Porous foam with bionic lotus seedpod surface structure and preparation thereof

Abstract

The invention provides porous foam with a bionic lotus seedpod surface structure and a preparation method of the porous foam, belongs to the technical field of photothermal conversion materials, and aims to solve the technical problem that a solar evaporator is poor in water evaporation performance and salt resistance. According to the invention, a vacuum solution pouring technology / salt template method / template auxiliary technology is combined to prepare the composite foam, and the composite foam has a surface hemispherical pore structure and a lower layer honeycomb hierarchical pore structure at the same time, which is benefited from unique surface and internal pore structures; the solar evaporator shows efficient and stable evaporation performance, high salt resistance, good self-cleaning capacity and the like in NaCl solutions with different concentrations, and the double-layer hierarchical pore composite foam has wide application prospects in sewage treatment and seawater desalination. The preparation method has the advantages of being simple in process, convenient to operate, controllable in surface pore structure and internal pore shape, capable of forming evaporators in complex shapes and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of photothermal conversion materials, and particularly relates to a water evaporator. Background Art

[0003] In 2024, Ma et al. designed a low-cost and high-efficiency fence solar evaporator using 3D printing technology. When tested under 1 sun illumination, the evaporator with a height of 18 mm and a gap width of 0.6 mm achieved a solar-driven water evaporation rate of 2.52 kg m - 2 h -1 . In addition, the device exhibited excellent salt tolerance and did not show salt accumulation or performance degradation during long-term use.

[0004] In 2024, Li et al. successfully prepared a cone array ultra-black (CAUB) surface using template replication and doctor blade coating techniques. A stainless steel template with regularly arranged micro-cone hole arrays was prepared using nanosecond laser ablation technology, and then an inverted cone array ultra-black (CAUB) surface was prepared by replicating this template. Through simulation and experiment, the relationship between the absorptivity (or reflectivity) of CAUB and its geometric parameters, layout, and material composition was revealed. The CAUB sample exhibited an absorbance as high as 99.35% in the UV-vis-NIR range and as high as 98% in the mid-infrared and far-infrared ranges. Under 1 sun illumination, the surface temperature of the sample reached 75 °C, corresponding to a photothermal conversion efficiency of 73.8%, exceeding many previously reported light-absorbing materials.

[0005] In 2023, Niu et al. designed an all-weather solar-driven interfacial evaporator with a sandwich structure. The top and bottom layers of the evaporator were composed of MnO2-modified cotton cloth for photothermal conversion and water transport, and the middle layer was composed of a phase change microcapsule / hydrogel composite material for heat storage and heat release. Under an irradiation of 1 kW m -2 , the evaporation rate of the evaporator was 2.67 kg m -2 h -1 , and the evaporation efficiency was 89.5%. In the dark, the heat released by the phase change layer supported an evaporation rate of 0.43 kg m -2 h -1 , which was 3.6 times that of pure water. In addition, the hybrid device was equipped with a thermoelectric module and achieved a stable output power of 0.42 W m -2 under 1 sun illumination and an extended output of 30 min in the dark.

[0006] In 2024, Lei et al. prepared a 3D-Felt fabric evaporator modified with MXene, chitosan, and dopamine with a concave array structure, which has a multi-layered network porous structure and adjustable concave dimensions. Due to its unique structural advantages, the evaporator has a high light absorption capacity (98.1%), balanced interfacial heating and water supply, effective vapor diffusion, and a low enthalpy of water evaporation. The 3D evaporator has an evaporation rate of up to 2.69 kg m -2 h -1 , a photothermal conversion efficiency of up to 97.09%, and an outdoor evaporation volume of up to 11.64 kg m -2 . It has high antibacterial properties, salt tolerance (200 hours in 15 wt% NaCl solution), and oil pollution resistance (underwater oil contact angle of 150°).

[0007] In 2024, Wang et al. designed a waffle-shaped solar evaporator (WSE). The WSE was fabricated via a zinc-assisted pyrolysis route, combining a low-cost biomass carbon source, recyclable zinc, and a molding process, which enables low-cost production without complex processing. Compared with traditional planar corrugated evaporators, the WSE features additional sidewalls for triggering convection with synergistic solute and thermo-Marangoni effects. Therefore, the WSE achieves spontaneous salt rejection and persistent evaporation stability, operating continuously in saline water for over 60 days without fouling.

[0008] In 2023, Wang et al. studied a double-sided carbon nanotube sponge (CNTS) for efficient solar-driven seawater evaporation. CNTS was synthesized by chemical vapor deposition and then prepared into double-sided CNTS through electrochemical treatment. Its top layer is a hydrophobic layer (light absorption layer), and the bottom layer is a hydrophilic layer (water transport layer). This structure effectively separates light absorption and water transport, reducing solar energy loss and salt deposition. Under 1 sun illumination, the evaporation rate of the double-sided CNTS reaches 3.0 kg m -2 h - -1, with an energy conversion efficiency of 95%, significant desalination effect on saline water, ion concentration meeting drinking water standards, and good long-term stability.

[0009] In 2024, He et al. prepared a wood interface solar steam generator (MIDW) with delignified linden as the substrate material and MXene as the photothermal conversion material. The inverted pyramid groove structure on its surface can reduce light reflection, enhance photothermal conversion efficiency, achieve thermal localization, and improve salt tolerance. Under 1 kW m -2 illumination, the seawater evaporation rate of the MIDW evaporator reaches 1.92 kg m -2 h - -1, and the generator has a simple preparation process, low cost, and high evaporation efficiency, providing a new approach for seawater desalination and wastewater treatment.

