Preparation method of composite interfacial evaporation material based on natural mulberry branches

Abstract

The application discloses a preparation method of a composite interfacial evaporation material based on natural mulberry branches, and belongs to the technical field of solar energy utilization and seawater desalination. The application aims at solving the problems of low durability and evaporation efficiency of existing biomass-based interfacial evaporation materials. The method comprises the following steps: one, substrate pretreatment; two, eutectic solvent treatment; three, silver nanoparticle loading; and four, silk fibroin self-assembly. The application is used for preparing the composite interfacial evaporation material based on natural mulberry branches.

Description

Technical Field

[0001] This invention belongs to the field of solar energy utilization and seawater desalination technology. Background Technology

[0002] In recent years, people's quality of life has generally improved, and the demand for water and the quality of water have continued to increase. This has made the development of seawater desalination technology imminent. In order to solve this problem, people have been increasing their efforts to develop renewable energy sources such as solar energy, wind energy, and tidal energy. However, the intermittency, uncertainty, and high cost of renewable energy have limited its further development. There is an urgent need for a high-efficiency, low-cost, and environmentally friendly solar-driven interface evaporation technology to stand out as an emerging solution. Its core lies in breaking through the multiple bottlenecks of traditional photothermal materials in terms of energy conversion efficiency, structural stability, and long-term operational reliability.

[0003] Currently, in the silkworm breeding process, a large amount of mulberry branches are left idle on the ground as agricultural waste. As a biomass material, mulberry branches have a certain water evaporation efficiency, but their durability is not high enough, and the evaporation efficiency remains in a low range. Summary of the Invention

[0004] This invention aims to address the problems of low durability and low evaporation efficiency in existing biomass-based interfacial evaporation materials, and thus provides a method for preparing a composite interfacial evaporation material based on natural mulberry branches.

[0005] A method for preparing a composite interfacial evaporation material based on natural mulberry branches, comprising the following steps:

[0006] I. Substrate Pretreatment:

[0007] Make multiple cuts along the length of the side of a natural mulberry branch, then spread one end of the bark layer outward along the cuts to form a multi-lobed structure, while keeping the other end of the bark layer connected to the xylem, thus obtaining a partially spread bark layer of the branch base.

[0008] II. Eutectic solvent treatment:

[0009] The pruning substrate with partially unfolded bark layer was heat-treated in a eutectic solvent, then washed and dried to obtain the substrate treated with the eutectic solvent.

[0010] III. Silver nanoparticle loading:

[0011] The substrate treated with a eutectic solvent was placed in a silver ammonia solution for reaction, and then washed and dried to obtain an interfacial evaporation material loaded with silver nanoparticles.

[0012] IV. Self-assembly of silk protein:

[0013] The interfacial evaporation material loaded with silver nanoparticles was immersed in a silk protein solution, pulled out, and then dried at room temperature. The immersion, pulling, and drying were repeated multiple times to obtain a composite interfacial evaporation material with a silk protein layer self-assembled on the surface.

[0014] The beneficial effects of this invention are:

[0015] 1. This invention uses agricultural waste (mulberry branches) and biological materials (silk) as the main raw materials, provides two clear pretreatment paths, has a simple preparation process, mild conditions, does not require complex equipment, is easy to select and adjust according to actual application needs, and has the potential for large-scale industrial production.

[0016] 2. This material enhances light absorption by peeling off the bark of mulberry branches and loading them with silk fibroin and silver nanoparticles, while simultaneously optimizing the surface microstructure. Under simulated sunlight, its water evaporation rate reaches 2.0088 kg·m³. -2 ·h -1 It exhibits excellent cycle stability (average evaporation rate retention rate > 98% after 10 hours of continuous cycle operation) and has broad application prospects in seawater desalination, wastewater treatment and other fields.

[0017] 3. This invention utilizes a closed-loop synergistic design—expanding the interface through peeling, enhancing cohesion with silk fibroin, and using DES-assisted silver loading—to achieve deep functional coupling among the components. DES treatment effectively removes waxy and other inert components from the biomass surface, increasing surface active sites and ensuring uniform loading of silver nanoparticles. Silver nanoparticle loading significantly improves the material's light absorption performance and prevents biofouling. Silk fibroin self-assembly further optimizes the material's long-term stability.

[0018] 4. The raw materials of this invention are widely available and inexpensive. The preparation process is simple and the conditions are mild. It does not require complex equipment or harsh environments and has the potential for large-scale production and application. It has broad application prospects in the fields of seawater desalination and industrial wastewater purification.

