Distillation membrane for synchronously desalting and degrading pollutants and preparation method thereof

Abstract

The invention discloses a distillation membrane capable of synchronously desalting and degrading pollutants and a preparation method thereof, the distillation membrane comprises a hydrophobic layer and a catalytic layer, the catalytic layer is deposited on the hydrophobic layer through an electrostatic spinning technology, and the catalytic layer is prepared from a nano photocatalyst and polymer powder, the nano photocatalyst is obtained by loading a metal precursor and an organic ligand on a two-dimensional nanosheet and then calcining the two-dimensional nanosheet. The prepared distillation membrane is placed in an assembly, the hot side is in contact with a hydrophobic membrane, the cold side is in contact with a catalytic layer, wastewater is introduced into the hot side, circulating condensate water is introduced into the cold side, a light source is turned on at the cold side, and the conductivity, the water yield and the pollutant concentration of the cold side are monitored within a certain time. The distillation membrane disclosed by the invention can completely degrade volatile organic compounds on the cold side while completely intercepting non-volatile substances on the hot side, and is beneficial to promoting the application of membrane distillation industrialization.

Description

Technical Field

[0001] The present invention relates to the technical field of distillation membranes, and particularly to a distillation membrane for synchronous desalination and degradation of pollutants and a preparation method thereof. Background Art

[0002] The treatment of high-salt wastewater is a major environmental protection issue faced by the current industrial development. In China, the output of high-salt wastewater accounts for 5% of the total wastewater and is still increasing at a rate of 2% per year. The treatment of high-salt wastewater has a high proportion in sewage treatment and is the focus and difficulty of wastewater treatment research. The total salt content of high-salt wastewater is greater than 1%, containing relatively high Cl - , SO4 2- , Na + and Ca 2+ and other inorganic ions, and also contains organic substances such as glycerol and medium- and low-carbon chain organic substances. Membrane distillation is an effective technology for treating high-salt water, which can efficiently intercept non-volatile substances by using low-grade heat sources. The membrane distillation method is driven by the vapor pressure difference on both sides of the membrane. The water in the feed liquid vaporizes on the surface of the hydrophobic membrane to form steam, which passes through the membrane pores and enters the cold side for condensation, while the non-volatile substances in the feed liquid are intercepted.

[0003] Compared with reverse osmosis and conventional distillation, membrane distillation has the advantages of simple equipment, the ability to utilize low-grade heat sources, and theoretically achieving 100% interception of non-volatile substances. However, volatile organic compounds have a relatively high Henry coefficient and molecular kinetic size similar to that of water molecules. It is difficult for traditional distillation membranes to intercept volatile components, thereby causing pollution to the produced water. In recent years, researchers have constructed a dense layer on the surface of the hydrophobic membrane through technical means to achieve synchronous interception of volatile and non-volatile substances. Chinese Patent CN116020280A dissolves polyvinyl alcohol (PVA), tannic acid (TA), and cellulose nanocrystals (CNC) in an ethanol aqueous solution. Through the slow evaporation of ethanol, hydrogen bonds between PVA, TA, and CNC are reconstructed to form a dense hydrogel on the surface of the hydrophobic membrane, which can prevent surfactants and salt crystallization from contacting the membrane and achieve efficient interception of pollutants. Chinese Patent CN115382403A prepares a multi-layer composite membrane on an electrospun membrane by using interfacial polymerization technology and rotary drop coating technology. The composite membrane includes a superhydrophobic layer, a superhydrophilic layer, and two FTC layers from bottom to top. By utilizing the interfacial layer effect of FTC, the interception of volatile and non-volatile substances during the membrane distillation process is achieved. However, the membrane structures in the above patents are complex, the preparation processes are cumbersome, and at the same time, pollutants cannot be completely removed only by interception means, resulting in environmental risks. Summary of the Invention

[0004] The object of the present invention is to provide a distillation membrane for synchronous desalination and degradation of pollutants and a preparation method thereof, so as to solve the problems of complex structure, cumbersome preparation process and inability to remove pollutants of the above-mentioned distillation membrane. The present invention uses electrospinning technology to load a high-performance photocatalyst on a hydrophobic substrate membrane to obtain a composite distillation membrane, which is composed of a hydrophobic substrate membrane and a catalytic layer. The hydrophobic substrate membrane has high hydrophobicity and can provide a transmembrane channel for water vapor on the hot side to achieve the retention of inorganic salts; the catalytic layer faces the cold side and generates superoxide radicals under light conditions to achieve the efficient degradation of volatile organic compounds.

