Method for realizing lignin-based derived carbon quantum dots based on surface modification

Abstract

The invention belongs to the field of nano material preparation, and particularly relates to a method for realizing lignin-based derived carbon quantum dots based on surface modification, which is characterized in that a lignin-based CQDs aqueous solution is subjected to oxidation treatment to obtain lignin-derived CQDs. Comprising the following steps: firstly, taking lignin as a raw material to obtain a lignin-based quantum dot aqueous solution; finally, slowly adding an oxidizing agent into the lignin-based quantum dot aqueous solution in batches to obtain lignin-based derivative CQDs; the benzenesulfonic acid and choline chloride system used in the invention is green and environment-friendly; the directional regulation and control of the fluorescence performance of the CQDs can be conveniently realized.

Description

Technical Field

[0001] The present invention belongs to the field of nanomaterial preparation, and specifically relates to a method for synthesizing lignin-derived carbon quantum dots (CQDs) based on surface modification. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] CQDs, due to their excellent optical properties, biocompatibility, low toxicity, and photostability, hold broad application prospects in optoelectronics, biomedicine, environmental monitoring, catalysis, and energy. Compared to traditional quantum dots (such as CdSe and PbS), lignin-based CQDs fundamentally avoid the risk of heavy metal toxicity while offering advantages such as a wide range of raw material sources and a highly sustainable process.

[0004] The preparation of existing biomass-based quantum dots (including cellulose and lignin derivatives) still faces significant challenges: First, they rely heavily on pretreatment processes for performance control, resulting in a single fluorescence emission spectrum and functionality, and the resulting CQDs generally only achieve monochromatic emission characteristics. Second, although the emission color range can be limitedly expanded through multi-step process optimization, the complex preparation process and high production costs seriously restrict their industrial application prospects. In particular, it is difficult to develop a systematic method for precisely controlling multicolor fluorescence through post-processing chemical modification based on the same raw material. This lack of technology directly limits the development of multifunctional biomass-based quantum dots. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for realizing lignin-based derived carbon quantum dots based on surface modification.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a method for realizing lignin-based derived carbon quantum dots based on surface modification, comprising: Lignin was pretreated with benzenesulfonic acid and choline chloride system to obtain the precursor of CQDs; hydrothermally treating the precursor of the CQDs to obtain a lignin-based CQDs aqueous solution; An oxidant is added to the lignin-based CQDs aqueous solution for oxidation treatment to obtain lignin-based derived carbon quantum dots.

[0007] The second aspect of the present invention provides lignin-derived carbon quantum dots prepared by the above method.

[0008] The third aspect of the present invention provides applications of the above-mentioned lignin-based derived carbon quantum dots in the fields of optoelectronic display and lighting, biomedicine and imaging, heavy metal ion detection, photocatalysis, and energy storage devices.

[0009] Beneficial effects of the present invention (1) Compared with the existing CQDs preparation method, the benzenesulfonic acid and choline chloride system used in the present invention is green and environmentally friendly, has a high quantum yield, and the emission wavelength of the obtained CQDs is 415nm-510nm.

[0010] (2) The directional control method of the present invention is simple and convenient for realizing directional control of the fluorescence properties of CQDs.

[0011] (3) The preparation method of the present invention is simple, practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0013] Figure 1 The fluorescence effect of CQDS before and after derivatization under 340nm ultraviolet light in Example 1; (a) CQDS without adding oxidant, (b) derivatized CQDS with adding oxidant nitric acid; Figure 2 The fluorescence effect of CQDS before and after derivatization under 440nm ultraviolet light in Example 2; (a) CQDS without adding oxidant, (b) derivatized CQDS with adding oxidant nitric acid. DETAILED DESCRIPTION

[0014] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0015] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in accordance with conventional methods in the art or according to product specifications. Similarly, unless otherwise specified, the test methods of the present invention are also tested in accordance with conventional methods in the art or the common methods or standards in the industry. In addition, any methods and materials similar to or equivalent to the described contents can be applied to the inventive method. The preferred embodiments and materials described herein are for demonstration purposes only.