[0019] 5. The present invention proposes a branch-cutting and spreading structure, which forms an open channel through the cutting and spreading, significantly enhancing the material's moisture transfer efficiency and heat localization effect, and improving evaporation performance. Attached Figure Description

[0020] Figure 1 A schematic diagram showing the pure water evaporation efficiency of the interfacial evaporation materials prepared in experiments 2 to 4 under simulated sunlight;

[0021] Figure 2 The graph shows the pure water evaporation efficiency of the interfacial evaporation material prepared in Example 1 over 10 cycles under simulated sunlight.

[0022] Figure 3Schematic diagram of the temperature rise of the interfacial evaporation materials prepared in experiments 2 to 4 under simulated sunlight;

[0023] Figure 4 The solar interface evaporation rate graph and the hourly solar intensity graph of the interfacial evaporation material prepared in Example 1 from 0:00 to 24:00 on a certain day are shown.

[0024] Figure 5 The graph shows the amount of pure water evaporation of the interfacial evaporation material prepared in Experiment 1 under simulated sunlight.

[0025] Figure 6 The graph shows the amount of pure water evaporation of the interfacial evaporation material prepared in Experiment 7 under simulated sunlight.

[0026] Figure 7 This is a schematic diagram illustrating the preparation of a branch substrate by unfolding a portion of the bark layer in step one of Examples;

[0027] Figure 8 This is a schematic diagram showing the pure water evaporation efficiency of the partially expanded bark layer of the branch substrate prepared in step one of Example 1, and the composite interface evaporation materials prepared in Example 1, Comparative Experiment 5, and Comparative Experiment 6 under simulated sunlight.

[0028] Figure 9 A scanning electron microscope image of the inner bark layer of the composite interfacial evaporation material with a surface self-assembled silk protein layer prepared in Example 1;

[0029] Figure 10 Scanning electron microscope (SEM) image of the outer xylem surface of the composite interfacial evaporation material with a self-assembled silk protein layer on its surface, prepared in Example 1. Detailed Implementation

[0030] Specific Implementation Method 1: This implementation method is a preparation method of a composite interfacial evaporation material based on natural mulberry branches, which is carried out according to the following steps:

[0031] I. Substrate Pretreatment:

[0032] Make multiple cuts along the length of the side of a natural mulberry branch, then spread one end of the bark layer outward along the cuts to form a multi-lobed structure, while keeping the other end of the bark layer connected to the xylem, thus obtaining a partially spread bark layer of the branch base.

[0033] II. Eutectic solvent treatment:

[0034] The pruning substrate with partially unfolded bark layer was heat-treated in a eutectic solvent, then washed and dried to obtain the substrate treated with the eutectic solvent.

[0035] III. Silver nanoparticle loading:

[0036] The substrate treated with a eutectic solvent was placed in a silver ammonia solution for reaction, and then washed and dried to obtain an interfacial evaporation material loaded with silver nanoparticles.

[0037] IV. Self-assembly of silk protein:

[0038] The interfacial evaporation material loaded with silver nanoparticles was immersed in a silk protein solution, pulled out, and then dried at room temperature. The immersion, pulling, and drying were repeated multiple times to obtain a composite interfacial evaporation material with a silk protein layer self-assembled on the surface.

[0039] In this specific implementation, the synergistic enhancement effect of silver nanoparticle loading, structure unfolding / exfoliation, and silk fibroin self-assembly was observed. A systematic seawater desalination evaporation experiment was conducted on the D3BUMBAg2-SF composite material, which combines sprue unfolding, silver loading, and silk self-assembly. Experimental results show that the combined material system exhibits optimal overall performance. Under the same solar irradiation conditions, the D3BUMBAg2-SF material exhibits the highest evaporation rate and cycling stability. Its performance advantage stems from the following synergistic mechanism:

[0040] The peeling structure optimizes moisture transport and heat localization: by spreading the branches through pruning, the evaporation interface is significantly increased, the resistance to moisture transport is reduced, and the light absorption and heat localization effects are enhanced.

[0041] Silver nanoparticle loading significantly improves photothermal conversion efficiency: uniform loading of silver particles enhances the material's light absorption capacity over a wide spectral range, thereby effectively increasing evaporation temperature and evaporation driving force.

[0042] Silk fibroin self-assembly enhances structural and functional stability: The silk fibroin layer not only enhances the mechanical strength and water resistance of the material, but also repairs the surface microstructure through its self-assembly behavior, further stabilizing the silver nanoparticles and delaying performance degradation.

[0043] The combination of these three elements forms a closed-loop synergistic system of "structural unfolding - photothermal enhancement - interface stabilization", which enables the material to maintain high evaporation performance while possessing excellent mechanical stability and resistance to biofouling.

