Preparation method of triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite membrane

Abstract

The invention discloses a preparation method of a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite membrane, which comprises the following steps: modifying a halloysite nanotube by an amino silane coupling agent to obtain an aminated halloysite nanotube; introducing hydroxyl by utilizing a ring-opening reaction of amino and glycidol, so as to obtain a hydroxylated halloysite-enriched nanotube; the preparation method comprises the following steps of: grafting triethanolamine on the surface by taking malonic acid as a'bridge 'by utilizing a reaction of hydroxyl and carboxyl to obtain a triethanolamine grafted modified halloysite nanotube; the preparation method comprises the following steps: under an alkaline condition, forming a three-dimensional network structure by taking diglycidyl ether as a cross-linking agent and taking hydroxyl on the surface of the halloysite nanotube grafted and modified by polyvinyl alcohol and triethanolamine as cross-linking sites, then carrying out vacuum filtration to form a membrane, removing alkaline substances, and drying to obtain the cross-linked composite membrane. According to the invention, the dispersibility of halloysite nanotubes in a resin body is improved, the problem of water solubility of PVA is solved, and the adsorption performance of heavy metal ions is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polyvinyl alcohol composite membranes, and particularly to a preparation method of a triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol crosslinked composite membrane. Background Art

[0002] As a natural clay mineral, halloysite nanotubes (HNTs) are often used as functional additives to enhance the adsorption efficiency of resin-based composites for heavy metal ions due to their unique hollow tubular structure, high specific surface area, and good biocompatibility. However, the high surface energy of HNTs leads to problems such as weak interfacial binding force and easy agglomeration with the resin matrix, seriously restricting the performance of HNTs. Existing modification technologies are limited by the lack of surface active reaction sites on HNTs (such as low density of natural hydroxyl groups), resulting in insufficient grafting rate of functional molecules and difficulty in effectively improving the compatibility with the matrix.

[0003] Polyvinyl alcohol (PVA), as a typical environmentally friendly film-forming material, has rich hydroxyl groups in its molecular chain that can form stable coordination bonds with heavy metal ions, showing unique advantages in the adsorption field. However, the water-soluble defect of PVA makes it easily dissolve in the aqueous phase during direct use, resulting in the loss of adsorbent, which greatly limits the engineering application of this material in heavy metal treatment scenarios. Summary of the Invention

[0004] Aiming at the above-mentioned defects of the existing technology, the present invention provides a preparation method of a triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol crosslinked composite membrane, which solves the problems of low grafting rate of surface functional molecules on halloysite nanotubes, poor dispersion of halloysite nanotubes and resin matrix, and easy residue of polyvinyl alcohol in aqueous solution, and realizes the efficient adsorption of heavy metal ions.

[0005] The technical solution of the present invention is as follows: A preparation method of a triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol crosslinked composite membrane, comprising the following steps: (1) Modify halloysite nanotubes with an amino-silane coupling agent to obtain amino-functionalized halloysite nanotubes; (2) Introduce hydroxyl groups on the surface of amino-functionalized halloysite nanotubes by the ring-opening reaction of amino groups and glycidol to obtain halloysite nanotubes with rich hydroxyl groups; (3) Ultrasonically disperse the halloysite nanotubes with rich hydroxyl groups in N , N -dicyclohexylcarbodiimide and 4-dimethylaminopyridine N , N [[ID=�3]]-dimethylformamide, under nitrogen protection, add malonic acid, carry out a stirring reaction, then add triethanolamine, continue the stirring reaction, filter, wash, and dry to obtain triethanolamine-grafted modified halloysite nanotubes; (4) Under alkaline conditions, using diglycidyl ether as a crosslinking agent, the hydroxyl groups on the surface of halloysite nanotubes grafted with polyvinyl alcohol and triethanolamine serve as crosslinking sites to form a three-dimensional network structure. Then, it is vacuum filtered into a film, and the alkaline substances are removed, followed by drying to obtain the crosslinked composite film.

