PVA-GO-coated UiO-66-coated PMIA photo-thermal composite film as well as preparation method and application thereof

Abstract

The invention discloses a PVA-GO-coated UiO-66-coated PMIA photo-thermal composite membrane as well as a preparation method and application thereof. The photo-thermal composite membrane is a composite membrane with a three-stage structure of a support layer, a middle layer and a separation layer. UiO-66 nanoparticles are firmly anchored on the surface of a PMIA primary membrane successfully through a spraying-phase inversion process, an intermediate layer with a uniform structure is formed, and PMIA molecular chains permeate and diffuse into mesopores on the surfaces of the UiO-66 nanoparticles to a certain extent at the initial stage of phase inversion; and finally, further spraying a PVA-GO mixed solution with a photo-thermal response function on the intermediate layer, wherein the separation layer and the intermediate layer form an interpenetrating structure. The composite membrane prepared by the innovative process not only has excellent desalting performance, but also has excellent long-term stability and photo-thermal response reversibility, realizes effective integration of the selective transmission capability of an MOF material and the photo-thermal conversion characteristic of GO, and provides a new way for developing a low-carbon and efficient water treatment technology.

Description

Technical Field

[0001] This invention relates to a photothermal composite film and its preparation method, specifically to a PVA-GO@UiO-66@PMIA photothermal composite film, its preparation method, and its application; belonging to the field of functional film technology. Background Technology

[0002] With global climate change, accelerated industrialization, and continuous population growth, freshwater resources are increasingly becoming a scarce natural resource. Oceans, widely distributed across the Earth, contain vast amounts of water resources, and achieving a sustainable supply of freshwater through seawater desalination technology has become one of the key approaches to solving global water security issues. Currently, the main desalination technologies fall into two categories: thermal and membrane methods. Thermal technologies, such as multi-effect evaporation (MED) and multi-stage flash evaporation (MSF), while widely used in industrial applications, are typically accompanied by high energy consumption and severe scaling problems during operation, making them difficult to align with the current development trends of green, low-carbon, energy-saving, and environmentally friendly practices.

[0003] While traditional membrane technologies, such as reverse osmosis (RO), offer high energy efficiency, they have limitations when treating high-concentration brine. Their operation relies on high pressures and requires strict control over influent water quality, thus limiting their application in specific scenarios such as high-salinity wastewater treatment. Against this backdrop, pervaporation (PV) technology, as a thermo-membrane coupling process, demonstrates unique application potential. Based on a dissolution-diffusion mechanism, water molecules selectively adsorb onto the membrane surface, then diffuse within the membrane and undergo a phase change, ultimately desorbing as vapor on the other side of the membrane, achieving separation. Pervaporation technology has a wide range of salt concentration adaptability, can treat various brine systems, and has low requirements for influent pretreatment. Furthermore, this technology can operate under low heat source conditions, effectively utilizing waste heat generated in industrial processes as an energy source, and can achieve efficient desalination while maintaining a suitable vacuum level in the system, without the need for high-pressure equipment, resulting in relatively low energy requirements. Therefore, pervaporation technology not only possesses excellent separation performance and operational flexibility, but also meets the current development needs of energy conservation and environmental friendliness. It is considered a promising seawater desalination and high-salinity wastewater treatment technology with significant application potential.

[0004] As a core component of membrane separation technology, the performance of membrane materials directly determines the efficiency of the pervaporation desalination process. A typical pervaporation desalination membrane is usually a composite structure consisting of a porous support layer and a dense separation layer, aiming to synergistically improve the overall performance of the composite membrane from both the dimensions of mass transfer efficiency and chemical stability.

[0005] Therefore, it is necessary to develop a composite membrane that exhibits excellent comprehensive performance in solar-driven pervaporation desalination through hierarchical structure design and process optimization, providing a new approach for developing low-carbon and efficient water treatment technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a PVA-GO@UiO-66@PMIA photothermal composite membrane, its preparation method, and its applications. The membrane utilizes a metal-organic framework material, UiO-66, with excellent water stability and structural tunability, combined with a polymer substrate to form a three-dimensional interlocked structure as the intermediate functional layer. This constructs a composite membrane with a three-tiered structure of "support layer-intermediate layer-separation layer." Through hierarchical design and process optimization, the overall performance of the composite membrane is synergistically improved in terms of both mass transfer efficiency and chemical stability. This effectively integrates the selective transport capability of MOF materials with the photothermal conversion characteristics of GO, exhibiting excellent comprehensive performance in solar-driven pervaporation desalination processes. This provides a new approach for developing low-carbon, high-efficiency water treatment technologies.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention discloses for the first time a PVA-GO@UiO-66@PMIA photothermal composite film, which is a three-level composite film with a "support layer-intermediate layer-separation layer". The support layer is a PMIA substrate, and the intermediate layer is composed of UiO-66 nanoparticles anchored to the surface of the PMIA nascent film through a spraying-phase inversion process. The nanoparticles and the PMIA polymer form a three-dimensional through-interlocking structure. In other words, the intermediate layer is composed of UiO-66 nanoparticles anchored to the surface of the PMIA substrate film through the spraying phase inversion process. By spraying MOF particles and combining the phase inversion process, the polymer film formation process can encapsulate, anchor, and chain-penetrate the MOF particles, forming an interlocking structure between the nanoparticles and the PMIA polymer. Even after cleaning, the nanoparticles can still maintain a firm anchorage. The UiO-66 particles and the PMIA substrate interface area form a three-dimensional interpenetrating structure, which is stable, firm, and has a uniform particle distribution. The separation layer is a PVA-GO separation layer formed on the intermediate layer. Since the sprayed solution is a non-crosslinked PVA-GO solution, the solution of the separation layer is spread and penetrates into the intermediate layer in a liquid state. The separation layer and the intermediate layer form an interpenetrating structure, which can avoid the adverse effects such as nanoparticle agglomeration caused by the direct blending of MOF materials into the PVA solution.

