Fully-hydrophobic ultrahigh-loading MOF (Metal Organic Framework) mixed matrix membrane as well as preparation method and application thereof

Abstract

The invention relates to a fully-hydrophobic ultrahigh-loading MOF (Metal Organic Framework) mixed matrix membrane as well as a preparation method and application thereof, and belongs to the technical field of membrane separation. The preparation method comprises the following steps: heating and melting a large-size hydrophobic MOF material, a high-molecular polymer and paraffin oil, molding through a high-temperature roller-to-roller hot pressing process to prepare a membrane material with the loading capacity of 92% or above and a multi-stage rough surface, and finally carrying out hydrophobic and oleophobic performance treatment through fluorosilane. The obtained mixed matrix membrane material has high flux and excellent anti-pollution and anti-infiltration capabilities, and is suitable for efficient desalination of complex wastewater.

Description

Technical Field

[0001] The present invention relates to a superhydrophobic ultra-high loading MOF mixed matrix membrane, a preparation method thereof and an application thereof, belonging to the technical field of membrane separation. Background Art

[0002] Membrane distillation technology combines distillation and membrane separation. Using a hydrophobic microporous membrane as a separation barrier and the vapor pressure gradient between the feed liquid and the permeate as the driving force, water vapor is transmitted through the membrane and collected on the condensation side, while salt ions and non-volatile components are retained. This technology has the advantages of low operating pressure, being able to treat high-salt and highly polluted wastewater, and being able to utilize industrial waste heat. However, it is difficult for membrane materials to simultaneously achieve high permeation flux and anti-pollution and anti-wetting properties. Generally, high-flux membrane materials need to have larger pore sizes, but this increases the risk of membrane wetting, resulting in the penetration of salt to the permeate side; while surface modification can improve anti-pollution and anti-wetting abilities, but it is prone to cause pore blockage and reduce the flux. Therefore, there is an urgent need to develop membrane materials with both high flux and anti-wetting and anti-pollution properties to meet the challenges of highly polluted industrial wastewater.

[0003] Metal-organic frameworks (MOFs) are crystalline porous materials formed by inorganic metal ions or metal clusters and organic ligands through coordination bonds to form ordered open channels. They have the advantages of structural diversity, high specific surface area, high porosity, and adjustable pore environment, and are ideal candidate materials for improving membrane distillation flux. However, challenges still exist in achieving high MOF loading in mixed matrix membranes, and problems such as aggregation and precipitation are prone to occur during the preparation process. The research group where the inventors are located previously applied for a patent "A preparation method of a porous material ultra-high loading mixed matrix membrane". The inventors further found through research that the mechanical strength of materials with a loading of more than 90% in the above patent cannot meet the actual test requirements and cannot be used in the field of membrane distillation technology. In addition, although superhydrophobic composite membranes help to improve anti-pollution and anti-wetting abilities during the desalination process, the flux is usually limited due to pore blockage. Currently, there is still a lack of systematic research on the application of superhydrophobic ultra-high loading MOF mixed matrix membranes in membrane distillation, and the trade-off relationship between flux and anti-pollution and anti-wetting properties still needs to be further explored. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a superhydrophobic ultra-high loading MOF mixed matrix membrane, a preparation method thereof and an application thereof. A self-supporting ultra-high loading MOF mixed matrix membrane with a multi-level rough surface is prepared by a high-temperature roll-to-roll hot pressing process, and a fluorosilane is coated on its surface to achieve hydrophobic and oleophobic properties. The obtained mixed matrix membrane material has both high flux and excellent anti-pollution and anti-wetting abilities, and is suitable for the efficient desalination of complex wastewater.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows.

[0006] A preparation method of a fully hydrophobic ultra-high loading MOF mixed matrix membrane, the method steps include:

[0007] (1) Mix hydrophobic MOF particles with a particle size of more than 400 nm, a polymer, and paraffin oil, heat and melt them, and stir evenly to obtain a casting solution; the polymer is composed of high-density polyethylene particles and ultra-high molecular weight polyethylene powder with a mass ratio of 3-4:1. The weight-average molecular weight (M w ) of the high-density polyethylene particles is above 40,000, and the density is 930 kg / m 3 ~970 kg / m 3 ; the weight-average molecular weight of the ultra-high molecular weight polyethylene powder is above 1.5 million;

[0008] (2) Coating the casting solution on a conveyor belt, and forming it by a high-temperature roll-to-roll hot pressing process; removing the paraffin oil, and after drying, obtaining an ultra-high loading MOF mixed matrix membrane with a thickness of more than 200 μm, and the loading of MOF is above 92 wt%;

[0009] (3) Coating an organic solution containing fluorosilane on the surface of the ultra-high loading MOF mixed matrix membrane, and performing a drying treatment at a temperature above 100 °C to obtain a fully hydrophobic ultra-high loading MOF mixed matrix membrane; the mass fraction of fluorosilane in the organic solution containing fluorosilane is 1.5%-3.5%, and the coating amount of the organic solution containing fluorosilane on each 1 cm 2 of the ultra-high loading MOF mixed matrix membrane is 400-600 μL.

