A pH-responsive, magnesium-iron-rich, double-coated controlled-release fertilizer and its preparation method

Abstract

This invention provides a pH-responsive, magnesium- and iron-rich, double-coated controlled-release fertilizer and its preparation method, belonging to the field of fertilizer preparation technology. The controlled-release fertilizer provided by this invention includes a fertilizer core, an inner ethyl cellulose membrane coating, and an outer shell. The fertilizer core is composed of urea, clay, and sodium polyacrylate. The outer shell covers the surface of the inner membrane and is composed of sequentially stacked iron-rich material layers and magnesium-rich gel layers. This invention employs an ammonia-etched silica template method to in-situ construct magnesium, a medium-element element, within a nano-silica mesoporous framework, forming intelligent microcapsules with pH-responsive characteristics. This allows for precise control of magnesium release in acidic soils and slow release in neutral or alkaline soils, improving magnesium nutrient utilization. Simultaneously, an antioxidant ferrous carrier is constructed using ascorbic acid and silicon-based materials, effectively stabilizing the ferrous ion form and overcoming the technical bottleneck of easy oxidation and inactivation in conventional iron fertilizers, thus improving the bioavailability of iron.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fertilizer preparation, and particularly relates to a pH-responsive magnesium-iron-rich double-layer coated controlled-release fertilizer and a preparation method thereof. BACKGROUND

[0002] Traditional coated controlled-release fertilizers mainly rely on the physical barrier effect of polymers to delay nutrient release, but lack an environmental response mechanism, and cannot dynamically adjust the release behavior according to soil conditions (such as pH). pH-sensitive materials such as sodium polyacrylate (PAANa) have been applied in the field of medical sustained-release, but their research in the fertilizer coating system is still insufficient. In the prior art, the combination of functional substances (such as trace elements) and fertilizers mostly adopts mechanical mixing or simple coating processes, which is difficult to achieve directional control of functional substances, and has the problems of complex process and high energy consumption.

[0003] The prior art has the following significant defects: first, ferrous ions (Fe 2+ ) in conventional iron fertilizers are easily oxidized into trivalent iron (Fe 3+ ) which is difficult for plants to absorb, resulting in low utilization rate of iron elements; second, the release of magnesium elements lacks an intelligent response mechanism and cannot be released on demand according to differences in soil pH; third, the combination of functional substances and the coating structure is rough, which not only cannot effectively maintain the stability of trace elements (such as oxidation resistance), but also is difficult to achieve the environment-responsive release of intermediate elements, seriously restricting the improvement of fertilizer nutrient utilization efficiency. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a pH-responsive magnesium-iron-rich double-layer coated controlled-release fertilizer, which has pH response characteristics and can achieve precise regulation and control of the rapid release of magnesium elements in acidic soil and the slow release of magnesium elements in neutral or alkaline soil, thereby improving the utilization rate of magnesium nutrients. At the same time, it can also effectively stabilize the form of ferrous ions, break through the technical bottleneck of the easy oxidation and inactivation of conventional iron fertilizers, and improve the biological effectiveness of iron elements.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0006] The present application provides a pH-responsive magnesium-iron-rich double-layer coated controlled-release fertilizer, which comprises a fertilizer core, an inner layer coating and an outer shell; the fertilizer core is composed of urea, clay and sodium polyacrylate; the inner layer coating is an ethyl cellulose film covering the surface of the fertilizer core; the outer shell covering the surface of the inner layer coating is composed of a layer of iron-rich material and a layer of magnesium-rich gel which are stacked in sequence; the layer of iron-rich material is composed of ORFFF, and the layer of magnesium-rich gel is composed of a PMFF@SA suspension;

[0007] The ORFFF is an ascorbic acid modified Fe(III) / SiO2 composite material, the PMFF@SA suspension is obtained by pouring the PMFF water suspension into a sodium alginate solution, and the PMFF is a pH responsive magnesium element modified nanosilica composite material.

[0008] Preferably, the mass ratio of urea, clay and sodium polyacrylate is (14-16):(290-310):(1.8-2.2), and the diameter of the fertilizer core is 4-6 mm.

[0009] Preferably, the mass of the ethyl cellulose film is 0.3%-0.5% of the mass of the fertilizer core.

[0010] Preferably, the preparation method of the ORFFF comprises the following steps: mixing acetylacetone iron, urea and nanosilica templates according to a mass ratio of (0.17-0.18):(0.48-0.50):(0.09-0.11), and then performing hydrothermal reaction at 180 ℃ for 12 h to obtain Fe(III) / SiO2; mixing Fe(III) / SiO2 and ascorbic acid according to a mass ratio of 1:(2-3) to obtain the ORFFF; and the preparation method of the nanosilica template comprises the following steps: mixing anhydrous ethanol, ammonia water and tetraethyl orthosilicate according to a volume ratio of 27:8:(3.9-4.5) to obtain the nanosilica template.

[0011] Preferably, the preparation method of the PMFF comprises the following steps: mixing anhydrous ethanol, ammonia water and tetraethyl orthosilicate according to a volume ratio of 27:8:(3.9-4.5) to obtain nanosilica templates; mixing the nanosilica templates, magnesium chloride hexahydrate, ammonium chloride and ammonia water, and then performing hydrothermal reaction at 140 ℃ for 10 h to obtain the PMFF.

[0012] Preferably, the mass-volume ratio of the nanosilica templates, magnesium chloride hexahydrate, ammonium chloride and ammonia water is 0.1 g:0.2 g:0.54 g:0.8-1.0 mL.

[0013] Preferably, the mass ratio of PMFF and sodium alginate is 1:3.

