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: 13Citation - Scopus: 15Ancillary Effects of Surfactants on Filtration of Low Molecular Weight Contaminants Through Cellulose Nitrate Membrane Filters(Elsevier Ltd., 2016) Olcay, Aybike Nil; Polat, Mehmet; Polat, Hürriyet; Polat, Mehmet; 04.01. Department of Chemistry; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyRemoval of contaminants with low molecular weight (<800 Dalton) requires the use of advanced separation techniques such as ultrafiltration (UF) or micellar enhanced ultrafiltration (MEUF). However, surface active agents invariably co-exist in waste waters along with these contaminants or they may be added intentionally as part of the separation process as in the case of MEUF. Though it is quite likely that both the filter medium and the contaminants would interact with the surfactant molecules or their micelles, there is not sufficient emphasis in the literature on the concomitant aspects of such interactions.The ancillary effects created by anionic (sodium dodecyl sulfate, SDS), cationic (hexadecyltrimethyl ammonium bromide, CTAB) and non-ionic (ethoxylated octylphenol, TX-100) surfactants on the mechanism and efficiency of the filtration process were investigated in this study. Methylene blue (MB) and cellulose nitrate membrane (CNM) filters were employed as model retentate and the separation medium. A combination of surface tension, contact angle and charge measurements demonstrated that the addition of surfactants had a remarkable effect on the filtration outcome. The effect depended on both the type and concentration of the surfactant and was manifested mainly through the creation of MB-surfactant entities which acted differently than the MB alone; but more importantly, through the interactions of the surfactant molecules/micelles and the MB-surfactant pairs with the separation membrane.Article Citation - WoS: 140Citation - Scopus: 171Physicochemical Characterization of Chitosan Extracted From Metapenaeus Stebbingi Shells(Elsevier Ltd., 2011) Küçükgülmez, Aygül; Çelik, Mehmet; Polat, Hürriyet; Şen, Didem; Polat, Hürriyet; Kadak, Ali Eslem; 04.01. Department of Chemistry; 04. Faculty of Science; 01. Izmir Institute of TechnologyIn this study, chitosan was extracted from Metapenaeus stebbingi shells. In order to determine physicochemical characteristics of the extracted chitosan, the yield, moisture and ash contents, degree of deacetylation, molecular weight, water and fat binding capacities, apparent viscosity and colour properties were measured using a variety of techniques including Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction. In addition, the physicochemical characteristics of the chitosan extracted from M. stebbingi shells were compared to commercial chitosan. The degree of deacetylation was calculated by the titration method and elemental analysis. The molecular weight was determined by viscosimetric methods. The results of the study indicate that shrimp shells are a rich source of chitosan as 17.48% of the shell's dry weight is consisted of this material. Extracted chitosan exhibited a lower molecular weight, higher degree of deacetylation, higher viscosity and higher water and fat binding capacities compared to the commercial chitosan.Article Citation - WoS: 23Citation - Scopus: 24Analytical Solution of Poisson-Boltzmann Equation for Interacting Plates of Arbitrary Potentials and Same Sign(Elsevier Ltd., 2010) Polat, Mehmet; Polat, Hürriyet; Polat, Mehmet; Polat, Hürriyet; 04.01. Department of Chemistry; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyEfficient calculation of electrostatic interactions in colloidal systems is becoming more important with the advent of such probing techniques as atomic force microscopy. Such practice requires solving the nonlinear Poisson-Boltzmann equation (PBE). Unfortunately, explicit analytical solutions are available only for the weakly charged surfaces. Analysis of arbitrarily charged surfaces is possible only through cumbersome numerical computations. A compact analytical solution of the one-dimensional PBE is presented for two plates interacting in symmetrical electrolytes. The plates can have arbitrary surface potentials at infinite separation as long they have the same sign. Such a condition covers a majority of the colloidal systems encountered. The solution leads to a simple relationship which permits determination of surface potentials, surface charge densities, and electrostatic pressures as a function of plate separation H for different charging scenarios. An analytical expression is also presented for the potential profile between the plates for a given separation. Comparison of these potential profiles with those obtained by numerical analysis shows the validity of the proposed solution. © 2009 Elsevier Inc. All rights reserved.Article Citation - WoS: 29Citation - Scopus: 38Encapsulating Fly Ash and Acidic Process Waste Water in Brick Structure(Elsevier Ltd., 2010) Köseoğlu, K.; Polat, Mehmet; Polat, Hürriyet; Polat, Mehmet; 04.01. Department of Chemistry; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyFly ash contains metals such as cadmium, iron, lead, aluminum and zinc in its structure in appreciable amounts. These metals can leach out into surface and ground waters if fly ash is not properly disposed of. A similar problem also exists for acidic process waste waters discharged by numerous industries. The purpose of this study was to utilize such wastes as additives in the production of construction quality bricks for the purpose of waste elimination. The bricks produced were subjected to flexural strength and water retention capacity tests along with heavy metal leaching