A composite material for simultaneously improving soil acidification and pesticide residues and a preparation method thereof

Abstract

The application discloses a composite material for simultaneously improving soil acidification and pesticide residue, wherein nano calcium hydroxide is loaded on active carbon as a carrier, and the mass ratio of the active carbon to the nano calcium hydroxide is 1: (0.9-1.5). The composite material is prepared by adding active carbon and sodium hydroxide solution into a calcium chloride solution in sequence under a nitrogen atmosphere, washing and drying the precipitate after the reaction, and the application of the composite material in simultaneously changing the pH value of acidic soil and adsorbing diuron and 3,4-dichloroaniline in the acidic soil. The composite material of the application loads nano calcium hydroxide on active carbon, and by limiting the mass ratio of the active carbon to nano calcium carbonate, the pH value of acidic soil can be effectively improved, and diuron and 3,4-dichloroaniline in the soil can be simultaneously adsorbed, so that the application is simple, and the problems of soil acidification and pesticide residue, two soil pollution problems, are solved.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation, specifically relating to a composite material and its preparation method that simultaneously improves soil acidification and pesticide residues. Background Technology

[0002] In recent years, my country's agricultural technology has developed rapidly, but this development has also brought many problems, the most serious of which is soil pollution. Soil pollution includes heavy metal pollution, pesticide and fertilizer residue pollution, biological pollution, and radioactive material pollution. Common remediation measures for soil pollution include soil covering, soil replacement, biological measures, and adding adsorbents to the soil. Adding adsorbents to the soil mainly reduces the transfer and migration capacity of pollutants, fixing them in a specific part of the soil, thereby preventing these pollutants from migrating into humans and plants and avoiding their damage to the ecological environment. Currently, we have found studies on adding biochar and bentonite as adsorbents to lead-contaminated soil, which can effectively reduce the concentration of lead ions in the soil. We have also found research on the adsorption of heavy metal ions and diuron using activated carbon, such as Yu Xiangyang et al.'s "Slow Adsorption of Diuron in Soil by Biochar and Its Influence on Desorption Behavior" and Du Ying's "Study on Adsorption of Residual Diuron in Soil by Biochar." However, soil pollution is not solely caused by pesticide residues, and diuron is not the only component of pesticide residues in soil. Therefore, how to solve multiple soil problems at once is a research direction in this field. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned technical problems and provide a composite material, preparation method and application that can simultaneously improve soil acidification and pesticide residues. This invention can not only effectively improve the pH value of acidic soil, but also simultaneously adsorb diuron and 3,4-dichloroaniline in the soil.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] A composite material that simultaneously improves soil acidification and pesticide residues, wherein the composite material is nano-calcium hydroxide loaded on activated carbon.

[0006] As a further technical solution, the mass ratio of the activated carbon and nano-calcium hydroxide mentioned above is 1:(0.9~1.5).

[0007] As a further technical solution, the mass ratio of the activated carbon and nano-calcium hydroxide mentioned above is 1:1.3.

[0008] As a further technical solution, the activated carbon mentioned above is bamboo shavings activated carbon, and the diameter of the nano-calcium hydroxide is 45-120 nm.

[0009] A method for preparing a composite material that simultaneously improves soil acidification and pesticide residues involves adding activated carbon and sodium hydroxide solution sequentially to a calcium chloride solution under a nitrogen atmosphere. After the reaction is complete, the precipitate is washed and dried to obtain the composite material.

[0010] As a further technical solution, the ratio of activated carbon, calcium chloride and sodium hydroxide mentioned above is 14-25g:0.3mol:0.6mol.

[0011] As a further technical solution, the preparation of the activated carbon described above includes the following steps:

[0012] (1) Mix bamboo shavings and phosphoric acid solution at a ratio of 1g:2-3mL evenly, and age at room temperature for 2-5 hours;

[0013] (2) Carbonize the aged mixture at 300-350℃ for 0.5-2h to obtain bamboo chip carbonized material;

[0014] (3) Activate the bamboo chip carbon at 450-500℃ for 1-1.5h, then cool, wash, dry and crush and sieve to obtain activated carbon.

