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Öğe Catalytic degradation of organic dye using reduced graphene oxide-polyoxometalate nanocomposite(Elsevier Science Sa, 2017) Ucar, Asuman; Findik, Mukerrem; Gubbuk, I. Hilal; Kocak, Nuriye; Bingol, HalukSilicotungstic acid (SiW) decorated reduced graphene oxide (rGO) nanocomposite (rGO-SiW) has been prepared and evaluated as a heterogeneous nanocatalyst for the degradation reactions of methylene blue (MB) and rhodamine B (RhB). The structural and morphological properties of rGO-SiW nanocomposite were investigated by various techniques such as Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), Atomic force microscopy (AFM) and Scanning electron microscope (SEM), which revealed the homogeneous and noncovalent anchoring of SiW nanoparticles on rGO sheets. The catalytic activity of rGO-SiW nanocomposite on the degradations of MB and RhB has been monitored using UV-visible absorption spectrometry in the presence of NaBH4 as the reducing agent at room temperature in water. The reduction reactions followed pseudo-first order kinetics and degradation were achieved in 34 min for MB and 81 min for RhB using rGO-SiW as catalysts. (C) 2017 Elsevier B.V. All rights reserved.Öğe ESR Characterization of Two Oxovanadium (IV) Schiff Base Complexes Derived from Tris(2-aminoethyl)amine(Taylor & Francis Inc, 2012) Sahin, Mustafa; Kocak, Nuriye; Sayin, Ulku; Yilmaz, MustafaThe compounds, C21H27N4O3(L-1) and C21H27N7(L-2), is a tripodal Schiff base that was obtained from the reaction of tris(2-aminoethyl)amine (tren) and furan-2-carbaldehyde and pyrole-2-carbaldehyde. The tripodal Schiff bases and their oxovanadium complexes have been characterized on the basis of the results of the elemental analysis, magnetic susceptibility measurements and spectroscopic studies FT-IR, H-1-NMR, UV-Vis, ESR, magnetic moment and thermal analysis (TGA). Job's method of continuous variation shows 3: 2 metal to ligand ratio.Öğe Insights into Components of Prospective Science Teachers' Mental Models and Their Preferred Visual Representations of Atoms(Mdpi, 2019) Derman, Aysegul; Kocak, Nuriye; Eilks, IngoThis study focused on determining the elements of mental models of atomic structure and views on visual representations of models of atomic structure in two sub-cohorts of student teachers studying at a university in Turkey. In total, 141 student teachers participated in this study. In the first cohort, the focus was on 73 freshman science student teachers' drawings of mental models of atomic structure. The analysis showed a wide variety of individual aspects in the students' minds when asked to sketch the structure of atoms. The majority of students preferred to draw two-dimensional structures, neglecting the atom's space-filling character. Concerning the details of atomic structure, the majority of students emphasized only the most essential components of atoms, namely protons, neutrons, and electrons. It was quickly recognizable that these elements were arranged according to different analogies or representations of historical models, particularly related to Bohr's atomic theory and different representations thereof. Overall, the different visual representations of atomic models the students see in school, almost exclusively serve as the basis for their ideas about atomic structure. Current atomic theory, like quantum mechanical models, are generally not used when students are asked for a contemporary model of atoms. Rather it seems that concreteness and functionality are the primary factors leading to the selection of an atomic model when requested. This study is supplemented by data collected from the second cohort of 68 prospective teachers consisting of a diverse group of students ranging from freshman to senior level. The students in this cohort were asked for their preferred illustrations of atoms in textbooks. Open-ended questions about atoms led to further insights. The analysis of the prospective teachers' drawings indicated that a more careful approach to teaching is necessary to clarify the relationships between different models of atomic structure and to allow students to understand what an appropriate and contemporary understanding of atomic structure should encompass.