Preparation method of tubular bifunctional membrane for rapidly detecting and removing mercury ions in wastewater

Abstract

The invention discloses a preparation method of a tubular bifunctional membrane for rapidly detecting and removing mercury ions in wastewater. The tubular bifunctional membrane is prepared by growing a mercaptan functionalized nitrogen-rich covalent organic polymer on the inner wall and the outer wall of a functionalized amino and aldehyde group Al2O3 ceramic tube in situ. The preparation method is simple, the process is easy to control, the inner side of the prepared tubular bifunctional membrane can be used for fluorescence detection of mercury ions, and the outer side of the prepared tubular bifunctional membrane can efficiently adsorb and remove the mercury ions; the tubular bifunctional membrane not only has high adsorption capacity and rapid adsorption kinetics, but also has high water flux, excellent mercury retention rate and fluorescence, so that the tubular bifunctional membrane becomes an efficient and practical method in wastewater treatment, and the risk of mercury ion leakage in the treatment process is remarkably reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional membrane preparation, and relates to a method for preparing a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater. Background Art

[0002] Mercury(II) (Hg 2+ ) is an environmental pollutant mainly present in surface water. Hg 2+ pollution poses a major threat to environmental health and can also cause irreversible damage to the human nervous, blood, immune and reproductive systems, attributed to its high toxicity and strong carcinogenic properties. However, reducing the mercury concentration in wastewater to meet strict wastewater discharge standards and drinking water standards (below 2 ppb) remains a major challenge. Therefore, implementing measures to detect, treat and recover mercury in the environment has important practical significance.

[0003] Among various technologies for treating mercury-containing wastewater, the adsorption separation method using porous adsorbents has become one of the most widely used and effective methods. However, this technology also has some disadvantages and limitations, such as the non-renewability of the adsorbent and the difficulty in separating it from water, etc. Adsorption membranes represent an innovative separation material that combines the advantages of membrane separation and adsorption. As a carrier for immobilizing adsorbents, adsorption membranes enable the capture of ions and the recovery of precious metals. This integration eliminates the need for an additional solid-liquid separation step, simplifies the recovery process, and improves the reusability of the adsorbent. Although traditional polymer membranes exhibit excellent heavy metal retention performance, the highly interconnected cross-linked network in polymer membranes results in low permeability, greatly limiting their wide application. To address this problem, developing mixed matrix membranes by mixing porous nanoparticles with polymers has proven to be an effective strategy. However, a high loading of nanoparticles may lead to poor dispersion and obvious aggregation, generating non-selective small voids and defects, thus affecting the performance of the membrane. In recent years, the method of in-situ growing nanoparticles has been applied to the preparation of membrane materials. This method customizes functional groups and pore structures according to specific separation systems, thereby controlling the growth direction of the membrane, preventing pore disorder, and promoting the diffusion of separated components.

[0004] Based on this, the present invention aims to provide a triazine-based thiol-functionalized nitrogen-rich covalent organic polymer material and in-situ grow it on the inner and outer walls of a ceramic tube to prepare a bilayer bifunctional membrane for detecting and removing Hg 2+ . Summary of the Invention

[0005] To solve the above technical problems, the present invention aims to provide a method for preparing a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater, which is prepared by in-situ growth of thiol-functionalized nitrogen-rich covalent organic polymers on the inner and outer walls of functionalized aldehyde group Al2O3 ceramic tubes. The preparation method of the present invention is simple, the process is easy to control, the inner side of the prepared tubular bifunctional membrane can be used for fluorescence detection of mercury ions, and the outer side can efficiently adsorb and remove mercury ions. The tubular bifunctional membrane not only has a high adsorption capacity and fast adsorption kinetics, but also its high water flux, excellent mercury retention rate and fluorescence make it an efficient and practical method in wastewater treatment, and significantly reduces the risk of mercury ion leakage during the treatment process.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater is carried out in the following steps in sequence:

[0008] S1. Preparation of functionalized amino and aldehyde group Al2O3 tubes

[0009] Soak a porous Al2O3 tube with a length of 5 cm and an inner diameter of 0.8 cm in boiling water at 100 °C for 1 - 2 h, then soak it in 1 M HCl solution for 5 - 6 h, rinse it with deionized water until neutral and dry it. Then, in an argon atmosphere, add 25 mL of 3-aminopropyltriethoxysilane solution at 110 °C and react for 1 - 2 h. Then, place it in 25 mL of 2,5-divinylterephthalaldehyde solution and react for 1 - 2 h. Wash it three times with ethanol and dry it to obtain functionalized amino and aldehyde group Al2O3 tubes.

