A polymer foam with high photothermal conversion efficiency and its preparation method

Abstract

This invention provides a polymer foam with high photothermal conversion efficiency and its preparation method. The polymer foam with high photothermal conversion efficiency includes a melamine three-dimensional foam skeleton and a monolayer MoS2 nanosheet polymerized in situ on the melamine three-dimensional foam skeleton. This method is based on the in situ polymerization process to uniformly introduce a monolayer of molybdenum disulfide into the three-dimensional polymer skeleton, thereby constructing a three-dimensional structured evaporator with high photothermal conversion efficiency, excellent salt crystallization resistance and simple processing technology.

Description

Technical Field

[0001] This invention relates to the field of advanced materials technology, and in particular to a polymer foam with high photothermal conversion efficiency and its preparation method. Background Technology

[0002] In recent years, Interfacial Solar Steam Generation (ISSG) technology has attracted widespread attention due to its low-carbon, sustainable, and highly efficient clean water production characteristics. The key factors affecting the performance of ISSG systems mainly include two aspects: one is the design of efficient and stable photothermal conversion materials, and the other is the evaporator structure configuration with good thermal management and steam transfer capabilities.

[0003] In the relatively mature two-dimensional (2D) evaporation membrane technology, the main development directions include improving photothermal conversion efficiency and achieving functional integration. For example, patent CN120173437A discloses a method for preparing a photothermal coating based on black TiO2. This coating has high hydrophilicity and strong light absorption capacity, and can guide light to reflect multiple times internally, thereby achieving near-omnidirectional absorption and significantly improving the utilization rate of solar energy and the water evaporation rate. Patent CN115925023A proposes a double-layer membrane structure evaporator, composed of a hydrophilic micro-nano photothermal layer and a hydrophobic low thermal conductivity insulation layer, which can effectively reduce heat loss and improve the solar-to-steam conversion efficiency, achieving an evaporation rate of 1.9 kg·m³. -2 ·h -1 Although two-dimensional evaporation membrane technology has made some breakthroughs, its structure is sensitive to the angle of light, its mechanical strength and resistance to salt crystallization are limited, and it relies on a hydrophilic thermal insulation substrate, making it difficult to achieve both long-term stability and large-scale engineering applications.

[0004] To overcome the inherent limitations of two-dimensional structures in terms of thermal localization, vapor diffusion, and salt resistance, three-dimensional (3D) evaporators have attracted widespread attention in recent years. 3D evaporators decouple the photothermal interface from the main water space through structural spatial decoupling, effectively reducing heat conduction losses and expanding the light absorption area and increasing vapor diffusion flux through multi-dimensional structural design. For example, patent CN119215438A provides a 3D solar evaporator composed of a hydrogel thin layer and a foam substrate, achieving an evaporation rate as high as 7.93 kg·m³. -2 ·h -1Furthermore, these technologies exhibit excellent resistance to salt crystallization in 3.5%-20% saline solutions. Patent CN119746438A, by constructing an inverted conical porous structure and utilizing the Donnan repulsion effect formed by accumulated electrolytes, effectively inhibits the migration of salt ions to the photothermal surface, reduces crystal precipitation, and improves long-term operational stability. Although the above technologies have improved evaporation performance and salt resistance, they still generally rely on surface coating or high-temperature impregnation processes of nanomaterials, which have problems such as the risk of material detachment, low utilization rate of the photothermal layer, and high processing complexity, thus restricting their large-scale application.

[0005] Therefore, there is an urgent need to develop a three-dimensional structured evaporator with high photothermal conversion efficiency, excellent salt crystallization resistance and simple processing technology, so as to realize the efficient, stable and scalable application of interfacial solar steam generation technology. Summary of the Invention

[0006] The purpose of this invention is to provide a polymer foam with high photothermal conversion efficiency and its preparation method. Based on the in-situ polymerization process, a single layer of molybdenum disulfide is uniformly introduced into a three-dimensional polymer skeleton to construct a three-dimensional structured evaporator with high photothermal conversion efficiency, excellent salt crystallization resistance and simple processing technology.

[0007] To achieve the above objectives, this technical solution provides a method for preparing polymer foam with high photothermal conversion efficiency, comprising the following steps:

[0008] S1: MoS2 dispersion is formed by dispersing monolayer MoS2 nanosheets in a liquid dispersion medium;

[0009] S2: Melamine and paraformaldehyde monomers are added to the MoS2 dispersion and then polymerized to obtain a melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets.

[0010] S3: The melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets is foamed at 60~70℃ to obtain polymer foam.

[0011] MoS2 nanosheets (<1 nm thick) can absorb 5-10% of incident light, exhibiting significantly higher absorption efficiency than traditional solar energy absorbing materials (such as GaAs, Si, and graphene), making them an ideal photothermal material. However, ultrathin materials have high surface energy, making them prone to agglomeration and stacking during application, resulting in a reduced specific surface area. This severely hinders the efficient conversion of their excellent photothermal performance to the macroscopic scale. Furthermore, as an inorganic nanomaterial, direct application of MoS2 can cause secondary water pollution. Therefore, this solution uniformly loads monolayer MoS2 nanosheets into a high-porosity photothermal composite foam material within a melamine foam (MF) three-dimensional framework. Melamine foam possesses advantages such as lightweight, high mechanical strength, a three-dimensional porous network structure, and good processing adaptability, making it suitable as a structural support for photothermal materials. This approach fixes the monolayer MoS2 without affecting its photothermal performance, thus overcoming application obstacles such as easy agglomeration, difficulty in separation, and poor environmental safety.

