A pH-responsive iron-based metal-organic framework fertilizer and a preparation method thereof

Abstract

The application relates to a pH response iron-based metal organic framework fertilizer and a preparation method thereof. A metal organic framework MIL-100(Fe) is stirred in a urea solution to obtain Urea@MIL-100(Fe) loaded with urea, the Urea@MIL-100(Fe) is coated in a silicate solution to obtain the metal organic framework fertilizer. The new metal organic framework fertilizer has a high nitrogen loading capacity of 25.5%, and the solution culture test results show that the new fertilizer has a good nutrient release characteristic of controlled release effect, is environment-friendly, and is matched with crop nutrient demand through excellent pH response characteristics, and the nutrient utilization rate is significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fertilizer manufacturing, and particularly relates to a pH-responsive iron-based metal-organic framework fertilizer and a preparation method thereof. BACKGROUND

[0002] The use of controlled-release fertilizers (CRFs) not only reduces nutrient losses due to volatilization and leaching, but also achieves a nutrient supply that matches crop growth. In addition, it also achieves one-time fertilization, thereby saving a large amount of labor. However, the large-scale application of controlled-release fertilizers is still limited. First, most commercial CRFs are expensive and have low nutrient release efficiency. Second, the coatings of current CRFs are usually made of petroleum-based synthetic materials such as polyolefins, acrylic resins and polysulfones. The production process of these synthetic materials is complex and often involves toxic chemicals. Although controlled-release fertilizers prepared from biological-based coating materials such as starch, lignin, cellulose and chitosan are environmentally friendly, the mechanical strength of the coating materials is usually poor, and the coating materials contain a large number of hydrophilic groups, which leads to too fast nutrient release rate, which greatly limits the development of biological-based slow / controlled-release fertilizers. Therefore, it is extremely important to develop new environmentally friendly nutrient slow / controlled-release carriers and delivery systems by using new materials and new technologies.

[0003] Nano delivery systems are expected to improve nutrient use efficiency and reduce environmental stress by controlling nutrient release. Among different nano carriers, core-shell nanoparticles have gradually attracted attention due to their integrated advantages, i.e., the ability to combine two separate materials into a new nano platform. Porous core-shell nanoparticles can effectively load target components, and their physical and chemical properties can also be easily designed according to the multifunctional shell. The multifunctionality of core-shell nanoparticles is an important condition for developing efficient and accurate "nutrient delivery systems".

[0004] Metal-organic frameworks (MOFs) are a class of most representative porous functional materials, which are formed by self-assembly of metal ions or ion clusters and organic ligands. Due to the advantages of large specific surface area, rich pore chemical environment and controllable structure, MOFs have been widely used in gas storage, separation, catalysis, drug carriers and other fields. Among many MOF materials, MIL-100(Fe) is a kind of transition metal MOF with rigid zeotype crystal structure. In addition to the properties possessed by general MOFs, iron also endows MIL-100(Fe) with non-toxic and environmentally friendly characteristics, greatly expanding its application range. Due to its nanoscale pore structure and high surface area, MIL-100(Fe) has been used in the fields of biological medicine, pesticides and fertilizers.

[0005] The rhizosphere soil pH is lower than the non-root base soil pH due to the influence of organic acids secreted by plant roots, and the development and application of pH-sensitive fertilizers are beneficial to reduce the slow release of nutrients in this scenario, reduce nutrient loss, and improve nutrient utilization. Current studies have combined cellulose-based hydrogel with MIL-100(Fe) to design a pH-sensitive cellulose / MOF hydrogel slow-release fertilizer. Although this type of slow-release fertilizer exhibits excellent water retention performance, the cost of this type of fertilizer is high, and the nutrient loading capacity is low; and in the cellulose / MOF hydrogel slow-release fertilizer, the nutrient carrier is the hydrogel, not the MIL-100(Fe), and the MIL-100(Fe) itself is only combined with the hydrogel to assist in reducing nutrient release by providing a curved path inside the hydrogel. In addition, the nitrogen loading capacity of existing metal organic framework is usually low, with a maximum of less than 10%. SUMMARY

[0006] The purpose of the present application is to overcome the defects of the prior art described above, and to provide a pH-responsive metal organic framework fertilizer with high nitrogen loading capacity and good slow-release effect and a preparation method thereof.