[0010] S2. Preparation of tubular bifunctional TBN-S-SH membrane

[0011] Place the functionalized amino and aldehyde group Al2O3 tubes in a three-necked flask, and add 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, 2,5-divinylterephthalaldehyde and dimethyl sulfoxide to it. React at 180 °C for 48 - 72 h under a nitrogen atmosphere. After natural cooling, add ethanedithiol and azobisisobutyronitrile, and react at 80 °C for 48 - 72 h. Wash it three times with acetone and dry it at 60 °C for 12 h to obtain a tubular bifunctional TBN-S-SH membrane.

[0012] As a limitation of the preparation method of the present invention, in step S1, the preparation method of the 3-aminopropyltriethoxysilane solution is: dissolve 0.44 g of 3-aminopropyltriethoxysilane in 25 mL of anhydrous toluene and stir evenly.

[0013] As another limitation of the preparation method of the present invention, in step S1, the preparation method of the 2,5-divinyl terephthalaldehyde solution is: dissolving 30 mg of 2,5-divinyl terephthalaldehyde in 25 mL of dimethyl sulfoxide (AR, analytical pure), and stirring evenly.

[0014] As the third limitation of the preparation method of the present invention, in step S1, the drying temperature is 60 °C and the time is 12 h.

[0015] As the fourth limitation of the preparation method of the present invention, in step S2, the molar ratio of 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, 2,5-divinyl terephthalaldehyde and dimethyl sulfoxide is 2:3:9400.

[0016] In the present invention, the molar ratio among 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, 2,5-divinyl terephthalaldehyde and dimethyl sulfoxide is crucial. When the molar ratio is 2:3:9400, the amino group and the aldehyde group in the reactants react in a suitable proportion. After the reaction is relatively complete, the formed film is more complete, and a defect-free TBN-S-SH film is formed; when the molar ratio is less than 2:3:9400, 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine is insufficient, so that some aldehyde groups in 2,5-divinyl terephthalaldehyde cannot react with the amino group, and there will be many exposed aldehyde groups, resulting in unstable TBN-S-SH crystal form, and further making the formed film have poor effect; when the molar ratio is greater than 2:3:9400, 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine is in excess, and the excessive amino group occupies the reaction sites, resulting in low crystallinity of the formed TBN-S-SH, thereby reducing the orderliness of the structure, and further making the formed film have poor effect.

[0017] As the fifth limitation of the preparation method of the present invention, in step S2, the molar ratio of ethanedithiol and azobisisobutyronitrile is 137:1.

[0018] In the present invention, the molar ratio of ethanedithiol to azobisisobutyronitrile affects the synthesis of the membrane. When the molar ratio is 137:1, the ethanedithiol reacts completely, enabling the mercapto groups to effectively bind to the ceramic tube membrane and enhancing the adsorption effect on mercury ions. When the molar ratio is greater than 137:1, the concentration of azobisisobutyronitrile is insufficient, resulting in incomplete reaction of ethanedithiol. Only a part of the mercapto groups bind to the ceramic tube membrane. The mercapto functional groups exhibit significant affinity for mercury ions, and strong interactions are achieved through coordination bonds and chemical complexation. These functional groups form stable complexes with mercury ions and provide specific binding sites for selective absorption, improving the adsorption effect of TBN-S-SH on mercury. The small number of mercapto groups affects the adsorption effect of mercury ions and thus the synthesis effect of the TBN-S-SH membrane. When the molar ratio is less than 137:1, it leads to an excessive concentration of the radical initiator azobisisobutyronitrile. Although azobisisobutyronitrile does not participate in the reaction, it can cause a high concentration of free radicals, resulting in side reactions, such as oxidizing some mercapto groups to disulfide bonds and reducing the effective adsorption sites.

[0019] As the sixth limitation of the preparation method of the present invention, in step S2, the molar ratio of 2,5-divinyl terephthalaldehyde to ethanedithiol is 1:183.

