Preparation method of hydrogel composite material for adsorbing heavy metals in soil

Abstract

The present invention relates to the technical field of soil remediation, and discloses a preparation method of a hydrogel composite material for soil heavy metal adsorption. A quaternary ammonium salt benzaldehyde crosslinking agent is crosslinked with the amino group of amino triazine modified polyvinyl alcohol to form a hydrogel composite material with a triazine-Schiff base crosslinked structure. It has the advantages of high water absorption rate and good water retention property. Moreover, the hydrogel molecular chain contains rigid benzene ring groups, forming a rigid chemical crosslinked network, which is beneficial to improving the mechanical strength of the hydrogel. The hydrogel composite material contains a triazine-Schiff base structure and can form coordination bonds with heavy metal ions such as cadmium, and adsorb heavy metal ions through chelation. And the hydrogel composite material contains a quaternary ammonium salt cationic structure and can form electrostatic interaction with Cr₂O₇²⁻, thereby carrying out adsorption. As a soil remediation material, the hydrogel composite material has good applications in aspects such as soil water retention and soil heavy metal adsorption.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and specifically to a preparation method of a hydrogel composite material for heavy metal adsorption in soil. Background Art

[0002] With the rapid development of industries such as mining, metallurgy, and electroplating, a large amount of heavy metal waste containing cadmium, lead, chromium, etc. will be generated. If these heavy metal wastes are not effectively treated and are randomly discarded in the natural environment, it will cause serious environmental pollution and pose a serious threat to the growth and reproduction of animals and crops in the soil. In recent years, the remediation of soil in the natural environment to reduce heavy metal pollution in the soil has been a research hotspot. Hydrogel materials have good hydrophilicity and water absorption properties and are widely used in the fields of soil remediation and environmental protection; Patent CN108148208B discloses that using wastewater containing hemicellulose as a solvent, mixing it with a hydrogel monomer and a crosslinking agent to obtain a crosslinked polymer hydrogel, which can be used as supplementary nutrition for crops and soil microorganisms, promoting the water retention performance in soil ecological improvers and playing a role in soil remediation. However, this hydrogel for soil improvement does not show an adsorption effect on heavy metal ions such as chromium and cadmium in the soil. Summary of the Invention

[0003] Technical problem to be solved: Provide a hydrogel composite material with high water absorption and water retention properties and high adsorption performance, which can be well used for heavy metal adsorption in soil and soil remediation.

[0004] Technical solution:

[0005] A preparation method of a hydrogel composite material: Add water, amino - triazine - modified polyvinyl alcohol, quaternary ammonium salt benzaldehyde crosslinking agent, and ethanol into a flask equipped with a condenser reflux tube, stir and react at a temperature of 80 - 95 °C for 3 - 8 h, cool to precipitate, filter, wash with ethanol, place the product in a dialysis bag, and dialyze and purify with distilled water to obtain the hydrogel composite material;

[0006] The chemical structure of the quaternary ammonium salt benzaldehyde crosslinking agent is:

[0007]

[0008] Further, the mass of the quaternary ammonium salt benzaldehyde crosslinking agent is 4 - 15% of the mass of the amino - triazine - modified polyvinyl alcohol.

[0009] Further, the volume of ethanol is 5 - 15% of the volume of water.

[0010] Further, the amino triazine modified polyvinyl alcohol is prepared as follows: Add N,N-dimethylformamide, polyvinyl alcohol, and sodium hydride into a flask equipped with a condenser reflux tube, introduce nitrogen, stir at room temperature for 1 - 3 h, then add 2-chloro-4,6-diamino-1,3,5-triazine, and react at a temperature of 130 - 150 °C for 6 - 12 h. Cool, pour the solution into water for precipitation, wash with water after filtration, and dry to obtain the amino triazine modified polyvinyl alcohol.

[0011] Further, the masses of sodium hydride and 2-chloro-4,6-diamino-1,3,5-triazine are respectively (5 - 25)% and (12 - 50)% of the mass of polyvinyl alcohol.

[0012] Further, the quaternary ammonium salt benzaldehyde crosslinker is prepared as follows:

[0013] (1) Add methanol, N,N-methylenebisacrylamide, and N,N,N'-trimethylethylenediamine into a flask equipped with a condenser reflux tube, react at a temperature of 55 - 65 °C for 10 - 18 h, concentrate to remove the solvent, and recrystallize the product from ethanol to obtain intermediate A.

[0014] (2) Add acetonitrile, intermediate A, and 4-chloromethylbenzaldehyde into a flask equipped with a condenser reflux tube, concentrate the solvent after the reaction, and recrystallize the product from ethanol to obtain the quaternary ammonium salt benzaldehyde crosslinker.

