A multilayer composite structure for achieving directional liquid transport and interface evaporation

Abstract

The present invention discloses a multilayer composite structure for realizing directional liquid transport and interface evaporation, which is composed of a hydrophobic metal grid layer, a hydrophilic layer and a photothermal coating from bottom to top. The present invention uses the moisture in the environment as the liquid transport target, and uses the hydrophobic metal grid layer to make water vapor adhere and condense; then under the action of the hydrophilic layer, water droplets pass through the mesh of the hydrophobic metal grid layer and are absorbed by the hydrophilic layer, so that the moisture is transported in an anti-gravity direction, or the water vapor directly passes through the mesh and is captured and absorbed by the hydrophilic layer, so that the humidity in the environment below the hydrophobic metal grid layer decreases, thereby achieving the purpose of dehumidification in a certain environmental area, and finally the photothermal coating realizes interface evaporation through solar evaporation technology, thereby releasing the moisture in the hydrophilic layer into the atmospheric space. The present invention realizes non-powered, anti-gravity directional liquid transport through a two-dimensional plane combining hydrophilic and hydrophobic, and then realizes a closed loop of liquid directional transport absorption and release in combination with solar evaporation technology.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid transport and interface evaporation, and in particular is a multilayer composite structure for realizing directional liquid transport and interface evaporation. Background Art

[0002] Unpowered directional liquid transport has broad application prospects, such as controllable microfluidics, directional drug delivery, controllable chemical reactions, and directional lubrication and anti-adhesion. Generally speaking, the power of the autonomous movement of liquid on the surface comes from the imbalance of surface energy or the imbalance of capillary force caused by the structure, while unidirectional movement is often caused by gradient surface tension, gradient Laplace pressure or anisotropic structure. The construction of inclined nanowire arrays or surface chemical infiltration gradients can achieve directional liquid transport, but these liquid transports have disadvantages such as slow speed and short distance. There are many phenomena of directional liquid movement in nature, typical of which are spider silk and cactus fog collection. As a result, materials such as one-dimensional bionic fiber silk and conical needles have been developed to achieve functions such as directional water collection. Inspired by cactus, the paper “Facile and Large-Scale Fabrication of a Cactus-Inspired Continuous Fog Collector, 30 January 2014” first fabricated an artificial fog collector on a large scale by integrating a cactus ridge-shaped hydrophobic conical microtip array with a hydrophilic cotton matrix. The new cactus-like atomizer can spontaneously and continuously collect, transport and store fog water, showing a high fog collection efficiency and has broad application prospects in areas where drinking water is scarce. However, it is difficult to use on two-dimensional surfaces and the directional transport of liquids is not good. Summary of the invention

[0003] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a multi-layer composite structure for achieving directional liquid transport and interface evaporation.

[0004] The technical solution of the present invention to solve the technical problem is to provide a multilayer composite structure for realizing directional liquid transport and interface evaporation, characterized in that the multilayer composite structure is composed of a hydrophobic metal grid layer, a hydrophilic layer and a photothermal coating from bottom to top; and the preparation method of the multilayer composite structure comprises the following steps:

[0005] Step 1, preparation of hydrophilic layer slurry: stirring and mixing the hydrophilic fiber and sodium alginate to obtain slurry; then pouring the slurry directly into the mold, or forming a hollow structure through a foaming process and then pouring the slurry into the mold;

[0006] Step 2: Preparation of a hydrophilic layer composited with a photothermal coating:

[0007] Copper chromium black powder or carbon nanotubes are attached to the surface of uncured slurry in a mold by self-embedding, and the mold with the slurry with copper chromium black powder or carbon nanotubes attached to the surface is dried to remove moisture to obtain a film or a three-dimensional structure; the film or the three-dimensional structure is immersed in a calcium chloride solution to cross-link the hydrophilic fiber and the sodium alginate to maintain the shape, thereby compounding the photothermal coating on one side of the hydrophilic layer; and the calcium ions remaining in the cross-linked film or the three-dimensional structure are removed to obtain a hydrophilic layer compounded with the photothermal coating;

