Method for preparing iron-based nano-fertilizer based on Joule thermal flash evaporation technology and application of iron-based nano-fertilizer in biological nitrogen fixation and yield increase of soybeans

Abstract

The invention relates to a method for preparing an iron-based nano-fertilizer based on a Joule thermal flash evaporation technology and application of the iron-based nano-fertilizer in biological nitrogen fixation and yield increase of soybeans, and the method comprises the following steps: preparing iron-based biochar: dissolving FeCl3 and dried coffee residue powder in deionized water according to a mass ratio of (0.5-1.5): 2, stirring for 10-14 hours at normal temperature, then standing until solid-liquid separation, pouring out redundant supernatant liquid, and drying to obtain the iron-based biochar; keeping solid precipitate, and drying; putting the dried solid into a crucible, compacting, putting into a muffle furnace, carrying out oxygen-limited pyrolysis at 700-1000 DEG C, cooling to room temperature, grinding, and sieving to obtain the iron-based biochar with the resistance of less than 300 ohm; and the iron-based biochar is loaded into a quartz tube for Joule flash evaporation, and the coffee residue source iron-based nano material is obtained. According to the method, goethite with higher solubility is obtained by using Joule flash evaporation through the combination of FeCl < 3 + > and coffee grounds, so that the biological nitrogen fixation and yield increase effects of soybeans are promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural fertilizers, and particularly relates to a method for preparing iron-based nano-fertilizer based on Joule heat flash evaporation technology and its application in biological nitrogen fixation and yield increase of soybeans. Background Art

[0002] As one of the widely cultivated food crops globally, soybeans are not only rich in high-quality plant protein and an important part of the human diet, but also important oil crops. Moreover, the biological nitrogen fixation ability of soybean root nodules can reduce the use of chemical fertilizers while ensuring yield, which is of great significance for promoting green agriculture. As a new type of high-efficiency fertilizer, nano-fertilizers have gradually come into people's view, mainly including inorganic nano-silicon fertilizers, nano-modified bio-based synergistic double-layer coated controlled-release fertilizers, nano-carbon fertilizers, etc. Through their unique nano-scale particle size effect, nano-fertilizers can significantly improve the utilization rate of fertilizers by plants, promote the absorption and transport of nutrients by soybean roots, and thus increase the yield and quality of soybeans. Among them, nano-carbon fertilizers are relatively the most economical because carbon-containing waste can be used as raw materials, and carbon fertilizers have high adsorption and slow-release properties, which can increase soil nutrients and promote the development of plant roots, thereby effectively promoting plant growth. Therefore, applying nano-carbon fertilizers to soybean cultivation is expected to become one of the important ways to improve China's self-sufficiency in soybeans and ensure food security. However, the preparation process of nano-carbon fertilizers is not easy. For example, the ball milling method generally grinds for several days, and the ultrasonic fragmentation method requires the addition of extra organic solvents; the chemical method generally adds strong acids and alkalis with strong corrosiveness, and needs to be washed repeatedly after preparation; the biological method (such as enzymatic hydrolysis) is rarely used due to high costs.

[0003] Chinese Patent CN118901728A discloses a method for preparing biomass-based nano-carbon. This patent uses current self-heating carbonization to prepare nano-biochar, effectively increasing soybean yield by about 25%. However, due to the lack of loading of additional nutrient elements, the yield increase rate of this material is not high. In view of this, this application makes improvements on this method to load appropriate nutrient elements on nano-carbon fertilizers, so as to achieve more effective biological nitrogen fixation and yield increase of soybeans. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing iron-based nano-fertilizer based on Joule heat flash evaporation technology and its application in biological nitrogen fixation and yield increase of soybeans. This method uses the combination of FeCl3 + coffee grounds to obtain goethite with higher solubility through Joule flash evaporation, thereby promoting biological nitrogen fixation and yield increase effects of soybeans.

