A modified MOF@HNTs / polypropylene composite coating layer, a preparation method and application thereof

Abstract

The application belongs to the technical field of functional materials, and provides a modified MOF@HNTs / polypropylene composite coating as well as a preparation method and application thereof. After copper nitrate trihydrate, 2,3,6,7,10,11-hexahydroxytriphenylamine hydrate and a solvent are mixed, halloysite nanotubes are added to react to obtain MOFs@HNT. The MOFs@HNT suspension, hexadecyl trimethoxysilane, tetraethyl orthosilicate and ammonia water are mixed to obtain hydrophobic modified MOFs@HNT. After the polypropylene solution and the hydrophobic modified MOFs@HNT are mixed and then solidified, the modified MOF@HNT / polypropylene composite coating is obtained. The MOFs@HNT endows the coating with solar light absorption capacity and photothermal conversion performance. The polypropylene matrix ensures good adhesion and chemical protection performance. The composite coating can also be applied in the field of self-cleaning car paint due to its excellent superhydrophobicity and self-cleaning performance, and effectively realizes automatic peeling of surface pollutants, and improves the convenience of vehicle appearance maintenance.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, and in particular to a modified MOF@HNTs / polypropylene composite coating, its preparation method, and its application. Background Technology

[0002] Superhydrophobic surfaces are a type of surface that achieves a Cassie-Baxter wetting state with a water contact angle greater than 150° and a roll-off angle less than 10° by constructing micro- and nano-level hierarchical rough structures and modifying them with low surface energy materials. This state can effectively delay water droplet freezing and reduce ice adhesion, making superhydrophobic surfaces a promising passive anti-icing strategy.

[0003] However, the micro-nano structure of traditional superhydrophobic coatings is easily damaged under long-term mechanical wear, contaminant deposition, or extreme low-temperature and high-humidity environments, leading to a decline in hydrophobic properties and a significant reduction in anti-icing effectiveness. Especially under sustained low-temperature conditions, passive anti-icing mechanisms alone are insufficient to completely prevent the formation and accumulation of ice crystals. Therefore, providing a hydrophobic coating that is easy to prepare, has excellent performance, and is highly adaptable to various environments has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to overcome the deficiencies in the prior art and provide a modified MOF@HNTs / polypropylene composite coating, its preparation method, and its application.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a modified MOF@HNTs / polypropylene composite coating, comprising the following steps: (1) Copper nitrate trihydrate, 2,3,6,7,10,11-hexahydroxytriphenylene hydrate and solvent were mixed and then halloysite nanotubes were added to react and MOFs@HNT were obtained; (2) Mix MOFs@HNT suspension, hexadecyltrimethoxysilane, tetraethyl silicate and ammonia to obtain hydrophobically modified MOFs@HNT; (3) After mixing the polypropylene solution and the hydrophobic modified MOFs@HNT, the mixture is cured to obtain the modified MOF@HNTs / polypropylene composite coating.

[0006] Preferably, the solvent in step (1) comprises N,N-dimethylformamide and water. The volume ratio of N,N-dimethylformamide to water is 1:5~15; The ratio of copper nitrate trihydrate, 2,3,6,7,10,11-hexahydroxytriphenylene hydrate, solvent, and halloysite nanotubes is 0.5~1.5g:6~7g:80~120mL:2~3g.

[0007] Preferably, the reaction temperature in step (1) is 80~90℃ and the time is ≥15h.

[0008] Preferably, the MOFs@HNT suspension in step (2) contains MOFs@HNT and a solvent; The solvents include ethanol, water, and ammonia. The volume ratio of ethanol, water, and ammonia is 80~100:8~10:1; The ratio of MOFs@HNT to solvent is 1g:80~120mL.

[0009] Preferably, in step (2), the ratio of MOFs@HNT, hexadecyltrimethoxysilane, tetraethyl silicate and ammonia in the MOFs@HNT suspension is 1g: 5~10mL: 1~2mL: 0.3~1mL.

[0010] Preferably, the mixing temperature in step (2) is 20~30℃ and the time is ≥2h.

[0011] Preferably, the polypropylene solution in step (3) contains atactic polypropylene and xylene; The ratio of random polypropylene to xylene is 0.3g: 20~30mL; In step (3), the mass ratio of hydrophobically modified MOFs@HNT to atactic polypropylene in the polypropylene solution is 1~5:1.

[0012] Preferably, the curing temperature in step (3) is 70~90℃ and the time is ≥2h.

[0013] The present invention also provides a method for preparing the modified MOF@HNTs / polypropylene composite coating to obtain the modified MOF@HNTs / polypropylene composite coating.

[0014] This invention also provides the application of the modified MOF@HNTs / polypropylene composite coating in hydrophobic materials and self-cleaning car covers.