[0009] Preferably, the preparation process of the aforementioned intermediate layer is as follows: the obtained UiO-66 powder is dispersed in ethanol to form a nano MOF ethanol dispersion, and then the nano MOF ethanol dispersion is sprayed onto the surface of the nascent membrane of the PMIA casting solution, and then placed in a deionized water coagulation bath at room temperature to prepare the intermediate layer through solvent-non-solvent exchange.

[0010] Preferably, the aforementioned photothermal composite membrane exhibits reversible photothermal response, and its permeation flux remains stable at 28.87 kg·m³ for 72 hours under conditions of 30°C and no light irradiation. -2 ·h -1 Near the target area, the rejection rate remained around 99.94%, demonstrating good steady-state performance. Under a feed temperature of 75℃ and an intermittent operating mode of 12 hours without light and 12 hours with 1.0 Sun illumination, the membrane exhibited excellent photothermal response reversibility: the flux during the light-free period was approximately 152.09 kg·m³. -2 ·h -1 The duration of illumination increased to 164.44 kg·m². -2 ·h -1 The increase was 8.12%, and the retention rate remained stable at around 99.89%.

[0011] This invention also discloses a method for preparing the aforementioned PVA-GO@UiO-66@PMIA photothermal composite film, comprising:

[0012] S1. Preparation of UiO-66@PMIA base film

[0013] UiO-66 powder was dispersed in an ethanol solution to form a nano MOF ethanol dispersion, which was then sprayed onto the surface of the nascent membrane of the PMIA casting solution. After that, it was placed in a deionized water coagulation bath at room temperature and the UiO-66@PMIA nanocomposite substrate was prepared by solvent-non-solvent exchange method.

[0014] S2. Preparation of PVA-GO separation layer solution

[0015] PVA and P(AA-AMPS) were dissolved in deionized water and stirred in an oil bath at 95°C for 12 hours until a transparent and homogeneous PVA / P(AA-AMPS) mixed solution was obtained. The solution was then allowed to stand to remove bubbles. A certain amount of the PVA / P(AA-AMPS) mixed solution was then taken out and GO dispersion was added to it so that the mass ratio of PVA / P(AA-AMPS) to GO was 5:1. The solution was sonicated for 30 minutes to obtain a clear brown PVA-GO separation layer preparation solution.

[0016] S3. Adhere the UiO-66@PMIA base film obtained in step S1 onto a glass plate. Spray the PVA-GO separation layer solution obtained in step S2 onto the UiO-66@PMIA base film using a spray gun. Then, place the sprayed PVA-GO@UiO-66@PMIA composite film at 200 mW·cm⁻¹. -1 PVA-GO@UiO-66@PMIA photothermal composite film was prepared by crosslinking under a xenon lamp for 1 h.

[0017] Preferably, the aforementioned UiO-66 powder is prepared in-house, and the preparation method is as follows:

[0018] (1) Preparation of organic ligand solution: Dissolve 1.994 g H2BDC in a mixed solvent consisting of 120 mL DMF and 30 mL FA, and sonicate for 30 min to ensure complete dissolution;

[0019] (2) Preparation of metal source solution: Dissolve 2.796 g ZrCl4 in another mixed solvent consisting of 120 mL DMF and 30 mL AA, and sonicate for 30 min to obtain a clear and transparent solution;

[0020] (3) Transfer the two solutions to a three-necked flask and mix them evenly. Stir magnetically in an oil bath at 100°C for 24 hours. After the reaction is complete, cool naturally to room temperature. Wash several times with DMF, EtOH and acetone in sequence. Dry under vacuum at 120°C for 12 hours to obtain UiO-66 powder.

[0021] More preferably, the preparation method of the aforementioned PMIA substrate casting solution is as follows: at room temperature, a certain amount of LiCl and DMAc solvent are stirred in a glass bottle for 30 min. After all the LiCl is dissolved, SE-11 is added to the solution and stirring is continued for 30 min until the solution is stable and homogeneous. Then, PMIA is added to the above solution and fully dissolved in an oven at 85 °C for 48 h to form a homogeneous casting solution.

[0022] More preferably, the concentration of UiO-66 in the aforementioned ethanol dispersion is 10~60 mg / ml.

[0023] More preferably, in step S2, the mass ratio of PVA to P(AA-AMPS) is 7:10, and the mass percentage of PVA in the PVA / P(AA-AMPS) mixed solution does not exceed 0.5%.

[0024] As mentioned above, a PVA-GO@UiO-66@PMIA photothermal composite membrane can be applied to a solar-driven pervaporation desalination membrane process.

[0025] The advantages of this invention are:

[0026] (1) In this invention, UiO-66 nanoparticles were successfully embedded and anchored on the surface of the PMIA nascent film through a spraying-phase conversion process. The phase conversion of the PMIA nascent film partially coated and anchored UiO-66. In the early stage of phase conversion, the PMIA molecular chains penetrated and diffused to a certain extent into the mesopores on the surface of the UiO-66 particles and were firmly connected in a locking state. During the curing process, the PMIA polymer film structure formed a three-dimensional mechanical interlocking structure with the UiO-66 interface region, which further stabilized the intermediate layer structure. Then, a PVA-GO mixed solution with photothermal response function was sprayed on the intermediate layer. The separation layer and the intermediate layer formed an interpenetrating structure and further crosslinked to form a dense separation layer. Finally, a PVA-GO@UiO-66@PMIA photothermal composite film with complete structure and both separation and photothermal conversion performance was formed.

