Flexible Fe / Cu-MOF-CC composite film material and preparation method and application thereof

Abstract

The invention discloses a flexible Fe / Cu-MOF (at) CC composite film material and a preparation method and application thereof.According to the method, impurities on the surface of a flexible substrate (carbon cloth) are removed through ultrasonic cleaning of acetone, ethyl alcohol and deionized water, then hydrophilic groups are introduced through activation of nitric acid, then FeCl3. 6H2O, CuCl2. 2H2O and 2, 5-dihydroxyterephthalic acid are dissolved in a DMF / methyl alcohol system to form a precursor solution, and the precursor solution is subjected to ultrasonic cleaning and drying to obtain the flexible Fe / Cu-MOF (at) CC composite film material. And performing in-situ growth of the Fe / Cu-MOF film on the activated substrate through a hydrothermal method. According to the technology, a Fe / Cu double-metal synergistic center is introduced, so that an MOF electronic structure is effectively regulated and controlled, the problems of weak interference capability and low dissociation efficiency of a water molecule hydrogen bond network caused by a single metal site and a fixed electronic structure of traditional MOFs are solved, the interface water evaporation performance of the material under a complex working condition is remarkably improved, and the preparation method is suitable for industrial production. The device is suitable for solar-driven seawater desalination and wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of interfacial solar water evaporation photothermal technology, and relates to a flexible Fe / Cu-MOF@CC composite thin film material, its preparation method and application. Background Technology

[0002] Against the backdrop of continuous global population growth, surging industrial and agricultural water demand, and low water resource utilization efficiency, freshwater scarcity has become one of the major challenges restricting sustainable social development. Seawater desalination and wastewater treatment are considered key approaches to alleviating the water crisis, especially solar-driven interfacial water evaporation technology, which has attracted widespread attention due to its green and low-energy consumption characteristics. In this technology, high-performance photothermal materials are the core for achieving efficient water evaporation.

[0003] Metal-organic frameworks (MOFs), a class of crystalline porous materials formed by the self-assembly of metal ions / clusters and organic ligands, have shown great potential in catalysis, sensing, energy storage, and environmental remediation due to their ultra-high specific surface area, tunable pore structure, abundant active sites, and good hydrophilicity. In recent years, MOFs have been widely used in electrochemical hydrogen production, carbon dioxide reduction, pollutant adsorption and separation, and solar water evaporation. Their unique porous structure not only facilitates the rapid transport of water molecules but also enables the activation of interfacial water through the interaction between metal nodes and water molecules, thereby reducing evaporation energy consumption. However, despite the many advantages of MOFs, their inherent fixed electronic structure and single metal active center limit their ability to regulate water molecules, making it difficult to achieve deep intervention and efficient dissociation of hydrogen bond networks. This severely restricts their application performance under complex conditions such as high-salinity wastewater treatment and long-term continuous operation. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a flexible Fe / Cu-MOF@CC composite thin film material, its preparation method, and its application. This solves the technical problem that MOFs, due to their inherent fixed electronic structure and single metal active center, are unable to deeply intervene in the hydrogen bond network of water molecules and achieve efficient dissociation, thus restricting their application in efficient water evaporation under complex working conditions.

[0005] This invention is achieved through the following technical solution: A method for preparing a flexible Fe / Cu-MOF@CC composite film includes the following steps: S1: The flexible substrate is cleaned sequentially with acetone, ethanol and deionized water in an ultrasonic environment to remove contaminants and impurities from the surface of the flexible substrate. S2: Place the cleaned flexible substrate in nitric acid to activate it; S3: FeCl3·6H2O, 2,5-dihydroxyterephthalic acid and CuCl2·2H2O are dissolved in DMF, and methanol is added. The mixture is then sonicated to obtain a Fe / Cu-MOF precursor solution. The activated flexible substrate is then immersed in the Fe / Cu-MOF precursor solution and subjected to a hydrothermal reaction to obtain the flexible Fe / Cu-MOF@CC composite film.

[0006] Preferably, during ultrasonic treatment, the frequency of the ultrasonic instrument is 30~50kHz.

[0007] Preferably, the activation treatment temperature is 70~85℃ and the treatment time is 3~5h.

[0008] Preferably, in the Fe / Cu-MOF precursor solution, the concentration of FeCl3·6H2O is 0.04~0.08M, the concentration of 2,5-dihydroxyterephthalic acid is 0.034~0.068M, and the concentration of CuCl2·2H2O is 0.04~0.08M.

[0009] Preferably, the molar ratio of FeCl3·6H2O, CuCl2·2H2O and 2,5-dihydroxyterephthalic acid is 1:(1~2):(0.85~1.7).

[0010] Preferably, the molar ratio of FeCl3·6H2O, CuCl2·2H2O and 2,5-dihydroxyterephthalic acid is 1:1:(0.85~1.7).

[0011] Preferably, the hydrothermal reaction temperature is 120~150℃ and the reaction time is 12~36h.

[0012] Preferably, the hydrothermal reaction is carried out at a temperature of 120°C for 24 hours.

