Preparation method of PVDF super-hydrophobic composite membrane
By coating the PVDF membrane surface with ZIF-8@MWCNT composite material and modifying it with FOTS, the problem of insufficient anti-wetting and anti-fouling properties of PVDF membranes during membrane distillation was solved, thereby improving the membrane's stability and permeation performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-05-03
- Publication Date
- 2026-04-07
AI Technical Summary
Existing PVDF membranes have shortcomings in terms of anti-wetting, anti-fouling, thermal stability, and high permeate flux during membrane distillation, which affect membrane separation efficiency.
By coating the surface of a PVDF membrane with ZIF-8@MWCNT composite material and modifying it with FOTS, a superhydrophobic layer is constructed to improve the hydrophobicity and stability of the membrane.
The superhydrophobicity of the PVDF membrane was achieved, which improved the membrane's antifouling and antiwetting properties, enhanced its thermal and chemical stability, and maintained high permeation flux and salt rejection rate.
Smart Images
Figure CN116422154B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the fields of membrane distillation and PVDF membrane composite technology, and particularly relates to a preparation method of a PVDF super-hydrophobic composite membrane. BACKGROUND
[0002] Membrane distillation (MD) is a heat-based membrane separation process that combines the advantages of both membrane separation and thermal distillation, in which a hydrophobic microporous membrane separates the feed liquid from the permeate liquid with a lower temperature, and the driving force for mass transfer in MD is not an applied pressure difference, concentration gradient or electric potential gradient, but a water vapor pressure difference caused by a temperature gradient across the membrane.
[0003] Membrane material as a microporous physical barrier is a crucial factor affecting the efficiency of MD. An ideal MD membrane must have excellent anti-wetting, anti-fouling, thermal stability and high permeation flux. Membrane wetting occurs during continuous MD operation, and better anti-wetting requires the membrane to have higher hydrophobicity and smaller pores with more uniform distribution. In addition, the MD membrane should have good chemical stability to cope with elevated operating temperatures and chemical cleaning. The above-mentioned related properties of the existing polyvinylidene difluoride (PVDF) membrane need to be further enhanced. Surface roughness and surface free energy are two key factors affecting the hydrophobicity of the PVDF membrane. A layer of ZIF-8@MWCNT composite material with functional groups is directly coated on the surface of the PVDF membrane through surface coating modification to achieve the purpose of super-hydrophobic modification of the PVDF membrane. SUMMARY
[0004] In view of the above problems existing in the prior art, the purpose of the application is to provide a preparation method of a PVDF super-hydrophobic composite membrane.
[0005] To achieve the above purpose, the application adopts the following technical scheme:
[0006] A preparation method of a PVDF super-hydrophobic composite membrane comprises the following steps:
[0007] 1) Synthesizing ZIF-8@MWCNT composite material;
[0008] 2) Dissolving ZIF-8@MWCNT and PVDF powder in ethanol;
[0009] 3) After ultrasonic treatment of the solution, the PVDF membrane is immersed in the solution, and then dried;
[0010] 4) The dried PVDF membrane obtained in step 3) is sealed with a silane coupling agent 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) in the same vessel for vaporization to obtain a modified PVDF super-hydrophobic composite membrane.
[0011] Preferably, in step 1), the ZIF-8@MWCNT composite material is synthesized, specifically including the following steps:
[0012] s1, carboxylated multi-walled carbon nanotubes (MWCNT) are ultrasonically dispersed in methanol, 2-methyl imidazole is added, and stirring and ultrasonic treatment are continued;
[0013] s2, a methanol solution of Zn(NO3)2·6H2O is added to the solution obtained in s1 under stirring, and after uniform mixing, centrifugation, washing and drying, a black solid is obtained.
[0014] Preferably, in step 2), the mass-volume ratio of ZIF-8@MWCNT and PVDF powder to ethanol solution is 0.01:30, and the unit of mass-volume ratio is gmL -1 .
[0015] Preferably, in step 3), the ultrasonic treatment time is 1h, the drying temperature is 70℃, and the drying time is 30min.
[0016] Preferably, in step 4), the vaporization temperature is 70℃, and the vaporization time is 8h.
