SA / EGCG@Ti / SA / PVDF sandwich membrane, its preparation method and application

Abstract

The present invention discloses a SA / EGCG@Ti / SA / PVDF sandwich membrane, its preparation method and application. The preparation method includes the following steps: mixing an epigallocatechin gallate solution and a titanium salt solution and reacting to obtain EGCG@Ti NPs; immersing a SA / PVDF substrate membrane in the mixed solution of EGCG@Ti NPs to obtain an EGCG@Ti / SA / PVDF membrane; and then coating a sodium alginate solution on the surface of the EGCG@Ti / SA / PVDF membrane to obtain a SA / EGCG@Ti / SA / PVDF sandwich membrane. The SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention can not only achieve the integrated removal of Cr(VI) and Cr(III) at low and high concentrations, but also achieve the efficient removal of organic dyes, and has high practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal and dye wastewater treatment, and particularly relates to a SA / EGCG@Ti / SA / PVDF sandwich membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Chromium (Cr) mainly enters the water environment through industrial production processes such as chromates, chrome pigments, electroplating, etc., and exists in the forms of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)). The traditional idea for treating the environmental problem of Cr(VI) pollution is to convert highly toxic Cr(VI) into low-toxicity Cr(III), and use Cr(III) as the final treatment product. However, Cr(III) is easily and rapidly oxidized to Cr(VI) under environmental conditions with oxygen and changes in acidity and alkalinity, thus causing secondary harm to the environment. In addition, organic pollutants generated in processes such as rubber, printing, leather, plastics, textiles, dyes, and pharmaceuticals complicate the water pollution problem, and new processes and technologies are urgently needed to address it. Therefore, converting Cr(VI) into Cr(III) and achieving the integrated removal of Cr(VI) and Cr(III), as well as co-removing other associated organic dyes in chromium-polluted water bodies, is a greener and more thorough treatment approach.

[0003] Currently, methods such as electrochemistry, photocatalysis, adsorption, and membrane separation are commonly used to reduce highly toxic Cr(VI) to low-toxicity Cr(III) and to achieve the removal of organic dyes. The adsorption method is simple to operate and has high economic benefits, but has disadvantages such as a long adsorption cycle and difficulty in recovering nanomaterials after adsorption. The membrane separation method has the advantages of high removal rate, high recovery rate, short circulation time, and high environmental benefits. More importantly, membrane technology is an effective way to solve the problems of nanomaterial recovery and metal ion leaching. Therefore, it is necessary to develop a green and efficient membrane for solving the problem of composite pollution of heavy metal chromium and organic dyes. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a SA / EGCG@Ti / SA / PVDF sandwich membrane, a preparation method thereof, and an application thereof, which can not only achieve the integrated removal of low-concentration and high-concentration Cr(VI) and Cr(III), but also achieve the efficient removal of organic dyes.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A preparation method of a SA / EGCG@Ti / SA / PVDF sandwich membrane, comprising the following steps:

[0007] S1. Mix the epigallocatechin gallate solution and the titanium salt solution, carry out the reaction, and after centrifugation, washing, and drying, obtain EGCG@Ti NPs;

[0008] S2. Coat the sodium alginate solution on the surface of the polyvinylidene fluoride membrane to obtain the SA / PVDF substrate membrane;

[0009] S3. Disperse the EGCG@Ti NPs obtained in step S1 in an organic solvent to obtain a mixed solution; steps S2 and S3 can be exchanged;

[0010] S4. Immerse the SA / PVDF substrate membrane obtained in step S2 into the mixed solution obtained in step S3, and dry it to obtain the EGCG@Ti / SA / PVDF membrane;

[0011] S5. Coat the sodium alginate solution on the surface of the EGCG@Ti / SA / PVDF membrane obtained in step S4, dry it, and then immerse it into a mixed solution of CaCl2 and H3BO3 to carry out a cross-linking reaction to obtain the SA / EGCG@Ti / SA / PVDF sandwich membrane.

[0012] In the above preparation method, preferably, in step S1, the molar ratio of epigallocatechin gallate in the epigallocatechin gallate solution to the titanium salt in the titanium salt solution is 1:1 to 2.5, and the titanium salt solution is a titanium sulfate solution.

