Self-cleaning radiative cooling coating based on biomass carbon quantum dots, its preparation method and application

Abstract

This invention discloses a self-cleaning radiative cooling coating based on biomass carbon quantum dots, its preparation method, and its application. The coating comprises a polymer film-forming resin, carbon quantum dots, and hollow glass microspheres; wherein the mass ratio of the polymer film-forming resin to the filler is 1:(0.1-0.5), and the mass ratio of the hollow glass microspheres to the carbon quantum dots is 1:(0.05-0.2). This invention synergistically enhances solar reflectivity through the photoluminescence properties of carbon quantum dots and the scattering properties of hollow glass microspheres, while simultaneously utilizing the synergistic effect of fluorinated resin and modified hollow glass microspheres to endow the coating with superhydrophobic self-cleaning function. A single layer of this coating can achieve a solar reflectivity >92%, mid-infrared emissivity >94%, and contact angle >150°, possessing both efficient daytime radiative cooling and long-lasting self-cleaning performance. It is particularly suitable for passive heat dissipation of outdoor equipment such as new energy vehicle charging piles, and features simple process, environmental friendliness, and excellent performance.

Description

Technical Field

[0001] This invention relates to the field of daytime radiation cooling and heat dissipation technology, specifically to a self-cleaning radiation cooling coating based on biomass carbon quantum dots, its preparation method, and its application. The coating is a self-cleaning radiation cooling coating based on photoluminescent quantum dots, which has photoluminescence, self-cleaning, and radiation cooling functions, and can be widely used for surface cooling. Background Technology

[0002] With the rapid popularization of new energy vehicles, charging piles, as core infrastructure, directly impact user experience and industry development in terms of performance and reliability. However, in high-power fast charging scenarios (such as 350kW or even higher), the power electronic devices, cables, and connectors inside the charging pile generate a large amount of heat due to high current (250A~600A) and high voltage (800V and above). If heat dissipation is not timely, it may lead to shortened equipment lifespan, decreased charging efficiency, and even extreme high temperatures may cause insulation material failure, resulting in safety hazards. Therefore, efficient heat dissipation technology has become a core challenge in charging pile design. Radiation cooling coatings for new energy vehicle charging piles are an emerging passive heat dissipation technology that achieves cooling by reflecting sunlight and radiating heat into outer space, and are expected to become an effective supplement or alternative to traditional active heat dissipation (such as air cooling and liquid cooling). Radiation cooling coatings can reduce the energy consumption of active heat dissipation, reduce the power consumption of fans or liquid cooling pumps (especially suitable for high-temperature areas), and improve overall energy efficiency.

[0003] However, existing radiation cooling coatings still have many shortcomings in practical applications: First, traditional coatings typically only possess a single radiation cooling function, and their cooling effect is limited under strong daytime sunlight due to sunlight absorption; second, when used outdoors for extended periods, dust easily accumulates on the surface, leading to decreased reflectivity and performance degradation; third, existing technologies often require multi-layered structural designs, resulting in complex manufacturing processes and making it difficult to achieve lightweight design and adaptability to irregularly shaped surfaces. Furthermore, how to achieve self-cleaning functionality and efficient cooling without sacrificing cooling performance remains a pressing technical challenge in this field.

[0004] To address the aforementioned issues, this invention discloses a self-cleaning radiation cooling coating with photoluminescence properties, which is expected to be applied in the field of cooling for new energy vehicle charging piles. Summary of the Invention

[0005] The purpose of this invention is to provide a self-cleaning radiation cooling coating based on biomass carbon quantum dots, its preparation method and application. This self-cleaning radiation cooling coating with photoluminescence properties has high solar reflectivity, high-medium infrared emissivity, excellent self-cleaning performance and photoluminescence enhancement function, bringing new possibilities for the rational design and sustainable development of next-generation smart coatings.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: On the one hand, the present invention proposes a self-cleaning radiation cooling coating based on biomass carbon quantum dots, comprising a polymer film-forming resin and fillers, wherein the fillers include modified hollow glass microspheres and fluorescent glass microspheres loaded with carbon quantum dots; The modified hollow glass microspheres are hollow glass microspheres that have been surface modified with a silane coupling agent; The fluorescent glass microspheres loaded with carbon quantum dots are a composite containing carbon quantum dots and hollow glass microspheres, wherein the carbon quantum dots are coated with polymer to form a core-shell structure and then loaded on the surface of the hollow glass microspheres. The polymeric film-forming resin is selected from at least one of fluoropolymers or organosilicon resins.

