Method for detecting h2s gas concentration based on metal organic framework-gold nanoparticle colorimetric gel patch

Abstract

The application discloses a kind of H2S gas concentration detection methods based on metal organic framework-gold nanoparticle colorimetric gel patch.In hot gel solution,metal organic framework solution,metal chloric acid solution are added and uniformly mixed,drop mixed solution into mould,after cooling,de-mould,place in H2S gas environment,photograph before and after response to extract color information change and then judge to obtain concentration.The application is simple to prepare,can be completed in 10min,improves the anti-interference ability of gas sensor to environmental humidity,improves the sensitivity of sensor,realizes the practical application in meat product packaging,realizes freshness detection under non-destructive condition.

Description

Technical Field

[0001] This invention relates to the field of gas sensing, and specifically to a colorimetric gel patch based on metal-organic framework-gold nanoparticles for colorimetric analysis of H2S gas. Background Technology

[0002] In recent years, gas sensing has become an important emerging research field, attracting great interest from many sectors such as environment, medicine, and food safety. Hydrogen sulfide (H2S) has been proven to be one of the malodorous gases in air pollution, an indicator of food spoilage, and a signal molecule for clinical diagnosis. Therefore, establishing an effective and sensitive method for H2S detection is crucial.

[0003] Compared to traditional detection methods such as chromatography and spectroscopy, electrochemical, fluorescence, and colorimetric sensing technologies have significantly improved in terms of sensitivity, portability, and ease of use. Colorimetry, in particular, is more intuitive, convenient, and inexpensive, requiring no external equipment and allowing for direct visual observation. However, most current gas sensors are based on a gas-solid phase model, limiting the selectable reaction systems, resulting in low sensitivity and significant susceptibility to gas flow rate and ambient humidity. Therefore, developing a stable and sensitive real-time monitoring technology that can withstand environmental interference is crucial.

[0004] The reduction of chloroauric acid to generate gold nanoparticles (AuNPs) using a reducing agent is a mature and sensitive colorimetric reaction widely used in the construction of colorimetric sensors. However, since the main component of the reaction is chloroaurate ions, this reaction must be carried out in solution, making it difficult to apply in gas detection. On the other hand, due to the inherent nucleation-growth process of gold nanoparticles, these sensors typically require sufficient reducing agent and incubation time, which is undoubtedly detrimental to rapid and sensitive responses. Summary of the Invention

[0005] To address the problems mentioned above, this invention proposes a method for preparing a colorimetric gel patch based on a metal-organic framework-gold nanoparticle and its application in the colorimetric analysis of H2S gas. The innovation lies in the construction and application of a novel high-sensitivity sensor. The method of this invention involves uniformly dispersing a metal-organic framework and chloroauric acid solution in an agarose gel to prepare a gel patch, which is then directly applied to the detection of H2S gas.

[0006] This invention simplifies the sensor fabrication process, enabling the rapid preparation of colorimetric gel patches based on metal-organic frameworks (MOFs) and gold nanoparticles. The microscopic aqueous environment provided by the gel ensures the smooth occurrence of ion reactions, effectively resisting interference from environmental humidity and airflow velocity. The pre-reduction effect of the MOF regulates the reaction process, significantly improving detection sensitivity. The gel patch can achieve stable and sensitive detection of H2S gas over a wide humidity range and at various airflow velocities, and has been successfully applied in meat product packaging, providing a valuable reference for non-destructive monitoring of freshness.

[0007] The technical solution adopted in this invention is as follows:

[0008] 1) Prepare chloroauric acid solution, metal-organic framework solution, and gel solution of a certain concentration;

[0009] 2) Add the chlorometallic acid solution and the metal-organic framework solution together to the gel solution at 60-80℃ and mix them evenly. Sonicate for a period of time at a certain intensity. After mixing, a large number of small-diameter metal nanoparticles appear. Small-diameter means that the particle size of the metal nanoparticles is smaller than that of the metal-organic framework particles. Then, drop the mixed solution into a customized mold, cool it and take it out to obtain a colorimetric gel patch.

[0010] 3) The colorimetric gel patch was placed in a known environment without H2S gas and in a test environment containing H2S gas to react. The colorimetric gel patch did not react when placed in the known environment without H2S gas. The corresponding H2S gas concentration was obtained based on the color change of the gel patch in the two environments.

[0011] The colorimetric gel patch prepared by this invention is a gel patch that does not regulate the growth and color development of gold nanoparticles based on a metal-organic framework. It is used for colorimetric analysis of H2S gas, thereby realizing real-time monitoring of H2S gas concentration.

[0012] The metal-organic frameworks mentioned include, but are not limited to, UIO-66-NH2, MOF-545, MIL-53(Fe), MIL-101(Fe), etc.