[0015] Further, the mass of 4-chloromethylbenzaldehyde in (2) is (180 - 230)% of the mass of intermediate A.

[0016] Further, the reaction in (2) is carried out at a temperature of 70 - 80 °C for 24 - 48 h.

[0017] Further, the application of the hydrogel composite material in the adsorption of heavy metals in soil.

[0018] Technical effect: The present invention uses sodium hydride as a catalyst to react polyvinyl alcohol and 2-chloro-4,6-diamino-1,3,5-triazine to obtain amino triazine modified polyvinyl alcohol; uses N,N-methylenebisacrylamide and N,N,N'-trimethylethylenediamine to carry out a Michael addition reaction, and then undergoes a quaternization reaction with 4-chloromethylbenzaldehyde to obtain a quaternary ammonium salt benzaldehyde crosslinker, and then uses its multiple aldehyde groups to carry out a crosslinking reaction with the amino groups of the amino triazine modified polyvinyl alcohol to form a hydrogel composite material with a triazine-Schiff base crosslinking structure of.

[0019] The polyvinyl alcohol-based hydrogel composite material of the present invention has a chemically crosslinked three-dimensional network structure. At the same time, the molecular chains of the polyvinyl alcohol hydrogel contain hydrophilic quaternary ammonium salt structures, significantly improving the hydrophilicity of the hydrogel, and having the advantages of high water absorption rate and good water retention. And the molecular chains of the hydrogel contain rigid benzene ring groups, forming a rigid chemical crosslinked network, which is beneficial to improving the mechanical strength of the hydrogel.

[0020] The hydrogel composite material of the present invention contains a triazine-Schiff base structure It can form coordination bonds with heavy metal ions such as cadmium, and adsorb heavy metal ions through chelation. The adsorption amount of Cd 2+ reaches up to 96.0%; and the hydrogel composite material contains a quaternary ammonium salt cation structure, which can form electrostatic interaction forces with Cr2O7 2- and thus adsorb. The adsorption rate of Cr2O7 2- reaches up to 98.5%. The hydrogel composite material is used as a soil remediation material and has good applications in aspects such as soil water retention and soil heavy metal adsorption. Brief Description of the Drawings

[0021] Figure 1 is the preparation reaction route of the quaternary ammonium salt benzaldehyde crosslinking agent.

[0022] Figure 2 is the preparation reaction route of amino triazine-modified polyvinyl alcohol. Detailed Embodiments

[0023] In the following description, for the purpose of illustration, in order to provide a comprehensive understanding of one or more embodiments, many specific details are set forth. However, it is obvious that these embodiments can also be implemented without these specific details. In other instances, well-known structures and devices are shown in block diagram form for the purpose of facilitating the description of one or more embodiments.

[0024] Example 1

[0025] Add 20 mL of methanol and 1.5 g of N,N-methylenebisacrylamide to a flask equipped with a reflux condenser 2.2 g of N,N,N'-trimethylethylenediamine React at a temperature of 60 °C for 10 h, concentrate to remove the solvent, and recrystallize the product in ethanol to obtain intermediate A.

[0026] Add 40 mL of acetonitrile, 2 g of intermediate A, and 3.6 g of 4-chloromethylbenzaldehyde to a flask equipped with a reflux condenser, and react at a temperature of 80 °C for 36 h. Concentrate the solvent, and recrystallize the product in ethanol to obtain the quaternary ammonium salt benzaldehyde crosslinking agent.

[0027] Add 250 mL of N,N-dimethylformamide, 20 g of polyvinyl alcohol, and 1 g of sodium hydride into a flask equipped with a condensing reflux tube. Introduce nitrogen gas and stir for 1 h at room temperature. Then add 2.4 g of 2-chloro-4,6-diamino-1,3,5-triazine and react at 130 °C for 12 h. Cool down, pour the solution into water for precipitation, wash with water after filtration, and dry to obtain amino triazine-modified polyvinyl alcohol.

[0028] Add 800 mL of water, 30 g of amino triazine-modified polyvinyl alcohol, 1.2 g of quaternary ammonium salt benzaldehyde crosslinker, and 40 mL of ethanol into a flask equipped with a condensing reflux tube. Stir and react at 90 °C for 8 h. Cool down to precipitate, filter, wash with ethanol, place the product in a dialysis bag, and dialyze and purify with distilled water to obtain a hydrogel composite material.

[0029] Example 2

[0030] Add 15 mL of methanol, 1.5 g of N,N-methylenebisacrylamide, and 2.4 g of N,N,N'-trimethylethylenediamine into a flask equipped with a condensing reflux tube. React at 65 °C for 10 h, concentrate to remove the solvent, and recrystallize the product from ethanol to obtain intermediate A.