[0005] The technical solution adopted by the present invention to solve the above technical problem is as follows:

[0006] In a first aspect, the present invention provides a method for preparing iron-based nano-fertilizer based on Joule heat flash evaporation technology. The preparation process of the method is as follows:

[0007] 1) Preparation of iron-based biochar: Dissolve FeCl3 and dried coffee residue powder in deionized water at a mass ratio of (0.5 - 1.5):2 and stir at room temperature for 10 - 14 h. Then let it stand until solid-liquid separation occurs, pour out the excess upper liquid, leave the solid precipitate, and dry it. The dried solid is loaded into a crucible, compacted, and placed in a muffle furnace for oxygen-limited pyrolysis at 700 - 1000 °C. After cooling to room temperature, grind and sieve it to obtain iron-based biochar FeBC with a resistance less than 300 Ω.

[0008] 2) Load the iron-based biochar FeBC into a quartz tube for Joule flash evaporation. Set the voltage of the Joule flash evaporation equipment to 150 - 170 V and the capacitance to 220 - 260 mF to obtain coffee residue-derived iron-based nano-material FeNM, which is the iron-based nano-fertilizer.

[0009] Further, in step 1), the ratio of the mass of the mixture after mixing FeCl3 and coffee residue powder to deionized water is: 40 - 60 g of the mixture: 0.8 - 1.2 L of deionized water.

[0010] In a second aspect, the present invention provides an iron-based nano-fertilizer prepared by using the above method.

[0011] Further, in the FeNM, goethite is the main component, the Fe content is not less than 1.40%, the hydrodynamic diameter of FeNM is not more than 800 nm, the absolute value of the Zeta potential is 30 - 34 mV. Preferably, the hydrodynamic diameter of FeNM is 705.55 ± 67.32 nm and the Zeta potential is 33.79 mV, and it stably exists in an aqueous solution.

[0012] In a third aspect, the present invention provides an application of the iron-based nano-fertilizer in soybean biological nitrogen fixation and yield increase. Mix 80 - 120 mg / kg of FeNM with 1.9 - 2.2 kg of soil evenly, water it to 55% - 65% of the maximum water content of the soil, balance for 10 days, and bury soybean seeds in it for soybean planting.

[0013] Further, maintain the field water holding capacity at 55% - 65%. At 90 days, the total nitrogen content in the leaves and roots is respectively above 28% and above 15%, which can effectively promote soybean biological nitrogen fixation.

[0014] The content of leghemoglobin in the root nodules treated with FeNM is 6.8 mg / g, which can effectively maintain the oxygen balance in the soybean plant and achieve effective yield increase of soybeans.

[0015] There are many types of free amino acids in soybeans treated with FeNM, and the contents of threonine (Thr), cysteine (Cys), and methionine (Met) are significantly increased, improving the quality of soybeans;

[0016] Among the light response curve parameters of soybean leaves treated with FeNM under light intensities of 0 - 1640 μmol / m 2 s, the maximum electron transfer efficiency ETR max is not less than 150, and at the same time, the minimum saturation light intensity E k is not less than 620, which can efficiently improve the key parameters of soybean photosynthesis, enhance the ability of soybeans to capture and convert light energy, enable them to maintain efficient photosynthesis in strong light environments, and contribute to improving the environmental adaptability and production potential of soybeans;

[0017] When detecting the number of grains and grain weight of grains at 115 days, they are greater than 9 and greater than 5 g / plant respectively, achieving a significant increase in yield.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] The present invention uses coffee grounds as a raw material and FeCl3 as an iron source, and prepares an iron-based nano-fertilizer through a flash Joule technology. The prepared iron-based nano-fertilizer can be used to promote biological nitrogen fixation and yield increase of soybeans. Compared with the prior art, the steps of adjusting the pH after dissolving FeCl3 in water are omitted, and the cumbersome hydrothermal reaction control procedure for doping iron is simplified. Through a 115-day pot experiment with soil application, it shows good effects in promoting soybean growth and nitrogen fixation.

[0020] The preparation method of the present invention, through the synergistic effect of the carbon source and the iron source, and through the rapid high temperature during the flash process, can decompose and recombine the stable chromite and magnetite in biochar to form goethite with higher solubility, thereby dissolving more free iron in the soil. At the same time, the appropriate flash process also makes the biochar particles smaller and less likely to agglomerate compared with commercial nano-iron fertilizers (nZVI). Therefore, it can effectively promote biological nitrogen fixation in soybean stems and leaves, with the total nitrogen content increasing by 22.33% and 19.22% respectively, and the soybean yield increasing by 44%, providing new technical support for the agricultural application of nanomaterials. Description of the Drawings

[0021] Figure 1 are the XRD patterns of nZVI, FeBC, and FeNM.

