A moisture-absorbing light-heat composite material, a preparation method and application thereof

Abstract

The application discloses a kind of hygroscopic photo-thermal composite material and its preparation method and application, belong to hygroscopic material technical field.The hygroscopic photo-thermal composite material provided by the application includes carbonizable polymer aerogel carrier, hygroscopic salt loaded in its pore and photo-thermal conversion layer generated in situ on at least one side of the carrier.The hygroscopic photo-thermal composite material and its preparation method provided by the application realize the decoupling of hygroscopic and desorption in space-time by the spatial selective distribution of photo-thermal conversion layer.Combined with the introduction of in-situ conversion interface, the problem of photo-thermal coating peeling and interface thermal mismatch is fundamentally avoided, the mass transfer resistance is reduced, and the hygroscopic kinetics performance and cycle stability are significantly improved.Meanwhile, the laser-induced process is a dry reagent-free process, which is green and efficient.The material can be widely used in atmospheric water collection, facility agriculture humidity regulation, industrial workshop water vapor recovery, building and indoor space dehumidification or photo-thermal antibacterial water collection and other fields.

Description

Technical Field

[0001] This invention belongs to the field of hygroscopic materials technology, specifically relating to a hygroscopic photothermal composite material, its preparation method, and its application. Background Technology

[0002] Atmospheric water harvesting technology, as one of the important ways to alleviate the global freshwater shortage problem, has received widespread attention in recent years. Besides freshwater harvesting in arid regions, it can be extended to emerging fields such as humidity control in facility agriculture, water vapor recovery in industrial workshops, dehumidification of buildings and indoor spaces, photothermal antibacterial water harvesting, and intelligent electromagnetic shielding, showing broad application prospects. Utilizing solar energy to drive hygroscopic materials to capture moisture from the air and achieve desorption and regeneration has become a research hotspot due to its low energy consumption and environmental friendliness. Aerogel materials, with their high specific surface area, high porosity, and excellent structural designability, are considered a highly promising class of hygroscopic carrier materials. Currently, researchers have proposed various schemes combining photothermal conversion materials with hygroscopic matrices to achieve solar-driven moisture absorption and desorption.

[0003] Chinese invention patent CN110330749B proposes a method for obtaining a highly absorbent polymer loaded on a three-dimensional graphene aerogel, employing a strategy of integrally mixing and freeze-drying the graphene and the hygroscopic polymer. However, the photothermal material is uniformly distributed within the aerogel, limiting the utilization rate of the photothermal components; the overall temperature rises under illumination, essentially constituting an intermittent cycle of "nighttime moisture absorption - daytime desorption"; and the preparation and use processes involve chemical reagent residues and waste emissions. Furthermore, the hygroscopic polymer is prone to dissolving or migrating from the framework during repeated water absorption and dehydration.

[0004] Chinese invention patent CN117164962B discloses a stable hygroscopic photothermal core-shell aerogel material, which uses an oxidative polymerization method to achieve complete encapsulation of the photothermal layer. However, its preparation relies on multi-step solution treatment and chemical initiators, making the process complex and posing a risk of reagent residue. Although its intrinsic hydrophobic properties prevent the loss of hygroscopic components, they increase the mass transfer resistance of water vapor diffusion inward, limiting the hygroscopic rate and saturated hygroscopic capacity. In addition, this core-shell structure is also an intermittent cycle, which cannot achieve continuous water collection around the clock.

[0005] Chinese invention patent CN120422532A proposes a sandwich-structured photothermal hygroscopic aerogel. This structure is formed by stepwise freeze-casting, creating upper and lower photothermal aerogel layers stacked with a middle pure cellulose layer, and incorporating through-pores to accelerate moisture diffusion. However, in this design, the photothermal and hygroscopic layers are physically stacked, meaning the heat generated by photothermal conversion must be transferred to the hygroscopic sites through the cellulose framework, resulting in a long heat conduction path and significant heat loss. Furthermore, during repeated moisture absorption-desorption cycles, the sandwich structure experiences interlayer stress due to differences in thermal expansion coefficients and uneven hygroscopic salt loading, leading to the risk of delamination after long-term cycling.

[0006] In addition, existing technologies also include physical composite methods such as spraying and dip coating. These processes have inherent defects: the photothermal layer of physical coating only has interfacial contact with the substrate, resulting in weak adhesion. It is prone to cracking and peeling under repeated moisture absorption-desorption and alternating hot and cold conditions, and has poor cycle stability. Particles introduced by spraying or dip coating can easily clog the mesopores of the aerogel surface, hindering water vapor transport and reducing moisture absorption kinetics. The dense coating on the surface can also form a "vapor support" effect, hindering the discharge of internally desorbed water vapor, increasing the internal pressure of the pores, and even inducing the collapse of the framework. Furthermore, the difference in the thermal expansion coefficients between the coating and the substrate leads to interfacial thermal mismatch stress, introducing additional interfacial thermal resistance, resulting in ineffective heat dissipation and making it impossible to achieve efficient and continuous water collection. Summary of the Invention

[0007] To address the shortcomings of existing photothermal aerogel materials in terms of structural design, mass transfer efficiency, heat management, and cycle stability, this invention provides a hygroscopic photothermal composite material, its preparation method, and its application. The aim is to achieve in-situ generation and spatially selective distribution of photothermal materials through structural innovation and process optimization, overcoming the limitations of intermittent cycling, increasing water absorption, preventing the loss of hygroscopic components, improving cycle stability and process control, and realizing high moisture absorption rate, high photothermal conversion efficiency, continuous water collection, and green and efficient preparation.

