Preparation method of electrostatic self-assembly modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel

Abstract

The invention discloses a preparation method of electrostatic self-assembly modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel, which comprises the following steps: carrying out surface modification on halloysite nanotubes by adopting cationic polyelectrolyte in an electrostatic assembly mode to obtain modified halloysite nanotubes with positive electrokinetic potential; the method comprises the following steps: modifying the surface of a modified halloysite nanotube with positive electrokinetic potential with negatively charged phytic acid in an electrostatic assembly manner to obtain a phytic acid functionalized halloysite nanotube; under the alkaline condition, 1, 3-diepoxybutane serves as a cross-linking agent, polyvinyl alcohol and the phytic acid functionalized halloysite nanotubes are subjected to a cross-linking reaction to form a three-dimensional network structure, finally, reaction liquid is freeze-dried, then alkaline matter is removed, and the electrostatic self-assembly modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel is obtained. According to the invention, the problems that polyvinyl alcohol is easy to remain in a solution and halloysite nanotubes are not easy to recycle are solved, and the adsorption performance on heavy metal ions is improved through synergistic interaction.

Description

Technical Field

[0001] The invention relates to the technical field of aerogels, and in particular to a method for preparing an electrostatically self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel. Background Art

[0002] Polyvinyl alcohol (PVA) molecular chains are rich in hydroxyl functional groups, which can form stable bonds with heavy metal ions through hydrogen bonding, complexation reactions and other mechanisms, thereby achieving effective adsorption of heavy metals. However, when polyvinyl alcohol is used alone as an adsorption material, due to the strong hydrophilicity of its molecular chain and the dissociation characteristics of some hydroxyl groups in aqueous solution, polyvinyl alcohol may swell or partially dissolve during the adsorption process, resulting in material loss and residue in the water.

[0003] Halloysite nanotubes (HNTs), used as adsorption materials, can easily form a stable suspension state in water, but are also difficult to recycle and reuse. Summary of the invention

[0004] In view of the above-mentioned defects in the prior art, the present invention provides a method for preparing an electrostatically self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel, which achieves efficient adsorption of heavy metal ions and solves the problems that polyvinyl alcohol is easily left in the solution and that halloysite nanotubes are difficult to recycle and reuse.

[0005] The technical solution of the present invention is as follows: A method for preparing an electrostatically self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel comprises the following steps: (1) Using an electrostatic assembly method, the surface of halloysite nanotubes was modified with a cationic polyelectrolyte to obtain modified halloysite nanotubes with a positive electrokinetic potential; (2) modifying the surface of the modified halloysite nanotubes with a positive electrokinetic potential obtained in step (1) with negatively charged phytic acid in an electrostatic assembly manner to obtain phytic acid-functionalized halloysite nanotubes; (3) Under alkaline conditions, 1,3-diethoxybutane was used as a cross-linking agent to form a three-dimensional network structure by cross-linking reaction between polyvinyl alcohol and phytic acid functionalized halloysite nanotubes. Finally, the reaction solution was freeze-dried and the alkaline substance was removed to obtain an electrostatically self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel.

[0006] Furthermore, the step (1) specifically comprises ultrasonically dispersing the halloysite nanotubes in deionized water, then adding sodium chloride and polydimethyldiallyl ammonium chloride, stirring at room temperature, filtering, washing and drying to obtain modified halloysite nanotubes with a positive zeta potential.

[0007] Further, the mass ratio of the halloysite nanotubes, sodium chloride, and polydimethyldiallylammonium chloride is 1:(0.6 - 1.2):(0.3 - 0.7).

[0008] Further, step (2) specifically involves slowly dripping an aqueous solution of phytic acid into a deionized water dispersion of modified halloysite nanotubes with a positive zeta potential, stirring at room temperature, followed by suction filtration, washing, and drying to obtain phytic acid-functionalized halloysite nanotubes.

[0009] Further, the concentration of the aqueous solution of phytic acid is 50% or 70%, and the mass ratio of phytic acid to the modified halloysite nanotubes with a positive zeta potential is (0.5 - 2):1.

[0010] Further, step (3) specifically includes ultrasonically dispersing the phytic acid-functionalized halloysite nanotubes in an aqueous solution of polyvinyl alcohol, then adding sodium hydroxide to adjust the pH value of the solution to 8 - 9, and finally adding 1,3-butadiene diepoxide for crosslinking reaction.

