A covalently reinforced and toughened graphene oxide composite film, its preparation method and its application

Abstract

This invention discloses a covalently reinforced and toughened graphene oxide composite film, its preparation method, and its applications. An aqueous solution of sulfosuccinic acid (SSA) and a monolayer graphene oxide (GO) aqueous dispersion are ordered to assemble a layered graphene oxide composite film. The film is then acidified with a certain amount of hydrochloric acid and placed in an oven at a specific temperature. Under heating conditions, GO and SSA covalently crosslink, yielding a covalently crosslinked GO-SSA graphene oxide composite film. The maximum strength and toughness of this film are increased by approximately 3 times and 4 times, respectively, compared to the unmodified film. Furthermore, due to the excellent photothermal properties of graphene oxide, this GO-SSA graphene oxide composite film can also be used as a substrate for solar water evaporation devices. The water evaporation rate of the pure GO film under 1 solar radiation intensity is 1.65 kg·m³. ‑2 ·h ‑1 GO-SSA graphene oxide composite membranes can increase the water evaporation rate to a maximum of 2.11 kg·m³. ‑2 ·h ‑1 This material has broad application prospects in the field of solar water evaporation.

Description

Technical Field

[0001] This invention relates to the design and optimization of graphene oxide composite films, specifically a covalently reinforced and toughened graphene oxide composite film, its preparation method, and its application in the field of solar water evaporation, belonging to the field of inorganic nanocomposite material preparation technology. Background Technology

[0002] Graphene oxide (GO), as a two-dimensional material, has attracted much attention in the field of materials science due to its unique physicochemical properties and microscopic layered structure. Current technology uses vacuum filtration to form interlocking layered structures of individual graphene oxide nanosheets at the micrometer scale, assembling them into self-supporting GO membranes. The resulting GO membranes are paper-like, exhibiting excellent flexibility and rigidity, with strength superior to other similar membrane materials. Unlike polymer membranes, GO membranes possess a multi-level layered structure, forming two-dimensional nanochannels in the horizontal direction and interlaced pores in the vertical direction. This allows water molecules to be transported in a tortuous manner between the GO nanosheet layers, giving the GO membrane excellent water permeability. Furthermore, the layered "channels" formed within it are nanometer-scale (approximately 0.8 nm), exhibiting excellent selective permeation characteristics; micrometer-sized molecules cannot pass through, allowing only small molecules such as water to pass freely. This unique layered membrane structure makes this material widely applicable in oil-water separation, water treatment, and solar water evaporation.

[0003] However, despite the enormous application potential of GO membranes in various fields, several technical problems still need to be solved in their practical use. First, the interlayer bonding strength of GO membranes mainly relies on van der Waals forces and some π-π stacking interactions, resulting in relatively low bonding strength. Because GO membranes have abundant hydrophilic carboxyl and hydroxyl functional groups, water molecules readily form hydrogen bonds with these functional groups when they enter the interlayer. As water molecules continuously penetrate, the interlayer spacing increases, and the π-π interactions between the graphene nanosheets gradually weaken. This leads to increasingly poor stability of the GO membrane during contact with water, severely limiting its practicality in aquatic applications.

[0004] Secondly, the room for optimization of the mechanical properties of GO membranes is limited. Although their strength and toughness are superior to traditional polymer membranes, they still cannot meet the requirements of some engineering applications demanding high strength and high toughness. Existing research has attempted to improve the mechanical properties of GO membranes through methods such as polymer composites, ionic bond modification, or hydrogen bond enhancement, but these modification methods have limitations to varying degrees. For example, the binding force of ionic and hydrogen bond modifications is relatively weak and cannot significantly improve the mechanical properties of GO membranes; while the strategy of modifying GO membranes through π-π stacking often faces problems of poor uniformity and low modification efficiency due to the structural characteristics of the modified molecules.

[0005] Furthermore, there is room for improvement in the photothermal conversion efficiency and water evaporation rate of GO films. GO, due to its black color and light absorption properties and certain photothermal conversion capabilities, is widely used in solar water evaporation. However, pure GO films are prone to degradation in photothermal performance due to swelling during long-term use, and their water evaporation efficiency is insufficient to meet the requirements of high-performance water treatment and evaporation devices. Existing research has shown that some GO films with optimized performance through surface modification or doping, while improving evaporation rates, often limit their large-scale application due to complex preparation processes and high costs.

[0006] In summary, existing graphene oxide (GO) membranes still exhibit significant shortcomings in terms of stability in aqueous environments, mechanical properties, and solar water evaporation efficiency. These deficiencies limit the application scope of GO membranes in practical applications. Therefore, how to further improve the water stability, mechanical properties, and photothermal performance of graphene oxide membranes to meet the needs of different fields is an urgent technical problem to be solved. Summary of the Invention

[0007] (a) The technical problem solved by the present invention To address the shortcomings of existing graphene oxide (GO) membranes, such as poor stability in aqueous environments, insufficient mechanical properties, and limited solar water evaporation efficiency, this invention aims to overcome at least one of the aforementioned and other technical problems in the prior art. It provides a covalently reinforced and toughened graphene oxide composite membrane, its preparation method, and its applications. By introducing sulfosuccinic acid (SSA) and graphene oxide for covalent cross-linking modification, and utilizing acidic conditions and heating to induce esterification between the carboxyl groups in the SSA molecules and the hydroxyl groups on the GO nanosheets to form COC covalent bonds, a cross-linked network with high bonding strength is constructed between the GO nanosheets, significantly improving the membrane's strength, toughness, and stability in water. Simultaneously, the hydrophilic sulfonic acid groups in SSA enhance the membrane's water absorption efficiency, effectively improving photothermal conversion performance and water evaporation efficiency. The GO composite membrane prepared by this invention not only has significantly improved mechanical properties but also exhibits excellent solar water evaporation performance, possessing broad application prospects.

