A photocatalytic self-cleaning BiOCl / COF composite film and a preparation method and application thereof

Abstract

The application relates to the field of membrane technology, in particular to a photocatalytic self-cleaning BiOCl / COF composite membrane and a preparation method and application thereof. BiOCl nanosheets and COF nanosheets with photocatalytic properties are respectively synthesized, and the two kinds of nanosheets are deposited on the surface of a polymer substrate membrane through a vacuum filtration technology. Since a large number of oxygen-containing groups in the COF nanosheets improve the dispersibility of the BiOCl nanosheets through hydrogen bond action, the disorderly stacking of the BiOCl is reduced in the stacking process. The addition of the COF assists the BiOCl nanosheets in forming interlayer channels with a screening effect, and the two kinds of nanosheets form a heterostructure, thereby enhancing the photocatalytic capacity of the composite membrane. The preparation method of the composite membrane is simple, the composite membrane has good permeability to dyes such as Evans blue, Congo red and rhodamine B, has excellent photocatalytic self-cleaning capacity, and can be applied to the separation of organic wastewater generated in the printing and dyeing industry.

Description

TECHNICAL FIELD

[0001] The application relates to the field of membrane technology, and in particular to a photocatalytic self-cleaning BiOCl / COF composite membrane and a preparation method and application thereof. BACKGROUND

[0002] Membrane separation technology has high separation efficiency and low energy consumption, and is widely applied to the field of water treatment. Membrane separation technology inevitably faces membrane pollution in a long-time filtration process. A membrane with photocatalytic self-cleaning capability can well alleviate the problem of membrane pollution, prolong the service life of the separation membrane, and photocatalysts can be loaded on the surface of the membrane through a vapor deposition method and a sol-gel method. However, the vapor deposition method has high cost and needs to use professional equipment and materials, and is prone to produce pollutants; the sol-gel method has a complicated process and high cost. Although the above two processes can prepare a separation membrane with photocatalytic self-cleaning characteristics, they have the defects of high cost, easy generation of waste and pollutants in the production process and the like. Therefore, it is necessary to develop a preparation method of a photocatalytic self-cleaning membrane which has a simple process, low cost and is environmentally friendly in the production process. SUMMARY

[0003] In order to solve the above problems, the application provides a photocatalytic self-cleaning BiOCl / COF composite membrane and a preparation method thereof. BiOCl nanosheets and COF nanosheets with photocatalytic characteristics are synthesized respectively, and the two kinds of nanosheets are deposited on the surface of a polymer substrate membrane through a vacuum filtration technology. A large number of oxygen-containing groups in the COF nanosheets improve the dispersibility of the BiOCl nanosheets through hydrogen bonding, and the disorderly stacking of the BiOCl is reduced in the stacking process. The addition of the COF assists the BiOCl nanosheets to form interlayer channels with a screening effect, and the two kinds of nanosheets form a heterostructure, thereby enhancing the photocatalytic capability of the composite membrane.

[0004] The application provides a preparation method of a photocatalytic self-cleaning BiOCl / COF composite membrane, which comprises the following steps:

[0005] (1) preparing BiOCl nanosheets: mixing bismuth nitrate, polyvinylpyrrolidone and ethylene glycol, stirring, then adding a chloride salt solution into the mixed solution, performing a hydrothermal reaction, adding appropriate ultrapure water after centrifugal washing, and preparing a BiOCl nanosheet dispersion liquid;

[0006] (2) preparing COF nanosheets: dissolving 2,5-diaminobenzenesulfonic acid and tri-aldehyde-based phloroglucinol in dimethyl sulfoxide solution respectively to obtain a 2,5-diaminobenzenesulfonic acid solution and a tri-aldehyde-based phloroglucinol solution, adding the tri-aldehyde-based phloroglucinol solution into the 2,5-diaminobenzenesulfonic acid solution drop by drop under stirring to obtain a mixed solution, and stirring for a certain time to obtain a COF dispersion liquid;

[0007] (3) Preparation of BiOCl / COF composite film: take an appropriate amount of bismuth oxychloride nanosheet dispersion liquid and COF dispersion liquid, dilute with ultrapure water, ultrasonic dispersion, after ultrasonic, the obtained mixed dispersion liquid is deposited on a polymer support substrate by vacuum filtration, dried to obtain a BiOCl / COF composite film.

[0008] In an embodiment of the present application, in step (1), the chloride salt solution is one of saturated sodium chloride, potassium chloride salt solution.

[0009] In an embodiment of the present application, in step (1), the amount of bismuth nitrate, polyvinylpyrrolidone and ethylene glycol is 465-505 mg: 380-420 mg: 14-25 mL.

[0010] In an embodiment of the present application, in step (1), the concentration of bismuth oxychloride nanosheet dispersion liquid is 1-2 mg / mL.