[0013] A flexible Fe / Cu-MOF@CC composite film was prepared by the method described above.

[0014] The above-mentioned flexible Fe / Cu-MOF@CC composite film is used in interfacial solar water evaporation.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for preparing a flexible Fe / Cu-MOF@CC composite film. This method effectively overcomes the limitation of water molecule control caused by the single metal center and fixed electronic structure of traditional MOF materials by constructing a bimetallic synergistically regulated MOF structure combined with a conductive flexible substrate. Firstly, Fe is introduced... 3+ With Cu2+ The bimetallic center, forming a heterometallic synergistic effect, not only modulates the electronic structure of the material and enhances charge transfer capability, but also provides diverse active sites, which is conducive to the synergistic activation of water molecules and weakens the hydrogen bond network between water molecules, promoting efficient dissociation of interfacial water. Secondly, the use of a flexible conductive substrate (such as carbon paper CC) followed by surface cleaning and nitric acid activation treatment enhances the interfacial bonding between the substrate and the MOF layer, while improving the overall conductivity and thermal conductivity of the material, which is beneficial for photothermal conversion and charge transport under solar excitation. The hydrothermal method for in-situ growth of Fe / Cu-MOF thin films on the substrate ensures the uniformity and stability of the material structure, avoiding the problems of easy agglomeration and difficult recycling of traditional powder materials, and improving durability under complex water quality conditions. The synergistic effect of bimetallic doping and interface engineering enables the material to maintain efficient water evaporation performance under complex operating conditions such as high salt and long-term operation. This method, through metal composition regulation and substrate design, fundamentally optimizes the interaction mechanism between MOF materials and water molecules, significantly enhancing its application potential in solar-driven interfacial water evaporation.

[0016] Furthermore, during ultrasonic treatment, the frequency of the ultrasonic instrument is 30~50kHz. Within this frequency range, ultrasound can generate a moderate cavitation effect. This effectively peels off and removes physically adsorbed impurities such as oil and dust from the surface of the carbon cloth, while avoiding the negative effects of excessively high or low frequencies (such as incomplete cleaning or excessive erosion of the carbon fiber matrix). This ensures a clean substrate surface, providing a consistent and highly active surface for subsequent activation and MOF growth, and improving the adhesion between the MOF film and the substrate.

[0017] Furthermore, the activation treatment is performed at a temperature of 70-85°C for 3-5 hours. Treating at 70-85°C for 3-5 hours effectively introduces oxygen-containing functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH) onto the carbon cloth surface through oxidation and etching, enhancing its surface hydrophilicity and chemical activity. This mild condition ensures sufficient activation to provide abundant anchor sites for MOF crystal nucleation, while preventing excessive oxidation from damaging the mechanical strength and conductivity of the carbon cloth, thus ensuring the flexibility and structural integrity of the final composite film.

[0018] Furthermore, in the Fe / Cu-MOF precursor solution, the concentrations of FeCl3·6H2O are 0.04–0.08 M, 2,5-dihydroxyterephthalic acid is 0.034–0.068 M, and CuCl2·2H2O is 0.04–0.08 M. Controlling the concentrations of each component within this specific range ensures a sufficient and balanced supply of reactants during the hydrothermal reaction. This is beneficial for forming a MOF crystal structure with high crystallinity and few defects. Too low a concentration will result in sparse MOF growth and insufficient thickness; too high a concentration may cause excessive supersaturation of the solution, leading to homogeneous nucleation of MOF particles in the solution rather than heterogeneous growth on the substrate, resulting in particle aggregation and film inhomogeneity. Therefore, this concentration range is conducive to preparing dense, continuous, and high-performance MOF composite films.

[0019] Furthermore, the molar ratio of FeCl3·6H2O, CuCl2·2H2O, and 2,5-dihydroxyterephthalic acid is 1:(1~2):(0.5~1.7), which is crucial for forming the bimetallic Fe / Cu-MOF structure. This ensures that Fe and Cu metal ions can coexist and synergistically participate in coordination reactions, forming a MOF with a heterostructure. This bimetallic synergistic effect is key to regulating the material's electronic structure, enriching active sites, enhancing photothermal conversion efficiency, and activating water molecules. A specific ratio range helps optimize the interaction between the bimetals, thereby maximizing their ability to interfere with and dissociate the hydrogen bond network of water molecules. More preferably, the molar ratio of FeCl3·6H2O, CuCl2·2H2O, and 2,5-dihydroxyterephthalic acid is 1:1:(0.85~1.7). Setting the molar ratio of FeCl3·6H2O to CuCl2·2H2O to 1:1 achieves optimal synergy between the Fe and Cu bimetallic sites. This equimolar ratio configuration helps to construct MOF crystals with balanced electronic structure and ideal distribution of active sites, thereby exerting the best synergistic effect in light absorption, charge separation and water molecule activation, and is an important ratio for obtaining high-performance photothermal evaporation materials.

