Metal organic framework saline alkali soil conditioner and preparation method thereof

Abstract

The invention discloses a metal organic framework saline alkali soil conditioner and a preparation method thereof. The modifier is formed by bridging coordination of a metal cluster, an inorganic ligand phosphoric acid, an organic ligand and a structure-directing agent urea under a hydrothermal condition. Wherein the metal cluster is ferric chloride hexahydrate and / or zinc sulfate heptahydrate; the organic ligand is one or a combination of two of oxalic acid dihydrate, citric acid monohydrate and tartaric acid; during the hydrothermal reaction, the molar ratio of the metal cluster to the phosphoric acid to the organic ligand to the urea to the deionized water is (1-2): 6: (1-2): (2.5-3): 100. The modifier disclosed by the invention not only has the function of improving saline-alkali soil, but also has the characteristic of slowly releasing a fertilizer, and can remarkably reduce the salinity effect caused by nutrients while providing sufficient nutrients for crops.

Description

Technical Field

[0001] The invention belongs to the field of soil conditioners, and in particular relates to a metal organic framework saline-alkali soil conditioner and a preparation method thereof. Background Art

[0002] Saline-alkali soil is caused by the alternating influence of climate, topography, soil texture, groundwater level, river and seawater, which causes a large amount of soluble salt to accumulate on the soil surface, destroying the physical, chemical and biological properties of the soil and affecting crop growth. Maximizing the development and utilization of saline-alkali land resources is of great significance to achieving sustainable agricultural development. Therefore, improving saline-alkali land is particularly important.

[0003] The improvement of saline-alkali soil is a systematic project with a long cycle and great challenges. At present, the improvement and management of saline-alkali soil include various approaches such as physical, chemical, water conservancy and biological. Whether it is the use of water conservancy irrigation facilities, the application of organic fertilizers, or the planting of salt-alkali tolerant crops, there are problems of slow results and high costs, which make it difficult to promote effectively. Chemical improvers are an economical and applicable method. They can retain water and fertilizer, improve the physical and chemical properties of the soil, reduce the aggregation of salt ions, and have a certain improvement effect. However, the effective improvement time of the current improvers is relatively short, and may even pose potential hazards to soil health. Therefore, there is an urgent need to develop a new type of green soil improver.

[0004] Metal-organic frameworks (MOFs) are a type of porous crystalline material formed by bridging coordination between inorganic metal ions or metal ion clusters and organic ligands. Due to their high specific area, diverse and adjustable pore structure, rich active sites, and easy modification and functionalization, they have been widely used in gas storage and separation, catalysis, sensing, adsorption, and drug carriers. Previously, there have been reports on the research of metal-organic frameworks in fertilizer controlled release. For example, Chinese patents ZL 202010424615.2 and ZL 202110166554.9 respectively disclose new fertilizers based on metal-organic framework materials and their preparation methods and methods for solid-phase synthesis of metal-organic framework fertilizers. These synthetic fertilizers have good slow-release properties, but there is a lack of research reports on the improvement of saline-alkali land. In addition, the applicant previously prepared a new type of Fe-MOF iron fertilizer through hydrothermal synthesis, but there were problems with the long reaction time (24 hours) and low nutrients (containing about 5.1% N, about 14.7% P and about 19.7% Fe). At the same time, it also did not involve research on the adsorption and improvement of saline-alkali soils. Summary of the invention

[0005] The first object of the present invention is to provide a metal organic framework saline-alkali soil conditioner.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A metal organic framework saline-alkali soil conditioner, wherein the conditioner is formed by bridging coordination of metal clusters, inorganic ligand phosphoric acid, organic ligands and structure directing agent urea under hydrothermal conditions;

[0008] Wherein, the metal cluster is ferric chloride hexahydrate and / or zinc sulfate heptahydrate; the organic ligand is one or a combination of two of oxalic acid dihydrate, citric acid monohydrate, and tartaric acid;

[0009] During the hydrothermal reaction, the molar ratio of the metal cluster, phosphoric acid, organic ligand, urea and deionized water is 1-2:6:1-2:2.5-3:100.

