Electrical properties of polycrystalline TiO<Subscript>2</Subscript>. Prolonged oxidation kinetics

The equilibration kinetics for polycrystalline TiO₂ was monitored during prolonged oxidation at 1,323 K and p(O₂)=75 kPa using the measurements of the electrical conductivity and thermoelectric power. The determined kinetic data indicate the presence of two kinetics regimes; the Regime I (rapid kinetics) and the Regime II (slow kinetics). The prolonged oxidation of TiO₂ is considered in terms of the formation of Ti vacancies at the surface and their subsequent transport into the bulk. This effect, also observed for TiO₂ single crystal, allows to obtain p-type TiO₂ without the incorporation of acceptor-type foreign ions into the TiO₂ lattice. This project was performed as part of the University of New South Wales Research and Development programme on solar-hydrogen.     

New β-isatin aldehyde-N,N′-thiocarbohydrazones: preparation,spectroscopic studies and DFT approach to antioxidant characteristics

Research on Chemical Intermediates - Five new Schiff bases of isatin and its derivatives were prepared from monothiocarbohydrazides and 5-chloro isatin. The chemical structures of the synthesized...     

Mapping fragmental drug-likeness in the MoStBioDat environment: intramolecular hydrogen bonding motifs in β-ketoenols

A detailed knowledge of hydrogen bond geometry and its directional preferences is vital for in silico investigations of the ligand-receptor short-range non-covalent interactions. The spatial arrangement of the carbonyl and hydroxyl groups seems to determine the capability of β-ketoenol derivatives to recognize the surrounding environment by forming inter- and intra-molecular hydrogen bonds (IHB). In the current study we examined the application of the MoStBioDat platform for a massive database screening of the IHB motifs in β-ketoenol subunits (O=C-C=C-OH). Then, the virtual 3D structural data derived from ZINC and PubChem repository were compared to the experimentally determined CSD data. Differences specific for each database were discovered, which indicated inaccuracies in the simulated data.     

Microstructure and Thermal Properties of Ethylene/Vinyl Chloride Copolymers

Abstract

The microstructure of ethylene/vinyl chloride (E/VC) copolymers, prepared by partial reduction of PVC with a variety of reagents, was analyzed using carbon-13 NMR spectroscopy. The effect of the reduction mechanism on the microstructure and stereochemistry of the copolymers was studied. The reduction with tri-n-butyltin hydride (TBTH) produced copolymers with higher degrees of alternating monomer units than copolymers obtained by reduction with lithium aluminum hydride (LAH). Reduction with lithium triethylborohydride (SH) produced blockier copolymers. The correlation of monomer sequence and distribution with thermal stability and dehydrochlorination rate in these copolymers was investigated. Partial reduction of PVC by all reagents was shown to produce E/VC copolymers with improved thermal stability compared to PVC. In the series of copolymers produced by TBTH reduction, improvement in thermal stability increased with an increase in E content and reached a maximum at 40% E content but dropped steadily thereafter. All copolymers from SH reduction showed a considerable drop in their dehydrochlorination rate compared to PVC. The stabilization effect reached a maximum at ～7 mol% E content and stayed constant throughout.     

Pharmacophore-based database mining for probing fragmental drug-likeness of diketo acid analogues

A number of the structurally diverse chemical compounds with functional diketo acid (DKA) subunit(s) have been revealed by combined online and MoStBiodat 3D pharmacophore-guided ZINC and PubChem database screening. We used the structural data available from such screening to analyse the similarities of the compounds containing the DKA fragment. Generally, the analysis by principal component analysis and self-organizing neural network approaches reveals four families of compounds complying with the chemical constitution (aromatic, aliphatic) of the compounds. From a practical point of view, similar studies may reveal potential bioisosteres of known drugs, e.g. raltegravir/elvitegravir. In this context, it seems that mono-halogenated aryl substructures with para group show the closest similarity to these compounds, in contrast to structures where the aromatic ring is halogenated in both ortho- and para-locations.     

