MXene-doped photothermal distillation membrane, preparation method and application thereof

Abstract

The application belongs to the technical field of separation membranes, and particularly relates to a MXene-doped photothermal distillation membrane as well as a preparation method and application thereof. In view of the defects and deficiencies of obvious temperature polarization, low flux, easy pollution and wetting in the existing membrane distillation technology, the application is based on the excellent photothermal conversion efficiency and anti-pollution property of MXene, and the MXene is compounded with hydrophilic materials such as graphene oxide, polymerized dopamine and chitosan, and then is deposited on the surface of a hydrophobic microporous membrane to form a photothermal composite layer, so that the composite membrane has a double-layer structure of a hydrophilic surface layer and a hydrophobic bottom layer, the photothermal conversion efficiency is relatively high, the photothermal membrane distillation has a high pollutant interception efficiency and a stable permeation flux when treating salt-containing organic wastewater, and the simultaneous improvement of indexes such as the photothermal membrane distillation heat efficiency, the anti-pollution performance and the permeation flux can be realized, and the application has a wide application prospect in the treatment of wastewater by membrane distillation and seawater desalination.

Description

Technical Field

[0001] This invention belongs to the field of separation membrane technology, specifically relating to an MXene-doped photothermal distillation membrane, its preparation method, and its application. Background Technology

[0002] Membrane distillation technology creates a vapor pressure difference across a hydrophobic microporous membrane by heating the feed water and cooling the product water. This vapor pressure difference forces water molecules in the wastewater through the membrane in gaseous form, where they are condensed and recovered on the other side. Compared to pressure-driven membrane separation processes such as reverse osmosis, membrane distillation can operate at atmospheric pressure, is highly adaptable to different wastewater types, produces high-quality effluent, and can utilize low-grade heat sources such as industrial waste heat to drive the membrane separation process. It demonstrates excellent application potential in the resource recovery and reuse of high-salt organic wastewater and in achieving near-zero discharge of industrial wastewater.

[0003] However, because membrane distillation requires water molecules to undergo a gas-liquid phase transition on the membrane surface, significant temperature polarization occurs, resulting in low thermal efficiency and low water flux. The development and application of photothermal distillation membranes can help overcome temperature polarization and improve thermal efficiency. Currently, photothermal materials with hydrophobic properties, such as noble metals, carbon nanotubes, and graphene, are commonly used to form a photothermal layer on the membrane surface. However, the deposition of these hydrophobic photothermal materials on the membrane surface may increase mass transfer resistance, leading to reduced flux. Moreover, the photothermal conversion efficiency of distillation membranes is relatively low. Introducing more efficient photothermal materials is expected to significantly improve the photothermal conversion efficiency of distillation membranes.

[0004] On the other hand, high-salt organic wastewater contains high concentrations and complex compositions of pollutants, leading to severe membrane fouling during membrane distillation and a rapid decline in distillation flux. Traditional photothermal materials may also adsorb pollutants from the wastewater, exacerbating membrane fouling or causing membrane wetting. This results in a decrease in both flux and pollutant removal efficiency during wastewater treatment, making it difficult to simultaneously achieve high thermal efficiency, high flux, and antifouling properties in membrane distillation. Therefore, improving the antifouling properties of the distillation membrane under localized heating conditions is crucial for the development of photothermal membrane distillation. Novel photothermal membrane materials need to be developed to simultaneously improve photothermal conversion efficiency, permeate flux, and antifouling performance. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings and deficiencies of existing membrane distillation technologies, such as significant temperature polarization, low flux, and susceptibility to fouling and wetting, by providing a high-flux, fouling-resistant photothermal composite membrane for photothermal membrane distillation. The photothermal composite membrane of this invention leverages the excellent photothermal conversion efficiency and antifouling properties of MXene. MXene is combined with hydrophilic materials such as graphene oxide, polymeric dopamine, and chitosan, and then deposited on the surface of a hydrophobic microporous membrane to form a photothermal composite layer. This results in a bilayer structure with a hydrophilic surface and a hydrophobic bottom layer, leading to high photothermal conversion efficiency. When treating saline organic wastewater, it exhibits high pollutant retention efficiency and stable permeate flux, simultaneously improving the thermal efficiency, antifouling performance, and permeate flux of photothermal membrane distillation. It has broad application prospects in membrane distillation for wastewater treatment and seawater desalination.

