Graphene composite hydrogel interfacial evaporation material and preparation method and application thereof

Abstract

The application belongs to the technical field of interfacial evaporation materials, and particularly relates to a graphene composite hydrogel interfacial evaporation material and a preparation method and application thereof. The composite hydrogel interfacial evaporation material comprises a hydrogel matrix and nitrogen-doped graphene oxide, and the nitrogen-doped graphene oxide is embedded into the hydrogel matrix through covalent bonding and hydrogen bonding. The hydrogel matrix comprises polyvinyl alcohol and polyethyleneimine. The hydrogel matrix has a double-network composite structure. Through construction of a double-polymerization network and directional water channels, the water evaporation rate is improved. The preparation process is simple, green and environmentally friendly. The obtained hydrogel has excellent photothermal performance, can realize evaporation enthalpy reduction and efficient seawater evaporation, and has good desalination effect on seawater.

Description

Technical Field

[0001] This invention belongs to the field of interfacial evaporation materials, specifically relating to a graphene composite hydrogel interfacial evaporation material, its preparation method, and its application. Background Technology

[0002] Seawater desalination technology is a key approach to solving the shortage of freshwater resources. Traditional seawater desalination technologies, such as reverse osmosis and multi-effect distillation, have high energy consumption (>3 kWh / m³). 3 However, solar energy faces challenges such as complex equipment and chemical pollution. Solar interfacial evaporation technology, with its zero carbon emissions, low cost, and distributed application, has become the most promising alternative. The selection of photothermal conversion materials and structural design are crucial for improving evaporation efficiency.

[0003] Common photothermal conversion materials are mainly divided into three categories: carbon-based materials (such as graphene, graphene oxide, and carbon nanotubes), metal-based nanomaterials (such as gold and silver nanoparticles), and inorganic semiconductor materials (such as black titanium dioxide and titanium trioxide). Among these, metal nanoparticles are prone to aggregation or oxidation, leading to a decrease in photothermal conversion effect and efficiency (e.g., Ag nanoparticles are unstable in biological environments). Semiconductor materials suffer from high electron-hole recombination rates, requiring heterojunction design for improvement. While carbon-based materials are stable, their limited efficiency as a single component and poor hydrophilicity make them unsuitable for meeting the long-term seawater evaporation requirements.

[0004] Hydrogel-based evaporators embed photothermal nanomaterials into a polymer network, endowing it with the ability to convert solar energy into heat energy, thus achieving efficient solar-driven water evaporation. Existing hydrogel-based evaporators still face two major technical bottlenecks: first, the polymer network is prone to swelling and disintegration under high-salt environments, leading to a decrease in evaporation rate; second, the interfacial bonding between the photothermal material and the hydrogel matrix is ​​weak, and phase separation easily occurs after long-term use. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a graphene composite hydrogel interfacial evaporation material, its preparation method, and its applications. Chemical modification of graphene oxide is achieved through hydrothermal reduction. Using polyvinyl alcohol and polyethyleneimine as gel network components, nitrogen-doped graphene oxide is linked with the gel network components via covalent bonds and hydrogen bonds to form a graphene composite hydrogel with a dual polymer network crosslinking. This hydrogel, as a solar interfacial evaporation material, exhibits excellent photothermal properties, enabling reduced enthalpy of evaporation, efficient seawater evaporation, and effective seawater desalination.

[0006] The technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a graphene composite hydrogel interfacial evaporation material, comprising a hydrogel matrix and nitrogen-doped graphene oxide, wherein the nitrogen-doped graphene oxide is embedded in the hydrogel matrix through covalent bonding and hydrogen bonding.

[0008] The hydrogel matrix includes polyvinyl alcohol and polyethyleneimine; the hydrogel matrix has a dual-network composite structure.

[0009] This invention uses polyvinyl alcohol (PVA) and polyethyleneimine (PEI) as gel network components. PVA is rich in hydroxyl groups; PII, one of the specific gel network components, is rich in nitrogen-containing groups such as primary, secondary, and tertiary amines. Through cross-linking polymerization of PVA and PII, a unique dual-network composite structure is formed, which can provide abundant functional groups to bind water molecules under saline conditions, thereby reducing the enthalpy of evaporation. N-GO is used as a photothermal material, embedded into the hydrogel matrix through covalent bonding and hydrogen bonding. A dual-polymer cross-linked graphene composite hydrogel material, PVA / PEI / N-GO, was constructed.

