A carbon-based self-cleaning membrane material for efficient separation of oil-water emulsions, its preparation method and application

Abstract

The present invention discloses a carbon-based self-cleaning membrane material for efficient separation of oil-water emulsions, its preparation method and application. The preparation method of the carbon-based self-cleaning membrane material comprises the following steps: subjecting acidified carbon nanotubes CNTs to polyethyleneimine PEI functionalization to obtain CNTs-PEI material; using vacuum-assisted filtration method to filter the CNTs-PEI dispersion onto a polyvinylidene fluoride PVDF membrane to obtain a CNTs-PEI membrane; filtering a Cu-ZnIn2S4 dispersion onto the CNTs-PEI membrane to obtain a carbon-based self-cleaning membrane material CNTs-PEI / CZIS for efficient separation of oil-water emulsions. The CNTs-PEI / CZIS membrane material of the present invention has a separation efficiency of 99.6±0.4% for chloroform / water emulsion, and has good broad-spectrum applicability, chemical adaptability and stability, and is a promising composite functional membrane material for recyclable and efficient separation of oil-water emulsions.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of oil-water separation composite membrane materials, and particularly relates to a carbon-based self-cleaning membrane material for efficiently separating oil-water emulsions, a preparation method thereof, and an application thereof. Background Art

[0002] The harmless treatment and resource utilization of oil-containing wastewater from petroleum, petrochemical, kitchen, etc. are important guarantees for water environment safety and industrial sustainable development. Traditional methods for treating oil-containing wastewater include sedimentation, flotation, adsorption, and filtration. Sedimentation and flotation are effective methods for separating oil-water mixtures, but it is difficult to treat emulsified oil. Adsorption separation usually uses porous materials such as sponges to adsorb and remove oil in wastewater, but these materials have a certain absorption rate and are difficult to recycle after saturation, which is likely to cause secondary pollution. The filtration separation method is based on the principle of pore size screening to treat oil-containing wastewater, and separation is carried out by selecting filtration separation materials with different pore sizes. The current operation method is mainly membrane separation. Existing membrane materials, such as polyvinylidene fluoride, polyethersulfone, etc., are prone to oil adhesion and fouling on the membrane surface during the oil-water separation process, resulting in membrane pore blockage, reduced separation efficiency, and increased energy consumption. Therefore, there is an urgent need to develop new membrane materials with excellent oil-water separation efficiency and anti-fouling performance to achieve stable and efficient oil-water separation effects.

[0003] Due to the high specific surface area and mechanical strength of carbon nanotubes, they are often used to modify the separation membrane, and hydrophilic and hydrophobic groups are introduced to construct a hydrophilic / underwater superoleophobic oil-water separation membrane. In addition, composite materials are one of the important development directions of functional materials. Under a suitable band gap, photocatalytic materials can achieve photocatalytic degradation of pollutants under the drive of visible light irradiation, and also have the advantages of stability, non-toxicity, self-cleaning, etc. Cu can be used as an effective platform for light-driven chemical reactions, and by combining with ternary sulfide ZnIn 2 S 4 to form a synergistic effect and improve the catalytic performance. Combining catalytic materials with membrane separation technology is a powerful means to degrade the oil stain remaining on the membrane surface or enhance the anti-fouling performance of the membrane material by using photocatalytic materials. Summary of the Invention

[0004] In order to overcome the disadvantages and deficiencies existing in the prior art, the purpose of the present invention is to provide a carbon-based self-cleaning membrane material for efficiently separating oil-water emulsions, a preparation method thereof, and an application thereof.

[0005] To achieve the above purpose, the following technical solutions are proposed:

[0006] A preparation method of a carbon-based self-cleaning membrane material for efficiently separating oil-water emulsions, comprising the following steps:

[0007] Step 1: Dissolve zinc salt, indium salt, and sulfur source in ultrapure water, adjust the pH value of the mixed solution to acidic, transfer the mixed solution to a hydrothermal reaction kettle, seal the hydrothermal reaction kettle, and place it in an oven for reaction. After the reaction is completed, wait for the reaction kettle to cool to room temperature, centrifuge, wash, and dry the precipitate to obtain the zinc indium sulfide composite material ZnIn 2 S 4 . Disperse the zinc indium sulfide composite material ZnIn 2 S 4 by ultrasonic dispersion in ultrapure water and mix it with a copper salt solution; under magnetic stirring and light irradiation, slowly inject a reducing solution and carry out a photoreduction reaction for 5 - 180 min to obtain Cu - ZnIn 2 S 4 .

