A self-powered flexible humidity sensor based on hydrogen bond organic framework and its preparation method and application

Abstract

The present invention discloses a self-powered flexible humidity sensor based on a hydrogen bond organic framework, a preparation method and an application thereof, comprising a symmetric electrode, a HOF / CNF electrolyte membrane located on one side of the symmetric electrode and a HOF / CNF / NaCl electrolyte membrane located on the other side of the symmetric electrode, wherein the HOF / CNF electrolyte membrane contacts the HOF / CNF / NaCl electrolyte membrane; the symmetric electrode is Ti3C2T x ‑MXene electrode, HOF is a hydrogen-bonded organic framework material synthesized with 1,2,4,5‑tetrakis(4‑carboxyphenyl)benzene as a precursor. The self-powered flexible humidity sensor of the present invention realizes the conversion of osmotic energy into electrical energy by regulating the salt ion concentration, exhibits good flexibility and low hysteresis characteristics, has a high sensitivity of 0.17μA / % RH, a fast response time of 1.06 s and stability for more than 200 cycles.

Description

Technical Field

[0001] The invention relates to a self-powered flexible humidity sensor based on a hydrogen bond organic framework, a preparation method and an application thereof, and belongs to the field of humidity sensors. Background Art

[0002] Traditional sensors are usually made based on the properties of metals and metal oxides, sulfur oxides and graphene materials. These materials usually have problems such as complex manufacturing processes, high costs, and heavy pollution. In addition, since most humidity sensors are based on resistors, capacitors, etc., they require external power supplies, which limits the use of the equipment.

[0003] Osmotic energy, especially the use of salt concentration differences between seawater and river water to generate electricity, is considered a key renewable and sustainable energy source to solve the global energy crisis. The osmotic energy system mainly uses the salt concentration gradient between seawater and rivers to directly convert osmotic pressure into electrical energy through ion transfer through cation or anion exchange membranes. However, there are various disadvantages in using the natural concentration difference between seawater and rivers to achieve power generation, such as the inability to find a suitable concentration difference interface and the difficulty in achieving large-scale application. In recent years, osmotic energy has been widely used in micro-energy, biomedicine and other fields.

[0004] As a new type of porous crystalline material, HOFs have the advantages of uniform pore structure, large specific surface area, adjustable pore size, and great surface modification potential, and have significant advantages in ion selectivity and osmotic energy conversion. The uniformly distributed hydrogen bonding sites of HOFs give them unique properties. Due to the presence of abundant reversible hydrogen bonds, the ion transport properties of HOFs vary greatly under high and low humidity conditions. The ion-selective transport of HOFs and the gated ion channel properties sensitive to humidity stimuli give them properties similar to those of cell membranes. At the same time, the metal-free properties of nanomaterials enhance their potential biocompatibility and safety, providing an important reference for flexible humidity sensors based on these nanomaterials to monitor the humidity of skin, fingers, sweat, and breath. Therefore, by constructing a concentration gradient in HOFs solid electrolytes, taking advantage of the multi-hydrogen bonding characteristics of HOFs, and using the difference in ion concentrations, effective humidity sensing can be achieved. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a self-powered flexible humidity sensor based on a hydrogen bond organic framework and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object, the present invention adopts a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework, comprising a symmetric electrode, a HOF / CNF electrolyte membrane located on one side of the symmetric electrode, and a HOF / CNF / NaCl electrolyte membrane located on the other side of the symmetric electrode, wherein the HOF / CNF electrolyte membrane is in contact with the HOF / CNF / NaCl electrolyte membrane;

[0007] The symmetrical electrode is Ti3C2T x - MXene electrode, HOF is a hydrogen-bonded organic framework material synthesized using 1,2,4,5-tetrakis(4-carboxyphenyl)benzene as a precursor.

[0008] As an improvement, the HOF / CNF electrolyte membrane is a solid electrolyte membrane formed by HOF-H4TCPB and CNF-C.

[0009] As an improvement, the HOF / CNF / NaCl electrolyte membrane is a solid electrolyte membrane formed by HOF-H4TCPB, CNF-C and NaCl.

[0010] As an improvement, the HOF / CNF electrolyte membrane overlaps the HOF / CNF / NaCl electrolyte membrane by 2-5 mm.

