Preparation method of plant-based carbon quantum dots, plant-based carbon quantum dots and application

Abstract

The invention discloses a preparation method of plant-based carbon quantum dots, the plant-based carbon quantum dots and application, and belongs to the technical field of carbon quantum dot corrosion inhibitors in electrolyte. The preparation method of the plant-based carbon quantum dots comprises the following steps: drying and grinding locust tree leaves to obtain locust tree leaf powder; dissolving the locust tree leaf powder in deionized water, and stirring until the locust tree leaf powder is completely dissolved to obtain a precursor solution; transferring the precursor solution into a reaction kettle for heating to obtain a reactant; and carrying out suction filtration and dialysis treatment on a reactant, and freeze-drying a solid substance to obtain the sophora japonica leaf-based carbon quantum dots. The prepared locust tree leaf-based carbon quantum dots are added into NaOH electrolyte as a corrosion inhibitor, so that the anode corrosion resistance of the aluminum air battery is improved, and the discharge performance is optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon quantum dot corrosion inhibitors in electrolytes, and in particular to a preparation method of plant-based carbon quantum dots, plant-based carbon quantum dots and applications thereof. Background Art

[0002] Lithium-ion batteries are currently the most mature and commercially viable battery technology. However, high material costs and safety issues related to thermal management are fundamental disadvantages of this battery system. Among various batteries, metal-air batteries have attracted much attention due to their high energy density, light weight, and safety. Aluminum reserves are abundant, economically feasible, and have a large volume capacity (8.04Ahcm -3 ), and is therefore widely considered a promising anode material for metal-air batteries. Aluminum-air batteries typically employ alkaline electrolytes (NaOH / KOH) to mitigate surface passivation and optimize discharge performance. However, the highly corrosive nature of alkaline electrolytes can lead to severe anode self-corrosion, shortening service life and raising serious safety concerns. Therefore, developing effective corrosion control strategies is crucial for the large-scale commercialization of aluminum-air batteries.

[0003] Methods for improving the corrosiveness of alkaline electrolytes in lithium-ion batteries include anode alloying, solid-state electrolytes, non-aqueous electrolytes, coating technologies, reversible oil-driven battery systems, and electrolyte additives. Among these methods, electrolyte additives have been widely studied due to their convenience and effectiveness. However, some additives require high dosages to be effective, negatively impacting discharge performance. Furthermore, these additives are environmentally unfriendly, which is inconsistent with the green and environmentally friendly design principles of aluminum-air batteries.

[0004] Carbon quantum dots (SCDs) are an emerging zero-dimensional nanomaterial with morphological characteristics such as nearly spherical shape and controllable size. They also have low toxicity, high chemical stability and good surface functionalization capabilities. With these advantages, carbon quantum dots have shown broad application prospects in many fields such as sensing, bioimaging, and energy. Traditional carbon quantum dots usually use small organic molecules as precursors, and have problems such as limited raw material sources and complex synthesis processes. In contrast, carbon quantum dots prepared with green plants as carbon sources can not only realize the resource utilization of plant waste, but also have the advantages of strong renewability, low cost, and environmental friendliness, becoming an important direction for promoting the development of green functional materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of plant-based carbon quantum dots, plant-based carbon quantum dots and applications, extract carbon quantum dots from locust leaves, and add the plant-based carbon quantum dots as corrosion inhibitors to NaOH electrolyte, thereby improving the corrosion resistance of the anode and optimizing the discharge performance of aluminum-air batteries.

[0006] To achieve the above object, the present invention provides a method for preparing plant-based carbon quantum dots, comprising the following steps:

[0007] S1, drying and grinding the leaves of Sophora japonica to obtain Sophora japonica leaf powder;

[0008] S2. Dissolve the Sophora japonica leaf powder in deionized water and stir until completely dissolved to obtain a precursor solution;

[0009] S3, transferring the precursor solution to a reactor for heating to obtain a reactant;

[0010] S4. After the reactants are filtered and dialyzed, the solid matter is freeze-dried to obtain plant-based carbon quantum dots.

[0011] Preferably, in S1, the drying temperature of the Sophora japonica leaves is 40° C.-50° C., the drying time is 36 hours-48 hours, and the powder particle size of the Sophora japonica leaves is less than 1.25 mm.

[0012] Preferably, in S2, 0.6 g to 1.5 g of Sophora japonica leaf powder is dissolved in every 100 ml of deionized water at a dissolution temperature of 60° C. to 80° C.

[0013] Preferably, in S3, the heating temperature is 160° C.-180° C., and the heating time is 15 hours-24 hours.