[0005] To achieve the above object, in the first aspect of the present invention, a distillation membrane for synchronous desalination and degradation of pollutants is provided. The distillation membrane includes a hydrophobic layer and a catalytic layer. The catalytic layer is deposited on the hydrophobic layer by electrospinning technology. The raw materials of the catalytic layer include a nano-photocatalyst and a polymer powder. The nano-photocatalyst is obtained by calcining a metal precursor and an organic ligand loaded on a two-dimensional nanosheet.

[0006] Preferably, the metal precursor includes at least one of indium nitrate, zinc nitrate, bismuth nitrate, titanium tetrachloride, nickel chloride, and manganese chloride; the organic ligand includes at least one of urea, 2-methylimidazole, and terephthalic acid.

[0007] Preferably, the two-dimensional nanosheet includes at least one of Mxene, MoS2, g-C3N4, and graphene oxide.

[0008] Preferably, the polymer powder includes at least one of polyacrylonitrile, polyethersulfone, and polyvinyl alcohol.

[0009] In the second aspect of the present invention, a preparation method of a distillation membrane for synchronous desalination and degradation of pollutants is provided, including the following steps:

[0010] S1: Load a metal precursor and an organic ligand on a two-dimensional nanosheet, and then perform calcination to obtain a nano-photocatalyst;

[0011] S2: Mix the nano-photocatalyst and the polymer powder in an organic solvent to obtain an electrospinning solution;

[0012] S3: By electrospinning technology, electrospin the electrospinning solution on the hydrophobic layer, and after drying and hot pressing, obtain the distillation membrane.

[0013] Preferably, in step S1, the metal precursor is dissolved in deionized water to form a metal solution, and at the same time, the organic ligand is dissolved in an organic solvent to form a ligand solution. The two-dimensional nanosheet is added to deionized water and ultrasonically treated to obtain a two-dimensional nanosheet dispersion;

[0014] Drop the ligand solution into the metal solution, and then add it to the two-dimensional nanosheet dispersion to obtain a mixture. Transfer the mixture to an autoclave for heating reaction. After the reaction is completed, centrifuge and dry to obtain a solid sample;

[0015] Calcine the solid sample to obtain a nano-photocatalyst.

[0016] Preferably, in step S1, the mass ratio of the metal precursor, the organic ligand, and the two-dimensional nanosheet is 1:(1-5):(1-5); the heating temperature is 100-150 °C, and the heating time is 15-20 h; the calcination temperature is 200-600 °C, and the calcination time is 3-8 h.

[0017] Preferably, in step S2, the organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; the mass ratio of the nano-photocatalyst, the polymer powder, and the organic solvent is 1:(1-5):(20-40).

[0018] Preferably, the specific process of electrospinning is as follows: preheat the electrospinning equipment to the set temperature, inject the prepared electrospinning solution into the spinneret at a constant rate through an injection pump, apply a high-voltage electric field between the spinneret and the collecting device, and fix the hydrophobic base film on the collecting device to ensure the flatness of the film surface. Place the hydrophobic base composite film deposited with the catalytic layer in a hot press for hot pressing to obtain a distillation membrane.

[0019] Preferably, the preheating temperature is 20-70 °C, the constant rate is 0.8-1 mL / h, and the diameter of the spinneret is 0.5-0.7 mm.

[0020] Preferably, in step S3, the hydrophobic layer is a hydrophobic base film, and the hydrophobic base film includes at least one of polytetrafluoroethylene, polypropylene, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene; the conditions for electrospinning are: voltage 10-30 kV, roller speed 50-200 rpm, spraying distance 5-25 cm, injection rate of the electrospinning solution 1-10 mL / h, and ambient humidity 30-70%.