[0012] Compared to traditional impregnation / coating processes, this method employs a mild and controllable loading method to achieve stable dispersion (loading of 0.01–1.0%, maintaining monolayer morphology) and robust integration of monolayer MoS2 within the porous MF framework. This significantly reduces the risk of agglomeration, thereby ensuring efficient conversion and sustainable operation of its photothermal performance on a macroscopic scale. Furthermore, this method offers advantages in high controllability and low cost; the loading can be adjusted as needed, avoiding material waste and supporting customized functionality and continuous-scale fabrication. Subsequent experiments show that the photothermal evaporator fabricated using this method achieves an evaporation rate of 2.61 kg·m³ under single-sided natural light conditions. -2 ·h -1 Furthermore, due to the light absorption area expansion effect brought about by the MF framework structure (up to 2 to 5 times the projected area), the overall evaporation rate can be further increased to 4 to 10 kg·m³. -2 ·h -1 Furthermore, this process is simple to prepare, requires no high temperature and high pressure conditions, and has a short cycle time. It is feasible for continuous and industrial-scale preparation and has good practical application prospects in freshwater production, wastewater purification, and salt lake extraction.

[0013] In step S1, the monolayer MoS2 nanosheets are either powder or suspension.

[0014] In some embodiments, the lateral dimensions of the monolayer MoS2 nanosheets are 50~200 nm.

[0015] In some embodiments, monolayer MoS2 nanosheets are dispersed in a liquid dispersion medium to form a dispersion by means of ultrasonic treatment or mechanical stirring. When ultrasonic treatment is used, the ultrasonic treatment conditions are a frequency of 20~50kHz, a power of 200~1000w, and a time of 10~60min. When mechanical stirring is used, the mechanical stirring speed is 5000~1500rpm and the time is 20~60min.

[0016] Preferably, the ultrasonic treatment time is 10~30 min.

[0017] In some embodiments, the mass concentration of MoS2 in the MoS2 dispersion is 1~10 mg / mL, preferably 2~5 mg / mL.

[0018] In some embodiments, the dispersion medium is selected as a liquid monomer or a comonomer, wherein the dispersion medium is selected from one or a combination of deionized water, methanol, ethanol, ethylene glycol, 1,4-butanediol, isopropanol, glycerol, and polyvinyl alcohol. Preferably, deionized water is selected as the dispersion medium, which can effectively ensure the stability of the system and its foaming compatibility.

[0019] In step S2, melamine and paraformaldehyde monomers are added to the MoS2 dispersion, and the pH of the mixed system is adjusted to be alkaline to obtain a mixed solution. The mixed solution is then subjected to a polymerization reaction under magnetic stirring to obtain a melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets.

[0020] In some embodiments, the molar ratio of melamine to paraformaldehyde is 1:2 to 1:4, and preferably, the molar ratio of melamine to paraformaldehyde is 1:3.

[0021] In some embodiments, an alkaline catalyst is added to adjust the pH of the mixture to 8-10, preferably 9.

[0022] In some embodiments, the alkaline catalyst is selected from one or a combination of sodium hydroxide, sodium carbonate, ammonia, and triethanolamine; preferably, the alkaline catalyst is selected from triethanolamine.

[0023] In some embodiments, the stirring rate of the magnetic stirrer is 600~1200 rpm, preferably 900 rpm.

[0024] In some embodiments, the reaction temperature is 80~90°C, preferably 85°C.

[0025] In some embodiments, the reaction time is 2 to 4 hours, preferably 3 hours.

[0026] In some embodiments, the mass fraction of MoS2 in melamine-formaldehyde resin is 0.01% to 1.0%, preferably, the mass fraction of MoS2 in melamine-formaldehyde resin is 0.1% to 1.0%.

[0027] In step S3, under controlled temperature conditions, the melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets undergoes in-situ polymerization and foaming to obtain polymer foam. The in-situ polymerization temperature is 80~90℃, and the in-situ polymerization reaction time is 2~4h.

[0028] In some embodiments, the foaming method is selected from either thermal foaming or microwave foaming, preferably, the foaming method is selected from microwave foaming.

[0029] In some embodiments, the foaming temperature is 60~70°C, preferably 70°C.

[0030] When microwave foaming is selected, the microwave power is 600~900W and the heating time is 5~15min. Preferably, the microwave power is 800W and the heating time is 10min.

[0031] In order to achieve uniform foaming and stable molding of foam, in some embodiments, a foaming agent, an emulsifier and a curing agent are added to a melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets and stirred to obtain a foaming liquid. The foaming liquid is then placed in a high-temperature environment for in-situ polymerization and foaming to obtain polymer foam.

[0032] In some embodiments, a foaming agent, an emulsifier, and a curing agent are added to a melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets and stirred to obtain a foaming solution, wherein the stirring time is 2-10 min and the stirring rate is 800-1500 rpm. Preferably, the stirring time is 5 min and the stirring rate is 1000 rpm.

[0033] In some embodiments, the foaming agent is a volatile organic solvent selected from one or any combination of n-pentane, isopentane, n-hexane, cyclohexane, petroleum ether, dichloromethane, diethyl ether, and methylcyclopentane, and the amount added is 10-20% of the mass of the reaction system, preferably 15% of the mass of the reaction system; the emulsifier can be selected from one or any combination of Tween (such as Tween 20, Tween 40, Tween 60, Tween 80), Span (such as Span 60), SDS (sodium dodecyl sulfate), and nonylphenol polyoxyethylene ether (NP-40), and the amount added is 1-5% of the mass of the reaction system, preferably 3% of the mass of the reaction system; the curing agent is an acidic catalyst, such as formic acid, hydrochloric acid, sulfuric acid, and oxalic acid, and the amount added is 5-15% of the mass of the reaction system, preferably 13% of the mass of the reaction system.

