A two-dimensional layered liquid crystal graphene-based aerogel interface evaporator and a preparation method thereof

Abstract

The application discloses a preparation method and application of an aerogel interface evaporator based on two-dimensional layered liquid crystal graphene oxide. The application takes aerogel as a base material, sprays liquid crystal graphene oxide, and obtains the interface evaporator through drying, light reduction and other processes. The application adopts a spraying method to load the liquid crystal graphene oxide on the aerogel, and uses a xenon lamp to irradiate and reduce the LGO film, thereby preparing the interface solar evaporator. The liquid crystal graphene oxide is sprayed on the aerogel, the graphene oxide dispersion liquid can quickly form the LGO film under the irradiation of the xenon lamp, the preparation time of the solar evaporator is greatly shortened, and the light reduction of the xenon lamp helps to increase the light-heat conversion performance and the evaporation rate of the evaporator. The evaporation rate of the aerogel evaporator with the two-dimensional ordered photo-thermal interface constructed by the method can reach 3.15 kg / m 2 ·h, and the aerogel evaporator has a wide application prospect in the field of solar seawater desalination.

Description

Technical Field

[0001] This invention belongs to the field of solar-powered seawater desalination, specifically relating to an aerogel interface evaporator based on two-dimensional layered liquid crystal graphene oxide and its preparation method. Background Technology

[0002] Seawater desalination and wastewater treatment are among the most important and effective ways to solve the problem of freshwater scarcity. Conventional seawater desalination methods include multi-stage distillation, multi-stage flash distillation, steam compression distillation, reverse osmosis, electrodialysis, ion exchange, and freezing, all of which consume large amounts of fossil fuels. Conventional wastewater treatment methods include gravity separation, centrifugation, filtration, membrane separation, biological oxidation ponds, anaerobic biological treatment, and biological contact oxidation. Some of these methods result in additional fossil fuel consumption, while others produce water with limited quality.

[0003] Solar energy is a renewable and clean energy source that is inexhaustible. Therefore, utilizing solar energy through light-to-thermal conversion for solar-driven water evaporation is one of the effective ways to achieve seawater desalination and wastewater treatment, thereby obtaining clean water. Although using solar evaporators for seawater desalination can effectively improve energy utilization, solar evaporators still face problems such as heat loss, low evaporation rates, and salt deposition.

[0004] Graphene oxide (GO)-based membranes possess sub-nanometer interlayer channels, enabling efficient water transport through a combination of spatial confinement, capillary action, and the Marangoni effect. Furthermore, the interlayer spacing of GO membranes is adjustable, allowing for the sieving of molecules of different sizes. GO is also an excellent photothermal material, thus GO membranes hold great promise for applications in solar evaporation. However, current methods for preparing GO membranes often encounter stacking defects and dead zones, affecting water mass transfer within the membrane and significantly reducing evaporation rates, thus limiting their application in solar evaporators. Additionally, most existing methods involve loading two-dimensional GO membranes onto other materials using vacuum filtration. While this method can effectively prepare GO membranes, it requires external energy input. If the amount of GO introduced is too large, the preparation time becomes extremely long when the deposited GO membrane thickness reaches micrometers. Therefore, rapidly preparing ordered two-dimensional GO membranes is crucial for improving evaporation rates. In addition, sufficient water supply and reduced heat loss are also key factors for improving the evaporation rate. However, the direct contact between the two-dimensional GO membrane and the water body will inevitably cause heat loss. Therefore, how to combine the two-dimensional GO membrane with a matrix material with excellent thermal insulation and water conveyance properties and how to further improve the evaporation rate have become the focus of research. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide an aerogel interface evaporator based on two-dimensional layered liquid crystal graphene oxide and its preparation method. Liquid crystal graphene oxide is loaded onto a substrate material with excellent thermal insulation and water transport properties via spraying. By adjusting parameters such as the concentration and loading amount of the liquid crystal graphene oxide, a high-evaporation-rate aerogel interface evaporator is achieved, thus solving the problem of low evaporation rates in existing graphene oxide film-based solar interface evaporators. The method of the present invention is easy to operate and convenient to use.