[0015] As a further technical solution, the phosphoric acid content in the phosphoric acid solution described above is 40% to 50% by mass.

[0016] Application of a composite material that simultaneously improves soil acidification and pesticide residues, the composite material being used to simultaneously alter the pH of acidic soils and absorb diuron and 3,4-dichloroaniline from acidic soils.

[0017] As a further technical solution, the pH value of the acidic soil is 3.50 to 4.50, the mixing ratio of the composite material and the acidic soil is (3 to 5) g: 1 kg, and the adsorption time of the composite material on the acidic soil is 300 to 360 min.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. The composite material of the present invention uses activated carbon as a carrier to load nano-calcium hydroxide. By limiting the mass ratio of activated carbon and nano-calcium carbonate, it can not only effectively improve the pH value of acidic soil, but also simultaneously adsorb diuron and 3,4-dichloroaniline in the soil. It is simple to use and solves the two soil pollution problems of soil acidification and pesticide residues.

[0020] 2. This invention improves the adsorption capacity of the product by preparing it under a nitrogen atmosphere, resulting in better overall adsorption of diuron and 3,4-dichloroaniline.

[0021] 3. When the composite material of the present invention is applied to acidic soil, by limiting the amount of input and the mass ratio of activated carbon and nano-calcium carbonate, it can not only improve the pH value of acidic soil to reach the pH value of 6.1 to 7.7 suitable for crop growth, thereby improving crop yield and quality, but also ensure the best comprehensive removal effect of diuron and 3,4-dichloroaniline (DCA) in the soil.

[0022] 4. This invention prepares activated carbon from bamboo shavings remaining after bamboo processing, thereby improving the utilization rate of bamboo shavings and providing a new approach to the preparation of activated carbon from bamboo shavings. Attached Figure Description

[0023] Figure 1 The graph shows the effect of different mass ratios of bamboo-based activated carbon and nano-calcium hydroxide in the composite material of this invention on the adsorption rates of diuron and 3,4-DCA in soil.

[0024] Figure 2 This is a graph showing the effect of different mass ratios of bamboo-based activated carbon and nano-calcium hydroxide in the composite material of this invention on soil pH.

[0025] Figure 3 SEM images of bamboo shavings activated carbon at different scales: (a) SEM image at a 5 μm scale; (b) SEM image at a 200 nm scale.

[0026] Figure 4 (c) SEM images of the composite material in Example 3 of the present invention at different scales; (d) SEM image at a 5 μm scale;

[0027] Figure 5 SEM images of activated carbon composite materials synthesized without nitrogen flow at different scales; (e) SEM image at 5 μm scale; (f) SEM image at 200 nm scale;

[0028] Figure 6 Fourier transform infrared spectra of different adsorbent materials;

[0029] Figure 7 The adsorption rates of diuron for different adsorbent materials;

[0030] Figure 8 The adsorption rates of 3,4-dichloroaniline (DCA) on different adsorbent materials;

[0031] Figure 9 The graph shows the effect of different amounts of the composite material of the present invention on the adsorption rates of diuron and 3,4-DCA. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited to the scope shown in the embodiments.

[0033] A composite material that simultaneously improves soil acidification and pesticide residues is disclosed. The composite material uses bamboo-based activated carbon as a carrier to support nano-calcium hydroxide. The diameter of the nano-calcium hydroxide is 45–120 nm. The mass ratio of bamboo-based activated carbon to nano-calcium hydroxide is 1:(0.9–1.5). Specific implementation examples are shown in Table 1.

[0034] Table 1

[0035]

[0036] A method for simultaneously improving soil acidification and pesticide residues using a composite material, comprising:

[0037] (1) Preparation of bamboo shavings activated carbon: Weigh 10g of dried and pulverized bamboo shavings to 60 mesh, measure 15mL of 40.8% phosphoric acid solution and mix with the raw bamboo shavings, stir evenly, and let it age at room temperature for 4h. The aged mixture is placed in a crucible and placed in a box-type resistance furnace, carbonized at 300℃ for 1.5h, and then activated at 450℃ for 1h in the box-type resistance furnace. After cooling, the activated raw material is taken out and rinsed multiple times with distilled water in a circulating water multi-purpose vacuum pump until neutral to wash away the phosphoric acid remaining in the activated raw material. The washed raw material is dried in an electric thermostatic drying oven, pulverized through 100 mesh after drying to obtain bamboo shavings activated carbon, which is then bagged for later use.