[0010] Preferably, in step (1), the particle size of the hydrophobic MOF particles is 400-2500 nm.

[0011] Preferably, in step (1), the hydrophobic MOF particles are one of hydrophobic ZIF series, hydrophobic UiO-66 series, hydrophobic MAF series, MIL-101 or FMOF-1. More preferably, the hydrophobic MOF particles are ZIF-8, ZIF-71, ZIF-7, UiO-66-(CF 3 ) 2 、UiO-66-(CH 3 ) 2 、MAF-X10, MAF-X13, MIL-101 or FMOF-1.

[0012] Preferably, in step (1), the heating and melting temperature is 200-250 °C.

[0013] Preferably, in step (1), the mass ratio of the paraffin oil to the hydrophobic MOF particles is 0.5-3:1.

[0014] Preferably, in step (2), the forming temperature of the hot roll-to-roll hot pressing process is 120-150 °C, and the conveyor belt speed is 40-60 rpm.

[0015] Preferably, in step (2), the thickness of the ultra-high loading MOF mixed matrix membrane is 200-400 μm.

[0016] Preferably, in step (2), the loading of MOF in the ultra-high loading MOF mixed matrix membrane is 92 wt%-96 wt%.

[0017] Preferably, in step (3), the fluorosilane is perfluorohexyltrimethoxysilane, perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltriethoxysilane, perfluorohexadecyltriethoxysilane, perfluorododecyltrichlorosilane, perfluorodecyltrichlorosilane or perfluorooctyltrichlorosilane.

[0018] Preferably, in step (3), the organic phase in the organic solution of the fluorosilane is n-hexane or ethanol.

[0019] Preferably, in step (3), the dipping method or the doctor blade method is used for coating.

[0020] Preferably, in step (3), the drying treatment temperature is 120-140 °C.

[0021] A fully hydrophobic ultra-high loading MOF mixed matrix membrane is prepared by the above method.

[0022] An application of the fully hydrophobic ultra-high loading MOF mixed matrix membrane described in the present invention in membrane distillation.

[0023] Preferably, the mixed matrix membrane is used for the membrane distillation treatment of industrial wastewater containing surfactants and oil pollutants.

[0024] Beneficial effects

[0025] The present invention provides a preparation method of a fully hydrophobic ultra-high loading MOF mixed matrix membrane. First, a large-sized hydrophobic MOF material is selected and heated and melted with a polymer and paraffin oil, and then a membrane material with a loading of more than 92% and a multi-level rough surface is prepared by a hot roll-to-roll hot pressing process. Finally, the hydrophobic and oleophobic properties are treated with fluorosilane. The obtained mixed matrix membrane material has both high flux and excellent anti-pollution and anti-wetting abilities, and is suitable for the efficient desalination of complex wastewater.

[0026] The method of the present invention is universal, time-consuming short, simple to operate, low-cost, and can achieve continuous production. By further regulating the loading amount of MOF, the process conditions of high-temperature roll-to-roll hot pressing, the content and coating amount of fluorosilane, the thickness, flux, and hydrophobic and oleophobic properties of the membrane can be accurately controlled.

[0027] During the membrane distillation process of the fully hydrophobic ultra-high loading amount MOF mixed matrix membrane of the present invention, the micron-sized channels and high porosity between MOF particles provide high permeation flux. The synergistic effect of the surface multi-level rough structure and the low surface energy fluorine-containing substance endows the membrane with fully hydrophobic characteristics. Its permeation flux is 1.5 times that of commercial membranes, and it can maintain high-efficiency desalination performance in the industrial wastewater environment containing surfactants and oil pollutants for a long time. Description of the Drawings

[0028] Figure 1 X-ray powder diffraction patterns of the MOF materials prepared in Examples 1, 3, and 4.

[0029] Figure 2 X-ray powder diffraction patterns of the MOF mixed matrix membranes with different loadings prepared in Examples 1-2 and Comparative Examples 1-5.

[0030] Figure 3 Nitrogen adsorption and desorption isotherms at 77K of the MOF materials prepared in Examples 1, 3, and 4.

[0031] Figure 4 Nitrogen adsorption and desorption isotherms of the MOF mixed matrix membranes with different loadings prepared in Examples 1-2 and Comparative Examples 1-5.

[0032] Figure 5 Nitrogen adsorption and desorption isotherms of the membranes before and after fluorination coating prepared in Example 1.

[0033] Figure 6 For the SiO prepared in Comparative Example 6 2 Nitrogen adsorption and desorption isotherm of the mixed matrix membrane.

[0034] Figure 7 Infrared spectra of the MOF mixed matrix membranes with different loadings prepared in Examples 1-2 and Comparative Examples 1-5.

[0035] Figure 8 Infrared spectra of the membranes before and after fluorination coating prepared in Example 1.

