Anita Trenczek-Zajac

Nanostructured TiO2-based gas sensors with enhanced sensitivity to reducing gases

2D TiO2 thin films and 3D flower-like TiO2-based nanostructures, also decorated with SnO2, were prepared by chemical and thermal oxidation of Ti substrates, respectively. The crystal structure, morphology and gas sensing properties of the TiO2-based sensing materials were investigated. 2D TiO2 thin films crystallized mainly in the form of rutile, while the flower-like 3D nanostructures as anatase. The sensor based on the 2D TiO2 showed the best performance for H2 detection, while the flower-like 3D nanostructures exhibited enhanced selectivity to CO(CH3)2 after sensitization by SnO2 nanoparticles. The sensor response time was of the order of several seconds. Their fast response, high sensitivity to selected gas species, improved selectivity and stability suggest that the SnO2-decorated flower-like 3D nanostructures are a promising material for application as an acetone sensor.

Study of N-doped TiO2 thin films forphotoelectrochemical hydrogengeneration from water

Abstract The present work deals with nitrogen-doped stoichiometric TiO2:N and non-stoichiometric TiO2−x:N thin films deposited by means of dc-pulsed reactive sputtering for application as photoanodes for hydrogen generation from water, using solar energy. Stoichiometric thin films of TiO2 crystallize as a mixture of anatase and rutile while rutile phase predominates in TiO2:N at higher nitrogen flow rates as shown by X-ray diffraction at grazing incidence, XRD GID. Lack of bulk nitridation of stoichiometric TiO2:N is indicated by valence-to-core X-ray emission spectroscopy, XES, analysis. The energy band gap as well as flat band potential remain almost unaffected by increasing nitrogen flow rate in this case. In contrast to that, non-stoichiometric thin films of TiO2‑x:N demonstrate systematic evolution of the structural, morphological, optical and photolectrochemical properties upon increasing level of nitrogen doping. Pronounced changes in the growth pattern of non-stoichiometric TiO2-x:N upon varied nitrogen flow rate, demonstrated by scanning electron microscopy, SEM, can be easily correlated with the crystallographic properties studied by XRD GID. Relative positions of Kβ’’ XES lines of the TiO2-x:N thin films, which depend strongly on the nature of the ligands and their local coordination, change with the increasing nitrogen flow. Doping of nonstoichiometric titanium dioxide with nitrogen shifts the absorption spectrum towards the visible range and increases considerably the flat band potential which is beneficial for water photolysis. Graphical Abstract

Pre- and post-oxidation treatment of titanium as a method of improving the response of TiO2-based photoanodes in PECs

TiO2-based photoanodes were prepared via thermal oxidation of titanium foils in air at 500–900∘C. Some of them were pre-treated via etching with HCl prior to oxidation, and others post-treated by means of sensitization with Ag2S or CdS. XRD analysis revealed that the formation of rutile is observed even at 500∘C. Etching prior to oxidation removes the Ti passivation layer and facilitates the oxidation process, and lowers the temperature at which the fundamental absorption edge is observed. The highest photocurrent values measured in a photoelectrochemical cell (PEC) were obtained for anodes etched prior to oxidation. Sensitization with CdS or Ag2S increased photocurrent drastically. It was demonstrated that pre- and post-treated TiO2-based photoanodes prepared in the process of thermal oxidation offer far better performance in PECs than those which had not been treated.