Production of Graphite Chloride and Bromide Using Microwave Sparks

Transcription

1 Supporting Information Production of Graphite Chloride and Bromide Using Microwave Sparks Jian Zheng, Hongtao Liu, Bin Wu, Chong-an Di, Yunlong Guo, Ti Wu, Gui Yu, Yunqi Liu, * and Daoben Zhu Key Laboratory of Organic Solids, National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing , P. R. China, liuyq@iccas.ac.cn Method Br 2 -adsorbed GS The GS was dispersed in liquid Br 2 for 10 h. The Br 2 -adsorbed GS was obtained after vacuum filtration. Cl 2 -adsorbed GS The GS was dispersed in liquid Cl 2 for 10 h. The Cl 2 -adsorbed GS was obtained after the excess Cl 2 was evaporated. Samples for AFM A piece of SiO 2 /Si chip was immerged into a G X solution for 1 h. Then the substrate was washed with DMF, picked up and dried with nitrogen. Finally, the substrate was annealed at 150 C under vacuum for 10 h. Patterned graphene electrode A G Cl film was spin-coated on the SiO 2 /Si substrate using a 0.5 mg/ml G Cl dispersion. The G Cl film needs to be annealed at 400 o C for 5 10 min before the next spin-coating. In order to obtain a 45 nm thick film, the spin-coating process was repeated ten times. Then the G Cl film was anealed at 600 o C for 15 mins in vacuum. A 70 nm Al layer was thermally evaporated through a shadow mask to fabricate S1

2 patterned Al electrodes. The substrate was then exposed in an O 2 plasma chamber for 5 min with 20 sccm O 2 flow with a pressure of 100 mtorr, and 150 W RF power. Finally, the patterned graphene electrode arrays were obtained by wet etching of the Al by immersing the substrate in 15 % FeCl 3 solution for 20 min at room temperature. The concentration of the G X dispersion As expected, the transmission electron microscope (TEM) and atomic force microscopy (AFM) measurements indicated that the graphite halide could be exfoliated into individual graphene halide sheets in dimethylformamide (DMF). More significantly, a similar degree of exfoliation was also attained for several other organic solvents in which stable graphite oxide dispersions could be prepared (namely N-methyl-2- pyrrolidone (NMP), dioxane, ethylene glycol and ortho-dichlorobenzene (ODCB)). The chemical modification enhances the dispersibility of the material, and thus the concentration of the G Br suspension after centrifugation in ODCB can reach about 0.12 mg/ml (G Cl 0.7 mg/ml), which is higher than the reported 1 value for pristine GS (0.03 mg/ml). Recycling use of unreacted graphite 50 µl 50% H 2 SO 4 was added into 90 mg unreacted graphite and grinded for 5 min, then the mixture was dried in vacuum for 3 h. At last the graphite powder was tableted to a compact disc at 36 MPa by a tableting machine. This graphite disc could re-expand with a microwave radiate and reacted with Cl 2 as a starting material. Characterization The samples were characterized by SEM (Hitachi S 4800, 15 kv), X-ray EDS, (fitted to the SEM), AFM (Multimode Nanoscope V), TEM (JEM 2010, 200 kv), SAED (fitted to the TEM), Raman spectrometer (Lab Ram HR800, with laser excitation at 514 nm), XPS (ESCA Lab220I XL), powder XRD (Rigaku D/max2500) and TGA (EXSTAR 6000 TG/DTA 6300). S2

3 Figure S1. Schematic illustration of the chlorination process. Graphite undergoes an expandsion of its volume in the hot sparks and emits large quantites of hot graphite flakes which can react directly with the halogen. The emitted hot graphite halide coated on the inside surface of the flask was rapidly cooled to ultralow temperature, thus avoiding thermal decomposion. Figure S2. AFM images of the graphene halides after annealing at 600 o C: (a) G Br, (b) G Cl. S3

4 Although the XPS analysis gives an accurate elemental composition, it characterizes the sample over a large area. EDS was performed to measure the elemental ratio in a selected small area on single graphite flake. Obvious halogen peaks can be clearly detected in each area of the graphite, while they are absent in the expanded graphite. Although the halogen was spread widely over the whole graphite flake, the halogen atoms were not homogenously spread on the same one graphite sheet (Fig. S6). As a result, we can deduce that the G X, which exfoliated from the inhomogenously modified graphene, also has an inhomogenous halogen content. The bromine content in the graphite bromide ranged between 2 and 8 atom%, while the chlorine content in the chlorinated samples ranged between 18 and 27 atom%. Figure S3. (a) SEM image of the brominated graphite sheet and (b) the EDS spectra taken from the area marked by the same colour dashed frame in the SEM image. The blue bar is 2000 nm. Figure S4. (a) SEM image of the chlorinated graphite sheet and (b) the EDS spectra taken from the area marked by the dashed frame in the SEM image. S4

5 Figure S5. Images shows halogen elemental distribution in the SEM images of (a) G Cl, (b) G Br. Figure S6. Wide survey XPS spectrum of the expanded graphite S5

6 Figure S7. High-resolution XPS Cl 2p spectra of the G Cl. Confirmation of the covalent bonding in G Cl and G Br by IR spectroscopy The interactions between GS and halogen atoms involve covalent bonding, as was shown by IR spectroscopy. The peak located at 838 cm 1 corresponds to stretching frequency of the C Br group 1 and that 847 cm 1 corresponds to the stretching frequency of the C Cl group. 2 These peaks were absent in the spectrum of pristine graphene. The peak at 1600 cm 1 in each spectrum corresponds to the C=C stretch. Figure S8. IR spectra of GS, G Br and G Cl. S6

7 Figure S9. TGA traces of G Cl. Figure S10. Wide survey XPS spectrum of G Cl after annealing at 600 o C. Figure S11. I ds V ds characteristics at various V g for the device in Fig. 4c. S7

8 Figure S12. Schematic illustration of the approach used to fabricate patterned graphene electrodes. Figure S13. a) Wide survey XPS spectra of G NHC 12 H 25. b) High-resolution XPS spectra of G NHC 12 H 25 showing the C N peak (~285.7 ev). S8

9 Figure S14. Wide survey XPS spectrum of the laurylamine-substituted G Cl. References (1) P. A. Troshin, S. I. Troyanov, Russ. Chem. Bull. 2004, 53, (2) F. N. Tebbe, J. Y. Becker, D. B. Chase, L. E. Firment, E. R. Holler, B. S. Malone, P. J. Krusic, E. Wasserman, J. Am. Chem. Soc. 1991, 113, S9