Pulsed laser based hierarchical porous structure aerogel and preparation method and application thereof

Abstract

The application discloses a kind of multi-level pore structure aerogel based on pulsed laser and preparation method and application, belong to solar energy conversion and utilization technical field.It is inorganic material containing silicon nano as freezing base element, biomass polymer is crosslinking agent, deionized water is solvent, three are uniformly mixed and stand to form hydrogel after solidification, then freeze to form ice crystal, then remove ice crystal to form micron-nanometer level porous aerogel using freeze drying technology;Finally, the micron-nanometer level aerogel obtained is customized punched using pulsed laser technology Millimeter hole, finally obtain millimeter-micron-nanometer multi-level pore aerogel.The application first uses the high single-pulse energy of laser, and the customization optimization regulation and control of millimeter level hole of aerogel is not limited by the size and shape of template, and only through simple programming can realize the diversified design of millimeter hole, which is simple, stable in process and good in reproducibility.

Description

Technical Field

[0001] This invention belongs to the field of aerogel material preparation technology, especially aerogel materials for solar energy conversion and utilization. Specifically, it relates to a method for preparing and applying a silicon-containing inorganic-organic composite aerogel with a customizable hierarchical porous structure of vertically oriented millimeter pores, three-dimensional interconnected micrometer-nano pores. Background Technology

[0002] With the increasing depletion of non-renewable energy sources, utilizing renewable energy for energy transition has become an important future development trend. Solar energy is characterized by its abundant resources and its green, clean, and pollution-free nature. Utilizing and converting solar energy to replace some of the consumption of fossil fuels is of great significance for environmental protection and sustainable development. Designing and developing lightweight, efficient, and scalable solar energy conversion materials is an important way to realize the practical application of solar energy.

[0003] Aerogel materials possess excellent characteristics such as low linear density, light weight, low thermal conductivity, large specific surface area, and high porosity, making them widely used in daily life and production. Aerogel materials are typically formed under supercritical drying or freeze-drying conditions, possessing a three-dimensional porous network framework structure. The pore structure characteristics are often influenced by both the freezing unit cells and the cross-linking strength. Chemical cross-linking or physical cross-linking is commonly used to ensure the strength of aerogels. Chemical cross-linking refers to the polymerization or copolymerization of monomers under the action of a chemical cross-linking agent, forming covalent bonds to construct a three-dimensional network structure. Physical cross-linking is a three-dimensional polymer network formed through physical forces such as hydrogen bonds, coordination bonds, van der Waals forces, and intermolecular entanglement. Selecting cross-linking agents with different characteristics can control the pore structure and cross-linking strength of aerogels, enabling them to meet the requirements of various service environments. Polyvinyl alcohol (PVA), rich in hydroxyl groups, is a widely used water-soluble polymer with excellent film-forming properties, thermal stability, adhesion, abrasion resistance, self-healing ability, and good mechanical strength. It also possesses outstanding biocompatibility, biodegradability, and non-toxicity, giving it unique advantages in environmental protection. Agar, a biocompatible polysaccharide, contains abundant carboxyl groups, dissolves in water at 90°C, and solidifies at room temperature, exhibiting excellent recyclability. Therefore, by selecting appropriate crosslinking agents and utilizing various crosslinking mechanisms, the crosslinking strength of aerogels can be effectively improved.

[0004] Aerogel materials, characterized by controllable pore structure and high porosity, are ideal for solar-driven water evaporation. They offer not only a considerable light-absorbing area but also abundant channels for water transport and steam escape. Therefore, aerogel materials have broad application prospects in solar-driven interfacial water evaporation for seawater desalination, wastewater treatment, and photothermal catalysis. However, the internal pore size of aerogels is often mesopore-like, ranging from 2-50 nm. Aerogels with a single-pore structure face limitations in water transport, light absorption, heat conduction, and energy utilization. Aerogels with a hierarchical pore structure undoubtedly provide a larger specific surface area for solar light absorption and can utilize capillary action through pore size control to improve water supply rates. Furthermore, constructing a through-pore structure within the aerogel can utilize the longitudinal salt concentration difference to create a surface tension gradient, leveraging the Marangoni effect to promote salt ion migration and thus achieving the anti-salt-precipitation design of the aerogel material. Furthermore, the synergistic utilization of the light absorption and mass exchange capabilities of aerogels within their millimeter-micrometer-nanometer hierarchical porous structure will unlock greater application potential in environmental protection fields such as seawater desalination, wastewater treatment, and air purification. Therefore, the pore size distribution and pore structure of aerogels require further regulation and optimization to ensure both structural integrity and multifunctionality.

