A renewable heavy metal wastewater filtration membrane and a method of making the same

Abstract

The application discloses a renewable heavy metal wastewater filtering membrane and a preparation method thereof. The preparation method of the renewable heavy metal wastewater filtering membrane comprises the following steps: S1, a poloxamer is grafted and polymerized on the surface of a base film to obtain a modified base film; and S2, the base film after the grafting and polymerization modification is soaked in a water solution of tannic acid, and the poloxamer on the surface of the base film is combined with the tannic acid to form a self-assembled tannic acid-poloxamer modification layer, so that the renewable heavy metal wastewater filtering membrane is obtained. The tannic acid-poloxamer modification layer of the filtering membrane prepared by the method is a composite layer formed by the hydrogen bond interaction between the phenolic hydroxyl of tannic acid and the ether bond of poloxamer, and the tannic acid-poloxamer modification layer is combined with the self-assembly characteristics of poloxamer and the heavy metal complexing characteristics and selectivity of tannic acid, so that the filtering membrane has the advantages of good heavy metal removal effect, strong renewability and simple process. When the filtering membrane is used for treating heavy metal wastewater, a large amount of complexing agent does not need to be added, and secondary filtration is not needed, so that the filtering membrane is more economical and environment-friendly.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental engineering water treatment, and more particularly relates to a renewable heavy metal wastewater filtration membrane and a preparation method thereof. BACKGROUND

[0002] Heavy metals enter water in the form of ions or hydrated ions, resulting in heavy metal wastewater, which can cause serious harm to organisms or human bodies if ingested. So far, the common techniques for treating heavy metal wastewater include precipitation, coagulation-flocculation, ion exchange, adsorption, and membrane separation. Membrane separation technology involves retaining heavy metal ions through a filtration membrane to achieve the enrichment of pollutants and obtain safely treated water. However, due to the extremely small size of heavy metal hydrated ions (0.1-1 nm), which is much smaller than the size of conventional filtration membranes (micron level), the use of membrane separation technology for heavy metal wastewater treatment generally requires a base membrane as a filtration membrane, and a modification layer is formed on the base membrane to strengthen its function of filtering heavy metal ions.

[0003] Polyphenolic compounds have complexation with various heavy metal ions, and thus are often used for heavy metal wastewater treatment. Tannic acid is the most abundant natural polyphenol, which is extracted from plants and is non-toxic. In terms of structure, tannic acid has a glucose core to form gallate esters, and each tannic acid molecule contains 25 phenolic hydroxyl groups, which can coordinate with heavy metal ions of different valence states to form stable complexes. In addition, tannic acid has obvious metal selectivity, and has obvious selectivity for divalent, trivalent, and other multivalent heavy metal ions, low coordination binding energy, and formation of stable metal complexes.

[0004] In the prior art, tannic acid is often combined with other substances such as chitosan and polyamine substances to react as a complexing agent to adsorb heavy metals during wastewater treatment. The complexing agent needs to be added directly into the wastewater to complex and remove heavy metals, which not only consumes a large amount of complexing agent, but also makes it difficult to achieve uniform combination when the complexing agent reacts with the wastewater, resulting in a low removal rate of heavy metal ions. Therefore, the prior art has poor renewability, causing resource waste, and needs to be combined with other heavy metal treatment methods, such as secondary filtration, to ensure the removal rate of heavy metal ions, which makes the process relatively complex. SUMMARY

[0005] The present application aims to solve the problems in the prior art, and provides a preparation method of a renewable heavy metal wastewater filtration membrane.

[0006] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0007] The present application provides a preparation method of a renewable heavy metal wastewater filtration membrane, comprising the following steps:

[0008] S1. grafting and polymerizing a layer of poloxamer on the surface of a base membrane to obtain a modified base membrane;

[0009] S2. soaking the base membrane after grafting and polymerization modification in a tannic acid aqueous solution, taking out after the poloxamer on the surface of the base membrane combines with the tannic acid to self-assemble, forming a tannic acid-poloxamer modification layer, and washing to remove the tannic acid on the surface of the base membrane that has not self-assembled, to obtain the renewable heavy metal wastewater filtration membrane;

[0010] In the step S2, the tannic acid-poloxamer modification layer is a composite layer formed by the multi-hydrogen bond interaction between the phenolic hydroxyl group of tannic acid and the ether bond of poloxamer.