[0015] This invention provides a modified MOF@HNTs / polypropylene composite coating. The MOFs@HNTs are obtained by mixing copper nitrate trihydrate, 2,3,6,7,10,11-hexahydroxytriphenylene hydrate, and a solvent, followed by the addition of halloysite nanotubes. A hydrophobic modified MOFs@HNTs are obtained by mixing a MOFs@HNTs suspension, hexadecyltrimethoxysilane, tetraethyl silicate, and ammonia. Finally, a polypropylene solution is mixed with the hydrophobic modified MOFs@HNTs and cured to obtain the modified MOF@HNTs / polypropylene composite coating.

[0016] This invention selects atactic polypropylene (aPP), which possesses inherent hydrophobicity, good chemical stability, and low cost, as the film-forming matrix. It innovatively introduces hydrophobically modified metal-organic frameworks / halostone nanotubes (MOFs@HNT) composite nanoparticles, which serve the dual function of photothermal fillers and micro / nanostructure building blocks. A simple one-step spraying method was used to successfully prepare a MOFs@HNT / aPP composite coating on the substrate surface. This design aims to achieve a synergistic integration of superhydrophobicity and photothermal conversion performance: MOFs@HNT not only provides the rough structure required to construct a superhydrophobic surface, but its MOF components also endow the coating with broad-spectrum solar light absorption and excellent photothermal conversion performance; the polypropylene matrix ensures good adhesion and chemical protection of the coating. This composite coating provides a new material selection and technical approach for intelligent anti-icing / de-icing protection of key equipment such as wind turbine blades, power transmission lines, and aerospace vehicles under cold conditions. Attached Figure Description

[0017] Figure 1 SEM images of halloysite nanotubes and MOFs@HNT in Example 1; Figure 2 XPS spectra of HNT and MOFs@HNT in Example 1; Figure 3 The infrared spectra of MOFs@HNT and hydrophobically modified MOFs@HNT in Example 1 are shown below. Figure 4 SEM images of modified MOF@HNTs / polypropylene composite coatings with different proportions in Example 1; Figure 5 The image shows the wettability of the modified MOF@HNTs / polypropylene composite coatings with different proportions in Example 1. Figure 6 The graph shows the photothermal conversion performance test results of the modified MOF@HNTs / polypropylene composite coating with a ratio of 4:1 of hydrophobic modified MOFs@HNTs and random polypropylene in the polypropylene solution in Example 1. Figure 7 The image shows the anti-icing results of the modified MOF@HNTs / polypropylene composite coating with a ratio of 4:1 in hydrophobic modified MOFs@HNTs and atactic polypropylene in the polypropylene solution in Example 1. Figure 8 This is a diagram showing the water droplet freezing process of the modified MOF@HNTs / polypropylene composite coating with a random polypropylene ratio of 4:1 in a polypropylene solution under a light intensity of 0.1 sun in Example 1. Figure 9The image shows the de-icing results of the modified MOF@HNTs / polypropylene composite coating with a ratio of 4:1 of hydrophobic modified MOFs@HNTs and random polypropylene in a polypropylene solution under 1 sun light intensity in Example 1. Figure 10 The diagram shows the self-cleaning performance of the modified MOF@HNTs / polypropylene composite coating with a ratio of 4:1 in hydrophobic modified MOFs@HNTs and atactic polypropylene in the polypropylene solution in Example 1. Figure 11 The mechanical durability results of the modified MOF@HNTs / polypropylene composite coating with a ratio of 4:1 in hydrophobic modified MOFs@HNTs and atactic polypropylene in the polypropylene solution are shown in Example 1. Figure 12 The graph shows the chemical stability results of the modified MOF@HNTs / polypropylene composite coating with a ratio of 4:1 in hydrophobic modified MOFs@HNTs and atactic polypropylene in the polypropylene solution in Example 1. Detailed Implementation

[0018] This invention provides a method for preparing a modified MOF@HNTs / polypropylene composite coating, comprising the following steps: (1) Copper nitrate trihydrate, 2,3,6,7,10,11-hexahydroxytriphenylene hydrate and solvent were mixed and then halloysite nanotubes were added to react and MOFs@HNT were obtained; (2) Mix MOFs@HNT suspension, hexadecyltrimethoxysilane, tetraethyl silicate and ammonia to obtain hydrophobically modified MOFs@HNT; (3) After mixing the polypropylene solution and the hydrophobic modified MOFs@HNT, the mixture is cured to obtain the modified MOF@HNTs / polypropylene composite coating.

[0019] In this invention, the solvent in step (1) comprises N,N-dimethylformamide and water.

[0020] In this invention, the volume ratio of N,N-dimethylformamide to water is preferably 1:5 to 15, more preferably 1:6 to 14, and even more preferably 1:8 to 12.