experiments in order to determine the applicability of the procedure and the best possible recipes. This paper summarizes the results obtained in these tests along with the possible mechanisms involved in stabilizing the two wastes in the brick structure. © 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 10Citation - Scopus: 10Determination of the Particle Interactions, Rheology and the Surface Roughness Relationship for Dental Restorative Ceramics(Elsevier Ltd., 2009) Kes, Mürşide; Polat, Hürriyet; Polat, Hürriyet; Polat, Mehmet; Aksoy, Gökhan; Polat, Mehmet; 04.01. Department of Chemistry; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe effect of inter-particle interactions on the slurry properties and the final surface roughness of the dental ceramic restoratives was investigated. A commercial dental ceramic powder, IPS Empress 2 veneer, was used as the raw material. The magnitudes of the particle-particle interactions were computed by the DLVO theory for the ceramic slurries of different electrolyte solutions (0.1 M, 0.25 M, 0.5 M, 0.75 M, 1 M NaCl and CaCl2). As expected, the energies of particle-particle interactions were influenced significantly by the presence of electrolytes. These computations demonstrated that addition of electrolytes leads to a progressive depression of the repulsive double layer forces. The absence of these forces should inevitably lead to agglomeration caused by the ever-present van der Waals forces. The rheological measurements carried out using the slurries with same solution properties supported the findings of the DLVO computations. It was found that dental ceramic slurries showed a Newtonian behavior in the absence of electrolytes, which is indicative of little or no agglomeration in the slurry. On the other hand, the same slurries displayed a non-Newtonian, shear thinning behavior in the presence of electrolytes which can be attributed to agglomeration or gelation. Roughness of the ceramic surfaces produced from these slurries was studied by SEM analysis and profilometer measurements. Contact angle studies were also carried out on the same surfaces. It was observed that the surface became rougher initially with electrolyte addition to a maximum, most probably due to formation of isolated agglomerates due to a reduction of the repulsive double layer forces. After reaching a maximum, surface roughness decreased to a much lower value with further increase in electrolyte concentration. This was most probably caused by the formation of a relatively homogeneous, gel-like structure within the extensively agglomerated slurry due to a complete collapse of the double layer.Article Citation - WoS: 98Citation - Scopus: 108Capacity and Mechanism of Phenol Adsorption on Lignite(Elsevier Ltd., 2006) Polat, Hürriyet; Polat, Mehmet; Molva, Murat; Polat, Hürriyet; Polat, Mehmet; 04.01. Department of Chemistry; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyA raw lignitic coal from Soma, Turkey was investigated to determine its potential as an adsorbent for phenol removal from wastewaters. Kinetic batch tests demonstrated that phenol could be completely removed from solution given sufficient solids loading and reaction time. The adsorption capacity of 10 mg/g obtained with the lignite is low compared to those achievable with activated carbons (around 300 mg/g). However, when normalized for the surface area, the adsorption capacity was much larger for the lignite (1.3 mg/m2) than that generally observed with activated carbons (0.05-0.3 mg/m2). Hydrogen-bonding of the phenolic -OH with the oxygen sites on the lignite surface is the most likely mechanism for adsorption. Though water molecules also have affinity for the same oxygen sites, lateral benzene ring interactions make phenol adsorption energetically more favorable. Since phenol molecules adsorbed in this fashion would project their benzene rings into solution, formation of a second layer through the action of the dispersive π-π interactions between the benzene rings is very likely. Residual water quality with respect to major elements and heavy metals was within acceptable limits defined by the ASTM standards. Dissolution of organic matter from the lignite was also observed to be negligible.Article Citation - WoS: 57Citation - Scopus: 62Effect of Various Treatment and Glazing (coating) Techniques on the Roughness and Wettability of Ceramic Dental Restorative Surfaces(Elsevier Ltd., 2006) Aksoy, Gökhan; Polat, Hürriyet; Polat, Hürriyet; Polat, Mehmet; Polat, Mehmet; Çoşkun, G.; 04.01. Department of Chemistry; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologySurface treatment procedures such as grinding and polishing are needed to provide the ceramic dental restorative materials with proper fitting and occlusion. The treated surfaces are customarily glazed to improve the strength and smoothness. Though smoothness and wetting of the dental surfaces are important to minimize bacterial plaque retention, influence of the surface treatment and glazing procedures on the final surface roughness and its correlation to wettability are overlooked. In this work, effect of various treatment (diamond fraising, stoning, sanding and aluminum oxide and rubber polishing) and glazing (auto and overglazing) techniques on the final roughness and the resulting wettability of dental ceramic surfaces were investigated using scanning electron microscopy (SEM) observations and atomic force microscopy (AFM) scans, 75 scans per sample. The surfaces were characterized and assigned an average roughness measure, Ra. The wettability of the same surfaces was evaluated using micro-contact angle measurements (25 micro-bubbles placed on a grid on each surface) to