A vermiculite-polyvinyl alcohol composite film and its preparation method and application

Abstract

The present invention discloses a vermiculite-polyvinyl alcohol composite film and its preparation method and application. The composition of the vermiculite-polyvinyl alcohol composite film of the present invention includes a laminated porous base film and a vermiculite-polyvinyl alcohol composite layer, and the composition of the vermiculite-polyvinyl alcohol composite layer includes vermiculite nanosheets and polyvinyl alcohol attached to the surface of the vermiculite nanosheets. The preparation method of the vermiculite-polyvinyl alcohol composite film of the present invention comprises the following steps: vermiculite nanosheets and polyvinyl alcohol are dispersed in a solvent to prepare a coating liquid, which is then applied to the surface of the porous base film and dried to obtain the vermiculite-polyvinyl alcohol composite film. The vermiculite-polyvinyl alcohol composite film of the present invention has the advantages of high selectivity for lithium ions and sodium ions, good mechanical properties and stability, and can be reused many times, and its preparation method is simple, energy consumption is low, cost is low, and applicability is wide, and it is suitable for large-scale industrial application.

Description

Technical Field

[0001] The present invention relates to the technical field of ion separation, and in particular to a vermiculite-polyvinyl alcohol composite membrane and a preparation method and application thereof. Background Art

[0002] Membrane separation technology is a separation technology that has rapidly emerged since the 1960s and has the functions of separation, concentration, purification and refinement. It has the advantages of high efficiency, energy saving, environmental protection, molecular-level filtration, simple and easy control of filtration process, etc. It is widely used in food, medicine, biology, environmental protection, chemical industry, metallurgy, energy, petroleum, water treatment, bionics, electronics and other fields, generating huge economic and social benefits, and has become one of the most important means in separation science today.

[0003] In recent years, porous membranes with ultrafast ion permeability and high ion selectivity have been widely used in fields such as mineral separation and water purification, achieving relatively promising results. However, existing porous membranes generally have low selectivity for lithium and sodium ions, poor stability, and a short service life. This significantly limits their application and makes it difficult to fully meet the growing demand for practical applications.

[0004] Therefore, it is of great significance to develop a porous membrane with high selectivity for lithium ions and sodium ions, good mechanical properties and stability, and can be reused multiple times. Summary of the Invention

[0005] The purpose of the present invention is to provide a vermiculite-polyvinyl alcohol composite film and a preparation method and application thereof.

[0006] The technical solution adopted by the present invention is:

[0007] A vermiculite-polyvinyl alcohol composite film comprises a laminated porous base film and a vermiculite-polyvinyl alcohol composite layer; the vermiculite-polyvinyl alcohol composite layer comprises vermiculite nanosheets and polyvinyl alcohol attached to the surface of the vermiculite nanosheets.

[0008] Preferably, the porous base membrane is one of nylon organic filter membrane, mixed cellulose ester membrane, polypropylene porous membrane, polyethersulfone porous membrane, porous ceramic membrane, and hollow fiber membrane.

[0009] Further preferably, the porous base membrane is a nylon organic filter membrane.

[0010] Preferably, the pores on the porous base membrane have a pore diameter of 100 nm to 600 nm.

[0011] Preferably, the mass ratio of vermiculite nanosheets to polyvinyl alcohol in the vermiculite-polyvinyl alcohol composite layer is 5:1-6.

[0012] More preferably, the mass ratio of vermiculite nanosheets to polyvinyl alcohol in the vermiculite-polyvinyl alcohol composite layer is 5:2-6.

[0013] More preferably, the mass ratio of vermiculite nanosheets to polyvinyl alcohol in the vermiculite-polyvinyl alcohol composite layer is 5:3-5.

[0014] Preferably, the vermiculite nanosheets have a diameter of 0.1 μm to 20 μm.

[0015] More preferably, the vermiculite nanosheets have a sheet diameter of 8 μm to 15 μm.