[0006] To achieve the above objectives, the present invention employs the following technical solutions:

[0007] An MXene-doped photothermal distillation membrane is provided, comprising a bilayer structure in which an MXene-doped hydrophilic surface layer is bonded to a hydrophobic bottom layer. The MXene-doped hydrophilic surface layer is a composite photothermal material of MXene and a hydrophilic polymer, and the hydrophobic bottom layer is a hydrophobic substrate membrane.

[0008] Furthermore, the hydrophilic polymer is polydopamine, polyvinyl alcohol, polyethylene glycol, polyethyleneimine, graphene oxide, chitosan, sodium alginate, cellulose, and copolymers or compositions thereof.

[0009] MXene is a two-dimensional transition metal carbide or nitride with the general formula M. n+1 X n , where M represents a transition metal (such as Sc, Ti, Zr, Hf, V, Nb, Ta, Cr and Mo), X is carbon or nitrogen, and n is a positive integer.

[0010] MXene can be obtained by using fluoride or alkaline etching of layered precursors of metal carbon / nitride.

[0011] A method for preparing the MXene-doped photothermal distillation film includes the following steps:

[0012] Step 1, Preparation of MXene-doped composite photothermal material: MXene and hydrophilic polymer were dissolved in deionized water and ultrasonically dispersed. Dopamine hydrochloride was then added and stirred at room temperature. Tris-HCl buffer solution was then added, and the mixture was placed in a water bath and stirred to react. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and vacuum dried to obtain solid powder of MXene-doped composite photothermal material.

[0013] Step 2, Treatment of hydrophobic base membrane: First, soak the hydrophobic base membrane in isopropanol, then soak it in deionized water and let it stand and dry. Then, soak the hydrophobic base membrane soaked in isopropanol and deionized water in Tris-HCl buffer solution of dopamine, stir and react at room temperature, then wash it several times with deionized water and let it dry for later use.

[0014] Step 3, Preparation of MXene-doped photothermal distillation membrane: The MXene-doped composite photothermal material solid powder obtained in Step 1 is dissolved in deionized water and ultrasonically dispersed. Then it is combined with the hydrophobic substrate membrane surface treated in Step 2. The membrane surface is then washed with deionized water and immersed in anhydrous ethanol to remove excess MXene-doped composite photothermal material, thus obtaining the MXene-doped photothermal distillation membrane.

[0015] Furthermore, in step 1, the mass ratio of MXene to hydrophilic polymer is 1 to 200:10, and the hydrophilic polymer is polydopamine, polyvinyl alcohol, polyethylene glycol, polyethyleneimine, graphene oxide, chitosan, sodium alginate, cellulose, and copolymers or compositions thereof, and the mass ratio of dopamine hydrochloride to MXene / hydrophilic polymer mixture is 1:1 to 5.

[0016] Furthermore, in step 1, the ultrasonic dispersion time is 0.5–2 h; the stirring time at room temperature is 0.5–2 h; the water bath temperature is 50–80 °C; the stirring reaction time in the water bath is 1–2 h, and the stirring speed is 400–900 rpm; the centrifugation time is 10–20 min, and the rotation speed is 3000–5000 rpm; and the washing is performed more than 3 times.

[0017] Furthermore, in steps 1 and 2, the concentration of the Tris-HCl buffer solution is 50 mmol / L and the pH is 8.5, and in step 2, the concentration of the Tris-HCl buffer solution for dopamine is 0.2–2 g / L.

[0018] Furthermore, in step 2, the hydrophobic base membrane is one of polytetrafluoroethylene, polyvinylidene fluoride, and polypropylene.

[0019] Furthermore, in step 2, the isopropanol soaking time is 1-2 hours, the deionized water soaking time is 6-14 hours, the stirring reaction time is 1-24 hours, and the washing is performed more than 3 times.

[0020] Furthermore, in step 3, the loading of the MXene-doped composite photothermal material on the treated hydrophobic substrate film surface is 0.1–5 mg / cm². 2 The method of combining the hydrophobic substrate film surface treated in step 2 is one of spraying, scraping, vacuum filtration, dip coating or electrospinning.

[0021] Furthermore, the ultrasonic treatment time in step 3 is 1 to 6 hours.