[0005] Currently, relatively mature aerogels include polymer-based aerogels and biomass aerogels. However, these organic aerogels are flammable, severely limiting their pore-forming technology and applications, and making precise pore size control and optimization difficult. In reported methods for constructing hierarchical porous structures, one or two pore-forming methods are usually used in combination. For example, Chinese patent CN109243849A discloses a method for preparing nitrogen-doped hierarchical porous graphene aerogel using CaCO3@polydopamine particles as templates, followed by acid washing to remove CaCO3 and thus form pores. However, this method introduces a template agent, requiring subsequent removal steps, making the process complex, and is not conducive to controlling pore morphology and structure. Chinese patent CN201910435537.3 discloses an inorganic nanofiber / organic polymer composite aerogel prepared by freeze casting, which has a "layer-stack-layer" structure, but can only provide micron-level channels, limiting its water and gas flux and mass exchange capacity. Chinese Patent 202110865371.6 discloses an emulsion template method for preparing aerogel materials. However, this method has weak control over the pore size distribution and pore structure of aerogels, making it difficult to precisely control the number and distribution of various pore types. Therefore, developing a simple, efficient, and precisely controllable technique for preparing hierarchical porous aerogels with optimized pore size, without the need for a pore-forming template, is of great significance for further improving their solar-driven water evaporation efficiency and expanding their application range. Summary of the Invention

[0006] To precisely control the pore structure characteristics and distribution of aerogel, this invention provides a multi-level porous aerogel based on pulsed laser. This aerogel not only has millimeter-micrometer-nanometer pore sizes, but also does not require a pore-forming agent template during preparation.

[0007] This invention also provides a method for preparing this aerogel and its applications.

[0008] To achieve the above objectives, the overall technical approach of this invention is as follows: First, utilizing the high melting point, excellent high-temperature stability, and high-temperature oxidation resistance of silicon-containing inorganic nanomaterials, polyvinyl alcohol, agar, and glutaraldehyde are used as crosslinking agents. Through the synergistic use of physical and chemical crosslinking mechanisms such as hydrogen bonding and polycondensation reactions, a silicon-containing inorganic-organic composite porous double-network aerogel is prepared. This aerogel not only utilizes the strength and toughness of the polymer materials to ensure its mechanical properties, but also leverages the characteristics of inorganic materials to improve the hardness and flame retardancy of the polyvinyl alcohol / agar aerogel, enhancing its ablation resistance and enabling diverse processing. Then, based on the preparation of the flame-retardant silicon-containing inorganic-organic nanogel, a simple and efficient process is developed using pulsed laser technology with high pulse energy and high processing efficiency. This process allows for precise control of the number and distribution of millimeter-sized pores, and the pore pattern can be customized.

[0009] The specific technical solution is as follows: a multi-level porous aerogel based on pulsed laser, characterized in that it uses silicon-containing nano-inorganic materials as freezing units, biomass polymers as cross-linking agents, and deionized water as solvents. After uniformly mixing and allowing the mixture to stand and solidify to form a silicon-containing inorganic-organic composite hydrogel, it is then frozen to form ice crystals. Next, freeze-drying technology is used to remove the ice crystals, thereby forming a micron-nano-scale silicon-containing inorganic-organic composite aerogel. Finally, pulsed laser technology is used to perform customized millimeter-hole punching on the obtained micron-nano-scale silicon-containing inorganic-organic composite aerogel. The rapid, high-energy, and customizable punching pattern of the laser is utilized to design the millimeter-hole diameter, shape, and number of pores in the aerogel, resulting in a millimeter-micron-nano-scale multi-level porous silicon-containing inorganic-organic composite aerogel with controllable process and capable of meeting the requirements of multiple scenarios and complex service environments.

[0010] Furthermore, the silicon-containing nano-inorganic materials include, but are not limited to, MoSi2, SiO2, Si3N4, etc.

[0011] Furthermore, the crosslinking agent includes at least polyvinyl alcohol, agar, and glutaraldehyde.

