Preparation method of integrated double-channel PCNFs / ZIF8-SA composite aerogel, product and application thereof

Abstract

The application provides a preparation method of integrated double-channel PCNFs / ZIF8-SA composite aerogel, a product and application thereof, and steps are as follows: step 1, sodium alginate (SA) and ZIF-8 are added into PCNFs suspension, and SA is fully dissolved by stirring until a uniform mixed solution is formed; the PCNFs are PAN / ZIF-8 / lignin / NaCl carbon nanofibers after hydrophilic modification; step 2, the mixed solution is poured into a mold, and directional freezing is carried out in a freeze dryer to obtain a composite aerogel columnar structure with a directional channel structure; step 3, the upper layer of the composite aerogel columnar structure is subjected to hydrophobic modification to form a hydrophobic layer with a certain thickness, and the lower layer is a hydrophilic layer, and the hydrophobic layer and the hydrophilic layer are integrated. The aerogel has a double-channel integrated special structure of fresh water channel and salt extraction channel, can extract accumulated salt from the side channel while realizing efficient solar seawater desalination, avoids the evaporation channel from being blocked, and greatly improves the evaporation efficiency and the stability of the composite aerogel.

Description

Technical field

[0001] The present invention relates to the technical field of composite aerogel materials, and in particular to a preparation method of an integrated, dual-pathway PCNFs / ZIF8-SA composite aerogel, and its products and applications. [Background Technology]

[0002] Traditional desalination technologies such as multi-stage flash evaporation, multi-effect distillation, and membrane technology have problems such as high energy consumption and environmental pollution. Solar-driven interfacial evaporation technology only uses sunlight and seawater to produce fresh water, and is a green and clean desalination technology. To date, various types of solar evaporators have been developed, such as evaporators based on hydrogels, membranes, plasmas and other materials. However, in actual use, these materials have many problems such as easy salt formation and clogging of evaporation channels, low reusability, and unstable evaporation efficiency. When desalination operations are carried out on the sea surface, the evaporator is easily blown over by strong sea breezes and stops working. In addition, these evaporators need to be connected to cotton cores for continuous water supply and require insulation materials for support. They have many components and need to be assembled, which is not conducive to industrial application.

[0003] Salt crystallization during the evaporation process is a major factor affecting the efficiency of solar desalination. Salt precipitation on the evaporator surface impairs light absorption and blocks water channels, thereby reducing evaporation efficiency. Current salt tolerance strategies primarily involve recirculating salt ions back into the water column. This not only increases salt concentration in the seawater, hindering the survival of marine life, but also neglects the processing and utilization of salt.

[0004] Sodium alginate (SA) is widely available, inexpensive, has excellent biodegradability and biocompatibility, and is rich in hydrophilic groups, making it an ideal material for preparing aerogels. In previous studies by the inventors, it was concluded that SA-based aerogels and membrane materials have excellent salt resistance and underwater oil pollution resistance (patent numbers: CN108905296B, CN106853296A). In order to improve the efficiency of solar desalination and its performance in actual seawater, the inventors' research group used SA as a substrate and prepared an integrated, salt-side-collecting, wind-resistant, dual-path composite aerogel CNFs / ZIF8-SA for solar desalination through directional freezing technology and surface wettability regulation. [Summary of the invention]

[0005] The technical problem to be solved by the present application is to provide a preparation method of integrated double-channel PCNFs / ZIF8-SA composite aerogel, a product thereof and an application thereof, so as to provide the double-channel integrated special structure of the composite aerogel, realize efficient solar seawater desalination, and accumulate salt from the side channel to avoid the blockage of the evaporation channel, thereby improving the evaporation efficiency and the stability of the composite aerogel.

[0006] The present application is implemented as follows:

[0007] The present application is implemented as follows:

[0008] In step 1, sodium alginate SA and ZIF-8 are added to a PCNFs suspension, and stirring is performed until the SA is fully dissolved, so as to form a uniform mixed solution; the PCNFs are hydrophilically modified PAN / ZIF-8 / lignin / NaCl carbon nanofibers; the mass ratio of the sodium alginate SA, ZIF-8 and PCNFs is 1.5:0.3:0.5-4:1:3.

[0009] In step 2, the mixed solution is poured into a mold, and directional freezing is performed in a freeze dryer under the condition of-80 DEG C vacuum freezing drying for 48 hours, so as to obtain a composite aerogel columnar structure with a directional channel structure.

[0010] In step 3, the upper layer of the composite aerogel columnar structure is hydrophobically modified to form a hydrophobic layer with a certain thickness, and the lower layer is a hydrophilic layer; the hydrophobic layer and the hydrophilic layer are integrated, and the PCNFs / ZIF8-SA composite aerogel is obtained.

