High Yield Synthesis of Aspect Ratio Controlled. Graphenic Materials from Anthracite Coal in

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1 Supporting Information High Yield Synthesis of Aspect Ratio Controlled Graphenic Materials from Anthracite Coal in Supercritical Fluids Suchithra Padmajan Sasikala 1, Lucile Henry 1, Gulen Yesilbag Tonga 2, Kai Huang 3, Riddha Das 2, Baptiste Giroire 1, Samuel Marre 1, Vincent M. Rotello 2, Alain Penicaud 3, Philippe Poulin 3 *, and Cyril Aymonier 1 * 1 CNRS, University of Bordeaux, ICMCB, UPR 9048, Pessac 33600, France 2 Department of Chemistry, University of Massachusetts Amherst, MA 01003, USA 3 Centre de Recherche Paul Pascal CNRS, University of Bordeaux, Pessac 33600, France 1

2 S1. Characterization techniques Optical characterizations were carried out on as obtained GQDs suspension in water. Luminescence spectra were recorded on a Fluorolog FL3 22 ihr320 spectrofluorimeter (Horiba Jobin Yvon) with two double grating monochromators (excitation and emission for the UV- visible studies). The excitation source was a 450 Watt Xenon lamp, excitation spectra were corrected for the variation of the incident lamp flux, as well as emission spectra for the transmission of the monochromator and the response of the photomultiplier (R928P photomultiplier). UV-vis absorption spectra were performed using a Carry 5000 (Varian) in the nm range. ATR-IR was carried out on solid samples using a MIRacle 10 from Shimadzu. XPS spectra were recorded on a Thermo Scientific K-Alpha spectrometer; a spot size of 250 mm was employed. For Surface-enhanced Raman spectroscopy, SERS substrates, covered by Ag particles (RANDA) were purchased from Integrated Optics. SERS substrates were washed with deionized water and ethanol before depositing GQDs. After the deposition of GQDs on the substrates, the coated surfaces were dried under vacuum at 50 C. Raman spectroscopic characterization was carried out on a Horiba Jobin Yvon Xplora (excitation wavelength: 638 nm) with a laser spot size of 1 μm. The spectra were calibrated in frequency using a piece of silicon prior to measurement. For GRs, they were deposited on the Si surface, and Raman spectra were recorded with an excitation wavelength of 532 nm. For Atomic force microscopy (AFM) of GQDs, samples were deposited on a freshly cleaved mica substrates. After the depostion on the substrates, the coated surfaces were dried under vacuum at room temperature and then washed carefully using deionized water. Finally, the mica substrates were dried at 100 C. GRs, due to their aggregating nature, ultrasonicated in ethanol for 10 minutes to disperse and immediately spin coated on prior ozone plasma etched Si/SiO 2 substrate. It is then dried at 100 C. AFM images in ambient air were acquired using a 2

3 Nanoscope III microscope operated in tapping mode using 8 nm radius tips MPP High resolution electron microscopy (HRTEM) was performed using a Jeol 2200FS, working at 200 kv. Samples were prepared by depositing a drop of GQDs suspensions onto coppercarbon grids. For imaging GRs, they were dispersed in ethanol via low power bath ultrasonication for 2 min before depositing on copper-carbon grids. S2. Preparation of thin film of GRs GRs dispersed in ethanol were vacuum filtrated through a millipore membrane, and immediately pressed the wet membrane with GRs side down to the surface of glass slide. It was then allowed to dry under room temperature under 1 kg weight overnight to adhere the film on to the glass surface. The transferred film was dried in an inert atmosphere at 200 C for 24 h. The two probes surface resistance of the film between silver electrodes is measured. 3

4 Figure S1. Representative molecular structure of anthracite coal. Grey, white, blue, red and yellow colors denote carbon, hydrogen, oxygen, nitrogen and sulfur atoms, respectively.. 4

5 Figure S2. Characterization of anthracite coal. (a) TEM image (b) and (c) SAED pattern for selected area under white and dark circles in (a), respectively. (d) Raman spectrum with 638 nm excitation (e) XPS survey, (f) High resolution C1s spectrum and (g) N1s spectrum. The high resolution C1s (284.3 ev) spectrum displayed presence of Csp 2, Csp 3, C-CO, C-O and C=O modes. The N1s spectra show the presence of pyridinic nitrogen (N1) at ev as the major fraction together with small amounts of pyrrolic (N2), graphitic/quaternary edge (N3) bulk (N4) and pyridinic N + O - (N5) nitrogens at 399.6, 400.6, 401.5, and ev, respectively. 5

