▎ 摘　　要

NOVELTY - Water-soluble graphene is prepared by reacting crystalline flake graphite with hydrogen peroxide in mixture of potassium nitrate and concentrated sulfuric acid to obtain graphene oxide suspension; reacting reduced graphene oxide, benzaldehyde and methylamino acetic acid in dimethylformamide (DMF) to obtain hydroxylated graphene; dissolving hydroxylated graphene and gamma -glycidoxypropyltrimethoxysilane (KH-560) in ethyl alcohol to obtain epoxy functionalized graphene; and reacting epoxy functionalized graphene with sulfanilic acid to obtain water-soluble sulfonated graphene. USE - Method of preparing water-soluble graphene (claimed). ADVANTAGE - The method introduces sulfonic acid group to graphene to prevent agglomeration phenomenon to occur in an aqueous solution of graphene. The graphene in aqueous solution has no environment pollution. In a dispersion experiment, 0.1 mg/ml graphene in surfactant-free neutral aqueous solution has stable dispersion with no layering phenomenon. Further, a graphene thin film material has conductivity of 1300 S/m. DETAILED DESCRIPTION - Preparation of water-soluble graphene comprises: (A) adding crystalline flake graphite to mixture of potassium nitrate and concentrated sulfuric acid under ultrasonic condition, uniformly mixing, in ice water bath, slowly adding potassium permanganate, then adjusting temperature of the system to 35-45 degrees C, high speed stirring for 6 hours, then slowly adding distilled water, raising temperature of the system to 60-80 degrees C and reacting for half an hour, adding distilled water and 30 mass% hydrogen peroxide and reacting for 5 minutes to obtain bright yellow graphene oxide mother liquid, washing with distilled water till pH is 6-8 to obtain purified graphene oxide, adding sodium dodecyl benzene sulfonate, ultrasonically mixing to obtain graphene oxide suspension, where ratio of crystalline flake graphite, potassium nitrate, potassium permanganate, concentrated sulfuric acid, distilled water and hydrogen peroxide is 1 g:1-1.8 g:6 g:30-60 mL:180 mL:6 mL; (B) adding graphene oxide suspension with hydrazine hydrate with stirring in 80 degrees C water bath condition and refluxing and reducing for 6-12 hours, cooling reaction system to room temperature, filtering, washing with anhydrous ethyl alcohol, and drying to obtain pure reduced graphene oxide, where volume ratio of graphene oxide suspension to hydrazine hydrate is 30 mL:60-80 mL; (C) adding reduced graphene oxide, benzaldehyde and methylamino acetic acid to dimethylformamide (DMF), ultrasonically dispersing, putting in oil bath of 110-130 degrees C stirring and refluxing, filtering when it is hot, centrifuging, repeatedly washing precipitate with anhydrous ethyl alcohol, and drying to obtain hydroxylated graphene; (D) dissolving hydroxylated graphene and gamma -glycidoxypropyltrimethoxysilane (KH-560) in ethyl alcohol under nitrogen protection, ultrasonically mixing, reacting at room temperature for 15-24 hours, washing with ethyl alcohol to remove unreacted KH560, filtering, and repeatedly flushing methanol to obtain epoxy functionalized graphene; and (E) charging the epoxy functionalized graphene and distilled water into a container, ultrasonically mixing, adding potassium hydroxide and sulfanilic acid at room temperature, stirring for 30 minutes, raising temperature to 80 degrees C and reacting for 24 hours, filtering reaction mixture through 0.22 mu m PTFE film, washing with distilled water, and vacuum drying to obtain target product water-soluble sulfonated graphene.