[0006] Further, in step (1), specifically, the halloysite nanotubes are dispersed in ethanol, ultrasonically dispersed evenly, and an amino-silane coupling agent is added, followed by reflux reaction at 80 - 90 °C for 10 - 16 h. Then, it is filtered, washed, and dried to obtain amino-functionalized halloysite nanotubes.

[0007] Further, in step (1), the mass ratio of halloysite nanotubes to the amino-silane coupling agent is 1:(0.1 - 0.5), and the amino-silane coupling agent is one of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

[0008] Further, in step (2), specifically, the amino-functionalized halloysite nanotubes are ultrasonically dispersed in an aqueous sodium hydroxide solution, and a solution of glycidol in ethanol is slowly added dropwise. The reaction is stirred at 60 - 80 °C, followed by filtration, washing, and drying to obtain halloysite nanotubes rich in hydroxyl groups.

[0009] Further, in step (2), the dosage ratio of amino-functionalized halloysite nanotubes to glycidol is 1 g:(20 - 40 mL), the concentration of the aqueous sodium hydroxide solution is 4 - 5% wt, and the volume ratio of glycidol to ethanol in the solution of glycidol in ethanol is 1:(1 - 1.5).

[0010] Further, in step (3), the halloysite nanotubes rich in hydroxyl groups, N , N - dicyclohexylcarbodiimide, 4-dimethylaminopyridine, malonic acid, and triethanolamine have a dosage ratio of 1 g:(1 - 2) g:(0.1 - 0.3) g:(0.4 - 0.8) g:(2 - 4 mL).

[0011] Further, in step (3), the stirring reaction is carried out at 30 - 50 °C for 8 - 12 h.

[0012] Further, in step (4), specifically, polyvinyl alcohol is stirred and dissolved in deionized water, and triethanolamine-grafted halloysite nanotubes are added. After ultrasonically dispersing evenly, sodium hydroxide is added to adjust the pH value of the solution to 8 - 9. Finally, diglycidyl ether is added, and the crosslinking reaction is carried out at 40 - 60 °C.

[0013] Further, in step (4), the dosage ratio of triethanolamine-grafted halloysite nanotubes, polyvinyl alcohol, and diglycidyl ether is 1 g:(1 - 3) g:(3 - 5) mL.

[0014] Further, the removal of the alkaline substance in step (4) is specifically to soak the suction filtration membrane in water at 40-50°C for 10-15 h and change the water every 1-3 h.

[0015] The present invention first aminosilylates halloysite nanotubes (HNTs) with an aminosilane coupling agent, and then introduces a large number of hydroxyl groups on the surface of HNTs through the ring-opening reaction of glycidol, significantly increasing the number of surface active sites; Subsequently, using malonic acid as a "bridge", triethanolamine (TEA) with multiple functional groups is efficiently grafted, further effectively improving the compatibility between HNTs and the resin matrix and the chelating ability for heavy metal ions. Finally, starting from the interface structure design, using diglycidyl ether as a crosslinking agent, promoting the covalent crosslinking reaction between triethanolamine-grafted modified halloysite nanotubes (TEA@HNTs) and polyvinyl alcohol in an alkaline solution to form a three-dimensional structure, which not only effectively improves the structural stability of the composite membrane, but also introduces more adsorption active sites (hydroxyl groups), and at the same time further strengthens the dispersion of HNTs in the matrix. Thus, by means of a simple vacuum filtration technique, a triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol crosslinked composite membrane (TEA@HNTs / PVA crosslinked composite membrane) with excellent structural stability and adsorption performance is prepared.

[0016] The advantages of the present invention compared with the prior art are as follows: (1) Through the synergistic effect of the hierarchical functionalization modification strategy and the crosslinking treatment technology, the present invention significantly improves the dispersion uniformity of HNTs in the resin matrix.