[0008] Alternatively, the mold containing the slurry is dried to remove moisture to obtain a film or a three-dimensional structure; the film or the three-dimensional structure is then immersed in a calcium chloride solution to allow the hydrophilic fibers and the sodium alginate to crosslink and maintain their shape; the calcium ions remaining in the cross-linked film or the three-dimensional structure are then removed to form a hydrophilic layer; an aqueous ammonium persulfate solution is then dripped onto the surface of the hydrophilic layer to wet the surface with the solution; the ammonium persulfate on the surface of the hydrophilic layer is then decomposed by reaction to generate oxidizing agents; a pyrrole ethanol solution is then dripped to react with the oxidizing ammonium persulfate to generate polypyrrole on the surface of the hydrophilic layer, thereby compounding the photothermal coating on one side of the hydrophilic layer to obtain a hydrophilic layer compounded with the photothermal coating;

[0009] Step 3, preparation of a hydrophobic metal mesh layer: remove surface stains, rust and oxide layer of the metal mesh or metal sheet with a porous structure in sequence; then immerse the metal mesh or metal sheet with a porous structure in a corrosive solution to produce a micro-nano structure on the surface of the metal mesh or metal sheet with a porous structure, then take it out, wash off the corrosive solution on the surface, dry its surface, and then immerse it in a PDMS solution to attach a hydrophobic layer to its surface, and then heat it to pre-cure the PDMS to form a PDMS colloid to obtain a hydrophobic metal mesh layer;

[0010] Step 4: Place the other side of the hydrophilic layer composited with the photothermal coating on the hydrophobic metal grid layer, bond the two together with PDMS colloid, and then completely cure the PDMS to obtain a multilayer composite structure that realizes directional liquid transport and interface evaporation.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] (1) The multilayer composite structure of the present invention has both hydrophilic and hydrophobic properties. Through a two-dimensional plane combining hydrophilicity and hydrophobicity, it realizes non-powered, anti-gravity directional liquid transport. Combined with solar evaporation technology, it realizes a closed loop of liquid directional transport absorption-release, meeting the needs of indoor and outdoor dehumidification, liquid conduction, fresh water acquisition, and industrial waste gas recovery. It has the advantages of easy water vapor collection, simple structure, low cost, green environmental protection, and stable performance.

[0013] (2) The present invention uses moisture in an indoor or outdoor environment as the target of liquid transport, and utilizes a hydrophobic metal mesh layer to allow moisture, steam and other water vapor to adhere and condense; then, under the action of the hydrophilic layer, water droplets pass through the mesh holes of the hydrophobic metal mesh layer and are absorbed by the hydrophilic layer, so that the moisture is transported in an anti-gravity direction, or the water vapor directly passes through the mesh holes and is captured and absorbed by the hydrophilic layer, so that the humidity in the environment below the hydrophobic metal mesh layer decreases, thereby achieving the purpose of dehumidification in a certain environmental area. Finally, the photothermal coating realizes interfacial evaporation through solar evaporation technology, thereby releasing the moisture in the hydrophilic layer into the atmosphere.

[0014] (3) The top of the multilayer composite structure of the present invention can block moisture. When moisture invades, it will be discharged from the hydrophilic layer, and the hydrophobic metal grid below will not be infiltrated, and the environmental humidity of the space area below will not be destroyed.

[0015] (4) The multi-layer composite structure of the present invention has a low manufacturing cost, flexible size and shape, and can be combined and tailored according to actual needs, and has the potential for large-scale industrial application; and it has obvious effects on water vapor removal and directional liquid transport, and can block the entry of liquid, thereby achieving environmentally friendly, cheap, fast, safe and efficient moisture removal, and providing a new solution for low-cost, large-scale dehumidification and directional liquid transport. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of the multi-layer composite structure of the present invention;

[0017] Figure 2 It is a functional principle diagram of the multilayer composite structure of the present invention;

[0018] Figure 3 The absorbance diagram of the multilayer composite structure prepared in Example 1 of the present invention in the ultraviolet-visible-near infrared (UV-VIS-NIR) spectrum with a wavelength between 200 and 2500 nm;

[0019] Figure 4 The absorbance diagram of the multilayer composite structure prepared in Example 2 of the present invention in the ultraviolet-visible-near infrared (UV-VIS-NIR) spectrum with a wavelength between 200 and 2500 nm;

[0020] Figure 5 This is a graph of the absorbance of the multilayer composite structure prepared in Example 3 of the present invention in the ultraviolet-visible-near infrared (UV-VIS-NIR) spectrum with a wavelength between 200 and 2500 nm.

