A type of carbon quantum dot based on distillers' grains, its preparation method and application

Abstract

This invention belongs to the field of nanomaterials technology, specifically relating to a distillery lees-based carbon quantum dot, its preparation method, and its application. The preparation method of the distillery lees-based carbon quantum dot includes the following steps: (1) preparing distillery lees powder; (2) reacting the distillery lees powder, polyethylene polyamine compound, and hydroxypropyl-β-cyclodextrin to obtain a reaction solution; (3) solid-liquid separation to obtain a carbon quantum dot solution; and (4) purification and drying to obtain distillery lees-based carbon quantum dots. This invention uses inexpensive and stable-source baijiu lees as a carbon source, polyethylene polyamine compound as a nitrogen source, and hydroxypropyl-β-cyclodextrin as an auxiliary agent, employing a simple, green, and low-energy-consumption synthesis process to prepare nitrogen-doped carbon quantum dots based on distillery lees. These carbon quantum dots can serve as highly efficient functional fillers, significantly improving the ionic conductivity of solid polymer electrolytes, and simultaneously solving the technical challenges faced in the industrialization of carbon quantum dots and the resource utilization of distillery lees.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, specifically relating to a distillers' grains-based carbon quantum dot, its preparation method, and its application. Background Technology

[0002] Carbon quantum dots, as a novel carbon-based nanomaterial with a size of less than 10 nanometers, have attracted much attention due to their excellent photoluminescence properties, good photostability, low toxicity, and excellent biocompatibility. Structurally, carbon quantum dots typically have a core-shell structure: the interior consists of sp... 2 or sp 3 The carbon core is composed of hybrid carbon, while the outer surface layer is rich in functional groups and heteroatom doping sites. This unique structure makes it a research hotspot in fields such as bioimaging, sensing and analysis, optoelectronic devices, and catalysis.

[0003] Currently, the synthesis methods for carbon quantum dots are mainly divided into two technical routes: the "top-down" method and the "bottom-up" method. The "top-down" method typically uses large-size carbon materials such as graphite and carbon nanotubes as raw materials, and breaks them down into nanoscale carbon dots through physical or chemical means (such as laser ablation, chemical oxidation, and electrochemical exfoliation). However, this type of method generally suffers from harsh reaction conditions, high energy consumption, low yield, and uneven product size distribution, making it difficult to meet the needs of large-scale production. The "bottom-up" method uses small organic molecules such as citric acid and glucose as precursors, and polymerizes and carbonizes them to form carbon dots through hydrothermal / solvothermal methods, microwave synthesis, or pyrolysis, which is currently the mainstream route for preparing carbon quantum dots. Among these, the hydrothermal method is the most widely used in laboratories due to its simple operation and mild conditions, and is particularly suitable for preparing carbon quantum dots with surfaces rich in oxygen-containing functional groups and good water solubility. Nevertheless, the industrial application of the "bottom-up" method still faces severe challenges: (1) High raw material costs: it relies on expensive high-purity chemicals as carbon sources; (2) Serious environmental pollution: some synthetic routes require the use of strong acids, strong bases or toxic organic solvents, resulting in secondary pollution and complex post-processing; (3) Poor biocompatibility of products: the residue of chemical reagents limits its application in food, cosmetics and biomedicine.

[0004] Therefore, researchers have turned to biomass as a green, low-cost carbon source. However, most reported biomass carbon sources, such as fruit and plant extracts, are food-grade raw materials, and their composition varies greatly depending on the place of origin and season, resulting in poor product uniformity. Furthermore, many biomass conversion processes still cannot completely eliminate their dependence on auxiliary chemical reagents or complex purification steps. Meanwhile, the liquor industry, as an important traditional industry in my country, generates a huge amount of solid waste—liquor lees—drinking during the brewing process. This lees is rich in protein, amino acids, cellulose, and other organic matter. However, its current main treatment method is low-value-added feed utilization, which is not only economically inefficient but also highly susceptible to fluctuations in the downstream livestock market. Once large quantities of lees accumulate, it not only wastes resources but also pollutes the environment.

