CN115304808B

CN115304808B - Sensitive material based on covalent organic framework film, humidity sensor and preparation method thereof

Info

Publication number: CN115304808B
Application number: CN202211029660.3A
Authority: CN
Inventors: 刘曰利; 梅傲寒; 陈文�
Original assignee: Shenzhen Research Institute Of Wuhan University Of Technology; Wuhan University of Technology WUT
Current assignee: Shenzhen Research Institute Of Wuhan University Of Technology; Wuhan University of Technology WUT
Priority date: 2022-08-25
Filing date: 2022-08-25
Publication date: 2023-05-23
Anticipated expiration: 2042-08-25
Also published as: CN115304808A

Abstract

The invention relates to a sensitive material based on a covalent organic framework film, a humidity sensor and a preparation method thereof, comprising the following steps: under the protective atmosphere, uniformly mixing a monomer of a COF-5 material with a solvent A to obtain a precursor solution; dripping the precursor solution onto the surface of the pretreated substrate, and placing the substrate and the open vessel filled with the solvent B into a reactor for sealing and preserving; and synthesizing a solid film on the surface of the substrate by a steam auxiliary method or/and a photochemical reaction method, and washing and drying to obtain the sensitive material. The humidity sensor includes interdigitated electrodes and a sensitive material. The covalent organic framework film sensitive material has high flexibility, is applied to a humidity sensor, and the manufactured humidity sensor is a high-performance flexible wearable sensor, can realize quick linear response in a full humidity range, has high performance consistency in bending states of different angles, and can be used for practical scene applications such as breath detection, fingertip contact and the like.

Description

Sensitive material based on covalent organic framework film, humidity sensor and preparation method thereof

Technical Field

The invention relates to the field of wearable sensors, in particular to a sensitive material based on a covalent organic framework film, a humidity sensor and a preparation method thereof.

Background

The humidity sensor can convert humidity information in air into electrical signals in real time, and plays an important role in the fields of human body respiration monitoring, agriculture and biological monitoring, industrial production monitoring, non-contact switches and the like. In order to realize the large-scale application of the humidity sensitive material in the future intelligent and integrated wearable device, the water molecule adsorption and desorption characteristics, the large-scale and high-sensitivity response characteristics and the flexibility of the material are required to be considered so as to meet the requirements of environment detection and health monitoring under specific conditions. However, most of the sensitive materials of high-performance humidity sensors are limited by the poor flexibility characteristic of inorganic materials, and generally depend on a rigid device structure to realize the humidity response performance, so that the application requirements of flexibility in wearable equipment are difficult to meet. Therefore, there is an urgent need to develop a film sensitive material having good flexibility and excellent humidity response characteristics.

Covalent Organic Frameworks (COFs) are an emerging class of porous materials that are of great interest and research due to their adjustable pore structure, high specific surface area, and good chemical and thermal stability. The unique porous structure and carrier transport characteristics of two-dimensional COFs ensure their interaction sites with water molecules and the function of transmitting humidity information out through electrical signals. However, in order to obtain COFs materials of high quality, solvothermal methods are generally used to heat the mixed solvent in which the monomer is dissolved in a closed vessel for several days under appropriate conditions of atmosphere, temperature, pressure and monomer concentration to ensure that the reversible process of covalent bond formation reduces the disorder inside the material. COFs materials synthesized by solvothermal methods are mostly highly insoluble powders, and their use in flexible devices is still very limited.

The in-situ preparation of the COFs film on the substrate is a reliable method for efficiently and stably preparing the flexible humidity sensitive material. This approach involves two problems: first, the thickness of the covalent organic framework film is difficult to control. In addition, during the synthesis process, deposition of oligomers, powders of COFs, and unreacted monomers tend to contaminate the film surface, degrading film quality. These problems have limited the research and development of novel COFs film preparation and purification techniques.

Disclosure of Invention

The invention aims to overcome the technical defects, and provides a sensitive material based on a covalent organic framework film, a humidity sensor and a preparation method thereof, wherein the sensitive material can be used for preparing a uniform covalent organic framework film, has good flexibility for the humidity sensor, and can realize quick linear response in a full humidity range.

