A composite sponge for seawater desalination and a method for preparing the same

Abstract

The present application relates to the technical field of polyurethane sponge, and particularly relates to a composite sponge for seawater desalination and a preparation method thereof.The composite sponge comprises the following steps: S1, pretreating the sponge; S2, placing the pretreated sponge, dopamine and lithium salt in a tris(hydroxymethyl)aminomethane hydrochloride buffer solution to perform a self-polymerization reaction; S3, soaking the polydopamine-lithium chloride modified sponge in an acidified carbon nanotube ethanol solution to perform ultrasonic treatment; and S4, spraying a n-hexane mixed solution of polydimethylsiloxane on the side surface of the acidified carbon nanotube modified sponge, and solidifying to obtain a multifunctional composite sponge.The present application endows the material with dynamic salt resistance by virtue of a biomimetic micro-nano structure design, solves the performance degradation problem caused by salt crystallization blockage of a traditional evaporator, and significantly prolongs the service life of the equipment.

Description

Technical Field

[0001] This invention relates to the field of polyurethane foam technology, and in particular to a composite foam for seawater desalination and its preparation method. Background Technology

[0002] Seawater desalination, a key technology for alleviating freshwater shortages, currently relies primarily on two main methods: membrane-based separation technologies (with reverse osmosis as the mainstream) and thermodynamic evaporation and condensation technologies (such as multi-stage flash evaporation and multi-effect distillation). Reverse osmosis technology dominates the global seawater desalination market due to its relatively low energy consumption, mature and efficient process, and relatively simple and flexible system operation, and is widely used for municipal water supply and industrial needs. In contrast, thermal desalination technologies exhibit better tolerance when treating extremely high salinity seawater or brackish water, and their core principles make them particularly suitable for integration into regions with abundant waste heat or inexpensive thermal energy. Thermal desalination creates a low-pressure environment to induce seawater flash evaporation or utilizes steam for repeated heat exchange evaporation in a multi-stage evaporator, ultimately collecting purified water through condensation.

[0003] However, reverse osmosis membranes are highly susceptible to fouling by naturally occurring microorganisms, colloidal substances, and dissolved inorganic salts in seawater. Fouling significantly reduces the membrane's permeability, leading to a decrease in water flux and forcing the system to increase operating pressure to maintain permeate production. This also drastically shortens the lifespan of expensive membrane elements. It not only increases the frequency and complexity of downtime cleaning and maintenance but also directly drives up the long-term operating and maintenance costs of the system. Furthermore, as the salinity of the feed seawater increases, the operating pressure required to overcome osmotic pressure rises sharply, posing a challenge to the membrane's chemical stability and pressure resistance, resulting in a significant decrease in the overall efficiency and economics of reverse osmosis in treating such high-salinity water.

[0004] The core of thermal energy transfer technology lies in evaporating seawater through heat, which means that the initial heat input is extremely large. Whether steam is generated by directly burning fossil fuels or by using waste heat from power plants or solar energy, acquiring and maintaining these heat sources constitutes the largest operating cost of the system. The high-temperature, multi-stage brine environment is highly corrosive to key metal equipment components such as pipes, heat exchangers, and evaporators, and salt scaling on heat transfer surfaces is also a significant problem. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a superhydrophobic-superhydrophilic multifunctional composite sponge for seawater desalination and its preparation method. The composite material exhibits excellent evaporation performance and salt resistance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a composite sponge for seawater desalination includes the following steps:

[0008] S1. Clean and dry the polyurethane sponge to obtain the pretreated sponge;

[0009] S2. The pretreated sponge, dopamine, and lithium salt were placed in a tris(hydroxymethyl)aminomethane hydrochloride buffer solution and subjected to a self-polymerization reaction under stirring to obtain the modified sponge.

[0010] S3. The modified sponge is immersed in an ethanol solution of acidified carbon nanotubes and subjected to ultrasonic treatment to obtain an acidified carbon nanotube modified sponge.

[0011] S4. Spray a mixed solution of polydimethylsiloxane and n-hexane onto the sides of the acidified carbon nanotube-modified sponge and cure it to obtain a multifunctional composite sponge.

[0012] Further, the cleaning in step S1 specifically involves: alternating squeezing with ethanol solution and deionized water 3-5 times in sequence, and drying at a temperature of 90-100℃.

