Preparation method and application of porous organic framework film ammonia gas sensor

Abstract

The invention provides a preparation method and application of a porous organic framework film ammonia gas sensor, and the preparation method comprises the following steps: S1, preparing an abietic acid solution, dropwise adding the abietic acid solution into ultrapure water, stirring to obtain a white emulsion, standing, centrifuging, carrying out suction filtration separation to obtain a white solid, and drying to obtain purified abietic acid; s2, dissolving cupric acetate and purified abietic acid in absolute ethyl alcohol according to a preset molar ratio, carrying out ultrasonic uniform mixing treatment, reacting in a constant-temperature oil bath at 55 DEG C for 5 hours, cooling to room temperature, pouring into ultrapure water to separate out a product, and carrying out suction filtration and drying to obtain a copper abietate porous organic framework; and S3, dissolving the copper abietate porous organic framework in dimethyl sulfoxide to prepare a dispersion liquid, sucking 2mL of the dispersion liquid, uniformly dispensing the dispersion liquid to two surfaces of a quartz crystal oscillator, and drying to form the porous organic framework film ammonia gas sensor. The preparation method has the beneficial effect that the porous organic framework ammonia gas sensor which has a high specific surface area, a regular pore structure and specific adsorption sites for ammonia gas can be prepared.

Description

Technical Field

[0001] This invention relates to the technical field of ammonia sensors, and more specifically, to a method for preparing and applying a porous organic framework thin-film ammonia sensor. Background Technology

[0002] Ammonia, as an important industrial gas and toxic pollutant, is increasingly in demand for precise detection in fields such as environmental monitoring, industrial safety, and food preservation. Quartz crystal microbalance (QCM) technology, due to its high sensitivity and ease of miniaturization, is considered one of the ideal platforms for developing novel gas sensors. The core performance of the QCM ammonia sensor lies in its surface-modified gas-sensitive membrane, which is responsible for the selective adsorption of the target gas and the resulting mass change.

[0003] Currently, the sensitive membrane materials used in QCM ammonia sensors mainly include metal oxides and organic polymers. However, these traditional materials still have significant limitations: First, their specific surface area is limited and the density of active sites is insufficient, resulting in low sensor sensitivity and difficulty in accurately detecting low concentrations of ammonia; second, these materials often form dense membrane layers through disordered stacking, resulting in high mass transfer resistance of gas molecules within the membrane, leading to slow sensor response and recovery speeds, making it difficult to meet the requirements of real-time monitoring; third, many materials also have an adsorption effect on water vapor, resulting in poor anti-interference ability and unsatisfactory selectivity in complex humidity environments.

[0004] Furthermore, a key technical challenge in the fabrication process of the sensitive membrane is how to stably and uniformly immobilize functional materials on the surface of the QCM electrode while simultaneously ensuring the openness of its porous structure and the accessibility of active sites. Traditional film-forming methods struggle to ensure high loading capacity while avoiding material agglomeration and pore blockage, which further restricts the improvement of sensor performance.

[0005] Therefore, there is an urgent need in the field for a new method for preparing a porous organic framework thin film ammonia sensor, which can give the porous organic framework ammonia sensor a high specific surface area, a regular pore structure and specific adsorption sites for ammonia. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to prepare a porous organic framework ammonia sensor with high specific surface area, regular pore structure and specific adsorption sites for ammonia. In order to overcome the defects of the prior art (or related art), the present invention provides a method for preparing a porous organic framework thin film ammonia sensor and its application.

[0007] This invention provides a method for preparing a porous organic framework thin-film ammonia sensor, comprising the following steps: Step S1: Dissolve rosin acid in anhydrous ethanol, filter to remove insoluble impurities to obtain rosin acid solution, then add the rosin acid solution dropwise to ultrapure water and stir rapidly to obtain a white emulsion, let it stand, and then separate it by centrifugation and vacuum filtration to obtain a white solid, and then dry the white solid to obtain purified rosin acid; Step S2: Copper acetate and the purified rosin acid are dissolved in anhydrous ethanol at a preset molar ratio and ultrasonically mixed evenly. Then, the mixture is reacted in a constant temperature oil bath at 55°C for 5 hours. After cooling to room temperature, the product is poured into ultrapure water to precipitate. After filtration and drying, a porous organic framework of copper rosin acid is obtained. Step S3: Dissolve the copper rosinate porous organic framework in dimethyl sulfoxide to prepare a dispersion of a preset concentration. Then, take 2 mL of the dispersion and uniformly drop it onto both sides of the quartz crystal oscillator. Dry it in a vacuum drying oven at 85°C to form a porous organic framework thin film ammonia sensor.

