A photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface and a preparation method and application thereof

Abstract

The application belongs to the field of water treatment, and particularly relates to a photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface and a preparation method and application thereof. A curing agent is mixed with polydimethylsiloxane (PDMS) to obtain a first polymer through stirring and vacuum defoaming; Fe3O4 powder is added to the first polymer to form a precursor liquid, the precursor liquid is subjected to gradient treatment, and a gradient polymer is obtained through vacuum defoaming; the gradient polymer is subjected to thermal curing, and the base evaporator is obtained through ethanol and water washing; the base evaporator is subjected to laser processing to make the surface of the base evaporator have groove and micropore structures, and the base evaporator is washed with ethanol and water and dried to obtain the photosensitive magnetic gradient structure PDMS evaporator. The photosensitive magnetic gradient structure is combined with the micro-nano composite surface, so that the evaporator is synergistically optimized in terms of light absorption, heat conduction and liquid transport, and the solar interface evaporation efficiency is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] The global supply and demand imbalance for freshwater resources is intensifying, making seawater desalination a key pathway to alleviate water scarcity. Traditional desalination technologies (such as distillation and reverse osmosis) generally suffer from bottlenecks such as high equipment investment, high energy consumption, and complex operation and maintenance, making them unsuitable for remote areas or decentralized water demand. Solar-powered interfacial evaporation technology, with its advantages of being clean and renewable, having high energy efficiency, and being environmentally friendly, has become a research hotspot for next-generation water purification technologies. Its core principle is to convert solar energy into localized heat energy through an evaporator, achieving efficient vaporization at the interface.

[0004] An efficient interfacial evaporator typically needs to meet several key performance requirements in tandem: excellent light absorption and photothermal conversion capabilities, effective heat localization management to minimize heat loss, and efficient moisture transport channels to ensure continuous and stable evaporation.

[0005] Polydimethylsiloxane (PDMS) is a polymer material with good chemical stability, thermal stability, and flexibility, and is often used as a matrix material for solar interfacial evaporators. To endow PDMS with photothermal conversion capabilities, researchers typically combine it with photothermal functional materials. Among these, iron(III) oxide (Fe3O4) nanoparticles are considered a promising photothermal dopant due to their broad-spectrum light absorption, good photothermal conversion performance, and certain magnetic response characteristics. Previous studies have prepared Fe3O4 / PDMS composite evaporation materials by uniformly mixing Fe3O4 nanoparticles with PDMS prepolymers, and applied them to the solar-powered seawater desalination process, achieving certain results in improving light absorption and evaporation performance.

[0006] However, existing Fe3O4 / PDMS composite evaporation materials still have certain shortcomings. On the one hand, the uniform distribution of Fe3O4 nanoparticles in the PDMS matrix allows heat generated by photothermal conversion to easily diffuse inward along the matrix, making it difficult to effectively confine at the gas-liquid evaporation interface, resulting in significant heat conduction losses and reduced interfacial evaporation efficiency. On the other hand, the uniform dispersion structure limits the number of Fe3O4 particles on the surface that can directly participate in light absorption, leaving room for improvement in the material's ability to capture incident light. Furthermore, traditional uniform composite structures lack continuous and efficient water transport channels, resulting in insufficient liquid replenishment capacity and difficulty in meeting the water transport requirements during long-term continuous evaporation. Meanwhile, existing research has largely focused on the uniform composite of Fe3O4 nanoparticles and the PDMS matrix, with less emphasis on further controlling the surface structure of the material through methods such as laser micro / nano processing, leading to significant limitations in enhancing light absorption, localizing heat, and optimizing water transport.

[0007] Therefore, there is an urgent need to design a novel interface evaporator with controllable structure, strong light absorption capacity and simple preparation process to achieve efficient and low-loss solar thermal evaporation. Summary of the Invention

[0008] In view of this, the present invention provides a photosensitive magnetic gradient structure PDMS evaporator with micro-nano composite surface, its preparation method and application.

[0009] In a first aspect, the present invention provides a method for preparing a photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface, comprising the following steps: (1) The curing agent is mixed with polydimethylsiloxane PDMS, and the mixture is stirred and vacuum defoamed to obtain the first polymer; (2) Add Fe3O4 powder to the first polymer to form a precursor liquid, perform gradient treatment on the precursor liquid, and obtain a gradient polymer by vacuum defoaming. (3) The gradient polymer is thermosetting and then rinsed with ethanol and water to obtain the basic evaporator; (4) The base evaporator is laser-processed to give the surface of the base evaporator a groove and microporous structure. After rinsing with ethanol and water and drying, it is obtained.

