Oleksiy V. Khavryuchenko

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

We investigated photoelectrodes based on TiO(2)-polyheptazine hybrid materials. Since both TiO(2) 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 TiO(2) (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 TiO(2) 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 IrO(2) nanoparticles as a co-catalyst. The quantum-chemical simulations demonstrate that the TiO(2)-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.

Visible‐Light Photooxidation of Water to Oxygen at Hybrid TiO2–Polyheptazine Photoanodes with Photodeposited Co‐Pi (CoOx) Cocatalyst

A cobalt oxide-based oxygen-evolving cocatalyst (Co-Pi) is photodeposited by visible-light irradiation onto nanocrystalline TiO(2)-polyheptazine (TiO(2)-PH) hybrid photoelectrodes in a phosphate buffer. The Co-Pi cocatalyst couples effectively to photoholes generated in the surface polyheptazine layer of the TiO(2)-PH photoanode, as evidenced by complete photooxidation of water to oxygen under visible-light (λ>420 nm) irradiation at moderate bias potentials. In addition, the presence of the cocatalyst also reduces significantly the recombination of photogenerated charges, particularly at low bias potentials, which is ascribed to better photooxidation kinetics resulting in lower accumulation of holes. This suggests that further improvements of photoconversion efficiency can be achieved if more effective catalytic sites for water oxidation are introduced to the surface structure of the hybrid photoanodes.

Focused enumeration and assessing the structural diversity of scaffold libraries: conformationally restricted bicyclic secondary diamines

Comprehensive enumeration of conformationally restricted bicyclic secondary diamines (CRDA) was performed within defined structural limits, yielding a library of all theoretically possible compounds of this class, potentially useful as building blocks for drug design. In order to assess structural diversity of the generated library, molecular geometries of the library members were optimized using DFT calculations. It was shown that the distance between the amino groups and their relative orientation in space vary widely over the whole library, which might be beneficial for diversity-oriented conformational restriction approach in drug discovery. There are many representatives of “three-dimensional” scaffolds in the CRDA library. Selected literature data on biological activity of the known CRDA derivatives were discussed, demonstrating utility of the CRDA scaffold hopping in drug design.

Synthesis and physicochemical characterization of two lead(II) complexes with O-, N-donor ligands. Lone pair functionality and crystal structure.

A dinuclear [Pb2(4-CHO-5-MeIm)6(NO3)2](NO3)2 (1) and a polynuclear [Pb(2-pzc)2(H2O)]n (2) complexes (where 5(4)-carbaldehyde-4(5)-methylimidazole (5(4)-CHO-4(5)-MeIm) and pyrazine-2-carboxylic acid (2-pzcH)) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. Structural determination for complex 1 reveals a cationic species [Pb(4-CHO-5-MeIm)3]2+ connected through bridging nitrate(V) ions. There are also an uncoordinated nitrate ions as counterions. Complex 2 is a three-dimensional architecture consisting of Pb6O12 building units. The pyrazine-2-carboxylato ligand behaves as a chelating agent and a bi-connective bridge. The coordination polyhedra around lead(II) ion could be described as a distorted docecahedron (1) or monocapped trigonal prism (2). The luminescent properties of 1 and 2 investigated in the solid state at room temperature indicate structure-dependent photoluminescent properties. The DFT calculations and the X-ray structural data point on rather hemidirected type of coordination around Pb(II) ions of 1 and 2.

Quantum chemical insight on vibration spectra of silica systems

A set of silicate ions and corresponding lithium salts have been quantum chemically (QC) simulated in a “free molecule” approach. The infrared (IR), inelastic neutron scattering (INS), and Raman spectra have been simulated and fitted to the experimentally registered ones. The complete assignment of the vibrational bands along with the intensities and potential energy distribution has been performed. The applicability of the traditionally used quasimolecule Si–O–Si model to the interpretation of bands near 440–480 cm− 1 and so-called “Boson” peak near 50 cm− 1 has been critically discussed.

