2H-or 1Tapos in the formula (I); method for producing phase transition metal disulfide nanosheets and use thereof

Abstract

Disclosed herein is a method of making transition metal disulfide (TMD) nanosheets in the 2H-or 1T '-phase state. The method includes the steps of: (a) discharging a TMD bulk at a low or high current density in a lithium battery to produce a lithiated TMD bulk; and (b) carrying out ultrasonic oscillation on the lithiated TMD block material in ethanol or water so as to strip the lithiated TMD block material sheet into a 2H-or 1T '-phase TMD nanosheet, wherein discharging the TMD bulk at a low or high current density can produce TMD nanosheets in a 2H-or 1T '-phase state, respectively; and the high current density is about 4 times of the low current density. The invention also discloses a device for detecting humidity. The device comprises an electrode which is characterized by comprising the TMD nanosheets in the 2H-or 1T '-phase state prepared by the method disclosed by the invention. The disclosure thus also includes methods of using the device to determine the humidity of gas exhaled from a nasal cavity or oral cavity of an individual.

Description

Cross-reference

[0001] This application claims all of the contents and rights of U.S. Provisional Application No. 63 / 562,652, filed on March 7, 2024. Background of the Invention

[0002] 1. Field of the Invention

[0003] The present invention generally relates to a method for preparing 2H- or 1T′-phase transition metal dichalcogenide (TMD) nanosheets (NSs), and the use of the 2H- or 1T′-phase TMD NSs for humidity monitoring.

[0004] 2. Prior Art

[0005] The crystal phase is a very important factor in determining the properties and applications of two-dimensional (2D) transition metal dichalcogenides (TMD) materials. Group VI TMDs, such as MoS2 and WS2, can exist in different phases (2H, 1T or 1T'), which are determined by the coordination geometry of the transition metal atoms. Group VI TMDs in the 1T (octahedral) and 1T' (distorted octahedral) phases exhibit metallic and semimetallic properties, respectively, making them potential candidates for energy storage, energy conversion and applications with excellent conductivity. In contrast, Group VI TMDs in the 2H phase (trigonal pyramid) are typical semiconductor materials with a band gap range of 1-2 eV, making them very suitable for use in nanoelectronics and nanooptics. The ability to prepare 2D Group VI TMDs (TMDs) with specific phases, particularly solution-processable TMDs, to tailor them for specific applications is crucial. Solution-processable TMDs are compatible with solution-based deposition techniques (e.g., inkjet printing, industrial roll-to-roll coating, droplet casting, and spin coating), enabling the facile and scalable fabrication of customized devices. While such printable 2D Group VI TMD materials can be fabricated via direct liquid-phase exfoliation in solvents and via solution exfoliation with intercalated foreign species (e.g., tetraalkylammonium ions, sulfates, and small molecules), the phase of the resulting 2D product is not tunable and remains identical to that of the original bulk material. Previous studies have shown that the 2H to 1T / 1T′ phase transition occurs during the exfoliation process of lithium intercalation between Group VI TMD layers, yielding 2D nanosheets (NSs) with mixed 2H and 1T / 1T′ phases. This is theoretically because lithium intercalation involves electron injection from the lithium s orbital into the transition metal d orbital to maintain overall charge neutrality. When the injected electrons exceed a certain threshold (for MoS2, this threshold is 0.29 electrons per unit cell), the stability of the 2H phase of Group VI TMDs becomes lower than that of the corresponding 1T or 1T' phases, leading to a phase transition. This phase transition implies the intercalation of lithium ions for exfoliation. This technique is theoretically a feasible means of preparing solution-processable Group VI TMDs with specific phases. However, this feasibility has not yet been experimentally demonstrated because the switch for phase switching remains unknown.

[0006] In view of this, the relevant field urgently needs to develop a method for preparing TMD nanosheets with specific 2H- or 1T′-phase. Summary of the Invention

[0007] An embodiment of the present invention relates to a method for manufacturing 2H- or 1T′-phase transition metal dichalcogenide (TMD) nanosheets, a device for manufacturing 2H- or 1T′-phase transition metal dichalcogenide (TMD) nanosheets, and a method for detecting humidity using the device.

[0008] Therefore, the primary object of the present invention is to provide a method for preparing 2H- or 1T′-phase transition metal dichalcogenide (TMD) nanosheets, comprising: (a) discharging the TMD bulk material at a low or high current density in a lithium battery to produce a lithiated TMD bulk material; and (b) ultrasonically vibrating the lithiated TMD bulk in ethanol or water to exfoliate the lithiated TMD bulk into 2H- or 1T′-phase TMD nanosheets; in: Discharging the TMD bulk at low or high current density can produce TMD nanosheets in the 2H- or 1T′-phase, respectively; and The high current density is approximately 4 times greater than the low current density.

[0009] According to an embodiment of the present invention, the lithium battery comprises: an anode made of lithium foil; A cathode composed of a TMD bulk material, carbon black, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP); and The electrolyte consists of LiPF6, ethyl carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0010] According to certain embodiments of the present invention, in step (a), the TMD bulk is discharged at a current density of 0.005 amperes per gram at a cutoff voltage of 0.9 volts; and in step (b), the lithiated TMD bulk is ultrasonically vibrated in ethanol to exfoliate the lithiated TMD bulk into 2H-phase TMD nanosheets.

