A method for preparing Janus ceramic membranes based on pre-wetting control

Abstract

This invention belongs to the field of membrane material preparation and modification technology, and relates to a method for pre-wetting the surface of a hydrophobic ceramic membrane. The ceramic membrane is immersed in a cyclohexane solution of perfluorooctyltrimethoxysilane for 3-4 hours. After immersion, the ceramic membrane is dried in an oven. An ethanol solution is forced to circulate through the ceramic membrane to pre-wet the separation layer. The pre-wetting process proposed in this invention is simple, highly controllable, and easily scaled up to pre-wet multi-channel hydrophobic ceramic membranes. This invention achieves coarse adjustment of the wetting degree by controlling the concentration of the ethanol-water solution, and further fine adjustment by combining the circulation time of the ethanol-water solution, thus achieving more precise control of the wetting degree and optimal improvement of the uniformity of the hydrophilic coating.

Description

Technical Field

[0001] This invention belongs to the field of membrane material preparation and modification technology, and relates to a method for preparing Janus ceramic membranes based on pre-wetting control. Background Technology

[0002] Ceramic membranes possess unique micro- and nano-structures, and due to their excellent thermal, mechanical, and chemical stability, they can be used in harsh chemical environments, including membrane separation, membrane distillation, and membrane dispersion. However, the inherent hydrophilic properties of ceramic membranes typically limit their application range. To broaden their applications, it is necessary to control the surface properties of the membrane. Surface wettability is one of the most important characteristics of the membrane. Inspired by mussels, depositing polydopamine coatings can improve the hydrophilicity of the material surface, thereby enhancing its antifouling and biocompatibility. Existing research has utilized this hydrophilic surface coating principle, combined with hydrophobic fibrous surface structures, to further enhance the material's hydrophilicity. Furthermore, this composite membrane with asymmetric wettability has been used as a gas distributor for aeration to generate microbubbles. The large specific surface area and self-compressibility of microbubbles enhance mass transfer. The surface wettability of the material itself has a significant impact on the adhesion, deposition behavior, and morphology of polydopamine coatings. This is particularly true when hydrophobic materials, including hydrophobic ceramic films, undergo hydrophilic modification by depositing dopamine on their surfaces. Due to the low surface energy of the hydrophobic ceramic film, air layers easily form on the film surface, hindering subsequent dopamine deposition and consequently reducing coating uniformity, thus affecting the hydrophilicity of the dopamine coating. Pre-wetting is an effective improvement method, but current research on pre-wetting is limited.

[0003] Pre-wetting processes primarily involve contacting the material with a wetting agent. Patent CN109550408A reports a method of immersing a ZrO2 ceramic membrane in ultrapure water for 2 hours to thoroughly wet all membrane pores. Then, a dopamine compound and amino (or mercapto) short-chain ethylene glycol molecules react to form a co-deposition layer on the ceramic membrane surface, resulting in a protein-resistant ceramic composite membrane. Patent CN111672339A reports a method for immersing a TiO2 ultrafiltration ceramic membrane in deionized water for 2 hours to thoroughly wet all membrane pores. The ceramic membrane is then placed in a mixed solution of dopamine compounds and polyethyleneimine to react, yielding a polydopamine-modified ceramic membrane. Both of these thorough immersion pre-wetting methods eliminate air layers on the membrane surface, allowing dopamine to deposit more firmly onto the ceramic membrane. While these methods can easily and thoroughly wet the material, they do not allow for control over the wetting area and degree of wetting. Furthermore, when the membrane surface is hydrophobic, the surface energy is low, the water permeation flux is low, and therefore the efficiency of water prewetting is low. Summary of the Invention

[0004] This invention proposes a novel method for preparing Janus ceramic membranes based on pre-wetting control, addressing the problems existing in traditional pre-wetting processes.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0006] A method for preparing Janus ceramic membranes with asymmetric wettability based on pre-wetting control, comprising the following steps:

[0007] (1) The pretreated ceramic membrane is immersed in a cyclohexane solution of perfluorooctyltrimethoxysilane for 3-4 hours, and the separation layer of the ceramic membrane is located on the inner wall of the tube.