[0021] Preferably, in step S3, the hot pressing temperature is 110-130 °C, the hot pressing pressure is 0.1-0.3 MPa, and the hot pressing time is 3-8 min.

[0022] The third aspect of the present invention provides an application of a distillation membrane for synchronous desalination and degradation of pollutants, and the application of the distillation membrane in the treatment of high-salt organic wastewater.

[0023] Preferably, the distillation membrane can treat high-salt organic wastewater in industries such as printing and dyeing, pharmaceutical, aquaculture, food, and electronics.

[0024] Therefore, the present invention adopts the above-mentioned distillation membrane for synchronous desalination and degradation of pollutants and its preparation method, which has the following beneficial effects:

[0025] (1) By loading a high-performance photocatalyst on a hydrophobic base membrane, the present invention realizes the interception of inorganic salts and the degradation of volatile organic compounds in high-salt feed liquid. While ensuring the permeation of water vapor, it can also degrade organic compounds under light or ultraviolet irradiation, which is applicable to the practical application of high-salt wastewater treatment and solves the problem that traditional membrane distillation technology only intercepts rather than removes organic compounds.

[0026] (2) The present invention composites the photocatalyst nanoparticles and the hydrophobic layer through electrospinning technology instead of directly coating the membrane to modify its performance. Compared with direct coating, electrospinning technology makes the distribution of catalysts on the membrane surface more uniform, increases the oxidation sites, can complete the modification with less raw materials, and the catalysts are firmly combined with the membrane and are not easy to fall off.

[0027] (3) In addition to degrading pollutants, the catalytic layer of the present invention can also enhance the photothermal conversion performance, and has excellent photothermal conversion performance in the design of the membrane. This layer can quickly absorb light energy and convert it into heat energy, so that the surface temperature of the membrane rises rapidly, which helps to improve the water flux of membrane distillation. Compared with traditional PVDF membranes or other membranes without photothermal conversion ability, the distillation membrane of the present invention can improve the evaporation efficiency in a shorter time.

[0028] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart for preparing the distillation membrane in Example 1;

[0030] Figure 2 is a SEM image of the catalytic layer thickness of the distillation membrane prepared in Example 1 and PAN nanofibers;

[0031] Figure 3 is the surface contact angle of the distillation membrane prepared in Example 1;

[0032] Figure 4 is the surface roughness of the distillation membrane prepared in Example 1;

[0033] Figure 5 is the change in the surface temperature of the distillation membrane prepared in Example 1;

[0034] Figure 6 is the flux, conductivity on the permeate side and degradation effect of PFOA on the hot side when the distillation membrane prepared in Example 2 irradiates the feed side;

[0035] Figure 7Flux, conductivity on the permeate side, and PFOA concentration variation diagrams of the distillation membrane prepared in Example 3 when irradiating the permeate side;

[0036] Figure 8 Flux of the distillation membrane prepared in Comparative Example 1, conductivity on the permeate side, and PFOA concentration on the hot side;

[0037] Figure 9 Flux of the distillation membrane prepared in Comparative Example 2, conductivity on the permeate side, and PFOA concentration on the hot side. Detailed implementation manners

[0038] The present invention will be further described below. It should be noted that this embodiment is based on the present technical solution, and detailed implementation manners and specific operation procedures are given, but the present invention is not limited to this embodiment.

[0039] Example 1

[0040] A preparation method of a distillation membrane for synchronous desalination and degradation of pollutants, comprising the following steps:

[0041] S1: First, stir and mix HCl (50 mL, 12 M) and LiF (2 g) to obtain a mixed solution. Secondly, slowly add the MAX phase Ti3AlC2 (2 g) precursor to the above mixed solution and continuously stir at 40 °C for 60 h. Then collect the etched Ti3C2 powder by centrifugation (5000 rpm), wash it several times with water until the pH is slightly acidic (pH 6.5). Finally, adopt a liquid-phase ultrasonic exfoliation technique in an inert gas and centrifuge at 5000 rpm for 1.5 h to obtain a well-dispersed Ti3C2 MXene solution, that is, a Ti3C2 Mxene dispersion.

