Effect of oxygen adsorption on magnetic properties of graphite

Boukhvalov, D. W.,Moehlecke, S.,da Silva, R. R.,Kopelevich, Y. American Physical Society 2011 Physical review. B, Condensed matter and materials Vol.83 No.23

Oxygen reduction reactions on pure and nitrogen-doped graphene: a first-principles modeling

Boukhvalov, Danil W.,Son, Young-Woo The Royal Society of Chemistry 2012 Nanoscale Vol.4 No.2

<P>Based on first principles density functional theory calculations we explored energetics of oxygen reduction reaction over pristine and nitrogen-doped graphene with different amounts of nitrogen doping. The process of oxygen reduction requires one more step than the same reaction catalyzed by metals. Results of calculations evidence that for the case of light doped graphene (about 4% of nitrogen) the energy barrier for each step is lower than for the same process on a Pt surface. In contrast to the catalysis on a metal surface the maximal coverage of doped graphene is lower and depends on the corrugation of graphene. Changes of the energy barriers caused by oxygen load and corrugation are also discussed.</P>

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>

First-Principles Modeling of the Polycyclic Aromatic Hydrocarbons Reduction

Boukhvalov, D. W.,Feng, X.,Mü,llen, K. American Chemical Society 2011 The Journal of Physical Chemistry Part C Vol.115 No.32

<P>Density functional theory modeling of the reduction of realistic nanographene molecules (C<SUB>42</SUB>H<SUB>18</SUB>, C<SUB>48</SUB>H<SUB>18</SUB>, and C<SUB>60</SUB>H<SUB>24</SUB>) by molecular hydrogen evidence of the presence of limits in the hydrogenation process. These limits caused the contentions between three-fold symmetry of polycyclic aromatic hydrocarbon molecules and two-fold symmetry of adsorbed hydrogen pairs. Increase in the binding energy between nanographenes during reduction is also discussed as a possible cause of the experimentally observed limited hydrogenation of studied nanographenes.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2011/jpccck.2011.115.issue-32/jp2024928/production/images/medium/jp-2011-024928_0002.gif'></P>

A Computational Investigation of the Catalytic Properties of Graphene Oxide: Exploring Mechanisms by using DFT Methods

Boukhvalov, Danil W.,Dreyer, Daniel R.,Bielawski, Christopher W.,Son, Young‐,Woo Wiley (John WileySons) 2012 ChemCatChem Vol.4 No.11

Penetration of alkali atoms throughout a graphene membrane: theoretical modeling.

Boukhvalov, D W,Virojanadara, C RSC Pub 2012 Nanoscale Vol.4 No.5

<P>Theoretical studies of penetration of various alkali atoms (Li, Na, Rb, Cs) throughout a graphene membrane grown on a silicon carbide substrate are reported and compared with recent experimental results. Results of first principles modeling demonstrate a rather low (about 0.8 eV) energy barrier for the formation of temporary defects in the carbon layer required for the penetration of Li at a high concentration of adatoms, a higher (about 2 eV) barrier for Na, and barriers above 4 eV for Rb and Cs. Experiments prove migration of lithium adatoms from the graphene surface to the buffer layer and SiC substrate at room temperature, sodium at 100 C and impenetrability of the graphene membrane for Rb and Cs. Differences between epitaxial and free-standing graphene for the penetration of alkali ions are also discussed.</P>

Development of Theoretical Descriptors for Cytotoxicity Evaluation of Metallic Nanoparticles

Boukhvalov, D. W.,Yoon, T. H. American Chemical Society 2017 Chemical research in toxicology Vol.30 No.8

<P>Motivated by the recent development of quantitative structure activity relationship (QSAR) methods in the area of nanotoxicology, we proposed an approach to develop additional descriptors based on results of first-principles calculations. For the evaluation of the biochemical activity of metallic nanoparticles, we consider two processes: ion extraction from the surface of a specimen to aqueous media and water dissociation on the surface. We performed calculations for a set of metals (Al, Fe, Cu, Ag, Au, and Pt). Taking into account the diversity of atomic structures of real metallic nanoparticles, we performed calculations for different models such as (001) and (111) surfaces, nanorods, and two different cubic nanoparticles of 0.6 and 0:3 nm size. Significant energy dependence of the processes from the selected model of nanoparticle suggests that for the coned description we should combine the calculations for several representative models. In addition to the descriptors of chemical activity of the metallic nanoparticles for the two studied processes, we propose descriptors for taking into account the dependence Of chemical activity from the size and shape of nanoparticles. Routes to minimization of computational costs for these calculations are also discussed.</P>