[0008] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a hygroscopic photothermal composite material, comprising a carbonizable polymer aerogel carrier, hygroscopic salt loaded in the pores of the carbonizable polymer aerogel carrier, and a photothermal conversion layer generated in situ on at least one side of the carbonizable polymer aerogel carrier.

[0009] Preferably, the carbonizable polymer aerogel carrier is a polyimide aerogel.

[0010] Preferably, the hygroscopic salt is a hygroscopic metal salt; the hygroscopic metal salt includes one or more of lithium chloride, calcium chloride, magnesium chloride, ferric chloride, zinc chloride, potassium chloride, lithium bromide and magnesium sulfate.

[0011] Preferably, the material of the photothermal conversion layer is laser-induced graphene.

[0012] Preferably, the moisture-absorbing salt loading accounts for 50-95% of the total mass of the moisture-absorbing photothermal composite material.

[0013] This invention also provides a method for preparing the hygroscopic photothermal composite material described above, comprising the following steps: After preparing a photothermal conversion layer on at least one side of a carbonizable polymer aerogel carrier, a hydrophilic treatment is performed to obtain a hydrophilic aerogel. The hydrophilic aerogel was soaked in a hygroscopic salt solution and then dried to obtain a hygroscopic photothermal composite material.

[0014] Preferably, when the material of the photothermal conversion layer is laser-induced graphene, the method for preparing the photothermal conversion layer is as follows: using a laser to perform laser scanning on the upper surface of the polyimide aerogel to directly generate the laser-induced graphene photothermal conversion layer in situ; the laser scanning conditions include: power of 1~10W, scanning speed of 50~500mm / s, scanning line spacing of 0.01~0.1mm, and scanning times of 1~3 times.

[0015] Preferably, the hydrophilic treatment is performed as plasma treatment in an oxygen-containing atmosphere.

[0016] Preferably, the plasma treatment conditions include: a power of 20~200W and a treatment time of 1~20min.

[0017] The present invention also provides the application of the hygroscopic photothermal composite material described in the above technical solution or the hygroscopic photothermal composite material prepared by the above technical solution in the fields of atmospheric water collection, humidity control in facility agriculture, water vapor recovery in industrial workshops, dehumidification of buildings and indoor spaces, photothermal antibacterial water collection, or intelligent electromagnetic shielding.

[0018] The present invention provides a hygroscopic photothermal composite material, comprising a carbonizable polymer aerogel carrier, hygroscopic salt loaded in the pores of the carbonizable polymer aerogel carrier, and a photothermal conversion layer generated in situ on at least one side of the carbonizable polymer aerogel carrier.

[0019] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following: (1) Strong interface bonding and excellent cycle stability. The laser-induced graphene photothermal layer of the present invention forms an "in-situ conversion interface without adhesive" between the polyimide aerogel carrier. The formation mechanism is as follows: when the high-energy laser beam irradiates the surface of the polyimide aerogel, the photothermal effect of the laser causes the C=O and CN bonds in the polyimide molecular chain to break, and the carbon atoms are recombined in situ into a three-dimensional porous graphene network structure. The laser-induced graphene is directly converted from the surface layer of the polyimide matrix, rather than an externally coated or deposited independent material layer. Therefore, there is no physical interface or adhesive layer between the two, which fundamentally avoids the problems of coating peeling and interface thermal mismatch. At the same time, the in-situ conversion interface has extremely strong bonding force and is not easy to peel or crack during repeated moisture absorption-desorption cycles of alternating hot and cold and volume expansion and contraction, giving the material excellent long-term cycle stability.

[0020] (2) Breaking through the limitations of intermittent circulation, achieving continuous water collection. This invention induces partial distribution of the photothermal conversion layer by laser, triggering local desorption under light irradiation. At the same time, relying on the inherently extremely low thermal conductivity of polyimide aerogel, water molecules can still be continuously captured in the low-temperature exposed area, unaffected by temperature rise, thus achieving decoupling of moisture absorption and desorption in time and space.

[0021] (3) Low mass transfer resistance and excellent hygroscopic kinetics. Polyimide aerogel itself has a three-dimensional interconnected network structure, in which water molecules can be rapidly transported. Furthermore, by combining plasma hydrophilic treatment to introduce oxygen-containing hydrophilic groups on the material surface, water molecules can directly enter the hygroscopic sites, resulting in low mass transfer resistance and significantly improved hygroscopic rate and saturated hygroscopic capacity, far exceeding traditional hygroscopic materials such as silica gel and MOF materials. In addition, this invention utilizes the customizability of laser-induced graphene technology to construct photothermal conversion zones on the surface of the aerogel, while the remaining exposed areas still retain sufficient direct capture channels for water molecules.

[0022] (4) Excellent mechanical properties and good structural stability. Traditional aerogels are usually brittle and have low mechanical strength. They are prone to skeleton collapse or cracking during repeated moisture absorption-drying cycles. The PI aerogel obtained in this invention has significant advantages in mechanical properties. The thermal imidization step converts PAA into PI. The intrinsic rigid aromatic heterocyclic molecular chain structure of PI endows the material with excellent mechanical strength and thermal stability. The strong π-π stacking effect and inter-chain interaction force between its molecular chains give the fiber skeleton high tensile strength and modulus. This is the fundamental reason why the mechanical properties of the aerogel of this invention are superior to most non-PI-based aerogels.

