Preparation method of colorimetric sensing gel for detecting formaldehyde and colorimetric sensing gel

Abstract

This invention discloses a method for preparing a colorimetric sensing gel for formaldehyde detection, and the corresponding colorimetric sensing gel. The preparation method includes the following steps: (1) grafting aldehyde groups; (2) grafting sensing molecules; (3) preparation of porous gel and core-shell structure. This invention uses chemical doping to graft amino-rich polyamine sensing molecules onto green and renewable calcium alginate to prepare a low-cost, green porous hydrogel for detecting formaldehyde concentration in the air.

Description

Technical Field

[0001] This invention belongs to the technical field of formaldehyde detection, and relates to a method for preparing a colorimetric sensing gel for formaldehyde detection and the colorimetric sensing gel itself. Background Technology

[0002] Formaldehyde (HCHO) is a highly reactive organic compound, widely used as an important chemical raw material in numerous fields, such as the medical industry, wood industry, textile industry, and construction industry. Free formaldehyde in these materials gradually volatilizes with airflow, entering indoor air and spreading into the environment, causing serious negative impacts on humans and the environment. For humans, long-term inhalation of formaldehyde can cause respiratory diseases and allergic reactions, and even lead to diseases such as nasopharyngeal carcinoma, nasal cavity cancer, and leukemia. Secondly, formaldehyde interacts with chemicals in the environment to form harmful air pollutants (such as ozone and fine particulate matter). These harmful air pollutants adversely affect air quality and plant growth. Since the release period of formaldehyde from indoor decoration materials can be as long as 15 years, there is currently no way to completely eliminate it. Regular testing of formaldehyde levels in the indoor environment is necessary, and removal should be carried out when levels exceed the standard to reduce its negative environmental impact.

[0003] Common methods for formaldehyde determination include instrumental methods, colorimetric sensing, and electrical transfer sensing. Instrumental methods are relatively accurate, but require on-site sampling and analysis back in a laboratory. The procedures are complex, time-consuming, and expensive, and require skilled operators. Electrical transfer sensing allows for on-site detection in a relatively short time, but the procedures are very complex and expensive, making it difficult to implement in ordinary households. Compared to these two methods, colorimetric sensing offers advantages such as simplicity, affordability, and on-demand testing. However, it lacks standardized operating procedures, calibration methods from metrology departments, and verification standards. However, if the goal is simply to understand the formaldehyde pollution level in indoor air and a test report is not required, colorimetric sensing is more suitable.

[0004] Colorimetric sensing consists of sensing molecules, a sensing substrate, and an indicator. Sensing molecules are reactants that can chemically react with formaldehyde. Indicators convert the concentration of the products generated by the reaction between the sensing molecules and formaldehyde into a color change that is perceptible to the human eye. The sensing substrate is the porous matrix to which the sensing molecules are attached. Commonly used sensing substrates include paper, cotton, organic polymers, and gels. Different substrates lead to variations in the absorption of sensing molecules, diffusion of the detected gas, and absorption, indirectly resulting in differences in detection time, sensitivity, and other detection results. Currently, formaldehyde detectors made from these substrates bind sensing molecules to the substrate surface through physical doping (hydrogen bonds, van der Waals forces). However, physical doping methods may suffer from problems such as weak absorption, long detection times, high storage requirements, and low sensitivity.

[0005] Currently, formaldehyde detectors fabricated on these substrates all bind sensor molecules to the substrate surface through physical doping (hydrogen bonds, van der Waals forces). However, existing physical doping methods suffer from problems such as weak adsorption of sensor molecules, long detection times, high storage requirements, and low sensitivity. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a colorimetric sensing gel for detecting formaldehyde and the colorimetric sensing gel itself.

[0007] According to one aspect of the present invention, a method for preparing a colorimetric sensing gel for detecting formaldehyde is provided, comprising the following steps:

[0008] (1) Grafting of aldehyde groups

[0009] First, dissolve 0.2wt%–2.5wt% sodium alginate in 39wt%–41wt% deionized water, and then add 0.1wt%–4.2wt% aldehyde and 6wt%–12.5wt% water. Stir for 20–45 minutes to prepare a transparent solution A.

