Calcium alginate composite film with anti-biofilm performance and preparation method and application thereof

Abstract

The present application relates to a kind of calcium alginate composite film with antibiofilm performance and its preparation method and application, the composite film is obtained by the surface of microfiltration membrane is coated with micro-nano coating, with superhydrophilic / underwater superoleophobicity, the micro-nano coating is the composite material of chitosan, silver nanoparticles and calcium alginate, micro-nano coating has fibrous three-dimensional porous structure, and silver nanoparticles are densely distributed on the surface and inside of coating.The calcium alginate composite film with antibiofilm performance provided by the present application provides micron pore structure by microfiltration membrane, and chitosan-coated silver nanoparticles provide nanostructure, so that the prepared composite film has superhydrophilic / underwater superoleophobicity, good antibacterial performance, good antibiofilm ability, can effectively separate oil-water mixture even oil-in-water emulsion stable to surfactant, and separation flux is high, can be applied to oil-water separation in complex water environment.

Description

Technical Field

[0001] This invention pertains to semi-permeable membranes used in separation processes or equipment, characterized by their materials. Specifically, it relates to a calcium alginate composite membrane with anti-biofilm properties, its preparation method, and its application in oil-water emulsion separation. Background Technology

[0002] Oily substances and organic solvents entering water bodies form oily wastewater, which seriously affects the environment and ecology, posing significant health risks. Therefore, how to efficiently, economically, and safely treat this oily wastewater has become an important issue for ecological protection. Oily wastewater is generally classified into two categories: stratified oil / water mixtures and oil-water emulsions. Stratified oil / water mixtures containing relatively large dispersed droplets (>20μm) are thermodynamically unstable, allowing the oil and water to separate naturally over time. The denser phase gradually settles, while the lighter phase floats to the top, making oil-water separation relatively easy. However, oil-water emulsions (<20μm) are thermodynamically stable colloidal dispersions, composed of micro / nano-sized droplets of dispersed phase within a continuous phase. Furthermore, the widespread use of surfactants makes oil-water emulsions typically very stable and difficult to separate naturally over time.

[0003] Traditional methods for treating oily wastewater include centrifugation, incineration, chemical dispersion, and biodegradation. These methods suffer from problems such as complex operation and high cost, and are not effective in treating oil-water emulsions. Membrane filtration technology is considered the most effective method for treating oil-water mixtures due to its low cost and simple operation, and has been widely used in industry. Especially in recent years, special wettability membrane separation technologies, such as superhydrophilic / subsea superoleophobic membranes, have been developed. These offer advantages such as simple operation, good separation effect, and fast processing rate, and are considered a more attractive oil-water separation method. However, they still struggle to separate oil-water emulsions.

[0004] Hydrogels, as hydrophilic polymers with swelling properties, are non-toxic and biocompatible. Rich in hydrophilic functional groups (hydroxyl, carboxyl, amino, and sulfhydryl groups), they exhibit strong hydrophilicity and are environmentally friendly, leading to their widespread application. Among various hydrogels, alginate, as a natural material, has attracted considerable attention due to its strong hydration ability. However, oily wastewater has a complex composition, containing not only emulsion droplets, dyes, and heavy metal ions, but also various bacteria. Bacteria easily contaminate and adhere to the surface of separation materials, causing biofouling. More specifically, bacterial biofilms can partially or completely cover the separation membrane surface, leading to pore blockage and a significant decrease in separation efficiency and flux. Therefore, developing oil-water emulsion separation membranes with anti-biofilm properties is of great significance. (Chang et al.)

[0005] (CN113101816A) prepared a composite membrane with anti-biofilm and emulsion separation properties using silver nitrate solution and cellulose nanocrystals, but its preparation process requires high parameters (high temperature, high pressure), resulting in low separation flux; only a simple paper diffusion experiment was conducted. Meng et al. (CN113069938A) obtained an antibacterial PTFE oil-water separation membrane using copolymer-modified polytetrafluoroethylene membranes, but its complex preparation process is a major drawback. Wu et al. (CN113750815A) disclosed a switchable emulsion-type oil-water separation nano-antibacterial membrane; however, the material used is fluorine-containing, which is not environmentally friendly. Summary of the Invention

[0006] To address the aforementioned shortcomings in the existing technology, this invention provides a calcium alginate composite membrane with anti-biofilm properties, its preparation method, and its application. This calcium alginate composite membrane exhibits superhydrophilic / underwater superoleophobic properties, good antibacterial properties, can inhibit biofilm formation, and can effectively separate surfactant-stabilized emulsions with high separation throughput.