[0008] (II) Technical Solution of the Invention The first objective of this invention is to provide a method for preparing a covalently reinforced and toughened graphene oxide composite film. A layered graphene oxide composite film is prepared using a vacuum filtration-induced self-assembly method. The film is then acidified by adding hydrochloric acid and heated in an oven to achieve covalent cross-linking within the GO nanosheets. By varying the amount of SSA added, a series of covalently reinforced and toughened GO-SSA graphene oxide composite films with different proportions are obtained. The implementation steps are as follows: SS1. Preparation of GO aqueous dispersion Aqueous dispersions of monolayer graphene oxide (GO) were prepared to ensure that the monolayer ratio of GO nanosheets was not less than 99.5%, the average radial size was 20–30 μm, and the GO concentration was controlled at 0.8–1.2 mg / mL, in order to provide a nanosheet base material with uniform dispersion. SS2. Prepare a sulfosuccinic acid (SSA) solution and mix. Weigh 100–400 mg of sulfosuccinic acid (SSA) with a mass fraction of 65–75 wt% using a balance and add it dropwise to an aqueous dispersion of graphene oxide (GO). The mass ratio of GO to SSA is controlled at 1:5 to 1:20. Stir the mixture for 5–8 hours to ensure that SSA and GO are fully mixed and obtain a mixed solution of GO and SSA. SS3. Ultrasonic dispersion Using water bath ultrasound, the mixed solution of GO and SSA prepared in step SS2 is placed in an ultrasonic water bath with a power of 90–110 W and ultrasonically dispersed for 5–10 min, with the ultrasonic temperature controlled not higher than 25℃, so that the GO nanosheets are fully dispersed and a uniform nanoscale suspension is formed. SS4. Vacuum Filtration-Induced Film Assembly The mixture of GO and SSA after ultrasonic dispersion in step SS3 was vacuum filtered through an aqueous microporous membrane with a pore size of 0.4–0.5 μm. The vacuum degree of filtration was not less than 0.08 MPa, which induced GO and SSA to self-assemble into a thin film with a micro-nano multi-level layered structure until a preliminary self-assembled film was formed. SS5. Acidification treatment After all the water has been drained, add 0.5–1 mL of 4–6 mol / L hydrochloric acid to the initially self-assembled membrane on the aqueous microporous filter membrane in step SS4, and continue vacuum filtration until the acidification solution is completely drained to obtain the acidified self-assembled membrane, and ensure that the hydroxyl groups on the surface of the GO nanosheets are fully exposed and can participate in subsequent chemical reactions. SS6. Heat treatment crosslinking The self-assembled membrane obtained in step SS5 after acidification is placed in a vacuum drying oven for heat treatment for 1-3 hours, with the temperature adjusted to 70-90 ℃ and the pressure to 0.8-1.2 atm, so that GO and SSA undergo a covalent cross-linking reaction. COC covalent bonds are formed through the esterification reaction of SSA carboxyl groups and GO hydroxyl groups to construct an interlayer cross-linking network with high bonding strength, and finally a covalently reinforced and toughened GO-SSA graphene oxide composite membrane is obtained. SS7 Performance Optimization The mass of SSA weighed in step SS2 was adjusted and mixed with an equal amount of GO aqueous solution. Steps SS3-SS6 were repeated to obtain a series of GO-SSA graphene oxide composite films with different SSA contents and different mechanical and photothermal properties. From these, the covalently reinforced and toughened graphene oxide composite film with the best mechanical strength and toughness was selected. The optimal ratio was determined, and the thickness of the resulting composite film with the best performance was controlled within the range of 3–5 μm, with a tensile strength of 400–420 MPa and a toughness of 10–12 MJ / m. 3 The water evaporation rate reached 2.0 kg·m -2 ·h -1 above.

[0009] The second objective of this invention is to provide a covalently reinforced and toughened graphene oxide composite film, which is prepared based on the above-mentioned method for preparing a covalently reinforced and toughened graphene oxide composite film.

[0010] The third objective of this invention is to provide an application of the above-mentioned covalently reinforced and toughened graphene oxide composite film as a substrate material in a solar water evaporation device.

[0011] The working principle of this invention: Many components of organisms in nature (such as animal bones, tendons, and nacreous layers of abalone shells) possess excellent mechanical properties, thanks to the sophisticated multi-level structure and abundant interfacial interactions of their constituent materials. Therefore, preparing inorganic nanomaterials with micro / nano-level, well-ordered orientations and modifying them with strong interfacial interactions is key to improving the macroscopic mechanical properties of inorganic nanomaterials. This invention introduces sulfosuccinic acid (SSA) and uses the hydrophilic organic small molecule SSA to covalently crosslink the layers of GO nanosheets. The resulting GO-SSA composite film has a micro / nano-level, multi-layered structure, and a covalent crosslinking network is formed between the GO nanosheets, thus significantly improving the strength and toughness of the GO-SSA graphene oxide composite film compared to the unmodified version. Simultaneously, the sulfonic acid groups on the SSA molecular chain have extremely strong hydrophilicity, which can enhance the water absorption capacity of the composite film and improve its evaporation efficiency in solar water evaporation. Furthermore, the two-dimensional nanochannels and interlaced pore structure of the GO nanosheets endow the film with excellent selective water molecule permeability. The uniform distribution of SSA effectively suppresses the defect of pure GO membranes easily swelling in water, and significantly improves the stability of composite membranes in humid environments.

[0012] (III) Technical Effects of the Invention Compared with existing technologies for preparing graphene oxide composite films, the covalently reinforced and toughened graphene oxide composite film, its preparation method, and its applications of the present invention have the following characteristics and advantages: (1) Using SSA, an organic small molecule with carboxyl groups at both ends of its molecular chain and containing hydrophilic sulfonic acid groups, as a crosslinking agent, SSA is esterified with the hydroxyl groups on GO nanosheets under acidic conditions and a certain temperature. This allows SSA to covalently crosslink the interlayer of GO nanosheets, forming a nano-toughened structure, thereby obtaining a covalently reinforced and toughened GO-SSA graphene oxide composite film. The prepared GO-SSA graphene oxide composite film has a maximum strength of 419 MPa and a toughness of 11 MJ / m. 3 A purer GO membrane (strength 126 MPa, toughness 2.6 MJ / m) 3 () has increased significantly.