[0013] In the above preparation method, preferably, in step S1, the temperature of the reaction is 40°C to 60°C, and the time of the reaction is 30 min to 60 min.

[0014] In the above preparation method, preferably, in step S1, the rotation speed of the centrifugation is 8000 rpm to 10000 rpm, the time of the centrifugation is 5 min to 10 min, the temperature of the drying is 60°C to 70°C, the time of the drying is 16 h to 24 h, and the drying is carried out under vacuum conditions.

[0015] In the above preparation method, preferably, in step S2, the mass percentage concentration of the sodium alginate solution is 0.05% to 0.1%;

[0016] And / or, in step S3, the mass percentage concentration of EGCG@Ti NPs in the mixed solution is 0.9% to 1%, the organic solvent is implemented in the form of an aqueous solution of the organic solvent, the mass percentage concentration of the aqueous solution of the organic solvent is 2% to 4%, and the aqueous solution of the organic solvent is a polyvinylpyrrolidone solution.

[0017] In the above preparation method, preferably, in step S4, the SA / PVDF substrate membrane is wetted before use, and the drying specifically includes: first, filtering and drying the water by vacuum filtration, and then air-drying at room temperature.

[0018] In the above preparation method, preferably, in step S5, the mass percentage concentration of the sodium alginate solution is 0.5% - 1%, and the preparation method of the mixed solution of CaCl2 and H3BO3 is: adding boric acid (solid powder) to a calcium chloride solution with a mass percentage concentration of 4% - 5% until the solution is saturated (i.e., boric acid no longer dissolves); the cross-linking reaction time is 20h - 24h, and the cross-linking reaction is carried out at room temperature.

[0019] As a general technical concept, the present invention also provides an SA / EGCG@Ti / SA / PVDF sandwich membrane prepared by the above preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane.

[0020] As a general technical concept, the present invention also provides an application of the above SA / EGCG@Ti / SA / PVDF sandwich membrane in treating heavy metal chromium-polluted water bodies and organic dye water bodies.

[0021] In the above application, preferably, when the SA / EGCG@Ti / SA / PVDF sandwich membrane treats a heavy metal chromium-polluted water body, it includes the following steps: placing the SA / EGCG@Ti / SA / PVDF sandwich membrane in the heavy metal chromium-polluted water body for adsorption to complete the treatment of the heavy metal chromium-polluted water body; the initial concentration of chromium in the heavy metal chromium-polluted water body ≤ 100mg / L;

[0022] When the SA / EGCG@Ti / SA / PVDF sandwich membrane treats an organic dye water body, it includes the following steps: placing the SA / EGCG@Ti / SA / PVDF sandwich membrane in the organic dye water body for adsorption to complete the treatment of the organic dye water body; the initial concentration of the organic dye in the organic dye water body is 30mg / L - 40mg / L, and the organic dye in the organic dye water body is at least one of methyl orange, methyl blue, and rhodamine B.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] The present invention provides a preparation method of an SA / EGCG@Ti / SA / PVDF sandwich membrane. First, epigallocatechin gallate (EGCG) is mixed with a titanium salt solution for reaction. Epigallocatechin gallate (EGCG) is a polyphenol richest in hydroxyl groups (-OH), and -OH can react with Ti 4+Chelate coordination is carried out with metal ions to form a Ti metal-polyphenol network structure, which can remove Cr(VI) through ion exchange, chelation / complexation, and reduction mechanisms; then, EGCG@Ti NPs are deposited on the surface of the SA / PVDF substrate membrane, and sodium alginate (SA) is coated to obtain the SA / EGCG@Ti / SA / PVDF sandwich membrane. For the SA / EGCG@Ti / SA / PVDF sandwich membrane prepared in the present invention, on the one hand, the SA on the surface layer and bottom layer of the membrane contains abundant carboxyl groups (-COOH) and -OH. The -OH can undergo anion exchange with Cr(VI) to remove Cr(VI), and the -COOH and -OH can also undergo complexation / chelation with Cr(III) to stabilize Cr(III); on the other hand, the surface of the EGCG@Ti NPs in the middle layer of the membrane contains abundant polyphenol functional groups and has strong reducing ability, which can undergo redox reaction with Cr(VI). Compared with the existing membranes, the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention has a unique structure, good hydrothermal stability and acid-base stability, and is a new type of green and economical material. It can not only achieve the integrated removal of low-concentration and high-concentration Cr(VI) and Cr(III) in simulated wastewater, but also achieve the efficient removal of organic dyes (such as methyl orange, methyl blue, rhodamine B), and has high practical value. In addition, the preparation method of the present invention has the advantages of rich raw material sources and simple operation.