In a first aspect, the present invention provides a method for preparing a sensitive material based on a covalent organic framework film, comprising the steps of:

(1) Under the protective atmosphere, uniformly mixing a monomer of a COF-5 material with a solvent A to obtain a precursor solution;

(2) Dripping the precursor solution on the surface of the pretreated substrate to obtain a substrate with the precursor solution; filling the solvent B into an open vessel to obtain a steam source; placing the substrate with the precursor solution and a steam source into a container capable of being sealed together, and sealing;

(3) And synthesizing a solid film on the surface of the substrate by a steam auxiliary method or/and a photochemical reaction method, and washing and drying to obtain the sensitive material.

Preferably, the protective atmosphere in step (1) is nitrogen.

Preferably, the precursor solution in step (1) is uniformly mixed by shaking and ultrasound.

Still more preferably, the ultrasonic power is 1500-2000W and the ultrasonic time is 20-30 min.

Further, in the step (1), monomers of the COF-5 material are 2,3,6,7,10, 11-hexahydroxytriphenyl and 1, 4-phenyldiboronic acid, the solvent A is a mixture of absolute ethyl alcohol and acetone, and the addition ratio of the 2,3,6,7,10, 11-hexahydroxytriphenyl, 1, 4-phenyldiboronic acid, the absolute ethyl alcohol and the acetone is (0.01-0.06) mmol (0.2-0.8) mL.

Further, in the step (2), the ratio of the volume of the precursor solution to the volume of the solvent B is (40 to 200 μl): (5-20) mL.

Further, in step (2), the substrate is polyimide, polyethylene terephthalate, borosilicate glass, porous fiber, conductive FTO glass, or flexible ITO/PEN; the solvent B is a mixture of 1,3, 5-trimethylbenzene and 1, 4-dioxane in any proportion.

Preferably, in step (2), the substrate pretreatment comprises cleaning, drying, inert gas purging, and plasma treatment.

Further, in the step (3), the steam assisted method is to react for 12-72 hours at the temperature of 5-30 ℃.

Further, in the step (3), the photochemical reaction method is that the room temperature is preserved for 3 to 24 hours, then the illumination is carried out for 3 to 9 hours under the ultraviolet light condition, and the reaction is continued for 3 to 36 hours; the ultraviolet light condition is provided by a Xe lamp or Hg lamp with 300w power and a dominant wavelength of 365 nm; the reaction temperature of the photochemical reaction method is 5-30 ℃.

In a second aspect, the present invention provides a sensitive material based on a covalent organic framework film.

In a third aspect, the present invention provides a humidity sensor comprising an interdigital electrode and the above-described sensing material, the sensing material comprising a substrate and a covalent organic framework film on the substrate, the interdigital electrode being located on a surface of the covalent organic framework film.

In a fourth aspect, the present invention provides a method for manufacturing a humidity sensor, comprising the steps of:

evaporating patterned Au on the surface of a covalent organic framework film of a sensitive material by a photoetching-evaporating method or a mask plate-evaporating method to form interdigital electrodes;

and (II) treating the sensitive material with the interdigital electrodes on the surface for 12-24 hours under constant temperature and constant humidity to obtain the humidity sensor.

Further, in the step (I), photoresist is spin-coated on the surface of the covalent organic framework film by the photoetching-vapor deposition method, and a patterned photoresist layer is formed through exposure and development; evaporating 30-100 nm Au on the photoresist layer;

the mask plate-evaporation method is to cover a metal mask plate on the surface of the covalent organic framework film and then evaporate 30-100 nm Au;

in the step (II), the temperature is 30-70 ℃ and the humidity is 30-70% in the constant temperature and constant humidity treatment.

Preferably, the spin-coating photoresist is performed at a rotation speed of 500-2500 rpm and baked at 70-110 ℃ for 1-3 min to obtain the photoresist layer.

Preferably, the exposure is to cover the surface of the photoresist with the photoetching mask plate with the interdigital electrode patterns with different pitches of 20-100 μm, expose for 5-10 s under an ultraviolet photoetching machine and bake for 1-3 min at 70-110 ℃.

Preferably, the development is to put the exposed material into a developing solution to oscillate for 60-120 s, so as to form a patterned photoresist layer.

Preferably, in the mask-vapor deposition method, the metal mask is a stainless steel plate with laser engraved electrode patterns, and the stainless steel plate is provided with interdigital electrode patterns with different pitches of 100-150 μm.

In a fifth aspect, the invention also provides the use of a sensitive material based on a covalent organic framework film in a humidity sensor.

