Abstract
The present invention discloses a graphene platelet fabrication method, which comprises Step (A): providing a highly-graphitized graphene having a graphitization degree of 0.8-1.0; and Step (B): providing a shear force acting on the highly-graphitized graphene to separate the highly-graphitized graphene into graphene platelets, wherein the graphene platelets have a length of 10-500 m and a width of 10-500 m and have a single-layer or multi-layer structure. The present invention also discloses a graphene platelet fabricated according to the abovementioned method.
Claims
1. A graphene platelet fabrication method comprising the steps of: Step (A): providing a liquid mixed with a highly-graphitized graphene having a graphitization degree of 0.8-1.0; and Step (B): passing the liquid through a circulation system containing a nozzle to make the liquid act on a surface or a lateral of the highly-graphitized graphene to provide a wet-type shear force acting on the highly-graphitized graphene to separate the highly-graphitized graphene into graphene platelets by a liquid action force opposite to the movement direction of the graphene platelets, wherein the highly-graphitized graphene is passed through elbows to make the liquid action force act on the lateral of the highly-graphitized graphene and separate the highly-graphitized graphene into the graphene platelets, and wherein the graphene platelets have a length of 10-500 m and a width of 10-500 m and have a single-layer or multi-layer structure.
2. The graphene platelet fabrication method according to claim 1, wherein the multi-layer structure of the graphene platelets has 2-50 layers of graphene planes.
3. The graphene platelet fabrication method according to claim 1, wherein the wet-type shear force is greater than a bonding force of the graphene platelets.
4. The graphene platelet fabrication method according to claim 1, wherein the liquid is selected from a group consisting of water, NMP (N-Methyl Pyrrolidone), surfactants, salt solutions, and combinations thereof.
5. The graphene platelet fabrication method according to claim 1, wherein the highly-graphitized graphene has a concentration of 0.5-50 wt % in the liquid.
6. The graphene platelet fabrication method according to claim 1, wherein the elbows have an angle of 30-150 degrees.
7. The graphene platelet fabrication method according to claim 1, wherein the highly-graphitized graphene is circulated in the circulation system for 1-900 cycles.
8. The graphene platelet fabrication method according to claim 1, wherein the circulation system applies the wet-type shear force of 1-500 MPa to the highly-graphitized graphene.
9. The graphene platelet fabrication method according to claim 4, wherein the highly-graphitized graphene is circulated in the circulation system for 200 cycles under the wet-type shear force of 200 MPa.
10. The graphene platelet fabrication method according to claim 1, wherein the liquid has a temperature of 25-100 C.
11. The graphene platelet fabrication method according to claim 1, further comprising Step (A1): undertaking a pre-treatment on the highly-graphitized graphene before Step (A) to swell the highly-graphitized graphene.
12. The graphene platelet fabrication method according to claim 6, wherein the pre-treatment is selected from a group consisting of an explosion method, a chemical exfoliation method, an ultrasonic method, a ball milling method, and combinations thereof.
13. A graphene platelet fabricated according to claim 1, wherein the graphene platelet has a length of 10-500 m and a width of 10-500 m and has a single-layer structure or a multi-layer structure.
14. The graphene platelet according to claim 8, having 2-50 layers of graphene planes.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1A and FIG. 1B respectively schematically show the processes of a graphene platelet fabrication method according to Embodiment I and Embodiment II of the present invention;
(2) FIG. 2 schematically shows a device according to Embodiment III of the present invention;
(3) FIG. 3 shows the result of the analysis of the platelet diameters Embodiment III of the present invention;
(4) FIG. 4A and FIG. 4B show the results of the analyses of the platelet diameters in Embodiment IV of the present invention;
(5) FIG. 5 shows the result of the analysis of the platelet diameters in Embodiment IV of the present invention; and
(6) FIG. 6 shows the result of the Raman spectrometric analysis in the experiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(7) The primary technical characteristic of the present invention is to use a method distinct from the conventional technology to fast fabricate large-area graphene platelets having perfect planar hexagonal network structure. Below, the present invention will be described in details with embodiments.