[0010] In 2024, Zhong et al. prepared a sulfonated carbonized corncob (SCC) evaporator using corncob as the carbon source and concentrated sulfuric acid as the sulfonating agent through a carbonization-sulfonation strategy. Its enthalpy of vaporization of water was as low as 1800 J / g, the evaporation rate reached 3.16 kg / m 2 ·h, the evaporation efficiency was 159%, and the electrostatic repulsion of sulfonic acid groups achieved effective separation of Na + and Cl−, enhancing the salt tolerance. This research provides an effective technology for regulating the water state of carbon-based solar interfacial evaporation devices at the molecular level and is of great significance for the research and development of biomass-based evaporation devices.

[0011] In 2024, Xiao et al. prepared a bionic evaporator containing a conductive hydrogel through 3D printing technology. It has excellent solar absorption, good mechanical properties, high water absorption, and low enthalpy of vaporization. The vertical microchannels in the hydrogel promote the transport of ions from the interface to the bulk of seawater, and the edge petal structure enables salt ions to crystallize at the edge. The two work together to inhibit salt crystallization.

[0012] In 2021, Zou et al. were inspired by the ultrafast liquid transport on the peristome surface of Nepenthes and the design of continuous arch bridges in architecture to prepare a bionic 3D arch solar evaporator. The evaporator was 3D printed from a composite resin containing carbon nanofibers and had a microcavity groove array bionic structure on the surface, which could form a double-layer continuous water film to achieve efficient solar water evaporation. Under 1 sun illumination, the evaporation rate was 1.64 kg m -2 h -1 , the efficiency was 91%, there was no salt precipitation accumulation after 200 h in 10 wt% NaCl solution, and the purified water met the WHO drinking water standard and could be used for wheat planting, demonstrating its application potential in agricultural planting.

[0013] In 2021, Li et al. introduced air into the hydrogel through a simple and controllable micropore generation method to synthesize a hierarchically porous aerogel with enhanced light absorption and heat localization capabilities. The aerogel uses chitosan-polyaniline copolymer (CP) as the light absorber and sodium alginate as the enhancer, and has a unique hierarchically porous structure with a pore size that can be regulated between 99 ± 49 μm and 316 ± 58 μm. Under 1 sun illumination, the evaporation rate of the aerogel reached 2.76 kgm -2 h -1 , the solar-steam conversion efficiency was 91.3%, and it showed excellent water purification performance under both simulated and natural sunlight, with significant treatment effects on artificial seawater and municipal wastewater.

[0014] In 2021, Lu et al. reported an effective method for efficient solar steam generation through the synergistic effect of an integrated hybrid hydrogel evaporator embedded with two-dimensional nanostructures and surface patterning. This improved surface-patterned evaporator can reduce the enthalpy of vaporization and induce the Marangoni effect near the evaporation surface, achieving an evaporation rate of 3.62 kg·m -2 h -1 , more than twice the theoretical limit of ordinary two-dimensional photothermal evaporators. This hybrid hydrogel provides a cost-effective approach to alleviating the shortage of clean water. It performs excellently in wastewater purification and seawater desalination and is expected to provide an ideal solution for the practical application of solar steam generation.

[0015] In 2019, Xu et al. were inspired by water lilies and proposed a hierarchical structure (WHS) for efficient and stable solar evaporation of high-salinity brine / wastewater until complete separation of water and solutes was achieved. After chemical etching, coating, and decoration treatment, the solar absorber at the top of this structure has a sunlight absorption rate of 98% and is hydrophobic; the bottom support is made of polystyrene with low thermal conductivity and has through holes. Experiments showed that when treating deionized water, 10 wt% brine, and 30 wt% wastewater with WHS, the evaporation rates were 1.31, 1.28, and 1.27 kg·m -2 h -1 , and the ion concentration decreased significantly. In experiments lasting 8 hours and 18 days continuously, WHS demonstrated a high evaporation rate, anti-pollution ability, and stability. Its average evaporation rate was higher than that of traditional solar absorbers, and there was no salt accumulation on the surface.

[0016] In 2022, Xu et al. were inspired by the structure of black hair and proposed a design strategy for a three-dimensional arched solar evaporator based on hydrophilic photothermal fibers for efficient water evaporation and long-term salt discharge. The melanin granules contained in black hair endow it with full-spectrum solar absorption and hydrophilic properties, and its surface temperature can rapidly increase under illumination. Its structure helps improve the photothermal conversion ability and hydration. Designing the photothermal layer as a three-dimensional arched structure can reduce the contact area with water, expand the evaporation area, reduce heat loss, and achieve efficient evaporation (the evaporation rate of black hair is 1.39 kg·m -2 ·h -1 , with an efficiency of 95.1%; that of carbon fiber oxide is 1.38 kg·m -2 ·h -1 , with an efficiency of 94.7%), and it can eliminate salt accumulation through Marangoni convection and capillary action, showing excellent desalination ability and durability in seawater desalination (it can evaporate outdoors continuously for 20 days), providing a new approach for the design and application of solar seawater desalination devices.