[0006] To achieve the above objectives, the present invention first provides a method for preparing an aerogel interface evaporator based on two-dimensional layered liquid crystal graphene oxide, comprising the following steps:

[0007] (1) Preparation of liquid crystal graphene oxide (LGO): Graphite powder was added to concentrated sulfuric acid and concentrated phosphoric acid, then potassium permanganate was added and stirred at room temperature until the reaction was complete. Then hydrogen peroxide solution was added dropwise to deionized water until the mixture turned golden yellow. The mixture was allowed to stand and separate into layers, centrifuged to collect the precipitate, washed several times with dilute hydrochloric acid solution and dialyzed in water to obtain LGO.

[0008] (2) Preparation of aerogel substrate: The polymer is dissolved to form a gel, which is placed on a copper platform connected to a vacuum freeze dryer and then freeze-dried in a directional manner to obtain aerogel;

[0009] (3) Preparation of interfacial solar evaporator: The LGO prepared in step (1) is sprayed onto the aerogel prepared in step (2), dried, and then the LGO film is reduced with a xenon lamp to obtain the interfacial solar evaporator.

[0010] In one embodiment of the present invention, the mass-to-volume ratio of graphite powder to concentrated sulfuric acid in step (1) is 1-4 g: 120-480 mL, and the volume ratio of concentrated sulfuric acid to concentrated phosphoric acid is 8:1-10:1.

[0011] In one embodiment of the present invention, the concentrated sulfuric acid in step (1) has a mass fraction of 80-98 wt%, and the concentrated phosphoric acid has a concentration of 85-90 wt%.

[0012] In one embodiment of the present invention, the amount of potassium permanganate added in step (1) is 4 to 10 times the mass of graphite powder.

[0013] In one embodiment of the present invention, the amount of potassium permanganate added in step (1) is 2 to 3 times the mass of graphite powder first, and then 1 to 2 times the mass of graphite powder every 24 hours, with a stirring time of 48 to 96 hours.

[0014] In one embodiment of the present invention, the volume ratio of deionized water to concentrated sulfuric acid in step (1) is 3 to 4:1, and the mass fraction of hydrogen peroxide is 30%.

[0015] In one embodiment of the present invention, the mass concentration of the dilute hydrochloric acid aqueous solution in step (1) is 1.5-2%, the dialysis time is 3-6 days, and the amount of dialysis solution used is 1.5-2L.

[0016] In one embodiment of the present invention, the polymer used in step (2) is any one or more of polyvinyl alcohol, sodium alginate, and cellulose nanofibers, the dissolution temperature is 60-90°C, the solvent is water, and the dissolution time is 1-3 hours.

[0017] In one embodiment of the present invention, the gel in step (2) is a gel formed by dissolving polyvinyl alcohol and glutaraldehyde in water, wherein the mass-to-volume ratio of polyvinyl alcohol and glutaraldehyde is (0.3-1) g:(0.04-0.25) mL, and the volume ratio of glutaraldehyde to water is 0.04-0.25:3-10.

[0018] In one embodiment of the present invention, the gel in step (2) is a gel formed by mixing polyvinyl alcohol, cellulose nanofibers and water, wherein the mass ratio of polyvinyl alcohol to cellulose nanofibers is 2-6:1-4, and the mass ratio of polyvinyl alcohol to water is (0.2-0.6):(3-10).

[0019] In one embodiment of the present invention, the gel in step (2) is a gel formed by sodium alginate, calcium chloride and water, wherein the mass-volume ratio of sodium alginate and calcium chloride is (0.3-1) g:(0.3-0.8) mL, and the volume ratio of calcium chloride and water is 0.3-0.8:3-10.

