Double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environment and preparation method of double-sided hydrogel colorimetric sensor

Abstract

The invention discloses a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in an extreme environment and a preparation method of the double-sided hydrogel colorimetric sensor, and belongs to the technical field of gas sensors. The double-sided hydrogel colorimetric sensor comprises a sponge network loaded with a CoCl2 / SbOCl color developing agent and a tough film loaded with the SbOCl color developing agent, wherein a sponge framework of the double-sided hydrogel colorimetric sensor is melamine resin nano sponge. The double-sided hydrogel colorimetric sensor has a double-sided characteristic, SbOCl is introduced, and heat resistance and durability are promoted by utilizing hydrophobicity and flame retardance of the SbOCl and a strong cross-linking effect of the SbOCl and PVA (Polyvinyl Alcohol); coCl2 is introduced, and on the basis of an ionic crosslinking and hydration action mechanism, the generation of ice crystals is remarkably inhibited, the anti-freezing performance is optimized, and the functional stability at low temperature is improved; a melamine resin nano sponge framework is introduced, so that the physical structure stability is fundamentally enhanced, and mechanical support and stress resistance are provided.

Description

Technical Field

[0001] The present application relates to the technical field of gas sensors, and in particular to a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments and a preparation method thereof. Background Art

[0002] As a highly flammable and explosive gas with a strong, pungent odor, high concentrations of H2S pose a significant threat to human health. H2S is a common gas in our daily lives, and trace amounts are also produced during human metabolism. H2S gas sensors based on sensing materials are not only convenient and easy to use, but also enable rapid detection at low cost and low power consumption compared to larger equipment.

[0003] Colorimetric sensors are currently effective tools for H2S detection due to their ability to respond in seconds, detect at room temperature, and monitor wirelessly. However, most colorimetric H2S gas sensors are limited to low-concentration detection, suffering from a narrow response range, low accuracy, and significant susceptibility to humidity and pH changes. Therefore, the development of a double-sided hydrogel colorimetric sensor and its preparation method for H2S leak detection in extreme environments is urgently needed. Summary of the Invention

[0004] In view of this, the present application provides a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments and a preparation method thereof. The double-sided hydrogel colorimetric sensor has double-sided characteristics, introduces SbOCl, and utilizes its hydrophobicity, flame retardancy and strong cross-linking effect with PVA to promote heat resistance and durability; introduces CoCl2, and based on the ionic cross-linking and hydration mechanism, significantly inhibits ice crystal formation, optimizes antifreeze performance, and improves functional stability at low temperatures; introduces a melamine resin nanosponge skeleton to fundamentally enhance the stability of the physical structure, provide mechanical support and stress resistance.

[0005] Specifically, the following technical solutions are included: In the first aspect, the present application provides a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments. The double-sided hydrogel colorimetric sensor includes a sponge network loaded with CoCl2 / SbOCl colorimetric agent and a tough film loaded with SbOCl colorimetric agent. The sponge skeleton of the double-sided hydrogel colorimetric sensor is a melamine resin nanosponge.

[0006] In some embodiments, the double-sided hydrogel colorimetric sensor has a length of 0.95-1.05 cm, a width of 0.55-0.65 cm, and a thickness of 0.75-0.85 cm, a thickness of the sponge network of 0.7-0.82, and a thickness of the tough film of 0.3-0.5 mm.

[0007] In some embodiments, the material loaded by the sponge network is CoCl2 / SbOCl / PVA / BA hydrogel, and the material loaded by the tough film is SbOCl / PVA / BA hydrogel.

[0008] In some embodiments, the average pore size of the sponge skeleton of the double-sided hydrogel colorimetric sensor is 50-70 nm.

[0009] In a second aspect, the present application provides a method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments, the preparation method comprising: Step 1, adding cobalt chloride hexahydrate to deionized water, and then adding to glycerol to obtain a CoCl2 solution; Step 2, adding antimony trichloride to anhydrous ethanol to obtain a SbCl3 solution; Step 3, mixing the CoCl2 solution and the SbCl3 solution, and then adding the high molecular weight polymer PVA and fully dissolving it in the solution to obtain a mixed solution; Step 4, adding a crosslinking agent, boric acid, to the mixed solution of step 3 to perform a crosslinking reaction to obtain a double-sided hydrogel precursor solution, CoCl2 / SbOCl / PVA / BA; Step 5: inject the double-sided hydrogel precursor solution CoCl2 / SbOCl / PVA / BA into the sponge and let it stand to obtain a double-sided hydrogel colorimetric sensor.