[0017] Currently, there are still some problems with the methods used to prepare special interface solar evaporators. For example, although the evaporator prepared with a special surface structure and rich internal pore channels improves its salt tolerance, the preparation process is complex. Some evaporators have excellent salt tolerance through the optimized design of structure and materials, but sometimes the evaporation efficiency is sacrificed. Therefore, it is still a challenge to prepare a solar evaporator with both good water evaporation performance and good salt tolerance. Summary of the Invention

[0018] Aiming at the technical problems of poor water evaporation performance and salt tolerance of solar evaporators, the present invention proposes a porous foam with a bionic lotus pod surface structure and a preparation method thereof. The composite foam is prepared by jointly using vacuum solution casting technology / salt template method / template-assisted technology. It has both a surface hemispherical pore structure and a lower-layer honeycomb-like hierarchical pore structure. Thanks to the unique surface and internal pore structures, the solar evaporator exhibits efficient and stable evaporation performance, high salt tolerance, and good self-cleaning ability in NaCl solutions with different concentrations. This double-layer hierarchical pore composite foam has broad application prospects in sewage treatment and seawater desalination. The preparation method has the advantages of simple process, convenient operation, controllable surface pore structure and internal pore morphology, and can form evaporators with complex shapes.

[0019] In order to achieve the above object, the technical solution of the present invention is realized as follows:

[0020] The present invention designs the surface structure of the interface solar evaporator. Inspired by the natural structure of the lotus pod and the cultural movable type printing technique, the porous foam obtained by using the designed template has high salt tolerance, excellent evaporation performance, good salt removal and self-cleaning ability, etc.

[0021] A porous foam with a bionic lotus pod surface structure, comprising a porous foam matrix, wherein photothermal particles are distributed in the porous foam matrix, and grooves are distributed on the upper surface of the porous foam matrix to form a bionic lotus pod surface structure.

[0022] The preparation method includes the following steps:

[0023] (1) Disperse and mix a polymer compound and photothermal particles into a solvent to prepare a mixed solution;

[0024] (2) Attach glue to small balls, then arrange a layer of the small balls with glue and cure them to bond the small balls together to obtain a surface structure template;

[0025] (3) Lay the surface structure template flat in the mold, then lay the pore-forming agent flat on the surface structure template to form a preform, and finally inject the mixed solution into the preform to form. After curing, remove the pore-forming agent and demold to obtain a water-porous foam with a bionic lotus surface structure (after demolding, small balls form groove structures on the upper surface of the porous foam matrix, and the distribution of the grooves is regulated by the arrangement of the small balls in the surface structure template).

[0026] The polymer compound is any one or more of polyacrylonitrile, polyurethane, polyvinyl alcohol, and cellulose acetate.

[0027] The photothermal particles are any one of graphite, graphene, graphene oxide, carbon black, carbon nanotubes, carbon fibers, polythiophene, polypyrrole, polyaniline, carbonized biomass, and iron tetroxide.

[0028] The solvent is any one or more of N,N-dimethylformamide, dichloromethane, tetrahydrofuran, dimethyl sulfoxide, or acetone.

[0029] In the step (1), the ratio of the polymer compound to the solvent is 0.1 - 0.3 g / mL, and the photothermal particles are 5 - 20 wt% of the polymer compound.

[0030] The diameter of the small balls is 2 - 6 mm; the small balls are glass balls.

[0031] The glue is silica gel, and the silica gel is PDMS glue.

[0032] The pore-forming agent is any one of sodium chloride, sucrose, or ammonium bicarbonate; the particle size of the pore-forming agent is 100 - 300 μm.

[0033] The curing method is solvent extraction; the method for removing the pore-forming agent is to soak the cured preform in water to dissolve the pore-forming agent.

[0034] The porous foam is used as a water evaporator.

[0035] Preferably, a method for preparing a porous foam with a bionic lotus surface structure is as follows:

[0036] (1) Weigh a certain amount of CNTs, pour them into an N,N-dimethylformamide (DMF) solution, and ultrasonically treat them at room temperature to obtain a uniformly dispersed CNTs suspension solution;

[0037] (2) Weigh a certain amount of CA and TPU, dissolve them in the suspension solution obtained in step (1), and use a constant temperature magnetic stirrer to completely dissolve them to obtain a well-dispersed and uniform CA / TPU / CNTs mixed solution, and then let it stand at room temperature for later use;

[0038] (3) Weigh a certain amount of polydimethylsiloxane (PDMS) A glue and B glue, mix the A glue and B glue in a certain proportion, and mix them with glass beads and stir to make the surface of the glass beads evenly adhere to the PDMS glue. Then arrange them in a metal mold with a size of 12 cm × 12 cm and a height of 2 cm. The arrangement method can be designed according to the required surface structure. After the arrangement is completed, put the mold into a vacuum drying oven for defoaming. After defoaming is completed, put the mold into an oven and keep it at a certain temperature for a period of time to make it form. After forming, demold and set aside for later use;

[0039] (4) First, put the template made in step (3) into a metal mold with a size of 12 cm × 12 cm, and then spread a certain amount of NaCl particles evenly on the template and apply pressure to form a dense NaCl preform. Then inject the CA / TPU / CNTs mixed solution obtained in step (2) into the NaCl preform with the assistance of a vacuum pump. After the preform is completely immersed, put it into a low-temperature refrigerator for pre-freezing.

[0040] (5) First, place the pre-frozen CA / TPU / CNTs / NaCl preform obtained in step (4) in a low-temperature ethanol bath and extract the solvent for a certain time by the solvent exchange method. Then take it out and soak it in deionized water for a certain time to remove the NaCl particles. Finally, freeze-dry and demold to successfully prepare a CA / TPU / CNTs solar water evaporator with a hemispherical surface structure.

