23 research outputs found
Paramagnetic properties of carbon-doped titanium dioxide
This paper reports the experimental results on paramagnetic properties of carbon-doped titanium dioxide. The electron paramagnetic resonance study of the samples has been carried out both in dark and under illumination. The nature of defects and their dynamics under illumination of carbon-doped TiO(2) samples is discussed
Dynamics of photogenerated charge carriers in TiO2 /MoO3, TiO2 /WO3 and TiO2 /V2O5 photocatalysts with mosaic structure
Titania is a widely used photocatalytic material possessing such advantages as low cost and high reactivity under the ultraviolet light illumination. However, the fast recombination of photoexcited charge carriers limits its application. Herein, we have synthesized original nanomaterials with mosaic structures that exhibited well-defined heterojunctions and new properties. Using SEM, XRD, EPR spectroscopy, photocatalytic measurements, and photoinduced pathphysiological activity of these photocatalysts, we studied the processes of charge carrier accumulation in TiO2 /MoO3, TiO2 /WO3, and TiO2 /V2 O5 under in situ UV illumination with emphasis on the charge exchange between energy levels of these nanosized semiconductors. It is shown that the accumulation of photoinduced charges occurs in two forms (i) filled electron traps corresponding to Ti4+ /Ti3+ levels and (ii) Mo5+ centers, both forms contributing to the photoinduced biocide activity of the samples. This work demonstrates that light exposure of heterostructure photocatalysts with mosaic surfaces produces different types of charge-trapping centers capable of interacting with molecular oxygen yielding peroxo species, which provide long-life light-induced âself-cleaningâ behavior. Such photoaccumulating materials open new opportunities in developing light-driven self-sterilization structures exhibiting a prolonged bactericidal effect up to 10 h after stopping light exposure. © 2020 by the authors. Licensee MDPI, Basel, Switzerland
Active Sites on Nanocrystalline Tin Dioxide Surface: Effect of Palladium and Ruthenium Oxides Clusters
Active sites of nanocrystalline tin
dioxide materials with variable particle size, surface area, and catalytic
modifiers were studied. Effect of palladium and ruthenium oxides clusters
on the activity and concentration of tin dioxide surface centers was
evaluated by temperature-programmed desorption techniques using probe
molecules, FTIR spectroscopy, EPR, and thermogravimetric methods.
The surface site concentration decrease was observed with an increase
of SnO<sub>2</sub> particle size and BET area decrease. The active
sites of SnO<sub>2</sub> were found to be selectively promoted by
the additives. Accumulation of surface OH groups including hydroxyl
spin centers and Broensted acid sites was characteristic for SnO<sub>2</sub>/PdO<sub><i>x</i></sub> nanocomposites as a result
of water chemisorption enhancement due to proposed electronic clustersâsupport
interaction. Ruthenium oxide was shown to increase the concentration
of chemisorbed oxygen species via oxygen spillover route
Photocatalytic CO2 Conversion Using Anodic TiO2 Nanotube-CuxO Composites
Nanosized titanium dioxide (TiO2) is currently being actively studied by the global scientific community, since it has a number of properties that are important from a practical point of view. One of these properties is a large specific surface, which makes this material promising for use in photocatalysts, sensors, solar cells, etc. In this work, we prepared photocatalysts based on TiO2 nanotubes for converting carbon dioxide (CO2) into energy-intensive hydrocarbon compounds. Efficient gas-phase CO2 conversion in the prepared single-walled TiO2 nanotube-CuxO composites was investigated. Parameters of defects (radicals) in composites were studied. Methanol and methane were detected during the CO2 photoreduction process. In single-walled TiO2 nanotubes, only Ti3+/oxygen vacancy defects were detected. The Cu2+ centers and O2− radicals were found in TiO2 nanotube-CuxO composites using the EPR technique. It has been established that copper oxide nanoparticles are present in the TiO2 nanotube-CuxO composites in the form of the CuO phase. A phase transformation of CuO to Cu2O takes place during illumination, as has been shown by EPR spectroscopy. It is shown that defects accumulate photoinduced charge carriers. The mechanism of methane and methanol formation is discussed. The results obtained are completely original and show high promise for the use of TiO2-CuxO nanotube composites as photocatalysts for CO2 conversion into hydrocarbon fuel precursors
Active Sites on Nanocrystalline Tin Dioxide Surface: Effect of Palladium and Ruthenium Oxides Clusters
Active sites of nanocrystalline tin
dioxide materials with variable particle size, surface area, and catalytic
modifiers were studied. Effect of palladium and ruthenium oxides clusters
on the activity and concentration of tin dioxide surface centers was
evaluated by temperature-programmed desorption techniques using probe
molecules, FTIR spectroscopy, EPR, and thermogravimetric methods.
The surface site concentration decrease was observed with an increase
of SnO<sub>2</sub> particle size and BET area decrease. The active
sites of SnO<sub>2</sub> were found to be selectively promoted by
the additives. Accumulation of surface OH groups including hydroxyl
spin centers and Broensted acid sites was characteristic for SnO<sub>2</sub>/PdO<sub><i>x</i></sub> nanocomposites as a result
of water chemisorption enhancement due to proposed electronic clustersâsupport
interaction. Ruthenium oxide was shown to increase the concentration
of chemisorbed oxygen species via oxygen spillover route
Photocatalytic CO<sub>2</sub> Conversion Using Anodic TiO<sub>2</sub> Nanotube-Cu<sub>x</sub>O Composites
Nanosized titanium dioxide (TiO2) is currently being actively studied by the global scientific community, since it has a number of properties that are important from a practical point of view. One of these properties is a large specific surface, which makes this material promising for use in photocatalysts, sensors, solar cells, etc. In this work, we prepared photocatalysts based on TiO2 nanotubes for converting carbon dioxide (CO2) into energy-intensive hydrocarbon compounds. Efficient gas-phase CO2 conversion in the prepared single-walled TiO2 nanotube-CuxO composites was investigated. Parameters of defects (radicals) in composites were studied. Methanol and methane were detected during the CO2 photoreduction process. In single-walled TiO2 nanotubes, only Ti3+/oxygen vacancy defects were detected. The Cu2+ centers and O2â radicals were found in TiO2 nanotube-CuxO composites using the EPR technique. It has been established that copper oxide nanoparticles are present in the TiO2 nanotube-CuxO composites in the form of the CuO phase. A phase transformation of CuO to Cu2O takes place during illumination, as has been shown by EPR spectroscopy. It is shown that defects accumulate photoinduced charge carriers. The mechanism of methane and methanol formation is discussed. The results obtained are completely original and show high promise for the use of TiO2-CuxO nanotube composites as photocatalysts for CO2 conversion into hydrocarbon fuel precursors
Doping nature of group V elements in ZnO single crystals grown from melts at high pressure
ZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb2O3, P, As, Sb and Zn3X2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of VZn and VZn-complexes was confirmed and their concentrations were measured. Estimates of the number of VZn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb)Zn-2VZn commonly regarded as responsible for acceptor properties in ZnO