[0011] The second aspect of the present invention further provides a method for preparing the self-powered flexible humidity sensor based on the hydrogen-bonded organic framework, comprising the following steps:

[0012] (1) Preparation of symmetrical electrodes;

[0013] (2) Take the HOF / CNF electrolyte solution and drop it on one of the symmetrical electrodes. After the drop casting is completed, put it into a vacuum drying oven for drying;

[0014] (3) Take the HOF / CNF / NaCl electrolyte solution and drop it on the other electrode of the symmetrical electrode. After the drop casting is completed, put it into a vacuum drying oven to dry.

[0015] As an improvement, the step (1) is specifically as follows: Ti3C2T x - The MXene solution was filtered to form a membrane, dried, and Ti3C2T x - The MXene film was laser engraved into electrodes 1-2 cm long and 0.3-0.8 cm wide.

[0016] It should be noted that the Ti3C2T x - MXene solution can be prepared by commercial products or common methods. For example, the self-preparation method is as follows: first, 15 ml of hydrochloric acid and 5 ml of deionized water are mixed and stirred for 3 minutes, then 1 g of LiF is weighed and added, and the reaction is carried out for 10 minutes. During the reaction, 1 g of MAX raw material (divided into multiple portions) is weighed; after the reaction is completed, a portion of raw material is added every 3 minutes, and the last portion is added and stirred for 10 minutes; then, after stirring, it is placed in a water bath (35°C) and stirred for 24 hours, and the liquid after the reaction is completed is transferred to a centrifuge tube and deionized water is added to 40-50 ml for centrifugal washing (3500rpm 5min), and this operation is repeated until the pH of the solution is close to neutral; the washed liquid is poured into a ventilation bottle for ventilation and ultrasound (argon, 60min); finally, the ultrasound-completed liquid is taken out and centrifuged (3500rpm 5min) to obtain a layered MXene solution.

[0017] As an improvement, the drying temperature of step (2) and step (3) is 50-70°C, and the drying time is 20-40 minutes.

[0018] As an improvement, the HOF / CNF electrolyte solution is a mixture of HOF-H4TCPB solution and CNF-C solution in a mass ratio of 1:(0.5-1.5);

[0019] The HOF / CNF / NaCl electrolyte solution is prepared by mixing a HOF-H4TCPB solution, a CNF-C solution and a NaCl solid in a mass ratio of 1:(0.5-1.5):(50-250).

[0020] It should be noted that the HOF-H4TCPB solution is obtained by the following method: a certain amount of 1,2,4,5-tetrakis(4-carboxyphenyl)benzene (H4TCPB) is dissolved in a DMF solution, and ultrasonicated until the solid is dispersed in the DMF solvent; the obtained dispersion is further dispersed in deionized water and stirred; the obtained solution is washed and filtered to form a solid film, and the mass is calibrated and then redispersed into a HOF-H4TCPB solution of a required fixed concentration.

[0021] In addition, the CNF-C solution is obtained by the following method: a CNF-C solution of a certain concentration is diluted with water.

[0022] As an improvement, the concentration of the HOF-H4TCPB solution is 2-4 mg / mL, and the concentration of the CNF-C solution is 1-3 mg / mL.

[0023] The third aspect of the present invention also provides an application of a humidity sensor for health monitoring in a flexible wearable device or as a humidity power generation device, wherein the humidity sensor is the self-powered flexible humidity sensor based on the hydrogen-bonded organic framework or the self-powered flexible humidity sensor based on the hydrogen-bonded organic framework obtained by the preparation method.

[0024] In order to facilitate a more detailed understanding of the present invention, the mechanism of the present invention is explained as follows:

[0025] The sensing mechanism of the self-powered flexible humidity sensor can be explained by the accumulation and consumption of ions under different humidity environments. In a low humidity environment, the transmission of sodium ions is hindered. In contrast, in a high humidity environment, the HOF / CNF porous membrane has excellent hydrophilicity, which is conducive to the adsorption of water molecules. The adsorption of water causes the electrolyte membrane to produce osmotic pressure due to the different concentrations of salt ions, and this osmotic pressure promotes the migration of sodium ions on the electrolyte interface. In addition, the migration of negatively charged Cl ions is inhibited by the HOF-H4TCPB membrane, which is also negatively charged, thereby generating a potential difference on the electrolyte membrane. This shows that carrier migration in the present invention is controlled by the difference in salt ion concentration.

