Preparation method of N-isopropylacrylamide-based hydrogel for solar-driven atmospheric water collection

Abstract

The invention discloses a preparation method of N-isopropylacrylamide-based hydrogel for solar-driven atmospheric water collection and a preparation method of the N-isopropylacrylamide-based hydrogel for solar-driven atmospheric water collection. The solar-driven atmospheric water collection N-isopropylacrylamide hydrogel is obtained through copolymerization of an N-isopropylacrylamide monomer and a cross-linking agent N, N '-methylene bisacrylamide, the polymerized hydrogel is soaked in a lithium chloride solution, and carboxylated carbon nanotubes are introduced into the hydrogel to prepare the hydrogel of a double-layer structure. The preparation method disclosed by the invention is simple; the lithium chloride-loaded poly (N-isopropylacrylamide-co-N, N '-methylene bisacrylamide) hydrogel containing the carboxylated carbon nanotubes has good moisture absorption performance in a relatively wide relative humidity range and excellent desorption performance under a sun illumination condition, and can be used for efficiently collecting water vapor in the atmosphere; the problem of fresh water resource shortage in arid regions is effectively relieved, and the method is particularly suitable for coastal regions with high relative humidity and sufficient illumination.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a method for preparing a solar-driven adsorption-type atmospheric water-collecting polyacrylamide hydrogel. Background Technology

[0002] Freshwater scarcity is a global challenge, with approximately 2-3 billion people worldwide currently facing freshwater shortages. Through the global water cycle, the Earth's atmosphere stores nearly 13,000 km³ of water, more than six times the volume of all the world's rivers combined. In recent years, atmospheric water harvesting has received widespread attention, including methods such as dew and fog collection. However, the effectiveness of these methods largely depends on local climatic conditions, particularly at low relative humidity (RH), and often requires additional energy input, making them unsuitable for arid regions with even scarcer resources. Adsorption-based atmospheric water harvesting is applicable to various environments, achieving water adsorption over a wider RH range without requiring additional energy input. Water release can be achieved solely through sunlight, making it particularly suitable for island regions with large diurnal temperature variations and abundant sunshine, where it better facilitates the adsorption and desorption of water vapor.

[0003] Bilayer hydrogels can effectively enhance photothermal response, thereby improving their desorption performance. The desorption performance of hydrogels can be further enhanced through the synergistic effect of N-isopropylacrylamide-based polymers and bilayer hydrogels. Using N-isopropylacrylamide as a monomer and N,N'-methylenebisacrylamide as a crosslinking agent, a poly(N-isopropylacrylamide-co-N,N'-methylenebisacrylamide) polymer hydrogel was prepared. Using hygroscopic lithium chloride (LiCl) as an adsorbent, and introducing carboxylated carbon nanotubes as photothermal materials, a bilayer composite hydrogel was prepared, achieving water vapor capture and efficient water release under natural light. The hydrogel exhibits superior desorption performance due to the combined effect of polymer chain conformational changes and the hydrogel's unique structure. Summary of the Invention

[0004] To address the problems existing in the background art, this invention provides a solar-driven atmospheric water-collecting N-isopropylacrylamide-based hydrogel. The hydrogel is formed by free radical polymerization of N-isopropylacrylamide monomer and N,N'-methylenebisacrylamide in a carboxylated carbon nanotube dispersion. The prepared hydrogel is then immersed in a hygroscopic salt solution to improve the binding force between the hydrogel and water molecules. The light-driven desorption adsorption-type atmospheric water-collecting polymer (N-isopropylacrylamide-co-N,N'-methylenebisacrylamide) hydrogel disclosed in this invention is simple to prepare. The prepared hydrogel can capture water molecules from the atmosphere over a wide range of relative humidity. Simultaneously, under sunlight irradiation, the carboxylated carbon nanotubes convert light energy into heat energy, raising the surface temperature of the hydrogel and releasing internal moisture as water vapor.

[0005] The technical solution adopted in this invention is: I. Atmospheric water-collecting polymer (N-isopropylacrylamide-co-N,N'-methylenebisacrylamide) hydrogel for solar-driven desorption is obtained by polymerizing N-isopropylacrylamide monomer and crosslinking agent N,N'-methylenebisacrylamide in a carboxylated carbon nanotube dispersion, and loading lithium chloride into the prepared hydrogel. This poly(N-isopropylacrylamide-co-N,N'-methylenebisacrylamide) / carboxylated carbon nanotube / lithium chloride hydrogel can capture water molecules from the atmosphere and store them in the hydrogel network. Under sunlight, the carboxylated carbon nanotubes in the hydrogel convert light energy into heat energy, causing the hydrogel temperature to rise and releasing water.

