Sulfonic acid covalent organic framework material, preparation method thereof and humidity sensor

Abstract

The present invention belongs to the field of gas humidity sensing and relates to a sulfonic acid covalent organic framework material, a preparation method thereof and a humidity sensor. The preparation method of the sulfonic acid covalent organic framework material provided by the present invention comprises the following steps: S1: dissolving 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde in octanoic acid to prepare solution A; S2: dissolving 2,5-diaminobenzenesulfonic acid in water to prepare solution B; S3: adding solution B dropwise to the upper layer of solution A and allowing to react; S4: after the reaction is completed, removing the upper clear liquid, dialyzing the lower red aqueous solution, and obtaining a sulfonic acid covalent organic framework material. The sulfonic acid covalent organic framework material provided by the present invention has the potential to become a humidity-sensitive material. The humidity sensor provided by the present invention is based on COF material and quartz crystal microbalance, has the advantages of good hydrophilicity, high sensitivity, fast response recovery, and good dynamic response, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the field of gas humidity sensing, and in particular to a sulfonic acid covalent organic framework material, a preparation method thereof, and a humidity sensor. Background Art

[0002] Covalent organic framework materials (COFs) are crystalline porous polymer materials composed of organic molecules connected by covalent bonds. COFs have the characteristics of low density, high specific surface area and easy modification and functionalization. Therefore, they are widely used in gas storage and separation, heterogeneous catalysis, photoelectric conduction, drug delivery and sensing. In the field of humidity sensing, humidity sensing is currently mainly based on the change of color and impedance of COFs at different humidity levels. For example, Pal et al. synthesized COF-TXDBA through Schiff base reaction and can detect environmental humidity by changing the impedance of COFs, but this humidity detection method is relatively cumbersome.

[0003] The humidity sensor consists of three parts: a humidity sensing device, a conversion device, and a measurement circuit. Its working principle is mainly to use the conversion element to convert the measured humidity into a physical quantity that is easy to analyze, and then measure it by the instrument. At present, the commonly used humidity sensors are mainly electrical humidity sensors, optical humidity sensors, and mass humidity sensors. The sensing of electrical humidity sensors depends on the change of electrical signals. Although it has the advantages of simple structure and low cost, its stability is poor and it cannot be used in high-demand scenarios; optical humidity sensors have the advantages of fast response speed and high sensitivity, but due to principle limitations, optical humidity sensors have poor anti-interference ability.

[0004] Mass humidity sensors are based on the mass effect of sensitive elements and are made by utilizing the relationship between the oscillator parameters (frequency, amplitude, wave velocity, etc.) of a specific shape of piezoelectric crystal and the change of its surface mass. They have the advantages of strong anti-interference ability and a wide range of applications.

[0005] Chinese invention patent publication number CN109883877A discloses a quartz crystal microbalance and humidity sensor based on metal-organic framework (MOF) materials. This humidity sensor uses MOF materials as humidity-sensitive materials, combined with a quartz crystal microbalance, to produce a humidity sensor capable of detecting humidity levels in the ppm range. However, MOFs are porous materials based on metal-organic coordination bonds, and their limited chemical bond strength leads to stability bottlenecks in their application. In particular, in aqueous conditions, metal ions easily hydrate with water molecules, affecting the MOF's pore structure and potentially significantly reducing the humidity sensor's detection accuracy.

[0006] In addition, there is currently no precedent for applying COFs materials to mass-type humidity sensors. Summary of the Invention

[0007] The object of the present invention is to provide a humidity sensor with good stability and high sensitivity based on a covalent organic framework material.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a sulfonic acid covalent organic framework material, which specifically comprises the following steps:

[0009] S1: dissolving 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde in octanoic acid to prepare solution A;

[0010] S2: dissolving 2,5-diaminobenzenesulfonic acid in water to prepare solution B;

[0011] S3: Add solution B dropwise to the upper layer of solution A and let it stand for reaction;

[0012] S4: After the reaction is completed, the upper clear liquid is removed and the lower red aqueous solution is dialyzed to obtain a sulfonic acid covalent organic framework material.

