Solar steam generator, method for blackening a surface of a three-dimensional porous material and applications

Abstract

The application provides a solar steam generator, a blackening method of a three-dimensional porous material surface and application. The blackening method comprises the following steps: S1, placing the three-dimensional porous material in a mixed solution containing tannic acid and sodium alginate, performing immersion treatment, and obtaining the three-dimensional porous material with a wet surface; S2, placing the three-dimensional porous material with the wet surface in a solution containing Fe 3+ , and performing cross-linking treatment; S3, performing flushing and drying treatment on the three-dimensional porous material after the cross-linking treatment, and obtaining the three-dimensional porous material with a blackened surface. The solar steam generator prepared by the blackening method has a water evaporation rate of more than 2.00kg m ‑2 h ‑1 . The purification performance of the SA / TA-Fe 3+ modified porous material on seawater, dye wastewater and heavy metal wastewater makes it expected to become a candidate product of a high-performance solar steam generator, and has great commercial application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of porous material surface blackening, and particularly relates to a solar steam generator, a three-dimensional porous material surface blackening method and application. BACKGROUND

[0002] In recent years, solar-driven interfacial water vapor power generation has been used to produce clean water from non-potable water resources, and is considered as an effective method to alleviate the impact of water crisis on human activities due to the abundant, renewable and pollution-free characteristics of solar energy. According to long-term research results, three basic characteristics of high-quality solar steam generators are summarized: (1) good light absorption performance to achieve the purpose of heating the evaporation surface; (2) stable thermal insulation layer to fix the generated heat at the air-water interface to generate steam; (3) hydrophilic porous structure to continuously transport water to the evaporation interface, which is crucial for water vapor evaporation.

[0003] Many three-dimensional (3D) porous materials, such as biomass materials, artificial gel materials and metal foams, have high specific surface area and hydrophilic characteristics. These inherent characteristics not only facilitate heat insulation and water transport, but also facilitate effective capture of sunlight after surface blackening treatment, thereby enhancing light absorption. Solar steam generators based on porous materials as substrates integrate light absorption, heat insulation and hydrophilic properties, and exhibit stable pure water evaporation rates, confirming the superiority of 3D porous materials as candidate materials for manufacturing high-performance evaporators. However, the current methods for introducing light absorption characteristics into 3D porous materials mainly include high-temperature carbonization, chemical etching, freeze-drying or spraying, which are only suitable for specific objects and have technical defects such as time-consuming, energy-consuming and even destroying the original surface hydrophilicity. Therefore, it is of great significance to develop a simple, time-saving and material-independent surface blackening strategy in the field of seawater desalination.

[0004] Therefore, it is necessary to design a solar steam generator, a three-dimensional porous material surface blackening method and application to solve the above problems. SUMMARY

[0005] The present application aims to provide a solar steam generator, a three-dimensional porous material surface blackening method and application.

[0006] To achieve the above-mentioned application purposes, the present application provides a three-dimensional porous material surface blackening method, which comprises the following steps:

[0007] S1, placing a three-dimensional porous material in a mixed solution containing tannic acid and sodium alginate for immersion treatment to form a uniform mixed layer on the surface of the three-dimensional porous material, thereby obtaining a three-dimensional porous material with a wet surface;

[0008] S2, placing the surface-wetted three-dimensional porous material into a solution containing Fe 3+ , to obtain a composite gel system formed by mixing tannic acid, sodium alginate and Fe 3 + , and performing cross-linking treatment for 0.5-10 min to obtain the three-dimensional porous material after cross-linking treatment;

[0009] S3, performing rinsing treatment on the three-dimensional porous material after cross-linking treatment to remove excess Fe 3+ solution, and performing drying treatment, so that a black interface gel layer is formed on the surface and inside the porous structure of the three-dimensional porous material, thereby obtaining the surface-blackened three-dimensional porous material.

[0010] As a further improvement of the present application, the concentration of the tannic acid in the mixed solution in step S1 is 0.2%-1.6%, and the concentration of the sodium alginate is 0.5%-4%.

[0011] As a further improvement of the present application, the concentration of the tannic acid in the mixed solution in step S1 is 0.4%, and the concentration of the sodium alginate is 2%.

