CN114053888A - Hydrophilic conductive distillation membrane and preparation method and use method thereof - Google Patents
Hydrophilic conductive distillation membrane and preparation method and use method thereof Download PDFInfo
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Abstract
The application relates to a hydrophilic conductive distillation membrane and a preparation method and a using method thereof. The hydrophilic conductive distillation membrane has a three-layer structure, a hydrophilic conductive layer, a hydrophobic insulating layer and a hydrophilic insulating layer are sequentially arranged from a feed liquid side to a water production side, a hydrophobic polyimide porous insulating film is firstly used as a substrate, and the surface of the substrate is sequentially subjected to activation, cleaning and drying pretreatment; depositing a hydrophilic conductive reduced graphene oxide film layer on one surface of the pretreated hydrophobic polyimide porous insulating film; and finally, depositing an insulating hydrophilic layer on the other surface of the pretreated hydrophobic polyimide porous insulating film to obtain the hydrophilic conductive distillation film. In specific use, the hydrophilic conductive layer is heated, and the purging cooling airflow is arranged on the water production side so as to maintain the temperature difference between the feed liquid side and the water production side at 5-50 ℃, so that the hydrophilic conductive distillation membrane has long-lasting high permeation flux under low energy consumption.
Description
Technical Field
The application relates to the technical field of water treatment membranes, in particular to a hydrophilic conductive distillation membrane and a preparation method and a use method thereof.
Background
Water is an essential resource for human survival. With the development of industrial society, water pollution and water resource shortage have become major challenges that restrict sustainable and high-quality development of human beings. Therefore, sewage treatment technology and water resource regeneration technology are becoming important green technologies in the current industrial society.
In the process of treating sewage, the membrane separation technology is a green technology which is most widely applied, and water and pollutants or impurities in a sewage mixing system are separated by a separation membrane through the driving of an external driving force, so that purified water can be obtained. At present, membrane separation technology is commonly used in the fields of brackish water and seawater desalination, advanced treatment of domestic and industrial wastewater and the like.
In order to improve the efficiency of membrane separation, in the traditional membrane distillation process, a method of circularly heating feed liquid is generally adopted, so that the temperature of the feed liquid is improved, and the water yield of the efficiency of membrane distillation is further improved. However, the cyclic heating of the feed liquid requires a large amount of heat energy, which is not environment-friendly and has high cost.
Conventional distillation membranes include both hydrophilic and hydrophobic membranes. For hydrophilic membranes, good solubility and permeability to water in the feed solution can be achieved, and high permeation flux can be obtained, so hydrophilic distillation membranes generally have higher permeation flux and membrane separation efficiency. However, since the hydrophilic film has wettability, it is not favorable for drying and reuse. For hydrophobic membranes, although they have the advantage of being easy to dry and reuse, their permeation flux is relatively small and the membrane separation is relatively inefficient.
Therefore, based on the above-mentioned shortcomings of the prior art membrane separation technology, the present application aims to provide a distillation membrane with low energy consumption and long-lasting high permeation flux.
Disclosure of Invention
In order to solve the problems of high energy consumption, insufficient permeation flux and the like in the existing membrane separation technology, the application provides a hydrophilic conductive distillation membrane and a preparation method and a use method thereof. The hydrophilic conductive distillation membrane of the present application is essentially a distillation membrane of a three-layer structure, the middle layer is a hydrophobic porous layer, and both outer surface layers are hydrophilic layers, so that the entire distillation membrane appears as a hydrophilic distillation membrane. Wherein, the hydrophilic layer of two surfaces is different, and the hydrophilic layer that is close to the feed liquid side has the electric conductivity, and the hydrophilic layer that is close to the side of producing water does not have the electric conductivity.
In order to provide a distillation membrane with low energy consumption and lasting high permeation flux, the application provides a preparation method of a hydrophilic conductive distillation membrane, which comprises the following steps:
(1) sequentially carrying out activation, cleaning and drying pretreatment on the surface of the substrate by taking the hydrophobic polyimide porous insulating film as the substrate;
(2) depositing a hydrophilic conductive reduced graphene oxide film layer on one surface of the pretreated hydrophobic polyimide porous insulating film;
(3) and depositing an insulating hydrophilic layer on the other surface of the pretreated hydrophobic polyimide porous insulating film.
