Method for preparing N-doped carbon dots and hydrogenation catalyst carrier based on biomass and eutectic solvent

Abstract

The invention relates to the technical field of biomass deep processing, and provides a method for preparing N-doped carbon dots and a hydrogenation catalyst carrier based on biomass and a deep eutectic solvent, and the method comprises the following steps: 1, mixing a biomass raw material, the deep eutectic solvent and an additive, and carrying out a reaction at 140-240 DEG C for 2-6 h to obtain a product 1; step 2, placing the product 1 in inert gas, and reacting at 150-260 DEG C for 1-4 hours to obtain a product 2; step 3, grinding and dissolving the product 2 to obtain a mixed solution, and carrying out suction filtration to respectively obtain a product 3 and an aqueous solution; wherein the product 3 is the hydrogenation catalyst carrier; and 4, dialyzing the aqueous solution for 24 hours to obtain a dialysis product, and carrying out rotary evaporation on the dialysis product to obtain the N-doped carbon dots. According to the method, a double-section heat treatment process is utilized, the product structure is regulated and controlled, and the yield of the eutectic solvent-biomass-based N-doped carbon dots is effectively increased.

Description

Technical Field

[0001] This invention relates to the field of biomass deep processing technology, and in particular to a method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and eutectic solvents. Background Technology

[0002] Carbon dots (CDs) are a novel class of fluorescent nanomaterials with dimensions smaller than 10 nanometers, composed of a carbon core and surface functional groups. Their unique physicochemical properties have shown great potential in biomedicine, environmental monitoring, and energy fields. Their core advantages lie in biocompatibility, low toxicity, and tunable optical properties, making them an ideal alternative to traditional quantum dots.

[0003] Biomass (such as straw and rice husks) is an abundant byproduct of agriculture and forestry, widely available and inexpensive. Using it for carbon dot production has positive implications for reducing carbon dot production costs and increasing the added value of the agricultural industry. Replacing petrochemical resources or fine chemicals as carbon sources with biomass aligns with green chemistry principles. This type of technology typically involves placing biomass feedstock in a solvent (water, methanol, ethanol, etc.) and producing renewable carbon dots in a one-pot process using hydrothermal / solvothermal methods in a sealed container such as a hydrothermal reactor.

[0004] The invention patent with publication number CN121022396A discloses a fluorescent carbon dot and a fluorescent hydrogel based on solvent stimulation response color change, as well as their preparation method and application; fluorescent carbon dots are obtained by mixing biomass carbon source and solvent and carrying out a solvothermal reaction, and then applied to fluorescent hydrogel-based information anti-counterfeiting encryption technology. The invention patent with publication number CN120192775A discloses a method for preparing polysaccharide-based fluorescent carbon dots with adjustable emission wavelength and its application; blue, green and yellow-green fluorescent carbon dots are prepared by mixing polysaccharides with different nitrogen dopants o-phenylenediamine, m-phenylenediamine and p-phenylenediamine respectively through hydrothermal reaction, with fluorescence quantum yield of 4.0-25.0%.

[0005] Eutectic solvents (DES) are an emerging class of "custom solvents" with advantages such as simple preparation, low cost, good biocompatibility, and tunable properties. They also exhibit good solubility in biomass and are used as solvents and dopants for the synthesis of biomass carbon dots (CDs). For example, Chongqing University introduced eutectic solvents into the traditional carbon dot synthesis process, achieving a fluorescence quantum yield of 20.43%, but the overall carbon dot yield was relatively low. Beijing Forestry University used hemicellulose and DES as raw materials to prepare carbon dots with a high fluorescence quantum yield of 23.45% via a solvothermal method, but the carbon dot yield was less than 10%. Patent and literature reviews reveal that most processes using DES as a solvent medium for carbon dot preparation do not discuss the carbon dot yield, and the low yield may be a common problem in such schemes.