[0007] Furthermore, the biomass carbon quantum dots are prepared from waste biomass via hydrothermal carbonization, and the waste biomass is selected from grapefruit peel, orange peel, tea leaves, or coffee grounds; grapefruit peel is preferred in this invention.

[0008] Furthermore, the core-shell structure uses polymethyl methacrylate as the core and branched polyethyleneimine as the shell, with the carbon quantum dots encapsulated within the core or shell.

[0009] This invention also proposes a method for preparing the self-cleaning radiation cooling coating based on biomass carbon quantum dots, comprising the following steps: (1) Prepare biomass carbon quantum dots by hydrothermal carbonization of waste biomass; (2) Preparation of fluorescent glass microspheres: Branched polyethyleneimine, carbon quantum dots and methyl methacrylate monomers are reacted in the presence of an initiator to form polymer core-shell particles coated with carbon quantum dots, which are then combined with hollow glass microspheres to obtain fluorescent glass microspheres loaded with carbon quantum dots. (3) Preparation of modified hollow glass microspheres: Disperse hollow glass microspheres in a solvent, add a catalyst and a silane coupling agent to carry out a surface modification reaction, and obtain the modified hollow glass microspheres; (4) Dissolve the polymer film-forming resin in the film-forming solvent, add the fluorescent glass microspheres obtained in step (2) and the modified hollow glass microspheres obtained in step (3), disperse them evenly, coat them on the substrate and cure them to obtain the coating.

[0010] Step (1) specifically involves washing the waste grapefruit peel multiple times with tap water and deionized water, then drying it to constant weight at 60 °C. Subsequently, the waste grapefruit peel is finely ground using a stainless steel grinder to pass through a 100-mesh sieve. The waste grapefruit peel powder and ethylenediamine are then accurately weighed into a polytetrafluoroethylene-lined autoclave, thoroughly mixed with an appropriate amount of deionized water, and reacted at a certain temperature for a period of time. After the reaction, the autoclave is naturally cooled to room temperature. The resulting product is then centrifuged at 10,000 rpm for 20 min, and then double-filtered using a 0.22 μm aqueous microporous membrane. The filtrate is collected and purified using a 500 Da dialysis bag for 12–48 h to obtain liquid carbon quantum dots. The liquid carbon quantum dots are then freeze-dried in liquid nitrogen to form a powder and kept below 4 °C for later use.

[0011] Step (2) specifically involves dissolving branched polyethyleneimine in water and thoroughly mixing it with a carbon quantum dot dispersion. The mixture is stirred at room temperature for 2 hours to induce crosslinking. The solution is then transferred to a water-jacketed flask equipped with a condenser, thermocouple, magnetic stirrer, and nitrogen inlet. The mixture is stirred and purged with Ar at a specific temperature for 30 minutes. Methyl methacrylate is added to the solution. After mixing for 5 minutes, an initiator is added to the stirred mixture to initiate polymerization. The mixture is then heated at a specific temperature under an Ar atmosphere for a specific time. After the reaction, a stable core-shell structured particle dispersion, PEI / PMMA@CDs, is obtained. This dispersion is then purified by centrifugation and washed with deionized water. Finally, the purified PEI / PMMA@CDs are stored at room temperature for subsequent use. The obtained core-shell structure and hollow glass microspheres, which have been ultrasonically cleaned and dried with ethanol, are mixed at a specific mass ratio and freeze-dried to obtain fluorescent glass microspheres.

[0012] Step (3) specifically involves: ultrasonically dispersing hollow glass microspheres in anhydrous ethanol, adding a catalyst and deionized water, heating and stirring the mixture in an oil bath, and then adding a silane coupling agent to react for a certain period of time. After cooling to room temperature, the product is centrifuged and washed twice with ethanol and deionized water to remove unreacted hollow glass microspheres and silane coupling agent. The product is then vacuum dried in an oven at 40-80℃ until constant weight is obtained, yielding modified hollow glass microspheres.

[0013] Step (4) specifically involves: adding the polymer film-forming resin to the film-forming solvent and magnetically stirring at room temperature to obtain a uniform solution. Then, the modified hollow glass microspheres and the hollow glass microspheres loaded with carbon quantum dots are added to the above solution in a certain proportion, and after thorough stirring and dispersion, a casting solution is obtained. The casting solution is coated onto the substrate, dried in air for 1 hour, and then dried in a 60°C oven for 2-24 hours to obtain the coating, which is a photoluminescent self-cleaning coating for daytime passive radiation cooling.

