Formation of N-doped Graphene Nanoribbons via Chemical Unzipping

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1 SUPPORTING INFORMATION FILE FOR: Formation of N-doped Graphene Nanoribbons via Chemical Unzipping Rodolfo Cruz-Silva 1, Aaron Morelos-Gómez 3, Sofia Vega-Díaz 1, Ferdinando Tristán- López 1, Ana L. Elias 2, Nestor Perea-López 2, Hiroyuki Muramatsu 3, Takuya Hayashi 1, Kazunori Fujisawa 1,Yoong A. Kim 1, Morinobu Endo 1, and Mauricio Terrones 1,2 1 Research Center for Exotic Nanocarbons, Shinshu University, Wakasato, Nagano , Japan. 2 Department of Physics, Department of Materials Science and Engineering & Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA 3 Faculty of Engineering, Shinshu University, Wakasato, Nagano , Japan Corresponding author M. Terrones; mut11@psu.edu; mtterrones@shinshu-u.ac.jp Supporting Information Table of contentts: Figure S1. a) SEM, b) diameter distribution, c) TEM, d) XPS and e) TGA of CNx- MWCNTs. Figure S2. SEM images of oxidized nitrogen doped graphene nanoribbons prepared at 60 C and oxidizer to nanotube mass ratio of a) 2.5:1 and b) 1:1. Figure S3. High resolution C 1s core-level spectra of ox-n-gnrs deconvoluted into components. Figure S4. FTIR spectra of a) Graphite oxide, and b) oxidized GNRs prepared from MWCNTs (ox-gnrs), c) oxidized graphene nanoribbons prepared from highly crystalline MWCNTs (ox-hc-gnrs), and d) ox-n-gnrs prepared from CNx-MWCNTs (ox-n-gnrs). Figure S5. XRD patterns (CuK of pristine nitrogen doped multiwalled carbon nanotubes (CNx-MWCNTs), oxidized nitrogen doped graphene nanoribbons (ox-n- GNRs), and nitrogen-doped graphene nanoribbons prepared by thermal reduction of ox- N-GNRs at 800 C and 300 C, (N-GNRs-red800 and N-GNRs-red300, respectively). Figure S6. TEM images of a) oxidized GNRs prepared from (pure carbon) MWCNTs, b) oxidized GNRs prepared from CNx-MWCNTs (ox-n-gnrs), c) Nitrogen-doped graphene nanoribbons reduced at 300 C (N-GNRs-red300), and d) Nitrogen doped graphene nanoribbons reduced at 800 C (N-GNRs-red800). Figure S7. a) Raman and b) UV-vis spectra of oxidized and reduced nanotubes. Table SI. Spectroscopic data from Raman and UV-Visible of the pure carbon and nitrogen containing oxidized graphene nanoribbons and their reduced samples. Figure S8. Cyclic voltammetry curves of graphene nanoribbons in H 2 SO 4 1 M aqueous solution.

2 b) a) 30 Counts CNx-MWCNT diameter (nm) d) 100 nm Intensity (a.u.) Element e) C 1s 100 Atomic % C 96.0 O 2.2 N 1.7 Fe % weight c) N 1s Fe 2p O 1s C weight loss peak Binding Energy (ev) % wt residue Temperature ( C) Figure S1. Nitrogen doped multiwalled carbon nanotubes (CNx-MWCNTs) used as starting material in this study. a) Scanning electron microcope image of the as obtained material after chemical vapor deposition (CVD), b) diameter distribution of the CNx-MWCNTs is bimodal. c) TEM images of a bundle of CNx-MWCNTs. Typical wall thickness is between 20 nm and 30 nm. d) XPS wide scan spectra of the CVD synthesized CNx-MWCNTs. Major features are the C, N and O 1s peak, and very weak Fe 2p peak, that indicates that most catalyst is encapsulated in carbon. e) Thermogravimetric analysis of the CNx-MWCNTs under air flow (300 ml/min). The residue consists mainly on ferric oxide due to the catalyst. The temperature degradation peak (492 C), is a relatively low value as compared with pure carbon MWCNTs (630 C). Lower crystallinity and the presence of defects on CNx-MWCNTs results in higher reactivity towards air oxidation as compared with pure carbon MWCNTs.

3 a) 2.5:1, C/O=2.51 b) 1:1; C/O=3.43 Figure S2. SEM images depicting the morphologies of the oxidized nitrogen-doped graphene nanoribbons (ox-n-gnrs) prepared at 60 C using a lower oxidizer to nanotube ratio: a) oxidizer/nanotube mass ratio 2.5:1.0, and b) oxidizer/nanotube mass ratio to 1:1. Green arrows point to flat nanoribbons, whereas blue arrows indicate "u" shape unzipped nanotubes.