[0041] In the present invention, cellulose acetate (CA) with good hydrophilicity and thermoplastic polyurethane (TPU) with excellent mechanical properties are used as the three-dimensional framework of the solar evaporator. Carbon nanotubes (CNTs) are used as the photothermal conversion material, and a self-made template of PDMS solution and glass beads is used. The CA / TPU / CNTs (CTC) composite foam is prepared by combining the salt template method / vacuum solution casting technique / template-assisted technique. The CTC is a solar evaporator with a hemispherical structure on the surface and a rich hierarchical pore structure inside. The CTC surface has characteristic structures such as side edges, basins, and plateaus. During the seawater desalination (seawater evaporation) process, since the evaporation rate and heat consumption rate on the plateaus of the CTC surface are higher than those in the basins, the salt concentration in the plateau part is higher than that in the basin part, and the temperature is lower than that in the basin part. A salt concentration gradient field and a temperature gradient field are formed at the side edge part of the CTC, thereby generating a surface tension gradient, enhancing the Marangoni flow, enabling the CTC evaporator to spontaneously avoid the formation of salt crystals and timely remove salt crystals, showing excellent salt tolerance. In addition, another reason for the excellent salt tolerance of the evaporator is that the honeycomb-like hierarchical pore structure in the lower layer of the CTC evaporator serves as a reservoir to provide sufficient moisture for seawater evaporation, shortening the downward migration path of salt ions, enabling the salt ions to circulate well inside the evaporator, avoiding the generation of high-concentration salt ions locally, and thus inhibiting the formation of salt crystals on the evaporation surface. Thanks to the above structural advantages, the CTC composite porous foam has achieved efficient and stable evaporation performance and salt tolerance in NaCl solutions with different concentrations. Inspired by the cultural movable type printing technology, the template used to manufacture the CTC solar interface evaporator is made of PDMS and glass balls. The template manufacturing method is simple, efficient, pollution-free, can regulate the surface structure morphology, and can be reused. The CTC interface solar evaporator has broad application prospects in sewage treatment and seawater desalination.

[0042] Advantages of the present invention:

[0043] (1) The preparation of the porous foam of the present invention has the advantages of simple process, convenient operation, and controllable pore structure.

[0044] (2) The template used to prepare the porous foam of the present invention can design the structure according to actual needs, imprint a specific structure on the surface of the porous foam, which is convenient for adjustment, has a simple process and is pollution-free.

[0045] (3) The porous foam of the present invention has a biomimetic lotus surface structure and an internal hierarchical pore structure. The synergistic effect of the two enables it to have excellent evaporation rate and evaporation efficiency, and at the same time has good salt tolerance, without secondary pollution problems, and has broad application prospects in the fields of seawater desalination and sewage purification. Description of the Drawings

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 It is a schematic diagram of the preparation steps for the CA / TPU / CNTs hemispherical surface solar water evaporator.

[0048] Figure 2 (a) Self-made solar water evaporation test system, (b) Schematic diagram of solar interfacial water evaporation simulation.

[0049] Figure 3 It is a structural diagram of the CTC solar evaporator with a bionic lotus surface structure.

[0050] Figure 4 (a) Distribution map of salt ion flow during the evaporation of brine by the evaporator without surface modification, (b) Distribution map of the internal salt ion flow state of the evaporator with the surface structure modified by the template of the present invention.

[0051] Figure 5 (a) Macroscopic physical diagrams of templates with ball diameters of 2mm, 3mm, 4mm, and 5mm respectively, (b) Macroscopic physical diagrams of interfacial solar evaporators with surface ball diameters of 3mm, 4mm, 5mm, and 6mm respectively.

[0052] Figure 6 (a) CTC-3 surface wettability test, (b) Mass change of CTC-3 before and after water absorption.

[0053] Figure 7 It is the photothermal conversion performance of the CTC-X evaporator; (a) Thermal conductivity of pure water and Examples 9, 8, Comparative Example 1, and Comparative Example 2; (b) Solar absorptance of Comparative Example 1, Comparative Example 2, and Example 1; (c) Curve graph of the surface temperature change of different evaporators under one sun intensity.

[0054] Figure 8 (a) Pure water evaporation rate of the CTC evaporator (Examples 1, 2, 3, 4, 5, and Comparative Examples 1 and 2) under one sun, (b) Pure water evaporation rate and efficiency of the CTC evaporator (Example 2) after 15 cycles under one sun, (c) Evaporation rate of simulated brine of the CTC evaporator (Examples 1, 2, 3, 4, 5, and Comparative Example 1) under one sun, (d) Seawater evaporation rate and efficiency of the CTC evaporator (Example 2) after 15 cycles under one sun.

[0055] Figure 9 Evaporation performance of the CTC evaporator (Examples 1, 2, 3, 4, 5 and Comparative Example 1) in salt water with different salt concentrations. (a) Evaporation performance of Comparative Example 1 at different brine concentrations; (b) Evaporation performance of Example 1 at different brine concentrations; (c) Evaporation performance of Example 2 at different brine concentrations; (d) Evaporation performance of Example 3 at different brine concentrations; (e) Evaporation performance of Example 4 at different brine concentrations; (f) Evaporation performance of Example 5 at different brine concentrations.

[0056] Figure 10 Evaporation performance of the CTC-3 evaporator (Example 2) in real outdoor environment for seawater. (a) Evaporation rate, accumulated water weight, and (b) Variations of solar flux, temperature, and humidity in the outdoor experiment; (c) Photo of the self-made outdoor experimental equipment; (d) Ion concentrations of seawater and collected distilled water.