[0022] An application of the MXene-doped photothermal distillation membrane is used for membrane distillation treatment of wastewater containing inorganic salts and / or organic matter.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] This invention prepares a photothermal composite membrane by doping MXene with hydrophilic materials such as graphene oxide (GO), polydopamine (PDA), and chitosan (CTS), leveraging the synergistic advantages of composite materials. The prepared photothermal composite membrane exhibits good stability, high photothermal efficiency, and high retention efficiency for most inorganic salts and organic substances. Utilizing the excellent photothermal conversion characteristics and hydrophilicity of materials such as MXene, GO, and PDA, the prepared hydrophilic-hydrophobic composite photothermal membrane can simultaneously improve membrane distillation thermal efficiency, antifouling properties, and permeation flux. Furthermore, the photothermal distillation membrane preparation process of this invention is simple and operates under mild conditions, thus broadening the applications of photothermal distillation membranes. Attached Figure Description

[0025] Figure 1 A schematic diagram of the preparation process of MXene-doped photothermal distillation film;

[0026] Figure 2 SEM image of MXene / GO / PDA composite photothermal material;

[0027] Figure 3 SEM cross-sectional image of the surface of the MXene-doped photothermal distillation film;

[0028] Figure 4 The contact angle between the surface of the MXene-doped photothermal distillation film and water;

[0029] Figure 5 This is a schematic diagram of a photothermal film distillation system;

[0030] Figure 6 The graph shows the photothermal properties of the MXene / GO / PDA composite distillation membrane. Detailed Implementation

[0031] Example 1

[0032] like Figure 1 As shown, a method for preparing an MXene-doped photothermal distillation film includes the following steps:

[0033] Step 1, Preparation of MXene-doped composite photothermal materials:

[0034] 1g of Ti3AlC2 powder was slowly added to 10mL of HCl solution containing 1g of LiF at a concentration of 9mol / L for chemical etching. The mixture was magnetically stirred in a water bath at 35℃ for 20h, then washed with deionized water and centrifuged at 3500rpm until the pH of the supernatant was about 6. The precipitate was then vacuum dried to obtain MXene.

[0035] MXene and graphene oxide (GO) were dissolved in deionized water at a mass ratio of 1:3 and ultrasonically dispersed for 1 h. Dopamine hydrochloride was then added to achieve a mass ratio of dopamine hydrochloride to MXene / GO mixture of 1:3. The mixture was stirred at room temperature for 1 h, followed by the addition of a 50 mmol / L Tris-HCl buffer solution (pH 8.5). The mixture was then placed in a 60°C water bath and stirred at 600 rpm for 12 h. After the reaction was complete, the mixture was cooled to room temperature, centrifuged at 4000 rpm for 15 min, washed at least three times, and vacuum dried to obtain a solid powder of MXene-doped composite photothermal material. Its surface morphology is as follows: Figure 2 As shown.

[0036] Step 2, Treatment of the hydrophobic basement membrane:

[0037] First, soak the hydrophobic polyvinylidene fluoride (PVDF) base membrane in isopropanol for 1 hour, then soak it in deionized water for 12 hours and let it stand and air dry. Next, soak the hydrophobic base membrane soaked in isopropanol and deionized water in a Tris-HCl buffer solution (50 mmol / L, pH=8.5) with a dopamine concentration of 1 g / L and stir at room temperature for 12 hours. Then wash it with deionized water more than 3 times and air dry for later use.

[0038] Step 3, Preparation of MXene-doped photothermal distillation film:

[0039] The MXene-doped composite photothermal material solid powder obtained in step 1 was dissolved in deionized water and ultrasonically dispersed for 2 hours. Then, the composite material was bonded to the surface of the hydrophobic substrate membrane treated in step 2 by vacuum filtration. The loading of the MXene-doped composite photothermal material on the treated hydrophobic substrate membrane surface was 3.5 mg / cm³. 2 The membrane surface is then washed with deionized water and immersed in anhydrous ethanol to remove excess MXene-doped composite photothermal material, thus obtaining the MXene-doped photothermal distillation membrane, the cross-sectional morphology of which is as follows. Figure 3 As shown, the MXene-doped composite photothermal material is bonded to the surface of the PVDF substrate. Hydrophilicity / hydrophobicity tests of the membrane surface show that the original hydrophobic PVDF substrate membrane has a water contact angle of 119.8°, while the contact angle of the membrane surface with water after loading the MXene composite material is as follows: Figure 4As shown, the contact angle decreased significantly to 68.7°, indicating that the surface of the composite membrane is hydrophilic, forming a bilayer composite membrane structure with a hydrophilic surface and a hydrophobic bottom layer.

