Low-dimensional oxygen-based iron nanosheets and manufacturing method thereof

Abstract

The present invention relates to iron oxide nanosheets and a method for manufacturing the same, and more specifically, to low-dimensional iron oxide (FeO) nanosheets synthesized using a surfactant-assisted method in which the shape and surface area of ​​the metal oxide can be easily controlled.

Description

Technology Field

[0001] The present invention relates to transition metal oxide nanosheets, and more specifically, to transition metal oxide nanosheets that can be utilized as electrochemical catalysts. Background Technology

[0003] Transition metal oxides are compounds of transition metals and oxygen ions. As compounds of metals and oxygen ions, transition metal oxides possess properties different from conventional semiconductor materials depending on the type of metal ion and the stoichiometric composition of cations and anions. For example, properties ranging from insulating properties that do not conduct electricity to superconducting properties with no electrical resistance can be realized.

[0004] Recently, among nanostructures, ultrathin nanosheets have established themselves as a favorable platform for maximizing electrochemical performance in energy conversion processes due to their unique advantages, such as a large specific surface area and highly exposed active sites. Furthermore, vertical stacking of materials composed of the same or different elements is simple and enables uniform transfer, making them suitable for numerous substrates.

[0005] To create two-dimensional (2D) nanosheet structures, there are top-down methods that convert from a higher dimension to a lower dimension and bottom-up methods that form structures using precursor ions. One bottom-up method is a surfactant-based method that allows for the easy synthesis of 2D nanosheet structures without limitations on the original crystal structure. The synthesized nanosheets can be transferred to any substrate for use.

[0006] In the present invention, chemically stable low-dimensional iron oxide nanosheets were prepared using a surfactant-assisted method. Furthermore, due to their structural characteristics, the iron oxide nanosheets prepared thereby can be utilized as electrochemical catalysts exhibiting good electrochemical reactivity and excellent stability. Prior art literature

[0008] Republic of Korea Registered Patent No. 10-2189302

[0009] Microwave Absorbing Properties of NiFe2O4 Nanosheets Synthesized Via a Simple Surfactant-Assisted Solution Route (Materials Research. 2016; 19(5): 1149-1154)Structure of single sheet iron oxides produced from surfactant interlayered green rust (Applied Clay Science Volume 170, 15 March 2019) The problem to be solved

[0010] The present invention has been devised to solve the above-mentioned problems, and the objective of the present invention is to provide transition metal oxide nanosheets that have good electrochemical reactivity and excellent stability.

[0011] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0013] To achieve the above objective, the present invention provides a method for manufacturing iron oxide nanosheets, characterized by comprising: a first step of preparing an iron precursor aqueous solution by mixing an iron precursor with hexamethylenetetramine; a second step of preparing a surfactant mixture by mixing sodium hexadecyl sulfate (SHS), a chloroform solution, and a surfactant; a third step of dispersing the surfactant mixture on the surface of the iron precursor aqueous solution; and a fourth step of synthesizing iron oxide nanosheets by heating the iron precursor aqueous solution in which the surfactant mixture is dispersed.

[0014] The above iron precursor may be iron(III) nitrate.

[0015] In the first step above, 5 to 9 mmol of the hexamethylenetetramine can be mixed with 1 mmol of the iron precursor.

[0016] In the second step above, the surfactant may be one or more selected from the group consisting of oleylamine and oleic acid.

[0017] The above surfactant may be added in an amount of 0.01 to 0.03 parts by weight per 100 parts by weight of the chloroform solution.

[0018] In the fourth step above, the aqueous mixture of nickel precursors to which the surfactant has been added can be heat-treated in an oven at 60 to 80°C for 2 to 4 hours.

[0019] The thickness of the iron oxide nanosheet above may be 5 to 15 nm.

[0020] The above iron oxide nanosheets can be synthesized by a surfactant-assisted method.

[0021] In addition, the present invention provides iron oxide nanosheets produced by the above-described manufacturing method.

[0022] In addition, the present invention provides an electrochemical catalyst comprising the above-mentioned iron oxide nanosheets. Effects of the invention

[0024] By means of the solution to the above problem, the present invention can provide low-dimensional iron oxide (FeO) nanosheets synthesized using a surfactant-assisted method, which facilitates the control of the shape and surface area of ​​the metal oxide.

[0025] In addition, according to one embodiment of the present invention, a precipitate is formed together during synthesis, so that the nanosheet has not only the composition of Fe(OH)2 but also the composition of Fe(OH)3, and as a result, an iron oxide nanosheet having good electrochemical reactivity and excellent stability can be provided.

[0026] In addition, the iron used in the iron oxide nanosheet according to the present invention is a material that can be easily obtained in its natural state, and has the advantage of being available at a lower cost compared to other transition metals, such as cobalt or nickel.