[0011] 2. The preparation method of the integrated double-channel PCNFs / ZIF8-SA composite aerogel according to claim 1, wherein the preparation process of ZIF-8 in step 1 is as follows:

[0012] 1.1. Preparation of ZIF-8: zinc nitrate hexahydrate Zn(NO3)2·6H2O is dissolved in methanol to prepare solution A, and 2-methylimidazole 2-MIM is dissolved in methanol to prepare solution B; then the two solutions A and B are quickly mixed, stirred and centrifuged, and the white precipitate is collected and dried to obtain ZIF-8.

[0013] Further, the preparation process of the PCNFs suspension in step 1 is as follows:

[0014] 1.2. Preparation of PAN / ZIF-8 / lignin / NaCl electrospun nanofiber membrane:

[0015] First, sodium chloride (NaCl) is added to an N,N-dimethylformamide (DMF) solution, ball-milled and allowed to stand. The upper layer of NaCl-containing solution and DMF solution are added to a container, and then ZIF-8 particles are added to the above solution. After ultrasonic treatment, polyacrylonitrile (PAN) is added and stirred for a period of time. Finally, lignin is added and stirred at 100°C to obtain an electrospinning precursor solution. The precursor solution is added to a syringe and electrospun at a propulsion rate of 0.3-0.6 mL / h and 16-22 kV to obtain a PAN / ZIF-8 / lignin / NaCl nanofiber membrane with uniform diameter, which is then dried at 60-80°C for later use.

[0016] 1.3 Preparation of PAN / ZIF-8 / lignin / NaCl electrospun carbon nanofiber membrane:

[0017] The PAN / ZIF-8 / lignin / NaCl nanofiber membrane was placed in a tubular furnace for high-temperature carbonization: first, the temperature was increased to 280°C at a heating rate of 5°C / min under a nitrogen atmosphere and maintained for 2 h. Then, the temperature was increased to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere and maintained for 2 h to obtain a PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane;

[0018] 1.4. Hydrophilic modification of PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane:

[0019] A certain volume of DA Tris-HCl buffer and ethanol were mixed and stirred to obtain a DA water / ethanol mixed solution. Subsequently, a PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane was placed in the mixed solution and floated for 2-6 hours to achieve hydrophilic modification of the composite membrane, thereby obtaining a hydrophilically modified PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane.

[0020] 1.5. Preparation of PAN / ZIF-8 / lignin / NaCl carbon nanofibers:

[0021] The hydrophilically modified PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane was cut into thin slices and homogenized in deionized water at 12000-13000 rpm using a homogenizer to obtain a uniform suspension of PCNFs.

[0022] Further, the preparation method of the composite aerogel columnar structure in step 2 is as follows: SA and ZIF-8 are added to the PCNFs suspension, stirred until the SA is fully dissolved, and a uniform mixture is formed; the mixture is poured into a polytetrafluoroethylene mold placed on a copper block, the copper block and the mold are placed in a Dewar flask, liquid nitrogen is added, and after freezing is completed, the sample is immediately transferred to a freeze dryer, vacuum freeze-dried at -80°C for 48h, and a composite aerogel columnar structure with a directional channel structure is obtained.

[0023] Further, the upper layer of the composite aerogel columnar structure in step 3 is modified as follows: a 2% methyltrimethoxysilane MTMS solution is prepared, and the composite aerogel columnar structure is modified by hydrophobic modification at the interface between the upper layer and the lower layer of the composite aerogel columnar structure, so that a hydrophobic layer with a certain thickness is formed on the upper layer of the composite aerogel columnar structure, and a hydrophilic layer is formed on the lower layer, and the hydrophobic layer and the hydrophilic layer are integrated, thereby obtaining a PCNFs / ZIF8-SA composite aerogel.

[0024] Further, the PCNFs / ZIF8-SA composite aerogel is an asymmetric wetting PCNFs / ZIF8-SA composite aerogel, and the thickness of the hydrophobic layer is less than the thickness of the hydrophilic layer.

[0025] Further, the thickness of the hydrophobic layer: the thickness of the hydrophilic layer = 1:1-1:7.

[0026] Further, the preparation method produces an integrated, double-channel PCNFs / ZIF8-SA composite aerogel.

[0027] Further, the application of the integrated, double-channel PCNFs / ZIF8-SA composite aerogel prepared by the preparation method, the PCNFs / ZIF8-SA composite aerogel is used for solar seawater desalination; the PCNFs / ZIF8-SA composite aerogel has a double-channel, the hydrophobic layer is located on the water surface, the top of the hydrophobic layer and the directional channel are a fresh water channel, and the side of the hydrophobic layer is a salt extraction channel; in the process of seawater desalination, water vaporizes into water vapor from the top of the fresh water channel and escapes, and accumulated salt is precipitated from the side of the salt extraction channel;

[0028] The hydrophilic layer is soaked in seawater to directionally transport seawater to the hydrophobic layer.