[0011] The renewable heavy metal wastewater filtration membrane prepared by the method comprises a base membrane and a tannic acid-poloxamer modification layer. The tannic acid-poloxamer modification layer is formed by the self-assembly of poloxamer and tannic acid, the multi-hydrogen bond interaction between the phenolic hydroxyl group of tannic acid and the ether bond of poloxamer, and the combination with the base membrane, so that a composite reinforced layer is formed on the surface of the base membrane. The tannic acid-poloxamer modification layer has good interception and adsorption effect on multiple heavy metals due to the self-assembly characteristics of poloxamer and the heavy metal complexing characteristics and selectivity of tannic acid. In addition, the tannic acid-poloxamer modification layer can deprotonate the phenolic hydroxyl group of tannic acid under weak alkaline conditions, so that the hydrogen bond between poloxamer and tannic acid is destroyed, and the structure of the self-assembled poloxamer and tannic acid is also destroyed, thereby making the heavy metal ions adsorbed by tannic acid fall off and be released in the solution, realizing the elution and recovery of heavy metal ions. The structure of poloxamer on the base membrane remains unchanged, and tannic acid can combine with poloxamer on the base membrane again, realizing the regeneration of the renewable heavy metal wastewater filtration membrane.

[0012] Further, in the step S2, the poloxamer on the surface of the base membrane combines with tannic acid, and the mass ratio of poloxamer to tannic acid used is 1:9-9:1.

[0013] Further, the poloxamer and tannic acid in step S2 are combined on the surface of the substrate membrane, and the mass ratio of the poloxamer to the tannic acid is 4:6-6:4.

[0014] Preferably, the poloxamer and tannic acid in step S2 are combined on the surface of the substrate membrane, and the mass ratio of the poloxamer to the tannic acid is 5:5.

[0015] Further, the self-assembly form in step S2 is combined by immersing the poloxamer-modified substrate membrane in a tannic acid aqueous solution, so that the poloxamer and the tannic acid are combined with each other by intermolecular hydrogen bonding.

[0016] Further, the concentration of the tannic acid aqueous solution is 1-10 mol / L, and the immersion is performed under the conditions of a temperature of 0-60°C and a pH value of 1-7, and the immersion time is 1 minute-24 hours.

[0017] Further, the washing in step S2 is washing with pure water or deionized water, and the washing time is 1-10 minutes.

[0018] Further, the poloxamer is grafted and polymerized on the surface of the substrate membrane in step S1, and the method is that the poloxamer is first capped with acrylate, and then the capped poloxamer is grafted on the surface of the substrate membrane.

[0019] The acrylate is capped at both ends of the poloxamer, so as to introduce an alkenyl group, so that the poloxamer can participate in the subsequent polymerization reaction and be loaded on the substrate membrane.

[0020] Further, the structure of the tannic acid-poloxamer modification layer in step S2 is as follows:

[0021]

[0022] In structure (I), the sum of x and z is 2-130, and y is 15-67.

[0023] The specific type of the above structure poloxamer has specific values of x, y, and z, and x and z do not need to be equal. For example, in poloxamer 188, the sum of x and z is 75-85, and y is 25-30.

[0024] Further, the poloxamer is one of poloxamer 127, poloxamer 188, poloxamer 338, and poloxamer 407.

[0025] Poloxamer is a non-ionic triblock copolymer composed of a central hydrophobic polyoxypropylene chain (PPO) connected to two hydrophilic polyethylene oxide (PEO) chains on the side.

[0026] Further, the base membrane in step S1 is one of an ultrafiltration membrane with a molecular weight cut-off of 1-500 kDa, a microporous membrane with a pore size of 0.1-1.2 μm, and a filter paper with a pore size of 2.5 μm.

[0027] Further, the material of the base membrane in step S1 is one of polyether sulfone, polysulfone, mixed cellulose, regenerated cellulose, polyvinyl chloride, polypropylene, and polytetrafluoroethylene.

[0028] The application also discloses the renewable heavy metal wastewater filtering membrane prepared by the preparation method.

[0029] The application also discloses application of the renewable heavy metal wastewater filtering membrane in heavy metal wastewater filtering.

