Composite hydrogel fibers for solar seawater desalination and methods of making the same

Abstract

The application discloses a preparation method of a composite hydrogel fiber for solar seawater desalination, and comprises the following steps: (1) sodium alginate powder is put into deionized water in 2-4 times for mixing to obtain a mixed solution; (2) the sodium alginate powder is completely dissolved by stirring, and primary defoaming is carried out for 1 h to obtain a sodium alginate solution; (3) MXene suspension is added into the sodium alginate solution to obtain a sodium alginate / MXene mixed solution; (4) secondary defoaming is carried out by ultrasonic for 30 min to obtain a sodium alginate / MXene spinning solution; (5) the sodium alginate / MXene spinning solution is loaded into a syringe and enters a CaCl2 coagulation bath to form uniform gel fibers, and the generated gel fibers are collected; and (6) glutaraldehyde is used for secondary crosslinking for 6-10 h, and then the gel fibers are soaked and washed in deionized water. On the basis of existing hydrogel evaporation materials, the evaporation rate and salt resistance and durability of the evaporator are maximally improved, and high-efficiency water transmission rate is realized and large-scale production is realized.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination technology, and in particular to a composite hydrogel fiber for solar-powered seawater desalination and its preparation method. Background Technology

[0002] With the increasing scarcity of global freshwater resources and the impacts of climate change, seawater desalination technology is becoming a crucial solution to the freshwater crisis. Seawater desalination technology has undergone continuous innovation, evolving from early simple distillation to today's reverse osmosis technology. However, environmental impact, energy consumption, and technological costs remain major challenges, severely hindering its further development. Solar energy is a green, environmentally friendly, and renewable clean energy source. Solar-driven interfacial evaporation (SDIE) technology has attracted considerable attention from researchers in recent years due to its economic efficiency, low energy consumption, and environmental friendliness, demonstrating great potential in the field of seawater desalination. In SDIE systems, photothermal materials such as carbon-based materials, metal-based nanoparticles, and inorganic semiconductor materials efficiently absorb sunlight and convert it into heat energy, thereby promoting evaporation at the evaporator-water-air interface. Among them, the two-dimensional transition metal carbide / nitride material MXene possesses unique electromagnetic wave absorption capabilities, efficiently absorbing a wide range of wavelengths from sunlight, including visible and near-infrared light. Furthermore, the nanostructure of MXene can induce localized surface plasmon resonance (LSPR), generating a concentrated enhancement effect of electromagnetic field on the material surface, thereby significantly improving the absorption and capture efficiency of light energy and converting it into heat energy, exhibiting the excellent characteristic of 100% internal photothermal conversion efficiency.

[0003] Common evaporator substrates today include aerogels, electrospun films, yarns, fabrics, and hydrogels. Hydrogel materials, as three-dimensional network cross-linked polymers containing a large number of water molecules, significantly improve evaporation efficiency and rate by reducing the enthalpy of vaporization and increasing thermal energy utilization. Current technologies for solar-powered seawater desalination photothermal interface water evaporation materials are as follows:

[0004] CN118594407A discloses a molybdenum disulfide-based hydrogel evaporator with adjustable pore structure, its preparation method, and its application. The method involves swelling polyvinyl alcohol in deionized water, then adding MoS2 nanoparticles and dissolving them. The mass ratio of polyvinyl alcohol to MoS2 nanoparticles is 72:(0.9–3.6), resulting in a mixture. Glutaraldehyde and hydrochloric acid are added to the mixture under stirring. The ratio of glutaraldehyde to MoS2 nanoparticles in Si is (80–120) μL:(0.09–0.36) g, resulting in a mixed system. This mixed system is then allowed to stand at room temperature in a sealed environment to obtain a crosslinked system. The crosslinked system is then frozen and dissolved, and excess glutaraldehyde is removed to obtain the molybdenum disulfide-based hydrogel evaporator with adjustable pore structure.

[0005] CN113943444A discloses a method for preparing a multi-level porous aero-hydrogel, its products, and applications, belonging to the field of solar energy application technology. First, a low-density, hydrophilic aerogel porous material is prepared by freeze-drying a Pickering emulsion gel. Then, a polyaniline aqueous dispersion, deionized water, and glutaraldehyde solution are added to an aqueous solution of sodium carboxymethyl cellulose nanoparticles, and acid is added dropwise to prepare an acidified polymer viscous aqueous solution. The aerogel is placed in the acidified polymer viscous aqueous solution to undergo a hydrogeling process. Through capillary forces and wetting effects, the aerogel and hydrogel are effectively cross-linked to obtain an aero-hydrogel with a multi-level porous structure, which is then used as a solar water evaporator.