6 Figure S3. (a) FTIR-ATR of anthracite coal, (b) TEM of anthracite coal after ultrasonication in water for 60 min. Inset is the optical image. 6

7 Figure S4. Supercritical water cutting of anthracite coal into GQDs as a function of time: TEM images after (a) 10 min, (b) 30 min, (c) 60 min, and (d) 120 min. Inset of a and b is respective high resolution TEM images. The white arrow denotes the portion which is magnified in (b). Graphene fringes are displayed. Inset of c and d are the respective SAED patterns. 7

8 Figure S5. PL-excitation spectra of GQDs-2 corresponding to different emission wavelengths. 8

9 Figure S6. Comparison experiment to show the effect of sch 2 O treatment on natural graphite flakes (Sigma Aldrich, 20µm flake size). (a) TEM image of an exfoliated graphite sheet, inset is the HRTEM image of the same. Graphene Quantum dots were seen on the surface of exfoliated sheets, (b) Raman spectra of (i) natural graphite (ii) exfoliated graphite sheet indicating few layers graphene, inset is the photograph of recovered sample from the reactor after removing the large flakes by 1000 rpm centrifugation, (iii) bottom portion and (iv) top 9

10 portion of the supernatant obtained after centrifugation. The TEM was done by drop casting the sample from (iv). The sample (iv) was then centrifuged at 7000 rpm for 60 min to separate the large flakes and recover the GQDs. The sediment with large flakes was used for recording Raman spectrum. (c,d) The HRTEM image of GQDs, (e) PL excitation spectrum and (f) PL emission spectra of GQDs. Inset is the photograph of GQDs excited at a wavelength of 365 nm. Figure S7. (a) PL- excitation spectrum of the product obtained after anthracite coal is treated with scetoh, insets are the optical images (i) under visible light and (ii) when excited by UV lamp at 365 nm, (b) PL -emission spectrum at an excitation wavelength of 380 nm. As shown the PL intensity is very low with board emission spectrum. 10

11 Figure S8. HRTEM analysis of sample obtained from scetoh treatment of anthracite coal for 60 min. Different images could be considered as anthracite coal at different stages of supercritical etching (a) a typical piece of multilayered coal particle undergoing etching, the highlighted part is magnified in (b) the formation of strips of higher aspect ratios can be clearly discerned from the emerging fringes, (c) ribbon like structures seen in another aggregate (d) a bunch of ribbons found with partially etched flakes obtained after 60 minutes. As mentioned in the main text, the partially etched and larger uncut sheets remain suspended in solution owing perhaps to the oxygenated defects on them during centrifugation. The conductive ribbon structures were obtained as precipitates; these were washed and centrifuged many cycles to achieve a reasonable homogeneity. 11

12 Figure S9. (a-c). Raman spectra of as obtained GRs deposited on a Si substrate. As shown a non-homogenous Raman spectrum with I D /I G values ranging up to 0.91 is obtained at different spots in the deposited sample under 532 nm excitation. 12

13 Figure S10. Effect of ethanol-water mixture on anthracite coal at 250 C and 20 MPa. (a) HRTEM image (b) PL performance of the product obtained after 1 h, at a 50:50 volume ratio of ethanol to water. (c) HRTEM image of the product obtained after 2 h, at 75:25 volume ratio of ethanol to water. (d) PL performance of the products obtained after (i) 1 h and (iii) 3 h, at 75:25 volume ratio of ethanol to water, (ii) after 1 h, at a 50:50 volume ratio of ethanol to water. In all these experiments the starting precursor concentration was 1mg/ml. (iv) PL performance of the products obtained at a starting precursor concentration of 3 mg/ml, after 1 h, at a 50:50 volume ratio of ethanol to water. Inset is the respective photograph of the products (from left to right-(iii), (i), and (iv), under UV lamp). Inset of (b) is that of (ii). 13

14 Figure S11. TEM images with different magnifications of a sheet structure obtained after scetoh treatment of anthracite coal. Intricate overlapping folds with long range array can be observed. This sheet remained suspended in ethanol, can not be precipitated under centrifugation. 14

15 Figure S12. (a) Quantum Yield (QY) calculation for GQDs-2 with respect to quinine sulfate standard. A 500 ppm stock solution of GQDs-2 was prepared by dispersing dried GQDs-2 powder in water. A 500 ppm stock solution of QS was prepared similarly. In order to adjust the absorbance below 0.1, prior to QY measurement, 0.9 ml of 500 ppm GQDs-2 was diluted to 10 ml. In the case of QS, 2 ml of 500 ppm QS was diluted to 12 ml. The dilution of these two solutions was used for further measurements involved in generating this graph. (b) Transmittance% of GRs film on the surface of glass slide. 15