[0006] Although numerous studies have demonstrated the potential of preparing high-value-added carbon dots from biomass feedstocks, significant challenges remain in the practical industrial application of this technology. Low carbon dot yields and fluorescence quantum yields, along with difficulties in utilizing byproducts, are common problems encountered in this type of process. Summary of the Invention

[0007] To address the aforementioned problems, this invention aims to provide a method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and eutectic solvents. The method utilizes the strong solubility of biomass in eutectic solvents to provide an excellent mass transfer environment for the synthesis of N-doped carbon dots, and can introduce some eutectic solvent fragments into the product structure. A two-stage heat treatment process is used to regulate the product structure, effectively improving the yield of eutectic solvent-biomass-based N-doped carbon dots.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, this application discloses a method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and a eutectic solvent, comprising the following steps: Step 1: Mix biomass raw materials, eutectic solvent and additives, and hydrothermally react at 140~240℃ for 2~6h to obtain product 1; Step 2: Place product 1 in an inert gas and calcine it at 150~260℃ for 1~4 hours to obtain product 2; Step 3: Grind and dissolve product 2 to obtain a mixture, and filter it to obtain product 3 and an aqueous solution respectively; Among them, product 3 is the hydrogenation catalyst support; Step 4: Dialyze the aqueous solution for 24 hours to obtain the dialysis product. Then, rotary evaporate the dialysis product to obtain N-doped carbon dots.

[0009] Furthermore, in step 1: Biomass raw materials include at least one of cellulose, lignin, straw, sawdust, bamboo shavings, peanut shells, rice husks, and corn cobs.

[0010] Furthermore, in step 1: The eutectic solvent is prepared by mixing a hydrogen bond acceptor and a hydrogen bond donor at 80°C; The hydrogen bond acceptors are choline chloride and / or guanidine hydrochloride. The hydrogen bond donor is at least one of urea, citric acid, ethylene glycol, glycerol, and oxalic acid.

[0011] Furthermore, in step 1: The additive is any one of ethylenediamine, p-phenylenediamine, m-phenylenediamine, and diethanolamine.

[0012] Furthermore, in step 1: The addition ratio of eutectic solvent to biomass raw material is 1~10 mL : 1g; The mass ratio of additives to biomass raw materials is 0.0001~0.01 : 1.

[0013] Furthermore, in step 2, the inert gas is any one of He, N2, and Ar.

[0014] Secondly, this application discloses an N-doped carbon dot, which is prepared by the above method.

[0015] Thirdly, this application discloses the use of N-doped carbon dots in metal ion detection.

[0016] Fourthly, this application discloses a hydrogenation catalyst support, which is prepared by the above method.

[0017] Fifthly, this application discloses the use of a hydrogenation catalyst support on a supported active metal.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes the strong solubility of eutectic solvents in biomass to provide an excellent mass transfer environment for the synthesis of N-doped carbon dots. It also allows for the introduction of some eutectic solvent fragments into the product structure. A two-stage heat treatment process is employed to regulate the product structure, effectively improving the yield of DES-biomass-based N-doped carbon dots. Simultaneously, N-doped carbon dots and a hydrogenation catalyst support are prepared. The resulting N-doped carbon dots exhibit high yields and fluorescence quantum yields. The hydrogenation catalyst support is loaded with active metals for the catalytic degradation of lignin. The overall product yield reaches 74-81%, significantly improving the raw material utilization rate and potential economic benefits in the traditional biomass N-doped carbon dot preparation process.

[0019] The fluorescence quantum yield of N-doped carbon dots produced by a single hydrothermal reactor reaction is no more than 6%, and using solid byproducts as hydrogenation catalyst supports in a single hydrothermal reactor reaction is also unacceptable, as the product is generally a sticky, tar-like substance. In this application, by adding tube furnace heating after a single hydrothermal reactor reaction, the yield of N-doped carbon dot products can be significantly improved. The reason is that the hydrothermal reactor is a closed environment, and the byproducts generated during the N-doped carbon dot synthesis process cannot be discharged, thus inhibiting the formation of N-doped carbon dots. However, during the subsequent tube furnace heating process, the byproducts of the N-doped carbon dot formation process leave in a gaseous state with the carrier gas, pushing the equilibrium towards the direction of N-doped carbon dot formation.