[0017] Preferably, in s1, the mass-volume ratio of MWCNT to methanol is 0.12:30, and the mass-volume ratio of added 2-methyl imidazole to MWCNT is 10.6:1-11:1.
[0018] Preferably, in s2, the mass-volume ratio of Zn(NO3)2·6H2O to methanol is 0.55:30-0.62:30.
[0019] Compared with the prior art, the present application has the following beneficial effects:
[0020] The application prepares ZIF-8@MWCNT composite material by in-situ growth method, wherein the carboxylated multi-walled carbon nanotube (MWCNT) provides nucleation sites for the growth of ZIF-8, is conducive to the fixation, growth and distribution of ZIF-8 on the MWCNT, further improves the dispersity of ZIF-8 nanoparticles in the solvent ethanol, and effectively avoids the aggregation of ZIF-8 on the PVDF membrane. Then the ZIF-8@MWCNT is mixed with a PVDF binder to be coated on the PVDF membrane, and 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (FOTS) is used to fluorinate the PVDF membrane to reduce the surface energy thereof. A ZIF-8@MWCNT super-hydrophobic layer is successfully constructed on the surface of the PVDF membrane, and the obtained ZIF-8@MWCNT / PVDF super-hydrophobic composite membrane has excellent anti-pollution and anti-wetting performance, good thermal stability and chemical stability, and has a high salt rejection rate and a high permeation flux. BRIEF DESCRIPTION OF DRAWINGS
[0021] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, when read in conjunction with the accompanying drawings:
[0022] Figure 1 (a) and 1(d) are SEM and TEM images of ZIF-8; Figure 1 (b) and 1(e) are SEM images of MWCNT; Figure 1 (c) and 1(f) are SEM images of ZIF-8@MWCNT.
[0023] Figure 2 FTIR spectra of MWCNT, ZIF-8 and ZIF-8@MWCNT.
[0024] Figure 3 PXRD patterns of MWCNT, ZIF-8 and ZIF-8@MWCNT.
[0025] Figure 4 a is the XPS spectrum of ZIF-8@MWCNT; Figure 4 (b)-4(e) are respectively the Zn2p, C1s, N1s and O1s energy spectrum of ZIF-8@MWCNT.
[0026] Figure 5 Thermogravimetric analysis curves of ZIF-8 and ZIF-8@MWCNT.
[0027] Figure 6The figure of UV absorption intensity of ZIF-8 and ZIF-8@MWCNT with time (insert: the photo of ZIF-8 and ZIF-8@MWCNT dispersion with time).
[0028] Figure 7 (a) and (b) are SEM images of the surface of PVDF membrane; Figure 7 (c) and (d) are SEM images of the surface of ZIF-8@MWCNT / PVDF membrane.
[0029] Figure 8 The figure of FTIR spectra of PVDF membrane and ZIF-8@MWCNT / PVDF superhydrophobic composite membrane.
[0030] Figure 9 The figure of CA of PVDF membrane and ZIF-8@MWCNT / PVDF superhydrophobic composite membrane.
[0031] Figure 10 (a) is the mechanical stability of ZIF-8@MWCNT / PVDF superhydrophobic composite membrane; Figure 10 (b) is the thermal stability of ZIF-8@MWCNT / PVDF superhydrophobic composite membrane; Figure 10 (c) is the acid and alkali stability of ZIF-8@MWCNT / PVDF superhydrophobic composite membrane.
[0032] Figure 11 (a) is the water flux of ZIF-8@MWCNT / PVDF superhydrophobic composite membrane in anti-pollution research; Figure 11 (b) is the average flux and salt rejection rate of ZIF-8@MWCNT / PVDF superhydrophobic composite membrane.
[0033] Figure 12 (a) and (b) are optical photos and surface scanning electron microscope images of PVDF membrane after anti-pollution experiment, respectively; Figure 12 (c) and (d) are optical photos and surface scanning electron microscope images of ZIF-8@MWCNT / PVDF superhydrophobic composite membrane after anti-pollution experiment, respectively.
[0034] Figure 13 The figure of water flux of ZIF-8@MWCNT / PVDF membrane and the conductivity of permeate in anti-wetting research process.
[0035] Figure 14 (a) is the water flux of ZIF-8@MWCNT / PVDF membrane in long-term performance test; Figure 14 (b) is the conductivity of permeate. DETAILED DESCRIPTION
[0036] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.
