Method for preparing Janus ceramic membrane based on pre-infiltration regulation

Abstract

The invention belongs to the technical field of membrane material preparation and modification, and relates to a method for pre-infiltrating the surface of a hydrophobic ceramic membrane. And soaking the ceramic membrane in a cyclohexane solution of perfluorooctyltrimethoxysilane for 3 to 4 hours. After dipping is completed, the ceramic membrane is placed in a drying oven to be dried. An ethanol solution is forced to circulate and pass through the ceramic membrane, and a ceramic membrane separation layer is subjected to pre-infiltration treatment; the pre-wetting process provided by the invention is simple in process, high in controllability and easy to amplify to pre-wet the hydrophobic ceramic membrane with a multi-channel structure. According to the method, coarse adjustment of the wetting degree is achieved by adjusting and controlling the concentration of the ethanol aqueous solution, fine adjustment of the wetting degree is further conducted by combining the circulation time of the ethanol aqueous solution, finer control over the wetting degree is overall achieved, and optimal improvement of the uniformity of the hydrophilic coating is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane material preparation and modification, and relates to a method for preparing a Janus ceramic membrane based on pre-wetting regulation. Background Art

[0002] Ceramic membranes have a special micro-nanostructure. Due to their good thermal stability, mechanical stability and chemical stability, they can be used in harsh chemical environments, including membrane separation, membrane distillation, membrane dispersion and other fields. Generally, ceramic membranes are limited in application due to their inherent hydrophilicity. In order to broaden their application range, it is necessary to regulate the surface properties of the membrane. The surface wettability of the membrane is one of its very important characteristics. Inspired by mussels in nature, the deposition of polydopamine coating can improve the hydrophilicity of the material surface, thereby improving the antifouling and biocompatibility of the material. Existing studies have used the principle of this hydrophilic surface coating and combined it with a hydrophobic fiber structure surface to make the material more hydrophilic, and used this composite membrane with asymmetric wettability as a gas distributor for aeration to generate microbubbles, and used the characteristics of large specific surface area and self-compression of microbubbles to achieve the purpose of enhancing mass transfer. The surface wettability of the material itself has a significant effect on the adhesion, deposition behavior and morphology of the polydopamine coating, especially when dopamine is deposited on the surface of hydrophobic materials including hydrophobic ceramic membranes for hydrophilic modification. Due to the low surface energy of the hydrophobic ceramic membrane itself, an air layer is easily formed on the membrane surface, which hinders the subsequent deposition of dopamine, and then causes the uniformity of the coating to decrease, thus affecting the hydrophilicity of the dopamine coating. Pre-wetting is an effective means of improvement, but there is currently little research on pre-wetting.

[0003] The pre-wetting process is mainly carried out by contacting the material with a wetting agent. Patent CN109550408A reports a method of immersing a ZrO2 ceramic membrane in ultrapure water for 2 hours, which can thoroughly wet all the membrane pores, and then react dopamine compounds and amino (or thiol) short-chain ethylene glycol molecules to form a co-deposition layer on the surface of the ceramic membrane to obtain a ceramic composite membrane that resists protein pollution. Patent CN111672339A reports a TiO2 ultrafiltration ceramic membrane immersion method, which pre-wets in deionized water for 2 hours to thoroughly wet all the membrane pores, and then places the ceramic membrane in a mixed solution of dopamine compounds and polyethyleneimine to react to obtain a polydopamine-modified ceramic membrane. Both of these pre-wetting methods with full immersion can eliminate the air layer on the membrane surface, so that dopamine is more firmly deposited on the surface of the ceramic membrane. Although the material can be simply and thoroughly wetted, the wetting area and degree of wetting cannot be controlled. In addition, when the membrane surface is hydrophobic, the surface energy is low and the water permeation flux is low, so the efficiency of pre-wetting with water is low. Summary of the invention

[0004] Aiming at the problems existing in the traditional pre-wetting process, the present invention proposes a novel method for preparing Janus ceramic membrane based on pre-wetting regulation.

[0005] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions: A method for preparing a Janus ceramic membrane with asymmetric wettability based on pre-wetting regulation, the steps are as follows: (1) Immersing the pretreated ceramic membrane in a cyclohexane solution of perfluorooctyltrimethoxysilane for 3-4 hours, wherein the separation layer of the ceramic membrane is located on the inner wall of the tube.

[0006] (2) After impregnation, the ceramic membrane is placed in an oven to dry.

