Preparation method and application of super-hydrophobic exfoliated graphite coating

Abstract

This invention relates to a method for preparing and applying a superhydrophobic expanded graphite coating. The invention addresses the problems of complex preparation processes, high costs, or insufficient mechanical stability in existing technologies. The method uses expanded graphite as the main raw material and adds epoxy resin to prepare a superhydrophobic expanded graphite coating with photothermal properties. The coating is uniformly sprayed onto the surface of circular nickel foam using a spraying technique, resulting in a multifunctional superhydrophobic expanded graphite photothermal evaporator with sustainability, corrosion resistance, recyclability, self-cleaning capabilities, and water purification abilities. This invention belongs to the field of superhydrophobic coating preparation technology.

Description

Technical Field

[0001] This invention relates to a method for preparing a graphite coating and its application, belonging to the field of superhydrophobic coating preparation technology. Background Technology

[0002] Under natural conditions, the evaporation rate of water is relatively low, around 1 kW·m - ² Under solar irradiance, it is typically only 0.3–0.4 kg·m² - ²·h - ¹, this approach struggles to meet practical application needs such as seawater desalination and wastewater reduction. To improve energy utilization efficiency, solar-driven interfacial evaporation technology has attracted widespread attention. By localizing heat on the evaporation surface, it can significantly reduce bulk heating losses, thereby improving evaporation efficiency. Currently, commonly used photothermal materials include metal oxides, metal nanoparticles, organic polymers, and carbon-based materials. Among these, while metal nanoparticles possess excellent light absorption properties, they suffer from high cost, easy aggregation, and insufficient long-term stability, hindering their practical application. Organic polymer materials, on the other hand, have limited weather resistance and thermal stability. In contrast, carbon-based materials, due to their wide availability, low cost, good chemical stability, and excellent broad-spectrum absorption characteristics, exhibit more prominent comprehensive advantages in the field of solar photothermal conversion and have become a key research focus.

[0003] Among numerous carbon-based materials, expanded graphite, due to its unique layered porous structure and excellent physicochemical properties, has gradually become an important candidate material in the field of interfacial evaporation. Expanded graphite possesses near-blackbody high light absorption capacity, and its loose porous structure enhances multiple reflections and scattering of light, thereby significantly improving solar energy capture efficiency. Simultaneously, graphite's excellent in-plane thermal conductivity facilitates rapid photothermal conversion and effectively concentrates heat at the evaporation interface, reducing heat loss to the bulk water phase. Furthermore, its interconnected pore network forms stable capillary water transport channels, ensuring a continuous water supply and maintaining the dynamic balance of the evaporation interface, thus achieving efficient and stable evaporation. Further, expanded graphite also features low density, high compressibility, and tunable structure, making it easy to composite with polymers or metal substrates to construct multifunctional evaporation structures. Compared with nanomaterials such as graphene and carbon nanotubes, its preparation process is simpler and the raw material cost is lower, making it more suitable for large-scale engineering applications. Therefore, constructing an evaporation material system based on expanded graphite that combines high photothermal conversion efficiency with structural stability has significant research value and application prospects.

[0004] However, in actual seawater desalination or high-salinity wastewater treatment processes, photothermal evaporation materials commonly face the problem of salt crystallization and deposition, severely restricting their long-term stable operation. As the evaporation process continues, salt ions undergo non-uniform nucleation on the evaporation surface and gradually accumulate, forming a crystal deposition layer. On the one hand, the salt crystal coverage significantly increases light reflection and scattering on the material surface, weakening light absorption capacity; on the other hand, the deposits clog material pores and evaporation channels, disrupting the original capillary water transport pathways and reducing water transport efficiency, thus leading to a significant decrease in the evaporation rate. Furthermore, repeated crystallization and dissolution processes can also cause material structural damage and interfacial instability, affecting its cycle life. While existing technologies employ methods such as constructing superhydrophobic surfaces, Janus structures, or introducing functional nanocomponents to inhibit salt adhesion and promote self-cleaning, these methods generally suffer from complex preparation processes, high costs, or insufficient mechanical stability, making it difficult to balance performance with practical application requirements. Therefore, developing a photothermal evaporation material system that combines high-efficiency photothermal conversion performance, excellent anti-salt deposition capability, good mechanical stability, and scalable preparation characteristics has become a key technical problem urgently needing to be solved in this field. Summary of the Invention

