A functionally layered monolithic gel solar evaporator and its preparation method and application

Abstract

The present application relates to the technical field of high-salinity wastewater treatment, and discloses a functionally layered integral gel solar evaporator as well as a preparation method and application thereof. The evaporator comprises, from top to bottom, a photothermal evaporation top layer, a heat storage middle layer and a water transmission bottom layer. The photothermal evaporation top layer is an oil-water dual-phase gel structure, and the oil phase containing a photothermal material is loaded in the water phase hydrophilic polymer network. The heat storage middle layer is also an oil-water dual-phase gel structure, and a phase change material is encapsulated in the oil phase droplets. The water transmission bottom layer is a single-phase hydrogel structure. The photothermal evaporation top layer, the heat storage middle layer and the water transmission bottom layer are simultaneously polymerized into an integral structure in situ in the vertical direction from a precursor solution. The present application polymerizes in situ by a one-pot method, and connects the functional layers into an integral whole without a physical interface through firm chemical bonds, so that the evaporator has excellent mechanical strength and chemical resistance, and can work stably in complex shale gas fracturing flowback fluid for a long time without delamination, swelling or degradation.

Description

Technical Field

[0001] This invention relates to the field of high-salt wastewater treatment technology, and more specifically, to a functionally layered integral gel solar evaporator, its preparation method, and its application. Background Technology

[0002] While hydraulic fracturing technology, heavily relied upon for shale gas development, brings enormous production, it also generates massive amounts of fracturing flowback fluid with extremely complex compositions. This flowback fluid is generally characterized by "three highs" (high suspended solids (SS), high total dissolved solids (TDS), and high chemical oxygen demand (COD), with its TDS often reaching tens of thousands of mg / L, and is widely recognized as one of the most difficult industrial wastewaters to treat.

[0003] Currently, there are two main types of technologies for the "zero discharge" treatment of such high-salinity wastewater: (1) Membrane technology (such as reverse osmosis, RO): Although membrane technology is mature in the conventional desalination field, when treating complex fracturing flowback fluid, its membrane elements are easily polluted and clogged by high concentrations of organic matter, inorganic salts and suspended solids, resulting in a sharp reduction in treatment efficiency, high operating costs and shortened membrane life, making it difficult to meet the requirements of long-term stable operation. (2) Thermal technology (such as multi-effect evaporation MVR): Thermal technology has strong adaptability to water quality and good desalination effect, and is currently the main means of treating high-salinity wastewater. However, its core drawback is the high energy consumption.

[0004] In recent years, solar interfacial evaporation technology has emerged due to its use of clean energy and low energy consumption. This technology confines the photothermal conversion process to the liquid interface, effectively reducing bulk heat loss and improving evaporation efficiency. Generally, a solar interfacial evaporation system consists of the following main parts: a solar absorption layer, a thermal insulation layer, a water supply channel, and a steam dissipation channel. Besides achieving self-floating properties for interfacial thermal positioning, an ideal solar interfacial evaporation system should also possess the following characteristics based on the entire light-heat-steam process: high-efficiency absorption and heat conversion within the solar spectrum; good insulation to confine heat to the evaporation front; a hydrophilic porous structure to facilitate water transport; and the ability to activate water (reduce the enthalpy of vaporization). By improving these characteristics of the solar interfacial evaporation system through methods such as selection of solar materials, light-heat energy conversion process, thermal localization design, water supply regulation, interface engineering, and biomimetic design, and supplemented by a good steam condensation and recovery system, the evaporation rate can be effectively increased, achieving highly efficient solar interfacial evaporation.

[0005] However, most existing evaporators achieve breakthroughs in only one aspect, then physically integrate different functional layers into a complete solar evaporator. This fabrication process is cumbersome and unsuitable for large-scale production. Furthermore, gaps inevitably exist between materials with different functions during physical integration, making them susceptible to contamination by wastewater or brine, and leading to issues such as multilayer delamination and poor salt resistance, thus affecting the evaporator's lifespan. In terms of thermal management, almost all rely on insulating substrate materials to reduce heat loss, lacking new thermal management mechanisms to further improve heat utilization, and suffer from nighttime evaporation interruptions. Regarding the study of interfacial wettability evaporation mechanisms, current understanding remains significantly limited due to the randomness of interfacial hydrophobic modification.

[0006] Therefore, how to further improve the photothermal conversion efficiency, overcome the problem of salt accumulation during the evaporation of high-salt shale gas flowback fluid, how to ensure sufficient water supply under the condition of good thermal insulation of interfacial photothermal vapor conversion, and how to accurately control the interfacial structure, and develop devices that can meet the requirements of low production cost, large-scale production, environmental friendliness, greenness and long service life are the urgent problems to be solved in the field of photothermal interfacial evaporation.

[0007] In view of the above, this application is hereby submitted. Summary of the Invention

[0008] To address the problems of the prior art, this invention provides a functionally layered monolithic gel solar evaporator, its preparation method, and its application. This invention integrates multiple separate functions that would otherwise require physical assembly into a continuous, interface-free, seamlessly integrated monolithic gel block material from top to bottom. This material possesses photothermal conversion, heat management, and water / salt transport functions, achieving synergistic optimization of light absorption, heat storage, and water transport within the same system. This solves problems such as interlayer instability, poor salt resistance, and low energy utilization.

[0009] This invention is achieved through the following technical solution:

[0010] In a first aspect, the present invention provides a functional layered integral gel solar evaporator, comprising a photothermal evaporation top layer, a heat storage middle layer, and a water transport bottom layer arranged sequentially from top to bottom;

[0011] The photothermal evaporation top layer has an oil-water biphase gel structure, with oil-phase microdroplets of photothermal material loaded within a hydrophilic polymer network in the aqueous phase.

[0012] The heat storage intermediate layer has an oil-water biphase gel structure, and phase change materials are encapsulated in the microdroplets of the oil phase.

[0013] The water transport substrate is a single-phase hydrogel structure;

[0014] The photothermal evaporation top layer, the heat storage intermediate layer, and the water transport bottom layer are formed by the simultaneous in-situ polymerization of the precursor solutions of each layer in a vertical direction to create an integrated structure.

[0015] This invention transforms multiple separate functions (photothermal, heat insulation, heat storage, water pumping, and salt discharge) that originally required physical assembly into a continuous, interface-free, and internally integrated monolithic gel block material with photothermal conversion, heat management, and water and salt transport functions from top to bottom using chemical means. This achieves synergistic optimization of light absorption, heat storage, and water transport within the same system, solving problems such as interlayer instability, poor salt resistance, and low energy utilization.

