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This paper describes determination of trace level of copper ions on a new type of modified glassy carbon paste electrode based on addition of different amount of Co-ferrites in glassy carbon paste (CoFeMGCPE). Co-ferrite nanoparticles with different amount of cobalt were synthesized and characterized using scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). A significant increase in current was achieved by introducing modifier in composition of the electrode in comparison with the bare glassy carbon paste electrode. Electrochemical parameters such as percentage of modifier, accumulation time and potential, pH and the optimized amount of cobalt in the ferrites were determined. The best voltammetric response was observed for Co0.5Fe0.5Fe2O4 when percentage of modifier was 3%. In acetate buffer solution, pH 4.5, thus prepared electrode displays selective detection toward copper ions, detection limit of 96 nM and it was successfully applied for the determination of copper ions in natural water samples, with satisfactory recovery.

Synthesis of monetite (CaHPO4) by means of mechanochemical treatment of brushite (CaHPO4∙2H2O) was studied. Start sample (Brushite) was obtained by precipitation method at room temperature. Particle size of brushite was reduced using vibromilling. The powders were analyzed by X-ray powder diffraction (XRPD). Microstructure and morphology was determined by means of scanning electron microscopy (SEM). Brunauer-Emmett-Teller (BET) method was used for examining specific surface area of obtained powders. It was found that five minutes of milling induces brushite-monetite phase transformation. This type of synthesis is cost-effective compared to the other used methods for synthesis of monetite.

Досадашња археолошка истраживања на данашњој територији Србије, довела су до открића великог броја налаза зидних слика из римског периода. У раду је обрађен материјал који потиче са археолошких налазишта Виминацијум, Сирмијум, Тимакум Минус, Сингидунум, Наис и Мансио Идимум, као и са појединих локалитета у Брестовику, Скобаљу, Бељини, Чачку, Бешкој, Чалми и Хртковцима. Материјал са археолошких налазишта Медијана и Феликс Ромулијана, није био доступан за обраду. Највише података нам пружају зидне слике из два римска града, Виминацијума и Сирмијума, са чијих локалитета је сачувано највише материјала. Обрађено сликарство потиче из профаних и фунерарних објеката. Један од циљева рада је био да се представи до сада необјављен материјал и направи сублимација са објављеним резултатима. Римљани који су живели на нашим просторима примењивали су различите типове малтера на којима се сликало. Од блатних са једним слојем малтера, преко вишеслојних, хидрауличних, до високоуглачаних у луксузнијим објектима. Такође, се на основу појединих примера може закључити да су на плафоне и зидове, антички мајстори постављали трску или пруће па тек потом малтер. На основу разнородности састава узоркованих малтера може се претпоставити да је коришћен агрегат који је био на располагању и не може се установити никакава законитост у саставу..., During the archaeological excavations in the territory of today’s Serbia, a large number of wall paintings from Roman period have been found until today. The material presented in this study originate from the archaeological sites of Viminacium, Sirmium, Timacum Minus, Singidunum, Naissus and Mansio Idimum, but also from the particular sites in Brestovik, Skobalj, Beljina, Čačak, Beška, Čalma and Hrtkovci. Material from the archaeological sites of Mediana and Felix Romuliana was not available for study. Most useful facts have been provided from the research of wall paintings found in two Roman cities, Viminacium and Sirmium, as mostly preserved ones. Studied paintings originate from secular and funeral building structures. One of the study aims is to present material unpublished so far and make sublimation with published results. Romans that lived in this territory applied different types of mortars as substrates for painting. It includes mud mortars in one layer, and lime ones, multilayered, non-hydraulic and hydraulic, rough and highly polished mortars. Also, according to some examples, it can be concluded that ancient artisans often used to put reed or wattle on walls and ceilings before the mortar. By analyzing different compositions of the studied mortars, it can be assumed that used aggregate was the most available one and no rule in composition can be found. During study of some examples, the traces from use of caliper, ruler, rope and stylus were found on intonaco surface. Data about renovation in the past (overpainting) have been obtained by fragments from Viminacium, Singidunum and Sirmium...