[0012] The following is a method for preparing the above-mentioned multi-level porous aerogel based on pulsed laser, including the following steps:

[0013] Step 1: Preparation of silicon-containing inorganic-organic composite hydrogels

[0014] First, weigh polyvinyl alcohol and agar, add deionized water and heat to dissolve the two powders to obtain a homogeneous solution. Then, add glutaraldehyde solution to the solution to crosslink it. Then, add silicon-containing nano-inorganic powder to the crosslinked solution to obtain a uniform silicon-containing inorganic-organic composite sol. After the silicon-containing inorganic-organic composite sol is allowed to stand and solidify, it forms a silicon-containing inorganic-organic hydrogel with a certain toughness.

[0015] Further: the concentration of polyvinyl alcohol in the silicon-containing inorganic-organic composite sol system is 1-4 wt%, the concentration of agar in the silicon-containing inorganic-organic composite sol system is 1-2 wt%, and the concentration of silicon-containing nano-inorganic powder in the silicon-containing inorganic-organic composite sol system is 0.02-1 wt%.

[0016] Further: The concentration of the glutaraldehyde solution is 50 wt%.

[0017] Step 2: Preparation of micron-nano-scale silicon-containing inorganic-organic composite aerogels

[0018] The silicon-containing inorganic-organic composite hydrogel obtained in step one was frozen to obtain ice crystals, and then vacuum freeze-dried to obtain a silicon-containing inorganic-organic composite aerogel with micron-nano scale.

[0019] Further: The freezing temperature range of the silicon-containing inorganic-organic composite hydrogel is -30 to -80℃. The lower the freezing temperature, the smaller the pore size, and the higher the temperature, the larger the pore size.

[0020] Step 3: Synthesis of millimeter-micrometer-nanoscale hierarchical porous silica-inorganic composite aerogels

[0021] The obtained micron-nano-scale silicon-containing inorganic-organic composite aerogel was processed to achieve a millimeter-pore structure using pulsed laser processing technology; the specific processing method is as follows:

[0022] The pulsed laser was set to a frequency of 20 Hz, a pulse width of 5000 Hz, a scanning speed of 50–150 mm / s, a laser power of 3–8%, and a laser spot size of 1 mm. Millimeter-hole shapes were designed and matrix-style punching programming was implemented. Subsequently, the laser source punched millimeter-holes in the micron-nano-scale silicon-containing inorganic-organic composite aerogel from top to bottom. Utilizing the high efficiency, speed, high energy, and customizable punching patterns of the laser, the millimeter-hole diameter, shape, and number of pores in the aerogel were designed, resulting in a millimeter-micron-nano-scale multi-level porous silicon-containing inorganic-organic composite aerogel with vertically oriented millimeter-hole shapes and adjustable porosity. In principle, the millimeter-hole diameter was controlled by a custom program and was unrestricted. The number of millimeter-hole meshes was determined by the pore density and aerogel area, also controlled by a custom program and was unrestricted. The porosity could be greater than 98%.

[0023] Furthermore, the shape of the millimeter aperture includes, but is not limited to, squares, circles, and polygons, and the distribution pattern of the millimeter aperture is not limited.

[0024] This invention relates to a multi-level porous aerogel based on pulsed laser technology, which can be used for solar-driven seawater desalination. The method of application involves combining the aerogel with polystyrene foam and absorbent fiber paper to assemble an evaporator. The silicon-containing inorganic-organic composite aerogel absorbs and converts solar energy to evaporate seawater and obtain fresh water. The polystyrene foam acts as an insulation layer for thermal management, suppressing heat conduction loss during photothermal evaporation. The hydrophilic fiber paper transports seawater through capillary action.

[0025] The method for testing the seawater desalination rate of the evaporator is as follows: the evaporator is placed on an analytical balance and irradiated with a simulated xenon lamp light source. The mass change of the evaporator at different times is continuously recorded by a computer connected to the balance, the mass loss is monitored, and the evaporation rate is calculated.

[0026] Compared with existing technologies, the technical solution provided by this invention has the following beneficial effects:

[0027] (1) This invention uses polyvinyl alcohol, agar, and glutaraldehyde as crosslinking agents. Polyvinyl alcohol has a large number of hydroxyl functional groups on its molecular chains, and agar contains a large number of carboxyl functional groups. The hydroxyl and carboxyl groups can form hydrogen bonds between the molecular chains to create a physical crosslinking network. The carboxyl and aldehyde groups can also undergo condensation reactions to form covalent bonds, thus creating a chemical crosslinking network. This dual-network structure not only forms a stable three-dimensional porous structure during freeze-drying but also further improves the strength of the aerogel. These characteristics not only help ensure the macroscopic shapeability of the aerogel and prevent volume shrinkage but also increase its compressive strength, improve its anti-swelling properties, and achieve excellent mechanical properties.

