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Membrane potentials for linearly varying fixed charges

Genç, Ayten

Article | 2009 | Turkish Journal of Engineering and Environmental Sciences33 ( 1 ) , pp.73 - 81

The membrane potentials for asymmetric membranes where fixed charges varied linearly with position were evaluated from the numerical solutions of Nernst-Planck flux and Donnan potential equations. The evaluated membrane potentials were compared with the results obtained from the conventional TMS theory where the fixed charge concentration in the membrane was assumed to be uniform. In the comparison, the number of fixed charges was kept constant by defining an average for the fixed charge concentration. The numerical results showed that the membrane potential increased in magnitude when the distributions of fixed charges at the membr . . .ane-solution interfaces were unequal. In addition, the deviation from TMS theory increased more as the charge difference at the interfaces increased. © TÜBİTAK Daha fazlası Daha az

Effects of acceptor phase and donor phase properties on sodium ions transport from aqueous solutions using liquid membrane systems

Altın, Süreyya | Demircioğlu, Nuhi | Peker, İbrahim | Altın, Ahmet

Article | 2007 | Colloids and Surfaces A: Physicochemical and Engineering Aspects306 ( 1-3 SPEC. ISS. ) , pp.14 - 21

In this study, the effects of the acceptor phase and the donor phase properties on sodium ion transport were examined in bulk liquid membrane systems. In the experiments, toluene and a mixture of toluene-dichloromethane (90-10%, v/v) containing 1 × 10-3 M DB18C6 (dibenzo18crown6) was used as the membrane. In order to examine the effects of different the acceptor phases, firstly H2SO4, HCl, HNO3, CH3COOH and distilled water were used as the acceptor phases. Furthermore, the experiments were performed by using various acid concentrations such as 2, 0.2 and 0.02 M of acids, as the acceptor phase. In the second part of the study, the ef . . .fect of donor phase on sodium ion transport was examined. For this examination, Na2SO4, NaNO3, NaOH and NaCl were applied. In order to determine the effect of the donor phase concentration, the experimentation was performed using 1.08 × 10-2, 2.17 × 10-2, 3.26 × 10-2 and 4.34 × 10-2 M concentrations of Na+ in form of NaCl. Finally, nonsteady-state kinetics was applied on all data obtained from the experiments and reaction constants (k1, k2, and k3) and the values of the Rmax, tmax, k1/k2 were calculated. Consequently, it was determined that the type and the concentration of the acceptor phase and the donor phase solutions were significant for transport efficiency in liquid membrane systems. The most efficient transport was obtained by applying 2 M H2SO4 and 2.17 × 10-2 M Na+ in form of NaCl. Besides, It was observed that there was a significant effect of the anion attached to the cation on transport efficiency. © 2007 Elsevier B.V. All rights reserved Daha fazlası Daha az

Experimental studies on the effect of electrode configuration in electrofiltration

Genç, Ayten | Tosun, İbrahim

Article | 2002 | Separation Science and Technology37 ( 13 ) , pp.3053 - 3064

Results from the electrofiltration of anatase (TiO2) particles in a water suspension and using three different electrode configurations are presented. The three electrode configurations studied were spot, foil, and mesh. For the first two configurations, the electric field was perpendicular to the direction of flow while for the mesh configuration it was opposite to the direction of flow. The percent gain volume filtrate and power consumption were measured for each electrode configuration. For a given percent gain volume filtrate, it was observed that the foil electrode configuration consumes the least power.

