Cellulose-based room temperature phosphorescent carbon quantum dots coating, and preparation method and application thereof

Abstract

The application discloses a cellulose-based room-temperature phosphorescent carbon quantum dot coating and a preparation method and application thereof, and belongs to the technical field of room-temperature phosphorescent coatings. The preparation method specifically comprises the following steps: (1) cellulose-based precursor solution preparation; (2) solvothermal carbonization and purification treatment; (3) urea modification treatment; and (4) coating compounding. The application takes natural cellulose as a green precursor, and through solvothermal nitrogen doping of cellulose and urea modification cooperation, in combination with rigid confinement of the waterborne polyurethane emulsion, a carbon quantum dot coating with long service life, color adjustment, and high-efficiency room-temperature phosphorescent performance is prepared. The coating is not only environment-friendly and simple in process, but also has excellent compatibility with a wood-based material, and has good mechanical performance and long-term stability, and can be widely applied to fields of high-end decoration, intelligent packaging and information encryption anti-counterfeiting and the like.

Description

Technical Field

[0001] This invention belongs to the field of room temperature phosphorescent coating technology, specifically relating to a cellulose-based room temperature phosphorescent carbon quantum dot coating, its preparation method, and its application. Background Technology

[0002] With the rapid development of the functional coatings industry, new coatings that combine luminescent properties with environmental friendliness are showing broad application prospects in fields such as architectural decoration, safety warnings, anti-counterfeiting labels, and bio-imaging auxiliary coatings. Room temperature phosphorescent materials, with their unique luminescent characteristics of long afterglow and long lifespan, can continue to emit light for several seconds to several minutes after the excitation source is turned off. Utilizing time-resolved technology, they can effectively avoid background fluorescence interference and achieve high-contrast signal recognition, making them a research hotspot in the field of luminescent materials in recent years.

[0003] However, most of the currently developed room-temperature phosphorescent coatings have significant technical shortcomings: early phosphorescent coatings mostly used inorganic sulfides and precious metal complexes containing heavy metals as the luminescent core, which are not only scarce in resources and expensive to prepare, but also pose a risk of biotoxicity from heavy metal leaching, completely failing to meet the environmental protection requirements of scenarios such as home and children's products. The emerging pure organic room-temperature phosphorescent materials mostly rely on complex small-molecule lattice structures to achieve triplet exciton stability. These materials are highly sensitive to environmental factors such as water and oxygen, and are prone to phosphorescence quenching in the daily use environment after coating film formation, making it difficult to maintain a stable long-afterglow luminescence effect.

[0004] In recent years, carbon quantum dots have been increasingly used in the preparation of luminescent coatings due to their advantages of low toxicity, ease of modification, and good optical stability. However, most existing carbon quantum dot-modified coatings use petroleum-based chemical raw materials as carbon sources. This not only results in high raw material costs and poor biocompatibility but also makes it difficult to achieve efficient room-temperature phosphorescence emission. Most products only produce ordinary fluorescence effects and cannot leverage the unique long afterglow advantage of room-temperature phosphorescent materials. Furthermore, current mainstream carbon quantum dot-modified coatings generally suffer from weak interfacial bonding between carbon quantum dots and the resin matrix, as well as uneven dispersion. After long-term use, defects such as luminescent layer peeling, insufficient coating hardness, and poor weather resistance are prone to occur. Some products also retain volatile organic solvents, failing to meet the current low-VOC environmental protection requirements of the coating industry.

[0005] In existing technologies, some studies have attempted to improve the stability of organic room-temperature phosphorescence by encapsulating it in a rigid polymer matrix. For example, phosphorescent small molecules are directly doped into polymer matrices such as PVA, using hydrogen bonding to restrict molecular vibrations and reduce non-radiative transitions. However, the phosphorescence quantum yield of these systems is generally low, and the matrix has poor water resistance, easily undergoing structural damage upon contact with water, making them completely unsuitable for coating applications in outdoor and high-humidity environments. Furthermore, the current preparation of carbon quantum dots mostly relies on non-renewable chemical raw materials as precursors, failing to fully utilize agricultural and forestry biomass resources. This not only contradicts the trend of green and low-carbon industrial development but also further increases the cost of large-scale production of functional phosphorescent coatings.

