Antifouling antibacterial nanofiltration membrane based on lawsone-iron coordination network and preparation method thereof

Abstract

A kind of antifouling antibacterial nanofiltration membrane based on lawsone-iron coordination network and preparation method.The present application belongs to nanofiltration membrane technical field.The purpose of the present application is to solve the technical problems that inorganic antibacterial metal nanoparticles on the existing antibacterial antifouling nanofiltration membrane are easy to fall off and flow loss, which leads to serious attenuation of antibacterial durability of nanofiltration membrane, and antibacterial, antifouling performance needs to be further improved.The nanofiltration membrane of the present application includes a substrate membrane and a lawsone-iron composite coating loaded thereon.The method of the present application: immerse the substrate membrane in a precursor solution containing iron and lawsone, and oscillate and deposit at room temperature.The present application uses lawsone with ortho-hydroxyl as a natural bacteriostatic agent, and the ortho-hydroxyl forms a stable five-membered ring coordination with iron as a reinforcing ligand, which realizes stable loading of metal ions while strengthening biological pollution control, significantly reduces the leakage of metal ions, guarantees the long-acting antibacterial antifouling performance of the composite membrane, and meets the green ecological requirements of environmental friendliness.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane technology, specifically relating to an antifouling and antibacterial nanofiltration membrane based on henna quinone-iron coordination network and its preparation method. Background Technology

[0002] Fluctuations in water quality caused by organic matter, trace pollutants, and bacterial growth place higher demands on existing water treatment processes. Traditional commercial nanofiltration membranes are often constrained by the trade-off between permeability and selectivity, making it difficult to simultaneously meet the dual requirements of high flux and high rejection rate in one-step membrane filtration. Furthermore, due to insufficient hydrophilicity of the membrane surface, microorganisms readily adhere to it, forming dense biofilms. Severe biofouling not only leads to a sharp decline in membrane flux and increased operating energy consumption but also forces water plants to frequently use large amounts of chemical cleaning agents. This significantly contradicts the environmentally friendly principles of low-chemical-consumption and low-emission treatment and may even cause irreversible damage to the membrane structure.

[0003] To address biofouling, existing anti-fouling modification strategies often employ physical blending, surface adsorption, or weak coordination to introduce inorganic antibacterial agents such as nano-silver and iron. However, these methods have serious drawbacks: firstly, under cross-flow shear stress and long-term continuous operation, the loaded nano-metal particles are easily and rapidly eluted and lost, leading to a significant decline in the membrane's antibacterial durability; more critically, the detached silver ions and other heavy metal residues enter water bodies or sludge systems, generating substantial secondary ecological risks. Therefore, there is an urgent need to develop a novel nanofiltration membrane that combines low environmental risk, long-lasting anti-biofouling properties, and the ability to overcome the permeability-selectivity constraint. This is of great significance for researching the synergistic reduction and control of carbon pollution in urban multi-media systems. Summary of the Invention

[0004] The purpose of this invention is to address the technical problems of existing antibacterial and antifouling nanofiltration membranes, which suffer from severe degradation of antibacterial durability due to the easy detachment and loss of inorganic antibacterial metal nanoparticles, and the need for further improvement in antibacterial and antifouling performance. This invention provides an antifouling and antibacterial nanofiltration membrane based on a henna quinone-iron coordination network and its preparation method.

[0005] The technical solution of the present invention is as follows: One of the objectives of this invention is to provide an antifouling and antibacterial nanofiltration membrane based on a henna quinone-iron coordination network. The nanofiltration membrane includes a base membrane and a henna quinone-iron composite coating loaded thereon. The Fe content in the coating is 2-4 at based on the amount of henna quinone.

[0006] Further specifying, the base film is polyamide.

[0007] Further specifying, the pore size of the basement membrane is 0.4-0.5 nm.

[0008] Further specified, the thickness of the henna quinone-iron composite coating is ≤20nm.

