Preparation method and application of nano-selenium particles

Abstract

The invention discloses a preparation method of nano-selenium particles. The preparation method comprises the following steps: S1, preparing a wood vinegar fermentation extracting solution which is used for providing an acidic reaction environment for synthesis of the nano-selenium particles and is used as a stabilizer and a morphology regulating agent; and S2, compounding the prepared pyroligneous fermentation extracting solution with ascorbic acid, sodium selenite, sodium carboxymethyl cellulose and cysteine, and carrying out controllable synthesis of nano-selenium particles in a stable system with a multi-component synergistic effect. The invention further discloses application of the obtained nano-selenium particles in selenium nutrient supplements and preparation of foliar fertilizers for selenium-rich agricultural product production.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizer raw material preparation technology, and in particular to a method for preparing and applying nano-selenium particles. Background Technology

[0002] Selenium is an essential micronutrient for humans and animals, possessing numerous important physiological functions such as antioxidation, immune enhancement, and prevention of cancer and Keshan disease. Humans primarily obtain selenium through consuming plant and animal-based foods, and the selenium content in food directly depends on the amount of selenium crops obtain from the soil or exogenous sources. However, large areas of selenium-deficient soil exist globally, resulting in generally low selenium content in agricultural products from these regions, failing to meet the daily selenium intake requirement (approximately 50-250 micrograms). Therefore, effectively increasing the selenium content of crop grains or edible parts through agricultural biofortification technology has become an important research direction in the fields of functional agriculture and nutritional health.

[0003] Currently, common methods of selenium supplementation in agriculture mainly include soil application and foliar spraying. While soil application of selenium fertilizers (such as sodium selenite) is simple, selenium is easily fixed in the soil in a poorly soluble form, resulting in low plant absorption and utilization rates, and easily leading to selenium loss and environmental pollution. In contrast, foliar spraying allows selenium nutrients to be directly absorbed by plants through leaf stomata and the cuticle, avoiding soil fixation. It has significant advantages such as high utilization rate, rapid effect, low dosage, and environmental friendliness.

[0004] In foliar selenium fertilizers, the form in which selenium exists is crucial to its bioavailability and safety. Traditional foliar selenium fertilizers mainly use inorganic selenium (such as sodium selenite, Na₂SeO₃) and organic selenium (such as selenoamino acids). However, both of these selenium sources have significant limitations. Inorganic selenium (especially sodium selenite), although inexpensive, is highly toxic to plants, has a narrow application concentration range, and even slightly high concentrations can cause plant toxicity and inhibit growth; furthermore, its conversion efficiency within plants is unstable, and its bioavailability to humans is relatively low. While organic selenium offers improvements in toxicity and bioavailability, its preparation process is complex, costly, and chemically unstable, making large-scale application in agricultural production difficult.

[0005] In recent years, the development of nanotechnology has provided new ideas for solving the above problems. Nanoscale selenium particles (selenium nanoparticles, SeNPs) exhibit superior properties compared to traditional inorganic and organic selenium due to their unique size and surface effects. Studies have shown that selenium nanoparticles have lower biotoxicity, higher bioactivity, and higher bioavailability. Because of their small particle size and large specific surface area, selenium nanoparticles can more easily penetrate the barrier of plant leaf surfaces, be absorbed and transported by plant cells, and thus accumulate more efficiently within the plant and be converted into selenoamino acids with nutritional value. Therefore, developing a high-absorption-efficiency and environmentally friendly selenium nanoparticle preparation technology suitable for foliar spraying has significant application prospects.

[0006] In existing technologies, the synthesis methods for nano-selenium mainly include physical, chemical, and biological methods. Physical methods are energy-intensive, require complex equipment, and have low yields, making them unsuitable for large-scale agricultural applications. Chemical reduction is the most commonly used method, typically employing reducing agents such as ascorbic acid (Vc) and sodium borohydride to reduce selenite to elemental selenium. However, this method faces two major challenges during synthesis: first, the aggregation of nanoparticles. Newly generated nano-selenium particles have high surface energy, making them prone to aggregation and Ostwald ripening, forming large-sized precipitates that lose their nano-properties, leading to decreased biological activity and easy clogging of spraying equipment; second, the uncontrollable morphology and size. Disordered nucleation and growth result in excessively wide nano-selenium particle size distribution and uneven morphology, affecting their stability and biological functions.

[0007] To address the challenges of aggregation and controlled synthesis, researchers typically add stabilizers or templates, such as various polymers (e.g., polyvinylpyrrolidone, PVP), surfactants, or organic acids. While these stabilizers can improve the dispersibility of selenium nanoparticles to some extent, many are synthetically produced chemicals, resulting in high costs and potential ecological safety risks in agricultural applications, which contradicts the principles of green agriculture. Furthermore, these synthetic systems are often conducted in purely chemical environments, leaving room for improvement in the compatibility (biocompatibility) of the products with the complex physiological environment of plants.

[0008] On the other hand, the search for green and sustainable synthetic raw materials has become a current research hotspot. Wood vinegar is a byproduct of biomass pyrolysis, with a complex composition containing hundreds of organic acids, phenols, ketones, aldehydes, and other organic components. It is commonly used in agriculture as a soil conditioner and plant growth promoter. Existing technologies have attempted to synthesize nanoparticles directly using wood vinegar or plant extracts as reducing media, but these methods often have the following shortcomings: 1. The composition of wood vinegar varies greatly from batch to batch, and direct use leads to poor reproducibility of the synthesis reaction, making it difficult to guarantee the yield, particle size and stability of nano selenium.

[0009] 2. The raw wood vinegar contains macromolecular impurities such as tar and a small amount of harmful components, which may have a negative impact on plants or interfere with the purity and performance of nano-selenium.

[0010] 3. The reducing and stabilizing abilities of the wood vinegar system are limited, and the synthesis efficiency is not high. It still needs to rely on strong chemical reducing agents or additional stabilizers, thus failing to fully realize the potential value of wood vinegar.