[0013] Further, in step S2, the mass ratio of the pretreated sponge, dopamine, and lithium salt is 1:(0.13-0.16):(2.6-3.1).

[0014] Furthermore, in step S2, the concentration of the tris(hydroxymethyl)aminomethane hydrochloride buffer solution is 0.12-0.15% w / v.

[0015] Furthermore, in step S2, the stirring speed is 500-600 rpm, the temperature of the self-polymerization reaction is 28-32℃, and the time is 24-48 h.

[0016] Furthermore, the lithium salt in step S2 is a water-soluble lithium salt.

[0017] Furthermore, in step S3, the concentration of the ethanol solution of acidified carbon nanotubes is 0.14-0.17 wt%.

[0018] Furthermore, in step S3, the frequency of ultrasonic treatment is 40-50kHz, the power is 200-300W, and the ultrasonic treatment time is 10-50min.

[0019] Furthermore, in step S4, the concentration of the polydimethylsiloxane n-hexane mixed solution is 1-6 wt%.

[0020] Furthermore, the curing temperature in step S4 is 80-100℃.

[0021] Furthermore, the lithium salt is selected from at least one of lithium chloride, lithium bromide, lithium nitrate, or lithium acetate.

[0022] According to another aspect of the present invention, a composite sponge prepared by the above-described preparation method is provided, the composite sponge having a central region and side regions surrounding the central region, wherein the central region is superhydrophilic and the side regions are superhydrophobic.

[0023] The beneficial effects of this invention are:

[0024] 1. The composite sponge prepared by the method of the present invention is simple to operate, consumes little energy, has a small volume and a short processing time, and is environmentally friendly and pollution-free.

[0025] 2. In the technical solution of this invention, the composite sponge achieves a dynamic balance between rapid capillary water transport and vapor diffusion by constructing a gradient wetting interface and a multi-level pore synergistic mechanism, based on a broad solar spectrum absorptivity (>95%), resulting in an evaporation rate of 2.04 kg·m³. -2 ·h -1 At the same time, the water contact angle reaches 157°.

[0026] 3. In the technical solution of this invention, the material is endowed with dynamic salt resistance characteristics through biomimetic micro-nano structure design. It can run continuously for 8 hours in a 20wt% high salinity water body without salt deposition, which solves the problem of performance degradation caused by salt crystal blockage in traditional evaporators and significantly extends the service life of the equipment. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 a is a schematic diagram illustrating the preparation of composite sponges obtained in one or more examples. Figure 1 b represents the biomimetic principle that was referenced in the design of this sponge structure. Figure 1 c represents five evaporator structure design examples based on the superhydrophobic / superhydrophilic structure of the sponge surface;

[0029] Figure 2 Scanning electron microscope images of composite sponge superhydrophobic and superhydrophilic layers prepared in one or more examples;

[0030] Figure 3 The graph shows the water contact angle test results of composite sponges prepared in one or more examples;

[0031] Figure 4 The resistance changes of composite sponges prepared in one or more examples under different ultrasonic times are shown in the graph.

[0032] Figure 5 The graph shows the variation of water contact angle of the composite sponges prepared in one or more examples;

[0033] Figure 6 The diagram shows the evaporation performance of composite sponges prepared in one or more examples, where... Figure 6 'a' represents the mass change of evaporators 1, 2, 3, 4, and 5. Figure 6 b represents the evaporation rate; Figure 6 c represents the mass changes of water, PU, ​​and evaporator 4 under darkness and 1 solar irradiance. Figure 6 d is the evaporation rate; Figure 6 e represents composite sponge at 1kW / m 2 2kW / m 2 and 3kW / m 2 Evaporation rate at the following levels Figure 6 f represents the change in mass;

[0034] Figure 7 This is a graph showing the salt resistance of composite sponges prepared in one or more examples, where... Figure 7 a is a diagram illustrating the seawater desalination mechanism of composite sponges. Figure 7 b represents the mass change of the composite sponge in different salt water solutions. Figure 7 c represents the corresponding evaporation rate and water contact angle. Figure 7 d represents the dissolution of a solid salt on the surface of a composite sponge for 5 minutes at a power density of 1 kW / m³. 2 Under light intensity; Figure 7 e represents the mass change of the composite sponge in the Bohai Sea over 10 hours. Figure 7 f is the evaporation rate;

