Gallic acid-based MOF gas sensitive material and preparation method and application thereof

Abstract

This invention discloses gallic acid-based MOF gas-sensitive materials, their preparation methods, and applications. The preparation method of the gallic acid-based MOF gas-sensitive material includes the following steps: dissolving a metal salt and gallic acid in an alkaline solution and reacting them at 110-150°C to obtain the gallic acid-based MOF gas-sensitive material; the metal salt is selected from one or more of the nitrates, sulfates, and hydrochlorides of cobalt, magnesium, and nickel; the molar ratio of the metal salt to gallic acid is 1:(1.5-2.5). This invention uses the gallic acid-based MOF gas-sensitive material to prepare QCM gas sensors, especially QCM-type ammonia sensors. Compared with Mg-Gallate MOF-based and Ni-Gallate MOF-based QCM gas sensors, the Co-Gallate MOF-based QCM gas sensor exhibits superior selectivity and good sensitivity for ammonia.

Description

Gallic acid-based MOF gas-sensitive materials, their preparation methods and applications Technical Field

[0001] This invention relates to the field of gas-sensitive materials technology, specifically to gallic acid-based MOF gas-sensitive materials, their preparation methods, and applications. Background Technology

[0002] The Quartz Crystal Microbalance (QCM) is a highly sensitive mass measurement instrument with advantages such as simple structure, low cost, high sensitivity, and measurement accuracy down to the nanogram level. Its applications can be further broadened by selectively depositing films on the metal electrodes (substrate), for example, by adding a selectively sensitive film to the electrode surface. When the sensitive film adsorbs gas, it causes a change in the frequency of the quartz crystal, which can be used to detect the gas being measured. Therefore, the material constituting the sensitive film (gas-sensitive material) is crucial to the QCM gas sensor.

[0003] Currently, various materials have been used to fabricate QCM-type gas sensors, such as metal oxides, polyaniline / titanium dioxide composites, triethanolamine, and polypropylene oxide. Metal oxides are the most studied class of gas-sensitive materials; metal oxide gas sensors detect the composition of gases in the surrounding environment by measuring their resistance values. Carbon nanotubes, as gas-sensitive materials, have a hollow structure and a large specific surface area, exhibiting a high adsorption capacity for gases. Conductive polymers are a class of organic semiconductor gas-sensitive materials, possessing excellent chemical stability and gas sensitivity. While these materials each have their advantages in application, they also have some drawbacks. For example, the preparation process of composite materials is complex and costly; metal oxide materials have poor selectivity, low sensitivity, and operate at high temperatures, resulting in high energy consumption; some materials have long response and recovery times for gas detection, leading to time-consuming experiments, and also suffer from poor stability and low repeatability.

[0004] Metal-organic frameworks (MOFs) are novel porous materials formed by the self-assembly of metal ions and organic ligands, exhibiting a periodic network structure. They possess high specific surface area and high porosity, making them highly promising for gas sensing applications. A QCM-type gas sensor using ZIF-90 as the sensing material demonstrates excellent sensitivity, fast response time, and high selectivity for acetone. A QCM-type pyridine sensor using the MOF MIL-101-Cr as the sensing material exhibits high sensitivity and fast response time for pyridine in the testing of nine volatile organic compounds, showing promise for practical applications in pyridine detection. However, most MOF materials still suffer from complex preparation methods, high raw material costs, and low physical or chemical stability. Therefore, there is an urgent need to find and develop a novel, reliable MOF material with good selectivity as the gas-sensing material for QCM-type gas sensors. Summary of the Invention

[0005] To address the aforementioned technical problems, the purpose of this invention is to provide gallic acid-based MOF gas-sensitive materials, their preparation methods, and applications.

[0006] The above-mentioned objective of this invention is achieved through the following technical solutions:

[0007] The first aspect of this invention provides a method for preparing gallic acid-based MOF gas-sensitive materials, comprising the following steps:

[0008] Metal salt and gallate acid are dissolved in an alkaline solution and reacted at 110-150℃ to obtain the gallate acid-based MOF gas-sensitive material.