[0014] The application further provides a preparation method of the controlled-release fertilizer, comprising the following steps: mixing urea, clay and sodium polyacrylate to granulate to obtain a fertilizer core; dissolving ethyl cellulose in an ethanol solution with a volume fraction of 70% to obtain a coating liquid, and then spraying the coating liquid onto the fertilizer core to obtain a core-coated fertilizer; spraying an ORFFF water suspension onto the surface of the core-coated fertilizer, and then spraying a PMFF@SA suspension onto the surface of the ORFFF layer, and repeating the steps of spraying the ORFFF water suspension first and then spraying the PMFF@SA suspension for 1-3 times to obtain the controlled-release fertilizer.

[0015] Preferably, the spraying amount of the ORFFF water suspension is calculated as 0.05% to 0.1% of the mass of the core-coated fertilizer in terms of iron element.

[0016] Preferably, the spraying amount of the PMFF@SA suspension is 10 mL:100 g in terms of the volume weight ratio of the core-coated fertilizer.

[0017] The present application has the following beneficial effects:

[0018] The pH-responsive magnesium-iron-rich double-layer coated controlled-release fertilizer provided by the present application uses an ammonia etching silicon oxide template method to construct magnesium, a medium element, in a nano-silicon dioxide mesoporous framework in situ, to form intelligent microcapsules with pH response characteristics, to realize precise regulation and control of the rapid release of magnesium in acidic soil and the slow release of magnesium in neutral or alkaline soil, and to improve the utilization rate of magnesium nutrients. Meanwhile, ascorbic acid and silicon-based materials are used to construct an antioxidant ferrous carrier, to effectively stabilize the ferrous ion form, to break through the technical bottleneck of the easy oxidation and inactivation of conventional iron fertilizers, and to improve the biological effectiveness of iron elements. The present application synergistically combines the two technologies to dynamically match the nutrient release law of the fertilizer and the crop demand, to reduce nutrient loss and environmental pollution, and to realize efficient use of medium and trace elements. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The present application is a schematic diagram of the structure of the pH-responsive magnesium-iron-rich double-layer coated controlled-release fertilizer and the principle of its action. DETAILED DESCRIPTION

[0020] The present application provides a pH-responsive magnesium-iron-rich double-layer coated controlled-release fertilizer, which comprises a fertilizer core, an inner layer coating, and an outer shell. The fertilizer core is composed of urea, clay, and sodium polyacrylate. The inner layer coating is an ethyl cellulose film covering the surface of the fertilizer core. The outer shell covering the surface of the inner layer coating is composed of a layer of iron-rich material and a layer of magnesium-rich gel stacked in sequence. The layer of iron-rich material is composed of ORFFF, and the layer of magnesium-rich gel is composed of PMFF@SA suspension.

[0021] The ORFFF is ascorbic acid-modified Fe(III) / SiO2 composite material, and the PMFF@SA suspension is obtained by pouring PMFF water suspension into sodium alginate solution. The PMFF is a pH-responsive magnesium element-modified nano-silicon dioxide composite material.

[0022] The present application is not particularly limited to the specific source of each raw material, and a conventional commercially available product can be used. In the present application, the mass ratio of urea, clay, and sodium polyacrylate is preferably (14-16):(290-310):(1.8-2.2), and more preferably 15:(295-305):(1.9-2.1), and the diameter of the fertilizer core is preferably 4-6 mm. The molecular chain of sodium polyacrylate (PAANa) contains a sodium carboxylate group (-COO - Na + In an acidic soil (pH<6): After the carboxyl group is protonated, the molecular chain repulsion is weakened, the molecular chain hydrogen bond is reorganized to cause swelling, and the micropore channels are formed to accelerate the diffusion of urea; and the clay enhances the particle compressive strength through a silicon-oxygen bond network.

[0023] In the present application, the ethyl cellulose film can be commercially available or self-prepared. In some embodiments of the present application, the ethyl cellulose is preferably derived from a plant straw cellulose etherification modification product, and the preparation method of the ethyl cellulose preferably comprises the following steps: plant straw is treated with a mixed solution of acetic acid and nitric acid to extract cellulose, the cellulose is added to a NaOH solution, and alkaline cellulose is prepared by negative pressure vacuum drying; the alkaline cellulose is mixed with toluene and bromoethane, and the ethyl cellulose is prepared by etherification reaction. In the present application, the plant straw preferably comprises at least one of wheat, rice, and corn. In the present application, the mass of the ethyl cellulose film is preferably 0.3%-0.5% of the mass of the fertilizer core, and more preferably 0.4% of the mass of the fertilizer core. The ethyl cellulose molecule contains an ethoxy group (-OC2H5), a hydrophobic long chain forms a molecular sieve network (pore size 0.5-1 nm), only allows water molecules to slowly penetrate and dissolve urea, prolongs the release period, and physically delays the initial release of urea to avoid seedling burn.

[0024] In the present application, the ORFFF is a pH-responsive antioxidant silicon-based nanocomposite derived from a nano-silicon-based material and ascorbic acid, and the preparation method of the ORFFF preferably comprises the following steps: acetylacetone iron, urea, and nano-silica template are mixed in a mass ratio of (0.17-0.18):(0.48-0.50):(0.09-0.11), hydrothermal reaction is carried out at 180°C for 12h to obtain Fe(III) / SiO2; Fe(III) / SiO2 is mixed with ascorbic acid in a mass ratio of 1:(2-3) to obtain ORFFF. In the present application, the mass ratio of acetylacetone iron, urea, and nano-silica template is preferably (0.17-0.18):0.49:0.10. In the present application, the preparation method of the nano-silica template preferably comprises the following steps: anhydrous ethanol, ammonia water, and tetraethyl orthosilicate are mixed in a volume ratio of 27:8:(3.9-4.5) to obtain the nano-silica template.

