A method for preparing a hydrogel for use in an air acidic gas stimulation application

Abstract

The application belongs to the technical field of production of responsive materials, and particularly relates to a preparation method of an air acidic gas stimulation responsive hydrogel, raw materials, acrylamide monomer, 1-vinylimidazole, maleimide, initiator, N,N-methylene bisacrylamide and water are uniformly mixed to obtain a gel precursor solution, and the hydrogel with acidic gas response is obtained after reaction at a certain temperature for a period of time. The preparation method is simple and easy to operate, and is environment-friendly, avoiding generation of organic acid wastewater and waste gas to pollute the environment, raw materials used in the method are easily obtained and low in price, and production cost is effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of responsive material production technology, specifically relating to a method for preparing a hydrogel that responds to acidic gas stimulation in the air. Background Technology

[0002] While industrial production brings new lifestyles to humanity, industrial pollution, especially the hazardous substances produced by chemical enterprises, also brings misfortune. Among these, acidic gases generated during industrial production can corrode factory equipment and precision instruments, causing losses in production and daily life. Therefore, testing for acidic components in the air is of great significance for ensuring the safety of life and property.

[0003] Currently, the technology for detecting acidic solutions is relatively mature, but reports on acidic gas components in the air are relatively few. Patent CN202110084436 discloses a covalent organic cage-like compound material with acid-stimulation-responsive function, its preparation method, and its application, successfully achieving the detection of acidic components in the air. However, the preparation of the organic cage-like compound material uses a large amount of organic acid, generating wastewater and waste gas, causing significant environmental pollution. In recent years, stimulus-responsive hydrogels, by combining stimulus-responsive groups with hydrophilic substances, have yielded a new type of intelligent responsive hydrogel with high flexibility, excellent stimulus responsiveness, and good processability. These hydrogels have broad application prospects in many fields such as biosensing, biomedicine, supercapacitors, smart wearables, electronic skin, and other intelligent devices, attracting widespread attention from researchers. For example, [Le XX,Shang H,Wu SS,Zhang JW,Liu MJ,Zheng YF,Chen T.Heterogeneous fluorescent organohydrogel enables dynamic anti-counterfeiting[J].AdvancedFunctional Materials,2021,31(52):2108365.] disclosed the introduction of fluorescent and pH-responsive spiropyran molecules and naphthalimide groups into a polymer gel network structure, in which PDMS (poly(N,N-dimethylacrylamide)) is used as the gel support. This gel has good application prospects in information anti-counterfeiting, but the high cost of structures such as spiropyran is not conducive to industrial application. In addition, grafting spiropyran structures into polymer structures increases the difficulty of synthesis due to the large steric hindrance of spiropyran.

[0004] Based on the current state of development, the controllable synthesis of high-performance acid gas sensing and detection materials using simple and environmentally friendly synthesis processes and low-cost materials remains a challenging problem. Summary of the Invention

[0005] To address the existing problems, this invention provides a method for preparing a hydrogel that responds to acidic gas stimulation in the air. This preparation method is simple, easy to operate, and environmentally friendly, avoiding the generation of organic acid wastewater and waste gas that pollute the environment. The raw materials used in this method are readily available and inexpensive, effectively reducing production costs.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a hydrogel responsive to acidic gases in air involves mixing raw materials: acrylamide monomers, 1-vinylimidazole, maleimide, initiator, N,N-methylenebisacrylamide, and water to obtain a gel precursor solution, and reacting it at a certain temperature for a period of time to obtain a hydrogel responsive to acidic gases.

[0008] Preferably, the raw materials, by mass percentage, include 1-60% acrylamide monomers, 0.01-5% 1-vinylimidazole, 0.01-5% maleimide, 0.001-1% initiator, 0.001-0.1% N,N-methylenebisacrylamide, and water as the balance.

[0009] More preferably, the mass ratio of 1-vinylimidazole to maleimide is 1:1.

