Graphene oxide film and preparation method therefor

Abstract

Disclosed in the present invention are a graphene oxide film and a preparation method therefor. The preparation method comprises the following steps: S1, mixing and dispersing a cross-linking agent solution and a graphene oxide dispersion to obtain a uniformly dispersed dispersion; S2, subjecting the dispersion to vacuum filtration on a substrate film, forming graphene oxide into a film by means of self-assembly, and drying same; and S3, stripping the film dried in step S2 from the substrate film, and then performing ultraviolet irradiation to obtain a surface-reduced graphene oxide film. In the present invention, while the stability of the graphene oxide film in water is improved, the impact on the water permeability of the film is relatively small, and relatively high treatment capacity is still maintained; and the present invention has a simple preparation process, is easy to operate and has good application prospects.

Description

A graphene oxide film and its preparation method Technical Field

[0001] This invention relates to the field of graphene films, and in particular to a graphene oxide film and its preparation method. Background Technology

[0002] Graphene oxide (GO) is the most common graphene derivative and a novel carbon material with excellent performance. It has received widespread attention in recent years. The basic structure of graphene oxide is similar to that of graphene, but the difference is that the surface and edges of graphene oxide are covered with abundant hydrophilic oxygen-containing functional groups (hydroxyl, carbonyl, carboxyl, etc.).

[0003] Graphene oxide membranes, formed by the self-assembly and stacking of single-atom sheets of graphene oxide, exhibit excellent permeability to water molecules while remaining completely impermeable to other liquids and even gases. Therefore, they have significant application value in water treatment, separation and purification of organic / water mixtures, and other fields. Due to the abundance of oxygen-containing functional groups on the graphene oxide membrane, it possesses good hydrophilicity, but this also leads to its instability in water. By modulating the oxygen-containing functional groups on graphene oxide, the stability of the graphene oxide membrane in water can be altered.

[0004] To date, existing reports on reduced graphene oxide membranes employ either physical reduction (calcination at 450-750℃) followed by filtration to form the membrane (Ming Wen, et al. Enhancing the selectivity of hydrogen isotopic water in membrane distillation by using graphene oxide. Journal of Membrane Science, 610, 118237, 2020) or chemical reduction (HI vapor reduction) after filtration of graphene oxide nanosheets (Aida Mohammadi, et al. New insights into the structure and chemical reduction of graphene oxide membranes for use in isotopic water separations. Journal of Membrane Science, 659, 120785, 2022). These methods all achieve a holistic reduction of the graphene oxide membrane, reducing the overall number of oxygen-containing functional groups and decreasing the interlayer spacing. However, while improving stability, they also significantly reduce the membrane's permeability and processing capacity.

[0005] Stable isotopes of hydrogen (protium H, deuterium D, and tritium T) have almost identical physicochemical properties, making their separation very difficult. Due to the selective permeability of graphene oxide membranes to water, and the slight difference in bond energy between hydrogen isotopes and oxygen-containing functional groups on the graphene oxide membrane, graphene oxide membranes can be used for the separation of hydrogen isotopes in water via air-gap membrane distillation.

[0006] Air-gap membrane distillation (AGMD) utilizes the air gap as a mass transfer resistance, avoiding direct contact between the liquid phase and the membrane surface, thereby improving the efficiency and stability of the distillation process. An AGMD apparatus consists of a membrane permeation cell, a steam generation section, and a condensate circulation section. One side of the membrane is in direct contact with the steam, while the condensate circulation section is in direct contact with a cold wall. An air gap exists between the membrane and the cold wall. Steam permeates through the membrane into the air gap, condenses into water upon encountering the cold wall, and the water flows down the cold wall and is collected through an outlet.

[0007] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, this invention provides a graphene oxide film and its preparation method.

[0009] The present invention adopts the following technical solution:

[0010] In a first aspect, a method for preparing a graphene oxide film is provided, comprising the following steps:

[0011] S1. Mix and disperse the crosslinking agent solution with the graphene oxide dispersion to obtain a uniformly dispersed dispersion.

[0012] S2. The dispersion is vacuum filtered on a base membrane, the graphene oxide self-assembles into a membrane, and then dried.

[0013] S3. The dried film from step S2 is peeled off from the base film and then subjected to ultraviolet irradiation to obtain a surface-reduced graphene oxide film.

[0014] Preferably, in step S1, the crosslinking agent is at least one of urea, ethylenediamine, m-phenylenediamine, and p-phenylenediamine.

[0015] Preferably, the crosslinking agent is p-phenylenediamine.

