Nanofiltration membrane based on tamarind gum as well as preparation method and application of nanofiltration membrane

Abstract

The invention provides a nanofiltration membrane based on tamarind gum and a preparation method and application thereof.The preparation method comprises the steps that firstly, halloysite is treated with a silane coupling agent, and modified halloysite is obtained; pre-treating the base membrane; adding aminated tamarind gum, sulfhydrylated tamarind gum and modified halloysite into water, and uniformly stirring to obtain a water-phase solution; the preparation method comprises the following steps: adding glycerol tri (1, 2-epoxy) propyl ether into ethanol, and uniformly stirring to obtain a glyceryl ether solution; the preparation method comprises the following steps: adding 1, 3, 6-naphthalene trisulfonyl chloride into normal hexane, and uniformly stirring to obtain an oil phase solution; finally, the pretreated base membrane is sequentially placed in a water phase solution, a glyceryl ether solution and an oil phase solution to be treated, and the nanofiltration membrane based on the tamarind gum is obtained. Compared with the prior art, the preparation method has the advantages that on the basis of tamarind gum, amination and sulfhydrylation are carried out on the tamarind gum, the composite nanofiltration membrane which is high in water flux and high in metal ion interception and can be used for the acid wastewater is constructed in cooperation with introduced modified halloysite, and the applicability and durability of the composite nanofiltration membrane to the acid wastewater are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel wastewater treatment, and particularly relates to a tamarind gum-based nanofiltration membrane, a preparation method thereof, and an application thereof. Background Art

[0002] The steel industry is one of the important basic industries in China. However, with the increase in the scale of the steel industry, the wastewater and environmental problems brought about by it need to be improved urgently. Among them, the desulfurization wastewater generated after desulfurization and denitrification is one of the wastewaters with relatively serious pollution. The desulfurization wastewater generally has a high acidity and contains rich ionic contents such as metals. If it cannot be effectively treated, it will pose a serious threat to the environment and human health. How to effectively treat it is crucial for environmental protection and sustainable development.

[0003] Nanofiltration membrane technology uses the pressure difference as the driving force, effectively intercepts specific ions, and has selective separation. It is widely used in the wastewater field, and it can effectively remove organic matters or heavy metal ions in water. However, generally, it is only applicable to neutral water. In wastewater with a high acidity, the treatment effect of the nanofiltration membrane will become worse. Therefore, it is necessary to improve the applicability of the nanofiltration membrane in acidic wastewater.

[0004] The patent with the publication number CN 114797471 A, which was published on July 29, 2022, discloses a crustacean biochar / sodium alginate composite gel nanofiltration membrane, a preparation method thereof, and an application thereof. It uses: cleaning and drying the shell of crustacean animals, then pyrolyzing at high temperature in a nitrogen atmosphere, and cleaning and drying after cooling to obtain crustacean biochar; ball-milling and modifying the crustacean biochar to obtain modified crustacean biochar; mixing the modified crustacean biochar with an anhydrous ethanol solution to obtain a mixed solution, and then making the modified crustacean biochar load on the substrate membrane through suction filtration to obtain a substrate membrane loaded with biochar; uniformly rod-coating a sodium alginate solution on the surface of the substrate membrane loaded with biochar, then transferring it to a CaCl2 solution for soaking to fully crosslink, and then cleaning and air-drying to obtain a crustacean biochar / sodium alginate composite gel nanofiltration membrane. However, it only discloses the application of the nanofiltration membrane in the separation and recovery of dye molecules / inorganic salt ions in dye wastewater, and does not disclose how to apply it in acidic wastewater. Summary of the Invention

[0005] The purpose of the present invention is to provide a tamarind gum-based nanofiltration membrane and a preparation method thereof. Based on tamarind gum, through its amination, mercaptanization, and synergistically introducing modified halloysite, a composite nanofiltration membrane with high water flux, high metal ion retention, and applicable to acidic wastewater is constructed, effectively improving its applicability and durability in acidic wastewater.

[0006] Another object of the present invention is to provide an application of a nanofiltration membrane based on tamarind gum for treating acidic wastewater, especially for treating desulfurization wastewater in the iron and steel industry. The nanofiltration membrane provided by the present invention can improve its applicability and application effect in acidic wastewater, reduce the treatment cost, extend the service life of the membrane, and at the same time reduce environmental pollution, which is of great significance for providing technical support for the sustainable development of the iron and steel industry.

[0007] The specific technical solution of the present invention is as follows:

[0008] A preparation method of a nanofiltration membrane based on tamarind gum, comprising the following steps:

[0009] 1) Treat halloysite with a silane coupling agent to obtain modified halloysite;

[0010] 2) Pretreat the base membrane;

[0011] 3) Add amino-functionalized tamarind gum, mercapto-functionalized tamarind gum and modified halloysite to water and stir evenly to obtain an aqueous solution; add tris(1,2-epoxy)propyl ether of glycerol to ethanol and stir evenly to obtain a glycerol ether solution; add 1,3,6-naphthalenetrisulfonyl chloride to n-hexane and stir evenly to obtain an oil phase solution;

[0012] 4) Immerse the pretreated base membrane obtained in step 2) in the aqueous solution, glycerol ether solution and oil phase solution in sequence for treatment. After washing, store it in deionized water to obtain a nanofiltration membrane based on tamarind gum.