[0007] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0008] A calcium alginate composite membrane with anti-biofilm properties is provided, which is obtained by coating a microfiltration membrane surface with a micro / nano coating. It exhibits superhydrophilic / superoleophobic properties underwater. The micro / nano coating is a composite material of chitosan, silver nanoparticles, and calcium alginate, possessing a fibrous three-dimensional porous structure with densely distributed silver nanoparticles on the coating surface and within the coating. Emulsion separation is achieved by utilizing the superhydrophilic and superoleophobic properties of the composite membrane surface and the nanoscale effect of the chitosan-encapsulated silver nanoparticle composite material. Positively charged chitosan (CS) and negatively charged sodium alginate (SA) in the raw materials can treat stable emulsions containing surfactants through electrostatic effects. Furthermore, the silver nanoparticles, encapsulated by chitosan, provide excellent sustained-release properties, continuously releasing silver ions and thus acting as an anti-biofilm agent.

[0009] According to the above scheme, the microfiltration membrane has a pore size of 2-5 μm and a thickness of 50-100 μm.

[0010] Preferably, the microfiltration membrane is one of nylon membrane, polyvinylidene fluoride membrane, polypropylene membrane, and glass fiber membrane.

[0011] According to the above scheme, the particle size of the silver nanoparticles in the calcium alginate composite membrane is 10-300 nm.

[0012] According to the above scheme, the calcium alginate composite membrane with anti-biofilm properties has a contact angle of 162.7-169.1° with hexane, toluene, and petroleum ether underwater, and is superhydrophilic in air. It takes only 2.0-3.0 seconds for a water droplet to be completely wetted, with 0ms as the time it takes for a water droplet to just touch the surface of the composite membrane.

[0013] This invention also includes a method for preparing the above-mentioned calcium alginate composite membrane with anti-biofilm properties, characterized by the following specific steps:

[0014] 1) Dissolve chitosan in an aqueous acetic acid solution to obtain a chitosan-acetic acid aqueous solution. Then add silver nitrate solution to the obtained chitosan-acetic acid aqueous solution and stir thoroughly under heating conditions. Then add sodium borohydride solution dropwise while stirring. Continue stirring and react for 90-180 min and then stop heating to obtain a chitosan-nano silver mixture.

[0015] 2) Add sodium alginate powder to the chitosan-nano silver mixture obtained in step 1) while stirring. Stir evenly at room temperature (15-35℃) and then filter to obtain sodium alginate / chitosan-nano silver mixture.

[0016] 3) Immerse the clean microfiltration membrane in the sodium alginate / chitosan-nano silver mixture obtained in step 2) for 5-30 minutes, then remove it and immerse it in calcium chloride solution for 5-30 minutes. Remove the membrane and dry it at room temperature to obtain the calcium alginate composite membrane with anti-biofilm properties.

[0017] According to the above scheme, the degree of deacetylation of the chitosan in step 1) is 70-100%, and the viscosity is 200-400 mPa·s.

[0018] According to the above scheme, the concentration of the acetic acid aqueous solution in step 1) is 0.1-1.0 mol / L.

[0019] According to the above scheme, the concentration of chitosan in the chitosan-acetic acid aqueous solution in step 1) is 2.0-3.0 g / L.

[0020] According to the above scheme, in step 1), the mass ratio of chitosan to silver nitrate in the silver nitrate solution is 5-6:1.

[0021] According to the above scheme, the concentration of the silver nitrate solution in step 1) is 0.1-1.0 mol / L.

[0022] According to the above scheme, the concentration of the sodium borohydride solution in step 1) is 0.1-1.0 mol / L.