[0008] The method for preparing a porous organic framework thin-film ammonia sensor of the present invention has the following advantages compared with the prior art: In this invention, step S1 involves the fine purification of rosin acid, effectively removing impurities from the raw materials. This ensures the purity of the starting material for the subsequent synthesis of the copper rosinate porous organic framework, fundamentally guaranteeing the consistency and repeatability of the final porous organic framework thin-film ammonia sensor material performance and avoiding interference from impurities on gas adsorption sites. Step S2 successfully constructs the copper rosinate porous organic framework through a coordination reaction between copper acetate and purified rosin acid under specific conditions. This framework has a regular porous structure and specific ammonia adsorption sites provided by copper ions, laying the material foundation for highly selective ammonia detection. Step S3 uses a drop-coating method to form a film on both sides of a quartz crystal oscillator. This method is simple and inexpensive. Drying under vacuum at 85°C effectively removes the solvent without damaging the film structure. The resulting film is firmly adhered and has a uniform thickness. This design allows the porous organic framework thin-film ammonia sensor to have a larger effective sensing area, thereby improving detection sensitivity and signal stability.

[0009] In one possible implementation, in step S1, the white solid is dried in a vacuum drying oven at 85°C for 12 hours.

[0010] Compared with existing technologies, the above-mentioned technical solution can reduce the boiling point of the solvent through a vacuum environment, so that moisture and residual ethanol can be removed efficiently even at a relatively low temperature of 85°C. This avoids the denaturation or decomposition of rosin acid that may be caused by high temperature, and ensures the chemical integrity of purified rosin acid.

[0011] In one possible implementation, in step S1, when the rosin acid solution is added dropwise to ultrapure water, the addition process is continuous and slow, and the rapid stirring time ends when the product precipitates.

[0012] Compared with existing technologies, the above-mentioned technical solution can achieve uniform dispersion and slow precipitation of rosin acid solution by combining "continuous dripping and slow precipitation" with "rapid stirring". This results in the formation of rosin acid solid particles with more uniform particle size and more regular morphology, reducing amorphous impurities or lattice defects caused by rapid precipitation. This provides morphological assurance for the subsequent synthesis of high-quality copper rosinate porous organic frameworks.

[0013] In one possible implementation, in step S2, the preset molar ratio of the copper acetate and the purified rosin acid is 1:0.99, 1:1.5, 1:2, 1:2.5, or 1:3.

[0014] Compared with existing technologies, the above technical solution can achieve different sensor sensitivities through multiple molar ratio options ranging from 1:0.99 to 1:3, thus providing services for various application scenarios.

[0015] In one possible implementation, in step S2, the product is dried in a vacuum drying oven at 100°C for 12 hours.

[0016] Compared with existing technologies, the above-mentioned technical solution can completely remove solvent molecules and water molecules embedded in the porous organic framework of copper rosinate during the synthesis process by vacuum drying at 100°C for 12 hours. This is beneficial to the activation and stabilization of the framework structure, ensuring that the final copper rosinate porous organic framework has open channels and a stable crystal structure, which is crucial for the rapid diffusion and reversible adsorption of gas molecules.

[0017] In one possible implementation, in step S3, the preset concentration of the dispersion is 0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, or 0.8 mg / mL.

[0018] Compared with existing technologies, the above technical solution can provide a concentration gradient from 0.4 mg / mL to 0.8 mg / mL. By controlling the concentration of the dispersion, the thickness of the sensitive film on the quartz crystal can be precisely controlled.

[0019] In one possible implementation, the ammonia sensitivity of the porous organic framework thin film ammonia sensor formed in step S3 is not less than 0.65 Hz / ppm.