Convenient synthesis and isolation of trifluoromethylthio-substituted building blocks

Various aryl-, heteroaryl-, and alkyl mercaptanes (RSH, 1a–r) were treated with a slight excess of NaH suspended in DMF to make the appropriate sodium thiolates (RSNa), which then reacted with 1.3 equivalent of CF₃I at room temperature for overnight to afford the appropriate trifluoromethyl sulfides (CF₃SR, 2) in fair to good yields. The radical chain alkylation reaction was effective without the use of UV irradiation with all but three substrates (thiosalicylic acid, 1k; 2-mercaptobenzimidazole, 1q; and 3-mercaptopropionic acid, 1r).Steam-distillation was found as an effective and easy to upscale means for the isolation of these volatile and water immiscible sulfides. The CF₃I reagent gas was conveniently weighed and delivered to the reaction mixture by the balloon technique or as a preliminary made stock solution in DMF or DMSO. The sulfides 2 obtained here were assayed by GC and characterized by ¹H, ¹³C, ¹⁹F NMR and MS spectroscopy.     

Fabrication and performance of nanoporous TiO2/SnO2 electrodes with a half hollow sphere structure for dye sensitized solar cells

The incorporation of nano-crystalline semiconductors with novel kinds of ordered microstructure is a very important area of research in the field of dye sensitized solar cells. A sol–gel method involving hydrolysis of titanium isopropoxide was used to form TiO₂ nanoparticles on the surface of SiO₂ spheres. In this process, 1, 5, or 10 wt% of SnCl₂.2H₂O was added to the sol–gel solution. To prepare TiO₂/SnO₂ nanoparticles with a half hollow sphere structure, SiO₂ was removed with NaOH solution. The crystal phase, crystal shape, and surface properties of the metal oxide nanocrystals were studied by x-ray diffraction and scanning electron microscopy. The photovoltaic performance of the TiO₂/SnO₂ nanoparticles with half hollow sphere structures was measured. The dye sensitized solar cell using nanoporous TiO₂ as electrode materials exhibits an overall conversion efficiency of 7.36% with a light intensity of 100 mW/cm². The short circuit photocurrent (I_sc), open circuit photovoltage (V_oc), and conversion efficiency (η) of these solar cells were improved over conventional materials.     

Toward sustainable energy: photocatalysis of Cr-doped TiO<Subscript>2</Subscript>: 1. electronic structure

The present chain of five papers considers the concept of defect engineering in processing TiO₂-based photosensitive semiconductors for solar-to-chemical energy conversion. The papers report the effect of chromium on the key performance-related properties of polycrystalline TiO₂ (rutile), including (i) electronic structure, (ii) chromium-related photocatalytic properties, (iii) oxygen-related photocatalytic properties, (iv) electrochemical coupling and (v) surface versus bulk properties. The present work reports the effect of chromium on defect disorder and the related electronic structure of TiO₂, including the band gap and mid-gap energy levels. It is shown that chromium incorporation into the TiO₂ lattice results in a decrease of the band gap from 3.04 eV for pure TiO₂ to 1.4 and 1.3 eV, for Cr-doped TiO₂ (1.365 at% Cr) after annealing at 1373 K in the gas phase of controlled oxygen activity, 21 kPa and 10^?10 Pa, respectively. The optical properties determined using the ultraviolet-vis spectroscopy (in the reflectance mode) indicate that chromium incorporation results in the formation of mid-band energy levels. In this work, we show that chromium at and above the concentrations levels of 0.04 and 0.376 at% results in the formation of acceptor-type energy levels at 0.57 and 1.16 eV (above the valence band), respectively, which are related to tri-valent chromium in titanium sites and titanium vacancies, respectively. Application of well-defined protocol leads to the determination of data that are well reproducible. The new insight involves the determination of the band gap of TiO₂ processed in the gas phase of controlled oxygen activity.

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