[0011] In an embodiment of the present application, in step (1), the hydrothermal reaction time is 3-12 h, and the temperature is 160-180℃.

[0012] In an embodiment of the present application, in step (2), the molar ratio of trihydroxybenzotriol to 2,5-diaminobenzenesulfonic acid is 1:1-3.

[0013] In an embodiment of the present application, in step (2), the concentration of COF dispersion liquid is 1-1.5 mg / mL.

[0014] In an embodiment of the present application, in step (2), the mixed solution is stirred for 1-3 days.

[0015] In an embodiment of the present application, in step (3), the drying time of the film is 12-48 h.

[0016] In an embodiment of the present application, in step (3), the polymer support substrate is one of nylon film, PVDF film, PAN film, PSF film and PES film.

[0017] In an embodiment of the present application, in step (3), the mass ratio of bismuth oxychloride nanosheet to COF is 1-5: 0.05-0.25.

[0018] The present application provides a photocatalytic self-cleaning BiOCl / COF composite film prepared by the above-mentioned method.

[0019] The present application also provides the application of the above-mentioned photocatalytic self-cleaning BiOCl / COF composite film in dye / water separation.

[0020] The present application has the following advantages:

[0021] (1) The application constructs a photocatalytic self-cleaning BiOCl / COF composite membrane by vacuum filtration, and the composite membrane generates free radicals under light to degrade pollutants on the membrane surface, dredge the pore structure of the membrane, restore the flux of the membrane, and prolong the service life of the membrane.

[0022] (2) The application constructs a BiOCl / COF heterojunction by vacuum filtration, and the formation of the heterojunction improves the light absorption capacity, increases the electron transfer rate, and enhances the photocatalytic capacity.

[0023] (3) The application constructs an interlayer channel with a dye screening function by COF-assisted dispersion of BiOCl nanosheets, thereby expanding the application range of two-dimensional nanomaterials in separation membranes.

[0024] (4) The BiOCl / COF composite membrane prepared in the application has photocatalytic self-cleaning properties, and the raw materials are easy to synthesize, the film forming process is simple, and the application has certain cost advantages.

[0025] (5) The composite membrane prepared in the application has excellent permeation flux (~33.4 L·m -2 ·h -1 ·bar -1 ) and separation performance (Congo red rejection rate 97.8%), and can be used for screening Evans blue dye / water solution, Congo red dye / water solution, rhodamine B dye / water solution, etc., and can be used for treating printing and dyeing wastewater; and after light irradiation, the flux recovery rate of the membrane is significantly improved from 61.9% to 97.6%, showing excellent anti-pollution performance. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a scanning electron microscope image of the BiOCl nanosheet prepared in Example 1 of the application;

[0027] Figure 2 It is a scanning electron microscope image of the COF nanosheet prepared in Example 1 of the application;

[0028] Figure 3 It is a scanning electron microscope image of the BiOCl / COF composite membrane prepared in Example 1 of the application;

[0029] Figure 4 It is a thickness change graph of the BiOCl / COF composite membrane prepared in the application with different proportions;

[0030] Figure 5 It is a scanning electron microscope image of the BiOCl nanosheet with different hydrothermal times. DETAILED DESCRIPTION

[0031] The application will be further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate but not to limit the scope of the application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content of the application, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] The reagents used in the embodiments of the application are as follows: sodium chloride (NaCl, 99.5%) was purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., 2,5-diaminobenzenesulfonic acid, polyvinylpyrrolidone (PVP, 99.5%) were purchased from Beijing Inokai Technology Co., Ltd., bismuth nitrate pentahydrate (Bi(NO3)3·5H2O, 99%), ethylene glycol (EG, 99.5%) were purchased from Shanghai Titan Science and Technology Co., Ltd., triformylphloroglucinol (TFP, 98%) was purchased from Jilin Zhongke Research Technology Co., Ltd.

[0033] The porous support membrane used in the embodiments of the application is a polyether sulfone ultrafiltration membrane (PES, 0.2 μm) produced by Jinteng Experimental Equipment Co., Ltd.

[0034] Example 1

[0035] (1) Preparation of bismuth oxychloride nanosheets: 0.486 g of bismuth nitrate and 0.4 g of polyvinylpyrrolidone were accurately weighed and dissolved in 25 mL of ethylene glycol solution. After stirring for 30 min, 10 mL of saturated sodium chloride aqueous solution was added dropwise (1 mL / min). After stirring for another 30 min, the mixed solution was poured into the inner liner of a 50 mL reaction kettle, and hydrothermal reaction was carried out at 160℃ for 9 h. After centrifugal washing, the lower precipitate was taken and dried in an oven at 60℃ to obtain BiOCl nanosheets. The BiOCl nanosheets were dispersed in ultrapure water to obtain a bismuth oxychloride nanosheet dispersion with a concentration of 1 mg / mL.

