An asymmetric iron oxide ceramic composite membrane and a preparation method and application thereof

Abstract

The application discloses a preparation method of an asymmetric iron oxide ceramic composite membrane, which comprises the following steps: step 1, obtaining iron hydroxide sol by subjecting an aqueous ferric chloride solution to a high-temperature hydrolysis reaction, cooling, and adding an aqueous polyvinyl alcohol solution into the iron hydroxide sol to obtain an iron oxide sol membrane solution; and step 2, immersing a ceramic microfiltration membrane into the iron oxide sol membrane solution obtained in the step 1, taking out, drying at room temperature, and microwave sintering to obtain the asymmetric iron oxide ceramic composite membrane. The new iron oxide membrane layer is formed on the surface of the ceramic microfiltration membrane by regulating the iron oxide sol membrane solution and the microwave sintering power and time. The sintering steps and time are greatly reduced, the energy required for sintering is saved, the membrane preparation cost is reduced, and the asymmetric iron oxide ceramic composite membrane has the advantages of high membrane flux and strong anti-pollution property.

Description

Technical Field

[0001] This invention relates to the field of ceramic membrane technology, specifically to an asymmetric iron oxide ceramic composite membrane, its preparation method, and its application. Background Technology

[0002] Desizing wastewater is generated during the pretreatment stage of dyeing and printing. It contains a large amount of organic matter, with a chemical oxygen demand (COD) exceeding 20 g / L. The total organic matter content accounts for more than 50% of the dyeing and printing wastewater, making it difficult to treat. Ceramic membranes, due to their advantages of good chemical stability, high mechanical strength, acid and alkali resistance, and high temperature resistance, are widely used in harsh environments with high temperature and strong alkalinity. However, desizing wastewater contains high molecular weight sizing agents (such as PVA and carboxymethyl cellulose), starch, and oils, which easily form a gel layer on the membrane surface or clog the membrane pores, leading to a sharp decrease in permeate flux. Once pollutants are adsorbed on the membrane surface, they are difficult to remove by conventional backwashing, requiring frequent chemical cleaning (such as with strong acids, strong alkalis, or oxidants), increasing equipment operation and maintenance costs.

[0003] Fe2O3 is considered a natural hydrophilic material, abundant and inexpensive. Due to the high hydrophilicity of nano-iron oxide particles, Fe2O3 nanoparticles deposited on the membrane surface result in minimal fouling tendency. Current technologies primarily modify the surface of ceramic membranes with Fe2O3 nanoparticles to enhance the hydrophilicity and oleophobicity of the membrane surface. However, these surface-modified iron oxide ceramic membranes still suffer from rapid decreases in permeate flux and require frequent cleaning in the treatment of desizing wastewater. In contrast, composite ceramic membranes with a complete iron oxide membrane layer exhibit superior antifouling performance in treating desizing wastewater, primarily due to their continuous and uniform surface characteristics. The complete membrane layer forms a dense cover, imparting high hydrophilicity to the entire membrane surface and effectively blocking the direct adhesion of hydrophobic organic matter. In comparison, ceramic membranes modified only with iron oxide have increased interparticle gaps and roughness, making it easier for pollutants to adhere and form a dense, difficult-to-remove fouling layer.Patent CN 113926321A describes the modification of Fe2O3 onto the surface of a ceramic microfiltration membrane to obtain an antifouling ceramic membrane. However, this patent explicitly states that Fe2O3 was only modified onto the surface of the ceramic microfiltration membrane. The iron hydroxide sol particles prepared in Example 2 of this patent have a particle size of only 40-50 nm. Under these conditions, a complete iron oxide film layer cannot be formed on the surface of a ceramic support with a pore size of 100 nm. Therefore, this patent lacks supporting data such as the pore size of the iron oxide film layer. Similarly, Barati N et al. (Barati N, Husein MM, Azaiez J. Modifying ceramic membranes with in situ grown iron oxide nanoparticles and their use for oily water treatment[J]. Journal of Membrane Science, 2020, 617:118641.) and Karnik BS et al. (Karnik BS, Baumann MJ, Masten SJ, et al. AFM and SEM characterization of iron oxide coated ceramic membranes[J]. Journal of Materials) Science, 2006, 41(20):6861-6870.) also modified the ceramic film surface with iron oxide nanoparticles, but the ceramic film surface disclosed in these literatures did not form a complete iron oxide film layer (Barati N et al. directly stated in the 8th and 9th lines of the 4th paragraph of Section 3.1.2 in their literature that they did not observe the formation of an additional layer composed only of nano-iron oxide; Karnik BS et al. showed the EDS energy spectrum of the iron oxide coated ceramic film prepared according to the method in the literature (Fig. 9b). It can be clearly seen from the figure that the surface of the modified ceramic film is mixed with chemical substances of different sizes and shapes (titanium dioxide, zirconium oxide, iron oxide and aluminum oxide), and the EDS energy spectrum signal response of Fe element is not uniform, indicating that the ceramic film is only modified with iron oxide on the surface. If a complete film layer is formed, the surface of the modified ceramic film should be composed of chemical substances of uniform size and similar shape, and the Fe element signal response in the EDS energy spectrum of Fe element should be uniform).