[0040] Example 2

[0041] A method for preparing an MXene-doped photothermal distillation film includes the following steps:

[0042] Step 1, Preparation of MXene-doped composite photothermal materials:

[0043] 1g of Ti3AlC2 powder was slowly added to 10mL of 50wt% hydrofluoric acid (HF) solution, and etched by stirring in a water bath at 25℃ for 24h. Then it was washed with deionized water and centrifuged at 3000rpm until the pH of the supernatant was about 6. The precipitate was then vacuum dried to obtain MXene.

[0044] MXene and chitosan (CTS) were dissolved in deionized water at a mass ratio of 20:1 and ultrasonically dispersed for 2 hours. Then, dopamine hydrochloride was added to make the mass ratio of dopamine hydrochloride to MXene / CTS mixture 1:1. The mixture was stirred at room temperature for 2 hours. Then, a Tris-HCl buffer solution with pH = 8.5 and a concentration of 50 mmol / L was added. The mixture was placed in an 80°C water bath and stirred at 400 rpm for 24 hours. After the reaction was completed, the mixture was cooled to room temperature, centrifuged at 5000 rpm for 10 minutes, washed more than 3 times, and vacuum dried to obtain MXene-doped composite photothermal material solid powder.

[0045] Step 2, Treatment of the hydrophobic basement membrane:

[0046] First, soak the hydrophobic polytetrafluoroethylene (PTFE) base membrane in isopropanol for 1.5 hours, then soak it in deionized water for 14 hours and let it stand and air dry. Next, soak the hydrophobic base membrane soaked in isopropanol and deionized water in a Tris-HCl buffer solution (50 mmol / L, pH=8.5) with a dopamine concentration of 0.2 g / L and stir at room temperature for 24 hours. Then wash it with deionized water more than 3 times and air dry for later use.

[0047] Step 3, Preparation of the photothermal distillation membrane:

[0048] The MXene-doped composite photothermal material solid powder obtained in step 1 was dissolved in deionized water and ultrasonically dispersed for 1 hour. Then, the composite material was bonded to the surface of the hydrophobic substrate membrane treated in step 2 using a scraping method. The loading of the MXene-doped composite photothermal material on the treated hydrophobic substrate membrane surface was 5 mg / cm³. 2The membrane surface was then washed with deionized water and immersed in anhydrous ethanol to remove excess MXene-doped composite photothermal material, thus obtaining the MXene-doped photothermal distillation membrane. Hydrophilicity / hydrophobicity tests showed that the contact angle between the MXene-doped photothermal distillation membrane and water was 66.5°.

[0049] Example 3

[0050] A method for preparing an MXene-doped photothermal distillation film includes the following steps:

[0051] Step 1, Preparation of MXene-doped composite photothermal materials:

[0052] 1g of Ti3AlC2 powder was slowly added to 10mL of HCl solution containing 1g of LiF at a concentration of 9mol / L for chemical etching. The mixture was then stirred in a water bath at 40℃ for 16h, washed with deionized water, and centrifuged at 5000rpm until the pH of the supernatant was about 6. The precipitate was then vacuum dried to obtain MXene.

[0053] MXene and polyvinyl alcohol (PVA) were dissolved in deionized water at a mass ratio of 1:10 and ultrasonically dispersed for 1 h. Then, dopamine hydrochloride was added to make the mass ratio of dopamine hydrochloride to MXene / GO mixture 1:5. The mixture was stirred at room temperature for 0.5 h, and then a Tris-HCl buffer solution with pH = 8.5 and a concentration of 50 mmol / L was added. The mixture was placed in a 50 °C water bath and stirred at 900 rpm for 2 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged at 3000 rpm for 20 min, washed more than 3 times, and vacuum dried to obtain MXene-doped composite photothermal material solid powder.

[0054] Step 2, Treatment of the hydrophobic basement membrane:

[0055] First, soak the hydrophobic polypropylene (PP) basement membrane in isopropanol for 2 hours, then soak it in deionized water for 6 hours and let it stand and air dry. Next, soak the hydrophobic basement membrane soaked in isopropanol and deionized water in a Tris-HCl buffer solution (50 mmol / L, pH=8.5) with a dopamine concentration of 2 g / L and stir at room temperature for 4 hours. Then wash it with deionized water more than 3 times and air dry for later use.

