Carbon nanotube-nanosilver gradient composite antibacterial film and preparation method thereof

Abstract

The application provides a carbon nanotube-nano silver gradient composite antibacterial composite film, the composite film is in asymmetric gradient distribution, and comprises a surface layer, a middle layer and a bottom layer; the surface layer is a nano silver and carbon nanotube composite layer; the middle layer is a carbon nanotube layer with a gradient structure; the bottom layer is a porous polymer base material; and the surface layer, the middle layer and the bottom layer are in gradient pore size increase. The composite antibacterial film of the application realizes synergistic antibacterial and filtration through the three-layer structure and the functional gradient.

Description

Technical Field

[0001] This invention relates to the field of filtration materials, specifically to a carbon nanotube-silver nano-gradient composite antibacterial membrane and its preparation method. Background Technology

[0002] Ultrafiltration membrane technology, as an important branch of membrane separation, is based on the core principle of sieving and cross-flow filtration, using pores with a diameter of 0.001-0.02 μm to trap suspended solids, bacteria, and large organic molecules. Due to its high efficiency and low energy consumption, ultrafiltration membranes have become a core separation technology in water treatment, biological separation, and food processing. However, traditional polymer ultrafiltration membranes (such as polyvinylidene fluoride (PVDF) and polyethersulfone (PES)) face multiple challenges in practical applications: membrane fouling (including adsorption of organic pollutants, formation of microbial biofilms, and inorganic scaling) leads to a permeate flux reduction of more than 30%-50%, requiring frequent chemical cleaning or high-pressure backflushing, significantly increasing operation and maintenance costs; simultaneously, pathogen residues caused by biological fouling (such as Escherichia coli and Staphylococcus aureus) may cause secondary pollution of the effluent, threatening public health.

[0003] To address these issues, researchers have introduced antibacterial functions through blending modification, surface grafting, or coating techniques. For example, silver nanoparticles (AgNPs) are widely used for membrane modification due to their broad-spectrum antibacterial properties, but their susceptibility to oxidative inactivation and the continuous release of Ag+ can lead to long-term toxicity risks. Graphene oxide (GO) inhibits microorganisms through physical retention and oxidative stress, but the stacking of layers can clog membrane pores, causing a decrease in flux (experiments show that the pure water flux of a PES membrane doped with 5 wt% GO is reduced by more than 40%). Quaternary ammonium polymers, while capable of disrupting bacterial cell membranes through electrostatic adsorption, suffer from poor chlorine resistance and easy leaching failure. Furthermore, the composite of single-functional materials often results in a trade-off in membrane performance—improved antibacterial properties often come at the cost of sacrificing mechanical strength (e.g., a 20%-30% decrease in elongation at break) or hydrophilicity.

[0004] In recent years, gradient composite strategies have provided a new direction for balancing antibacterial properties, antifouling properties, and mechanical properties. For example, by constructing gradient structure membranes with AgNPs enriched on the surface and carbon nanotubes (CNTs) loaded internally through electrospinning, bacteria can be rapidly inactivated in the outer layer (sterilization rate >90% within 2 hours of contact), while the inner CNT network inhibits Ag+ oxidation through electron transfer, prolonging the antibacterial period. Simultaneously, the directional arrangement of CNTs (e.g., vertical arrays) can form rapid mass transfer channels, mitigating flux decay (compared to homogeneous membranes, gradient membranes show a 25% increase in flux recovery in bovine serum albumin filtration). Nevertheless, the uniformity of nanomaterial dispersion in polymer matrices (e.g., CNT aggregation leading to membrane defects), interfacial compatibility (e.g., weak binding between AgNPs and PVDF causing detachment), and environmental safety (e.g., the impact of long-term Ag+ release on aquatic ecosystems) remain key challenges restricting their large-scale application. Summary of the Invention

[0005] The technical problem to be solved: The purpose of this invention is to provide a carbon nanotube-silver nano-gradient composite antibacterial membrane, which achieves a good antibacterial and filtration effect through the three-layer structure and the synergistic effect of functional gradient antibacterial and filtration.

[0006] Technical solution: A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer. The surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate. The surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0007] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0008] S1. Add PVDF and PVP to DMAc, stir to dissolve, and obtain PVDF casting solution;

[0009] S2. The casting solution is scraped into a liquid film with a thickness of 80-150um, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film;

[0010] S3. Disperse hydroxylated carbon nanotubes in deionized water to prepare a carbon nanotube dispersion;

[0011] S4. Add the carbon nanotube dispersion to the chitosan solution to prepare mixed solutions of different concentrations;

[0012] S5. The mixed solution is coated onto the base film in order of increasing concentration. Each time the base film is coated, it is placed between two parallel electrodes. An alternating electric field is applied during the drying process to obtain a base film of carbon nanotubes with a gradient structure.