[0009] The second objective of this invention is to provide a method for preparing an antifouling and antibacterial nanofiltration membrane based on a henna quinone-iron coordination network, the method comprising the following steps: (1) FeCl3·6H2O and henna quinone were mixed evenly in anhydrous ethanol solution to obtain a precursor solution; (2) The basement membrane, which has been soaked in deionized water overnight, is immersed in the precursor solution and deposited under oscillation conditions. After washing, an antifouling and antibacterial nanofiltration membrane based on the henna quinone-iron coordination network is obtained.

[0010] Further specified, the concentration of FeCl3·6H2O in the precursor solution in step (1) is 0.05-0.4 mg / mL, and the concentration of henna quinone is 0.05-0.2 mg / mL.

[0011] Further, the oscillation rate in step (2) is 60-100 rpm and the oscillation time is 0.5-4 h.

[0012] Further specified, the nanofiltration membrane obtained in step (2) is used to treat wastewater containing bacteria.

[0013] To further specify, the bacteria are Escherichia coli, and the wastewater also contains inorganic salts, with an E. coli concentration of 2 × 10⁻⁶. 6 CFU·mL -1 The concentration of inorganic salts is 0-2 g / L.

[0014] To further specify, the inorganic salt is one or more of sodium sulfate, magnesium sulfate, magnesium chloride, and sodium chloride.

[0015] The advantages of this invention compared to existing technologies are: (1) The preparation method of the composite nanofiltration membrane of the present invention has the advantages of short cycle, simple process, and strong economic applicability. In the multi-cycle operation process and stability test, the coating of the composite membrane did not peel off, and it has strong physical and chemical stability; (2) The composite nanofiltration membrane prepared by this invention achieves a synergistic improvement in permeate flux and salt rejection rate, breaking through the trade-off between permeate performance and separation performance, and exhibits high permeate flux, high selectivity and tolerance to complex influent water quality. When treating secondary effluent containing bacteria, the composite membrane exhibits excellent anti-biofouling performance, and the decrease in membrane flux is significantly slowed down during continuous operation, effectively alleviating membrane fouling; (3) The composite nanofiltration membrane prepared in this invention forms a composite nanofiltration membrane by loading an ultrathin coating of rhododendron quinone-metal network onto a polyamide-based nanofiltration membrane. This enhances the hydrophilicity of the membrane surface and minimizes additional mass transfer resistance, thereby improving the permeation mass transfer efficiency. In addition, more importantly, through screening, rhododendron quinone with ortho-hydroxyl groups is selected as a natural antibacterial agent. This not only solves the problem of insufficient antibacterial and antifouling performance of nanofiltration membranes, but also allows the ortho-hydroxyl group to form a stable five-membered ring coordination with iron as a reinforcing ligand. This achieves stable loading of metal ions while enhancing biofouling control, significantly reducing metal ion leakage. The long-term antibacterial and antifouling performance of the composite membrane is also guaranteed, while meeting the environmentally friendly green ecological requirements. Attached Figure Description