[0007] (3) The ethanol solution is forced to circulate through the ceramic membrane tube to pre-wet the inner surface of the ceramic membrane.

[0008] (4) The dopamine solution is forced to circulate through the ceramic membrane tube to perform dopamine deposition. After the deposition is completed, the dopamine solution is cleaned and dried to prepare a Janus ceramic membrane with asymmetric wettability.

[0009] 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, ultrasonicate for 0.5-1h and then dry it; the concentration of the cyclohexane solution of perfluorooctyltrimethoxysilane is 0.001-0.01 mol / L, and the immersion temperature is 25-35°C.

[0010] Preferably, in step (2), the drying temperature is 65-75° C. and the drying time is at least 12 h.

[0011] Preferably, in step (3), the concentration of the ethanol solution is 8-12% vol, the pre-wetting treatment 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.

[0012] Preferably, the dopamine solution is prepared in step (4) by adjusting the pH of a 3.8-4.5 g / L dopamine aqueous solution to 8.4-8.6 using a 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.

[0013] The present invention strictly controls the process of pre-wetting treatment, effectively improves the efficiency of dynamic deposition of dopamine on the surface of hydrophobic ceramic membrane, improves the uniformity of hydrophilic coating, and further improves the uniformity of gas dispersion into liquid of ceramic membrane. The pre-wetted ceramic membrane has broad application prospects in systems with strict requirements for gas feed, such as difficult to dissolve systems, violent reactions, and systems with too fast reaction process and easy to produce by-products.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are: 1. The pre-wetting process proposed in the present invention is simple in technology, highly controllable, and can be easily expanded to pre-wetting a hydrophobic ceramic membrane with a multi-channel configuration.

[0015] 2. The present invention achieves a rough adjustment of the wetting degree by regulating the concentration of the ethanol aqueous solution, and further fine-tunes the wetting degree in combination with the circulation time of the ethanol aqueous solution, thereby achieving a more precise control of the wetting degree as a whole and achieving optimal improvement in the uniformity of the hydrophilic coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 and Figure 2 are the water contact angles of ceramic membranes, Figure 1 is the static contact angle; Figure 2 is the dynamic contact angle.

[0017] Figure 3 Surface FESEM images of ceramic membranes, where (a) is JCM, (b) is JCM-P, and (c) is CM.

[0018] Figure 4 Figure 2 is the curve of dissolved oxygen changing with time, where (a) is the pre-wetting test result of ethanol aqueous solution with different concentrations, and (b) is the test result of different pre-wetting time. DETAILED DESCRIPTION

[0019] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0020] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0021] Example 1 This example provides a process for preparing a pre-wetted tubular Janus ceramic membrane with asymmetric wettability.

[0022] (1) Preparation of hydrophobic ceramic membrane A single-tube alumina ceramic membrane (separation layer located on the inner wall of the membrane, length 6.0 cm, average pore size of separation layer 200 nm, outer diameter 12 mm, inner diameter 8 mm) was taken and ultrasonically cleaned for 30 min using a cleaning solution. The cleaning solution was a mixed solution of water, acetone and ethanol in a volume ratio of 1:1:1. The ceramic membrane was then heated at 70o C oven for 12 h, and then naturally cooled to room temperature, which was recorded as CM.

[0023] Preparation of hydrophobic ceramic membrane by in-situ grafting of hydrophobic groups by immersion method: Prepare 0.005 mol / L perfluorooctyltrimethoxysilane (PFTMS) cyclohexane solution, immerse the ceramic membrane in the filtration bottle containing the above solution, and use a water ring vacuum pump to suck for 10 minutes. After taking out, place the ceramic membrane vertically in a beaker, pour the above solution into it until the membrane tube is submerged, and carry out grafting reaction for 3 hours under heating in a 30°C water bath. After the reaction is completed, wash with water and ethanol for 5 minutes each to remove the residual solution, and then o C for 12 h to obtain a hydrophobic film, which was named OCM.

[0024] (2) Pre-wetting of hydrophobic ceramic membrane Prepare 200 mL of 8% ethanol solution for later use. Prepare 200 mL of 4 g / L dopamine (DA) aqueous solution, adjust the pH of the DA aqueous solution to 8.5 with Tris buffer solution (50 g / L tris(hydroxymethyl)aminomethane solution), and then place the DA aqueous solution in a 30°C water bath for later use.