[0013] Step 1) specifically includes:

[0014] 1-1) Perform alkali activation treatment on halloysite nanotubes to obtain pretreated halloysite;

[0015] 1-2) Use an amino silane coupling agent and a mercapto silane coupling agent to perform composite modification on the pretreated halloysite to obtain modified halloysite;

[0016] In step 1-1), the alkali activation treatment is specifically: treat with a sodium hydroxide solution of 0.2-0.3 mol / L, the dosage ratio of halloysite nanotubes to the sodium hydroxide solution is 1 g:20-30 mL, and the alkali activation treatment time is 20-40 minutes at room temperature.

[0017] Step 1-2) is specifically: add the pretreated halloysite, amino silane coupling agent, and mercapto silane coupling agent with a mass ratio of 1:(0.09-0.1):(0.05-0.06) to an 85-90 wt% ethanol aqueous solution and stir for 1-2 hours, then raise the temperature to 60-70 °C and stir for 1-2 hours, wash and dry to obtain modified halloysite; among them, the amino silane coupling agent is amino silane coupling agent KH550, and the mercapto silane coupling agent is mercapto silane coupling agent KH580.

[0018] In step 2), the pre-treated base film means: placing the base film in a sodium hydroxide solution for pre-activation; then uniformly coating the modified halloysite dispersion on the surface of the pre-activated base film and drying it naturally to obtain the pre-treated base film;

[0019] In step 2), the base film is a PAN ultrafiltration membrane or a PPS membrane; the concentration of the sodium hydroxide solution is 0.1 - 0.12 mol / L; the pre-activation temperature is 40 - 50 °C and the time is 20 - 40 minutes; the preparation method of the modified halloysite dispersion is: mixing the modified halloysite, amino-functionalized tamarind gum and water evenly to obtain it; where the mass ratio of the modified halloysite, amino-functionalized tamarind gum and deionized water is 5:(20 - 25):500; the coating amount of the modified halloysite dispersion is 50 - 60 mg / m 2 。

[0020] In step 3), the solid content of the aqueous solution is 0.25 - 0.32 wt%, where the mass ratio of the amino-functionalized tamarind gum, mercapto-functionalized tamarind gum and modified halloysite is (0.14 - 0.17):(0.08 - 0.1):

[0021] (0.03 - 0.05); the concentration of glycerol tris(1,2-epoxy)propylether in the glycerol ether solution is 0.1 - 0.15 wt%; the concentration of 1,3,6-naphthalenetrisulfonyl chloride in the oil phase solution is 0.2 - 0.25 wt%.

[0022] In step 3), the preparation method of the mercapto-functionalized tamarind gum includes the following steps:

[0023] S2.1: Adding tamarind gum to a nitric acid solution, oscillating and activating it at room temperature for 5 - 6 hours, washing and freeze-drying to obtain activated tamarind gum;

[0024] S2.2: Adding the activated tamarind gum to an aqueous sodium periodate solution, stirring for 3 - 4 hours, adding ethylene glycol for neutralization, centrifuging and washing with water; obtaining pre-treated tamarind gum;

[0025] S2.3: Adding the pre-treated tamarind gum, cysteine, carbodiimide hydrochloride and N-hydroxysuccinimide to toluene in turn, under nitrogen protection, stirring and reacting at 40 - 50 °C for 4 - 6 hours, washing and freeze-drying to obtain the mercapto-functionalized tamarind gum.

[0026] Preferably, in the raw materials for activating tamarind gum, the mass ratio of tamarind gum to nitric acid solution is 1:(40 - 60); the concentration of the nitric acid solution is 0.45 - 0.5 mol / L; in the raw materials for pretreating tamarind gum, the mass ratio of activated tamarind gum to sodium periodate is 1.5:1, and the concentration of the aqueous sodium periodate solution is 5 - 10 wt%; in the raw materials for thiolating tamarind gum, the mass ratio of pretreated tamarind gum to cysteine is 1:(1 - 1.2); the mass ratio of tamarind gum, carbodiimide hydrochloride, and N-hydroxysuccinimide is 10:2.5:1;

[0027] In steps 2) and 3), the preparation method of the amidated tamarind gum is as follows:

[0028] S1.1: Add tamarind gum to N-methyl-pyrrolidone, heat up to 90 - 95 °C and stir for 2 - 3 hours, cool to room temperature, add triethylamine, stir for 1 - 1.5 hours under ice bath, dropwise add acryloyl chloride, continue to stir for 3 - 4 hours, wash and freeze-dry to obtain alkenyl tamarind gum;

[0029] S1.2: Add alkenyl tamarind gum to dimethyl sulfoxide, then add ethyl diazoacetate and diazoseryl, stir at room temperature for 24 - 28 hours, wash and freeze-dry to obtain amidated tamarind gum.

[0030] In the preparation method of the amidated tamarind gum, in the raw materials for alkenyl tamarind gum, the mass ratio of tamarind gum, triethylamine, and acryloyl chloride is (1.2 - 1.5):4:2; in the raw materials for amidated tamarind gum, the mass ratio of alkenyl tamarind gum, dimethyl sulfoxide, ethyl diazoacetate, and diazoseryl is 5:80 - 100:0.4 - 0.5:0.8 - 1.