[0026] The beneficial effects of the present invention are:

[0027] 1. The self-powered flexible humidity sensor based on the hydrogen-bonded organic framework of the present invention realizes the conversion of osmotic energy into electrical energy by regulating the salt ion concentration, exhibits good flexibility and low hysteresis characteristics, has a high sensitivity of 0.17μA / % RH, a fast response time of 1.06 s and stability of more than 200 cycles.

[0028] 2. The self-powered flexible humidity sensor based on the hydrogen-bonded organic framework of the present invention can not only be used as a fast-response high-performance humidity sensor, but also can be used as a humidity power generation device to provide a higher electrical signal output.

[0029] 3. The self-powered flexible humidity sensor based on the hydrogen-bonded organic framework of the present invention can monitor the breathing of people in running and stationary states. In addition, the present invention has the characteristics of flexibility, biocompatibility, and environmental friendliness, and is suitable for application in the development of flexible wearable electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of a self-powered flexible humidity sensor according to Embodiment 1 of the present invention;

[0031] Figure 2 This is a schematic diagram of ion transmission of the HOF / CNF / NaCl electrolyte membrane used in the self-powered flexible humidity sensor of Example 1 of the present invention;

[0032] Figure 3This is a humidity sensing mechanism diagram of the self-powered flexible humidity sensor according to Example 1 of the present invention;

[0033] Figure 4 The current density and power density curve of the self-powered flexible humidity sensor of the present invention as a humidity power generation device;

[0034] Figure 5 Response recovery time curve of the self-powered flexible humidity sensor of the present invention;

[0035] Figure 6 The humidity response curve of the self-powered flexible humidity sensor of the present invention in an environment of 14% RH~90% RH;

[0036] Figure 7 The self-powered flexible humidity sensor of the present invention is about 200 cycles of humidity response curve in 90% RH environment within 2000s;

[0037] Figure 8 The self-powered flexible humidity sensor of the present invention is used as a contactless switch to generate different response curves for different distances of 1 mm, 3 mm, and 5 mm;

[0038] Fig. 9 This is the breathing monitoring curve of a human body in a running state and a stationary state by the self-powered flexible humidity sensor of the present invention. DETAILED DESCRIPTION

[0039] The following embodiments are further descriptions of the content of the present invention as an explanation of the technical content of the present invention, but the essential content of the present invention is not limited to the following embodiments. Ordinary technicians in this field can and should know that any simple changes or replacements based on the essential spirit of the present invention should fall within the scope of protection required by the present invention.

[0040] Example 1

[0041] A method for preparing a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework comprises the following steps:

[0042] (1) Extraction of Ti3C2T x -MXene solution, and filtered to form a membrane. The mass of the membrane after drying was 30 mg. x -MXene film is laser engraved into electrodes with a length of 1.5 cm and a width of 0.5 cm to make symmetrical electrodes;

[0043] (2) 3 mg / mL HOF-H4TCPB solution and 2 mg / mL CNF-C (carboxylated cellulose nanofiber) solution were mixed at a mass ratio of 1:1 and stirred for 30 min to prepare a HOF / CNF electrolyte solution;

[0044] (3) 3 mg / mL HOF-H4TCPB solution, 2 mg / mL CNF-C solution and NaCl solid were mixed at a mass ratio of 1:1:150 and stirred for 30 min to prepare a HOF / CNF / NaCl electrolyte solution;

[0045] (4) The Ti3C2T obtained in step (1) x -MXene symmetric electrodes are pasted on a PET substrate (2 cm*2 cm), and the spacing between the symmetric electrodes is controlled at 2-5 mm;

[0046] (5) Apply the uniformly dispersed HOF / CNF electrolyte solution in step (2) to the Ti3C2T x -MXene symmetrical electrode and dried in a vacuum oven at 60 °C for 30 min to obtain the HOF / CNF electrolyte membrane;

[0047] (6) Apply the uniformly dispersed HOF / CNF / NaCl electrolyte solution in step (3) to the Ti3C2T x -MXene symmetric electrode and dried in a vacuum drying oven at 60 °C for 30 min to obtain a HOF / CNF / NaCl electrolyte membrane. The schematic diagram of ion transport of the HOF / CNF / NaCl electrolyte membrane is shown in Figure 2 As shown; at the same time, the HOF / CNF electrolyte membrane and the HOF / CNF / NaCl electrolyte membrane are ensured to contact each other (the contact size is about 3 mm) to form an ion transmission channel, that is, Figure 1 The self-powered flexible humidity sensor shown.