[0017] (2) The present invention selects diglycidyl ether as a crosslinking agent, and constructs a stable three-dimensional network structure through the covalent crosslinking reaction between PVA and the surface hydroxyl groups of TEA@HNTs, effectively solving the water solubility problem of PVA.

[0018] (3) Through the synergistic strengthening of the chelation adsorption effect between TEA@HNTs and the PVA crosslinking network, the present invention realizes a significant improvement in the adsorption performance of the composite membrane for heavy metal ions. Description of the Drawings

[0019] Figure 1 SEM image of the TEA@HNTs / PVA crosslinked composite membrane prepared in Example 1. Specific 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 a triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol crosslinked composite membrane, comprising the following steps: (1) 1 g of HNTs (Xianfeng Nano, CAS No.: 1332 - 58 - 7, product number: 103763) was dispersed in ethanol and ultrasonically dispersed evenly. 0.1 g of 3 - aminopropyltrimethoxysilane was added, and the mixture was refluxed at 80 °C for 16 h. After filtration, washing, and drying, amino - modified HNTs were obtained.

[0023] (2) 1 g of the prepared amino - modified HNTs was ultrasonically dispersed in an aqueous sodium hydroxide solution (4% wt). A mixture of 20 mL of glycidol and 20 mL of absolute ethanol was slowly added dropwise, and the mixture was stirred at 60 °C for 12 h. After filtration, washing, and drying, hydroxy - rich HNTs were obtained.

[0024] (3) 1 g of the prepared hydroxy - rich HNTs was added to a solution of 1 g N , N - dicyclohexylcarbodiimide and 0.1 g of 4 - dimethylaminopyridine in N , N - dimethylformamide. After ultrasonic dispersion, 0.4 g of malonic acid was added under nitrogen protection. After stirring at 30 °C for 12 h, 2 mL of triethanolamine was added dropwise, and the mixture was continuously stirred at 30 °C for 12 h. After filtration, washing, and drying, TEA@HNTs were obtained.

[0025] (4) 1 g of PVA (molecular weight 65,000 - 75,000) was stirred and dissolved in deionized water. 1 g of the prepared TEA@HNTs was added, and after ultrasonic dispersion, sodium hydroxide was added to adjust the pH of the solution to 8. Finally, 3 mL of diglycidyl ether was slowly added dropwise, and the mixture was stirred at 40 °C for 14 h. A part of the reaction solution was taken for vacuum filtration. The filter membrane was immersed in warm water at 40 °C for 15 h, and the water was changed every 3 h. After drying, a TEA@HNTs / PVA cross - linked composite membrane was obtained. Its SEM image is as shown in Figure 1 shown, indicating that the composite membrane has a rich pore structure.

[0026] The adsorption performance test experiment of the TEA@HNTs / PVA cross - linked composite membrane prepared in Example 1 is as follows: In a flask, 100 mL of an aqueous solution with a lead ion (lead nitrate as the reagent) concentration of 100 mg / L was prepared. After adjusting the pH of the solution to 7 with 0.1 M NaOH, the prepared TEA@HNTs / PVA cross - linked composite membrane was added. Then, in a constant - temperature shaker at 30 °C, adsorption was carried out at a rotation speed of 200 rpm for 3 h. After adsorption, the supernatant was taken, and the concentration of lead ions in the supernatant was measured by ICP - OES. The adsorption capacity of the adsorbent material for lead ions ( Q , mg / g) was calculated by the following formula, and the results are listed in Table 1.

[0027] Q = (C 0 - 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).

[0028] Example 2

[0029] A preparation method of triethanolamine grafted modified halloysite nanotube - polyvinyl alcohol crosslinked composite membrane, comprising the following steps: (1) Disperse 1 g of HNTs (Xianfeng Nano, CAS No.: 1332 - 58 - 7, product number: 103763) in ethanol, ultrasonically disperse evenly, add 0.3 g of 3 - aminopropyltriethoxysilane, reflux and react at 85 °C for 13 h, filter, wash, and dry to obtain amino - functionalized HNTs.