[0006] Therefore, how to develop a new type of functional coating with renewable cellulose as the core precursor, which has high stable room temperature phosphorescence properties, is environmentally friendly and low in toxicity, has strong adhesion and excellent weather resistance, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a cellulose-based room temperature phosphorescent carbon quantum dot coating, its preparation method and application, so as to overcome the shortcomings of the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a cellulose-based room-temperature phosphorescent carbon quantum dot coating specifically includes the following steps: (1) Preparation of cellulose-based precursor solution Cellulose, nitrogen source and solvent are stirred until dissolved to obtain cellulose-based precursor solution; (2) Solvent thermal carbonization and purification treatment A cellulose-based precursor solution was subjected to a solvothermal reaction, and after natural cooling, it was centrifuged, filtered, and dialyzed to obtain a cellulose-based carbon quantum dot solution. (3) Urea modification treatment Cellulose-based carbon quantum dot solution, urea and water are stirred until dissolved, evaporated, and ground to obtain urea-modified cellulose-based carbon quantum dots; (4) Coating composite The cellulose-based room temperature phosphorescent carbon quantum dot coating is obtained by mixing urea-modified cellulose-based carbon quantum dots and water-based polyurethane emulsion evenly.

[0010] Furthermore, in step (1) above, the cellulose is microcrystalline cellulose, waste pulp cellulose or cellulose extracted from agricultural straw, with a purity ≥90%; the nitrogen source is o-phenylenediamine, m-phenylenediamine or p-phenylenediamine; the solvent is sulfoxide, acetone or N,N-dimethylformamide (DMF); the ratio of cellulose, nitrogen source and solvent is 0.01g:0.03g:20mL.

[0011] The further beneficial effect of the above method lies in the fact that nitrogen-doped carbon quantum dots are prepared by using natural cellulose as the carbon source, o-phenylenediamine / m-phenylenediamine / p-phenylenediamine as the nitrogen source, and sulfoxide, acetone, and DMF as solvents, respectively, via a one-pot solvothermal carbonization reaction. The introduction of the nitrogen source allows for the tuning of the surface functional groups and electronic structure of the carbon quantum dots, providing a foundation for room-temperature phosphorescence performance.

[0012] Furthermore, in step (1) above, the stirring temperature is room temperature and the stirring time is 30 minutes.

[0013] Furthermore, in step (2) above, the equipment for the solvothermal reaction is a polytetrafluoroethylene-lined hydrothermal reactor and a forced-air drying oven, with a temperature of 160℃ and a time of 6h; the centrifugation speed is 8000r / min and the time is 30min; the filtration uses a 0.22μm filter membrane; the dialysis uses a dialysis bag with a molecular weight cutoff of 1000Da, with a time of 72h and water changed every 8h.

[0014] The further beneficial effect of the above-mentioned method is that the purity and dispersion stability of carbon quantum dots are ensured through centrifugation, filtration, and dialysis purification.

[0015] Furthermore, in step (3) above, the ratio of cellulose-based carbon quantum dot solution, urea and water is 10mL:2g:20mL; the stirring temperature is 50℃ and the time is 30min; the evaporation equipment is an evaporating dish and an oven, the temperature is 150℃ and the time is 2.5h.

[0016] The further beneficial effect of the above-mentioned method is that, through the interaction between urea and the hydroxyl groups on the surface of carbon quantum dots, a rigid network structure is formed, which further suppresses the nonradiative transition of the excited triplet state of carbon quantum dots, significantly prolongs the phosphorescence lifetime and improves the luminescence intensity, while enhancing the compatibility between carbon quantum dots and waterborne polyurethane emulsions.

[0017] Furthermore, in step (4) above, the solid content of the waterborne polyurethane emulsion is 40%-50%, preferably 45%; the mass ratio of urea-modified cellulose-based carbon quantum dots to waterborne polyurethane emulsion is (2-2.5):100, preferably 2.5:100; the stirring temperature is room temperature, the stirring speed is 3000 r / min, and the stirring time is 20 min.

[0018] The further beneficial effect of the above method lies in the fact that urea-modified carbon quantum dots and waterborne polyurethane emulsion are mixed in an optimized ratio and uniformly dispersed by high-speed stirring. The waterborne polyurethane emulsion not only possesses excellent film-forming properties and environmental friendliness, but its carboxyl and ester groups on its molecular chain can also form hydrogen bonds with the functional groups on the surface of carbon quantum dots, constructing a rigid confined environment, stabilizing triplet excitons, and synergistically improving room-temperature phosphorescence performance.

[0019] This invention also claims protection for a cellulose-based room-temperature phosphorescent carbon quantum dot coating prepared by the above-described method.