[0034] In some preferred embodiments, 10-20% n-pentane, 1-5% Tween 80, and 8-15% formic acid are added to the reaction system of the melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets. This combination can effectively control the bubble generation rate and size distribution during the foaming process, improving the repeatability and structural integrity of foam molding. In some embodiments, the stirring rate of the foaming solution is 800-1500 rpm, and the stirring time is 2-10 min.

[0035] In some embodiments, the proportions of foaming agent, emulsifier, and curing agent are adjusted to control the pore size of the polymer foam to be 50-200 μm, the porosity to be 40-95%, and the foam density to be 10-50 kg / m³. 3 .

[0036] To further improve the environmental stability and safety of polymer foam, the preparation method of this polymer foam with high photothermal conversion efficiency includes:

[0037] S4: Formaldehyde removal, cooling, demolding and drying of polymer foam.

[0038] In some embodiments, the polymer foam is placed in an oven at 80-120°C and heated for 2-5 hours to promote the release of residual formaldehyde and further curing of the polymer cross-linked structure. Preferably, the oven temperature is 100°C and the heating time is 2 hours.

[0039] In some embodiments, the demolded polymer foam is dried in a hot air drying oven at 60°C for 6-12 hours, or naturally dried at room temperature for 24-48 hours.

[0040] To further enhance the performance of polymer foam in interfacial solar evaporation, the preparation method of this polymer foam with high photothermal conversion efficiency includes:

[0041] S5: Functionalize the surface of the polymer foam, wherein the functionalization method includes any one of plasma treatment, silane coupling modification, electrodeposition of hydrophilic coating, etc.

[0042] The specific functional treatments are adjusted according to actual product requirements. By functionalizing the surface of polymer foam, its surface hydrophilicity and anti-fouling ability can be enhanced, and its water vapor evaporation efficiency and service life can be improved.

[0043] Furthermore, the polymer foam prepared by this method can be processed by cutting, die-cutting, and compression molding according to application requirements to adapt to the structure of interfacial steam generators in different scenarios. For example, the foam can be prepared into cylindrical, square, disc-shaped, or other irregularly shaped parts with a thickness of 3~100mm to adapt to engineering devices such as portable evaporators and floating desalination devices; the foam can also be prepared into a layered structure and coupled with a multi-stage heat recovery system to further improve energy utilization efficiency.

[0044] In addition, to enhance structural diversity and functionality, in some embodiments, a modifier is added to the melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets. The modifier is selected from one or more of urea, oleylamine, ethylene glycol, and polyvinyl alcohol. Preferably, the modifier is urea or ethylene glycol.

[0045] Secondly, unlike the aforementioned method of dispersing monolayer MoS2 nanosheets into a dispersion and then polymerizing them with melamine and paraformaldehyde to obtain a melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets, this scheme can first polymerize a liquid-phase resin precursor system containing condensable functional groups of melamine, and then uniformly disperse monolayer MoS2 nanosheets into the liquid-phase resin precursor system to prepare monolayer MoS2 modified melamine foam by in-situ foaming.

[0046] Specifically, this solution provides a method for preparing polymer foam with high photothermal conversion efficiency, including the following steps:

[0047] S1: Prepare a resin solution containing melamine prepolymer;

[0048] S2: MoS2 nanosheets were ultrasonicated and concentrated, and then dispersed in a liquid dispersion medium to form MoS2 gel.

[0049] S3: MoS2 gel was dispersed in a resin solution containing melamine prepolymer and ultrasonically treated to obtain a melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets.

[0050] S4: The melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets is foamed at 60~70℃ to obtain polymer foam.

[0051] In step S1, the resin solution containing melamine prepolymer is a melamine-formaldehyde resin solution or a melamine-urea-formaldehyde resin mixture.

[0052] When the resin solution containing melamine prepolymer is a melamine-formaldehyde resin solution, melamine powder and formaldehyde aqueous solution are mixed and stirred in a high-temperature environment. The pH value of the mixed system is adjusted to alkaline and the reaction is carried out to obtain the melamine-formaldehyde resin solution.

[0053] In some embodiments, the molar ratio of melamine powder to formaldehyde aqueous solution is 1:1.5 to 1:4, and preferably, the molar ratio of melamine powder to formaldehyde aqueous solution is 1:3.

[0054] In some embodiments, melamine powder and formaldehyde aqueous solution are mixed and stirred at 80-90°C, wherein the stirring rate is 600-1200 rpm. Preferably, melamine powder and formaldehyde aqueous solution are mixed and stirred at 85°C, wherein the stirring rate is 900 rpm.

[0055] In some embodiments, an alkaline catalyst is used to adjust the pH of the mixture to 8-10, preferably to 9.

[0056] In some embodiments, the pH of the mixture is adjusted to alkaline and the reaction is carried out for 2-4 hours to obtain a melamine-formaldehyde resin solution, which is then cooled to room temperature. Preferably, the reaction is carried out for 3 hours to obtain the melamine-formaldehyde resin solution.

[0057] When the resin solution containing melamine prepolymer is a melamine-urea-formaldehyde resin mixture, melamine powder and formaldehyde aqueous solution are mixed and stirred at 80-90℃. The pH of the mixture is adjusted to alkaline and reacted to obtain a melamine-formaldehyde resin solution. Urea and formaldehyde aqueous solution are mixed and the pH is adjusted to alkaline and reacted at 70-80℃. Then, the pH of the mixture is adjusted to acidic and urea is added to continue the reaction. The pH of the mixture is then adjusted to alkaline to obtain a urea-formaldehyde resin solution. The melamine-formaldehyde resin solution and the urea-formaldehyde resin solution are mixed and stirred to obtain a melamine-urea-formaldehyde resin mixture.