[0005] To address the problems of complex preparation processes, high costs, or insufficient mechanical stability in existing technologies, this invention proposes a method for preparing and applying a superhydrophobic expanded graphite coating.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: The preparation method of the superhydrophobic expanded graphite coating of the present invention is achieved through the following steps: Step 1: Weigh out expanded graphite, anhydrous ethanol, and deionized water, place them in a ball mill jar, and add zirconia balls for ball milling; separate the dispersion from the zirconia balls by filtration, and place the unmodified dispersion in a beaker for later use; Step 2: Add the ammonia solution to the unmodified dispersion obtained in Step 1 and stir in a heat-collecting constant-temperature magnetic stirrer; Step 3: Then, ammonia, tetraethyl orthosilicate and perfluorodecyltriethoxysilane are added to the dispersion obtained in step 2, and the mixture is stirred in a constant temperature water bath to carry out the modification treatment and obtain the modified dispersion. Step 4: Add two-component epoxy resin to the modified dispersion obtained in Step 3, and mix evenly with magnetic stirring at a constant temperature to obtain a superhydrophobic expanded graphite coating. Step 5: Spray the superhydrophobic expanded graphite coating obtained in Step 4 onto the substrate surface, and dry and cure to obtain a superhydrophobic expanded graphite coating.

[0007] Furthermore, in step 1, the mass of expanded graphite is 0.05~0.40 g, the amount of anhydrous ethanol is 40~160 ml, the amount of deionized water is 6~40 ml, the mass ratio of dispersion to zirconia balls is 2~4:1, the ball milling speed is 100~600 r / min, and the ball milling time is 2~10 h.

[0008] Furthermore, in step 2, the amount of ammonia is 1-4 ml, the temperature of magnetic stirring is 20-80 ℃, and the stirring time is 5-120 min.

[0009] Furthermore, in step 3, the amount of ammonia is 0.5-8 ml, the amount of tetraethyl orthosilicate is 0.5-8 ml, the amount of perfluorodecyltriethoxysilane is 0.1-1.5 ml, the constant temperature water bath stirring temperature is 20-80℃, and the constant temperature water bath stirring time is 12-72 h.

[0010] Furthermore, in step 4, the mass ratio of A and B components in the two-component epoxy resin is 1.5~6:1, the total amount of A and B components in each 100 ml modified dispersion is 0.5~12 g, the constant temperature magnetic stirring temperature is 40~80℃, and the constant temperature magnetic stirring time is 10~120 min.

[0011] Furthermore, in step 5, the spraying rate is 20~150 ml / min, the spraying distance is 25 cm~40 cm, the spray gun nozzle diameter is 0.4~1.5 mm, the drying temperature is 50~90℃, and the curing time is 12~72 h.

[0012] Furthermore, in step 5, the substrate surface is one of glass sheet, nickel foam disc, resin sheet or metal sheet.

[0013] The superhydrophobic expanded graphite coating described in this invention is applied to the fields of seawater desalination, self-cleaning, and wastewater evaporation and volume reduction treatment.

[0014] The beneficial effects of this invention are: 1. The process of this invention is simple and energy-saving: This invention is based on expanded graphite with broad spectrum absorption, high thermal conductivity and low cost for photothermal conversion. Fluorination modification technology makes expanded graphite superhydrophobic, and epoxy resin is added to improve the wear resistance of the coating. The preparation process is simple.

[0015] 2. This invention exhibits excellent salt corrosion resistance: F-EGP@SiO2@1.5epoxy and F-EGP@SiO2@3epoxy coated photothermal evaporators, after being immersed in salt water with salinities of 3.5wt%, 10wt%, and 20wt% respectively for 7 days, still maintain structural integrity and superhydrophobicity, with water contact angles greater than 140°. Furthermore, the average evaporation efficiency of this photothermal evaporator is consistently above 1.41 kg·m³ over 2 hours. -2 h -1 The above solutions address the problem of traditional superhydrophobic coatings being prone to corrosion in high-humidity salt spray environments.

[0016] 3. This invention features long-term stability and recyclability: Under one solar radiation intensity, the photothermal evaporator continuously simulates seawater evaporation for 8 hours, 7 cycles. Tests show that the average photothermal evaporation efficiency of the coating remains at 1.62 kg·m³. -2 h -1 No obvious salt crystallization was observed on the surface and inside of the photothermal evaporator, which maintains a complete porous structure and can achieve long-term performance stability and recyclability.