[0023] (5) High utilization rate of photothermal materials and localization of heat. The present invention uses laser-induced technology to generate a photothermal conversion layer in situ on the surface of aerogel. The photothermal materials are only distributed on the surface and can all participate in light absorption, effectively avoiding the waste of photothermal materials. At the same time, the extremely low thermal conductivity of the aerogel matrix can localize the heat generated by photothermal conversion, effectively avoiding heat conduction to the interior and loss to the environment, and significantly improving the heat utilization efficiency.

[0024] (6) Green and efficient preparation process. The present invention adopts laser-induced technology as a one-step dry process, which does not require the introduction of any chemical reagents. It is a green processing technology with zero chemical reagents, which fundamentally avoids the use of toxic reagents and the emission of waste. Laser processing is a digital and programmable process with short processing time and high production efficiency. Different shapes and photothermal patterns can be quickly customized on the surface of aerogel according to application requirements without the need for an additional composite photothermal layer, which simplifies the structure and process. At the same time, when the fiber dispersion concentration is not less than 1.2wt%, the aerogel skeleton strength is sufficient to support it to maintain the pore structure without collapse during conventional drying. It can be directly dried in an oven, which further shortens the preparation cycle, reduces energy consumption, and is conducive to large-scale continuous production.

[0025] (7) Multi-scenario application adaptability. The moisture-absorbing photothermal composite material of the present invention has the comprehensive advantages of high moisture absorption capacity, fast moisture absorption rate, high photothermal conversion efficiency, excellent cycle stability and green and efficient preparation. It can be widely used in atmospheric water collection, humidity control in facility agriculture, water vapor recovery in industrial workshops, dehumidification of buildings and indoor spaces, photothermal antibacterial water collection and intelligent electromagnetic shielding, etc., and has significant industrial application prospects and commercial value. Attached Figure Description

[0026] Figure 1 A photograph of the hygroscopic photothermal composite material prepared in Example 1; Figure 2 Test diagram of the hygroscopic photothermal composite material prepared in Example 1 for bending; Figure 3 The graph shows the test results of the moisture absorption-desorption performance of the hygroscopic photothermal composite material prepared in Example 1 under light-driven conditions. Figure 4 To simulate the temperature change of the hygroscopic photothermal composite material prepared in Example 1 under sunlight irradiation for 30 minutes after desorption, an infrared camera was used to capture the sample temperature change. Figure 5 To simulate the temperature change of the hygroscopic photothermal composite material prepared in Example 1 under sunlight irradiation, an infrared camera was used to capture the temperature change of the sample side desorption over 8 hours. Figure 6 The moisture absorption diagram shows the amount of moisture absorbed by the hygroscopic photothermal composite material prepared in Example 2. Figure 7 SEM image of the hygroscopic photothermal composite material prepared in Example 2; Figure 8 The hygroscopic kinetics of the hygroscopic photothermal composite material under different salt loading rates (A) and the salt loading rate of the samples impregnated with solutions of different salt concentrations (B) are shown in the figure. Figure 9 Images of the 5% salt solution-impregnated samples prepared in Example 2 at different time points showing moisture absorption. Figure 10 Images of samples immersed in salt solutions of different concentrations at different time periods showing moisture absorption. Figure 11 The graph shows the moisture absorption performance of commercial silica gel in Comparative Example 1. Detailed Implementation

[0027] The present invention provides a hygroscopic photothermal composite material, comprising a carbonizable polymer aerogel carrier, hygroscopic salt loaded in the pores of the carbonizable polymer aerogel carrier, and a photothermal conversion layer generated in situ on at least one side of the carbonizable polymer aerogel carrier.

[0028] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0029] In one embodiment, the carbonizable polymer aerogel carrier is a polyimide (PI) aerogel; the aerogel material used in this invention has high thermal stability and carbonizable properties, and can form a graphene structure under laser induction.

[0030] As one embodiment, the preparation method of the polyimide (PI) aerogel includes the following steps: Nanofiber membranes are obtained by electrospinning a spinning solution containing polyamic acid (PAA). The nanofiber membrane was freeze-dried, and the resulting aerogel with a three-dimensional interconnected network structure was subjected to thermal imidization treatment in an air atmosphere to obtain a polyimide aerogel.

[0031] As one embodiment, the method for preparing the polyamic acid (PAA)-containing spinning solution is as follows: polyamic acid (PAA) is dissolved in a polar solvent to obtain a polyamic acid (PAA)-containing spinning solution; the mass fraction of the polyamic acid (PAA)-containing spinning solution is 8-20%, and in a specific embodiment it is 18%; the polar solvent is selected from one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc), and in a specific embodiment it is N,N-dimethylacetamide.

[0032] In this embodiment of the invention, the spinning solution containing PAA has a mass fraction of 18%, and the polar solvent used is DMAc.

[0033] In one embodiment, the equipment used for electrospinning is an electrospinning apparatus; the conditions for electrospinning include: voltage of 8~20kV, specifically 15kV in this embodiment; receiving distance of 10~25cm, specifically 18cm in this embodiment; spinning solution supply rate of 0.2~2mL / h, specifically 0.8mL / h in this embodiment; relative humidity of the environment of 0~60%, specifically 40% in this embodiment; using a roller or flat plate receiver to collect fibers; and spinning time of 2~8h, specifically 4h in this embodiment.