[0008] Step 2: Carbon nanotubes CNTs are treated by heating and acidification in a mixed solution of concentrated H 2 SO 4 / concentrated HNO 3 . After that, let it stand to remove the supernatant, wash the lower layer product with distilled water until neutral, and dry it to obtain acidified carbon nanotubes CNTs - COOH.

[0009] Step 3: Ultrasonically disperse the acidified carbon nanotubes CNTs - COOH obtained in Step 2 and polyethyleneimine PEI in water, and then successively undergo centrifugation, washing, and drying to obtain PEI - functionalized CNTs, denoted as CNTs - PEI.

[0010] Step 4: Disperse the CNTs - PEI obtained in Step 3 with water to obtain a dispersion, and filter the dispersion onto a hydrophilic polyvinylidene fluoride PVDF membrane to obtain a CNTs - PEI membrane.

[0011] Step 5: Disperse Cu - ZnIn 2 S 4 with water to obtain a dispersion, and filter the dispersion onto the CNTs - PEI membrane obtained in Step 4 to obtain a CNTs - PEI / Cu - ZnIn 2 S 4 composite membrane, and thus the preparation is completed.

[0012] Furthermore, the zinc salt in Step 1 is zinc nitrate, zinc sulfate, zinc chloride, zinc phosphate, zinc acetate, zinc citrate, zinc isooctanoate, or zinc glycinate, the indium salt is indium nitrate, indium sulfate, indium chloride, indium phosphate, indium acetate, or indium citrate, and the sulfur source is thioacetamide, thiourea, ammonium sulfide, or sodium thiosulfate. The molar ratio of the zinc salt, indium salt, and sulfur source fed is 2 - 3:4 - 6:8 - 12.

[0013] Further, the copper salt in Step 1 is copper nitrate, copper chloride, copper phosphate, copper acetate or sodium copper ethylenediaminetetraacetate, and the mass ratio of the copper salt to the indium zinc sulfide material is 0.1-2:10.

[0014] Further, the reducing solution in Step 1 is hydrazine, sodium borohydride, potassium borohydride, ethanol, ammonia water or sodium sulfite. The concentration of the reducing solution is 0.01-0.6 mol / L, the molar ratio to the copper salt is 3-15:1, and the injection rate of the reducing solution is 2-3 drops per second.

[0015] Further, in Step 2, during the heating and acidification of carbon nanotubes CNTs, the volume ratio of concentrated H 2 SO 4 solution to concentrated HNO 3 solution is 1-4:1, preferably 2-3:1. The mass fraction of concentrated H 2 SO 4 solution is 95-98%, and the mass fraction of concentrated HNO 3 solution is 65-70%. The temperature of the heating and acidification treatment is 60-80 °C, and the time is 0.5-2 h.

[0016] In Step 2 of the present invention, the acidified CNTs are functionalized with PEI, so that the CNTs-PEI surface contains hydrophilic amino and carboxyl groups and has a high affinity for water.

[0017] Further, in Step 3, the dispersion concentrations of acidified carbon nanotubes CNTs-COOH and polyethyleneimine PEI in water are 0.05-0.2 g / L and 0.5-2 g / L respectively, preferably 0.08-0.12 g / L and 0.8-1.2 g / L respectively; the ultrasonic dispersion time in Step 3 is 0.5-2 h.

[0018] Further, in Step 4, under the condition of 0.9 bar (90 kpa), the vacuum-assisted filtration method is used to deposit carbon nanotubes on the hydrophilic polyvinylidene fluoride (PVDF) membrane to form a thin film.

[0019] The present invention also discloses the application of the carbon-based self-cleaning membrane material for efficiently separating oil-water emulsions in membrane separation of oil-water emulsions. After the membrane separation is completed, the following regeneration treatment steps are further included: alternately washing with alcohol and water 2-4 times to remove part of the oil components, and then performing visible light irradiation treatment on the membrane.

[0020] The CNTs-PEI / CZIS composite membrane of the present invention has excellent hydrophilic-lipophobic properties and special wettability, making the CNTs-PEI / CZIS composite membrane a promising membrane separation material for efficient separation of oil-water emulsions. Taking chloroform / water (C / W) emulsion as an example, the separation flux of the CNTs-PEI / CZIS composite membrane is (2070 ± 19 L m -2 h -1 bar -1 ), and the separation efficiency can reach 99.6 ± 0.4%.