[0025] In the present application, ascorbic acid reduces Fe 3+ to Fe 2+ , and forms a chelate, with the oxidation potential reduced from +0.77V to -0.18V, thereby improving the retention rate of Fe 2+ ; by being compounded with silicon-based nanomaterials to form a novel anti-oxidation ferrous-silicon-based nanocomposite, the technical problem that conventional iron fertilizer Fe(II) is easily oxidized into Fe(III) which is difficult for plants to absorb and utilize is solved, and the utilization rate of trace element iron fertilizer is improved; according to XPS characterization, the proportion of Fe 2+ in the ORFFF of the present application is up to 89%, and is still maintained at more than 82% after 30 days of storage at room temperature. The ORFFF directly contacts the environment and preferentially responds to water penetration to release iron.

[0026] In the present application, the PMFF is a silicon-based nanomagnesium fertilizer, and the preparation method of the PMFF preferably comprises the following steps: mixing anhydrous ethanol, ammonia water and tetraethyl orthosilicate according to a volume ratio of 27:8:(3.9~4.5) to obtain a nanosilica template; in the present application, the volume ratio of the anhydrous ethanol, the ammonia water and the tetraethyl orthosilicate is preferably 27:8:(4.1~4.4). Ammonia catalyzes the hydrolysis and condensation of tetraethyl orthosilicate: , to form a mesoporous structure (pore size 5~10 nm) to provide an anchoring site for Mg 2+ . In the present application, magnesium chloride hexahydrate is used as a magnesium source, ammonium chloride provides NH4+ to promote ion exchange, and an ammonia water solution maintains an alkaline environment. The nanosilica template, the magnesium chloride hexahydrate, the ammonium chloride and the ammonia water are mixed, and hydrothermal reaction is carried out at 140℃ for 10h to obtain the PMFF. In the present application, the mass / volume ratio of the nanosilica template, the magnesium chloride hexahydrate, the ammonium chloride and the ammonia water is preferably 0.1g:0.2g:0.54g:0.8~1.0mL.

[0027] In the present application, the PMFF directly constructs magnesium elements in situ on the nanosilica mesoporous framework by ammonia etching the silicon template method to form pH-sensitive microcapsules. In an acidic soil environment (pH<6), H + ion exchange reaction occurs on the carrier framework: , which leads to rapid release of magnesium ions; while in a neutral / alkaline soil (pH≥7), the carrier structure is stable, and Mg 2+ is slowly released by diffusion, so as to automatically adjust the release rate of magnesium elements according to the pH of the soil and improve the utilization rate of magnesium elements.

[0028] The structure of the pH-responsive magnesium-rich and iron-rich double-layer coated controlled-release fertilizer of the present application and the principle of the function are shown in Figure 1 .

[0029] In the present application, the mass ratio of PMFF to sodium alginate is preferably 1:3. The PMFF@SA suspension prepared by pouring the PMFF aqueous suspension into the sodium alginate solution is used as the outer shell, and the-COO of sodium alginate reacts with the Ca 2+ Gelation: ; form a protective layer to delay the decomposition of PMFF.

[0030] The present application directly constructs the medium element magnesium in situ on nanosilica by using ammonia etching silicon oxide template method, and loads the magnesium in microcapsules, and modifies the coating layer of the microcapsules, so that the microcapsules can have sensitivity to pH, can automatically release magnesium element according to different pH, and improves the nutrient utilization rate of magnesium element. The ascorbic acid and silicon-based nanomaterials are compounded to form a new type of antioxidant ferrous-silicon-based nanocomposite, which solves the problem that the conventional Fe (II) is easily oxidized into Fe (III) which is difficult for plants to absorb and utilize, and improves the fertilizer utilization rate of trace element iron.

[0031] The present application also provides a preparation method of the controlled-release fertilizer, comprising the following steps: mixing urea, clay and sodium polyacrylate to granulate to obtain a fertilizer core; dissolving ethyl cellulose in an ethanol solution with a volume fraction of 70% to obtain a coating liquid, spraying the coating liquid onto the fertilizer core to obtain a core-coated fertilizer; spraying an ORFFF aqueous suspension onto the surface of the core-coated fertilizer, and then spraying a PMFF@SA suspension onto the surface of the ORFFF layer, repeating the steps of spraying the ORFFF aqueous suspension and then spraying the PMFF@SA suspension for 1-3 times to obtain the controlled-release fertilizer.

[0032] In the present application, the spraying amount of the ORFFF aqueous suspension is calculated according to 0.05%-0.1% of the mass of the iron element in the core-coated fertilizer, and the spraying amount here refers to the total spraying amount of all times. The spraying amount of the PMFF@SA suspension is preferably 10 mL:100 g of the volume weight ratio of the core-coated fertilizer, and the spraying amount here refers to the total spraying amount of all times.

[0033] The technical solutions provided by the present application will be described in detail below in combination with embodiments, but they should not be understood as limiting the scope of protection of the present application.

[0034] In the following examples, if not specifically stated, the conventional methods are used.

[0035] In the following examples, the materials, reagents, etc. used, if not specifically stated, can be obtained from commercial channels.

[0036] Example 1

[0037] The application discloses a pH-responsive magnesium-iron-rich double-layer coated controlled-release fertilizer, which is composed of a fertilizer core, an inner layer coating and an outer layer shell; the fertilizer core is composed of urea, clay and sodium polyacrylate; the inner layer coating is an ethyl cellulose film covering the surface of the fertilizer core; the outer layer shell covering the surface of the inner layer coating is composed of a stacked iron-rich material layer and a magnesium-rich gel layer; the iron-rich material layer is composed of ORFFF, and the magnesium-rich gel layer is composed of a PMFF@SA suspension; the ORFFF is an ascorbic acid modified Fe(III) / SiO2 composite material, the PMFF@SA suspension is obtained by pouring PMFF water suspension into a sodium alginate solution, and the PMFF is a pH-responsive magnesium element modified nanosilica composite material.

[0038] The preparation method is as follows:

[0039] S1: preparation of the fertilizer core

[0040] Urea powder, clay and polyacrylate sodium (PAANa) are uniformly mixed according to a mass ratio of 15:300:2, and then added into a granulator to prepare the fertilizer core, wherein the particle size of the fertilizer core is controlled to be 5 mm.