[0036] Figure 9 High-resolution C1s X-ray photoelectron spectroscopy of ZIF-8PE MMM-92%-FDTS prepared in Example 1.

[0037] Figure 10Scanning electron microscope images of MOF mixed matrix membranes with different loadings prepared in Example 1 and Comparative Examples 1-5.

[0038] Figure 11 Water contact angle images of MOF mixed matrix membranes with different loadings prepared in Examples 1-2 and Comparative Examples 1-5.

[0039] Figure 12 Images of different liquid contact angles of the membrane before and after fluorination prepared in Example 1.

[0040] Figure 13 Vacuum membrane distillation performance images of MOF mixed matrix membranes with different loadings prepared in Example 1 and Comparative Examples 1-5.

[0041] Figure 14 Vacuum membrane distillation performance images of ZIF-8PE MMM-92%-FDTS prepared in Example 1 at different temperatures.

[0042] Figure 15 Vacuum membrane distillation performance images of ZIF-8PE MMM-92%-FDTS prepared in Example 1 at different vacuum degrees.

[0043] Figure 16 Vacuum membrane distillation performance images of ZIF-8PE MMM-92%-FDTS prepared in Example 1 at different salt concentrations.

[0044] Figure 17 Anti-wetting vacuum membrane distillation performance images of ZIF-8PE MMM-92%-FDTS prepared in Example 1.

[0045] Figure 18 Anti-fouling vacuum membrane distillation performance images of ZIF-8PE MMM-92%-FDTS prepared in Example 1.

[0046] Figure 19 Vacuum membrane distillation performance images of the SiO 2 mixed matrix membrane prepared in Comparative Example 6.

[0047] Figure 20 Static toluene vapor adsorption and desorption curves of ZIF-8 prepared in Example 1 at 60 °C.

[0048] Figure 21 Cyclic adsorption performance images of ZIF-8PE MMM-92%-FDTS prepared in Example 1 for toluene in vacuum membrane distillation tests. Detailed implementation manners

[0049] The present invention will be further described in detail below in conjunction with specific embodiments. Unless otherwise specified, the methods are conventional methods, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0050] X-ray powder diffractometer: The instrument model is Rigaku MiniFlex600, manufactured by Rigaku Corporation, Japan. Among them, the X-ray source is Cu-Kα (λ = 0.154056 nm), the voltage is 40 kV, and the current is 50 mA.

[0051] Infrared spectrometer: Model Bruker ALPHA, wavelength range 400 cm -1 ~4000 cm -1 ,manufactured by Bruker Corporation, USA.

[0052] Gas sorption analyzer: Model Quantachrome (ASiQMVH002-5), manufactured by Quantachrome Corporation, USA; at 77 K, nitrogen is used to measure the specific surface area and pore size distribution of the sample. The specific surface area is calculated based on the Brunauer-Emmett-Teller (BET) theory, and the pore size distribution is analyzed using the non-local density functional theory. Before testing, the sample is vacuum pretreated at 120 °C for 12 hours to remove the residual solvent in the pores.

[0053] Vapor sorption analyzer: Model Belsorp Instrument Max analyzer, the test relative pressure range is 0.05~0.95, and the vapor sorption curves at different temperatures are measured. Before testing, the sample is dried under vacuum at 120 °C for 12 h to remove the residual solvent molecules in the pores.

[0054] Field emission scanning electron microscope: Model ZEISS SUPRA-55 scanning electron microscope, the working conditions of the instrument are a working voltage of 5 kV and a current of 10 μA.

[0055] Contact angle measuring instrument: Model SCI3000 contact angle measuring instrument, which can measure the contact angles of different liquids such as water, ethanol, toluene, and oil on the membrane surface.

[0056] X-ray photoelectron spectrometer: Model Thermo Fisher Scientific K-Alpha+, monochromatic Al Ka X-ray source (1486.6 eV), power 72 W (12 kV, 6 mA). A low-energy argon ion gun (≤10 eV) is used to neutralize the charge accumulation, the background signal is subtracted, and the spectrum is fitted with a Gaussian-Lorentz curve.

[0057] Membrane distillation performance test: A vacuum membrane distillation device is used to evaluate the desalination performance of the membrane material. The effective membrane area for testing is 9 cm 2, the feed volume was 1000 mL, the temperature was controlled at 70 °C, and the hot feed liquid was circulated on the membrane surface at a set flow rate. A vacuum of approximately 15 mbar was maintained on the other side by a vacuum pump, so that the water vapor permeated through the membrane and was evacuated, and condensed and recovered in the cooling water at 5 °C. The transmembrane water vapor flux was calculated by measuring the mass of the permeate, and the sodium chloride rejection rate was evaluated by monitoring the conductivity of the permeate.

