H2S gas concentration detection method of colorimetric gel patch based on metal organic framework-gold nanoparticles

Abstract

The invention discloses a H2S gas concentration detection method of a colorimetric gel patch based on metal organic framework-gold nanoparticles. Adding a metal organic framework solution and a chlorine metal acid solution into the hot gel solution, uniformly mixing, dripping the mixed solution into a mold, cooling, demolding, placing in an H2S gas environment, shooting pictures before and after response, extracting color information change, and judging to obtain the concentration. According to the present invention, the preparation is simple, the preparation can be completed within 10 min, the anti-interference ability of the gas sensor on the environmental humidity is improved, the sensitivity of the sensor is improved, the practical application in the meat product package is achieved, and the freshness detection under the nondestructive condition is achieved.

Description

Technical Field

[0001] The present invention relates to the field of gas sensing, and in particular to a method for colorimetric analysis of H2S gas using a colorimetric gel patch based on a metal organic framework-gold nanoparticle. Background Art

[0002] In recent years, gas sensing has become an important and emerging research field, attracting significant interest in a wide range of fields, including the environment, medicine, and food safety. Hydrogen sulfide (H2S) has been shown to be a major odorous gas in atmospheric pollution, an indicator of food spoilage, and a signal molecule for clinical diagnosis. Therefore, developing effective and sensitive H2S detection methods is crucial.

[0003] Compared with traditional detection methods such as chromatography and spectroscopy, sensing technologies such as electrochemistry, fluorescence, and colorimetry have greatly improved in sensitivity, portability, and simplicity. Colorimetry is more intuitive, convenient, and inexpensive, requiring no external equipment and allowing for direct visual observation. However, most current gas sensors are gas-solid phase models, with limited selectable reaction systems, low sensitivity, and significant influences on gas flow rate and ambient humidity. Therefore, developing a stable, sensitive, and real-time monitoring technology that can withstand environmental interference is crucial.

[0004] The reduction of chloroauric acid with a reducing agent to form gold nanoparticles (AuNPs) is a well-established, sensitive colorimetric reaction widely used in the construction of colorimetric sensors. However, because the main component of the reaction is the chloroaurate ion, the reaction must be carried out in solution, making it difficult to apply to gas detection. Furthermore, due to the inherent nucleation-growth process of gold nanoparticles, these sensors typically require sufficient reducing agent and incubation time, which is undoubtedly unfavorable for fast and sensitive responses. Summary of the Invention

[0005] To address the aforementioned issues, this paper proposes a method for preparing a colorimetric gel patch based on a metal-organic framework (MOF) and gold nanoparticles, and its application in H2S gas colorimetric analysis. The innovation lies in the construction and application of a new highly sensitive sensor. The method evenly disperses the MOF and chloroauric acid solution in an agar gel to prepare the gel patch, which can be directly applied to H2S gas detection.

[0006] This invention simplifies the sensor fabrication process and enables the rapid preparation of a colorimetric gel patch based on a metal-organic framework (MOF)-gold nanoparticle-based material. The microscopic aqueous environment provided by the gel ensures the smooth occurrence of ionic reactions, effectively counteracting interference from ambient humidity and airflow velocity. The pre-reduction effect of the MOF regulates the reaction process, significantly improving detection sensitivity. The gel patch enables stable and sensitive detection of H2S gas across a wide humidity range and at various airflow velocities. It has also proven successful in meat packaging, providing valuable insights for non-destructive freshness monitoring.

[0007] The technical solutions adopted in the present invention are as follows:

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

[0009] 2) Adding the chlorometallic acid solution and the metal-organic framework solution to a gel solution at 60-80°C and uniformly mixing them, the mixture is sonicated at a certain intensity for a period of time to produce a large number of small-sized metal nanoparticles. Small-sized metal nanoparticles are smaller than the metal-organic framework particles. The mixed solution is then dripped into a custom mold, cooled, and removed to obtain a colorimetric gel patch.