[0010] Preferably, the amide monomer is one of acrylamide, methacrylamide, N-butylacrylamide, N-ethylacrylamide, and N-hydroxyacrylamide.

[0011] Preferably, the temperature is 50-95℃ and the time period is 10-24h.

[0012] Preferably, the initiator is ammonium persulfate or potassium persulfate.

[0013] The principle of this invention is as follows:

[0014]

[0015] This invention combines the characteristics of gel copolymers with the strong electron-withdrawing properties of maleimide containing a five-membered ring to synthesize a new maleimide gel copolymer, which has been successfully used for acid-base chromogenic color change to detect acidic gas components in mixed gases. Maleimide is a strong electron-withdrawing monomer. After copolymerization with the heterocyclic 1-vinylimidazolium, the electron cloud distribution of the imidazole group is changed. The copolymerization of the two monomers gives the structure a pink (red) structural color. Since the imidazole group is a basic functional group, under the stimulation of acidic components, the N atom of the imidazole group is protonated to form a salt structure, and the polymer color changes from pink to colorless. When the basic components continue to stimulate, the ammonium salt structure becomes N atoms, completing the deprotonation reaction, and the color changes from colorless to pink.

[0016] This invention uses maleimide and 1-vinylimidazole as responsive groups, acrylamide as the backbone, and N,N-methylenebisacrylamide to connect the gel network to prepare a hydrogel with acid gas responsiveness, which has important application prospects in the detection of acid gas components. This invention provides a stimulus-responsive polymer system containing a stable five-membered ring maleimide structural unit, which has the advantages of simple synthesis, easy control of chain structure, rapid response to multiple stimuli, and low cost of maleimide.

[0017] In this invention, the acidic gas component in the mixed gas comes into contact with a large number of water molecules on the surface of the hydrogel, enters the gel structure, and rapidly undergoes a protonation reaction with the imidazole groups in the gel backbone structure. This causes the gel to change from red (pink) to colorless, enabling rapid detection of the acidic component. The entire reaction process is completed within 5 seconds. When the reacted gel encounters alkaline gas components such as ammonia, it undergoes deprotonation and then rapidly changes from colorless and transparent to red (pink). The entire process is repeated 50 times with excellent reversible cyclic stability. Furthermore, tensile strength testing of the gel reveals good mechanical properties, making it suitable for various applications. For example, the gel can be used as a detection device in the sensor field, providing assurance for repeated stimulus-response tests and gel handling. The hydrogel prepared by this invention exhibits stimulus responsiveness to hydrochloric acid, acetic acid, trifluoroacetic acid, nitric acid, and hydrofluoric acid in the air, demonstrating excellent versatility.

[0018] This invention provides a method for preparing a hydrogel that responds to acidic gas stimulation in air. This method yields a novel gel copolymer based on maleimide and vinylimidazolium, and its colorimetric properties are used to detect the presence of acidic gas components in a mixed gas. The method exhibits fast response time and good mechanical properties. Verification has shown that the gel copolymer has excellent reversible cycle stability. Furthermore, the preparation method is simple, environmentally friendly, and low in cost. Attached Figure Description

[0019] Figure 1 Infrared structural characterization images of Examples 1-5;

[0020] Figure 2 The color of the hydrogel prepared in Example 1 changes in response to stimulation by acidic components in the air;

[0021] Figure 3 The image shows the SEM structure of the hydrogel prepared in Example 1.

[0022] Figure 4 The images show the hydrogels prepared in Comparative Examples 1 and 2. On the left, A is the hydrogel prepared in Comparative Example 1, and on the right, B is the hydrogel prepared in Comparative Example 2.

[0023] Figure 5The thermal analysis diagram of the hydrogel prepared in Example 4 is shown.