[0008] (2) After impregnation, place the ceramic film in an oven to dry.

[0009] (3) Force the ethanol solution to circulate through the ceramic membrane tube to pre-wet the inner surface of the ceramic membrane.

[0010] (4) The dopamine solution is forced to circulate through the ceramic membrane tube to deposit dopamine. After the deposition is completed, it is cleaned and dried to prepare an asymmetric wettability Janus ceramic membrane.

[0011] Preferably, the ceramic membrane in step (1) is a single-tube alumina ceramic membrane, and the pretreatment process is to place the membrane tube in a mixed solution of water, acetone and ethanol, sonicate for 0.5-1h and then dry it; the concentration of the perfluorooctyltrimethoxysilane cyclohexane solution is 0.001-0.01mol / L and the immersion temperature is 25-35℃.

[0012] Preferably, the drying temperature in step (2) is 65-75℃ and the drying time is at least 12h.

[0013] Preferably, in step (3), the concentration of the ethanol solution is 8-12% vol, the pre-wetting time is 0.5-4.5 min, and the flow rate of the ethanol solution in the ceramic membrane tube is 3-6 cm / s.

[0014] Preferably, the dopamine solution in step (4) is prepared by adjusting the pH of a 3.8-4.5 g / L dopamine aqueous solution to 8.4-8.6 using Tris buffer solution; the deposition time is 1.4-1.6 h; and the flow rate of the dopamine solution in the ceramic membrane tube is 3-6 cm / s.

[0015] This invention strictly controls the pre-wetting process, effectively improving the efficiency of dynamic dopamine deposition on the surface of hydrophobic ceramic membranes, enhancing the uniformity of the hydrophilic coating, and thus improving the uniformity of gas dispersion into the liquid. Pre-wetting ceramic membranes have broad application prospects in systems with strict requirements for gas feed, such as poorly soluble systems, systems with vigorous reactions, and systems where rapid reactions easily generate byproducts.

[0016] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0017] 1. The prewetting process proposed in this invention is simple, highly controllable, and easy to scale up to prewetting of hydrophobic ceramic membranes with multi-channel configurations.

[0018] 2. This invention achieves coarse adjustment of wetting degree by regulating the concentration of ethanol aqueous solution, and further fine adjustment of wetting degree by combining the circulation time of ethanol aqueous solution, thus achieving more precise control of wetting degree and optimal improvement of hydrophilic coating uniformity. Attached Figure Description

[0019] Figure 1 and Figure 2 All are water contact angles of ceramic membranes, among which Figure 1 This is the static contact angle; Figure 2 This refers to the dynamic contact angle.

[0020] Figure 3 The images are FESEM images of the ceramic film surface, where (a) is JCM, (b) is JCM-P, and (c) is CM.

[0021] Figure 4 The figures show the dissolved oxygen variation curves over time, where (a) represents the detection results of pre-wetting with ethanol aqueous solutions of different concentrations, and (b) represents the detection results of different pre-wetting times. Detailed Implementation

[0022] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0023] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0024] Example 1

[0025] This embodiment provides a process for preparing a pre-wetted tubular Janus ceramic membrane with asymmetric wettability.

[0026] (1) Preparation of hydrophobic ceramic membrane

[0027] A single-tube alumina ceramic membrane (with the separation layer located on the inner wall of the membrane, 6.0 cm in length, an average pore size of 200 nm, an outer diameter of 12 mm, and an inner diameter of 8 mm) was ultrasonically cleaned for 30 min using a cleaning solution consisting of a 1:1:1 mixture of water, acetone, and ethanol. The ceramic membrane was then ultrasonically cleaned at 70°C. o Dry in an oven at temperature C for 12 hours, then allow to cool naturally to room temperature. This is denoted as CM.