[0021] In this invention, the preferred ratio of copper nitrate trihydrate, 2,3,6,7,10,11-hexahedroxytriphenylene hydrate, solvent, and halloysite nanotubes is 0.5~1.5g:6~7g:80~120mL:2~3g, more preferably 0.6~1.4g:6.2~6.8g:85~115mL:2.2~2.8g, and even more preferably 0.8~1.2g:6.4~6.6g:90~110mL:2.4~2.6g.

[0022] In this invention, the mixing time in step (1) is preferably ≥10 min, more preferably ≥20 min, and even more preferably ≥30 min.

[0023] In this invention, the reaction temperature in step (1) is preferably 80~90℃, more preferably 82~88℃, and even more preferably 84~86℃; the time is preferably ≥15h, more preferably ≥18h, and even more preferably ≥20h; the rotation speed is preferably 400~600rpm, more preferably 450~550rpm, and even more preferably 480~520rpm.

[0024] In this invention, after the reaction in step (1) is completed, the resulting suspension is filtered and the solid is dried. The drying temperature is preferably 80~90℃, more preferably 82~88℃, and even more preferably 84~86℃. MOFs@HNT are obtained by drying to constant weight.

[0025] In this invention, the MOFs@HNT suspension in step (2) contains MOFs@HNT and a solvent.

[0026] In this invention, the solvent comprises ethanol, water, and ammonia.

[0027] In this invention, the volume ratio of ethanol, water and ammonia is preferably 80~100:8~10:1, more preferably 85~95:8.5~9.5:1, and even more preferably 88~92:8.8~9.2:1.

[0028] In this invention, the preferred ratio of MOFs@HNT to solvent is 1g:80~120mL, more preferably 1g:85~115mL, and even more preferably 1g:90~110mL.

[0029] In this invention, MOFs@HNT are dispersed in a solvent and stirred and sonicated sequentially. The stirring time is preferably ≥10 min, more preferably ≥20 min, and more preferably ≥30 min; the sonication time is preferably ≥5 min, more preferably ≥10 min, and more preferably ≥20 min; after sonication, a MOFs@HNT suspension is obtained.

[0030] In this invention, the preferred ratio of MOFs@HNT, hexadecyltrimethoxysilane, tetraethyl silicate and ammonia in the MOFs@HNT suspension in step (2) is 1g:5~10mL:1~2mL:0.3~1mL, more preferably 1g:6~9mL:1.2~1.8mL:0.4~0.8mL, and even more preferably 1g:7~8mL:1.4~1.6mL:0.5~0.7mL.

[0031] In this invention, the mixing temperature in step (2) is preferably 20~30℃, more preferably 22~28℃, and even more preferably 24~26℃; the time is preferably ≥2h, more preferably ≥3h, and even more preferably ≥4h.

[0032] In this invention, after mixing in step (2), the mixture is centrifuged, filtered, and dried to obtain hydrophobically modified MOFs@HNT.

[0033] In this invention, the polypropylene solution in step (3) contains atactic polypropylene and xylene.

[0034] In this invention, the preferred ratio of atactic polypropylene to xylene is 0.3g:20~30mL, more preferably 0.3g:22~28mL, and even more preferably 0.3g:24~26mL.

[0035] In this invention, random polypropylene and xylene are mixed. The mixing temperature is preferably 90~110℃, more preferably 95~105℃, and even more preferably 98~102℃. The mixing time is preferably ≥4h, more preferably ≥5h, and even more preferably ≥6h. Stirring is maintained during the mixing process to obtain a polypropylene solution.

[0036] In this invention, the mass ratio of hydrophobically modified MOFs@HNT to atactic polypropylene in the polypropylene solution in step (3) is preferably 1~5:1, more preferably 2~4:1, and even more preferably 2.5~3:1.

[0037] In this invention, the mixing in step (3) is ultrasound, and the mixing time is preferably ≥30 min, more preferably ≥50 min, and even more preferably ≥60 min.

[0038] In this invention, the curing temperature in step (3) is preferably 70~90℃, more preferably 75~85℃, and even more preferably 78~82℃; the time is preferably ≥2h, more preferably ≥3h, and even more preferably ≥4h.

[0039] The present invention also provides a method for preparing the modified MOF@HNTs / polypropylene composite coating to obtain the modified MOF@HNTs / polypropylene composite coating.

[0040] This invention also provides the application of the modified MOF@HNTs / polypropylene composite coating in hydrophobic materials and self-cleaning car covers.

[0041] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] The specifications and manufacturers of each material in the embodiments are shown in Table 1.

