Janus ceramic membrane with gradient wettability and preparation method and application thereof

Abstract

The application discloses a gradient-wetting Janus ceramic membrane and a preparation method and application thereof. In the preparation, a porous ceramic substrate with hydrophilic double main surfaces is taken, one main surface of the porous ceramic substrate is treated with a solution containing a hydrophobic modifier (without contacting the other main surface), a photocatalyst is loaded on the treated surface, and at least three continuous sub-regions are divided, different-length activation radiation is applied to each sub-region to form a gradient-wetting region with a water contact angle gradually changing along a preset direction, and finally, the photocatalyst is removed and dried. The obtained membrane has an asymmetric structure, one side has precisely regulated gradient-wetting, and the other side remains hydrophilic. When the membrane is applied to scenes such as carbon capture and regeneration of waste heat recovery of gas, the surface wettability of the membrane can be accurately matched with a local thermodynamic and concentration environment along the way, heat and mass transfer can be strengthened, surface self-cleaning can be realized, the performance of the membrane is superior to that of a traditional membrane, and the energy-saving and consumption-reducing potential is great.

Description

Technical Field

[0001] This invention relates to the field of advanced materials manufacturing technology, and in particular to a Janus ceramic membrane with gradient wettability, its preparation method, and its application. Background Technology

[0002] Among carbon capture, utilization, and storage (CCUS) technologies, chemical absorption based on alkaline absorbents is considered one of the most promising solutions due to its technological maturity. However, this technology faces a bottleneck of high energy consumption during the regeneration of CO2-rich absorbent solutions (rich liquid). Rich liquid regeneration requires temperatures above 110°C to release CO2, and the required reboiler load constitutes a major part of the system's operating cost. To address this, researchers have developed a rich solution split (RS) process. By splitting a portion of the cold rich liquid, it exchanges heat with the high-temperature regeneration gas (a mixture of CO2 and water vapor) discharged from the regeneration tower in a heat exchanger before entering the regeneration tower, thereby recovering the waste heat of the regeneration gas and reducing the reboiler load. In recent years, porous commercial ceramic membrane heat exchangers (Chinese patent CN201710371929.9) have enhanced waste heat recovery through heat and mass transfer coupling, introducing water vapor / liquid water mass transfer to supplement the single heat conduction of conventional heat exchangers, further improving waste heat recovery performance and energy saving potential.

[0003] However, existing commercial ceramic membranes have inherent limitations, creating intractable technical contradictions. On the one hand, traditional ceramic membrane heat exchangers use hydrophilic ceramic membranes such as alumina (Al2O3). When high-temperature regeneration gas contacts the membrane surface, water vapor condenses on the membrane surface to form a continuous water film. This water film not only constitutes a significant thermal resistance, hindering heat transfer, but also requires the latent heat of water vapor condensation to pass through the liquid film and the membrane substrate via heat conduction to be transferred to the cold rich liquid. This results in low heat transfer efficiency and heat loss. At the same time, the water film may cause droplets to flow back to the regeneration tower, and under certain pressures, the cold rich liquid may even permeate to the gas phase side, weakening the energy-saving effect. On the other hand, although conventional hydrophobic ceramic membranes can promote the droplet condensation of water vapor, the condensed water droplets quickly detach to keep the membrane surface exposed and improve the heat transfer coefficient on the gas phase side, the internal pores of the completely hydrophobic membrane are mostly filled with gas. The thermal conductivity of gas is much lower than that of liquid, which leads to a significant reduction in the effective thermal conductivity of the membrane, offsetting the heat transfer advantage of droplet condensation. In addition, the gas in the membrane pores may allow CO2 in the regeneration gas to permeate to the cold rich liquid side under the drive of partial pressure difference, increasing the CO2 load of the rich liquid and indirectly increasing the regeneration energy consumption.

[0004] More importantly, there are still deep-seated unresolved technical problems in this field: while simple Janus membranes (a special membrane material with different wettability on both sides) are superior to homogeneous membranes, they are still a "one-size-fits-all" solution, ignoring the highly non-uniform physical reality of the process environment in actual heat exchange equipment such as transport membrane condensers (TMCs). Computational fluid dynamics (CFD) simulations and experiments have confirmed that there are significant axial gradients of temperature and water vapor concentration along the gas flow direction within the gas channel. The inlet end has a high temperature, high water vapor concentration, and strong condensation driving force, while the outlet end has a low temperature, low water vapor concentration, and weak condensation driving force. This means that any surface with a single fixed wettability (whether hydrophilic, hydrophobic, or with a fixed hydrophobic contact angle) cannot operate optimally along the entire membrane length. Extreme hydrophobicity is required at the inlet to maximize dropwise condensation (DWC) efficiency, while hydrophilicity may be required at the outlet to capture and transport residual trace amounts of condensate using capillary forces.

[0005] Therefore, existing technologies (including simple Janus membranes) are unable to adapt to dynamic requirements that change along the process due to their limited surface properties, which has become the fundamental bottleneck restricting the further improvement of TMC performance. There is an urgent need in this field for new membrane design concepts and feasible preparation methods to create membranes with spatially customizable surface properties, enabling them to intelligently adapt to local process conditions and break through the performance ceiling of existing membrane technologies. Summary of the Invention

[0006] This invention aims to overcome the fundamental limitation of existing membrane materials (including hydrophilic membranes, hydrophobic membranes, and simple hydrophilic-hydrophobic Janus membranes) in adapting to non-uniform process environments due to their uniform surface wettability. The core technical problem this invention addresses is to provide a Janus ceramic membrane with gradient wettability, its preparation method, and its applications. This gradient wettability structure aims to achieve optimal matching between the local wetting characteristics of the membrane surface and the varying local thermodynamics and component concentration environment along the heat and mass transfer equipment, thereby maximizing the synergistic heat and mass transfer efficiency over the entire functional length of the membrane.