[0034] In one embodiment, the freeze-drying involves adding water to the nanofiber membrane, mechanically breaking it down to form a fiber dispersion; injecting the fiber dispersion into a mold, first freezing it in a freezing device, and then transferring it to a freeze dryer for freeze-drying; the water is deionized water; the solid content of the fiber dispersion is 0.3~3wt%, specifically 0.9wt% in this embodiment; the fiber dispersion further includes a crosslinking agent; the crosslinking agent is triethylamine; the amount of crosslinking agent added is 0.05~0.3 times the mass of the nanofiber membrane, specifically 0.2 times in this embodiment; adding the crosslinking agent can improve the uniformity of fiber dispersion in water; the mold is a container with a customizable shape; the freezing temperature is -80~-4℃, specifically -20℃ in this embodiment; the freezing time is 2~12h, specifically 6h in this embodiment; the freeze-drying is carried out under an absolute pressure <100Pa; the freeze-drying time is 12~48h, specifically 24h in this embodiment.

[0035] In one embodiment, the equipment used for the thermal imidization treatment is a muffle furnace; the thermal imidization treatment includes a first stage treatment and a second stage treatment in sequence; the temperature of the first stage treatment is 200~250℃, specifically 220℃ in this embodiment, and the holding time is 0.5~1h, specifically 1h in this embodiment; the temperature of the second stage treatment is 350~400℃, specifically 360℃ in this embodiment, and the holding time is 1~2h, specifically 1h in this embodiment; the heating rate to the first stage treatment and the second stage treatment is independently 5~10℃ / min, specifically 5℃ / min in this embodiment; after the thermal imidization treatment, it is naturally cooled to room temperature to obtain polyimide aerogel.

[0036] In one embodiment, the hygroscopic salt is a hygroscopic metal salt; the hygroscopic metal salt includes one or more of lithium chloride, calcium chloride, magnesium chloride, ferric chloride, zinc chloride, potassium chloride, lithium bromide, and magnesium sulfate. Another embodiment is lithium chloride (LiCl) and / or calcium chloride (CaCl2), with lithium chloride being the specific embodiment. The hygroscopic salt loading accounts for 50-95% of the total mass of the hygroscopic photothermal composite material, with 68% in a specific embodiment (corresponding to a sample impregnated with a 3% salt solution). Different salts have different hygroscopic capacities and desorption temperatures, and can be flexibly selected according to the target humidity environment.

[0037] In one embodiment, the photothermal conversion layer is made of laser-induced graphene (LIG). A binder-free in-situ conversion interface is formed between the laser-induced graphene layer and the carbonizable polymer aerogel carrier, and the interface exhibits a customizable pattern distribution.

[0038] In one embodiment, the carbonizable polymer aerogel carrier is in the form of sheets or blocks, with a thickness of 1~10mm, and in a specific embodiment, it is 3~5mm.

[0039] In this invention, the carbonizable polymer aerogel carrier is composed of a three-dimensional nanofiber network structure formed by electrospinning, freeze-drying, and thermal imidization of electrospun polyamic acid (PAA). The aerogel matrix is ​​uniformly loaded with hygroscopic lithium chloride (LiCl). The photothermal conversion layer is located on the upper surface of the aerogel matrix or in a specific patterned area. It is a porous graphene layer (LIG) generated in situ by laser scanning. The LIG layer and the aerogel matrix form an in-situ conversion interface without additional adhesive. The aerogel has a three-dimensional interconnected open-pore structure, which is composed of electrospun nanofibers overlapping each other. The overall material can be customized into any shape according to mold or application requirements.

[0040] The present invention also provides a method for preparing the above-mentioned hygroscopic photothermal composite material, comprising the following steps: After preparing a photothermal conversion layer on at least one side of a carbonizable polymer aerogel carrier, a hydrophilic treatment is performed to obtain a hydrophilic aerogel. The hydrophilic aerogel was soaked in a hygroscopic salt solution and then dried to obtain a hygroscopic photothermal composite material.

[0041] The present invention involves preparing a photothermal conversion layer on at least one side of a carbonizable polymer aerogel carrier, followed by hydrophilic treatment to obtain a hydrophilic aerogel.

[0042] As one implementation method, when the photothermal conversion layer material is laser-induced graphene (LIG), the method for preparing the photothermal conversion layer is as follows: A laser is used to scan the upper surface of the polyimide aerogel, directly generating the laser-induced graphene (LIG) photothermal conversion layer in situ. The laser scanning conditions include: power of 1~10W (2W in a specific embodiment), scanning speed of 50~500mm / s (250mm / s in a specific embodiment), scanning line spacing of 0.01~0.1mm (0.01mm in a specific embodiment), and 1~3 scans (1 in a specific embodiment). The laser is a CO2 laser, a semiconductor laser, or a fiber laser, specifically a CO2 laser. For graphene induction using a semiconductor laser or fiber laser, only the laser power and wavelength need to be sufficient to induce a photothermal carbonization reaction in the polymer precursor. Patterns (such as full coverage, grids, serpentine patterns, etc.) can be designed as needed, resulting in a black porous graphene layer on the surface after treatment. The present invention controls the distribution density and pattern of the laser-induced graphene photothermal layer by adjusting the power, speed and spacing of the laser scanning.

[0043] In one embodiment, the hydrophilic treatment is plasma treatment in an oxygen-containing atmosphere; the oxygen-containing atmosphere is oxygen or air; plasma hydrophilic treatment introduces oxygen-containing hydrophilic groups into the composite material, changing the composite material from hydrophobic to hydrophilic, which can promote the salt impregnation effect or water adsorption.