Elevated concentrations of arsenic in groundwater, which is used as a source for drinking water, is a worldwide problem. Use of TiO2 and iron doped TiO2 synthesized by a microwave-assisted hydrothermal method for As(III) and As(V) removal were examined. Synthesized sorbents were characterized with XRD and nitrogen physisorption. Synthesized sorbents have predominantly anatase structure, and no peaks for iron could be observed. Doping of iron increases the surface area of synthesized sorbents. Sorption experiments show that increase of iron in sorbents increases the sorption capacity for As(III) and As(V). Increase of pH from 3 to 11 has no influence on As(III) sorption but decreases the sorption of As(V). Batch isotherm studies were performed to determine the binding capacities of As(III) and As(V). As(III) followed the Freundlich isotherm model, while for As(V) a better fit was with the Langmuir isotherm. The results of competition of SO42- and PO43- anions on adsorption of As(III) indicated that both anions reduced substantially the efficiency of adsorption on both adsorbents while for As(V) only the presence of PO43- anion interfered with adsorption. Testing 10Fe/TiO2 sorbent with arsenic contaminated natural water showed that this material could be used for removal of arsenic to the level recommended by WHO without pretreatment.

This paper describes the preparation of a new sensor based on Zn-ferrite modified glassy carbon paste electrode and its electrochemical application for the determination of trace Cd(II) ions in waste waters using differential pulse anodic stripping voltammetry (DPASV). Different Zn/Ni ferrite nanoparticles were synthesized and characterized using scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). The prepared ferrite nanoparticles were used for the preparation of Zn-ferrite-modified glassy carbon paste electrode (ZnMGCPE) for determination of Cd(II) at nanomolar levels in waste water at pH 5. The different parameters such as conditions of preparation, Zn2+/Ni2+/Fe2+ ratio and electrochemical parameters, percentage of modifier, accumulation time, pH and accumulation potential were investigated. Besides, interference measurements were also evaluated under optimized parameters. The best voltammetric response was observed for ZnFe2O4 modifier, when the percentage of modifier was 3%, accumulation time 9 min, pH of supporting electrolyte 5 and accumulation potential -1.05 V. Thus prepared electrode displays excellent response to Cd(II) with a detection limit of 0.38 ppb, and selective detection toward Cd(II) was achieved.

Sub-micronic, spherical Y2O3:Yb/Er particles comprising clustered nano-units (70 nm) were prepared via ultrasonic spray pyrolysis from pure nitrate precursor solutions with different Yb/Er dopant ratios. The particles were additionally thermally treated at 1100 °C for 12, 24 and 48 h. The structural and morphological characteristics of particles were studied by X-ray powder diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy dispersive X-ray analysis and specific surface area (BET) and were further correlated with their advanced optical properties. For the recorded up-conversion emissions, originating from the following Er3+ transitions: [2H9/2→4I15/2] in blue (407–420 nm); [2H11/2, 4S3/2→4I15/2] green: 510–590 nm; and [4F9/2→4I15/2] in red (640–720 nm) spectral region, the corresponding lifetimes were acquired in the wide temperature range (10–300 K). The most intense green up-conversion emission with the long decay of 550 ms is recorded for Y1.97Yb0.02Er0.01O3 particles thermally treated at 1100 °C for 24 h.

Fe-doped TiO2 photocatalysts with different contents of Fe (0.5, 1.6, 3.4 and 6.4 %) were synthesized by a microwave-hydrothermal method and characterized by X-ray diffraction analysis, N-2 physisorption at 77 K and UV-Vis spectrometry. The characterization showed that the Fe ions were highly dispersed in the TiO2 lattice. It was found that all the synthesized catalysts had a mesoporous structure and that Fe-doping increased the BET surface area. The UV-Vis study showed that the absorption spectra were shifted to longer wavelengths (red shift) with increasing dopant concentration. The photocatalytic activity of the samples was evaluated by the decolorization of the textile dye Reactive Blue 52 (RB) in aqueous solutions under sun-like radiation in the presence of H2O2 (a heterogeneous photo-Fenton process). The photocatalyst with 3.4 % Fe was found to be the most efficient in the presence of H2O2. The effect of the initial pH of the dye solution was assessed and dissolution of iron ions was studied as a function of pH value. It was concluded that decolorization was more favorable in acidic pH, and that at pH values >4, the release of Fe ions into the solution was negligible. Photocatalytic degradation of 4-chlorophenol (4-CP) was investigated under the optimal conditions and it was shown that the catalyst was capable of degrading colorless pollutants.