[0011] In summary, there is an urgent need in this field to develop a novel method for preparing nano-selenium. This method should meet the needs of agricultural applications, namely: (1) the process is green and safe, and the raw materials used are environmentally friendly; (2) the prepared nano-selenium particles have good water solubility, high dispersibility, uniform particle size, and controllable morphology; (3) the product has excellent biocompatibility and is easily absorbed and utilized by plants; and (4) the preparation process is stable, reproducible, and suitable for large-scale production. Existing technologies have not yet provided a satisfactory solution that can simultaneously and effectively address all of the above problems. Summary of the Invention

[0012] The purpose of this invention is to provide a method for preparing and applying nano-selenium particles, which meets the needs of agricultural applications for green and safe processes, environmentally friendly raw materials, products with excellent biocompatibility, and easy absorption and utilization by plants; as well as stable and reproducible preparation processes suitable for large-scale production. A first aspect of the present invention is to provide a method for preparing selenium nanoparticles, comprising: S1, Preparation of wood vinegar fermentation extract to provide an acidic reaction environment for the synthesis of selenium nanoparticles and to act as a stabilizer and morphology regulator; S2, based on the prepared wood vinegar fermentation extract, is compounded with ascorbic acid, sodium selenite, sodium carboxymethyl cellulose and cysteine ​​to carry out the controllable synthesis of selenium nanoparticles in a stable system with synergistic effects of multiple components.

[0013] Preferably, S1 includes: S11, Obtain raw materials and perform pretreatment on the raw materials, and prepare crude wood vinegar based on the pretreated raw materials; S12, ferment the crude wood vinegar to degrade and transform the harmful components in the crude wood vinegar, and enrich the active components that are beneficial to the synthesis of nano-selenium particles; S13, the fermented wood vinegar material is separated, distilled and purified using physical methods to obtain a pure wood vinegar fermentation extract.

[0014] Preferably, S11 includes: (1) Obtaining raw materials and pre-treating them, including: First, the collected agricultural and forestry timber is cleaned by rinsing it with a high-pressure water gun to remove inorganic impurities. Then, place it in a cool, ventilated, and dark environment to air dry naturally for about a week, thereby controlling the moisture content of the wood to 18%-22%. After air drying, use a stainless steel saw to break the wood into small pieces with a volume of 20-30 cubic centimeters as pre-treatment raw materials. (2) High-temperature pyrolysis and collection of the pretreated raw materials, including: The treated wood blocks are packed tightly but not compacted into a high-temperature resistant steel mesh basket, and then quickly transferred to a high-temperature pyrolysis furnace. Inert gas is immediately introduced to completely remove air from the furnace and create an absolutely oxygen-deficient or oxygen-free environment. The temperature is increased to 780℃-820℃ and maintained at this temperature for 1-2 hours for pyrolysis. The mixed flue gas generated by pyrolysis is discharged from the pyrolysis furnace and sent to a natural air-cooled or water-cooled condensation system. The mixed flue gas flows in the condenser tubes and exchanges heat with the ambient air. The condensable vapor components are condensed as the original wood vinegar liquid into brown to dark brown liquid products, which are collected in a special corrosion-resistant container to form crude wood vinegar. The remaining non-condensable gas is recovered as fuel to provide part of the energy for the pyrolysis process.

[0015] Preferably, S12 includes: (1) Preparation of fermentation substrate, including: Weigh the following solid materials by weight: 10 parts wood ash, 20 parts sawdust, 2 parts humic acid, and 5 parts superphosphate; among which, wood ash is used to provide potassium and various trace elements, and to adjust pH; sawdust is used as a carbon source and physical carrier for microorganisms; humic acid is used as a natural organic colloid to adsorb harmful substances and promote the reproduction of microorganisms; and superphosphate is used to provide phosphorus and calcium. The solid materials are mixed evenly in a fermentation pot. Then, clean water is slowly added while stirring until the moisture content of the fermentation material reaches 65%±2% to form the first water mixture. Ten parts of a high-temperature fiber-decomposing bacteria agent are added to the first water mixture to form a fermentation substrate. The high-temperature fiber-decomposing bacteria agent is used to decompose cellulose and hemicellulose in sawdust and produce small molecules to provide initial energy for the fermentation system. The high-temperature fiber-decomposing bacteria agent includes pyrolytic cellulose clostridium or thermophilic actinomycetes. (2) Adding diluted crude wood vinegar to the fermentation substrate and starting fermentation, including: Prepare a 100-fold volume dilution of crude wood vinegar, i.e., mix 1 volume part of crude wood vinegar with 99 volume parts of water; The crude wood vinegar dilution, which is equal to the total water volume of the fermentation material, is slowly added to the fermentation pot, and the stirring device is started to ensure that all materials are highly homogenized. The crude wood vinegar dilution, which is equal to the total water volume of the fermentation material, means that the crude wood vinegar dilution has a volume equal to that of the previously added water. The fermentation pot is sealed, and a microporous ventilation system is retained to ensure the normal respiration of aerobic and facultative anaerobic bacteria. The fermentation temperature is 33℃-37℃, and the fermentation cycle lasts for 2 months to obtain the fermented wood vinegar material.

[0016] Preferably, S13 includes: (1) Performing primary separation and decolorization on the fermented wood vinegar material, including: First, the fermented material is separated into solid and liquid components using a plate and frame filter press or centrifuge to remove solid residue and obtain a clear fermentation broth. The clarified fermentation broth was transferred to a large PET plastic bucket and left to stand at room temperature for more than 3 months for aging. The liquid naturally settled and separated into three layers by gravity: supernatant, intermediate main liquid, and bottom sediment. The intermediate liquid was precisely extracted. Add 3-4% of the total mass of powdered activated carbon to the obtained intermediate liquid, stir thoroughly for at least 30 minutes under a stirrer, then let stand for 24 hours to allow the adsorbed activated carbon to settle, and then filter through a precision filter to obtain the decolorized wood vinegar fermentation liquid. (2) Distill the decolorized wood vinegar fermentation liquid and collect the fraction, including: The decolorized wood vinegar fermentation liquid is injected into a distillation apparatus for atmospheric or vacuum distillation. By precisely controlling the heating temperature, the fraction with a boiling point between 100°C and 120°C is collected. The final distillate was stored in brown glass bottles as wood vinegar fermentation extract, protected from light, for later use.