[0030] (2) Ultrasonically disperse 1 g of the obtained amino - functionalized HNTs in an aqueous sodium hydroxide solution (4.5% wt), slowly dropwise add a mixed solution of 30 mL of glycidol and 37.5 mL of absolute ethanol, stir and react at 70 °C for 10 h, filter, wash, and dry to obtain hydroxy - rich HNTs.

[0031] (3) Add 1 g of the obtained hydroxy - rich HNTs to a solution containing 1.5 g N , N -dicyclohexylcarbodiimide and 0.2 g of 4 - dimethylaminopyridine N , N -dimethylformamide, ultrasonically disperse evenly, under nitrogen protection, add 0.6 g of malonic acid, stir and react at 40 °C for 10 h, then dropwise add 3 mL of triethanolamine, continue to stir and react at 40 °C for 10 h, filter, wash, and dry to obtain TEA@HNTs.

[0032] (4) Stir and dissolve 2 g of PVA (molecular weight 65,000 - 75,000) in deionized water. Add 1 g of the prepared TEA@HNTs. After ultrasonic dispersion until homogeneous, add sodium hydroxide to adjust the pH value of the solution to 8.5. Finally, slowly dropwise add 4 mL of diglycidyl ether. Stir and react at 50 °C for 11 h. Take a part of the reaction solution for vacuum filtration. Immerse the filtration membrane in warm water at 45 °C for 12.5 h and change the water every 2 h. Dry to obtain the TEA@HNTs / PVA crosslinked composite membrane. The adsorption capacity of lead ions is measured according to the adsorption performance experiment of the product in Example 1, and the results are listed in Table 1.

[0033] Example 3

[0034] A preparation method of a triethanolamine grafted modified halloysite nanotube - polyvinyl alcohol crosslinked composite membrane, comprising the following steps: (1) Disperse 1 g of HNTs (Xianfeng Nano, CAS No.: 1332 - 58 - 7, product number: 103763) in ethanol. After ultrasonic dispersion until homogeneous, add 0.5 g of 3 - aminopropyltriethoxysilane. Reflux and react at 90 °C for 10 h. Filter, wash, and dry to obtain amino - functionalized HNTs.

[0035] (2) Ultrasonically disperse 1 g of the prepared amino - functionalized HNTs in an aqueous sodium hydroxide solution (5% wt). Slowly dropwise add a mixture of 40 mL of glycidol and 60 mL of absolute ethanol. Stir and react at 80 °C for 8 h. Filter, wash, and dry to obtain hydroxyl - rich HNTs.

[0036] (3) Add 1 g of the prepared hydroxyl - rich HNTs to a solution containing 2 g N , N - dicyclohexylcarbodiimide and 0.3 g of 4 - dimethylaminopyridine N , N - dimethylformamide. After ultrasonic dispersion until homogeneous, under nitrogen protection, add 0.8 g of malonic acid. Stir and react at 50 °C for 8 h, then dropwise add 4 mL of triethanolamine. Continue to stir and react at 50 °C for 8 h. Filter, wash, and dry to obtain TEA@HNTs.

[0037] (4) Stir and dissolve 3 g of PVA (molecular weight 65,000 - 75,000) in deionized water. Add 1 g of the prepared TEA@HNTs. After ultrasonic dispersion to be uniform, add sodium hydroxide to adjust the pH value of the solution to 9. Finally, slowly dropwise add 5 mL of diglycidyl ether. Stir and react at 60 °C for 8 h. Take a part of the reaction solution for vacuum filtration. Immerse the filtration membrane in warm water at 50 °C for 10 h and change the water every 1 h. Dry to obtain the TEA@HNTs / PVA crosslinked composite membrane. The adsorption capacity of lead ions is determined according to the adsorption performance experiment of the product in Example 1. The results are listed in Table 1.

