Lignin-based carbon quantum dot coating and preparation method and application thereof

Abstract

The application discloses a kind of lignin-based carbon quantum dots coating and its preparation method and application, belong to functional coating technical field.The preparation method specifically includes the following steps: (1) lignin-based precursor solution preparation;(2) solvothermal reaction and purification treatment;(3) coating compound.The present application uses industrial byproduct lignin as carbon source, by solvothermal carbonization reaction preparation high quantum yield nitrogen-doped carbon quantum dots, again with water-based resin compound forms dual-function coating with efficient ultraviolet shielding and fluorescent alarm, while ensuring that coating and wood substrate good compatibility.The coating not only can efficiently block full-band ultraviolet, protect wood substrate from aging, also can be directly fed back coating integrity and protection state by fluorescence signal change, and preparation process green environmental protection, simple process, suitable for large-scale production, can be widely used in wood material protection, intelligent packaging, health monitoring and other fields, has important scientific value and market prospect.

Description

Technical Field

[0001] This invention relates to the field of functional coatings technology, specifically to a lignin-based carbon quantum dot coating, its preparation method, and its application. Background Technology

[0002] UV-shielding functional coatings, by intercepting or converting high-energy ultraviolet radiation in the 280-400nm wavelength band, can effectively delay the photo-oxidative aging of polymer materials and wood-based substrates, preventing problems such as yellowing, chalking, and strength reduction. They have been widely used in furniture, construction, packaging, and other fields. With industry development, coatings with only protective functions can no longer meet the needs of high-end applications, and multifunctional coatings that combine protection and intelligent response characteristics have become a research hotspot.

[0003] Wood-based materials (such as engineered wood and solid wood) are core substrates for furniture and construction. Their wood fibers and adhesives are extremely sensitive to ultraviolet (UV) radiation, and prolonged exposure to sunlight can easily lead to aging and failure. Traditional UV protection solutions mainly rely on petroleum-based organic absorbers (such as benzotriazoles) or inorganic nanoparticles (such as ZnO and TiO2), but these solutions have several drawbacks: organic absorbers are prone to photodegradation leading to "light depletion," while inorganic particles have poor dispersibility and may cause degradation of the resin matrix. Furthermore, both lack a functional state feedback mechanism, making it impossible to directly assess protective efficacy. In addition, existing coatings often use toxic solvents, lacking environmental friendliness, and their interfacial compatibility with wood-based substrates needs improvement.

[0004] Lignin, a byproduct of the papermaking industry, is the second most abundant natural aromatic polymer. Its intrinsic UV absorption capabilities are endowed by phenolic hydroxyl groups and conjugated carbonyl groups in its molecular structure, and it exhibits a synergistic compatibility with wood-based substrates. Converting lignin into carbon quantum dots (CQDs) not only preserves its UV absorption properties but also imparts fluorescence functionality, providing an ideal material for constructing integrated "protection-warning" coatings. However, current technologies for preparing lignin-based carbon quantum dots still suffer from complex processes, low quantum yields, poor dispersibility with resin matrices, and insufficient functional synergy, hindering their large-scale application.

[0005] Therefore, how to prepare a green, efficient, functionally synergistic, and industrially scalable lignin-based carbon quantum dot coating is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a lignin-based carbon quantum dot coating, its preparation method and application, so as to overcome the shortcomings of the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a lignin-based carbon quantum dot coating specifically includes the following steps: (1) Preparation of lignin-based precursor solution Lignin, nitrogen dopant and solvent are stirred until dissolved to obtain lignin-based precursor solution; (2) Solvent thermal reaction and purification treatment The lignin-based precursor solution was subjected to a hydrothermal reaction, naturally cooled, centrifuged, filtered, and dialyzed to obtain a lignin-based carbon quantum dot solution. (3) Coating composite Under stirring conditions, a lignin-based carbon quantum dot solution is added dropwise to an aqueous resin. After the addition is complete, stirring continues, and the mixture is allowed to stand naturally to defoam, thus obtaining a lignin-based carbon quantum dot coating.

[0009] Furthermore, in step (1) above, the nitrogen dopant is o-phenylenediamine, m-phenylenediamine or p-phenylenediamine; the solvent is sulfoxide (DMSO), acetone or N,N-dimethylformamide (DMF); the ratio of lignin, nitrogen dopant and solvent is 0.01g:0.03g:20mL.

[0010] The further beneficial effect of the above-mentioned method lies in the fact that the present invention uses lignin as the carbon source, o-phenylenediamine, m-phenylenediamine, or p-phenylenediamine as the nitrogen dopant, and sulfoxide, acetone, or N,N-dimethylformamide as the solvent to prepare carbon quantum dots through a one-pot solvothermal carbonization reaction. By matching the nitrogen dopant with the solvent, the particle size and surface functional groups of the carbon quantum dots are controlled, thereby enhancing the synergistic effect of ultraviolet absorption and fluorescence emission.