[0012] As a further improvement of the present application, the concentration of Fe 3+ in the solution containing Fe 3+ is 0.5%-4%, and the solution containing Fe 3+ is one of FeCl3 solution and Fe2(SO4)3 solution.

[0013] As a further improvement of the present application, in step S1, the immersion treatment is complete immersion treatment on the surface and inside of the three-dimensional porous material, or complete immersion treatment on the surface and partial immersion treatment on the inside of the three-dimensional porous material.

[0014] As a further improvement of the present application, in step S1, the immersion treatment is complete immersion treatment on the surface and inside of the three-dimensional porous material, or complete immersion treatment on the surface and partial immersion treatment on the inside of the three-dimensional porous material.

[0015] As a further improvement of the present application, the three-dimensional porous material is one of melamine formaldehyde sponge, diatom ooze, biomass wood, metal nickel foam and metal copper foam.

[0016] As a further improvement of the present application, in step S2, the cross-linking time is 5-8 min.

[0017] To achieve the above-mentioned purposes, the application further provides a solar steam generator prepared by the above-mentioned blackening method of the surface of the three-dimensional porous material; the solar steam generator comprises a three-dimensional porous material substrate and a black interface gel layer loaded on the surface and inside the porous structure of the three-dimensional porous material substrate; the black interface gel layer is a composite gel system composed of tannic acid, sodium alginate and Fe 3+ .

[0018] As a further improvement of the application, the water evaporation rate of the solar steam generator reaches 2.63 kg m - 2 h -1 ; exhibits superhydrophilic and superoleophobic properties; the light absorption performance reaches 98% or above; and does not significantly deform under a weight of 900 times its own weight.

[0019] To achieve the above-mentioned purposes, the application further provides the above-mentioned blackening method of the surface of the three-dimensional porous material and the application of the above-mentioned solar steam generator in seawater desalination.

[0020] The application has the following beneficial effects:

[0021] 1. The blackening method of the surface of the three-dimensional porous material provided by the application can simultaneously perform surface modification and blackening treatment on the porous material by using the SA / TA-Fe 3+ system, and can also form a black micro-flake structure dispersed in the porous structure of the material or adhered to the skeleton. 3+ Based on the coordination effect between the phenolic hydroxyl group of tannic acid TA and Fe 3+ , a black complex (TA-Fe 3+ ) can be generated, so that the material has excellent light absorption performance. In addition, Fe 3+ can be chelated with the 1,4-linked alpha-l-guluronic acid (G unit) of sodium alginate SA, so that the sodium alginate SA is cross-linked to form a gel structure, thereby improving the stability of the light absorption material. In the application, the tannic acid-Fe 3+ system and the sodium alginate-Fe 3+ system are compounded under the action of Fe 3+The composite gel system formed by mixing the three is loaded on the surface and inside of the porous material (based on the actual application needs, according to the specific process of the impregnation treatment, the mixed gel system can be completely loaded inside the porous material or only loaded in a certain thickness) to form a micro-flake structure (black interface gel layer), which can significantly improve the mechanical properties of the porous material and will not be significantly deformed under the weight of 900 times its own weight, overcoming the technical defect that the porous material is compressed and deformed under stress.

[0022] 2、The method for blackening the surface of the three-dimensional porous material provided by the application, the sodium alginate is used to make the complex formed by the tannic acid and the ferric ion firmly adhere to the skeleton of the porous material, thereby enhancing the stability of the material itself and overcoming the technical defect that the coating without the sodium alginate hydrogel is thin and the amount of tannic acid TA modification is small in the prior art. In addition, the sodium alginate hydrogel layer can increase the coating thickness, so that more tannic acid TA adheres to the sponge skeleton. At the same time, the sodium alginate gel layer can make the material have excellent underwater oil-repellent property and extremely weak adhesion, as well as high-efficiency water purification function, so that it is suitable for use in an oil pollution environment.

