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

Abstract

The invention discloses a preparation method of a triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film, comprising the steps of: modifying halloysite nanotubes by an aminosilane coupling agent to obtain amination halloysite nanotubes; utilizing the ring-opening reaction of amino and glycidol to introduce hydroxyl groups to obtain hydroxylation-rich halloysite nanotubes; utilizing the reaction of hydroxyl and carboxyl groups, using malonic acid as a "bridge", grafting triethanolamine on the surface to obtain triethanolamine-grafted modified halloysite nanotubes; under alkaline conditions, using diglycidyl ether as a cross-linking agent, the hydroxyl groups on the surfaces of polyvinyl alcohol and triethanolamine-grafted modified halloysite nanotubes are cross-linking sites to form a three-dimensional network structure, followed by vacuum filtration to form a film, and removing alkaline substances, and drying to obtain a cross-linked composite film. The present invention improves the dispersibility of halloysite nanotubes in a resin body and solves the water-solubility problem of PVA, thereby improving the adsorption performance of heavy metal ions.

Description

Technical Field

[0001] The invention relates to the technical field of polyvinyl alcohol composite films, in particular to a method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film. Background Art

[0002] Halloysite nanotubes (HNTs), a natural clay mineral, are often used as functional additives to enhance the adsorption of heavy metal ions in resin-based composites due to their unique hollow tubular structure, high specific surface area, and good biocompatibility. However, the high surface energy of HNTs leads to dispersibility challenges such as weak interfacial bonding with the resin matrix and easy agglomeration, which severely restricts their performance. Existing modification technologies are limited by the lack of active reaction sites on the HNT surface (e.g., the low density of natural hydroxyl groups), resulting in insufficient grafting efficiency of functionalized molecules and difficulty in effectively improving compatibility with the matrix.

[0003] Polyvinyl alcohol (PVA) is a typical environmentally friendly film-forming material. The abundant hydroxyl groups in its molecular chain can form stable coordination bonds with heavy metal ions, demonstrating unique advantages in the adsorption field. However, PVA's water solubility makes it easily soluble in water when used directly, resulting in adsorbent loss, which greatly limits its engineering application in heavy metal treatment scenarios. Summary of the Invention

[0004] In response to the above-mentioned defects in the prior art, the present invention provides a method for preparing a triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film, which solves the problems of low grafting rate of functionalized molecules on the surface of halloysite nanotubes, poor dispersibility of halloysite nanotubes and resin matrix, and easy residue of polyvinyl alcohol in the aqueous solution, thereby achieving efficient adsorption of heavy metal ions.

[0005] The technical solution of the present invention is as follows: a method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film, comprising the following steps:

[0006] (1) Halloysite nanotubes are modified by an aminosilane coupling agent to obtain amino-modified halloysite nanotubes;

[0007] (2) Using the ring-opening reaction of amino groups with glycidol, hydroxyl groups were introduced onto the surface of aminated halloysite nanotubes to obtain hydroxyl-rich halloysite nanotubes;

[0008] (3) Ultrasonic dispersion of hydroxylated halloysite nanotubes in a solution N , N -dicyclohexylcarbodiimide and 4-dimethylaminopyridine N , N- dimethylformamide, under nitrogen protection, adding malonic acid, stirring and reacting, then adding triethanolamine, continuing to stir and react, filtering, washing, and drying to obtain triethanolamine-grafted halloysite nanotubes;

[0009] (4) Under alkaline conditions, diglycidyl ether was used as a crosslinking agent, and polyvinyl alcohol and triethanolamine were grafted to modify the hydroxyl groups on the surface of halloysite nanotubes as crosslinking sites to form a three-dimensional network structure. The membrane was then vacuum filtered to form a membrane, and the alkaline substances were removed and dried to obtain a crosslinked composite membrane.

[0010] Furthermore, the step (1) specifically comprises dispersing the halloysite nanotubes in ethanol, uniformly dispersing by ultrasonication, adding an aminosilane coupling agent, and reacting under reflux at 80-90° C. for 10-16 hours, filtering, washing, and drying to obtain the amino-treated halloysite nanotubes.