[0021] The hydrophilic functional groups (-COOH, -NH 2 ), imparted by the PEI functionalization of the present invention, effectively prevent oil from adhering to the inner / outer surface of the membrane. The excellent photocatalytic performance of Cu-ZnIn 2 S 4 can catalytically degrade the residual oil components and other impurities, and the two complement each other to endow the CNTs-PEI / CZIS composite membrane with extremely strong self-cleaning ability.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1) A series of CNTs-PEI / CZIS composite membranes were designed and prepared by using polymer functionalization and vacuum-assisted filtration method. By acidifying carbon nanotubes and functionalizing polyethyleneimine, rich hydrophilic functional groups were imparted to it, making the CNTs-PEI / CZIS composite membrane have excellent hydrophilic-lipophobic properties and special wettability, and effectively preventing oil from adhering to the inner / outer surface of the membrane. The excellent photocatalytic characteristics of Cu-ZnIn 2 S 4 can catalytically degrade the residual oil components and other impurities on the membrane, effectively enhancing the anti-fouling performance of the membrane material.

[0024] 2) Taking chloroform / water (C / W) emulsion as an example, the separation flux of the CNTs-PEI / CZIS composite membrane is (2070 ±19 L m -2 h -1 bar -1 ), and the separation efficiency can reach 99.6 ± 0.4%. Through cyclic experiments and fouling resistance experiments with different emulsions, it is further shown that the CNTs-PEI / CZIS has good chemical adaptability, high stability of the composite membrane, can be recycled, and has self-cleaning and broad-spectrum applicability, and is a promising composite functional membrane material for efficient separation of oil-water emulsions. Description of the Drawings

[0025] Figure 1XRD spectra of the CNTs-PEI, CNTs-PEI / ZIS, and CNTs-PEI / CZIS composite membrane materials prepared in Example 1;

[0026] Figure 2 Cu-ZnIn prepared for Example 1 2 S 4 EDS elemental distribution maps;

[0027] Figure 3 Comparison chart of the separation flux and separation efficiency of the composite membrane materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 for chloroform / water (C / W);

[0028] Figure 4 Comparison chart of the water flux before and after the separation of chloroform / water (C / W) emulsion by the CNTs-PEI / CZIS composite membrane material prepared in Example 1;

[0029] Figure 5 Recycling effect diagram of the CNTs-PEI / CZIS composite membrane material prepared in Example 1;

[0030] Figure 6 Effect diagram of the CNTs-PEI / CZIS composite membrane material prepared in Example 1 for separating different oil-in-water emulsions. Detailed implementation manners

[0031] The present invention will be further described below in conjunction with examples and the accompanying drawings of the specification, but the protection scope of the present invention is not limited thereto.

[0032] Example 1 Preparation of CNTs-PEI / CZIS composite membrane material;

[0033] Preparation of CNTs-PEI / CZIS self-cleaning membrane material:

[0034] 1) Carbon nanotubes (CNTs, purity > 95%, ID: 5 - 10 nm, OD: 10 - 20 nm, Length: 10 - 30 nm, purchased from Macklin Reagent Co., Ltd.) were heated in a mixed solution of 95 - 98% H 2 SO 4 and 70% HNO 3 at 70 °C for 2 h in a volume ratio of 3:1; after heating, the solution was allowed to stand to remove the supernatant, distilled water was added to the lower layer solution, and the above steps were repeated 3 times or more until neutral after the solution was allowed to stand and layer; the obtained neutral solution was filtered and washed to remove impurities; the black substance obtained by filtration was placed in a vacuum drying oven and dried at 40 °C overnight to obtain acidified carbon nanotubes, denoted as CNTs-COOH;

[0035] 2) Disperse 0.02 g of acidified carbon nanotubes (CNTs-COOH) and 0.2 g of polyethyleneimine (PEI, molecular weight 43.04, purity 50%, purchased from Ron Reagent Co., Ltd.) in 200 mL of ultrapure water and ultrasonically disperse for 1 h; centrifuge the mixed solution at 8000 r / min for 10 min, remove the supernatant, wash the precipitate with ultrapure water 3 - 5 times, and dry at 30 °C to obtain PEI-functionalized CNTs, denoted as CNTs-PEI;

[0036] 3) Prepare a 100 mg / L CNTs-PEI dispersion using an aqueous solvent; using the vacuum-assisted filtration method, filter 10 mL of the dispersion onto a polyvinylidene fluoride membrane (PVDF, pore size 0.45 μm, purchased from Shanghai Titan Technology Co., Ltd.) with an effective area of 40 cm 2 to obtain a 40 cm 2 CNTs-PEI membrane;

