Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 14Citation - Scopus: 25Kinetic and Equilibrium Studies of Adsorption of Ss-Glucuronidase by Clinoptilolite-Rich Minerals(Elsevier Ltd., 2015) Demirbüker Kavak, Dilek; Ülkü, SemraThe adsorption of the bacterial β-glucuronidase (GUS) enzyme, which is thought to be responsible for the production of reactive metabolites related to some diseases and cancer development, by clinoptilolite-rich mineral was investigated. Batch experiments were performed to analyze of the effects of the clinoptilolite amount and particle size, initial GUS concentration, shaking rate, pH and temperature on the adsorption equilibrium and kinetics. Adsorption equilibrium data were interpreted in terms of Langmuir and Freundlich isotherms; and they were well represented by the Langmuir isotherm model. The percentage of GUS removal by the clinoptilolite-rich mineral was changed in the range of 9.4-54.4% depending on its initial concentration. The kinetic data were analyzed using external film diffusion, intraparticle diffusion, pseudo-first-order and pseudo-second-order models and both external film and intraparticle diffusion appeared to be effective in GUS adsorption. Thermodynamic studies indicated that GUS adsorption is exothermic, physical and spontaneous at the temperatures investigated (288-310 K)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: 13Citation - Scopus: 14Characterization and Dehydration Behavior of a Natural, Ammonium Hydroxide, and Thermally Treated Zeolitic Tuff(Taylor and Francis Ltd., 2011) Narin, Güler; Balköse, Devrim; Ülkü, SemraAqueous NH4OH-treated and subsequently calcined forms of local natural zeolitic tuff were characterized by different techniques including scanning electron microscopy (SEM), X-ray powder diffraction, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), volumetric N2 adsorption at -196°C, thermogravimetry (TG), differential scanning calorimetry (DSC), and transmittance infrared spectroscopy. The dehydration behavior of the samples was investigated using an in situ temperature-programmed diffuse reflectance Fourier transform infrared spectroscopy (TP-DRIFTS) method under vacuum. The DRIFTS spectra recorded yielded information about the effect of the NH4OH treatment and subsequent calcination on the dehydration behavior of the natural zeolite.Changes in the infrared bands corresponding to vibrations of the O-H and N-H bonds upon in situ heating under vacuum were analyzed.Article Citation - WoS: 35Citation - Scopus: 41Batch and Column Studies on Heavy Metal Removal Using a Local Zeolitic Tuff(Elsevier Ltd., 2010) Balköse, Devrim; Ülkü, Semra; Can, ÖzgeIon exchange is considered to be one of the most cost effective methods if low cost ion exchangers such as natural zeolites are used in waste water treatment. In this study, a zeolitic tuff rich in clinoptilolite from Gördes Manisa Turkey was examined to evaluate its ion exchange performance for the removal of copper, nickel and cobalt ions from metal (II) nitrate solutions at various concentrations by performing both batch and packed column experiments. A clinoptilolite tuff with purity around 60% was used in ion exchange experiments. Copper, nickel and cobalt exchange capacities of the tuff were determined as 8.3mg (0.26meq) Cu2+/g, 6.6mg (0.23meq) Ni2+/g and 4.5mg (0.15meq) Co2+/g, respectively. The equilibrium behavior of the system was best described by classical Langmuir model. The experimental breakthrough curves from the column experiments were fitted to solid diffusion control model. The study showed that efficient metal ion removal can be done by using the local clinoptilolite rich tuff. © 2010 Elsevier B.V.Article Citation - WoS: 10Citation - Scopus: 10Clinoptilolite-Rich Mineral as a Novel Carrier for the Active Constituents Present in Ginkgo Biloba Leaf Extract(Elsevier Ltd., 2008) Göktaş, Selda; Ülkü, Semra; Bayraktar, OğuzThe possible use of clinoptilolite-rich mineral as a novel carrier for the active constituents present in Ginkgo biloba leaf extract solutions was investigated. The flavonoid aglycone constituents were found to be selectively adsorbed on the clinoptilolite surface. The antioxidant activity determinations of the extract solutions were performed by the Trolox Equivalent Antioxidant Capacity (TEAC) assay. The antioxidant activity measurements performed for the Ginkgo leaf extract solutions showed decreasing antioxidant activities due to adsorption. The decrease in antioxidant activity was attributed to the adsorption of phenolic constituents on the clinoptilolite surface.Article Citation - WoS: 29Citation - Scopus: 31Cure Kinetics of Epoxy Resin-Natural Zeolite Composites(Springer Verlag, 2008) Cansever Erdoğan, Beyhan; Seyhan, Abdullah Tuğrul; Ocak, Yılmaz; Tanoğlu, Metin; Balköse, Devrim; Ülkü, SemraThe cure kinetics of epoxy resin and