[0006] CN117362763A discloses a method for preparing a self-floating, high-efficiency solar water evaporation material containing hydrophobic aerogel. The material consists of hydrophobic aerogel powder, a photothermal conversion material, and a polymer hydrogel. The preparation method involves dispersing the hydrophobic aerogel powder and the photothermal conversion material in a polymer aqueous solution through high-speed stirring, followed by the addition of a crosslinking agent to obtain the self-floating, high-efficiency solar water evaporation hydrogel material containing hydrophobic aerogel.

[0007] Based on the aforementioned patented technologies, it is evident that there are currently various methods for preparing hydrogels, including self-assembly template methods, freeze-thaw processes, and physical cross-linking through electrostatic interactions, hydrogen bonds, and chain entanglement via ionic interactions. Chemical cross-linking includes radiation cross-linking, ultraviolet cross-linking, and chemical modification, which connect different polymer chains or monomers together via covalent bonds. It is worth noting that although many studies have achieved excellent water transport performance, high evaporation rates, and stable salt resistance in evaporators through the formation of three-dimensional gel networks and structural engineering, some complex processes, repeated freeze-thaw cycles, and long-term freeze-drying techniques are difficult to scale up for production, and certain limitations remain. Furthermore, the tightly packed and tortuous water transport channels of traditional hydrogels are not conducive to water transport in SDIE (Self-Containing Electrolyte), failing to promptly transport salt from the evaporation surface back to the bulk water, leading to salt accumulation on the evaporation surface. Salt accumulation, on the one hand, blocks the amount of sunlight reaching the evaporator's photothermal material, reducing photothermal conversion efficiency and evaporation rate; on the other hand, it can also clog the evaporator's water supply channels and steam release, reducing evaporator performance and affecting its service life. Therefore, how to maximize the evaporation rate and salt resistance of the evaporator based on existing hydrogel evaporation materials, achieve high-efficiency water transport rate, realize large-scale production, reduce production costs, and realize industrial application has become a problem that technicians in the field of solar seawater desalination urgently need to solve. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a composite hydrogel fiber for solar seawater desalination that can maximize the evaporation rate and salt resistance of the evaporator based on the existing hydrogel evaporation materials, achieve high water transport rate and enable large-scale production, as well as the preparation method thereof.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing composite hydrogel fibers for solar-powered seawater desalination, comprising the following steps:

[0010] (1) Add sodium alginate powder to deionized water in 2-4 portions and mix to obtain a mixed solution with a mass fraction of 40-60 g / L;

[0011] (2) Stir vigorously at a speed of 300-400r / min until the sodium alginate powder is completely dissolved, and then perform initial defoaming at a speed of 150-250r / min for 1 hour to obtain sodium alginate solution.

[0012] (3) Add MXene suspension with a mass fraction of 40-60 mg / mL to sodium alginate solution to obtain sodium alginate / MXene mixed solution with a mass fraction of 40-60 g / L;

[0013] (4) Continue stirring for 20-40 minutes until the sodium alginate / MXene mixed solution is fully mixed. After stirring, sonicate for 30 minutes to perform secondary degassing to obtain sodium alginate / MXene spinning solution.

[0014] (5) Load the sodium alginate / MXene spinning solution into a syringe, use a micro-injection pump to press the spinning solution out of the spinneret to form a thin stream, enter the CaCl2 coagulation bath to form uniform gel fibers, and collect the generated gel fibers.

[0015] (6) The collected gel fibers are cross-linked with glutaraldehyde for 6-10 hours, and then soaked and washed in deionized water to obtain composite hydrogel fibers.

[0016] In the above-mentioned method for preparing composite hydrogel fibers for solar seawater desalination, in step (1), sodium alginate powder is added to deionized water in three separate batches and mixed to obtain a mixed solution with a mass fraction of 50 g / L.

[0017] In the above-mentioned method for preparing composite hydrogel fibers for solar seawater desalination, in step (2), the dissolution stirring speed is 350 r / min, and the initial defoaming stirring speed is 200 r / min.