[0010] In some other embodiments, the mass ratio of nitrogen-doped graphene oxide to the hydrogel matrix is ​​(0.009-0.01):1; the mass ratio of polyvinyl alcohol to polyethyleneimine is (2-4):1, the number average molecular weight of polyvinyl alcohol is 89,000-98,000, and the number average molecular weight of polyethyleneimine is 18 million-100,000.

[0011] Specifically, the mass ratio of nitrogen-doped graphene oxide to the hydrogel matrix is ​​0.009:1, 0.0095:1, or 0.01:1; the mass ratio of polyvinyl alcohol to polyethyleneimine is 2:1, 3:1, or 4:1. This ensures that the network has sufficient cross-linking density while still retaining a large number of hydrophilic groups (-OH, -NH2) exposed in water, giving the hydrogel high water content and good swelling properties. The number average molecular weight of polyvinyl alcohol is 85,000-100,000, and the number average molecular weight of polyethyleneimine is 1,800-100,000. More specifically, the mass ratio of polyvinyl alcohol to polyethyleneimine is 3:1, with the number average molecular weight of polyvinyl alcohol being 89,000, 90,000, 95,000, or 98,000; and the number average molecular weight of polyethyleneimine being 1,800, 10,000, 70,000, or 100,000.

[0012] Polyvinyl alcohol (PVA) possesses excellent hydrophilicity and film-forming ability. Its high molecular weight, longer chains, and stronger entanglement form the main mechanical framework of hydrogels, providing strength and toughness. Polyethylene imine (PEI), on the other hand, has a larger molecular weight range than PVA, a highly branched structure, and numerous amine groups. A single PEI molecule can simultaneously form hydrogen bonds with hydroxyl groups on multiple PVA chains, acting as a multifunctional crosslinking point. This structure significantly improves crosslinking efficiency, substantially enhancing the network's rigidity and stability. Combining the long-chain framework of PVA with the highly efficient crosslinking points of PEI produces a synergistic effect, enabling the formed hydrogel to effectively dissipate energy and maintain structural stability under stress.

[0013] In some other embodiments, the pyridine nitrogen content in the dual-polymer network crosslinked graphene composite hydrogel interfacial evaporation material is 5.0-6.0 wt%, at 1 kW·m -2 Under light conditions, the evaporation rate in 3.5 wt% brine is >2.36 kg·m³. -2 ·h -1 Specifically, the pyridine nitrogen content is 5.0, 5.5, or 6.0 wt%, at 1 kW·m -2 The evaporation rates of 3.5 wt% brine under illumination were 2.03, 2.05, 2.36, and 2.31 kg·m⁻¹, respectively. -2 ·h -1 .

[0014] In nitrogen-doped graphene oxide, hydrogen bonds form between the pyridine nitrogen / carbon surface and water molecules, weakening the hydrogen bond interactions between water clusters. This allows water molecules to escape more easily, reducing the energy required for evaporation. Nitrogen-doped graphene oxide also exhibits good hydrophilicity.

[0015] In a second aspect, the present invention provides a method for preparing the interfacial evaporation material of the dual polymer network crosslinked graphene composite hydrogel, comprising the following steps:

[0016] (1) Add graphene oxide to deionized water and stir to mix evenly to prepare graphene oxide dispersion;

[0017] (2) Ammonium citrate was added to the graphene oxide dispersion, and the mixture was ultrasonically treated and stirred at room temperature to obtain a mixed solution. The mixed solution was transferred to a hydrothermal reactor and subjected to a hydrothermal reduction reaction to obtain nitrogen-doped graphene oxide.

[0018] (3) Dissolve polyvinyl alcohol and polyethyleneimine in deionized water, stir and mix evenly to obtain a gel precursor solution;

[0019] (4) Add nitrogen-doped graphene oxide to the gel precursor solution and stir to mix evenly. Add hydrochloric acid solution to adjust the pH, and then add glutaraldehyde to carry out cross-linking reaction to obtain the reaction product. The reaction product is subjected to directional freezing (the solution is placed in a polytetrafluoroethylene directional freezing mold and directionally frozen in liquid nitrogen until the sample is completely solidified for 5-15 minutes) and freeze-thaw to obtain the composite hydrogel. After soaking and washing with deionized water, the graphene composite hydrogel interface evaporation material with double polymer network cross-linking is obtained.