[0020] Furthermore, the hydrothermal reaction temperature is 120–150 °C, and the reaction time is 12–36 h. Hydrothermal methods are commonly used to prepare MOF materials, and the temperature and time directly determine the crystal growth quality. The temperature range of 120–150 °C provides sufficient reactivity to drive the coordination reaction between metal ions and organic ligands, forming highly crystalline MOFs. The reaction time of 12–36 h ensures that the crystals have sufficient time to nucleate, grow, and firmly anchor on the carbon cloth substrate. This mild reaction condition is conducive to forming uniform, dense MOF films with strong adhesion to the substrate, while avoiding crystal structure damage or film detachment caused by excessively vigorous reactions. The reaction temperature of 120 °C and the reaction time of 24 h are optimized optimal conditions. Under these conditions, the nucleation and growth rates of MOF crystals reach an optimal balance, enabling the preparation of Fe / Cu-MOF@CC composite films with the highest crystallinity, most regular morphology, and most stable performance. This condition ensures the consistency and reproducibility of preparation results between batches, which is of great significance for the controllable preparation and potential large-scale application of high-performance materials. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 X-ray diffraction images of the original flexible substrate (i.e., carbon cloth CC) and the Fe / Cu-MOF@CC thin film (FCMC) prepared in Example 1 of this invention; Figure 2 The images shown are SEM and EDS images of the Fe / Cu-MOF@CC thin film prepared in Example 1 of the present invention; wherein, (a) and (b) are SEM images of the original carbon cloth at different magnifications; (c) and (d) are SEM images of the prepared Fe / Cu-MOF@CC at different magnifications; (e) and (f) are EDS images of Fe and Cu elements in the Fe / Cu-MOF@CC thin film. Figure 3 The XPS spectrum of the Fe / Cu-MOF@CC thin film prepared in Example 1 of this invention is shown below. Figure 4 The Raman spectrum of Fe / Cu-MOF@CC prepared in Example 1 of this invention; Figure 5 The mass loss curve of the Fe / Cu-MOF@CC thin film prepared in Example 1 of this invention under one sun; Figure 6 Water contact angle test results for the original carbon cloth and the Fe / Cu-MOF@CC thin film prepared in Example 1 of this invention; Figure 7 The image shows the DSC spectrum of Fe / Cu-MOF@CC obtained in Example 1 of this invention. Detailed Implementation

[0023] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0024] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0025] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0026] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0027] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0028] This invention provides a method for preparing a flexible Fe / Cu-MOF@CC composite film, comprising the following steps: S1: The flexible substrate is cleaned sequentially with acetone, ethanol and deionized water in an ultrasonic environment to remove contaminants and impurities from the surface of the flexible substrate. The flexible substrate is carbon cloth, and more preferably hydrophobic carbon cloth; Preferably, during ultrasonic treatment, the frequency of the ultrasonic instrument is 30~50kHz; Wash with acetone, anhydrous ethanol and deionized water for 20 minutes in sequence.

[0029] S2: Place the cleaned flexible substrate in nitric acid to activate it; The concentration of the nitric acid is 65%~68%; The activation treatment is performed at a temperature of 70-85°C for 3-5 hours; preferably, the activation treatment is performed at a temperature of 80°C for 4 hours. S3: FeCl3·6H2O, 2,5-dihydroxyterephthalic acid and CuCl2·2H2O are dissolved in DMF, and methanol is added. The mixture is then sonicated to obtain a Fe / Cu-MOF precursor solution. The activated flexible substrate is then immersed in the Fe / Cu-MOF precursor solution and subjected to a hydrothermal reaction to obtain the flexible Fe / Cu-MOF@CC composite film.

[0030] In the Fe / Cu-MOF precursor solution, the concentration of FeCl3·6H2O is 0.04~0.08M, the concentration of 2,5-dihydroxyterephthalic acid is 0.034~0.068M, and the concentration of CuCl2·2H2O is 0.04~0.08M. The molar ratio of FeCl3·6H2O, CuCl2·2H2O and 2,5-dihydroxyterephthalic acid is 1:(1~2):(0.85~1.7), preferably 1:1:(0.85~1.7).

[0031] The hydrothermal reaction temperature is 120~150℃ and the reaction time is 12~36h. Preferably, the hydrothermal reaction temperature is 120℃ and the reaction time is 24h. Furthermore, after the hydrothermal reaction is completed, the material is naturally cooled and removed, washed with DMF and ethanol to remove unreacted reactants, and dried at 60°C overnight (12h) to obtain the flexible Fe / Cu-MOF@CC composite thin film material.

[0032] In addition, the present invention also discloses a flexible Fe / Cu-MOF@CC composite film prepared by the above method.

