Preparation method and application of biomass hybrid hydrogel evaporator

Abstract

The present invention relates to the technical field of solar thermal conversion and water treatment, and in particular to a preparation method and application of a biomass hybrid hydrogel evaporator. The preparation method comprises the following steps: S1, preparing a solar absorber, and S2, preparing a hydrogel evaporator; applying the prepared biomass hybrid hydrogel evaporator to the purification of salty water resources. The biomass hybrid hydrogel evaporator prepared by the present invention has the advantages of reducing evaporation enthalpy, improving material hydrophilicity, and excellent light absorption and heat conversion capabilities, high evaporation efficiency, and can stably combine the anti-polyelectrolyte effect of zwitterionic hydrogels, thereby solving the problems of salt crystallization and difficult evaporation in salty water.

Description

Technical Field

[0001] The present invention relates to the technical field of solar thermal conversion and water treatment, and in particular to a preparation method and application of a biomass hybrid hydrogel evaporator. Background Art

[0002] Water is one of Earth's most abundant resources, yet available freshwater resources are extremely limited. Common existing water recovery methods include reverse osmosis, multi-stage flash evaporation, and membrane distillation, but all suffer from high energy consumption, severe pollution, and expensive equipment. Solar interfacial evaporation technology utilizes solar energy to separate water and impurities through evaporation in an evaporator. This technology can alleviate water shortages by leveraging sustainable energy and potential freshwater resources, offering advantages such as low energy consumption, environmental friendliness, simplicity, and efficiency. Water in hydrogels exists in three states: free water, intermediate water, and bound water. The latter can reduce the energy requirement for evaporation. Furthermore, hydrogels are hydrophilic polymers with three-dimensional network structures and highly tunable physicochemical properties, making them promising solar evaporators. In particular, polyzwitterionic hydrogels exhibit a unique anti-polyelectrolyte effect in high-salinity environments. This unique salt response can decompose their relatively collapsed cohesive state into chain expansion and greater water absorption, facilitating the coordination of a wider range of salt species and enabling more stretched conformations for water capture within the hydrogel.

[0003] The key to interfacial evaporation is selecting the right solar absorber to efficiently convert solar energy into the heat required for vaporization. Compared to other photothermal conversion materials like metals and semiconductors, carbon-based materials, such as graphene and carbon nanotubes, offer the advantages of natural broadband light absorption and abundant sources. Biochar, in particular, is low-cost, easy to prepare, and has a broad absorption band, making it an effective absorber across the solar spectrum. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a preparation method and application of a biomass hybrid hydrogel evaporator. The technical solution of the present invention is: a preparation method based on a biomass hybrid hydrogel evaporator, comprising the following steps:

[0005] S1. Preparation of solar absorber

[0006] S1-1. Dry the waste biomass and place it in a porcelain boat, then transfer it to a tube furnace. Under a protective atmosphere, heat the tube furnace from room temperature to 400-800°C at a rate of 5-10°C / min and maintain for 1 hour. After cooling to room temperature, take it out and grind it to obtain biochar material.

[0007] S1-2, the obtained biochar material was acid-washed with a 3-5% HNO3 solution, kept for 12-15 hours, and then washed with water 3-5 times until the water flow was neutral, taken out and dried at 30-50°C, and then ball-milled for 10-12 hours until it passed through a 100-200 mesh sieve to obtain a solar absorber;

[0008] S2. Preparation of hydrogel evaporator

[0009] S2-1. Dissolve the polyzwitterionic hydrogel in deionized water at a mass ratio of 2-4:6-8, and stir until transparent to obtain solution A.

[0010] S2-2, preparing an initiator at a mass ratio of initiator to solution A of 0.04 to 0.06:10, and then preparing a crosslinker at a volume ratio of crosslinker to solution A of 1:100 to 130, then adding the initiator and crosslinker to solution A obtained in S2-1, mixing, and ultrasonicating for 10 to 20 minutes under the conditions of an ultrasonic temperature of 15°C, an ultrasonic frequency of 40 kHz, and an ultrasonic power of 360 W to obtain a hydrogel precursor solution;

[0011] S2-3, dispersing the solar absorber obtained in S1-2 in deionized water to obtain solution B;

[0012] S2-4, adding solution B obtained in S2-3 to the hydrogel precursor solution obtained in S2-2 at a volume ratio of 1:10, mixing, and ultrasonicating for 12 to 17 minutes under the conditions of an ultrasonic temperature of 15°C, an ultrasonic frequency of 40 kHz, and an ultrasonic power of 360 W to obtain a mixed solution, and then adding tetramethylethylenediamine at a volume ratio of 40 to 50 μL of tetramethylethylenediamine: 100 mL of the mixed solution, and aerating with nitrogen for 25 to 35 minutes to obtain liquid C;

[0013] S2-5. Liquid C is injection molded and sealed at 85-95° C., reacted for 3.5-4.5 hours to obtain a hydrogel, and then soaked in deionized water for 20-24 hours, and dried to obtain a biomass hybrid hydrogel evaporator.

