Organic-inorganic composite gel transparent soil and preparation method thereof

Abstract

The application discloses an organic-inorganic composite gel transparent soil and a preparation method thereof, and belongs to the technical field of materials. The transparent soil is prepared by forming a three-dimensional gel ball of polysaccharide and clay in a magnesium ion solution with a certain concentration, and then coating the three-dimensional gel ball with silicon dioxide. The transparent soil can be used for observing plant root systems by stacking and filling water, and can be used as a culture medium for plant culture. The transparent soil has the advantages that the structure of the transparent soil is similar to that of real soil aggregates, the organic-inorganic composite is formed mainly by inorganic minerals and supplemented by organic components, and a silicon dioxide coating layer is formed on the surface, so that the transparent soil has mechanical support and good stability without affecting the transparency. The application has the advantages of environmental friendliness, low cost and adaptability to complex experimental scenes, and can be used for plant culture and real-time observation of plant root growth.

Description

Technical Field

[0001] This invention belongs to the field of materials technology and relates to an organic-inorganic composite gel transparent soil and its preparation method. Background Technology

[0002] Roots serve as a bridge between plants and their soil environment, providing essential resources and support while also helping plants adapt to complex environmental conditions through various mechanisms. They are a core component of plant growth, development, and ecosystem function. Root phenotypes are key indicators of plant growth and environmental adaptation, revealing their role by quantifying various root characteristics. However, the inherent opacity of soil makes studying and quantifying root biological processes extremely difficult. Researchers initially used hydroponics to observe plant root growth. While this method is suitable for rapid and simple root observation and nutrient absorption studies, it has limitations in simulating soil environments and studying rhizosphere microorganisms. Other researchers used transparent gels as culture media. Although this method is closer to the natural soil environment than hydroponics and suitable for high-resolution imaging and rhizosphere microbiology studies, these gels are composed of organic polymers and cannot simulate the composition of soil, which is primarily inorganic minerals with supplementary organic components. To address the challenges of hydroponics and gel culture, the development of a transparent soil material that closely resembles real soil and can monitor plant root growth processes offers a new solution for plant root research.

[0003] An existing patent (application number US201816107512A) describes the creation of hydrogel beads by mixing gellan gum and sodium alginate. This allows for the adjustment of the size and porosity of the hydrogel spheres, providing heterogeneous, aerated, and porous conditions for plant growth, thus achieving an environment closer to natural soil. Another patent (application number CN202311749915.8) describes the creation of a transparent soil material by dripping gellan gum and hydroxyethyl cellulose solution into a magnesium-containing MS nutrient mixture. This material exhibits high transparency and stability, and the roots cultivated in this substrate show a high similarity to the traits expressed by roots under natural soil conditions. However, both of these patents have a single gel composition, consisting entirely of organic matter, making them easily degradable, and their structures differ significantly from real soil.

[0004] The most fundamental structure of real soil is aggregates. Soil aggregates are three-dimensional structures composed of various minerals, organic materials, and biological materials. This structure is crucial for soil functions, such as stabilizing organic matter, storing and supplying water, and promoting microbial diversity. No research reports have been found on the preparation of transparent organic-inorganic composite gel soil by mimicking the structure of real soil aggregates through organic-inorganic composites and constructing a silica coating layer on the surface. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems and provide a method for preparing transparent soil with a realistic soil structure that can be used for plant cultivation and root phenotypic observation. This invention maintains the transparency of the transparent soil system while altering its internal composition, resulting in a transparent soil material with a three-dimensional structure similar to real soil.

[0006] To achieve the above objectives, the present invention is based on the following: Lithium magnesium silicate is a layered silicate mineral with a lamellar structure similar to clay minerals in soil. Furthermore, it can rapidly disperse in water to form a transparent thixotropic gel with minimal impact on transparency, making it suitable as a clay colloid in transparent soil. In addition, numerous studies have demonstrated (e.g., Li D et al., Comprehensive Reviews in Food Science and Food Safety, 20, 5345-5369, 2021) that alginate, as a biopolymer, can form an "egg-box" model gel with a three-dimensional molecular network through selective binding with polyvalent cations. This gel exhibits high water absorption and retention properties similar to soil organic components, making it an ideal matrix material for preparing transparent soil. Sodium alginate can also be compounded with other materials to enhance the properties of the matrix material itself while also endowing the material with multifunctionality. Therefore, sodium carboxymethyl cellulose is added to the sodium alginate solution to make the gel structure dense; and after the sodium alginate gel is formed, the surface of the gel material is chemically modified by hydrolyzing tetraethyl orthosilicate (TEOS) through the sol-gel method to prepare a silica layer to improve the stability of sodium alginate gel spheres, reduce their degradability, and better simulate soil characteristics.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] In a first aspect, an organic-inorganic composite gel transparent soil is provided, the transparent soil comprising silica-modified magnesium lithium silicate composite polymer hydrogel microspheres, made from the following raw materials in the following mass percentages:

[0009] 1.4% polysaccharide, 2.8-5.6% clay, 1.55-3.1% silica, 0.05% crosslinking agent, balance deionized water;

[0010] The polysaccharide is a mixture of sodium alginate and sodium carboxymethyl cellulose in a mass ratio of 1:1; preferably, the ratio of β-D-mannuronic acid (M) to α-L-guluronic acid (G) is <1, and the degree of substitution (DS, i.e., the average number of carboxymethyl groups on each glucose unit) of sodium carboxymethyl cellulose is 0.9~1.2.

[0011] The clay is lithium magnesium silicate;

[0012] The silica is formed by the hydrolysis and condensation of tetraethyl orthosilicate via a sol-gel method; the crosslinking agent is magnesium chloride hexahydrate or magnesium sulfate heptahydrate.

[0013] Secondly, a method for preparing organic-inorganic composite gel transparent soil is provided, comprising the following steps:

[0014] (1) Add the organic components and clay colloids to deionized water in sequence, and stir at room temperature until the solution is clear and transparent to obtain an organic-inorganic mixture.

[0015] (2) The organic-inorganic mixture was squeezed into the stirred crosslinking agent solution by a syringe through a syringe pump. After crosslinking and curing for 0.5 h, it was filtered out and washed with deionized water to obtain organic-inorganic composite gel balls.

[0016] (3) Mix tetraethyl orthosilicate, anhydrous ethanol and deionized water, adjust the pH to 2-4 with dilute hydrochloric acid, stir rapidly at room temperature for 6 h until completely transparent, and then heat in an 80℃ water bath until the anhydrous ethanol is completely evaporated to obtain tetraethyl orthosilicate hydrolysate.

[0017] (4) The organic-inorganic composite gel spheres and tetraethyl orthosilicate hydrolysate were mixed at a mass ratio of 1:2 and stirred and condensed at room temperature for 3 h to obtain the organic-inorganic composite gel spheres. The mixture was filtered out and washed with deionized water to obtain the transparent soil.

[0018] In some preferred embodiments, the syringe in step (2) of the present invention is 20 ml 1.2# (the actual size can be determined by the size of the transparent soil hydrogel microspheres to be prepared), the injection pump speed is 4 mm / min, the drop height is 1 cm above the liquid surface, the concentration of the cross-linked metal ion salt solution is 0.05 mol / L, and the stirring speed of the magnesium chloride solution is 100 r / min.

[0019] Preferably, in step (3) of the present invention, the mass ratio of tetraethyl silicate, anhydrous ethanol and deionized water is 1:3:6 to 1:6:12.

[0020] Thirdly, an application of organic-inorganic composite gel transparent soil is provided. After stacking and filling with water, the transparent soil material can be used for plant cultivation and root phenotypic observation.

[0021] Compared with other methods, the beneficial technical effects of this invention are:

[0022] (1) Compared with existing transparent soil, this invention simulates the chemical composition and aggregate structure of soil, with inorganic minerals as the main component and organic components as the auxiliary component, realizing organic-inorganic composite, which changes the situation that existing transparent soil is mainly composed of organic matter;

[0023] (2) This invention uses a sol-gel method to coat amorphous silica onto the surface of transparent soil. By combining the flexibility of sodium alginate organic gel with the stability of silica inorganic material, the durability of the gel is improved, the physical and chemical properties of transparent soil are optimized, and it is closer to real soil. Attached Figure Description

[0024] Figure 1 Scanning electron microscope images of organic-inorganic composite gel transparent soil No. 2 at 35x (A) and 2kx (B);

[0025] Figure 2 The images show the effects of organic-inorganic composite gel transparent soil #2 without filling (A) and with water filling (B);

[0026] Figure 3 Diagram showing the water-holding capacity of transparent soil from organic-inorganic composite gels;

[0027] Figure 4 Collapse curve of transparent soil from organic-inorganic composite gel;

[0028] Figure 5 Photographs of Arabidopsis thaliana roots after 14 days of growth in real soil (A) and transparent organic-inorganic composite gel soil (B). Detailed Implementation

[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0030] Example 1: Preparation of transparent soil.