[0020] This invention also claims protection for the application of a cellulose-based room-temperature phosphorescent carbon quantum dot coating prepared by the above-described method in high-end decoration, intelligent interactive packaging, or information encryption and anti-counterfeiting. Specifically, in the field of information encryption and anti-counterfeiting, the coating of this invention can form concealed patterns through screen printing or inkjet printing, requiring ultraviolet light excitation and delayed observation (≥5s) to decrypt the information, and different nitrogen source-solvent combinations correspond to specific phosphorescent colors and lifetime codes.

[0021] A method for preparing a board containing a cellulose-based room temperature phosphorescent carbon quantum dot coating obtained by the above preparation method includes the following steps: applying the coating to the surface of a pretreated wood substrate, drying, cooling and then repeating the application, drying again, and allowing it to cool naturally to form a room temperature phosphorescent coating.

[0022] Furthermore, the aforementioned wood-based material is a engineered wood product, preferably particleboard; the pretreatment includes sanding with 400-600 grit sandpaper, wiping with anhydrous ethanol to remove oil, and air drying; the thickness of a single brush coating is 50-80 μm; the drying equipment is a forced-air drying oven at a temperature of 60°C for 1 hour; the re-drying equipment is a forced-air drying oven at a temperature of 70°C for 1.5 hours.

[0023] The further beneficial effect of adopting the above-mentioned method is that a uniform coating is formed on the surface of the pretreated artificial board through a two-coat process, the curing temperature and time are controlled to ensure a strong bond between the coating and the substrate, while retaining excellent room temperature phosphorescence properties and mechanical properties.

[0024] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: 1. Green and sustainable: Using natural cellulose (such as waste pulp and straw) as raw materials to achieve high-value utilization of biomass resources.

[0025] 2. Excellent phosphorescence performance: Through synergistic regulation of nitrogen doping and urea modification, carbon quantum dots (particle size 3-10nm) achieve a room temperature phosphorescence lifetime of ≥10s (excitation wavelength 365nm) and a fluorescence quantum yield of ≥25% (tested according to GB / T 38250 standard); after QUV accelerated aging for 1000h, the phosphorescence intensity retention rate is ≥75% and the afterglow time decay rate is ≤30%; the phosphorescence color can be tuned from blue to orange-red, which is far superior to traditional cellulose-based luminescent materials; and the phosphorescence performance is responsive to environmental humidity, pH or volatile organic compounds.

[0026] 3. Good interfacial compatibility: Cellulose-based carbon quantum dots and wood-based substrates have the advantage of "homogeneous enhancement". Combined with urea modification and resin composite process, the compatibility and adhesion of the coating are improved. The coating adhesion reaches level 1 (tested by cross-cut test according to GB / T9286-1998), the pencil hardness is ≥2H (tested according to GB / T 6739-2022), and the visible light transmittance is ≥80% (400-800nm), without affecting the original decorative effect of wood.

[0027] 4. Strong process adaptability: The preparation process uses conventional equipment, and the coating can be achieved by brushing, roller coating or spraying. The curing conditions are mild, adaptable to existing artificial board production lines, and suitable for large-scale production.

[0028] 5. Wide range of applications: Combining long-life room temperature phosphorescence and environmental responsiveness, it can be applied to high-end decoration, intelligent interactive packaging or information encryption and anti-counterfeiting fields, with huge market potential.

[0029] In summary, this invention utilizes natural cellulose as a green precursor and, through the synergistic effect of solvothermal nitrogen doping of cellulose and urea modification, combined with the rigid confinement effect of waterborne polyurethane emulsion, produces a carbon quantum dot coating with long lifespan, tunable color, and high-efficiency room-temperature phosphorescence properties. This coating is not only environmentally friendly and simple to process, but also exhibits excellent compatibility with wood-based substrates, good mechanical properties, and long-term stability, making it widely applicable in high-end decoration, smart packaging, and information encryption and anti-counterfeiting fields. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 The preparation method of urea-modified cellulose-based carbon quantum dots (o-phenylenediamine-thionyl chloride system) specifically includes the following steps: (1) Preparation of cellulose-based precursor solution Take a 250mL beaker, add 0.01g microcrystalline cellulose (95% purity) and 0.03g o-phenylenediamine, add 20mL thionyl chloride solvent, and stir magnetically at room temperature for 30min until the solid is completely dissolved to obtain a uniform and transparent cellulose-based precursor solution. (2) Solvent thermal carbonization treatment The cellulose-based precursor solution was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, sealed, and placed in a forced-air drying oven for reaction at 160 °C for 6 h. (3) Purification treatment After the reaction was completed, the product was allowed to cool naturally to room temperature. The product was then poured into a centrifuge tube and centrifuged at 80,000 r / min for 30 min. The supernatant was then filtered through a 0.22 μm filter membrane to remove any residual residue. The filtrate was then transferred to a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed in deionized water for 72 h. The deionized water was changed every 8 h to obtain a pure cellulose-based carbon quantum dot solution. (4) Urea modification treatment Take 10 mL of cellulose-based carbon quantum dot solution, add 2 g of urea and 20 mL of deionized water, heat and stir at 50 °C for 30 min until the urea is completely dissolved, transfer to a 100 mL evaporating dish, place in an oven at 150 °C and heat for 2.5 h, evaporate the water to obtain a fluffy solid, grind it into powder to obtain urea-modified cellulose-based carbon quantum dots with a yield of 26% and a particle size of 5.3 ± 0.8 nm.

