Hydrogel evaporator with solar-driven water evaporation and thermoelectric power generation performance and preparation method thereof

Abstract

The invention discloses a hydrogel evaporator with solar-driven water evaporation and thermoelectric power generation performance and a preparation method of the hydrogel evaporator, and relates to the technical field of porous material preparation. The preparation method comprises the following steps: preparing a Pickering emulsion from a photothermal conversion material, a hydrogel monomer and nanocellulose or a derivative thereof, and then carrying out free radical polymerization to prepare the hydrogel evaporation material; the hydrogel can efficiently realize dual effects of solar-driven water evaporation and thermoelectric power generation, has remarkable high evaporation rate and stable output voltage, effectively overcomes the bottleneck of symbiosis of fresh water and electric power, and shows huge application potential in the field of evaporation-driven power generation. The method has the remarkable technical advantages that the preparation process is simple and easy to implement, the method is suitable for industrial large-scale production, and the manufacturing cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of porous material preparation, and particularly to a hydrogel evaporator with both solar-driven water evaporation and thermoelectric power generation performance and a preparation method thereof. Background Art

[0002] To alleviate the increasing demand for fresh water, researchers have shown great interest in the combination of seawater desalination technology and evaporation-driven watervoltaic effect. Compared with other materials, hydrogels have a lower evaporation enthalpy and abundant capillary water transport channels, and are widely used in the field of solar water evaporation. In addition, as a material with high water absorption and water retention properties, the unique physical and chemical properties of hydrogels provide new possibilities for watervoltaic power generation.

[0003] However, the performance of hydrogel-based electroosmotic devices (EHD) is affected by various factors, among which the Zeta potential is an important parameter. The Zeta potential is a key index characterizing the surface charge properties of colloidal particles, which directly affects the stability and dispersibility of the colloidal system. In hydrogel-based EHD, changes in the Zeta potential may affect processes such as the charge distribution state inside the hydrogel, the ion migration rate, and the interfacial charge transport, thereby affecting the output voltage of the device.

[0004] Since photothermal conversion materials with different micro-morphologies will endow hydrogels with different micro-surface structures and different surface areas, which in turn affect the distribution state of ion exchange sites in the hydrogel, this will affect the charge separation efficiency and power generation performance of EHD. Therefore, when designing and preparing hydrogel-based EHD, it is necessary to fully consider the influence of different photothermal conversion materials on the internal micro-structure of hydrogels, and higher power generation performance can be achieved by regulating and optimizing the surface structure. Summary of the Invention

[0005] The purpose of the present invention is to provide a hydrogel evaporator with both solar-driven water evaporation and thermoelectric power generation performance and a preparation method thereof to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above purpose, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a preparation method of a hydrogel evaporation material, including the following steps:

[0008] Prepare a Pickering emulsion from a photothermal conversion material, a hydrogel monomer, and nanocellulose or its derivative, and then prepare the hydrogel evaporation material through free radical polymerization.

[0009] Further, the photothermal conversion material includes carbon nanotubes and polypyrrole.

[0010] Further, the nanocellulose includes cellulose nanocrystals or cellulose nanofibers; the nanocellulose derivative includes sodium carboxymethyl cellulose.

[0011] Further, the hydrogel monomer includes acrylamide.

[0012] Further, the preparation method includes the following steps:

[0013] Prepare carbon nanotubes, hydrogel monomers and nanocellulose or its derivatives into Pickering emulsion 1;

[0014] Prepare polypyrrole, hydrogel monomers and nanocellulose or its derivatives into Pickering emulsion 2;

[0015] After that, the Pickering emulsion 1 and the Pickering emulsion 2 are subjected to free radical polymerization to obtain the hydrogel evaporation material.

[0016] Further, the free radical polymerization uses tetramethylethylenediamine as a catalyst.

[0017] In the preparation process of the Pickering emulsion of the present invention, N, N'-methylenebisacrylamide is used as a crosslinking agent and potassium persulfate is used as an initiator.

[0018] The organic solvent used in the preparation process of the Pickering emulsion of the present invention is immiscible with water and includes dichloromethane, 1,2-dichloroethane, chloroform, n-hexane or cyclohexane.

[0019] Further, the mass concentration ratio of carbon nanotubes in the Pickering emulsion 1 to polypyrrole in the Pickering emulsion 2 is 0.25-0.5%: 0.25-0.5%.

[0020] Further, the mass concentration of the nanofiber material and its derivatives in both the Pickering emulsion 1 and the Pickering emulsion 2 is 0.25-1%.