[0010] As a preferred embodiment, the hydrothermal condition is 110-120° C. for 18-20 h.

[0011] Furthermore, the hydrothermal condition is 120° C. for 18 h.

[0012] As a preferred embodiment, the metal cluster is ferric chloride hexahydrate or a combination of ferric chloride hexahydrate and zinc sulfate heptahydrate.

[0013] Furthermore, when the metal cluster is a combination of ferric chloride hexahydrate and zinc sulfate heptahydrate, the molar ratio of ferric chloride hexahydrate and zinc sulfate heptahydrate is 1:1; and the molar amounts of ferric chloride hexahydrate and zinc sulfate heptahydrate are equal to the molar amounts when ferric chloride hexahydrate is the only metal cluster.

[0014] As a preferred embodiment, the organic ligand is oxalic acid dihydrate, or a combination of oxalic acid dihydrate and citric acid monohydrate, or oxalic acid dihydrate and tartaric acid.

[0015] Furthermore, when the organic ligand is a combination of oxalic acid dihydrate and citric acid monohydrate, or oxalic acid dihydrate and tartaric acid, the molar ratio of the two organic acids is 1:1;

[0016] The molar amount of each of the two organic acids is equal to the molar amount when oxalic acid is used as the only organic ligand.

[0017] As a preferred embodiment, the metal cluster is ferric chloride hexahydrate, and the organic ligand is oxalic acid dihydrate and tartaric acid;

[0018] During the hydrothermal reaction, the molar ratio of ferric chloride hexahydrate, phosphoric acid, oxalic acid dihydrate, tartaric acid, urea and deionized water is 1:6:1:1:2.5:100.

[0019] The second object of the present invention is to provide a method for preparing the above-mentioned improver, comprising:

[0020] Weighing the metal cluster, phosphoric acid, organic ligand and urea in molar ratio and dissolving them in deionized water to obtain a mixed solution;

[0021] The mixed solution is poured into a reaction kettle and sealed, and then transferred to an oven for reaction;

[0022] After the kettle body is cooled to room temperature, the reactants are taken out and filtered with filter paper, and then washed with deionized water and dried to obtain the product.

[0023] As a preferred embodiment, the filtered reactant is dried at 60°C to obtain a product.

[0024] The technical solution of the present invention is to prepare a metal organic framework modifier with inorganic metal ion clusters, phosphoric acid, natural organic acid organic ligands and urea, and apply the modifier to saline-alkali soil. Since the framework material itself contains a microporous structure, it has a certain adsorption capacity for salt ions, and NH4 + -N is located in the internal gap of the framework as a guest molecule to maintain charge balance, and in the process of slow release of nitrogen, the framework material will also adsorb salt ions such as K / Na / Ca / Mg under the action of electrostatic force. On the other hand, the metal framework structure can slowly release nutrients such as nitrogen, phosphorus and iron to enhance soil fertility. In addition, it can also lower soil pH and reduce the degree of soil alkalinity. By adsorbing soil salt ions and lowering pH, the modifier can reduce soil salinity. In a preferred embodiment, the present invention introduces the natural organic ligand tartaric acid as a functional ligand with both hydroxyl and carboxyl coordination active groups, presenting a variety of bridging coordination modes, and can also meet the coordination modes with different metals. In addition, the present invention relates to two different organic / inorganic ligands competing for coordination modes to affect MOFs, thereby modifying MOFs to a certain extent.