[0007] To achieve the above objectives, the present invention first provides a method for preparing a Janus ceramic membrane with gradient wettability, comprising:

[0008] S10, a porous ceramic substrate is provided, the porous ceramic substrate having a first main surface and a second main surface disposed opposite to each other, both the first main surface and the second main surface being hydrophilic;

[0009] S20, the solution containing the hydrophobic modifier is brought into contact with the first main surface to react, while ensuring that the second main surface does not come into contact with the solution;

[0010] S30, a photocatalyst is loaded on the first main surface, and the loaded first main surface is selectively divided into regions to form at least three spatially continuous sub-regions to be treated.

[0011] S40, applying activation radiation with different irradiation durations to multiple sub-regions to be treated, so that the first main surface forms a gradient wettability region with continuous or discrete wettability levels; in the gradient wettability region, the water contact angle of different wettability sub-regions increases or decreases sequentially along the gradient preset direction.

[0012] S50, the photocatalyst loaded on the first main surface is removed and dried in a manner that does not affect the gradient wettability region, to obtain a Janus ceramic film with gradient wettability.

[0013] Preferably, in step S10, the porous ceramic substrate includes any one of an alumina ceramic membrane, a titanium dioxide ceramic membrane, and a silicon dioxide ceramic membrane.

[0014] Preferably, in step S20: the hydrophobic modifier can be a fluoroalkyl silane reagent, including 1H,1H,2H,2H-perfluorooctyltriethoxysilane or 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

[0015] Preferably, in step S30, the photocatalyst is titanium dioxide nanoparticles.

[0016] Preferably, in step S40: an opaque shield is used to shield multiple sub-regions to be processed for different durations, and the actual duration of each sub-region to be processed receiving activation radiation is controlled by the difference in shielding duration, and the shielding duration is proportional to the final hydrophobicity formed by the corresponding sub-region to be processed; the light source for activation radiation is a high-pressure mercury lamp that can emit 365nm light.

[0017] Preferably, in step S40: the gradient wettability region sequentially includes a spatially continuous strong hydrophobic region, a weak hydrophobic region, a weak hydrophilic region, a hydrophilic region, and a strong hydrophilic region along the preset gradient direction;

[0018] Among them, the water contact angle of the strongly hydrophobic region is >110°; the water contact angle of the weakly hydrophobic region is >90° and ≤110°; the water contact angle of the weakly hydrophilic region is >40° and ≤90°; the water contact angle of the hydrophilic region is >10° and ≤40°; and the water contact angle of the strongly hydrophilic region is <<10°.

[0019] In a second aspect, the present invention also provides a Janus ceramic membrane with gradient wettability, which is prepared by the method for preparing a Janus ceramic membrane with gradient wettability as described in any of the above claims.

[0020] Preferably, the Janus ceramic membrane has a hydrophilic surface and a wettability gradient surface arranged opposite to each other. The wettability gradient surface can induce condensed droplets to spontaneously migrate from the strongly hydrophobic region to the weakly hydrophobic region or the hydrophilic region.

[0021] Thirdly, the present invention also provides the application of the Janus ceramic membrane with gradient wettability as described above in the preparation of heat and mass transfer equipment.

[0022] Preferably, the heat and mass transfer device includes a transport membrane condenser with a Janus ceramic membrane, which is used to recover waste heat from a gas stream containing condensable components, and the gradient of the wettability gradient surface is pre-directed in the same direction as the flow direction of the gas stream.

[0023] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a Janus ceramic film with gradient wettability, its preparation method, and its application. The preparation method includes: First, providing a porous ceramic substrate having a first main surface and a second main surface arranged opposite to each other, both of which are hydrophilic; Second, contacting a solution containing a hydrophobic modifier with the first main surface to react, while ensuring that the second main surface does not contact the solution; Third, loading a photocatalyst onto the first main surface and selectively dividing the loaded first main surface into at least three spatially continuous sub-regions to be treated; Fourth, applying activation radiation with different irradiation durations to the multiple sub-regions to be treated, causing the first main surface to form a gradient wettability region with continuous or discrete wetting levels; In the gradient wettability region, the water contact angle of different wetting sub-regions increases or decreases sequentially along a predetermined gradient direction; Finally, removing the photocatalyst loaded on the first main surface in a manner that does not affect the gradient wettability region and drying it to obtain a Janus ceramic film with gradient wettability. The gradient wettability Janus ceramic membrane prepared in this invention employs an asymmetric structural design, with one surface possessing a precisely controllable wettability gradient while the other surface remains hydrophilic. When applied to fluid systems containing condensing components (such as waste heat recovery from regenerated gas in carbon capture processes), it allows for precise matching of the wettability of different regions on the membrane surface with the changing local thermodynamics and concentration environment along the process. The hydrophobic region promotes efficient droplet condensation to enhance heat transfer, while the hydrophilic region enhances mass transfer through capillary effects. Simultaneously, the surface energy gradient induces condensate droplets to spontaneously migrate from the hydrophobic to the hydrophilic region, achieving self-cleaning and continuous renewal of the membrane surface. Experiments demonstrate that the heat and mass transfer performance of this gradient membrane is significantly superior to traditional hydrophilic membranes, hydrophobic membranes, and simple hydrophilic-hydrophobic Janus membranes, exhibiting great application potential in the field of energy conservation and emission reduction. Attached Figure Description

[0024] Figure 1 A flowchart illustrating the preparation method of a Janus ceramic membrane with gradient wettability provided in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram illustrating the mechanism by which the Janus ceramic membrane with gradient wettability enhances heat and mass transfer in an embodiment of the present invention.

