A graphene-based material for use as a slow-release fertilizer and a method for preparing and using the same

Abstract

The application discloses a graphene-based material used as slow-release fertilizer and a preparation method and application thereof. The synthesized reduced graphene oxide film can be used as a novel trace metal element carrier and has the unique performance of slowly releasing ions, can make the metal elements be efficiently and slowly released to soil and be converted into the exchangeable state which can be easily absorbed by plants, and is especially beneficial to the establishment of high-nutrition soil, and provides favorable conditions for subsequent planting of crops rich in nutrition elements.

Description

Technical Field

[0001] This invention belongs to the field of slow-release fertilizer technology, specifically relating to a graphene-based material used as a slow-release fertilizer, its preparation method, and its application. Background Technology

[0002] Membrane technology is one of the most important high technologies of the 21st century, and it is now widely used in agriculture, chemical industry, environmental monitoring, biomedicine, and charge conduction. The membrane loading, selectivity, and transmembrane flux depend on the membrane pore size, chemical function, and applied pressure. Based on the principles of membrane adsorption-controlled release, charge conduction, and controlled release, membrane technology is now more widely used in agriculture for pesticide enhancement, slow release and precision delivery of fertilizers, agricultural irrigation, and crop quality optimization.

[0003] Graphene is considered by many scientists to be a revolutionary material of the future. It contains π-electron-rich aromatic rings, with sp... 2 Two-dimensional carbon nanomaterials, composed of hexagonal honeycomb lattices formed by hybrid orbitals, include monolayer graphene-based films, which can be considered the thinnest films in the world. Graphene oxide, as an important derivative of graphene-based materials, possesses a large surface area and high functional group content. The introduction of oxygen-containing groups not only endows graphene oxide with chemical stability but also provides surface modification active sites and a large specific surface area for the synthesis of graphene-based and graphene oxide-based materials, and serves as a preferential adsorption site for many ions. Unlike two-dimensional planes, three-dimensional graphene oxide spheres not only have high free volume and excellent compressibility but can also achieve close packing of thin films without reducing the effective specific surface area. Researchers have demonstrated that composite three-dimensional wrinkled graphene oxide exhibits excellent high water permeability, selectivity, and photoreactivity. Furthermore, the addition of silver ions based on the above research enhances its high stability, anti-aggregation properties, and photocatalytic performance.

[0004] Besides major nutrients such as nitrogen, phosphorus, and potassium, plant growth and soil health also depend on micronutrients such as iron (Fe), manganese (Mn), zinc (Zn), boron (B), molybdenum (Mo), and copper (Cu). In agricultural applications, adding micronutrients can not only compensate for nutrient deficiencies but also improve soil productivity. For example, zinc plays a crucial role in plant photosynthesis, sugar production, and sugar consumption, while boron plays a key role in regulating plant hormone levels and promoting normal plant growth. Micronutrients are usually added to the soil in the form of chemical salts such as oxides, sulfates, chloride ions, and nitrates. However, adding them in this form results in a rapid dissolution rate, causing them to be washed into deeper soil layers, preventing plants from obtaining nutrients.

[0005] Therefore, it is essential to design a new material with controlled-release fertilizer properties to improve the effectiveness of micronutrients by controlling the release rate of nutrients. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the object of the present invention is to overcome the shortcomings of the prior art and provide a graphene-based material for use as a slow-release fertilizer.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including,

[0010] A reduced graphene oxide-based film, and trace metal elements loaded on the surface of the reduced graphene oxide-based film; wherein the loading amount of the trace metal elements based on the reduced graphene oxide-based film is 8% to 50%.

[0011] As a preferred embodiment of the graphene-based material used as a slow-release fertilizer according to the present invention, the loading of the trace metal elements based on the reduced graphene oxide-based film is 10% to 35%.

[0012] As a preferred embodiment of the graphene-based material used as a slow-release fertilizer according to the present invention, the trace metal elements include one or more of zinc, iron, copper, manganese, cobalt, molybdenum, chromium, nickel, vanadium, and tin.

[0013] As a preferred embodiment of the graphene-based material used as a slow-release fertilizer according to the present invention, the trace metal elements include one or more of zinc, iron, copper, and manganese.

[0014] Another object of the present invention is to provide a method for preparing graphene-based materials for use as slow-release fertilizers.