[0031] In step 4), first dip-coat the pretreated substrate film in an aqueous solution for 30 - 40 minutes, air-dry at room temperature; then transfer it to a glycerol ether solution and oscillate and immerse it at room temperature for 15 - 30 minutes, then heat-treat it at 60 - 80 °C for 10 - 20 minutes; then transfer it to an oil-phase solution and oscillate and immerse it at room temperature for 30 - 40 minutes, then heat-treat it at 50 - 60 °C for 5 - 15 minutes; finally wash it and store it in deionized water to obtain a composite nanofiltration membrane.

[0032] A nanofiltration membrane based on tamarind gum provided by the present invention is prepared by the above method. The water flux of the nanofiltration membrane based on tamarind gum ≥ 22 L / (m 2 h); soak it in a 40 wt% sulfuric acid solution at room temperature for 5 days, take it out, wash it with deionized water, and test the rejection rate of 2000 ppm magnesium sulfate at 0.5 Mpa ≥ 90%; wash it, soak it again for 30 days, and test the rejection rate ≥ 88%.

[0033] The present invention provides an application of a nanofiltration membrane based on tamarind gum for treating acidic metal wastewater, especially for treating desulfurization wastewater in the iron and steel industry, and for intercepting metal ions in acidic iron and steel wastewater.

[0034] The design concept of the present invention is as follows:

[0035] In the present invention, halloysite nanotubes are first treated with a sodium hydroxide solution, which can not only clean the surface, remove impurities, and prepare for subsequent modification, but also increase the number of surface hydroxyl groups, improve the reaction activity, and then treated with an amino-silane coupling agent KH550 and a mercapto-silane coupling agent KH580, which can introduce functional groups such as amino and mercapto groups, change the surface charge and chemical properties, not only enhance the chemical bonding between halloysite and the base membrane, but also improve the dispersion stability of halloysite in the coating film. The addition of ethanol in the solvent further improves the dispersibility. The modified halloysite may have stronger adsorption capacity and selectivity, which is helpful for intercepting metal ions. Moreover, the covalent bonding (Si-O-Si) of the silane coupling agent makes the modified halloysite more stable at low pH, avoiding structural disintegration, so that the prepared nanofilm has stable properties under pickling conditions.

[0036] Then, by pre-activating the surface of the base membrane in advance, its surface energy is increased, the adhesion and compatibility with the modified halloysite are enhanced, and more reaction sites are formed, which is beneficial to the uniform deposition of the modified halloysite; then the modified halloysite dispersion liquid is pre-deposited on its surface, effectively improving the adhesion of the subsequent coating film and increasing the interfacial property between the coating film and the base membrane. In addition, due to the modified halloysite contained in the modified halloysite dispersion liquid, pre-deposition can form protrusions on the surface, increase the membrane surface area and contact sites, extend the action time of metal ions and the membrane; it also helps to form interfacial pores, improve the water flux, and at the same time, halloysite itself has a charge, which can improve the interception of metal ions. The addition of amino-functionalized tamarind gum may have more amino groups, which are protonated and positively charged under acidic conditions, but may form coordination bonds with metal ions through complexation, improving the metal ion interception rate.

[0037] After pretreatment, a coating film is constructed with amino-functionalized tamarind gum, mercapto-functionalized tamarind gum, and modified halloysite as basic raw materials; an interpenetrating crosslinked network is formed, and the formation of the crosslinked network effectively improves the physical properties of the surface coating film. While ensuring the water flux and metal ion interception, its durability in acidic solutions is enhanced. Moreover, the complexation of amino and mercapto groups directly fixes metal ions, improving the metal ion interception rate.

[0038] In the present invention, tamarind gum is a natural plant gum with acid resistance, heat resistance, salt resistance and freeze resistance; it has good application potential for acidic steel wastewater. Amination and mercaptanization treatments are beneficial to the formation of a cross-linked network and can improve its applicability. The preparation of aminated tamarind gum is as follows: First, it is grafted with acryloyl chloride to make it contain unsaturated bonds, and then it reacts with ethyl diazoacetate and diazoserin to form a nitrogen-containing heterocycle (pyrazoline) while grafting amino groups and other groups, thus obtaining it. The preparation of mercaptanized tamarind gum is as follows: It is successively activated and pretreated in a nitric acid solution and a sodium periodate aqueous solution; then, with the assistance of carbodiimide hydrochloride and N-hydroxysuccinimide, cysteamine is grafted to obtain a mercapto-containing substance. Modified halloysite is also prepared using an amino-silane coupling agent and a mercapto-silane coupling agent. The three substances form an interpenetrating cross-linked network under the cross-linking of subsequent tris(1,2-epoxy)propyl ether and 1,3,6-naphthalenetrisulfonyl chloride; effectively improving the membrane quality and water flux; at the same time, due to the good adsorption of metal ions by the nitrogen-containing heterocycle and the coordination with metal ions, the metal rejection rate can be effectively improved; in addition, the durability under acidic conditions can also be improved. Functional groups such as amino and mercapto in the material can chelate and electrostatically adsorb metal ions, enhancing the interception ability of metal ions, and the dense coating structure formed by dip coating and heat treatment can effectively intercept metal ions and improve the rejection rate. Moreover, the present invention controls the preparation conditions and the raw material dosage ratio to improve its comprehensive performance. The epoxy group of tris(1,2-epoxy)propyl ether undergoes a ring-opening reaction with amino or hydroxyl groups to form a covalent cross-linked network, enhancing the mechanical strength and chemical stability of the membrane structure and preventing swelling or degradation in an acidic environment. 1,3,6-Naphthalenetrisulfonyl chloride in the oil phase undergoes an interfacial polymerization reaction with the amino group (-NH2) of the pre-deposited layer to form a dense layer, which has the effect of reducing the adsorption of hydrophobic pollutants (such as oils) and avoiding membrane pore blockage. And when prepared in the order of the present invention, the dense hydrophobic layer and the underlying hydrophilic layer form an osmotic pressure gradient, accelerating the transfer of water molecules (high water flux), while restricting the diffusion of metal ions. And through heat treatment, the cross-linking reaction in the coating further proceeds, improving the mechanical strength and selectivity of the coating and the stability of the nanofiltration membrane.