[0010] In some embodiments, in step 1, the volume of deionized water is 11.5-12.5 mL, the volume of glycerol is 2.5-3.5 mL, the total volume of water and glycerol is 15 mL, the mass of cobalt chloride hexahydrate is 0.5-0.54 g, and the mass fraction of CoCl2 solution is 3.06-3.31 wt%.

[0011] In some embodiments, the mass of antimony trichloride in step 2 is 0.95-1.05 g, and the mass fraction of the SbCl 3 solution is 24.08-26.62 wt %.

[0012] In some embodiments, the mass of the high molecular weight polymer PVA in step 3 is 2.3-2.5 g, and the mass of the high molecular weight polymer PVA in step 3 is 2.3-2.5 g. 2+ With Sb 3+ Carry out preliminary ion crosslinking, the reaction temperature of crosslinking reaction is 70~80 o C.

[0013] In some embodiments, the mass of the boric acid in step 4 is 0.35-0.37 g.

[0014] In some embodiments, the reaction temperature after adding boric acid in step 4 is 60-80 o C.

[0015] The beneficial effects of the technical solutions provided by the embodiments of the present application include at least: The present invention provides a double-sided hydrogel colorimetric sensor for H2S leak monitoring in extreme environments and its preparation method. This double-sided hydrogel colorimetric sensor features dual-sided properties. The introduction of SbOCl utilizes its hydrophobicity, flame retardancy, and strong crosslinking with PVA to enhance heat resistance and durability. The introduction of CoCl2 significantly inhibits ice crystal formation, optimizes antifreeze performance, and enhances functional stability at low temperatures through ionic crosslinking and hydration mechanisms. Furthermore, the introduction of a melamine resin nanosponge skeleton fundamentally enhances physical structural stability, providing mechanical support and stress resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 A schematic diagram of the structure of a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided in an embodiment of the present application; Figure 2 Schematic diagram of the preparation process of a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided in an embodiment of the present application; Figure 3 The sensor signal effect diagram of the double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided by the embodiment of the present application: (a) The effect of SbCl3 and CoCl2 at different ratios on the tough film sensor signal, (b) The effect of SbCl3 and CoCl2 at different ratios on the sponge network sensor signal; Figure 4 Response curve renderings of a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided by an embodiment of the present application: (a) Response curve of the tough film at H2S concentrations of 1 to 280 ppm, (b) Response curve of the sponge network at H2S concentrations of 1 to 300 ppm; Figure 5Dynamic response effect diagram of the tough film of the double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided in the embodiments of the present application: (a) schematic diagram of the response of the tough film in H2S atmosphere, (b) dynamic sensing curve of the tough film under 1-280 ppm H2S, (c) dynamic response curve of the tough film in 280 ppm H2S, (d) linear fitting effect diagram of the response of the tough film and gas concentration, (e) response difference effect diagram of the tough film under 0.1-0.9 ppm H2S gas concentration, (f) selectivity of the tough film in air, N2, C6H6, C2H2, CH4, O2, CO2, NO2, SO2, NH3 and H2S atmospheres; Figure 6 Dynamic response effect diagram of the sponge network of the double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided in the embodiments of the present application: (a) schematic diagram of the response of the sponge network in H2S atmosphere, (b) dynamic sensing curve of the sponge network under 1-280 ppm H2S, (c) dynamic response curve of the sponge network in 280 ppm H2S, (d) linear fitting effect diagram of the response of the sponge network and gas concentration, (e) response difference effect diagram of the sponge network under 0.1-0.9 ppm H2S gas concentration, (f) selectivity of the sponge network in air, N2, C6H6, C2H2, CH4, O2, CO2, NO2, SO2, NH3 and H2S atmospheres; Figure 7 The double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided by the embodiment of the present application has different ratios of SbCl3 and CoCl2 (a) at 25 o C, color response effect diagram under 40% RH, (b) double-sided hydrogel sensor with different concentrations of SbOCl and CoCl2 at -20 o C storage for 0~96 h. (c) shows the mass retention rate curve of the double-sided hydrogel sensor with different concentrations of SbOCl and CoCl2 at 50 o Mass retention curves of sensors with different pore sizes after storage in an oven at 25 o C, double-sided response effect diagram under 40% RH, (e) sensors with different pore size sponges at -20 o C storage for 0~96 h. (f) Mass retention curve of sensors with different pore size sponges at 50 o C for 0-10 h; Figure 8The double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided in the embodiment of the present application (a) is stored at -20 o Response of the tough film to 280 ppm H2S at 0-96 h under 40°C. (b) Storage at -20 o Response of the sponge network to 300 ppm H2S at 0-96 h under 50 °C. (c) o Response of the sensor's tough film to 280 ppm H2S at 0-10 h; (d) stored at 50 o Response value of the sensor sponge network to 300 ppm H2S at 0-10 h; Figure 9 The present invention provides a double-sided sensing mechanism of a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments; Figure 10 The operation process of the DF-LSTM gas concentration prediction model of the double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided in the embodiment of the present application; Figure 11 Application test diagrams of the double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments provided in the embodiments of the present application: (a) H2S concentration value for detecting the degree of chicken spoilage within 0 to 7 days, (b) H2S concentration for detecting the degree of egg spoilage within 1 to 50 days, and (c) schematic diagram of remote real-time monitoring of H2S leakage and alarm functions. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0019] In order to make the technical solutions and advantages of the present application clearer, the implementation methods of the present application will be described in further detail below with reference to the accompanying drawings.

