KR102308365B1 - Electrochemical system for selective fluorine removal - Google Patents

Abstract

An electrochemical system for removing selected fluorine according to an embodiment of the present invention includes: a central flow path providing a path through which influent water containing ions can move; a working electrode disposed on one side of the central flow path to selectively adsorb target negative ions; a counter electrode disposed on the other side of the central flow path to adsorb positive ions; and a cation exchange membrane disposed between the counter electrode and the central flow path.

Description

ELECTROCHEMICAL SYSTEM FOR SELECTIVE FLUORINE REMOVAL

The present invention relates to an electrochemical system for selective fluorine removal.

In the world, the value of water as a resource is increasing due to the deepening of drought caused by global warming, the depletion of groundwater, the progress of desertification, and the increase in the use of living and industrial water due to population growth and industrialization. Desalination is emerging as a new issue.

In general, for desalination of seawater, an electrodialysis method using an ion exchange membrane, a reverse osmosis membrane method, an evaporation method in which seawater is changed into steam to desalinate, a freezing method, and a method using solar heat are used. In addition, the currently commercialized desalination technology is an evaporation process by applying heat to separate salts and a reverse osmosis membrane process using a membrane that allows only water to pass through.

In addition, desalination technologies using electrochemical methods such as double capacitive desalination process and battery desalination process are being developed. .

However, the above technique has the following problems.

Capacitive desalination process, which is an environment-friendly and energy-efficient technology for general water-based ion removal, uses the principle that an electric double layer is formed on the surface of the electrode when an electric potential is applied between the two electrodes.

This desalination technology mainly uses an activated carbon electrode with a large surface area as a material for the anode and cathode. However, since the activated carbon has no selectivity to cations or anions, when it is used as an electrode material, other ions are also removed when the target ions are removed to a certain level or more, which causes unnecessary energy consumption. Accordingly, there is a need for a desalting process capable of selectively removing specific ions.

In particular, fluorine has recently been present in high concentrations in groundwater in many countries, causing numerous health problems, and the need for its removal is being emphasized. Development of an electrode capable of effectively removing the fluoride ion and an electrochemical system using the same research is needed.

Embodiments of the present invention are proposed to solve the above problems, and to provide an electrochemical system for selective fluorine removal that minimizes energy loss that may occur when unnecessary negative ions are removed.

An electrochemical system for selective fluorine removal according to an embodiment of the present invention includes a central flow path providing a path through which influent water containing ions can move; a working electrode disposed on one side of the central flow path to selectively adsorb target negative ions; a counter electrode disposed on the other side of the central flow path to adsorb positive ions; and a cation exchange membrane disposed between the counter electrode and the central flow path.

In addition, the working electrode includes a reduced graphene oxide/hydroxyapatite compound having a structure in which hydroxyapatite is grown on reduced graphene oxide.

In addition, the reduced graphene oxide/hydroxyapatite compound is formed by hydrothermal synthesis of a mixture in which calcium nitrate tetrahydrate, ammonium phosphate, cetrimonium bromide and sodium citrate are added to an aqueous solution of graphene oxide.

In addition, in the reduced graphene oxide/hydroxyapatite compound, the reduced graphene oxide may impart electrical conductivity, and the hydroxyapatite may have high selectivity for the target anion.

In addition, the hydroxyapatite may be grown as a seed with calcium ions disposed at the center of an arrangement connected to carbon atoms of the reduced graphene oxide.

In addition, the hydroxyapatite may include 35 to 91 parts by weight based on 100 parts by weight of the reduced graphene oxide/hydroxyapatite compound.

^{In addition, the target anion is ion-exchanged with the hydroxide ions (OH −} ) of the reduced graphene oxide/hydroxyapatite compound and adsorbed to the working electrode.

In addition, the counter electrode may include activated carbon.

The electrochemical system for selective fluorine removal according to embodiments of the present invention can minimize energy loss that may occur when unnecessary negative ions are removed.

1 is a schematic view for explaining an electrochemical system for selective fluorine removal according to an embodiment of the present invention.
2 is a view for explaining the synthesis process of the reduced graphene oxide / hydroxyapatite compound according to an embodiment of the present invention.
3 is a view for explaining the structure of the reduced graphene oxide / hydroxyapatite compound according to an embodiment of the present invention.
4 is a view for explaining the principle of the reduced graphene oxide / hydroxyapatite compound selectively removes fluorine according to an embodiment of the present invention.
5 is a view showing the fluorine adsorption performance according to the hydroxyapatite content of the electrochemical system for selective fluorine removal according to an embodiment of the present invention.
6 is a view showing anion removal performance according to an electrochemical system in a mixed solution in relation to selective fluorine removal according to an embodiment of the present invention.
7 is a view showing a result of measurement of fluorine removal according to a voltage level of an electrochemical system for selective fluorine removal according to an embodiment of the present invention.
8 is a view showing results for evaluating the stability and desorption degree of the electrochemical system for selective fluorine removal according to an embodiment of the present invention.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Examples of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, and the scope of the present invention is as follows It is not limited to an Example.