[0058] Example 1

[0059] (1) Dissolve 2.2600 g of Zn(NO 3 ) 2 ·6H 2 O in 50 mL of methanol, dissolve 2.6200 g of 2-methylimidazole in 50 mL of methanol, mix the two solutions, and react at room temperature for 24 h. Centrifuge, wash three times with methanol, and dry in a vacuum oven at 120 °C for 12 h to obtain the ZIF-8 solid material.

[0060] (2) Grind the ZIF-8 solid with a mortar to a uniform powder, and then place the ZIF-8 powder, high-density polyethylene particles (HDPE, Sigma-Aldrich, melt index = 2.2 g / 10 min), and ultra-high molecular weight polyethylene powder (UHMWPE, Alfa Aesar, molecular weight 3 - 6 million) in a 50 °C electrothermal constant temperature blast dryer and preheat for 4 h to remove moisture.

[0061] (3) Mix 0.4600 g of ZIF-8 powder, 0.0320 g of high-density polyethylene, 0.0080 g of ultra-high molecular weight polyethylene with 0.3 mL of paraffin oil, heat and melt at 210 °C and perform mechanical stirring until a viscous and uniform casting solution is formed.

[0062] (4) Place the obtained casting solution on a conveyor belt rotating at 40 rpm and perform forming using a roll-to-roll hot pressing process at 140 °C. After cooling to room temperature, immerse the obtained membrane in 80 mL of dichloromethane overnight to remove the paraffin oil lubricant. Dry at room temperature to obtain the ZIF-8PE MMM-92% membrane.

[0063] (5) Dissolve 1.5 wt% of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FDTS) in n-hexane and ultrasonically form a uniform solution. Subsequently, take 0.7 mL of this solution and uniformly coat it on the surface of a 1.5 cm * 1.5 cm ZIF-8PE MMM-92% membrane, and dry in an oven at 120 °C for 2 hours to finally obtain the fully hydrophobic ZIF-8PE MMM-92%-FDTS.

[0064] Example 2

[0065] On the basis of Example 1, change the mixing of 0.4600 g of ZIF-8, 0.0320 g of high-density polyethylene, 0.0080 g of ultra-high molecular weight polyethylene with 0.3 mL of paraffin oil in step (3) to the mixing of 0.4800 g of ZIF-8 powder, 0.0160 g of high-density polyethylene, 0.004 g of ultra-high molecular weight polyethylene with 0.28 mL of paraffin oil, and keep the other step conditions unchanged to prepare the fully hydrophobic ZIF-8PE MMM-96%-FDTS.

[0066] Example 3

[0067] (1) Dissolve 2.1951 g of Zn(CH 3 COO) 2 ·2H 2 O in 100 mL of N,N-dimethylformamide, dissolve 2.3600 g of benzimidazole in 100 mL of methanol, mix the two solutions, and stir at room temperature for 1 h. Centrifuge, wash three times with methanol, and dry in a vacuum oven at 80 °C for 12 h to obtain the ZIF-7 solid material.

[0068] (2) Grind the ZIF-7 solid with a mortar to a uniform powder, then place the ZIF-7 powder, high-density polyethylene particles (HDPE, Sigma-Aldrich, melt index = 2.2 g / 10 min), and ultra-high molecular weight polyethylene powder (UHMWPE, Alfa Aesar, molecular weight 3-6 million) in a 50 °C electrothermal constant temperature blast dryer and preheat for 4 h to remove moisture.

[0069] (3) Mix 0.4600 g of ZIF-7 powder, 0.0320 g of high-density polyethylene, and 0.0080 g of ultra-high molecular weight polyethylene with 0.3 mL of paraffin oil, and mechanically stir the mixture at 210 °C until a viscous and uniform film-forming material is formed.

[0070] (4) Place the obtained film-forming material on a conveyor belt rotating at 40 rpm and carry out forming by a roll-to-roll hot pressing process at 140 °C. After cooling to room temperature, immerse the obtained film in 80 mL of dichloromethane overnight to remove the paraffin lubricant. Finally, dry at room temperature to obtain the ZIF-7PE MMM-92% film.

[0071] (5) Dissolve 1.5 wt% of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FDTS) in n-hexane and ultrasonically form a uniform solution. Subsequently, take 0.7 mL of this solution and uniformly coat the surface of a 1.5 cm * 1.5 cm ZIF-7PE MMM-92% film, and dry in an oven at 120 °C for 2 h to finally obtain the fully hydrophobic ZIF-7PE MMM-92%-FDTS.

[0072] Example 4

[0073] (1) Dissolve 0.2970 g of Zn(CH 3 COO) 2 in 60 mL of methanol, and dissolve 0.8760 g of 4,5-dichloroimidazole in 60 mL of methanol. Mix the two solutions and react at room temperature for 24 h. Then, remove the methanol solution, replace it with chloroform three times, soak and wash for three days, and finally dry in a vacuum oven at 50 °C for 24 h to obtain the ZIF-71 solid material.

[0074] (2) Use a mortar to grind the ZIF-71 solid into a uniform powder. Then, preheat the ZIF-71 powder, high-density polyethylene particles, and ultra-high molecular weight polyethylene powder in a 50 °C electrothermal constant temperature blast dryer for 4 h to remove moisture.