[0011] According to an embodiment of the present invention, the 2H-phase TMD nanosheets are 2H-phase WS2 nanosheets, 2H-phase TaS2 nanosheets, 2H-phase TiS2 nanosheets, 2H-phase WSe2 nanosheets, 2H-phase TaSe2 nanosheets, or 2H-phase TiSe2 nanosheets.

[0012] According to some optional embodiments of the present invention, the method further comprises: (c) collecting the 2H-phase TMD nanosheets produced in step (b) by centrifugation; and (d) Re-dispersing the product of step (c) in ethanol to form a 2H-phase TMD nanosheet dispersion.

[0013] According to other embodiments of the present invention, in step (a), the TMD bulk is discharged at a current density of 0.02 amperes per gram at a cutoff voltage of 0.7 volts; and in step (b), the lithiated TMD bulk is ultrasonically vibrated in water to exfoliate the lithiated TMD bulk into 1T′-phase TMD nanosheets.

[0014] According to an embodiment of the present invention, the 1T′-phase TMD nanosheet is a 1T′-phase MoS2 nanosheet, a 1T′-phase WS2 nanosheet, a 1T′-phase TaS2 nanosheet, a 1T′-phase TiS2 nanosheet, a 1T′-phase MoSe2 nanosheet, a 1T′-phase WSe2 nanosheet, a 1T′-phase TaS2 nanosheet, or a 1T′-phase TiSe2 nanosheet.

[0015] According to some optional embodiments of the present invention, the method further comprises: (c) collecting the 1T′-phase TMD nanosheets produced in step (b) by centrifugation; and (d) Re-dispersing the product of step (c) in water to form a 1T′-phase TMD nanosheet dispersion.

[0016] Therefore, a secondary object of the present invention is to provide a humidity detection device. The device comprises an electrode having a polymer substrate and a plurality of 2H- or 1T′-phase TMD nanosheets deposited on the polymer substrate, wherein the 2H- or 1T′-phase TMD nanosheets are produced using the method of the present invention, and the electrode has a response time of less than 0.5 seconds and a recovery time of about 1 second at a relative humidity of about 60% to about 75%.

[0017] According to an embodiment of the present invention, the 2H-phase TMD nanosheets are 2H-phase WS2 nanosheets, 2H-phase TaS2 nanosheets, 2H-phase TiS2 nanosheets, 2H-phase WSe2 nanosheets, 2H-phase TaSe2 nanosheets, or 2H-phase TiSe2 nanosheets.

[0018] According to an embodiment of the present invention, the electrode comprises a plurality of 2H-phase WS2 nanosheets disposed on a polymer substrate, and the response time of the electrode is approximately 0.48 seconds and the recovery time is approximately 0.32 seconds.

[0019] According to a specific embodiment of the present invention, the 1T′-phase TMD nanosheets are 1T′-phase MoS2 nanosheets, 1T′-phase WS2 nanosheets, 1T′-phase TaS2 nanosheets, 1T′-phase TiS2 nanosheets, 1T′-phase MoSe2 nanosheets, 1T′-phase WSe2 nanosheets, 1T′-phase TaS2 nanosheets, or 1T′-phase TiSe2 nanosheets.

[0020] According to a preferred embodiment of the present invention, the electrode comprises a plurality of 1T′-phase WS2 nanosheets disposed on a polymer substrate, and the response time of the electrode is approximately 0.3 seconds and the recovery time is approximately 1.2 seconds.

[0021] A third object of the present invention is to provide a method for measuring the humidity of air exhaled from the nasal cavity or oral cavity of a subject. The method comprises the following steps: (a) allowing the gas to contact the device of the present invention; (b) measuring the current intensity generated when the electrode contacts the gas; (c) interpolating the current intensity measured in step (b) from a standard graph of relative humidity (RH) and current intensity to calculate the humidity of the gas; in, The standard diagram is generated by plotting a plurality of known current intensities of the electrodes against their corresponding humidity.

[0022] According to certain embodiments of the present invention, the device includes an electrode comprising a plurality of 2H-phase WS2 nanosheets disposed on a polymer substrate, and the electrode has a response time of approximately 0.48 seconds and a recovery time of approximately 0.32 seconds.

[0023] According to another embodiment of the present invention, the device includes an electrode comprising a plurality of 1T′-phase WS2 nanosheets disposed on a polymer substrate, and the electrode has a response time of approximately 0.3 seconds and a recovery time of approximately 1.2 seconds.

[0024] In all embodiments of the invention, the individual is a human.

[0025] Details of one or more embodiments of the present invention can be found in the following detailed description of the invention. Other features and advantages of the present invention can also be found in the detailed description of the invention and the scope of claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The details of the present invention can be better understood through the following drawings and their descriptions, wherein

[0027] Figure 1is a flow chart of a method 10 for producing 2H- or 1T′-phase TMD nanosheets according to a preferred embodiment of the present invention;

[0028] Figure 2a Figure 2 is the VIS-NIR absorption spectrum of a 2H- or 1T′-phase TMD nanosheet solution produced by exfoliation according to the method of the present invention, where A, B, and C represent characteristic absorption peaks in the 2H-phase WS2, and the inset is a photograph of the 2H- or 1T′-phase TMD nanosheet solution.