Classification of carbon materials for developing structure-properties relationships based on the aggregate state of the precursors

Abstract Modern carbon science lacks an efficient structure-related classification of materials. We present an approach based on dividing carbon materials by the aggregate state of the precursor. The common features in the structure of carbon particles that allow putting them into a group are discussed, with particular attention to the potential energy stored in the carbon structure from differ- ent rates of relaxation during the synthesis and prearrangement of structural motifs due to the effect of the precursor structure .

Preparation of binary M/Mn (M = Co, Cu, Zn) oxide catalysts by thermal degradation of heterobimetallic complexes

Abstract Thermal degradation of heterobimetallic complexes [M 2 Mn(OAc) 6 (dipy) 2 ] (M = Cu ( 1 ), Co ( 2 ), Zn ( 3 ); dipy = 2,2-dipyridile) and freezly dried mixtures of corresponding metal acetates in stoichiometric ratio M(OAc) 2 :Mn(OAc) 2 = 2:1 has been examined with TG/DTA (in dynamic air and under N 2 atmosphere) and with thermo-programmed desorption mass-spectrometry. The products of 2 decomposition in air has been studied with SEM/EDX, indicating formation of highly dispersed oxide system.

Quantum chemical study of water impact on the calcium hydroxyapatite

Structure and infra-red spectra of Ca5(PO4)3OH·xH2O (where x = 1-3) clusters were simulated by ab initio quantum chemical method. Evolution of the H-bonding character upon increase of water content and corresponding changes of the IR spectra in the ν(H-O) vibrations region are discussed.

Surface characterization of ZnO/ZnMn{sub 2}O{sub 4} and Cu/Mn{sub 3}O{sub 4} powders obtained by thermal degradation of heterobimetallic complexes

From the selective transformation of the heterometallic (Zn-Mn or Cu-Mn) carboxylate complexes with 2,2 Prime -bipyridyl by thermal degradation at relatively low (350 Degree-Sign C) temperature, it was possible to get either well defined spinel ZnMn{sub 2}O{sub 4} over zinc oxide or well dispersed copper particles surrounded by a manganese oxide (Mn{sub 3}O{sub 4}) in a core-shell like structure. Morphology of the powder surface was examined by scanning electron microscopy with energy dispersive X-ray microanalysis (SEM/EDX). Surface composition was determined by X-ray photoelectron spectroscopy (XPS). Specific surface of the powders by nitrogen adsorption was found to be 33{+-}0.2 and 9{+-}0.06 m{sup 2} g{sup -1} for Zn-Mn and Cu-Mn samples, respectively, which is comparable to those of commercial products. - Graphical abstract: From the selective transformation of heterometallic (Zn-Mn or Cu-Mn) carboxylate complexes, it was possible to get either well defined spinel ZnMn{sub 2}O{sub 4} over zinc oxide or well dispersed copper particles surrounded by a manganese oxide (Mn{sub 3}O{sub 4}) in a core-shell like structure. Highlights: Black-Right-Pointing-Pointer Thermal degradation of heterometallic complexes results in fine disperse particles. Black-Right-Pointing-Pointer Core-shell Cu/Mn{sub 3}O{sub 4} particles are obtained. Black-Right-Pointing-Pointer ZnMn{sub 2}O{sub 4} spinel layer covers ZnO particles.

Formation process, reactivity and physicochemical properties of SiO nanoparticles: spectroscopic and computational study

Synthesis and spectral (infrared, Raman and inelastic neutron scattering) examination of SiO thin film, powder and products of their oxidation are reported. Processes of SiO formation and interaction with small species, occurring in gas phase, have been simulated in molecular approach by PM3 quantum chemical (QC) method. The QC-simulated model of the SiO nanoparticle was used as a basic model to QC simulate the interaction of SiO molecules and nanoparticle with O2, CO and H2O in the cluster approach. Structures of nanoparticles, resulting from such interaction, and their vibrational spectra have been QC simulated. Inverted vibrational problems have been solved in each case in order to verify the QC-evaluated models. Mechanism of the SiO high-temperature oxidation in gas phase is proposed and discussed. QC-evaluated models and complete range of corresponding theoretical and experimental vibration spectra represent molecular interactions with the nanoparticles of SiO and related changes in spectral characteristics.