[0043] Table 1. Specifications and Suppliers of Various Materials

[0044] Example 1

[0045] 0.97 g of copper nitrate trihydrate and 6.5 g of HHTP were added sequentially to 100 ml of DMF / H2O mixture (v / v = 1 / 10) and stirred for 10 min. Then, 2.5 g of HNT nanotubes were added to the above solution, and the mixture was stirred in a water bath (85℃, 500 r / min) for 15 h to form a MOFs@HNT suspension. Finally, the MOFs@HNT nanotubes were filtered and dried in an oven at 85℃ to obtain MOFs@HNT.

[0046] 1 g of MOFs@HNT was dispersed in 100 ml of solvent (ethanol, water, and ammonia in a volume ratio of 90:9:1), stirred for 10 min, and then sonicated at 25 °C for 5 min. Subsequently, 5 ml of HDTMS and 1 ml of TEOS were added to the suspension, followed by the addition of 0.3 mL of ammonia. The mixture was stirred at 25 °C for 2 h to form a MOFs@HNT suspension. Finally, the hydrophobically modified MOFs@HNT was obtained by centrifugation, filtration, and drying.

[0047] First, add 0.3 g of aPP to 20 mL of xylene. Stir the mixture at 100 °C for 4 h using a magnetic stirrer to obtain a polypropylene solution. Add MOFs@HNT to the polypropylene solution according to the following ratios (the mass ratio of hydrophobic modified MOFs@HNT to atactic polypropylene in the polypropylene solution is 1:1, 2:1, 3:1, 4:1, and 5:1, respectively). After ultrasonic dispersion for 30 min, spray the mixture onto the substrate surface and cure it at 80 °C for 2 h to obtain a modified MOF@HNTs / polypropylene composite coating.

[0048] The microstructure of pristine halloysite nanotubes (HNTs) and MOFs@HNTs was systematically characterized using scanning electron microscopy (SEM), and the results are as follows: Figure 1 As shown, Figure 1 In the images, (a) represents halloysite nanotubes (HNTs), and (b) represents MOFs@HNTs. The original HNTs exhibit a typical one-dimensional hollow tubular structure with smooth, uniform wall surfaces, free of significant defects or deposits, and with sharp, clear outlines, consistent with the intrinsic morphological characteristics of natural halloysite nanotubes. After in-situ growth and modification with MOFs, the tubular framework of the HNTs remains intact, but the surface morphology undergoes a significant transformation: the originally smooth walls are tightly covered by a large number of uniformly distributed secondary nanostructures. These secondary structures are orderly anchored along the HNT axis, forming dense nanocrystal clusters in local areas, with tight interfacial bonding and no obvious detachment or aggregation.

[0049] XPS analysis was performed on HNT and MOFs@HNT, and the resulting XPS spectra are shown below. Figure 2 As shown, Figure 2 In the image, (a) shows the full-range spectrum of HNT and MOFs@HNT, (b) shows the high-resolution spectrum of Cu2p, (c) shows the high-resolution spectrum of C, and (d) shows the high-resolution spectrum of Si. It can be observed that the Cu2p spectrum of MOFs@HNT clearly shows four binding energy peaks: 934.7 eV, 941.5 eV, 944.8 eV, and 954.6 eV. The first peak corresponds to Cu2p... 3 / 2 The second and third peaks correspond to satellite peaks of Cu(II), and the fourth peak corresponds to Cu 2p. 1 / 2 .

[0050] To investigate whether hexadecyltrimethoxysilane (HDTMS) successfully modified MOFs@HNT, the complex before and after modification was characterized using infrared spectroscopy. The results are as follows: Figure 3 As shown, Figure 3 In the image, (a) shows the FTIR spectra of MOFs@HNT and hydrophobically modified MOFs@HNT, (b) shows the XPS spectrum of hydrophobically modified MOFs@HNT, and (c) shows the XRF spectrum of hydrophobically modified MOFs@HNT. From (a), it can be seen that compared to MOFs@HNT, the hydrophobically modified MOFs@HNT exhibits better XRF performance at 2850 cm⁻¹. -1 and 2940 cm -1 The new peaks appearing nearby correspond to the stretching and bending vibrations of CH, respectively. In summary, HDTMS has been successfully grafted onto the MOFs@HNT surface. As shown in (b), the Cu peak signal is missing, while the C peak signal is enhanced. This is because HDTMS covers the MOFs@HNT, and the XPS detection depth is very shallow, only a few nanometers, indicating a good modification effect. As shown in (c), the Cu element is uniformly distributed in the sample, indicating that the synthesized MOFs@HNT is very uniform, which is beneficial to the photothermal conversion performance of the coating.

