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Isopiestic Determination of Osmotic and Activity Coefficients of the {yNaH(2)PO(4) + (1-y)Na2HPO4}(aq) System at T=298.15 K
No full textIsopiestic measurements have been made for aqueous solutions of the common sodium cation mixtures of NaH2PO4 and Na2HPO4 at T = 298.15 +/- 0.01 K, at NaH2PO4 ionic strength fractions y = (0, 0.24851, 0.49862, 0.74544, and 1), where the ionic strength fractions were calculated by assuming complete electrolytic dissociation of NaH2PO4 as 1:1 and Na2HPO4 as 2:1 electrolytes; CaCl2(aq) was used as the reference standard solution. Model parameters for an extended form of Pitzer's ion-interaction model and also for the Clegg-Pitzer-Brimblecombe equations based on the mole-fraction-composition scale were evaluated at T = 298.15 K for both NaH2PO4(aq) and Na2HPO4(aq) using the isopiestic results from this study (17 values each) together with numerous critically assessed osmotic coefficients for both electrolytes taken from the published literature. The thermodynamic models for NaH2PO4(aq) extend to m = 7.5 mol.kg(-1), whereas those for Na2HPO4(aq) extend to m = 2.6050 mol.kg(-1), which is well above the solubility limit for the thermodynamically stable phase Na2HPO4 center dot 12H(2)O(cr). The 51 osmotic coefficients for the ternary mixtures were treated with these two models together with Scatchard's neutral-electrolyte model; one previous set of osmotic coefficient values for {yNaH(2)PO(4) + (1 - y)Na2HPO4}(aq) mixtures was found in the literature [Scharge, T.; et al. J. Chem. Thermodyn. 2015, 80, 172-183], and hence an analysis and comparison were made of our results with theirs
Improvement and modification of the energy-dispersive X-ray fluorescence method for the determination of metal elements in cement leachates - A chemometric approach
No full textA modification of an analytical procedure for the energy-dispersive X-ray fluorescence (EDXRF) quantification of ten chemical elements (As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb and Zn) in the leachates obtained from cement binders was developed. Twenty-nine testing samples were used in the experiment. All samples were based on Portland cement. Fly ash of different origin, zeolite and bentonite were employed as mineral additives in the cement binders. Distilled water was used as the leachate. Validation of the modified EDXRF procedure was conducted in terms of limits of detection and quantification, working range, linearity, selectivity, precision, trueness, and robustness. Traceability of the procedure was established using certified reference materials. Uncertainty of measurement was confirmed via an "in-house" laboratory validation approach. The expanded uncertainties for the ten analysed elements were obtained for the entire working range of the EDXRF method. Robustness of the modified EDXRF procedure was assessed by means of a chemometric in-house approach. The results obtained by the modified X-ray fluorescence method were additionally correlated to those acquired by inductively coupled plasma optical emission spectrometry to confirm that EDXRF could be used as an effective and reliable alternative method for analysis of cement leachates
Temperature and pH growth profile prediction of newly isolated bacterial strains from alkaline soils
No full textBACKGROUND Soil microorganisms can form complex and varied communities which interact with each other in many different ways depending on environmental conditions. These microbial diversities are accompanied by different metabolic paths and adaptability reflected even in extreme environments. In recent decades, the biodiversity of microbes in extreme environments has been in scientific focus because such specifically adapted bacteria can improve bioremediation processes in industrial and agricultural applications. Instead of the time-consuming process of identification of new bacterial strains from habitats rich in microbiota, artificial neural networks have been proposed as a mapping model for resolving the problem of prediction of microbial behaviour. RESULTS The occurrence and diversity of alkaliphilic sporogenic bacteria in alkaline soils were investigated. For this purpose, soil samples were collected from various locations: leached soil from the Danube river, cement factory wastewater accumulation, deposit of limestone near the Besenovo lake and the Beli Majdan cave in the Fruska gora mountain. According to the obtained results, two empirical models were developed that gave a good fit to experimental data and were able to predict successfully the pH and temperature growth profiles of the natural isolates. The artificial neural network models showed a reasonably good predictive capability (overall R-2 for temperature growth profile was 0.727, while the overall R-2 for pH growth profile was 0.906). CONCLUSIONS The developed mathematical models provided adequate precision for practical study in the microbiology laboratory and scale-up processes for a wide range of laboratory and industrial applications, where specifically adapted microbial communities are needed
Porous cordierite-supported polyethyleneimine composites for nickel(II) and cadmium(II) ions removal
No full textIndustrial/technological growth is directly connected with environmental pollution, but its influence can be minimized through pollution abatement approaches such as the treatment of industrial wastewater. In this study, novel porous amine-functionalized silicate minerals, specifically, cordierite was investigated for the removal of toxic heavy metals from industrial wastewaters. Cordierite supports were synthesized by mixing MgO, Al2O3, and SiO2 powders in 2:2:5 molar ratios, and mechanically activated via ball milling in ethanol for 10, 40, or 80 min. Pellets were sintered by heating in air at 20 degrees C min(-1) to 1,350 degrees C, for 2 h. Porous supports were produced by coarsely crushing the sintered pellets and mixing the crushed and sieved cordierite powder with 20 wt.% of a pore-forming agent, either nanocellulose or yeast. The resulting pellets were sintered by heating at 5 degrees C min(-1) to 700 degrees C in air. The synthetic cordierite support was modified by treatment in poly-ethylenimine. Activated supports were then tested for the removal of Ni2+ and Cd2+ ions. The phase composition of the cordierite supports was analyzed by the X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Analysis of adsorption isotherms, kinetics, and thermodynamic parameters indicated that adsorption was a spontaneous, endothermic process with a maximum adsorption capacity of 36 mg g(-1) for Cd2+ and 43 mg g(-1) for Ni2+. This work has shed light on the mechanism of heavy metal removal from the aquatic medium using the novel hybrid functionalized cordierite-based ceramic