[0041] S2: preparation of an ethyl cellulose-ethanol composite coating solution

[0042] 1. Ethyl cellulose synthesis:

[0043] 80% by volume of acetic acid and 69% by volume of nitric acid are mixed according to a volume ratio of 10:1 to obtain a mixed solution; dry plant straw (wheat) is soaked in the mixed solution according to a ratio of 100g of the plant straw to 200mL of the mixed solution, and heated in a 90℃ water bath for 3h to obtain cellulose;

[0044] The cellulose is added into a NaOH solution with a concentration of 18wt%, and the mass-volume ratio of the cellulose to the NaOH solution with a concentration of 18wt% is 150g:1L; the mixture is stirred at 25℃ for 1.5h, and then subjected to negative pressure filtration under a negative pressure of greater than or equal to 0.08MPa; and the alkaline cellulose is prepared by negative pressure vacuum drying (the negative pressure vacuum drying is performed under the conditions of 60℃, a vacuum degree of-0.1MPa and drying for 12h).

[0045] The prepared basic cellulose, toluene, and bromoethane are mixed in an amount of 100 g of basic cellulose, 800 mL of toluene (solvent), and 250 mL of bromoethane (etherifying agent), and after mixing, are added to a 2L high-pressure reaction kettle to prepare ethyl cellulose by etherification. The specific operation of the etherification reaction is as follows: the materials are added to the high-pressure reaction kettle, then N2 is used to replace the air 2-3 times, the temperature is raised to 60°C, the stirring speed is 260 rpm, and the reaction is carried out for 20 h (pressure ≤0.5 MPa); after cooling to 25°C, the mixture is taken out after pressure relief, and ethyl cellulose is obtained.

[0046] 2. Ethyl cellulose-ethanol composite film coating solution:

[0047] The ethyl cellulose is dissolved in an ethanol solution with a volume fraction of 70% to prepare a 10% (w / v) solution (i.e., 10 g of ethyl cellulose is added to every 100 mL of ethanol solution), and the solution is continuously stirred at 45°C for 10-20 min using a magnetic stirrer until the solution is uniformly mixed, and then is cooled to room temperature to obtain a pH-responsive ethyl cellulose-ethanol composite coating solution, which is cooled for standby use.

[0048] S3: Preparation of an environment-responsive core-coated fertilizer

[0049] The fertilizer core prepared in S1 is placed in a drum, and the initial rotating speed of the coating machine is set to 50 r / min, and is preheated at 80°C for 15 min.

[0050] Then, the ethyl cellulose-ethanol composite coating solution prepared in S2 is uniformly sprayed onto the surface of the granular fertilizer core, and the granular fertilizer core is continuously and uniformly turned at a rotating speed of 40 r / min, and the above process is repeated 4 times until the amount of ethyl cellulose film reaches 0.4% of the mass of a single fertilizer core.

[0051] Then, the rotating speed is further reduced to 20 r / min and the machine continues to work for 10 min until the granular fertilizer is completely dried, and an environment-responsive core-coated fertilizer is obtained.

[0052] S4: Preparation of PMFF and ORFFF

[0053] 1. Preparation of PMFF

[0054] 1) Preparation of nano-silica template

[0055] The anhydrous ethanol and ammonia water are uniformly mixed under magnetic stirring, and then the tetraethyl orthosilicate is quickly added. The volume ratio of anhydrous ethanol, ammonia water, and tetraethyl orthosilicate is 27:8:4.2. The mixed solution is centrifuged, washed repeatedly with deionized water and anhydrous ethanol under ultrasonic, and fully dried to obtain a white product, nano-silica template.

[0056] 2) Synthesis of PMFF

[0057] The nanosilica template was dispersed in deionized water at a mass:volume ratio of 0.1 g:20 mL (i.e., 20 mL of deionized water was added for every 0.1 g of nanosilica template), and was dispersed in deionized water by ultrasonic to form solution A;

[0058] The magnesium chloride hexahydrate, ammonium chloride and ammonia were sequentially dissolved in deionized water, and were uniformly mixed under magnetic stirring to form solution B, wherein the mass ratio of the magnesium chloride hexahydrate, the ammonium chloride and the nanosilica template was 0.2 g:0.54 g:0.1 g, the volume:mass ratio of the ammonia and the nanosilica template was 1 mL:0.1 g, and the volume:mass ratio of the deionized water and the nanosilica template was 30 mL:0.1 g;

[0059] Solution A and solution B were transferred into a high-pressure reaction kettle and heated at 140°C for 10 h. The product was collected after being washed by centrifugation with anhydrous ethanol and deionized water for 3 times, and was dried in a vacuum oven at 60°C overnight to obtain a white product, which was PMFF.

[0060] 2. Preparation of ORFFF

[0061] The nanosilica template (prepared in step 1 above) was ultrasonically dispersed in 20 mL of deionized water at a mass:volume ratio of 0.1 g:20 mL to form solution C.

[0062] The ferric acetylacetonate, urea and anhydrous ethanol were sequentially dissolved in 25 mL of deionized water to form solution D, and the ratio of the nanosilica template, the ferric acetylacetonate, the urea, the anhydrous ethanol and the deionized water was 0.1 g:0.5 mmol (converted to a mass of 176 mg of ferric acetylacetonate (calculated according to a molecular weight of 352.17)):8 mmol (converted to a mass of 480 mg):5 mL:25 mL.

[0063] Solution C and solution D were transferred into a high-pressure reaction kettle and heated at 180°C for 12 h, and were washed with anhydrous ethanol and deionized water for at least 3 times. Finally, the washed reddish-brown product was dried in a vacuum oven at 60°C overnight to obtain Fe(III) / SiO2.