[0010] 3) The colorimetric gel patch is placed in a known environment without H2S gas and in a test environment containing H2S gas for reaction. The colorimetric gel patch does not react when placed in the known environment without H2S gas. The corresponding H2S gas concentration is obtained based on the color change of the gel patch in the known environment and the test environment.

[0011] The colorimetric gel patch prepared by the present invention is not based on a gel patch that regulates the growth and coloration of gold nanoparticles using a metal organic framework, and is used for H2S gas colorimetric analysis, thereby realizing real-time H2S gas concentration monitoring.

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

[0013] In the step 1), the metal organic framework solution adopts UIO-66-NH2 solution, and the UIO-66-NH2 solution 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 as follows:

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

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

[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 metal nanoparticles with color change, including gold nanoparticles, silver nanoparticles, etc. The chlorometallic acid is chloroauric acid or chlorosilveric acid.

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

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

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

[0022] In the step 1), the concentration of the chlorometallic acid solution is 1-10 mM, the concentration of the UIO-66-NH2 solution is 0.5-10 mg / mL, and in the 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), which can ensure that the system is in optimal reaction conditions.

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

[0024] In the step 2), ultrasonic mixing is used for uniform mixing, with an ultrasonic intensity of 7-9 and a time of 10-30s to ensure uniform dispersion and fluidity of the solution;

[0025] In step 2), the volume of the mixed solution dripped into the mold is based on filling the mold, usually 200-400 μL, so that a gel patch of appropriate thickness can be obtained;

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

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

[0028] In step 3), the same experiment is performed multiple times with different H2S gas concentrations to obtain corresponding color changes of the colorimetric gel patch. A curve relationship is established by fitting the color change of the colorimetric gel patch in each experiment and the corresponding H2S gas concentration. The color of the colorimetric gel patch after being placed in a 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 RGB data using Image J software, and converting the RGB values into LAB.

[0030] In the specific implementation of the experimental test, the prepared gel patch can be placed in a culture dish and placed in a sealed bag together. H2S gas is introduced into the bag at a fixed airflow rate for reaction, and the color change is observed. The 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 based on the color change before and after the reaction combined with a pre-calibrated curve relationship between the color change and the H2S gas concentration.

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

[0032] In a specific embodiment of the present invention, the prepared metal-organic framework-gold nanoparticle gel patch was subjected to H2S gas response in a sealed bag. The patch was then removed and tested to obtain performance data. The gel patch's morphology, structure, and colorimetric properties were further characterized using electron microscopy, thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, mobile phone photography, and Image J software.

[0033] This invention utilizes a gel as a carrier to implement a gold nanoparticle growth system for gas sensing. The pre-reduction of the zirconium-based metal-organic framework UIO-66-NH2 regulates the reaction process, enabling sensitive detection of H2S gas. The gel's rich microscopic water environment provides resistance to interference from ambient humidity and airflow velocity, resulting in a novel colorimetric sensor capable of stable and sensitive H2S gas detection across a wide humidity range and various airflow velocities.

[0034] The invention is simple to prepare, requiring only 10 minutes. The microscopic water environment of the gel improves the gas sensor's ability to resist interference from ambient humidity, regulates the growth of gold nanoparticles, and increases sensor sensitivity, enabling practical application within meat product packaging and enabling non-destructive freshness detection.

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

[0036] 1. The preparation process of the present invention is simple, and only heating and cooling are required to obtain the sensor. The preparation process of the sensor can be completed within 10 minutes, saving preparation time. Moreover, this method can be implemented only by a heating plate, reducing instrument costs and being convenient and fast.

[0037] 2. Using gel as a carrier, the gold nanoparticle growth system was applied to the field of gas sensing. At the same time, the gel's rich microscopic water environment was utilized to achieve resistance to interference from ambient humidity and airflow velocity.

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

[0039] 4. The significant color change caused by the growth of gold nanoparticles can be detected by naked eyes and instruments, and the color change of the gel patch can be directly quantified, which has the advantages of being simple, efficient and can be detected 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 the ambient gas and the non-destructive monitoring of the freshness of meat products in packaging.

