual mass percentage of the composite membrane increases with the increase of PMo 12 The concentration of PMo increased steadily, indicating that 12 It exists in the composite film and its content is relatively high.

[0091] Figure 11 PMo in the present invention 12 , PES blank film and composite film X-ray photoelectron spectroscopy (XPS). Figure 11 It can be seen that compared with the PES blank membrane, the composite membrane clearly has Mo characteristic peaks, indicating that PMo 12 It exists in the composite film and its content is relatively high.

[0092] Figure 12 The different PMo in the present invention 12 The PMo content in the composite membrane prepared by the casting solution with a concentration of 12 The content of PMo is obtained by using concentrated hydrochloric acid to decompose the membrane per unit area. 12 The dissolution of PMo in each composite membrane can be directly measured by membrane digestion experiment. 12 Content, by Figure 12 It can be seen that as the PMo in the casting solution 12 With the increase of concentration, PMo in the composite membrane 12 The content showed an upward trend.

[0093] Figure 13 is the water contact angle (WCA) of the PES blank film and the composite film in the present invention. Figure 13 It can be seen that the WCA decreased from 65.7±1.2° for the PES blank membrane to 52.5±2.8° for the PES-P3 composite membrane, indicating that the addition of PMo 12 By increasing the pore density on the membrane surface, water molecules are promoted to diffuse into the membrane, thereby reducing WCA. 12 The excellent hydrophilicity of the membrane also increases.

[0094] Figure 14 PMo in the present invention 12 Zeta potential diagram. The zeta potential of the membrane was measured using 1 mM KCl as the electrolyte to test the charge characteristics of the membrane at pH 3-10.

[0095] Figure 15 It is the zeta potential diagram of the PES blank membrane and the composite membrane in the present invention. Figure 14 、 Figure 15 It can be seen that compared with the PES blank membrane, the composite membrane contains PMo 12 , the electronegativity is stronger, thereby effectively reducing the deposition of negatively charged organic pollutants on the membrane surface by enhancing the charge repulsion, and alleviating the problem of organic pollution on the membrane surface.

[0096] Figure 16 The molecular weight cutoffs (MWCOs) of the blank PES membrane and the composite membrane of the present invention are determined by the MWCOs of the membrane when the retention rate of the membrane for PEG of different molecular weights (10, 20, 100, 300 and 600 kDa) is 90%. Figure 16 It can be seen that the MWCOs of PES, PES-P1, PES-P2 and PES-P3 are 87.14, 78.73, 72.99 and 68.46 kDa, respectively. 12 As the content increases, the cut-off molecular weight gradually decreases.

[0097] Figure 17 is the effective pore size distribution and average pore size of the PES blank membrane and composite membrane in the present invention. Figure 17 It can be seen that PMo 12 The effective pore size of the membrane decreases as the concentration increases, but this is not related to Figure 3 The SEM image results contradict each other. Figure 7 、 Figure 8 Based on the study of membrane selective layer thickness in

[15] , it can be inferred that this contradiction is caused by the increase in the thickness of the membrane selective layer. The excessive thickness of the selective layer hinders the penetration of the pore-forming agent PEG, resulting in a decrease in the effective pore size.

[0098] Figure 18 This is a test of the separation performance of the blank PES membrane and the composite membrane in the present invention. Under room temperature conditions, the permeability and selectivity of the membrane were examined using deionized water and BSA solution in a cross-flow mode. The flow rate of the feed liquid in the device was 0.6m / s and the operating pressure was 0.1MPa, i.e. 1bar. Figure 18 It can be seen that the water flux of the PES blank membrane is 169.33±47.93 L·m -2 ·h -1 The water flux of the PES-P2 composite membrane increased to 572.67±21.73LMH, while the water flux of the PES-P3 composite membrane was 540.33±26.84LMH, which was slightly lower than that of the PES-P2 composite membrane. The PES-P2 composite membrane had the highest water flux, which increased by 238% compared with the PES blank membrane. This phenomenon is caused by the following factors: First, with the increase of PMo 12 The increase in concentration, the more PMo 12 The clusters are exposed on the membrane surface, providing more hydrophilic sites and promoting the water molecule permeation process. Secondly, compared with the PES blank membrane, the PES-P2 composite membrane has a higher pore density and porosity, which reduces the water molecule mass transfer resistance and improves the water flux. At the same time, due to the PMo 12 The concentration increases, resulting in a high viscosity of the casting solution, which reduces the pore density and porosity of the PES-P3 composite membrane, increases the mass transfer resistance of water molecules through the membrane, and reduces the water flux. 12 With the increase of concentration, the thickness of the membrane selective layer gradually increases, which hinders the permeation process of water molecules and causes the water flux of the PES-P3 composite membrane to decrease. Figure 18 It can be seen that the BSA rejection rate increased from 98.62±0.49% of the PES blank membrane to 99.49±0.33% of the PES-P3 composite membrane. 12 The selectivity of ultrafiltration membrane is determined by the effective pore size. Figure 17 It can be seen that PMo 12 As the concentration increases, the effective pore size of the membrane decreases, so the BSA retention rate also increases with the increase of PMo 12 Increases with the increase of concentration.