[0048] The humidity sensing mechanism of the self-powered flexible humidity sensor prepared in Example 1 is as follows Figure 3 As shown in the figure, in a low humidity environment, the transmission of sodium ions is hindered. In contrast, in a high humidity environment, the porous structure of the HOF / CNF electrolyte membrane has excellent hydrophilicity, which is conducive to the adsorption of water molecules. The adsorption of water causes the electrolyte membrane to produce osmotic pressure due to the different concentrations of salt ions. This osmotic pressure promotes the migration of sodium ions at the electrolyte interface. In addition, the migration of negatively charged Cl ions is inhibited by the HOF-H4TCPB membrane, which is also negatively charged, thereby generating a potential difference on the electrolyte membrane.

[0049] Example 2

[0050] The mass ratio of HOF-H4TCPB solution, CNF-C solution and NaCl solid in step (3) of Example 1 was 1:1:150, which was replaced with 1:1:50. The remaining steps were the same as in Example 1.

[0051] Example 3

[0052] The mass ratio of HOF-H4TCPB solution, CNF-C solution and NaCl solid in step (3) of Example 1 was 1:1:150, which was replaced with 1:1:100. The remaining steps were the same as in Example 1.

[0053] Example 4

[0054] The mass ratio of HOF-H4TCPB solution, CNF-C solution and NaCl solid in step (3) of Example 1 was 1:1:150, which was replaced with 1:1:200. The remaining steps were the same as in Example 1.

[0055] Example 5

[0056] The mass ratio of HOF-H4TCPB solution, CNF-C solution and NaCl solid in step (3) of Example 1 was 1:1:150, which was replaced with 1:1:250. The remaining steps were the same as in Example 1.

[0057] Example 6

[0058] The self-powered flexible humidity sensor (MHCNM) prepared in Example 1 is used as a humidity power generation device, which can stably output a current of 8 μA within 1000 s, and can still output a current of 4 μA after 40000 s, demonstrating excellent humidity power generation capability. Figure 4 Demonstrated MHCNM as a humidity power generation device with a maximum output of 164 mA / m 2 The current density is 5.625 m W / m 2 power density.

[0059] Example 7

[0060] The self-powered flexible humidity sensor (MHCNM) of the present invention has excellent sensing performance, high sensitivity and fast response speed. Taking the self-powered flexible humidity sensor prepared in Example 1 as an example, the humidity response performance is tested under the environmental conditions of relative humidity of 14% RH~90% RH:

[0061] like Figure 5 As shown, MHCNM is able to respond and recover quickly, with a response time of only 1.06 s and a recovery time of only 1.41 s.

[0062] like Figure 6 As shown in the figure, MHCNM can respond to humidity from 14% RH to 90% RH and has good discrimination for different humidity levels. Figure 7 Up to 200 humidity cycles demonstrate that the present invention has good stability as a humidity sensor, which indicates that it has practical application value.

[0063] Example 8

[0064] The self-powered flexible humidity sensor (MHCNM) of the present invention has good biocompatibility, high flexibility and excellent sensing performance, which makes the present invention have application potential in contactless switches and flexible wearable devices.

[0065] Taking the self-powered flexible humidity sensor prepared in Example 1 as an example, Figure 8 The response curves of MHCNM to human fingers are shown at distances of 1 mm, 3 mm and 5 mm, respectively, which indicates that the present invention is suitable for application in a contactless environment. Fig. 9 The invention shows that the present invention can monitor the breathing of people in motion and people in a static state. The breathing rate and water content produced in these two environments are different, and this change is sensitively recorded by the sensor. The invention provides a new reference for the application of flexible wearable devices in the field of health monitoring.