[0029] Further, a layer of polyamide nanofiltration membrane is arranged at the bottom of the PCNFs / ZIF8-SA composite aerogel for solar seawater desalination, and the salt extracted from the side is collected; treatment of the aqueous solution of the salt with carbonate can obtain battery-grade Li2CO3 powder, realizing collection of lithium ions in seawater.

[0030] The present application has the following advantages:

[0031] The PCNFs / ZIF8-SA composite aerogel has a multistage pore structure. The composite aerogel has parallel directional channels of about 30-50 microns by directional freezing, and the directional channels are penetrated by PAN / ZIF-8 / lignin / NaCl carbon nanofiber filaments of about 200 nm. The nanofiber filaments have mesopore and micropore structures formed by ZIF-8 and lignin pyrolysis. In addition, the PCNFs / ZIF8-SA composite aerogel is inlaid with porous material ZIF-8 with a diameter of about 50 nm. Due to the capillary effect, the parallel channels can continuously transport water from the bottom to the upper layer. The introduction of carbon nanofiber filaments and ZIF-8 increases the specific surface area and porosity of the PCNFs / ZIF8-SA composite aerogel. The micropores and mesopores in the composite aerogel can reduce the interaction between water molecules, thereby reducing the evaporation enthalpy and greatly improving the interfacial evaporation rate.

[0032] In addition, the present application can prepare an asymmetric wetting structure by adjusting the wettability and water entry height of the hydrophobic layer and the hydrophilic layer, so as to ensure that the aerogel can float on the sea surface without sinking, so that the PCNFs / ZIF8-SA composite aerogel has the characteristics of wind resistance. In addition, the special structure design of the double channel (fresh water channel and salt extraction channel) can realize efficient solar seawater desalination, extract accumulated salt from the side channel, avoid blocking the evaporation channel, improve the evaporation efficiency and the stability of the composite aerogel, and at the same time, the composite aerogel can also be applied to lithium extraction from salt lakes, and help to reserve resources. BRIEF DESCRIPTION OF DRAWINGS

[0033] The present application will be further described below with reference to the accompanying drawings and examples.

[0034] Figure 1 SEM image of PCNFs in Example 1 of the present application.

[0035] Figure 2 Preparation flow chart of PCNFs / ZIF8-SA composite aerogel of the present application.

[0036] Figure 3Schematic diagram of the PCNFs / ZIF8-SA composite aerogel structure of the present invention.

[0037] Figure 4 Schematic diagram of the wettability analysis of the PCNFs / ZIF8-SA composite aerogel of the present invention.

[0038] Figure 5 This is the UV-visible-near-infrared absorption spectrum of the PCNFs / ZIF8-SA composite aerogel of the present invention.

[0039] Figure 6 This is a graph showing the evaporation rate of the PCNFs / ZIF8-SA composite aerogel of the present invention in 10 wt% salt water under 1 sunlight intensity.

[0040] Figure 7 Schematic diagram of the interface evaporation of PCNFs / ZIF8-SA composite aerogel of the present invention.

[0041] Figure 8 This is a diagram showing the salt formation of the PCNFs / ZIF8-SA composite aerogel of the present invention before and after evaporation under different sunlight intensities and different salt concentrations.

[0042] Figure 9 Schematic diagram of the cyclic stability test of the PCNFs / ZIF8-SA composite aerogel of the present invention under 1 sunlight intensity and 20% salt water. [Specific implementation method]

[0043] The following will be combined with the Figure 1-9 The technical solutions of the present invention are clearly and completely described in the following and in detail. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention. If specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0044] 1. Product Preparation

[0045] Example 1:

[0046] This embodiment first provides a PAN / ZIF-8 / lignin / NaCl porous carbon nanofiber, the preparation method of which includes the following steps:

[0047] 1. Preparation of ZIF-8

[0048] Solution A was prepared by dissolving 4.461 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) in methanol, and solution B was prepared by dissolving 9.852 g of 2-methylimidazole (2-MIM) in methanol. Solutions A and B were quickly mixed, stirred, and centrifuged. The white precipitate was collected and dried to obtain ZIF-8.