[0021] The second technical solution of the present invention is to provide a hydrogel evaporation material prepared by the above preparation method.

[0022] The third technical solution of the present invention is to provide an application of the above hydrogel evaporation material as an evaporation-driven power generation material.

[0023] The hydrogel evaporation material prepared by the present invention can be used as a hydrogel evaporator in the field of evaporation-driven power generation.

[0024] In the present invention, the synergistic effect of carbon nanotubes and polypyrrole endows the hydrogel with excellent photothermal conversion efficiency, enabling it to rapidly heat up under solar irradiation and promote water evaporation. Meanwhile, using the gel monomer as the matrix ensures the mechanical stability and good water absorption of the material, further enhancing its feasibility and reliability in practical applications. In addition, the unique structural design enables the hydrogel to effectively resist the accumulation of pollutants during long-term use, ensuring the long-term stability of its performance.

[0025] The present invention uses carbon nanotubes and polypyrrole as photothermal conversion materials, polyacrylamide as the gel matrix, and through the Pickering emulsion templating method combined with in-situ radical polymerization technology, successfully prepares a multifunctional hydrogel. The advantage of the Pickering emulsion templating method combined with in-situ radical polymerization technology lies in its unique porous structure and preparation mechanism. The Pickering emulsion stabilizes the oil-water interface through solid particles, forming a highly open porous network, significantly increasing the specific surface area, thereby improving the water evaporation efficiency. At the same time, this porous structure can efficiently absorb solar energy and convert it into heat energy, further enhancing the evaporation effect. Moreover, in terms of thermoelectric power generation, the porous material prepared by this technology has good thermal stability and electrical properties, and can effectively collect waste heat and convert it into electrical energy. Therefore, this hydrogel can not only efficiently achieve solar-driven water evaporation and thermoelectric power generation, but also has excellent seawater desalination ability and anti-pollution performance. Experimental results show that this material has a significant high evaporation rate and a stable output voltage, showing great application potential in the field of evaporation-driven power generation, effectively overcoming the bottleneck of the coexistence of fresh water and electricity.

[0026] There is a unique synergistic effect among the three raw materials used in the present invention: carbon nanotubes have excellent mechanical and electrical properties, polypyrrole is a conductive polymer with good conductivity and electrochemical properties, while polyacrylamide has good water absorption and flexibility. The combination of the three can simultaneously achieve mechanical enhancement, improvement of electrical properties, and optimization of water absorption, and this synergistic effect has not been fully explored in existing research.

[0027] The present invention discloses the following technical effects:

[0028] The present invention uses the Pickering emulsion templating method combined with in-situ radical polymerization to prepare a hydrogel evaporation material with both solar-driven water evaporation and thermoelectric power generation performance. This hydrogel-based evaporation material exhibits superior performance and can meet the actual application requirements in the field of solar evaporation-driven power generation.

[0029] The hydrogel evaporator prepared by the present invention has an extremely high evaporation rate and excellent output voltage, ensuring efficient energy conversion. Moreover, the preparation process is simple and easy to implement, suitable for large-scale industrial production, reducing the manufacturing cost and improving the economic benefits. Brief Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0031] Figure 1 Infrared thermal image photos of pure water and different MFTP-PAM hydrogels irradiated under 1 Sun for 15 min.

[0032] Figure 2 In [the figure], a is the evaporation mass loss diagram of pure water irradiated under 1 Sun for 2 h and the evaporation mass loss diagram of tap water with different MFTP-PAM hydrogels irradiated under 1 Sun for 2 h, b is the evaporation mass loss diagram of 3.5 wt% NaCl solution with different MFTP-PAM hydrogels irradiated under 1 Sun for 2 h, c is the evaporation rate diagram of different MFTP-PAM hydrogels in tap water and 3.5 wt% NaCl solution irradiated under 1 Sun for 2 h; d is the change in color and absorption spectrum of methylene blue solution before and after purification using the M4F2T1P1-PAM hydrogel evaporator.

[0033] Figure 3 In [the figure], a is the test device diagram of different MFPT-PAM hydrogels, b is the Zeta potential of different ratios of CMC / CNT and CNF / PPy aqueous dispersions, c is the output voltage of different MFTP-PAM hydrogels in 3.5 wt% NaCl solution.

[0034] Figure 4 In [the figure], a is the output voltage of different MFPT-PAM hydrogels irradiated under 1 Sun in DI water; b is the output voltage of different MFPT-PAM hydrogels in 3.5 wt% NaCl solution without light irradiation.