[0017] 4. This invention has excellent water treatment capabilities: This photothermal evaporator can remove salt ions, including Na+. + Mg 2+ Ca 2+ K + The removal rate reaches 99.99%, and the purified water meets the drinking water standards stipulated by the World Health Organization; it has high photothermal evaporation efficiency and purification capacity for sewage such as cola, coffee, and Liuchi Lake Water Industry. Attached Figure Description

[0018] Figure 1 These are microscopic morphology images of the EGP coating, EGP@SiO2 coating, F-EGP coating, and F-EGP@SiO2 coating corresponding to Comparative Examples 1-4 of this invention.

[0019] Figure 2 This is a self-cleaning test of the F-EGP@SiO2 coatings prepared in Comparative Examples 4-6 of this invention.

[0020] Figure 3 These are macroscopic photographs and static contact angle data of the three coatings of this invention (Comparative Examples 1, 3, and 4) against room temperature liquids.

[0021] Figure 4 This invention describes the rebound behavior of water droplets on three coatings: EGP in Comparative Example 1, F-EGP in Comparative Example 3, and F-EGP@SiO2 in Comparative Example 4.

[0022] Figure 5This invention describes the lifting behavior of oil droplets on three coatings: EGP in Comparative Example 1, F-EGP in Comparative Example 3, and F-EGP@SiO2 in Comparative Example 4.

[0023] Figure 6 This invention presents the self-cleaning tests of three coatings—EGP in Comparative Example 1, F-EGP in Comparative Example 3, and F-EGP@SiO2 in Comparative Example 4—under ambient temperature and hot liquid conditions.

[0024] Figure 7 These are macroscopic morphology images of F-EGP@SiO2, F-EGP@SiO2@1.5epoxy, F-EGP@SiO2@3epoxy, F-EGP@SiO2@4.5epoxy and F-EGP@SiO2@6epoxy obtained in Comparative Example 4 and Examples 1-4 of this invention.

[0025] Figure 8 The F-EGP@SiO prepared in Comparative Example 4 and Examples 1-4 of this invention 2、 The photothermal evaporation rates of the F-EGP@SiO2@1.5epoxy, F-EGP@SiO2@3epoxy, F-EGP@SiO2@4.5epoxy, and F-EGP@SiO2@6epoxy coatings.

[0026] Figure 9 The mechanical properties of the F-EGP@SiO2@1.5epoxy and F-EGP@SiO2@3epoxy coatings prepared in Examples 1 and 2 of this invention are tested.

[0027] Figure 10 The contact angle and macroscopic morphology of the F-EGP@SiO2@1.5epoxy and F-EGP@SiO2@3epoxy coatings prepared in Examples 1 and 2 of this invention after salt spray testing are shown. Detailed Implementation

[0028] Specific Implementation Method 1: The steps of the preparation method of the superhydrophobic expanded graphite coating described in this implementation method include: Step 1: Under conditions of -30 to 200℃, the water contact angle on the coating surface can reach more than 150°, and the oil contact angle on the coating surface is >150°. Water droplets can bounce multiple times on the coating surface, with no less than 8 bounces, showing excellent static and dynamic superhydrophobic properties. Step 2: After being worn for 1000 revolutions on an ASTM standard Taber abrasion tester at 60 r / min with a CS-10 grinding wheel, the coating still maintains its hydrophobic properties. Water droplets can quickly bounce off the worn area without any adhesion. Step 3: After continuous spraying with 5 wt% sodium chloride solution in a salt spray test chamber for 7 days, the water contact angle of the coating is still greater than 140°, the macroscopic morphology of the surface does not change significantly, and the coating does not peel off, showing excellent salt spray corrosion resistance. Step 4: After immersing in 3.5 wt%, 10 wt%, and 20 wt% sodium chloride solutions for 7 days respectively, the water contact angle of the coating is greater than 140°, the surface remains hydrophobic, and the structural integrity is good. Step 5: After immersing in an acidic or alkaline solution with pH 2-7 for 7-14 days, the coating maintains its superhydrophobicity and structural integrity. Step 6: Within the wavelength range of 200 nm–2500 nm, the coating exhibits an average light absorption rate of 89.3% under sunlight illumination, at a solar irradiance of 1 kW·m². - Under these conditions, the surface temperature of the coating can be stably maintained above 60℃; Step 7: In the 12-hour photothermal evaporation experiment, the average photothermal evaporation efficiency of the coating was 1.55 kg·m³. - ²·h - ¹, with a maximum evaporation efficiency of 1.63 kg·m - ²·h - ¹; Step 8: In the cyclic photothermal evaporation test, after 8 hours of continuous photothermal evaporation and repeated 7 times, the average photothermal evaporation efficiency of the coating remained at 1.62 kg·m³. - ²·h - ¹ No obvious salt crystallization was observed on the surface or inside, maintaining a complete porous structure.