[0014] Furthermore, in step S1-1, the waste biomass is coconut shell, sorghum straw or sludge;

[0015] Note: The above-mentioned biomass is a type of carbon-rich natural resource with the characteristics of sustainability, renewable, biodegradable and low cost.

[0016] Furthermore, in step S1-2, the polyzwitterionic hydrogel is [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide, the initiator is ammonium persulfate, and the cross-linking agent is polyethylene glycol diacrylate;

[0017] Description: Polyzwitterionic hydrogel has a good anti-polyelectrolyte effect. It can more effectively capture and retain water when treating salty water resources, while lowering the salt crystallization threshold, thereby improving the recovery efficiency of water resources. Ammonium persulfate as an initiator can improve the efficiency of the polymerization reaction and the completeness of the monomer reaction to a certain extent. Polyethylene glycol diacrylate as a cross-linking agent can react with the hydrogel monomer to form a more stable and tough hydrogel network structure, thereby improving its water absorption performance, water retention capacity and mechanical strength.

[0018] Furthermore, in step S2-3, the mass ratio of the solar absorber to deionized water is 1:10;

[0019] Note: Adding solar absorbers in the above proportions can make the gel have better light-to-heat conversion ability, improve the state of water molecules inside the gel, and increase evaporation efficiency.

[0020] Furthermore, in step S2-5, the liquid C is stabilized before the gelation reaction.

[0021] The stabilization treatment method comprises: injecting nitrogen gas with a purity of 99.9% to 99.99% into a high-pressure container containing liquid tetrahydrazide polydimethylsiloxane at a volume ratio of 18 to 22:1, adjusting the temperature of the high-pressure container to 85 to 95° C. and the pressure to 5 to 15 MPa, stirring and diffusing the container for 3 to 6 hours until bubbles are generated, then reducing the pressure in the container at a rate of 0.25 to 0.5 MPa / min until the bubbles solidify to obtain tetrahydrazide polydimethylsiloxane foam, ultrasonically immersing the tetrahydrazide polydimethylsiloxane foam in liquid C at a mass ratio of 0.3 to 0.5:1 and mixing for 15 to 30 minutes, finally dropwise adding a pH adjuster until the pH of the solution is 4.5 to 5.5, and mixing to obtain stabilized liquid C;

[0022] Among them, the nitrogen injection speed is 900-1000Nm 3 / h, the ultrasonic immersion temperature is 25-30°C, the ultrasonic frequency is 10-12kHz, and the ultrasonic power is 160-180W;

[0023] Description: Low surface tension tetrahydrazide polydimethylsiloxane foam helps lower the energy threshold for water evaporation, making it easier for water molecules to transform from liquid to gas. Mixing liquid C with low surface tension tetrahydrazide polydimethylsiloxane foam can effectively increase the evaporation rate of the evaporator. Tetrahydrazide polydimethylsiloxane foam has a low thermal conductivity coefficient, which can reduce heat loss on the surface of the hydrogel evaporator and help maintain a high temperature environment inside the evaporator, thereby accelerating water evaporation. By adjusting the pH value of the solution to 4.5-5.5, the swelling rate of the hydrogel can be improved. This optimization helps the hydrogel evaporator maintain stable performance during long-term use, thereby achieving more efficient and stable water evaporation.

[0024] Furthermore, the pH regulator is a hydroxyethylidene diphosphonic acid solution with a concentration of 80 to 100 mg / L or a sodium hydroxide solution with a concentration of 0.5 to 2 mol / L;

[0025] Explanation: The reason why hydroxyethylidene diphosphonic acid solution is used as the regulator is that the anions formed after the dissociation of hydroxyethylidene diphosphonic acid in water form stable complexes or chelates with metal ions such as calcium and magnesium, thereby preventing these metal ions from forming precipitation during the concentration process; secondly, hydroxyethylidene diphosphonic acid can change the kinetic process of crystal growth, making it difficult for crystals to form or the formed crystals are relatively loose and difficult to adhere to the evaporator surface.

[0026] Furthermore, the prepared biomass hybrid hydrogel evaporator is applied to the purification of saline water resources;

[0027] Description: The biomass hydrogel evaporator prepared by the present invention has the advantages of reducing evaporation enthalpy, improving material hydrophilicity, and excellent light absorption and heat conversion capabilities. It has high evaporation efficiency and excellent salt crystallization evaporation ability, which can effectively solve the problems of salt crystallization and difficult evaporation in saline water bodies.