[0020] The preparation process is simple and environmentally friendly. Graphene oxide is chemically modified through hydrothermal reduction, and polyvinyl alcohol and polyethyleneimine are used as gel network components. Through covalent bonding and hydrogen bonding enhancement, a graphene composite hydrogel with a dual polymer network crosslinking is formed. This composite hydrogel exhibits excellent photothermal properties, enabling reduced enthalpy of vaporization, efficient seawater evaporation, and effective seawater desalination.

[0021] In some other embodiments, in step (1), the concentration of the graphene oxide dispersion is 8-12 mg / L; specifically, the concentration of the graphene oxide dispersion is 8, 10, or 12 mg / L. Within this concentration range, the graphene oxide is more uniformly dispersed.

[0022] In step (2), the mass ratio of graphene oxide to ammonium citrate in the graphene oxide dispersion is 1:(1-7), the ultrasonic treatment time is 1-3 h, and the stirring time is 20-50 min; the hydrothermal reduction reaction temperature is 100-150 ℃, and the time is 9-12 h. Specifically, the mass ratio of graphene oxide to ammonium citrate in the graphene oxide dispersion is 1:1, 1:3, 1:5, or 1:7, the ultrasonic treatment time is 1, 2, or 3 h, and the stirring time is 20, 30, 40, or 50 min; the hydrothermal reduction reaction temperature is 100, 120, 140, or 150 ℃, and the time is 9, 10, 11, or 12 h. Within this range, the oxygen-containing / nitrogen-containing functional groups (-COOH, -OH, -N-) on the modified nitrogen-doped graphene oxide can react with the -OH of PVA and the -NH3 of PEI. + / -NH2 + It forms hydrogen bonds and electrostatic interactions, firmly anchoring it in the polymer network. Simultaneously, its sheet-like structure itself acts as a physical cross-linking point and a reinforcing filler. This ensures its long-term, stable, and efficient photothermal conversion performance.

[0023] In some other embodiments, in step (3), the mass ratio of polyvinyl alcohol to polyethyleneimine is (2-4):1, the number average molecular weight of polyvinyl alcohol is 89,000-98,000, the number average molecular weight of polyethyleneimine is 18,000-100,000, the reaction temperature for stirring and mixing is 85-95°C, and the reaction time is 20-50 min.

[0024] In some other embodiments, in step (4), the mass ratio of nitrogen-doped graphene oxide to hydrogel matrix is ​​(0.009-0.01):1, and the stirring is carried out at room temperature for 20-25 h.

[0025] The pH is 1-2, the concentration of hydrochloric acid is 0.8-1.2 mol / L, the amount of glutaraldehyde solution added is 200-400 μL, and the concentration of glutaraldehyde solution is 20-30 wt%.

[0026] Specifically, the concentration of hydrochloric acid is 0.8, 1.0 or 1.2 mol / L, the amount of glutaraldehyde solution added is 200, 300 or 400 μL, and the concentration of glutaraldehyde solution is 20, 25 or 30 wt%.

[0027] Under hydrochloric acid conditioning conditions, the amino groups of PEI are highly protonated and positively charged (-NH3). + / -NH2 + Glutaraldehyde (GA) forms strong hydrogen bonds with the hydroxyl groups (-OH) of PVA, and also exhibits electrostatic attraction with partially negatively charged PVA or anions in solution. The highly branched structure of PEI itself makes it an efficient physical cross-linking site. GA reacts with the primary amine groups (-NH2) of PEI through a Schiff base reaction to form imine bonds (-C=N-), while GA can also undergo acetalization with the hydroxyl groups of PVA. This forms a strong and stable covalent cross-linked network, significantly improving the mechanical strength, elastic modulus, swelling resistance, and long-term stability of the hydrogel.

[0028] Thirdly, this invention provides the application of the dual-polymer network crosslinked graphene composite hydrogel interfacial evaporation material of the first aspect in seawater desalination. This hydrogel evaporator exhibits a rich hydrophilic pore structure; simultaneously, it possesses photothermal properties and excellent evaporation performance, and can be used to achieve efficient light-driven interfacial seawater desalination.

[0029] In some other embodiments, the seawater desalination method involves placing a graphene composite hydrogel interfacial evaporation material as the interfacial evaporation material.