[0011] Further, the dosage ratio of the phytic acid-functionalized halloysite nanotubes, polyvinyl alcohol, and 1,3-butadiene diepoxide is 1 g:(1 - 3) g:(7 - 15) mL.

[0012] Further, the crosslinking reaction in step (3) is carried out by stirring at 30 - 50 °C for 10 - 16 h.

[0013] Further, the freeze-drying in step (3) is to freeze-dry the reaction solution at -50 - -40 °C for 30 - 50 h.

[0014] Further, removing the alkaline substance in step (3) specifically involves soaking the freeze-dried sample in water at 30 - 50 °C for 8 - 12 h, and changing the water every 1 - 3 h.

[0015] First, the present invention utilizes the negative charge characteristics on the surface of halloysite nanotubes (HNTs) to modify a layer of cationic polyelectrolyte (polydimethyldiallylammonium chloride) on its surface through electrostatic interaction, forming modified halloysite nanotubes (p-HNTs) with a positive zeta potential. Subsequently, based on the principle of electrostatic adsorption again, phytic acid molecules rich in phosphate groups are adsorbed on the surface of p-HNTs to form phytic acid-functionalized halloysite nanotubes (PA-p-HNTs). Further, the composite structural nanomaterial (PA-p-HNTs) is blended with an aqueous solution of polyvinyl alcohol (PVA), and 1,3-diepoxybutane is introduced as a crosslinking agent to promote the chemical crosslinking reaction between the epoxy groups in 1,3-diepoxybutane and the phosphate groups, hydroxyl groups on the surface of PA-p-HNTs, and the hydroxyl groups on the PVA molecular chain in an alkaline solution. Finally, through freeze-drying treatment and removal of alkaline substances, a crosslinked composite aerogel material with porosity, excellent structural stability, and adsorption performance is obtained.

[0016] The advantages of the present invention compared with the prior art are as follows: (1) The composite aerogel prepared by the present invention not only has a rich pore structure, but also integrates the unique structural characteristics of halloysite nanotubes, the charge regulation ability of cationic electrolytes, the excellent adsorption performance of phytic acid, and the rich reactive hydroxyl groups of polyvinyl alcohol. Thanks to the excellent interfacial compatibility, the four form a deep combination and synergistic effect in adsorption performance, greatly improving its adsorption performance for heavy metal ions.

[0017] (2) The present invention introduces 1,3-diepoxybutane as a crosslinking agent into the composite system to form a three-dimensional network structure through chemical crosslinking reaction, which not only introduces more hydroxyl groups, optimizes the interfacial pore structure, but also improves the structural stability of the aerogel, effectively solving the problems that polyvinyl alcohol is easily left in the solution and halloysite nanotubes are not easy to recycle and reuse. Description of the Drawings

[0018] Figure 1 The zeta potential curves of the original HNTs, p-HNTs, and PA-p-HNTs prepared in Example 1 in an aqueous dispersion with a pH of 7.

[0019] Figure 2 The SEM image of the electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol crosslinked composite aerogel prepared in Example 1. Detailed Embodiments

[0020] The present invention will be further described below in conjunction with embodiments, but it is not intended to limit the present invention.

[0021] Example 1

[0022] A preparation method of electrostatic self-assembled decorated halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel, comprising the following steps: (1) Ultrasonically disperse 1 g of halloysite nanotubes (Xianfeng Nano, CAS No.: 1332-58-7, product number: 103763) in deionized water, and successively add 0.6 g of sodium chloride and 0.3 g of polydimethyldiallylammonium chloride (Wuxi Tianxin Chemical Co., Ltd., product model: PDLS41). At room temperature, continuously stir for 2 h, then perform suction filtration, washing, and drying to obtain p-HNTs. It can be Figure 1 seen that the surface of HNTs is negatively charged, and after adsorbing cationic polyelectrolyte on its surface, the surface of p-HNTs becomes positively charged.

[0023] (2) Ultrasonically disperse 1 g of the prepared p-HNTs in deionized water, then dropwise add 1 g of an aqueous solution of phytic acid with a concentration of 50%. Continuously stir at room temperature for 5 h, then perform suction filtration, washing, and drying to obtain PA-p-HNTs. It can be Figure 1 seen that due to the introduction of phytic acid, the surface of PA-p-HNTs is negatively charged again.