Embodiment I
(8) Embodiment I involves a method using a dry-type shear force to separate highly-graphitized graphene. Refer to FIG. 1A a diagram showing the process of a graphene platelet fabrication method according to Embodiment I of the present invention. Firstly, place a highly-graphitized graphene 10 on a fixing platform 11. Next, use a pushing device 12 to provide a dry-type shear force. In Embodiment I, the dry-type shear force acts on the surface of the highly-graphitized graphene 10, separating the highly-graphitized graphene 10 into graphene platelets 101. In Embodiment I, the highly-graphitized graphene 10 has a graphitization degree of 0.95 and is 100 m in width and 100 m in length. The shear force is a mechanical force generated by the pushing device 12. The mechanical force is parallel to the movement direction of the graphene platelets 101 (as indicated by the arrow) and greater than the Van der Waals bonding force of the graphene platelets 101. Modifying the intensity of the mechanical force not only can separate the highly-graphitized graphene 10 but also can control the number of the layers of graphene planes of a graphene platelet 101. In Embodiment I, the obtained graphene platelet 101 has 2-5 layers of graphene planes. In Embodiment I, as the highly-graphitized graphene 10 has a pretty high graphitization degree, the obtained graphene platelets 101 have a width of 100 m and a length of 100 m and still have a perfect planar hexagonal network structure.
Embodiment II
(9) Embodiment II involves another method using a dry-type shear force to separate highly-graphitized graphene. Refer to FIG. 1B a diagram showing the process of a graphene platelet fabrication method according to Embodiment II of the present invention. In Embodiment II, it is similar to Embodiment I: a highly-graphitized graphene 20 is placed on a fixing platform 21, and a pushing device 22 is used to provide a dry-type shear force acting on the highly-graphitized graphene 20 for separating the highly-graphitized graphene 20 into graphene platelets 201. In Embodiment II, it is different from Embodiment I: the dry-type shear force generated by the pushing device 22 (the mechanical force indicated by the arrow) acts on the lateral side of the highly-graphitized graphene 20. In Embodiment II, the distance between the pushing device 22 and the fixing platform 21 is carefully adjusted to precisely control the number of the layers of graphene planes of the obtained graphene platelets 201. In Embodiment II, the obtained graphene platelet 201 has 2 layers of graphene planes. In Embodiment II, the obtained graphene platelets 201 also have a width of 100 m and a length of 100 m and also have a perfect planar hexagonal network structure.
Embodiment III
(10) In addition to using the dry-types shear forces introduced in Embodiments I and II, the present invention also uses a wet-type shear force to separate the highly-graphitized graphene, wherein the highly-graphitized graphene is mixed with a fluid, and the fluid is circulated in a circulation system containing nozzles. Refer to FIG. 2 showing a device according to Embodiment III. The circulation system 3 comprises two feeding ports 32 and a discharging port 33, wherein the discharging port 33 is connected with the feeding ports 32 (not shown in the drawing) for circulation of the fluid. In one embodiment, a pressurizing system (not shown in the drawing) is used to make the fluid flow through nozzles 30 where the fluid generates a fluid action force functioning as a wet-type shear force. The present invention does not particularly limit the type of the pressurizing system as long as the pressurizing system can make fluid generate the required fluid action force. In order to separate the highly-graphitized graphene more efficiently, elbows 34 are arranged before the nozzles 30, whereby the highly-graphitized graphene carried by the fluid will be turned by 90 degrees while passing through the elbows 34. Thus, the fluid action force will act on the lateral side of the highly-graphitized graphene and separate the highly-graphitized graphene.
(11) The objective of Embodiment III is to separate the highly-graphitized graphene with a wet-type shear force, which is provided by the circulation system 3 shown in FIG. 2 and different from the dry-type shear forces. In Embodiment III, the highly-graphitized graphene has a graphitization degree of 0.95 and has a length of 100 m and a width of 100 m. In Embodiment III, the fluid is NMP (N-Methyl Pyrrolidone); the concentration of the highly-graphitized graphene is 1 wt %; the temperature of the fluid is between 25 and 35 C. during all the fabrication process.