[0010] (2) Grafting of sensing molecules

[0011] Dissolve 0.5wt%–8wt% of polyamine in 33wt%–46wt% deionized water to prepare solution B;

[0012] Then, solution B is added dropwise to solution A at a rate of 4-8 ml / min. After the addition is complete, the mixture is stirred for 1-4 hours at 20-35℃ and 300-1000 rpm to obtain a uniform light pink emulsion.

[0013] Add 0.01wt% to 0.84wt% of indicator to the emulsion and stir for 0.5 to 2 hours to ensure that the indicator is evenly dispersed in the emulsion, forming a rose-red emulsion C;

[0014] (3) Preparation of porous gels and core-shell structures

[0015] Emulsion C is added dropwise to a 2-10 wt% divalent cation solution and reacted for 20-120 min to gel the gel. The gel spheres are then added to a 5-20 wt% alcohol solution and stirred for 2-10 min to adsorb an epoxy resin layer onto the surface of the gel spheres. Finally, the gel is filtered and freeze-dried at -50°C for 12-48 h to obtain the amino-rich colorimetric sensing gel for formaldehyde detection.

[0016] In some embodiments, the stirring step in the aldehyde grafting is vigorous stirring, thereby preparing a transparent solution A.

[0017] In some embodiments, the grafting of the sensing molecules involves grafting amino-rich polyamine sensing molecules onto the surface of calcium alginate, which is a porous substrate, via acetal and elimination reactions, thereby improving the adsorption strength of the sensing molecules.

[0018] In some embodiments, the sensing indicator is bound to the sensing molecule and sensing substrate by hydrogen bonds and van der Waals forces, thereby rapidly and accurately sensing changes in the sensing molecule and thus precisely sensing changes in formaldehyde content.

[0019] In some embodiments, during the preparation steps of the porous gel and the core-shell structure, the porous hydrogel rich in polar groups is formed by a double substitution reaction with divalent cations. In addition, an epoxy resin protective shell is formed on the surface of the hydrogel through the core-shell structure to isolate it from interference from the external environment.

[0020] In some embodiments, the aldehydes include either glutaraldehyde or adipaldehyde, or any combination thereof.

[0021] In some embodiments, the polyamine includes any one of polyethyleneimine and branched polyethyleneimine, or any combination thereof.

[0022] In some embodiments, the alcohol solution includes any one or any combination thereof, such as an ethanol solution containing epoxy resin, an aqueous solution containing polyvinyl alcohol, or a combination thereof.

[0023] In some embodiments, the indicator includes any one or any combination of phenolphthalein, catechol purple, m-cresol purple, and benzyl alcohol.

[0024] In some embodiments, the divalent cation solution includes any one of CaCl2, CaCO3, sodium silicate, Al2(SO4)3, CaSO4, AlCl3, FeCl3, FeCl2, Fe(NO3)2, Fe(NO3)3, or any combination thereof.

[0025] According to a second aspect of the present invention, a colorimetric sensing gel is provided, the colorimetric sensing gel being prepared in the above embodiments, wherein amino sensing molecules are grafted onto the surface of the porous material calcium alginate.

[0026] The method for preparing an amino-rich colorimetric sensing gel for detecting formaldehyde according to the present invention has at least one or at least a portion of the following advantages:

[0027] 1. Grafting sensing molecules into porous substrates

[0028] To overcome the problems of weak adsorption of sensing molecules, long detection time, complex storage, and low sensitivity associated with physical doping methods, this invention employs acetal and elimination reactions to successfully graft amino-rich sensing molecules onto the surface of a porous substrate. The prepared colorimetric sensing gel exhibits significantly improved performance, achieving a sensitivity of 0.02 mg / m³. 3 The shortest detection time is only 10 minutes, while the detection limit can be reduced to 0.06 mg / m³. 3 .