[0014] Preferably, in said S4, the freezing temperature of freeze drying is -80°C to -85°C, and the drying time is 36 hours to 48 hours.

[0015] The plant-based carbon quantum dots were prepared using the above preparation method.

[0016] Application of plant-based carbon quantum dots in aluminum-air battery electrolytes.

[0017] Preferably, the concentration of the strong alkaline electrolyte in the aluminum-air battery electrolyte is 4M.

[0018] Preferably, the strong alkaline electrolyte is sodium hydroxide.

[0019] Preferably, the concentration of the plant-based carbon quantum dots is 0.2 g L -1 .

[0020] The advantages and positive effects of the preparation method of plant-based carbon quantum dots, plant-based carbon quantum dots and applications of the present invention are:

[0021] 1. The hydrothermal method used in the present invention prepares SCDs with uniform morphology and a particle size of less than 10 nm. The preparation method is simple and easy to operate.

[0022] 2. When the concentration of SCDs is 0.2 g L -1 Whencorr 27.5 mA cm -1 down to 16.1 mA cm -1 Polarization curves calculated a corrosion inhibition efficiency of 41.5%. Furthermore, the charge transfer resistance increased, resulting in a corrosion inhibition efficiency of 40.4% calculated using electrochemical impedance spectroscopy. Sophora japonica leaf-based carbon quantum dots possess aluminophilic functional groups, which allow molecules to adsorb to the aluminum metal surface. This modulates the reaction kinetics between the electrode and electrolyte, promotes uniform and controllable corrosion of the aluminum anode, and inhibits hydrogen evolution side reactions.

[0023] 3. The electrolyte prepared by the present invention has improved electrochemical stability and can effectively inhibit hydrogen evolution reaction when used on the surface of aluminum anode;

[0024] 4. The electrolyte prepared by the present invention can effectively improve the discharge performance of aluminum-air batteries when used in aluminum-air batteries. When SCDs are present in the electrolyte, the capacity density can reach 1538.5 mAh g -1 , energy density can be as high as 1800.0Whkg -1 , the anode utilization rate also increased significantly to 51.7%.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a process flow chart of an embodiment of the present invention;

[0027] Figure 2 AFM images of SCDs prepared according to the present invention;

[0028] Figure 3 AFM image of particle size analysis of SCDs prepared in an embodiment of the present invention;

[0029] Figure 4 TEM images of SCDs prepared in accordance with an embodiment of the present invention;

[0030] Figure 5 TEM image particle size analysis diagram of SCDs prepared in an embodiment of the present invention;

[0031] Figure 6 Nyquist diagrams of the embodiments and comparative examples of the present invention;

[0032] Figure 7 Bode diagrams of the embodiments and comparative examples of the present invention, including impedance-frequency and phase angle-frequency diagrams;

[0033] Figure 8 Polarization curves of the embodiments of the present invention and the comparative example;

[0034] Figure 9 A comparison diagram of the electrochemical windows of the embodiments of the present invention and the comparative examples;

[0035] Figure 10 The graph of the amount of hydrogen released over time for the examples of the present invention and the comparative example;

[0036] Figure 11 The aluminum-air battery composed of the embodiment of the present invention and the comparative example is -2 The constant current discharge curve diagram below;

[0037] Figure 12 Polarization curves and power density curves of aluminum-air batteries composed of embodiments of the present invention and comparative examples;

[0038] Figure 13 The voltage curves of the aluminum-air batteries composed of the embodiments of the present invention and the comparative examples at different current densities;

[0039] Figure 14 The intermittent discharge curves of the aluminum-air batteries composed of the embodiments of the present invention and the comparative examples are shown;

[0040] Figure 15 The limit discharge curves of the aluminum-air batteries composed of the embodiments of the present invention and the comparative examples;

[0041] Figure 16 This is a microscopic surface SEM image of an aluminum plate after the aluminum metal was immersed in the electrolyte prepared in the embodiment of the present invention for 0.5 h;

[0042] Figure 17 The microscopic surface SEM image of the aluminum plate after the aluminum metal was immersed in the electrolyte prepared in the comparative example of the present invention for 0.5 h;

[0043] Figure 18 CLSM image of the aluminum plate after the aluminum metal was immersed in the electrolyte prepared in the embodiment of the present invention for 0.5 h;

[0044] Figure 19 This is a CLSM image of an aluminum plate after metallic aluminum was immersed in the electrolyte prepared in the comparative example of the present invention for 0.5 h. DETAILED DESCRIPTION

[0045] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. In the event of any inconsistency, the meaning described in this specification or the meaning derived from the contents recorded in this specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0046] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0047] like Figure 1 As shown, a method for preparing plant-based carbon quantum dots comprises the following steps:

[0048] S1. Dry the leaves of Sophora japonica at 40-50° C. for 36-48 hours, and grind them to obtain Sophora japonica leaf powder with a particle size of less than 1.25 mm.