[0057] Figure 11 Purification ability of the CTC evaporator for dye wastewater. (a) UV-visible spectra and corresponding digital photos of MB, (b) MO, and (c) Rhb before and after treatment, and (d) Evaporation rates of different dyes by CTC-3 under sunlight irradiation. Detailed implementation manners

[0058] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0059] Examples 1-9

[0060] A preparation method of a solar water evaporator with a bionic lotus surface structure, using CA and TPU as the base materials of the evaporator and CNTs as the photothermal materials of the evaporator. The preparation process is as Figure 1 shown, including the following steps:

[0061] (1) Weigh 0.576 g of CNTs, pour them into 60 mL of N,N-dimethylformamide (DMF) solution, and ultrasonically treat for 4 h at 25 °C to obtain a uniformly dispersed CNT suspension solution;

[0062] (2) Weigh a total of 7.2 g of CA and TPU, with the mass ratio of CA to TPU being 10:0 - 0:10. Dissolve them in the suspension solution obtained in step (1), and use a constant temperature magnetic stirrer to process for 16 h until completely dissolved to obtain a well-dispersed and uniform CA / TPU / CNTs mixed solution. The mass ratio of CNTs to the polymer (TPU / CA) is 8 wt%, and then let it stand at room temperature for later use.

[0063] (3) Weigh a certain amount of PDMS component A and B. Mix A and B in a ratio of 1:1, and mix them with glass beads by stirring to make the surface of the glass beads evenly adhere to the PDMS glue. Then arrange them in a metal mold with an area of 12 cm × 12 cm and a height of 2 cm. Adjust the size of the surface bionic lotus structure by adjusting the diameter of the glass beads. In this invention, the diameters of the glass beads are mainly explored to be 2 mm, 3 mm, 4 mm, 5 mm, and 6 mm respectively. After the arrangement is completed, put the mold into a vacuum drying oven for defoaming, and then put the mold into an oven and keep it at 60 °C for 7 h to make it form. After the templates with various different ball diameters are formed, demold them for later use.

[0064] (4) First, put the template made in step (3) into a metal mold with a size of 12 cm × 12 cm, and then spread 80 g (212 - 300 μm) of NaCl particles on the template and apply pressure to form a dense NaCl preform. Then inject the CA / TPU / CNTs mixed solution obtained in step (2) into the NaCl preform with the assistance of a vacuum pump. After the preform is completely immersed, put it into the refrigerator for pre-freezing.

[0065] (5) First, place the pre-frozen CA / TPU / CNTs / NaCl preform obtained in step (4) in an ethanol bath at -75 °C for 72 h, extract the solvent by the solvent exchange method, then take it out and soak it in deionized water for 48 h to remove the NaCl particles. Finally, freeze-dry and demold to successfully prepare a CA / TPU / CNTs solar water evaporator with a bionic lotus surface structure. (Hereinafter referred to as "CTC-x", where x is the size of the ball diameter).

[0066] Examples 1 - 9 prepare the solar evaporator according to the above preparation steps, and the specific process parameters are shown in Table 1:

[0067] Table 1 List of process parameters in Examples 1 - 9

[0068]

[0069]

[0070] Comparative Example 1

[0071] (1) Weigh 0.576 g of CNTs and pour them into 60 mL of DMF solution. Sonicate the solution at 25 °C for 3 h to obtain a uniformly dispersed CNTs suspension solution.

[0072] (2) Weigh a total of 7.2 g of CA and TPU with a mass ratio of CA to TPU of 1:1 and dissolve them in the suspension solution obtained in step (1). Use a thermostatic magnetic stirrer to stir for 8 h until completely dissolved to obtain a well-dispersed and uniform CA / TPU / CNTs mixed solution. The mass ratio of CNTs to the polymer (TPU / CA) is 8 wt%. Then let it stand at room temperature for later use.

[0073] (3) First, spread 80 g of NaCl particles (212 - 300 μm) evenly on a metal mold with an area of 12 cm × 12 cm and apply pressure to form a dense NaCl preform. Then inject the CA / TPU / CNTs mixed solution obtained in step (2) into the NaCl preform with the assistance of a vacuum pump. After the preform is completely immersed, place it in the refrigerator for pre-freezing.

[0074] (4) First, place the pre-frozen CA / TPU / CNTs / NaCl composite obtained in step (3) in an ethanol bath at -75 °C for extraction and freezing for 72 h. Then take it out and soak it in deionized water for 48 h to remove the NaCl particles. Finally, freeze-dry it for 72 h to successfully prepare a CA / TPU / CNTs solar water evaporator without a biomimetic lotus surface structure (hereinafter referred to as CTC).

[0075] Comparative Example 2

[0076] (1) Weigh a total of 7.2 g of CA and TPU with a mass ratio of CA to TPU of 1:1 and dissolve them in 60 mL of DMF solution. Use a thermostatic magnetic stirrer to stir for 8 h until completely dissolved to obtain a well-dispersed and uniform CA / TPU mixed solution. Then let it stand at room temperature for later use.

[0077] (2) First, spread 80 g of NaCl particles (212 - 300 μm) evenly on a metal mold with an area of 12 cm × 12 cm and apply pressure to form a dense NaCl preform. Then inject the CA / TPU mixed solution obtained in step (1) into the NaCl preform with the assistance of a vacuum pump. After the preform is completely immersed, place it in the refrigerator for pre-freezing.

[0078] (3) First, the pre-frozen CA / TPU / NaCl composite obtained in step (2) was placed in an ethanol bath at -75 °C for extraction and freezing for 72 h, then taken out and soaked in deionized water for 48 h to remove NaCl particles, and finally freeze-dried for 72 h to successfully prepare a CA / TPU solar water evaporator without the bionic lotus surface structure and the photothermal conversion material CNTs (hereinafter referred to as CT).