Fuel cell application of tungsten carbide is revisited starting with four different tungsten carbide precursors used for high temperature synthesis. It was shown that the final products greatly depend on the nature of the precursor. Using tungsten peroxide/2-propanol derived precursor almost pure WC was obtained which was subjected to further electrochemical investigation. It was shown that it is necessary to decorate WC with Pt nanoparticles in order to obtain satisfactory fuel cell performance, but catalytic activity of Pt/WC anode catalyst is not expected to overcome the activity of Pt/C. It is argued that new synthetic routes for the preparation of WC should be directed towards obtaining highly dispersed WC, that is, WC with high external surface area available for Pt deposition, rather than high specific surface area WC with large contribution of micropores having no importance when it comes to the use of WC as a catalyst support. The true benefit of the use of WC as catalyst support is found in increased CO tolerance/CO oxidation activity of WC-supported Pt catalysts. Qualitative mechanistic view on increased CO oxidation activity of Pt/WC is offered. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

High energy ball milling was used in order to improve dispersion of metal oxide in Ag-SnO2 electrical contact materials. The processed Ag-SnO2 (92:8) and Ag-SnO2In2O3 (87.8:9.30:2.9) powder mixtures were subsequently consolidated to bulk solid pieces by conventional powder metallurgy method. The characterization of the prepared samples included microstructural analysis by XRD and SEM, as well as measurements of physical properties such as density, hardness and electrical conductivity. The results of X-Ray analysis point to reduction of crystallite size after milling of about ten times. Microstructures of sintered Ag-SnO2 and Ag-SnO2 In2O3 materials display very fine dispersion of the oxide components in silver matrix. Somewhat higher uniformity was obtained for Ag-SnO2 In2O3 material which was illustrated by results of SEM analysis and more consistent microhardness values. The obtained values of studied physical properties were found to be in accordance with observed higher dispersion of metal oxide particles and comparable to properties of commercial electrical contact materials of this type., Metoda visokoenergetskog mehaničkog mlevenja je primenjena za pripremu elektrokontaktnih materijala na bazi Ag-SnO2 sa ciljem postizanja visokog stepena disperzije čestica metalnih oksida u srebrnoj matrici. Smeše prahova sastava Ag- SnO2 (92:8) i Ag-SnO2In2O3 (87.8:9.30:2.9) su posle mlevenja procesuirane konvencionalnim tehnikama metalurgije praha. Karakterizacija sinterovanih uzoraka obuhvatila je mikrostrukturnu analizu (XRD, SEM) kao i merenje važnijih fizičkih svojstava: gustina, tvrdoća i električna provodljivost. Rezultati XRD analize su pokazali značajno smanjenje veličine kristalita od oko deset puta. Mikrostrukturna analiza sinterovanih materijala ukazala je na veoma finu i uniformnu disperziju oksidnih komponenti u srebrnoj matrici. SEM mikrofotografije takođe pokazuju veću uniformnost mikrostrukture uzorka Ag-SnO2In2O3 što potvrđuju i ujednačenije vrednosti mikrotvrdoće dobijene za ovaj materijal. Izmerene vrednosti analiziranih fizičkih svojstava su u saglasnosti sa postignutim većim stepenom disperzije čestica metalnih oksida u srebrnoj matrici i uporedive su sa svojstvima komercijalnih elektrokontaktnih materijala ovog tipa.

The evolution of the magnetic state, crystal structure and microstructure parameters of nanocrystalline zinc-ferrite, tuned by thermal annealing of similar to 4 nm nanoparticles, was systematically studied by complementary characterization methods. Structural analysis of neutron and synchrotron x-ray radiation data revealed a mixed cation distribution in the nanoparticle samples, with the degree of inversion systematically decreasing from 0.25 in an as-prepared nanocrystalline sample to a non-inverted spinel structure with a normal cation distribution in the bulk counterpart. The results of DC magnetization and Mossbauer spectroscopy experiments indicated a superparamagnetic relaxation in similar to 4 nm nanoparticles, albeit with different freezing temperatures T-f of 27.5 K and 46 K, respectively. The quadrupole splitting parameter decreases with the annealing temperature due to cation redistribution between the tetrahedral and octahedral sites of the spinel structure and the associated defects. DC magnetization measurements indicated the existence of significant interparticle interactions among nanoparticles (superspins). Additional confirmation for the presence of interparticle interactions was found from the fit of the Tf(H) dependence to the AT line, from which a value of the anisotropy constant of K-eff = 5.6 x 10(5) erg cm(-3) was deduced. Further evidence for strong interparticle interactions was found from AC susceptibility measurements, where the frequency dependence of the freezing temperature T-f(f) was satisfactory described by both Vogel-Fulcher and dynamic scaling theory, both applicable for interacting systems. The parameters obtained from these fits suggest collective freezing of magnetic moments at T-f.

