KR20180040743A - Ionic diode membrane comprising branched nanopore and method for preparing thereof - Google Patents

Abstract

The present invention relates to an ionic diode membrane having ion selectivity and ion rectification characteristics by integration of branched nanopores and a preparing method thereof. More specifically, the present invention relates to an ionic diode membrane in an integrated form of branch-structured nanopores, wherein in the inside of a membrane, as the nanopores continue to diverge, the number of nanopores per unit area gradually increases and a diameter of the pores and an interval between the pores gradually decrease along a nanoporous axis, and wherein an ion concentration gradient due to structural asymmetry of the nanopores is induced along the nanoporous axis, thereby expressing ion rectification characteristics and expressing high-ion selectivity and low-membrane resistance characteristics at the same time, and to a preparing method of an ionic diode membrane, wherein various membrane characteristics of the ionic diode membrane, such as rectification characteristics, ion selectivity, membrane resistance and the like can be controlled by regulating anodizing process conditions to freely control a form of the ionic diode membrane according to a design.

Description

[0001] The present invention relates to an ion diode membrane including nanopores of a branched type,

The present invention relates to an ion diode membrane having ion selective and ion rectifying properties by integrating nanopores of a branched type and a manufacturing method thereof. More particularly, the present invention relates to an ion diode membrane having nanopore spaced along a nanopore axis As the number of nano pores gradually increases and the pore diameter and spacing of the pore space gradually decrease, the nano pores of the branch structure are integrated, and the ion concentration gradient due to the structural asymmetry of the nano pore is induced along the nano pore axis An ion diode membrane that exhibits ionic rectification characteristics and exhibits high ion selectivity and low film resistance characteristics and an ion diode membrane that can control the shape of the ion diode membrane according to design by controlling the anodization process conditions, Selectivity, and membrane resistance. The present invention relates to a method of manufacturing an ion-diode membrane.

The origin of the ion exchange membrane was first discovered by Oswald in 1890, and by Donnan in 1930, the Donnan exclusion phenomenon, which is the selective permeation of the corresponding ions by the ionic bonding of the fixed ions within the ion exchange membrane, I started with understanding. Ion exchange membranes are mainly composed of polymeric materials and inorganic materials. They are classified into cation exchange membranes and anion exchange membranes depending on the membrane functional groups. Since the cation exchange membrane has negative charge functional groups such as SO ₃ , COO, PO ₃ ² , -PO ₃ H, and -C ₆ H ₄ O, it excludes anions and selectively permeates cations. On the other hand, the anion exchange membrane has positive charge functional groups such as -NH ₃ ⁺ , -NRH ₂ ⁺ , -NR ₂ H ⁺ , -NR ₃ ⁺ , -PR ₃ ⁺ , and -SR ²⁺ to selectively transmit anions.

Ion exchange membranes are traditionally used in a variety of industries including electrical desalination technology, acid / alkali production, removal of heavy metals from industrial wastewater, desalination of seawater, production of ultrapure water from the semiconductor industry, preparation of salt from seawater, and recovery of organic acids and amino acids from fermentation industries Has been applied in the field. In recent years, however, the ion exchange membrane having new functions and characteristics has been demanded as it has been widely used beyond the conventional application fields.

Ion exchange membranes are used as core materials that determine performance and cost in fields such as membrane-storage seawater desalination, reverse electrodialysis, fuel cells, redox flow cells, etc., And membrane resistance, low mechanical, chemical, and thermal durability, commercialization of related industries is hindered. Since the 1980s, cost-effective membranes have been developed in Tokuyama Corporation, Asahi Chemical, DuPont, etc., but the cost and membrane resistance of the membranes are still considerably high to achieve economical efficiency. Therefore, a next generation ion exchange membrane capable of replacing existing ion exchange membranes, low membrane resistance, high permeation selectivity, excellent mechanical, chemical, thermal stability, and low production cost has long been demanded.