[0015] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including,

[0016] A mixture of graphene oxide aqueous solution and trace metal elements is atomized and treated. The atomized droplets are then transported to a tubular alumina reactor by nitrogen gas and reacted at a high temperature of 50℃~450℃ for 1~10s. The reactants are loaded onto a cellulose ester matrix inside the membrane filter through a membrane filter, thus obtaining a graphene oxide-based material loaded with trace metal elements.

[0017] The amount of trace metal element added is 8 to 50 mg / L per 100 mg / L of graphene oxide aqueous solution.

[0018] Preferably, the high-temperature reaction temperature is 100℃~300℃ and the high-temperature reaction time is 1~3s.

[0019] In a preferred embodiment of the method for preparing the graphene-based material used as a slow-release fertilizer according to the present invention, the atomization is performed at a pressure of 10-20 psi at room temperature.

[0020] Preferably, the atomization is performed at room temperature and a pressure of 13.5 to 14.5 psi.

[0021] In a preferred embodiment of the method for preparing the graphene-based material used as a slow-release fertilizer according to the present invention, the atomized droplets are then transported to a tubular alumina reactor by nitrogen gas, wherein the transport flow rate is 10-20 L / min.

[0022] Preferably, the conveying flow rate is 12-13 L / min.

[0023] In a preferred embodiment of the method for preparing the graphene-based material used as a slow-release fertilizer according to the present invention, the method for preparing the aqueous solution of graphene oxide includes:

[0024] Expanded graphite was dispersed in concentrated sulfuric acid and cooled in an ice-water bath. Sodium nitrate and potassium permanganate were then slowly added to the mixture, which was then refrigerated to obtain mixture I.

[0025] Mixture I was stirred at a constant temperature and then cooled in an ice-water bath. Deionized water was added to dilute it, and then 10% hydrogen peroxide was added dropwise until no more bubbles were generated, resulting in a suspension.

[0026] The suspension was filtered and washed sequentially with hydrochloric acid solution and deionized water. The filtrate was then placed in a dialysis bag, dispersed with deionized water, and immersed in deionized water for dialysis until impurity ions in the suspension were removed. After dialysis, the supernatant was removed, deionized water was added, and the mixture was ultrasonically dispersed and centrifuged to obtain an aqueous solution of graphene oxide.

[0027] Another object of the present invention is to provide an application of graphene-based materials in improving the nutrient content of soil crops.

[0028] Another object of the present invention is to provide an application of graphene-based materials in the construction of highly nutrient-rich soils.

[0029] Beneficial effects of this invention:

[0030] The graphene-based material provided by this invention, when used as a slow-release fertilizer, has the unique property of slowly releasing ions as a novel carrier of trace metal elements. This enables trace metal elements to be efficiently and slowly released into the soil and transformed into an exchangeable state that is easily absorbed by plants. This is not only particularly beneficial for establishing nutrient-rich soil, but also provides favorable conditions for the subsequent planting of nutrient-rich crops. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0032] Figure 1 The image shows TEM images of the zinc-loaded graphene oxide material prepared in Example 1 of this invention before and after reduction.

[0033] Figure 2 This is a curve fitting diagram of the C1s spectrum of the graphene oxide material prepared by loading zinc element before and after reduction in Example 1 of the present invention.

[0034] Figure 3 The images show TEM images of the graphene-based material prepared in Comparative Example 1 of this invention before and after loading zinc.

[0035] Figure 4 The images show TEM images of the graphene-based material prepared in Comparative Example 2 of this invention before and after loading zinc.

[0036] Figure 5 The graph shows the release rates of different graphene-based materials obtained in this invention. Detailed Implementation

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0039] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0040] The aqueous solution of graphene oxide used in the specific embodiments of this invention was synthesized according to the following method:

[0041] 1g of expanded graphite was dispersed in 75mL of 98% concentrated sulfuric acid, cooled to 0°C in an ice-water bath, and 2.5g of sodium nitrate and 15g of potassium permanganate were slowly added. The mixture was then refrigerated at 4°C for 24 hours.

[0042] The above mixture was stirred at 35°C for 2 hours, cooled in an ice-water bath, and then diluted with 917 mL of deionized water. 10% hydrogen peroxide was added dropwise until no more bubbles were generated, resulting in a suspension.