[0023] According to the above scheme, the molar ratio of sodium borohydride in the sodium borohydride solution to silver nitrate in the silver nitrate solution in step 1) is 1.2-2:1.

[0024] According to the above scheme, the heating temperature in step 1) is 40-60℃.

[0025] According to the above scheme, the mass-volume ratio of sodium alginate powder to chitosan-nano silver mixture in step 1) is 1-5 g / L.

[0026] According to the above scheme, the concentration of the calcium chloride solution in step 2) is 4-10 wt%.

[0027] The present invention also includes the application of the above-mentioned calcium alginate composite membrane with anti-biofilm properties in the field of oil-water emulsion separation.

[0028] The beneficial effects of this invention are as follows: 1. The calcium alginate composite membrane with anti-biofilm properties provided by this invention possesses superhydrophilic / underwater superoleophobic properties. The microfiltration membrane provides a micron-sized pore structure, and the chitosan-encapsulated silver nanoparticles provide a nanostructure, enabling the prepared composite membrane to exhibit superhydrophilic / underwater superoleophobic properties, good antibacterial performance, and excellent anti-biofilm ability. It can effectively separate oil-water mixtures and even surfactant-stabilized oil-in-water emulsions, and has a high separation flux, making it suitable for oil-water separation in complex aquatic environments. 2. The preparation method of this invention is simple, time-saving, and energy-efficient, showing promising prospects for industrial application. Attached Figure Description

[0029] Figure 1 Photographs showing the contact angles of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 1 of this invention with toluene, n-hexane, and petroleum ether in water.

[0030] Figure 2 Photographs showing the contact angles of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 2 with toluene, n-hexane, and petroleum ether in water.

[0031] Figure 3 Photographs showing the contact angles of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 3 with toluene, n-hexane, and petroleum ether in water.

[0032] Figure 4 Photographs showing the contact angles of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 4 with toluene, n-hexane, and petroleum ether in water.

[0033] Figure 5 The XRD pattern of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 5;

[0034] Figure 6 The image shows the FE-SEM image of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 6.

[0035] Figure 7The ATR-FTIR spectrum of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 7;

[0036] Figure 8 EDS spectrum of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 8;

[0037] Figure 9 Photographs of culture tubes containing Escherichia coli and Staphylococcus aureus prepared in Example 8 with calcium alginate composite membrane having anti-biofilm properties.

[0038] Figure 10 SEM images of the original N66 nylon microfiltration membrane and the calcium alginate composite membrane with anti-biofilm properties prepared in Example 8 after culturing in Staphylococcus aureus solution for 24 h;

[0039] Figure 11 The graph shows the change in water contact angle of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 9.

[0040] Figure 12 Photographs showing the contact angles of the calcium alginate composite membrane with anti-biofilm properties prepared in Example 10 with toluene, n-hexane, and petroleum ether in water.

[0041] Figure 13 The image shows the separation process of water-in-toluene emulsion and the comparison between the filtrate and the emulsion using the calcium alginate composite membrane with anti-biofilm properties prepared in Example 10.

[0042] Figure 14 Optical micrographs of the emulsion and filtrate before and after separation of the water-in-toluene emulsion with sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), and Tween 80 prepared in Example 10, which has anti-biofilm properties.

[0043] Figure 15 Crystal violet staining images of the calcium alginate composite membrane with anti-biofilm properties prepared in Examples 6-10, which inhibits biofilm formation in S. aureus. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0045] Example 1

[0046] A calcium alginate composite membrane with anti-biofilm properties is prepared by the following steps:

[0047] 1) Pretreatment of microfiltration membranes

[0048] N66 nylon microporous filter membranes with a pore size of 5μm and a thickness of 100μm were ultrasonically cleaned with anhydrous ethanol and deionized water for 10 minutes in sequence to remove the substances adhering to the surface. They were then dried in an oven at 60℃ and stored for later use.

