Janus photothermal distillation membrane for oily wastewater of a ship and preparation method thereof

Abstract

The application provides a Janus photothermal distillation membrane for oily wastewater of a ship and a preparation method thereof, and belongs to the technical field of oil-water separation membrane materials. In the application, an adhesive layer is modified on a polytetrafluoroethylene (PTFE) membrane substrate, and then carbon nanotubes (CNT) are sprayed on the adhesive layer to obtain a CNT / PTFE membrane, so that the conversion of photothermal conversion is effectively promoted and the photothermal material is prevented from falling off; polyvinyl alcohol-tannic acid (PVA-TA) with rich hydroxyl groups is in-situ gelled on the CNT / PTFE membrane to form a uniform hydrophilic and oleophobic hydrogel layer, the layer is integrated on the membrane surface and strengthens the 'pollution resistance' mechanism, and finally the obtained photothermal Janus distillation membrane has excellent firmness and durability, anti-wetting property and anti-pollution performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of oil-water separation membrane materials, in particular to a Janus photothermal distillation membrane for ship oily sewage and a preparation method thereof. BACKGROUND

[0002] Ship oily sewage has always been an important source of marine pollution. Its easy spreadability, non-degradability and toxicity of oil pollution mixture bring certain difficulty to the treatment and standard discharge of ship oily sewage, seriously threatening the ecological balance of the ocean and near sea areas, and being contrary to the current low-pollution, sustainable and green ocean ecological development mode. Therefore, efficient and economical ship oily sewage treatment technology is urgently needed. At present, common ship oily sewage treatment methods include physical method, chemical method, physical-chemical method and biological method. Among them, membrane separation technology has the advantages of simple operation, easy control, no need for additional chemical reagents, environmental friendliness and continuous operation, and is considered as one of the most promising water treatment technologies in the 21st century.

[0003] Compared with traditional pressure-driven membrane separation technology, photothermal membrane distillation (PMD) has been widely used in oily salt sewage treatment field due to its small operation pressure requirement (can run at low pressure or even no pressure), high water quality, low energy consumption, wide application range and high evaporation efficiency. Research has found that the photothermal effect can reduce the viscosity of oil in high-concentration oily wastewater, increase the flowability of oil to speed up water evaporation, and greatly improve the oil-water separation efficiency. Especially, the use of renewable energy solar energy can meet the sustainable development demand of green ocean construction which requires saving resources, meeting environmental and ecological requirements and obtaining good economic benefits. Enhancing the anti-oil pollution ability of the distillation membrane is another key and difficulty to ensure the efficient and stable treatment of ship oily sewage by membrane distillation. Due to the hydrophobic interaction, oil droplets can be quickly adsorbed to the surface of the hydrophobic membrane, and then cause the membrane pores to be blocked and wetted, which seriously inhibits the transportation of water vapor and finally reduces the durability of the membrane. Therefore, designing a photothermal antifouling distillation membrane is the key to expanding the application of membrane distillation in high-difficulty ship oily sewage.

[0004] Recent research results show that Janus oil-water separation membranes with different wettabilities can effectively treat complex high-salt oily wastewater. The membrane combines a hydrophilic and oleophobic top layer with a hydrophobic bottom layer with low surface energy and high roughness, which shows effective repellency to surfactants and oily substances, thereby realizing excellent anti-oil pollution and anti-wetting performance. However, the interface of the traditional Janus membrane has poor adhesion, which may cause the photothermal material to fall off, thereby deteriorating the evaporation performance in long-time membrane distillation experiments. Therefore, there is an urgent need for a photothermal Janus oil-water separation membrane with a strong layer structure to achieve the purpose of treating ship oily sewage. SUMMARY

[0005] The present application aims to provide a Janus photo-thermal distillation membrane for oily wastewater of a ship and a preparation method thereof, for solving the above technical problems.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The present application provides a preparation method of a Janus photo-thermal distillation membrane for oily wastewater of a ship, which comprises the following steps:

[0008] 1) mixing carbon nanotubes in an acidic solvent for acidification treatment, and obtaining acidified carbon nanotubes after filtration, drying and grinding;