The method can realize controllable preparation of the thickness of the covalent organic framework film, and has the characteristics of low cost, simple method, good repeatability, green production and the like. The covalent organic framework film sensitive material has high flexibility, is applied to a humidity sensor, and the manufactured humidity sensor is a high-performance flexible wearable sensor, can realize quick linear response in a full humidity range, has high performance consistency in bending states of different angles, and can be used for practical scene applications such as breath detection, fingertip contact and the like.

Compared with the prior art, the invention has the beneficial effects that:

1. according to the invention, the covalent organic framework film is synthesized by adopting a photochemical reaction method or a steam auxiliary method, and the solvent B serving as a steam source is independently placed in an open vessel and is naturally volatilized in a closed reactor together with the substrate, so that the organic solvent residue in the preparation process is avoided, and a uniform covalent organic framework film is formed on the substrate. The high specific surface area and ordered pore structure of the covalent organic framework enable a large number of borate active sites in the plane to be exposed and have Lewis acid-base interaction with water molecules, so that the covalent organic framework has excellent humidity response characteristics as a sensitive layer. Meanwhile, the unique nano-pore structure and interlayer conjugated stacking of the covalent organic framework provide efficient mass transfer channels and carrier transmission paths, so that the sensor based on the covalent organic framework film shows quick response and recovery characteristics to humidity.

2. The covalent organic framework film prepared by the invention has uniform surface morphology, so that the resistance between grain boundaries and grains is reduced, carrier defect sites are reduced, the adsorption capacity of the material is improved, and the problem that the response of the current covalent organic framework material in the sensing field is generally lower is solved; the humidity sensor prepared by the invention can realize detection of human respiratory humidity and humidity response when fingertips are in non-contact approach, and can realize quick response/recovery in the change of 11% -98% of relative humidity.

3. The covalent organic framework film prepared by the invention has excellent flexibility, and the sensor can still maintain stable humidity sensitivity under the condition of bearing thousands of times of bending and bending for 90 degrees, so that the problem of lack of flexible high-sensitivity humidity sensitive materials in the field is solved, and the covalent organic framework film has great potential in future integrated and intelligent sensing devices.

In the method, a photochemical reaction method or a steam auxiliary method is adopted, a specific raw material proportion is combined, a volatile solvent is selected to dissolve covalent organic framework monomers to form a precursor solution, and the precursor solution is volatilized on a substrate and then grows in situ to obtain the solid film. The preparation method provided by the invention effectively avoids the residue of organic solvent in the preparation process, and can realize that the covalent organic framework film is free from impurities or byproducts after vacuum drying, and the obtained film has good quality. Meanwhile, the thickness of the obtained film can be controlled and the film can be uniformly formed by adjusting the concentration and the volume of the precursor solution.

Drawings

FIG. 1 shows the characterization of the morphology of the COF-5 film prepared on polyimide substrates according to example 1, wherein FIG. 1a is a 2000-magnification SEM image and FIG. 1b is a 10000-magnification SEM image.

FIG. 2 shows the IR spectrum of the COF-5 film prepared in example 2.

FIG. 3 is a water contact angle test result of the surface of the COF-5 film prepared in example 3, wherein FIG. 3a is an initial state of water drops after dropping on the surface of the COF-5 film, and FIG. 3b is a stable state of water drops after dropping for 30 seconds after spreading on the surface of the COF-5 film.

FIG. 4 shows the results of the crystal structure test of the surface of the COF-5 film prepared in example 4.

Fig. 5 is a humidity response curve result of the flexible wearable humidity sensor prepared in application example 1 under the conditions of straight, 30 ° bending and 90 ° bending.

Fig. 6 is a humidity response result of the flexible wearable humidity sensor prepared in application example 2 when the fingertip of the human body is close.

Detailed Description

The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

The covalent organic framework film sensitive material adopts polyimide, polyethylene terephthalate, porous fiber, flexible ITO/PEN film and the like as a flexible substrate, and the covalent organic framework film is grown on the substrate by any one of the following two preparation methods.

(1) And (3) photochemistry reaction synthesis:

step A1. Under the nitrogen atmosphere, adding 2,3,6,7,10, 11-hexahydroxy triphenyl, 1, 4-benzene diboronic acid, absolute ethyl alcohol and acetone according to the adding ratio of 0.01-0.06 mmol to 0.2-0.8 mL, and adding the 2,3,6,7,10, 11-hexahydroxy triphenyl and 1, 4-benzene diboronic acid into the mixed solution of the absolute ethyl alcohol and the acetone to form a mixture.