[0025] Under hydrothermal conditions, the present invention uses hexahydrate ferric chloride heptahydrate / zinc sulfate as inorganic metal clusters, natural organic acids such as dihydrate oxalic acid / monohydrate citric acid / tartaric acid as organic ligands, and urea as a structure-directing agent and phosphoric acid to synthesize a series of metal organic framework modifiers. The framework is rich in nitrogen, phosphorus and iron nutrients. Through soil cultivation experiments, it is found that the framework has good slow-release nutrient performance. In addition, through simulated saline-alkali soil test tests, it is found that the modifier can effectively reduce soil pH and reduce salt. Therefore, the metal framework modifier of the present invention simultaneously has controlled-release nutrient performance and improved saline-alkali soil characteristics, explores the improvement effect of MOFs on saline-alkali soil, broadens the scope of application of MOFs, and effectively supports the efficient utilization of saline-alkali soil resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the cumulative release rate of mineral nitrogen in saline-alkali soil (%).

[0027] Figure 2 is the cumulative release rate of available phosphorus in saline-alkali soil (%).

[0028] Figure 3Salt content and pH of different treatment groups.

[0029] Figure 4 Potassium / sodium / calcium / magnesium contents in different treatment groups. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The methods described are conventional methods unless otherwise specified, and reference can be made to previous published literature (Wu Ke, Zhou Jianmin, Du Changwen. Preparation of a new type of iron fertilizer based on metal organic frameworks [J]. Journal of Huazhong Agricultural University, 2023, 42(6): 73-79).

[0031] Example 1

[0032] This embodiment provides a method for preparing a metal organic framework saline-alkali soil conditioner, which specifically comprises the following steps:

[0033] Weigh the substrate raw materials in molar ratio: ferric chloride hexahydrate (FeCl3·6H2O): phosphoric acid (H3PO4): oxalic acid dihydrate (H2C2O4·2H2O): urea (CO(NH2)2): deionized water = 1:6:1:2.5:100. Dissolve the raw materials ferric chloride hexahydrate, phosphoric acid, oxalic acid dihydrate, and urea completely in deionized water, and mix them thoroughly with a glass rod. Pour the mixed solution into a reactor (Xi'an Changyi Instrument Equipment Co., Ltd.), tighten and seal the lid, and then transfer it to a 120 ℃ oven for reaction for 18 hours. After the reactor body cools to room temperature, open the reactor, filter the reactants with filter paper, wash them three times with deionized water, and then dry them at 60 ℃ to obtain the product. Compared with the previous Fe-MOF type new iron fertilizer (Comparative Example 1), the preparation method of this embodiment adjusts the substrate molar ratio and hydrothermal synthesis conditions, increases the hydrothermal synthesis temperature, and shortens the reaction time. Compared with Comparative Example 1, the nutrient phosphorus content, iron content and pH reduction rate of the metal organic framework modifier prepared in this embodiment are greatly improved, as shown in Table 1.

[0034] Example 2

[0035] The only difference between this embodiment and embodiment 1 is that the organic ligand oxalic acid is replaced by oxalic acid and tartaric acid (C4H6O6) (1:1), and the molar ratio of the reaction substrates is ferric chloride hexahydrate: phosphoric acid: oxalic acid dihydrate: tartaric acid: urea: deionized water = 1:6:1:1:2.5:100.

[0036] Example 3

[0037] The only difference between this embodiment and embodiment 1 is that the inorganic metal cluster ferric chloride hexahydrate is replaced by ferric chloride hexahydrate and zinc sulfate heptahydrate (ZnSO4·7H2O) (1:1), and the molar ratio of the reaction substrates is ferric chloride hexahydrate: zinc sulfate heptahydrate: phosphoric acid: oxalic acid dihydrate: urea: deionized water = 1:1:6:1:2.5:100.

[0038] Example 4

[0039] The only difference between this embodiment and embodiment 1 is that the organic ligand oxalic acid is replaced by oxalic acid and citric acid monohydrate (H8C6O7·H2O) (1:1), and the molar ratio of the reaction substrates is ferric chloride hexahydrate: phosphoric acid: oxalic acid dihydrate: citric acid monohydrate: urea: deionized water = 1:6:1:1:2.5:100.

[0040] Example 5

[0041] The difference between this embodiment and embodiment 1 is only that the ratio of urea substrate is different, and the molar ratio of the reaction substrate is ferric chloride hexahydrate: phosphoric acid: oxalic acid dihydrate: urea: deionized water = 1:6:1:3:100.

