Patent Application
20250162900
The present application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2023-0160327 filed on Nov. 20, 2023, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.
The present invention relates to a halogen-free MXene with improved stability due to the absence of halogen elements on its surface, and a method for manufacturing the same.
MXene is a two-dimensional material obtained from a MAX phase with a three-dimensional crystal structure consisting of M layer, A layer, and X layer. In 2011, a research team led by Professor Michel W. Barsoum at Drexel University succeeded in transforming a three-dimensional titanium-aluminum carbide, the MAX phase, into a two-dimensional structure with completely different properties by selectively removing an aluminum layer therefrom using a hydrofluoric acid. The research team named the two-dimensional material obtained by exfoliating the MAX phase as “MXene.” The MXene has electrical conductivity and strength similar to those of a graphene, and is known to be available to a variety of application technologies ranging from energy storage devices to biomedical applications, electromagnetic wave shielding, and composites.
The MXene can also be obtained by using a strong acid such as a hydrofluoric acid or a hydrochloric acid as an etchant for the MAX phase material. However, the strong acid such as the hydrofluoric acid or the hydrochloric acid used in synthesis of the MXene is harmful to the health of workers and generates by-products containing halogen elements, thereby increasing the cost of chemical waste disposal.
Further, the MXene material synthesized with the hydrofluoric acid and the hydrochloric acid-based etchants contains halogen elements as a surface functional group, and these halogen elements make the MXene material highly reactive. Therefore, the MXene, which has high reactivity, has low oxidation stability, and decomposes into a metal oxide and an amorphous carbon as time elapses, making long-term storage almost impossible.
Furthermore, when the MXene containing the halogen elements is oxidized and decomposed, halogen ions are released on its surface, which may cause contamination and malfunction of electronic devices to which the MXene is applied. Additionally, in case the MXene is applied to biosensors, etc., there is a problem that the halogen ions released from the surface of MXene may cause cytotoxicity.
A first purpose of the present invention is to provide a halogen-free MXene that does not have a harmful effect on the health of workers by not using a strong acid such as a hydrofluoric acid or a hydrochloric acid during its manufacturing process, and a method for manufacturing the same.
A second purpose of the present invention is to provide a halogen-free MXene that has excellent chemical stability and oxidation stability and does not decompose easily over time to allow for long-term storage, and a method for manufacturing the same.
A third purpose of the present invention is to provide a halogen-free MXene that does not cause contamination or malfunction of electronic devices due to halogen ions even when used in the electronic devices, and does not cause cytotoxicity even when applied to biological electronic devices such as biosensors; and a method for manufacturing the same.
In order to achieve the purposes of the present invention, the present invention provides a halogen-free MXene represented by the following formula (1), that has no halogen in its surface functional group by performing an etching process to generate MXene from a MAX phase material, and after the etching process, performing an impurity removal treatment process of etching and removing impurities using a halogen-free etchant and a halogen-free post-treatment agent, respectively.
Mn+1XnTx [Formula 1]
The MXene may be formed of a single layer.
In order to achieve the above purposes, the present invention also provides a method for manufacturing a halogen-free MXene, comprising a first step of mixing a saturated sodium hydroxide solution with a MAX phase material and heat treating the same; and a second step of removing impurities by treating a product obtained after the heat treatment with a halogen-free post-treatment agent.
The MAX phase material may be a material represented by the following formula 2.
Mn+1AXn [Formula 2]
The first step may include etching the MAX phase material at a high temperature of 200° C. or higher using the halogen-free etchant.
The halogen-free etchant may be a saturated sodium hydroxide solution with a concentration of 60 to 90%.
The first step may be performed at a temperature of 200 to 350° C. for a period of 24 hours or more to less than 96 hours.
The second step may be performed for 5 to 30 minutes using the halogen-free post-treatment agent selected from the group consisting of nitric acid, sulfuric acid, and phosphoric acid.
After the second step, the method of the present invention may further comprise a third step of performing exfoliation of a single layer by adding an organic solvent selected from the group consisting of DMSO (Dimethylsulfoxide), TMAOH (Tetramethylammonium hydroxide), and TBAOH (Tetrabutylammonium hydroxide) to the halogen-free MXene from which the impurities have been removed.