[0030] Further, the heavy metal ions in the heavy metal wastewater are one or any combination of Co 2+ , Cu 2+ , Ni 2+ , Pb 2+ , Fe 3+ , Cd 2+ , Zn 2+ and Mn 2+ .

[0031] Further, the total concentration of the heavy metal ions is 0.01 mmol / L-10 mol / L.

[0032] The application also discloses a regeneration method of the renewable heavy metal wastewater filtering membrane, which comprises the following steps: first, placing the used renewable heavy metal wastewater filtering membrane in an alkaline solution with a pH value of 8 or above to remove the tannin acid layer; then, soaking the membrane in a tannin acid aqueous solution, taking out the membrane after poloxamer on the surface of the base membrane and tannin acid are recombined and self-assembled, and cleaning to remove tannin acid on the surface of the base membrane which is not self-assembled, so as to obtain the regenerated heavy metal wastewater filtering membrane.

[0033] Further, the pH value is 8-11.

[0034] More preferably, the pH value of the alkaline solution is 9-10.

[0035] Further, the alkaline solution is one of NaOH, KOH, Na2CO3, NaHCO3 or K2CO3 dissolved in water.

[0036] Further, the time for placing the renewable heavy metal wastewater filtering membrane in the alkaline solution is 10 minutes or above.

[0037] Preferably, the time for placing the renewable heavy metal wastewater filtering membrane in the alkaline solution is 10 minutes.

[0038] Further, the tannic acid aqueous solution has a concentration of 1-10 mol / L, and the soaking condition is that the temperature is 0-60 DEG C, the pH value is 1-7, and the soaking time is 1 minute-24 hours.

[0039] Further, the cleaning is cleaning with pure water or deionized water, and the cleaning time is 1-10 minutes.

[0040] The application further discloses a method for eluting heavy metal ions from the renewable heavy metal wastewater filtering membrane after filtering the heavy metal ions, and comprises the following steps: placing the heavy metal ion filtering membrane in a weak alkaline solution with a pH value of 8 or above for elution.

[0041] The renewable heavy metal wastewater filtering membrane prepared by the method is deprotonated under weak alkaline conditions, the hydrogen bond between poloxamer and tannic acid is destroyed, the self-assembled structure of poloxamer and tannic acid is also destroyed, so that the heavy metal ions adsorbed by tannic acid are released in the solution, the elution and recovery of the heavy metal ions can be realized, and the structure of poloxamer on the base membrane is unchanged.

[0042] Further, the pH value is 8-11.

[0043] More preferably, the pH value of the weak alkaline solution is 9-10.

[0044] Further, the weak alkaline solution is formed by dissolving one of NaOH, KOH, Na2CO3, NaHCO3 or K2CO3 in water.

[0045] Further, the renewable heavy metal wastewater filtering membrane is placed in the weak alkaline solution with a pH value of 8 or above for elution, and the elution time is 10 minutes or above.

[0046] Preferably, the elution time is 10 minutes.

[0047] The application has the following beneficial effects:

[0048] (1) The preparation method of the renewable heavy metal wastewater filter membrane developed by the application can make the conventional filter membrane obtain the effect of filtering heavy metal ions, and is used for treating various heavy metal ion wastewater; the renewable heavy metal wastewater filter membrane comprises a base membrane and a tannic acid-poloxamer modification layer; the tannic acid-poloxamer modification layer forms a composite layer through the hydrogen bond interaction between the phenolic hydroxyl of tannic acid and the ether bond of poloxamer, and is combined with the base membrane, so that a composite reinforced layer is formed on the surface of the base membrane; the self-assembly characteristics of poloxamer and the heavy metal complexing characteristics and selectivity of tannic acid are combined, and the interception and adsorption of various heavy metals have good effects, and the heavy metal removal rate is high.

[0049] (2) In the filter membrane prepared by the preparation method of the renewable heavy metal wastewater filter membrane, the tannic acid-poloxamer modification layer makes the heavy metal ions adsorbed by tannic acid fall off and be released in the solution under weak alkaline conditions, realizes the elution and recovery of heavy metal ions, the structure of poloxamer on the base membrane is unchanged, tannic acid is combined with poloxamer on the base membrane again, and the renewable heavy metal wastewater filter membrane is regenerated and reused, so that the renewability is high and the service life of the membrane is prolonged.