Step A2, oscillating and ultrasonic treating the mixture for a period of time to obtain a uniform and clear precursor solution.

Step A3. Drop-coating 40-200. Mu.L of precursor solution on the surface of the cleaned substrate, placing the substrate and a culture dish containing 5-20 mL of 1:1 (volume ratio) mixed solution of 1,3, 5-trimethylbenzene and 1, 4-dioxane into a closed container (transparent container), and sealing.

A4, preserving a transparent closed container (a substrate with a precursor solution coated therein) for 3-24 hours at room temperature, placing under a Xe lamp, irradiating with light with a dominant wavelength of 365nm (or ultraviolet irradiation under an Hg lamp) for 3-9 hours at 300w power, continuing to react for 3-36 hours, cleaning, and vacuum drying to obtain the covalent organic framework film sensitive material.

(2) Synthesizing by a steam auxiliary method:

step B1, adding 2,3,6,7,10, 11-hexahydroxy triphenyl, 1, 4-benzene diboronic acid, absolute ethyl alcohol and acetone into a mixed solution of absolute ethyl alcohol and acetone according to the adding ratio of 0.01-0.06 mmol to 0.2-0.8 mL in a nitrogen atmosphere to form a mixture.

And step B2, oscillating and ultrasonic treating the mixture for a period of time to obtain a uniform and clear precursor solution.

B3, dripping 40-200 mu L of precursor solution on the surface of the cleaned substrate, placing the substrate and a culture dish containing 5-20 mL of 1:1 mixed solution of 1,3, 5-trimethylbenzene and 1, 4-dioxane into a closed container, and sealing.

Step B4., volatilizing the precursor solution after reacting for 12-72 hours to obtain a white solid film. And taking out the substrate, cleaning, and then carrying out vacuum drying to obtain the covalent organic framework film sensitive material.

In the steps, the covalent organic framework film can be prepared on the surface of a substrate made of polyimide, polyethylene terephthalate, borosilicate glass, porous fiber, conductive FTO glass or flexible ITO/PEN and the like.

The selected flexible substrate is pretreated, firstly, the flexible substrate is respectively cleaned in deionized water and ethanol for 15-20 min under the ultrasonic power of 1000-2000W, then is dried for 20-30 min under the environment of 70-80 ℃, and the surface of the substrate is purged for 3-5 min by inert gas to remove surface air and liquid, wherein the inert gas is one of argon and nitrogen; finally, the surface is treated by oxygen plasma.

In the steps A2 and B2, the ultrasonic power is 1500-2000W, and the ultrasonic time is 20-30 min. In the step A4, the reaction is preserved for 3 to 24 hours at room temperature, which means that the solvent is fully volatilized, the subsequent illumination reaction is facilitated, and the total reaction time is reduced (the same is true in the 12 hours before the reaction in the actual step B4, and the reaction in the solvent volatilization stage is slower).

The two methods are subjected to the same steam-assisted reaction, and the synthesis temperature of the covalent organic framework film is 5-30 ℃ in the steam-assisted and photochemical methods; wherein, the reaction time required by the photochemical method is shorter, preferably 3-9 hours of illumination, and the reaction is continued for 12-24 hours; the reaction time in the steam assisted process is preferably from 12 to 72 hours.

Preferably, the monomer concentration in the precursor solution of the covalent organic framework film is 0.01 mmol/mL-0.06 mmol/mL, and the volume of the precursor solution dropwise added on the flexible substrate is 40-200 mu L.

In the preparation method, the formation mode is different from that of the traditional COF-5; separating the mixed solvent from the monomer by a steam auxiliary method, wherein the monomer is dissolved by absolute ethyl alcohol and acetone (solvent A), and the solvent A is volatile liquid and replaces the traditional high-boiling mixed solvent so as to realize the deposition of the COF-5 film in the solvent volatilization process; the 1:1 mixed solution (solvent B) of 1,3, 5-trimethylbenzene and 1, 4-dioxane is taken as a steam source to be independently placed in a culture dish and is naturally volatilized together with a substrate in a closed container, wherein the solvent effect corresponding to the composition of the solvent B can obviously influence the growth process of the COF, and the optimal reaction result can be realized by adopting the 1,3, 5-trimethylbenzene and the 1, 4-dioxane. The removal of solvent B does not allow the reaction to proceed and the formation of the desired covalent organic framework film. Meanwhile, the surface of the substrate is subjected to plasma treatment, and liquid with different volumes is dripped and spread out to cover the whole surface; the thickness of the prepared covalent organic framework film can be controlled by the volume and the concentration of the dropwise added precursor solution, and uniform preparation in the micron-scale range can be realized. The covalent organic framework film material prepared by the invention is COF-5 connected by a boric acid ester bond structure.