[0075] (3) Mix 0.4600 g of ZIF-71 powder, 0.0320 g of high-density polyethylene (HDPE, Sigma-Aldrich, melt index = 2.2 g / 10 min), 0.0080 g of ultra-high molecular weight polyethylene (UHMWPE, Alfa Aesar, molecular weight 3 - 6 million), and 0.3 mL of paraffin oil. Mechanically stir the mixture at 210 °C until a viscous and uniform casting film material is formed.

[0076] (4) Place the obtained casting film material on a conveyor belt rotating at 40 rpm and form it using a roll-to-roll hot pressing process at 140 °C. After cooling to room temperature, immerse the obtained film in 80 mL of dichloromethane overnight to remove the paraffin lubricant. Finally, dry at room temperature to obtain the ZIF-71PE MMM-92% film.

[0077] (5) Dissolve 1.5 wt% of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FDTS) in n-hexane and ultrasonically form a uniform solution. Then, take 0.7 mL of this solution and uniformly coat it on the surface of a 1.5 cm * 1.5 cm ZIF-71PE MMM-92% film, and dry it in an oven at 120 °C for 2 h to finally obtain the fully hydrophobic ZIF-71PE MMM-92%-FDTS.

[0078] Example 5

[0079] In the vacuum membrane distillation process, volatile organic compounds (VOCs) often co-evaporate with water molecules, resulting in a decrease in the purity of the produced water. ZIF-8 with a swinging effect was screened out from a variety of hydrophobic MOF materials, and it was proven by the Bayer vapor adsorption curve that high-efficiency adsorption of VOCs can be achieved. Based on the membrane material of Example 1, membrane distillation tests were carried out on a 10.5 wt% sodium chloride solution containing 200 ppm of toluene at 70 °C and a vacuum of 85 kPa to evaluate the conductivity and toluene concentration in the permeate, and cyclic tests were also carried out.

[0080] Comparative Example 1

[0081] On the basis of Example 1, changing the mixing of 0.4600 g of ZIF-8, 0.0320 g of high-density polyethylene, 0.0080 g of ultra-high molecular weight polyethylene and 0.3 mL of paraffin oil in step (3) to the mixing of 0.3250 g of ZIF-8, 0.1400 g of high-density polyethylene, 0.0350 g of ultra-high molecular weight polyethylene and 0.97 mL of paraffin oil, with other step conditions remaining unchanged, ZIF-8PE MMM-66%-FDTS was prepared.

[0082] Comparative Example 2

[0083] On the basis of Example 1, changing the mixing of 0.4600 g of ZIF-8, 0.0320 g of high-density polyethylene, 0.0080 g of ultra-high molecular weight polyethylene and 0.3 mL of paraffin oil in step (3) to the mixing of 0.3750 g of ZIF-8, 0.1000 g of high-density polyethylene, 0.0250 g of ultra-high molecular weight polyethylene and 0.9 mL of paraffin oil, with other step conditions remaining unchanged, ZIF-8PE MMM-75%-FDTS was prepared.

[0084] Comparative Example 3

[0085] On the basis of Example 1, changing the mixing of 0.4600 g of ZIF-8, 0.0320 g of high-density polyethylene, 0.0080 g of ultra-high molecular weight polyethylene and 0.3 mL of paraffin oil in step (3) to the mixing of 0.4000 g of ZIF-8, 0.0800 g of high-density polyethylene, 0.0200 g of ultra-high molecular weight polyethylene and 0.63 mL of paraffin oil, with other step conditions remaining unchanged, ZIF-8PE MMM-81%-FDTS was prepared.

[0086] Comparative Example 4

[0087] On the basis of Example 1, changing the mixing of 0.4600 g of ZIF-8, 0.0320 g of high-density polyethylene, 0.0080 g of ultra-high molecular weight polyethylene and 0.3 mL of paraffin oil in step (3) to the mixing of 0.4250 g of ZIF-8, 0.0600 g of high-density polyethylene, 0.0150 g of ultra-high molecular weight polyethylene and 0.45 mL of paraffin oil, with other step conditions remaining unchanged, ZIF-8PE MMM-85%-FDTS was prepared.

[0088] Comparative Example 5

[0089] On the basis of Example 1, in step (3), the mixture of 0.4600 g of ZIF-8, 0.0320 g of high-density polyethylene, 0.0080 g of ultra-high molecular weight polyethylene and 0.3 mL of paraffin oil was changed to the mixture of 0.4500 g of ZIF-8, 0.0400 g of high-density polyethylene, 0.0100 g of ultra-high molecular weight polyethylene and 0.34 mL of paraffin oil, and the conditions of other steps remained unchanged, and ZIF-8PE MMM-89%-FDTS was prepared.