[0044] Comparative experiments further confirmed that materials employing only one or two of these technologies exhibited lower evaporation efficiency, cycle stability, or structural integrity compared to systems combining all three. This fully demonstrates that the deep integration of silver nanoparticle loading, peeling structure modification, and silk fibroin self-assembly is a key pathway to achieving efficient and stable solar interfacial evaporation.

[0045] This embodiment provides a solar-driven water treatment solution integrating structure and function. Its core innovation lies in a three-step synergistic process: increasing the evaporation interface through peeling, enhancing mechanical stability through the self-assembly of silk fibroin, and stabilizing the load on silver nanoparticles with the assistance of a eutectic solvent. This achieves a high-value composite of agricultural waste (mulberry branches) and biomaterials (silk). The self-assembly capability of silk fibroin is cleverly utilized to repair and strengthen the exposed fiber structure after peeling, while simultaneously constructing an ideal active interface. This results in a uniform and robust load on silver nanoparticles, enabling the material to simultaneously possess efficient photothermal evaporation and excellent durability. This embodiment effectively solves a series of problems associated with traditional biomass evaporation materials, such as insufficient efficiency, susceptibility to structural damage, and susceptibility to biofouling. It not only opens up new avenues for the resource utilization of mulberry branches but also provides a new material foundation for developing high-performance, long-life, and green economic solar water treatment devices, showing significant application potential in seawater, freshwater, and wastewater treatment.

[0046] The beneficial effects of this embodiment are:

[0047] 1. This implementation method uses agricultural waste (mulberry branches) and biological materials (silk) as the main raw materials, provides two clear pretreatment paths, has a simple preparation process, mild conditions, does not require complex equipment, is easy to select and adjust according to actual application needs, and has the potential for large-scale industrial production.

[0048] 2. This material enhances light absorption by peeling off the bark of mulberry branches and loading them with silk fibroin and silver nanoparticles, while simultaneously optimizing the surface microstructure. Under simulated sunlight, its water evaporation rate reaches 2.0088 kg·m³. -2 ·h -1 It exhibits excellent cycle stability (average evaporation rate retention rate > 98% after 10 hours of continuous cycle operation) and has broad application prospects in seawater desalination, wastewater treatment and other fields.

[0049] 3. This embodiment utilizes a closed-loop synergistic design—expanding the interface through peeling, enhancing cohesion with silk fibroin, and using DES-assisted silver loading—to achieve deep functional coupling among the components. DES treatment effectively removes waxy and other inert components from the biomass surface, increasing surface active sites and ensuring uniform loading of silver nanoparticles. The silver nanoparticle loading significantly improves the material's light absorption performance and prevents biofouling. Silk fibroin self-assembly further optimizes the material's long-term stability.

[0050] 4. The raw materials for this method are widely available and inexpensive. The preparation process is simple and the conditions are mild. It does not require complex equipment or harsh environments and has the potential for large-scale production and application. It has broad application prospects in the fields of seawater desalination and industrial wastewater purification.

[0051] 5. This embodiment proposes a branch-cutting and unfolding structure, which forms an open channel through the cutting and unfolding, significantly enhancing the material's moisture transfer efficiency and heat localization effect, and improving evaporation performance.

[0052] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the outward extension of the bark layer in step one accounts for 40% to 60% of the total length of the natural mulberry branch. Everything else is the same as in Specific Implementation Method One.

[0053] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the eutectic solvent mentioned in step two is composed of choline chloride and oxalic acid, and the molar ratio of choline chloride to oxalic acid is (1~2):1; the mass ratio of the partially expanded bark layer of the pruning substrate to the volume ratio of the eutectic solvent in step two is 1g:(15~25)mL. Everything else is the same as in Specific Implementation Method One or Two.

[0054] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the heat treatment described in step two is specifically carried out at a temperature of 50℃ to 100℃ for 0.5h to 4h. Everything else is the same as in Specific Implementation Methods One to Three.

[0055] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the silver ammonia solution mentioned in step three is prepared according to the following steps: adding ammonia water dropwise to the silver nitrate solution until the solution becomes clear; the concentration of the silver nitrate solution is 0.05 mol / L to 0.15 mol / L; the concentration of the ammonia water is 0.05 mol / L to 0.15 mol / L; and the volume ratio of the silver nitrate solution to the ammonia water is 1:(15~25). Everything else is the same as in Specific Implementation Methods One to Four.

[0056] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the mass ratio of the substrate after eutectic solvent treatment in step three to the volume ratio of the silver ammonia solution is 1g:(15~25)mL. Everything else is the same as in Specific Implementation Methods One to Five.