Öğe Mechanical and thermal studies on epoxy toluene oligomer-modified epoxy resin/marble waste composites(Wiley, 2012) Ahmetli, Gulnare; Kocak, Nuriye; Dag, Mustafa; Kurbanli, RefikaIn this research, marble dust waste was recycled as raw material for the preparation of composite materials. Epoxy toluene oligomer (ETO) was synthesized from toluene and epichlorohydrin, which was used as a comatrix in 50 wt% with commercial epoxy resin (ER). Its chemical structure was characterized with Fourier transform infrared spectroscopy and chemical analyses. The rigid filler used in epoxy polymer matrix was the marble processing waste obtained from wastewater using different coagulants, such as sepiolite, zeolite, or pumice. The thermal and mechanical properties of the composites were evaluated with thermogravimetric and mechanical analyses. The results showed that the marble wastes with all coagulants can significantly improve the thermal stability of an ERETO matrix at temperatures above 350 degrees C. Composites exhibited a higher thermal degradation temperature with a much higher char yield. Surface hardness and tensile strength of the composites were higher than those of pure epoxy polymer matrix, as well. Scanning electron microscopy was used for the characterization of surface and cross-sections of the composites to verify the results. POLYM. COMPOS., 2012. (c) 2012 Society of Plastics EngineersÖğe A Novel Chitosan Nanoparticle-Schiff Base Modified Carbon Paste Electrode as a Sensor for the Determination of Pb(II) in Waste Water(Esg, 2013) Kucukkolbasi, Semahat; Erdogan, Zehra Ozden; Barek, Jiri; Sahin, Mustafa; Kocak, NuriyeThis paper describes the preparation and electrochemical application of a modified carbon paste electrode with a new kind of chitosan nanoparticle-Schiff base for the determination of Pb(II) ions in waste water using differential pulse anodic stripping voltammetry (DPASV). Firstly a new kind of chitosan nanoparticle-Schiff base (CNSB) was synthesized by chitosan nanoparticle reaction with 2,4-dihydroxybenzaldehyde. CNSB structure was characterized by FT-IR spectroscopy, elemental analysis, particle size and zeta potential. Afterwards, a novel, simple and effective chemically modified carbon paste electrode with CNSB was prepared and characterized using scanning electronic microscopy (SEM-EDX) and anodic stripping voltammetry. The modified electrode showed only one oxidation peak in the anodic scan at -0.35 V (vs. Ag/AgCl) for the oxidation of Pb(II). The electrochemical properties and applications of the modified electrode, including the pH, supporting electrolyte, preconcentration time, reduction potential and time, and percentage of modifier were investigated. The best voltammetric response was observed for a paste composition of 73.7% (w/w) of graphite powder, 5.3% (w/w) of chitosan and 21% (w/w) of paraffin oil, with 0.2 mol L-1 NaAc solution at pH 6.0 as supporting electrolyte, preconcentration time of 600 s, a reduction potential of -0.1 V and reduction time of 10 s. The new electrode displays excellent response to Pb(II) which is linear in the range from 1x10(-6) to 1x10(-4) mol L-1, with a correlation coefficient of 0.998 and a detection limit of 7.24x10(-7) mol L-1.Öğe Self-assembly of a new building block of {BMo12O40} with excellent catalytic activity for methylene blue(Pergamon-Elsevier Science Ltd, 2019) Findik, Mukerrem; Ucar, Asuman; Colak, Alper Tolga; Sahin, Onur; Bingol, Haluk; Sayin, Ulku; Kocak, NuriyeA novel organic-inorganic hybrid of 2,2'-bipyridyl (2,2'-bipy) linked covalently with the first inorganic framework based on boron-containing Keggin-type heteropolymolybdate anion [BMo12O40](5-) has been hydrothermally synthesized in aqueous solution. The crystal structure was fully characterized by elemental analyses, single crystal X-ray diffraction, Fourier-transform infrared spectrum (FT-IR), powder X-ray diffraction (XRD), Ultraviolet-visible spectroscopy (UV-Vis) and electron paramagnetic resonance (EPR) analysis. The catalytic performance of the synthesized catalyst was studied in degradation of methylene blue (MB) at ambient temperature. The catalyst exhibited excellent degradation against MB with a rate constant of 0.506/m, which was much higher than those by other polyoxometalate catalysts. Moreover, it was found to be easily separated from the reaction solution and recycled up to five times without significant loss of degradation activity. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Synthesis and characterization of novel nano-chitosan Schiff base and use of lead (II) sensor(Elsevier Science Bv, 2012) Kocak, Nuriye; Sahin, Mustafa; Kucukkolbasi, Semahat; Erdogan, Zehra OzdenA new kind of nano-chitosan Schiff base ligand (CHNS) with particle size of 34 nm was formed by the reaction between the 2-amino groups of glucosamine residue of nano-chitosan and a 2,5-dihydroxybenzaldehyde. The chemical structures of the nano-chitosan and nano-chitosan Schiff base were characterized by FT-IR spectra, particle sizer, zeta potential, and elemental analysis. A new, simple and effective chemically modified carbon paste electrode with CHNS was prepared and used as a lead (II) sensor. The prepared electrode was characterized using scanning electronic microscopy (SEM-EDX) and cyclic voltammetry (CV). The modified electrode showed only one oxidation peak in the anodic scan at -0.34 V (vs. Ag/AgCl) for the oxidation of lead (II). The dedection limit (LOD) was calculated as 1.36 x 10(-7) for a 10-min preconcentration time at pH 6.0. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.Öğe Synthesis and Characterization of Sporopollenin-Supported Schiff Bases and Ruthenium(III) Sorption Studies(Springer, 2012) Sahin, Mustafa; Gubbuk, Ilkay Hilal; Kocak, NuriyeTwo Schiff base derivatives, (2-pycolylimino)benzen-1,4-diol and (2-pyridylimino)benzen-1,4-diol) were immobilized onto sporopollenin (Lycopodium clavatum) surfaces. The compounds were fully characterized by an infrared spectroscopy, elemental analysis, scanning electron microscopy, and X-ray diffraction techniques. The sorption capacities of the immobilized surfaces toward Ru(III) ions were investigated by batch sorption experiments. For the sorption experiment, the Ru(III) concentration, initial pH, and the temperature effects were studied. The isotherm data of Ru(III) ions were correlated reasonably well as a Freundlich sorption isotherm. The thermodynamic studies showed that the Ru(III) sorption onto immobilized sporopollenin derivatives is a non-spontaneous, endothermic and physical reaction.Öğe Synthesis of asymmetrical tridendate Schiff bases and metal complexes and investigation of anticarcinogen effects on human colon and cervical cancers(Taylor & Francis Inc, 2017) Sahin, Mustafa; Korkmaz, Hatice; Kocak, Nuriye; Sahin, Ozlem; Karakurt, Serdar; Yilmaz, MustafaThe metal complexes of Zn(II), Ni(II), Cu(II) and Pb(II) with asymmetrical Schiff bases were synthesized. The asymmetrical Schiff base was obtained through the condensation of 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde and biphenyl-4-carbaldehyde. The new Schiff base ligands (L-1' and L-2') and their metal complexes were characterized by TG/DTG, FT-IR, H-1-NMR, UV-Vis, ESR, powder XRD, elemental analysis, magnetic moment and fluorescence studies. The powder XRD studies indicate that Co(II) and Cu(II) complexes are amorphous, while Ni(II) and Zn(II) complexes are crystalline. The anticarcinogenic effects of L-1' and L-2' were also investigated against colon (SW-620) and cervical cancer (HeLa) cell lines and compound L-2' was found to possess the highest anticarcinogenic potential, with 16.7 mu M and 27.5 mu M of IC50 values for HeLa and SW620 cells, respectively.Öğe The Use of Voltammetry for Sorption Studies of Pb2+ from Aqueous Media using Schiff Base Immobilized Biologic Polymer Material(Springer International Publishing Ag, 2013) Kucukkolbasi, Semahat; Erdogan, Zehra Ozden; Kocak, Nuriye; Sahin, Mustafa; Gubbuk, Ilkay HilalAdsorption by low-cost adsorbents and biosorbents is recognized as an effective and economic method for low-concentration heavy metal. The purpose of this study was to investigate the possibility of the utilization of N,N'-bis(2,5-dihydroxybenzylidene)-1, 4-diaminobenzene (DHDB)-immobilized sporopollenin (Schiff base-immobilized sporopollenin, Sp-DHDB) as a sorbent for removal of lead (II) ion from aqueous solution. The effects of different parameters (such as sorbate concentration, sorbent dosage, and pH of the medium) were investigated by differential pulse anodic stripping voltammetry (DPASV) technique. The experimental data were analyzed by the Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) isotherms. Equilibrium data fitted well with the Freundlich model and the procedure developed was successfully applied for the removal of lead ions in aqueous solutions. This investigation reveals a new, simple, environmentally friendly, and cost-effective method for the removal of lead ions from aqueous solutions by a new Sp-DHDB material.Öğe Zn(II), Ni(II), Cu(II) and Pb(II) complexes of tridentate asymmetrical Schiff base ligands: Synthesis, characterization, properties and biological activity(Pergamon-Elsevier Science Ltd, 2013) Sahin, Mustafa; Kocak, Nuriye; Erdenay, Damla; Arslan, UgurNew asymmetrical tridentate Schiff base ligands were synthesized using 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde, 9-anthracenecarboxaldehyde. Schiff base ligands and their metal complexes were synthesised and characterized by using FT-IR, H-1 NMR, C-13 NMR, UV-Vis, XRD, ESR, elemental analysis and fluorescence studies. The antimicrobial activity of the ligands and their metal complexes were studied against Staphylococcus aureus ATCC 29213, S. aureus ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853. The determination of the antibacterial activity was done using the broth microdilution methods. In general, it has been determined that the studied compounds have MIC values similar to Gram-positive and Gram-negative bacteria. It has been found that Ni, Pb, Zn derivatives of HL1A and ZnL(2)A has lower MIC values than ampicillin for P. aeruginosa ATCC 27853 strain. (c) 2012 Elsevier B.V. All rights reserved.