[0020] In one possible embodiment, the present invention also provides an application of a porous organic framework thin film ammonia sensor prepared by the above-described method in the field of ammonia detection. Attached Figure Description

[0021] Figure 1 This is a flowchart of the steps of the present invention; Figure 2 The diagram shows the experimental results of the treated and untreated rosin acid gas-sensitive materials in the present invention under two humidity ranges of 11%-84% RH and 11%-97% RH. In the diagram, (a) represents the humidity-sensing linear characteristic curves of the treated and untreated rosin acid gas-sensitive materials under the humidity range of 11%-84% RH, (b) represents the humidity-sensing linear characteristic curves of the treated and untreated rosin acid gas-sensitive materials under the humidity range of 11%-97% RH, and (c) represents the humidity response of the treated and untreated rosin acid gas-sensitive materials at the same concentration. Detailed Implementation

[0022] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] See Figure 1 This invention discloses a method for preparing a porous organic framework thin-film ammonia sensor, comprising the following steps: Step S1, Purification and Pretreatment of Rosin Acid Raw Material This step aims to remove impurities such as oxidized resin acids from the rosin acid raw material, improving the uniformity and performance reproducibility of the subsequently synthesized materials. Specifically, approximately 5 grams of rosin acid (analytical grade, purity approximately 75%) is weighed and placed in an Erlenmeyer flask, 100 ml of anhydrous ethanol is added, and the mixture is magnetically stirred in a 40°C water bath until completely dissolved, yielding a rosin acid solution. This solution is then filtered through a 0.22 μm PTFE membrane to remove insoluble impurities. Next, under high-speed stirring (e.g., 800 rpm), the filtrate is slowly and continuously added dropwise to 500 ml of ultrapure water using a constant-pressure dropping funnel. The rosin acid rapidly precipitates in the unsuitable solvent water, forming a stable white emulsion. This white emulsion is allowed to stand and age for 2 hours to allow complete crystal growth. Then, the emulsion is heated to 8000 mL / min. Centrifuge at rpm for 10 minutes, collect the white precipitate at the bottom, and wash it three times with ultrapure water. Finally, place the obtained white solid in a vacuum drying oven and dry it at 85°C for 12 hours to obtain high-purity rosin acid powder. Store it in a sealed container for later use. This purification process effectively avoids the interference of impurities on the subsequent porous framework structure, which is the key to ensuring the consistency of sensor performance. Step S2, Synthesis of copper rosinate porous organic framework (Cu-AA POF) This step is crucial for constructing a core functional material with specific ammonia recognition sites. First, copper acetate monohydrate (Cu(CH3COO)2·H2O) and the purified rosin acid obtained in step S1 are accurately weighed and mixed according to a preset molar ratio. The molar ratio can be selected from a series of ratios such as 1:0.99, 1:1.5, 1:2, 1:2.5, and 1:3 to control the density of copper sites in the framework and the pore structure of the material. A preferred embodiment is to use a molar ratio of 1:1.5. Both were dissolved together in 50 mL of anhydrous ethanol. The mixture was then placed in a CNC ultrasonic cleaner and sonicated at 40 kHz and 300 W for 30 minutes to ensure thorough mixing and the formation of a homogeneous precursor solution. The reaction system was then transferred to a 55°C constant-temperature oil bath and reacted under reflux for 5 hours. This mild reaction temperature and sufficiently long reaction time are conducive to the formation of a well-crystallized and structurally stable coordination polymer framework. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting blue or blue-green reaction... The liquid is poured into a large amount (e.g., 200 ml) of ultrapure water under vigorous stirring to precipitate the target product. The precipitate is collected by vacuum filtration and washed alternately with ethanol and ultrapure water to remove unreacted raw materials and byproducts. Finally, the filter cake is placed in a vacuum drying oven and dried at 100°C for 12 hours to obtain a powder of copper rosinate porous organic framework. The copper ions (Cu²⁺) of the material synthesized in this step can act as Lewis acid sites and interact specifically with ammonia molecules (Lewis bases), which is the basis for realizing highly selective ammonia sensing. Step S3: Assembly of QCM sensor device and preparation of sensitive membrane This step transforms the functional powder material into a sensing element that can be directly used for detection. First, the copper rosinate porous organic framework powder synthesized in step S2 is lightly ground in an agate mortar and then dispersed in dimethyl sulfoxide (DMSO) solvent. A uniform and stable dispersion is prepared by magnetic stirring and short-term sonication (e.g., 15 minutes). The concentration of the dispersion can be adjusted according to the required film thickness, typically ranging from 0.4 mg / mL to 0.8 mg / mL, such as 0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, and 0.8 mg / mL. A best-performing example uses a concentration of 0.6 mg / mL. Before coating, the QCM wafer (e.g., a baseband 20) needs to be... Pretreatment was performed on the QCM crystal oscillator (with a silver electrode diameter of 4 mm) by ultrasonic cleaning with anhydrous ethanol and ultrapure water for 5 minutes in sequence, followed by drying with high-purity nitrogen. Then, using a calibrated micropipette, 2 μL of the above dispersion was accurately pipetted and carefully and evenly dropped onto the active area of ​​the silver electrode. To ensure uniform film coverage and sufficient active area, the same drop-coating operation was performed on both sides of the crystal oscillator. The coated sensor was then placed horizontally in a vacuum drying oven and dried at 85°C for 1 hour. This process completely removed the DMSO solvent, allowing the copper rosinate porous organic framework to form a firm, uniform, and porous sensitive film on the electrode surface, ultimately producing a porous organic framework thin film ammonia sensor.