[0057] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the reaction described in step three is specifically carried out at a temperature of 40℃~60℃ for 1h~3h. Everything else is the same as Specific Implementation Methods One to Six.

[0058] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the silk protein solution described in step four is specifically prepared according to the following steps:

[0059] ① The silkworm cocoons are boiled in a sodium carbonate solution to degummify them, then washed with pure water. The degumming and washing process is repeated twice, and finally dried to obtain degummed silk. The mass percentage of the sodium carbonate solution is 0.05%~0.2%. The mass ratio of the silkworm cocoons to the volume of the sodium carbonate solution is 1g:(30~50)mL.

[0060] ② Add degummed silk to the ternary solution and heat at 70℃~80℃ until completely dissolved. Dialyze using a dialysis bag with a molecular weight cutoff of 8000 Daltons~14000 Daltons for 2-3 days to obtain a silk protein solution with a concentration of 1wt%~3wt%. The ternary solution is composed of calcium chloride, ethanol, and water, with a molar ratio of calcium chloride to ethanol of 1:(1~3) and a molar ratio of calcium chloride to water of 1:(7~9). The mass ratio of degummed silk to the ternary solution is 1:(15~25). Other steps are the same as in specific embodiments one to seven.

[0061] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the mass ratio of the interfacial evaporation material loaded with silver nanoparticles to the volume ratio of the silk protein solution in step four is 1 g:(15~25) mL. Everything else is the same as in Specific Implementation Methods One to Eight.

[0062] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that: in step four, the interfacial evaporation material loaded with silver nanoparticles is immersed in a silk fibroin solution at a flow rate of 0.25 cm·s⁻¹. -1 ~0.75cm·s -1 The sample is lifted out quickly and then dried at room temperature for 5 to 15 minutes. This process of soaking, lifting, and drying is repeated 2 to 4 times. Other procedures are the same as those in specific embodiments one through nine.

[0063] The beneficial effects of the present invention are verified using the following embodiments:

[0064] Example 1:

[0065] A method for preparing a composite interfacial evaporation material based on natural mulberry branches, comprising the following steps:

[0066] I. Substrate Pretreatment:

[0067] Make four cuts along the length of a natural mulberry branch (MB) with a diameter of 1cm and a length of 2cm, extending to the xylem. Then, spread one end of the bark layer outward along the cuts to form a four-lobed structure, while keeping the other end of the bark layer connected to the xylem, to obtain a partially spread bark layer of the whole branch base (marked as BUMB).

[0068] The outward extension of the bark layer accounts for 50% of the total length of the natural mulberry branch, and the thickness of the bark layer is 0.2 cm;

[0069] II. Eutectic solvent treatment:

[0070] The partially expanded bark layer of the pruning substrate was placed in a eutectic solvent (DES) and treated at 95°C for 3 hours. It was then washed with deionized water until neutral and finally dried at 50°C to obtain the substrate treated with the eutectic solvent (D3BUMB).

[0071] The eutectic solvent is composed of choline chloride and oxalic acid, and the molar ratio of choline chloride to oxalic acid is 3:2.

[0072] The mass ratio of the partially expanded bark layer of the pruning substrate to the volume ratio of the eutectic solvent is 1g:20mL.

[0073] III. Silver nanoparticle loading:

[0074] The substrate treated with eutectic solvent was placed in silver ammonia solution and reacted at 50°C for 2 hours. It was then washed with deionized water and finally dried at 60°C to obtain the interfacial evaporation material loaded with silver nanoparticles (labeled as D3BUMBAg2).

[0075] The silver ammonia solution is prepared by the following steps: adding ammonia water dropwise to a silver nitrate solution until the solution becomes clear; the concentration of the silver nitrate solution is 0.1 mol / L, and the concentration of the ammonia water is 0.1 mol / L; the volume ratio of the silver nitrate solution to the ammonia water is 1:20.

[0076] The mass ratio of the substrate treated with the eutectic solvent to the volume ratio of the silver ammonia solution is 1g:20mL.

[0077] IV. Self-assembly of silk protein:

[0078] Interfacial evaporation material loaded with silver nanoparticles was immersed in a silk fibroin solution at a velocity of 0.5 cm·s. -1 The material was quickly lifted out and dried at room temperature for 10 minutes. The process of immersion, lifting, and drying was repeated twice to obtain a composite interfacial evaporation material with a self-assembled silk protein layer on the surface (labeled as D3BUMBAg2-SF2).

