JP6679117B2 - Nanocarbon separation membrane, nanocarbon composite separation membrane, and method for producing nanocarbon separation membrane - Google Patents

Description

The present invention relates to a nanocarbon separation membrane, a nanocarbon composite separation membrane, and a method for manufacturing a nanocarbon separation membrane.
The present application claims priority based on Japanese Patent Application No. 2016-209841 filed in Japan on October 26, 2016, and the content thereof is incorporated herein.

  The separation membrane (water treatment membrane) used for water treatment includes a UF membrane (Ultrafiltration Membrane: ultrafiltration membrane), an NF membrane (Nanofiltration Membrane: nanofiltration membrane), an RO membrane (ReverseOsmosis Membrane: reverse osmosis membrane), and FO membrane (Forward Osmosis Membrane: forward osmosis membrane) and the like. The separation membrane is not limited to water treatment but is widely used for gas separation and the like.

  In recent years, in order to improve robustness such as chemical resistance, heat resistance, and durability, the use of nanocarbon materials for separation membranes has been studied.

For example, Non-Patent Document 1 describes a separation membrane produced by vacuum filtration of a dispersion liquid in which graphene oxide pieces are dispersed. In addition, for example, Non-Patent Document 2 describes a separation membrane in which graphene oxide pieces are crosslinked with 1,3,5-benzenetricarbonyltrichloride (TMC). Further, for example, Non-Patent Document 3 describes a method of producing an NF film by vacuum-filtering a dispersion liquid in which graphene oxide pieces and multi-wall carbon nanotubes (hereinafter referred to as MWCNT) are dispersed on a porous substrate. ing.
As a method for producing graphene oxide pieces, a method using graphite as a raw material is known (see, for example, the methods described in Patent Document 1 and Non-Patent Document 4).

JP, 2014-201492, A JP, 2013-18673, A JP, 2005-343726, A

Renlong Liu, et al. Carbon, 77, (2014) 933-938. Meng Hu and Baoxia Mi. Environ.Sci.Technol, 2013,47,3715-3723. Yi Han, Yanqiu Jiang, and Chao Gao. ACS Appl. Mater. Interfaces 2015,7,8147-8155. Marcano, D. C. et al. Improved synthesis of graphene oxide.ACS Nano 4, (2010) 4806-4814.

  However, none of the separation membranes has sufficient characteristics. One of the performances and characteristics required of the separation membrane is the water permeability and the separation performance of the separation target. These have a correlation that when one of them is increased, the other decreases, and a separation membrane sufficiently satisfying both the water permeation performance and the separation performance of the separation target has not been obtained.

  Further, the separation films described in Non-Patent Document 1 and Non-Patent Document 3 also have a problem that graphene oxide pieces are separated during use. This is because the graphene oxide pieces are easily dispersed in water or the like. On the other hand, in the separation membrane described in Non-Patent Document 2, graphene oxide pieces are cross-linked. Therefore, the graphene oxide pieces are unlikely to be separated from each other. However, since it is crosslinked by organic molecules, the robustness of the separation membrane cannot be sufficiently enhanced.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a nanocarbon separation membrane having both excellent water permeability and excellent separation performance.

  The present inventors have found that by cross-linking a plurality of graphene oxide pieces with a divalent cation and inserting a double-wall carbon nanotube between the layers, a nanocarbon separation membrane having excellent separation performance can be obtained. It was That is, the present invention provides the following means in order to solve the above problems.

A first aspect of the present invention is a nanocarbon separation membrane described in (1) below.
(1) The nanocarbon separation membrane of the first aspect of the present invention is present so as to overlap each other when viewed in the thickness direction, and a plurality of graphene oxide pieces that are crosslinked with each other by a divalent cation, and the plurality of graphene oxide pieces. A double wall carbon nanotube inserted between layers of the double wall carbon nanotube, wherein the mass ratio of the graphene oxide piece to the total mass of the graphene oxide piece and the double wall carbon nanotube is more than 0 mass% and 70 mass% or less. Is 30% by mass or more and less than 100% by mass.

(2) In the nanocarbon separation membrane according to (1) above, the mass ratio of the graphene oxide pieces to the total mass of the graphene oxide pieces and the double wall carbon nanotubes is 30% by mass or more and 70% by mass or less, and the double wall carbon The mass ratio of the nanotubes may be 30% by mass or more and 70% by mass or less.

(3) In the nanocarbon separation membrane according to any one of (1) or (2) above, the divalent cation may be a calcium ion.

The second aspect of the present invention is the following nanocarbon composite separation membrane described in (4).
(4) A nanocarbon composite separation membrane according to a second aspect of the present invention is provided with the nanocarbon separation membrane according to any one of (1) to (3) above and one surface side of the nanocarbon separation membrane. And a porous membrane supporting the nanocarbon separation membrane.

(5) In the nanocarbon composite separation membrane according to (4) above, the nanocarbon separation membrane and the porous membrane may be adhered to each other.

(6) In the nanocarbon composite separation membrane according to (5) above, the nanocarbon separation membrane and the porous membrane may be adhered by a polyvinyl alcohol membrane.

A third aspect of the present invention is a method for producing a nanocarbon separation membrane described in (7) below.
(7) The method for producing a nanocarbon separation membrane according to the third aspect of the present invention comprises a step of applying a dispersion liquid in which graphene oxide pieces and double-wall carbon nanotubes are dispersed, and drying to form a carbon membrane. And a step of immersing the carbon film in a solution in which a divalent cation is dissolved.