As an alternative to this, attention has been focused on asymmetric ion exchange membranes with conical pores. Such membranes are known to exhibit low membrane resistance and high permeation selectivity. US Patent Application Publication No. US 2003-0159985 discloses a process for producing a membrane using polyimide. However, due to the nature of the process, the porosity of the membrane The ion conductivity is lower than that of the conventional ion exchange membrane, and it is impossible to control the pore shape of the membrane, so that it is difficult to apply variously. In addition, since the cone-shaped pores in this ion exchange membrane are morphologically formed in such a manner that small pores and large pores correspond one to the other, the pore density (area of pores per unit area) of one side of the membrane made of small pores is very low No, the performance of the membrane deteriorates.

Therefore, it is necessary to develop a new type of high-performance ion diode membrane that can maximize ion rectification characteristics and membrane performance while maintaining the meat hole density, and the technology of ion-diode membrane fabrication process that can freely control membrane characteristics .

In order to solve the above-mentioned problems, the present invention has a branch structure in which the number of nano pores per unit area, the spacing of the pore spaces and the pore diameter of the pore vary along the nano pores, The pore density (the area of the pores per unit area) of one side of the membrane made of the small pores can be greatly increased and the ratio of the surface area per unit volume of the large pores and the small pores can be maximized to provide ions having excellent rectifying properties, It is an object of the present invention to provide an ion diode membrane fabrication method capable of integrating a diode film, nano pores having a high pore size, and controlling the shape of pores in the membrane by controlling process conditions to control rectification characteristics and membrane resistance. .

The ion diode membrane of the present invention is an ion diode membrane comprising a plurality of nano-pores present on one side of the membrane and a plurality of outlets that are nano-pores present on the other side of the membrane, wherein the inlet and outlet have a number of pores and a diameter And are interconnected within the membrane, wherein the nanopore comprises one or more branches in which the passage in the pore is divided into a plurality of branches according to a depth change.

The ion-diode membrane fabrication method of the present invention comprises the steps of: (a) preparing a metal and an electrolyte for anodization; (b) performing an anodic oxidation to form an oxide of the ion diode film; (c) removing the metal to obtain a porous template of oxide; And (d) removing the lower portion of the porous template to obtain a penetrating ion diode membrane. In the step (b), a multi-potential rectangular pulse anodizing process is performed, Support section; And a branch in which the passage in the pore is divided into a plurality of branches according to a change in depth, an oxide of an ion diode film including a nanopore of a branch shape is formed.

According to the manufacturing method of the present invention, it is possible to manufacture an ion diode film having a low film resistance and excellent rectifying characteristics by controlling the shape of the pores in the film by controlling the anodizing process conditions, have. It should be understood that the effects of the present invention are not limited to the above effects and include all effects that can be deduced from the detailed description of the present invention or the configuration of the invention described in the claims.

1 is a schematic view of an ion diode membrane in which nano pores of a branch shape are integrated according to an embodiment of the present invention.
2 is a flow chart illustrating a process of fabricating an ion diode membrane according to one embodiment of the present invention.
FIG. 3 is a schematic diagram showing a multi-potential rectangular pulse anodic oxidation method for controlling the morphology of nanopores according to an embodiment of the present invention.
4 is a photomicrograph view of an ion diode membrane fabricated in an embodiment of the present invention.
5 is a current-voltage curve of the ion diode film fabricated in an embodiment of the present invention.
6 is a graph showing the open-circuit voltage and the short-circuit current of the ion diode membrane of the present invention measured in seawater (500 mM NaCl) and fresh water condition (10 mM NaCl).

Hereinafter, the present invention will be described in more detail with reference to the drawings. The invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly explain the present invention, parts not related to the description are omitted, and like parts are denoted by similar reference numerals throughout the specification.

In this specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" with another part in between . Also, when an element is referred to as "comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

In the present specification, the term " nano-pore structure " means that the passage in the pore from the inlet to the outlet has a shape in which the passage in the pore is divided into a plurality of branches according to the depth variation. For example, The diameter of the pores is larger than the diameter of the outlet and the number of pores per unit area increases as the passage progresses from the inlet to the outlet, and the pore spacing and pore diameter decrease.