[0035] Figure 5 Output voltages of MFT-PAM hydrogel (a) and FTP-PAM hydrogel (b) in 3.5 wt% NaCl solution.

[0036] Figure 6 In [the figure], a is the SEM image of F1P1-PAM hydrogel, b is the SEM image of F2P1-PAM hydrogel.

[0037] Figure 7 Flow chart for preparing MFTP-PAM hydrogel in Embodiment 1 of the present invention. Detailed Embodiments

[0038] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be construed as a limitation on the present invention, but rather as a more detailed description of certain aspects, features, and implementation schemes of the present invention.

[0039] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0040] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0041] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0042] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0043] It should be noted that the aspects not described in detail in the present invention are all conventional operating means in the art and are not the focus of the present invention.

[0044] The chemical reagents and raw materials used in the embodiments of the present invention are all of analytical purity or higher purity.

[0045] Example 1

[0046] (1) Preparation of Polypyrrole (PPy)

[0047] Weigh 0.67 mL of pyrrole monomer and dissolve it in 40 mL of deionized water. Weigh 4.866 g of ferric chloride and dissolve it in 10 mL of deionized water. Both solutions are placed in an ice-water bath and kept at a constant temperature for 1 h. Under the condition of the ice-water bath, the ferric chloride solution is slowly added dropwise to the stirred pyrrole monomer solution, and after the addition is complete, continue for 2 h. The obtained black solution is centrifuged and washed with water multiple times to separate the polypyrrole, which is then dried for standby.

[0048] (2) Preparation of CMC / CNF / CNT emulsion

[0049] Prepare different CMC / CNF / CNT emulsions according to Table 1: First, fix the mass fraction of nanofiber (CNF) at 0.5 wt%, and prepare CMC / CNF aqueous dispersions with the mass ratios of sodium carboxymethyl cellulose (CMC) to CNF being 2:1, 1:1, and 1:2 respectively (i.e., the mass fractions of CMC are 1 wt%, 0.5 wt%, and 0.25 wt% respectively). Add a certain mass of carbon nanotubes (CNT) to the above aqueous dispersions respectively, and configure CMC / CNF / CNT aqueous dispersions with different ratios through ultrasonic treatment and stirring for 3 h.

[0050] Table 1

[0051]

[0052]

[0053] Add 0.16 g of AM (acrylamide), 0.0128 g of MBA (N,N'-methylenebisacrylamide), and 0.008 g of KPS (potassium persulfate) to 1.6 mL of the above different CMC / CNF / CNT aqueous dispersions respectively. After stirring and dissolving evenly, it serves as the aqueous phase. Add 0.4 mL of cyclohexane (CYH) to the above solutions respectively according to the volume ratio of water to oil being 4:1. After ultrasonic treatment and shaking by hand 5 times, Pickering emulsion (CMC / CNF / CNT emulsion) is prepared.

[0054] (3) Preparation of CNF / PPy emulsion

[0055] As shown in Table 2, weigh a certain mass of PPy and prepare CNF / PPy aqueous dispersions with the mass fraction of CNF being 0.5 wt% and the mass fractions of PPy being 0.5 wt% and 0.25 wt% respectively.

[0056] Table 2

[0057]

[0058] To 0.8 mL of the above CNF / PPy aqueous dispersion, 0.08 g of AM, 0.0064 g of MBA, and 0.004 g of KPS were added. After stirring and dissolving evenly, it was used as the aqueous phase. According to the volume ratio of water to oil of 4:1, 0.2 mL of cyclohexane (CYH) was added to the above solution respectively. After ultrasonic treatment and hand shaking 5 times, a Pickering emulsion (CNF / PPy emulsion) was prepared.

[0059] (4) 8 μL of tetramethylethylenediamine was added to the CMC / CNF / CNT emulsion prepared in step (2), and at the same time, 4 μL of tetramethylethylenediamine was added to the CNF / PPy aqueous dispersion prepared in step (3). After the addition was completed, it was shaken vigorously for 15 s. Then, the two emulsions were poured into the mold from both ends respectively. After that, the mold was transferred to a water bath at 35 °C and reacted for 30 min to obtain a polyacrylamide-based polymer hydrogel containing cyclohexane. After that, it was freeze-dried for 48 h and then rehydrated to obtain a lamellar MFTP-PAM hydrogel composed of two gels spliced together.