[0037] Example 1
[0038] A method for preparing a PVDF superhydrophobic composite membrane includes the following steps:
[0039] 1) Synthesize ZIF-8@MWCNT composite material, including the following steps:
[0040] s1. Disperse 0.1200g MWCNT in 30mL methanol by ultrasonication, add 1.2978g 2-methylimidazole, stir for 15min, and continue ultrasonication for 15min.
[0041] s2. Add 30 mL of methanol solution containing 0.5866 g Zn(NO3)2·6H2O to the solution obtained in s1 under stirring, and continue stirring at room temperature for 1 h; centrifuge the resulting mixed solution at 8000 rpm for 10 min, then repeat the centrifugation and washing three times with 10 mL of methanol, and dry at 100℃ for 12 h to obtain black solid ZIF-8@MWCNT.
[0042] To compare the performance of ZIF-8@MWCNT composite materials and ZIF-8 nanomaterials, ZIF-8 nanomaterials were synthesized: 1.2978 g of 2-methylimidazole and 0.5866 g of Zn(NO3)2·6H2O were dissolved in 30 mL of methanol solution respectively. The Zn(NO3)2·6H2O methanol solution was poured into the 2-methylimidazole methanol solution while stirring, and stirring was continued for 1 h to obtain a white turbid solution. The white turbid solution was centrifuged at 8000 rpm for 10 min, washed three times with 10 mL of methanol, and dried at 100 °C for 12 h to obtain white solid ZIF-8 nanomaterials.
[0043] The ZIF-8 and ZIF-8@MWCNT obtained in step 1) were structurally characterized and analyzed:
[0044] The morphology and structure of ZIF-8, MWCNT, and ZIF-8@MWCNT were characterized by scanning electron microscopy (SEM). Figure 1 As shown in (a), the ZIF-8 particles have a diameter of approximately 50 nm and exhibit good uniformity. Their spherical crystal shape is a result of hexagonal shape transformation, due to the minimization of the ZIF-8 surface energy caused by the SEM electron beam. MWCNTs have a smooth surface and a diameter of approximately 20 nm. Figure 1(b) A large number of ZIF-8 nanoparticles adhered to MWCNTs, almost completely covering the surface of the MWCNT walls, exhibiting a distinct string-like morphology. Figure 1 (c)). Furthermore, the particle size of ZIF-8 attached to MWCNTs is close to that of pure ZIF-8, indicating that the introduction of MWCNTs has no effect on the growth of ZIF-8. Figure 1 As shown in (d)-(f), 50 nm ZIF-8 is grown on the outer surface of MWCNT, possibly because MWCNT provides many nucleation sites for ZIF-8 growth. Compared with ZIF-8, ZIF-8 grown on MWCNT has better dispersibility, which improves the aggregation problem of ZIF-8 nanoparticles.
[0045] Figure 2 Fourier transform infrared (FTIR) spectra of ZIF-8, MWCNT, and ZIF-8@MWCNT. At 3134 cm⁻¹ -1 and 2927cm -1 The absorption peaks at 1580 cm⁻¹ represent the CH side chains of the imidazole ring in ZIF-8. -1 The peak at 1178 cm corresponds to the C=N stretching vibration. -1 and 996cm -1 The peak at that location belongs to the stretching vibration of CN. The infrared characteristic peaks of ZIF-8@MWCNT and ZIF-8 are almost identical in position, indicating that ZIF-8 nanoparticles have been successfully grown on the MWCNT surface.
[0046] Figure 3 The results show that the characteristic diffraction peaks of ZIF-8@MWCNT and ZIF-8 are basically the same. The diffraction peaks at 2θ = 7.3°, 10.3°, 12.7°, 14.7°, 16.9° and 18.0° correspond to the (011), (002), (112), (022), (013) and (222) lattice planes of ZIF-8 nanoparticles, respectively. This indicates that ZIF-8 still maintains its original framework structure after the introduction of MWCNT. The growth of ZIF-8 nanoparticles on the surface of MWCNT does not affect the crystal structure of ZIF-8.