[0013] (2) This invention significantly improves the stability of GO membranes in water through covalent crosslinking, solving the problem of easy swelling of pure GO membranes in humid environments. Pure GO membranes have abundant hydrophilic carboxyl and hydroxyl functional groups, and can form two-dimensional nanochannels in the horizontal direction and have an interlaced pore structure in the vertical direction, allowing water molecules to pass through. GO membranes themselves are black and have a certain photothermal conversion capacity, therefore, this material can be applied to solar water evaporation devices. However, pure GO membranes are prone to swelling and instability when exposed to water. The covalently crosslinked graphene oxide composite membrane prepared in this invention has some oxygen-containing functional groups between GO layers covalently crosslinked, improving the stability of the graphene oxide composite membrane when exposed to water. In addition, the GO-SSA graphene oxide composite membrane has hydrophilic sulfonic acid groups, which helps to improve the water absorption efficiency of the membrane.

[0014] (3) The GO-SSA composite membrane of the present invention exhibits excellent performance in solar water evaporation, with significant improvements in photothermal conversion efficiency and evaporation rate. The evaporation rate of the pure graphene oxide film reaches 1.65 kg·m under irradiation with 1 solar intensity. -2 ·h -1 The GO-SSA graphene oxide composite membrane of this invention can increase the water evaporation rate to a maximum of 2.11 kg·m³. -2 ·h -1 This technological effect makes the material potentially widely applicable in the field of solar water distillation, such as solar seawater desalination and water resource recycling.

[0015] (4) The preparation method used in this invention is simple and controllable. The performance of the composite membrane can be precisely controlled by adjusting the ratio of GO to SSA. The entire preparation process is carried out under mild conditions, without the need for complex instruments and equipment or harsh reaction conditions, and has good prospects for industrial application. In addition, the raw materials used are widely available and have low cost, which further enhances the practical value of this technology. Attached Figure Description

[0016] Figure 1This is a flowchart illustrating the process of preparing the covalently reinforced and toughened graphene oxide composite film according to the present invention. Figure 2 This is a schematic diagram illustrating the preparation of the covalently reinforced and toughened graphene oxide composite film according to the present invention. Figure 3 The images show the microstructure and sulfur elemental analysis of the GO-SSA graphene oxide composite film. Image A is a scanning electron microscope image of the cross-sectional structure of the GO-SSA graphene oxide composite film, Image B is the sulfur elemental distribution map of the corresponding region in Image A, and Image C is the sulfur elemental spectrum of the GO-SSA graphene oxide composite film in X-ray photoelectron spectroscopy (XPS). Figure 4 The figures are spectral characterization diagrams, where Figure A is the infrared spectrum of the GO film and the GO-SSA graphene oxide composite film; Figure B is the X-ray diffraction pattern of the GO film and the GO-SSA graphene oxide composite film; Figure C is the X-ray photoelectron spectrum of the GO film; and Figure D is the X-ray photoelectron spectrum of the GO-SSA graphene oxide composite film. Figure 5 The figures show a comparison of the mechanical properties of GO-SSA graphene oxide composite films. Figure A shows the stress-strain curves of GO film and GO-SSA graphene oxide composite film; Figure B shows a comparison of the strength and toughness of GO-SSA graphene oxide composite film and GO composite films modified by other methods. Figure 6 The graphs show the solar water evaporation performance of GO membrane and GO-SSA graphene oxide composite membrane. Graph A shows the temperature rise data of pure water, GO membrane, and GO-SSA graphene oxide composite membrane under 1 solar radiation intensity. Graph B shows the water loss data of pure water, GO membrane, and GO-SSA graphene oxide composite membrane under 1 solar radiation intensity. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be described in more detail below with reference to the accompanying drawings. The described embodiments are some, but not all, of the embodiments of this invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0018] This invention aims to provide a covalently reinforced and toughened graphene oxide composite membrane, its preparation method, and its applications. By introducing sulfosuccinic acid (SSA) and graphene oxide for covalent cross-linking modification, and utilizing acidic conditions and heating to induce esterification between the carboxyl groups in the SSA molecules and the hydroxyl groups on the GO nanosheets to form COC covalent bonds, a cross-linked network with high bonding strength is constructed between the GO nanosheets, significantly improving the membrane's strength, toughness, and stability in water. Simultaneously, the hydrophilic sulfonic acid groups in SSA can enhance the membrane's water absorption efficiency, effectively improving photothermal conversion performance and water evaporation efficiency.

[0019] Example 1 like Figure 1 , 2 As shown, the method for preparing the covalently reinforced and toughened graphene oxide composite film of the present invention mainly includes the following steps in its implementation: SS1. Preparation of GO aqueous dispersion: Prepare an aqueous dispersion of monolayer graphene oxide to ensure that the monolayer ratio of GO nanosheets is not less than 99.5%, the average radial size is 20–30 μm, and the GO concentration is controlled at 0.8–1.2 mg / mL, in order to provide a nanosheet base material with uniform dispersion.

[0020] SS2. Preparation and mixing of sulfosuccinic acid (SSA) solutions: First, weigh a series of 70 wt% SSA aqueous solutions using a balance and add them to the prepared GO aqueous solution, stirring until well mixed. The mass ratios of GO and SSA are 1:5, 1:10, 1:15, and 1:20, respectively. Stir the mixed solution for 5–8 hours to ensure thorough mixing of SSA and GO, obtaining a mixed solution of the two.

[0021] SS3. Ultrasonic dispersion: Using a water bath, place the mixed solution of GO and SSA prepared in step SS2 in an ultrasonic water bath with a power of 90–110 W and ultrasonically disperse for 5–10 min, controlling the ultrasonic temperature not to exceed 25℃, so that the GO nanosheets are fully dispersed and a uniform nanoscale suspension is formed.

[0022] SS4. Vacuum Filtration-Induced Film Assembly: The ultrasonically dispersed mixture of GO and SSA was poured into a vacuum filtration flask, and a layered film was prepared by vacuum filtration-induced self-assembly. Specifically, the mixture was vacuum filtered through an aqueous microporous membrane with a pore size of 0.4–0.5 μm and a vacuum degree of not less than 0.08 MPa to induce GO and SSA to self-assemble into a film with a micro-nano multi-level layered structure until a preliminary self-assembled film was formed.