In the sensitive material prepared by the invention, the thickness of the covalent organic framework film is preferably 1-30 mu m.

The invention provides a high-sensitivity wearable humidity sensor based on a flexible film sensitive material, which comprises a sensitive material based on a covalent organic framework film and a flexible wearable interdigital electrode; wherein: covalent organic framework film materials are prepared on a plurality of flexible substrates by adopting a photochemical method and a steam-assisted synthesis method; the flexible wearable sensor is manufactured on the surface of a covalent organic framework film by a photoetching technology and a mask evaporation technology, namely the humidity sensor is of a layered structure and sequentially comprises a substrate layer, a covalent organic framework film layer and interdigital electrodes from bottom to top.

In the preparation method of the flexible wearable humidity sensor, the flexible wearable interdigital electrode is prepared on the surface of the covalent organic framework film which grows uniformly on the surface by any one of a photoetching method and a metal mask coverage method:

(1) The preparation method of the interdigital electrode comprises the following steps:

and step C1, spin-coating photoresist on the surface of the covalent organic framework film at a rotating speed of 500-2500 rpm for 2-4 mu m, and baking at 70-110 ℃ (preferably 70-90 ℃) for 1-3 min.

Step C2. is to cover the surface of the photoresist with the photoetching mask plates with the interdigital electrode patterns with different pitches of 20-100 μm, expose for 5-10 s under an ultraviolet photoetching machine, and bake for 1-3 min at 70-110 ℃.

Step C3., the film is put into a developing solution to oscillate for 60-120 s, a patterned photoresist layer is formed, and 30-100 nm Au is evaporated on the surface of the photoresist layer.

And step C4, processing the film with the patterned Au evaporated on the surface at the constant temperature and humidity within the humidity range of 30-70 ℃ and 30-70% for 12-24 hours to obtain the humidity sensor with stable performance based on the covalent organic framework film sensitive layer.

(2) The preparation method of the interdigital electrode by the stainless steel mask plate method comprises the following steps:

and D1, placing the flexible substrate prepared into the covalent organic framework film into an evaporation instrument, covering a metal mask plate with 100-150 mu m interdigital electrodes at different intervals, and evaporating 30-100 nm Au.

And D2., processing the film with the patterned Au evaporated on the surface for 12-24 hours at constant temperature and humidity (30-70 ℃ and 30-70% humidity) to obtain the humidity sensor with stable performance based on the covalent organic framework film sensitive layer.

The photolithography mask in the step C2 is any one of a glass mask plated with patterned metal chromium and a polymer mask printed with patterned electrodes. The metal mask plate in the step D1 is a stainless steel plate for carving the electrode pattern by laser.

The humidity sensor prepared by the invention adopts the humidity-sensitive flexible covalent organic framework film sensitive material, can realize the linear response of the logarithmic value of the resistance in the range of 11% -98% relative humidity, and has excellent performance consistency under different bending angles.

The invention is further illustrated by the following specific examples.

Example 1

The preparation method of the COF-5 film provided in the embodiment 1 comprises the following steps:

step 1, cutting a polyimide substrate with the thickness of 0.125mm into a rectangle with proper size, respectively putting into deionized water and absolute ethyl alcohol for ultrasonic cleaning for 15min, and then treating the surface for 90s by using oxygen plasma.

Step 2. Under nitrogen atmosphere, 0.04mmol 2,3,6,7,10,11-hexahydroxytriphenyl, 0.04mmol of 1, 4-benzenediboronic acid are dissolved in 1mL of absolute ethanol and acetone 1:1, oscillating for 3min, and then performing ultrasonic treatment for 20min at 1500W power to obtain a clear precursor solution.

And 3, dripping the obtained precursor solution on the cleaned polyimide substrate in a volume of 50 mu L.

Step 4. The polyimide substrate with the precursor solution spread thereon is placed in a closed vessel filled with nitrogen gas along with a petri dish with a 1:1 mixture of 1,3, 5-trimethylbenzene and 1, 4-dioxane added thereto in an amount of 14 mL.

