Atmospheric hygroscopic material for ecological restoration of arid-semi-arid regions and preparation method of atmospheric hygroscopic material

Abstract

The invention relates to the technical field of hygroscopic materials, and particularly discloses an atmospheric hygroscopic material for ecological restoration of arid-semi-arid regions and a preparation method of the atmospheric hygroscopic material. The method comprises the following steps: firstly preparing gel containing a heat-conducting material, acrylamide and isopropyl acrylamide, freeze-drying the swelled gel, soaking the gel in a moisture-absorbing salt water solution to load moisture-absorbing salt, taking out and drying. The temperature sensitivity of isopropylacrylamide is retained through copolymerization of acrylamide and isopropylacrylamide monomers, meanwhile, higher hydrophilic performance is given to isopropylacrylamide, a high-molecular polymer can absorb liquid drops formed by deliquescence of moisture absorption salt, continuous adsorption of the moisture absorption salt is kept, and the polymerized gel has higher moisture absorption capacity and water yield. The prepared atmospheric hygroscopic material provides a new way for supplying water required by ecological restoration plants in arid-semi-arid regions, water vapor is collected without depending on an external device in use, and the water production process is free of energy consumption and emission and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of hygroscopic materials, and in particular relates to an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas and a preparation method thereof. Background Art

[0002] After ecological restoration in arid and semi-arid areas, natural precipitation is unable to provide the water required for the survival of ecological restoration plants, and they have to rely on artificial maintenance, which is extremely costly and consumes a large amount of liquid fresh water resources in the area. After watering is stopped, the survival rate is low, and the problem of water source required by ecological restoration plants is very serious.

[0003] Atmospheric water harvesting refers to the process of capturing and collecting liquid water from the air. Currently, there are a lot of studies in areas lacking fresh water resources, mainly used to provide drinking water for human survival and water for production activities. Water molecules in the air are captured by hygroscopic materials, and water vapor and liquid water are released by heating the hygroscopic agent to achieve liquid water collection. It has the advantages of wide climate adaptability and low energy consumption, but it usually relies on the use of container devices to collect and condense the water vapor released by the adsorption material for use, which is difficult to apply on ecological restoration slopes with limited terrain conditions. Therefore, it is urgent to develop new hygroscopic materials to continuously provide the water needed by ecological restoration plants. Summary of the invention

[0004] The purpose of the present invention is to provide an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas and a preparation method thereof in view of the deficiencies in the prior art. The thermosensitivity of isopropyl acrylamide is retained while giving it stronger hydrophilicity through copolymerization of acrylamide and isopropyl acrylamide monomers. The hygroscopic salt has good water absorption performance but is easy to deliquesce, resulting in performance degradation. The high molecular polymer can absorb droplets formed by the deliquescing of the hygroscopic salt, maintain continuous adsorption of the hygroscopic salt, and make the polymer gel have greater moisture absorption and water production.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] The invention provides a method for preparing an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas. The method comprises the following steps: dispersing acrylamide and isopropyl acrylamide monomers in water to dissolve the monomers to obtain a polymer solution, wherein the mass concentration of the polymer solution is 10% to 25%, and the mass ratio of the acrylamide monomer to the isopropyl acrylamide monomer is 1:0.5 to 1:1.5; then adding a heat-conducting substance and dispersing the substance uniformly to obtain a mixed suspension; adding a cross-linking agent, an initiator and a catalyst to perform ultrasonic reaction to obtain a composite hydrogel, washing away unreacted monomers with ultrapure water, placing the composite hydrogel in ultrapure water to swell the composite hydrogel, performing freeze drying, and soaking the composite hydrogel in a hygroscopic salt solution, taking the composite hydrogel out and performing drying to obtain the atmospheric hygroscopic material.

[0007] Furthermore, the thermally conductive material includes any one of nano carbon powder, nano graphite powder, carbon black, conductive alumina powder, polyaniline or polypyrrole.

[0008] Furthermore, the mass fraction of the heat-conducting substance in the mixed suspension is 1.5% to 3%.

[0009] Furthermore, the cross-linking agent is N,N-methylenebisacrylamide.

[0010] Furthermore, the mass ratio of the N,N-methylenebisacrylamide to the mixed suspension is 1:1000 to 1:250.