[0031] Add 60 mL of acetonitrile, 2 g of intermediate A, and 4.2 g of 4-chloromethylbenzaldehyde into a flask equipped with a condensing reflux tube. React at 75 °C for 48 h, concentrate the solvent, and recrystallize the product from ethanol to obtain the quaternary ammonium salt benzaldehyde crosslinker.

[0032] Add 300 mL of N,N-dimethylformamide, 20 g of polyvinyl alcohol, and 2 g of sodium hydride into a flask equipped with a condensing reflux tube. Introduce nitrogen gas and stir for 2 h at room temperature. Then add 4.5 g of 2-chloro-4,6-diamino-1,3,5-triazine and react at 130 °C for 12 h. Cool down, pour the solution into water for precipitation, wash with water after filtration, and dry to obtain amino triazine-modified polyvinyl alcohol.

[0033] Add 800 mL of water, 30 g of amino triazine-modified polyvinyl alcohol, 2 g of quaternary ammonium salt benzaldehyde crosslinker, and 60 mL of ethanol into a flask equipped with a condensing reflux tube. Stir and react at 95 °C for 3 h. Cool down to precipitate, filter, wash with ethanol, place the product in a dialysis bag, and dialyze and purify with distilled water to obtain a hydrogel composite material.

[0034] Example 3

[0035] Add 20 mL of methanol, 1.5 g of N,N-methylenebisacrylamide, and 2.4 g of N,N,N'-trimethylethylenediamine into a flask equipped with a condensing reflux tube. React at 55 °C for 18 h, concentrate to remove the solvent, and recrystallize the product from ethanol to obtain intermediate A.

[0036] Add 60 mL of acetonitrile, 2 g of intermediate A, and 4.6 g of 4-chloromethylbenzaldehyde into a flask equipped with a condenser reflux tube, react at 70 °C for 48 h, concentrate the solvent, and recrystallize the product from ethanol to obtain the quaternary ammonium salt benzaldehyde crosslinker.

[0037] Add 400 mL of N,N-dimethylformamide, 20 g of polyvinyl alcohol, and 3.5 g of sodium hydride into a flask equipped with a condenser reflux tube, introduce nitrogen, stir at room temperature for 2 h, then add 8 g of 2-chloro-4,6-diamino-1,3,5-triazine, react at 150 °C for 6 h, cool, pour the solution into water for precipitation, wash with water after filtration, and dry to obtain the amino triazine-modified polyvinyl alcohol.

[0038] Add 800 mL of water, 30 g of amino triazine-modified polyvinyl alcohol, 3.2 g of quaternary ammonium salt benzaldehyde crosslinker, and 80 mL of ethanol into a flask equipped with a condenser reflux tube, stir and react at 95 °C for 6 h, cool to precipitate, filter, wash with ethanol, place the product in a dialysis bag, and dialyze and purify with distilled water to obtain the hydrogel composite material.

[0039] Example 4

[0040] Add 20 mL of methanol, 1.5 g of N,N-methylenebisacrylamide, and 2.2 g of N,N,N'-trimethylethylenediamine into a flask equipped with a condenser reflux tube, react at 65 °C for 10 h, concentrate to remove the solvent, and recrystallize the product from ethanol to obtain intermediate A.

[0041] Add 40 mL of acetonitrile, 2 g of intermediate A, and 3.6 g of 4-chloromethylbenzaldehyde into a flask equipped with a condenser reflux tube, react at 75 °C for 24 h, concentrate the solvent, and recrystallize the product from ethanol to obtain the quaternary ammonium salt benzaldehyde crosslinker.

[0042] Add 400 mL of N,N-dimethylformamide, 20 g of polyvinyl alcohol, and 5 g of sodium hydride into a flask equipped with a condenser reflux tube, introduce nitrogen, stir at room temperature for 3 h, then add 10 g of 2-chloro-4,6-diamino-1,3,5-triazine, react at 150 °C for 10 h, cool, pour the solution into water for precipitation, wash with water after filtration, and dry to obtain the amino triazine-modified polyvinyl alcohol.

[0043] Add 800 mL of water, 30 g of amino triazine-modified polyvinyl alcohol, 4.5 g of quaternary ammonium salt benzaldehyde crosslinker, and 120 mL of ethanol into a flask equipped with a condenser reflux tube, stir and react at 80 °C for 8 h, cool to precipitate, filter, wash with ethanol, place the product in a dialysis bag, and dialyze and purify with distilled water to obtain the hydrogel composite material.