The third step may be performed at a temperature of 25 to 45° C. for 3 to 5 hours.
Hereinafter, a halogen-free MXene and a manufacturing method thereof related to the present invention will be described in more detail with reference to the drawings.
A halogen-free MXene according to an embodiment of the present invention can be represented by the following formula (1) that has no halogen in its surface functional group by performing an etching process to generate MXene from a MAX phase material, and after the etching process, performing an impurity removal treatment process of etching and removing impurities using a halogen-free etchant and a halogen-free post-treatment agent, respectively.
Mn+1XnTx [Formula 1]
In other words, since the halogen-free MXene according to the present invention is manufactured by etching and removing impurities with a halogen-free etchant and a halogen-free post-treatment agent in the process of manufacturing the MXene from the MXene phase material, it is characterized by the absence of halogens such as fluoride (F), chloride (CI), bromide (Br), and iodide (I) that may exist on the surface of conventional MXene. Therefore, the surface of MXene is relatively stabilized and has excellent oxidation stability, so that it does not decompose into a metal oxide and an amorphous carbon even when stored for a long time and can maintain a high preservation state.
In addition, since the halogen-free MXene does not contain halogen elements on its surface, it has an advantage that can prevent contamination or malfunction of electrochemical devices due to halogen ion emission even when applied to the electrochemical devices such as semiconductor devices, batteries, capacitors, and photoelectric devices.
Moreover, since the halogen-free MXene does not contain halogen and thus exhibits high biocompatibility, it can be applied to various technical fields such as biosensors, neural electrodes, biomedical polymers, and implant materials that can be applied to a human body.
The MAX phase material may be a material represented by the following formula 2.
Mn+1AXn [Formula 2]
The halogen-free etchant may be a basic material that generates ions capable of nucleophilic attack on the MAX phase material, and may be, for example, a material selected from the group consisting of potassium hydroxide (KOH), ammonium hydroxide (NH4OH), and sodium hydroxide (NaOH). Specifically, the halogen-free etchant may be sodium hydroxide (NaOH). Herein, the sodium hydroxide may be used in the form of a saturated solution with a concentration of 60 to 90%.
The MXene manufactured using the halogen-free etchant, which is a supersaturated solution of sodium hydroxide (NaOH), can be defined as, for example, MXene as shown in the following formula 3.
NaOH-Mn+1XnTx [Formula 3]
More specifically, the MXene may be formed as MXene of NaOH—Ti3C2Tx type.
The halogen-free post-treatment agent acts to neutralize the surface of MXene etched by the basic halogen-free etchant, and perform further exfoliation and processing of the MXene more smoothly by removing impurities such as aluminum hydroxide and NTO composites (compounds containing elements selected from the group consisting of sodium (Na), titanium (Ti), and oxygen (O)) with low water solubility present on the surface of MXene. This halogen-free post-treatment agent may be selected from the group consisting of, for example, nitric acid, sulfuric acid, and phosphoric acid.
The halogen-free MXene may also be formed into a thinner and lighter MXene by, for example, exfoliating it with an organic solvent selected from the group consisting of DMSO (Dimethylsulfoxide), TMAOH (Tetramethylammonium hydroxide), and TBAOH (Tetrabutylammonium hydroxide) to form MXene of a single layer. For example, by intercalating TMA+ cations using TMA in Ti3C2Tx MXene from which impurities have been removed, multi-layer Ti3C2Tx MXene can be exfoliated into single layer Ti3C2Tx MXene.
For reference, the MXene can be synthesized into a film only in case it is exfoliated, and the exfoliated MXene can be used in the form of solution by dispersing it in water. Further, if the MXene is not exfoliated, the liquid dispersion and film synthesis may become difficult.
The present invention also provides a method for manufacturing a halogen-free MXene, comprising a first step of mixing a saturated sodium hydroxide solution with a MAX phase material and heat treating the same; and a second step of removing impurities by treating a product obtained after the heat treatment with a halogen-free post-treatment agent.
