A leaf surface control composite material and a preparation method and application thereof

Abstract

The application discloses a kind of leaf surface resistance control composite material and preparation method and application thereof, the leaf surface resistance control composite material includes core material with resistance control effect, and shell layer is coated on core material;Wherein, core material is any one of MOFs, sodium silicate, sodium selenate, zinc chloride, ferric sulfate and humic acid;Shell layer is formed by sodium alginate.The shell layer sodium alginate of leaf surface resistance control composite material in the application has affinity with waxy layer of plant leaf surface, prolongs the residence time of leaf surface resistance control composite material on leaf surface, beneficial to the iron ion in leaf surface resistance control composite material into leaf surface tissue, to inhibit Cd in plant tissue migration and transformation, so that Cd only enriches in leaf, reduces the transport to other parts, especially alleviate Cd to grain transport in rice filling period.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of heavy metal pollution prevention and control of agricultural products, and particularly relates to a leaf surface blocking and controlling composite material and a preparation method and application thereof. BACKGROUND

[0002] There are a large number of technologies for passivation of As and Cd in soil, reducing the absorption and transport of available As and Cd by rice, but the chemical behavior of As and Cd in soil is opposite, making the traditional single method of blocking and controlling the absorption of As and Cd by rice unsuitable. It is difficult to simultaneously block and control the migration and accumulation of As and Cd in soil to rice. Therefore, it is urgent to develop a new technology for simultaneously blocking and controlling the migration and accumulation of As and Cd to rice grains.

[0003] At present, various technologies are used to cooperatively block and control the accumulation of As and Cd in rice. The effective methods in practice are: water management, soil passivation agent and foliar inhibitor, etc. The water management method can effectively alleviate the absorption and transport of Cd by rice, but the blocking and control effect on As is not obvious. Although Honma et al. proposed that when the Eh in soil is equal to -73 mV and the pH is 6.2, water management can most effectively block and control the absorption of As and Cd by rice. However, it is difficult to continuously maintain the Eh and pH in the actual field.

[0004] Soil passivation method: In recent years, a large number of reports have shown that by adding various in-situ passivation agents to soil, the amount of bioavailable As and Cd in soil can be reduced, thereby reducing the content of As and Cd in rice grains. This method has significant effect, good stability during the growth cycle of rice, relatively low cost, simple operation, and can achieve the purpose of repairing while producing. However, this method lacks long-term stability study of the passivation agent. In practice, the paddy field will undergo a dry-wet cycle every year and various fertilizers will be added again. In this process, Cd, As and other heavy metals are likely to be reactivated, and there is a risk of secondary release. In addition, the number of articles on soil passivation agents is increasing year by year, especially the blocking and control methods for compound contaminated soil are reported in large numbers, and the market is flooded with a large number of related passivation agents, which seriously puzzles the selection and use of agricultural technology workers. The selection of low-accumulation varieties is also a feasible method, mainly using gene splicing technology, which is expected to realize the rapid screening and cultivation of low-arsenic and low-cadmium accumulation rice varieties. However, there are many types of rice in China, and the region is vast. It is necessary to cultivate low-accumulation rice varieties according to different places. The variety selection not only has a long cycle, high cost, but also has certain contingency in success rate.

[0005] Compared with other technologies, leaf surface control technology shows excellent superiority in relieving heavy metal stress on plants, and its importance is focused on high efficiency, easy operation, and low cost, and is widely used in large-scale agricultural intensive production of rice. At present, the main leaf surface control agents are sodium silicate, sodium selenate, zinc chloride, and ferric sulfate. Because the rice leaf surface has a thin wax layer, it is difficult for inorganic solution type leaf surface control agents to adhere to the leaf surface, which greatly reduces the application efficiency (more than 95% cannot enter the leaf, but falls in the farmland), so it is necessary to spray 3-4 times of leaf surface control agents; in addition, low concentration of inorganic solution type leaf surface control agents has almost no effect, and high concentration will seriously burn the leaf surface, causing sharp yield reduction. In order to overcome the problems of inorganic leaf surface control agents, nanomaterials are widely used in the research and application of leaf surface control agents, such as CuO-NPs, ZnO-NPs, CeO2-NPs and FeO-NPs. Although the residence time of leaf surface control agents on the leaf surface can be increased, due to their large volume and potential toxicity, new problems such as plant absorption and transportation difficulties may be encountered.

[0006] Therefore, it is urgent to develop a leaf surface inhibitor with strong affinity to leaves, long life and resistance to leaf burning to delay the accumulation of As and Cd in rice grains. SUMMARY

[0007] In order to solve the existing problems, one of the purposes of the present application is to provide a leaf surface control composite material.