[0013] In step 1), the metal-organic framework solution is UIO-66-NH2 solution, which is prepared using ZrCl4, 2-amino-1,4-terephthalic acid and benzoic acid. That is, the metal-organic framework is a colorless metal-organic framework UIO-66-NH2 with reducing properties.

[0014] The UIO-66-NH2 solution was prepared in the following manner:

[0015] 1.1) Dissolve ZrCl4, 2-amino-1,4-terephthalic acid and benzoic acid in DMF, add hydrochloric acid to form a mixture;

[0016] 1.2) The mixture was then transferred to a container and sonicated. After that, it was reacted at 120°C for 24 hours. After the reaction, it was cooled to room temperature and washed multiple times with DMF and methanol to obtain UIO-66-NH2. It was dried overnight to obtain metal-organic framework UIO-66-NH2 powder.

[0017] 1.3) Weigh 1-20 mg of dried UIO-66-NH2 powder into a 5 mL centrifuge tube, add 2 mL of ultrapure water, and sonicate until the powder is evenly dispersed to prepare a 0.5-10 mg / mL UIO-66-NH2 solution.

[0018] The nanoparticles are any type of metal nanoparticles that have color-changing properties, including gold nanoparticles, silver nanoparticles, etc., and the chlorometallic acid is chloroauric acid or chlorosilicic acid.

[0019] In step 1), the gel solution is any non-reducing, colorless, and transparent gel, including but not limited to agar gel solution, silk fibroin gel solution, sodium alginate gel solution, polyethylene glycol gel, etc.

[0020] In step 1), the gel solution is an agar gel solution, specifically:

[0021] Weigh 0.04-0.4g of agar powder into a beaker, add 5mL of ultrapure water, seal the beaker with aluminum foil, place it on a heating plate, set the temperature to 100-150℃, and heat for 2-5 minutes until boiling to prepare a colorless and transparent agar gel solution with a mass fraction of 0.08-0.8%.

[0022] In step 1), the concentration of the chlorometallic acid solution is 1-10 mM, and the concentration of the UIO-66-NH2 solution is 0.5-10 mg / mL. In step 2), the mass fraction of the gel solution is 0.08-0.8%, and the volume ratio of the chlorometallic acid solution, UIO-66-NH2 solution, and gel solution is 1:1:(3-18). This ensures that the system is under optimal reaction conditions.

[0023] In step 2), the temperature of the gel solution is 60-80℃;

[0024] In step 2), the uniform mixing method is ultrasonic mixing, with an ultrasonic intensity of 7-9 and a time of 10-30s, which makes the dispersion uniform and ensures that the solution has fluidity.

[0025] In step 2), the volume of the mixed solution dropped into the mold is determined by filling the mold, usually 200-400 μL, so as to obtain a gel patch of appropriate thickness.

[0026] In step 2), the mold used has a diameter of 1-2 cm and a depth of 1-2 mm. The material is any one of polytetrafluoroethylene, glass, and plastic, including but not limited to polytetrafluoroethylene, Teflon, metal, etc.

[0027] In step 2), cooling is performed at 0-4°C for 3-5 minutes to completely transform the gel into a non-flowing phase.

[0028] In step 3), different H2S gas concentrations are set in advance and the same experiment is performed multiple times to obtain the color change of the corresponding colorimetric gel patch. The color change of the colorimetric gel patch under each experiment and the corresponding H2S gas concentration are fitted to establish a curve relationship. The color of the colorimetric gel patch after being placed in the test environment containing H2S gas is substituted into the curve relationship to obtain the corresponding H2S gas concentration.

[0029] The fluorescence intensity of the gel patch was measured by taking pictures with a mobile phone, extracting the RGB data using ImageJ software, and converting the RGB values ​​into LAB.

[0030] In specific experimental tests, the prepared gel patch can be placed in a petri dish and then placed in a sealed bag. H2S gas is introduced into the bag at a fixed gas flow rate to carry out the reaction. The color change is observed, and images of the gel patch before and after the reaction are taken with a mobile phone and the color information is extracted. The corresponding H2S gas concentration is obtained by combining the color change before and after the reaction with the pre-calibrated curve relationship between the color change and the H2S gas concentration.

[0031] In step 4), the concentration of H2S gas introduced is 0.01ppm-10ppm, the gas introduction time is 5-20min, and the reaction time after introduction is 60-90min.

[0032] In a specific embodiment of the present invention, the metal-organic framework-gold nanoparticle gel patch prepared above is subjected to H2S gas response in a sealed bag, and then the reacted metal-organic framework-gold nanoparticle gel patch is taken out for measurement to obtain the performance results of the gel patch. The morphology, structure, and colorimetric properties of the gel patch are further characterized by electron microscopy, thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, mobile phone photography, and ImageJ software.