[0043] The above suspension was filtered and washed three times with 20% hydrochloric acid solution and deionized water. The resulting filtrate was placed in a dialysis bag, dispersed with deionized water, and dialyzed in deionized water for seven days. After dialysis, the supernatant was removed, deionized water was added, and the mixture was ultrasonically dispersed for 4 hours and centrifuged for 2 hours to obtain an aqueous solution of graphene oxide.

[0044] Unless otherwise specified, all raw materials and reagents used in this invention are commercially available in the field.

[0045] The atomizer used in this invention is a colliison atomizer, and the tubular alumina reactor is a tubular aerosol reactor (FuAR, 1m×25mmID).

[0046] Example 1

[0047] This embodiment provides a method for preparing zinc-loaded reduced graphene oxide, specifically as follows:

[0048] 1) The graphene oxide aqueous solution and zinc powder were mixed at a ratio of 16.7 mg / L of zinc element per 100 mg / L of graphene oxide aqueous solution and then atomized at room temperature with an atomization pressure of 14 psi.

[0049] 2) The atomized droplets are then transported to a tubular alumina reactor by nitrogen at a flow rate of 12.4 L / min. The reaction is carried out at 200 °C for 2 s. The reactants are loaded onto the cellulose ester matrix inside the membrane filter through the membrane filter, thus obtaining zinc-loaded reduced graphene oxide material, denoted as RGO--Zn1.

[0050] Figure 1 (a) is a TEM image of the zinc-loaded reduced graphene oxide material prepared in this embodiment. Figure 1 (b) is a diagram of reduced graphene oxide without zinc loading prepared by the method of this embodiment. It can be seen that after loading zinc, the cross-section of the material has a laminated microstructure. Figure 2 (a) is a curve fitting diagram of the C1s spectrum of the material prepared in this embodiment; Figure 2 (b) is a curve fitting diagram of the C1s spectrum of the unloaded zinc-containing reduced graphene oxide prepared according to the method of this embodiment. It can be seen that after the adsorption of zinc, the corresponding peak appeared in the measured spectrum of the RGO--Zn1 material, which confirms that zinc ions were successfully attached to the reduced graphene oxide film. The content of CC groups increased, the content of CO groups decreased, and the binding of the C= peak shifted to a higher binding energy, which proves that the metal ions were loaded on the reduced graphene oxide film and adsorbed at the wrinkles of the reduced graphene oxide.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that the high-temperature reaction temperature in step 2) is adjusted to 400°C, while the remaining steps are the same as in Example 1. Specifically:

[0053] 1) The graphene oxide aqueous solution and zinc powder were mixed at a ratio of 16.7 mg / L of zinc element per 100 mg / L of graphene oxide aqueous solution and then atomized at room temperature with an atomization pressure of 14 psi.

[0054] 2) The atomized droplets are then transported to a tubular alumina reactor with nitrogen at a flow rate of 12.4 L / min. The reactor is reacted at 400°C for 2 seconds. The reactants are then loaded onto a cellulose ester matrix inside a membrane filter, thus obtaining a zinc-loaded three-dimensional graphene oxide material, denoted as CGO--Zn1. Figure 3 The TEM image of the zinc-loaded graphene oxide-based material prepared in this comparative example shows that the graphene spheres with zinc ions form an isotropic black solid with a rough microstructure on both the surface and cross-section.

[0055] Comparative Example 2

[0056] This comparative example provides a method for preparing a graphene-based material loaded with zinc, specifically as follows:

[0057] The graphene oxide aqueous solution and zinc were mixed evenly at a ratio of 16.7 mg / L of zinc per 100 mg / L of graphene oxide aqueous solution to obtain a uniformly dispersed mixed aqueous solution.

[0058] The mixed aqueous solution was dropped onto a cellulose ester matrix using a dropper, and then dried to form a film, thus obtaining the zinc-loaded graphene oxide material, denoted as GO--Zn1. Figure 4 The TEM image shows the zinc-loaded graphene-based material prepared in this comparative example. It can be seen that this comparative example produces an anisotropic, very smooth, and almost featureless surface.

[0059] Study on the sustained-release properties of materials

[0060] The dissolution rate of zinc was determined using the vacuum filtration method. Since preliminary experiments revealed significant differences in dissolution among the samples within the first 600 minutes, the amount of zinc released over 600 minutes was used to represent the sustained-release effect. Lower release amounts indicated better sustained-release effects. The results are shown in Table 1.