[0047] Figure 4 (a) is the XPS spectrum of ZIF-8@MWCNT, indicating that ZIF-8@MWCNT contains Zn, O, N, and C elements. Figure 4 (b), Zn2p 3 / 2 and Zn2p 1 / 2 Peaks were observed at 1021.7 eV and 1044.7 eV, respectively. Figure 4(c) indicates that the C1s peak consists of four peaks at 284.2 eV, 284.6 eV, 285.7 eV, and 289.7 eV, corresponding to CC / C=C, CN, CO, and OC=O, respectively. For example... Figure 4 As shown in (d), the N1s peak at 399.4 eV is attributed to the nitrogen atom of 2-methylimidazole, and the peak at 398.8 eV is attributed to the secondary amine group. Figure 4 (e) shows the O1s energy spectrum of ZIF-8@MWCNT, with the peak at 529.6 eV being Zn-O, and the peaks at 532.2 eV, 534.3 eV, and 530.7 eV being CO, C=O, and O=CO, respectively.
[0048] Figure 5 Thermogravimetric analysis (TGA) spectra of ZIF-8 and ZIF-8@MWCNT were used to investigate the thermal stability of the ZIF-8@MWCNT composite. In the temperature range of 30–300 °C, the weight loss rates of ZIF-8 and ZIF-8@MWCNT were 2.1% and 3.5%, respectively, mainly attributed to the removal of guest molecules from the skeletal cavities. In the temperature range of 300 °C–800 °C, the weight loss trends of ZIF-8 and ZIF-8@MWCNT were basically the same, indicating gradual skeletal collapse.
[0049] Figure 6 To evaluate the dispersibility of ZIF-8 and ZIF-8@MWCNT in ethanol, time-resolved photographs and the relationship between UV absorption peak intensity and time were used. Even after 48 hours, the stability of ZIF-8 and ZIF-8@MWCNT in the ethanol dispersion remained unchanged, with no significant aggregation. Further verification using the UV absorption intensity-time relationship confirmed the good stability of ZIF-8 and ZIF-8@MWCNT in ethanol after 48 hours. Therefore, ethanol will be used as the solvent to prepare the PVDF coating solution for ZIF-8@MWCNT in the synthesis of the ZIF-8@MWCNT / PVDF superhydrophobic composite film.
[0050] 2) Dissolve 0.01g ZIF-8@MWCNT and 0.01g PVDF powder in 30mL ethanol;
[0051] 3) After sonication for 1 hour, immerse the PVDF membrane in it, immerse it at room temperature for 10 minutes, and then dry it at 70℃ for 30 minutes;
[0052] 4) Place the dried PVDF membrane and 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) in the same container and seal it. Vaporize it at 70℃ for 8 hours to obtain the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane.
[0053] The ZIF-8@MWCNT / PVDF superhydrophobic composite membrane obtained in step 4) was characterized and analyzed for performance:
[0054] Figure 7 SEM images of the PVDF membrane and the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane. Figure 7 (a) and (b) show that compared to the ZIF-8@MWCNT / PVDF membrane surface, the PVDF membrane surface is smoother and has lower roughness, thus exhibiting poorer hydrophobicity. Figure 7 As shown in (c) and (d), a large number of nanoscale protrusions exist on the surface of the ZIF-8@MWCNT / PVDF film, indicating that ZIF-8@MWCNT was successfully loaded onto the PVDF base film.
[0055] Figure 8 The images show the FTIR spectra of the PVDF membrane and the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane. Compared to the PVDF membrane, the ZIF-8@MWCNT / PVDF membrane exhibits better FTIR at 1275 cm⁻¹. -1 The absorption peak with lower transmittance is observed at the β phase of the PVDF film because the ZIF-8@MWCNT / PVDF composite film is coated with ZIF-8@MWCNT composite material. Therefore, a ZIF-8@MWCNT / PVDF superhydrophobic composite film was successfully prepared using ZIF-8@MWCNT composite material and FOTS.
[0056] Figure 9 For example, PVDF membrane and ZIF-8@MWCNT / PVDF superhydrophobic composite membrane CA. Figure 9 As shown, the CA of the ZIF-8@MWCNT / PVDF film is significantly increased, indicating that the modified film has good superhydrophobicity, which can be attributed to the formation of cavitation by ZIF-8@MWCNT on the PVDF base film and the presence of an ultra-low surface energy FOTS coating.
