CN110723725B - Low-power laser reduction graphene film and preparation method thereof - Google Patents
Low-power laser reduction graphene film and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a method for improving laser reduction efficiency of a graphene oxide film by a freeze-drying method. The method comprises the following steps: (1) preparing a graphene oxide dispersion liquid; (2) placing the graphene oxide dispersion liquid obtained in the step (1) on a substrate to prepare a graphene oxide dispersion liquid film; (3) freeze-drying the graphene oxide dispersion liquid film obtained in the step (2) to prepare a graphene oxide film; (4) and (4) reducing the graphene oxide film obtained in the step (3) by laser irradiation to obtain a graphene film. The method greatly reduces the laser power, can utilize a low-power laser with the power as low as 1mW, reduces the graphene by one-step forming, has simple process, low price and environmental protection, and is suitable for large-scale production. The graphene film prepared by the invention has a three-dimensional and porous internal structure and a high specific surface area.
Description
Technical Field
The invention belongs to the technical field of graphene materials, and particularly relates to a method for improving laser reduction efficiency of a graphene oxide film by a freeze-drying method.
Background
Since the discovery in 2004, graphene has been widely studied and proved to be a material with excellent properties, such as excellent electrical conductivity, good thermal conductivity, and large specific surface area, and has been paid more and more attention by researchers. Many methods for preparing graphene have been reported so far, including mechanical exfoliation, silicon carbide pyrolytic epitaxial growth, chemical vapor deposition, graphene oxide reduction, and the like. The chemical vapor deposition method and the graphene oxide reduction method belong to simple and easy methods. The graphene oxide reduction method mainly refers to a Hummers method and a series of improved Hummers methods, and is characterized in that a strong oxidation mode is utilized, graphite powder is subjected to post-treatment, steps such as chemical oxidation stripping and centrifugation are carried out, a graphene oxide solution with a certain concentration is obtained, and then the graphene is obtained after reduction treatment (for example, vitamin C and hydrazine hydrate are added for chemical reduction, or laser and the like are utilized for irradiating graphene oxide for illumination reduction).
Compared with a chemical reduction method, the illumination reduction method can be directly applied to reduction of the graphene oxide film, and specific patterns and images are formed by irradiation of the selected area. However, the physical and chemical properties of graphene prepared by the graphene oxide reduction method are controlled by the reduction efficiency (e.g., the higher the reduction degree, the higher the conductivity), and therefore, the improvement of the reduction efficiency of graphene oxide is the key to prepare high-quality graphene.
Chinese patent document CN107161990A discloses a method for preparing a reduced graphene oxide functional heterogeneous thin film by using a laser technique one-step method, but in order to realize one-step reduction, the laser source power used therein is high (from 10W LED laser to 120W carbon dioxide laser); when a low power laser (such as a DVD optical engraving recorder) is used, as reported by Cai et al in matrix Research Express vol.4(2017)036304, multiple times of restoration (up to 25 times) are required to achieve the desired restoration effect, which greatly prolongs the time consumption of the restoration process.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method for improving the laser reduction efficiency of a graphene oxide film by a freeze-drying method. The method is wide in application range, the laser reduction of the graphene oxide film can be realized by lasers with different use powers (for example, the power is as low as 1mW), illustratively, the graphene can be reduced by one-step forming by using a laser with low power (for example, a DVD laser light engraving machine) with the power of 5mW, and compared with other modes in the prior art, the method has the characteristics of simplicity and convenience in operation, high efficiency and the like.
The purpose of the invention is realized by the following technical scheme.
A method of preparing a graphene film, the method comprising the steps of:
(1) preparing a graphene oxide dispersion liquid;
(2) placing the graphene oxide dispersion liquid obtained in the step (1) on a substrate to prepare a graphene oxide dispersion liquid film;
(3) freeze-drying the graphene oxide dispersion liquid film obtained in the step (2) to obtain a graphene oxide film;
(4) and (4) reducing the graphene oxide film obtained in the step (3) by laser irradiation to obtain a graphene film.
According to an embodiment of the present invention, in step (1), the preparation of the graphene oxide dispersion is not particularly limited, and may be commercially available or may be prepared by a conventional preparation method known to those skilled in the art; illustratively, the graphene oxide dispersion is prepared by an oxidation exfoliated graphite method (Hummers method) or a modified oxidation exfoliated graphite method. The source of the graphite is not particularly limited, and conventional graphite known to those skilled in the art may be used, and illustratively, nano graphite, natural flake graphite, and the like. The mesh number of the graphite is also not particularly limited, and may be, for example, 100-.