In the present specification, the term " branch " means a region in which one of the passages in the pore is divided into two or more fork (passage), the spacing of the space, the diameter of the pore, and the number per unit area. This is done by artificially adjusting the applied voltage. &Quot; Section " means an area between a branch and a branch, or an area between an inlet (or outlet) and a branch, and refers to a space where the number of pores per unit area is constant. The term " inlet " is defined as a pore on a surface having a large pore diameter and a large space distance on both sides of the ion diode membrane. The " outlet " is defined as pores on the opposite surface of the inlet. And is defined to facilitate understanding of the present invention.

The ion diode membrane of the present invention is an ion diode membrane comprising a plurality of nano-pores present on one side of the membrane and a plurality of outlets that are nano-pores present on the other side of the membrane, wherein the inlet and outlet have a number of pores and a diameter And the nano pores include one or more branches in which the passage in the pore is divided into a plurality of branches according to the depth change, and in some cases, the nano pores do not branch according to the depth change, A relatively long support section may be included. The support section serves to improve the durability of the ion diode membrane.

The ion diode membrane of the present invention can be classified into a cation diode membrane having a negative charge function on the surface of the membrane and an anion diode membrane having a positive charge function on the surface of the membrane. In order to control the characteristics of the ion diode membrane, the shape of the nanopores of the branch shape (thickness of the membrane, the diameter of the inlet and outlet and the distance of the gas space, the number of sections and branches, the diameter in each section, Etc.) or the distribution of positive charge / negative charge or the type of functional group can be controlled.

The shape of the nano pores of the ion diode membrane includes one or more branches in which the passage in the pore is divided into a plurality of branches according to a depth change from the inlet to the outlet, and relatively non-branched, that is, And may include non-branching support sections. In this structure, the ion flow rate is very fast and the separation rate can be improved. Depending on the application, the type of charge, the distribution of charge, the type of nanopore (ie, the thickness of the membrane, the diameter of the inlet and outlet and the distance of the air space, the number of sections and branches, the diameter of the section, .

Nano pores including one or more branches where the passage in the pore is divided into a plurality of branches according to the depth of the nano pores in the form of gaps, that is, from the inlet to the outlet, are different from the general nano pores by the structural asymmetry, And it shows the rectification characteristic in the ion flow in the electrolyte. Although not particularly limited, the characteristics of the ion diode film of the present invention can be controlled through various designs. For example, by designing a relatively short length of a section having a small passage diameter used for separation of ions or molecules in nanopores, the resistance can be reduced to facilitate the flow of ions or molecules, and in this case, The section can be designed to be long. In addition, it is possible to increase the selectivity of ions by designing a relatively long section with a relatively small diameter, or to reduce the resistance by designing a relatively long section having a large diameter, thereby facilitating the flow of molecules or ions.

FIG. 1 is a schematic view of an ion diode film having nano pores and nano pores in a branched form according to an embodiment of the present invention. The nano pores in the form of nano pores are nano pores in the form of one or more branches in which the passage in the pore from the inlet to the outlet is divided into a plurality of branches. The number of the sections is determined according to the number of the branches, N-1, the number of intervals is defined as N. Each section consists of pores of the same diameter and the distance between the pores is constant. The diameter of the pore and the distance of the pore space change while the pore branches, and the pore of the section n and the section of the section n + 1 are connected to each other. The length of each section, the distance of the space, and the diameter can be variously adjusted depending on the application.

The support section is made for the purpose of mechanical durability (mechanical strength) of the ion diode membrane. Generally, as the thickness of the film decreases, the resistance of the film decreases, so that the flow rate of the ions improves but the durability of the film decreases. Therefore, the length of the section having relatively large diameter nano pores having a small influence on the resistance of the membrane can be made long, and the support section for improving the durability while minimizing the decrease of the ion flow rate can be manufactured. The support section is a section that is relatively long in shape compared to other sections of the ion diode membrane. In addition, the ion diode membrane of the present invention is an asymmetric membrane composed of the same material composed of a branch and a support section having a separation function, and exhibits a high separation rate as compared with a symmetric membrane, and is prevented from clogging by foreign substances.