[0026] Figure 3 A schematic diagram of the two-stage process flow for the preparation method of the Janus ceramic membrane with gradient wettability provided in this embodiment 1;

[0027] Figure 4 Schematic diagrams of the structure of the commercial hydrophilic membrane provided in Comparative Example 1 and the Janus ceramic membranes with gradient wettability prepared in Examples 1-3;

[0028] Figure 5 The graph shows a performance comparison between the commercial hydrophilic membrane provided in Comparative Example 1 and the Janus ceramic membranes with gradient wettability prepared in Examples 1-3. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see Figure 1 , Figure 1 A flowchart illustrating a method for preparing a Janus ceramic membrane with gradient wettability, provided in an embodiment of the present invention; wherein, the preparation method specifically includes:

[0031] S10 provides a porous ceramic substrate having a first main surface and a second main surface disposed opposite to each other, both of which are hydrophilic.

[0032] Specifically, step S10 also includes:

[0033] Firstly, a porous ceramic substrate is provided, which includes any one of alumina ceramic membrane, titanium dioxide ceramic membrane, and silicon dioxide ceramic membrane.

[0034] Subsequently, the porous ceramic substrate is cleaned under ultrasonic conditions to remove impurities and activate surface hydroxyl groups; finally, it is dried at a suitable temperature for later use; wherein, the porous ceramic substrate has a first main surface and a second main surface arranged opposite to each other, and both the first main surface and the second main surface are hydrophilic.

[0035] Specifically, step S10 uses a porous ceramic material with strong compatibility, such as alumina, titanium dioxide, or silicon dioxide, as the substrate. It combines ultrasonic cleaning to remove impurities and activate surface hydroxyl groups, followed by drying. This not only ensures the initial hydrophilicity of the substrate's two surfaces, laying a uniform and stable foundation for subsequent wettability modification, but also improves the substrate's cleanliness and surface reactivity, reduces interference from subsequent processes, and ensures the final membrane product's preparation quality and performance stability.

[0036] S20, the solution containing the hydrophobic modifier is brought into contact with the first main surface to react, while ensuring that the second main surface does not come into contact with the solution.

[0037] Specifically, step S20 also includes:

[0038] First, the hydrophobic modifier is dissolved in an anhydrous organic solvent (such as anhydrous ethanol) to prepare a modified solution of a specific concentration; wherein, the hydrophobic modifier is a fluoroalkylsilane reagent, including 1H,1H,2H,2H-perfluorooctyltriethoxysilane or 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

[0039] Next, the modified solution is brought into contact with the first main surface to react, while ensuring that the second main surface does not come into contact with the modified solution. At this time, after the modified solution comes into contact with the first main surface, a grafting reaction occurs. After the reaction is carried out at a set time and temperature, a layer of chemically bonded hydrophobic molecules is uniformly grafted onto the first main surface. Meanwhile, since the second main surface does not come into contact with the modified solution, it can prevent the modified solution from penetrating into the membrane pores and the opposite surface.

[0040] Finally, the modified membrane was removed, ultrasonically cleaned with a solvent to remove the physically adsorbed hydrophobic modifier, and then dried. This yielded a Janus ceramic membrane with one side uniformly hydrophobic and the other side remaining hydrophilic.

[0041] Furthermore, in step S20, a modified solution was prepared using a fluoroalkylsilane reagent, allowing only the first main surface to react while strictly isolating the second main surface. A chemically bonded hydrophobic molecular layer was formed through a grafting reaction. Combined with ultrasonic cleaning to remove physically adsorbed components and drying treatment, this process achieved uniform hydrophobicity of the first main surface while fully preserving the hydrophilicity of the second main surface. At the same time, it avoided the penetration and contamination of the modified solution into the membrane pores and the opposite side surface. This successfully prepared a basic Janus ceramic membrane with one side hydrophobic and one side hydrophilic, laying a precise and controllable structural foundation for the subsequent construction of gradient wettability.

[0042] S30, a photocatalyst is loaded onto the first main surface, and the loaded first main surface is selectively divided into regions to form at least three spatially continuous sub-regions to be treated.

[0043] Specifically, step S30 also includes:

[0044] First, the hydrophobic surface of the Janus membrane prepared in step S20 is brought into contact with a suspension containing a photocatalyst, so that the photocatalyst particles are uniformly attached to the hydrophobic surface. Then the membrane is dried. The photocatalyst is titanium dioxide nanoparticles.

[0045] Then, the first main surface after loading is selectively divided into regions to form at least three spatially continuous sub-regions to be processed.

[0046] Specifically, step S30 involves uniformly loading titanium dioxide nanoparticle photocatalysts onto the hydrophobic first host surface and selectively dividing it into at least three spatially continuous sub-regions to be treated. This provides a catalytic reaction basis for subsequent regulation of the wettability gradient through light radiation. Furthermore, the multi-region design creates spatial conditions for achieving continuous or discrete wettability hierarchical differences, ensuring that a gradient wettability structure can be accurately constructed subsequently. This lays a crucial foundation for adapting the membrane surface to the local environment that changes along the process.