[0005] Meanwhile, in the field of solid-state batteries, solid polymer electrolytes have attracted widespread attention due to their potential to replace traditional liquid electrolytes in flexible devices and high-safety batteries. Among them, polymer electrolyte systems represented by polyethylene oxide (PEO) are the most widely studied. However, the application of PEO-based solid electrolytes faces a key technical bottleneck: because PEO molecular chains easily arrange themselves in a regular pattern at room temperature to form crystalline regions, they severely hinder ion migration, resulting in extremely low ionic conductivity (typically below 10). -6 The S / cm ratio is insufficient to meet the needs of practical applications.

[0006] To address this issue, a common modification strategy is to add inorganic nanofillers (such as silica, alumina, etc.) to the polymer matrix to suppress polymer crystallization and provide additional ion transport pathways. However, traditional inorganic nanofillers often suffer from the following problems: (1) the particles are prone to agglomeration in the polymer matrix, leading to non-uniform performance; (2) the interfacial compatibility between the inorganic filler and the organic polymer matrix is ​​poor, easily forming obstacles to ion transport. Therefore, developing a novel functional nanofiller that is well-compatible with the polymer matrix and can efficiently promote ion transport is of great significance for promoting the development of solid polymer electrolytes. Summary of the Invention

[0007] Based on this, in order to address the aforementioned needs in the existing technology, the purpose of this invention is to provide a method for preparing water-soluble carbon quantum dots using baijiu lees as raw material. This method is simple, low-cost, and environmentally friendly. The carbon quantum dots can serve as highly efficient functional fillers, significantly improving the ionic conductivity of solid polymer electrolytes. This method can simultaneously solve the technical challenges faced in the industrialization of carbon quantum dots and the resource utilization of baijiu lees.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) The lees of the liquor are dried and pulverized to obtain liquor lees powder; (2) Mix the distiller's grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, and place them in a reaction vessel to carry out the reaction to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is (0.01-0.1):1; (3) The reaction solution is subjected to solid-liquid separation to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified and dried to obtain distillers grains-based carbon quantum dots.

[0009] Most solid polymer electrolytes originate from matrices with simple functional groups, exhibiting characteristics such as low ionic conductivity, reduced mechanical properties after modification, poor electrochemical stability, and low lithium-ion transfer numbers. Therefore, designing and applying multifunctional carbon quantum dots to solid polymer electrolytes is a novel strategy to address the electrochemical performance issues of these electrolytes. To this end, this invention uses baijiu (Chinese liquor) lees as biomass, polyethylenepolyamine compounds as the nitrogen source, and hydroxypropyl-β-cyclodextrin as an auxiliary nitriding molecule to prepare nitrogen-doped carbon quantum dots. The type of lees is not particularly limited; any commonly used lees in the field is acceptable. Specifically, this invention uses sorghum lees.

[0010] Nitrogen-doped carbon quantum dots (CNQDs) can serve as nanofillers for solid polymer electrolytes (SPEs), improving their performance and ionic conductivity. Generally, smaller particle sizes are more beneficial for conductivity improvement but also more prone to aggregation, hindering their intended function. CNQDs, with their abundant hydrophilic / hydrophobic groups, exhibit excellent water / oil solubility, allowing for thorough dispersion in electrolyte solutions. Furthermore, the rich oxygen-containing functional groups on their surface provide Lewis acid-base reaction sites, effectively promoting salt dissociation and anion adsorption in SPEs, ultimately significantly enhancing ion mobility. Moreover, the surface structure of CNQDs can provide lithium-ion transport channels, further improving the ionic conductivity of SPEs.

[0011] In one embodiment, the drying temperature in step (1) is 40-60°C, and the drying time is 24-48 hours. Further, the drying temperature is 40°C, 45°C, 50°C, 55°C, or 60°C. Specifically, the drying temperature is 45-55°C. A suitable drying temperature can promote the thoroughness of the drying process and improve drying efficiency.