[0014] In step (1) of this invention, to optimize the synthesis of carbon quantum dots and achieve high fluorescence intensity and fluorescence yield, the mass ratio of waste grapefruit peel powder to deionized water used for dissolution and dispersion is 1:(1-50). Preferably, it is 1:(5-20).

[0015] In step (1) of the present invention, the hydrothermal temperature is 120~250 ℃, preferably 180~220 ℃.

[0016] In step (1) of this invention, the hydrothermal time is 1~12 h, preferably 2~10 h. In step (2) of this invention, considering that the proportion of carbon quantum dots directly affects the fluorescence performance, dispersion stability, coating effect and final application performance of the material, the mass ratio of carbon quantum dots to methyl methacrylate is (0.01~0.1):1, preferably (0.01~0.05):1.

[0017] In step (2) of this invention, the mass ratio of branched polyethyleneimine to methyl methacrylate is (0.01-1):1, preferably (0.03-0.1):1.

[0018] The initiator in step (2) of this invention is selected from potassium persulfate, tert-butyl hydroperoxide, ammonium persulfate, and potassium persulfate / sodium bisulfite. Since too high an initiator may cause explosive polymerization and too low an initiator may result in insufficient reaction, the mass ratio of initiator to methyl methacrylate is (0.05-5):100, preferably (0.5-2):100.

[0019] In step (2) of this invention, the dropping rate of methyl methacrylate is 0.5-2 mL / min, and the polymerization reaction time is preferably 3-6 h.

[0020] In step (2) of this invention, in order to successfully synthesize the core-shell structure of carbon quantum dots loaded with polymethyl methacrylate as the core and polyethyleneimine as the shell, the reaction temperature is 30~90℃ and the reaction time is 1~12 h.

[0021] In step (2) of this invention, in order to make carbon quantum dots uniformly dispersed on the surface of hollow glass microspheres and give full play to their fluorescence performance, the mass ratio of PEI / PMMA@CDs to hollow glass microspheres is (3-15):1.

[0022] In step (3) of this invention, the amount of anhydrous ethanol used is such that the particle concentration is between 0.1-5 wt%.

[0023] In step (3) of this invention, the ultrasonic dispersion power is 30W-700W and the time is 10-60min.

[0024] The catalyst mentioned in step (3) of this invention is selected from at least one of the following: dilute hydrochloric acid, glacial acetic acid, ammonia water, and the mass ratio of the catalyst to the aqueous ethanol solution is (0.01-0.2):1.

[0025] In step (3) of this invention, the molar ratio of deionized water to silane coupling agent is (0.1-0.4):1.

[0026] In step (3) of this invention, the heating temperature is 40℃-80℃, the time is 2-24h, and the stirring speed is controlled at 100-1000rpm.

[0027] In step (3) of this invention, the silane coupling agent is selected from at least one of 3-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, hexadecyltrimethoxysilane, and perfluorodecyltriethoxysilane, and the mass ratio of the silane coupling agent to the aqueous ethanol solution is (0.01-0.1):1.

[0028] In step (4) of this invention, the mass ratio of polymer film-forming resin to film-forming solvent is 1:(0.1-0.85).

[0029] In step (4) of the present invention, the polymer film-forming resin is selected from at least one of the following: polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, perfluoroalkoxy resin, ethylene-tetrafluoroethylene copolymer, methyl silicone resin, phenyl silicone resin, methylphenyl silicone resin, epoxy modified organosilicon resin, polyester modified organosilicon resin, preferably polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0030] In step (4) of this invention, the film-forming solvent is selected from at least one of the following: ethyl acetate, acetone, xylene, tetrahydrofuran, isopropanol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, N-methylpyrrolidone, dimethylformamide, and n-butanol.

[0031] In step (4) of this invention, the initial mixing speed of the polymer film-forming resin is 300-500 rpm and the time is 30-60 min.

[0032] In step (4) of this invention, the rotation speed after adding filler (hollow glass microspheres, fluorescent glass microspheres) is 200-800 rpm and the time is 1-4h.

[0033] In step (4) of this invention, the hollow glass microspheres are purchased directly from the market. Considering the scattering effect and dispersion stability of the coating surface, the average size is controlled at 0.5-15μm.