[0047] S40, applying activation radiation with different irradiation durations to multiple sub-regions to be treated, so that the first main surface forms a gradient wettability region with continuous or discrete wettability levels; in the gradient wettability region, the water contact angle of different wettability sub-regions increases or decreases sequentially along the gradient preset direction.

[0048] Specifically, in step S40: an opaque shield is used to shield multiple sub-regions to be treated for different durations. The actual duration of activation radiation received by each sub-region to be treated is controlled by the difference in shielding duration, and the shielding duration is proportional to the final hydrophobicity of the corresponding sub-region to be treated; wherein, activation radiation includes ultraviolet light irradiation treatment.

[0049] In one embodiment, the gradient wettability region sequentially includes a spatially continuous strong hydrophobic region, a weak hydrophobic region, a weak hydrophilic region, a hydrophilic region, and a strong hydrophilic region along a predetermined gradient direction; the water contact angle of the strong hydrophobic region is >110°; the water contact angle of the weak hydrophobic region is >90° and ≤110°; the water contact angle of the weak hydrophilic region is >40° and ≤90°; the water contact angle of the hydrophilic region is >10° and ≤40°; and the water contact angle of the strong hydrophilic region is ≤10°.

[0050] Furthermore, step S40 controls the activation radiation duration of different sub-regions to be treated by using an opaque shield. Combining the direct proportionality between shielding duration and hydrophobicity, a gradient wettability region with continuous or discrete wetting level differences (such as a classification of strong hydrophobicity, weak hydrophobicity, weak hydrophilicity, hydrophilicity, and strong hydrophilicity) is precisely constructed on the first main surface. This achieves an orderly variation of the water contact angle along a preset direction, allowing the membrane surface to adapt to the changing local environment in subsequent applications. This provides core structural support for improving heat and mass transfer performance. At the same time, this control method is precise and controllable, ensuring the stability and consistency of the gradient wettability.

[0051] S50, the photocatalyst loaded on the first main surface is removed and dried in a manner that does not affect the gradient wettability region, to obtain a Janus ceramic film with gradient wettability.

[0052] Specifically, step S50 also includes:

[0053] After the activation radiation is completed, the membrane is ultrasonically cleaned with ultrapure water to thoroughly remove the photocatalyst particles on the surface, and then dried again to finally obtain the finished product - the Janus ceramic membrane with gradient wettability.

[0054] Specifically, step S50 removes photocatalyst particles from the first main surface through ultrasonic cleaning with ultrapure water, while avoiding any impact on the already formed gradient wettability region. Combined with subsequent drying, this process thoroughly removes any catalytic components that are not needed to be retained, preventing them from interfering with the membrane's heat and mass transfer performance. It also stabilizes and solidifies the constructed gradient wettability structure, ultimately producing a high-performance, pure, and structurally stable gradient wettability Janus ceramic membrane, ensuring the reliability of the finished membrane in applications.

[0055] In a second aspect, the present invention also provides a Janus ceramic membrane with gradient wettability, which is prepared by the method for preparing a Janus ceramic membrane with gradient wettability as described in any of the above claims.

[0056] Janus ceramic membranes have a hydrophilic surface and a wettability gradient surface that are arranged opposite to each other. The wettability gradient surface can induce condensed droplets to spontaneously migrate from the strongly hydrophobic region to the weakly hydrophobic region or the hydrophilic region.

[0057] Specifically, the gradient wettability Janus ceramic membrane provided by this invention forms an asymmetric structure of "hydrophilic surface + wettability gradient surface" based on the aforementioned preparation method. Its wettability gradient surface can induce condensate droplets to spontaneously migrate from the strongly hydrophobic region to the weakly hydrophobic region or the hydrophilic region. This not only solves the performance bottleneck of uniform wettability of traditional membranes, but also provides structural support for the membrane surface to adapt to the local environment that changes along the process, simultaneously enhance heat and mass transfer and achieve self-cleaning, thus ensuring efficient application in scenarios such as carbon capture.

[0058] Thirdly, the present invention also provides the application of the Janus ceramic membrane with gradient wettability as described above in the preparation of heat and mass transfer equipment.

[0059] Specifically, the heat and mass transfer equipment includes a transport membrane condenser with a Janus ceramic membrane, which is used to recover waste heat from a gas stream containing condensable components, and the gradient of the wettability gradient surface is pre-directed in the same direction as the flow direction of the gas stream; wherein, the aforementioned waste heat is the waste heat recovered from the high-temperature gas (high-temperature regeneration gas, containing water vapor and carbon dioxide) at the top outlet of the regeneration tower in the CO2 chemical absorption process.

[0060] Furthermore, the above design allows different regions of the membrane surface to precisely match the temperature and concentration environment of the gas along the process—the hydrophobic region promotes efficient droplet condensation to enhance heat transfer, and the hydrophilic region enhances mass transfer through capillary effect. It also enables the surface to self-clean through spontaneous droplet migration, significantly improving the efficiency of waste heat recovery and effectively reducing the regeneration energy consumption of the CO2 capture process, providing key equipment support for energy saving and consumption reduction in carbon capture systems.

[0061] Please see Figure 2 , Figure 2 This is a schematic diagram illustrating the mechanism of enhanced heat and mass transfer using a Janus ceramic membrane with gradient wettability prepared according to an embodiment of the present invention. The diagram depicts the scenario of water vapor-containing gas flowing through a gradient wettability surface: in the hydrophobic zone at the inlet, efficient droplet condensation occurs due to the surface hydrophobicity, resulting in a significant high heat flux; in the hydrophilic zone at the outlet, strong capillary action is generated due to hydrophilicity, ultimately achieving a high condensate flux. Crucially, Figure 2 The middle arrow clearly indicates the "self-driven transport" phenomenon in which condensate droplets spontaneously migrate from the hydrophobic region to the hydrophilic region under the drive of the surface free energy gradient force.