[0023] 3、The solar steam generator prepared by the method for blackening the surface of the three-dimensional porous material provided by the application has a water evaporation rate of more than 2.00 kg m -2 h -1 . Whether in high-concentration salt water, real environment or long-term application, it can maintain high and stable water production. Based on the SA / TA-Fe 3+ modified porous material, the purification performance on seawater, dye wastewater and heavy metal wastewater makes it expected to become a candidate product of high-efficiency solar steam generator and has great commercial application value. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The method for blackening the surface of the three-dimensional porous material and the MF-SA / TA-Fe 3+ performance characterization diagram provided by the application Figure 1 a is a flow chart of the interface gel blackening method; Figure 1 b and Figure 1 c, d are SEM images of the original MF and the prepared MF-SA / TA-Fe 3+ outer surface, the scale is 300 μm, 30 μm; Figure 1 e is an element mapping image of the prepared MF-SA / TA-Fe 3+ outer surface, the scale is 100 μm.

[0025] Figure 2 The MF-SA / TA-Fe 3+Reaction principle and mechanical property characterization figure Figure 2 a is the reaction between TA, SA and Fe in Example 2 and Comparative Examples 2-3 3+ , and the corresponding mechanical stability test; Figure 2 b and Figure 2 c are the XRD and XPS spectra of MF-SA / TA-Fe provided in Example 2, respectively; 3+ Figure 2 d is the o1s curve fitting result of MF-SA / TA-Fe 3+ ; Figure 2 e and Figure 2 f are photos of MF of different shapes and modified by different substances (Examples 11-13), respectively; Figure 2 g and Figure 2 h are the lightness proof and compression test figure of MF-SA / TA-Fe 3+ , respectively.

[0026] Figure 3 Black MF-SA / TA-Fe provided in Example 2 of the present application 3+ Self-floating figure of the sponge in water.

[0027] Figure 4 MF-SA / TA-Fe provided in the present application 3+ Light absorption performance and evaporation performance characterization figure Figure 4 a, b, c are pure water, unprocessed MF of Comparative Example 1 and MF-SA / TA-Fe 3+ of the present application, respectively; Figure 4 d is the change of the surface temperature of the sample with irradiation time; Figure 4 e is the absorption, scattering and reflection of light on the surface of MF-SA / TA-Fe 3+ ; Figure 4 f is the change of water vapor generation mass with time under simulated sunlight irradiation and non-irradiation; Figure 4 g is the evaporation rate of different samples; Figure 4 h is the evaporation rate of MF-SA / TA-Fe -2 of the present application under 1 kW m 3+ of sunlight irradiation in the circulating water evaporation experiment; Figure 4 i is the evaporation rate comparison figure of the obtained sample with other reported samples.

[0028] Figure 5 Black MF-SA / TA-Fe provided in Example 2 of the present application 3+ Characterization figure of the oil-repellent performance and water purification performance of the sponge Figure 5 a is the underwater oil contact angle characterization of different oily droplets on the surface of MF-SA / TA-Fe 3+ ;​Figure 5 b is the rolling behavior characterization on the surface of the oil (dichloromethane) in MF-SA / TA-Fe 3+ Rolling behavior characterization on the surface and low adhesion proof; Figure 5 c is the dissolution process of the salt on the surface of MF-SA / TA-Fe 3+ Evaporation rate between different concentrations of NaCl solution; Fig. d is the dissolution process of the surface; Figure 5 e, f, g, h are characterization figures of purifying methylene blue dye wastewater, methyl orange dye wastewater, simulated seawater and heavy metal wastewater, respectively; Figure 5 i is the ion removal rate of simulated seawater and heavy metal wastewater.

[0029] Figure 6 UV / vis / NIR absorption spectrum of the porous material provided for Example 2 and Comparative Example 1 of the present application.

[0030] Figure 7 Black MF-SA / TA-Fe provided for Example 2 of the present application 3+ Evaporation performance of the sponge Figure 7 a is the MF-SA / TA-Fe 3+ Photos of sample scalability proof; Figure 7 b is the MF-SA / TA-Fe 3+ Outdoor evaporation experiment figure of the evaporator Figure 7 c is the outdoor evaporator temperature and solar power density Figure 7 d is the evaporation rate and water vapor generation mass change figure of the evaporator system.

[0031] Figure 8 Photos of different samples and corresponding UV / vis / NIR absorption spectra provided for Examples 1-5 of the present application, with a surface blackening time of 8 minutes.

[0032] Figure 9 Sample photos of different surface blackening times (SA, TA and Fe 3+ The concentrations of SA, TA and Fe are 2%, 0.4% and 2%, respectively.

[0033] Figure 10 Water contact angle characterization figure on the surface of the unprocessed MF provided for Comparative Example 1 of the present application.