[0020] For clarity, the embodiments of the present application will be described in further detail below with reference to the accompanying drawings.

[0021] In the first aspect, the present application provides a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments, such as Figure 1The double-sided hydrogel colorimetric sensor consists of a sponge network (1) loaded with a CoCl2 / SbOCl colorimetric reagent and a flexible film (2) loaded with a SbOCl colorimetric reagent. The sponge framework of the double-sided hydrogel colorimetric sensor is a melamine resin nanosponge. The sponge network (1) loaded with the CoCl2 / SbOCl colorimetric reagent is pink, while the flexible film (2) loaded with the SbOCl colorimetric reagent is white.

[0022] In some embodiments, the double-sided hydrogel colorimetric sensor can be 1 cm long, 0.6 cm wide, and 0.8 cm thick, with the sponge network 1 having a thickness of 0.76 cm and the tough film 2 having a thickness of 0.4 mm. This configuration is beneficial for broadening the sensor's detection range and improving detection accuracy.

[0023] In some embodiments, the material loaded on the sponge network 1 is CoCl2 / SbOCl / PVA / BA hydrogel, and the material loaded on the tough film 2 is SbOCl / PVA / BA hydrogel, thereby forming a double-sided hydrogel system with double-sided properties.

[0024] In some embodiments, the average pore size of the sponge skeleton of the double-sided hydrogel colorimetric sensor can be 60 nm. This configuration improves the mass retention and structural stability of the double-sided hydrogel colorimetric sensor. The hydrogel is cross-linked within the nanoporous sponge skeleton, forming a denser and more stable three-dimensional network structure, making the device more stable. The synergy between the nanosponge, SbOCl, and CoCl2 also enhances mass retention and structural stability.

[0025] In summary, the present application provides a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments. The double-sided hydrogel colorimetric sensor has double-sided characteristics, introduces SbOCl, and utilizes its hydrophobicity, flame retardancy and strong cross-linking effect with PVA to promote heat resistance and durability; introduces CoCl2, based on the ionic cross-linking and hydration mechanism, significantly inhibits ice crystal formation, optimizes antifreeze performance, and improves functional stability at low temperatures; introduces a melamine resin nanosponge skeleton to fundamentally enhance the stability of the physical structure, provide mechanical support and stress resistance.

[0026] In a second aspect, the present application provides a method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments, the preparation method comprising: Step 1, adding cobalt chloride hexahydrate to deionized water, and then adding glycerol to obtain a CoCl2 solution; Step 2, adding antimony trichloride to anhydrous ethanol to obtain a SbCl3 solution; Step 3, mixing the CoCl2 solution and the SbCl3 solution, and then adding the high molecular weight polymer PVA and fully dissolving it in the solution to obtain a mixed solution; Step 4, adding a crosslinking agent, boric acid, to the mixed solution of step 3 to perform a crosslinking reaction to obtain a double-sided hydrogel precursor solution, CoCl2 / SbOCl / PVA / BA; Step 5: injecting the double-sided hydrogel precursor solution CoCl2 / SbOCl / PVA / BA into the sponge and allowing it to stand to obtain the double-sided hydrogel colorimetric sensor.

[0027] In some embodiments, in step 1, the volume of deionized water is 11.5-12.5 mL, the volume of glycerol is 2.5-3.5 mL, the total volume of water and glycerol is 15 mL, the mass of cobalt chloride hexahydrate is 0.5-0.54 g, and the mass fraction of CoCl2 solution is 3.06-3.31 wt%.

[0028] In some embodiments, the mass of antimony trichloride in step 2 is 0.95-1.05 g, and the mass fraction of the SbCl 3 solution is 24.08-26.62 wt %.

[0029] In some embodiments, the mass of the high molecular weight polymer PVA in step 3 is 2.3-2.5 g, and the mass of the high molecular weight polymer PVA in step 3 is 2.3-2.5 g. 2+ With Sb 3+ Carry out preliminary ion crosslinking, the reaction temperature of crosslinking reaction is 70~80 o C.