An experimental study of CO2 separation using a silica based composite membrane

Yıldırım, Yılmaz | Hughes, Ronald

Article | 2003 | Process Safety and Environmental Protection: Transactions of the Institution of Chemical Engineers, Part B81 ( 4 ) , pp.257 - 261

In this investigation, the preparation and gas selectivity characteristics of an 'ultrafine' composite ceramic membrane are reported. A dip-coating technique was used to prepare a thin selective membrane on a commercially available ceramic macroporous filter (SCT, France). The permeabilities of H2, N2 and CO2 were measured at temperatures of 25-470°C and average pressures of 1-2 bar. The separation of CO2/N2 binary mixtures was also performed. The separation factors for CO2 were found to be higher than that of the Knudsen separation mechanism at room and high temperature. The potential applications of these membranes to CO2 separati . . .on at these temperatures are discussed on the basis of measured selectivity values Daha fazlası Daha az

Development of statistical models for trihalomethane (THM) removal in drinking water sources using carbon nanotubes (CNTs)

Özdemir, Kadir | Güngör, Ömer

Article | 2018 | Water SA44 ( 4 ) , pp.680 - 690

This research developed models using the multiple linear regression technique for prediction of trihalomethane (THM) removal from chlorinated drinking water sources through a combination of a coagulation process with carbon nanotubes (CNTs). Terkos Lake water (TLW), Buyukçekmece Lake water (BLW) and Ulutan Lake water (ULW) samples were coagulated by a conventional coagulant (alum) and increasing doses of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) with the addition of alum. Also, chlorination experiments were conducted with water reservoirs from TLW, BLW and ULW, with different water quality re . . .garding bromide concentration and organic matter content. The factors studied affecting THM removal were contact time, chlorine dose, coagulation process, total organic carbon (TOC), and specific ultraviolet absorbance (SUVA). Statistical analysis of the results focused on the development of multiple regression models, as Models 1 and 2, for predicting total trihalomethane (TTHM) based on the use of contact time, SWCNTs and MWCNTs doses, chlorine dose and TOC. When the two models were compared, Model 1 proved best suited to describe THM removal for the three water sources. The developed models provided satisfactory estimations of THM removal; the model regression coefficients for Models 1 and 2 were 0.88 and 0.77, respectively. Furthermore, the root-mean-square error (RMSE) values of 0.083 and 0.126 confirm the reliability of the two models. The results show that THM removal can be simply predicted by using the multiple linear regression technique in chlorinated drinking water sources. © 2018, South African Water Research Commission. All rights reserved Daha fazlası Daha az

Water quality monitoring with emphasis on estimation of point and diffuse pollution sources

Albek, Erdem Ahmet | Göncü, Serdar | Uygun, Burcu Şimşek | Albek, Mine | Avdan, Zehra Yiğit | Güngör, Ömer

Article | 2019 | Global Nest Journal21 ( 2 ) , pp.163 - 171

Population growth, urbanization and anthropogenic activities are becoming a serious problem for water resources in Turkey, which necessitates their monitoring and maintenance of water quality. In this study, water quality was implemented in the Porsuk Stream in Inner Anatolia, Turkey. Water samples were collected at monthly intervals between the period of 2008-2010 at four selected stations. Twenty one water quality parameters were measured which are water temperature (T), pH, dissolved oxygen (DO), electrical conductivity (EC), salinity, turbidity, chloride, suspended solids, dissolved solids, organic nitrogen (Org-N), ammonium nit . . .rogen (NH3-N), nitrite nitrogen (NO2-N), nitrate nitrogen (NO3-N), total organic carbon, biological oxygen demand (BOD), chemical oxygen demand (COD), total coliform, alkalinity, orthophosphate phosphorus (PO4 3--P), total phosphorus and chlorophyll-a. The monitoring was conducted to see how the water quality changed along the stream in response to various anthropogenic activities. Besides, a paired t-test was utilized to determine the concentration differences at stations above and below the single most important point source of pollutants (Eskisehir city). Moreover, a regression model was used to establish relations between water quality parameters and flow and to estimate nonpoint source loadings. © 2019 Global NEST Printed in Greece Daha fazlası Daha az

Wild-growing Rosa heckeliana Tratt.: phenolic constituents with cytotoxic and antioxidative properties