[0024] Figure 6 The stress-strain curve of the hydrogel prepared in Example 5 is shown. Detailed Implementation

[0025] The technical solutions in this embodiment will be described in detail below, but the described embodiments are only some embodiments of the present invention and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this application.

[0026] Example 1

[0027] A method for preparing a hydrogel responsive to acidic gases in air:

[0028] 4.0g of acrylamide monomer, 0.1g of 1-vinylimidazole, 0.1g of maleimide, 0.01g of ammonium persulfate, 0.005g of N,N-methylenebisacrylamide, and 10mL of deionized water were mixed evenly. The mixed liquid was then poured into a mold and subjected to free radical polymerization in a 70℃ oven for 8 hours to prepare a fully solid red transparent hydrogel, named Ionogel-1.

[0029] Ionogel-1 gel was cut into regular shapes and placed in a sealed flask. A mixed gas containing hydrogen chloride was introduced. The HCl component in the mixed gas came into contact with a large number of water molecules on the gel surface, and the gel changed from red to colorless, forming a rapid detection of acidic components. When the gel after the reaction came into contact with ammonia, it quickly changed from colorless and transparent to red, showing reversible cycle stability.

[0030] Example 2

[0031] A method for preparing a hydrogel responsive to acidic gases in air:

[0032] 4.0g acrylamide monomer, 0.1g 1-vinylimidazole, 0.1g maleimide, 0.01g ammonium persulfate, 0.003g N,N-methylenebisacrylamide, and 10mL deionized water were mixed evenly. The mixed liquid was then poured into a mold and subjected to free radical polymerization in a 70℃ oven for 8 hours to prepare a fully solid pink transparent hydrogel, named Ionogel-2.

[0033] Ionogel-2 gel was cut into regular shapes and placed in a sealed flask. A mixed gas containing hydrogen chloride was introduced. The HCl component in the mixed gas came into contact with a large number of water molecules on the gel surface, and the gel changed from pink to colorless, forming a rapid detection of acidic components. When the gel after the reaction came into contact with ammonia, it quickly changed from colorless and transparent to pink, showing reversible cycle stability.

[0034] Example 3

[0035] A method for preparing a hydrogel responsive to acidic gases in air:

[0036] 4.0g of acrylamide monomer, 0.01g of 1-vinylimidazole, 0.01g of maleimide, 0.005g of ammonium persulfate, 0.002g of N,N-methylenebisacrylamide, and 10mL of deionized water were mixed evenly. The mixed liquid was then poured into a mold and subjected to free radical polymerization in an oven at 75℃ for 10h to prepare a completely solid, light pink, transparent hydrogel, named Ionogel-3.

[0037] Ionogel-3 gel was cut into regular shapes and placed in a sealed flask. A mixed gas containing hydrogen chloride was introduced. The HCl component in the mixed gas came into contact with a large number of water molecules on the gel surface, and the gel changed from light pink to colorless, forming a rapid detection of acidic components. When the gel after the reaction came into contact with ammonia, it quickly changed from light pink to colorless, showing reversible cycle stability.

[0038] Example 4

[0039] A method for preparing a hydrogel responsive to acidic gases in air:

[0040] 3.5g of acrylamide monomer, 0.1g of maleimide, 0.1g of 1-vinylimidazole, 0.01g of ammonium persulfate, 0.003g of N,N-methylenebisacrylamide, and 10mL of deionized water were mixed evenly. The mixed liquid was then poured into a mold and subjected to free radical polymerization in an oven at 75℃ for 10h to prepare a fully solid pink transparent hydrogel, named Ionogel-4.

[0041] Ionogel-6 gel was cut into regular shapes and placed in a sealed flask. A mixed gas containing trifluoroacetic acid was introduced. The trifluoroacetic acid component in the mixed gas came into contact with a large number of water molecules on the gel surface, and the gel changed from pink to colorless, forming a rapid detection of acidic components. When the gel after the reaction came into contact with ammonia, it quickly changed from colorless and transparent to pink, showing reversible cycle stability.