[0011] Furthermore, in step (1), the mass ratio of the halloysite nanotubes to the aminosilane coupling agent is 1:(0.1-0.5), and the aminosilane coupling agent is one of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

[0012] Furthermore, the step (2) specifically comprises ultrasonically dispersing the amino-treated halloysite nanotubes in a sodium hydroxide aqueous solution, slowly adding a solution of glycidol in ethanol, stirring and reacting at 60-80° C., filtering, washing, and drying to obtain hydroxylated halloysite nanotubes.

[0013] Furthermore, in the step (2), the ratio of the amount of the aminated halloysite nanotubes to the amount of glycidol is 1 g:(20-40 mL), the concentration of the sodium hydroxide aqueous solution is 4-5% wt, and the volume of glycidol to ethanol in the glycidol-ethanol solution is 1:(1-1.5).

[0014] Furthermore, in step (3), the hydroxylated halloysite nanotubes, N , N The usage ratio of 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).

[0015] Furthermore, the stirring reaction in step (3) is carried out at 30-50° C. for 8-12 hours.

[0016] Furthermore, the step (4) specifically comprises stirring and dissolving polyvinyl alcohol in deionized water, adding triethanolamine grafted modified halloysite nanotubes, uniformly dispersing by ultrasonication, adding sodium hydroxide, adjusting the pH value of the solution to 8-9, and finally adding diglycidyl ether to carry out a cross-linking reaction at 40-60°C.

[0017] Furthermore, in step (4), the usage ratio of triethanolamine grafted modified halloysite nanotubes, polyvinyl alcohol and diglycidyl ether is 1 g: (1-3) g: (3-5) mL.

[0018] Furthermore, the alkaline substances in step (4) are removed by soaking the filtration membrane in water at 40 to 50° C. for 10 to 15 hours, and changing the water every 1 to 3 hours.

[0019] This invention first modifies halloysite nanotubes (HNTs) by amino-modification using an aminosilane coupling agent. A large number of hydroxyl groups are then introduced onto the HNT surface via a glycidol ring-opening reaction, significantly increasing the number of surface active sites. Subsequently, triethanolamine (TEA), a multifunctional group, is efficiently grafted onto the HNTs using malonic acid as a bridge, further enhancing the HNTs' compatibility with the resin matrix and their ability to chelate heavy metal ions. Finally, based on interfacial structural design, diglycidyl ether is used as a crosslinker to promote the covalent crosslinking reaction between the TEA-grafted halloysite nanotubes (TEA@HNTs) and polyvinyl alcohol (PVA) in an alkaline solution, forming a three-dimensional structure. This not only effectively improves the structural stability of the composite membrane, but also introduces more adsorption active sites (hydroxyl groups) and further enhances the dispersion of the HNTs in the matrix. Consequently, a TEA@HNTs / PVA cross-linked composite membrane with excellent structural stability and adsorption performance (TEA@HNTs / PVA cross-linked composite membrane) was prepared using a simple vacuum filtration technique.

[0020] The advantages of the present invention compared with the prior art are:

[0021] (1) The present invention significantly improves the dispersion uniformity of HNTs in the resin matrix through the synergistic effect of graded functional modification strategy and cross-linking treatment technology.

[0022] (2) The present invention uses diglycidyl ether as a cross-linking agent, and constructs a stable three-dimensional network structure through the covalent cross-linking reaction between PVA and the surface hydroxyl groups of TEA@HNTs, which effectively solves the water solubility problem of PVA.

[0023] (3) The present invention achieves a significant improvement in the adsorption performance of the composite membrane for heavy metal ions by synergistically enhancing the chelating adsorption effect between TEA@HNTs and the PVA cross-linked network. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the TEA@HNTs / PVA cross-linked composite film prepared in Example 1. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the examples, but are not intended to limit the present invention.

[0026] Example 1

[0027] A method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film comprises the following steps:

[0028] (1) Disperse 1 g of HNTs (Xianfeng Nano, CAS No.: 1332-58-7, Product No.: 103763) in ethanol and disperse them evenly by ultrasonication. Add 0.1 g of 3-aminopropyltrimethoxysilane and reflux at 80 °C for 16 h. Filter, wash, and dry to obtain amino HNTs.

[0029] (2) 1 g of the prepared amino HNTs was ultrasonically dispersed in a sodium hydroxide aqueous solution (4% wt), and a mixture of 20 mL of propylene oxide and 20 mL of anhydrous ethanol was slowly added dropwise. The mixture was stirred at 60 °C for 12 h, filtered, washed, and dried to obtain hydroxylated HNTs.