[0037] 4) Cu-ZnIn 2 S 4 , abbreviated as CZIS, prepare a 100 mg / L Cu-ZnIn 2 S 4 dispersion using an aqueous solvent for later use; filter 25 mL of the Cu-ZnIn 2 S 4 dispersion onto the 40 cm 2 CNTs-PEI membrane prepared in step 3) to obtain a CNTs-PEI / CZIS composite membrane. 2 S 4

[0038] 5) ZnIn 2 S 4 , abbreviated as ZIS, prepare a 100 mg / L ZnIn 2 S 4 dispersion using an aqueous solvent for later use; filter 25 mL of the ZnIn 2 S 4 dispersion onto the 40 cm 2 CNTs-PEI membrane prepared in step 3) to obtain a CNTs-PEI / ZIS composite membrane. 2 S 4

[0039] Preparation of the above-mentioned ZnIn 2 S 4 material: Dissolve 0.068 g of ZnCl 2 , 0.239 g of InCl 2 ​​· 4H 2 O and 0.15 g CH 3 CSNH 2 were dissolved in 40 mL of ultrapure water and magnetically stirred for 30 min to form a mixed metal salt solution; the mixed solution was transferred to a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner; the hydrothermal reaction kettle was sealed and placed in an oven, and kept at 160 °C for 16 h; after the reaction was completed, the precipitate was cooled to room temperature and centrifugally washed several times with ultrapure water and absolute ethanol to obtain a dark yellow solid material, which was placed in a vacuum oven at 60 °C and vacuum dried for 12 h to obtain ZnIn 2 S 4 materials.

[0040] Preparation of the above Cu-ZnIn 2 S 4 materials: 4.2 mg of CuCl 2 was ultrasonically dissolved in 5 mL of ultrapure water to prepare a copper ion solution for standby; 14.3 mg of NaBH 4 was ultrasonically dissolved in 5 mL of ultrapure water to prepare an aqueous sodium borohydride solution for standby; 100 mg of the prepared ZnIn 2 S 4 materials were ultrasonically dispersed in 40 mL of water, mixed with the prepared copper ion solution, transferred to a quartz photoreactor after ultrasonic treatment, and the dissolved oxygen was removed by nitrogen bubbling. Using a 300 W xenon lamp as the experimental light source, under magnetic stirring, the aqueous sodium borohydride solution was injected at a rate of 2 drops per second. After the dropping was completed, the reaction continued for 60 min to complete the photodeposition reaction, and the temperature was kept at room temperature in a constant temperature water bath during the reaction; after the reaction was completed, the residual salts were removed by centrifugal washing with ultrapure water and absolute ethanol, and dried in a vacuum oven at 60 °C for 12 hours to obtain Cu-ZnIn 2 S 4 materials.

[0041] The XRD patterns of the CNTs-PEI film, CNTs-PEI / ZIS composite film and CNTs-PEI / CZIS composite film prepared by Example 1 are as Figure 1 shown. The prepared CNTs-PEI materials have obvious standard diffraction peaks of carbon-based materials, corresponding to the (002) and (110) crystal planes of carbon materials. In the XRD patterns of the CNTs-PEI / ZIS and CNTs-PEI / CZIS composite films, the characteristic diffraction peaks of ZIS can be clearly observed, corresponding to the (006), (102), (110) and (116) crystal planes of hexagonal ZIS (JCPDS No. 72-0773), indicating that CZIS and CNTs-PEI have been successfully compounded. Among them, in the XRD pattern of the CNTs-PEI / CZIS composite film, due to the low loading amount of Cu, its characteristic diffraction peaks are not obvious.

[0042] Cu-ZnIn 2 S 4 The corresponding EDS elemental distribution map is as Figure 2 shown. The Zn, In, S, and Cu elements of the material are evenly distributed, indicating that Cu can be evenly distributed on ZIS by in-situ photochemical deposition method.

[0043] Example 2 Emulsion separation performance of CNTs-PEI / CZIS composite membrane material

[0044] By preparing different types of oil / water (O / W) emulsions and calculating the permeation flux and separation efficiency of the emulsions, the separation performance of the membrane material was evaluated. The steps for preparing the emulsions are as follows: Add 0.8 g of emulsifier Tween-80 (polyoxyethylene sorbitan monooleate) and 4 mL of oil (the oil is selected from chloroform, dichloromethane, hexane, toluene, silicone oil, or soybean oil) to 120 mL of water, and stir vigorously for 8 h to obtain chloroform / water (C / W) emulsion, dichloromethane / water (D / W) emulsion, n-hexane / water (H / W) emulsion, toluene / water (T / W) emulsion, silicone oil / water (Si / W) emulsion, and soybean oil / water (So / W) emulsion respectively.