The lattice constant of the ion diode film of the present invention is not particularly limited, but may be 2 to 1,000 nm, for example, 2 to 800 nm, for example, 2 to 600 nm, and may be determined by the following Equation 1 in the manufacturing process. Further, although not particularly limited, the ratio of the lattice constant at the inlet and the outlet may be more than 1: 1 to 2,000, for example, more than 1: 1 to 1,000.

[Equation 1]

Lattice constant (d _n ) (nm) = 2.5 (nm / V) x U _n (V)

(Where d _n is the lattice constant of the n section and U _n is the applied voltage of the n section).

The ion diode membrane of the present invention is not particularly limited, but it may be an ion diode membrane having a surface of 2 to 1,000 and being charged positively or negatively.

In addition, the initial diameter of the nano pores can be determined according to the type and voltage of the electrolyte, as can be seen from the experiment of Example 1 below.

The nanostructure layer formed at this time has a hexagonal structure. The diameter of the pores can be controlled after the anodic oxidation through the isotropic etching process. The final diameter of the nano pores obtained by isotropic etching is larger than the initial diameter or smaller than the lattice constant Lt; / RTI > When uniform pores are not required as in the case of the ion diode membrane of the present invention, anodic oxidation can be carried out under various electrolyte and voltage conditions according to Equation 1. In the case of 1 M sulfuric acid or oxalic acid, for example, 2.5 nm It is also possible to manufacture nanopores of lattice constant. The anodic oxidation conditions of the present invention are not limited to those shown in Table 1, but can be expanded to various conditions enabling porous anodization.

A method of manufacturing an ion-diode membrane of the present invention includes the steps of: (a) preparing a metal and an electrolyte for anodizing; (b) performing an anodic oxidation to form an oxide of the ion diode film; (c) removing the metal to obtain a porous template of oxide; And (d) removing the lower portion of the porous template to obtain a penetrating ion diode membrane. In the step (b), a multi-potential rectangular pulse anodizing process is performed, Support section; And a branch in which the passage in the pore is divided into a plurality of branches according to a change in depth, an oxide of an ion diode film including a nanopore of a branch shape is formed.

The anodic oxidation method may be used for the ion diode membrane production method of the present invention. Anodic oxidation is one of the surface treatment techniques for metal. It has been widely used to prevent corrosion by forming an oxide film on the surface of metal or to color metal. Recently, however, nanostructures such as nano dots, nanowires, nanotubes, and nanorods Is known as a method for directly forming a template for forming a bare structure or a template for forming a bare structure. Examples of the metal capable of forming the nanostructure by the anodic oxidation include aluminum (Al), titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), niobium (Nb), tungsten Can be used. Among them, aluminum anodic oxide film is easy to manufacture and unlike other metals using fluorine ion, it is relatively safe to handle the electrolyte, and it is easy to control the distance (lattice constant) between the diameter, length and pore size of the nanopore. It has been widely used. Aluminum is electrochemically anodized in an aqueous solution containing an electrolyte such as sulfuric acid, oxalic acid, selenic acid or phosphoric acid to form a thick porous anodic oxide film on the surface. This anodic oxide film forms a porous layer in which pores having regular intervals are grown in the direction perpendicular to the outer surface from the inner metal. The self - alignment of the nanopores is determined by the specific voltage and temperature of the electrolyte. Anodization at these self - aligned conditions can produce nanotubes in which the nanopores are densely arranged. In particular, the anodic alumina nanotemplate is used in various fields as nanotemplate manufacturing technology because it is easy and economical to control the nanopores.

The method for producing an ion-diode membrane of the present invention may further comprise the following steps after the step (a):

(a-1) pre-anodizing the metal to form an oxide on the metal surface; And

(a-2) selectively removing the oxide from the metal.

The pre-anodizing step may be an anodizing step with an electrolyte, and may be performed under the same voltage conditions as one section of the anodizing step of step (b) described later. The aligned pores can be obtained more than when the processes (a-1) and (a-2) are performed, and as a result, the ion flow rate can be improved.