[0061] Table 1

[0062]

[0063] Furthermore, inductively coupled plasma optical emission spectrometry (ICP-MS) was used to further investigate the ion release rates of the materials. The prepared RGO-Zn1, CGO-Zn1, and GO-Zn1 materials were freeze-dried, ground into powder, shaped into small cubes using a press, and then analyzed by ICP-MS. The release rates of each material are shown below. Figure 5 As shown.

[0064] From Table 1 and Figure 5 It can be seen that although the evaluation methods are different, the zinc loaded on the GO-Zn1 material is released instantaneously upon dissolution, while the zinc loaded on the RGO-Zn1 and CGO-Zn1 materials is released slowly. This indicates that the GO-Zn1 material does not have a sustained-release effect, while the RGO-Zn1 and CGO-Zn1 materials do have sustained-release properties.

[0065] Study on the stability performance of soil

[0066] The zinc-loaded graphene-based materials prepared by RGO-Zn1, CGO-Zn1, and GO-Zn1 in the above examples and comparative examples were ground into powder and used as zinc fertilizer. Their stability in soil application was investigated by comparing them with commercially available zinc fertilizer ZnSO4 (ZnSO4 purity ≥ 95%, content ≥ 35%). The specific experimental methods are as follows:

[0067] A 20ml glass syringe was used as the container for the simulated soil column. Each column was filled with a soil-river sand mixture to a mark of 10ml. Then, zinc fertilizer was added to the surface of the soil column at a dosage of 10mg. The mixture was stirred in a glass beaker, and the leachate was collected in a beaker. Pure water was added to the simulated soil column until it was saturated. After standing for 12 hours, leaching experiments were started. Leaching experiments were conducted every 12 hours for a total of 7 times. The filtrate was collected, and the zinc ion content in the leachate was measured. The results are shown in Table 2.

[0068] Table 2

[0069]

[0070] As shown in Table 2, the graphene-based zinc-loaded materials of this invention effectively increase the zinc content in the soil. While commercially available zinc fertilizers can also increase the zinc content in the soil to some extent, these fertilizers are sulfides, and the sulfate ions they contain react with certain inorganic ions in the environment, leading to the formation of toxic and harmful byproducts. Although GO-Zn1 materials can exist stably in the soil, as previous studies have shown, GO-Zn1 does not possess slow-release properties and is therefore unsuitable as a slow-release carrier for trace elements. In contrast, RGO-Zn1 and GGO-Zn1 exhibit good stability in the soil and possess slow-release properties, making them suitable as slow-release carriers for trace elements.

[0071] Research on improving soil crop nutrient performance

[0072] Water, ZnSO4, GO-Zn1, RGO-Zn1, and CGO-Zn1 were added to the soil and ground into granules. The granules were diluted with water to obtain an aqueous solution. The soil was stirred to ensure even distribution of the solution. The 'Nipponbare' rice variety was selected, and the seeds were germinated in a constant temperature and humidity chamber. Once the seeds showed signs of sprouting, they were placed in germination bags and transferred to a light-curing incubator. After 10 days, rice seedlings of the same height were transplanted into the prepared soil. After transplanting, the seedlings were continuously watered with the experimental solution, ensuring the water level was approximately 2 cm above the soil surface. After 14 days, rice seedlings were obtained. The seedling samples were processed using microwave digestion with nitric acid. The zinc content in the rice seedlings was determined using ICP-MS, and the results are shown in Table 3.

[0073] Table 3

[0074]

[0075]

[0076] Table 3 shows that the zinc content in rice seedlings grown using GGO-Zn1 as a carrier was too low. This may be due to the soil particles' adsorption of GGO-Zn1 limiting its transformation and movement from the soil to the plant, or the zinc ion adsorption being controlled by the strong adhesion of oxygen-containing functional groups on the CGO surface, leading to excessive zinc ions being strongly adsorbed on the CGO surface and unable to act quickly within the plant. In contrast, the rice grown using RGO-Zn1 had the highest zinc content at 229.1 mg / kg, significantly higher than that of rice grown with traditional zinc fertilizers. Therefore, this newly developed material, RGO-Zn, can be used to develop controlled-release fertilizers to provide nutrients to plants, improve plant productivity, and minimize nutrient loss.