[0024] (3) Stir and dissolve 1 g of polyvinyl alcohol (Sangon Biotech (Shanghai) Co., Ltd., molecular weight 65,000 - 75,000) in deionized water, then add 1 g of the prepared PA-p-HNTs, ultrasonically disperse evenly, add sodium hydroxide to adjust the pH value of the solution to 8, then slowly dropwise add 7 mL of 1,3-diepoxybutane, stir and react at 30 °C for 16 h. After freeze-drying the reaction solution at -40 °C for 50 h, soak the sample in warm water at 30 °C for 12 h, and change the water every 3 h. Take out the sample and dry it to obtain electrostatic self-assembled decorated halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel. Its SEM image is as Figure 2 shown, and it can be seen that it has a rich pore structure.

[0025] The adsorption performance experiment of the electrostatic self-assembled decorated halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel prepared in Example 1 is as follows: Prepare 100 mL of an aqueous solution with a lead ion (lead nitrate as the reagent) concentration of 100 mg / L in a flask. After adjusting the pH of the solution to 7 with 0.1 M NaOH, add the prepared electrostatic self-assembled decorated halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel, and then in a 30 o °C constant temperature shaker, adsorb at a rotation speed of 200 rpm for 3 h. After adsorption, take the supernatant, use ICP-OES to measure the concentration of lead ions in the supernatant, and calculate the adsorption amount of the adsorption material for lead ions through the following formula ( Q , mg / g), and the results are listed in Table 1.

[0026] Q = (C 0 -[[]] C C t ) V / M Q is the adsorption capacity (mg / g); C 0 is the initial concentration of heavy metal ions (mg / L); C t is the concentration of heavy metal ions after adsorption (mg / L); V is the volume of the solution (L); M is the mass of the adsorbent (g).

[0027] Example 2

[0028] A preparation method of electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel, comprising the following steps: (1) Ultrasonically disperse 1 g of halloysite nanotubes (Xianfeng Nano, CAS No.: 1332-58-7, product number: 103763) in deionized water, sequentially add 0.9 g of sodium chloride and 0.5 g of polydimethyldiallylammonium chloride (Wuxi Tianxin Chemical Co., Ltd., product model: PDLS41), and continuously stir at room temperature for 3 h, then filter, wash, and dry to obtain p-HNTs.

[0029] (2) Ultrasonically disperse 1 g of the prepared p-HNTs in deionized water, then dropwise add 2.5 g of an aqueous solution of phytic acid with a concentration of 50%, continuously stir at room temperature for 6.5 h, then filter, wash, and dry to obtain PA-p-HNTs.

[0030] (3) Stir and dissolve 2 g of polyvinyl alcohol (Sangon Biotech (Shanghai) Co., Ltd., molecular weight 65,000 - 75,000) in deionized water, then add 1 g of the prepared PA-p-HNTs, ultrasonically disperse evenly, add sodium hydroxide to adjust the pH value of the solution to 8.5, then slowly dropwise add 11 mL of 1,3-diepoxybutane, stir and react at 40 °C for 13 h, freeze-dry the reaction solution at -45 °C for 40 h, then soak the sample in warm water at 40 °C for 10 h and change the water every 2 h, take out the sample and dry it to obtain electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel, and its adsorption performance is measured according to the adsorption performance experiment of the product in Example 1, and the results are listed in Table 1.

[0031] Example 3

[0032] A preparation method of electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel, comprising the following steps: (1) Ultrasonically disperse 1 g of halloysite nanotubes (Xianfeng Nano, CAS No.: 1332 - 58 - 7, product number: 103763) in deionized water. Sequentially add 1.2 g of sodium chloride and 0.7 g of polydimethyldiallylammonium chloride (Wuxi Tianxin Chemical Co., Ltd., product model: PDLS41). At room temperature, continuously stir for 4 h, then perform suction filtration, washing, and drying to obtain p - HNTs.

[0033] (2) Ultrasonically disperse 1 g of the prepared p - HNTs in deionized water, and then dropwise add 2.9 g of an aqueous solution of phytic acid with a concentration of 70%. Continuously stir at room temperature for 8 h, then perform suction filtration, washing, and drying to obtain PA - p - HNTs.