[0028] Furthermore, the application method is as follows: the biomass hybrid hydrogel evaporator is floated on the water surface through an isolation layer, and evaporation of the solar-driven interface can be performed under sunlight; the isolation layer is PVA sponge or foam;

[0029] Description: The use of an isolation layer can effectively prevent the hydrogel evaporator from direct contact with the water body, reducing the heat loss of the water body during the evaporation process, thereby improving the efficiency of the evaporator. At the same time, the isolation layer can also serve as a supporting material to keep the position of the hydrogel evaporator stable and prevent it from moving or deforming due to water flow or other factors during the evaporation process.

[0030] PVA sponge or foam serves as an isolation layer, which itself has a certain ability to absorb and retain water. This material can continuously provide a water source for the hydrogel evaporator and promote the transfer of water molecules to the evaporator surface through its pore structure. This water transfer ability ensures that the evaporator can maintain a stable evaporation rate under continuous light. By floating the hydrogel evaporator on the water surface and performing solar-driven evaporation, this technology can be applied to a wider range of water environments, such as lakes, rivers, and seawater. This technology is not only suitable for the recovery and purification of freshwater resources, but can also be used in fields such as seawater desalination.

[0031] Furthermore, the isolation layer is wrapped with a hydrophilic material;

[0032] Description: Hydrophilic materials can quickly absorb and transfer water to the surface of the hydrogel evaporator, which helps to form a uniform and continuous water film on the evaporator surface; the uniform distribution of the water film helps to improve the evaporation efficiency of the evaporator because water molecules can more effectively contact solar radiation and convert into water vapor; and hydrophilic materials generally have good thermal conductivity, which can help heat transfer to the evaporator surface faster, thereby accelerating the evaporation rate of water.

[0033] Compared with the existing technology, the beneficial effects of the present invention are:

[0034] (1) The biomass hybrid hydrogel evaporator prepared by the present invention has the advantages of reducing evaporation enthalpy, improving material hydrophilicity, and excellent light absorption and heat conversion capabilities, high evaporation efficiency, and can stably combine the anti-polyelectrolyte effect of zwitterionic hydrogel, solving the problems of salt crystallization and difficult evaporation in saline water bodies; at the same time, the preparation process of the present invention is simple, easy to operate, and low in price, and can be promoted and applied on a large scale. It is a green and efficient new method with industrial application prospects.

[0035] (2) The present invention combines biochar as an absorbent with polyzwitterionic hydrogel to collect sunlight and convert it into thermal energy, which is then used in situ for the evaporation of water contained in the molecular network. At the same time, the unique anti-polyelectrolyte effect can effectively address the problem of salt in potential freshwater resources and alleviate the occurrence of salt crystallization. Waste biomass is used as the raw material of the absorbent, which is widely available, easy to obtain, and environmentally friendly, thus realizing the "resourceization" of waste disposal and achieving the purpose of "treating waste with waste."

[0036] (3) The present invention stabilizes liquid C before gelation, and utilizes tetrahydrazide polydimethylsiloxane foam with low surface tension to effectively reduce the energy threshold of water evaporation, thereby effectively improving the evaporation rate of the evaporator. The low thermal conductivity of tetrahydrazide polydimethylsiloxane foam is utilized to effectively reduce the heat loss on the surface of the hydrogel evaporator, maintain a high temperature environment inside the evaporator, and thus accelerate the evaporation of water. By preparing a pH regulator with excellent photothermal conversion performance and excellent biological contamination resistance, the swelling rate of the hydrogel is effectively improved, thereby optimizing the hydrogel evaporator to maintain stable performance during long-term use, and at the same time, it also plays a certain limiting role on the deposition of salt, thereby achieving more efficient and stable water evaporation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a comparison chart of the evaporation rates of the hydrogel evaporator obtained by carbonizing sorghum straw at 400°C, 600°C, and 800°C and without biochar hybridization;

[0038] Figure 2 This is a comparison chart of the evaporation rates of different biomasses carbonized at 600°C, conventional solar evaporation without the aid of an evaporator, and a hydrogel evaporator prepared without biochar hybridization;

[0039] Figure 3 This is a comparison chart of the long-period evaporation rate of the hydrogel evaporator in Example 1 of the present invention;

[0040] Figure 4 This is a comparison chart of the evaporation rates of the biomass hybrid hydrogel evaporators prepared in Examples 1 to 24 and Control Groups 1 to 5 of the present invention. DETAILED DESCRIPTION

[0041] In order to further illustrate the approach and effects achieved by the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with experiments.