Specifically, the activation treatment is:
and activating the surface of the hydrophobic polyimide porous insulating film by using potassium hydroxide, sodium ethoxide or potassium persulfate as an activator, wherein the concentration of the activator is 0.01-0.05mol/L, and the activation time is 1-5 min. Through the activation treatment, the wettability of the surface of the hydrophobic polyimide porous insulating film can be properly improved, a small amount of free radicals are formed, and the subsequent deposition of a hydrophilic film layer is facilitated.
Wherein, if the concentration of the activator exceeds 0.05mol/L, the activator destroys not only the hydrophobicity of the surface of the hydrophobic polyimide porous insulating film but also the hydrophobicity of the interior of the substrate throughout the porous structure by penetrating into the interior of the substrate during the activation treatment; if the concentration of the activator is less than 0.01mol/L, there is a problem that the wettability of the substrate surface cannot be effectively improved. Similarly, the time of the activation treatment needs to be well controlled, and when the time of the activation treatment is too long, particularly after more than 5min, even if the concentration of the activator is less than 0.01mol/L, there is a risk of destroying the hydrophobicity inside the substrate of the entire porous structure; when the time of the activation treatment is too short, particularly less than 1min, there is also a problem that the wettability of the substrate surface cannot be effectively improved.
Further, the step (2) is specifically:
mixing the components in a mass ratio of 1: and (1) dispersing the phytic acid and graphene oxide sheets in the (1-5) into deionized water to obtain a mixed dispersion liquid, loading the phytic acid and graphene oxide sheets in the mixed dispersion liquid on one surface of the hydrophobic polyimide porous insulating film pretreated in the step (1) in a filter pressing or spraying mode, and then carrying out heat treatment in an oven at the temperature of 80-100 ℃ for 1-2h to mutually crosslink and solidify a small amount of free radicals on the surfaces of the phytic acid, graphene oxide and polyimide to obtain an intermediate product A.
Then, reducing the intermediate product A by using high-purity nitrogen to obtain an intermediate product B; the reduction temperature is 300-350 ℃, and the reduction time is 20-30min, so that the graphene oxide is reduced into the reduced graphene oxide, and the conductivity is improved.
And finally, soaking the intermediate product B in 1-3mmol/L ferric chloride solution for 10-20min to complex iron ions on the surface of the intermediate product B, thereby obtaining the hydrophilic conductive reduced graphene oxide membrane layer.
The graphene oxide has good hydrophilicity and poor conductivity, and the reduced graphene oxide has good conductivity and poor hydrophilicity. In order to prepare a hydrophilic and conductive film layer on one surface of a hydrophobic polyimide porous insulating film, the inventors found that a complex of phytic acid and iron ions used for the surface of a graphene oxide nanosheet can be used on a reduced graphene oxide sheet to not only extend super-hydrophilic performance but also obtain excellent conductivity, and the reduced graphene oxide can provide excellent conductivity without affecting the overall hydrophilicity due to the reduction of oxygen-containing groups on the surface of the graphene oxide.
Moreover, the hydrophilic phytic acid and the iron ions can be complexed to quickly wet water molecules on the surface and promote the water molecules on the surface to be dissolved, so that the water molecules are guided to be quickly transmitted between the reduced graphene oxide sheets and reach the middle hydrophobic polyimide porous insulating film.
Particularly, the reduced graphene oxide has excellent conductivity, and the feed liquid in the area near the distillation membrane can be locally and effectively heated by electrifying and heating the hydrophilic conductive reduced graphene oxide membrane layer, so that the permeation and transmission of water molecules are promoted, and the permeation flux and the transmission efficiency are improved. By electrifying and heating the hydrophilic conductive reduced graphene oxide membrane layer, the feed liquid in the area near the distillation membrane is only locally and effectively heated, and energy waste caused by heating all the feed liquid is avoided.
Further, in the step (3), the insulating hydrophilic layer is an MOF-silicone porous film layer doped with MOF (Metal-Organic-framework material) and having silicone as a matrix material.
Further, the MOF material comprises one or more of CAU-1, ZIF-8 and NH 2-UiO-66. The particle size of the MOF material is 0.05-1 um.