[0079] Figure 2 The self-made solar water evaporation test system and the schematic diagram of solar interfacial water evaporation simulation are given. As shown in the figure, the solar simulator uses a xenon lamp (CEL-HXF300) equipped with an AM 1.5G filter, and a photometer (CEL-NP2000-2A, China) is used to measure the light intensity. The change of water mass over time during the evaporation process was measured with an analytical balance (GT204, Shanghai Youke Instrument Co., Ltd.) with an accuracy of 0.1 mg, and communicated with the computer in real time to evaluate the evaporation rate and evaporation efficiency. The water temperature and the temperature of the evaporation surface of the evaporator were measured and recorded with a thermocouple power meter (HT-9815) and an infrared (IR) camera (FLIRA615, USA). In this experiment, a glass beaker was used as the water container, and the dust-free paper was folded into two parts. One part was placed on polyethylene (PE) foam used as insulation and support material, and the other part was immersed in water. The evaporator with an effective evaporation area of 5 cm 2 was placed on the dust-free paper. The position of the light source was adjusted so that the simulated solar energy was perpendicularly irradiated on the evaporation surface of the evaporator.

[0080] Inspired by the movable type printing technique, through the salt template method / vacuum solution casting technique / template-assisted technique, with CA having good hydrophilicity and TPU having excellent mechanical properties as the three-dimensional skeleton of the solar evaporator, CNTs as the photothermal conversion material, and a self-made template of PDMS solution and glass beads, a CTC solar water evaporator with a bionic lotus surface structure was prepared. The CTC surface prepared in Example 2 has characteristic structures of side edges, basins, and plateaus ( Figure 3) During the seawater desalination (seawater evaporation) process, since the evaporation rate and heat consumption rate on the plateau of the CTC surface are higher than those in the basin, the salt concentration of the plateau part is higher than that of the basin part, and the temperature is lower than that of the basin part. A salt concentration gradient field and a temperature gradient field are formed at the side edges of the CTC, thereby generating a surface tension gradient, enhancing the thermal Marangoni effect, enabling the CTC evaporator to spontaneously avoid the formation of salt crystals and timely remove salt crystals, showing excellent salt tolerance performance. In addition, another reason for the excellent salt tolerance performance of the evaporator is that the honeycomb-like multi-level pore structure in the lower layer of the CTC evaporator serves as a reservoir to provide sufficient moisture for seawater evaporation, shortening the downward migration path of salt ions, enabling the salt ions to circulate well inside the evaporator, avoiding the generation of high-concentration salt ions locally, and thus inhibiting the formation of salt crystals on the evaporation surface. The internal salt ion flow state of the evaporator without a surface modification structure and the internal salt ion flow state of the evaporator with the surface structure modified by the template of the present invention are as Figure 4 shown Figure 4 (a) Salt ion flow distribution diagram during the evaporation of brine by the evaporator without surface modification, (b) Salt ion flow state distribution diagram inside the evaporator with the surface structure modified by the template of the present invention. Figure 5 The PDMS template used to prepare the solar evaporator with a bionic lotus surface structure and the macroscopic physical diagrams of the solar evaporators prepared in Examples 2, 3, 4, and 5 are given.

[0081] Figure 6 The wetting performance and water absorption rate of the CTC-3 (Example 2) evaporator are given, which have important effects on the evaporation performance of the evaporator. As Figure 6 (a) shows, the CTC-3 evaporator has good hydrophilic performance, and the water contact angle of its surface structure drops to 61° within 4.89 s. As Figure 6 (b) shows, the mass of the dry CTC-3 is 0.4095 g, and after reaching the water absorption balance, its mass is 3.1200 g. The water absorption rate of CTC-3 is 761.9%. These results indicate that the CTC evaporator has good hydrophilic performance and water transmission and storage capabilities, providing good conditions for efficient solar water evaporation.

[0082] The thermal conductivity, as a key parameter to measure the heat conduction ability of materials, directly affects the heat transfer efficiency, energy utilization, and evaporation rate of the evaporator. A low thermal conductivity helps to reduce the loss of heat during the transfer process, enabling more input energy to be used for the evaporation of the liquid rather than being dissipated in the form of heat conduction inside the evaporator material. Figure 7 (a) gives the thermal conductivities of pure water and Examples 9, 6, Comparative Example 1, and Comparative Example 2. It can be seen from the figure that the thermal conductivities of the CA foam, TPU foam, and CT are 0.24 W m -1 K -1, 0.19 W m -1 K -1 and 0.28 W m -1 K -1 , while the thermal conductivity of CTC is 0.46 W m - 1 K -1 . The addition of CNTs improves the thermal conductivity of the evaporator, but it is still lower than that of pure water (0.6 W m -1 K -1 ). Therefore, the CTC evaporator can concentrate heat energy on the evaporator for photothermal conversion under sunlight irradiation. In a solar-driven evaporator, the light absorption rate is a key factor affecting the solar energy utilization efficiency. A UV-Vis-NIR spectrometer is used to evaluate the light absorption ability of the evaporator. As Figure 7 (b) shows, the pure CT foam evaporator without the addition of the photothermal conversion material CNTs has a very low absorption rate of solar energy. However, after preparing and introducing a lotus-like surface structure on its surface, the incident sunlight absorption rate of the CTC-0 (Comparative Example 1) evaporator increases to 87.9%. Further introducing CNTs, the incident sunlight absorption rate of the CTC-3 evaporator further increases to 89.1%. These results indicate that the introduction of the lotus-like surface structure and the photothermal material CNTs can significantly improve the light absorption performance of the evaporator, thereby enhancing its solar energy utilization efficiency. Figure 7 (c) gives a graph showing the surface temperature change during the evaporation process of different evaporators under sunlight recorded using an infrared camera. It can be seen that except for the small change in the surface temperature of the CT evaporator, the surface temperatures of other CTC evaporators all rapidly increase from about 30 °C to about 40 °C within 10 minutes, indicating that the CTC evaporator can quickly convert light into heat and increase its surface temperature.