[0016] Preferably, in the dispersion of step S1, the concentration of the crosslinking agent is greater than 0 and ≤75mg / L.

[0017] Preferably, the concentration of the crosslinking agent is 75 mg / L.

[0018] Preferably, in the dispersion of step S1, the concentration of graphene oxide is 0.1-1 mg / L, more preferably 0.5 mg / L. Preferably, in step S1, dispersion is performed by ultrasonication, with an ultrasonic power of 4-40 kHz and an ultrasonication time of 30-60 min.

[0019] Preferably, in step S2: the vacuum degree of the vacuum filtration is -0.09 MPa; the base membrane is at least one of a mixed cellulose membrane, a PVDF hydrophilic membrane, and a PTFE hydrophobic membrane, and the pore size of the base membrane is 0.2-1 μm; the drying temperature is 20-60℃, and the drying time is 12-24 h.

[0020] Preferably, in step S3, the power of the ultraviolet lamp used for ultraviolet irradiation is 90-320W, and the irradiation time is 0.5-24h.

[0021] Preferably, in step S2, 10-30 mL of the dispersion is vacuum filtered on the base membrane; in step S3, the thickness of the first membrane is 100-600 nm.

[0022] In a second aspect, a graphene oxide film is provided, which is prepared by the preparation method described in the first aspect.

[0023] Preferably, the thickness of the graphene oxide film is 100-600 nm, and the interlayer spacing is greater than 0.820 nm and ≤0.914 nm.

[0024] The present invention has the following advantages:

[0025] (1) Adding a crosslinking agent can not only shorten the self-assembly time of the membrane (the membrane formation time of this invention is only about one-sixth of the time required for filtration of graphene oxide dispersion without crosslinking agent), but also regulate and stabilize the interlayer spacing of the graphene oxide membrane (by controlling the concentration of the crosslinking agent, the interlayer spacing of the graphene oxide membrane can be regulated. At the same time, the crosslinking agent can stabilize the interlayer spacing of the membrane and reduce the hydration effect of the membrane (hydration effect: when the membrane is immersed in water, water molecules insert into the membrane to form a hydration layer, resulting in a larger interlayer spacing)). Taking p-phenylenediamine as a crosslinking agent as an example, when the concentration of p-phenylenediamine varies in the range of 0-75 mg / L, the interlayer spacing of the graphene oxide membrane can vary between 0.820-0.914 nm.

[0026] (2) Through the synergistic effect of crosslinking and UV irradiation surface reduction, UV irradiation only reduces the membrane surface (the degree of surface reduction can be controlled by controlling the UV irradiation time and / or power), which improves the hydrophobicity of the membrane surface. At the same time, the crosslinking agent ensures that the membrane still maintains a high level of interlayer channels for water molecule transport, which greatly improves the stability of the graphene oxide membrane in aqueous solution.

[0027] Therefore, this invention improves the stability of graphene oxide membranes in water while having little impact on the membrane's permeability, retaining high processing capacity. Furthermore, the preparation process is simple, easy to operate, and has good application prospects. Attached Figure Description

[0028] Figure 1 is a cross-sectional SEM image of the graphene oxide film prepared in Example 1 of the present invention;

[0029] Figure 2 is a surface SEM image of the graphene oxide film prepared in Example 1 of the present invention;

[0030] Figure 3 shows the interlayer spacing data of graphene oxide films obtained by crosslinking different concentrations of p-phenylenediamine according to Examples 1-4 and Comparative Example 1 of the present invention.

[0031] Figure 4 is a photograph of the graphene oxide film prepared in Example 1 of the present invention.

[0032] Figure 5 is a comparison of the stability of the graphene oxide membrane prepared in Example 1 of the present invention and the original GO membrane in water.

[0033] Figure 6 is a comparison of the infrared spectral data of the film after peeling in Example 1 before and after UV irradiation;

[0034] Figure 7 is a comparison of the XRD data of the film after peeling in Example 1 before and after UV irradiation. Detailed Implementation

[0035] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0036] This invention provides a method for preparing a graphene oxide film, comprising the following steps:

[0037] S1. Mix and disperse the crosslinking agent solution with the graphene oxide dispersion to obtain a uniformly dispersed dispersion (this dispersion is the crosslinked graphene oxide dispersion).

[0038] S2. The dispersion is vacuum filtered on a base membrane, the graphene oxide self-assembles into a membrane, and then dried.

[0039] S3. The dried film from step S2 is peeled off from the base film and then subjected to ultraviolet irradiation to obtain a surface-reduced graphene oxide film.