[0013] S6. The base film prepared in step S5 is immersed in silver nitrate solution, and then hydrazine hydrate is added for reduction to obtain a carbon nanotube-silver nano-gradient composite antibacterial composite film.

[0014] Preferably, the mass ratio of PVDF to PVP is 15-20:1, and the concentration of PVDF in the PVDF casting solution is 6-10 wt%.

[0015] Preferably, the PVDF casting solution also contains carboxylated carbon nanotubes, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1-2 wt%.

[0016] Preferably, the concentration of the carbon nanotube dispersion is 2-3 wt%.

[0017] Preferably, the concentration of the chitosan solution is 0.2–0.5 wt%, and the carbon nanotube content in the mixed solutions of different concentrations is 0.1–0.3 wt%, 0.4–0.6 wt%, and 0.7–1 wt%, respectively.

[0018] Preferably, the electric field strength of the alternating current field is 1500–3000 V·cm⁻¹, and the frequency is 1–3 Hz.

[0019] Preferably, the concentration of the silver nitrate solution is 0.3–0.8 mol / L, the reduction temperature is 80–90°C, and the time is 10–20 h. Beneficial effects: The carbon nanotube-silver nanogradient composite antibacterial membrane of the present invention has the following advantages:

[0020] 1. In this invention, the composite antibacterial membrane exhibits an asymmetric gradient distribution. The surface layer consists of high-density silver nanoparticles embedded with a small amount of CNTs, providing strong antibacterial properties and reducing bacterial adhesion. The middle layer has a gradient-increasing CNT content (vertically oriented), forming water channels and enhancing conductivity. The bottom layer is a porous polymer substrate doped with sparse CNTs, which can maintain the mechanical strength of the membrane.

[0021] 2. In this invention, the three-layer structure achieves synergistic antibacterial and filtration effects through functional gradient. The effect from the surface to the bottom layer is as follows: surface antibacterial (AgNP) → middle conductive (CNT-induced electric field anti-biofilm) → bottom layer traps macromolecular pollutants, thus achieving a very good antibacterial and filtration effect.

[0022] 3. In this invention, the process parameters are optimized to form a gradient pore structure, wherein the surface pore size is 20-50nm (for bacterial retention), the middle layer is 50-100nm (for low transmission resistance), and the bottom layer is 100-200nm (for high throughput), which further improves the filtration effect. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments:

[0024] Example 1

[0025] A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer, wherein the surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate, and the surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0026] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0027] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 15:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 6wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1wt%.

[0028] S2. The casting solution is coated into a liquid film with a thickness of 100 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Hydroxylated carbon nanotubes are dispersed in deionized water to prepare a carbon nanotube dispersion with a concentration of 2 wt%;

[0029] S4. The carbon nanotube dispersion was added to a 0.5 wt% water-soluble chitosan solution to prepare mixed solutions of different concentrations. The carbon nanotube contents in the mixed solutions of different concentrations were 0.1 wt%, 0.4 wt%, and 0.7 wt%, respectively.

[0030] S5. The mixed solution is coated onto the base film in order of decreasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 1500 V·cm is applied during the drying process. -1 A base film of carbon nanotubes with a gradient structure was obtained at a frequency of 3 Hz.

[0031] S6. The base film prepared in step S5 is immersed in a silver nitrate solution with a concentration of 0.3 mol / L, and then hydrazine hydrate is added for reduction. The reduction temperature is 80℃ and the time is 20h to obtain a carbon nanotube-silver nanogradient composite antibacterial composite film.

[0032] Example 2

[0033] A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer, wherein the surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate, and the surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0034] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0035] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 20:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 10wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 2wt%.

[0036] S2. The casting solution is scraped into a liquid film with a thickness of 90 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film;

[0037] S3. Disperse hydroxylated carbon nanotubes in deionized water to prepare a carbon nanotube dispersion with a concentration of 3wt%;

[0038] S4. Add the carbon nanotube dispersion to a 0.2wt% water-soluble chitosan solution to prepare mixed solutions of different concentrations. The carbon nanotube contents in the mixed solutions of different concentrations are 0.3wt%, 0.6wt%, and 1wt%, respectively.

