A method for preparing silver nanoparticle-grafted modified ceramic membranes

Abstract

This invention relates to the field of separation membrane materials technology, specifically a method for preparing a silver nanoparticle-grafted modified ceramic membrane. The method involves cleaning and soaking a ceramic membrane; then reacting the ceramic membrane in an ethanol solution of (3-mercaptopropyl)trimethoxysilane, followed by drying to obtain a ceramic membrane grafted with (3-mercaptopropyl)trimethoxysilane; next, immersing the obtained ceramic membrane in an aqueous solution of silver nitrate, followed by drying to obtain a ceramic membrane with silver ions coordinated on its surface and pore walls; finally, immersing the ceramic membrane in an aqueous solution of a reducing agent to obtain a ceramic membrane grafted with silver nanoparticles. This invention features a simple process, mild reaction conditions, and does not damage the membrane microstructure. The prepared membrane has a uniformly distributed layer of silver nanoparticles on its pore walls, which has little impact on the permeate flux of the ceramic membrane, fully utilizing the large specific surface area of ​​the nanoparticles, resulting in a large contact area with bacteria in the water and good antibacterial properties.

Description

Technical Field

[0001] This invention patent relates to the field of separation membrane material technology, specifically a method for preparing a silver nanoparticle grafted modified ceramic membrane. Background Technology

[0002] Ceramic membranes are thin-film materials with highly efficient separation functions, made from inorganic metal oxides or non-metal oxides through high-temperature sintering. Ceramic membranes possess characteristics such as high temperature resistance, chemical corrosion resistance, good mechanical strength, strong antimicrobial ability, high permeability, strong washability, narrow pore size distribution, and long service life.

[0003] Currently, ceramic membranes are mainly used in domestic wastewater treatment and advanced drinking water purification. However, a bottleneck in their application is unavoidable membrane fouling, which leads to reduced membrane permeate flux, decreased water production efficiency, and increased operating and maintenance costs. The main components causing membrane fouling are microorganisms and their metabolic secretions, which accumulate, multiply, and compact on the membrane surface.

[0004] However, existing ceramic membranes produced using domestic and international technologies, as well as those already used in wastewater treatment and drinking water purification, only possess simple separation functions and lack antibacterial and bactericidal capabilities. There are numerous reports on antibacterial functional modifications to ceramic membranes. The main approach involves incorporating nano-metal particles into the ceramic membrane matrix and separation layer during the membrane preparation process, followed by high-temperature sintering. However, this approach suffers from the problem of nano-metal particles being easily embedded by ceramic particles, resulting in a weak antibacterial effect. Another approach involves in-situ growth of nano-metal particles on the pore walls and surface of the ceramic membrane. This method is feasible, but the nanoparticles tend to aggregate, clogging the membrane pores and reducing the membrane's porosity and filtration efficiency. Yet another antibacterial method involves grafting quaternary ammonium zwitterions onto the ceramic membrane surface, but this method has been found to have poor antibacterial effects. Finally, a method involves coating the ceramic membrane surface with a titanium dioxide nanolayer, which exhibits excellent antibacterial and bactericidal effects under ultraviolet light. However, this approach is difficult to implement in engineering projects. Large-scale engineering projects cannot integrate ultraviolet light onto the ceramic membrane surface, primarily due to the high turbidity in wastewater hindering ultraviolet irradiation.

[0005] Patent (Application No.: 202210573330.4) discloses a method for preparing an antibacterial ceramic membrane, which involves grafting inexpensive copper nanoparticles onto the surface and pore walls of a ceramic membrane at room temperature using a chemical grafting method for antibacterial purposes. However, the actual antibacterial effect is very limited and cannot achieve the purpose of practical engineering applications. This may be due to the weak coordination bond of N-Cu, leading to copper particle loss. Therefore, this invention uses a thiol-containing silane coupling agent to firmly and uniformly fix silver nanoparticles onto the pore walls and surface of the ceramic membrane through S-Ag bonds, thereby achieving super-strong antibacterial and bactericidal effects, ensuring stable ceramic membrane flux, and high filtration efficiency. Summary of the Invention

[0006] This invention addresses the unavoidable microbial contamination of ceramic membranes in wastewater treatment or deep drinking water purification, which leads to reduced membrane separation efficiency and increased membrane operation and maintenance costs, as well as the problems existing in the various antibacterial technologies already disclosed. It proposes a method that utilizes the abundant hydroxyl functional groups on the surface of ceramic membranes as active sites and anchors nano-silver particles on the surface and pore walls of ceramic membranes through chemical grafting to endow ceramic membranes with super-strong antibacterial and bactericidal functions.