[0041] In summary, the present invention solves the problem that traditional gas sensors are severely disturbed by ambient humidity and airflow velocity, and realizes the preparation of efficient metal-organic framework-gold nanoparticle gel patches with high stability and high sensitivity. The gel patches can realize the detection of H2S gas in ambient gas and non-destructive monitoring of freshness in meat product packaging. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0043] Figure 2 This is a representation diagram of the gel patch preparation process and the gold nanoparticle growth process; Figure 2 AC are scanning electron micrographs 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 microscopy images of UIO-66-NH2, UIO-66-NH2 / AG before and after the reaction of UIO-66-NH2 / AG with H2S, respectively; Figure 2 G is the X-ray diffraction pattern of UIO-66-NH2, UIO-66-NH2 / AG before and after the reaction of UIO-66-NH2 / AG with H2S; Figure 2 H is the infrared characterization of UIO-66-NH2, UIO-66-NH2 / AG before and after the reaction of UIO-66-NH2 / AG with H2S; Figure 2 I is the thermogravimetric analysis characterization diagram of UIO-66-NH2 / AG before and after the reaction of UIO-66-NH2 / AG with H2S.

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

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

[0046] Figure 5This is a picture of the actual application of UIO-66-NH2 / AG patch for freshness detection in packaging; Figure 5 A is a schematic diagram of in-packaging detection; Figure 5 B is a diagram of the actual device used in packaging; Figure 5 C is the curve of A value change over time and the actual picture of UIO-66-NH2 / AG used in chicken packaging at room temperature, and the bottom is the blank control; Figure 5 D is the curve of A value change over time and the actual picture when UIO-66-NH2 / AG is used in chicken packaging at 4°C. The blank control is shown below.

[0047] Figure 6 This is a schematic diagram of the UIO-66-NH2 / PbCA2 test on H2S gas detection performance and humidity resistance. Figure 6 A is a schematic diagram of the response of the UIO-66-NH2 / PbCA2 patch to H2S concentration; Figure 6 B: Schematic diagram of the humidity resistance of the UIO-66-NH2 / PbCA2 patch. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the technical solution of the present invention, the method provided by the present invention is described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

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

[0050] Example 1:

[0051] This embodiment is applied in a standard gas environment with known concentration, 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 and sonicate for 15 minutes. React at 120°C for 24 hours. Cool to room temperature, then wash three times with DMF and methanol to yield UIO-66-NH₂, which is then dried at 70°C overnight.

[0054] Step 2: First, add 0.04g of agar to 5mL of water and heat to 120°C to boil the agar to obtain a homogeneous solution. Then, add 500μL of 1mg / mL UIO-66-NH2 and 500μL of 4mM chloroauric acid solution to 4mL of the hot agar solution, and sonicate for 10s to obtain a homogeneous solution. Each 200μL portion of the solution is dripped onto a polytetrafluoroethylene template with a diameter of 1cm and a thickness of 2mm. Cool at 4°C for 3 minutes. After solidification, demold the sample to obtain a UIO-66-NH2 / AG patch for use.

[0055] (2) Gel patch preparation process and characterization of gold nanoparticle response process

[0056] like Figure 2 As shown in Figure A, the prepared UIO-66-NH2 is a rough surface sphere with a diameter of 20-50nm. It is dispersed in a hot agar solution together with a chloroauric acid solution. When cooled, the agar units are connected by covalent or non-covalent bonds to form a three-dimensional network structure. The agar units are then captured by hydrogen bonds with water molecules to form a colloid, which presents a porous structure formed by stacking sparse network membranes formed by cross-linking agar molecules. The colloid appears colorless and transparent under sunlight. ( Figure 2 B, 2C and illustrations).

