Method for preparing carbon quantum dot nano-fertilizer by using humic acid and application thereof

Abstract

The application discloses a method for preparing carbon quantum dot nanofertilizer by using humic acid and application thereof, and comprises the following steps: uniformly mixing humic acid and dodecylbenzene, and then performing ball milling to obtain humic acid after ball milling; taking the humic acid after ball milling and a nitrogen dopant as raw materials to perform hydrothermal reaction, collecting supernatant after reaction, filtering the supernatant, freeze-drying the filtrate, and obtaining carbon quantum dot nanofertilizer, wherein the nitrogen dopant is one or more of diaminocyclohexane and diethylenetriamine. The application takes humic acid as a precursor, takes diaminocyclohexane or diethylenetriamine as a nitrogen source to perform nitrogen doping modification, adjusts the fluorescence wavelength of the carbon quantum dots prepared from humic acid, and improves the fluorescence quantum yield and biocompatibility of the carbon quantum dots; the prepared carbon quantum dot nanofertilizer can promote the growth and development of small rape, the release of root exudates, and the activation of nitrogen and phosphorus in the rhizosphere soil of rape.

Description

Technical Field

[0001] This invention relates to the technical field of nano-fertilizers, specifically to a method for preparing carbon quantum dot nano-fertilizers using humic acid and its application. Background Technology

[0002] Currently, a significant gap remains in global food security, primarily due to factors such as climate change, declining soil quality, water scarcity, and rising fertilizer costs. While chemical fertilizers are essential agricultural inputs, excessive application leads to agricultural non-point source pollution, increased greenhouse gas emissions, and soil acidification. Therefore, improving crop yields and nutrient utilization while reducing environmental pollution risks is crucial for addressing global food and environmental security issues. With the development of nanotechnology, numerous nanomaterials have been developed and applied in research areas such as plant nutrient management, crop stress resistance, environmental protection, and controlled-release pesticides. Compared to metal-based nanomaterials, carbon-based nanomaterials exhibit higher biocompatibility, lower environmental toxicity, and lower accumulation. Furthermore, carbon-based nanomaterials are widely available, offer cost advantages, and align better with the principles of green agricultural development.

[0003] Humic acid plays a crucial role in agricultural production, possessing functions such as improving soil structure, enhancing fertilizer efficiency, increasing crop yield and quality, and increasing soil carbon sequestration. Humic acid is mainly extracted from mineral raw materials such as lignite, weathered coal, and peat, or derived from biomass fermentation, making it widely available and inexpensive. Humic acid possesses various functional groups, including carboxyl, phenolic hydroxyl, quinone, and aromatic rings, which form the basis for its diverse agricultural applications. Developing functional fertilizers using humic acid to improve crop yield, promote nutrient absorption, and enhance crop stress resistance is a hot research topic in the agricultural field.

[0004] Chinese patent document CN114426270A discloses a method for preparing coal-based graphene quantum dots. This method uses coal-based raw materials and nitric acid as raw materials, and prepares graphene carbon quantum dots through an oxidation reaction under microwave digestion conditions. This method reduces the severity of the oxidation reaction and shortens the reaction time. However, this method uses a large amount of concentrated acid, which has certain adverse effects on the environment. Chinese patent document CN118126723A discloses a method for carbon fixation, pollution reduction, and increased farmland yield. This method proposes a novel nickel catalyst that improves the growth efficiency of carbon nanotubes under low temperature and low pressure conditions, while also improving the selectivity and yield of the carbon nanotube generation reaction. However, the carbon nanomaterial reaction steps proposed by this method are complex, and the reactor needs to be purged with hydrogen for a long time, resulting in high preparation costs. In the study "Formation of carbon quantum dots and graphenenanosheets from different abundant carbonaceous materials" published in the journal *Diamond and Related Materials*, Saikia M et al. prepared carbon quantum dots through a hydrothermal synthesis method using a mixture of coal-derived humic acid and water. The preparation method is simple, but the quantum yield of carbon quantum dots prepared by this method is only 2.38%. Therefore, it is of great significance to provide a simple, efficient, green, environmentally friendly method for preparing carbon quantum dots using humic acid with high fluorescence quantum yield. Summary of the Invention

