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N. Paunović

Bio: N. Paunović is an academic researcher from University of Belgrade. The author has contributed to research in topics: Phonon & Raman spectroscopy. The author has an hindex of 11, co-authored 35 publications receiving 499 citations.

Papers
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Journal ArticleDOI
TL;DR: The results showed that ferromagnetic ordering rapidly degrades with Pr doping, and the suppression of ferromagnetism can be explained in terms of the different dopant valence state, the different nature of the vacancies formed in Pr-doped samples and their ability/disability to establish the feromagnetic ordering.
Abstract: Ce1−xPrxO2−δ (0 ≤ x ≤ 0.4) nanocrystals were synthesized by self-propagating method and thoroughly characterized using X-ray diffraction, Raman and X-ray photoelectron spectroscopy and magnetic measurements. Undoped CeO2 nanocrystals exhibited intrinsic ferromagnetism at room temperature. Despite the increased concentration of oxygen vacancies in doped samples, our results showed that ferromagnetic ordering rapidly degrades with Pr doping. The suppression of ferromagnetism can be explained in terms of the different dopant valence state, the different nature of the vacancies formed in Pr-doped samples and their ability/disability to establish the ferromagnetic ordering.

142 citations

Journal ArticleDOI
TL;DR: In this paper, a powder mixture of BaO and TiO2 was treated in a planetary ball mill in an air atmosphere for up to 1 h, using zirconium oxide vial and zirconsium oxide balls as the milling medium.
Abstract: Barium titanate, BaTiO3 ceramic powders were prepared by mechanochemical synthesis and by the Pechini method. A powder mixture of BaO and TiO2 was treated in a planetary ball mill in an air atmosphere for up to 1 h, using zirconium oxide vial and zirconium oxide balls as the milling medium. After 60 min BaTiO3 phase was formed. In both ways BaTiO3 ceramics were sintered after 2 h on 1300 ◦C without pre-calcinations step. The heating rate was 10◦C min−1. The formation of phase and crystal structure of BaTiO3 was approved by X-ray diffraction analysis and the Raman spectroscopy. The morphology and microstructure of obtained powders were examined by scanning electron microscopy method. Sharp phase transition from ferroelectric to paraelectric state was observed. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials.

56 citations

Journal ArticleDOI
26 Sep 2014-Langmuir
TL;DR: Ultrafine CeO2-δ nanopowder, prepared by a simple and cost-effective self-propagating room temperature synthesis method (SPRT), showed high adsorption capability for removal of different azo dyes.
Abstract: Ultrafine CeO2-δ nanopowder, prepared by a simple and cost-effective self-propagating room temperature synthesis method (SPRT), showed high adsorption capability for removal of different azo dyes. Batch type of adsorption experiments with fixed initial pH value were conducted for the removal of Reactive Orange 16 (RO16), Methyl Orange (MO), and Mordant Blue 9 (MB9). The equilibrium adsorption data were evaluated using Freundlich and Langmuir isotherm models. The Langmuir model slightly better describes isotherm data for RO16 and MO, whereas the Freundlich model was found to best fit the isotherm data for MB9 over the whole concentration range. The maximum adsorption capacities, determined from isotherm data for MO, MB9, and RO16 were 113, 101, and 91 mg g(-1) respectively. The adsorption process follows the pseudo-second-order kinetic model indicating the coexistence of chemisorption and physisorption. The mechanism of azo dye adsorption is also discussed.

45 citations

Journal ArticleDOI
TL;DR: In this paper, a soft mechanochemical reaction leading to formation of the MnFe 2 O 4 spinel phase was followed by X-ray diffraction, Raman spectroscopy, scanning and transmission microscopy and magnetization measurements.

44 citations

Journal ArticleDOI
TL;DR: In this paper, room temperature ferromagnetism was observed in undoped and Fe2+(3+)-doped CeO2 nanocrystals, associated with the presence of magnetic ions mediated by single charged O2− vacancies.
Abstract: Room-temperature ferromagnetism was observed in undoped and Fe2+(3+)-doped CeO2 nanocrystals. In Fe-doped samples the enhancement of ferromagnetic ordering occurs by changing the valence state of Fe ions, whereas Raman spectra demonstrated strong electron-molecular vibrational coupling and increase in oxygen vacancy concentration. Air annealing showed degradation of ferromagnetic ordering and appearance of hematite phase in Fe3+-doped sample. The observed ferromagnetic coupling in Fe-doped samples, associated with the presence of magnetic ions mediated by single charged O2− vacancies, demonstrated that valence state of dopant has a strong influence on magnetic properties of CeO2 nanoparticles.