[0064] The ascorbic acid was dissolved in deionized water as a reducing agent at a mass:volume ratio of 0.30 g:50 mL, and then the Fe(III) / SiO2 was added into a round-bottom flask, and the mixture was stirred and dispersed uniformly, and the mass ratio of the Fe(III) / SiO2 and the ascorbic acid was 1:3. Subsequently, the solvent was evaporated at 60°C and under negative pressure using a rotary evaporator to obtain a reddish-brown product ORFFF.

[0065] S5: Preparation of the suspension PMFF@SA

[0066] Sodium alginate was dissolved in deionized water at a mass:volume of 0.3 g:20 mL, stirred with a magnetic stirrer until completely dissolved to obtain a sodium alginate solution;

[0067] Then the PMFF prepared by S4 was dispersed in distilled water at a mass:volume of 0.1 g:10 mL to obtain a suspension, the suspension was poured into the sodium alginate solution, the volume ratio of the suspension and the sodium alginate solution was 1:2, the mixture was shaken with a shaker at a speed of 500 r / min for 10 min to obtain a uniform PMFF@SA suspension, and the concentration of the sodium alginate solution was maintained at 1.5%.

[0068] S6: Double-layered envelope construction

[0069] The environment-responsive core coated fertilizer prepared by S3 was placed in a rotating drum;

[0070] The ORFFF prepared by S4 was dispersed in deionized water and then sprayed onto the surface of the fertilizer particles in the rotating drum, and the total spraying amount was controlled at 0.05% of the total mass of the iron element in the environment-responsive core coated fertilizer prepared by S3.

[0071] Then the PMFF@SA suspension prepared by S5 was slowly sprayed onto the surface of the rotating fertilizer particles, and an outer gel film shell was formed under the condition of continuous rotation for 10 min, and the crosslinking reaction was completed;

[0072] The above steps were repeated 3 times (referring to the 2 steps of spraying ORFFF and then spraying PMFF@SA suspension, which were repeated 3 times), and the total amount of PMFF@SA suspension used was 10% (v / w) of the mass of the environment-responsive core coated fertilizer prepared by S3, that is, 10 mL of PMFF@SA suspension was used per 100 g of the environment-responsive core coated fertilizer prepared by S3, to obtain a pH-responsive magnesium-iron-rich double-layered coated controlled-release fertilizer.

[0073] Example 2

[0074] A pH-responsive magnesium-iron-rich double-layered coated controlled-release fertilizer, which is composed of a fertilizer core, an inner layer coating and an outer shell; the fertilizer core is composed of urea, clay and sodium polyacrylate; the inner layer coating is an ethyl cellulose film covering the surface of the fertilizer core; the outer shell covering the surface of the inner layer coating is composed of a layer of iron-rich material and a layer of magnesium-rich gel stacked in turn; the iron-rich material layer is composed of ORFFF, and the magnesium-rich gel layer is composed of PMFF@SA suspension; the ORFFF is ascorbic acid modified Fe(III) / SiO2 composite material, and the PMFF@SA suspension is obtained by pouring PMFF water suspension into sodium alginate solution; the PMFF is a pH-responsive magnesium element modified nanosilica composite material.

[0075] The preparation method is as follows:

[0076] S1: Preparation of fertilizer core

[0077] Urea powder, clay and sodium polyacrylate (PAANa) were mixed uniformly in a mass ratio of 14:290:1.8, and then added to a granulator to prepare the fertilizer core, with the particle size of the fertilizer core controlled at 4 mm.

[0078] S2: Preparation of ethyl cellulose-ethanol composite coating solution

[0079] Ethyl cellulose was dissolved in an ethanol solution with a volume fraction of 70% to prepare a 10% (w / v) solution (i.e., 10 g of ethyl cellulose was added to 100 mL of ethanol solution). The solution was continuously stirred at 45°C using a magnetic stirrer for 10-20 min until it was uniformly mixed, and then cooled to room temperature to obtain a pH-responsive ethyl cellulose-ethanol composite coating solution, which was cooled for standby use.

[0080] S3: Preparation of environment-responsive core-coated fertilizer

[0081] The fertilizer core prepared in S1 was placed in a drum, and the initial rotating speed of the coating machine was set to 50 r / min. The granules were preheated at 80°C for 15 min.

[0082] Then, the ethyl cellulose-ethanol composite coating solution prepared in S2 was uniformly sprayed onto the surface of the granular fertilizer core. The granular fertilizer core was continuously and uniformly turned at a rotating speed of 40 r / min. The above process was repeated 4 times until the amount of ethyl cellulose film reached 0.3% of the mass of a single fertilizer core.

[0083] Then, the rotating speed was further reduced to 20 r / min and the machine continued to work for 10 min until the fertilizer granules were completely dried, obtaining an environment-responsive core-coated fertilizer.

[0084] S4: Preparation of PMFF and ORFFF

[0085] 1. PMFF preparation

[0086] 1) Preparation of nano-silica template

[0087] Anhydrous ethanol and ammonia water were mixed uniformly under magnetic stirring, and then tetraethyl orthosilicate was quickly added. The volume ratio of anhydrous ethanol, ammonia water and tetraethyl orthosilicate was 27:8:3.9. The mixed solution was centrifuged, washed repeatedly with deionized water and anhydrous ethanol under ultrasonic, and dried to obtain a white product, nano-silica template.

[0088] 2) PMFF synthesis

[0089] The nano-silica template is dispersed in deionized water at a mass:volume ratio of 0.1 g:20 mL (i.e. 20 mL of deionized water is added for every 0.1 g of nano-silica template), and is dispersed in deionized water by ultrasonic to form solution A;

[0090] The magnesium chloride hexahydrate, ammonium chloride and ammonia are sequentially dissolved in deionized water, and are uniformly mixed under magnetic stirring to form solution B, wherein the mass ratio of the magnesium chloride hexahydrate, ammonium chloride and nano-silica template is 0.2 g:0.54 g:0.1 g, the volume mass ratio of the ammonia and nano-silica template is 0.8 mL:0.1 g, and the volume mass ratio of the deionized water and nano-silica template is 30 mL:0.1 g;

[0091] The solution A and solution B are transferred to a high-pressure reaction kettle and heated at 140°C for 10 h. The product is collected after being washed by centrifugation with anhydrous ethanol and deionized water for 3 times, and is dried in a vacuum oven at 60°C overnight to obtain a white product, which is PMFF.

