Preparation method and application of ZIF-8 / PEDOT: PSS composite material and flexible humidity sensor

Abstract

The invention relates to the technical field of sensors, in particular to a preparation method and application of a ZIF-8 / PEDOT: PSS composite material and a flexible humidity sensor, and the flexible humidity sensor comprises a flexible substrate, a metal layer interdigital electrode which is subjected to laser photoetching on the substrate, a humidity-sensitive coating which is coated on the metal layer interdigital electrode, and a conductivity measurement external circuit, different from a traditional humidity sensor for measuring the absolute humidity of the environment, the flexible humidity sensor made of the ZIF-8 / PEDOT: PSS composite material can provide a brand-new respiration monitoring means for users in the field of medical treatment and public health by monitoring humidity changes of respiration and different parts of the body. The flexible humidity sensor based on ZIF-8 / PEDOT: PSS realizes great potential in non-contact detection of human body humidity and respiratory health. A result shows that the ZIF-8 / PEDOT: PSS has a very excellent application prospect in a humidity detection material.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically to a ZIF-8 / PEDOT:PSS composite material, a method for preparing a flexible humidity sensor, and its application. Background Technology

[0002] Humidity is a crucial factor to consider in many industries, and humidity sensors play an irreplaceable role in scenarios such as weather forecasting, industrial production, medical monitoring, and smart homes. Their ability to detect changes in ambient humidity and convert them into electrical signals provides the technological foundation for precise air humidity control. During the COVID-19 pandemic, highly contagious respiratory viruses can spread rapidly among people, and monitoring the humidity of human respiration can provide biophysical information, including health status. Therefore, developing high-performance humidity sensors for non-contact respiratory monitoring and detecting human perspiration can effectively detect changes in human bodily functions among different users, thereby reducing the risk of cross-infection between them.

[0003] With the rise of the Internet of Things (IoT) and wearable devices, the limitations of traditional humidity sensors in terms of comfort and mechanical adaptability are becoming increasingly apparent. Developing flexible humidity sensors with excellent sensing performance and high structural stability is imperative. In particular, the demand for flexible humidity sensors is significant as a crucial component of non-contact wearable sensing devices, offering application value in medical fields such as respiratory monitoring and skin perspiration detection. They also play a vital role in improving comfort and the accuracy and timeliness of data acquisition in human-computer interaction.

[0004] Human body humidity detection, as a widely used human-computer interaction platform, needs to provide both an accurate and comfortable sensory experience, as well as the ability to resist external environmental interference. Inspired by traditional human body humidity detection, non-contact human body humidity detection holds promise. Although significant progress has been made in humidity-sensitive materials in recent years, integrating these ideal functions into a single material remains challenging.

[0005] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of how to develop a high-performance humidity sensor for non-contact respiratory monitoring and detection of human sweating, which can effectively detect changes in human bodily functions of different users, thereby reducing the risk of cross-infection between different users. This invention provides a method for preparing a ZIF-8 / PEDOT:PSS composite material and a flexible humidity sensor, as well as its application.

[0007] To achieve the above objectives, this invention discloses a method for preparing ZIF-8 / PEDOT:PSS composite materials, comprising the following steps:

[0008] S1, Zinc nitrate hexahydrate and 2-methylimidazole were mixed in a methanol solution and stirred for 1 hour. The resulting suspension was then centrifuged and dried to obtain ZIF-8.

[0009] S2, ZIF-8, EDOT and PSS are uniformly mixed with ultrapure water, and then APS is added to initiate the polymerization of EDOT and PSS. The mixture is stirred at room temperature for 24 hours to ensure that the components are fully mixed, thus obtaining the ZIF-8 / PEDOT:PSS composite material.

[0010] In step S1, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:2.

[0011] In step S2, the amount of ZIF-8 used is 0.2 mmol, the amount of EDOT used is 110 μL, the amount of PSS used is 155 μL, and the amount of APS used is 0.3165 g.

[0012] The present invention also discloses the ZIF-8 / PEDOT:PSS composite material prepared by the above preparation method.

[0013] This invention also discloses a method for preparing a flexible humidity sensor made of ZIF-8 / PEDOT:PSS composite material, comprising the following steps:

[0014] A1, the metal layer is processed into a metal layer interdigitated electrode;

[0015] A2. The ZIF-8 / PEDOT:PSS composite material is uniformly drop-coated onto the interdigitated metal electrode and dried to ensure that the ZIF-8 / PEDOT:PSS composite material adheres firmly to form a humidity-sensitive coating. Metal wires are led out from both ends of the interdigitated electrode to obtain a flexible humidity sensor made of ZIF-8 / PEDOT:PSS composite material.