[0013] Currently, the preparation methods of COFs include mechanical grinding, microwave synthesis, and solvent thermal methods. Among them, mechanical grinding and microwave synthesis can only be processed into solid powder materials by direct tableting, and the COFs powder samples prepared by tableting have poor solubility, low conductivity efficiency, and cannot be connected to the device. The solvent thermal method has high reaction temperature, long reaction time, and consumes a large amount of solvent, with the disadvantages of high energy consumption and high production cost. The present invention adopts interfacial polymerization to prepare sulfonic acid covalent organic framework materials. The reaction conditions of this preparation method are mild. At the same time, the whole process conditions of synthesizing sulfonic acid covalent organic framework materials using this method are controllable.

[0014] Preferably, the molar ratio of the 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde to 2,5-diaminobenzenesulfonic acid is 1:(1-2).

[0015] The second aspect of the present invention provides a sulfonic acid covalent organic framework material prepared by the preparation method of the first aspect.

[0016] The sulfonate loading amount of the sulfonic acid covalent organic framework material provided by the present invention reaches 3.2 mmol / g or more, which makes the sulfonic acid covalent organic framework material provided by the present invention have good water retention.

[0017] The third aspect of the present invention provides a humidity sensor, which includes a quartz crystal microbalance and the sulfonic acid covalent organic framework material described in the second aspect. The quartz crystal microbalance includes an electrode, and the sulfonic acid covalent organic framework material is coated on part or all of the surface of the electrode of the quartz crystal microbalance.

[0018] The humidity sensor provided by the present invention combines the sulfonic acid covalent organic framework material of the second aspect and a quartz crystal microbalance for the first time. The humidity sensor obtained has the advantages of high sensitivity and high precision of the quartz crystal microbalance sensor and good water retention of the sulfonic acid covalent organic framework material.

[0019] Preferably, the resonant frequency of the humidity sensor is 19-21 MHz.

[0020] Preferably, the coating amount of the sulfonic acid covalent organic framework material is at least 170 ng.

[0021] Preferably, the humidity sensor further includes an oscillation circuit for collecting sensing data and a computer for processing the sensing data.

[0022] A fourth aspect of the present invention provides a method for preparing a humidity sensor, comprising the following steps:

[0023] SA: Preparation of sulfonic acid covalent organic framework materials;

[0024] SB: Preparation of aqueous solution of sulfonic acid covalent organic framework material;

[0025] SC: A sulfonic acid covalent organic framework material aqueous solution is added dropwise to the electrode surface of a quartz crystal microbalance and dried to obtain a humidity sensor.

[0026] Preferably, in step SB, the concentration of the aqueous solution of the sulfonic acid covalent organic framework material is 0.1-0.5 mg / mL.

[0027] In the above-mentioned preparation method of the humidity sensor, the sulfonic acid covalent organic framework material is directly coated on the surface of the quartz crystal microbalance. This preparation method has the advantage of simple operation.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention provides a sulfonic acid covalent organic framework material, which has excellent water retention properties, making the sulfonic acid covalent organic framework material have the potential to become a humidity-sensitive material;

[0030] 2. The preparation method of the sulfonic acid covalent organic framework material provided by the present invention has controllable parameters, mild reaction conditions, and broad application prospects;

[0031] 3. This invention is the first to combine a sulfonic acid covalent organic framework material with a quartz crystal microbalance to fabricate a humidity sensor. This humidity sensor exhibits excellent sensing performance in the humidity range of 11% to 97%, providing new research ideas for the development of subsequent humidity sensors.

[0032] 4. The preparation method of the humidity sensor provided by the present invention is simple to operate and has the potential for large-scale production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The experimental results of the contact angle analysis in Example 3;

[0034] Figure 2 The measurement results of the frequency response of the humidity sensor in Example 4;

[0035] Figure 3 Response and recovery curves of the QCM-1 measured continuously under the lowest (11% RH) and highest (97% RH) humidity environments in Example 6;

[0036] Figure 4 Response and recovery curves of the QCM-2 measured continuously under the lowest (11% RH) and highest (97% RH) humidity environments in Example 6;

[0037] Figure 5 Response and recovery curves of the QCM-3 measured continuously under the lowest (11% RH) and highest (97% RH) humidity environments in Example 6;

[0038] Figure 6 Response and recovery curves of the QCM-4 measured continuously under the lowest (11% RH) and highest (97% RH) humidity environments in Example 6;

[0039] Figure 7 The response and recovery curves of the QCM-5 measured continuously in the lowest (11% RH) and highest (97% RH) humidity environments in Example 6 are shown in FIG.