[0016] The top layer of this invention, a photothermal evaporation layer, is an oil-water biphase gel structure. Its continuous hydrophilic polymer network disperses oil-phase microdroplets loaded with photothermal materials. This oil-water biphase gel structure differs from conventional oil-water biphase structures formed by network interpenetration or solvent miscibility. The oil-water biphase gel structure of this invention is a microphase separation structure formed on the basis of an emulsion system, in which oil droplets are dispersed in an island-like form within the aqueous phase. Its working principle is as follows: the photothermal material efficiently absorbs sunlight and converts it into heat energy, localizing it at the evaporation interface; simultaneously, the micro-hydrophobic regions constructed on the surface by the oil-phase microdroplets effectively reduce the enthalpy of water evaporation, increase the gas-liquid-solid three-phase contact line to accelerate water evaporation, and inhibit the initial nucleation of salt ions from the source.

[0017] Unlike existing post-modification techniques for functional layers using coupling agents or plasma treatment, this invention uses a functional precursor emulsion to introduce a hydrophobic oil phase into the top hydrogel of the photothermal evaporation layer. This creates island-like hydrophobic microregions at the evaporation interface, thereby modulating the hydrophilicity and hydrophobicity of the material surface and achieving pre-modification of the evaporation interface's hydrophilicity and hydrophobicity. The hydrophilic hydrogel top hydrogel with hydrophobic island-like microregions allows water to concentrate mainly in the hydrophilic regions, forming a water film with increased thickness. This weakens the interaction between the outermost water molecules and the hydrogel surface, making evaporation easier and enabling ultra-fast evaporation. At the same time, appropriate hydrophobicity does not affect water transport in the top hydrothermal evaporation layer, ensuring a continuous and sufficient supply of water molecules during interfacial evaporation, thus guaranteeing a stable and efficient evaporation rate and achieving a balance between heat localization and water transport.

[0018] The intermediate heat storage layer in the middle of this invention also has an oil-water biphase gel structure. Similar to the surface evaporation layer, it also embeds dispersed oil droplets in a continuous hydrogel network. The difference is that its oil phase microdroplets encapsulate phase change materials. Its working principle is as follows: During the day, this layer absorbs excess heat conducted from the top layer of photothermal evaporation and stores the energy as latent heat through the melting of the phase change material. At the same time, the oil phase component and the gel matrix together form a thermal barrier to prevent heat loss to the water below. At night, as the ambient temperature decreases, the phase change material solidifies and releases latent heat, providing heat feedback to the top evaporation interface and driving the continuous evaporation of water at night. This achieves a thermal management mechanism of storing heat during the day and releasing heat at night, maintaining continuous evaporation day and night, and realizing all-weather water production.

[0019] The bottom water transport layer of this invention is a single-phase porous hydrophilic hydrogel structure rich in interconnected micron-sized channels. Its working principle is as follows: through capillary action, source water at the bottom is continuously pumped to the top evaporation interface to meet the evaporation requirements; simultaneously, these open porous structures also provide efficient convection and diffusion channels for salt ions. When the salinity of the evaporation surface increases due to water evaporation, high-concentration salt ions can rapidly diffuse through these channels into the lower-concentration bulk solution, achieving dynamic equilibrium and exchange of salts.

[0020] The three functional layers of this invention achieve dynamic salt resistance and self-cleaning through the synergistic effect of multiple mechanisms. The hydrophobic microregions in the top layer inhibit salt crystal nucleation at the source; the large pores in the bottom layer provide a high-speed channel for salt to flow back into the bulk solution; and crucially, the phase change heat storage and nighttime heat feedback function of the middle layer not only drives nighttime evaporation, but its slow and continuous evaporation process is also sufficient to redissolve the trace amounts of salt crystals that may have precipitated on the surface during daytime evaporation, restoring a clean surface at night. This dynamic self-cleaning cycle of daytime salt precipitation and nighttime salt dissolution enables the evaporator to operate stably for a long time even in high-salinity solutions.

[0021] In one specific embodiment, the water transport substrate is polymerized from an aqueous precursor solution, which contains water-soluble or hydrophilic polymer materials, crosslinking agents, and initiators.

[0022] In one specific embodiment, the heat storage intermediate layer is formed by oil-water biphase precursor emulsion polymerization. The oil-water biphase precursor emulsion is obtained by homogenizing and emulsifying an aqueous phase containing polyvinyl alcohol, a crosslinking agent, and an initiator, and an oil phase containing lauryl methacrylate, a phase change material, and a crosslinking agent.

[0023] In one specific embodiment, the photothermal evaporation top layer is formed by oil-water biphase precursor emulsion polymerization. The oil-water biphase precursor emulsion is obtained by homogenizing and emulsifying an aqueous phase containing water-soluble or hydrophilic polymer materials, photothermal materials, crosslinking agents, and initiators, and an oil phase containing lauryl methacrylate, phase change materials, and crosslinking agents.

[0024] In one specific embodiment, the water-soluble or hydrophilic polymer material is one or more selected from polyvinyl alcohol, polyacrylamide, polyacrylic acid, and polyvinylpyrrolidone. Polyvinyl alcohol is preferred in this invention.

[0025] In one specific embodiment, the phase change material is solid paraffin or oleogloss, wherein the oleogloss comprises a gelling agent HSA (12-hydroxystearic acid) and a light oil capable of forming an oleogloss with HSA. Liquid paraffin and HSA are preferred in this invention. That is, by adding HSA, the dispersed oil phase in the heat storage intermediate layer undergoes a reversible thermotropic gel-sol transition, thereby achieving latent heat energy storage through phase change. The amount of HSA added to the oil phase is 5-10 wt%, preferably 5 wt%.

[0026] In one specific embodiment, the photothermal material is MXene, rGO (reduced graphene oxide), carbon black, or metal nanoparticles. MXene is preferably used in this invention; the amount of MXene added in the aqueous phase is >0.5 mg / mL, preferably 1 mg / mL.

[0027] Secondly, the present invention provides a method for preparing a functionally layered monolithic gel solar evaporator, comprising the following steps:

[0028] (1) Take water-soluble or hydrophilic polymer materials, add them to water, heat and stir to dissolve, add N,N-dimethylacetamide, crosslinking agent and initiator to the solution, and continue stirring until uniform to obtain water transport bottom layer precursor solution, i.e. precursor I;

[0029] (2) Take water-soluble or hydrophilic polymer materials, add them to water, heat and stir to dissolve, and add to the solution Pluronic F127 (poloxam F127), crosslinking agent and initiator, stirred continuously until homogeneous to obtain an aqueous phase;

[0030] Take lauryl methacrylate, phase change material, and crosslinking agent, heat and stir to obtain an oil phase;

[0031] The oil phase was slowly added to the aqueous phase under stirring, and the mixture was homogenized and emulsified to obtain the precursor emulsion of the thermal storage intermediate layer, namely precursor II.