[0025] Sodium alginate (SA) used in the present invention is a material with excellent biocompatibility, biodegradability, and renewability, and has viscosity and film-forming ability. In addition, the polyvinylidene fluoride membrane (PVDF) used in the present invention has excellent hydrophobicity and mechanical properties and can be used as a substrate membrane to improve the separation performance. Description of the Drawings

[0026] Figure 1 It is the yield and the removal effect diagram of hexavalent chromium for EGCG@Ti NPs, EGCG@Zn NPs, and EGCG@Ni NPs in Example 2 of the present invention.

[0027] Figure 2 It is the pure water flux and the removal effect diagram of hexavalent chromium for PVDF membrane, SA / PVDF substrate membrane, EGCG@Ti / SA / PVDF membrane, and SA / EGCG@Ti / SA / PVDF sandwich membrane in Example 3 of the present invention.

[0028] Figure 3 It is the retention flux and the removal effect diagram of hexavalent chromium of the SA / EGCG@Ti / SA / PVDF sandwich membrane over time in Example 4 of the present invention.

[0029] Figure 4This is the removal effect diagram of SA / EGCG@Ti / SA / PVDF sandwich membrane for different concentrations of hexavalent chromium in Example 5 of the present invention.

[0030] Figure 5 This is the removal effect diagram of SA / EGCG@Ti / SA / PVDF sandwich membrane for different dyes in Example 7 of the present invention.

[0031] Figure 6 This is the cycle number-removal effect diagram corresponding to the removal of hexavalent chromium by SA / EGCG@Ti / SA / PVDF sandwich membrane in Example 8 of the present invention. Detailed implementation manners

[0032] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are all commercially available.

[0033] Example 1:

[0034] A preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention includes the following steps:

[0035] (1) Preparation of EGCG@Ti NPs

[0036] According to the volume ratio of epigallocatechin gallate solution and Ti(SO4)2 solution being 1:1, and the molar ratio of epigallocatechin gallate in the epigallocatechin gallate solution to Ti(SO4)2 in the Ti(SO4)2 solution being 1:2.5, pour the epigallocatechin gallate solution into the Ti(SO4)2 solution at one time, continuously react in a water bath at 60 °C for 30 min. After the reaction is completed, centrifuge the reaction product at 10000 rpm for 5 min, remove the supernatant, and then centrifuge with deionized water at 10000 rpm for multiple times until the supernatant is colorless. Dry in vacuum at 60 °C for 16 h, and repeatedly grind with an agate mortar until it becomes a uniform powder to obtain EGCG@Ti NPs, and its yield is 53.26%.

[0037] (2) Preparation of SA / EGCG@Ti / SA / PVDF sandwich membrane

[0038] (1.1) Use a glass rod to scrape a layer of sodium alginate solution (SA) with a mass percentage concentration of 0.05% on the surface of a commercial polyvinylidene fluoride membrane (PVDF membrane) as a protective layer, and air-dry at room temperature to obtain an SA / PVDF substrate membrane.

[0039] In this step, scraping SA is to prevent the leaching of EGCG@Ti NPs and Ti, thereby avoiding the loss of the EGCG@Ti NPs component in the sandwich membrane.

[0040] (1.2) First, prepare a polyvinylpyrrolidone solution (PVP solution) with a mass percentage concentration of 2%, and then disperse the EGCG@Ti NPs obtained in step (1) into the PVP solution and mechanically stir for 10 min to obtain a mixed solution; the mass percentage concentration of EGCG@Ti NPs in this mixed solution is 1.0%.

[0041] (1.3) After wetting the SA / PVDF substrate membrane obtained in step (1.1), fix it in a vacuum filtration funnel, add 10 mL of the mixed solution obtained in step (1.2), drain the water, and air-dry at room temperature to obtain the EGCG@Ti / SA / PVDF membrane.