[0016] A surface-modified synthesis method for lignin-derived CQDs involves oxidizing an aqueous solution of lignin-derived CQDs to produce the lignin-derived CQDs. Specifically, lignin is used as the raw material to produce an aqueous solution of lignin-derived CQDs. Finally, an oxidant is added to the aqueous solution in batches to produce the lignin-derived CQDs.

[0017] In some embodiments, the lignin is selected from alkali lignin, and at least one of lignins obtained by separating and extracting coniferous wood, hardwood wood and grass raw materials by alkali cooking and pulping and then using acid precipitation method.

[0018] Preferably, the lignin is separated and extracted by acid precipitation (H2SO4 solution with pH = 3.0 ± 0.2) after pulping coniferous wood (such as pine, spruce), hardwood (such as eucalyptus, birch) and grass raw materials (such as wheat straw, reed, and phragmites australis) by alkaline cooking (such as sulfate process, caustic soda-anthraquinone process).

[0019] Preferably, the purity of lignin is 85-90%.

[0020] Preferably, the moisture content of lignin is 1-3%.

[0021] Preferably, the lignin particle size is 80-100 mesh.

[0022] Preferably, the molecular weight of lignin is between 4000 and 7000.

[0023] The pretreatment solvent will affect the fluorescence properties and yield of CQDs. Therefore, the present invention studies the types of pretreatment solvents. In some embodiments, the benzenesulfonic acid and choline chloride system is a choline chloride and p-toluenesulfonic acid or a choline chloride and 2,4-diaminobenzenesulfonic acid system to better improve the fluorescence properties of CQDs, increase the yield, and achieve directional regulation of the fluorescence properties of CQDs.

[0024] Preferably, the purity of choline chloride, p-toluenesulfonic acid, and 2,4-diaminobenzenesulfonic acid is 95-99%.

[0025] The ratio of choline chloride to p-toluenesulfonic acid affects its physicochemical properties, solubility, conductivity, etc. Therefore, the present invention studies the ratio of choline chloride to p-toluenesulfonic acid. In some embodiments, the molar ratio of choline chloride to p-toluenesulfonic acid is 1:1.5~2.5; in order to better improve the fluorescence properties of CQDs and increase the yield.

[0026] The ratio of choline chloride to 2,4-diaminobenzenesulfonic acid affects its physicochemical properties, solubility, conductivity, etc. Therefore, the present invention studies the ratio of choline chloride to 2,4-diaminobenzenesulfonic acid. In some embodiments, the molar ratio of choline chloride to 2,4-diaminobenzenesulfonic acid is 1:2~4; in order to better improve the fluorescence properties of CQDs and increase the yield.

[0027] The amount of lignin used will affect the treatment effect of the pretreatment solvent. Therefore, the present invention studies the ratio of lignin to choline chloride and p-toluenesulfonic acid. In some embodiments, the mass ratio of lignin to choline chloride and p-toluenesulfonic acid is 1:1~2:2.4~4; to better improve the pretreatment effect of lignin.

[0028] The amount of lignin used will affect the treatment effect of the pretreatment solvent. Therefore, the present invention studies the ratio of lignin to choline chloride and 2,4-diaminobenzenesulfonic acid. In some embodiments, the mass ratio of lignin to choline chloride and 2,4-diaminobenzenesulfonic acid is 1:1~2:2.7~5; to better improve the pretreatment effect of lignin.

[0029] Temperature and time also affect the effect of pretreatment. Therefore, the present invention has studied the temperature and time of pretreatment. In some embodiments, the pretreatment conditions are a treatment temperature of 80-100°C and a treatment time of 50-65 minutes; in some embodiments, the pretreatment conditions are a treatment temperature of 80-95°C and a treatment time of 50-65 minutes; in some embodiments, the pretreatment conditions are a treatment temperature of 80-100°C and a treatment time of 50-60 minutes. Those skilled in the art can select and adjust the pretreatment conditions according to different pretreatment solvents.

[0030] Preferably, the preparation process for the lignin-based quantum dot aqueous solution is as follows: First, lignin is pretreated with a benzenesulfonic acid and choline chloride system to produce a CQD precursor. The process is as follows: A lignin sample, choline chloride, and p-toluenesulfonic acid are uniformly mixed and then heated at 80-95°C for 50-65 minutes. The mass ratio of lignin sample to choline chloride to p-toluenesulfonic acid is 1:1-2:2.4-4.