[0032] (3) Take water-soluble or hydrophilic polymer materials, add them to water, heat and stir to dissolve, and add to the solution PluronicF127, crosslinking agent, and initiator are stirred continuously until homogeneous. Then, the photothermal material is added and dispersed evenly to obtain an aqueous phase.

[0033] Take lauryl methacrylate, liquid paraffin, and a crosslinking agent, heat and stir to obtain an oil phase;

[0034] The oil phase is slowly added to the aqueous phase under stirring and homogenized emulsified. The volume ratio of the oil phase is 30%~70%, and the photothermal evaporation top layer precursor emulsion, namely precursor III, is obtained.

[0035] (4) Precursor I, precursor II and precursor III are poured into the mold in sequence to form layers in the vertical direction. The mixture is thermally initiated and polymerized in a water bath at 65~75℃ for 1.5~2.5 h to obtain a functional layered integral gel solar evaporator.

[0036] This invention involves layering different precursor solutions and casting them in layers. By utilizing molecular diffusion between the liquids to form a smooth transition interface, and through in-situ polymerization using a "one-pot" method, all monomers are simultaneously cross-linked and cured in their respective regions and at the interlayer interfaces, forming a single gel block with a hydrophilic hydrogel at the bottom, an oil phase of photothermal material and a phase change material oil phase introduced at the top and middle, respectively. The three functions (light absorption, thermal management and water transport) are vertically and continuously distributed, and the internal structure is tightly connected by chemical bonds, forming a seamless single gel block.

[0037] This invention utilizes a "one-pot" in-situ polymerization process, which connects the functional layers of the evaporator into a seamless, interface-free whole through strong chemical bonds, rather than a physical assembly of the functional layers. This integral structure endows the evaporator with excellent mechanical strength and chemical resistance, enabling it to operate stably for a long time in the complex shale gas fracturing flowback fluid without delamination, swelling, or degradation. Its structural stability far exceeds that of existing physically assembled evaporators.

[0038] The gel evaporator produced by this invention not only possesses the water transport network of a hydrogel and the ability to reduce the enthalpy of vaporization of water, but also exhibits the self-floating and anti-fouling properties of an oil phase. Furthermore, combined with a heat insulation layer capable of phase change energy storage and insulation, its evaporation rate can reach 2.80 kg·m³. -2 Daily water production reaches 9.64 kg·m -2 This provides an efficient and stable solution for the low-energy treatment of high-salinity industrial wastewater.

[0039] In one specific embodiment, the thickness ratio of the top layer of photothermal evaporation, the intermediate layer of heat storage, and the bottom layer of water transport is (0.5~1.5):(0.5~1.5):(0.5~2.5).

[0040] Thirdly, the present invention provides the application of the functionally layered integral gel solar evaporator or the gel solar evaporator prepared by the preparation method in high-salt wastewater.

[0041] Specifically, it can be applied to high-salt shale gas backflow hydraulic fracturing wastewater, seawater desalination, high-salt chemical waste liquid, and other fields requiring efficient interface evaporation; the photothermal materials, phase change heat storage agents, and hydrophilic gel components can all be flexibly replaced according to different scenarios. As long as the layered synergistic structure with continuous physical interface and the hydrophobic island + hydrophilic network structure of the evaporation interface are maintained, the performance advantages of the gel solar evaporator of this invention can be realized.

[0042] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0043] 1. The present invention provides a functionally layered monolithic gel solar evaporator, its preparation method and application. It integrates multiple separate functions (photothermal, heat insulation, heat storage, water pumping and salt discharge) that originally required physical assembly by means of physical means. By adopting the "one-pot method" in-situ polymerization, it forms a seamless, interface-free, internally integrated monolithic single gel block material with photothermal conversion, heat management and water and salt transport functions. The functional layers are connected by strong chemical bonds to form a single gel block material. It integrates the functions of photothermal conversion, heat management and water and salt transport from top to bottom. It achieves synergistic optimization of light absorption, heat storage and water transport within the same system, and solves problems such as interlayer instability, poor salt resistance and low energy utilization.

[0044] 2. The present invention provides a functional layered integral gel solar evaporator, its preparation method, and its application. The top layer of the photothermal evaporation layer adopts a structure in which oil-phase microdroplets loaded with photothermal materials are dispersed in a continuous hydrophilic polymer network. The photothermal materials efficiently absorb sunlight and convert it into heat energy, which is localized at the evaporation interface. At the same time, the introduced hydrophobic oil-phase microdroplets can form island-shaped hydrophobic microregions at the evaporation interface, realizing the pre-modification of the hydrophilicity and hydrophobicity of the evaporation interface. On the one hand, the oil phase can effectively reduce the enthalpy of water evaporation, increase the gas-liquid-solid three-phase contact line to accelerate water evaporation, and inhibit the initial nucleation of salt ions from the source. On the other hand, the hydrophilic hydrogel with hydrophobic island-shaped microregions can make water mainly concentrate in the hydrophilic region, forming a water film with increased thickness, which weakens the interaction between the outermost water molecules and the surface of the hydrogel, thus making it easier to evaporate and achieving ultra-fast evaporation.

[0045] 3. This invention provides a functional layered integral gel solar evaporator, its preparation method, and its application. The central heat storage layer is also an oil-water biphase gel structure, similar to the surface evaporation layer. It also embeds dispersed oil droplets in a continuous hydrogel network. The difference is that its oil phase droplets encapsulate phase change materials. Its working principle is as follows: During the day, this layer absorbs excess heat conducted from the top layer of the photothermal evaporation layer. The energy is stored as latent heat through the melting of the phase change material. At the same time, the oil phase component and the gel matrix together form a thermal barrier to prevent heat loss to the water below. At night, as the ambient temperature decreases, the phase change material solidifies and releases latent heat, providing heat feedback to the top evaporation interface and driving the continuous evaporation of water at night. This achieves a thermal management mechanism of storing heat during the day and releasing heat at night, maintaining continuous evaporation day and night, and realizing all-weather water production.

[0046] 4. This invention provides a functional layered integral gel solar evaporator, its preparation method, and its application. The bottom water transport layer of this invention is a single-phase porous hydrophilic hydrogel structure, rich in interconnected micron-sized channels. Its working principle is as follows: through capillary action, the source water at the bottom is continuously pumped to the top evaporation interface to meet the evaporation requirements; simultaneously, these open porous structures also provide efficient convection and diffusion channels for salt ions. When the salinity of the evaporation surface increases due to water evaporation, high-concentration salt ions can quickly diffuse into the lower-concentration bulk solution through these channels, achieving dynamic balance and exchange of salts.