In addition, the method for producing an ion-diode membrane of the present invention may further include: (e) surface-treating the ion-diode membrane by a method selected from the group consisting of a silanization step, a layered self-assembly method and a hydrothermal synthesis method. Anodized ion diode membranes can control the type and charge density of surface charge by surface treatment, and thus can be fabricated as cationic or anion exchange membranes. As the surface treatment method, there are a method using a silane process using an anodized oxide -OH, a layered self-assembly method using a charged polymer electrolyte, or a hydrothermal synthesis method, and the kind and density of the surface charge on the surface of the ion- Can be adjusted.

FIG. 2 illustrates a method of manufacturing an ion diode membrane using anodization according to an embodiment of the present invention. The method includes: (a) preparing a metal (an aluminum foil) for anodization and an electrolyte; (a-1) pre-anodizing the metal to form an oxide on the metal surface; (a-2) selectively removing the oxide from the metal; (b) performing an anodic oxidation to form an oxide of the ion diode film; (c) removing the metal to obtain a porous template of oxide; (d) removing the lower portion of the porous template to obtain a penetrating ion diode membrane, and (e) a surface treatment step for adjusting the surface charge density of the ion diode membrane. The anodization step (b) may be carried out on the aluminum foil (a) without going through the steps (a-1) and (a-2). After step (a-1), it is immersed in the electrolyte solution of (a-1) for a long time and isotropically etched to cope with step (a-2). The surface treatment of (e) may be carried out after the step (b) or (c).

The lattice constant of each section of the ion diode film can be determined by controlling the applied voltage in the anodic oxidation process according to the following equation (1) in steps (a-1) and (b) In general, the pore alignment can be improved by adjusting the lattice constants to be the same by applying the same voltage to one section of the step (a-1) and the step (b).

[Equation 1]

Lattice constant (d _n ) (nm) = 2.5 (nm / V) x U _n (V)

(Where d _n is the lattice constant of the n section and U _n is the applied voltage of the n section).

Referring to Table 1, the lattice constant of the nanoporous layer can be controlled according to the kind of the electrolyte and the voltage applied to the anodic oxidation, and the initial diameter is determined according to the electrolyte and the voltage. The nanostructure layer formed at this time has a hexagonal system structure. The diameter of the pores can be controlled after the anodic oxidation through the isotropic etching process. The final diameter of the nanopores obtained by isotropic etching is larger than the initial diameter or smaller than the lattice constant Lt; / RTI >

The unaligned pores produced by the pre-anodization process of (a-1) have an ordered hexagonal structure when the anodization of step (b) is performed after the step (a-2) pore diameter becomes uniform. However, when uniform pores are not required as in the case of the ion diode membrane of the present invention, anodic oxidation may proceed under various electrolyte and voltage conditions according to Equation 1. For example, in 1 M sulfuric acid or oxalic acid, 2.5 nm It is also possible to manufacture nanoporous lattice constants. Therefore, the anodic oxidation condition of the present invention can be expanded to various conditions enabling porous anodic oxidation.

FIG. 3 is a schematic view showing a multistage square pulse anodic oxidation method for controlling the morphology of nano pores according to an embodiment of the present invention, in order to facilitate understanding of step b) of FIG. 2. In general, the isotropic etching is caused by the electrolyte during the anodic oxidation process, and the isotropic etching rate is influenced by the used electrolyte and temperature, so that the pore shape can be controlled by considering this.

First, the shape of the ion diode membrane such as the total thickness of the membrane, the length of the supporting section, the number of sections, the length of the nanopore, the lattice constant, and the diameter of each section including the inlet and the outlet are designed according to the use of the ion diode membrane, And the process temperature. The growth rate (v _n ) and the isotropic etch rate (v _e ) of the anodic oxide are determined according to the electrolyte and the process temperature. The growth rate also depends on the applied voltage in addition to the type of electrolyte and the process temperature.