[0034] (3) Stir and dissolve 3 g of polyvinyl alcohol (Sangon Biotech (Shanghai) Co., Ltd., molecular weight 65,000 - 75,000) in deionized water. Then add 1 g of the prepared PA - p - HNTs, ultrasonically disperse them evenly, add sodium hydroxide to adjust the pH value of the solution to 9, and then slowly dropwise add 15 mL of 1,3 - diepoxybutane. Stir and react at 50 °C for 10 h. After freeze - drying the reaction solution at - 50 °C for 30 h, soak the sample in warm water at 50 °C for 8 h and change the water every 1 h. Take out the sample and dry it to obtain an electrostatic self - assembled modified halloysite nanotube - polyvinyl alcohol cross - linked composite aerogel. Its adsorption performance is measured according to the adsorption performance experiment of the product in Example 1, and the results are listed in Table 1.

[0035] Comparative Example 1 Stir and dissolve 1 g of polyvinyl alcohol (Sangon Biotech (Shanghai) Co., Ltd., molecular weight 65,000 - 75,000) in deionized water. Then add 1 g of the original HNTs (Xianfeng Nano, CAS No.: 1332 - 58 - 7, product number: 103763), ultrasonically disperse them evenly, add sodium hydroxide to adjust the pH value of the solution to 8, and then slowly dropwise add 7 mL of 1,3 - diepoxybutane. Stir and react at 30 °C for 16 h. After freeze - drying the reaction solution at - 40 °C for 50 h, soak the sample in warm water at 30 °C for 12 h and change the water every 3 h. Take out the sample and dry it to obtain an HNTs / PVA composite aerogel. Its adsorption performance is measured according to the adsorption performance experiment of the product in Example 1, and the results are listed in Table 1.

[0036] Comparative Example 2 Dissolve 1 g of polyvinyl alcohol (Sangon Biotech (Shanghai) Co., Ltd., molecular weight 65,000 - 75,000) by stirring in deionized water, then add 1 g of p-HNTs (prepared according to step (1) in Example 1), disperse evenly by ultrasonic treatment, add sodium hydroxide to adjust the pH value of the solution to 8, then slowly dropwise add 7 mL of 1,3-diepoxybutane, stir and react at 30 °C for 16 h. After freeze-drying the reaction solution at -40 °C for 50 h, soak the sample in warm water at 30 °C for 12 h and change the water every 3 h. Take out the sample and dry it to obtain the p-HNTs / PVA composite aerogel. Its adsorption performance was measured according to the adsorption performance experiment of the product in Example 1, and the results are listed in Table 1.

[0037] Comparative Example 3 Dissolve 1 g of polyvinyl alcohol (Sangon Biotech (Shanghai) Co., Ltd., molecular weight 65,000 - 75,000) by stirring in deionized water, then add 1 g of the prepared PA-p-HNTs (prepared according to steps (1) and (2) in Example 1), disperse evenly by ultrasonic treatment. After freeze-drying the dispersion at -40 °C for 50 h, obtain the PA-p-HNTs / PVA composite aerogel. Its adsorption performance was measured according to the adsorption performance experiment of the product in Example 1, and the results are listed in Table 1.

[0038] Table 1 Adsorption amounts of lead ions by the aerogels prepared in Examples 1 - 3 and Comparative Examples 1 - 3

[0039] It can be seen from the results that the electrostatic self-assembly decorated halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel prepared in the examples of the present invention, on the one hand, realizes the perfect combination and synergistic effect of the unique structural characteristics of halloysite nanotubes, the excellent adsorption performance of cationic electrolytes, phytic acid and the rich active hydroxyl groups of polyvinyl alcohol, and on the other hand, realizes the effective cross-linking between halloysite nanotubes and polyvinyl alcohol, not only optimizing the pore structure of the aerogel, but also introducing more active hydroxyl groups with adsorption performance, and at the same time promoting the dispersion of halloysite nanotubes. Therefore, the prepared aerogel has excellent adsorption performance for lead ions, and the highest adsorption amount can reach 339 mg / g.