[0004] Microwave sintering offers numerous advantages, including rapid and uniform heating, high efficiency and energy saving, and no heat source pollution, attracting significant attention from materials scientists. Since 1998, the Materials Research Society (MRS) has discussed microwave sintering technology as a special topic. Currently, microwave sintering is primarily applied in materials preparation, where it aims to achieve densification and macroscopic performance control, overcoming challenges related to size effects and temperature uniformity. In the membrane field, the focus is on the precise control of membrane microstructure, balancing porosity, separation efficiency, and mechanical stability. Fe is considered a microwave absorbing material with significant absorption properties, especially at high frequencies, making it an excellent material for microwave sintering. How to apply microwave sintering to the preparation of ceramic membranes to create composite ceramic membranes with a complete iron oxide film layer, higher permeation flux, and stronger resistance to membrane fouling is a pressing problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to address the problems of rapid decrease in permeate flux and poor antifouling ability when using existing iron oxide-modified ceramic membranes to treat desizing wastewater, and to provide a method for preparing an asymmetric iron oxide ceramic membrane. This invention rapidly prepares an iron oxide membrane layer on the surface of a ceramic microfiltration membrane using microwave sintering. The asymmetric iron oxide ceramic membrane prepared by this method exhibits high permeate flux and superior antifouling performance in the treatment of desizing wastewater.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0007] A method for preparing an asymmetric iron oxide ceramic composite film includes the following steps:

[0008] Step 1: Ferric chloride aqueous solution is subjected to high-temperature hydrolysis reaction to obtain ferric hydroxide sol, cooled, and polyvinyl alcohol aqueous solution is added to obtain ferric hydroxide sol film-forming solution;

[0009] Step 2: Immerse the ceramic microfiltration membrane in the iron oxide sol membrane-forming solution obtained in Step 1, remove it, dry it, and microwave sinter it to obtain the final product.

[0010] In step 1, the high-temperature hydrolysis is performed by adding the ferric chloride aqueous solution dropwise into boiling water and reacting at a temperature of 90–100°C for 0.1–12 hours; the cooling is performed by cooling to 70–90°C.

[0011] In step 1, after adding polyvinyl alcohol aqueous solution to the ferric hydroxide sol, the mixture is stirred and reacted at a temperature of 70-90°C for 10-30 minutes to obtain the ferric hydroxide sol film-forming solution.

[0012] In step 1, the solid content of ferric hydroxide in the ferric hydroxide sol film-forming solution is 0.1-0.6 wt%.