[0040] In the above technical solution, the interlayer spacing of the graphene oxide film can be controlled by adjusting the concentration of the crosslinking agent, and the degree of surface reduction can be controlled by adjusting the time and / or power of ultraviolet irradiation. The synergistic effect of crosslinking and ultraviolet irradiation surface reduction can improve the stability of the graphene oxide film in water and ensure its high processing capacity.

[0041] In a preferred embodiment, in step S1, the crosslinking agent is at least one of urea, ethylenediamine, m-phenylenediamine, and p-phenylenediamine; more preferably, the crosslinking agent is p-phenylenediamine.

[0042] In a preferred embodiment, in the dispersion of step S1, the concentration of the crosslinking agent is greater than 0 and ≤75 mg / L, preferably 75 mg / L.

[0043] In a preferred embodiment, the concentration of graphene oxide in the dispersion in step S1 is 0.1-1 mg / L, preferably 0.5 mg / L. In a preferred embodiment, in step S1, dispersion is performed by ultrasonication at a power of 4-40 kHz for a duration of 30-60 min.

[0044] In a preferred embodiment, in step S2: the vacuum degree of the vacuum filtration is -0.09 MPa; the base membrane is at least one of a mixed cellulose membrane, a PVDF hydrophilic membrane, and a PTFE hydrophobic membrane, and the pore size of the base membrane is 0.2-1 μm; the drying temperature is 20-60℃, and the drying time is 12-24 h.

[0045] In a preferred embodiment, in step S3, the power of the ultraviolet lamp used for ultraviolet irradiation is 90-320W, and the irradiation time is 0.5-24h.

[0046] In a preferred embodiment, in step S2, 10-30 mL of the dispersion is vacuum filtered on a base membrane; in step S3, the thickness of the first membrane is 100-600 nm.

[0047] A specific embodiment of the present invention also provides a graphene oxide film, which is prepared by the aforementioned preparation method.

[0048] In a preferred embodiment, the thickness of the graphene oxide film is 100-600 nm, and the interlayer spacing is greater than 0.820 nm and ≤0.914 nm.

[0049] The following describes specific embodiments of the present invention.

[0050] Example 1

[0051] This embodiment provides a graphene oxide film, the preparation method of which includes the following steps:

[0052] Dissolve 300 mg of p-phenylenediamine in 1 L of deionized water to prepare a 300 mg / L p-phenylenediamine aqueous solution; take 100 mg of monolayer graphene oxide powder with a diameter of 0.5–5 μm and a thickness of 0.8–1.2 nm, add it to 100 mL of water, and sonicate at 40 kHz for 30 min to prepare a 1 mg / mL graphene oxide dispersion.

[0053] Take 5 mL of the above p-phenylenediamine solution, 10 mL of the above graphene oxide dispersion, and 5 mL of deionized water, mix them, and then ultrasonically disperse for 30 min to obtain a dispersion in which the concentration of p-phenylenediamine is 75 mg / L.

[0054] Using a mixed cellulose membrane with a pore size of 0.2 μm as the base membrane, the obtained dispersion was vacuum filtered under vacuum with a vacuum pump pressure of -0.09 MPa.

[0055] After filtration, the membrane was dried at room temperature for 24 hours. After peeling, the membrane was placed under a 192W UV lamp for 4 hours to obtain a partially reduced graphene oxide membrane with high water stability and high processing capacity. The cross-sectional SEM image and surface SEM image of the graphene oxide membrane are shown in Figures 1 and 2, respectively. As shown in Figure 3, the interlayer spacing of the graphene oxide membrane is 0.914 nm. Figure 4 shows a photograph of the actual graphene oxide membrane. Figure 6 shows a comparison of the infrared spectral data of the membrane before and after UV irradiation in Example 1. Figure 7 shows a comparison of the XRD data of the membrane before and after UV irradiation in Example 1. The membrane before UV irradiation is represented by "GO" in Figures 6 and 7, and the membrane after UV irradiation is represented by "GO-UV" in Figures 6 and 7.

[0056] When the graphene oxide membrane prepared in this invention is applied to an air-gap membrane distillation experiment, the water permeation flux (the volume of water passing through a unit area of ​​membrane per unit time, i.e., membrane flux, i.e., permeation flux) is 11.8 L·m⁻¹. In the air-gap membrane distillation experiment, the water sample permeating through the membrane is collected, and the membrane flux can be calculated by recording the time taken, the effective membrane area, and the amount of water sample obtained. -2 ·h -1 .

[0057] Example 2

[0058] The difference from Example 1 is that the concentration of p-phenylenediamine in the dispersion is 12.5 mg / L, as shown in Figure 3, and the interlayer spacing of the graphene oxide film is 0.828 nm.