[0016] Preferably, the vermiculite nanosheets are prepared by the following method: dispersing vermiculite in a saturated sodium chloride solution, condensing and refluxing at 110°C to 130°C for 20h to 30h, filtering, repeatedly rinsing the filtered solid with water and ethanol, and then dispersing it in a lithium chloride solution, condensing and refluxing at 110°C to 130°C for 20h to 30h, filtering, repeatedly rinsing the filtered solid with water and ethanol, and then dispersing it in water and centrifuging to obtain a precipitate to obtain vermiculite nanosheets (Reference: Shao J, Raidongia K, Koltonow AR, et al. Self-assembled two-dimensional nanofluidic proton channels with high thermal stability[J]. NATURE COMMUNICATIONS. 2015, 6).

[0017] Preferably, the viscosity of the polyvinyl alcohol is 5.2 mPa·s to 6.0 mPa·s, and the alcoholysis degree is 98.0 mol% to 99.0 mol%.

[0018] A method for preparing the above-mentioned vermiculite-polyvinyl alcohol composite membrane comprises the following steps: dispersing vermiculite nanosheets and polyvinyl alcohol in a solvent to prepare a coating solution, coating the solution on the surface of a porous base membrane, and drying the solution to obtain the vermiculite-polyvinyl alcohol composite membrane.

[0019] Preferably, a method for preparing the vermiculite-polyvinyl alcohol composite membrane as described above comprises the following steps: mixing a vermiculite nanosheet dispersion and a polyvinyl alcohol dispersion, stirring and dispersing the mixture and ultrasonically dispersing the mixture to prepare a coating liquid, which is then coated on the surface of a porous base membrane and dried to obtain a vermiculite-polyvinyl alcohol composite membrane.

[0020] Preferably, the stirring and dispersing is carried out at room temperature (15° C. to 25° C.), with a stirring speed of 100 rpm to 6000 rpm and a stirring time of 25 min to 35 min.

[0021] Preferably, the ultrasonic dispersion is carried out under the conditions of an ultrasonic power of 10W to 50W and an ultrasonic frequency of 50 Hz, and the ultrasonic dispersion time is 5 minutes to 30 minutes.

[0022] Preferably, the coating method is one of suction filtration, scraping, spraying and spin coating.

[0023] Preferably, the drying method is one of natural drying, forced air drying, vacuum drying and desiccant drying.

[0024] More preferably, the drying method is vacuum drying.

[0025] Preferably, the vacuum drying is carried out at 120° C. to 200° C., and the drying time is 24 h to 96 h.

[0026] Application of the above-mentioned vermiculite-polyvinyl alcohol composite membrane for selective separation of lithium ions and sodium ions.

[0027] The beneficial effects of the present invention are: the vermiculite-polyvinyl alcohol composite membrane of the present invention has the advantages of high selectivity for lithium ions and sodium ions, good mechanical properties and stability, and can be reused multiple times. In addition, its preparation method is simple, energy consumption is low, cost is low, and applicability is wide, and it is suitable for large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 3 is a scanning electron microscope image of the vermiculite nanosheets in the embodiment.

[0029] Figure 2 3 is a scanning electron microscope image of the surface of the vermiculite-polyvinyl alcohol composite film with a mass ratio of vermiculite nanosheets to polyvinyl alcohol of 5:5 in the embodiment.

[0030] Figure 3 3 is a scanning electron microscope image of a cross section of a vermiculite-polyvinyl alcohol composite film having a mass ratio of vermiculite nanosheets to polyvinyl alcohol of 5:5 in the embodiment.

[0031] Figure 4 This is a graph showing the test results of the permeability of the nylon organic filter membrane in the comparative example to lithium ions and sodium ions.

[0032] Figure 5 1 is a graph showing the test results of the lithium ion permeability of vermiculite-polyvinyl alcohol composite membranes with different vermiculite nanosheets and polyvinyl alcohol mass ratios in the examples.

[0033] Figure 6 1 is a graph showing the test results of the sodium ion permeability of vermiculite-polyvinyl alcohol composite membranes with different vermiculite nanosheets and polyvinyl alcohol mass ratios in the examples.