[0042] Example 1: A method for preparing a biomass hybrid hydrogel evaporator, comprising the following steps:

[0043] S1. Preparation of solar absorber

[0044] S1-1. Dry the waste biomass and place it in a porcelain boat, then transfer it to a tube furnace. Under a protective atmosphere, heat the tube furnace from room temperature to 600°C at a rate of 5°C / min and maintain it for 1 hour. After cooling to 26°C, take it out and grind it to obtain a biochar material; wherein the protective atmosphere is argon and the waste biomass is sorghum straw;

[0045] S1-2, the obtained biochar material was acid-washed with a 4% HNO3 solution, kept for 14 hours, and then washed with water seven times until the water flow was neutral. The biochar material was taken out and dried at 40°C, and then ball-milled for 12 hours until it passed through a 100-mesh sieve to obtain a solar absorber;

[0046] S2. Preparation of hydrogel evaporator

[0047] S2-1. Dissolve a polyzwitterionic hydrogel in deionized water at a mass ratio of 3:7 and stir until transparent to obtain a solution A; the polyzwitterionic hydrogel is [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide;

[0048] S2-2, preparing an initiator at a mass ratio of initiator to solution A of 0.05:10, and then preparing a crosslinker at a volume ratio of crosslinker to solution A of 1:160, then adding the initiator and crosslinker to solution A obtained in S2-1, mixing, and ultrasonicating for 15 minutes under the conditions of an ultrasonic temperature of 15°C, an ultrasonic frequency of 40 kHz, and an ultrasonic power of 360 W to obtain a hydrogel precursor solution; the initiator is ammonium persulfate, and the crosslinker is polyethylene glycol diacrylate;

[0049] S2-3, dispersing the solar absorber obtained in S1-2 in deionized water to obtain solution B; the mass ratio of the solar absorber to deionized water is 1:10;

[0050] S2-4, adding solution B obtained in S2-3 to the hydrogel precursor solution obtained in S2-2 at a volume ratio of 1:101, mixing, and ultrasonically treating for 15 min under the conditions of an ultrasonic temperature of 15°C, an ultrasonic frequency of 40 kHz, and an ultrasonic power of 360 W to obtain a mixed solution, and then adding tetramethylethylenediamine at a volume ratio of 45 μL:100 mL of the mixed solution, and aerating with nitrogen for 30 min to obtain liquid C;

[0051] S2-5, injection molding liquid C in a sealed state at 90° C., reacting for 4 hours to obtain a hydrogel, and then soaking it in deionized water for 22 hours to obtain a biomass hybrid hydrogel evaporator;

[0052] This embodiment also provides an application method, in which the prepared biomass hybrid hydrogel evaporator is applied to the purification of salt water resources;

[0053] The application method is as follows: the biomass hybrid hydrogel evaporator is floated on the water surface through an isolation layer, and solar-driven interface evaporation can be performed under sunlight; the isolation layer is PVA sponge; the isolation layer is wrapped with a hydrophilic material; in this embodiment, the hydrophilic material is dust-free paper.

[0054] Example 2: Different from Example 1, in step S1-1, the waste biomass is coconut shell.

[0055] Example 3: Different from Example 1, in step S1-1, the waste biomass is sludge.

[0056] Example 4: Different from Example 1, in step S1-1, the temperature of the tubular furnace is raised from room temperature to 400°C at a heating rate of 5°C / min.

[0057] Example 5: Different from Example 1, in step S1-1, the temperature of the tubular furnace is raised from room temperature to 800°C at a heating rate of 5°C / min.

[0058] Example 6: Different from Example 1, in step S1-2, the obtained biochar material is acid-washed with a 3% HNO3 solution, kept for 12 hours, and then washed with water 7 times until the water flow is neutral, taken out and dried at 30°C.

[0059] Example 7: Different from Example 1, in step S1-2, the obtained biochar material is acid-washed with a 5% HNO3 solution, kept for 15 hours, and then washed with water 9 times until the water flow is neutral, taken out and dried at 50°C.

[0060] Example 8: Different from Example 1, in step S2-1, the polyzwitterionic hydrogel is dissolved in deionized water at a mass ratio of 2:8.

[0061] Example 9: Different from Example 1, in step S2-1, the polyzwitterionic hydrogel is dissolved in deionized water at a mass ratio of 4:6.

[0062] Example 10: Different from Example 1, in step S2-2, the initiator is prepared according to the mass ratio of initiator: solution A of 0.04:10, and the cross-linker is prepared according to the volume ratio of cross-linker: solution A of 1:150. Then, the initiator and cross-linker are added to the solution A obtained in S2-1, mixed and ultrasonicated for 10 minutes.

[0063] Example 11: Different from Example 1, in step S2-2, the initiator is prepared according to the mass ratio of initiator: solution A of 0.06:10, and the cross-linker is prepared according to the volume ratio of cross-linker: solution A of 1:200. Then the initiator and cross-linker are added to the solution A obtained in S2-1, mixed and ultrasonicated for 20 minutes.