40 citations


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TL;DR: The results indicated that the RGO/MnFe2O4/PVDF composites show the most excellent wave absorption properties, and the wave absorbing mechanism can be attributed to the dielectric loss, magnetic loss and the synergetic effect between RGO+Mn Fe 2O4, RGO-PV DF and MnFe2 O4+PvDF.
Abstract: MnFe2O4 nanoparticles have been synthesized on a large scale by a simple hydrothermal process in a wild condition, and the RGO/MnFe2O4 nanocomposites were also prepared under ultrasonic treatment based on the synthesized nanoparticles. The absorption properties of MnFe2O4/wax, RGO/MnFe2O4/wax and the RGO/MnFe2O4/PVDF (polyvinylidene fluoride) composites were studied; the results indicated that the RGO/MnFe2O4/PVDF composites show the most excellent wave absorption properties. The minimum reflection loss of RGO/MnFe2O4/PVDF composites with filler content of 5 wt % can reach −29.0 dB at 9.2 GHz, and the bandwidth of frequency less than −10 dB is from 8.00 to 12.88 GHz. The wave absorbing mechanism can be attributed to the dielectric loss, magnetic loss and the synergetic effect between RGO+MnFe2O4, RGO+PVDF and MnFe2O4+PVDF.

653 citations

Journal ArticleDOI
TL;DR: The review would be an excellent resource for researchers who are currently focusing on metal oxide-based materials for water remediation as well as for those who are interested in adsorptive and photocatalytic applications of metal oxides and their composites.

409 citations

Journal Article
TL;DR: In this paper, it was shown that ZnO samples can be magnetic even without transition-metal doping and also suggests that introducing Zn vacancy is a natural and an effective way to fabricate magnetic ZNO nanostructures.
Abstract: Extensive calculations based on density functional theory have been carried out to understand the origin of magnetism in undoped ZnO thin films as found in recent experiments. The observed magnetism is confirmed to be due to Zn, instead of O, vacancy. The main source of the magnetic moment, however, arises from the unpaired 2p electrons at O sites surrounding the Zn vacancy with each nearest-neighbor O atom carrying a magnetic moment ranging from 0.490 to 0.740 B. Moreover, the study of vacancy-vacancy interactions indicates that in the ground state, the magnetic moments induced by Zn vacancies prefer to ferromagnetically couple with the antiferromagnetic state lying 44 meV higher in energy. Since this is larger than the thermal energy at room temperature, the ferromagnetic state can be stable against thermal fluctuations. Calculations and discussions are also extended to ZnO nanowires that have larger surface to volume ratio. Here, the Zn vacancies are found to lead to the ferromagnetic state too. The present theoretical study not only demonstrates that ZnO samples can be magnetic even without transition-metal doping but also suggests that introducing Zn vacancy is a natural and an effective way to fabricate magnetic ZnO nanostructures. In addition, vacancy mediated magnetic ZnO nanostructures may have certain advantages over transition-metal doped systems in biomedical applications.

357 citations

Journal ArticleDOI
TL;DR: In this article, a Ni/CeO2 solid is exposed to CH4 and CO2 in a cyclic way to restore the oxygen capacity of the support and remove residual carbon formed at the surface.
Abstract: Chemical looping dry reforming of methane (CLDRM) is performed by exposing a Ni/CeO2 solid to CH4 and CO2 in a cyclic way. The solid acts as an oxygen vector producing syngas (CO + H2) during exposure to CH4, and is re-oxidized during exposure to CO2. Absence of CO2 during syngas production allows suppressing reverse water gas shift reaction and reaching high selectivity. Exposure to CO2 restores the oxygen capacity of the support and removes residual carbon formed at the surface, thus fully regenerating the catalyst. Solids were characterized by TPR, XRD, Raman scattering, and XPS. Results show that part of the Ni is reduced and remain in metallic state during the looping process. On the other hand, Ni2+ species in strong interaction with Ce cations are observed even after exposure to methane. Both Ni species play important roles on reactants activation and oxygen supply by the solid. Ni loading is a crucial parameter for controlling the reduction behavior of the support and therefore for CLDRM process optimization.

191 citations

Journal ArticleDOI
TL;DR: These new material systems can be of importance where the presence of oxygen vacancies is essential or in applications where a narrow band gap is desirable, and Interestingly, the band gap values are relatively invariant with respect to the composition or thermal treatments.
Abstract: New multicomponent equiatomic rare earth oxides (ME-REOs) containing 3-7 rare earth elements (Ce, Gd, La, Nd, Pr, Sm and Y) in equiatomic proportions are synthesized using nebulized spray pyrolysis. All the systems crystallized as a phase pure fluorite type (Fm3[combining macron]m) structure in spite of the high chemical complexity. A nominal increase in the lattice parameter compared to CeO2 is observed in all ME-REOs. X-ray photoelectron spectroscopy performed on the ME-REOs confirmed that all the constituent rare earth elements are present in the 3+ oxidation state, except for Ce and Pr which are present in 4+ and in a mixed (3+/4+) oxidation state, respectively. The presence of Ce4+ contributes substantially to the observed stability of the single phase structure. These new oxide systems have narrow direct band gaps in the range of 1.95-2.14 eV and indirect band gaps in the range of 1.40-1.64 eV, enabling light absorption over the entire visible spectral range. Furthermore, the oxygen vacancy concentration rapidly increases and then saturates with the number of rare earth elements that are incorporated into the ME-REOs. The lowering of the band gap is found to be closely related to the presence of multivalent Pr. Interestingly, the band gap values are relatively invariant with respect to the composition or thermal treatments. Considering the high level of oxygen vacancies present and the observed low band gap values, these new material systems can be of importance where the presence of oxygen vacancies is essential or in applications where a narrow band gap is desirable.

180 citations