[0018] In the above-mentioned method for preparing composite hydrogel fibers for solar seawater desalination, in step (3), the mass fraction of MXene suspension is 50 mg / mL, the mass fraction of sodium alginate / MXene mixed solution is 50 g / L, and the volume ratio of sodium alginate solution to MXene solution is 14:1.

[0019] In the above-described method for preparing composite hydrogel fibers for solar-powered seawater desalination, step (5) involves using a micro-injection pump with an extrusion speed of 0.5-0.7 mm / s. -1 The concentration of CaCl2 in the coagulation bath is 5-15 wt%.

[0020] In the above-mentioned method for preparing composite hydrogel fibers for solar seawater desalination, in step (6), the secondary crosslinking time of glutaraldehyde is 8 hours.

[0021] In the above-described method for preparing composite hydrogel fibers for solar-powered seawater desalination, step (5) involves using a micro-injection pump with an extrusion speed of 0.6 mm / s. -1 The concentration of the CaCl2 coagulation bath was 10 wt%.

[0022] A composite hydrogel fiber for solar-powered seawater desalination is prepared by the above-described method.

[0023] The aforementioned composite hydrogel fiber for solar-powered seawater desalination has an expansion ratio of 700-900%, a saturated water content of 85-95%, and a fiber toughness of 2-2.6 MJ / m. 3 .

[0024] The aforementioned composite hydrogel fiber for solar-powered seawater desalination has a diameter of 0.5-1.1 mm and a tensile breaking stress of 2-6 MPa.

[0025] The advantages of this invention regarding the composite hydrogel fiber for solar-powered seawater desalination and its preparation method are as follows: Based on physically cross-linked hydrogels, combined with wet spinning technology from textile production processes, sodium alginate and MXene are used as spinning solutions, and calcium chloride is used as a coagulation bath to prepare the hydrogel fibers. During water transport in the evaporator, the dual effects of the multi-level pores within the hydrogel fibers and the capillary effect between fibers endow the evaporator with excellent water transport performance. In experiments, the optimal porosity of the capillary effect between fibers is determined by adjusting the number of fibers in the evaporator, thus ensuring sufficient water supply, a high evaporation rate, and timely salt reflux. Based on the widespread availability and efficient utilization of solar energy, this invention maximizes the evaporation rate and salt resistance of the evaporator compared to existing hydrogel evaporation materials, achieving a high water transport rate and enabling large-scale production. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the preparation process and principle of the composite hydrogel fiber of the present invention;

[0027] Figure 2 This is a morphology diagram of the composite hydrogel fiber obtained in Example 2 of the present invention;

[0028] Figure 3 This is an EDS elemental distribution diagram of the composite hydrogel fiber prepared in Example 2 of the present invention;

[0029] Figure 4 The image shown is an FTIR image of the composite hydrogel fiber obtained in Example 2 of this invention.

[0030] Figure 5 High-resolution XPS spectra of C1s, Ti2p, Cl2p, Ca2p and O1s in the composite hydrogel fiber prepared in Example 2 of the present invention.

[0031] Figure 6 The graph shows the water transport rate test results for composite hydrogel fibers with porosities of 3%, 10%, and 15%. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] like Figure 1 As shown, a method for preparing composite hydrogel fibers for solar-powered seawater desalination includes the following steps:

[0036] (1) Add sodium alginate powder to deionized water in 2-4 portions and mix to obtain a mixed solution with a mass fraction of 40-60 g / L;

[0037] (2) Stir vigorously at a speed of 300-400r / min until the sodium alginate powder is completely dissolved, and then perform initial defoaming at a speed of 150-250r / min for 1 hour to obtain sodium alginate solution.

[0038] (3) Add MXene suspension with a mass fraction of 40-60 mg / mL to sodium alginate solution to obtain sodium alginate / MXene mixed solution with a mass fraction of 40-60 g / L;

[0039] (4) Continue stirring for 20-40 minutes until the sodium alginate / MXene mixed solution is fully mixed. After stirring, sonicate for 30 minutes to perform secondary degassing to obtain sodium alginate / MXene spinning solution.

[0040] (5) Load the sodium alginate / MXene spinning solution into a syringe, use a micro-injection pump to press the spinning solution out of the spinneret to form a thin stream, enter the CaCl2 coagulation bath to form uniform gel fibers, and collect the generated gel fibers; there is no stretching force during the fiber generation and collection process.