Wherein, by depositing an insulating hydrophilic layer on the other surface of the hydrophobic polyimide porous insulating film, a three-layer structure of hydrophilic conductivity/hydrophobic insulation/hydrophilic insulation can be obtained. The hydrophilic conductive layer can be heated, so that the potential energy of water molecules on the feed liquid side is relatively high, and the potential energy of water molecules on the water production side is relatively low, and the water molecules have the driving force for conveying from the feed liquid side to the water production side. Meanwhile, as the water production side is also a hydrophilic insulating layer, the hydrophilic insulating layer tends to wet and dissolve water molecules with high potential energy, namely, water molecule conveying channels formed through holes of the middle hydrophobic insulating layer tend to "pull" the water molecules wetted and dissolved in the hydrophilic conductive layer on the feed liquid side into the hydrophilic insulating layer on the water production side. Moreover, the water molecule conveying channel formed by the through holes of the middle hydrophobic insulating layer has extremely small and almost negligible conveying resistance to water molecules, so that the water molecules on the feed liquid side can be driven by relatively small potential energy to realize the transmission from the hydrophilic conductive layer to the hydrophilic insulating layer. The distillation membranes of the present application can be used over time and maintain high permeate flux and transport efficiency.
Still further, both surfaces of the hydrophobic polyimide porous insulation film used herein have through holes, the average diameter of the through holes is 0.1 to 5um, the opening ratio of both surfaces of the hydrophobic polyimide porous insulation film is 50% or more, and the thickness of the hydrophobic polyimide porous insulation film is 20 to 50 um.
And, preferably, the average diameter (D, in um) of the through-hole and the thickness (h, in um) should also satisfy the following relationship: d/h is not less than 1/50. The diameter of the through hole is too small compared with the thickness of the membrane, so that the transmission resistance of water molecules in the middle hydrophobic insulating layer is increased, and the permeation flux and the transmission efficiency of the distillation membrane are not facilitated.
The application also provides a hydrophilic conductive distillation membrane which has a three-layer structure, wherein the hydrophilic conductive layer, the hydrophobic insulating layer and the hydrophilic insulating layer are sequentially arranged from the feed liquid side to the water production side, and the hydrophilic conductive distillation membrane is prepared by the preparation method of the hydrophilic conductive distillation membrane.
Further, this application still provides a use method of hydrophilic electrically conductive distillation membrane, hydrophilic electrically conductive distillation membrane has three layer construction, is hydrophilic conducting layer, hydrophobic insulating layer, hydrophilic insulating layer from the feed liquid side to producing the water side in proper order, sets up hydrophilic conducting layer in the feed liquid side, and hydrophilic insulating layer sets up in producing the water side, heats hydrophilic conducting layer to set up in producing the water side and sweep the cooling air current, in order to maintain the difference in temperature of feed liquid side and producing the water side at 5-50 ℃.
The purging cooling airflow is arranged on the water production side, so that the heating effect of the heat radiation of the hydrophilic conducting layer for power-on heating on the water production side can be reduced. The temperature difference between the feed liquid side and the water production side is further maintained at 5-50 ℃, so that water molecules on the feed liquid side and the water production side have proper potential energy difference, and the stability and the durability of permeation flux and the transmission efficiency of a distillation membrane are ensured.
Detailed Description
The present invention is further illustrated by the following examples, which are intended to facilitate the understanding of the present application and are not intended to be limiting in any way.
Example 1
A preparation method of a hydrophilic conductive distillation membrane, which has a three-layer structure and is sequentially provided with a hydrophilic conductive layer, a hydrophobic insulating layer and a hydrophilic insulating layer from a feed liquid side to a water production side, comprises the following steps:
first, a suitable hydrophobic polyimide porous insulating film is selected as a substrate, and the hydrophobic polyimide porous insulating film used in this embodiment has an average diameter of through holes of about 1um, an opening ratio of the surface of about 55.2%, and a thickness of about 24.5 um.
Then, activating the hydrophobic polyimide porous insulating film substrate by using 0.02mol/L sodium hydroxide solution as an activating agent, immersing the hydrophobic polyimide porous insulating film substrate in the 0.02mol/L sodium hydroxide solution for 3min, and after the activation treatment is finished, sequentially carrying out cleaning and drying pretreatment.