The method for manufacturing the halogen-free MXene according to the present invention is carried out in a simple and convenient process of heat-treating the MXene in a single reactor using the saturated sodium hydroxide solution without using compounds containing halogen elements and removing impurities using the halogen-free post-treatment agent, compared to the conventional method of manufacturing MXene, which is carried out by a process of etching the MAX phase material using fluorine-containing compounds such as lithium fluoride (LiF), sodium fluoride (NaF), and magnesium fluoride (MgF2) or strong acids such as chlorofluoric acid (HF), hydrochloric acid (HCl), and sulfuric acid (HSO4). Therefore, the method according to the present invention does not have a harmful effect on the health of workers, and makes it possible to manufacture the MXene of a high purity more quickly with the impurities removed.
The first step may be performed in a hydrothermal reactor having a pressure of 1 to 10 bar at a temperature of 200 to 350° C. for a period of 24 hours or more to less than 96 hours. The hydrothermal reactor used in this first step may be, for example, a batch-type hydrothermal synthesis reactor equipped with a cover, a leakage prevention device, and a stirring impeller on the main body.
The second step may be performed for 5 to 30 minutes using the halogen-free post-treatment agent selected from the group consisting of nitric acid, sulfuric acid, and phosphoric acid.
Further, after the second step, the method of the present invention may further comprise a third step of performing exfoliation of a single layer by adding an organic solvent selected from the group consisting of DMSO (Dimethylsulfoxide), TMAOH (Tetramethylammonium hydroxide), and TBAOH (Tetrabutylammonium hydroxide) to the halogen-free MXene from which the impurities have been removed. This third step may be performed at a temperature of 25 to 45° C. for 3 to 5 hours.
Hereinafter, with reference to Examples and Drawings, the halogen-free MXene and its manufacturing method according to the present invention will be described in more detail.
As a halogen-free etchant, 50 mL of NaOH aqueous solution with a saturated concentration of 27.5M was used to manufacture MXene with a molecular formula of Ti3C2Tx by heating a MAX phase material with a molecular formula of Ti3AlC2 in a hydrothermal reaction vessel at a temperature of 270° C. for 72 hours (First step).
The manufactured MXene with the molecular formula Ti3C2Tx was post-treated (washed) at a room temperature for 5 minutes using phosphoric acid as a halogen-free post-treatment agent to remove impurities (Second step). In this case, the removed impurities were found to be aluminum hydroxide or NTO (Na—Ti—O) composites.
A single layer halogen-free MXene (NaOH—Ti3C2Tx) was manufactured by adding TMAOH to the halogen-free MXene of the molecular formula Ti3C2Tx from which the impurities were removed and reacting the mixture at a temperature of 25° C. for 3 to 5 hours to exfoliate a multi-layer halogen-free MXene (Third step).
A single layer halogen-free MXene was manufactured in the same manner as in Example 1, except that a NaOH aqueous solution having a concentration of 20M was used as a halogen-free etchant during the process for manufacturing the halogen-free MXene.
A single layer halogen-free MXene was manufactured in the same manner as in Example 1, except that a NaOH aqueous solution having a concentration of 10M was used as a halogen-free etchant during the process for manufacturing the halogen-free MXene.
A single layer halogen-free MXene was manufactured in the same manner as in Example 1, except that a NaOH aqueous solution having a concentration of 5M was used as a halogen-free etchant during the process for manufacturing the halogen-free MXene.
A MXene (Minimally Intensive Layer Delamination MXene, MILD-Ti3C2Tx) was manufactured in the same manner as in Example 1, except that a HCl—LiF aqueous solution was used as an etchant during the process for manufacturing the halogen-free MXene.
When comparing the halogen-free MXene of Example 1 with the MXene of the Comparative Example, as can be seen from the graphs of
In the graph (a) of
Shown in (a) of
Eventually, it can be seen from (a), (b), and (c) of
As a result of the film analysis, it can be confirmed through the analysis of contact angle (CA) that the MXene of Example 1 has no fluorine functional group and contains many —OH or —O— functional groups so that NaOH—Ti3C2Tx of Example 1 exhibits greater hydrophilicity than MILD-Ti3C2Tx of Comparative Example. In addition, when looking at (b) and (c) of
When looking at (a) of
Further, when checking (d) of
Shown in (e) and (f) of
Shown in (a), (b), and (c) of
When looking at (c) of
That is, the table of
In
Examples 3 and 4 were described to compare how the NTO contents changes depending on a concentration of NaOH used as the etchant. In Examples 3 and 4, the NaOH-MXene was synthesized using NaOH at a significantly lower concentration (5M, 10M) than the NaOH concentration of 27.5M used when originally synthesizing NaOH-MXene (the acid treatment (second step) was not performed). It was confirmed from Examples 3 and 4 that ratios of NTO impurities were higher.