[0035] Figure 8 The diagram shows the seawater desalination and water purification effects of the composite sponges prepared in one or more examples, where... Figure 8 a represents the resistance of different water samples: seawater, tap water, collected water, and deionized water; Figure 8 b represents the pH values ​​of the solutions before and after purification for pH=2 (HCl) and pH=13 (NaOH). Figure 8 c shows a comparison of the UV-Vis absorption spectra of methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) before and after purification (the inset shows a color comparison of the freshwater before and after purification). Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention provides a method for preparing a composite sponge for seawater desalination, comprising the following steps:

[0038] S1. Clean and dry the polyurethane sponge to obtain the pretreated sponge;

[0039] S2. The pretreated sponge, dopamine and lithium salt were placed in a tris(hydroxymethyl)aminomethane hydrochloride buffer solution and subjected to self-polymerization reaction under stirring to obtain polydopamine-lithium chloride modified sponge.

[0040] S3. The polydopamine-lithium chloride modified sponge was immersed in an ethanol solution of acidified carbon nanotubes and subjected to ultrasonic treatment to obtain an acidified carbon nanotube modified sponge.

[0041] S4. Spray a mixed solution of polydimethylsiloxane and n-hexane onto the sides of the acidified carbon nanotube-modified sponge and cure it to obtain a multifunctional composite sponge.

[0042] In the preparation method provided by the present invention, the cleaning step in step S1 is preferably: alternatingly squeezing with ethanol solution and deionized water 3-5 times, specifically 3 times, 4 times and 5 times.

[0043] In the preparation method provided by the present invention, the drying temperature in step S1 is preferably 90-100℃, specifically 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃ and 100℃.

[0044] In the preparation method provided by the present invention, the preferred mass ratio of the pretreated sponge, dopamine and lithium salt in step S2 is 1:(0.13-0.16):(2.6-3.1), specifically 1:0.13:2.6, 1:0.14:2.6, 1:0.15:2.6, 1:0.16:2.6, 1:0.13:2.7, 1:0.14:2.8, 1:0.15:2.9, 1:0.16:3.0, 1:0.13:3.1 and 1:0.16:3.1.

[0045] In the preparation method provided by the present invention, the concentration of the tris(hydroxymethyl)aminomethane hydrochloride buffer solution in step S2 is preferably 0.12-0.15% w / v, specifically 0.12% w / v, 0.13% w / v, 0.14% w / v and 0.15% w / v.

[0046] In the preparation method provided by the present invention, the stirring speed in step S2 is preferably 500-600 rpm, specifically 500 rpm, 550 rpm and 600 rpm.

[0047] In the preparation method provided by the present invention, the temperature of the self-polymerization reaction in step S2 is preferably 28-32°C, specifically 28°C, 29°C, 30°C, 31°C and 32°C.

[0048] In the preparation method provided by the present invention, the self-polymerization reaction time in step S2 is preferably 24-48 h, specifically 24 h, 36 h and 48 h.

[0049] In the preparation method provided by the present invention, the lithium salt in step S2 is preferably a water-soluble lithium salt, specifically selected from lithium chloride, lithium bromide, lithium nitrate or lithium acetate, and more specifically, selected from lithium chloride.

[0050] In the preparation method provided by the present invention, the concentration of the ethanol solution of acidified carbon nanotubes in step S3 is preferably 0.14-0.17 wt%, specifically 0.14 wt%, 0.15 wt%, 0.16 wt%, and 0.17 wt%.

[0051] In the preparation method provided by the present invention, the frequency of ultrasonic treatment in step S3 is preferably 40-50 kHz, specifically 40 kHz, 42 kHz, 45 kHz, 48 kHz and 50 kHz.

[0052] In the preparation method provided by the present invention, the power of ultrasonic treatment in step S3 is preferably 200-300W, specifically 200W, 250W and 300W.

[0053] In the preparation method provided by the present invention, the ultrasonic treatment time in step S3 is preferably 10-50 min, specifically 10 min, 20 min, 30 min, 40 min and 50 min.