[0028] (2) This invention prepares an inorganic-organic composite aerogel and enhances its flame-retardant properties by adding silicon-containing inorganic nanomaterials, making it processable by pulsed laser. Compared with existing technologies, this invention is the first to utilize pulsed laser impact to customize and optimize the millimeter-scale pores of aerogels. It is not limited by template size and shape, and diverse millimeter-scale pore designs can be achieved through simple programming. The method is simple, the process is stable, reproducible, convenient, efficient, low-cost, green, and pollution-free. The pore structure can be controlled over a wide range, and precise structural matching designs can be made according to different application scenarios. It has good commercial application prospects in multiple fields and has the potential for large-scale promotion and application.

[0029] (3) This invention, through multi-component material composites and a clever hierarchical porous structure design, yields a silicon-containing inorganic-organic composite aerogel with a millimeter-micrometer-nanometer hierarchical porous structure that combines vertical orientation and three-dimensional connectivity. This optimizes the pore size distribution, increases the specific surface area, improves its anti-swelling performance, and enhances its water transport performance, mass exchange efficiency, and self-cleaning function. This results in a good evaporation rate in solar-driven seawater desalination, demonstrating its application prospects in solar energy conversion and utilization, including but not limited to seawater desalination and wastewater treatment. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. The accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the preparation process of the millimeter-micrometer-nanoscale porous structure MoSi2 aerogel of the present invention.

[0032] Figure 2 These are macroscopic photographs of the millimeter-micrometer-nanoscale porous structure MoSi2 aerogels of Examples 1-3 of the present invention before and after pulsed laser punching.

[0033] Figure 3 The image shown is a SEM image of the multi-level porous structure MoSi2 aerogel in Embodiment 1 of the present invention, consisting of four images: a, b, c, and d. Image a represents the micron-nano-scale pore structure on the surface of the MoSi2 aerogel, image b represents the microstructure within the millimeter-scale channels of the MoSi2 aerogel after laser punching, image c represents the internal pore structure of the original MoSi2 aerogel, and image d represents a magnified view of the microstructure within the millimeter-scale channels of the MoSi2 aerogel.

[0034] Figure 4 Density diagrams of the original MoSi2 aerogel and the hierarchical porous MoSi2 aerogel synthesized in Examples 1-3 of this invention.

[0035] Figure 5 The swelling properties of the original MoSi2 aerogel and the hierarchical porous MoSi2 aerogel synthesized in Examples 1-3 are shown in the figure.

[0036] Figure 6a and 6b The images show actual test results of the aerogel before and after adding MoSi2 nanomaterials according to this invention.

[0037] Figure 7a and 7bThe graphs show the mass loss and evaporation rate of the original MoSi2 aerogel and the hierarchical porous MoSi2 aerogels of Examples 1-3 within 60 minutes under one times the intensity of sunlight.

[0038] Figure 8 These are physical images showing the self-dissolution of salt content over time in the original MoSi2 aerogel and the hierarchical porous MoSi2 aerogels of Examples 1-3 of this invention. Detailed Implementation

[0039] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0040] It should be noted that the original MoSi2 aerogel mentioned in this invention refers to micron-nano-scale MoSi2 aerogel that has not been laser-punched.

[0041] Example 1

[0042] Example 1 uses the preparation of MoSi2 aerogel with a macroscopic pore matrix of 5*5 circular pores as an example, referring to... Figure 1 This invention illustrates the preparation method and application of MoSi2 aerogel with a millimeter-micrometer-nanometer hierarchical porous structure, comprising the following steps:

[0043] Step 1: Preparation of MoSi2 hydrogel

[0044] First, weigh 2 wt% agar and 1 wt% polyvinyl alcohol powder into a beaker, add 100 ml of deionized water, and heat to 90°C. Stir magnetically for 1 hour to dissolve the two powders and obtain a homogeneous solution. Then, add 100 μL of 50 wt% glutaraldehyde solution and continue stirring for 10 minutes. Next, slowly add 0.02 wt% MoSi2 powder to the above solution and stir magnetically until a uniform black solution is obtained.

