Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Conference Object Antioxidant, Antimicrobial and Cytotoxic Activities of Some Turkish Plant Extracts(John Wiley and Sons Inc., 2006) Altıok, Evren; Asbagh, L. Abbasi; Bulut, Çisem; Ülkü, Semra; Bayraktar, OğuzPlant extracts have been known to possess notable biological activity, including antioxidant, antimicrobial and cytotoxic properties. There is a growing interest in the use of natural products in the human food industries as consumer resistance to synthetic additives increases. These products can be used to improve human health. In vitro antioxidant, antimicrobial and cytotoxic activities of ethanol extracts of some plants from Urla region in Turkey were investigated. Plant materials were collected from Pistacia lentiscus, Vitex agnus-castus, Cistus creticus and Nerium oleander in October, November and December.Article Citation - WoS: 3Citation - Scopus: 5Adsorption Characteristics of Lead-, Barium- and Hydrogen-Rich Clinoptilolite Mineral(SAGE Publications Inc., 2003) Çakıcıoğlu Özkan, Seher Fehime; Ülkü, SemraThe carbon dioxide and water vapour adsorption properties of local clinoptilolite-rich material, both as the original and as lead-, barium- and hydrogen-rich forms, were examined. The lead- and barium-rich forms were prepared by treatment of the original clinoptilolite with Pb(NO3)2 and BaCl2 respectively, while the hydrogen-rich form was prepared by NH4Cl and heat treatment. Water and CO2 adsorption experiments were conducted in a volumetric system under static conditions, with low-pressure adsorption data being used for the characterization of the natural, Pb-rich, Ba-rich and H-rich clinoptilolite samples. Although the existence of barium-exchange was not noted, an appreciable decrease in CO2 adsorption was observed with the Pb-rich and H-rich forms due to a decrease in the electrostatic interaction between the surface and the adsorbate. Application of the Dubinin-Astakhov equation to the water adsorption data established the existence of micropores of different sizes that exhibited different adsorption mechanisms.Article Citation - WoS: 9Citation - Scopus: 8Measurement of Ternary Polymer/Solvent Equilibrium Data by Vapor-Phase Infrared Spectroscopy(Elsevier Ltd., 2009) Yürekli, Yılmaz; Alsoy Altınkaya, SacideVapor-liquid equilibrium (VLE) data for binary toluene/PVAC, methanol/PVAC and ternary toluene/methanol/PVAC systems have been measured at 100 °C by using vapor-phase infrared spectroscopy. Binary data have been compared with literature data measured by different experimental techniques and agreement between our measurements and others was found to be good. The ternary VLE data indicate that the solubility of methanol in PVAC is not influenced by the presence of toluene, while the solubility of toluene is lowered due to presence of methanol. To predict ternary VLE data, the Entropic free volume and Kannan free volume models and the Flory-Huggins theory were used. The predictive abilities of Flory-Huggins theory and the Kannan free volume model are similar and better than that of the Entropic free volume model.Article Citation - WoS: 40Citation - Scopus: 46Influence of Tert-Amine Groups on the Solubility of Polymers in Co2(Elsevier Ltd., 2009) Kılıç, Sevgi; Wang, Yang; Johnson, J. Karl; Beckman, Eric J.; Enick, Robert M.There is a need to develop new, non-fluorous polymers that are highly soluble in CO2. Experimental evidence indicates that tertiary amine and pyridine groups may exhibit favorable Lewis acid-Lewis base type interactions with CO2. It is therefore reasonable to assume that incorporation of tertiary amines into the side chain or backbone of non-fluorous polymers may impart a degree of CO2-solubility to the polymer. We present experimental results for eight different tert-amine-containing polymers. Of these polymers, only propyl dimethylamine-functionalized poly(dimethylsiloxane) is soluble in CO2 at temperatures and pressures accessible in our experiments, but even this polymer is less soluble than non-functionalized poly(dimethylsiloxane) at the same chain length. We have performed ab initio calculations on tertiary amine-containing moieties representative of some of the polymers examined experimentally. Our calculations confirm that amine-CO2 interactions are indeed energetically favorable. However, we also find that the moiety self-interactions are typically more favorable than the CO2-moiety interactions. This indicates that the lack of solubility of