Due to its excellent electrical, thermal and mechanical properties, graphene has broad application prospects in materials science, energy, and biomedicine. At present, the preparation method of graphene powder is commonly used chemical redox method. In the process of reducing graphene oxide, the main reducing agents selected are hydrazine hydrate and its derivatives, NaBH₄, p-phenylenediamine, sulfur-containing compounds, etc. Most reducing agents are toxic and explosive, which is not conducive to large-scale production. Guo Shouwu and others proposed that Vitamin C is an effective reducing agent, but the relatively high price of Vitamin C limits the large-scale production of graphene. Therefore, Ma Qi et al. proposed a graphene preparation method using guanidine hydrochloride as a reducing agent, as follows:

(1) Add graphite oxide to double distilled water, treat with a cell disruptor for 20-90 minutes, and then continue ultrasonic treatment with ultrasound for 10-60 minutes to obtain a uniformly dispersed graphene oxide dispersion. The concentration of the graphene oxide dispersion is preferably 0.1-10 mg/mL.

(2) Add a soluble high molecular polymer (polyvinylpyrrolidone, polyacrylamide, polyvinyl alcohol, polyethylene glycol, hydroxymethyl cellulose, polyacrylic acid) to the graphene oxide dispersion.the mass concentration of the high molecular polymer in the mixed solution is 0.01-0.1 mg/mL, and the mixed solution of high molecular polymer and graphene oxide is obtained after ultrasonic dispersion for 5-30 minutes.

(3) Add guanidine hydrochloride to the mixed solution obtained in step (2). The mass ratio of guanidine hydrochloride to graphene oxide is 10:1-100:1. At the same time, add alkaline solution (alkaline solution is selected from mass percentage 10%-28% ammonia water, 0.1-5mol/L NaOH solution, 0.1-5mol/L KOH solution) adjust the pH to 8-12, place it in an oil bath and stir the reaction, the temperature of the oil bath is 60-100℃， The reaction time is 1-5 hours , and then centrifuged and washed to obtain water-soluble graphene.

The preparation process is simple, the equipment requirements are low, and the graphene is easily prepared in large quantities. The presence of soluble high-molecular polymers greatly improves the water solubility of graphene, and at the same time facilitates the further preparation of graphene films. Guanidine hydrochloride is used as a reducing agent to prepare graphene that can be stably dispersed in an aqueous solution, and the graphene thus prepared can be used to construct sensors and electrical devices.

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