[0029] Figure 2b is a photoluminescence spectrum of a 2H- or 1T′-phase WS2 sheet according to a preferred embodiment of the present invention;

[0030] Figure 2c 1 is a Raman spectrum of WS2 bulk and 2H- or 1T′-phase WS2 flakes according to a preferred embodiment of the present invention;

[0031] Figure 2d It is an XPSW4f optical spectrum of WS2 bulk material and 2H- or 1T′-phase WS2 sheet according to a preferred embodiment of the present invention;

[0032] Figure 3a is the current / relative humidity curve of the 2H-phase WS2 humidity sensor of the present invention, and the inset is an enlarged view between low relative humidity of 15% and 50%;

[0033] Figure 3b is based on Figure 3a Dynamic humidity response time and recovery time measured by the 2H-phase WS2 humidity sensor at different relative humidity;

[0034] Figure 3c is based on Figure 3a Dynamic humidity response and recovery curves of the 2H-phase WS2 humidity sensor measured at 60-75% relative humidity;

[0035] Figure 3d yes Figure 3c The enlarged view of the response and recovery curves, where τ 上升 and τ 下降 Represents response time and recovery time respectively;

[0036] Figure 3e is based on Figure 3a Response and recovery curves of the 1T′-phase WS2 humidity sensor measured at 60-75% relative humidity;

[0037] Figure 3f yes Figure 3e The enlarged view of the response and recovery curves, where τ 上升and τ 下降 Represents response time and recovery time respectively;

[0038] Figure 4a This is a curve showing the 2H-phase WS2 humidity sensor monitoring nasal humidity according to a preferred embodiment of the present invention;

[0039] Figure 4b Plotting the quantitative monitoring results of finger distance and device under 10V bias, with the inset showing the finger approaching the device; and

[0040] Figure 4c FIG. 4 is a dynamic current curve diagram of a preferred embodiment of the present invention, which is obtained when a finger approaches the WS2 humidity sensor. DETAILED DESCRIPTION

[0041] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the disclosed descriptions and drawings are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0042] 1. Methods for fabricating 2H- or 1T′-phase TMD nanosheets

[0043] The primary purpose of this invention is to propose a method for producing 2H- or 1T′-phase TMD nanosheets by electrochemically inserting lithium at low and high current densities in lithium batteries and exfoliating them in solution. Figure 1 .

[0044] Accordingly, a lithium battery required for carrying out the method of the present invention is first constructed. Specifically, a slurry consisting of TMD bulk powder, carbon black, and polyvinylidene fluoride (PVDF) is mixed with N-methylpyrrolidone (NMP) to form a mixture to form a cathode. This cathode is combined with an anode (i.e., lithium foil) and an electrolyte to form a lithium battery. According to a preferred embodiment, the electrolyte is prepared by dissolving LiPF6 in a mixture of ethyl carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. Once the battery is constructed, a bias voltage can be applied to it to cause lithium ions to be embedded in the cathode.

[0045] The method of the present invention begins by discharging the lithium battery at a low or high current density to produce lithiated TMD bulk ( Figure 1 According to an embodiment of the present invention, discharging a lithium battery at a low or high current density can generate 2H- or 1T′-phase TMD nanosheets, respectively, wherein the high current density is about 4 times that of the low current density.

[0046] After the electrochemical insertion of lithium, the lithiated TMD bulk material can be subjected to ultrasonic vibration in ethanol or water to exfoliate the lithiated TMD bulk material into 2H- or 1T′-phase TMD nanosheets ( Figure 1 , step 102).

[0047] According to certain embodiments, in step 101, a TMD bulk material is discharged in a lithium battery at a current density of 0.005 amperes per gram at a cutoff voltage of 0.9 volts to produce a lithiated TMD bulk material. Furthermore, in step 102, the lithiated TMD bulk material is ultrasonically agitated in ethanol to exfoliate the lithiated TMD bulk material into 2H-phase TMD nanosheets. Examples of 2H-phase TMD nanosheets that can be prepared using the method of the present invention include, but are not limited to, 2H-phase WS2 nanosheets, 2H-phase TaS2 nanosheets, 2H-phase TiS2 nanosheets, 2H-phase WSe2 nanosheets, 2H-phase TaSe2 nanosheets, or 2H-phase TiSe2 nanosheets. The 2H-phase TMD nanosheets are preferably 2H-phase WS2 nanosheets.

[0048] In other embodiments, in step 101, the TMD bulk material is discharged in a lithium battery at a current density of 0.02 amperes per gram at a cutoff voltage of 0.7 volts to produce a lithiated TMD bulk material; and in step 102, the lithiated TMD bulk material is ultrasonically agitated in water to exfoliate the lithiated TMD bulk material into 1T′-phase TMD nanosheets. Examples of 1T′-phase TMD nanosheets that can be prepared using the method of the present invention include, but are not limited to, 1T′-phase MoS2 nanosheets, 1T′-phase WS2 nanosheets, 1T′-phase TaS2 nanosheets, 1T′-phase TiS2 nanosheets, 1T′-phase MoSe2 nanosheets, 1T′-phase WSe2 nanosheets, 1T′-phase TaS2 nanosheets, or 1T′-phase TiSe2 nanosheets. The 1T′-phase TMD nanosheets are preferably 1T′-phase WS2 nanosheets.

