Electronic Supplementary Material Determination of quantitative structure property and structure process relationships for graphene production in water Thomas J. Nacken, Cornelia Damm, Haichen Xing, Andreas Rüger, and Wolfgang Peukert ( ) Institute of Particle Technology (LFG), Friedrich-Alexander University Erlangen-Nürnberg (FAU), Cauerstrasse 4, 91058 Erlangen, Germany Supporting information to DOI 10.1007/s12274-014-0694-6 Influence of cut size on product yield First we show the cut size (x = 400 nm in Fig. S1 and x = 200 nm in Fig. S2) with respect to the surfactant concentration used during the initial studies in a shaking device (LAU Disperser), which was used to evaluate the optimum amount of surfactant for processing. The dependency of dispersed carbon concentration and achieved production rate obtained after the delamination process respectively are plotted vs. process time and different applied cut sizes (Figs. S3 and 4). Figure S1 Dispersed carbon concentration for different TW80 concentration for cut size of 400 nm using a shaking plate (LAU disperser) with different times of processing. 100 µm ZrO 2 beads were used as delamination media and the carbon concentration was fixed to 1 wt.%. Address correspondence to wolfgang.peukert@fau.de
Figure S2 Dispersed carbon concentration for different TW80 concentration for a cut size of 200 nm using a shaking plate (LAU disperser) with different times of processing. 100 µm ZrO 2 beads were used as delamination media and the carbon concentration was fixed to 1 wt.%. Figure S3 Dispersed carbon concentration as a function of process time in a stirred media mill operating with a stirrer rotation speed of 1,000 rpm and 100 µm ZrO 2 beads for different cut sizes of the subsequent centrifugation step. A 1 wt.% suspension of graphite was delaminated in an aqueous solution of 0.1 wt.% TW80. Figure S4 Dispersed carbon production rate (dcpr) for 1 wt.% graphite in an aqueous solution of 0.1 wt.% TW80 using 100 µm ZrO 2 beads, a stirrer rotation speed of 1,000 rpm in a stirred media mill PE075 as a function of the cut size of the subsequent centrifugation step. www.editorialmanager.com/nare/default.asp
Statistical Raman spectroscopy evaluation Discussed are typical spectra obtained during Raman mapping and an exemplary fitting of the 2D-peak by a Lorentz-function for I G > 300 counts (Fig. S5 left spectrum) and I G < 300 counts (Fig. S3 right spectrum). Spectra with a G-peak intensity of < 300 counts demonstrate a poor quality for fitting. Directly connected is the influence of the neglected spectra during evaluation for the mapped and actually evaluated area, as displayed in Fig. S6. In total 2,914 spectra where analyzed with G-peak intensity > 300 counts, a representative example of the obtained mean values and related standard deviations for mentioned data in the manuscript is depicted in Fig. S7 (compare Fig. 2). Figure S5 Example for selection of Raman spectra for statistical evaluation. Exemplary Raman spectra of a recorded Raman map for a processed sample. Left picture represents a typical evaluated spectrum with I G > 300 counts. Right spectrum represents a typical neglected spectrum with I G < 300 counts. Figure S6 Influence of selection by I G > 300 counts to evaluated surface. Example of a map of the maximum intensity of the G-peak plotted two dimensionally over the measured surface during mapping. Different intensities are distinguished by the color scheme of the legend. Red color represents intensity equivalent for noise (left map) or total neglected area as for too low intensities for good evaluation (right map). www.thenanoresearch.com www.springer.com/journal/12274 Nano Research
Figure S7 Combined plot of all spectra evaluated during a Raman mapping. 2D-FWHM data plotted vs D/G ratio obtained from all fitted spectra during a typical Raman mapping. Calculated mean value and standard deviation marked in red. Influence of viscosity on obtained product concentration The influence of viscosity on the dispersed carbon and FLG yield obtained after delamination in a stirred media mill is displayed in Fig. S8. Figure S8 Influence of viscosity on dispersed carbon and FLG concentration after 90 min of delamination using a stirrer rotation speed of 1,000 rpm and 100 µm ZrO 2 beads as a function of dispersing medium viscosity. Product morphology obtained by Atomic Force Microscopy imaging The efficiency of exfoliation can, in addition to Raman spectroscopy, be determined by measuring the height of flakes found on the wafer via atomic force microscopy. Figures S9 and S10 show characteristic atomic force microscopy images of samples processed by stirred media delamination with TW80 as surfactant. During coating concentration effects can lead to aggregation of stabilized flakes [S1, S2]. As already small residues of stabilizing agents or additives for adjusting the viscosity, which are not completely removed from the sheet surface, contribute directly to the height of the flake, it is difficult to get the correct number of layers directly from the measured height. Depending on the surfactant used as stabilizing agent the height of a monolayer can vary between 0.6 3 nm [S3, S4]. www.editorialmanager.com/nare/default.asp
Figure S9 (a) AFM image of a 30 min processed sample using a stirrer rotation speed of 500 rpm and 30 µm ZrO 2 beads with 3 representative flakes marked. (b) Cross sections of the marked flakes 1 3. Figure S10 (a) AFM image of a 30 min processed sample using a stirrer rotation speed of 1,000 rpm and 100 µm ZrO 2 beads and a viscosity of 1.29 mpa s with 5 representative flakes marked. (b) Cross sections of the marked flakes 1 4, 6,7. (c) Crop of flake 5. (d) cross section of flake 5. Discussion of autogenously delamination by wet media comminution Besides the discussed impact of two colliding beads for a delamination event in the manuscript, also collisions between two carbon particles may contribute to SI and SN and therefore to E m. However, for ZrO 2 bead diameters of 30 and 100 μm respectively, SI for a collision is higher by the factor of 10 and 374, respectively, in comparison with SI for a collision of two 20 μm carbon particles (representing the mean feed particle size). For the amounts of carbon and ZrO 2 beads used in typical delamination experiments the number of 100 and 30 μm ZrO 2 beads, respectively, inside the milling chamber is higher by the factor of two and about 10 2 in comparison with the number of carbon particles. Thus, for bead collision the product of SI and SN is always at least two orders of magnitude larger than for collision of two 20 μm carbon particles. Therefore, for the experimental set up used, the contribution of collisions between particles to delamination can be neglected. www.thenanoresearch.com www.springer.com/journal/12274 Nano Research
References [S1] Coleman, J. N. Liquid exfoliation of defect-free graphene. Acc. Chem. Res. 2012, 1, 14 22. [S2] Paton, K. R.; Varrla, E.; Backes, C.; Smith, R. J.; Khan, U.; O Neill, A.; Boland, C.; Lotya, M.; Istrate, O. M., King, P.; et al. Scalable production of large quantities of defect-free few-layer graphene by shear exfoliation in liquids, Nat. Mater. 2014, 6, 624 630. [S3] Bourlinos, A. B.; Georgakilas, V.; Zboril, R.; Steriotis, T. A., Stubos, A. K.; et al. Liquid-phase exfoliation of graphite towards solubilized graphenes. Small 2009, 16, 1841 1845. [S4] Green, A. A.; Hersam, M. C. Solution phase production of graphene with controlled thickness via density differentiation. Nano Lett. 2009, 12, 4031 4036. www.editorialmanager.com/nare/default.asp