And 5, taking out the substrate after reacting for 72 hours at room temperature, and vacuum drying after nitrogen purging the surface for 3 minutes to obtain the sensitive material based on the covalent organic framework film, wherein the thickness distribution of the covalent organic framework film is 4.4 mu m.

Example 2

The preparation method of the COF-5 film provided in the embodiment 2 comprises the following steps:

step 1, cutting a polyethylene terephthalate substrate with the thickness of 0.1mm into a rectangle with a proper size, respectively putting into deionized water and absolute ethyl alcohol for ultrasonic cleaning for 20min, and then treating the surface for 60s by using oxygen plasma.

Step 2. Under nitrogen atmosphere, 0.06mmol 2,3,6,7,10,11-hexahydroxytriphenyl, 0.06mmol of 1, 4-benzenediboronic acid are dissolved in 1mL of absolute ethanol and acetone 1:1, oscillating for 3min, and then performing ultrasonic treatment for 20min at 1500W power to obtain a clear precursor solution.

And 3, dripping the obtained precursor solution on the cleaned polyimide substrate in a volume of 100 mu L.

Step 4. Polyimide substrates with different volumes of precursor solutions spread out were placed in a closed vessel filled with nitrogen, along with a petri dish with 10mL of a 1:1 mixture of 1,3, 5-trimethylbenzene and 1, 4-dioxane added.

And 5, taking out the substrate after reacting for 72 hours at room temperature, and vacuum drying after nitrogen purging the surface for 3 minutes to obtain the sensitive material based on the covalent organic framework film, wherein the thickness of the covalent organic framework film is distributed at 23.14 mu m.

Example 3

The preparation method of the COF-5 film provided in the embodiment 3 comprises the following steps:

step 1, cutting a polyethylene terephthalate substrate with the thickness of 0.1mm into a rectangle with proper size, respectively putting into deionized water and absolute ethyl alcohol for ultrasonic cleaning for 20min, and then treating the surface for 60s by using oxygen plasma.

And 3, dripping the obtained precursor solution on the cleaned polyethylene terephthalate substrate in a volume of 80 mu L.

Step 4. Polyimide substrates with different volumes of precursor solutions spread out are placed in a closed vessel filled with nitrogen gas along with 14mL of a 1:1 mixture of 1,3, 5-trimethylbenzene and 1, 4-dioxane.

And 5, taking out the substrate after reacting for 24 hours at room temperature, and vacuum drying after nitrogen purging the surface for 3 minutes to obtain the sensitive material based on the covalent organic framework film, wherein the covalent organic framework film has good crystallinity.

Example 4

The photochemical preparation method of the COF-5 film provided in the embodiment 4 comprises the following steps:

And 3, dripping the obtained precursor solution on the cleaned polyimide substrate in a volume of 80 mu L.

Step 4, putting the polyimide substrate spread with different volumes of precursor solution and 10mL of 1:1 mixed solution of 1,3, 5-trimethylbenzene and 1, 4-dioxane into a glass closed container filled with nitrogen, and preserving for 24 hours at room temperature.

And 5, placing the substrate and the sealed glass container under an Hg lamp for ultraviolet irradiation, wherein the irradiation time is 9h.

And 6, standing the container after ultraviolet irradiation is finished, continuously reacting for 24 hours, taking out the substrate, purging the surface with nitrogen for 3 minutes, and then performing vacuum drying to obtain the sensitive material based on the covalent organic framework film.

Application example 1

The preparation method of the COF-5 film humidity sensor provided in application example 1 comprises the following steps:

step 1. The flexible substrate with the covalent organic framework film prepared in the embodiment 1 is placed into an evaporation instrument, metal masks with 100-150 mu m of different spacing interdigital electrodes are covered and then 30nm of Au is evaporated, then the masks are taken down, and nitrogen is purged for 3min.

And 2, processing the film with the patterned Au evaporated on the surface for a period of time at 70 ℃ and 40% humidity to obtain the humidity sensor with stable performance based on the covalent organic framework film sensitive layer.

Application example 2

The preparation method of the COF-5 film humidity sensor provided in application example 2 comprises the following steps:

step 1. The surface of the covalent organic framework film obtained in example 1 was spin coated with ROL-7133 photoresist at 2000 rpm, baked at 110℃for 90 seconds and cooled to room temperature.