[0040] In the aerogel prepared in Comparative Example 1, the synergistic adsorption effect of the cationic electrolyte and phytic acid is lacking, and there are fewer hydroxyl groups on the surface of halloysite, resulting in the inability to form an effective cross-linked structure with polyvinyl alcohol. In Comparative Example 2, the synergistic adsorption effect of phytic acid is lacking, and an effective cross-linking still cannot be formed between the halloysite nanotubes and the resin. In Comparative Example 3, although the synergistic effect among the halloysite nanotubes, the cationic electrolyte, phytic acid and polyvinyl alcohol is achieved, no cross-linking agent is added, and no cross-linking reaction occurs between the filler and the resin. Cross-linking modification is not achieved in Comparative Examples 1-3. This not only fails to fully exert the synergistic adsorption effect among the components, but also reduces the porosity of the aerogel and lacks the abundant active hydroxyl groups introduced by cross-linking. It can be seen that the aerogels prepared in Comparative Examples 1-3 cannot be compared with the cross-linked aerogel prepared in the Examples in terms of porosity, interfacial bonding and synergistic effect. Therefore, their adsorption performance is far inferior to that of the Examples of the present invention.

Claims

1. A preparation method of an electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel, characterized in that, It includes the following steps: (1) By means of electrostatic assembly, the halloysite nanotubes are surface-modified with a cationic polyelectrolyte to obtain modified halloysite nanotubes with a positive zeta potential; (2) By means of electrostatic assembly, negatively charged phytic acid is modified on the surface of the modified halloysite nanotubes with a positive zeta potential obtained in the step (1) to obtain phytic acid-functionalized halloysite nanotubes; (3) Under alkaline conditions, using 1,3-diepoxybutane as a cross-linking agent, polyvinyl alcohol reacts with the phytic acid-functionalized halloysite nanotubes by cross-linking reaction to form a three-dimensional network structure. Finally, the reaction solution is freeze-dried, and then the alkaline substances are removed to obtain an electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel.

2. The preparation method of the electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel according to claim 1, characterized in that, The step (1) specifically is to ultrasonically disperse the halloysite nanotubes in deionized water, then add sodium chloride and poly(dimethyldiallylammonium chloride), stir at room temperature, then filter, wash, and dry to obtain modified halloysite nanotubes with a positive zeta potential.

3. The preparation method of the electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel according to claim 2, wherein, The mass ratio of the halloysite nanotubes, sodium chloride, and poly(dimethyldiallylammonium chloride) is 1:(0.6 - 1.2):(0.3 - 0.7).

4. The preparation method of the electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol crosslinked composite aerogel according to claim 1, characterized in that, The step (2) specifically is to slowly drip the aqueous solution of phytic acid into the deionized water dispersion of the modified halloysite nanotubes with a positive zeta potential, stir at room temperature, then filter, wash, and dry to obtain phytic acid-functionalized halloysite nanotubes.

5. The preparation method of the electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel according to claim 4, characterized in that, The concentration of the aqueous solution of phytic acid is 50% or 70%, and the mass ratio of phytic acid to the modified halloysite nanotubes with a positive zeta potential is (0.5 - 2):

1.

6. The preparation method of the electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel according to claim 1, characterized in that, The step (3) specifically includes ultrasonically dispersing the phytic acid-functionalized halloysite nanotubes in an aqueous solution of polyvinyl alcohol, then adding sodium hydroxide to adjust the pH value of the solution to 8 - 9, and finally adding 1,3-diepoxybutane to carry out the cross-linking reaction.

7. The preparation method of the electrostatic self-assembled decorated halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel according to claim 6, characterized in that, The dosage ratio of the phytic acid-functionalized halloysite nanotubes, polyvinyl alcohol, and 1,3-diepoxybutane is 1 g:(1 - 3) g:(7 - 15) mL.

8. The preparation method of the electrostatic self-assembled decorated halloysite nanotube-polyvinyl alcohol crosslinked composite aerogel according to claim 6, characterized in that, In the step (3), the cross-linking reaction is carried out by stirring at 30 - 50 °C for 10 - 16 h.

9. The preparation method of the electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel according to claim 1, wherein, In the step (3), the freeze-drying is to freeze-dry the reaction solution at -50 - -40 °C for 30 - 50 h.

10. The preparation method of the electrostatic self-assembled modified halloysite nanotube-polyvinyl alcohol cross-linked composite aerogel according to claim 1, wherein, In the step (3), the removal of the alkaline substances specifically is to soak the freeze-dried sample in water at 30 - 50 °C for 8 - 12 h, and change the water every 1 - 3 h.

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