[0057] In order to understand the response mechanism of the gel patch, the response process was also 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 in the mixture. At this time, the gel patch did not show obvious color change ( Figure 2 D, 2E and illustrations). This is because UIO-66-NH2 has weak reducing properties and can reduce chloroauric acid, but its reducing ability is limited, and only small-sized gold nanoparticles can be produced. When it continues to react with H2S, the diameter of the nanoparticles increases significantly to the same level as UIO-66-NH2, and the color of the gel patch changes significantly ( Figure 2 F and inset). This indicates that H2S continues to undergo redox reaction with chloroauric acid, causing the original gold nanoparticles to further grow.

[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 preparation process of the sensor and the response process of gold nanoparticles.

[0059] Figure 2G is the XRD result. The characteristic peak of agar gel (5°) indicates its amorphous structure. UIO-66-NH2 / AG has a clear corresponding crystal diffraction peak position, indicating that the UIO-66-NH2 / AG gel patch was successfully prepared. The UIO-66-NH2 / AG gel patch before and after the reaction with H2S has a clear crystal diffraction peak at 30°. Compared with before the reaction, the half-peak width of the diffraction peak is significantly improved, indicating that the crystal growth is more complete. FT-IR spectrum qualitatively explains the preparation and response process ( Figure 2 H), UIO-66-NH2 / AG shows a new emission peak at 581nm, which is derived from the vibration of the benzene ring skeleton, indicating that MOF is successfully loaded on the sensor. UIO-66-NH2 shows a new emission peak at 500-700cm before and after the reaction with chloroauric acid. -1 The conjugated structure of the benzene ring was observed to change within the range of 1370 cm -1 A new characteristic absorption peak of the nitro group (-NO2) was observed at , but the peak intensity was weak, indicating that the reduction site of UIIO-66-NH2 was the amino group on the benzene ring of the ligand, and a nitro intermediate may have been generated during the process.

[0060] Rich water content is necessary to ensure the growth and color development of gold nanoparticles in the gel. The water content of the prepared sensor was measured by TGA. Figure 2 As shown in Figure 1, the mass loss of AG gel in the range of 0-100 °C is nearly 98%, which is due to the large amount of water volatilization in this temperature range. After the addition of MOF and chloroauric acid, UIO-66-NH2 / AG loses about 80% of its weight in the range of 0-100 °C. 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] First, by monitoring the color reaction of H2S standard solution to chloroauric acid solution, it was determined that the colorimetric quantitative detection of the UIO-66-NH2 / AG patch was feasible, laying the foundation for the subsequent development of a colorimetric sensor suitable for H2S gas. Using hydrogen sulfide standard solution as the only reducing agent to react with chloroauric acid solution, after a period of time, the solution turned from light yellow to purple and exhibited an ultraviolet absorption peak at 435nm, which is consistent with the absorption peak of the standard gold nanoparticle solution ( Figure 3 A).

[0063] In order to obtain better sensing performance, the contact time and incubation time of the sensor were optimized. Figure 3As shown in Figure B, for the same airflow concentration, the initial color of UIO-66-NH2 / AG darkens 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 within the sensor continuously migrate toward the surface, where a large number of gold nanoparticles accumulate, deepening the color. This also explains why UIO-66-NH2 / AG appears yellow instead of the standard purple-red. Furthermore, after cessation of contact with hydrogen sulfide gas, the color of the gel 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 chloroauric acid within.

[0064] Under the above optimized conditions, UIO-66-NH2 / AG was placed in H2S gas with different concentrations for detection. Figure 3 As shown in C, as the H2S concentration increases, the color of UIO-66-NH2 / AG changes, and this change can also be directly observed by the naked eye ( Figure 3 C illustration). As the concentration increases, the red color becomes darker and the red color range value A value continues to increase. Therefore, the calibration curve is constructed with the A value as the vertical axis. UIO-66-NH2 / AG shows a good linear relationship in the range of 0-10ppm, and the linear regression equation is: y = 0.8761x + 1.0869 (R 2 =0.9875), the detection limit of UIO-66-NH2 / AG was 14.6 ppb (S / N=3, Figure 3 C), outperforming other hydrogen sulfide colorimetric sensors and reducing the detection limit by 2 orders of magnitude compared to commercial lead acetate test paper.

