KR20140127514A - Capacitive deionization device including carbon electrode having hierarchically porous structure - Google Patents

Abstract

The disclosed capacitive deionization device includes a pair of electrodes, and a separation membrane arranged between the pair of electrodes. At least one electrode between the electrodes includes a carbon electrode, wherein the carbon electrode has micropores with a diameter less than 2 nm and a volume of 1 cm^3/g or more, and large pores with a diameter of 2 nm or more and a volume of 4 cm^3/g or more.

Description

TECHNICAL FIELD [0001] The present invention relates to a capacitive desalination apparatus having a carbon electrode having a hierarchical pore structure,

The present invention relates to a capacitive desalination apparatus, and more particularly, to a capacitative desalination apparatus having a carbon electrode of a hierarchical pore structure.

As living water or industrial water, water is very important in human life. However, in modern times, water contains heavy metals, nitrate nitrogen, and fluoride ions, and when people drink water containing such substances for a long time, they can be very harmful to health. Thus, numerous water treatment techniques have been developed, such as reverse osmosis (RO), electrodialysis (ED), and ion exchange (EDI) methods, but these techniques must meet high cost and high risk technical conditions. For example, reverse osmosis systems require high pressures and pretreatment processes and also cause high volume of concentrated water. Therefore, even if there is a high-efficiency thin-film technology, it requires a very dangerous and expensive process for the operation. In the case of electrodialysis, since the high pressure is required, the electricity consumption is large and the membrane fouling from the hard- And the generation process is complicated. Ion exchange using ion exchange resins has the disadvantage that it causes secondary pollution due to various chemical substances and it is very difficult to remove total dissolved solids (TDS).

Accordingly, a capacitive deionization (CDI) system using a water purification technique using an electro-absorption and electric double charge principle has been developed in order to overcome the above disadvantages. The stack of CDI is composed of a support plate, a current supply plate, an electrode, a gasket, and an electrode separator. The current supply plate receives the current from the power supply and makes a positive electrode or negative electrode on the electrode attached to the current supply plate, and the negative ions and the positive ions are attracted to the respective electrodes according to the electrical attraction.

As the electrode material of the storage desalination technique, carbon which can relatively easily realize a high specific surface area is used. The most widely used activated carbon has a very high specific surface area due to the development of micropores having a size of 2 nm or less (~ 2000 m ² / g), but the pore size, And consequently exhibits low speed characteristics. On the other hand, in the case of carbon aerogels, medium and large pores having a size of 2 nm or more are developed, which exhibits excellent speed characteristics, but exhibits low specific surface area and thus low capacitance due to lack of micropores.

Therefore, in order to improve the performance of the capacitive desalination technique, it is necessary to develop an electrode material having a high ionic rate characteristic and a high capacitance.

An object of the present invention is to provide a capacitive desalination apparatus using an electrode material having a high ionic rate characteristic and a high electrostatic capacity.

According to an embodiment of the present invention, a capacitive desalination apparatus includes a pair of electrodes and a separator disposed between the electrodes. Wherein at least one of the electrodes includes a carbon electrode having a hierarchical pore structure, the carbon electrode has a volume of pores having a diameter of less than 2 nm of 1 cm 3 / g or more, a volume of pores having a diameter of 2 nm or more of 4 cm 3 / to be.

According to one embodiment, the specific surface area of the carbon electrode is about 2,000 m 2 / g or more.

According to one embodiment, the storage and desalination apparatus further includes a current collector connected to the carbon electrode, and the current collector includes graphite.

According to one embodiment, the carbon electrode has a capacitance of at least 60 F / g when charged and discharged at a frequency of 1 Hz in a 1 M NaCl electrolyte.

According to an embodiment, the carbon electrode may have a volume of ultrafine pores having a diameter of less than 0.8 nm of 0.5 cm 3 / g or more, a volume of micropores having a diameter of 0.8 nm or more and less than 2 nm of 0.5 cm 3 / The volume of the mesopores having a pore size of 2 nm or more and less than 50 nm is 2 cm 3 / g or more, and the volume of the pores having a diameter of 50 nm or more is 2 cm 3 / g or more.

According to embodiments of the present invention, by using a carbon electrode having a hierarchical pore structure, a high electrostatic capacity can be obtained simultaneously with a high ion movement speed. Thus, desalination performance can be greatly improved.