[0009] 2) mixing dopamine hydrochloride and polyethyleneimine in a buffer solution to obtain an adhesive liquid, and loading the adhesive liquid on a PTFE membrane to obtain a modified PTFE membrane containing an adhesive layer;

[0010] 3) mixing the acidified carbon nanotubes in ethanol, and spraying the obtained acidified carbon nanotube mixture on the modified PTFE membrane containing the adhesive layer to obtain a CNT / PTFE membrane;

[0011] 4) mixing polyvinyl alcohol and tannic acid in a mixed solvent, and spraying the obtained polyvinyl alcohol-tannic acid mixture on the CNT / PTFE membrane to obtain a Janus photo-thermal distillation membrane for oily wastewater of a ship after gelation.

[0012] Further, the acidic solvent comprises sulfuric acid and nitric acid, and the volume ratio of the sulfuric acid and the nitric acid is 2-5:1.

[0013] Further, the acidification treatment is carried out under heating, the heating temperature is 70-90℃, and the acidification treatment time is 2-4h.

[0014] Further, the mass ratio of the dopamine hydrochloride and the polyethyleneimine is 1:1-1.5, the buffer solution is Tris-HCl buffer solution, and the concentration of the polyethyleneimine in the buffer solution is 2-3mg / L.

[0015] Further, the loading time of the adhesive liquid on the PTFE membrane is 10-14h, and the temperature of the adhesive liquid is 40-60℃.

[0016] Further, the concentration of the acidified carbon nanotube mixture is 1-3mg / mL, and the spraying volume of the acidified carbon nanotube mixture is 1-3mL.

[0017] Further, in the step 4), the mixed solvent comprises ethanol and water in a volume ratio of 1:1-2, the concentration of polyvinyl alcohol in the polyvinyl alcohol-tannic acid mixed solution is 20-30 mg / mL, and the concentration of tannic acid is 20-30 mg / mL.

[0018] Further, the polyvinyl alcohol-tannic acid mixed solution is subjected to water bath heating treatment before spraying, the water bath heating temperature is 80-100 DEG C, and the water bath heating time is 5-7 h; the volume of the polyvinyl alcohol-tannic acid mixed solution sprayed is 1-2 mL.

[0019] The application further provides a Janus photothermal distillation membrane for oily wastewater of a ship.

[0020] The application has the following beneficial effects:

[0021] The application modifies an adhesive layer on a hydrophobic PTFE base film, then sprays a photothermal material, carbon nanotube (CNT), onto the adhesive layer to form a middle layer, which endows the film with excellent photothermal conversion performance and prevents the photothermal material from falling off; subsequently, a polyvinyl alcohol-tannic acid (PVA-TA) hydrogel coating layer with rich hydroxyl groups is coated to form a uniform hydrophilic and oleophobic layer, and finally a Janus photothermal distillation membrane with excellent firmness is obtained. In addition, a series of photothermal membrane distillation experiments are carried out, which prove that the Janus photothermal distillation membrane (HC1 / PTFE membrane) for oily wastewater of a ship of the application has excellent anti-wetting and anti-fouling properties, and is suitable for treating real oily wastewater of a ship with complex components in practical applications. The application proposes a feasible method for preparing a photothermal distillation membrane with anti-wetting and anti-fouling properties. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The surface SEM images and cross-sectional SEM images of the Janus photothermal distillation membrane for oily wastewater of a ship obtained in Example 1 of the application are shown in (a) PTFE, (b) HC1 / PTFE, (c) HC2 / PTFE and (d) HC3 / PTFE membrane surface SEM images; (e) PTFE and (f) HC1 / PTFE membrane cross-sectional SEM images;

[0023] Figure 2 The surface AFM images of (a) PTFE and (b) HC1 / PTFE membranes are shown in the figure;

[0024] Figure 3 The air-water contact angle (WCAs) and underwater oil contact angle (UOCAs) of (a) PTFE and HC1 / PTFE membranes and (b) the underwater oil dynamic contact process diagram of PTFE and HC1 / PTFE membranes are shown in the figure;

[0025] Figure 4(a) surface temperature and infrared thermography of HC1 / PTFE membranes at different light intensities and (b) UV-Vis-NIR absorption spectra of PTFE and HC1 / PTFE membranes;