[0079] The silk fibroin solution is prepared according to the following steps:

[0080] ① The silkworm cocoons are boiled in a sodium carbonate solution for 30 minutes to degumme them, then washed with pure water. The degumming and washing process is repeated twice, and finally dried to obtain degummed silk. The sodium carbonate solution has a mass percentage of 0.5% and the mass ratio of the silkworm cocoons to the volume of the sodium carbonate solution is 1g:40mL.

[0081] ② Add degummed silk to the ternary solution and heat at 75°C until completely dissolved. Dialyze using an MD 77 (8000-14000) dialysis bag for 3 days to obtain a silk protein solution with a concentration of approximately 2 wt%. The ternary solution is composed of calcium chloride, ethanol, and water, with a molar ratio of calcium chloride to ethanol of 1:2 and a molar ratio of calcium chloride to water of 1:8. The mass ratio of degummed silk to the ternary solution is 1:20.

[0082] The mass ratio of the interfacial evaporation material loaded with silver nanoparticles to the volume ratio of the silk protein solution is 1 g: 20 mL.

[0083] Comparative Experiment 1: This comparative experiment differs from Example 1 in that, in step two, the partially unfolded bark layer of the branch substrate is replaced with a bark substrate (Bark). Specifically, the bark substrate is bark peeled from natural mulberry branches, with a thickness of 0.2 cm and an area of ​​1.57 cm². 2 In step two, the DES treatment time is shortened to 1 / 6 h; in step three, the reaction time is shortened to 1.5 h; step four is cancelled; the interfacial evaporation material with silver nanoparticles loaded in step three is labeled as D. 1 / 6 Ag 1.5 Everything else is the same as in Example 1.

[0084] Comparative Experiment 2: This comparative experiment differs from Example 1 in that: the treatment of natural mulberry branches in step 1 is omitted; step 4 is omitted; steps 2 and 3 are performed directly using natural mulberry branches with a diameter of 1 cm and a length of 2 cm; the interfacial evaporation material loaded with silver nanoparticles obtained in step 3 is labeled D3MBAg2. Everything else is the same as in Example 1.

[0085] Comparative Experiment 3: This comparative experiment differs from Example 1 in that: the treatment of natural mulberry branches in step 1 is omitted; steps 2 and 4 are omitted; step 3 is performed directly using natural mulberry branches with a diameter of 1 cm and a length of 2 cm; the interfacial evaporation material loaded with silver nanoparticles obtained in step 3 is labeled MBAg2. Everything else is the same as in Example 1.

[0086] Comparative Experiment 4: This comparative experiment differs from Example 1 in that: the treatment of natural mulberry branches in step 1 is omitted; steps 3 and 4 are omitted; step 2 is performed directly using natural mulberry branches with a diameter of 1 cm and a length of 2 cm; the substrate treated with eutectic solvent in step 2 is labeled D3MB. Everything else is the same as in Example 1.

[0087] Comparative Experiment 5: This comparative experiment differs from Example 1 in that steps 2 and 3 are omitted; only steps 1 and 4 are performed. The composite interfacial evaporation material with a self-assembled silk protein layer on its surface obtained in step 4 is labeled BUMB-SF2. Everything else is the same as in Example 1.

[0088] Comparative Experiment Six: This comparative experiment differs from Example One in that step two is omitted; only steps one, three, and four are performed. The composite interfacial evaporation material with a self-assembled silk protein layer on its surface obtained in step four is labeled BUMBAg2-SF2. Everything else is the same as in Example One.

[0089] Comparative Experiment Seven: This comparative experiment differs from Example One in that: in step two, the partially unfolded bark layer of the branch substrate was replaced with a bark substrate (Bark). Specifically, the bark substrate is bark peeled from natural mulberry branches, with a thickness of 0.2 cm and an area of ​​1.57 cm². 2 In step two, the DES treatment time is shortened to 30 minutes, and in step three, the reaction time is shortened to 1 hour. Step four is divided into two groups, with one group repeating the impregnation, lifting, and drying process twice (labeled as D). 0.5 Ag1-SF2), a set of repeated immersion, lifting and drying 4 times (marked as D) 0.5 (Ag1-SF4). Everything else is the same as in Example 1.