[0038] Comparative Example 1 Stir and dissolve 1 g of PVA (molecular weight 65,000 - 75,000) in deionized water. Add 1 g of raw HNTs. After ultrasonic dispersion to be uniform, add sodium hydroxide to adjust the pH value of the solution to 8. Finally, slowly dropwise add 3 mL of diglycidyl ether. Stir and react at 40 °C for 14 h. Take a part of the reaction solution for vacuum filtration. Immerse the filtration membrane in warm water at 40 °C for 15 h and change the water every 3 h. Dry to obtain the HNTs / PVA crosslinked composite membrane.

[0039] Comparative Example 2 (1) Add 1 g of raw HNTs to a solution containing 1 g N , N -dicyclohexylcarbodiimide and 0.1 g of 4-dimethylaminopyridine N , N -dimethylformamide. After ultrasonic dispersion to be uniform, under nitrogen protection, add 0.4 g of malonic acid. Stir and react at 30 °C for 12 h, then dropwise add 2 mL of triethanolamine and continue to stir and react at 30 °C for 12 h. Filter, wash, and dry to obtain TEA@HNTs.

[0040] (2) Stir and dissolve 1 g of polyvinyl alcohol (molecular weight 65,000 - 75,000) in deionized water. Add the 1 g of prepared TEA@HNTs. After ultrasonic dispersion to be uniform, add sodium hydroxide to adjust the pH value of the solution to 8. Finally, slowly dropwise add 3 mL of diglycidyl ether. Stir and react at 40 °C for 14 h. Take a part of the reaction solution for vacuum filtration. Immerse the filtration membrane in warm water at 40 °C for 15 h and change the water every 3 h. Dry to obtain the TEA@HNTs / PVA crosslinked composite membrane.

[0041] Table 1 Adsorption amounts of lead ions by the composite membranes prepared in Examples 1 - 3 and Comparative Examples 1 - 2

[0042] It can be seen from the results that the TEA@HNTs / PVA crosslinked composite membrane prepared in the embodiment of the present invention contains abundant adsorption sites. Moreover, based on the excellent interfacial compatibility between TEA@HNTs and PVA, the strong combination and synergistic effect of the two in adsorption performance can be fully exerted. At the same time, the crosslinking improves the porosity of the composite membrane. Therefore, the prepared TEA@HNTs / PVA crosslinked composite membrane has excellent adsorption performance for lead ions, and the adsorption capacity can reach 366 mg / g.

[0043] In contrast, in Comparative Example 1, since the HNTs were not functionalized and modified, the lack of surface active groups on the HNTs limited both the generation of effective adsorption sites and caused agglomeration due to the weak interfacial binding between the filler and the matrix, seriously restricting the synergistic adsorption efficiency of the composite system. Although in Comparative Example 2, an attempt was made to directly graft triethanolamine, but limited by the density of surface reactive sites on the HNTs, the actual grafting rate was low, and the improvement effect on the dispersion of the nano-filler was limited. The two comparative examples were significantly inferior to the example group in key indicators such as interfacial interaction, filler dispersion, the number of active sites, and synergistic adsorption efficiency. Therefore, their adsorption performance was far inferior to that of the examples.

Claims

1. A preparation method of a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol crosslinked composite membrane, characterized in that, It includes the following steps: (1) Modify halloysite nanotubes with an amino-silane coupling agent to obtain amino-functionalized halloysite nanotubes; (2) Introduce hydroxyl groups on the surface of the amino-functionalized halloysite nanotubes by the ring-opening reaction of amino groups with glycidol to obtain halloysite nanotubes rich in hydroxyl groups; (3) Ultrasonically disperse the hydroxy-rich halloysite nanotubes in a solution containing N , N -dicyclohexylcarbodiimide and 4-dimethylaminopyridine in N , N -dimethylformamide. Under nitrogen protection, add malonic acid and carry out a stirring reaction. Then add triethanolamine and continue the stirring reaction. Filter, wash, and dry to obtain triethanolamine-grafted modified halloysite nanotubes; (4) Under alkaline conditions, using diglycidyl ether as a crosslinking agent, and the hydroxyl groups grafted and modified on the surface of halloysite nanotubes by polyvinyl alcohol and triethanolamine as crosslinking sites to form a three-dimensional network structure, then vacuum filter to form a film, remove alkaline substances, and dry to obtain a crosslinked composite film.