[0023] SS5. Acidification treatment: After all the water has been removed, add 0.5–1 mL of 4–6 mol / L hydrochloric acid to the filtered membrane, and then continue filtration until the liquid is completely removed to acidify the membrane and obtain an acidified self-assembled membrane, ensuring that the hydroxyl groups on the surface of the GO nanosheets are fully exposed and can participate in subsequent chemical reactions.

[0024] SS6. Heat Treatment Crosslinking: The filtered membrane is placed in a vacuum drying oven and heated for 1-3 hours, with the temperature adjusted to 70–90 °C and the pressure to 0.8–1.2 atm. During this process, GO and SSA undergo covalent crosslinking, and the esterification reaction of SSA carboxyl groups and GO hydroxyl groups forms COC, which in turn forms covalent bonds to construct an interlayer crosslinked network with high bonding strength, thus ultimately obtaining GO-SSA graphene oxide composite membranes with varying degrees of covalent crosslinking.

[0025] SS7. Performance Optimization: Adjust the mass of SSA weighed in step SS2 and blend it with an equal amount of GO aqueous solution. Repeat steps SS3-SS6 to obtain a series of GO-SSA graphene oxide composite films with different SSA contents and different mechanical and photothermal properties. From these, screen out the covalently reinforced and toughened graphene oxide composite film with the best mechanical strength and toughness. Determine the optimal ratio and ensure that the thickness of the resulting composite film with the best performance is controlled within the range of 3–5 μm, the tensile strength reaches 400–420 MPa, and the toughness reaches 10–12 MJ / m. 3 The water evaporation rate reached 2.0 kg·m -2 ·h -1 above.

[0026] Preferably, in the above steps, the GO aqueous solution is a graphene oxide aqueous dispersion with a monolayer ratio >99.5%, an average radial dimension of 20-30 μm, and active groups such as carboxyl, epoxy, and hydroxyl groups on its surface. A film with a micro-layered structure can be prepared by vacuum filtration. The SSA is a 70 wt% SSA aqueous solution. The covalent crosslinking of GO and SSA occurs under acidic and heating conditions, where the hydroxyl groups on the GO surface undergo esterification with the carboxyl groups on the small molecule SSA. The resulting COC covalent bonds cause interlayer covalent crosslinking of the GO nanosheets, thereby improving the strength and toughness of the GO-SSA graphene oxide composite film. Because the small molecule SSA molecular chain contains hydrophilic sulfonic acid groups, the hydrophilicity of the GO-SSA graphene oxide composite film is also improved, significantly increasing its solar water evaporation efficiency. The thickness of the GO-SSA graphene oxide composite film obtained by this invention ranges from 3 to 5 micrometers.

[0027] Preferably, in step SS1 above, the preparation process of the GO aqueous dispersion includes: dispersing graphite oxide powder at a concentration of 0.8-1.2 mg / mL in deionized water, performing ultrasonic exfoliation for 60-90 min using a probe-type ultrasonic device with a power of 400-600W, controlling the temperature to not exceed 15 ℃ during the ultrasonication process using an ice-water bath, and then centrifuging at a speed of 4000-6000 rpm for 10-20 min, collecting the supernatant to obtain a GO aqueous dispersion with a monolayer rate of not less than 99.5%.

[0028] Preferably, in step SS2 above, the mixing process of GO and SSA further includes: using a magnetic stirrer during the stirring process, controlling the rotation speed to 300-500 rpm, maintaining the stirring temperature at 20-25 ℃, taking samples every 2 hours to test the dispersion stability of the mixture using dynamic light scattering method, ensuring the uniform dispersion of GO nanosheets, until the measured particle size distribution curve remains stable.

[0029] Preferably, in step SS3 above, the temperature range of the ultrasonic water bath is controlled between 20 and 25 ℃, and the ultrasonic process is carried out in an intermittent manner, that is, after working for 2 minutes, it is paused for 1 minute, and the cycle is repeated 3-5 times. At the same time, a thermometer is used to monitor the solution temperature in real time. When the temperature exceeds 25 ℃, the ultrasonic process is stopped immediately and resumed after the temperature drops below 20 ℃, so as to further reduce the probability of particle sedimentation and enhance the dispersion effect of the mixed solution, thereby improving the microstructure uniformity and film quality of the subsequent film layer.

[0030] Preferably, in step SS4 above, the method of inducing self-assembly of the membrane using vacuum filtration includes at least the following sub-steps: SS41. Solution pretreatment: Let the ultrasonically dispersed GO and SSA mixture obtained in step SS3 stand for 2–5 min to ensure solution homogeneity and avoid affecting the uniform formation of the membrane due to particle aggregation or sedimentation. SS42. Initial filtration operation: With the vacuum pump off, add the settled GO and SSA mixture to the vacuum filtration device, ensuring that the mixture evenly covers the filter membrane surface; SS43. Start vacuum filtration: Let the mixed solution of GO and SSA stand in the vacuum filtration device for 2–5 min to ensure that the GO and SSA molecules are in full contact with the filter membrane. Then, gradually turn on the vacuum pump to perform vacuum filtration, control the vacuum degree between 0.08–0.10 MPa, and ensure that the filtration speed is slow and uniform to avoid defects or damage to the membrane surface due to liquid flow impact. SS44. Microstructure control of membrane layer: During the filtration process, GO nanosheets in the GO and SSA mixed solution gradually deposit on the filter membrane to form a layered microstructure, while SSA small molecules are distributed between the GO nanosheet layers and deposited together on the filter membrane. By adjusting the filtrate discharge rate in real time, the deposition rate and distribution of GO and SSA on the filter membrane surface are optimized to ensure that the final membrane has a good micro-nano multi-level layered structure. SS45. Complete filtration and drying: Continue filtration until the water is completely removed and a uniform, dense graphene oxide composite membrane mixed with SSA is formed on the surface of the filter membrane. After stopping the vacuum pump, remove the filter membrane and place it in a ventilated environment to air dry naturally or in a dry environment at a temperature of 25–35°C for 30–60 minutes to remove residual moisture and avoid high temperature causing membrane instability or loosening of structure.