[0029] Example Example 1 1. A method for preparing a superhydrophobic expanded graphite coating, comprising the following steps: (1) Weigh 0.18 g of expanded graphite, 80 mL of anhydrous ethanol, and 16 mL of deionized water, place them in a ball mill jar, and add zirconia balls at a mass ratio of 3:1. Ball mill at 400 r / min for 6 h. Separate the dispersion from the zirconia balls by filtering them through a sieve, and place the unmodified dispersion in a beaker for later use.

[0030] (2) Add 2 mL of ammonia solution to the unmodified dispersion obtained in step (1) and stir for 20 min in a heat-collecting constant temperature magnetic stirrer at 50°C.

[0031] (3) Then, 2 mL of ammonia, 2 mL of tetraethyl orthosilicate and 0.6 mL of perfluorodecyltriethoxysilane were added to the dispersion obtained in step (2), and the mixture was stirred in a constant temperature water bath at 50°C for 24 h to carry out the modification treatment and obtain the modified dispersion.

[0032] (4) Add two-component epoxy resin to the modified dispersion obtained in step (3), keeping the mass ratio of A glue to B glue at 3:1. The total amount of two-component epoxy resin A glue and B glue in every 100ml of modified dispersion is 1.5 g. Stir magnetically at 50℃ for 20 min to obtain superhydrophobic expanded graphite coating.

[0033] (5) Spray the superhydrophobic expanded graphite coating obtained in step (4) onto the surface of a glass slide or nickel foam substrate, and dry and cure it in an oven at 60°C for 24 h to obtain a superhydrophobic expanded graphite coating, denoted as F-EGP@SiO2@1.5epoxy coating.

[0034] The macroscopic morphology of the F-EGP@SiO2@1.5epoxy coating prepared in this embodiment is shown in the figure below. Figure 7 As shown in (b).

[0035] The photothermal evaporation rate of the F-EGP@SiO2@1.5epoxy coating prepared in this embodiment is as follows: Figure 8 As shown, Figure 8 It can be seen that the average evaporation rate of the F-EGP@SiO2@1.5epoxy coating is 1.312 kg·m. -2 h -1 .

[0036] The mechanical properties of the F-EGP@SiO2@1.5epoxy coating prepared in this embodiment are as follows: Figure 9 As shown in (ab), by Figure 9 (ab) shows that after 1000 r of wear, water droplets flowing through the wear area of ​​the F-EGP@SiO2@1.5epoxy coating will quickly bounce off, and the coating surface will still maintain hydrophobic properties.

[0037] The contact angle and macroscopic morphology of the F-EGP@SiO2@1.5epoxy coating prepared in this embodiment after salt spray testing are as follows: Figure 10 As shown in (a, c), by Figure 10 As shown in (a, c), the hydrophobic properties of the F-EGP@SiO2@1.5epoxy coating decreased before and after the salt spray test, while the macroscopic morphology remained unchanged.

[0038] Comparative Example 1: As described in Example 1, the difference is that the modification treatment in steps (2) and (3) was not performed, nor was step (4). The unmodified dispersion obtained in step (1) was directly sprayed onto the surface of the glass substrate and dried and cured in an oven at 60°C for 24 hours to obtain an expanded graphite coating, which is referred to as EGP coating.

[0039] The microstructure of the EGP coating prepared in this comparative example is shown in the figure below. Figure 1 As shown in (a), by Figure 1 (a) It can be seen that the EGP coating has a granular structure and is relatively scattered.

[0040] Macroscopic photographs and static contact angle data of the EGP coating prepared in this comparative example are shown below. Figure 3 As shown, by Figure 3 It can be seen that the EGP coating has a water contact angle of 141.6°, exhibiting hydrophobic properties, while the oil contact angle is only 9°, proving that the EGP coating is only hydrophobic and not oleophobic.

[0041] The water droplet rebound behavior of the EGP coating prepared in this comparative example is as follows: Figure 4 As shown in (a), by Figure 4 As shown in (a), a water droplet can bounce back about 3 times on the EGP coating.