[0060] Table 3 shows the concentrations of CMC, CNF, CNT in the CMC / CNF / CNT emulsion and the concentration of PPy in the CNF / PPy emulsion used for different MFTP-PAM hydrogels.

[0061] Table 3

[0062]

[0063]

[0064] An infrared thermal imager was used to dynamically monitor the temperature changes of pure water and the composite hydrogel prepared in Example 1 under 1 Sun radiation. The results are shown in Figure 1 .

[0065] From Figure 1It can be seen that after 15 minutes of illumination, due to the high thermal conductivity and light transmittance of pure water, the water temperature at the bottom is close to that at the surface, which are 27.8 °C and 26.2 °C respectively. When the evaporation stabilizes, the surface temperature of the self-floating MFTP-PAM hydrogel reaches a maximum of 39.6 °C and a minimum of 34.2 °C, and the temperature difference between the bottom and the top is about 7 - 8 °C. As can be seen from the figure, the top temperature slowly transfers to the bottom water body, forming a certain temperature difference, which avoids a large amount of heat loss caused by directly heating the water body. Except for M2F1T1P1-PAM and M4F2T1P1-PAM hydrogels, the surface temperature of the remaining hydrogels gradually increases with the increase of CNT or PPy content. This may be because the excessive CMC content in M2F1T1P1-PAM and M4F2T1P1-PAM hydrogels results in smaller pore sizes in the hydrogel structure, causing a higher diffuse reflectance on the hydrogel surface, thereby reducing the photothermal conversion efficiency. All in all, the MFTP-PAM hydrogel has excellent photothermal conversion ability, which will help improve the steam generation efficiency.

[0066] The water evaporation performance of the MFTP-PAM hydrogel was tested by simulating a solar lamp. The MFTP-PAM hydrogel was cut into appropriate sizes, fixed on a floating support material, and placed in a container filled with tap water or simulated seawater (3.5 wt% NaCl solution). The container was placed on an analytical balance to record the initial mass. The simulated solar lamp was turned on, and the light intensity was set to 1 kW / m 2 , and the mass change was recorded every 5 minutes. The water evaporation rate was calculated based on the mass change, the evaporation curve was plotted, and the photothermal conversion and evaporation performance of the hydrogel were analyzed. The results are as Figure 2 shown.

[0067] Figure 2 In it, a is the evaporation mass loss diagram of pure water irradiated under 1 Sun for 2 h and the evaporation mass loss diagram of tap water with different MFTP-PAM hydrogels irradiated under 1 Sun for 2 h, b is the evaporation mass loss diagram of 3.5 wt% NaCl solution with different MFTP-PAM hydrogels irradiated under 1 Sun for 2 h, and c is the evaporation rate diagram of different MFTP-PAM hydrogels in tap water and 3.5 wt% NaCl solution irradiated under 1 Sun for 2 h. It can be seen that the evaporation mass loss of all the composite hydrogels prepared in the experimental examples is significantly higher than that of tap water. According to Figure 2 a and Figure 2 b, the average evaporation rates for tap water were further calculated to be 1.45, 1.53, 1.41, 1.43, 1.44, 1.23 kg m -2 h -1, the average evaporation rates of the simulated seawater are 0.98, 0.95, 0.94, 0.96, 1.01, 1.02 kg m -2 h -1 , as Figure 2 shown in c. Among them, the tap water evaporation rate of the M4F2T1P1-PAM hydrogel is the highest (1.53 kg m -2 h -1 ), and the simulated seawater evaporation rate of the M1F2T1P1-PAM hydrogel is the highest (1.02 kg m -2 h -1 ). This may be because when evaporating tap water, the higher concentration of CMC helps to reduce the evaporation enthalpy of the hydrogel, while when the evaporation object is a high-concentration NaCl solution, the capillary channels inside the hydrogel with less CMC dosage are richer, which helps the transportation of high-concentration liquids.

[0068] In addition, to prove the water purification performance of the MFTP-PAM hydrogel evaporator, the M4F2T1P1-PAM hydrogel was directly put into the methylene blue waste liquid and treated for 5 hours. Then, the water obtained by purifying the waste liquid with the hydrogel was detected by an ultraviolet-visible spectrophotometer. The absorption peak belonging to methylene blue disappeared in the obtained absorption spectrum ( Figure 2 d), indicating that the hydrogel evaporator has water purification performance.