[0029] 2. Combination of sensing indicators

[0030] To improve the sensing accuracy of the sensor indicator, this invention uses hydrogen bonding and van der Waals forces to tightly attach the sensor indicator containing polar groups to the sensing molecule and the sensing substrate. This method enables the sensor indicator to rapidly and accurately detect changes in the sensing molecule, thereby achieving precise sensing of changes in formaldehyde content and improving the accuracy of the colorimetric sensing gel.

[0031] 3. Preparation of core-shell structure

[0032] Currently, a key problem commonly found in various colorimetric detectors is their extreme sensitivity to the external environment. Therefore, they require strict sealing before detection to isolate them from external interference factors, which inconveniences transportation and storage and easily leads to damage. To address this challenge, this invention employs an innovative core-shell structure method, forming an epoxy resin protective shell on the surface of the colorimetric sensing gel. This effectively isolates the effects of the external environment, improving detection accuracy and extending service life. The detector prepared in this way has a shelf life of over 6 months, greatly facilitating transportation and storage.

[0033] 4. Material selection for sensing molecules and porous substrates

[0034] Calcium alginate has attracted much attention due to its numerous outstanding characteristics, including non-toxicity, non-polluting nature, low cost, wide availability, renewability, and high porosity. Furthermore, its abundant hydroxyl and carboxyl groups enable it to efficiently adsorb formaldehyde. Given these excellent properties, this invention intelligently selects calcium alginate, a green biomass material, as a porous substrate to reduce product costs and improve the accuracy of formaldehyde detection. In addition, polyamines such as polyethyleneimine possess many advantages, such as low cost, stable performance, excellent biocompatibility, and abundant amino groups. Therefore, this invention selects polyamines such as polyethyleneimine as sensing molecules to further enhance the efficiency of this technology. These two materials not only achieve significant improvements in sensitivity, detection time, and detection limit, but also inherit the advantages of low cost and simple preparation process of physical grafting.

[0035] Other objects and advantages of the invention will become apparent from the following description of embodiments of the invention with reference to the accompanying drawings, and will help to provide a comprehensive understanding of the invention. Attached Figure Description

[0036] The present invention will be further described in detail with reference to the accompanying drawings, in which:

[0037] Figure 1 A flowchart illustrating a method for preparing a colorimetric sensing gel for formaldehyde detection according to an embodiment of the present invention;

[0038] Figure 2 The morphology of the hydrogel prepared by the method for preparing a colorimetric sensing gel for formaldehyde detection according to an embodiment of the present invention, wherein, Figure 2 a and Figure 2 b is a scanning electron microscope image of the colorimetric sensing gel at different magnifications. Figure 2 c is a photograph of a colorimetric sensing gel with a shell structure. Figure 2 d is a photograph of the colorimetric sensing gel after the shell has been removed;

[0039] Figure 3 A time-optimized view of a colorimetric sensing gel according to an embodiment of the present invention, wherein, Figure 3 Figure a shows the changes in the L, a, and b values ​​of the colorimetric sensing gel over time in formaldehyde gas. Figure 3 b is a graph showing the evolution of the corresponding color difference value of the colorimetric sensing gel over time. Figure 3 c represents the overall trend of color change of the colorimetric sensing gel in formaldehyde gas over time.

[0040] Figure 4 To provide sensitivity and selectivity to formaldehyde concentration according to one embodiment of the present invention, wherein Figure 4 A is a view showing the trend of color difference values ​​of the colorimetric sensor gel as formaldehyde concentration increases. Figure 4Figure b shows a comparison of the color difference values ​​of the colorimetric sensing gel in various common indoor pollutant gases. Figure 4 c is a view of the color change trend of the colorimetric sensing gel at different formaldehyde concentrations. Figure 4 d is a view comparing the color changes of the colorimetric sensing gel in various indoor pollutant gases;