[0034] In step (4) of the present invention, in order to balance cooling efficiency and mechanical properties, the mass ratio of polymer film-forming resin to filler (hollow glass microspheres, fluorescent glass microspheres) is preferably 1: (0.1-0.5).

[0035] In step (4) of the present invention, in order to achieve scattering complementarity, the preferred mass ratio of modified hollow glass microspheres to fluorescent glass microspheres is 1:(0.05-0.2).

[0036] This invention innovatively introduces photoluminescent carbon quantum dots that can absorb ultraviolet light under sunlight and convert it into visible light, enhancing their emission in the visible light spectrum. The high-to-medium infrared emissivity is achieved through the organic polymer substrate and filler molecular structure, resulting in high emission in the mid-infrared band. Excellent self-cleaning functionality is achieved through fluorinated polymers. During hydrothermal carbonization, biomass undergoes a series of transformations, including hydrolysis, dehydration, decarboxylation, aromatization, and recondensation, ultimately producing carbon quantum dots. Producing carbon quantum dots from biomass not only achieves mild reaction conditions and a simple preparation process but also provides an environmentally friendly method to mitigate pollution and address the energy crisis associated with traditional carbon sources such as coal and oil. By introducing a core-shell structure to protect the carbon quantum dots, the shell physically isolates the surface from oxidation by substances such as oxygen or water. Simultaneously, the core-shell structure prevents direct contact between the carbon quantum dots and the organic polymer substrate, avoiding fluorescence attenuation due to π-π stacking or energy transfer.

[0037] Thirdly, this invention provides the application of the above-described coating or the coating prepared by the above-described method in equipment heat dissipation, particularly in the heat dissipation of charging piles for new energy vehicles. The photoluminescent daytime radiation cooling coating of this invention can be used for heat dissipation in charging piles for new energy vehicles, thereby effectively insulating and cooling the temperature, and is a promising candidate in advanced thermal management.

[0038] Compared with existing technologies, the advantages of this invention are: (1) The preparation process of carbon quantum dots is of great significance for solving pollution, curbing carbon dioxide emissions and reducing the burden of expensive waste disposal by transforming biological waste into sustainable high-value materials.

[0039] (2) The present invention avoids the quenching problem caused by aggregation by chemically and physically combining carbon quantum dots and hollow glass microspheres.

[0040] (3) The high density and high stability of the CF bonds in the PVDF-HFP matrix give it high surface energy and UV resistance and mechanical durability, thus giving the coating excellent hydrophobic self-cleaning ability and ensuring long-term outdoor stability.

[0041] (4) Compared with traditional radiation cooling coatings, this design combines high reflectivity and high radiation characteristics with engineering practicality: a single layer coating can achieve efficient heat dissipation, avoiding the complex process of multi-layer structures; at the same time, its lightweight characteristics and flexible film-forming ability make it easy to adapt to the irregular surface of charging piles.

[0042] (5) The solar reflectivity and infrared emissivity of the radiation cooling coating prepared by the present invention can reach more than 90%. Attached Figure Description

[0043] Figure 1 Scanning electron microscopy imaging of the PEI / PMMA@CDs prepared for this invention. Detailed Implementation

[0044] To enable those skilled in the art to better understand this invention, it is further described below with reference to specific embodiments.

[0045] Example 1: Preparation of carbon quantum dots

[0046] Waste grapefruit peels were washed multiple times with tap water and deionized water and then dried to constant weight at 60 °C. Subsequently, the waste grapefruit peels were finely ground using a stainless steel grinder to pass through a 100-mesh sieve. 1 g of the waste grapefruit peel powder was then precisely weighed into a polytetrafluoroethylene-lined autoclave, thoroughly mixed with 0.4 mL of ethylenediamine and 10 g of deionized water, and reacted at 180 °C for 5 h. After the reaction, the autoclave was allowed to cool naturally to room temperature. The resulting product was then centrifuged at 10,000 rpm for 20 min and double-filtered using a 0.22 μm aqueous microporous membrane. The filtrate was collected and purified using a 500 Da dialysis bag for 24 h to obtain liquid carbon quantum dots. The liquid carbon quantum dots were then lyophilized with liquid nitrogen and freeze-dried to form a powder, which was maintained below 4 °C for later use.

[0047] Examples 2-5: Preparation of carbon quantum dots

[0048] The preparation methods of Examples 2-5 are basically the same as those of Example 1, except for the hydrothermal temperature, hydrothermal time and solid-liquid ratio (mass ratio of waste grapefruit peel powder to deionized water). The specific parameters and the performance of the obtained carbon quantum dots are shown in Table 1 below.