[0020] The eutectic solvent decomposes itself and combines with the biomass structure to generate a fluorescent structure. On the other hand, it slowly decomposes during the temperature-controlled heating process in the tube furnace (the temperature is near the initial pyrolysis temperature of the eutectic solvent, but slightly higher), which to some extent protects the surface functional groups of the N-doped carbon dots, thereby ensuring the fluorescence quantum yield of the N-doped carbon dots. Attached Figure Description

[0021] Figure 1 The following are fluorescence characteristic diagrams of N-doped carbon dots in Example 3 of the present invention, wherein (a) is the excitation and emission spectrum; (b) is the lifetime decay spectrum; (c) is the fluorescence emission spectrum at different excitation wavelengths; (d) is the fluorescence emission spectrum at different storage times; (e) is the curve of F / F0 (the ratio of fluorescence intensity of N-doped carbon dot solution with added NaCl / KCl to that without added NaCl / KCl) as a function of the concentration of additive NaCl / KCl; and (f) is the effect of solvent pH on fluorescence quantum yield.

[0022] Figure 2 The N-doped carbon dots synthesized in Example 3 of this invention are used to measure the effects of different metal ion concentrations in solution. The results of the degree detection are shown in the figure; where (a) is Fe 3+ (b) is CrO4 2- (c) is Ru 3+ .

[0023] Figure 3 This is a GCMS total ion chromatogram of the hydrogenation catalyst supported on a carrier with 3% Ru, synthesized in Example 3 of the present invention, after catalytic degradation of dealkalized lignin. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0025] Please see Figures 1-3 This application discloses a method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and a eutectic solvent, comprising the following steps: Step 1: Mix biomass raw materials, eutectic solvent and additives in a hydrothermal reactor and react hydrothermally at 140~240℃ for 2~6 hours to obtain product 1; Among them, biomass raw materials include at least one of cellulose, lignin, straw, sawdust, bamboo shavings, peanut shells, rice husks and corn cobs; It should be noted that the eutectic solvent in step 1 is prepared by mixing hydrogen bond acceptors and hydrogen bond donors at 80°C; The hydrogen bond acceptors are choline chloride and / or guanidine hydrochloride. The hydrogen bond donor is at least one of urea, citric acid, ethylene glycol, glycerol, and oxalic acid; The additive is any one of ethylenediamine, p-phenylenediamine, m-phenylenediamine, and diethanolamine; It should also be noted that the addition ratio of the eutectic solvent to the biomass raw material is 1~10 mL : 1g; The mass ratio of additives to biomass raw materials is 0.0001~0.01 : 1.

[0026] Step 2: Place product 1 in an inert gas and calcine it at 150~260℃ for 1~4 hours to obtain product 2; In step 2, the inert gas is any one of He, N2, and Ar.

[0027] Step 3: Grind and dissolve product 2 to obtain a mixture, and filter it to obtain product 3 and an aqueous solution respectively; Product 3 is the hydrogenation catalyst support; and the hydrogenation catalyst support obtained in this step can be directly loaded with Ru. If the hydrogenation catalyst support is to be stored, it needs to be dried in an oven at 110 degrees Celsius for 1 hour.

[0028] Step 4: Dialyze the aqueous solution for 24 hours to obtain the dialysis product. Then, rotary evaporate the dialysis product to obtain N-doped carbon dots.

[0029] The tools used for dialysis include dialysis bags (MWCO=1000 Da); rotary evaporation is performed at 80 degrees Celsius, and only water needs to be evaporated.

[0030] Example 1 The method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and eutectic solvent is as follows: 5g of straw powder (100-200 mesh), 25 mL of eutectic solvent (choline chloride-urea, molar ratio 1:1), and 0.7 mg of ethylenediamine are placed in a hydrothermal reactor. The volume ratio of the eutectic solvent to the biomass raw material is 5 mL / g. The hydrothermal reactor is sealed and heated at 240℃ for 6 hours. The product in the hydrothermal reactor is removed and placed in a tube furnace. N2 gas is introduced and heated at 220℃ for 2 hours. The product heated in the tube furnace is ground and dissolved in a small amount of water. The solid product obtained after filtration is the hydrogenation catalyst support. The resulting aqueous solution is dialyzed in a dialysis bag (MWCO=1000 Da) for 24 hours. The dialyzed product is taken and rotary evaporated. The solid obtained is the N-doped carbon dots.