[0047] 5. This invention provides a functionally layered integral gel solar evaporator, its preparation method, and its application. The three functional layers, through the synergistic effect of multiple mechanisms, achieve dynamic salt resistance and self-cleaning. The hydrophobic microdomains in the top layer inhibit salt crystal nucleation at the source; the large pores in the bottom layer provide a high-speed channel for salt to flow back to the bulk solution; most importantly, the phase change heat storage and nighttime heat feedback function of the middle layer not only drives nighttime evaporation, but more importantly, its slow and continuous evaporation process is sufficient to redissolve the trace amounts of salt crystals that may precipitate on the surface during daytime evaporation, restoring a clean surface at night. This dynamic self-cleaning cycle of daytime salt precipitation and nighttime salt dissolution enables the evaporator to operate stably for a long time even in high-salinity solutions.

[0048] 6. The present invention provides a functional layered integral gel solar evaporator, its preparation method and application. Through in-situ polymerization using a "one-pot method", the functional layers of the evaporator are connected by strong chemical bonds to form a seamless whole without physical interfaces. It is not a physical assembly of the functional layers. This integral structure gives the evaporator excellent mechanical strength and chemical resistance, enabling it to work stably in the complex shale gas fracturing flowback fluid for a long time without delamination, swelling or degradation. Its structural stability far exceeds that of existing physically assembled evaporators.

[0049] 7. The functional layered integral gel solar evaporator, its preparation method, and its application provided in this invention not only possess the water transport network and the ability to reduce the enthalpy of water vaporization of hydrogels, but also exhibit the self-floating and anti-fouling properties imparted by the oil phase. Combined with a phase-change energy storage and heat insulation layer, its evaporation rate can reach 2.80 kg·m³. -2 Daily water production reaches 9.64 kg·m -2 This provides an efficient and stable solution for the low-energy treatment of high-salinity industrial wastewater;

[0050] 8. The present invention provides a functional layered integral gel solar evaporator, its preparation method and application. The "one-pot" preparation process is simple, the raw materials used are all inexpensive and readily available chemical products, the cost is low, no complex and expensive equipment is required, and it is suitable for large-scale industrial applications, making it possible to mass-produce this high-performance evaporator. Attached Figure Description

[0051] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 A schematic diagram illustrating the fabrication of the functionalized layered gel solar evaporator FG-SWE provided in Embodiment 1 of the present invention;

[0053] Figure 2 Actual images and basic characterization of the FG-SWE gel evaporator provided for embodiments of the present invention: (ac) SEM images of different layers of the FG-SWE gel evaporator; (d) FTIR spectra; (e) viscoelasticity test;

[0054] Figure 3 Contact angle and water content variation curves of the FG-SWE gel evaporator provided in the embodiments of the present invention: Microscopic images of the emulsion (a) magnified 10 times; (b) magnified 40 times; (c) Statistical diagram of oil droplet size in the emulsion; (d) Contact angle of different FG-SWE gel evaporators; (e) Water content of different FG-SWE gel evaporators;

[0055] Figure 4 The effect of the hydrophilicity / hydrophobicity of the evaporation surface on the evaporation performance of the FG-SWE gel evaporator provided for embodiments of the present invention: (a) temperature change curves of different FG-SWE gel evaporator surfaces; (b) evaporation mass change curves of different FG-SWE gel evaporators;

[0056] Figure 5 The photothermal performance of the FG-SWE gel evaporator provided in the embodiments of the present invention includes: (a) the average light absorption rate of the FG-SWE gel evaporator containing MXene and the gel evaporator without MXene; (b) the average light absorption rate of the FG-SWE gel evaporators with different MXene contents; and (c) the infrared monitoring results of the FG-SWE gel evaporator during the illumination process.

[0057] Figure 6 The evaporation performance of the FG-SWE gel evaporator for pure water provided in the embodiments of the present invention is as follows: (a) The evaporation performance of FG-SWE gel and pure water at 1 kW·m -2 (a) Mass change curves of FG-SWE gel and pure water under light intensity for 1 hour of illumination and 1 hour of no illumination; -2 Surface temperature changes after 1 hour of illumination under light intensity and 1 hour of no illumination;

[0058] Figure 7 DSC curves of the FG-SWE gel evaporator provided in the embodiments of the present invention: (left) DSC curve of HSA liquid paraffin oil gel; (right) DSC curve of FG-SWE gel;

[0059] Figure 8 Salt resistance and stability test results of the FG-SWE gel evaporator provided in the embodiments of the present invention: (a) under 12 h of light irradiation; (b) top photograph after 4 h of light off; (c) 25 wt% concentrated brine under single solar irradiation conditions (1 kW·m -2 (d) Evaporation rate variation curves after 15 consecutive cycles of continuous operation (on / off every 12 hours);

[0060] Figure 9 Test results of the desalination performance of the FG-SWE gel evaporator provided in the embodiments of the present invention: (a) Schematic diagram of the evaporation device; (b) TDS of the backflow liquid before and after evaporation; (c) Ion content of the backflow liquid before and after evaporation; (d) Outdoor light intensity and ambient temperature; (e) Outdoor evaporation performance of the multilayer gel evaporator. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0062] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0063] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0064] Example 1

[0065] This invention provides a method for preparing a functionally layered monolithic gel solar evaporator pair, comprising the following steps:

[0066] (1) Preparation of precursor I

[0067] First, accurately weigh the PVA powder. Then, with mechanical stirring at 600 rpm, pour the weighed PVA powder into a three-necked flask containing a certain amount of deionized water. Raise the water bath temperature to 90 ℃, install the reflux device, and stir for 1 h to obtain a colorless and transparent 10 wt% PVA aqueous solution. Remove the solution, cool it, and seal it for later use.

[0068] Weigh 10 g of 10 wt% PVA aqueous solution, then add 3.0 g DMA, 20 mg crosslinking agent MBA and 15 mg water-soluble initiator V50, and stir continuously until homogeneous to obtain the water transport bottom layer precursor solution, named precursor I.

[0069] (2) Preparation of precursor II

[0070] Weigh 10 g of a 10 wt% PVA aqueous solution, and add 0.1 g of [unspecified ingredient] while stirring. PluronicAfter F127 and 100 μL of SDS (sodium dodecyl sulfate) aqueous solution (1 wt%) were completely dissolved, 3.0 g of DMA, 20 mg of crosslinking agent MBA, and 15 mg of initiator V50 were added to form an aqueous phase solution. Then, 6.3 g of LMA, 15.8 g of liquid paraffin, and 0.02 g of oil phase crosslinking agent EGDMA were weighed out, stirred evenly, and preheated in a 70°C water bath. Under magnetic stirring, purified organic gelling agent HSA powder was added until completely dissolved, with HSA accounting for 5% of the total mass fraction of the oil phase. Finally, at 70°C, the prepared oil phase was slowly added to the aqueous phase under stirring, and emulsified at 20,000 r / h for 5 min using a homogenizing high-speed emulsifier to form a homogeneous white emulsion, which was then obtained as the precursor emulsion for the heat storage intermediate layer and named precursor II.