[0038] (2) Add 250 mL of 0.3 mol / L calcium chloride solution to a three-necked flask. Before the reaction, purge with nitrogen to remove dissolved oxygen and carbon dioxide. Then add bamboo shavings activated carbon and stir for 0.5 h. Slowly add 0.6 mol / L sodium hydroxide solution at 0.2–1.0 mL / min while stirring and purging with nitrogen. After the sodium hydroxide solution has been added, continue purging with nitrogen and stirring for 30 min. After the reaction, wash the precipitate eight times with distilled water at 90–100 °C and freeze-dry to obtain activated carbon-supported nano-calcium hydroxide nanocomposite material.

[0039] Based on the above preparation parameters, composite materials with different proportions in Examples 1-4 were prepared by controlling the amount of bamboo shavings activated carbon added. The material proportions of bamboo shavings activated carbon, calcium chloride, and sodium hydroxide are shown in Table 2.

[0040] Table 2

[0041]

[0042] Application and Comparative Experiments of Composite Materials

[0043] Soil sampling: Soil samples were collected using a five-point sampling method from sugarcane fields in Laibin City, Guangxi Province. After collection, the soil samples were air-dried, impurities were removed, crushed, and sieved through a 60-mesh sieve. The samples were then uniformly mixed and stored for testing. The soil pH ranged from 3.50 to 4.50. In this application example, the soil pH was 4.35, indicating severe soil acidification.

[0044] (1) Effect of the mass ratio of bamboo-based activated carbon and nano-calcium hydroxide on the remediation effect of sugarcane soil

[0045] Experimental Procedure: 10g of soil was taken and mixed with 25mL of a 20mg / L diuron and 3,4-DCA mixed solution. Then, 0.03g of activated carbon composite materials from Examples 1-4 (different mass ratios) was added for adsorption for 300min. The adsorption reaction was then carried out using a benchtop constant-temperature shaker at 150r / min and 298.15K. After the corresponding adsorption time, the mixture was centrifuged at 4000r / min for 10min. The supernatant was collected and filtered through a 0.22μm microporous membrane. The concentrations of remaining diuron and 3,4-DCA in the solution were determined and calculated using high-performance liquid chromatography (HPLC). The experiment was repeated three times, and the average value was taken. The adsorption effects of the activated carbon composite materials from Examples 1-4 on diuron and 3,4-DCA in soil are as follows: Figure 1 As shown.

[0046] from Figure 1 It can be seen that the adsorption rates of diuron and 3,4-DCA in the soil significantly increase with the increase of the mass ratio of bamboo-based activated carbon to nano-calcium hydroxide. When the mass ratio of bamboo-based activated carbon to nano-calcium hydroxide is 1:1.3, the adsorption rates of diuron and 3,4-DCA in the soil by the activated carbon composite material are 97.67% and 95.87%, respectively, which is the optimal adsorption effect. Afterward, with further increases in the mass ratio, the adsorption rate of diuron remains basically unchanged, while the adsorption rate of 3,4-DCA decreases slightly.