[0049] Optionally, the obtained 2H- or 1T′-phase TMD nanosheets can be collected by centrifugation ( Figure 1 , step 103), then the collected 2H- or 1T′-phase TMD nanosheets are redispersed in ethanol or water to prepare a 2H- or 1T′-phase TMD nanosheet dispersion ( Figure 1 , step 104). The obtained 2H- or 1T′-phase TMD nanosheet dispersion can be used to construct a device (eg, an electrode) required for subsequent applications (eg, humidity detection).

[0050] 2. Humidity sensor

[0051] The 2H- or 1T′-phase TMD nanosheets of the present invention can absorb water molecules and are suitable for sensing humidity in an environment. Therefore, the 2H- or 1T′-phase TMD nanosheet dispersion can be used to construct a humidity sensor suitable for humidity sensing.

[0052] To this end, the above-mentioned 2H- or 1T′-phase TMD nanosheet dispersion is applied to the surface of a polymer substrate by droplet coating and allowed to dry at room temperature. Next, a thin layer of conductive material, generally a metal such as gold, palladium, gold / palladium alloy, and the like, is sputtered on the dried polymer substrate surface. Examples of polymer substrates suitable for use in the present invention include, but are not limited to, nylon, polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), and the like. According to a preferred embodiment of the present invention, different volumes of the above-mentioned 2H- or 1T′-phase TMD nanosheet dispersion are coated on PET, and then a gold layer (thickness of about 200 nm) is sputtered on it to produce the desired electrode.

[0053] Therefore, a second object of the present invention is to provide a device suitable for sensing humidity, for example, a device for sensing the humidity of breath exhaled from a person's nasal or oral cavity. The device is characterized by comprising the aforementioned electrode. According to a preferred embodiment of the present invention, the electrode comprises a 2H- or 1T′-phase TMD nanosheet produced by the aforementioned method of the present invention. At a relative humidity (RH) of 60% to 75%, the device can detect humidity in less than 1 second and can resume sensing again in approximately 1 second.

[0054] According to certain embodiments of the present invention, the device comprises an electrode comprising multiple layers of 2H-phase TMD nanosheets (e.g., 2H-phase WS2 nanosheets) prepared by the method of the present invention, and the electrode has a response time of approximately 0.48 seconds and a recovery time of approximately 0.32 seconds. According to other embodiments of the present invention, the device comprises an electrode comprising multiple layers of 1T′-phase WS2 nanosheets prepared by the method of the present invention, and the electrode has a response time of approximately 0.3 seconds and a recovery time of approximately 1.2 seconds.

[0055] 3. Methods of sensing humidity

[0056] The present disclosure also includes a method of using the device of the present invention to measure the humidity of exhaled air from the nasal or oral cavity of an individual.

[0057] According to an embodiment of the present invention, the device of the present invention is placed below the nostrils or in front of the mouth of an individual to capture water molecules in the exhaled air from the individual's nasal cavity or mouth. The method comprises the following steps: (a) allowing the gas to contact the device of the present invention; (b) measuring the current intensity generated after the gas contacts the electrode; (c) interpolating the current intensity measured in step (b) from a standard graph of relative humidity (RH) and current intensity to calculate the humidity of the gas; in, The standard graph is generated by plotting a plurality of known current intensities of the electrodes against their corresponding humidity.

[0058] According to certain embodiments of the present invention, the device includes an electrode comprising a plurality of 2H-phase WS2 nanosheets disposed on a PET substrate, and the electrode has a response time of approximately 0.48 seconds and a recovery time of approximately 0.32 seconds at a relative humidity between approximately 60% and approximately 75%.

[0059] According to another embodiment of the present invention, the device includes an electrode comprising a plurality of 1T′-phase WS2 nanosheets disposed on a PET substrate, and the electrode has a response time of about 0.3 seconds and a recovery time of about 1.2 seconds at a relative humidity between about 60% and about 75%.

[0060] In all embodiments of the invention, the individual is a human.

[0061] The present invention will be described below based on embodiments. The embodiments provided are merely examples, and the scope of the present invention is not limited to the disclosed embodiments.

[0062] Example

[0063] Materials and Methods

[0064] Synthesis of 2H- or 1T′-phase TMD nanosheets

[0065] Using electrochemical lithium insertion and exfoliation technology, a button cell with a copper foil coated WS2 bulk material as the cathode (weighing about 5 mg), a lithium foil as the anode, and LiPF6 dissolved in a mixture of ethyl carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 was used as the electrolyte. A current discharge was applied to allow lithium to be inserted into the WS2 bulk material at the cathode. After completion, Li was carefully removed from the button cell. xThe WS2 was removed and ultrasonically shaken in a solvent to obtain WS2 nanosheets. To obtain 2H-phase WS2 nanosheets, the lithium battery was discharged at a current density of 0.005 A / g at a cutoff voltage of 0.9 V; to obtain 1T′-phase WS2 nanosheets, the lithium battery was discharged at a current density of 0.02 A / g at a cutoff voltage of 0.7 V. Furthermore, ultrasonic shaking was performed in ethanol to obtain 2H-phase WS2 nanosheets, and ultrasonic shaking was performed in water to obtain 1T′-phase WS2 nanosheets. After ultrasonic shaking, the exfoliated nanosheets were collected by centrifugation and resuspended in a solvent for subsequent use.

