H 9500 system

Ex situ characterization methods for natural graphite and as-produced GO were including X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and micro Raman spectroscopy. For XRD, the dried GO powder was used as sample. The XRD was performed by BRUKER D2 PHASER- X-ray Powder Diffractometer (Bremen, Germany) (Cu Kα, λ = 1.54Å). For TEM, samples were prepared by dispersing GO in ethanol and then dropped onto 300 mesh holey lacy carbon grids on cupper support (Ted Pella, Inc., Redding, CA, USA) at ambient condition. The TEM images were observed by Hitachi H-9500 system, Japan. For XPS and Raman, the samples were prepared by dispersing GO in ethanol. Then thin sample films were prepared on Si wafer and dried in a hot air oven at 60 °C. XPS (VG ESCALAB 250; Thermo Fisher Scientific, Waltham, MA, USA) was performed using a monochromatic Al Kα X-ray radiation (10 kV and 10 mA). The source power was set to 72 W, and pass energies of 200 eV for survey scans and 50 eV for high-resolution scans. Raman scattering studies were performed at room temperature with a JASCO 5100 spectrometer (533 nm; JASCO, Tokyo, Japan).