Guanidine hydrochloride, which is often used as an intermediate in medicines, pesticides, dyes and other organic compounds, is an important raw material for sulfonamides and folic acid; it can be used as a strong denaturants in the extraction of total RNA from cells, and used for denaturation and complexation of proteins. It can be used as an antistatic agent for synthetic fibers. In addition, it can also be used as a reducing agent to prepare graphene.

Graphene is a two-dimensional crystal composed of carbon atoms with only one layer of atomic thickness. It is an ultra-thin material with high strength and toughness. It has a large breaking strength which is 200 times more than steel. It has 20% stretching range and excellent electrical conductivity.

Due to its unique quantum effect and excellent electrical, thermal and mechanical properties, graphene has broad application in nanoelectronic devices and integrated circuits, flexible electronic devices, ultra-high sensitive sensor devices and other new electronic devices, composite materials, solar cells, super capacitors, hydrogen storage materials, etc.

The Existing Preparation Method

At present, preparation methods of graphene mainly include physical mechanical stripping method, vapor deposition method and chemical method. Mechanical methods include micro-mechanical stripping methods, epitaxial growth methods and heating of SiC. It is difficult to prepare graphene with large area and uniformly thick.

Compared with physical methods, chemical method for preparing graphene has a high yield. It has the advantages of simple preparation method, low cost and large-scale production, and thus becomes a common method for preparing graphene. However, in the reduction of graphene oxide, the selected reducing agents are mainly hydrazine hydrate and its derivatives, NaBH4, p-phenylenediamine, sulfur compounds, etc. Most of the reducing agents are toxic and explosive, which is not conducive to large scale production.

Therefore, it is necessary to develop a simple, efficient, low-cost and environmentally friendly method.

The researchers developed a method for preparing graphene with guanidine hydrochloride (CAS 50-01-1) as a reducing agent [1]:

(3) Adding guanidine hydrochloride to the above mixed solution, the mass ratio of guanidine hydrochloride to graphene oxide is 10:1~100:1, and adding alkaline solution (10%~28% ammonium hydroxide, 0.1~5mol/L NaOH solution, 0.1~5mol/L KOH solution) to adjust the pH to 8~12, stir in the oil bath (60~100°C), the reaction time is 1~5h. The water-soluble graphene is obtained by centrifuging and washing.

The preparation method has the advantages of simple preparation process, low equipment requirement, and easy preparation of graphene in large quantities; the presence of the soluble high molecular polymer greatly improves the water solubility of the graphene, and is also beneficial to the further preparation of the graphene film. Guanidine hydrochloride (Guanidinium chloride) can be used as a reducing agent to prepare graphene which can be stably dispersed in an aqueous solution, and the prepared graphene can be used for constructing sensor and electrical device.

Reference

[1] Ma Qi, Song Jinping, Guo Yong, et al. A method for preparing graphene with guanidine hydrochloride as a reducing agent. CN104261393B, 29 June 2016.