[0083] Figure 8 gives the pure water evaporation rate and evaporation efficiency, and the simulated seawater evaporation rate and evaporation efficiency of CTC evaporators such as Examples 1, 2, 3, 4, 5, and Comparative Examples 1 and 2 under one sunlight irradiation. It can be seen from the figure that when the surface hemispherical diameter is 3 mm, the evaporation rate and evaporation efficiency of the CTC evaporator for pure water and simulated seawater are the fastest. This is mainly because the water film layer in the interconnected pores on the evaporator surface maximally satisfies solar-driven evaporation, which can not only prevent the excess water from being heated by solar energy, but also form a rich water-air interface, expanding the evaporation area. Therefore, determining the balance between solar-driven interfacial heating and the water supply rate (thin water layer) is crucial for efficient steam generation. From Figure 8 (b) and (d), it can be seen that with the increase in the number of evaporation cycles, the evaporation rate and evaporation efficiency of the CTC-3 evaporator do not change significantly. After 15 cycles, it still maintains a high evaporation rate and evaporation efficiency.

[0084] During the seawater desalination process, salt deposition is the main problem that the evaporator cannot maintain high evaporation efficiency for a long time. The salt accumulated inside the evaporator will clog the water conveyance channels, thereby blocking the steam diffusion channels and reducing the evaporation rate. The salt accumulation on the evaporation surface will severely limit the solar light absorption rate and reduce the evaporation rate. Therefore, how to solve the salt deposition problem of the evaporator and improve the salt tolerance of the evaporator still poses a huge challenge. To evaluate the influence of the lotus-leaf-like surface structure on the salt tolerance of the evaporator, evaporation experiments were conducted on the evaporators of Examples 1-5 and Comparative Example 1 in simulated brine concentrations of 0, 5, 10, 15, 20, and 25 wt%. As can be seen from Figure 9 (a-f), the evaporation rate of the CTC evaporator slightly decreases with the increase in the simulated brine concentration, and the evaporation performance of Example 2 is the best. For the evaporator without the lotus-leaf-like structure whose surface is not treated with a template, the evaporation rate decreases significantly with the increase in the brine concentration.

[0085] To evaluate the practical performance of the CTC evaporator, an outdoor experiment was conducted on the evaporator of Example 2 under natural conditions. As can be seen from Figure 10 (a and b), the evaporation performance of the CTC-3 evaporator is directly proportional to the light intensity and ambient temperature. The higher the light intensity and ambient temperature, the better the evaporation performance of the evaporator. At around 12:00 noon, the light intensity reaches a maximum of 1102 W / m 2 , the outdoor temperature reaches 30.7 °C, and the evaporation rate reaches 4.8 kg m -2 h -1 . In addition, under outdoor conditions where the average solar light intensity and ambient temperature are 740 W / m 2 and 22.7 °C respectively, CTC-3 can produce 27.8 kg m -2 of fresh water within 6 h. Figure 11 (c) is the evaporation equipment self-made in the laboratory. Figure 11 (d) shows the water purification ability of the CTC evaporator, that is, the concentration changes of K + , Na + , Ca 2+ , and Mg 2+ plasma were measured before and after seawater evaporation and desalination. The concentration of Na + decreased from 1.08×10 4 mg L -1 to 2.2548 mg L -1 , and the removal rate was 99.9%. In addition, the ion concentrations of K + , Mg 2+ , and Ca 2+ decreased to 1.167 mg L -1 , 0.0159 mg L -1and 0.2408 mg / L -1 , meeting the requirements of the World Health Organization's ion concentration standards for drinking water.

[0086] An ideal solar evaporator should not only achieve the conversion of light energy to steam energy but also have the ability to handle complex water sources, including inorganic salts, organic matter, and biological fouling. By treating three different dye solutions (MB, MO, and Rhb), the ability of the CTC-3 (Example-3) evaporator to handle complex water sources was further investigated. The color change of the dye solution and the disappearance of the typical absorption peaks of MB (665 nm), MO (465 nm), and Rhb (550 nm) demonstrated the excellent purification ability of the CTC evaporator for organic dyes ( Figure 11 (a-c)). When treating MB, CR, and MO solutions, the evaporation rates were 1.92, 1.9, and 1.95 kg m -2 / h -1 , respectively, and there was no significant decrease compared with the evaporation rate of pure water ( Figure 11 (d)). The results showed that the prepared CTC evaporator has great potential in treating various complex wastewaters (not just seawater).

[0087] Example 10

[0088] A preparation method of a solar water evaporator with a bionic lotus surface structure, comprising the following steps:

[0089] (1) Weigh 2 g of CNTs, pour them into 100 mL of N,N-dimethylformamide (DMF) solution, and ultrasonically treat for 5 h at 25 °C to obtain a uniformly dispersed suspension solution;

[0090] (2) Weigh 10 g of CA and PAN, with the mass ratio of CA to PAN being 1:5, dissolve them in the suspension solution obtained in step (1), and use a constant-temperature magnetic stirrer to treat for 16 h to completely dissolve them, obtaining a well-dispersed and uniform mixed solution, and then let it stand at room temperature for later use;

[0091] (3) Weigh a certain amount of component A and component B of PDMS, mix component A and component B in a ratio of 1:1, mix them with glass balls with a diameter of 4 mm and stir, so that the surface of the glass balls is evenly attached with PDMS glue, and then arrange them in a metal mold with an area of 12 cm × 12 cm and a height of 2 cm. After the arrangement is completed, put the mold into a vacuum drying oven for defoaming, and then put the mold into an oven and keep it at 60 °C for 8 h to make it form. After the templates with different ball diameters are formed, demold and keep for later use.