[0042] Comparative Example 1

[0043] This embodiment is prepared according to the Fe-MOF type new iron fertilizer synthesized in the previously published literature. The difference from Example 1 is that the hydrothermal reaction conditions are 24 hours at 100°C, and the molar ratio of the substrates is ferric chloride hexahydrate: phosphoric acid: oxalic acid dihydrate: urea: deionized water = 1:5:3:3:80.

[0044] Comparative Example 2

[0045] The only difference between this embodiment and embodiment 1 is that the organic ligand oxalic acid is replaced by tartaric acid, and the molar ratio of the reaction substrates is ferric chloride hexahydrate: phosphoric acid: tartaric acid: urea: deionized water = 1:6:1:2.5:100.

[0046] Comparative Example 3

[0047] The difference between this embodiment and embodiment 1 is that the organic ligand oxalic acid is replaced by citric acid. The molar ratio of the reaction substrates is ferric chloride hexahydrate: phosphoric acid: citric acid monohydrate: urea: deionized water = 1:6:1:2.5:100.

[0048] Comparative Example 4

[0049] The only difference between this embodiment and embodiment 1 is that the ratio of phosphoric acid and urea substrates is different, and the molar ratio of the reaction substrates is ferric chloride hexahydrate: phosphoric acid: oxalic acid dihydrate: urea: deionized water = 1:5:1:2.5:100.

[0050] Example 6

[0051] This example uses soil experiments to test the nutrient and salinity improvement effects of the metal organic framework modifiers prepared in Examples 1-5 and Comparative Examples 1-4. The test environment is as follows:

[0052] Soil cultivation: The soil used is saline-alkali soil, and its physical and chemical properties are as follows: organic matter 12.45 g·kg -1 , total nitrogen 0.62g·kg -1 , ammonium nitrogen 1.22 mg kg -1 , nitrate nitrogen 12.47 mg kg -1 , available phosphorus 6.72 mg kg -1 , effective iron 8.73 mg kg -1 , pH 9.02, salt content 0.44%, and conductivity 6328.82 us / cm. Soil samples (100 g) were placed in a Petri dish with a diameter of 8 cm, and the soil moisture was uniformly adjusted to 38% (w / w).

[0053] There were two treatments: control and MOF. The control did not use MOF, while the MOF was used at a nitrogen content of 75 kg N / ha. Each treatment was repeated three times. All culture dishes were placed in a constant temperature incubator (PPX-450B, Saifu Corporation, China) at 25°C, and plastic wrap was loosely covered on the pot mouth to reduce soil moisture evaporation. 36 soil samples were collected on the 1st, 3rd, 5th, 10th, 20th and 30th days of cultivation, and all soil samples were naturally air-dried and sieved.

[0054] The mineral nitrogen (ammonium nitrogen and nitrate nitrogen) content of soil samples was determined using a Smart Chem 200 automatic analyzer (AMS Alliance, Frepillon, France). The available phosphorus and available iron contents in the soil were measured using an ICP-OES spectrometer (iCAP 7000, ThermoFisher Scientific, USA). The soil pH was determined using a pH acidometer (Orion StarA211, Thermo Fisher Scientific, USA).

[0055] At the same time, 5 g of the saline-alkali soil was weighed and placed in a 50 mL centrifuge tube. 25 mL of deionized water was added. Two treatments were set up, 0.2 g of MOF treatment (each embodiment and comparative example) and a control (blank group) without MOF were added, and each treatment was repeated 3 times. Then the above samples were placed on a shaker and shaken at 200 r / min for 12 h at 25 ° C. After the end, the liquid in the tube was taken for analysis. The K / Na / Ca / Mg in the liquid was determined by ICP-OES spectrometer, the soil conductivity was determined by conductivity meter (SD30, Mettler Toledo, Zurich, Switzerland), the total amount of water-soluble salt in the soil was determined by residue drying-mass method, and the pH acidity meter was used to determine the soil pH.