[0066] Based on the ion concentration difference sensing mechanism, the present invention successfully prepared a self-powered flexible humidity sensor (MHCNM) using HOF-H4TCPB solid electrolyte and MXene symmetric electrode. In the HOF-H4TCPB electrolyte, the Na ion concentration gradient has a reversible effect on the Na ion migration barrier, resulting in efficient Na ion migration. The humidity sensor has high current response (8 μA), fast response and recovery ability (1.06 s / 1.41 s), and long-term cycle stability (greater than 200 cycles). It should be noted that the response of this humidity sensor based on osmotic energy conversion does not depend on specific electrode materials and shows certain flexibility. In addition, the humidity sensor can also be used as humidity power generation, with long-lasting stability and high current response, no external power supply is required, strong self-power supply capability, low power consumption, simple preparation, and easy low-cost large-scale production.

[0067] It should be noted that the above-described embodiments of the present invention are only explanations and clarifications for those skilled in the art to understand the technical essence of the present invention, so the technical contents described are not intended to limit the substantial protection scope of the present invention. The substantial protection scope of the present invention shall be subject to the claims. Those skilled in the art should know that any modifications, equivalent substitutions and improvements based on the substantial spirit of the present invention shall be within the substantial protection scope of the present invention.

Claims

1. A self-powered flexible humidity sensor based on a hydrogen-bonded organic framework, characterized in that: It includes a symmetrical electrode, a HOF / CNF electrolyte membrane located on one side of the symmetrical electrode, and a HOF / CNF / NaCl electrolyte membrane located on the other side of the symmetrical electrode, wherein the HOF / CNF electrolyte membrane is in contact with the HOF / CNF / NaCl electrolyte membrane; The symmetrical electrode is Ti3C2T x -MXene electrode, HOF is a hydrogen-bonded organic framework material synthesized using 1,2,4,5-tetrakis(4-carboxyphenyl)benzene as a precursor.

2. A self-powered flexible humidity sensor based on a hydrogen-bonded organic framework according to claim 1, characterized in that: The HOF / CNF electrolyte membrane is a solid electrolyte membrane formed by HOF-H4TCPB and CNF-C.

3. A self-powered flexible humidity sensor based on a hydrogen-bonded organic framework according to claim 1, characterized in that: The HOF / CNF / NaCl electrolyte membrane is a solid electrolyte membrane formed by HOF-H4TCPB, CNF-C and NaCl.

4. The self-powered flexible humidity sensor based on a hydrogen-bonded organic framework according to claim 1, characterized in that: The HOF / CNF electrolyte membrane overlaps the HOF / CNF / NaCl electrolyte membrane by 2-5 mm.

5. A method for preparing a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Preparation of symmetrical electrodes; (2) Take the HOF / CNF electrolyte solution and drop it on one of the symmetrical electrodes. After the drop casting is completed, put it into a vacuum drying oven for drying; (3) Take the HOF / CNF / NaCl electrolyte solution and drop it on the other electrode of the symmetrical electrode. After the drop casting is completed, put it into a vacuum drying oven to dry.

6. The method for preparing a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework according to claim 5, characterized in that: The step (1) is specifically as follows: Ti3C2T x -MXene solution was filtered to form a membrane, dried, and Ti3C2T x -MXene film is laser engraved into electrodes with a length of 1-2 cm and a width of 0.3-0.8 cm.

7. The method for preparing a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework according to claim 5, characterized in that: The drying temperature of step (2) and step (3) is 50-70° C., and the drying time is 20-40 min.

8. The method for preparing a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework according to claim 5, characterized in that: The HOF / CNF electrolyte solution is prepared by mixing a HOF-H4TCPB solution and a CNF-C solution in a mass ratio of 1:(0.5-1.5); The HOF / CNF / NaCl electrolyte solution is prepared by mixing a HOF-H4TCPB solution, a CNF-C solution and a NaCl solid in a mass ratio of 1:(0.5-1.5):(50-250).

9. The method for preparing a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework according to claim 8, characterized in that: The concentration of the HOF-H4TCPB solution is 2-4 mg / mL, and the concentration of the CNF-C solution is 1-3 mg / mL.

10. An application of a humidity sensor in a flexible wearable device for health monitoring or as a humidity power generation device, characterized in that: The humidity sensor is a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework as described in any one of claims 1-4 or a self-powered flexible humidity sensor based on a hydrogen-bonded organic framework obtained by the preparation method described in any one of claims 5-9.

Images