[0022] Figure 2 is the XRD pattern of the rubber + FeSO4 carbonized and then flashed.

[0023] Figure 3 are the XPS total spectra of FeNM, the rubber + FeSO4 carbonized and then flashed, and the corn straw + FeCl3 carbonized and then flashed.

[0024] Figure 4 Comparison diagrams of the hydrodynamic diameters and zeta potentials of nZVI, FeBC, and FeNM.

[0025] Figure 5 Comparison diagram of iron ion contents in soils with different treatments.

[0026] Figure 6 Comparison diagram of total nitrogen contents in the roots and leaves of soybean plants under different treatments.

[0027] Figure 7 Comparison diagram of the number and weight (fresh weight) of soybean seeds after 115 days of growth of soybean plants under different treatments.

[0028] Figure 8 Comparison diagram of free amino acid contents in soybean seeds under different treatments.

[0029] Figure 9 Comparison diagram of leghemoglobin contents in soybean root nodules under different treatments.

[0030] Figure 10 Comparison diagram of light response curves of leaves under different treatments. Specific implementation manners

[0031] The present invention will be further explained below in conjunction with embodiments and the accompanying drawings, but this is not used to limit the protection scope of the present application.

[0032] The present invention selects economic coffee grounds as raw materials and common iron salts (FeCl3) as iron sources, and through the Joule flash evaporation technology, aims to obtain an economic, green, and high-performance iron-based nano-fertilizer, which is used to promote the growth of soybeans and biological nitrogen fixation, and achieve the dual goals of recycling solid waste resources and sustainable agricultural development.

[0033] The coffee grounds in the present invention have a particle size of about 1-2 mm and are derived from discarded coffee residues. Without complex treatment processes such as grinding of small particle sizes, they are directly combined with FeCl3 for use, ensuring that the iron element content is neither too low nor too high, so that it can be carried out under a suitable flash evaporation process to obtain an iron-based nano-fertilizer mainly composed of goethite.

[0034] Example 1

[0035] The method for preparing an iron-based nano-fertilizer based on the Joule heat flash evaporation technology in this example is as follows:

[0036] 1) Preparation of iron-based biochar: Dissolve FeCl3 and dried coffee ground powder in deionized water at a certain mass ratio of 1:2 (50 g mixture: 1 L deionized water), stir at room temperature on a magnetic stirrer for 12 h to enable the coffee grounds to fully absorb iron elements, then let it stand until solid-liquid separation occurs, pour out the excess upper liquid, leave the solid precipitate, and dry it. The dried solid is loaded into a crucible, compacted, and placed in a muffle furnace for oxygen-limited pyrolysis at 700 °C. After cooling to room temperature, it is ground and passed through a 100-mesh sieve to obtain iron-based biochar FeBC with a resistance less than 300 Ω, and its Fe element content is approximately 1.6%.

[0037] 2) Preparation of iron-based nanomaterials: Load the iron-based biochar FeBC into a quartz tube with an inner diameter of 15 mm, and plug graphite stoppers at both ends to compact the biochar. Set the voltage of the Joule flash evaporation equipment to 170 V and the capacitance to 240 mF, and then perform Joule flash evaporation to obtain coffee ground-derived iron-based nanomaterials (FeNM). Since the resistance of the iron-based biochar FeBC prepared in step 1) is less than 300 Ω, it can ensure the progress of the Joule flash evaporation process. If the resistance is too large, it is not conducive to the Joule flash evaporation process.

[0038] The present invention can achieve effective doping of iron by mixing iron salts with raw materials and pyrolysis. Successful doping is a necessary basis for subsequent experiments. The key to realizing biological carbon fixation and yield increase of soybeans in this application lies in the appropriate dissolution of free iron after the material is applied to the soil. The key to dissolving free iron lies in decomposing and recombining chromite and magnetite in the iron-based biochar under an appropriate flash evaporation voltage (130 - 170 V). If the voltage is too low, iron ore recombination cannot be achieved, and if the voltage is too high, iron elements are easily volatilized. The preparation of traditional nano-carbon fertilizers (such as ball milling method) only physically reduces the particle size of biochar, and its composition will not change. The iron-based biochar of the present invention realizes the recombination of iron ore after flash evaporation.