[0020] In the present invention, the molar ratio of 2,5-divinyl terephthalaldehyde to ethanedithiol affects the effect of the finally prepared TBN-S-SH membrane. When the molar ratio is 1:183, after forming the TBN-V membrane, the double bonds can react with sufficient ethanedithiol, and then the mercapto groups bind to the membrane to form the TBN-S-SH membrane. When the molar ratio is greater than 1:183, the ethanedithiol is in excess, causing waste and poor economic efficiency. When the molar ratio is less than 1:183, the reaction effect is poor. The amount of ethanedithiol is too small, resulting in uneven binding of the mercapto functional groups to the membrane, thus affecting the adsorption effect of the TBN-S-SH membrane.

[0021] Since the surface of Al2O3 is usually relatively inert and the interfacial interaction with the TBN-S-SH material is weak, the TBN-S-SH material cannot grow stably and firmly on the ceramic tube. Therefore, in the present invention, the Al2O3 ceramic tube is modified with amino and aldehyde groups. 3-aminopropyltriethoxysilane has the function of surface modification, which promotes the formation of coordination bonds between the 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine ligand and the aminoaluminum substrate, significantly enhances the growth ability of TBN-S-SH on the ceramic tube, and improves the interaction between Al2O3 and 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, thereby improving the adhesion of the TBN-S-SH film, and thus improving the stability and service life of the film. In addition, the application of TBN-S-SH powder is limited by the difficulty of its separation and recovery. The fine TBN-S-SH powder is prone to agglomeration, forming larger particle clusters, which makes it difficult for them to be evenly dispersed in the liquid medium. After adsorbing mercury, it is necessary to wash to remove residual impurities and solvents. However, due to the agglomeration phenomenon of TBN-S-SH powder, it is difficult to completely remove impurities. Moreover, the TBN-S-SH powder has a small size, and there will inevitably be losses during the separation and recovery process, making it difficult to reuse. In addition, the powder is prone to agglomeration, resulting in a decrease in the effective specific surface area and a decline in the adsorption performance. Growing the TBN-S-SH material in-situ on the surface of the ceramic tube can enable it to form a continuous and evenly distributed film layer instead of independent particles, which makes the material structure more stable, not easy to fall off or agglomerate. Moreover, growing the TBN-S-SH material in-situ on the modified Al2O3 ceramic tube can be reused, improving the durability of the material.

[0022] The tubular bifunctional TBN-S-SH film of the present invention has strong fluorescence characteristics and high sensitivity to Hg 2+ ions. The coordination between the mercapto group of the outer TBN-S-SH film and mercury ions, the coordination complexation between the lone pair electrons on N and mercury ions, and the cation-π effect generated by the conjugated π electrons enable it to adsorb mercury ions; in the absence of adsorbed mercury ions, the TBN-S-SH film emits fluorescence at 365 nm, and with the adsorption of mercury ions, the fluorescence weakens. This characteristic allows real-time monitoring of the saturation level of mercury ion adsorption in the inner TBN-S-SH film and provides an indication of potential mercury ion leakage.

[0023] As an overall technical solution of the present invention, each step is closely related and mutually influential, and they jointly determine the morphological characteristics and performance of the product.

[0024] The above technical solution has the following advantages or beneficial effects:

[0025] 1. The tubular bifunctional TBN-S-SH membrane prepared by the present invention can detect mercury ions in wastewater on the inner side, adsorb and remove mercury ions on the outer side, and the adsorption capacity for mercury ions reaches 99.3%.

[0026] 2. The tubular bifunctional TBN-S-SH membrane prepared by the present invention can recover a relatively high membrane flux after being washed with water and can be recycled.

[0027] 3. The preparation method of the present invention is simple, the process is easy to control, and it is suitable for large-scale industrial production.

[0028] The present invention is applicable to the preparation of the tubular bifunctional TBN-S-SH membrane.