[0028] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims. Brief explanation of the drawing

[0031] Figure 1 shows a schematic diagram of an iron oxide nanosheet photograph and synthesis according to an embodiment of the present invention. Figure 2 shows the AFM analysis results of iron oxide nanosheets according to one embodiment of the present invention. Figure 3 shows the XPS analysis results of iron oxide nanosheets according to one embodiment of the present invention. Figure 4 shows the results of electrochemical analysis of iron oxide nanosheets according to an embodiment of the present invention, including (a) Linear Sweep Voltammetry (LSV), (b) Tafel slope, and (c) Chronopotetiometry (CP) analysis. Specific details for implementing the invention

[0032] The terms used in this invention have been selected based on currently widely used general terms, taking into account their functions within the invention; however, these terms may vary depending on the intent of those skilled in the art, case law, the emergence of new technologies, etc. Additionally, in specific cases, terms have been arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, the terms used in this invention should be defined not merely by their names, but based on their meanings and the overall content of the invention.

[0033] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0034] When a part of a specification is described as “comprising” a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0035] Embodiments of the present invention are described below with reference to the attached drawings so that those skilled in the art can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0037] The present invention will be described in detail below.

[0039] The present invention provides a method for manufacturing iron oxide nanosheets, characterized by comprising: a first step of preparing an iron precursor aqueous solution by mixing an iron precursor with hexamethylenetetramine; a second step of preparing a surfactant mixture by mixing sodium hexadecyl sulfate (SHS), a chloroform solution, and a surfactant; a third step of dispersing the surfactant mixture on the surface of the iron precursor aqueous solution; and a fourth step of synthesizing iron oxide nanosheets by heat-treating the iron precursor aqueous solution in which the surfactant mixture is dispersed.

[0040] The above iron precursor may be of a conventional type used as an iron source in the manufacture of iron oxide. Preferably, the iron precursor may be iron(III) nitrate, but is not limited thereto.

[0041] In the first step above, 5 to 9 mmol of the hexamethylenetetramine may be mixed with 1 mmol of the iron precursor. Preferably, 7 mmol of the hexamethylenetetramine may be mixed with 1 mmol of the iron precursor, but is not limited thereto.

[0042] In the second step above, the surfactant may be one or more selected from the group consisting of oleylamine and oleic acid.

[0043] The above surfactant may be added in an amount of 0.01 to 0.03 parts by weight per 100 parts by weight of the chloroform solution. Preferably, 0.024 parts by weight may be added per 100 parts by weight of the chloroform solution, but is not limited thereto.

[0044] After the third step above, the aqueous iron precursor solution in which the surfactant mixture is dispersed may be exposed to air for 20 to 40 minutes. Preferably, it may be exposed for 30 minutes, but is not limited thereto.

[0045] In the fourth step above, the aqueous mixture of nickel precursors to which the surfactant has been added may be heated in an oven at 60 to 80°C for 2 to 4 hours. Preferably, it may be heated in an oven at 70°C for 3 hours, but is not limited thereto. According to one embodiment of the present invention, nanosheets can be synthesized widely and in large quantities at the water-air interface even at a relatively low temperature during iron oxide synthesis.

[0046] The thickness of the iron oxide nanosheet above may be 5 to 15 nm.

[0047] The above iron oxide nanosheets can be synthesized by a surfactant-assisted method. According to one embodiment of the present invention, an anionic surfactant was used in the surfactant-assisted method, which means that the part of the surfactant that ionizes and exhibits surface activity upon dissolving in water becomes an anion. The anion formed at this time reacts with the cation of the aqueous solution to form nanosheets at the interface. When synthesizing iron oxide nanosheets through the above surfactant-assisted method, the shape and surface area of ​​the metal oxide can be easily controlled. According to one embodiment of the present invention, since the valence of the iron nitrate used is trivalent, when synthesizing iron oxide nanosheets through the surfactant-assisted method, an iron oxide (III) precipitate is formed, and a substance that appears red when viewed below the water interface can be formed (Fig. 1).

[0048] After the above fourth step, the synthesized iron oxide nanosheets can be scooped using any substrate. According to one embodiment of the present invention, scooping can be performed using a Si wafer substrate coated with SiO2, but is not limited thereto.

[0049] In addition, the present invention provides iron oxide nanosheets produced by the above-described manufacturing method.

[0050] In addition, the present invention provides an electrochemical catalyst comprising the above-mentioned iron oxide nanosheets.

[0051] The iron oxide nanosheet according to the present invention has a precipitate formed together during synthesis, so the nanosheet has not only the composition of Fe(OH)2 but also the composition of Fe(OH)3, and for this reason, it has good electrochemical reactivity and excellent stability, which can improve the efficiency of energy storage devices.

[0053] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0055] Example 1. FeO / Fe(OH) 3 Nanosheet synthesis

[0056] FeO / Fe(OH)3 nanosheets were synthesized using a surfactant-assisted method. During the synthesis process, 5 mM iron(III) nitrate was mixed with 30 mL of deionized water, and 35 mM hexamethylenetetramine (HMTA) was mixed with the same amount of deionized water as iron(III) nitrate. These two aqueous solutions were then mixed to prepare a total of 60 mL of aqueous solution in a glass container. Subsequently, 40 μL of a surfactant mixture containing 0.0024 g of oleylamine and 10 g of chloroform containing 0.028 g of sodium hexadecyl sulfate was dispersed onto the surface of the aqueous solution. The aqueous solution was then exposed to air for 30 minutes. After 30 minutes, the glass container was placed in a convection oven set to 70°C and heat-treated for 3 hours. After removing the glass container from the oven, the FeO / Fe(OH)3 nanosheets synthesized at the water-air interface were scooped using a substrate such as a Si wafer coated with SiO2.