[0031] Preferably, the lignin-based CQD aqueous solution is prepared using lignin as the raw material. The preparation process for the lignin-based quantum dot aqueous solution is as follows: First, lignin is pretreated with a benzenesulfonic acid and choline chloride system to obtain a CQD precursor. The lignin sample, choline chloride, and 2,4-diaminobenzenesulfonic acid are uniformly mixed and then heated at 80-100°C for 50-60 minutes. The mass ratio of lignin sample to choline chloride to 2,4-diaminobenzenesulfonic acid is 1:1-2:2.7-5.

[0032] The hydrothermal temperature affects the formation of the carbon core of CQDs and the composition of its surface functional groups, thereby affecting the particle size and optical properties of CQDs. Therefore, the temperature and time of the hydrothermal reaction are studied in the present invention. In some embodiments, the hydrothermal treatment is performed at 180-220°C for 8-12 hours to better improve the fluorescence properties and yield of CQDs.

[0033] In some embodiments, after the hydrothermal treatment, deionized water is added to terminate the reaction. Deionized water at 0-4°C is added dropwise to the reaction system at a rate of 4-6.5 mL / min. The mass-to-volume ratio of lignin to deionized water is 1 g:30 mL.

[0034] The type of oxidant will affect the effect of directional regulation. Therefore, the present invention studies the type of oxidant. In some embodiments, the oxidant is nitric acid; so as to better achieve directional regulation of the fluorescence properties of CQDs.

[0035] The concentration of the oxidant will also affect the effect of directional regulation. Therefore, the present invention studies the concentration of the oxidant. In some embodiments, the concentration of the nitric acid solution is 62%~72%; so as to better achieve directional regulation of the fluorescence properties of CQDs.

[0036] In some embodiments, the concentration of nitric acid is 62% to 72% (mass fraction).

[0037] The ratio of CQDs to nitric acid will affect the effect of directional regulation. Therefore, the present invention studies the ratio of CQDs to nitric acid. In some embodiments, the volume ratio of the lignin-based CQDs aqueous solution to nitric acid is 1:5~20 to better achieve directional regulation of the fluorescence properties of CQDs.

[0038] The process steps of oxidation treatment will affect the efficiency and effect of directional regulation. Therefore, the present invention studies the specific steps of oxidation treatment. In some embodiments, the specific steps of oxidation treatment include: adding nitric acid solution to the lignin-based CQDs aqueous solution and standing for 3 to 5 hours to improve the efficiency and effect of directional regulation.

[0039] Preferably, nitric acid is added dropwise to the CQDs aqueous solution at a rate of 2.5-4.5 mL / min.

[0040] Preferably, after nitric acid is added to the CQDs solution, the solution is allowed to stand for 3 to 5 hours.

[0041] In order to obtain derivative CQDs, the reaction products need to be post-treated. Therefore, the present invention studies the specific process of post-treatment. In some embodiments, it also includes: filtering, dialyzing, and freeze-drying the reaction system after oxidation treatment to obtain derivative CQDs.

[0042] Preferably, the oxidant is added to the lignin-based CQDs aqueous solution, and nitric acid is added to the CQDs solution. After the treatment is completed, the reaction system is filtered with a 0.22 μm microporous filter element, and the obtained filtrate is then placed in a 3000 Da dialysis bag and dialyzed for 48 hours, and freeze-dried at minus 50°C to obtain the derived CQDs.

[0043] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0044] Example 1 (1) Commercial alkali lignin (purity of 95%, particle size of 90 mesh, water content of 2%, molecular weight of 5200) was used as the lignin sample. The lignin sample, choline chloride, and p-toluenesulfonic acid were mixed evenly at a mass volume ratio of 1 g:2 g:3.7 g and then heated (80°C, 65 min) to obtain a precursor of CQDs. The precursor of CQDs was hydrothermally treated (220°C, 12 h). After the reaction, 4°C deionized water was added dropwise (5 mL / min) to the reaction system at a mass volume ratio of 1 g:30 mL to obtain a lignin-based CQDs aqueous solution.