[0029] The technical solutions of the present invention will be further described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments. Description of the Drawings

[0030] Figure 1 XRD patterns of TBN-S-SH prepared in Comparative Example 1 of the present invention and TBN-V prepared in step (1) of Comparative Example 1;

[0031] Figure 2 SEM images of TBN-S-SH prepared in Comparative Example 1 of the present invention, where: (a) is the SEM image of TBN-S-SH at 9K magnification, (b) is the SEM image of TBN-S-SH at 3.5K magnification, (c) is the SEM image of TBN-S-SH at 1K magnification, and (d) is the SEM image of TBN-S-SH at 500 magnification;

[0032] Figure 3 SEM image of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention at 5K magnification;

[0033] Figure 4 BET characterization diagrams of TBN-S-SH prepared in Comparative Example 1 of the present invention and TBN-V prepared in step (1) of Comparative Example 1;

[0034] Figure 5 Adsorption isotherms of TBN-S-SH prepared in Comparative Example 1 of the present invention and TBN-V prepared in step (1) of Comparative Example 1 for Hg 2+ ;

[0035] Figure 6Fluorescence effect diagrams of TBN-S-SH prepared in Comparative Example 1 of the present invention and TBN-V prepared in step (1) of Comparative Example 1, where: (a) is the luminescence spectrum diagram of TBN-V and TBN-S-SH in water under 365 nm ultraviolet light excitation, and (b) is TBN-S-SH in water containing different concentrations of Hg 2+ Relative fluorescence intensity diagram in water;

[0036] Figure 7 In-situ growth diagram of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention;

[0037] Figure 8 Comparison diagram of fluorescence effects of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention and the blank tube under ultraviolet light irradiation in different solutions, where: (a) is the comparison diagram of fluorescence effects under ultraviolet light irradiation in dichloromethane solution, and (b) is the comparison diagram of fluorescence effects under ultraviolet light irradiation in mercury nitrate solution;

[0038] Figure 9 Interception performance diagram of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention for different metals;

[0039] Figure 10 Anti-pollution performance diagram of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention. Detailed implementation manners

[0040] The following embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Therefore, the detailed descriptions in the embodiments of the present invention provided below are not intended to limit the scope of the claimed invention, but merely represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention.

[0041] In the present invention, unless otherwise specified, all devices and raw materials can be purchased from the market or are commonly used in this industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0042] Example 1

[0043] This example prepares a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater, and its preparation process and steps are as follows:

[0044] S1. Preparation of functionalized amino and aldehyde group Al2O3 tubes

[0045] Soak a porous Al2O3 tube with a length of 5 cm and a diameter of 0.8 cm in boiling water at 100 °C for 1 h, then soak it in 1 M HCl solution for 5 h, rinse it with deionized water until neutral, and dry it at 60 °C for 12 h. Then, place it in an argon atmosphere and react it with 25 mL of 3-aminopropyltriethoxysilane solution (prepared by dissolving 0.44 g of 3-aminopropyltriethoxysilane in 25 mL of anhydrous toluene) at 110 °C for 1 h. Then, place it in 25 mL of 2,5-divinylterephthalaldehyde solution (prepared by dissolving 30 mg of 2,5-divinylterephthalaldehyde in 25 mL of dimethyl sulfoxide) and react for 1 h. Wash it three times with ethanol and dry it at 60 °C for 12 h to obtain a functionalized amino- and aldehyde-group-containing Al2O3 tube;

[0046] S2. Preparation of tubular bifunctional TBN-S-SH membrane

[0047] Place the functionalized amino- and aldehyde-group-containing Al2O3 tube in a three-necked flask, add 0.15 mmol of 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, 0.225 mmol of 2,5-divinylterephthalaldehyde, and 705 mmol of dimethyl sulfoxide. React at 180 °C for 48 h under a nitrogen atmosphere. After natural cooling, add 41 mmol of ethanedithiol and 0.3 mmol of azobisisobutyronitrile, and react at 80 °C for 48 h. Then wash it three times with acetone and dry it at 60 °C for 12 h to obtain a tubular bifunctional TBN-S-SH membrane.

[0048] Example 2

[0049] In this example, a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater is prepared. The preparation process and steps are as follows:

[0050] S1. Preparation of functionalized amino- and aldehyde-group-containing Al2O3 tube

[0051] Soak a porous Al2O3 tube with a length of 5 cm and an inner diameter of 0.8 cm in boiling water at 100 °C for 1.5 h, then soak it in 1 M HCl solution for 5.5 h, rinse it with deionized water until neutral, and dry it at 60 °C for 12 h. Then, place it in an argon atmosphere and react it with 25 mL of 3-aminopropyltriethoxysilane solution (prepared by dissolving 0.44 g of 3-aminopropyltriethoxysilane in 25 mL of anhydrous toluene) at 110 °C for 1.5 h. Then, place it in 25 mL of 2,5-divinylterephthalaldehyde solution (prepared by dissolving 30 mg of 2,5-divinylterephthalaldehyde in 25 mL of dimethyl sulfoxide) and react for 1.5 h. Wash it three times with ethanol and dry it at 60 °C for 12 h to obtain a functionalized amino- and aldehyde-group-containing Al2O3 tube;