[0077] Example 2

[0078] This embodiment was used to investigate the effect of micronutrient loading on the performance of the material as a slow-release fertilizer. Specifically, the amount of zinc added in step 1) of Example 1 was adjusted to 8.3, 11.1, 16.7, 33.3, and 50 mg / L of zinc added per 100 mg / L of graphene oxide aqueous solution. The remaining steps were the same as in Example 1. RGO-Zn with different zinc content was obtained in this embodiment. The slow-release performance and the ability to improve soil crop nutrient performance of different materials in this embodiment were determined by vacuum filtration. The results are shown in Table 4.

[0079] Table 4

[0080]

[0081] As can be seen from Table 4, the zinc loading amount did not have a significant effect on its slow release rate. The reason for the significant increase in release when the loading amount was 50% is presumably because the loading saturation of the carrier material had been reached at this point, so the excess zinc ions were unstable and prone to burst release. In addition, the high zinc loading amount did not further enhance the nutrients it provided to soil crops.

[0082] Example 3

[0083] This embodiment was used to investigate the effect of the preparation temperature of RGO-Zn material on the performance of the material as a slow-release fertilizer. Specifically, the high-temperature reaction temperature in step 2) of Example 1 was adjusted to 100℃, 150℃, 200℃, 250℃, and 300℃, while the remaining steps were the same as in Example 1. RGO-Zn synthesized at different temperatures in this embodiment was obtained. The slow-release performance and the ability to improve soil crop nutrients of different materials in this embodiment were determined by vacuum filtration. The results are shown in Table 5.

[0084] Table 4

[0085]

[0086] As can be seen from Table 5, graphene materials loaded with zinc ions have better slow-release performance under high temperature conditions. This is because graphene at high temperature can exhibit better adsorption stability. However, when applied to soil crops, the nutrient absorption effect of crops is lower at higher temperatures. This is because oxygen-containing functional groups at high temperatures cause zinc ions to be strongly adsorbed on the surface of the carrier material, thus preventing them from acting quickly on crops.

[0087] Example 4

[0088] This embodiment is used to explore the feasibility of preparing slow-release fertilizers by loading other types of trace elements using the method of the present invention. Specifically, the zinc element in step 1) of Example 1 is adjusted to iron, copper, manganese, iodine, selenium and fluorine respectively. The remaining steps are the same as in Example 1. RGO-V materials loaded with different trace elements are obtained in this embodiment. The slow-release performance of different materials in this embodiment is determined by vacuum filtration method. The results are shown in Table 6.

[0089] Table 6

[0090]

[0091]

[0092] As can be seen from Table 6, the method of the present invention is applicable to most metallic trace elements, but has no obvious sustained-release effect on non-metallic trace elements.

[0093] Example 5

[0094] 1) The graphene oxide aqueous solution and zinc powder were mixed at a ratio of 16.7 mg / L of zinc element per 100 mg / L of graphene oxide aqueous solution and then atomized at room temperature with an atomization pressure of 10 psi.

[0095] 2) The atomized droplets are then transported to a tubular alumina reactor by nitrogen at a flow rate of 10 L / min. The reaction is carried out at 200°C for 1 second. The reactants are loaded onto the cellulose ester matrix inside the membrane filter through a membrane filter, thus obtaining zinc-loaded reduced graphene oxide material, denoted as RGO--Zn2.

[0096] Example 6

[0097] 1) The graphene oxide aqueous solution and zinc powder were mixed at a ratio of 16.7 mg / L of zinc element per 100 mg / L of graphene oxide aqueous solution and then atomized at room temperature with an atomization pressure of 18 psi.

[0098] 2) The atomized droplets are then transported to a tubular alumina reactor by nitrogen at a flow rate of 18 L / min. The reaction is carried out at 200°C for 5 s. The reactants are loaded onto the cellulose ester matrix inside the membrane filter through a membrane filter, thus obtaining zinc-loaded reduced graphene oxide material, denoted as RGO--Zn3.

[0099] Example 7

[0100] 1) The graphene oxide aqueous solution and zinc powder were mixed at a ratio of 16.7 mg / L of zinc element per 100 mg / L of graphene oxide aqueous solution and then atomized at room temperature with an atomization pressure of 16 psi.

[0101] 2) The atomized droplets are then transported to a tubular alumina reactor by nitrogen at a flow rate of 12 L / min. The reaction is carried out at 200°C for 2 seconds. The reactants are loaded onto the cellulose ester matrix inside the membrane filter through a membrane filter, thus obtaining zinc-loaded reduced graphene oxide material, denoted as RGO--Zn4.