[0008] The technical scheme for solving the above technical problems of the present application is as follows:

[0009] A leaf surface control composite material, comprising a core material with a control effect, and a shell layer coated on the core material;

[0010] The core material is any one of MOFs, sodium silicate, sodium selenate, zinc chloride, ferric sulfate and humic acid.

[0011] The shell layer is formed by sodium alginate.

[0012] On the basis of the above technical scheme, the present application can also be improved as follows:

[0013] Further, the core material is MOFs.

[0014] Further, the MOFs are Fe-MOFs; specifically, the Fe-MOFs are composed of iron ions as the center, and then the iron ions are combined with terephthalic acid through coordination bond.

[0015] The second purpose of the present application is to provide a preparation method of a leaf surface control composite material, comprising the following steps:

[0016] Step S1, after dispersing the core material in the solvent, heating, then adding sodium alginate and making it completely dissolved to prepare a mixture;

[0017] Step S2, drop the mixture into the CaCl2 solution drop by drop and crosslinking reaction to prepare a foliar control composite material in the form of beads.

[0018] Further, the solvent in step S1 is deionized water; the heating temperature in step S1 is 316-338K.

[0019] Further, the concentration of the core material in the mixture is 3-7% w / v, and the concentration of sodium alginate in the mixture is 0.6-1.1% w / v.

[0020] Further, the crosslinking reaction time in step S2 is 30-60min, and the crosslinking reaction condition is room temperature.

[0021] Further, the mass ratio of sodium alginate to CaCl2 is 0.8:0.7-1.2:1.3.

[0022] The third object of the present application is the application of the foliar control composite material in controlling the transport of As and Cd in plants.

[0023] Further, the plant is at least one of wheat, corn, sorghum and rice.

[0024] The present application has the following beneficial effects:

[0025] 1. The core material in the present application is preferably Fe-MOFs, and the shell layer coated on the Fe-MOFs is sodium alginate. In the present application, Fe is not only a nutrient required by plants, but also can alleviate the stress of heavy metals on plants, and sodium alginate can not only increase the affinity of Fe-MOFs with the leaf surface to avoid shedding after spraying, but also can control the pore size and surface charge through post-functionalization to load the required target ions or groups.

[0026] 2. The shell layer of the foliar control composite material in the present application has affinity with the wax layer of the plant leaf surface, prolonging the residence time of the foliar control composite material on the leaf surface, which is beneficial for the iron ions in the foliar control composite material to enter the leaf surface tissue, thereby inhibiting the migration and transformation of Cd in plant tissues, making Cd only enriched in the leaves, reducing the transport to other parts, and especially alleviating the transport of Cd to the grains during the filling period of rice.

[0027] In addition, since the sodium alginate has affinity with the wax layer of the leaf surface, it prolongs the control time of the foliar control composite material to a certain extent, so that only one spraying is needed, and it is effective for the subsequent growth period after spraying. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Fig. 6 is a structural characterization diagram of the leaf surface resistance control composite material, wherein a is a thermogravimetric diagram of MIL-100@SA, b is an XRD diagram of MIL-100@SA, c-e are XPS (1S of O, 1S of C, 2p of Fe) characterization diagrams of MIL-100@SA, and f is a TEM diagram of MIL-100@SA;

[0029] Figure 2 Fig. 8 is a diagram of the determination of the Fe content in the leaves of rice at different periods between the growth periods of rice; 57

[0030] Figure 3 Fig. 9 is a test diagram of the influence of the leaf surface resistance control composite material on rice, wherein a is a result diagram of the influence of the leaf surface resistance control composite material on As and Cd in rice grains, b is a result diagram of the influence of the leaf surface resistance control composite material on the yield of rice, c is a result diagram of the influence of the leaf surface resistance control composite material on the dry weight of rice, and d is a result diagram of the influence of the leaf surface resistance control composite material on the relative content of chlorophyll in the leaves of rice at different growth periods of rice;

[0031] Figure 4 Fig. 10 is a schematic diagram of the test results of the wetting angle, wherein (a) is a result diagram of the wetting angle test of the traditional resistance control agent, and (b) is a result diagram of the wetting angle test of the leaf surface resistance control composite material;

[0032] Figure 5 Fig. 11 is a result diagram of the metal content in the leaves, wherein (a) is a result diagram of the content of arsenic and cadmium elements in the leaves, and (b) is a result diagram of the content of iron elements in the leaves;

[0033] Figure 6 Fig. 12 is a diagram of the element analysis in the leaves. DETAILED DESCRIPTION

[0034] The principles and features of the present application are described below in combination with the drawings, and the examples are only used to explain the present application and are not used to limit the scope of the present application. If the specific conditions are not indicated in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not indicated by the manufacturer, they are all conventional products that can be purchased on the market.