FIG. 1 is a side view schematically showing a thermal desalination apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a pore structure of a carbon electrode of a thermal decomposition apparatus according to an embodiment of the present invention. Referring to FIG.
3 is a scanning electron microscope (SEM) photograph of the carbon material of Example 1. Fig.
4 is a graph showing the nitrogen isothermal adsorption / desorption experiment results for the carbon material of Example 1. Fig.
5 is a graph showing the CV test results of the electrodes of Example 1, Comparative Example 1 and Comparative Example 2 measured at 2 mV / s.
6 is a graph showing the CV test results of the electrodes of Example 1, Comparative Example 1 and Comparative Example 2 measured at 100 mV / s.
7 is a graph showing the EIS test results of the electrodes of Example 1, Comparative Example 1 and Comparative Example 2. Fig.
8 is a graph showing the conductivity of the effluent of the charge and discharge apparatus of Example 1, Comparative Example 1 and Comparative Example 2. Fig.
FIG. 9 is a graph showing the volumes according to the pore sizes of Examples 1, 2, and 3. FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. It is to be understood that the invention is not to be limited to the specific embodiments disclosed and that all changes which fall within the spirit and scope of the present invention are intended to be illustrative, , ≪ / RTI > equivalents, and alternatives.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "comprises", "having", and the like are used to specify that a feature, a number, a step, an operation, an element, a part or a combination thereof is described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

FIG. 1 is a side view schematically showing a thermal desalination apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating a pore structure of a carbon electrode of a thermal decomposition apparatus according to an embodiment of the present invention. Referring to FIG.

Referring to FIG. 1, the apparatus for depolarization includes a pair of carbon electrodes 20 and a separator 30 disposed between the electrodes. The carbon electrodes 20 are connected to a power source, one of which functions as an anode and the other of which functions as a cathode. The storage and desalination apparatus may include a pair of current collectors 10 connected to the electrodes 20, respectively.

The separator 30 is disposed between the carbon electrodes 20 to prevent a short circuit between the electrodes. The separation membrane 30 may include a polymer such as polyethylene, polyimide, nylon, polycarbonate, acrylic, and Teflon. The separation membrane 30 may have a hollow structure or the like and the brine supplied to the storage and desalination unit may move between the carbon electrodes 20 through the separation membrane 30.

The current collector 10 supplies a current to the carbon electrode 20 and protects the carbon electrode 20. The current collector 10 may include carbon, specifically, graphite. The current collector 10 may be omitted depending on the configuration of the carbon electrode.

The carbon electrode 20 has a hierarchical pore structure including voids of different sizes, as shown in Fig. Specifically, the volume of pores having a diameter of less than about 2 nm is about 1 cm 3 / g or more, and the volume of pores having a diameter of about 2 nm or more is about 4 cm 3 / g or more. The specific surface area of the carbon electrode may be about 2,000 m 2 / g or more. More preferably, the volume of micropores having a diameter of less than about 0.8 nm is about 0.5 cm 3 / g or more, the volume of micropores having a diameter of about 0.8 nm or more and less than about 2 nm is about 0.5 cm 3 / g or more, The volume of the mesopores having a pore size of 2 nm or more and less than about 50 nm is about 2 cm 3 / g or more, and the volume of pores having a diameter of about 50 nm or more is about 2 cm 3 / g or more. Further, the carbon electrode may have a capacitance of at least 60 F / g at a frequency of 1 Hz when charged and discharged in a 1 M NaCl electrolyte.

The carbon electrode may be formed by heat-treating a mixture of an inorganic precursor, an organic precursor, and a first solvent to synthesize an inorganic-organic skeleton structure, washing the inorganic-organic skeleton structure with a second solvent, The organic-inorganic skeleton structure can be obtained by thermally decomposing the inorganic-organic skeleton structure in a temperature range.

As the inorganic precursor, metal ions or metal clusters may be used. Zinc nitrate tetrahydrate or Zinc nitrate hexahydrate may be used in the present embodiment, but it is not limited thereto. In addition, ions or clusters made of one or more metals belonging to Groups 1 to 16 of the Periodic Table of Elements may be used .