[0026] Figure 5 (a) PTFE membranes and (b) HC1 / PTFE membranes at 1.0 kW·m -2 (a) permeate flux and salt rejection curves of HC1 / PTFE membranes at different light intensities and (b) UV-Vis-NIR absorption spectra of PTFE and HC1 / PTFE membranes;

[0027] Figure 6 (a) PTFE membranes and (b) HC1 / PTFE membranes at 1 kW·m -2 (a) permeate flux and salt rejection curves of HC1 / PTFE membranes at different light intensities and (b) UV-Vis-NIR absorption spectra of PTFE and HC1 / PTFE membranes;

[0028] Figure 7 (a) PTFE membranes and (b) HC1 / PTFE membranes at 1 kW·m -2 (a) permeate flux and salt rejection curves of HC1 / PTFE membranes at different light intensities and (b) UV-Vis-NIR absorption spectra of PTFE and HC1 / PTFE membranes. DETAILED DESCRIPTION

[0029] The present application provides a preparation method of a Janus photo-thermal distillation membrane for oily wastewater of a ship, the method comprising the following steps:

[0030] 1) carbon nanotubes are mixed in an acidic solvent for acidification treatment, and after filtration, drying and grinding, acidified carbon nanotubes are obtained;

[0031] 2) dopamine hydrochloride and polyethyleneimine are mixed in a buffer solution to obtain an adhesive liquid, which is loaded on a PTFE membrane to obtain a modified PTFE membrane containing an adhesive layer;

[0032] 3) the acidified carbon nanotubes are mixed in ethanol, and the obtained acidified carbon nanotube mixture is sprayed on the modified PTFE membrane containing the adhesive layer to obtain a CNT / PTFE membrane;

[0033] 4) polyvinyl alcohol and tannic acid are mixed in a mixed solvent, and the obtained polyvinyl alcohol-tannic acid mixture is sprayed on the CNT / PTFE membrane, and after gelation, a Janus photo-thermal distillation membrane for oily wastewater of a ship can be obtained.

[0034] In the present application, the acidic solvent comprises sulfuric acid and nitric acid, and the volume ratio of the sulfuric acid and the nitric acid is 2-5:1, preferably 3-4:1, and further preferably 3:1.

[0035] In the present application, the acidification treatment is carried out under heating, the temperature of the heating is 70-90℃, preferably 75-85℃, further preferably 80℃; the time of the acidification treatment is 2-4h, preferably 3h.

[0036] In the present application, the mass ratio of the dopamine hydrochloride and the polyethyleneimine is 1:1-1.5, preferably 1:1; the buffer is Tris-HCl buffer, and the concentration of the polyethyleneimine in the buffer is 2-3mg / L, preferably 2mg / L.

[0037] In the present application, the time of loading the adhesive liquid on the PTFE film is 10-14h, preferably 12h; the temperature of the adhesive liquid is 40-60℃, preferably 45-55℃, further preferably 50℃.

[0038] In the present application, the concentration of the acidified carbon nanotube mixed liquid is 1-3mg / mL, preferably 2mg / mL; the volume of the acidified carbon nanotube mixed liquid sprayed is 1-3mL, preferably 2mL.

[0039] In the present application, in the step 4), the mixed solvent comprises ethanol and water in a volume ratio of 1:1-2, preferably 1:1; the concentration of the polyvinyl alcohol in the polyvinyl alcohol-tannic acid mixed liquid is 20-30mg / mL, preferably 22-29mg / mL, further preferably 25-28.5mg / mL; the concentration of the tannic acid is 20-30mg / mL, preferably 22-29mg / mL, further preferably 25-28.5mg / mL.

[0040] In the present application, the polyvinyl alcohol-tannic acid mixed liquid is heated in water bath before spraying, the water bath heating temperature is 80-100℃, preferably 85-95℃, further preferably 90℃; the water bath heating time is 5-7h, preferably 6h; the volume of the polyvinyl alcohol-tannic acid mixed liquid sprayed is 1-2mL, preferably 1mL.

[0041] The present application also provides a Janus photothermal distillation membrane for oily wastewater of a ship.