[0042] (1.4) Spin-coat a 0.5% SA solution by mass percentage concentration on the surface of the EGCG@Ti / SA / PVDF membrane obtained in step (1.3) as a surface isolation layer. This step is to fix the EGCG@Ti NPs, and the SA layer can provide adsorption sites to adsorb Cr(III) after the reduction of Cr(VI) and prevent the escape of Cr(III) ions from the membrane surface; then, place this sandwich membrane in an oven at 50 °C and dry it until there is no residue of sodium alginate on the surface, and then immerse it in a mixed solution of CaCl2 and H3BO3 and crosslink at room temperature for 20 h to obtain the SA / EGCG@Ti / SA / PVDF sandwich membrane, which is stored moist.

[0043] In this step, the preparation method of the mixed solution of CaCl2 and H3BO3 is as follows: first, prepare a calcium chloride solution with a mass percentage concentration of 4%, and then add boric acid (solid powder) until the solution is saturated, that is, until boric acid no longer dissolves.

[0044] Comparative Example 1:

[0045] A Zn metal polyphenol nanomaterial, comprising the following steps:

[0046] According to the volume ratio of the epigallocatechin gallate solution to the Zn(CH3COO)2 solution being 1:1, pour the epigallocatechin gallate solution into the Zn(CH3COO)2 solution at one time, wherein the molar ratio of epigallocatechin gallate in the epigallocatechin gallate solution to Zn(CH3COO)2 in the Zn(CH3COO)2 solution is 1:2.5, continuously react in a 60 °C water bath for 30 min, the reaction solution changes from colorless to milky white, and a white product is rapidly produced to obtain the Zn metal polyphenol nanomaterial, denoted as EGCG@Zn NPs, and its yield is 16.75%.

[0047] Comparative Example 2:

[0048] A Ni metal polyphenol nanomaterial, comprising the following steps:

[0049] According to the volume ratio of epigallocatechin gallate solution and Ni(CH3COO)2 solution being 1:1, the epigallocatechin gallate solution was poured into the Ni(CH3COO)2 solution at one time. Among them, the molar ratio of epigallocatechin gallate in the epigallocatechin gallate solution to Ni(CH3COO)2 in the Ni(CH3COO)2 solution was 1:2.5. The reaction was continuously carried out in a water bath at 60 °C for 30 min. The reaction solution rapidly produced a light green product, and the Ni metal polyphenol nanomaterial was obtained, denoted as EGCG@Ni NPs, and its yield was 13.03%.

[0050] Comparative Example 3:

[0051] A Cu metal polyphenol nanomaterial, comprising the following steps:

[0052] According to the volume ratio of epigallocatechin gallate solution and CuS04 solution being 1:1, the epigallocatechin gallate solution was poured into the CuSO4 solution at one time. Among them, the molar ratio of epigallocatechin gallate in the epigallocatechin gallate solution to CuS04 in the CuS04 solution was 1:2.5. The reaction was continuously carried out in a water bath at 60 °C for 30 min. The reaction solution changed from blue to dark green, and after standing overnight, a very small amount of dark green product was produced, and the yield was extremely low.

[0053] Comparative Example 4:

[0054] A Fe metal polyphenol nanomaterial, comprising the following steps:

[0055] According to the volume ratio of epigallocatechin gallate solution and FeCl3 solution being 1:1, the epigallocatechin gallate solution was poured into the FeCl3 solution at one time. Among them, the molar ratio of epigallocatechin gallate in the epigallocatechin gallate solution to FeCl3 in the FeCl3 solution was 1:2.5. The reaction was continuously carried out in a water bath at 60 °C for 30 min. The reaction solution changed from orange-yellow to light black, and after standing at room temperature overnight, the solution turned black and a very small amount of black product was produced, and the yield was extremely low.

[0056] Comparative Example 5:

[0057] A Co metal polyphenol nanomaterial, comprising the following steps:

[0058] The volume ratio of the epigallocatechin gallate solution to the Co(NO)3 solution is 1:1. The epigallocatechin gallate solution is poured into the Co(NO)3 solution at one time. Among them, the molar ratio of epigallocatechin gallate in the epigallocatechin gallate solution to Co(NO)3 in the Co(NO)3 solution is 1:2.5. The reaction is continuously carried out in a water bath at 60 °C for 30 min. The reaction solution changes from a darker pink to a lighter pink, and no product is formed.

