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Your search keyword '"Khavryuchenko, Oleksiy V."' showing total 115 results
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115 results on '"Khavryuchenko, Oleksiy V."'

20. Enabling visible-light water photooxidation by coordinative incorporation of Co(II/III) cocatalytic sites into organic-inorganic hybrids: Quantum-chemical modeling and photoelectrochemical performance

Author

Khavryuchenko, Oleksiy V., Lidong Wang, Mitoraj, Dariusz, Peslherbe, Gilles H., and Beranek, Radim

Abstract

Coordinative incorporation of Co(II/III) cocatalytic sites into organic-inorganic hybrids of TiO2 and “polyheptazine” (PH, poly(aminoimino)heptazine, melon or “graphitic carbon nitride”) has been investigated both by quantum-chemical calculations and experimental techniques. Specifically, density-functional theory (DFT) calculations (PBE/def2-TZVPP) suggest that Co(II/III) and Zn(II) ions adsorb in nano-cavities at the surface of the hybrid PH–TiO2 cluster, a prediction which can be further confirmed experimentally by 15N nuclear magnetic resonance in the case of the Zn complex. The absorption spectra of the complexes were characterized by time-dependent DFT calculations, suggesting a change of color upon Co ion binding which can in fact be observed with the naked eye. Hybrid TiO2–PH photoelectrodes were impregnated with Co(II) ions from aqueous cobalt nitrate solutions. Optical absorption data suggest that Co(II) ions are predominantly present as single ions coordinated within the nitrogen cavities of TiO2-PH, and any undesired blocking of light absorption is negligible. The cobalt-induced cocatalytic sites can efficiently couple to the holes photogenerated by visible light in TiO2-PH, leading to complete oxidation of water to dioxygen. Our results indicate that coordinative incorporation of metal ions into well-designed surface sites in the light absorber is sufficient to drive complex multielectron transformations in artificial photosynthetic systems.

Published
2015
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46. A density-functional theory investigation of the structural and spin properties of (PO2)4(WO3)8 model bronzes

Author

Khavryuchenko, Oleksiy V., Stus, Nataliya V., and Peslherbe, Gilles H.

Subjects
*DENSITY functionals, *TUNGSTEN bronze, *X-ray diffraction, *TEMPERATURE effect, *OCTAHEDRA, *X-ray crystallography
Abstract

Abstract: Plane-wave density-functional theory calculations of P4W8O32 mono-phosphate tungsten bronzes with pentagonal tunnels demonstrate that (1) these materials possess a ground (singlet) state structure of orthorombic symmetry, as observed by X-ray diffraction crystallography at room temperature; (2) open-shell states lie very close in energy to the ground state and are significantly populated at room temperature; and (3) these low-lying states are likely to be implicated in the formation of a superstructure due to the tilting of WO6 octahedra (Peierls-like structural transformations) upon temperature decrease. The latter finding is consistent with the existence of a low-temperature incommensurate structure, as evidenced by the satellite peaks observed in X-ray diffraction patterns. [Copyright &y& Elsevier]

Published
2012
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48. Visible-light photocurrent response of TiO2–polyheptazine hybrids: evidence for interfacial charge-transfer absorption.

Author

Bledowski, Michal, Wang, Lidong, Ramakrishnan, Ayyappan, Khavryuchenko, Oleksiy V., Khavryuchenko, Volodymyr D., Ricci, P. Carlo, Strunk, Jennifer, Cremer, Till, Kolbeck, Claudia, and Beranek, Radim

Abstract

We investigated photoelectrodes based on TiO2–polyheptazine hybrid materials. Since both TiO2 and polyheptazine are extremely chemically stable, these materials are highly promising candidates for fabrication of photoanodes for water photooxidation. The properties of the hybrids were experimentally determined by a careful analysis of optical absorption spectra, luminescence properties and photoelectrochemical measurements, and corroborated by quantum chemical calculations. We provide for the first time clear experimental evidence for the formation of an interfacial charge-transfer complex between polyheptazine (donor) and TiO2 (acceptor), which is responsible for a significant red shift of absorption and photocurrent response of the hybrid as compared to both of the single components. The direct optical charge transfer from the HOMO of polyheptazine to the conduction band edge of TiO2 gives rise to an absorption band centered at 2.3 eV (540 nm). The estimated potential of photogenerated holes (+1.7 V vs. NHE, pH 7) allows for photooxidation of water (+0.82 V vs. NHE, pH 7) as evidenced by visible light-driven (λ ＞ 420 nm) evolution of dioxygen on hybrid electrodes modified with IrO2 nanoparticles as a co-catalyst. The quantum-chemical simulations demonstrate that the TiO2–polyheptazine interface is a complex and flexible system energetically favorable for proton-transfer processes required for water oxidation. Apart from water splitting, this type of hybrid materials may also find further applications in a broader research area of solar energy conversion and photo-responsive devices. [ABSTRACT FROM AUTHOR]

Published
2011
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49. Effect of spin catalysis in H2S oxidation: A quantum chemical insight

Author

Khavryuchenko, Volodymyr D., Khavryuchenko, Oleksiy V., and Lisnyak, Vladyslav V.

Subjects
*HYDROGEN sulfide, *OXIDATION, *QUANTUM chemistry, *QUINONE, *SURFACE chemistry, *ACTIVATED carbon, *RADICALS (Chemistry), *DESULFURIZATION
Abstract

Abstract: Reactions of H2S with quinones and a model carbonic cluster, mimicking an active centre on the surface of active carbon have been quantum chemically simulated. Energetic parameters of elementary steps have been computed. An impact of spin state of the system on the reaction pathway has been formulated, demonstrating that the processes studied belong to the realm of spin chemistry. It is shown that the carbon matrix acts as source of spin density and, thus, can itself promote the reaction of sulphidic radicals generation, which are usually spin-forbidden. [Copyright &y& Elsevier]

Published
2010
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50. INTERACTION OF THE DIOXYGEN MOLECULE WITH THE C96H24 POLYAROMATIC HYDROCARBON CLUSTER:: A QUANTUM CHEMICAL INSIGHT.

Author

Khavryuchenko, Volodymyr D., Tarasenko, Yurij A., Strelko, Volodymyr V., Khavryuchenko, Oleksiy V., and Lisnyak, Vladyslav V.

Subjects
QUANTUM chemistry, HYDROCARBONS, AROMATIC compounds, OXYGEN, ADSORPTION (Chemistry)
Abstract

Interaction of the previously described [V. D. Khavryuchenko, Y. A. Tarasenko, V. V. Strelko, O. V. Khavryuchenko and V. V. Lisnyak, Quantum chemical study of polyaromatic hydrocarbons in high multiplicity states, Int. J. Modern. Phys. B21, 4507 (2007), in press] polyaromatic hydrocarbon (PAH) C96H24 with dioxygen molecule and KO2 have been quantum chemically examined. The probability of existence of the oxygen superoxide ion-radical O2 adsorbed on the surface of the PAH is critically discussed. [ABSTRACT FROM AUTHOR]

Published
2008
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