[0033] This invention utilizes a gel as a carrier to apply a gold nanoparticle growth system to the field of gas sensing. By regulating the reaction process through the pre-reduction of the zirconium-based metal-organic framework UIO-66-NH2, sensitive detection of H2S gas is achieved. The rich micro-aqueous environment of the gel resists interference from ambient humidity and airflow velocity, resulting in a novel colorimetric sensor capable of stable and sensitive detection of H2S gas under a wide humidity range and various airflow velocity conditions.

[0034] This invention is simple to prepare, taking only 10 minutes. Utilizing the microscopic aqueous environment of the gel improves the gas sensor's resistance to interference from ambient humidity, regulates the growth process of gold nanoparticles, and enhances the sensor's sensitivity. This enables practical application within meat product packaging, achieving freshness detection under non-destructive conditions.

[0035] The metal-organic framework-gold nanoparticle gel patch prepared by the method of this invention has the following advantages:

[0036] 1. The preparation process of this invention is simple, requiring only heating and cooling. The sensor preparation process can be completed within 10 minutes, saving preparation time. Moreover, this method can be achieved using only a heating plate, reducing instrument costs and making it convenient and quick.

[0037] 2. By using gel as a carrier, the gold nanoparticle growth system was applied to the field of gas sensing. Simultaneously, the rich micro-aqueous environment of the gel enabled resistance to interference from environmental humidity and airflow velocity.

[0038] 3. The reaction process is regulated to the critical value for color development through the pre-reduction effect of the metal-organic framework UIO-66-NH2. At this point, only a very small amount of H2S is needed to grow and develop the color of gold nanoparticles, effectively improving the detection sensitivity.

[0039] 4. The significant color change caused by the growth of gold nanoparticles can be determined by naked eye and instruments to detect the effect, and the color change of the gel patch can be directly used to quantify the result, which has the advantages of being simple, efficient and on-site.

[0040] 5. By integrating the moisture resistance of the gel, the pre-reduction effect of UIO-66-NH2, and the color signal response performance of gold nanoparticles, the prepared UIO-66-NH2 / AG patch can realize the detection of H2S gas in ambient gas and non-destructive monitoring of freshness in meat product packaging.

[0041] In summary, this invention solves the problem of traditional gas sensors being severely affected by environmental humidity and airflow velocity, and realizes the preparation of a highly efficient metal-organic framework-gold nanoparticle gel patch with high stability and high sensitivity. The gel patch can be used to detect H2S gas in the environment and to monitor the freshness of meat products in packaging without damage. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the present invention;

[0043] Figure 2 These are characterization diagrams of the gel patch preparation process and the gold nanoparticle growth process; Figure 2 AC are scanning electron microscope images of UIO-66-NH2, UIO-66-NH2 / AG at high magnification, and UIO-66-NH2 / AG at low magnification, respectively; Figure 2 DF are transmission electron micrographs of UIO-66-NH2, UIO-66-NH2 / AG before and after the reaction with H2S, respectively. Figure 2 G represents the X-ray diffraction patterns of UIO-66-NH2, UIO-66-NH2 / AG before and after the reaction with H2S; Figure 2 H represents the infrared characterization images of UIO-66-NH2, UIO-66-NH2 / AG before and after the reaction with H2S; Figure 2 I represents the thermogravimetric analysis characterization diagrams of UIO-66-NH2 / AG before and after the reaction with H2S.

[0044] Figure 3 This is a graph showing the H2S gas detection performance of the UIO-66-NH2 / AG patch in this invention; Figure 3 A is the absorbance curve of chloroauric acid solution before and after the reaction with H2S; Figure 3 B is the curve showing the change of the A value of UIO-66-NH2 / AG over time after different response times compared to H2S; Figure 3 C represents the standard curves of the response of UIO-66-NH2 / AG to different concentrations of H2S.

[0045] Figure 4 This is a performance diagram of the UIO-66-NH2 / AG patch in this invention regarding environmental interference; Figure 4 A represents the H2S gas response results of UIO-66-NH2 / AG under different humidity levels and at 0.5, 1, and 5 ppm. Figure 4 B represents the response of UIO-66-NH2 / AG to 1 ppm H2S at different flow rates; Figure 4 C represents the relationship between the A value of UIO-66-NH2 / AG and time at 4℃ and room temperature; Figure 4 D represents the selectivity result for UIO-66-NH2 / AG.