[0025] The pre-wetting device can have many forms, and this embodiment provides one of them: the device of this embodiment includes 1 membrane assembly, 2 beakers, 1 peristaltic pump, and 2 three-way valves. The membrane assembly mainly includes 1 single-layer cylindrical stainless steel shell, 2 end sealing ring covers, and 2 sealing ring clamps. There is an outlet on both end faces of the assembly cylinder. The ceramic membrane tube is placed in the assembly cylinder and the two ends of the membrane tube are extended out of the end face by an appropriate length so that the gaskets can be put on both ends of the membrane tube and fit the outlet of the assembly cylinder. Then one of the sealing ring covers is put on the outlet of the cylinder, and the sealing ring clamp is used to clamp the membrane assembly and the sealing ring cover tightly. Finally, the bolts on the sealing ring clamp are tightened. The other end of the cylinder is sealed by the same sealing method. The sealing ring covers are provided with liquid flow ports so that the inlet and outlet ends of the entire membrane assembly can be connected with a hose. The membrane assembly is fixed vertically on the iron frame. The inlet end of the membrane assembly (the lower part of the membrane assembly) is connected to a flow channel of the three-way valve. The other two flow channels of the three-way valve are connected to the beaker containing ethanol solution and the beaker containing DA solution with hoses. The outlet end of the membrane assembly is connected to a flow channel of another three-way valve, and the other two flow channels are connected to the beaker containing ethanol solution and the beaker containing DA solution with hoses. Then the hose part between the inlet of the membrane assembly and the three-way valve at the inlet end of the membrane assembly is fastened with a peristaltic pump, and the speed is set. Before the pre-wetting begins, adjust the inlet and outlet three-way valves respectively, and form a closed loop with the hose to form the membrane assembly and the ethanol solution as a whole. Turn on the pump to pump the ethanol solution into the membrane assembly, flow through the inner surface of the hydrophobic ceramic membrane in the membrane assembly to drive away the air layer, and then flow back to the beaker. The pre-wetting process is carried out in a cyclic circulation manner, and the cycle time is strictly controlled to be 0.5min. The peristaltic pump controls the liquid flow rate on the inner surface of the membrane tube to be 4cm / s.

[0026] (3) Preparation of Janus ceramic membranes with asymmetric wettability by dynamic deposition of DA When the pre-wetting time reaches 0.5 min, the flow direction of the inlet and outlet three-way valves is quickly adjusted to make the membrane assembly and the DA solution form a closed loop as a whole. The DA solution is circulated with a circulation time of 1.5 h and a liquid flow rate of 3.0 cm / s on the membrane surface of the peristaltic pump to prepare a Janus ceramic membrane with asymmetric wettability.

[0027] Cleaning the Janus ceramic membrane: After the deposition is completed, remove the membrane tube and rinse it with water for 5 minutes to remove the residual solution. o The Janus ceramic membrane prepared by the above steps was named JCM-P.

[0028] A Janus ceramic membrane with DA deposited directly without a pre-wetting process was prepared for comparison and named JCM.

[0029] The ceramic film prepared in this example was tested for contact angle. The results are as follows: Figure 1 and 2 As shown, from Figure 1 It can be seen 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 penetration rate on the hydrophilic surface of JCM-P is higher than that of JCM, indicating that the hydrophilicity of the deposited DA coating is significantly enhanced after pre-wetting the hydrophobic membrane.

[0030] The ceramic membrane prepared in this example was characterized by SEM. Figure 3 .from Figure 3 It can be seen that the DA coating of JCM has obvious prominent 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, which indicates that the pre-wetting process has a significant improvement on the DA deposition process.

[0031] Example 2 This example provides a process for preparing a pre-wetted tubular Janus ceramic membrane with asymmetric wettability.

[0032] (1) Preparation of hydrophobic ceramic membrane The alumina ceramic membrane was taken and ultrasonically cleaned for 30 minutes using a cleaning solution, which was a mixed solution of water, acetone, and ethanol in a volume ratio of 1:1:1. o C oven for 12 h, and naturally cooled to room temperature, which was recorded as CM.

[0033] Preparation of hydrophobic ceramic membrane by in-situ grafting of hydrophobic groups by immersion method: Prepare 0.005 mol / L perfluorooctyltrimethoxysilane cyclohexane solution, immerse the ceramic membrane in the suction bottle containing the above solution, and use a water ring vacuum pump to suck for 10 minutes. After taking it out, place the ceramic membrane vertically in a beaker, pour the above solution into it until the membrane tube is submerged, and carry out grafting reaction for 3 hours under heating in a water bath at 25°C. After the reaction is completed, wash with water and ethanol for 5 minutes each to remove the residual solution, and then heat at 75 o C for 13 h to obtain a hydrophobic film.