Mixing the components in a mass ratio of 1: 2, dispersing the phytic acid and graphene oxide sheets in deionized water to obtain a mixed dispersion liquid, loading the phytic acid and graphene oxide sheets in the mixed dispersion liquid on one surface of the pretreated hydrophobic polyimide porous insulating film in a spraying mode, and then carrying out heat treatment for 2 hours in an oven at 90 ℃ to enable a small amount of free radicals on the surfaces of the phytic acid, graphene oxide and polyimide to be cross-linked and cured mutually, so as to obtain an intermediate product A.
And (3) reducing the intermediate product A for 20min at 300 ℃ by using high-purity nitrogen as a reducing agent to obtain an intermediate product B.
And (3) soaking the intermediate product B in a 2mmol/L ferric chloride solution for 15min to complex iron ions on the surface of the intermediate product B, so as to obtain a hydrophobic polyimide porous insulating film with a hydrophilic conductive reduced graphene oxide film layer on the surface.
And spraying a ZIF-8-organosilicon precursor solution on the other surface of the hydrophobic polyimide porous insulating film, and then drying in an oven at 80 ℃ for 2 hours to obtain a ZIF-8-organosilicon porous film layer on the other surface of the hydrophobic polyimide porous insulating film, wherein the particle size of ZIF-8 is about 0.5 um.
Example 2
A preparation method of a hydrophilic conductive distillation membrane, which has a three-layer structure and is sequentially provided with a hydrophilic conductive layer, a hydrophobic insulating layer and a hydrophilic insulating layer from a feed liquid side to a water production side, comprises the following steps:
first, a suitable hydrophobic polyimide porous insulating film is selected as a substrate, and the hydrophobic polyimide porous insulating film used in this embodiment has an average diameter of through holes of about 0.2um, an opening ratio of a surface of about 52.3%, and a thickness of about 26.5 um.
Then, activating the hydrophobic polyimide porous insulating film substrate by using 0.02mol/L sodium hydroxide solution as an activating agent, immersing the hydrophobic polyimide porous insulating film substrate in the 0.02mol/L sodium hydroxide solution for 3min, and after the activation treatment is finished, sequentially carrying out cleaning and drying pretreatment.
Mixing the components in a mass ratio of 1: 3, dispersing the phytic acid and graphene oxide sheets in deionized water to obtain a mixed dispersion liquid, loading the phytic acid and graphene oxide sheets in the mixed dispersion liquid on one surface of the pretreated hydrophobic polyimide porous insulating film in a spraying mode, and then carrying out heat treatment for 2 hours in a 90-DEG C oven to enable a small amount of free radicals on the surfaces of the phytic acid, graphene oxide and polyimide to be cross-linked and cured mutually, so as to obtain an intermediate product A.
And (3) reducing the intermediate product A for 20min at 300 ℃ by using high-purity nitrogen as a reducing agent to obtain an intermediate product B.
And (3) soaking the intermediate product B in a 2mmol/L ferric chloride solution for 15min to complex iron ions on the surface of the intermediate product B, so as to obtain a hydrophobic polyimide porous insulating film with a hydrophilic conductive reduced graphene oxide film layer on the surface.
And spraying a ZIF-8-organosilicon precursor solution on the other surface of the hydrophobic polyimide porous insulating film, and then drying in an oven at 80 ℃ for 2 hours to obtain a ZIF-8-organosilicon porous film layer on the other surface of the hydrophobic polyimide porous insulating film, wherein the particle size of ZIF-8 is about 0.5 um.
Example 3
A preparation method of a hydrophilic conductive distillation membrane, which has a three-layer structure and is sequentially provided with a hydrophilic conductive layer, a hydrophobic insulating layer and a hydrophilic insulating layer from a feed liquid side to a water production side, comprises the following steps:
first, a suitable hydrophobic polyimide porous insulating film is selected as a substrate, and the hydrophobic polyimide porous insulating film used in this embodiment has an average diameter of through holes of about 0.5um, an opening ratio of the surface of about 51.0%, and a thickness of about 22.8 um.
Then, activating the hydrophobic polyimide porous insulating film substrate by using 0.04mol/L sodium hydroxide solution as an activating agent, immersing the hydrophobic polyimide porous insulating film substrate in the 0.04mol/L sodium hydroxide solution for 2min, and after the activation treatment is finished, sequentially carrying out cleaning and drying pretreatment.