[0016] In step A1, the specific processing procedure is as follows: the flexible PI film is fixed on the substrate; the designed electrode pattern is imported into the operating software, and the parameters of the laser lithography system are set to lithographically imprint interdigitated electrodes onto the flexible PI film.

[0017] In step A1, the interdigitated metal electrode comprises multiple metal deposition layers composed of Au, Ni, and Cu.

[0018] In step A1, the width of the interdigitated fingers of the metal layer interdigitated electrode and the gap between adjacent interdigitated fingers are both 100 μm, and the number of pairs of interdigitated fingers in the metal layer is 20.

[0019] The present invention also discloses a flexible humidity sensor of ZIF-8 / PEDOT:PSS composite material prepared by the above preparation method, comprising a flexible substrate, interdigitated metal electrodes laser-lithographically formed on the substrate, a humidity-sensitive coating coated on the interdigitated metal electrodes, and an external circuit for measuring conductivity.

[0020] The present invention also discloses the application of the above-mentioned ZIF-8 / PEDOT:PSS composite material flexible humidity sensor in non-contact human body humidity detection.

[0021] The humidity sensing mechanism of the PEDOT:PSS / ZIF-8 composite material is based on the synergistic effect of enhanced ion conduction formed after ZIF-8 absorbs moisture and the structural response of PEDOT:PSS. ZIF-8 adsorbs water molecules due to its high specific surface area and open metal sites, triggering a proton conduction mechanism; the hydrophilic sulfonic acid groups in PEDOT:PSS dissociate to generate... This forms ion channels, transforming the material into an ion-electron hybrid conductor. The interface between the two is connected by hydrogen bonds to form a proton exchange pathway. After ZIF-8 absorbs moisture and expands, it forms a water-mediated 3D permeation network with PEDOT, synergistically improving conductivity and achieving a highly sensitive nonlinear response to humidity.

[0022] Compared with existing technologies, the advantages of this invention are as follows: The flexible humidity sensor based on the ZIF-8 / PEDOT:PSS composite material in this invention, due to its porous and adjustable structure of the metal-organic framework material, achieves high-performance and fast-response humidity detection. The flexible humidity sensing material and flexible device based on the ZIF-8 / PEDOT:PSS composite material obtained by the method described in this invention can achieve sensitive detection of humidity changes during respiration at room temperature, with a response time as low as 5 seconds, exhibiting characteristics of operating at room temperature, high sensitivity, and fast response time. The impedance of the flexible humidity sensor based on the ZIF-8 / PEDOT:PSS composite material is in the megaohm range, with extremely low power consumption; it can be mass-produced and packaged. Attached Figure Description

[0023] Figure 1 The microstructure characteristics of the ZIF-8 / PEDOT:PSS-2 composite material are shown by scanning electron microscopy (SEM) images, (a) 500 nm, (b) 2 μm;

[0024] Figure 2 A schematic diagram of the structure of a flexible humidity sensor made of ZIF-8 / PEDOT:PSS composite material;

[0025] Figure 3 The response recovery curve of the flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material in the range of 25-93%RH.

[0026] Figure 4 Fitting curves of the response value and relative humidity of the flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material for the range of 25-93%RH;

[0027] Figure 5 The response time and recovery time of the flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material under specific humidity conditions;

[0028] Figure 6 The response curves of the flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material when a person speaks different words;

[0029] Figure 7 The response curves of a flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material under different bending and flat conditions for testing a specific humidity.

[0030] Figure 8 The resistance response curves of the flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material at distances of 5 mm, 10 mm and 15 mm from a wet finger.

[0031] Figure 9 The dynamic changes in the response of the flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material to different nasal breathing frequencies (fast and slow);

[0032] Figure 10 The dynamic changes in the response of the flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material to oral and nasal breathing conditions.