2. The preparation method of the triethanolamine-grafted and modified halloysite nanotube-polyvinyl alcohol crosslinked composite film according to claim 1, wherein the specific step (1) is to disperse halloysite nanotubes in ethanol, ultrasonically disperse them evenly, add an amino-silane coupling agent, and reflux and react at 80-90 °C for 10-16 h, filter, wash, and dry to obtain amino-functionalized HNTs.

3. The preparation method of the triethanolamine-grafted and modified halloysite nanotube-polyvinyl alcohol crosslinked composite film according to claim 2, wherein the mass ratio of halloysite nanotubes to the amino-silane coupling agent in the step (1) is 1:(0.1-0.5), and the amino-silane coupling agent is one of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

4. The preparation method of the triethanolamine-grafted and modified halloysite nanotube-polyvinyl alcohol crosslinked composite film according to claim 1, wherein the specific step (2) is to ultrasonically disperse the amino-functionalized halloysite nanotubes in an aqueous sodium hydroxide solution, slowly dropwise add a solution of glycidol in ethanol, stir and react at 60-80 °C, filter, wash, and dry to obtain halloysite nanotubes rich in hydroxyl groups.

5. The preparation method of the triethanolamine-grafted and modified halloysite nanotube-polyvinyl alcohol crosslinked composite film according to claim 4, wherein the dosage ratio of the amino-functionalized halloysite nanotubes to glycidol in the step (2) is 1 g:(20-40 mL), the concentration of the aqueous sodium hydroxide solution is 4-5% wt, and the volume ratio of glycidol to ethanol in the solution of glycidol in ethanol is 1:(1-1.5).

6. The preparation method of the triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol crosslinked composite membrane according to claim 1, wherein in the step (3), the dosage ratio of the hydroxy-rich halloysite nanotubes, N , N -dicyclohexylcarbodiimide, 4-dimethylaminopyridine, malonic acid and triethanolamine is 1 g: (1-2) g: (0.1-0.3) g: (0.4-0.8) g: (2-4 mL).

7. The preparation method of the triethanolamine-grafted and modified halloysite nanotube-polyvinyl alcohol crosslinked composite film according to claim 1, wherein the stirring reaction in the step (3) is carried out at 30-50 °C for 8-12 h.

8. The preparation method of the triethanolamine-grafted and modified halloysite nanotube-polyvinyl alcohol crosslinked composite film according to claim 1, wherein the specific step (4) is to stir and dissolve polyvinyl alcohol in deionized water, add triethanolamine-grafted and modified halloysite nanotubes, ultrasonically disperse them evenly, add sodium hydroxide, adjust the pH value of the solution to 8-9, and finally add diglycidyl ether to carry out a crosslinking reaction at 40-60 °C.

9. The preparation method of the triethanolamine-grafted and modified halloysite nanotube-polyvinyl alcohol crosslinked composite film according to claim 8, wherein the dosage ratio of the triethanolamine-grafted and modified halloysite nanotubes, polyvinyl alcohol, and diglycidyl ether in the step (4) is 1 g:(1-3) g:(3-5) mL.

10. The preparation method of the triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol crosslinked composite membrane according to claim 1, wherein the removal of the basic substance in the step (4) is specifically to soak the suction filtration membrane in water at 40-50 °C for 10-15 h, and change the water every 1-3 h.

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