[0042] The technical solutions provided by the present application will be described in detail below in combination with the embodiments, but they should not be understood as limiting the scope of protection of the present application.

[0043] Example 1

[0044] 1) 2 g of carbon nanotubes were dissolved in a mixed solvent (80 mL, H2SO4 / HNO3 = 3:1, v / v) at 80 °C for 3 h, and then the mixed solution was diluted to 2 L, left to precipitate and the supernatant was removed. After vacuum filtration, freeze-drying and grinding, acidified carbon nanotube powder was obtained.

[0045] 2) Dopamine hydrochloride (2 mg / L) and polyethyleneimine (2 mg / L) were dissolved in Tris-HCl buffer, stirred at 500 rpm for 5 min, and then a polytetrafluoroethylene film was placed on the above solution at 50 °C for 12 h. The PDA / PEI modified PTFE film was named P-PTFE.

[0046] 3) Acidified carbon nanotubes were dissolved in anhydrous ethanol to obtain a 2 mg / mL acidified carbon nanotube mixture, and then treated with an ultrasonic crusher for 30 min. Different volumes (1 mL, 2 mL and 3 mL) of acidified carbon nanotube mixture were sucked into an airbrush. Then it was uniformly sprayed on P-PTFE to obtain CNT / PTFE film, abbreviated as C n / PTFE (n represents the volume of acidified carbon nanotube mixture).

[0047] 4) 3 g of polyvinyl alcohol and 3 g of tannic acid were dissolved in a mixed solvent (105 mL, ethanol / deionized water = 1:1, v / v). Then heated in a 90 °C water bath for 6 h, and then 1 mL of the above polyvinyl alcohol-tannic acid mixture was added to the airbrush. Then, these liquids were uniformly sprayed on the surface of C n / PTFE. After the solvent evaporated, a hydrogel coated film was obtained, named HC n / PTFE (n represents the volume of CNTs). The final oily water of ship was stored in deionized water with Janus photo-thermal distillation film for subsequent testing.

[0048] Test Example

[0049] The HC1 / PTFE, HC2 / PTFE and HC3 / PTFE films obtained in Example 1 were characterized and tested for performance.

[0050] Test method: The surface morphology of the film was observed by field emission scanning electron microscope (FESEM, FEI, quanta 250 FEG). The light absorption rate of the film was measured by ultraviolet-visible-near infrared (UV-vis-NIR) spectrophotometer system (UH4150, Hitachi). The surface roughness of the film was characterized by atomic force microscope (AFM, JPK, NanoWizard4). The wettability of the film was characterized by measuring the water contact angle (WCA) and underwater oil contact angle (UOCA) in air using an optical goniometer (HARKE-SPCAX1S, China). The infrared thermal imager (Infra-Tec, ) Monitor the surface temperature change of the membrane. 1.0 kW·m -2 The light intensity of 1 corresponds to 1 sun light intensity. The mass and conductivity were measured by an electronic balance and a conductivity meter, respectively.

[0051] (1) Surface morphology:

[0052] As shown in [ Figure 1 (a)], the original hydrophobic polytetrafluoroethylene (PTFE) membrane exhibited a rough and porous morphology with a unique fibrous nodule mesh arrangement structure. Figure 1 (b-d) can be seen that the smooth hydrogel layer and the CNT photothermal intermediate layer embedded under the hydrogel layer. At the same time, [ Figure 1 (e-f)] cross-sectional contrast diagram can also show that the Janus photothermal distillation membrane has a clear hierarchical structure.

[0053] (2) AFM test:

[0054] As can be seen from [ Figure 2 (a)] and [ Figure 2 (b)], the Rq value of the original substrate is 223 nm, and the Rq value of the HC1 / PTFE membrane is 27.3 nm, and the significant decrease in Rq value shows that the roughness of the membrane surface is greatly reduced, which further provides supplementary evidence for the successful construction of the smooth hydrogel layer.

