Liquid nanobiostimulant composition containing carbon nanodots prepared by distillation carbonization and in situ quenching and uses thereof

Abstract

This invention relates to a method for producing a liquid composition that converts carbon- and nitrogen-containing organic compounds into carbon-containing nanodots based on distillation carbonization and in-situ quenching processes, and to the liquid nanobiostimulant composition obtained therefrom, as well as the agricultural use of said composition.

Description

Technical Field

[0001] This invention relates to a production method based on distillation carbonization and in-situ quenching (DICQ), which converts carbon- and nitrogen-containing organic compounds into a liquid composition containing carbon nanodots; it also relates to the liquid nanobiostimulant composition obtained by this method and its agricultural applications. Background Technology

[0002] Currently, a wide variety of biostimulants are used in agriculture, aiming to promote plant growth, enhance stress resistance, and improve nutrient absorption. However, a large portion of existing products are single-component or have a narrow activity spectrum, and are usually based solely on amino acids, organic acids, or microbial-derived components. This makes it difficult for them to simultaneously and effectively support multiple physiological processes such as plant growth, photosynthesis, stress regulation, and nutrient absorption.

[0003] Carbon nanodots (CNDs) are carbon-based nanomaterials that have gained significant attention in recent years for their application as biostimulants in agriculture. These nanoparticles, typically 1-10 nm in diameter, are dispersed in water and possess various functional groups on their surface, exhibiting multiple functions such as promoting plant growth, enhancing photosynthetic efficiency, promoting nutrient absorption, and strengthening plant stress resistance. Beyond agriculture, CNDs are also applied in research areas such as medicine, imaging, sensor technology, and drug delivery systems. Currently, there are various methods for synthesizing CNDs, mainly divided into two categories: top-down and bottom-up methods. In agricultural applications, the preferred method is usually the bottom-up method, which involves the controlled carbonization of carbon- and nitrogen-containing organic compounds under high temperature, high pressure, or specific energy input conditions.

[0004] In recent years, although CNDs have attracted much attention as a new generation of agricultural biostimulants, existing CND production technologies still have significant drawbacks, such as high energy consumption, long reaction times, reliance on specialized equipment (such as autoclaves and microwave reactors), and difficulty in large-scale production. Most production methods first obtain solid products and then convert them back into liquids through additional processing steps, resulting in longer production cycles, higher costs, and increased process complexity.

[0005] These technological bottlenecks hinder the widespread industrial application of carbon nanoparticle-based biostimulants, making it difficult to achieve sustainable economic development and limiting their broad application in agriculture. Furthermore, the use of toxic solvents or high-pressure systems in some methods also poses environmental risks and occupational health and safety hazards. Summary of the Invention

[0006] The main objective of this invention is to provide an energy-saving, low-equipment-requirement, and easily scalable method for production. This method uses at least one organic acid selected from monocarboxylic acids, dicarboxylic acids, or tricarboxylic acids as a carbon source, and simultaneously combines it with a nitrogen-containing organic compound selected from primary or secondary amines, amino alcohols, alkylamines, ethoxylated amines, fatty acid-derived amines, amide amines, or polyfunctional polyamines as a nitrogen source to convert the carbon nanoparticles into carbon nanodots. After conversion, the resulting carbon nanodots are compounded with organic and / or inorganic auxiliary components to prepare a multi-component liquid nanobiostimulant composition.

[0007] The resulting composition is designed to simultaneously support multiple physiological processes, such as plant growth, photosynthesis, stress resistance, nutrient uptake, and yield enhancement. Furthermore, because the composition is in a ready-to-use liquid form, it can be used either as a standalone biostimulant or in synergistic use with fertilizers.

[0008] Another objective of this invention is to provide an innovative production method based on "distillation carbonization and in-situ quenching," thereby developing an economical, efficient, environmentally friendly, low-energy-consumption alternative suitable for industrial production. In this way, the invention not only solves the problems of existing technologies but also contributes to achieving the sustainable development goals of modern agriculture.