[0049] S2. Dissolve the Sophora japonica leaf powder in deionized water and stir until completely dissolved to obtain a solution.

[0050] Dissolve 0.6g-1.5g of Sophora japonica leaf powder in every 100ml of deionized water at a dissolution temperature of 60℃-80℃.

[0051] S3. Transfer the solution to a reactor and heat it to obtain a reactant. The heating temperature is 160° C. to 180° C. and the heating time is 15 hours to 24 hours.

[0052] S4. After the reactants are filtered and dialyzed, they are freeze-dried at -80°C to -85°C in a vacuum environment for 36 hours to 48 hours to obtain plant-based carbon quantum dots.

[0053] Example

[0054] A method for preparing plant-based carbon quantum dots comprises the following steps:

[0055] S1. Dry the leaves of Sophora japonica at 40-50° C. for 36-48 hours, and grind them to obtain Sophora japonica leaf powder with a particle size of less than 1.25 mm.

[0056] S2. Dissolve 5 g of Sophora japonica leaf powder in 500 ml of deionized water and stir thoroughly at 70° C. until completely dissolved to obtain a precursor solution.

[0057] S3. Transfer the precursor solution to a reactor and heat it at 170° C. for 20 to 24 hours to fully carbonize and cross-link the precursor to obtain a reactant.

[0058] S4. After the reactants were filtered and dialyzed, they were freeze-dried at -80°C to -85°C in a vacuum environment for 36 hours to 48 hours to obtain 0.1 g of Sophora japonica leaf-based carbon quantum dots (SCDs).

[0059] In order to study the morphology and particle size of SCDs, the obtained SCDs were characterized by combining AFM and TEM. Figure 2 As shown in Figure 2, the AFM images show that SCDs are spherical, and the height distribution of two carbon quantum dot calibration points (1, 2) was analyzed by NanoScopeAnalysis software. Figure 3The heights of the two calibration points are between 2nm and 4nm. Figure 4 As shown in FIG, TEM images also show that the morphology of the SCDs prepared in the embodiment is spherical. The particle size analysis of the TEM images was performed using ImageJ software. Figure 5 The particle size of SCDs is mainly distributed in the range of 4nm-9nm, with an average particle size of about 7nm. This shows that carbon quantum dots were successfully prepared using the method described in this example.

[0060] Weigh 16g of NaOH and dissolve it in deionized water. After cooling to room temperature, dilute to 100ml in a 100mL volumetric flask to obtain 100ml of a 4M sodium hydroxide solution, which serves as the comparative electrolyte. Weigh 0.2g of the SCDs prepared in Example 1 and add them to 100ml of a 4M sodium hydroxide solution, then sonicate until homogeneous. This serves as the example electrolyte.

[0061] In the study of the effect of SCDs corrosion inhibitors on the discharge performance of aluminum-air batteries, the aluminum anode was commercial aluminum and the cathode was a commercial air cathode. The electrochemical test used a three-electrode system, where aluminum and copper conductors were welded and sealed with epoxy resin adhesive (reaction area 1 cm 2 ) as the working electrode. The counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. In the electrochemical window test, both the working and counter electrodes were platinum electrodes, and the reference electrode was a Hg / HgO electrode.

[0062] The aluminum anode needs to be pretreated before use. The pretreatment steps include: polishing the aluminum anode with sandpaper. The order of sandpaper used is 400 mesh, 800 mesh, 1200 mesh, and 2000 mesh. Then, ultrasonic cleaning is performed with deionized water and anhydrous ethanol. Finally, drying is performed to ensure that the surface of the aluminum anode is smooth and flat.

[0063] In order to further study the interface reaction kinetics of aluminum anode, EIS and polarization curve tests were carried out on the examples and comparative examples. Figure 6 The curves of the embodiment and the comparative example show similar shape characteristics, indicating that the introduction of SCDs does not change the dissolution mechanism of aluminum, but rather hinders the dissolution of Al corresponding to the inductance loop in the high-frequency region into Al + Process and Al corresponding to the second inductor loop + Oxidized to Al 3+ The inductive loop in the mid-frequency region originates from the competitive adsorption of the oxidation intermediates formed during the Al dissolution process, the intermediates during the hydrogen evolution process, and the SCDs molecules on the aluminum surface.