[0052] S2. Preparation of Tubular Bifunctional TBN-S-SH Membrane

[0053] Place the functionalized amino- and aldehyde-group-containing Al2O3 tube in a three-necked flask, and add 0.15 mmol of 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, 0.225 mmol of 2,5-divinylterephthalaldehyde, and 705 mmol of dimethyl sulfoxide thereto. React at 180 °C for 60 h under a nitrogen atmosphere. After natural cooling, add 41 mmol of ethanedithiol and 0.3 mmol of azobisisobutyronitrile, and react at 80 °C for 60 h. Then wash three times with acetone and dry at 60 °C for 12 h to obtain the tubular bifunctional TBN-S-SH membrane.

[0054] Example 3

[0055] In this example, a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater is prepared, and the preparation process and steps are as follows:

[0056] S1. Preparation of Functionalized Amino- and Aldehyde-Group-Containing Al2O3 Tube

[0057] Immerse a porous Al2O3 tube with a length of 5 cm and an inner diameter of 0.8 cm in boiling water at 100 °C for 2 h, then immerse it in a 1 M HCl solution for 6 h, rinse with deionized water until neutral, and dry at 60 °C for 12 h. Then, in an argon atmosphere, add 25 mL of 3-aminopropyltriethoxysilane solution (prepared by dissolving 0.44 g of 3-aminopropyltriethoxysilane in 25 mL of anhydrous toluene) at 110 °C and react for 2 h. Then place it in 25 mL of 2,5-divinylterephthalaldehyde solution (prepared by dissolving 30 mg of 2,5-divinylterephthalaldehyde in 25 mL of dimethyl sulfoxide) and react for 2 h. Wash three times with ethanol and dry at 60 °C for 12 h to obtain the functionalized amino- and aldehyde-group-containing Al2O3 tube;

[0058] S2. Preparation of Tubular Bifunctional TBN-S-SH Membrane

[0059] Place the functionalized amino and aldehyde group Al2O3 tubes in a three-necked flask, and add 0.15 mmol of 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, 0.225 mmol of 2,5-divinyl terephthalaldehyde and 705 mmol of dimethyl sulfoxide thereto. Under a nitrogen atmosphere, react at 180 °C for 72 h. After natural cooling, add 41 mmol of ethanedithiol and 0.3 mmol of azobisisobutyronitrile, and react at 80 °C for 72 h. Wash three times with acetone and dry at 60 °C for 12 h to obtain a tubular bifunctional TBN-S-SH membrane.

[0060] Comparative example

[0061] In order to explore the influence of different parameters or different raw materials in the preparation process of the present invention on the performance of the product of the present invention, the following comparative experiments were specifically carried out. The following comparative examples respectively prepared different functional membranes, specifically as follows:

[0062] Comparative example 1

[0063] This comparative example prepares a bifunctional covalent organic polymer material. The preparation process is similar to that of Example 1, except that the material does not grow on the Al2O3 ceramic tube. The specific preparation process and steps are as follows:

[0064] (1) Mix 0.15 mmol of 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine and 0.225 mmol of 2,5-divinyl terephthalaldehyde with 705 mmol of dimethyl sulfoxide evenly, and place it on an ultrasonic oscillator for ultrasonic oscillation for 20 min. Subsequently, place the solution in a nitrogen atmosphere, heat it under magnetic stirring to reflux to 180 °C, react for 48 h, naturally cool to room temperature, filter, and then carry out continuous Soxhlet extraction with 160 mL of methanol, 160 mL of tetrahydrofuran and 160 mL of dichloromethane respectively. Subsequently, dry it under vacuum at 80 °C overnight to obtain TBN-V;

[0065] (2) Place TBN-V and 0.3 mmol of azobisisobutyronitrile in a three-necked flask, add 41 mmol of ethanedithiol under an argon atmosphere, reflux at 80 °C for 48 h, filter, wash three times with acetone, and then dry under vacuum at 60 °C overnight to obtain TBN-S-SH.