[0058] The section on preparing the melamine-formaldehyde resin solution in the melamine-urea-formaldehyde resin mixture is as described above. The following section will focus on the method for preparing the urea-formaldehyde resin solution.

[0059] In some embodiments, urea and formaldehyde aqueous solutions are mixed and the pH is adjusted to 7.5-8.5, then placed in a high-temperature environment (70-80°C) for 30-60 minutes. Subsequently, the pH of the mixture is adjusted to 4, and urea is added again for 1 hour. Then, the pH of the mixture is adjusted to 7.5-8.5 to obtain a urea-formaldehyde resin solution.

[0060] In some embodiments, the mass ratio of melamine-formaldehyde resin solution to urea-formaldehyde resin solution is 0.5 to 2:1, and preferably, the mass ratio of melamine-formaldehyde resin solution to urea-formaldehyde resin solution is 1:1.

[0061] In some embodiments, melamine-formaldehyde resin solution and urea-formaldehyde resin solution are mixed and stirred at high temperature for 30 minutes to obtain melamine-urea-formaldehyde resin mixture.

[0062] In step S2, the monolayer MoS2 nanosheets are either powder or suspension.

[0063] In some embodiments, the lateral dimensions of the monolayer MoS2 nanosheets are 50~200 nm.

[0064] In some embodiments, monolayer MoS2 nanosheets are concentrated by ultrasonic treatment or centrifugation, and MoS2 nanosheets are dispersed by a liquid dispersion medium to obtain MoS2 gel.

[0065] In some embodiments, the dispersion medium is selected as a liquid monomer or a comonomer, wherein the dispersion medium is selected from one or a combination of deionized water, methanol, ethanol, ethylene glycol, 1,4-butanediol, isopropanol, glycerol, and polyvinyl alcohol. Preferably, the dispersion medium is ethylene glycol to form a MoS2-ethylene glycol gel.

[0066] In step S3, the MoS2 gel is dispersed in a melamine resin solution and then ultrasonically treated to obtain a melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets. The ultrasonic treatment frequency is 10-50 kHz, the power is 200-1000 W, and the time is 10-30 min. Preferably, the ultrasonic treatment frequency is 50 kHz, the power is 800 W, and the time is 15 min.

[0067] In some embodiments, the mass fraction of MoS2 in melamine-formaldehyde resin is 0.01% to 1.0%, preferably, the mass fraction of MoS2 in melamine-formaldehyde resin is 0.1% to 1.0%.

[0068] The technical features of the polymer foam obtained by subsequent in-situ foaming of the melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets in Example 2 are the same as those in Example 1, so they will not be repeated here.

[0069] Thirdly, this solution provides a polymer foam with high photothermal conversion efficiency, which is prepared by the above-mentioned polymer foam with high photothermal conversion efficiency. The polymer foam with high photothermal conversion efficiency includes: a melamine three-dimensional foam skeleton and a single layer of MoS2 nanosheets polymerized in situ on the melamine three-dimensional foam skeleton.

[0070] In some embodiments, the polymer foam has a pore size of 50-200 μm, a porosity of 40-95%, and a density of 10-50 kg / m³.

[0071] In some embodiments, polymer foam is used directly in natural water bodies to achieve stable solar-driven steam output through its self-floating properties and high photothermal conversion efficiency.

[0072] In some embodiments, polymer foam can be die-cut, hot-pressed, or cold-pressed into shapes such as cylinders, spheres, rectangles, and cones for use in solar steam generators with different structural forms.

[0073] In some embodiments, polymer foam is used in solar steam generation devices for complex aquatic environments, exhibiting excellent photothermal performance, self-floating characteristics, and structural adjustability.

[0074] In some embodiments, the solar steam generator is an interface-type solar steam generator, and the steam output efficiency can be optimized by adjusting the foam thickness (3~200 mm), evaporator height (5~100 mm), surface porosity (40-95%), and hydrophilic / hydrophobic modification treatment.

[0075] Compared with existing technologies, this technical solution has the following characteristics and beneficial effects:

[0076] This method utilizes an in-situ polymerization process to uniformly introduce monolayer molybdenum disulfide (ML-MoS2) into the three-dimensional polymer framework of melamine, constructing a molecularly dispersed photothermal functional composite foam. This foam exhibits excellent photothermal properties and structural stability, possesses good self-floating ability, and can be directly applied to natural water bodies for efficient solar-driven steam generation. Furthermore, through synergistic control of the foam's macroscopic structure and microscopic interfaces, while maintaining the material's lightweight and high porosity, the light absorption efficiency, photothermal conversion efficiency, and evaporation rate are effectively improved. Experimental results show that the foam material exhibits stable steam output performance under natural light conditions, making it suitable for various applications such as seawater desalination, salt lake extraction, and wastewater purification, demonstrating good engineering adaptability and potential for large-scale production.

[0077] This solution has at least the following technical advantages:

[0078] (1) Excellent dispersibility and structural stability: Through in-situ polymerization / foaming process, monolayer MoS2 nanosheets are uniformly introduced into the melamine foam skeleton to achieve molecular-level dispersion in the polymer matrix. This strategy effectively prevents the aggregation of MoS2 nanosheets during the composite process, thereby significantly improving the photothermal conversion efficiency of the material and enabling it to achieve efficient photothermal performance conduction and utilization on a macroscopic scale.