[0028] In-situ grafting of hydrophobic groups to prepare hydrophobic ceramic membranes via immersion method: A 0.005 mol / L cyclohexane solution of perfluorooctyltrimethoxysilane (PFTMS) was prepared. The ceramic membrane was immersed in a vacuum flask containing this solution, and vacuumed for 10 min using a water ring vacuum pump. After removal, the ceramic membrane was placed vertically in a beaker, and the above solution was poured in until the membrane was submerged. The grafting reaction was carried out in a 30°C water bath for 3 h. After the reaction, the membrane was washed with water and ethanol for 5 min each to remove residual solution, and then the membrane was heated to 70°C. o After drying at C for 12 hours, a hydrophobic membrane was obtained and named OCM.

[0029] (2) Prewetting of hydrophobic ceramic membranes

[0030] Prepare 200 mL of 8% (v / v) ethanol solution for later use. Prepare 200 mL of 4 g / L dopamine (DA) aqueous solution, and adjust the pH of the DA aqueous solution to 8.5 with Tris buffer solution (50 g / L tris(hydroxymethyl)aminomethane) solution. Then place the DA aqueous solution in a 30°C water bath for constant temperature until use.

[0031] The pre-wetting device can take many forms, and this embodiment provides one of them: The device in this embodiment includes one membrane module, two beakers, one peristaltic pump, and two three-way valves. The membrane module mainly includes three parts: one single-layer cylindrical stainless steel shell, two end sealing ring caps, and two sealing ring retainers. Each end face of the module body has an outlet. The ceramic membrane tube is placed in the module body and the two ends of the membrane tube extend an appropriate length from the end face so that the gaskets are fitted on the two ends of the membrane tube and fit against the outlet of the module body. Then, one of the sealing ring caps is fitted on the outlet of the body. The sealing ring retainers are used to lock the membrane module and the sealing ring cap tightly. Finally, the bolts on the sealing ring retainers are tightened. The other end of the body is sealed by the same sealing method. Each sealing ring cap has a liquid outlet so that the inlet and outlet ends of the entire membrane module can be connected by a hose. The membrane module is vertically fixed on an iron stand. The inlet end (lower part of the membrane module) is connected to one port of a three-way valve. The other two ports of the three-way valve are connected via hoses to beakers containing ethanol solution and DA solution, respectively. The outlet end of the membrane module is connected to one port of another three-way valve. The other two ports are also connected via hoses to beakers containing ethanol solution and DA solution, respectively. Then, the hose section between the membrane module inlet and the three-way valve at the inlet end is secured with a peristaltic pump, and the pump speed is set. Before pre-wetting begins, adjust the inlet and outlet three-way valves to form a closed loop between the membrane module and the ethanol solution through the hoses. Turn on the pump to pump the ethanol solution into the membrane module, allowing it to flow over the inner surface of the hydrophobic ceramic membrane to dispel the air layer, and then return to the beakers. This pre-wetting process is carried out in a circulating manner, with the circulation time strictly controlled at 0.5 minutes. The peristaltic pump controls the liquid flow rate on the inner surface of the membrane tube to 4 cm / s.

[0032] (3) Dynamic deposition of DA to prepare Janus ceramic films with asymmetric wettability

[0033] When the pre-wetting time reaches 0.5 min, the flow direction of the inlet and outlet three-way valves is quickly adjusted so that the membrane module and DA solution form a closed loop. The DA solution is then circulated for 1.5 h. The liquid flow rate on the membrane surface of the peristaltic pump is 3.0 cm / s, thus preparing a Janus ceramic membrane with asymmetric wettability.

[0034] Cleaning the Janus ceramic membrane: After deposition, remove the membrane tube and rinse continuously with water for 5 minutes to remove residual solution, then rinse at 70°C. o Dry at C for 12 hours. The Janus ceramic membrane prepared by the above steps is named JCM-P.

[0035] Janus ceramic films with direct DA deposition without pre-wetting were prepared for comparison and named JCM.

[0036] The ceramic film prepared in this embodiment was subjected to contact angle testing, and the results are as follows: Figure 1 and 2 As shown, from Figure 1 It can be seen from this that the hydrophilicity of the hydrophilic surface of JCM-P is higher than that of JCM. Figure 2 It can be seen that the water permeation rate on the hydrophilic surface of JCM-P is higher than that of JCM, indicating that the hydrophilicity of the DA coating deposited after pre-wetting the hydrophobic membrane is significantly enhanced.