(n 구간의 최소직경)보다 전해액에 노출된 시간, 즉 기공 형성 후부터 누적된 양극산화 공정시간만큼 직경이 증가하므로 수학식 3에 의해 결정된다. 도 3의 b)에서는 U₁에서 U₂로 낮아진 인가전압에서 2번째 양극산화를 수행하면 기공 내 통로에서 분기가 일어나면서 2번째 사각펄스 양극산화를 통해 분기가 일어나 1구간 아래에 2구간이 형성되고, 형성된 2구간의 격자상수(d₂)와 길이(L₂), 직경(D₂)은 2구간의 인가전압(U₂)과 인가전압에서 양극산화물의 성장속도(v₂), 전압인가 시간(t₂)과 주기 시간(T₂)으로부터 결정된다. 여기서 1구간의 다공의 직경은 2구간에서의 전해액과 공정온도가 1구간과 동일한 경우에 2구간의 등방성 식각속도는 1구간과 동일하므로, T₂에 의존하여 수학식 3에 따라 증가한다.First, in Fig. 3 (a), the first rectangular pulse anodization is performed to fabricate one section including the inlet surface. Where the square pulse is an applied voltage calculated by Equation 1 and a square pulse of 0 V according to the design. The total number N of square pulses and the total number N of ion diode film sections are equal to each other. 3 (d) is a schematic diagram showing the time-voltage curve of multi-potential rectangular pulse anodization. That is, a total of N square pulse anodizing processes performed at different applied voltages according to the design can form an ion diode film having N sections in total. The first section corresponding to a) of FIG. 3 is formed through the first rectangular pulse anodization process. The lattice constant d ₁ and the length L ₁ and the diameter D ₁ of the first section can be calculated by dividing the growth rate v ₁ of the anodic oxide at an applied voltage U ₁ and the isotropic etching rate v _e), it is determined by equation 1, 2, and 3 from the voltage application time (t ₁₎ and the cycle time (t _1). In general, the anodic oxide isotropically etched by the electrolyte in the anodic oxidation process, so that the pores formed by the anodic oxidation during the period of exposure to the electrolyte are increased in diameter by isotropic etching. Therefore, the diameter of the pore (D _n ) is calculated by the 10% porosity`s role

(the minimum diameter of the section n), that is, the diameter of the anodization process accumulated from the time of formation of the pores increases. 3 b), when the second anodization is performed at a lower applied voltage from U ₁ to U ₂ , the branching occurs in the passage in the pore, branching occurs through the second square pulse anodization, and two sections are formed under one section The lattice constant d ₂ , the length L ₂ and the diameter D _{2 of the} formed two sections are set so that the applied voltage U ₂ of the two sections and the growth rate v ₂ of the anodic oxide at the applied voltage, Is determined from the time t ₂ and the cycle time T ₂ . In this case, the diameter of the pore of the first section is increased according to Equation (3) depending on T ₂ because the isotropic etch rate of the two sections is the same as the first section when the electrolyte and the process temperature in the two sections are equal to one section.

&Quot; (2) "

(Where L _n is the length of the n section, v _n is the growth rate of the anodic oxide in the n section, and t _n is the voltage application time in the n section).

&Quot; (3) "

(And wherein R, D _n is the diameter of the pores of the n sections, d _n is the lattice constant of the n sections, v _e is the isotropic etching rate, T _i is the period of time in the i interval, N is a total of two of the interval chat.)

)으로 결정된다. 또한, N번의 사각펄스 양극산화를 실시하여 완성된 이온다이오드막의 i 번째 구간의 다공직경(D_i) 은 i 번째에서 N 번째까지 누적된 주기시간 (

) 으로부터 결정된다. 위의 원리를 이용하면 설계에 따라 저온 양극산화 시간, 고온 양극산화의 각 사이클에서의 주기시간과 전압인가 시간을 조절하여, 이온다이오드막 내부의 나노다공 형태를 자유롭게 조절할 수 있으며, 다양한 특성의 이온다이오드막 제조가 가능하다.The lattice constant d _i , the length L _i and the diameter D _{i of the i-} th section in the case of performing the i-th multistage rectangular pulse anodic oxidation process as described above are determined on the assumption that the electrolytic solution and the process temperature do not fluctuate, is the i interval voltage (U _i) and the rate of growth of anodic oxide on the applied voltage (v _i), an isotropic etching speed (v _e), equation voltage from the application time (t _i) and the cycle time (t _i) 2 And < / RTI > The thickness of the entire ion diode film is the sum of the lengths of all the sections (

). Further, the porous diameter (D _i) of the i-th ion diodes film interval completed by performing a single square pulse anodizing is N times the cumulative period from the i-th to N-th (

). By using the above principle, it is possible to freely control the nanoporous form in the ion diode film by controlling the low-temperature anodization time, the cycle time and the voltage application time in each cycle of the high-temperature anodization according to the design, Diode film fabrication is possible.