  The nanocarbon separation membrane according to the first aspect of the present invention has excellent separation performance.

It is a perspective schematic diagram which shows the preferable example of the nanocarbon composite separation membrane which concerns on the 1st aspect of this invention. It is a cross-sectional schematic diagram which shows the preferable example of the nanocarbon composite separation membrane which concerns on the 1st aspect of this invention. It is a scanning electron microscope (SEM) image of a graphene oxide piece simple substance. It is a transmission electron microscope (TEM) image of a graphene oxide piece simple substance. It is a transmission electron microscope (TEM) image of a nanocarbon separation membrane. It is a transmission electron microscope (TEM) image of a nanocarbon separation membrane. It is the figure which showed typically the manufacturing method of the nanocarbon composite separation membrane concerning this embodiment. The results of FTIR measurement of Reference Comparative Examples 2, 2-1 and 2-2 are shown. The results of Raman spectroscopy measurement of Reference Comparative Examples 2, 2-1 and 2-2 are shown. The analysis result of the C1s spectrum obtained by the XPS measurement of Reference Comparative Example 2-1 is shown. The analysis result of the C1s spectrum obtained by the XPS measurement of Reference Comparative Example 2-2 is shown. The analysis result of the C1s spectrum obtained by the XPS measurement of Reference Comparative Example 2 is shown. The analysis result of the Cl2p spectrum obtained by the XPS measurement of Reference Comparative Example 2 is shown. The analysis result of the Ca2p spectrum obtained by the XPS measurement of Reference Comparative Example 2 is shown. 5 is a photograph of the surface of the carbon nanocomposite separation membrane after the treatment of Example 4. 3 is a photograph of the surface of the carbon nanocomposite separation membrane after the treatment of Example 1. The results of FTIR measurement before and after heating the polyvinyl alcohol film are shown.

Hereinafter, preferred examples and preferred embodiments of the present invention will be described. The present invention is not limited to these examples and embodiments. Within the scope of the present invention, preferable changes and / or additions can be made as necessary. Unless otherwise specified, the number, amount, material, shape, position, type, etc. may be changed, added, or omitted as necessary. It should be noted that in the drawings used in the following description, in order to make the features easy to understand, parts and configurations may be enlarged, reduced, deformed, or omitted for convenience.
<Nanocarbon composite separation membrane>
FIG. 1 is a schematic perspective view of a nanocarbon composite separation membrane according to the first aspect of the present invention. FIG. 2 is a schematic cross-sectional view of the nanocarbon composite separation membrane according to the first aspect of the present invention. In FIG. 1, each component is illustrated separately for easy understanding.

  The nanocarbon composite separation membrane 100 shown in FIGS. 1 and 2 has a nanocarbon separation membrane 10, an adhesive layer 20, and a porous membrane 30. The nanocarbon separation membrane 10 is a functional membrane having a high filtration function. The porous membrane 30 is a support membrane that supports the nanocarbon separation membrane 10 and enhances the mechanical strength of the nanocarbon composite separation membrane 100 as a whole. The nanocarbon composite separation membrane 100 can be used for both gas phase separation and liquid phase separation depending on the application. Hereinafter, the liquid phase separation will be mainly described.

(Nanocarbon separation membrane)
The nanocarbon separation film 10 includes a graphene oxide (GO (abbreviation of graphene oxide)) piece 1 and a double wall carbon nanotube (hereinafter, referred to as “DWCNT” (abbreviation of Double Wall Carbon Nanotube)) 2. DWCNT2 is a double-walled carbon nanotube. The DWCNT may have a structure in which at least two carbon nanotubes having different inner diameters are overlapped. The presence of graphene oxide so as to overlap each other when viewed in the thickness direction may mean that at least some of the graphene oxide overlaps each other when viewed in the thickness direction.

  FIG. 3 is a scanning electron microscope (SEM) image of the graphene oxide piece 1 alone. Further, FIG. 4 is a transmission electron microscope (TEM) image of the graphene oxide piece 1 alone.

  The graphene oxide piece 1 is a piece of graphene oxide. Graphene oxide is a material in which an oxygen-containing functional group selected from an epoxy group, a carboxyl group, a carbonyl group, a hydroxyl group, and the like is bonded to a monolayer of graphene. Graphene oxide is also known as a material that becomes graphite when reduced.

  The thickness of the graphene oxide piece 1 is one carbon atom and is about 1 to 1.5 nm. The size of the graphene oxide piece 1 in the in-plane direction can be appropriately designed. The average diameter in the in-plane direction of the graphene oxide piece 1 shown in FIG. 3 is 12 μm.

  Here, the average diameter was determined as follows. First, the dispersion liquid in which the graphene oxide pieces 1 are dispersed is dropped on a Si substrate and dried. Next, the Si substrate is observed by SEM, and the circumscribed ellipse of the graphene oxide piece 1 is drawn. At this time, the graphene oxide pieces 1 are not selected so that the circumscribed ellipse cannot be drawn by aggregation. Then, the major axis of the obtained circumscribed ellipse is measured. The same operation was performed on 90 pieces of graphene oxide pieces 1 and the average value was calculated to obtain the average diameter.

  A part of the graphene oxide piece 1 is open (see a dotted line area in FIG. 4). In other words, the surface of the graphene oxide piece 1 may be provided with one or more holes (openings). This hole functions as a flow path for the fluid that passes through the nanocarbon separation membrane 10.