[0020] In one embodiment of the present invention, the freezing temperature in step (2) is -100 to -60°C, the freezing time is 2 to 5 hours, the vacuum degree of the vacuum freeze dryer is 0.1 to 20 Pa, and the drying time is 48 to 96 hours.

[0021] In one embodiment of the present invention, the LGO concentration used in step (3) is 1-20 mg / mL, preferably 10-20 mg / mL, and the surface area of ​​the aerogel is 10-15 cm². -2 The volume of LGO is 0.5 to 2 mL.

[0022] In one embodiment of the present invention, the spraying distance in step (3) is 10-15 cm and the spraying pressure is 30-50 bar.

[0023] In one embodiment of the present invention, the drying temperature in step (3) is 45-60°C and the drying time is 5-10 hours.

[0024] In one embodiment of the present invention, the reduction light intensity of the xenon lamp in step (3) is 1-3 KW / m. 2 •h, the reduction time is 2 to 10 hours.

[0025] Based on the above method, this invention provides an aerogel interface evaporator based on two-dimensional layered LGO.

[0026] This invention relates to the application of a two-dimensional layered LGO-based aerogel interface evaporator prepared by the above method in the field of solar seawater desalination.

[0027] The beneficial effects of this invention are as follows:

[0028] (1) The present invention uses a spraying method to load liquid crystal graphene oxide onto aerogel and uses xenon lamp irradiation to reduce the LGO film to prepare an interfacial solar evaporator. By spraying liquid crystal graphene oxide onto aerogel, the graphene oxide dispersion can quickly form an LGO film under xenon lamp irradiation, which greatly shortens the preparation time of the solar evaporator. Furthermore, xenon lamp irradiation reduction helps to increase the photothermal conversion performance and evaporation rate of the evaporator.

[0029] (2) By adding potassium permanganate in batches, the present invention helps to control the oxidation rate of graphene in order to prepare large-sized LGO nanosheets. As the LGO concentration increases, the interaction between layers is enhanced and an ordered liquid crystal phase is formed, which can effectively improve the stacking defects and dead zones in the film-making process, increase the transport rate of water molecules and inhibit salt deposition.

[0030] (3) The aerogel material prepared by the method of the present invention has a vertical pore structure, which can effectively promote water transport capacity, so that water can be transported to the evaporation interface and reduce heat loss.

[0031] (4) The aerogel evaporator with a two-dimensional ordered photothermal interface constructed using the method of this invention exhibits excellent evaporation performance, with an evaporation rate as high as 3.15 kg / m³. 2 ·h is beneficial for alleviating water and energy shortages and has broad application prospects in the field of solar-powered seawater desalination. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of the aerogel prepared in Example 1 of the present invention.

[0033] Figure 2 This is a scanning electron microscope image of the two-dimensional ordered photothermal interface layer prepared in Example 1 of the present invention. Detailed Implementation

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] Methods for testing evaporation rate:

[0036] The parameters were selected under xenon lamp irradiation at 1 solar intensity, using water as the evaporator. The interfacial evaporator was placed in polystyrene foam, and then placed in a beaker containing the evaporator. The mass loss in the beaker was recorded every 5 minutes at 25°C, and the evaporation rate and evaporation efficiency were calculated using formulas.

[0037] Formula for water evaporation rate:

[0038]

[0039] Where m0 is the initial mass of the device, m1 is the mass of the device after evaporation for a certain period of time, s represents the projected area of ​​the aerogel evaporator, and t is the time of sunlight irradiation.

[0040] Evaporation efficiency formula:

[0041]

[0042] Where v is the water evaporation rate (kg / m³) measured by the solar evaporator. 2 •h, total water evaporation minus natural evaporation without sunlight exposure); Q i The solar radiation intensity provided per hour (1KW / m) 2 ·h), H LV It is the total enthalpy change of the liquid-gas phase transition (2257 KJ / kg).