[0066] Comparative example 2

[0067] This comparative example prepares a tubular bifunctional membrane. The preparation process is similar to that of Example 1, except that in step S1, 3-aminopropyltriethoxysilane solution is not added.

[0068] Comparative Example 3

[0069] In this comparative example, a tubular bifunctional membrane was prepared. The preparation process was similar to that of Example 1, except that in step S1, the 2,5-divinylterephthalaldehyde solution was not added.

[0070] Comparative Example 4

[0071] In this comparative example, a tubular bifunctional membrane was prepared. The preparation process was similar to that of Example 1, except that in step S2, 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine was not used, but the following substances were used:

[0072] Group A: 6-(4'-(bis(4'-(4,6-diamino-1,3,5-triazin-2-yl)biphenyl-4-yl)amino)biphenyl-4-yl)-1,3,5-triazine-2,4-diamine.

[0073] Group B: 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)[1,1':3',1''-terphenyl]-4,4'-diyl)-1,3,5-triazine-2,4-diamine.

[0074] Group C: 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl))phenyl)[1,1':3',1'-triphenyl]-4,4'''-diyl)-1,3,5-triazine-2,4-diamine.

[0075] Comparative Example 5

[0076] In this comparative example, a tubular bifunctional membrane was prepared. The preparation process was similar to that of Example 1, except that in step S2, ethanedithiol and azobisisobutyronitrile were not added.

[0077] Comparative Example 6

[0078] In this comparative example, a tubular bifunctional membrane was prepared. The preparation process was similar to that of Example 1, except that in step S2, 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine was not added.

[0079] Comparative Example 7

[0080] In this comparative example, a tubular bifunctional membrane was prepared. The preparation process was similar to that of Example 1, except that in step S2, 2,5-divinylterephthalaldehyde was not added.

[0081] Comparative Example 8

[0082] In this comparative example, a tubular bifunctional membrane is prepared. The preparation process is similar to that of Example 1, except that step S1 is not performed, that is, the Al2O3 ceramic tube is not subjected to amino and aldehyde functionalization treatment.

[0083] Performance Testing

[0084] The materials prepared in Examples 1-3 and Comparative Examples 1-8 were subjected to relevant performance tests, and the specific test results are as follows:

[0085] like Figure 1 , which is the XRD diagram of TBN-S-SH prepared in Comparative Example 1 of the present invention and TBN-V prepared in step (1) of Comparative Example 1. It can be seen from the figure that both TBN-S-SH and TBN-V have relatively broad XRD spectra, indicating that the crystallinity of the two materials is relatively low and suitable for adsorbing mercury ions.

[0086] like Figure 2 , which are SEM images of TBN-S-SH prepared in Comparative Example 1 of the present invention, wherein: (a) is a SEM image of TBN-S-SH at 9K times, (b) is a SEM image of TBN-S-SH at 3.5K times, (c) is a SEM image of TBN-S-SH at 1K times, and (d) is a SEM image of TBN-S-SH at 500 times. It can be seen from the figures that TBN-S-SH is a block particle with a diameter of about 5 μm.

[0087] like Figure 3 , which is a SEM image of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention at 5K times. It can be seen from the figure that the TBN-S-SH powder grows well on the ceramic tube to form a membrane.

[0088] like Figure 4 , which is the BET characterization diagram of TBN-S-SH prepared in Comparative Example 1 of the present invention and TBN-V prepared in step (1) of Comparative Example 1. Nitrogen adsorption measurement shows that both TBN-V and TBN-S-SH maintain relatively high specific surface areas, which are 817m 2 / g and 726m 2 / g, indicating that the accessibility of the pores is retained after modification. The pore size distribution was analyzed by DFT method, and the results showed that the pore width of TBN-S-SH was narrower than that of TBN-V, indicating that TBN-S-SH had a higher pore utilization rate.

[0089] like Figure 5 , is the TBN-S-SH prepared in Comparative Example 1 of the present invention and the TBN-V prepared in step (1) of Comparative Example 1 to Hg 2+ The adsorption isotherm of TBN-V for Hg2+ The adsorption capacity was 689 mg / g. After grafting mercapto groups, the adsorption capacity of TBN-S-SH for Hg 2+ reached 1107 mg / g. This is because the addition of mercapto groups showed significant affinity for mercury ions, and strong interactions were achieved through coordination bonds and chemical complexation, thus enhancing the ability of the material to adsorb mercury ions.