[0049] 2) Preparation of sodium alginate / chitosan-silver nano-solution

[0050] 0.2 g of chitosan (70% degree of deacetylation, 200 mPa·s viscosity) was added to 100 mL of 0.1 mol / L acetic acid aqueous solution and stirred at room temperature until completely dissolved to obtain chitosan-acetic acid aqueous solution. 1 mL of 0.1 mol / L silver nitrate solution was added to 47 mL of chitosan-acetic acid aqueous solution and heated to 40 °C and stirred for 30 min. Then, 2 mL of sodium borohydride solution (0.1 mol / L concentration) was added dropwise while stirring. The reaction was continued for 90 min and then heating was stopped to obtain a chitosan-nano silver mixture. 0.05 g of sodium alginate powder was added to the obtained chitosan-nano silver mixture while stirring and stirred at room temperature for 2 h. The mixture was filtered through filter paper to obtain a uniform sodium alginate / chitosan-nano silver mixture.

[0051] 3) Preparation of calcium alginate composite membrane for emulsion separation with antibacterial activity

[0052] The N66 nylon microporous filter membrane, after being cleaned in step 1), was first immersed in the sodium alginate / chitosan-nano silver mixture obtained in step 2) for 5 minutes. After that, it was taken out and immersed in calcium chloride solution (5g of calcium chloride dissolved in 100mL of deionized water) for 5 minutes. The membrane was then taken out and dried at room temperature to obtain an emulsion separation calcium alginate composite membrane with anti-biofilm properties.

[0053] To test the hydrophobicity of the composite membrane prepared in this embodiment underwater, the composite membrane was fixed underwater, and 3 μL of an oily substance (one of toluene, n-hexane, or petroleum ether) was dripped below the composite membrane using a bent-tip syringe. The oily substance floated to the surface and contacted the composite membrane. The contact angles of the composite membrane with toluene, n-hexane, and petroleum ether in water were photographed as shown in the images. Figure 1 As shown, the measured contact angles were 168.2°, 165.5°, and 164.8°, indicating that the composite membrane has underwater superoleophobic properties.

[0054] Example 2

[0055] An emulsion separation calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the microfiltration membrane in step 1) is a polyvinylidene fluoride membrane with a pore size of 5 μm.

[0056] Figure 2The images show the contact angles of the emulsion separation calcium alginate composite membrane obtained in this embodiment with toluene, n-hexane, and petroleum ether in water. The contact angles measured with 3 μL of toluene, n-hexane, and petroleum ether were 165.0°, 163.4°, and 162.7°, respectively, indicating that the composite membrane has superoleophobic properties underwater.

[0057] Example 3

[0058] An emulsion separation calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the microfiltration membrane in step 1) is a polypropylene membrane with a pore size of 5 μm.

[0059] Figure 3 The images show the contact angles of the emulsion separation calcium alginate composite membrane obtained in this embodiment with toluene, n-hexane, and petroleum ether in water. The contact angles measured with 3 μL of toluene, n-hexane, and petroleum ether were 167.1°, 164.2°, and 163.8°, respectively, indicating that the composite membrane has superoleophobic properties underwater.

[0060] Example 4

[0061] An emulsion separation calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the microfiltration membrane in step 1) is a glass fiber membrane with a pore size of 5 μm.

[0062] Figure 4 The images show the contact angles of the composite membrane obtained in this embodiment with toluene, n-hexane, and petroleum ether in water. The contact angles measured with 3 μL of toluene, n-hexane, and petroleum ether were 169.1°, 165.5°, and 163.9°, respectively, indicating that the composite membrane has underwater superoleophobic properties.

[0063] Example 5

[0064] An emulsion separation calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the concentration of the acetic acid aqueous solution in step 2) is 1.0 mol / L.

[0065] Figure 5 The figure shows the XRD pattern of the composite film prepared in this embodiment. The diffraction peaks from 2θ = 10° to 30° are the diffraction peaks of the original film. In this embodiment, the diffraction peaks from 2θ = 30° to 80° are consistent with the standard spectrum of silver nanoparticles (AgNPs) JCPDS 04-0783. The diffraction peaks at 2θ = 38.4°, 44.3°, 64.5° and 77.4° correspond to the lattice planes (111), (200), (220) and (311) of the cubic crystal structure of AgNPs, respectively, indicating that silver nanoparticles were successfully loaded.