[0025] In this embodiment of the invention, the ammonia sensor prepared by the above preparation method, after third-party testing and verification, has a detection sensitivity of 0.65 Hz / ppm or higher for ammonia, demonstrating excellent detection capability. This ammonia sensor can be integrated with a miniature intelligent detection system containing a microprocessor, WiFi or Bluetooth module to realize real-time acquisition and wireless transmission of ammonia concentration signals, and remote monitoring and result display via smartphone WeChat mini-programs, etc.

[0026] In this embodiment of the invention, considering that impurities in rosin acid may affect its crystallization tendency and thus have a certain impact on the morphology and gas sensing characteristics of the sensitive membrane, step S1 of this invention purifies the rosin acid and studies the hygroscopic characteristics of the rosin acid sensitive membrane material before and after treatment. The treated rosin acid is dissolved in DSMO to prepare five solutions of different concentrations (0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, and 0.8 mg / mL). 2 mL of the prepared solution is evenly drop-coated onto a quartz crystal using a micropipette, coating each side. The crystals are then dried in a vacuum drying oven at 85 ℃ to obtain rosin acid sensitive membranes, named QCM-A, QCM-B, QCM-C, QCM-D, and QCM-E, respectively. Similarly, untreated rosin acid (75%) is dissolved in DSMO to prepare five solutions of different concentrations (0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, and 0.8 mg / mL). (0.5 mg / mL, 0.7 mg / mL and 0.8 mg / mL) 2 mL of the prepared solution was pipetted evenly onto a quartz crystal oscillator, with each side being coated. The rosin acid sensitive membranes were then dried in a vacuum drying oven at 85 ℃ and named QCM-a, QCM-b, QCM-c, QCM-d and QCM-e, respectively. Tables 1 and 2 below record some gas-sensitive parameters of rosin acid-sensitive materials: Table 1. Basic Information of Untreated Rosin Acid Sensitive Membrane QCM Table 2 Basic information of the treated rosin acid sensitive membrane QCM As shown in Tables 1 and 2 above, the frequency changes (response values) of QCM-A, QCM-B, QCM-C, QCM-D, and QCM-E in an 11%-97% RH humidity environment are -270 Hz, -468 Hz, -897 Hz, -1309 Hz, and -2043 Hz, respectively; while the frequency changes of QCM-a, QCM-b, QCM-c, QCM-d, and QCM-e in the same 11%-97% RH humidity environment are -403 Hz, -975 Hz, -1205 Hz, -1660 Hz, and -4923 Hz, respectively. Figure 2(a) and (b) in the figure are the humidity-sensing linear characteristic curves of the treated and untreated rosin acid gas-sensitive materials under two humidity ranges of 11%-84% RH and 11%-97% RH, respectively. The inset shows the corresponding logarithmic fitting curves. The purified rosin acid gas-sensitive materials have good logarithmic fitting linearity under humidity environments of 11%-84% RH and 11%-97% RH. The logarithmic fitting correlation coefficients of QCM-A, QCM-B, QCM-C, QCM-D and QCM-E under the conditions of 11-84% RH and 11-97% RH are 0.9949, 0.9969, 0.9975, 0.9958, 0.9886 and 0.9911, 0.9981, 0.9956, 0.9919, 0.9889, respectively. Untreated rosin acid gas-sensitive materials exhibited good logarithmic linearity under 11-84% RH conditions, with logarithmic correlation coefficients of 0.9961, 0.9964, 0.9970, 0.9920, and 0.9831 for QCM-a, QCM-b, QCM-c, QCM-d, and QCM-e, respectively. Figure 2 Figure (c) compares the response of treated and untreated rosin acid gas-sensitive materials to humidity at the same concentration. The figure shows that the response values ​​of the untreated rosin acid gas-sensitive material are all higher than those of the treated material, indicating that the purification treatment of rosin acid is effective and feasible. The purification treatment removes some hydrophilic impurities, while also combining... Figure 2 In (a) and (b), it was found that the treated rosin acid gas-sensitive material had good logarithmic linearity in both 11-84% RH and 11-97% RH humidity environments, while the untreated rosin acid gas-sensitive material had poor logarithmic linearity in the 11-97% RH humidity range. This phenomenon may be caused by impurities in the rosin acid raw material. Therefore, subsequent experiments used treated rosin acid as raw material to prepare copper rosin acid porous organic frameworks.