[0043] Example 1

[0044] A method for preparing an aerogel interfacial evaporator based on two-dimensional layered LGO includes the following steps:

[0045] (1) Preparation of liquid crystal graphene oxide (LGO): 2g of 325-mesh flake graphite was added to 240mL of 98wt% concentrated sulfuric acid and 27mL of 86wt% concentrated phosphoric acid. After stirring evenly, 6g of potassium permanganate was slowly added, and stirring was continued at a constant speed at room temperature. 2g of potassium permanganate was added every 24 hours for a total of 3 times. After the reaction was completed, the mixture was slowly poured into 800mL of deionized water, and 30wt% hydrogen peroxide was added dropwise until the mixture turned golden yellow. The mixture was allowed to stand and separate into layers. The precipitate was collected by centrifugation and washed several times with 1.8% dilute hydrochloric acid and deionized water until the pH value was close to 5-6 to obtain LGO.

[0046] (2) Dissolve 0.5g polyvinyl alcohol and 0.126mL glutaraldehyde in 5mL water at 90℃, remove air bubbles under vacuum, then add 0.05mL 1.2mol / L hydrochloric acid solution, let stand for 1h to form a gel, freeze on a copper platform at -70℃ for 2h, freeze dry under vacuum for 48h at a vacuum degree of 5Pa to obtain aerogel.

[0047] (3) Spray 1 mL of 15 mg / mL LGO onto the aerogel. The aerogel surface is circular with a surface area of ​​10 cm². -2 Dry in an oven at 45℃, then place under light intensity of 1KW / m 2 An interfacial evaporator was obtained by irradiating the sample under a xenon lamp for 2 hours.

[0048] The interfacial evaporator prepared in Example 1 was characterized, and the results are shown in the figure. Figures 1-2 . Figure 1 The image shown is a scanning electron microscope image of the hydrophilic aerogel prepared in Example 1 of this invention. The aerogel exhibits a vertical pore structure. Figure 2 The image shown is a scanning electron microscope image of the two-dimensional photothermal interface layer prepared in Example 1 of the present invention. The cross-section shows a two-dimensional layered structure, indicating that the two-dimensional layered film was successfully prepared.

[0049] Example 2

[0050] The difference between Example 2 and Example 1 is that the concentration of LGO in step (3) is different. In Example 2, the concentration of LGO in step (3) is 1 mg / mL.

[0051] Example 3

[0052] The difference between Example 3 and Example 1 is that the concentration of LGO in step (3) is different. In Example 3, the concentration of LGO in step (3) is 5 mg / mL.

[0053] Example 4

[0054] The difference between Example 4 and Example 1 is that the concentration of LGO in step (3) is different. In Example 4, the concentration of LGO in step (3) is 10 mg / mL.

[0055] Example 5

[0056] The difference between Example 5 and Example 1 is that the concentration of LGO in step (3) is different. In Example 5, the concentration of LGO in step (3) is 20 mg / mL.

[0057] The interfacial evaporators prepared in Examples 1-5 were tested. The results are shown in Table 1.

[0058] Table 1. Evaporation rates of the interfacial evaporators prepared in Examples 1-5

[0059] test LGO concentration (mg / mL) <![CDATA[Evaporation rate (kg / m 2 ·h)]]> Evaporation efficiency (%) Example 1 15 3.15 198 Example 2 1 2.48 155 Example 3 5 2.64 165 Example 4 10 2.82 177 Example 5 20 2.96 186

[0060] As shown in Table 1, when the total LGO loading remains constant, both the evaporation rate and evaporation efficiency initially increase and then decrease with increasing concentration. The evaporation rate and evaporation efficiency reach their maximum at an LGO concentration of 15 mg / mL, both reaching 3.15 kg / mL. 2 ·h and 198%.

[0061] Example 6

[0062] The difference between Example 6 and Example 1 is that the volume of LGO in step (3) is different. In Example 6, the volume of LGO in step (3) is 0.5 mL.