[0050] (3) The preparation method of the renewable heavy metal wastewater filter membrane is simple, the base membrane is combined with the tannic acid-poloxamer modification layer, heavy metals can be directly filtered, a large amount of complexing agent does not need to be added in wastewater, the method is more environmentally friendly, and secondary filtration is not needed. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 It is a preparation schematic diagram of the renewable heavy metal wastewater filter membrane.

[0052] Figure 2 It is a schematic diagram of poloxamer terminated with acrylate in Example 1.

[0053] Figure 3 It is a scanning electron microscope image of the renewable heavy metal wastewater filter membrane in Example 1.

[0054] Figure 4 It is a Fourier infrared spectrum diagram of the renewable heavy metal wastewater filter membrane in Example 1.

[0055] Figure 4 In the table, a denotes tannic acid, b denotes a poloxamer, and c denotes a composite reinforced layer formed by the hydrogen bond interaction of tannic acid and poloxamer on the base membrane.

[0056] Figure 5 It is a heavy metal wastewater filtering process schematic diagram.

[0057] Figure 6 It is a regeneration and heavy metal ion elution process schematic diagram of the renewable heavy metal wastewater filter membrane.

[0058] Figure 1 、 Figure 2 and Figure 5 The rectangular block represents the base membrane, the wavy line represents the poloxamer, and the snowflake shape represents the tannic acid. DETAILED DESCRIPTION

[0059] The present application will be further described by the following description of the drawings and specific examples, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0060] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0061] The base membrane herein refers to a membrane or filter paper having a certain pore size and capable of attaching the composite reinforcement layer in the present application thereto.

[0062] Example 1 Preparation of a renewable heavy metal wastewater filtration membrane

[0063] A method for preparing a renewable heavy metal wastewater filtration membrane, as shown in Figure 1 , specifically comprising the following steps:

[0064] S1. Grafting and polymerizing a layer of poloxamer 188 on the surface of a polypropylene base membrane with a pore size of 0.22 μm to obtain a modified base membrane; the specific steps are as follows:

[0065] (1) The poloxamer 188 is capped with acrylate. In a round-bottom flask, 15 g of poloxamer is dissolved in 60 mL of benzene. Then 2.73 mL (19.6 mmol) of triethylamine and 1.58 mL (19.5 mmol) of acryloyl chloride are added to the flask, and the reaction mixture is stirred at 80°C for 3 hours. The reaction mixture is filtered, and the filtrate is dropped into excess hexane. The precipitate is dried under reduced pressure at 40°C for 24 hours, as shown in Figure 2 , to form a polymerizable acryl monomer at both ends, i.e. to obtain poloxamer capped with acrylate.

[0066] (2) Then graft and polymerize poloxamer on the polypropylene microporous filter membrane. Namely, the cleaned and weighed 0.22 μm polypropylene filter membrane is soaked in a 10 mM solution of p-benzoquinone in n-heptane for 1 hour; the polypropylene filter membrane is taken out, washed with acetone, dried, placed in a container, 5 mL of poloxamer diacrylate monomer solution is added, and after irradiation with ultraviolet light for half an hour, it is taken out, washed for 5 minutes and dried, to obtain a polypropylene filter membrane modified with poloxamer on the surface.

[0067] According to the needs, the above-mentioned base film can also be an ultrafiltration membrane with a molecular weight cut-off of 1-500 kDa, a microporous filter membrane with a pore size of 0.1-1.2 μm, or a filter paper with a pore size of 2.5 μm; the material used for the base film can be polyether sulfone, polysulfone, mixed cellulose, regenerated cellulose, polyvinyl chloride, or polypropylene or polytetrafluoroethylene; and according to the actual needs, the poloxamer can be poloxamer 127, poloxamer 338, or poloxamer 407. Due to the similar structures, all of them can achieve the purpose of forming a modified layer on the surface of the base film.