[0027] In this embodiment of the invention, an application of a porous organic framework thin film ammonia sensor prepared by the above-described method in the field of ammonia detection is also disclosed. This application has a wide range of scenarios, including but not limited to industrial environmental safety monitoring (such as chemical plants and refrigeration workshops), agricultural livestock and poultry house environmental monitoring, food packaging leakage indication, and medical breath analysis.

[0028] In the description of this invention, the references to "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0029] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a porous organic framework thin-film ammonia sensor, characterized in that, Includes the following steps: Step S1: Dissolve rosin acid in anhydrous ethanol, filter to remove insoluble impurities to obtain rosin acid solution, then add the rosin acid solution dropwise to ultrapure water and stir rapidly to obtain a white emulsion, let it stand, and then separate it by centrifugation and vacuum filtration to obtain a white solid, and then dry the white solid to obtain purified rosin acid; Step S2: Copper acetate and the purified rosin acid are dissolved in anhydrous ethanol at a preset molar ratio and ultrasonically mixed evenly. Then, the mixture is reacted in a constant temperature oil bath at 55°C for 5 hours. After cooling to room temperature, the product is poured into ultrapure water to precipitate. After filtration and drying, a porous organic framework of copper rosin acid is obtained. Step S3: Dissolve the copper rosinate porous organic framework in dimethyl sulfoxide to prepare a dispersion of a preset concentration. Then, take 2 mL of the dispersion and uniformly drop it onto both sides of the quartz crystal oscillator. Dry it in a vacuum drying oven at 85°C to form a porous organic framework thin film ammonia sensor.

2. The preparation method according to claim 1, characterized in that, In step S1, the white solid is dried in a vacuum drying oven at 85°C for 12 hours.

3. The preparation method according to claim 1, characterized in that, In step S1, when the rosin acid solution is added dropwise to ultrapure water, the addition process is continuous and slow, and the rapid stirring time ends when the product precipitates.

4. The preparation method according to claim 1, characterized in that, In step S2, the preset molar ratio of copper acetate and purified rosin acid is 1:0.99, 1:1.5, 1:2, 1:2.5, or 1:

3.

5. The preparation method according to claim 1, characterized in that, In step S2, the product is dried in a vacuum drying oven at 100°C for 12 hours.

6. The preparation method according to claim 1, characterized in that, In step S3, the preset concentration of the dispersion is 0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, or 0.8 mg / mL.

7. The preparation method according to claim 1, characterized in that, The ammonia sensitivity of the porous organic framework thin film ammonia sensor formed in step S3 is not less than 0.65 Hz / ppm.

8. The application of a porous organic framework thin film ammonia sensor prepared by any one of the preparation methods described in claims 1-7 in the field of ammonia detection.

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