[0090] Under simulated sunlight conditions, the evaporation rate of pure water prepared in Example 1 and the comparative experiment was tested: Example 1, D3BUMBAg2-SF2, showed an evaporation rate of 2.0088 kg·m³ for pure water under simulated sunlight conditions. -2 ·h -1 Comparative Experiment 1D 1 / 6 Ag 1.5 Under simulated sunlight conditions, the evaporation rate of pure water is 0.7827 kg·m³. -2 ·h -1 In comparative experiment two, under simulated sunlight conditions, the evaporation rate of pure water using D3MBAg2 was 1.6908 kg·m³. -2 ·h -1 In comparative experiment three, under simulated sunlight conditions, the evaporation rate of pure water using MBAg2 was 1.5480 kg·m³. -2 ·h -1 In comparative experiment four, the D3MB, under simulated sunlight conditions, showed an evaporation rate of 1.3860 kg·m³ for pure water. -2 ·h -1 In comparative experiment five, under simulated sunlight conditions, the evaporation rate of pure water using BUMB-SF2 was 1.5942 kg·m³. -2 ·h -1 In comparative experiment six, under simulated sunlight conditions, the evaporation rate of pure water from BUMBAg2-SF2 was 1.7928 kg·m³. -2 ·h -1 Comparative Experiment 7D 0.5Under simulated sunlight conditions, Ag1-SF2 has an evaporation rate of 0.5816 kg·m³ for pure water. -2 ·h -1 .

[0091] Figure 1 This diagram illustrates the evaporation efficiency of the interfacial evaporation materials prepared in experiments two through four under simulated sunlight. As shown in the figure, under simulated sunlight conditions, the evaporation rates of MBAg2, D3MB, and D3MBAg2 are 1.5480 kg·m³, respectively. -2 ·h -1 1.3860 kg·m -2 ·h -1 and 1.6908 kg·m -2 ·h -1 The evaporation rates of both were much greater than those of MB, proving that both silver loading and DES treatment had a significant effect on improving the evaporation performance of MB. Moreover, the evaporation efficiency of D3MBAg2 was greater than that of MBag2 and D3MB, which were treated with only one factor, proving that silver loading and DES treatment had a synergistic effect.

[0092] Cyclic testing was performed on the interfacial evaporation material prepared in Example 1:

[0093] (1) Light source conditions: A xenon lamp simulating sunlight is used, and the light intensity is calibrated in real time throughout the process to ensure that the light intensity of each cycle is without deviation, simulating the natural sunlight irradiation environment;

[0094] (2) Environmental conditions: The room temperature is kept constant, and the ambient temperature is maintained at 25±5℃. o C; The relative humidity of the environment is kept constant at 55±5%; The test environment is free from wind disturbance and direct sunlight, and the fluctuations in ambient airflow, temperature and humidity should be avoided to prevent interference with the evaporation test data;

[0095] (3) Single cycle process: Fix the interfacial evaporation material prepared in Example 1 on the surface of pure water to ensure that the material floats completely and adheres to the liquid surface without tilting; turn on the simulated sunlight source and irradiate continuously for 1 hour to complete a single cycle test; after the single cycle is completed, take out the material, let it air dry naturally to remove residual moisture on the surface, and restore the material to its initial dry state and microstructure.

[0096] (4) Continuous cycle operation: Strictly repeat the above single cycle operation and complete 10 independent cycle experiments in a row; the single cycle duration is 1 hour and the total number of cycles is 10. Before each cycle experiment, water is replenished to a fixed level to eliminate experimental errors caused by water loss and ensure that the test substrate conditions of each group are consistent.

[0097] Figure 2The figure shows the pure water evaporation efficiency of the interfacial evaporation material prepared in Example 1 during 10 cycles under simulated sunlight. As can be seen from the figure, after 10 consecutive cycles (1 hour per cycle), the evaporation rate of the first cycle was 2.0088 kg·m³. -2 ·h -1 Similarly, the evaporation rates for subsequent cycles are 2.0514 kg·m³. -2 ·h -1 2.1288 kg·m -2 ·h -1 1.9788 kg·m -2 ·h -1 1.9338 kg·m -2 ·h -1 1.9578 kg·m -2 ·h -1 1.8522 kg·m -2 ·h -1 1.8756 kg·m -2 ·h -1 1.9848 kg·m -2 ·h -1 and 1.9644 kg·m -2 ·h -1 The first evaporation rate was 2.0088 kg·m³. -2 ·h -1 Based on this, the evaporation rate retention rate for the first cycle is (2.0088 / 2.0088)×100%=100%, and so on. The subsequent retention rates are 102%, 106%, 98%, 96%, 97%, 92%, 93%, 99% and 98%, respectively. The average evaporation rate retention rate is >98%, and the evaporation efficiency remains relatively stable, proving that the material has good cycle stability and durability.

[0098] Figure 3 The figure shows the temperature rise of the interfacial evaporation materials prepared in experiments 2 to 4 under simulated sunlight. As can be seen from the figure, the heating rate and maximum temperature of MBAg2, D3MB, and D3MBAg2 are significantly higher than those of MB, indicating that both silver loading and DES treatment can increase their thermal conductivity, but neither is as good as D3MBAg2, further demonstrating the synergistic effect of silver loading and DES treatment.