The diameter and the amount of holes formed in the graphene oxide piece 1 can be arbitrarily selected and can be controlled by changing the degree of oxidation of the graphene oxide piece 1. The average diameter of the holes formed in the graphene oxide piece 1 is preferably 0.5 nm or more and 5 nm or less, and more preferably 1 nm or more and 3 nm or less.
The area of the holes is preferably 0.5% or more and 5% or less of the area of graphene oxide (GO).

FIG. 5 is a transmission electron microscope (TEM) image of a nanocarbon separation membrane, which is a preferred example of the present invention.
As shown in FIG. 5, the DWCNT2 in the nanocarbon separation membrane has a length of 500 nm or more, and the distance between adjacent DWCNT2 is about 100 nm at the maximum.

  FIG. 6 is a transmission electron microscope (TEM) image of the nanocarbon separation membrane, and is an enlarged view of a part of FIG. 5.

  As shown in FIG. 6, in the TEM image, there is a difference in how the holes (see the dotted line area in FIG. 6) of the graphene oxide piece 1 are viewed. This is because it is different whether the hole of the graphene oxide piece 1 on the front side of the paper surface or the hole of the graphene oxide piece 1 on the back side of the paper surface is viewed. In other words, this image shows that the graphene oxide pieces 1 are present so as to overlap each other when viewed in the thickness direction. Note that “existing so as to overlap with each other” means that at least some of the graphene oxide pieces overlap with each other.

  Further, in FIG. 6, a part of the DWCNT 2 can be confirmed through the hole (see a dotted region in FIG. 6), and the other part can be confirmed through the carbon atoms forming the graphene oxide piece 1. That is, the DWCNT 2 is located deeper in the drawing than the graphene oxide piece 1. Focusing on the hole portion, carbon atom dots are also confirmed inside the hole. That is, the graphene oxide piece 1 exists on the back side of the paper with respect to the DWCNT 2. That is, the DWCNT 2 is sandwiched between the graphene oxide pieces 1 that are present so as to overlap each other when viewed from the thickness direction.

  The DWCNT 2 has a diameter of about several nm to several tens of nm and is thicker than the thickness of the graphene oxide piece 1. Therefore, when at least one DWCNT 2 is sandwiched between the plurality of graphene oxide pieces 1, the space between the stacked graphene oxide pieces 1 is increased. The diameter of DWCNT2, the innermost inner diameter of DWCNT2, and the length of DWCNT2 may be arbitrarily selected.

  The average interplanar distance of the graphene oxide pieces in the case of only the graphene oxide pieces 1 is 7.7Å. When DWCNT2 is sandwiched, the average interplane distance is 7.7Å or more. The average surface distance is obtained from the peak value obtained by X-ray diffraction. The average interplanar distance of the graphene oxide pieces in the nanocarbon separation membrane of the present invention can be arbitrarily changed by changing the conditions and the like.

  As the average interplanar distance of the graphene oxide piece 1 increases, the flow path of the fluid passing through the nanocarbon separation membrane 10 expands. That is, in the case of liquid phase separation, water permeability increases. On the other hand, the spread of the average face-to-face distance is Å unit, which is small. Therefore, it is possible to prevent the separation characteristic of the separation object from being greatly deteriorated.

  The mass ratio of the graphene oxide pieces 1 to the total mass of the graphene oxide pieces and the double-walled carbon nanotubes is 70% by mass or less and larger than 0% by mass. The mass ratio of DWCNT2 to the total mass of graphene oxide pieces and double-walled carbon nanotubes is 30% by mass or more and less than 100% by mass. When the ratio of the graphene oxide piece 1 to the DWCNT 2 is within this range, it is possible to prevent the performance of one of the water permeability and the separation property of the separation target from being significantly deteriorated.

  Further, the mass ratio of the graphene oxide pieces 1 to the total mass of the graphene oxide pieces and the double-walled carbon nanotubes is preferably 30% by mass or more and 70% by mass or less, and more preferably 40% by mass or more and 70% by mass or less. It is more preferable that the content is 50% by mass or more and 70% by mass or less. The mass ratio of DWCNT2 to the total mass of graphene oxide pieces and double-walled carbon nanotubes is preferably 30 mass% or more and 70 mass% or less, more preferably 30 mass% or more and 60 mass% or less, and 30 mass% or less. % Or more and 50% by mass or less is more preferable. The total mass ratio of the graphene oxide piece 1 and the DWCNT 2 is 100% by mass.

The plurality of graphene oxide pieces 1 are cross-linked with each other by divalent cations. The graphene oxide piece 1 has at least one oxygen-containing functional group selected from an epoxy group, a carboxyl group, a carbonyl group, a hydroxyl group, and the like.
The divalent cation coordinates near the oxygen-containing functional group of the graphene oxide piece 1 and cross-links the adjacent graphene oxide pieces 1. When the plurality of graphene oxide pieces 1 are crosslinked, the nanocarbon separation membrane 10 becomes strong.

  Generally, the graphene oxide piece 1 has high dispersibility in water. Therefore, if the graphene oxide pieces 1 are simply stacked, the graphene oxide pieces 1 may be separated from the nanocarbon separation film 10 when water is passed. In particular, in the case of a cross flow in which water flows in a direction parallel to the film surface of the nanocarbon separation film 10, the graphene oxide piece 1 is likely to peel off.