Further, the number of pores per unit area of the section can be determined by the following equation (4).

&Quot; (4) "

(Where N / P _n is the number of pores per cm ^{2 of the} section n, and d _n is the lattice constant of the section n).

Also, since the above process can be simply controlled through a program, the number of sections (N) can be very large, thereby enabling precise shape control.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the scope of the present invention is not limited thereto.

[Example]

1. The lattice constant of the ion diode film and the initial diameter of the pores

Table 1 below shows the initial diameters and lattice constants of the pores when the electrolyte and the applied voltage were differently measured under the conditions described by using an electron microscope.

The results of Table 1 correspond to Equation (1), and it can be seen that the lattice constant of the nanoporous layer can be controlled according to the kind of the electrolyte and the applied voltage for the anodic oxidation, and the initial diameter is determined according to the electrolyte and the voltage.

2. Manufacture of ion diode membrane

After the aluminum foil was immersed in acetone, the organic matter was washed with ultrasonic and immersed in water (HCl (hydrochloric acid) 20 ml + HNO ₃ (nitric acid) 10 ml + distilled water 70 ml + HF (hydrofluoric acid) 1 ml) After removal, it was washed with distilled water. The aluminum foil from which the impurities were removed was heat-treated for 5 hours in an N ₂ atmosphere at 500 ° C, and electrolytic polishing was performed to remove fine irregularities on the aluminum surface. A smooth aluminum foil surface-treated as described above 40V, and then subjected to a pre-anodization using an aqueous solution of 0.3M oxalic acid as an electrolyte at 10 ℃, chromate, the oxide formed from the anodizing solution (1.8g 7.1g CrO ₃ + H ₃ PO ₄ (85%) + fill up to 100 mL). It was confirmed by electron microscope that a 100 nm hexagonal system pattern remained on the aluminum surface from which the oxide was removed.

The diameter of the inlet of the ion diode membrane was 47 nm, the lattice constant was 100 nm, the diameter of the outlet was 4.2 nm, the lattice constant was 12.5 nm, the total thickness of the membrane was 60 μm, and the number of sections was 351. Also, the support section was included in one section including the entrance, and the remaining sections were designed to have the same length. The process temperature was 10 ° C, and the isotropic etching rate was 0.566143 nm / hr. The growth rate at each applied voltage was calculated in advance and was 85nm / min at 40V and 4.92nm / min at 5V. For the aluminum foil with hexagonal pattern, an ion diode membrane was fabricated by conducting multi - potential square - pulse anodization at 10 ℃ using an aqueous solution of oxalic acid (40V, 0.3M), which was the same as the pre - anodic oxidation condition. At this time, the anodization time was determined according to the formulas (2) and (3) according to the design, and the process was performed for 23 hours 43 minutes and 49 seconds. After the anodic oxidation process was completed, the anodized aluminum was immersed in 1M SnCl ₄ solution to remove the anodic oxide film containing the nanopores.

The resulting anodic oxide film was clogged with one pore, so that the bottoms of the pores were wet etched with a chromic acid aqueous solution to prepare an ion diode film through the inlet and the outlet. The prepared ion diode membrane was immersed in a 1: 100 solution of 3-mercaptopropyl trimethoxysilane (MPTS, HS (CH ₂ ) ₃ Si (OCH ₃ ) ₃ ) and acetone for 12 hours The surface was treated to introduce the -SH functional group on the surface, and washed with acetone. Thereafter, the ion diode film was immersed in a 30% H ₂ O ₂ aqueous solution for one day and then dried. The surface of the anodized oxide generally has an -OH functional group, but the ionization membrane having the -SO ₃ H functional group by the above-mentioned silanization process and hydrogen peroxide treatment was prepared. The ion diode film prepared as described above is photographed by an electron microscope and is shown in FIG. 4, and morphological control by multi-potential square pulse anodization can be confirmed according to the design.