[0037] The ceramic film prepared in this embodiment was characterized by SEM, and the results are as follows: Figure 3 .from Figure 3 As can be seen, the DA coating of JCM has obvious agglomerates, which makes the surface of the coating rougher, while the uniformity of the DA coating of JCM-P is significantly better than that of JCM. This indicates that the pre-wetting process has a significant improvement on the DA deposition process.

[0038] Example 2

[0039] This embodiment provides a process for preparing a pre-wetted tubular Janus ceramic membrane with asymmetric wettability.

[0040] (1) Preparation of hydrophobic ceramic membrane

[0041] An alumina ceramic membrane was taken and ultrasonically cleaned for 30 minutes using a cleaning solution consisting of a 1:1:1 mixture of water, acetone, and ethanol (volume ratio). The ceramic membrane was then ultrasonically cleaned at 70°C. o Dry in an oven at temperature C for 12 hours, then allow to cool naturally to room temperature. This is recorded as CM.

[0042] In-situ grafting of hydrophobic groups to prepare hydrophobic ceramic membranes using the immersion method: A 0.005 mol / L cyclohexane solution of perfluorooctyltrimethoxysilane was prepared. The ceramic membrane was immersed in a vacuum flask containing this solution, and the flask was evacuated for 10 minutes using a water ring vacuum pump. After evacuation, the ceramic membrane was removed and placed vertically in a beaker. The solution was poured in until the membrane was submerged, and the grafting reaction was carried out in a 25°C water bath for 3 hours. After the reaction, the membrane was washed with water and ethanol for 5 minutes each to remove residual solution, and then the membrane was heated to 75°C. o The hydrophobic membrane was obtained by drying at C for 13 hours.

[0043] (2) Prewetting of hydrophobic ceramic membranes

[0044] Prepare 200 mL of 10% ethanol solution for later use. Prepare 200 mL of 4 g / L dopamine aqueous solution and adjust the pH of the DA aqueous solution to 8.5 with Tris buffer solution. Then place the DA aqueous solution in a 30℃ water bath for constant temperature and use.

[0045] The pre-wetting cycle time was controlled at 1.0 min, and the peristaltic pump controlled the liquid flow rate on the membrane surface at 6 cm / s.

[0046] (3) Dynamic deposition of DA to prepare Janus ceramic films with asymmetric wettability

[0047] When the pre-wetting time reaches 0.5 min, the flow direction of the inlet and outlet three-way valves is quickly adjusted so that the membrane module and DA solution form a closed loop. The DA solution is then circulated for 1.5 h. The liquid flow rate on the membrane surface of the peristaltic pump is 3.5 cm / s, thus preparing a Janus ceramic membrane with asymmetric wettability.

[0048] Cleaning the Janus ceramic membrane: After deposition, remove the membrane tube and rinse continuously with water for 5 minutes to remove residual solution, then rinse at 70°C. o Dry at C for 12 hours.

[0049] Example 3

[0050] This embodiment provides a process for preparing a pre-wetted tubular Janus ceramic membrane with asymmetric wettability.

[0051] (1) Preparation of hydrophobic ceramic membrane

[0052] An alumina ceramic membrane was taken and ultrasonically cleaned for 30 minutes using a cleaning solution consisting of a 1:1:1 mixture of water, acetone, and ethanol (volume ratio). The ceramic membrane was then ultrasonically cleaned at 70°C. o Dry in an oven at C for 12 hours, then allow to cool naturally to room temperature.

[0053] In-situ grafting of hydrophobic groups to prepare hydrophobic ceramic membranes using the immersion method: A 0.005 mol / L cyclohexane solution of perfluorooctyltrimethoxysilane was prepared. The ceramic membrane was immersed in a vacuum flask containing this solution, and the flask was evacuated for 10 minutes using a water ring vacuum pump. After evacuation, the ceramic membrane was removed and placed vertically in a beaker. The solution was poured in until the membrane was submerged, and the grafting reaction was carried out in a 30°C water bath for 3 hours. After the reaction, the membrane was washed with water and ethanol for 5 minutes each to remove residual solution, and then the membrane was heated to 70°C. o The hydrophobic membrane was obtained by drying at C for 12 hours.