[0035] Example 1

[0036] A preparation method of a leaf surface resistance control composite material, comprising the following steps:

[0037] Step 1, synthesis of Fe-MOFs

[0038] ​Dissolve 0.1 mmol FeCl3·6H2O in 17 mL DMF to obtain solution A; dissolve 0.5 mmol terephthalic acid (C8H6O4) in 10 mL DMF to obtain solution B. Then, drop solution B into solution A drop by drop using a dropper, and then add 3 mL triethylamine solution to obtain a uniform solution. Finally, transfer the mixture into a 100 mL Teflon-lined stainless steel autoclave and react at 180°C for 12 hours. After the reaction is completed, centrifugally wash the orange-red precipitate obtained by using DMF and methanol three times each, and then soak the orange-red precipitate in methanol for three days to obtain Fe-MOFs (referred to as MIL-100).

[0039] Step 2, synthesis of MIL-100@SA

[0040] Step S1, disperse the Fe-MOFs prepared in step 1 in deionized water and magnetically stir for 30 min to mix them uniformly, then heat the mixture to 323 K in a water bath and stir vigorously, and finally slowly add sodium alginate (SA) to completely dissolve it to obtain a mixture; wherein the concentration of Fe-MOFs in the mixture is 5% w / v, and the concentration of sodium alginate is 0.8% w / v.

[0041] Step S2, cool the mixture to room temperature, and drop the CaCl2 solution drop by drop to obtain beads; then crosslink for 45 min, filter, wash with deionized water multiple times to remove residues and solution, and freeze-dry for 24 h to obtain the MIL-100@SA foliar control composite in the form of beads; wherein the mass ratio of sodium alginate to CaCl2 is 1:1.

[0042] The w / v in this embodiment is g / mL.

[0043] Example 2

[0044] A preparation method of a foliar control composite material, comprising the following steps:

[0045] Step 1, synthesis of Fe-MOFs

[0046] Dissolve 0.1 mmol FeCl3·6H2O in 17 mL DMF to obtain solution A; dissolve 0.5 mmol terephthalic acid (C8H6O4) in 10 mL DMF to obtain solution B. Then, drop solution B into solution A drop by drop using a dropper, and then add 3 mL triethylamine solution to obtain a uniform solution. Finally, transfer the mixture into a 100 mL Teflon-lined stainless steel autoclave and react at 180°C for 12 hours. After the reaction is completed, centrifugally wash the orange-red precipitate obtained by using DMF and methanol three times each, and then soak the orange-red precipitate in methanol for three days to obtain Fe-MOFs (referred to as MIL-100).

[0047] Step 2, synthesis of MIL-100@SA

[0048] Step S1, the Fe-MOFs prepared in step 1 were dispersed in deionized water and magnetically stirred for 30 min to mix evenly, then heated to 316K in a water bath and stirred vigorously, and finally slowly added sodium alginate (SA) to completely dissolve to prepare a mixture; wherein the concentration of Fe-MOFs in the mixture was 3% w / v, and the concentration of sodium alginate was 0.6% w / v.

[0049] Step S2, the mixture was cooled to room temperature, and CaCl2 solution was added dropwise to obtain beads; then crosslinked for 30 min, filtered, washed with deionized water several times to remove residues and solution, and freeze-dried for 24 h to obtain MIL-100@SA foliar control composite in the form of beads; wherein the mass ratio of sodium alginate to CaCl2 was 1:1.

[0050] The w / v in this embodiment is g / mL.

[0051] Example 3

[0052] A preparation method of a foliar control composite material, comprising the following steps:

[0053] Step 1, synthesis of Fe-MOFs

[0054] Dissolve 0.1 mmol FeCl3·6H2O in 17 mL DMF, mix evenly to obtain solution A; dissolve 0.5 mmol terephthalic acid (C8H6O4) in 10 mL DMF to obtain solution B. Then, use a dropper to add solution B dropwise to solution A, then add 3 mL triethylamine solution, and obtain a uniform solution. Finally, transfer the mixture to a 100 mL Teflon-lined stainless steel autoclave and react at 180°C for 12 hours. After the reaction is completed, wash the obtained orange-red precipitate with DMF and methanol three times each, and then soak the precipitate in methanol for three days to obtain Fe-MOFs (abbreviated as MIL-100).