[0079] (2) High-efficiency photothermal evaporation performance: The prepared photothermal functional foam can achieve self-floating operation without additional auxiliary structures, and has excellent photothermal conversion and steam output capabilities. Under standard sunlight conditions, the foam surface temperature can reach 70℃, and the single-sided evaporation rate can reach 2.61 kg·m -2 ·h -1 Furthermore, due to the light absorption area expansion effect brought about by the MF framework structure (2-5 times the projected area), the overall evaporation efficiency can be further improved to 4-10 kg·m³. -2 ·h -1 It exhibits excellent interfacial steam generation efficiency.

[0080] (3) Strong processability and long service life: Foam materials have good dimensional stability and shape plasticity in structural design, which facilitates die cutting and multi-scale molding. At the same time, the in-situ fixation strategy effectively inhibits the shedding or migration of monolayer MoS2 during long-term use, greatly reduces the loss of photothermal components, and extends the service life of the material.

[0081] (4) Wide range of applications: The preparation process of this invention is simple, the raw materials are cheap and readily available, and it has good scalability. The foam material is suitable for various solar-driven interfacial evaporation applications such as seawater desalination, salt lake salt extraction, and sewage purification, and has the potential for rapid deployment and industrialization. Attached Figure Description

[0082] Figure 1 These are physical images of monolayer MoS2 modified melamine foams of different concentrations prepared in Example 1 and digital photographs of them floating in water.

[0083] Figure 2 SEM image of the monolayer MoS2 modified melamine foam prepared in Example 1;

[0084] Figure 3 Comparison of water contact angle tests for monolayer MoS2-modified melamine foam prepared in Example 1;

[0085] Figure 4 Fluorescence confocal images of pure melamine foam and monolayer MoS2-modified melamine foam prepared in Example 1 at an excitation wavelength of 532 nm;

[0086] Figure 5 Raman spectra of monolayer MoS2-modified melamine foams with different contents prepared in Example 1;

[0087] Figure 6 The UV-Vis-NIR absorption spectra of monolayer MoS2 modified melamine foams of different concentrations prepared in Example 1 are shown.

[0088] Figure 7 Temperature-time curves of dry and wet surfaces of a single-layer MoS2-modified melamine foam with a content of 0.3% prepared in Example 1 under sunlight irradiation.

[0089] Figure 8 A comparison of the water evaporation rates of a single-layer MoS2-modified melamine foam with a content of 0.3% prepared in Example 1 and pure water under sunlight and dark conditions.

[0090] Figure 9 The evaporation rate curve of the monolayer MoS2 modified melamine foam prepared in Example 1 during a 50-h seawater evaporation cycle test.

[0091] Figure 10 The graph shows the measured performance of the single-layer MoS2 modified melamine foam prepared in Example 1 under outdoor conditions.

[0092] Figure 11 The diagram shows the water evaporation performance of a surface-coated monolayer MoS2-modified melamine foam prepared as a comparative example under sunlight conditions. Detailed Implementation

[0093] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0094] Those skilled in the art should understand that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] Example 1

[0096] The monolayer MoS2 nanosheets were uniformly dispersed in melamine-formaldehyde resin, and the monolayer MoS2 modified melamine foam was prepared by in-situ foaming. This Example 1 includes the following steps: (1) Melamine powder and formaldehyde aqueous solution with a mass fraction of about 37% were mixed at a molar ratio of 1:3, heated and stirred at 85°C at a stirring rate of 900 rpm, and the pH was adjusted to 9 with triethanolamine. The reaction was carried out for 3 hours to prepare a transparent melamine-formaldehyde resin solution, which was then cooled to room temperature for later use.

[0097] (2) The monolayer MoS2 nanosheets were concentrated by ultrasonication or centrifugation and then ethylene glycol was used to form MoS2-ethylene glycol gel.

[0098] (3) Use the resin solution obtained in step (1) to rinse and redisperse the MoS2-ethylene glycol gel obtained in step (2), and then sonicate it (frequency 50kHz, power 800w, time 15min) to obtain a melamine-formaldehyde resin solution with a uniform dispersion of monolayer MoS2.

[0099] (4) Add a foaming agent, an emulsifier, and a curing agent to the dispersion system obtained in step (3): the foaming agent is n-pentane, and the amount added is 15% of the mass of the dispersion; the emulsifier is Tween 80, and the amount added is 3% of the mass of the dispersion; the curing agent is anhydrous formic acid, and the amount added is 13% of the mass of the dispersion.

[0100] (5) The obtained foaming liquid is stirred rapidly at room temperature to make it uniformly emulsified and foamed. The stirring time is 5 min and the stirring speed is 1000 rpm to obtain the foaming liquid.

[0101] (6) The foaming liquid was placed in a microwave reactor and heated to foam and form. The power was 800W and the time was 10min. Then the formed foam was placed in a vacuum drying oven to cure and remove residual formaldehyde. The temperature was 100℃ and the time was 2h to obtain a single-layer MoS2 modified melamine foam material. The mass of single-layer MoS2 added accounted for 0.01-1.0wt% of the resin mass.

[0102] This Example 1 conducted experiments with different concentrations.

[0103] Example 2:

[0104] Monolayer MoS2 nanosheets were uniformly dispersed in a liquid monomer or comonomer, and monolayer MoS2-modified melamine foam was prepared by in-situ polymerization and foaming. This Example 2 includes the following steps:

[0105] (1) Weigh a single layer of MoS2 nanosheets and add them to a certain volume of deionized water. Disperse them by ultrasound to obtain a stable MoS2 dispersion. The ultrasound treatment time is 30 minutes.