[0069] The electricity generated by evaporation drive within 30 min under 1 Sun light intensity of different MFTP-PAM hydrogels prepared in the examples was measured using an electrochemical workstation. The test results are as Figure 3 shown.

[0070] During the test, the MFPT-PAM hydrogel was placed on a glass slide, and a copper sheet was connected to the terminal clip to assemble an EHD, and its output voltage was measured. The test device diagram is as Figure 3 shown in a.

[0071] Figure 3 b shows the Zeta potentials of CMC / CNF / CNT aqueous dispersions and CNF / PPy aqueous dispersions with different ratios. It can be seen from the figure that as the dosage of CMC decreases, the absolute value of the Zeta potential of the CMC / CNT aqueous dispersion gradually decreases from 67.4 mV to 45 mV, while the output voltage value of the MFTP-PAM hydrogel does not conform to the change law of the absolute value of the Zeta potential. From Figure 3c It can be seen that when CMC is 1wt%, the output voltages of M2F1T1P1-PAM and M4F2T1P1-PAM hydrogels reach 450mV and 430mV respectively, while when the CMC mass fraction is 0.5wt%, the output voltage of M2F2T1P1-PAM hydrogel is the highest, reaching 470mV. When the amount of CMC is further reduced to 0.25wt%, the output voltage of the hydrogel decreases significantly, still at 332mV. This can be explained by the fact that when the amount of CMC is too much, although the absolute value of Zeta potential increases, the influence of Zeta potential on the output voltage of the hydrogel has reached the highest level at this time, and the charge density in the solution has reached saturation, which has a certain inhibition on the movement of ions in the nanochannel. Therefore, increasing the amount of CMC leads to a lower output voltage.

[0072] The present invention further measured the output voltage of the MFTP-PAM hydrogel in 3.5wt% NaCl solution under DI water and no light conditions, and the results showed that the output voltage was lower than the output voltage in 3.5wt% NaCl solution under light conditions. Figure 4 It can be seen from a that when the CNT dosage is fixed at 0.5wt%, the output voltage value of MFTP-PAM hydrogel increases with the increase of CMC dosage, while when the CNT dosage is fixed at 0.25wt%, the output voltage value of MFTP-PAM hydrogel decreases with the increase of CMC dosage (M2F1T1P1-PAM>M1F1T1P1-PAM>M1F2T2P2-PAM). Since the evaporation object is DI water (deionized water), at this time, CMC, as a polyelectrolyte, its own carboxyl group helps to ionize the protons in the water. When the dosage is too high, the pore structure in the hydrogel is dense and compact. At this time, the MFTP-PAM hydrogel with a higher CMC dosage has a higher CMC distribution in its pore structure, so the output voltage generated is also higher. In addition, when the CNT dosage is too high, although a conductive network is formed, it is not conducive to ion transmission. Excessive CMC dosage may also lead to ion migration obstruction. When the content of both CNT and CMC is low, ion migration and conductivity reach a balance, so the MF2T1P1-PAM hydrogel obtains the maximum output voltage (245mV) in DI water. As shown in 4b, under no light conditions, the output voltage of the MFTP-PAM hydrogel in 3.5wt% NaCl solution within 30min is stable between 250 and 350mV, which is lower than its output voltage in DI water under 1Sun irradiation for 30min. This shows that the MFTP-PAM hydrogel is suitable for constructing EHD driven power generation for seawater desalination synergistic evaporation.

[0073] For comparative experiments, the PPy in the above-mentioned MFTP-PAM hydrogel was replaced with CNT in equal amounts, and then a hydrogel without PPy (MFT-PAM hydrogel, correspondingly labeled as M2F1T1P0-PAM, M4F2T1P0-PAM, M1F1T1P0-PAM, M2F2T1P0-PAM, M1F2T2P0-PAM, M1F2T1P0-PAM) was prepared; and the CMC in M4F2T1P1-PAM and M1F1T1P1-PAM was omitted to prepare a hydrogel without CMC (FTP-PAM hydrogel, labeled as M0F2T1P1-PAM and M0F1T1P1-PAM respectively), and the output voltages of the two hydrogels in 3.5 wt% NaCl solution under 1 Sun light illumination conditions were tested respectively. The results showed that the output voltages of MFT-PAM hydrogel and FTP-PAM hydrogel were both lower than those of MFTP-PAM hydrogel under the same conditions.

[0074] Figure 5 Output voltages of MFT-PAM hydrogel (a) and FTP-PAM hydrogel (b) in 3.5 wt% NaCl solution.