[0041] (6) The collected gel fibers are cross-linked with glutaraldehyde for 6-10 hours, and then soaked and washed in deionized water to obtain composite hydrogel fibers.

[0042] The auxiliary agents used in this invention are as follows: Ti3C2Tx (MXene, 50 mg / ml, Jinan Sanchuan), sodium alginate (SA, 280 mPa·s, Qingdao Haizhilin), and calcium chloride (CaCl2, 96%, Sinopharm Chemical Reagent Co., Ltd.). All chemical reagents used met analytical purity standards and can be directly used in experiments without additional purification.

[0043] This invention employs a mature wet spinning method from the textile industry to prepare continuous hydrogel fibers, such as... Figure 1 As shown, using sodium alginate and MXene as spinning solutions and calcium chloride solution as the coagulation bath, the preparation process has advantages such as high coagulation efficiency, low cost, environmental friendliness and safety, and ease of large-scale production. The G unit (α-L-guluronic acid unit) in the sodium alginate molecular chain contains some freely moving carboxylic acid groups (-COO). - MXenes are rich in polar functional groups such as hydroxyl (-OH) and oxygen (-O) at their ends. When mixed, these groups form hydrogen bonds. Simultaneously, physical entanglement of long sodium alginate molecular chains may occur between the MXene sheets. The combined effect of these forces enhances the dispersibility and stability of the mixed solution system. When exposed to polyvalent cations such as Ca... 2+ At this time, the carboxylic acid groups on the G units of sodium alginate bind with calcium ions, forming stable bridges between molecular chains and constructing a three-dimensional network structure. This physical cross-linking process is a key step in the formation of hydrogels. In this study, increasing the solution concentration increases the number of cross-linking points within the hydrogel fibers to further enhance their strength.

[0044] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0045] Example 1:

[0046] A method for preparing composite hydrogel fibers for solar-powered seawater desalination includes the following steps:

[0047] (1) Sodium alginate powder was added to deionized water in two batches and mixed to obtain a mixed solution with a mass fraction of 40 g / L.

[0048] (2) Stir vigorously at 300 r / min until sodium alginate powder is completely dissolved, and then perform initial defoaming at 150 r / min for 1 hour to obtain sodium alginate solution.

[0049] (3) Add MXene suspension with a mass fraction of 40 mg / mL to sodium alginate solution to obtain sodium alginate / MXene mixed solution with a mass fraction of 40 g / L; wherein the volume ratio of sodium alginate solution to MXene solution is 14:1.

[0050] (4) Continue stirring for 20 minutes until the sodium alginate / MXene mixed solution is fully mixed. After stirring, sonicate for 30 minutes to perform secondary degassing to obtain sodium alginate / MXene spinning solution.

[0051] (5) The sodium alginate / MXene spinning solution is loaded into a syringe. A micro-injection pump is used to expel the spinning solution from the spinneret to form a thin stream, which enters the CaCl2 coagulation bath to form uniform gel fibers. The generated gel fibers are collected. No stretching force is applied during fiber generation and collection. The extrusion speed of the micro-injection pump is 0.5 mm / s. -1 The concentration of the CaCl2 coagulation bath was 5 wt%.

[0052] (6) The collected gel fibers were cross-linked with glutaraldehyde for 6 hours, and then soaked and washed in deionized water to obtain composite hydrogel fibers.

[0053] The composite hydrogel fiber prepared in this embodiment for solar seawater desalination has an expansion ratio of 700%, a saturated water content of 85%, and a fiber toughness of 2 MJ / m. 3 The diameter is 0.5 mm, and the measured tensile fracture stress is 2 MPa.

[0054] Example 2:

[0055] A method for preparing composite hydrogel fibers for solar-powered seawater desalination includes the following steps:

[0056] (1) Sodium alginate powder was added to deionized water in three portions and mixed to obtain a mixed solution with a mass fraction of 50 g / L.

[0057] (2) Stir vigorously at 350 r / min until sodium alginate powder is completely dissolved, and then perform initial defoaming at 200 r / min for 1 hour to obtain sodium alginate solution.

[0058] (3) Add MXene suspension with a mass fraction of 50 mg / mL to sodium alginate solution to obtain sodium alginate / MXene mixed solution with a mass fraction of 50 g / L; wherein the volume ratio of sodium alginate solution to MXene solution is 14:1.