[0034] Figure 11 Water contact angle characterization figure on the surface of MF-SA / TA-Fe 3+ provided for Example 2 of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be described in detail below in combination with the drawings and specific embodiments.

[0036] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0037] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0038] Please see Figure 1 As shown, the present invention provides a method for blackening the surface of a three-dimensional porous material, which includes the following steps:

[0039] S1, the three-dimensional porous material is placed in a mixture containing tannic acid and sodium alginate for impregnation treatment, forming a uniform mixed layer on the surface of the three-dimensional porous material, resulting in a surface-wetted three-dimensional porous material.

[0040] S2, placing a surface-wetted three-dimensional porous material in a Fe-containing environment. 3+ In a solution, tannic acid, sodium alginate, and Fe were obtained. 3 + The composite gel formed by mixing the three components is subjected to cross-linking treatment for 0.5 to 10 minutes to obtain a cross-linked three-dimensional porous material.

[0041] S3, the cross-linked three-dimensional porous material is rinsed to remove excess Fe. 3+ The solution is dried, and a black interface gel layer is formed on both the surface and inside the porous structure of the three-dimensional porous material, thereby obtaining a surface-blackened three-dimensional porous material.

[0042] Preferably, in the mixture of step S1, the concentration of tannic acid is 0.2% to 1.6% and the concentration of sodium alginate is 0.5% to 4%.

[0043] Preferably, in the mixture of step S1, the concentration of tannic acid is 0.4% and the concentration of sodium alginate is 2%.

[0044] Preferably, the Fe-containing 3+ In the solution, Fe 3+ The concentration is 0.5% to 4%; the Fe-containing 3+ The solution is either FeCl3 solution or Fe2(SO4)3 solution.

[0045] Preferably, in step S1, the impregnation treatment is complete impregnation treatment of the surface and interior of the three-dimensional porous material; or complete impregnation of the surface and partial impregnation of the interior of the three-dimensional porous material.

[0046] Preferably, in step S1, the impregnation treatment is complete impregnation treatment of the surface and interior of the three-dimensional porous material; or complete impregnation of the surface and partial impregnation of the interior of the three-dimensional porous material.

[0047] Preferably, the three-dimensional porous material is one of melamine formaldehyde sponge, diatom ooze, biomass wood, metal nickel foam, and metal copper foam.

[0048] Preferably, in step S2, the crosslinking time is 5-8 min.

[0049] Example 1

[0050] The embodiment 1 of the present application provides a blackening method for the surface of a three-dimensional porous material, which comprises the following steps:

[0051] S1, a piece of melamine formaldehyde (MF) sponge (size 3.5 cm x 3.0 cm x 2.0 cm) is completely immersed in a mixture containing tannic acid (TA) and sodium alginate (SA) to wet the outer surface and form a uniform mixed layer. The concentration of tannic acid (TA) is 0.2%, and the concentration of sodium alginate (SA) is 2%.

[0052] S2, the wet sponge is crosslinked in a FeCl3 solution (concentration 2%) for 8 min.

[0053] S3, the crosslinked sponge is washed with water several times to remove the excess FeCl3 solution in the sponge, and is dried to obtain a three-dimensional porous material with a blackened surface, modified MF sponge (denoted as MF-SA / TA-Fe 3+ ), which is a solar steam generator.

[0054] Comparative Example 1

[0055] Melamine formaldehyde (MF) sponge is used as a blank control.

[0056] Comparative Example 2

[0057] The difference from Example 1 is that only sodium alginate (SA) is used for impregnation treatment of the porous material.

[0058] Comparative Example 3

[0059] The difference from Example 1 is that only tannic acid (TA) is used for impregnation treatment of the porous material.

[0060] Examples 2-5

[0061] The difference from Example 1 is that the concentration of tannic acid (TA) is different, as shown in the table below. Everything else is the same as in Example 1 and will not be repeated here.

[0062] Example Tannic acid TA (%) Example 1 0.2 Example 2 0.4 Example 3 0.8 Example 4 1.2 Example 5 1.6

[0063] Examples 6-10

[0064] The difference from Example 1 is that the surface blackening time (crosslinking time) is different, as shown in the table below. Everything else is the same as in Example 1, and will not be repeated here.