[0021] In the figure, there are photothermal coating 1, hydrophilic layer 2, and hydrophobic metal grid layer 3. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the claims of the present invention.

[0023] The present invention provides a multilayer composite structure for realizing directional liquid transport and interface evaporation (hereinafter referred to as the multilayer composite structure), characterized in that the multilayer composite structure is composed of a hydrophobic metal grid layer 3, a hydrophilic layer 2 and a photothermal coating 1 from bottom to top; the hydrophobic metal grid layer 3 is roughened by a metal surface to produce a surface micro-nano structure, and then formed by a hydrophobic treatment; the hydrophilic layer 2 is tightly attached to the hydrophobic metal grid layer 3; the photothermal coating 1 is directly attached to the hydrophilic layer 2; and the preparation method of the multilayer composite structure comprises the following steps:

[0024] Step 1, preparation of slurry for hydrophilic layer 2: mixing hydrophilic fiber and sodium alginate uniformly to obtain slurry; then directly pouring the slurry into a mold, or forming a hollow structure through a foaming process and then pouring the slurry into the mold;

[0025] Preferably, in step 1, the foaming process is: stirring and mixing the slurry, a 30% by volume aqueous hydrogen peroxide solution and polyoxyethylene-8-octylphenyl ether evenly, and then standing and foaming for 1 to 2 hours; the ratio of the mass of the slurry, the volume of the hydrogen peroxide solution, and the volume of the polyoxyethylene-8-octylphenyl ether is 10g:1 to 2mL:0.05 to 0.1mL.

[0026] Preferably, in step 1, the hydrophilic fiber is at least one of wood fiber, silk, rabbit hair fiber, bamboo fiber, cotton fiber, hemp fiber, plant shell fiber and straw fiber.

[0027] Preferably, in step 1, the mass ratio of hydrophilic fiber to sodium alginate is 1:1-10.

[0028] Preferably, in step 1, the mold can be 3D printed into any shape according to demand.

[0029] Step 2: Preparation of the hydrophilic layer 2 composited with the photothermal coating 1:

[0030] Copper chromium black powder or carbon nanotubes are attached to the surface of the uncured slurry in the mold by self-embedding, and the mold with the slurry with copper chromium black powder or carbon nanotubes attached to the surface is dried to remove moisture, so as to obtain a flat film or three-dimensional structure with a certain shape; the film or three-dimensional structure is then immersed in a calcium chloride solution to make the hydrophilic fiber and sodium alginate cross-linked to maintain the shape, so that the photothermal coating 1 is composited on one side of the hydrophilic layer 2; and the calcium ions remaining in the cross-linked film or three-dimensional structure are removed to obtain the hydrophilic layer 2 composited with the photothermal coating 1;

[0031] Alternatively, the mold containing the slurry is dried to remove moisture to obtain a flat film or three-dimensional structure with a certain shape; then the film or three-dimensional structure is immersed in a calcium chloride solution to make the hydrophilic fiber and sodium alginate cross-linked to maintain the shape; then the cross-linked film or three-dimensional structure removes the residual calcium ions in the system to form a hydrophilic layer 2; then a 5-10wt% ammonium persulfate aqueous solution is dripped on the surface of the hydrophilic layer 2 to make the surface wetted by the solution; then the reaction is carried out at 50-60°C for 0.5-2h to decompose the ammonium persulfate on the surface of the hydrophilic layer, thereby generating oxidizing properties; then a 5-10wt% pyrrole ethanol solution is dripped and reacted with the oxidizing ammonium persulfate at 50-60°C for 1-2h to generate polypyrrole on the surface of the hydrophilic layer, thereby compounding the photothermal coating 1 on one side of the hydrophilic layer 2 to obtain a hydrophilic layer 2 compounded with the photothermal coating 1;

[0032] Preferably, in step 2, the particle size of the copper chrome black powder is less than 5 μm (preferably 2.5 μm); the specific process is: sieving the copper chrome black powder with a sieve to obtain uniform particles with a particle size of less than 5 μm.