[0017] Preferably, S2 includes: S21, Prepare a reaction mother liquor based on the prepared wood vinegar fermentation extract; S22, Add reactants to the reaction mother liquor in a specific order, the reactants including ascorbic acid, sodium selenite, sodium carboxymethyl cellulose and cysteine; S23, after the controllable synthesis of nano-selenium particles, a reaction product is obtained. During the reaction, the changes in materials and the pH value of the reaction system are monitored. Monitoring the pH value of the reaction system includes monitoring whether the pH value of the system is naturally maintained in the acidic range of 3-4 during the reaction. S24, the reaction products are separated and post-processed.

[0018] Preferably, S21 includes: (1) Take 1 part by weight of the wood vinegar fermentation extract and place it in a reaction vessel; (2) Add 50 times the volume of water to the 1 part by weight of the wood vinegar fermentation extract for dilution. The diluted solution constitutes the reaction mother liquor.

[0019] Preferably, S22 includes: One of the reactants is added sequentially to the reaction mother liquor while continuously stirring: Sodium carboxymethyl cellulose, 2 parts by weight; Cysteine, 2 parts by weight; Ascorbic acid, 2 parts by weight; Sodium selenite, 1 part by weight.

[0020] Preferably, S24 includes: After the reaction was completed, the resulting dark red nano-selenium sol was centrifuged. After centrifugation, the supernatant was an almost colorless waste liquid, and the bottom precipitate was the nano-selenium particles. The bottom precipitate was washed 2-3 times alternately with anhydrous ethanol and deionized water to remove residual reactants and soluble byproducts. Finally, the washed wet precipitate was placed in a vacuum drying oven and dried at 40℃-50℃ for 6-12 hours to obtain dry, dark red to brick red nano-selenium powder.

[0021] The second aspect of the present invention is to provide the application of the nano-selenium particles prepared in the first aspect in the formulation of selenium nutrient fortifiers and foliar fertilizers for the production of selenium-enriched agricultural products.

[0022] The method and application provided by this invention have the following beneficial technical effects: Through a complete, precise, and controllable process, crude wood vinegar derived from agricultural and forestry waste is first transformed into a stable and functional fermentation extract. This extract is then used in conjunction with various stabilizers, reducing agents, and a selenium source to construct a synergistic reaction system, successfully producing novel selenium nanoparticles with high yield, uniform particle size, regular morphology, and excellent stability. This preparation method is green, economical, and highly reproducible, and the resulting product demonstrates significant application potential and market value in the field of selenium enrichment in agriculture. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for preparing nano-selenium particles according to an embodiment of the present invention.

[0024] Figure 2 This is a flowchart of step S1 of the method for preparing nano-selenium particles according to an embodiment of the present invention.

[0025] Figure 3 This is a flowchart of step S2 of the method for preparing nano-selenium particles according to an embodiment of the present invention.

[0026] Figure 4 This is a schematic diagram of the morphology of the reaction products determined by field emission scanning electron microscopy according to an embodiment of the present invention. Figure 5 This is a schematic diagram showing the appearance of the nano-selenium ion solution prepared according to an embodiment of the present invention after it has been placed in a reagent bottle. Detailed Implementation

[0027] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0028] Example 1 like Figure 1 As shown, this embodiment provides a method for preparing nano-selenium particles, including: S1, Preparation of wood vinegar fermentation extract to provide an acidic reaction environment for the synthesis of selenium nanoparticles and to act as a stabilizer and morphology regulator; The wood vinegar fermentation extract is a key component of this invention. It not only provides a suitable acidic reaction environment for the synthesis of selenium nanoparticles, but its complex organic components also act as natural stabilizers and morphology modifiers, synergistically working with subsequently added chemical stabilizers to ensure the high stability and uniformity of the selenium nanoparticles. The preparation process involves a multi-step, refined purification and biotransformation process.

[0029] like Figure 2 As shown, in a preferred embodiment, S1 includes: S11, Obtain raw materials and perform pretreatment on the raw materials, and prepare crude wood vinegar based on the pretreated raw materials; The quality of the raw wood vinegar is fundamental to all subsequent processes. This invention preferably uses broadleaf wood, such as oak, elm, or birch, because its dense wood produces higher levels of organic acids and phenolic substances after pyrolysis, which are beneficial for subsequent fermentation and functionalization. Coniferous wood, due to its higher resin content, may result in excessive tar content in the raw wood vinegar and should be used with caution.

[0030] In a preferred embodiment, S11 includes: (1) Obtaining raw materials and pre-treating them, including: The collected agricultural and forestry timber is first cleaned by rinsing it with a high-pressure water gun to remove inorganic impurities such as mud and dust. Then, place it in a cool, well-ventilated, and dark environment to air dry naturally. The air drying time is approximately one week, thereby controlling the moisture content of the wood to about 20% (preferably, the moisture content can range from 18% to 22%). This moisture content level is optimized: excessive moisture will consume a large amount of energy for evaporation during pyrolysis, leading to incomplete pyrolysis and a decrease in the proportion of small-molecule organic acids in the product; while excessively low moisture content may make the wood too flammable, causing it to carbonize rapidly in the early stages of pyrolysis, affecting the yield and composition of the wood vinegar. After air drying, the wood is broken down into small pieces of 20-30 cubic centimeters using a stainless steel saw as pretreatment raw material. This volume range is chosen to achieve a balance between uniform heat transfer during pyrolysis and ease of material handling. If the pieces are too large, internal pyrolysis will be incomplete; if the pieces are too small, they will easily leak through the steel mesh, and excessive packing will hinder the escape of volatile gases.