[0049] Table 1 Comparison of test results in Examples 1-5

[0050] Example 6: Preparation of fluorescent glass microspheres 0.33 g of branched polyethyleneimine was dissolved in water and thoroughly mixed with 0.04 g of carbon quantum dot dispersion. The mixture was stirred at room temperature for 2 h to induce crosslinking. The solution was then transferred to a water-jacketed flask equipped with a condenser, thermocouple, magnetic stirrer, and nitrogen inlet. The mixture was stirred and purged with Ar at 80 °C for 30 min. 4 g of methyl methacrylate was added to the solution. After mixing for 5 min, 1 mL of 100 mM tert-butyl hydroperoxide was added to the stirred mixture to initiate polymerization. The mixture was then heated at 80 °C under an Ar atmosphere for 2 h to obtain a stable particulate dispersion. This dispersion was subsequently purified by centrifugation and washed with deionized water. Finally, the purified PEI / PMMA@CDs were stored at room temperature for later use. The resulting core-shell structure and hollow glass microspheres, ultrasonically cleaned and dried with ethanol, were mixed at a mass ratio of 4:1 and freeze-dried to obtain fluorescent glass microspheres.

[0051] Example 7: Coating Preparation and Performance Testing

[0052] Two g of hollow glass microspheres were dispersed in 100 mL of anhydrous ethanol, and 200 μL of ammonia and 3 mL of deionized water were added. The mixture was heated to 80 °C in an oil bath and stirred at 800 rpm for 30 min. Then, 200 μL of perfluorodecyltriethoxysilane was added, and the reaction was continued for 2 h. After cooling to room temperature, the product was centrifuged and washed twice with ethanol and deionized water to remove unreacted nanoparticles and silane coupling agent. The product was then vacuum dried in a 60 °C oven to constant weight to obtain modified hollow glass microspheres.

[0053] 5g of polyvinylidene fluoride-hexafluoropropylene was added to 4.5g of ethyl acetate, and the mixture was magnetically stirred at 400rpm for 1h at room temperature to obtain a homogeneous solution. 1.50g of modified hollow glass microspheres and 0.17g of fluorescent glass microspheres prepared in Example 6 were added to the above solution, and the mixture was stirred thoroughly at 600rpm for 3h to obtain a casting solution. The casting solution was coated onto a substrate, dried in air for 1h, and then dried in an oven at 60℃ for 4h to obtain a photoluminescent self-cleaning coating for daytime passive radiative cooling.

[0054] The solar reflectance (0.3-2.5 μm) of the sample was tested using a UV-Vis-NIR spectrophotometer equipped with a standard integrating sphere attachment. Simultaneously, the radiation characteristics of the coating in the mid-infrared band (2.5-25 μm) were tested using a Fourier transform infrared spectrometer equipped with an integrating sphere attachment. The contact angle of the coating was measured using an optical contact angle measuring device to evaluate its hydrophobicity and self-cleaning effect.

[0055] Comparative Example 1

[0056] The difference between Comparative Example 1 and Example 7 is that unmodified hollow glass microspheres were used instead of modified hollow glass microspheres in the steps, while other conditions remained the same.

[0057] Comparative Example 2

[0058] The difference between Comparative Example 2 and Example 7 is that only 1.67g of unmodified hollow glass microspheres were added in the steps, and fluorescent glass microspheres were not added, while other conditions were the same.

[0059] Comparative Example 3

[0060] The difference between Comparative Example 3 and Example 7 is that only 1.67g of modified hollow glass microspheres were added in the steps, and fluorescent glass microspheres were not added, while other conditions remained the same. The relevant performance test results are shown in Table 2.

[0061] Table 2 Comparison of test results between Example 7 and Comparative Examples 1-3

[0062] Examples 8-11: Coating performance with different filler ratios The preparation methods of Examples 8-11 are basically the same as those of Example 7, except that the amount of modified hollow glass microspheres and fluorescent glass microspheres added in the steps is different. The specific ratios and coating properties are shown in Table 3.