[0046] Figure 5This is a diagram illustrating the practical application of the UIO-66-NH2 / AG patch in packaging for freshness detection. Figure 5 A is a schematic diagram of the testing process in the packaging; Figure 5 B is a diagram of the actual device used in the packaging; Figure 5 C represents the curve and actual image of UIO-66-NH2 / AG used in chicken packaging at room temperature, with the blank control shown below. Figure 5 D represents the curve and actual image of the A value changing over time when UIO-66-NH2 / AG is used in chicken packaging at 4℃. Below is the blank control.

[0047] Figure 6 This is a schematic diagram illustrating the performance of UIO-66-NH2 / PbCA2 in detecting H2S gas and its resistance to humidity interference. Figure 6 A is a schematic diagram of the concentration response of the UIO-66-NH2 / PbCA2 patch to H2S; Figure 6 B: Schematic diagram of the humidity interference resistance of the UIO-66-NH2 / PbCA2 patch. Detailed Implementation

[0048] To enable those skilled in the art to better understand the technical solution of the present invention, the method provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0049] The embodiments of the present invention are as follows:

[0050] Example 1:

[0051] This embodiment describes its application in a standard gas environment with known concentrations, and includes the following steps:

[0052] (1) Preparation of UIO-66-NH2 / AG patch

[0053] Step 1: Dissolve 0.1864 g of ZrCl4, 0.1328 g of 2-amino-1,4-terephthalic acid, and 1.464 g of benzoic acid in 28 mL of DMF, then add 144 μL of hydrochloric acid. Transfer the mixture to a sealed Teflon container, sonicate for 15 min, react at 120 °C for 24 h, cool to room temperature, wash three times with DMF and methanol to obtain UIO-66-NH2, and dry overnight at 70 °C.

[0054] Step 2: First, add 0.04g of agar to 5mL of water and heat to 120℃ to boil the agar, obtaining a homogeneous solution. Then, add 500μL of 1mg / mL UIO-66-NH2 and 500μL of 4mM chloroauric acid solution to 4mL of hot agar solution, and sonicate for 10s to obtain a homogeneous solution. Drop 200μL of the solution into a 1cm diameter, 2mm thick polytetrafluoroethylene template, cool at 4℃ for 3min, and demold the solidified sample to obtain a UIO-66-NH2 / AG patch for later use.

[0055] (2) Characterization of gel patch preparation process and gold nanoparticle response process

[0056] like Figure 2 As shown in Figure A, the prepared UIO-66-NH2 consists of rough-surfaced spheres with a diameter of 20-50 nm. These spheres, along with a chloroauric acid solution, are dispersed in a hot agar solution. Upon cooling, the agar units are linked by covalent or non-covalent bonds, forming a three-dimensional network structure. Water molecules are trapped by hydrogen bonds formed between the agar units, creating a colloid. This results in a porous structure formed by the sparse, interconnected network of agar molecules, exhibiting a colorless and transparent colloid under sunlight. Figure 2 B, 2C and illustrations).

[0057] To understand the response mechanism of the gel patch, the response process was characterized. TEM results showed that when chloroauric acid solution and UIO-66-NH2 were mixed, a large number of nanoparticles with a particle size much smaller than UIO-66-NH2 appeared. At this point, the gel patch did not exhibit a significant color change. Figure 2 (D, 2E and illustrations). This is because UIO-66-NH2 has weak reducing properties and can reduce chloroauric acid, but the reducing power is limited, only producing small-sized gold nanoparticles. However, upon continued reaction with H2S, the diameter of the nanoparticles significantly increases to the same level as UIO-66-NH2, at which point the color of the gel patch changes noticeably. Figure 2 (F and illustration). This shows that H2S continues to undergo a redox reaction with chloroauric acid, causing the original gold nanoparticles to grow further.

[0058] Other characterization methods, such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA), were used to comprehensively analyze the sensor fabrication process and the response process of gold nanoparticles.

[0059] Figure 2G represents the XRD results; the characteristic peak (5°) of the agarose gel indicates its amorphous structure. UIO-66-NH2 / AG exhibits a clearly corresponding crystal diffraction peak position, indicating successful preparation of the UIO-66-NH2 / AG gel patch. The UIO-66-NH2 / AG gel patch before and after the H2S reaction shows a distinct crystal diffraction peak at 30°, and compared to before the reaction, the full width at half maximum (FWHM) of this diffraction peak is significantly increased, indicating more complete crystal growth. FT-IR spectroscopy qualitatively explains the preparation and response process. Figure 2 H), a new emission peak appears at 581 nm for UIO-66-NH2 / AG, which originates from the vibration of the benzene ring skeleton, indicating that the MOF has been successfully loaded onto the sensor. Meanwhile, UIO-66-NH2 exhibits emission peaks at 500-700 cm⁻¹ before and after its reaction with chloroauric acid. -1 Changes in the conjugated structure of the benzene ring were observed within a certain range, at 1370 cm⁻¹. -1 A new characteristic absorption peak for the nitro group (-NO2) was observed, but the peak intensity was weak. This indicates that the reducing site of UIIO-66-NH2 is the amino group on the benzene ring in the ligand, and a nitro intermediate may have been generated during the process.

