Solar interface evaporator with adjustable pores and vertical channels

Abstract

The invention discloses a solar interface evaporator with adjustable pores and vertical channels, which comprises a container for storing seawater to be evaporated, a heat absorption and heat conduction layer floating on the seawater to be evaporated is arranged in the container, a cylindrical three-dimensional evaporation part for continuously evaporating the seawater is arranged on the heat absorption and heat conduction layer, and the vertical channels are communicated with the cylindrical three-dimensional evaporation part. The cylindrical three-dimensional evaporation part downwards penetrates through the lower surface of the heat absorption and heat conduction layer and extends below the seawater surface, the fixing device is used for connecting the cylindrical three-dimensional evaporation part to the heat absorption and heat conduction layer, and heat insulation layers are arranged on the surfaces of the side wall and the bottom of the container respectively. The heat supply / heat insulation model is adopted, the'heat evaporation 'theory is used as the inventive concept, efficient water transmission, high evaporation rate and large-scale production are achieved, and the heat supply / heat insulation model is combined, so that popularization in practical application can be greatly promoted in the future.

Description

Technical Field

[0001] The present invention relates to the technical field of seawater desalination, and particularly to a solar interfacial evaporator with adjustable pores and vertical channels. Background Art

[0002] Solar energy is a green, environmentally friendly and renewable clean energy. Due to its economic efficiency, low energy consumption and environmental friendliness, the solar-driven interfacial evaporation (SDIE) technology has attracted the attention of many researchers in recent years and shown great development prospects in the field of seawater desalination. In the SDIE system, photothermal materials such as carbon-based materials, metal-based nanoions, and inorganic semiconductor materials efficiently absorb sunlight and convert it into heat energy, thereby promoting the interfacial evaporation at the evaporator-water-air interface. Among them, the two-dimensional transition metal carbide / nitride material MXene has a unique electromagnetic wave absorption ability and can efficiently absorb a wide range of wavelengths such as visible light and near-infrared light in sunlight. In addition, the nanostructure of MXene can cause the local surface plasmon resonance effect (LSPR), generating an enhanced effect of electromagnetic field concentration on the material surface, thereby significantly improving the absorption and capture efficiency of light energy and converting it into heat energy, showing an excellent characteristic of 100% internal photothermal conversion efficiency.

[0003] Common evaporator substrates currently include aerogels, electrospun films, yarns, fabrics, hydrogels, etc. As a three-dimensional network cross-linked polymer containing a large number of water molecules, hydrogel materials have achieved a significant improvement in evaporation efficiency and rate by reducing the evaporation enthalpy of water and increasing the utilization efficiency of thermal energy. During the assembly of the evaporation system, thermal insulation foam is usually used to connect the evaporator and bulk water. For 2DSDIE, the thermal insulation foam can localize heat on the evaporator surface to prevent heat from transferring downward through heat conduction, thereby improving the thermal efficiency of the overall evaporation system. For 3DSDIE, previous studies have shown that a three-dimensional evaporator can obtain additional energy from bulk water and the surrounding environment. While the thermal insulation foam hinders the heat conduction loss from the evaporator to the bulk water, it also hinders the energy extraction of the evaporator and is not suitable for three-dimensional evaporators. In addition, many researchers have focused on reducing the heat loss of the evaporation system but have overlooked the universality of solar energy in the natural environment. The advantages of solar energy-driven evaporation should be fully utilized, combined with the characteristics of three-dimensional evaporators, to enhance the evaporation potential on the side of the evaporator and improve the rate of the entire evaporation system. To this end, many researchers have improved the salt tolerance of hydrogels through porous structure design. For example, Peng's team designed and developed a foam-based inverse phase transition-induced polymer / nanofiller foam hydrogel using ultra-high-speed stirring foaming (35,000 rpm), with the bubble phase as the matrix and the hydrogel as the dispersed phase, promoting the fabrication of a hierarchical pore structure. Yu's team prepared a vertically channeled hydrogel with an oriented structure as a water transport path through directional freezing with liquid nitrogen. Although these structural designs are different, they all improve the water supply efficiency by designing the evaporator structure to form a salt concentration gradient between the bulk water and the evaporator surface, and utilize the driving forces of convection and diffusion to fully dissolve and transport salt ions into the bulk water.

[0004] The existing technologies for solar desalination photothermal interfacial water evaporation materials are as follows:

[0005] CN117647019A discloses a solar interfacial evaporation device, its preparation method and application. The solar interfacial evaporation device of the present invention includes a substrate and a photothermal conversion structure disposed on the substrate. The photothermal conversion structure is composed of modified loofah columnar bodies distributed in a circular array. The modified loofah columnar bodies include carbonized loofah columnar bodies and PVA / ppy composite materials attached to the carbonized loofah columnar bodies.

[0006] CN117209000A discloses an integrated multifunctional solar evaporator for better achieving the balance of water transport, salt tolerance and heat supply, belonging to the technical field of functional materials. The present invention provides an integrated multifunctional solar evaporator. The evaporator includes a water evaporation layer, a heating layer and a thermal insulation layer. The water evaporation layer is a hydrophilic aerogel with a vertically oriented structure, and the heating layer is a photothermal hydrophobic film.

[0007] CN117362763A discloses a preparation method of a hydrophobic aerogel self-floating high-efficiency solar water evaporation material. This material consists of hydrophobic aerogel powder, a photothermal conversion material, and a polymer hydrogel. The preparation method is to disperse the hydrophobic aerogel powder and the photothermal conversion material into an aqueous polymer solution through high-speed stirring, and then add a cross-linking agent to obtain the hydrophobic aerogel self-floating high-efficiency solar water evaporation hydrogel material.

[0008] Combined with the above patent technology, it can be seen that the structures and preparation methods of hydrogels are diverse at present, including physical cross-linking formed by self-assembly template method, freeze-thaw process, ionic interaction, etc. through electrostatic interaction, hydrogen bond, chain entanglement, etc. Chemical cross-linking formed by covalently connecting different polymer chains or monomers through radiation cross-linking, ultraviolet cross-linking, chemical modification, etc. It is worth mentioning that although many studies have achieved excellent water transportation performance, high evaporation rate and stable anti-salt performance of the evaporator through the formation of a three-dimensional gel network and structural engineering research. However, some complex processes, repeated freeze-thaw cycles, and long-time freeze-drying and other technologies are difficult to achieve large-scale application in production, and there are still certain limitations. Moreover, the tightly tortuous water transport channels of traditional hydrogels are not conducive to the water transport of SDIE, and cannot timely transport the salt on the evaporation surface back to the bulk water, resulting in salt accumulation on the evaporation surface energy. On the one hand, the salt accumulation blocks the amount of sunlight reaching the photothermal material of the evaporator, reducing the photothermal conversion efficiency and evaporation rate. On the other hand, it also blocks the water supply and steam release of the water channels of the evaporator, reducing the performance of the evaporator and affecting its service life. And the traditional heat insulation model separates the evaporator from the bulk water, reducing the heat loss to the outside in the form of conduction, convection and radiation during the evaporation process, not only improving the thermal efficiency of the whole system, but also helping to reduce additional energy consumption. However, in actual operation, the advantage of solar energy driving cannot be fully exerted and utilized, and the light, heat, and radiation effects of solar energy conduction, convection and radiation cannot be maximally reflected in the whole evaporation system. That is to say, except for using solar radiation for photothermal conversion at the evaporator interface, the universality of solar radiation cannot be fully utilized, resulting in the inability to maximize the evaporation efficiency.