[0054] In the preparation method provided by the present invention, the concentration of the polydimethylsiloxane n-hexane mixed solution in step S4 is preferably 1-6 wt%, specifically 1 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt% and 6 wt%.

[0055] In the preparation method provided by the present invention, the curing temperature in step S4 is preferably 80-100℃, specifically 80℃, 85℃, 90℃, 95℃ and 100℃.

[0056] For clarity, the following examples and comparative models will be used to provide a detailed description.

[0057] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.

[0058] Figure 1c shows five evaporator structure design examples based on the superhydrophobic / superhydrophilic structure of the sponge surface. Unless otherwise specified, evaporator 4 is used as an example in the following embodiments and comparative examples.

[0059] Example 1: The specific preparation process is as follows Figure 1 As shown. The preparation steps are as follows:

[0060] A1. Cut the polyurethane foam into small squares of 2×2×2cm, about 0.24g, and squeeze them three times alternately with ethanol solution and deionized water. Then dry them at 90℃ until constant weight.

[0061] A2. Add 0.24g of tris(hydroxymethyl)aminomethane hydrochloride to 200mL of deionized water to prepare a buffer solution with a pH of 8.5. Add the sponge obtained in step A1 and 0.4g of dopamine hydrochloride to the buffer solution, add 0.62g of lithium chloride, put it in an oil bath at 30℃ and stir mechanically for 24h. Take it out and dry it at 100℃.

[0062] A3. Place the multi-walled carbon nanotubes in 65% concentrated nitric acid and reflux at 100°C for 4 hours. After centrifugation, wash with deionized water until neutral and vacuum dry at 60°C for 12 hours. Weigh 150 mg of acidified carbon nanotubes and disperse them in 150 mL of ethanol solution by ultrasonication. Immerse the sponge obtained in step A2 in the solution and then use an ultrasonic cell disruptor to sonicate for 40 minutes to anchor the multi-walled carbon nanotubes onto the polyurethane sponge skeleton. After removal, place it in an oven at 100°C to dry again. The frequency of ultrasonic treatment is 40 kHz and the power is 200 W.

[0063] A4. Weigh 1g of polydimethylsiloxane (PDMS), 0.1g of curing agent tetraethyl orthosilicate, and 18.9g of n-hexane and mix them to prepare a 5wt% PDMS solution. Spray the PDMS solution onto the sides of the polyurethane sponge obtained in step A3 and dry and cure it in an oven at 100℃ to obtain a multifunctional composite sponge with superhydrophobic sides and superhydrophilic center.

[0064] Example 2: The difference between this example and Example 1 is that a 4wt% PDMS solution is prepared, while the other steps are the same as in Example 1.

[0065] Example 3: The difference between this example and Example 1 is that a 3wt% PDMS solution is prepared, while the remaining steps are the same as in Example 1.

[0066] Example 4: The difference between this example and Example 1 is that a 2wt% PDMS solution is prepared, while the remaining steps are the same as in Example 1.

[0067] Example 5: The difference between this example and Example 1 is that a 1wt% PDMS solution is prepared, while the remaining steps are the same as in Example 1.

[0068] Example 6: The difference between this example and Example 1 is that lithium bromide is used instead of lithium chloride to prepare a 6wt% PDMS solution, while the rest of the steps are the same as in Example 1.

[0069] Comparative Example 1: The difference between this comparative example and Example 1 is that only polyurethane foam is used, and dopamine and lithium chloride are not added. The remaining steps are the same as in Example 1.

[0070] Comparative Example 2: The difference between this comparative example and Example 1 is that lithium chloride is not added, but the other steps are the same as in Example 1.

[0071] Comparative Example 3: The difference between this comparative example and Example 1 is that dopamine is not added, but the rest of the steps are the same as in Example 1.

[0072] Comparative Example 4: The difference between this comparative example and Example 1 is that step A4 is not performed, i.e., PDMS is not soaked. The remaining steps are the same as in Example 1.

[0073] The microstructure of the composite sponge prepared in Example 1 was observed using a scanning electron microscope as follows: Figure 2 As shown, Figure 2 a is a superhydrophilic layer. Figure 2 be is a superhydrophobic layer.