Mixing the components in a mass ratio of 1: 1, dispersing the phytic acid and graphene oxide sheets in deionized water to obtain a mixed dispersion liquid, loading the phytic acid and graphene oxide sheets in the mixed dispersion liquid on one surface of the pretreated hydrophobic polyimide porous insulating film in a spraying mode, and then carrying out heat treatment for 2 hours in an oven at 80 ℃ to enable a small amount of free radicals on the surfaces of the phytic acid, graphene oxide and polyimide to be crosslinked and cured mutually, so as to obtain an intermediate product A.
And (3) reducing the intermediate product A for 20min at 330 ℃ by using high-purity nitrogen as a reducing agent to obtain an intermediate product B.
And (3) soaking the intermediate product B in a 3mmol/L ferric chloride solution for 10min to complex iron ions on the surface of the intermediate product B, thereby obtaining a hydrophobic polyimide porous insulating film with a hydrophilic conductive reduced graphene oxide film layer on the surface.
And spraying NH 2-UiO-66-organic silicon precursor solution on the other surface of the hydrophobic polyimide porous insulating film, and then drying in an oven at 85 ℃ for 2 hours to obtain an NH 2-UiO-66-organic silicon porous film layer on the other surface of the hydrophobic polyimide porous insulating film, wherein the grain diameter of NH2-UiO-66 is about 0.3 um.
Example 4
A preparation method of a hydrophilic conductive distillation membrane, which has a three-layer structure and is sequentially provided with a hydrophilic conductive layer, a hydrophobic insulating layer and a hydrophilic insulating layer from a feed liquid side to a water production side, comprises the following steps:
first, a suitable hydrophobic polyimide porous insulating film is selected as a substrate, and the hydrophobic polyimide porous insulating film used in this embodiment has an average diameter of through holes of about 4um, an opening ratio of the surface of about 58.4%, and a thickness of about 35.8 um.
Then, activating the hydrophobic polyimide porous insulating film substrate by using 0.05mol/L sodium hydroxide solution as an activating agent, immersing the hydrophobic polyimide porous insulating film substrate in the 0.05mol/L sodium hydroxide solution for 1min, and after the activation treatment is finished, sequentially carrying out cleaning and drying pretreatment.
Mixing the components in a mass ratio of 1: 5, dispersing the phytic acid and graphene oxide sheets in deionized water to obtain a mixed dispersion liquid, loading the phytic acid and graphene oxide sheets in the mixed dispersion liquid on one surface of the pretreated hydrophobic polyimide porous insulating film in a spraying mode, and then carrying out heat treatment for 1h in an oven at 100 ℃ to enable a small amount of free radicals on the surfaces of the phytic acid, graphene oxide and polyimide to be crosslinked and cured mutually, so as to obtain an intermediate product A.
And (3) reducing the intermediate product A for 25min at 350 ℃ by using high-purity nitrogen as a reducing agent to obtain an intermediate product B.
And (3) soaking the intermediate product B in a 3mmol/L ferric chloride solution for 20min to complex iron ions on the surface of the intermediate product B, thereby obtaining a hydrophobic polyimide porous insulating film with a hydrophilic conductive reduced graphene oxide film layer on the surface.
And spraying the CAU-1-organic silicon precursor solution on the other surface of the hydrophobic polyimide porous insulating film, and then drying in a 90 ℃ oven for 2 hours to obtain a CAU-1-organic silicon porous film layer on the other surface of the hydrophobic polyimide porous insulating film, wherein the particle size of CAU-1 is about 1 um.
Comparative example 1
A method for preparing a distillation membrane having only a two-layer structure, a hydrophilic conductive layer on the feed liquid side, a hydrophobic insulating layer on the water producing side, and a hydrophilic conductive layer and a hydrophobic insulating layer according to example 1.
A hydrophobic polyimide porous insulating film with an average diameter of through holes of about 1um, an opening ratio of a surface of about 55.2% and a thickness of about 24.5um is used as a substrate, one surface of the substrate is activated for 3min by using a 0.02mol/L sodium hydroxide solution, and then cleaning and drying pretreatment are carried out.