[0031] Preferably, in step SS5 above, the hydrochloric acid is added gradually, with each addition controlled at 20-30% of the total amount, to ensure that the acid solution is evenly distributed on the film surface. Vacuum filtration is performed after each addition to ensure that the acidification process is uniform and sufficient, avoiding insufficient or over-acidification in certain areas that could affect the exposure of the hydroxyl groups on the GO nanosheets. Furthermore, 0.5-1 wt% of ethanol or isopropanol is added to the hydrochloric acid solution during the acidification process as an auxiliary agent to improve the acidification efficiency and slow down the shrinkage of the film structure, so as to maintain the uniformity and integrity of the film after acidification and provide a better structural basis for subsequent crosslinking.

[0032] Preferably, in step SS6 above, the heat treatment crosslinking process further includes: controlling the pressure of the vacuum drying oven at 0.8–1.2 atmospheres, and increasing the temperature gradient during heating, gradually increasing it from an initial temperature of 50–60 ℃ to 70–90 ℃, to avoid deformation or delamination of the membrane layer due to rapid heating, while ensuring that the esterification reaction proceeds fully. After the temperature reaches 70–90 ℃, it is kept at a constant temperature for 2 hours, and then naturally cooled to room temperature at a cooling rate of 1 ℃ / min. The entire heat treatment process is carried out under nitrogen protection, with the nitrogen flow rate controlled at 100–150 mL / min, which further enhances the stability of the membrane structure, improves the mechanical properties and water stability of the GO-SSA composite membrane, and ensures the long-term performance of the finished membrane in complex environments.

[0033] Preferably, in step SS7 above, SSA is modified by adding polyhydroxy compounds (such as glycerol, sorbitol) or amino compounds (such as ethylenediamine, triethanolamine) as functional group modifiers, so that it can form a more stable covalent cross-linked network with GO nanosheets during acidification and heat treatment. By optimizing the mass ratio of GO to SSA to 1:10 to 1:25, the thickness and interlayer structure of the film are systematically controlled, and the photothermal conversion efficiency of the composite film under 1 solar intensity is further improved, thereby screening out GO-SSA composite films with higher photothermal conversion efficiency.

[0034] Example 2 As a more specific example, in the implementation of Example 2: First, the graphene oxide dispersion was diluted to a concentration of 1 mg / mL GO dispersion, and 20 mL was prepared for later use. 100 mg of a 70 wt% SSA aqueous solution was weighed and added dropwise to the prepared 20 mL GO dispersion, with continuous mechanical stirring during the addition. Stirring continued for approximately 10 hours after the addition was complete. Then, an ultrasonic water bath with a power of 100 W was used, with the ultrasonic temperature not exceeding 25 ℃, for 10 min to fully disperse the GO nanosheets. At this point, the solution was brown and translucent. The mixture was poured into a vacuum filtration flask for vacuum filtration using an aqueous filter membrane with a pore size of 0.45 μm. After the liquid was dried, a black, opaque film was deposited on the filter membrane. The vacuum filtration device was stopped, the vacuum tube was removed, and 5 mol / L hydrochloric acid was added dropwise to the filtration flask. Vacuum filtration continued until the membrane was completely acidified. After the liquid was drained again, the filter membrane was removed and placed in an oven at 80 °C. During the heating process, the black film gradually detached from the filter membrane, forming an independent film; this heating process took approximately 1 hour. When the temperature reached 80 °C, the acidified GO nanosheets and SSA began an esterification reaction, which took approximately 1 hour, resulting in a covalently cross-linked GO-SSA graphene oxide composite membrane. Infrared spectroscopy characterization of the obtained GO-SSA graphene oxide composite membrane revealed that, after this reaction time, the membrane reached a density of ~10³² cm⁻¹. -1 A characteristic peak appeared at this location. Subsequently, extending the time the film was placed in the oven did not change this characteristic peak, indicating that the reaction conditions and time were sufficient to allow the hydroxyl groups on the GO nanosheets to fully react with the carboxyl groups on the SSA. Parallel samples of the GO-SSA graphene oxide composite film obtained by this method showed an average tensile strength of 159 MPa and an average toughness of 3.7 MJ / m. 3 .

[0035] Example 3 As another preferred example, in this embodiment 3, the graphene oxide dispersion was diluted to a GO dispersion with a concentration of 1 mg / mL, and 20 mL was set aside. 200 mg of a 70 wt% SSA aqueous solution was weighed and added dropwise to the prepared 20 mL GO dispersion, with continuous mechanical stirring during the addition. Stirring continued for approximately 10 hours after the addition was complete. Then, an ultrasonic water bath with a power of 100 W was used, with the ultrasonic temperature not exceeding 25 °C, for 10 minutes to fully disperse the GO nanosheets. At this point, the solution was brown and translucent. The mixture was poured into a vacuum filtration flask for vacuum filtration using an aqueous filter membrane with a pore size of 0.45 μm. After the liquid was dried, a black opaque film was deposited on the filter membrane. The vacuum filtration device was stopped, the vacuum tube was removed, and 5 mol / L hydrochloric acid was added dropwise to the filtration flask. Vacuum filtration continued until the membrane was completely acidified. After the liquid was drained again, the filter membrane was removed and placed in an oven at 80 °C. During the heating process, the black film gradually detached from the filter membrane, forming an independent film; this heating process took approximately 1 hour. When the temperature reached 80 °C, the acidified GO nanosheets and SSA began an esterification reaction, which took approximately 1 hour, resulting in a covalently cross-linked GO-SSA graphene oxide composite membrane. Infrared spectroscopy characterization of the obtained GO-SSA graphene oxide composite membrane revealed that, after this reaction time, the membrane reached a density of ~10³² cm⁻¹. -1 A characteristic peak appeared at this location. Subsequently, extending the time the film was placed in the oven did not change this characteristic peak, indicating that the reaction conditions and time were sufficient to allow the hydroxyl groups on the GO nanosheets to fully react with the carboxyl groups on the SSA. Parallel samples of the GO-SSA graphene oxide composite film obtained by this method showed an average tensile strength of 251 MPa and an average toughness of 7.4 MJ / m. 3 .