[0007] To achieve the above technical purpose, the following technical solutions are adopted in the present application:

[0008] A preparation method of a metal organic framework fertilizer, wherein MIL-100(Fe) is immersed in a urea (CO(NH2)2) solution and shaken to obtain a metal organic framework loaded with urea (Urea@MIL-100(Fe)), and the Urea@MIL-100(Fe) is coated with a silicate solution to obtain the metal organic framework fertilizer.

[0009] As a preferred embodiment, the MIL-100(Fe) is immersed in a urea solution and shaken, and then vacuum dried after centrifugation to obtain Urea@MIL-100(Fe).

[0010] As a preferred embodiment, the MIL-100(Fe) is immersed in a urea solution and shaken at room temperature.

[0011] As a preferred embodiment, the MIL-100(Fe) is immersed in a urea solution and shaken for 24-36 hours.

[0012] As a preferred embodiment, the concentration of the urea solution is 0.8-1.2 mol / L.

[0013] As a preferred embodiment, the Urea@MIL-100(Fe) is immersed in a silicate solution and stirred, then filtered and washed with deionized water, and dried to obtain the metal organic framework fertilizer.

[0014] As a preferred embodiment, the concentration of the silicate solution is greater than 0.1 mol / L.

[0015] As a preferred embodiment, the molar ratio of the reactant raw materials is MIL-100(Fe): urea (CO(NH2)2): silicate = 1:5-10:2-4.

[0016] As a preferred embodiment, the silicate is sodium silicate.

[0017] Another object of the present application is to provide the metal organic framework fertilizer prepared by the above preparation method, which takes urea as the guest molecule, MIL-100(Fe) as the porous core material, and silicon dioxide as the shell.

[0018] The present application has the following beneficial effects:

[0019] (1) The present application uses metal organic framework MIL-100(Fe) and realizes efficient loading of nutrients by using a simple adsorption strategy, and further coats silicon dioxide to synthesize a metal organic framework fertilizer. Through element composition analysis, the framework contains nitrogen, iron and silicon nutrient elements.

[0020] (2) The nitrogen loading capacity of the metal organic framework new fertilizer synthesized by the present application is significantly improved, and can reach 25.5% at the highest, while the highest nutrient loading capacity of the existing fertilizer of this type is less than 10%.

[0021] (3) Through the nutrient release test at different pH values, the pH-responsive metal organic framework fertilizer of the present application has good pH-responsive release characteristics and excellent slow-release performance. The pH response is the intelligent feature of the fertilizer, which can better match the nutrient demand of crops, and thus can significantly improve the nutrient utilization efficiency.

[0022] (4) The fertilizer preparation method of the present application is simple, and can obtain a new fertilizer with high nutrient loading capacity, good slow-release effect and pH response performance by using relatively inexpensive raw materials and simple synthesis steps, which has economic and practicality. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is an electron microscope image of the MOFs prepared in Example 1.

[0024] Figure 2 is the nitrogen release curve of the MOFs prepared in Example 1 under different pH conditions.

[0025] Figure 3 is the nitrogen release curve of the MOFs prepared in Example 2 under different pH conditions.

[0026] Figure 4Nitrogen release curves of MOFs prepared in Example 3 under different pH conditions. DETAILED DESCRIPTION

[0027] The technical solutions of the present application are further described below in conjunction with the accompanying drawings and specific examples.

[0028] The metal organic framework MIL-100(Fe) is prepared by using the existing method, and the preparation method is as follows:

[0029] 1 mole of ferric chloride (FeCl3·6H2O) and 1 mole of 1,3,5-benzenetricarboxylic acid (H3BTC) are dissolved in 0.3 moles of N,N-dimethylformamide (DMF) in a beaker, the mixture is stirred at room temperature for 1 h, then the mixed solution is transferred to a polytetrafluoroethylene lined reaction kettle, sealed completely, the reaction temperature is set to 150°C, and the reaction time is 48 h. After the reaction is completed, after the temperature drops to room temperature, the product is collected by centrifugation after washing with ethanol for 3 times. The purified product is dried in an oven at 50°C for 12 h to obtain the metal organic framework MIL-100(Fe).