[0032] Example 2 The preparation method of urea-modified cellulose-based carbon quantum dots (m-phenylenediamine-acetone system) differs from that in Example 1 only in that o-phenylenediamine is replaced with m-phenylenediamine and thionyl chloride is replaced with acetone.

[0033] Example 3 The preparation method of urea-modified cellulose-based carbon quantum dots (p-phenylenediamine-DMF system) differs from that in Example 1 only in that o-phenylenediamine is replaced with p-phenylenediamine and thionyl chloride is replaced with DMF.

[0034] Example 4 The preparation method of cellulose-based room temperature phosphorescent carbon quantum dot coating specifically includes the following steps: Take 0.5g of the urea-modified cellulose-based carbon quantum dots prepared in Example 1, add 20g of waterborne polyurethane emulsion (solid content 45%), place it in a high-speed disperser, and stir at 3000r / min for 30min to obtain a uniform and stable cellulose-based room temperature phosphorescent carbon quantum dot coating.

[0035] Example 5 The preparation method of cellulose-based room temperature phosphorescent carbon quantum dot coating differs from that of Example 4 only in that the urea-modified cellulose-based carbon quantum dots obtained in Example 2 are used.

[0036] Example 6 The preparation method of cellulose-based room temperature phosphorescent carbon quantum dot coating differs from that of Example 4 only in that the urea-modified cellulose-based carbon quantum dots obtained in Example 3 are used.

[0037] Example 7 A method for preparing a substrate containing a cellulose-based room-temperature phosphorescent carbon quantum dot coating, characterized by comprising the following steps: (1) Substrate pretreatment Select particleboard as the substrate, cut it into 10cm×10cm×5mm specimens, sand it smooth with 400-grit sandpaper, wipe the surface with anhydrous ethanol to remove oil, and let it air dry for 2 hours before use. (2) Coating forming The coating prepared in Example 2 was applied evenly to the surface of the artificial board using a wool brush in a "horizontal first, then vertical" pattern, with the coating thickness controlled at 60 μm. The board was then placed in a 60°C forced-air drying oven for 1 hour to pre-cur it. After cooling to room temperature, the coating was applied once more and then placed in a 70°C forced-air drying oven for 1.5 hours to dry. The board was then allowed to cool naturally to room temperature to form a room temperature phosphorescent coating.

[0038] Example 8 The method for preparing a board containing a cellulose-based room temperature phosphorescent carbon quantum dot coating differs from that in Example 7 only in that the cellulose-based room temperature phosphorescent carbon quantum dot coating obtained in Example 5 is applied.

[0039] Example 9 The method for preparing a board containing a cellulose-based room temperature phosphorescent carbon quantum dot coating differs from that in Example 7 only in that the cellulose-based room temperature phosphorescent carbon quantum dot coating obtained in Example 6 is applied.

[0040] Performance testing The boards prepared in Examples 7-9 were tested for their room temperature phosphorescent coatings according to relevant standards, and the results are shown in Table 1.

[0041] Table 1. Performance test results of room temperature phosphorescent coatings on substrates in Examples 7-9

[0042] As shown in Table 1, the room temperature phosphorescent coating of the substrate in Example 7 has the best overall performance, the longest phosphorescence lifetime, and the highest quantum yield, making it the preferred option.

[0043] The above experiments demonstrate that this invention achieves highly efficient room-temperature phosphorescence performance through the synergistic effect of solvothermal nitrogen doping of cellulose and urea modification, combined with the rigid confinement effect of waterborne polyurethane emulsion. Simultaneously, it leverages the "homogeneous synergistic" advantage of cellulose and wood-based substrates to improve coating compatibility and adhesion. This invention clarifies the optimal process for carbon quantum dot preparation and modification, demonstrates key parameters for coating composite and coating formation, verifies the excellent performance of the coating through standardized testing, and compares the effects of different nitrogen source-solvent combinations, providing a basis for process optimization. Those skilled in the art can appropriately adjust parameters such as the type of nitrogen source, solvent type, and amount of carbon quantum dots added within the scope of this invention according to actual application needs, all of which can achieve the technical effects of this invention.