[0009] The metal salt is selected from one or more of the nitrates, sulfates and hydrochlorides of cobalt, magnesium and nickel; the molar ratio of the metal salt to gallic acid is 1:(1.5-2.5), preferably 1:2.

[0010] Furthermore, the alkaline solution is an aqueous solution of potassium hydroxide or an aqueous solution of sodium hydroxide.

[0011] Further, dissolve 1-3g of the metal salt in 30-50mL of alkaline solution.

[0012] Furthermore, the concentration of the alkaline solution is 0.1-0.5M.

[0013] Furthermore, the reaction time is 12-36 hours.

[0014] Furthermore, it also includes an activation treatment at 110-150°C after the reaction is completed.

[0015] Furthermore, the activation treatment time is 12-30 hours.

[0016] In a specific embodiment, a metal salt and gallic acid are mixed at a certain molar ratio, dissolved in an alkaline solution, and ultrasonically treated for 20-60 minutes. The mixture is then sealed in a polytetrafluoroethylene-lined stainless steel autoclave and placed in an oven at 110-150°C for 12-36 hours. The autoclave is removed, cooled to room temperature, and the product is obtained by centrifugation. The product is then washed 3-5 times with water and ethanol, respectively, and activated in a vacuum oven at 100-150°C for 12-30 hours to obtain the gallic acid-based MOF gas-sensitive material.

[0017] The second aspect of the present invention provides a gallic acid-based MOF gas-sensitive material prepared by the method described in the first aspect.

[0018] The third aspect of this invention provides the application of the gallic acid-based MOF gas-sensitive material described in the second aspect in the preparation of a QCM gas sensor.

[0019] A fourth aspect of the present invention provides a QCM gas sensor comprising the gallic acid-based MOF gas-sensitive material described in the second aspect.

[0020] In a specific embodiment, a dispersion of gallic acid-based MOF gas-sensitive material is coated onto the substrate of the QCM gas sensor.

[0021] Furthermore, the concentration of the gallic acid-based MOF gas-sensitive material dispersion is 1-5 mg / mL, preferably 1 mg / mL.

[0022] Furthermore, the gallic acid-based MOF gas-sensitive material dispersion is prepared by dissolving the gallic acid-based MOF gas-sensitive material in a solvent.

[0023] Furthermore, the solvent is selected from one or more of methanol, ethanol, and water.

[0024] In a specific embodiment, 3-5 μL of gallic acid-based MOF gas-sensitive material dispersion is dropped onto the center of the QCM gas sensor substrate and dried at room temperature for 1-5 hours.

[0025] The fifth aspect of this invention provides the application of the QCM gas sensor described in the fourth aspect in the detection of ammonia.

[0026] The beneficial effects of this invention are:

[0027] This invention synthesizes a simple and low-cost gallic acid-based MOF material (M-Gallate MOF, M = Co, Ni, Mg), and uses it as a gas-sensitive material to prepare a QCM gas sensor. Experiments on gas detection using the three gallic acid-based MOF materials revealed that the Co-Gallate MOF-based QCM gas sensor exhibits superior selectivity and better sensitivity for ammonia compared to the Mg-Gallate MOF-based and Ni-Gallate MOF-based QCM gas sensors. Attached Figure Description

[0028] Figure 1 shows the XRD patterns of the Co-Gallate MOF of Example 1, the Mg-Gallate MOF of Example 2, and the Ni-Gallate MOF of Example 3.

[0029] Figure 2 is a comparison of the detection performance of QCM gas sensors prepared from the gas-sensitive materials of Examples 1-3 at 60% RH for 100 ppm NH3.

[0030] Figure 3 shows the single-response recovery time curves of QCM gas sensors prepared from the gas-sensitive materials of Examples 1-3 at 60% RH to 100ppm NH3; where a is Co-Gallate MOF, b is Mg-Gallate MOF, c is Ni-Gallate MOF, and d is a response time comparison graph.