[0010] This invention uses polydimethylsiloxane (PDMS) as the matrix material and introduces Fe3O4 magnetic nanoparticles as the photothermal conversion medium. A gradient distribution of Fe3O4 along the thickness direction is achieved through magnetic field manipulation or gravity sedimentation. Subsequently, a picosecond laser is used to ablate the Fe3O4-rich surface, forming microporous and trench array structures while simultaneously removing part of the surface PDMS layer, exposing more Fe3O4 particles. This constructs a micro / nano composite surface structure that combines light-trapping effects and superhydrophilic properties. The entire design achieves directional optimization of light absorption and heat conduction, concentrating heat at the evaporation interface and significantly improving the solar energy interface evaporation efficiency.

[0011] Preferably, in step (1), the curing agent is a platinum catalyst; In step (1), the mass ratio of polydimethylsiloxane PDMS to curing agent is 8-12:1.

[0012] In step (1), the stirring is specifically: stirring clockwise for 14-16 minutes, and then stirring counterclockwise for 14-16 minutes; the vacuum defoaming time is 15-30 minutes.

[0013] Preferably, in step (2), the particle size of the Fe3O4 powder is 20-200 nm, and the mass ratio of Fe3O4 powder to polydimethylsiloxane PDMS in the precursor fluid is 1:(1-5).

[0014] Preferably, in step (2), the gradient processing includes magnetic field manipulation or gravity settling; The magnetic field modulation specifically involves placing the precursor fluid in a neodymium iron boron magnet with a magnetic field strength of 0.1-0.5 T. The gravity sedimentation specifically involves allowing the precursor fluid to stand for 1-2 hours.

[0015] This invention employs either magnetic field manipulation or gravity sedimentation for gradient processing, providing a flexible option. The principle behind achieving gradient distribution using these two methods is primarily based on the directional migration and spatial enrichment behavior of Fe3O4 particles in the liquid precursor.

[0016] The magnetic field manipulation method involves placing the PDMS / Fe3O4 precursor in an external magnetic field environment before it solidifies. Fe3O4 particles exhibit magnetic response characteristics and are driven by magnetic force to migrate directionally along the magnetic field direction. When the magnetic field direction is set perpendicular to the sample thickness direction, the Fe3O4 particles gradually aggregate towards the side closest to the magnetic source. Subsequently, through heating or static solidification, the spatial distribution of the particles is fixed, thereby forming a gradient structure with Fe3O4 content varying from high to low along the thickness direction.

[0017] The gravity sedimentation principle utilizes the density difference between Fe3O4 particles and the PDMS precursor. In the liquid system before solidification, the Fe3O4 particles have a higher density and will slowly settle downwards under the influence of gravity. By controlling the precursor viscosity, particle content, settling time, and solidification time, the particles can be fixed at different depths before complete sedimentation, ultimately forming a gradient distribution along the thickness direction.

[0018] Therefore, both methods induce directional migration of Fe3O4 particles before material curing, and then fix the particle distribution through the curing process, thereby achieving a gradient structure in the thickness direction. Magnetic field modulation mainly relies on the magnetic response characteristics of Fe3O4, which has directional controllability; gravity sedimentation mainly relies on the density difference between the particles and the matrix.

[0019] A magnetic field strength of 0.1-0.5 T provides a moderate attraction to Fe3O4 particles, enabling directional migration of particles along the magnetic field direction (thickness direction) while avoiding excessive aggregation and agglomeration due to an overly strong magnetic field, thus ensuring the continuity of the gradient distribution. A standing period of 1-2 hours ensures significant enrichment of Fe3O4 particles along the thickness direction due to density differences, forming a stable gradient distribution. This avoids an indistinct gradient due to insufficient standing time or excessive particle settling due to excessive time, which could negatively impact the surface structure.

[0020] Preferably, in step (2), the vacuum defoaming time is 15-30 min.

[0021] Preferably, in step (3), the thermosetting temperature is 100-150℃ and the thermosetting time is 25-35min. This temperature range enables PDMS to be fully and rapidly cured.

[0022] In step (3), the rinsing process is carried out in an ultrasonic environment with an ultrasonic power of 90-110W. Each rinsing session lasts for 8-15 minutes, and the number of rinsing sessions is 4-6. Ultrasonic rinsing can more effectively remove surface residues after curing.

[0023] Preferably, in step (4), the laser processing parameters are: laser wavelength of 1064 nm, pulse duration of 0.1-50 ps, ​​average power of 5-50 W, scanning speed of 50-500 mm / s, and single pulse energy of 50-500 μJ. These laser processing parameters enable fine etching at the micro-nano scale.