[0039] S5. The mixed solution is coated onto the base film in order of decreasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 3000 V·cm is applied during the drying process. -1 A base film of carbon nanotubes with a gradient structure was obtained at a frequency of 1 Hz.

[0040] S6. The base film prepared in step S5 is immersed in a 0.5 mol / L silver nitrate solution, and then hydrazine hydrate is added for reduction at a temperature of 90℃ for 10 h to obtain a carbon nanotube-silver nanogradient composite antibacterial composite film.

[0041] Example 3

[0042] A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer, wherein the surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate, and the surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0043] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0044] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 16:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 7wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1.4wt%.

[0045] S2. The casting solution is coated into a liquid film with a thickness of 120 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Hydroxylated carbon nanotubes are dispersed in deionized water to prepare a carbon nanotube dispersion with a concentration of 2 wt%;

[0046] S4. The carbon nanotube dispersion was added to a 0.7wt% water-soluble chitosan solution to prepare mixed solutions of different concentrations. The carbon nanotube contents in the mixed solutions of different concentrations were 0.15wt%, 0.45wt%, and 0.78wt%, respectively.

[0047] S5. The mixed solution is coated onto the base film in order of decreasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 1800 V·cm is applied during the drying process. -1 A base film of carbon nanotubes with a gradient structure was obtained at a frequency of 1 Hz.

[0048] S6. The base film prepared in step S5 is immersed in a silver nitrate solution with a concentration of 0.25 mol / L, and then hydrazine hydrate is added for reduction. The reduction temperature is 85℃ and the time is 15h to obtain a carbon nanotube-silver nanogradient composite antibacterial composite film.

[0049] Example 4

[0050] A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer, wherein the surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate, and the surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0051] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0052] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 18:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 9wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1.8wt%.

[0053] S2. The casting solution is coated into a liquid film with a thickness of 122 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Hydroxylated carbon nanotubes are dispersed in deionized water to prepare a carbon nanotube dispersion with a concentration of 3 wt%;

[0054] S4. The carbon nanotube dispersion was added to a 0.4 wt% water-soluble chitosan solution to prepare mixed solutions of different concentrations. The carbon nanotube contents in the mixed solutions of different concentrations were 0.2 wt%, 0.5 wt%, and 0.8 wt%, respectively.

[0055] S5. The mixed solution is coated onto the base film in order of decreasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 2500 V·cm is applied during the drying process. -1 A base film of carbon nanotubes with a gradient structure was obtained at a frequency of 3 Hz.

[0056] S6. The base film prepared in step S5 is immersed in a silver nitrate solution with a concentration of 0.55 mol / L, and then hydrazine hydrate is added for reduction. The reduction temperature is 90℃ and the time is 16h to obtain a carbon nanotube-silver nanogradient composite antibacterial composite film.

[0057] Example 5

[0058] A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer, wherein the surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate, and the surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0059] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0060] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 17:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 8wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1.6wt%.

[0061] S2. The casting solution is coated into a liquid film with a thickness of 118 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Hydroxylated carbon nanotubes are dispersed in deionized water to prepare a carbon nanotube dispersion with a concentration of 2.5 wt%;

[0062] S4. The carbon nanotube dispersion was added to a 0.3 wt% water-soluble chitosan solution to prepare mixed solutions of different concentrations. The carbon nanotube contents in the mixed solutions of different concentrations were 0.25%, 0.55 wt%, and 0.95 wt%, respectively.

[0063] S5. The mixed solution is coated onto the base film in order of decreasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 2000 V·cm is applied during the drying process. -1 A base film of carbon nanotubes with a gradient structure was obtained at a frequency of 2Hz.

[0064] S6. The base film prepared in step S5 is immersed in a silver nitrate solution with a concentration of 0.62 mol / L, and then hydrazine hydrate is added for reduction. The reduction temperature is 85℃ and the time is 15h to obtain a carbon nanotube-silver nanogradient composite antibacterial composite film.

[0065] Comparative Example 1

[0066] A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer, wherein the surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer, and the bottom layer is a porous polymer substrate, and the surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0067] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0068] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 17:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 8wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1.6wt%.

[0069] S2. The casting solution is coated into a liquid film with a thickness of 118 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Hydroxylated carbon nanotubes are dispersed in deionized water to prepare a carbon nanotube dispersion with a concentration of 2.5 wt%;

[0070] S4. Add the carbon nanotube dispersion to a 0.3wt% water-soluble chitosan solution to prepare a mixed solution, wherein the carbon nanotube content in the mixed solution is 0.55wt%.

