WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 17Citation - Scopus: 20Preparation and Characterization of Antibacterial Cobalt-Exchanged Natural Zeolite/Poly(vinyl Alcohol) Hydrogels(Springer Verlag, 2014) Narin, Güler; Bulut Albayrak, Çisem; Ülkü, SemraIn the present study, potential application of the local clinoptilolite-rich natural zeolite in formulation of antibacterial hydrogels was investigated. The zeolite powder exchanged with cobalt(II) ions was used in preparation of the zeolite/poly(vinyl alcohol) hydrogel films in different amounts. The films were physically crosslinked by the freezing-thawing method and characterized for their crystallinity, surface and cross sectional morphology, chemical composition, thermal behaviour, mechanical properties, swelling and dissolution behaviours, and antibacterial activities against a Gram-negative bacteria. The films with 0.48 wt% and higher cobalt-exchanged zeolite contents showed antibacterial activity. Addition of the zeolite powder in the formulations did not cause significant changes in the other properties of the films.Article Citation - WoS: 11Citation - Scopus: 11Comparison of Uniform and Non-Uniform Pressure Approaches Used To Analyze an Adsorption Process in a Closed Type Adsorbent Bed(Springer Verlag, 2013) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraHeat and mass transfer in an annular adsorbent bed filled with silica gel particles is numerically analyzed by uniform and non-uniform pressure approaches. The study is performed for silica gel-water pair, particle radius from 0.025 to 1 mm and two bed radii of 10 and 40 mm. For uniform pressure approach, the energy equation for the bed and the mass transfer equation for the particle are solved. For non-uniform pressure approach, the continuity and Darcy equations due to the motion of water vapor in the bed are added, and four coupled partial differential equations are solved. The changes of the adsorbate concentration, pressure, and temperature in the bed throughout the adsorption process for both approaches are obtained and compared. The obtained results showed that the particle size plays an important role on the validity of uniform pressure approach. Due to the interparticle mass transfer resistance, there is a considerable difference between the results of the uniform pressure and non-uniform pressure approaches for the beds with small size of particles such as 0.025 mm.Article Citation - WoS: 5Citation - Scopus: 8Investigation of Structural Properties of Clinoptilolite Rich Zeolites in Simulated Digestion Conditions and Their Cytotoxicity Against Caco-2 Cells in Vitro(Springer Verlag, 2013) Kavak, Dilek Demirbüker; Ülkü, SemraThe use of the clinoptilolite rich natural zeolites in biomedical applications such as in anticancer therapy, drug or drug support systems and as nutritive supplement is highly dependent on their behavior in digestive conditions. Aim of this study is to investigate structural stability of clinoptilolite rich natural zeolites in simulated digestion conditions and their interactions with digestive media and with Caco-2 (human colon adenocarcinoma) cells. X-ray Diffraction (XRD), Fourier Transform InfraRed (FTIR), Scanning Electron Microscopy (SEM) and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analyses of the clinoptilolite rich zeolite samples showed that zeolites preserved their structural stabilities during in vitro digestion. Slight interactions were detected in UV measurements of the digestive liquid media and FTIR spectra of the intestinal digested media powders. SEM results implied that zeolites might have a role in the aggregation of the digestive enzymes. Cytotoxicity test using colon cancer cells showed that clinoptilolite rich natural zeolites have cytotoxic effect against Caco-2 cells and cytotoxicity did not significantly change with respect to simulated digestion process.Article Citation - WoS: 10Citation - Scopus: 11Removal of Bacteria by Clinoptilolite Rich Mineral and Its Surfactant Modified Forms(Springer Verlag, 2013) Cansever Erdoğan, Beyhan; Ülkü, SemraBatch experiments were carried out to understand the potential values of clinoptilolite rich mineral and its surfactant modified forms in the removal of Gram-positive and Gram-negative bacteria. Zeta potential and Fourier Transform IR analysis were performed to explain the possible interactions between the bacteria and the zeolite samples. The results revealed that hydrogen bonding was significant mechanism in the removal of bacteria with clinoptilolite rich mineral and anionic surfactant modified clinoptilolite rich mineral whereas both attractive electrostatic forces and hydrogen bonding were dominant mechanism in the removal of bacteria with cationic surfactant modified clinoptilolite rich mineral. Cationic and anionic surfactant modified clinoptilolite rich mineral are promising materials in removal of bacteria studies.Article Citation - WoS: 17Citation - Scopus: 23Synthesis of Zinc Borate by Inverse Emulsion Technique for Lubrication(Springer Verlag, 2011) Atakul Savrık, Sevdiye; Balköse, Devrim; Ülkü, SemraLubricating oil additives based on boron compounds are promising materials for lubrication due to their tribological advantages such as antiwear efficiency, good film strength, and high temperature resistance. This article deals with the preparation of zinc borate particles that are well dispersed and colloidally stabilized in mineral oil. This method starts with preparing two inverse emulsions (water-in-oil) with sorbitan monostearate (Span 60) as a surfactant, light neutral oil as a continuous phase, and the aqueous solutions of borax decahydrate (Na2B4O7·10H 2O) and zinc nitrate (Zn(NO3)2·6H 2O) as the dispersed phases. The produced particles were zinc borate crystals having both rod-like and spherical morphologies, and the diameters of spherical particles were changing between 20 and 30 nm. FTIR spectra of the obtained particles showed the characteristic peaks of trihedral borate (B(3)-O) and tetrahedral borate (B(4)-O) groups as well as