The macroscopically-zoned grandite from the garnetite skarn of Meka Presedla (Kopaonik Mountain, Serbia) was studied with optical microscopy, electron microprobe analysis (EMPA), Fourier transform infra-red (FT–IR), and Raman methods. The EMPA results indicate that the main core–rim compositional variations (Ca2.93–2.97Mn0.05–0.06Mg0.00–0.01Al1.14–1.26Fe3+0.72–0.83Ti0.00–0.02Si2.97–3.02O12) slightly differ along the zones, showing evidence for a quasi-cyclic alternation of the oscillatory zoning nature. Among this, considerable variation is observed only by the Al–Fe3+ substitutions in the octahedral site. The EMPA also indicate that the grandite zones compositionally vary, mostly within ±1 and ±2 mol% of the homogeneity level range, that is, Grs64±1Adr36±1Sps2 (A), Grs62±1Adr38±1Sps2 (B), Grs59±2Adr40±2Sps2 (C), Grs58±2Adr41±2Sps2 (D), and Grs58±1Adr41±1Sps2 (E). Therefore, the investigated garnet can be considered as relatively highly homogeneous. The majority of compositions lie within the narrow miscibility region of 0.58±2

Ten nepheline single crystals from five different localities representing rocks from nepheline-syenite pegmatites to urtite, ijolite and cancrinite-ijolite were investigated chemically and structurally. The chemical compositions were determined by electron microprobe, whereas the crystal structures were refined against X-ray diffraction data to R values of 0.022–0.031. In all cases the crystal structures conformed to space group P63, but at the same time all crystals produced some satellite reflections testifying to the modulation effects in their structure. This work confirms the presence of satellite reflections as a universal property of nepheline and resolves some controversy about this issue present in older works. The samples show a range of compositions with variable excess of Si over Al combined with vacancies in the alkaline sites. Vacancies are present exclusively in the symmetric ditrigonal channels occupied preferentially by K atoms in natural nepheline. The influence of the variable amounts of K, Na and vacancies to the increase of volume at this site is shown to be in the order ¿>K>Na. It has been confirmed that natural nepheline can partly depart from Loewenstein’s rule and show some degree of disorder in the Si/Al distribution. Most of the samples revealed a practically full Si-Alordering, but the crystals from one of the nepheline-syenite pegmatites in Langesundsfjord, Norway and from the type locality of ijolite, Iivaara, Finland, showed a disorder of 10–20% suggesting a different cooling history for these rocks.

Pure and Pt-doped ZnO nanophase particles were synthesized by ultrasonic spray pyrolysis. The particles were obtained through the decomposition of zinc nitrate and with a newly developed Pt(IV) complex with 1,3 -propylenediamine-NN'-diacetate tetradentate class ligand (pdda). The complex was characterized by elemental analysis, electronic absorption and infrared spectroscopy. The form of the determined complex structure {trans-[Pt(pdda)Br-2]center dot H2O} implies that Pt(IV) ion has a distorted octahedral coordination due to intramolecular N-H center dot center dot center dot Br interaction. The results of structural refinement (cell parameters, bond lengths, and ion occupancy) of ultrasonically derived pure and Pt-doped ZnO particles suggest either the formation of Zn-i interstitials or platinum ion incorporation into the ZnO lattice in octahedral interstitial positions, respectively. A well-crystallized hexagonal wurtzite structure of ZnO was pronounced in all investigated samples [JCPDS card 36-1415, Joint Committee on Powder Diffraction Standards, defined by International Centre for Diffraction Data (www.icdd.com)]. Phase determination also indicated the presence of a nitrate hydroxide hydrate phase (JCPDS card 24-1460), as a result of incomplete precursor decomposition and a spinel Zn2PtO4 phase (below 1.0 wt%) located in the boundary region for a Pt-doped ZnO sample. Based on x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analyses, it was shown that the different particle growing morphologies, which were either spheroidally or pyramidally shaped, were influenced by the precursor chemistry, processing parameters and the presence of platinum ions. The composite internal particle structure revealed by transmission electron microscopy and selected area electron diffraction analyses, implied that the secondary particles represent an assembly of primary particles sized under 60 nm aroused during the processes of nucleation, grow