[0060] A high water content is essential for the growth and color development of gold nanoparticles within the gel. The water content of the prepared sensor was determined by TGA. Figure 2 As shown in Figure I, the AG gel loses nearly 98% of its mass in the 0-100℃ range, which is due to the large amount of water evaporation in this temperature range. After the addition of MOF and chloroauric acid, UIO-66-NH2 / AG loses about 80% of its weight in the 0-100℃ range. Therefore, it can be seen that the prepared sensor has a very high water content.

[0061] (3) Detection of H2S gas by UIO-66-NH2 / AG.

[0062] Firstly, by monitoring the colorimetric reaction of H2S standard solution with chloroauric acid solution, the feasibility of colorimetric quantitative detection using the UIO-66-NH2 / AG patch was confirmed, laying the foundation for the subsequent development of a colorimetric sensor suitable for H2S gas. Using hydrogen sulfide standard solution as the sole reducing agent in the reaction with chloroauric acid solution, after a period of time, the solution changed from pale yellow to purple and exhibited a UV absorption peak at 435 nm, consistent with the absorption peak of the standard gold nanoparticle solution. Figure 3 A).

[0063] To achieve better sensing performance, the sensor's contact time and incubation time were optimized. The results are as follows: Figure 3As shown in Figure B, for the same concentration of gas flow, the initial color of UIO-66-NH2 / AG deepens with increasing ventilation time. This is because the sensor actively captures H2S molecules, which accumulate on the surface of UIO-66-NH2 / AG. Chloroaurate ions inside the sensor continuously migrate to the surface, and the accumulation of numerous gold nanoparticles on the surface further deepens the color. This also explains why UIO-66-NH2 / AG appears yellow instead of the standard purplish-red. Simultaneously, after stopping contact with hydrogen sulfide gas, the gel color gradually deepens with increasing incubation time. This is because the hydrogen sulfide captured on the surface of UIO-66-NH2 / AG gradually diffuses inward and reacts with the chloroaurate inside.

[0064] Under the optimized conditions described above, UIO-66-NH2 / AG was placed in H2S gas of different concentrations for detection. For example... Figure 3 As shown in Figure C, the color of UIO-66-NH2 / AG changes with increasing H2S concentration; this change can also be observed directly with the naked eye. Figure 3 (C Illustration). As the concentration increases, the red color deepens, and its red gamut value A continuously increases. Therefore, a standard curve is constructed using the A value as the ordinate. UIO-66-NH2 / AG exhibits a good linear relationship in the range of 0-10 ppm, and the linear regression equation is: y = 0.8761x + 1.0869 (R²). 2 =0.9875), the detection limit of UIO-66-NH2 / AG was 14.6 ppb (S / N = 3, ). Figure 3 C) It is superior to other hydrogen sulfide colorimetric sensors, with a detection limit that is reduced by two orders of magnitude compared to commercial lead acetate test strips.

[0065] Test results

[0066] 1) Stability of UIO-66-NH2 / AG patch

[0067] In real-world testing applications, the environment is complex and ever-changing. Temperature, humidity, airflow speed, and other gas components can all interfere with the normal operation of the sensor. To better evaluate the practical application capabilities of UIO-66-NH2 / AG, its resistance to environmental interference was tested. First, the sensor's stability was examined under room temperature and 4°C refrigeration conditions, and the results are as follows: Figure 4 As shown in Figure A, UIO-66-NH2 / AG can maintain a good morphology and no significant color change within 10 days at room temperature, and can be stored for more than 15 days at 4℃, indicating that the prepared sensor has good stability.

[0068] 2) INO-66-NH2 / AG patch's resistance to environmental humidity interference

[0069] Humidity is the most common interference factor in gas sensing. The response of UIO-66-NH2 / AG to 0.5, 1, and 5 ppm H2S gas under different humidity conditions was compared. At room temperature, the A values ​​of UIO-66-NH2 / AG to 1 ppm H2S under different humidity conditions were 2.67, 3.64, 2.45, 5.21, 6.20, and 8.34, with a standard deviation of 1.44. It also showed good response to other concentrations of H2S. Figure 4 B). This demonstrates that UIO-66-NH2 / AG can adapt well to ambient humidity and maintain good detection performance within a range of 0-100% RH. This is thanks to the abundant water content provided by the gel substrate; drastic changes in ambient humidity do not have an unacceptable impact on the internal liquid phase environment of UIO-66-NH2 / AG within the response time.