[0059] (4) Continue stirring for 30 minutes until the sodium alginate / MXene mixed solution is fully mixed. After stirring, sonicate for 30 minutes to perform secondary degassing to obtain sodium alginate / MXene spinning solution.

[0060] (5) The sodium alginate / MXene spinning solution is loaded into a syringe. A micro-injection pump is used to expel the spinning solution from the spinneret to form a thin stream, which enters the CaCl2 coagulation bath to form uniform gel fibers. The generated gel fibers are collected. No stretching force is applied during fiber generation and collection. The extrusion speed of the micro-injection pump is 0.6 mm / s. -1 The concentration of the CaCl2 coagulation bath was 10 wt%.

[0061] (6) The collected gel fibers were cross-linked with glutaraldehyde for 8 hours, and then soaked and washed in deionized water to obtain composite hydrogel fibers.

[0062] The composite hydrogel fiber prepared in this embodiment for solar-powered seawater desalination has an expansion ratio of 819%, a saturated water content of 89.1%, and a fiber toughness of 2.34 MJ / m. 3 The diameter is 0.8 mm, and the measured tensile fracture stress is 4 MPa.

[0063] When the SA / MXene spinning solution is 1 wt%, the low concentration and viscosity make it difficult to form continuous and stable hydrogel fibers (S1) when extruded from the spinneret. However, excessively high concentrations and viscosities of the SA / MXene spinning solution lead to difficulties in stirring the sodium alginate solution. Furthermore, Ca... 2+ The slow diffusion rate affected the formation speed of the hydrogel fibers, and the final concentration of the SA / MXene mixed solution was determined to be 5 wt% (S1). Hydrogel fibers with diameters of 0.8, 1.5, and 2.5 mm were prepared by changing the needle and adjusting the advance speed of the microinjection pump (S2). Based on preliminary experiments and considering subsequent porosity adjustments, the final determined hydrogel fiber diameter for assembling the evaporator was 0.8 mm, and the injection pump advance speed was 0.6 mm / s. -1 .

[0064] Example 3:

[0065] A method for preparing composite hydrogel fibers for solar-powered seawater desalination includes the following steps:

[0066] (1) Sodium alginate powder was added to deionized water in four portions and mixed to obtain a mixed solution with a mass fraction of 60 g / L.

[0067] (2) Stir vigorously at 400 r / min until sodium alginate powder is completely dissolved, and then perform initial defoaming at 250 r / min for 1 hour to obtain sodium alginate solution.

[0068] (3) Add MXene suspension with a mass fraction of 60 mg / mL to sodium alginate solution to obtain sodium alginate / MXene mixed solution with a mass fraction of 60 g / L; wherein the volume ratio of sodium alginate solution to MXene solution is 14:1.

[0069] (4) Continue stirring for 40 minutes until the sodium alginate / MXene mixed solution is fully mixed. After stirring, sonicate for 30 minutes to perform secondary degassing to obtain sodium alginate / MXene spinning solution.

[0070] (5) The sodium alginate / MXene spinning solution is loaded into a syringe. A micro-injection pump is used to expel the spinning solution from the spinneret to form a thin stream, which enters the CaCl2 coagulation bath to form uniform gel fibers. The generated gel fibers are collected. No stretching force is applied during fiber generation and collection. The extrusion speed of the micro-injection pump is 0.7 mm / s. -1 The concentration of the CaCl2 coagulation bath was 15 wt%.

[0071] (6) The collected gel fibers were cross-linked with glutaraldehyde for 10 hours, and then soaked and washed in deionized water to obtain composite hydrogel fibers.

[0072] The composite hydrogel fiber prepared in this embodiment for solar-powered seawater desalination has an expansion ratio of 900%, a saturated water content of 95%, and a fiber toughness of 2.6 MJ / m. 3 The diameter is 1.1 mm, and the measured tensile breaking stress is 6 MPa.