[0033] This invention also discloses the application of the flexible Fe / Cu-MOF@CC composite film in interfacial solar water evaporation. Thanks to the synergistic electronic activation of water molecules by the Fe / Cu bimetallic sites, this material can significantly reduce the enthalpy of water evaporation to 970 J·g. -1 Simultaneously, its superhydrophilic properties enable ultra-rapid wetting within 20ms, effectively reducing thermodynamic energy consumption and accelerating the kinetic water supply process. Under one day of sunlight, the evaporator exhibits a high efficiency of 2.31 kg·m³. -2 ·h -1The excellent evaporation rate of Fe / Cu-MOF@CC demonstrates a remarkable synergistic effect between photothermal conversion and water transport. Addressing the common problem of salt accumulation in high-salinity wastewater treatment, Fe / Cu-MOF@CC exhibits strong salt ion reflux capability and self-regeneration characteristics: even with a large amount of salt crystals deposited on the surface, the rapid water transport achieved through its fully hydrophilic channels allows the salt crystals to completely dissolve and reflux back into the bulk solution within 90 minutes, ensuring long-term stable operation of the device in complex salt environments. Furthermore, this material combines excellent mechanical flexibility, high hydrophilic flux, and efficient physical retention of organic pollutants, effectively removing dye pollutants (such as RhB) from water and exhibiting good comprehensive purification performance. These characteristics make Fe / Cu-MOF@CC a promising candidate for applications in solar-powered seawater desalination and complex wastewater treatment. The bimetallic electronic structure modulation and fully hydrophilic interface design strategy proposed in this work provides important design ideas and practical pathways for developing a new generation of high-efficiency, salt-resistant, and recyclable solar-driven water evaporation devices, promoting the development of high-performance environmental functional materials.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0036] Example 1 A method for producing a flexible Fe / Cu-MOF@CC composite thin film material includes: (1) Pretreatment of carbon cloth: First, cut the purchased carbon cloth into 3cm×3cm pieces, and then clean the carbon cloth with acetone and ethanol at 50kHz for 20min. During this period, it is cleaned with deionized water.

[0037] (2) Carbon cloth activation: The treated carbon cloth is immersed in concentrated nitric acid and treated in a constant temperature water bath at 80°C for 4 hours to introduce carboxylic acid groups and enhance surface activity. It is then rinsed repeatedly with deionized water until neutral and vacuum dried at 60°C overnight for use.

[0038] (3) Preparation of Fe / Cu-MOF precursor solution: Weigh FeCl3·6H2O (0.04M), 2,5-dihydroxyterephthalic acid (0.034M) and CuCl2·2H2O (0.04M) into 28mL of DMF, add 4mL of methanol, and sonicate for 30min to mix the system evenly.

[0039] (4) The activated carbon cloth is immersed in the Fe / Cu-MOF precursor solution to ensure complete wetting. Then it is transferred to a high-pressure reactor and hydrothermally synthesized at 120°C for 24 hours to allow MOF to nucleate and grow on the surface of the carbon cloth. After natural cooling, it is taken out, washed with DMF and ethanol to remove unreacted substances, and dried at 60°C overnight to obtain the flexible Fe / Cu-MOF@CC composite film material.

[0040] To assess the rate of solar vapor generation, the fabricated flexible Fe / Cu-MOF@CC composite thin film material and evaporator were placed on an electronic balance. The device was then irradiated with a xenon lamp solar simulator at one solar intensity, and the mass change due to moisture evaporation was continuously recorded.

[0041] Example 2 This embodiment discloses a method for preparing a flexible Fe / Cu-MOF@CC composite thin film material, including the following steps: (1) Clean the substrate In a 30kHz CNC ultrasonic cleaning instrument, carbon cloth (3cm×3cm) was cleaned sequentially with water, acetone, anhydrous ethanol, and deionized water for 20 minutes, and then placed in a disposable petri dish to dry at room temperature for 12 hours.

[0042] (2) Matrix activation The treated carbon cloth was immersed in 65% concentrated nitric acid and treated in a constant temperature water bath at 70°C for 5 hours to introduce carboxylic acid groups and enhance surface activity. It was then repeatedly rinsed with deionized water until neutral and vacuum dried overnight at 60°C for later use.

[0043] (3) Preparation of flexible Fe / Cu-MOF@CC thin films FeCl3·6H2O (0.04M), 2,5-dihydroxyterephthalic acid (0.034M), and CuCl2·2H2O (0.04M) were weighed into 28 mL of DMF, and 4 mL of methanol was added. The mixture was sonicated for 30 min to ensure homogeneity. The activated carbon cloth was immersed in the precursor solution, ensuring complete wetting, and then transferred to a high-pressure reactor. Hydrothermal synthesis was carried out at 120 °C for 30 h to allow MOF nucleation and growth on the carbon cloth surface. After natural cooling, the material was removed, washed with DMF and ethanol to remove unreacted substances, and dried overnight at 60 °C to obtain the flexible Fe / Cu-MOF@CC composite thin film material.

[0044] Experimental Example 3 A method for preparing a flexible Fe / Cu-MOF@CC composite thin film material includes the following steps: (1) Clean the substrate In a 50kHz CNC ultrasonic cleaning instrument, carbon cloth (3cm×3cm) was cleaned sequentially with water, acetone, anhydrous ethanol, and deionized water for 20 minutes, and then placed in a disposable petri dish to dry at room temperature for 12 hours.