An equimolar mixtures of starting ZnO and Cr2O3 powders were mechanically activated by grinding using a planetary ball mill for various periods of time (40-320min). Formation of nanocrystalline ZnCr2O4 as normal spine] structure at room temperature is detected in all samples-after ball-milling. A detailed XRD structural analysis (the relative phase abundances of different phases, lattice parameter changes, site occupancy, the average primary crystallite sizes, crystal lattice microstrains) is realized by the pattern decomposition technique, performed in accordance with the procedure based on Rietveld software KOALARIET-XFIT. Due to the importance of cation distribution on the chemical and physical properties of spinels, a study of site occupation factors of ZnCr2O4 spinels has been undertaken. The calculation based on the atomistic methods for the description of the perfect and defect spinel ZnCr2O4 crystal lattice is applied and the presence of the individual structural defects is determined.

Pure and Pt-doped ZnO nanophase particles were synthesized by ultrasonic spray pyrolysis. The particles were obtained through the decomposition of zinc nitrate and with a newly developed Pt(IV) complex with 1,3 -propylenediamine-NN'-diacetate tetradentate class ligand (pdda). The complex was characterized by elemental analysis, electronic absorption and infrared spectroscopy. The form of the determined complex structure {trans-[Pt(pdda)Br-2]center dot H2O} implies that Pt(IV) ion has a distorted octahedral coordination due to intramolecular N-H center dot center dot center dot Br interaction. The results of structural refinement (cell parameters, bond lengths, and ion occupancy) of ultrasonically derived pure and Pt-doped ZnO particles suggest either the formation of Zn-i interstitials or platinum ion incorporation into the ZnO lattice in octahedral interstitial positions, respectively. A well-crystallized hexagonal wurtzite structure of ZnO was pronounced in all investigated samples [JCPDS card 36-1415, Joint Committee on Powder Diffraction Standards, defined by International Centre for Diffraction Data (www.icdd.com)]. Phase determination also indicated the presence of a nitrate hydroxide hydrate phase (JCPDS card 24-1460), as a result of incomplete precursor decomposition and a spinel Zn2PtO4 phase (below 1.0 wt%) located in the boundary region for a Pt-doped ZnO sample. Based on x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analyses, it was shown that the different particle growing morphologies, which were either spheroidally or pyramidally shaped, were influenced by the precursor chemistry, processing parameters and the presence of platinum ions. The composite internal particle structure revealed by transmission electron microscopy and selected area electron diffraction analyses, implied that the secondary particles represent an assembly of primary particles sized under 60 nm aroused during the processes of nucleation, grow

Nanophase phosphor particles in the complex Y3Al5O12Ce system were synthesized from aerosols of 0.06 mol/dm3 nitrate solution ultrasonically generated with frequency of 8105 s-1 and thermally treated at 1273 to 1473 K. The secondary particles obtained are spherical, and range in size from 300- 800 nm. TEM reveals a composite secondary particle structure comprised of clusters of < 60 nm primary particles. XRD of the as-synthesized powders indicates the presence of poorly crystallized phases. The phase development and structural changes, followed using a Koalariet-Xfit program, identifies the target cubic YAG - Y3AI5O12 being prevalent after annealing at 1073 K, with The YAG content increases with temperature. Both CeÛ2 and monoclinic Y4AI2O9 are present in lower concentration. EDX analysis verifies a uniform distribution of the constitutive elements inside the secondary particles. Photoluminescence measurements show an emission spectrum peak maximum at 537 nm for the thermally treated particles, which is attributed to the phase content of the powder.

An equimolar mixtures of starting ZnO and Cr2O3 powders were mechanically activated by grinding using a planetary ball mill for various periods of time (40-320min). Formation of nanocrystalline ZnCr2O4 as normal spine] structure at room temperature is detected in all samples-after ball-milling. A detailed XRD structural analysis (the relative phase abundances of different phases, lattice parameter changes, site occupancy, the average primary crystallite sizes, crystal lattice microstrains) is realized by the pattern decomposition technique, performed in accordance with the procedure based on Rietveld software KOALARIET-XFIT. Due to the importance of cation distribution on the chemical and physical properties of spinels, a study of site occupation factors of ZnCr2O4 spinels has been undertaken. The calculation based on the atomistic methods for the description of the perfect and defect spinel ZnCr2O4 crystal lattice is applied and the presence of the individual structural defects is determined.