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In situ single-step reduction of bromine-intercalated graphite to covalently brominated and alkylated/ brominated graphene Mustafa Kemal Bayazit1,a) 1

Sabanci University Nanotechnology Research and Application Center, Tuzla, Istanbul 34956, Turkey Address all correspondence to this author. e-mail: [email protected]

a)

Received: 11 February 2020; accepted: 20 April 2020

Developing easy and effective surface functionalization approaches has required to facilitate the processability of graphene while seeking novel application areas. Herein, an in situ single-step reductive covalent bromination of graphene has been reported for the first time. Highly brominated graphene flakes (>3% Br) were prepared by only subjecting the bromine-intercalated graphite flakes to a reduction reaction with reactive lithium naphthalide. The bromine-functionalized graphene was characterized by X-ray photoelectron spectroscopy and thermogravimetric analysis. Results revealed that Br2 molecules acted as both an intercalating agent for the graphite and a reactant for the surface functionalization of the graphene. After brominating, the remaining negative charges on the reduced graphene surface were further used for the dual surface functionalization of graphene with a long-chain alkyl group (∼1% dodecyl group addition). The functionalized graphenes were also characterized by Fourier transform infrared and Raman spectroscopy.

Introduction Since its discovery [1, 2], the extraordinary chemical and physical properties of graphene caused an explosion in many research areas. To take advantage of its fascinating properties, graphene solutions have been prepared in aqueous or organic media [3, 4]. However, an appropriate concentration and the stability of final solution have become main issues while seeking bulk application areas such as composites [5]. Many dispersion strategies to overcome the poor dispersibility of graphene have been reported [3, 4, 6, 7]. Among these strategies, similar to single-walled carbon nanotube (SWCNT) chemistry [8, 9, 10, 11, 12, 13, 14, 15], chemical modification of graphene surface has gained much attention, and several covalent strategies have been developed to create functional surface moieties. Surface modification of graphene has increased its processability in solution phase, besides they facilitated their interaction with various matrices such as polymers [5, 16]. Disruptive surface modification techniques that follow the oxidation of graphite using strong acids (Hummers’ method) to produce graphene oxide have usually been preferred because of

ª Materials Research Society 2020

its simplicity [17]. However, the defective surface of the produced graphene has limited its use in applications requiring high electrical conductivity, but they have been successfully applied for the applications where bulk graphene materials are needed. Also, more sophisticated surface modification techniques have been used to create functional graphene surfaces, and these techniques have provided more control over the surface modi