Examples of the metal atoms include Li, Na, K, Mg, Ca, Sr, Ba, Sc, Y, Zr, Hf, V, Ti, Nb, Ta, Cr, Mo, W, Mn, Re, Cu, Zn, Ag, Pt, Pd, Ni, Cd, Rb, Be, Ru, Os, Rh, Ir, Au, Hg, Al, Ga, In, Si, Ge, Sn, Pb, ≪ / RTI >

As the organic precursor, terephthalic acid, amino-benzene dicarboxylate and naphthalene dicarboxylate may be used, but the present invention is not limited thereto. In addition, halide (F Organic materials including at least one of chlorine (Cl), bromine (Br), and iodine (I)), N, O, S, B, P, Si and Al can be used.

More specifically, examples of organic precursors include isocyanates (OC≡N), isocyanates (N═C═S), nitriles (C≡N), nitroso (-N═O), nitro (NO 2) Aliphatic or aromatic hydrocarbon compounds containing at least one of phosphate (PO3-4) and the like may be used.

Examples of such derivatives include benzene, naphthalene, carboxylate, trimecic acid, biphenyl, bipyridyl ((C5H4N) 2), and pyridine (C5H5N). Aliphatic compounds can be linear, branched, or cyclic, and aromatic compounds are possible in both forms in which one or more benzene rings are present one after the other.

The organic precursor may be an organic ligand. Representative examples of the organic ligand that can be used include 2-anilino-5-bromoterephthalic acid, 2-trifluoromethoxy terephthalic acid, nitroterephthalic acid, cis-cyclobutane-1,2-dicarboxylic acid, 2,5-thiophenedicarboxylic acid (Trifluoromethoxy) terephthalic acid, 1,3,5-benzenetricarboxylic acid, 3,3-bis (triphenylmethoxy) terephthalic acid, Fluoromethyl) -1-oxo-5-isobenzofurancarboxylic acid (3,3-bis (trifluoromethyl) -1-oxo-5-isobenzofurancarboxylic acid, pyrene- 2,7-dicarboxylate, terphenyl-4,4-dicarboxylate, 4,4,4-tricarboxytriphenylamine, 4,4,4-tris (N, N-bis (4-carboxyphenyl) amino) triphenylamine), and the like .

As the solvent for dissolving the inorganic and organic precursors, N, N'-dimethylformamide or N, N'-diethylformamide may be used. In addition, water, alcohol, ketone, nitrite, etc. may be used.

More specific examples of the solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, formic acid, acetic acid, propionic acid ), Butanoic acid, acetonitrile, cyanobenzene, acetone, methylene chloride, 1,2-dichloroethane, formamide t-butylacetamide, tetrahydrofuran, dioxane, dimethyl sulphoxide (DMSO), and the like can be used. , Sodium hydroxide (NaOH), ether, N-methyl-2-pyrrolidone (NMP) and 1-ethyl-3-methyl imidazolium bromide -methyl imidazolium bromide) can be used.

Any inorganic precursor and organic precursor can be dissolved, and any solvent that can withstand a hydrothermal reaction or a solvothermal reaction can be used without limitation. Mixtures of up to 1 wt% water and a single solvent can be used for synthesis. In the case of mixed solvents, the mass ratio of water can be adjusted to 1 wt% or more within the range of making crystals.

In order to synthesize the inorganic-organic skeleton structure, the mixture may be stirred at 10 to 1000 rpm for 10 minutes to 48 hours, and the heat treatment may be performed at a temperature ranging from room temperature to 80 ° C. to 150 ° C. at a rate of 1 ° C./min to 5 ° C. / min, maintaining the temperature at the highest temperature for 3 hours to 72 hours, and then cooling to room temperature. Stirring of the mixture can be carried out before the heat treatment. The heat treatment process can be either a hydrothermal treatment or a non-hydrothermal treatment. The maximum temperature for raising the temperature, the temperature raising rate and the maximum temperature holding time may be changed depending on the kinds of inorganic precursors, organic precursors and solvents.