Application of Contemporary Extraction Techniques for Elements and Minerals Recovery from Stinging Nettle Leaves
No full textStinging nettle (Urtica dioica L.) is a perennial plant belonging to the Urticaceae family. Several studies have reported the presence of the different classes of chemical compounds, which expressed a beneficial effect on human health. Among them there are elements and minerals that are essential for the proper functioning of organism. Mineral occurrence requires analytical data about the content. For such purposes was developed and validated a method based on the optical emission spectroscopy coupled with inductively coupled plasma (ICP-OES). Minerals and elements were extracted using two conventional methods (Soxhlet and maceration) and two non-conventional (ultrasound- and microwave-assisted techniques). The extracts were analyzed resulting in high diversity in the composition. Non-conventional techniques showed better results, since those extracts possessed high content of the macroelements and iron as well, instead the toxic elements were found in trace amoun
Supercritical fluid extraction of raspberry seed oil: Experiments and modelling
No full textThe aim of this study was the optimization of supercritical fluid extraction (SFE) of raspberry seed oil. Sequential extraction kinetic modelling and artificial neural networks (ANN) were used for this purpose. SFE was performed according to the broaden Box-Behnken experimental design with pressure, temperature and CO2 flow rate as independent variables, while the influence of particle size on extraction kinetics and adjustable model parameters was additionally evaluated. Five empirical kinetic equations and mass-transfer model proposed by Sovova were utilized for extraction kinetics modelling. According to appropriate statistical parameters (R-2, SSE and AARD), the mass-transfer model exhibited the best fit of experimental data. The initial mass-transfer rate of extraction curve was used as a response variable in ANN optimization. SFE should be performed at elevated pressure and CO2 flow rate, while temperature and particle size should be held at a lower level in order to achieve a maximal initial mass-transfer rate
Serbian aromatized wine "Bermet": Electrochemical, chemiluminescent and spectrophotometric determination of antioxidant activity
No full textSerbian aromatized wine "Bermet" from grapes grown on Fruska Gora Mountain has been in production since the 15th century. Ten commercial Bermets produced according to the traditional procedure by different manufacturers, and six prepared within the scope of this study were assessed for antioxidant (AO) activity using electrochemical, chemiluminescent and spectrophotometric AO assays. Direct current polarographic assay based on the decrease of anodic current of [hydrogen(peroxido)(1-)]hydroxidomercury(II) complex formation in alkaline H2O2 solution at potential of mercury oxidation, chemiluminescent H2O2 scavenging assay, as well as commonly used spectrophotometric assays (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) based Trolox equivalent antioxidant capacity (TEAC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP)) were used. Total phenolic content (TPC) was determined by Folin-Ciocalteu assay. The results obtained were correlated using regression analysis, ANOVA and F-test. An integrated approach to AO capacity determination allowed a more comprehensive comparison between samples. The approach is based on the introduction of the relative antioxidant capacity index, calculated by assigning each AO assay equal weight, and by PCA analysis. In addition, the introduction of phenolic antioxidant coefficients, calculated as the ratio between individual AO capacity and TPC, enabled a better understanding of their relation
Effect of laser shock peening with and without protective coating on the microstructure and mechanical properties of Ti-alloy
No full textOwing to their good mechanical properties, titanium based alloys are used for machine parts and devices that operate in demanding regimes and environmental conditions. Laser shock peening (LSP) is an innovative technique for improvement of the surface and mechanical characteristics of the material. In this paper, LSP is employed for additional improvement of already good characteristics of Ti- alloy. Laser shock peening is performed on alloy surface, with and without protective and transparent layer and obtained microstructure, surface characteristics and mechanical properties are compared. LSP improved the surface topology and microhardness of material, producing overall better results when the Ti-alloy surface was coated by transparent and protective layer
Luminescent lanthanide beta-diketonate complexes: insights into the role of the coordination environment on the photophysical properties of lanthanide ions
No full textThis thesis consists of five chapters which divide the thesis into three parts. The first part consists of an introduction which provides a background on lanthanides, luminescence and introduces the topics which are covered in the PhD work of this thesis, presented in Chapter 1. The second part consists of three chapters and contains the experimental work and their results, as presented in Chapters 2 to 4. In the final part the general conclusions are presented and an outlook given based on the research and work done during this PhD thesis.