[0042] S2: Dissolve 2.04 g of In(NO3)3·4.5H2O in 16 mL of deionized water to obtain a metal solution. At the same time, dissolve 2.0 g of urea in 10 mL of ethanol to form a ligand solution. Dropwise add the ligand solution to the metal solution at room temperature and stir for 2 h, and then add the Ti3C2 Mxene dispersion to obtain a mixture.

[0043] Transfer the mixture to an autoclave, react at 120 °C for 17 h, centrifuge and separate, then dry in a vacuum drying oven to obtain a solid sample. Then the solid sample is calcined in air at 300 °C for 5 h to obtain an In2O3@Mxene nano-photocatalyst ( Figure 1 as shown in A).

[0044] S3: Dissolve 3 g of PAN powder and 0.2 g of In2O3@Mxene nano-photocatalyst in 6.8 g of DMF solution, dissolve at 80 °C for 2 h to obtain a 3 wt% PAN solution, that is, an electrospinning solution.

[0045] S4: Electrospin the In2O3@MXene catalytic layer on the PVDF membrane (hydrophobic layer) using electrospinning technology, and obtain the In2O3@MXene / PVDF catalytic distillation membrane after hot pressing by a plastic machine (as shown in Figure 1 Figure B);

[0046] The specific process of electrospinning is as follows: Preheat the electrospinning equipment to the set temperature, inject the prepared electrospinning solution into the spinneret at a constant rate through an injection pump, apply a high-voltage electric field between the spinneret and the collection device, and fix the PVDF membrane on the collection device to ensure the flatness of the membrane surface. Place the hydrophobic base composite membrane deposited with the catalytic layer in a hot press for hot pressing to obtain the distillation membrane;

[0047] The conditions for electrospinning are: the preheating temperature is 50 °C, the constant rate is 1 mL / h, the spinneret diameter is 0.6 mm, the voltage is 20 kV, the roller speed is 100 rpm, the spraying distance is 15 cm, the injection rate of the electrospinning solution is 5 mL / h, and the environmental humidity is 50%;

[0048] The hot pressing temperature is 120 °C, the hot pressing pressure is 0.1 MPa, and the hot pressing time is 5 min.

[0049] Example 2

[0050] The difference between this example and Example 1 is: the type of two-dimensional nanosheets is different. The two-dimensional nanosheets used in this example are graphene oxide (GO) nanosheets. The metal precursor indium nitrate (In(NO3)3·4.5H2O) is loaded on the graphene oxide (GO) nanosheets by the hydrothermal method of Example 1 to form the In2O3@GO catalyst, and the catalyst is anchored on the PVDF membrane by electrospinning technology to obtain the In2O3@GO / PVDF catalytic membrane.

[0051] The preparation process of the GO dispersion is as follows: Add graphite powder (1 g) to the mixed acid of sulfuric acid (98%, 120 mL) and phosphoric acid (13 mL), stir for 30 min, slowly add potassium permanganate (6 g) at 20 °C and react for 12 h. Transfer the reaction solution to an ice bath, slowly add deionized water (200 mL), and then dropwise add hydrogen peroxide (5 mL) until the solution turns bright yellow. Wash alternately with 5% hydrochloric acid and deionized water until the pH of the supernatant is 7. Dissolve the graphite oxide in deionized water and ultrasonically exfoliate for 30 min, centrifuge at 3000 rpm for 30 min, and collect the supernatant to obtain the GO dispersion.

[0052] Example 3

[0053] The difference between this example and Example 1 lies in that the types of two-dimensional nanosheets are different. The two-dimensional nanosheets used in this example are carbon nitride (g-C3N4) nanosheets. The metal precursor indium nitrate (In(NO3)3·4.5H2O) is loaded onto the carbon nitride (g-C3N4) nanosheets by the hydrothermal method of Example 1 to form an In2O3@g-C3N4 catalyst, and the catalyst is anchored on the PVDF membrane by electrospinning technology to obtain an In2O3@g-C3N4 / PVDF catalytic membrane.