[0009] The method includes the following steps: concentrating the aqueous precursor solution by distillation; carbonizing by increasing the temperature; and, after the carbonization stage, converting the medium into a liquid state by controlled addition of liquid. The resulting liquid composition preferably contains, in addition to carbon nanodots, plant secondary metabolites, vitamins, amino acids, organic acids, polyamino acids and / or various inorganic nanoparticles (e.g., SiO2, TiO2, ZnO, CuO, Fe3O4, etc.), as well as secondary metabolites obtained from microorganisms.

[0010] This liquid nano-biostimulant promotes plant growth, enhances photosynthetic activity, resists oxidative stress, supports physiological processes such as rooting, flowering, and fruiting, improves nutrient absorption efficiency, enhances disease resistance, and increases plant tolerance to adverse conditions. This composition can be applied to plants via foliar spraying or soil application. When added to conventional fertilizer formulations, it can synergistically enhance fertilizer efficacy by promoting nutrient absorption in plants. Attached Figure Description

[0011] Figure 1 UV-Vis spectrum of carbon nanodots.

[0012] Figure 2 Fourier transform infrared spectrum of carbon nanodots.

[0013] Figure 3 Particle size distribution of carbon nanodots.

[0014] Figure 4Zeta potential diagram of carbon nanodots. Detailed Implementation

[0015] This invention provides a liquid nanobiostimulant composition prepared by a method based on distillation carbonization and in-situ quenching, wherein carbon nanodots (CNDs) are directly stabilized in the liquid phase. The method uses at least one organic acid selected from monocarboxylic acids, dicarboxylic acids, or tricarboxylic acids as a carbon source, and simultaneously uses a nitrogen-containing organic compound as a nitrogen source, such as primary or secondary amines, amino alcohols, alkylamines, ethoxylated amines, fatty acid-derived amines, amide amines, or polyfunctional polyamines.

[0016] First, to ensure a clear understanding of the scope of this invention, the technical terms and concepts used throughout are defined. These definitions aim to ensure consistency in terminology and to clearly express the technical content. The following describes terms and concepts crucial for understanding the composition and manufacturing process of the nano-biostimulant of this invention: Carbon nanodots (CNDs): Nanoscale particles, typically 1-10 nm in diameter, made from carbon, with a semi-crystalline structure and various functional groups on their surface, are soluble in water and organic solvents. Because their surface functional groups can interact with plant physiology, they exhibit good compatibility with biological systems.

[0017] Distillation-Carbonization and In-situ Quenching (DICQ) Method: An innovative production method that directly synthesizes carbon nanodots in the liquid phase through a controlled distillation and thermal carbonization process of carbon- and nitrogen-containing organic compounds. This method yields a direct liquid product without the need for solid-phase separation or re-dissolution steps.

[0018] Organic acids: Monocarboxylic acids, dicarboxylic acids, or tricarboxylic acids containing a carboxyl group (-COOH) are used as carbon sources in the preparation of carbon nanodots. These compounds also have phytostimulatory (biostimulant) effects, which help maintain the structural integrity and functional effectiveness of the composition.

[0019] Nitrogen-containing organic compounds—primary or secondary amines, amino alcohols, alkylamines, ethoxylated amines, fatty acid-derived amines, amide amines, or polyfunctional polyamines—are used in the synthesis process to form functional groups on the surface. These compounds enhance biological effects by forming structures such as amino groups (-NH2), thereby promoting the interaction between carbon nanodots and plants.

[0020] Nanobiostimulant composition: A liquid-phase plant support product containing, in addition to carbon nanodots, an organic matrix, vitamins, amino acids, polyamino acids, and optional inorganic nanoparticles, which can enhance plant growth and improve its resistance to environmental stresses.

[0021] Organic matrix: refers to the organic components in the composition other than carbon nanoparticles. This organic matrix is ​​composed of organic acids, amino acids, vitamins, and plant secondary metabolites, and it enriches the overall biological function of the product through synergistic effects.

[0022] Inorganic nanoparticles: Metal oxide-based nanoparticles, such as ZnO, SiO2, TiO2, CuO, Fe2O3, and MnO2. These nanoparticles can exhibit functions such as supporting plant growth, antibacterial activity, or stress relief, and can be selectively added to compositions.