[0027] (2) In the composite membrane prepared by this invention, UiO-66 is firmly embedded between the support layer and the separation layer, which not only enhances the interlayer bonding strength but also plays a key role in regulating the structure and performance of the separation layer. Firstly, the highly ordered microporous structure provides nanoscale transport channels for water molecules, promoting the diffusion of water molecules within the membrane and thus increasing water flux. Secondly, as a low thermal conductivity material, UiO-66 can slow down heat loss during thermal crosslinking, forming a local thermal aggregation effect, and promoting the formation of a more complete and uniform in-situ self-crosslinking network of PVA molecules. This dual-action mechanism synergistically improves the overall performance of the composite membrane from two dimensions: mass transfer efficiency and chemical stability. Under 30°C feeding conditions, the permeation flux increased from 25.55 ± 0.97 kg·m³ under no light conditions. -2 ·h -1 Gradually increased to 28.95±0.35 kg·m under 2.0 Suns illumination. -2 ·h -1 The flux increased by 13.31%, while the rejection rate remained above 99.9%. Under high-temperature feeding conditions of 75℃, a similar trend of increasing flux with increasing light intensity was observed, from 156.57 ± 10.29 kg·m³. -2 ·h -1 Increased to 176.73 ± 7.03 kg·m -2 ·h -1 The increase was 12.88%, and the retention rate remained above 99.8%.

[0028] (3) The photothermal composite membrane prepared by the present invention not only has excellent desalination performance, but also excellent long-term desalination stability and photothermal response reversibility. That is, through hierarchical optimization design and process optimization, the selective transport capability of MOF material and the photothermal conversion characteristics of GO are effectively integrated. It can exhibit excellent comprehensive performance in the solar-driven pervaporation desalination process, providing a new way for developing low-carbon and efficient water treatment technology. Attached Figure Description

[0029] Figure 1 Examples 1-4 (from top to bottom) are SEM images of the PMIA substrate and the nanocomposite substrate containing the UiO-66 intermediate layer.

[0030] Figure 2 Examples 1-4 (from top to bottom) are SEM images of the cross-sections of the PMIA substrate and the nanocomposite substrate containing the UiO-66 intermediate layer.

[0031] Figure 3 The images show surface SEM characterizations of the composite films prepared in Examples 1-4 (from top to bottom);

[0032] Figure 4 SEM images of the PMIA substrate and the nanocomposite substrate containing the UiO-66 intermediate layer in comparative examples and Examples 5, 6, 2, and 7 (from left to right);

[0033] Figure 5 SEM images of the composite films of comparative examples and Examples 5, 6, 2, and 7 (from left to right);

[0034] Figure 6 The above are surface XRD patterns of the nanocomposite substrates containing the UiO-66 intermediate layer in Examples 1-4.

[0035] Figure 7 The XRD patterns of the composite films in Examples 1-4 are shown.

[0036] Figure 8 The surface AFM of the composite films in Examples 1-4 is shown, where (a1-d1) are three-dimensional morphology images and (a2-d2) are two-dimensional morphology images.

[0037] Figure 9 The graph shows the temperature change of the membrane surface during the crosslinking process. From top to bottom, a~g correspond to Examples 1~7, and h is the comparative example. From left to right, 1~5 correspond to 5 min, 10 min, 15 min, 20 min, and 60 min, respectively.

[0038] Figure 10 The graph shows the pervaporation performance test results for all the obtained examples and comparative examples;

[0039] Figure 11 The graph shows the effect of different light irradiations on the pervaporation and desalination of the composite membrane in Example 2 at 30°C.

[0040] Figure 12 The graph shows the effect of different light irradiations on the pervaporation and desalination of the composite membrane in Example 2 at 75°C.

[0041] Figure 13 The graph shows the effect of different temperatures on the pervaporation and desalination of the composite membrane in Example 2.

[0042] Figure 14 The graph shows the long-term stability of the composite membrane of Example 2 under pervaporation at 30°C.

[0043] Figure 15 The graph shows the long-term stability of the composite membrane of Example 2 under pervaporation at 75°C. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0045] Unless otherwise specified, all reagents used in this invention (except for deionized water) are commercially available, and preferred methods are shown in Table 1 below:

[0046]

[0047] Table 1. List of preferred sources of raw materials used in this invention

[0048] This invention discloses a PVA-GO@UiO-66@PMIA photothermal composite film, and the preparation process of each embodiment includes the following steps:

[0049] (I) Synthesis of UiO-66

[0050] First, the metal source and organic ligand solutions were prepared separately. 1.994 g of H₂BDC was dissolved in a mixed solvent consisting of 120 mL DMF and 30 mL FA, and sonicated for 30 min to ensure complete dissolution. Simultaneously, 2.796 g of ZrCl₄ was dissolved in another mixed solvent consisting of 120 mL DMF and 30 mL AA, and sonicated for 30 min as well, yielding a clear and transparent solution.

[0051] Subsequently, the two solutions were transferred to a three-necked flask and mixed thoroughly. The reaction system was placed in an oil bath at 100°C and magnetically stirred for 24 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. It was then washed several times with DMF, EtOH, and acetone, and dried under vacuum at 120°C for 12 h to obtain UiO-66 powder.

[0052] (II) Preparation of UiO-66@PMIA nanocomposite substrate

[0053] First, casting solutions with different PMIA contents were prepared. At room temperature, a certain amount of LiCl and DMAc solvent were stirred in a glass bottle for 30 min. After all the LiCl was dissolved, SE-11 was added to the solution, and stirring continued for another 30 min until the solution was stable and homogeneous. Then, a certain amount of PMIA was added to the above solution, and the solution was thoroughly dissolved in an oven at 85 ℃ for 48 h to form a homogeneous casting solution. The composition of each casting solution is shown in Table 2. Membranes with different PMIA contents are denoted as x-PMIA membranes (x=9, 10, 11, or 12). The prepared casting solutions were removed from the oven and allowed to stand at room temperature for 2 hours for degassing treatment before use.