[0106] (2) The MoS2 aqueous dispersion was transferred to a three-necked flask, and melamine and paraformaldehyde were added in appropriate amounts according to a molar ratio of melamine to paraformaldehyde of 1:3. The pH was adjusted to 9 using sodium hydroxide. The mixture was reacted under magnetic stirring (stirring speed of 900 rpm) at a reaction temperature of 85°C for 3 hours to obtain a melamine-formaldehyde resin dispersion doped with monolayer MoS2 nanosheets.

[0107] (3) After the reaction is complete, cool to room temperature, and add emulsifier, foaming agent and curing agent to the obtained dispersion in sequence, and stir rapidly to obtain foamed liquid. The stirring speed is 1000 rpm, the stirring time is 5 min, the emulsifier is Tween 80, and the amount added is 3% of the system mass; the foaming agent is n-pentane, and the amount added is 15% of the system mass; the curing agent is anhydrous formic acid, and the amount added is 13% of the system mass.

[0108] (4) The foaming liquid obtained in step (3) is placed in a microwave oven and heated to foam. The microwave power is 800 W and the heating time is 10 minutes. Then it is transferred to a vacuum drying oven and cured at 100°C to further remove residual formaldehyde. The curing time is 2 hours, and finally a melamine foam material loaded with a single layer of MoS2 is obtained.

[0109] Example 3:

[0110] A preferred mixture of MF and UF is used as a resin precursor for preparing MoS2 modified foam materials. Example 3 includes the following steps:

[0111] (1) Add formaldehyde aqueous solution (mass fraction of about 37%) and melamine powder to the reaction vessel according to the required molar ratio, place it in an electromagnetic constant temperature water bath, control the stirring speed at 900 rpm, and slowly add NaOH solution with a concentration of about 10% to adjust the pH of the system to 9. React at 85℃ for 3 hours to obtain a melamine-formaldehyde resin solution with a concentration of about 60-70%, and cool it for later use.

[0112] (2) Mix formaldehyde aqueous solution (mass fraction of about 37%) with urea in proportion, place in a constant temperature water bath, stir at 900 rpm, adjust pH to 7.8, heat to 75°C and react for 50 minutes (preferably 50 minutes), during which the pH is adjusted to about 4 and the second part of urea is added, react for 1 hour, and finally adjust the pH to 7.8 to prepare urea-formaldehyde resin (UF), and cool for later use;

[0113] (3) Mix the MF and UF resin liquid obtained in steps (1) and (2) at a mass ratio of 1:1 and stir at high speed for 30 minutes to obtain a melamine-urea-formaldehyde resin mixture.

[0114] (4) The monolayer MoS2 aqueous dispersion was concentrated by centrifugation and redispersed with ethylene glycol to obtain MoS2 gel. This gel was added to the resin mixture obtained in step (3), and the MoS2 was uniformly dispersed by ultrasonic vibration or high-speed stirring to obtain a MoS2 / resin dispersion. The mass of monolayer MoS2 added accounted for 0.01~1.0 wt% of the resin mass.

[0115] (5) Add emulsifier, foaming agent and curing agent to the dispersion obtained in step (4). The emulsifier is Tween 80, and the mass content is 5% of the resin dispersion. The foaming agent is n-pentane, and the mass content is 15% of the resin dispersion. The curing agent is anhydrous formic acid, and the mass content is 10% of the resin dispersion. Stir quickly for 5 minutes, and control the stirring speed at 1000 rpm to obtain foaming liquid.

[0116] (6) The foaming liquid is placed in a microwave reactor and heated to form foam at a power of 800 W for 10 minutes. Then the formed foam is placed in a vacuum drying oven and cured at 100°C for 2 hours to remove residual formaldehyde and complete the curing of the foam structure, thus obtaining a high-performance single-layer MoS2 modified melamine-urea-formaldehyde foam material.

[0117] Comparative Example 1

[0118] This comparative example proposes a "post-molding loading" modification method. By loading a single layer of MoS2 onto the surface of a melamine foam skeleton, it achieves a comparison with in-situ foaming modification. This method facilitates the analysis of the effects of different modification strategies and is applicable to applications requiring controllable adjustment of MoS2 loading. Specifically, it includes the following sequential steps:

[0119] (1) Select commercially available melamine foam as the load matrix. The melamine foam has a density of about 24 kg / m³ and a porosity of about 90%. After cutting the foam into the required size, use deionized water to clean the surface impurities. Wash it 1 to 3 times. After cleaning, let it air dry naturally to ensure that the surface is dry and free of contamination.

[0120] (2) The monolayer MoS2 nanosheets were dispersed in a liquid medium by ultrasonication or high-speed stirring. The selected medium was deionized water. In order to improve the adhesion of MoS2 on the foam surface, a certain proportion of binder was added to the dispersion. The binder was an aqueous polyurethane dispersion with a mass content controlled at 20 wt%. The ultrasonic time was 30 minutes and the stirring speed was 1000 rpm to obtain a stable MoS2 dispersion.

[0121] (3) Apply the MoS2 dispersion prepared in step (2) to the melamine foam prepared in step (1) by uniform coating, impregnation or spraying (preferably impregnation), and use static adsorption or vacuum-assisted permeation to fully wet and adhere MoS2 to the surface of the foam skeleton. The adsorption or permeation time is controlled within 30 minutes;

[0122] (4) The loaded foam is placed in a vacuum drying oven and the drying temperature is controlled at 60°C for 8 hours to effectively remove residual liquid and promote the curing and adhesion of the binder, and finally obtain a MoS2 modified foam material with stable surface load.