[0054] (2) Prewetting of hydrophobic ceramic membranes

[0055] Prepare 200 mL of 8% (v / v) ethanol solution for later use. Prepare 200 mL of 4 g / L dopamine aqueous solution and adjust the pH of the DA aqueous solution to 8.5 with Tris buffer solution. Then place the DA aqueous solution in a 30℃ water bath for constant temperature and use.

[0056] The pre-wetting cycle time was controlled at 4.5 min, and the peristaltic pump controlled the liquid flow rate on the membrane surface at 3 cm / s.

[0057] (3) Dynamic deposition of DA to prepare Janus ceramic films with asymmetric wettability

[0058] When the pre-wetting time reaches 0.5 min, the flow direction of the inlet and outlet three-way valves is quickly adjusted so that the membrane module and DA solution form a closed loop. The DA solution is then circulated for 1.5 h. The liquid flow rate on the membrane surface of the peristaltic pump is 4 cm / s, thus preparing a Janus ceramic membrane with asymmetric wettability.

[0059] Cleaning the Janus ceramic membrane: After deposition, remove the membrane tube and rinse continuously with water for 5 minutes to remove residual solution, then rinse at 70°C. o Dry at C for 12 hours.

[0060] SEM analysis showed that the uniformity of the Janus ceramic film DA coating with asymmetric wettability obtained in Examples 2 and 3 was not significantly different from that in Example 1.

[0061] JCM-P as a gas distributor for dispersion performance testing.

[0062] 1. Dispersion performance test of JCM-P in oxygen-water system

[0063] Aeration is a crucial process in biofilm reactor systems, water treatment systems, and chemical catalytic reaction systems. The oxygenation performance of a system directly affects its operational efficiency and energy consumption. Within each system, gas solubility and gas-phase transfer efficiency are key factors influencing aeration performance. For poorly soluble systems, such as oxygen-water two-phase systems, liquid film resistance is high, and traditional blower aeration achieves an oxygen transfer efficiency of only 5-10%, indicating significant potential for improvement in dissolved oxygen efficiency. Ceramic membrane aeration, as a microbubble aeration method, is currently a hot research topic.

[0064] This embodiment uses an oxygen-water two-phase system and examines the aeration performance of JCM-P using three parameters: total oxygen transfer coefficient, oxygenation capacity, and oxygen utilization rate.

[0065] The testing method is as follows: Oxygen at a constant flow rate of 25 mL / min is bubbled into the membrane distributor, allowing oxygen to pass through the separation layer from the outer surface of the membrane tube and enter the interior. A constant flow of water is pumped from the storage tank to shear the dispersed microbubbles, controlling the liquid flow velocity at the membrane surface to 4 cm / s. The water is then returned to the storage tank. This process requires the use of commercially available, custom-made membrane modules to ensure that gas can only enter the interior of the membrane tube from the tube wall, while the aqueous phase only flows through the tube side. The change in dissolved oxygen in the water over time is obtained through a data acquisition system, and the dissolved oxygen concentration in the water corresponding to the aeration time t is recorded. Ct Dissolved oxygen saturation value C S (The maximum value measured on-site after a sufficiently long period of stable aeration) The total oxygen transfer coefficient, oxygenation capacity, and oxygen utilization rate are calculated using the method described in CJ / T 475-2015 "Determination of Oxygen Mass Transfer Performance of Microporous Aerators in Clear Water", thereby comparing the dispersion performance of each gas distributor.

[0066] The test results are shown in Table 1 below.

[0067] Table 1. Test results of dissolved oxygen dispersion performance of each membrane tube during aeration

[0068]

[0069] As shown in Table 1, the dissolved oxygen content of JCM-P (JCM / 8%-0.5min) prepared in Example 1 was significantly higher than that of the other membrane distributors, and its oxygen content increased at a faster rate than that of the other distributors. This indicates that the pre-wetting process significantly enhances the dispersion performance of this material.