[0009] Therefore, how to make full use of solar energy driving, maximize the conduction, convection and radiation of solar energy, realize the thermal evaporation of seawater, further improve the evaporation efficiency, evaporation rate and salt tolerance durability, and achieve a high water transport rate and large-scale production, and reduce production costs has become a difficult problem that technicians in the field of solar desalination urgently need to solve. Summary of the Invention

[0010] Aiming at the deficiencies of the existing technology, the technical problem to be solved by the present invention is to provide a solar interface evaporator with adjustable pores and vertical channels that makes full use of solar energy drive, maximizes the comprehensive utilization of solar energy, realizes the thermal evaporation of seawater, and realizes a high water transmission rate, further improving the evaporation efficiency, evaporation rate and salt tolerance durability.

[0011] To solve the above technical problems, the technical solution adopted by the present invention is: a solar interface evaporator with adjustable pores and vertical channels, including a container for storing seawater to be evaporated. A heat-absorbing and heat-conducting layer floating on the seawater to be evaporated is arranged in the container. A columnar three-dimensional evaporation component for continuously evaporating seawater is arranged on the heat-absorbing and heat-conducting layer. The columnar three-dimensional evaporation component extends downward through the lower surface of the heat-absorbing and heat-conducting layer and extends below the seawater surface. And a fixing device for connecting the columnar three-dimensional evaporation component to the heat-absorbing and heat-conducting layer. Heat-insulating layers are respectively arranged on the surfaces of the side wall and the bottom of the container.

[0012] For the above-mentioned solar interface evaporator with adjustable pores and vertical channels, the columnar three-dimensional evaporation component is composed of a number of short fibers arranged vertically in combination, and the protruding length of the short fibers on the surface of the heat-absorbing and heat-conducting layer is 1-3 cm.

[0013] For the above-mentioned solar interface evaporator with adjustable pores and vertical channels, the columnar three-dimensional evaporation component is composed of 240-280 short fibers arranged vertically in combination. The diameter of the short fibers is 0.5-1.1 mm, and the porosity between the short fibers is 3%-15%.

[0014] For the above-mentioned solar interface evaporator with adjustable pores and vertical channels, the fixing device includes an upper clamping member and a lower clamping member respectively arranged on the surface and the bottom surface of the heat-absorbing and heat-conducting layer, and a fastening screw passing through the heat-absorbing and heat-conducting layer for locking the upper and lower clamping members. A plurality of limiting support rods for longitudinally restricting the short fibers are arranged upward on the upper clamping member along the vertical direction, and a plurality of locking members for laterally restricting the short fibers are arranged on the limiting support rods.

[0015] For the above-mentioned solar interface evaporator with adjustable pores and vertical channels, the surface of the limiting support rod is provided with grooves for snap-fitting and positioning with the locking members, and a plurality of grooves are arranged along the length direction of the limiting support rod.

[0016] For the above-mentioned solar interface evaporator with adjustable pores and vertical channels, the upper and lower clamping members are of an annular structure, and the limiting support rods are uniformly arranged along the axial direction of the annular structure and fixedly connected to the annular structure.

[0017] For the above-mentioned solar interface evaporator with adjustable pores and vertical channels, the heat-absorbing and heat-conducting layer is black honeycomb Oxford cloth, and the heat-insulating layer is foam.

[0018] The above-mentioned solar interface evaporator with adjustable pores and vertical channels, wherein the short fibers are composite hydrogel fibers, which are prepared and cut by wet spinning technology, and the preparation method comprises the following steps:

[0019] (1) Put sodium alginate powder into deionized water in 2 - 4 times and mix to obtain a mixed solution with a mass fraction of 40 - 60 g / L;

[0020] (2) Stir strongly at a speed of 300 - 400 r / min until the sodium alginate powder is completely dissolved, and then carry out primary defoaming for 1 h at a speed of 150 - 250 r / min to obtain a sodium alginate solution;

[0021] (3) Add an MXene suspension with a mass fraction of 40 - 60 mg / mL to the sodium alginate solution to obtain a sodium alginate / MXene mixed solution with a mass fraction of 40 - 60 g / L, wherein the volume ratio of the sodium alginate solution to the MXene solution is 14:1;

[0022] (4) Continue to stir for 20 - 40 min until the sodium alginate / MXene mixed solution is fully mixed, and after stirring, perform ultrasonic treatment for 30 min for secondary defoaming to obtain a sodium alginate / MXene spinning solution;

[0023] (5) Load the sodium alginate / MXene spinning solution into a syringe, and use a micro-injection pump to press the spinning stock solution out of the spinneret needle at a speed of 0.5 - 0.7 mms -1 to form a thin stream, and enter a coagulation bath with a concentration of 5 - 15 wt% of CaCl 2 to form uniform gel fibers, and collect the generated gel fibers;

[0024] (6) Crosslink the collected gel fibers with glutaraldehyde for 6 - 10 h secondarily, and then soak and wash them in deionized water to obtain composite hydrogel fibers.

[0025] For the above-mentioned solar interface evaporator with adjustable pores and vertical channels, in the step (5), the extrusion speed of the micro-injection pump is 0.6 mms -1 , and the concentration of the CaCl 2 coagulation bath is 10 wt%.

[0026] For the above-mentioned solar interface evaporator with adjustable pores and vertical channels, the swelling ratio of the composite hydrogel fiber is 700 - 900%, the saturated water content is 85 - 95%, and the fiber toughness is 2 - 2.6 MJ / m 3 .

[0027] The advantages of the solar interface evaporator with adjustable pores and vertical channels in the present invention are as follows: Based on physically cross-linked hydrogels, combined with the wet spinning technology in textile production processes, using sodium alginate and MXene as the spinning dope and calcium chloride as the coagulation bath to prepare composite hydrogel fibers, and further assembling them into a hydrogel fiber evaporator with vertical channels. During the water transport process in the evaporator, the dual effects of the multi-level pores inside the hydrogel fibers and the capillary effect between the fibers endow the evaporator with excellent water transport performance. By adjusting the number of fibers in the evaporator, the optimal porosity of the capillary effect between the fibers is determined, thus having sufficient water supply, a high evaporation rate, and timely salt reflux. Compared with the traditional heat insulation model, the present invention adopts a heat supply / heat insulation model, with the "thermal evaporation" theory as the inventive concept, using honeycomb Oxford cloth as the heat source to heat bulk water for supplying heat to the evaporator, and white foam to prevent the heated bulk water from dissipating heat. After testing, the evaporation rates of a 3-cm evaporator in the heat insulation model and the heat supply / model are 3.62 kgm -2 h -1 and 8.09 kgm -2 h -1， respectively. The evaporation system combines a condensation device and conducts an outdoor experiment for 9 h, and the evaporation amount reaches 64.74 kgm -2 (the maximum solar irradiance is 0.67 KWm -2 ). It realizes efficient water transport, a high evaporation rate, and large-scale production. Combined with the heat supply / heat insulation model, it may greatly promote the popularization in practical applications in the future. Based on the existing hydrogel evaporation materials, the evaporation rate and salt tolerance durability of the evaporator are maximally improved, and efficient water transport rate and large-scale production are achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of the external structure of the solar interface evaporator of the present invention;

[0029] Figure 2 is Figure 1 a partially enlarged view of part A in

[0030] Figure 3 is a schematic diagram of the full cross-sectional structure of the solar interface evaporator of the present invention;