[0042] The droplet lifting behavior of the EGP coating prepared in this comparative example is as follows: Figure 5 As shown in (a), by Figure 5 As shown in (a), oil droplets spread directly on the EGP coating, which is consistent with its non-oleophobic properties.

[0043] The self-cleaning tests of the EGP coating prepared in this comparative example under room temperature liquid and hot liquid conditions are as follows: Figure 6 As shown in (a), by Figure 6 (a) It can be seen that powder residue still remains on the surface of the EGP coating after rinsing.

[0044] Comparative Example 2: As described in Example 1, the difference is that in step (3), 2 mL of ammonia and 2 mL of tetraethyl orthosilicate were added for modification, but perfluorodecyltriethoxysilane (PFDTES) was not added. Step (4) was also omitted, and the obtained modified dispersion was directly sprayed onto the surface of a glass slide substrate and dried and cured in an oven at 60°C for 24 h to obtain an expanded graphite coating, denoted as EGP@SiO2 coating.

[0045] The microstructure of the EGP@SiO2 coating prepared in this comparative example is shown in the figure below. Figure 1 As shown in (b), by Figure 1 (b) It can be seen that the surface of the EGP@SiO2 coating is mainly occupied by spherical silica particles, while expanded graphite particles occupy only a small part.

[0046] Comparative Example 3: As described in Example 1, the difference is that in step (3), 2 mL of ammonia and 0.6 mL of fluorosilane (PFDTES) (correct name confirmed) were added for modification treatment, but tetraethyl orthosilicate was not added. Step (4) was also not performed. The obtained modified dispersion was directly sprayed onto the surface of the glass slide substrate and dried and cured in an oven at 60°C for 24 h to obtain an expanded graphite coating, denoted as F-EGP coating.

[0047] The microstructure of the F-EGP coating prepared in this comparative example is shown in the figure below. Figure 1 As shown in (c), by Figure 1 (c) It can be seen that the graphite particles on the surface of the F-EGP coating are in an agglomerated state.

[0048] The water droplet rebound behavior of the F-EGP coating prepared in this comparative example is as follows: Figure 4 As shown in (b), by Figure 4 As shown in (b), water droplets can bounce back about 6 times on the F-EGP coating.

[0049] The oil droplet lifting behavior of the F-EGP coating prepared in this comparative example is as follows: Figure 5 As shown in (b), by Figure 5 As shown in (b), the oil droplets cannot be pulled up again after contacting the F-EGP coating, but remain on the coating surface in the form of droplets.

[0050] The self-cleaning tests of the F-EGP coating prepared in this comparative example under room temperature liquid and hot liquid conditions are as follows: Figure 6 As shown, by Figure 6 It can be seen that the F-EGP coating surface remains clean after rinsing.

[0051] Comparative Example 4: As described in Example 1, except that step (4) was not performed, the obtained modified dispersion was directly sprayed onto the surface of the glass slide substrate and dried and cured in an oven at 60°C for 24 h to obtain an expanded graphite coating, denoted as F-EGP@SiO2 coating.

[0052] The microstructure of the F-EGP@SiO2 coating prepared in this comparative example is shown in the figure below. Figure 1 As shown in (d), by Figure 1 (d) The F-EGP@SiO2 coating is covered with dense SiO2 microparticles on the expanded graphite, and the agglomeration of this coating is more obvious than that of the EGP coating.

[0053] The self-cleaning test of the F-EGP@SiO2 coating prepared in this comparative example is as follows: Figure 2 As shown, by Figure 2 It can be seen that the coating exhibits excellent superhydrophobic and amphoteric properties when using glass slides, resin sheets, or metal plates as substrates.

[0054] Macroscopic photographs and static contact angle data of the F-EGP@SiO2 coating prepared in this comparative example are shown below. Figure 3 As shown, Figure 3 As shown, the F-EGP@SiO2 coating exhibits water contact angles greater than 150° for oil, tea, coffee, milk, and water, demonstrating its superhydrophobic and dihydrophobic properties.

[0055] The water droplet rebound behavior of the F-EGP@SiO2 coating prepared in this comparative example is as follows: Figure 4 As shown in (c), by Figure 4 As shown in (c), water droplets can bounce back about 10 times on the F-EGP@SiO2 coating.

