K. I. Papazova

Photocatalytic oxidation of pharmaceuticals on thin nanostructured Zinc Oxide films

The photocatalytic activity of thin ZnO films in the photocatalytic oxidation of the pharmaceuticals, paracetamol and chloramphenicol (Levomycetin) is reported. The films annealed at 500°C exhibit the highest activity. They have a wurtzite-like structure and consist of conducting branches, which are the spinodal decomposition products.

Synthesis and characterization of nanostructured zinc oxide layers for sensor applications

Fractal structures and arrays of nanowires based on zinc oxide are fabricated by two different methods, sol-gel dip-coating and chemical bath deposition combined with sol-gel synthesis. The gas-sensitive properties of the structures are analyzed. It is found that the greatest sensitivity to reducing ethanol vapor is exhibited by the structure with a lower layer in the form of an array of zinc-oxide nanowires modified by four immersions in a copper nitrate solution.

The thermovoltaic effect in zinc oxide inhomogeneously doped with mixed-valence impurities

The thermovoltaic effect has been for the first time observed in zinc oxide. The samples had the form of ZnO/ZnO–Me sandwich structures (Me = Cu, Fe) formed by the sol–gel method. An electromotive force of 1–10 mV appeared in the temperature range of 200–300°C.

Study of the photocatalytic and sensor properties of ZnO/SiO 2 nanocomposite layers

ZnO/SiO2 nanocomposite layers are deposited onto glass substrates by the sol-gel method. The fraction of SiO2 is 20%. The layers are produced by single or double deposition and sol centrifugation. To study the photocatalytic properties of the samples, experiments are performed on the decomposition of Malachite Green oxalate in aqueous solutions under the action of light in the ultra-violet and visible (UV/VIS) spectral ranges. The gas-sensitive properties of the layers are examined by impedance spectroscopy in various gas atmospheres. In all experiments, double-layer ZnO/SiO2 nanocomposites exhibit a higher efficiency, compared with the rest of the samples, irrespective of the irradiation type. The double-layer samples also show the best sensitivity to acetone and isopropanol vapors.

Structures of Nanowires with Zn-ZnO:CuO Junctions for Detecting Ethanol Vapors

The synthesis of ZnO-ZnO:CuO structures in the form of overlapping layers of nanowires of pure and copper oxide-doped zinc oxide is described. These structures are tested as ethanol vapor sensors. The following two-stage method is used to form ZnO:CuO nanowires. At the first stage, ZnO nanowires are formed by chemical deposition from a solution. At the second stage, arrays of ZnO nanowires are coated with a copper-containing layer. The CuO content on the surface of ZnO nanowires is changed by varying the number of immersions in a Cu(NO3)2 solution. The formed structures are studied by scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray analysis. The interaction of the grown sensor structures with ethanol vapors is analyzed by measuring the potential difference between the layers of pure zinc oxide and copper oxide-modified zinc oxide in the temperature range 190–300°C. The response of the sensor is investigated at various ethanol vapor concentrations and detection temperatures.

A new type of gas sensor based on the thermovoltaic effect in zinc oxide inhomogeneously doped with mixed-valence impurities

We propose a new type of potentiometric gas sensor operating on the basis of the thermovoltaic effect in uniformly heated (without temperature gradients) ZnO/ZnO–Fe sandwich structures obtained by the sol–gel method. It is established that a significant contribution to the gas responsivity of sensors is related to the thickness of the upper doped layer of the structure.

Study of the photodegradation of brilliant green on mechanically activated powders of zinc oxide

A study of the photocatalytic activity of commercial and mechanically activated zinc oxide powders has been carried out based on the example of the decomposition of Brilliant Green. The goal of this work was to study the effect of the grinding time (0, 1, 3, 5, and 7 min) on the structure of zinc oxide and its photocatalytic activity under visible and ultraviolet (UV) radiation. It has been found that, when UV radiation is used, the constant of the dye oxidation rate for samples activated for 1 min increases compared with unactivated powders, whereas further mechanical activation leads to a decrease in the photocatalytic activity. When using visible radiation, samples activated for 1 min showed the minimum photocatalytic activity and further mechanical activation led to an increase in the efficiency of photocatalysis.

Green synthesis of UV and visible light active TiO2/WO3 powders and films for malachite green and ethylene photodegradation

Powder nanocomposites of TiO2/WO3 are prepared by a simple solid-state thermal procedure from commercial oxide powders and cast thereafter as a film coating on TLC substrate. The WO3 content in the powder composites is varied from 0.5 to 50%. The phase composition and morphology of titania/tungsten composites and films is characterized by SEM and X-ray analysis. The photocatalytic activity of TiO2/WO3 powders is tested in the degradation of malachite green dye in aqueous solutions under UV and visible light irradiation. The effect of preparation temperature on the photocatalytic activity is also investigated. It is found out that the mixed powder of 5%WO3 manifests the best photocatalytic performance. The prepared powder photocatalyst is deposited as a film coating on TLC sheet for gas-phase application. The as-obtained composite coated photocatalysts with 5%WO3 are tested for air purification from ethylene contamination under UV and visible light illumination. The TiO2/WO3 coated photocatalysts show always a higher efficiency in comparison to that of the pure TiO2.