[0013] When the polyvinyl alcohol content C in the ferric hydroxide sol film-forming solution in step 1 is in the range of 0.25wt% ≤ C < 0.5wt%, then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 400-600W, and the microwave sintering time is 3-5min; or, during the microwave sintering process, the microwave power first linearly increases from 0 to the target power within 2-3min, and then sintersects at a constant target power for 1-2min, the target power being 400-600W.

[0014] In step 1, the polyvinyl alcohol content C in the ferric hydroxide sol film-forming solution is in the range of 0.5wt% ≤ C ≤ 0.75wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 600-800W, and the microwave sintering time is 3-5min; or, during the microwave sintering process, the microwave power first linearly increases from 0 to the target power within 2-3min, and then sintersects at a constant target power for 2-3min, the target power being 600-800W.

[0015] In step 1, the polyvinyl alcohol content (C) in the ferric hydroxide sol film-forming solution is in the range of 0.75wt% < C ≤ 1wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 600-800W, and the microwave sintering time is 4-5min; or, during the microwave sintering process, the microwave power first linearly increases from 0 to the target power within 2-3min, and then sintersects at a constant target power for 3-4min, the target power being 600-800W.

[0016] The polyvinyl alcohol in question is polyvinyl alcohol type 124.

[0017] In step 1, the particle size of the ferric hydroxide colloid in the ferric hydroxide sol film-forming solution is 100-200 nm.

[0018] In step 2, the room temperature drying refers to drying at room temperature for 6 to 24 hours.

[0019] In step 2, the material of the ceramic microfiltration membrane is any one or a combination of several of alumina, titanium dioxide, zirconium oxide and silicon dioxide.

[0020] The ceramic microfiltration membrane is a common microporous ceramic membrane that can be purchased from the market.

[0021] In step 2, the ceramic microfiltration membrane is cleaned before being immersed in the ferric hydroxide sol membrane-forming solution. The preferred cleaning method is to immerse the ceramic microfiltration membrane in water and heat it to boiling, maintaining the boiling for 60 minutes to remove impurities from its surface and pores.

[0022] In step 2, before immersing the ceramic microfiltration membrane in the ferric hydroxide sol membrane-forming solution, the ferric hydroxide sol membrane-forming solution is subjected to degassing treatment; the preferred method for degassing treatment is to stir the ferric hydroxide sol membrane-forming solution in a degassing mixer at 2000 r / min for 3 minutes, and then degas at 2200 r / min for 5 minutes.

[0023] The asymmetric iron oxide ceramic composite film prepared by the above method is also within the scope of protection of this invention.

[0024] The present invention also claims protection for the application of the asymmetric iron oxide ceramic composite membrane prepared by the above preparation method in the treatment of desizing wastewater in the printing and dyeing industry.

[0025] Preferably, when using the asymmetric iron oxide ceramic composite membrane to treat desizing wastewater from the printing and dyeing industry, the filtration method is cross-flow filtration, the transmembrane pressure difference is 1–2 bar, and the membrane surface velocity is 1–1.5 m·s. -1 The operating temperature is 50-70℃.

[0026] Beneficial effects:

[0027] (1) This invention prepares an asymmetric iron oxide ceramic composite film by microwave sintering. Microwave sintering can achieve bulk heating through the dielectric loss inside the material, and the heating rate is fast (up to 1000℃ / min). Compared with conventional sintering, microwave sintering shortens the film preparation time by 50-90% and reduces energy consumption by 30-70%, which greatly reduces the film preparation steps and time, reduces energy consumption, and thus effectively reduces the film preparation cost.

[0028] (2) This invention forms a new iron oxide membrane layer on the surface of a ceramic microfiltration membrane by controlling the composition of the iron hydroxide sol membrane-forming solution, the microwave sintering frequency, and the time. This reduces the degree of scaling on the membrane and increases the membrane permeation flux during the treatment of desizing wastewater. Moreover, the rapid sintering of microwave sintering inhibits excessive grain growth, resulting in a more uniform membrane pore size distribution and optimizing the membrane microstructure. It also avoids the organic matter volatilization pollution caused by prolonged high temperatures in traditional sintering. Due to the uniform heating characteristics of microwaves, the resulting iron oxide nanoparticles are more uniform, increasing the porosity of the resulting iron oxide membrane layer and reducing the isoelectric point of the membrane surface. Furthermore, due to the electrostatic repulsion, the degree of scaling on the iron oxide membrane is further reduced during the treatment of desizing wastewater, and the permeation flux is further increased.