[0064] Example 12: Different from Example 1, in step S2-4, solution B obtained in S2-3 was added to the hydrogel precursor solution obtained in S2-2 at a volume ratio of 1:9, mixed and then ultrasonically treated for 12 minutes to obtain a mixed solution, and then tetramethylethylenediamine was added at a volume ratio of 40 μL:100 mL of tetramethylethylenediamine: mixed solution, and nitrogen was passed through for 25 minutes to obtain liquid C.

[0065] Example 13: Different from Example 1, in step S2-4, solution B obtained in S2-3 was added to the hydrogel precursor solution obtained in S2-2 at a volume ratio of 1:11, mixed and then ultrasonically treated for 17 minutes to obtain a mixed solution, and then tetramethylethylenediamine was added at a volume ratio of 50 μL:100 mL of tetramethylethylenediamine: mixed solution, and nitrogen was passed through for 35 minutes to obtain liquid C.

[0066] Example 14: Different from Example 1, in step S2-5, liquid C is injection molded in a sealed state at 85°C, reacted for 3.5 hours to obtain a hydrogel, and then soaked in deionized water for 20 hours to obtain a biomass hybrid hydrogel evaporator.

[0067] Example 15: Different from Example 1, in step S2-5, liquid C is injection molded in a sealed state at 95°C, reacted for 4.5 hours to obtain a hydrogel, and then soaked in deionized water for 24 hours to obtain a biomass hybrid hydrogel evaporator.

[0068] Example 16: Different from Example 1, in step S2-5, the liquid C is stabilized before the gelation reaction.

[0069] The stabilization treatment method is as follows: nitrogen gas with a purity of 99.95% is injected into a high-pressure container containing liquid tetrahydrazide polydimethylsiloxane at a volume ratio of 20:1, the temperature of the high-pressure container is adjusted to 90°C and the pressure is 10 MPa, and the mixture is stirred and diffused for 4.5 hours until bubbles are generated, and then the pressure in the container is reduced at a rate of 0.35 MPa / min until the bubbles solidify to obtain tetrahydrazide polydimethylsiloxane foam, and the tetrahydrazide polydimethylsiloxane foam is ultrasonically immersed in liquid C at a mass ratio of 0.4:1 and mixed for 22 minutes. In this embodiment, the pH of the solution is measured to be 6, and finally a pH adjuster is added dropwise to the solution pH = 5.0, and the stabilized liquid C is obtained by mixing; the pH adjuster is a 90 mg / L hydroxyethylidene diphosphonic acid solution;

[0070] Among them, the nitrogen injection speed is 950Nm 3 / h, the ultrasonic immersion temperature was 27°C, the ultrasonic frequency was 14kHz, and the ultrasonic power was 170W.

[0071] Example 17: The difference from Example 16 is that nitrogen with a purity of 99.9% is added at a volume ratio of 18:1 at a speed of 900 Nm 3 The solution is injected into a high-pressure container containing liquid tetrahydrazide polydimethylsiloxane at an injection rate of / h.

[0072] Example 18: The difference from Example 16 is that nitrogen with a purity of 99.99% is added at a volume ratio of 22:1 at a speed of 1000 Nm 3 The solution is injected into a high-pressure container containing liquid tetrahydrazide polydimethylsiloxane at an injection rate of / h.

[0073] Example 19: Different from Example 16, the temperature of the high-pressure container is adjusted to 85°C and the pressure is 5 MPa, and the mixture is stirred and diffused for 3 hours until bubbles are generated, and then the pressure in the container is reduced at a rate of 0.25 MPa / min until the bubbles solidify.

[0074] Example 20: Different from Example 16, the temperature of the high-pressure container is adjusted to 95°C and the pressure is 15 MPa, and the mixture is stirred and diffused for 6 hours until bubbles are generated, and then the pressure in the container is reduced at a rate of 0.5 MPa / min until the bubbles solidify.

[0075] Example 21: Different from Example 16, the tetrahydrazide polydimethylsiloxane foam is ultrasonically immersed in liquid C and mixed for 15 minutes, and finally a pH adjuster is added dropwise until the pH of the solution is 4.5, and the mixture is mixed to obtain stabilized liquid C; wherein, the ultrasonic immersion temperature is 25°C, the ultrasonic frequency is 10kHz, and the ultrasonic power is 160W.

[0076] Example 22: Different from Example 16, the tetrahydrazide polydimethylsiloxane foam is ultrasonically immersed in liquid C and mixed for 30 minutes, and finally a pH adjuster is added dropwise until the pH of the solution is 5.5, and the mixture is mixed to obtain stabilized liquid C; wherein, the ultrasonic immersion temperature is 30°C, the ultrasonic frequency is 12kHz, and the ultrasonic power is 180W.

