CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Chinese Patent Application No. 201810262140.4, filed on Mar. 28, 2018, and the disclosures of which are hereby incorporated by reference.

FIELD

The present disclosure relates to the field of producing graphene nano materials, and in particular relates to a method of producing graphene.

BACKGROUND

Graphene has great potential application prospects in various fields such as batteries, electronic devices, optical devices, and biomedical applications due to its excellent mechanical properties, optical properties, electrical and thermal conductivity properties, and excellent biocompatibility. Using a mild method for large-scale production of high-quality graphene is the core and key to achieve the true realization of graphene applications.

At present, researchers have developed a variety of graphene production techniques, especially in the large-scale preparation, mainly including graphene oxide chemical exfoliation, electrochemical exfoliation, ultrasonic exfoliation, stabilizer grinding-assisted exfoliation and other methods. Chemically exfoliated graphene has a significant decrease in its comprehensive performance due to changes in functional groups, which greatly limits its practical application. Although methods such as grinding exfoliation have advantages in large-scale preparation, the layer number of graphene flake produced is too high, and the quality is greatly limited. Ultrasound-assisted exfoliation is conducted under mild conditions, and the graphene flakes produced have a low layer number and few defects, and can be directly prepared as a solvent dispersion system that can be further applied. However, it is difficult for ultrasonic exfoliation method to achieve large-scale production, and there are technical barriers which are not possible to be solved in large-scale preparation and application.

SUMMARY

An object of the present disclosure is to provide a method of producing graphene. The method of the present disclosure can achieve large-scale production while ensure the quality of the graphene flakes.

The present disclosure provides a method of producing graphene, comprising:

A) mixing graphite powders with a silk fibroin nanofiber solution, performing mechanical stirring to exfoliate graphite to form graphene flakes;

wherein the silk fibroin nanofibers in the silk fibroin nanofiber solution have a crystallinity of 40% or above; the silk fibroin nanofibers have a diameter of 10 to 30 nm; the silk fibroin nanofibers have a length of 100 nm to 3 μm;

the mechanical stirring has a shearing speed of 1,000 to 50,000 rpm; and the duration of the mechanical stirring is 10 min to 6 h;

B) centrifuging the solution obtained in step A) after exfoliation to remove unexfoliated graphite; and

C) centrifuging the centrifuged solution obtained in step B), and separating graphene from the silk fibroin nanofibers to obtain the graphene.

Preferably, the mechanical stirring is performed at the temperature of 10 to 40° C.

Preferably, the device for the mechanical stirring has a volume of 1 L-100 L.

Preferably, the silk fibroin nanofibers have a beta-sheet crystal structure.

Preferably, the silk fibroin nanofiber solution has a mass concentration of 0.1-3%.

Preferably, the mass ratio of the dry silk fibroin nanofibers used to prepare the silk fibroin nanofiber solution to the graphite powders is 1: (1-100).

Preferably, the centrifuging in step B) is performed at the speed of 500-5,000 rpm; the duration of the centrifuging in step B) is 5 min to 2 h.

Preferably, the centrifuging in step C) is performed at the speed of 8,000-20,000 rpm; and the duration of the centrifuging in step C) is 5-60 min.

Preferably, the graphene has 5 layers or fewer and a lateral size of 100 nm-2 μm.

The present disclosure provides a method of producing graphene, comprising: A) mixing graphite powders with a silk fibroin nanofiber solution, performing mechanical stirring to exfoliate graphite to form graphene flakes; wherein the silk fibroin nanofibers in the silk fibroin nanofiber solution have a crystallinity of 40% or above; the silk fibroin nanofibers have a diameter of 10 to 30 nm; the silk fibroin nanofibers have a length of 100 nm to 3 μm; the mechanical stirring has a shearing speed of 1,000 to 50,000 rpm; and the duration of the mechanical stirring is 10 min to 6 h; B) centrifuging the solution obtained in step A) after exfoliation to remove unexfoliated graphite; and C) centrifuging the centrifuged solution obtained in step B), and separating graphene from the silk fibroin nanofibers to obtain the graphene. By exploring the stirring condition and optimizing the silk protein, the present disclosure realizes the production of high-quality graphene which can be dispersed in water or other water-organic solvent composite solvent under the condition of high-speed stirring treatment, obtaining high concentration and high yield of the graphene in aqueous solution (the highest concentration of 10 mg/ml or above and the highest yield of higher than 30%), which are significantly higher than that of the graphene prepared by high-speed stirring and exfoliation in the prior art.