[0064] In order to better quantify the corrosion inhibition effect of SCDs on Al in 4 M NaOH, the EIS test results were fitted, as shown in Table 1. The relevant parameters include solution resistance (R s ), charge transfer resistance (R ct,1 ), constant phase angle element (CPE1), inductor (L), inductive resistor (R), charge transfer resistor (R ct,2 ) and constant phase element (CPE2). The corrosion inhibition efficiency (ηEIS) is calculated using Equations 1 and 2.

[0065] R P =R ct,1 +R ct,2 (1)

[0066]

[0067] Table 1 EIS test results fitting table

[0068]

[0069]

[0070] The results showed that 0.2 g L -1 SCDs can make R ct，1 Increase by two times, making R ct，2 The corrosion inhibition efficiency was increased by 1.5 times, and reached 40.4%. Preliminary results show that SCDs can effectively adsorb on the surface of aluminum and block direct contact between Al and the electrolyte environment.

[0071] Figure 7 The Bode diagrams of the embodiments and comparative examples of the present invention show that 0.2 g L -1 The addition of SCDs significantly improves the impedance modulus and phase angle, further proving the interface modification effect of SCDs on Al.

[0072] Figure 8 The polarization curves of the embodiments of the present invention and the comparative example are shown in FIG. Figure 8 The results show that the addition of SCDs causes a decrease in both the cathode and anode parts of the curve. However, the decrease in the anode part is more significant than that in the cathode part, indicating that SCDs inhibit corrosion mainly by reducing the anode dissolution rate and improve the occurrence of hydrogen evolution reaction to a certain extent. The corrosion potential (E corr ), corrosion current density (i corr ), cathode and anode slopes (β c / β a ), as shown in Table 2. The corrosion inhibition efficiency calculated by Formula 3 reaches 41.5%, which is consistent with the calculation results of EIS.

[0073]

[0074] Table 2 Extrapolation calculation results

[0075]

[0076]

[0077] Figure 9 The electrochemical window comparison diagram of the embodiment of the present invention and the comparative example is shown in FIG. Figure 9 As shown, linear sweep voltammetry reveals the overpotential of the hydrogen evolution reaction with and without the introduction of SCDs. In the example, the hydrogen evolution overpotential of the aluminum anode is 50 mV higher than that of the electrolyte in the comparative example. This increase in potential indicates a hysteresis in hydrogen reduction and a widening of the electrochemical stability window. This demonstrates the effectiveness of SCDs in suppressing the hydrogen evolution side reaction and optimizing the electrolyte.

[0078] Figure 10 The graph of the amount of hydrogen released over time for the examples of the present invention and the comparative example is shown in FIG. Figure 10 As shown in the figure, the amount of hydrogen evolution after adding SCDs is significantly lower than that of the control.

[0079] Figure 11 The aluminum-air battery composed of the embodiment of the present invention and the comparative example is -2 The constant current discharge curve is shown in Figure 1. After the 1-hour discharge test, the mass difference of the aluminum block before and after discharge is weighed and the average discharge voltage is read. The key parameters of the battery (Q: capacity density; U: a : anode utilization; W: power density) is calculated:

[0080]

[0081] Here, I represents the discharge current (mA), t represents the discharge time (h), Δm refers to the weight loss of aluminum before and after discharge (g), F is the Faraday constant (C / mol), and E represents the average discharge voltage (V). The mass loss and discharge voltage of the comparative example are 0.026g and 1.11V, respectively. The relevant parameters of the corresponding embodiment are 0.013g and 1.17V. Figure 11 As shown in FIG, the embodiment increases the capacity density of the aluminum-air battery from 769.2 mAh g -1 Increased to 1538.5mAh g -1 The calculated anode utilization rate increased from 25.8% to 51.7%; the power density increased from 853.8Wh kg -1 Increased to 1800.0Wh kg -1 .

[0082] Figure 12 Figure 2 is the polarization curve and power density curve of the aluminum-air battery composed of the embodiment of the present invention and the comparative example. Figure 12 As shown in the figure, the addition of SCDs increases the maximum output power of AAB from 50.8 mW cm -2 Increased to 60.0 mW cm -2 .