By separating the graphene oxide pieces 1 from each other, exfoliation of the graphene oxide pieces 1 can be suppressed.
Further, the DWCNT 2 sandwiched between the graphene oxide pieces 1 also becomes difficult to be detached from the layers.

  The divalent cation may be any ionic species as long as it can contribute to crosslinking. From the viewpoint of easy availability, at least one of calcium ion and magnesium ion is preferable.

  As described above, in the nanocarbon separation film 10 according to the present embodiment, the layers of the graphene oxide piece 1 are appropriately expanded by the DWCNT 2. Therefore, the nanocarbon separation membrane 10 according to the present embodiment is excellent as a separation membrane in both water permeability and separation characteristics of the object to be separated.

Further, the graphene oxide pieces 1 are cross-linked by the divalent cations. Therefore, peeling of the graphene oxide piece 1 is suppressed during use. Therefore, the solution can be supplied to the nanocarbon separation membrane 10 by cross flow.
The thickness of the nanocarbon separation membrane may be arbitrarily selected.

(Porous membrane)
The porous membrane 30 is arranged on one surface side of the nanocarbon separation membrane 10. The porous membrane 30 supports the nanocarbon separation membrane 10 and enhances the mechanical strength of the nanocarbon composite separation membrane 100 as a whole.

  As shown in FIGS. 1 and 2, the porous film 30 has a hole 31 inside. By having the hole portion 31 inside, water permeability is provided in the thickness direction. The hole 31 does not have to be a hole extending in the thickness direction as shown in the drawing. In practice, it may be a connecting hole in which a plurality of minute holes are connected.

  As the porous membrane 30, a known porous substrate can be selected and used as long as it has water permeability and mechanical strength. For example, a resin film made of polyimide, polysulfone, polyether sulfone, or the like having communication holes, porous alumina, or the like can be used as the porous film 30. When the adhesive layer 20 described below is formed by cross-linking by heat, light or the like, it is particularly preferable to use polysulfone having high heat resistance. The thickness of the porous film may be arbitrarily selected.

(Adhesive layer)
The adhesive layer 20 adheres the nanocarbon separation membrane 10 and the porous membrane 30. As the adhesive layer 20, a material that does not significantly impair the water permeability and can adhere the nanocarbon separation membrane 10 and the porous membrane 30 can be used.

  The material of the adhesive layer can be arbitrarily selected. For example, polyvinyl alcohol or the like can be used. By providing uncrosslinked polyvinyl alcohol between the nanocarbon separation membrane 10 and the porous membrane 30 and crosslinking the polyvinyl alcohol, these can be bonded.

  When the dead end flow in which the liquid is passed from the direction perpendicular to the in-plane direction of the nanocarbon composite separation membrane 100 is performed, the nanocarbon separation membrane 10 is hardly separated from the porous membrane 30. On the other hand, when crossflow is performed in which the liquid flows in a direction parallel to the in-plane direction of the nanocarbon composite separation membrane 100, the nanocarbon separation membrane 10 is easily separated from the porous membrane 30. Therefore, when the nanocarbon composite separation membrane 100 is cross-flowed, it is particularly preferable to provide the adhesive layer 20. The thickness of the adhesive layer may be arbitrarily selected.

  As described above, the nanocarbon composite separation membrane 100 according to the present embodiment includes the nanocarbon separation membrane 10 having excellent water permeability and excellent separation characteristics of the separation target. Therefore, the separation characteristics are excellent.

  In addition, since one surface of the nanocarbon separation membrane 10 is supported by the porous membrane 30, the mechanical strength of the nanocarbon composite separation membrane 100 can be increased. Furthermore, by adhering the nanocarbon separation membrane 10 and the porous membrane 30 with the adhesive layer 20, it is possible to prevent the nanocarbon separation membrane 10 from peeling off during use.

<Nanocarbon composite separation membrane>
FIG. 7 is a diagram schematically showing the method for manufacturing the nanocarbon composite separation membrane according to the present embodiment.

  As shown in this order in FIGS. 7A to 7D, in the nanocarbon composite separation membrane 100 according to the present embodiment, the step of forming the adhesive layer 20 on one surface of the porous membrane 30 and the adhesive layer 20. And a step of forming the nanocarbon separation film 10 on the surface on which is formed.

The nanocarbon separation membrane 10 includes a step of applying a dispersion liquid in which the graphene oxide pieces 1 and the DWCNT 2 are dispersed onto the surface of the porous membrane 30 on which the adhesive layer 20 is formed, and drying the carbon membrane to form a carbon membrane. The membrane is dipped in a solution of divalent cations.
The thickness of the graphene oxide piece 1 used for manufacturing can be arbitrarily selected, but is preferably about 1 to 1.5 nm.
The average diameter (outer diameter) of DWCNT2 used for manufacturing may be arbitrarily selected. Further, the innermost inner diameter of DWCNT2 may be arbitrarily selected. The length of DWCNT2 may also be arbitrarily selected.
In the dispersion liquid, the mass ratio of the graphene oxide piece 1 to the total mass of the graphene oxide piece 1 and the DWCNT 2 can be arbitrarily selected, but for example, it is preferably 30% by mass or more and 70% by mass or less, and 40% by mass or more 70 It is more preferably at most 50% by mass, and particularly preferably at least 50% by mass and at most 70% by mass. The mass ratio of DWCNT2 to the total mass of the graphene oxide pieces and the double-wall carbon nanotubes can be arbitrarily selected, but is preferably 30% by mass or more and 70% by mass or less, and 30% by mass or more and 60% by mass or less. Is more preferable, and particularly preferably 30% by mass or more and 50% by mass or less.
Hereinafter, a specific description will be given based on FIG. 7.