[0024] Preferably, in step (4), the trench spacing is 10-200μm, the trench depth is 40-150μm, the trench width is 100-250μm; the micropore spacing is 200-500μm, the micropore diameter is 100-200μm, and the micropore depth is 300-600μm. In step (4), the rinsing process is carried out in an ultrasonic environment with an ultrasonic power of 90-110W. Each rinsing session lasts 8-15 minutes, and the number of rinsing sessions is 4-6. The grooves and micropores within this size range can form an interlaced micro-nano structure, maximizing multiple reflections and scattering of light and enhancing the light-trapping effect. At the same time, the size matching of the grooves and micropores can construct an efficient capillary transport network, ensuring rapid water migration.

[0025] In a second aspect, a photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface is provided, obtained by the preparation method described in the first aspect.

[0026] Thirdly, the present invention provides the application of the photosensitive magnetic gradient structure PDMS evaporator with micro-nano composite surface described in the second aspect in water purification and solar interface evaporation.

[0027] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) This invention combines a photosensitive magnetic gradient structure with a micro-nano composite surface to achieve synergistic optimization of the evaporator in terms of light absorption, heat conduction and liquid transport. The gradient distribution of Fe3O4 constructs a heat flow guiding path, while the micro-nano structure increases the effects of multiple reflections and light capture. The two work together to enable the evaporator to maintain efficient and stable thermal management performance under strong light.

[0028] (2) This invention uses gradient treatment to enrich Fe3O4 particles along the thickness direction on the evaporation surface, forming a gradient distribution with high concentration on the surface and low concentration at the bottom, thus achieving a coordinated match between light absorption and thermal conductivity. This structure ensures that the heat generated by photothermal conversion is mainly concentrated in the evaporation interface region, while the PDMS matrix with low Fe3O4 concentration at the bottom can play an excellent role in heat insulation, effectively preventing heat from diffusing into the matrix and water, significantly reducing heat loss and improving energy utilization.

[0029] (3) This invention utilizes picosecond lasers to perform fine etching on Fe3O4-rich surfaces, fabricating a composite structure of micropore arrays and trench arrays. This results in a light-trapping structure and superhydrophilic properties on the surface, significantly enhancing light absorption and water transport capabilities, thereby achieving a higher evaporation rate and a more stable evaporation process. During laser processing, some surface PDMS is removed, exposing more Fe3O4 particles and forming a light-trapping structure. This structure increases the multiple reflections and scattering of light on the material surface, greatly enhancing the broad-spectrum absorption capacity, enabling the material to absorb more solar energy and convert it into heat energy, thus improving evaporation efficiency. Simultaneously, the micron-sized trenches and micropores, together with the exposed nano-sized Fe3O4 particles, endow the surface with superhydrophilicity. The superhydrophilic surface can rapidly adsorb and transport liquid, ensuring continuous liquid supply to the evaporation interface, forming a stable photothermal evaporation channel. This solves the problems of insufficient water transport channels and low liquid supply efficiency in existing materials, which is beneficial for continuous evaporation processes.

[0030] (4) The preparation process of the present invention is simple and controllable, requiring no complex chemical etching or template assistance. The structure can be constructed simply by magnetic field or gravity control and laser processing. This process has good repeatability, is suitable for large-scale production, reduces production costs, and provides convenience for practical applications.

[0031] (5) The evaporator of the present invention has the advantages of high efficiency of photothermal conversion, low heat loss and stable water transport capability. It has broad application prospects not only in the fields of water purification such as seawater desalination and sewage purification, as well as in the field of solar interface evaporation, but can also be extended to various engineering fields such as photothermal energy conversion, interface thermal management and environmental purification. Attached Figure Description