[0039] Compared with the prior art, the present invention is based on tamarind gum, and through its amination and mercaptanization, and synergistically introducing modified halloysite, constructs a composite nanofiltration membrane with high water flux and high metal ion interception, which can be used for acidic wastewater, effectively improving its applicability and durability for acidic wastewater. Detailed implementation mode

[0040] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] The test materials, reagents, etc. used in the following embodiments can be obtained from commercial channels without special instructions.

[0042] For those not specifying specific technologies or conditions in the embodiments, they can all be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications.

[0043] It should be noted that in the present invention, "parts" refer to parts by mass; there are no special restrictions on the purchase manufacturers of all raw materials involved in the present invention. Exemplarily, including: in the following embodiments, the diameter of halloysite nanotubes is 50-300 nm, and the brand is Xianfeng Nano; the brand of tamarind gum is Libangda; the CAS number of acryloyl chloride is 814-68-6, the CAS number of ethyl diazoacetate is 623-73-4, the CAS number of azaserine is 115-02-6, the CAS number of glycerol tris(1,2-epoxy)propyl ether is 13236-02-7, and the CAS number of 1,3,6-naphthalenetrisulfonyl chloride is 67294-61-5; the above and other raw materials are all commercially available.

[0044] Preparation of amino-functionalized tamarind gum:

[0045] S1.1: Add 15 parts of tamarind gum to 150 parts of N-methyl-pyrrolidone, heat to 90 °C and stir for 2 hours, cool to room temperature, add 40 parts of triethylamine, stir for 1 hour under ice bath, dropwise add 20 parts of acryloyl chloride, continue to stir for 4 hours, wash and freeze-dry to obtain vinyl tamarind gum;

[0046] S1.2: Add 5 parts of vinyl tamarind gum to 100 parts of dimethyl sulfoxide, add 0.45 part of ethyl diazoacetate and 1 part of azaserine, stir at room temperature for 24 hours, wash and freeze-dry to obtain amino-functionalized tamarind gum.

[0047] Preparation of mercapto-functionalized tamarind gum:

[0048] S2.1: Add tamarind gum to a 0.45 mol / L nitric acid solution, and the mass ratio of tamarind gum to nitric acid solution is 1:50. Oscillate and activate at room temperature for 5 hours, wash and freeze-dry to obtain activated tamarind gum;

[0049] S2.2: Add the activated tamarind gum into an aqueous solution of sodium periodate at 5 wt%, with the mass ratio of the activated tamarind gum to sodium periodate being 1.5:1. Stir for 3 hours, add ethylene glycol for neutralization, centrifuge, and wash with water to obtain the pretreated tamarind gum.

[0050] S2.3: Add the pretreated tamarind gum, cysteine, carbodiimide hydrochloride, and N-hydroxysuccinimide into toluene in sequence. Under nitrogen protection, stir and react at 50 °C for 5 hours, wash, and freeze-dry to obtain the thiolated tamarind gum. The mass ratio of the pretreated tamarind gum to cysteine is 1:1. The masses of the tamarind gum, carbodiimide hydrochloride, N-hydroxysuccinimide, and toluene are 10:2.5:1:100.

[0051] Example 1

[0052] A preparation method of a nanofiltration membrane based on tamarind gum, comprising the following steps:

[0053] Step 1 Modify halloysite:

[0054] 1-1): Place halloysite nanotubes in a 0.25 mol / L sodium hydroxide solution, with the ratio of halloysite nanotubes to the sodium hydroxide solution being 1 g:25 mL. Conduct alkali activation treatment at room temperature for 30 minutes to obtain the pretreated halloysite.

[0055] 1-2): Add the pretreated halloysite, amino-silane coupling agent KH550, and mercapto-silane coupling agent KH580 with a mass ratio of 1:0.1:0.05 into a 90 wt% ethanol aqueous solution (prepare 50 mL of ethanol aqueous solution for 1 g of pretreated halloysite) and stir for 1 hour, then raise the temperature to 60 °C and stir for 2 hours, wash and dry to obtain the modified halloysite.

[0056] Step 2 Pretreat the base membrane:

[0057] Mix the modified halloysite, amidated tamarind gum, and deionized water according to a mass ratio of 5:20:500, and mix evenly to obtain the modified halloysite dispersion. Place the base membrane (PAN ultrafiltration membrane with a molecular weight cut-off of 50,000) in a 0.1 mol / L sodium hydroxide solution for pre-activation, with the pre-activation temperature being 40 °C and the time being 30 minutes. Uniformly coat the modified halloysite dispersion on the surface of the pre-activated base membrane; dry naturally to obtain the pretreated base membrane. Among them, the dosage of the modified halloysite dispersion is calculated according to 50 mg / m 2 Coat;

[0058] Step 3 Prepare the solution:

[0059] 3-1): Add aminated tamarind gum, mercapto-tamarind gum, and modified halloysite with a mass ratio of 0.15:0.1:0.05 to deionized water and stir evenly to obtain an aqueous solution with a solid content of 0.30 wt%;

[0060] 3-2): Add tris(1,2-epoxy)propyl ether to ethanol and stir evenly to obtain a glycerol ether solution with a concentration of 0.12 wt%;

[0061] 3-3): Add 1,3,6-naphthalenetrisulfonyl chloride to n-hexane and stir evenly to obtain an oil-phase solution with a concentration of 0.23 wt%;

[0062] Step 4 Prepare the composite nanofiltration membrane:

[0063] Immerse the pretreated substrate membrane in the aqueous solution for 30 minutes, air-dry at room temperature; transfer it to the glycerol ether solution and oscillate and immerse it at room temperature for 20 minutes, then heat-treat it at 70 °C for 20 minutes; transfer it to the oil-phase solution and oscillate and immerse it at room temperature for 30 minutes, then heat-treat it at 50 °C for 10 minutes; finally, wash it and store it in deionized water to obtain the composite nanofiltration membrane.

[0064] Example 2

[0065] A preparation method of a nanofiltration membrane based on tamarind gum, comprising the following steps:

[0066] Step 1 Modify halloysite:

[0067] 1-1) Place halloysite nanotubes in a 0.25 mol / L sodium hydroxide solution, with the ratio of halloysite nanotubes to sodium hydroxide solution being 1 g:25 mL, and perform alkali activation treatment at room temperature for 30 minutes to obtain pretreated halloysite;

[0068] 1-2) Add pretreated halloysite, amino-silane coupling agent KH550, and mercapto-silane coupling agent KH580 with a mass ratio of 1:0.1:0.05 to a 90 wt% ethanol aqueous solution ((50 mL ethanol aqueous solution is prepared according to 1 g pretreated halloysite)) and stir for 1 hour, heat up to 60 °C and stir for 2 hours, wash and dry to obtain modified halloysite;

[0069] Step 2 Pretreat the substrate membrane:

[0070] Mix modified halloysite, aminated tamarind gum, and deionized water according to a mass ratio of 5:20:500, and mix evenly to obtain a modified halloysite dispersion; place the substrate membrane (PAN ultrafiltration membrane with a molecular weight cut-off of 50,000) in a 0.1 mol / L sodium hydroxide solution for pre-activation, with the pre-activation temperature being 40 °C and the time being 30 minutes; evenly coat the modified halloysite dispersion on its surface; air-dry naturally to obtain the pretreated substrate membrane; the coating amount of the modified halloysite dispersion is 50 mg / m2 ;

[0071] Step 3: Prepare the solution:

[0072] 3-1) Add aminated tamarind gum, mercapto-tamarind gum, and modified halloysite with a mass ratio of 0.17:0.1:0.05 to deionized water and stir evenly to obtain an aqueous solution with a solid content of 0.30 wt%;

[0073] 3-2) Add tris(1,2-epoxy)propyl ether to ethanol and stir evenly to obtain a glycerol ether solution with a concentration of 0.15 wt%;

[0074] 3-3) Add 1,3,6-naphthalenetrisulfonyl chloride to n-hexane and stir evenly to obtain an oil-phase solution with a concentration of 0.25 wt%;

[0075] Step 4: Prepare the composite nanofiltration membrane:

[0076] Immerse the pretreated substrate membrane in the aqueous solution for 30 minutes, air-dry at room temperature; transfer it to the glycerol ether solution and oscillate and impregnate at room temperature for 20 minutes, heat-treat at 70 °C for 20 minutes; transfer it to the oil-phase solution and oscillate and impregnate at room temperature for 30 minutes; set the temperature at 50 °C and heat-treat for 10 minutes, wash, and store in deionized water to obtain the composite nanofiltration membrane.

[0077] Example 3

[0078] A preparation method of a nanofiltration membrane based on tamarind gum, comprising the following steps:

[0079] Step 1: Modify halloysite:

[0080] 1-1) Place halloysite nanotubes in a 0.25 mol / L sodium hydroxide solution, with the ratio of halloysite nanotubes to sodium hydroxide solution being 1 g:25 mL, and perform alkali activation treatment at room temperature for 30 minutes to obtain pretreated halloysite;

[0081] 1-2) Add the pretreated halloysite, amino-silane coupling agent KH550, and mercapto-silane coupling agent KH580 with a mass ratio of 1:0.1:0.05 to a 90 wt% ethanol aqueous solution (50 mL of ethanol aqueous solution is prepared for 1 g of pretreated halloysite) and stir for 1 hour, heat up to 60 °C and stir for 2 hours, wash and dry to obtain modified halloysite;

[0082] Step 2: Pretreat the substrate membrane:

[0083] Mix modified halloysite, aminated tamarind gum, and deionized water in a mass ratio of 5:20:500, and mix well to obtain a modified halloysite dispersion; place the base membrane (PAN ultrafiltration membrane with a molecular weight cut-off of 50,000) in a 0.1 mol / L sodium hydroxide solution for pre-activation, with a pre-activation temperature of 40 °C and a time of 30 minutes; evenly coat the modified halloysite dispersion on its surface; dry naturally to obtain a pretreated base membrane; the coating amount of the modified halloysite dispersion is 60 mg / m 2 ;

[0084] Step 3 Prepare the solution:

[0085] 3-1) Add aminated tamarind gum, mercapto-functionalized tamarind gum, and modified halloysite with a mass ratio of 0.14:0.08:0.03 to deionized water and stir evenly to obtain an aqueous solution with a solid content of 0.25 wt%;

[0086] 3-2) Add tris(1,2-epoxy)propyl ether to ethanol and stir evenly to obtain a glycerol ether solution with a concentration of 0.1 wt%;

[0087] 3-3) Add 1,3,6-naphthalenetrisulfonyl chloride to n-hexane and stir evenly to obtain an oil-phase solution with a concentration of 0.2 wt%;

[0088] Step 4 Prepare the composite nanofiltration membrane:

[0089] Immerse the pretreated base membrane in the aqueous solution for 30 minutes and air-dry at room temperature; transfer it to the glycerol ether solution and oscillate and impregnate at room temperature for 20 minutes, set the temperature at 70 °C and heat-treat for 20 minutes; transfer it to the oil-phase solution and oscillate and impregnate at room temperature for 30 minutes; set the temperature at 50 °C and heat-treat for 10 minutes, wash, and store in deionized water to obtain the composite nanofiltration membrane.

[0090] Comparative Example 1

[0091] A preparation method of a nanofiltration membrane based on tamarind gum, including the following steps: carried out according to Example 1, the difference is that aminated tamarind gum is used alone; specifically as follows:

[0092] Step 1 Modify halloysite:

[0093] 1-1) Place halloysite nanotubes in a 0.25 mol / L sodium hydroxide solution, with a ratio of halloysite nanotubes to sodium hydroxide solution of 1 g:25 mL, and perform alkali activation treatment at room temperature for 30 minutes to obtain pretreated halloysite;

[0094] 1-2) The pretreated halloysite, amino-silane coupling agent KH550, and mercapto-silane coupling agent KH580 with a mass ratio of 1:0.1:0.05 were successively added to an aqueous ethanol solution of 90 wt%, stirred for 1 hour, heated to 60 °C, stirred for 2 hours, washed and dried to obtain modified halloysite;

[0095] Step 2 Pretreatment of the base membrane:

[0096] The modified halloysite, amidated tamarind gum, and deionized water were mixed at a mass ratio of 5:20:500, and after mixing evenly, a modified halloysite dispersion was obtained; the base membrane was pre-activated in a 0.1 mol / L sodium hydroxide solution at a pre-activation temperature of 40 °C for 30 minutes; the modified halloysite dispersion was evenly coated on its surface; and it was naturally dried to obtain the pretreated base membrane; among the raw materials of the modified halloysite dispersion, 50 mg / m of the modified halloysite dispersion was coated 2 ;

[0097] Step 3 Preparation of solutions:

[0098] 3-1): Amidated tamarind gum and modified halloysite with a mass ratio of 0.25:0.05 were added to deionized water and stirred evenly to obtain an aqueous solution with a solid content of 0.30 wt%;

[0099] 3-2): Tris(1,2-epoxy)propyl ether of glycerol was added to ethanol and stirred evenly to obtain a glycerol ether solution with a concentration of 0.12 wt%;

[0100] 3-3) 1,3,6-Naphthalenetrisulfonyl chloride was added to n-hexane and stirred evenly to obtain an oil-phase solution with a concentration of 0.23 wt%;

[0101] Step 4 Preparation of the composite nanofiltration membrane:

[0102] The pretreated base membrane was dip-coated in the aqueous solution for 30 minutes and air-dried at room temperature; transferred to the glycerol ether solution and oscillated and impregnated at room temperature for 20 minutes, heat-treated at a set temperature of 70 °C for 20 minutes; transferred to the oil-phase solution and oscillated and impregnated at room temperature for 30 minutes; set the temperature at 50 °C and heat-treated for 10 minutes, washed, and stored in deionized water to obtain the composite nanofiltration membrane.

[0103] Comparative Example 2

[0104] A preparation method of a nanofiltration membrane based on tamarind gum, comprising the following steps: carried out according to Example 1, except that the ratio of amidated tamarind gum and mercaptoated tamarind gum was adjusted, and the rest was the same as in Example 1; specifically as follows:

[0105] Step 1 Modified halloysite:

[0106] 1-1): Place halloysite nanotubes in a 0.25 mol / L sodium hydroxide solution. The ratio of halloysite nanotubes to the sodium hydroxide solution is 1 g:25 mL. Perform alkali activation treatment at room temperature for 30 minutes to obtain pretreated halloysite;

[0107] 1-2): Add pretreated halloysite, amino-silane coupling agent KH550, and mercapto-silane coupling agent KH580 with a mass ratio of 1:0.1:0.05 to a 90 wt% ethanol aqueous solution in sequence and stir for 1 hour. Then, raise the temperature to 60 °C and stir for 2 hours. Wash and dry to obtain modified halloysite;

[0108] Step 2 Pretreat the base membrane:

[0109] Mix modified halloysite, aminated tamarind gum, and deionized water in a mass ratio of 5:20:500, and mix evenly to obtain a modified halloysite dispersion; Place the base membrane in a 0.1 mol / L sodium hydroxide solution for pre-activation; Uniformly coat the modified halloysite dispersion on its surface; Dry naturally to obtain a pretreated base membrane; The coating amount of the modified halloysite dispersion is 50 mg / m 2 ;

[0110] Step 3 Prepare the solution:

[0111] 3-1): Add aminated tamarind gum, mercapto-tamarind gum, and modified halloysite with a mass ratio of 0.1:0.15:0.05 to deionized water and stir evenly to obtain an aqueous solution with a solid content of 0.30 wt%;

[0112] 3-2) Add tris(1,2-epoxy)propyl ether to ethanol and stir evenly to obtain a glycerol ether solution with a concentration of 0.12 wt%;

[0113] 3-3) Add 1,3,6-naphthalenetrisulfonyl chloride to n-hexane and stir evenly to obtain an oil-phase solution with a concentration of 0.23 wt%;

[0114] Step 4 Prepare the composite nanofiltration membrane:

[0115] Immerse the pretreated base membrane in the aqueous solution for 30 minutes and air-dry at room temperature; Transfer it to the glycerol ether solution and oscillate and impregnate for 20 minutes. Set the temperature at 70 °C and heat-treat for 20 minutes; Transfer it to the oil-phase solution and oscillate and impregnate for 30 minutes; Set the temperature at 50 °C and heat-treat for 10 minutes. Wash and store it in deionized water to obtain the composite nanofiltration membrane.

[0116] Comparative Example 3

[0117] A preparation method of a nanofiltration membrane based on tamarind gum, including the following steps: Conduct according to Example 1, except that the base membrane is not pretreated with the modified halloysite dispersion, and the rest is the same as Example 1; Specifically as follows:

[0118] Step 1 Modify halloysite:

[0119] 1-1) Place halloysite nanotubes in a 0.25 mol / L sodium hydroxide solution. The ratio of halloysite nanotubes to the sodium hydroxide solution is 1 g:25 mL. Conduct alkali activation treatment at room temperature for 30 minutes to obtain pretreated halloysite;

[0120] 1-2) Add pretreated halloysite, amino-silane coupling agent KH550, and mercapto-silane coupling agent KH580 with a mass ratio of 1:0.1:0.05 to a 90 wt% ethanol aqueous solution in sequence, stir for 1 hour, heat up to 60 °C and stir for 2 hours, wash and dry to obtain modified halloysite;

[0121] Step 2 Pretreat the base membrane:

[0122] Place the base membrane in a 0.1 mol / L sodium hydroxide solution for pre-activation; wash and air-dry naturally to obtain a pretreated base membrane;

[0123] Step 3 Prepare the solution:

[0124] 3-1) Add amidated tamarind gum, mercapto-tamarind gum, and modified halloysite with a mass ratio of 0.15:0.1:0.05 to deionized water and stir evenly to obtain an aqueous solution with a solid content of 0.30 wt%;

[0125] 3-2) Add tris(1,2-epoxy)propyl ether to ethanol and stir evenly to obtain a glycerol ether solution with a concentration of 0.12 wt%;

[0126] 3-3) Add 1,3,6-naphthalenetrisulfonyl chloride to n-hexane and stir evenly to obtain an oil-phase solution with a concentration of 0.23 wt%;

[0127] Step 4 Prepare the composite nanofiltration membrane:

[0128] Immerse the pretreated base membrane in the aqueous solution for 30 minutes and air-dry at room temperature; transfer it to the glycerol ether solution and oscillate and impregnate for 20 minutes, set the temperature at 70 °C and conduct heat treatment for 20 minutes; transfer it to the oil-phase solution and oscillate and impregnate for 30 minutes; set the temperature at 50 °C and conduct heat treatment for 10 minutes, wash, and store it in deionized water to obtain the composite nanofiltration membrane.

[0129] Comparative Example 4

[0130] A preparation method of a nanofiltration membrane based on tamarind gum, comprising the following steps: Based on Example 1, the difference is that halloysite nanotubes are directly introduced, and the rest is the same as Example 1; specifically as follows:

[0131] Step 1: Prepare halloysite nanotubes for standby;

[0132] Step 2: Halloysite nanotubes, amidated tamarind gum, deionized water, and deionized water are mixed evenly according to a mass ratio of 5:20:500 to obtain a halloysite dispersion; the base membrane is pre-activated in a 0.1 mol / L sodium hydroxide solution; the halloysite dispersion is evenly coated on its surface; and it is naturally dried to obtain a pretreated base membrane; the coating amount of the halloysite dispersion is 50 mg / m 2 ;

[0133] Step 3: Prepare solutions:

[0134] 3-1): Amidated tamarind gum, mercapto-functionalized tamarind gum, and modified halloysite with a mass ratio of 0.15:0.1:0.05 are added to deionized water and stirred evenly to obtain an aqueous solution with a solid content of 0.30 wt%;

[0135] 3-2): Tris(1,2-epoxy)propyl ether is added to ethanol and stirred evenly to obtain a glycerol ether solution with a concentration of 0.12 wt%;

[0136] 3-3): 1,3,6-Naphthalenetrisulfonyl chloride is added to n-hexane and stirred evenly to obtain an oil-phase solution with a concentration of 0.23 wt%;

[0137] Step 4: Prepare a composite nanofiltration membrane:

[0138] The pretreated base membrane is dip-coated in the aqueous solution for 30 minutes and air-dried at room temperature; it is transferred to the glycerol ether solution and oscillated and impregnated for 20 minutes, heat-treated at a temperature of 70°C for 20 minutes; it is transferred to the oil-phase solution and oscillated and impregnated for 30 minutes; heat-treated at a temperature of 50°C for 10 minutes, washed, and stored in deionized water to obtain a composite nanofiltration membrane.