[0044] In one embodiment, the plasma treatment in an oxygen-containing atmosphere involves placing an aerogel with a photothermal conversion layer in a plasma treatment device and performing plasma treatment in an oxygen-containing atmosphere to introduce hydrophilic functional groups such as hydroxyl and carboxyl groups onto the surface of the photothermal conversion layer and the aerogel. The plasma treatment conditions include: a power of 20-200W (200W in a specific embodiment) and a treatment time of 1-20 minutes (5 minutes in a specific embodiment).

[0045] After obtaining the hydrophilic aerogel, the present invention soaks the hydrophilic aerogel in a hygroscopic salt solution and then dries it to obtain a hygroscopic photothermal composite material.

[0046] As one embodiment, the method for preparing the hygroscopic salt solution is as follows: dissolving the hygroscopic salt in an aqueous solution or an ethanol solution, specifically in an aqueous solution; the mass fraction of the hygroscopic salt solution is 1-25%, specifically 3-10%; the soaking involves completely immersing the hydrophilic aerogel in the hygroscopic salt solution; the soaking time is 2-24 hours, specifically 12 hours, to allow the hygroscopic salt to be fully adsorbed into the three-dimensional porous framework of the aerogel. The drying process is freeze-drying or oven drying, specifically freeze-drying in this embodiment. The freeze-drying involves first freezing the material in a freezing device, then transferring it to a freeze dryer for further freeze-drying. The freezing temperature is -80 to -30°C, specifically -70°C in this embodiment. The freezing time is 2 to 12 hours, specifically 6 hours in this embodiment. The freeze-drying is performed under an absolute pressure <100 Pa. The freeze-drying time is 12 to 48 hours, specifically 24 hours in this embodiment. The oven drying process involves drying the material in an oven to constant weight. The oven drying temperature is 80 to 150°C, specifically 120°C in this embodiment, and the drying time is 4 to 12 hours, specifically 6 hours in this embodiment. When the fiber dispersion concentration is below 1.2 wt%, the drying is freeze-drying; when the fiber dispersion concentration is not less than 1.2 wt%, the drying is oven drying or freeze-drying. Furthermore, the resulting hygroscopic photothermal composite material can be cut or edge-sealed according to application requirements.

[0047] The raw materials used in the preparation of the hygroscopic photothermal composite material in this invention can all be obtained through commercial channels (PAA powder can be purchased from reagent companies or synthesized according to known methods, LiCl is analytical grade, and deionized water can be prepared in-house or purchased commercially). The entire preparation process can be carried out under conventional laboratory conditions.

[0048] To address the problems in existing technologies, this invention essentially provides a hygroscopic photothermal composite material and its preparation method, comprehensively improving material performance. Specifically, this invention utilizes laser-induced technology to generate a laser-induced graphene photothermal layer in situ on the surface of polyimide aerogel, forming a binder-free in-situ conversion interface between the two. This fundamentally avoids coating peeling and interfacial thermal mismatch problems, endowing the material with excellent long-term cycling stability. Through the partial distribution of the photothermal conversion layer, local desorption is triggered at high-temperature photothermal sites under illumination, while low-temperature exposed areas continuously capture water molecules, achieving temporal and spatial decoupling of hygroscopic absorption and desorption. Combined with the intrinsically extremely low thermal conductivity of polyimide aerogel, heat is regionalized, significantly improving thermal utilization efficiency. The exposed areas retain sufficient direct capture channels for water molecules, and combined with plasma hydrophilic treatment to introduce oxygen-containing hydrophilic groups, allowing water molecules to directly enter the hygroscopic sites, resulting in low mass transfer resistance and fast hygroscopic rate.

[0049] Meanwhile, this invention employs a laser-induced one-step dry process, which requires no chemical reagents, has a short processing time, high production efficiency, and can be dried in a conventional oven by adjusting the fiber concentration, further shortening the preparation cycle and reducing energy consumption. This meets the needs of industrial production and aligns with current societal requirements for energy and environmental development.

[0050] The present invention also provides the application of the hygroscopic photothermal composite material described in the above technical solution or the hygroscopic photothermal composite material prepared by the preparation method described in the above technical solution in the fields of atmospheric water collection, humidity control in facility agriculture, water vapor recovery in industrial workshops, dehumidification of buildings and indoor spaces, photothermal antibacterial water collection, or intelligent electromagnetic shielding.

[0051] In one implementation method, the facility agriculture refers to greenhouses.

[0052] The present invention does not have any particular limitation on the application of the moisture-absorbing photothermal composite material, and any application method known in the art can be used.

[0053] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0054] Example Unless otherwise specified, the process conditions and parameters in the following embodiments are consistent with those in the basic embodiments. Subsequent embodiments only describe the changed experimental conditions.

[0055] The preparation method of the hygroscopic photothermal composite material includes the following steps: (1) Electrospinning: First, a polymer spinning solution is prepared. PAA powder is dissolved in N,N-dimethylacetamide (DMAc) to prepare a spinning solution with a mass fraction of 18%. Then, the spinning solution is injected into the electrospinning device. The process parameters are: voltage 15kV, receiving distance 18cm, spinning solution supply rate 0.8mL / h, relative humidity 40%, fiber is collected using a flat plate receiver, and spinning time is 4h to obtain PAA nanofiber membrane.

[0056] (2) Freeze-drying: The PAA nanofiber membrane obtained in step (1) was added to deionized water and mechanically crushed to form a fiber dispersion with a solid content of 0.9 wt%. A crosslinking agent (triethylamine, the amount added is 0.2 times the mass of PAA) was added to improve the uniformity of fiber dispersion in water. The dispersion was injected into a mold and first placed in a freezing device for freezing at a freezing temperature of -20℃ for 6 hours. Then it was transferred to a freeze dryer and dried for 24 hours under an absolute pressure of <100Pa to obtain an aerogel with a three-dimensional interconnected network structure.