[0044] Comparative Example 1

[0045] The difference between Comparative Example 1 and Example 1 is that the amino triazine-modified polyvinyl alcohol was not crosslinked using a quaternary ammonium salt benzaldehyde crosslinking agent.

[0046] Add 800 mL of water, 30 g of amino triazine-modified polyvinyl alcohol to a flask equipped with a condenser reflux tube, stir and dissolve at a temperature of 90 °C, cool to 60 °C, stand for defoaming, place the solution in a freezer at -25 °C for 12 h, and then thaw at room temperature for 6 h. Repeat the freezing-thawing process 3 times to obtain a hydrogel composite material.

[0047] Comparative Example 2

[0048] The difference between Comparative Example 2 and Example 1 is that glutaraldehyde of equal mass was used to replace the quaternary ammonium salt benzaldehyde crosslinking agent to crosslink the amino triazine-modified polyvinyl alcohol.

[0049] Add 800 mL of water, 30 g of amino triazine-modified polyvinyl alcohol, 1.2 g of glutaraldehyde, and 40 mL of ethanol to a flask equipped with a condenser reflux tube, stir and react at a temperature of 90 °C for 8 h, cool to precipitate, filter, wash with ethanol, place the product in a dialysis bag, and dialyze and purify with distilled water to obtain a hydrogel composite material.

[0050] Determination of the water absorption rate of the hydrogel composite material: Weigh a certain mass (m) of the hydrogel composite material, place it in distilled water, soak it at room temperature for 6 h, take out the hydrogel, dry the excess water, and weigh it as m1; calculate the water absorption rate Q. Place the water-absorbed hydrogel at room temperature for 168 h, then dry the excess water and weigh it as m2; calculate the water retention rate W. Water absorption rate Q = (m1 - m) / m; Water retention rate W = (m2 / m1) × 100%.

[0051] Table 1 Test of water absorption rate and water retention rate of hydrogel composite materials

[0052] Water absorption rate (g / g) Water retention rate (%) Example 1 31.4 91.1 Example 2 60.9 83.9 Example 3 56.4 81.6 Comparative Example 4 39.8 88.7 Comparative Example 1 2.9 39.6 Comparative Example 2 8.6 72.1

[0053] In Examples 1-4, a quaternary ammonium salt benzaldehyde crosslinking agent was used to crosslink with the amino group of the amino triazine-modified polyvinyl alcohol to obtain a polyvinyl alcohol-based hydrogel composite material with a chemically crosslinked three-dimensional network structure. At the same time, the polyvinyl alcohol hydrogel molecular chain contains a hydrophilic quaternary ammonium salt structure, which significantly improves the hydrophilicity of the hydrogel and has the advantages of high water absorption rate and good water retention property.

[0054] Comparative Example 1 used the freezing-thawing method to prepare a polyvinyl alcohol-based hydrogel composite material, which does not contain a hydrophilic quaternary ammonium salt structure and does not form a chemically crosslinked three-dimensional network structure, and has poor water absorption rate and water retention property.

[0055] In Comparative Example 2, glutaraldehyde was used to replace the quaternary ammonium salt benzaldehyde crosslinker to crosslink amino - triazine - modified polyvinyl alcohol. It does not contain a hydrophilic quaternary ammonium salt structure, and the water absorption rate and water retention capacity of the hydrogel composite material are not good.

[0056] The tensile strength of the hydrogel composite material was tested according to the method of GB / T1040.1 - 2006.

[0057] Table 2 Test of water absorption rate and water retention rate of hydrogel composite material

[0058] Tensile strength (MPa) Example 1 0.51 Example 2 0.59 Example 3 0.72 Comparative Example 4 0.66 Comparative Example 1 0.19 Comparative Example 2 0.37

[0059] In Examples 1 - 4, a quaternary ammonium salt benzaldehyde crosslinker was used to carry out a crosslinking reaction with the amino group of amino - triazine - modified polyvinyl alcohol. The hydrogel molecular chain contains a rigid benzene ring group, forming a rigid chemical crosslinking network, which is beneficial to improving the mechanical strength of the hydrogel.

[0060] In Comparative Example 1, a freeze - thaw method was used to obtain a polyvinyl alcohol - based hydrogel composite material, which did not form a rigid chemical crosslinking network and had the lowest tensile strength.

[0061] The hydrogel molecular chain of Comparative Example 2 does not contain a rigid benzene ring group, and the tensile strength of the hydrogel is not good.