[0030] In some embodiments, the mass of the boric acid in step 4 is 0.35-0.37 g.

[0031] In some embodiments, the reaction temperature after adding boric acid in step 4 is 60-80 o C.

[0032] Preferably, the preparation process of the double-sided hydrogel colorimetric sensor is as follows Figure 2 First, prepare 12 mL of deionized water and 3 mL of glycerol (Gly). Add 0.52 g of cobalt chloride hexahydrate (CoCl2·6H2O) to 12 mL of deionized water, then add 3 mL of glycerol. Stir evenly at room temperature (RT) on a magnetic stirrer to obtain a CoCl2 solution. Next, add 1 g of antimony trichloride (SbCl3) to 5 mL of anhydrous ethanol while stirring to obtain a SbCl3 solution. After mixing, quickly transfer the mixture to a circulating water bath and heat at 70 oThe mixture was stirred at room temperature. 2.4 g of polyvinyl alcohol (PVA) was then slowly added to the mixed solution. The circulating water bath temperature was raised to 75°C and stirred for 8 hours. 0.36 g of boric acid (BA) was then added to the mixed solution and stirred for another hour to obtain the double-sided hydrogel precursor solution, CoCl2 / SbOCl / PVA / BA. The sponge was evenly divided into 2 cm x 1 cm x 0.5 cm sections, rinsed by immersion in pure water, and then placed in a 60°C oven for 4 hours. The precursor solution, CoCl2 / SbOCl / PVA / BA, was injected into the sponge, thoroughly soaked, and ultrasonically cleaned for 1 hour. After standing at room temperature for 12 hours, a double-sided hydrogel colorimetric sensor with double-sided properties was obtained. This double-sided hydrogel colorimetric sensor comprises a sponge network 1 loaded with CoCl2 / SbOCl colorimetric reagents and a tough film 2 loaded with SbOCl colorimetric reagents.

[0033] It should be noted that the introduced SbCl3, a Lewis acid, rapidly hydrolyzes in water to form the highly hydrophobic SbOCl. SbOCl is stable and hydrophobic. Due to the effective support provided by the sponge for the gel system and the effects of gravity during static operation, some SbOCl is evenly distributed within the sponge network 1, while the remaining portion sinks to the bottom due to gravitational potential energy, becoming the primary component of the tough film 2.

[0034] The effects of different ratios of SbCl3 and CoCl2 on the double-sided hydrogel colorimetric sensor were tested. The ratios were calculated based on the molar concentration ratio of the two in the total mixed solution, with a total volume of 20 mL. It was determined that a molar concentration ratio of 1:1 was the best. In the preferred embodiment above, 0.52g:1g is converted to a molar concentration of 200:219.1mM. Figure 3 (a), When the ratio of SbCl3 to CoCl2 increases (0:1 to 1:1), the response value of the tough film 2 increases from 0 to 44.86. When the ratio continues to increase (1.5:1 to 2:1), the response value of the tough film 2 begins to decrease. This may be because too little SbCl3 will lead to the incompleteness of the tough film 2, resulting in a low response value. Excessive SbCl3 participation makes the tough film 2 more hydrophobic and increases the thickness, affecting the diffusion of gas and the color development reaction, resulting in a loss of the response value of the tough film 2. Figure 3 (b) shows a similar pattern, that is, when the ratio of SbCl3 to CoCl2 is 1:1, the response of sponge network 1 reaches the highest value. Therefore, 1:1 is the optimal molar concentration ratio of SbCl3 to CoCl2.

[0035] The response time of the double-sided hydrogel colorimetric sensor in H2S is also an important parameter in the detection process. Figure 4 (a) with Figure 4(b) shows the response curves of the tough film 2 at H2S concentrations of 1-280 ppm and the sponge network 1 at H2S concentrations of 1-300 ppm. The response value increases significantly with the increase of reaction time. The t res Within 25s. Including the reserved observation time (5s), the optimal exposure time (time to reach stable full response) is 30s, at which point the sensor response is basically saturated in each stage. It should be noted that the sensor response time is defined as t res . t res It is the response time for the sensor color to change by 90% after the target gas is introduced.