[0030] In some other embodiments, the concentration of seawater is 3.0-3.5 wt%.

[0031] The beneficial effects of this invention are:

[0032] (1) In this invention, polyvinyl alcohol and polyethyleneimine are used as gel network components. Polyvinyl alcohol is rich in hydroxyl groups. Polyethyleneimine, one of the specific gel network components, is rich in nitrogen-containing groups such as primary amines, secondary amines, and tertiary amines on its chain. Through cross-linking polymerization of polyvinyl alcohol and polyethyleneimine, a unique double-network composite structure is formed, which can provide abundant functional groups under saline conditions to bind water molecules and thus reduce the enthalpy of evaporation. Using N-GO as a photothermal material, it is embedded into the hydrogel matrix through covalent bonding and hydrogen bonding to construct a double-polymerized network cross-linked graphene composite hydrogel material PVA / PEI / N-GO.

[0033] (2) The synthesis steps of this invention are simple, and the raw materials used are inexpensive, readily available, and environmentally friendly. The N-GO after hydrothermal treatment with ammonium citrate contains 5.5% pyridine nitrogen. Hydrogen bonds are formed between the nitrogen / carbon surface and water molecules, which weakens the hydrogen bond interaction between water clusters, making it easier for water molecules to escape. This reduces the energy required for evaporation and significantly improves photothermal performance. The introduction of N-GO into the composite hydrogel network lays the foundation for seawater desalination in solar interfacial evaporation.

[0034] (3) During the seawater desalination process, the amino group of polyethyleneimine, one of the components of the composite hydrogel, becomes positively charged after protonation, which can effectively react with Na+. + Electrostatic repulsion effectively prevents salt accumulation; simultaneously, the vertically arranged hierarchical pore structure constructed through directional freezing enhances rapid water transport, achieving efficient seawater desalination. Therefore, the composite hydrogel achieves the core mechanism of efficient seawater desalination, encompassing the synergistic effects of "rapid water transport - thermal localization - ion repulsion." The overall structure of the composite hydrogel in this invention provides it with a certain degree of impact resistance to seawater and exhibits good mechanical properties.

[0035] (4) The enthalpy of water evaporation of the graphene composite hydrogel material with dual polymer network crosslinking in this invention is 1625 J / g; by introducing polymer molecules and constructing directional water channels, the evaporation capacity of seawater and good impact resistance are improved, with a 1kW·m -2 Under illumination, the evaporation rate of 3.5 wt% NaCl is 2.36 kg·m⁻². -2 ·h -1 It can achieve efficient evaporation of seawater. Attached Figure Description

[0036] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0037] Figure 1 The enthalpy diagram of evaporation of the composite hydrogel in Example 1;

[0038] Figure 2 The graph shows the evaporation rate of the composite hydrogels in Examples 1-4;

[0039] Figure 3 The XPS spectrum of the pyridine nitrogen content of the composite hydrogel in Example 1 is shown.

[0040] Figure 4 The images show digital images and infrared thermal images of the surface temperature of the composite hydrogel interface evaporation material prepared in Example 1. Among them, a is a digital image of the surface steady-state temperature under 1 sun simulated sunlight irradiation, b is an infrared thermal image of the evaporator under 1 sun simulated sunlight irradiation for 0 min, and c is an infrared thermal image of the evaporator under 1 sun simulated sunlight irradiation for 60 min.

[0041] Figure 5 The figures show the hydrophilicity test results of the nitrogen-doped graphene oxide material prepared in Example 1, where a is the contact angle at 0 s, b is the contact angle at 0.05 s, and c is the contact angle at 0.1 s. Detailed Implementation

[0042] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0043] This invention addresses the shortcomings of single carbon-based materials, such as poor hydrophilicity and low mechanical strength, which make them unsuitable for long-term seawater evaporation. Nitrogen-doped modification of graphene oxide is achieved through hydrothermal reduction. The resulting nitrogen-doped graphene oxide exhibits unique sp... 2 The hybrid carbon network and the defect structure introduced by nitrogen doping can achieve nearly 95% absorption of the solar spectrum over a wide wavelength range (200-2500nm), and the local thermal effect generated by the non-radiative recombination of electron-hole pairs is significantly better than that of traditional carbon materials.