[0045] The permeation flux ( J ) is an important index to evaluate the separation performance of the composite membrane. A large permeation flux means that water molecules pass through the membrane quickly; a small permeation flux means that the diffusion rate of water molecules from outside the membrane to inside the membrane is slow. The calculation formula is as follows:

[0046] ;

[0047] In the formula, —— Permeated water volume, L;

[0048] A —— Effective membrane area, m 2 ;

[0049] —— Operating time, h;

[0050] —— Transmembrane pressure difference, bar.

[0051] During the membrane separation process, different solute molecules have different permeation properties. By measuring the oil concentration in the liquid before and after filtration by TOC, the separation efficiency R (%) of the membrane material for the emulsion was calculated, and the formula is as follows:

[0052] ;

[0053] In the formula, C 0 —— Oil concentration of the initial emulsion, mg / L;

[0054] C f ——Oil concentration in the filtrate, mg / L.

[0055] Taking chloroform / water (C / W) emulsion as an example, when the filtration pressure is 0.3 bar, by measuring the volume of permeated water for separating 50 mL of emulsion within 30 min and the oil concentrations in the liquid before and after filtration, the permeation flux and separation efficiency of the emulsion are calculated. According to this test condition, the separation fluxes and efficiencies of the CNTs-PEI membrane, CNTs-PEI / ZIS composite membrane, and CNTs-PEI / CZIS composite membrane prepared in Example 1 for separating chloroform / water (C / W) for 30 min are as Figure 3 shown (the separation flux is a bar chart, and the separation efficiency is a dotted line chart).

[0056] From Figure 3 it can be seen that the CNTs-PEI membrane has a relatively high separation flux for C / W emulsion (2150 ± 69 L m -2 h -1 bar -1 ), and the separation efficiency is 92.4 ± 0.3%. After modification with ZIS or CZIS, the pores of the CNTs-PEI / ZIS composite membrane and CNTs-PEI / CZIS composite membrane are slightly affected, the separation flux decreases slightly, but the separation efficiencies are increased to 98.5 ± 0.7% and 99.6 ± 0.4% respectively. In addition, due to the modification of CuNPs on the surface of ZIS, a larger specific surface area and more active sites than pure ZIS are provided, and the separation flux of the CNTs-PEI / CZIS composite membrane (2070 ± 19 L m -2 h -1 bar -1 )is higher than that of the CNTs-PEI / ZIS composite membrane (1920 ± 100 L m -2 h -1 bar -1 ).

[0057] Preparation of the CNTs*-PEI composite membrane material in Comparative Example 1

[0058] Dissolve 0.02 g of carbon nanotubes (CNTs) and 0.2 g of polyethyleneimine (PEI) in 200 mL of ultrapure water, and ultrasonically disperse for 1 h; centrifuge the mixed solution at 8000 r / min for 10 min, remove the supernatant, wash the precipitate with ultrapure water 3 - 5 times, and dry at 30 °C to obtain PEI-functionalized CNTs, denoted as CNTs*-PEI; prepare a 100 mg / L CNTs*-PEI dispersion; using the vacuum-assisted filtration method, filter 10 mL of the dispersion onto a polyvinylidene fluoride (PVDF) membrane with an effective area of 40 cm 2 to obtain the CNTs*-PEI membrane.

[0059] Comparative Example 2 Preparation of CNTs-PAA / CZIS Composite Membrane Material

[0060] 1) Ultrasonically disperse 0.15 g of carbon nanotubes in 150 mL of acetone, add 3.0 g of acrylic acid (AA) and 0.065 g of recrystallized benzoyl peroxide (BPO), and stir at 75 °C for 8 h under N 2 atmosphere. Collect the prepared CNTs-PAA by filtration, wash it 3 times with deionized water, and dry at 30 °C to obtain CNTs modified with hydrazide functional groups, denoted as CNTs-PAA;

[0061] 2) Prepare a 100 mg / L CNTs-PAA dispersion; using the vacuum-assisted filtration method, filter 10 mL of the dispersion onto a polyvinylidene fluoride (PVDF) membrane with an effective area of 40 cm 2 to obtain the CNTs-PAA membrane;