[0036] The performance of the double-sided hydrogel colorimetric sensor, which was constructed with a molar concentration ratio of SbCl₃ to CoCl₂ of 1:1 and a total Gly content of 15% (i.e., volume ratio of the total solution), was tested. First, the sensing properties of the tough film 2 of the double-sided hydrogel colorimetric sensor were tested. Figure 5 (a) Shows the response effect of the double-sided hydrogel colorimetric sensor in H2S gas. Figure 5 (b) shows the dynamic sensing curve of the flexible film 2 under 1-280 ppm H2S. The flexible film 2 of the sensor exhibits reliable response elasticity when the H2S concentration increases. Figure 5 (c) is the response curve of the tough film 2 in 280 ppm H2S. It can be observed that the t res The detection time was 22 s, and the total detection time was less than 30 s, demonstrating the rapid detection characteristics of the double-sided hydrogel colorimetric sensor. Figure 5 (d) shows a good linear fit between the response of tough film 2 and the increase in gas concentration (50 ppm each time). According to the linear fitting function (y = 0.128x + 10.404, R 2 =95.68%), and the theoretical LOD (lower limit of detection) of the response of tough film 2 was calculated to be 0.12 ppm. Figure 5 (e) shows the response difference under H2S gas concentration of 0.1~0.9 ppm. It can be seen that the sensor still has a good response at a concentration of 0.2-0.9 ppm. The experiment verifies that the LOD of the response of the tough film 2 can reach 0.2 ppm.

[0037] Since some gases often appear together with H2S in certain application contexts. Selectivity is the key feature of the double-sided hydrogel colorimetric sensor. In order to test the selectivity of the tough film 2, 11 identical sensors were prepared and placed in 11 independent detection chambers, and 11 gases (air, N2, C6H6, C2H2, CH4, O2, CO2, NO2, SO2, NH3 and H2S) were introduced into each chamber respectively. The controlled gas concentration was 280 ppm, and the tough film 2 in the H2S gas showed obvious color changes, which can also be identified by the naked eye. In the gas environment of air, N2, C6H6, C2H2, CH4, O2, CO2, NO2, SO2 and NH3, the sensor showed almost no change. As Figure 5 (f) The sensitivity of flexible film 2 to H2S differs significantly from that of other gases. H2S was also tested in the presence of 280 ppm of N2, C6H6, C2H2, CH4, O2, CO2, NO2, SO2, NH3, and pure air to simulate the presence of complex gas interferences during sensor detection. Relative standard deviation (RSD) was used to assess the differences; an RSD of less than 10% indicates minimal fluctuation in the test results.

[0038] Figure 6 (a) Shows the response effect of the double-sided hydrogel colorimetric sensor sponge network 1 in H2S gas. Figure 6 (b) shows the good response of sponge network 1 under 1-300 ppm H2S, Figure 6 (c) shows the t of sponge network 1 at 300 ppm. res The response of sponge network 1 to H2S gas at 1-300 ppm showed a good linear fit, as shown in Figure 1. Figure 6 (d). Based on the linear fitting function (y = 0.152x + 5.983, R 2 =94.64%), the LOD of sponge network 1 is 0.25 ppm. As shown in 6(e), the experiment verified that sponge network 1 can achieve H2S resolution at low concentrations, with an actual LOD of 0.3 ppm. Further, the excellent selectivity and H2S resolution ability of sponge network 1 under complex gas conditions were verified, as shown in Figure 6 (f).

[0039] The mass retention rate was introduced to quantify the antifreeze, heat resistance and water retention properties of the double-sided hydrogel colorimetric sensor. The molar concentrations of CoCl2 and SbCl3 solutions in the hydrogel precursor solution were controlled to be 50mM~300mM (the concentrations of the two solutions were kept consistent at 1:1). Based on this, the hydrogel was synthesized and tested to find the optimal concentration. Finally, it was found that the best effect was achieved when both were 200mM. At this time, the mass ratio of CoCl2 to SbCl3 was 0.52g:1g. The molar concentrations of CoCl2 and SbCl3 solutions were controlled to be 50:50mM, 100:100mM, 200:200mM, 250:250mM, and 300:300mM, and were named Co-Sb-50, Co-Sb-100, Co-Sb-200, Co-Sb-250 and Co-Sb-300, respectively. These sensors were tested at 25 o C. The color response at 40% RH is as follows Figure 7 (a) The Co-Sb-200 tough film 2 and sponge network 1 have the largest response values. o C constant temperature refrigerator for 0~96h, and calculate the mass retention rate every 12h. Figure 7 (b) Co-Sb-50, Co-Sb-100, Co-Sb-200, Co-Sb-250 and Co-Sb-300 sensors at -20 o C storage 0 ~ 96h mass retention rate curve, at -20 o After freezing at 50 °C for 96 h, Co-Sb-200 showed the highest mass retention. o In the mass retention curve of C stored in the oven for 0~10h, the mass retention rate of Co-Sb-200 is the highest, such as Figure 7 Therefore, after comprehensive consideration, the concentrations of SbOCl and CoCl2 were both selected to be 200 mM.