[0059] Example 2:

[0060] An application of the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention in treating heavy metal chromium-polluted water bodies includes the following steps:

[0061] Dilute the K2Cr2O7 solution with a concentration of 100 mg / L with ultrapure water (Milli-Q water) to obtain a Cr(VI) solution with a concentration of 50 mg / L; weigh 20 mg of EGCG@Ti NPs in Example 1, EGCG@Zn NPs in Comparative Example 1, and EGCG@Ni NPs in Comparative Example 2 and add them to a conical flask containing 20 mL of 50 mg / L Cr(VI) solution. Fix the conical flask in a constant temperature water bath oscillator for an adsorption experiment at room temperature, 130 rpm, and 24 h. After the adsorption reaction is completed, filter through a 0.22 μm filter membrane to complete the treatment of Cr(VI) in the solution. Measure the concentration of Cr(VI) in the solution on an ultraviolet spectrophotometer.

[0062] Figure 1 This is the yield and the removal effect diagram of hexavalent chromium for EGCG@Ti NPs, EGCG@Zn NPs, and EGCG@Ni NPs in Example 2 of the present invention. From Figure 1 It can be seen that the removal rates of Cr(VI) by EGCG@Ti NPs, EGCG@Zn NPs, and EGCG@Ni NPs are 65.69%, 64.49%, and 61.45% respectively.

[0063] Example 3:

[0064] An application of the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention in treating heavy metal chromium-polluted water bodies includes the following steps:

[0065] Dilute the K2Cr2O7 solution with a concentration of 100 mg / L with ultrapure water (Milli-Q water) to obtain a Cr(VI) solution with a concentration of 20 mg / L; take the effective area of 12.56 cm 2In Example 1, the PVDF membrane, SA / PVDF substrate membrane, EGCG@Ti / SA / PVDF membrane, and SA / EGCG@Ti / SA / PVDF sandwich membrane were fixed in a vacuum filtration funnel, and deionized water was filtered at 0.1 MPa until the flux was stable. Then, the Cr(VI) solution was intercepted for 180 min, and the filtrate was passed through a 0.22-μm filter membrane to complete the treatment of Cr(VI) in the solution. The concentration of Cr(VI) in the solution was measured on an ultraviolet spectrophotometer.

[0066] Figure 2 This is the pure water flux and the removal effect diagram of hexavalent chromium of the PVDF membrane, SA / PVDF substrate membrane, EGCG@Ti / SA / PVDF membrane, and SA / EGCG@Ti / SA / PVDF sandwich membrane in Example 3 of the present invention. Figure 2 In it, A is the PVDF membrane, B is the SA / PVDF substrate membrane, C is the EGCG@Ti / SA / PVDF membrane, and D is the SA / EGCG@Ti / SA / PVDF sandwich membrane. From Figure 2 It can be seen that the pure water fluxes of the PVDF membrane, SA / PVDF substrate membrane, EGCG@Ti / SA / PVDF membrane, and SA / EGCG@Ti / SA / PVDF sandwich membrane are 4686.11 L / m 2 ·h, 2914.80 L / m 2 ·h, 1534.06 L / m 2 ·h, 171.40 L / m 2 ·h, respectively. In the same time, the higher the pure water flux of the membrane, the faster the water passes through the membrane. When the pure water is replaced with a Cr(VI) solution, the faster the Cr(VI) solution passes through the membrane, the shorter the contact time between Cr(VI) and the membrane, and the relatively lower the removal rate of Cr(VI). When the PVDF membrane, SA / PVDF substrate membrane, EGCG@Ti / SA / PVDF membrane, and SA / EGCG@Ti / SA / PVDF sandwich membrane intercept for 180 min, the removal rates of Cr(VI) are 0.00%, 4.83%, 70.12%, and 100%, respectively.

