arXiv subjects

Vitaly Chaban

Publications and source records attributed to Vitaly Chaban.

14 recordsLinked to original sources

arXiv2016

The Haber Process Made Efficient by Hydroxylated Graphene

The Haber-Bosch process is the main industrial method for producing ammonia from diatomic nitrogen and hydrogen. Very demanding energetically, it uses an iron catalyst, and requires high temperature and pressure. Any improvement of the Haber process will have an extreme scientific and economic impact. We report a significant increase of ammonia production using hydroxylated graphene. Exploiting the polarity difference between N2/H2 and NH3, as well as the universal proton acceptor behavior of NH3, we demonstrate a strong shift of the equilibrium of the Haber-Bosch process towards ammonia. Hydroxylated graphene provides the polar environment favoring the forward reaction, and remain stable under the investigated thermodynamic conditions. Ca. 50 kJ mol-1 enthalpy gain and ca. 60-70 kJ mol-1 free energy gain are achieved at 298-1300 K and 1-1000 bar, strongly shifting the reaction equilibrium towards the product. A clear microscopic interpretation of the observed phenomenon is given using electronic structure calculations and real-time reactive simulations. The demonstrated principle can be applied with many polar groups functionalizing a substrate with a high surface area, provided that the system is chemically inert to H2, N2 and NH3. The modified Haber-Bosch process is of significant importance to the chemical industry, since it provides a substantial increase of the reaction yield while decreasing the temperature and pressure, thereby, reducing the cost.

physics.chem-ph↗

arXiv2015

Halogenation Thermodynamics of Pyrrolidinium-Based Ionic Liquids

Room-temperature ionic liquids (RTILs) exhibit large difference between melting and boiling points. They are highly tunable thanks to numerous accessible combinations of the cation and the anion. On top of that, cations can be functionalized using methods of organic chemistry. This paper reports gas-phase thermodynamics (enthalpy, entropy, Gibbs free energy) of the halogenation reactions (fluorination, chlorination, bromination) involving protonated pyrrolidine C4H10N+, protic N-ethylpyrrolidinium C4H9N(C2H5)+, and aprotic N-ethyl-N-methylpyrrolidinium C4H8N(CH3)(C2H5)+ cations. Substitution of all symmetrically non-equivalent hydrogen atoms was compared based of the thermodynamic favorability. Fluorination of all sites is much more favorable than chlorination, whereas chlorination is somewhat more favorable than bromination. This is not trivial, since electronegative fluorine and chlorine have to compete for the already insufficient number of electrons with other atoms belonging to the pyrrolidinium-based cations. The difference between different reaction sites within the cations is modest, although it often exceeds kT at simulated temperatures. The correlation between thermodynamics and electronic density distribution has been established, which allows new simple prediction of the reaction pathways. The reported results inspire further chemical modifications of the pyrrolidinium-based RTILs to achieve ever finer tunability of physical chemical properties.

cond-mat.mtrl-sci↗

arXiv2015

Negatively Charged Silver-Doped Gold Nanoscale Clusters

Gold nanoparticles (GNPs) constitute a breakthrough in modern chemistry. The recent success in the synthesis and total structure determination of the precise-composition GNPs provides exciting opportunities for fundamental studies and development of novel applications. GNPs allow for specific number of alien metal atoms to be incorporated into the gold core. Doping tunes optical, structural, and electronic properties of the nanostructure. This work examines silver-doped negatively charged Au25Ag25-N (N=1,2,3) GNPs using PM7-MD. GNP is shown to accommodate multiple silver atoms, whereas silver atoms prefer to create Au2 clusters at the surface. Silver-gold binding appears inferior to the gold-gold binding.

cond-mat.mtrl-sci↗

arXiv2015

Solvation of the Fluorine Containing Anions and Their Lithium Salts in Propylene Carbonate and Dimethoxyethane