[0011] Furthermore, the initiator is potassium persulfate or ammonium persulfate.

[0012] Furthermore, the mass ratio of the initiator to the mixed suspension is 1:200 to 1:120.

[0013] Furthermore, the concentration of the hygroscopic salt solution is 2-5 mol / mL, wherein the mass ratio of calcium chloride to lithium chloride is 1:4-1:9.

[0014] Furthermore, the mass ratio of calcium chloride to lithium chloride is 1:4 to 1:9.

[0015] Furthermore, the catalyst is N,N,N',N'-tetramethylethylenediamine or N,N,-dimethylbenzylamine.

[0016] Furthermore, the volume ratio of the catalyst to the mixed suspension is 1:(200-400).

[0017] The second object of the present invention is to provide an atmospheric moisture absorbing material prepared by the above-mentioned preparation method.

[0018] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0019] (1) The present invention provides a method for preparing an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas. The method first prepares a gel containing a thermal conductive material, acrylamide and isopropyl acrylamide, freeze-dries the swollen gel, and then soaks the gel in a hygroscopic salt solution to load the hygroscopic salt, takes it out and dries it. The thermosensitivity of isopropyl acrylamide is retained by copolymerizing acrylamide and isopropyl acrylamide monomers, while giving it stronger hydrophilic properties. The high molecular polymer can absorb droplets formed by the deliquescence of the hygroscopic salt, maintain the continuous adsorption of the hygroscopic salt, and make the polymer gel have a larger moisture absorption and water production.

[0020] (2) The atmospheric hygroscopic material prepared by the present invention provides a new way to supply the water required by plants for ecological restoration in arid and semi-arid areas. During use, it does not rely on external devices to collect water vapor, and the water production process is energy-free and emission-free, which is environmentally friendly.

[0021] (3) The present invention provides a method for preparing an atmospheric hygroscopic material, which is simple to operate and convenient for field operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a photo of the atmospheric moisture absorbing material prepared by the present invention;

[0023] Figure 2 A graph showing the dynamic contact angle test results of the atmospheric hygroscopic material provided by the present invention;

[0024] Figure 3 A diagram showing the application of the atmospheric moisture absorbing material provided by the present invention in a field vegetation hole;

[0025] Figure 4 The swelling rate diagram of atmospheric hygroscopic materials in pure water at 10°C at different mass ratios of NIPAM / AM;

[0026] Figure 5 It is the adsorption rate curve of atmospheric hygroscopic materials under different humidity conditions at a temperature of 15°C;

[0027] Figure 6 This is the curve of the change of residual water content and temperature of the gel of the atmospheric hygroscopic material under fixed light intensity at 20℃. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present invention clearer, the specific embodiments of the present invention are further described in detail below in conjunction with specific examples and drawings. If no specific test method, instrument or condition is specified in the examples, it is carried out according to the technology or condition described in the literature in this field or according to the product instructions. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0029] The invention provides an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas, comprising a hydrogel body copolymerized from acrylamide and isopropylacrylamide monomers, and hygroscopic salts and heat-conducting materials distributed in the pores of the hydrogel. The preparation method comprises the following steps: firstly preparing a gel containing a heat-conducting material, acrylamide (AM) and isopropylacrylamide (NIPAM), freeze-drying the swollen gel, then soaking the gel in a hygroscopic salt solution to load the hygroscopic salt, and drying the gel after taking it out to obtain a composite hygroscopic material.

[0030] The specific preparation process is as follows: AM and NIPAM are dispersed in water and ultrasonically shaken for 30 to 60 minutes to dissolve them to obtain a polymer solution; then a heat conductive material is added, and the mixture is evenly dispersed by stirring and ultrasonicating for 2 to 4 hours to obtain a mixed suspension; a cross-linking agent, an initiator and a catalyst are added and reacted under ultrasonication for 10 to 30 minutes to obtain a composite hydrogel, and after the unreacted monomers are rinsed off with ultrapure water, the composite hydrogel is placed in ultrapure water for 24 hours to swell, removed and freeze-dried for 24 to 48 hours, and soaked in a hygroscopic saline solution, and then taken out and dried, the drying temperature is 60 to 80°C, and the drying time is 48 to 72 hours.

