Abstract
The electrochemical exfoliation of graphite has been considered to be an effective approach for the mass production of high-quality graphene due to its easy, simple, and eco-friendly synthetic features. However, water dispersion of graphene produced in the electrochemical exfoliation method has also been a challenging issue because of the hydrophobic properties of the resulting graphene. In this study, we report the electrochemical exfoliation method of producing water-dispersible graphene that importantly contains the relatively low oxygen content of <10% without any assistant dispersing agents. Through the mild in situ sulfate functionalization of graphite under alkaline electrochemical conditions using a pH buffer, the highly water-dispersible graphene could be produced without any additional separation processes of sedimentation and/or centrifugation. We found the resulting graphene sheets to have high crystalline basal planes, lateral sizes of several μm, and a thickness of <5 nm. Furthermore, the high aqueous dispersion stability of as-prepared graphene could be demonstrated using a multi-light scattering technique, showing very little change in the optical transmittance and the terbiscan stability index over time.
Highlights
When a voltage is applied to a graphite electrode, few-layer graphene sheets are exfoliated from the graphite layers over successive reaction steps, including the formation of graphite intercalation compounds (GICs), expansion of the graphite layer through gas-evolving electrolysis, and exfoliation of graphite layers in various electrolytes (Parvez et al, 2014)
We report the preparation of highly waterdispersible graphene through the mild in situ sulfate functionalization of graphite manipulated by controlling the reaction of persulfate (S2O82−) ions to graft sulfate (R–OSO3−) groups onto the graphene sheets during the electrochemical reactions
The persulfate anion (S2O82−), a strong oxidant (E0 2.01 V) (Yuan et al, 2014), undergoes chemical or thermal dissociation to become an intermediate of sulfate free radicals (SO4_−), which can be readily converted to hydroxyl free radicals (_OH) in aqueous solution via a radical interconversion reaction
Summary
Atomically thin carbon layers exfoliated from graphite in which multiple layers of sp2bonded carbon atoms are arranged in a hexagonal lattice, has been standing at the center of materials due to its great potential applications in next-generation electronic devices (Kwon et al, 2020; Alonso et al, 2018), energy conversion and storage devices (Jang et al, 2021; Tanguy et al, 2020), catalysis (Hwang et al, 2019; Lu et al, 2016), and other functional composites (Ryu et al, 2020; Wu et al, 2017) owing to its unique electrical, mechanical, optical, and chemical properties (Kwon et al, 2017; Dong et al, 2017; Kim et al, 2019). The electrochemical exfoliation of graphite has been performed by changing the electrolyte type to control the characteristics of the resulting graphene sheets, such as their lateral size, thickness, and electronic and chemical properties (Yang et al, 2016). We report the preparation of highly waterdispersible graphene through the mild in situ sulfate functionalization of graphite manipulated by controlling the reaction of persulfate (S2O82−) ions to graft sulfate (R–OSO3−) groups onto the graphene sheets during the electrochemical reactions. In our electrochemical regime of mild in situ sulfate functionalization, the highly water-dispersible graphene could be prepared with a relatively lower oxygen content of
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