[0044] Using polyvinyl alcohol and polyethyleneimine as the gel network components, a three-dimensional network structure with directional water transport channels is constructed by cross-linking the two polymer molecules. Nitrogen-doped graphene oxide is then covalently embedded into the cross-linked network to enhance hydrogen bonding, forming a nitrogen-doped graphene oxide-hydrogel heterostructure with photothermal effects, exhibiting significantly improved tensile strength and salt resistance. This composite system achieves stable integration of the photothermal unit and the hydrophilic matrix through hydrogen-bonded networks formed by the covalent bonding of the amino and hydroxyl groups of the gel network with graphene, providing a material basis for developing novel evaporators with high evaporation flux.

[0045] The graphene oxide (GO) used in this embodiment of the invention can be prepared by existing methods, such as the modified Hummers method, through acidic oxidation exfoliation. For example, the modified Hummers method can be used to perform strong acidic oxidation exfoliation on 325-mesh graphite powder to obtain graphene oxide (GO). For specific methods, please refer to WS Hummers, RE Offeman, Preparation of Graphitic Oxide, J Am Chem Soc 80(6) (1958) 1339-1339.

[0046] Example 1

[0047] A graphene composite hydrogel interfacial evaporation material and its synthesis method, comprising the following steps:

[0048] (1) Add GO to deionized water and stir for 10 min to make the solution evenly dispersed to prepare a GO dispersion with a concentration of 10 mg / mL.

[0049] (2) Add ammonium citrate (the mass ratio of ammonium citrate to GO is 5:1) to the GO dispersion, sonicate and stir for 30 min at room temperature to obtain a mixture; transfer the mixture to a hydrothermal reactor and heat at 120°C for 12 hours to obtain nitrogen-doped graphene oxide.

[0050] (3) Weigh polyvinyl alcohol (number average molecular weight of about 89,000-98,000) and polyethyleneimine (number average molecular weight of about 1,800), dissolve them in deionized water, wherein the mass ratio of polyvinyl alcohol to polyethyleneimine is 3:1, and stir at 90°C for 30 min to obtain a gel precursor solution.

[0051] (4) Nitrogen-doped graphene oxide (mass ratio of gel precursor solution to nitrogen-doped graphene oxide is 0.0095:1) was added to the gel precursor solution and stirred at room temperature for 24 hours. Hydrochloric acid was added to adjust the pH of the solution to 1, and then glutaraldehyde crosslinking agent (300 μL, concentration 25 wt%) was added and stirred evenly to carry out the crosslinking reaction. The reaction product was directionally frozen and freeze-thawed at -20℃ to obtain the composite hydrogel. After soaking and washing with deionized water, the double polymer network crosslinked graphene composite hydrogel interface evaporation material was obtained and labeled as PVA / PEI / N-GO. 1-5 .

[0052] Example 2

[0053] A graphene composite hydrogel interfacial evaporation material and its synthesis method are disclosed. Unlike Example 1, in step (2) of the synthesis method in this example, the mass ratio of ammonium citrate and GO is 1:1. Other preparation methods are consistent with Example 1, resulting in a graphene composite hydrogel interfacial evaporation material with a dual polymer network crosslinking, denoted as PVA / PEI / N-GO. 1-1 .

[0054] Example 3

[0055] A graphene composite hydrogel interfacial evaporation material and its synthesis method are disclosed. Unlike Example 1, in step (2) of the synthesis method in this example, the mass ratio of ammonium citrate and GO is 3:1. Other preparation methods are consistent with Example 1, resulting in a graphene composite hydrogel interfacial evaporation material with a dual polymer network crosslinking, denoted as PVA / PEI / N-GO. 1-3 .

[0056] Example 4

[0057] A graphene composite hydrogel interfacial evaporation material and its synthesis method are disclosed. Unlike Example 1, in step (2) of the synthesis method in this example, the mass ratio of ammonium citrate and GO is 7:1. Other preparation methods are consistent with Example 1, resulting in a graphene composite hydrogel interfacial evaporation material with a dual polymer network crosslinking, denoted as PVA / PEI / N-GO. 1-7 .

[0058] Example 5

[0059] A graphene composite hydrogel interface evaporation material and its synthesis method are different from those in Example 1. In step (3) of the synthesis method in this example, polyethyleneimine (number average molecular weight of 10,000) is used. Other preparation methods are the same as in Example 1 to obtain a graphene composite hydrogel interface evaporation material with dual polymer network crosslinking, denoted as PVA / PEI1 / N-GO.