[0123] This scheme includes physical images of monolayer MoS2-modified melamine foams of different concentrations prepared in Example 1, and digital photos taken of them floating in water, as shown below. Figure 1 As shown, Figure 1 From right to left, the images show monolayer MoS2-modified melamine foams with MoS2 contents of 0%, 0.03%, 0.1%, 0.3%, 0.6%, and 1.0%. It can be seen that when the MoS2 content is 0.1%, the overall foam color exhibits the unique yellow-green hue of monolayer MoS2 nanosheets, and the color gradually deepens with increasing MoS2 loading. Simultaneously, the modified foam with a MoS2 content of 0.3% was observed using scanning electron microscopy (SEM), and the imaging results are as follows... Figure 2 As shown, the results indicate that the foam maintains a typical interconnected three-dimensional network pore structure, providing abundant channels for water transport. Further comparison of the water contact angle test results for samples with 0% and 0.3% content yields the following results: Figure 3 As shown, the MoS2 loading did not significantly weaken the intrinsic superhydrophilic properties of melamine foam.

[0124] In addition, pure melamine foam and 0.3% monolayer MoS2 modified foam were imaged using a laser confocal fluorescence microscope with an excitation wavelength of 532 nm. The imaging results are as follows: Figure 4 As shown, the results indicate that pure melamine foam did not show obvious fluorescence, while the modified foam had a unique fluorescence signal of monolayer MoS2 nanosheets evenly distributed along the skeleton, indicating that the MoS2 nanosheets were uniformly dispersed in the matrix and did not show obvious aggregation.

[0125] Raman spectra of monolayer MoS2-modified melamine foam with different contents in Example 1 are shown below. Figure 5 As shown, it can be seen that with the increase of MoS2 loading, at 602, 674, and 750 cm⁻¹, -1 The peak disappears at 975cm. -1 The peak intensity decreased significantly at 379.6 and 400.9 cm⁻¹, while the intensity decreased at 479.6 and 400.9 cm⁻¹. -1 Two distinct peaks appear at this point, corresponding to the E of monolayer MoS2. 2g 1 and A g 1 Raman mode, with a frequency difference of approximately 21.3 cm. -1 This indicates that in MoS2-MF, MoS2 nanosheets exist in a monolayer or few-layer form; the UV-Vis-NIR absorption spectra of monolayer MoS2-modified melamine foams of different concentrations prepared in Example 1 are shown below. Figure 6As shown, with the increase of MoS2 loading, the absorption of the foam across the entire spectrum is significantly enhanced, especially in the near-infrared region, demonstrating the excellent light absorption performance of the foam. The temperature-time curves of the dry and wet surfaces of the 0.3% MoS2-modified melamine foam prepared in Example 1 under sunlight irradiation are shown below. Figure 7 As shown, under sunlight, the sample's temperature can be stably maintained at approximately 70℃ and 40℃ in both dry and wet states, respectively, exhibiting excellent light response and stability. The comparison of water evaporation rates between the 0.3% MoS2-modified melamine foam prepared in Example 1 and pure water under sunlight and dark conditions is shown in the figure. Figure 8 As shown, the evaporation rate of pure water under dark conditions is measured to be 0.14 kg·m³. -2 ·h -1 Under one ray of sunlight, the evaporation rate is 0.48 kg·m³. -2 ·h -1 The net evaporation rate is 0.34 kg·m³. -2 ·h -1 This result is very close to the reported data. When using 3D MoS2-MF for testing, the water evaporation rate of MoS2-MF under dark conditions was 0.43 kg·m³. -2 ·h -1 The stable evaporation rate of MoS2-MF under one sun was 2.61 kg·m³. -2 ·h -1 The net evaporation rate is 2.18 kg·m³. -2 ·h -1 This is more than six times the amount of water that evaporates directly, a figure that also exceeds the theoretical limit of 1.47 kg·m³ for traditional single-stage 2D evaporators. -2 ·h -1 .

[0126] It is worth noting that even under dark conditions, the water evaporation rate of the 3D evaporator is much higher than that of pure water, approaching the evaporation rate of pure water under one day of sunlight. This is mainly attributed to the porous structure of MoS2-MF, which allows water to be distributed on the evaporator surface through capillary action, forming a thin water film that promotes water evaporation. The evaporation rate curve of the monolayer MoS2-modified melamine foam prepared in Example 1 during a 50-hour seawater evaporation cycle test is shown in the figure. Figure 9 As shown, the seawater evaporation rate remains relatively stable at 2.10 kg·m³. -2 ·h -1The results, around [timeframe missing], confirm the excellent long-term stability and reliability potential of this evaporator. The measured performance of the single-layer MoS2 modified melamine foam prepared in Example 1 under outdoor conditions is as follows: Figure 10 As shown, during the 12-day test, the average evaporation rate of the MoS2-MF evaporator remained stable at 4-6 times that of seawater, demonstrating its excellent evaporation performance and stable reliability.

[0127] To further compare the advantages of this process, the water evaporation performance of MoS2-modified melamine foam prepared based on post-processing was compared under standard sunlight conditions. Figure 11 As shown, the water evaporation rate of this process shows a significant performance degradation compared to the in-situ molding process. This is mainly because the binder clogs the pores of the melamine foam during the post-processing, resulting in a significant reduction in water transport capacity and thus greatly reducing the water evaporation rate. This also demonstrates the advanced nature and superiority of the in-situ molding process.