[0031] (2) High-temperature pyrolysis and collection of the pretreated raw materials, including: The treated wood blocks are packed tightly but not compacted into a high-temperature resistant steel mesh basket, and then quickly transferred to a high-temperature pyrolysis furnace. Inert gases such as nitrogen or carbon dioxide are immediately introduced to completely remove air from the furnace, creating an absolutely oxygen-deficient or oxygen-free environment. This is a crucial step to prevent the wood from burning and oxidizing, ensuring the pyrolysis reaction produces the target product in a targeted manner. The temperature is increased to 800°C (preferred implementation, an acceptable temperature range after increase is 780°C-820°C), and maintained at this temperature for 1-2 hours. 800°C is an optimized choice, at which cellulose, hemicellulose, and lignin can undergo sufficient thermal decomposition to generate volatile components rich in small molecule organic acids (such as acetic acid and propionic acid), phenols, ketones, and alcohols, while avoiding excessive decomposition that generates too many non-condensable permanent gases. The mixed flue gas generated during pyrolysis is discharged from the pyrolysis furnace and fed into a natural air-cooled or water-cooled condensation system. A preferred embodiment of the invention uses natural air cooling because the slow condensation process facilitates the effective separation and condensation of components with different boiling points, reducing the water content in the subsequent liquid. The mixed flue gas flows within the condenser tubes, exchanging heat with the ambient air. The condensable vapor components (i.e., the original wood vinegar solution) condense into a brownish-black to dark brown liquid product, which is collected in a dedicated corrosion-resistant container. This is the crude wood vinegar solution. The remaining non-condensable gases (mainly CO, H2, CH4, etc.) can be recovered as fuel, providing some energy for the pyrolysis process.

[0032] S12, ferment the crude wood vinegar to degrade and transform the harmful components in the crude wood vinegar, and enrich the active components that are beneficial to the synthesis of nano-selenium particles; The composition of crude wood vinegar is complex and unstable, containing aldehydes, ketones, and other substances that may inhibit plant growth, as well as some large-molecule tar. Through a specific fermentation process, harmful components can be degraded and transformed, while active components beneficial to the synthesis of nano-selenium can be enriched.

[0033] In a preferred embodiment, S12 includes: (1) Preparation of fermentation substrate, including: Accurately weigh the following solid materials by weight: 10 parts wood ash, 20 parts sawdust, 2 parts humic acid, and 5 parts superphosphate; among which, wood ash is used to provide potassium and various trace elements, and to adjust pH; sawdust is used as a carbon source and physical carrier for microorganisms; humic acid is used as a natural organic colloid to adsorb harmful substances and promote the reproduction of microorganisms; and superphosphate is used to provide phosphorus and calcium. The solid materials are mixed evenly in a fermentation vessel. Then, clean water is slowly added while stirring, until the moisture content of the fermentation material reaches 65% (±2%), forming the first water mixture. This water activity is optimal for the growth and metabolic activities of most microorganisms. Ten parts of a high-temperature fiber-decomposing bacteria agent are added to the first water mixture to form a fermentation substrate. In a preferred embodiment, the high-temperature fiber-decomposing bacteria agent is used to effectively decompose cellulose and hemicellulose in sawdust, producing small molecules such as sugars, providing initial energy for the entire fermentation system. This agent includes, but is not limited to, pyrolytic cellulose-decomposing Clostridium and thermophilic actinomycetes. (2) Adding diluted crude wood vinegar to the fermentation substrate and starting fermentation, including: Prepare a 100-fold volume dilution of crude wood vinegar, i.e., mix 1 part by volume of crude wood vinegar with 99 parts by volume of water. The 100-fold dilution ratio aims to reduce the initial impact of the high concentration of organic acids and phenols in the crude wood vinegar on the fermentation inoculant, while providing an abundant organic carbon source; The crude wood vinegar dilution, equal in volume to the total water volume of the fermentation materials, is slowly added to the fermentation pot, and the stirring device is started to ensure that all materials (including solid materials, water, high-temperature fiber decomposition bacteria agent and wood vinegar dilution) are highly homogenized. The crude wood vinegar dilution, equal in volume to the total water volume of the fermentation materials, means that the crude wood vinegar dilution has the same volume as the previously added water. The fermentation pot is sealed, with microporous ventilation to ensure normal respiration of both aerobic and facultative anaerobic bacteria. The fermentation temperature is precisely controlled at 35℃ (range 33℃-37℃), which is the optimal activity temperature range for the selected thermophilic fiber-decomposing bacteria. The fermentation process lasts for two months, yielding the completed wood vinegar material. During this long process, the microbial community undergoes significant succession: initially, fiber-decomposing bacteria are active, decomposing wood fibers; in the middle stage, various bacteria and fungi utilize the wood vinegar and fiber decomposition products for metabolism, degrading some irritating macromolecules (such as formaldehyde and furfural) and converting some organic acids into more complex esters, lactones, and other biologically active substances.

[0034] S13, the fermented wood vinegar material is separated, distilled and purified using physical methods to obtain a pure wood vinegar fermentation extract; After fermentation, the resulting mixture is still complex and needs to be separated and purified by physical methods to obtain a relatively stable and pure extract suitable for the synthesis of nano-selenium.

[0035] In a preferred embodiment, S13 includes: (1) Performing primary separation and decolorization on the fermented wood vinegar material, including: First, the fermented material is separated into solid and liquid components using a plate and frame filter press or centrifuge to remove solid residue and obtain a clear fermentation broth. The clarified fermentation broth was transferred to a large PET plastic drum and left to stand at room temperature for at least 3 months for aging. During this long period of standing, the liquid naturally settles and separates into three layers by gravity, typically consisting of a supernatant, a medium-sized main liquid, and a bottom sediment. The medium-sized liquid was precisely extracted; this part is considered to be the core portion with the most homogeneous composition and the fewest impurities after biotransformation and physical sedimentation. Add 3-4% (by weight) of powdered activated carbon to the obtained intermediate liquid. Activated carbon has a large specific surface area and abundant microporous structure, which can effectively adsorb pigments, residual trace amounts of tar, and any possible odor substances in the liquid. Stir thoroughly (for at least 30 minutes) to ensure full contact between the activated carbon and the liquid. Then let it stand for 24 hours to allow the saturated activated carbon to settle. Filter the solution through a precision filter (such as a 0.45μm microporous membrane) to obtain a decolorized wood vinegar fermentation liquid with a lighter color and significantly improved transparency. (2) Distill the decolorized wood vinegar fermentation liquid and collect the fraction, including: The decolorized wood vinegar fermentation broth is injected into a distillation apparatus for atmospheric or vacuum distillation. By precisely controlling the heating temperature, fractions with boiling points between 100°C and 120°C are collected. This temperature range is chosen based on the boiling points of the main active components in the wood vinegar, ensuring the effective collection of key organic acids such as acetic acid (boiling point approximately 118°C) and propionic acid (boiling point approximately 141°C, although their azeotropic point changes in aqueous solution), as well as some low-boiling-point alcohols, esters, and ketones. Higher-boiling-point components such as water, heavy phenols, and tar remain in the distillation residue and are thus removed.