[0031] In some embodiments, the thermal conductive material is selected from nano-carbon powder, nano-graphite powder, carbon black, conductive alumina powder, polyaniline, polypyrrole, etc.; the cross-linking agent is selected from N,N-methylenebisacrylamide (MBA); the initiator is selected from potassium persulfate or ammonium persulfate (APS); the catalyst is selected from N,N,N',N'-tetramethylethylenediamine, or N,N,-dimethylbenzylamine; and the hygroscopic salt is selected from calcium chloride and lithium chloride.

[0032] In a specific embodiment, acrylamide and isopropyl acrylamide monomers are dispersed and dissolved in water at a mass ratio of 1:0.5 to 1:1.5 to obtain a polymer solution, and the mass concentration of the polymer solution is 10% to 25%. The amount of heat conductive material added can be 15% to 30% of the mass fraction of the mixed suspension, the mass ratio of the mass of the cross-linking agent added to the mass of the mixed suspension is 1:1000-1:250, the mass ratio of the initiator added to the mass of the mixed suspension is 1:200 to 1:120, and the volume ratio of the catalyst to the mixed suspension is 1:(200 to 400).

[0033] The following is a detailed description of a method for preparing an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas provided by the present invention with reference to specific embodiments.

[0034] Example 1

[0035] This embodiment provides a method for preparing an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas.

[0036] The specific steps are as follows:

[0037] (1) Weigh 0.4g AM and 0.6g NIPAM into a beaker, add 8g ultrapure water and sonicate for 60min to completely dissolve them, weigh 0.3g 1 micron nanocarbon powder and add it into the solution and sonicate for 2h. Add 3mL MBA solution with a concentration of 0.016g / mL and 0.5mL APS solution with a concentration of 0.05g / mL, sonicate for 5min, drop 20μl N,N,N',N'-tetramethylethylenediamine, continue sonicating for 15min and let stand for 10h.

[0038] (2) The gel was repeatedly soaked and rinsed with ultrapure water for 5 times to remove unreacted monomers, then soaked for 24 hours, taken out and put into the refrigerator for freezing, and after it was completely frozen, put into the freeze dryer for 48 hours. Add 4.44g CaCl 2 Stir and dissolve 6.78g LiCl, soak the freeze-dried gel in the solution for 24h, take it out and put it in a 70℃ forced air drying oven for 48h.

[0039] Example 2

[0040] This embodiment provides a method for preparing an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas.

[0041] The method is basically the same as Example 1, except that the masses of the AM and NIPAM monomers described in step (1) are 0.66 g and 0.33 g respectively.

[0042] Example 3

[0043] This embodiment provides a method for preparing an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas.

[0044] The method is basically the same as Example 1, except that the amount of ultrapure water used in step (1) is 5 g, the mass of nano-carbon powder is 0.15 g, the amount of MBA solution used is 1.5 ml, and the amount of APS solution used is 0.3 ml.

[0045] Example 4

[0046] This embodiment provides a method for preparing an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas.

[0047] The same as Example 1, except that the mass of the hygroscopic salt in step (2) is 2.77 gCaCl 2 and 9.54gLiCl.

[0048] Example 5

[0049] This embodiment is a method for using hygroscopic materials on low and gentle slopes. The composite hygroscopic material soaked in hygroscopic salt solution is dried and chopped into small pieces with a diameter of about 3 mm. The composite hygroscopic material: sand and soil are mixed and stirred at a mass ratio of 1:3 to 1:7, and evenly sprinkled in a circle with a radius of 3 cm around the roots of plants with a thickness of 5 mm.

[0050] Example 6

[0051] This embodiment is a method for using hygroscopic materials in vegetation holes. The composite hygroscopic material soaked in hygroscopic salt solution is dried and cut into 5 mm thick slices, which are covered on the soil at the opening of the vegetation hole. It absorbs water vapor and condensed water in the air at night and releases liquid water to replenish the underlying soil after light during the day.

[0052] Comparative Example 1

[0053] The difference from Example 1 is that 1 g NIPAM is used as the polymer material and no nano carbon powder is added.