[0056] The test results of Examples 1-5 and Comparative Examples 1-4 are shown in Table 1:

[0057] Table 1 Nutrient content of metal organic framework modifiers and their salt-alkali modification effects

[0058]

[0059] It can be seen that the present invention prepares a series of metal organic framework modifiers under hydrothermal reaction, and the average nutrient content of this type of modifier is: C about 5.32%, N about 4.61%, P about 17.01%, Fe about 20.79%, Zn about 10.44%, and after applying the modifier, the soil pH is reduced by an average of about 16.05%, and desalination is about 7.85%. When the modifier is applied in saline-alkali soil, the cumulative nitrogen release rate in 30 days is about 11.03%, showing a good nutrient controlled release effect. While providing sufficient nutrients to crops, it can significantly reduce the salt effect brought by the nutrients themselves. Compared with the comparative example, the nutrient content and salt-alkali improvement effect of the embodiment are improved to a certain extent, so the synthesized metal organic framework modifier can reduce soil saline-alkali stress and improve saline-alkali soil.

Claims

1. A metal organic framework saline-alkali soil conditioner, characterized in that: The modifier is formed by bridging coordination of metal clusters, inorganic ligand phosphoric acid, organic ligands and structure-directing agent urea under hydrothermal conditions; Wherein, the metal cluster is ferric chloride hexahydrate and / or zinc sulfate heptahydrate; the organic ligand is one or a combination of two of oxalic acid dihydrate, citric acid monohydrate, and tartaric acid; During the hydrothermal reaction, the molar ratio of the metal cluster, phosphoric acid, organic ligand, urea and deionized water is 1-2:6:1-2:2.5-3:

100.

2. The improver according to claim 1, characterized in that The hydrothermal condition is 110-120° C. for 18-20 hours.

3. The improver according to claim 2, characterized in that The hydrothermal condition is 120° C. for 18 h.

4. The improver according to claim 1, characterized in that The metal cluster is ferric chloride hexahydrate or a combination of ferric chloride hexahydrate and zinc sulfate heptahydrate.

5. The improver according to claim 4, characterized in that When the metal cluster is a combination of ferric chloride hexahydrate and zinc sulfate heptahydrate, the molar ratio of ferric chloride hexahydrate and zinc sulfate heptahydrate is 1:1; and the molar amounts of ferric chloride hexahydrate and zinc sulfate heptahydrate are equal to the molar amounts when ferric chloride is the only metal cluster.

6. The improver according to claim 1, characterized in that The organic ligand is a combination of oxalic acid dihydrate, oxalic acid dihydrate and citric acid monohydrate, or oxalic acid dihydrate and tartaric acid.

7. The improver according to claim 6, characterized in that When the organic ligand is a combination of oxalic acid dihydrate and citric acid monohydrate, or oxalic acid dihydrate and tartaric acid, the molar ratio of the two organic acids is 1:1; The molar amount of each of the two organic acids is equal to the molar amount when oxalic acid dihydrate is used as the only organic ligand.

8. The improver according to claim 1, characterized in that The metal cluster is ferric chloride hexahydrate, and the organic ligands are oxalic acid dihydrate and tartaric acid; During the hydrothermal reaction, the molar ratio of ferric chloride hexahydrate, phosphoric acid, oxalic acid dihydrate, tartaric acid, urea and deionized water is 1:6:1:1:2.5:

100.

9. The method for preparing the improver according to any one of claims 1 to 8, characterized in that: include: Weighing the metal cluster, phosphoric acid, organic ligand and urea in molar ratio and dissolving them in deionized water to obtain a mixed solution; The mixed solution is poured into a reaction kettle and sealed, and then transferred to an oven for reaction; After the kettle body is cooled to room temperature, the reactants are taken out and filtered with filter paper, and then washed with deionized water and dried to obtain the product.

10. The preparation method according to claim 9, characterized in that The filtered reactant was dried at 60 °C to obtain the product.

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