title: Transformation of hydrogen titanate nanoribbons to TiO2 nanoribbons and the influence of the transformation strategies on the photocatalytic performance.
abstract: The influence of the reaction conditions during the transformation of hydrogen titanate nanoribbons to TiO2 nanoribbons on the phase composition, the morphology, the appearance of the nanoribbon surfaces and their optical properties was investigated. The transformations were performed (i) through a heat treatment in oxidative and reductive atmospheres in the temperature range of 400-650 °C, (ii) through a hydrothermal treatment in neutral and basic environments at 160 °C, and (iii) through a microwave-assisted hydrothermal treatment in a neutral environment at 200 °C. Scanning electron microscopy investigations showed that the hydrothermal processing significantly affected the nanoribbon surfaces, which became rougher, while the transformations based on calcination in either oxidative or reductive atmospheres had no effect on the morphology or on the surface appearance of the nanoribbons. The transformations performed in the reductive atmosphere, an NH3(g)/Ar(g) flow, and in the ammonia solution led to nitrogen doping. The nitrogen content increased with an increasing calcination temperature, as was determined by X-ray photoelectron spectroscopy. According to electron paramagnetic resonance measurements the calcination in the reductive atmosphere also resulted in a partial reduction of Ti(4+) to Ti(3+). The photocatalytic performance of the derived TiO2 NRs was estimated on the basis of the photocatalytic oxidation of isopropanol. After calcinating in air, the photocatalytic performance of the investigated TiO2 NRs increased with an increased content of anatase. In contrast, the photocatalytic performance of the N-doped TiO2 NRs showed no dependence on the calcination temperature. An additional comparison showed that the N-doping significantly suppressed the photocatalytic performance of the TiO2 NRs, i.e., by 3 to almost 10 times, in comparison with the TiO2 NRs derived by calcination in air. On the other hand, the photocatalytic performance of the hydrothermally derived TiO2 NRs was additionally improved by a subsequent heat treatment in air.
authors.affiliation: Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia ; Jožef Stefan International Postgraduate School, Jamova cesta 39, SI-1000 Ljubljana, SIovenia.
authors.forename: Melita
authors.initials: M
authors.lastname: Rutar
authors.affiliation: Slovenian National Building and Civil Engineering Institute, Dimičeva 12, SI-1000 Ljubljana, Slovenia.
authors.forename: Nejc
authors.initials: N
authors.lastname: Rozman
authors.affiliation: Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Matej
authors.initials: M
authors.lastname: Pregelj
authors.affiliation: Chimie des Interactions Plasma Surface, CIRMAP, University of Mons, 23 Place du Parc, B-7000 Mons, Belgium.
authors.forename: Carla
authors.initials: C
authors.lastname: Bittencourt
authors.affiliation: Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva cesta 5, SI-1000 Ljubljana, Slovenia.
authors.forename: Romana
authors.initials: R
authors.lastname: Cerc Korošec
authors.affiliation: Slovenian National Building and Civil Engineering Institute, Dimičeva 12, SI-1000 Ljubljana, Slovenia.
authors.forename: Andrijana
authors.initials: A
authors.lastname: Sever Škapin
authors.affiliation: Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Aleš
authors.initials: A
authors.lastname: Mrzel
authors.affiliation: Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Srečo D
authors.initials: SD
authors.lastname: Škapin
authors.affiliation: Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Polona
authors.initials: P
authors.lastname: Umek
keywords: doping; nanoribbon; photocatalytic performance; titanate; titanium dioxide (TiO2); transformation