Specifically, taking a graphene oxide dispersion liquid of 2.4mg/ml as an example, the graphene oxide dispersion liquid can be prepared by the following method: graphite powder is used as a raw material, graphene oxide is prepared by an improved Hummers method, and the steps mainly comprise oxidizing natural graphite and ultrasonically stripping to obtain uniformly dispersed graphene oxide colloidal suspension. For example, 20ml of phosphoric acid and 180ml of concentrated sulfuric acid are firstly added into a three-neck flask with ice bath, 1.5g of graphite powder (8000 meshes) and 9g of potassium permanganate are added in turn in small amount for many times, the mixture reacts for 12 hours at 50 ℃, and after the mixture is cooled to normal temperature,adding 300ml deionized ice blocks; the reaction was poured into a large beaker and 6ml of 30% H was added2O2And 100mL of hydrochloric acid, repeatedly centrifuging, and washing with deionized water until the solution is neutral; after ultrasonic treatment, putting the mixture into a dialysis bag for dialysis for 2 weeks to prepare a graphene oxide solution; then, graphene oxide solid is obtained through freeze-drying, and the solid is taken out and diluted to 2.4 mg/ml.
According to an embodiment of the present invention, in step (1), the concentration of the graphene oxide dispersion liquid will affect the film forming property and the laser reduction efficiency, and is preferably 0.001mg/ml to 20 mg/ml; for example, 0.01mg/ml to 20 mg/ml; more preferably, the concentration of the graphene oxide dispersion liquid is 0.1mg/ml to 10.0 mg/ml; for example, the concentration is not in the range of 0.1mg/ml to 5.0 mg/ml.
According to the embodiment of the present invention, in the step (2), the method of placing the graphene oxide dispersion on the surface of the substrate may be selected according to the thickness of the film, the application field, the substrate material, and the like, and is not limited to any one of dropping coating, pouring, dipping, screen printing, inkjet printing, roll coating, spray coating, blade coating, and spin coating. The substrate is selected from a common substrate for preparing a membrane material, which does not react with the graphene oxide dispersion liquid and the graphene oxide membrane; for example, the material may be any of quartz glass, single crystal silicon, Polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), Polyimide (PI), DVD disk, Polyethylene (PE), and polyvinyl chloride (PVC).
According to an embodiment of the present invention, in step (3), the temperature and time of the freeze-drying are not particularly limited, and may be performed according to a conventional choice of those skilled in the art; illustratively, the temperature of the freeze-drying is below-5 ℃, such as-50 ℃ to-5 ℃, and further such as-30 ℃ to-10 ℃; the freeze-drying time is 10 minutes or more, for example, 10 minutes to 72 hours, further for example, 20 minutes to 36 hours, further for example, 30 minutes to 12 hours, and it is sufficient to ensure complete drying. The freeze-drying is preferably carried out under vacuum conditions, for example, under vacuum conditions of 200Pa or less, and further, for example, under vacuum conditions of 1 to 50Pa, and further, for example, under vacuum conditions of 1 to 10 Pa. Through the freeze drying treatment of the graphene oxide dispersion liquid, the one-step forming reduction of a subsequent graphene oxide film under the irradiation of low-power laser can be realized; the freeze drying process creates a three-dimensional porous graphene structure, effectively reduces the heat conduction of graphene, and is beneficial to improving the photo-thermal reduction efficiency.
According to an embodiment of the present invention, in step (3), the graphene oxide film after freeze-drying has a thickness of 10nm to 300 μm, for example, 1 μm to 60 μm.
According to an embodiment of the present invention, in the step (4), the power of the laser irradiation is 1mW to 100W; the total time of laser irradiation is 1-120 minutes; preferably, the power of laser irradiation is 5 mW-1W; the total time of laser irradiation is 3-20 minutes; after laser irradiation, the yellowish-brown graphene oxide film is reduced to a black graphene film.
The invention also provides the following technical scheme:
the graphene film is prepared by the preparation method of the graphene film.
According to the invention, the interior of the graphene film is three-dimensional and porous, and has a high specific surface area.
The invention has the beneficial effects that:
(1) the invention provides a method for preparing a graphene film by a laser reduction method, which improves the laser reduction efficiency by freeze-drying a graphene oxide dispersion liquid, has simple process, low price and environmental friendliness, and is suitable for large-scale production.
(2) The invention provides a method for preparing a graphene film by a laser reduction method, which greatly reduces laser power and can reduce graphene by one-step forming by using a low-power laser (such as a DVD laser engraving machine).
