title: Formation of nitrogen-doped graphene nanoribbons via chemical unzipping.
abstract: In this work, we carried out chemical oxidation studies of nitrogen-doped multiwalled carbon nanotubes (CNx-MWCNTs) using potassium permanganate in order to obtain nitrogen-doped graphene nanoribbons. Reaction parameters such as oxidation reaction, reaction time, the oxidizer to nanotube mass ratio, and the temperature were varied, and their effect was carefully analyzed. The presence of nitrogen atoms makes CNx-MWCNTs more reactive toward oxidation when compared to undoped multiwalled carbon nanotubes (MWCNTs). High-resolution transmission electron microscopy studies indicate that the oxidation of the graphitic layers within CNx-MWCNTs results in the unzipping of large diameter nanotubes and the formation of a disordered oxidized carbon coating on small diameter nanotubes. The nitrogen content within unzipped CNx-MWCNTs decreased as a function of the oxidation time, temperature, and oxidizer concentration. By controlling the degree of oxidation, the N atomic % could be reduced from 1.56% in pristine CNx-MWCNTs down to 0.31 atom % in nitrogen-doped oxidized graphene nanoribbons. A comparative thermogravimetric analysis reveals a lower thermal stability of the (unzipped) oxidized CNx-MWCNTs when compared to MWCNT samples. The oxidized graphene nanoribbons were chemically and thermally reduced and yielded nitrogen-doped graphene nanoribbons (N-GNRs). The thermal reduction at relatively low temperature (300 °C) results in graphene nanoribbons with 0.37 atom % of nitrogen. This method represents a novel route to preparation of bulk quantities of nitrogen-doped unzipped carbon nanotubes, which is able to control the doping level in the resulting reduced GNR samples. Finally, the electrochemical properties of these materials were evaluated.
authors: Research Center for Exotic Nanocarbons, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan.
authors: Rodolfo
authors: R
authors: Cruz-Silva
authors: Aaron
authors: A
authors: Morelos-Gómez
authors: Sofia
authors: S
authors: Vega-Díaz
authors: Ferdinando
authors: F
authors: Tristán-López
authors: Ana L
authors: AL
authors: Elias
authors: Nestor
authors: N
authors: Perea-López
authors: Hiroyuki
authors: H
authors: Muramatsu
authors: Takuya
authors: T
authors: Hayashi
authors: Kazunori
authors: K
authors: Fujisawa
authors: Yoong Ahm
authors: YA
authors: Kim
authors: Morinobu
authors: M
authors: Endo
authors: Mauricio
authors: M
authors: Terrones