[0083] Figure 13 The discharge voltage curves of the aluminum-air batteries composed of the embodiments of the present invention and the comparative examples at different current densities are shown. Figure 14 The intermittent discharge curves of the aluminum-air batteries composed of the embodiments of the present invention and the comparative examples are shown in FIG. Figure 15 The limit discharge curves of the aluminum-air batteries of the embodiments of the present invention and the comparative examples are shown in FIG. Figure 13 The addition of SCDs enables aluminum-air batteries to better adapt to discharge at different current densities. This phenomenon is particularly evident at high current densities. In addition, this study simulated the battery discharge-relaxation process to examine the battery's cycle performance. Figure 14 As shown, the embodiment can make the aluminum-air battery -2 In the case of discharge, the discharge voltage is higher and more stable. Figure 15 As shown in the figure, the electrolyte of the embodiment improves the open circuit voltage and discharge voltage of the aluminum-air battery under two discharge conditions. -2 The improvement was about 1.5 times at 60 mA cm -2 The discharge test increased by about 1.9 times. These results show that the addition of SCDs optimizes the surface state of aluminum and significantly improves battery performance.

[0084] CLSM and SEM were used to evaluate the microscopic surface of aluminum after immersion in the electrolyte of the embodiment and comparative example. Figure 16 This is a microscopic surface SEM image of an aluminum plate after the aluminum metal is immersed in the electrolyte prepared in the embodiment of the present invention for 0.5 hours. Figure 17 This is a microscopic surface SEM image of an aluminum plate after metallic aluminum was immersed in the electrolyte prepared in the comparative example of the present invention for 0.5 h. Figure 16 、 17 As shown in FIG. 1 , after 0.5 h of immersion, obvious corrosion marks appeared on the aluminum surface, indicating that the NaOH solution triggered a corrosion reaction on the aluminum surface. The aluminum surface after immersion in the example was smoother than that after immersion in the comparative example, and no corrosion products accumulated.

[0085] Figure 18 CLSM image of aluminum plate after metal aluminum was immersed in the electrolyte prepared in the embodiment of the present invention for 0.5h. Figure 19CLSM image of aluminum plate after immersing aluminum in the electrolyte prepared in the comparative example of the present invention for 0.5h. Figure 18 、 19 As shown, after immersion for 0.5 h, the surface roughness of the aluminum in the embodiment is 0.778 μm, which is significantly lower than 1.842 μm of the comparative example.

[0086] Therefore, the preparation method of plant-based carbon quantum dots described in the present invention is adopted - carbon quantum dots are extracted from locust leaves, and the plant-based carbon quantum dots are added to the NaOH electrolyte as a corrosion inhibitor, which improves the corrosion resistance of the anode of the aluminum-air battery and optimizes the discharge performance.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing plant-based carbon quantum dots, characterized in that: The following steps are involved: S1, drying and grinding the leaves of Sophora japonica to obtain Sophora japonica leaf powder; S2. Dissolve the Sophora japonica leaf powder in deionized water and stir until completely dissolved to obtain a precursor solution; S3, transferring the precursor solution to a reactor for heating to obtain a reactant; S4. After the reactants are filtered and dialyzed, the solid matter is freeze-dried to obtain plant-based carbon quantum dots.

2. The method for preparing plant-based carbon quantum dots according to claim 1, wherein: In the above-mentioned S1, the drying temperature of the locust tree leaves is 40° C.-50° C., the drying time is 36 hours-48 hours, and the particle size of the powder of the locust tree leaves is less than 1.25 mm.

3. The method for preparing plant-based carbon quantum dots according to claim 1, wherein: In the above S2, 0.6g-1.5g of Sophora japonica leaf powder is dissolved in every 100ml of deionized water at a dissolution temperature of 60°C-80°C.

4. The method for preparing plant-based carbon quantum dots according to claim 1, wherein: In the step S3, the heating temperature is 160° C. to 180° C., and the heating time is 15 hours to 24 hours.

5. The method for preparing plant-based carbon quantum dots according to claim 1, wherein: In the step S4, the freeze-drying temperature is -80°C to -85°C, and the drying time is 36 hours to 48 hours.

6. Plant-based carbon quantum dots prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the plant-based carbon quantum dots as claimed in claim 6 in an aluminum-air battery electrolyte.

8. The use of the plant-based carbon quantum dots in an aluminum-air battery electrolyte according to claim 7, characterized in that: The concentration of the strong alkaline electrolyte in the aluminum-air battery electrolyte is 4M.

9. The use of the plant-based carbon quantum dots in an aluminum-air battery electrolyte according to claim 8, characterized in that: The strong alkaline electrolyte is sodium hydroxide.

10. The use of the plant-based carbon quantum dots in an aluminum-air battery electrolyte according to claim 8, characterized in that: The concentration of the plant-based carbon quantum dots is 0.2 gL -1 .

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