[0067] Example 4:

[0068] An application of the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention in treating heavy metal chromium-polluted water bodies at different time periods, including the following steps:

[0069] Dilute a K2Cr2O7 solution with a concentration of 100 mg / L with ultrapure water (Milli-Q water) to obtain a Cr(VI) solution with a concentration of 20 mg / L; take an effective area of 12.56 cm 2In Example 1, the SA / EGCG@Ti / SA / PVDF sandwich membrane was fixed in a vacuum filtration funnel, and deionized water was filtered at 0.1 MPa until the flux was stable. Then, the Cr(VI) solution was intercepted for 10 min to 180 min, and 1.5 mL of filtrate was taken every 10 min and filtered through a 0.22 μm filter membrane. The concentration of Cr(VI) in the solution was measured on an ultraviolet spectrophotometer, and the total Cr concentration was measured in an inductively coupled plasma mass spectrometer (ICP-MS).

[0070] Figure 3 This is the interception flux and the removal effect diagram of hexavalent chromium over time of the SA / EGCG@Ti / SA / PVDF sandwich membrane in Example 4 of the present invention. From Figure 3 It can be seen that when the interception time is 150 min and 180 min, the removal rate of Cr(VI) is 100%, and the Cr(VI) interception fluxes are 63.88 L / m 2 ·h and 56.73 L / m 2 ·h, respectively. In addition, in the filtrate collected at 180 min, the total Cr concentration is lower than the detection limit of ICP-MS, that is, when Cr(VI) is reduced to Cr(III), the positively charged Cr(III) will be electrostatically attracted by the negatively charged sandwich membrane so that Cr(III) will not leach out.

[0071] Example 5:

[0072] An application of the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention in treating water bodies polluted by heavy metals with different concentrations of chromium, comprising the following steps:

[0073] The 100 mg / L K2Cr2O7 solution was diluted with ultrapure water (Milli-Q water) to obtain Cr(VI) solutions with concentrations of 0.5 mg / L, 1 mg / L, mg / L, 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, 10 mg / L, 20 mg / L, 30 mg / L, and 100 mg / L; the SA / EGCG@Ti / SA / PVDF sandwich membrane in Example 1 with an effective area of 12.56 cm 2 was placed in a petri dish, and the above-prepared Cr(VI) solutions with different concentrations were added, and the mixture was left standing at room temperature for adsorption for 12 h. After the reaction ended, the filtrate was filtered through a 0.22 μm filter membrane. The concentration of Cr(VI) in the solution was measured on an ultraviolet spectrophotometer.

[0074] Figure 4 This is the removal effect diagram of the SA / EGCG@Ti / SA / PVDF sandwich membrane on different concentrations of hexavalent chromium in Example 5 of the present invention. From Figure 4It can be seen that as the initial concentration of Cr(VI) increases, the removal ability of the SA / EGCG@Ti / SA / PVDF sandwich membrane for Cr(VI) slightly weakens. That is, when the Cr(VI) concentration increases from 0.5 mg / L to 100 mg / L, the removal rate of the SA / EGCG@Ti / SA / PVDF sandwich membrane for Cr(VI) decreases from 100% to 94.82%, and its removal rate still remains at a high level.

[0075] Example 6:

[0076] An application of the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention in treating heavy metal chromium-polluted water bodies, specifically using the SA / EGCG@Ti / SA / PVDF sandwich membrane to treat electroplating wastewater, includes the following steps:

[0077] Obtain typical Cr electroplating wastewater from a company in Guilin, Guangxi, and dilute the Cr(VI) concentration in the Cr electroplating wastewater to 17.22 mg / L with ultrapure water. Take the SA / EGCG@Ti / SA / PVDF sandwich membrane in Example 1 with an effective area of 12.56 cm 2 Place it in a petri dish, add the above 20 mL of Cr electroplating wastewater, and let it stand at room temperature for adsorption for 24 h. Measure the concentration of Cr(VI) in the solution on an ultraviolet spectrophotometer.

[0078] Table 1 Element contents (mg / L) of electroplating wastewater before and after 24 h of adsorption

[0079] Element Cr(VI) Cr(III) Na K Ca Co Ni Cu Zn Ag Before reaction 17.2200 / 7.3657 0.2879 0.0589 0.0025 0.0541 0.4008 0.0516 0.0565 After reaction 0.0000 0.5713 1.4472 0.0000 0.0000 0.0000 0.0000 0.0000 0.0359 0.0000

[0080] As can be seen from Table 1, after the Cr electroplating wastewater is treated with the SA / EGCG@Ti / SA / PVDF sandwich membrane, the removal rate of Cr(VI) in the Cr electroplating wastewater containing various interfering ions is 100%, and the removal rate of total chromium (including Cr(VI) and Cr(III)) is as high as 96.68%.