[0063] Table 3 Comparison of test results in Examples 7-11

[0064] Performance Analysis: Table 1 shows that in the hydrothermal preparation of carbon quantum dots, hydrothermal temperature has the greatest impact on the formation process, followed by the solid-liquid ratio, while hydrothermal time has the least impact. Considering both the yield and cost-effectiveness of carbon quantum dots, the optimal conditions were determined as follows: hydrothermal temperature of 180℃, hydrothermal duration of 5 h, and solid-liquid ratio of 1:10. Hydrothermal temperature, reaction time, and solid-liquid ratio affect the fluorescence intensity and quantum yield of carbon quantum dots by regulating carbon nucleus formation, surface functional group modification, and defect state distribution: temperature determines the degree of carbonization of the carbon source (low temperature generates small sp² domains that emit blue light, while high temperature expands the conjugated structure, causing a redshift but potentially quenching); time affects the uniformity of carbon nuclei and surface passivation (insufficient time leads to defects, while excessive time causes aggregation); the solid-liquid ratio changes the precursor concentration (low concentration results in small size and high quantum yield, while high concentration easily leads to aggregation and reduced luminescence efficiency). The synergistic effect of these three factors optimizes the balance between surface states and lattice defects, thereby regulating the luminescence performance.

[0065] The reflectance of the samples in the solar band (0.3-2.5 μm) was measured using a UV-Vis-NIR spectrophotometer equipped with a standard integrating sphere attachment. Simultaneously, the radiation characteristics of the coating in the mid-infrared band (2.5-25 μm) were measured using a Fourier transform infrared spectrometer equipped with an integrating sphere attachment. The contact angle of the coating was measured using an optical contact angle measuring device to evaluate its hydrophobicity and self-cleaning properties. The results are shown in Tables 2 and 3.

[0066] As shown in Table 2, the photoluminescent self-cleaning coating provided in Example 7, through the synergistic combination of perfluorodecyltriethoxysilane-modified hollow glass microspheres and fluorescent glass microspheres, exhibits excellent daytime passive radiative cooling performance and self-cleaning function. Test results show that the coating of Example 7 has a solar reflectance of 92.3%, a mid-infrared emissivity of 94.1%, and a contact angle of 152.5°, significantly better than the control groups such as Comparative Example 1. Comparative Example 1, using an unmodified hollow glass microsphere coating, has a solar reflectance reduced to 83.2%, a mid-infrared emissivity of 87.4%, and a contact angle of 85.2°; the performance of the coating in Comparative Example 2, without fluorescent glass microspheres, further declines; while Comparative Example 3, although using modified microspheres but without adding fluorescent components, has a slightly lower solar reflectance than Example 7. These comparative experiments fully demonstrate the synergistic effect of perfluorosilane surface modification and fluorescent components: the modified microspheres not only enhance the hydrophobicity of the coating by introducing low surface energy groups (-CF3 / -CF2), but also improve the mid-infrared radiation efficiency; the fluorescent microspheres further optimize the solar reflection performance through ultraviolet light conversion.

[0067] Table 3 measures the effect of different filler ratios on the reflectivity, emissivity, and contact angle of the coating. In Examples 8-10, insufficient microsphere content resulted in inadequate scattering and weak interface effects. In Example 7, the microspheres generated interface-polarized phonons, broadening the radiation peak to 6-25 μm. In Example 11, the microspheres agglomerated, creating light scattering dead zones, resulting in actual reflectivity lower than theoretically calculated values. Increased porosity also reduced infrared emissivity. Furthermore, excessively high microsphere content weakened the PVDF-HFP coating capacity, leading to decreased mechanical strength. Example 7, through a precise ratio of 22.5% hollow microspheres + 2.5% fluorescent microspheres, optimized optical, thermal, and surface properties, overcoming the traditional material contradiction of "high reflectivity equals low emissivity" or "superhydrophobicity equals easy detachment." The perfluorosilane-modified microspheres formed a chemical-physical dual bond with the PVDF-HFP matrix, achieving a balance between high emissivity and mechanical strength.

[0068] It is evident that the beneficial effects of this invention are mainly reflected in the following aspects: 1. Triple Function Synergy: (1) Photoluminescence function: Carbon quantum dots derived from waste biomass emit visible light when excited by sunlight (especially ultraviolet light). This "down-conversion" process not only gives the coating an indication or marking function in the dark environment, but more importantly, it converts harmful ultraviolet light that is easily absorbed by materials into visible light that is not easily absorbed, thereby reducing the heat input of solar radiation from the source. Together with the scattering effect of hollow glass microspheres, it increases the solar reflectivity of the coating to more than 90% (up to 92.3%).