[0062] The technical solution of the present invention will now be further described with reference to specific embodiments.

[0063] Example 1 (CM-Ⅳ):

[0064] This embodiment 1 provides a Janus ceramic film with four-zone gradient wettability and its preparation method. The preparation method innovatively employs a two-stage process (stage one is the uniform hydrophobication of one side of the substrate surface, and stage two is the selective photocatalytic reduction of the hydrophobic surface to construct gradient wettability), such as... Figure 3 As shown: Figure 3 (a) shows the first-stage unilateral hydrophobic modification device; Figure 3 Figure (b) illustrates the second-stage selective shading and UV photocatalytic reduction process used to construct the wettability gradient.

[0065] Specifically, the method for preparing a Janus ceramic membrane with four-zone gradient wettability provided in Example 1 includes the following steps:

[0066] Step 1, Substrate Pretreatment: A commercially available flat alumina ceramic membrane (CM-Ⅰ) with dimensions of 160mm × 80mm × 5mm (length × width × thickness) and an average pore size of 30nm was selected as the substrate. First, the membrane was thoroughly rinsed sequentially with pure acetone (>5min), ethanol (>5min), and ultrapure water (>5min) under ultrasonic conditions, and then dried in an oven at 65℃ for 12h.

[0067] Step 2, preparation of hydrophobic modifier solution: Dissolve the hydrophobic modifier, such as a fluoroalkylsilane (FAS) reagent (e.g., 1H,1H,2H,2H-perfluorooctyltriethoxysilane, C6), in an anhydrous organic solvent (e.g., anhydrous ethanol) to prepare a modified solution of a specific concentration (e.g., 0.001 mol / L).

[0068] Step 3, Single-sided grafting reaction: The pretreated ceramic substrate is installed in a specially designed membrane tank. A 0.001 mol / L anhydrous ethanol solution of C6 (1H,1H,2H,2H-perfluorooctyltriethoxysilane) is used as the modifier solvent and pumped into one channel of the membrane tank at a flow rate of 50 mL / min to contact the membrane surface to be modified and initiate a grafting reaction. Simultaneously, CO2 gas is introduced into the other channel of the membrane tank and a certain pressure is maintained (forming a transmembrane pressure barrier) to prevent the modifier solvent from permeating. By controlling the grafting reaction time, the water contact angle of this side surface reaches a uniform hydrophobic state of 120±4° (hydrophobic modification by immersion method).

[0069] Step 4, Post-processing: After the reaction is complete, the modified membrane is taken out and ultrasonically cleaned with ultrapure water to remove the physically adsorbed hydrophobic modifier. Then it is dried at 65°C for 12 hours. Thus, a Janus ceramic membrane with one side being uniformly hydrophobic and the other side remaining hydrophilic is obtained.

[0070] Step 5, Photocatalyst loading (attaching TiO2 to hydrophobic surface of ceramic membrane): The Janus membrane with one side hydrophobicized as prepared above is placed in the membrane cell again, so that its hydrophobic surface is in contact with the suspension containing photocatalyst (such as 10 wt.% TiO2 nanoparticles), and flows through its hydrophobic surface at a flow rate of 20 mL / min for 30 min, so that the photocatalyst particles are uniformly attached to the hydrophobic surface. Then the membrane is dried in an oven at 65°C for at least 12 h.

[0071] Step Six, Selective Masking: Using an opaque masking material (such as black PTFE tape), the hydrophobic surface loaded with the photocatalyst is selectively masked according to a preset gradient pattern. Areas that need to maintain strong hydrophobicity are completely masked, while areas that need to reduce hydrophobicity or restore hydrophilicity are exposed: The dried, TiO2-coated hydrophobic surface is evenly divided into four regions (A, B, C, and D) along its length (160 mm), each region being 40 mm long. These regions are selectively masked using black PTFE tape.

[0072] Step 7, Differentiated Irradiation (UV lighting converts hydrophobic surface to hydrophilic surface): The masked membrane is placed under an activation radiation source (such as a high-pressure mercury lamp, 365nm) for irradiation. The key to this invention lies in applying differentiated irradiation durations to different exposure areas. The longer the irradiation time, the higher the degree of photocatalytic degradation of hydrophobic molecules, and the weaker the surface hydrophobicity (lower water contact angle, WCA). By precisely controlling the masking time for each area and the total irradiation time, a stepped wettability gradient consisting of multiple areas with different WCA values ​​can be constructed on the membrane surface.

[0073] Specifically, the membrane was exposed to ultraviolet light (UV light) for a total duration of 64 minutes under a high-pressure mercury lamp. The following differentiated irradiation scheme was used: Area A: Black PTFE tape was used throughout the process. Area B: The area is shielded from all UV light to preserve its original strong hydrophobicity (measured WCA 121.0±3.7°). Area C: After 62 minutes of irradiation, the tape is removed, exposing the area to UV light for 2 minutes, aiming to reduce its WCA to the weak hydrophobic range of 90-110° (measured WCA 108.5±3.4°). Area D: After 48 minutes of irradiation, the tape is removed, exposing the area to UV light for 16 minutes, aiming to reduce its WCA to the weak hydrophilic range of 40-90° (measured WCA 58.6±2.6°). Area D: The area is not shielded from the beginning and is exposed to UV light for 64 minutes, aiming to restore it to a strong hydrophilic state (measured WCA << 10° and close to 0°, << 10° means much less than 10°). Figure 4 As shown in (c).