[0068] S2. The base film after graft polymerization modification is immersed in a 1 mol / L tannic acid aqueous solution. The volume of the tannic acid aqueous solution is adjusted so that the mass ratio of poloxamer to tannic acid used for forming the tannic acid-poloxamer modified layer satisfies 5:5. The immersion conditions are as follows: the temperature is 28°C, the pH value is 7, and the immersion time is 1 hour. After that, the base film is taken out. At this time, the poloxamer on the surface of the base film combines with the tannic acid to complete self-assembly, and a tannic acid-poloxamer modified layer is formed. The tannic acid-poloxamer modified layer is a complex layer formed by the interaction of the multiple hydrogen bonds between the phenolic hydroxyl groups of tannic acid and the ether bonds of poloxamer. Then, the base film surface is washed with pure water to remove the tannic acid that has not self-assembled, and a renewable heavy metal wastewater filtration membrane is obtained.

[0069] According to the actual needs, the modified base film is immersed in a 1-10 mol / L tannic acid aqueous solution under the conditions of a temperature of 0-60°C and a pH value of 1-7 for 1 minute to 24 hours. The poloxamer on the surface of the base film can combine with the tannic acid to complete self-assembly. After the self-assembly of the poloxamer and the tannic acid is completed, the excess tannic acid is removed using pure water, and the elution time is 1-10 minutes.

[0070] Example 2: Preparation of a renewable heavy metal wastewater filtration membrane

[0071] The renewable heavy metal wastewater filtration membrane is prepared according to the method of Example 1, except that the mass ratio of poloxamer to tannic acid used for the combination of poloxamer and tannic acid satisfies 1:9.

[0072] Example 3: Preparation of a renewable heavy metal wastewater filtration membrane

[0073] The renewable heavy metal wastewater filtration membrane is prepared according to the method of Example 1, except that the mass ratio of poloxamer to tannic acid used for the combination of poloxamer and tannic acid satisfies 9:1.

[0074] Experimental Example 1: Characterization of the self-assembly structure

[0075] 1. Experimental method

[0076] The renewable heavy metal wastewater filtering membrane prepared in Example 1 was characterized by scanning electron microscopy and Fourier infrared spectroscopy to verify the self-assembly structure thereof.

[0077] 2. Experimental results

[0078] The results are shown in Figure 3 and Figure 4 It can be seen from Figure 3 that a dense composite reinforcing layer is formed on the surface of the base membrane, and in combination with Figure 4 , it can be seen that the composite reinforcing layer is a tannic acid-poloxamer modified layer formed by self-assembly combination of poloxamer and tannic acid, and contains characteristic absorption peaks of both. From the above experimental results, it can be concluded that the structure of poloxamer and tannic acid after self-assembly combination is as follows:

[0079]

[0080] In the above structure, the structure with a benzene ring is tannic acid, and the polymer above the tannic acid which is hydrogen-bonded thereto is poloxamer 188 (commercially available), and the sum of x and z in the copolymer is 75-85, and y is 25-30.

[0081] Experimental Example 2 Removal of heavy metals by different treatment methods

[0082] 1. Experimental method

[0083] The renewable heavy metal wastewater filtering membrane of Example 1 above, Comparative Example 1 (prepared according to the preparation method of Example 1, except that after the first reinforcing layer is prepared, no tannic acid is soaked to obtain a filtering membrane without a tannic acid layer), was connected to a filtering device and added to the wastewater containing heavy metal ions in Table 1-5, and a heavy metal ion filtering test was performed; and the same kind and volume of wastewater was added to 20 mol / L excess tannic acid complex, and then the filtering membrane obtained in Comparative Example 1 was used for filtering, as Comparative Example 2. The time used for filtering was recorded, and the filtrate was collected; the concentration of heavy metal ions in the solution before and after filtering was measured by flame atomic absorption spectroscopy; and the membrane flux and removal rate were calculated.

[0084] Table 1 Wastewater sample number content and concentration

[0085]

[0086]