[0047] from Figure 2It can be seen that the soil pH gradually increases with the increase of the mass ratio of bamboo-based activated carbon to nano-calcium hydroxide. After 300 minutes of adsorption reaction with the activated carbon composite material of bamboo-based activated carbon and nano-calcium hydroxide in Example 1 (mass ratio 1:0.9), the soil pH increased from 4.35 to 5.54. After 300 minutes of adsorption reaction with the activated carbon composite material of bamboo-based activated carbon and nano-calcium hydroxide in Example 2 (mass ratio 1:1.1), the soil pH increased from 4.35 to 5.77. Although the soil pH increased after adsorption, it did not reach the optimal soil pH for sugarcane growth. After 300 minutes of adsorption reaction with the activated carbon composite material of bamboo shavings activated carbon and nano-calcium hydroxide in a mass ratio of 1:1.3 (Example 3), the pH increased from 4.35 to 6.21. At this point, the pH of the soil after adsorption was 6.0–6.5, ensuring optimal pesticide removal and significantly improving soil acidification. Under the same experimental conditions, after adsorption with the activated carbon composite material of bamboo shavings activated carbon and nano-calcium hydroxide in a mass ratio of 1:1.5 (Example 4), the soil pH increased from 4.35 to 7.8, slightly exceeding the optimal pH range for sugarcane soil: 6.1–7.7. Furthermore, the adsorption rates of diuron and 3,4-DCA in the soil by the activated carbon composite material were 97.51% and 95.47%, respectively, showing a decrease in both adsorption rates. This is because diuron is easily hydrolyzed under acidic conditions but relatively stable under neutral conditions. Therefore, the adsorption rate of diuron by the activated carbon composite material is higher in acidic solutions, and the adsorption amount tends to stabilize as the pH gradually increases. Furthermore, the adsorption capacity of diuron in soil by the activated carbon composite material decreased with increasing pH. Under low pH conditions, the active groups in the soil protonated, increasing the adsorption sites for diuron molecules on the soil surface, which was beneficial for soil absorption of diuron. Conversely, increasing the soil pH caused the active groups in the soil to ionize, and diuron molecules competed with water molecules for adsorption sites on the soil surface, thus reducing soil adsorption of diuron. For 3,4-DCA in soil, when the pH value was greater than 3, the adsorption effect of 3,4-DCA increased with increasing pH, then decreased with further increases in pH, reaching a maximum at pH 6.5. Meanwhile, organic pollutants in molecular form were more easily adsorbed by the soil. Under alkaline conditions, both diuron and 3,4-DCA were easily dissociated, so the adsorption rate decreased as the solution pH increased to an alkaline state. Finally, the optimal comprehensive soil remediation effect was achieved when the mass ratio of bamboo-based activated carbon to nano-calcium hydroxide in Example 3 was 1:1.3.

[0048] (2) The effect of different adsorbents on the remediation effect of sugarcane soil

[0049] Bamboo shavings activated carbon (AC): The bamboo shavings activated carbon prepared in step (1) of Example 7 was used. Its morphology and structure are as follows... Figure 3 As shown.

[0050] Activated carbon composite material (C&[Ca(OH)2&N2]) synthesized by nitrogen gas: The product of Example 3 obtained by the preparation method of Example 7. Morphological structure as follows... Figure 4 As shown.

[0051] Activated carbon composite material (AC&Ca(OH)2) synthesized without nitrogen gas: Based on Example 7, the product obtained by changing step (2) to not introducing nitrogen gas. Morphological structure as follows... Figure 5 As shown.

[0052] Depend on Figure 3 It can be seen that the surface of bamboo shavings activated carbon is relatively smooth, with many pores, and the pores are relatively intact; from Figure 4 It can be seen that the activated carbon composite material synthesized by nitrogen gas exhibits reduced surface porosity and the appearance of numerous particulate solids, indicating that calcium hydroxide has been loaded onto the activated carbon. Figure 5 It can be seen that the surface of the activated carbon composite material synthesized without nitrogen becomes rough and granular solids appear, but some irregular pore structures are generated. It is considered that carbon dioxide in the air reacts with some calcium hydroxide to form calcium carbonate, which causes the surface of the activated carbon composite material to become rough and the pores to expand irregularly.

[0053] Infrared spectra of bamboo shavings activated carbon (AC), activated carbon composite material synthesized with nitrogen gas (C&[Ca(OH)2&N2]), and activated carbon composite material synthesized without nitrogen gas (AC&Ca(OH)2) are shown below. Figure 6 As shown, by Figure 6 It can be seen that in the infrared spectrum of bamboo shavings activated carbon (AC), 1037.7 cm⁻¹ -1 It is the bending vibration peak of the hydroxyl group, 1000–1750 cm⁻¹ -1 There are also some small absorption peaks within the range, corresponding to C—C, C—H stretching vibration peaks, etc. In the infrared spectrum of the activated carbon composite material (C&[Ca(OH)2&N2]) synthesized under nitrogen, the peaks are 405.1, 871.8, and 1475.544 cm⁻¹. -1 The peaks are Ca-OH stretching vibration peaks, and all of the above characteristic peaks indicate that Ca(OH)2 has been well loaded onto activated carbon.