[0081] Example 7:

[0082] An application of the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention in treating organic dye water bodies includes the following steps:

[0083] Dilute methyl orange solution, methylene blue solution, and rhodamine B solution with a concentration of 50 mg / L with ultrapure water (Milli-Q water) to obtain methyl orange solution, methylene blue solution, and rhodamine B solution with a concentration of 30 mg / L; take the SA / EGCG@Ti / SA / PVDF sandwich membrane with an effective area of 12.56 cm 2In Example 1, the SA / EGCG@Ti / SA / PVDF sandwich membrane was placed in a petri dish, and 20 mL of the above-prepared methyl orange solution, methyl blue solution, and rhodamine B solution were added respectively. The adsorption reaction was allowed to proceed at room temperature for 24 h. After the reaction, the filtrate was filtered through a 0.22 μm filter membrane. The concentrations of methyl orange, methyl blue, and rhodamine B in the solution were measured on an ultraviolet spectrophotometer.

[0084] Figure 5 This is the removal effect diagram of different dyes by the SA / EGCG@Ti / SA / PVDF sandwich membrane in Example 7 of the present invention. From Figure 5 It can be seen that the removal rates of methyl orange, methyl blue, and rhodamine B by the SA / EGCG@Ti / SA / PVDF sandwich membrane are 95.82%, 95.10%, and 98.37% respectively.

[0085] Example 8:

[0086] To investigate the reusability of the SA / EGCG@Ti / SA / PVDF sandwich membrane in treating heavy metal chromium-polluted water, specifically, the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention was used to treat electroplating wastewater, including the following steps:

[0087] (1) The concentration of Cr(VI) in the Cr electroplating wastewater was diluted to 17.22 mg / L with ultrapure water. An SA / EGCG@Ti / SA / PVDF sandwich membrane with an effective area of 12.56 cm 2 from Example 1 was placed in a petri dish, and 20 mL of the above-mentioned Cr electroplating wastewater was added. The adsorption was allowed to proceed at room temperature for 24 h to complete one cycle.

[0088] (2) After completing one cycle, the SA / EGCG@Ti / SA / PVDF sandwich membrane adsorbed with Cr(VI) in step (1) was placed in a petri dish containing 50 mL of 0.1 mol / L H2SO4 solution. After desorbing at room temperature for 12 h, the membrane was placed in a vacuum filtration funnel for filtration, and the membrane was washed repeatedly with deionized water until the filtrate was neutral to obtain a regenerated SA / EGCG@Ti / SA / PVDF sandwich membrane.

[0089] (3) Steps (1) and (2) were repeated a total of 4 times to complete the cycle experiment. The concentration of Cr(VI) in the solution was measured on an ultraviolet spectrophotometer.

[0090] Figure 6 This is the cycle number-removal effect diagram corresponding to the removal of hexavalent chromium by the SA / EGCG@Ti / SA / PVDF sandwich membrane in Example 8 of the present invention. From Figure 6It can be seen that the removal rate of Cr(VI) in Cr electroplating wastewater by the SA / EGCG@Ti / SA / PVDF sandwich membrane is 100%; at the same time, after 5 adsorption-desorption cycles of the SA / EGCG@Ti / SA / PVDF sandwich membrane, the removal rate of the sandwich membrane for Cr(VI) electroplating wastewater is still 100%.

[0091] Generally speaking, the SA / EGCG@Ti / SA / PVDF sandwich membrane of the present invention exhibits excellent Cr(VI) and dye removal capabilities in both simulated water samples and actual water bodies, and is an ideal choice for treating Cr(VI)-polluted wastewater.