[0070] 2. Effects of different prewetting parameters

[0071] The effects of different pre-wetting conditions on the dispersion performance of the membrane tubes were investigated by varying the pre-wetting time or the concentration of the ethanol solution. Unless otherwise specified, the conditions were consistent with those in Example 1. For ease of description, JCM-P prepared with different pre-wetting concentration parameters was named JCM-P / n%-0.5min, where the pre-wetting time was 0.5 min; JCM-P prepared with different pre-wetting time parameters was named JCM-P / 8%-t, where the volume fraction of the EtOH aqueous solution was 8%.

[0072] 2.1 Effect of Ethanol Concentration

[0073] The ethanol volume percentage was adjusted to 4%, 12%, 16%, and 50%, respectively, while the other conditions remained the same as in Example 1. The test was conducted using the method described in CJ / T 475-2015, "Determination of Oxygen Transfer Performance of Microporous Aerators in Clear Water". The test results are as follows: Figure 4 (a) and Table 2 below, where JCM-P / 8%-0.5min is the prepreg film prepared in Example 1.

[0074] Table 2 Effect of Ethanol Concentration on Test Results

[0075]

[0076] according to Figure 4As shown in (a) and Table 2 above, with the increase of pre-wetting concentration, both the saturated oxygen concentration and the oxygen dissolution rate show an overall trend of first increasing and then decreasing, and the dissolved oxygen dispersion performance of JCM-P / n%-0.5min is better than that of JCM. Therefore, the concentration of pre-wetting agent has a significant impact on the dispersion effect of the material.

[0077] 2.2 Effect of Pre-wetting Time

[0078] The pre-wetting time was adjusted sequentially to 1.5 min, 2.5 min, 3.5 min, 4.5 min, and 10 min, with all other conditions remaining the same as in Example 1. The effect of pre-wetting time was investigated using the test method in CJ / T475-2015, "Determination of Oxygen Transfer Performance of Microporous Aerators in Clear Water". Figure 4 As shown in (b) and Table 3, with the increase of prewetting time, both the saturated oxygen concentration and the oxygen dissolution rate generally show a trend of first increasing and then decreasing, and the dissolved oxygen dispersion performance of JCM-P / 8%-2.5min is the best. Therefore, prewetting time has a significant impact on the dispersion effect of the material.

[0079] Table 3. Effect of Pre-wetting Time on Test Results

[0080]

[0081] 3. Average diameter (d), polydispersity index (PDI), and gas holdup testing

[0082] The testing apparatus used the same membrane module as in the dissolved oxygen test described above. A polymethyl methacrylate (PMMA) visualization module was fixed to the top of the membrane module (outlet on the membrane tube). A gas flow meter controlled air to pass through the shell side of the membrane module at a constant flow rate of 25 mL / min. After being dispersed by a single-tube ceramic membrane, the gas entered the channel of the membrane tube. Water entered the membrane module through a peristaltic pump and flowed through the inner membrane surface of the membrane tube at a flow rate of 4 cm / s, shearing the microbubbles. Dynamic bubble images in the visualization module were recorded by a high-speed camera for analysis. The average diameter (d) and polydispersity index (PDI) were calculated from the sizes of microbubbles with a total number greater than 500 in the bubble images to evaluate the characteristics of the dispersed microbubble size. PDI is the ratio of the sample standard deviation to the mean; the smaller the value, the less the bubble size deviates from the main body size. The gas holdup was determined by the volume expansion method, i.e., the liquid in the visualization module was retained during stable aeration. After the bubbles escaped, the change in the liquid level drop was recorded by a camera to reflect the retention performance of the aeration system for microbubbles.

[0083] 3.1 Effect of Pre-wetting Solution Concentration

[0084] The preparation of the pre-wetted membrane was the same as in 2.1, and the measurement results are shown in Table 4 below.

[0085] Table 4. Test results of dispersion performance of pre-wetted membranes

[0086]

[0087] Compared to JCM, the average bubble size of JCM-P / n%-0.5min initially decreased and then slowly increased with increasing pre-wetting concentration, reaching a minimum of 295 μm. This indicates that pre-wetting can reduce bubble size, but excessively high or low ethanol concentrations significantly affect the pre-wetting effect. Table 4 shows that the polydispersity index initially decreased and then increased, indicating that excessively high or low ethanol concentrations also significantly affect the uniformity of microbubble dispersion by the membrane distributor.