[0041] Figure 5 This is a view of the stability / lifespan of a colorimetric sensing gel according to an embodiment of the present invention, wherein... Figure 5 a is a view showing the changing trends of L, a, and b values ​​after a certain period of time, before and after detection, for the colorimetric sensing gel. Figure 5 b is a view showing the color difference between samples at different times and the sample at day 0 in air without formaldehyde concentration, and the color difference between samples at different times and the sample at day 0 after exposure to formaldehyde gas. Figure 5 c uses the same time frame as a baseline, showing the results at 0.1 mg / m³. 3 Samples under formaldehyde concentration conditions and 0 mg / m³ 3 A view of the color difference values ​​of the sample under formaldehyde concentration conditions. Figure 5 d is a photograph of the colorimetric sensing gel at different times. Detailed Implementation

[0042] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In this specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation thereof.

[0043] Furthermore, in the following detailed description, numerous specific details are set forth for ease of explanation to provide a thorough understanding of the embodiments disclosed herein. However, it will be apparent that one or more embodiments may be practiced without these specific details.

[0044] See Figure 1 According to the inventive concept of the present invention, a method for preparing a colorimetric sensing gel for detecting formaldehyde is provided, and the specific preparation process is as follows:

[0045] (1) Grafting of aldehyde groups

[0046] First, dissolve 0.2wt%–2.5wt% sodium alginate in 39wt%–41wt% deionized water, and then add 0.1wt%–4.2wt% aldehyde and 6wt%–12.5wt% water. Stir for 20–45 minutes to prepare a transparent solution A.

[0047] (2) Grafting of sensing molecules

[0048] Dissolve 0.5wt%–8wt% of polyamine in 33wt%–46wt% deionized water to prepare solution B;

[0049] Then, solution B is added dropwise to solution A at a rate of 4-8 ml / min. After the addition is complete, the mixture is stirred for 1-4 hours at 20-35℃ and 300-1000 rpm to obtain a uniform light pink emulsion.

[0050] Add 0.01wt% to 0.84wt% of indicator to the emulsion and stir for 0.5 to 2 hours to ensure that the indicator is evenly dispersed in the emulsion, forming a rose-red emulsion C;

[0051] (3) Preparation of porous gels and core-shell structures

[0052] Emulsion C is added dropwise to a 2-10 wt% divalent cation solution and reacted for 20-120 min to gel the gel. The gel spheres are then added to a 5-20 wt% alcohol solution and stirred for 2-10 min to adsorb an epoxy resin layer onto the surface of the gel spheres. Finally, the gel is filtered and freeze-dried at -50°C for 12-48 h to obtain the amino-rich colorimetric sensing gel for formaldehyde detection.

[0053] Specifically, the stirring step in the grafting of the aldehyde group involves vigorous stirring to prepare a transparent solution A.

[0054] The grafting of the sensing molecules involves grafting amino-rich polyamine sensing molecules onto the surface of calcium alginate, which is a porous substrate, through acetal and elimination reactions.

[0055] In the preparation steps of porous gel and core-shell structure, an epoxy resin protective shell is formed on the surface of the hydrogel.

[0056] In some embodiments, the aldehydes include either glutaraldehyde or adipaldehyde, or any combination thereof.

[0057] In some embodiments, the polyamine includes any one of polyethyleneimine and branched polyethyleneimine, or any combination thereof.

[0058] In some embodiments, the alcohol solution includes any one or any combination thereof, such as an ethanol solution containing epoxy resin, an aqueous solution containing polyvinyl alcohol, or a combination thereof.

[0059] In some embodiments, the indicator includes any one or any combination of phenolphthalein, catechol purple, m-cresol purple, and benzyl alcohol.

[0060] In some embodiments, the divalent cation solution includes any one of CaCl2, CaCO3, sodium silicate, Al2(SO4)3, CaSO4, AlCl3, FeCl3, FeCl2, Fe(NO3)2, Fe(NO3)3, or any combination thereof.