[0057] (3) Thermal imidization: The aerogel obtained in step (2) is placed in a muffle furnace and thermal imidized in a normal air atmosphere. The temperature is increased to 220°C at 5°C / min and held for 1 hour, then increased to 360°C at 5°C / min and held for 1 hour, and then naturally cooled to room temperature to obtain polyimide (PI) aerogel.

[0058] (4) Laser-induced in-situ generation of graphene (LIG): A CO2 laser is used to scan the upper surface of the aerogel obtained in step (3) to directly generate the LIG photothermal conversion layer in situ. The laser process parameters are: power 2W, scanning speed 250mm / s, scanning line spacing 0.01mm, scanning times 1, and a black porous graphene layer is formed on the surface.

[0059] (5) Plasma treatment: The aerogel with LIG layer obtained in step (4) is placed in a plasma treatment device and plasma treatment is carried out in an oxygen atmosphere to introduce hydrophilic functional groups such as hydroxyl and carboxyl groups on the surface of LIG and aerogel. The treatment parameters are: power 200W, treatment time 5min.

[0060] (6) Lithium chloride solution immersion: Prepare a lithium chloride (LiCl) aqueous solution with a mass fraction of 3%. Immerse the aerogel treated in step (5) completely in the solution for 12 hours to allow LiCl to be fully adsorbed into the three-dimensional porous framework of the aerogel. After removal, freeze at -70℃ for 6 hours, then transfer to a freeze dryer and dry at an absolute pressure <100Pa for 24 hours to obtain a surface-in-situ laser-induced graphene functionalized hygroscopic photothermal composite material, in which the LiCl loading accounts for 68% of the total mass of the hygroscopic photothermal composite material (when the salt solution concentration is 3%), and the thickness is 3 mm. In addition, the obtained aerogel can be cut or edge-encapsulated according to application requirements.

[0061] The above-mentioned hygroscopic photothermal composite material was subjected to moisture absorption at 25℃ and 70% relative humidity for 24 hours, and the moisture absorption reached 3.7 g / g (Note: This is the measured value of a sample impregnated with a 3% salt solution concentration; higher moisture absorption can be obtained by increasing the salt concentration); under one standard sunlight (100 mW / cm²), the moisture absorption reached 3.7 g / g. 2 Under irradiation, the surface temperature rises to 65°C within 10 minutes.

[0062] Example 1 The fiber dispersion liquid had a solid content of 3wt%, an aerogel thickness of 5mm, and a salt solution concentration of 3%. After being immersed in the salt solution, it was dried in a high-temperature oven at 120℃ for 6 hours until constant weight, thus obtaining the LIG-PI aerogel composite material.

[0063] The hygroscopic photothermal composite material prepared in Example 1 is as follows: Figure 1 As shown; Figure 2 The test image shows the hygroscopic photothermal composite material prepared in Example 1, which is formed by bending. Figure 2 It is evident that the aerogel and photothermal layer have a strong interface, excellent mechanical properties, and good structural stability.

[0064] (1) Test of the hygroscopic-desorption properties of materials under light-driven illumination The LIG-PI aerogel composite material (initial sample mass approximately 0.3015 g) prepared in Example 1 of this invention was placed in a constant temperature and humidity chamber. The ambient temperature was controlled at 25±1℃ and the relative humidity at 40±2% to simulate the atmospheric environment of arid or semi-arid regions. A simulated solar light source (light intensity 1.0 kW·m²) was used. -2 The sample surface was vertically irradiated with an AM 1.5G filter, and the change in sample mass over time was recorded in real time. The results are as follows: Figure 3 As shown.

[0065] Depend on Figure 3The test results show that in the initial stage after illumination (0-60 min), the sample mass exhibits a rapid decline trend, indicating that the LIG photothermal conversion layer efficiently captures light energy and converts it into heat energy, causing the surface temperature to rise rapidly (measured by infrared thermal imaging, the surface temperature reached 70℃). This drives the rapid release of captured water molecules from the lithium chloride hygroscopic sites loaded in the surface channels. During the illumination period of 60-300 min and longer, the sample mass did not exhibit the desorption rate decay or even stagnation seen in conventional photothermal desorption materials. Instead, it maintained a continuous and stable net mass decline trend, fully demonstrating that the low thermal conductivity of the lower PI aerogel effectively confines the heat generated by the photothermal layer to the upper layer of the material. The lithium chloride loaded in the pores of the lower aerogel, with its high hygroscopic activity, continuously captures water vapor from the environment while surface desorption occurs, and migrates to the surface through the continuous interconnected channels of the aerogel, achieving real-time regeneration and continuous replenishment of the hygroscopic sites. Figure 3 It is evident that the sample did not reach a state of complete desorption even after 8 hours of sunlight exposure. Furthermore, this test was conducted under conditions of high fiber density, low humidity, and low salt load, indicating that in practical applications, by reducing fiber density and increasing salt load, the moisture absorption and desorption rates can be quickly balanced, thus achieving continuous water production.

[0066] (2) The surface temperature distribution of the LIG-PI aerogel composite material prepared in Example 1 of this invention was monitored in real time under simulated sunlight using an infrared thermal imager. The sample was placed under a simulated solar light source (light intensity 1.0 kW·m). -2 The temperature changes of the illuminated side (front) and the shaded side (side) are as follows: Figure 4 and 5 As shown.