[0036] Example 4 As another preferred example, in this embodiment 4, the graphene oxide dispersion was diluted to a GO dispersion with a concentration of 1 mg / mL, and 20 mL was set aside. 300 mg of a 70 wt% SSA aqueous solution was weighed and added dropwise to the prepared 20 mL GO dispersion, with continuous mechanical stirring during the addition. Stirring continued for approximately 10 hours after the addition was complete. Then, an ultrasonic water bath with a power of 100 W was used, with the ultrasonic temperature not exceeding 25 °C, for 10 minutes to fully disperse the GO nanosheets. At this point, the solution was brown and translucent. The mixture was poured into a vacuum filtration flask for vacuum filtration using an aqueous filter membrane with a pore size of 0.45 μm. After the liquid was dried, a black, opaque film was deposited on the filter membrane. The vacuum filtration device was stopped, the vacuum tube was removed, and 5 mol / L hydrochloric acid was added dropwise to the filtration flask. Vacuum filtration continued until the membrane was completely acidified. After the liquid was drained again, the filter membrane was removed and placed in an oven at 80 °C. During the heating process, the black film gradually detached from the filter membrane, forming an independent film; this heating process took approximately 1 hour. When the temperature reached 80 °C, the acidified GO nanosheets and SSA began an esterification reaction, which took approximately 1 hour, resulting in a covalently cross-linked GO-SSA graphene oxide composite membrane. Infrared spectroscopy characterization of the obtained GO-SSA graphene oxide composite membrane revealed that, after this reaction time, the membrane reached a density of ~10³² cm⁻¹. -1 A characteristic peak appeared at this location. Subsequently, extending the time the film was placed in the oven did not change this characteristic peak, indicating that the reaction conditions and time were sufficient to allow the hydroxyl groups on the GO nanosheets to fully react with the carboxyl groups on the SSA. Parallel samples of the GO-SSA graphene oxide composite film obtained by this method showed an average tensile strength of 419 MPa and an average toughness of 11 MJ / m. 3 .

[0037] Example 5 As another preferred example, in this embodiment 5, the graphene oxide dispersion was diluted to a GO dispersion with a concentration of 1 mg / mL, and 20 mL was set aside. 400 mg of a 70 wt% SSA aqueous solution was weighed and added dropwise to the prepared 20 mL GO dispersion, with continuous mechanical stirring during the addition. Stirring continued for approximately 10 hours after the addition was complete. Then, an ultrasonic water bath with a power of 100 W was used, with the ultrasonic temperature not exceeding 25 °C, for 10 minutes to fully disperse the GO nanosheets. At this point, the solution was brown and translucent. The mixture was poured into a vacuum filtration flask for vacuum filtration using an aqueous filter membrane with a pore size of 0.45 μm. After the liquid was dried, a black, opaque film was deposited on the filter membrane. The vacuum filtration device was stopped, the vacuum tube was removed, and 5 mol / L hydrochloric acid was added dropwise to the filtration flask. Vacuum filtration continued until the membrane was completely acidified. After the liquid was drained again, the filter membrane was removed and placed in an oven at 80 °C. During the heating process, the black film gradually detached from the filter membrane, forming an independent film; this heating process took approximately 1 hour. When the temperature reached 80 °C, the acidified GO nanosheets and SSA began an esterification reaction, which took approximately 1 hour, resulting in a covalently cross-linked GO-SSA graphene oxide composite membrane. Infrared spectroscopy characterization of the obtained GO-SSA graphene oxide composite membrane revealed that, after this reaction time, the membrane reached a density of ~10³² cm⁻¹. -1 A characteristic peak appeared at this location. Subsequently, extending the time the film was placed in the oven did not change this characteristic peak, indicating that the reaction conditions and time were sufficient to allow the hydroxyl groups on the GO nanosheets to fully react with the carboxyl groups on the SSA. Parallel samples of the GO-SSA graphene oxide composite film obtained by this method showed an average tensile strength of 162 MPa and an average toughness of 4.2 MJ / m. 3 .

[0038] Structural and performance characterization of GO-SSA graphene oxide composite film like Figure 2-6 As shown, the structure and properties of the covalently reinforced and toughened graphene oxide composite membrane (GO-SSA composite membrane) of the present invention have been comprehensively characterized by microscopic features and performance tests, demonstrating its excellent mechanical properties, chemical structural characteristics and solar water evaporation performance.

[0039] Figure 2The diagram illustrates the preparation of the covalently reinforced and toughened graphene oxide composite membrane (GO-SSA composite membrane) according to the present invention: A well-mixed aqueous dispersion of GO and SSA is self-assembled into a layered film using vacuum filtration. After the film is fully acidified with hydrochloric acid and heated in an oven, a covalently cross-linked GO-SSA graphene oxide composite membrane is obtained. The diagram illustrates the interlayer cross-linking structure formed by covalent bonds between small-molecule SSA and GO nanosheets: hydroxyl groups in the GO nanosheets and carboxyl groups in the SSA organic molecule form covalent bonds through esterification, resulting in interlayer cross-linking of the GO nanosheets and thus improving the mechanical properties of the GO-SSA graphene oxide composite membrane.

[0040] Figure 3 The images show the microstructure and sulfur element analysis of the GO-SSA graphene oxide composite film. Image A is a cross-sectional scanning electron microscope image of the GO-SSA graphene oxide composite film, showing that the film has a micro-layered structure. Image B shows that a large amount of sulfur is distributed between the layers of the GO-SSA graphene oxide composite film, indicating that SSA is uniformly distributed between the GO nanosheets. Image C, through sulfur element spectrum in X-ray photoelectron spectroscopy, further shows that SSA has entered the interlayer of GO nanosheets.

[0041] Figure 4 The image shows the spectral characterization: Figure A shows the infrared spectra of the GO film and the GO-SSA graphene oxide composite film. The modified GO-SSA has an infrared spectrum of ~1032 cm⁻¹. -1 A new absorption peak appears at ~1224 cm⁻¹, which is a characteristic peak of COC, indicating the formation of covalent bonds. -1 The significantly enhanced CO absorption peak at position A indicates a significantly increased number of CO bonds in the GO-SSA graphene oxide composite film compared to the pure GO film, further illustrating the formation of COC covalent bonds within the GO-SSA graphene oxide composite film. Figure B shows the X-ray diffraction patterns of the GO film and the GO-SSA graphene oxide composite film. The diffraction peak of the GO-SSA graphene oxide composite film shows a significant blue shift compared to the pure GO film, indicating that the addition of SSA increases the interlayer spacing of the GO nanosheets, suggesting that SSA in the GO-SSA graphene oxide composite film is inserted into the interlayer of the GO nanosheets. Figure C shows the X-ray photoelectron spectrum of the GO film; Figure D shows the X-ray photoelectron spectrum of the GO-SSA graphene oxide composite film. Compared to Figure C, the significantly increased intensity of the CO absorption peak at approximately 288 eV indicates the formation of new CO chemical bonds, further demonstrating the formation of COC covalent bonds within the GO-SSA graphene oxide composite film.