  First, as shown in FIG. 7A, a porous film 30 is prepared. The porous film 30 is used by selecting it from those mentioned above.

  Next, as shown in FIG. 7B, the adhesive layer 20 is formed on one surface of the porous film 30. The adhesive layer 20 can be formed by means such as coating. For example, the adhesive layer 20 can be formed on one surface of the porous film 30 by immersing the porous film 30 in an aqueous solution of polyvinyl alcohol, or by applying the aqueous solution to the film and drying it.

  Next, as shown in FIG. 7C, the dispersion liquid 11 in which the graphene oxide pieces 1 and the DWCNT 2 are dispersed is applied to the surface on which the adhesive layer 20 is formed. The method of application is not particularly limited. You may arbitrarily select and use it from a well-known method. For example, when spray coating is performed from the nozzle, shearing force is applied to the dispersion liquid 11 at the nozzle tip, and the dispersibility of the graphene oxide piece 1 and the DWCNT 2 is enhanced.

  The dispersion liquid 11 is obtained by, for example, mixing a first dispersion liquid in which the graphene oxide pieces 1 are dispersed and a second dispersion liquid in which DWCNT2 is dispersed.

  The first dispersion liquid is obtained, for example, by the following procedure. First, the graphene oxide piece 1 is prepared. The graphene oxide piece 1 is obtained by a known method using graphite as a raw material (for example, the method described in Patent Document 1 or Non-Patent Document 4). The graphene oxide piece 1 has high dispersibility in water. Therefore, the first dispersion liquid can be obtained simply by adding it to water.

  Then, the second dispersion liquid is obtained, for example, by the following procedure. First, DWCNT2 is manufactured. DWCNT2 can be produced by a general synthesis method. For example, there are methods such as arc discharge method, laser ablation method, and CVD (chemical vapor deposition method). The CVD method includes a substrate method and a vapor phase flow method. The substrate method includes a method of synthesizing carbon nanotubes on a substrate on which a metal layer having a thickness of several nm to several μm is deposited, and a method of synthesizing carbon nanotubes by supporting transition metal part particles on a simple substance such as zeolite or ceramic. . The vapor phase flow method is a method of synthesizing carbon nanotubes by reacting catalyst fine particles and a raw material gas in a high temperature area in a reaction tube. The catalyst fine particles are obtained by spraying the precursor compound on the reaction tube and thermally decomposing the precursor compound at the reaction tube inlet. The catalyst fine particles and the raw material gas are sent into the reaction tube by the carrier gas. Specifically, the DWCNT manufacturing method described in Patent Document 2 or Patent Document 3 can be given as an example.

The DWCNT2 thus prepared is added to an aqueous solution selected as necessary to obtain a second dispersion liquid. As the aqueous solution, for example, a sodium polystyrene sulfonate (PSS) aqueous solution, a sodium dodecyl sulfate aqueous solution, a sodium deoxycholate aqueous solution, or the like can be used.
Next, the first dispersion liquid and the second dispersion liquid are mixed and, if necessary, diluted to obtain a dispersion liquid 11.

  The dispersion liquid 11 after coating is dried, for example, naturally dried to obtain a carbon film. The carbon film is preferably heated together with the porous film 30. When the adhesive layer is crosslinked by heat, when polyvinyl alcohol is used as the adhesive layer, the polyvinyl alcohol of the adhesive layer 20 is crosslinked by heating, and the adhesiveness between the carbon film and the porous film 30 is increased, It also exhibits water resistance. Also, excess water can be removed.

  Finally, the carbon film formed by applying the dispersion liquid 11 is dipped in a solution in which divalent cations are dissolved. For example, when calcium ions are used as divalent cations, they are immersed in a solution in which calcium chloride is dissolved. By being immersed in a solution in which cations are dissolved, the graphene oxide pieces 1 are crosslinked with each other via the cations. The solvent of the solution may be arbitrarily selected. The divalent cation can be arbitrarily selected, and examples thereof include calcium ion and magnesium ion.

  As described above, according to the method for manufacturing a nanocarbon separation membrane of the present embodiment, a predetermined nanocarbon separation membrane can be easily obtained. Further, by using this method for producing a nanocarbon separation membrane, a nanocarbon composite separation membrane can be easily obtained.

  Further, according to the method for manufacturing a nanocarbon separation membrane of the present embodiment, the fluid of the nanocarbon separation membrane can be obtained by simply mixing the first dispersion liquid in which the graphene oxide pieces 1 are dispersed and the second dispersion liquid in which DWCNT2 is dispersed. It is possible to control the flow path through which That is, the water permeability and separation performance of the nanocarbon separation membrane can be easily controlled.

  Further, according to the method for producing a nanocarbon separation membrane of the present embodiment, the nanocarbon separation membrane can be produced by applying the dispersion liquid. Therefore, it becomes easy to increase the area of the nanocarbon separation membrane.

  The nanocarbon separation membrane, the nanocarbon composite separation membrane, and the method for manufacturing the nanocarbon separation membrane have been described above. The present invention may be variously modified without departing from the spirit of the invention.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
As Example 1, a nanocarbon composite separation membrane having a nanocarbon separation membrane composed of 30 mass% graphene oxide pieces and 70 mass% DWCNT was produced. Specifically, the nanocarbon composite separation membrane of Example 1 was produced by the following procedure.