[0055] (3) Contact angle test:

[0056] [ Figure 3 (a)] The wettability and oleophobicity of PTFE membrane and HC1 / PTFE membrane are intuitively illustrated by water contact angle (WCA) and underwater oil contact angle (UOCA) measurements. The high WCA (>126°) on both sides of PTFE accompanied by low UOCA (<22°) indicates that the original substrate is essentially hydrophobic and oleophilic, which may lead to poor permeation flux and cannot resist oil. In contrast, the HC1 / PTFE membrane shows excellent oleophobicity on the front side, with a UOCA of 138.3°, which is due to the highly hydrated nature of the hydrogel layer, which endows the modified membrane with oil resistance. As shown in [ Figure 3 (b)], the oil droplets do not adhere to the modified membrane at all, showing its excellent anti-oil pollution performance.

[0057] (4) Photothermal performance test:

[0058] The surface temperature change of HC1 / PTFE membrane under different light intensity conditions was monitored during the PMD experiment using an infrared thermal imager. As can be seen from [ Figure 4 (a)], when the solar light intensity increases from 0 kW·m -2 to 1.5 kW·m -2At this time, the surface temperature of HC1 / PTFE membrane rapidly increased from 48.1℃ to 52.7℃. It can be seen that the HC1 / PTFE membrane has excellent photothermal performance, which can be applied to the evaporation of high-salt oil-containing wastewater.

[0059] In order to further verify the excellent light-heat conversion performance of HC1 / PTFE membrane, the light absorption performance thereof was characterized by using ultraviolet-visible-near infrared (UV-Vis-NIR) spectrum test. Figure 4 (b) As shown in the drawings, in the wavelength range of 200-2500 nm, the PTFE membrane has obviously lower light absorption rate in the whole spectral region. In contrast, the average light absorption rate of HC1 / PTFE membrane is 91.5%, which is 4.7 times of that of PTFE membrane, which is conducive to subsequent light-heat conversion and solar steam generation. These results show that carbon nanotubes can expand the propagation path of light to obtain better light absorption rate.

[0060] (5) Anti-wetting performance test:

[0061] A mixture of a representative surfactant (SDS) and 3.5wt% NaCl solution was used as feed to evaluate the anti-wetting performance of HC1 / PTFE membrane and control PTFE membrane. From the 60th minute, SDS was added every 2 hours to gradually increase the SDS concentration in the feed solution to 0.4mM. Figure 5 (a-b) As shown in the drawings, in the first hour of the feed without SDS, each membrane showed relatively stable permeation flux and ideal salt rejection rate (>99.9%). However, the salt rejection rate of PTFE membrane decreased significantly after 0.4mM SDS was added. In contrast, even under the condition of feed containing 0.4mM SDS and 7 hours of PMD test time, the modified membrane still showed excellent permeation flux and desalination rate Figure 5 (b). These results confirm that the Janus photothermal distillation membrane prepared in the application has excellent anti-wetting characteristics for ship oily wastewater.

[0062] (6) Anti-fouling performance test:

[0063] A salt solution containing 1000ppm n-hexadecane was used as feed solution to evaluate the anti-fouling performance of the membrane. The permeation flux of PTFE membrane decreased sharply Figure 6 (a) after the start of PMD test, which indicates that the control PTFE membrane is seriously contaminated by oily substances, which in turn leads to a significant reduction in water production flux. In contrast, HC1 / PTFE membrane shows stable permeation flux and excellent salt rejection rate Figure 6 (b) throughout the test. These results confirm that HC1 / PTFE membrane has excellent anti-oil pollution ability.

[0064] (7) Membrane durability test:

[0065] The practical durability of HC1 / PTFE membranes in treating complex oily salt wastewater was verified by treating simulated ship oily wastewater (real seawater, 0.4 M SDS, 1000 ppm n-hexadecane) in a 10-hour PMD experiment. Shortly after the start of the PMD experiment, a rapid decrease in the desalination rate of the PTFE membrane was observed[ Figure 7 (a)]. In addition, the sudden increase in permeation flux also indicated that the PTFE membrane was wetted, allowing the feed liquid to pass through the membrane pores. In contrast, the HC1 / PTFE membrane maintained a stable permeation flux and excellent desalination rate (>99.9%) throughout the 10-hour experiment[ Figure 7 (b)], reflecting its excellent practical durability. These results indicate that the Janus photo-thermal distillation membranes prepared in this application have good application prospects in the treatment of real high-salt wastewater with complex components.