Electrolyte solutions based on the propylene carbonate (PC)-dimethoxyethane (DME) mixtures are of significant importance and urgency due to emergence of lithium-ion batteries. Solvation and coordination of the lithium cation in these systems have been recently attended in detail. However, analogous information concerning anions (tetrafluoroborate, hexafluorophosphate) is still missed. This work reports PM7-MD simulations (electronic-structure level of description) to include finite-temperature effects on the anion solvation regularities in the PC-DME mixture. The reported result evidences that the anions appear weakly solvated. This observation is linked to the absence of suitable coordination sites in the solvent molecules. In the concentrated electrolyte solutions, both BF4 and PF6 prefer to exist as neutral ion pairs (LiBF4, LiPF6).

cond-mat.mtrl-sci↗

arXiv2015

Solvation of Lithium Ion in Dimethoxyethane and Propylene Carbonate

Solvation of the lithium ion (Li+) in dimethoxyethane (DME) and propylene carbonate (PC) is of scientific significance and urgency in the context of lithium-ion batteries. I report PM7-MD simulations on the composition of Li+ solvation shells (SH) in a few DME/PC mixtures. The equimolar mixture features preferential solvation by PC, in agreement with classical MD studies. However, one DME molecule is always present in the first SH, supplementing the cage formed by five PC molecules. As PC molecules get removed, DME gradually substitutes vacant places. In the PC-poor mixtures, an entire SH is populated by five DME molecules.

cond-mat.mtrl-sci↗

arXiv2015

Hydrogen Fluoride Capture by Imidazolium Acetate Ionic Liquid

Extraction of hydrofluoric acid (HF) from oils is a drastically important problem in petroleum industry, since HF causes quick corrosion of pipe lines and brings severe health problems to humanity. Some ionic liquids (ILs) constitute promising scavenger agents thanks to strong binding to polar compounds and tunability. PM7-MD simulations and hybrid density functional theory are employed here to consider HF capture ability of ILs. Discussing the effects and impacts of the cation and the anion separately and together, I will evaluate performance of imidazolium acetate and outline systematic search guidelines for efficient adsorption and extraction of HF.

cond-mat.mtrl-sci↗

arXiv2014

Competitive Solvation of the Imidazolium Cation by Water and Methanol

Imidazolium-based ionic liquids are widely used in conjunction with molecular liquids for various applications. Solvation, miscibility and similar properties are of fundamental importance for successful implementation of theoretical schemes. This work reports competitive solvation of the 1,3-dimethylimidazolium cation by water and methanol. Employing molecular dynamics simulations powered by semiempirical Hamiltonian (electronic structure level of description), the local structure nearly imidazolium cation is described in terms of radial distribution functions. Although water and methanol are chemically similar, water appears systematically more successful in solvating the 1,3-dimethylimidazolium cation. This result fosters construction of future applications of the ternary ion-molecular systems.

physics.chem-ph↗

arXiv2014

Systematic Refinement of Canongia Lopes-Padua Force Field for Pyrrolidinium-Based Ionic Liquids

Reliable force field (FF) is a central issue in successful prediction of physical chemical properties via computer simulations. Together with the original CL-P parameters, our force field fosters computational investigation of ionic liquids. In addition, the reported results shed more light on the chemical nature of cation-anion binding in various families of RTILs.

cond-mat.mtrl-sci↗

arXiv2014

Computationally Efficient Prediction of Area per Lipid

Area per lipid (APL) is an important property of biological and artificial membranes. Newly constructed bilayers are characterized by their APL and newly elaborated force fields must reproduce APL. Computer simulations of APL are very expensive due to slow conformational dynamics. The simulated dynamics increases exponentially with respect to temperature. APL dependence on temperature is linear over an entire temperature range. I provide numerical evidence that thermal expansion coefficient of a lipid bilayer can be computed at elevated temperatures and extrapolated to the temperature of interest. Thus, sampling times to predict accurate APL are reduced by a factor of ~10.