[0007] The technical solution for preparing a silver nanoparticle grafted modified ceramic membrane according to the present invention includes the following steps: Step 1: Pretreatment of ceramic membrane surface: The flat ceramic membrane is ultrasonically cleaned for 20 min, and then soaked in ethanol solution for 1 h to remove impurities from its surface and pores. The structure of the membrane surface is as follows: ; Step 2: Grafting (3-mercaptopropyl)trimethoxysilane onto the ceramic membrane: The pretreated ceramic membrane from Step 1 was immersed in an ethanol solution of (3-mercaptopropyl)trimethoxysilane of a certain concentration for 12 h, then its surface was repeatedly rinsed with anhydrous ethanol and vacuum dried at 60 ℃ to obtain a flat ceramic membrane grafted with (3-mercaptopropyl)trimethoxysilane. The reaction process is as follows:

[0008] Step 3, coordinating silver ions: The ceramic membrane obtained in Step 2 was immersed in an aqueous solution of silver nitrate of a certain concentration for 12 h, then rinsed repeatedly with deionized water several times, and vacuum dried at 60 ℃ to obtain a flat ceramic membrane with silver ions coordinated on the surface and pore walls. The reaction process is as follows:

[0009] Step 4, Self-assembly of silver nanoparticles: The ceramic membrane obtained in Step 3 was immersed in an aqueous solution containing a certain concentration of reducing agent for 1 hour, and repeatedly rinsed with deionized water to obtain a flat ceramic membrane grafted with silver nanoparticles. The reaction process is as follows:

[0010] Preferably, in step 1 of the above preparation method, the ceramic film is a composite ceramic film of one or more of alumina, titanium oxide, zirconium oxide, silicon oxide and silicon carbide.

[0011] As a further preferred embodiment, in step 1 of the above preparation method, the ceramic membrane is made of alumina and silicon carbide; its shape is one of flat plate, tubular, or dense multi-channel.

[0012] Preferably, in step 2 of the above preparation method, the concentration of (3-mercaptopropyl)trimethoxysilane is 10~30 mmol / L.

[0013] Preferably, in step 3 of the above preparation method, the concentration of silver nitrate is 0.1~3 mmol / L.

[0014] Preferably, in step 4 of the above preparation method, the reducing agent is either sodium borohydride or hydrazine hydrate.

[0015] Preferably, in step 4 of the above preparation method, the concentration of the reducing agent is 0.05~0.3 mol / L.

[0016] The present invention has the following beneficial effects: (1) This invention uses a silane coupling agent containing thiol to firmly anchor nano-silver particles uniformly on the pore walls and surface of the ceramic membrane through S-Ag bonds, thereby achieving super antibacterial and bactericidal effects, ensuring stable flux of the ceramic membrane and high filtration efficiency.

[0017] (2) The nano-silver particle modified ceramic membrane prepared by the present invention, after being soaked in water for 24 hours, has a slow-release silver ion content of only 0.0017 mg / L, which is far lower than the 0.05 mg / L specified in the "Drinking Water Quality Standard (CJ94-2005)", showing excellent safety performance; (3) The preparation method is simple and the reaction conditions are mild; (4) The ceramic membrane has the property of being resistant to organic solvents, and the preparation process will not damage the membrane microstructure; (5) The preparation method involves uniformly distributing a layer of nano-silver particles on the pore walls of the ceramic membrane, which has little effect on the permeation flux of the ceramic membrane. This may be based on the boundary slip effect of the nanoparticles. (6) The preparation method involves uniformly distributing a layer of nano-silver particles on the surface of the ceramic membrane and the pore walls, giving full play to the large specific surface area characteristics of nanoparticles, resulting in a large contact area with bacteria in the water and good antibacterial performance. Detailed Implementation The present invention will be further illustrated below with examples, but these are not intended to limit the scope of the invention.

[0018] Example 1 The flat silicon carbide ceramic diaphragm was ultrasonically cleaned for 20 min and then soaked in ethanol solution for 1 h to remove impurities from its surface and pores. Example 2 Step 1: Ultrasonically clean the flat silicon carbide ceramic diaphragm for 20 min, and then soak it in ethanol solution for 1 h to remove impurities from its surface and pores. Step 2: Immerse the ceramic membrane after the pretreatment in Step 1 in an ethanol solution of 20 mmol / L (3-mercaptopropyl)trimethoxysilane for 1 h, then rinse its surface repeatedly with anhydrous ethanol, and dry it under vacuum at 60 °C to obtain a flat silicon carbide ceramic membrane grafted with (3-mercaptopropyl)trimethoxysilane. Step 3: Immerse the ceramic membrane obtained in Step 2 in a 2 mmol / L silver nitrate aqueous solution for 24 h, then rinse it repeatedly with deionized water until the washing solution is colorless, and vacuum dry it at 60 °C to obtain a flat silicon carbide ceramic membrane with silver ions coordinated on the surface and pore walls. Step 4: Immerse the ceramic membrane obtained in Step 3 in a 0.2 mol / L aqueous solution of hydrazine hydrate for 1 h, and rinse repeatedly with deionized water to obtain a flat silicon carbide ceramic membrane grafted with silver nanoparticles. The pretreated planar silicon carbide ceramic membrane from Example 1 was tested for pure water flux. Under constant negative pressure of -0.02 MPa and a temperature of 20 °C, deionized water was filtered using an immersion filtration method. The pure water flux of the membrane in Example 1 was 1078 LMH. Under the same testing conditions, the pure water flux of the membrane in Example 2 was 1356 LMH. This indicates that the modification of the planar silicon carbide ceramic membrane surface and pore walls with nanoparticles does not significantly affect the permeation flux of the membrane. The main reason why the pure water flux of the membrane in Example 2 is higher than that in Example 1 is likely due to a boundary slip effect: nanoparticles have a high specific surface area, exhibiting more MO dangling bonds and abundant surface hydroxyl groups, thus exhibiting a strong binding interaction with water molecules. This strong interaction results in an ordered arrangement of water molecules on the silicon carbide membrane surface, and the closer to the solid surface, the stronger the molecular order. This ordered layer of liquid molecules reduces the friction between water and the solid surface, thereby generating fluid slip and improving the hydrophilicity of the membrane.