Rather, these examples are provided so that this disclosure will be more thorough and complete, and will fully convey the spirit of the invention to those skilled in the art.

In addition, in the following drawings, each component is exaggerated for convenience and clarity of description, and the same reference numerals refer to the same elements in the drawings. As used herein, the term “and/or” includes any one and all combinations of one or more of those listed items.

The terminology used herein is used to describe specific embodiments, not to limit the present invention.

As used herein, the singular forms may include the plural forms unless the context clearly dictates otherwise. Also, as used herein, “comprise” and/or “comprising” refers to the presence of the recited shapes, numbers, steps, actions, members, elements, and/or groups of those specified. will,

It does not exclude the presence or addition of one or more other shapes, numbers, movements, members, elements and/or groups.

1 is a schematic view for explaining an electrochemical system for selective fluorine removal according to an embodiment of the present invention, and FIG. 2 is a synthesis process of reduced graphene oxide/hydroxyapatite compound according to an embodiment of the present invention 3 is a view for explaining the structure of the reduced graphene oxide / hydroxyapatite compound according to an embodiment of the present invention.

The present invention is a technology for reversibly removing ions in influent using an electrochemical system capable of adsorption and desorption of ions.

In addition, the present invention is characterized in that the reduced graphene oxide / hydroxyapatite compound is included in the electrode side in the electrochemical system for selective fluorine removal.

Referring to FIG. 1 , the electrochemical system for selective fluorine removal according to an embodiment of the present invention is disposed on one side of the central flow path 100, which provides a path through which influent water containing ions can move. A working electrode 200 for selectively adsorbing target anions, a counter electrode 300 disposed on the other side of the central flow path to adsorb cations, and a cation exchange membrane 400 disposed between the counter electrode and the central flow path. can

The central flow path 100 moves influent water including seawater, salt water, wastewater, and groundwater to a space between the working electrode 200 and the counter electrode 300 .

In addition, the influent may include cations and anions capable of electrochemical reaction with the electrode, and in particular, the anions include fluorine ions (F ^- ), nitrate ions (NO ₃ ^- ), chlorine ions (Cl ^- ). can

In addition, the influent flowing into or discharged from the central flow path 100 is a water- _{soluble substance such as NaCl, H 2} SO ₄ , HCl, NaOH, KOH, Na ₂ NO ₃ and propylene carbonate (Propylene Carbonate, PC), diethyl carbonate ( Diethyl Carbonate, DEC) and an organic material such as Tetrahydrofuran (THF) may be included.

The working electrode 200 may include a reduced graphene oxide/hydroxyapatite compound (Reduced Graphene Oxide/Hydroxyapatite composite, rGO/HA).

Specifically, the reduced graphene oxide / hydroxyapatite compound is a reduced graphene oxide (Reduced Graphene Oxide) that can impart electrical conductivity to hydroxyapatite having high selectivity for fluorine by hydrothermal synthesis (HydroThermal Synthesis) is a substance

Such a reduced graphene oxide / hydroxyapatite compound is calcium nitrate tetrahydrate (Ca(NO ₃ )4H ₂ O), ammonium phosphate ((NH _{4 )2PO 4} ), cetrimonium in a graphene oxide aqueous solution (Graphene Oxide Solution) It is formed by hydrothermal synthesis after ultrasonication of a mixture containing bromide (Cetrimonium Bromide) and sodium citrate (Trisodium Citrate).

Specifically, in the process of hydrothermal synthesis of reduced graphene oxide/hydroxyapatite compound, first, graphene oxide is reduced to form reduced graphene oxide, and calcium ions ( the Ca ^{+ 2)} are arranged. At this time, the calcium ion (Ca ^{2 +} ) may serve as an anchor to hold the phosphate ion (PO ₄ ^2- ) and the hydroxide ion (OH ^{− ) on the reduced graphene oxide.}

Accordingly, hydroxyapatite is formed by ionic bonding of calcium ions, phosphate ions, and hydroxide ions, and calcium ions disposed at the center of an arrangement connected to carbon atoms of the reduced graphene oxide may be grown as seeds.