[0065] Example Surface blackening time (min) Example 1 8.0 Example 6 0.5 Example 7 2.0 Example 8 4.0 Example 9 6.0 Example 10 10

[0066] Examples 11-13

[0067] The difference from Example 1 is that the type of porous material is different. Everything else is the same as in Example 1, and will not be repeated here.

[0068] Example Porous material type Example 1 Melamine formaldehyde (MF) sponge Example 11 Inorganic diatomaceous mud Example 12 Biomass wood Example 13 Metallic nickel foam

[0069] Examples 14-17

[0070] The difference from Example 1 is that sodium alginate (SA) and Fe 3+ The concentrations are different, as shown in the table below. Everything else is the same as in Example 1, and will not be repeated here.

[0071] Example Sodium alginate SA (%) Fe 3+ (%)]]> Example 1 2.0 2.0 Example 14 1.0 2.0 Example 15 3.0 2.0 Example 16 2.0 1.0 Example 17 2.0 3.0

[0072] Performance analysis was performed on Examples 1-17 and Comparative Examples 1-3.

[0073] Please see Figure 1 As shown, the surface blackening method provided in Embodiment 1 of the present invention, compared with the interconnected porous structure of the original MF sponge in Comparative Example 1, ( Figure 1 (as shown in b), modified MF sponge (represented as MF-SA / TA-Fe) 3+ The scanning electron microscope reveals a more complex porous structure, in which numerous micro-flakes are clearly visible dispersed within the pores of the sponge or adhered to its framework. Figure 1 (as shown in c and d). Figure 1 Elemental mapping analysis in e showed that the aforementioned microsheets were composed of C, O, and Fe elements, while N elements appeared only on the framework, not as a component of the microsheets. All of these results strongly confirm that the black complex was successfully modified onto the MF surface. It is worth noting that this surface blackening modification method does not involve expensive reagents, additional light-absorbing substances, or toxic solvents, making it environmentally friendly and cost-effective.

[0074] Please see Figure 2As shown, based on the technical mechanism of the interface gel blackening treatment, due to the coordination effect between the phenolic hydroxyl group of tannic acid TA and Fe 3+ , a black complex (TA-Fe 3+ ) can be generated, so that the porous material has good light absorption performance. In addition, Fe 3+ can be chelated with the 1,4-linked α-l-guluronic acid (G unit) of sodium alginate SA, promoting the cross-linking of sodium alginate SA to form a gel structure, and improving the stability of the light absorption material. Figure 2 In a, experiments were performed by wetting the MF sponge with SA and FeCl3 solution (Comparative Example 2), wetting the MF sponge with TA and FeCl3 solution (Comparative Example 3), and wetting the MF sponge with SA / TA mixture and FeCl3 solution (Example 2), respectively. It can be clearly seen from Figure 2 that the system composed of sodium alginate SA and Fe 3+ in Comparative Example 2 can form a stable gel structure, but cannot achieve surface blackening, while in the tannic acid TA and Fe 3+ system of Comparative Example 3, a large number of black TA-Fe 3+ can be quickly generated on the surface of the MF sponge, but the binding force between the black complex and the MF sponge is poor, and ultrasonic treatment (10 seconds) will cause the complex to fall off from the sponge matrix. Only in the SA / TA mixture and FeCl3 system of Example 2, the successful cross-linking reaction between SA, TA and Fe 3+ can form black micro-flakes dispersed in the pore structure or adhered to the skeleton Figure 2 (b-d), which helps to achieve surface blackening of the material, and based on the high stability and high adhesion of the composite gel system formed by mixing tannic acid, sodium alginate and Fe 3+ , it remains stable and does not fall off after 6h of ultrasonic treatment.

[0075] Further, according to the interface gel blackening method provided by the present application, various shapes (triangular, circular, rectangular or pentagonal, Figure 2 e) and different surface chemical porous materials (inorganic diatom ooze, biomass wood and metal nickel foam, Figure 2 f) provided by Examples 11-13 can be flexibly converted into black materials. Figure 2 g shows that the evaporator is light in quality, Figure 2 h shows that the evaporator has good mechanical properties. Even if compressed by a heavy object (about 900 times its own weight), the MF-SA / TA-Fe 3+ does not deform significantly, that is, the tannic acid-Fe 3+ system and the sodium alginate-Fe 3+The mixed gel system formed by mixing and dispersing the two systems mentioned above forms a micro-sheet structure (black interface gel layer) on the surface of porous materials and inside the porous structure (the inside of the porous structure can be fully or partially impregnated as needed). This can significantly improve the mechanical properties of porous materials, which helps to maintain stable water transport channels and thermal insulation performance after long-term steam generation.