[0102] Example 8

[0103] 1) The graphene oxide aqueous solution and zinc powder were mixed at a ratio of 16.7 mg / L of zinc element per 100 mg / L of graphene oxide aqueous solution and then atomized at room temperature with an atomization pressure of 12 psi.

[0104] 2) The atomized droplets are then transported to a tubular alumina reactor by nitrogen at a flow rate of 16 L / min. The reaction is carried out at 200°C for 3 seconds. The reactants are loaded onto the cellulose ester matrix inside the membrane filter through a membrane filter, thus obtaining zinc-loaded reduced graphene oxide material, denoted as RGO--Zn5.

[0105] The sustained-release effect of the reduced graphene oxide materials prepared in Examples 5 to 8 was tested. The test results showed that the RGO--Zn2 to RGO--Zn5 obtained in Examples 5 to 8 of the present invention all had sustained-release performance comparable to RGO--Zn1 in Example 1.

[0106] In summary, the graphene-based material provided by this invention, when used as a slow-release fertilizer, has the unique property of slowly releasing ions as a novel carrier of trace metal elements. This enables trace metal elements to be efficiently and slowly released into the soil and converted into an exchangeable state that is easily absorbed by plants. This is not only particularly beneficial for establishing nutrient-rich soil, but also provides favorable conditions for the subsequent planting of nutrient-rich crops.

[0107] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A graphene-based material for use as a slow-release fertilizer, characterized in that: include, A reduced graphene oxide-based film, and trace metal elements loaded on the surface of the reduced graphene oxide-based film; wherein the loading amount of the trace metal elements based on the reduced graphene oxide-based film is 8% to 50%. The preparation method of the graphene-based material is as follows: A mixture of graphene oxide aqueous solution and trace metal elements is atomized and treated. The atomized droplets are then transported to a tubular alumina reactor by nitrogen gas and reacted at a high temperature of 200℃~300℃ for 1~10s. The reactants are loaded onto a cellulose ester matrix inside the membrane filter through a membrane filter, thus obtaining a graphene oxide-based material loaded with trace metal elements. The amount of trace metal element added is 8 to 50 mg / L per 100 mg / L of graphene oxide aqueous solution.

2. The graphene oxide-based material used as a slow-release fertilizer as described in claim 1, characterized in that: The loading of the trace metal elements on the reduced graphene oxide-based film is 10% to 35%.

3. The graphene-based material used as a slow-release fertilizer as described in claim 1, characterized in that: The trace metal elements include one or more of zinc, iron, copper, manganese, cobalt, molybdenum, chromium, nickel, vanadium, and tin.

4. The graphene-based material used as a slow-release fertilizer as described in claim 1, characterized in that: The trace metal elements include one or more of zinc, iron, copper, and manganese.

5. The graphene-based material used as a slow-release fertilizer as described in claim 1, characterized in that: The atomization is performed at room temperature and a pressure of 10–20 psi.

6. The graphene-based material used as a slow-release fertilizer as described in claim 1, characterized in that: The atomized droplets are then transported to a tubular alumina reactor via nitrogen gas at a flow rate of 10–20 L / min.

7. The graphene-based material used as a slow-release fertilizer as described in claim 1, characterized in that: The method for preparing the aqueous solution of graphene oxide includes, Expanded graphite was dispersed in concentrated sulfuric acid and cooled in an ice-water bath. Sodium nitrate and potassium permanganate were then slowly added to the mixture, which was then refrigerated to obtain mixture I. Mixture I was stirred at a constant temperature and then cooled in an ice-water bath. Deionized water was added to dilute it, and hydrogen peroxide was added dropwise until no more bubbles were generated, resulting in a suspension. The suspension was filtered and washed sequentially with hydrochloric acid solution and deionized water. The filtrate was then placed in a dialysis bag, dispersed with deionized water, and immersed in deionized water for dialysis until impurity ions in the suspension were removed. After dialysis, the supernatant was removed, deionized water was added, and the mixture was ultrasonically dispersed and centrifuged to obtain an aqueous solution of graphene oxide.

8. The application of graphene-based materials used as slow-release fertilizers as described in any one of claims 1 to 4 in improving soil crop nutrient content.

9. The application of graphene-based materials used as slow-release fertilizers as described in any one of claims 1 to 4 in the establishment of highly nutrient-rich soils.

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