[0011] Furthermore, in step (1) above, the stirring temperature is room temperature and the stirring time is 30 minutes.

[0012] Furthermore, in step (2) above, the hydrothermal reaction equipment is a polytetrafluoroethylene-lined hydrothermal reactor, the temperature is 180℃, and the time is 10h; the centrifugation speed is 10000rpm / min, and the time is 15min; the filtration uses a 0.22μm filter membrane; the dialysis uses a dialysis bag with a molecular weight cutoff of 1000Da, the time is 48h, and the water is changed every 6h.

[0013] The further beneficial effect of the above method is that the purity and dispersion stability of carbon quantum dots are ensured through centrifugation, filtration, and dialysis purification. The final lignin-based carbon quantum dots have a particle size of 4-7 nm, a fluorescence quantum yield of ≥27% (tested according to GB / T38250 standard), and an absorption efficiency of ≥85% in the 280-400 nm ultraviolet band.

[0014] Furthermore, in step (3) above, the aqueous resin is at least one of aqueous acrylic emulsion, aqueous polyurethane and aqueous epoxy resin, preferably aqueous acrylic emulsion; the ratio of lignin-based carbon quantum dot solution to aqueous resin is 10 mL: 10 g.

[0015] The further beneficial effect of the above-mentioned method is that the present invention uses water-based resin as the base resin, which ensures low VOC emissions in the coating and meets the requirements of green production.

[0016] Furthermore, in step (3) above, the stirring speed is 350 r / min; the dropping rate is 1 drop / 2 s; the stirring time is 30 min; and the settling time is 20 min.

[0017] The further beneficial effect of the above-mentioned method is that the present invention achieves uniform dispersion of carbon quantum dots in resin by controlling the acceleration rate of carbon quantum dot droplets and stirring parameters, thereby avoiding agglomeration.

[0018] This invention also claims protection for a lignin-based carbon quantum dot coating prepared by the above-described method.

[0019] This invention also claims protection for the application of a lignin-based carbon quantum dot coating prepared by the above method in high-end weather-resistant decoration, intelligent packaging monitoring, or health early warning of wood materials.

[0020] In the field of intelligent packaging monitoring, the coating of this invention is applied as a photosensitive label to the surface of wooden packaging. When the cumulative ultraviolet radiation dose exceeds 500 MJ / m², it can detect the ultraviolet radiation. 2 When the fluorescence intensity decay rate is ≥30%, it enables monitoring of light exposure during storage and transportation.

[0021] A method for preparing a board containing a lignin-based 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 by brushing or spraying, controlling the coating thickness to 20~30μm, drying or baking to form a lignin-based carbon quantum dot coating, thus obtaining the board.

[0022] This invention applies a coating to the surface of a pretreated wood substrate using a brush or spray process, controlling the coating thickness and curing (drying or baking) conditions to form a coating with high transparency, strong adhesion, and dual functional properties. Under natural light, the coating retains the original appearance of the wood, and under ultraviolet excitation (254nm or 365nm), it emits visible fluorescence. The fluorescence intensity decreases linearly with ultraviolet aging time, allowing for a direct assessment of the coating's protective efficacy through changes in the fluorescence signal, achieving a synergy between protective function and status warning.

[0023] Furthermore, the aforementioned wood-based material is particleboard, fiberboard, plywood, or solid wood panel.

[0024] Furthermore, the above pretreatment includes sanding with 400-600 grit sandpaper, wiping with anhydrous ethanol to remove oil, and drying at 60°C for 2 hours.

[0025] Furthermore, the spray gun pressure for the above-mentioned spraying is 0.3 MPa.

[0026] Furthermore, the drying temperature mentioned above is room temperature, and the time is 18 hours.

[0027] Furthermore, the drying temperature was 70°C and the drying time was 1 hour.

[0028] 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 high-value utilization Using lignin, an industrial byproduct, as raw material, the process achieves "waste treatment with waste." The raw material is low-cost and widely available, and the preparation process leaves no toxic solvent residues, meeting environmental protection requirements.

[0029] 2. Dual-function synergistic effect The coating combines high-efficiency UV shielding (UV shielding rate ≥90%, UVA band 320~400nm, UVB band 280~320nm) with fluorescent warning function. Its UV shielding efficiency is significantly better than that of traditional coatings, and the fluorescent signal can intuitively reflect the coating status, solving the pain point of "unvisible function" of traditional protective materials.