[0074] Step 8, final processing: After irradiation, the membrane is ultrasonically cleaned with ultrapure water for 10 minutes to completely remove TiO2 particles from the surface, and then dried again to finally obtain a Janus ceramic membrane with gradient wettability of different surface WCA regions on the hydrophobic side.

[0075] Specifically, the relationship between the process parameters of the Janus ceramic film prepared in Example 1 and the resulting surface wettability is shown in Table 1 below:

[0076] Table 1: Relationship between process parameters and surface wettability in Example 1

[0077]

[0078] Table 1 demonstrates the controllability of the method of the present invention, precisely linking the controllable process variable (UV irradiation time) with the final material surface property (water contact angle), thus proving the reliability and repeatability of the method.

[0079] Example 2 (CM-Ⅱ):

[0080] This embodiment 2 provides a Janus ceramic membrane with dual-zone gradient wettability (one side is a hydrophilic surface, and the other side is a dual-zone wettability gradient surface) and its preparation method. One side of the Janus ceramic membrane is a hydrophilic surface, and the other side is a hydrophilic-hydrophobic hybrid surface. The direction of its wettability gradient is consistent with the flow direction of the stripped gas. The preparation method provided in this embodiment 2 is largely the same as the preparation method provided in embodiment 1, with the only difference being:

[0081] Step Six, Selective Masking: Using an opaque masking material (such as black PTFE tape), the hydrophobic surface loaded with the photocatalyst is selectively masked according to a preset gradient pattern. Areas that need to maintain strong hydrophobicity are completely masked, while areas that need to reduce hydrophobicity or restore hydrophilicity are exposed: The dried, TiO2-coated hydrophobic surface is uniformly divided into two regions, A and B, along its length (160 mm), with each region being 80 mm long. These regions are selectively masked using black PTFE tape.

[0082] Step 7, Differentiated Irradiation: The membrane was exposed to a high-pressure mercury lamp using the following differentiated UV irradiation scheme: Area A: Completely shielded with black PTFE tape, receiving no UV irradiation to preserve its original strong hydrophobicity (measured WCA 121.0 ± 3.7°); Area B: No shielding from the beginning, exposed to UV light for 64 minutes, aiming to restore it to a hydrophilic state (measured WCA close to 0°). Figure 4 As shown in (b).

[0083] Example 3 (CM-VI):

[0084] This embodiment 3 provides a Janus ceramic membrane with six-zone gradient wettability (one side is a hydrophilic surface, and the other side is a six-zone wettability gradient surface) and its preparation method. The preparation method provided in this embodiment 3 is largely the same as the preparation method provided in embodiment 1, with the only difference being:

[0085] Step Six, Selective Masking: Using an opaque masking material (such as black PTFE tape), the hydrophobic surface loaded with the photocatalyst is selectively masked according to a preset gradient pattern. Areas that need to maintain strong hydrophobicity are completely masked, while areas that need to reduce hydrophobicity or restore hydrophilicity are exposed: The dried, TiO2-coated hydrophobic surface is evenly divided along its length (160 mm) into six regions: A, B, C, D, E, and F, each region being 26.67 mm long. These regions are selectively masked using black PTFE tape.

[0086] Step 7, Differentiated Irradiation: The membrane was exposed to a high-pressure mercury lamp and subjected to the following differentiated UV irradiation scheme: Area A: Covered entirely with black PTFE tape, it was not exposed to any UV light to preserve its original strong hydrophobicity (measured WCA of 121.0 ± 3.7°); Area B: After 62 minutes of irradiation, the tape was removed, exposing it to UV light for 2 minutes, with the goal of reducing its WCA to the weak hydrophobic range of 105-110° (measured WCA of 108.5 ± 3.4°); Area C: After 60 minutes of irradiation, the tape was removed, exposing it to UV light for 4 minutes. The target for irradiation zone D was to reduce its WCA to the weakly hydrophobic range of 85-105° (measured WCA was 96.5±10.6°). For zone D, after 48 minutes of irradiation, the tape was removed, and the zone was exposed to UV light for 16 minutes, with the goal of reducing its WCA to the weakly hydrophilic range of 40-90° (measured WCA was 58.6±2.6°). For zone E, after 32 minutes of irradiation, the tape was removed, and the zone was exposed to UV light for 32 minutes, with the goal of restoring it to a hydrophilic state (measured WCA was 35.5±5.7°). For zone F, no shielding was applied from the beginning, and the zone was exposed to UV light for 64 minutes, with the goal of restoring it to a hydrophilic state (measured WCA close to 0°). Figure 4 As shown in (d).

[0087] Comparative Example 1:

[0088] Comparative Example 1 provides a commercial hydrophilic membrane with two opposing hydrophilic surfaces, and the measured WCA is close to 0°. Figure 4 As shown in (a).

[0089] Specifically, the performance of the commercial hydrophilic membrane provided in Comparative Example 1 and the Janus ceramic membranes with gradient wettability provided in Examples 1-3 were evaluated in a simulated transport membrane condenser (TMC) system. The performance of the Janus ceramic membranes with gradient wettability provided in Examples 1-3 was evaluated using a simulated transport membrane condenser experimental platform and compared with the commercial hydrophilic membrane (CM-I, Comparative Example 1). Simulated regeneration gas (a mixture of water vapor and CO2) was countercurrently contacted with a low-temperature MEA-rich solution (a CO2-rich aqueous ethanolamine solution) on both sides of the membrane. The heat recovery flux (Q) was calculated by measuring the temperature difference and flow rate at the inlet and outlet of the rich solution, as well as the amount of condensate transported across the membrane. heat ) and water recycling flux (J H2O ),like Figure 5 As shown.