[0061] According to another aspect of the present invention, a colorimetric sensing gel is provided, the colorimetric sensing gel being prepared in the above embodiments, wherein amino sensing molecules are grafted onto the surface of the porous material calcium alginate.

[0062] The following specific examples illustrate the preparation process of the formaldehyde-rich colorimetric sensing gel for detecting formaldehyde and the colorimetric sensing gel obtained by the preparation method of the present invention.

[0063] Example 1

[0064] (1) Dissolve 1.5g sodium alginate in 48.5g deionized water, and add 1.5g glutaraldehyde and 14g water to it. Stir vigorously for 20min to make a transparent solution A.

[0065] (2) Dissolve 3g of polyethyleneimine in 47g of deionized water to make solution B.

[0066] Then, solution B was added dropwise to solution A at a rate of 5 ml / min. After the addition was complete, the mixture was stirred at 25°C and 500 rpm for 1 hour to obtain a uniform light pink emulsion. Then, 0.1 g of phenolphthalein was added to the emulsion and stirred for 0.5–2 hours to ensure that the phenolphthalein was evenly dispersed in the solution, forming a rose-red emulsion C.

[0067] (3) Emulsion C was added dropwise to a 3 wt% CaCl2 solution and reacted for 25 min to gel the gel. The gel spheres were then immersed in an ethanol solution containing 10 wt% epoxy resin and stirred for 2 min to adsorb a layer of epoxy resin onto the surface of the gel spheres. Finally, the gel was filtered and freeze-dried at -50°C for 15 h to obtain the colorimetric hydrogel, which is the amino-rich colorimetric sensing gel for formaldehyde detection of the present invention.

[0068] Example 2

[0069] (1) Dissolve 2g of sodium alginate in 48g of deionized water, and add 3g of glutaraldehyde and 12g of water to it. Stir vigorously for 30 minutes to make a transparent solution A.

[0070] (2) Dissolve 7g of polyethyleneimine in 43g of deionized water to make solution B.

[0071] Then, solution B was added dropwise to solution A at a rate of 6 ml / min. After the addition was complete, the mixture was stirred at 28°C and 600 rpm for 3 hours to obtain a uniform light pink emulsion. Next, 0.5 g of phenolphthalein was added to the emulsion and stirred for 2 hours to ensure that the phenolphthalein was evenly dispersed in the solution, forming a rose-red emulsion C.

[0072] (3) Emulsion C was added dropwise to a 5 wt% CaCl2 solution and reacted for 30 min to gel the gel. The gel spheres were then immersed in an ethanol solution containing 17 wt% epoxy resin and stirred for 5 min to adsorb a layer of epoxy resin onto the surface of the gel spheres. Finally, the gel was filtered and freeze-dried at -50°C for 24 h to obtain the colorimetric hydrogel, which is the amino-rich colorimetric sensing gel for formaldehyde detection of the present invention.

[0073] See Figure 2 As shown, regarding the colorimetric sensing gel prepared in Example 2, according to Figure 2 a and Figure 2 As can be seen from b, the grafted gel exhibits a honeycomb structure with a pore wall thickness of approximately 1.4 μm and a pore size of approximately 2 μm. This unique honeycomb-like porous structure provides a channel for formaldehyde gas to enter the gel interior. According to... Figure 2 As can be seen from c, the colorimetric sensing gel is coated with a layer of transparent epoxy resin, which can isolate it from interference from the external environment. After removing the shell, the actual object is shown in the image below. Figure 2 As shown in d.