[0076] Please see Figure 3 As shown, due to the black MF-SA / TA-Fe prepared in Example 2 of this invention 3+ Sponges can float in water, therefore, simulated sunlight (1kW m²) can be studied using infrared thermal imagers. -2 The dynamic temperature change of the evaporator. For example... Figure 4 As shown in 4a and 4b, due to their lack of light absorption properties, neither pure water nor the unprocessed MF in Comparative Example 1 showed significant temperature changes; after 20 minutes of irradiation, the temperature rise was approximately 4.9 °C and 5.1 °C, respectively. Figure 4 d). However, once the black MF-SA / TA-Fe is placed... 3+ When a sponge is placed under simulated sunlight, its surface temperature will rise rapidly and significantly. Figure 4 c) After irradiation for 20 minutes, the temperature rise can reach approximately 19.2℃. MF-SA / TA-Fe 3+ It exhibits excellent photothermal properties, mainly due to the prepared black SA / TA-Fe 3+ It possesses high light absorption performance and a micro-thin sheet structure. For example... Figure 4 As described in e, irradiation with MF-SA / TA-Fe 3+ Sunlight on the surface will be absorbed, reflected, or scattered. Clearly, the microplates on the porous structure can significantly increase the probability of light reflection, and even multiple reflections can be observed within the structure, thus allowing the evaporator to more effectively capture sunlight to heat the water on the evaporator surface. Such excellent light absorption and photothermal properties make MF-SA / TA-Fe... 3+ It shows great promise as a high-performance evaporator for generating steam.

[0077] exist Figure 4 In section f, the mass change of water under constant sunlight was tested. Clearly, the evaporation rates of pure water and unprocessed MF were low, at 0.472 kg m³, respectively. -2 h -1 and 0.636 kg m -2 h -1 . Add MF-SA / TA-Fe 3+ After the evaporator, due to the heat generation induced by light absorption, the steam rate is greatly accelerated, resulting in a significant increase in the evaporation rate to 2.63 kg m³. -2 h -1 (Figure 4 g), and good evaporation performance can be maintained stable during long-term use Figure 4 h). Moreover, for these substances modified by the proposed interfacial gelation blackening method (wood, foamed nickel and diatom ooze in Examples 11-13), the evaporation rate is significantly improved to 2.00 kg m -2 h -1 Above, higher than similar materials in existing reports Figure 4 i). These results strongly demonstrate the effectiveness of the interfacial gelation blackening method provided by the present application for improving solar-driven steam generation performance, and the versatility for different materials.

[0078] In Figure 5 a, the underwater oleophobicity of MF-SA / TA-Fe 3+ was evaluated. For some commonly used oils, MF-SA / TA-Fe 3+ prepared in Example 2 exhibited underwater superoleophobicity and extremely weak adhesion, so that oil droplets could quickly roll off the surface without contamination Figure 5 b, Figure 6 shown). The excellent underwater superoleophobicity of MF-SA / TA-Fe 3+ can be attributed to the superhydrophilic SA / TA-Fe 3+ gel structure, which can absorb a large amount of water and form a hydration layer on the surface to prevent oil contamination. Therefore, due to the continuous upward transport of water inside the evaporator, MF-SA / TA-Fe 3+ The salt on the surface is easily dissolved Figure 5 c), and ensures that the evaporator maintains stable steam generation capacity even in high salinity seawater Figure 5 d). Subsequently, different solutions such as dye wastewater, simulated seawater and heavy metal wastewater were tested to evaluate the purification effect of the prepared MF-SA / TA-Fe 3+ on wastewater. As shown in Figure 5 e and Figure 5 f, compared with dye wastewater, the collected water became clear, and there were no ultraviolet characteristic peaks of methylene blue and methyl orange in the condensed water after solar evaporation. In addition, the concentrations of Na + , Mg 2+ , K + , Ca 2+ in the purified simulated seawater and the concentrations of Fe 3+ , Cu 2+ , Ni 2+ , Mn 2+ , Sn 2+ in the heavy metal wastewater were greatly reduced Figure 5 g and h). The ion removal rate was higher than 99% Figure 5i) meets the health drinking water standards set by the World Health Organization (WHO). The above shows that the MF-SA / TA-Fe 3+ has excellent underwater oleophobicity and extremely weak adhesion, and water purification function.