[0032] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0033] Figure 1 This is a schematic diagram of the photosensitive magnetic gradient structure PDMS evaporator with micro-nano composite surface of the present invention; Figure 2 Scanning electron microscope (SEM) image of a photosensitive magnetic gradient structure PDMS evaporator with a micro / nano composite surface prepared in Example 4 of this invention; Figure 3 This is a physical image of the photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface prepared in Example 4 of the present invention; Figure 4SEM image of a photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface prepared in Example 4 of this invention; Figure 5 The energy dispersive spectroscopy (EDS) analysis diagram of the light-absorbing layer of the photosensitive magnetic gradient structure PDMS evaporator with micro-nano composite surface prepared in Example 4 of the present invention; Figure 6 EDS analysis diagram of the insulation layer of the photosensitive magnetic gradient structure PDMS evaporator with micro-nano composite surface prepared in Example 4 of this invention; Figure 7 The contact angle test of the photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface prepared in Example 4 of the present invention is shown in the figure. a represents the water droplet before contact with the micro-nano composite surface; b represents the water droplet starting to move downwards; and c represents the water droplet after contact with the micro-nano composite surface. Figure 8 The graph shows the mass change of the evaporators prepared in Examples 1-4 and Comparative Examples 1-3 of this invention during evaporation tests. Figure 9 Graphs showing the evaporation rate and evaporation efficiency of the evaporators prepared in Examples 1-4 and Comparative Examples 1-3 of this invention during evaporation tests. Figure 10 Infrared thermal image of the evaporator prepared in Comparative Example 4 under one illumination intensity; Figure 11 Infrared thermal image of the evaporator prepared for Comparative Example 2 under one illumination intensity; Figure 12 Infrared thermal imaging of the evaporator prepared in Example 4 under one light intensity; Figure 13 This is a graph showing the mass change of the evaporator prepared in Example 3 of the present invention during evaporation tests under different salt concentrations. Figure 14 The evaporation efficiency graph of the evaporator prepared in Example 3 of the present invention was obtained during evaporation tests under different salt concentrations. Detailed Implementation

[0034] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0036] Example 1 This embodiment provides a photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface and its preparation method.

[0037] like Figure 1 The diagram shows a schematic of the photosensitive magnetic gradient structure PDMS evaporator with a micro / nano composite surface according to the present invention. The evaporator consists of a PDMS substrate layer, an Fe3O4 gradient distribution layer, and a micro / nano composite surface formed by laser processing. The bottom PDMS layer provides flexible support and thermal insulation, effectively preventing heat from diffusing downwards. The middle layer, through the action of a magnetic field or gravity, causes Fe3O4 particles to gradually accumulate to the surface in the thickness direction, forming a concentration gradient from shallow to deep. The surface layer, after being ablated by a picosecond laser, forms a regular array of micropores and grooves, and possesses superhydrophilic characteristics, which can promote capillary replenishment of moisture.

[0038] Specifically, the following steps are included: (1) Mix 4g of polydimethylsiloxane (PDMS) and 0.4g of platinum catalyst, stir clockwise for 15min, then stir counterclockwise for 15min, and then defoam under vacuum for 30min to obtain the first polymer, and pour it into a container with an area of ​​2×2 cm². 2 In a mold with a depth of 3mm.

[0039] (2) Add 2.2g of Fe3O4 nanoparticles (20nm) to the first polymer to form a precursor liquid. Place the mold in a neodymium iron boron magnet environment with a surface magnetic field strength of 0.5 T to make the Fe3O4 particles move in a direction. Then defoam under vacuum for 30min to obtain a gradient polymer.

[0040] (3) The obtained gradient polymer mold is placed in a forced-air drying oven and heated at 105°C for 30 min. After curing, the cured sample is taken out of the mold and placed in anhydrous ethanol and distilled water for ultrasonic cleaning 4 times. The ultrasonic power is 100W and each time is 10 min to remove surface residues and obtain the basic evaporator.

[0041] (4) The basic evaporator was fixed on a picosecond laser processing platform and processed using a laser with a wavelength of 1064 nm and a pulse width of 15 ps. The average laser power was controlled at 16 W, the scanning speed was 100 mm / s, and the single pulse energy was 462 μJ. First, a groove array structure was formed on the surface with a groove spacing of 200 μm, a depth of 150 μm, and a width of 200 μm. Then, a micropore array was processed with a micropore spacing of 250 μm, a micropore diameter of 200 μm, and a micropore depth of 500 μm. After laser processing, the sample was ultrasonically cleaned four times with anhydrous ethanol and distilled water. The ultrasonic power was 100 W, and each time it lasted for 10 min. Finally, it was dried to obtain the final product.

[0042] Example 2 This embodiment provides a photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface and its preparation method.

[0043] Specifically, the following steps are included: (1) Mix 4g of polydimethylsiloxane (PDMS) and 0.4g of platinum catalyst, stir clockwise for 15min, then stir counterclockwise for 15min, and then defoam under vacuum for 30min to obtain the first polymer, and pour it into a container with an area of ​​2×2 cm². 2 In a mold with a depth of 3mm.

[0044] (2) Add 2.2g of Fe3O4 nanoparticles (20nm) to the first polymer to form a precursor liquid. Let the precursor liquid stand for 2 h to allow the Fe3O4 particles to settle naturally due to the density difference. Then defoam under vacuum for 30 min to obtain a gradient polymer.

[0045] (3) The obtained gradient polymer mold is placed in a forced-air drying oven and heated at 105°C for 30 min. After curing, the cured sample is taken out of the mold and placed in anhydrous ethanol and distilled water for ultrasonic cleaning 4 times. The ultrasonic power is 100W and each time is 10 min to remove surface residues and obtain the basic evaporator.