[0016] Figure 1 EDS image of iron on the surface of the nanofiltration membrane prepared in Example 1; Figure 2 XPS spectra of the nanofiltration membrane and the surface layer of the substrate membrane prepared in Example 1; Figure 3 This is a TEM image of a cross-section of the nanofiltration membrane prepared in Example 1; Figure 4 The diagram shows the filtration system device involved in Application Example 1; where 1 is the inlet tank, 2 is the pressure pump, 3 is the nanofiltration membrane tank, 4 is the nanofiltration membrane module, 5 is the clear water tank, 6 is the data acquisition system, and 7 is the electronic balance. Figure 5 The pure water flux diagram is shown for the nanofiltration membrane FLNF prepared in Example 1 and the original substrate membrane. Figure 6 This is a comparison of the salt rejection rates of the nanofiltration membrane FLNF prepared in Example 1 and the original substrate membrane for four inorganic salts: sodium sulfate, magnesium sulfate, magnesium chloride, and sodium chloride. Figure 7 A comparison of the normalized membrane flux of the nanofiltration membrane FLNF prepared in Example 1 under a multi-cycle fouling-cleaning cycle with the original substrate membrane; Figure 8 Comparison of the nanofiltration membrane FLNF prepared in Example 1 under multi-cycle fouling-cleaning and the biofilm on the surface of the original basement membrane; Figure 9 The graph shows the change in iron leakage of the nanofiltration membrane prepared in Example 1 over time during a long-term process. Figure 10 Comparison of simulated cell images of the quinone-iron system used in the composite nanofiltration membranes prepared in Example 1 and Comparative Example 2; (a) Example 1, (b) Comparative Example 2; Figure 11 The radial distribution function of the quinone-iron system used in the composite nanofiltration membranes prepared in Example 1 and Comparative Example 2 is compared. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0019] The nanofiltration membrane water flux tested in the following examples was calculated according to the following formula: (1) In formula (1) J – Osmium flux, L·m -2 ·h -1 ·bar -1 ; V – Volume of the filtered solution, in L; A – Effective filtration area of ​​the nanofiltration membrane, in meters. 2 ; T—Measurement filtration time interval, h; P – Operating pressure, bar.

[0020] The rejection rate of inorganic salts by nanofiltration membranes is calculated using the following formula: (2) In formula (2) R – Solute rejection rate, % C p —Through the concentration of solute in the liquid, mg·L -1 ; C f —Solute concentration in influent, mg·L -1 .

[0021] Example 1: The preparation method of the antifouling and antibacterial nanofiltration membrane based on the henna quinone-iron coordination network in this example is carried out according to the following steps: Step 1: Rinse the commercial polyamide substrate membrane (Pristine NF, pore size 0.5 nm) with deionized water until the residual protective agent on the surface is removed, and soak it in deionized water overnight to ensure that the membrane is in a stable hydration state; Step 2: Mix FeCl3·6H2O and henna quinone in anhydrous ethanol solution until homogeneous to obtain a precursor solution with FeCl3·6H2O concentration of 0.2 mg / mL and henna quinone concentration of 0.1 mg / mL; Step 3: Immerse the treated basement membrane in the precursor solution and deposit it for 2 h at room temperature and 80 rpm. After washing with deionized water, an antifouling and antibacterial nanofiltration membrane (FLNF) based on henna quinone-iron coordination network is obtained.

[0022] Comparative Example 1: Without any modification, the original polyamide nanofiltration membrane used in Example 1 was simply washed with deionized water.

[0023] Comparative Example 2: The difference between this comparative example and Example 1 is that in step 2, henna quinone is replaced with juglone, and the FeCl3·6H2O concentration is adjusted to 0.5 mg / mL. Other steps and parameters are the same as in Example 1. The resulting nanofiltration membrane is designated NFFJ.

[0024] Figure 1 An EDS image of the surface of the nanofiltration membrane prepared in Example 1 is shown, which shows that iron is uniformly distributed on the membrane surface. Figure 2 XPS spectra of the nanofiltration membrane prepared in Example 1 and the original membrane of Comparative Example 1 are compared, with the characteristic peak of Fe2p confirming successful iron loading. Table 1 shows the elemental composition of the nanofiltration membrane prepared in Example 1, the original membrane of Comparative Example 1, and the nanofiltration membrane of Comparative Example 2. The microscopic TEM characterization of the nanofiltration membrane prepared in Example 1 is as follows: Figure 3 As shown, the radial thickness of the coating is controlled within an ultrathin range of 20 nm.