  First, a first dispersion liquid in which graphene oxide pieces having an average diameter of 12 μm were dispersed was prepared using graphite (product number 332461, manufactured by Sigma-Aldrich Co., Ltd.) as a raw material. The first dispersion liquid was prepared as follows.

A first 95 wt% _H 2 SO ₄ aqueous solution 200 mL, and aqueous _H 3 PO ₄ 40mL of 85% by weight, were mixed, further added graphite 5g, were mixed with a magnetic stirrer. Next, 25 g of KMnO ₄ was slowly added to the mixed solution. At this time, the color of the liquid changed from black to green. The temperature of this liquid was raised to 40 ° C. over 5 minutes and kept at 40 ° C. for 1 hour. After 1 hour, the graphite peeled off and the liquid became a paste. The resulting paste was further mixed with a Teflon bar at 40 ° C. for 2.5 hours. Then, the paste after mixing was cooled to room temperature.

Then, a mixed solution of 40 mL of 35% H ₂ O ₂ aqueous solution and 600 mL of cold water at 5 ° C. or lower was slowly poured into this paste. When the mixture was poured, the paste generated heat and foamed.
And the obtained mixed liquid was left still overnight or more.

The liquid left to stand was separated into a supernatant and a precipitate. The supernatant was removed by decantation to obtain a precipitate. The obtained precipitate was added to and dispersed in a 5% by mass H ₂ SO ₄ aqueous solution (1 L).

  Then, the operation of adding the dispersion liquid to pure water, centrifuging it, and then dispersing it in pure water was repeated 5 times to clean the dispersion medium. In this process, the precipitate after centrifugation has two layers. The lower layer was graphite that was not exfoliated from each other, and the upper layer was exfoliated graphene oxide pieces that absorbed water. By removing the lower layer, a first dispersion liquid having a solid content concentration of 0.9 mass% was obtained. The obtained first dispersion liquid was diluted with water, dropped on a Si substrate, and the dried sample was observed by SEM. As a result, the average diameter of graphene oxide pieces was 12 μm.

  Then, a second dispersion liquid was prepared. DWCNT (outer diameter 1.8 nm, inner diameter 1.2 nm, as observed by TEM) was dispersed in a 0.5% by mass sodium deoxycholate aqueous solution to prepare a second dispersion liquid. The diameter of DWCNT in the second dispersion was about several nm.

  Then, the obtained first dispersion liquid and the second dispersion liquid were mixed and diluted to obtain a dispersion liquid. Nanocarbon consisting of graphene oxide pieces and DWCNT is dispersed in the dispersion liquid. The composition ratio of nanocarbon in the dispersion liquid was 30% by mass of graphene oxide pieces and 70% by mass of DWCNT. The concentration of nanocarbon in the solvent was 0.8 mg / mL.

  A commercially available polysulfone film (GR40PP manufactured by Alfa Label Co., size 50 mm × 50 mm) was prepared as the porous film. Then, the polysulfone film was immersed in a 1% by mass aqueous polyvinyl alcohol solution (manufactured by Sigma-Aldrich: molecular weight 31,000-50,000, saponified product of 98 to 99%) for 1 hour. The polysulfone membrane after immersion was air-dried in a standing state. As a result, the surface of the polysulfone film was coated with polyvinyl alcohol.

  Next, the dispersion liquid was sprayed onto the porous film coated with polyvinyl alcohol using an air brush (HP-BCS manufactured by Anest Iwata). Then, the porous film was dried in an air atmosphere at 100 ° C. for 1 hour. At this time, the polyvinyl alcohol was crosslinked, and the porous film and the carbon film formed by drying the dispersion liquid adhered to each other.

  Finally, the obtained laminated film was immersed in a calcium chloride solution for 1 hour. The calcium chloride solution had a calcium chloride concentration of 5% by mass, and the solvent of the calcium chloride solution was a mixture of ethanol and water in a volume ratio of 1: 3. Then, the laminated film after the immersion was dried. Drying was performed by first air-drying, once immersing in ethanol for 1 hour, and then air-drying again.

(Examples 2 and 3)
In Examples 2 and 3, nanocarbon composite separation membranes were produced by the same procedure as in Example 1 except that the mixing ratio of the first dispersion liquid and the second dispersion liquid was changed.
The composition ratio of the obtained nanocarbon separation membrane is as follows.
Example 2: Graphene oxide pieces (50% by mass), DWCNT (50% by mass)
Example 3: Graphene oxide pieces (70% by mass), DWCNT (30% by mass)

(Comparative Example 1)
In Comparative Example 1, a nanocarbon composite separation membrane was produced by the same procedure as in Example 1 except that the mixing ratio of the first dispersion liquid and the second dispersion liquid was changed.
The composition ratio of the nanocarbon separation membrane of Comparative Example 1 was 90% by mass of graphene oxide pieces and 10% by mass of DWCNT.

(Comparative example 2)
In Comparative Example 2, a nanocarbon composite separation membrane was produced by the same procedure as in Example 1 except that the first dispersion was used as the dispersion and the second dispersion was not used.
That is, the composition ratio of the nanocarbon separation membrane of Comparative Example 2 was 100% by mass of graphene oxide pieces.