[0042] Example 5

[0043] A method for preparing a hydrogel responsive to acidic gases in air:

[0044] 4.0g acrylamide monomer, 0.08g maleimide, 0.08g 1-vinylimidazole, 0.01g ammonium persulfate, 0.003g N,N-methylenebisacrylamide, and 10mL deionized water were mixed evenly. The mixed liquid was then poured into a mold and subjected to free radical polymerization in an oven at 80℃ for 12h to prepare a fully solid pink transparent hydrogel, named Ionogel-5.

[0045] Ionogel-5 gel was cut into regular shapes and placed in a sealed flask. A mixed gas containing hydrogen fluoride was introduced. The hydrogen fluoride component in the mixed gas came into contact with a large number of water molecules on the gel surface, and the gel changed from pink to colorless. This rapid detection of acidic components was achieved. When the gel after the reaction came into contact with ammonia, it quickly changed from colorless and transparent to pink, demonstrating reversible cycle stability.

[0046] Comparative Example 1

[0047] A method for preparing a hydrogel responsive to acidic gases in air:

[0048] 3.5g acrylamide monomer, 0.3g maleimide, 0.01g ammonium persulfate, 0.01g N,N-methylenebisacrylamide and 10mL deionized water were mixed evenly. Finally, the mixed liquid was poured into a mold and subjected to free radical polymerization in an oven at 75℃ for 10h to prepare a solid, colorless and transparent hydrogel called Ionogel-6.

[0049] Comparative Example 2

[0050] A method for preparing a hydrogel responsive to acidic gases in air:

[0051] 3.5g of acrylamide monomer, 0.3g of 1-vinylimidazole, 0.01g of ammonium persulfate, 0.01g of N,N-methylenebisacrylamide and 10mL of deionized water were mixed evenly. Finally, the mixed liquid was poured into a mold and subjected to free radical polymerization in an oven at 75℃ for 10h to prepare a solid, colorless and transparent hydrogel, named Ionogel-7.

[0052] Test case

[0053] The resins obtained by freeze-drying the gels from Examples 1-5 were then subjected to structural characterization, such as... Figure 1 The image shown is the infrared spectrum of the gel resin structure, 3400 cm⁻¹. -1 The peak at 3450 cm⁻¹ is the absorption peak of the amine group. -1The absorption peak for the imine group is 1700 cm⁻¹. -1 The infrared absorption peak for carbonyl groups is in the range of 1750-2200 cm⁻¹. -1 The polymer showed no double bond peaks and was smooth, indicating that the three monomers had completely polymerized. The structure of the gel polymer was determined by characterizing the polymer with infrared spectroscopy.

[0054] In Example 1, the prepared Ionogel-1 was a bright red color. It was cut into regular shapes and placed in a sealed flask. A mixed gas containing hydrogen chloride was introduced. The HCl component in the mixed gas came into contact with a large number of water molecules on the gel surface, entered the gel structure, and rapidly protonated with the imidazole groups in the gel backbone. The gel changed from red to colorless, enabling rapid detection of acidic components, such as... Figure 2 As shown. When the reacted gel comes into contact with ammonia, it quickly changes from colorless and transparent to red, exhibiting reversible cycle stability.

[0055] Figure 3 This is a SEM image of the lyophilized Ionogel-1 hydrogel prepared in Example 1. Figure 3 As shown, the gel surface consists of a porous structure with pore sizes of 10-20 micrometers. The pores are relatively dense, and the surface is relatively smooth. This porous microstructure is mainly due to the highly cross-linked physical network formed by maleimide and acrylamide linked by chemical bonds (amide bonds). Therefore, based on this porous and dense cross-linked network structure, on the one hand, it is beneficial to improve the mechanical strength and performance of the gel; on the other hand, this dense porous structure increases the porosity of the gel, increasing the exposure space of the chromogenic groups (imidazole). When the stimulating factor comes into contact with the gel, it is easier to contact the imidazole groups, rapidly undergoing a protonation reaction, producing a reversible color cycle, greatly saving the stimulus response time, and making it more conducive to the occurrence of the stimulus response.