Mixing the components in a mass ratio of 1: 1, dispersing the phytic acid and graphene oxide sheets in deionized water to obtain a mixed dispersion liquid, loading the phytic acid and graphene oxide sheets in the mixed dispersion liquid on one surface of the pretreated hydrophobic polyimide porous insulating film in a spraying mode, and then carrying out heat treatment for 2 hours in an oven at 80 ℃ to enable a small amount of free radicals on the surfaces of the phytic acid, graphene oxide and polyimide to be crosslinked and cured mutually, so as to obtain an intermediate product A.
And (3) reducing the intermediate product A for 20min at 330 ℃ by using high-purity nitrogen as a reducing agent to obtain an intermediate product B.
And (3) soaking the intermediate product B in a 3mmol/L ferric chloride solution for 10min to complex iron ions on the surface of the intermediate product B, thereby obtaining the distillation membrane of the comparative example 1.
Comparative example 2
A method for preparing a distillation membrane having only a two-layer structure, which is different from comparative example 1 only in that: the hydrophilic conducting layer is positioned on the water producing side, and the hydrophobic insulating layer is positioned on the feed liquid side. The rest is exactly the same as in comparative example 1.
Comparative example 3
A preparation method of a distillation membrane, the distillation membrane has a three-layer structure, and a hydrophilic layer, a hydrophobic insulating layer and a hydrophilic insulating layer are sequentially arranged from a feed liquid side to a water production side, and the preparation method comprises the following steps:
first, a suitable hydrophobic polyimide porous insulating film is selected as a substrate, and the hydrophobic polyimide porous insulating film used in this embodiment has an average diameter of through holes of about 1um, an opening ratio of the surface of about 55.2%, and a thickness of about 24.5 um.
Then, activating the hydrophobic polyimide porous insulating film substrate by using 0.02mol/L sodium hydroxide solution as an activating agent, immersing the hydrophobic polyimide porous insulating film substrate in the 0.02mol/L sodium hydroxide solution for 3min, and after the activation treatment is finished, sequentially carrying out cleaning and drying pretreatment.
Mixing the components in a mass ratio of 1: 2, dispersing the phytic acid and graphene oxide sheets in deionized water to obtain a mixed dispersion liquid, loading the phytic acid and graphene oxide sheets in the mixed dispersion liquid on one surface of the pretreated hydrophobic polyimide porous insulating film in a spraying mode, and then carrying out heat treatment for 2 hours in an oven at 90 ℃ to enable a small amount of free radicals on the surfaces of the phytic acid, graphene oxide and polyimide to be cross-linked and cured mutually, so as to obtain an intermediate product A.
And (3) soaking the intermediate product A in a 2mmol/L ferric chloride solution for 15min to complex iron ions on the surface of the intermediate product A, so as to obtain a hydrophobic polyimide porous insulating film with a hydrophilic graphene oxide film layer on the surface.
And (3) spraying a ZIF-8-organic silicon precursor solution on the other surface of the hydrophobic polyimide porous insulating film, wherein the particle size of the ZIF-8 is about 0.5um, and then drying in an oven at 80 ℃ for 2 hours to obtain the distillation film of the comparative example 3.
To better evaluate the performance of the distillation membranes of the present application, the distillation membranes of examples 1-4 and comparative examples 1-3 were subjected to the following performance tests:
1. hydrophilicity test
The contact angle of the distillation films prepared in examples 1 to 4 with water was measured using a contact angle tester, and the measurement results are shown in table 1.
2. Pure water flux test
The pure water flux of the distillation membranes of examples 1 to 4 and comparative examples 1 to 3 was tested at a pressure of 0.1 MPa; the test results are shown in Table 1.
3. Permeation flux test
The permeation flux of each distillation membrane was tested with 0.35 wt.% NaCl solution as the distillate feed. Meanwhile, the permeation flux of each distillation membrane was tested here after the distillation membrane was continuously used for 60 days.
Wherein, during the permeation flux test, the distillation membranes of examples 1-4 and comparative examples 1-2 were heated and a purge cooling gas stream was provided on the water production side of the distillation membranes to maintain the temperature difference between the feed side and the water production side at about 15 ℃. The distillation membrane of comparative example 3 was not heated.
Meanwhile, comparative example 4 was provided, and the distillation membrane of comparative example 4 was the same as that of example 1 except that the distillation membrane of comparative example 4 was not heated. The specific test results are shown in table 1.