[0045] (2) Matrix activation The cleaned carbon cloth was immersed in concentrated nitric acid and treated in a constant temperature water bath at 85°C for 3 hours to introduce carboxylic acid groups and enhance surface activity. It was then repeatedly rinsed with deionized water until neutral and vacuum dried at 60°C overnight for later use.

[0046] (3) Preparation of flexible Fe / Cu-MOF@CC thin films FeCl3·6H2O (0.08M), 2,5-dihydroxyterephthalic acid (0.068M), and CuCl2·2H2O (0.08M) were weighed into 28 mL of DMF, and 4 mL of methanol was added. The mixture was sonicated for 30 min to ensure homogeneity. The activated carbon cloth was immersed in the precursor solution, ensuring complete wetting, and then transferred to a high-pressure reactor. Hydrothermal synthesis was carried out at 130 °C for 25 h to allow MOF nucleation and growth on the carbon cloth surface. After natural cooling, the material was removed, washed with DMF and ethanol to remove unreacted substances, and dried overnight at 60 °C to obtain the flexible Fe / Cu-MOF@CC composite thin film material.

[0047] Experiment Example 4 This embodiment discloses a method for preparing a flexible Fe / Cu-MOF@CC composite thin film material, including the following steps: (1) Clean the substrate In a CNC ultrasonic cleaning instrument with a frequency of 30-50kHz, carbon cloth (2cm×2cm) was cleaned sequentially with water, acetone, anhydrous ethanol, and deionized water for 20 minutes, and then placed in a disposable petri dish to dry at room temperature for 12 hours.

[0048] (2) Matrix activation The treated carbon cloth was immersed in concentrated nitric acid and treated in a constant temperature water bath at 82°C for 4 hours to introduce carboxylic acid groups and enhance surface activity. It was then repeatedly rinsed with deionized water until neutral and vacuum dried overnight at 60°C for later use.

[0049] (3) Preparation of flexible Fe / Cu-MOF@CC thin films FeCl3·6H2O (0.04M), 2,5-dihydroxyterephthalic acid (0.068M), and CuCl2·2H2O (0.04M) were weighed into 28 mL of DMF, and 4 mL of methanol was added. The mixture was sonicated for 30 min to ensure homogeneity. The activated carbon cloth was immersed in the precursor solution, ensuring complete wetting, and then transferred to a high-pressure reactor. Hydrothermal synthesis was carried out at 130 °C for 20 h to allow MOF nucleation and growth on the carbon cloth surface. After natural cooling, the material was removed, washed with DMF and ethanol to remove unreacted substances, and dried overnight at 60 °C to obtain the flexible Fe / Cu-MOF@CC composite thin film material.

[0050] Experimental Example 5 This embodiment discloses a method for preparing a flexible Fe / Cu-MOF@CC composite thin film material, including the following steps: (1) Clean the substrate In a 40kHz CNC ultrasonic cleaning instrument, carbon cloth (3cm×3cm) was cleaned sequentially with water, acetone, anhydrous ethanol, and deionized water for 20 minutes, and then placed in a disposable petri dish to dry at room temperature for 12 hours.

[0051] (2) Matrix activation The treated carbon cloth was immersed in 68% concentrated nitric acid and treated in a constant temperature water bath at 80°C for 4 hours to introduce carboxylic acid groups and enhance surface activity. It was then repeatedly rinsed with deionized water until neutral and vacuum dried overnight at 60°C for later use.

[0052] (3) Preparation of flexible Fe / Cu-MOF@CC thin films FeCl3·6H2O (0.04M), 2,5-dihydroxyterephthalic acid (0.034M), and CuCl2·2H2O (0.04M) were weighed into 28 mL of DMF, and 4 mL of methanol was added. The mixture was sonicated for 30 min to ensure homogeneity. The activated carbon cloth was immersed in the precursor solution, ensuring complete wetting, and then transferred to a high-pressure reactor. Hydrothermal synthesis was carried out at 150 °C for 12 h to allow MOF nucleation and growth on the carbon cloth surface. After natural cooling, the material was removed, washed with DMF and ethanol to remove unreacted substances, and dried overnight at 60 °C to obtain the flexible Fe / Cu-MOF@CC composite thin film material.

[0053] Experimental Example 6 This embodiment discloses a method for preparing a flexible Fe / Cu-MOF@CC composite thin film material, including the following steps: (1) Clean the substrate In a CNC ultrasonic cleaning instrument with a frequency of 30-50kHz, carbon cloth (3cm×3cm) was cleaned sequentially with water, acetone, anhydrous ethanol, and deionized water for 20 minutes, and then placed in a disposable petri dish to dry at room temperature for 12 hours.

[0054] (2) Matrix activation The treated carbon cloth was immersed in concentrated nitric acid and treated in a constant temperature water bath at 80°C for 4 hours to introduce carboxylic acid groups and enhance surface activity. It was then repeatedly rinsed with deionized water until neutral and vacuum dried overnight at 60°C for later use.