[0092] 2. Preparation of ORFFF

[0093] The nano-silica template (prepared in step 1 above) is ultrasonically dispersed in 20 mL of deionized water at a mass:volume ratio of 0.09 g:20 mL to form solution C.

[0094] The ferric acetylacetonate, urea and anhydrous ethanol are sequentially dissolved in 25 mL of deionized water to form solution D, and the ratio of the nano-silica template, ferric acetylacetonate, urea, anhydrous ethanol and deionized water is 0.09 g:0.18 g:0.50 g:5 mL:25 mL.

[0095] The solution C and solution D are transferred to a high-pressure reaction kettle and heated at 180°C for 12 h, and are washed with anhydrous ethanol and deionized water for at least 3 times. Finally, the washed reddish-brown product is dried in a vacuum oven at 60°C overnight to obtain Fe(III) / SiO2.

[0096] The ascorbic acid is dissolved in deionized water as a reducing agent at a mass:volume ratio of 0.30 g:50 mL, and then the Fe(III) / SiO2 is added into a round-bottom flask, and the mixture is stirred and dispersed uniformly, and the mass ratio of the Fe(III) / SiO2 and ascorbic acid is 1:2. Subsequently, the solvent is evaporated by using a rotary evaporator at 60°C and under negative pressure to obtain a reddish-brown product ORFFF.

[0097] S5: Preparation of suspension PMFF@SA

[0098] Sodium alginate was dissolved in deionized water at a mass:volume of 0.3 g:20 mL, stirred with a magnetic stirrer until completely dissolved to obtain a sodium alginate solution;

[0099] Then the PMFF prepared in S4 was dispersed in distilled water at a mass:volume of 0.1 g:10 mL to obtain a suspension, the suspension was poured into the sodium alginate solution, and the volume ratio of the suspension to the sodium alginate solution was 1:2. The mixture was shaken with a shaker at a speed of 500 r / min for 10 min to obtain a uniform PMFF@SA suspension, and the concentration of the sodium alginate solution was maintained at 1.5%.

[0100] S6: Double-layered envelope construction

[0101] The environment-responsive core coated fertilizer prepared in S3 was placed in a rotating drum;

[0102] The ORFFF prepared in S4 was dispersed in deionized water and then sprayed onto the surface of the fertilizer particles in the rotating drum, and the total spraying amount was controlled at 0.1% of the total mass of the iron element in the environment-responsive core coated fertilizer prepared in S3.

[0103] Then the PMFF@SA suspension prepared in S5 was slowly sprayed onto the surface of the rotating fertilizer particles, and an outer gel membrane shell was formed under the condition of continuous rotation for 10 min, and the crosslinking reaction was completed;

[0104] The above steps were repeated 3 times (referring to the steps of spraying ORFFF first, and then spraying PMFF@SA suspension, which were repeated 3 times), and the total amount of PMFF@SA suspension used was 10% (v / w) of the mass of the environment-responsive core coated fertilizer prepared in S3, i.e. 10 mL of PMFF@SA suspension was used per 100 g of the environment-responsive core coated fertilizer prepared in S3, to obtain a pH-responsive magnesium-iron-rich double-layered coated controlled-release fertilizer.

[0105] Comparative Example 1

[0106] 1. Fertilizer core and inner layer envelope: same as steps S1-S3 of Example 1.

[0107] 2. Difference in outer layer structure:

[0108] The synthesis step of PMFF was omitted, and the following steps were used instead:

[0109] a. 0.3 g of magnesium chloride hexahydrate was weighed and dissolved in 10 mL of deionized water to obtain solution B;

[0110] b. 0.1 g of sodium alginate was weighed and dissolved in 20 mL of deionized water to obtain solution A;

[0111] c. Pour solution B into solution A (volume ratio of solution B to solution A is 1:2), oscillate at 500 r / min for 10 min to form Mg-Alg suspension.

[0112] Spraying process:

[0113] The Mg-Alg suspension is sprayed onto the surface of the ORFFF layer instead of PMFF@SA (the amount is the same as in Example 1), and the remaining steps are the same as in Example 1.

[0114] That is, the coated fertilizer of Comparative Example 1 actually has a core, an ethyl cellulose inner layer film, and an ORFFF layer, and the PMFF@SA layer is replaced by the Mg-Alg suspension.

[0115] Test Example 1

[0116] Take 10 g of the coated controlled-release fertilizer prepared in Example 1 and Comparative Example 1, respectively, crush and pass through a 100-mesh sieve to obtain a uniform granular sample. Perform the following experiments (5 parallel experiments for each group):

[0117] I. pH-responsive release experiment

[0118] 1. Buffer solution preparation:

[0119] pH 5.0 buffer: 0.1M acetic acid-sodium acetate system (simulating acidic soil);

[0120] pH 7.5 buffer: 0.1M Tris-HCl system (simulating neutral soil).

[0121] 2. Release kinetics test:

[0122] Take 50 mg of the test sample and place it in a dialysis bag (molecular weight cutoff 3500 Da), immerse it in 200 mL of buffer, and oscillate at 37°C (100 rpm). Sampling time points: 0.5 h, 2 h, 6 h, 12 h, 24 h, 48 h.