And 2, covering a photoetching mask plate with 20-50 mu m interdigital electrode patterns at different intervals on the surface of the photoresist, exposing for 6s in an ultraviolet photoetching machine, and then baking for 90s at 110 ℃.

And step 3, putting the film into a developing solution, oscillating for 80 seconds to form a patterned photoresist layer, and evaporating 50nm Au on the surface of the photoresist layer.

And 4, placing the substrate into a photoresist removing solution, soaking for 4 hours, oscillating, stripping the redundant photoresist and Au layer attached to the surface of the COF-5 film, blowing for 5 minutes by using nitrogen, and drying at 70 ℃.

And 5, carrying out vacuum drying treatment on the film with the patterned Au on the surface for a period of time to obtain the humidity sensor with stable performance based on the covalent organic framework film sensitive layer.

Test analysis

The surface morphology of the COF-5 film prepared in example 1 is shown in FIG. 1. Under different magnification, it can be clearly seen that the surface of the formed film presents a uniform fiber structure, and the whole forms mutually communicated pore channels. The morphology can provide a large specific surface area for the sensor sensitive layer, so that more active sites are exposed to interact with water molecules, and the response capability of the sensor is improved. Meanwhile, the uniform surface morphology is beneficial to reducing electronic defects at the grain boundary of the surface of the material, improving the resistance change of the sensitive layer adsorbed water molecules and further improving the sensitivity of the sensor.

Inventive example 2The infrared spectrum of the COF-5 film is shown in FIG. 2. The infrared spectrum result in FIG. 2 shows that the prepared COF-5 film is at 1395cm ^-1 And 1345cm ^-1 The telescopic vibration peak of B-O bond in boric acid group appears at 1242cm ^-1 A C-O bond stretching vibration peak in the borate group appears at the position, which indicates the formation of covalent bonds in the COF-5 structure.

The results of the water contact angle test of the surface of the COF-5 film in example 3 of the present invention are shown in FIG. 3. The contact angle of water on the surface of the prepared COF-5 film was 104.7 DEG at the initial stage of dropping (a graph), and after the spreading process was continued for 30 seconds (b graph), the water drop was spread and the contact angle was maintained at 39.8 deg. This indicates that the hydrophilic surface of the COF-5 film can enhance its adsorption ability to water molecules in a humid environment, exhibiting a greater degree of humidity-sensitive response characteristics.

The XRD spectrum of the COF-5 film prepared in example 4 of the present invention is shown in FIG. 4. Diffraction peaks of the prepared COF-5 film at 3.42 degrees, 5.93 degrees, 6.88 degrees and 9.10 degrees correspond to (100), (110), (200) and (210) crystal faces of the COF-5 crystal respectively. (100) The high intensity of diffraction peaks of the crystal faces indicates that the COF-5 has a good periodic structure in the growth of the two-dimensional plane.

FIG. 5 shows the results of the humidity sensor performance test of application example 1 in a 15% -84% humidity environment formed by gradually dripping deionized water into the test cavity to heat and volatilize and continuously introducing artificial dry air. The result shows that the humidity response performance of the sensor is stable in the 4000s test process, the resistance change spans 4 orders of magnitude, and the logarithmic function of the resistance and the humidity show a nearly linear change relation. Meanwhile, the sensor shows high performance consistency under the conditions of straight, 30-degree bending and 90-degree bending of humidity sensitivity performance test results and humidity response functions, when the humidity is below 50%, the bending has no obvious influence on the performance of the device, and when the humidity is higher, the sensor with 90-degree bending has the humidity response functions which are more in line with the linear relation, which is probably caused by the acceleration of desorption of water molecules in the material under the bending state.

Fig. 6 is a response curve of a device when a human fingertip is close to the sensor obtained in application example 2. As a result, the surface sensor can capture a small amount of water vapor volatilized from the skin of a human fingertip and generate an obvious response when the distance is small, so that the sensor has application potential in a non-contact switch.

Comparative example 1

The preparation method of the covalent organic framework film is replaced by the preparation method in CN201911273052.5, so that the one-dimensional rod-like crystal material is obtained, the macroscopic appearance is a white powder indissolvable in an organic solvent, and a film with uniform thickness and controllable thickness cannot be formed on the surface of the flexible substrate. The one-dimensional rod-shaped crystals are distributed in organic solvents such as acetone to form slurry, and a film formed by dripping the slurry on the surface of the interdigital electrode is easy to fall off in the bending process, so that the film cannot be used in the field of wearable humidity sensing detection.