4 a) ox-n-gnrs 20 C C/O= % 17% 14% 9% b) ox-n-gnrs 40 C C/O= % 29% 13% 46% Intensity [a.u.] c) ox-n-gnrs 60 C C/O= % 23% 20% 34% d) ox-n-gnrs 80 C C/O= % 25% 14% 34% e) ox-n-gnrs 60 C 2.5:1 oxidizer ratio 60 C C/O= % 24% 46% 12% f) ox-n-gnrs 60 C 1:1 oxidizer ratio 60 C C/O= % 12% 10% 64% Binding energy [ev] Figure S3. High resolution C 1s core-level spectra of ox-n-gnrs. Deconvolution shows the individual contribution of oxygenated species. a), b), c) and d) show the C 1s peak of nitrogen-doped oxidized graphene nanoribbons (ox-n-gnrs) prepared at 20 C, 40 C, 60 C and 80 C, respectively. e) and f) show the C 1s peak of oxidized nitrogen doped graphene nanoribbons (ox-n-gnrs) prepared at 60 C using a lower ratio of oxidizer/nanotube ratio. e) oxidizer/nanotube mass ratio to 2.5:1.0, and f) oxidizer/nanotube mass ratio to 1:1.

5 a) Graphite oxide Transmittance (A.U) O-H C-H b) ox-gnrs c) ox-hc-gnrs HOH C/O=2.33 C/O=3.12 C/O=2.44 d) ox-n-gnrs C/O= Wavenumber (cm -1 ) Figure S4. Fourier-Transformed Infrared Spectroscopy spectra of a) Graphite oxide, and b) oxidized GNRs prepared from MWCNTs (ox-gnrs), c) oxidized graphene nanoribbons prepared from highly crystalline MWCNTs (ox-hc-gnrs), and d) ox-n- GNRs prepared from CNx-MWCNTs (ox-n-gnrs). There is a striking similarity in the relative abundance of different functional groups between graphite oxide and oxidized pure carbon multiwalled nanotubes. On the other hand, ox-n-gnrs have greater abundance of carbonyl groups.

6 Intensity (arb. units) CNx-MWCNTs ox-n-gnrs (001) GO N-GNRs-red800 N-GNRs-red300 C/O=49.00 C/O=2.16 C/O=19.7 C/O=15.2 (002)* Figure S5. XRD patterns (CuK of pristine nitrogen doped multiwalled carbon nanotubes (CNx-MWCNTs), oxidized nitrogen doped graphene nanoribbons (ox-n- GNRs), and nitrogen-doped graphene nanoribbons prepared by thermal reduction of ox- N-GNRs at 800 C and 300 C, (N-GNRs-red800 and N-GNRs-red300, respectively). The C/O atomic ratio was calculated by XPS and indicates the degree of oxidation. After oxidation of CNx-MWCNTs, a peak indicating exfoliation of the graphitic layers appears close to 10, and disappears after thermal treatment.

7 a) ox GNRs C/O=3.12 b) ox N GNRs C/O= nm c) N GNRs red300 C/O= nm 100 nm d) N GNRs red800 C/O= nm Figure S6. TEM images of a) oxidized GNRs prepared from (pure carbon) MWCNTs, b) oxidized GNRs prepared from CNx-MWCNTs (ox-n-gnrs), c) Nitrogen-doped graphene nanoribbons reduced at 300 C (N-GNRs-red300), and d) Nitrogen doped graphene nanoribbons reduced at 800 C (N-GNRs-red800). While nanoribbons reduced at 300 C show a flat ribbon morphology of several microns long, reduction at 800 C leads to significant fragmentation of the nanostructures.

8 a) CNx-MWNTs b) Intensity (arb. units) N-GNRs-redNH2 GNRs-redNH2 N-GNRs-red800 N-GNRs-red300 ox-gnrs ox-n-gnrs Absorbance (arb. units) CNx-MWCNTs ox-gnrs GNRs-redNH2 GNRs-red800 ox-n-gnrs N-GNRs-redNH2 N-GNRs-red Raman shift (cm -1 ) Wavelength (nm) Figure S7. a) Raman and b) UV-vis spectra of pristine nitrogen doped carbon nanotubes (CNx- MWCNTs), oxidized graphene nanoribbons (ox-gnrs) and oxidized nitrogen doped graphene nanoribbons (ox-n-gnrs), N-doped graphene nanoribbons obtained by thermal reduction at 300 C (N-GNRs-red300) and 800 C (N-GNRs-red800), and chemically reduced GNRs (GNRsredNH2) and chemically reduced N doped GNRs (N-GNRs-redNH2).

9 Table SI. Spectroscopic data from Raman and UV-Visible of the pure carbon and nitrogen containing oxidized graphene nanoribbons and their corresponding chemically and thermally reduced graphene nanoribbons samples. Sample UV Vis Rama n I G cm 1 I D /I G CNxP MWCNTs ox N GNRs ox GNRs N GNRs rednh GNRs rednh N GNRs red N GNRs red i (ma) a) GNRs-red E (V vs Ag AgCl) i (ma) b) N-GNRs-redNH E (V vs Ag AgCl) 500 mv/s 200 mv/s 100 mv/s 50 mv/s 25 mv/s 10 mv/s Figure S8. Cyclic voltammetry curves of graphene nanoribbons in H 2 SO 4 1 M aqueous solution: a) Graphene nanoribbons after oxidation of MWCNTs and thermally reduced at 800 C, and b) nitrogen doped graphene nanoribbons obtained by oxidation of CNx- MWCNTs and reduced with hydrazine (N-GNRs-redNH2).