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sp-Electron Magnetic Clusters with a Large Spin in Graphene
Boukhvalov, Danil W.,Katsnelson, Mikhail I. American Chemical Society 2011 ACS NANO Vol.5 No.4
<P>Motivated by recent experimental data (Sepioni, M.; <I>et al. Phys. Rev. Lett</I>. <B>2010</B>, <I>105</I>, 207−205), we have studied the possibility of forming magnetic clusters with spin <I>S</I> > <SUP>1</SUP>/<SUB>2</SUB> on graphene by adsorption of hydrogen atoms or hydroxyl groups. Migration of hydrogen atoms and hydroxyl groups on the surface of graphene during the delamination of HOPG led to the formation of seven atom or seven OH-group clusters with <I>S</I> = <SUP>5</SUP>/<SUB>2</SUB> that were of a special interest. The coincidence of symmetry of the clusters with the graphene lattice strengthens the stability of the cluster. For (OH)<SUB>7</SUB> clusters that were situated greater than 3 nm from one another, the reconstruction barrier to a nonmagnetic configuration was approximately 0.4 eV, whereas for H<SUB>7</SUB> clusters, there was no barrier and the high-spin state was unstable. Stability of the high-spin clusters increased if they were formed on top of ripples. Exchange interactions between the clusters were studied and we have shown that the ferromagnetic state is improbable. The role of the chemical composition of the solvent used for the delamination of graphite is discussed.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-4/nn103510c/production/images/medium/nn-2010-03510c_0001.gif'></P>
Origin of Anomalous Water Permeation through Graphene Oxide Membrane
Boukhvalov, Danil W.,Katsnelson, Mikhail I.,Son, Young-Woo American Chemical Society 2013 Nano letters Vol.13 No.8
<P>Water inside the low-dimensional carbon structures has been considered seriously owing to fundamental interest in its flow and structures as well as its practical impact. Recently, the anomalous perfect penetration of water through graphene oxide membrane was demonstrated although the membrane was impenetrable for other liquids and even gases. The unusual auxetic behavior of graphene oxide in the presence of water was also reported. Here, on the basis of first-principles calculations, we establish atomistic models for hybrid systems composed of water and graphene oxides revealing the anomalous water behavior inside the stacked graphene oxides. We show that formation of hexagonal ice bilayer in between the flakes as well as melting transition of ice at the edges of flakes are crucial to realize the perfect water permeation across the whole stacked structures. The distance between adjacent layers that can be controlled either by oxygen reduction process or pressure is shown to determine the water flow thus highlighting a unique water dynamics in randomly connected two-dimensional spaces.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-8/nl4020292/production/images/medium/nl-2013-020292_0005.gif'></P>