[0054] Comparative Example 2

[0055] The difference from Comparative Example 2 is that 1 g AM is used as the polymer material.

[0056] The swelling properties and water release ratios of Example 1, Comparative Example 1 and Comparative Example 2 were tested. The swelling property of Example 1 was 24.72 g / g, slightly lower than 26.74 g / g of Comparative Example 2 but much higher than 17.47 g / g of Comparative Example 1. Example 1 can achieve 75.3% water release, which is 31.3% higher than the average water production of Comparative Example 1.

[0057] refer to Figure 1 Figure a shows the freeze-dried composite gel, which has a large number of pore structures inside that can load hygroscopic salts, and figure b shows the swollen gel after soaking in hygroscopic salts.

[0058] refer to Figure 2 In the figure, a, b, and c are images of a water droplet on the surface of a dry hygroscopic material at 1s, 5s, and 10s, respectively. The contact angle measurement reflects the hydrophilicity and adsorption properties of the gel.

[0059] refer to Figure 3 The atmospheric hygroscopic material prepared in Example 1 was tested for application in vegetation holes. 50 g of soil with a fixed moisture content was placed in a culture dish, and the composite hygroscopic gel was wrapped with gauze and placed in the dish and weighed and recorded, and the changes in soil moisture content and gel moisture content were continuously monitored.

[0060] refer to Figure 4 , is the swelling rate of the composite gel copolymerized by AM and NIPAM in different mass ratios. It can be seen that the higher the AM content, the greater the swelling degree.

[0061] refer to Figure 5 , which are the adsorption curves of atmospheric hygroscopic materials under four different humidity conditions at 20°C, proving that adsorption can also be achieved under low humidity conditions of 30% RH, and the adsorption amount under high humidity conditions at the same time is far greater than that under low humidity.

[0062] refer to Figure 6, which is a trend chart of the temperature and moisture content of the atmospheric hygroscopic material itself under the conditions of 20℃ and light intensity 15wLUX.

[0063] In the absence of conflict, the above embodiments and features in the embodiments may be combined with each other.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an atmospheric hygroscopic material for ecological restoration in arid and semi-arid areas, characterized in that: Acrylamide and isopropylacrylamide monomers are dispersed and dissolved in water to obtain a polymer solution, wherein the mass concentration of the polymer solution is 10% to 20%, and the mass ratio of acrylamide monomer to isopropylacrylamide monomer is 1:0.5 to 1:1.5; then a heat conductive material is added and dispersed evenly to obtain a mixed suspension; a crosslinking agent, an initiator and a catalyst are added to perform ultrasonic reaction to obtain a composite hydrogel, unreacted monomers are washed away with ultrapure water, the composite hydrogel is placed in ultrapure water for swelling, freeze-dried, soaked in a hygroscopic saline solution, taken out and dried to obtain an atmospheric hygroscopic material.

2. The preparation method according to claim 1, characterized in that The heat-conducting material includes any one of nano carbon powder, nano graphite powder, carbon black, conductive alumina powder, polyaniline or polypyrrole.

3. The preparation method according to claim 2, characterized in that: The mass fraction of the heat-conducting material in the mixed suspension is 1.5% to 3%.

4. The preparation method according to claim 1, characterized in that: The cross-linking agent is N,N-methylenebisacrylamide, and the mass ratio of N,N-methylenebisacrylamide to the mixed suspension is 1:1000 to 1:

250.

5. The preparation method according to claim 1, characterized in that: The initiator is potassium persulfate or ammonium persulfate.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the initiator to the mixed suspension is 1:200 to 1:

120.

7. The preparation method according to claim 1, characterized in that: The hygroscopic salts are calcium chloride and lithium chloride.

8. The preparation method according to claim 7, characterized in that: The concentration of the hygroscopic salt solution is 2-5 mol / mL, wherein the mass ratio of calcium chloride to lithium chloride is 1:4-1:

9.

9. The preparation method according to claim 3, characterized in that: The catalyst is N,N,N',N'-tetramethylethylenediamine or N,N,-dimethylbenzylamine, and the volume ratio of the catalyst to the mixed suspension is 1:(200-400).

10. An atmospheric hygroscopic material prepared by the preparation method according to any one of claims 1 to 9.

Images