[0034] (2) Pre-wetting of hydrophobic ceramic membrane Prepare 200 mL of 10% ethanol solution for standby use, prepare 200 mL of 4 g / L dopamine aqueous solution, adjust the pH of the DA aqueous solution to 8.5 with Tris buffer solution, and then place the DA aqueous solution in a 30°C water bath for constant temperature standby use.

[0035] The pre-wetting cycle time was controlled to be 1.0 min, and the peristaltic pump controlled the liquid flow rate on the membrane surface to be 6 cm / s.

[0036] (3) Preparation of Janus ceramic membranes with asymmetric wettability by dynamic deposition of DA When the pre-wetting time reaches 0.5 min, the flow direction of the inlet and outlet three-way valves is quickly adjusted to make the membrane assembly and the DA solution form a closed loop as a whole. The DA solution is circulated with a circulation time of 1.5 h and a liquid flow rate of 3.5 cm / s on the membrane surface of the peristaltic pump to prepare a Janus ceramic membrane with asymmetric wettability.

[0037] Cleaning the Janus ceramic membrane: After the deposition is completed, remove the membrane tube and rinse it with water for 5 minutes to remove the residual solution. o C for 12 h.

[0038] Example 3 This example provides a process for preparing a pre-wetted tubular Janus ceramic membrane with asymmetric wettability.

[0039] (1) Preparation of hydrophobic ceramic membrane The alumina ceramic membrane was taken and ultrasonically cleaned for 30 minutes using a cleaning solution, which was a mixed solution of water, acetone, and ethanol in a volume ratio of 1:1:1. o C oven for 12 h and then naturally cooled to room temperature.

[0040] Preparation of hydrophobic ceramic membrane by in-situ grafting of hydrophobic groups by immersion method: Prepare 0.005 mol / L perfluorooctyltrimethoxysilane in cyclohexane solution, immerse the ceramic membrane in the filtration bottle containing the above solution, and use a water ring vacuum pump to suck for 10 minutes. After taking it out, place the ceramic membrane vertically in a beaker, pour the above solution into it until the membrane tube is submerged, and carry out grafting reaction for 3 hours under heating in a 30°C water bath. After the reaction is completed, wash with water and ethanol for 5 minutes each to remove the residual solution, and then heat it at 70 o C for 12 h to obtain a hydrophobic film.

[0041] (2) Pre-wetting of hydrophobic ceramic membrane Prepare 200 mL of 8% ethanol solution for standby use, prepare 200 mL of 4 g / L dopamine aqueous solution, adjust the pH of the DA aqueous solution to 8.5 with Tris buffer solution, and then place the DA aqueous solution in a 30°C water bath for constant temperature standby use.

[0042] The pre-wetting cycle time was controlled to be 4.5 min, and the peristaltic pump controlled the liquid flow rate on the membrane surface to be 3 cm / s.

[0043] (3) Preparation of Janus ceramic membranes with asymmetric wettability by dynamic deposition of DA When the pre-wetting time reaches 0.5 min, the flow direction of the inlet and outlet three-way valves is quickly adjusted to make the membrane assembly and the DA solution form a closed loop as a whole. The DA solution is circulated with a circulation time of 1.5 h and a liquid flow rate of 4 cm / s on the membrane surface of the peristaltic pump to prepare a Janus ceramic membrane with asymmetric wettability.

[0044] Cleaning the Janus ceramic membrane: After the deposition is completed, remove the membrane tube and rinse it with water for 5 minutes to remove the residual solution. o C for 12 h.

[0045] Through SEM detection, the uniformity of the DA coating of the asymmetric wettability Janus ceramic membrane prepared in Examples 2 and 3 is not much different from that in Example 1.

[0046] JCM-P is used as a gas distributor for dispersion performance test.

[0047] 1. Test on the dispersion performance of JCM-P in oxygen-water system Aeration is an important process in biofilm reactor systems, water treatment systems, chemical catalytic reaction systems, etc. The oxygenation performance of the system directly affects the operating effect and energy consumption of the system. In each system, the solubility of the gas and the gas phase transfer efficiency are important factors affecting the aeration performance. For poorly soluble systems, such as the oxygen-water two-phase system, the liquid film resistance is large, and the oxygen transfer efficiency of traditional forced aeration is only 5-10%. There is still great potential for improving the aeration dissolved oxygen efficiency. Among them, ceramic membrane aeration as a microbubble aeration method is currently a hot research and development hotspot.