[0071] S5. The mixed solution is coated onto the base film in order of decreasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 2000 V·cm is applied during the drying process. -1 A base film of carbon nanotubes with a gradient structure was obtained at a frequency of 2Hz.

[0072] S6. The base film prepared in step S5 is immersed in a 0.5 mol / L silver nitrate solution, and then hydrazine hydrate is added for reduction at a temperature of 85℃ for 15 h to obtain a carbon nanotube-silver nanogradient composite antibacterial composite film.

[0073] Comparative Example 2

[0074] A carbon nanotube gradient composite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer and a bottom layer, wherein the surface layer is a carbon nanotube layer with a gradient structure and the bottom layer is a porous polymer substrate, and the surface layer and the bottom layer have a gradient increase in pore size.

[0075] The above-mentioned method for preparing the carbon nanotube gradient composite antibacterial film includes the following steps:

[0076] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 17:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 8wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1.6wt%.

[0077] S2. The casting solution is coated into a liquid film with a thickness of 118 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Hydroxylated carbon nanotubes are dispersed in deionized water to prepare a carbon nanotube dispersion with a concentration of 2.5 wt%;

[0078] S4. The carbon nanotube dispersion was added to a 0.3 wt% water-soluble chitosan solution to prepare mixed solutions of different concentrations. The carbon nanotube contents in the mixed solutions of different concentrations were 0.25%, 0.55 wt%, and 0.95 wt%, respectively.

[0079] S5. The mixed solution is coated onto the base film in order of decreasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 2000 V·cm is applied during the drying process. -1A carbon nanotube gradient composite antibacterial composite film was obtained at a frequency of 2Hz.

[0080] Comparative Example 3

[0081] A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer, wherein the surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate, and the surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0082] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0083] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 17:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 8wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1.6wt%.

[0084] S2. The casting solution is coated into a liquid film with a thickness of 118 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Hydroxylated carbon nanotubes are dispersed in deionized water to prepare a carbon nanotube dispersion with a concentration of 2.5 wt%;

[0085] S4. The carbon nanotube dispersion was added to a 0.3 wt% water-soluble chitosan solution to prepare mixed solutions of different concentrations. The carbon nanotube contents in the mixed solutions of different concentrations were 0.25%, 0.55 wt%, and 0.95 wt%, respectively.

[0086] S5. The mixed solution is coated onto the base film in order of increasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 2000 V·cm is applied during the drying process. -1 A base film of carbon nanotubes with a gradient structure was obtained at a frequency of 2Hz.

[0087] S6. The base film prepared in step S5 is immersed in a silver nitrate solution with a concentration of 0.32 mol / L, and then hydrazine hydrate is added for reduction. The reduction temperature is 85℃ and the time is 15h to obtain a carbon nanotube-silver nanogradient composite antibacterial composite film.

[0088] Comparative Example 4

[0089] A carbon nanotube-silver nanocomposite antibacterial composite membrane, wherein the composite membrane is asymmetrically gradient distributed and includes a surface layer, an intermediate layer and a bottom layer, wherein the surface layer is a composite layer of silver nanotubes and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate, and the surface layer, intermediate layer and bottom layer exhibit a gradient increase in pore size.

[0090] The preparation method of the above-mentioned carbon nanotube-silver nanocomposite antibacterial film includes the following steps:

[0091] S1. Add PVDF and PVP to DMAc, with a mass ratio of PVDF to PVP of 30:1, stir to dissolve, add carboxylated carbon nanotubes, and continue stirring until homogeneous to obtain PVDF casting solution. The concentration of PVDF in the PVDF casting solution is 8wt%, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1.6wt%.

[0092] S2. The casting solution is coated into a liquid film with a thickness of 118 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Hydroxylated carbon nanotubes are dispersed in deionized water to prepare a carbon nanotube dispersion with a concentration of 2.5 wt%;

[0093] S4. The carbon nanotube dispersion was added to a 0.3 wt% water-soluble chitosan solution to prepare mixed solutions of different concentrations. The carbon nanotube contents in the mixed solutions of different concentrations were 0.25%, 0.55 wt%, and 0.95 wt%, respectively.

[0094] S5. The mixed solution is coated onto the base film in order of decreasing concentration. After each coating, the base film is placed between two parallel electrodes. An alternating electric field with a field strength of 2000 V·cm is applied during the drying process. -1 A base film of carbon nanotubes with a gradient structure was obtained at a frequency of 2Hz.

