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Pap Zs.,University of Szeged | Pap Zs.,Babes - Bolyai University | Mogyorosi K.,University of Szeged | Vereb G.,University of Szeged | And 5 more authors.
Journal of Molecular Structure | Year: 2014

As visible light driven photocatalysis became more and more intensively studied, the first commercial products showed up on the market. Simultaneously controversial results appeared in the literature generating an intensive debate regarding the advantages and draw-backs of nitrogen doping of titania. Hence, the present work focuses on two commercially available and four sol-gel made nitrogen modified titania powders regarding their structure and activity. It is demonstrated that the interstitial nitrogen entities "leak out" from the catalysts if the material is irradiated with UV light, while substitutional nitrogen remains stable. However, the latter one was proven to be less important in the photocatalytic point of view. These observations were also valid in the case of sol-gel made nitrogen modified titanias. Furthermore, the results obtained after applying different spectroscopic methods (IR, XPS and DRS) shown that the yellow color of the titanias, does not necessary mean that a successful doping is achieved. © 2014 Elsevier B.V. All rights reserved.

Vereb G.,University of Szeged | Gyulavari T.,University of Szeged | Pap Z.,University of Szeged | Pap Z.,Babes - Bolyai University | And 5 more authors.
RSC Advances | Year: 2015

The characteristic properties and the resulted photocatalytic efficiencies of rutile-phase titanium dioxides were investigated in the present study. A series of rutile with different primary particle sizes (5.2-290 nm) were produced by a sol-gel method followed by calcination and were characterized by XRD, DRS, TEM, XPS, EPR, IR and N2 adsorption. Their photocatalytic efficiencies were determined in the decomposition of phenol, and in the inactivation of E. coli bacteria under visible light irradiation. The results were compared with the photocatalytic performance of commercial Aldrich rutile and Aeroxide P25 powders. Of the non-commercial products, the TiO2 with the smallest particle size displayed the highest efficiency, while the surface-normalized photocatalytic performance was significantly higher for the larger rutile particles. This can be explained by the red shift of light absorption at higher calcination temperatures. Although Aldrich rutile and the corresponding laboratory-made photocatalyst exhibited similar structural features (e.g. particle size, specific surface area, morphology and light absorption), the latter proved to be less efficient despite its Ti3+ content (while Aldrich rutile contains only Ti4+). The main reason for the much higher photocatalytic performance was the presence of Ti-O-O- entities on the surface of Aldrich rutile. On the basis of these results, in the case of rutile-phase titanium dioxide, the presence of Ti-O-O- entities was more beneficial, than the presence of Ti3+ and low-binding-energy oxygen (which indicates defects) in relation with the photocatalytic performance under visible light irradiation. This journal is © The Royal Society of Chemistry.

Szekely I.,Babes - Bolyai University | Kovacs G.,Babes - Bolyai University | Kovacs G.,University of Szeged | Kovacs G.,Institute for Interdisciplinary Research on Bio Nano science | And 7 more authors.
Materials | Year: 2016

A traditional semiconductor (WO3) was synthesized from different precursors via hydrothermal crystallization targeting the achievement of three different crystal shapes (nanoplates, nanorods and nanostars). The obtained WO3 microcrystals were analyzed by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). These methods contributed to the detailed analysis of the crystal morphology and structural features. The synthesized bare WO3 photocatalysts were totally inactive, while the P25/WO3 composites were efficient under UV light radiation. Furthermore, the maximum achieved activity was even higher than the bare P25's photocatalytic performance. A correlation was established between the shape of the WO3 crystallites and the observed photocatalytic activity registered during the degradation of different substrates by using P25/WO3 composites. © 2016 by the authors.

Kovacs G.,Babes - Bolyai University | Kovacs G.,University of Szeged | Fodor S.,Babes - Bolyai University | Vulpoi A.,Babes - Bolyai University | And 10 more authors.
Journal of Catalysis | Year: 2015

As shape tailoring is gaining more attention in the field of photocatalysis, exploration of the impact of noble metal (Pt) nanoparticles' morphology on the activity of TiO2-Pt nanocomposites is inevitable. Spherical and polyhedral Pt nanoparticles have been synthesized by chemical reduction, while Aldrich anatase, Aldrich rutile, and Aeroxide P25 were used as base photocatalysts. The nanocomposites were analyzed using DRS, XRD, and HRTEM to uncover morphological, optical, and structural peculiarities of the composite photocatalysts. The importance of the Pt nanoparticles' geometry was proven at three levels: (i) UV light-driven photodegradation of three model pollutants: phenol, methyl orange, and oxalic acid; (ii) the primary degradation intermediates' evolution profile in the case of phenol degradation; and (iii) photocatalytic H2 production. © 2015 Elsevier Inc. All rights reserved.

Vajda K.,University of Szeged | Kasa Z.,University of Szeged | Dombi A.,University of Szeged | Nemeth Z.,University of Szeged | And 10 more authors.
Nanoscale | Year: 2015

One of the most fundamental aspects of the heterogeneous catalysis field is the manipulation of the catalysts' activity. In photocatalysis this is carried out by maximizing the right crystal plane of a semiconductor oxide. Until now, most of the papers have achieved this by a combination of different oxides, with noble metals and sometimes with carbon nanomaterials. In this work MWCNTs (multiwalled carbon nanotubes) were applied as "crystallization promoters" in a very simple, safe, one-step hydrothermal method. By this method TiO2 nano/micro crystals with exposed {001} facets were obtained in the first step. The next episode in the crystal manipulation "saga" was the modification of the (001) crystallographic plane's structure by creating ordered/own faceted "crystallographic holes". These elements are capable of further enhancing the obtained activity of titania microcrystals to a higher extent, as shown by the UV driven photocatalytic phenol degradation experiments. The appearance of the holes was "provoked" by simple calcination and their presence and influence were demonstrated by XPS and HRTEM. This journal is © The Royal Society of Chemistry.

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