[0033] Figure 11 The dynamic changes in skin response values ​​at different times after applying hand cream using a flexible humidity sensor made of ZIF-8 / PEDOT:PSS-2 composite material;

[0034] Figure 12 Comparison of the response values ​​(a) and dynamic response changes (b) of flexible humidity sensors made of ZIF-8 / PEDOT:PSS-1, ZIF-8 / PEDOT:PSS-2 and ZIF-8 / PEDOT:PSS-3 composite materials when detecting humidity from 25% to 93%. Detailed Implementation

[0035] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0036] Example 1

[0037] The materials used in this embodiment include water, poly(3,4-ethylenedioxythiophene)PEDOT, poly(styrene sulfonic acid)PSS, zinc nitrate hexahydrate, 2-methylimidazole, and ammonium persulfate APS.

[0038] The preparation method of the humidity-sensitive material (ZIF-8 / PEDOT:PSS composite material) in this embodiment includes the following steps:

[0039] ZIF-8 was first prepared by mixing zinc nitrate hexahydrate and 2-methylimidazole in a methanol solution at a molar ratio of 1:2. After stirring for one hour, ZIF-8 was collected by centrifugation. 0.0228 g (0.1 mmol) of ZIF-8, 110 μL of EDOT, and 155 μL of PSS were then mixed uniformly with 20 mL of ultrapure water and stirred for 20 min. Then, 0.3165 g of APS was added to initiate the polymerization of EDOT and PSS. The reaction was maintained at room temperature for 24 hours. The resulting black solution was designated as the ZIF-8 / PEDOT:PSS-1 composite material.

[0040] Example 2

[0041] The preparation method of the humidity-sensitive material (ZIF-8 / PEDOT:PSS composite material) in this embodiment includes the following steps:

[0042] ZIF-8 was first prepared by mixing zinc nitrate hexahydrate and 2-methylimidazole in a methanol solution at a molar ratio of 1:2. After stirring for one hour, ZIF-8 was collected by centrifugation. 0.0455 g (0.2 mmol) of ZIF-8, 110 μL of EDOT, and 155 μL of PSS were then mixed uniformly with 20 mL of ultrapure water and stirred for 20 min. Then, 0.3165 g of APS was added to initiate the polymerization of EDOT and PSS. The reaction was maintained at room temperature for 24 hours. The resulting black solution was designated as the ZIF-8 / PEDOT:PSS-2 composite material.

[0043] SEM image of ZIF-8 / PEDOT:PSS-2 composite material as shown below Figure 1 As shown in the scanning electron microscope (SEM) image, the surface of the composite material has some spherical structures, which is consistent with the dodecahedral structure of ZIF-8. This indicates that the ZIF-8 material has been successfully attached to the PEDOT:PSS material. The sensor surface exhibits a large number of wrinkles. These structural characteristics endow the sensor with good hygroscopicity, providing favorable conditions for humidity detection.

[0044] Example 3

[0045] The preparation method of the humidity-sensitive material (ZIF-8 / PEDOT:PSS composite material) in this embodiment includes the following steps:

[0046] ZIF-8 was first prepared by mixing zinc nitrate hexahydrate and 2-methylimidazole in a methanol solution at a molar ratio of 1:2. After stirring for one hour, ZIF-8 was collected by centrifugation. 0.0683 g (0.3 mmol) of ZIF-8, 110 μL of EDOT, and 155 μL of PSS were then mixed with 20 mL of ultrapure water and stirred for 20 min. 0.3165 g of APS was then added to initiate the polymerization of EDOT and PSS. The reaction was maintained at room temperature for 24 hours. The resulting black solution was designated as the ZIF-8 / PEDOT:PSS-3 composite material.

[0047] Example 4

[0048] Reference Figure 2 This diagram illustrates the overall structure of a flexible humidity sensor based on ZIF-8 / PEDOT:PSS composite material. The diagram clearly depicts the sensor's design layout, providing a basic framework for subsequent analysis.

[0049] In this embodiment, a flexible humidity sensor is prepared using the ZIF-8 / PEDOT:PSS-2 composite material obtained in Example 2.

[0050] A flexible humidity sensor based on ZIF-8 / PEDOT:PSS-2 composite material includes: a flexible substrate, interdigitated electrodes, and a humidity-sensitive coating coated on the interdigitated electrodes; the humidity-sensitive coating is a ZIF-8 / PEDOT:PSS-2 composite material, and the flexible substrate is PI.

[0051] After depositing an appropriate amount of ZIF-8 / PEDOT:PSS-2 composite material on the interdigitated electrode, the positive and negative electrodes of the interdigitated electrode are connected to the external circuit for conductivity measurement to obtain a flexible humidity sensor.