[0092] (4) First, place the template made in step (3) into a metal mold with a size of 12 cm × 12 cm. Then, spread 80 g of NaCl particles (212 - 300 μm) evenly on the template and apply pressure to form a dense NaCl preform. Next, inject the mixed solution obtained in step (2) into the NaCl preform with the assistance of a vacuum pump. After the preform is completely immersed, place it in the refrigerator for pre-freezing.

[0093] (5) First, place the preform obtained in step (4) in an ethanol bath at -75 °C for 72 h, extract the solvent through the solvent exchange method, then take it out and soak it in deionized water for 48 h to remove the NaCl particles. Finally, freeze-dry and demold to successfully prepare a solar water evaporator with a bionic lotus surface structure.

[0094] Example 11

[0095] A preparation method of a solar water evaporator with a bionic lotus surface structure, comprising the following steps:

[0096] (1) Weigh 0.5 g of graphene and pour it into 100 mL of N,N-dimethylformamide (DMF) solution. Ultrasonically treat it at 25 °C for 5 h to obtain a uniformly dispersed suspension solution.

[0097] (2) Weigh 10 g of polyurethane and dissolve it in the suspension solution obtained in step (1). Use a constant-temperature magnetic stirrer to treat it for 16 h to completely dissolve it, obtaining a well-dispersed and uniform mixed solution, and then let it stand at room temperature for later use.

[0098] (3) Weigh a certain amount of PDMS component A glue and B glue, mix A glue and B glue in a ratio of 1:1, mix it with glass balls with a diameter of 4 mm and stir to make the surface of the glass balls evenly adhere to PDMS glue, and then arrange them in a metal mold with an area of 12 cm × 12 cm and a height of 2 cm. After the arrangement is completed, place the mold in a vacuum drying oven for defoaming, and then place the mold in an oven and keep it at 60 °C for 8 h to make it form. After the templates with various different ball diameters are formed, demold and reserve them for later use.

[0099] (4) First, place the template made in step (3) into a metal mold with a size of 12 cm × 12 cm. Then, spread 80 g of NaCl particles (100 - 300 μm) evenly on the template and apply pressure to form a dense NaCl preform. Next, inject the mixed solution obtained in step (2) into the NaCl preform with the assistance of a vacuum pump. After the preform is completely immersed, place it in the refrigerator for pre-freezing.

[0100] (5) First, place the preform obtained in step (4) in an ethanol bath at -75°C and freeze it for 72 h. Extract the solvent through the solvent exchange method, then take it out and soak it in deionized water for 48 h to remove NaCl particles. Finally, freeze-dry and demold to successfully prepare a solar water evaporator with a biomimetic lotus surface structure.

[0101] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A porous foam with a bionic lotus seedpod surface structure, characterized in that, It includes a porous foam matrix in which photothermal particles are distributed, and grooves are distributed on the upper surface of the porous foam matrix to form a bionic lotus pod surface structure.

2. The preparation method of the porous foam with a bionic lotus seedpod surface structure according to claim 1, characterized in that, It includes the following steps: (1) Disperse and mix a polymer compound and photothermal particles into a solvent to prepare a mixed solution; (2) Attach glue to the small balls, then arrange a layer of the small balls with glue and cure them to bond the small balls together to obtain a surface structure template; (3) Lay the surface structure template flat in a mold, then lay a porogen flat on the surface structure template to form a preform, and finally inject the mixed solution into the preform to form. After curing, remove the porogen and demold to obtain a porous foam with a bionic lotus pod surface structure.

3. The preparation method of the porous foam with a bionic lotus surface structure according to claim 2, characterized in that, The polymer compound is any one or more of polyacrylonitrile, polyurethane, polyvinyl alcohol, and cellulose acetate.

4. The preparation method of the porous foam with a bionic lotus surface structure according to claim 3, characterized in that, The photothermal particle is any one of graphite, graphene, graphene oxide, carbon black, carbon nanotubes, carbon fibers, polythiophene, polypyrrole, polyaniline, carbonized biomass, and iron tetroxide.

5. The preparation method of the porous foam with a bionic lotus seedpod surface structure according to claim 4, characterized in that, The solvent is any one or more of N,N-dimethylformamide, dichloromethane, tetrahydrofuran, dimethyl sulfoxide, or acetone.

6. The preparation method of the porous foam with a bionic lotus pod surface structure according to any one of claims 1-5, characterized in that, In the step (1), the ratio of the polymer compound to the solvent is 0.1-0.3 g / mL, and the photothermal particle is 5-20 wt% of the polymer compound.

7. The preparation method of the porous foam with a bionic lotus surface structure according to claim 2, characterized in that, The diameter of the small balls is 2-6 mm; the small balls are glass balls.

8. The preparation method of the porous foam with a bionic lotus surface structure according to claim 7, characterized in that, The glue is silica gel, and the silica gel is PDMS glue.

9. The preparation method of the porous foam with a bionic lotus surface structure according to claim 2, characterized in that, The porogen is any one of sodium chloride, sucrose, or ammonium bicarbonate; the particle size of the porogen is 100-300 μm.

10. The preparation method of the porous foam with a bionic lotus seedpod surface structure according to claim 2, characterized in that, The curing method is solvent extraction; the method for removing the porogen is to soak the cured preform in water to dissolve the porogen.

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