[0012] In one embodiment, the polyethylene polyamine compound in step (2) is one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and hexaethyleneheptamine.

[0013] Polyethylene polyamine compounds contain multiple nitrogen atoms and reactive amino groups. Under high temperature and pressure conditions, and with the assistance of hydroxypropyl-β-cyclodextrin, the nitrogen atoms of these compounds can not only chemically embed into the carbon framework of the forming carbon quantum dots, achieving a high level of nitrogen doping, but also the amino groups can undergo amidation reactions with carboxyl and carbonyl groups on the carbon quantum dot surface, directly grafting onto the carbon dot surface. This not only provides abundant surface functional groups, enhancing water solubility and fluorescence properties, but also effectively "passivates" defect states on the carbon dot surface, significantly improving yield.

[0014] Specifically, various polyethylene polyamine compounds with different molecular weights can be used for doping. Smaller molecular weight polyethylene polyamine compounds, with their short chains, high reactivity, and low steric hindrance, can rapidly and extensively penetrate into carbon precursors, achieving nitrogen intercalation in the early stages and within the carbon core. This facilitates the formation of cores with high nitrogen doping concentrations and promotes the formation of graphitic nitrogen and pyridine nitrogen. Larger molecular weight polyethylene polyamine compounds, with their longer chains, higher nitrogen content, greater steric hindrance, and relatively milder reactions, tend to react more readily on or near the surface of the carbon core due to their larger molecular structure. They provide more abundant surface nitrogen functional groups and, due to their longer, more flexible chains, more easily interact with hydroxypropyl-β-cyclodextrin, thus effectively performing surface passivation and functionalization. The mixed use of various polyethylene polyamine compounds with different molecular weights can achieve uniform, gradient doping from the bulk phase to the surface. For example, a mixture of diethylenetriamine and tetraethylenepentamine in a molar ratio of (0.1-10):1 can be used. Specifically, a mixture of diethylenetriamine and tetraethylenepentamine in a ratio of 0.1:1, 0.3:1, 0.5:1, 0.8:1, 1:1, 3:1, 5:1, 8:1, or 10:1 can be used. Further, a mixture of diethylenetriamine and tetraethylenepentamine in a ratio of (0.3-0.8):1 can be used.

[0015] Compared to β-cyclodextrin, hydroxypropyl-β-cyclodextrin possesses a cyclic cavity structure that is hydrophobic internally and hydrophilic externally. Before the reaction, it can encapsulate hydrophobic aromatic intermediate molecules produced by the decomposition of baijiu lees, preventing these precursors from prematurely agglomerating or forming large carbon slag masses. This provides a confined reaction space at the nanoscale, which is beneficial for generating more uniformly sized carbon quantum dots. Furthermore, the cavity of hydroxypropyl-β-cyclodextrin can also weakly interact with polyethylenepolyamine compound molecules, enriching them around the carbon precursors. This is equivalent to targeted delivery of the nitrogen source to the carbon core growth interface, improving the efficiency and controllability of nitrogen doping, especially promoting the formation of more graphitic nitrogen or pyridine nitrogen. Moreover, hydroxypropyl-β-cyclodextrin itself is a carbohydrate that can be partially carbonized at high temperatures, participating in the formation of carbon cores or surface modification, introducing more oxygen-containing functional groups, resulting in better dispersion and less agglomeration of the final nitrogen-doped carbon quantum dots. This is beneficial for uniform composite formation with solid polymer electrolytes. As an auxiliary agent, the main function of hydroxypropyl-β-cyclodextrin is to promote nitrogen doping of carbon quantum dots. Its dosage should not be too high, otherwise it will not only affect the formation of carbon quantum dots and reduce the purity of the product, but also, excessive hydroxypropyl-β-cyclodextrin will act as an isolation layer, hindering the effective contact between polyethylene polyamine compounds and carbon precursors, and thus preventing the effective nitrogen doping reaction.