[0051] The morphology of modified MOF@HNTs / polypropylene composite coatings with different hydrophobic modified MOFs@HNTs and random polypropylene ratios in polypropylene solutions was characterized by SEM. The results are as follows: Figure 4 As shown, Figure 4In the figures, (a) to (e) are composite coatings with a ratio of 1:1, 2:1, 3:1, 4:1, and 5:1 of hydrophobically modified MOFs@HNT and atactic polypropylene in the polypropylene solution at a depth of 100 μm; (f) to (j) are composite coatings with a ratio of 1:1, 2:1, 3:1, 4:1, and 5:1 of hydrophobically modified MOFs@HNT and atactic polypropylene in the polypropylene solution at a depth of 10 μm. Compared with pure aPP, the surface of MOFs@HNT / aPP coatings with different ratios will have a portion of MOFs@HNT coated with aPP resin to a certain extent. When MOFs@HNT:aPP=1:1, the content of MOFs@HNT is relatively low, and the coating surface has some protrusions, accompanied by a large number of flat areas, which are composed of atactic polypropylene with very poor crystallinity. As the content of MOFs@HNT increases, the flat areas on the coating surface gradually decrease, and the secondary micro-nano structures formed by MOFs@HNT gradually appear. When the ratio of MOFs@HNT:aPP is 4:1, the mixture reaches its optimal state, exhibiting the best surface microstructure. However, as the MOFs@HNT content further increases, MOFs@HNT become dominant, leading to significant agglomeration. The resin is unable to hold the MOFs@HNT in place, resulting in a substantial decrease in the coating's mechanical properties and eventual peeling.

[0052] The wettability of modified MOF@HNTs / polypropylene composite coatings with different ratios was tested using a contact angle meter. The results are as follows: Figure 5As shown, the ratio of hydrophobically modified MOFs@HNT to aPP has a significant impact on the hydrophobicity of the coating: at a ratio of 1:1, the coating exhibits poor hydrophobicity, with a contact angle of only 120.3° and a roll-off angle greater than 120°, indicating strong adhesion of water to the surface and almost no water droplet roll-off. With increasing MOFs@HNT content, the hydrophobicity of the coating surface gradually improves. At a ratio of 2:1, the contact angle increases to 140.5°, while the roll-off angle decreases to 38°. At a ratio of 3:1, the contact angle reaches 148.7°, and the roll-off angle further decreases to 12°. At a ratio of 4:1, the contact angle continues to increase to 162.5°, and the roll-off angle drops to as low as 3°, demonstrating excellent superhydrophobic properties. When the MOFs@HNT content continues to increase, reaching a ratio of 5:1, the contact angle of the coating begins to show a decreasing trend. Overall, the hydrophobicity of the coating increases with the increase of the MOFs@HNT addition ratio, but excessive addition is detrimental to the coating's wettability. Analysis of the coating's surface morphology reveals that the change in wettability is due to alterations in its structure. Insufficient MOFs@HNT results in exposed aPP on the coating surface, leading to surface inhomogeneity and poor hydrophobicity. At a 3:1 ratio, the coating surface tends towards uniformity, but the micro / nano structure of MOFs@HNT is not fully realized, resulting in a coating that approaches superhydrophobicity. At a 4:1 ratio, a multi-level micro / nano structure forms on the coating surface, achieving a good superhydrophobic state. However, as MOFs@HNT continues to be added, aggregation begins, leading to a decrease in hydrophobicity.

[0053] The following tests were conducted using a modified MOF@HNTs / polypropylene composite coating with a ratio of 4:1, with the coated glass and the original glass used as a control.

[0054] Photothermal conversion performance was tested using a xenon lamp to simulate sunlight, and a thermal infrared imager was used to record the temperature change of the coating surface at room temperature (20℃±1℃). The results are as follows: Figure 6 As shown, Figure 6 In the image, (a) shows the temperature-time curve at 0.1 sun, (b) shows the infrared thermal image at 0.1 sun, (c) shows the temperature-time curve at 1 sun, and (d) shows the infrared thermal image at 1 sun. 1 sun = 96 mW / cm² 2As shown in (a), the surface temperature of the original glass did not change significantly with the extension of illumination time, increasing by only 2.4℃ after 5 minutes of illumination; the surface temperature of the coated glass showed a significant upward trend, especially in the first 2 minutes of illumination, with a rapid heating rate of 17.5℃, after which the heating rate gradually slowed down and stabilized. After 5 minutes of illumination, the surface temperature of the coated glass reached 41.3℃, an increase of 21.3℃ from the initial temperature; (b) shows that the surface temperature of the coated glass increased significantly with the increase of illumination time, while the temperature change of the original glass was slight; (c) shows that after 5 minutes of illumination, the surface temperature of the original glass increased by only 20.2℃, while the surface temperature of the coated glass increased by 48.4℃, reaching a final temperature of 68.4℃, demonstrating excellent photothermal conversion capability. The corresponding infrared thermal imaging image in (d) further confirms the significant increase in the surface temperature of the coating, and the final surface temperature of the coating also increases with the increase of light intensity. This phenomenon is mainly attributed to the MOFs@HNT component introduced into the coating. When the light intensity increases, this component can absorb more light energy and release more heat through its excellent photothermal conversion ability, thereby increasing the surface temperature of the coating.