[0073] The performance test results of the composite hydrogel fiber prepared by the preparation method described in Example 2 of this invention and its specific applications are as follows:

[0074] like Figure 2 As shown, where, Figure 2 a is a SEM image of the SA / MXene hydrogel fiber surface. Figure 2 bd is a SEM image of the pore structure of the SA / MXene hydrogel fiber cross section. Figure 2 e shows a SEM image of the outer wall of the SA / MXene hydrogel fiber. After lyophilization, the morphology of the SA / MXene hydrogel fiber was observed using scanning electron microscopy (SEM), as shown below. Figure 2 As shown in Figure a, the hydrogel fibers have a smooth and flat surface, demonstrating the reliability and superiority of wet spinning technology in hydrogel fiber forming. The fiber surface also exhibits some distinct lamellae (S4a, b), which may be formed by MXene nanosheets embedded in the hydrogel fibers. Figure 2bd shows that the hydrogel fiber cross-section has circular or elliptical hierarchical pores (S4c,d) of 24-120 μm. MXene and sodium alginate were processed using Ca... 2+ The physical cross-linking process forms pore walls of 1-15 μm and fiber outer walls of about 80 μm. Figure 2 e). SA@MX hydrogel fibers have a smooth and thick outer wall and a multi-level porous structure, which not only gives the hydrogel fibers excellent mechanical properties but also facilitates water transport during evaporation. The relevant parameters of the hydrogel fibers are evaluated by comparing their weight after swelling equilibrium and their dry weight. The swelling ratio (SR) and saturated water content (SWC) can be calculated using the following formulas:

[0075]

[0076] Where m s It is the weight of the hydrogel fiber after it has swelled and reached equilibrium during molding, in m. d This refers to the weight of the hydrogel fiber after it has been completely dried. Multiple measurements were taken and averaged to calculate the swelling ratio (S5a) and saturated water content (S5b) of the hydrogel fiber, which were 819% and 89.1%, respectively. This indicates that the hydrogel fiber possesses excellent water absorption capacity and a porous structure. Despite the high swelling ratio, the hydrogel fiber maintains its structural integrity through cross-linking between internal molecular chains, while also exhibiting excellent mechanical strength and properties. A hydrogel fiber with a diameter of only 0.8 mm can lift a 150 g weight (S6a), and its breaking stress can reach 4 MPa (S6b) under tensile testing.

[0077] like Figure 3 As shown in the EDS image, elements such as Ca, O, and Ti are clearly distributed on the fiber surface. 2+ The hydrogel formed by crosslinking with carboxyl ions in sodium alginate, and the uniform distribution of Ca elements, indicate that the crosslinking reaction proceeded relatively evenly during wet spinning, further demonstrating that the hydrogel fibers formed a stable gel network structure. The Ti elements originated solely from MXene, and their uniform distribution verifies the thorough integration of MXene and sodium alginate. The relatively concentrated elemental distribution may be due to the distribution of larger-diameter MXene nanosheets on the fiber surface.

[0078] like Figure 4 As shown, the molecular structures of SA hydrogel fibers and SA / MX hydrogel fibers were analyzed using Fourier transform infrared spectroscopy (FTIR). For SA hydrogel fibers, the molecular structure at 3254 cm⁻¹... -1 The broad peak at 1593 cm⁻¹ is due to the stretching vibration of the hydroxyl group (-OH). -1 and 1413cm -1 There are two COOs- Asymmetric and symmetric stretching vibration peaks, 1030 cm⁻¹ -1 A CO stretching vibration peak is present. After introducing MXene into SA hydrogel fibers, the position of the peak in the Fourier transform infrared spectrum changes, with both peak broadening and intensity decrease. The shift in the hydroxyl stretching vibration peak of SA / MXene indicates the formation of hydrogen bonds between the terminal groups -O and -OH of MXene and the COO- and -OH of sodium alginate. Furthermore, because Ca... 2+ The addition of SA's -O and COO- with Ca 2+ The coordination interactions between them may cause changes in the width of characteristic peaks. XPS technology was used to analyze the bonding and surface structure changes of the synthesized SA@MX. The presence of Ti elements in the XPS full spectrum (S7) indicates the successful addition of MXene.