[0139] Performance test: The nanofiltration membranes prepared in Example 1 and Comparative Examples 1-4 are subjected to relevant performance tests; the water flux of the prepared composite nanofiltration membrane is tested; it is soaked in a 40 wt% sulfuric acid solution at room temperature for 5 days, taken out, washed with deionized water, and the rejection rate A of 2000 ppm magnesium sulfate is tested at 0.5 Mpa; washed with distilled water, soaked in a 40 wt% sulfuric acid solution at room temperature for 30 days again, and the rejection rate B is tested; the obtained data are shown in Table 1 below.

[0140] Table 1 Test results of the nanofiltration membranes in Example 1 and Comparative Examples 1-4

[0141]

[0142] Conclusion: Based on amino-functionalized tamarind gum, mercapto-functionalized tamarind gum, and modified halloysite, a composite nanofiltration membrane with high water flux and high metal ion retention for acidic wastewater was constructed. From the data of Example 1 and Comparative Examples 1-4, it can be seen that the introduction of specifically prepared amino-functionalized tamarind gum and mercapto-functionalized tamarind gum, the limitation of their ratio, the pretreatment of the base with a modified halloysite dispersion, and the modification of halloysite nanotubes play an important role in improving its application and durability in acidic wastewater.

[0143] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of a nanofiltration membrane based on tamarind gum, characterized in that, The preparation method comprises the following steps: 1) Treat halloysite with a silane coupling agent to obtain modified halloysite; 2) Pretreat the base membrane; 3) Add amidated tamarind gum, mercapto - modified tamarind gum and modified halloysite into water and stir evenly to obtain an aqueous solution; add tris(1,2 - epoxy)propyl ether of glycerol into ethanol and stir evenly to obtain a glycerol ether solution; add 1,3,6 - naphthalenetrisulfonyl chloride into n - hexane and stir evenly to obtain an oil - phase solution; 4) Treat the pretreated base membrane obtained in step 2) successively in the aqueous solution, glycerol ether solution and oil - phase solution, wash it, and store it in deionized water to obtain a tamarind - gum - based nanofiltration membrane.

2. The preparation method according to claim 1, characterized in that, Step 1) specifically includes: 1 - 1) Perform alkali activation treatment on halloysite nanotubes to obtain pretreated halloysite; 1 - 2) Compound - modify the pretreated halloysite with an amino - silane coupling agent and a mercapto - silane coupling agent to obtain modified halloysite.

3. The preparation method according to claim 2, wherein Step 1 - 2) is specifically as follows: Add pretreated halloysite, amino - silane coupling agent, and mercapto - silane coupling agent with a mass ratio of 1:(0.09 - 0.1):(0.05 - 0.06) successively into an ethanol aqueous solution with a concentration of 85 - 90wt%, stir for 1 - 2 hours, raise the temperature to 60 - 70°C and stir for 1 - 2 hours, wash and dry to obtain modified halloysite.

4. The preparation method according to claim 1, characterized in that, In step 2), the pretreated base membrane refers to: Place the base membrane in a sodium hydroxide solution for pre - activation; then evenly coat the surface of the pre - activated base membrane with the modified halloysite dispersion; dry naturally to obtain the pretreated base membrane.

5. The preparation method according to claim 4, characterized in that, The preparation method of the modified halloysite dispersion is: Mix modified halloysite, amidated tamarind gum and water evenly to obtain it; the mass ratio of modified halloysite, amidated tamarind gum and deionized water is 5:(20 - 25):

500.

6. The preparation method according to claim 1, characterized in that, In step 3), the mass ratio of amidated tamarind gum, mercapto - modified tamarind gum and modified halloysite is (0.14 - 0.17):(0.08 - 0.1):(0.03 - 0.05).

7. The preparation method according to claim 1 or 6, characterized in that, In step 3), the preparation method of the mercapto - modified tamarind gum comprises the following steps: S2.1: Add tamarind gum into a nitric acid solution, oscillate and activate it at room temperature, wash and freeze - dry to obtain activated tamarind gum; S2.2: Add the activated tamarind gum into an aqueous sodium periodate solution, stir and react, add ethylene glycol for neutralization, centrifuge, and wash with water; obtain pretreated tamarind gum; S2.3: Add the pretreated tamarind gum, cysteine, carbodiimide hydrochloride, and N - hydroxysuccinimide into toluene successively, under nitrogen protection, heat and stir for 4 - 6 hours, wash and freeze - dry to obtain mercapto - modified tamarind gum.

8. The preparation method according to claim 1 or 6, characterized in that, The preparation method of the amidated tamarind gum described in steps 2) and 3) is: S1.1: Add tamarind gum into N - methyl - pyrrolidone, raise the temperature to 90 - 95°C and stir to react, cool to room temperature, add triethylamine, stir to react under ice - bath conditions, drop - add acryloyl chloride, and continue to stir to react, wash and freeze - dry to obtain alkenyl tamarind gum; S1.2: Add the alkenyl tamarind gum into dimethyl sulfoxide, add ethyl diazoacetate and diazoserin, stir to react at room temperature, wash and freeze - dry to obtain amidated tamarind gum.

9. A tamarind gum-based nanofiltration membrane prepared by the preparation method according to any one of claims 1-8.

10. Use of the tamarind gum-based nanofiltration membrane according to claim 9, characterized in that, The tamarind gum-based nanofiltration membrane is used for treating acidic metal wastewater.

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