[0049] 2. Preparation of PAN / ZIF-8 / lignin / NaCl electrospinning nanofiber membrane

[0050] NaCl was first added to a DMF solution, ball-milled, and allowed to stand. 0.5 mL of the upper NaCl solution and 5.5 mL of DMF solution were then added to a beaker. 0.6 g of ZIF-8 particles were then added to the solution. After ultrasonic treatment for 60 minutes, 0.35 g of PAN was added and stirred for 24 hours. Finally, 0.35 g of lignin was added and stirred at 100°C for 1 hour to prepare the electrospinning precursor solution. The precursor solution was added to a syringe and electrospun at a propulsion rate of 0.6 mL / h and 22 kV to obtain a PAN / ZIF-8 / lignin / NaCl nanofiber membrane with uniform diameter. The membrane was then dried at 80°C for later use.

[0051] 3. Preparation of PAN / ZIF-8 / lignin / NaCl electrospun carbon nanofiber membrane

[0052] The PAN / ZIF-8 / lignin / NaCl nanofiber membrane was placed in a crucible and carbonized in a tube furnace. First, the temperature was raised to 280°C at a rate of 5°C / min under a nitrogen atmosphere and held for 2 hours. Then, the temperature was raised to 900°C at a rate of 5°C / min under a nitrogen atmosphere and held for 2 hours, resulting in a PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane.

[0053] 4. Hydrophilic modification of PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane

[0054] A certain volume of DA Tris-HCl buffer and ethanol was added to a beaker and magnetically stirred for 5 minutes to obtain a DA water / ethanol mixed solution. Subsequently, a PAN / ZIF-8 / lignin / NaCl composite membrane was placed in this mixed solution and floated for 4 hours to achieve hydrophilic modification of the composite membrane.

[0055] 5. Preparation of PAN / ZIF-8 / lignin / NaCl carbon nanofibers

[0056] 0.5 g of the hydrophilically modified PAN / ZIF-8 / lignin / NaCl nanofiber membrane was cut into thin slices and homogenized in deionized water at 13,000 rpm for 30 min to obtain a uniform solution, which is a suspension of PCNFs. The scanning electron microscope image of the above PCNFs suspension is shown in Figure 2. Figure 1 As shown, from Figure 1 It can be seen that after the carbonization of nanofibrils, ZIF-8 and lignin are pyrolyzed to form mesoporous and microporous structures.

[0057] Example 2:

[0058] The differences from Example 1 are: in step 2, the propulsion rate is 0.5 mL / h, the voltage is 19 kV, the amount of DMF solution is 4 mL, and the amount of ZIF-8 is 0.4 g; in step 5, the amount of PAN / ZIF-8 / lignin / NaCl nanofiber membrane is 1 g, and the homogenizer speed is 12000 rpm. The other operations and amounts are exactly the same as in Example 1.

[0059] Example 3:

[0060] The differences from Example 1 are: in step 2, the propulsion rate is 0.3 mL / h, the voltage is 16 kV, the amount of DMF solution is 5 mL, and the amount of ZIF-8 is 0.5 g; in step 5, the amount of PAN / ZIF-8 / lignin / NaCl nanofiber membrane is 1.5 g, and the homogenizer speed is 12500 rpm. The other operations and amounts are exactly the same as in Example 1.

[0061] Example 4:

[0062] PCNFs / ZIF8-SA composite aerogel was prepared using the raw materials prepared in Example 1, and the preparation method thereof comprised the following steps:

[0063] 1.5g SA and 0.3g ZIF-8 were added to the PCNFs suspension and stirred until SA was fully dissolved and a uniform mixture was formed. The mixture was poured into a polytetrafluoroethylene mold on a copper block, and the copper block and the mold were placed in a Dewar flask. Liquid nitrogen was added and the sample was immediately transferred to a freeze dryer after freezing. It was vacuum freeze-dried at -80°C for 48 hours to obtain an aerogel with a directional channel structure. Then, a 2% mass fraction of MTMS solution was prepared to regulate the wettability of the aerogel: the filter paper was moistened with the hydrolyzed MTMS solution, and then the filter paper was covered on the upper surface of the aerogel for 3s to obtain a PCNFs / ZIF8-SA composite aerogel with asymmetric wettability. The specific preparation process is as follows: Figure 2 The structure of the prepared PCNFs / ZIF8-SA composite aerogel is shown in Figure 3As shown, the present invention performs hydrophobic modification on the upper layer of the composite aerogel columnar structure to form a hydrophobic layer 1 with a certain thickness, and the lower layer is a hydrophilic layer 2, and the PCNFs / ZIF8-SA composite aerogel is subjected to directional freezing to obtain penetrating directional channels 3.

[0064] Example 5:

[0065] The difference from Example 4 is that the amount of SA is 1 g, and the other operations and amounts are exactly the same as those in Example 4.

[0066] Example 6:

[0067] The difference from Example 4 is that the amount of SA is 2 g, and the other operations and amounts are exactly the same as those in Example 4.

[0068] Example 7:

[0069] The difference from Example 4 is that the filter paper is in contact with the aerogel surface for 10 seconds, and the other operations and amounts are exactly the same as in Example 4.