[0045] The black solution obtained above was poured into a pre-made mold with dimensions of 100*100*10mm. After standing for 5 minutes, the solution solidified to form a MoSi2 hydrogel with a certain degree of toughness.

[0046] Step 2: Preparation of MoSi2 aerogel with micron-nanoscale porous structure

[0047] The MoSi2 hydrogel obtained in step one was frozen at -80°C for 24 hours to allow it to solidify into ice crystals. Subsequently, the frozen gel was removed and vacuum dried in a freeze dryer at -80°C for 48 hours to obtain a MoSi2 aerogel with a micron-nano scale pore structure.

[0048] Step 3: Synthesis of millimeter-micrometer-nanoscale porous MoSi2 aerogel

[0049] The aerogel from step two was cut to obtain square aerogels with dimensions of 30*30mm. A pulsed laser was used to perform customized millimeter-hole pattern punching on the obtained micron-nano-scale MoSi2 aerogel. The laser frequency was set to 20, pulse width to 5000, speed to 100mm / s, and laser power to 8%. The hole shape was set to a circle with a diameter of 1mm, and the hole spacing was set. A 5*5 matrix of circular holes was programmed for design. Then, the laser was activated, and the laser source punched millimeter holes in the MoSi2 aerogel from top to bottom. After approximately 30 seconds, the laser punching was completed, resulting in the desired pattern. Figure 2 The image shown has a P5x5 pattern and, as Figure 3 The image shows a MoSi2 aerogel with vertically oriented through-holes in millimeters and three-dimensional interconnected micron-nano hierarchical pores.

[0050] (5) Solar thermal seawater desalination application

[0051] The water evaporation rate of the P5x5 hierarchical MoSi2 aerogel in Example 1 was tested to be 1.39 kg·m³. -2 ·h -1 .

[0052] Example 2

[0053] Example 2 uses the preparation of MoSi2 aerogel with a 6*6 circular pore matrix in millimeter pores as an example. The preparation method is basically the same as in Example 1. The difference is that, in order to verify the controllability of the millimeter pore mesh number of the aerogel in this invention while ensuring that the macroscopic shape does not collapse, the programming design of the 5*5 matrix circular pores in step 3 of Example 1 is changed to the programming of the 6*6 matrix circular pores. Other parameters and operating steps of the pulsed laser remain unchanged, and the following result is obtained: Figure 2 The multi-level porous aerogel with a pore size of 6x6 mm shown is illustrated.

[0054] The water evaporation rate of the P6x6 hierarchical MoSi2 aerogel in Example 2 was tested to be 1.26 kg·m³. -2 ·h -1 .

[0055] Example 3

[0056] Example 3 uses the preparation of MoSi2 aerogel with a macroscopic pore matrix of 7*7 square holes as an example. The preparation method is basically the same as in Example 1. The difference is that, in order to verify the precise customization of the millimeter-level pore pattern of the aerogel in this invention, the programming design of the 5*5 matrix circular holes in step 3 of Example 1 was changed to the programming of the 7*7 matrix square holes. Other parameters and operating steps of the pulsed laser remain unchanged, resulting in the following... Figure 2 The multi-level porous aerogel with a pore size of P7x7 mm is shown.

[0057] The water evaporation rate of the P7x7 hierarchical MoSi2 aerogel in Example 3 was tested to be 1.13 kg·m³. -2 ·h -1 .

[0058] Figure 2 These are macroscopic photographs of the millimeter-micrometer-nanometer hierarchical porous MoSi2 aerogels of Examples 1-3 of this invention before and after pulsed laser punching. As can be seen from the figures, the MoSi2 aerogels prepared by this invention exhibit good macroscopic formability, with no surface cracks or significant shrinkage deformation, and possess excellent cutability. After pulsed laser punching, the aerogels did not show any destructive phenomena such as ablation or structural collapse. Furthermore, with the increase in millimeter pore mesh size and changes in pore shape, the aerogels maintained stable macroscopic structural characteristics, enabling customized millimeter pore pattern processing, adjustable mesh size, and controllable pore size distribution. After immersion in water, the surface of the hierarchical porous MoSi2 aerogels turned black due to the removal of gelling agents; however, the pore shape did not collapse, and the macroscopic shape of the aerogels remained intact, demonstrating that the hierarchical porous aerogels maintained excellent strength and toughness.

