The electrical conductivity and the transient photoconductivity of Ag/TiO2 nanoplates were studied at 300K, both in vacuum and in air. A solvothermal method was used for the preparation of anatase TiO2 nanoplates and the embedding of Ag nanoparticles was achieved via the photoreduction of AgNO3 under UVA irradiation. The particle size was controlled by varying the time of illumination and the obtained Ag nanoparticles sizes were in a range of 5–20nm. The Ag/TiO2 nanoplates were characterized by X-ray diffraction (XRD) and transition electron microscopy (TEM). The electrical conductivity and the photoconductivity responses were investigated. The influence of environment was also discussed. For some periods of UVA illumination time, photoconductivity reaches higher values in comparison with the pure TiO2 anatase nanoplates. In air, the influence of the adsorbed on the surface oxygen is obvious, resulting in high recombination rates.

The photoinduced processes of pristine and Mg2+-doped anatase nanopowders with the exposed {0 0 1} facets synthesized by a solvothermal method, using HF as the capping agent, were investigated by EPR spectroscopy. The adsorbed fluoride ions on the {0 0 1} facets of the as-prepared anatase samples have been removed by NaOH washing (washed samples) or calcination at 600 °C (calcined samples). EPR spectra monitored at 100 K for the as-prepared and washed anatase nanopowders characterized with high percentage of the exposed {0 0 1} facets, evidenced the presence of paramagnetic signals attributed to the intrinsic Ti3+ centers with narrow-line axially symmetric spectrum (g⊥ = 1.988, g∥ = 1.956) and holes (O−) characterized with g-tensor g⊥ = 2.006, g∥ = 2.003 already before exposure. Upon in situ UV exposure under air, the intensity of EPR signals of Ti3+ and O− increased significantly and two additional signals compatible with the photogenerated O2− and O2H were observed. A series of indirect EPR techniques, e.g., spin trapping using 5,5-dimethyl-1-pyrroline N-oxide (DMPO), hindered amine oxidation, or reduction of radical cation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate), were applied to follow the reactions in the irradiated TiO2 dispersions. While in the irradiated aerated aqueous media all anatase samples revealed the generation of DMPO-OH spin-adduct, upon UV exposure of the as-prepared samples in deaerated acetonitrile, the formation of a unique EPR spectrum attributed to DMPO-F was found. The DMPO-F spin-adduct is most probably produced by the inverted spin trapping mechanism via interaction of DMPO+ with the surface fluorides.

•Ti3+ and O− EPR signals of Mg2+-doped anatase powders with exposed {001} facets.•UV-induced OH radical generation in TiO2 aqueous media monitored by spin trapping.•UV-induced DMPO-F formation via surface fluorides in acetonitrile under argon.•F− ions on exposed {001} facets enhance the photoinduced redox processes on TiO2.

Ag nanoparticles were photodeposited on the {1 0 1} crystal facets of the TiO2 anatase nanoplates. This was achieved with the photoreduction of AgNO3 in methanol solution in which TiO2 anatase nanoplates were suspended while UVA irradiation was performed. The size range of the photodeposited silver nanoparticles was between 5 and 20 nm. The manipulation of their size was achieved by controlling the UVA light irradiation period of time whereas the formation on the specific facet of the TiO2 anatase nanocrystal was managed by using methanol as a hole scavenger. The silver ions (Ag) were photoreduced by the electrons that were photogenerated due to the TiO2 anatase nanoplates irradiation with UVA light. The photocatalytic activity of the nanocomposites was examined in NO oxidation, showing a higher photocatalytic activity and photonic efficiency in comparison to the pure TiO2 anatase nanoplates. (C) 2014 Elsevier B.V. All rights reserved.

The photocatalytic activity of TiO2 and magnesium doped TiO2 nanocrystals in dopant range of 2-6.2 at%, was studied. The doped and undoped nanocrystals with exposed {0 0 1} crystal facets were synthesized by a solvothermal method. Several studies have shown that the (0 0 1) surface of the TiO2 anatase crystal is more reactive than the thermodynamically stable (1 0 1) surface. The crystal structure as well as the shape of the TiO2 and Mg2+/TiO2 anatase nanoparticles were determined using two different techniques, such as X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), which both lead to the agreeable conclusion that the nanocrystals are in the form of plates. Chemical analysis of the photocatalyst was carried out with X-ray photoelectron spectroscopy (XPS) and showed the presence of magnesium ions in the TiO2 nanoplates. UV-vis diffuse reflectance spectroscopy (DRS) showed that there is an adsorption shift for doped TiO2 to visible light region.The photocalaytic efficiency of the synthesized catalysts was investigated by the photocatalytic oxidation of the gaseous nitric oxide (NO) and decomposition of the gaseous acetaldehyde (CH3 CHO) under UV irradiation. It was demonstrated that the low Mg2+ doped catalysts exhibited higher photocatalytic activity than the pure TiO2. The optimal concentration of dopant that is beneficial for the photocatalytic activity was studied. (c) 2013 Elsevier B.V. All rights reserved.