[0036] The final distillate was stored as wood vinegar fermentation extract in brown glass bottles, protected from light, for later use. This wood vinegar fermentation extract exhibits stable composition and minimal batch-to-batch variation, laying a solid foundation for the reproducible and controllable synthesis of nano-selenium. In this embodiment, the wood vinegar fermentation extract is a colorless or slightly yellow transparent liquid with a mild smoky aroma and no irritating odor.

[0037] S2, based on the prepared wood vinegar fermentation extract, is compounded with ascorbic acid, sodium selenite, sodium carboxymethyl cellulose and cysteine ​​to carry out the controllable synthesis of selenium nanoparticles in a stable system with synergistic effects of multiple components.

[0038] This invention utilizes the wood vinegar fermentation extract prepared above, and combines it with ascorbic acid, sodium selenite, sodium carboxymethyl cellulose and cysteine ​​to efficiently and controllably reduce and generate nano-selenium particles in a stable reaction system with multi-component synergistic effects.

[0039] like Figure 3 As shown, in a preferred embodiment, S2 includes: S21, Prepare a reaction mother liquor based on the prepared wood vinegar fermentation extract, including: (1) Take 1 part by weight of the wood vinegar fermentation extract and place it in a reaction vessel; (2) Add 50 times the volume of water (e.g., 1 part of extract to 50 parts of water) to 1 part by weight of the wood vinegar fermentation extract for dilution. The diluted solution constitutes the reaction mother liquor. Dilution is used to adjust the concentration of the extract to an optimized level that provides a suitable acidic environment (pH usually between 3 and 4) without causing excessively high organic acid concentration, which would lead to excessively rapid selenium nucleus formation and uneven particle size.

[0040] S22, Add reactants to the reaction mother liquor in a specific order, the reactants including ascorbic acid, sodium selenite, sodium carboxymethyl cellulose, and cysteine, comprising: While continuously stirring (preferably using a magnetic stirrer at 300-500 rpm), add one of the reactants sequentially to the mother liquor: Sodium carboxymethyl cellulose (CMC-Na), 2 parts by weight. CMC-Na is preferentially added as a polymeric template agent and steric stabilizer, allowing it to fully hydrate and extend in solution to form a network structure, providing a pre-set template and steric hindrance for the subsequent nucleation and growth of selenium nanoparticles.

[0041] Cysteine, 2 parts by weight. Cysteine ​​acts as a small molecule stabilizer and ligand; its thiol and amino groups specifically interact with the selenium precursor.

[0042] Ascorbic acid (Vc), 2 parts by weight. Ascorbic acid acts as the main reducing agent with a moderate reduction potential, thereby gradually reducing Se(IV) in sodium selenite to Se(O).

[0043] Sodium selenite (Na2SeO3), 1 part by weight. Added as a selenium source, either last or in batches after the other components are thoroughly mixed, to control the initial nucleation rate.

[0044] This order of addition is optimized. First, stabilizers (CMC-Na and cysteine) are added to form a stable "reaction microenvironment," then a reducing agent (Vc) is added to create a reducing atmosphere, and finally, reactants (sodium selenite) are introduced. This allows for effective stabilization after "explosive nucleation," which is beneficial for obtaining nanoparticles with uniform particle size.

[0045] S23, after the controllable synthesis of selenium nanoparticles, a reaction product is obtained. During the reaction, the changes in materials and the pH value of the reaction system are monitored, including: (1) After adding the reactants to the mother liquor in a specific order, continue stirring. The reaction system will gradually change. The initial colorless or pale yellow solution will gradually turn red or orange-red within 10-30 minutes at room temperature (25±5℃), indicating that elemental selenium nuclei have begun to form and grow. As the reaction proceeds, the color gradually deepens, eventually becoming a stable, transparent, deep red sol. The total reaction time is controlled within 3 hours to ensure that the reduction reaction is complete.

[0046] (2) During the reaction, the pH value of the system is naturally maintained in the acidic range of 3-4. This is because the wood vinegar fermentation extract provides a certain buffering capacity. This acidic environment is not only required for ascorbic acid to exert its best reducing activity, but also conducive to the protonation of cysteine ​​amino groups.

[0047] S24, separating and post-processing the reaction products, including: After the reaction was completed, the resulting dark red nano-selenium sol was centrifuged. In this embodiment, the sol was centrifuged at 10,000 rpm for 15 minutes. After centrifugation, the supernatant was an almost colorless waste liquid, and the bottom precipitate was the target product - nano-selenium particles. The bottom precipitate was washed 2-3 times alternately with anhydrous ethanol and deionized water to remove residual reactants and soluble byproducts. Finally, the washed wet precipitate was placed in a vacuum drying oven and dried at 40℃-50℃ for 6-12 hours to obtain dry, dark red to brick red nano-selenium powder. This powder is easy to store and transport, and can be redispersed in the aqueous phase when needed to form a stable nano-selenium suspension.

[0048] The reaction mechanism in this embodiment is explained as follows: The unique, multi-component synergistic reaction mechanism ingeniously solves the problems of nucleation, growth and stabilization in the synthesis of nano-selenium.

[0049] 1. Reduction reaction kinetics: As shown in the ionic reaction equation: .

[0050] Ascorbic acid (C6H8O6) acts as an electron donor, under acidic conditions, to convert selenite ions (… (where Se is in the +4 valence) is reduced to elemental selenium (Se 0 Wood vinegar fermentation extract provided It not only drives the reaction but also forms a buffer system through its organic acid components, keeping the reaction pH stable within the optimal range and preventing rapid particle aggregation caused by drastic pH fluctuations.