[0031] Transparent soil was prepared according to the formula in the table below. The organic components and clay were added to deionized water in sequence according to the ratio. The mixture was stirred at room temperature until the solution was clear and transparent. It was then poured into a 20 ml 1.2# syringe, attached to a syringe pump, and squeezed through the syringe pump at a speed of 4 mm / min. The mixture was dripped into a 0.05 mol / L magnesium chloride hexahydrate solution stirred at 100 r / min from a height of 1 cm above the liquid surface. After cross-linking and solidification for 0.5 h, it was filtered out and washed with deionized water to obtain organic-inorganic composite gel spheres.

[0032] Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a mass ratio of 1:3:6 to 1:6:12. The pH was adjusted to between 2 and 4 with dilute hydrochloric acid. The mixture was stirred at 600 r / min at room temperature for 6 h until it became completely transparent. Then, it was heated in an 80℃ water bath until the anhydrous ethanol was completely evaporated to obtain a tetraethyl orthosilicate hydrolysate.

[0033] Organic-inorganic composite gel spheres and tetraethyl orthosilicate hydrolysate were mixed at a mass ratio of 1:2 and stirred and condensed at room temperature for 3 h to obtain organic-inorganic composite gel spheres. The spheres were filtered out and washed with deionized water to obtain the transparent soil in which the silica content of 1-3# was 3.1% and the silica content of 4-6# was 1.55%.

[0034] The resulting transparent soil was freeze-dried and imaged using a scanning electron microscope at 35x and 2kx magnification, as shown below. Figure 1 As shown in (A) and (B), it can be seen that the prepared transparent soil has pores of varying sizes, which are similar to the capillary pores in the soil aggregate structure. Furthermore, the cementation characteristics brought about by polysaccharides can be observed, indicating that the prepared transparent soil has a similar aggregate structure to real soil.

[0035] Table 1 Transparent Soil Formulation (The remainder is deionized water)

[0036]

[0037] Example 2: Evaluation of transparency of transparent soil.

[0038] Transparent soil samples 1-3# prepared in Example 1 (the coating effect of 1-3# is slightly better than that of 4-6#, and the presentation effect is better; 1-3# will be shown in subsequent examples) were selected and placed into 12.5 mm × 12.5 mm × 45 mm cuvettes. Water was added to submerge the transparent soil. Using pure water as the 100% transmittance, the transmittance at 680 nm (visible light) and 1000 nm (infrared light) was measured using a spectrophotometer. The results are shown in the table below. Transparent soil samples 1-3# achieved a transmittance of >60% at 1000 nm. The prepared transparent soil was then placed into 25 ml petri dishes, which were filled with water. After filling, the text at the bottom of the petri dish could be observed under visible light, such as... Figure 2 As shown, a transparent effect can be achieved.

[0039] Table 2. Statistical table of light transmittance of transparent soil

[0040]

[0041] Example 3: Evaluation of the water-holding capacity of transparent soil.

[0042] The transparent soil samples #1-3 prepared in Example 1 were soaked in pure water for 24 hours to maximize water-holding capacity. 4-5 g of each sample was taken, surface moisture was blotted off, and the initial mass was recorded. The samples were then placed in 10 ml centrifuge tubes and placed in a constant 25°C light incubator for natural water loss under 16 hours of light / 8 hours of darkness. The mass was measured every 24 hours, and the percentage relative to the initial mass was calculated. This was recorded continuously for 14 days. The results are as follows: Figure 3 As shown in the image, the transparent soil retains 50% of its original mass after two weeks, demonstrating good water retention capacity.

[0043] Example 4: Evaluation of the compressibility of transparent soil.

[0044] The transparent soil samples #1-3 prepared in Example 1 were subjected to mechanical tests on an electronic universal testing machine to simulate the maximum pressure that particles can withstand when compressed and collapsed in a semi-closed system. The organic-inorganic composite gel transparent soil, with its surface moisture removed, was added to a graduated cylinder containing 10 ml of water to make a volume of 12 ml. The resulting 2 ml volume of transparent soil was then filtered out, its surface moisture removed again, and loaded into a 10 ml syringe. Compression was performed from an initial position of 30 mm at a compression rate of 5 mm / min to obtain the maximum pressure. The maximum compressive stress results are shown in the table below, and the compressive stress-strain curves are shown in the figure. Figure 4 As shown, of the three transparent soils, soil #2 has the best resistance to compression.