[0088] 3.2 Effect of Pre-wetting Time

[0089] The preparation of the pre-wetted membrane was the same as in section 2.2, and the measurement results are shown in Table 5 below.

[0090] Table 5. Test results of dispersion performance of pre-wetted membranes

[0091]

[0092] According to the test results in Table 5, compared with JCM, the average bubble size of JCM-P / 8%-t initially decreased slightly with increasing pre-wetting time, then increased, reaching a minimum of 233 μm. However, after a pre-wetting time of 10 min, the average bubble size became too large, indicating that adjusting the time can reduce bubble size to some extent. The polydispersity index showed the same trend, and the gas holdup also increased with prolonged pre-wetting time. However, this trend reached an inflection point after excessively long pre-wetting times. For example, after 10 min of pre-wetting, the gas holdup decreased from a maximum of 1.34% to a minimum of 0.88%, indicating that excessively long pre-wetting times affect the uniformity of the bubble cluster.

[0093] In wastewater treatment processes, aeration systems often require the injection of large amounts of air into the water to provide sufficient dissolved oxygen for biochemical reactions, thereby enhancing the treatment of pollutants. Aeration systems consume approximately 50% of the electricity required for wastewater treatment plants, and the low oxygen mass transfer efficiency of commonly used aeration methods is one reason for this high energy consumption. The oxygen supply capacity of an aeration system is generally evaluated using parameters such as the total oxygen mass transfer coefficient and oxygen transfer efficiency. The particle size of the bubble swarm is significantly correlated with both the air holdup and the oxygen transfer coefficient. Reducing the bubble particle size is an effective way to improve oxygen supply efficiency. Therefore, the application of ceramic membrane distributors with microporous structures is gradually being promoted. Considering that the volume change of microbubbles generated by dispersed air during their ascent in water is relatively small, it is beneficial to reveal the specific size and distribution of microbubble swarms controllably generated using JCM-P as a distributor, thus guiding the development and preparation of JCM-P.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing Janus ceramic membranes with asymmetric wettability based on pre-wetting control, characterized in that, The steps are as follows: (1) The pretreated ceramic membrane is immersed in a cyclohexane solution of perfluorooctyltrimethoxysilane for 3-4 hours, and the separation layer of the ceramic membrane is located on the inner wall of the tube. (2) After impregnation, place the ceramic film in an oven to dry; (3) The ethanol solution is forced to circulate through the ceramic membrane tube to pre-wet the inner surface of the ceramic membrane. (4) The dopamine solution is forced to circulate through the ceramic membrane tube to deposit dopamine. After the deposition is completed, it is cleaned and dried to prepare an asymmetric wettability Janus ceramic membrane. In step (3), the concentration of the ethanol solution is 8-12% vol, the pre-wetting time is 0.5-4.5 min, and the flow rate of the ethanol solution in the ceramic membrane tube is 3-6 cm / s.

2. The method for preparing Janus ceramic membranes with asymmetric wettability based on pre-wetting control according to claim 1, characterized in that, The ceramic membrane mentioned in step (1) is an alumina ceramic membrane. The pretreatment process is to place the membrane tube in a mixed solution of water, acetone and ethanol, sonicate for 0.5-1h and then dry it. The concentration of the perfluorooctyltrimethoxysilane cyclohexane solution is 0.001-0.01mol / L and the immersion temperature is 25-35℃.

3. The method for preparing Janus ceramic membranes with asymmetric wettability based on pre-wetting control according to claim 1, characterized in that, In step (2), the drying temperature is 65-75℃ and the drying time is at least 12 hours.

4. The method for preparing Janus ceramic membranes with asymmetric wettability based on pre-wetting control according to claim 1, characterized in that, The dopamine solution in step (4) is prepared by adjusting the pH of a 3.8-4.5 g / L dopamine aqueous solution to 8.4-8.6 using Tris buffer solution; the deposition time is 1.4-1.6 h; and the flow rate of the dopamine solution in the ceramic membrane tube is 3-6 cm / s.

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