[0051] 2. Synergistic effect of multiple stabilization mechanisms: (1) Electrostatic stabilization mechanism (dominated by cysteine ​​and wood vinegar): In the acidic environment of the reaction system, the α-amino group (-NH2) in the cysteine ​​molecule will be protonated to form a positively charged ammonium ion. .These The group preferentially adsorbs onto the negatively charged selenite ions through electrostatic attraction. An initial "guiding layer" forms around the intermediate valence state ions of selenium. When Se... 0 After the atoms are reduced, these protonated amino groups are further anchored to the surface of the newly formed selenium nanoparticles, giving them a net positive charge. Simultaneously, some positively charged organic components in the wood vinegar fermentation extract are also adsorbed onto the particle surface, collectively constructing a strong positively charged double layer. According to the DLVO theory, the particles generate a strong electrostatic repulsion due to their shared positive charge, effectively overcoming the aggregation tendency caused by van der Waals attraction.

[0052] (2) Steric hindrance stabilization mechanism (dominated by sodium carboxymethyl cellulose): CMC-Na is a long-chain anionic polysaccharide polymer. It fully extends in solution, and its molecular chains are physically adsorbed onto the surface of the selenium nanoparticles, forming a thick polymeric protective layer. When two particles coated with CMC-Na approach each other, their outer polymeric chains physically overlap and compress, leading to a reduction in the conformational entropy of the chain segments, thus generating a strong repulsive force—steric hindrance. This physical barrier effect, complementing the aforementioned electrostatic repulsion, constitutes a more robust "electrostatic-steric hindrance" composite stabilization mechanism, ensuring the stability of the selenium nanoparticle sol during long-term storage.

[0053] (3) Template effect and morphology control (achieved through the synergistic effect of CMC-Na and cysteine): The long-chain structure of CMC-Na can form micro-regions similar to "nanoreactors" in solution, which restricts the free diffusion of selenium atoms and the disordered growth of the lattice, thereby guiding nano-selenium to form a spherical structure with the lowest energy and uniform size. The coordination effect of cysteine ​​guides the directional deposition of selenium atoms at the molecular level, further finely controlling the growth process of the nucleus. The synergy of the two ultimately achieves precise control over the particle size (90-150 nm) and spherical morphology of nano-selenium.

[0054] To fully verify the feasibility, repeatability, and superiority of the present invention, the following series of detailed embodiments and comparative examples are provided.

[0055] Example 1: Synthesis of Nano-Selenium under Standard Process Procedure: The wood vinegar fermentation extract was prepared according to step S1. All chemical reagents were of analytical grade.

[0056] Process phenomena: About 15 minutes after adding sodium selenite, the solution began to turn light pink, and then the color gradually deepened until it turned bright red after 1 hour. When the reaction ended after 3 hours, it was a transparent dark wine-red sol. No precipitate was produced during the entire process.

[0057] Yield calculation: After the reaction, the mass of the dried selenium nanoparticle powder was accurately weighed. Three parallel experiments were conducted, with yields of 95.6%, 93.8%, and 96.1%, respectively, resulting in an average yield of 95.2%. Calculation formula: Yield (%) = (actual mass of nano-selenium / theoretical mass of selenium calculated based on sodium selenite feed amount) × 100%.

[0058] Example 2: Effect of dilution ratio on wood vinegar fermentation extract Keep all other conditions exactly the same as in Example 1, only change the dilution factor of the wood vinegar fermentation extract.

[0059] (1) Group: Group A: Diluted 25 times.

[0060] Group B: Diluted 50 times (standard conditions).

[0061] Group C: Diluted 100 times.

[0062] (2) Results: Group A: The reaction started quickly, and the color deepened rapidly, but the selenium nanoparticles eventually showed slight sedimentation after standing for 24 hours, and the absolute value of the Zeta potential was slightly lower, indicating slightly poor stability. This is because the acidity and organic matter concentration were too high, nucleation was too rapid and excessive, and the stabilizer was insufficient to completely cover all the nuclei.

[0063] Group B: Performed best, with stable sol and narrow particle size distribution.

[0064] Group C: The reaction started slowly, the color was lighter, the reaction was incomplete, and the yield decreased to about 85%. This was due to insufficient acidity and effective stabilizing components.

[0065] Example 3: Relationship between stabilizer type and dosage Keeping all other conditions the same as in Example 1, the stable system was modified.

[0066] (1) Group: Group D: Only 2 portions of CMC-Na were used.

[0067] Group E: Only 2 portions of cysteine ​​were used.

[0068] Group F: Use 1 part CMC-Na and 1 part cysteine.

[0069] Group G (Standard): Use 2 parts CMC-Na and 2 parts cysteine.

[0070] Group H: Two portions of commercially available polyvinylpyrrolidone (PVP K30) were used to replace CMC-Na and cysteine.

[0071] (2) Results: Group D: The particles are relatively large with a wide particle size distribution (150-300nm), and they tend to aggregate after long-term static storage.

[0072] Group E: The sol is red, but has a high zeta potential and is mainly electrostatically stable. It is sensitive to salinity, and the addition of a small amount of NaCl will trigger aggregation.

[0073] Group F: The effect is better than that of Groups D and E, but the stability is still not as good as that of Group G.

[0074] Group G: Best overall performance.

[0075] Group H: It can synthesize nano-selenium, but the cost is high, and the biocompatibility of the product in plants may not be as good as the green and stable system of this invention.

[0076] Comparative Example 1: Unfermented wood vinegar The crude wood vinegar prepared using the same source and method was directly used for the synthesis of nano-selenium (replacing the wood vinegar fermentation extract) after simple filtration and dilution, with other conditions the same as in Example 1.

[0077] Results: The reaction solution was dark red and turbid, with a large amount of brick-red precipitate forming during the reaction, failing to form a stable sol. After drying, the product showed severe agglomeration and poor water redispersibility. This demonstrates that crude wood vinegar, without biological fermentation and physical purification, has a complex composition and contains impurities that promote agglomeration, making it unsuitable for synthesizing high-quality nano-selenium.

[0078] Comparative Example 2: Wood-free vinegar fermentation extract system Instead of using wood vinegar fermentation extract, deionized water was adjusted to pH 3.5 with dilute hydrochloric acid (HCl) as the reaction medium. Other components and amounts were the same as in Example 1.

[0079] Results: Although red selenium nanoparticles could be generated, the reaction rate was slower, the product particle size distribution was wider (80-200 nm), and the synthesized selenium nanoparticle sol showed significant aggregation and sedimentation after one week. This demonstrates that a single chemical acid cannot replace the complex organic components provided by the wood vinegar fermentation extract and their synergistic effect in the stabilization mechanism.