[0040] The average pore size of the sponge is also a key factor affecting stability. Three types of sensors were prepared using sponges with average pore sizes of 60 nm, 0.5 mm, and 2.5 mm, respectively named Sponge-1, Sponge-2, and Sponge-3. The above steps were repeated, and Sponge-1, Sponge-2, and Sponge-3 were placed at 25 o C, observe the double-sided response at 40% RH, store at -20 o C for 0~96h and 50 o C for 0~10h, and calculate the mass retention rate during the process. Figure 7 (d), Figure 7 (e) and Figure 7(f) It can be seen that Sponge-1 has the best response performance and the highest mass retention rate. Therefore, choosing a melamine resin nanosponge with an average pore size of 60 nm as the internal skeleton can further improve the structural stability of the double-sided hydrogel.

[0041] The concentrations of SbOCl and CoCl2 (200 mM) and the average pore size of the sponge skeleton of the double-sided hydrogel colorimetric sensor (60 nm) were determined to further test the stability of the double-sided hydrogel colorimetric sensor. The double-sided hydrogel colorimetric sensors prepared in the same batch were stored at -20 o C for 0-96h, gas response test every 12h, tough film 2 is used to detect 280 ppm H2S, sponge network 1 is used to detect 300 ppm H2S. Figure 8 (a) and Figure 8 (b) As the storage time increases from 12h to 96h, the response values of the tough film 2 and sponge network 1 of the double-sided hydrogel colorimetric sensor remain basically unchanged (RSD=0.784%, RSD=0.464%). o C working environment still has a stable response. Similarly, the double-sided hydrogel colorimetric sensor is placed at 50 o C for 0~10h, perform H2S response test every 2h, such as Figure 8 (c) and Figure 8 (d) As the storage time increases from 2h to 10h, the response values of the tough film 2 and sponge network 1 of the double-sided hydrogel colorimetric sensor remain basically unchanged (RSD=0.851%, RSD=1.215%). o C's working environment is stable.

[0042] The above tests show that the antifreeze performance, thermal stability, and water retention properties of the double-sided hydrogel colorimetric sensor make the hydrogel-based colorimetric H2S sensor highly adaptable to the environment and have excellent stability, breaking the limitation of durability and broadening the application range of hydrogel-based sensors.

[0043] like Figure 9The response mechanism of the double-sided hydrogel colorimetric sensor is mainly attributed to the high sensitivity and interaction of SbCl3 and CoCl2 to H2S. The introduced SbCl3, as a Lewis acid, can quickly hydrolyze in water to form highly hydrophobic SbOCl. SbOCl is stable and hydrophobic. Due to the effective loading and management of the nanosponges, part of the SbOCl is evenly distributed in the sponge network 1, and the other part sinks to the bottom due to gravitational potential energy, serving as the main component of the tough film 2. CoCl2 is a highly hygroscopic salt and is introduced as the main color developer of the sponge network 1. Co in CoCl2 2+ (Electron configuration is [Ar]3d 7 ) has an empty d orbital. The H2O molecule is a Lewis base, in which the O atom has a lone pair of electrons. The lone pair of electrons of the O atom will fill the Co 2+ The empty d orbital of the ion forms a coordination bond, thus forming the hydrated ion [Co(H2O)6] 2+ , pink in the tough film 2. When the tough film 2 and sponge network 1 of the double-sided hydrogel colorimetric sensor are placed in increasing concentrations of H2S gas, both gradually turn brown-black, which is due to the SbO and Co in the double-sided hydrogel. 2+ The effective adsorption of H2S generates brown-black Sb2S3 and CoS, which makes the double-sided hydrogel colorimetric sensor respond in color. This process is shown in equations (1) to (3): (1) (2) (3) (4) In addition, the double-sided hydrogel colorimetric sensor showed excellent stability during storage and operation. In addition to being a color developer, SbOCl and CoCl2 also have high stability. The single network of PVA / BA hydrogel can no longer support the pursuit of stability in real applications, although it has good biocompatibility and is simple to prepare. The double-sided hydrogel colorimetric sensor is made by introducing SbO - and Co 2+ An ultra-stable ternary network structure was constructed. The chemical reactions during the hydrogel formation process are shown in equations (5) to (10), where [-CH2-CH(OH)-]n refers to the PVA structural unit with a degree of polymerization of n. SbOCl and CoCl2 can not only act as catalysts to increase the crosslinking reaction rate in a system containing borax, but also SbO + with [Co(H2O)6] 2+It also forms coordination bonds with the hydroxyl (OH) groups on the PVA molecular chains, creating a multilayer bridging structure, further increasing the degree and strength of crosslinking, thereby improving the physical stability of the double-sided hydrogel. Ultimately, based on the ternary network structure formed by the simultaneous crosslinking of PVA with SbOCl, CoCl2, and borax, the double-sided hydrogel colorimetric sensor exhibits excellent environmental adaptability and stable performance, making it a stable and reliable colorimetric H2S sensor.