[0033] Preferably, in step 2, the process for removing moisture is: drying in an oven at 50-60° C. for 1-6 hours; the cross-linking process is: immersing in a 1-10wt% calcium chloride solution for 1-2 hours; and the process for removing residual calcium ions in the cross-linked film or three-dimensional structure is: immersing in deionized water to remove residual calcium ions in the system, and then drying in a natural environment to remove moisture in the system.

[0034] Preferably, in step 2, the ratio of the volume of the ammonium persulfate aqueous solution to the surface area of ​​the hydrophilic layer 2 is 1-5 mL: 20-40 cm 2 .

[0035] Step 3, preparation of the hydrophobic metal mesh layer 3: remove surface stains, rust and oxide layer of the metal mesh or the metal sheet with a porous structure in sequence; then immerse the metal mesh or the metal sheet with a porous structure in a corrosive solution to produce a micro-nano structure on the surface of the metal mesh or the metal sheet with a porous structure, then take it out, wash off the corrosive solution on the surface, dry it to keep its surface dry, then immerse it in a PDMS solution to attach a hydrophobic layer to its surface, and then heat it to pre-cure the PDMS to form a PDMS colloid with a certain viscosity and stability, thereby obtaining a hydrophobic metal mesh layer 3;

[0036] Preferably, in step 3, the preparation process of the metal mesh is: weaving the metal wire into a mesh structure through a weaving process of reeding and reeding to form a metal mesh; the preparation process of the metal sheet with a porous structure is: subjecting the metal sheet to a metal engraving process to have a porous structure of a certain size and shape, thereby forming a metal sheet with a porous structure. The metal is copper, iron or stainless steel.

[0037] Preferably, in step 3, the process for removing surface stains is: repeatedly rinsing with water and ethanol; the process for removing rust is: grinding and removing rust with fine sandpaper; the process for removing the oxide layer is: soaking in hydrochloric acid with a concentration of 1 to 2 mol / L for 5 to 10 minutes to remove the oxide layer, and then rinsing with hydrochloric acid and drying to avoid the influence of hydrochloric acid on subsequent steps.

[0038] Preferably, in step 3, the corrosive solution is a mixed solution of 2-3 mol / L sodium hydroxide and 0.1-0.2 mol / L ammonium persulfate, or a mixed solution of 200-300 g / L copper chloride, 100-150 g / L organic small molecule carboxylic acid, 4-5 g / L azole corrosion inhibitor and 4-5 g / L low foam wetting agent;

[0039] When a mixed solution consisting of 2-3 mol / L sodium hydroxide and 0.1-0.2 mol / L ammonium persulfate is used, a metal mesh or a metal sheet with a porous structure is immersed in the mixed solution at room temperature for 5-10 minutes until the color of the mixed solution changes from colorless to blue-black and the reaction is complete;

[0040] When a mixed solution consisting of 200-300 g / L of copper chloride, 100-150 g / L of organic small molecule carboxylic acid, 4-5 g / L of azole corrosion inhibitor and 4-5 g / L of low foaming wetting agent is used, a metal mesh or a metal sheet with a porous structure is immersed in it at 90-100°C for 15-20 minutes until the color of the mixed solution changes from blue to black, indicating that the reaction is complete.

[0041] Preferably, in step 3, the organic small molecule carboxylic acid is formic acid, acetic acid or propionic acid; the azole corrosion inhibitor is mercaptobenzothiazole, benzotriazole or methylbenzotriazole; the low foaming wetting agent is ethylene oxide adduct, polyether silicone or non-ionic fluorocarbon polymer; the mixed solution is preferably a mixed solution composed of 200-300 g / L of cupric chloride, 100-150 g / L of propionic acid, 4-5 g / L of mercaptobenzothiazole and 4-5 g / L of polyether silicone.

