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Haspel H.,University of Szeged | Bugris V.,University of Szeged | Kukovecz A.,University of Szeged | Kukovecz A.,MTA SZTE Lendulet Porous Nanocomposites Research Group
Journal of Physical Chemistry C | Year: 2013

Broadband dielectric spectroscopy (BDS) measurements have been carried out on a nanostructured hydrophilic model system to gain insight into the atomistic level mechanism of adsorption-induced dielectric changes. Titanate nanowires (TiONWs) were investigated between 10 mHz and 1 MHz under various humidity conditions. The processes contributing to the measured dielectric response were identified, and their dependence on water surface coverage was discussed in detail. Three relaxation processes and an imperfect ionic conduction were found in the investigated frequency window. Exponential relationships were found between the different dielectric quantities and the amount of adsorbed water. The conductivity variation originates from the exponentially increasing charge carrier concentration, while the relaxations in the middle frequency range have a common, interfacial origin. The high-frequency loss process arises from the orientation relaxation of a real dipolar moiety of the system. © 2013 American Chemical Society. Source

Haspel H.,University of Szeged | Laufer N.,University of Szeged | Bugris V.,University of Szeged | Ambrus R.,University of Szeged | And 3 more authors.
Journal of Physical Chemistry C | Year: 2012

Elongated oxide nanostructures have gained much attention in the past decade due to their unique mechanical, optical, and electrical properties. Despite the vast amount of theoretical and experimental work on these materials, the mechanism of water-related electrical conduction in these systems has remained unsolved. In this study, the charge transport processes in hydrothermally synthesized trititanate nanowires (TiONW) at varying relative humidity (RH) have been investigated. Parameters characterizing these processes were extracted from dielectric spectroscopy (DRS) and ionic transient current (ITIC) measurements at room temperature. The dc conductivity varies exponentially with increasing RH. It is suggested to stem mainly from the exponentially increasing charge carrier concentration, while carrier mobility seems to have a much weaker influence on the long-range charge transport. The changes in the constituent parameters of dc conductivity are thought to be due to the changes in the amount, surface structure, and thermodynamic state of adsorbed water, which has been confirmed in the case of ionic mobility with moisture sorption and calorimetric (DSC) investigations. However, the microscopic origin of the exponentially increasing carrier concentration with RH still remains an open question. © 2012 American Chemical Society. Source

Madarasz D.,University of Szeged | Szenti I.,University of Szeged | Sapi A.,University of Szeged | Halasz J.,University of Szeged | And 4 more authors.
Chemical Physics Letters | Year: 2014

Titanate nanotubes were utilized in Ca2+ and Mg2+ removal in a continuous ion-exchange unit. Three consecutive water softening-regeneration cycles were performed. The highest measured value of the total ion-exchange capacity was 1.2 mmol g-1 which decreased to 0.66 mmol g-1 in the third cycle. The capacity loss was due to the irreversible binding of Ca2+ ions to very strong adsorption sites, while the Mg2+/Na+ exchange was reversible. A relatively fast initial adsorption step and a subsequent slower concentration decrease were the two processes that governed the kinetics of the ion exchange reaction.© 2013 Elsevier B.V. All rights reserved. Source

Haspel H.,University of Szeged | Bugris V.,University of Szeged | Kukovecz A.,University of Szeged | Kukovecz A.,MTA SZTE Lendulet Porous Nanocomposites Research Group
Langmuir | Year: 2014

The temperature dependence of dielectric processes in humid titanate nanowires was investigated via broadband dielectric spectroscopy under quasi-isosteric conditions in the temperature range of 150-350 K. It was found that the dynamic parameters obtained from low-temperature measurements cannot describe the dielectric behavior of the system above 273 K, implying changes in the dynamics of the corresponding dielectric processes. The calculated activation energies and pre-exponential factors counterintuitively increase linearly with the amount of adsorbed water, and a compensation effect was also found to apply to all contributions in the TiONW spectra. © 2014 American Chemical Society. Source

Potari G.,University of Szeged | Madarasz D.,University of Szeged | Nagy L.,University of Szeged | Laszlo B.,University of Szeged | And 9 more authors.
Langmuir | Year: 2013

High-aspect-ratio titanate nanotubes (NT) and nanowires (NW) were produced by the hydrothermal conversion of TiO2 at 400 K. The titanate morphology was studied by high-resolution transmission electron microscopy (HRTEM). The formation of ordered titanate nanoobjects depended on the time of conversion. Shorter synthesis times favored hollow nanotube production while during prolonged treatment the thermodynamically more stable nanowires were formed. Titanate nanotubes and nanowires were decorated by Rh nanoparticles. The structure and stability of titanate nanocomposites were studied by thermal gravimetric (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS), Fourier transformed infrared spectroscopic (FTIR), and Raman spectroscopic methods. The nanowires preserve their structure up to 850 K, while the nanotubes start to recrystallize above 600 K. FTIR measurements showed that the water and hydroxyl content gradually decreased with increasing temperature in both cases. XPS data revealed the existence of high binding energy, highly dispersed Rh species on both supports. A small portion of Rh may participate in an ion exchange process. Support transformation phenomena were observed in Rh containing titanate nanowires and nanotubes. Rh decorated nanowires transform into the β-TiO2 structure, whereas their pristine counterparts' recrystallize into anatase. The formation of anatase was dominant during the thermal annealing process in both acid treated and Rh decorated nanotubes. Transformation to anatase was enhanced in the presence of Rh. The average diameters Rh nanoparticles were 4.9 ± 1.4 and 2.8 ± 0.7 nm in the case of nanowires and nanotubes, respectively. © 2013 American Chemical Society. Source

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