[0070] 3) Iso-66-NH2 / AG patch's ability to resist airflow velocity interference

[0071] The gas flow rate determines the amount of target molecules the sensor can contact within a specified time. However, in this work, the gas flow rate has almost no impact on the sensing performance. The changes in the sensor's A value after reacting the prepared UIO-66-NH2 / AG with H2S gas at a concentration of 5 ppm and flow rates of 200, 300, 600, 900, 1200, and 1500 mL / min are shown. Figure 4 As shown in Figure C, the A values ​​of UIO-66-NH2 / AG after the response were 7.00, 8.16, 10.51, 8.48, 8.44, and 9.55, respectively, with a standard deviation of 1.05, indicating that UIO-66-NH2 / AG can adapt well to changes in gas flow rate. This may be because the response of H2S gas to the gel sensor relies not only on the static diffusion of gas molecules but also on the active adsorption of H2S molecules by water molecules. Even if the gas flow rate changes significantly, the electrostatic interaction between water molecules and H2S molecules does not change significantly.

[0072] 4) Specificity

[0073] The interference immunity of UIO-66-NH2 / AG to other potential gas molecules in actual products and the environment was also evaluated. Among the 12 selected gases, UIO-66-NH2 / AG only showed a significant response and a visually noticeable color change to H2S gas. Figure 4 (D and illustrations) The reaction with other gases is negligible, indicating that UIO-66-NH2 / AG has good selectivity.

[0074] Example 2:

[0075] This embodiment describes its application in an environment with unknown gas concentrations at room temperature. It includes the following steps:

[0076] 1) Preparation of UIO-66-NH2 / AG patch

[0077] Step 1: Dissolve 0.1864 g of ZrCl4, 0.1328 g of 2-amino-1,4-terephthalic acid, and 1.464 g of benzoic acid in 28 mL of DMF, then add 144 μL of hydrochloric acid. Transfer the mixture to a sealed Teflon container, sonicate for 15 min, react at 120 °C for 24 h, cool to room temperature, wash three times with DMF and methanol to obtain UIO-66-NH2, and dry overnight at 70 °C.

[0078] Step 2: First, add 0.04g of agar to 5mL of water and heat to 120℃ to boil the agar solution, obtaining a homogeneous solution. Then, add 500μL of 1mg / mL UIO-66-NH2 and 500μL of 4mM chloroauric acid solution to 4mL of hot agar solution, and sonicate for 10s to obtain a homogeneous solution. Drop 200μL of the solution into a 1cm diameter, 2mm thick polytetrafluoroethylene template, cool at 4℃ for 3min, and demold the solidified sample to obtain a UIO-66-NH2 / AG patch for later use.

[0079] 2) Monitoring the freshness of chicken packaging at room temperature

[0080] The practical application capability of UIO-66-NH2 / AG was evaluated by applying it to chicken packaging for meat freshness testing. Figure 5 The schematic diagram of A shows UIO-66-NH2 / AG fixed on the inner surface of the chicken's plastic packaging. Over time, the meat decomposes, releasing H2S. The higher the degree of decomposition, the higher the hydrogen sulfide concentration. The actual device is as follows... Figure 5 As shown in Figure B, UIO-66-NH2 / AG was colorless and transparent on day 0, but after 3 days, it turned a visible purple. The relationship between the A value of UIO-66-NH2 / AG and time at room temperature was recorded, as follows: Figure 5 As shown in Figure C, the label's A value increased from -0.58 to 2.55 within 3 days and remained constant for the next 4 days. During this period, the quality of the chicken rapidly declined, with significant water loss and obvious spoilage, emitting a foul odor. However, in empty packages without chicken, the label remained colorless, with a color difference value of around -0.52, showing no significant change over time.

[0081] Example 3:

[0082] This embodiment illustrates its application in an environment with unknown gas concentrations at 4°C. It includes the following steps:

[0083] 1) Preparation of UIO-66-NH2 / AG patch

[0084] Step 1: Dissolve 0.1864 g of ZrCl4, 0.1328 g of 2-amino-1,4-terephthalic acid, and 1.464 g of benzoic acid in 28 mL of DMF, then add 144 μL of hydrochloric acid. Transfer the mixture to a sealed Teflon container, sonicate for 15 min, react at 120 °C for 24 h, cool to room temperature, wash three times with DMF and methanol to obtain UIO-66-NH2, and dry overnight at 70 °C.

[0085] Step 2: First, add 0.04g of agar to 5mL of water and heat to 120℃ to boil the agar solution, obtaining a homogeneous solution. Then, add 500μL of 1mg / mL UIO-66-NH2 and 500μL of 4mM chloroauric acid solution to 4mL of hot agar solution, and sonicate for 10s to obtain a homogeneous solution. Drop 200μL of the solution into a 1cm diameter, 2mm thick polytetrafluoroethylene template, cool at 4℃ for 3min, and demold the solidified sample to obtain a UIO-66-NH2 / AG patch for later use.