[0077] Example 23: The difference from Example 16 is that the pH regulator is a hydroxyethylidene diphosphonic acid solution with a concentration of 80 mg / L.

[0078] Example 24: The difference from Example 16 is that the pH regulator is a 100 mg / L hydroxyethylidene diphosphonic acid solution.

[0079] Experimental Example: The description of this experimental example is based on the scheme described in Example 1, and is intended to illustrate the practical application effect of the present invention.

[0080] The hydrogel evaporator was floated in a beaker containing 100 mL of 10 wt% NaCl saline through a PVA sponge. The beaker was placed on an electronic balance and placed directly below a solar simulator equipped with an AM1.5G filter. The distance between the surface of the hydrogel in the evaporation layer of the evaporator and the light source was measured and calibrated using a solar power meter so that the light intensity received on the surface was 1 standard sunlight intensity (1 kW / m 2 ), the test was carried out at room temperature of 25±1°C and a humidity of approximately 50%. During the evaporation process, the electronic balance data was recorded every 10 minutes to obtain the mass loss under light. At the same time, a dark evaporation experiment was carried out, that is, the analytical balance was covered with tin foil. In a completely light-proof environment, the mass loss under dark evaporation was recorded in the same manner. After the evaporation process stabilized, the steady-state evaporation rate V was calculated using the following formula:

[0081]

[0082] Where: M is the net total mass loss (mass loss under light conditions minus mass loss under dark evaporation, kg); A is the area of ​​the evaporation layer hydrogel (m 2 ); T is the total evaporation time (h).

[0083] Figure 1 In the equation, Control is the evaporation rate of the hydrogel evaporator without biochar hybridization; So400-PZH represents the evaporation rate of the hydrogel evaporator prepared by carbonizing sorghum straw at a temperature of 400°C, i.e., Example 4; So600-PZH represents the evaporation rate of the hydrogel evaporator prepared by carbonizing sorghum straw at a temperature of 600°C, i.e., Example 1; So800-PZH represents the evaporation rate of the hydrogel evaporator prepared by carbonizing sorghum straw at a temperature of 600°C, i.e., Example 5; Figure 1 It can be seen that the evaporation rate of the biomass hybrid hydrogel evaporator prepared at 600 °C is the best, so Example 1 is selected as the optimal solution;

[0084] Figure 2 In the equation, Pure Water represents traditional solar evaporation without the aid of an evaporator; Control represents the evaporation rate of a hydrogel evaporator without biochar hybridization; Co600-PZH represents the evaporation rate of a hydrogel evaporator made from coconut shell at a carbonization temperature of 600°C, i.e., Example 2; So600-PZH represents the evaporation rate of a hydrogel evaporator made from sorghum straw at a carbonization temperature of 600°C, i.e., Example 1; Sw600-PZH represents the evaporation rate of a hydrogel evaporator made from sludge at a carbonization temperature of 600°C, i.e., Example 3; Figure 2It can be seen that the evaporation rate of the hydrogel evaporator obtained after carbonization of coconut shell and sorghum straw at 600℃ is better, while the evaporation rate of the hydrogel evaporator obtained after carbonization of sludge at 600℃ is smaller than that of the hydrogel evaporator obtained after carbonization of coconut shell and sorghum straw at 600℃, but it is improved compared with traditional solar evaporation and hydrogel evaporator without biochar hybridization. It can be seen that the evaporation effect of the hydrogel evaporator after biomass hybridization is better.

[0085] Figure 3 The hydrogel evaporator prepared in Example 1 was used for 7 consecutive evaporations, and it was found that the evaporation rate did not change much and was relatively stable;

[0086] 1. Investigate the effect of the preparation method of the hydrogel evaporator on the evaporation performance of the obtained hydrogel evaporator

[0087] Control group 1: Different from Example 1, the polyzwitterionic hydrogel uses commercially available 3-[(3-acrylamidopropyl)dimethylammonium]propionate polymer.

[0088] Control group 2: Different from Example 1, the mass ratio of the solar absorber to deionized water is 1:9.

[0089] Control group 3: Different from Example 16, liquid C was not mixed with tetrahydrazide polydimethylsiloxane.

[0090] Control group 4: Different from Example 16, the tetrahydrazide polydimethylsiloxane was not subjected to foaming treatment.

[0091] Control group 5: Different from Example 16, a commercially available nitric acid solution with a concentration of 90 mg / L was used as the pH regulator.