[0059] Example 3

[0060] The difference from Example 1 is that the concentration of p-phenylenediamine in the dispersion is 25 mg / L, as shown in Figure 3, and the interlayer spacing of the graphene oxide film is 0.831 nm.

[0061] Example 4

[0062] The difference from Example 1 is that the concentration of p-phenylenediamine in the dispersion is 50 mg / L, as shown in Figure 3, and the interlayer spacing of the graphene oxide film is 0.844 nm.

[0063] Comparative Example 1

[0064] The difference from Example 1 is that no crosslinking agent was used. Instead, 20 mL of graphene oxide dispersion (graphene concentration of 0.5 mg / L) was directly filtered to form a film (referred to as the "original GO membrane"), as shown in Figure 3. The interlayer spacing of this graphene oxide membrane is 0.820 nm. The stability of the graphene oxide membrane obtained in Example 1 (referred to as "this product" in Figure 5) was compared with that of the original GO membrane in Comparative Example 1, and the results are shown in Figure 5.

[0065] Comparative Example 2

[0066] When a high-temperature reduced graphene oxide membrane (preparation method see "Ming Wen, et al. Enhancing the selectivity of hydrogen isotopic water in membrane distillation by using graphene oxide. Journal of Membrane Science, 610, 118237, 2020") was applied to an air-gap membrane distillation experiment, the water permeation flux was 0.47 L·m⁻¹. -2 ·h -1 .

[0067] Comparative Example 3

[0068] When HI-reduced graphene oxide membranes (preparation method see "Aida Mohammadi, et al. New insights into the structure and chemical reduction of graphene oxide membranes for use in isotopic water separations. Journal of Membrane Science, 659, 120785, 2022") were applied to air-gap membrane distillation experiments, the water permeation flux was 6.06 L·m⁻¹. -2 ·h -1 .

[0069] Applying the graphene oxide membrane in this invention to the field of AGMD fully considers the influence of hydration. Specifically, due to the hydration of the membrane, the interlayer spacing may not remain stable for a long time. This invention improves the stability of the membrane in water by generating hydrophobicity through UV reduction and inhibiting hydration through crosslinking. The graphene oxide membrane in this invention has the advantages of controllable interlayer spacing, good stability in water, and high processing capacity.

[0070] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for preparing a graphene oxide film, characterized in that, Includes the following steps: S1. Mix and disperse the crosslinking agent solution with the graphene oxide dispersion to obtain a uniformly dispersed dispersion. S2. The dispersion is vacuum filtered on a base membrane, the graphene oxide self-assembles into a membrane, and then dried. S3. The dried film from step S2 is peeled off from the base film and then subjected to ultraviolet irradiation to obtain a surface-reduced graphene oxide film.

2. The preparation method according to claim 1, characterized in that: In step S1, the crosslinking agent is at least one of urea, ethylenediamine, m-phenylenediamine, and p-phenylenediamine; preferably, the crosslinking agent is p-phenylenediamine.

3. The preparation method according to claim 1, characterized in that: In the dispersion of step S1, the concentration of the crosslinking agent is greater than 0 and ≤75 mg / L, preferably, the concentration of the crosslinking agent is 75 mg / L.

4. The preparation method according to claim 1, characterized in that: In the dispersion of step S1, the concentration of graphene oxide is 0.1-1 mg / L, preferably 0.5 mg / L.

5. The preparation method according to claim 1, characterized in that: In step S1, dispersion is achieved by ultrasound, with a power of 4-40 kHz and an ultrasound duration of 30-60 min.

6. The preparation method according to claim 1, characterized in that, In step S2: the vacuum degree of the vacuum filtration is -0.09MPa; the base membrane is at least one of mixed cellulose membrane, PVDF hydrophilic membrane, and PTFE hydrophobic membrane, and the pore size of the base membrane is 0.2-1μm; the drying temperature is 20-60℃, and the drying time is 12-24h.

7. The preparation method according to claim 1, characterized in that: In step S3, the power of the ultraviolet lamp used for ultraviolet irradiation is 90-320W, and the irradiation time is 0.5-24h.

8. The preparation method according to claim 1, characterized in that: In step S2, 10-30 mL of the dispersion is vacuum filtered on the base membrane; in step S3, the thickness of the first membrane is 100-600 nm.

9. A graphene oxide film, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The graphene oxide film as described in claim 9, characterized in that, The thickness of the graphene oxide film is 100-600 nm, and the interlayer spacing is greater than 0.820 nm and ≤0.914 nm.

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