[0055] (3) Preparation of flexible Fe / Cu-MOF@CC thin films FeCl3·6H2O (0.04M), 2,5-dihydroxyterephthalic acid (0.034M), and CuCl2·2H2O (0.04M) were weighed into 28 mL of DMF, and 4 mL of methanol was added. The mixture was sonicated for 30 min to ensure homogeneity. The activated carbon cloth was immersed in the precursor solution, ensuring complete wetting, and then transferred to a high-pressure reactor. Hydrothermal synthesis was carried out at 120 °C for 36 h to allow MOF nucleation and growth on the carbon cloth surface. After natural cooling, the material was removed, washed with DMF and ethanol to remove unreacted substances, and dried overnight at 60 °C to obtain the flexible Fe / Cu-MOF@CC composite thin film material.

[0056] The technical effects of the present invention are illustrated by the following characteristics, wherein: Figure 1 The figures show X-ray diffraction (XRD) images of the original flexible substrate (carbon cloth CC) and the Fe / Cu-MOF@CC thin film (FCMC) prepared in Example 1 of this invention. As can be seen from the figures, the XRD pattern of the original carbon cloth shows a typical broad peak around 26°, which is a characteristic peak of the (002) crystal plane of carbon materials (graphite). This indicates that the carbon cloth is mainly composed of amorphous carbon or microcrystalline graphite, with relatively low crystallinity and a simple structure. In contrast, the XRD pattern of the Fe / Cu-MOF@CC composite film shows multiple sharp and high-intensity diffraction peaks in the range of 5° to 30°. These newly appearing peak positions highly coincide with the characteristic peaks of typical MOF materials, clearly indicating that well-crystallized Fe / Cu-MOF crystals were successfully grown on the carbon cloth substrate. Compared with the original carbon cloth, the composite film has sharper peaks and higher peak intensities, indicating that the introduction of MOF significantly improves the overall crystallinity of the material.

[0057] Figure 2The images show SEM and EDS images of the Fe / Cu-MOF@CC thin film prepared in Example 1 of this invention. (a) and (b) are SEM images of the original carbon cloth at different magnifications; (c) and (d) are SEM images of the prepared Fe / Cu-MOF@CC at different magnifications; (e) and (f) are EDS images of Fe and Cu elements in the Fe / Cu-MOF@CC thin film. As can be seen from the images, the carbon cloth is composed of a large number of parallel carbon fibers with smooth and clean surfaces and uniform diameters, exhibiting a typical woven structure. This provides a good flexible substrate and conductive network for subsequent MOF material loading. Compared to the original carbon cloth, the fiber surface of the composite film is no longer smooth but is tightly coated with a large number of nanoscale particles. These particles exhibit regular polyhedral or quasi-spherical morphologies, uniform size, and are evenly distributed on the fiber surface without obvious aggregation or shedding. This indicates that Fe / Cu-MOF crystals have been successfully and uniformly grown on the carbon fiber surface, forming a composite structure. This micro / nano structure not only effectively increases the specific surface area of ​​the material, which is beneficial for light absorption and water molecule adsorption, but also provides abundant active sites for photothermal conversion. Furthermore, through methods such as... Figure 2 Figures (e) and (f) clearly show that the distribution of Fe (green) and Cu (yellow) elements on the material surface highly overlaps and covers a wide area, perfectly consistent with the particle distribution area in the SEM image. This strongly demonstrates that the Fe and Cu bimetallic sites have been successfully introduced and uniformly distributed in the MOF structure, forming a bimetallic synergistic composite material. The uniformity of elemental distribution further indicates that during the synthesis process, the two metal ions and organic ligands underwent effective co-assembly, rather than forming separate single metal phases. Therefore, the SEM and EDS results jointly confirm that Fe / Cu-MOF has been successfully and uniformly loaded onto the surface of carbon fiber, forming a structurally complete bimetallic composite film with uniform elemental distribution. This microstructure provides important structural support for the material's applications in photothermal conversion, water evaporation, and ion transport.

[0058] Figure 3 The XPS spectrum of the Fe / Cu-MOF@CC thin film prepared in Example 1 of this invention is shown. Multiple characteristic peaks can be clearly observed in the figure, corresponding to different elements: a C1s peak at approximately 284 eV, an N1s peak at approximately 400 eV, an O1s peak at approximately 532 eV, a Fe 2p peak at approximately 711 eV, and a Cu 2p peak at approximately 934 eV. The presence of these peaks indicates that carbon, nitrogen, oxygen, iron, and copper elements were successfully introduced into the composite material, consistent with the raw material composition, confirming the successful synthesis and loading of Fe / Cu-MOF. Furthermore, no obvious impurity peaks were observed, indicating high material purity and a controllable synthesis process.