[0034] Figure 7Graph showing the selectivity test results of vermiculite-polyvinyl alcohol composite membranes with different vermiculite nanosheet and polyvinyl alcohol mass ratios in the examples. DETAILED DESCRIPTION

[0035] The present invention will be further explained and illustrated below with reference to specific embodiments.

[0036] Example:

[0037] A vermiculite-polyvinyl alcohol composite film, the preparation method of which comprises the following steps:

[0038] 1) 2 g of vermiculite (sheet diameter of 1 mm to 5 mm) was added to 200 mL of saturated sodium chloride solution, condensed and refluxed at 120 ° C for 24 h, filtered, and the filtered solid was repeatedly rinsed with water and ethanol and dispersed in a lithium chloride solution prepared by 84.78 g of lithium chloride and 200 mL of deionized water, condensed and refluxed at 120 ° C for 24 h, filtered, and the filtered solid was repeatedly rinsed with water and ethanol, dispersed in deionized water and centrifuged at a speed of 8000 rpm for 30 min. The precipitate was taken to obtain vermiculite nanosheets (SEM image as shown in FIG). Figure 1 As shown, single-layer structure, sheet diameter is 8μm to 15μm);

[0039] 2) adding 200 mg of vermiculite nanosheets to 100 mL of deionized water and ultrasonically dispersing the mixture for 12 h at a power of 30 W, a frequency of 50 Hz, and a dispersion time of 15 min to obtain a 2 mg / mL dispersion of vermiculite nanosheets. Furthermore, adding 2 g of polyvinyl alcohol (viscosity of 5.2 mPa·s to 6.0 mPa·s and a degree of alcoholysis of 98.0% mol% to 99.0% mol%) to 400 mL of deionized water and stirring and dispersing the mixture at 95° C. for 2 h to obtain a 5 mg / mL dispersion of polyvinyl alcohol.

[0040] 3) adding 5 mL of the vermiculite nanosheet dispersion and 2 mL of the polyvinyl alcohol dispersion into 50 mL of deionized water, stirring and dispersing at room temperature for 30 min at a stirring speed of 2000 rpm, and then ultrasonically dispersing for 10 min at an ultrasonic power of 30 W and an ultrasonic frequency of 50 Hz to obtain a coating solution;

[0041] 4) Pour the coating liquid onto the surface of a nylon organic filter membrane (pore size is 200 nm), filter it, and then vacuum dry it at 120°C for 24 hours to obtain a vermiculite-polyvinyl alcohol composite membrane (surface scanning electron microscopy image as shown in FIG. Figure 2 The cross-sectional SEM images are shown in Figure 3 As shown, the vermiculite-polyvinyl alcohol composite film presents a layered structure, the thickness of the composite film is about 3 μm, and the mass ratio of vermiculite nanosheets and polyvinyl alcohol in the vermiculite-polyvinyl alcohol composite layer is 5:5);

[0042] 5) Vermiculite-polyvinyl alcohol composite films with a mass ratio of vermiculite nanosheets to polyvinyl alcohol of 5:1, 5:2, 5:3, 5:4 and 5:6 were prepared respectively by referring to the methods of steps 1) to 4).

[0043] Comparative Example:

[0044] Nylon organic filter membrane (pore size is 200 nm, same as in the embodiment).

[0045] Performance testing:

[0046] 1) The ion permeability test of the nylon organic filter membrane (i.e., blank substrate) in the comparative example was performed using a LiCl solution with a concentration of 0.2 mol / L and a NaCl solution with a concentration of 0.2 mol / L. At the same time, a conductivity meter was used to collect data and calculate the permeation rates of lithium ions and sodium ions. The permeability test results of the nylon organic filter membrane for lithium ions and sodium ions are shown as follows: Figure 4 shown.

[0047] Depend on Figure 4 It can be seen that both lithium ions and sodium ions can quickly permeate through the nylon organic filter membrane, and the difference in their permeation rates is very small, indicating that the nylon organic filter membrane has poor selectivity for lithium ions and sodium ions.