the specific peaks of the sorbitan monostearate. TG showed 30.42% and 22.08% mass loss at 600 °C for the samples prepared by inverse emulsion and precipitation techniques, respectively. The endothermic peak at 50 °C is observed due to the melting of sorbitan monostearate and the heat of melting is evaluated as -3.50 J/g. Tribological studies revealed that sorbitan monostearate not only outperformed as a dispersing agent of inorganic particles, but also it proved to be an anti-wear agent. Zinc borate produced by precipitation decreased the wear scar diameter from 1.402 to 0.639 mm and the friction coefficient from 0.099 to 0.064. The inverse emulsion was effective in decreasing wear scar diameter and the friction coefficient by lowering them to 0.596 and 0.089 mm, respectively.Article Citation - WoS: 23Citation - Scopus: 25Microcalorimetric Investigation of Water Vapor Adsorption on Silica Gel(Springer Verlag, 2011) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraWater vapor adsorption on silica gel was investigated using Tian-Calvet-type microcalorimetry. Differential heat of adsorption data was obtained. The setup of microcalorimetry was used volumetric system to determine adsorption isotherms of water vapor-silica gel. The Langmuir model was used in the interpretation of the adsorption data. The Clausius-Clapeyron diagram was also given. Effective mass diffusivity of water vapor in the silica gel particle as a function of temperature was also determined. The silica gel, which was degassed under vacuum at 10 -7 mbar and 120 °C for 18 h, was found to adsorb 0.6, 0.98, 1.1, 1.4, 2, 3.5, 11, 13, and 14 wt% water vapor at 120, 110, 100, 90, 75, 60, 40, 35, and 30 °C, respectively. The diffusivities of water vapor inside the silica gel for short- and long-range periods were described using kinetics data as a function of temperature in the Arrhenius form.Conference Object Citation - WoS: 22Citation - Scopus: 24Characterization of Poly(vinyl Chloride) Powder Produced by Emulsion Polymerization(Springer Verlag, 2010) Atakul Savrık, Sevdiye; Balköse, Devrim; Ulutan, Sevgi; Ülkü, SemraThe effect of emulsion process formulation ingredients on the morphology, structure, and properties of polyvinyl chloride (PVC) powder has been considered in this study. PVC powder was extracted with ethanol and films were obtained by solvent casting from tetrahydrofurane. Characterization of powders, films, and ethanol extract was performed through FTIR spectroscopy, DSC, AFM, SEM, EDX analysis, methylene blue, and nitrogen adsorption. PVC powder was composed of spheres of a large particle size range from 10 nm to 20 μm as shown by SEM. The specific surface area of the PVC powder was determined as 16 and 12 m 2 g-1 from methylene blue adsorption at 25 °C and from N2 adsorption at -196 °C, respectively. AFM indicated the surface roughness of the films obtained by pressing the particles was 25.9 nm. Density of PVC powder was determined by helium pycnometry as 1.39 g cm -3. FTIR spectroscopy indicated that it contained carbonyl and carboxylate groups belonging to additives such as surface active agents, plasticizers, and antioxidants used in production of PVC. These additives were 1.6% in mass of PVC as determined by ethanol extraction. EDX analysis showed PVC particles surfaces were coated with carbon-rich materials. The coatings had plasticizer effect since, glass transition temperature was lower than 25 °C for PVC powder and it was 80 °C for ethanol extracted powders as found by using differential scanning calorimetry. These additives from polymerization process made PVC powder more thermally stable as understood from Metrom PVC thermomat tests as well. © 2010 Akadémiai Kiadó, Budapest, Hungary.Article Citation - WoS: 22Citation - Scopus: 28The Effect of Zinc Stearate on Thermal Degradation of Paraffin Wax(Springer Verlag, 2008) Gönen, Mehmet; Balköse, Devrim; İnal, Fikret; Ülkü, SemraIn this research, the effects of zinc stearate addition on paraffin wax degradation were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The apparent activation energies of wax decomposition in nitrogen and air atmospheres were determined as 76 and 37 kJ mol-1, respectively applying Kissinger method to TG data. The degradation rate constants of paraffin containing zinc stearate (0.1-0.5%) were found to be almost two times greater than that of paraffin only in air atmosphere. However, zinc stearate did not affect the rate constants in nitrogen significantly.Article Citation - WoS: 26Citation - Scopus: 28Thermal Stability of Ag-Exchanged Clinoptilolite Rich Mineral(Springer Verlag, 2008) Akdeniz, Yelda; Ülkü, SemraThermal stability of clinoptilolite rich mineral from Western Anatolia, Turkey and its Ag-exchange forms was investigated. Parent mineral of different sizes were heated up to 1000°C with heating rate of 2 and 10°C min -1 using differential thermal analyzer (DTA) and thermogravimetric analyzer (TG). Ag exchange was conducted both in conventional constant temperature waterbath and microwave at 40, 60 and 80°C. The exchanged minerals were then characteized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), DTA and TG. The particle size and heating rate do not have significant effect on the thermal behavior of the parent mineral and no structural changes were observed with Ag exchange, only decomposition temperature was lowered. It was finally concluded that, Ag-exchanged clinoptilolite rich minerals were less thermally stable compared to parent mineral that does not affect their use for possible applications.Article Citation - WoS: 7Citation - Scopus: 7Water vapour adsorption on DNA(Springer Verlag, 2008) Balköse, Devrim; Alp, Burcu; Ülkü, SemraDNA adsorbed very low amount of water at low relative humidities, amount of adsorption increased to 140% at 98% relative humidity at 25°C. Heat of adsorption was 109 kJ mol-1 H2O for the increase of moisture content from 0 to 1.96%. At higher moisture contents the heat released approached heat of condensation of water vapour on free liquid surface, 40 kJ mol-1 H2O.