[0071] (3) Preparation of precursor III

[0072] 10 mg of MXene powder was added to 10 mL of the aqueous solution described in step (2) and dispersed evenly. Then, 6.3 g of LMA, 15.8 g of liquid paraffin, and 20 mg of oil phase crosslinking agent EGDMA were weighed and stirred evenly to obtain the oil phase. The oil and water phases were mixed, with the oil phase accounting for 30% of the volume. The mixture was emulsified for 5 min at 20000 r / h using a homogenizing high-speed emulsifier to form a photothermal evaporation top-layer precursor emulsion, named Precursor III.

[0073] (4) Finally, as Figure 1 As shown, precursor I, precursor II and precursor III were poured into the mold in sequence and polymerized in a 70°C water bath for 2 hours to obtain the functionalized layered gel solar evaporator FG-SWE.

[0074] Performance Characterization

[0075] 1. Structural and compositional characterization of the FG-SWE gel solar interfacial evaporator

[0076] Visually, the gel can be divided into three layers. The top layer, C1, is the photothermal evaporation layer. Due to the presence of the light-absorbing material MXene, layer C1 is pure black, which is beneficial for absorbing light energy. The middle layer, C2, is the heat storage layer and is milky white. The bottom layer, C3, is the water transport layer and is transparent.

[0077] Figure 2 Image ac is a SEM image of a cross-section of the gel FG-SWE evaporator. It can be seen that all three functional layers have a porous structure, with the C3 water transport layer (…) Figure 2 c) The internal pore structure is the most abundant, with pore sizes ranging from 15 to 40 µm. This abundant pore structure effectively promotes the upward transport of water molecules. Simultaneously, due to C1 ( Figure 2a) and C2 ( Figure 2 (b) The layer contains an oil phase, and distinct circular oil droplet shapes can be observed. This proves that the multilayer gel has a continuous, monolithic structure at the microscopic level.

[0078] The prepared multilayer gel FG-SWE was immersed in acetone to remove liquid paraffin and unreacted monomers, and then vacuum dried to determine its infrared spectrum, verifying the successful preparation and chemical composition of the functionalized layered gel solar evaporator FG-SWE. Figure 2 As shown in d, at 3449 cm -1 A broad peak is present nearby, primarily attributed to the -OH stretching vibrations on the PVA chains within the underlying hydrogel framework, linked by intramolecular and intermolecular hydrogen bonds. Additionally, a peak is observed at 2923 cm⁻¹. -1 and 2857 cm -1 Two very sharp and strong absorption peaks were observed at 1730 cm⁻¹, corresponding to the asymmetric and symmetric stretching vibrations of -CH₂, respectively, proving that the LMA monomer had been successfully polymerized into the polymer network, forming the hydrophobic structural domains of the intermediate and top layers. Simultaneously, two independent carbonyl absorption peaks were observed in the FTIR spectrum: at 1730 cm⁻¹. -1 The strong absorption peak at 1641 cm⁻¹ is due to the C=O stretching vibration of the ester group in LMA, while the peak at 1641 cm⁻¹ is due to the stretching vibration of the ester group in LMA. -1 Another strong absorption peak corresponds to the C=O stretching vibration of the amide I band in PDMA. The simultaneous appearance of characteristic peaks for both ester and amide groups confirms the successful construction of a hydrophilic-hydrophobic biphase polymer network, i.e., these three layers form a single entity. Subsequently, frequency scanning tests showed that: across the entire frequency scanning range (0.1-100 s⁻¹), -1 The elastic modulus (G') of the multilayer gel FG-SWE is approximately 15.9 kPa, which is not significantly dependent on frequency and is always greater than the viscous modulus (G"), exhibiting typical gel properties. Figure 2 e).

[0079] 2. Contact Angle and Equilibrium Moisture Content Test of Gel Solar Interfacial Evaporator FG-SWE

[0080] Microscopic images of the emulsion prepared in Example 1 of this invention, as shown below. Figure 3 As shown in a (10x magnification) and 3b (40x magnification), Figure 3 c represents the statistical diagram of oil droplet size. It can be seen that the evaporation interface in Example 1 of this invention exhibits a multiphase system resembling an emulsion, where oil droplets are dispersed like islands within the aqueous phase. In the hydrophilic hydrogel evaporator with hydrophobic island-like structures, water mainly concentrates in the hydrophilic region, forming a water film of increased thickness. This weakens the interaction between the outermost water molecules and the hydrogel surface, making evaporation easier and enabling ultra-fast evaporation.

[0081] Based on Example 1, this invention adjusts the oil-water ratio in the C1 layer, with the oil phase volume percentages being 0%, 30%, 50%, and 70%, respectively, thereby sequentially preparing C1 layers (labeled OW0, OW30 (Example 1 of this invention), OW50, and OW70) containing approximately 0%, 30%, 50%, and 70% hydrophobic area, respectively. Figure 3 The contact angle test shows that the surface hydrophobicity increases with the increase of the hydrophobic area of ​​the evaporation interface. The water content variation curves of FG-SWE gel evaporators with different hydrophobic C1 layers are shown below. Figure 3 As shown in e, the equilibrium water content of the FG-SWE gel ranges from 7.5 to 13.5 g / g, indicating that the overall change in equilibrium water content is not significant after the appropriate introduction of the hydrophobic oil phase. This demonstrates that appropriate hydrophobicity at the evaporation interface has little impact on water transport and should ensure a continuous and sufficient supply of water molecules during interfacial evaporation, thereby guaranteeing a stable and efficient evaporation rate.

[0082] FG-SWE-0, FG-SWE-30 (Example 1 of this invention), FG-SWE-50, and FG-SWE-70 with different surface hydrophilicity and hydrophobicity were prepared using oil phase volume fractions of 0%, 30%, 50%, and 70% in the C1 layer, respectively. The effect of surface hydrophilicity and hydrophobicity on the performance of the FG-SWE gel evaporator was studied, and the results are as follows: Figure 7 As shown.