[0056] The oil droplet pulling behavior of the F-EGP@SiO2 coating prepared in this comparative example is as follows: Figure 5 As shown in (c), by Figure 5 As shown in (c), on the F-EGP@SiO2 coating, the oil droplets can leave the coating surface again with the pipette after going through the entire lifting process.

[0057] The self-cleaning tests of the F-EGP@SiO2 coating prepared in this comparative example under room temperature liquid and hot liquid conditions are as follows: Figure 6 As shown, by Figure 6 It can be seen that the surface of the F-EGP@SiO2 coating remains clean after rinsing.

[0058] The macroscopic morphology of the F-EGP@SiO2 coating prepared in this comparative example is shown in the figure below. Figure 7 As shown in (a).

[0059] The photothermal evaporation rate of the F-EGP@SiO2 coating prepared in this embodiment is as follows: Figure 8 As shown, Figure 8 As shown, the average evaporation rate of the F-EGP@SiO2 coating is 1.302 kg·m⁻². -2 h -1 .

[0060] Comparative Example 5: As described in Comparative Example 4, except that it was sprayed onto the surface of a resin sheet substrate.

[0061] The self-cleaning test of the F-EGP@SiO2 coating prepared in this comparative example is as follows: Figure 2 As shown in (b).

[0062] Comparative Example 6: As described in Comparative Example 4, except that it is sprayed onto the surface of a copper substrate.

[0063] The self-cleaning test of the F-EGP@SiO2 coating prepared in this comparative example is as follows: Figure 2 As shown in (c).

[0064] Example 2: As described in Example 1, the difference is that the total amount of two-component epoxy resin A and B in every 100 ml of modified dispersion is 3 g, denoted as F-EGP@SiO2@3epoxy coating.

[0065] The macroscopic morphology of the F-EGP@SiO2@3epoxy coating prepared in this embodiment is shown in the figure below. Figure 7 As shown in (c).

[0066] The photothermal evaporation rate of the F-EGP@SiO2@3epoxy coating prepared in this embodiment is as follows: Figure 8 As shown, Figure 8 As shown, the average evaporation rate of the F-EGP@SiO2@3epoxy coating is 1.324 kg·m⁻¹. -2 h -1 .

[0067] The mechanical properties of the F-EGP@SiO2@3epoxy coating prepared in this embodiment are as follows: Figure 9 (cd) shown, Depend on Figure 9 (cd) shows that after the F-EGP@SiO2@3epoxy coating is worn for 400 r, the water droplets that flow through it will adhere to the surface of the worn coating, and the hydrophobic properties of the coating will be destroyed.

[0068] The contact angle and macroscopic morphology of the F-EGP@SiO2@3epoxy coating prepared in this embodiment after salt spray testing are as follows: Figure 10 As shown in (b) and (d), by Figure 10 (b, d) show that the hydrophobic properties of the F-EGP@SiO2@3epoxy coating decreased before and after the salt spray test, while the macroscopic morphology did not change significantly.

[0069] Example 3: As described in Example 1, except that the total amount of two-component epoxy resin A and B in every 100 ml of modified dispersion is 4.5 g, denoted as F-EGP@SiO2@4.5epoxy coating.

[0070] The macroscopic morphology of the F-EGP@SiO2@4.5epoxy coating prepared in this embodiment is shown in the figure below. Figure 7 As shown in (d).

[0071] The photothermal evaporation rate of the F-EGP@SiO2@4.5epoxy coating prepared in this embodiment is as follows: Figure 8 As shown, Figure 8 As shown, the average evaporation rate of the F-EGP@SiO2@4.5epoxy coating is 1.284 kg·m⁻¹. -2 h -1 .

[0072] Example 4: As described in Example 1, the difference is that the total amount of two-component epoxy resin A and B in every 100 ml of modified dispersion is 6 g, denoted as F-EGP@SiO2@6epoxy coating.

[0073] The macroscopic morphology of the F-EGP@SiO2@6epoxy coating prepared in this embodiment is shown in the figure below. Figure 7 As shown in (e).

[0074] The photothermal evaporation rate of the F-EGP@SiO2@6epoxy coating prepared in this embodiment is as follows: Figure 8 As shown, Figure 8 As shown, the average evaporation rate of the F-EGP@SiO2@6epoxy coating is 1.296 kg·m⁻¹. -2 h -1 .