[0031] Figure 4 shows the selectivity test results of the QCM gas sensor prepared by the gas-sensitive material in Example 1 for 100 ppm of different gases.

[0032] Figure 5 shows a comparison of the detection performance of the Co-Gallate MOF-based QCM gas sensor for 50-300 ppm NH3 at room temperature and 60% RH, as well as the repeatability curve for detecting 100 ppm NH3. Among them, a is the corresponding curve for different concentrations (50, 100, 200, 300 ppm) of NH3, b is the linear fitting curve of the response value and concentration for different concentrations (50, 100, 200, 300 ppm) of NH3, and c is the repeatability curve for detecting 100 ppm NH3 by the Co-Gallate MOF-based QCM gas sensor at 60% RH. Detailed Implementation

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0036] Example 1

[0037] A method for preparing a co-gallate MOF (co-gallate MOF) gas-sensitive material includes the following steps:

[0038] 1.903 g of CoCl2·6H2O and 2.722 g of gallic acid were mixed in a 1:2 molar ratio and dissolved in 40 mL of 0.16 MkOH aqueous solution. After sonication for 30 min, the mixture was sealed in a stainless steel autoclave lined with polytetrafluoroethylene and reacted in an oven at 120 °C for 24 h. The autoclave was removed, cooled to room temperature, and the product was obtained by centrifugation. The product was then washed three times with water and ethanol, respectively. The sample was activated in a vacuum oven at 120 °C for 24 h to obtain the Co-Gallate MOF gas-sensitive material.

[0039] Example 2

[0040] A method for preparing a gallic acid-based MOF (Mg-Gallate MOF) gas-sensitive material includes the following steps:

[0041] 1.626 g of MgCl₂·6H₂O and 2.722 g of gallic acid were mixed in a 1:2 molar ratio and dissolved in 40 mL of 0.5 MkOH aqueous solution. After sonication for 30 min, the mixture was sealed in a stainless steel autoclave lined with polytetrafluoroethylene and reacted in an oven at 120 °C for 24 h. The autoclave was removed, cooled to room temperature, and the product was obtained by centrifugation. The product was then washed three times with water and ethanol, respectively. The sample was activated in a vacuum oven at 120 °C for 24 h to obtain the Mg-Gallate MOF gas-sensitive material.

[0042] Example 3

[0043] A method for preparing a gallic acid-based MOF (Ni-Gallate MOF) gas-sensitive material includes the following steps:

[0044] 1.903 g NiCl2·6H2O and 2.722 g gallic acid were mixed in a 1:2 molar ratio and dissolved in 40 mL of 0.16 MkOH solution. After sonication for 30 min, the mixture was sealed in a stainless steel autoclave lined with polytetrafluoroethylene and reacted in an oven at 120 °C for 24 h. The autoclave was removed, cooled to room temperature, and the product was obtained by centrifugation. The product was then washed three times with water and ethanol, respectively. The sample was activated in a vacuum oven at 120 °C for 24 h to obtain the Ni-Gallate MOF gas-sensitive material.

[0045] Figure 1 shows the X-ray diffraction (XRD) patterns of the Co-Gallate MOF of Example 1, the Mg-Gallate MOF of Example 2, and the Ni-Gallate MOF of Example 3. As can be seen from Figure 1, by comparing with the simulated standard Gallate MOF, the present invention successfully prepared these MOFs.

[0046] Application examples

[0047] The substrate of the QCM gas sensor was cleaned with ethanol and deionized water. After cleaning, the substrate was fixed on a horizontal plane. 10 mg of the gas-sensitive material prepared in Examples 1-3 was dispersed in 10 mL of methanol and sonicated for 10 minutes to prepare a dispersion with a concentration of 1 mg / mL. 3 μL of the dispersion was dropped onto the center of the QCM gas sensor substrate and dried at room temperature for 2 hours.