[0066] Example 6

[0067] An emulsion separation calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the concentration of silver nitrate solution in step 2) is 0.5 mol / L.

[0068] Figure 6 The image shows the FE-SEM image of the composite membrane prepared in this embodiment. As can be seen from the image, a micro-nano coating is uniformly coated on the surface of the microfiltration membrane. The micro-nano coating is composed of chitosan, calcium alginate and silver nanoparticles, and has a fibrous three-dimensional porous structure. Silver nanoparticles are densely distributed on the surface of the coating, and the particle size of the silver nanoparticles is 10-50 nm.

[0069] Example 7

[0070] A calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the concentration of silver nitrate solution in step 2) is 1.0 mol / L.

[0071] Figure 7 The ATR-FTIR spectrum of the composite membrane prepared in this embodiment is shown, and compared with that of the N66 nylon microporous filter membrane used as raw material. The absorption peaks of the two membranes are at 3400 cm⁻¹. -1 Near the nylon membrane, the absorption peak intensity of SA / CS-Ag 1.0@NM is higher than that of the nylon membrane, which is attributed to the absorption band of the -OH stretching vibration in SA; 1500 cm⁻¹ -1 The nearby peak is attributed to SA-COO - Asymmetric tensile vibration at C=O. At 1671 cm⁻¹. -1 The new peak is attributed to the stretching vibration of NH in CS; 1305 cm⁻¹ -1 The absorption peak at 1029 cm⁻¹ is attributed to the C-S stretching vibration of the aromatic amine. -1 The absorption peak at 831 cm⁻¹ is due to the C-OH stretching vibration of secondary alcohols; the peak at 831 cm⁻¹ is due to the C-OH stretching vibration of secondary alcohols. -1 The nearby peaks are attributed to the CH bending vibration in CS, indicating that SA and CS were successfully loaded onto the filter membrane.

[0072] Example 8

[0073] An emulsion separation calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the heating temperature in step 2) is 60°C.

[0074] Figure 8 The EDS spectrum of the composite membrane prepared in this embodiment shows five elemental peaks (C, O, Ca, Ag, and N). Among all elements, C, N, and O are the basic constituent elements of the nylon membrane. The presence of Ag indicates the successful loading of silver nanoparticles, and the presence of Ca indicates that Ca... 2+It was successfully cross-linked with SA and loaded onto the filter membrane.

[0075] Figure 9 The images show test tubes containing the composite membrane prepared in this embodiment against *Escherichia coli* and *Staphylococcus aureus*. The antibacterial activity of this embodiment was evaluated using a bacterial suspension immersion experiment. The activated bacteria were diluted to 10... 6 CFU / mL, take 500 μL of the solution as a concentration of 10. 6 Add CFU / mL of Escherichia coli or Staphylococcus aureus to 4.5 mL of LB liquid medium in a test tube to bring the final bacterial concentration to 10. 5 CFU / mL. The composite membrane prepared in this example was placed in a test tube and then cultured in a constant temperature shaker at 200 rpm and 37°C for 16 h. The bacterial solution in the photo was clear, indicating that the composite membrane prepared in this example has antibacterial effect against both Gram-negative bacteria (E. coli) and Gram-positive bacteria (S. aureus).

[0076] The anti-biofilm performance of the composite membrane prepared in this embodiment was evaluated using a biofilm formation inhibition assay. The composite membrane prepared in this embodiment was placed in a 6-well plate, and the revived S. aureus bacterial culture was inoculated into TSB medium containing 1 wt% sucrose to achieve a final bacterial concentration of 10. 7 CFU / mL, add 3 mL of bacterial culture to each well, and incubate at 37℃ for 24 h. Use the original N66 nylon microporous membrane as a control. Wash the cultured membrane material three times with PBS buffer, and then fix it with 2.5 wt% glutaraldehyde solution at 4℃ for 5 h. Observe the bacteria on the membrane surface using SEM. Figure 10 The image shows SEM images of the original N66 nylon microporous filter membrane and the composite membrane prepared in this embodiment after culturing in Staphylococcus aureus solution for 24 hours. The image shows that there are many Staphylococcus aureus bacteria on the surface of the original N66 nylon microporous filter membrane, while no bacteria were observed in the composite membrane prepared in this embodiment, indicating that the composite membrane prepared in this embodiment has a certain anti-biofilm ability.