[0066] Preparation of devices containing WS2 nanosheets

[0067] PET (1.5 x 1.5 cm²) was thoroughly cleaned in an ultrasonic bath and then sequentially rinsed with detergent-containing water, acetone, deionized water, and isopropyl alcohol, each cleaning step lasting 15 minutes. After cleaning, the aforementioned 2H- or 1T′-phase TMD nanosheet dispersion (32 mg / L) was applied to the PET surface via droplet coating and allowed to dry at room temperature. Next, a gold layer approximately 200 nm thick was sputtered onto the dried PET substrate using a pre-designed metal mask using a QUORUM #Q150TS dual-target sputtering system.

[0068] To fabricate the WS2 nanosheet sensing array, the PET substrate is cleaned using the aforementioned cleaning procedure. Next, a gold-based circuit is sputtered onto the PET substrate using a pre-designed metal shield in a QUORUM#Q150TS dual-target sputtering system. A customized metal mask with a rectangular array pattern is then affixed to the circuit. A 32 mg / L dispersion of WS2 nanosheets in either the 2H- or 1T′-phase is then applied to the PET surface using a droplet coating process. After the solution has completely dried, the mask is carefully removed, leaving the WS2 nanosheets on the substrate pattern.

[0069] Humidity sensing test

[0070] Humidity sensing is performed in a customized, sealed container. Humidity is controlled by precisely adjusting the mass flow rate of dry or humid argon gas flowing into the container. The carrier carrying the chip is then connected to an external measuring instrument (Keysight BISOOA semiconductor analyzer) for testing. In the breathing test, the humidity sensor is placed under the nose or on a mask to monitor the humidity in exhaled breath at different breathing rates. In the finger approach humidity sensing test, the sensor is placed horizontally and then the finger is gradually approached from above. In the non-contact positioning test, the finger is maintained at a certain height above the sensing array, and the current of each sensor is measured. In the voice recognition test, the sensor is placed approximately 5 cm in front of the individual's mouth, and the current change caused by the individual reading English words of varying lengths is recorded. The current changes of all sensors are recorded in real time using the Keysight BISOOA semiconductor analyzer.

[0071] Example 1: Fabrication and Analysis of 2H- or 1T′-Phase TMD Nanosheets

[0072] 1.1 WS2 nanosheets in 2H- or 1T′-phase

[0073] In this example, 2H- or 1T′-phase WS2 nanosheets were produced according to the procedures described in "Materials and Methods." Briefly, coin-type lithium batteries containing bulk WS2 cathodes were discharged at either low (0.005 A / g, 0.9 V) or high (0.02 A / g, 0.7 V) current densities to produce 2H- or 1T′-phase WS2 nanosheets. UV-visible, Raman, and X-ray photoelectron spectroscopy were then analyzed, and the results are shown in Figure 2.

[0074] The 2H-phase WS2 nanosheet dispersion prepared by lithium insertion driven by low current density is light green and has a clear absorption peak in the visible light range, as shown in its UV-visible spectrum ( Figure 2a ), confirming that 2H-phase WS2 nanosheets with semiconductor properties are formed at low current density. In contrast, the 1T′-phase WS2 nanosheet dispersion produced at high current density is black and has no absorption peak in the visible light range ( Figure 2a ), indicating that a phase transition occurs at high current density and 1T′-phase WS2 nanosheets with semi-metallic properties are formed.

[0075] The above results can be further confirmed by photoluminescence (PL) spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The main PL peak of WS2 nanosheets prepared at low current density represents its semiconductor properties ( Figure 2b In the Raman spectrum of WS2 nanosheets produced by low current density, there are only two main peaks representing the 2H-phase, which appear at 350 cm-1 In-plane photon E 1 2g and appears at 419.2cm -1 Out-of-plane photon A 1 g ( Figure 2c ). On the contrary, in the low-frequency region of the Raman spectrum of 1T′-phase WS2 nanosheets generated at high current density, there are three J1, J2 and J3 peaks representing the 1T′-phase ( Figure 2c The yields of 2H- and 1T′-phase WS2 nanosheets were 100% and 67%, respectively, which can be confirmed by deconvolution of the W4f region in the XPS spectrum ( Figure 2d ).

[0076] Aberration-corrected annular dark-field scanning transmission electron microscopy (ADF-STEM) was used to further examine the phases of the exfoliated WS2 nanosheets. The individual W and S atoms in the 2H-phase WS2 nanosheets produced by low-density current stripping have a hexagonal lattice structure representative of the 2H-phase, while the one-dimensional zigzag W atomic chains in the WS2 nanosheets produced by high-density current stripping represent the 1T′-phase. It should be noted that small areas of the 2H-phase can also be observed in the images, indicating that the WS2 nanosheets produced at high current density coexist with both the 2H- and 1T′-phases, with the 1T′-phase being the predominant phase. Sulfur vacancies can also be observed in the ADF-STEM images of the 2H- or 1T′-phase WS2 nanosheets obtained (data not shown), and electron paramagnetic resonance (EPR) results indicate that the 2H-phase WS2 nanosheets have more sulfur vacancies than the 1T′-phase WS2 nanosheets (data not shown).