[0090] Please see Figure 5 , Figure 5This is a performance comparison diagram of the commercial hydrophilic membrane provided in Comparative Example 1 and the Janus ceramic membranes with gradient wettability prepared in Examples 1-3; wherein, Figure 5 In the graph (A), the horizontal axis represents the inlet temperature of the rich solvent (K), and the vertical axis represents the heat recovery flux (MJ / m³). 2 h); Figure 5 In the graph (B), the horizontal axis represents the inlet temperature of the rich solution (in K), and the vertical axis represents the water recovery flux (H2O / H2O(g)flux, in kg / m³). 2 h); Figure 5 The horizontal axis of (C) represents the inlet flow rate of stripped gas, in N / m³. 3 h), with the vertical axis representing the heat recovery flux (unit: MJ / m). 2 h); Figure 5 The horizontal axis of (D) represents the inlet flow rate of regenerated gas (in N / m³). 3 h), water recovery flux (unit: kg / m³) 2 h).

[0091] Depend on Figure 5 It can be seen that under typical operating conditions (e.g., regeneration gas inlet temperature 363K, rich liquid inlet temperature 313K, regeneration gas flow rate 3.6Nm), 3 The performance of different membranes was tested ( / h), and the results are summarized in Table 2 below:

[0092] Table 2 Comparative analysis of heat and mass transfer performance of different types of membranes

[0093]

[0094] Specifically, the data in Table 2 fully demonstrates that the comprehensive performance of the gradient wettability Janus ceramic membranes prepared in Examples 1-3 of this invention is significantly superior to that of the commercial hydrophilic membrane in Comparative Example 1 (CM-I). More importantly, this data further highlights the core principle that "the refinement of gradient wettability design is positively correlated with membrane performance"—compared to CM-II, which only has a simple two-zone gradient, CM-VI, with its six-zone refined gradient design, exhibits superior heat and mass transfer capabilities. Specifically, the heat recovery flux of CM-VI is 9.2% higher than that of the commercial hydrophilic membrane. This quantitative result directly verifies the core design concept of this invention: by precisely matching the membrane surface wettability with the local process environment, the overall heat and mass transfer efficiency can be significantly enhanced. The essential reason for this performance improvement stems from the synergistic effect of the aforementioned "spatial optimization synergistic mechanism" and "surface energy gradient-induced self-driven transport effect," which together construct an efficient heat and mass transfer path.

[0095] Compared with the prior art, the preparation method provided by the present invention and the resulting gradient wettability Janus ceramic film have the following significant but not obvious beneficial effects:

[0096] (1) Spatial optimization of the synergistic transport mechanism to maximize performance: This invention adheres to the design concept of "tailor-made" and uses a gradient structure to form functional zones on the membrane surface. In high-temperature and high-steam-concentration regions such as the gas inlet, the strongly hydrophobic region (e.g., contact angle WCA>110°) can maximize droplet condensation (DWC) efficiency and obtain an extremely high heat transfer coefficient; in the downstream region with lower steam concentration, the moderately hydrophobic and hydrophilic regions (e.g., WCA≤40°) can efficiently capture and transport residual moisture by virtue of lower nucleation energy barriers and strong capillary forces, maximizing mass transfer and latent heat recovery. This synergistic effect of optimization along the process breaks through the performance bottleneck of a single wettable surface and achieves a significant improvement in overall performance. Experimental data show that the heat recovery flux of the optimized gradient membrane (CM-VI) is 9.2% higher than that of commercial hydrophilic membranes.

[0097] (2) Passive, surface energy gradient-induced self-driven condensate transport: The wettability gradient (WCA gradient) constructed along the film surface generates a surface free energy gradient. This energy gradient provides an internal driving force for condensate droplets without the need for external energy, enabling them to spontaneously and directionally migrate from the low surface energy hydrophobic region to the high surface energy hydrophilic region. This self-cleaning or self-refreshing effect can continuously remove droplets from the high-efficiency heat transfer hydrophobic region, preventing "flooding" from forming an adiabatic liquid film, thereby always maintaining the hydrophobic region in the peak heat transfer state of the region with the strongest condensation driving force. This mechanism has been directly confirmed by visualization experiments.

[0098] (3) Quantifiable and superior comprehensive performance: The combined effect of the aforementioned synergistic effect and self-driving mechanism brings about a measurable performance leap. Under experimental conditions simulating carbon capture and waste heat recovery, the Janus membrane (CM-VI) with fine gradients (such as a six-zone gradient) prepared in this invention achieves a heat recovery flux of 13.60 MJ / (m²). 2 h) is not only significantly higher than commercial hydrophilic membranes (CM-I), but also superior to membranes with only simple gradients (such as two-zone gradients) (CM-II), while also exhibiting superior water recovery flux, providing direct quantitative evidence for the technological superiority of the invention.

[0099] (4) By adjusting exposure parameters (such as exposure pattern, exposure time, etc.), the present invention can obtain photoresist patterns with different morphologies, thereby flexibly controlling the array arrangement, size and spacing of Janus ceramic films with gradient wetting properties in the horizontal direction. Compared with the traditional process that relies on a fixed template (such as anodized aluminum template), this control path does not require template replacement, is simpler to operate, more flexible and more efficient, and can quickly adapt to the structural design requirements of diverse devices.