[0077] Example 9

[0078] A calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the concentration of sodium borohydride solution used in step 2) is 1.2 mol / L.

[0079] Figure 11 The graph shows the change in water contact angle of the composite membrane prepared in this embodiment. The measurement was obtained using 3 μL of water. The water contact angle was 47° 100 ms after water contacted the composite membrane prepared in this embodiment, and it became 0° after 2566 ms, indicating that the composite membrane prepared in this embodiment has superhydrophilic properties.

[0080] Example 10

[0081] A calcium alginate composite membrane with anti-biofilm properties is prepared in a manner similar to that of Example 1, except that the soaking time in sodium alginate / chitosan-nano silver solution and calcium chloride solution in step 3) is 30 min.

[0082] Figure 12 The images show the contact angles of the composite membrane obtained in this embodiment with toluene, n-hexane, and petroleum ether in water. The contact angles measured with 3 μL of toluene, n-hexane, and petroleum ether were 161.3°, 155.7°, and 154.9°, respectively, indicating that the composite membrane has superoleophobic properties underwater.

[0083] 0.05 g SDS was added to 99 mL of deionized water, and the mixture was magnetically stirred for 1 min to disperse the surfactant SDS. Then, 1 mL of toluene was added, and stirring was continued for 30 min to obtain an SDS-stabilized water-in-toluene emulsion. The composite membrane prepared in this example was cut into small circular pieces with a diameter of 2 cm and placed in a self-made simple oil-water separator. The SDS-stabilized water-in-toluene emulsion prepared above was stirred and then added through the upper glass tube. Figure 13 The image on the left shows the separation process of the SDS-stabilized water-in-toluene emulsion using the composite membrane prepared in this embodiment. Due to the hydrophilic nature of the composite membrane, deionized water can permeate through it. Simultaneously, because the composite membrane material possesses underwater oleophobic properties, the oil phase is isolated at the top, thus achieving oil-water separation at room temperature and atmospheric pressure. Subsequently, the oil content and oil droplet size in the filtrate were detected using an optical microscope and a laser particle size analyzer. A comparison image of the emulsion and the filtrate after separation is shown below. Figure 13 On the right, the emulsion appears as an opaque milky white liquid, and the filtrate after separation is clear and transparent, with a separation flux of up to 874 L·m⁻¹. -2 h -1 The separation efficiency reached 99.73%.

[0084] 0.05g of different surfactants (SDS, CTAB, Tween 80) were added to 99mL of deionized water and magnetically stirred for 1min to disperse the surfactants. Then, 1mL of toluene was added and stirring was continued for 30min to obtain three different types of water-in-toluene emulsions: anionic, cationic, and nonionic water-in-toluene emulsions. Figure 14 Optical microscope images of the water-in-toluene emulsion and filtrate before and after separation of the composite membrane prepared in this embodiment with SDS, CTAB, and Tween 80 added, respectively, show that there are obvious oil droplets in the emulsion before separation, while no obvious oil droplets are observed in the filtrate after separation.

[0085] The composite membranes obtained in Examples 6-10 and the original N66 nylon microporous membranes were placed in 6-well plates, and the revived S. aureus bacterial culture was inoculated into TSB medium containing 1 wt% sucrose to achieve a final bacterial concentration of 10. 7 Add 3 mL of bacterial suspension (CFU / mL) to each well and incubate at 37°C for 24 h. After incubation, aspirate the cell suspension, rinse the membrane material three times with PBS buffer, and remove the membrane material. Then fix the biomembrane in the well with methanol for 15 min, and stain with 600 μL of crystal violet solution (0.1 wt%) for 5 min. After staining, wash with deionized water until the washings are no longer purple, and observe the biomembrane. Figure 15 The images show crystal violet staining images of the composite membranes and original membranes prepared in Examples 6-10, and their inhibitory effect on S. aureus biofilm formation. The images show that stained biofilm remains in the wells after culturing with the original membranes, while no obvious stained biofilm remains are observed in the wells after culturing with the examples. This indicates that the composite membranes prepared in Examples 6-10 have the ability to inhibit biofilm formation.