[0030] 3. Excellent interface compatibility Lignin-based carbon quantum dots exhibit good compatibility with wood-based substrates and water-based resins. The coating adhesion reaches Grade 1 (tested according to GB / T 9286-1998 cross-cut test), the pencil hardness is ≥2H (tested according to GB / T 6739-2022), and the visible light transmittance is ≥85% (400~800nm), without affecting the original decorative effect of the wood.

[0031] 4. Simple process, can be scaled up The entire preparation process uses conventional equipment (hydrothermal reactor, stirrer, spray gun), the process parameters are easy to control, the solvent can be recycled, the production cost is low, and it is suitable for industrial-scale production.

[0032] 5. Wide range of applications It can be applied to high-end furniture, outdoor wooden building materials, museum display cases, smart wooden packaging and other fields, and has multiple functions such as protection, warning and traceability, with huge market potential.

[0033] In summary, this invention uses lignin, an industrial byproduct, as a carbon source to prepare nitrogen-doped carbon quantum dots with high quantum yield through a solvothermal carbonization reaction. These quantum dots are then composited with an aqueous resin to form a coating that combines highly efficient UV shielding with fluorescent warning functions, while ensuring good compatibility between the coating and the wood substrate. This coating not only effectively blocks ultraviolet light across the entire spectrum, protecting the wood substrate from aging, but also provides intuitive feedback on coating integrity and protection status through changes in fluorescence signals. Furthermore, the preparation process is green and environmentally friendly, simple, and suitable for large-scale production. It can be widely applied in fields such as wood material protection, smart packaging, and health monitoring, demonstrating significant scientific value and market potential. Detailed Implementation

[0034] 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.

[0035] Example 1 The preparation method of lignin-based carbon quantum dot solution (o-phenylenediamine-DMSO system) specifically includes the following steps: (1) Preparation of lignin-based precursor solution Take a 250mL beaker, add 0.01g of industrial lignin (purity ≥90%) and 0.03g of o-phenylenediamine, add 20mL of DMSO solvent, and stir magnetically at room temperature for 30min until the solid is completely dissolved to obtain a uniform and transparent lignin-based precursor solution. (2) Solvent thermal reaction The lignin-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 180 °C for 10 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 10,000 rpm for 15 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 48 h, with the deionized water being replaced every 6 h, to obtain a pure lignin-based carbon quantum dot solution.

[0036] Example 2 The preparation method of lignin-based carbon quantum dot solution (m-phenylenediamine-acetone system) differs from that in Example 1 only in that o-phenylenediamine is replaced with m-phenylenediamine and DMSO is replaced with acetone.

[0037] Example 3 The preparation method of lignin-based carbon quantum dot solution (p-phenylenediamine-DMF system) differs from that in Example 1 only in that o-phenylenediamine is replaced with p-phenylenediamine and DMSO is replaced with DMF.

[0038] Example 4 The preparation method of lignin-based carbon quantum dot coatings specifically includes the following steps: Take 10g of aqueous acrylic emulsion (solid content 40%) and place it in a 50mL three-necked flask. Install a mechanical stirrer and set the speed to 350r / min. Use a dropper to slowly add 10mL of the lignin-based carbon quantum dot solution prepared in Example 1 to the aqueous acrylic emulsion at a rate of 1 drop / 2s. After the addition is complete, continue stirring for 30min to ensure that the carbon quantum dots are evenly dispersed. Turn off the stirrer and let it stand for 20min to naturally defoam, and obtain the lignin-based carbon quantum dot coating.

[0039] Example 5 The method for preparing lignin-based carbon quantum dot coatings differs from that in Example 4 only in that the lignin-based carbon quantum dot solution prepared in Example 2 is added dropwise.

[0040] Example 6 The method for preparing lignin-based carbon quantum dot coatings differs from that in Example 4 only in that the lignin-based carbon quantum dot solution prepared in Example 3 is added dropwise.

[0041] Example 7 The preparation method of the board containing lignin-based carbon quantum dot coating specifically includes the following steps: (1) Substrate pretreatment Medium-density fiberboard (MDF) was selected as the substrate, cut into 100mm×100mm×5mm specimens, sanded smooth with 400-grit sandpaper, wiped with anhydrous ethanol to remove oil, and dried at 60℃ for 2 hours for later use. (2) Coating application The lignin-based carbon quantum dot coating prepared in Example 4 was uniformly sprayed onto the pretreated substrate surface using a small spray gun (pressure 0.3 MPa), and the coating thickness was controlled at 25 μm (estimated by the difference in quality before and after coating). (3) Curing The specimen was placed in a dark and ventilated place and dried at room temperature for 18 hours to form a lignin-based carbon quantum dot coating.

[0042] Example 8 The method for preparing the board containing lignin-based carbon quantum dot coating differs from that of Example 7 only in that the lignin-based carbon quantum dot coating obtained in Example 5 is sprayed.