(3) The low-power graphene film prepared by laser reduction has a three-dimensional and porous internal structure and a large specific surface area, and can be applied to supercapacitors, sensors and the like.
Drawings
Fig. 1 is a photo photograph of the graphene oxide film of example 1.
Fig. 2 is a comparative graph of the photolithographic reduction of the graphene oxide film of example 1.
Fig. 3 is a scanning electron microscope image of the photolithographically reduced graphene film of example 1.
FIG. 4 is a comparative graph of the photolithographic reduction of the graphene oxide film of example 2.
FIG. 5 is a comparative graph of the photolithographic reduction of the graphene oxide film of example 3.
FIG. 6 is a comparative graph of the photolithographic reduction of the graphene oxide film of example 4.
FIG. 7 is a comparative graph of the photolithographic reduction of the graphene oxide film of example 5.
Detailed Description
The preparation method of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
Example 1
A graphene oxide dispersion liquid film was formed on a quartz glass substrate by a dropping method using 2mg/ml of the graphene oxide dispersion liquid (prepared by the method described above). And freezing the obtained liquid membrane at-30 ℃, then placing the liquid membrane in a vacuum environment at-10 ℃ and 200Pa, and carrying out freeze drying for 48 hours to obtain the graphene oxide membrane. And irradiating the graphene oxide film by using 5mW laser for 10 minutes to prepare the graphene film.
Examples 2 to 10
The steps of examples 2 to 10 were the same as in example 1 except that the graphene oxide dispersion and the concentration thereof, the temperature and time and pressure of freeze-drying, the laser power, and the irradiation time were different from each other, as specifically shown in table 1.
Comparative example 1 (lyophilized, not laser reduced)
Taking 2mg/ml of graphene oxide dispersion liquid, and forming a graphene oxide dispersion liquid film on a quartz glass substrate by a dropping coating method. And freezing the obtained liquid membrane at-30 ℃, then placing the liquid membrane in a vacuum environment at-50 ℃ and 200Pa, and carrying out freeze drying for 48 hours to obtain the graphene oxide membrane.
Comparative example 2 (chemical reduction)
Carrying out 100W ultrasonic treatment on 2.0mg/ml graphene oxide dispersion liquid for 1h to uniformly disperse the graphene oxide dispersion liquid, adding hydrazine hydrate (2.0ml/100ml dispersion liquid), heating in a water bath at 90 ℃ for 24h, filtering by using a glass funnel, and respectively carrying out centrifugal washing on 5 times by using a mixed solution (1: 1 volume ratio) of deionized water and methanol to obtain the graphene prepared by a chemical reduction method. Adding deionized water to adjust the volume, and preparing a graphene solution with the concentration of 2.4mg/ml by a chemical reduction method; through a drop coating method, a liquid film is formed on a quartz glass substrate, and the graphene film is prepared after drying for 120 minutes at 25 ℃.
Comparative example 3 (non-lyophilized + laser reduction)
Taking 2mg/ml of graphene oxide dispersion liquid, and forming a graphene oxide dispersion liquid film on a quartz glass substrate by a dropping coating method. And naturally drying the film at 25 ℃ for 120 minutes to prepare the graphene oxide film. The graphene oxide film was irradiated with 5mW of laser light for 10 minutes to prepare a graphene film.
TABLE 1 specific parameters of the examples and comparative examples
In addition, in example 1, the photo graph of the graphene oxide film is shown in fig. 1, and as shown in fig. 1, the graphene oxide film prepared by freeze drying is grayish brown in color and rough in surface, which is different from the sample formed by air drying. The photoetching reduction contrast diagram of the graphene oxide film is shown in FIG. 2, and as shown in FIG. 2, the formed graphene film is naturally air-dried, and the photoetching reduction trace is not obvious; the graphene film formed by freeze drying has obvious photoetching reduction traces and shows a square pattern. Meanwhile, the observation result of the scanning electron microscope (fig. 3) shows that the graphene film generated after the laser reduction is porous.
In example 2, the photo-etching reduction contrast diagram of the graphene oxide film is shown in fig. 4, as shown in fig. 4, the photo-etching reduction trace is not obvious when the graphene film formed by natural air drying is used; the graphene film formed by freeze drying has obvious photoetching reduction traces and shows a square pattern.