[0056] Step 3, Preparation of the photothermal distillation membrane:

[0057] The MXene-doped composite photothermal material solid powder obtained in step 1 was dissolved in deionized water and ultrasonically dispersed for 6 hours. Then, the composite material was bonded to the surface of the hydrophobic substrate film treated in step 2 by spraying. The loading of the MXene-doped composite photothermal material on the treated hydrophobic substrate film surface was 0.5 mg / cm³. 2The membrane surface was then washed with deionized water and immersed in anhydrous ethanol to remove excess MXene-doped composite photothermal material, thus obtaining the MXene-doped photothermal distillation membrane. Hydrophilicity / hydrophobicity tests showed that the contact angle between the MXene-doped photothermal distillation membrane and water was 72.3°.

[0058] Example 4

[0059] This embodiment provides a method for using an MXene-doped photothermal composite membrane for membrane distillation to treat saline organic wastewater. The specific steps are as follows:

[0060] The photothermal composite membrane from Example 1 was used for membrane distillation treatment of wastewater containing 3000 mg / L NaCl and 50 mg / L humic acid. The photothermal membrane distillation system (such as...) Figure 5 (As shown) The hot and cold side cycling temperatures were set to 20℃ and 50℃ respectively. The photothermal performance test results of the composite film surface after 30s of sunlight exposure under one sunlight condition are as follows. Figure 6 As shown, when the membrane surface temperature rises to 57.6℃, the average permeate flux of membrane distillation is 30.7 L / m³. 2 The MXene-doped photothermal composite membrane exhibits a 53% increase in flux compared to a single-layer PVDF hydrophobic membrane and a salt rejection rate exceeding 99.5%, indicating that the membrane distillation flux and pollutant rejection performance are beneficial for improving membrane distillation efficiency.

[0061] Example 5

[0062] This embodiment provides a method for using an MXene-doped photothermal composite membrane for membrane distillation to treat saline organic wastewater. The specific steps are as follows:

[0063] The photothermal composite membrane from Example 1 was used for membrane distillation treatment of wastewater from an actual industrial park. The COD concentration was 250–350 mg / L, and the conductivity was 3.8–4.5 mS / cm. The circulating temperatures of the hot and cold sides of the photothermal membrane distillation system were set to 20°C and 50°C, respectively. A photothermal membrane distillation experiment was conducted under sunlight conditions, and the average permeate flux was 28.5 L / m³. 2 The MXene-doped photothermal composite membrane exhibits a 39% higher efficiency in treating pollutants compared to a single-layer PVDF hydrophobic membrane, with a pollutant retention efficiency exceeding 99%, demonstrating its excellent treatment effect on actual industrial wastewater.

[0064] Example 6

[0065] This embodiment provides a method for using an MXene-doped photothermal composite membrane for membrane distillation to treat saline organic wastewater. The specific steps are as follows:

[0066] The photothermal composite membrane from Example 2 was used for membrane distillation treatment of wastewater containing 1000 mg / L CaSO4 and 50 mg / L sodium dodecyl sulfate (SDS) surfactant. The circulating temperatures of the hot and cold sides of the photothermal membrane distillation system were set to 20°C and 50°C, respectively. Under both sunlight irradiation conditions, the surface temperature of the composite membrane rose to 61.5°C after 30 seconds of illumination, and the average membrane distillation flux was 36.4 L / m³. 2 The flux density of the MXene-doped photothermal composite film is 48% higher than that of a single-layer PTFE hydrophobic film, and the conductivity of the produced water remains below 5 μS / cm, indicating that the MXene-doped photothermal composite film has excellent flux enhancement and anti-wetting properties.

[0067] Example 7

[0068] This embodiment provides a method for using an MXene-doped photothermal composite membrane for membrane distillation to treat saline organic wastewater. The specific steps are as follows:

[0069] The photothermal composite membrane from Example 3 was used for membrane distillation treatment of wastewater containing 3000 mg / L NaCl and 100 mg / L mineral oil. The circulating temperatures of the hot and cold sides of the photothermal membrane distillation system were set to 20°C and 40°C, respectively. Under two solar illumination conditions, the surface temperature of the composite membrane rose to 58.5°C after 60 seconds of illumination, and the average membrane distillation flux was 16.7 L / m³. 2 The efficiency of the photothermal composite membrane is 38% higher than that of a single-layer PP hydrophobic membrane, and the retention efficiency of mineral oil is higher than 99.5%, indicating that the photothermal composite membrane has a good treatment effect on oily and salty wastewater.

[0070] Comparative Example

[0071] This comparative example provides a method for preparing a GO / PDA composite membrane without MXene doping and its application in membrane distillation for treating saline organic wastewater. The specific steps are as follows:

[0072] The PVDF hydrophobic base membrane was soaked in isopropanol and deionized water for 1 h and 12 h respectively, and then allowed to stand and air dry. It was then soaked in Tris-HCl buffer solution (50 mmol / L, pH=8.5) with a dopamine concentration of 1 g / L and stirred at room temperature for 12 h. After that, it was washed with deionized water more than 3 times and then air dried for later use.