[0055] The sample was placed on a cooling platform set at -20℃. After the temperature stabilized, 20 μL of deionized water was added to the sample surface using a pipette. The entire process of the water droplet from contact with the substrate to complete freezing was observed and recorded in real time, and the results were captured with a camera. Figure 7 As shown, Figure 7 In the figure, (a) is the original glass and (b) is the coated glass. As can be seen from the figure, the entire freezing process is mainly divided into two stages: the pre-cooling stage and the ice growth stage. In the pre-cooling stage, due to the increased reflectivity of ice to light, the water droplets gradually become turbid; in the ice growth stage, the ice interface slowly grows from the bottom to the top, eventually forming an ice block with a pointed tip.

[0056] For the original glass, the precooling phase lasted only 26 s, and the freezing process was completed in 43 s. In contrast, the precooling phase of the droplets on the coated glass surface lasted 220 s, and the complete freezing time reached 440 s, which is about 10 times that of the original glass.

[0057] This significant delay in icing is primarily attributed to the unique surface properties of the superhydrophobic coating. On one hand, the air layer trapped within the rough structure of the coating has a low thermal conductivity, effectively slowing down heat conduction between the water droplet and the substrate. On the other hand, the high contact angle of the coating significantly reduces the actual contact area between the water droplet and the solid surface, thereby further delaying heat transfer and ice crystal nucleation.

[0058] To further simulate the anti-icing performance of the coating in a real-world environment, both the original and coated glass slides were placed on a cold stage at -20°C. 20 μL of deionized water was dropped onto each slide, and they were continuously irradiated under 0.1°C sunlight. The icing behavior of the water droplets was observed and recorded. The results are as follows: Figure 8 As shown, Figure 8 In the diagram, (a) represents the original glass and (b) represents the coated glass. The experimental results show that under simulated sunlight conditions, water droplets on the surface of the original glass begin to become cloudy at 18 s, marking the end of the pre-cooling stage, and freeze completely at 48 s. This freezing rate is basically consistent with that of the original glass under no-light conditions, indicating that even with weak light, ordinary glass is unlikely to slow down the freezing process at low temperatures.

[0059] In contrast, the coated glass surface exhibited significantly better anti-icing performance. Water droplets only became turbid after 470 s and did not freeze completely until 950 s. Compared to the original glass, the coating improved the icing delay time by nearly 20 times. This superior performance is mainly attributed to the synergistic effect of the coating's photothermal effect and superhydrophobic properties: under low-intensity light, the coating absorbs light energy and converts it into heat, slowing down the heat exchange between the water droplets and the cold surface. At the same time, the air layer trapped on the coating surface further reduces the heat conduction efficiency, thereby effectively inhibiting the formation and growth of ice crystals.

[0060] The above results demonstrate that the prepared photothermal superhydrophobic coating can significantly delay the surface icing process in everyday low-temperature environments, showing potential as a passive anti-icing solution. This coating is expected to be applied to aircraft wings, high-voltage transmission lines, wind turbine blades, and other applications, improving equipment operational safety in winter conditions while reducing energy consumption and maintenance costs associated with traditional active de-icing methods.

[0061] The raw glass and coated glass were placed on a cooling platform at -20°C, and water droplets were dropped onto their surfaces and allowed to freeze completely. Subsequently, a xenon lamp was turned on to irradiate the samples with a light intensity of 1 sun, and the morphological changes of the ice droplets were recorded in real time. The de-icing performance results are as follows: Figure 9 As shown, Figure 9 In the image, (a) represents the original glass and (b) represents the coated glass. It can be observed that the ice droplets on the original glass surface showed no obvious signs of melting after 300 seconds of continuous irradiation, remaining frozen. However, the ice droplets on the coated glass surface began to melt at the bottom after only 20 seconds of irradiation. As the irradiation time increased, the coating continued to absorb light energy and convert it into heat, causing the surface temperature to rise continuously. By 83 seconds, the ice droplets had completely melted into liquid water, and the droplets were transparent, indicating that the coating possesses a rapid-response photothermal de-icing capability under light irradiation.

[0062] This result fully verifies that the prepared coating has both good photothermal conversion efficiency and superhydrophobic properties, and can achieve rapid active de-icing in low-temperature environments.