[0090] Comparative Example 6

[0091] (1) Use a mortar to grind SiO 2 solid into a uniform powder, and then place the SiO 2 powder, high-density polyethylene particles and ultra-high molecular weight polyethylene powder in a 50 °C electrothermal constant temperature blast dryer and preheat for 4 h to remove moisture.

[0092] (2) Mix 0.4600 g of SiO 2 , 0.0320 g of high-density polyethylene, 0.0080 g of ultra-high molecular weight polyethylene and 0.3 mL of paraffin oil, and mechanically stir the mixture at 210 °C until a viscous and uniform film-forming material is formed.

[0093] (3) Place the obtained film-forming material on a conveyor belt with a rotation speed of 40 rpm and use a roll-to-roll hot pressing process to form at 140 °C. After cooling to room temperature, immerse the obtained film in 80 mL of dichloromethane overnight to remove the paraffin lubricant. Finally, dry at room temperature to obtain SiO 2 PE MMM-92% film.

[0094] (4) Dissolve 1.5 wt% of 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyltrimethoxysilane (FDTS) in n-hexane and ultrasonically form a uniform solution. Subsequently, take 0.7 mL of this solution and uniformly coat it on the surface of a 1.5 cm * 1.5 cm SiO 2 PE MMM-92% film, and dry it in an oven at 120 °C for 2 hours to finally obtain a superhydrophobic SiO 2 PE MMM-92%-FDTS.

[0095] Performance characterization:

[0096] (1) Powder X-ray diffraction test results

[0097] The X-ray powder diffraction patterns of the three MOFs of ZIF-8, ZIF-7 and ZIF-71 prepared in Examples 1, 3 and 4 are shown in detail in Figure 1 , which match their simulated powder phases, indicating that the three MOF materials were successfully synthesized. Figure 2The X-ray powder diffraction patterns of ZIF-8 / PE MMMs in Examples 1-2 and Comparative Examples 1-5 show that the characteristic peaks of ZIF-8 and PE appear simultaneously, and the topological structure of ZIF-8 is maintained during the high-temperature hot pressing process.

[0098] (2) Gas adsorption test results

[0099] As Figure 3 shown, the 77K nitrogen adsorption / desorption isotherms of three MOFs, ZIF-8, ZIF-7, and ZIF-71, prepared in Examples 1, 3, and 4 indicate that the three MOFs have a high BET specific surface area. Figure 4 The nitrogen adsorption / desorption isotherms at 77K of PE mixed matrix membranes (MMMs) with different ZIF-8 loadings in Examples 1-2 and Comparative Examples 1-5 are shown. The results show that as the ZIF-8 loading increases, the BET specific surface area of the membrane gradually increases. Specifically, the BET specific surface areas of ZIF-8 / PE MMMs with ZIF-8 loadings of 66wt%, 75wt%, 81wt%, 85wt%, 89wt%, 92wt%, and 96wt% are 965, 1137, 1307, 1450, 1567, 1670, and 1707 m 2 g -1 . Figure 5 It shows that the specific surface area of the membrane after fluorination modification remains basically unchanged, and the pore size distribution also does not change significantly, indicating that the fluorine chains do not block the pores of ZIF-8. Figure 6 Exhibits the BET specific surface area of the SiO 2 / PE MMM-92% membrane in Comparative Example 6 is 51 m 2 g -1 , proving that there are almost no micropores in its membrane material.

[0100] (3) Infrared spectroscopy test results

[0101] As Figure 7 shown, the infrared spectra of ZIF-8 / PE MMMs in Examples 1-2 and Comparative Examples 1-5 contain the characteristic peaks of PE and ZIF-8. From the relative intensities of the peaks at 2845 cm -1 and 2915 cm -1 , it can be seen that as the loading increases, the intensity of the PE characteristic peak gradually weakens, indicating a decrease in the proportion of the polymer. Figure 8 The ZIF-8 / PE MMM-92wt%-FDTS in -1 shows a C-F stretching vibration peak at 1211 cm

[0102] (5) X-ray photoelectron spectroscopy test results

[0103] To further analyze the surface chemical composition of ZIF-8PE MMM-92wt%-FDTS in Example 1, X-ray photoelectron spectroscopy was used for testing. Figure 9 The results showed that C-C, -CF 2 and -CF 3 groups were present in the membrane, further proving the success of surface fluorination of the membrane.

[0104] (6) Results of scanning electron microscope testing

[0105] As Figure 10 shown, in Example 1 and Comparative Examples 1-5, with the increase in the ZIF-8 loading amount, the wrinkled morphology dominated by the polymer in the mixed matrix membrane gradually changed to a multi-level rough structure jointly constructed by the polymer and rhombic dodecahedron ZIF-8.