[0042] Preferably, in step 3, the concentration of the PDMS solution is 10-50 wt %, and the immersion time is 5-30 s; the PDMS pre-curing process is: heating at a temperature of 20-100° C. for 1-2 h.

[0043] Step 4: Place the other side of the hydrophilic layer 2 composited with the photothermal coating 1 on the hydrophobic metal grid layer 3, bond the two together with PDMS colloid, and then completely cure the PDMS to obtain a multilayer composite structure (referred to as a multilayer composite structure) that realizes directional liquid transport and interface evaporation.

[0044] Preferably, in step 4, the process for completely curing PDMS is: heating at a temperature of 20 to 100° C. for 1 to 24 hours.

[0045] Preferably, the contact angle of the hydrophobic metal grid layer 3 is 135-145°, and the rolling angle is 120-130°.

[0046] Preferably, the size and shape of the multi-layer combined structure are flexible and can be freely combined and tailored according to actual application needs to meet the specific requirements of fixed scenes in production and life.

[0047] The functional principle of the multilayer composite structure of the present invention is (such as Figure 2 As shown in the figure): the hydrophobic metal mesh layer is used to make moisture, steam and other water vapor adhere and condense; then under the action of the hydrophilic layer, water droplets are absorbed by the hydrophilic layer through the mesh of the hydrophobic metal mesh layer, so that the water is transported in an anti-gravity direction, or the water vapor directly passes through the mesh and is captured and absorbed by the hydrophilic layer, so that the humidity in the environment below the hydrophobic metal mesh layer decreases, thereby achieving the purpose of dehumidification in a certain environmental area. Finally, the photothermal coating realizes interfacial evaporation through solar evaporation technology, thereby releasing the water in the hydrophilic layer into the atmospheric space. When water invades, it will be discharged from the hydrophilic layer, and the hydrophobic metal mesh below it will not be infiltrated, and the environmental humidity of the space area below it will not be destroyed.

[0048] Example 1

[0049] Step 1, mixing wood fiber and sodium alginate in a mass ratio of 1:5 to obtain a slurry, and then pouring the slurry into a mold for forming;

[0050] Step 2, sieving the copper chromium black powder with a sieve to obtain uniform particles with a particle size of no more than 2.5 μm; then attaching the sieved copper chromium black powder to the surface of the uncured slurry in the mold by self-embedding, placing the mold with the slurry with the copper chromium black powder attached to the surface in an oven for drying to obtain a flat film with a certain shape, and then immersing the film in a 10wt% calcium chloride solution for 1 hour to crosslink the fiber and sodium alginate to maintain the shape; then immersing the cross-linked film in deionized water to remove residual calcium ions in the system, and finally drying in a natural environment to remove moisture in the system to obtain a hydrophilic layer composited with a photothermal coating;

[0051] Step 3, weave the copper wire into a mesh structure through a weaving process of reeding and reeding; then rinse the metal mesh repeatedly with water and ethanol to remove surface stains, and polish it with fine sandpaper to remove rust, then soak it in 1mol / L hydrochloric acid for 5 minutes to remove the oxide layer, then rinse the hydrochloric acid and dry it; then soak it in a mixed solution of 2.5mol / L sodium hydroxide and 0.13mol / L ammonium persulfate for 5 minutes to produce a micro-nano structure on its surface; then take it out, wash off the corrosive solution on the surface, dry its surface, and then immerse it in a 10wt% PDMS solution for 10s to attach a hydrophobic layer to its surface, and then heat it in a 50°C oven for 1h to pre-cure the PDMS to form a PDMS colloid to obtain a hydrophobic metal mesh layer;

[0052] Step 4: Place the other side of the hydrophilic layer composited with the photothermal coating on the hydrophobic metal grid layer, bond the two together with PDMS colloid, and then heat in an oven at 100° C. for 1 hour to completely cure the PDMS to obtain a multilayer composite structure.

[0053] The dehumidification efficiency of the prepared multilayer composite structure is 0.653 kg·m -2 ·h -1 , the solar evaporation rate is 1.51 kg·m -2 ·h -1 , the solar evaporation conversion efficiency is 90.8%. Figure 3 It can be seen that the absorptivity of the multilayer composite structure in the ultraviolet-visible-near infrared (UV-VIS-NIR) with a wavelength between 200 and 2500 nm is about 0.95.