[0080] Product characterization data: 1. Particle size analysis: The nano-selenium sol obtained in Example 1 was analyzed using a Malvern Zeta potential and particle size analyzer. The results showed that its hydrodynamic particle size was mainly distributed in the range of 90-150 nm, and the polydispersity index (PDI) was less than 0.2, indicating that the particle size distribution was concentrated and the monodispersity was good.

[0081] 2. Morphological observation: Take the sample from Example 1, dilute it, and drop it onto a silicon wafer for observation using a field emission scanning electron microscope (FE-SEM). For example... Figure 4 The SEM images clearly show that the prepared selenium nanoparticles are regular spherical or near-spherical in shape, with smooth surfaces, clear separation between particles, and no obvious adhesion or agglomeration, which is consistent with the particle size analysis results.

[0082] 3. For example Figure 5 As shown, stability test: The nano-selenium sol prepared in Example 1 was sealed in a transparent glass reagent bottle and stored at room temperature in the dark.

[0083] (1) After standing for 1 hour, 48 hours and 1 month: the color of the sol did not change significantly and there was no sediment at the bottom of the bottle.

[0084] (2) After standing for 2 months: the sol remains transparent red, with only a very small amount of sediment at the bottom that can only be found by careful observation. It can be completely dispersed again by gently shaking.

[0085] (3) After standing for 3 months: the color darkened slightly, some particles sank to the bottom of the bottle, but most particles remained suspended, exhibiting stability far superior to the comparative example. This excellent stability is attributed to the aforementioned "electrostatic-steric hindrance" composite stabilization mechanism. It only becomes cloudy when shaken.

[0086] (4) After standing for 6 months: most of the particles sank to the bottom of the bottle and clear liquid appeared on the top. However, after shaking, it immediately returned to the original uniform dispersion state, indicating that the deposition was mainly caused by gravity and the stability of the nano-ions was not destroyed.

[0087] Examples of the formulation and application of nano-selenium foliar fertilizer The ultimate application of the nano-selenium particles prepared by this invention is as a highly efficient and safe selenium nutrient fortifier for the formulation of foliar fertilizers for the production of various selenium-enriched agricultural products.

[0088] 1. Example of foliar fertilizer formula: Nano-selenium powder (based on elemental selenium): 0.1%; Urea: 15%; Potassium dihydrogen phosphate: 5%; Potassium chloride: 3%; Surfactant (e.g., Tween-80): 0.1%; Deionized water: Replenish to 100%; The above components are mixed, and the nano-selenium powder is uniformly dispersed in the liquid by shear emulsification or high-speed stirring to obtain nano-selenium foliar fertilizer.

[0089] 2. Application Example: Tomato Foliar Spraying Experiment (1) Method: Select tomato plants with uniform growth and spray them with the above-prepared nano-selenium foliar fertilizer at the initial flowering stage, fruit setting stage, and fruit enlargement stage, respectively. Use an equal amount of basic fertilizer solution without nano-selenium as a control. Each spray should be applied until both sides of the leaves are evenly moistened.

[0090] (2) Results: Compared with the control group, the tomato plants sprayed with nano-selenium foliar fertilizer had darker green leaves and a lower incidence of plant diseases.

[0091] Samples were collected and tested after the fruit matured: the selenium content of tomatoes in the control group was undetectable or extremely low (<0.01 mg / kg); the selenium content of tomatoes in the experimental group was significantly increased, reaching 0.15-0.25 mg / kg, which meets the national industry standard for selenium-enriched agricultural products.

[0092] Furthermore, the experimental group of tomatoes showed increased levels of vitamin C and soluble solids (sugar content). This indicates that the nano-selenium foliar fertilizer of this invention can not only effectively enrich selenium but also stimulate plant metabolism and improve fruit quality.

[0093] To verify the effectiveness and scalability of this invention, as well as the practicality and value of nano-selenium fertilizer, biological samples of apples, persimmons, and nectarines were sent for testing (the testing institution was a mineral resources testing center under the Ministry of Natural Resources). The results are as follows: Table 1. Comparison of selenium content between nano-selenium foliar fertilizer and basal fertilizer applied to apple trees. Table 2. Comparison of selenium content between nano-selenium foliar fertilizer and basal fertilizer applied to persimmons. Table 3. Comparison of selenium content between nano-selenium foliar fertilizer and basal fertilizer applied to nectarines. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for preparing nano-selenium particles, characterized in that, The method comprises the following steps: S1, preparing wood vinegar fermentation extract for providing an acidic reaction environment for the synthesis of nano selenium particles and serving as a stabilizer and a morphology regulator; S2, based on the prepared wood vinegar fermentation extract, performing a complex synthesis of nano selenium particles in a stable system with the synergistic effect of multiple components by compounding with ascorbic acid, sodium selenite, sodium carboxymethyl cellulose and cysteine.

2. The method of claim 1, wherein the nano-selenium particles are prepared by the process of claim 1. The S1 comprises: S11, obtaining raw materials and pretreating the raw materials, and preparing crude wood vinegar based on the pretreated raw materials; S12, fermenting the crude wood vinegar to degrade and transform harmful components in the crude wood vinegar and enrich active components beneficial to the synthesis of nano selenium particles; S13, separating, rectifying and purifying the fermented wood vinegar material by a physical method to obtain pure wood vinegar fermentation extract.

3. The method for preparing nano-selenium particles according to claim 2, characterized in that, The S11 comprises: (1) obtaining raw materials and pretreating the raw materials, including: First, cleaning the surface of collected agricultural and forestry wood by using a high-pressure water gun to remove inorganic impurities; Subsequently, placing the wood in a cool, ventilated and light-avoiding environment for natural air drying, and the natural air drying time is about one week, so that the moisture content of the wood is controlled to be 18%-22%; After the air drying is completed, the wood is decomposed into small pieces with a volume of 20-30 cubic centimeters by using a stainless steel saw as pretreated raw materials; (2) high-temperature pyrolysis and collection of the pretreated raw materials, including: tightly but not compactly packing the treated wood pieces into a high-temperature-resistant steel mesh basket, and then quickly transferring them into a high-temperature pyrolysis furnace; immediately introducing inert gas to completely remove air in the furnace to achieve an absolute oxygen-deficient or oxygen-free environment; programmed heating to 780-820°C, and maintaining pyrolysis at this temperature for 1-2 hours; guiding the mixed flue gas generated by pyrolysis out of the pyrolysis furnace and into a natural air cooling or water cooling condensing system, and the mixed flue gas flows in the condensing tube and exchanges heat with the ambient air, wherein the condensable vapor components are condensed into brown to black brown liquid products as wood vinegar crude liquid, which is collected in a dedicated corrosion-resistant container to form crude wood vinegar, and the remaining non-condensable gas is recovered as fuel to provide part of the energy for the pyrolysis process.