[0092] Conclusion: Figure 4From the comparison of Examples 1 to 24, it can be seen that the parameter changes during the preparation method of the hydrogel evaporator have little effect on the evaporation performance of the hydrogel evaporator. From the comparison of Examples 1, 8 to 9 and Control Group 1, it can be seen that the polyzwitterionic hydrogel is selected. Although acrylamide-based polymers can form an interpenetrating double network structure to improve mechanical strength, this structure may cause the flexibility of the hydrogel to decrease. The decrease in the flexibility of the hydrogel may reduce its surface area or change its shape, thereby affecting the surface area and efficiency of water evaporation. A larger surface area usually contributes to faster water evaporation, and the decrease in flexibility may limit this advantage of the hydrogel. In addition, the decrease in flexibility may change the surface absorbance of the hydrogel, thereby affecting its absorption and utilization of solar radiation, thereby indirectly affecting the evaporation efficiency; [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide (SBMA) as a zwitterionic monomer can provide physical crosslinking through its strong dipole and the association between molecular chains, thereby enhancing the mechanical properties of the hydrogel. The mechanical reinforcement of the hydrogel helps to reduce rupture during the evaporation process. or deformation, thereby indirectly helping to maintain a higher evaporation efficiency; and the methacryloyl compound can not only improve the mechanical strength of the hydrogel, but also has good water retention, frost resistance, self-healing and transparency, etc. Good water retention can maintain a moist state for a longer time, thereby continuously carrying out the evaporation process; good frost resistance, then it can maintain a liquid or stable structure at low temperatures and continue to evaporate; excellent self-healing property, can quickly restore its structure and function after being slightly damaged, thereby maintaining the stability of evaporation performance, higher transparency can more fully absorb sunlight, thereby improving evaporation efficiency; from the comparison of Example 1 and Control Group 2, it can be seen that a too high proportion of solar absorber will cause the evaporation performance of the hydrogel evaporator to be weakened. Although the solar absorber can improve the hydrogel's ability to absorb sunlight, a too high proportion may cause the absorber to aggregate, forming an area with low photothermal conversion efficiency, thereby reducing the overall evaporation efficiency. A too high proportion of solar absorber will also destroy the network structure of the hydrogel, reduce its water retention capacity, and further cause the hydrogel to lose water too quickly during the evaporation process, thereby reducing its evaporation efficiency and durability;

[0093] From the comparison of Examples 1 to 15 and Examples 16 to 24, it can be seen that the stabilization treatment of liquid C in Examples 16 to 24 significantly improves the evaporation performance of the hydrogel evaporator compared to Example 1. This shows that the stabilization treatment can effectively reduce the adhesion of salt and other pollutants on the evaporation interface, improve the sustainable use of the evaporator, and further improve the evaporation efficiency of the hydrogel evaporator. From an economic perspective, Example 16 is the optimal solution.

[0094] From Example 16 and the comparison between control groups 3 and 4, it can be seen that since tetrahydrazide polydimethylsiloxane can form reversible covalent bonds (such as acylhydrazone bonds) with other components in the hydrogel, this helps to construct a self-repairing system. When the hydrogel evaporator is damaged during use, these reversible covalent bonds can prompt the hydrogel to self-repair, thereby maintaining the stability and durability of its evaporation performance, thereby improving the evaporation rate and evaporation efficiency of the hydrogel evaporator; however, from the comparison between Example 16 and control group 4, it can be seen that the evaporation performance of tetrahydrazide polydimethylsiloxane after foaming treatment is better. The main reason is that the tetrahydrazide polydimethylsiloxane after foaming treatment has a larger specific surface area, which helps to increase the contact area between the hydrogel evaporator and the air, thereby improving the evaporation efficiency. The foam structure can effectively disperse the liquid, making the hydrogel evaporate more evenly. and high efficiency, and because the tetrahydrazide polydimethylsiloxane foam itself has good thermal stability and thermal conductivity, when mixed with the hydrogel precursor solution, these properties can be transferred to the hydrogel, enabling it to remain stable at higher temperatures and transfer heat more efficiently, thereby further promoting water evaporation; and from the comparison of Example 16, Example 23 to Example 24 and Control Group 5, it can be seen that the use of a 90 mg / L hydroxyethylidene diphosphonic acid solution as a pH regulator significantly improves the evaporation performance of the hydrogel evaporator compared to directly using a 90 mg / L nitric acid solution. The main reason is that the anions formed after the dissociation of hydroxyethylidene diphosphonic acid in water can prevent the metal ions in the evaporator from precipitating during the concentration process; and hydroxyethylidene diphosphonic acid can change the kinetic process of crystal growth, making it difficult for crystals to adhere to the evaporator surface.

[0095] In summary, the stabilization treatment of liquid C according to the method provided in this application before gelation has a more prominent effect on the evaporation performance of the hydrogel evaporator. At the same time, the foaming treatment of tetrahydrazide polydimethylsiloxane also has a good improvement effect on the evaporation performance of the hydrogel evaporator.