epoxy resin containing 10 mass% of natural zeolite were investigated using differential scanning calorimetry (DSC). The conformity of the cure kinetic data of epoxy and epoxy-zeolite system was checked with the auto-catalytic cure rate model. The results indicated that the hydroxyl group on the zeolite surface played a significant role in the autocatalytic reaction mechanism. This group was able to form a new transition state between anhydride hardener and epoxide group. The natural zeolite particles acted as catalyst for the epoxy system by promoting its curing rate.Article Citation - WoS: 12Citation - Scopus: 17Diffusion Mechanism of Water Vapour in a Zeolitic Tuff Rich in Clinoptilolite(Springer Verlag, 2008) Çakıcıoğlu Özkan, Seher Fehime; Ülkü, SemraThe adsorption kinetics of H2O in a clinoptilolite rich zeolitic tuff was experimentally investigated at 18°C. In the identification of the diffusion mechanism the isothermal adsorption model equation was used. It was found out that the intraparticle mass transfer becomes more dominant over the heat transfer with increase in particle size and the adsorptive dose pressure. Although initially intraparticle mass transfer was the controlling resistance later external heat transfer also contributes to the transfer mechanism.Article Citation - WoS: 19Citation - Scopus: 21Microwave Effect on Ion-Exchange and Structure of Clinoptilolite(Springer Verlag, 2007) Akdeniz, Yelda; Ülkü, SemraThe effect of microwave irradiation on the ion exchange degree and structure of clinoptilolite mineral has been examined in comparison with the conventional heat treatment in waterbath. Clinoptilolite-rich mineral from the Western Anatolia, Bigadiç region was used for the experimental study. The mineral was mainly clinoptilolite (80-85%) and additionally, quartz (5-10%), and analcime+mordenite (<5%) were found as co-existing minerals. The mineral was stable towards dehydration and maintains its original structure up to 800°C. The BET and Langmuir surface areas of the sample were found to be 22 and 17m2/g for N2 adsorption and 28 and 22m2/g for Ar adsorption, respectively. For the exchange experiments, clinoptilolite rich mineral was treated with 1N NaCl salt solution both in a microwave unit and waterbath for 10min, 1h and 2h at 80°C. The waterbath treatment with the same conditions was continued for two additional weeks. The chemical composition of the parent and Na-exchanged forms of the clinoptilolite rich minerals were analyzed by using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Microwave treatment was found to be more rapid and effective for ion exchange compared to conventional waterbath treatment. Additionally, the XRD results reveal that microwave irradiation has zero effect on the structure of the clinoptilolite rich mineral.Article Citation - WoS: 112Citation - Scopus: 130The Effect of Hcl Treatment on Water Vapor Adsorption Characteristics of Clinoptilolite Rich Natural Zeolite(Elsevier Ltd., 2005) Çakıcıoğlu Özkan, Fehime; Ülkü, SemraIn this study, water vapor adsorption properties of the clinoptilolite rich zeolite tuff, from Bigadic (Turkey), and its modified forms were examined. The modified forms were obtained by treating the tuff with HCl solutions (0.032, 0.16, 0.32, 1.6 or 5 M) at 25,40,75 and 100°C for 3 h. Infrared spectroscppy and water vapor adsorption were used for the characterization of the zeolites. Langmuir, BET and Dubinin-Raduschevich methods were applied in the analysis of water vapor adsorption data. Applications of Dubinin Raduschevich equation to the water adsorption data displayed that the super-micropore volume was not very sensitive to acid treatment. It was found out that the Langmuir surface area and ultra-micropore volume depend on the degree of the removal of aluminum from the structure.Article Citation - WoS: 249Citation - Scopus: 268Silver, Zinc, and Copper Exchange in a Na-Clinoptilolite and Resulting Effect on Antibacterial Activity(Elsevier Ltd., 2004) Top, Ayben; Ülkü, SemraAg+-Na+, Zn2+-Na+, and Cu2+-Na+ equilibria for clinoptilolite-rich mineral from Gördes (Western Anatolia) were investigated at 25 °C and 0.1 N total solution normality. While silver exchange was favorable over the whole concentration range, zinc and copper were partially exchanged and preferred only at low concentrations. The standard free energies of exchanges for Ag+-Na+, Zn2+-Na+, and Cu2+-Na+ pairs were found as -6.0, 2.03, and 3.09 kJ/equiv., respectively. From these values, selectivity sequence was determined as Ag+>Na+ >Zn2+>Cu2+. Antibacterial activities of the exchanged samples were measured as a function of exchange level against Pseudomonas aeruginosa and Escherichia coli. Considering the selectivity sequence of the clinoptilolite and antibacterial activity results, Ag-clinoptilolite seemed to be promising antibacterial material.