[0040] Figure 8 : is the dynamic response characteristic curve of each humidity sensor in Example 7. DETAILED DESCRIPTION

[0041] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only intended to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter ranges described in the present invention. Reasonable variations derived therefrom are still within the scope of protection of the claims of the present invention.

[0042] It should be noted that the endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0043] Although it has been demonstrated that porous materials such as MOFs combined with a quartz crystal microbalance (QCM) have the potential to become humidity sensors, there are currently no reports on humidity sensors based on covalent organic framework materials and QCMs. Therefore, a specific embodiment of the present invention provides a method for preparing a sulfonic acid-based covalent organic framework material, which specifically includes the following steps:

[0044] S1: dissolving 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde in octanoic acid to prepare solution A;

[0045] S2: dissolving 2,5-diaminobenzenesulfonic acid in water to prepare solution B;

[0046] S3: Add solution B dropwise to the upper layer of solution A and let it stand for reaction;

[0047] S4: After the reaction is completed, the upper clear liquid is removed and the lower red aqueous solution is dialyzed to obtain a sulfonic acid covalent organic framework material.

[0048] In some specific embodiments, the molar ratio of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde to 2,5-diaminobenzenesulfonic acid is 1:(1-2).

[0049] The sulfonic acid covalent organic framework material prepared according to the above method has a sulfonate loading amount of more than 3.2 mmol / g, which makes the sulfonic acid covalent organic framework material have good water retention performance.

[0050] A specific embodiment of the present invention also provides a humidity sensor, which includes a quartz crystal microbalance and the aforementioned sulfonic acid covalent organic framework material. The quartz crystal microbalance includes an electrode, and the sulfonic acid covalent organic framework material is coated on part or all of the surface of the electrode of the quartz crystal microbalance.

[0051] The humidity sensor of the above embodiment is manufactured by the following steps:

[0052] SA: Preparation of sulfonic acid covalent organic framework materials;

[0053] SB: Prepare an aqueous solution of a sulfonic acid covalent organic framework material, the concentration of which is 0.1-0.5 mg / mL;

[0054] SC: A sulfonic acid covalent organic framework material aqueous solution is added dropwise to the electrode surface of a quartz crystal microbalance and dried to obtain a humidity sensor.

[0055] In the above embodiment, a sulfonic acid covalent organic framework material thin film can be formed on the surface of the quartz crystal microbalance electrode by dropping a sulfonic acid covalent organic framework material aqueous solution onto the surface of the quartz crystal microbalance electrode and drying the solution.

[0056] The working principle of the humidity sensor provided by the above embodiment is as follows: when the humidity sensor is in a humidity environment of 11% to 97% and the ambient humidity rises, the sulfonic acid covalent organic framework material film, which is a humidity-sensitive material, will absorb water and change its own mass due to the change in ambient humidity. The changed mass can be reflected according to the oscillation frequency of the quartz crystal microbalance. Therefore, it is only necessary to collect and measure the change in the oscillation frequency of the quartz crystal microbalance through an oscillation circuit to reversely obtain the ambient humidity data.

[0057] The technical scheme of the present invention is further described below by specific examples, unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as those skilled in the art to which the present invention belongs. In some cases, this paper is for illustrating or facilitating the definition of terms with conventional understanding meanings for the purpose of quoting, and such limitations herein should not be construed as representing that there are significant differences from conventional understandings in this area. The technical methods described herein or cited are generally fully understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available reagents and instruments is carried out according to the scheme and parameters given by the manufacturer.

[0058] In a specific embodiment of the present invention, the saturated salt solution shown in Table 1 is used to provide the corresponding relative humidity.

[0059] Table 1

[0060]

[0061] Example 1

[0062] Preparation of sulfonic acid-based covalent organic framework materials.

[0063] S1: 0.1 mM 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde was sonicated for 30 min and then dissolved in 20 mL of octanoic acid to prepare solution A;

[0064] S2: 0.1 mM 2,5-diaminobenzenesulfonic acid was sonicated for 30 min and then dissolved in 30 mL of water to prepare solution B;

[0065] S3: Add solution B dropwise to the upper layer of solution A and let it react at 20°C for 3 days;

[0066] S4: After the reaction is completed, the upper clear liquid is removed and the lower red aqueous solution is dialyzed for 2 days to obtain a sulfonic acid covalent organic framework material dispersion. The concentration of the sulfonic acid covalent organic framework material is calibrated to 1 mg / mL by dry weighing method.

