Tetrapyrrole bizirconium complexes as active catalysts for ethylene polymerization

Ethylene polymerization was carried out by using a group of new dizirconium(IV) tetrapyrrole complexes as catalysts and MAO as co-catalyst under 1 atmosphere pressure of ethylene gas at 25 and 40°C. The highest value of catalyst activity was obtained at 40°C by using bizirconium complexes including one calix[4]pyrrole between two zirconium centers and two terminal chlorines, while zirconium(IV) complexes with coordinated THF, almost have not catalytic activity. The maximum catalytic activity mounted to 830 kg/mol·bar·h by Zr₂(Cy₄ Pyr ₄)Cl₄. The results show that the structure of the coordination sphere of zirconium(IV) has great influence on the rate of polymerization, molar masses of forming polymer, and its molecular mass distribution. Correspondence: Sajjad Mohebbi, Chemistry Department, University of Kurdistan, P.O. Box 66176-416, Sanandaj, Iran.     

Photocatalytic Oxidation Based on Modified Titanium Dioxide with Reduced Graphene Oxide and CdSe/CdS as Nanohybrid Materials

Photocatalytic activity of TiO₂ nanoparticles in the visible light region was enhanced. TiO₂–CdSe and TiO₂–CdSe/CdS nanohybrids were supported on the reduced graphene oxide. These nanohybrid materials were applied as photocatalyst toward oxidation of aromatic alcohols under a mild condition and the molecular oxygen as oxidant. A plausible mechanism for the photocatalytic oxidation was also proposed. Desired nanohybrids were obtained via in situ fixation of CdSe/CdS on the surface of nanosheets of reduced graphene oxide (rGO). Finally, it was modified by TiO₂ sol nanoparticles through a hydrothermal method. The obtained nanomaterials, were characterized by SEM, TEM imaging, XRD, EDAX, DRS and XPS analyses. The size of nanohybrids materials were distributed mostly in a narrow range of 50–65 and 60–75 nm for TiO₂–rGO–CdSe and TiO₂–rGO–CdSe/CdS, respectively. These photocatalysts showed high catalytic activity under visible light irradiation in a short reaction time and even higher selectivity rather than UV irradiation. The yield of catalytic oxidation increased at least 25–30% for TiO₂–CdSe/CdS on rGO, which could be related to its higher light sensitivity and lower energy band gap. The photocatalysts were recycled and reused 8 times without significant loss of their activities due to their stability under visible light.     

Fabrication of a nanostructured TiO2/carbon nanotube composite electrode for voltammetric and impedimetric determination of NTO explosive in the water and soil samples

An electrochemical oxidation route was developed for sensitive and selective assay of nitrotriazolone (NTO) explosive in some environmental samples on a multi-walled carbon nanotube (MWCNTs)/TiO₂ nanocomposite paste electrode, for prevention of the analytical interference of conventional reducible energetic compounds. Detailed evaluations were made for the electrochemical behaviour of NTO on the modified electrode by adsorptive stripping voltammetry, electrochemical impedance spectroscopy (EIS) and chronoamperometry techniques in the pH range of 2.0–10.0. Parameters such as diffusion coefficient constant of NTO were calculated, and various experimental conditions were also optimised. Under optimal conditions the calibration curve had two linear dynamic ranges of 130.0–3251.5 μg L^?1 and 6.5–26.0 mg L^?1 with a detection limit of 26.0 μg L^?1 (0.2 μmol L^?1) and precision of <3%. This electrochemical sensor was further applied to determine NTO in real soil and water samples with satisfactory results.     

Recent synthetic strategies toward the synthesis of spirocyclic compounds comprising six-membered carbocyclic/heterocyclic ring systems

Molecular Diversity - Spirocyclic compounds fascinate the synthetic chemists due to their privileged ring system and efficacy in drug discovery. Many natural compounds comprise spirocyclic moiety...