[0075] Experimental Example 1: Because expanded graphite, after modification, possesses superhydrophobic and amphoteric properties, it means that if dirt accumulates on the coating surface, it can be washed away with various liquids, thus enabling the coating's sustainable application. To verify this application, we conducted self-cleaning tests on three coatings. White powder was spread evenly on the coating surface to simulate the dust particle adhesion problem encountered in real-world applications, and then tap water was used to simply rinse the coating surface with a dropper. The experimental results are as follows... Figure 6 As shown, powder residue remained on the EGP coating surface after rinsing, while the surfaces of both F-EGP and F-EGP@SiO2 coatings remained clean. This indicates that the self-cleaning properties of the F-EGP and F-EGP@SiO2 coatings are superior to those of the unmodified EGP coating.

[0076] To explore the difference in self-cleaning performance between F-EGP and F-EGP@SiO2 coatings, we replaced the room temperature water used in the self-cleaning test with near-boiling hot water. Figure 6The self-cleaning test of three coatings—EGP, F-EGP, and F-EGP@SiO2—under high-temperature liquid conditions was also demonstrated. The EGP coating's hydrophobic properties were compromised by simple rinsing with a high-temperature liquid, with the coating even peeling off, proving its inability to withstand high temperatures and limiting its applications. While the F-EGP coating could have surface dust removed by the high-temperature liquid, water droplets remained after rinsing, indicating that the superhydrophobic and amphoteric properties of the F-EGP coating were compromised by the high-temperature liquid. In contrast, the F-EGP@SiO2 coating remained clean after rinsing with a high-temperature liquid, with no dust or water droplets remaining. This fully demonstrates the superior superhydrophobic and amphoteric properties of the F-EGP@SiO2 coating, unaffected by high-temperature liquids, proving its sustainable application and relatively long service life.

[0077] Experimental Example 2: The F-EGP coating prepared above has excellent superhydrophobic properties, with a water contact angle of over 150°. However, due to the weak adhesion between the coating and the substrate, it is easily damaged by external forces, which limits the application of the coating. In this section, to enhance the adhesion between the coating and the substrate, we propose to add different amounts of two-component epoxy resin (formulations shown in Table 1 below) to the superhydrophobic expanded graphite coating, thereby improving the coating strength.

[0078] Table 1 Epoxy Resin Formulation Table

[0079] The macroscopic morphology of the photothermal evaporators made with expanded graphite coatings of different formulations is as follows: Figure 8 As shown.

[0080] Experimental Example 3: To investigate the effect of epoxy resin content on the photothermal evaporation efficiency of the coating, we placed the sample under a xenon lamp to simulate solar radiation intensity and explored the photothermal evaporation efficiency of five different photothermal evaporators. The weight loss in the beaker was recorded every ten minutes, simulating the evaporation rate of seawater. The evaporation efficiency was then calculated using the formula... The photothermal evaporation efficiency is calculated as follows: Figure 8 It can be seen that the average evaporation rate of the F-EGP coating is 1.302 kg·m. -2 h -1In comparison, adding 1.5 g and 3 g of epoxy resin can improve the photothermal evaporation efficiency of the coating. This is because the F-EGP coating has poor adhesion and is prone to peeling. However, the photothermal coating adhering to the nickel foam skeleton does not peel off after adding epoxy resin, thus relatively increasing the photothermal evaporation area of ​​the coating. However, when the amount of epoxy resin added increases to 4.5 g and 6 g, the photothermal evaporation efficiency of the coating decreases. This is because the addition of epoxy resin affects the light absorption capacity of the coating, thus leading to a decrease in evaporation efficiency. At the same time, the superhydrophobic properties of the coating change with the increase of epoxy resin content. As shown in the figure, when the epoxy resin content increases to 6 g, the contact angle decreases from 156.8° to 132.1°.

[0081] Experiment Example 4: After optimizing the formulation, to investigate the mechanical properties of the superhydrophobic F-EGP coating, we used the Taber abrasion technique according to ASTM standards to conduct surface wear tests on the coating. The experiment used a CS-10 grinding wheel, adjusted to a speed of 60 r / min, and after a certain number of revolutions, the wettability of the coating was tested. The results are as follows: Figure 9 As shown in (b), after 1000 r of wear, water droplets flowing through the worn area of ​​the EG@1.5epoxy coating bounce off quickly, and the coating surface still maintains its hydrophobic properties; as follows: Figure 9 (d) After 400 r of wear, water droplets will adhere to the surface of the worn F-EGP@SiO2@3epoxy coating, thus damaging the hydrophobic properties of the coating.