[0005] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for preparing carbon quantum dot nano-fertilizer using humic acid and its application. The method uses a one-step hydrothermal method to synthesize carbon quantum dot nano-fertilizer with good water solubility and high biocompatibility. It is simple to operate, green and pollution-free, and has low production cost.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing carbon quantum dot nano-fertilizer using humic acid, comprising the following steps:

[0008] (1) Humic acid and dodecylbenzene are mixed evenly and then ball-milled to obtain ball-milled humic acid;

[0009] (2) Using ball-milled humic acid and nitrogen dopant as raw materials, a hydrothermal reaction was carried out. After the reaction, the supernatant was collected, filtered, and the filtrate was freeze-dried to obtain carbon quantum dot nano-fertilizer.

[0010] The nitrogen dopant is one or more of diaminocyclohexane and diethylenetriamine.

[0011] Preferably, in step (1), the amount of dodecylbenzene added is 0.1% to 0.3% of the mass of humic acid, and the particle size of dodecylbenzene is 10-20 μm.

[0012] Preferably, in step (1), the ball milling conditions are: grinding at a speed of 200-400 r / min for 8-12 hours.

[0013] Preferably, in step (2), the mass ratio of humic acid to nitrogen dopant is 10:(1-4).

[0014] Preferably, in step (2), the hydrothermal reaction conditions are: the solid-liquid ratio of the hydrothermal reaction is 1g:(80~120)ml; the reaction temperature is 210℃~240℃; the reaction time is 6~10h; and the reaction pH is 9.5-10.5.

[0015] Preferably, in step (2), the filtration method is to use a 1000Da dialysis bag for dialysis for 46-50 hours.

[0016] In a second aspect, the present invention provides a carbon quantum dot nanofertilizer prepared using the above method.

[0017] A third aspect of the present invention provides the application of the above-mentioned carbon quantum dot nanofertilizer in promoting crop growth.

[0018] In a fourth aspect, the present invention provides the application of the above-described carbon quantum dot nanofertilizer in any of the following (1)-(3):

[0019] (1) Promotes the release of root exudates from rapeseed;

[0020] (2) Promotes the activation of nitrogen in the rhizosphere soil of rapeseed;

[0021] (3) Promote the activation of phosphorus in the rhizosphere soil of rapeseed.

[0022] Preferably, the rapeseed root exudate is betaine, phenylalanine, leucine, or glycine.

[0023] As a preferred option, the specific method for the above application is as follows:

[0024] The above-mentioned carbon quantum dot nano-fertilizers can be applied to crops by soil mixing or foliar spraying.

[0025] When applied by mixing with soil, the dosage of carbon quantum dot nano-fertilizer is 1.0–20.0 mg / kg soil.

[0026] When using foliar spraying, the carbon quantum dot solution is sprayed evenly onto the crop, with a concentration of 0.1–5.0 g / L.

[0027] The beneficial effects of this invention are:

[0028] 1. This invention uses humic acid as a precursor to prepare carbon quantum dots through a simple hydrothermal synthesis reaction. The preparation process is green and environmentally friendly, simple, and has a short reaction time, which can extend the agricultural industrial chain of humic acid. This invention uses diaminocyclohexane or diethylenetriamine as nitrogen sources for nitrogen doping modification, adjusting the fluorescence wavelength of carbon quantum dots prepared from humic acid, improving the fluorescence quantum yield and biocompatibility of carbon quantum dots. Compared with common urea and ethylenediamine, diethylenetriamine has more amino functional groups, which can effectively provide nitrogen in the synthesis of carbon quantum dots, thereby achieving high nitrogen doping efficiency, which helps to improve the fluorescence performance of carbon quantum dots and also helps to improve the quantum yield. Diaminocyclohexane has a cyclic structure, which can improve the morphology and size distribution of carbon quantum dots, enhance the optical properties and stability of carbon quantum dots, and improve the fluorescence yield. Compared with ethylenediamine, neither of these materials is toxic and is safer and more environmentally friendly.