[0099] Figure 4The graphs show the solar interfacial evaporation rate of the interfacial evaporation material prepared in Example 1 from 0:00 to 24:00 on a certain day, as well as the hourly solar intensity graph. As can be seen from the graphs, the performance of the material in Example 1 under actual varying light conditions (from 0:00 to 24:00 on a certain day) shows that its pure water evaporation rate follows the same trend as the real-time solar intensity variation, reaching a maximum value of 2.1894 kg·m³ at 13:00. -2 ·h -1 This verified its reliability and practicality under unsteady natural light.

[0100] Figure 5 The figure shows the pure water evaporation rate of the interfacial evaporation material prepared in Experiment 1 under simulated sunlight. As can be seen from the figure, with the support of silver loading, the intact mulberry bark structure can effectively utilize photothermal energy. Its heat preservation effect overcomes the temperature loss caused by simple structural exposure, thus maximizing the evaporation performance. Therefore, the intact mulberry bark structure was preserved during the preparation of D3BUMBAg2-SF.

[0101] Figure 6 The figure shows the pure water evaporation rate of the interfacial evaporation materials prepared in Experiment 7 under simulated sunlight. As can be seen from the figure, the interfacial evaporation material dipped twice in silk fibroin solution has a higher evaporation rate than the material dipped four times. For mulberry branch blocks with a naturally hierarchical porous structure, there is an optimal threshold for the number of times silk fibroin is impregnated. Dipping twice forms an ultra-thin functional layer on the surface of the wood block and the inner walls of the pores, improving hydrophilicity while maximizing the preservation of the wood block's own pore structure and evaporative active surface, thus optimizing heat and mass transfer. The thicker coating formed by dipping four times partially blocks the natural water-carrying micropores of the wood block, increasing mass transfer resistance and ultimately leading to a decrease in evaporation performance.

[0102] Figure 7 This is a schematic diagram of the preparation of a branch substrate by unfolding a portion of the bark layer in step one of the embodiments; as shown in the figure, it illustrates the way the BUMB is cut and the general structure of the sample.

[0103] Figure 8 This diagram illustrates the pure water evaporation efficiency of the partially expanded bark layer of the prepared branch substrate from Example 1 (Step 1), and the composite interfacial evaporation materials prepared in Example 1, Comparative Experiment 5, and Comparative Experiment 6 under simulated sunlight. As shown in the diagram, the evaporation rates of BUMB, BUMB-SF2, BUMBAg2-SF2, and D3BUMBAg2-SF are 1.3674 kg·m³. -2 ·h -1 1.5942 kg·m -2 ·h -1 1.7928 kg·m -2 ·h -1and 2.0088 kg·m -2 ·h -1 This demonstrates that independent techniques such as peeling structure modification, silk fibroin self-assembly, silver nanoparticle loading, and DES pretreatment can be effectively integrated and synergistically responded in composite systems, gradually and significantly improving the overall performance of interfacial evaporation materials.

[0104] Figure 9 This is a scanning electron microscope (SEM) image of the inner bark layer of the composite interfacial evaporation material with a self-assembled silk fibroin layer prepared in Example 1. The modified inner bark surface is smooth and continuous, exhibiting a dense, thin-film structure formed by the self-assembly of silk fibroin, without obvious exposed fiber defects or local agglomeration. The silk fibroin constructs a uniform and homogeneous active interface on the inner bark surface, rich in amino and hydroxyl groups. Uniform and firm anchoring of silver nanoparticles can also be observed, ensuring the stability and consistency of photothermal properties of the material during long-term use.

[0105] Figure 10 This is a scanning electron microscope (SEM) image of the outer xylem surface of the composite interfacial evaporation material with a self-assembled silk fibroin layer prepared in Example 1. After peeling, the natural fibrous structure of the mulberry branch xylem is exposed, while the silk fibroin, through self-assembly, uniformly coats and fills the interfiber gaps and cell wall pores of the xylem, effectively repairing the interfacial defects caused by peeling. The image shows that the xylem vessels, fibers, and other structures are continuously covered by silk fibroin, and the inner walls of the pores are uniformly modified by the protein layer, forming a stable interface rich in active sites. Uniform loading of silver nanoparticles can also be observed.