[0090] Such as Figure 6 , which are the fluorescence effect diagrams of TBN-S-SH prepared in Comparative Example 1 of the present invention and TBN-V prepared in step (1) of Comparative Example 1. Among them: (a) is the luminescence spectrogram of TBN-V and TBN-S-SH in water under 365 nm ultraviolet light excitation, and (b) is the relative fluorescence intensity diagram of TBN-S-SH in water containing different concentrations of Hg 2+ . It can be seen from Figure (a) that the fluorescence of TBN-S-SH is three times that of TBN-V; it can be seen from Figure (b) that TNB-S-SH has an obvious fluorescence quenching effect. As the concentration of Hg 2+ increases, the fluorescence intensity of TBN-S-SH gradually decreases, thus affirming the occurrence of fluorescence quenching.

[0091] Such as Figure 7 , which is the in-situ growth diagram of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention. It can be seen from the figure that the functionalization treatment for amino and aldehyde group modification can enhance the interaction between Al2O3 and 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, improve the adhesion of the TBN-S-SH membrane, and thus improve the stability and service life of the membrane. In addition, the application of TBN-S-SH powder is limited by the difficulty of its separation and recovery, and it is difficult to reuse. Moreover, the powder is prone to agglomeration, resulting in a decrease in the effective specific surface area and a decline in adsorption performance. In-situ growing the TBN-S-SH material on the surface of the ceramic tube can enable it to form a continuous and evenly distributed membrane layer instead of independent particles, which makes the material structure more stable, not easy to fall off or agglomerate, and thus better adsorb mercury ions.

[0092] Such as Figure 8, which is the fluorescence quenching diagram of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention. Among them: (a) is the comparison diagram of the fluorescence effects of the TBN-S-SH tube and the blank tube under ultraviolet light irradiation in dichloromethane solution, and (b) is the comparison diagram of the fluorescence effects of the TBN-S-SH tube and the blank tube under ultraviolet light irradiation in mercury nitrate solution. It can be seen from the figure that the TBN-S-SH tube will produce a fluorescence phenomenon under ultraviolet light irradiation in dichloromethane solution, while a fluorescence quenching phenomenon will occur in mercury nitrate solution. Thus, it can be shown that the TBN-S-SH membrane has a good fluorescence detection effect on Hg 2+ has a good fluorescence detection effect.

[0093] Such as Figure 9 , which is the rejection performance diagram of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention for different metals. It can be seen from the figure that the tubular bifunctional TBN-S-SH membrane has outstanding adsorption capacities for mercury, silver, and copper ions, reaching 99.3%, 89%, and 80% respectively, while the adsorption capacities for iron, magnesium, and sodium are relatively weak. This is because the sulfur and nitrogen chelating groups in the TBN-S-SH structure preferentially bind to soft acid metal ions to form stable covalent bonds, while the interaction with metal ions existing in hard acids is relatively small. Therefore, the adsorption capacities for iron, magnesium, and sodium are relatively weak.

[0094] Such as Figure 10 , which is the anti-fouling performance diagram of the tubular bifunctional TBN-S-SH membrane prepared in Example 1 of the present invention. It can be seen from the figure the changes in the fouling and membrane flux of the TBN-S-SH membrane by pollutants bovine serum albumin (BSA) and humic acid (HA) during three filtration cycles. Both BSA and HA cause a decrease in membrane flux within 10 minutes of feeding. As the filtration continues, the pollutants gradually accumulate on the membrane surface and within its layered structure, resulting in a sharp decrease in membrane flux and finally tending to be stable. However, after a 15-minute water rinse of the membrane, the flux is significantly restored. This shows that the tubular bifunctional TBN-S-SH membrane has extremely strong anti-fouling properties and can be recycled.

