X. Zhang, Y. Huang, S. Chen, N.Y. Kim, W. Kim, D. Schilter, M. Biswal, B. Li, Z. Lee, S. Ryu, C.W. Bielawski, W.S. Bacsa, R.S. Ruoff
CEMES-CNRS et Université de Toulouse,
Keywords: graphene, functionalisation, graphane
Summary:Functionalization of graphene has a strong effect on its physical and chemical properties. Completely hydrogenated graphene (graphane) is predicted to have a large band-gap1; graphane has not been synthesized. Density functional theory calculations predict the formation of ferromagnetic domains2 in partially hydrogenated graphene. We show here how graphene or few layer graphene with one to three layers can be efficiently hydrogenated using ‘Birch-type’ reduction. Mechanically-exfoliated as well as CVD grown graphene were employed using Li and methanol as a reducing reagent and H2O as the proton donor. The degree of hydrogenation depends on the reducing reagent and number of layers, and the graphene samples were dehydrogenated upon thermal annealing in Argon atmosphere (300C-700C). The degree of hydrogenation was estimated by analysis of the Raman bands and it was found that the reactivity under the Birch conditions is independent of stacking orientation for those stacking orientations studied. Evolution of Raman maps as a function of reduction time revealed that hydrogenation proceeds onward from edges or defects. Edge sealed graphene was found to be inert to the reagents employed. Functionalization of isotope labeled few layer graphene made evident that all the layers are reduced to the same extent. This shows that the reaction proceeds from the perimeter to the interior where the reducing agent can intercalate between the graphene layers. Hydrogenation was found to create strain in the graphene layers, which was detected from Raman spectroscopy and transmission electron microscopy data. Furthermore, hydrogenation changed the optical transmission and fluorescence. Higher fluorescence emission was observed at graphene edges. Our results6 give a detailed insight on the reaction mechanism of hydrogenation of graphene using efficient Birch-type reduction. This work was supported by IBS-R019- D1. References 1. Sofo, J. O.; Chaudhari, A. S.; Barber, G. D., Graphane: A Two-Dimensional Hydrocarbon. Phys Rev B 2007, 75, 153401. 2. Zhou, J.; Wang, Q.; Sun, Q.; Chen, X. S.; Kawazoe, Y.; Jena, P., Ferromagnetism in Semihydrogenated Graphene Sheet. Nano Lett 2009, 9, 3867-3870. 3. Yang, Z. Q.; Sun, Y. Q.; Alemany, L. B.; Narayanan, T. N.; Billups, W. E., Birch Reduction of Graphite. Edge and Interior Functionalization by Hydrogen. J Am Chem Soc 2012, 134, 18689-18694. 4. Schafer, R. A.; Englert, J. M.; Wehrfritz, P.; Bauer, W.; Hauke, F.; Seyller, T.; Hirsch, A., On the Way to Graphane Pronounced Fluorescence of Polyhydrogenated Graphene. Angew Chem Int Edit 2013, 52, 754-757. 5. Whitener, K. E.; Lee, W. K.; Campbell, P. M.; Robinson, J. T.; Sheehan, P. E., Chemical Hydrogenation of Single-layer Graphene Enables Completely Reversible Removal of Electrical Conductivity. Carbon 2014, 72, 348-353. 6. Xu Zhang, Yuan Huang, Shanshan Chen, Na Yeon Kim, Wontaek Kim, David Schilter, Mandakini Biswal, Baowen Li, Zonghoon Lee, Sunmin Ryu, Christopher W. Bielawski, Wolfgang S. Bacsa & Rodney S. Ruoff, Birch-type hydrogenation of few- layer graphenes: products and mechanistic implications, Jounal of the American Chemical Society 138 (2016) 14980.