[0006] Solar-driven atmospheric water-collecting N-isopropylacrylamide-based hydrogels are mainly prepared by free radical copolymerization of polymer monomers and crosslinking agents in a photothermal material dispersion, followed by swelling with deionized water and freeze-drying, and then freeze-drying after solution immersion. This process yields poly(N-isopropylacrylamide-co-N,N'-methylenebisacrylamide)-carboxylated carbon nanotube-lithium chloride hydrogels, i.e., N-isopropylacrylamide-based hydrogels.

[0007] The poly(N-isopropylacrylamide-co-N,N'-methylenebisacrylamide) has the following structural formula: II. A method for preparing solar-driven atmospheric water-collecting polymer (N-isopropylacrylamide-co-N,N'-methylenebisacrylamide) hydrogels. The preparation method includes the following steps: 1) Add the polymer monomer and crosslinking agent to deionized water and stir until homogeneous, then add the photoinitiator, and stir until homogeneous in the dark to obtain the precursor solution; The polymer monomer includes one or more of acrylamide, N-isopropylacrylamide, acrylic acid, and acrylate; the crosslinking agent is N,N'-methylenebisacrylamide; by mass parts, the polymer monomer is 1 part, deionized water is 1-100 parts, and crosslinking agent is 0.001-1 part; the photoinitiator includes one or more of benzoyl and its derivatives, acylphosphine oxides, and α-hydroxy ketones and their derivatives; by mass parts, the ratio of photoinitiator to deionized water is 1:1-1000; 2) Take the precursor solution from step 1), shield it from light, and pass it through an inert gas to remove oxygen. This solution is denoted as solution A. Step 2) specifically refers to: Take 1-10 mL of the precursor solution from step 1), shield it from light, and pass it through an inert gas to remove oxygen for 1-100 min. This solution is denoted as solution A. 3) Take the precursor solution from step 1), add the photothermal material, then shield it from light and pass inert gas to remove oxygen, and record it as solution B; Step 3) specifically refers to: Take 1-10 mL of the precursor solution from step 1), add the photothermal material, then shield it from light and pass an inert gas through it to remove oxygen for 1-100 min, and record it as solution B; The added photothermal material is one or more of carboxylated carbon nanotubes, carbon nanotubes, graphene, graphene oxide, carbon black, Mxene, polypyrrole, and polydopamine; by mass, the photothermal material is 1 part and the solvent water is 1-100 parts; the inert gas is one or more of nitrogen and argon. 4) Take solution B, cure it under a UV lamp, add solution A, and then cure it under a UV lamp again to obtain a bilayer poly hydrogel; Step 4) specifically involves: Take 0.1-1 mL of solution B, cure it under a 100 W UV lamp for 1-100 min, then add 0.1-10 mL of solution A, and then cure it under a 100 W UV lamp for 1-100 min to obtain a bilayer poly hydrogel; solution B is 1 part by volume and solution A is 0.1-10 parts. 5) The bilayer poly hydrogel obtained in step 4) was soaked in deionized water and then freeze-dried to constant weight. It was then soaked in a hygroscopic salt solution and freeze-dried to constant weight to obtain the final product.

[0008] Step 5) specifically involves: The bilayer poly hydrogel obtained in step 4) was soaked in 1-100 mL of deionized water for 1-100 h and then freeze-dried to constant weight. It was then soaked in 1-100 mL of hygroscopic salt solution for 1-100 h and then freeze-dried to constant weight to obtain poly(N-isopropylacrylamide-co-N,N'-methylenebisacrylamide)-carboxylated carbon nanotube-lithium chloride hydrogel. The hygroscopic salt includes one or more of lithium chloride, calcium chloride, cobalt chloride, and magnesium chloride; the mass fraction of the hygroscopic salt solution is 1-45 wt%.

[0009] The preparation method disclosed in this invention is simple. The poly(N-isopropylacrylamide-co-N,N'-methylenebisacrylamide) hydrogel containing carboxylated carbon nanotubes loaded with lithium chloride exhibits good hygroscopic properties over a wide range of relative humidity and excellent desorption properties under sunlight conditions. It can efficiently collect water vapor from the atmosphere, effectively alleviating the problem of freshwater shortage in arid areas, and is especially suitable for coastal areas with high relative humidity and abundant sunshine.

[0010] The beneficial effects of this invention are: 1. The preparation process of solar-driven atmospheric water-collecting polymer (N-isopropylacrylamide-co-N, N'-methylenebisacrylamide) hydrogel is simple, the raw materials are common and readily available, and it has high application potential.