[0066] Example 2

[0067] 1) Dissolve 2 g of carbon nanotubes in a mixed solvent (100 mL, H2SO4 / HNO3 = 4:1, v / v) at 80°C for 3 h, then dilute the mixed solution to 2 L, let it settle and remove the supernatant. Then, after vacuum filtration, freeze-drying treatment and grinding, acidified carbon nanotube powder is obtained.

[0068] 2) Dissolve dopamine hydrochloride (2 mg / L) and polyethyleneimine (3 mg / L) in Tris-HCl buffer, stir at 500 rpm for 5 min, then load the polytetrafluoroethylene membrane on the above solution at 50°C for 12 h. The PDA / PEI modified PTFE membrane is named P-PTFE.

[0069] 3) Dissolve the acidified carbon nanotubes in anhydrous ethanol to obtain a 2 mg / mL acidified carbon nanotube mixture, then treat with an ultrasonic crusher for 30 min. 1 mL of the acidified carbon nanotube mixture is sucked into an airbrush. Then, it is uniformly sprayed on the P-PTFE to obtain a CNT / PTFE membrane.

[0070] 4) Dissolve 3 g of polyvinyl alcohol and 3 g of tannic acid in a mixed solvent (105 mL, ethanol / deionized water = 1:1, v / v). Then heat in a 90°C water bath for 6 h, then add 1 mL of the above polyvinyl alcohol-tannic acid mixture to the airbrush. Then, these liquids are uniformly sprayed on the CNT / PTFE surface. After the solvent evaporates, a hydrogel-coated membrane is obtained, named HCNT / PTFE. The final ship oily wastewater is stored in deionized water with the Janus photo-thermal distillation membrane for future testing.

[0071] Example 3

[0072] The water bath temperature of step 4) in Example 1 was changed to 100℃, the water bath time was changed to 5h, the spraying volume of polyvinyl alcohol-tannic acid mixture was changed to 2mL, and the other conditions were the same as in Example 1.

[0073] Example 4

[0074] The amount of polyvinyl alcohol in step 4) of Example 1 was changed to 2.5g, the amount of tannic acid was changed to 2.2g, and the other conditions were the same as in Example 1.

[0075] Example 5

[0076] 1) 2g of carbon nanotubes were dissolved in a mixed solvent (100mL, H2SO4 / HNO3=3:1, v / v) at 70℃ for 4h, and then the mixed solution was diluted to 2L, allowed to stand and precipitate, and the supernatant was removed. After vacuum filtration and freeze-drying treatment, the acidified carbon nanotube powder was ground to obtain.

[0077] 2) Dopamine hydrochloride (2mg / L) and polyethyleneimine (3mg / L) were dissolved in Tris-HCl buffer, stirred at 500rpm for 5min, and then a polytetrafluoroethylene film was placed on the above solution at 50℃ for 12h. The PDA / PEI modified PTFE film was named P-PTFE.

[0078] 3) The acidified carbon nanotubes were dissolved in anhydrous ethanol to obtain a 1mg / mL acidified carbon nanotube mixture, and then treated with an ultrasonic crusher for 30min. 2mL of the acidified carbon nanotube mixture was sucked into a spray gun. Then it was uniformly sprayed on P-PTFE to obtain a CNT / PTFE film.

[0079] 4) 3g of polyvinyl alcohol and 3g of tannic acid were dissolved in a mixed solvent (105mL, ethanol / deionized water=1:1, v / v). Then heated in a 90℃ water bath for 6h, and then 1mL of the above polyvinyl alcohol-tannic acid mixture was added to the spray gun. Then, these liquids were uniformly sprayed on the surface of CNT / PTFE. After the solvent was evaporated, a hydrogel-coated film was obtained, named HCNT / PTFE. The final ship oil-containing wastewater was stored in deionized water with Janus photo-thermal distillation film for future testing.

[0080] Example 6

[0081] The concentration of the acidified carbon nanotube mixture in Example 5 was changed to 3mg / mL, the spraying volume of the acidified carbon nanotube mixture was changed to 1mL, and the other conditions were the same as in Example 1.