[0067] Infrared camera captured the temperature change of the sample during desorption over 30 minutes. Figure 4 Under a simulated sunlight source, the sample temperature rises to 66℃ in 10 minutes and to 70.3℃ in 30 minutes, and then stabilizes at 60~70℃.

[0068] Infrared camera images of the temperature change of the sample side desorption over 8 hours are shown below. Figure 5 As shown.

[0069] Figure 4 and 5The test results show that after 30 seconds of illumination, the temperature on the front of the sample rapidly rises to approximately 43.5°C, indicating that the LIG photothermal conversion layer has highly efficient photothermal response characteristics. As the illumination time extends to 4 hours, the upper layer temperature reaches approximately 60.2°C, and the lower layer temperature is approximately 43.5°C, as seen from the side. Even after 8 hours of illumination, the upper layer temperature remains at approximately 60.0°C, while the lower layer temperature is approximately 38.3°C, indicating a continued temperature difference. Furthermore, the aerogel thickness is only 5 mm; increasing the aerogel thickness can further amplify the temperature difference. This strongly demonstrates that the hygroscopic layer and photothermal layer of the material in this invention are not simply physically superimposed, but rather achieve functional synergy through thermal gradient-driven processes, thereby endowing the material with the core capability of continuous water production under sustained illumination.

[0070] Example 2 The fiber dispersion liquid has a solid content of 0.9wt%, a thickness of 3mm, a salt solution concentration of 5%, and an ambient humidity of 30%RH.

[0071] (1) Testing the moisture absorption properties of materials under low humidity conditions The LIG-PI aerogel composite material (lithium chloride loading of approximately 77%) prepared in Example 2 of this invention was placed in a constant temperature and humidity chamber. The ambient temperature was controlled at 25±1℃ and the relative humidity at 30±2% (simulating the atmospheric environment of arid / semi-arid regions). The change in material mass over time was recorded, and the moisture uptake per unit mass of material (1.85 g / g) was calculated. The results are as follows: Figure 6 As shown.

[0072] Depend on Figure 6 It is evident that the material of this invention exhibits excellent moisture absorption rate and capacity under low water vapor partial pressure conditions. The mechanism lies in the following: lithium chloride, through a freeze-drying process, is confined and distributed in the mesoporous channels of the PI aerogel in the form of nanocrystals, resulting in a large specific surface area and uniform dispersion, maximizing the exposure of effective moisture absorption sites; simultaneously, the interconnected pore structure of the PI aerogel ensures rapid transport and diffusion of water vapor, eliminating the mass transfer resistance caused by surface densification in traditional coating processes.

[0073] (2) Microscopic morphological characterization The microstructure of the LIG-PI aerogel composite material prepared in Example 2 of this invention was characterized using scanning electron microscopy (SEM), and the results are as follows: Figure 7 As shown.

[0074] Test results and mechanism analysis: from Figure 7The SEM images clearly show that after impregnation with 5wt% LiCl solution, the three-dimensional interconnected nanofiber network structure of the aerogel remains intact, without obvious framework collapse or pore shrinkage. This proves that the LIG-then-salt impregnation process and subsequent freeze-drying process used in this invention cause minimal damage to the matrix structure, and the interconnected porous framework of the PI aerogel is effectively preserved. The LiCl particles on the fiber surface exhibit a uniform, thin-layer distribution with uniform particle size, and no obvious aggregates or large-sized crystal precipitation are observed. This indicates that the loading at 5wt% salt concentration is within the ideal range—ensuring sufficient hygroscopic active sites without damaging the porous structure of the aerogel. At the 60μm scale, the aerogel surface pores are uniformly distributed and unobstructed. This interconnected pore structure provides low-resistance channels for the rapid diffusion and transport of water vapor, which is the structural basis for the rapid hygroscopic response of the material under low humidity conditions.

[0075] (3) Hygroscopic kinetics of fiber dispersion liquid with a solid content of 0.9 wt% and a thickness of 3 mm under different salt loading rates. Figure 8 (A) and the salt loading rate of samples impregnated with solutions of different salt concentrations ( Figure 8 (B)

[0076] The 5% salt solution impregnated sample prepared in Example 2 is shown in the following images at different time periods, illustrating the actual moisture absorption. Figure 9 As shown in the image. Images of samples soaked in salt solutions of different concentrations at different time periods show the actual moisture absorption. Figure 10 As shown.

[0077] Hygrokinetic curves of fiber dispersion liquid with a solid content of 0.9 wt% under different salt loading rates ( Figure 8 As shown in Figure A), the sample absorbed moisture for 24 hours in a 75±2%RH environment, reaching a maximum moisture absorption of 4.11 g / g. After being transferred to a 92±2%RH environment for 76 hours, the moisture absorption reached 7.59 g / g. The sample with the highest moisture absorption did not exhibit salt leakage. This indicates that the sample immersed in 5% salt solution showed no salt leakage after 100 hours of high humidity. Excessively high salt concentrations can lead to salt leakage. The sample immersed in 7% salt solution showed slight salt leakage after 58 hours of high humidity. The sample immersed in 9% salt solution showed no salt leakage after 24 hours of immersion in a 75±2%RH environment, but leakage began to appear after 13 hours of immersion in a 92±2%RH environment. However, for practical applications involving continuous water collection, the results still meet the experimental requirements.

[0078] Comparative Example 1 Moisture absorption performance of commercial silica gel: Commercially available silica gel (high-absorption silica gel, Mofanke) was used as a comparison.