[0079] Most importantly, the interface gel blackening method proposed in the present application can also be flexibly used to modify large-size materials, which is very important for promoting the conversion of materials from the laboratory to practical use. Figure 7 a shows that the modified MF-SA / TA-Fe 3+ with a size of 50cm x 50cm x 1cm (which can be easily scaled up further), the surface modification cost (modification depth is about 1mm) is calculated to be about 0.5$, which proves the feasibility and low cost of the proposed large-area material method. Outdoor experiments were carried out under sufficient light conditions to study the practical application potential of MF-SA / TA-Fe 3+ . As shown in Figure 7 b, a simple device was designed and prepared, and the sample was used to absorb sunlight and convert it into heat to generate steam, and the formed water was condensed into water and flowed along the spherical collector. Due to the changes in ambient temperature and radiation intensity, the mass of water changes with time, and strong sunlight and higher ambient temperature are conducive to more efficient generation of water vapor. In the open field Figure 7 c and d), the average evaporation rate was calculated to be 1.05kg m -2 h -1 -1 2 after solar irradiation from 8:30am to 15:30pm. This means that 1m 3+ of MF-SA / TA-Fe 3+ can produce at least 7.35L of clean water per day under sufficient sunlight to meet the daily water needs of 3 adults.

[0080] Please refer to Figure 8 to 9 , in examples 1 to 10, the concentration of tannic acid TA in the mixture varies between 0.2% and 1.6%, and the blackening time varies between 0.5-10 minutes. According to the light absorption of the obtained material, it is determined that the ideal concentration of tannic acid TA is 0.4%, and a short time of about 8 minutes is sufficient to complete the surface blackening treatment, without the need for excessive use of modifiers and long-term treatment.

[0081] Please refer to Figure 10 to 11 , as shown in the comparison of the water wetting properties of the sponge in Comparative Example 1 and the modified sponge in Example 2 of the present application, it can be seen that the water wetting properties of the sponge before and after modification do not change, and still have superhydrophilic properties, which is convenient for water to be transported inside the sponge.

[0082] In Examples 14-17, sodium alginate (SA) and Fe 3+The influence of the concentration change of the sodium alginate SA on the performance of the modified sponge is that: if the concentration of the sodium alginate SA is too high, the viscosity is too high, it is difficult to wet the internal pores of the sponge, and uneven black hydrogel appears on the internal surface of the sponge. If the concentration of the sodium alginate SA is too low, the gel layer modified on the skeleton of the sponge is too thin, more TA cannot be modified on the skeleton, and even the black hydrogel cannot be generated on the sponge, so that the blackening degree of the sponge is not high.

[0083] In conclusion, the application provides a solar steam generator, a blackening method for a surface of a three-dimensional porous material and application. The blackening method comprises the following steps: S1, placing the three-dimensional porous material in a mixed solution containing tannic acid and sodium alginate, performing immersion treatment, forming a uniform mixed layer on the surface of the three-dimensional porous material, and obtaining a surface-wetted three-dimensional porous material; S2, placing the surface-wetted three-dimensional porous material in a solution containing Fe 3+ , forming a cross-linking system composed of tannic acid, sodium alginate and Fe 3+ , and performing cross-linking treatment for 0.5-10 min to obtain a cross-linked three-dimensional porous material; S3, performing rinsing treatment on the cross-linked three-dimensional porous material to remove excess Fe 3+ solution, and performing drying treatment, so that a black interfacial gel layer is formed on the surface and in the porous structure of the three-dimensional porous material, thereby obtaining a surface-blackened three-dimensional porous material. The SA / TA-Fe 3+ system composed of sodium alginate, tannic acid and iron ions is used to perform surface modification and blackening treatment on the porous material, and at the same time, a black micro-flake structure dispersed in the porous structure of the material or adhered to the skeleton can be formed. Based on the coordination effect between the phenolic hydroxyl group of tannic acid and Fe 3+ , a black complex can be generated, so that the material has excellent light absorption performance. In addition, Fe 3+ can be chelated with sodium alginate to promote the cross-linking of sodium alginate to form a gel structure, thereby improving the stability of the light absorption material. In addition, the micro-flake structure formed by the above cross-linking system on the surface and in the porous structure of the porous material can significantly improve the mechanical performance of the porous material, overcoming the technical defect that the porous material is compressed and deformed under stress.