4. The method for preparing nano-selenium particles according to claim 3, characterized in that, The S12 comprises: (1) preparing a fermentation substrate, including: measuring the following solid materials by weight: 10 parts of wood ash, 20 parts of sawdust, 2 parts of humic acid and 5 parts of superphosphate; wherein the wood ash is used to provide potassium and various trace elements and adjust the pH; the sawdust is used as a carbon source and a physical carrier for microorganisms; the humic acid is used as a natural organic colloid to adsorb harmful substances and promote microbial reproduction; the superphosphate is used to provide phosphorus and calcium elements; mixing the solid materials uniformly in a fermentation pot, and then slowly adding clean water while stirring until the moisture content of the fermentation material reaches 65%±2% to form a first water mixture; The first water mixture is added with 10 parts of high-temperature fiber-decomposing bacteria agent to form a fermentation substrate, the high-temperature fiber-decomposing bacteria agent is used to decompose cellulose and hemicellulose in sawdust and generate small molecular substances, and provides initial energy for the fermentation system; the high-temperature fiber-decomposing bacteria agent includes Clostridium thermocellum or thermophilic actinomyces; (2) adding a crude wood vinegar liquid diluent to the fermentation substrate and starting fermentation, comprising: A crude wood vinegar liquid diluent with a volume of 100 times is prepared, that is, 1 volume part of crude wood vinegar liquid is mixed with 99 volume parts of water; An equal amount of the crude wood vinegar liquid diluent to the total water amount of the fermentation material is slowly added to the fermentation pot, and a stirring device is started to ensure that all the materials are highly homogenized, wherein the equal amount of the crude wood vinegar liquid diluent to the total water amount of the fermentation material means that the crude wood vinegar liquid diluent has an equal volume to the previous added water; The fermentation pot is sealed, and a microporous aeration device is retained to ensure normal respiration of aerobic and facultative anaerobic bacteria, the fermentation temperature is 33-37°C, and the fermentation period lasts for 2 months to obtain a fermented wood vinegar liquid material.

5. The method for preparing nano-selenium particles according to claim 4, characterized in that, The S13 comprises: (1) primary separation and decolorization of the fermented wood vinegar liquid material, comprising: First, the fermented material is subjected to solid-liquid separation by a plate-and-frame filter press or a centrifuge, and the solid residue is discarded to obtain a clarified fermentation liquid; The clarified fermentation liquid is transferred to a large PET plastic barrel and aged at room temperature for more than 3 months, and the liquid is naturally deposited and stratified by gravity into three layers of supernatant, middle body liquid and bottom sediment, and the middle layer liquid is accurately intercepted; 3-4% of the total mass of the obtained middle layer liquid is added to the powder activated carbon, and sufficient stirring is performed under a stirrer for at least 30 minutes, and then it is statically placed for 24 hours, so that the activated carbon saturated with adsorption is settled, and then filtered through a precision filter to obtain a decolorized wood vinegar liquid fermentation liquid; (2) distillation of the decolorized wood vinegar liquid fermentation liquid and collection of the distillate, comprising: The decolorized wood vinegar liquid fermentation liquid is injected into a distillation device for atmospheric or reduced pressure distillation, and by accurately controlling the heating temperature, the distillate with a boiling point of 100-120°C is collected; The finally obtained distillate is stored in a brown glass bottle as a wood vinegar liquid fermentation extract, and is stored in the dark for standby use.

6. The method for preparing nano-selenium particles according to claim 5, characterized in that, The S2 comprises: S21, configuring a reaction mother liquor based on the prepared wood vinegar liquid fermentation extract; S22, adding reactants to the reaction mother liquor in a specific order, the reactants including ascorbic acid, sodium selenite, carboxymethyl cellulose sodium and cysteine; S23, obtaining a reaction product after the controllable synthesis reaction of nano selenium particles, and monitoring the change of the material and the pH value of the reaction system during the reaction; the monitoring of the pH value of the reaction system includes monitoring whether the pH value of the system during the reaction is naturally maintained in an acidic range of 3-4; S24, separating and post-treating the reaction product.

7. The method for preparing nano-selenium particles according to claim 6, characterized in that, The S21 comprises: (1) 1 part by weight of wood vinegar liquid fermentation extract is measured and placed in a reaction container; (2) 50 times volume of water is added to the 1 part of the wood vinegar fermentation extract solution for dilution, and the diluted solution constitutes the reaction mother liquor. 8.The method of claim 7, wherein the selenium nanoparticles have a diameter of 1-100 nm. The S22 comprises: Under continuous stirring, one of the reactants is added to the reaction mother liquor in sequence: Sodium carboxymethyl cellulose, 2 parts by weight; Cysteine, 2 parts by weight; Ascorbic acid, 2 parts by weight; Sodium selenite, 1 part by weight.

9. The method for preparing nano-selenium particles according to claim 8, characterized in that, The S24 comprises: After the reaction is completed, the obtained deep red nano-selenium sol is subjected to centrifugal treatment, and after centrifugation, the supernatant is almost colorless waste liquid, and the bottom precipitate is the nano-selenium particles; The bottom precipitate is washed with anhydrous ethanol and deionized water alternately for 2-3 times to remove residual reactants and soluble by-products; Finally, the washed wet precipitate is placed in a vacuum drying oven and dried at 40-50°C for 6-12 hours to obtain dry, deep red to brick red nano-selenium powder.

10. The application of the nano-selenium particles obtained by the preparation method of any one of claims 1-9 in the preparation of selenium nutritional supplements and foliar fertilizers for the production of selenium-rich agricultural products.

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