[0045] (2) The oxidant (nitric acid, concentration 62%, 5°C) was added dropwise (3.5 mL / min) to the lignin-based CQDs aqueous solution, with a volume ratio of 20:1. After the addition was completed, the solution was allowed to stand for 4 hours. After the treatment, the reaction system was filtered using a 0.22 μm microporous filter element, and the filtrate was collected and placed in a 3000 Da dialysis bag for 48 hours of dialyzation. The solution was then freeze-dried at -50°C to obtain the derived CQDs.

[0046] Example 2 (1) Sulfonated lignin (90% purity, 100 mesh particle size, 2% water content, molecular weight 4200) was used as the lignin sample. The lignin sample, 2,4-diaminobenzenesulfonic acid, and choline chloride were mixed uniformly at a mass volume ratio of 1 g:2 g:4.2 g and then heated (90°C, 60 min) to obtain a CQDs precursor. The CQDs precursor was hydrothermally treated (220°C, 12 h). After the reaction, 4°C deionized water was added dropwise (5 mL / min) to the reaction system at a mass volume ratio of 1 g:30 mL to obtain a lignin-based CQDs aqueous solution.

[0047] (2) The oxidant (nitric acid, concentration 62%~72%, 3℃) was added dropwise (3.5mL / min) to the lignin-based CQDs aqueous solution, with a volume ratio of 5:1. After the addition was completed, the solution was allowed to stand for 4 hours. After the treatment, the reaction system was filtered using a 0.22 μm microporous filter element, and the filtrate was collected and placed in a 3000Da dialysis bag for 48 hours of dialyzation. The solution was then freeze-dried at -50℃ to obtain the derived CQDs.

[0048] Example 3 (1) Commercial alkali lignin (purity of 95%, particle size of 90 mesh, water content of 2%, molecular weight of 5200) was used as the lignin sample. The lignin sample, choline chloride, and p-toluenesulfonic acid were mixed evenly at a mass volume ratio of 1 g:2 g:3.7 g and then heated (95°C, 50 min) to obtain the precursor of CQDs. The precursor of CQDs was hydrothermally treated (220°C, 12 hours). After the reaction, 0°C deionized water was added dropwise (5 mL / min) to the reaction system at a mass volume ratio of 1 g:30 mL to obtain a lignin-based CQDs aqueous solution.

[0049] (2) The oxidant (nitric acid, concentration 72%, 5°C) was added dropwise (3.5 mL / min) to the lignin-based CQDs aqueous solution, with a volume ratio of 5:1. After the addition was completed, the solution was allowed to stand for 4 hours. After the treatment, the reaction system was filtered using a 0.22 μm microporous filter element, and the filtrate was collected and placed in a 3000 Da dialysis bag for 48 hours of dialyzation. The solution was then freeze-dried at -50°C to obtain the derived CQDs.

[0050] Example 4 (1) Commercial alkali lignin (purity of 95%, particle size of 90 mesh, water content of 2%, molecular weight of 5200) was used as the lignin sample. The lignin sample, choline chloride, and p-toluenesulfonic acid were mixed evenly at a mass volume ratio of 1 g:2 g:3.7 g and then heated (88°C, 58 min) to obtain a CQDs precursor. The CQDs precursor was hydrothermally treated (220°C, 12 h). After the reaction, 4°C deionized water was added dropwise (5 mL / min) to the reaction system at a mass volume ratio of 1 g:30 mL to obtain a lignin-based CQDs aqueous solution.

[0051] (2) The oxidant (nitric acid, concentration 67%, 4°C) was added dropwise (3.5 mL / min) to the lignin-based CQDs aqueous solution, with a volume ratio of 12:1. After the addition was completed, the solution was allowed to stand for 4 hours. After the treatment, the reaction system was filtered using a 0.22 μm microporous filter element, and the filtrate was collected and placed in a 3000 Da dialysis bag for 48 hours of dialyzation. The solution was then freeze-dried at -50°C to obtain the derived CQDs.

