MTA SZTE Lendulet Porous Nanocomposites Research Group

Szeged, Hungary

MTA SZTE Lendulet Porous Nanocomposites Research Group

Szeged, Hungary
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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.

Gyori Z.,MTA SZTE Lendulet Porous Nanocomposites Research Group | Konya Z.,University of Szeged | Konya Z.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Kukovecz A.,MTA SZTE Lendulet Porous Nanocomposites Research Group | Kukovecz A.,University of Szeged
Applied Catalysis B: Environmental | Year: 2015

In this paper we describe the use of differently sized PbSe quantum dots as photosensitizers for anatase TiO2 nanowires under visible light illumination. After the organometallic synthesis of PbSe quantum dots with three different average diameters (1.8, 2.5 and 4.7nm), the nanocrystals were attached to the surface of nanowires with thioglycolic acid as a linker molecule. These quantum dot decorated nanowires were used as photocatalyst in the methyl orange degradation model reaction with promising results. The best performance achieved was 90% degradation of the initial concentration of methyl orange in six hours over 2.5nm PbSe quantum dot sensitized nanowires using a 40W quartz UV lamp equipped with a 400nm cut-off filter. © 2015 Elsevier B.V.

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.

Mahajan A.,Campus Universitario | Kingon A.,Brown University | Kukovecz A.,University of Szeged | Kukovecz A.,MTA SZTE Lendulet Porous Nanocomposites Research Group | And 2 more authors.
Materials Letters | Year: 2013

Carbon nanotubes (CNTs) have unique physical properties. This has been the driver for the current exploitation of their use in different advanced applications, such as in composite nanoscale devices. If a thermal treatment is required for the fabrication of the composite, the thermal decomposition behavior of the tubes is a key aspect in the integration process. Within this context, the thermal decomposition of multiwall CNTs (MWCNTs) under different conditions was studied in this work by DTA/TG, XRD, RAMAN spectroscopy and electron microscopy. Purified MWCNTs are stable up to 420 °C in air, as no weight loss occurs in TG/DTA analysis under non isothermal conditions but morphology changes were observed for isothermal conditions at 400 °C by Raman spectroscopy. In oxygen-rich atmosphere MWCNTs started to oxidized at 200 °C. However in argon-rich atmosphere and under a high heating rate MWCNTs remain stable up to 1300 °C with a minimum sublimation. The activation energy for the decomposition of MWCNTs in air was calculated to lie between 80 and 108 kJ/mol. These results have broad implications for the expanded use of MWCNTs in composites with functional complex oxides that usually require synthesis temperature above 650 °C. © 2012 Elsevier B.V.

Bogya E.S.,Babes - Bolyai University | Bogya E.S.,MTA SZTE Lendulet Porous Nanocomposites Research Group | Karoly Z.,Hungarian Academy of Sciences | Barabas R.,Babes - Bolyai University
Ceramics International | Year: 2015

Silica-doped hydroxyapatite as a bioactive coating presents some advantages compared to the pure one, such as: increased in vivo bioactivity and early bone ingrowth. The aim of this study is to obtain a deposition of silica-doped hydroxyapatite on magnesium alloy plates by atmospheric plasma spraying. The coating material was prepared by a precipitation method with sodium silicate addition as a source of silica, and various methods were used to characterize it. Spraying conditions including powder feed rate and current values were varied. The coating properties were defined by determining the purity, phase composition, morphology and corrosion protection of the HAP-Si deposits on the magnesium plates. © 2015 Elsevier Ltd and Techna Group S.r.l.

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.

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.

Pusztai P.,University of Szeged | Simon T.,University of Szeged | Kukovecz A.,University of Szeged | Kukovecz A.,MTA SZTE Lendulet Porous Nanocomposites Research Group | And 2 more authors.
Journal of Molecular Structure | Year: 2013

Until now one-dimensional CePO4 nanostructures were investigated mainly from the characterization and photoluminescent property improvement point of view. In this study we present a structural stability test of CePO 4 nanowires prepared at ambient temperature. The calcination of the nanowires was carried out at 400 °C, 600 °C, 800 °C and 1000 °C for 1 h in air atmosphere, the morphological and surface changes were monitored by transmission electron microscopy (TEM) and nitrogen adsorption technique. An increase in average diameter and a decrease in specific surface area with increasing temperature were observed indicating a sintering process above 600 °C. The phase transition of the nanowires was investigated by X-ray diffractometry (XRD), Raman and infrared spectroscopy. The XRD study showed the recrystallization of the nanowires from hexagonal to monoclinic phase at 600 °C which was further confirmed by Raman and IR spectroscopy. © 2012 Elsevier B.V. All rights reserved.

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.

Bogya E.S.,MTA SZTE Lendulet Porous Nanocomposites Research Group | Szilagyi B.,Babes - Bolyai University | Kukovecz A.,MTA SZTE Lendulet Porous Nanocomposites Research Group
Carbon | Year: 2016

The heat transfer coefficient between a single water droplet and a multiwall carbon nanotube film (buckypaper) was measured for pristine and for carboxy functionalized nanotubes by infrared thermography. The value for non-functionalized nanotubes (438 Wm-2 K-1) was more than twice as large as that for functionalized ones (204 Wm-2 K-1) even though the water to nanotube affinity is larger in the latter case as indicated by contact angle measurement. This apparent contradiction can be explained by the hydrophilic surface pinning of the droplet and the vertically periodic layered structure of the buckypaper. © 2016 Elsevier Ltd.All rights reserved.

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