[0043] Example 9 The method for preparing the board containing lignin-based carbon quantum dot coating differs from that of Example 7 only in that the lignin-based carbon quantum dot coating obtained in Example 6 is sprayed.

[0044] Performance testing 1. Carbon quantum dots The lignin-based carbon quantum dot solutions prepared in Examples 1-3 were freeze-dried to obtain lignin-based carbon quantum dots. Their yield, particle size and fluorescence quantum yield were tested (according to GB / T 38250 standard, with quinine sulfate as a reference). The results are shown in Table 1.

[0045] Table 1 Performance test results of lignin-based carbon quantum dots in Examples 1-3

[0046] As shown in Table 1, the particle size of the lignin-based carbon quantum dots in Examples 1-3 is 4~7nm, and the fluorescence quantum yield is ≥27% (tested according to GB / T 38250 standard).

[0047] 2. Panel coating The coatings of the plates prepared in Examples 7-9 were tested according to relevant standards, and the results are shown in Table 2.

[0048] Table 2 Performance test results of the coatings on the substrates in Examples 7-9

[0049] As shown in Table 2, the coatings of the substrates in Examples 7-9 possess both high-efficiency UV shielding (UV shielding rate ≥90%, UVA band 320~400nm, UVB band 280~320nm) and fluorescent warning function. Adhesion reaches Grade 1 (tested according to GB / T 9286-1998 cross-cut test), pencil hardness ≥2H (tested according to GB / T 6739-2022), and visible light transmittance ≥85% (400~800nm). Among these, the lignin-based carbon quantum dots in Example 7 exhibit the best overall performance, with the highest fluorescence quantum yield and UV shielding rate, making it the preferred option.

[0050] 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 lignin-based carbon quantum dot coating, characterized in that, Specifically, the following steps are included: (1) Preparation of lignin-based precursor solution Lignin, nitrogen dopant and solvent are stirred until dissolved to obtain lignin-based precursor solution; (2) Solvent thermal reaction and purification treatment The lignin-based precursor solution was subjected to a hydrothermal reaction, naturally cooled, centrifuged, filtered, and dialyzed to obtain a lignin-based carbon quantum dot solution. (3) Coating composite Under stirring conditions, the lignin-based carbon quantum dot solution is added dropwise to the aqueous resin. After the addition is complete, stirring is continued, and the mixture is allowed to stand naturally to defoam, thus obtaining the lignin-based carbon quantum dot coating.

2. The method for preparing a lignin-based carbon quantum dot coating according to claim 1, characterized in that, In step (1), the nitrogen dopant is o-phenylenediamine, m-phenylenediamine or p-phenylenediamine; the solvent is sulfoxide, acetone or N,N-dimethylformamide; and the ratio of lignin, nitrogen dopant and solvent is 0.01g:0.03g:20mL.

3. The method for preparing a lignin-based 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 lignin-based carbon quantum dot coating according to claim 1, characterized in that, In step (2), the hydrothermal reaction equipment is a polytetrafluoroethylene-lined hydrothermal reactor, the temperature is 180℃, and the time is 10h; the centrifugation speed is 10000rpm / min, and the time is 15min; the filtration uses a 0.22μm filter membrane; the dialysis uses a dialysis bag with a molecular weight cutoff of 1000Da, the time is 48h, and the water is changed every 6h.

5. The method for preparing a lignin-based carbon quantum dot coating according to claim 1, characterized in that, In step (3), the aqueous resin is at least one of aqueous acrylic emulsion, aqueous polyurethane and aqueous epoxy resin; the ratio of the amount of lignin-based carbon quantum dot solution to aqueous resin is 10 mL: 10 g.

6. The method for preparing a lignin-based carbon quantum dot coating according to claim 1, characterized in that, In step (3), the stirring speed is 350 r / min; the dripping rate is 1 drop / 2 s; the stirring time is 30 min; and the settling time is 20 min.

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

8. The application of a lignin-based carbon quantum dot coating prepared by any one of claims 1-6 in high-end weather-resistant decoration, intelligent packaging monitoring, or health early warning of wood materials.

9. A method for preparing a board containing a lignin-based 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 by brushing or spraying, with the coating thickness controlled at 20~30μm, and then dried or oven-dried to form a lignin-based carbon quantum dot coating.

10. A method for preparing a board containing a lignin-based carbon quantum dot coating according to claim 9, characterized in that, The wood substrate is particleboard, fiberboard, plywood, or solid wood board; the pretreatment includes sanding with 400-600 grit sandpaper, wiping with anhydrous ethanol to remove oil, and drying at 60°C for 2 hours; the spray gun pressure for spraying is 0.3 MPa; the drying temperature is room temperature and the time is 18 hours; the baking temperature is 70°C and the time is 1 hour.

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