[0031] Figure 4 is Figure 2 a partially enlarged view of part B in

[0032] Figure 5 is a schematic diagram of the preparation process and application of the composite hydrogel fiber of the present invention;

[0033] Figure 6 is a morphology diagram of the composite hydrogel fiber prepared in Example 2 of the present invention;

[0034] Figure 7 EDS elemental distribution map of the composite hydrogel fiber prepared in Example 2 of the present invention;

[0035] Figure 8 FTIR image of the composite hydrogel fiber prepared in Example 2 of the present invention;

[0036] Figure 9 High-resolution XPS spectra of C1s, Ti2p, Cl2p, Ca2p and O1s in the composite hydrogel fiber prepared in Example 2 of the present invention;

[0037] Figure 10 Water transmission rate test diagrams of composite hydrogel fibers with porosity of 3%, 10% and 15% respectively;

[0038] Figure 11 In which, b is the ultraviolet-visible-near-infrared absorption spectrum of SHF and SMHF evaporators, and c is the test diagram of the temperature change at the top of the evaporator under one sunlight irradiation;

[0039] Figure 12 In which, d is the reflection schematic diagram of incident light entering the interior of the evaporator, e is the infrared image of the top of the SMHF-P10 evaporator under one sunlight for 200 s, and f is the heat insulation, heat supply and heat supply / heat insulation model image;

[0040] Figure 13 Infrared images of the heat insulation and heat supply / heat insulation models under one sunlight irradiation;

[0041] Figure 14 Evaporation mass change diagrams of heat insulation, heat supply and heat supply / heat insulation models at different heights (0, 1, 2 and 3 cm) under one sunlight irradiation;

[0042] Figure 15 In which, e is the bulk water temperature change trend diagram of different evaporation models, and f is the water weight loss test diagram of the SMHF-P1 evaporator under different simulated sunlight irradiations;

[0043] Figure 16 In which, g is the water weight loss diagram of the SMHF-P10 evaporator at different salt concentrations, and h is the schematic diagram of salt reflux in the evaporator;

[0044] Figure 17 In which, i is the self-cleaning dissolution test diagram of NaCl on the surface of the SMHF-P10 evaporator, and j is the performance comparison diagram of the SMHF-P10 evaporator and other three-dimensional evaporators. Detailed implementation manners

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "front end", "back end", "both ends", "one end", "the other end", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0047] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" 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 directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] As Figures 1-4 shown, a solar interface evaporator with adjustable pores and vertical channels includes a container 2 for storing seawater 1 to be evaporated. An endothermic and heat-conducting layer 3 floating on the seawater 1 to be evaporated is arranged in the container 2, and the endothermic and heat-conducting layer 3 is a black honeycomb Oxford cloth. A columnar three-dimensional evaporation component 4 for continuously evaporating seawater is arranged on the endothermic and heat-conducting layer 3. The columnar three-dimensional evaporation component 4 extends downward through the lower surface of the endothermic and heat-conducting layer 3 and extends below the seawater surface, and a fixing device 5 for connecting the columnar three-dimensional evaporation component 4 to the endothermic and heat-conducting layer 3. Heat-insulating layers 6 are respectively arranged on the side wall and the bottom surface of the container 2, and the heat-insulating layer 6 is foam.

[0049] The columnar three-dimensional evaporation component 4 is composed of a number of short fibers 7 arranged vertically. The protruding length of the short fibers 7 on the surface of the heat absorption and heat conduction layer 3 is 1-3 cm. Specifically, the columnar three-dimensional evaporation component 4 of the present invention is composed of 240-280 short fibers 7 arranged vertically, among which, 260 is preferred. The diameter of the short fiber 7 is 0.5-1.1 mm, and the porosity between the short fibers 7 is 3%-15%. The fixing device 5 includes an upper clamping member 8 and a lower clamping member 9 respectively arranged on the surface and the bottom surface of the heat absorption and heat conduction layer 3, and a fastening screw 10 passing through the heat absorption and heat conduction layer 3 for locking the upper clamping member 8 and the lower clamping member 9. A plurality of limiting support rods 11 for longitudinally restricting the short fibers 7 are arranged upward on the upper clamping member 8 in the vertical direction, and a plurality of locking members 12 for laterally restricting the short fibers 7 are arranged on the limiting support rods 11. The surface of the limiting support rod 11 is provided with grooves for snap-fitting and positioning with the locking member 12, and a plurality of grooves are arranged along the length direction of the limiting support rod 11. Since the grooves are snap-fitted and installed with the locking member 12, they are not marked in the drawings. In the present invention, the upper clamping member 8 and the lower clamping member 9 are of an annular structure, and the limiting support rods 11 are uniformly arranged along the axial direction of the annular structure and are fixedly connected to the annular structure.

[0050] Due to the special working environment of the present invention, in order to avoid the influence of seawater corrosion on the service life of the evaporator, components such as the upper clamping member 8, the lower clamping member 9, the limiting support rod 11, and the locking member 12 are all made of materials such as polyethylene or PVC. The limiting support rod 11 and the upper clamping member 8 can be integrally manufactured or connected by conventional component connection techniques such as binding. At the same time, the locking member 12 can be made of conventional elastic or inelastic materials such as elastic ropes and plastic snap rings. By adjusting the lateral binding force of the locking member 12 on the short fiber cluster, the porosity between the short fibers 7 can be flexibly adjusted in cooperation with the number of short fibers 7. The overall structure of the fixing device 5 used for restricting the short fibers 7 in the present invention has no obstruction to the conduction, convection and radiation of sunlight, and does not affect the lateral evaporation of seawater, effectively ensuring the optimal seawater evaporation efficiency and evaporation speed.

[0051] The black honeycomb Oxford cloth is used as a heating source to preheat the bulk water during the evaporation process, promoting evaporation during the water transfer process. The white foam is used as a heat insulation material. After the bulk water is heated, it prevents the heat of the bulk water from dissipating into the air, ensuring that the bulk water has a relatively high temperature and enhancing the evaporation rate. When the temperature of the Oxford cloth rises to heat the bulk water, due to the temperature gradient, the hydrogel fiber evaporator will spontaneously absorb heat from the Oxford cloth and the bulk water, converting the cold evaporation on the side and bottom of the evaporator into hot evaporation. As the evaporation proceeds and heat is lost, the temperature of the evaporator decreases, and the side of the evaporator becomes cold evaporation again. Compared with traditional heat insulation models and heat supply models, the honeycomb Oxford cloth heating the bulk water is beneficial to increasing the heat absorption of the evaporator and hot evaporation during the water transfer process, further demonstrating the superiority of the white foam in preventing heat loss of the bulk water and highlighting the advantages of the heat supply model by maintaining the high temperature of the bulk water.

[0052] As Figure 5 shown, a preparation method of a composite hydrogel fiber for solar seawater desalination includes the following steps:

[0053] (1) Put the sodium alginate powder into deionized water in 2 - 4 portions and mix to obtain a mixed solution with a mass fraction of 40 - 60 g / L.

[0054] (2) Stir vigorously at a speed of 300 - 400 r / min until the sodium alginate powder is completely dissolved, and then perform primary defoaming for 1 h at a speed of 150 - 250 r / min to obtain a sodium alginate solution.

[0055] (3) Add an MXene suspension with a mass fraction of 40 - 60 mg / mL to the sodium alginate solution to obtain a sodium alginate / MXene mixed solution with a mass fraction of 40 - 60 g / L.