[0074] according to Figure 3 As can be seen from a, over time, the L of the colorimetric sensing gel... * The value gradually increases, indicating that the color of the sensor ball is gradually becoming brighter. * The value of b gradually decreases, indicating that the red color of the sensor ball is gradually fading. While b * The value increases slowly, but shows a gradual yellowing trend. According to... Figure 3 As can be seen from b, when the colorimetric sensing gel (colorimetric sensing gel sensor ball) is placed in formaldehyde gas for about 5 minutes, a color change occurs, ΔE * The value is approximately 5.87. A noticeable color change occurs after about 10 minutes of placement. When the sensor is placed for more than 30 minutes, ΔE... * The slope increases sharply. After approximately 30 minutes, ΔE... * x It reaches its maximum value of 13.31. Then, as time continues to increase, △E * The slope of 0 gradually decreases, ΔE * x Gradually decreasing. Furthermore, according to... Figure 3As can be seen from c, as the time increases from 0 min, the color of the corresponding colorimetric sensing gel also changes, gradually changing from dark red to light red.

[0075] according to Figure 4 a and Figure 4 c shows that the colorimetric sensing gel, in environments with low and high concentrations of formaldehyde gas, ΔE * The zero value and formaldehyde gas concentration both increased linearly. More importantly, the lowest detection limit of this colorimetric sensing gel was 0.06 mg / m³. 3 The levels are significantly lower than the WHO-set threshold for formaldehyde concentration in indoor air. Furthermore, the sensitivity can reach 0.02 mg / m³. 3 .

[0076] The colorimetric sensing gel was exposed to various common indoor pollutant gases, such as formaldehyde, CO2, NO2, NH3, benzene, toluene, methanol, and ethanol. According to... Figure 4 b and Figure 4 As can be seen from d, the colorimetric sensing gel only showed a significant colorimetric response in formaldehyde gas. Other interfering gases did not cause any significant color change in the colorimetric sensing gel.

[0077] Figure 5 a is a view showing the changing trends of L, a, and b values ​​after a certain period of time, before and after detection, for the colorimetric sensing gel. Figure 5 b is a view showing the color difference between samples at different times and the sample at day 0 in air without formaldehyde concentration, and the color difference between samples at different times and the sample at day 0 after exposure to formaldehyde gas. Figure 5 c uses the same time frame as a baseline, showing the results at 0.1 mg / m³. 3 Samples under formaldehyde concentration conditions and 0 mg / m³ 3 A view of the color difference values ​​of the sample under formaldehyde concentration conditions. Figure 5 d shows the actual images of the colorimetric sensing gel at different times. Formaldehyde concentrations were measured on the colorimetric sensing gel after 0 days, 7 days, 30 days, 3 months, and 6 months in a normal external environment (25℃, 40%, indoors). Figure 5 a- Figure 5 As shown in d. Since the color difference value did not change significantly, the presence of the shell can extend the shelf life of the colorimetric sensing gel to 6 months.

[0078] See Table 1, which shows the results of the colorimetric sensing gel obtained in Example 2 of the present invention for detecting the formaldehyde concentration in actual indoor air.

[0079] Table 1 shows the actual formaldehyde concentration in indoor air.

[0080]

[0081] Four common indoor locations (bedroom, wardrobe, desk, and office) were selected, and formaldehyde was tested at the same locations using three different methods, as shown in Table 1. Compared with the national standard method (AHMT spectrophotometry) and commercial testing reagents, colorimetric sensing gel detection is practically feasible. Furthermore, compared with commercially available testing reagents, the results obtained by colorimetric sensing gel are relatively more accurate.

[0082] Example 3

[0083] (1) Dissolve 2.5g sodium alginate in 48.5g deionized water, and add 4g glutaraldehyde and 10g water to it. Stir vigorously for 30min to make a transparent solution A.

[0084] (2) Dissolve 5g of polyethyleneimine in 45g of deionized water to make solution B.

[0085] Then, solution B was added dropwise to solution A at a rate of 7 ml / min. After the addition was complete, the mixture was stirred at 30°C and 800 rpm for 4 hours to obtain a uniform light pink emulsion. Then, 0.7 g of phenolphthalein was added to the emulsion and stirred for 1.5 hours to ensure that the phenolphthalein was evenly dispersed in the solution, forming a rose-red emulsion C.