[0100] In summary, unlike existing technologies, this invention provides a Janus ceramic membrane with gradient wettability, its preparation method, and its application. The preparation method includes: first, providing a porous ceramic substrate having a first main surface and a second main surface arranged opposite to each other, both of which are hydrophilic; second, contacting a solution containing a hydrophobic modifier with the first main surface to react, while ensuring that the second main surface does not contact the solution; third, loading a photocatalyst onto the first main surface and selectively dividing the loaded first main surface into at least three spatially continuous sub-regions to be treated; fourth, applying activation radiation with different irradiation durations to the multiple sub-regions to be treated, so that the first main surface forms a gradient wettability region with continuous or discrete wetting level differences; in the gradient wettability region, the water contact angle of different wetting sub-regions increases or decreases sequentially along a predetermined gradient direction; finally, removing the photocatalyst loaded on the first main surface in a manner that does not affect the gradient wettability region and drying it to obtain a Janus ceramic membrane with gradient wettability. The gradient wettability Janus ceramic membrane prepared in this invention employs an asymmetric structural design, with one surface possessing a precisely controllable wettability gradient while the other surface remains hydrophilic. When applied to fluid systems containing condensing components (such as waste heat recovery from regenerated gas in carbon capture processes), it allows for precise matching of the wettability of different regions on the membrane surface with the changing local thermodynamics and concentration environment along the process. The hydrophobic region promotes efficient droplet condensation to enhance heat transfer, while the hydrophilic region enhances mass transfer through capillary effects. Simultaneously, the surface energy gradient induces condensate droplets to spontaneously migrate from the hydrophobic to the hydrophilic region, achieving self-cleaning and continuous renewal of the membrane surface. Experiments demonstrate that the heat and mass transfer performance of this gradient membrane is significantly superior to traditional hydrophilic membranes, hydrophobic membranes, and simple hydrophilic-hydrophobic Janus membranes, exhibiting great application potential in the field of energy conservation and emission reduction.

[0101] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0102] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a Janus ceramic membrane having gradient wettability, characterized by, include: S10, a porous ceramic substrate is provided, the porous ceramic substrate having a first main surface and a second main surface disposed opposite to each other, both the first main surface and the second main surface being hydrophilic; S20, the solution containing the hydrophobic modifier is brought into contact with the first main surface to react, while ensuring that the second main surface does not come into contact with the solution; the hydrophobic modifier is a fluoroalkylsilane reagent; S30, a photocatalyst is loaded onto the first main surface, and the loaded first main surface is selectively divided into regions to form at least three spatially continuous sub-regions to be treated; the photocatalyst is titanium dioxide nanoparticles. S40, activation radiation with different irradiation durations is applied to the multiple sub-regions to be treated, so that the first main surface forms a gradient wettability region with continuous or discrete wettability levels; in the gradient wettability region, the water contact angle of different wettability sub-regions increases or decreases sequentially along the gradient preset direction. S50, the photocatalyst loaded on the first main surface is removed and dried in a manner that does not affect the gradient wettability region, to obtain a Janus ceramic film with gradient wettability.

2. The method for preparing a Janus ceramic membrane with gradient wettability according to claim 1, characterized in that, In step S10, the porous ceramic substrate includes any one of alumina ceramic membrane, titanium dioxide ceramic membrane, and silicon dioxide ceramic membrane.

3. The method for preparing a Janus ceramic membrane with gradient wettability according to claim 1, characterized in that, In step S20: the fluoroalkylsilane reagent includes 1H,1H,2H,2H-perfluorooctyltriethoxysilane or 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

4. The method for preparing a Janus ceramic membrane with gradient wettability according to claim 1, characterized in that, In step S40: an opaque shield is used to shield multiple sub-regions to be processed for different durations. The actual duration of activation radiation received by each sub-region to be processed is controlled by the difference in shielding duration. The shielding duration is proportional to the final hydrophobicity of the corresponding sub-region to be processed. The light source for the activation radiation is a high-pressure mercury lamp that emits 365nm light.

5. The method for preparing a Janus ceramic membrane with gradient wettability according to claim 4, characterized in that, In step S40: the gradient wettability region sequentially includes a spatially continuous strong hydrophobic region, a weak hydrophobic region, a weak hydrophilic region, a hydrophilic region, and a strong hydrophilic region along the preset gradient direction; Wherein, the water contact angle of the strongly hydrophobic region is >110°; the water contact angle of the weakly hydrophobic region is >90° and ≤110°; the water contact angle of the weakly hydrophilic region is >40° and ≤90°; the water contact angle of the hydrophilic region is >10° and ≤40°; and the water contact angle of the strongly hydrophilic region is <<10°.

6. A Janus ceramic membrane with gradient wettability, characterized in that, It is prepared by the method for preparing Janus ceramic membrane with gradient wettability as described in any one of claims 1 to 5.

7. The Janus ceramic membrane with gradient wettability according to claim 6, characterized in that, The Janus ceramic membrane has a hydrophilic surface and a wettability gradient surface arranged opposite each other. The wettability gradient surface induces condensed droplets to spontaneously migrate from the strongly hydrophobic region to the weakly hydrophobic region or the hydrophilic region.

8. The application of a Janus ceramic membrane with gradient wettability as described in claim 7 in the fabrication of heat and mass transfer equipment.

9. The application according to claim 8, characterized in that, The heat and mass transfer device includes a transport membrane condenser with the Janus ceramic membrane, the transport membrane condenser being used to recover waste heat from a gas stream containing condensable components, and the gradient preset direction of the wettability gradient surface being consistent with the flow direction of the gas stream.

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