The inorganic-organic skeleton structure is filtered from the first solvent, and then impregnated with the usable second solvent candidate group. The step of impregnating the second solvent candidate group may be carried out by repeating the washing by immersing and draining over 2 to 30 times at intervals of 30 minutes to 24 hours. As the second solvent, dimethylformamide may be used. Subsequently, additional washing may be repeated with the use of anhydrous volatile solvent. Representative examples of anhydrous volatile solvents include anhydrous ethanol, anhydrous acetone, and anhydrous chloroform.

The inorganic-organic skeleton structure is impregnated with a second solvent and pyrolyzed at a rate of 2 ° C / min to 10 ° C / min from 500 ° C to 1500 ° C under a low-activity or inert gas. For example, it may be maintained at the maximum temperature for 1 hour to 72 hours and then cooled to room temperature.

Through the above process, a carbon material derived from an inorganic-organic skeleton structure can be obtained.

Before performing the pyrolysis, the inorganic-organic skeleton structure may be dried to remove the second solvent, but it is preferable that the second solvent or the volatile solvent is pyrolyzed in the state where the second solvent or the volatile solvent remains without drying . In the pyrolysis process, the second solvent or the volatile solvent volatilizes or decomposes, thereby enabling formation of a hierarchical pore structure having various sizes.

The capacitor type desalination apparatus according to an embodiment of the present invention uses a carbon electrode having a hierarchical pore structure, so that it can have a high ion migration rate and a large capacitance simultaneously. Thus, desalination performance can be greatly improved.

Hereinafter, a method of fabricating a carbon electrode of a storage type desalination apparatus according to an embodiment of the present invention and an effect of a storage type desalination apparatus using the carbon electrode will be described with reference to specific examples and experimental examples.

Example 1

0.784 g of zinc nitrate and 0.166 g of terephthalic acid were dissolved in 30 ml of N, N'-diethylformamide, and then the temperature was raised to 105 ° C at a rate of 2 ° C / min in a furnace. To obtain an inorganic-organic skeleton structure which is a cube crystal. The inorganic-organic skeleton structure was cooled to room temperature, washed with dimethylformamide, purged with nitrogen gas in a tube furnace, heated to 900 ° C at a heating rate of 5 ° C / min, , The mixture was kept at that temperature for 3 hours and then cooled to room temperature to obtain a carbon body.

Next, the carbon body, the conductor (Super P), and the binder (PTFE) were mixed at a weight ratio of 86: 7: 7 to prepare a sheet-shaped electrode. The active material was used to provide high specific surface area, the conductor to increase the conductivity of the electrode, and the binder to hold the two materials in an electrode form.

Next, the electrode was cut into a circle having a diameter of 50 mm to prepare a carbon electrode, and a storage and desalination apparatus including the carbon electrode, a graphite current collector, and a nylon separator was prepared.

Example 2

A storage demineralizer was prepared in substantially the same manner as in Example 1, except that it was washed with dimethylformamide and then again washed with chloroform.

Example 3

A condensation desalination apparatus was prepared in substantially the same manner as in Example 1, except that it was washed with dimethylformamide and then dried at about 150 ° C for about 24 hours.

Comparative Example 1

A capacitive desalination apparatus was prepared in the same manner as in Example 1, except that a carbon electrode containing activated carbon was used in place of the carbon body of Example 1.

Comparative Example 2

A capacitive desalination apparatus was prepared in the same manner as in Example 1, except that a carbon electrode including carbon aerogels was used in place of the carbon bodies of Example 1.

Experimental Example 1

3 is a scanning electron microscope (SEM) photograph of the carbon body of Example 1. Fig. Referring to FIG. 3, it can be seen that the carbon bodies retain particles in the form of a split surface, and that the three-dimensional porous structure is regularly developed with reference to an enlarged photograph.

In order to investigate the surface area of the carbon body, a nitrogen isothermal adsorption / desorption experiment was carried out, and the result thereof (Adsorption: Desorption: Desorption amount, Relative pressure: partial pressure) was shown in FIG. Referring to FIG. 4, it was confirmed that the adsorbed amount of nitrogen in the carbon material was about 3500 cm 3 / g (P / P ₀ = 0.99), and the specific surface area was about 3000 m 2 / g. As a result, it can be seen that the carbon body has well-developed small pores with large pores.

Experimental Example 2

In order to analyze the electrochemical characteristics of the electrodes of Example 1, Comparative Example 1 and Comparative Example 2, electrochemical characteristics of the electrodes were measured using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) The dose was measured. As the electrolyte, 1 M NaCl was used.