[0084] The above examples are only used to illustrate the technical solutions of the application and not to limit the application. Although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the application.

Claims

1. A method for blackening a surface of a three-dimensional porous material, characterized by: It comprises the following steps: S1, the three-dimensional porous material is placed in a mixed solution containing tannic acid and sodium alginate for immersion treatment, a uniform mixed layer is formed on the surface of the three-dimensional porous material, and a three-dimensional porous material with a wet surface is obtained; the concentration of the tannic acid is 0.2%-1.6%; the concentration of the sodium alginate is 0.5%-4%; S2, placing the surface-wetted three-dimensional porous material in a solution containing Fe 3+ , to obtain a composite gel system formed by mixing tannic acid, sodium alginate and Fe 3+ , and performing cross-linking treatment for 0.5-10 min to obtain a cross-linked three-dimensional porous material; the concentration of Fe 3+ in the solution containing Fe 3+ is 0.5%-4%. S3, rinsing the three-dimensional porous material after the cross-linking treatment to remove excess Fe 3+ solution and drying treatment, a black interfacial gel layer is formed on the surface and inside the porous structure of the three-dimensional porous material, thereby obtaining a three-dimensional porous material with a blackened surface; The SA / TA-Fe system is composed of sodium alginate, tannic acid and iron ions 3+ The system can perform surface modification and blackening treatment on the three-dimensional porous material, and can also form black micro-flake structures dispersed in the porous structure of the three-dimensional porous material or adhered to the framework.

2. The method of blackening a three-dimensional porous material surface according to claim 1, wherein: In the mixed solution of step S1, the concentration of the tannic acid is 0.4%; the concentration of the sodium alginate is 2%.

3. The method of blackening a three-dimensional porous material surface of claim 1, wherein: The solution containing Fe 3+ is one of FeCl3 solution, Fe2(SO4)3 solution.

4. The method of blackening a three-dimensional porous material surface of claim 1, wherein: In step S1, the immersion treatment is complete immersion treatment on the surface and inside of the three-dimensional porous material; or complete immersion treatment on the surface and partial immersion treatment on the inside of the three-dimensional porous material.

5. The method of blackening a three-dimensional porous material surface of claim 1, wherein: The three-dimensional porous material is one of melamine formaldehyde sponge, diatom ooze, biomass wood, metal nickel foam and metal copper foam.

6. The method of blackening a three-dimensional porous material surface of claim 1, wherein: In step S2, the crosslinking time is 5-8 min.

7. A solar steam generator characterized by: The solar steam generator is prepared by the blackening method of the three-dimensional porous material surface according to any one of claims 1 to 6; the solar steam generator comprises a three-dimensional porous material substrate and a black interface gel layer loaded on the surface and inside the porous structure of the three-dimensional porous material substrate; the black interface gel layer is a composite gel system formed by mixing tannic acid, sodium alginate and Fe 3+ and the like. The solar steam generator is prepared by the blackening method of the three-dimensional porous material surface according to any one of claims 1 to 6; the solar steam generator comprises a three-dimensional porous material substrate and a black interface gel layer loaded on the surface and inside the porous structure of the three-dimensional porous material substrate; the black interface gel layer is a composite gel system formed by mixing tannic acid, sodium alginate and Fe 3+ and the like.

8. The solar steam generator of claim 7, wherein: The water evaporation rate of the solar steam generator reaches 2.63 kg m -2 h -1 ; exhibits super-hydrophilic and super-oleophobic properties; light absorption performance reaches 98% and above; does not deform significantly under 900 times its own weight.

9. Application of the method for blackening the surface of the three-dimensional porous material according to any one of claims 1-6 to the field of seawater desalination.

10. Application of the solar steam generator according to any one of claims 7-8 to the field of seawater desalination.

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