[0029] 2. The carbon quantum dots prepared by this invention have high biocompatibility, high water solubility and low toxicity, and are easily absorbed and utilized by crops. When used as nano-fertilizers, they can show relatively obvious effects at low doses.

[0030] 3. The humic acid used in this invention is processed by ball milling. Humic acid is a natural macromolecule, and the yield of carbon quantum dots prepared directly by hydrothermal method is only 2% to 4%. This invention increases the number of small molecule humic acid particles by ball milling pretreatment, and the proportion of humic acid particles with a particle size <10nm is significantly increased, thereby improving the yield and efficiency of hydrothermal preparation of carbon quantum dots.

[0031] 4. The carbon quantum dot nano-fertilizer prepared by this invention, when applied to corn in the form of foliar spray, can promote the growth and development of corn; when mixed with soil and planted with rapeseed, it can promote the growth and development of rapeseed, and can promote the release of rapeseed root exudates (betaine, phenylalanine, leucine or glycine), promote the activation of nitrogen in rapeseed rhizosphere soil, and promote the activation of phosphorus in rapeseed rhizosphere soil. Attached Figure Description

[0032] Figure 1 This is a high-resolution transmission electron microscope image of the carbon quantum dot nanofertilizer obtained in Example 1.

[0033] Figure 2 Example 2: SPAD value of maize leaves during the tasseling stage treated with carbon quantum dot nano-fertilizer.

[0034] Figure 3 The graph shows the results of the aboveground dry weight, grain weight, and harvest index of maize treated with carbon quantum dot nano-fertilizer in Example 2.

[0035] Figure 4Example 3: Treatment of rhizosphere soil nitrogen content in rapeseed using carbon quantum dot nano-fertilizer.

[0036] Figure 5 Example 3: Treatment of the rhizosphere soil of rapeseed with carbon quantum dot nano-fertilizer to increase effective phosphorus and alkaline phosphatase activity. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0038] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0039] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0040] The dodecylbenzene used in this invention has a particle size of 10-20 μm.

[0041] Example 1: Preparation of carbon quantum dot nano-fertilizer:

[0042] (1) Weigh 10.0g of humic acid and 20.0mg of dodecylbenzene, mix them and grind them in a planetary ball mill at 300r / min for 10h to obtain ball-milled humic acid;

[0043] (2) Weigh 1.5g of ball-milled humic acid and 0.3g of diethylenetriamine, dissolve them in 150ml of deionized water, adjust the pH to 10 using NaOH solution, stir evenly with a glass rod, transfer the mixed solution to a high-pressure reactor, heat at 240℃ for 8h, and after the reaction cools down, obtain carbon quantum dot supernatant. Dialyze with a dialysis bag with a molecular weight cutoff of 1000Da for 48h to remove small molecule impurities, and freeze-dry to obtain carbon quantum dot nano-fertilizer.

[0044] The humic acid carbon quantum dots obtained in this embodiment were characterized by high-resolution transmission electron microscopy, such as... Figure 1 As shown in the transmission electron microscope (TEM) image, the carbon quantum dots prepared in this embodiment are spherical with good dispersibility, and the particle size is between 0.5 and 6 nm.