[0054]

[0055] Table 2. Summary of Raw Material Composition and Content of Casting Solution

[0056] Subsequently, a certain amount of UiO-66 powder prepared in step S1 was taken and prepared into ethanol dispersions with concentrations of 0, 10, 20, 40, and 60 mg / ml, respectively. The dispersions were ultrasonically treated for 1 h to obtain a uniform white dispersion. The completely degassed casting solution was then coated onto a nonwoven fabric using a 150 μm thick doctor blade. The UiO-66 ethanol dispersion was then sprayed onto the membrane surface, and the membrane was placed in a deionized water coagulation bath at room temperature. Solvent-nonsolvent exchange was then performed to prepare the membrane.

[0057] Finally, the prepared membranes were stored in deionized water for later use. Membranes with different UiO-66 dispersion amounts were denoted as n-UiO-66@PMIA. For example, a membrane with a PMIA content of 11 and a 40 mg / mL UiO-66 dispersion was sprayed on it and was denoted as 40-UiO-66@11-PMIA.

[0058] (III) Preparation of PVA-GO separation layer solution

[0059] 0.35 g PVA and 0.5 g P(AA-AMPS) were dissolved in 69.15 g deionized water and stirred in an oil bath at 95 °C for 12 h until a clear and homogeneous PVA solution was obtained. The solution was then allowed to stand to remove bubbles. A certain amount of PVA / P(AA-AMPS) solution was then taken out and GO dispersion was added to it so that the mass ratio of PVA / P(AA-AMPS) to GO was 5:1. The solution was sonicated for 30 min to obtain a clear brown PVA-GO separation layer preparation solution.

[0060] (iv) Preparation of PVA-GO@UiO-66@PMIA photothermal composite film

[0061] The UiO-66@PMIA base film was adhered to a glass plate, and PVA-GO solution was sprayed onto the UiO-66@PMIA base film using a spray gun. The sprayed PVA-GO@UiO-66@PMIA composite film was then placed at 200 mW·cm⁻¹. -1 PVA-GO@UiO-66@PMIA photothermal composite film was prepared by crosslinking under a xenon lamp for 1 h.

[0062] The preparation methods of Examples 1 to 7 are as described above, with the main differences being the PMIA content and the UiO-66 dispersion amount, as detailed in Table 3:

[0063]

[0064] Table 3. Summary of Raw Material Contents for Each Example and Comparative Example

[0065] Structural characterization

[0066] (1) Microstructure characterization of PVA-GO@UiO-66@PMIA photothermal composite film

[0067] Characterized using scanning electron microscopy (SEM, Zeiss GeminiSEM 360, ZEISS, Germany).

[0068] Surface morphology sample preparation: Cut out samples with an area of ​​0.5 cm × 0.5 cm from each film with scissors, and stick them on the electron microscope test stage with conductive adhesive.

[0069] Sample preparation for cross-sectional morphology: The membrane was cut into strips with scissors, and then the sample was placed in liquid nitrogen with tweezers. After waiting for 20 seconds, the sample was quenched and then dried in an oven. The sample was then attached to the electron microscope test stage with conductive adhesive.

[0070] To better observe the microstructure of the film, the surface and cross-section of the film need to be sputtered with gold for 120 seconds (Q150RES, USA) before scanning observation to enhance the conductivity of the sample.

[0071] The intermediate products from Examples 1-4—x-PMIA series membranes without UiO-66 nanoparticles and nanocomposite substrate series membranes containing UiO-66 intermediate layers—were subjected to SEM characterization to study the effect of PMIA content on membrane microstructure.

[0072] from Figure 1 The SEM images (a1)-(d1) and (a2)-(d2) show that as the PMIA content decreases, the porosity of the PMIA base film surface gradually increases, and the porosity phenomenon is most significant when the PMIA content is 9%.

[0073] Further observation Figure 1 As can be seen from (a3)-(d3) and (a4)-(d4), although the surface of the nanocomposite substrate containing the UiO-66 intermediate layer is coated with a UiO-66 layer, the coating cannot completely cover the macroporous structure of the film surface. In particular, obvious pore defects can still be seen in the sample with a PMIA content of 9%.

[0074] SEM cross-section of x-PMIA series membranes Figure 2 As can be observed in (a1)-(d1) and (a2)-(d2), the internal pore size of the membrane increases and the pore wall structure gradually becomes more open as the PMIA content decreases. This trend suggests that lower concentrations of polymer solution facilitate the formation of more developed porous interconnected structures during phase separation, thereby providing a more efficient pathway for mass transport.

[0075] Further observation Figure 2 As can be seen from (a3)-(d3) and (a4)-(d4), UiO-66 particles are uniformly embedded inside the PMIA matrix, forming a closely bonded interface structure. This indicates that the spraying process successfully achieved effective loading and fixation of UiO-66 inside the membrane, and this composite structure can enhance the mechanical stability of the membrane.

[0076] The thickness of the nanocomposite substrate series films containing UiO-66 interlayers was systematically measured, and the results are shown in Table 4. With decreasing PMIA content, the film thickness gradually decreased from 84.90±0.95 μm to 77.14±1.79 μm. This trend is mainly attributed to the decrease in polymer solids content in the casting solution, leading to a decrease in system viscosity and increased fluidity, thus facilitating the penetration of the casting solution into the underlying nonwoven fabric support during film formation. This process affects matrix formation during the phase transformation stage, ultimately resulting in a correspondingly thinner cured film.