[0046] (4) The basic evaporator was fixed on a picosecond laser processing platform and processed using a laser with a wavelength of 1064 nm and a pulse width of 15 ps. The average laser power was controlled at 16 W, the scanning speed was 100 mm / s, and the single pulse energy was 462 μJ. First, a groove array structure was formed on the surface with a groove spacing of 200 μm, a depth of 150 μm, and a width of 200 μm. Then, a micropore array was processed with a micropore spacing of 250 μm, a micropore diameter of 200 μm, and a micropore depth of 500 μm. After laser processing, the sample was ultrasonically cleaned four times with anhydrous ethanol and distilled water. The ultrasonic power was 100 W, and each time it lasted for 10 min. Finally, it was dried to obtain the final product.

[0047] Example 3 The difference between this embodiment and Embodiment 1 is that the mass of the Fe3O4 nanoparticles in this embodiment is 2.93g, while all other conditions are the same.

[0048] Example 4 The difference between this embodiment and Embodiment 1 is that the mass of the Fe3O4 nanoparticles in this embodiment is 4.4g, while all other conditions are the same.

[0049] Comparative Example 1 (1) Mix 4g of polydimethylsiloxane (PDMS) and 0.4g of platinum catalyst, stir clockwise for 15min, then stir counterclockwise for 15min, and then defoam under vacuum for 30min to obtain the first polymer, and pour it into a container with an area of ​​2×2 cm². 2 In a mold with a depth of 3mm.

[0050] (2) Add 2.2 g Fe3O4 nanoparticles (20 nm) to the first polymer to form a precursor liquid, and then defoam under vacuum for 30 min to obtain the polymer.

[0051] (3) Place the obtained polymer mold into a forced-air drying oven and heat it at 105℃ for 30 minutes. After curing, take out the cured sample from the mold and place it in anhydrous ethanol and distilled water for ultrasonic cleaning 4 times. The ultrasonic power is 100W and each time is 10 minutes to remove surface residues and obtain the basic evaporator.

[0052] (4) The basic evaporator was fixed on a picosecond laser processing platform and processed using a laser with a wavelength of 1064 nm and a pulse width of 15 ps. The average laser power was controlled at 16 W, the scanning speed was 100 mm / s, and the single pulse energy was 462 μJ. First, a groove array structure was formed on the surface with a groove spacing of 200 μm, a depth of 150 μm, and a width of 200 μm. Then, a micropore array was processed with a micropore spacing of 250 μm, a micropore diameter of 200 μm, and a micropore depth of 500 μm. After laser processing, the sample was ultrasonically cleaned four times with anhydrous ethanol and distilled water. The ultrasonic power was 100 W, and each time it lasted for 10 min. Finally, it was dried to obtain the final product.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that step (4) is not performed in this comparative example, while all other conditions are the same.

[0054] Comparative Example 3 (1) Mix 4g of polydimethylsiloxane (PDMS) and 0.4g of platinum catalyst, stir clockwise for 15min, then stir counterclockwise for 15min, and then defoam under vacuum for 30min to obtain the first polymer, and pour it into a container with an area of ​​2×2 cm². 2 In a mold with a depth of 3mm.

[0055] (2) Add 2.2g of Fe3O4 nanoparticles (50nm) to the first polymer to form a precursor liquid, and then defoam under vacuum for 30min to obtain the polymer.

[0056] (3) Place the obtained polymer mold into a forced-air drying oven and heat it at 105℃ for 30 minutes. After curing, take out the cured sample from the mold and place it in anhydrous ethanol and distilled water for ultrasonic cleaning 4 times. The ultrasonic power is 100W and each time is 10 minutes to remove surface residues and obtain the basic evaporator.

[0057] Comparative Example 4 (1) Mix 4g of polydimethylsiloxane (PDMS) and 0.4g of platinum catalyst, stir clockwise for 15min, then stir counterclockwise for 15min, and then defoam under vacuum for 30min to obtain the first polymer, and pour it into a container with an area of ​​2×2 cm². 2 In a mold with a depth of 3mm.

[0058] (2) The polymer was then defoamed under vacuum for 30 minutes to obtain the polymer.

[0059] (3) Place the obtained polymer mold into a forced-air drying oven and heat it at 105℃ for 30 minutes. After curing, take out the cured sample from the mold and place it in anhydrous ethanol and distilled water for ultrasonic cleaning 4 times. The ultrasonic power is 100W and each time is 10 minutes to remove surface residues and obtain a pure PDMS evaporator.