(12) Refer to FIG. 3 showing the relationships between the values of the shear force and the average platelet diameters of the graphene platelets, wherein the horizontal axis represents the wet-type shear force (MPa) and the vertical axis represents the platelet diameter (m). The relationships are obtained via circulating the NMP solution containing the highly-graphitized graphene in the circulation system 3 for 1 cycle in the circulation system 3 under different values of the wet-type shear force. Refer to Curve D50 in FIG. 3. While the wet-type shear force is not applied, the original average platelet diameter is 28 m. While the wet-type shear force is increased to 50 MPa, the average platelet diameter decreases to 15 m. While the wet-type shear force is increased to 200 MPa, the average platelet diameter decreases to 9 m. FIG. 3 shows that the greater the wet-type shear force, the smaller the average platelet diameter of the obtained graphene platelets. Therefore, the wet-type shear force can indeed separate the highly-graphitized graphene into the graphene platelets.
Embodiment IV
(13) The objective of Embodiment IV is to evaluate the effect of the number of circulation cycles on the platelet diameter of the graphene platelets in the circulation system 3. In Embodiment IV, it is similar to Embodiment III: the highly-graphitized graphene has a graphitization degree of 0.95 and has a length of 100 m and a width of 100 m; the fluid is NMP (N-Methyl Pyrrolidone); the concentration of the highly-graphitized graphene is 1 wt %.
(14) Refer to FIG. 4A showing the relationships between the number of circulation cycles and the average diameters of the graphene platelets, wherein the horizontal axis represents the number of circulation cycles and the vertical axis represents the platelet diameter (m). The relationships are obtained via circulating the NMP solution containing the highly-graphitized graphene for 1-500 cycles in the circulation system 3 under a wet-type shear force of 200 MPa. Refer to Curve D50 in FIG. 4A. While the number of circulation cycles has reached 200, the average platelet diameter is 0.4 m. While the number of circulation cycles exceeds 300, the average platelet diameter increases to 1 m, however. While the number of circulation cycles exceeds 500, the average platelet diameter further increases to 1.3 m. It is a hypothesis for such a result: while the number of circulation cycles is increased, the friction between the fluid and the circulation system causes the temperature of the fluid to rise; the temperature rise further causes the re-agglomeration (thermally-induced agglomeration) of the graphene platelets dispersed in the fluid.
(15) In order to prove the abovementioned hypothesis, the graphene platelets, which are obtained by 500 cycles of circulations under a wet-type shear force of 200 MPa, is further circulated for 1 cycle under a wet-type shear force of 50 MPa to disperse the agglomerated graphene platelets. Refer to FIG. 4B showing the relationships between the number of circulation cycles and the average diameters of the graphene platelets, wherein the horizontal axis represents the particle size distribution and the vertical axis represents the platelet diameter (m). The fluids are respectively circulated for 200 cycles and 500 cycles under a wet-type shear force of 200 MPa. Then, the fluid, which has been circulated for 500 cycles, is further circulated for 1 cycle under a shear force of 50 MPa (the recirculation process). FIG. 4B shows that the diameter of the graphene platelets of the group of 200 MPa/200 cycles is similar to the diameter of the graphene platelets of the group of [200 MPa/500 cycles+50 MPa/1 cycle] for various grain sizes. The result proves that the graphene platelets indeed re-agglomerate because of the temperature rise of the fluid.
(16) From FIG. 4A and FIG. 4B, the following facts are learned: the average diameter of graphene platelets decreases with the increase of the number of circulation cycles; while the number of circulation cycles exceeds 200, the dispersed graphene platelets re-agglomerate because of the temperature rise of the fluid; a smaller wet-type shear force can be used to re-separate the thermally-agglomerated graphene platelets.
(17) Therefore, it can be concluded from Embodiments III and IV: either of a higher wet-type shear force or a higher number of circulation cycles favors separation of highly-graphitized graphene into graphene platelets; the fluid temperature needs carefully controlling lest the dispersed graphene platelets be thermally agglomerated.