[0045] Example 2: Preparation of carbon quantum dot nano-fertilizer:

[0046] (1) Weigh 10.0g of humic acid and 20.0mg of dodecylbenzene, mix them and grind them in a planetary ball mill at 300r / min for 10h to obtain ball-milled humic acid;

[0047] (2) Weigh 1.5g of ball-milled humic acid and 0.3g of diaminocyclohexane, dissolve them in 150ml of deionized water, adjust the pH to 10 using NaOH solution, stir evenly with a glass rod, transfer the mixed solution to a high-pressure reactor, heat at 240℃ for 8h, and after the reaction cools down, obtain carbon quantum dot supernatant. Dialyze with a dialysis bag with a molecular weight cutoff of 1000Da for 48h to remove small molecule impurities, and freeze-dry to obtain carbon quantum dot nano-fertilizer.

[0048] Example 3: Preparation of carbon quantum dot nano-fertilizer:

[0049] (1) Weigh 10.0g of humic acid and 20.0mg of dodecylbenzene, mix them and grind them in a planetary ball mill at 300r / min for 10h to obtain ball-milled humic acid;

[0050] (2) Weigh 1.5g of ball-milled humic acid, 0.15g of diethylenetriamine and 0.15g of diaminocyclohexane, dissolve them in 150ml of deionized water, adjust the pH to 10 using NaOH solution, stir evenly with a glass rod, transfer the mixed solution to a high-pressure reactor, heat at 240℃ for 8h, and after the reaction cools, obtain carbon quantum dot supernatant. Dialyze with a dialysis bag with a molecular weight cutoff of 1000Da for 48h to remove small molecule impurities, and freeze-dry to obtain carbon quantum dot nano-fertilizer.

[0051] Comparative Example 1:

[0052] Weigh 1.5g of humic acid and 0.3g of diethylenetriamine, dissolve them in 150ml of deionized water, adjust the pH to 10 using NaOH solution, stir evenly with a glass rod, transfer the mixed solution to a high-pressure reactor, heat at 240℃ for 8h, and after the reaction cools, obtain carbon quantum dot supernatant. Dialyze the supernatant using a dialysis bag with a molecular weight cutoff of 1000Da for 48h to remove small molecule impurities, and freeze-dry to obtain carbon quantum dot nano-fertilizer.

[0053] Comparative Example 2:

[0054] (1) Weigh 10.0g of humic acid and 20.0mg of dodecylbenzene, mix them and grind them in a planetary ball mill at 300r / min for 10h to obtain ball-milled humic acid;

[0055] (2) Weigh 1.5g of ball-milled humic acid and 0.3g of ethylenediamine, dissolve them in 150ml of deionized water, adjust the pH to 10 using NaOH solution, stir evenly with a glass rod, transfer the mixed solution to a high-pressure reactor, heat at 240℃ for 8h, and after the reaction cools down, obtain carbon quantum dot supernatant. Dialyze the supernatant using a dialysis bag with a molecular weight cutoff of 1000Da for 48h to remove small molecule impurities, and freeze-dry to obtain carbon quantum dot nano-fertilizer.

[0056] Comparative Example 3:

[0057] (1) Weigh 10.0g of humic acid and 20.0mg of dodecylbenzene, mix them and grind them in a planetary ball mill at 300r / min for 10h to obtain ball-milled humic acid;

[0058] (2) Weigh 1.5g of ball-milled humic acid and 0.3g of urea, dissolve them in 150ml of deionized water, adjust the pH to 10 using NaOH solution, stir evenly with a glass rod, transfer the mixed solution to a high-pressure reactor, heat at 240℃ for 8h, and after the reaction cools down, obtain carbon quantum dot supernatant. Dialyze with a dialysis bag with a molecular weight cutoff of 1000Da for 48h to remove small molecule impurities, and freeze-dry to obtain carbon quantum dot nano-fertilizer.