[0077] After spraying the PVA-GO solution, the PVA-GO@UiO-66@x-PMIA composite films obtained in Examples 1-4 were characterized by SEM, and the results are as follows: Figure 3 As shown. From the surface morphology Figure 3As can be observed in (a1)-(d1) and (a2)-(d2), the outline of UiO-66 particles gradually becomes clearer as the PMIA content decreases. This is mainly attributed to the increased porosity of the base film surface when the PMIA content decreases, which makes it easier for the PVA-GO solution to penetrate into the porous substrate during film formation, resulting in a decrease in the thickness of the surface separation layer and a corresponding weakening of the coverage effect on the underlying UiO-66 structure. Furthermore, from the cross-sectional images of the composite membrane (a3)-(d3) and (a4)-(d4), it can be seen that as the PMIA content decreases, the thickness of the PVA-GO separation layer gradually decreases from 124.99±9.04 nm to 92.35±9.29 nm (see Table 4). This indicates that a lower separation layer thickness can reduce mass transfer resistance and is beneficial for increasing permeation flux.

[0078]

[0079] Table 4. Film thickness overview for different PMIA contents

[0080] Figure 4 From left to right are the SEM characterization images of the intermediate layer of the comparative examples and Examples 5, 6, 2, and 7. The PMIA content is 11% in all examples, and the UiO-66 spraying concentrations are 0, 10, 20, 40, and 60 mg / mL, respectively. Figure 4 As shown, with the increase of UiO-66 spraying concentration, the UiO-66 loading on the membrane surface gradually increases, and the particle distribution uniformity is improved. However, when the spraying concentration increases to 60 mg / mL, due to the tendency of UiO-66 to become supersaturated in the ethanol dispersion system, significant particle agglomeration occurs. This phenomenon not only affects the atomization uniformity of the spray gun but also forms agglomerates on the membrane surface, thus adversely affecting the uniformity and continuity of the composite membrane structure. Figure 5 It is evident that even after further coating the n-UiO-66@PMIA substrate with a PVA-GO layer, the resulting PVA-GO@n-UiO-66@PMIA composite film still clearly displays the outline characteristics of the underlying UiO-66. Particularly under a high concentration of 60 mg / mL, the PVA-GO coating layer still cannot completely conceal the aggregated morphology of UiO-66, indicating that the surface PVA-GO layer is relatively thin, and the aggregated structure of the underlying UiO-66 has a certain influence on the surface morphology.

[0081] (2) Characterization of the crystal structure of PVA-GO@UiO-66@PMIA photothermal composite film

[0082] The crystal structure was characterized using an X-ray diffractometer (D / max-2550, Rigaku Smart Lab, Japan).

[0083] like Figure 6As shown, the UiO-66@PMIA film in the intermediate layer of samples 1-4 all showed diffraction peaks at 2θ≈7.5° and 8.7°, corresponding to the (111) and (002) crystal planes of UiO-66, respectively, and their positions are consistent with the reference spectrum of pure UiO-66 powder. Figure 1 This confirms that the crystal structure of UiO-66 is maintained after recombination.

[0084] XRD analysis of the PVA-GO / UiO-66@x-PMIA composite membrane, such as Figure 7 As shown, even after covering with a PVA-GO layer, the characteristic diffraction peaks of UiO-66 are still clearly observed at 2θ≈7.5° and 8.7° in the spectrum. This phenomenon indicates that the surface PVA-GO separation layer is relatively thin and insufficient to completely shield the diffraction signal of the underlying UiO-66, thus indirectly confirming that the PVA-GO layer has a small thickness, which is beneficial for reducing mass transfer resistance and thus obtaining better mass transfer flux.

[0085] (3) Surface roughness characterization of PVA-GO@UiO-66@PMIA photothermal composite film

[0086] The surface topology of the composite film was systematically characterized using an ultra-high vacuum scanning probe microscope (AFM, UHV AFM / STM, BRUKER, Germany), obtaining corresponding three-dimensional morphology images, two-dimensional morphology images, and average roughness (R). a ) data, such as Figure 8 As shown in the figure. The results show that in Examples 1-4, as the PMIA content decreased, the average roughness of the film surface increased significantly from 27.50±0.59 nm to 40.93±1.54 nm, and the three-dimensional morphology images also intuitively reflected the upward trend of roughness.

[0087] The applicant's analysis suggests that the roughness variation can be attributed to the following mechanisms: As the PMIA content decreases, the viscosity of the casting solution correspondingly decreases. During the UiO-66 spraying process, particles are more easily embedded within the casting solution, leading to a decrease in the uniformity of their distribution after film formation. This, in turn, results in an uneven morphology for the subsequent PVA-GO layer. Furthermore, the reduced PMIA content also increases the porosity and pore structure of the base film surface, making it easier for the PVA-GO solution to penetrate the substrate, further exacerbating the increase in surface roughness. These changes in surface morphology will significantly impact the separation behavior of the composite membrane.

[0088] Performance testing

[0089] (1) Thermal insulation performance of PVA-GO@UiO-66@PMIA photothermal composite film

[0090] The PVA-GO@UiO-66@x-PMIA photothermal composite films prepared in each embodiment were tested at a power density of 0.2 W·cm⁻¹. -2 Crosslinking was performed under visible light using a xenon lamp light source. The temperature change of the film surface over 60 minutes was investigated. Temperature data were acquired using a thermal infrared imager. The results are as follows: Figure 9 As shown in Table 5, the membrane surface temperature showed a continuous upward trend with the extension of illumination time, and the membrane surface temperature of each embodiment reached above 72°C within 60 minutes. This temperature condition can effectively meet the requirements of the PVA crosslinking reaction for a continuously high-temperature environment, thereby promoting the formation of a dense network structure. In contrast, the surface temperature of the composite membrane without UiO-66 coating in the comparative example was only 68.5°C.