[0065] Test situation

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

[0067] In actual detection application scenarios, the environment is complex and changeable. Temperature, humidity, air flow velocity, other gas components, etc. may interfere with the normal operation of the sensor. In order to better measure the practical application capability of UIO-66-NH2 / AG, its ability to resist environmental interference was tested. First, the stability of the sensor was investigated under room temperature and 4℃ refrigeration conditions. The results are as follows: Figure 4 As shown in A, UIO-66-NH2 / AG can maintain a good morphology without obvious color change at room temperature for 10 days, and can be stored for more than 15 days at 4°C, indicating that the prepared sensor has good stability.

[0068] 2) UIO-66-NH2 / AG patch's ability to resist interference from ambient humidity

[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 at different humidity levels was compared. At room temperature, the A values of UIO-66-NH2 / AG to 1 ppm H2S at different humidity levels were 2.67, 3.64, 2.45, 5.21, 6.20, and 8.34, respectively, with a standard deviation of 1.44. It also has good response to other concentrations of H2S ( Figure 4 B) This demonstrates that UIO-66-NH2 / AG is well-adapted to ambient humidity, maintaining excellent detection performance within a range of 0-100% RH. This is due to the abundant moisture provided by the gel base, which allows drastic changes in ambient humidity to have no unacceptable impact on the liquid phase within UIO-66-NH2 / AG within the response time.

[0070] 3) Anti-interference ability of UIO-66-NH2 / AG patch to airflow velocity

[0071] The airflow rate determines the amount of target molecules that the sensor can contact within a specified time. However, in this work, the airflow rate has almost no effect on the sensing performance. The changes in the A value of the sensor after the prepared UIO-66-NH2 / AG was reacted with H2S gas with a concentration of 5 ppm and flow rates of 200, 300, 600, 900, 1200, and 1500 mL / min. Figure 4 As shown in Figure C, the A values of UIO-66-NH2 / AG after 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 anti-interference ability of UIO-66-NH2 / AG to other potential gas molecules in actual products and environments was also evaluated. Among the 12 selected gases, UIO-66-NH2 / AG only produced a significant response and visible color change to H2S gas ( Figure 4 D and inset), the response to other gases is negligible, indicating that UIO-66-NH2 / AG has good selectivity.

[0074] Example 2:

[0075] This embodiment is applied to an environment with unknown gas concentration 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 and sonicate for 15 minutes. React at 120°C for 24 hours. Cool to room temperature, then wash three times with DMF and methanol to yield UIO-66-NH₂, which is then dried at 70°C overnight.

[0078] Step 2: First, add 0.04g of agar to 5mL of water and heat to 120°C to boil the agar solution to obtain a homogeneous solution. Then, add 500μL of 1mg / mL UIO-66-NH2 and 500μL of 4mM chloroauric acid solution to 4mL of the hot agar solution, and sonicate for 10s to obtain a homogeneous solution. Each 200μL portion of the solution is dripped onto a polytetrafluoroethylene template with a diameter of 1cm and a thickness of 2mm. Cool at 4°C for 3min. After solidification, demold the sample to obtain a UIO-66-NH2 / AG patch for use.

[0079] 2) Freshness monitoring of chicken packaging at room temperature

[0080] The practical application capability of UIO-66-NH2 / AG was evaluated by applying the prepared UIO-66-NH2 / AG to chicken packaging for meat freshness detection. Figure 5 Schematic diagram of A, UIO-66-NH2 / AG is fixed on the inner surface of the chicken plastic packaging. As time goes by, the meat becomes corrupted and releases H2S. The higher the degree of corruption, the higher the concentration of hydrogen sulfide. Figure 5 As shown in B, UIO-66-NH2 / AG was colorless and transparent on day 0, and after 3 days, UIO-66-NH2 / AG showed a purple color visible to the naked eye. The relationship between the A value of UIO-66-NH2 / AG at room temperature and time was recorded, as shown in Figure 5 As shown in Figure C, the label's A value increased from -0.58 to 2.55 over three days and remained constant for the next four days. During this period, the chicken's quality rapidly deteriorated, with significant water loss, obvious signs of spoilage, and a foul odor. However, in the empty packaging without the chicken, the label remained colorless, with a color difference value of approximately -0.52, showing no significant change over time.