[0052] Next, a humidity response test was conducted on the sensor. The humidity sensor was placed in a dry cavity of about 5 cubic centimeters. The cavity was then filled with saturated salt solutions of different salts to achieve a stable relative humidity. The resistance change of the flexible humidity sensor was measured by a digital source meter, and the sensitivity of the flexible humidity sensor was calculated according to formula (1).

[0053]

[0054] Where Ra is the base resistance of the sensor exposed to air, and Rg is the base resistance of the gas being analyzed. After testing, the sensor is placed in a standard glass desiccator and stored at room temperature.

[0055] The prepared sensor was placed in environments with varying humidity levels: 25%, 33%, 43%, 59%, 75%, 85%, and 93% RH, obtained from saturated salt solutions of CH3COOK, MgCl2, K2CO3, NaBr, NaCl, KCl, and KNO3, respectively. Specifically, the interdigitated electrode with a flexible substrate was placed inside a sealed bottle at the top, with the bottom of the bottle containing saturated salt solutions. For example, a saturated CH3COOK aqueous solution (25% RH) meant the relative humidity of the space above the bottle was 43% RH at room temperature.

[0056] The changes in resistance under different humidity levels were recorded using an external circuit, as shown below. Figure 3 As shown (25%, 33%, 43%, 59%, 75%, 85%, and 93% RH represent relative humidity).

[0057] The fitted curves of response and relative humidity shown have response values ​​of 2461, 1248, 464, 178, 128, and 33 for relative humidity ranges of 33-93%. The fitting equation for the sensor's response to different humidity levels as a function of RHX can be expressed as follows:

[0058]

[0059] Regression coefficient (R) 2 The value is 0.9809, such as Figure 4 As shown in the figure, this indicates that the response to an increase in RH concentration is exponential.

[0060] Figure 5 The response-recovery curves are shown for RH from 25% to 93%; the response-recovery times are ~238 s and ~135 s, respectively.

[0061] The prepared flexible humidity sensor was tested for speech recognition accuracy.

[0062] The flexible substrate of the sensor is attached to the opening at a certain distance. The figure shows that the ZIF-8 / PEDOT:PSS-2 humidity sensor can detect different voice signals. When a human emits different command signals (Hi! or Hello!), the sensor can identify changes in humidity in the air at room temperature and convert them into dynamic response value changes, which are then converted into sound signals. The results are as follows... Figure 6 As shown. From Figure 6 As can be seen, the sensor of the present invention has the advantages of being able to recognize simple language well and responding quickly.

[0063] The prepared flexible humidity sensor was subjected to a bending resistance test:

[0064] The image shows a comparison of the resistance changes of the ZIF-8 / PEDOT:PSS-2 flexible humidity sensor after being folded at 45°, 90°, and 135° with those of the folded sensor at 93% RH. Figure 7 As can be seen, the folded sensor still achieves the same response as the folded sensor. However, due to the folding effect, the relative interaction of molecules in the material increases, leading to a slight increase in the adsorption and desorption time for water molecules. This has no special impact on the detection of physiological signals from human body parts. This demonstrates that the sensor in this embodiment has excellent resistance to bending and humidity response performance.

[0065] Testing the changes in perspiration on different parts of the human body using the prepared flexible humidity sensor:

[0066] Figure 8 The display shows the response curves of the ZIF-8 / PEDOT:PSS-2 sensor to changes in human body humidity at different distances (5-15 mm) from a human finger. When the finger is 5-15 mm above the sensor, the higher humidity on the finger triggers the sensor's response; the closer the distance, the higher the response, and the higher the peak value of the resistance fluctuation when converted into a resistance signal. This demonstrates that the sensor of this invention has excellent sensitivity for detecting changes in perspiration in different parts of the human body.

[0067] The dynamic response changes of the fabricated flexible humidity sensor under the same nasal breathing frequencies (fast and slow) were tested, demonstrating the dynamic changes in the sensor's response under different nasal breathing frequencies (fast and slow). Figure 9 During rapid nasal breathing, the response values ​​fluctuate more significantly, with clearer peaks and troughs. Conversely, the slower the breathing rate, the more dispersed the waveform and the smaller the vibration amplitude. This highlights the ZIF-8 / PEDOT:PSS humidity sensor's ability to accurately detect different breathing patterns and effectively capture relevant health information.