[0091] The test results show that the introduction of UiO-66 provides a certain thermal insulation effect on the PMIA matrix and PVA-GO layer, and provides a more continuous and stable thermal environment for the in-situ self-crosslinking reaction of PVA.

[0092]

[0093] Table 5. Summary of film surface temperature change data for each embodiment and comparative example.

[0094] (2) Characterization of the desalination performance of PVA-GO@UiO-66@PMIA photothermal composite film

[0095] The pervaporation separation performance of the composite membrane was tested using a pervaporation membrane separation test device.

[0096] The testing method is as follows: The membrane is cut into a circle with a diameter of 6 cm, fixed in the membrane cell, and connected to a pervaporation testing device. The feed solution, i.e., a 3.5 wt.% NaCl solution, is poured into the feed tank, and the feed pump is started until the flow meter reading stabilizes at 2.0 L / min. -1 Turn on the heating switch. When the feed liquid temperature on the feed side reaches 75.0℃, turn on the vacuum pump. After the vacuum gauge reading stabilizes, open the vacuum pipeline valve and use the liquid nitrogen condenser to collect the permeate from the permeate side. At the same time, use a stopwatch to record the time taken, weigh the permeate, and test the conductivity. Test three membranes of each type.

[0097] Among them, the permeation flux J w (Kg·m) -2 ·h -1 The calculation method is as follows:

[0098]

[0099] In the formula, J w Permeation flux, in kg·m -2 ·h -1m represents the product water mass in kg; A represents the effective membrane area in m². 2 ; The experimental time is expressed in hours (h).

[0100] The salt rejection rate is calculated as follows: Substitute the conductivity values ​​of the product water from the feed side and the permeate side into the standard conductivity curve of sodium chloride solution, and calculate the concentration of NaCl solution on both the feed side and the permeate side. The calculation formula is:

[0101]

[0102] In the formula, R is the retention rate (%), and C p This represents the concentration of the osmotic salt solution, in mg·L⁻¹. -1 C f This refers to the concentration of the salt solution on the feed side, in mg·L. -1 .

[0103] The pervaporation performance of the prepared PVA-GO@UiO-66@PMIA composite membrane was tested under conditions of a feed temperature of 75℃ and a NaCl solution mass fraction of 3.5%. The test results are as follows: Figure 10 As shown: With the decrease of PMIA content, the permeation flux of the composite membrane decreased from 121.33 ± 7.96 kg·m -2 ·h -1 It increased significantly to 207.98±59.14 kg·m -2 ·h -1 The rejection rate decreased from 99.97±0.04% to 91.65±13.57%. This trend is mainly attributed to the following structural evolution: as the PMIA content decreases, the open porosity of the base membrane increases and the pores expand, especially when the PMIA content is 10%, large pore defects appear; at the same time, the thickness of the PVA-GO separation layer decreases and the mass transfer resistance decreases, which together contribute to a significant increase in water flux.

[0104] However, as mentioned earlier, a decrease in PMIA content leads to increased membrane surface roughness and the formation of more wrinkles in the PVA-GO layer. While these wrinkles help increase the effective adsorption area for water molecules, their binding stability may decrease, posing a risk of delamination and thus affecting the long-term operational stability of the membrane. Particularly at a PMIA content of 9%, the probability of membrane surface defects increases significantly, resulting in decreased retention performance and increased data fluctuations. This inverse relationship between permeate flux and retention rate is consistent with the typical "trade-off" effect in membrane separation processes.

[0105] like Figure 10 As shown, as the UiO-66 spraying concentration increased to 40 mg / mL, the permeation flux of the composite membrane increased from 122.97 ± 17.91 kg·m -2·h -1 Increased to 148.00±3.87 kg·m -2 ·h -1 Meanwhile, the rejection rate increased from 99.70±0.21% to 99.95±0.32%. The sample without UiO-66 coating lacked an effective thermal barrier, resulting in greater heat loss during PVA crosslinking. PVA and P(AA / AMPS) failed to fully crosslink to form a dense network, resulting in structural defects and thus poor salt rejection performance.

[0106] It can be seen that the UiO-66 introduced by the spray-phase inversion of the present invention can be uniformly loaded on the PMIA matrix. This tightly embedded and oriented structure has excellent stability and can effectively anchor UiO-66, so that it can exert a variety of enhanced mass transfer effects: (1) UiO-66 itself has good hydrophilicity, which is conducive to the adsorption and transfer of water molecules; (2) As a porous material, UiO-66 provides additional transport channels for water molecules, thereby promoting a further increase in permeation flux; (3) The thermal insulation effect of the UiO-66 layer helps PVA to be more fully crosslinked, further promoting a slight increase in the rejection rate.

[0107] However, we found that when the spray concentration increased to 60 mg / mL, UiO-66 exhibited localized agglomeration due to uneven dispersion, and structural defects were easily formed after PVA-GO coverage, resulting in a decrease in retention rate to 99.57±0.32%. Simultaneously, excessively high loading also increased the water mass transfer resistance, causing the flux to drop to 138.47±18.22 kg·m³. -2 ·h -1 Furthermore, data volatility has intensified.

[0108] Therefore, considering the balance between penetration and rejection rate, Example 2, with a PMIA content of 11% and a UiO-66 spraying amount of 40 mg / mL, is the optimal example and will be used as an example for further in-depth research.