[0106] The experiments above show that the original peeled structure (BUMB) without any functionalization already possesses a certain foundation for water transport and evaporation. Introducing a silk fibroin self-assembled layer (BUMB-SF2) enhances the hydrophilicity and structural integrity of the material surface, laying the interfacial foundation for further loading of functional nanoparticles. Loading silver nanoparticles (BUMBAg2-SF2) significantly improves light absorption and photothermal conversion capabilities, thereby significantly accelerating the evaporation process. The system pretreated with DES before silver loading and silk fibroin modification (D3BUMBAg2-SF2) exhibits better performance because DES promotes the formation of the substrate framework, providing more attachment sites for silver nanoparticles. This results in a more uniform distribution and stronger bonding of silver nanoparticles, and a denser and more stable silk fibroin self-assembled layer. Ultimately, optimal synergy is achieved between photothermal conversion, water transport, and structural stability, resulting in the highest level of evaporation performance.

Claims

1. A method for preparing a composite interfacial evaporation material based on natural mulberry branches, characterized in that... It is done in the following steps: I. Substrate Pretreatment: Make multiple cuts along the length of the side of a natural mulberry branch, then spread one end of the bark layer outward along the cuts to form a multi-lobed structure, while keeping the other end of the bark layer connected to the xylem, thus obtaining a partially spread bark layer of the branch base. II. Eutectic solvent treatment: The pruning substrate with part of the bark layer unfolded was heat-treated in a eutectic solvent, then washed and dried to obtain the substrate treated with the eutectic solvent. III. Silver nanoparticle loading: The substrate treated with a eutectic solvent was placed in a silver ammonia solution for reaction, and then washed and dried to obtain an interfacial evaporation material loaded with silver nanoparticles. IV. Self-assembly of silk protein: The interfacial evaporation material loaded with silver nanoparticles was immersed in a silk protein solution, pulled out, and then dried at room temperature. The immersion, pulling, and drying were repeated multiple times to obtain a composite interfacial evaporation material with a silk protein layer self-assembled on the surface.

2. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... In step one, the outward extension of the bark layer accounts for 40% to 60% of the total length of the natural mulberry branch.

3. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... The eutectic solvent mentioned in step two is composed of choline chloride and oxalic acid, and the molar ratio of choline chloride to oxalic acid is (1~2):1; the mass ratio of the partially expanded bark layer of the pruning substrate to the volume ratio of the eutectic solvent in step two is 1g:(15~25)mL.

4. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... The heat treatment described in step two is specifically performed at a temperature of 50℃~100℃ for 0.5h~4h.

5. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... The silver ammonia solution mentioned in step three is prepared according to the following steps: ammonia water is added dropwise to the silver nitrate solution until the solution becomes clear; the concentration of the silver nitrate solution is 0.05 mol / L to 0.15 mol / L; the concentration of the ammonia water is 0.05 mol / L to 0.15 mol / L; and the volume ratio of the silver nitrate solution to the ammonia water is 1:(15~25).

6. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... The mass ratio of the substrate after eutectic solvent treatment to the volume ratio of silver ammonia solution in step three is 1g:(15~25)mL.

7. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... The reaction described in step three is specifically carried out at a temperature of 40℃~60℃ for 1h~3h.

8. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... The silk protein solution mentioned in step four is prepared according to the following steps: ① The silkworm cocoons are boiled in a sodium carbonate solution to degummify them, then washed with pure water. The degumming and washing process is repeated twice, and finally dried to obtain degummed silk. The mass percentage of the sodium carbonate solution is 0.05%~0.2%. The mass ratio of the silkworm cocoons to the volume of the sodium carbonate solution is 1g:(30~50)mL. ② Add degummed silk to the ternary solution and heat at 70℃~80℃ until completely dissolved. Dialyze the solution for 2-3 days using a dialysis bag with a molecular weight cutoff of 8000 Daltons~14000 Daltons to obtain a silk protein solution with a concentration of 1wt%~3wt%. The ternary solution is composed of calcium chloride, ethanol and water, and the molar ratio of calcium chloride to ethanol is 1:(1~3), and the molar ratio of calcium chloride to water is 1:(7~9). The mass ratio of degummed silk to the ternary solution is 1:(15~25).

9. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... The mass ratio of the interfacial evaporation material loaded with silver nanoparticles to the volume ratio of the silk protein solution in step four is 1 g:(15~25) mL.

10. The method for preparing a composite interfacial evaporation material based on natural mulberry branches according to claim 1, characterized in that... In step four, the interfacial evaporation material loaded with silver nanoparticles is immersed in a silk fibroin solution at a velocity of 0.25 cm·s. -1 ~0.75cm·s -1 Pull it out quickly, then dry it at room temperature for 5 to 15 minutes. Repeat the soaking, pulling and drying process 2 to 4 times.

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