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The microstructural characterization and adsorption properties of metakaolin (MK) and alkali-activated metakaolin, known as geopolymer materials (GP) were investigated. The structure and properties of the metakaolin and obtained geopolymer were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Furthermore, based on the analysis of adsorption efficiency, microstructure and mineral structure, the difference between geopolymer and metakaolin on the performance of immobilizing heavy metals have been discussed. The kinetics of adsorption can be represented by pseudo-second order equation. The results of lead ions adsorption experiments were best fitted by Freundlich adsorption isotherm for both investigated adsorbents. The highest removal efficiencies of alkali-activated material based on metakaolin was found 97.5% at pH 4 and metakaolin removal efficiencies was found 92% at pH 5.5.[Projekat Ministarstva nauke Republike Srbije, br. III 45012 i br. 172007]

Lipophilicity of twelve synthesized chalcones, whose ring B is a ortho, meta or para monosubstituted with alkyl, oxyalkyl groups or halogens was determined by reverse phase liquid chromatography, using octadecyl-functionalized (RP-18) silica gel as a stationary phase and two-component mixture of methanol/water as a mobile phase. Linear dependence of logk’ values of the volume fraction of methanol in the mobile phase was determined for all analyzed compounds, with high coefficient of correlation (r > 0.99). Extrapolation of the line to 0% methanol concentration resulted in the capacity factor of chromatographic system where water is the mobile phase (logkw). For five standard substances, chemically similar to chalcones, logkw values were determined under experimental conditions and they were correlated with logP values of those compounds available in the literature. logPEXP values of synthesized chalcones were calculated on the basis of the created standard curve. In order to estimate the relevance of the experimentally obtained logP values for chalcones, correlation of logPEXP values with the logP values obtained through various computational procedures was performed using linear regression analysis. Statistical parameters of dependence showed that the best matching of the results had been achieved with ChemOffice program, suggesting that this program is suitable for calculating logP values of newly-synthesized chalcones, as well as of compounds structurally similar to chalcones. [Projekat Ministarstva nauke Republike Srbije, br. OI 172041]

Majority of lead content found in the environment is the result of human activities. Heavy metals can be hazardous because they tend to bioaccumulate. Complexation-microfiltration process for the removal of Pb(II) ions was studied. The aim of microfiltration of the model wastewater containing heavy metal ions was finding an optimum ratio between the concentrations of the complexing agent and metal, and determining the most favorable pH value. The microfiltration experiments were carried out in a stirred dead-end cell. Diethylaminoethyl cellulose (DEAE 23) was selected as the complexing agent. Versapor membranes were used to separate formed polymer-metal complex. The concentration of heavy metal ions after microfiltration in aqueous solution was determined using the atomic absorption spectroscopy (AAS). Effects on the amount of complexing agent, concentration of metal ion, pH value and operating pressure on the flux, J, and rejection coefficient, R, were investigated. Experimental results indicate that the pH of the solution has considerable influence on the rejection coefficient. An increase in pH and the amount of complexing agents enabled us to obtain very high retention coefficient (99%).

The first successful attempt to electrodeposit ZnMn alloy coatings from alkaline bath was made only a few years ago. In this kind of solution, potassium pyrophosphate (K4P2O7) serves both as a complexing agent and as the basic electrolyte. The aim of this work was to study the electrodeposition process and properties of ZnMn alloy coatings deposited from pyrophosphate solution, with a new kind of alkaline pyrophosphate bath. Namely, chloride salts were used as the source of metal ions and ascorbic acid was used as reducing agent. The composition of the plating solution was as follows: 1 mol dm-3 K4P2O7 + 0.017 mol dm-3 ascorbic acid + 0.05 mol dm-3 ZnCl2 + 0.05 mol dm-3 MnCl2•4H2O. Cathodic processes during the alloy electrodeposition were investigated using linear voltammetry. The influence of addition of small amounts of ascorbic acid on the cathodic processes was established. It was shown that this substance inhibits hydrogen evolution and increases the current efficiency of alloy deposition. The current efficiency in the plating bath examined was in the range of 25 and 30%, which was quite higher as compared to the results reported in the literature for electrodeposition of ZnMn alloy from pyrophosphate bath. Electrodeposition of ZnMn alloys was performed galvanostatically on steel panels, at current densities of 20120 mA cm-2. The coatings with the best appearance were obtained at current densities between 30 and 80 mA cm-2. The surface morphology studies, based on atomic force microscopy measurements, showed that morphology of the deposits is highly influenced by deposition current density. ZnMn coating deposited at 30 mA cm-2 was more compact and possessed more homogeneous structure (more uniform agglomeration size) than the coating deposited at 80 mA cm-2. Such dependence of morphology on the current density could be explained by the high rate of hydrogen evolution reaction during the electrodeposition process.

Sintering kinetics of the mechanically activated ZnO-TiO2 system was studied. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill for different time intervals from 0 to 300 minutes. Formal phenomenological analyses were performed in order to describe the specimen’s behavior during isothermal sintering at 1100oC. Non-isothermal sintering was investigated by dilatometer measurements up to 1100oC with a constant heating rate. The Dorn method was applied in order to give information on the activation energy. .

The aim of this work was analysis of isothermal sintering of zinc titanate ceramics doped with MgO obtained by mechanical activation. Mixtures of ZnO, TiO2 and MgO (0, 1.25 and 2.5%) were mechanically activated 15 minutes in a planetary ball mill. The powders obtained were pressed under different pressures and the results were fitted with a phenomenological compacting equation. Isothermal sintering was performed in air for 120 minutes at four different temperatures. Structural characterization of ZnO-TiO2-MgO system after milling was performed at room temperature using XRPD measurements. DTA measurements showed different activation energies for pure and doped ZnO-TiO2 systems. Thus addition of MgO stabilizes the crystal structure of zinc titanate.

Reduction of the specific surface area of porous ZnO during the sintering process was studied. ZnO powder was sintered at temperatures from 673 K to 1173 K. The decrease in the specific surface area was observed as a function of temperature and sintering time. Two different models were involved in order to define the appropriate parameters. The Arrhenius equation was used to give information on the activation energy of sintering. The LSE method was applied for determining optimum parameter values.