[0054] Experimental procedure: 10g of soil was mixed with 25mL of a 20mg / L diuron and 3,4-DCA mixed solution. Then, 0.0260g of activated carbon, 0.0600g each of nitrogen-synthesized activated carbon composite material and nitrogen-free activated carbon composite material were added to the solution. The adsorption times were 30, 60, 120, 180, 240, 300, 360, and 420min, respectively. The adsorption reaction was carried out using a benchtop constant temperature shaker at 150r / min and 298.15K. After the corresponding adsorption time, the solution was centrifuged at 4000r / min for 10min. The supernatant was collected and filtered through a 0.22μm microporous membrane. The concentrations of diuron and 3,4-DCA remaining in the solution were determined and calculated using high performance liquid chromatography. The experiment was repeated 3 times, and the average value of the results was taken.

[0055] The adsorption effects of different adsorbents on diuron and 3,4-DCA in soil are as follows: Figure 7 and Figure 8 As shown:

[0056] Depend on Figure 7 and Figure 8It can be seen that the adsorption capacity of different adsorbents for diuron and 3,4-DCA is as follows: activated carbon composite material synthesized with nitrogen gas > activated carbon composite material synthesized without nitrogen gas > bamboo shavings activated carbon. The adsorption rates for diuron and 3,4-DCA are both: diuron > 3,4-DCA. With the extension of the shaking adsorption time, the adsorption rates of diuron and 3,4-DCA of the three different adsorbents gradually increase. However, with the extension of the adsorption time, the increasing trend gradually slows down. Among them, the adsorption rate of bamboo shavings activated carbon reaches the maximum value when the shaking adsorption time is 240 min, at which time the adsorption rates for diuron and 3,4-DCA are 94.28% and 93.80%, respectively. After that, the adsorption rate remains basically unchanged and tends to stabilize. The adsorption rates of diuron and 3,4-DCA for both activated carbon composite materials tended to stabilize after 300 min of adsorption reaction. Specifically, the activated carbon composite material synthesized under nitrogen gas showed adsorption rates of 97.57% and 95.87% for diuron and 3,4-DCA, respectively, while the activated carbon composite material synthesized without nitrogen gas showed adsorption rates of 97.56% and 95.33%, respectively. Afterward, the adsorption rates remained essentially constant, reaching an equilibrium state. This is because at the beginning of adsorption, there were relatively more adsorption sites on the surface of the bamboo-based activated carbon. Furthermore, the relatively high initial concentrations of diuron and 3,4-DCA in the solution resulted in greater kinetic energy for adsorption and transfer, leading to a rapid adsorption rate for the activated carbon composite material. Subsequently, as the number of adsorption sites on the surface of the adsorbent material decreased, the removal rate gradually slowed down, and the adsorption sites on the surface of the activated carbon composite material became saturated after 300 min. Furthermore, the adsorption rates of diuron and 3,4-DCA of the activated carbon composite material synthesized under nitrogen protection were greater than those of the activated carbon composite material synthesized without nitrogen protection, indicating that the activated carbon composite material synthesized under nitrogen protection conditions has a better adsorption effect and a more significant removal rate of pesticides in sugarcane soil.

[0057] The effects of different adsorbents on soil pH changes are shown in Table 3:

[0058] Table 3

[0059]

[0060] Table 3 shows that bamboo-based activated carbon had a relatively small impact on soil pH. After 240 minutes of adsorption, the soil pH increased from 4.35 to 4.38 by only 0.03 units, and then stabilized. The activated carbon composite material had a larger impact on soil pH, and there was no significant difference in soil pH changes between synthesizing the composite material under nitrogen protection and other conditions. After 300 minutes of adsorption, the soil pH increased from 4.35 to 6.21, an increase of 1.86 units, and then stabilized. The experimental data indicate that the activated carbon composite material can effectively improve soil acidification, and the activated carbon composite material synthesized under nitrogen protection has a higher adsorption rate.