[0109] (3) Test on the effect of light and temperature on the performance of composite membrane

[0110] The effect of different light intensities on the pervaporation performance of the PVA-GO@UiO-66@PMIA photothermal composite membrane prepared in Example 2 was investigated. The experiment was conducted at different light intensities (0, 0.5, 1.0, 1.5, and 2.0 Suns, i.e., 0–2 kw / cm²). -2 The membrane performance was tested under xenon lamp illumination conditions, with feed temperatures of 30℃ and 75℃ and NaCl mass fraction of 3.5%.

[0111] like Figure 11As shown, under feeding conditions of 30℃, with increasing light intensity, the permeation flux increased from 25.55 ± 0.97 kg·m⁻² under no light conditions. -2 ·h -1 Gradually increased to 28.95±0.35 kg·m under 2.0 Suns illumination. -2 ·h -1 The increase reached 13.31%, while the retention rate remained above 99.94%.

[0112] like Figure 12 As shown, under high-temperature feeding conditions of 75℃, the flux also showed an increasing trend with increasing light intensity, from 156.57±10.29 kg·m⁻². -2 ·h -1 Increased to 176.73 ± 7.03 kg·m -2 ·h -1 The increase was 12.88%, while the rejection rate remained above 99.82%. Under applied light intensity, the GO in the composite membrane exhibited excellent photothermal conversion capabilities, converting absorbed photon energy into heat energy. This energy conversion process selectively induces a local temperature gradient at the membrane-liquid interface, enhancing the thermal kinetic energy of water molecules and reducing the apparent activation energy they need to overcome during permeation and phase transition within the membrane. Simultaneously, the photothermal effect of GO provides additional heat energy at this phase transition point, effectively compensating for heat loss caused by water vaporization and mitigating the negative impact of temperature polarization. Therefore, illumination can effectively improve the performance of the photothermal composite membrane during the pervaporation process.

[0113] Furthermore, the pervaporation performance of a 3.5 wt.% NaCl solution was tested at different feed temperatures: 30℃, 45℃, 60℃, and 75℃. The results are as follows: Figure 13 As shown, as the feed temperature increased from 30°C to 75°C, the membrane permeation flux increased from 25.55 ± 0.97 kg·m⁻². -2 ·h -1 Significantly increased to 156.57±10.29 kg·m -2 ·h -1This is mainly attributed to the significant increase in vapor pressure on the feed side caused by increased temperature, which strengthens the vapor pressure difference across the membrane. This enhanced mass transfer driving force directly promotes the increase in water flux. Simultaneously, the increased temperature also intensifies the thermal motion of PVA polymer chains, correspondingly weakening intermolecular forces and causing thermal expansion of the polymer network. The permeability and diffusion capacity of water molecules are further enhanced at high temperatures, jointly promoting the increase in free volume within the membrane. This may cause a slight expansion of the transport channels within the membrane, providing more potential transmembrane pathways for Na⁺ and Cl⁻ ions, resulting in a slight decrease in the rejection rate from 99.96±0.06% to 99.84±0.12%, reflecting a slight decrease in ion selectivity at high temperatures. Under a light intensity of 1.0 Sun, the flux increases corresponding to different feed temperatures (30℃, 45℃, 60℃, 75℃) were 9.20%, 5.80%, 6.03%, and 9.97%, respectively, further demonstrating the general enhancing effect of photothermal effect on the mass transfer process across different temperature ranges.

[0114] (4) Long-term stability test of PVA-GO@UiO-66@PMIA photothermal composite film

[0115] The composite membrane was subjected to a 72-hour pervaporation long-term stability test, and the results are as follows: Figure 14 and Figure 15 As shown.

[0116] Under conditions of 30°C and no light, the osmotic flux remained stable at 28.87 kg·m³. -2 ·h -1 The flux fluctuated within a certain range, but the rejection rate remained at approximately 99.94%, demonstrating good steady-state performance. Under feed conditions of 75℃ and an intermittent operation mode of 12 hours without light and 12 hours with 1.0 Sun illumination, the membrane exhibited excellent photothermal response reversibility: the flux during the light-free period was approximately 152.09 kg·m³. -2 ·h -1 The duration of illumination increased to 164.44 kg·m -2 ·h -1 The improvement reached 8.12%, and the retention rate remained stable at around 99.89%. This result indicates that the PVA-GO@UiO-66@PMIA photothermal composite film prepared in this invention maintained its inherent structure during 72 hours of continuous testing, demonstrating the excellent stability of the nanocomposite substrate prepared by spraying-phase transformation. It did not detach under high temperature and vacuum conditions and exhibited excellent long-term operational stability and photothermal cycling durability under different temperature and illumination conditions.

[0117] In summary, this invention first successfully embedded and anchored UiO-66 nanoparticles onto the surface of a PMIA nascent film using a self-developed spraying-phase inversion process. Phase inversion occurred through the PMIA nascent film, partially coating and anchoring the UiO-66. Furthermore, during the initial phase inversion, the PMIA molecular chains penetrated and diffused to a certain extent into the mesopores on the surface of the UiO-66 particles, forming a secure interlocking structure. During the curing process, the PMIA polymer film structure forms a three-dimensional mechanical interlocking structure with the UiO-66 interface region, further stabilizing the intermediate layer structure. Subsequently, a photothermal responsive coating was further sprayed onto the intermediate layer. A PVA-GO mixed solution, with the separation layer and intermediate layer forming an interpenetrating structure, further cross-links to form a dense separation layer, possessing both separation and photothermal conversion properties, ultimately forming a structurally complete PVA-GO@UiO-66@PMIA photothermal composite membrane. This photothermal composite membrane not only has excellent desalination performance but also excellent long-term desalination stability and photothermal response reversibility. That is, through hierarchical design and process optimization, the selective transport capability of MOF materials and the photothermal conversion characteristics of GO are effectively integrated, demonstrating excellent comprehensive performance in solar-driven pervaporation desalination processes, providing a new approach for developing low-carbon and efficient water treatment technologies.