[0062] 3) Cu-ZnIn 2 S 4 , abbreviated as CZIS, dissolve Cu-ZnIn 2 S 4 in an aqueous solvent to prepare a 100 mg / L Cu-ZnIn 2 S 4 dispersion for standby; filter 25 mL of the Cu-ZnIn 2 CNTs-PAA membrane to obtain the CNTs-PAA / CZIS composite membrane. 2 S 4 4) ZnIn

[0063] S 2 S 4 , abbreviated as ZIS, dissolve ZnIn 2 S4 The material was formulated into a 100 mg / L ZnIn 2 S 4 dispersion for standby; 25 mL of ZnIn 2 was filtered through the CNTs-PAA membrane prepared in step 2), 2 S 4 and a CNTs-PAA / ZIS composite membrane was obtained.

[0064] Among them, in Comparative Example 2, the preparation steps of Cu-ZnIn 2 S 4 and ZnIn 2 S 4 were repeated as in Example 1.

[0065] Comparative Example 3 Emulsion separation performance of CNTs*-PEI and CNTs-PAA / CZIS composite membrane materials

[0066] Referring to the emulsion separation conditions in Example 2, a chloroform / water (C / W) emulsion was selected as the separation object.

[0067] The separation fluxes and efficiencies of the CNTs*-PEI membrane in Comparative Example 1, the CNTs-PAA membrane in Comparative Example 2, the CNTs-PAA / ZIS composite membrane, and the CNTs-PAA / CZIS composite membrane for the separation of chloroform / water (C / W) for 30 min are as Figure 3 shown. The separation flux of the CNTs*-PEI membrane for the C / W emulsion was relatively low, only (1420 ± 53 L m -2 h -1 bar -1 ), and the separation efficiency was 83.1 ± 0.2%. Both the separation flux and the separation efficiency were significantly lower than those of the CNTs-PEI membrane prepared from acidified carbon nanotubes in Example 2, indicating that the acidification treatment of carbon nanotubes can effectively improve the hydrophilicity of carbon nanotube membrane materials and thus enhance the separation performance of the membrane materials.

[0068] The separation flux of the CNTs-PAA membrane for the C / W emulsion could reach (1840 ± 53 L m -2 h -1 bar -1 ), and the separation efficiency was 91.2 ± 0.4%. After modification with ZIS or CZIS, the pores of the CNTs-PAA / ZIS composite membrane and the CNTs-PAA / CZIS composite membrane were slightly affected, and the separation fluxes decreased to 1600 ± 80 L m -2 h -1 bar -1 and 1740 ± 20 Lm -2 h-1 bar -1 , but the separation efficiencies were increased to 95.3 ± 0.2% and 96.7 ± 0.5% respectively. Similarly, since CuNPs are modified on the surface of ZIS, providing a larger specific surface area and more active sites than pure ZIS, the separation flux of the CNTs-PAA / CZIS composite membrane is higher than that of the CNTs-PAA / ZIS composite membrane.

[0069] By comparing the permeation flux and separation efficiency of the composite membranes for C / W emulsions, it can be seen that the separation performance of the CNTs-PEI, CNTs-PEI / ZIS, and CNTs-PEI / CZIS composite membranes is significantly better than that of the CNTs-PAA, CNTs-PAA / ZIS, and CNTs-PAA / CZIS composite membranes. This may be because the acidified CNTs are functionalized with PEI, making the surface of CNTs-PEI contain hydrophilic amino and carboxyl groups, which have a high affinity for water.

[0070] Example 3 Self-cleaning performance of the CNTs-PEI / CZIS composite membrane material;

[0071] Referring to the emulsion separation conditions in Example 2, a chloroform / water (C / W) emulsion was selected as the separation object, and the antifouling performance of the membrane material, that is, the self-cleaning performance, was tested by calculating the water flux before and after the separation of the C / W emulsion to evaluate the practical application and comprehensive performance of the membrane. The CNTs-PEI / CZIS composite membrane prepared in Example 1 was used for evaluation. The initial / recovered water fluxes (initial, after emulsion separation, after water washing, after sunlight irradiation) of the CNTs-PEI / CZIS composite membrane during the separation of the C / W emulsion are as Figure 4 shown. The initial water flux of the CNTs-PEI / CZIS composite membrane for the separation of pure water at a pressure of 0.3 bar for 30 min ( J 0 ) is 13090 ± 940 L m -2 h -1 bar -1 . The obtained membrane is denoted as the initial membrane. After the initial membrane is separated from chloroform / water (C / W) at a pressure of 0.3 bar for 30 min according to the emulsion separation conditions in Example 2, the water flux of the membrane tested by separating pure water at a pressure of 0.3 bar for 30 min ( J 1 ) is as low as 2070 ± 19 L m -2 h -1 bar -1 . This can be attributed to the aggregation and adhesion of oil droplets in the emulsion on the surface and inside of the membrane. The obtained membrane is denoted as the membrane after emulsion separation.