Meanwhile, the calcium ions may be uniformly dispersed and disposed on the reduced graphene oxide, whereby the reduced graphene oxide/hydroxyapatite compound has a structure in which hydroxyapatite is uniformly dispersed in the reduced graphene oxide and grown. can

In other words, the working electrode 200 may include reduced graphene oxide/hydroxyapatite compound formed through hydrothermal synthesis of growing hydroxyapatite on reduced graphic oxide, and the reduced graphene oxide/hydroxyapatite compound is It is possible to selectively remove fluorine ions.

In addition, in the electrochemical system for selective fluorine removal according to an embodiment of the present invention, the working electrode 200 includes a reduced graphene oxide/hydroxyapatite compound, wherein the hydroxyapatite is the reduced graphene oxide/hydroxyapatite compound. It is preferable to include 35 to 91 parts by weight based on 100 parts by weight.

The counter electrode 300 may use an activated carbon-based material having a high specific surface area, and may include, for example, activated carbon, activated carbon powder, activated carbon fiber, carbon nanotube, carbon airgel, and the like, but is not necessarily limited thereto. In an embodiment of the present invention, the counter electrode 300 preferably includes activated carbon.

That is, the counter electrode 300 may be an activated carbon electrode having cation selectivity, and may attract and adsorb cations contained in influent water.

In addition, since the counter electrode 300 has a large surface area, it has excellent advantages in relatively stable capacity characteristics in influent water, but the resistance of the activated carbon itself is not small, and the surface characteristic is hydrophobic, so it is not friendly with water. Performance can be improved by applying an ion exchange material such as calcium alginate to the counter electrode 300 .

The cation exchange membrane 400 may selectively pass cations from the influent.

The electrochemical system of the present invention removes ions in the influent water by adsorbing ions to the electrode surface when an electric potential is applied, but inevitably, some of the charge required for ion adsorption may be wasted. For example, power may be consumed to repel positively charged ions present on the electrode surface.

That is, the cation exchange membrane 400 relieves the above-described electrostatic charge ion repulsion, thereby dramatically improving ion adsorption performance and charge efficiency.

In addition, as the cation exchange membrane 400 , NaSS-MAA-MMA copolymer may be used, and may be installed to be spaced apart from the counter electrode 300 or coated on the counter electrode 300 .

4 is a view for explaining the principle of the reduced graphene oxide / hydroxyapatite compound selectively removes fluorine according to an embodiment of the present invention.

Hereinafter, an operating principle of the electrochemical system for selective fluorine removal according to an embodiment of the present invention will be described.

1 and 4, when electric energy is applied by connecting the counter electrode 300 and the working electrode 200 in one circuit, the cations present in the space of the central flow path 100 are the cation exchange membrane 400. It passes through and is adsorbed to the counter electrode 300 due to an electrochemical reaction with the counter electrode 300 .

In addition, negative ions existing in the space of the central flow path 100 move in the direction of the working electrode 200 due to an electrochemical reaction with the working electrode 200 .

Specifically, fluorine ions (F ⁻ ), which are negative ions, diffuse and move around the working electrode 200 , and a difference in concentration of fluorine ions occurs at the center of the central flow path 100 and at the periphery of the working electrode 200 . .

Accordingly, fluorine ions may be adsorbed to the hydroxyapatite included in the working electrode 200 by a concentration gradient without external energy.

Specifically, fluorine ions are ion-exchanged with hydroxide ions (OH-) of hydroxyapatite using a high concentration gradient as a driving force to be adsorbed to the hydroxyapatite. That is, hydroxide ions and fluorine ions capable of ion exchange with the central flow path 100 may be selectively removed through an electrochemical reaction with the working electrode 200 .

On the other hand, in the electrochemical system for selective fluorine removal according to an embodiment of the present invention, the adsorption process of fluorine ions is a negative voltage applied to the counter electrode 300 and a (+) voltage applied to the working electrode 200 . , and when the adsorption capacity of the working electrode 200 is saturated, no more fluorine ions can be adsorbed, so that the ions of the influent can come out as they are in the effluent.

Therefore, the electrochemical system for selective fluorine removal according to an embodiment of the present invention requires a desorption process of fluorine ions, and the desorption process desorbs ions adsorbed on the working electrode 200 and the counter electrode 300 . In order to regenerate the electrodes, the electrodes are shorted or a potential opposite to the adsorption potential is applied.