[0059] Figure 3 The images show SEM images of the hierarchical porous MoSi2 aerogel in Embodiment 1 of this invention. Image a shows that the surface of the un-laser-punched MoSi2 aerogel has an elliptical micron-sized pore structure with numerous nanopores uniformly distributed on the network framework. Image b shows that after pulsed laser processing, the pore framework with through-holes carbonizes at high temperature, turning black and breaking cross-links, forming a layered stacked microstructure. Image d is a magnified view of image b, showing wrinkles on the surface of the broken pore framework and a layered, interstitial structure. Image c shows the internal pore structure of the un-laser-punched MoSi2 aerogel, revealing a relatively large aerogel framework with unidirectional through-holes.

[0060] Figure 4 This is a density diagram of the original MoSi2 aerogel and the hierarchical porous MoSi2 aerogels of Examples 1-3 of this invention. Their densities are 0.039, 0.036, 0.034, and 0.033 g / cm³, respectively. 3 As can be seen from the figure, the density of aerogel gradually decreases as the number of millimeter pores increases, but the difference is small, indicating that laser punching has little impact on the quality of aerogel.

[0061] Figure 5The graph shows the swelling ratios of the original MoSi2 aerogel and the hierarchical porous MoSi2 aerogels of Examples 1-3. The swelling ratios are 17.3%, 18.8%, 19.3%, and 21.4%, respectively. As can be seen from the graph, the swelling ratio gradually increases with the increase of the millimeter pore size of the aerogel, demonstrating that the water absorption capacity of the aerogel is enhanced and the water saturation is increased. This is because, compared to the original MoSi2 aerogel with a higher degree of cross-linking, the presence of millimeter pores provides more permeation pathways for the aqueous solution, and the broken cross-links reduce the osmotic resistance of the aqueous solution, enabling the hierarchical porous aerogel with more millimeter pores to absorb more water in the same amount of time.

[0062] Figure 6a and 6b The images show actual test results of the aerogels before and after the addition of MoSi2 nanomaterials, representing the flame retardant properties of the aerogels according to this invention. As can be seen from the images, before the addition of MoSi2 nanomaterials, the polyvinyl alcohol / agar aerogel continued to burn for 14 seconds, while the polyvinyl alcohol / agar / MoSi2 aerogel stopped burning spontaneously after 14 seconds, demonstrating that the addition of MoSi2 nanomaterials enhanced the flame retardant properties of the aerogel. This is likely because MoSi2 has high-temperature stability and can act as a thermal insulator, forming a good physical barrier during combustion and effectively preventing the continued combustion of adjacent parts.

[0063] Figure 7a and 7b The graphs show the mass loss and evaporation rate of the original MoSi2 aerogel and the hierarchical porous MoSi2 aerogels of Examples 1-3 within 60 minutes under one times the intensity of sunlight. Figure 7a Mass loss diagram and Figure 7b The evaporation rate diagram shows that the original MoSi2 aerogel maintains a relatively rapid mass loss during the first 30 minutes of evaporation. However, the mass loss slows down significantly between 30 and 60 minutes. This is because the original MoSi2 aerogel has a high degree of cross-linking, resulting in slower water supply, and the water supply rate cannot keep up with the evaporation rate. However, when the number of millimeter-sized through-holes is P5x5, the evaporation rate increases significantly due to the faster water supply. When the number of millimeter-sized through-holes further increases, the evaporation rate decreases again, because the increased pore size leads to a decrease in the light absorption area. Therefore, controlling the appropriate pore size to minimize area loss while increasing the water supply rate and ensuring water supply capacity can effectively improve the solar evaporation performance of hierarchical porous MoSi2 aerogels.

[0064] Figure 8The figures show physical images of the salt self-dissolution of the original MoSi2 aerogel and the hierarchical porous MoSi2 aerogels of Examples 1-3. As can be seen from the figures, when salt is deposited on the surface of different aerogels, the salt dissolution efficiency decreases over time in the following order: P7x7 > P6x6 > P5x5 > original MoSi2 aerogel. Compared to the original micron-nano structure aerogel, the increase in millimeter pore size improves the internal mass transfer efficiency of the MoSi2 aerogel, endowing it with self-cleaning function, further demonstrating the necessity of designing and constructing millimeter-micron-nano hierarchical porous aerogels.