[0030] (3) Add 1g of the prepared hydroxylated HNTs to a solution containing 1g N , N -dicyclohexylcarbodiimide and 0.1 g of 4-dimethylaminopyridine N , N -dimethylformamide, ultrasonically dispersed uniformly, added 0.4 g of malonic acid under nitrogen protection, stirred and reacted at 30 ° C for 12 h, then added 2 mL of triethanolamine dropwise, and continued to stir and react at 30 ° C for 12 h, filtered, washed and dried to obtain TEA@HNTs.

[0031] (4) 1 g of PVA (molecular weight 65,000-75,000) was stirred and dissolved in deionized water, and 1 g of the prepared TEA@HNTs was added. After ultrasonic dispersion, sodium hydroxide was added to adjust the pH value of the solution to 8. Finally, 3 mL of diglycidyl ether was slowly added dropwise. The reaction was stirred at 40 °C for 14 h. A portion of the reaction solution was vacuum filtered and the filter membrane was soaked in warm water at 40 °C for 15 h. The water was changed every 3 h and dried to obtain a TEA@HNTs / PVA cross-linked composite membrane. Its SEM image is shown in FIG. Figure 1 As shown, the composite membrane has a rich pore structure.

[0032] The adsorption performance test experiment of the TEA@HNTs / PVA cross-linked composite membrane prepared in this Example 1 is as follows:

[0033] A 100 mL aqueous solution of 100 mg / L lead ion (lead nitrate as a reagent) was prepared in a flask. After adjusting the solution pH to 7 with 0.1 M NaOH, the prepared TEA@HNTs / PVA cross-linked composite membrane was added. The membrane was then adsorbed in a 30°C constant temperature oscillator at 200 rpm for 3 hours. After adsorption, the supernatant was collected and the lead ion concentration in the supernatant was determined by ICP-OES. The adsorption capacity of lead ions by the adsorbent was calculated using the following formula ( Q , mg / g), and the results are listed in Table 1.

[0034] Q =( C 0 - C t ) V / M

[0035] 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).

[0036] Example 2

[0037] A method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film comprises the following steps:

[0038] (1) Disperse 1 g of HNTs (Xianfeng Nano, CAS No.: 1332-58-7, Product No.: 103763) in ethanol and disperse them evenly by ultrasonication. Add 0.3 g of 3-aminopropyltriethoxysilane and reflux at 85 °C for 13 h. Filter, wash, and dry to obtain amino HNTs.

[0039] (2) 1 g of the prepared amino HNTs was ultrasonically dispersed in a sodium hydroxide aqueous solution (4.5% wt), and a mixture of 30 mL of propylene oxide and 37.5 mL of anhydrous ethanol was slowly added dropwise. The mixture was stirred at 70 °C for 10 h, filtered, washed, and dried to obtain hydroxylated HNTs.

[0040] (3) Add 1g of the prepared hydroxylated HNTs to a solution of 1.5g N , N -dicyclohexylcarbodiimide and 0.2 g of 4-dimethylaminopyridine N , N-dimethylformamide, ultrasonically dispersed uniformly, added 0.6 g of malonic acid under nitrogen protection, stirred and reacted at 40 ° C for 10 h, then added 3 mL of triethanolamine dropwise, and continued to stir and react at 40 ° C for 10 h, filtered, washed and dried to obtain TEA@HNTs.

[0041] (4) 2 g of PVA (molecular weight 65,000-75,000) was stirred and dissolved in deionized water, and 1 g of the prepared TEA@HNTs was added. After ultrasonic dispersion, sodium hydroxide was added to adjust the pH value of the solution to 8.5. Finally, 4 mL of diglycidyl ether was slowly added dropwise. The reaction was stirred at 50 °C for 11 h. A portion of the reaction solution was vacuum filtered and the filter membrane was soaked in warm water at 45 °C for 12.5 h. The water was changed every 2 h and the membrane was dried to obtain a TEA@HNTs / PVA cross-linked composite membrane. The adsorption capacity of the membrane for lead ions was measured according to the adsorption performance experiment of the product in Example 1. The results are listed in Table 1.