[0031] Example 2 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this embodiment is the same as in Example 1. The only difference is that the eutectic solvent in this embodiment is guanidine hydrochloride-citric acid.

[0032] Example 3 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this embodiment is the same as in Example 2. The only difference is that the biomass used in this embodiment is cellulose.

[0033] Comparative Example 1 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as that in Example 1. The only difference is that the eutectic solvent in this comparative example is choline chloride-citric acid.

[0034] Comparative Example 2 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as that in Example 1. The only difference is that the eutectic solvent in this comparative example is choline chloride-ethylene glycol.

[0035] Comparative Example 3 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as that in Example 1. The only difference is that the eutectic solvent in this comparative example is choline chloride-glycerol.

[0036] Comparative Example 4 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as that in Example 1. The only difference is that the eutectic solvent in this comparative example is choline chloride-oxalic acid.

[0037] Comparative Example 5 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as that in Example 2. The only difference is that the eutectic solvent in this comparative example is guanidine hydrochloride-urea.

[0038] Comparative Example 6 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as that in Example 2. The only difference is that the eutectic solvent in this comparative example is guanidine hydrochloride-ethylene glycol.

[0039] Comparative Example 7 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as in Example 2. The only difference is that the eutectic solvent in this comparative example is guanidine hydrochloride-glycerol.

[0040] Comparative Example 8 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as that in Example 2. The only difference is that the eutectic solvent in this comparative example is guanidine hydrochloride-oxalic acid.

[0041] Comparative Example 9 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as in Example 3. The only difference is that the biomass in this comparative example is lignin.

[0042] Comparative Example 10 The method for preparing N-doped carbon dots and hydrogenation catalyst supports in this comparative example is the same as in Example 3. The only difference is that the biomass used in this comparative example is poplar wood chips.

[0043] The performance of the N-doped carbon dots and hydrogenation catalyst supports synthesized in the embodiments and comparative examples of this invention will be studied below. 1. Yield calculation of N-doped carbon dots and support (1) Experimental methods The yield of N-doped carbon dots was calculated by dividing the mass of N-doped carbon dots by the total mass of biomass and DES. The fluorescence quantum yield of N-doped carbon dots was determined by an FLS920 fluorescence spectrometer, and the catalytic effect of the hydrogenation catalyst was quantitatively analyzed by gas chromatography and gas chromatography-mass spectrometry.

[0044] (2) Experimental results The yields and fluorescence quantum yields of the N-doped carbon dots synthesized in Examples 1-3 of this invention were 12.7%, 16.7%, and 21.3%, respectively; the fluorescence quantum yields of the N-doped carbon dots were 21.6%, 37.7%, and 47.5%, respectively; and the yields of the hydrogenation catalyst support were 48.8%, 52.3%, and 62.3%, respectively. The yields of N-doped carbon dots synthesized in Comparative Examples 1-10 of this invention were 12.6%, 15.1%, 6.4%, 4.8%, 15.6%, 16.3%, 10.5%, 8.7%, 16.7%, and 19.3%, respectively; the fluorescence quantum yields of N-doped carbon dots were 20.7%, 11.9%, 15.4%, 14.7%, 21.7%, 18.6%, 25.5%, 24.2%, 11.4%, and 37.2%, respectively; and the yields of hydrogenation catalyst supports were 58.8%, 64.2%, 46.4%, 37.5%, 48.5%, 51.3%, 44.6%, 51.8%, 70.3%, and 67.4%, respectively.

[0045] Example 3 exhibits the highest N-doped carbon dot yield and fluorescence quantum yield. This is because the N-doped carbon dots prepared using the method of Example 3 contain significantly more N and O functional groups on their surface than those in other groups. These functional groups combine with the unsaturated aromatic structures on the surface of the N-doped carbon dots to form abundant photoluminescent active sites, thereby enabling the N-doped carbon dots prepared using the method of Example 3 to have the highest fluorescence quantum yield.