[0067] Example 2

[0068] Humidity sensor assembly.

[0069] The five quartz crystal microbalance (QCM) elements used in this example were from Yangxing Technology. They had a fundamental frequency of 20 MHz and silver electrodes with a diameter of 4 mm. After exposing the silver electrodes, they were cleaned with ethanol and water to ensure that the surfaces were free of dirt. The frequencies of the cleaned and dried QCM elements were measured and the relevant data recorded.

[0070] The sulfonic acid covalent organic framework material dispersion prepared in Example 1 was diluted with ddH2O. The concentrations of the diluted sulfonic acid covalent organic framework material solutions were 0.1 mg / mL, 0.2 mg / mL, 0.3 mg / mL, 0.4 mg / mL, and 0.5 mg / mL, respectively.

[0071] The above five concentrations of sulfonic acid covalent organic framework material solutions were respectively added dropwise onto the surfaces of five quartz crystal microbalance silver electrodes. After drying in a vacuum oven at 85°C, humidity sensors were obtained. The five humidity sensors were labeled as QCM-1 (0.1 mg / mL), QCM-2 (0.2 mg / mL), QCM-3 (0.3 mg / mL), QCM-4 (0.4 mg / mL), and QCM-5 (0.5 mg / mL). The frequencies of the five humidity sensors were measured and recorded.

[0072] Connect the five humidity sensors mentioned above to the oscillation circuit board, and store all components in a dry container.

[0073] Example 3

[0074] Contact angle analysis.

[0075] The sulfonic acid covalent organic framework material solutions of five concentrations prepared in Example 2 were added dropwise onto a smooth quartz glass and dried to form a COF film. The contact angle of the corresponding COF film was measured using a contact angle meter. The relevant results are shown in Table 2 and Figure 1 shown.

[0076] Table 2

[0077]

[0078] From Table 2 and Figure 1 It can be seen that as the mass of the sulfonic acid covalent organic framework material film increases, the water contact angle gradually decreases, which means that the hydrophilicity of the material gradually increases, which means that the covalent organic framework material provided by the present invention has good hydrophilicity.

[0079] Example 4

[0080] Frequency response.

[0081] Using the five humidity sensors prepared in Example 2, the frequency variation of the sensors was measured in a humidity environment ranging from 11% to 97% and a linear fit was performed. The relevant experimental results are shown in Table 3 and Figure 2 As shown, Figure 2 A in the figure is the frequency response curve of the corresponding humidity sensor under different humidity conditions. Figure 2 B in FIG is the frequency logarithmic fitting curve of the corresponding humidity sensor under different humidity conditions.

[0082] Table 3

[0083]

[0084] From Table 3 and Figure 2 It can be seen that under the ambient humidity of 11%~97%, the frequency shift of the five humidity sensors shows an upward trend with the increase of humidity, indicating that they have strong humidity sensing characteristics, and the frequency change value increases with the increase of the concentration of sulfonic acid covalent organic framework material. The logarithm of the frequency change has a good linear fitting effect with the relative humidity, and the five humidity sensors all have a good linear correlation coefficient.

[0085] Example 5

[0086] Sensitivity test.

[0087] A frequency meter was used to measure the frequency values ​​of five quartz crystal microbalances before and after coating the sulfonic acid covalent organic framework material film. According to the simplified Sauerbrey equation (1), the film mass can be obtained. The relevant results are shown in Table 4.

[0088] The table shows that as the mass of the sulfonic acid covalent organic framework film increases, the sensitivity of the humidity sensor increases. Sensitivity is defined as the slope of the QCM frequency change versus relative humidity fitting curve, indicating the speed of the frequency output when the humidity changes. The calculation formula is shown in Equation (1).

[0089] (1)

[0090] Where, is the frequency change value, is the QCM fundamental frequency, 20 MHz, is the membrane mass, and A is the area of ​​the QCM silver electrode.

[0091] Table 4

[0092]

[0093] Example 6

[0094] Response-recovery time determination.