[0077] Transmission electron microscopy (TEM) images revealed that the lateral dimensions of the 2H- and 1T′-phase WS2 nanosheets ranged from 300-600 nm and 100-200 nm, respectively. SEM images confirmed the synthesis of large quantities of 2H- or 1T′-phase WS2 nanosheets. Atomic force microscopy (AFM) images revealed a thickness of approximately 1.8 nm for the 2H-phase WS2 nanosheets and 1.2 nm for the 1T′-phase WS2 nanosheets, indicating that the 2H-phase WS2 nanosheets formed were likely bilayers, while the 1T′-phase WS2 nanosheets were likely monolayers.

[0078] 1.2 2H- or 1T′-phase WSe2 nanosheets

[0079] Phase-tunable WSe2 nanosheets can also be prepared according to steps similar to the method described in Example 1.1 (data not shown).

[0080] 1.3 1T′-phase MoS2 nanosheets

[0081] In addition, the method described in this disclosure is not suitable for the preparation of 1T′-phase MoS 2 nanosheets (data not shown).

[0082] Example 2: Humidity sensor made with 2H- or 1T′-phase TMD nanosheets of Example 1

[0083] In this embodiment, a humidity sensor was fabricated using the 2H- or 1T′-phase TMD nanosheets prepared in Example 1, following the procedures described in "Materials and Methods." Briefly, a dispersion of the 2H- or 1T′-phase WS2 nanosheets was applied to a PET surface using a droplet coating method. After the solution dried completely, gold was sputtered onto the surface to serve as electrodes. The resulting device was used to measure humidity at various humidity levels (RH%). The results are shown in Figure 2. Figures 3a-3f .

[0084] like Figure 3a As shown in Figure 2, as the relative humidity increases from 15% to 90%, the current intensity of the device also increases by two orders of magnitude, indicating that the device can be used to sense humidity. When the relative humidity exceeds 65%, the device containing 2H-phase WS2 nanosheets shows a strong response, indicating that the humidity sensor can be used in high humidity environments, such as monitoring respiratory rate and contactless positioning interface. The dynamic humidity sensing response and recovery time results of the device containing 2H-phase WS2 nanosheets are shown in Figure 2. Figure 3b The results in the figure show that the response of the 2H-phase WS2 nanosheet device under different humidity conditions has excellent selectivity and reproducibility. Figure 3c The results show the reproducible results of dynamic humidity sensing of 2H-phase WS2 nanosheet devices from 60% to 75% relative humidity (RH), with sensing and recovery times of less than 1 second. Figure 3d ) shows that the response and recovery times of the 2H-phase WS2 nanosheet device are 0.48 seconds and 0.32 seconds, respectively. The response and recovery times of the 1T′-phase WS2 nanosheet device are 0.3 seconds and 1.2 seconds, respectively. Figure 3e and 3f Compared to the 2H-phase WS2 nanosheet humidity sensor, the 1T′-phase WS2 nanosheet humidity sensor has a faster response time but requires a longer recovery time. This difference may be attributed to the more negative absorption energy of water molecules in the 1T′-phase WS2 nanosheet relative to the 2H phase, meaning that water molecules are more easily adsorbed on the 1T′-phase WS2 nanosheet. Conversely, water molecules are less likely to desorb from the 1T′-phase WS2 nanosheet, resulting in a longer recovery time.

[0085] Compared to other humidity sensors, the 2H-phase or 1T′-phase WS2 nanosheet humidity sensors disclosed herein have very fast response and recovery times (data not shown). This is due to the ultrathin structure of the WS2 nanosheets and the abundant sulfur vacancies, which give the devices very short response and recovery times. Specifically, the 1T′-phase WS2 nanosheets of the present invention have a single-layer structure, while the 2H-phase WS2 nanosheets have a double-layer structure, which is significantly thinner than other humidity sensor materials (data not shown). The 2H-phase or 1T′-phase WS2 nanosheets disclosed herein have a high specific surface area, resulting in a larger number of atoms being exposed on the surface, thereby enhancing the interaction with water molecules. Such a high specific surface area can enhance the adsorption of water molecules, resulting in substantial current changes and greater sensitivity to humidity changes. Furthermore, the ultrathin structure of these two-dimensional materials promotes rapid adsorption and desorption of water molecules, thereby enabling rapid response and recovery. Furthermore, the 2H-phase or 1T′-phase WS2 nanosheets disclosed herein possess numerous sulfur vacancies, which enhance conductivity, thereby shortening response time and improving recovery speed. These factors fully explain the extremely short response and recovery times of the 2H-phase or 1T′-phase WS2 nanosheets disclosed herein. Based on these considerations, the following embodiments utilize 2H-phase WS2 nanosheets for humidity sensing applications.

[0086] Example 3: Various applications of the device containing the 2H-phase WS2 nanosheets of Example 1

[0087] 3.1 Breath monitoring device

[0088] The 2H-phase WS2 nanosheet humidity sensor was subjected to various bending cycles and its response current intensity at 65% RH was analyzed to investigate its mechanical properties. The 2H-phase WS2 nanosheet humidity sensor exhibited excellent flexibility, with the response current intensity remaining nearly unchanged even after 1,300 bending cycles (data not shown). This is likely due to the inherent flexibility of the ultra-thin two-dimensional 2H-phase WS2 nanosheet, which exhibits a tensile strength at break of approximately 25-30%. These properties significantly contribute to the stability of the device. Therefore, the 2H-phase WS2 nanosheet humidity sensor of this embodiment is being used to detect, diagnose, and treat the breath of patients with early-stage, slow-progressing diseases that lack sufficient monitoring indicators, such as cancer, diabetes, or sleep apnea-hypopnea syndrome. During operation, the 2H-phase WS2 nanosheet humidity sensor of this embodiment is fixed below the patient's nasal cavity for monitoring.