[0063] Example 7

[0064] The difference between Example 7 and Example 1 is that the volume of LGO in step (3) is different. In Example 7, the volume of LGO in step (3) is 1.5 mL.

[0065] Example 8

[0066] The difference between Example 8 and Example 1 is that the volume of LGO in step (3) is different. In Example 8, the volume of LGO in step (3) is 2 mL.

[0067] The interfacial evaporators prepared in Examples 6-8 were tested. The results are shown in Table 2.

[0068] Table 2. Evaporation rates of the interfacial evaporators prepared in Examples 6-8

[0069] test LGO volume (mL) <![CDATA[Evaporation rate (kg / m 2 ·h)]]> Evaporation efficiency (%) Example 6 0.5 2.86 179 Example 7 1.5 3.02 189 Example 8 2 2.95 185

[0070] As shown in Table 2, with the increase of LGO dosage, the evaporation rate and evaporation efficiency first increase and then decrease.

[0071] Example 9

[0072] The difference between Example 9 and Example 1 lies in the preparation method of the aerogel in step (2). The preparation method of the aerogel in step (2) of Example 9 is as follows:

[0073] Dissolve 0.5g sodium alginate in 5mL of water at 60℃, remove air bubbles under vacuum, then add 0.5mL of 0.1mol / L calcium chloride solution to form a gel. Freeze on a copper platform at -70℃ for 2h, then freeze-dry under vacuum for 48h at a vacuum degree of 5Pa to obtain an aerogel.

[0074] The evaporation rate of the interfacial evaporator prepared in Example 9 was tested to be 2.54 kg / m³. 2 ·h.

[0075] Example 10

[0076] The difference between Example 10 and Example 1 lies in the preparation method of the aerogel in step (2). The preparation method of the aerogel in step (2) of Example 10 is as follows:

[0077] 0.2g of cellulose nanofibers were added to 2mL of water, and 0.3g of polyvinyl alcohol was added to 3mL of water and dissolved at 90℃. The air bubbles were removed under vacuum, and the mixture was mixed evenly to form a gel. The gel was then frozen on a copper table at -70℃ for 2h and freeze-dried under vacuum for 48h at a vacuum degree of 5Pa to obtain an aerogel.

[0078] The evaporation rate of the interfacial evaporator prepared in Example 10 was tested to be 2.34 kg / m³. 2 ·h.

[0079] Example 11

[0080] The difference between Example 11 and Example 1 is that the xenon lamp irradiation time in step (3) is different. In Example 11, the xenon lamp irradiation time in step (3) is 10 hours.

[0081] The evaporation rate of the interfacial evaporator prepared in Example 11 was tested to be 3.12 kg / m³. 2 The value of ·h indicates that the irradiation time has little effect; in fact, longer xenon lamp irradiation can actually reduce the evaporation rate.

[0082] Example 12

[0083] The difference between Example 12 and Example 1 is that in step (1), 12g of potassium permanganate is added at once and the reaction is carried out for 24 hours.

[0084] The evaporation rate of the interfacial evaporator prepared in Example 12 was tested to be 3.04 kg / m³. 2 ·h.

[0085] Comparative Example 1

[0086] The difference between Comparative Example 1 and Example 1 is that the xenon lamp irradiation step in step (3) is omitted.

[0087] When the interface evaporator is not irradiated with a xenon lamp, the color of the two-dimensional photothermal interface becomes lighter, and the photothermal conversion performance of the resulting evaporator weakens, reaching only 86% of that after irradiation.

[0088] Comparative Example 2

[0089] 1 mL of 15 mg / mL LGO was dispersed in 50 mL of aqueous solution and loaded onto a macroporous polyethersulfone membrane by vacuum filtration, with a membrane preparation time of up to 10 hours; while the spray coating method can complete the membrane preparation in a few minutes.