[0011] 2. The solar-driven atmospheric water-collecting polymer (N-isopropylacrylamide-co-N, N'-methylenebisacrylamide) hydrogel can achieve good moisture absorption and desorption properties under different environmental conditions.

[0012] 3. The atmospheric water-collecting polymer (N-isopropylacrylamide-co-N, N'-methylenebisacrylamide) hydrogel driven by sunlight does not require additional energy input during desorption, making it suitable for various working scenarios and reducing energy consumption. Attached Figure Description

[0013] Figure 1 The moisture absorption curve of Example 1 is shown under environmental conditions of 25°C and 90% relative humidity.

[0014] Figure 2 The desorption curve of Example 1 under 1 kW·m⁻² illumination is shown. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] The present invention will be described in more detail below with reference to embodiments, but the present invention is not limited thereto. For those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the protection scope of the present invention. Contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0017] The embodiments of the present invention are as follows: Example 1: Step 1: Add NIPAM (2.9989 g, 0.0265 mol) to 30 mL of deionized water, add MBA (0.1118 g, 0.7 mmol), and stir until completely dissolved (40℃, 500 rpm). Step 2: Add α-KGA (0.0310 g, 0.2 mmol), and stir in the dark until completely dissolved to obtain the precursor solution. Step 3: Take 4 mL of the precursor solution and label it Solution A, then purge with Ar for 20 min in the dark to remove oxygen. Step 4: Take 2 mL of the precursor solution and label it Solution B, add CNT-COOH (9.2 mg), stir in the dark until CNT-COOH is completely dissolved, and then purge with Ar for 20 min to remove oxygen. Step 5: Transfer Solution B to a mold and cure under a 100 W UV lamp for 20 min to obtain a hydrogel containing a CNT-COOH photothermal layer. Step 6: Transfer Solution A to a mold again and cure under a 100 W UV lamp for 20 min to obtain a bilayer poly (NIPAM-co-MBA) hydrogel was obtained by immersing the hydrogel in 15 mL of deionized water for 24 h to allow it to fully swell. The surface was then dried and frozen in a freezer for 12 h. After freeze-drying to constant weight, PNIPAMM-CNT-1.5 hydrogel was obtained.

[0018] LiCl (214.2835 g, 5.0550 mol) was added to 500 mL of deionized water and stirred thoroughly to dissolve it, resulting in a 30 wt% LiCl solution. 15 mL of the LiCl solution was taken, and the prepared PNIPAMM-CNT-1.5 hydrogel was immersed in the LiCl solution for 36 h. The surface was wiped dry and placed in a freezer for 12 h. After freeze-drying to constant weight, PNIPAMM-CNT-1.5-LiCl-30 hydrogel was obtained.

[0019] The results are as follows Figure 1 and Figure 2 As shown.

[0020] Example 2: Step 1: Add NIPAM (2.9989 g, 0.0265 mol) to 30 mL of deionized water, add MBA (0.1118 g, 0.7 mmol), and stir until completely dissolved (40℃, 500 rpm). Step 2: Add α-KGA (0.0310 g, 0.2 mmol), and stir in the dark until completely dissolved to obtain the precursor solution. Step 3: Take 4 mL of the precursor solution and label it Solution A, then purge with Ar for 20 min in the dark to remove oxygen. Step 4: Take 2 mL of the precursor solution and label it Solution B, add CNT-COOH (14.9 mg), stir in the dark until CNT-COOH is completely dissolved, and then purge with Ar for 20 min to remove oxygen. Step 5: Transfer Solution B to a mold and cure under a 100 W UV lamp for 20 min to obtain a hydrogel containing a CNT-COOH photothermal layer. Step 6: Transfer Solution A to a mold again and cure under a 100 W UV lamp for 20 min to obtain a bilayer poly (NIPAM-co-MBA) hydrogel was obtained by immersing the hydrogel in 15 mL of deionized water for 24 h to allow it to fully swell. The surface was then dried and placed in a freezer for 12 h. After freeze-drying to constant weight, PNIPAMM-CNT-2.5 hydrogel was obtained.

[0021] LiCl (214.2835 g, 5.0550 mol) was added to 500 mL of deionized water and stirred thoroughly to dissolve it, resulting in a LiCl solution with a mass fraction of 30 wt%. 15 mL of the LiCl solution was taken and the prepared PNIPAMM-CNT-2.5 hydrogel was immersed in the LiCl solution for 36 h. The surface was wiped dry and the hydrogel was placed in a freezer for 12 h. After freeze-drying to constant weight, PNIPAMM-CNT-2.5-LiCl-30 hydrogel was obtained.