[0048] This example adopts an oxygen-water two-phase system, and uses three parameters, namely, total oxygen transfer coefficient, oxygenation capacity, and oxygen utilization rate, to investigate the aeration performance of JCM-P.

[0049] The test method is: 25mL / min of constant flow of oxygen is blown into the membrane distributor, so that oxygen enters the membrane tube from the outer surface through the separation layer, and a constant flow of water is pumped from the storage tank to shear the dispersed microbubbles, and the liquid flow rate on the membrane surface is controlled to be 4cm / s, and then the water flows back to the storage tank. This process requires the use of commercially available customized membrane components to ensure that the gas can only enter the membrane tube from the tube wall of the membrane tube, and the water phase only flows through the tube of the membrane tube. The change of dissolved oxygen in water over time is obtained through the data acquisition system, and the dissolved oxygen concentration in water corresponding to the aeration time t is recorded. C t , saturation value of dissolved oxygen C S(The maximum value of the on-site measurement after stable aeration for a long enough time). The method described in “Determination of Oxygen Mass Transfer Performance of Clean Water with Microporous Aerators” CJ / T 475-2015 was used to solve the values ​​of total oxygen transfer coefficient, oxygenation capacity and oxygen utilization rate, so as to compare the dispersion performance of each gas distributor.

[0050] The test results are shown in Table 1 below.

[0051] Table 1 Test results of dissolved oxygen dispersion performance of each membrane tube aeration According to Table 1, the dissolved oxygen content of JCM-P (JCM / 8%-0.5min) prepared in Example 1 is significantly higher than that of the other membrane distributors, and the rising rate of its oxygen content is faster than that of the other distributors. It can be seen that the pre-wetting process significantly enhances the dispersion performance of the material.

[0052] 2. Effect of different pre-wetting parameters By changing the pre-wetting time or the concentration of the ethanol solution, the influence of different pre-wetting conditions on the dispersion performance of the membrane tube was investigated. Among them, the conditions not specifically stated are consistent with those in Example 1. For the convenience of description, the JCM-P prepared with different pre-wetting concentration parameters is named JCM-P / n%-0.5min, and the pre-wetting time is 0.5min; the JCM-P prepared with different pre-wetting time parameters is named JCM-P / 8%-t, and the volume fraction of the EtOH aqueous solution is 8%.

[0053] 2.1 Effect of ethanol concentration The volume percentage of ethanol was adjusted to 4%, 12%, 16%, and 50%, respectively. The other conditions were the same as those in Example 1. The test was carried out using the method described in "Determination of Oxygen Mass Transfer Performance of Clean Water with Microporous Aerator" CJ / T 475-2015. The test results are as follows: Figure 4 (a) and as shown in Table 2 below, in which JCM-P / 8%-0.5min is the prepreg film prepared in Example 1.

[0054] Table 2 Effect of ethanol concentration on test results according to Figure 4 (a) and Table 2 above show that with the increase of pre-wetting concentration, the saturated oxygen concentration and oxygen dissolution rate show a 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 the pre-wetting agent has a significant effect on the dispersion effect of the material.

[0055] 2.2 Effect of pre-wetting time The pre-wetting time was adjusted to 1.5min, 2.5min, 3.5min, 4.5min, and 10min in sequence. The other conditions were consistent with those in Example 1, and the effect of the pre-wetting time was investigated by the test method in "Determination of Oxygen Mass Transfer Performance of Clean Water with Microporous Aerator" CJ / T475-2015. Figure 4 (b) and Table 3 show that with the increase of pre-wetting time, the saturated oxygen concentration and 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, the pre-wetting time has a significant effect on the dispersion effect of the material.

[0056] Table 3 Effect of pre-wetting time on test results 3. Average diameter (d), polydispersity index (PDI) and gas holdup test The test device uses the same membrane assembly as in the above-mentioned dissolved oxygen test. The visualization assembly made of polymethyl methacrylate (PMMA) is fixed on the top of the membrane assembly (the outlet on the membrane tube). The gas flowmeter controls the air to pass through the membrane assembly shell at a constant flow rate of 25 mL / min. The gas is dispersed by the single-tube ceramic membrane and enters the channel of the membrane tube. Water enters the membrane assembly through a peristaltic pump and flows through the inner membrane surface of the membrane tube at a flow rate of 4 cm / s to shear the microbubbles. The dynamic bubble image in the visualization assembly is recorded by a high-speed camera for analysis. The size of microbubbles with a total number of more than 500 in the bubble image is counted to calculate the average diameter (d) and polydispersity index (PDI) to evaluate the characteristics of the dispersed microbubble size. PDI is the ratio of the sample standard deviation to the average value. The smaller the value, the smaller the degree to which the bubble size deviates from the main size. The gas holdup is determined by the volume expansion method, that is, the liquid in the visualization assembly is retained during the stable operation of the aeration process. After the bubbles escape, the camera is used to record the change in the height of the liquid level drop, which is used to reflect the aeration system's retention performance for microbubbles.