[0082] The Janus photothermal distillation membrane prepared in Example 6 was subjected to a 12h treatment PMD experiment simulating ship oily wastewater (containing 35g / L sodium chloride, 1200ppm lubricating oil), and the photothermal membrane exhibited excellent oil pollution resistance and stable permeation flux throughout the entire operation, and the salt rejection rate was always greater than 99.9%.

[0083] From the above examples, the present application provides a Janus photothermal distillation membrane for ship oily wastewater and a preparation method thereof. The present application effectively promotes photothermal conversion and prevents photothermal material from falling off by modifying an adhesive layer on a PTFE membrane substrate, and then spraying carbon nanotubes, a photothermal material, onto the adhesive layer to obtain a CNT / PTFE membrane. A uniform hydrophilic and oleophobic hydrogel layer is formed on the CNT / PTFE membrane by in-situ gelation of polyvinyl alcohol-tannic acid (PVA-TA) with abundant hydroxyl groups, which integrates and strengthens the "pollution resistance" mechanism on the membrane surface. The final photothermal Janus distillation membrane has excellent firmness, durability, anti-wetting, anti-pollution and anti-pollution durability.

[0084] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A method for preparing a Janus photo-thermal distillation membrane for oily wastewater of a ship, characterized by, The method comprises the following steps: 1) mixing carbon nanotubes in an acidic solvent for acidification treatment, and obtaining acidified carbon nanotubes after filtration, drying and grinding; 2) mixing dopamine hydrochloride and polyethyleneimine in a buffer solution to obtain an adhesive liquid, and loading the adhesive liquid on a PTFE membrane to obtain a modified PTFE membrane containing an adhesive layer; 3) mixing the acidified carbon nanotubes in ethanol, and spraying the obtained acidified carbon nanotube mixture on the modified PTFE membrane containing the adhesive layer to obtain a CNT / PTFE membrane; 4) mixing polyvinyl alcohol and tannic acid in a mixed solvent, and spraying the obtained polyvinyl alcohol-tannic acid mixture on the CNT / PTFE membrane to obtain a Janus photothermal distillation membrane for ship oily wastewater after gelation. The concentration of the acidified carbon nanotube mixture is 1-3 mg / mL, and the volume of the acidified carbon nanotube mixture sprayed is 1-3 mL.

2. The method for preparing the Janus photothermal distillation membrane for oily wastewater from ships according to claim 1, characterized in that, The acidic solvent comprises sulfuric acid and nitric acid, and the volume ratio of the sulfuric acid to the nitric acid is 2-5:

1.

3. The method for preparing a Janus photo-thermal distillation membrane for oily wastewater of a ship according to claim 1 or 2, characterized in that, The acidification treatment is carried out under heating, the heating temperature is 70-90℃, and the acidification treatment time is 2-4 h.

4. The method for preparing the Janus photothermal distillation membrane for oily wastewater from ships according to claim 3, characterized in that, The mass ratio of dopamine hydrochloride to polyethyleneimine is 1:1-1.5, the buffer solution is Tris-HCl buffer solution, and the concentration of polyethyleneimine in the buffer solution is 2-3 mg / L.

5. The method for preparing Janus photothermal distillation membrane for ship oily wastewater according to claim 1, 2, or 4, characterized in that, The adhesive liquid is loaded on the PTFE membrane for 10-14 h, and the temperature of the adhesive liquid is 40-60℃.

6. The method for preparing the Janus photothermal distillation membrane for oily wastewater from ships according to claim 5, characterized in that, In step 4), the mixed solvent comprises ethanol and water in a volume ratio of 1:1-2, the concentration of polyvinyl alcohol in the polyvinyl alcohol-tannic acid mixture is 20-30 mg / mL, and the concentration of tannic acid is 20-30 mg / mL.

7. The method for preparing the Janus photothermal distillation membrane for oily wastewater from ships according to claim 6, characterized in that, The polyvinyl alcohol-tannic acid mixture is heated in a water bath before spraying, the water bath heating temperature is 80-100℃, the water bath heating time is 5-7 h, and the volume of the polyvinyl alcohol-tannic acid mixture sprayed is 1-2 mL.

8. The Janus photothermal distillation membrane for ship oily wastewater prepared by the preparation method of any one of claims 1-7.

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