[0118] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A PVA-GO@UiO-66@PMIA photothermal composite film, characterized in that, The composite membrane has a three-level structure of "support layer-intermediate layer-separation layer". The support layer is a PMIA substrate; the intermediate layer is composed of UiO-66 nanoparticles anchored to the surface of the PMIA primary membrane through a spray-phase inversion process, and the nanoparticles and PMIA polymer form a three-dimensional through-interlocked structure; the separation layer is a PVA-GO separation layer formed on the surface of the intermediate layer, and the separation layer and the intermediate layer form an interpenetrating structure.

2. The PVA-GO@UiO-66@PMIA photothermal composite film according to claim 1, characterized in that, The preparation process of the intermediate layer is as follows: UiO-66 powder is dispersed in ethanol to form a nano MOF ethanol dispersion, and then the nano MOF ethanol dispersion is sprayed onto the surface of the nascent membrane of the PMIA casting solution to undergo a spraying-phase inversion process. Then it is placed in a deionized water coagulation bath at room temperature, and after a further solvent-non-solvent exchange process, a nano MOF composite substrate with a UiO-66 intermediate layer is prepared.

3. The PVA-GO@UiO-66@PMIA photothermal composite film according to claim 1, characterized in that, The photothermal composite membrane exhibits reversible photothermal response, and its permeation flux remains stable at 28.87 kg·m³ after 72 hours under 30°C and no light conditions. -2 ·h -1 The rejection rate remained around 99.94%, demonstrating good steady-state performance. Under feed conditions of 75℃ and an intermittent operation mode of 12 hours without light and 12 hours with 1.0 Sun illumination, the membrane exhibited excellent photothermal response reversibility: the flux during the light-free period was 152.09 kg·m³. -2 ·h -1 The duration of illumination increased to 164.44 kg·m -2 ·h -1 The increase was 8.12%, and the retention rate remained stable at around 99.89%.

4. The method for preparing a PVA-GO@UiO-66@PMIA photothermal composite film as described in claim 1, characterized in that, include: S1. Preparation of UiO-66@PMIA nanocomposite substrate UiO-66 powder was dispersed in an ethanol solution to form a nano MOF ethanol dispersion, which was then sprayed onto the surface of the nascent membrane in the PMIA casting solution. After that, it was placed in a deionized water coagulation bath at room temperature and the UiO-66@PMIA nanocomposite substrate was prepared by solvent-non-solvent exchange method. S2. Preparation of PVA-GO separation layer solution PVA and P(AA-AMPS) were dissolved in deionized water and stirred in an oil bath at 95°C for 12 h until a transparent and homogeneous PVA / P(AA-AMPS) mixed solution was obtained. The solution was then allowed to stand to remove bubbles. A certain amount of the PVA / P(AA-AMPS) mixed solution was then taken out and GO dispersion was added to it. The mass ratio of PVA / P(AA-AMPS) to GO was 5:

1. The solution was sonicated for 30 min to obtain a clear brown PVA-GO separation layer preparation solution. S3. Adhere the UiO-66@PMIA substrate film obtained in step S1 onto a glass plate. Spray the PVA-GO separation layer solution obtained in step S2 onto the UiO-66@PMIA nanocomposite substrate using a spray gun. Then, place the sprayed PVA-GO@UiO-66@PMIA composite film at 200 mW·cm⁻¹. -1 PVA-GO@UiO-66@PMIA photothermal composite film was prepared by crosslinking under a xenon lamp for 1 h.

5. The method for preparing a PVA-GO@UiO-66@PMIA photothermal composite film according to claim 4, characterized in that, The UiO-66 powder was prepared in-house using the following method: (1) Preparation of organic ligand solution: Dissolve 1.994 g H2BDC in a mixed solvent consisting of 120 mL DMF and 30 mL FA, and sonicate for 30 min to ensure complete dissolution; (2) Preparation of metal source solution: Dissolve 2.796 g ZrCl4 in another mixed solvent consisting of 120 mL DMF and 30 mL AA, and sonicate for 30 min to obtain a clear and transparent solution; (3) Transfer the two solutions to a three-necked flask and mix them evenly. Stir magnetically in an oil bath at 100°C for 24 h. After the reaction is complete, cool naturally to room temperature. Wash several times with DMF, EtOH and acetone in sequence. Dry under vacuum at 120°C for 12 h to obtain UiO-66 powder.

6. The method for preparing a PVA-GO@UiO-66@PMIA photothermal composite film according to claim 4, characterized in that, The preparation method of the PMIA substrate casting solution is as follows: at room temperature, a certain amount of LiCl and DMAc solvent are stirred in a glass bottle for 30 min. After all the LiCl is dissolved, SE-11 is added to the solution and stirring is continued for 30 min until the solution is stable and homogeneous. Then, PMIA is added to the above solution and fully dissolved in an oven at 85 °C for 48 h to form a homogeneous casting solution.

7. The method for preparing a PVA-GO@UiO-66@PMIA photothermal composite film according to claim 4, characterized in that, The concentration of UiO-66 in the ethanol dispersion is 10~60 mg / ml.

8. The method for preparing a PVA-GO@UiO-66@PMIA photothermal composite film according to claim 4, characterized in that, In step S2, the mass ratio of PVA to P(AA-AMPS) is 7:10, and the mass percentage of PVA in the PVA / P(AA-AMPS) mixed solution does not exceed 0.5 wt.%.

9. The PVA-GO@UiO-66@PMIA photothermal composite membrane as described in any one of claims 1 to 3 is used in a solar-driven pervaporation desalination membrane process.

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