[0023] pH range: This refers to the pH value being adjustable within the range of 4-10 to maintain the chemical stability of the composition and its compatibility with plants. This range allows the product to be flexibly applied to different application conditions and plant species.

[0024] Liquid: This refers to the product's uniform fluid physical form, suitable for direct foliar spraying or soil application. This characteristic gives it the advantages of easy application and rapid bioavailability.

[0025] Fertilizer formulation: refers to a chemical or organic mixture used in agricultural production to provide plants with essential nutrients. The compositions of this invention can be used in conjunction with such fertilizers and help to improve their effectiveness.

[0026] Synergistic effect: This refers to the interaction exhibited when nano-biostimulant compositions are used in conjunction with fertilizer formulations. This effect helps to mutually promote plant growth and improve fertilizer utilization efficiency.

[0027] Within the framework of these definitions, the production methods and final product compositions described below differ from existing systems in terms of technical characteristics and functional advantages.

[0028] Preparation of initial solution Organic acids (preferably with a chain length of C2-C) will be used as carbon sources. 10 A homogeneous initial solution is prepared by mixing at least one of the following: monocarboxylic acids, dicarboxylic acids, or tricarboxylic acids (e.g., acetic acid, lactic acid, gluconic acid, citric acid, malic acid, hexanoic acid, octanoic acid, etc.) with purified water. The total concentration of the homogeneous initial solution is 2-25%.

[0029] The pH of the solution was adjusted to the range of 4-10. The components in this solution play a crucial role in the formation of carbon cores and the determination of surface functional group structures.

[0030] Thermal carbonization and distillation concentration The prepared initial solution was heated in a controlled manner in a semi-closed system without an inert atmosphere. The first heating stage proceeded relatively rapidly within a temperature range of 140-190℃. The second heating stage proceeded more slowly and in a controlled manner within a temperature range of 190-250℃. During both heating stages, water in the solution evaporated, and the solution viscosity increased. Simultaneously, the carbonization reaction began. Through these reactions, organic compounds decomposed and condensed, forming carbon nuclei and generating carbon nanodots with a particle size of 1-5 nm (see...). Figure 3 (Particle size distribution diagram).

[0031] In-situ quenching After the carbonization reaction is complete, preheated pure water or a suitable carrier liquid can be added to the reaction medium in a controlled, stepwise manner without the need for a cooling system. This process allows for a controlled decrease in temperature, enabling the carbon nanoparticles to transfer into the liquid phase. The technical advantage of this process is that carbon nanoparticles can be directly stabilized in a liquid suspension without passing through a solid phase.

[0032] Figure 4 The zeta potential spectrum shown demonstrates this stability, indicating that the particles maintain long-term colloidal stability due to surface charge and electrostatic repulsion. Therefore, time-consuming and energy-intensive additional steps, such as curing, re-dissolving, or filtration, are eliminated, simplifying and accelerating the production process. Furthermore, the carbon nanodots retain their surface functional groups after synthesis and are integrated into the final product without losing their potential for biological interactions, thereby improving the product's effectiveness and applicability.

[0033] In another embodiment of the invention, the liquid mixture obtained after carbonization may be supplemented with the following components: • Organic acids, amino acids, polyamino acids, vitamins • Plant secondary metabolites • Optionally, inorganic nanoparticles, such as ZnO, SiO2, TiO2, and CuO, can be added. These components are added to enhance the product’s biostimulant effects, improve its stability, and expand its functional properties.

[0034] The liquid nanobiostimulant composition developed within the scope of this invention comprises the following main components: • Carbon nanodots (CNDs) • Organic matrix • Inorganic nanoparticles Carbon nanodots (CNDs) The main active ingredient of the composition of this invention is carbon nanodots. These nanodots are obtained through controlled synthesis of a monocarboxylic acid, dicarboxylic acid, or tricarboxylic acid as the carbon source, combined with a nitrogen-containing organic compound (selected from at least one of primary or secondary amines, amino alcohols, alkylamines, ethoxylated amines, fatty acid-derived amines, amide amines, or polyfunctional polyamines) as the nitrogen source. The synthesis process employs distillation carbonization and in-situ quenching. The average particle size ranges from 1 to 5 nm (see [link to original text]). Figure 3 (Particle size distribution diagram).