[0046] 2. Optical characteristics and ion detection of N-doped carbon dots The optical characteristics of the N-doped carbon dots prepared in Example 3 of this invention are as follows: Figure 1 As shown, the maximum excitation wavelength of the N-doped carbon dot aqueous solution (0.01 mg / mL) is 403 nm, and the maximum emission wavelength is 468 nm. Figure 1 a). The fluorescence lifetime of N-doped carbon dots is 10.12 ns ( Figure 1 b). Changing the excitation wavelength affects the fluorescence intensity and maximum emission wavelength of N-doped carbon dots, indicating that N-doped carbon dots exhibit photoluminescence characteristics. Figure 1 c). Dispersing N-doped carbon dots in NaCl or KCl solutions of different concentrations showed little effect on the fluorescence emission intensity of the N-doped carbon dots, indicating that the aqueous solution of N-doped carbon dots has good salt resistance. Figure 1 d). After 12 weeks, the fluorescence emission spectrum of the N-doped carbon dot aqueous solution remained consistent with that of the freshly prepared solution, indicating that the CD-R structure has good stability. Figure 1 e). The quantum yield (QY) of N-doped carbon dots exhibits pH dependence, remaining stable in solutions with pH values ​​between 6 and 9, but significantly decreasing when the pH deviates from this range. Figure 1 f).

[0047] The N-doped carbon dots obtained in Example 3 were used for Fe 3+ CrO4 2- and Ru 3+ The test yielded a standard curve as follows: Figure 2 As shown, Fe3+ CrO4 2- and Ru 3+ R of the standard curve 2 All values ​​were greater than 0.99, and the detection limit was greater than 0.01 ppm.

[0048] 3. Performance of hydrogenation catalyst supported with 3% Ru on the catalytic degradation of dealkalized lignin (1) Metal loading method The hydrogenation catalyst supports in the above examples and comparative examples can all be prepared by impregnation with 3% Ru. The preparation method is as follows: Catalyst Ru / CN: The obtained hydrogenation catalyst support CN is placed in water, an appropriate amount of RuCl3 is weighed and dissolved in the aforementioned water containing CN, commercially available concentrated ammonia is added to adjust the pH to 8-10, stirred at room temperature for 1-3 hours, and allowed to stand for 10-15 hours, filtered, and the resulting precipitate is placed in a muffle furnace and heated at 200℃ for 2 hours, and then reduced with hydrogen at 200℃ for 1-3 hours in a tube furnace to obtain the Ru / CN catalyst, wherein the Ru content is 3-10% of the support mass, and the mass ratio of the support CN to the volume ratio of water is 1 g: (4-6) mL.

[0049] The experimental methods used in the above embodiments and comparative examples are as follows: Metal ion fluorescence detection experiment: Weigh different masses of various metal compounds into 10 mL centrifuge tubes, add the prepared N-doped carbon dot solution, and shake well to ensure that the metal ion concentration in the system is 0.5, 5, 10, 20, 40, 60, 100, 200, 300, and 400 μmol / L, and the solution volume is 10 mL. Prepare a stock solution sample. Use 391 nm as the excitation wavelength and measure the fluorescence intensity at 468 nm, and record the fluorescence emission spectrum of the solution. To ensure the validity of the experiment, multiple experiments should be conducted and compared.

[0050] Catalytic hydrogenolysis experiment: 0.1 g catalyst (3% Ru / CN) and 1 g dealkalized lignin were placed in a 50 mL reactor, 20 mL ethanol was added, and 1 MPa hydrogen gas was introduced. The reaction was carried out at 220 °C for 2-6 hours.

[0051] (2) Catalytic degradation effect The statistical results of the effects of the hydrogenation catalyst supports prepared in Examples 1-3 and Comparative Examples 1-10 of this invention on the catalytic degradation of alkali-free lignin are shown in Tables 1, 2 and 3 below.

[0052] Table 1. Effect of 3% Ru supported on hydrogenation catalyst support on the catalytic degradation of alkali-free lignin in Example 1 and Comparative Examples 1-4

[0053] Table 2. Effects of 3% Ru loaded on the hydrogenation catalyst support on the catalytic degradation of alkali-free lignin in Examples 2 and Comparative Examples 5-8.