[0070] Example 8:

[0071] The difference from Example 4 is that the time the filter paper contacts the aerogel surface is 15 seconds, and the other operations and dosages are exactly the same as those in Example 12.

[0072] Example 9:

[0073] The difference from Example 4 is that the filter paper is in contact with the aerogel surface for 20 seconds, and the other operations and amounts are exactly the same as in Example 4.

[0074] The thickness of the hydrophobic layer and the hydrophilic layer of the PCNFs / ZIF8-SA composite aerogel prepared in the above example are shown in Table 1 below:

[0075] Table 1 Thickness and ratio of hydrophobic layer and hydrophilic layer in the embodiment

[0076] serial number Hydrophobic layer thickness (cm) Hydrophilic layer thickness (cm) Hydrophobic layer: hydrophilic layer Example 4 0.5 3.5 1:7 Example 7 2 2 1:1 Example 8 3 1 3:1 Example 9 4 0 1:0

[0077] As can be seen from Table 1, the thickness of the hydrophobic layer after hydrophobic modification can be controlled by controlling the contact time between the MTMS solution wetting filter paper and the aerogel surface.

[0078] 2. Performance measurement:

[0079] 1. The wettability analysis of the PCNFs / ZIF8-SA composite aerogel prepared in Example 4 was carried out. The specific process is as follows: Figure 4 As shown in Figure 1, a is the asymmetric wettability diagram of PCNFs / ZIF8-SA composite aerogel; b is the water contact angle diagram of the upper surface hydrophobic layer and the underlying hydrophilic layer of PCNFs / ZIF8-SA composite aerogel.

[0080] from Figure 4 As shown in the figure, the contact angle of the hydrophobic layer is 138.21°, indicating that the prepared composite aerogel has good hydrophobicity. The hydrophilic layer of the composite aerogel rapidly absorbs water within 70 ms, indicating that the hydrophilic layer of the PCNFs / ZIF8-SA composite aerogel has good hydrophilicity. During evaporation, the composite aerogel can quickly replenish water from the water below, preventing the amount of water evaporated per unit time from exceeding the amount of water replenished, which would reduce the evaporation rate.

[0081] 2. The light absorption capacity of PCNFs / ZIF8-SA composite aerogel was tested using UV-visible spectrophotometer. Figure 5 As shown. Figure 5 It can be seen that within the wavelength range of 250-2500 nm, the light absorption rate of the photothermal layer of the PCNFs / ZIF8-SA composite aerogel of the present invention can reach 93%, which indicates that the PCNFs / ZIF8-SA composite aerogel has excellent light absorption performance.

[0082] 3. A commercial polyamide nanofiltration membrane was added to the bottom of the PCNFs / ZIF8-SA composite aerogel prepared in Example 4 to conduct a solar desalination experiment. Figure 6 As shown. Figure 6 It can be seen that under 1 sun intensity and 10 wt% salt water, the evaporation rate of PCNFs / ZIF8-SA composite aerogel is maintained at 2.297 kg m -2 h -1 ~2.36kg m - 2 h -1 Since the particle size of divalent ions is much larger than that of monovalent ions, the use of polyamide nanofiltration membrane can make Na + 、Li + , K + ions pass through, while Mg in seawater 2+ , Ca 2+ Ions are intercepted by the nanofiltration membrane in the water body. During the interface evaporation process, Na + 、Li + , K + As water molecules enter the PCNFs / ZIF8-SA composite aerogel from bottom to top, water evaporates at the top of the composite aerogel due to heat, and the accumulated salt precipitates from the side of the hydrophobic layer, such as Figure 7 As shown, Figure 7(a) shows the macroscopic surface of the PCNFs / ZIF8-SA composite aerogel before interfacial evaporation; (b) shows salt crystals extracted from the side channels of the PCNFs / ZIF8-SA composite aerogel after interfacial evaporation. The salts extracted from the side channels are collected, and the resulting salt crystals are NaCl, LiCl, and KCl. Treating their aqueous solutions with carbonates can produce battery-grade Li2CO3 powder, contributing to the conservation of lithium resources.

[0083] 4. The PCNFs / ZIF8-SA composite aerogel prepared in Example 5 was placed in 3.5 wt% salt water under 1 sun intensity for seawater desalination experiment. After evaporation for 12 h, the evaporation rate was calculated to be 3.462 kg m -2 h -1 The reason why PCNFs / ZIF8-SA composite aerogel can achieve a high freshwater vaporization rate is that during the evaporation process, the accumulated salt crystallizes on the side of the hydrophobic layer and does not block the freshwater evaporation channel.