[0025] Table 1. Surface elemental composition of the original basement membrane and FLNF and NFFJ nanofiltration membranes

[0026] Table 1 shows the XPS elemental composition of the membrane surface in Example 1. As the modification group with the best permeability improvement in the FeCl3·6H2O and juglone coating modification study, the mass ratio of FeCl3·6H2O to juglone in the coating composition of Example 1 is 2:1, and the molar ratio is approximately 1.29:1 ≈ 1:1. Correspondingly, the NFFJ membrane in Comparative Example 2, as the best modified membrane for the FeCl3·6H2O and juglone coating, has a mass ratio of FeCl3·6H2O to juglone in its coating composition of 0.5:1, and the molar ratio is approximately 0.32:1 ≈ 1:3. It is worth noting that the Fe element content on the surface of the NFFJ membrane is approximately 1%, while the Fe element content of the FLNF membrane shown in Table 1 is approximately 3%. The consistency between the XPS elemental content and the optimal modification molar ratio confirms that juglone per unit molar mass can complex more iron ions, thereby achieving a stronger improvement in hydrophilicity and permeability flux.

[0027] Table 2. Comparison of water contact angles on nanofiltration membrane surfaces between Example 1 and Comparative Example 2

[0028] Table 2 shows a comparison of the water contact angle and permeation performance of the nanofiltration membranes prepared in Example 1 and Comparative Example 2. The water contact angle of the iron-juglone composite nanofiltration membrane (NFFJ) prepared in Comparative Example 2 was 39.3°, while the water contact angle of the iron-hennaquinone composite nanofiltration membrane (FLNF) prepared in Example 1 was 28°. The significantly reduced contact angle demonstrates the excellent hydrophilicity of the iron-hennaquinone coating.

[0029] Application Example 1: The nanofiltration membrane prepared in Example 1 was used in... Figure 4 The filtration system shown was in operation. During the experiment, the nanofiltration membrane was installed in the nanofiltration membrane module, and the operating pressure was set to 4 bar. Before the formal experiment, the nanofiltration membrane was pre-run to a stable state, and relevant performance tests were carried out under the set pressure conditions.

[0030] Example 1: Membrane permeation / separation performance test: The entire filtration process (pure water) was monitored by software. The filtrate mass was collected at 6-second intervals, with the mass recorded every 6 seconds. The effective filtration area was 28.7 cm². 2 The pure water flux results are as follows: Figure 5 As shown, thanks to the improved hydrophilicity, the membrane's permeation flux increased from 11.1 ± 0.6 L·m in Comparative Example 1 to that of the original membrane. -2 ·h -1 ·bar -1 The efficiency was increased to 14.5 ± 2.2 L·m⁻¹ of the nanofiltration membrane prepared in Example 1. -2 ·h -1 ·bar -1 This represents an increase of approximately 28%.

[0031] At the same time, such as Figure 6 As shown, the nanofiltration membrane prepared in Example 1 showed varying degrees of improvement in the salt rejection rates of four salts, Na2SO4, MgSO4, MgCl2, and NaCl (all at a concentration of 2.0 g / L), compared to the original membrane in Comparative Example 1. The rates increased from 94.8%, 91.1%, 42.2%, and 39.9% to 98.3%, 95.8%, 56.7%, and 46.4%, respectively. This indicates that the coating improved the separation performance of the nanofiltration membrane by enhancing the size repulsion effect.

[0032] Example 2: Membrane biofouling control during multi-cycle operation: Prepare a solution containing NaCl (8.0 mM), NaHCO3 (0.5 mM), NH4Cl (0.4 mM), CaCl2 (0.2 mM), KH2PO4 (0.2 mM), MgSO4 (0.15 mM), glucose (0.6 mM), and Escherichia coli (2 × 10⁻⁶). 6 CFU mL -1 The simulated secondary effluent (ATCC 25922) was used as the influent, containing E. coli, and subjected to a constant pressure of 4 bar. Figure 4 The filtration system shown underwent a multi-cycle continuous fouling-cleaning experiment. After three cycles of filtration-cleaning, each lasting 100 minutes and lasting approximately 400 minutes, physical cleaning was performed. Details of the normalized membrane flux changes are available in [link to relevant documentation]. Figure 7 The results showed that the specific flux of the nanofiltration membrane prepared in Example 1 was significantly higher than that of the original membrane in Comparative Example 1 in each operating cycle. After three cycles of fouling, the flux of the nanofiltration membrane in Example 1 could be restored to 85% of its initial state, while the original membrane in Comparative Example 1 could only be restored to 48% of its initial state. This proves that membrane fouling was alleviated, indicating that the composite nanofiltration membrane has significantly enhanced antifouling performance and can maintain a stable high flux.