Claims

1. A calcium alginate composite membrane with anti-biofilm properties, characterized in that, It is obtained by coating the surface of a microfiltration membrane with a micro-nano coating, and has superhydrophilic / underwater superoleophobic properties. The micro-nano coating is a composite material of chitosan, silver nanoparticles and calcium alginate. The micro-nano coating has a fibrous three-dimensional porous structure, with silver nanoparticles densely distributed on the surface and inside of the coating.

2. The calcium alginate composite membrane with anti-biofilm properties according to claim 1, characterized in that, The microfiltration membrane has a pore size of 2-5 μm and a thickness of 50-100 μm.

3. The calcium alginate composite membrane with anti-biofilm properties according to claim 1, characterized in that, The microfiltration membrane is one of nylon membrane, polyvinylidene fluoride membrane, polypropylene membrane, and glass fiber membrane.

4. The calcium alginate composite membrane with anti-biofilm properties according to claim 1, characterized in that, The silver nanoparticles have a particle size of 10-300 nm.

5. The calcium alginate composite membrane with anti-biofilm properties according to claim 1, characterized in that, The calcium alginate composite membrane with anti-biofilm properties has a contact angle of 162.7-169.1° with hexane, toluene, and petroleum ether underwater. It is superhydrophilic in air, with 0ms as the moment a water droplet just contacts the surface of the composite membrane, and the water droplet can be completely wetted in only 2.0-3.0s.

6. A method for preparing a calcium alginate composite membrane with anti-biofilm properties as described in any one of claims 1-5, characterized in that, The specific steps are as follows: 1) Dissolve chitosan in an aqueous acetic acid solution to obtain a chitosan-acetic acid aqueous solution. Then add silver nitrate solution to the obtained chitosan-acetic acid aqueous solution and stir thoroughly under heating conditions. Then add sodium borohydride solution dropwise while stirring. Continue stirring and react for 90-180 min and then stop heating to obtain a chitosan-nano silver mixture. 2) Add sodium alginate powder to the chitosan-silver nano mixture obtained in step 1) while stirring. Stir evenly at room temperature and then filter to obtain sodium alginate / chitosan-silver nano mixture. 3) Immerse the clean microfiltration membrane in the sodium alginate / chitosan-nano silver mixture obtained in step 2) for 5-30 minutes, then remove it and immerse it in calcium chloride solution for 5-30 minutes. Remove the membrane and dry it at room temperature to obtain the calcium alginate composite membrane with anti-biofilm properties.

7. The method for preparing the calcium alginate composite membrane with anti-biofilm properties according to claim 6, characterized in that, Step 1) The degree of deacetylation of the chitosan is 70-100%, and the viscosity is 200-400 mPa·s; the concentration of the acetic acid aqueous solution is 0.1-1.0 mol / L; and the concentration of chitosan in the chitosan acetic acid aqueous solution is 2.0-3.0 g / L.

8. The method for preparing the calcium alginate composite membrane with anti-biofilm properties according to claim 6, characterized in that, In step 1), the mass ratio of chitosan to silver nitrate in the silver nitrate solution is 5-6:1; the concentration of the silver nitrate solution is 0.1-1.0 mol / L; the concentration of the sodium borohydride solution is 0.1-1.0 mol / L; the molar ratio of sodium borohydride in the sodium borohydride solution to silver nitrate in the silver nitrate solution is 1.2-2:1; the heating temperature is 40-60℃; and the mass-volume ratio of sodium alginate powder to chitosan-nano silver mixture is 1-5 g / L.

9. The method for preparing the calcium alginate composite membrane with anti-biofilm properties according to claim 6, characterized in that, Step 2) The concentration of the calcium chloride solution is 4-10 wt%.

10. The application of a calcium alginate composite membrane with anti-biofilm properties as described in any one of claims 1-5 in the field of oil-water emulsion separation.

Images