[0084] 5. In the application of seawater desalination and simulated high-concentration salt water evaporation, the PCNFs / ZIF8-SA composite aerogel of the present invention has a high evaporation rate, see Figure 8 As shown in the figure, a is the initial state of PCNFs / ZIF8-SA composite aerogel. Under 1 sun intensity and 3.5wt% salt water, PCNFs / ZIF8-SA composite aerogel has no obvious salt crystallization after the 30min evaporation experiment (as shown in the figure). Figure 8 b); Under 6 sun intensity, in 20wt% salt water, after 30min evaporation experiment, only part of the salt crystallized on the side of PCNFs / ZIF8-SA composite aerogel, and did not affect the light absorption of the aerogel surface (as shown in Fig. Figure 8 c). In addition, the stable evaporation rate of PCNFs / ZIF8-SA composite aerogel in 20 wt% salt solution under 1 sun intensity is 2.293 kg m -2 h -1 , which is higher than the evaporation rate of some evaporators reported so far in 3.5wt% salt solution under 1 sun intensity.

[0085] 5. The PCNFs / ZIF8-SA composite aerogel of the present invention has good cyclic stability. The PCNFs / ZIF8-SA composite aerogel was placed in a 20 wt% salt solution under 1 sun intensity for cyclic testing. The results are as follows: Figure 9 As shown. Figure 9 It can be seen that the composite aerogel of the present invention can run stably for 20 cycles, and the evaporation rate is 1.975 kg m -2 h -1 -2kg m -2 h -1, the evaporation rate is almost constant, which indicates that the PCNFs / ZIF8-SA composite aerogel has good stability.

[0086] 6. Wind and reverse resistance: When tested for wind and reverse resistance in simulated sea winds, the fan's maximum wind force reached the equivalent of a natural force 3 wind. At this point, the PCNFs / ZIF8-SA composite aerogel prepared in Example 4 stably floated on the water. In the absence of storms or unusual weather conditions, wind forces on the sea surface typically range from force 1 to force 3. Therefore, the PCNFs / ZIF8-SA composite aerogel of the present invention was able to float on the sea surface without capsizing, demonstrating a certain degree of wind and reverse resistance.

[0087] In summary, the present invention has the following advantages:

[0088] 1. The present invention uses SA as the aerogel substrate, which is low-priced, has excellent biodegradability and biocompatibility, and does not damage the environment. SA has abundant hydrophilic groups, which can quickly transport water and ensure a stable water supply during the evaporation process. SA has good salt tolerance and good underwater oil pollution resistance, so that the composite aerogel can remain clean in real seawater without affecting evaporation efficiency.

[0089] 2. The present invention introduces carbonized, modified and homogenized PAN / ZIF-8 / lignin / NaCl carbon nanofibers (PCNFs) in the aerogel preparation process to strengthen the multi-level pore structure for nano-confinement ( Figure 1 After carbonization of the nanofibrils, ZIF-8 and lignin are pyrolyzed to form mesoporous and microporous structures, providing a high specific surface area and porosity. The micropores and mesopores can reduce the interaction between water molecules, thereby reducing the evaporation enthalpy and increasing the interfacial evaporation rate.

[0090] 3. The directional channels 3 of the PCNFs / ZIF8-SA composite aerogel prepared by the directional freeze-drying technology of the present invention are 30-50 μm in size and have a good capillary effect. They can continuously transport water from the bottom to the upper layer, ensuring an adequate water supply during the evaporation process. At the same time, ZIF-8 with an average diameter of about 50 nm is embedded in the PCNFs / ZIF8-SA composite aerogel, which plays a nano-confinement role on water molecules, effectively reduces the evaporation enthalpy, and saves energy. Since ZIF-8 is a porous material with a high specific surface area, its penetration into the PCNFs / ZIF8-SA composite aerogel can promote the transmission of water vapor, reduce the resistance of water vapor during the transmission process, and thus increase the evaporation rate.

[0091] 4. The PCNFs / ZIF8-SA composite aerogel of the present invention has a hydrophobic upper layer 1 and a hydrophilic lower layer 5. During evaporation, the composite aerogel can quickly replenish water from the water below through the hydrophilic layer 2, preventing the amount of water evaporated per unit time from exceeding the amount of water replenished, which would reduce the evaporation rate.