[0075] As Figure 5 can be seen from a, the output voltage values of all hydrogels without PPy were relatively low, not exceeding 135 mV at most. After losing the asymmetric microstructure constructed by PPy, the internal microstructure of the hydrogel containing only CNT was relatively rough, with a larger surface area, thus providing more charge distribution sites, resulting in a higher charge density inside the MFT-PAM hydrogel.

[0076] The CMC and CNT in M2F1T1P1-PAM and M4F2T1P1-PAM were omitted to prepare F1P1-PAM hydrogel and F2P1-PAM hydrogel. From the SEM photos of F1P1-PAM hydrogel and F2P1-PAM hydrogel ( Figure 6 a and Figure 6 b), it can be seen that regularly shaped dot-like PPy particles were distributed on the micro surface of the FP-PAM hydrogel, and the pore walls were relatively smooth, providing fewer charge distribution sites. The charge density inside the hydrogel was lower than that of the MFP-PAM hydrogel, and the charge density difference caused by the Zeta potential difference resulted in a larger potential difference at both ends of the MFTP-PAM hydrogel, thus generating a higher output voltage. In addition, due to the larger number of charge distribution sites inside the MFT-PAM hydrogel, there would be more charge transport paths, which helped to improve the charge transport efficiency. While the number of charge distribution sites in the FP-PAM hydrogel was less, and the resulting difference in charge transport efficiency between the two would also cause more charges to accumulate in the MFT-PAM hydrogel, thereby generating a larger potential difference. And inFigure 5 In Figure b, the output voltage values of all hydrogels without CMC do not exceed 110 mV, verifying that the Zeta potential difference provided by CMC and the carboxylic acid groups contribute to increasing the charge density of the EDL in the ion channels of the hydrogel and improving the output voltage in hydrovoltaic power generation.

[0077] Figure 7 This is the flow chart for preparing the MFTP-PAM hydrogel in Example 1 of the present invention.

[0078] Currently, the pore structure of the hydrogel evaporator prepared by the traditional free radical polymerization method is not uniform enough, which may lead to poor mechanical properties of the material, being fragile and prone to powdering. The evaporation rate is about 1.4 kg m -2 h -1 , the light absorption rate is generally about 70%-80%, and it is prone to approaching blockage in a high salinity environment, affecting the evaporation effect. The evaporation rate of the existing self-healing hydrogel evaporator is about 1.78 kg m -2 h -1 , the light absorption rate is about 77.5%-80.75%, and the light absorption efficiency in the full spectrum range is relatively low. Moreover, in high salinity (20%) salt water, the evaporation rate of the self-healing hydrogel evaporator will decrease significantly, and after continuous operation for 10 days, the evaporation rate gradually decreases, and the structural stability is poor. The hydrogel evaporator prepared by the emulsion template method + free radical polymerization method of the present invention exhibits remarkable salt tolerance and thermal management ability in a high salt environment, and at the same time has excellent mechanical properties. For example, the M1F2T1-PAM hydrogel obtains the maximum compressive stress (115.36 KPa), which is suitable for long-term use in complex environments.

[0079] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a hydrogel evaporation material, characterized in that: The following steps are involved: The photothermal conversion material, the hydrogel monomer and the nanocellulose or its derivatives are prepared into a Pickering emulsion, and then free radical polymerization is performed to prepare the hydrogel evaporation material.

2. The preparation method according to claim 1, characterized in that: The photothermal conversion material includes carbon nanotubes and polypyrrole.

3. The preparation method according to claim 1, characterized in that: The nanocellulose includes cellulose nanocrystals or cellulose nanofibers; the nanocellulose derivative includes sodium carboxymethyl cellulose.

4. The preparation method according to claim 1, characterized in that: The hydrogel monomer includes acrylic amine.

5. The preparation method according to claim 2, characterized in that: The following steps are involved: The carbon nanotubes, the hydrogel monomer and the nanocellulose or its derivatives are prepared into a Pickering emulsion 1; Prepare Pickering emulsion 2 by using polypyrrole, hydrogel monomer and nanocellulose or its derivatives; Then, the Pickering emulsion 1 and the Pickering emulsion 2 are subjected to free radical polymerization to prepare the hydrogel evaporation material.

6. The preparation method according to claim 5, characterized in that: The free radical polymerization uses tetramethylethylenediamine as a catalyst.

7. The hydrogel evaporation material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the hydrogel evaporative material as claimed in claim 7 as an evaporation driven power generation material.

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