Comparative example 2

The reaction temperature in step 5 was set to 50℃and the other conditions were the same as in example 1.

As a result, it was found that the precursor solution was rapidly volatilized on the surface of the flexible substrate, and thus the synthesized COF-5 film could not completely cover the substrate, and the surface morphology and film thickness were uneven, and the film crystallization strength was greatly lowered. Thus, at higher temperatures, the reaction temperature of 5-30℃is preferred in the present invention, which is detrimental to the polymerization and crystallization process of the reactive monomer of COF-5 in the precursor solution.

The invention provides a high-sensitivity wearable humidity sensor based on a flexible film sensitive material and a preparation method thereof, wherein a covalent organic framework film is used as a humidity sensitive material in the method, and a photochemical method and a steam-assisted synthesis method are involved; the invention discloses a flexible wearable humidity sensor manufactured by a plurality of flexible substrates, which relates to a photoetching process and a mask evaporation process, and interdigital electrodes with different sizes are prepared on the surface of a covalent organic framework film. In the covalent organic framework film prepared by the invention, the sensor has quick response/recovery performance due to the strong hydrophilic characteristic of the borate ester bond and the uniform and porous characteristics of the film, and the logarithmic function of the resistance of the sensor has a linear relation with the environmental humidity. The covalent organic framework film prepared by the steam assisted method has the characteristics of adjustable thickness and high flexibility, and the prepared humidity sensor has excellent performance consistency under any bending angle, can realize the functions of human respiration monitoring, humidity change detection when fingertips are close, and the like, and has huge application prospects of wearable electronic devices and medical monitoring.

The above-described embodiments of the present invention do not limit the scope of the present invention. Any other corresponding changes and modifications made in accordance with the technical idea of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a sensitive material based on a covalent organic framework film, comprising the steps of:

(2) Dripping the precursor solution onto the surface of the pretreated substrate, placing the substrate and the open vessel filled with the solvent B into a reactor, and sealing;

(3) Synthesizing a solid film on the surface of a substrate by a steam auxiliary method or/and a photochemical reaction method, and cleaning and drying to obtain the sensitive material;

in the step (1), monomers of the COF-5 material are 2,3,6,7,10, 11-hexahydroxytriphenyl and 1, 4-phenyldiboronic acid, a solvent A is a mixture of absolute ethyl alcohol and acetone, and the addition ratio of the 2,3,6,7,10, 11-hexahydroxytriphenyl, 1, 4-phenyldiboronic acid, the absolute ethyl alcohol and the acetone is (0.01-0.06) mmol (0.2-0.8) mL;

in the step (2), the substrate is polyimide, polyethylene terephthalate, borosilicate glass, porous fiber, conductive FTO glass or flexible ITO/PEN; the solvent B is a mixture of 1,3, 5-trimethylbenzene and 1, 4-dioxane in any proportion.

2. The method for preparing a sensitive material based on a covalent organic framework film according to claim 1, wherein in step (2), the ratio of the volume of the precursor solution dispensed to the volume of the solvent B is (40-200 μl): (5-20) mL.

3. The method for preparing a sensitive material based on a covalent organic framework film according to claim 1, wherein in the step (3), the steam assisted method is carried out at 5-30 ℃ for 12-72 hours.

4. The method for preparing the sensitive material based on the covalent organic framework film according to claim 1, wherein in the step (3), the photochemical reaction method is that the sensitive material is preserved for 3-24 hours at room temperature, then is irradiated for 3-9 hours under the ultraviolet light condition, and then is continuously reacted for 3-36 hours; the ultraviolet light conditions were provided by a 300w power, dominant wavelength 365nm Xe lamp or Hg lamp.

5. A sensitive material based on a covalent organic framework film produced by the production method according to any one of claims 1 to 4.

6. A humidity sensor comprising an interdigitated electrode and a sensing material of claim 5 comprising a substrate and a covalent organic framework film disposed on the substrate, the interdigitated electrode being disposed on a surface of the covalent organic framework film.

7. The method for manufacturing a humidity sensor as claimed in claim 6, comprising the steps of:

8. The method of claim 7, wherein in step (i), the photo-etching-vapor deposition method is to spin-coat a photoresist on the surface of the covalent organic framework film, and form a patterned photoresist layer by exposure and development; evaporating 30-100 nm Au on the photoresist layer;