[0044] (5) (6) (7) (8) (9) (10) Long-term storage can lead to a slight decrease in response value (RSD <2.5%). Although the double-sided hydrogel colorimetric sensor is very stable, it is inevitably affected by the negative effects of hydrogel dehydration. Algorithms can be used to address this issue in detection applications. The performance loss of the double-sided hydrogel colorimetric sensor is mainly due to changes in time. If the impact of time changes on the response of both sides of the double-sided hydrogel colorimetric sensor is fully considered, the error can be effectively compensated.

[0045] In some embodiments, a double-sided feature-based long short-term memory (DF-LSTM) network model was designed to enable rapid and accurate H2S detection using a double-sided hydrogel colorimetric sensor in practical applications, improving its feasibility and reliability in diverse applications. The DF-LSTM model can bind time series during training, effectively inheriting valid information from past events and better handling the long-term dependency between response values and gas concentrations. With the help of the DF-LSTM, the double-sided hydrogel colorimetric sensor can more accurately monitor H2S concentrations.

[0046] Figure 10The DF-LSTM process is shown. The receptive region in the original image is segmented using YOLOv8. Image data of the double-sided response of the double-sided hydrogel colorimetric sensor is fed into the DF-LSTM as the primary input. The RGB map of the original image is extracted, the image is resized, and the pixel values are normalized (3×224×224). The double-sided feature data x(R1, G1, B1, R2, G2, B2) in the input layer is bounded to a time series with four time steps, with the training data for each time step being input. The timestamp-bound double-sided feature data X = [x1, x2, x3, x4] is progressively fed into the Long Short-Term Memory Network (LSTM). At each time step, the LSTM unit calculates its forget gate, input gate, candidate cell state, and output gate. The forget gate determines whether to forget useless data from the previous time step. The input gate controls which new information should be written to the cell state. The candidate cell states provide possible new memory values. Finally, the cell state Ct and hidden state ht are updated to be passed to the next time step. At each time step in the sequence, the hidden state ht calculated by the hidden layer of LSTMd (LSTM-hidden layer) is used as the output (LSTM-output). This state is ultimately mapped to the output layer through two fully connected layers (Fc_1, Fc_2), resulting in the predicted H2S concentration. The DF-LSTM can be installed on smart terminals, enabling fast and convenient H2S detection while avoiding accuracy errors caused by long-term use. This allows the double-sided hydrogel colorimetric sensor to achieve nearly 100% monitoring accuracy, enabling intelligent, ultra-high-precision H2S detection for multi-domain applications.

[0047] In some embodiments, the double-sided hydrogel colorimetric sensor can be used for food monitoring and H2S leak warning.

[0048] Antifreeze properties of double-sided hydrogel colorimetric sensor (operating temperature range can be as low as -20 o C), giving it significant advantages for food safety testing at low temperatures. The double-sided hydrogel colorimetric sensor can be used not only as a smart food refrigerator magnet at home, but also for smart packaging of refrigerated products in supermarkets and freshness monitoring during cold chain transportation.

[0049] like Figure 11(a) On the third day of meat storage, visual observation revealed little change in the meat's condition. However, the color of the double-sided hydrogel colorimetric sensor changed significantly, with response values (ΔE) reaching 9.76 for the tough film 2 and 4.28 for the sponge network 1, respectively, and a detected H2S concentration of 2.58 ppm. Continued monitoring until the seventh day revealed that the meat had deteriorated, with response values (ΔE) increasing to 14.02 for the tough film 2 and 6.2 for the sponge network 1, respectively, and a detected H2S concentration of 10.12 ppm. This demonstrates that H2S generated by meat deterioration can be sensitively captured by the double-sided hydrogel colorimetric sensor.

[0050] In addition, if Figure 11 (b) The wired transmission camera module was replaced with a wireless transmission camera module (HSD-VC403W, 8.5 megapixels, 2.4G wireless USB 3.0). This was combined with a double-sided hydrogel colorimetric sensor and a smartphone application loaded with DF-LSTM to design a remote H2S monitoring and alarm system. The double-sided hydrogel colorimetric sensor offers low power consumption, continuous and spontaneous color signal feedback, and long-term stable performance. The double-sided response captured by the camera is then displayed on a smartphone via wireless transmission, enabling timely, convenient, and secure observation from the factory to the office. Because the smartphone application incorporates cloud technology, users can simultaneously upload data to cloud storage, ultimately enabling multi-terminal access and remote H2S monitoring.