[0056] (4) Continue stirring for 20 - 40 min until the sodium alginate / MXene mixed solution is fully mixed. After stirring, perform ultrasonic treatment for 30 min for secondary defoaming to obtain a sodium alginate / MXene spinning solution.

[0057] (5) Load the sodium alginate / MXene spinning solution into a syringe, and use a microinjection pump to press the spinning stock solution out of the spinneret needle to form a thin stream, which enters the CaCl 2 coagulation bath to form uniform gel fibers, and collect the generated gel fibers; there is no action of any drawing force during the fiber generation and collection process.

[0058] (6) Crosslink the collected gel fibers with glutaraldehyde for 6 - 10 h for the second time, and then soak and wash them in deionized water to obtain the composite hydrogel fiber.

[0059] The information of the additives used in the present invention is as follows: Ti3C2Tx (MXene, 50 mg / ml, Jinan Sanchuan), sodium alginate (SA, 280 mPa·s, Qingdao Haizhilin), calcium chloride (CaCl 2 , 96%, Sinopharm Chemical Reagent Co., Ltd.). All the chemical reagents used meet the analytical purity standard and can be directly applied to the experiment without additional purification treatment.

[0060] The present invention adopts the mature wet spinning method in the textile industry to prepare continuous hydrogel fibers. As Figure 1 shown, using sodium alginate and MXene as the spinning dope and calcium chloride solution as the coagulation bath, the preparation process has the advantages of high coagulation efficiency, low cost, environmental friendliness and safety, and easy large-scale production. The G unit (α-L-guluronic acid unit) in the sodium alginate molecular chain contains some freely movable carboxylic acid groups (-COO - ), and the ends of MXene are rich in polar functional groups such as hydroxyl (-OH) and oxygen (-O). After mixing, hydrogen bonds will be formed, and at the same time, physical entanglement of the long molecular chains of sodium alginate may occur between the MXene sheets. The combined action of these forces can enhance the dispersibility and stability of the mixed solution system. When contacting with polyvalent cation Ca 2+ , the carboxylic acid groups on the G unit of sodium alginate combine with calcium ions, forming stable bridges between the molecular chains and constructing a three-dimensional network structure. This physical cross-linking process is the key step in forming the hydrogel. In the present invention, the strength of the hydrogel fiber is further increased by increasing the solution concentration to increase the cross-linking points inside the hydrogel fiber.

[0061] Utilizing the solar-driven interfacial evaporation technology (SDIE) combined with the low evaporation enthalpy of the hydrogel is one of the key ways to solve the fresh water crisis. The prepared sodium alginate / MXene hydrogel fiber, due to the dual effects of the porous structure inside the fiber and the capillary force between the fibers, can endow the SMHF evaporator with efficient water transport performance. The excellent water transport performance can dissolve salt particles and return them to the bulk water due to multiple aspects. The hydrophilicity of the hydrogel fiber promotes the adsorption and diffusion of water molecules on the material surface. The porous structure inside the fiber allows water molecules to flow inside the fiber. At the same time, the capillary force caused by the reasonable fiber distance between the fibers enhances the speed and height of water transport, accelerating the movement of water and quickly dissolving salt particles. It solves the problem that the traditional hydrogel with a tight and tortuous water transport channel is not conducive to the water transport of SDIE and cannot timely transport the salt on the evaporation surface back to the bulk water, resulting in salt accumulation on the evaporation surface energy. At the same time, it avoids the defects that on the one hand, the salt accumulation blocks the light reaching the photothermal material of the evaporator, reducing the photothermal conversion efficiency and evaporation rate, and on the other hand, it also blocks the water supply and steam release of the evaporator water channel, reducing the performance of the evaporator and affecting the service life.

[0062] The present application will be specifically described below through specific embodiments. The following embodiments are only partial embodiments of the present application and do not limit the present application.

[0063] Example 1:

[0064] A preparation method of a composite hydrogel fiber for solar desalination of seawater, comprising the following steps:

[0065] (1) Put sodium alginate powder into deionized water in two portions and mix to obtain a mixed solution with a mass fraction of 40 g / L;

[0066] (2) Stir strongly at a speed of 300 r / min until the sodium alginate powder is completely dissolved, and then carry out primary defoaming for 1 h at a speed of 150 r / min to obtain a sodium alginate solution;

[0067] (3) Add an MXene suspension with a mass fraction of 40 mg / mL to the sodium alginate solution to obtain a sodium alginate / MXene mixed solution with a mass fraction of 40 g / L; wherein, the volume ratio of the sodium alginate solution to the MXene solution is 14:1;

[0068] (4) Continue stirring for 20 min until the sodium alginate / MXene mixed solution is fully mixed, and after stirring, perform ultrasonic treatment for 30 min for secondary defoaming to obtain a sodium alginate / MXene spinning solution;

[0069] (5) Load the sodium alginate / MXene spinning solution into a syringe, and use a micro-injection pump to press the spinning stock solution out of the spinneret needle to form a thin stream, which enters the CaCl 2 coagulation bath to form uniform gel fibers, and collect the generated gel fibers. There is no action of any drawing force during the fiber generation and collection process. The extrusion speed of the micro-injection pump is 0.5 mms -1 , and the concentration of the CaCl 2 coagulation bath is 5 wt%.

[0070] (6) Crosslink the collected gel fibers with glutaraldehyde for 6 h secondarily, and then soak and wash them in deionized water to obtain the composite hydrogel fiber.

[0071] The swelling ratio of the composite hydrogel fiber for solar desalination of seawater prepared in this example is 700%, the saturated water content is 85%, the fiber toughness is 2 MJ / m 3 , the diameter is 0.5 mm, and the measured tensile fracture stress is 2 MPa.

[0072] Example 2:

[0073] A preparation method of a composite hydrogel fiber for solar desalination, comprising the following steps:

[0074] (1) Put sodium alginate powder into deionized water in three portions and mix to obtain a mixed solution with a mass fraction of 50 g / L;

[0075] (2) Stir vigorously at a speed of 350 r / min until the sodium alginate powder is completely dissolved, and then perform primary defoaming for 1 h at a speed of 200 r / min to obtain a sodium alginate solution;

[0076] (3) Add an MXene suspension with a mass fraction of 50 mg / mL to the sodium alginate solution to obtain a sodium alginate / MXene mixed solution with a mass fraction of 50 g / L; wherein, the volume ratio of the sodium alginate solution to the MXene solution is 14:1;

[0077] (4) Continue stirring for 30 min until the sodium alginate / MXene mixed solution is fully mixed, and perform secondary degassing by ultrasonic treatment for 30 min after stirring to obtain a sodium alginate / MXene spinning solution;

[0078] (5) Load the sodium alginate / MXene spinning solution into a syringe, and use a micro-injection pump to press the spinning dope out of the spinneret needle to form a thin stream, which enters the CaCl 2 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. The extrusion speed of the micro-injection pump is 0.6 mms -1 and the concentration of the CaCl 2 coagulation bath is 10 wt%;

[0079] (6) Crosslink the collected gel fibers with glutaraldehyde for 8 h secondarily, and then soak and wash them in deionized water to obtain the composite hydrogel fiber.

[0080] The swelling ratio of the composite hydrogel fiber for solar desalination prepared in this example is 819%, the saturated water content is 89.1%, the fiber toughness is 2.34 MJ / m 3 and the diameter is 0.8 mm, and the measured tensile fracture stress is 4 MPa.