[0042] Figure 5The mechanical properties of GO-SSA composite films are compared in the following figures: Figure A shows the stress-strain curves of GO film and a series of GO-SSA graphene oxide composite films: 1 is the stress-strain curve of pure GO film; 2 is the stress-strain curve of GO-SSA graphene oxide composite film reinforced and toughened by covalent bonds with a GO to SSA mass percentage of 1:5; 3 is the stress-strain curve of GO-SSA graphene oxide composite film reinforced and toughened by covalent bonds with a GO to SSA mass percentage of 1:10; 4 is the stress-strain curve of GO-SSA graphene oxide composite film reinforced and toughened by covalent bonds with a GO to SSA mass percentage of 1:15; and 5 is the stress-strain curve of GO-SSA graphene oxide composite film reinforced and toughened by covalent bonds with a GO to SSA mass percentage of 1:20. The above data shows that the GO-SSA graphene oxide composite film, with a GO to SSA mass percentage of 1:15, exhibits the best mechanical properties through covalent reinforcement and toughening. Figure B compares the strength and toughness of the GO-SSA graphene oxide composite film with GO films modified by other methods. The data in the figure indicate that the GO-SSA graphene oxide composite film possesses comprehensive advantages in both strength and toughness, with strength and toughness increased by approximately 3 times and 4 times, respectively, compared to pure GO films.

[0043] Figure 6 The solar water evaporation performance curves of GO membrane and GO-SSA graphene oxide composite membrane are shown in Figure A: Figure A shows the temperature rise data of pure water, GO membrane, and GO-SSA graphene oxide composite membrane under one solar radiation intensity. The results show that the GO-SSA graphene oxide composite membrane has the highest temperature rise efficiency. Figure B shows the water evaporation data of pure water, GO membrane, and GO-SSA graphene oxide composite membrane under one solar radiation intensity. The results show that the GO-SSA graphene oxide composite membrane has the highest water evaporation efficiency, reaching 2.11 kg·m³. -2 ·h -1 .

[0044] In summary, the covalently reinforced and toughened graphene oxide-SSA composite membrane prepared in this invention combines multiple advantages in mechanical properties, chemical stability, and photothermal performance. Its covalently cross-linked network significantly enhances the structural stability of the membrane, while the introduction of SSA molecules improves the hydrophilicity and water evaporation efficiency of the composite membrane. Measurement results show that its maximum strength and toughness are approximately 3 times and 4 times higher than before modification, respectively, and the water evaporation rate is increased to a maximum of 2.11 kg·m³. -2 ·h -1 These properties make this material promising for applications in fields such as solar water evaporation, seawater desalination, and water resource recycling.

[0045] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A method for preparing a covalently reinforced and toughened graphene oxide composite film, characterized in that, The preparation method is implemented in the following steps: SS1. Prepare an aqueous dispersion of monolayer graphene oxide (GO) to ensure that the monolayer content of GO nanosheets is not less than 99.5%, the average radial size is 20–30 μm, and the GO concentration is controlled at 0.8–1.2 mg / mL, in order to provide a nanosheet base material with uniform dispersion. SS2. Weigh 100–400 mg of sulfosuccinic acid (SSA) with a mass fraction of 65–75 wt% using a balance and add it dropwise to the aqueous dispersion of graphene oxide (GO). The mass ratio of GO to SSA is controlled at 1:5 to 1:

20. Stir the mixture for 5–8 hours to ensure that SSA and GO are fully mixed to obtain a mixed solution of GO and SSA. SS3. Using water bath ultrasound, place the mixed solution of GO and SSA prepared in step SS2 in an ultrasonic water bath with a power of 90–110 W for ultrasonic dispersion for 5–10 min, and control the ultrasonic temperature not to exceed 25℃, so that the GO nanosheets are fully dispersed and a uniform nanoscale suspension is formed. SS4. The ultrasonically dispersed mixture of GO and SSA was vacuum filtered through an aqueous microporous membrane with a pore size of 0.4–0.5 μm. The vacuum degree of the filtration was not less than 0.08 MPa, which induced GO and SSA to self-assemble into a thin film with a micro-nano multi-level layered structure until a preliminary self-assembled film was formed. SS5. After all the water has been drained, add 0.5–1 mL of hydrochloric acid with a concentration of 4–6 mol / L to the initially self-assembled membrane on the aqueous microporous filter membrane in step SS4, and continue vacuum filtration until the acidification solution is completely drained to obtain the acidified self-assembled membrane, and ensure that the hydroxyl groups on the surface of the GO nanosheets are fully exposed and can participate in subsequent chemical reactions. SS6. Place the acidified self-assembled membrane obtained in step SS5 into a vacuum drying oven for heat treatment for 1-3 hours, adjusting the temperature to 70-90 ℃ and the pressure to 0.8-1.2 atm, so that GO and SSA undergo a covalent cross-linking reaction. Through the esterification reaction of SSA carboxyl groups and GO hydroxyl groups, COC covalent bonds are formed to construct an interlayer cross-linking network with high bonding strength, and finally a covalently reinforced and toughened GO-SSA graphene oxide composite membrane is obtained. SS7. The SSA mass taken in step SS2 is blended with the same content of GO aqueous solution, and steps SS3-SS6 are repeated to obtain a series of GO-SSA graphene oxide composite films with different SSA contents and different mechanical properties and photothermal properties, from which a covalently bonded enhanced and toughened graphene oxide composite film with optimal mechanical strength and toughness is screened, and the thickness of the obtained optimal performance composite film is controlled within the range of 3-5 μm, the tensile strength reaches 400-420 MPa, the toughness reaches 10-12 MJ / m 3 , and the water evaporation rate reaches 2.0 kg·m -2 ·h -1 above.