[0057] Stability test:
[0058] like Figure 10 As shown in (a) and (b), the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane was subjected to ultrasonic treatment for 1 hour and immersion in a 70℃ hot water bath for a certain period of time. A comparison of the CA (chemical stability) of the ZIF-8@MWCNT / PVDF composite membrane before treatment revealed that the ZIF-8@MWCNT / PVDF membrane exhibited stronger mechanical and thermal stability. Figure 10 As shown in (c), after soaking in an aqueous solution with pH 3-11 for 4 hours, the contact angle of the ZIF-8@MWCNT / PVDF membrane remained almost unchanged, demonstrating excellent chemical stability.
[0059] Membrane distillation performance testing:
[0060] (1) Figure 11 The water flux, average water flux, and salt rejection ratio of the PVDF membrane and the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane are given. Figure 11 As shown in (a), at the beginning of the MD process, the water flux of the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane was slightly lower than that of the PVDF membrane. This is because the ZIF-8@MWCNT composite material, after being loaded onto the PVDF membrane, blocked a small number of membrane pores, leading to a decrease in the composite membrane porosity and pore size, and an increase in the mass transfer resistance of steam through the membrane. As the MD process progressed, the water flux of the PVDF membrane gradually decreased, exhibiting a precipitous drop at 3 hours, and decreasing to 0 μm at 4 hours. -2 h -1 At this point, the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane's flux decreased slowly but it could still be used normally. The water flux of the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane surpassed that of the PVDF membrane at approximately 3.5 hours, while the ZIF-8@MWCNT / PVDF composite membrane only showed a significant decrease at 6 hours. The rate of decrease in water flux for the ZIF-8@MWCNT / PVDF composite membrane was slower than that for the PVDF membrane. The PVDF membrane has poor hydrophobicity and is more easily fouled by the feed liquid, while the ZIF-8@MWCNT / PVDF membrane is more hydrophobic and less prone to fouling by the feed liquid, indicating that the ZIF-8@MWCNT / PVDF composite membrane possesses superior antifouling capabilities.
[0061] After the MD experiment, the average flux and sodium chloride rejection of the PVDF membrane and the ZIF-8@MWCNT / PVDF composite membrane were as follows: Figure 11 As shown in (b), the average water flux of the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane is lower than that of the PVDF membrane. This is mainly due to the shorter operating time, faster descent rate, and relatively larger initial water flux of the PVDF membrane. Throughout the MD experiment, the salt rejection rates of both the PVDF membrane and the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane were above 99.99%, indicating that the modification of the PVDF membrane by ZIF-8@MWCNT did not reduce the salt rejection rate of the PVDF membrane.
[0062] (2) A 25% NaCl solution close to a saturated NaCl solution was selected as the feed liquid for the MD test to study the membrane's antifouling properties. To observe the sodium chloride crystals on the membrane surface, the fouled membrane was removed from the membrane module after the test and air-dried at room temperature. Figure 12 Optical photographs and SEM images of PVDF films and ZIF-8@MWCNT / PVDF superhydrophobic composite films are shown. Figure 12 As shown in (a) and (c), there are large transparent salt crystals on the surface of the PVDF membrane, while no obvious salt crystals were observed on the surface of the composite membrane.Figure 12 Images (b) and (d) are SEM images of the PVDF membrane and the ZIF-8@MWCNT / PVDF composite membrane, further verifying that no obvious salt crystals were present on the surface of the composite membrane, while those on the PVDF membrane were. Large salt particles were clearly visible on the surface of the PVDF membrane after the MD test, clogging the membrane pores, consistent with the experimental results showing a sharp decrease in water flux with prolonged operation time during the MD process. In contrast, the ZIF-8@MWCNT / PVDF membrane exhibited less surface fouling, and its water flux decreased more gradually with prolonged operation time. It can be seen that the ZIF-8@MWCNT / PVDF composite membrane has stronger antifouling properties than the PVDF membrane, while also possessing a good salt rejection rate (up to 99.99%).