[0048] 2) adopting the LiCl solution with a concentration of 0.2mol / L and the NaCl solution with a concentration of 0.2mol / L to carry out ion permeability test on the vermiculite-polyvinyl alcohol composite membranes with different vermiculite nanosheets and polyvinyl alcohol mass ratios in the embodiment, and collecting data with a conductivity meter at the same time, calculating the permeation rate of lithium ions and sodium ions and the selectivity of the composite membrane (permeation rate of selectivity=permeation rate of lithium ions / permeation rate of sodium ions). The permeability test results of the vermiculite-polyvinyl alcohol composite membranes with different vermiculite nanosheets and polyvinyl alcohol mass ratios to lithium ions are as follows: Figure 5 As shown in the figure, the test results of sodium ion permeability are as follows Figure 6 As shown, the selective test results are as follows Figure 7 shown.

[0049] Depend on Figures 5-7 It can be seen that the lithium ion permeability of the vermiculite-polyvinyl alcohol composite membrane is much higher than that of the sodium ion, and with the increase of the polyvinyl alcohol doping ratio, the selectivity shows a trend of first increasing and then decreasing. When the mass ratio of vermiculite nanosheets to polyvinyl alcohol is 5:4, the selectivity reaches the maximum value, indicating that the vermiculite-polyvinyl alcohol composite membrane of the present invention has high selectivity for lithium ions and sodium ions.

[0050] 3) The test found that: the vermiculite-polyvinyl alcohol composite membranes with different vermiculite nanosheets and polyvinyl alcohol mass ratios in the examples did not change significantly after being immersed in deionized water at room temperature for 2 months; the vermiculite-polyvinyl alcohol composite membranes with different vermiculite nanosheets and polyvinyl alcohol mass ratios in the examples were used to selectively separate lithium ions and sodium ions. After repeated use 10 times, the selectivity of the vermiculite-polyvinyl alcohol composite membrane for lithium ions and sodium ions did not show a significant decrease.

[0051] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A vermiculite-polyvinyl alcohol composite film, characterized in that: The composition includes a laminated porous base film and a vermiculite-polyvinyl alcohol composite layer; the vermiculite-polyvinyl alcohol composite layer includes vermiculite nanosheets and polyvinyl alcohol attached to the surface of the vermiculite nanosheets; the pores on the porous base film have a pore diameter of 100nm to 600nm; the mass ratio of vermiculite nanosheets to polyvinyl alcohol in the vermiculite-polyvinyl alcohol composite layer is 5:1 to 6; and the diameter of the vermiculite nanosheets is 0.1μm to 20μm.

2. The vermiculite-polyvinyl alcohol composite film according to claim 1, characterized in that: The porous base membrane is one of a nylon organic filter membrane, a mixed cellulose ester membrane, a polypropylene porous membrane, a polyethersulfone porous membrane, a porous ceramic membrane, and a hollow fiber membrane.

3. The vermiculite-polyvinyl alcohol composite film according to claim 1 or 2, characterized in that: The viscosity of the polyvinyl alcohol is 5.2 mPa·s to 6.0 mPa·s, and the alcoholysis degree is 98.0 mol% to 99.0 mol%.

4. A method for preparing a vermiculite-polyvinyl alcohol composite film according to any one of claims 1 to 3, characterized in that: The following steps are involved: Vermiculite nanosheets and polyvinyl alcohol are dispersed in a solvent to prepare a coating liquid, which is then coated on the surface of a porous base film and dried to obtain a vermiculite-polyvinyl alcohol composite film.

5. The preparation method according to claim 4, characterized in that: The coating method is one of suction filtration, scraping, spraying and spin coating.

6. The preparation method according to claim 4 or 5, characterized in that: The drying method is one of natural drying, forced air drying, vacuum drying and desiccant drying.

7. Use of the vermiculite-polyvinyl alcohol composite membrane according to any one of claims 1 to 3 for selective separation of lithium ions and sodium ions.

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