For example, referring to FIG. 1 , the desorption process proceeds due to a (+) voltage applied to the counter electrode 300 and a (-) voltage applied to the working electrode 200, in which case the electrodes are charged The electrode is regenerated by rapidly desorbing the adsorbed ions as they lose or have the opposite charge.

Example One

working electrode Produce

As a working electrode, a reduced graphene oxide/hydroxyapatite compound electrode having a hydroxyapatite (HA) content of 48wt% was prepared, and the working electrode was calcium nitrate tetrahydrate (Ca(NO ₃ )4H in an aqueous solution based on graphene oxide). ₂ O), ammonium phosphate ((NH ₄ )2PO ₄ ), cetrimonium bromide, and sodium citrate (Trisodium Citrate) were added to a mixed solution added by hydrothermal synthesis.

Specifically, first, 282 mg of calcium nitrate tetrahydrate and 54 mL of double distilled water were added to 36 mL of an aqueous solution of graphene oxide to prepare a first mixture. Then, 309.6 mg of sodium citrate, 94.68 mg of ammonium phosphate and 45 mL of secondary distilled water were mixed to prepare a second mixture.

At this time, the graphene oxide aqueous solution preferably contains 5 g of graphene oxide per 1 liter.

Then, the mixed solution obtained by mixing the first mixture and the second mixture was sonicated for 30 minutes using a sonicator.

Thereafter, the ultrasonically treated mixed solution was hydrothermally synthesized at 180 degrees Celsius for 24 hours.

Then, the hydrothermal synthesized mixed solution was subjected to vacuum filtration using a nanopore filter, mixed with ethanol and second distilled water to wash off impurities sufficiently, and then dried at 40 degrees Celsius for 24 hours. .

Finally, the dried mixed solution was made into a slurry and kneaded to make a sheet-shaped electrode using a roll presser. The thickness of the electrode thus made was about 300 μm.

In addition, reduced graphene oxide/hydroxyapatite compound electrodes of 35 and 91 wt% of hydroxyapatite (HA) were prepared in the same manner as above, and the reduced graphene oxide/hydroxyapatite compound electrodes of 35 and 91 wt% of the electrode were 48 wt% In comparison with the reduced graphene oxide/hydroxyapatite compound electrode, the content of calcium nitrate tetrahydrate, ammonium phosphate, cetrimonium bromide, and sodium citrate was added in 1/2 times and 2 times, respectively.

Electrochemical system configuration for selective fluorine removal

An activated carbon electrode is used as a counter electrode, and a reduced graphene oxide/hydroxyapatite compound electrode is used as a working electrode. It consists of an electrode, and a cation exchange membrane disposed at adjacently spaced apart positions of the counter electrode.

Experimental example 1 - Evaluation of fluorine adsorption performance by content and time

In the fluorine adsorption performance experiment, a cell composed of a working electrode and a counter electrode was formed in a solution containing the same number of moles ^{of fluorine ions (F -} ), chlorine ions (Cl ^- ), and nitrate ions (PO ₄ ^{2- ), and voltage was applied.} did.

In addition, as a working electrode, an activated carbon electrode used in an existing capacitive desalination system, a reduced graphene oxide electrode, and reduced graphene oxide / containing hydroxyapatite content of 35wt%, 48wt% and 91wt% A hydroxyapatite compound (Reduced Graphene Oxide/Hydroxyapatite) electrode was used.

5 is a view showing the fluorine adsorption performance according to the hydroxyapatite content of the electrochemical system for selective fluorine removal according to an embodiment of the present invention.

Referring to FIG. 5 , it can be seen that when a reduced graphene oxide/hydroxyapatite compound electrode is used as a working electrode, more fluorine ions are removed than when an activated carbon electrode or a reduced graphene on-side electrode not containing hydroxyapatite is used. can

In addition, the reduced graphene oxide/hydroxyapatite compound electrode showed better fluorine ion adsorption performance as the hydroxyapatite content increased.

Concentration changes of fluorine ions, chlorine ions, and nitrate ions were measured for 250 minutes under a voltage condition of 1.2 V using a reduced graphene oxide/hydroxyapatite compound electrode containing a hydroxyapatite content of 48 wt% as a working electrode.

6 is a view showing anion removal performance according to an electrochemical system in a mixed solution in relation to selective fluorine removal according to an embodiment of the present invention.

Referring to FIG. 6 , it can be seen that the amount of change in the concentration of fluorine ions after the evaluation process is larger than the amount of change in the concentration of chlorine ions and nitrate ions.