[0030] The nutrient release determination method in the example is as follows:

[0031] Three buffer systems of pH 5.0 (acetic acid-sodium acetate buffer), pH 7.0 (deionized water) and pH 9.0 (borax buffer) are prepared respectively. 3 g of Urea@MIL-100(Fe)@silica is accurately weighed and placed in a 150 mL glass bottle, 100 mL of buffer (pH 5.0, 7.0, 9.0 respectively) is added, the bottle is tightly capped and placed in a constant temperature incubator at 25°C, 3 parallel experiments are set for each treatment. On the 1st, 3rd, 5th, 7th, 14th, 28th, 42nd and 56th day, the solution is poured out and 100 mL of the corresponding buffer is added again. The content of urea in the solution is determined by p-dimethylaminobenzaldehyde colorimetry, and the cumulative release rate of nutrients is calculated.

[0032] Example 1

[0033] Urea@MIL-100(Fe)@silica was prepared according to the following procedure. 0.011 mol (about 3 g) of MIL-100(Fe) was placed in 100 mL of urea solution (0.83 mol / L) and shaken at room temperature for 24 h at 120 rpm. After centrifugation, the Urea@MIL-100(Fe) was dried. 10 g of sodium silicate (Na2SiO3·9H2O) was dissolved in 200 mL of water to obtain a silicate solution (0.175 mol / L), and the pH was adjusted to about 5 with an HC1 solution. 0.009 mol (about 3 g) of Urea@MIL-100(Fe) was added to the silicate solution. After stirring at 50 °C for 2 h at a stirring rate of 120 rpm, Urea@MIL-100(Fe)@silica was obtained by filtration and washing with deionized water, and drying. Figure 1 .

[0034] The nitrogen content of Urea@MIL-100(Fe)@silica prepared in Example 1 was 24-26%.

[0035] The nutrient release period of Urea@MIL-100(Fe)@silica prepared in Example 1 was 50 d, 18 d and 7 d at pH 5, 7 and 9, respectively, as determined by the nutrient release experiment, as shown in Table 1. Figure 2 The release period was defined as the time required for the cumulative release rate to reach 80% of the total nutrient.

[0036] Example 2

[0037] Example 2 differed from Example 1 only in that the urea solution concentration was 0.5 mol / L and the silicate solution concentration was 0.087 mol / L (0.018 mol (about 5 g) of sodium silicate (Na2SiO3·9H2O) was dissolved in 200 mL of water).

[0038] The nitrogen content of Urea@MIL-100(Fe)@silica prepared in Example 2 was 8-10%, indicating that the urea solution concentration had a significant effect on the nutrient loading of Urea@MIL-100(Fe)@silica.

[0039] The nutrient release period of Urea@MIL-100(Fe)@silica prepared in Example 2 was 24 d, 12 d and 3 d at pH 5, 7 and 9, respectively, as determined by the solution culture experiment, as shown in Table 2. Figure 3 This indicated that too little sodium silicate (Na2SiO3·9H2O) was added, resulting in less silica coated on Urea@MIL-100(Fe), which in turn caused the nutrient release period of Urea@MIL-100(Fe)@silica to be shortened.

[0040] Example 3

[0041] Example 3 differs from Example 1 only in that the urea solution concentration is 1.16 mol / L and the silicate solution is 0.087 mol / L.

[0042] The nitrogen content of Urea@MIL-100(Fe)@silica prepared in Example 3 is 23-26%, indicating that when the urea solution reaches a certain concentration, the urea loading of Urea@MIL-100(Fe)@silica does not increase with the increase of the urea solution concentration.