[0059] Figure 4The image shows the Raman spectrum of Fe / Cu-MOF@CC prepared in Example 1 of this invention. As can be seen from the figure, ~3100 cm⁻¹ -1 (Marked as FW) is attributed to very strong hydrogen bonding or specific lattice vibrational coupling. ~3200cm -1 This is typically attributed to the OH stretching vibration in a strong hydrogen-bonded network, corresponding to bound water or interlayer water. This indicates the presence of numerous hydrophilic sites (such as metal clusters or functional groups) on the surface of Fe / Cu-MOF materials, capable of adsorbing water molecules through strong hydrogen bonding to form a stable hydrated layer. This is crucial for constructing water transport channels and activating interfacial water. ~3100cm -1 And ~3200cm -1 FW stands for free / weakly hydrogen-bonded water; ~3400cm -1 This is typically attributed to a weak hydrogen bond network or the OH stretching vibration of free water. These water molecules may be located within the pores of the MOF or in the material's loose structure, where they are less bound and have better mobility. ~3600 cm⁻¹ -1 (Labeled as IW) is typically attributed to isolated hydroxyl groups or weakly bound physisorbed water (such as non-hydrogen-bonded OH). This may originate from uncoordinated hydroxyl groups on the MOF surface or from a small number of physisorbed water molecules. ~3400cm -1 And ~3600 cm -1 IW stands for isolated / weakly bound water / hydroxyl group; The peak intensity ratio of IW to FW is approximately 1:1.1, indicating the presence of a significant proportion of free or weakly bound water in the material. In photothermal evaporation applications, weakly bound water molecules are more easily evaporated because they require less energy to break hydrogen bonds. Therefore, this Raman characteristic suggests that the Fe / Cu-MOF@CC material possesses excellent water molecule activation capabilities and potentially high evaporation efficiency.

[0060] Furthermore, the spectrum exhibits broadened peaks, a typical characteristic of the disordered hydrogen bond network in amorphous or microcrystalline materials. This indirectly confirms that MOF materials possess abundant porous structures and surface functional groups, resulting in water molecules existing in various chemical environments. Therefore, Raman spectroscopy analysis shows that Fe / Cu-MOF@CC materials can adsorb a large number of water molecules, and these water molecules exist in multiple states ranging from strongly bound to weakly bound. In particular, the presence of a high proportion of weakly bound water (FW) is beneficial for reducing the energy consumption of water evaporation, thereby improving the performance of solar-driven water evaporation. This result provides important mechanistic support for the application of this material in the field of photothermal evaporation.

[0061] Figure 5The figure shows the mass loss curve of the Fe / Cu-MOF@CC thin film prepared in Example 1 of this invention under sunlight. As can be seen from the figure, the mass of the film exhibits a highly linear decreasing trend during the 60-minute continuous illumination test. This indicates that the system has reached a steady-state photothermal evaporation process. Under steady-state conditions, the heat generated by light absorption is stably used for the phase change (evaporation) of liquid water, without performance fluctuations caused by material failure, dry burning, or obstructed water transport. The figure shows that the mass change is approximately -2.3 kg m over 60 minutes (i.e., 1 hour). -2 Therefore, the average evaporation rate of this material under one sun can be estimated to be approximately 2.3 kg / m³. -2 h -1 This evaporation rate is significantly higher than the natural evaporation rate of pure water (typically around 0.5~0.6 kg m³). -2 h -1 The results indicate that the Fe / Cu-MOF@CC thin film possesses excellent photothermal conversion capabilities, efficiently converting solar energy into heat energy to drive water evaporation. This superior evaporation performance is attributed to the material's properties. Firstly, both the MOF material itself and the carbon cloth substrate exhibit good light absorption over a wide spectral range. Secondly, the Raman spectroscopy reveals a high proportion of weakly bound water, meaning water molecules are more easily evaporated. Simultaneously, the porous structure and hydrophilicity of the MOF facilitate a continuous water supply. Furthermore, the Fe / Cu bimetallic sites may enhance the photogenerated carrier separation efficiency, further improving the photothermal conversion efficiency. These results strongly demonstrate the significant potential of the Fe / Cu-MOF@CC thin film prepared in this invention for solar-driven water evaporation applications.

[0062] Figure 6The figures show the water contact angle test results for the original carbon cloth and the Fe / Cu-MOF@CC film prepared in Example 1 of this invention. As can be seen from the figures, the water droplet just contacts the surface of the original carbon cloth at 0 seconds. Subsequently, over a period of 20 to 120 seconds, although the contact angle decreases, it remains at a relatively large angle (greater than 90°), and the water droplet does not completely penetrate or spread within a longer time (120 seconds). This indicates that the surface of the original carbon cloth is hydrophobic. This hydrophobicity usually stems from the low surface energy of the carbon material itself and the smooth structure of the fiber surface, which is unfavorable for the rapid adsorption and transport of water molecules. In contrast, water exhibits an extremely fast response on the Fe / Cu-MOF@CC composite film surface. From the initial contact at 0 seconds, to 0.01 seconds, 0.02 seconds… up to 0.05 seconds, the water droplet spreads rapidly, and the contact angle decreases sharply. Within an extremely short time (far less than 0.05 seconds), the water droplet has completely wetted the surface and begins to penetrate inward, exhibiting an instantaneous wetting phenomenon. This clearly demonstrates that the Fe / Cu-MOF@CC film surface possesses excellent hydrophilicity, even reaching a superhydrophilic state. This is primarily due to the introduction of the MOF material, which brings a large number of polar functional groups (such as hydroxyl and carboxyl groups) and metal active sites (Fe, Cu). These hydrophilic groups significantly increase the surface energy of the material, enhancing its adsorption force on water molecules. Furthermore, the rough nanoparticle structure revealed by SEM images further promotes water spreading and penetration through capillary forces. This transformation from hydrophobic to superhydrophilic is crucial for water evaporation at the solar interface. Superhydrophilicity ensures that liquid water can be rapidly and continuously transported from the bottom to the photothermal conversion layer (i.e., the MOF surface) through capillary action, thereby maintaining a continuous and efficient evaporation process, preventing dry burning due to insufficient water replenishment, and ensuring the stability of the high evaporation rate.