[0062] Soil metal ion adsorption simulation experiment: Weigh 100 g of natural soil, crush and dry it, mix it with 10 mg of cadmium nitrate or potassium dichromate, add it to 400 mL of water, and stir well to prepare a simulated soil solution. Take the supernatant and determine the concentration C of Cd 2+ or Pb 2+ in the simulated soil solution by atomic absorption spectrophotometry; add 0.3 g of the hydrogel composite material, stir and adsorb for 4 h, and determine the concentration C1 of Cd 2+ or Pb 2+ in the solution, and calculate the adsorption rate A. A=(C - C1) / C×100%. C is the concentration of metal ions in the soil solution before adsorption, and C1 is the concentration of metal ions in the soil solution after adsorption.

[0063] Table 3 Test of adsorption performance of water - absorbing resin

[0064]

[0065] The hydrogel composite materials prepared in Examples 1 - 4 contain a triazine - Schiff base structure which can form coordination bonds with heavy metal ions such as cadmium and adsorb heavy metal ions through chelation. The adsorption amount of Cd 2+ reaches up to 96.0% at most; and the hydrogel composite material contains a quaternary ammonium cation structure, which can react with Cr2O7 2-Form an electrostatic interaction force to perform adsorption on Cr2O7 2- The highest adsorption rate reaches 98.5%.

[0066] The hydrogel composite of Comparative Example 1 does not contain a triazine-Schiff base structure and a quaternary ammonium salt cation structure, and has low chelation and electrostatic interaction with Cd 2+、 Cr2O7 2- resulting in poor adsorption performance.

[0067] The hydrogel composite of Comparative Example 2 does not contain a quaternary ammonium salt cation structure, and has low electrostatic interaction with Cr2O7 2- resulting in poor adsorption performance.

Claims

1. A method for preparing a hydrogel composite material, characterized in that: The hydrogel composite material is prepared according to the following method: water, aminotriazine-modified polyvinyl alcohol, quaternary ammonium benzaldehyde crosslinking agent, and ethanol are added to a flask equipped with a condenser reflux tube, stirred and reacted at a temperature of 80-95° C. for 3-8 hours, cooled to precipitate, filtered, washed, and the product was placed in a dialysis bag and dialyzed with distilled water for purification to obtain a hydrogel composite material; The chemical structure of the quaternary ammonium salt benzaldehyde cross-linking agent is: The aminotriazine-modified polyvinyl alcohol is prepared according to the following method: N,N-dimethylformamide, polyvinyl alcohol, and sodium hydride are added to a flask equipped with a condenser reflux tube, nitrogen is introduced, and the mixture is stirred at room temperature for 1-3 hours, and then 2-chloro-4,6-diamino-1,3,5-triazine is added. After the reaction, the mixture is cooled, and the solution is poured into water for precipitation. The solution is filtered, washed, and dried to obtain the aminotriazine-modified polyvinyl alcohol. The masses of the sodium hydride and 2-chloro-4,6-diamino-1,3,5-triazine are (5-25)% and (12-50)% of the mass of the polyvinyl alcohol, respectively.

2. The method for preparing a hydrogel composite material according to claim 1, wherein: The mass of the quaternary ammonium salt benzaldehyde cross-linking agent is 4-15% of the mass of the aminotriazine modified polyvinyl alcohol.

3. The method for preparing a hydrogel composite material according to claim 1, wherein: The volume of ethanol is 5-15% of the volume of water.

4. The method for preparing a hydrogel composite material according to claim 1, wherein: The reaction is carried out at a temperature of 130-150° C. for 6-12 hours.

5. The method for preparing a hydrogel composite material according to claim 1, wherein: The quaternary ammonium salt benzaldehyde cross-linking agent is prepared as follows: (1) Methanol, N,N-methylenebisacrylamide, and N,N,N'-trimethylethylenediamine were added to a flask equipped with a reflux tube, and the mixture was reacted at a temperature of 55-65°C for 10-18 hours. The solvent was removed by concentration, and the product was recrystallized to obtain intermediate A; (2) Add acetonitrile, intermediate A, and 4-chloromethylbenzaldehyde to a flask equipped with a condenser reflux tube, concentrate the solvent after the reaction, and recrystallize the product to obtain a quaternary ammonium salt benzaldehyde cross-linking agent.

6. The method for preparing a hydrogel composite material according to claim 5, wherein: The mass of 4-chloromethylbenzaldehyde in (2) is (180-230)% of the mass of intermediate A.

7. The method for preparing a hydrogel composite material according to claim 5, wherein: The reaction in (2) is carried out at a temperature of 70-80°C for 24-48 hours.

8. Use of the hydrogel composite material obtained by the preparation method according to any one of claims 1 to 7 in the adsorption of heavy metals in soil.

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