[0063] To evaluate the self-cleaning performance of the prepared coating, carbon black was evenly sprinkled on the surfaces of both the original and coated glass. The coating was then tilted at a certain angle, and the removal of contaminants was observed by adding deionized water. The results are as follows: Figure 10 As shown, Figure 10 In the image, (a) is the original glass and (b) is the coated glass. The state of the carbon black powder on the surface of the original glass after being impacted by water is as follows: Due to the lack of superhydrophobic properties on the glass surface, water is difficult to form effective rolling or sliding on its surface and cannot carry away the carbon black powder. A large amount of powder remains in the original area, and it even diffuses due to the wetting and impact of water, resulting in extremely poor self-cleaning effect. However, the state of the carbon black powder on the surface of the coated glass after being impacted by water is as follows: Water quickly forms droplets on the non-sticky superhydrophobic coating surface and rolls (or slides). With the help of the droplet carrying effect, the carbon black powder is efficiently peeled off and carried away from the coating surface by the water flow, leaving only a very small amount of powder, resulting in a significant self-cleaning effect.

[0064] The experimental results show that the coating imparts extremely low surface energy, a suitable rough structure, and high contact angle-low roll-off angle characteristics to the glass surface, making it easy for water to roll off and carry away contaminants, thus achieving excellent self-cleaning function. In contrast, untreated glass cannot achieve effective self-cleaning due to differences in surface properties.

[0065] The wear resistance and impact resistance of the coating were tested using sandpaper abrasion and drop impact tests. In the sandpaper abrasion test, the coated sample was placed face down on 1000-grit sandpaper, and a 50 g weight was applied as a normal force. A horizontal force was then applied, causing the sample to move 10 cm laterally and longitudinally. The contact angle and roll-off angle of the coating were measured after each complete stroke (i.e., every 10 cm of wear). In the drop impact test, the superhydrophobic coating sample was fixed at a 45° angle to the horizontal plane, and sand was continuously dripped from a funnel at a height of 50 cm directly above the sample to impact the coating surface. The contact angle and roll-off angle of the coating were measured after every 20 g of sand was added. The test results are as follows: Figure 11 As shown, Figure 11In the figures, (a) shows the results of the sandpaper abrasion test, and (b) shows the results of the drop sand impact test. The hydrophobic properties of the coating showed a slow decreasing trend with increasing abrasion distance and continuous drop sand impact. When the abrasion distance reached 110 cm, the contact angle of the coating surface remained at 150.4°, and the roll-off angle was below 10°. After a 140 g drop sand impact, the contact angle of the coating surface still reached 152.2°, and the roll-off angle was below 10°, maintaining its superhydrophobic state. These two experiments combined demonstrate that the prepared coating possesses excellent mechanical stability. This performance is mainly attributed to the synergistic effect of the coating surface chemical composition and microstructure. On one hand, atactic polypropylene (aPP) effectively enhances the interfacial adhesion between the coating and the glass substrate, effectively preventing MOFs@HNT from detaching under external impact or abrasion. On the other hand, the multi-level rough structure constructed by the MOFs@HNT material itself provides the coating with good structural redundancy; even if the surface is partially damaged during abrasion, the coating retains sufficient roughness to maintain its superhydrophobic properties.

[0066] To evaluate the chemical stability of the coating in corrosive media, it was immersed in hydrochloric acid solution (pH=1) and 3.5 wt.% NaCl solution, respectively. The change in surface wettability with immersion time was investigated, and the results are as follows: Figure 12 As shown, Figure 12 In the figures, (a) is a 3.5 wt.% NaCl solution and (b) is a hydrochloric acid solution with pH=1. As shown in the figure, the contact angle of the coating surface decreases with increasing immersion time, while the roll-off angle continues to increase. However, even after continuous immersion in acid or salt solutions for more than 100 h, the coating still maintains good superhydrophobic properties, with the contact angle consistently above 153° and the roll-off angle remaining below 10°. This excellent chemical stability is mainly attributed to the fact that when the superhydrophobic coating is immersed in liquid, the air layer trapped by its rough surface structure forms a stable gas film barrier, effectively isolating the corrosive solution from direct contact with the coating surface, thereby significantly delaying the damage of the corrosive medium to the coating's microstructure and chemical composition.

[0067] In summary, the prepared superhydrophobic coating exhibits excellent chemical stability in strong acid and salt water environments, and has the potential for long-term application under complex corrosive conditions.

[0068] As demonstrated by the examples, this invention uses atactic polypropylene (aPP) as the matrix and introduces hydrophobically modified metal-organic frameworks / halostone nanotube composite fillers (MOFs@HNT) to successfully construct an intelligent anti-icing coating that combines superhydrophobicity with high-efficiency photothermal conversion capabilities. This coating achieves dual functions of "passive anti-icing" and "active photothermal de-icing" through the synergistic effect of micro / nanostructure design and photothermal functional fillers. Details are as follows: (1) Hydrophobic properties The coating surface forms a stable micro-nano composite rough structure with a static water contact angle (WCA) of 162.5° and a roll-off angle (SA) of less than 3°. The droplets roll off in a spherical shape, which conforms to the Cassie-Baxter wetting state and provides a structural basis for self-cleaning and anti-icing functions.