Experimental example 2 - Evaluation of fluorine adsorption performance by voltage

The adsorption performance of fluorine was evaluated using a reduced graphene oxide/hydroxyapatite compound electrode containing a hydroxyapatite content of 48wt% as a working electrode. , 1.2V and 1.5V were applied to evaluate the fluorine adsorption performance for 20 minutes.

In relation to this, FIG. 7 is a view showing a measurement result of fluorine removal according to a voltage level of an electrochemical system for selective fluorine removal according to an embodiment of the present invention.

As a result of the experiment, the fluorine removal performance increased as the voltage increased, and then decreased again due to side reactions such as water decomposition when a potential of 1.5V was applied. As a result, the fluoride ion was removed the most at 1.2V.

Experimental example 3 - by cycle Fluorine adsorption performance evaluation

The stability of the electrode and the flexibility of fluorine ion adsorption/desorption were evaluated for 40 minutes using a reduced graphene oxide/hydroxyapatite compound electrode containing a hydroxyapatite content of 48wt% as a working electrode, followed by an adsorption experiment for 20 minutes, and the remaining The desorption experiment was carried out for 20 minutes.

Here, the reduced graphene oxide/hydroxyapatite compound electrode and the reduced graphene oxide in which a total of 50 cycles were performed under a voltage condition of 1.2V, an adsorption experiment for 20 minutes and a desorption experiment for 20 minutes as one cycle / The fluorine adsorption performance of the hydroxyapatite compound electrode was evaluated.

8 is a view showing results for evaluating the stability and desorption degree of the electrochemical system for selective fluorine removal according to an embodiment of the present invention.

As a result of the experiment, it can be confirmed that there is almost no difference in the fluorine adsorption performance between the reduced graphene oxide/hydroxyapatite compound electrode subjected to 50 cycles and the reduced graphene oxide/hydroxyapatite compound electrode subjected to one cycle.

Accordingly, it can be confirmed that the electrochemical system for selective fluorine removal according to an embodiment of the present invention can be reused and has excellent stability even in repeated fluorine ion adsorption and desorption processes.

The electrochemical system for selective fluorine removal according to an embodiment of the present invention has been described as a specific embodiment, but this is only an example, and the present invention is not limited thereto, and the widest scope according to the basic idea disclosed in the present specification should be interpreted as having A person skilled in the art may implement a pattern of a shape not specified by combining or substituting the disclosed embodiments, but this also does not depart from the scope of the present invention. In addition, those skilled in the art can easily change or modify the disclosed embodiments based on the present specification, and it is clear that such changes or modifications also fall within the scope of the present invention.

100: central euro
200: working electrode
300: counter electrode
400: cation exchange membrane

Claims (8)

a central flow path providing a path for the influent containing ions to move;
a working electrode disposed on one side of the central flow path to selectively adsorb fluorine ions;
a counter electrode disposed on the other side of the central flow path to adsorb positive ions; and
A cation exchange membrane disposed between the counter electrode and the central flow path; including,
The working electrode is
A reduced graphene oxide/hydroxyapatite compound having a structure in which hydroxyapatite is grown on reduced graphene oxide,
In the reduced graphene oxide / hydroxyapatite compound, the reduced graphene oxide imparts electrical conductivity, and the hydroxyapatite is an electrochemical system for selective fluorine removal having selectivity for the fluorine ion.
delete The method of claim 1,
The reduced graphene oxide / hydroxyapatite compound,
An electrochemical system for selective fluorine removal formed by hydrothermal synthesis of a mixture of calcium nitrate tetrahydrate, ammonium phosphate, cetrimonium bromide, and sodium citrate in an aqueous solution of graphene oxide.
delete 4. The method of claim 3,
The hydroxyapatite is
An electrochemical system for selective fluorine removal in which calcium ions disposed at the center of an arrangement connected to carbon atoms of the reduced graphene oxide are grown as seeds.
6. The method of claim 5,
The hydroxyapatite is
An electrochemical system for selective fluorine removal comprising 35 to 91 parts by weight based on 100 parts by weight of the reduced graphene oxide/hydroxyapatite compound.
7. The method of claim 6,
The fluorine ion is
An electrochemical system for selectively removing fluorine adsorbed to the working electrode by ion exchange with hydroxide ions (OH-) of the reduced graphene oxide/hydroxyapatite compound.
8. The method of claim 7,
The opposite electrode is
An electrochemical system for selective fluorine removal comprising activated carbon.

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