[0048] Test case

[0049] The gas is detected using the QCM gas sensor prepared in the application example. The detection method is as follows:

[0050] The QCM gas sensor is placed inside the gas chamber and connected to the oscillation circuit and frequency counter. The oscillation circuit and frequency counter are turned on, and after the equipment has preheated for 10 minutes, background gas (N2 with a certain humidity) is introduced, and the sensor frequency change is measured. Once the baseline frequency stabilizes, the test gas (several types of test gases, with nitrogen as the background gas and the same humidity) is introduced under the control of a flow meter. After 300 seconds, the background gas is introduced, and then the process is switched to the next concentration. This process yields the response recovery curve of the QCM gas sensor.

[0051] The performance of QCM gas sensors prepared from the gas-sensitive materials in Examples 1-3 in detecting ammonia was compared. The response to 100 ppm NH3 was detected at 60% humidity (RH). The results are shown in Figure 2. Under 60% RH conditions, the QCM gas sensor prepared from Co-Gallate MOF has the highest response value compared to the other two sensors.

[0052] The single-response recovery times of the QCM gas sensors prepared from the gas-sensitive materials of Examples 1-3 at 60% RH were compared for 100 ppm NH3, as shown in Figure 3. The response and recovery times of the Co-Gallate MOF-based QCM gas sensor in Example 1 were 36 s and 86 s, respectively; the response and recovery times of the Mg-Gallate MOF-based QCM gas sensor in Example 2 were 52 s and 210 s, respectively; and the response and recovery times of the Ni-Gallate MOF-based QCM gas sensor in Example 3 were 82 s and 279 s, respectively. The Co-Gallate MOF-based QCM gas sensor exhibited shorter response and recovery times compared to the other two sensors.

[0053] The QCM gas sensor prepared by the gas-sensitive material in Example 1 was tested for selectivity to 100 ppm of different gases. The gases to be tested were ammonia (NH3), hydrogen sulfide (H2S), acetone, trimethylamine, and ethanol. The test results are shown in Figure 4. The QCM gas sensor of the present invention has high selectivity to NH3.

[0054] The detection performance of the Co-Gallate MOF-based QCM gas sensor for 50-300 ppm NH3 was investigated at room temperature and 60% RH. As shown in Figures 5a and 5b, the response of the Co-Gallate MOF-based QCM gas sensor to NH3 continuously increased from 50 ppm to 300 ppm, increasing from 48 Hz to 95 Hz, with the response value showing a linear correlation with concentration. The repeatability of the Co-Gallate MOF-based QCM gas sensor for detecting 100 ppm NH3 at 60% RH was studied. As shown in Figure 5c, the Co-Gallate MOF-based QCM gas sensor exhibited high repeatability for 100 ppm NH3.

[0055] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An application of a quartz crystal microbalance gas sensor in the detection of ammonia, characterized in that, The quartz crystal microbalance gas sensor comprises gallic acid-based MOF gas-sensitive material. 3-5 μL of a gallic acid-based MOF gas-sensitive material dispersion is dropped onto the center of the QCM gas sensor substrate. The gallic acid-based MOF gas-sensitive material dispersion is prepared by dissolving the gallic acid-based MOF gas-sensitive material in a solvent, and the concentration of the gallic acid-based MOF gas-sensitive material dispersion is 1-5 mg / mL. The preparation method of the gallic acid-based MOF gas-sensitive material includes the following steps: dissolving a metal salt and gallic acid in an alkaline solution and reacting at 110-150 °C to obtain the gallic acid-based MOF gas-sensitive material. The metal salt is selected from one or more of the nitrates, sulfates, and hydrochlorides of cobalt, magnesium, and nickel. The molar ratio of the metal salt to gallic acid is 1:(1.5-2.5).

2. The application according to claim 1, characterized in that, The concentration of the alkaline solution is 0.1-0.5 M.

3. The application according to claim 1, characterized in that, Dissolve 1-3 g of metal salt in 30-50 mL of alkaline solution.

4. The application according to claim 1, characterized in that, The reaction time is 12-36 h.

5. The application according to claim 1, characterized in that, It also includes an activation treatment at 110-150 °C after the reaction is completed.

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