[0086] 2) Monitoring the freshness of chicken packaging at 4℃

[0087] The prepared UIO-66-NH2 / AG was applied to chicken packaging for meat freshness testing to evaluate its practical application capability. Figure 5 A schematic diagram shows UIO-66-NH2 / AG fixed on the inner surface of the chicken's plastic packaging. Over time, the meat decomposes, releasing H2S; the higher the degree of decomposition, the higher the hydrogen sulfide concentration. Considering that chicken is mostly stored refrigerated in real life, the experiment was conducted at 4°C. Figure 5 As shown in Figure D, within packaging containing chicken, UIO-66-NH2 / AG also changed from colorless to red. However, it took 7 days to reach the same color difference value, and the color difference value remained unchanged for the next 7 days. This is because microbial activity is slow at 4°C, thus slowing down the spoilage rate. This result demonstrates that UIO-66-NH2 / AG also performs well under refrigeration conditions.

[0088] Comparative Example 1:

[0089] To verify the excellent properties of gold nanoparticles, the chloroauric acid solution was replaced with the same amount of lead acetate solution, and UIO-66-NH2 / PbCA2 gel was prepared.

[0090] (1) Preparation of UIO-66-NH2 / PbCA2 patch

[0091] Step 1: Dissolve 0.1864 g of ZrCl4, 0.1328 g of 2-amino-1,4-terephthalic acid, and 1.464 g of benzoic acid in 28 mL of DMF, then add 144 μL of hydrochloric acid. Transfer the mixture to a sealed Teflon container, sonicate for 15 min, react at 120 °C for 24 h, cool to room temperature, wash three times with DMF and methanol to obtain UIO-66-NH2, and dry overnight at 70 °C.

[0092] Step 2: First, add 0.04g of agar to 5mL of water and heat to 120℃ to boil the agar, obtaining a homogeneous solution. Then, add 500μL of 1mg / mL UIO-66-NH2 and 500μL of 4mM lead acetate solution to 4mL of hot agar solution, and sonicate for 10s to obtain a homogeneous solution. Drop 200μL of the solution into a polytetrafluoroethylene template with a diameter of 1cm and a thickness of 2mm, cool at 4℃ for 3min, and demold the solidified sample to obtain a UIO-66-NH2 / PbCA2 patch for later use.

[0093] (2) Detection of H2S gas by UIO-66-NH2 / PbCA2.

[0094] Lead acetate is the raw material for commercial H2S test strips. It produces a noticeable black color change upon contact with H2S; the higher the H2S concentration, the darker the black. The prepared UIO-66-NH2 / PbCA2 patch was placed in H2S gas of different concentrations for detection. For example... Figure 6 As shown in Figure A, the color of UIO-66-NH2 / PbCA2 changes with increasing H2S concentration; this change is not easily observed with the naked eye. Figure 6 (Illustration A). Similarly, using the rate of change of A as the ordinate to measure the magnitude of the change, it does not exhibit a good linear relationship in the range of 0-25 ppm, indicating that the role of metal nanoparticles in this system is irreplaceable.

[0095] Test results:

[0096] 1) INO-66-NH2 / PbCA2 patch's resistance to environmental humidity interference

[0097] Although lead acetate exhibits poor responsiveness to H2S, the high water content of the gel allows UIO-66-NH2 / PbCA2 to demonstrate good resistance to humidity interference. The responsiveness of UIO-66-NH2 / PbCA2 to H2S gas at different humidity levels (0.5, 1, and 5 ppm) was compared. At room temperature, the A values ​​of UIO-66-NH2 / PbCA2 to 1 ppm H2S under different humidity conditions were -0.39, -0.38, -0.24, -0.35, 0.23, and -0.17, with a standard deviation of 0.21. It also showed good responsiveness to other concentrations of H2S. Figure 6 B). This indicates that UIO-66-NH2 / PbCA2 can adapt well to ambient humidity and maintain good detection performance in the range of 0-100% RH. This is due to the abundant water content provided by the gel substrate; drastic changes in ambient humidity do not have an unacceptable impact on the internal liquid phase environment of UIO-66-NH2 / PbCA2 within the response time.

[0098] As can be seen from the above implementation examples, in the embodiments, UIO-66-NH2 can regulate the growth process of gold nanoparticles, improve the sensitivity of the sensor, realize practical application in meat product packaging, and achieve freshness detection under non-destructive conditions.