[0029] (3) Microwave sintering has a significant effect on the uniform sintering of porous structures or composite membranes, avoiding delamination between membrane layers. In this invention, the ceramic membrane coated with iron hydroxide sol is calcined using a microwave method, which greatly improves the bonding strength of iron oxide nanoparticles on the surface of the ceramic membrane, and improves the operational stability of the resulting iron oxide ceramic membrane. Attached Figure Description

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0031] Figure 1 Scanning electron microscope (SEM) images of the original alumina ceramic film and the ceramic films prepared in Examples 1, 2, 1, and 2 are shown. Specifically, image a is an SEM image of the surface (left) and cross-section (right) of the original alumina ceramic film; image b is an SEM image of the surface (left) and cross-section (right) of the asymmetric iron oxide ceramic composite film prepared in Example 1; image c is an SEM image of the surface (left) and cross-section (right) of the asymmetric iron oxide ceramic composite film prepared in Example 2; image d is an SEM image of the surface (left) and cross-section (right) of the ceramic film prepared in Comparative Example 1; and image e is an SEM image of the surface (left) and cross-section (right) of the ceramic film prepared in Comparative Example 2.

[0032] Figure 2 The images show the elemental distribution map and EDS spectrum obtained from EDS scanning of the asymmetric iron oxide ceramic composite film prepared in Example 1; where, a is the EDS spectrum obtained from energy dispersive spectroscopy scanning of the asymmetric iron oxide ceramic composite film surface; b is the surface morphology map of the asymmetric iron oxide ceramic composite film; c is the Al elemental distribution map of the asymmetric iron oxide ceramic composite film surface; d is the O elemental distribution map of the asymmetric iron oxide ceramic composite film surface; and e is the Fe elemental distribution map of the asymmetric iron oxide ceramic composite film surface.

[0033] Figure 3 The pressure-flow curves (Figure a) and pore size distribution diagrams (Figure b) obtained by measuring the pore size distribution of the original alumina ceramic membrane and the asymmetric iron oxide ceramic composite membrane prepared in Example 1 using the bubble pressure method are shown.

[0034] Figure 4 The diagram shows the pure water flux of the original alumina ceramic membrane in Example 3, the ceramic membranes prepared in Comparative Example 2 and Example 1.

[0035] Figure 5 The graph shows the flux changes during the treatment of desizing wastewater by the original alumina ceramic membrane in Example 4, the ceramic membrane with iron oxide only modified on the surface, and the asymmetric iron oxide ceramic composite membrane prepared in Example 1.

[0036] Figure 6 This is a comparison chart showing the membrane flux recovery rates of the original alumina ceramic membrane in Example 4, the ceramic membrane with iron oxide only modified on the surface, and the asymmetric iron oxide ceramic composite membrane prepared in Example 1 after treating desizing wastewater. Detailed Implementation

[0037] The present invention will be further described below with reference to the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0038] Example 1

