Green and facile production of high-quality graphene from graphite by the combination of hydroxyl radicals and electrical exfoliation in different electrolyte systems.

A novel, simple and efficient method by the combination of hydroxyl radicals and electrical exfoliation of graphite for the green production of high-quality graphene from graphite was first developed in our self-manufactured exfoliation apparatus. In this work, we focused on the investigation of the roles of various electrolyte systems for the exfoliation of graphite. Sodium chloride, sodium hydroxide, poly vinyl pyrrolidone (PVP), dodecyl trimethyl ammonium bromide (DTAB) and sodium dodecyl benzene sulfonate (SDBS) were tested as the electrolyte. The yields of the graphene product in sodium hydroxide, PVP, DTAB, sodium chloride and SDBS electrolyte system were 32.9%, 34.0%, 45.2%, 77.5% and 83.5%, respectively. The experimental result demonstrated that graphite can be successfully exfoliated to graphene in these electrolytes, with SDBS showing the best exfoliation effect. We further investigated the effects of process parameters on the graphite exfoliation in the SDBS system by single factor experiments. The obtained optimal process parameters were as follows: graphite dosage, 5.0 g; SDBS solution concentration, 10.0% (w/v); applied current strength, 10 mA; air flow, 1.0 L h; and exfoliation time, 3 h. At these conditions, the yield of the graphene product was 89.7%. TEM results revealed that the graphene product possessed the characteristic features of a thin-layer graphene sheet. XRD results showed that the graphene products still maintained the structures of carbon atoms or molecules. FT-IR and Raman results indicated that the products exhibited the characteristic peaks and the absorption peaks of graphene. AFM test results revealed that the layer number of graphene product obtained was about 2, while the layer numbers of the graphene products obtained from sodium hydroxide, PVP, DTAB and sodium chloride systems were 30, 20, 4 and 3, respectively, at the same experimental conditions. The observed exfoliation effect in the SDBS system was due to its good electrical conductivity, which was favorable for the formation of hydroxyl radicals in exfoliation. Furthermore, SDBS has good hydrophilic properties and can enable even dispersion of graphite in the system. These two effects facilitated the exfoliation of graphite to form good-quality graphene. SDBS as the electrolyte did not corrode the electrode, and it could be recycled; also, it does not pollute the environment and reduces the production cost, which is favorable for mass production.