[0083] from Figure 4 The temperature curves show that under standard sunlight (1 sun), the temperature of all FG-SWE gels rapidly increased in the open environment and stabilized at around 32℃, significantly higher than the 27℃ of pure water. This is mainly due to their excellent photothermal conversion and heat localization capabilities; their surface temperature increases with increasing hydrophobic area, with FG-SWE-70 reaching a maximum of 35℃. The evaporation mass change curves of FG-SWE gels with different surface hydrophilicity and hydrophobicity are shown in Figure 1. Figure 4 As shown in b, the evaporation rate exhibits a non-linear relationship with surface hydrophobicity, initially increasing and then decreasing. FG-SWE-30 showed the highest water evaporation rate, approximately 2.80 kg·m³. -2 ·h -1 The evaporation rates of FG-SWE-0, FG-SWE-50, and FG-SWE-70 were approximately 2.32, 2.45, and 1.81 kg·m³, respectively. -2 ·h -1 These rates all far exceed the evaporation rate of pure water (0.4 kg·m³). -2 ·h -1The superior evaporation performance described above is attributed to its unique island-shaped surface structure. This is because appropriately increasing the hydrophobicity of the evaporation surface effectively weakens the bond between the outermost water molecules and the gel surface, and extends the three-phase contact line, thereby significantly enhancing the water vaporization process. However, when the hydrophobic area ratio is too high, although its surface temperature is the highest, the effective evaporation area and the continuous supply of water molecules begin to be limited, leading to a decrease in the overall evaporation rate. Therefore, the excellent performance of FG-SWE-30 is the result of achieving an optimal balance between heat management and mass transfer.

[0084] 3. Photothermal and evaporation performance tests of the FG-SWE gel solar interfacial evaporator

[0085] The light absorption properties of FG-SWE gel in the spectral range of 200-2500 nm were measured using UV-Vis-NIR. Figure 5 As can be seen from Figure a, the FG-SWE gel sample with the addition of 1 mg / mL MXene material (Example 1 of this invention) showed an increase in average light absorption rate in the ultraviolet-visible to near-infrared region from 35% to over 95% compared to the gel sample without MXene. Furthermore, the light absorption rate also increased continuously with the increase in MXene content.

[0086] Furthermore, based on Example 1, this invention investigated the effects of adding 0.05 mg / mL, 0.1 mg / mL, 0.2 mg / mL, 0.5 mg / mL, and 1 mg / mL MXene (named FG-SWE-M0.05, FG-SWE-M0.1, FG-SWE-M0.2, FG-SWE-M0.5, and FG-SWE-M1 (Example 1 of this invention)) to the aqueous phase of the C1 layer on photothermal performance. The results are as follows: Figure 5 As shown in b, it can be seen that when the MXene content is 0.5 mg / mL, the FG-SWE gel sample already achieves a light absorption rate of over 95% in the UV-Vis to near-infrared region. Therefore, the FG-SWE gel exhibits excellent light absorption performance. Figure 5Infrared monitoring results during the irradiation process show that in the initial stage of irradiation (0-1500 s), the light energy absorbed by the evaporator is mainly concentrated at the top, and the surface temperature of the top rises rapidly from 25°C to approximately 35°C. Subsequently, in the quasi-steady-state evaporation stage (1500-4000 s), the rate of surface temperature increase slows significantly, eventually stabilizing at around 37°C. At this point, evaporation has reached dynamic equilibrium, and the heat energy converted from solar energy is mainly used to efficiently drive the evaporation of water molecules at the interface. In addition, some heat is transferred to the water body below through thermal conduction, causing the temperature of the water body in the middle and bottom of the gel to rise slowly as well. Because the FG-SWE gel evaporator of this invention also contains a phase change heat storage layer, after 4000 s of continuous irradiation, the temperature of the water body at the bottom only rises from 25°C to approximately 29°C, with a total temperature rise of approximately 4°C. The heat is effectively localized at the evaporation interface, allowing solar energy to be efficiently used in the interface evaporation process.

[0087] Figure 6 The evaporation performance of the FG-SWE gel evaporator for pure water in Embodiment 1 of the present invention is shown. Figure 6 The mass change curve of a is shown in the figure at 1 kW·m -2 During the first 60 minutes of light irradiation, the evaporation rates of FG-SWE gel and pure water were 1.519 kg·m³, respectively. -2 ·h -1 and 0.719 kg·m -2 ·h -1 The FG-SWE gel evaporator of Example 1 of this invention exhibits excellent solar interface evaporation performance. Furthermore, during the dark evaporation phase after the lights are turned off (60-120 min), the FG-SWE gel evaporator of Example 1 of this invention can continuously evaporate, with an average evaporation rate of 0.594 kg·m³. -2 ·h -1 It is nearly twice that of pure water. The mechanism of this behavior can be understood from... Figure 6 The explanation is found in the surface temperature change of b. For example... Figure 6 As shown in b, under illumination, the surface temperature of FG-SWE rapidly increases and stabilizes at approximately 35°C, significantly higher than the approximately 26°C of pure water. When the light source is turned off, the temperature decrease rate of FG-SWE is significantly lower than that of pure water, and it consistently remains at a higher temperature level than pure water. This indicates that the phase change material inside the FG-SWE gel stores thermal energy under illumination and releases it in the dark, thus providing energy for continuous evaporation at night. This phase change heat storage capability enables the FG-SWE gel to achieve the potential for all-weather water production.

[0088] In addition, to verify the effect of different thicknesses of the top and bottom layers on the evaporation rate and evaporation amount of the FG-SWE gel evaporator, based on Example 1, after fixing the thickness of the heat storage intermediate layer to 1 cm, the evaporation rate and evaporation amount of the FG-SWE gel evaporator with different top and bottom layer thicknesses were investigated, and the results are shown in Table 1.

[0089] When the thickness of the top layer of photothermal evaporation is fixed, the evaporation rate initially increases and then decreases with increasing thickness of the bottom water transport layer (C3). This is because the bottom water transport layer not only transports moisture to the evaporation interface but also acts as an insulating layer, preventing heat from being conducted from the evaporation zone to the lower bulk water. When the thickness increases from 1.5 cm to 2.0 cm, the thermal shielding effect is enhanced, effectively reducing heat loss and thus improving evaporation efficiency. However, when the thickness is too large, the water transport path becomes longer, and the hydrodynamic force provided by capillary action is insufficient to match the evaporation demand of the top layer. The excessively long water transport path leads to insufficient water supply capacity, which in turn limits the evaporation rate.

[0090] Similarly, when the thickness of the bottom water transport layer is fixed, there is also an optimal value for the thickness of the top C1 layer in photothermal evaporation. For example, when the C3 layer thickness is 2.0 cm, as the C1 layer thickness increases from 0.2 cm to 0.6 cm, the evaporation rate increases from 2.18 kg·m³. -2 ·h -1 Increased to a peak of 2.45 kg·m -2 ·h -1 At this point, a thicker C1 layer allows for more efficient absorption of sunlight and conversion into heat energy, enhancing the localization of heat at the evaporation interface. However, when the thickness further increases to 0.8 cm, the evaporation rate decreases slightly. This may be because an excessively thick photothermal layer increases thermal resistance, causing some heat to dissipate inside the evaporator rather than being used for the phase change of water. Therefore, the evaporation performance of the FG-SWE gel evaporator of this invention is the result of a synergistic balance between heat management (light absorption efficiency, insulation effect) and mass transfer (water transport capacity). When the C3 layer is 2.0 cm and the C1 layer is 0.6 cm, the evaporation rate of the FG-SWE gel evaporator reaches a maximum of 2.45 kg·m³. -2 ·h -1 .