[0036] (2) Preparation of covalent organic framework nanosheets: 8.53 mg of 2,5-diaminobenzenesulfonic acid and 6.3 mg of triformylphloroglucinol were dissolved in 5 mL of dimethyl sulfoxide solution, respectively. The triformylphloroglucinol solution was added dropwise to the 2,5-diaminobenzenesulfonic acid solution under stirring at a speed of 100 rpm. Then the mixed solution was gently stirred for 24 h to obtain a COF dispersion.

[0037] (3) Preparation of bismuth oxychloride / covalent organic framework composite membrane: 4 mL of BiOCl nanosheet dispersion with a concentration of 1 mg / mL and 0.1 mL of COF dispersion with a concentration of 1.5 mg / mL were taken, and 200 mL of ultrapure water was added to prepare a mixed dispersion. The nanosheets were deposited on the PES polymer substrate by vacuum suction filtration, and dried at 45℃ for 24 h to obtain a BiOCl / COF composite membrane.

[0038] Comparative Example 1

[0039] The COF addition amount in the step (3) is adjusted to 0, as shown in Table 1, and the rest of the implementation conditions are as in Example 1.

[0040] Examples 2-5

[0041] The COF addition amount in the step (3) is adjusted to 0.05, 0.1, 0.2, and 0.25 mg, respectively, as shown in Table 1, and the rest of the implementation conditions are as in Example 1.

[0042] Test Example 1

[0043] The photocatalytic self-cleaning BiOCl / COF composite membranes prepared in Examples 1-5 and Comparative Example 1 are tested for permeation flux and retention rate by a dead-end filtration device. The specific test procedure is as follows: the test membrane is placed in the dead-end filtration device, and an ultrapure water solution is added to the device. A pressure of 2 bar is used for pre-pressing for 1 h. After the permeation flux of the membrane is stabilized, a pressure of 1 bar is used to test the permeation flux of the membrane. Then, a 50 ppm dye solution is added to the dead-end device. After 10 mL of the solution permeates (to avoid the adsorption of the membrane), an appropriate amount of the permeate is taken, and the change in absorbance of the solution is tested by a UV-visible spectrophotometer, so as to calculate the retention rate. The results are shown in Table 1.

[0044] Table 1 Permeation flux and Congo red retention rate of photocatalytic self-cleaning BiOCl / COF composite membranes prepared in Examples 1-5 and Comparative Example 1

[0045]

[0046] As can be seen from the data in Table 1, as the relative addition ratio of COF increases, the interlayer channel of the separation membrane becomes increasingly regular. As shown in Table 1, as the loading amount of COF increases, the thickness of the composite membrane does not increase but decreases, which also confirms the ordered assembly of nanosheets. The retention rate of the composite membrane for Congo red / water solution gradually increases, and according to the limitation of the trade-off effect, the permeation flux of the separation membrane gradually decreases. Figure 4

[0047] Examples 6-9

[0048] The BiOCl addition amount in step (1) is adjusted, as shown in Table 2, and the rest of the implementation conditions are as in Example 1.

[0049] Test Example 2

[0050] The photocatalytic self-cleaning BiOCl / COF composite membranes prepared in Examples 6-9 are tested. The results are shown in Table 2.

[0051] Table 2 Permeation flux and Congo red retention rate of photocatalytic self-cleaning BiOCl / COF composite membranes prepared in Examples 6-9

[0052] ​

[0053]

[0054] From the data in Table 2, it can be seen that as the BiOCl addition amount increases, the regularity of the interlayer channel of the separation membrane becomes higher, which gives the membrane gradually increasing dye rejection rate, however, due to the limitation of trade-off effect, the permeation flux of the separation membrane shows a downward trend.

[0055] Examples 10-12

[0056] Adjust the hydrothermal time of BiOCl in step (1) (as shown in Table 3), and the rest of the implementation conditions are as in Example 1.

[0057] Test Example 3

[0058] The photocatalytic self-cleaning BiOCl / COF composite membranes prepared in Examples 10-12 were tested. The results are shown in Table 3.

[0059] Table 3 Permeation flux and Congo red rejection rate of photocatalytic self-cleaning BiOCl / COF composite membranes prepared in Examples 10-12

[0060]

[0061] From the data in Table 3, it can be seen that as the hydrothermal time of BiOCl nanosheets increases, the permeation flux of the corresponding membrane gradually increases, and the rejection rate shows a downward trend. It is speculated that the reason may be that the size of BiOCl nanosheets becomes larger due to the extension of the hydrothermal time. Since BiOCl nanosheets have poor dispersibility in water, an excessively large sheet size is not conducive to the dispersion of COF nanosheets through hydrogen bonding. The stacking of nanosheets is no longer ordered, and the disordered stacking during assembly increases the permeation flux of the membrane, and correspondingly reduces the rejection rate of the membrane.

