Chemistry / Kimya
Permanent URI for this collectionhttps://hdl.handle.net/11147/4072
Browse
10 results
Search Results
Article Citation - WoS: 16Citation - Scopus: 19Designing of Spherical Chitosan Nano-Shells With Micellar Cores for Solvation and Safeguarded Delivery of Strongly Lipophilic Drugs(Elsevier Ltd., 2017) Cihan, Esra; Polat, Mehmet; Polat, HürriyetChitosan is a very effective biopolymer for drug delivery purposes due to its biocompatibility, positive charge and exceptionally pH sensitive degradability behavior in an aqueous medium. Nevertheless, its inability for dissolving lipophilic drug active material and the difficulties in controlling the size and shape of the synthesized particles in nanometer range are critical drawbacks in its effective use. In this study, a synthesis procedure which addresses both issues simultaneously is presented. The procedure is based on initial dissolution of lipophilic drug molecules within the hydrophobic cores of the micelles of a bio-compatible block-copolymer by ionic gelation and subsequent formation of a chitosan shell by polymerization around the micellar structures. Well-formed, hollow and perfectly spherical chitosan particles (nano-shells) in the 30–300 nm size range could be successfully manufactured. Characterization by STEM, TEM, AFM, FTIR and DLS, DLS-LDV techniques showed clearly that the drug was successfully incorporated into the chitosan structure. It was demonstrated that the particles enveloped the micelle(s) of a Pluronic copolymer (P-123) whose hydrophobic cores contained a strongly hydrophobic drug Probucol. The chitosan nano-shells are expected to act as an agent protecting the integrity of the drug-loaded micelles in the body fluid while providing a pH sensitive release medium. The drug uptake by the chitosan particles was very high. A very sharp increase in the amount of the drug released with a slight change in the acidity of the medium was an indication of the potential of the manufactured chitosan nano-shells as pH sensitive, target specific delivery vehicles for drug release.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, HürriyetRemoval 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: 23Citation - Scopus: 24Analytical Solution of Poisson-Boltzmann Equation for Interacting Plates of Arbitrary Potentials and Same Sign(Elsevier Ltd., 2010) Polat, Mehmet; Polat, HürriyetEfficient 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, HürriyetFly 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; Keleşoğlu, Serkan; Polat, Mehmet; Aksoy, GökhanThe 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; Molva, Murat; Polat, MehmetA 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, Mehmet; Çoşkun, G.Surface 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: 123Citation - Scopus: 131A New Methodology for Removal of Boron From Water by Coal and Fly Ash(Elsevier Ltd., 2004) Polat, Hürriyet; Vengosh, Avner; Pankratov, Irena; Polat, MehmetHigh 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: 198Citation - Scopus: 210Physical and Chemical Interactions in Coal Flotation(Elsevier Ltd., 2003) Polat, Mehmet; Polat, Hürriyet; Chander, SubhashCoal flotation is a complex process involving several phases (particles, oil droplets and air bubbles). These phases simultaneously interact with each other and with other species such as the molecules of a promoting reagent and dissolved ions in water. The physical and chemical interactions determine the outcome of the flotation process. Physical and chemical interactions between fine coal particles could lead to aggregation, especially for high rank coals. Non-selective particle aggregation could be said to be the main reason for the selectivity problems in coal flotation. It should be addressed by physical (conditioning) or chemical (promoters) pretreatment before or during flotation. Although the interactions between the oil droplets and coal particles are actually favored, stabilization of the oil droplets by small amounts of fine hydrophobic particles may lead to a decrease in selectivity and an increase in oil consumption. These problems could be remedied by use of promoters that modify the coal surface for suitable particle-particle, droplet-particle and particle-bubble contact while emulsifying the oil droplets. The role of promoters may be different for different types of coals, however. They could be employed as modifiers to increase the hydrophobicity of low rank coals whereas their main role might be emulsification and aggregation control for high rank coals. In this paper, a detailed description of the various phases in coal flotation, their physical and chemical interactions with each other in the flotation pulp, the major parameters that affect these interactions and how these interactions, in turn, influence the flotation process are discussed.Article Citation - WoS: 20Citation - Scopus: 23Electrostatic Charge on Spray Droplets of Aqueous Surfactant Solutions(Elsevier Ltd., 2000) Polat, Mehmet; Polat, Hürriyet; Chander, SubhashElectrostatic charges on individual spray droplets were measured using a refined form of the Millikan oil drop method. The measurement system consisted of three main sections; a droplet generation cell, a settling column and a charge measurement chamber. The trajectories required for calculation of charge were determined using a high-speed motion analyzer coupled to a long-focal-length microscope. Charges on droplets were manipulated by the addition of surface-active agents into the spray solution. Droplet charge was a function of the type and concentration of the surfactant added. For ionic surfactants, it showed a maximum at low surfactant concentrations, decreased with further surfactant addition and was constant after the CMC. The charge on cationic surfactants was always more than that observed with the anionic surfactants. Nonionic surfactants displayed a steady increase in droplet charge with increasing concentration. The charges were lower compared to the ionic surfactants. (C) 2000 Elsevier Science Ltd. Electrostatic charges on individual spray droplets were measured using a refined form of the Millikan oil drop method. The measurement system consisted of three main sections; a droplet generation cell, a settling column and a charge measurement chamber. The trajectories required for calculation of charge were determined using a high-speed motion analyzer coupled to a long-focal-length microscope. Charges on droplets were manipulated by the addition of surface-active agents into the spray solution. Droplet charge was a function of the type and concentration of the surfactant added. For ionic surfactants, it showed a maximum at low surfactant concentrations, decreased with further surfactant addition and was constant after the CMC. The charge on cationic surfactants was always more than that observed with the anionic surfactants. Nonionic surfactants displayed a steady increase in droplet charge with increasing concentration. The charges were lower compared to the ionic surfactants.