Looking at overall change in the XRD peak (MAX→MXene) before and after etching of the MAX phase material, the peak change was not confirmed because there was no crystallinity of the NTO (impurities) before and after the acid treatment ([1]), which is a treatment process of the post-treatment agent. Therefore, after increasing crystallinity of the NTO through heat treatment in [2], the peak was reconfirmed. In addition, in [1], a change in the XRD peak before and after exfoliation of the MXene using TMAOH was confirmed.
The XRD peak ([2]) of NTO (impurities) before and after the acid treatment ([1]) and NTO (impurities) according to the presence or absence of heat treatment process to reconfirm the XRD peak after securing crystallinity of the impurities (NTO) without the acid treatment (through the heat treatment) was confirmed.
The graph [1] in
Herein, the black pattern indicates that only the etching of the first step was performed and no heat treatment was performed to ensure crystallinity of the NTO. The red pattern indicates that peaks (24.57-27.42) that appear to be the impurities were confirmed by heat treatment to increase crystallinity of the NTO after the etching of the first step.
Further, it can be confirmed from the graph [2] of
The table of
Looking at the results for the MXene (before heat treatment and before acid treatment) having many impurities, which was not subjected to the second step after treatment of the first step, the MXene (before acid treatment), which was subjected to additional heat treatment in the first step for checking the presence or absence of amorphous impurities, and the MXene (after acid treatment), by which the impurities were removed through the first and second steps, respectively, it can be confirmed that the ratios (0.26, 0.28) of the impurity elements (Na, Ti) on a surface of the MXene (after acid treatment) material that was subjected to both the first and second steps are detected lower than the ratios (0.34, 0.33) of the impurity elements (Na, Ti) on a surface of the MXene (before heat treatment) material that was not subjected to the second step after treatment of the first step and the ratios (0.95, 0.77) of the impurity elements (Na, Ti) on a surface of the MXene (after heat treatment) material that was subjected to additional heat treatment in the first step for checking the presence or absence of amorphous impurities. These results can be seen as proving that transformation of the MAX phase material (Ti3AlC2) into the MXene (NaOH—Ti3C2Tx), which was subjected to both the first and second steps, has effectively been performed.
Hereinafter, it is described that experimental results in which a MAX phase material other than the previously discussed MAX phase material (Ti3AlC2) is transformed to the MXene.
The graph [1] of
The photograph [2] of
The SEM image [3] of
The graph [1] of
The photograph [2] of
The SEM image [3] of
In conclusion, it can be confirmed that since the NaOH—Ti3CNTx MXene and the NaOH—Ti2CTx MXene also showed the SEM images of absorption peaks, water dispersion states, and single layer flakes similar to those of the MXene (NaOH—Ti3C2Tx) of Example 1, they had similar deformation of the halogen-free MXene.
That is, it has been demonstrated from
The effects of the present invention obtained through the above-described solution are as follows.
Since the MXene is manufactured by performing the etching process to generate MXene from the MAX Phase material, and after the etching process, performing the impurity removal treatment process using the halogen-free etchant and the halogen-free post-treatment agent, a halogen functional group such as fluorine is not present on the surface of MXene not to have any harmful effects on the health of workers.
Due to the absence of the halogen functional group on the surface of MXene, the MXene has excellent chemical stability and oxidation stability and does not decompose easily over time to allow for long-term storage.
Even in case used in the electronic devices, the MXene does not cause contamination or malfunction of the devices due to halogen ions, and can be implemented as MXene which does not cause cytotoxicity even when applied to biological electronic devices such as biosensors.
The foregoing description is merely illustrative, and various modifications can be made without departing from the scope and technical spirit of the described embodiments by a person who has an ordinary knowledge in the technical field to which the present invention. The above-described embodiments can be implemented individually or in any combination.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2023-0160327 | Nov 2023 | KR | national |