[0051] By simulating H2S leakage in a closed environment and giving a real-time alarm, it was verified that the double-sided hydrogel colorimetric sensor can be used for H2S leakage warning. 0~10 ppm of H2S was input into the transmission mode detection chamber, and the system monitored the concentration changes throughout the process. The threshold value can be set in advance in the smartphone application. Referring to the national occupational safety standard (GBZ 2.1-2019), the H2S concentration threshold is set at 6.7 ppm. The monitoring data during the experiment will be transmitted to the App in real time. Figure 11 (c) When the H2S concentration is below 6.7 ppm, the smartphone displays a green "SAFE:)." As more H2S is introduced until the concentration exceeds the threshold, the smartphone displays a red "Danger!" sign. When the H2S is turned off, the H2S concentration drops below the threshold, causing the green "SAFE:)" sign to reappear. Therefore, the double-sided hydrogel colorimetric sensor can achieve remote, real-time monitoring of H2S and provide timely alerts for potential H2S leaks.

[0052] In summary, the present application provides a method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments. The double-sided hydrogel colorimetric sensor prepared by this method has double-sided characteristics. SbOCl is introduced to promote heat resistance and durability by utilizing its hydrophobicity, flame retardancy and strong cross-linking effect with PVA; CoCl2 is introduced to significantly inhibit ice crystal formation based on the ionic cross-linking and hydration mechanism, optimize antifreeze performance, and improve functional stability at low temperatures; and a melamine resin nanosponge skeleton is introduced to fundamentally enhance the stability of the physical structure, provide mechanical support and stress resistance.

[0053] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the present invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only.

[0054] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. Double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments, characterized by: The double-sided hydrogel colorimetric sensor comprises a sponge network (1) loaded with a CoCl2 / SbOCl color developer and a tough film (2) loaded with a SbOCl color developer. The sponge skeleton of the double-sided hydrogel colorimetric sensor is a melamine resin nanosponge.

2. The double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 1, characterized in that: The double-sided hydrogel colorimetric sensor has a length of 0.95-1.05 cm, a width of 0.55-0.65 cm, and a thickness of 0.75-0.85 cm. The thickness of the sponge network (1) is 0.7-0.82 cm, and the thickness of the tough film (2) is 0.3-0.5 mm.

3. The double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 1, characterized in that: The material loaded on the sponge network (1) is CoCl2 / SbOCl / PVA / BA hydrogel, and the material loaded on the tough film (2) is SbOCl / PVA / BA hydrogel.

4. The double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 1, characterized in that: The average pore size of the sponge skeleton of the double-sided hydrogel colorimetric sensor is 50-70 nm.

5. The method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 1, characterized in that: The preparation method comprises: Step 1, adding cobalt chloride hexahydrate to deionized water, and then adding glycerol to obtain a CoCl2 solution; Step 2, adding antimony trichloride to anhydrous ethanol to obtain a SbCl3 solution; Step 3, mixing the CoCl2 solution and the SbCl3 solution, and then adding the high molecular weight polymer PVA and fully dissolving it in the solution to obtain a mixed solution; Step 4, adding a crosslinking agent, boric acid, to the mixed solution of step 3 to perform a crosslinking reaction to obtain a double-sided hydrogel precursor solution, CoCl2 / SbOCl / PVA / BA; Step 5: injecting the double-sided hydrogel precursor solution CoCl2 / SbOCl / PVA / BA into the sponge and allowing it to stand to obtain the double-sided hydrogel colorimetric sensor.

6. The method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 5, characterized in that: In step 1, the volume of deionized water is 11.5-12.5 mL, the volume of glycerol is 2.5-3.5 mL, the total volume of water and glycerol is 15 mL, the mass of cobalt chloride hexahydrate is 0.5-0.54 g, and the mass fraction of CoCl2 solution is 3.06-3.31 wt%.

7. The method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 5, characterized in that: In step 2, the mass of antimony trichloride is 0.95-1.05 g, and the mass fraction of the SbCl3 solution is 24.08-26.62 wt%.

8. The method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 5, characterized in that: The mass of the high molecular weight polymer PVA in step 3 is 2.3~2.5g, and 2+ With Sb 3+ Carry out preliminary ion crosslinking, the reaction temperature is 70~80 o C.

9. The method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 5, characterized in that: The mass of boric acid in step 4 is 0.35~0.37g.

10. The method for preparing a double-sided hydrogel colorimetric sensor for H2S leakage monitoring in extreme environments according to claim 5, characterized in that: The reaction temperature after adding boric acid in step 4 is 60~80 o C.

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