[0054] The preparation process of the g-C3N4 dispersion is as follows: Immerse the g-C3N4 powder in sulfuric acid (98%, 50 mL) and stir for 6 h. Wash the acid solution with deionized water until the pH = 7. Perform exfoliation by ultrasonic fragmentation in an ice bath for 30 min, centrifuge at 3000 rpm for 30 min, and collect the supernatant to obtain the g-C3N4 dispersion.

[0055] Example 4

[0056] The difference between this example and Example 1 lies in that the types of two-dimensional nanosheets are different. The two-dimensional nanosheets used in this example are molybdenum disulfide (MoS2) nanosheets. The metal precursor indium nitrate (In(NO3)3·4.5H2O) is loaded onto the molybdenum disulfide (MoS2) nanosheets by the hydrothermal method described in Example 1 to form an In2O3@MoS2 catalyst, and the catalyst is anchored on the PVDF membrane by electrospinning technology to obtain an In2O3@MoS2 / PVDF catalytic membrane.

[0057] The preparation process of the MoS2 dispersion is as follows: Add MoS2 powder (50 mg) to 50 mL of N-methylpyrrolidone and stir for 6 h to obtain a suspension. Use an ultrasonic fragmentation instrument to ultrasonically treat the above solution for 30 min under ice bath conditions, centrifuge at 3000 rpm for 30 min, and collect the supernatant to obtain the MoS2 dispersion.

[0058] Example 5

[0059] The difference between this example and Example 1 lies in that the types of metal precursors are different. The metal precursor used in this example is Zn(NO3)2·6H2O. The metal precursor zinc nitrate (Zn(NO3)2·6H2O) is loaded onto the MXene nanosheets by the hydrothermal method of Example 1 to form a ZnO@MXene catalyst, and the catalyst is anchored on the PVDF membrane by electrospinning technology to obtain a ZnO@MXene / PVDF catalytic membrane.

[0060] Example 6

[0061] The difference between this example and Example 1 lies in the type of metal precursor. The metal precursor used in this example is Bi(NO3)3.5H2O. The metal precursor bismuth nitrate (Bi(NO3)3·5H2O) is loaded onto MXene nanosheets by the hydrothermal method of Example 1 to form a Bi2O3@MXene catalyst, and the catalyst is anchored on a PVDF membrane by electrospinning technology to obtain a Bi2O3@MXene / PVDF catalytic membrane.

[0062] Example 7

[0063] The difference between this example and Example 1 lies in the type of metal precursor. The metal precursor used in this example is TiCl4. The metal precursor titanium tetrachloride (TiCl4) is loaded onto MXene nanosheets by the hydrothermal method of Example 1 to form a TiO2@MXene catalyst, and the catalyst is anchored on a PVDF membrane by electrospinning technology to obtain a TiO2@MXene / PVDF catalytic membrane.

[0064] Comparative Example 1

[0065] A commercial PVDF membrane (Millipore HVHP04700) was used for performance testing.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that the metal solution was not mixed with the Ti3C2 Mxene dispersion liquid. The specific preparation process is as follows:

[0068] S1: Dissolve 2.04 g of In(NO3)3·4.5H2O in 16 mL of deionized water to obtain a metal solution. At the same time, dissolve 2.0 g of urea in 10 mL of ethanol to form a ligand solution. Drop the ligand solution into the metal solution at room temperature and stir for 2 h to obtain a mixture.

[0069] Transfer the mixture to an autoclave, react at 120 °C for 17 h, centrifuge and separate, then dry in a vacuum drying oven to obtain a solid sample. Then, the solid sample is calcined in air at 300 °C for 5 h to obtain an In2O3 nano-photocatalyst.

[0070] S2: Dissolve 3 g of PAN powder and 0.2 g of In2O3 nano-photocatalyst in 6.8 g of DMF solution, and dissolve at 80 °C for 2 h to obtain a 3 wt% PAN solution, which is the electrospinning solution.