correlate the final surface roughness and wettability. The results show that overglazing prevails over surface irregularities from different treatment procedures and provides homegeneously smooth surfaces with mean Ra < 10 nm. It also produces uniformly wetted surfaces with low contact angles around 20°. The autoglazed surfaces are less smooth (mean Ra around 50 nm) and displays sporadic topographic irregularities. They display larger and less uniform contact angles ranging between 35° and 50°. The results suggest that overglazing should be preferred after surface treatment to obtain a smooth and well-wetted dental ceramic surface.Article Citation - WoS: 259Citation - Scopus: 284Heavy Metal Removal From Waste Waters by Ion Flotation(Elsevier Ltd., 2007) Polat, Hürriyet; Erdoğan, D.; Polat, Hürriyet; 04.01. Department of Chemistry; 04. Faculty of Science; 01. Izmir Institute of TechnologyFlotation studies were carried out to investigate the removal of heavy metals such as copper (II), zinc (II), chromium (III) and silver (I) from waste waters. Various parameters such as pH, collector and frother concentrations and airflow rate were tested to determine the optimum flotation conditions. Sodium dodecyl sulfate and hexadecyltrimethyl ammonium bromide were used as collectors. Ethanol and methyl isobutyl carbinol (MIBC) were used as frothers. Metal removal reached about 74% under optimum conditions at low pH. At basic pH it became as high as 90%, probably due to the contribution from the flotation of metal precipitates.Article Citation - WoS: 123Citation - Scopus: 131A New Methodology for Removal of Boron From Water by Coal and Fly Ash(Elsevier Ltd., 2004) Polat, Hürriyet; Vengosh, Avner; Polat, Mehmet; Polat, Hürriyet; 04.01. Department of Chemistry; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyHigh levels of boron concentrations in water present a serious problem for domestic and agriculture utilizations. The recent EU drinking water directive defines an upper limit of 1 mgB/I. In addition, most crops are sensitive to boron levels >0.75 mg/1 in irrigation water. The boron problem is magnified by the partial (∼60%) removal of boron in reverse osmosis (RO) desalination due to the poor ionization of boric acid and the accumulation of boron in domestic sewage effluents. Moreover, high levels of boron are found in regional groundwater in some Mediterranean countries, which requires special treatment in order to meet the EU drinking water regulations. Previous attempts to remove boron employed boron-specific ion-exchange resin and several cycles of RO desalination under high pH conditions. Here, we present an alternative methodology for boron removal by using coal and fly ash as adsorbents. We conducted various column and batch experiments that explored the efficiency of boron removal from seawater and desalinated seawater using several types of coal and fly ash materials under controlled conditions (pH, liquid/solid ratio, time of reaction, pre-treatment, regeneration). We examined the effect of these factors on the boron removal capacity and the overall chemical composition of the residual seawater. The results show that the selected coal and fly ash materials are very effective in removing boron such that the rejection ratio of boron can reach 95% of the initial boron content under certain optimal conditions (e.g., pH = 9, L/S = 1/10, reaction time > 6 h). Our experiments demonstrated that use of glycerin enables regeneration of boron uptake into coal, but the boron uptake capacity of fly ash reduces after several cycles of treatment-reaction. The boron removal is associated with Mg depletion and Ca enrichment in the residual seawater and conversely with relative Mg enrichment and Ca depletion in the residual fly ash. We propose that the reaction of Ca-rich fly ash with Mg-rich seawater causes co-precipitation of magnesium hydroxide in which boron is co-precipitated. The new methodology might provide an alternative technique for boron removal in areas where coal and fly ash are abundant.Article Citation - WoS: 5Citation - Scopus: 7Alumina/Water Suspensions in the Presence of Peo-Ppo Triblock Copolymers(Elsevier Ltd., 2004) Şakar Deliormanlı, Aylin; Polat, Hürriyet; Polat, Hürriyet; Çiftçioğlu, Muhsin; Şakar Deliormanlı, Aylin Müyesser; 03.02. Department of Chemical Engineering; 04.01. Department of Chemistry; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe aim of this study was to investigate the stability and dispersion behaviour of aqueous alumina suspensions in the presence of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) type triblock copolymers. For this purpose alumina suspensions at various solids loadings were prepared using four different methods. These are: Method I: powder and water were stirred only; Method II: powder and water were stirred and ultrasonic treatment was applied; Method III: powder and water were stirred in the presence of block copolymers; Method IV: powder and water were stirred and ultrasonic treatment was applied in the presence of block copolymers. These suspensions were characterized by means of rheological measurements. Sedimentation and turbidity measurements were also conducted to support these results and to investigate the stability of these systems for longer times. Surface tension measurements were performed to investigate the adsorption behaviour of block copolymers onto alumina surface. It was found that the use of PEO-PPO-PEO type triblock copolymers improved the dispersion behaviour of aqueous alumina suspensions in the presence of ultrasonic treatment at low solids loadings. However their effect was not significant at high solids loadings and without ultrasonic treatment.