[0081] Example 3:

[0082] This example describes the application of the method to an unknown gas concentration environment at 4°C. The method 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 and sonicate for 15 minutes. React at 120°C for 24 hours. Cool to room temperature, then wash three times with DMF and methanol to yield UIO-66-NH₂, which is then dried at 70°C overnight.

[0085] Step 2: First, add 0.04g of agar to 5mL of water and heat to 120°C to boil the agar solution to obtain a homogeneous solution. Then, add 500μL of 1mg / mL UIO-66-NH2 and 500μL of 4mM chloroauric acid solution to 4mL of the hot agar solution, and sonicate for 10s to obtain a homogeneous solution. Each 200μL portion of the solution is dripped onto a polytetrafluoroethylene template with a diameter of 1cm and a thickness of 2mm. Cool at 4°C for 3min. After solidification, demold the sample to obtain a UIO-66-NH2 / AG patch for use.

[0086] 2) Freshness monitoring of chicken in packaging at 4°C

[0087] The prepared UIO-66-NH2 / AG was applied to chicken packaging to detect meat freshness to evaluate the practical application capability of UIO-66-NH2 / AG. Figure 5 Schematic diagram of A, UIO-66-NH2 / AG is fixed on the inner surface of the chicken plastic packaging. As time goes by, the meat becomes corrupted and releases H2S. The higher the degree of corruption, the higher the concentration of hydrogen sulfide. Considering that in real life, chicken is mostly refrigerated, the experiment was conducted at 4℃. Figure 5 As shown in Figure D, inside the package containing chicken, UIO-66-NH2 / AG also changed from colorless to red. However, it took seven days to reach the same color difference, and the color difference remained constant over the next seven days. This is because microbial activity is slow at 4°C, slowing spoilage. This result demonstrates that UIO-66-NH2 / AG also works well under refrigerated conditions.

[0088] Comparative Example 1:

[0089] In order to verify the excellent properties of gold nanoparticles, the chloroauric acid solution was replaced with the lead acetate solution with the same content 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 and sonicate for 15 minutes. React at 120°C for 24 hours. Cool to room temperature, then wash three times with DMF and methanol to yield UIO-66-NH₂, which is then dried at 70°C overnight.

[0092] Step 2: First, add 0.04g of agar to 5mL of water and heat to 120°C to boil the agar to obtain a homogeneous solution. Then, add 500μL of 1mg / mL UIO-66-NH2 and 500μL of 4mM lead acetate solution to 4mL of the hot agar solution. Ultrasonicate for 10 seconds to obtain a homogeneous solution. Each 200μL portion of the solution is dripped onto a 1cm diameter, 2mm thick polytetrafluoroethylene template. Cool at 4°C for 3 minutes. After solidification, demold the sample to obtain a UIO-66-NH2 / PbCA2 patch for use.

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

[0094] Lead acetate is the raw material of commercial H2S test paper. It will produce a significant black change after contact with H2S. The higher the H2S concentration, the darker the black. The prepared UIO-66-NH2 / PbCA2 patch was placed in H2S gas with different concentrations for detection. Figure 6 As shown in A, as the H2S concentration increases, the color of UIO-66-NH2 / PbCA2 changes, and this change is not obvious even when observed with the naked eye ( Figure 6 A (inset). Similarly, the change rate of the A value is used as the ordinate to measure the magnitude of the change. It does not have 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 situation:

[0096] 1) Anti-interference ability of UIO-66-NH2 / PbCA2 patch to ambient humidity

[0097] Although lead acetate has a poor response to H2S, thanks to the rich water content of the gel, UIO-66-NH2 / PbCA2 still shows good resistance to humidity interference. The response of UIO-66-NH2 / PbCA2 to 0.5, 1, and 5 ppm H2S gas at different humidity levels 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, respectively, with a standard deviation of 0.21. It also has good response to other concentrations of H2S ( Figure 6 B) This demonstrates that UIO-66-NH2 / PbCA2 is well adapted to ambient humidity, maintaining excellent detection performance within a range of 0-100% RH. This is due to the abundant moisture provided by the gel base, which allows drastic changes in ambient humidity to have no unacceptable impact on the liquid phase within UIO-66-NH2 / PbCA2 within the response time.