[0044] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a cellulose-based room-temperature phosphorescent carbon quantum dot coating, characterized in that, Specifically, the following steps are included: (1) Preparation of cellulose-based precursor solution Cellulose, nitrogen source and solvent are stirred until dissolved to obtain cellulose-based precursor solution; (2) Solvent thermal carbonization and purification treatment A cellulose-based precursor solution was subjected to a solvothermal reaction, and after natural cooling, it was centrifuged, filtered, and dialyzed to obtain a cellulose-based carbon quantum dot solution. (3) Urea modification treatment Cellulose-based carbon quantum dot solution, urea and water are stirred until dissolved, evaporated, and ground to obtain urea-modified cellulose-based carbon quantum dots; (4) Coating composite The cellulose-based room temperature phosphorescent carbon quantum dot coating is obtained by mixing urea-modified cellulose-based carbon quantum dots and water-based polyurethane emulsion evenly.

2. The method for preparing a cellulose-based room-temperature phosphorescent carbon quantum dot coating according to claim 1, characterized in that, In step (1), the cellulose is microcrystalline cellulose, waste pulp cellulose or cellulose extracted from agricultural straw; the nitrogen source is o-phenylenediamine, m-phenylenediamine or p-phenylenediamine; the solvent is sulfoxide, acetone or N,N-dimethylformamide; the ratio of cellulose, nitrogen source and solvent is 0.01g:0.03g:20mL.

3. The method for preparing a cellulose-based room-temperature phosphorescent carbon quantum dot coating according to claim 1, characterized in that, In step (1), the stirring temperature is room temperature and the stirring time is 30 minutes.

4. The method for preparing a cellulose-based room-temperature phosphorescent carbon quantum dot coating according to claim 1, characterized in that, In step (2), the equipment for the solvothermal reaction is a polytetrafluoroethylene-lined hydrothermal reactor and a forced-air drying oven, with a temperature of 160°C and a time of 6 hours; the centrifugation speed is 80,000 r / min and the time is 30 minutes; the filtration uses a 0.22 μm filter membrane; the dialysis uses a dialysis bag with a molecular weight cutoff of 1000 Da and a time of 72 hours, with water changed every 8 hours.

5. The method for preparing a cellulose-based room-temperature phosphorescent carbon quantum dot coating according to claim 1, characterized in that, In step (3), the ratio of the cellulose-based carbon quantum dot solution, urea and water is 10mL:2g:20mL; the stirring temperature is 50℃ and the time is 30min; the evaporation equipment is an evaporating dish and an oven, the temperature is 150℃ and the time is 2.5h.

6. The method for preparing a cellulose-based room-temperature phosphorescent carbon quantum dot coating according to claim 1, characterized in that, In step (4), the solid content of the aqueous polyurethane emulsion is 40%-50%; the mass ratio of the urea-modified cellulose-based carbon quantum dots to the aqueous polyurethane emulsion is (2-2.5):100; the stirring temperature is room temperature, the stirring speed is 3000 r / min, and the stirring time is 20 min.

7. A cellulose-based room-temperature phosphorescent carbon quantum dot coating prepared by the preparation method according to any one of claims 1-6.

8. The application of a cellulose-based room temperature phosphorescent carbon quantum dot coating prepared by any one of claims 1-6 in high-end decoration, intelligent interactive packaging, or information encryption and anti-counterfeiting.

9. A method for preparing a substrate containing a cellulose-based room-temperature phosphorescent carbon quantum dot coating obtained by any one of the preparation methods described in claims 1-6, characterized in that, Specifically, the following steps are included: The coating is applied to the pretreated wood substrate surface, dried, cooled, and then applied again, dried again, and allowed to cool naturally to form a room temperature phosphorescent coating.

10. The method for preparing a board containing a cellulose-based room-temperature phosphorescent carbon quantum dot coating according to claim 9, characterized in that, The wood substrate is a engineered wood product; the pretreatment includes sanding with 400-600 grit sandpaper, wiping with anhydrous ethanol to remove oil, and air drying; the thickness of a single coating applied by brushing is 50-80 μm; the drying equipment is a forced-air drying oven at a temperature of 60°C for 1 hour; the re-drying equipment is a forced-air drying oven at a temperature of 70°C for 1.5 hours.

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