[0039] Accurately weigh 1.29 g of FeCl3·6H2O compound and add it to 50 mL of deionized water. Sonicate for 5 min to dissolve completely. Then, add it dropwise to 40 mL of pre-boiled deionized water and heat in an oil bath to 100 °C. Continue the reaction for 3 h, then cool to 80 °C to obtain ferric hydroxide sol. Next, take 10 mL of 10 wt% PVA aqueous solution and add it dropwise to the above ferric hydroxide sol. Stir and react at 80 °C for 20 min. Finally, cool naturally to room temperature to obtain a ferric hydroxide sol film-forming solution with a ferric hydroxide solid content of 0.5% and a PVA content of 1 wt%. Mix the solution at 2000 r / min for 3 min and deaerator at 2200 r / min for 5 min in a mixer-deaerator. Repeat the mixing and deaerator process 3 times. The particle size of the ferric hydroxide colloid was measured to be 100–200 nm. A sheet-type alumina ceramic membrane (Nanjing Membrane Materials Industry Technology Research Institute Co., Ltd., 3cm in diameter, 2mm thick) with an average pore size of 100nm was cleaned with deionized water and dried at 110℃ for 4 hours. The cleaned alumina ceramic membrane was immersed in ferric hydroxide sol film-forming solution for 1 minute, then removed at a speed of 10mm / s, naturally air-dried for 12 hours, and then sintered in a microwave sintering furnace at a constant power of 800W for 4 minutes to obtain the asymmetric ferric oxide ceramic composite membrane of the present invention.

[0040] The microstructure of the original alumina ceramic film and the asymmetric iron oxide ceramic composite film prepared in this embodiment were analyzed using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown in Figure a (sheet alumina ceramic film) and Figure b (asymmetric iron oxide ceramic composite film), comparing the microstructure of the ceramic film surface before and after coating with the film-forming solution, it was found that compared with the original alumina ceramic film, a new iron oxide film layer with a thickness of 0.5 μm was formed on the surface of the asymmetric iron oxide ceramic composite film, with smaller nanoparticles and a smoother surface.

[0041] Surface EDS energy dispersive spectroscopy analysis was performed on the original alumina ceramic film and the asymmetric iron oxide ceramic composite film prepared in this embodiment. The results are as follows: Figure 2 As shown, comparing the elements on the surface of the original alumina ceramic film and the asymmetric iron oxide ceramic composite film prepared in this embodiment, it was found that since the surface of the asymmetric iron oxide ceramic composite film is a new iron oxide film layer, there is an obvious Fe element signal response on its surface, with the Fe element accounting for 20.4 wt%.

[0042] The pore size of the asymmetric iron oxide ceramic composite membrane prepared in this embodiment was determined by the bubble pressure method. The results are as follows: Figure 3 As shown, the pore size of the asymmetric iron oxide ceramic composite film prepared by this method is found to be between 100 and 120 nm, which is consistent with... Figure 1 The results of the SEM images shown in Figure b are consistent, with a porosity of 35-41%.

[0043] Example 2

[0044] Accurately weigh 1.29 g of FeCl3·6H2O compound and add it to 50 mL of deionized water. Sonicate for 5 min to dissolve completely. Then, add it dropwise to 40 mL of pre-boiled deionized water and heat in an oil bath to 100 °C. Continue the reaction for 3 h, then cool to 80 °C to obtain ferric hydroxide sol. Next, take 10 mL of 10 wt% PVA aqueous solution and add it dropwise to the above ferric hydroxide sol. Stir and react at 80 °C for 20 min. Finally, cool naturally to room temperature to obtain a ferric hydroxide sol film-forming solution with a ferric hydroxide solid content of 0.5% and a PVA content of 1 wt%. Mix the solution at 2000 r / min for 3 min and deaerator at 2200 r / min for 5 min in a mixer-deaerator. Repeat the mixing and deaerator process 3 times. The particle size of the ferric hydroxide colloid was measured to be 100–200 nm. A sheet-type alumina ceramic membrane (Nanjing Membrane Materials Industry Technology Research Institute Co., Ltd., 3cm in diameter, 2mm thick) with an average pore size of 100nm was cleaned with deionized water and dried at 110℃ for 4 hours. The cleaned alumina ceramic membrane was then immersed in ferric hydroxide sol film-forming solution for 1 minute, removed at a speed of 10mm / s, and allowed to air dry naturally for 12 hours. After that, it was placed in a microwave sintering furnace where the power was linearly increased from 0 to 800W within 2 minutes, and then sintered at 800W for 3 minutes to obtain an asymmetric ferric oxide ceramic composite membrane.