Claims

1. An atmospheric water-collecting N-isopropylacrylamide-based hydrogel for solar-driven applications, characterized in that: The process mainly involves free radical copolymerization of polymer monomers and crosslinking agents in a photothermal material dispersion, followed by swelling with deionized water and freeze-drying, and then freeze-drying after immersion in solution to obtain poly(N-isopropylacrylamide-co-N,N'-methylenebisacrylamide)-carboxylated carbon nanotube-lithium chloride hydrogel.

2. The method for preparing a solar-driven atmospheric water-collecting N-isopropylacrylamide-based hydrogel according to claim 1, characterized in that... Includes the following steps: 1) Add the polymer monomer and crosslinking agent to deionized water and stir until homogeneous, then add the photoinitiator, and stir until homogeneous in the dark to obtain the precursor solution; 2) Take the precursor solution from step 1), shield it from light, and pass it through an inert gas to remove oxygen. This solution is denoted as solution A. 3) Take the precursor solution from step 1), add the photothermal material, then shield it from light and pass inert gas to remove oxygen, and record it as solution B; 4) Take solution B, cure it under a UV lamp, add solution A, and then cure it under a UV lamp again to obtain a bilayer poly hydrogel; 5) The bilayer poly hydrogel obtained in step 4) was soaked in deionized water and then freeze-dried to constant weight. It was then soaked in a hygroscopic salt solution and freeze-dried to constant weight to obtain the final product.

3. The method for preparing a solar-driven atmospheric water-collecting N-isoacrylamide hydrogel according to claim 2, characterized in that: In step 1), The polymer monomer includes one or more of acrylamide, N-isopropylacrylamide, acrylic acid, and acrylate. The crosslinking agent is N,N'-methylenebisacrylamide.

4. The method for preparing a solar-driven adsorption-type atmospheric water-collecting N-isopropylacrylamide hydrogel according to claim 2, characterized in that: In step 1), by mass parts, the polymer monomer is 1 part, the deionized water is 1-100 parts, and the crosslinking agent is 0.001-1 part.

5. The method for preparing a solar-driven adsorption-type atmospheric water-collecting N-isopropylacrylamide hydrogel according to claim 2, characterized in that: In step 1), the photoinitiator includes one or more of benzoyl and its derivatives, acylphosphine oxides, and α-hydroxy ketones and their derivatives; The ratio of photoinitiator to deionized water in step 1) is 1:1-1000 by mass.

6. The method for preparing a solar-driven adsorption-type atmospheric water-collecting N-isopropylacrylamide hydrogel according to claim 2, characterized in that: Step 2) specifically refers to: Take 1-10 mL of the precursor solution from step 1), shield it from light, and pass it through an inert gas to remove oxygen for 1-100 min. This solution is denoted as solution A.

7. The method for preparing a solar-driven adsorption-type atmospheric water-collecting N-isopropylacrylamide hydrogel according to claim 2, characterized in that: Step 3) specifically refers to: Take 1-10 mL of the precursor solution from step 1), add the photothermal material, then shield it from light and pass an inert gas through it to remove oxygen for 1-100 min, and record it as solution B; The added photothermal material is one or more of carboxylated carbon nanotubes, carbon nanotubes, graphene, graphene oxide, carbon black, Mxene, polypyrrole, and polydopamine; By mass, the photothermal material is 1 part and the solvent water is 1-100 parts.

8. A method for preparing a solar-driven adsorption-type atmospheric water-collecting N-isopropylacrylamide hydrogel according to claim 6 or 7, characterized in that: The inert gas is one or more of nitrogen and argon.

9. The method for preparing a solar-driven adsorption-type atmospheric water-collecting N-isopropylacrylamide hydrogel according to claim 2, characterized in that: Step 4) specifically involves: Take 0.1-1 mL of solution B, cure it under a 100 W UV lamp for 1-100 min, then add 0.1-10 mL of solution A, and then cure it under a 100 W UV lamp for 1-100 min to obtain a bilayer poly hydrogel. Solution B is 1 part by volume, and solution A is 0.1-10 parts.

10. The method for preparing a solar-driven adsorption-type atmospheric water-collecting N-isoacrylamide hydrogel according to claim 2, characterized in that: Step 5) specifically involves: The bilayer poly hydrogel obtained in step 4) was soaked in 1-100 mL of deionized water for 1-100 h and then freeze-dried to constant weight. It was then soaked in 1-100 mL of hygroscopic salt solution for 1-100 h and then freeze-dried to constant weight to obtain poly(N-isopropylacrylamide-co-N,N'-methylenebisacrylamide)-carboxylated carbon nanotube-lithium chloride hydrogel. The hygroscopic salt includes one or more of lithium chloride, calcium chloride, cobalt chloride, and magnesium chloride; The mass fraction of hygroscopic salt solutions is 1-45 wt%.

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