cond-mat.mtrl-sci↗

arXiv2014

Annealing Relaxation of Ultrasmall Gold Nanostructures

Except serving as an excellent gift on proper occasions, gold finds applications in life sciences, particularly in diagnostics and therapeutics. These applications were made possible by gold nanoparticles, which differ drastically from macroscopic gold. Versatile surface chemistry of gold nanoparticles allows coating with small molecules, polymers, biological recognition molecules. Theoretical investigation of nanoscale gold is not trivial, because of numerous metastable states in these systems. Unlike elsewhere, this work obtains equilibrium structures using annealing simulations within the recently introduced PM7-MD method. Geometries of the ultrasmall gold nanostructures with chalcogen coverage are described at finite temperature, for the first time.

cond-mat.mtrl-sci↗

arXiv2014

The Thiocyanate Anion is a Primary Driver of Carbon Dioxide Capture by Ionic Liquids

Carbon dioxide, CO2, capture by room-temperature ionic liquids (RTILs) is a vivid research area featuring both accomplishments and frustrations. This work employs the PM7-MD method to simulate adsorption of CO2 by 1,3-dimethylimidazolium thiocyanate at 300 K. The obtained result evidences that the thiocyanate anion plays a key role in gas capture, whereas the impact of the 1,3-dimethylimidazolium cation is mediocre. Decomposition of the computed wave function on the individual molecular orbitals confirms that CO2-SCN binding extends beyond just expected electrostatic interactions in the ion-molecular system and involves partial sharing of valence orbitals.

cond-mat.mtrl-sci↗

arXiv2014

Competitive Solvation of (Bis)(trifluoromethanesulfonyl)imide Anion by Acetonitrile and Water

Competitive solvation of an ion by two or more solvents is one of the key phenomena determining the identity of our world. Solvation in polar solvents frequently originates from non-additive non-covalent interactions. Pre-parametrized potentials poorly capture these interactions, unless the force field derivation is repeated for every new system. Development cost increases drastically as new chemical species are supplied. This work represents an alternative simulation approach, PM7-MD, by coupling the latest semiempirical parametrization, PM7, with equation-of-motion propagation scheme and temperature coupling. Using a competitive solvation of (bis)(trifluoromethanesulfonyl)imide anion in acetonitrile and water, the work demonstrates efficiency and robustness of PM7-MD.

cond-mat.mtrl-sci↗

arXiv2014

Nanoscale Carbon Greatly Enhances Mobility of a Highly Viscous Ionic Liquid

Ability to encapsulate molecules is one of the outstanding features of nanotubes. The encapsulation alters physical and chemical properties of both nanotubes and guest species. The latter normally form a separate phase, exhibiting drastically different behavior compared to bulk. Ionic liquids (ILs) and apolar carbon nanotubes (CNTs) are disparate objects; nevertheless, their interaction leads to spontaneous CNT filling with ILs. Moreover, ionic diffusion of highly viscous ILs can increase 5-fold inside CNTs, approaching that of molecular liquids, even though the confined IL phase still contains exclusively ions. We exemplify these unusual effects by computer simulation on a highly hydrophilic, electrostatically structured, and immobile 1-ethyl-3-methylimidazolium chloride, [C2C1IM][Cl]. Self-diffusion constants and energetic properties provide microscopic interpretation of the observed phenomena. Governed by internal energy and entropy rather than external work, the kinetics of CNT filling is characterized in detail. The significant growth of the IL mobility induced by nanoscale carbon promises important advances in electricity storage devices.

cond-mat.mtrl-sci↗

arXiv2011

Strength and structure of carbon-carbon reinforced composite

The atomistic simulations of carbon nanotube (CNT) - carbon reinforced composite material are reported. The studied composite samples were obtained by impregnating certain amounts of CNTs (3,3) and (6,6) into pristine graphite matrix. The addition of CNTs is found to be of significant usefulness for nanotube-reinforced carbon composites since it allows to achieve extreme lightness and strength. Being impregnated into graphite matrix, nanotubes are able to increase the critical component of its highly anisotropic Young modulus by 2-8 times. The linear thermal expansion coefficients do not exceed 1E-5 K-1, making these composites applicable for aviation and space vehicles. The dispersion of CNTs within graphite matrix was found to drastically influence composite properties.

cond-mat.mtrl-sci↗