[0069] (2) High-efficiency radiation cooling function: Fluoropolymers such as PVDF-HFP have intrinsically high emissivity in the mid-infrared band (especially 8-13μm); the introduction of hollow glass microspheres can effectively scatter sunlight and enhance the infrared emission interface; the microspheres modified with perfluorosilane are coupled with the PVDF-HFP matrix interface, which can excite interface polarized phonons, further broadening and enhancing the radiation capability in the mid-infrared band, so that the infrared emissivity of the coating reaches more than 94%. The synergy between light conversion and high scattering and high radiation breaks through the contradiction that traditional materials cannot achieve both high reflectivity and high emission.

[0070] (3) Long-lasting self-cleaning function: Both PVDF-HFP resin and perfluorosilane modified microspheres are rich in low surface energy -CF2- / CF3 groups, which makes the coating surface form a stable superhydrophobic state (water contact angle >150°), with excellent water repellency and anti-fouling ability. Pollutants are difficult to adhere to, and even if they do, they are easily washed away by rainwater, thus maintaining the optical cleanliness of the coating surface for a long time and ensuring the long-lasting stability of radiative cooling performance.

[0071] 2. Unique structural design solves key technical problems: (1) A creative PEI / PMMA core-shell structure is used to load carbon quantum dots. This structure encapsulates the carbon quantum dots, physically isolating them from oxygen, moisture, and other carbon quantum dots. This effectively solves the oxidation, aggregation, and fluorescence quenching problems that easily occur when carbon quantum dots are directly doped, ensuring the long-term stability of their fluorescence performance.

[0072] (2) Surface grafting modification of hollow glass microspheres using perfluorosilanes. The modified microspheres are rich in fluorinated long chains, which not only have excellent compatibility with the PVDF-HFP matrix, enhancing the filler-matrix interfacial bonding force and improving the mechanical strength of the coating, but also introduce these low surface energy groups to the coating surface, which is key to achieving superhydrophobic self-cleaning. At the same time, this modification optimizes the interfacial optical properties, which is beneficial to infrared emission.

[0073] 3. Harmony between environmental friendliness and high performance: Carbon quantum dots are prepared from waste grapefruit peels and other biomass, achieving high-value utilization of waste resources and conforming to the concept of green chemistry. Through optimized composite processes, multiple functions can be integrated with a simple single-layer coating process, avoiding complex and expensive multi-layer coating or nanoimprinting processes. It is low-cost, easy to scale up production and construction, and is particularly suitable for the surfaces of large or irregularly shaped equipment such as charging piles.

[0074] 4. Excellent Overall Performance: Experimental data show that the coating prepared in the preferred embodiment of this invention has a solar reflectivity of up to 92.3%, a mid-infrared emissivity of 94.1%, and a water contact angle of 152.5°, demonstrating excellent heat dissipation potential and superhydrophobic properties. Compared with the unmodified sample without added fluorescent components, the performance improvement is significant, proving that there is a clear synergistic enhancement effect among the components, rather than a simple additive effect.

[0075] In summary, this invention, through an innovative combination of biomass-sourced carbon quantum dots, perfluorosilane-modified hollow glass microspheres, and a fluoropolymer matrix, and utilizing a core-shell structure to protect the carbon quantum dots, successfully prepared a multifunctional coating that combines efficient radiative cooling (reflectivity >92%, emissivity >94%), superhydrophobic self-cleaning (contact angle >150°), and photoluminescence. This coating has a simple and environmentally friendly preparation process, making it particularly suitable for thermal management of outdoor electronic devices such as new energy vehicle charging piles, and possesses significant application value.

[0076] The above embodiments of the present invention are for illustrative purposes only and are not intended to limit the present invention. Any modifications or changes that conform to the scope of protection defined in the claims of this application and their equivalent technical solutions shall be deemed to be included within the scope of the claims of this patent.

Claims

1. A self-cleaning radiative cooling coating based on biomass carbon quantum dots, characterized in that, It includes a polymeric film-forming resin and fillers, wherein the fillers include modified hollow glass microspheres and fluorescent glass microspheres loaded with carbon quantum dots; The modified hollow glass microspheres are hollow glass microspheres that have been surface modified with a silane coupling agent; The fluorescent glass microspheres loaded with carbon quantum dots are a composite containing carbon quantum dots and hollow glass microspheres, wherein the carbon quantum dots are coated with polymer to form a core-shell structure and then loaded on the surface of the hollow glass microspheres. The polymeric film-forming resin is selected from at least one of fluoropolymers or organosilicon resins.