[0062] Take the photocatalytic self-cleaning membrane prepared in Example 1, and change the cleaning conditions after membrane fouling.

[0063] The photocatalytic self-cleaning BiOCl / COF composite membrane prepared in Example 1 was tested for self-cleaning performance. In three cycles of experiments, first, the membrane was tested for pure water flux for 0.5 h, then the simulated pollutant (soybean oil) was added, and the membrane was tested for flux for 1 h, the membrane surface was irradiated for 2 h, and then the pure water flux was tested for 0.5 h, and the process was repeated three times. The results are shown in Table 4.

[0064] Table 4 Long-term emulsion flux changes of different membrane samples prepared in Example 1

[0065]

[0066]

[0067] Due to the introduction of BiOCl and COF nanosheets with photocatalytic function on the surface of the membrane, the flux recovery rate of the membrane is significantly improved from 61.9% to 97.6% after light irradiation, showing excellent anti-pollution performance.

[0068] Comparative Example 2

[0069] Omit BiOCl in step (3), and the rest of the implementation conditions are as in Example 1, to prepare a pure COF membrane.

[0070] BiOCl membranes, COF membranes, and BiOCl / COF membranes with the same loading amount were respectively prepared for testing, and the results are shown in Table 5.

[0071] Table 5 Permeation flux and Congo red rejection rate of the photocatalytic self-cleaning BiOCl / COF composite membrane prepared in Comparative Example 2

[0072]

[0073] As can be seen from the data in Table 5, a single BiOCl membrane or COF membrane exhibits poor rejection rate or excessively low permeation flux, while a small amount of COF nanosheets is incorporated into the BiOCl dispersion to assist in dispersing the BiOCl nanosheets, making the bismuth oxychloride stack more orderly, forming complete screening channels, and compared with the pure COF membrane, the composite membrane exhibits good permeability.

[0074] The above provided examples are not intended to limit the scope covered by the present application, and the described steps are not intended to limit the execution order. Those skilled in the art can make obvious improvements to the present application in combination with existing common knowledge, which also falls within the protection scope defined by the claims of the present application.

Claims

1. A method for preparing a photocatalytically self-cleaning bismuth oxychloride / covalent organic framework composite membrane, characterized in that, Includes the following steps: (1) Bismuth nitrate, polyvinylpyrrolidone and ethylene glycol were mixed, and chloride salt solution was added to carry out hydrothermal reaction. After centrifugation and washing, ultrapure water was added to obtain bismuth oxychloride nanosheet dispersion. (2) Dissolve 2,5-diaminobenzenesulfonic acid and trialdehyde phloroglucinol in dimethyl sulfoxide solution to obtain 2,5-diaminobenzenesulfonic acid solution and trialdehyde phloroglucinol solution respectively. Add the trialdehyde phloroglucinol solution dropwise to the 2,5-diaminobenzenesulfonic acid solution to obtain a mixed solution and stir for a certain time to obtain COF dispersion. (3) Take bismuth oxychloride nanosheet dispersion and COF dispersion, add ultrapure water, sonicate, and then deposit the resulting mixed dispersion on the polymer support substrate by vacuum filtration and drying to obtain BiOCl / COF composite membrane.

2. The method for preparing a photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite film according to claim 1, characterized in that, In step (1), the chloride salt solution is either a saturated sodium chloride or potassium chloride solution; the hydrothermal reaction time is 3 to 12 hours and the temperature is 160 to 180°C.

3. The method for preparing a photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite film according to claim 1, characterized in that, In step (1), the amounts of bismuth nitrate, polyvinylpyrrolidone, and ethylene glycol are 465–505 mg: 380–420 mg: 14–25 mL.

4. The method for preparing a photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite film according to claim 1, characterized in that, In step (1), the concentration of the bismuth oxychloride nanosheet dispersion is 1-2 mg / mL.

5. The method for preparing a photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite membrane according to claim 1, characterized in that, In step (2), the concentration of the COF dispersion is 1 to 1.5 mg / mL.

6. The method for preparing a photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite film according to claim 1, characterized in that, In step (2), the molar ratio of trialdehyde phloroglucinol to 2,5-diaminobenzenesulfonic acid is 1:1 to 3.

7. The method for preparing a photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite membrane according to claim 1, characterized in that, In step (3), the mass ratio of bismuth oxychloride nanosheets to COF is 1-5:0.05-0.

25.

8. The method for preparing a photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite film according to claim 1, characterized in that, In step (3), the polymer support substrate is one of nylon film, PVDF film, PAN film, PSF film, and PES film.

9. The photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite membrane prepared by the method according to any one of claims 1 to 8.

10. The application of the photocatalytic self-cleaning bismuth oxychloride / covalent organic framework composite membrane according to claim 9 in the field of dye separation.

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