(Comparative Example 3)
In Comparative Example 3, a nanocarbon composite separation membrane was produced by the same procedure as in Example 1 except that the second dispersion was used as the dispersion and the first dispersion was not used.
That is, the composition ratio of the nanocarbon separation membrane of Comparative Example 3 was set to 100% by mass of DWCNT.

<Evaluation of nanocarbon composite separation membrane>
The water permeability and the NaCl removal rate of the nanocarbon composite separation membranes of Examples 1 to 3 and Comparative Examples 1 to 3 were measured. Specifically, a 0.2% concentration aqueous sodium chloride solution was fed to the membrane at 300 mL / min by cross flow to measure the water permeation rate and the NaCl removal rate of the nanocarbon composite separation membrane.

The amount of water permeation was calculated from the results of water permeability measurement at a pressure of 5.0 MPa.
The NaCl removal rate was obtained by cutting out the membrane into a circle with a diameter of 25 mm and using a cross flow filter (manufactured by Tosk Corp.).
NaCl removal rate [%] = {1-NaCI concentration [mass%] of permeated water / NaCl concentration [mass%] of raw water} × 100

  The measurement results are shown in Table 1. In Table 1, GO indicates graphene oxide pieces, DWCNT indicates double-wall carbon nanotubes, and PVA indicates polyvinyl alcohol.

  As described above, the nanocarbon composite separation membranes of Examples 1 to 3 in which the ratio of graphene oxide pieces and DWCNT were within the predetermined range were more water permeable than the nanocarbon composite separation membranes of Comparative Example 1 and Comparative Example 2. The quantity has improved significantly. Although the NaCl removal rate was somewhat lowered, about 40% was sufficient depending on the application, and a sufficient NaCl removal rate was shown. Applications include, for example, a nanofiltration membrane for removing divalent ions and separation of organic substances. In Comparative Example 3 consisting of DWCNT only, water freely flowed and no desalting performance was confirmed.

<Bridge between graphene oxides>
A study was conducted to confirm that graphene oxides were cross-linked by divalent cations.
The examination was performed by Fourier transform infrared spectroscopy (FTIR) measurement, Raman spectroscopy measurement, and X-ray photoelectron spectroscopy (XPS) measurement.

  The measurement was carried out by a reference comparative example 2 consisting of graphene oxide pieces only, and a sample stopped before the sample of the reference comparative example 2 was immersed in the calcium chloride solution (hereinafter referred to as reference comparative example 2-1: calcium chloride solution). And the sample of Reference Comparative Example 2 was stopped before being immersed in the calcium chloride solution and heated at 100 ° C. (hereinafter referred to as Reference Comparative Example 2-2: No immersion in calcium chloride solution). ) And 3 samples.

  In Reference Comparative Example 2, the dispersion liquid used in Comparative Example 2 was applied on a Si substrate instead of the porous film, and the same procedure including dipping in a calcium chloride solution was performed to prepare a nanocarbon on the Si substrate. A separation membrane was formed. Hereinafter, those formed on the Si substrate will be referred to as reference comparative examples and the like. Reference Comparative Example 2 corresponds to one produced under the same conditions as Comparative Example 2, and other Reference Examples and Reference Comparative Examples also have the same correspondence relationship.

FIG. 8 shows the results of FTIR measurement of Reference Comparative Examples 2, 2-1 and 2-2. FTIR was performed by the total reflection measurement (ATR) method. The observed peaks of FTIR measurement are CO (alkoxy / alkoxide, 1042cm ^-1 ), CO (carboxy, 1410cm ^-1 ), C = C (aromatic, 1620cm ^-1 ), C = O (carboxy / carbonyl, 1716cm ^-1 ). , OH (3300 cm ^-1 ).

When the relative comparison is performed using the C = C peak as a reference, the intensity of the C—O and C═O peaks of the reference comparative example ₂ subjected to the CaCl ₂ treatment is higher than that of the reference comparative example 2-1 before the treatment. It's going down. This is because the Ca ²⁺ ion is coordinated with the oxygen ion, so that the relative intensities of the C—O and C═O peaks based on the C═C peak are reduced.

FIG. 9 shows the results of Raman spectroscopic measurement of Reference Comparative Examples 2, 2-1 and 2-2.
The D (1350 cm ⁻¹ ) / G (1600 cm ⁻¹ ) ratio in the result of Raman spectroscopy measurement was 0.92 in Reference Comparative Example 2-1, 0.84 in Reference Comparative Example 2-2, and 0 in Reference Comparative Example 2. It was 0.87.

Comparing Reference Comparative Example 2-1 and Reference Comparative Example 2-2, the D / G ratio of Reference Comparative Example 2-2 is smaller.
The G band is a peak derived from a graphite structure, and the D band is a defect derived peak. Therefore, the smaller D / G ratio means the higher crystallinity. Reference Comparative Example 2-2 is obtained by heating Reference Comparative Example 2-1 at 100 ° C., and it is considered that part of graphene oxide was reduced by heating and the graphene structure was approached.

  On the other hand, when comparing Reference Comparative Example 2-2 and Reference Comparative Example 2, the D / G ratio of Reference Comparative Example 2 is large. It is considered that the coordination of calcium ions caused disorder in the crystal arrangement.