[0059] Test Example: Determination of quantum yield of carbon quantum dot nanofertilizers prepared in Example 1 and Comparative Example 1:

[0060] The fluorescence quantum yield of carbon quantum dot nanofertilizers prepared in Example 1 and Comparative Example 1 was determined using a fluorescence spectrophotometer with a relative method. Specifically, Rhodamine 6G was selected as the standard substance for determining the fluorescence quantum yield. The absorbance of the carbon quantum dot solution prepared with humic acid was adjusted to be similar to that of Rhodamine 6G at an excitation wavelength of 340 nm. The fluorescence emission intensity of the carbon quantum dot solution and Rhodamine 6G was measured, the integrated fluorescence area of ​​the carbon quantum dots was calculated, and the fluorescence quantum yield of the carbon quantum dots was calculated according to the fluorescence quantum yield formula, as shown in Table 1.

[0061] Table 1. Effect of ball milling on the fluorescence quantum yield of humic acid carbon quantum dots

[0062]

[0063]

[0064] As can be seen from Table 1, the fluorescence quantum yield of the carbon quantum dot nanofertilizers prepared in Examples 1-3 of the present invention is significantly higher than that of the carbon quantum dot nanofertilizers prepared in Comparative Examples 1-3. In addition, the fluorescence quantum yield of the carbon quantum dot nanofertilizer prepared by combining diethylenetriamine and diaminocyclohexane in Example 3 is higher than that prepared by using only diethylenetriamine in Example 1 and only diaminocyclohexane in Example 2. This indicates that the combination of diethylenetriamine and diaminocyclohexane in the present invention has a synergistic effect in improving the fluorescence quantum yield of carbon quantum dot nanofertilizers.

[0065] Experiment 1: Experiment on the promotion of maize growth and development by carbon quantum dot nano-fertilizer:

[0066] Test method:

[0067] The carbon quantum dot nano-fertilizer prepared in Example 1 was applied to corn by foliar spraying, as follows:

[0068] Weigh 0.4g of carbon quantum dots and dissolve them in 1L of water. Add 0.2ml of alkyl glucoside surfactant to obtain a carbon quantum dot solution with a concentration of 0.4g / L. On a sunny day, spray twice each at the corn tasseling stage and the tasseling stage. The sprayed carbon quantum dot droplets are evenly distributed on the corn leaves. The control group is sprayed with an equal amount of water.

[0069] 2. Test metrics:

[0070] The SPAD value of leaves was measured during the tasseling stage of maize, and the results are as follows: Figure 2 As shown.

[0071] like Figure 2 As shown, the SPAD value of the control group leaves was 56.1, while the SPAD value of the treated group maize leaves was 60.2, an increase of 7.31%.

[0072] The biomass, yield, and harvest index of maize were measured at harvest time, and the results are as follows: Figure 3 As shown.

[0073] like Figure 3 As shown, the aboveground biomass of maize in the control group was 16235.8 kg / ha, and the yield was 8792.6 kg / ha; the aboveground biomass of maize in the treatment group was 16977.5 kg / ha, and the yield was 9707.2 kg / ha, representing increases of 4.57% and 10.4%, respectively. The maize harvest index in the control group was 54.2%, while that in the treatment group was 57.2%, an increase of 5.58% year-on-year.

[0074] Experiment Example 2: Experiment on the promotion of rapeseed growth and development by carbon quantum dots:

[0075] 1. Test method:

[0076] The carbon quantum dot nano-fertilizer prepared in the example was mixed with soil and then used to plant rapeseed, as detailed below:

[0077] Weigh 10 mg of carbon quantum dot nano-fertilizer and mix it thoroughly with 1.0 kg of test soil to prepare mixed soil with a carbon quantum dot addition of 10 mg / kg. The control group was soil without carbon quantum dot nano-fertilizer. Sow rapeseed and irrigate regularly.

[0078] 2. Test metrics:

[0079] 2.1 Harvest 30 days after planting and measure the root biomass, single plant biomass, and plant height of the rapeseed.

[0080] 2.2 Rapeseed root exudate release test:

[0081] Root exudates were collected 20 days after planting, and the types and contents of root exudates were measured by high performance liquid chromatography.