[0072] Perform the first regeneration on the separated emulsion membrane, wash it alternately with water / alcohol three times, dry it at 30 °C, and then measure the water flux of the membrane that separates pure water for 30 min under a pressure of 0.3 bar ( J 2 ), which is restored to 5630 ± 370 L m -2 h -1 bar -1 . This indicates that water and alcohol cannot play a role in deep cleaning, and the obtained membrane is recorded as the regenerated membrane after water washing.

[0073] Perform another regeneration on the regenerated membrane after water washing. Irradiate the composite membrane with a 300 W xenon lamp to simulate sunlight for 30 min, and then separate pure water for 30 min under a pressure of 0.3 bar. The recovered water flux of the CNTs-PEI / CZIS composite membrane ( J 3 ) is restored to 13010 ± 830 L m -2 h -1 bar -1 . This indicates that the membrane has good visible light absorption and self-cleaning ability.

[0074] Example 4 Stability of CNTs-PEI / CZIS Composite Membrane Material

[0075] Referring to the emulsion separation conditions in Example 2, select chloroform / water (C / W) emulsion as the separation object, and use the CNTs-PEI / CZIS composite membrane of Example 1 to perform multiple cyclic separations on the C / W emulsion. Each emulsion separation experiment is to continuously separate the chloroform / water (C / W) emulsion for 60 min under a pressure of 0.3 bar. Record the separation data in two time periods of 0 - 30 min and 30 - 60 min of the separation time, that is, record two sets of experimental data for each emulsion separation experiment, and calculate the corresponding separation flux and separation efficiency according to the formula in Example 2.

[0076] After each emulsion separation experiment, regenerate the membrane. First, wash the composite membrane alternately with alcohol / water three times, dry it at 30 °C, and then irradiate it with a 300 W xenon lamp to simulate sunlight for 30 min to obtain the regenerated composite membrane, which is then used for the next emulsion separation experiment.

[0077] According to the above experimental process, the experimental results of the CNTs-PEI / CZIS composite membrane of Example 1 for multiple cyclic separations of the C / W emulsion are shown in Figure 5 . Judge its stability by the separation flux and separation efficiency of the composite membrane for multiple separations of the C / W emulsion, so as to evaluate the actual application prospect of the CNTs-PEI / CZIS composite membrane. From Figure 5It can be seen from [Figure] that the recycling effect of the CNTs-PEI / CZIS composite membrane (the separation flux is a line graph, and the separation efficiency is a dot graph). During multiple cycles, the separation efficiency of the CNTs-PEI / CZIS composite membrane for the C / W emulsion always remained above 95%, and the separation flux remained stable.

[0078] Example 5 Application Performance Evaluation of CNTs-PEI / CZIS Composite Membrane Materials

[0079] Referring to the emulsion separation conditions in Example 2, to evaluate the actual performance of the CNTs-PEI / CZIS composite membrane prepared in Example 1, the separation performance tests were also carried out on other emulsions. The separation results of different water-in-oil emulsions are as Figure 6 shown (the separation flux is a bar graph, and the separation efficiency is a dotted line graph), including D / W emulsion, H / W emulsion, T / W emulsion, So / W emulsion, Si / W emulsion. The separation fluxes are 2150 ± 69, 4880 ± 450, 6470 ± 500, 4130 ± 310, and 2380 ± 100 L m -2 h -1 bar -1 , and the separation efficiencies are 98.5 ± 0.5%, 96.4 ± 0.6%, 99.7 ± 0.3%, 97.6 ± 0.4%, and 97.4 ± 0.6%, respectively. This indicates that the CNTs-PEI / CZIS composite membrane has good practical applicability, can separate a variety of emulsions and all show high separation efficiency, further demonstrating its excellent hydrophilic and oleophobic properties.