[0079] like Figure 5 As shown, the disappearance of the Ti-C bond in the C1s spectrum proves that the sodium alginate molecular chain interacts with the MXene nanosheets. The Ti2p spectrum shows characteristic binding energy peaks at 455.2 eV, 456.8 eV, and 458.5 eV, corresponding to Ti-C, Ti-O, and Ti-O2, respectively. In the Ca2p spectrum, the binding energy of 347.7 eV corresponds to the Ca 2p3 / 2 peak, while the Ca 2p1 / 2 peak is located at a higher binding energy of 351.28 eV, and its peak intensity is generally weaker than that of the Ca 2p3 / 2 peak. For the Cl 2p XPS, a peak is shown at a binding energy of 198.3 eV, attributed to the presence of Cl 2p3 / 2, which is 1.6 eV lower than the Cl 2p1 / 2 binding energy. These two elements interact in the SA@MX hydrogel fibers with Ca... 2+ and Cl - The presence of this form demonstrates that calcium chloride, acting as a coagulation bath, facilitated the successful synthesis of hydrogel fibers. The peaks in the O 1s spectrum at 529.8, 532.1, 531.2, 533.4, and 534.8 eV represent C-Ti-O, C–Ti–(OH), and C–Ti–(OH), respectively. x、 C=O and H2O ads This indicates that Ti forms a bonding bond with the -OH group in the sodium alginate molecular chain. Compared to sodium alginate fibers, the hydroxyl peak of the mixed sodium alginate fibers containing MXene and sodium alginate shifts to a lower wavelength, indicating that the sodium alginate molecular chain is rich in carboxylic acid (COO-) and -OH groups, which can form hydrogen bonds with the terminal -O and -OH groups of MXene.

[0080] Excellent water transport performance ensures timely water supply to the interfacial evaporation surface, which is beneficial to improving the evaporation rate of the evaporator. The hydrophilicity of hydrogel fibers refers to their ability to attract water, promoting adsorption and diffusion on the fiber surface through forces such as hydrogen bonds. Using a water contact angle instrument, a water droplet was completely absorbed in just 103 ms, indicating the excellent hydrophilicity of hydrogel fibers. For vertical channel evaporators, the hydrophilicity of the evaporator material is generally used to transport bulk water from bottom to top to the evaporator surface via capillary forces. For the hydrogel fiber evaporator studied in this paper, water transport relies on the hierarchical pore structure of the fibers themselves and the combined effect of capillary forces between the fibers. Capillary action is generated by the interaction (adhesive force) between the surface tension of the liquid and the solid surface, causing the liquid to rise or fall within small pores or narrow spaces. This effect allows bulk water to move upwards along the surface when it comes into contact with the hydrogel fiber surface, and this effect is the dominant factor in the water transport process. Using a PE ring with a diameter of 13.5 mm as the quantitative area, the effect of the evaporator's porosity (P) on water transport performance was determined by varying the number of internal fibers. Based on previous experimental comparisons, SHF evaporators with the same height of 3 cm but different porosities (P) were finally selected. Evaporators with porosities of 3%, 10%, and 15% (named SHF-P3, SHF-P10, and SHF-P15, respectively) were selected for further study. Figure 6 As shown, the transport height of dyed water in the SHF evaporator is compared. Based on capillary pressure and capillary rise equations:

[0081] P c =2σcos(θ) / R

[0082] h=σcos(θ) / ρgR

[0083] Where h is the height the liquid rises in the capillary, σ is the surface tension of the liquid, θ is the contact angle, ρ is the density of the liquid, g is the acceleration due to gravity, and R is the radius of the capillary (which can be analogously considered as half the distance between the fibers). According to the two equations, both the capillary pressure Pc and the height the liquid rises h are inversely proportional to the fiber spacing R; that is, the smaller the fiber spacing, the greater the capillary pressure and the greater the height the liquid rises. (Comparison) Figure 6When the evaporator porosity was reduced from 15% to 10%, the distance between fibers decreased, leading to a higher water transport height. However, when the evaporator porosity was reduced to 3%, the water transport efficiency actually decreased. This is because in a porous fiber bundle evaporator, the capillary force between fibers is also affected by factors such as surface properties and fiber bundle structure. Under the direct influence of capillary action, the greater the capillary pressure, the greater the height the liquid may rise in the capillary tube. However, the increase in capillary pressure also increases the flow resistance of the liquid in the smaller pores between the fibers, making it difficult for the liquid to move between the fibers and reducing the transport efficiency. Therefore, an evaporator with a porosity of 10% was used for subsequent experiments.