[0092] 5. Most of the existing evaporators are composed of a photothermal layer, a water transport layer, a support layer, an insulation layer and a water transport cotton core. There are many parts and they cannot achieve self-floating and wind-resistant reversal functions on the sea surface. The PCNFs / ZIF8-SA composite aerogel of the present invention is integrated, and the hydrophobic layer 1 (which also has a photothermal effect) and the hydrophilic layer 2 (which plays a water transport role) are a whole. The traditional hydrophobic modification method is to immerse the aerogel directly in the solution. Due to the high siphon rate of the aerogel, it quickly absorbs the solution and it is difficult to control the thickness of the hydrophobic layer. The present invention uses MTMS solution to wet the filter paper, and then covers the filter paper on the upper surface of the aerogel for modification, which can reduce the siphon rate of the aerogel and regulate to obtain aerogels with different hydrophobic layer thicknesses. In addition, the PCNFs / ZIF8-SA composite aerogel is light in weight, 11 cm 3 The composite aerogel weighs 0.5g and can be supported by a dandelion. Its thin hydrophobic layer (1) and thick hydrophilic layer (2) structure enable it to float on the sea surface and resist wind reversal. During evaporation, only the hydrophobic layer floats on the water surface, while the hydrophilic layer is submerged and weighs a certain amount, making it less likely to capsize. Therefore, the PCNFs / ZIF8-SA composite aerogel of the present invention can float on the sea surface without capsizing, demonstrating a certain degree of wind reversal resistance.

[0093] 6. The PCNFs / ZIF8-SA composite aerogels of the present invention exhibit a high evaporation rate, which is due to their unique dual-pathway design: water vaporizes from the top of the hydrophobic layer, while salt is extracted from the side, thus avoiding clogging the evaporation channels for desalination. Furthermore, the evaporation rate of the PCNFs / ZIF8-SA composite aerogels remains stable in saline solutions ranging from 3.5 wt% to 20 wt%, demonstrating their excellent salt tolerance and suitability for interfacial evaporation of high-concentration saltwater.

[0094] 7. The PCNFs / ZIF8-SA composite aerogel of the present invention has good cyclic stability, which is due to: (1) the design of the dual-channel PCNFs / ZIF8-SA composite aerogel. The dual channels of the freshwater channel and the salt side mining channel ensure that the evaporation channel of the PCNFs / ZIF8-SA composite aerogel will not be blocked by salt crystals, so that the composite aerogel maintains good stability; (2) thanks to the good salt resistance and underwater oil resistance of SA, the PCNFs / ZIF8-SA composite aerogel can remain clean in real seawater, so that the composite aerogel has long-term stability.

[0095] 8. The existing salt tolerance strategy is to return salt to the water body. When large-scale seawater desalination is carried out, the salt ion concentration in the seawater will increase, affecting the living environment of marine organisms. In addition, the processing and utilization of salt crystals are missed. Unlike the former, the salt precipitated during the solar seawater desalination process of the present invention will not flow back into the water body. Its crystallization will be on the side of the PCNFs / ZIF8-SA composite aerogel, which can prevent the vaporization channel from being blocked by salt crystals and affecting the evaporation rate. At the same time, the salt precipitated on the side can be collected and separated by chemical precipitation to obtain lithium. After purification, it can be used in the battery industry, which is expected to alleviate the problem of lithium supply shortage.

[0096] Although the specific embodiments of the present invention are described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an integrated, dual-pathway PCNFs / ZIF8-SA composite aerogel, characterized by: The method steps are as follows: Step 1: Add sodium alginate SA and ZIF-8 to a PCNFs suspension and stir until SA is fully dissolved and a uniform mixture is formed; the PCNFs are hydrophilically modified PAN / ZIF-8 / lignin / NaCl carbon nanofibers; the mass ratio of sodium alginate SA, ZIF-8, and PCNFs is 1.5:0.3:0.5-4:1:3; The preparation process of the PCNFs suspension in step 1 is as follows: a. Preparation of PAN / ZIF-8 / lignin / NaCl electrospinning nanofiber membrane: Sodium chloride (NaCl) is first added to an N,N-dimethylformamide (DMF) solution, ball-milled, and allowed to stand. The upper NaCl solution and DMF solution are then added to a container. ZIF-8 particles are then added to the above solution. After ultrasonic treatment, polyacrylonitrile (PAN) is added and stirred for a period of time. Finally, lignin is added and stirred at 100°C to obtain an electrospinning precursor solution. The precursor solution is added to a syringe and electrospun at a propulsion rate of 0.3-0.6 mL / h and 16-22 kV to obtain a PAN / ZIF-8 / lignin / NaCl nanofiber membrane with uniform diameter. The membrane is then dried at 60-80°C for later use. b. Preparation of PAN / ZIF-8 / lignin / NaCl electrospun carbon nanofiber membrane: The PAN / ZIF-8 / lignin / NaCl nanofiber membrane was placed in a tubular furnace for high-temperature carbonization: first, the temperature was increased to 280°C at a heating rate of 5°C / min under a nitrogen atmosphere and maintained for 2 h. Then, the temperature was increased to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere and maintained for 2 h to obtain a PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane. c. Hydrophilic modification of PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane: A certain volume of DA Tris-HCl buffer and ethanol were mixed and stirred to obtain a DA water / ethanol mixed solution. Subsequently, a PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane was placed in the mixed solution and floated for 2-6 hours to achieve hydrophilic modification of the composite membrane, thus obtaining a hydrophilically modified PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane. d. Preparation of PAN / ZIF-8 / lignin / NaCl carbon nanofibers: The hydrophilically modified PAN / ZIF-8 / lignin / NaCl carbon nanofiber membrane was cut into thin slices and homogenized in deionized water at 12000-13000 rpm using a homogenizer to obtain a uniform suspension of PCNFs; Step 2: Pour the mixed solution into a mold, place it in a freeze dryer for directional freezing, and vacuum freeze-dry it at −80°C for 48 h to obtain a composite aerogel columnar structure with a directional channel structure; Step 3: The upper layer of the composite aerogel columnar structure is hydrophobically modified to form a hydrophobic layer with a certain thickness, and the lower layer is a hydrophilic layer, and the hydrophobic layer and the hydrophilic layer are integrated to obtain the PCNFs / ZIF8-SA composite aerogel.