[0095] In addition, Hg 2+ solution filtration and retention tests were carried out on the materials prepared in Examples 1-3 and Comparative Examples 2-8. The specific test results are shown in the following table:

[0096]

[0097] Since the TBN-S-SH prepared in Comparative Example 1 is in powder form, it is impossible to carry out Hg 2+ solution filtration and retention tests on it. In addition, in Comparative Example 4 of the present invention, tubular bifunctional TBN-S-SH membranes were prepared using different reactants. From the above table of Hg 2+It can be seen from the solution filtration retention test that the adsorption capacity of the tubular bifunctional TBN-S-SH membrane prepared from the reactants selected in the comparative example 4A-C groups for mercury ions is inferior to that of the reactants used in the technical solution of the present invention. The reason is as follows: 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine can effectively promote charge separation due to its excellent conjugation characteristics and electron-rich group structure in its chemical composition. The conjugated structure provides a channel for electron transfer and more active sites, while the lone pair electrons of the electron-rich group can coordinate with mercury ions. The two work together to significantly improve the adsorption efficiency of TBN-S-SH for mercury ions; while 6-(4'-(bis(4'-(4,6-diamino-1,3,5-triazin-2-yl)biphenyl-4-yl)amino)biphenyl-4-alkyl)-1,3,5-triazine-2,4-diamine (comparative example 4A group) forms a larger conjugated ring compared to 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, and can allocate fewer mercapto groups. The fewer mercapto groups result in a decrease in the efficiency of adsorbing mercury ions; in 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)[1,1':3',1”-terphenyl]-4,4'-diyl]1,3,5-triazine-2,4-diamine (comparative example 4B group) and 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl))phenyl)[1,1':3',1'-triphenyl]-4,4”'-diyl]-1,3,5-triazine-2,4-diamine (comparative example 4C group), after replacing N with a benzene ring or 1,3,5-triphenylbenzene, the nitrogen content decreases, the total content of mercapto groups decreases, and the coordination ability with mercury ions is weak, resulting in a low efficiency of adsorbing mercury ions.

[0098] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A preparation method of a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater, characterized in that, Proceed in the following steps in sequence: S1. Preparation of functionalized amino- and aldehyde-group-containing Al2O3 tubes Immerse a porous Al2O3 tube with a length of 5 cm and an inner diameter of 0.8 cm in boiling water at 100 °C for 1 - 2 h, then immerse it in 1 M HCl solution for 5 - 6 h. After rinsing with deionized water until neutral and drying, in an argon atmosphere, add 25 mL of 3-aminopropyltriethoxysilane solution at 110 °C and react for 1 - 2 h. Then place it in 25 mL of 2,5-divinylterephthalaldehyde solution and react for 1 - 2 h. After washing three times with ethanol and drying, functionalized amino- and aldehyde-group-containing Al2O3 tubes are obtained; S2. Preparation of tubular bifunctional TBN-S-SH membranes Place the functionalized amino- and aldehyde-group-containing Al2O3 tubes in a three-necked flask, and add 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine, 2,5-divinylterephthalaldehyde, and dimethyl sulfoxide. Under a nitrogen atmosphere, react at 180 °C for 48 - 72 h. After natural cooling, add ethanedithiol and azobisisobutyronitrile, and react at 80 °C for 48 - 72 h. Wash three times with acetone and dry at 60 °C for 12 h to obtain tubular bifunctional TBN-S-SH membranes.

2. The preparation method of a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater according to claim 1, characterized in that In step S1, the preparation method of the 3-aminopropyltriethoxysilane solution is: dissolve 0.44 g of 3-aminopropyltriethoxysilane in 25 mL of anhydrous toluene and stir evenly.

3. The preparation method of a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater according to claim 1, characterized in that, In step S1, the preparation method of the 2,5-divinylterephthalaldehyde solution is: dissolve 30 mg of 2,5-divinylterephthalaldehyde in 25 mL of dimethyl sulfoxide and stir evenly.

4. The preparation method of a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater according to claim 1, characterized in that, In step S1, the drying temperature is 60 °C and the time is 12 h.

5. The preparation method of a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater according to claim 1, characterized in that, In step S2, the molar ratio of 6-(4-(bis(4-(4,6-diamino-1,3,5-triazin-2-yl)phenyl)amino)phenyl)-1,3,5-triazine-2,4-diamine to 2,5-divinylterephthalaldehyde and dimethyl sulfoxide is 2:3:9400.

6. The preparation method of a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater according to claim 1, characterized in that, In step S2, the molar ratio of ethanedithiol to azobisisobutyronitrile is 137:

1.

7. The preparation method of a tubular bifunctional membrane for rapid detection and removal of mercury ions in wastewater according to claim 1, characterized in that, In step S2, the molar ratio of 2,5-divinylterephthalaldehyde to ethanedithiol is 1:183.

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