[0081] When the SA / MXene spinning dope is 1 wt%, the relatively low concentration and viscosity make it difficult to form continuous and stable hydrogel fibers when extruded from the spinneret needle. However, when the concentration and viscosity of the SA / MXene spinning dope are too high, it will cause difficulties in stirring the sodium alginate solution. In addition, Ca 2+The diffusion rate is slow, which affects the forming speed of the hydrogel fiber. Finally, the concentration of the SA / MXene mixed solution is determined to be 5 wt% (S1). By replacing the needle and adjusting the propulsion speed of the micro-injection pump, hydrogel fibers with diameters of 0.8, 1.5, and 2.5 mm can be prepared. Through preliminary experiments and considering subsequent pore adjustment problems, the diameter of the hydrogel fiber for assembling the evaporator is finally determined to be 0.8 mm, and the propulsion speed of the injection pump is 0.6 mm / s -1 .

[0082] Example 3:

[0083] A preparation method of a composite hydrogel fiber for solar seawater desalination, comprising the following steps:

[0084] (1) Put sodium alginate powder into deionized water in 4 portions and mix to obtain a mixed solution with a mass fraction of 60 g / L;

[0085] (2) Stir strongly at a speed of 400 r / min until the sodium alginate powder is completely dissolved, and then perform primary defoaming for 1 h at a speed of 250 r / min to obtain a sodium alginate solution;

[0086] (3) Add an MXene suspension with a mass fraction of 60 mg / mL to the sodium alginate solution to obtain a sodium alginate / MXene mixed solution with a mass fraction of 60 g / L; wherein, the volume ratio of the sodium alginate solution to the MXene solution is 14:1;

[0087] (4) Continue stirring for 40 min until the sodium alginate / MXene mixed solution is fully mixed. After stirring, perform ultrasonic treatment for 30 min for secondary defoaming to obtain a sodium alginate / MXene spinning solution;

[0088] (5) Load the sodium alginate / MXene spinning solution into a syringe, and use a micro-injection pump to press the spinning stock solution out of the spinneret needle to form a thin stream, which enters the CaCl 2 coagulation bath to form uniform gel fibers. The generated gel fibers are collected, and there is no stretching force during the fiber generation and collection process. The extrusion speed of the micro-injection pump is 0.7 mm / s -1 , CaCl 2 The concentration of the coagulation bath is 15 wt%;

[0089] (6) Crosslink the collected gel fibers with glutaraldehyde for 10 h for the second time, and then soak and wash them in deionized water to obtain the composite hydrogel fiber.

[0090] The swelling ratio of the composite hydrogel fiber for solar seawater desalination prepared in this example is 900%, the saturated water content is 95%, and the fiber toughness is 2.6 MJ / m 3, with a diameter of 1.1 mm, and the measured tensile fracture stress is 6 MPa.

[0091] The performance test results of the composite hydrogel fiber prepared by the preparation method described in Example 2 of the present invention and its specific applications are as follows:

[0092] As Figure 6 shown, where Figure 6 a is the SEM image of the surface of the SA / MXene hydrogel fiber, Figure 6 b-d are the SEM images of the cross-sectional pores of the SA / MXene hydrogel fiber, Figure 6 e is the SEM image of the outer wall of the SA / MXene hydrogel fiber. After freeze-drying the hydrogel fiber, the morphology of the SA / MXene hydrogel fiber was observed by scanning electron microscopy (SEM). As Figure 6 shown in a, the hydrogel fiber has a flat and smooth surface, proving the reliability and superiority of the wet spinning technology applied to the formation of hydrogel fibers. There are also some obvious lamellae (S4a, b) on the fiber surface, which may be formed by the embedding of MXene nanosheets into the hydrogel fiber. Figure 6 b-d show that the cross-section of the hydrogel fiber has circular or elliptical multi-level pores (S4c, d) with a size of 24-120 μm. The physical cross-linking of MXene and sodium alginate by Ca 2+ forms pore walls with a size of 1-15 μm, and a fiber outer wall of about 80 μm ( Figure 6 e). The outer wall of the SA@MX hydrogel fiber is flat and thick, and has a multi-level pore structure inside. On the one hand, it can endow the hydrogel fiber with excellent mechanical properties, and at the same time is beneficial to the water transport performance during the evaporation process. The relevant parameters of the hydrogel fiber, the swelling ratio (SR) and the saturated water content (SWC), can be calculated by the following formulas:

[0093]

[0094] where m s is the weight of the hydrogel fiber after swelling equilibrium during forming, and m d is the weight of the hydrogel fiber after complete drying. Taking the average value of multiple measurements, the swelling ratio (S5a) and the saturated water content (S5b) of the hydrogel fiber are calculated to be 819% and 89.1% respectively. It shows that the hydrogel fiber has excellent water absorption ability and porous structure. Although the swelling ratio of the hydrogel fiber is very high, it can still maintain the integrity of its structure through the cross-linking between internal molecular chains, and at the same time has excellent mechanical strength and mechanical properties. The hydrogel fiber with a diameter of only 0.8 mm can lift a 150 g weight, and the fracture stress can reach 4 MPa under the test of a tensile machine.

[0095] AsFigure 7 As shown, it can be clearly seen from the EDS image that elements such as Ca, O, and Ti are distributed on the fiber surface, and Ca 2+ crosslinks with the carboxyl ions in sodium alginate to form a hydrogel. The uniform distribution of Ca elements indicates that the crosslinking reaction proceeds relatively uniformly during the wet spinning process, further indicating that the hydrogel fiber forms a stable gel network structure. Among them, the Ti element only comes from MXene. The uniform distribution of the Ti element verifies the sufficient fusion of MXene and sodium alginate. The relatively concentrated element distribution may be caused by the distribution of larger-diameter MXene nanosheets on the fiber surface.

[0096] As Figure 8 shown, the molecular structures of SA hydrogel fibers and SA / MX hydrogel fibers were analyzed by Fourier transform infrared spectroscopy (FTIR). For SA hydrogel fibers, a broad peak appears at 3254 cm -1 , which is caused by the stretching vibration of hydroxyl groups (-OH). There are two asymmetric and symmetric stretching vibration peaks of COO -1 at 1593 cm -1 and 1413 cm - , and a C-O stretching vibration peak exists at 1030 cm -1 . After introducing MXene into SA hydrogel fibers, the positions of the peaks in the Fourier transform infrared spectroscopy curve change, and at the same time, the peaks broaden and the intensity weakens. The stretching vibration peak of the hydroxyl group of SA / MXene shifts, indicating that hydrogen bonds are formed between the terminal groups -O and -OH of MXene and COO- and -OH of sodium alginate. In addition, due to the addition of Ca 2+ , the coordination between -O and COO- of SA and Ca 2+ may cause changes in the width of the characteristic peaks. XPS technology was used to analyze the bonding and surface structure changes of the synthesized SA@MX. The appearance of the Ti element in the full XPS spectrum (S7) indicates the successful addition of MXene.