[0052] Experimental Example 1 The lignin-based CQDs and the derived CQDs prepared in the above example were irradiated with ultraviolet light and tested by fluorescence spectrophotometry, with the excitation wavelength of 280-480 nm (interval of 20 nm) as the excitation wavelength. The results showed that the fluorescence first increased and then decreased. Figure 1 In (a), the fluorescence intensity of lignin-based CQDs is the largest when the excitation wavelength is 340 nm, and the corresponding emission wavelength is 415 nm. Figure 2 In (a), the fluorescence intensity of lignin-based CQDs is the largest when the excitation wavelength is 440 nm, and the corresponding emission wavelength is 510 nm.

[0053] Figure 1 (b) is the same as “ Figure 1 The corresponding "in (a)" and the derived carbon quantum dots obtained by oxidation have an emission wavelength of 422 nm when the excitation wavelength is 350.

[0054] Figure 2 (b) is the same as " Figure 1 The corresponding "in (a)" is the derived carbon quantum dots obtained by oxidation, and when the excitation wavelength is 440 nm, the corresponding emission wavelength is 515 nm.

[0055] It can be seen that after adding an oxidant to derivatize CQDS, the fluorescence properties of the derived CQDS are significantly changed. It can be seen that the present invention achieves directional regulation of the fluorescence properties of CQDs.

[0056] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for realizing lignin-based derived carbon quantum dots based on surface modification, characterized in that: include: Lignin was pretreated with benzenesulfonic acid and choline chloride system to obtain the precursor of CQDs; hydrothermally treating the precursor of the CQDs to obtain a lignin-based CQDs aqueous solution; An oxidant is added to the lignin-based CQDs aqueous solution for oxidation treatment to obtain lignin-based derived carbon quantum dots.

2. The method for realizing lignin-based derived carbon quantum dots based on surface modification according to claim 1, characterized in that: The lignin is selected from alkali lignin, and at least one of lignins obtained by separating and extracting coniferous wood, broadleaf wood and grass raw materials through alkali cooking and pulping and then using acid precipitation method.

3. The method for realizing lignin-based derived carbon quantum dots based on surface modification according to claim 1, characterized in that: The benzenesulfonic acid and choline chloride system is a choline chloride and p-toluenesulfonic acid system or a choline chloride and 2,4-diaminobenzenesulfonic acid system; Alternatively, the molar ratio of choline chloride to p-toluenesulfonic acid is 1:1.5-2.5; Alternatively, the molar ratio of choline chloride to 2,4-diaminobenzenesulfonic acid is 1:2 to 4; Alternatively, the mass ratio of lignin to choline chloride and p-toluenesulfonic acid is 1:1~2:2.4~4; Alternatively, the mass ratio of lignin to choline chloride and 2,4-diaminobenzenesulfonic acid is 1:1~2:2.7~5.

4. The method for realizing lignin-based derived carbon quantum dots based on surface modification according to claim 1, characterized in that: The pretreatment conditions are as follows: a treatment temperature of 80-100°C and a treatment time of 50-65 minutes; Alternatively, the pretreatment conditions are a treatment temperature of 80-95° C. and a treatment time of 50-65 min; Alternatively, the pretreatment conditions are a treatment temperature of 80-100° C. and a treatment time of 50-60 min.

5. The method for realizing lignin-based derived carbon quantum dots based on surface modification according to claim 1, characterized in that: The hydrothermal treatment is carried out at 180-220° C. for 8-12 hours.

6. The method for realizing lignin-based derived carbon quantum dots based on surface modification according to claim 1, characterized in that: The oxidant is nitric acid; Or, the concentration of nitric acid solution is 62%~72%; Alternatively, the volume ratio of the lignin-based CQDs aqueous solution to nitric acid is 1:5~20.

7. The method for realizing lignin-based derived carbon quantum dots based on surface modification according to claim 1, characterized in that: The specific steps of the oxidation treatment include: adding nitric acid solution dropwise to the lignin-based CQDs aqueous solution and allowing it to stand for 3 to 5 hours.

8. The method for realizing lignin-based derivative carbon quantum dots based on surface modification according to claim 1, characterized in that: Also includes: The reaction system after oxidation treatment is filtered, dialyzed and freeze-dried.

9. Lignin-based derived carbon quantum dots prepared by the method according to any one of claims 1 to 8.

10. Application of the lignin-derived carbon quantum dots according to claim 9 in the fields of optoelectronic display and lighting, biomedicine and imaging, heavy metal ion detection, photocatalysis, and energy storage devices.

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