[0071] S3: Use electrospinning technology to electrospin an In2O3 catalytic layer on a PVDF membrane (hydrophobic layer), and obtain an In2O3 / PVDF catalytic distillation membrane after hot pressing by a plastic machine;

[0072] The specific process of electrospinning is as follows: Preheat the electrospinning equipment to the set temperature, inject the prepared electrospinning solution into the spinneret at a constant rate through an injection pump, apply a high-voltage electric field between the spinneret and the collection device, and fix the PVDF membrane on the collection device to ensure the flatness of the membrane surface. Place the hydrophobic base composite membrane deposited with the catalytic layer in a hot press for hot pressing to obtain a distillation membrane;

[0073] The conditions for electrospinning are: preheating temperature is 50 °C, constant rate is 1 mL / h, spinneret diameter is 0.6 mm, voltage is 20 kV, roller rotation speed is 100 rpm, spraying distance is 15 cm, injection rate of the electrospinning solution is 5 mL / h, and environmental humidity is 50%;

[0074] The hot pressing temperature is 120 °C, the hot pressing pressure is 0.1 MPa, and the hot pressing time is 5 min.

[0075] Test Examples

[0076] (1) Characterize the distillation membrane of Example 1.

[0077] ① Characterize the membrane surface morphology using a scanning electron microscope.

[0078] Paste a membrane sample of appropriate size onto the sample stage with conductive glue and sputter coat with gold for 30 s; during testing, send the membrane into the electron microscope cavity for observation. The results show that a uniform PAN nanofiber layer with a thickness of 40 μm is deposited on the surface of PVDF ( Figure 2 A), and the continuous overlap of PAN nanofibers generates interconnected pores throughout the layer, and abundant In2O3@MXene nanosheets are clearly detected on the fibers, indicating that the catalyst has been successfully loaded on the membrane surface ( Figure 2 B).

[0079] ② Use a contact angle measuring instrument to measure the contact angle of the membrane.

[0080] Use a contact angle instrument to characterize the hydrophilicity and hydrophobicity of the double-layer membrane. The test results show that the In2O3@MXene / PVDF membrane has Janus hydrophilic and hydrophobic properties. The upper In2O3@MXene catalytic layer is hydrophilic with a contact angle of 84.5°, and the lower PVDF layer is hydrophobic with a contact angle of 129° ( Figure 3 ).

[0081] ③ Use a metallurgical microscope to measure the membrane roughness.

[0082] Cut the membrane sample into small rectangular strips and lay them flat on the microscope lens. The test results show that after electrospinning combined with In2O3@MXene nanoparticles, the roughness of the PVDF membrane increases from 1.37 μm ( Figure 4A) Increased to 3.62 μm for the In2O3@MXene / PVDF membrane ( Figure 4 B), and the increased roughness is beneficial to increasing the solid-liquid contact area.

[0083] ④ Photothermal conversion performance test.

[0084] An infrared camera was used to monitor the temperature changes of the two membranes under 1 kW / m 2 light irradiation. Under 30 minutes of light irradiation, the temperature of the commercial PVDF (Comparative Example 1) increased slightly (∼2 °C), while the upper surface temperature of the In2O3@MXene / PVDF membrane (Example 1) rapidly increased to ∼60 °C within 5 minutes ( Figure 5 A and Figure 5 B), indicating that the catalytic layer has good photothermal conversion performance and helps to improve the membrane flux.

[0085] (2) The performance of the distillation membranes of Example 1 and Comparative Examples 1 to 2 was tested.

[0086] The test procedure was as follows:

[0087] A direct contact membrane distillation (DCMD) device was used to evaluate the performance of the In2O3@MXene / PVDF catalytic distillation membrane. An NaCl solution with a perfluorooctanoic acid (PFOA) concentration of 75 mg / L was prepared as the feed liquid, and the feed liquid was circulated and adsorbed in the membrane module at a flow rate of 0.5 m / s for 10 min by a gear pump, and then heated to 80 ± 2 °C with a constant temperature water bath. Deionized water was selected on the permeate side, and the temperature of the permeate side was maintained at 20 ± 2 °C, and the permeate was circulated at a flow rate of 0.5 m / s by a gear pump. During the experiment, a conductivity meter was used to monitor the conductivity of the produced water on the permeate side in real time, and the flux was recorded according to the change of the balance on the permeate side. A mercury lamp was set on the feed liquid side. The flux value J (kg / m 2 h) was calculated by Equation 1:

[0088] J = Δm / At (1)

[0089] In the formula, Δm (kg) is the mass difference of pure water measured by an analytical balance within the time interval t (h), and A (m 2 ) is the effective membrane area.