[0035] Depending on the precursor used, its surface chemistry includes functional groups such as carboxyl (-COOH), hydroxyl (-OH), amino (-NH2), and carbonyl (-C=O) (see [link to relevant documentation]). Figure 2 FTIR spectrum). In the UV-Vis spectrum of carbon nanodots ( Figure 1 In UV-Vis spectra, strong π-π transitions near 275 nm typically correspond to structures containing aromatic rings and conjugated double bonds (e.g., graphite carbon cores and double bonds), while weak n-π transitions near 320 nm indicate the presence of carboxyl groups (-COOH), carbonyl groups (-C=O), and other oxygen-containing functional groups.

[0036] These functional groups facilitate the penetration of carbon nanodots through plant cell membranes, enhancing nutrient absorption and transport, promoting photosynthesis and metabolism, resisting oxidative stress by acting as antioxidants, and exhibiting hormone-like effects to promote plant growth. During synthesis, organic acids (preferably with a chain length of C2-C) are used. 10 Monocarboxylic acids, dicarboxylic acids, or tricarboxylic acids (e.g., acetic acid, lactic acid, gluconic acid, citric acid, malic acid, hexanoic acid, octanoic acid) and nitrogen-containing organic compounds (preferably primary or secondary amines, amino alcohols, alkylamines, ethoxylated amines, fatty acid-derived amines, amide amines, or polyfunctional polyamines; e.g., ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane (putrescine), diethylenetriamine (DETA), triethylenetetramine (TETA), monoethanolamine, diethanolamine, triethanolamine, aminoethylethanolamine, oleylamine, laurylamine, PEG amine, etc.) in a total concentration of 2-25% (w / w) are used to optimize surface functional groups.

[0037] In this respect, carbon nanodots not only function as carriers or structural components, but also as effective stimulants and bioactive regulators.

[0038] This matrix serves as a carrier system, stabilizing carbon nanodots and supporting their bioactivity. It comprises naturally derived substances such as organic acids, amino acids and polyamino acids, vitamins, plant secondary metabolites, and microbial fermentation extracts. These components not only enhance the colloidal stability of the carbon nanodots but also provide multifaceted support for plant growth.

[0039] Inorganic nanoparticles In one embodiment of the present invention, inorganic nanoparticles may be added to the composition during or after production as a source of micronutrients and a physiological activator. At least one of the following nanoparticles may be used: • ZnO: Helps with cell division and hormone synthesis.

[0040] • SiO2: Increases cell wall rigidity and enhances stress resistance.

[0041] • TiO2: Enhances light absorption and promotes photosynthesis.

[0042] • CuO: plays an effective role in the defense system and contributes to enzyme activity.

[0043] • Fe3O4 / Fe2O3: Supports chlorophyll synthesis and alleviates iron deficiency symptoms.

[0044] • MnO2: Regulates photosynthetic enzyme activity and plays a role in reducing oxidative stress.

[0045] • MgO: plays a role in the center of chlorophyll and is effectively involved in energy metabolism.

[0046] • CaCO3: Helps with cell wall structure and provides calcium supplementation.

[0047] These nanoparticles not only provide essential nutrients but also enhance the synergistic effect of the nanobiostimulant composition.

[0048] The liquid composition of this invention is a colloidal suspension whose physical properties can be optimized according to the intended use. The pH value of the composition can be adjusted within the range of 4-10, thus flexibly adapting to different agricultural applications. Its viscosity can also be optimized according to the application method, enabling effective delivery through various methods such as foliar spraying or drip irrigation. Furthermore, carbon nanoparticles and other auxiliary components maintain long-term colloidal stability, preserve the physical integrity of the product, and ensure its uniform distribution throughout its shelf life.

[0049] This invention is formulated as a multifunctional biostimulant designed to improve plant health and productivity in agricultural applications. Specifically, it promotes early growth by accelerating root and shoot development, while simultaneously enhancing photosynthetic efficiency to optimize energy production processes. The composition activates the plant's antioxidant defense system, endowing it with the ability to resist oxidative stressors and improving its adaptability to abiotic stresses such as extreme temperatures, drought, or salinity. Furthermore, it enhances the plant's uptake of micronutrients and macronutrients, thereby providing balanced support for plant metabolism. When applied in combination with conventional fertilizers, this composition has a synergistic effect, significantly increasing total crop yield.