[0016] In one embodiment, the mass ratio of the polyethylene polyamine compound to the distiller's grains powder in step (2) is (0.5-1):1. Further, it can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1. Specifically, it can be (0.6-0.8):1. An appropriate amount of polyethylene polyamine compound can sufficiently dope carbon quantum dots, improving the ionic conductivity of the solid electrolyte.

[0017] There is no particular limit to the amount of water used, as long as the components are fully dispersed. Specifically, the mass-to-volume ratio of the distiller's grains powder to water is (1-10) g : (50-100) mL.

[0018] In one embodiment, the reaction temperature in step (2) is 170-200°C, and the reaction time is 10-14 hours. Specifically, the reaction vessel can be placed in an oven, and the reaction temperature can be 170°C, 180°C, 185°C, 190°C, or 200°C. Further, the reaction temperature is 180-190°C. A suitable reaction temperature can both promote the carbonization process and prevent excessive carbonization and decomposition due to excessively high temperatures.

[0019] In one embodiment, the solid-liquid separation in step (3) includes centrifugation and filtration processes.

[0020] In one embodiment, the centrifugation speed is 8000-12000 r / min, and the filtration process uses a filter membrane with a pore size of no more than 0.22 μm. Specifically, the centrifugation speed can be 8000 r / min, 9000 r / min, 10000 r / min, 11000 r / min, or 12000 r / min.

[0021] In one embodiment, the purification process in step (4) uses a dialysis membrane with a molecular weight cutoff of 500 Da. Specifically, deionized water can be used for dialysis purification; the drying process is freeze drying.

[0022] On the other hand, the present invention also provides distillers' grains-based carbon quantum dots prepared by the above method and solid polymer electrolytes containing the quantum dots.

[0023] Nitrogen-doped carbon quantum dots synthesized with the aid of hydroxypropyl-β-cyclodextrin are expected to have smaller size distribution, higher nitrogen doping uniformity, richer surface functional groups and dispersion stability, making them particularly suitable as nanofillers for solid polymer electrolytes to improve their ionic conductivity.

[0024] The addition of nitrogen-doped carbon quantum dots increases the degree of amorphization within the solid polymer electrolyte, thereby lowering the activation energy for lithium-ion migration and effectively improving ionic conductivity. Furthermore, with the assistance of hydroxypropyl-β-cyclodextrin, the edge nitrogen in the carbon quantum dots plays a crucial role in the interaction between the solid polymer electrolyte chains and lithium ions, granting the constrained lithium ions greater freedom and further enhancing the ionic conductivity of the polymer / nitrogen-doped carbon quantum dot composite electrolyte.

[0025] Specifically, the solid polymer electrolyte comprises a polymer matrix, a lithium salt, and distillers' grains-based carbon quantum dots. The solid polymer electrolyte can be prepared using conventional processes in the art: the polymer matrix, lithium salt, and distillers' grains-based carbon quantum dots are dissolved and dispersed together in an organic solvent to form a mixed solution; the mixed solution is then cast into a film, and the solvent is removed to obtain the solid polymer electrolyte.

[0026] In one embodiment, the polymer matrix is ​​polyethylene oxide; the lithium salt is lithium perchlorate; and the amount of distillers' grains-based carbon quantum dots added is 0.5-2% of the mass of polyethylene oxide. Further, the mass ratio of polyethylene oxide, lithium perchlorate, and distillers' grains-based carbon quantum dots is 500:60:5.

[0027] Beneficial effects: (1) This invention uses non-grain, inexpensive, and stable-source baijiu lees as a carbon source and employs a simple, green, and low-energy-consumption hydrothermal process to prepare nitrogen-doped carbon quantum dots with good water solubility. These carbon quantum dots can serve as highly efficient functional fillers, significantly improving the ionic conductivity of solid polymer electrolytes, and can simultaneously solve the technical challenges faced in the industrialization of carbon quantum dots and the resource utilization of baijiu lees.

[0028] (2) Polyethylene polyamine compounds contain multiple nitrogen atoms and active amino groups. Under high temperature and high pressure conditions and with the assistance of hydroxypropyl-β-cyclodextrin, polyethylene polyamine compounds can achieve high levels of nitrogen doping and provide abundant surface functional groups, thereby enhancing water solubility and improving quantum yield.