[0055] Step 2, synthesis of MIL-100@SA

[0056] Step S1, the Fe-MOFs prepared in step 1 were dispersed in deionized water and magnetically stirred for 30 min to mix evenly, then heated to 338K in a water bath and stirred vigorously, and finally slowly added sodium alginate (SA) to completely dissolve to prepare a mixture; wherein the concentration of Fe-MOFs in the mixture was 7% w / v, and the concentration of sodium alginate was 1.1% w / v.

[0057] Step S2: Cool the mixture to room temperature and add it dropwise to a CaCl2 solution to obtain beads; then crosslink for 60 min and filter, rinse repeatedly with deionized water to remove residues and solution, freeze dry for 24 h to obtain bead-shaped MIL-100@SA leaf surface resistance control composite material; wherein, the mass ratio of sodium alginate to CaCl2 is 1.2:1.3.

[0058] In this embodiment, w / v is g / mL.

[0059] Test Analysis:

[0060] 1. Characterization of the structure of composite materials with blade resistance control

[0061] The leaf surface resistance control composite material (MIL-100@SA) prepared in Example 1 was characterized, and the test results are as follows: Figure 1 As shown, a is the thermogravimetric spectrum of MIL-100@SA, b is the XRD pattern of MIL-100@SA, ce are the XPS (1S of O, 1S of C, 2p of Fe) characterization patterns of MIL-100@SA, and f is the TEM image of MIL-100@SA.

[0062] from Figure 1 As can be seen from this, the present invention has successfully synthesized nanoscale MIL-100@SA materials.

[0063] 2. Performance testing and analysis of blade resistance control composite materials

[0064] The specific test analysis is as follows:

[0065] The experimental field for this test was located at E115°30′14″, N27°18′53″ in Yongfeng County, Ji'an City, Jiangxi Province, China. Sixteen paddy fields were selected in this area as the research area, and each paddy field was designed as a 5m*6m square. Each replicate paddy field contained 20 rice plants, and Lingliangyou 45 was planted in the paddy fields.

[0066] During the test, the rice was divided into three groups: control group (CK): rice leaves were sprayed with water during the tillering stage; MIL-100 group: rice leaves were sprayed with MIL-100 (w / v, 1.5%) during the tillering stage; MIL-100@SA group: rice leaves were sprayed with MIL-100@SA (w / v, 1.5%) during the tillering stage; the irrigation method during the planting process was consistent with the local conventional rice planting method.

[0067] At 24 h after foliar application at the tillering stage, two rice leaves were collected (3 treatments, 4 replicates, n = 24) and immediately stored in liquid nitrogen and then in a -80 °C freezer. The subsequent rice plants were continued to be grown in a traditional manner, keeping the soil flooded until harvest. Sixteen plant tissues (3 replicates per treatment) included root (n = 16), leaf (new and old leaves, n = 16), stem (basal stem and nodal, n = 16), and grain (n = 16).

[0068] The test results are as follows:

[0069] (1) The Fe content in the leaves of rice at different stages between the growth stages of rice 57 Fe content determination

[0070] The test was performed by using 0.1% dilute nitric acid to rinse different leaves at the same position of the same rice plant at different stages during the growth of rice. The rinsing solution was used to determine the Fe content by inductively coupled plasma mass spectrometry (ICP-MS), and the test results are shown in 57 . Figure 2 .

[0071] As can be seen from Figure 2 , the application of foliar control agent MIL-100@SA at the tillering stage of rice can still detect MIL-100@SA from the tillering stage to the harvest stage (i.e. about 30d), which indicates that MIL-100@SA has a long leaf residence time and is helpful for the absorption of Fe and SA by rice. Compared with traditional foliar control agents such as silicon preparations, selenium preparations, sulfur-rich foliar fertilizers, and magnesium sulfate or magnesium nitrate, which need to be sprayed frequently (2-3 times), MIL-100@SA (sprayed once) is almost effective throughout the growth period of rice.

[0072] (2) Test of the effect of foliar control composite material (MIL-100@SA) on rice

[0073] The test results are shown in Figure 3 , wherein a is the effect on As and Cd in rice grains; b is the effect on rice yield; c is the effect on the dry weight of rice; and d is the effect on the relative content of chlorophyll in the leaves of rice at different growth stages.

[0074] As shown in Figure 3 a, MIL-100 and MIL-100@SA significantly reduced the content of inorganic As (iAs) and Cd in the grains. Among them, MIL-100 reduced iAs and Cd in the grains by 32% and 36%, respectively, while MIL-100@SA reduced iAs and Cd in the grains by 45% and 66%, respectively. Therefore, MIL-100@SA can significantly control the absorption and transport of As and Cd by rice, and the control effect is much better than that of MIL-100 alone.