[0019] The flat-plate silicon carbide ceramic membranes prepared in Examples 1 and 2 were used to treat domestic sewage. The water samples were from rural domestic sewage in Zhejiang Province. The process used was membrane bioreactor (MBR), i.e., a decentralized integrated domestic sewage treatment equipment. The stability of the membrane's permeate flux was tested under a constant negative pressure of -0.02 MPa and a temperature of 20 ℃ to evaluate the membrane's antibacterial performance. The evaluation results are shown in the table below: Time (days) 1 5 10 15 20 Example 1 (LMH) 33 25 22 20 20 Example 2 (LMH) 38 36 35 34 34 Compared to the original membrane of Example 1, the silver nanoparticle grafted and modified ceramic membrane prepared in Example 2 exhibited better stable permeation flux, indicating that the flat silicon carbide ceramic membrane of Example 2 has excellent antibacterial properties.

[0020] The antibacterial properties of the plate-shaped silicon carbide ceramic membranes prepared in Examples 1 and 2 were tested using the plate count method. The test bacteria were Escherichia coli (E) and Staphylococcus aureus (S). The test results are as follows: strains Blank control Example 1 Example 2 <![CDATA[S(10 -4 )]]> 873 728 0 <![CDATA[E(10 -4 )]]> 856 791 0 The comparison of total bacterial counts showed that Example 2 successfully prepared a ceramic membrane with excellent antibacterial properties.

[0021] Example 3 Following the same steps as in Example 2, alumina, titanium dioxide, zirconium oxide, and silicon dioxide were used as ceramic films for preparation. Since the main function of this invention is the technical effect produced after grafting on the surface of the ceramic film, the products obtained by grafting modification with these base films have similar technical effects as those in the examples after comparative testing. In the tests on Escherichia coli (E) and Staphylococcus aureus (S), the same effects as those in the examples were also observed.

[0022] Example 4 Following the same steps as in Example 2, experiments were conducted using (3-mercaptopropyl)trimethoxysilane at concentrations of 10 mmol / L and 30 mmol / L, and the following results were obtained: The tested bacteria were Escherichia coli (E) and Staphylococcus aureus (S), and the test results are as follows:

[0023] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. All equivalent variations and modifications described in accordance with the scope of the present invention and the description should fall within the scope of the present invention.

Claims

1. A method for preparing a silver nanoparticle-grafted modified ceramic membrane, characterized in that, Includes the following steps: Step 1: Ultrasonically clean the ceramic membrane for 20 min, then soak it in ethanol solution for 1 h to remove impurities from its surface and pores. Step 2: Immerse the ceramic membrane after the pretreatment in Step 1 in an ethanol solution of (3-mercaptopropyl)trimethoxysilane of a certain concentration for 12 h, then rinse its surface repeatedly with anhydrous ethanol, and dry it under vacuum at 60 °C to obtain a ceramic membrane grafted with (3-mercaptopropyl)trimethoxysilane. Step 3: Immerse the ceramic membrane obtained in Step 2 in an aqueous solution of silver nitrate of a certain concentration for 12 h, then rinse it repeatedly with deionized water several times, and dry it under vacuum at 60 °C to obtain a ceramic membrane with silver ions coordinated on the surface and pore walls. Step 4: Immerse the ceramic membrane obtained in Step 3 in an aqueous solution containing a certain concentration of reducing agent for 1 hour, and rinse repeatedly with deionized water to obtain a ceramic membrane grafted with silver nanoparticles; the reducing agent is either sodium borohydride or hydrazine hydrate.

2. The preparation method according to claim 1, characterized in that... The ceramic membrane is a composite ceramic membrane made of one or more of the following: alumina, titanium dioxide, zirconium oxide, silicon dioxide, and silicon carbide.

3. The preparation method according to claim 2, characterized in that... The ceramic film is alumina or silicon carbide; Its shape can be one of flat plate, tubular, or dense multi-channel.

4. The preparation method according to claim 1, characterized in that... The concentration of the (3-mercaptopropyl)trimethoxysilane is 10~30 mmol / L.

5. The preparation method according to claim 1, characterized in that... The concentration of silver nitrate is 0.1~3 mmol / L.

6. The preparation method according to claim 1, characterized in that... The concentration of the reducing agent is 0.05~0.3 mol / L.

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