[0097] As Figure 9 shown, the disappearance of the Ti-C bond in the C1s spectrum proves the interaction between the molecular chain of sodium alginate and the MXene nanosheet. From the spectrum of Ti2p, characteristic peaks with binding energies at 455.2 eV, 456.8 eV, and 458.5 eV are observed, corresponding to Ti-C, Ti-O, and Ti-O 2. In the spectrum of Ca 2p, 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 usually weaker than that of the Ca 2p3 / 2 peak. For the XPS of Cl 2p, a peak is shown at a binding energy of 198.3 eV, which is attributed to the presence of Cl 2p3 / 2. This peak is 1.6 eV lower than the binding energy of Cl 2p1 / 2. These two elements exist in the form of Ca 2+ and Cl - in the SA@MX hydrogel fiber, simultaneously proving that calcium chloride as a coagulation bath promotes the successful synthesis of the hydrogel fiber. The O 1s spectral peaks at 529.8, 532.1, 531.2, 533.4, and 534.8 eV are C-Ti-O, C–Ti–(OH) x、 C=O and H 2 O ads , indicating that the bonding of Ti with the -OH groups in the alginate molecular chain produces binding bonds. Compared with alginate fibers, the hydroxyl peak of the mixed alginate fibers of MXene and alginate shifts to the low wave band, indicating that the alginate molecular chain is rich in carboxylic acid (COO-) and -OH groups, which can form hydrogen bond interactions with the terminal -O and -OH groups of MXene.

[0098] Excellent water transport performance can ensure the timely water supply to the interface evaporation surface, which is beneficial to improving the evaporation rate of the evaporator. The hydrophilicity of the hydrogel fiber refers to the ability to attract water, and it attracts water molecules through forces such as hydrogen bonds to promote adsorption and diffusion on the fiber surface. Using a water contact angle instrument for testing, it only takes 103 ms for the water droplet to be completely absorbed, indicating that the hydrogel fiber has excellent hydrophilicity. For vertical channel evaporators, generally, the hydrophilicity of the evaporator material is utilized to transport bulk water from bottom to top to the evaporator surface through capillary force. For the hydrogel fiber evaporator of the present invention, water transport depends on the combined action of the hierarchical pore structure of the fiber itself and the capillary force between the fibers. Among them, the capillary action is generated by the interaction (adhesion force) between the surface tension of the liquid and the solid surface, causing the liquid to rise or fall in small pores or narrow spaces. This effect enables bulk water to move upward along the surface when it contacts the surface of the hydrogel fiber for water transport, and it dominates the water transport process. Taking a PE ring with a diameter of 13.5 mm as the quantitative area, the influence of the porosity (P) of the evaporator on the water transport performance is determined by changing the number of internal fibers. According to the previous experimental comparison, finally, SHF evaporators with the same height of 3 cm but different porosities (P) are selected. Evaporators with porosities of 3%, 10%, and 15% (named SHF-P3, SHF-P10, and SHF-P15 respectively) are selected for research. As Figure 10As shown, the transport height of the dyed water in the SHF evaporator was compared. According to the capillary pressure and capillary rise equation:

[0099]

[0100] h = σcos(θ) / ρgR

[0101] where h is the height of the liquid rising 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 analogized to half of the fiber - to - fiber distance). According to the two equations, it can be known that both the capillary pressure Pc and the liquid rising height h are inversely proportional to the fiber spacing R, that is, the smaller the fiber spacing, the greater the capillary pressure and the liquid rising height. Comparing Figure 10 , after the evaporator void fraction is reduced from 15% to 10%, as the void fraction decreases, the fiber - to - fiber distance decreases, and the water transport height of the fibers is higher. However, when the evaporator void fraction is reduced to 3%, the water transport effect decreases instead. This is because in the porous fiber bundle evaporator, the capillary force between the 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. However, the increase in capillary pressure will also increase 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 the subsequent experiment.

[0102] As Figure 11 shown, in order to evaluate the light absorption ability of the evaporator, the light absorption characteristics of the SHF and SMHF evaporators in the ultraviolet - visible - near - infrared (UV - Vis - NiR) range were studied. As Figure 11 shown in b, compared with SHF, the addition of MXene endows SMHF with excellent light absorption ability, having a wide and strong light absorption rate in the range of 280 - 2500 nm, and showing extremely low reflectivity and transmittance. In addition, the porosity and vertical channels of the evaporator further promote the multiple scattering and absorption of sunlight by extending the propagation path of the incident light, as Figure 11 shown in c, indicating that this structural design effectively improves the ability to capture incident light. For solar - driven interfacial evaporation technology, the photothermal conversion performance of the evaporator interface plays a crucial role in increasing the evaporation rate.

[0103] As Figure 12 shown, a thermal imager was used to test and study the temperature rise of the hydrogel fiber evaporator ( Figure 12 e), under a simulated solar illumination intensity of one sun (1KWm -2) Under such conditions, the operating evaporator responds rapidly. The surface temperature rises rapidly to 25.5 °C within 5 s, continues to rise, and reaches about 30 °C around 180 s, and stabilizes at 30.2 °C at 200 s. The surface of the SA@MX hydrogel evaporator heats up rapidly in a short time, which fully demonstrates its excellent photothermal conversion ability. Figure 12 d). The excellent high conductivity of MXene and the abundant terminal functional groups (-OH, -O) exhibit excellent electromagnetic wave absorption ability. When the frequency of the incident light matches the plasma resonance frequency of MXene, local surface plasmon resonance (LSPR) will occur. This enables MXene to efficiently capture the radiant energy in sunlight and convert it into heat energy, enhancing the photothermal conversion efficiency. In addition, the vertical channel design of the hydrogel fiber evaporator can confine the heat in a smaller area, enhancing the local thermal effect on the evaporator surface and further improving the photothermal conversion efficiency.

[0104] The thermal conductivity of the materials was tested using the hot wire method. The thermal conductivities of the bulk hydrogel and the hydrogel fiber are 0.5641 and 0.1927 Wm-1K-1, respectively. Since the saturated water content of the hydrogel is as high as 89.1% (Figure S5b), the thermal conductivity of the bulk hydrogel is close to that of bulk water (0.6 Wm-1K-1). When hydrogel fibers with a diameter of only 0.8 mm are prepared and assembled into the SMHF evaporator, the thermal conductivity decreases due to the pores between the fibers (the thermal conductivity of air is approximately 0.026 Wm-1K-1). Therefore, the heat of the evaporator only stays on the surface of the evaporator irradiated by simulated sunlight without transferring downward, verifying the excellent performance of the vertical channel hydrogel evaporator in thermal localization. This thermal localization ability is crucial for improving the performance of solar evaporators because it effectively reduces heat loss, ensuring that most of the absorbed solar energy is directly used to heat the interfacial liquid, thus promoting the evaporation process and demonstrating excellent thermal management ability.

[0105] During the assembly of the evaporation system, a popular method is to adopt a thermal insulation model to separate the evaporator from the bulk water, reducing heat loss through conduction, convection, and radiation during evaporation. This not only improves the thermal efficiency of the entire system but also helps reduce additional energy consumption. However, in actual operation, the advantage of solar energy drive should be fully utilized and reflected in the entire evaporation system. In addition to using solar radiation for photothermal conversion at the evaporator interface, the extensive nature of solar radiation should also be used to heat the bulk water. For example Figure 12As shown, the present invention uses Oxford cloth with special honeycomb texture to maximize the absorption of sunlight to heat bulk water, uses white foam to reduce the heat loss of high-temperature bulk water, assembles a heat supply / heat insulation model, and uses traditional heat insulation models and heat supply models for comparison. According to the second law of thermodynamics, the surface temperature (T1) of the evaporator of the heat supply / heat insulation model is lower than the temperature of the bulk water (T2), and energy tends to transfer from high temperature to low temperature. Therefore, when the temperature of the Oxford cloth rises to heat the bulk water, due to the temperature gradient, the hydrogel fiber evaporator will spontaneously absorb heat from the Oxford cloth and the bulk water, changing the cold evaporation on the bottom side of the evaporator to hot evaporation. As evaporation proceeds and heat is lost, the temperature of the evaporator decreases, and the side of the evaporator becomes cold evaporation again. In COMSOL, a model of the fiber spacing was built according to the porosity and assembled into an evaporator, and numerical simulation was used to calculate the pressure and heat transfer of the SMHF-P10 evaporator. Figure 12 As shown, the water pressure distribution shows that the SMHF-P10 evaporator generates surface negative pressure, which combines with the capillary force between the fibers to jointly drive the water transport in the channel.