[0092] As mentioned above, it is only a preferred embodiment of the present invention, and it does not impose any formal restrictions on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A preparation method of SA / EGCG@Ti / SA / PVDF sandwich membrane, characterized in that, It includes the following steps: S1. Mix the epigallocatechin gallate solution and the titanium salt solution, carry out a reaction, and after centrifugation, washing, and drying, obtain EGCG@Ti NPs; S2. Coat the sodium alginate solution on the surface of the polyvinylidene fluoride membrane to obtain the SA / PVDF substrate membrane; S3. Disperse the EGCG@Ti NPs obtained in step S1 in an organic solvent to obtain a mixed solution; steps S2 and S3 can be exchanged; S4. Immerse the SA / PVDF substrate membrane obtained in step S2 into the mixed solution obtained in step S3, and dry it to obtain the EGCG@Ti / SA / PVDF membrane; S5. Coat the sodium alginate solution on the surface of the EGCG@Ti / SA / PVDF membrane obtained in step S4, dry it, and then immerse it in a mixed solution of CaCl2 and H3BO3 to carry out a cross-linking reaction to obtain the SA / EGCG@Ti / SA / PVDF sandwich membrane.

2. The preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane according to claim 1, characterized in that, In step S1, the molar ratio of epigallocatechin gallate in the epigallocatechin gallate solution to the titanium salt in the titanium salt solution is 1:1 - 2.5, and the titanium salt solution is a titanium sulfate solution.

3. The preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane according to claim 2, wherein, In step S1, the temperature of the reaction is 40°C - 60°C, and the time of the reaction is 30 min - 60 min.

4. The preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane according to any one of claims 1 to 3, characterized in that, In step S1, the rotation speed of the centrifugation is 8000 rpm - 10000 rpm, the time of the centrifugation is 5 min - 10 min, the temperature of the drying is 60°C - 70°C, the time of the drying is 16 h - 24 h, and the drying is carried out under vacuum conditions.

5. The preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane according to any one of claims 1 to 3, characterized in that, In step S2, the mass percentage concentration of the sodium alginate solution is 0.05% - 0.1%; And / or, in step S3, the mass percentage concentration of EGCG@Ti NPs in the mixed solution is 0.9% - 1%, the organic solvent is implemented in the form of an aqueous solution of the organic solvent, the mass percentage concentration of the aqueous solution of the organic solvent is 2% - 4%, and the aqueous solution of the organic solvent is a polyvinylpyrrolidone solution.

6. The preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane according to any one of claims 1 to 3, characterized in that, In step S4, the SA / PVDF substrate membrane is wetted before use, and the drying specifically is: first vacuum filter to drain the water, and then air dry at room temperature.

7. The preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane according to any one of claims 1 to 3, characterized in that, In step S5, the mass percentage concentration of the sodium alginate solution is 0.5% - 1%, and the preparation method of the mixed solution of CaCl2 and H3BO3 is: add boric acid to the calcium chloride solution with a mass percentage concentration of 4% - 5% until the solution is saturated; the time of the cross-linking reaction is 20 h - 24 h, and the cross-linking reaction is carried out at room temperature.

8. An SA / EGCG@Ti / SA / PVDF sandwich membrane prepared by the preparation method of the SA / EGCG@Ti / SA / PVDF sandwich membrane according to any one of claims 1 - 7.

9. An application of the SA / EGCG@Ti / SA / PVDF sandwich membrane according to claim 8 in treating heavy metal chromium-polluted water bodies and organic dye water bodies.

10. The application according to claim 9, wherein, When the SA / EGCG@Ti / SA / PVDF sandwich membrane is used to treat heavy metal chromium-polluted water, the following steps are included: placing the SA / EGCG@Ti / SA / PVDF sandwich membrane in the heavy metal chromium-polluted water for adsorption to complete the treatment of the heavy metal chromium-polluted water; the initial concentration of chromium in the heavy metal chromium-polluted water is ≤ 100 mg / L; When the SA / EGCG@Ti / SA / PVDF sandwich membrane is used to treat organic dye water, the following steps are included: placing the SA / EGCG@Ti / SA / PVDF sandwich membrane in the organic dye water for adsorption to complete the treatment of the organic dye water; the initial concentration of the organic dye in the organic dye water is 30 mg / L to 40 mg / L, and the organic dye in the organic dye water is at least one of methyl orange, methyl blue, and rhodamine B.

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