[0050] This invention provides a liquid nanobiostimulant composition containing carbon nanodots, designed for wide application across various plant species and agricultural environments. The product can be used in multiple crop production systems, including vegetables, fruits, grains, legumes, industrial crops, and ornamental plants, serving as an adjunct biological agent in both organic and conventional agricultural practices. It effectively enhances plant resistance to various stresses such as drought, salinity, cold, and disease. The composition aims to improve plant growth performance, increase stress resistance, and enhance overall agricultural productivity. The product can be applied to agricultural production through three main methods. For foliar spraying, the dosage is 0.2-2 L / ha, diluted with water to 1000 L; this method is preferably suitable for key growth stages such as shoot growth, flowering, and fruit setting, and provides rapid effects. For soil application, the dosage is 1-5 L / ha, mixed with irrigation water or fertilizer solution, which promotes root development, enhances soil microbial communities, and optimizes nutrient absorption. In addition, this product can be added to liquid fertilizer formulations at a rate of 3-15% (by volume), especially to compound nitrogen, phosphorus, and potassium fertilizers and micronutrient fertilizers, where it can produce a synergistic effect and improve nutrient absorption and utilization efficiency.

[0051]

[0052] Table 1. pH stability results

[0053] Table 2. Long-term stability results Stability tests (Table 1) showed that the liquid composition containing carbon nanodots maintained its efficacy over a wide pH range suitable for agricultural applications. Particularly noteworthy was the high colloidal stability observed in the pH range of 4.0–8.0, with particle sizes remaining stable between 1.5–1.6 nm and a Zeta potential of approximately -30 mV, confirming the maintenance of the physicochemical integrity of the dispersion. A strong UV-Vis peak observed at 275 nm indicates the preservation of the carbon core structure, while a weak peak near 320 nm confirms the presence of surface functional groups (carbonyl and amino groups). These data demonstrate that the synthesized carbon nanodots have been successfully integrated into the liquid formulation without loss of their functional surface properties.

[0054] Long-term stability tests (Table 2) evaluated the product's storage performance under different temperature conditions. After 30 days of storage at 4°C and 25°C, particle size growth was minimal and appearance changes were negligible, indicating that the product remains stable throughout its shelf life. Significant turbidity and a small amount of precipitation were observed at 40°C; therefore, a storage temperature range of 4–25°C is recommended. These results confirm that the carbon nanodot-containing biostimulant composition remains stable both post-production and pre-application, ensuring safe and reliable use in agricultural practices.

[0055] From an application perspective, this composition has a user-friendly structure and can be used directly without any pretreatment. Foliar spraying is recommended in the early morning or evening, while for soil application, adequate soil moisture enhances product efficacy. The composition can be easily applied using standard agricultural equipment and provides a solution that aligns with modern agricultural principles, including efficiency, environmental friendliness, and sustainability.

[0056] In the method of this invention, the "Distillation Carbonization and In-situ Quenching (DICQ)" process enables the direct synthesis of carbon nanodots (CNDs) in the liquid phase, completely eliminating the solid-liquid conversion step. Therefore, no additional operations such as filtration, centrifugation, or redissolution are required, and the production line can continuously produce liquid products after a single-stage carbonization process of 1-5 hours. This method uses a simple distillation apparatus operating at atmospheric pressure, eliminating the need for traditional autoclaves, microwaves, or inert atmosphere systems, thus significantly reducing energy consumption and equipment investment.

[0057] This method, through a controlled combination of stepwise heating and simultaneous addition of hot water, can prepare carbon nanodots (CNDs) with a particle size of 1-5 nm and a surface rich in functional groups such as carboxyl, hydroxyl, and amino groups. These surface chemical properties exhibit a high affinity for plant cell walls, thus directly promoting various physiological benefits when applied to leaves or roots, including rapid absorption, enhanced photosynthetic capacity, activation of antioxidant defense systems, and improved nutrient transport.