In example 3, the photo-etching reduction contrast of the graphene oxide film is shown in fig. 5, and as shown in fig. 5, the photo-etching reduction trace is not obvious when the graphene film formed by natural air drying is used; the graphene film formed by freeze drying has obvious photoetching reduction traces and shows a square pattern.
In example 4, the photo-etching reduction contrast of the graphene oxide film is shown in fig. 6, and as shown in fig. 6, the photo-etching reduction trace is not obvious when the graphene film formed by natural air drying is used; the graphene film formed by freeze drying has obvious photoetching reduction traces and shows a square pattern.
In example 5, the photo-etching reduction contrast of the graphene oxide film is shown in fig. 7, and as shown in fig. 7, the photo-etching reduction trace is not obvious when the graphene film formed by natural air drying is used; the graphene film formed by freeze drying has obvious photoetching reduction traces and shows a square pattern.
The resistance of the graphene film or graphene oxide film of each example and comparative example was measured by a two-probe method using a multimeter with a fixed probe spacing of 1.4cm, and the measurement results are shown in table 2.
TABLE 2 two-probe method resistance measurement results of graphene films or graphene oxide films of each example and comparative example
As can be seen from the above examples, when the laser power and the photolithography time are the same, the lower the freeze-drying temperature or the lower the freeze-drying pressure is, the higher the reduction efficiency is (the lower the resistance of the obtained graphene thin film is); the higher the concentration of the graphene oxide is, the thickness of the finally prepared graphene film is correspondingly increased; the laser reduction efficiency can be effectively improved by increasing the laser power or prolonging the laser photoetching time, and the resistance of the obtained graphene film is reduced.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (17)
1. A method of preparing a graphene film, the method comprising the steps of:
(1) preparing a graphene oxide dispersion liquid;
(2) placing the graphene oxide dispersion liquid obtained in the step (1) on a substrate to prepare a graphene oxide dispersion liquid film;
(3) freeze-drying the graphene oxide dispersion liquid film obtained in the step (2) to prepare a graphene oxide film;
(4) and (4) reducing the graphene oxide film obtained in the step (3) by laser irradiation to obtain a graphene film.
2. The method according to claim 1, wherein in the step (1), the concentration of the graphene oxide dispersion is 0.001mg/ml to 20 mg/ml.
3. The method according to claim 2, wherein in the step (1), the concentration of the graphene oxide dispersion is 0.01mg/ml to 20 mg/ml.
4. The method according to claim 3, wherein in the step (1), the concentration of the graphene oxide dispersion is 0.1mg/ml to 10 mg/ml.
5. The preparation method according to claim 1, wherein in the step (2), the graphene oxide dispersion is placed on the surface of the substrate by any one method selected from the group consisting of dropping coating, pouring, dipping, screen printing, ink-jet printing, roll coating, spray coating, knife coating, and spin coating.
6. The production method according to claim 1, wherein in the step (2), the substrate is selected from any one of quartz glass, single crystal silicon, Polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), Polyimide (PI), DVD disc, Polyethylene (PE), or polyvinyl chloride (PVC).
7. The production method according to any one of claims 1 to 6, wherein in the step (3), the temperature of the freeze-drying is from-50 ℃ to-5 ℃; the freeze-drying time is 10 minutes to 72 hours.
8. The method according to claim 7, wherein in the step (3), the temperature of the freeze-drying is from-30 ℃ to-10 ℃; the freeze-drying time is 30 minutes to 12 hours.
9. The production method according to any one of claims 1 to 6, wherein in the step (3), the freeze-drying is carried out under a vacuum atmosphere at a pressure of 200Pa or less.
10. The method according to claim 9, wherein the degree of vacuum in the step (3) is 1 to 50 Pa.
11. The method according to claim 10, wherein the degree of vacuum in the step (3) is 1 to 10 Pa.
12. The method according to claim 7, wherein in the step (3), the freeze-drying is carried out under a vacuum atmosphere at a pressure of 200Pa or less.
13. The method according to claim 12, wherein the degree of vacuum in the step (3) is 1 to 50 Pa.
14. The method according to claim 12, wherein the degree of vacuum in the step (3) is 1 to 10 Pa.
15. The production method according to any one of claims 1 to 6, wherein in the step (3), the thickness of the graphene oxide film after freeze-drying is 10nm to 300 μm.
16. The method according to claim 15, wherein in the step (3), the thickness of the graphene oxide film after freeze-drying is 1 to 60 μm.
17. The production method according to any one of claims 1 to 6, wherein in the step (4), the power of the laser irradiation is 1mW to 100W; the total time of the laser irradiation is 1 minute to 120 minutes.
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