2. The method for preparing an integrated, dual-path PCNFs / ZIF8-SA composite aerogel according to claim 1, characterized in that: The preparation process of ZIF-8 in step 1 is as follows: Zinc nitrate hexahydrate Zn(NO3)2·6H2O was dissolved in methanol to prepare solution A, and 2-methylimidazole 2-MIM was dissolved in methanol to prepare solution B. Solutions A and B were then quickly mixed, stirred, and centrifuged. The white precipitate was collected and dried to obtain ZIF-8.

3. The method for preparing an integrated, dual-path PCNFs / ZIF8-SA composite aerogel according to claim 1, characterized in that: The preparation method of the composite aerogel columnar structure in step 2 is as follows: SA and ZIF-8 are added to the PCNFs suspension and stirred until the SA is fully dissolved and a uniform mixed solution is formed; the mixed solution is poured into a polytetrafluoroethylene mold placed on a copper block, the copper block and the mold are placed in a Dewar flask, liquid nitrogen is added, and after freezing, the sample is immediately transferred to a freeze dryer and vacuum freeze-dried at −80°C for 48 hours to obtain a composite aerogel columnar structure with a directional channel structure.

4. The method for preparing an integrated, dual-path PCNFs / ZIF8-SA composite aerogel according to claim 1, characterized in that: The hydrophobic modification of the upper layer of the composite aerogel columnar structure in step 3 is specifically as follows: a 2% by mass methyltrimethoxysilane MTMS solution is prepared, and the aerogel is hydrophobically modified at the interface between the solution and the upper layer of the composite aerogel columnar structure, so that a hydrophobic layer with a certain thickness is formed on the upper layer of the composite aerogel columnar structure, and the lower layer is a hydrophilic layer, and the hydrophobic layer and the hydrophilic layer are integrated to obtain the PCNFs / ZIF8-SA composite aerogel.

5. The method for preparing an integrated, dual-path PCNFs / ZIF8-SA composite aerogel according to claim 1, characterized in that: The PCNFs / ZIF8-SA composite aerogel is a PCNFs / ZIF8-SA composite aerogel with asymmetric wettability, and the thickness of the hydrophobic layer is less than the thickness of the hydrophilic layer.

6. The method for preparing an integrated, dual-path PCNFs / ZIF8-SA composite aerogel according to claim 5, characterized in that: The thickness of the hydrophobic layer: the thickness of the hydrophilic layer = 1:1-1:

7.

7. An integrated, dual-channel PCNFs / ZIF8-SA composite aerogel prepared according to the preparation method according to any one of claims 1 to 6.

8. An application of an integrated, dual-pathway PCNFs / ZIF8-SA composite aerogel prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The PCNFs / ZIF8-SA composite aerogel is used for solar seawater desalination. The PCNFs / ZIF8-SA composite aerogel has dual passages: the hydrophobic layer is located on the water surface, the top of the hydrophobic layer and the directional channel serve as freshwater passages, and the side of the hydrophobic layer serves as a salt extraction passage. During the desalination process, water evaporates from the top freshwater passage into water vapor and escapes, while accumulated salt precipitates from the side salt extraction passages. The hydrophilic layer is immersed in seawater for directionally transporting seawater to the hydrophobic layer.

9. The use of an integrated, dual-path PCNFs / ZIF8-SA composite aerogel according to claim 8, characterized in that: A polyamide nanofiltration membrane is set at the bottom of the PCNFs / ZIF8-SA composite aerogel to carry out solar seawater desalination and collect the salt mined from the side; the aqueous solution is treated with carbonate to obtain battery-grade Li2CO3 powder, realizing the collection of lithium ions in seawater.

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