[0039] Conduct relevant growth applications and relevant tests on the above-mentioned iron-based nano-fertilizer:

[0040] Soybean growth experiment: Collect clean and pollution-free surface soil from farmland, air-dry it naturally and pass it through a 2-mm sieve, and load it into plastic flower pots with air holes at the bottom. Each pot contains 2.0 kg of soil. Mix 100 mg / kg FeNM and FeBC evenly with the soil, use the soil without adding any improvement materials as a control, water it to 55% - 65% of the maximum water content of the soil, and balance for about 10 days. During this period, germinate soybean seeds. After 5 days of germination, select seeds with similar growth conditions and bury them in the soil, about 1 - 2 cm from the soil surface, 4 seeds per pot. Then keep the field water holding capacity at 55% - 65% and carry out normal planting management. Detect the total nitrogen, leghemoglobin content in nodules, and chlorophyll fluorescence after about 90 days, and detect the relevant indexes of the grains after about 115 days.

[0041] Material characterization: The crystal structure of the material was analyzed by X-ray diffraction. Jade 6.0 was used to identify the XRD characteristics, bands, and spectral features. The hydrodynamic diameter and zeta potential were measured using a nanoparticle size and zeta potential analyzer.

[0042] Total nitrogen determination: 0.1 g of plant roots or leaves was taken and digested with H2SO4 and H2O2 (v / v = 5 / 3) at 160 °C for 1.5 h. After cooling, it was diluted to 100 mL, and finally the total nitrogen content was determined using a flow injection analyzer.

[0043] Free amino acid determination: Fresh soybean seeds were ground into powder, passed through a 100-mesh sieve, dissolved in hydrochloric acid, and then precipitated with sulfosalicylic acid to precipitate proteins. After centrifugation, it was filtered through a membrane, and the types and contents of free amino acids were detected using an amino acid analyzer.

[0044] Determination of leghemoglobin content in nodules: 0.5 g of fresh nodules was added to 2 mL of 0.1 mol / L phosphate buffer (pH = 6.8) and ground into a homogenate. The homogenate was filtered, and the filtered liquid was centrifuged at 100 g and 4 °C for 15 min. The obtained supernatant was centrifuged again at 20000 g and 4 °C for 20 min. 100 μL of the supernatant was added to 2 mL of buffer. The mixture was shaken well, and the absorbance value at a wavelength of 540 nm was measured to calculate the leghemoglobin content in nodules.

[0045] Measurement of the light response curve of leaves: The light response curve of leaves was measured using a chlorophyll fluorometer. The sample was exposed to 10 light intensity gradients (0 - 1640 μmol / m 2 s) to obtain the rapid light response curve.

[0046] Next, to further illustrate the advantages of the present invention, FeCl3 and coffee grounds were replaced with FeSO4 and rubber or corn straw, and carbonization and flash evaporation were carried out with the same operations for comparison.

[0047] Obtaining of nano zero-valent iron (nZVI) in the present invention: nZVI was purchased from Macklin Pharmaceutical Company, with a diameter of 100 nm. The drug was used as received, and nZVI was used as a traditional iron fertilizer for comparison.

[0048] First, the XRD patterns of three iron-based fertilizers were compared (see Figure 1)。The nZVI shows strong diffraction peaks at 44.7°, 65.0°, and 82.3°, which are in complete agreement with the crystal planes of Fe in the standard card (PDF#99 - 0064). The diffraction peaks of FeBC at 23.7° and 43.9° correspond to the (002) and (100) planes of amorphous carbon, respectively, which are typical characteristic peaks of biochar. In addition, FeBC contains abundant minerals, mainly including goethite, chromite, and magnetite, etc. Except for goethite, chromite and magnetite are both stable iron ore types that are not easily decomposed. After FJH treatment, FeNM shows enhanced asymmetric (002) and (100) peaks, indicating that the graphitization degree of FeNM is much stronger than that of FeBC. This is because the stable chromite and magnetite in FeBC decompose and recombine at extremely high temperatures, forming more goethite, making it easier to dissolve free iron in the soil for plant absorption and utilization than iron - based biochar and nano - zero - valent iron materials (see Figure 5 ). Figure 5 In Figure 5 , FeNM can dissolve out more iron ions. The main reason is that the solubility of goethite is lower than that of chromite and magnetite.