[0087] 2. Experimental results

[0088] The filtering process of the renewable heavy metal wastewater filtering membrane is shown in Figure 5From the figures, it can be seen that the tannin-poloxamer modification layer on the renewable heavy metal wastewater filtration membrane can intercept heavy metal ions, while water molecules can freely pass through the renewable heavy metal wastewater filtration membrane. The specific experimental results obtained by the above experimental method are shown in Table 2. It can be seen that the renewable heavy metal wastewater filtration membrane in Example 1 can effectively remove heavy metal ions in heavy metal wastewater, and the membrane flux is above 5000. For pure solutions and mixed solutions of various different heavy metal ions, the removal rate is more than 93%, and with the increase of wastewater treatment capacity, the membrane flux and removal rate do not fluctuate significantly. The efficiency and flux of Example 2 are low (single heavy metal removal rate is 83.5%, and average removal rate of multiple heavy metals is 82.4%), because too much tannin is unstable on the membrane, which affects the flux and also falls through the filtration membrane with the metal; the efficiency of Example 3 is low, because there is too little tannin, which affects the interception of heavy metals (single heavy metal removal rate is 65.6%, and average removal rate of multiple heavy metals is 59.9%). In addition, through comparison of different heavy metal ions, it can be seen that tannin has obvious complex selectivity for heavy metal ions, and Fe 3+ has the best removal effect, which is consistent with the stability of the phenolic hydroxyl complex. Finally, the addition of other metal ions (such as Na + ) without complexation does not affect the removal of heavy metal ions.

[0089] The efficiency of Comparative Example 1 is very low and almost has no heavy metal interception effect, because poloxamer itself has no heavy metal complexation or adsorption effect and can only rely on the physical interception of limited self-assembly structure; the efficiency of Comparative Example 2 is also not high (single heavy metal removal rate is 32.9%, and average removal rate of multiple heavy metals is 33.6%), although the heavy metal ions in the wastewater solution are pre-complexed with excess tannin to form complex molecules, when passing through the poloxamer layer, the tannin complexed with heavy metal ions directly passes through the filtration membrane due to the occupied sites, and a small part is successfully intercepted by poloxamer to form hydrogen bonds. Moreover, the introduction of excess tannin also brings trouble to subsequent removal. The heavy metal removal effect of Examples 1-3 is higher than that of Comparative Examples 1-2, which shows that the tannin-poloxamer modification layer formed by the self-assembly combination of poloxamer and tannin has a more significant removal effect than poloxamer alone or the composite layer formed by poloxamer and tannin without forming a specific structure for heavy metal removal.

[0090] Table 2 Removal of metal ions by different treatment methods

[0091]

[0092]

[0093] Note: The unit of membrane flux is L·m -2 ·h-1 • bar -1 ; " / " means no such metal ion.

[0094] Regeneration and recycling of the renewable heavy metal wastewater filtration membrane of experimental example 3

[0095] The regeneration and recycling of the renewable heavy metal wastewater filtration membrane of the present application is shown in Figure 6 After filtering heavy metals, the renewable heavy metal wastewater filtration membrane is placed in a weak alkaline solution, the tannin acid phenolic hydroxyl group is deprotonated, which leads to the destruction of the hydrogen bond between poloxamer and tannin acid, and the structure of the self-assembled combination of poloxamer and tannin acid is also destroyed, so that the heavy metal ions adsorbed by tannin acid fall off and are released in the solution to realize the elution and recovery of heavy metal ions, while the structure of poloxamer on the substrate membrane remains unchanged.

[0096] 1. Experimental method

[0097] The renewable heavy metal wastewater filtration membrane of example 1 is regenerated and recycled for 1-5 times and 100 times, and 100 mL of wastewater No. 1 and 5 in Table 1 is filtered respectively, and the membrane flux and removal rate are measured, and the regeneration method is: after use, the renewable heavy metal wastewater filtration membrane is soaked in 10 mL of NaOH aqueous solution with pH value of 10 at room temperature for 10 minutes, and the soaking time is more than 10 minutes, which can realize the separation of heavy metals and tannin acid from the filtration membrane combined with poloxamer, according to the needs, KOH, Na2CO3, NaHCO3 or K2CO3 aqueous solution can also be used to prepare the solution with the same pH value, in fact, the aqueous solution is a weak alkaline solution with pH value greater than 8, preferably, the weak alkaline solution with pH value of 8-11 can better realize the separation of heavy metals and tannin acid from the filtration membrane combined with poloxamer on the renewable heavy metal wastewater filtration membrane, and realize the elution of heavy metal ions, more preferably, the pH value of the weak alkaline solution is 9-10; after soaking, the filtration membrane is washed with deionized water for three times, and then soaked in 1 mol / L tannin acid solution according to the method of example 1, and stirred at room temperature for 1 hour. After taking out the filtration membrane, washing it with water for three times, the regenerated heavy metal wastewater filtration membrane is obtained. The alkaline solution after soaking is collected and concentrated by distillation to obtain enriched heavy metal ions. According to the actual needs, after washing the renewable heavy metal wastewater filtration membrane soaked in weak alkaline solution to remove the residual weak alkaline solution, it is soaked in tannin acid aqueous solution, the concentration of tannin acid aqueous solution is 1-10 mol / L, the soaking conditions of tannin acid are that the temperature is 0-60℃, the pH value is 1-7, the soaking time is 1 minute-24 hours, and the surface of the substrate membrane is washed to remove the tannin acid which is not self-assembled, and the washing time is 1-10 minutes, which can realize the regeneration of the renewable heavy metal wastewater filtration membrane.