[0090] The PFOA degradation rate (%) was calculated by Equation 2:

[0091] R = (C0 - C t ) / C0 × 100% (2)

[0092] In the formula, C0 is the initial concentration of PFOA (mg / L), and C t is the concentration of PFOA at time t (mg / L).

[0093] The test results are shown inFigure 6 , Figure 8 and Figure 9 .

[0094] Figure 6 A shows that when the mercury lamp is set on the stock solution side, the In2O3@MXene / PVDF membrane (Example 1) can retain 99% of NaCl, and the conductivity on the permeate side remains below 5 μS / cm. At the same time, due to the high photothermal conversion efficiency of the catalytic layer, the flux of the In2O3@MXene / PVDF membrane remains above 34 kg / m 2 h. On the other hand, the catalytic distillation membrane has high catalytic activity, more than 90% of PFOA is degraded, and it has good reusability, retaining more than 85% of the removal rate after 5 cycles ( Figure 6 B).

[0095] The membrane test results of Comparative Example 1 show that the flux of the commercial PVDF membrane slowly decreases from 25.5 kg / m 2 h to 23.8 kg / m 2 h. The gradual decrease in flux may be caused by concentration polarization ( Figure 8 A). Due to the poor photothermal conversion effect on the surface of the PVDF membrane under light, in contrast, the In2O3@MXene / PVDF membrane shows higher and more stable flux, which is 34 kg / m 2 h. The concentration of PFOA in the feed liquid gradually increases with the increase of the running time, which is due to the lack of catalytic degradation effect of the PVDF membrane and the continuous entry of pure water into the permeate side, resulting in the gradual increase of the PFOA concentration ( Figure 8 B).

[0096] Due to the excellent thermal and electrical conductivity of two-dimensional nanosheets, the photothermal conversion efficiency can be improved under light conditions. At the same time, its excellent electron transport ability promotes the separation of photo-generated carriers and improves the photocatalytic performance. However, compared with Example 1, the flux of the In2O3 / PVDF membrane in Comparative Example 2 decreases to 23.5 kg / m 2 h, and the degradation rate of PFOA is greatly reduced. The final concentration of PFOA is still 48 mg / L ( Figure 9 ). This shows the importance of first loading the In2O3 catalyst on two-dimensional nanosheets to form a composite catalyst and then adding a polymer for electrospinning in the present invention.

[0097] (3) Test the performance of the distillation membranes of Examples 1 to 7.

[0098] The test process is as follows:

[0099] The performance of the distillation membranes of the examples and comparative examples was evaluated using a direct contact membrane distillation (DCMD) device. An NaCl solution with a perfluorooctanoic acid (PFOA) concentration of 75 mg / L was prepared as the feed liquid, and the feed liquid was circulated and adsorbed in the membrane module at a flow rate of 0.5 m / s for 10 min by a gear pump, and then heated to 80 ± 2 °C with a constant temperature water bath. Deionized water was selected on the permeate side, and the temperature of the permeate side was maintained at 20 ± 2 °C, and the permeate was circulated at a flow rate of 0.5 m / s by a gear pump. During the experiment, a conductivity meter was used to monitor the conductivity of the produced water on the permeate side in real time, and the flux was recorded according to the change of the balance on the permeate side. A mercury lamp was set on the permeate side to shield the influence of inorganic salts on degradation. The calculation method of the flux value and the calculation method of the PFOA degradation rate were the same as those in the above test example (2). The performance test results of the distillation membranes of Examples 1 to 7 are shown in Table 1.

[0100] Table 1 Performance test results of the distillation membranes of Examples 1 to 7

[0101]

[0102] Figure 7 A shows that the flux of the In2O3@MXene / PVDF membrane (Example 1) can be stabilized at 29 kg / m 2 h, with a high retention rate for NaCl, and the conductivity of the permeate side is less than 5 μS / cm. When the mercury lamp is set on the permeate side, the initial concentration of PFOA entering the permeate side is about 10 mg / L. Under light irradiation, the In2O3@MXene / PVDF membrane can effectively remove most of the PFOA on the permeate side, and the concentration of PFOA in the final product water is below 1 mg / L, indicating its high degradation efficiency for PFOA ( Figure 7 B).