amine-containing polymers in CO2 is a direct result of strong polymer-polymer interactions.Article Citation - WoS: 11Citation - Scopus: 15Supercritical Carbon Dioxide Drying of Methanol-Zinc Borate Mixtures(American Chemical Society, 2009) Gönen, Mehmet; Balköse, Devrim; Gupta, Ram B.; Ülkü, SemraSupercritical carbon dioxide (CO 2) drying of zinc borate species was investigated to evaluate possible chemical alterations in the product during the drying. Methanol-wetted zinc borates produced either from borax decahydrate and zinc nitrate hexahydrate (2ZnO · 3B 2O 3 ·7H 2O) or from zinc oxide and boric acid (2ZnO · 3B 2O 3 ·3H 2O) were dried by both conventional and supercritical carbon dioxide drying methods. Zinc borate samples dried by both techniques were characterized using analytical titration, X-ray powder diffraction (XRD), thermo gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, elemental analysis, and scanning electron microscopy (SEM). It was found that while zinc borate obtained from zinc oxide and boric acid did not have any chemical interaction with CO 2, carbonates were formed on the surface of zinc borate obtained from borax decahydrate and zinc nitrate hexahydrate. The main factor for the carbonate formation during supercritical CO 2 drying is anticipated as the structural differences of zinc borate species. CO 2 is a nonpolar solvent, and it does not usually react with polar substances unless water is present in the medium. While 2ZnO · 3B 2O 3 ·3H 2O had three bound OH groups, 2ZnO · 3B 2O 3 ·7H 2O had five bound OH groups and one mole of water of crystallization. It is proposed that the water of crystallization reacts with CO 2 forming carbonic acid. Then, carbonic acid, which is stronger than boric acid, substitutes borate ions from their zinc salts.Article Citation - WoS: 68Citation - Scopus: 75Air-Water Exchange of Polychlorinated Biphenyls (pcbs) and Organochlorine Pesticides (ocps) at a Coastal Site in Izmir Bay, Turkey(Elsevier Ltd., 2008) Odabaşı, Mustafa; Çetin, Banu; Demircioğlu, Eylem; Sofuoğlu, AysunThe air-water exchange of polychlorinated biphenyl (PCB) and organochlorine pesticides (OCPs) were investigated using paired air-water samples (n = 16) collected in July and February-March, 2005 from Guzelyali Port in Izmir Bay, Turkey. Atmospheric PCBs and OCPs were mainly in gas-phase in both periods. However, their dissolved and particle-phase water concentrations were comparable. For PCBs, 3 and 4-Cl congeners were dominant while chlorpyrifos, endosulfans and HCHs were the most abundant OCPs for all samples. Especially in summer, calculated net gas-exchange PCB fluxes were mainly volatilization from the water ranging from - 0.2 (volatilization, PCB-101) to - 30.0 (volatilization, PCB-31) ng m- 2 day- 1. For OCPs, net flux ranged from - 0.03 (volatilization, cis-nonachlor) to 1568 (deposition, endosulfan I) ng m- 2 day- 1 and they have seasonal variations with generally deposition in winter and volatilization in summer. However, endosulfan I, II, endosulfan sulfate, α- and γ-HCH deposited in both periods. The calculated residence times of PCBs and OCPs in the water column indicated that the gas-exchange in the Bay is at least as or a more important mechanism than advection. Annual gaseous absorption and volatilization fluxes were calculated and were used along with the estimated dry deposition fluxes and wet deposition fluxes measured recently at a suburban site in Izmir to determine the relative contributions of different atmospheric mechanisms to the pollutant inventory of the Bay water column. Results suggested that the relative contributions of all studied mechanisms to the water column PCB and OCP inventories were significant.Article Citation - WoS: 21Citation - Scopus: 23Adsorption of Anionic Polyelectrolyte and Comb Polymers Onto Lead Magnesium Niobate(Elsevier Ltd., 2008) Şakar-Deliormanlı, Aylin; Çelik, Erdal; Polat, MehmetThis paper presents the results concerning the adsorption mechanism of polyacrylic acid (PAA) and polyacrylic acid/polyethylene oxide (PAA/PEO) comb polymer onto lead magnesium niobate (PMN) powders. In the study adsorption behavior of PAA and PAA/PEO onto PMN surface were determined in aqueous solutions and the influence of pH and ionic strength was investigated. Results showed that adsorption of PAA or PAA/PEO increased with decreasing pH of the suspensions. The increase in the ionic strength or the presence of divalent cations caused an increase in the adsorption of both