[0045] The microstructure of the asymmetric iron oxide ceramic film prepared in this embodiment was analyzed using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown in Figure c, comparing the microstructure of the ceramic film surface before and after coating with the film-forming solution, it was found that compared to the original alumina ceramic film ( Figure 1 a) A new iron oxide film layer with a thickness of about 0.6 μm was also formed on the surface of the asymmetric iron oxide ceramic film. The pore size of the film is between 105 and 124 nm, and the porosity is 35 to 41%.

[0046] Comparative Example 1

[0047] Accurately weigh 1.29 g of FeCl3·6H2O compound and add it to 50 mL of deionized water. Sonicate for 5 min to dissolve completely. Then, add it dropwise to 40 mL of pre-boiled deionized water and heat in an oil bath to 100 °C. Continue the reaction for 3 h, then cool to 80 °C to obtain ferric hydroxide sol. Next, add 10 mL of 10 wt% PVA aqueous solution dropwise to the above ferric hydroxide sol. Stir and react at 80 °C for 20 min, and finally cool naturally to room temperature to obtain a ferric hydroxide sol film-forming solution with a solid content of 0.5%. Mix the solution at 2000 r / min for 3 min and degas at 2200 r / min for 5 min in a mixer-degassing machine. Repeat the mixing and degassing process 3 times. The particle size of the ferric hydroxide colloid was measured to be 100–200 nm. A sheet-type alumina ceramic membrane (Nanjing Membrane Materials Industry Technology Research Institute Co., Ltd., diameter 3 cm, membrane thickness 2 mm) with an average pore size of 100 nm was cleaned with deionized water and dried at 110 °C for 4 h. After immersing the cleaned alumina ceramic membrane in ferric hydroxide sol for 1 minute, it was removed at a speed of 10 mm / s and allowed to air dry naturally for 12 hours. Then, it was placed in a microwave sintering furnace and the power was linearly increased from 0 to 600W within 3 minutes. Finally, it was sintered at 600W for 4 minutes to obtain an asymmetric ferric oxide ceramic membrane.

[0048] The microstructure of the asymmetric iron oxide ceramic film prepared in this comparative example was analyzed using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown in Figure d, comparing the microstructure of the ceramic film surface before and after coating with the film-forming solution, it was found that compared with the original alumina ceramic film ( Figure 1 a) A new iron oxide film layer with a thickness of 2 μm was formed on the surface of the asymmetric iron oxide ceramic film. The surface nanoparticles were smaller and the surface was smoother. However, due to the excessively long overall sintering time, the surface of the iron oxide film layer became dense and the channels were not obvious, indicating the formation of a dense layer. The pure water flux test showed that the pure water flux was 0, which also indicated the formation of a dense layer and made it unsuitable for application.

[0049] Comparative Example 2

[0050] Accurately weigh 1.29 g of FeCl3·6H2O compound and add it to 50 mL of deionized water. Sonicate for 5 min to dissolve completely. Then, add it dropwise to 40 mL of pre-boiled deionized water and heat in an oil bath to 100 °C. Continue the reaction for 3 h, then cool to 80 °C to obtain ferric hydroxide sol. Next, add 10 mL of 10 wt% PVA aqueous solution dropwise to the above ferric hydroxide sol. Stir and react at 80 °C for 20 min, and finally cool naturally to room temperature to obtain a ferric hydroxide sol film-forming solution with a solid content of 0.5%. Mix the solution at 2000 r / min for 3 min and degas at 2200 r / min for 5 min in a mixer-degassing machine. Repeat the mixing and degassing process 3 times. The particle size of the ferric hydroxide colloid was measured to be 100–200 nm. A sheet-type alumina ceramic membrane (Nanjing Membrane Materials Industry Technology Research Institute Co., Ltd., diameter 3 cm, membrane thickness 2 mm) with an average pore size of 100 nm was cleaned with deionized water and dried at 110 °C for 4 h. After immersing the cleaned alumina ceramic membrane in ferric hydroxide sol for 1 minute, it was removed at a speed of 10 mm / s and allowed to air dry naturally for 12 hours. Then, it was placed in a microwave sintering furnace and sintered at a constant 600 W for 4 minutes to obtain an asymmetric ferric oxide ceramic membrane.