[0056] The gels obtained in Comparative Examples 1-2, from Figure 4 As can be seen from the figure, the gel color of Ionogel-6 is shown in Figure A, and the gel color of Ionogel-7 is shown in Figure B. Both gels are colorless and transparent, indicating that the color of the gel is controlled by maleimide and vinylimidazole. It is the combined control of these two substances that allows the gel to quickly change from red to colorless under acid stimulation, with a clear color difference. However, the gels of Comparative Example 1 and Comparative Example 2 did not achieve such an effect.

[0057] The resin after lyophilization of the gel prepared in Example 4 was subjected to thermogravimetric analysis, such as... Figure 5It can be seen that the gel polymer exhibits almost no thermal decomposition below 200℃, indicating that the polymer can withstand high temperatures up to 200℃. At 300℃, only a 10% mass loss occurs. Further heating to 350℃ results in a significant mass loss, indicating that the polymer's maximum heat resistance temperature is 350℃. Between 350-450℃, the polymer decomposes relatively completely, with 20wt% remaining even at 700℃. In summary, maleimide, utilizing a five-membered heterocyclic structure, can significantly improve the heat resistance of polymers. The gel polymer prepared in this invention exhibits high thermal stability.

[0058] The mechanical properties of the gels prepared in Examples 1-5 and Comparative Examples 1-2 were tested, and the results are shown in Table 1. Figure 6 The stress-strain curves of the hydrogel prepared in Example 5 are shown. All of the above-mentioned gels exhibit good mechanical properties. This is because the acrylamide structure contains amino groups, and the maleimide and imidazole structures contain nitrogen elements, which form hydrogen bonds with water molecules. As the hydrogen bond content in the gel increases, the tensile strength and elongation at break of the gel improve, meeting different requirements such as stretching, cutting, and assembly, making them more suitable for various applications, such as in the sensor field.

[0059] Table 1. Mechanical property test results of all-solid gels prepared in Examples 1-5 and Comparative Examples 1-2

[0060]

[0061] This invention provides a method for preparing a hydrogel that responds to acidic gas stimulation in air. This method yields a novel gel copolymer based on maleimide and vinylimidazolium, and its colorimetric properties are used to detect the presence of acidic gas components in a mixed gas. The method exhibits fast response time and good mechanical properties. Verification has shown that the gel copolymer has excellent reversible cycle stability. Furthermore, the preparation method is simple, environmentally friendly, and low in cost.

Claims

1. A method for preparing a hydrogel responsive to acidic gases in air, characterized in that, The raw materials, namely acrylamide monomers, 1-vinylimidazole, maleimide, initiator, N,N-methylenebisacrylamide and water, are mixed evenly to obtain a gel precursor solution. After reacting at 50-95℃ for 10-24h, a hydrogel with acid gas response is obtained. The raw materials, by mass percentage, include 1-60% acrylamide monomers, 0.01-5% 1-vinylimidazole, 0.01-5% maleimide, 0.001-1% initiator, 0.001-0.1% N,N-methylenebisacrylamide, and water as the balance.

2. The method for preparing a hydrogel responsive to acidic gases in air according to claim 1, characterized in that, The mass ratio of 1-vinylimidazole to maleimide is 1:

1.

3. The method for preparing a hydrogel responsive to acidic gases in air according to claim 1, characterized in that, The acrylamide monomer is one of acrylamide, methacrylamide, N-butylacrylamide, N-ethylacrylamide, and N-hydroxyacrylamide.

4. The method for preparing a hydrogel responsive to acidic gases in air according to claim 1, characterized in that, The initiator is ammonium persulfate or potassium persulfate.

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