The photocatalytic activity of TiO2 and manganese doped TiO2 nanoplates with various manganese atomic percentages, in the range of 2-7%, was studied. The undoped and doped nanoplates with exposed {001} facets were produced by a solvothermal method. The crystal structure as well as the shape of the TiO2 and Mn4+/TiO2 anatase nanoparticles was determined with X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Both techniques revealed that the nanocrystals are in the form of plates. Moreover, the anisotropic peak broadening of the X-ray diffraction patterns was studied using the Rietveld refining method. Chemical analysis of the photocatalyst that was carried out with X-ray photoelectron spectroscopy (XPS) showed the presence of manganese ions in the.TiO2 anatase matrix. The Density Functional Theory (OFT) calculations exhibited a decrease in the energy gap and an increase in the density of the electronic stated inside the gap for the doped TiO2 These observations were in agreement with the results of the UV visible diffuse reflectance spectroscopy (DRS) that demonstrated an adsorption shift towards the visible region for the same samples.The photocatalytic activity of the synthesized catalysts was investigated by the photocatalytic oxidation of the gaseous nitric oxide (NO) and decomposition of the gaseous acetaldehyde (CH3CHO) under visible light irradiation. The optimal concentration of dopant that improves the photocatalytic activity of the nanoplates was determined. (C) 2014 Elsevier B.V. All rights reserved.

•Anatase TiO2 hollow microspheres with dominant {001} facets were synthesized by a solvothermal method.•Electrical conductivity was studied in vacuum and in air.•Environment influences significantly the conductivity.•Different conduction mechanisms act at different temperature regions.

Nanosized anatase TiO2 powders with dominant {001} facets were prepared by solvothermal reaction of titanium isopropoxide in the presence of hydrofluoric acid as a capping agent. Two kinds of samples, as prepared and calcinated at 600 degrees C were fabricated and their UV-Visible and transient photoconductivity were investigated in vacuum and in air. The photoconductivity reaches high values and is sensitive on the environment. Thermal treatment improves the crystalline quality and enhances the amount of created excess charge carriers. (C) 2013 Elsevier B.V. All rights reserved.

TiO2 anatase nanoplates were fabricated by a solvothermal method using titanium isopropoxide as a titanium precursor and HF as a capping agent in order to enhance the formation of the {0 0 1} crystal facets of the anatase crystal. Two different surface modification procedures were applied in order to remove the adsorbed fluoride anions on the {0 0 1} crystal facets of the nanoplates. The first procedure was by calcining the as-prepared TiO2 anatase nanoplates up to 600 degrees C and the second one was by washing them with a NaOH aqueous solution. Importantly, the surface modification procedure leads to the formation of two different morphologies of the TiO2 anatase nanoplates which exhibited tunable photocatalytic selectivity in air pollutants purification. The calcined nanoplates became larger and their {1 0 1} crystal facets expanded by shrinking the {0 0 1} crystal facets. In contrast the washed nanoplates maintained their shape which was formed by the solvothermal method. All samples that were calcined or washed, exhibited high photonic efficiency for air pollutants oxidation. The calcined TiO2 anatase nanoplates exhibited the best photocatalytic activity in oxidizing the NO gas to NO2 and NO3- whereas the washed TiO2 anatase nanoplates, preserving the initial morphology, exhibited the best photocatalytic activity in decomposing acetaldehyde. The dominant exposed {1 0 1) or {0 0 1} crystal facets of the TiO2 anatase nanoplates is the key factor in tuning the adsorption selectivity of the air pollutants. (c) 2013 Elsevier B.V. All rights reserved.

TiO2 anatase nanoplates, hollow microspheres and microcrystals with exposed {001} crystal facets were fabricated via a solvothermal-hydrothermal method at 180 degrees C for 24 hours using titanium isopropoxide or titanium tetrafluoride as a titanium precursor, ethanol or distilled water as a solvent and lastly hydrofluoric acid as the enhancer for the formation of the TiO2 anatase {001} crystal facets. All samples were calcined at 600 degrees C in order to remove the fluoride atoms adsorbed on the photocatalysts surface. This paper presents the influence of different TiO2 anatase structures in their photocatalytic activity. The photocatalytic evaluation of all TiO2 anatase structures with exposed {001} crystal facets was obtained by oxidizing the NO gas to NO2 and NO3- and then calculating their photonic efficiency. Commercial TiO2 photocatalyst P25 by Evonik Degussa was used as a reference. The TiO2 anatase nanoplates were the structure that exhibited the best photocatalytic activity of all TiO2 anatase structures, including the used reference P25 by Evonik Degussa.

TiO2 anatase nanoplates and hollow microspheres were fabricated by a solvothermal–hydrothermal method using titanium isopropoxide as a titanium precursor and hydrofluoric acid as a capping agent in order to enhance the formation of the {001} crystal facets of the anatase nanocrystals.

Nanostructured powders of titanium dioxide anatase nanoplates with dominant highly reactive {001} facets were fabricated using a solvothermal method. Two kinds of samples, as prepared and calcinated at 600 degrees C, were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrical conductivity in vacuum and in air. The dependence of the conductivity versus the inverse of temperature in the temperature range 150-440 K indicated the contribution of at least two conduction mechanisms in vacuum. The electron transport was controlled by partially depleted of charge carriers grains and adiabatic small polaron conduction in the high temperature regime and by Mott variable-range hopping (VRH) at lower temperatures. The environment was found from the experimental results to influence significantly the electrical conductivity values and its temperature dependence. A decrease with temperature in air is observed in the ranges 290-370 and 285-330 K for the as prepared and the calcinated sample respectively. Potential barriers caused by partial depletion of carriers at grain boundaries control the electrical conductivity behavior in air at high temperatures and VRH in the lower temperature regime. (C) 2012 Elsevier B.V. All rights reserved.