[0054] Table 3. Effect of 3% Ru loaded on the hydrogenation catalyst support on the catalytic degradation of alkali-free lignin in Example 3 and Comparative Examples 9-10

[0055] As can be seen from Tables 1, 2, and 3, the catalyst prepared from the hydrogenation catalyst support obtained in Example 3 exhibits the best catalytic degradation effect on dealkalized lignin. The surface of the hydrogenation catalyst support prepared in Example 3 contains abundant pyrrole N, which forms a coordination structure with the Ru precursor during loading, thereby promoting metal dispersion, regulating the valence electron configuration of the metal, and obtaining better catalytic hydrogenation activity. This results in the catalyst exhibiting the best catalytic degradation effect on dealkalized lignin.

[0056] The above-mentioned hydrogenation catalyst support was loaded with 3% Ru (3% Ru / CN) for alkali-removing lignin catalytic degradation. Its GCMS total ion chromatogram and product comparison with the catalyst supported on commercial activated carbon (3% Ru / commercial activated carbon) are shown below. Figure 3 As shown. From Figure 3 It is evident that 3% Ru / CN exhibits better performance than 3% Ru / commercial activated carbon in the catalytic degradation of dealkalized lignin, both in terms of monophenol product yield and selectivity. Nine major monophenol compounds (guaiacol, p-propylphenol, 4-propyl-2-methoxyphenol, isoeugenol, coniferol, dihydroconiferol, 4-hydroxy-3-methoxyphenylpropanal, 4-methyl-2,6-dimethoxyphenol, and 3-(4-hydroxy-3,5-dimethoxyphenyl)propanal) account for 71% of the total aromatic monomer products, with an aromatic monomer yield of 18.5% and an ethyl acetate-soluble yield of 66.2%.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and a eutectic solvent, characterized in that, Includes the following steps: Step 1: Mix biomass raw materials, eutectic solvent and additives, and hydrothermally react at 140~240℃ for 2~6h to obtain product 1; Step 2: Place product 1 in an inert gas and calcine it at 150~260℃ for 1~4 hours to obtain product 2; Step 3: Grind and dissolve product 2 to obtain a mixture, and filter it to obtain product 3 and an aqueous solution respectively; Among them, product 3 is the hydrogenation catalyst support; Step 4: Dialyze the aqueous solution for 24 hours to obtain the dialysis product. Then, rotary evaporate the dialysis product to obtain N-doped carbon dots.

2. The method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and a eutectic solvent according to claim 1, characterized in that, In step 1: Biomass raw materials include at least one of cellulose, lignin, straw, sawdust, bamboo shavings, peanut shells, rice husks, and corn cobs.

3. The method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and a eutectic solvent according to claim 1, characterized in that, In step 1: The eutectic solvent is prepared by mixing a hydrogen bond acceptor and a hydrogen bond donor at 80°C; The hydrogen bond acceptors are choline chloride and / or guanidine hydrochloride. The hydrogen bond donor is at least one of urea, citric acid, ethylene glycol, glycerol, and oxalic acid.

4. The method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and a eutectic solvent according to claim 1, characterized in that, In step 1: The additive is any one of ethylenediamine, p-phenylenediamine, m-phenylenediamine, and diethanolamine.

5. The method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and a eutectic solvent according to claim 1, characterized in that, In step 1: The addition ratio of eutectic solvent to biomass feedstock is 1~10 mL : 1g; The mass ratio of additives to biomass raw materials is 0.0001~0.01 :

1.

6. The method for preparing N-doped carbon dots and hydrogenation catalyst supports based on biomass and a eutectic solvent according to claim 1, characterized in that: In step 2, the inert gas is any one of He, N2, and Ar.

7. An N-doped carbon dot, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. The use of the N-doped carbon dots according to claim 7 in metal ion detection.

9. A hydrogenation catalyst support, characterized in that, It is prepared by the method described in any one of claims 1-6.

10. Use of the hydrogenation catalyst support according to claim 9 on a supported active metal.

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