[0063] Figure 7The figure shows the DSC spectrum of Fe / Cu-MOF@CC prepared in Example 1 of this invention. As can be seen, pure water exhibits a sharp and strong endothermic peak at approximately 15 min, corresponding to the liquid-gas phase transition (evaporation) of water. This is a typical manifestation of the latent heat absorbed by bulk liquid water when reaching its boiling point or evaporating under specific conditions. In contrast, the endothermic peak of water confined within Fe / Cu-MOF@CC shifts towards a shorter time (approximately 13-14 min). In DSC testing, this typically indicates a lower temperature or faster response to the phase transition. This suggests that water molecules in the MOF material are affected by surface interactions, weakening their hydrogen bond network and making them more susceptible to phase transitions. For pure water, the area under the peak is 2444 J / g, a value close to the theoretical latent heat of vaporization of water (approximately 2260 J / g), representing the energy required to break the strong hydrogen bond network in bulk water. The peak area under the confined water is significantly reduced, to only 1258 J / g, which means that the energy required to convert water molecules in the MOF channels or surface into a gaseous state is greatly reduced (only about half that of pure water). This directly confirms the inference from Raman spectroscopy that water molecules on the material surface are in a weakly bound state. The microstructure of this weakly bound water (free water or weakly hydrogen-bonded water) is closer to that of the gaseous state, thus resulting in a lower phase transition energy barrier. In addition, the sharp peak shape of pure water indicates a concentrated and intense phase transition, while the peak shape of confined water is relatively broadened and the lag time is shortened, indicating that the evaporation of water molecules in porous media is a complex process affected by pore structure, surface diffusion, and heat and mass transfer, but its overall thermal response speed is faster. Therefore, Fe / Cu-MOF@CC materials can significantly reduce the enthalpy of water vaporization. This low-energy evaporation characteristic is due to the unique microenvironment of MOF pre-activating water molecules and weakening their hydrogen bonding.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a flexible Fe / Cu-MOF@CC composite film, characterized in that, Includes the following steps: S1: The flexible substrate is cleaned sequentially with acetone, ethanol and deionized water in an ultrasonic environment to remove contaminants and impurities from the surface of the flexible substrate. S2: Place the cleaned flexible substrate in nitric acid to activate it; S3: FeCl3·6H2O, 2,5-dihydroxyterephthalic acid and CuCl2·2H2O are dissolved in DMF, and methanol is added. The mixture is then sonicated to obtain a Fe / Cu-MOF precursor solution. The activated flexible substrate is then immersed in the Fe / Cu-MOF precursor solution and subjected to a hydrothermal reaction to obtain the flexible Fe / Cu-MOF@CC composite film.

2. The method for preparing a flexible Fe / Cu-MOF@CC composite film according to claim 1, characterized in that, During ultrasonic treatment, the frequency of the ultrasonic instrument is 30~50kHz.

3. The method for preparing a flexible Fe / Cu-MOF@CC composite film according to claim 1, characterized in that, The activation treatment is performed at a temperature of 70-85°C for 3-5 hours.

4. The method for preparing a flexible Fe / Cu-MOF@CC composite film according to claim 1, characterized in that, In the Fe / Cu-MOF precursor solution, the concentration of FeCl3·6H2O is 0.04~0.08M, the concentration of 2,5-dihydroxyterephthalic acid is 0.034~0.068M, and the concentration of CuCl2·2H2O is 0.04~0.08M.

5. The method for preparing a flexible Fe / Cu-MOF@CC composite film according to claim 1, characterized in that, The molar ratio of FeCl3·6H2O, CuCl2·2H2O, and 2,5-dihydroxyterephthalic acid is 1:(1~2):(0.85~1.7).

6. The method for preparing a flexible Fe / Cu-MOF@CC composite film according to claim 5, characterized in that, The molar ratio of FeCl3·6H2O, CuCl2·2H2O and 2,5-dihydroxyterephthalic acid is 1:1:(0.85~1.7).

7. The method for preparing a flexible Fe / Cu-MOF@CC composite film according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 120-150°C for 12-36 hours.

8. The method for preparing a flexible Fe / Cu-MOF@CC composite film according to claim 6, characterized in that, The hydrothermal reaction was carried out at a temperature of 120°C for 24 hours.

9. A flexible Fe / Cu-MOF@CC composite film, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The application of the flexible Fe / Cu-MOF@CC composite film as described in claim 9 in interfacial solar water evaporation.

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