Atomic and electronic structure of a copper/graphene interface as prepared and 1.5 years after

Boukhvalov, D.W.,Bazylewski, P.F.,Kukharenko, A.I.,Zhidkov, I.S.,Ponosov, Yu. S.,Kurmaev, E.Z.,Cholakh, S.O.,Lee, Y.H.,Chang, G.S. Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.426 No.-

<P><B>Abstract</B></P> <P>We report the results of X-ray spectroscopy and Raman measurements of as-prepared graphene on a high quality copper surface and the same materials after 1.5 years under different conditions (ambient and low humidity). The obtained results were compared with density functional theory calculations of the formation energies and electronic structures of various structural defects in graphene/Cu interfaces. For evaluation of the stability of the carbon cover, we propose a two-step model. The first step is oxidation of the graphene, and the second is perforation of graphene with the removal of carbon atoms as part of the carbon dioxide molecule. Results of the modeling and experimental measurements provide evidence that graphene grown on high-quality copper substrate becomes robust and stable in time (1.5 years). However, the stability of this interface depends on the quality of the graphene and the number of native defects in the graphene and substrate. The effect of the presence of a metallic substrate with defects on the stability and electronic structure of graphene is also discussed</P> <P><B>Highlights</B></P> <P> <UL> <LI> Proposed model of step by step perforation of graphene on metals during process of oxidation. </LI> <LI> Modeling and measurements demonstrate important role of substrate quality for protective properties of graphene. </LI> <LI> Effect of imperfectness of carbon sheet and substrate to electronic structure of graphene are shown. </LI> <LI> Key conditions for long-term anti-corrosion protection are discussed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Luminescent metal-organic frameworks for the detection of nitrobenzene in aqueous media

Vellingiri, Kowsalya,Boukhvalov, Danil W.,Pandey, Sudhir Kumar,Deep, Akash,Kim, Ki-Hyun Elsevier 2017 Sensors and actuators. B Chemical Vol.245 No.-

<P><B>Abstract</B></P> <P>The feasibility of highly water stable Zr-based metal organic frameworks (MOFs: UiO-66-NH<SUB>2</SUB>) as a sensing probe material was explored for the detection of the electron deficient nitrobenzene (NB) molecule in an aqueous phase. The probe system was highly sensitive toward the NB molecule within the range of 10–100ppm with a linear range of 0–30ppm and a quenching efficiency of around 95% (at 100ppm). The limit of detection (LOD) of the proposed probe was estimated to be 0.9ppm. In contrast, this method was not affected sensitively by potential interferences such as other aromatic compounds. For instance, benzene (B), toluene (T), and chlorobenzene (CB) showed reduced quenching efficiencies (<40%). The specificity toward NB molecules for the proposed probe was appreciable in the presence of co-existing components (B, T, and CB). DFT calculations showed that the sensing mechanism was ascribable to electron transfer from the excited missed-linker induced sites of the ZrOH to the NB molecule. This interaction was confirmed by an FTIR analysis of the UiO-66-NH<SUB>2</SUB>-NB material. Therefore, the proposed UiO-66-NH<SUB>2</SUB> probe can be used as a potent sensing material for the NB even at low concentrations in an aqueous medium.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Quenching mechanism of the metal-organic frameworks (MOFs) is good for sensing hazardous compounds. </LI> <LI> The environmental significance of nitro aromatic compounds is well known due to their health impacts. </LI> <LI> The sensing efficiency of a Zr-based MOFs (UiO-66-NH<SUB>2</SUB>) is assessed against the detection of nitrobenzene. </LI> <LI> The performance of UiO-66-NH<SUB>2</SUB> was demonstrated along with the temporal stability and regenerability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>