[0095] S6. The base film prepared in step S5 is immersed in a silver nitrate solution with a concentration of 0.1 mol / L, and then hydrazine hydrate is added for reduction. The reduction temperature is 85℃ and the time is 15h to obtain a carbon nanotube-silver nanogradient composite antibacterial composite film.

[0096] Table 1 Pore size distribution of each layer of the composite membrane

[0097] Average surface pore size (nm) Average pore size of intermediate layer (nm) Average pore size of the bottom layer (nm) Example 1 32.3 65.6 133.9 Example 2 28.9 78.9 152.3 Example 3 42.3 59.6 145.9 Example 4 44.5 82.3 188.7 Example 5 38.9 66.1 172.6 Comparative Example 1 22.3 55.7 158.9 Comparative Example 2 / 72.1 156.5 Comparative Example 3 35.6 56.9 165.4 Comparative Example 4 65.9 56.2 89.9

[0098] As shown in the table above, the surface layer pore size ranges from 28.9 to 44.5 nm, the middle layer pore size ranges from 59.6 to 82.3 nm, and the bottom layer pore size ranges from 133.9 to 188.7 nm. The surface layer is used to retain bacteria, the middle layer has low transport resistance, and the bottom layer has high water flux. The performance in Table 2 was tested according to the GB / T 32360-2015 ultrafiltration membrane test method, and the membrane's antibacterial rate (E. coli) was also tested.

[0099] Table 2 Composite Membrane Filtration Performance Test

[0100]

[0101] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A carbon nanotube-silver nanocomposite antibacterial membrane, characterized in that: The composite antibacterial film has an asymmetric gradient distribution, including a surface layer, an intermediate layer and a bottom layer. The surface layer is a composite layer of silver nanoparticles and carbon nanotubes, the intermediate layer is a carbon nanotube layer with a gradient structure, and the bottom layer is a porous polymer substrate. The surface layer, intermediate layer and bottom layer have a gradient increase in pore size.

2. A method for preparing the carbon nanotube-silver nanocomposite antibacterial membrane as described in claim 1, characterized in that, Includes the following steps: S1. Add PVDF and PVP to DMAc, stir to dissolve, and obtain PVDF casting solution; S2. The casting solution is coated into a liquid film with a thickness of 80-150 μm, and then immersed in a coagulation bath to solidify into a film, thus obtaining the bottom base film; S3. Disperse hydroxylated carbon nanotubes in deionized water to prepare a carbon nanotube dispersion; S4. Add the carbon nanotube dispersion to the chitosan solution to prepare mixed solutions of different concentrations; S5. The mixed solution is coated onto the base film in order of increasing concentration. Each time the base film is coated, it is placed between two parallel electrodes. An alternating electric field is applied during the drying process to obtain a base film of carbon nanotubes with a gradient structure. S6. The base film prepared in step S5 is immersed in silver nitrate solution, and then hydrazine hydrate is added for reduction to obtain a carbon nanotube-silver nano-gradient composite antibacterial composite film.

3. The method for preparing the carbon nanotube-silver nanocomposite antibacterial membrane according to claim 2, characterized in that: The mass ratio of PVDF to PVP is 15–20:1, and the concentration of PVDF in the PVDF casting solution is 6–10 wt%.

4. The method for preparing the carbon nanotube-silver nanocomposite antibacterial membrane according to claim 3, characterized in that: The PVDF casting solution also contains carboxylated carbon nanotubes, and the content of carboxylated carbon nanotubes in the PVDF casting solution is 1-2 wt%.

5. The method for preparing the carbon nanotube-silver nanocomposite antibacterial membrane according to claim 2, characterized in that: The concentration of the carbon nanotube dispersion is 2–3 wt%.

6. The method for preparing the carbon nanotube-silver nanocomposite antibacterial membrane according to claim 2, characterized in that: The concentration of the chitosan solution is 0.2–0.5 wt%, and the carbon nanotube content in the mixed solutions of different concentrations is 0.1–0.3 wt%, 0.4–0.6 wt%, and 0.7–1 wt%, respectively.

7. The method for preparing the carbon nanotube-silver nanocomposite antibacterial membrane according to claim 2, characterized in that: The electric field strength of the alternating current is 1500–3000 V·cm. -1 The frequency is 1 to 3 Hz.

8. The method for preparing the carbon nanotube-silver nanocomposite antibacterial membrane according to claim 2, characterized in that: The concentration of the silver nitrate solution is 0.1–0.5 mol / L, the reduction temperature is 80–90°C, and the time is 10–20 h.

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