[0043] Through the solution culture test, the nutrient release period of Urea@MIL-100(Fe)@silica prepared in Example 3 under the conditions of pH 5, 7, and 9 is 28d, 16d, and 5d, respectively, as shown in Figure 4 , indicating that insufficient addition of sodium silicate will affect the coating effect of Urea@MIL-100(Fe) and thus affect its nutrient release effect.

[0044] Example 4

[0045] Example 4 differs from Example 1 only in that the urea solution concentration is 1.16 mol / L and the silicate solution is 0.26 mol / L (0.053 mol (about 15 g) of sodium silicate (Na2SiO3·9H2O) is dissolved in 200 mL of water).

[0046] The nitrogen content of Urea@MIL-100(Fe)@silica prepared in Example 4 is 23-26%.

[0047] Through the solution culture test, the nutrient release period of Urea@MIL-100(Fe)@silica prepared in Example 3 under the conditions of pH 5, 7, and 9 is 28d, 16d, and 5d, respectively, as shown in

[0048] Example 5

[0049] Example 5 differs from Example 1 only in that 0.009 mol of Urea@MIL-100(Fe) is added to the silicate solution. Stirring is carried out at 50°C for 5h.

[0050] The nitrogen content of Urea@MIL-100(Fe)@silica prepared in Example 5 is 23-26%, indicating that increasing the stirring time has no obvious effect on the nutrient loading of Urea@MIL-100(Fe)@silica.

[0051] Example 6

[0052] Example 6 differs from Example 1 only in that the urea solution concentration is 1.16 mol / L, the silicate solution is 0.26 mol / L, and 0.009 mol Urea@MIL-100(Fe) is added to the silicate solution. Stirring is performed at 50 °C for 5 h.

[0053] The nitrogen content of Urea@MIL-100(Fe)@silica prepared in Example 6 is 23-26%.

[0054] Example 7

[0055] Example 7 differs from Example 1 only in that 0.009 mol MIL-100(Fe) is placed in 100 mL of urea solution (0.83 mol / L) and is soaked and shaken at room temperature for 12 h.

[0056] The nitrogen content of Urea@MIL-100(Fe)@silica prepared in Example 7 is 5-8%, indicating that insufficient soaking and shaking time can significantly affect the nitrogen loading of Urea@MIL-100(Fe)@silica.

[0057] Example 8

[0058] Example 8 differs from Example 1 only in that 0.009 mol MIL-100(Fe) is placed in 100 mL of urea solution (0.83 mol / L) and is soaked and shaken at room temperature for 36 h.

[0059] The nitrogen content of Urea@MIL-100(Fe)@silica prepared in Example 8 is 23-27%, indicating that soaking and shaking for more than 24 h does not significantly increase the nitrogen content of Urea@MIL-100(Fe)@silica.

Claims

1. A method for preparing a pH-responsive iron-based metal-organic framework fertilizer, characterized in that, The metal organic framework MIL-100(Fe) is immersed in a 0.8-1.2 mol / L urea solution and shaken for 24-36 h to obtain a urea-loaded metal organic framework Urea@MIL-100(Fe), and the Urea@MIL-100(Fe) is coated with a sodium silicate solution with a concentration greater than 0.1 mol / L to obtain the metal organic framework fertilizer. The molar ratio of the reactant raw materials is: MIL-100(Fe): urea: sodium silicate = 1:5-10:2-4. The MIL-100(Fe) is immersed in a urea solution and shaken, centrifuged, and vacuum dried to obtain Urea@MIL-100(Fe).

2. The production method according to claim 1, characterized by, The MIL-100(Fe) is immersed in a urea solution and shaken at room temperature.

3. The production method according to claim 1 or 2, characterized by, The Urea@MIL-100(Fe) is immersed in a sodium silicate solution, stirred at 40-60 DEG C for 1-5 h, then filtered and washed with deionized water, and dried to obtain the metal organic framework fertilizer.

4. The production method according to claim 1, characterized by, The metal organic framework fertilizer uses urea as a guest molecule, MIL-100(Fe) as a porous core material, and silicon dioxide as a shell.

5. The metal organic framework fertilizer produced by the method of any one of claims 1-4, characterized by, ​

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