In one embodiment of the present invention, the anodized ion diode membrane can control the type and charge density of the surface charge by surface treatment, and thus can be fabricated as a cation exchange membrane or anion exchange membrane. Surface treatment methods typically include the type and density of the surface charge on the surface of the ion diode membrane using a method using a silane process using an anodized oxide -OH, a layered self-assembly method using a charged polymer electrolyte, or a hydrothermal synthesis method Can be adjusted.

FIG. 5 shows the rectification characteristics of ions in a current-voltage curve of a cation and an anion diode film surface-treated with -SO ₃ H and -NH ₂ by a silanization process according to an embodiment of the present invention. NaCl aqueous solution and exhibited a high ion diode characteristic of a rectification ratio of 500 or more.

FIG. 6 shows an open circuit voltage and a short-circuit current in a seawater (500 mM NaCl) and a fresh water condition (10 mM NaCl) of the prepared ion diode membrane, and an energy production of about 3.4 W / m 2 was possible. This value is about 17 times higher than the conventional commercialized ion exchange membrane.

Claims (11)

A plurality of entrances that are nanopores present on one side of the membrane,
An ion diode membrane comprising a plurality of outlets which are nanopores present on the other side of the membrane,
Wherein the inlet and outlet are different in pore number and diameter and are connected to each other within the membrane,
Wherein the nano-pores include one or more branches in which a passage in the pore is divided into a plurality of branches according to a depth change. The nano-pore structure according to claim 1, wherein the nano-pores include: a support section in which a passage in the pore does not branch according to a change in depth; And a branch in which the passage in the pore is divided into a plurality of branches according to the depth change. 2. The ion diode membrane of claim 1, wherein the ratio of the lattice constant of the inlet and the outlet is greater than 1: 1 and 2,000. The ion diode membrane according to claim 1, wherein the material of the ion diode film is an oxide of a metal selected from the group consisting of aluminum, titanium, zirconium, hafnium, tantalum, niobium and tungsten. The ion diode membrane according to claim 1, wherein the rectification ratio is 2 to 1,000, and the surface is positively charged or negatively charged. (a) preparing a metal and an electrolyte for anodizing;
(b) performing an anodic oxidation to form an oxide of the ion diode film;
(c) removing the metal to obtain a porous template of oxide; And
(d) removing the lower portion of the porous template to obtain a penetrating ion diode membrane,
Performing a multistage rectangular pulse anodization process in the step (b), wherein the passage in the pore does not branch according to the depth change; And a branch in which the passage in the pore is divided into a plurality of branches according to the depth change,
A method of manufacturing an ion diode membrane. The method according to claim 6, further comprising, after the step (a), further comprising the steps of:
(a-1) pre-anodizing the metal to form an oxide on the metal surface; And
(a-2) selectively removing the oxide from the metal. 7. The method according to claim 6, wherein in step (b), the lattice constant of the ion diode film is determined according to the following equation (1).
[Equation 1]
Lattice constant (d _n ) (nm) = 2.5 (nm / V) x U _n (V)
(Where d _n is the lattice constant of the n section and U _n is the applied voltage of the n section). The method according to claim 6, wherein the length (L _n ) of the support section is determined according to the following equation (2) in the step (b).
&Quot; (2) "

(Where L _n is the length of the n section, v _n is the growth rate of the anodic oxide in the n section, and t _n is the voltage application time in the n section). The method according to claim 6, wherein the diameter (D _n ) of the pores is determined according to the following equation (3) in the step (b).
&Quot; (3) "

(Where D _n is the diameter of the pore in the n section, d _n is the lattice constant in the n section, v _e is the growth rate of the anodic oxide in the e section, T _i is the cycle time in the i section, N is the total number of intervals.) 7. The method of manufacturing an ion-diode membrane according to claim 6, further comprising the step of: (e) surface-treating the ion-diode membrane by a method selected from the group consisting of a silanization process, a layered self-assembly process and a hydrothermal synthesis process.

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