[0063] (3) In the anti-wetting test, a 3.5% NaCl solution was used as the feed solution, and sodium dodecyl sulfate (SDS) solution was added to it to gradually increase the SDS concentration in the feed solution. The SDS concentration increased by 0.2 mmol / L every 2 hours. -1 This is done to gradually reduce the surface tension of the feed liquid. Figure 13 The water flux and permeate conductivity of the PVDF membrane and the ZIF-8@MWCNT / PVDF composite membrane were measured during the anti-wetting test. After 1 hour of operation, the feed solution was replaced with a solution containing 0.2 mmol / L. -1 When SDS is in a 3.5% NaCl solution, the water flux of the PVDF membrane suddenly drops to 0 Lm. -2 h -1 Furthermore, the permeate-side conductivity increases. Based on the degree of wetting, this phenomenon indicates complete membrane pore wetting, caused by the addition of SDS to the feed solution, which reduces the surface tension of the feed solution. This allows the permeate to directly enter the feed solution through the membrane pores, preventing the DCMD from functioning properly. Therefore, for solutions containing SDS, the hydrophobicity of the PVDF membrane is insufficient, and the membrane pores are easily wetted. Compared to the PVDF membrane, the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane exhibits better performance at 2.0 mmol / L... -1 Even under these conditions, the ZIF-8@MWCNT / PVDF composite membrane remains usable, and its permeate conductivity remains consistently low, indicating that it can still prevent salt from passing through. The superhydrophobicity of the ZIF-8@MWCNT / PVDF composite membrane prevents SDS-containing feed solutions from easily wetting the membrane pores; only water vapor can pass through. This allows the composite membrane to maintain stable water flux and salt rejection rate during DCMD, thus extending its service life. Therefore, compared to PVDF membranes, the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane also exhibits anti-wetting properties.
[0064] (4) Using a 3.5% NaCl solution with a salt concentration close to that of real seawater as the feed liquid, a MD test was conducted for 48 hours to investigate the long-term stability of PVDF membrane and ZIF-8@MWCNT / PVDF superhydrophobic composite membrane. Figure 14 The water flux and permeate conductivity of the PVDF membrane and the ZIF-8@MWCNT / PVDF composite membrane were measured during medium- and long-term performance tests. Figure 14 (a) indicates that the initial flux values of the PVDF membrane and the ZIF-8@MWCNT / PVDF superhydrophobic composite membrane are similar, approximately 17 Lm. -2 h -1 During the period from 0h to 48h, the water flux of the PVDF membrane continuously decreased, reaching 0 Lm at 44h. -2 h -1 The rate of decrease in water flux of the ZIF-8@MWCNT / PVDF composite membrane was less than that of the PVDF membrane, which is consistent with the experimental results in step (1), indicating that the ZIF-8@MWCNT / PVDF composite membrane has better antifouling ability and superior stability. Figure 14 As shown in (b), after a long-term MD test of 48 h, the cold-side permeate conductivity of the PVDF membrane and the ZIF-8@MWCNT / PVDF composite membrane were 13.1 ± 0.2 μS / cm, respectively. -1 and 5.0±0.1μScm -1 Compared to the permeate conductivity of PVDF membranes, the permeate conductivity of the ZIF-8@MWCNT / PVDF composite membrane is only 8.1 μS / cm lower. -1 This is because as the DCMD operates for a longer period, the PVDF membrane pores gradually become wetted, leading to an increase in permeate conductivity. Simultaneously, fouling deposits on the PVDF membrane surface clog the pores, reducing membrane flux and delaying pore wetting, thus acting as a filter and inhibiting the rise in permeate conductivity to some extent. Therefore, under the combined effect of these two factors, the permeate conductivity of the PVDF membrane ultimately shows a slight increase compared to the composite membrane.
[0065] It is evident that the method of the present invention can improve the performance of the PVDF membrane by grafting ZIF-8@MWCNT composite material onto the PVDF membrane surface, thereby increasing the surface roughness of the PVDF membrane. FOTS reduces the surface energy of the PVDF membrane, and the superhydrophobic composite membrane exhibits excellent antifouling properties, stable and excellent antiwetting properties, and a high salt rejection rate.
[0066] Example 2
[0067] 1) A method for preparing ZIF-8@MWCNT composite material, comprising the following steps:
[0068] s1. Disperse 0.1200g MWCNT in 30mL methanol by ultrasonication, add 1.2217g 2-methylimidazole, stir for 15min, and continue ultrasonication for 15min.