TABLE 1
As can be seen from table 1, the hydrophilic conductive distillation membrane of the present application has excellent hydrophilicity, has high pure water flux and permeation flux, and can maintain high permeation flux after being continuously used for 60 days. Especially, under the distillation process that the hydrophilic conductive layer is heated and the purging cooling airflow is arranged on the water producing side, the high permeation flux can be more effectively maintained for a long time.
Claims (9)
1. A preparation method of a hydrophilic conductive distillation membrane, wherein the hydrophilic conductive distillation membrane has a three-layer structure and comprises a hydrophilic conductive layer, a hydrophobic insulating layer and a hydrophilic insulating layer from a feed liquid side to a water production side in sequence, and the preparation method comprises the following steps:
(1) sequentially carrying out activation, cleaning and drying pretreatment on the surface of the substrate by taking the hydrophobic polyimide porous insulating film as the substrate;
(2) depositing a hydrophilic conductive reduced graphene oxide film layer on one surface of the pretreated hydrophobic polyimide porous insulating film;
(3) and depositing an insulating hydrophilic layer on the other surface of the pretreated hydrophobic polyimide porous insulating film.
2. The method for preparing a hydrophilic conductive distillation membrane according to claim 1, wherein the activation treatment is:
and activating the surface of the hydrophobic polyimide porous insulating film by using potassium hydroxide, sodium ethoxide or potassium persulfate as an activator, wherein the concentration of the activator is 0.01-0.05mol/L, and the activation time is 1-5 min.
3. The method for preparing a hydrophilic conductive distillation membrane according to claim 1 or 2, wherein the step (2) is:
mixing the components in a mass ratio of 1: dispersing the phytic acid and graphene oxide sheets in (1-5) into deionized water to obtain a mixed dispersion liquid, loading the phytic acid and graphene oxide sheets in the mixed dispersion liquid on one surface of the hydrophobic polyimide porous insulating film pretreated in the step (1) in a filter pressing or spraying mode, and then carrying out heat treatment in an oven at 80-100 ℃ for 1-2h to enable a small amount of free radicals on the surfaces of the phytic acid, graphene oxide and polyimide to be mutually crosslinked and cured to obtain an intermediate product A;
then, reducing the intermediate product A by using high-purity nitrogen to obtain an intermediate product B; the reduction temperature is 300-350 ℃, and the reduction time is 20-30min, so that the graphene oxide is reduced into reduced graphene oxide, and the conductivity is improved;
and finally, soaking the intermediate product B in 1-3mmol/L ferric chloride solution for 10-20min to complex iron ions on the surface of the intermediate product B, thereby obtaining the hydrophilic conductive reduced graphene oxide membrane layer.
4. The method of claim 3, wherein in the step (3), the insulating hydrophilic layer is a MOF-organosilicon porous membrane layer doped with MOF and prepared from organosilicon serving as a matrix material.
5. The method for preparing the hydrophilic conductive distillation membrane as claimed in claim 4, wherein the MOF material comprises one or more of CAU-1, ZIF-8, NH2-UiO-66, and/or the particle size of the MOF material is 0.05-1 um.
6. The method of claim 1 or 2, wherein the average diameter D of the through holes of the porous insulating film of hydrophobic polyimide is 0.1 to 5um, and/or the opening ratio of both surfaces of the porous insulating film of hydrophobic polyimide is 50% or more, and/or the thickness h of the porous insulating film of hydrophobic polyimide is 20 to 50 um.
7. The method of claim 6, wherein the average diameter D of the through holes and the thickness h satisfy the following relationship: d/h is not less than 1/50.
8. A hydrophilic conductive distillation membrane having a three-layer structure comprising, in order from a feed liquid side to a water producing side, a hydrophilic conductive layer, a hydrophobic insulating layer, and a hydrophilic insulating layer, wherein the hydrophilic conductive distillation membrane is produced by the method of any one of claims 1 to 7.
9. The method of claim 8, wherein the hydrophilic conductive distillation membrane is used by disposing the hydrophilic conductive layer on the feed liquid side, disposing the hydrophilic insulating layer on the water production side, heating the hydrophilic conductive layer, and disposing the purge cooling gas flow on the water production side to maintain the temperature difference between the feed liquid side and the water production side at 5-50 ℃.
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