[0082] This is because as the epoxy resin content increases, the surface energy of the coating changes, and the intrinsic contact angle decreases. The rough structure formed during the spraying process of the F-EGP@SiO2@3epoxy coating has a significant impact on its hydrophobic properties. During the wear process, the rough structure is gradually destroyed, and the hydrophobic properties of the coating will decrease. On the other hand, the F-EGP@SiO2@1.5epoxy coating has a relatively low epoxy resin content, and the coating surface still has a low surface energy. Although the rough structure is destroyed in the experiment, the low surface energy of the coating can still achieve the surface hydrophobicity.

[0083] Experimental Example 5: Two coatings, F-EGP@SiO2@1.5epoxy and F-EGP@SiO2@3epoxy, were placed in a salt spray test chamber. A 5wt% sodium chloride salt spray was used to simulate a corrosive environment. Changes in the contact angle and surface morphology of the coatings were observed after 1, 3, 5, and 7 days of the experiment. Figure 10 It can be observed that the hydrophobic properties of the coating decreased before and after the salt spray test, while the macroscopic morphology did not change significantly.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a superhydrophobic expanded graphite coating, characterized in that, The specific steps include: Step 1: Weigh out expanded graphite, anhydrous ethanol, and deionized water, place them in a ball mill jar, and add zirconia balls for ball milling; separate the dispersion from the zirconia balls by filtration, and place the unmodified dispersion in a beaker for later use; Step 2: Add the ammonia solution to the unmodified dispersion obtained in Step 1 and stir in a heat-collecting constant-temperature magnetic stirrer; Step 3: Then, ammonia, tetraethyl orthosilicate and perfluorodecyltriethoxysilane are added to the dispersion obtained in step 2, and the mixture is stirred in a constant temperature water bath to carry out the modification treatment and obtain the modified dispersion. Step 4: Add two-component epoxy resin to the modified dispersion obtained in Step 3, and mix evenly with magnetic stirring at a constant temperature to obtain a superhydrophobic expanded graphite coating. Step 5: Spray the superhydrophobic expanded graphite coating obtained in Step 4 onto the substrate surface, and dry and cure to obtain a superhydrophobic expanded graphite coating.

2. The method for preparing a superhydrophobic expanded graphite coating according to claim 1, characterized in that, In step 1, the mass of expanded graphite is 0.05~0.40 g, the amount of anhydrous ethanol is 40~160 ml, the amount of deionized water is 6~40 ml, the mass ratio of dispersion to zirconia balls is 2~4:1, the ball milling speed is 100~600 r / min, and the ball milling time is 2~10 h.

3. The method for preparing a superhydrophobic expanded graphite coating according to claim 1, characterized in that, In step 2, the amount of ammonia water is 1-4 ml, the temperature of magnetic stirring is 20-80 ℃, and the stirring time is 5-120 min.

4. The method for preparing a superhydrophobic expanded graphite coating according to claim 1, characterized in that, In step 3, the amount of ammonia is 0.5-8 ml, the amount of tetraethyl orthosilicate is 0.5-8 ml, the amount of perfluorodecyltriethoxysilane is 0.1-1.5 ml, the constant temperature water bath stirring temperature is 20-80℃, and the constant temperature water bath stirring time is 12-72 h.

5. The method for preparing a superhydrophobic expanded graphite coating according to claim 1, characterized in that, In step 4, the mass ratio of A and B components in the two-component epoxy resin is 1.5~6:

1. The total amount of A and B components in each 100 ml modified dispersion is 0.5~12 g. The constant temperature magnetic stirring temperature is 40~80 ℃, and the constant temperature magnetic stirring time is 10~120 min.

6. The method for preparing a superhydrophobic expanded graphite coating according to claim 1, characterized in that, In step 5, the spraying rate is 20~150 ml / min, the spraying distance is 25 cm~40 cm, the spray gun nozzle diameter is 0.4~1.5 mm, the drying temperature is 50~90℃, and the curing time is 12~72 h.

7. The method for preparing a superhydrophobic expanded graphite coating according to claim 1, characterized in that, In step 5, the substrate surface is one of the following: a glass sheet, a nickel foam disc, a resin sheet, or a metal sheet.

8. The application of a superhydrophobic expanded graphite coating prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The superhydrophobic expanded graphite coating is applied in the fields of seawater desalination, self-cleaning, and wastewater evaporation and volume reduction treatment.

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