[0069] (2) Photothermal conversion performance

[0070] MOFs@HNT fillers impart excellent broadband light absorption and heat conversion capabilities to the coating: at 1 sun (100 mW / cm²), 2 Under simulated illumination, the surface temperature rises to 68.4℃ within 5 minutes; under weak light conditions of 0.1 sun, it can still rise to 21.3℃, showing good weak light response characteristics.

[0071] (3) Anti-icing and de-icing performance

[0072] Delayed icing under no light: In a low-temperature environment of -20℃, the superhydrophobic surface significantly inhibits ice nucleation, extending the water droplet icing time to 440 s (10 times faster than the original glass); Delayed icing under 0.1 sun light: Under weak light irradiation, the weak photothermal effect, combined with the superhydrophobicity, further extends the icing time to 950 s; Active de-icing under 1 sun light: The pre-formed ice layer completely melts within 83 s under 1 sun light, confirming its rapid active de-icing capability.

[0073] (4) Self-cleaning performance

[0074] As the water droplets roll off, they can efficiently carry away simulated surface contaminants (such as toner), demonstrating excellent self-cleaning performance.

[0075] (5) Overall stability

[0076] The stability of the coating was tested by experiments including sandpaper abrasion, sand drop impact, and chemical liquid immersion. The results showed that the coating maintained good superhydrophobicity after being subjected to 110 cm sandpaper abrasion, 140 g sand drop impact, and 100 h of acid and salt solution immersion, respectively, and had excellent mechanical durability and chemical stability.

[0077] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a modified MOF@HNTs / polypropylene composite coating, characterized in that, Includes the following steps: (1) Copper nitrate trihydrate, 2,3,6,7,10,11-hexahydroxytriphenylene hydrate and solvent were mixed and then halloysite nanotubes were added to react and MOFs@HNT were obtained; (2) Mix MOFs@HNT suspension, hexadecyltrimethoxysilane, tetraethyl silicate and ammonia to obtain hydrophobically modified MOFs@HNT; (3) After mixing the polypropylene solution and the hydrophobic modified MOFs@HNT, the mixture is cured to obtain the modified MOF@HNTs / polypropylene composite coating.

2. The method for preparing the modified MOF@HNTs / polypropylene composite coating as described in claim 1, characterized in that, The solvent in step (1) contains N,N-dimethylformamide and water. The volume ratio of N,N-dimethylformamide to water is 1:5~15; The ratio of copper nitrate trihydrate, 2,3,6,7,10,11-hexahydroxytriphenylene hydrate, solvent, and halloysite nanotubes is 0.5~1.5g:6~7g:80~120mL:2~3g.

3. The method for preparing the modified MOF@HNTs / polypropylene composite coating as described in claim 2, characterized in that, The reaction temperature in step (1) is 80~90℃ and the time is ≥15h.

4. The method for preparing the modified MOF@HNTs / polypropylene composite coating as described in claim 3, characterized in that, In step (2), the MOFs@HNT suspension contains MOFs@HNT and solvent; The solvents include ethanol, water, and ammonia. The volume ratio of ethanol, water, and ammonia is 80~100:8~10:1; The ratio of MOFs@HNT to solvent is 1g:80~120mL.

5. The method for preparing the modified MOF@HNTs / polypropylene composite coating as described in claim 4, characterized in that, In step (2), the ratio of MOFs@HNT, hexadecyltrimethoxysilane, tetraethyl silicate and ammonia in the MOFs@HNT suspension is 1g: 5~10mL: 1~2mL: 0.3~1mL.

6. The method for preparing the modified MOF@HNTs / polypropylene composite coating as described in claim 5, characterized in that, The mixing temperature in step (2) is 20~30℃, and the time is ≥2h.

7. The method for preparing the modified MOF@HNTs / polypropylene composite coating as described in claim 6, characterized in that, The polypropylene solution in step (3) contains atactic polypropylene and xylene; The ratio of random polypropylene to xylene is 0.3g: 20~30mL; In step (3), the mass ratio of hydrophobically modified MOFs@HNT to atactic polypropylene in the polypropylene solution is 1~5:

1.

8. The method for preparing the modified MOF@HNTs / polypropylene composite coating as described in claim 7, characterized in that, In step (3), the curing temperature is 70~90℃ and the time is ≥2h.

9. The modified MOF@HNTs / polypropylene composite coating prepared by the method according to any one of claims 1 to 8.

10. The application of the modified MOF@HNTs / polypropylene composite coating of claim 9 in hydrophobic materials and self-cleaning car covers.

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