[0089] like Figure 4aAs shown, the current value varies with breathing rate. Within the first 3-7 seconds of the measurement, the subject inhaled deeply and exhaled a relatively high-humidity breath, causing the current to rise and fall significantly. Next, the subject breathed rapidly and irregularly for 8 seconds, causing the current to exhibit low-amplitude, high-frequency fluctuations. These results demonstrate that the ultrafast response and recovery characteristics of the 2H-phase WS2 nanosheet humidity sensor of this embodiment enable real-time and accurate respiratory monitoring. Furthermore, the WS2 nanosheet humidity sensor can also be used to test the protective effectiveness of various face masks, a crucial characteristic.

[0090] 3.2 Language Identification Device

[0091] This embodiment provides a prototype of a speech recognition device. When a person speaks, the pronunciation of different words will cause changes in the content of water molecules in the exhaled breath. The ultra-fast response and recovery characteristics of the 2H-phase WS2 nanosheet humidity sensor enable it to detect the humidity of the exhaled breath in real time when speaking (data not shown). Therefore, a current change curve corresponding to each spoken word can be generated, and the characteristic current curve of each spoken word (for example, "Hi", "people", "thank you", "you are welcome", "question", "unbelievable", "beautiful", etc.) can be recorded. The high reproducibility of the device in this embodiment once again shows the potential of the device in future speech recognition applications.

[0092] 3.3 Devices with contactless interfaces

[0093] The remote controllability of the disclosed device makes it have the potential for future applications in electronic products, especially contactless switches and local zero-contact interface devices. Humidity detection is an attractive signal that can promote the development of such new applications. The high sensitivity and fast response characteristics of the disclosed 2H-phase WS2 nanosheet humidity sensor can definitely meet the needs of real-time local non-contact interface. Figure 4b As shown, using a human finger as a moisture source (inset), quantitative monitoring results at a 10V bias voltage reveal an exponential relationship between finger distance and the current of the WS2 nanosheet humidity sensor. When the finger is approximately 6mm vertically from the sensor, the sensor begins to exhibit a slight current response, which increases significantly as the finger approaches. Figure 4cThis graph shows the dynamic current curve measured as a finger approaches the WS2 humidity sensor in an indoor environment. Thanks to the ultra-fast response and recovery characteristics of the 2H-phase WS2 nanosheet humidity sensor, the current increases with the finger's approach, with virtually no pause. Furthermore, the 2H-phase WS2 nanosheet humidity sensor exhibits excellent stability, remaining virtually unchanged after exposure to 65% RH and room temperature for 96 hours.

[0094] Due to the excellent response capability of WS2 nanosheets, a local non-contact interface can be realized by using a WS2 nanosheet humidity sensor array. Based on this, a 5 cm square WS2 nanosheet humidity sensor array was fabricated on a PET substrate. The fabricated local non-contact interface still retains flexibility, and its response and recovery time remain almost unchanged (relative to the unbent device) even when bent (data not shown). It is known that the local non-contact interface made using WS2 nanosheets can clearly distinguish the relative position and depth of two fingers (data not shown). When the vertical distance of the two fingers from the sensor is represented by different colors on the current distribution diagram, the individual positions of the two fingers can be seen. By incorporating the finger position and depth information into a 3D cuboid, a 3D model that can simulate the actual position of the two fingers can be reconstructed. These results show that the local non-contact interface made using WS2 nanosheets can use water vapor signals to reconstruct the spatial distribution of individuals. In addition, due to its fast response and recovery characteristics, the local non-contact interface disclosed in the present invention can be used to achieve real-time local monitoring.

[0095] In summary, the present disclosure demonstrates that by electrically switching the phase transition during the exfoliation process using electrochemical lithium intercalation, a phase-switchable and solution-processable WS2 monolayer or bilayer can be fabricated from bulk material. Specifically, the present disclosure demonstrates that driving lithium intercalation at low current densities can produce a 2H-phase WS2 bilayer; conversely, driving lithium intercalation at high current densities can produce a 1T′-phase WS2 monolayer.

[0096] Although the above embodiments disclose specific embodiments of the present invention, they are not intended to limit the present invention. Those skilled in the art may make various changes and modifications without departing from the principles and spirit of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined by the accompanying patent applications.

Claims

1. A method for producing 2H- or 1T′-phase transition metal dichalcogenide (TMD) nanosheets, comprising: (a) discharging the TMD bulk material at a low or high current density in a lithium battery to produce a lithiated TMD bulk material; and (b) ultrasonically vibrating the lithiated TMD bulk material in ethanol or water to exfoliate the lithiated TMD bulk material into TMD nanosheets; in: Discharging the TMD bulk at low or high current density can produce TMD nanosheets in the 2H- or 1T′-phase, respectively; and The high current density is approximately 4 times greater than the low current density.