[0060] Experimental Example 1: Characterization like Figure 2 The image shown is a scanning electron microscope (SEM) image of a photosensitive magnetic gradient structure PDMS evaporator with a micro / nano composite surface prepared in Example 4 of this invention. It can be seen that after picosecond laser processing, a micro / nano composite snowflake-like structure composed of an interwoven array of micropores and grooves is formed. Numerous nanoparticle protrusions and pores are scattered on the inner walls and surface of the grooves, significantly improving the overall surface roughness. The synergistic effect of the microstructure and nanoparticles greatly enhances multiple reflections and scattering of light, thereby achieving broad-spectrum absorption and efficient photothermal conversion. Simultaneously, the exposed Fe3O4 particles on the surface can generate a localized heating effect under light irradiation, promoting the vaporization of water molecules at the interface. The superhydrophilic surface structure ensures a continuous flow of liquid into the evaporation area, forming a stable photothermal evaporation channel.

[0061] like Figure 3 The image shown is an optical photograph of the photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface prepared in Example 4 of this invention. It can be seen that the evaporator exhibits a clear gradient distribution characteristic, with the upper layer being a light-absorbing layer with good light absorption capabilities and the lower layer being a heat-insulating layer that provides support and insulation. This indicates that the prepared evaporator successfully constructed a gradient structure with synergistic light absorption and heat insulation.

[0062] like Figure 4The image shown is a SEM image of the photosensitive magnetic gradient structure PDMS evaporator with a micro / nano composite surface prepared in Example 4 of this invention. It can be seen that a regular trench array structure is formed on the evaporator surface, and the trenches and their surrounding areas have obvious micro / nano snowflake-like structures, indicating that laser processing effectively constructed a multi-scale micro / nano composite surface. This structure is beneficial for enhancing surface roughness and light-harvesting ability, thereby improving the photothermal conversion and interfacial evaporation performance of the evaporator.

[0063] like Figure 5 The image shown is an EDS analysis diagram of the light-absorbing layer of the photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface prepared in Example 4 of this invention. It can be seen that C, O, and Fe are the main elements detected in the light-absorbing layer, with a high Fe content, indicating that the Fe3O4 magnetic photothermal component was successfully introduced and enriched in the light-absorbing layer region, possessing efficient photothermal conversion capability.

[0064] like Figure 6 The image shown is an EDS analysis diagram of the photosensitive magnetic gradient structure PDMS evaporator insulation layer with a micro-nano composite surface prepared in Example 4 of this invention. It can be seen that C and O elements were mainly detected in the insulation layer, with no obvious Fe element signal detected, indicating that the Fe3O4 magnetic photothermal component is mainly distributed in the upper light-absorbing layer, while the insulation layer basically maintains the compositional characteristics of the PDMS matrix. This result further proves that the evaporator successfully constructed a gradient structure with a separated light-absorbing layer and insulation layer, which is beneficial for achieving the synergistic effect of upper-layer photothermal conversion and lower-layer heat barrier.

[0065] like Figure 7 As shown, this is a contact angle test of a PDMS evaporator with a micro / nano composite surface fabricated in Example 4 of the present invention. The dynamic process of water droplets contacting the evaporator surface was recorded using a contact angle meter. The test results show that, as... Figure 7 As shown in Figure c, when a water droplet contacts the micro / nano composite surface, its contact angle is 0°, exhibiting excellent superhydrophilic properties. This superhydrophilic surface facilitates rapid capillary transport of water, ensuring a continuous water supply to the evaporation interface, thereby maintaining a stable photothermal evaporation process.

[0066] Experimental Example 2: Evaporation Test Indoors, a xenon lamp was used to simulate sunlight conditions. An evaporator was placed in an evaporating dish containing 3.5 wt% saline solution to construct an interfacial evaporation test system. The system was then placed under a xenon lamp to test its evaporation performance. During the experiment, the light intensity was set to the irradiance of a standard solar irradiance, i.e., 1000 W / m². 2Before the test, the initial mass of the evaporation system was recorded using a high-precision electronic balance. Subsequently, evaporation experiments were conducted for 1 hour on Examples 1-4 and Comparative Examples 1-3, with the mass of the evaporation system recorded every 10 minutes. Based on the change in the mass of the evaporation system during the test, and in conjunction with the evaporation area of ​​the evaporator, the amount of brine evaporated per unit area was calculated, thus obtaining the variation law of the evaporation amount per unit area of ​​the evaporator over time.