[0095] The response-recovery time refers to the time required for the sensor frequency shift to reach 90% of the total frequency shift change during the process of moisture absorption and dehumidification. Figure 3 The response and recovery curves of the QCM-1 under continuous measurements at the lowest (11% RH) and highest (97% RH) humidity environments are shown; Figure 4 The response and recovery curves of the QCM-2 under continuous measurement in the lowest (11% RH) and highest (97% RH) humidity environments are shown; Figure 5 The response and recovery curves of the QCM-3 under continuous measurement in the lowest (11% RH) and highest (97% RH) humidity environments are shown; Figure 6 The response and recovery curves of the QCM-4 under continuous measurement in the lowest (11% RH) and highest (97% RH) humidity environments are shown; Figure 7 The response and recovery curves of the QCM-5 are shown for continuous measurements at the lowest (11% RH) and highest (97% RH) humidity levels. The response and recovery times of QCM-1, QCM-2, QCM-3, QCM-4, and QCM-5 are shown in Table 5. QCM-2 exhibits excellent response / recovery performance (15 seconds and 1 second, respectively).

[0096] Table 5

[0097]

[0098] Example 7

[0099] Dynamic response characteristics determination.

[0100] Five humidity sensors were placed in the humidity generator in sequence. The humidity increased from the minimum value of 11% RH to the maximum value of 97% RH, and then decreased from the maximum value of 97% RH to the minimum value of 11% RH. The response time of each device was 10 minutes, and the dynamic response characteristic curve was as follows: Figure 4 As shown in Table 6, the reaction is essentially stable after 10 minutes, and the results are relatively accurate. The humidity hysteresis measurement results of the humidity sensor in the range of 11% RH to 97% RH are shown in Table 6. In the range of 11% RH to 97% RH, the maximum humidity hysteresis is 15.40%.

[0101] Table 6

[0102]

[0103] As can be seen from Table 6, the humidity hysteresis of the humidity sensor provided by the present invention is good. The reason for the humidity hysteresis is that during the humidity increase process, due to the adsorption of water molecules in the salt solution, as the humidity increases, the adsorption amount of water molecules increases, the film thickness increases, and the output frequency of the sensor decreases. Conversely, during the decrease process, the adsorption amount of water molecules decreases, the film thickness decreases, and the vibration frequency of the sensor decreases. However, since the sulfonic acid covalent organic framework material film previously adsorbed a certain amount of water molecules to form a surface state, the water molecules cannot be completely desorbed, and residues are formed on the surface of the sulfonic acid covalent organic framework material film, resulting in a low output frequency and hysteresis.

[0104] As can be seen from Examples 1 to 7, the humidity sensor provided by the present invention has the advantages of good hydrophilicity, high sensitivity, fast response-recovery, and good dynamic response, and has broad application prospects.

[0105] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A humidity sensor, characterized in that: The humidity sensor includes a quartz crystal microbalance sulfonic acid covalent organic framework material, the quartz crystal microbalance includes an electrode, the sulfonic acid covalent organic framework material is coated on part or all of the surface of the electrode of the quartz crystal microbalance, and the sulfonic acid covalent organic framework material is prepared by the following steps: S1: dissolving 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde in octanoic acid to prepare solution A, wherein the molar ratio of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde to 2,5-diaminobenzenesulfonic acid is 1:(1-2); S2: dissolving 2,5-diaminobenzenesulfonic acid in water to prepare solution B; S3: Add solution B dropwise to the upper layer of solution A and let it react at 20°C for 3 days; S4: After the reaction is completed, the upper clear liquid is removed and the lower red aqueous solution is dialyzed to obtain a sulfonic acid covalent organic framework material.

2. The humidity sensor according to claim 1, wherein The resonant frequency of the humidity sensor is 19-21 MHz.

3. The humidity sensor according to claim 1, wherein The coating amount of the sulfonic acid covalent organic framework material is at least 170 ng.

4. The humidity sensor according to claim 1, wherein The humidity sensor further comprises an oscillating circuit for collecting sensing data and a computer for processing the sensing data.

5. A method for preparing the humidity sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: SA: Preparation of sulfonic acid covalent organic framework materials; SB: Preparation of aqueous solution of sulfonic acid covalent organic framework material; SC: A sulfonic acid covalent organic framework material aqueous solution is added dropwise to the electrode surface of a quartz crystal microbalance and dried to obtain a humidity sensor.

6. The preparation method according to claim 5, wherein In the step SB, the concentration of the aqueous solution of the sulfonic acid covalent organic framework material is 0.1-0.5 mg / mL.

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