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© 2016 Elsevier LtdThe electrical conductivity and the transient photoconductivity of Ag/TiO2 nanoplates were studied at 300 K, 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 5–20 nm. 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.

Ag nanoparticles were photodeposited on the {101} 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 20nm. 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. © 2014 Elsevier B.V.

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 {001} crystal facets of the anatase crystal. Two different surface modification procedures were applied in order to remove the adsorbed fluoride anions on the {001} crystal facets of the nanoplates. The first procedure was by calcining the as-prepared TiO2 anatase nanoplates up to 600°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 {101} crystal facets expanded by shrinking the {001} 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 {101} or {001} crystal facets of the TiO2 anatase nanoplates is the key factor in tuning the adsorption selectivity of the air pollutants. © 2013 Elsevier B.V.

Introduction: 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. Methods: These different morphological structures of TiO2 anatase can be achieved by only changing the solvent, keeping the amount of the precursor and of the capping agent identical during the solvothermal-hydrothermal process. Results and discussion: After calcination of the samples, the adsorbed fluoride atoms on the {001} crystal facets of the TiO2 anatase nanocrystals were completely removed from their surface according to XPS analysis. The calcined TiO2 anatase structures were higher crystallized and the specific surface area of the catalysts increased, enhancing their photocatalytic activity in comparison to the non-calcined TiO2 anatase structures. All TiO2 anatase samples with adsorbed as well as non-adsorbed fluoride atoms on their {001} crystal facets, exhibited a higher photonic efficiency than Degussa P25, which was used as a reference. Conclusion: The fluoride free TiO2 anatase nanoplates exhibited the best photocatalytic activity in oxidizing the NO gas to NO2 and NO3-. © 2012 Springer-Verlag.