[0051] The microstructure of the asymmetric iron oxide ceramic film prepared in this comparative example was analyzed using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown in Figure e, comparing the microstructure of the ceramic film surface before and after coating with the film-forming solution, it was found that compared to the original alumina ceramic film ( Figure 1 a) A complete iron oxide film layer did not form on the surface of the asymmetric iron oxide ceramic film, and the film surface remained very rough. This is because the sintering microwave power was low, and incomplete sintering resulted in residual PVA on the film surface, preventing the formation of a complete iron oxide film layer. The cross-section also shows that no obvious iron oxide layer was formed. Figure 1 (See right figure). However, the incomplete iron oxide layer on the surface of the ceramic film will gradually peel off, rendering it unusable.

[0052] Example 3

[0053] Pure water flux tests were conducted using the original alumina ceramic membrane, the asymmetric iron oxide ceramic membrane prepared in Example 1, and Comparative Example 2. During the experiments, the transmembrane pressure difference was 0.5 bar, the membrane surface velocity was 1 m / s, and the operating temperature was 20°C. The experimental results are as follows: Figure 4 As shown, the results indicate that the stable flux of the original alumina ceramic membrane is 262 L·m. -2 ·h -1 The stable flux of the asymmetric iron oxide ceramic membrane prepared in Example 1 was 213 L·m. -2 ·h -1The flux was reduced by 20% compared to the original ceramic membrane because the increased loading of the new iron oxide layer improved the overall membrane resistance. Similarly, the asymmetric iron oxide ceramic membrane prepared in Comparative Example 2 had a stable flux of 230 L·m⁻¹. -2 ·h -1 The flux was reduced by 12% compared to the original ceramic membrane. However, because a complete iron oxide film layer was not formed, the flux reduction was not as significant as in Example 1.

[0054] Example 4

[0055] Continuous concentration and separation experiments were conducted on desizing wastewater (from a company in Quanzhou) using a raw alumina ceramic membrane, the asymmetric iron oxide ceramic composite membrane prepared in Example 1 of this invention, and a ceramic membrane prepared in Example 2 of patent CN 113926321A with iron oxide modified only on the ceramic membrane surface. The desizing wastewater had a COD of 10000–18000 mg / L, a pH of 12–14, and its main components were 3–10 g / L starch and 1–3 g / L polyvinyl alcohol. During membrane separation, the transmembrane pressure difference was 1 bar, the membrane surface velocity was 1.5 m / s, and the operating temperature was 70℃. Membrane flux was measured during the separation process. The experimental results are as follows: Figure 5 As shown, the results indicate that after 210 min of operation, the permeation flux of the original alumina ceramic membrane was 60 L·m⁻¹. -2 ·h -1 The permeation flux of the ceramic membrane modified only with iron oxide was 69 L·m. -2 ·h -1 The asymmetric iron oxide ceramic membrane prepared in Example 1 had a permeation flux of 85 L·m⁻¹. -2 ·h -1 The flux increased by 41.6% compared to the original ceramic membrane and by 23.2% compared to the ceramic membrane modified with iron oxide alone. At this point, the feed solution was concentrated by 2 times or more, indicating that the asymmetric iron oxide ceramic composite membrane has better antifouling performance.