[0068] Figure 10 The figure shows the dynamic changes in the response of the flexible humidity sensor in this embodiment to the breathing state through the mouth and nose. As shown in the figure, the flexible humidity sensor responds more significantly to the humidity generated by oral breathing, indicating that the humidity level of oral exhalation is higher.

[0069] Figure 11 This diagram illustrates the dynamic response of the flexible humidity sensor in this embodiment to changes in skin humidity over a certain period of time after using different hand creams. Tests were conducted at equal intervals after using different hand creams. Figure 11 As shown, the fitted curve of the test response value and relative humidity can be combined. Figure 4 The calculation of the relative humidity of the skincare product indicates that the flexible humidity sensor described in this invention can meet the needs of daily life for identifying the moisturizing level of skincare products.

[0070] Example 5

[0071] Flexible humidity sensors were fabricated using the composite materials obtained in Examples 1-3. The influence of the composite materials on the performance of the final sensors was investigated. Figure 12 (a) and Figure 12 As shown in (b), the comparison of the response values ​​of ZIF-8 with different molar amounts to 93% humidity and the dynamic response diagram of the resistance indicate that the composite material has the best response to humidity when the amount of ZIF-8 added during the synthesis process is 0.2 mmol.

[0072] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A method for preparing a ZIF-8 / PEDOT:PSS composite material, characterized in that, Includes the following steps: S1, Zinc nitrate hexahydrate and 2-methylimidazole were mixed in a methanol solution and stirred for 1 hour. The resulting suspension was then centrifuged and dried to obtain ZIF-8. S2, ZIF-8, EDOT and PSS are uniformly mixed with ultrapure water, and then APS is added to initiate the polymerization of EDOT and PSS. The mixture is stirred at room temperature for 24 hours to ensure that the components are fully mixed, thus obtaining the ZIF-8 / PEDOT:PSS composite material.

2. The method for preparing a ZIF-8 / PEDOT:PSS composite material as described in claim 1, characterized in that, In step S1, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:

2.

3. The method for preparing a ZIF-8 / PEDOT:PSS composite material as described in claim 1, characterized in that, In step S2, the amount of ZIF-8 used is 0.2 mmol, the amount of EDOT used is 110 μL, the amount of PSS used is 155 μL, and the amount of APS used is 0.3165 g.

4. A ZIF-8 / PEDOT:PSS composite material prepared by the preparation method according to any one of claims 1 to 3.

5. A method for preparing a flexible humidity sensor made of ZIF-8 / PEDOT:PSS composite material, characterized in that, Includes the following steps: A1, the metal layer is processed into a metal layer interdigitated electrode; A2, uniformly drop-coat the ZIF-8 / PEDOT:PSS composite material as described in claim 4 onto the interdigitated metal electrode, dry it to make the ZIF-8 / PEDOT:PSS composite material firmly adhere to form a humidity-sensitive coating, and lead out metal wires at both ends of the interdigitated electrode to obtain a flexible humidity sensor of ZIF-8 / PEDOT:PSS composite material.

6. The method for preparing a flexible humidity sensor made of ZIF-8 / PEDOT:PSS composite material as described in claim 5, characterized in that, In step A1, the specific processing procedure is as follows: the flexible PI film is fixed on the substrate; the designed electrode pattern is imported into the operating software, and the parameters of the laser lithography system are set to lithographically imprint interdigitated electrodes onto the flexible PI film.

7. The method for preparing a flexible humidity sensor made of ZIF-8 / PEDOT:PSS composite material as described in claim 5, characterized in that, In step A1, the interdigitated metal electrode comprises multiple metal deposition layers composed of Au, Ni, and Cu.

8. The method for preparing a flexible humidity sensor made of ZIF-8 / PEDOT:PSS composite material as described in claim 5, characterized in that, In step A1, the width of the interdigitated fingers of the metal layer interdigitated electrode and the gap between adjacent interdigitated fingers are both 100 μm, and the number of pairs of interdigitated fingers in the metal layer is 20.

9. A flexible humidity sensor made of ZIF-8 / PEDOT:PSS composite material, prepared by the method described in any one of claims 5 to 8, characterized in that, It includes a flexible substrate, interdigitated metal electrodes lithographically formed on the substrate, a humidity-sensitive coating on the interdigitated metal electrodes, and an external circuit for conductivity measurement.

10. The application of the ZIF-8 / PEDOT:PSS composite flexible humidity sensor as described in claim 9 in non-contact human body humidity detection.

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