Embodiment V
(18) The present invention is Mainly characterized in applying a shear force to highly-graphitized graphene to overcome the Van der Waals bonding force between the graphene layers and separate the highly-graphitized graphene into graphene platelets. In Embodiment V, before a wet-type shear force is used to separate the highly-graphitized graphene, a pre-treatment is used to swell the highly-graphitized graphene, increasing the interplanar distance (d.sub.(0002)) between graphene layers and decreasing the Van der Waals bonding force between the graphene layers, whereby the graphene platelets are more easily separated. In Embodiment V, an explosion method is used to realize the pre-treatment, decreasing the Van der Waals bonding force between the graphene layers and favoring the separation of the highly-graphitized graphene.
(19) Refer to FIG. 5 showing the analysis of the diameters of graphene platelets, wherein the horizontal axis represents the number of circulation cycles and the vertical axis represents the diameter of the graphene platelets (m). In Embodiment V, it is similar to Embodiment III: the NMP solution containing the highly-graphitized graphene is circulated in the circulation system 3 for 1-200 cycles under a wet-type shear force of 200 MPa. However, in Embodiment V, it is different Embodiment III: the highly-graphitized graphene is pre-treated with an explosion method beforehand to reduce the Van der Waals bonding force between graphene layers. Refer to Curve D50 in FIG. 5. Curve D50 shows that the average platelet diameter is 0.5 m while the number of circulation cycles has reached 100 and that the average platelet diameter is 0.4 m while the number of circulation cycles has reached 200. In comparison with FIG. 4A, it is learned that the 100 cycles of circulations are sufficient to effectively separate the highly-graphitized graphene having been pre-treated by the explosion method. However, no matter whether the highly-graphitized graphene is pre-treated by an explosion method, the separated graphene platelets will have similar sizes as long as the number of circulation cycles has exceeded 100. It indicates that the graphene platelet fabrication method of the present invention can also cooperate with the conventional technology to fast fabricate graphene platelets having a perfect planar hexagonal network structure.
Experiment
(20) In the present invention, a Raman spectrometer is used to analyze the completeness of the planar structures of the obtained graphene platelets and the number of the layers of the multi-layer structure thereof. The graphene platelets used in the experiment is obtained via circulating the highly-graphitized graphene in the circulation system 3 shown in FIG. 2 for 200 cycles under a wet-type shear force of 200 MPa. Refer to FIG. 6 showing the result of the Raman spectrometric analysis of the abovementioned graphene platelets, wherein the horizontal axis represents the Raman shift (cm.sup.1) and the vertical axis represents the absorption intensity (a.u.). The Raman spectrum of the conventional graphene has three characteristic peaks: respectively the D band at 1364 cm.sup.1 involved with the Sp.sup.3 bonding of carbon atoms; the G band at 1586 cm.sup.1 involved with the Sp.sup.2 bonding of carbon atoms; and the 2D band at 2710 cm.sup.1, which will deviate slightly with the variation of the number of the graphene layers of the graphene platelets. In FIG. 6, the ratio of the intensity of the D band at 1364 cm.sup.1 to the intensity of the G band at 1586 cm.sup.1 confirms that the graphene platelets fabricated by the method of the present invention has a pretty fine planar hexagonal network structure; the characteristic peak of the 2D band at 2710 cm.sup.1 indicates that the multi-layer structure of the graphene platelets has 5 layers of graphene planes. Via an optical microscope, the obtained graphene platelets are detected to have a length of 100 m and a width of 100 m, which indicates that the method of the present invention would not damage the planar structure of the graphene platelets.
(21) From Embodiment IV, Embodiment V and the Experiment, it is learned that the wet-type shear force generated by a circulation system containing nozzles can fast separate the highly-graphitized graphene into graphene platelets. Thus is proved that the graphene platelet fabrication method of the present invention can fast fabricate graphene platelets having more perfect planar hexagonal network structure.
(22) The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Any modification or variation according to the spirit of the present invention is to be also included within the scope of the present invention, which is based on the claims stated below.