[0042] Example 3

[0043] A method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film comprises the following steps:

[0044] (1) Disperse 1 g of HNTs (Xianfeng Nano, CAS No.: 1332-58-7, Product No.: 103763) in ethanol and disperse them evenly by ultrasonication. Add 0.5 g of 3-aminopropyltriethoxysilane and reflux at 90 °C for 10 h. Filter, wash, and dry to obtain amino HNTs.

[0045] (2) 1 g of the prepared amino HNTs was ultrasonically dispersed in a sodium hydroxide aqueous solution (5% wt), and a mixture of 40 mL of propylene oxide and 60 mL of anhydrous ethanol was slowly added dropwise. The mixture was stirred at 80 °C for 8 h, filtered, washed, and dried to obtain hydroxylated HNTs.

[0046] (3) Add 1g of the prepared hydroxylated HNTs to a solution containing 2g N , N -dicyclohexylcarbodiimide and 0.3 g of 4-dimethylaminopyridine N , N -dimethylformamide, ultrasonically dispersed uniformly, added 0.8 g of malonic acid under nitrogen protection, stirred and reacted at 50 ° C for 8 h, then added 4 mL of triethanolamine dropwise, and continued to stir and react at 50 ° C for 8 h, filtered, washed and dried to obtain TEA@HNTs.

[0047] (4) 3 g of PVA (molecular weight 65,000-75,000) was stirred and dissolved in deionized water, and 1 g of the prepared TEA@HNTs was added. After ultrasonic dispersion, sodium hydroxide was added to adjust the pH value of the solution to 9. Finally, 5 mL of diglycidyl ether was slowly added dropwise. The reaction was stirred at 60 °C for 8 h. A portion of the reaction solution was vacuum filtered and the filter membrane was soaked in warm water at 50 °C for 10 h. The water was changed every 1 h and the membrane was dried to obtain a TEA@HNTs / PVA cross-linked composite membrane. The adsorption capacity of the membrane for lead ions was measured according to the adsorption performance experiment of the product in Example 1. The results are listed in Table 1.

[0048] Comparative Example 1

[0049] 1 g of PVA (molecular weight 65,000-75,000) was stirred and dissolved in deionized water. 1 g of original HNTs was added and ultrasonically dispersed. Then, sodium hydroxide was added to adjust the pH of the solution to 8. Finally, 3 mL of diglycidyl ether was slowly added dropwise. The reaction was stirred at 40°C for 14 hours. A portion of the reaction solution was vacuum filtered and the filtered membrane was immersed in warm water at 40°C for 15 hours. The water was changed every 3 hours and dried to obtain an HNTs / PVA cross-linked composite membrane.

[0050] Comparative Example 2

[0051] (1) Add 1g of original HNTs to a solution containing 1g N , N -dicyclohexylcarbodiimide and 0.1 g of 4-dimethylaminopyridine N , N -dimethylformamide, ultrasonically dispersed uniformly, added 0.4 g of malonic acid under nitrogen protection, stirred and reacted at 30 ° C for 12 h, then added 2 mL of triethanolamine dropwise, and continued to stir and react at 30 ° C for 12 h, filtered, washed and dried to obtain TEA@HNTs.

[0052] (2) 1 g of polyvinyl alcohol (molecular weight 65,000-75,000) was stirred and dissolved in deionized water, and 1 g of the prepared TEA@HNTs was added. After ultrasonic dispersion, sodium hydroxide was added to adjust the pH value of the solution to 8. Finally, 3 mL of diglycidyl ether was slowly added dropwise. The reaction was stirred at 40 °C for 14 h. Part of the reaction liquid was vacuum filtered and the filtration membrane was soaked in warm water at 40 °C for 15 h. The water was changed every 3 h and dried to obtain the TEA@HNTs / PVA cross-linked composite membrane.

[0053] Table 1 Adsorption capacity of lead ions by the composite membranes prepared in Examples 1-3 and Comparative Examples 1-2

[0054]

[0055] The results show that the TEA@HNTs / PVA cross-linked composite membrane prepared in this embodiment of the present invention contains abundant adsorption sites. Furthermore, the excellent interfacial compatibility between TEA@HNTs and PVA allows for the powerful combination and synergistic enhancement of their adsorption performance. Furthermore, the cross-linking enhances the porosity of the composite membrane. Consequently, the resulting TEA@HNTs / PVA cross-linked composite membrane exhibits excellent adsorption performance for lead ions, with an adsorption capacity of up to 366 mg / g.