[0061] (3) The effect of the amount of activated carbon composite material added in this invention on the remediation effect on sugarcane soil

[0062] Experimental procedure: Take 10g of soil and mix it with 25mL of a mixed solution of diuron and 3,4-DCA with a concentration of 20mg / L. Then, add 0.015g, 0.025g, 0.03g, 0.035g, 0.04g, 0.045g, and 0.5g of the composite material from Example 3. The adsorption time is 300min. The adsorption reaction is carried out in a benchtop constant temperature shaker at a speed of 150r / min and a temperature of 298.15K. After the corresponding adsorption time, the mixture is centrifuged at a speed of 4000r / min for 10min. The supernatant is taken out and filtered through a 0.22μm microporous membrane. The concentrations of diuron and 3,4-DCA remaining in the solution are determined and calculated by high performance liquid chromatography. The experiment is repeated 3 times and the average value is taken.

[0063] Calcium hydroxide increases soil pH by increasing the concentration of hydroxide ions in the soil solution, and since hydroxide ions are directly produced by the hydrolysis of calcium hydroxide, it has a significant impact on soil pH changes. The sugarcane soil used in the experiment had an initial pH of 4.35, indicating severe soil acidification. Figure 9 It can be seen that the adsorption rates of the composite material of this invention for diuron and 3,4-DCA increase with the increase of the input amount. Table 3 shows that adding 0.03g of the composite material in this experiment increased the soil pH from 4.35 to 6.21, an increase of 1.86 units. At this point, the adsorption rate of diuron was 97.67%, and the adsorption rate of 3,4-DCA was 95.87%. When the addition amount was 0.5g of the composite material, the soil pH increased from 4.35 to 7.8 units. At this point, the adsorption rate of diuron was 97.68%, and the adsorption rate of 3,4-DCA was 94.61%, with the adsorption capacity of diuron being greater than that of 3,4-DCA. However, after adding 0.05g of activated carbon composite material, the soil pH was higher than the optimal pH for sugarcane growth. Furthermore, the excessive application of calcareous soil conditioners can lead to an imbalance of various nutrients in the soil, thereby inhibiting crop absorption of nutrients and causing negative effects such as reduced crop yield. Therefore, the soil pH value after adsorption being within the optimal pH range for sugarcane growth and the soil acidification degree being improved as much as possible helps to increase the adsorption rate of diuron and 3,4-DCA by activated carbon composite material. The optimal addition amount of composite material is 0.03g.

[0064] The above embodiments are merely specific examples to further illustrate the purpose, technical solution, and beneficial effects of the present invention, and the present invention is not limited thereto. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the disclosure of the present invention are included within the protection scope of the present invention.

Claims

1. Use of a composite material for simultaneously improving soil acidification and pesticide residues, characterized in that: The application of the composite material to simultaneously change the pH value of acidic soil and adsorb linuron and 3,4-dichloroaniline in acidic soil; The composite material is active carbon loaded with nano calcium hydroxide, and the mass ratio of the active carbon to the nano calcium hydroxide is 1:1.

3. The composite material is prepared by adding active carbon and sodium hydroxide solution into calcium chloride solution under nitrogen atmosphere, and then washing and drying the precipitate. The active carbon is bamboo chip active carbon, and the diameter of the nano calcium hydroxide is 45-120 nm.

2. Use of a composite material for simultaneously improving soil acidification and pesticide residues according to claim 1, characterized in that: The ratio of the active carbon, calcium chloride and sodium hydroxide is 14-25 g:0.3 moL:0.6 moL.

3. Use of a composite material for simultaneously improving soil acidification and pesticide residues according to claim 1, characterized in that: The preparation of the active carbon comprises the following steps: (1) mixing bamboo chips with phosphoric acid solution at a ratio of 1 g:2-3 mL, and aging at room temperature for 2-5 hours; (2) carbonizing the aged mixture at 300-350 ℃ for 0.5-2 hours to obtain bamboo chip carbonization product; (3) activating the bamboo chip carbonization product at 450-500 ℃ for 1-1.5 hours, and then cooling, washing, drying and crushing to obtain the active carbon.

4. Use of a composite material for simultaneously improving soil acidification and pesticide residues according to claim 3, characterized in that: The mass content of phosphoric acid in the phosphoric acid solution is 40%-50%.

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