[0086] (3) Emulsion C was added dropwise to a 6 wt% CaCl2 solution and reacted for 45 min to gel the gel. The gel spheres were then immersed in an ethanol solution containing 19 wt% epoxy resin and stirred for 9 min to adsorb a layer of epoxy resin onto the surface of the gel spheres. Finally, the gel was filtered and freeze-dried at -50°C for 36 h to obtain the colorimetric hydrogel, which is the amino-rich colorimetric sensing gel for formaldehyde detection of the present invention.

[0087] Example 4

[0088] (1) Dissolve 3g of sodium alginate in 47g of deionized water, and add 5g of glutaraldehyde and 10g of water to it. Stir vigorously for 40min to make a transparent solution A.

[0089] (2) Dissolve 9g of polyethyleneimine in 50g of deionized water to make solution B.

[0090] Then, solution B was added dropwise to solution A at a rate of 8 ml / min. After the addition was complete, the mixture was stirred at 30°C and 900 rpm for 4 hours to obtain a uniform light pink emulsion. Then, 1 g of phenolphthalein was added to the emulsion and stirred for 2 hours to ensure that the phenolphthalein was evenly dispersed in the solution, forming a rose-red emulsion C.

[0091] (3) Emulsion C was added dropwise to a 7 wt% CaCl2 solution and reacted for 50 min to gel the gel. The gel balls were then immersed in an ethanol solution containing 20 wt% epoxy resin and stirred for 10 min to adsorb a layer of epoxy resin onto the surface of the gel balls. Finally, the gel balls were filtered and freeze-dried at -50°C for 48 h to obtain a colorimetric hydrogel, namely the amino-rich colorimetric gel for formaldehyde detection of the present invention.

[0092] This invention employs a chemical doping method to graft amino-rich polyamines, such as polyethyleneimine, onto green and renewable calcium alginate, preparing a low-cost, eco-friendly porous hydrogel for detecting formaldehyde concentration in the air. Furthermore, this study utilizes a core-shell structure to form a protective shell on the surface of the colorimetric sensing gel, isolating it from external environmental influences and improving detection accuracy while extending its lifespan. Research results show that this colorimetric sensing gel exhibits high sensitivity, excellent detection limit, and short detection time. Its sensitivity can reach 0.02 mg / m³. 3 The detection limit is as low as 0.06 mg / m³. 3 The detection time is as short as 10 minutes. Furthermore, it exhibits excellent selectivity among common indoor pollutants and is unaffected by temperature (≤70℃) and humidity (20%–70%). More importantly, due to its core-shell structure, it can resist external environmental interference and has a shelf life of at least 6 months, facilitating transportation and storage. In addition, compared to formaldehyde detectors prepared by physical doping methods, the formaldehyde detector prepared in this invention is lower in cost and has a simpler preparation process.

[0093] The method for preparing an amino-rich colorimetric sensing gel for detecting formaldehyde according to the present invention has at least one of the following advantages, or at least a portion thereof:

[0094] 1. Grafting sensing molecules into porous substrates

[0095] To overcome the problems of weak adsorption of sensing molecules, long detection time, complex storage, and low sensitivity associated with physical doping methods, this invention employs acetal and elimination reactions to successfully graft amino-rich sensing molecules onto the surface of a porous substrate. The prepared colorimetric sensing gel exhibits significantly improved performance, achieving a sensitivity of 0.02 mg / m³. 3 The shortest detection time is only 10 minutes, while the detection limit can be reduced to 0.06 mg / m³. 3 .

[0096] 2. Combination of sensing indicators

[0097] To improve the sensing accuracy of the sensor indicator, this invention uses hydrogen bonding and van der Waals forces to tightly attach the sensor indicator containing polar groups to the sensing molecule and the sensing substrate. This method enables the sensor indicator to rapidly and accurately detect changes in the sensing molecule, thereby achieving precise sensing of changes in formaldehyde content and improving the accuracy of the colorimetric sensing gel.