[0054] Example 2

[0055] Step 1, bamboo fiber and sodium alginate are mixed evenly in a mass ratio of 1:10 to obtain a slurry, and then the slurry is subjected to a foaming process, and each 10g of the slurry is stirred and mixed evenly with 1mL of a 30% by volume aqueous hydrogen peroxide solution and 0.1mL of polyoxyethylene-8-octylphenyl ether, and the mixture is allowed to stand for foaming for 1h to obtain a hollow structure, and then the slurry is poured into a mold for molding;

[0056] Step 2: attach the carbon nanotubes to the surface of the uncured slurry in the mold by self-embedding, put the mold with the slurry attached to the surface of the carbon nanotubes into an oven for drying, and obtain a flat three-dimensional structure with a certain shape, and then immerse the three-dimensional structure in a 1% calcium chloride solution for 1 hour to cross-link the fibers and sodium alginate to maintain the shape; then immerse the cross-linked three-dimensional structure in deionized water to remove the residual calcium ions in the system, and finally dry it in a natural environment to remove the moisture in the system to obtain a hydrophilic layer composited with a photothermal coating;

[0057] Step 3, weave the stainless steel wire into a mesh structure through a weaving process of reeding and reeding; then rinse the metal mesh repeatedly with water and ethanol to remove surface stains, and polish and remove rust with fine sandpaper, then soak it in 1mol / L hydrochloric acid for 5min to remove the oxide layer, then rinse the hydrochloric acid and dry it; then soak it in a mixed solution consisting of 300g / L copper chloride, 100g / L propionic acid, 5g / L mercaptobenzothiazole, and 5g / L polyether silicone and corrode it at 90°C for 5min, repeat 3 times, so that a micro-nano structure is generated on its surface; then take it out, wash off the corrosive solution on the surface, dry its surface, and then immerse it in a 20wt% PDMS solution for 30s to attach a hydrophobic layer to its surface, and then heat it in a 50°C oven for 1h to pre-cure the PDMS to form a PDMS colloid to obtain a hydrophobic metal mesh layer;

[0058] Step 4: Place the other side of the hydrophilic layer composited with the photothermal coating on the hydrophobic metal grid layer, bond the two together with PDMS colloid, and then heat in an oven at 100° C. for 1 hour to completely cure the PDMS to obtain a multilayer composite structure.

[0059] The dehumidification efficiency of the obtained multilayer composite structure is 0.658 kg·m -2 ·h -1 , the solar evaporation rate is 1.61 kg·m -2 ·h -1 , the solar evaporation conversion efficiency is 91.7%. Figure 4 It can be seen that the absorptivity of the multilayer composite structure in the ultraviolet-visible-near infrared (UV-VIS-NIR) with a wavelength between 200 and 2500 nm is about 0.95.

[0060] Example 3

[0061] Step 1, mixing wood fiber and sodium alginate in a mass ratio of 1:5 to obtain a slurry, and then pouring the slurry into a mold for forming;

[0062] Step 2, placing the mold filled with the slurry in an oven for drying to obtain a flat three-dimensional structure with a certain shape, and then immersing the three-dimensional structure in a 10% calcium chloride solution for 1 hour to crosslink the fibers and sodium alginate to maintain the shape; then immersing the cross-linked three-dimensional structure in deionized water to remove the residual calcium ions in the system, and drying in a natural environment to remove the moisture in the system to form a hydrophilic layer; then dripping 1mL of ammonium persulfate aqueous solution (10wt%) on the surface of the hydrophilic layer to wet the surface of the hydrophilic layer; then drying the film or three-dimensional structure with the wet surface again at 50°C for 1 hour to decompose the ammonium persulfate on its surface, thereby generating oxidizing properties; then dripping 5% pyrrole ethanol solution on the surface of the hydrophilic layer, reacting with the oxidizing ammonium persulfate at 60°C for 1 hour to generate polypyrrole on the surface of the hydrophilic layer, thereby compounding the photothermal coating 1 on one side of the hydrophilic layer 2 to obtain a hydrophilic layer 2 compounded with the photothermal coating 1;