[0057] 3.1 Effect of pre-wetting solution concentration The pre-wetting membrane was prepared in the same manner as in 2.1, and the measurement results are shown in Table 4 below.

[0058] Table 4 Dispersion performance test results of pre-wetted membrane Compared with JCM, the average bubble size of JCM-P / n%-0.5min decreases first and then increases slowly with the increase of pre-wetting concentration, and the minimum value drops to 295μm, indicating that pre-wetting can reduce the bubble size, but too high or too low ethanol concentration will have a great impact on the pre-wetting effect. The polydispersity index in Table 4 shows a trend of first decreasing and then increasing, indicating that too high or too low ethanol concentration will also have a great impact on the uniformity of microbubbles dispersed by the membrane distributor.

[0059] 3.2 Effect of pre-wetting time The preparation of the pre-wetted membrane is consistent with that in 2.2, and the measurement results are shown in Table 5 below.

[0060] Table 5 Dispersion performance test results of pre-wetted membrane According to the test results in Table 5, compared with JCM, the average bubble size of JCM-P / 8%-t first slightly decreases and then increases with the increase of pre-wetting time, and the minimum value is 233μm. However, after the pre-wetting time reaches 10min, the average bubble size is too large, indicating that the bubble size can be reduced to a certain extent by regulating the time. The change of the polydispersity index also shows the same trend. The gas holdup also tends to increase with the extension of the pre-wetting time, but after the pre-wetting time is too long, this trend has an inflection point. For example, after 10min of pre-wetting, the gas holdup decreases from the highest value of 1.34 (%) to the lowest value of 0.88 (%), indicating that too long a pre-wetting time will affect the uniformity of the bubble group.

[0061] In the aeration system of the sewage treatment process, a large amount of air is often required to be blown into the water body to provide sufficient dissolved oxygen for the biochemical reaction to enhance the treatment effect of water pollutants. The power consumption of the aeration system accounts for about 50% of the sewage treatment plant, and the low oxygen mass transfer efficiency in the commonly used aeration methods is one of the reasons for the high energy consumption. The oxygen supply capacity of the aeration system is generally evaluated by parameters such as the total oxygen mass transfer coefficient and the oxygen transfer efficiency. The particle size of the bubble group is significantly related to the gas content and the oxygen transfer coefficient. Reducing the bubble particle size is an effective way to improve the oxygen supply efficiency. Therefore, the application of ceramic membrane distributors with microporous structures is gradually promoted. Considering that the volume of microbubbles generated by dispersed air changes little during the rising process in water, it is helpful to reveal the specific size and distribution of the microbubble group that can be controlled by JCM-P as a distributor, thereby guiding the development and preparation of JCM-P.

[0062] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a Janus ceramic membrane with asymmetric wettability based on pre-wetting regulation, characterized in that: Here are the steps: (1) immersing the pretreated ceramic membrane in a cyclohexane solution of perfluorooctyltrimethoxysilane for 3-4 hours, wherein the separation layer of the ceramic membrane is located on the inner wall of the tube; (2) After impregnation, the ceramic membrane is placed in an oven for drying; (3) forcing the ethanol solution 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 perform dopamine deposition. After the deposition is completed, the dopamine solution is cleaned and dried to prepare a Janus ceramic membrane with asymmetric wettability.

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

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

4. The method for preparing a Janus ceramic membrane with asymmetric wettability based on pre-wetting regulation according to claim 1, characterized in that: In step (3), the concentration of the ethanol solution is 8-12% vol, the pre-wetting treatment 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.

5. The method for preparing a Janus ceramic membrane with asymmetric wettability based on pre-wetting regulation according to claim 1, characterized in that: The dopamine solution is prepared in step (4) by adjusting the pH of a 3.8-4.5 g / L dopamine aqueous solution to 8.4-8.6 using a 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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