[0065] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions conceived without inventive effort should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A multi-level porous aerogel based on pulsed laser, characterized in that, It uses silicon-containing inorganic nanomaterials as the freezing unit, biomass polymers as the crosslinking agent, and deionized water as the solvent. After uniformly mixing and allowing the mixture to solidify, a silicon-containing inorganic-organic composite hydrogel is formed. Then, it is frozen to form ice crystals. Next, freeze-drying technology is used to remove the ice crystals, thereby forming a micron-nano-scale silicon-containing inorganic-organic composite aerogel. Finally, pulsed laser technology is used to perform customized millimeter-pore punching on the obtained micron-nano-scale silicon-containing inorganic-organic composite aerogel. Taking advantage of the laser's fast, high-energy, and customizable punching pattern characteristics, the millimeter-pore diameter, pore shape, and pore number of the aerogel can be designed, resulting in a millimeter-micron-nano-scale multi-level porous silicon-containing inorganic-organic composite aerogel with controllable process and capable of meeting the requirements of multiple scenarios and complex service environments.

2. The multi-level porous aerogel based on pulsed laser as described in claim 1, characterized in that, The silicon-containing nano-inorganic materials mentioned include, but are not limited to, MoSi2, SiO2 and Si3N4.

3. The multi-level porous aerogel based on pulsed laser as described in claim 1, characterized in that, The crosslinking agent includes at least polyvinyl alcohol, agar, and glutaraldehyde.

4. A method for preparing a multi-level porous aerogel based on pulsed laser as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Preparation of silicon-containing inorganic-organic composite hydrogels First, polyvinyl alcohol and agar are weighed, deionized water is added and heated to dissolve the two powders to obtain a homogeneous solution. Then, glutaraldehyde solution is added to the solution to crosslink the powders. Subsequently, silicon-containing nano-inorganic powder is added to the crosslinked solution to obtain a uniform silicon-containing inorganic-organic composite sol. After the silicon-containing inorganic-organic composite sol is allowed to stand and solidify, it forms a silicon-containing inorganic-organic composite hydrogel with a certain toughness. Step 2: Preparation of micron-nano-scale silicon-containing inorganic-organic composite aerogels The silicon-containing inorganic-organic composite hydrogel obtained in step one was frozen to obtain ice crystals, and then vacuum freeze-dried to obtain a silicon-containing inorganic-organic composite aerogel with micron-nano scale. Step 3: Synthesis of millimeter-micrometer-nanoscale hierarchical porous silica-inorganic composite aerogels The obtained micron-nano-scale silicon-containing inorganic-organic composite aerogel was processed to achieve a millimeter-pore structure using pulsed laser processing technology; the specific processing method is as follows: The pulsed laser was set to a frequency of 20, a pulse width of 5000, a scanning speed of 50–150 mm / s, a laser power of 3–8%, and a laser spot size of 1 mm. The shape of the millimeter holes was designed and matrix punching programming was performed. Subsequently, the laser source punched millimeter holes in the micron-nano-scale silicon-containing inorganic-organic composite aerogel from top to bottom. Utilizing the high efficiency, speed, high energy, and customizable punching pattern of the laser, the millimeter hole diameter, hole shape, and number of pores in the aerogel were designed to obtain a multi-level millimeter-micron-nano multi-level porous silicon-containing inorganic-organic composite aerogel with vertically oriented millimeter hole shapes and adjustable porosity.

5. The method for preparing a multi-level porous aerogel based on pulsed laser as described in claim 4, characterized in that, In step one, the concentration of polyvinyl alcohol in the silicon-containing inorganic-organic composite sol system is 1-4 wt%, the concentration of agar in the silicon-containing inorganic-organic composite sol system is 1-2 wt%, and the concentration of silicon-containing nano-inorganic powder in the silicon-containing inorganic-organic composite sol system is 0.02-1 wt%.

6. The method for preparing a multi-level porous aerogel based on pulsed laser as described in claim 4, characterized in that, In step two, the freezing temperature range of the silicon-containing inorganic-organic composite hydrogel is -30 to -80℃.

7. The method for preparing a multi-level porous aerogel based on pulsed laser as described in claim 4, characterized in that, The millimeter hole shapes include, but are not limited to, square, circular, and polygonal shapes.

8. An application of a multi-level porous aerogel based on pulsed laser as described in any one of claims 1-3 in solar energy conversion and utilization.

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