[0123] Magnesium ion concentration detection:

[0124] Take 5 mL of solution each time (while adding an equal amount of fresh buffer), and use an atomic absorption spectrometer (AAS) to determine the Mg 2+ concentration and calculate the cumulative release rate:

[0125]

[0126] The results of the environment-responsive magnesium-rich iron double-layer coated controlled-release fertilizer obtained in Example 1 are shown in Table 1 (the release difference multiple in Table 1 refers to the release difference multiple of the magnesium release rate at pH 5.0 and the magnesium release rate at pH 7.5), which shows that the magnesium release rate at 24 h under acidic conditions (pH 5.0) is 78.5%, which is significantly higher than that under neutral conditions (28.3%), and the difference is 2.8 times. It is confirmed that the nano-silicon dioxide carrier in the PMFF has a pH response in H + Corrosion under acceleration Mg 2+ Dissolution. The release rate in an acidic environment within 48 h is >90%, which meets the demand of the crop growth cycle.

[0127] Table 1 Results of the pH response release experiment of the coated controlled-release fertilizer obtained in Example 1

[0128]

[0129] The results of the coated controlled-release fertilizer obtained in Comparative Example 1 are shown in Table 2 (the release difference multiple in Table 2 refers to the release difference multiple of the magnesium release rate at pH 5.0 and the magnesium release rate at pH 7.5), which shows that the fertilizer without the PMFF@SA layer has a magnesium release rate of only 31.6% at 24 h under pH 5.0, which proves the necessity of the outer coating for the pH response. The common Mg-Alg gel layer has no pH response channel structure (compared with the 5-10 nm mesoporous structure of PMFF), and the magnesium ions are only released by diffusion, which leads to a difference of <5% in the magnesium release rate between acidic and neutral soils (only 31.6% at 24 h under pH 5.0, which is much lower than 78.5% of the present application); the cumulative magnesium release rate in acidic and neutral soils within 48 h is >50%, which increases the risk of nutrient loss.

[0130] Table 2 Results of the pH response release experiment of the coated controlled-release fertilizer obtained in Comparative Example 1

[0131]

[0132] II. Ferrous ion (Fe 2+ ) retention rate test:

[0133] Verify the stabilizing effect of ascorbic acid modification on ferrous ions.

[0134] 1. Take 0.5 g of the ORFFF material prepared in Example 1 and store it in an open container in a constant temperature and humidity box at 25°C / 60% RH;

[0135] Take samples at 0 days (initial), 15 days, and 30 days;

[0136] Determine the Fe 2+ content (Fe 2+ / (Fe 2+ + Fe 3+ )) by X-ray photoelectron spectroscopy (XPS);

[0137] The standard curve was established by iron standard solution, and the iron form was verified by atomic absorption spectrometry (AAS).

[0138] The results are shown in Table 3.

[0139] Table 3 Ferrous ion (Fe 2+ ) retention rate test results

[0140]

[0141] 2. Mechanism analysis:

[0142] Ascorbic acid forms a stable complex through chelation:

[0143]

[0144] The oxidation potential of this chelate is reduced to -0.18V (normal Fe 2+ is +0.77V), inhibiting oxidation and providing sustained and effective iron nutrition for crops.

[0145] Comparative Example 2

[0146] Fertilizer core, inner layer film and magnesium layer are the same as steps S1-S3 and PMFF@SA of Example 1.

[0147] Iron layer difference:

[0148] Omit: ascorbic acid reduction step of ORFFF;

[0149] Alternative steps:

[0150] a. Mix acetylacetone iron: urea: SiO2 template = 0.175: 0.49: 0.10 by mass ratio;

[0151] b. Hydrothermal reaction at 180℃ for 12h to prepare Fe(III) / SiO2 (unreduced);

[0152] c. Directly use Fe(III) / SiO2 powder to disperse in water (without adding ascorbic acid).

[0153] Spraying process:

[0154] Replace ORFFF with Fe(III) / SiO2 aqueous dispersion to spray on the surface of the inner layer film (iron element accounts for 0.08%), and the rest is the same as step S6 of Example 1.

[0155] Test Example 2

[0156] Take the fertilizer obtained in Comparative Example 2 to test the ferrous ion (Fe 2+Retention rate test, test method same as test example 1. Results shown in Table 4. Indicate that in unmodified Fe(III) / SiO2, the initial non-plant effective iron: 100% is Fe 3+ (crop absorption rate <10%); low ferrous ion conversion rate and no protection: 30 days later, effective Fe 2+ accounting for only 40.8% (while the corresponding value of ORFFF in Table 3 is 82.3%).

[0157] Table 4 Ferrous ion (Fe 2+ ) retention rate test results

[0158]

[0159] From the results of test example 1 and test example 2, it can be seen that the present application constructs a pH-responsive PMFF carrier (Mg 2+ loading capacity 12.3wt%), 0.5h rapid release of 10.2% magnesium in acidic soil (4.9 times higher than in neutral environment), 24h cumulative release rate reached 78.5%; simultaneously using ascorbic acid chelation technology to improve the retention rate of ferrous ion in ORFFF to 82.3% in 30 days, breaking through the bottleneck of iron fertilizer oxidation.

[0160] Test example 3

[0161] Test crop: tomato; plastic pot specifications: pot bottom diameter 15cm, pot opening diameter 20cm, height 18cm; test fertilizers are the fertilizer samples prepared by example 1, comparative example 1 and comparative example 2.