[0106] As Figure 13 shown, the numerical simulation of the steady-state temperature distribution of the SMHF-P10 evaporator was carried out through a porous medium heat transfer model, and the simulation results are close to the experimental results. This further illustrates that the reasonable design of the vertical channels and the fiber spacing promotes the water transport and excellent photothermal performance of the SMHF-P10 evaporator.

[0107] In the heat supply / heat insulation model, the honeycomb Oxford cloth is the heat source, and the white foam is the heat insulation model. In the previous experiment, during the water transport process of the heat supply / heat insulation model, part of the bulk water was used for the hot evaporation on the side of the evaporator, thus reducing the surface water transfer rate. Therefore, when the height is greater than 3.5 cm, the surface will dry out due to insufficient water supply. Therefore, SMHF-P10 hydrogel fiber evaporators with heights of 0 cm, 1 cm, 2 cm, and 3 cm were designed, and the evaporation rates of different evaporation models were measured under a simulated solar light intensity. As Figure 14 shown, as the height increases, the evaporation rate also increases. This is because for a three-dimensional evaporator, under the condition of the same projected area, the side area provides an additional water / air interface, and the higher the height, the larger the evaporation area, which greatly improves the evaporation rate of the evaporator. Evaporation tests were carried out on evaporators with different porosities, and the evaporation rates of 3%, 10%, and 15% were 7.71 kg m-2 h-1, 8.09 kg m-2 h-1, and 7.0 kg m-2 h-1 respectively, further proving the superiority of the 10% porosity evaporator. Water evaporation experiments were carried out using SHF-P10 and SMHF-P10 materials, and the evaporation rates were 5.02 kg m-2 h-1 and 8.09 kg m-2 h-1 respectively ( Figure 14) demonstrated the positive role of MXene photothermal materials in promoting solar-driven interfacial evaporation. At the same time, the evaporation rates of the evaporation models from large to small are the heat supply / heat insulation model, the heat supply model, and the heat insulation model, with evaporation rates of 8.09, 5.49, and 3.62 kg m-2 h-1, respectively. This indicates that compared with the heat insulation model and the heat supply model, the honeycomb Oxford cloth heating of bulk water is beneficial to increasing the heat absorption of the evaporator and the thermal evaporation during the water transfer process, and more reflects the superiority of the white foam in preventing the heat loss of bulk water, highlighting the advantage of the heat supply model by maintaining the high temperature of bulk water.

[0108] As Figure 15 shown, the advantage of the heat supply / heat insulation system is also reflected in its ability to extend the high evaporation rate. As Figure 15 shown in e, the heating of bulk water in different evaporation systems was recorded. After a period of irradiation, the stable temperatures of the heat insulation model, the heat supply model, and the heat supply / heat insulation model were 26, 38.7, and 45.6 °C, respectively. For the two heat supply systems, after turning off the simulated sunlight, the evaporation rate of bulk water can still be maintained higher than that of the heat insulation system during the cooling process. This performance is beneficial to the potential of the evaporator in practical applications. In addition, in many studies, in order to demonstrate the superiority of the evaporator performance, relatively high solar irradiances (2, 3, 4, 5 sun) are often used for water evaporation tests, and there are very few studies on low solar irradiances. However, in the actual natural environment, the maximum solar irradiance in most areas is usually around 0.8 KW m-2. Therefore, it is particularly important for the evaporation system to still have a high evaporation rate under low solar irradiances. As Figure 15 shown in f, the present invention simulated low solar irradiances (0.8, 0.6, 0.4, 0.2 KW m-2) for experiments. As the solar irradiance decreased, the evaporation rates were 8.09 (45.6 °C), 6.45 (39.8 °C), 5.92 (35.3 °C), 4.36 (33 °C), 2.95 (30.2 °C) kg m-2 h-1, respectively. The evaporation rate of 4.36 kg m-2 h-1 of the heat supply / heat insulation system under 0.4 KW m-2 simulated sunlight exceeded the evaporation rate of 3.62 kg m-2 h-1 of the heat insulation system under 1 KW m-2 simulated sunlight. These tests further fully demonstrated the superiority of the heat supply / heat insulation system compared with the heat insulation system and its great potential in practical applications in the natural environment.

[0109] As Figure 16As shown, the heating / thermal insulation model significantly improves the evaporation rate through the combined action of multiple aspects. Therefore, the salt tolerance of the evaporator is crucial. In practical applications, salt crystallization can prevent sunlight from reaching the evaporator surface, weaken the effect of the evaporator capturing and converting solar energy, and lead to a decrease in the overall photothermal conversion efficiency. At the same time, it may also block the water transmission channels for evaporation and the paths for steam escape, affecting the continuity of the seawater desalination process. Under simulated solar irradiance intensity, the evaporation rates of the SMHF-P10 evaporator in pure water, 3.5 wt% brine, and 10 wt% brine are 8.09, 8.04, and 7.02 kg m-2 h-1( Figure 16 g, h). Ten-hour (10 times) water evaporation experiments were continuously carried out, and the average water evaporation rates of 3.5 wt% brine and 10 wt% brine are 7.8 and 7.4 kg m-2 h-1, respectively. In the 3.5 wt% brine with less salt, the water evaporation rate fluctuates less. In the 10 wt% brine, the evaporation rate decreases with time, and the lowest evaporation rate is 6.79 kg m-2 h-1 at the 8th hour of the experiment, and then it starts to increase. The higher evaporation rate and the phenomenon of first decreasing and then increasing of the SMHF-10 evaporator are because after the surface steam escapes under the action of photothermal conversion, salt ions are left behind. As evaporation proceeds, the concentration at the evaporation interface of the evaporator approaches saturation, creating a concentration difference with the bottom bulk water. These differences cause a surface tension gradient to form between the surface and the bottom of the evaporator. Under the Marangoni effect, the surface tension gradient drives the flow of water, transferring salt from the evaporation area to the bulk water through water reflux, keeping the salt concentration on the evaporation surface always below the saturation value and avoiding the appearance of salt crystallization. The present invention also simulates the situation of alternating day and night tests during actual operation. Taking 10 wt% as an example, the evaporation rate of the evaporator decreases from 8.02 to 7.27 kg m-2 h-1 after 10 h, and then it undergoes dark evaporation for 10 h under dark conditions. At this time, the process of salt ion dissolution and reflux to the bulk water is still ongoing, and the evaporation rate returns to 7.95 kg m-2 h-1 the next day. This phenomenon indicates that the evaporator has strong self-cleaning ability, stability, and durability in the heating / thermal insulation model. Therefore, even after continuous evaporation for 10 h in 10 wt% concentrated brine, the evaporation surface still remains wet, and no salt crystallization precipitates, further demonstrating the excellent salt tolerance of the vertical channel hydrogel evaporator.

