Abstract:

Functionalized graphene has attracted significant interest over the past decade due to its unique physical properties and potential applications. Graphene oxide (GO), a readily scaled-up product, is a basic material for further functionalization. Using reductive processes, highly conductive reduced graphene oxide (RGO) can be obtained, which exhibits electrical and optical properties analogous to those of graphene. Moreover, due to the presence of oxygen-containing functional groups, its chemical reactivity and electronic properties can be easily tailored by chemical doping with nitrogen. However, developing strategies for doping graphene is challenging and the fundamental roles of the doping atom configuration and its environment on the resulting properties of graphene remain poorly understood. These properties are important for electrical and catalytic applications of graphene. Thus, synthesizing specific configurations of nitrogen-doped graphene and consequently investigating the electrical and catalytic properties of the product is imperative. Herein, we demonstrate an approach that allows for successful production of nitrogen-functionalized RGO using Schiff base condensation between the amino groups in an o-aryl diamine compound and the carbonyl groups in GO. Three typical nitrogen-containing species including o-phenylenediamine (OPD), 2, 3-diaminopyridine (23DAP), and bis(trifluoromethyl)-1, 2-diaminobenzene (BTFMDAB) were used for functionalizing the GO samples, and the corresponding RGO derivatives (OPD-RGO, 23DAP-RGO, and BTF-RGO) were obtained by thermal annealing. Pyrazine nitrogen was successfully introduced into graphitic framework, as confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, thermal gravimetric analysis (TGA), Raman, and X-ray photoelectron spectroscopy (XPS). Field-effect transistors (FETs) based on the BTF-RGO exhibited hole-dominated ambipolar field-effect behavior with a Dirac point at a 9 V gate voltage and hole mobilities up to 2.5 times that of RGO. The weak p-type doping effect originated from the strongly electron-withdrawing trifluoromethyl groups. By studying the OPD-RGO and 23DAP-RGO-based FETs, containing pyrazine nitrogen and mixed pyrazine/pyridine nitrogen, respectively, we found that pyrazine nitrogen provided weak n-type doping effects, while pyridine nitrogen exhibited weak p-type doping effects due to its electron-withdrawing ability. Enhanced p-type doping effect was accompanied by the introduction of groups with stronger electron-withdrawing ability into the graphitic framework. Impressively, pyridine nitrogen in the pyrazine nitrogen-doped RGO yielded a weak p-type doped graphene due to the electron-withdrawing effect of the pyridine nitrogen. Nitrogen-doped graphene can be finely tuned from weak n-type to weak p-type doping by adjusting the electron-withdrawing ability of o-aryl diamine compounds. This study demonstrates the effect of nitrogen configuration and its surrounding environment on the electrical properties of RGOs, providing additional possible applications.

Key words: Reduced graphene oxide, Nitrogen doping, Schiff base reaction, Electron-withdrawing group, Field-effect transistor