[0074] (I) Contact Angle Test: The static contact angle of the composite sponges prepared in Examples 1-6 and Comparative Examples 1-4 was measured using an optical water contact angle meter (TZL-900). The measurement method was as follows: the water contact angle of three different locations on the surface was measured and the average value was taken. The variation of the water contact angle is shown in the figure. Figure 5 and Figure 3 As shown, when the concentration of PDMS was 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, and 6wt%, the water contact angles were 147°, 150°, 152°, 153°, 157°, and 157°, respectively. The water contact angles in Comparative Examples 1-4 were 133°, 88°, 96°, and 0°, respectively.

[0075] (II) Conductivity Test: The superhydrophobic-superhydrophilic multifunctional composite sponge prepared in Example 1 was tested on three different areas of its surface using a four-probe conductivity meter. The average value was taken to reduce the error in the actual resistance measurement. The conductivity variation is shown below. Figure 4 As shown.

[0076] (III) Evaporation Performance Test: The prepared composite sponge was placed under a xenon lamp to simulate the actual lighting conditions. The evaporator was encased in polystyrene foam and suspended in a beaker filled with deionized water. The solar-driven steam generation performance was tested using a solar simulator (PLS-SXE 300) and the spectrum was calibrated using an optical element (AM 1.5). The solar radiation density was measured using a light power meter (PL-MW 2000). The mass change of water was recorded in real time using a high-precision electronic microbalance. The water evaporation rate was calculated using the formula m = dm / (S•t), where dm is the water mass loss (in kg) and S is the light-receiving area of ​​the evaporator (projected area of ​​sunlight) (in m²). 2 ), t is the light exposure time (in hours).

[0077] like Figure 6 As shown in cd, in Comparative Example 1, the evaporation rates under darkness and one ray of sunlight were 0.12 kg·m³, respectively. -2 ·h -1 0.41 kg·m -2 ·h -1 The evaporation rate in Example 1 was significantly increased to 2.04 kg·m³. -2 ·h -1 .like Figure 6 ef, at 1kW / m 2 2kW / m 2 3kW / m 2 Under sunlight, the evaporation efficiency of Example 1 was 2.04 kg·m³. -2 ·h -1 3.05 kg·m -2 ·h -1 3.94 kg·m -2 ·h -1 .

[0078] (IV) Salt resistance test: The composite sponge prepared in Example 1 was placed under a xenon lamp to simulate the light conditions in the actual environment. The evaporator was wrapped in polystyrene foam and suspended in beakers filled with water of different salinities (3.5wt%, 10wt%, 15wt%, 20wt%).

[0079] like Figure 7 As shown in the desalination mechanism of a, during the seawater evaporation process, the sponge has a rich three-dimensional porous structure inside, which can quickly adsorb salt water into the pores through capillary action. When water is transported to the sponge surface, the evaporation process (especially when combined with photothermal materials) preferentially converts water molecules into vapor, while salt ions are trapped due to their large size and limited solubility, thus achieving the separation of salt and water.

[0080] like Figure 7 As shown in b, the evaporation efficiency of the prepared composite sponge in water with different salinities decreases slightly with increasing concentration, while the water contact angle remains above 150°. Furthermore, as... Figure 7 As shown in Figure d, the solid salt completely dissolved on the sponge surface within 5 minutes. Figure 7 As shown in ef, the composite sponge can maintain a stable evaporation efficiency in natural seawater for a long time, and there is no salt accumulation on the sponge.

[0081] The catechol groups of polydopamine (PDA) "lock in" Li through chelation. + Significantly reduces free Li + The concentration of Cl makes it unable to react with Cl. - They combine to form LiCl crystal nuclei. Furthermore, the chelation process is reversible; when the salt concentration in the environment fluctuates, PDA releases or captures LiCl crystals. + To maintain the metastable state of the solution and avoid local supersaturation that could lead to crystallization. Meanwhile, Cl... - The amino groups of PDA are fixed by hydrogen bonds and electrostatic interactions, even with a small amount of free Li + Existence, Cl - The diffusion path is also prolonged, and the nucleation probability is significantly reduced. Furthermore, because PDA is rich in hydroxyl and amino groups, it has strong hydrophilicity and can adsorb a large number of water molecules to form a stable hydrated layer. This hydrated layer encapsulates Li… + and Cl - This system maintains the dissolved state of salts and prevents rapid crystallization under dry conditions. Simultaneously, the strong hygroscopicity of LiCl and the hydrophilic network of PDA create a synergistic effect, forming a "self-moisturizing" system. This system can lock in some of the moisture at the evaporation interface, delaying salt supersaturation even in low-humidity environments, achieving long-term stability of evaporation efficiency, and preventing salt deposition on the sponge surface.