[0060] Example 6

[0061] A graphene composite hydrogel interface evaporation material and its synthesis method are different from those in Example 1. In step (3) of the synthesis method in this example, polyethyleneimine (number average molecular weight of 70,000) is used. Other preparation methods are the same as in Example 1 to obtain a graphene composite hydrogel interface evaporation material with dual polymer network crosslinking, denoted as PVA / PEI7 / N-GO.

[0062] Example 7

[0063] A graphene composite hydrogel interfacial evaporation material and its synthesis method are disclosed. Unlike Example 1, in step (3) of the synthesis method in this example, polyethyleneimine (number-average molecular weight of 100,000) is used. Other preparation methods are the same as in Example 1, resulting in a graphene composite hydrogel interfacial evaporation material with a dual polymer network crosslinking, denoted as PVA / PEI. 10 / N-GO.

[0064] Comparative Example 1

[0065] A graphene composite hydrogel interface evaporation material and its synthesis method are different from those in Example 1. In this embodiment, step (2) is omitted in the synthesis method, that is, the graphene oxide is not modified by nitrogen doping. The graphene oxide from step (1) is directly added to the gel precursor solution. Other preparation methods are the same as in Example 1. A graphene composite hydrogel interface evaporation material with dual polymer network crosslinking is obtained, which is denoted as PVA / PEI / GO.

[0066] Comparative Example 2

[0067] A graphene composite hydrogel interfacial evaporation material and its synthesis method are disclosed. Unlike Example 1, in step (3) of the synthesis method in this example, polyethyleneimine (number-average molecular weight approximately 1800) is replaced in equal amounts with polyvinyl alcohol, dissolved in deionized water to prepare a gel precursor solution. Other preparation methods are consistent with Example 1, resulting in a graphene composite hydrogel interfacial evaporation material, denoted as PVA / N-GO.

[0068] Comparative Example 3

[0069] A graphene composite hydrogel interfacial evaporation material and its synthesis method are disclosed. Unlike Example 1, in step (3) of the synthesis method in this example, polyvinyl alcohol is added and replaced in equal amounts with polyethyleneimine (number-average molecular weight approximately 1800), dissolved in deionized water to prepare a gel precursor solution. Other preparation methods are the same as in Example 1, resulting in a graphene composite hydrogel interfacial evaporation material, denoted as PEI / N-GO.

[0070] Comparative Example 4

[0071] A graphene composite hydrogel interface evaporation material and its synthesis method are different from those in Example 1. In the synthesis method (3) of this example, an additional polymer such as polyvinyl acid is added, and the mass ratio of polyvinyl alcohol, polyethyleneimine and polyvinyl acid is 3:0.5:0.5. The other preparation methods are the same as those in Example 1, and a graphene composite hydrogel interface evaporation material with dual polymer network crosslinking is obtained, which is denoted as PVA / PEI / PAA / N-GO.

[0072] Performance testing

[0073] 1. The method for testing the enthalpy of evaporation is as follows: The composite hydrogel interfacial evaporation material is placed in an aluminum pan with a perforated cover and heated from 40 ℃ to 180 ℃ at a linear heating rate of 5 ℃ / min. The evaporation performance of the prepared composite hydrogel interfacial evaporation material is tested using a self-made seawater evaporation test device. The specific process is as follows:

[0074] A self-made seawater evaporation experimental apparatus includes a xenon lamp, an evaporating dish, a precision electronic balance, and insulating foam. The evaporating dish contains brine (NaCl concentration 3.5wt%-25wt%), and a composite hydrogel interfacial evaporation material and insulating foam are arranged sequentially from top to bottom within the dish. The evaporating dish is placed on the precision electronic balance. The xenon lamp (1kW·m²) is used. -2 The simulated sunlight is emitted and vertically irradiated onto the surface of the composite hydrogel interface evaporation material; a precision electronic balance is used to monitor the mass change of the simulated seawater in the evaporation dish in real time; and thermal insulation foam is used to block the simulated sunlight.

[0075] 2. The formula for calculating the evaporation rate of composite hydrogel interfacial evaporation materials is as follows:

[0076] ;

[0077] in, ρ is the evaporation rate; m is the mass change of the brine during the experiment, in kg; A is the vertical projected area of ​​the solar interface evaporator's illuminated surface, in m². 2 t represents the evaporation time, measured in hours (h).