[0162] The experiment was carried out in the new fertilizer and green agricultural institute of Xinyangfeng agricultural technology Co., Ltd. The experiment was set up with two factors, i.e. soil type (acidic soil, pH 5.5; calcareous soil, pH 7.80) and fertilizer (the slow-release fertilizer prepared in example 1, comparative example 1 and 2), a total of 6 treatments were set up, i.e. AcT1, AcT2, AcT3, AlT1, AlT2 and AlT3 (wherein Ac represents acidic soil; Al represents calcareous soil; T1 represents the fertilizer sample prepared in example 1; T2 represents the fertilizer sample prepared in comparative example 1; T3 represents the fertilizer sample prepared in comparative example 2), the tomato planting container was a plastic flowerpot, 1.5 kg of soil (acidic soil, calcareous soil) was put into each pot, all nitrogen, phosphorus and potassium fertilizers were applied as base fertilizer, full-grain and uniform-size tomato seeds were selected, 5 seeds were sowed in each pot with a burial depth of 1.5 cm, the fertilizer was applied at a position 4 cm below the seeds, 5 g of the slow-release fertilizer prepared in example 1, comparative example 1 or comparative example 2 was applied in each pot, the sowing was carried out in a way of watering-sowing-covering, the seedlings were thinned 7 days after sowing, and 3 tomato seedlings were planted. All the pots were cultured in an artificial climate room, the temperature was set to 25℃, the daily light length was set to 16 h, and the light intensity was about 900 μmol (m 2 ·s). Each treatment was repeated 3 times, and the random block arrangement was adopted, and unified management measures were taken for all treatments during the experiment. After 45 days of culture, the mature plants were harvested for determination of various indexes.

[0163] The dry weight of tomato plants: the tomato plants were killed in an oven at 105℃ for 30 min, and then dried at 80℃ to a constant weight, and the weight was determined by an electronic balance; the magnesium content of the plants was determined by atomic absorption spectrophotometry after nitric acid-perchloric acid digestion; the iron content of the plants was determined by atomic absorption spectrophotometry in the same way as the magnesium content, i.e. after nitric acid-perchloric acid digestion.

[0164] The results are shown in table 5. It is shown that PMFF and ORFFF are sensitive to pH value, the release amounts of magnesium and Fe (II) are different in different soil of different pH value, and the release amounts can be controlled according to the change of pH value, so as to meet the requirements of magnesium and iron in different growth stages of crops, and the double-layer film structure (ethyl cellulose inner layer + PMFF@SA / ORFFF outer layer) of the application can realize the dynamic matching of magnesium and iron release and crop demand.

[0165] Table 5: results of different groups

[0166]

[0167] Note: Ac in Table 5 represents acid soil; Al represents lime soil; T1 represents the fertilizer sample prepared in Example 1; T2 represents the fertilizer sample prepared in Comparative Example 1; and T3 represents the fertilizer sample prepared in Comparative Example 2.

[0168] The above only is the preferred embodiment of the present application, it should be pointed out that, for the ordinary skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A pH-responsive, magnesium-iron-rich double-layer coated controlled-release fertilizer, characterized in that, The application relates to a controlled-release fertilizer, which comprises a fertilizer core, an inner layer coating and an outer layer shell; the fertilizer core is composed of urea, clay and sodium polyacrylate; the inner layer coating is an ethyl cellulose film covering the surface of the fertilizer core; the outer layer shell covering the surface of the inner layer coating is composed of an iron-rich material layer and a magnesium-rich gel layer which are stacked in sequence; the iron-rich material layer is composed of ORFFF, and the magnesium-rich gel layer is composed of PMFF@SA suspension; The ORFFF is ascorbic acid modified Fe(III) / SiO2 composite material, the PMFF@SA suspension is obtained by pouring PMFF water suspension into sodium alginate solution, and the PMFF is pH responsive magnesium element modified nano silicon dioxide composite material. The preparation method of the controlled-release fertilizer comprises the following steps: mixing urea, clay and sodium polyacrylate to granulate a fertilizer core; dissolving ethyl cellulose in 70% ethanol solution to obtain a coating liquid, and spraying the coating liquid onto the fertilizer core to obtain a core-coated fertilizer; spraying ORFFF water suspension onto the surface of the core-coated fertilizer, then spraying PMFF@SA suspension onto the surface of the ORFFF layer, and repeating the steps of spraying ORFFF water suspension and then spraying PMFF@SA suspension for 1-3 times to obtain the controlled-release fertilizer. The spraying amount of the ORFFF water suspension is calculated according to 0.05%-0.1% of iron element in the core-coated fertilizer. The spraying amount of the PMFF@SA suspension is 10 mL:100 g of the volume weight ratio of the core-coated fertilizer.

2. The controlled-release fertilizer of claim 1, wherein, The mass ratio of urea, clay and sodium polyacrylate is (14-16):(290-310):(1.8-2.2), and the diameter of the fertilizer core is 4-6 mm.

3. The controlled-release fertilizer of claim 1, wherein, The mass of the ethyl cellulose film is 0.3%-0.5% of the mass of the fertilizer core.

4. The controlled-release fertilizer of claim 1, wherein, The preparation method of the ORFFF comprises the following steps: Mixing acetylacetone iron, urea and nano silicon dioxide templates according to the mass ratio of (0.17-0.18):(0.48-0.50):(0.09-0.11), and carrying out hydrothermal reaction at 180 DEG C for 12 hours to obtain Fe(III) / SiO2; mixing Fe(III) / SiO2 and ascorbic acid according to the mass ratio of 1:(2-3) to obtain ORFFF; the preparation method of the nano silicon dioxide template comprises the following steps: mixing anhydrous ethanol, ammonia water and tetraethyl orthosilicate according to the volume ratio of 27:8:(3.9-4.5) to obtain a nano silicon dioxide template. The preparation method of the PMFF comprises the following steps: mixing anhydrous ethanol, ammonia water and tetraethyl orthosilicate according to the volume ratio of 27:8:(3.9-4.5) to obtain a nano silicon dioxide template; mixing the nano silicon dioxide template, magnesium chloride hexahydrate, ammonium chloride and ammonia water, and carrying out hydrothermal reaction at 140 DEG C for 10 hours to obtain PMFF.

5. The controlled-release fertilizer of claim 1, wherein, The mass-volume ratio of the nano silicon dioxide template, magnesium chloride hexahydrate, ammonium chloride and ammonia water is 0.1 g:0.2 g:0.54 g:0.8-1.0 mL.

6. The controlled-release fertilizer of claim 5, wherein, The mass ratio of PMFF and sodium alginate is 1:

3.

7. The controlled-release fertilizer of claim 1, wherein, ​

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