[0069] s2. Add 30 mL of methanol solution containing 0.5866 g Zn(NO3)2·6H2O to the solution obtained in s1 under stirring, and continue stirring at room temperature for 1 h; centrifuge the resulting mixed solution at 8000 rpm for 10 min, then repeat the centrifugation and washing three times with 10 mL of methanol, and dry at 100℃ for 12 h to obtain black solid ZIF-8@MWCNT.
[0070] 2) Dissolve 0.01g ZIF-8@MWCNT and 0.01g PVDF powder in 30mL ethanol;
[0071] 3) After sonication for 1 hour, immerse the PVDF membrane in it, immerse it at room temperature for 10 minutes, and then dry it at 70℃ for 30 minutes;
[0072] 4) Place the dried PVDF membrane and 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) in the same container and seal it. Vaporize it at 70℃ for 8 hours to obtain ZIF-8@MWCNT / PVDF superhydrophobic composite membrane.
[0073] Example 3
[0074] 1) Synthesize ZIF-8@MWCNT composite material, including the following steps:
[0075] s1. Disperse 0.1200g MWCNT in 30mL methanol by ultrasonication, add 1.3235g 2-methylimidazole, stir for 15min, and continue ultrasonication for 15min.
[0076] s2. Add 30 mL of methanol solution containing 0.5866 g Zn(NO3)2·6H2O to the solution obtained in s1 under stirring, and continue stirring at room temperature for 1 h; centrifuge the resulting mixed solution at 8000 rpm for 10 min, then repeat the centrifugation and washing three times with 10 mL of methanol, and dry at 100℃ for 12 h to obtain black solid ZIF-8@MWCNT.
[0077] 2) Dissolve 0.01g ZIF-8@MWCNT and 0.01g PVDF powder in 30mL ethanol;
[0078] 3) After sonication for 1 hour, immerse the PVDF membrane in it, immerse it at room temperature for 10 minutes, and then dry it at 70℃ for 30 minutes;
[0079] 4) Place the dried PVDF membrane and 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) in the same container and seal it. Vaporize it at 70℃ for 8 hours to obtain ZIF-8@MWCNT / PVDF superhydrophobic composite membrane.
[0080] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.
Claims
1. A method for preparing a PVDF superhydrophobic composite membrane, characterized in that, Includes the following steps: 1) Synthesis of ZIF-8@MWCNT composite material, including: s1. Carboxylated multi-walled carbon nanotubes were ultrasonically dispersed in methanol, and 2-methylimidazole was added and stirred before ultrasonication was continued. s2. Add the Zn(NO3)2·6H2O methanol solution to the solution obtained in s1 under stirring. After mixing evenly, centrifuge, wash and dry to obtain a black solid. 2) Dissolve ZIF-8@MWCNT and PVDF powder in ethanol; 3) After sonicating the solution, immerse the PVDF membrane in it and then dry it; 4) The dried PVDF membrane obtained in step 3) and the silane coupling agent 1H,1H,2H,2H-perfluorooctyltrichlorosilane were placed in the same container and sealed for vaporization to obtain a modified PVDF superhydrophobic composite membrane.
2. The method for preparing the PVDF superhydrophobic composite membrane according to claim 1, characterized in that, In step 2), the mass-to-volume ratio of ZIF-8@MWCNT and PVDF powder to ethanol solution is 0.01:30, and the unit of mass-to-volume ratio is g / mL. -1 .
3. The method for preparing the PVDF superhydrophobic composite membrane according to claim 1, characterized in that, In step 3), the ultrasonic time is 1 hour, the drying temperature is 70℃, and the drying time is 30 minutes.
4. The method for preparing the PVDF superhydrophobic composite membrane according to claim 1, characterized in that, In step 4), the vaporization temperature is 70℃ and the vaporization time is 8h.
5. The method for preparing the PVDF superhydrophobic composite membrane according to claim 1, characterized in that, In s1, the mass-to-volume ratio of MWCNT to methanol is 0.12:30, and the mass-to-volume ratio of 2-methylimidazole to MWCNT is 10.6:1 to 11:
1.
6. The method for preparing the PVDF superhydrophobic composite membrane according to claim 1, characterized in that, In s2, the mass-volume ratio of Zn(NO3)26H2O to methanol is 0.55:30 to 0.62:30.