[0082] (V) Seawater Desalination and Water Purification: Natural Bohai Sea water (40.6169°N, 120.8107°L) was used to demonstrate the purification capacity of the composite sponge prepared in Example 1 by evaporating acidic and alkaline solutions and various organic aqueous solutions, including hydrochloric acid, sodium hydroxide, Rhodamine B (RhB, 10 mg / L), methylene blue (MB, 10 mg / L), and methyl orange (MO, 10 mg / L), for wastewater treatment. Condensate was collected in a sealed 1000 mL beaker. The ion concentration of the condensate collected from seawater using the composite sponge was very low, such as... Figure 8 As shown in Figure a. Meanwhile, the water collected in the acid / alkaline solution has a pH of 7, as... Figure 8 As shown in b. (As shown in...) Figure 8 As shown in Figure c, the peak absorbance of the water purified by different dyes is close to zero, indicating that the dye concentration in the purified water is extremely low.

[0083] In summary, a series of tests have shown that the composite sponge prepared by this invention exhibits different characteristics in terms of contact angle, conductivity, evaporation performance, salt resistance, seawater desalination, and water purification. The composite sponge prepared in the examples shows better overall performance than the comparative examples. It can effectively avoid salt deposition and maintain stable evaporation efficiency during seawater evaporation. It also has good purification effects on acid and alkali solutions and various dye solutions in wastewater treatment.

[0084] In the description of this specification, the references to terms such as "embodiment," "comparative example," and "various embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or comparative example is included in at least one embodiment or comparative example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or comparative example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or comparative examples.

[0085] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite sponge for seawater desalination, characterized in that, Includes the following steps: S1. Clean and dry the polyurethane sponge to obtain the pretreated sponge; S2. The pretreated sponge, dopamine, and lithium salt were placed in a tris(hydroxymethyl)aminomethane hydrochloride buffer solution and subjected to a self-polymerization reaction under stirring to obtain the modified sponge. S3. The modified sponge is immersed in an ethanol solution of acidified carbon nanotubes and subjected to ultrasonic treatment to obtain an acidified carbon nanotube modified sponge. S4. Spray the polydimethylsiloxane-hexane mixture solution onto the side perimeter of the acidified carbon nanotube modified sponge, and cure it to obtain a multifunctional composite sponge. In step S2, the mass ratio of the pretreated sponge, dopamine, and lithium salt is 1:(0.12-0.18):(2.4-3.4). The concentration of the tris(hydroxymethyl)aminomethane hydrochloride buffer solution is 0.11-0.16% w / v; The lithium salt is selected from at least one of lithium chloride, lithium bromide, lithium nitrate or lithium acetate.

2. The preparation method according to claim 1, characterized in that, The cleaning process in step S1 involves alternating squeezing with ethanol solution and deionized water 3-5 times, followed by drying at a temperature of 90-100℃.

3. The preparation method according to claim 1, characterized in that, In step S2, the stirring speed is 500-600 rpm, the temperature of the self-polymerization reaction is 28-32℃, and the time is 24-48 h.

4. The preparation method according to claim 1, characterized in that, In step S3, the concentration of the ethanol solution of acidified carbon nanotubes is 0.13-0.18 wt%.

5. The preparation method according to claim 1, characterized in that, In step S3, the ultrasonic treatment frequency is 38-52kHz, the power is 200-300W, and the ultrasonic treatment time is 15-45min.

6. The preparation method according to claim 1, characterized in that, In step S4, the concentration of the polydimethylsiloxane-hexane mixed solution is 1.5-5.5 wt%. The curing temperature is 75-105℃.

7. A composite sponge prepared by the method according to any one of claims 1-6, characterized in that, Composite sponges have a central region and side regions surrounding the central region; The middle region is superhydrophilic, while the side regions are superhydrophobic.

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