[0091] Table 1

[0092]

[0093] 4. Thermodynamic performance testing of FG-SWE gel solar interfacial evaporator

[0094] The intermediate layer of the gel solar interface evaporator FG-SWE is a phase change thermal storage layer. The introduction of phase change materials enables the management of heat dissipation, potentially improving the evaporator's evaporation performance. Similar to the surface evaporation layer, the intermediate layer of the FG-SWE gel evaporator also embeds dispersed oil droplets within a continuous hydrogel network. Unlike the photothermal evaporation layer C1, these oil droplets contain HSA, which imparts a reversible thermotropic gel-sol transition to the droplets.

[0095] Figure 7 DSC curves were obtained for FG-SWE gel and HAS liquid paraffin oil gel with 0 wt%, 5 wt%, and 10 wt% HSA (named FG-SWE0, FG-SWE5, and FG-SWE10, respectively) added to the C2 layer oil phase. The DSC curves of both FG-SWE gel and HAS liquid paraffin oil gel (right figure) show two broad peaks, one of which is an endothermic peak at 66.3℃ (T...). m ) and the exothermic peak located at 69.6℃ (T crys Furthermore, the positions of these two peaks are consistent with those of HSA liquid paraffin oil gel. T gel (Left figure) They are almost identical. In addition, the peaks on the DSC curve of FG-SWE gel are wider than those of HSA liquid paraffin, which may be due to the introduction of more solvents such as water and liquid paraffin into the whole gel system, and the peak positions also show a slight shift.

[0096] The thermal properties of HSAFG-SWE gels with different contents are shown in Table 2. It can be seen that the melting enthalpy of FG-SWE-10 gel is 125.8 kJ·kg. -1 This proves that it has good latent heat storage capacity.

[0097] Table 2

[0098]

[0099] 5. Salt resistance test of FG-SWE gel solar interfacial evaporator

[0100] The salt resistance and long-term stability of the FG-SWE gel evaporator of Example 1 of this invention were investigated. First, after 8 hours of continuous light evaporation in 10 wt% standard saline solution, only a small amount of salt crystals precipitated on the surface of the FG-SWE gel evaporator of Example 1. Figure 8 a). Subsequently, when the light source was turned off, the salt crystals accumulated on the surface were completely redissolved within 4 hours, restoring a clean evaporation surface. Figure 8(b) It exhibits excellent self-cleaning ability. This is mainly because after the lights are turned off, the heat source for evaporation changes from the irradiant heat energy of the light to the heat energy released by the latent heat of phase change. The evaporation rate also decreases significantly, allowing more water to remain on the evaporation surface. This causes the salt crystals that would otherwise form due to long-term evaporation to be dissolved, thus achieving self-cleaning and effectively preventing salt accumulation.

[0101] Figure 8 The diagram (cd) illustrates the long-term evaporation stability of the FG-SWE gel evaporator of Example 1 of this invention. Throughout the 15-cycle test, the evaporation rate under illumination remained consistently high, stabilizing at approximately 3.0 kg·m³ in each illumination phase. -2 ·h -1 The dark phase stabilizes at approximately 2.0 kg·m³. -2 ·h -1 The performance showed almost no degradation throughout the cycle, demonstrating its robustness under intermittent light conditions. Furthermore, in a long-term 30-day continuous evaporation test, the evaporation rate only decreased from the initial approximately 2.70 kg·m³. -2 ·h -1 It slowly decreased to approximately 2.45 kg·m -2 ·h -1 The performance retention rate is as high as 90.7%. It can be seen that, thanks to the unique continuous layered structure and hydrogel network of this invention, the FG-SWE gel evaporator can achieve efficient water transport and salt ion exchange, effectively avoiding salt crystallization and accumulation on the evaporation surface, and exhibiting excellent anti-salt fouling ability.

[0102] 6. Test of backflow liquid desalination performance of FG-SWE gel solar interfacial evaporator

[0103] To verify the practical application effect, the FG-SWE gel evaporator prepared in Example 1 of this invention was placed in an outdoor evaporation device to desalinate the shale gas fracturing flowback fluid. For example... Figure 9 As shown in Figure a, the outdoor evaporation device is made of transparent acrylic glass to ensure sufficient light exposure, and the generated vapor condenses at the top of the device and enters the right side of the device. Inside the device is a 6 cm diameter FG-SWE gel evaporator for photothermal evaporation.

[0104] The FG-SWE gel evaporator with the optimal evaporation performance obtained in the aforementioned study (based on Example 1, with a C1 layer thickness of 0.6 cm, a C2 layer thickness of 1 cm, and a C3 layer thickness of 2.0 cm) was used as the research object and placed in... Figure 9 The evaporation unit of a performs desalination and purification treatment on the return liquid. Figure 9b shows the curves of solar irradiance and ambient temperature changing over time in a real-world environment. Solar irradiance peaks at noon (approximately 0.9 kW·m). -2 The ambient temperature fluctuated between 25-34℃. The device was placed on a laboratory rooftop to measure water quality changes under outdoor conditions. Under real sunlight, the evaporator's water production performance was as follows: Figure 9 As shown in c. During the daytime (approximately 8:00-18:00), the cumulative water production reaches approximately 15 kg·m³. -2 Thanks to the heat storage and release effect of the phase change layer, the device can still continuously produce about 2 kg·m³ of water during the night after sunset (18:00 to 8:00 the next day). -2 This results in a daily water production of approximately 17 kg·m³ for a single evaporator. -2 Furthermore, the treated water was evaluated, and the results were as follows: Figure 9 As shown in d. Before treatment, the total dissolved solids (TDS) of all five groups of reflux liquid samples were below 8 × 10⁻⁶. 4 The TDS values ​​of all samples were around mg / L, but after evaporation and purification, they dropped to below 125 mg / L, a reduction of approximately three orders of magnitude, meeting the requirements of my country's "Standards for Drinking Water Quality" (<1000 mg / L, GB5749—2006). Furthermore, from... Figure 9 As can be seen from e, after the shale gas fracturing fluid flowback fluid is evaporated by the FG-SWE gel evaporator, its K + Ca 2+ Na + Mg 2+ Ba 2+ The mass concentrations of the five main ions were reduced by 3 to 4 orders of magnitude compared with the original solution, all below 10 mg / L, indicating that the FG-SWE gel evaporator has good desalination performance and can be applied to the treatment of shale gas fracturing flowback fluid generated in different development stages.