[0056] After 210 min of continuous concentration experiment, the membrane surface was rinsed with pure water for 60 min and backwashed for 5 min, respectively. The membrane flux was measured again, and the membrane flux recovery rate was calculated. The experimental results are as follows: Figure 6As shown, the results indicate that the flux recovery rate of the original alumina ceramic membrane was 42% under pure water rinsing and 67% under backwashing. The flux recovery rate of the ceramic membrane modified with iron oxide alone was 49% under pure water rinsing and 76% under backwashing. In contrast, the flux recovery rate of the asymmetric iron oxide ceramic membrane prepared in Example 1 increased to 57% under pure water rinsing and 82% under backwashing, representing increases of 36% and 22% respectively compared to the original ceramic membrane, and increases of 16.3% and 8% respectively compared to the iron oxide-modified ceramic membrane. The flux recovery performance of the asymmetric iron oxide ceramic composite membrane prepared by this invention is improved.

[0057] This invention provides an asymmetric iron oxide ceramic composite film and its preparation and application, along with related ideas and methods. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing an asymmetric iron oxide ceramic composite film, characterized in that, Includes the following steps: Step 1: Ferric chloride aqueous solution is subjected to high-temperature hydrolysis reaction to obtain ferric hydroxide sol, cooled, and polyvinyl alcohol aqueous solution is added to obtain ferric hydroxide sol film-forming solution; Step 2: Immerse the ceramic microfiltration membrane in the ferric hydroxide sol membrane-forming solution obtained in Step 1, remove it, dry it at room temperature, and sinter it using microwave to obtain the final product. In step 1, the solid content of ferric hydroxide in the ferric hydroxide sol film-forming solution is 0.1 ~ 0.6 wt%; the polyvinyl alcohol is polyvinyl alcohol type 124; the high-temperature hydrolysis is: adding the ferric chloride aqueous solution dropwise to boiling water and reacting at a temperature of 90 ~ 100℃ for 0.1 ~ 12 h; In step 1, the polyvinyl alcohol content (C) in the ferric hydroxide sol film-forming solution ranges from 0.25 wt% to C < 0.5 wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 400 ~ 600 W, and the microwave sintering time is 3 ~ 5 min; or, during the microwave sintering process, the microwave power first linearly increases from 0 to the target power within 2 ~ 3 min, and then sintersects at a constant target power for 1 ~ 2 min, the target power being 400 ~ 600 W. In step 1, the polyvinyl alcohol content (C) in the ferric hydroxide sol film-forming solution ranges from 0.5 wt% ≤ C ≤ 0.75 wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 600 ~ 800 W, and the microwave sintering time is 3 ~ 5 min; or, during the microwave sintering process, the microwave power first linearly increases from 0 to the target power within 2 ~ 3 min, and then sintersects at a constant target power for 2 ~ 3 min, the target power being 600 ~ 800 W. In step 1, the polyvinyl alcohol content (C) in the ferric hydroxide sol film-forming solution is in the range of 0.75 wt% < C ≤ 1 wt%; then in step 2, the microwave power is constant during the microwave sintering process, the microwave power is 600 ~ 800 W, and the microwave sintering time is 4 ~ 5 min; or, during the microwave sintering process, the microwave power first linearly increases from 0 to the target power within 2 ~ 3 min, and then sintersects at a constant target power for 3 ~ 4 min, the target power being 600 ~ 800 W.

2. The preparation method according to claim 1, characterized in that, In step 1, the cooling process involves cooling the temperature to 70-90°C.

3. The preparation method according to claim 1, characterized in that, In step 1, after adding polyvinyl alcohol aqueous solution to the ferric hydroxide sol, the mixture is stirred and reacted at a temperature of 70-90℃ for 10-30 minutes to obtain the ferric hydroxide sol film-forming solution.

4. The asymmetric iron oxide ceramic composite film prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the asymmetric iron oxide ceramic composite membrane according to claim 4 in the treatment of desizing wastewater in the printing and dyeing industry.

6. The application according to claim 5, characterized in that, When using the aforementioned asymmetric iron oxide ceramic composite membrane to treat desizing wastewater from the printing and dyeing industry, the filtration method is cross-flow filtration, the transmembrane pressure difference is 1~2 bar, and the membrane surface velocity is 1~1.5 m·s. -1 The operating temperature is 50 ~ 70℃.

Images