[0078] 3. Test method for complete vaporization temperature: DSC test is used under a nitrogen atmosphere. The termination temperature (T) is extrapolated from the main endothermic peak of the DSC curve. e ).

[0079] 4. Obtain the enthalpy of evaporation using the peak comprehensive analysis function in the DSC analysis software, and indirectly obtain the total heat of evaporation by calculating the area of ​​the peak.

[0080] like Figure 1 The enthalpy diagram of evaporation of the composite hydrogel prepared in Example 1 is shown below. Figure 1 It can be seen that its enthalpy of evaporation is 1625 J / g.

[0081] like Figure 2 Examples 1-4 show composite hydrogels with different mass ratios of ammonium citrate and GO at 1 kW·m -2 The evaporation rate under light conditions at a brine concentration of 3.5 wt%. (From...) Figure 2It can be seen that as the ammonium citrate content in nitrogen-doped graphene oxide decreases, the evaporation rate of the composite hydrogel first increases and then decreases. When the mass ratio of GO to ammonium citrate is 1:5 (Example 1), the evaporation rate is the highest at 2.36 kg·m³. -2 ·h -1 .

[0082] To further verify the evaporation rate of the composite hydrogel prepared in Example 1 in salt water of different concentrations, the composite hydrogel prepared in Example 1 was sequentially subjected to evaporation at 1 kW·m -2 Evaporation rates were measured under illumination and with saline concentrations of 3.5 wt%, 20 wt%, and 25 wt%, respectively, and the measured evaporation rates were 2.36, 2.23, and 2.13 kg·m³, respectively. -2 ·h -1 .

[0083] Figure 3 The XPS spectrum of the pyridine nitrogen content of the composite hydrogel prepared in Example 1 is shown below. Figure 3 It can be seen that its pyridine nitrogen content is 5.5%.

[0084] Depend on Figure 4 As shown in 'a', under simulated sunlight irradiation (1 sun), the surface temperature of the composite hydrogel rises to 40 ℃ within 2.5 min, and the highest temperature remains at 50 ℃ within 60 min. The initial surface temperature of the composite hydrogel (0 min) is 30 ℃. Figure 4 (b) Maintain at 50 °C for 60 min ( Figure 4 (c) This further illustrates the excellent photothermal conversion effect of the composite hydrogel.

[0085] Depend on Figure 5 It can be seen that the contact angle of nitrogen-doped graphene oxide starts from 0 s ( Figure 5 a) 0.05 s ( Figure 5 (b) and 0.1 s ( Figure 5 The contact angle under c) gradually decreased to 0°, and the water droplet completely disappeared within 0.1s, indicating that it has strong hydrophilicity.

[0086] Table 1 shows the performance of the composite hydrogel interfacial evaporation material measured in this invention. The evaporation rate is measured at 1 kW·m⁻¹. -2 The values ​​were measured under illumination at a saline concentration of 3.5 wt%.

[0087] Table 1 shows the performance of the examples and comparative examples.

[0088]

[0089] As shown in Table 1, the vaporization transition of the hydrogel reflects the ability of water to escape from the hydration network of the hydrogel. The temperature required for complete vaporization of water in the hydrogel is related to the content of BW (bound water). The complete vaporization temperature of Example 1 is only 115℃. The enthalpy of evaporation of water in the hydrogel was determined by DSC. The enthalpy of evaporation of water in Example 1 is 1625 J / g, indicating that the energy of water evaporation is effectively reduced.

[0090] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A graphene composite hydrogel interfacial evaporation material, characterized in that, It includes a hydrogel matrix and nitrogen-doped graphene oxide, wherein the nitrogen-doped graphene oxide is embedded in the hydrogel matrix through covalent bonding and hydrogen bonding; The hydrogel matrix is ​​composed of polyvinyl alcohol and polyethyleneimine; the hydrogel matrix has a dual-network composite structure. The preparation method of the graphene composite hydrogel interface evaporation material includes the following steps: (1) Add graphene oxide to deionized water and stir to mix evenly to prepare graphene oxide dispersion; (2) Add ammonium citrate to the graphene oxide dispersion, and sonicate and stir at room temperature to obtain a mixture; transfer the mixture to a hydrothermal reactor and carry out a hydrothermal reduction reaction to obtain nitrogen-doped graphene oxide; (3) Dissolve polyvinyl alcohol and polyethyleneimine in deionized water, stir and mix evenly to obtain a gel precursor solution; (4) Add nitrogen-doped graphene oxide to the gel precursor solution and stir to mix evenly. Add hydrochloric acid solution to adjust the pH, and then add glutaraldehyde solution to carry out cross-linking reaction to obtain the reaction product. The reaction product is subjected to directional freezing and freezing-thawing to obtain composite hydrogel. After soaking and washing with deionized water, the graphene composite hydrogel interface evaporation material with double polymer network cross-linking is obtained.