[0067] The evaporation rate is calculated based on the mass change of the evaporation system within 1 hour, i.e., the mass loss is divided by the effective evaporation area of ​​the evaporator and the test time. The evaporation efficiency is calculated using the formula η = m × hν / (Copt × P0). Where m is the net evaporation rate, obtained by subtracting the natural evaporation rate under shaded conditions from the evaporation rate under standard solar irradiance; hν is the equivalent enthalpy of vaporization of water during solar-driven evaporation; and P0 is the irradiance power at one standard solar irradiance intensity, i.e., 1 kW / m². 2 Copt represents the optical focusing factor at the evaporation interface. The test results for evaporation rate and evaporation efficiency are shown in Table 1.

[0068] Table 1. Evaporation rates and evaporation efficiencies of the evaporators prepared in Examples 1-4 and Comparative Examples 1-3.

[0069] like Figure 8 The figure shows the mass change of the evaporators prepared in Examples 1-4 and Comparative Examples 1-3 of the present invention during evaporation tests.

[0070] like Figure 9 The figures shown are evaporation rate and evaporation efficiency graphs of the evaporators prepared in Examples 1-4 and Comparative Examples 1-3 of this invention during evaporation tests.

[0071] As shown in Table 1, the photosensitive magnetic gradient structure PDMS evaporators with micro-nano composite surfaces prepared in each embodiment of the present invention all exhibit excellent evaporation performance. Among them, Example 4 has the highest evaporation rate and evaporation efficiency, reaching 3.12 kg·m³, respectively. -2 ·h -1 The success rate was 86.5%, significantly better than the control group 1-3.

[0072] Comparing Example 1 and Comparative Example 1, it can be seen that, under the same Fe3O4 content and laser processing parameters, Example 1, which uses magnetic field control to achieve gradient distribution, has a higher evaporation rate and efficiency than Comparative Example 1, which has uniformly dispersed Fe3O4. This demonstrates that by enriching Fe3O4 on the surface through gradient treatment, the heat generated by photothermal conversion can be more effectively localized at the evaporation interface, reducing heat conduction loss into the water body and thus improving evaporation efficiency.

[0073] Comparing Example 1 and Comparative Example 2, it can be seen that Comparative Example 2, which did not undergo laser processing, had an evaporation rate of 2.53 kg·m³. -2 ·h -1 The evaporation efficiency was 68.8%, the lowest among all examples and comparative examples. This indicates that an unprocessed flat surface cannot form an effective light-trapping structure and superhydrophilic channels, severely limiting both light absorption and water transport capabilities. In contrast, Example 1, after laser processing, showed a significant performance improvement, confirming that the trench / micropore array constructed by picosecond lasers is crucial for enhancing light trapping, increasing evaporation area, and promoting water replenishment.

[0074] Comparing Examples 1, 3, and 4, it can be seen that the evaporation performance of the evaporator increases with the increase of the proportion of Fe3O4 powder in the precursor liquid. When the mass ratio of Fe3O4 to PDMS increases from 1:1.8 (Example 1) to 1:1 (Example 4), the evaporation rate increases from 2.88 kg·m³. -2 ·h -1 Increased to 3.12 kg·m -2 ·h -1 The efficiency increased from 79.3% to 86.5%. This indicates that appropriately increasing the content of photothermal conversion materials can enhance the overall light absorption and photothermal conversion capabilities of the materials, thereby improving evaporation performance.

[0075] Comparing the performance of Comparative Example 2 and Comparative Example 3, it can be seen that the evaporation rate of Comparative Example 3 is slightly higher than that of Comparative Example 2, but far lower than that of all examples that underwent gradient treatment and laser processing. Combined with the fact that the performance of Comparative Example 1 is lower than that of Example 1, it can be further confirmed that simply relying on uniformly dispersed photothermal materials or merely performing surface structuring cannot achieve the optimal coupling of heat localization and water transport. Only by combining the magnetic field / gravity-induced Fe3O4 gradient distribution with laser-processed micro / nano composite surfaces can the advantages of efficient photothermal conversion, interfacial heat localization, and rapid water transport be synergistically utilized, thereby obtaining the best solar interfacial evaporation performance.

[0076] like Figure 10 , Figure 11 and Figure 12 The image shown is an infrared thermal image of Comparative Example 4, Comparative Example 2, and Example 4 under one light intensity. It can be seen that the surface temperature of each sample increases to varying degrees with increasing illumination time. Figure 10 As shown, the pure PDMS sample prepared in Comparative Example 4 showed a small temperature increase, with the surface temperature rising only from 24.9℃ to 35.7℃, indicating that its light absorption and photothermal conversion capabilities are relatively weak. Figure 11 As shown, Comparative Example 2 exhibits a significant temperature increase after illumination, reaching a maximum temperature of 89.8℃, indicating that the introduction of Fe3O4 effectively enhances the photothermal response of the material. In contrast, as... Figure 12As shown, the surface temperature increase in Example 4 was the most significant, reaching a final temperature of 101.4℃, which was significantly higher than that of pure PDMS and Comparative Example 2. This result indicates that the gradient distribution of the magnetic photothermal components and the laser-constructed micro / nano composite surface in Example 4 can synergistically enhance light absorption and photothermal conversion, thereby endowing the evaporator with excellent solar thermal conversion performance.