[0049] In contrast, using rubber as the raw material and FeSO4 as the iron source, its XRD pattern does not show the goethite peak, but shows the peaks of FeS and iron nitride, both of which are iron phases that are not easily soluble. At the same time, based on the XPS spectrum ( Figure 3 ), the Fe content in FeNM is 1.59%, while the Fe content in the rubber + FeSO4 carbonized and flash - evaporated is only 0.2%, and its XPS total spectrum also has only extremely low Fe 2p peaks, indicating that FeSO4 is not suitable for this step. Replacing coffee grounds with corn straw and still using FeCl3 as the iron source can obtain a higher Fe 2p peak than FeSO4, but it is still lower compared to using coffee grounds as the raw material. The Fe content is 1.09%. The above results illustrate the necessity of using coffee grounds as the raw material and FeCl3 as the iron source in this process, and emphasize the significant advantage of the synergistic effect of the coffee grounds + FeCl3 combination compared to other combinations.

[0050] Figure 4It was shown that the hydrodynamic diameters of nZVI, FeBC, and FeNM were 3260 ± 212 nm, 829.13 ± 97.88 nm, and 705.55 ± 67.32 nm, respectively, indicating that FeNM had the smallest particle size and could be more readily absorbed and utilized by plant roots. The Zeta potentials of the materials were -0.48 mV, 37.37, and 33.79 mV, respectively. The larger the absolute value of the Zeta potential, the higher the charge density on the particle surface, the greater the electrostatic repulsion between particles, the less likely the particles are to aggregate, and the more stable the system. Therefore, it can be seen that the nZVI aqueous solution was the least stable and had the greatest tendency to agglomerate, while FeBC and FeNM were relatively stable, with comparable stabilities. However, FeNM had a smaller particle size and exhibited good dispersibility and absorption effects in aqueous solutions.

[0051] The total nitrogen content in plants after 90 days of soybean growth was measured ( Figure 6 ). For both the total nitrogen content in leaves and roots, the FeNM treatment had the highest value. Compared with the control treatment (Control), the total nitrogen in roots and leaves increased by 22.33% and 19.22%, respectively, indicating that the application of FeNM could effectively promote biological nitrogen fixation in soybeans.

[0052] The number of soybean grains and biomass after 115 days of treatment with the three materials were measured ( Figure 7 ). The results showed that the number of grains and biomass of all iron-based material treatments were higher than those of the control, and among them, the FeNM treatment had the highest number of grains and biomass. Compared with the control treatment, the number of soybean grains in the soil treated with FeNM increased by 44%, and the grain weight increased by 45.9%, achieving a significant increase in yield.

[0053] The types and contents of free amino acids in soybean grains of the control group and the FeNM treatment were compared ( Figure 8 ). For both the types and contents of amino acids, the FeNM treatment was higher than that of the control. Amino acids such as threonine (Thr), cysteine (Cys), and methionine (Met) play key roles in protein synthesis and functional regulation, and their contents were significantly increased after the FeNM treatment, which significantly improved the quality of soybeans.

[0054] Soybean root nodules play an important role in the nitrogen fixation process of soybeans, converting free nitrogen in the air into ammonia and providing nitrogen nutrition for soybeans. Leghemoglobin in root nodules is a protein present in root nodule cells, and it mainly plays a role in regulating the oxygen concentration during the growth of soybeans because too high an oxygen concentration will inactivate nitrogenase. Figure 9 It was shown that the content of leghemoglobin in root nodules of the FeNM treatment was the highest, increasing by 11.90% compared with the control treatment, which could effectively maintain the oxygen balance in soybean plants and thus achieve effective yield increase in soybeans.