[0029] (3) Nitrogen-doped carbon quantum dots synthesized with the aid of hydroxypropyl-β-cyclodextrin have smaller size distribution, higher nitrogen doping uniformity, richer surface functional groups and dispersion stability, making them particularly suitable as nanofillers for solid polymer electrolytes and improving their ionic conductivity. Attached Figure Description

[0030] Figure 1 Transmission electron microscopy image of the distillers' grains-based carbon quantum dots prepared in Example 10; Figure 2 High-magnification transmission electron microscope image of the distillers' grains-based carbon quantum dots prepared in Example 10; Figure 3 Transmission electron microscopy (TEM) image of the solid product prepared for Comparative Example 1. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0032] Performance testing: Under the same conditions, the ionic conductivity of the solid polymer electrolytes prepared in Examples 1-10 and Comparative Examples 2-3 was tested on an electrochemical workstation: polyethylene oxide, lithium perchlorate, and distillers' grains-based carbon quantum dots were dissolved and dispersed together in anhydrous acetonitrile to form a mixed solution; the mixed solution was cast into a film and dried to obtain the solid polymer electrolyte; the mass ratio of polyethylene oxide, lithium perchlorate, and distillers' grains-based carbon quantum dots was 500:60:5.

[0033] Example 1 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 40°C for 48 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, place them in a reaction vessel and react at 170°C for 14 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.01:1; the polyethylene polyamine compound is diethylenetriamine; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.5:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 6.16 × 10⁻⁶. -5 S / cm.

[0034] Example 2 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 60°C for 24 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, place them in a reaction vessel and react at 200°C for 10 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.1:1; the polyethylene polyamine compound is triethylenetetramine; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 1:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 9.05 × 10⁻⁶. -5 S / cm.

[0035] Example 3 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 50°C for 35 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, and place them in a reaction vessel and react at 190°C for 12 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.06:1; the polyethylene polyamine compound is diethylenetriamine; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.8:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 7.69 × 10⁻⁶. -5 S / cm.

[0036] Example 4 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 42℃ for 26 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, place them in a reaction vessel and react at 175°C for 11 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.02:1; the polyethylene polyamine compound is tetraethylenepentamine; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.6:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 6.75 × 10⁻⁶. -5 S / cm.

[0037] Example 5 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 50°C for 35 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, place them in a reaction vessel and react at 190°C for 12 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.06:1; the polyethylene polyamine compound is tetraethylenepentamine; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.8:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 8.12 × 10⁻⁶. -5 S / cm.

[0038] Example 6 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 45°C for 42 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, and place them in a reaction vessel to react at 180°C for 13 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.05:1; the polyethylene polyamine compound is a mixture of diethylenetriamine and triethylenetetramine in a molar ratio of 0.1:1; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.6:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 8.87 × 10⁻⁶. -5 S / cm.

[0039] Example 7 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 50°C for 35 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, and place them in a reaction vessel to react at 190°C for 12 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.06:1; the polyethylene polyamine compound is a mixture of diethylenetriamine and tetraethylenepentamine in a molar ratio of 2:1; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.8:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 8.33 × 10⁻⁶. -5 S / cm.

[0040] Example 8 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 55℃ for 30h, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, and place them in a reaction vessel and react at 190°C for 12 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.08:1; the polyethylene polyamine compound is a mixture of triethylenetetramine and tetraethylenepentamine in a molar ratio of 0.7:1; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.9:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 9.01 × 10⁻⁶. -5 S / cm.

[0041] Example 9 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 48°C for 36 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, place them in a reaction vessel and react at 180°C for 12.5 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.04:1; the polyethylene polyamine compound is a mixture of diethylenetriamine and triethylenetetramine in a molar ratio of 10:1; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.7:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 7.36 × 10⁻⁶. -5 S / cm.