[0090] Comparative Example 3

[0091] The difference between Comparative Example 3 and Example 1 is that the aerogel from step (2) was directly impregnated in LGO, resulting in a two-dimensional layered film with uneven thickness.

[0092] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing an aerogel interface evaporator based on two-dimensional layered liquid crystal graphene oxide, characterized in that, Includes the following steps: (1) Preparation of liquid crystal graphene oxide: Graphite powder was added to concentrated sulfuric acid and concentrated phosphoric acid, then potassium permanganate was added and stirred at room temperature until the reaction was complete. Then hydrogen peroxide solution was added dropwise to deionized water until the mixture turned golden yellow. The mixture was allowed to stand and separate into layers, centrifuged to collect the precipitate, washed several times with dilute hydrochloric acid solution and dialyzed in water to obtain LGO. (2) Preparation of aerogel substrate: The polymer is dissolved to form a gel, which is placed on a copper platform connected to a vacuum freeze dryer and subjected to directional freeze drying to obtain an aerogel; the gel is a gel formed by dissolving polyvinyl alcohol and glutaraldehyde in water, wherein the mass-volume ratio of polyvinyl alcohol to glutaraldehyde is (0.3~1) g:(0.04~0.25) mL, and the volume ratio of glutaraldehyde to water is 0.04~0.25:3~10; (3) Preparation of interfacial solar evaporator: The LGO prepared in step (1) is sprayed onto the aerogel prepared in step (2), dried at 45~60 ℃ for 5~10 h, and then the LGO film is reduced with a xenon lamp to obtain the interfacial solar evaporator.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass-to-volume ratio of graphite powder to concentrated sulfuric acid is 1-4 g: 120-480 mL, the amount of potassium permanganate added is 4-10 times the mass of graphite powder, the volume ratio of concentrated sulfuric acid to concentrated phosphoric acid is 8:1-10:1, the mass fraction of the concentrated sulfuric acid is 80-98 wt%, and the mass fraction of the concentrated phosphoric acid is 85-90 wt%.

3. The preparation method according to claim 1, characterized in that, In step (1), the amount of potassium permanganate added is 2 to 3 times the weight of graphite powder first, and then 1 to 2 times the weight of graphite powder every 24 hours. The stirring time is 48 to 96 hours.

4. The preparation method according to claim 1, characterized in that, In step (1), the volume ratio of deionized water to concentrated sulfuric acid is 3~4:1, the mass fraction of hydrogen peroxide is 30%, the mass concentration of dilute hydrochloric acid aqueous solution is 1.5~2%, the dialysis time is 3~6 days, and the volume of dialysis solution used is 1.5~2 L.

5. The preparation method according to claim 1, characterized in that, The polymer used in step (2) is any one or more of polyvinyl alcohol, sodium alginate, and cellulose nanofibers. The dissolution temperature is 60~90℃, the solvent is water, and the dissolution time is 1 h~3 h.

6. The preparation method according to claim 1, characterized in that, The freezing temperature in step (2) is -100 ~ -60 ℃, the freezing time is 2 ~ 5 h, the vacuum degree of the vacuum freeze dryer is 0.1 ~ 20 Pa, and the drying time is 48 ~ 96 h.

7. The preparation method according to claim 1, characterized in that, The LGO concentration used in step (3) is 1~20 mg / mL, and the surface area of ​​the aerogel is 10~15 cm². -2 The LGO volume is 0.5~2 mL, the spraying distance is 10~15 cm, the spraying pressure is 30~50 bar, and the xenon lamp reduction light intensity is 1~3 KW / m. 2 •h, the reduction time is 2~10 h.

8. An aerogel interface evaporator based on two-dimensional layered liquid crystal graphene oxide prepared by the method according to any one of claims 1 to 7.

9. The application of the aerogel interface evaporator based on two-dimensional layered liquid crystal graphene oxide as described in claim 8 in the field of solar seawater desalination.

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