2. The method for preparing a covalently reinforced and toughened graphene oxide composite film according to claim 1, characterized in that: In step SS1 above, the preparation process of the GO aqueous dispersion includes: dispersing graphite oxide powder at a concentration of 0.8-1.2 mg / mL in deionized water, performing ultrasonic exfoliation for 60-90 min using a probe-type ultrasonic device with a power of 400-600W, controlling the temperature to not exceed 15 ℃ during the ultrasonic process using an ice-water bath, and then centrifuging at a speed of 4000-6000 rpm for 10-20 min, collecting the supernatant to obtain a GO aqueous dispersion with a monolayer rate of not less than 99.5%.

3. The method for preparing a covalently reinforced and toughened graphene oxide composite film according to claim 1, characterized in that: In step SS2 above, the mixing process of GO and SSA further includes: using a magnetic stirrer during the stirring process, controlling the speed to 300-500 rpm, maintaining the stirring temperature at 20-25 ℃, taking samples every 2 hours to test the dispersion stability of the mixture by dynamic light scattering method, ensuring the uniform dispersion of GO nanosheets, until the measured particle size distribution curve remains stable.

4. The method for preparing a covalently reinforced and toughened graphene oxide composite film according to claim 1, characterized in that: In step SS3 above, the temperature range of the ultrasonic water bath is controlled between 20 and 25 ℃. The ultrasonic process adopts an intermittent ultrasonic method, that is, working for 2 minutes and then pausing for 1 minute, and repeating the cycle 3-5 times. At the same time, a thermometer is used to monitor the solution temperature in real time. When the temperature exceeds 25 ℃, the ultrasonic process is stopped immediately and resumed after the temperature drops below 20 ℃. This is to further reduce the probability of particle sedimentation and enhance the dispersion effect of the mixed solution, thereby improving the microstructure uniformity and film quality of the subsequent film layer.

5. The method for preparing a covalently reinforced and toughened graphene oxide composite film according to claim 1, characterized in that: In step SS4 above, the method of inducing self-assembly into a membrane using vacuum filtration includes at least the following sub-steps: SS41. Solution Pretreatment Let the ultrasonically dispersed GO and SSA mixture obtained in step SS3 stand for 2–5 min to ensure solution homogeneity and avoid affecting the uniform formation of the membrane due to particle aggregation or sedimentation. SS42. Initial Filtering Operation With the vacuum pump off, add the settled GO and SSA mixture to the vacuum filtration device to ensure that the mixture evenly covers the filter membrane surface. SS43. Start vacuum filtration Allow the mixed solution of GO and SSA to stand in a vacuum filtration apparatus for 2–5 minutes to ensure GO... After the SSA molecules have come into full contact with the filter membrane, the vacuum pump is gradually turned on to perform vacuum filtration, controlling the vacuum level between 0.08 and 0.10 MPa, and ensuring that the filtration speed is slow and uniform to avoid defects or damage to the membrane surface caused by liquid flow impact. SS44. Microscopic Regulation of Membrane Layers During the filtration process, GO nanosheets in the GO and SSA mixed solution gradually deposit on the filter membrane to form a layered microstructure, while SSA small molecules are distributed between the GO nanosheet layers and deposited together on the filter membrane. By adjusting the filtrate discharge rate in real time, the deposition rate and distribution of GO and SSA on the filter membrane surface are optimized to ensure that the final membrane has a good micro-nano multi-level layered structure. SS45. Complete filtration and drying. The filtration operation continues until the water is completely drained, until a uniform and dense graphene oxide composite membrane mixed with SSA is formed on the surface of the filter membrane. After stopping the vacuum pump, the filter membrane is removed and placed in a ventilated environment to air dry naturally or in a dry environment at a temperature of 25–35°C for 30–60 minutes to remove residual moisture and avoid high temperature causing the membrane morphology to be unstable or the structure to be loose.

6. The method for preparing a covalently reinforced and toughened graphene oxide composite film according to claim 1, characterized in that: In step SS5 above, hydrochloric acid is added gradually, with each addition controlled at 20-30% of the total amount to ensure uniform distribution of the acid solution on the film surface. Vacuum filtration is performed after each addition to ensure uniform and sufficient acidification and avoid insufficient or excessive acidification in certain areas, which could affect the exposure of the hydroxyl groups of the GO nanosheets. In addition, 0.5-1 wt% of ethanol or isopropanol is added to the hydrochloric acid solution as an auxiliary agent during the acidification process to improve the acidification efficiency and slow down the shrinkage of the film structure.

7. The method for preparing a covalently reinforced and toughened graphene oxide composite film according to claim 1, characterized in that: In step SS6 above, the heat treatment crosslinking process further includes: controlling the pressure of the vacuum drying oven at 0.8–1.2 atmospheres, and increasing the temperature gradient during the heating process, so that the initial temperature of 50–60 ℃ is gradually increased to 70–90 ℃. After the temperature reaches 70–90 ℃, it is kept at a constant temperature for 2 hours, and then naturally cooled to room temperature at a cooling rate of 1 ℃ / min. The entire heat treatment process is carried out under nitrogen protection, and the nitrogen flow rate is controlled at 100–150 mL / min.

8. The method for preparing a covalently reinforced and toughened graphene oxide composite film according to claim 1, characterized in that: In step SS7 above, SSA is modified by adding polyhydroxy or amino compounds as functional group modifiers, so that it can form a more stable covalent cross-linked network with GO nanosheets during acidification and heat treatment. By optimizing the mass ratio of GO to SSA to 1:10 to 1:25, the thickness and interlayer structure of the film are systematically controlled, further improving the photothermal conversion efficiency of the composite film under one solar radiation intensity.

9. A covalently reinforced and toughened graphene oxide composite film, characterized in that, The graphene oxide composite film is prepared based on the covalent bond-reinforced and toughened graphene oxide composite film preparation method according to any one of claims 1 to 8.

10. The application of the covalently reinforced and toughened graphene oxide composite film of claim 9 as a substrate material in a solar water evaporation device.

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