2. The method according to claim 1, wherein the lithium battery comprises: an anode made of lithium foil; A cathode composed of a TMD bulk material, carbon black, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP); and The electrolyte consists of LiPF6, ethyl carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

3. The method according to claim 2, wherein: In step (a), the TMD bulk is discharged at a current density of 0.005 amperes per gram at a cutoff voltage of 0.9 volts; and In step (b), the lithiated TMD bulk material is subjected to ultrasonic vibration in ethanol to exfoliate the lithiated TMD bulk material into 2H-phase TMD nanosheets.

4. The method according to claim 3, wherein the 2H-phase TMD nanosheets are 2H-phase WS2 nanosheets, 2H-phase TaS2 nanosheets, 2H-phase TiS2 nanosheets, 2H-phase WSe2 nanosheets, 2H-phase TaSe2 nanosheets, or 2H-phase TiSe2 nanosheets.

5. The method according to claim 3, further comprising: (c) collecting the 2H-phase TMD nanosheets produced in step (b) by centrifugation; and (d) Re-dispersing the product of step (c) in ethanol to form a 2H-phase TMD nanosheet dispersion.

6. The method according to claim 2, wherein In step (a), the TMD bulk is discharged at a current density of 0.02 A / g and a cutoff voltage of 0.7 V; and In step (b), the lithiated TMD bulk material is subjected to ultrasonic vibration in water to exfoliate the lithiated TMD bulk material into 1T′-phase TMD nanosheets.

7. The method according to claim 6, wherein the 1T′-phase TMD nanosheets are 1T′-phase MoS2 nanosheets, 1T′-phase WS2 nanosheets, 1T′-phase TaS2 nanosheets, 1T′-phase TiS2 nanosheets, 1T′-phase MoSe2 nanosheets, 1T′-phase WSe2 nanosheets, 1T′-phase TaS2 nanosheets, or 1T′-phase TiSe2 nanosheets.

8. The method of claim 7, further comprising: (c) collecting the 1T′-phase TMD nanosheets produced in step (b) by centrifugation; and (d) Re-dispersing the product of step (c) in water to form a 1T′-phase TMD nanosheet dispersion.

9. A device for detecting humidity, comprising an electrode having a polymer substrate and a plurality of 2H- or 1T′-phase TMD nanosheets deposited on the polymer substrate, wherein the 2H- or 1T′-phase TMD nanosheets are manufactured by the method of claim 1, and the electrode has a response time of less than 0.5 seconds and a recovery time of about 1 second at a relative humidity of about 60% to about 75%.

10. The device according to claim 9, wherein In step (a), the TMD bulk is discharged at a current density of 0.005 amperes per gram at a cutoff voltage of 0.9 volts; and In step (b), the lithiated TMD bulk material is subjected to ultrasonic vibration in ethanol to exfoliate the lithiated TMD bulk material into 2H-phase TMD nanosheets.

11. The device according to claim 10, wherein the 2H-phase TMD nanosheets are 2H-phase WS2 nanosheets, 2H-phase TaS2 nanosheets, 2H-phase TiS2 nanosheets, 2H-phase WSe2 nanosheets, 2H-phase TaSe2 nanosheets, or 2H-phase TiSe2 nanosheets.

12. The device according to claim 11, wherein the 2H-phase TMD nanosheets are 2H-phase WS2 nanosheets, and the response time of the electrode is about 0.48 seconds and the recovery time is about 0.32 seconds.

13. The device according to claim 9, wherein In step (a), the TMD bulk is discharged at a current density of 0.02 A / g and a cutoff voltage of 0.7 V; and In step (b), the lithiated TMD bulk material is subjected to ultrasonic vibration in water to exfoliate the lithiated TMD bulk material into 1T′-phase TMD nanosheets.

14. The device according to claim 13, wherein the 1T′-phase TMD nanosheets are 1T′-phase MoS2 nanosheets, 1T′-phase WS2 nanosheets, 1T′-phase TaS2 nanosheets, 1T′-phase TiS2 nanosheets, 1T′-phase MoSe2 nanosheets, 1T′-phase WSe2 nanosheets, 1T′-phase TaS2 nanosheets, or 1T′-phase TiSe2 nanosheets.

15. The device according to claim 14, wherein the 1T'-phase TMD nanosheet is a 1T'-phase WS2 nanosheet, and the response time of the electrode is about 0.3 seconds and the recovery time is about 1.2 seconds.

16. A method for measuring the humidity of air exhaled from the nasal cavity or oral cavity of a subject, comprising: (a) contacting the gas with the apparatus according to claim 9; (b) measuring the intensity of the current generated when the electrode contacts the gas; (c) interpolating the current intensity measured in step (b) from a standard graph of relative humidity (RH) and current intensity to calculate the humidity of the gas; in, The standard diagram is generated by plotting a plurality of known current intensities of the electrodes against their corresponding humidity. 17 . The method according to claim 16 , wherein the electrode comprises a plurality of 2H-phase TMD nanosheets deposited on the polymer substrate, and the response time of the electrode is about 0.48 seconds and the recovery time is about 0.32 seconds.

18. The method according to claim 16, wherein the electrode comprises a plurality of 1T'-phase TMD nanosheets deposited on the polymer substrate, and the response time of the electrode is about 0.3 seconds and the recovery time is about 1.2 seconds.

19. The method of claim 16, wherein the subject is a human.

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