[0106] (7) Results of static contact angle testing

[0107] As Figure 11 shown, in Examples 1-2 and Comparative Examples 1-5, the surface of the pure PE membrane was dense and smooth, and the water contact angle was 87.1°. As the ZIF-8 loading amount increased from 66wt% to 96wt%, due to the gradual increase in its surface roughness, the water contact angle of the membrane increased from 118° to 150°. Then, the contact angle of ZIF-8PE MMM-92wt%-FDTS was measured to evaluate the surface wettability of liquids with different surface tensions, including water, 1.5 mM SDS, ethanol, toluene, and mineral oil. As Figure 12 shown, after fluorination modification, the water contact angle increased from 149° to 152°, the 1.5 mM SDS contact angle increased from 115° to 147°, the ethanol contact angle changed from complete wetting to 101°, and the mineral oil contact angle increased from 42° to 103°. The fluorination treatment significantly improved the hydrophobic and oleophobic properties of the material.

[0108] (8) Influence of MOF mixed matrix membranes with different loading amounts on vacuum membrane distillation performance

[0109] As Figure 13 shown, in Example 1 and Comparative Examples 1-5, as the ZIF-8 loading amount increased from 66wt% to 92wt%, the permeation flux of ZIF-8PE MMMs increased from 7 L·m -2 ·h -1 to 68 L·m -2 ·h -1 , and at the same time, the conductivity of the permeate was stabilized at 8 μS cm -1 . In contrast, the permeation flux of the commercial PVDF membrane under the same conditions was 23 L·m -2 ·h -1 , and the conductivity was about 101 μS cm -1 .

[0110] (9) Influence of Different Temperatures on the Performance of Vacuum Membrane Distillation

[0111] In Example 1, under the conditions of a feed of 10.5 wt% NaCl solution and a vacuum degree of 85 kPa, the vacuum membrane distillation performance at 40 - 80 °C was tested. As Figure 14 shown, as the temperature of the feed liquid increased from 40 °C to 80 °C, the permeation flux of ZIF-8PE MMM-92wt%-FDTS increased from 9.12 L·m -2 ·h -1 to 70.12 L·m -2 ·h -1 , while the conductivity of the permeate remained at about 8 μS cm -1 . The increase in temperature promoted the evaporation of water on the membrane surface and increased the temperature difference across the membrane, thus accelerating the transport of water vapor molecules in the membrane pores and increasing the permeation flux.

[0112] (10) Influence of Different Vacuum Degrees on the Performance of Vacuum Membrane Distillation

[0113] In Example 1, under the conditions of a feed liquid of 10.5 wt% NaCl solution and a temperature of 70 °C, the vacuum membrane distillation performance in the range of 45 - 85 kPa of vacuum degree was tested. As Figure 15 shown, as the vacuum degree increased from 45 kPa to 85 kPa, the permeation flux of ZIF-8PE MMM-92wt%-FDTS increased from 12.67 L·m -2 ·h -1 to 62.27 L·m -2 ·h -1 , while the conductivity of the permeate remained at about 8 μS cm -1 . The increase in vacuum degree increased the vapor pressure difference across the membrane and improved the permeation flux.

[0114] (11) Influence of Different Salt Solution Concentrations on the Performance of Vacuum Membrane Distillation

[0115] In Example 1, at a temperature of 70 °C and a vacuum degree of 85 kPa, as the NaCl concentration increased, the permeation flux showed a downward trend, as Figure 16 shown. When the NaCl concentration of the feed liquid increased to 31.5 wt%, the permeation flux of the commercial PVDF-FDTS membrane decreased to 3 L·m -2 ·h -1 , and the conductivity of the permeate was about 100 μS·cm -1 or so. In contrast, although the permeation flux of ZIF-8PE MMM-92wt%-FDTS decreased, it still maintained a relatively high flux (50 L·m -2 ·h -1), while the conductivity of the permeate remains at 10 μS cm -1 Below, its application potential in treating high-concentration brine is demonstrated.

[0116] (12) Evaluation of the anti-wetting performance of membrane distillation

[0117] In Example 1, after adding 0.1 mM sodium dodecyl sulfate (SDS) to the feed salt solution, the hydrophobic tails of SDS adsorbed on the membrane surface, causing the pores of the commercial PVDF-FDTS membrane to gradually become wet. The dissolved salts permeated into the distillate, the flux gradually increased, and the salt rejection rate decreased to 82%. However, ZIF-8PE MMM-92wt%-FDTS still had good anti-wetting performance and stable salt rejection performance for 0.4 mM SDS, and could operate continuously for 600 min, as Figure 17 shown.

[0118] (13) Evaluation of the anti-fouling performance of membrane distillation

[0119] Due to its rough surface structure and ultra-low surface energy, ZIF-8PE MMM-92wt%-FDTS could still maintain a stable water flux and excellent salt rejection rate within 600 minutes when the mineral oil concentration in the original solution was as high as 1000 ppm, as Figure 18 shown.

[0120] (14) Vacuum membrane distillation performance of the ultra-high loading SiO 2 mixed matrix membrane

[0121] In Comparative Example 6, under the conditions of a 10.5 wt% NaCl solution, a temperature of 70 °C, and a vacuum of 85 kPa, the water flux of the SiO 2 mixed matrix membrane was only 28.7 L·m -2 ·h -1 , as Figure 19 shown.