[0098] 2. Experimental results

[0099] The experimental results are shown in Table 3. As shown in Table 3, the performance of the renewable heavy metal wastewater filtration membrane is substantially unchanged in terms of membrane flux and removal rate in cycles 1-5. In cycle 100, the membrane flux is 5300, which is 96% of the initial value, and the average removal rate is still above 90%. It can be seen that the membrane flux and removal rate of the renewable heavy metal wastewater filtration membrane are still at a high level in cycles 1-100 of a single heavy metal and multiple heavy metals. The renewable heavy metal wastewater filtration membrane has a high renewable ability.

[0100] Table 3 Membrane flux and average removal rate of metal ions in different cycles

[0101]

[0102] Note: The unit of membrane flux is L·m -2 ·h -1 ·bar -1 ; " / " indicates that there is no such metal ion.

[0103] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples. Any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method for preparing a renewable heavy metal wastewater filtration membrane, characterized by, The method comprises the following steps: S1. grafting and polymerizing a layer of poloxamer on the surface of a base membrane to obtain a modified base membrane; S2. soaking the base membrane modified by grafting and polymerization in a tannic acid aqueous solution, taking out after the poloxamer on the surface of the base membrane and the tannic acid are combined and self-assembled to form a tannic acid-poloxamer modification layer, and cleaning to remove the tannic acid that is not self-assembled on the surface of the base membrane to obtain the renewable heavy metal wastewater filtration membrane; In step S2, the tannic acid-poloxamer modification layer is a complex layer formed by the interaction of multiple hydrogen bonds between the phenolic hydroxyl groups of tannic acid and the ether bonds of poloxamer. In step S2, the poloxamer on the surface of the base membrane is combined with tannic acid, and the mass ratio of poloxamer to tannic acid used is 1:9-9:

1.

2. The production method according to claim 1, characterized by, In step S2, the self-assembled form is combined by soaking the base membrane modified with poloxamer in a tannic acid aqueous solution to make the poloxamer and tannic acid combined with each other by intermolecular hydrogen bond interaction.

3. The preparation method according to claim 1, characterized in that, In step S1, the method for grafting and polymerizing a layer of poloxamer on the surface of the base membrane is to first end-cap the poloxamer with acrylate and then graft the end-capped poloxamer on the surface of the base membrane.

4. The method of claim 1, wherein, The structure of the tannic acid-poloxamer modification layer in step S2 is: （I） In structure (I), the sum of x and z is 2-130, and y is 15-67.

5. The renewable heavy metal wastewater filtration membrane prepared by the method according to any one of claims 1-4.

6. The application of the renewable heavy metal wastewater filtration membrane according to claim 5 in heavy metal wastewater filtration.

7. The method for regenerating the renewable heavy metal wastewater filtration membrane according to claim 5, wherein, The method comprises the following steps: first, placing the used renewable heavy metal wastewater filtration membrane in a weak alkaline solution with a pH value of 8-11 to remove the tannic acid layer; then, soaking it in a tannic acid aqueous solution, taking it out after the poloxamer on the surface of the base membrane and the tannic acid are recombined and self-assembled, and cleaning to remove the tannic acid that is not self-assembled on the surface of the base membrane to obtain the regenerated heavy metal wastewater filtration membrane.

8. The regeneration method according to claim 7, characterized by, The weak alkaline solution is formed by dissolving one of NaOH, KOH, Na2CO3, NaHCO3 or K2CO3 in water.

9. The regeneration method according to claim 7, characterized by, The time for placing the renewable heavy metal wastewater filtration membrane in the weak alkaline solution with a pH value of 8-11 is more than 10 minutes.

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