polyelectrolytes. It was observed that the adsorption reaches a maximum when PAA is fully complexed in solution. On the other hand, the increase in the adsorption of PAA/PEO onto PMN in the presence of monovalent or divalent salt was attributed to the decrease in the electrostatic forces rather than complex formation with the divalent metal ions in solution. Turbidity measurements showed that there is no complex formation between the divalent metal ions and PAA/PEO comb polymers due to shielding effect of the PEO teeth.Article Citation - WoS: 53Citation - Scopus: 60Supercritical Deposition of Pt on Sno2-Coated Al2o3 Foams: Phase Behaviour and Catalytic Performance(Elsevier Ltd., 2008) Garrido, G. Incera; Patcas, F. C.; Upper, G.; Türk, M.; Yılmaz, Selahattin; Kraushaar-Czarnetzki, B.Deposition and reduction of an organometallic platinum complex from a supercritical Pt(COD)Me2/CO2 solution was carried out to produce Pt/SnO2 catalysts supported on Al2O3 foams for CO oxidation at moderate temperatures. The phase behaviour of the complex in supercritical carbon dioxide was investigated to find the optimum pressure and temperature conditions for the deposition. For the Pt(COD)Me2/CO2 mixture, the melting point decreased with increasing pressure from 378 K at 0.1 MPa to 360 K at 25.6 MPa. Additional investigations showed that the solubility of Pt(COD)Me2 in CO2 increases from 5.9 × 10-4 mol/mol at 11.2 MPa and 313 K to 3.4 × 10-3 mol/mol at 29.6 MPa and 353 K. The supercritical deposition yielded catalysts with highly dispersed platinum nanoparticles of approx. 3 nm having a narrow size distribution and thus, a superior activity towards oxidation of carbon monoxide in comparison to a catalyst prepared by the conventional aqueous impregnation of Pt.Article Citation - WoS: 3Citation - Scopus: 4Phase Formation and Microstructure of Nd +3 Doped Pb(mg 1/3nb 2/3)o 3 Prepared by Sol-Gel Method(Springer Verlag, 2008) Şakar-Deliormanlı, Aylin; Polat, Mehmet; Çelik, Erdal; Şakar Deliormanlı, Aylin Müyesser; Polat, MehmetThe aim of this study was to investigate the effects of the rare earth element neodymium on the phase formation and microstructural development of relaxor ferroelectric lead magnesium niobate, Pb(Mg 1/3 Nb 2/3)O 3 (PMN) system. Perovskite phase PMN powders were prepared using the sol - gel method and the effect of neodymium doping was investigated at different doping levels ranging from 0.1 mol% to 30 mol%. The precursors employed in the sol - gel process were lead (II) acetate, magnesium ethoxide, and niobium (V) ethoxide. All the experiments were performed at room temperature while the calcination temperatures ranged between 800 °C and 1,100 °C. Results showed that it was possible to obtain the pure perovskite phase at 950 °C using the sol - gel method. Nd +3 addition influenced the phase formation and microstructure of the multicomponent system. Pyrochlore was detected along with the perovskite phase above 10 mol% Nd. Results also demonstrated that grain size of the synthesized powders depended on the Nd +3 concentration.Article Citation - WoS: 14Citation - Scopus: 18Rheological Behavior of Pmn Gels for Solid Freeform Fabrication(Elsevier Ltd., 2008) Şakar Deliormanlı, Aylin; Çelik, Erdal; Polat, MehmetLead magnesium niobate (PMN) is a relaxor ferroelectric material and have widespread applications in the manufacture of multilayer electronic devices such as ceramic capacitors, actuators and transducers. The dielectric constant of this electrostrictive material is much higher than the well known ferroelectric barium titanate. However, aqueous processing of PMN is not investigated yet especially for the novel wet shaping fabrication. In this study, concentrated aqueous colloidal PMN gels have been designed to use in the robocasting process. Concentrated PMN suspensions were stabilized by polyacrylic acid and then gelation induced by changing the pH or ionic strength of the suspension or by addition of a cationic polyelectrolyte to the system. Through this procedure it was essential to understand the solid-liquid transition under shear to explore the feasibility of forming without excessive use of polymers. Therefore, rheological response of the samples having a gel network was investigated. Results showed that gelation induced by cationic polyethylene imine or by multivalent salts were successful methods in preparation of PMN gels. However, gelation induced by changing the pH of the suspension was challenging due to ion dissolution from PMN surface.