[0103] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A distillation membrane for synchronous desalination and degradation of pollutants, characterized in that: The distillation membrane comprises a hydrophobic layer and a catalytic layer. The catalytic layer is deposited on the hydrophobic layer by electrospinning technology. The raw materials of the catalytic layer include a nano-photocatalyst and polymer powder. The nano-photocatalyst is obtained by calcining a metal precursor and an organic ligand supported on a two-dimensional nanosheet.

2. The distillation membrane for synchronous desalination and degradation of pollutants according to claim 1, characterized in that: The metal precursor includes at least one of indium nitrate, zinc nitrate, bismuth nitrate, titanium tetrachloride, nickel chloride, and manganese chloride; The organic ligand includes at least one of urea, 2-methylimidazole, and terephthalic acid.

3. A distillation membrane for synchronous desalination and degradation of pollutants according to claim 1, characterized in that: The two-dimensional nanosheet includes at least one of Mxene, MoS2, g-C3N4, and graphene oxide.

4. A distillation membrane for synchronous desalination and degradation of pollutants according to claim 1, characterized in that: The polymer powder includes at least one of polyacrylonitrile, polyethersulfone, and polyvinyl alcohol.

5. The preparation method of a distillation membrane for synchronous desalination and degradation of pollutants according to any one of claims 1 to 4, characterized in that: It includes the following steps: S1: Load the metal precursor and the organic ligand on the two-dimensional nanosheet, and then perform calcination to obtain the nano-photocatalyst; S2: Mix the nano-photocatalyst and the polymer powder in an organic solvent to obtain an electrospinning solution; S3: Through electrospinning technology, electrospin the electrospinning solution on the hydrophobic layer, and after drying and hot pressing, obtain the distillation membrane.

6. The preparation method of a distillation membrane for synchronous desalination and degradation of pollutants according to claim 5, characterized in that: In step S1, dissolve the metal precursor in deionized water to form a metal solution, and at the same time dissolve the organic ligand in an organic solvent to form a ligand solution. Add the two-dimensional nanosheet to deionized water and perform ultrasonic treatment to obtain a two-dimensional nanosheet dispersion; Drop the ligand solution into the metal solution, then add it to the two-dimensional nanosheet dispersion to obtain a mixture. Transfer the mixture to an autoclave for heating reaction. After the reaction is completed, perform centrifugation and drying to obtain a solid sample; Calcine the solid sample to obtain the nano-photocatalyst.

7. The preparation method of a distillation membrane for synchronous desalination and degradation of pollutants according to claim 6, characterized in that: In step S1, the mass ratio of the metal precursor, the organic ligand, and the two-dimensional nanosheet is 1: (1-5): (1-5); the heating temperature is 100-150 °C, the heating time is 15-20 h; the calcination temperature is 200-600 °C, and the calcination time is 3-8 h.

8. The preparation method of a distillation membrane for synchronous desalination and degradation of pollutants according to claim 5, characterized in that: In step S2, the organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; the mass ratio of the nano-photocatalyst, the polymer powder, and the organic solvent is 1: (1-5): (20-40).

9. The preparation method of a distillation membrane for synchronous desalination and degradation of pollutants according to claim 5, characterized in that: In step S3, the hydrophobic layer is a hydrophobic base membrane, and the hydrophobic base membrane includes at least one of polytetrafluoroethylene, polypropylene, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene; the conditions for electrospinning are: voltage 10-30 kV, roller speed 50-200 rpm, spraying distance 5-25 cm, injection rate of the electrospinning solution 1-10 mL / h, and environmental humidity 30-70%.

10. Use of a distillation membrane for synchronous desalination and degradation of pollutants according to any one of claims 1 to 4, characterized in that: Application of the distillation membrane in the treatment of high-salt organic wastewater.

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