Claims

1. A preparation method based on biomass hybrid hydrogel evaporator, characterized in that: The following steps are involved: S1. Preparation of solar absorber S1-1. The waste biomass is dried and placed in a porcelain boat, and then transferred to a tube furnace. Under a protective atmosphere, the tube furnace is heated from room temperature to 400-800°C at a rate of 5°C / min and maintained for 1 hour. After cooling to room temperature, the waste biomass is taken out and ground to obtain a biochar material; S1-2. The obtained biochar material is acid-washed with a 3-5% HNO3 solution, maintained for 12-15 hours, and then washed with water 7-9 times until the water flow is neutral. The biochar material is taken out and dried at 30-50°C, and then ball-milled for 10-12 hours until it passes through a 100-200 mesh sieve to obtain a solar energy absorber; wherein the polyzwitterionic hydrogel is [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide, the initiator is ammonium persulfate, and the cross-linking agent is polyethylene glycol diacrylate; S2. Preparation of hydrogel evaporator S2-1. Dissolve the polyzwitterionic hydrogel in deionized water at a mass ratio of 2-4:6-8, and stir until transparent to obtain solution A. S2-2, preparing an initiator at a mass ratio of initiator to solution A of 0.04 to 0.06:10, and then preparing a cross-linker at a volume ratio of cross-linker to solution A of 1:150 to 200, then adding the initiator and cross-linker to solution A obtained in S2-1, mixing, and ultrasonicating for 10 to 20 minutes under the conditions of an ultrasonic temperature of 15°C, an ultrasonic frequency of 40 kHz, and an ultrasonic power of 360 W to obtain a hydrogel precursor solution; S2-3, dispersing the solar absorber obtained in S1-2 in deionized water to obtain solution B; S2-4, adding solution B obtained in S2-3 to the hydrogel precursor solution obtained in S2-2 at a volume ratio of 1:10, mixing, and ultrasonicating for 12-17 min under the conditions of ultrasonic temperature of 15°C, ultrasonic frequency of 40 kHz, and ultrasonic power of 360 W to obtain a mixed solution, and then adding tetramethylethylenediamine at a volume ratio of 40-50 μL:100 mL of the mixed solution, and aerating with nitrogen for 25-35 min to obtain liquid C; S2-5, injection molding liquid C in a sealed state at 85-95° C., reacting for 3.5-4.5 hours to obtain a hydrogel, and then soaking it in deionized water for 20-24 hours to obtain a biomass hybrid hydrogel evaporator; In step S2-5, the liquid C is stabilized before the gelation reaction. The stabilization treatment method comprises: injecting nitrogen gas with a purity of 99.9% to 99.99% into a high-pressure container containing liquid tetrahydrazide polydimethylsiloxane at a volume ratio of 18 to 22:1, adjusting the temperature of the high-pressure container to 85 to 95° C. and the pressure to 5 to 15 MPa, stirring and diffusing the container for 3 to 6 hours until bubbles are generated, then reducing the pressure in the container at a rate of 0.25 to 0.5 MPa / min until the bubbles solidify to obtain tetrahydrazide polydimethylsiloxane foam, ultrasonically immersing the tetrahydrazide polydimethylsiloxane foam in liquid C at a mass ratio of 0.3 to 0.5:1 and mixing for 15 to 30 minutes, finally dropwise adding a pH adjuster until the pH of the solution is 4.5 to 5.5, and mixing to obtain stabilized liquid C; Among them, the nitrogen injection speed is 900~1000Nm 3 / h, the ultrasonic immersion temperature is 25-30°C, the ultrasonic frequency is 10-12kHz, and the ultrasonic power is 160-180W; the pH regulator is a hydroxyethylidene diphosphonic acid solution with a concentration of 80-100 mg / L.

2. The preparation method of a biomass hybrid hydrogel evaporator according to claim 1, characterized in that: In step S1-1, the waste biomass is coconut shell, sorghum straw or sludge.

3. The preparation method of a biomass hybrid hydrogel evaporator according to claim 1, characterized in that: In step S2-3, the mass ratio of the solar absorber to deionized water is 1:

10.

4. The use of a biomass hybrid hydrogel evaporator prepared by the method according to any one of claims 1 to 3, characterized in that: It is used in the purification of salt water resources.

5. The application of a biomass hybrid hydrogel evaporator according to claim 4, characterized in that: The application method is as follows: the biomass hybrid hydrogel evaporator is floated on the water surface through an isolation layer, and evaporation of the solar-driven interface can be carried out under sunlight; the isolation layer is PVA sponge or foam.

6. The application of a biomass hybrid hydrogel evaporator according to claim 4, characterized in that: The isolation layer is wrapped with hydrophilic material.

Images