  10A to 10C show respective analysis results of C1s spectra obtained by XPS measurement of Reference Comparative Examples 2, 2-1 and 2-2. 10A shows the analysis result of Reference Comparative Example 2-1, FIG. 10B shows the analysis result of Reference Comparative Example 2-2, and FIG. 10C shows the analysis result of Reference Comparative Example 2.

  Comparing FIG. 10A and FIG. 10B, the peak ratio of C—O and COO is small with the C = C peak as a reference. It is considered that part of graphene oxide was reduced by heating and oxygen element was released.

  Further, when comparing FIG. 10B and FIG. 10C, the peak ratio of C—O and COO becomes smaller with reference to the C = C peak. It is considered that this is because the amount of detected CO and COO peaks decreased due to the coordination of calcium ions with oxygen element.

  11A and 11B show analysis results of Cl2p spectrum and Ca2p spectrum obtained by XPS measurement of Reference Comparative Example 2. FIG. 11A shows the analysis result of the Cl2p spectrum, and FIG. 11B shows the analysis result of the Ca2p spectrum.

As shown in FIG. 11A, in Reference Comparative Example 2, the peak of Ca was detected, but the peak of Cl was not detected. That is, it can be seen that in Reference Comparative Example 2, CaCl ₂ is incorporated as Ca rather than remaining.

  From the above experimental results, it can be said that calcium ions coordinate with oxygen and crosslink graphene oxides.

<Examination of presence or absence of adhesive layer>
A nanocarbon composite separation membrane of Example 1 and a nanocarbon composite separation membrane obtained by removing the adhesive layer from Example 1 (hereinafter referred to as Example 4) were prepared. Example 4 is different in that the polysulfone film was not immersed in an aqueous polyvinyl alcohol solution in the manufacturing process of Example 1.

  To the carbon nanocomposite separation membranes of Example 1 and Example 4, a 0.2% concentration sodium chloride aqueous solution was fed at a flow rate of 300 ml / min at a pressure of 2 to 5 MPa by cross flow.

  12A and 12B are photographs of the surface of the carbon nanocomposite separation membrane after the treatments of Example 1 and Example 4. FIG. 12A is a surface photograph of the carbon nanocomposite separation membrane of Example 4 23 hours after starting the supply of the aqueous sodium chloride solution. FIG. 12B is a surface photograph of the carbon nanocomposite separation membrane of Example 1 70 hours after the supply of the aqueous sodium chloride solution was started.

  In the carbon nano-composite separation membrane of Example 4, the carbon nano-separation membrane is peeled off due to the flow of the supplied liquid (the portion shown by the arrow in FIG. 12A). On the other hand, as shown in FIG. 12B, the carbon nanocomposite separation membrane of Example 1 did not peel off.

  That is, by providing the adhesive layer, it is possible to prevent the carbon nano separation membrane from being separated from the carbon nano composite separation membrane. In particular, when supplying a liquid to the carbon nanocomposite separation membrane by cross flow, it is preferable to provide an adhesive layer. On the other hand, when the liquid or gas is supplied by the dead end flow, it can be used without the adhesive layer.

<Confirmation of hardening of adhesive layer>
FIG. 13 shows the results of FTIR measurement before and after heating polyvinyl alcohol.
As shown in FIG. 13, when normalized by the 854 cm ⁻¹ peak, the peak at 1141 cm ⁻¹ increased. This indicates the heat curing of the polyvinyl alcohol film.
That is, the polyvinyl alcohol film is sufficiently crosslinked when dried in an atmosphere of 100 ° C. for 1 hour.

  It is an object of the present invention to provide a nanocarbon separation membrane having both excellent water permeability and separation performance.

1 Graphene oxide pieces,
2 double wall carbon nanotubes (DWCNT),
10 Nanocarbon separation membrane,
11 dispersion liquid 20 adhesive layer,
30 porous membrane,
31 holes,
100 Nano carbon composite separation membrane

Claims (7)

A plurality of graphene oxide pieces existing so as to overlap each other when viewed from the thickness direction and cross-linked with each other by a divalent cation,
And a double-wall carbon nanotube inserted between layers of the plurality of graphene oxide pieces,
The mass ratio of the graphene oxide pieces to the total mass of the graphene oxide pieces and the double-wall carbon nanotubes is more than 0 mass% and 70 mass% or less, and the mass ratio of the double-wall carbon nanotubes is 30 mass% or more and less than 100 mass%. , Nano carbon separation membrane.   The mass ratio of the graphene oxide pieces to the total mass of the graphene oxide pieces and the double wall carbon nanotubes is 30% by mass or more and 70% by mass or less, and the mass ratio of the double wall carbon nanotubes is 30% by mass or more and 70% by mass or less. Item 2. The nanocarbon separation membrane according to item 1.   The nanocarbon separation membrane according to claim 1, wherein the divalent cation is calcium ion. A nanocarbon separation membrane according to any one of claims 1 to 3,
A nanocarbon composite separation membrane, which is disposed on one side of the nanocarbon separation membrane and has a porous membrane supporting the nanocarbon separation membrane.   The nanocarbon composite separation membrane according to claim 4, wherein the nanocarbon separation membrane and the porous membrane are adhered to each other.   The nanocarbon composite separation membrane according to claim 5, wherein the nanocarbon separation membrane and the porous membrane are bonded with polyvinyl alcohol. A step of applying a dispersion liquid in which graphene oxide pieces and double-wall carbon nanotubes are dispersed, and drying to form a carbon film;
And a step of immersing the carbon membrane in a solution in which a divalent cation is dissolved.