[0058] Experimental Example 1. AFM Analysis

[0059] AFM analysis was performed to measure the thickness of the iron oxide nanosheets, and the results are shown in Figure 2. As a result of the AFM analysis, the thickness of the iron oxide nanosheets was approximately 11 nm, which is thicker than other nanosheets, which are thin at 3 to 4 nm.

[0061] Experimental Example 2. XPS Analysis

[0062] Pt was deposited on a Si wafer coated with SiO2, and nanosheets synthesized at the water-air interface were scooped and X-ray Photoelectron Spectroscopy (XPS) analysis was performed, as shown in Figure 3.

[0063] Referring to Figure 3, XPS composition analysis results showed that in O1s, the components were found in the order of Fe(OH)3 >> Fe(OH)2 > FeOOH, while in 2p, they were found in the order of Fe(OH)2 > Fe(OH)3 > FeOOH. Generally, iron hydroxide and iron oxyhydroxide were found in large quantities, which are well known as materials possessing electrochemical properties. This implies that the synthesized iron oxide nanosheets can possess electrochemical properties. Based on the above results, electrochemical analysis was performed to confirm the electrochemical properties of the iron oxide nanosheets.

[0065] Experimental Example 3. Electrochemical Analysis

[0066] To analyze the electrochemical properties, FeO / Fe(OH)3 nanosheets synthesized on an FTO substrate at the water-air interface were scooped and analyzed instead of a Si wafer coated with SiO2, and this is shown in Figure 4.

[0067] When using an FTO substrate, the Oxygen Evolution Reaction (OER) is measured under alkaline conditions. The results of the FeO / Fe(OH)3 OER analysis show that the overpotential point, which can be considered the starting point of catalytic activity for LSV, begins at approximately 1.58 V, and the Tafel slope exhibits a very stable value of 42 mV / dec. The CP also demonstrates stability; CP is considered stable when the voltage remains constant over time without noise. Actual measurements show that it remained constant for 50 hours at the same voltage. In other words, the LSV results indicate that the material possesses electrochemical catalytic characteristics, and the Tafel slope and CP results demonstrate that stability is maintained.

[0069] Specific embodiments of the present invention have been examined so far. Those skilled in the art will understand that the present invention may be embodied in modified forms without departing from the essential characteristics of the invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the claims, not by the foregoing description, and all variations within the scope of equivalents should be interpreted as being included in the present invention.

Claims

Claim 1 A first step of preparing an aqueous iron precursor solution by mixing iron(III) nitrate and hexamethylenetetramine; a second step of preparing a surfactant mixture by mixing sodium hexadecyl sulfate (SHS), a chloroform solution, and a surfactant; a third step of dispersing the surfactant mixture on the surface of the aqueous iron precursor solution; and a fourth step of synthesizing iron oxide nanosheets by heating the aqueous iron precursor solution in which the surfactant mixture is dispersed; wherein the iron(III) nitrate and hexamethylenetetramine are mixed in a molar ratio of 1:7, and the iron oxide nanosheets are, in the Fe 2p spectrum obtained by X-ray photoelectron spectroscopy (XPS) analysis, Fe(OH) 2, A method for manufacturing iron oxide nanosheets characterized by peak intensity or area ratios appearing in the order of Fe(OH)3 and FeOOH, and peak intensity or area ratios appearing in the order of Fe(OH)3, Fe(OH)2 and FeOOH in the O1s spectrum. Claim 2 delete Claim 3 delete Claim 4 A method for manufacturing iron oxide nanosheets according to claim 1, wherein in the second step, the surfactant is one or more selected from the group consisting of oleylamine and oleic acid. Claim 5 A method for manufacturing iron oxide nanosheets according to claim 1, characterized in that the surfactant is added in an amount of 0.01 to 0.03 parts by weight per 100 parts by weight of the chloroform solution. Claim 6 A method for manufacturing iron oxide nanosheets according to claim 1, characterized in that, in the fourth step, the aqueous iron precursor solution in which the surfactant mixture is dispersed is heated in an oven at 60 to 80°C for 2 to 4 hours. Claim 7 A method for manufacturing iron oxide nanosheets according to claim 1, characterized in that the thickness of the iron oxide nanosheet is 5 to 15 nm. Claim 8 A method for manufacturing iron oxide nanosheets according to claim 1, characterized in that the iron oxide nanosheets are synthesized by a surfactant-assisted method. Claim 9 Iron oxide nanosheets manufactured by the manufacturing method of claim 1 Claim 10 Electrochemical catalyst comprising iron oxide nanosheets according to claim 9

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