[0110] As Figure 17 shown, the same mass of NaCl particles is placed on the evaporator surface to evaluate the self-cleaning of the SMHF-P3, SMHF-P10, and SMHF-P15 evaporators. From Figure 17As can be seen from i-j, the NaCl particles on the surface of SMHF-P10 significantly decreased and dissolved into the bulk water within 5 minutes, while only surface wetting occurred for the NaCl particles of SA@MX-3% and SA@MX-15%. The excellent water transport performance of SMHF-P10, which can dissolve salt particles and reflux them to the bulk water, is attributed to multiple aspects. The hydrophilicity of the hydrogel fibers promotes the adsorption and diffusion of water molecules on the material surface. The porous structure inside the fibers enables water molecules to flow inside the fibers. At the same time, the capillary force caused by the reasonable fiber distance between the fibers enhances the speed and height of water transport, accelerates the movement of water, and rapidly dissolves salt particles. By comparison, the SMHF-P10 hydrogel fiber evaporator of the present invention combines a heat supply / heat insulation model, and has obvious advantages in evaporation rate among three-dimensional evaporators. This performance improvement is mainly due to the characteristics of the hydrogel material, the vertical channels of the evaporator, the integrated design of the heat supply / heat insulation model and other factors.

[0111] In summary, the present invention prepares hydrogel fibers with multi-level pores and further assembles them into a three-dimensional evaporator with vertical channels. Combining with the wet spinning technology of the textile industry is conducive to realizing the continuous preparation of hydrogel fibers and large-scale applications in production and life. The fiber vertical array helps to reflect sunlight multiple times, improving the photothermal conversion efficiency and confining the heat to the surface of the evaporator. Introducing MXene as a photothermal material enables the evaporator to have photothermal conversion properties and at the same time promotes the activation of water in the polymer network to reduce the evaporation enthalpy. Finally, for the efficient utilization of solar energy, a heat supply / heat insulation model is innovatively constructed. The honeycomb Oxford cloth is used as a heat source to preheat the bulk water in advance, and the white foam is used as a heat insulation material for heat preservation. This model enables the three-dimensional evaporator to obtain a maximum of 0.008 W of energy from the outside world. The bottom of the evaporator absorbs heat from the high-temperature bulk water, making part of the side cold evaporation become hot evaporation with a high evaporation rate. Part of the side can still absorb additional energy from the surrounding environment for cold evaporation. The evaporation rate of this evaporation model under one sun illumination is 8.09 kg m -2 h -1 , and continuous evaporation outdoors for 7 hours results in an evaporation amount as high as 67.47 kg m -2 . Under the combined action of the multi-level voids inside the fibers and the capillary force between the fibers, the evaporator can still ensure timely water supply at the top of the evaporator under the influence of side hot evaporation. It can continuously evaporate for ten hours (1 sun) in 10 wt% salt water without salt crystallization on the surface, showing excellent self-cleaning ability. The design and application of the heat supply / heat insulation model provide a new assembly idea for the three-dimensional evaporator, maximizing the advantage that the three-dimensional evaporator can obtain additional energy from the surrounding environment and the bulk water.

[0112] Certainly, the above description is not a limitation of the present invention, nor is the present invention limited to the above examples. Those of ordinary skill in the art, within the scope of the essence of the present invention, any changes, modifications, additions or substitutions should fall within the protection scope of the present invention.

Claims

1. A solar interface evaporator with adjustable pores and vertical channels, comprising a container for storing seawater to be evaporated, characterized in that: The container is provided with a heat-absorbing and heat-conducting layer floating on the seawater to be evaporated, a columnar three-dimensional evaporation component for continuously evaporating the seawater is provided on the heat-absorbing and heat-conducting layer, the columnar three-dimensional evaporation component extends downward through the lower surface of the heat-absorbing and heat-conducting layer to below the surface of the seawater, and a fixing device for connecting the columnar three-dimensional evaporation component to the heat-absorbing and heat-conducting layer, and heat insulation layers are respectively provided on the surfaces of the side walls and the bottom of the container.

2. The solar interface evaporator with adjustable pores and vertical channels according to claim 1, characterized in that: The columnar three-dimensional evaporation component is composed of a plurality of short fibers arranged vertically, and the protruding length of the short fibers on the surface of the heat absorption and heat conduction layer is 1-3 cm.

3. The solar interface evaporator with adjustable pores and vertical channels according to claim 2, characterized in that: The columnar three-dimensional evaporation component is composed of 240-280 short fibers arranged vertically, the diameter of the short fibers is 0.5-1.1 mm, and the void ratio between the short fibers is 3%-15%.

4. The solar interface evaporator with adjustable pores and vertical channels according to claim 1, characterized in that: The fixing device includes an upper clamping piece and a lower clamping piece respectively arranged on the surface and bottom surface of the heat-absorbing and heat-conducting layer, and a fastening screw passing through the heat-absorbing and heat-conducting layer for locking the upper and lower clamping pieces. A plurality of limiting support rods for longitudinally restraining the short fibers are arranged on the upper clamping piece along the vertical direction and extending upward, and a plurality of locking pieces for transversely restraining the short fibers are arranged on the limiting support rods.

5. The solar interface evaporator with adjustable pores and vertical channels according to claim 4, characterized in that: A groove for clamping and positioning with the locking piece is provided on the surface of the position-limiting support rod, and a plurality of grooves are provided along the length direction of the position-limiting support rod.

6. The solar interface evaporator with adjustable pores and vertical channels according to claim 4, characterized in that: The upper and lower clamping members are annular structures, and the limiting support rods are evenly arranged along the axial direction of the annular structure and are fixedly connected to the annular structure.

7. The solar interface evaporator with adjustable pores and vertical channels according to claim 1, characterized in that: The heat-absorbing and heat-conducting layer is black honeycomb Oxford cloth, and the heat-insulating layer is foam.

8. The solar interface evaporator with adjustable pores and vertical channels according to any one of claims 1 to 7, characterized in that: The short fibers are composite hydrogel fibers, which are prepared and cut by wet spinning technology, and the preparation method thereof comprises the following steps: (1) Add sodium alginate powder into deionized water 2-4 times and mix to obtain a mixed solution with a mass fraction of 40-60 g / L; (2) Stir vigorously at a speed of 300-400 r / min until the sodium alginate powder is completely dissolved, and then perform initial defoaming at a speed of 150-250 r / min for 1 hour to obtain a sodium alginate solution; (3) adding a MXene suspension having a mass fraction of 40-60 mg / mL to the sodium alginate solution to obtain a sodium alginate / MXene mixed solution having a mass fraction of 40-60 g / L, wherein the volume ratio of the sodium alginate solution to the MXene solution is 14:1; (4) Continue stirring for 20-40 min until the sodium alginate / MXene mixed solution is fully mixed. After the stirring is completed, perform secondary degassing by ultrasonication for 30 min to obtain a sodium alginate / MXene spinning solution; (5) Load the sodium alginate / MXene spinning solution into a syringe and use a microinjection pump at a speed of 0.5-0.7 mms -1 The spinning solution is pressed out from the spinneret at a speed to form a thin stream, which enters a CaCl2 coagulation bath with a concentration of 5-15wt% to form a uniform gel fiber, and the generated gel fiber is collected; (6) The collected gel fibers were cross-linked with glutaraldehyde for 6-10 hours, and then immersed in deionized water for washing to obtain composite hydrogel fibers.

9. The solar interface evaporator with adjustable pores and vertical channels according to claim 5, characterized in that: In step (5), the extrusion speed of the microinjection pump is 0.6 mms -1 , the concentration of CaCl2 coagulation bath is 10wt%.

10. The solar interface evaporator with adjustable pores and vertical channels according to claim 8, characterized in that: 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 .

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