[0073] A 5 mg / L GO aqueous solution was ultrasonically treated for 1 hour, and GO was then bound to the surface of a dopamine-treated PVDF membrane by a scraping method. The membrane surface was then washed with deionized water and immersed in anhydrous ethanol to remove excess GO, thus obtaining a GO / PDA composite membrane without MXene doping.

[0074] A GO / PDA composite membrane was used for membrane distillation to treat wastewater containing 3000 mg / L NaCl and 50 mg / L humic acid. The hot and cold side circulation temperatures of the membrane distillation system were set to 20℃ and 50℃, respectively. Under 30 seconds of sunlight irradiation, the membrane surface temperature showed no significant change, and the average permeate flux was 22.6 L / m³. 2 ·h.

[0075] Comparative tests have demonstrated that the preparation method of the photothermal distillation membrane prepared by MXene doping is simple and has good photothermal performance. When used for membrane distillation treatment of high-salt organic wastewater, it has an anti-fouling effect that slows down flux decline. Therefore, the MXene-doped photothermal distillation membrane described in this invention not only has good anti-fouling performance for wastewater treatment, but is also an energy-saving and consumption-reducing material.

Claims

1. A method for preparing an MXene-doped photothermal distillation film, comprising the following steps: Step 1, Preparation of MXene-doped composite photothermal materials: 1g of Ti3AlC2 powder was slowly added to 10mL of 50wt% hydrofluoric acid solution, and etched by stirring in a water bath at 25℃ for 24h. Then it was washed with deionized water and centrifuged at 3000rpm until the pH of the supernatant was 6. The precipitate was vacuum dried to obtain MXene. MXene and chitosan CTS were dissolved in deionized water at a mass ratio of 20:1 and ultrasonically dispersed for 2 hours. Then, dopamine hydrochloride was added to make the mass ratio of dopamine hydrochloride to MXene / CTS mixture 1:

1. The mixture was stirred at room temperature for 2 hours. Then, a Tris-HCl buffer solution with pH=8.5 and a concentration of 50 mmol / L was added. The mixture was placed in an 80°C water bath and stirred at 400 rpm for 24 hours. After the reaction was completed, the mixture was cooled to room temperature, centrifuged at 5000 rpm for 10 minutes, washed more than 3 times, and vacuum dried to obtain MXene-doped composite photothermal material solid powder. Step 2, Treatment of the hydrophobic basement membrane: First, the PTFE hydrophobic base membrane was soaked in isopropanol for 1.5 hours, then soaked in deionized water for 14 hours and allowed to stand and air dry. Then, the hydrophobic base membrane soaked in isopropanol and deionized water was soaked in a Tris-HCl buffer solution with a dopamine concentration of 0.2 g / L (50 mmol / L, pH=8.5) and stirred at room temperature for 24 hours. Then, it was washed with deionized water more than 3 times and air dried for later use. Step 3, Preparation of the photothermal distillation membrane: The MXene-doped composite photothermal material solid powder obtained in step 1 was dissolved in deionized water and ultrasonically dispersed for 1 hour. Then, the composite material was bonded to the surface of the hydrophobic substrate membrane treated in step 2 using a scraping method. The loading of the MXene-doped composite photothermal material on the treated hydrophobic substrate membrane surface was 5 mg / cm³. 2 Then, the membrane surface is washed with deionized water and then immersed in anhydrous ethanol to remove excess MXene-doped composite photothermal material, thus obtaining the MXene-doped photothermal distillation membrane. Hydrophilicity and hydrophobicity tests on the membrane surface showed that the contact angle between the MXene-doped photothermal distillation membrane and water was 66.5°. The prepared photothermal distillation membrane was used for membrane distillation treatment of wastewater containing 1000 mg / L CaSO4 and 50 mg / L sodium dodecyl sulfate surfactant. The circulating temperatures of the hot and cold sides of the photothermal membrane distillation system were set to 20℃ and 50℃, respectively. Under two solar illumination conditions, the surface temperature of the photothermal distillation membrane rose to 61.5℃ after 30 seconds of illumination, and the average membrane distillation flux was 36.4 L / m³. 2 The conductivity of the produced water remained below 5 μS / cm throughout the process.

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