[0075] As Figure 3 b shows and Table 1 shows that compared with the CK group, the test group of spraying MIL-100 and MIL-100@SA on the leaf surface does not improve the parameters of rice (grain, plant height, tillering) (Table 1). Therefore, the effect of diluting heavy metal accumulation by increasing biomass is not significant.

[0076] As Figure 3 c shows that the dry fresh weight ratio of harvested rice plants is between 80% and 82%, and studies have shown that spraying MIL-100@SA on the leaf surface does not enhance the photosynthesis and organic carbon accumulation of rice. However, compared with the CK group, the SPAD index of spraying MIL-100@SA on the leaf surface is significantly increased (d), indicating that spraying the experimental blocking agent can alleviate the stress of heavy metals on rice leaves, which is conducive to improving the metabolic capacity of chloroplasts and improving the tolerance of rice leaves to heavy metals. Figure 3

[0077] Table 1 Physiological parameters of rice after spraying

[0078]

[0079] (3) Wetting angle measurement of the composite material in the application

[0080] The traditional blocking agent (commercially available solution-state leaf blocking agent: Fengfeng rich foliar fertilizer of Foshan Ironman Environmental Protection Technology Co., Ltd.) and the leaf blocking composite material (MIL-100@SA) prepared in Example 1 were subjected to wetting angle test analysis, and the test results are shown in Figure 4 , wherein (a) is the wetting angle test result of the traditional blocking agent, and (b) is the wetting angle test result of the leaf blocking composite material.

[0081] As can be seen from Figure 4 , compared with the traditional blocking agent, the wetting angle of the leaf blocking composite material in the application is significantly reduced, which helps to increase the affinity of the leaf blocking composite material to the rice leaves, prolong the residence time of MIL-100 on the surface of the rice leaves, and increase the action time of the leaf blocking composite material on the rice.

[0082] (4) Analysis of elements in the rice leaf surface after spraying

[0083] The main analysis is the elements in the rice leaf surface 24 hours after spraying in the tillering stage, and the test results are shown in Figure 5 , wherein (a) is the distribution diagram of As and Cd in the leaf, and (b) is the distribution of Fe element in the leaf.

[0084] As can be seen from Figure 5 ​The results show that the Fe content in the leaves of the group sprayed with MIL-100@SA was significantly higher than that of the group sprayed with MIL-100 and the control group (CK group). Simultaneously, the Cd content in the leaves was significantly increased, while the As content was significantly decreased. This indicates that Fe intake alters the distribution of heavy metals within the plant, with Cd mainly accumulating in the leaves, thus mitigating its translocation to the grains.

[0085] (5) For the leaves 111 Cd and 57 Fe micro-area analysis

[0086] Elemental analysis of the blades was performed using laser ablation tandem inductively coupled plasma mass spectrometry (LA-ICP-MS). Detailed test results can be found in [link to relevant documentation]. Figure 6 ;from Figure 6 It can be seen that after spraying MIL-100@SA, Fe was mainly found in the main veins of rice leaves; Cd and Fe showed the same distribution trend, indicating that after Fe ions entered the plant tissue, they inhibited the migration and transformation of Cd between plant tissues, causing Cd to accumulate only in the leaves and reducing its translocation to other parts, especially alleviating the translocation of Cd to grains during the rice grain-filling period.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A leaf surface resistance control composite material, characterized in that, It includes a core material with a barrier function, and a shell layer covering the core material; wherein the core material is Fe-MOFs; and the shell layer is formed of sodium alginate. The preparation method of the blade resistance control composite material includes the following steps: Step S1: Disperse the core material in a solvent and heat it, then add sodium alginate and promote its complete dissolution to obtain a mixture; Step S2: The mixture is added dropwise to CaCl2 solution and cross-linked to obtain a bead-shaped leaf surface resistance control composite material.

2. The blade resistance control composite material according to claim 1, characterized in that, The solvent in step S1 is deionized water; the heating temperature in step S1 is 316~338K.

3. The blade resistance control composite material according to claim 1, characterized in that, The concentration of the core material in the mixture is 3-7% w / v, and the concentration of sodium alginate in the mixture is 0.6-1.1% w / v.

4. The blade resistance control composite material according to claim 1, characterized in that, The crosslinking reaction time in step S2 is 30-60 min, and the crosslinking reaction condition is room temperature.

5. The blade resistance control composite material according to claim 1, characterized in that, The mass ratio of sodium alginate to CaCl2 is 0.8:0.7~1.2:1.

3.

6. The application of the leaf surface barrier composite material according to claim 1 in controlling the transport of As and Cd in plants.

7. The application according to claim 6, characterized in that, The plant is at least one of wheat, corn, sorghum, and rice.

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