[0079] Dry the silica gel at 120℃ to constant weight, and take about 0.15g and place it in a constant temperature and humidity chamber at 25±1℃ and 90±2% relative humidity for 12h to absorb moisture.

[0080] Test results: The moisture absorption of the sample reached 0.31 g / g (e.g., ... Figure 11 (As shown).

[0081] Compared with Example 2, it can be found that the material of the present invention is significantly superior to traditional commercial moisture-absorbing materials in terms of both moisture absorption capacity and moisture absorption kinetics. Its advantages stem from the three-dimensional through-structured nanofiber network structure of the material of the present invention and the uniform nano-dispersion of lithium chloride on the fiber surface. The two work together to achieve a high exposure rate of moisture absorption sites and low resistance diffusion of water vapor.

[0082] Compared to other patents mentioned in the research background, the present invention has superior moisture absorption performance, and can achieve simultaneous moisture absorption and desorption, and has strong interfacial bonding.

[0083] Application Example 1: Application of the material of the present invention in humidity control and irrigation water recycling in facility agriculture The LIG-PI aerogel composite material prepared in Example 1 of this invention is installed on the side or top of a greenhouse, and its working mode is as follows: During nighttime or periods without sunlight, the lithium chloride hygroscopic sites loaded within the pores of the lower PI aerogel actively capture water vapor from the high-humidity air inside the greenhouse, storing it as hydrated salts within the nanopores. This process reduces the relative humidity inside the greenhouse, inhibiting diseases such as gray mold induced by high humidity; it also locks the water vapor in liquid form within the material, avoiding water waste caused by ventilation and dehumidification. Simultaneously, the low thermal conductivity of the PI aerogel provides some insulation during this stage, reducing heat loss from the greenhouse.

[0084] During daytime or periods of sunshine, the upper LIG photothermal conversion layer converts solar energy into heat, driving the desorption and release of water molecules trapped within the pores. Due to the insulating properties of the PI aerogel, the heat is localized to the surface, ensuring desorption efficiency while preventing excessively high temperatures in the lower layers from affecting the regeneration of moisture absorption sites. The released water vapor, after condensation and collection, can be used to supplement crop irrigation. Simultaneously, the low thermal conductivity of the PI aerogel can block some external heat from being conducted into the greenhouse during summer, reducing the greenhouse's heat load.

[0085] The material of this invention exhibits parallel and overlapping hygroscopic absorption and desorption in space and time. Even during periods of sunlight, the lower hygroscopic sites continuously capture moisture from the high-humidity air inside the greenhouse, enabling the material to simultaneously perform the dual functions of desorption and water production, as well as hygroscopic dehumidification under sunlight conditions. This continuous operating mode breaks through the intermittent cycle of "nighttime hygroscopic absorption - daytime desorption" of traditional hygroscopic materials, integrating greenhouse humidity control with irrigation water recycling to achieve low-energy and sustainable humidity management in facility agriculture.

[0086] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A moisture-absorbing, photothermal composite material, characterized in that, It includes a carbonizable polymer aerogel carrier, hygroscopic salts loaded in the pores of the carbonizable polymer aerogel carrier, and a photothermal conversion layer generated in situ on at least one side of the carbonizable polymer aerogel carrier.

2. The moisture-absorbing and photothermal composite material according to claim 1, characterized in that, The carbonizable polymer aerogel carrier is a polyimide aerogel.

3. The moisture-absorbing and photothermal composite material according to claim 1, characterized in that, The hygroscopic salt is a hygroscopic metal salt; the hygroscopic metal salt includes one or more of lithium chloride, calcium chloride, magnesium chloride, ferric chloride, zinc chloride, potassium chloride, lithium bromide and magnesium sulfate.

4. The hygroscopic and photothermal composite material according to claim 1, characterized in that, The photothermal conversion layer is made of laser-induced graphene.

5. The hygroscopic photothermal composite material according to claim 1 or 3, characterized in that, The hygroscopic salt loading accounts for 50-95% of the total mass of the hygroscopic photothermal composite material.

6. The method for preparing the hygroscopic photothermal composite material according to any one of claims 1 to 5, characterized in that, Includes the following steps: After preparing a photothermal conversion layer on at least one side of a carbonizable polymer aerogel carrier, a hydrophilic treatment is performed to obtain a hydrophilic aerogel. The hydrophilic aerogel was soaked in a hygroscopic salt solution and then dried to obtain a hygroscopic photothermal composite material.

7. The preparation method according to claim 6, characterized in that, When the material of the photothermal conversion layer is laser-induced graphene, the method for preparing the photothermal conversion layer is as follows: a laser is used to perform laser scanning on the upper surface of the polyimide aerogel to directly generate the laser-induced graphene photothermal conversion layer in situ; the conditions for laser scanning include: power of 1~10W, scanning speed of 50~500mm / s, scanning line spacing of 0.01~0.1mm, and scanning times of 1~3 times.

8. The preparation method according to claim 6, characterized in that, The hydrophilic treatment is performed by plasma treatment in an oxygen-containing atmosphere.

9. The preparation method according to claim 8, characterized in that, The conditions for plasma treatment include: power of 20~200W and treatment time of 1~20min.

10. The application of the hygroscopic photothermal composite material according to any one of claims 1 to 5 or the hygroscopic photothermal composite material prepared by the preparation method according to any one of claims 6 to 9 in the fields of atmospheric water collection, humidity control in facility agriculture, water vapor recovery in industrial workshops, dehumidification of buildings and indoor spaces, photothermal antibacterial water collection, or intelligent electromagnetic shielding.

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