[0098] 3. Preparation of core-shell structure

[0099] Currently, a key problem commonly found in various colorimetric detectors is their extreme sensitivity to the external environment. Therefore, they require strict sealing before detection to isolate them from external interference factors, which inconveniences transportation and storage and easily leads to damage. To address this challenge, this invention employs an innovative core-shell structure method, forming an epoxy resin protective shell on the surface of the colorimetric sensing gel. This effectively isolates the effects of the external environment, improving detection accuracy and extending service life. The detector prepared in this way has a shelf life of over 6 months, greatly facilitating transportation and storage.

[0100] 4. Material selection for sensing molecules and porous substrates

[0101] Calcium alginate has attracted much attention due to its numerous outstanding characteristics, including non-toxicity, non-polluting nature, low cost, wide availability, renewability, and high porosity. Furthermore, its abundant hydroxyl and carboxyl groups enable it to efficiently adsorb formaldehyde. Given these excellent properties, this invention intelligently selects calcium alginate, a green biomass material, as a porous substrate to reduce product costs and improve the accuracy of formaldehyde detection. In addition, polyamines such as polyethyleneimine possess many advantages, such as low cost, stable performance, excellent biocompatibility, and abundant amino groups. Therefore, this invention selects polyamines such as polyethyleneimine as sensing molecules to further enhance the efficiency of this technology. These two materials not only achieve significant improvements in sensitivity, detection time, and detection limit, but also inherit the advantages of low cost and simple preparation process of physical grafting.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a colorimetric sensing gel for detecting formaldehyde, comprising the following steps: (1) Grafting of aldehyde groups First, 0.2wt% to 2.5wt% sodium alginate is dissolved in 39wt% to 41wt% deionized water, and 0.1wt% to 4.2wt% aldehyde substance, 6wt% to 12.5wt% water are added thereto, stirred for 20 to 45 min to prepare a transparent solution A, wherein the aldehyde substance includes any one or any combination of glutaraldehyde and adipaldehyde; (2) Grafting of sensing molecules 0.5wt% to 8wt% polyamine is dissolved in 33wt% to 46wt% deionized water to prepare solution B, wherein the polyamine includes any one or any combination of polyethyleneimine and branched polyethyleneimine; Then, solution B is added dropwise to solution A at a speed of 4 to 8 ml / min, and after the dropwise addition is completed, stirring is performed at 20 to 35℃ and 300 to 1000 rpm for 1 to 4 h to obtain a uniform light pink emulsion; 0.01wt% to 0.84wt% indicator is further added to the emulsion and stirred for 0.5 to 2 h to uniformly disperse the indicator in the emulsion, forming a magenta emulsion C; (3) Preparation of porous gel and core-shell structure The emulsion C is added dropwise to a 2 to 10wt% divalent cation solution to react for 20 to 120 min to gel, the gel ball is added to a 5 to 20wt% alcohol solution and stirred for 2 to 10 min to adsorb a layer of epoxy resin on the surface of the gel ball, and finally it is filtered and freeze-dried at -50℃ for 12 to 48 h to obtain the amino-rich colorimetric sensing gel for detecting formaldehyde, wherein the divalent cation solution is a CaCl2 solution.

2. The method according to claim 1, wherein the amino-rich polyamine sensing molecules are grafted onto the surface of calcium alginate, which is a porous substrate, through acetal reaction and elimination reaction.

3. The method according to claim 1, wherein in the step of preparing the porous gel and core-shell structure, a layer of epoxy resin protective shell is formed on the surface of the colorimetric sensing gel.

4. The method according to claim 1, wherein the alcohol solution includes any one or any combination of an epoxy resin-containing ethanol solution and a polyvinyl alcohol-containing aqueous solution.

5. The method according to claim 4, wherein the indicator includes any one or any combination of phenothalin, catechol violet, m-cresol purple and resorcinol benzyl alcohol.

6. A colorimetric sensing gel, which is prepared according to any one of claims 1 to 5, wherein the surface of calcium alginate, which is a porous substrate, is grafted with amino sensing molecules. ​ ​ ​ ​

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