[0042] Example 10 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 50°C for 35 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, and place them in a reaction vessel to react at 190°C for 12 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.06:1; the polyethylene polyamine compound is a mixture of diethylenetriamine and tetraethylenepentamine in a molar ratio of 0.5:1; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.8:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 9.12 × 10⁻⁶. -5 S / cm.

[0043] Comparative Example 1 A method for preparing a solid product includes the following steps: (1) Dry the lees of Baijiu at 50°C for 35 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and ethanol, place them in a reaction vessel and react at 190°C for 12 h. The product is in the form of a turbid liquid. The mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.06:1. The polyethylene polyamine compound is a mixture of diethylenetriamine and tetraethylenepentamine in a molar ratio of 0.5:1. The mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.8:1. The mass-volume ratio of distillers' grains powder to ethanol is 1 g: 70 mL. (3) Centrifuge the turbid liquid at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain the solution; (4) The solution was purified by dialysis with a molecular weight cutoff of 500 Da and freeze-dried to obtain a solid product with poor water solubility.

[0044] Comparative Example 2 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 50°C for 35 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, β-cyclodextrin and water, and place them in a reaction vessel to react at 190°C for 12 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of β-cyclodextrin to polyethylene polyamine compound is 0.06:1; the polyethylene polyamine compound is a mixture of diethylenetriamine and tetraethylenepentamine in a molar ratio of 0.5:1; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.8:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 1.35 × 10⁻⁶. -5 S / cm.

[0045] Comparative Example 3 A method for preparing distillers' grains-based carbon quantum dots includes the following steps: (1) Dry the lees of Baijiu at 50°C for 35 hours, and then pulverize them to obtain lees powder; (2) Mix the distillers' grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, and place them in a reaction vessel to react at 190°C for 12 h to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is 0.2:1; the polyethylene polyamine compound is a mixture of diethylenetriamine and tetraethylenepentamine in a molar ratio of 0.5:1; the mass ratio of polyethylene polyamine compound to distillers' grains powder is 0.8:1; the mass-volume ratio of distillers' grains powder to water is 1 g: 70 mL; (3) Centrifuge the reaction solution at 10000 r / min, take the supernatant, and then filter it with a 0.22 μm filter membrane to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified using a dialysis membrane with a molecular weight cutoff of 500 Da, and then freeze-dried to obtain distillers' grains-based carbon quantum dots. The ionic conductivity of the resulting solid polymer electrolyte was measured to be 3.37 × 10⁻⁶. -5 S / cm.

[0046] Figure 1 The image shows a transmission electron microscope (TEM) image of the distillers' grains-based carbon quantum dots prepared in Example 10. The image shows that the product consists of uniformly dispersed near-spherical nanoparticles with a particle size distribution concentrated between 2 and 6 nm. Figure 2 The image shown is a high-magnification transmission electron microscope (TEM) image of the distillers' grains-based carbon quantum dots prepared in Example 10. The high-resolution TEM image shows clear lattice fringes, proving that well-crystallized hybrid aromatic carbon cores are formed inside the carbon quantum dots. Figure 3 The image shows a transmission electron microscope (TEM) image of the solid product prepared in Comparative Example 1. It can be seen from the image that the obtained product consists of irregular, severely aggregated carbonaceous particles with a size exceeding several hundred nanometers, rather than the desired carbon quantum dots. Therefore, under the process conditions of this invention, carbon quantum dots cannot be prepared using ethanol as a solvent.

[0047] As can be seen from the above figures and data, this invention uses non-grain, inexpensive, and stable-source baijiu (Chinese liquor) lees as a carbon source, and employs a simple, green, and low-energy-consumption synthesis process to prepare nitrogen-doped carbon quantum dots. These carbon quantum dots can serve as highly efficient functional fillers, significantly improving the ionic conductivity of solid polymer electrolytes, and simultaneously solving the technical challenges faced in the industrialization of carbon quantum dots and the resource utilization of baijiu lees. The polyethylenepolyamine compound contains multiple nitrogen atoms and active amino groups. Under high temperature and high pressure conditions, and with the assistance of hydroxypropyl-β-cyclodextrin, the polyethylenepolyamine compound can achieve a high level of nitrogen doping and provide abundant surface functional groups, enhancing water solubility and improving quantum yield. The nitrogen-doped carbon quantum dots synthesized with the assistance of hydroxypropyl-β-cyclodextrin exhibit smaller size distribution, higher nitrogen doping uniformity, richer surface functional groups, and better dispersion stability, making them particularly suitable as nanofillers for solid polymer electrolytes to improve their ionic conductivity.