[0122] (15) Removal performance of VOCs during membrane distillation by the ultra-high loading ZIF-8 mixed matrix membrane

[0123] As Figure 20 shown, according to Example 5, the Bayer vapor adsorption curve at 60 °C shows that even under high-temperature conditions, toluene vapor can still quickly enter the ZIF-8 pores and there is no obvious desorption in the low-pressure region. As Figure 21 shown, the ZIF-8PE MMM-92wt%-FDTS membrane not only achieved efficient desalination but also effectively intercepted toluene molecules, making the toluene concentration in the permeate far lower than the 0.7 ppm safety limit and could operate stably for five cycle tests.

[0124] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention shall be regarded as being within the protection scope of the present invention.

Claims

1. A method for preparing a fully hydrophobic ultra-high loading MOF mixed matrix membrane, characterized in that: The method steps include: (1) mixing hydrophobic MOF particles with a particle size of 400 nm or more, a high molecular weight polymer and paraffin oil, heating and melting, and stirring uniformly to obtain a casting solution; the high molecular weight polymer is composed of high-density polyethylene particles and ultra-high molecular weight polyethylene powder in a mass ratio of 3 to 4:1, the weight average molecular weight of the high-density polyethylene particles is more than 40,000, and the density is 930 kg / m 3 ~970kg / m 3 ;The weight average molecular weight of ultra-high molecular weight polyethylene powder is above 1.5 million; (2) coating the casting solution on a conveyor belt and forming the film by a high-temperature roll-to-roll hot pressing process; removing the paraffin oil and drying the film to obtain an ultra-high MOF loading mixed matrix membrane with a thickness of more than 200 μm and a MOF loading of more than 92 wt%; (3) coating an organic solution containing fluorine silane on the surface of the ultra-high loading MOF mixed matrix membrane, and drying the membrane at 100° C. or above to obtain a fully hydrophobic ultra-high loading MOF mixed matrix membrane; wherein the mass fraction of fluorine silane in the organic solution containing fluorine silane is 1.5% to 3.5%, and the mass fraction of fluorine silane per 1 cm 2 The coating amount of the fluorosilane-containing organic solution on the ultra-high loading MOF mixed matrix membrane is 400-600 μL.

2. The method for preparing a fully hydrophobic ultra-high loading MOF mixed matrix membrane according to claim 1, characterized in that: In step (1), the particle size of the hydrophobic MOF particles is 400 to 2500 nm; and / or, the hydrophobic MOF particles are one of the hydrophobic ZIF series, the hydrophobic UiO-66 series, the hydrophobic MAF series, MIL-101 or FMOF-1; and / or, the heating melting temperature is 200-250°C; And / or, the mass ratio of the paraffin oil to the hydrophobic MOF particles is 0.5 to 3:

1.

3. The method for preparing a fully hydrophobic ultra-high loading MOF mixed matrix membrane according to claim 2, characterized in that: In step (1), the hydrophobic MOF particles are ZIF-8, ZIF-71, ZIF-7, UiO-66-(CF3)2, UiO-66-(CH3)2, MAF-X10, MAF-X13, MIL-101 or FMOF-1.

4. The method for preparing a fully hydrophobic ultra-high loading MOF mixed matrix membrane according to claim 1, characterized in that: In step (2), the high-temperature roller-to-roller hot pressing process molding temperature is 120-150° C., and the conveyor belt speed is 40-60 rpm.

5. The method for preparing a fully hydrophobic ultra-high loading MOF mixed matrix membrane according to claim 1, characterized in that: In step (2), the thickness of the ultra-high loading MOF mixed matrix membrane is 200 to 400 μm; And / or, the MOF loading of the ultra-high MOF mixed matrix membrane is 92 wt% to 96 wt%.

6. The method for preparing a fully hydrophobic ultra-high loading MOF mixed matrix membrane according to claim 1, characterized in that: In step (3), the fluorosilane is perfluorohexyltrimethoxysilane, perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltriethoxysilane, perfluorohexadecyltriethoxysilane, perfluorododecyltrichlorosilane, perfluorodecyltrichlorosilane or perfluorooctyltrichlorosilane; And / or, the organic phase in the organic solution of fluorine-containing silane is n-hexane or ethanol.

7. The method for preparing a fully hydrophobic ultra-high loading MOF mixed matrix membrane according to claim 1, characterized in that: In step (3), the coating is performed by immersion or scraping; And / or, the drying temperature is 120-140°C.

8. A fully hydrophobic ultra-high loading MOF mixed matrix membrane, characterized in that: It is prepared by the method according to any one of claims 1 to 7.

9. Use of the fully hydrophobic ultra-high loading MOF mixed matrix membrane as claimed in claim 8 in membrane distillation.

10. The use according to claim 9, wherein the mixed matrix membrane is used in the membrane distillation treatment of industrial wastewater containing surfactant and oil pollutants.

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