[0077] To verify the evaporation performance of the prepared evaporator under different salt concentrations, the PDMS / Fe3O4 evaporator prepared in Example 3 was placed in 3.5wt%, 7wt%, 15wt%, and 25wt% sodium chloride (NaCl) solutions for evaporation tests. Figure 13 As shown, the test results indicate that the mass of each solution system continuously decreased with prolonged illumination time, demonstrating that the evaporator can stably perform interfacial evaporation under different salt concentrations. Figure 14 As shown, as the salt concentration increased from 3.5 wt% to 25 wt%, the evaporation rate increased from 3.01 kg·m³. -2 ·h -1 Decreased to 2.18 kg·m -2 ·h -1 However, it still maintains a high evaporation rate even under a high-salt environment of 25 wt%. This result indicates that the gradient PDMS / Fe3O4 evaporator prepared in this invention has good salt-resistant evaporation capability. This is because Fe3O4 particles can enhance photothermal conversion and concentrate heat at the evaporation interface, while the surface grooves and microstructures formed by laser processing can increase the evaporation area, promote water transport, and alleviate salt accumulation, thereby ensuring the continuous and stable operation of the evaporation process.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating a photosensitive magnetic gradient structure PDMS evaporator with a micro / nano composite surface, characterized in that, Includes the following steps: (1) The curing agent is mixed with polydimethylsiloxane PDMS, and the mixture is stirred and vacuum defoamed to obtain the first polymer; (2) Add Fe3O4 powder to the first polymer to form a precursor liquid, perform gradient treatment on the precursor liquid, and obtain a gradient polymer by vacuum defoaming. (3) The gradient polymer is thermosetting and then rinsed with ethanol and water to obtain the basic evaporator; (4) The base evaporator is laser-processed to give the surface of the base evaporator a groove and microporous structure. After rinsing with ethanol and water and drying, the product is obtained. In step (1), the curing agent is a platinum catalyst; In step (1), the mass ratio of polydimethylsiloxane PDMS to curing agent is 8-12:1; In step (1), the stirring specifically involves: stirring clockwise for 14-16 minutes, and then stirring counterclockwise for 14-16 minutes; the vacuum defoaming time is 15-30 minutes. In step (2), the particle size of the Fe3O4 powder is 20-200 nm, and the mass ratio of Fe3O4 powder to polydimethylsiloxane PDMS in the precursor fluid is 1:(1-5). In step (2), the gradient processing includes magnetic field manipulation or gravity settling; The magnetic field modulation specifically involves placing the precursor fluid in a neodymium iron boron magnet with a magnetic field strength of 0.1-0.5 T. The gravity sedimentation specifically involves allowing the precursor fluid to stand for 1-2 hours.

2. The preparation method according to claim 1, characterized in that, In step (2), the vacuum defoaming time is 15-30 min.

3. The preparation method according to claim 1, characterized in that, In step (3), the thermosetting temperature is 100-150℃ and the thermosetting time is 25-35min; In step (3), the rinsing process is carried out in an ultrasonic environment with an ultrasonic power of 90-110W, each rinsing time is 8-15 minutes, and the number of rinsing times is 4-6.

4. The preparation method according to claim 1, characterized in that, In step (4), the parameters used in the laser processing are: laser wavelength of 1064nm, pulse duration of 0.1-50ps, average power of 5-50W, scanning speed of 50-500mm / s, and single pulse energy of 50-500μJ.

5. The preparation method according to claim 1, characterized in that, In step (4), the trench spacing is 10-200μm, the trench depth is 40-150μm, and the trench width is 100-250μm; the micropore spacing is 200-500μm, the micropore diameter is 100-200μm, and the micropore depth is 300-600μm. In step (4), the rinsing process is carried out in an ultrasonic environment with an ultrasonic power of 90-110W, each rinsing time is 8-15 minutes, and the number of rinsing times is 4-6.

6. A photosensitive magnetic gradient structure PDMS evaporator with a micro-nano composite surface obtained by the preparation method according to any one of claims 1-5.

7. The application of the photosensitive magnetic gradient structure PDMS evaporator with micro-nano composite surface as described in claim 6 in water purification and solar interface evaporation.

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