[0098] As can be seen from the above implementation cases, 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, the present invention uses gel as a carrier to realize the application of gold nanoparticle growth system in the field of gas sensing, regulates the reaction process through the pre-reduction effect of UIO-66-NH2, and realizes sensitive detection of H2S gas; utilizes the rich microscopic water environment of gel to achieve resistance to interference from ambient humidity and airflow velocity, and prepares a new colorimetric sensor that can stably and sensitively detect H2S gas in a wide humidity range and under various airflow velocity conditions.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the method of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for detecting H2S gas concentration using a colorimetric gel patch based on a metal organic framework-gold nanoparticles, characterized by: The following steps are involved: 1) Prepare chloroauric acid solution, metal-organic framework solution, and gel solution; 2) adding the chlorometallic acid solution and the metal organic framework solution to the gel solution at 60-80°C and uniformly mixing them, resulting in the formation of small-sized metal nanoparticles. The mixed solution is then dripped into a mold, cooled, and removed to obtain a colorimetric gel patch. 3) The colorimetric gel patch is placed in a known environment without H2S gas and in a test environment containing H2S gas, and the corresponding H2S gas concentration is obtained based on the color change of the gel patch in the two environments.

2. The method for detecting H2S gas concentration using a colorimetric gel patch based on a metal organic framework-gold nanoparticle according to claim 1, characterized in that: In the step 1), the metal organic framework solution adopts UIO-66-NH2 solution, and the UIO-66-NH2 solution is prepared using ZrCl4, 2-amino-1,4-terephthalic acid and benzoic acid.

3. The method for detecting H2S gas concentration using a colorimetric gel patch based on a metal organic framework-gold nanoparticle according to claim 2, characterized in that: The UIO-66-NH2 solution was prepared as follows: 1.1) Dissolve ZrCl4, 2-amino-1,4-terephthalic acid, and benzoic acid in DMF, and add hydrochloric acid to form a mixture; 1.2) The mixture was transferred to a container for ultrasonic treatment and then reacted at 120°C for 24 hours. After the reaction, the mixture was cooled to room temperature and washed with DMF and methanol multiple times to obtain UIO-66-NH2, which was then dried overnight to obtain UIO-66-NH2 powder of the metal-organic framework; 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.

4. The method for detecting H2S gas concentration using a colorimetric gel patch based on a metal organic framework-gold nanoparticle according to claim 1, characterized in that: The nanoparticles are any metal nanoparticles with color change, including gold nanoparticles, silver nanoparticles, etc., and the chlorometallic acid is chloroauric acid or chlorosilveric acid.

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

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

7. The method for detecting H2S gas concentration using a metal organic framework-gold nanoparticle colorimetric gel patch according to claim 1, characterized in that: In the step 1), the concentration of the chlorometallic acid solution is 1-10 mM, the concentration of the UIO-66-NH2 solution is 0.5-10 mg / mL, and in the 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).

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

9. The method for detecting H2S gas concentration using a colorimetric gel patch based on a metal organic framework-gold nanoparticle according to claim 1, characterized in that: In step 3), the same experiment is performed multiple times with different H2S gas concentrations to obtain corresponding color changes of the colorimetric gel patch. A curve relationship is established by fitting the color change of the colorimetric gel patch in each experiment and the corresponding H2S gas concentration. The color of the colorimetric gel patch after being placed in a test environment containing H2S gas is substituted into the curve relationship to obtain the corresponding H2S gas concentration.

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