2. The self-cleaning radiative cooling coating based on biomass carbon quantum dots according to claim 1, characterized in that, The biomass carbon quantum dots are prepared from waste biomass via hydrothermal carbonization, and the waste biomass is selected from grapefruit peel, orange peel, tea leaves, or coffee grounds.

3. The self-cleaning radiative cooling coating based on biomass carbon quantum dots according to claim 1, characterized in that, The mass ratio of the polymer film-forming resin to the filler is 1:(0.1-0.5); the mass ratio of the modified hollow glass microspheres to the fluorescent glass microspheres loaded with carbon quantum dots is 1:(0.05-0.2).

4. The self-cleaning radiative cooling coating based on biomass carbon quantum dots according to claim 1, characterized in that, The core-shell structure uses polymethyl methacrylate as the core and branched polyethyleneimine as the shell, with the carbon quantum dots encapsulated within the core or shell.

5. The self-cleaning radiative cooling coating based on biomass carbon quantum dots according to claim 1, characterized in that, The polymeric film-forming resin is selected from at least one of the following: polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, perfluoroalkoxy resin, ethylene-tetrafluoroethylene copolymer, methyl silicone resin, phenyl silicone resin, methylphenyl silicone resin, epoxy-modified silicone resin, and polyester-modified silicone resin.

6. The method for preparing a self-cleaning radiation cooling coating based on biomass carbon quantum dots as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Prepare biomass carbon quantum dots by hydrothermal carbonization of waste biomass; (2) Preparation of fluorescent glass microspheres: Branched polyethyleneimine, carbon quantum dots and methyl methacrylate monomers are reacted in the presence of an initiator to form polymer core-shell particles coated with carbon quantum dots, which are then combined with hollow glass microspheres to obtain fluorescent glass microspheres loaded with carbon quantum dots. (3) Preparation of modified hollow glass microspheres: Disperse hollow glass microspheres in a solvent, add a catalyst and a silane coupling agent to carry out a surface modification reaction, and obtain the modified hollow glass microspheres; (4) Dissolve the polymer film-forming resin in the film-forming solvent, add the fluorescent glass microspheres obtained in step (2) and the modified hollow glass microspheres obtained in step (3), disperse them evenly, coat them on the substrate and cure them to obtain the coating.

7. The method for preparing a self-cleaning radiation cooling coating based on biomass carbon quantum dots according to claim 6, characterized in that, In step (1), the hydrothermal temperature is 180~220℃; the hydrothermal time is 2~10 h; in step (2), the mass ratio of carbon quantum dots to methyl methacrylate is (0.01~0.05):1; the mass ratio of branched polyethyleneimine to methyl methacrylate is (0.03-0.1):1; the initiator is selected from one of potassium persulfate, tert-butyl hydroperoxide, ammonium persulfate, and potassium persulfate / sodium bisulfite; the mass ratio of the initiator to methyl methacrylate is (0.5-2):100; the reaction temperature for forming the polymer core-shell particles coated with carbon quantum dots is 30~90℃, and the reaction time is 1~12 h; the mass ratio of the polymer core-shell particles coated with carbon quantum dots to hollow glass microspheres is (3-15):

1.

8. The method for preparing a self-cleaning radiation cooling coating based on biomass carbon quantum dots according to claim 6, characterized in that, In step (3), the catalyst is selected from at least one of the following: dilute hydrochloric acid, glacial acetic acid, and ammonia; the silane coupling agent is selected from at least one of 3-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, hexadecyltrimethoxysilane, and perfluorodecyltriethoxysilane.

9. The method for preparing a self-cleaning radiation cooling coating based on biomass carbon quantum dots according to claim 6, characterized in that, In step (4), the mass ratio of the polymer film-forming resin to the film-forming solvent is 1:(0.1-0.85); the film-forming solvent is selected from at least one of the following: ethyl acetate, acetone, xylene, tetrahydrofuran, isopropanol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, N-methylpyrrolidone, dimethylformamide, n-butanol; the fluorescent glass microspheres obtained in step (2) and the modified hollow glass microspheres obtained in step (3) are used as fillers, and the mass ratio of the polymer film-forming resin to the filler is 1:(0.1-0.5); the mass ratio of the modified hollow glass microspheres obtained in step (3) to the fluorescent glass microspheres obtained in step (2) is 1:(0.05-0.2).

10. The application of a coating as described in any one of claims 1-5 or a coating prepared by the preparation method as described in any one of claims 6-9 in heat dissipation of equipment, characterized in that, The device is a charging pile for new energy vehicles.

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