[0048] Specifically, compared to Example 10, Comparative Example 1, which used ethanol for a solvothermal reaction, failed to yield carbon quantum dots, indicating that water as the reaction medium is a key and necessary condition for the efficient conversion of baijiu lees into high-quality carbon quantum dots. Compared to Example 10, Comparative Example 2 used β-cyclodextrin as an auxiliary agent. Since β-cyclodextrin lacks an amphiphilic structure, it cannot interact with polyethylene polyamine molecules, resulting in reduced nitrogen doping efficiency and hindering the formation of graphitic nitrogen or pyridine nitrogen. Compared to Example 10, Comparative Example 3 used excessive amounts of hydroxypropyl-β-cyclodextrin. As an auxiliary agent, the main function of hydroxypropyl-β-cyclodextrin is to promote nitrogen doping of carbon quantum dots. Excessive hydroxypropyl-β-cyclodextrin not only affects the formation of carbon quantum dots, leading to reduced product purity, but also acts as an isolation layer, hindering effective contact between polyethylene polyamine compounds and carbon precursors, preventing effective nitrogen doping and thus reducing the conductivity of the prepared solid electrolyte membrane.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing distillers' grains-based carbon quantum dots, characterized in that, Includes the following steps: (1) The lees of the liquor are dried and pulverized to obtain liquor lees powder; (2) Mix the distiller's grains powder, polyethylene polyamine compound, hydroxypropyl-β-cyclodextrin and water, and place them in a reaction vessel to carry out the reaction to obtain a reaction solution containing carbon quantum dots; the mass ratio of hydroxypropyl-β-cyclodextrin to polyethylene polyamine compound is (0.01-0.1):1; (3) The reaction solution is subjected to solid-liquid separation to obtain a carbon quantum dot solution; (4) The carbon quantum dot solution was purified and dried to obtain distillers grains-based carbon quantum dots.

2. The method for preparing distillers' grains-based carbon quantum dots as described in claim 1, characterized in that, The drying temperature in step (1) is 40-60℃ and the time is 24-48h.

3. The method for preparing distillers' grains-based carbon quantum dots as described in claim 1, characterized in that, The polyethylene polyamine compound in step (2) is one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and hexaethyleneheptamine.

4. The method for preparing distillers' grains-based carbon quantum dots as described in claim 1, characterized in that, In step (2), the mass ratio of the polyethylene polyamine compound to the distiller's grains powder is (0.5-1):

1.

5. The method for preparing distillers' grains-based carbon quantum dots as described in claim 1, characterized in that, The reaction temperature in step (2) is 170-200℃, and the reaction time is 10-14h.

6. The method for preparing distillers' grains-based carbon quantum dots as described in claim 1, characterized in that, The solid-liquid separation in step (3) includes centrifugation and filtration processes.

7. The method for preparing distillers' grains-based carbon quantum dots as described in claim 6, characterized in that, The centrifugation speed is 8000-12000 r / min, and the filtration process uses a filter membrane with a pore size of no more than 0.22 μm.

8. The method for preparing distillers' grains-based carbon quantum dots as described in claim 1, characterized in that, In step (4), the purification process uses a dialysis membrane with a molecular weight cutoff of 500 Da, and the drying process is freeze drying.

9. A type of distillers' grains-based carbon quantum dot, characterized in that, It is prepared by the method for preparing a distillers' grains-based carbon quantum dot according to any one of claims 1-8.

10. A solid polymer electrolyte, characterized in that, It comprises a polymer matrix, a lithium salt, and the distillers grains-based carbon quantum dots as described in claim 9.

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