[0084] In summary, this invention utilizes solar-driven interfacial evaporation (SDIE) technology combined with the low enthalpy of vaporization of hydrogels, representing a key approach to solving the freshwater crisis. The prepared sodium alginate / MXene hydrogel fibers, through the combined effect of their porous internal structure and interfiber capillary forces, endow the SMHF evaporator with highly efficient water transport performance. This superior water transport performance, capable of dissolving salt particles and returning them to the bulk water, is attributed to several factors. The hydrophilicity of the hydrogel fibers promotes the adsorption and diffusion of water molecules on the material surface. The porous internal structure of the fibers allows water molecules to flow within the fibers. Simultaneously, the appropriate fiber spacing induces capillary forces that enhance the speed and height of water transport, accelerating water movement and rapidly dissolving salt particles. This solves the problem of traditional hydrogels' tightly packed and tortuous water transport channels being unfavorable for SDIE water transport, failing to promptly transport salt from the evaporation surface back to the bulk water, thus leading to salt accumulation on the evaporation surface. Furthermore, it avoids the drawbacks of salt accumulation: on the one hand, it blocks sunlight from reaching the evaporator's photothermal material, reducing photothermal conversion efficiency and evaporation rate; on the other hand, it clogs the evaporator's water supply channels and steam release, reducing evaporator performance and affecting its service life.

[0085] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should be protected by the present invention.

Claims

1. A method for the preparation of composite hydrogel fibers for solar seawater desalination, characterized by, The method comprises the following steps: (1) Put sodium alginate powder into deionized water in 2-4 times for mixing to obtain a mixed solution with a mass fraction of 40-60 g / L; (2) Stir intensively at a speed of 300-400 r / min until the sodium alginate powder is completely dissolved, and then perform primary defoaming at a speed of 150-250 r / min for 1 h to obtain a sodium alginate solution; (3) Add MXene suspension with a mass fraction of 40-60 mg / mL into the sodium alginate solution to obtain a sodium alginate / MXene mixed solution with a mass fraction of 40-60 g / L; (4) Continue to stir for 20-40 min until the sodium alginate / MXene mixed solution is fully mixed, and then perform secondary defoaming by ultrasonic for 30 min to obtain a sodium alginate / MXene spinning solution; (5) Put the sodium alginate / MXene spinning solution into a syringe, use a micro-injection pump to press the spinning solution from a spinning needle to form a stream, and then enter a CaCl2 coagulation bath to form uniform gel fibers, and collect the generated gel fibers; (6) Use glutaraldehyde to perform secondary crosslinking on the collected gel fibers for 6-10 h, and then immerse the gel fibers in deionized water for washing to obtain a composite hydrogel fiber.

2. The method for the preparation of composite hydrogel fibers for solar seawater desalination according to claim 1, characterized by: In the step (1), the sodium alginate powder is put into deionized water in 3 times for mixing to obtain a mixed solution with a mass fraction of 50 g / L.

3. The method for the preparation of composite hydrogel fibers for solar seawater desalination according to claim 1, characterized by: In the step (2), the stirring speed for dissolving is 350 r / min, and the stirring speed for primary defoaming is 200 r / min.

4. The method for the preparation of composite hydrogel fibers for solar seawater desalination according to claim 1, characterized by: In the step (3), the mass fraction of the MXene suspension is 50 mg / mL, and the mass fraction of the sodium alginate / MXene mixed solution is 50 g / L, wherein the volume ratio of the sodium alginate solution to the MXene solution is 14:

1.

5. The method for the preparation of composite hydrogel fibers for solar seawater desalination according to claim 1, characterized by: The extrusion speed of the micro-injection pump used in the step (5) is 0.5-0.7 mms -1 The concentration of the CaCl2 coagulating bath is 5-15 wt%.

6. The method for the preparation of composite hydrogel fibers for solar seawater desalination according to claim 1, characterized by: In the step (6), the secondary crosslinking time using glutaraldehyde is 8 h.

7. The method for the preparation of composite hydrogel fibers for solar seawater desalination according to claim 5, characterized by: The extrusion speed of the micro-injection pump used in the step (5) is 0.6 mms -1 The concentration of the CaCl2 coagulation bath is 10 wt%.

8. A composite hydrogel fiber for solar powered seawater desalination, characterized by: The composite hydrogel fiber is prepared by the preparation method in any one of claims 1-7.

9. The composite hydrogel fiber for solar seawater desalination according to claim 8, characterized by: The composite hydrogel fiber has an expansion ratio of 700-900%, a saturated water content of 85-95%, and a fiber toughness of 2-2.6 MJ / m 3 .

10. The composite hydrogel fiber for solar seawater desalination according to claim 8, characterized by: The diameter of the composite hydrogel fiber is 0.5-1.1 mm, and the tensile fracture stress is 2-6 MPa.

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