[0056] In contrast, Comparative Example 1 lacks functional modification of the HNTs, resulting in a lack of active groups on the HNT surface. This not only limits the generation of effective adsorption sites, but also leads to agglomeration due to the weak filler-matrix interface, severely restricting the synergistic adsorption performance of the composite system. Comparative Example 2 attempts direct grafting of triethanolamine, but the density of reactive sites on the HNT surface limits the actual grafting rate, resulting in limited improvement in nanofiller dispersion. Both comparative examples significantly underperform the examples in key metrics such as interfacial interaction, filler dispersion, number of active sites, and synergistic adsorption performance, resulting in adsorption performance far inferior to that of the examples.

Claims

1. A method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film, characterized in that: The following steps are involved: (1) Halloysite nanotubes are modified by an aminosilane coupling agent to obtain amino-modified halloysite nanotubes; (2) Using the ring-opening reaction of amino groups with glycidol, hydroxyl groups were introduced onto the surface of aminated halloysite nanotubes to obtain hydroxyl-rich halloysite nanotubes; (3) Ultrasonic dispersion of hydroxylated halloysite nanotubes in a solution N , N -dicyclohexylcarbodiimide and 4-dimethylaminopyridine N , N - dimethylformamide, under nitrogen protection, adding malonic acid, stirring and reacting, then adding triethanolamine, continuing to stir and react, filtering, washing, and drying to obtain triethanolamine-grafted halloysite nanotubes; (4) Under alkaline conditions, diglycidyl ether was used as a crosslinking agent, and polyvinyl alcohol and triethanolamine were grafted to modify the hydroxyl groups on the surface of halloysite nanotubes as crosslinking sites to form a three-dimensional network structure. The membrane was then vacuum filtered to form a membrane, and the alkaline substances were removed and dried to obtain a crosslinked composite membrane.

2. The method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film according to claim 1, wherein the step (1) specifically comprises dispersing the halloysite nanotubes in ethanol, uniformly dispersing them by ultrasonication, adding an aminosilane coupling agent, and reacting under reflux at 80-90°C for 10-16 hours, filtering, washing, and drying to obtain the amino-modified halloysite nanotubes.

3. The method for preparing a triethanolamine-grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film according to claim 2, wherein the mass ratio of the halloysite nanotube to the aminosilane coupling agent in step (1) is 1:(0.1-0.5), and the aminosilane coupling agent is one of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

4. The method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film according to claim 1, wherein the step (2) specifically comprises ultrasonically dispersing the amination-modified halloysite nanotubes in an aqueous sodium hydroxide solution, slowly adding a solution of ethanol containing propylene oxide, stirring and reacting at 60-80°C, filtering, washing, and drying to obtain hydroxylation-rich halloysite nanotubes.

5. The method for preparing a triethanolamine-grafted halloysite nanotube-polyvinyl alcohol cross-linked composite film according to claim 4, wherein the ratio of the amount of the aminated halloysite nanotubes to the amount of glycidol in step (2) is 1 g:(20-40 mL), the concentration of the sodium hydroxide aqueous solution is 4-5% wt, and the volume ratio of glycidol to ethanol in the glycidol-ethanol solution is 1:(1-1.5).

6. The method for preparing triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film according to claim 1, wherein in step (3), the hydroxylated halloysite nanotubes, N , N The usage ratio of 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 method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film according to claim 1, wherein the stirring reaction in step (3) is carried out at 30-50°C for 8-12 hours.

8. The method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film according to claim 1, wherein the step (4) specifically comprises stirring and dissolving polyvinyl alcohol in deionized water, adding triethanolamine grafted modified halloysite nanotubes, ultrasonically dispersing the mixture uniformly, adding sodium hydroxide, adjusting the pH value of the solution to 8-9, and finally adding diglycidyl ether to carry out a cross-linking reaction at 40-60°C.

9. The method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite film according to claim 8, wherein the usage ratio of the triethanolamine grafted modified halloysite nanotube, polyvinyl alcohol and diglycidyl ether in step (4) is 1 g: (1-3) g: (3-5) mL.

10. The method for preparing a triethanolamine grafted modified halloysite nanotube-polyvinyl alcohol cross-linked composite membrane according to claim 1, wherein the alkaline substance is removed in step (4) by soaking the filtration membrane in water at 40-50°C for 10-15 hours, and changing the water every 1-3 hours.

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