[0099] Therefore, this invention utilizes a gel as a carrier to realize the application of a gold nanoparticle growth system in the field of gas sensing. By regulating the reaction process through the pre-reduction effect of UIO-66-NH2, sensitive detection of H2S gas is achieved. By utilizing the rich microscopic water environment of the gel, resistance to interference from environmental humidity and airflow velocity is achieved, and a novel colorimetric sensor capable of stable and sensitive detection of H2S gas under a wide humidity range and various airflow velocity conditions is prepared.

[0100] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the method of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for detecting H2S gas concentration based on a colorimetric gel patch of metal-organic framework-gold nanoparticles, characterized in that: Includes the following steps: 1) Prepare chloroauric acid solution, metal-organic framework solution, and gel solution; In step 1), the metal-organic framework solution is UIO-66-NH2 solution, which is prepared using ZrCl4, 2-amino-1,4-terephthalic acid and benzoic acid. 2) Add chloroauric acid solution and metal-organic framework solution together to gel solution at 60-80℃ and mix evenly. After mixing, small-diameter metal nanoparticles appear. Then, drop the mixed solution into a mold, cool it and take it out to obtain colorimetric gel patch. 3) Place the colorimetric gel patch in a known environment without H2S gas and in a test environment containing H2S gas, and obtain the corresponding H2S gas concentration based on the color change of the gel patch in the two environments.

2. The method for detecting H2S gas concentration based on a colorimetric gel patch of metal-organic framework-gold nanoparticles according to claim 1, characterized in that: The UIO-66-NH2 solution was prepared in the following manner: 1.1) Dissolve ZrCl4, 2-amino-1,4-terephthalic acid and benzoic acid in DMF, add hydrochloric acid to form a mixture; 1.2) The mixture was then transferred to a container and sonicated. After that, it was reacted at 120°C for 24 h. After the reaction, it was cooled to room temperature and washed multiple times with DMF and methanol to obtain UIO-66-NH2. It was dried overnight to obtain metal-organic framework UIO-66-NH2 powder. 1.3) Weigh the dried UIO-66-NH2 powder into a centrifuge tube, add ultrapure water, and sonicate until the powder is evenly dispersed to prepare a UIO-66-NH2 solution.

3. The method for detecting H2S gas concentration based on a colorimetric gel patch of metal-organic framework-gold nanoparticles according to claim 1, characterized in that: In step 1), the gel solution is any non-reducing, colorless, and transparent gel, including agar gel solution, silk fibroin gel solution, sodium alginate gel solution, and polyethylene glycol gel.

4. The method for detecting H2S gas concentration based on a colorimetric gel patch of metal-organic framework-gold nanoparticles according to claim 1, characterized in that: In step 1), the gel solution is an agar gel solution, specifically: Weigh agar powder into a beaker, add 5 mL of ultrapure water, seal the beaker with aluminum foil, place it on a heating plate, set the temperature to 100-150℃, heat for 2-5 min until boiling, and prepare an agar gel solution with a mass fraction of 100-150℃.

5. The method for detecting H2S gas concentration based on a colorimetric gel patch of metal-organic framework-gold nanoparticles according to claim 1, characterized in that: In step 1), the concentration of the chlorometallic acid solution is 1-10 mM, and the concentration of the UIO-66-NH2 solution is 0.5-10 mg / mL. In step 2), the mass fraction of the gel solution is 0.08-0.8%, and the volume ratio of the chlorometallic acid solution, the UIO-66-NH2 solution, and the gel solution is 1:1:(3-18).

6. The method for detecting H2S gas concentration based on a colorimetric gel patch of metal-organic framework-gold nanoparticles according to claim 1, characterized in that: In step 2), the temperature of the gel solution is 60-80℃; In step 2), the uniform mixing method is ultrasonic mixing, with an ultrasonic intensity of 7-9 and a time of 10-30 s; In step 2), the volume of the mixed solution dripped into the mold is such that it fills the mold completely; In step 2), the mold used has a diameter of 1-2 cm and a depth of 1-2 mm, and the material is any one of polytetrafluoroethylene, glass, or plastic. In step 2), cooling is performed at 0-4°C for 3-5 minutes to completely transform the gel into a non-flowing phase.

7. The method for detecting H2S gas concentration based on a colorimetric gel patch of metal-organic framework-gold nanoparticles according to claim 1, characterized in that: In step 3), different H2S gas concentrations are set in advance and the same experiment is performed multiple times to obtain the color change of the corresponding colorimetric gel patch. The color change of the colorimetric gel patch under each experiment and the corresponding H2S gas concentration are fitted to establish a curve relationship. The color of the colorimetric gel patch after being placed in the test environment containing H2S gas is substituted into the curve relationship to obtain the corresponding H2S gas concentration.

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