[0045] Table 3. Statistical table of compressibility of transparent soil

[0046]

[0047] Example 5: Effects of plant culture and root phenotype observation in transparent soil.

[0048] The No. 2 transparent soil prepared in Example 1 (selecting transparent soil with the best physical properties) was added to a 20 ml transparent container, and 1 / 2 Hoagland nutrient solution was added to cover the transparent soil. Arabidopsis seeds were added to centrifuge tubes filled with water and vernalized at 5°C for 72 h, then sown into the transparent soil. Sterilized cultivated soil was set up as a control group, also sown with Arabidopsis seeds. Both groups were placed in a 25°C light incubator for a 16 h light / 8 h dark cycle. After the seeds reached the seedling stage, the seedlings from the control group were compared with those grown in the transparent soil. The actual results are as follows: Figure 5 As shown, transparent soil can be used for soil plant culture and root phenotyping.

[0049] Example 6: Stability evaluation of transparent soil.

[0050] Take 4-5 g of the transparent soil No. 2 prepared in Example 1, absorb the residual moisture on the surface, and place it in a 20 ml container. Add water to cover the transparent soil and store it at a constant temperature of 25°C for 28 days. Record the mass every 7 days and calculate the percentage of the original mass. In addition, take the transparent soil near the plant roots in Example 5 and perform the same operation. The results are shown in Table 4. It can be seen that whether the transparent soil is stored in pure water or used for plant cultivation, it can still maintain about 93% of the original mass after 28 days. Therefore, it will not shrink in size like the organic transparent soil, so it has high stability.

[0051] Table 4. Statistical Table of Changes in the Storage Quality of Transparent Soil

[0052]

[0053] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. An organic-inorganic composite gel transparent soil, characterized in that, The transparent soil comprises silica-modified magnesium lithium silicate composite polymer hydrogel microspheres, made from the following raw materials in the indicated mass percentages: 1.4% polysaccharide, 2.8-5.6% lithium magnesium silicate, 1.55-3.1% silica, 0.05% crosslinking agent, balance water; The polysaccharide is a mixture of sodium alginate and sodium carboxymethyl cellulose; The sodium alginate and sodium carboxymethyl cellulose are mixed in a mass ratio of 1:1; the ratio of β-D-mannuronic acid to α-L-guluronic acid in the sodium alginate is <1, and the degree of substitution of sodium carboxymethyl cellulose is 0.9~1.

2. The silica is formed by the hydrolysis and condensation of tetraethyl orthosilicate via a sol-gel method.

2. The organic-inorganic composite gel transparent soil as described in claim 1, characterized in that, The crosslinking agent is magnesium chloride hexahydrate or magnesium sulfate heptahydrate.

3. A method for preparing the organic-inorganic composite gel transparent soil according to any one of claims 1-2, characterized in that, Includes the following steps: Polysaccharide, lithium magnesium silicate, and water were mixed and stirred at room temperature until the solution became clear and transparent. Droplets were formed and cross-linked and solidified to obtain organic-inorganic composite gel spheres. A silica-modified layer was prepared by hydrolysis and condensation via sol-gel method.

4. The method for preparing organic-inorganic composite gel transparent soil as described in claim 3, characterized in that, After the solution is stirred until it is clear and transparent, droplets are formed using a syringe and dropped into the stirred crosslinking agent. The syringe size is determined by the size of the hydrogel microspheres to be prepared, the injection pump speed is 4 mm / min, the drop height is 1 cm above the liquid surface, the crosslinking agent is a metal ion salt solution with a concentration of 0.05 mol / L, and the solution stirring speed is 100 r / min.

5. The method for preparing organic-inorganic composite gel transparent soil as described in claim 3, characterized in that, The preparation of the silica-modified layer by hydrolysis-condensation via sol-gel method includes: mixing tetraethyl orthosilicate, anhydrous ethanol, and water, adjusting the pH to 2-4, stirring at room temperature until completely transparent, and then heating in an 80°C water bath until the anhydrous ethanol is completely evaporated to obtain a hydrolysate; mixing the organic-inorganic composite gel spheres and the hydrolysate at a mass ratio of 1:2, stirring at room temperature to condense and obtain the organic-inorganic composite gel spheres, and then filtering and washing them.

6. The method for preparing organic-inorganic composite gel transparent soil as described in claim 5, characterized in that, The mass ratio of tetraethyl orthosilicate, anhydrous ethanol, and water is 1:3:6 to 1:6:

12.

7. Use of the organic-inorganic composite gel transparent soil according to claim 1, characterized in that: Used for plant culture and for observing root phenotypes.

Images