[0099] Figure 19 It is the PMo in the PES-P2 composite membrane of the present invention. 12 Leaching risk test in circulating solution. Using 1L deionized water as feed solution, the composite membrane was continuously operated at 1 bar, the permeate was returned to the feed solution, and the PMo content in the solution was tested at different times. 12The amount of (calculated based on the measured Mo concentration). Figure 19 It can be seen that the Mo concentration in the solution increased to about 23.5 μg / L within 30 minutes after the experiment using 500 mL of deionized water for 700 minutes of circulation filtration. This may be due to the physical adsorption of PMo inside the membrane. 12 It is difficult to remove by surface washing or soaking, but it is washed out under pressure. The leaching concentration of Mo is much lower than the 70μg / L specified in the Chinese Drinking Water Quality Standard (GB5749-2006). At the same time, the PMo 12 The leaching rate of α-D-glucan was only ∼5.0 wt %, which is negligible relative to the total loading, indicating that the composite membrane has excellent long-term stability.

[0100] Figure 20 This is a test of the static anti-organic pollution performance of the PES blank membrane and the PES-P2 composite membrane in the present invention. Figure 20 It can be seen that in the static pollution experiment, the adsorption capacity of BSA and humic acid (HA) by PES-P2 composite membrane was 87.9±26.2 and 63.7±11.2 mg / m 2 , which is much lower than 218.2±27.9 and 168.8±30.6 mg / m 2 .

[0101] Figure 21 、 Figure 22 、 Figure 23 This is a test of the dynamic anti-organic pollution performance of the PES blank membrane and the PES-P2 composite membrane in the present invention. Figure 23 It can be seen that with BSA and HA solutions as test solutions, the water flux decrease value (Fd) of the PES-P2 composite membrane is higher than that of the PES blank membrane. Figure 21 、 Figure 22 It can be seen that the overall water flux of the PES-P1 composite membrane is higher than that of the PES blank membrane. Compared with the PES blank membrane, the water flux recovery value (Fr) of the PES-P2 composite membrane is higher and the irrecoverable flux value (Fir) is lower, indicating that the PES-P2 composite membrane has better resistance to organic fouling. This may be due to the blending of PMo 12 This enhances the hydrophilicity and electronegativity of the membrane surface. On the one hand, the increased hydrophilicity reduces the deposition of hydrophobic contaminants on the membrane surface. On the other hand, the electronegativity enhances the charge repulsion effect between the membrane surface and negatively charged contaminants, reducing the deposition of negatively charged organic contaminants on the membrane surface.

[0102] Figure 24 This is a test of the anti-biological contamination performance of the PES blank membrane and the PES-P2 composite membrane in the present invention. Figure 24In the figure, (a) is the blank control group, that is, the growth of the diluted solution of E. coli culture on the surface of LB agar medium; (b) and (c) are the growth of the diluted solution of culture on the surface of LB agar medium after E. coli was mixed with PES blank membrane and PES-P2 composite membrane for 2 hours; (d) is a comparison chart of the number of E. coli colonies and sterilization activity in (b) and (c). Figure 24 In (d), it can be seen that the E. coli colony counts of the blank control group, PES blank membrane and PES-P2 composite membrane are 284±7, 258±5 and 9±4, respectively. The inset in (d) shows the bactericidal activity of PES blank membrane and PES-P2 composite membrane. The inset in (d) shows that the bactericidal activity of PES blank membrane and PES-P2 composite membrane is 9.3±1.6% and 96.9±1.2%, respectively, indicating that the blended PMo 12 It can significantly enhance the anti-biological fouling ability of the composite membrane.

Claims

1. A method for preparing a PES composite ultrafiltration membrane loaded with POMs, characterized in that: The following steps are involved: Step 1: Prepare a casting solution: Dissolve PES and PEG in DMF, place the solution in a 70°C oil bath, and stir to uniformly dissolve PES and PEG to obtain a basement membrane solution; dissolve phosphomolybdic acid in DMF to prepare a phosphomolybdic acid-DMF solution; add the phosphomolybdic acid-DMF solution to the basement membrane solution, and continue stirring in a 70°C oil bath; let it stand for degassing overnight to obtain a casting solution containing phosphomolybdic acid; Step 2: Preparing a PES composite ultrafiltration membrane loaded with POMs: at room temperature, pouring the casting solution obtained in step 1 onto a glass plate, spreading it, letting it stand, and then immersing it in deionized water at room temperature. The casting solution undergoes phase separation and solidification, and then the membrane is separated from the glass plate to obtain a PES composite ultrafiltration membrane; after removing the PES composite ultrafiltration membrane, immersing it in deionized water to remove residual solvents and additives, thereby obtaining a PES composite ultrafiltration membrane loaded with POMs; The mass fraction of phosphomolybdic acid in the phosphomolybdic acid-DMF solution in step 1 is 0.45% to 1.35%. The molecular weight of PEG in step 1 is 20,000. The mass fractions of PES and PEG in the basement membrane solution in step 1 are 20% and 8%, respectively. The phosphomolybdic acid in the casting solution is partially assembled into the microstructure of the PES membrane, and the remaining free phosphomolybdic acid transfers PEG from the casting solution to the coagulation bath during the phase inversion process, and the hydrogen bond between the phosphomolybdic acid and PEG accelerates the release of PEG.

2. The PES composite ultrafiltration membrane loaded with POMs obtained by the preparation method according to claim 1.

3. Use of the PES composite ultrafiltration membrane loaded with POMs according to claim 2 in water treatment.

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