[0033] Furthermore, the biofilm on the surface of the nanofiltration membrane after a single cycle (100 min of operation) of fouling was compared. Figure 8 As shown, the biofilm thickness on the surface of the nanofiltration membrane prepared in Example 1 after contamination was significantly lower than that of the original membrane in Comparative Example 1, with the average biofilm volume reduced by about 70%, indicating that the modified composite membrane effectively inhibited biofouling on the membrane surface.

[0034] Example 3: Membrane stability test The nanofiltration membrane prepared in Example 1 was subjected to static leaching metal leakage tests in three different pH environments (pH=3, 7, and 11) to evaluate the metal leakage of the coating and thus assess the chemical stability of the modified membrane in the water treatment process. Figure 9 The cumulative iron leakage of the FLNF membrane prepared in Example 1 over 10 consecutive days under different pH conditions is shown. As shown in the figure, iron leakage is less (<5 ng / cm³) under neutral and alkaline conditions. 2 Despite the detection of increased leakage (<25 ng / cm) in a strongly acidic environment. 2 However, overall, the leakage of metal ions on the surface of the FLNF membrane remains relatively restrained and stable, which ensures the integrity of the coating, long-term biofouling control capabilities, and environmental friendliness during long-term service.

[0035] Simulation calculations, using theoretical calculations, illustrate the differences in the binding of the two quinones to iron. Stability is supported by simulation calculations, such as... Figure 10 and Figure 11 As shown, henna quinone exhibits a stronger tendency to bind with ferric ions and a higher radial distribution function, which helps to explain the stability of its coating at the molecular level.

[0036] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A nonfouling and antibacterial nanofiltration membrane based on henna quinone-iron coordination network, characterized in that, The nanofiltration membrane comprises a base membrane and an on-site quinone-iron composite coating, wherein the Fe content in the coating is 2-4 at based on the amount of quinone.

2. The nanofiltration membrane according to claim 1, characterized in that, The basement membrane is made of polyamide.

3. The nanofiltration membrane according to claim 1, characterized in that, The pore size of the basement membrane is 0.4-0.5 nm.

4. The nanofiltration membrane according to claim 1, characterized in that, The thickness of the henna quinone-iron composite coating is ≤20nm.

5. The method for preparing the nanofiltration membrane according to any one of claims 1-4, characterized in that, The method described: (1) FeCl3·6H2O and henna quinone were mixed evenly in anhydrous ethanol solution to obtain a precursor solution; (2) The basement membrane, which has been soaked in deionized water overnight, is immersed in the precursor solution and deposited under oscillation conditions. After washing, an antifouling and antibacterial nanofiltration membrane based on the henna quinone-iron coordination network is obtained.

6. The method according to claim 5, characterized in that, The concentration of FeCl3·6H2O in the precursor solution in step (1) is 0.05-0.4 mg / mL, and the concentration of henna quinone is 0.05-0.2 mg / mL.

7. The method according to claim 5, characterized in that, The oscillation rate in step (2) is 60-100 rpm and the oscillation time is 0.5-4 h.

8. The method according to claim 5, characterized in that, The nanofiltration membrane obtained in step (2) is used to treat wastewater containing bacteria.

9. The method according to claim 8, characterized in that, The bacteria are Escherichia coli, and the wastewater also contains inorganic salts. The concentration of E. coli is 2 × 10⁻⁶. 6 CFU·mL -1 The concentration of inorganic salts is 0-2 g / L.

10. The method according to claim 9, characterized in that, The inorganic salt is one or more of sodium sulfate, magnesium sulfate, magnesium chloride, and sodium chloride.

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