[0105] In summary, this invention successfully constructs a three-layer evaporator with a vertically continuous structure using a "one-pot" polymerization process. The top layer is responsible for efficient photothermal conversion, the middle layer achieves phase change heat storage and insulation, and the bottom layer ensures rapid water transport. The synergistic effect of these functional layers significantly improves the overall evaporation performance.

[0106] This invention effectively reduces the enthalpy of water vaporization through optimized interfacial surface wettability and a porous network structure, thereby achieving high-efficiency evaporation in the FG-SWE evaporator. In practical applications, under standard sunlight intensity, the interfacial evaporation rate of the FG-SWE evaporator of this invention for processing actual return liquid can reach up to 2.80 kg·m³. -2 ·h -1The average photothermal conversion efficiency exceeds 96%. Furthermore, due to the energy storage-heat release effect of the intermediate phase change layer, the evaporator can operate continuously day and night, achieving a daily water production of up to 17 kg·m³ in real-world outdoor environments. -2 This demonstrates its immense application potential. Furthermore, the unique structure of the FG-SWE evaporator endows it with excellent salt resistance and long-term operational stability. Its porous hydrogel network and surface wettability regulation effectively inhibit the accumulation of salt crystals at the evaporation interface and possess a nighttime self-cleaning function. In a 30-day continuous long-term operation test, the evaporation performance retention rate reached 90.7%, proving its structural stability and reliable performance, meeting the stringent requirements of industrial wastewater treatment scenarios.

[0107] Finally, the FG-SWE evaporator of this invention can reduce the total dissolved solids (TDS) of the return liquid from 8 × 10⁻⁶ to 10⁻⁶. 4 The concentration of sodium chloride (Na+) drops to below 125 mg / L, with the main salt ion being Na+. + Ca 2+ The removal rate of wastewater (including salts) exceeds 99.9%, and the quality of the produced water is superior to the national drinking water quality standards (GB5749-2006). This demonstrates the significant effect in treating high-salt shale gas fracturing flowback fluid, achieving effective purification and resource utilization of high-salt wastewater, and providing a feasible zero-discharge treatment scheme for high-salt shale gas fracturing flowback fluid.

[0108] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A functionally layered integral gel solar evaporator, characterized in that, It includes, from top to bottom, a photothermal evaporation top layer, a thermal storage middle layer, and a water transport bottom layer; The photothermal evaporation top layer has an oil-water biphase gel structure, with oil phase microdroplets containing photothermal materials loaded within the hydrophilic polymer network of the aqueous phase. The heat storage intermediate layer has an oil-water biphase gel structure, and phase change materials are encapsulated in the microdroplets of the oil phase. The water transport substrate is a single-phase hydrogel structure; The photothermal evaporation top layer, the heat storage intermediate layer, and the water transport bottom layer are formed by the simultaneous in-situ polymerization of the precursor solutions of each layer in a vertical direction.

2. The functional layered integral gel solar evaporator according to claim 1, characterized in that, The water transport substrate is polymerized from an aqueous precursor solution, which contains water-soluble or hydrophilic polymer materials, crosslinking agents, and initiators.

3. The functional layered integral gel solar evaporator according to claim 1, characterized in that, The thermal storage intermediate layer is formed by oil-water biphase precursor emulsion polymerization. The oil-water biphase precursor emulsion is obtained by homogenizing and emulsifying an aqueous phase containing polyvinyl alcohol, crosslinking agent, and initiator and an oil phase containing lauryl methacrylate, phase change material, and crosslinking agent.

4. The functional layered integral gel solar evaporator according to claim 1, characterized in that, The photothermal evaporation top layer is formed by oil-water biphase precursor emulsion polymerization. The oil-water biphase precursor emulsion is obtained by homogenizing and emulsifying an aqueous phase containing water-soluble or hydrophilic polymer materials, photothermal materials, crosslinking agents, and initiators, and an oil phase containing lauryl methacrylate, phase change materials, and crosslinking agents.

5. A functional layered integral gel solar evaporator according to any one of claims 2 to 4, characterized in that, The water-soluble or hydrophilic polymer material is one or more of polyvinyl alcohol, polyacrylamide, polyacrylic acid, and polyvinylpyrrolidone.

6. A functional layered integral gel solar evaporator according to claim 4, characterized in that, The phase change material is a solid paraffin or an oleogloss, wherein the oleogloss includes a gelling agent HSA and a light oil that can form an oleogloss with HSA.

7. A functional layered integral gel solar evaporator according to claim 3 or 4, characterized in that, The photothermal material is made of MXene, rGO, carbon black, or metal nanoparticles.

8. A method for preparing the functionally layered monolithic gel solar evaporator according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Take water-soluble or hydrophilic polymer materials, add them to water, heat and stir to dissolve, add N,N-dimethylacetamide, crosslinking agent and initiator to the solution, and continue stirring until uniform to obtain water transport bottom layer precursor solution, i.e. precursor I; (2) Take water-soluble or hydrophilic polymer materials, add them to water, heat and stir to dissolve, and add to the solution Pluronic F127, crosslinking agent and initiator, stir continuously until homogeneous to obtain an aqueous phase; Take lauryl methacrylate, phase change material, and crosslinking agent, heat and stir to obtain an oil phase; The oil phase was slowly added to the aqueous phase under stirring, and the mixture was homogenized and emulsified to obtain the precursor emulsion of the thermal storage intermediate layer, namely precursor II. (3) Take water-soluble or hydrophilic polymer materials, add them to water, heat and stir to dissolve, and add to the solution Pluronic F127, crosslinking agent and initiator, stir continuously until uniform, then add photothermal material and disperse evenly to obtain aqueous phase; Take lauryl methacrylate, liquid paraffin, and a crosslinking agent, heat and stir to obtain an oil phase; The oil phase was slowly added to the aqueous phase under stirring, and the mixture was homogenized and emulsified to obtain the photothermal evaporation top layer precursor emulsion, namely precursor III; (4) Precursor I, precursor II and precursor III are poured into the mold in sequence to form layers in the vertical direction. The layers are thermally initiated and polymerized in a water bath at 65~75℃ for 1.5~2.5 h to obtain a functional layered integral gel solar evaporator.

9. The method for preparing the functional layered integral gel solar evaporator according to claim 8, characterized in that, The thickness ratio of the top layer of photothermal evaporation, the middle layer of thermal storage, and the bottom layer of water transport is (0.5~1.5):(0.5~1.5):(0.5~2.5).

10. The application of the functional layered integral gel solar evaporator according to any one of claims 1 to 7, or the gel solar evaporator prepared by the preparation method according to claim 8 or 9, in high-salt wastewater.

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