[0063] Step 3, the iron sheet is subjected to a metal engraving process to make it have a pore structure of a certain size and shape; then the metal sheet with the pore structure is repeatedly rinsed with water and ethanol to remove surface stains, and is polished with fine sandpaper to remove rust, and then immersed in 1mol / L hydrochloric acid for 5min to remove the oxide layer, and then the hydrochloric acid is rinsed and dried; then immersed in a mixed solution of 2.5mol / L sodium hydroxide and 0.13mol / L ammonium persulfate for 5min to produce a micro-nano structure on its surface, then taken out, the corrosive solution on the surface is washed off, and then the surface is dried, and then immersed in a 10wt% PDMS solution for 10s to attach a hydrophobic layer to its surface, and then heated in a 50°C oven for 1h to pre-cure the PDMS to form a PDMS colloid to obtain a hydrophobic metal grid layer;

[0064] Step 4: Place the other side of the hydrophilic layer composited with the photothermal coating on the hydrophobic metal grid layer, bond the two together with PDMS colloid, and then heat them in an oven at 100°C for 2 hours to completely cure the PDMS to obtain a multilayer composite structure.

[0065] The dehumidification efficiency of the prepared multilayer composite structure is 0.647 kg·m -2 ·h -1 , the solar evaporation rate is 1.52 kg·m -2 ·h -1 , the solar evaporation conversion efficiency is 88.5%. Figure 5 It can be seen that the absorptivity of the multilayer composite structure in the ultraviolet-visible-near infrared (UV-VIS-NIR) with a wavelength between 200 and 2500 nm is about 0.87.

[0066] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A multilayer composite structure for achieving directional liquid transport and interface evaporation, It is characterized in that The multi-layer composite structure is composed of a hydrophobic metal grid layer, a hydrophilic layer and a photothermal coating from bottom to top; and the preparation method of the multi-layer composite structure comprises the following steps: Step 1, preparation of hydrophilic layer slurry: stirring and mixing the hydrophilic fiber and sodium alginate to obtain slurry; then pouring the slurry directly into the mold, or forming a hollow structure through a foaming process and then pouring the slurry into the mold; Step 2: Preparation of a hydrophilic layer composited with a photothermal coating: Copper chromium black powder or carbon nanotubes are attached to the surface of uncured slurry in a mold by self-embedding, and the mold with the slurry with copper chromium black powder or carbon nanotubes attached to the surface is dried to remove moisture to obtain a film or a three-dimensional structure; the film or the three-dimensional structure is immersed in a calcium chloride solution to cross-link the hydrophilic fiber and the sodium alginate to maintain the shape, thereby compounding the photothermal coating on one side of the hydrophilic layer; and the calcium ions remaining in the cross-linked film or the three-dimensional structure are removed to obtain a hydrophilic layer compounded with the photothermal coating; Alternatively, the mold containing the slurry is dried to remove moisture to obtain a film or a three-dimensional structure; the film or the three-dimensional structure is then immersed in a calcium chloride solution to allow the hydrophilic fibers and the sodium alginate to crosslink and maintain their shape; the calcium ions remaining in the cross-linked film or the three-dimensional structure are then removed to form a hydrophilic layer; an aqueous ammonium persulfate solution is then dripped onto the surface of the hydrophilic layer to wet the surface with the solution; the ammonium persulfate on the surface of the hydrophilic layer is then decomposed by reaction to generate oxidizing agents; a pyrrole ethanol solution is then dripped to react with the oxidizing ammonium persulfate to generate polypyrrole on the surface of the hydrophilic layer, thereby compounding the photothermal coating on one side of the hydrophilic layer to obtain a hydrophilic layer compounded with the photothermal coating; Step 3, preparation of a hydrophobic metal mesh layer: remove surface stains, rust and oxide layer of the metal mesh or metal sheet with a porous structure in sequence; then immerse the metal mesh or metal sheet with a porous structure in a corrosive solution to produce a micro-nano structure on the surface of the metal mesh or metal sheet with a porous structure, then take it out, wash off the corrosive solution on the surface, dry its surface, and then immerse it in a PDMS solution to attach a hydrophobic layer to its surface, and then heat it to pre-cure the PDMS to form a PDMS colloid to obtain a hydrophobic metal mesh layer; Step 4: Place the other side of the hydrophilic layer composited with the photothermal coating on the hydrophobic metal grid layer, bond the two together with PDMS colloid, and then completely cure the PDMS to obtain a multilayer composite structure that realizes directional liquid transport and interface evaporation.

2. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 1, It is characterized in that In step 1, the hydrophilic fiber is at least one of wood fiber, silk, rabbit hair fiber, bamboo fiber, cotton fiber, hemp fiber, plant shell fiber and straw fiber.

3. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 1, It is characterized in that In step 1, the mass ratio of the hydrophilic fiber to the sodium alginate is 1:1-10.

4. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 1, It is characterized in that In step 2, the process for removing moisture is: placing in an oven at 50-60° C. and drying for 1-6 hours; the cross-linking process is: immersing in a 1-10wt% calcium chloride solution for 1-2 hours; and the process for removing residual calcium ions in the cross-linked film or three-dimensional structure is: immersing in deionized water to remove residual calcium ions in the system, and then drying in a natural environment to remove moisture in the system.

5. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 1, It is characterized in that In step 2, the ratio of the volume of the ammonium persulfate aqueous solution to the surface area of ​​the hydrophilic layer is 1-5 mL: 20-40 cm 2 ; The mass fraction of the ammonium persulfate aqueous solution is 5~10wt%; the ammonium persulfate decomposition process is: react at 50~60℃ for 0.5~2h; the mass fraction of the pyrrole ethanol solution is 5~10wt%; the process for generating polypyrrole is: react with oxidizing ammonium persulfate at 50~60℃ for 1~2h.

6. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 1, It is characterized in that In step 3, the process for removing surface stains is: repeatedly rinsing with water and ethanol; the process for removing rust is: grinding with sandpaper to remove rust; the process for removing the oxide layer is: soaking in 1-2 mol / L hydrochloric acid for 5-10 minutes to remove the oxide layer, then rinsing with hydrochloric acid and drying to avoid the influence of hydrochloric acid on subsequent steps.

7. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 1, It is characterized in that In step 3, the corrosive solution is a mixed solution consisting of 2-3 mol / L sodium hydroxide and 0.1-0.2 mol / L ammonium persulfate, or a mixed solution consisting of 200-300 g / L copper chloride, 100-150 g / L organic small molecule carboxylic acid, 4-5 g / L azole corrosion inhibitor and 4-5 g / L low foam wetting agent; When a mixed solution consisting of 2-3 mol / L sodium hydroxide and 0.1-0.2 mol / L ammonium persulfate is used, the metal mesh or metal sheet with a porous structure is immersed in it at room temperature for 5-10 minutes until the color of the mixed solution changes from colorless to blue-black and the reaction is completed; When a mixed solution consisting of 200-300 g / L of copper chloride, 100-150 g / L of organic small molecule carboxylic acid, 4-5 g / L of azole corrosion inhibitor and 4-5 g / L of low foaming wetting agent is used, the metal mesh or metal sheet with a porous structure is immersed in it at 90-100°C for 15-20 minutes until the color of the mixed solution changes from blue to black and the reaction is completed.

8. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 7, It is characterized in that In step 3, the organic small molecule carboxylic acid is formic acid, acetic acid or propionic acid; the azole corrosion inhibitor is mercaptobenzothiazole, benzotriazole or methylbenzotriazole; the low foam wetting agent is ethylene oxide adduct, polyether silicone or non-ionic fluorocarbon polymer compound.

9. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 1, It is characterized in that In step 3, the concentration of the PDMS solution is 10-50wt%, and the immersion time is 5-30s; the PDMS pre-curing process is: heating at 20-100°C for 1-2h.

10. The multilayer composite structure for realizing directional liquid transport and interface evaporation according to claim 1, It is characterized in that In step 4, the process for fully curing PDMS is: heating at a temperature of 20-100°C for 1-24h.

Images