Claims

1. Application of a carbon-based self-cleaning membrane material for efficient separation of oil-water emulsions in membrane separation of oil-water emulsions, characterized in that The method for preparing the carbon-based self-cleaning membrane material comprises the following steps: Step 1: The carbon nanotubes CNTs are heated and acidified in a mixed solution of concentrated H2SO4 / concentrated HNO3, and then the supernatant is removed by standing, and the lower layer product is washed with distilled water until it is neutral, and dried to obtain acidified carbon nanotubes CNTs-COOH; Step 2: The acidified carbon nanotubes CNTs-COOH obtained in step 1 are ultrasonically dispersed in water together with polyethyleneimine PEI, and then centrifuged, washed, and dried in sequence to obtain PEI-functionalized CNTs, which are recorded as CNTs-PEI; Step 3: dispersing the CNTs-PEI obtained in step 2 with water to obtain a dispersion, filtering the dispersion onto a hydrophilic polyvinylidene fluoride (PVDF) membrane to obtain a CNTs-PEI membrane; Step 4: Disperse Cu-ZnIn2S4 with water to obtain a dispersion, and filter the dispersion onto the CNTs-PEI membrane obtained in step 3 to obtain a CNTs-PEI / Cu-ZnIn2S4 composite membrane, and the preparation is completed; Step 1: During the heating and acidification of carbon nanotubes CNTs, the volume ratio of concentrated H2SO4 solution to concentrated HNO3 solution is 1-4:1, the mass fraction of concentrated H2SO4 solution is 95-98%, and the mass fraction of concentrated HNO3 solution is 65-70%; the temperature of the heating and acidification treatment is 60-80 °C, and the time is 0.5-2 h; The ultrasonic dispersion time in step 2 is 0.5-2 h; In step 2, the dispersion concentrations of the acidified carbon nanotubes CNTs-COOH and polyethyleneimine PEI in water are 0.08-0.12 g / L and 0.5-1.0 g / L, respectively; After the membrane separation is completed, the following regeneration treatment step is also included: after washing with alcohol and water alternately for 2-4 times to remove part of the oil component, the membrane is irradiated with visible light.

2. The application of a carbon-based self-cleaning membrane material for separating oil-water emulsions efficiently as claimed in claim 1 in membrane separation of oil-water emulsions, characterized in that The preparation method of Cu-ZnIn2S4 comprises the following steps: S1: Dissolve zinc salt, indium salt and sulfur source in ultrapure water, adjust the pH value of the mixed solution to acidic, transfer the mixed solution to a hydrothermal reactor, seal the hydrothermal reactor and place it in an oven for reaction; after the reaction is completed, wait for the reactor to cool to room temperature, centrifuge, wash and dry the precipitate to obtain the sulfur-indium-zinc composite material ZnIn2S4; S2: Ultrasonic dispersion of the sulfur-indium-zinc composite material ZnIn2S4 obtained in step S1 in ultrapure water and mixing with a copper salt solution; injecting a reducing solution under magnetic stirring and light irradiation to perform a photodeposition reaction for 5-180 min to obtain Cu-ZnIn2S4.

3. The application of a carbon-based self-cleaning membrane material for separating oil-water emulsions efficiently as claimed in claim 2 in membrane separation of oil-water emulsions, characterized in that The zinc salt in step S1 is zinc nitrate, zinc sulfate, zinc chloride, zinc phosphate, zinc acetate, zinc citrate, zinc isooctanoate or zinc glycinate, the indium salt is indium nitrate, indium sulfate, indium chloride, indium phosphate, indium acetate or indium citrate, and the sulfur source is thioacetamide, thiourea, ammonium sulfide or sodium thiosulfate; the molar ratio of the zinc salt, indium salt and sulfur source is 2-3:4-6:8-12; the reaction temperature in step S1 is 140-180°C, and the reaction time is 10-20 h.

4. The use of a carbon-based self-cleaning membrane material for efficiently separating oil-water emulsions as claimed in claim 2 in membrane separation of oil-water emulsions, characterized in that In step S2, the copper salt is copper nitrate, copper chloride, copper phosphate, copper acetate or ethylenediaminetetraacetic acid copper sodium salt, and the mass ratio of copper to indium zinc sulfide material is 0.1-2:10; The reducing solution in step S2 is an aqueous solution of hydrazine, sodium borohydride, potassium borohydride, ethanol, ammonia water or sodium sulfite, the concentration of the reducing solution is 0.01-0.6 mol / L, the molar ratio of the reducing solution to the copper salt is 3-15:1, and the injection speed of the reducing solution is 2-3 drops per second.

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