[0058] Furthermore, this invention can integrate carbon nanodots (CNDs) with components such as organic acids, amino acids / polyamino acids, vitamins, and plant secondary metabolites, as well as optional inorganic nanoparticles (such as ZnO, SiO2, TiO2, and CuO) into a single formulation. When this multi-component liquid nanobiostimulant composition is added to fertilizer tank mixes or foliar sprays, it produces a synergistic effect, thereby achieving simultaneous nutrient supplementation and biostimulation within the same application period.

[0059] Therefore, DICQ-based production lines offer significant technological advantages, including simplified equipment requirements, low-temperature and low-energy operation, short process times, and direct liquid output, all of which collectively reduce production costs. The resulting functional CND compositions offer a wide range of benefits, promoting plant growth, enhancing stress resistance, and contributing to increased yields.

Claims

1. A method for preparing a liquid nanobiostimulant composition containing carbon nanodots to promote plant growth, comprising the following steps: - A homogeneous starting solution is prepared by mixing at least one organic acid as a carbon source and at least one nitrogen-containing organic compound as a nitrogen source with water, wherein the pH of the solution is adjusted to the range of 4-10. - The solution is heated in a semi-closed system without an inert atmosphere, first rapidly in a temperature range of 140-190°C, and then slowly and in a controlled manner in a temperature range of 190-250°C to carry out distillation concentration and thermal carbonization reaction. - After the carbonization reaction is complete, no cooling system is needed. Simply add preheated free water or a suitable carrier liquid to the reaction medium to directly obtain stable carbon nanoparticles in the liquid phase.

2. The method according to claim 1, characterized in that, Add at least one of the following substances to the final product: organic acids, amino acids, polyamino acids, vitamins, plant secondary metabolites, or inorganic nanoparticles selected from ZnO, SiO2, TiO2, and CuO.

3. The organic acid according to claim 1, characterized in that, It contains at least one of monocarboxylic acid, dicarboxylic acid, or tricarboxylic acid, preferably having a C2-C ratio. 10 Chain length.

4. The nitrogen-containing organic compound according to claim 1, characterized in that, It contains at least one of primary or secondary amines, amino alcohols, alkyl amines, ethoxylated amines, fatty acid-derived amines, amide amines, or polyfunctional polyamines.

5. The starting solution according to claim 1, characterized in that, The content of at least one organic acid as a carbon source and at least one nitrogen-containing organic compound as a nitrogen source is in the range of 2-25% (w / w) of the total solution.

6. A nano-biostimulant composition prepared by in-situ quenching, characterized in that, It contains carbon nanodots and an organic matrix.

7. The composition according to claim 3, characterized in that, It contains at least one inorganic nanoparticle.

8. The composition according to claim 3 or 4, characterized in that, The average particle size of the carbon nanodots is in the range of 1-5 nm.

9. The composition according to any one of claims 3-5, characterized in that, The surface of the carbon nanodots contains carboxyl (-COOH), hydroxyl (-OH), amino (-NH2) and / or carbonyl (-C=O) functional groups.

10. The composition according to any one of claims 3-6, characterized in that, The organic matrix contains organic acids, amino acids and / or polyamino acids, vitamins, plant secondary metabolites and / or microbial fermentation extracts.

11. The composition according to claim 3, characterized in that, The inorganic nanoparticles contain at least one selected from ZnO, SiO2, TiO2, CuO, Fe3O4, Fe2O3, MnO2, MgO, and CaCO3.

12. The composition according to any one of claims 3-8, characterized in that, It is a liquid-phase colloidal suspension containing carbon nanoparticles that are stable to maintain a uniform distribution.

13. The composition according to any one of claims 3-9, characterized in that, Its pH value is in the range of 4-10, and the viscosity value can be optimized according to the application type.

14. The composition according to any one of claims 3-10, characterized in that, Its application method is suitable for foliar spraying, drip irrigation, or mixing with fertilizer.

15. Use of the composition according to any one of claims 3-11 in agriculture for promoting plant growth.

16. Use of the composition according to any one of claims 3-11 for promoting root development and supporting shoot growth.

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