In Chapter 1 a general background is provided, which consists of an overview of lanthanides and luminescence, presented in the first two sections of this chapter. The 3rd section provides a background on the sensitization of lanthanide ions with organic molecules, followed by a short discussion of different types of sensitization mechanisms. In the 4th section the quenching of luminescence and possible quenching mechanisms are discussed, while in the 5th section of this Chapter a background is given on temperature-dependent luminescence, types of measurement which can be employed and different types of temperature sensors. In the 6th section the coordination chemistry of lanthanide ions and some types of the used ligands is discussed. In the last section of this Chapter the aim of this PhD thesis is presented.
Chapter 2 is the first out of three chapters in which the experimental work and results of this thesis are presented. In this Chapter the synthesis of tetrakis lanthanide beta-diketonate complexes, structural studies, and their luminescence and temperature sensing properties are described. Furthermore, by co-crystallization of two homonuclear complexes, heteronuclear complexes containing two different lanthanide ions with different ratios could be obtained. All complexes have been structurally characterized with single-crystal XRD analysis, photoluminescence and for temperature sensing with temperature-dependent luminescence showing promising results regarding the sensitivity.
Chapter 3 presents the work on temperature sensors based on poly(methyl-methacrylate) (PMMA) doped with tris lanthanide beta-diketonate complexes based on the same -diketone ligands as in Chapter 3, however here the visible-emitting lanthanide ions (Eu3+, Tb3+ and Sm3+) were used and also tppo was used to form water-free complexes. The main part in this Chapter is on the synthesis and temperature-dependent luminescence of PMMA films doped with Tb3+ – Eu3+ or Tb3+ – Sm3+ complexes. Also, silica nanoparticles were prepared, which were afterwards coated with PMMA films and their sensitivity and temperature-dependent luminescence was investigated in water for these samples. The developed PMMA films and coated silica nanoparticles show one of the highest sensitivity properties for the physiological temperature range reported to date. Besides the temperature sensing properties, the lanthanide beta-diketonate complexes were characterized before the films were made.
Chapter 4 describes the work on the study of vibration quenching of C-H and O-H oscillators on the near-infrared emission of NIR emitting lanthanide ions (Nd3+, Er3+, Yb3+ and Sm3+) by Förster resonance energy transfer (FRET). Here two series of tris -diketonate complexes with slightly different ligands were synthesized. Both ligands were based on the 4,4,4-trifluoro-1-phenyl-1,3-butadion ligand where for ligand L1 a H atom is present in the p-position of the phenyl ring and for ligand L2 this p-position of the phenyl ring is substituted with a Cl atom, whereas for the water-free complexes the triphenylphosphine oxide (tppo) ligand was used.
Chapter 5 summarizes the main findings of this PhD thesis and gives an outlook and suggestions for further research based on the results of this work
Elderberry (Sambucus nigra L.) juice as a novel functional product rich in health-promoting compounds
No full textThe medicinal herbs of the Balkan Peninsula are highly represented in traditional medicine. The connection between traditional and modern life and health is reflected in the creation of new food products with added value. In this study, the plant species Sambucus nigra L. was used to obtain freshly pressed juice, whose chemical composition and various biological activities were evaluated. The most abundant compounds were phenolic acids: protocatechuic and chlorogenic acid, as well as flavonoids: quercetin-3-O-hexoside, quercetin, and rutin. The analyzed juice was very rich in total phenolic compounds (1945 mg GAE per mL juice), and a significant anthocyanin concentration was observed (30.85 mg Cy-3-GE per mL juice). Bioactivity testing revealed that elderberry juice was an extremely potent agent in the process of neutralizing NO free radicals (53.06 g TE per L juice), while in reducing over-enzyme activity, the best result was achieved in the inhibition of tyrosinase enzyme (54.70 mg KAE per g of juice)