[0128] In summary, the polymer foam with high photothermal conversion efficiency provided by this solution effectively avoids the aggregation of monolayer MoS2 nanosheets, ensuring their uniform dispersion and fixation within the melamine foam matrix. This achieves efficient conversion of its excellent photothermal properties to a macroscopic scale. Furthermore, through process optimization, a monolayer MoS2-modified melamine foam for seawater desalination interfacial solar steam generation system can be prepared. By controlling the macroscopic and microscopic structures, the light absorption rate, photothermal conversion efficiency, and steam generation rate of the composite foam can be improved, with a maximum water evaporation rate reaching 2.61 kg·m³. -2 ·h -1 This technology has advantages such as simplicity, environmental friendliness, low cost, and high processability, and is expected to be rapidly scaled up and produced, thus enabling large-scale applications in wastewater treatment, seawater desalination, salt lakes, and seawater extraction.

[0129] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for producing a polymer foam having a high light-to-heat conversion efficiency, characterized by, The method comprises the following steps: S1: dispersing monolayer MoS2 nanosheets in a liquid dispersion medium to form a MoS2 dispersion; S2: adding melamine and paraformaldehyde monomers to the MoS2 dispersion to obtain a melamine formaldehyde resin dispersion doped with monolayer MoS2 nanosheets by re-polymerization; S3: allowing the melamine formaldehyde resin dispersion doped with monolayer MoS2 nanosheets to undergo in-situ polymerization and foaming under temperature control to obtain a polymer foam, wherein the in-situ polymerization temperature is 80-90 DEG C, the in-situ polymerization time is 2-4 h, and the foaming temperature is 60-70 DEG C.

2. A method for producing a polymer foam having a high light-heat conversion efficiency, characterized by, The method comprises the following steps: S1: preparing a resin solution containing melamine pre-polymer, wherein the resin solution containing melamine pre-polymer is a melamine formaldehyde resin solution or a melamine-urea-formaldehyde resin mixture S2: dispersing monolayer MoS2 nanosheets in a liquid dispersion medium to form a MoS2 gel after ultrasonic treatment and concentration; S3: dispersing the MoS2 gel in the resin solution containing melamine pre-polymer and performing ultrasonic treatment to obtain a melamine formaldehyde resin dispersion doped with monolayer MoS2 nanosheets; S4: allowing the melamine formaldehyde resin dispersion doped with monolayer MoS2 nanosheets to undergo in-situ polymerization and foaming under temperature control to obtain a polymer foam, wherein the in-situ polymerization temperature is 80-90 DEG C, the in-situ polymerization time is 2-4 h, and the foaming temperature is 60-70 DEG C.

3. The method of claim 2, wherein the polymer foam has a high light-to-heat conversion efficiency. When the resin solution containing melamine pre-polymer is a melamine formaldehyde resin solution, melamine powder and an aqueous formaldehyde solution are mixed and stirred in a high-temperature environment, the pH value of the mixed system is adjusted to be alkaline, and reaction is performed to obtain the melamine formaldehyde resin solution; when the resin solution containing melamine pre-polymer is a melamine-urea-formaldehyde resin mixture, melamine powder and an aqueous formaldehyde solution are mixed and stirred at 80-90 DEG C, the pH value of the mixed system is adjusted to be alkaline, and reaction is performed to obtain the melamine formaldehyde resin solution; urea and an aqueous formaldehyde solution are mixed and stirred at 70-80 DEG C after the pH value is adjusted to be alkaline, then the pH value of the mixed system is adjusted to be acidic, and then urea is continuously added for reaction, and then the pH value of the mixed system is adjusted to be alkaline to obtain a urea formaldehyde resin solution; The melamine formaldehyde resin solution and the urea formaldehyde resin solution are mixed and stirred to obtain a melamine-urea-formaldehyde resin mixture.

4. The method for preparing polymer foam with high photothermal conversion efficiency according to claim 1 or 2, characterized in that, The mass fraction of MoS2 in the melamine formaldehyde resin is 0.01%-1.0%.

5. The method for preparing polymer foam with high photothermal conversion efficiency according to claim 1 or 2, characterized in that, A foaming agent, an emulsifying agent and a curing agent are added to the melamine formaldehyde resin dispersion doped with monolayer MoS2 nanosheets and stirred to obtain a foaming liquid.

6. The method for preparing polymer foam with high photothermal conversion efficiency according to claim 1 or 2, characterized in that, The surface of the polymer foam is subjected to functionalization treatment.

7. The method for preparing polymer foam with high photothermal conversion efficiency according to claim 1 or 2, characterized in that, The dispersion medium is selected from one or a combination of deionized water, methanol, ethanol, ethylene glycol, 1, 4-butanediol, isopropanol, glycerol and polyvinyl alcohol.

8. A polymer foam having high photothermal conversion efficiency, characterized by, It comprises: a melamine three-dimensional foam framework and monolayer MoS2 nanosheets in-situ polymerized on the melamine three-dimensional foam framework, wherein the loading amount of the monolayer MoS2 nanosheets is 0.01-1.0%, the monolayer MoS2 nanosheets maintain a monolayer state, and the polymer foam with high light-heat conversion efficiency is prepared according to the preparation method of claim 1 or 2.

9. The polymeric foam with high photothermal conversion efficiency according to claim 8, wherein, Polymer foam has pore size of 50-200 microns, porosity of 40-95%, and density of 10-50 kg / m³.

10. The polymeric foam with high photothermal conversion efficiency according to claim 8, wherein, The polymer foam is directly used in natural water bodies, and through its self-floating performance and high light-heat conversion efficiency, stable solar-driven steam output is realized, which is used in solar steam generation devices of different structures.

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