5 is a graph showing the CV test results of the electrodes of Example 1, Comparative Example 1 and Comparative Example 2 measured at 2 mV / s. Fig. 6 is a graph showing the results of comparison 5 is a graph showing the results of CV experiments of the electrodes of Example 1 and Comparative Example 2.

Referring to FIGS. 5 and 6, all three kinds of carbon electrodes exhibit an ideal rectangular shape at a low scanning speed (2 mV / s), while activated carbon (Comparative Example 1) at a high scanning speed (100 mV / It can be seen that the shape of the carbon electrode is distorted and that the micropores in the activated carbon are not suitable for the fast movement of the ions. In addition, in the case of a material having medium pores such as carbon aerogels (Comparative Example 2), low carbon electrostatic capacity is exhibited, while the carbon material (Example 1) develops up to the micropores and exhibits both high capacitance and speed characteristics .

7 is a graph showing the EIS test results of the electrodes of Example 1, Comparative Example 1 and Comparative Example 2. Fig. Referring to FIG. 7, the activated carbon (Comparative Example 1) exhibits a low electrostatic capacity at a high frequency region (1-10 Hz) and has poor speed characteristics. However, the carbon body (Example 1) Specifically, a capacitance of at least 60 F / g when charged and discharged at a frequency of 1 Hz, and its size is also higher than that of carbon aerogels (Comparative Example 2).

Experimental Example 3

In order to evaluate the desalting performance of the storage and desalination apparatuses of Example 1, Comparative Example 1 and Comparative Example 2, 10 mM NaCl was pumped for 10 minutes at a potential of 1.2 V for charging, A potential of 0 V was applied for 10 minutes and the conductivity of the effluent was measured in real time. The results are shown in FIG. Conductivity values varying with time are divided by the weight of the electrode (specific deionization capacity or salt adsorption capacity, mg / g).

Referring to FIG. 8, it can be confirmed that the electrochemical de-ionization apparatus of Example 1 removes ions at a higher rate than the apparatus of Comparative Examples.

Experimental Example 4

FIG. 9 is a graph showing the volumes according to the pore sizes of Examples 1, 2, and 3. FIG.

Referring to FIG. 9, it can be seen that the carbon electrodes of Examples 1 and 2 can have pores of various sizes, compared to Example 3 which has undergone the drying process. In addition, it was confirmed that the pore size was different according to the pore size of Example 1 washed with dimethylformamide and Example 2 washed with chloroform, which is a volatile solvent, and the pore structure can be changed by changing the solvent. In addition, it can be seen that the carbon electrode obtained using dimethylformamide rather than chloroform, which is a volatile solvent, has a larger total pore volume.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. It can be understood that it is possible.

The storage and desalination apparatus according to the present invention can be used for desalination, softening, production of ultrapure water, removal of ionic pollutants, concentration of valuable metals, and the like.

Claims (6)

A pair of electrodes; And
And a separator disposed between the electrodes,
Wherein at least one of the electrodes comprises a carbon electrode, the carbon electrode has a hierarchical pore structure in which the volume of pores having a diameter of less than 2 nm is not less than 1 cm 3 / g and the volume of pores having a diameter of 2 nm or more is not less than 4 cm 3 / / RTI > The device of claim 1, wherein the specific surface area of the carbon electrode is not less than about 2,000 m 2 / g. The apparatus of claim 1, further comprising a current collector connected to the carbon electrode. The apparatus of claim 3, wherein the current collector comprises graphite. The apparatus of claim 1, wherein the carbon electrode has a capacitance of at least 60 F / g at a frequency of 1 Hz when charged and discharged in a 1 M NaCl electrolyte. The carbon electrode according to claim 1, wherein the carbon electrode has a volume of ultrafine pores having a diameter of less than 0.8 nm of 0.5 cm 3 / g or more, a volume of micropores having a diameter of 0.8 nm or more and less than 2 nm of 0.5 cm 3 / Wherein the volume of the mesopores of 2 nm or more and less than 50 nm is 2 cm 3 / g or more and the volume of the pores having a diameter of 50 nm or more is 2 cm 3 / g or more.

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