2. The graphene composite hydrogel interfacial evaporation material according to claim 1, characterized in that, The mass ratio of nitrogen-doped graphene oxide to hydrogel matrix is ​​(0.009-0.01):1, the mass ratio of polyvinyl alcohol to polyethyleneimine is (2-4):1, the number average molecular weight of polyvinyl alcohol is 89,000-98,000, and the number average molecular weight of polyethyleneimine is 18 million-100,000.

3. The graphene composite hydrogel interfacial evaporation material according to claim 1, characterized in that, The pyridine nitrogen content in the graphene composite hydrogel interfacial evaporation material with dual polymer network crosslinking is 5.0-6.0 wt%, and it is used in a 1kW·m -2 Under light conditions, the evaporation rate in 3.5 wt% brine is >2.36 kg·m³. -2 ·h -1 .

4. A method for preparing the graphene composite hydrogel interfacial evaporation material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Add graphene oxide to deionized water and stir to mix evenly to prepare graphene oxide dispersion; (2) Add ammonium citrate to the graphene oxide dispersion, and sonicate and stir at room temperature to obtain a mixture; transfer the mixture to a hydrothermal reactor and carry out a hydrothermal reduction reaction to obtain nitrogen-doped graphene oxide; (3) Dissolve polyvinyl alcohol and polyethyleneimine in deionized water, stir and mix evenly to obtain a gel precursor solution; (4) Add nitrogen-doped graphene oxide to the gel precursor solution and stir to mix evenly. Add hydrochloric acid solution to adjust the pH, and then add glutaraldehyde solution to carry out cross-linking reaction to obtain the reaction product. The reaction product is subjected to directional freezing and freezing-thawing to obtain composite hydrogel. After soaking and washing with deionized water, the graphene composite hydrogel interface evaporation material with double polymer network cross-linking is obtained.

5. The preparation method of the graphene composite hydrogel interfacial evaporation material according to claim 4, characterized in that, In step (1), the concentration of the graphene oxide dispersion is 8-12 mg / L; In step (2), the mass ratio of graphene oxide to ammonium citrate in the graphene oxide dispersion is 1:(1-7), the ultrasonic treatment time is 1-3h, the stirring time is 20-50min, the temperature of the hydrothermal reduction reaction is 100-150℃, and the time is 9-12h.

6. The preparation method of the graphene composite hydrogel interfacial evaporation material according to claim 4, characterized in that, In step (3), the mass ratio of polyvinyl alcohol to polyethyleneimine is (2-4):1, the number average molecular weight of polyvinyl alcohol is 89,000-98,000, the number average molecular weight of polyethyleneimine is 18,000-100,000, the reaction temperature for stirring and mixing is 85-95℃, and the reaction time is 20-50 min.

7. The preparation method of the graphene composite hydrogel interfacial evaporation material according to claim 4, characterized in that, In step (4), the mass ratio of nitrogen-doped graphene oxide to hydrogel matrix is ​​(0.009-0.01):1, and the stirring is carried out at room temperature for 20-25 h. The pH is 1-2, the concentration of the hydrochloric acid is 0.8-1.2 mol / L, the amount of glutaraldehyde solution added is 200-400 μL, and the concentration of the glutaraldehyde solution is 20-30 wt%.

8. The application of the graphene composite hydrogel interfacial evaporation material according to any one of claims 1-3 in seawater desalination.

9. The application according to claim 8, characterized in that, The method of seawater desalination is to use graphene composite hydrogel interfacial evaporation material as the interfacial evaporation material.

10. The application according to claim 9, characterized in that, The concentration of seawater is 3.0-3.5 wt%.

Images