[0055] The Fe element plays an important role in photosynthesis. Iron can participate in photosynthetic electron transport, affect chlorophyll synthesis, and participate in the regulation of enzyme activity in photosynthesis, etc. The fitting results of the light response curves of soybean leaves at 90 days are as Figure 10 shown in and Table 1. In the table, R 2 are all higher than 0.99, showing a good correlation. The parameter α reflects the light energy utilization efficiency, ETR max is the maximum electron transport efficiency, and E k is the minimum saturation light intensity, which reflects the tolerance of the sample to strong light. The ETR max and E k of FeNM are both the largest, indicating its maximum electron transport efficiency and the strongest tolerance to strong light. This shows that FeNM can efficiently improve the key parameters of soybean photosynthesis, enhance the ability of soybeans to capture and convert light energy, enable them to maintain efficient photosynthesis in strong light environments, and contribute to improving the environmental adaptability and production potential of soybeans.

[0056] Table 1 Light response curve parameters of soybean leaves under different treatments

[0057]

[0058] Matters not described in the present invention are applicable to the prior art.

Claims

1. A method for preparing iron-based nano-fertilizer based on Joule heating flash evaporation technology, characterized in that, The preparation process of the method is as follows: 1) Preparation of iron-based biochar: Dissolve FeCl3 and dried coffee ground powder in deionized water at a mass ratio of (0.5 - 1.5):2, and stir at room temperature for 10 - 14 h. Then let it stand until solid-liquid separation occurs, pour out the excess upper liquid, leave the solid precipitate, and dry it. The dried solid is loaded into a crucible, compacted, and placed in a muffle furnace for oxygen-limited pyrolysis at 700 - 1000 °C. After cooling to room temperature, grind and sieve it to obtain iron-based biochar FeBC with a resistance less than 300 Ω. 2) Load the iron-based biochar FeBC into a quartz tube for Joule flash evaporation. Set the voltage of the Joule flash evaporation equipment to 150 - 170 V and the capacitance to 220 - 260 mF to obtain coffee ground-derived iron-based nanomaterial FeNM, which is the iron-based nano-fertilizer.

2. The method according to claim 1, wherein In step 1), the ratio of the mass of the mixture after mixing FeCl3 and coffee ground powder to deionized water is: 40 - 60 g of the mixture: 0.8 - 1.2 L of deionized water.

3. An iron-based nano-fertilizer is prepared by the method described in claim 1 or 2.

4. The iron-based nano-fertilizer according to claim 3, characterized in that, In the said FeNM, goethite is the main component, the Fe content is not less than 1.40%, the hydrodynamic diameter of FeNM is not more than 800 nm, the absolute value of the Zeta potential is 30 - 34 mV. Preferably, the hydrodynamic diameter of FeNM is 705.55 ± 67.32 nm and the Zeta potential is 33.79 mV, and it stably exists in the aqueous solution.

5. Use of the iron-based nano-fertilizer according to claim 3 or 4 in biological nitrogen fixation and yield increase of soybeans, characterized in that, Mix 80 - 120 mg / kg of FeNM evenly with 1.9 - 2.2 kg of soil, water it to 55% - 65% of the maximum water content of the soil, balance for 10 days, and bury soybean seeds in it for soybean planting.

6. The application according to claim 5, characterized in that, Maintain the field water holding capacity at 55% - 65%. At 90 days, the total nitrogen content in the leaves and roots is above 28% and above 15% respectively, which can effectively promote biological nitrogen fixation of soybeans. The content of leghemoglobin in the root nodules treated with FeNM is 6.8 mg / g, which can effectively maintain the oxygen balance in the soybean plant and achieve effective yield increase of soybeans. The types of free amino acids in the soybean grains treated with FeNM are more, and the contents of threonine (Thr), cysteine (Cys), and methionine (Met) are significantly increased, improving the quality of soybeans. The light response curve parameters of FeNM-treated soybean leaves under light intensities of 0 to 1640 μmol / m 2 s show that the maximum electron transfer efficiency ETR max is not less than 150, and at the same time the minimum saturation light intensity E k is not less than 620. These are key parameters that can efficiently improve soybean photosynthesis, enhance the ability of soybeans to capture and convert light energy, enable them to maintain efficient photosynthesis in strong light environments, and contribute to improving the environmental adaptability and production potential of soybeans; When detecting at 115 days, the number of grains and the grain weight of the grains are greater than 9 and greater than 5 g / plant respectively, achieving a substantial yield increase.

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