[0082] 2.3 The contents of ammonium nitrogen and nitrate nitrogen in the rhizosphere soil of rapeseed were tested 20 days after planting;

[0083] Soil ammonium nitrogen and nitrate nitrogen were determined by ultraviolet spectrophotometry, referring to GB / T 32737-2016 "Determination of Nitrate Nitrogen in Soil by Ultraviolet Spectrophotometry";

[0084] 2.4 At 20 days after planting, the available phosphorus content and alkaline phosphatase activity in the rhizosphere soil of rapeseed were tested.

[0085] Available phosphorus in the soil was determined by sodium bicarbonate extraction-molybdenum antimony spectrophotometry, referring to NY / T 1121.7-2014, "Soil Testing Part 7: Determination of Available Phosphorus in Soil"; soil alkaline phosphatase activity was determined by disodium phenyl phosphate colorimetric method, referring to "Soil Agricultural Chemical Analysis Methods" edited by Lu Rukun.

[0086] 3. Experimental Results:

[0087] Table 2. Plant height, root biomass, and single-plant biomass of rapeseed treated with carbon quantum dots.

[0088]

[0089] As shown in Table 2, the plant height, root biomass per plant, and biomass per plant in the control group were 24.2 cm, 6.5 g, and 189.8 g, respectively. In the treatment group, the plant height, root biomass per plant, and biomass per plant were 25.6 cm, 8.1 g, and 227.7 g, respectively, representing increases of 5.8%, 19.9%, and 24.6%.

[0090] Table 3. Content of root exudates from rapeseed treated with carbon quantum dots.

[0091]

[0092] Table 3 shows that the number of root exudates from the control group and the treatment group were 124 and 126 respectively, with no significant difference. The contents of betaine, phenylalanine, leucine, and glycine in the root exudates of the control group were 1.46, 0.43, 0.85, and 4.39 μg / s, respectively. -1 h -1 The contents of betaine, phenylalanine, leucine, and glycine in the root exudates of the treated group of rapeseed were 2.28, 0.52, 1.27, and 6.24 μg per plant, respectively. -1 h -1These figures represent increases of 56.1%, 20.9%, 49.4%, and 42.1%, respectively.

[0093] Depend on Figure 4 It can be seen that the contents of ammonium nitrogen and nitrate nitrogen in the root soil of rapeseed in the control group were 10.2 mg / kg and 25.4 mg / kg, respectively, while the contents of ammonium nitrogen and nitrate nitrogen in the root soil of rapeseed in the treatment group were 14.4 mg / kg and 29.6 mg / kg, respectively, which increased by 41.1% and 16.5%.

[0094] Depend on Figure 5 It can be seen that the available phosphorus content and alkaline phosphatase activity in the root soil of rapeseed in the control group were 33.3 mg / kg and 79.8 mg / kg / h, respectively, while the ammonium nitrogen and nitrate nitrogen content in the root soil of rapeseed in the treatment group were 41.2 mg / kg and 127.7 mg / kg / h, respectively, which increased by 23.7% and 60.0%.

[0095] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for improving the fluorescence quantum yield of humic acid carbon quantum dot nanofertilizers, characterized in that, The humic acid carbon quantum dot nano-fertilizer is prepared by the following method: (1) Weigh 10.0g of humic acid and 20.0mg of dodecylbenzene, mix them and grind them in a planetary ball mill at 300r / min for 10h to obtain ball-milled humic acid; (2) Weigh 1.5g of ball-milled humic acid, 0.15g of diethylenetriamine and 0.15g of diaminocyclohexane, dissolve them in 150ml of deionized water, adjust the pH to 10 using NaOH solution, stir evenly with a glass rod, transfer the mixed solution to a high-pressure reactor, heat at 240℃ for 8h, and after the reaction cools, obtain carbon quantum dot supernatant. Dialyze with a dialysis bag with a molecular weight cutoff of 1000Da for 48h to remove small molecule impurities, and freeze-dry to obtain carbon quantum dot nano-fertilizer.

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