Çoruh, Nursen | Özdoğan, Nizamettin

Article | 2017 | Turkish Journal of Biology41 ( 1 ) , pp.195 - 212

Rosa heckeliana, as one of the wild-growing species of the family Rosacea, has a wide use in the folk medicine; however, scientifically there is very little known about it. Our objective was to examine the antioxidative and antiproliferative properties of Rosa heckeliana root extract and its phenolics. The phenolic constituents, namely catechin, caffeic acid, and ellagic acid, were obtained by the methods of extraction, fractionation, and purification through column chromatography. The DPPH and ABTS radical scavenging assays and total flavonoid content analysis were employed as the current antioxidant methods over the crude extract . . .and fractionated parts. Among the extracts/fractions, the ethyl acetate fraction exhibited the highest amount of flavonoid content (4.58 ± 0.018 µg CE/ mg of extract). The ethyl acetate fraction also displayed high antioxidative properties for DPPH (EC50 value: 2.78 ± 0.01 µg/mL) and ABTS scavenging capacities (586 ± 6.64 µM trolox as TEAC value). Additionally, the antiproliferative properties of the crude extract and the ethyl acetate fraction and its isolated constituents were evaluated for two breast cancer cell lines (MCF-7 and MDA-MB-231) using the XTT method. Acetate fraction over the cells of MCF-7 and MDA-MB-231 resulted in ED50 values of 61.18 ± 0.99 µg/mL and 62.54 ± 2.01 µg/mL, respectively. The isolated phenolic constituents were twice as effective as the ethyl acetate fraction on both MCF-7 and MDA-MB-231 cells. Rosa heckeliana, as one of the wild-growing species of the family Rosacea, has a wide use in the folk medicine; however, scientifically there is very little known about it. Our objective was to examine the antioxidative and antiproliferative properties of Rosa heckeliana root extract and its phenolics. The phenolic constituents, namely catechin, caffeic acid, and ellagic acid, were obtained by the methods of extraction, fractionation, and purification through column chromatography. The DPPH and ABTS radical scavenging assays and total flavonoid content analysis were employed as the current antioxidant methods over the crude extract and fractionated parts. Among the extracts/fractions, the ethyl acetate fraction exhibited the highest amount of flavonoid content (4.58 ± 0.018 µg CE/ mg of extract). The ethyl acetate fraction also displayed high antioxidative properties for DPPH (EC50 value: 2.78 ± 0.01 µg/mL) and ABTS scavenging capacities (586 ± 6.64 µM trolox as TEAC value). Additionally, the antiproliferative properties of the crude extract and the ethyl acetate fraction and its isolated constituents were evaluated for two breast cancer cell lines (MCF-7 and MDA-MB-231) using the XTT method. Acetate fraction over the cells of MCF-7 and MDA-MB-231 resulted in ED50 values of 61.18 ± 0.99 µg/mL and 62.54 ± 2.01 µg/mL, respectively. The isolated phenolic constituents were twice as effective as the ethyl acetate fraction on both MCF-7 and MDA-MB-231 cells Daha fazlası Daha az

Novel Enzymatic Rhodium Modified Poly(styrene-g-oleic amide) Film Electrode for Hydrogen Peroxide Detection

Kılıç, Muhammet Samet | Korkut, Şeyda | Hazer, Baki

Article | 2017 | Electroanalysis29 ( 10 ) , pp.2377 - 2384

Newly synthesized poly(styrene-g-oleic amide) was coated onto a rhodium nanoparticle modified glassy carbon (GC) surface for the fabrication of horseradish peroxidase based biosensor used for hydrogen peroxide detection. The rhodium modifed electrode presented ten times higher signal than unmodified electrode even at low elecrtroactive enzyme quantity by enhancing the electron transfer rate at the applied potential of -0.65 V. The biosensor designed by under the optimized rhodium electrodeposition time exhibited a fast response less than 5 s, an excellent operational stability with a relative standard deviation of 0.6 % (n=6), an ac . . .curacy of 96 % and a large linear range between 50 µM and 120 mM for hydrogen peroxide. Detection limit and the sensitivity parameters were calculated to be 44 µM and 57 µA mM-1 cm-2, respectively by preserving its entire initial response up to the 15 days, while only 20 % of its initial response was lost at the end of one month. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei Daha fazlası Daha az

Separation of Cd(II) from aqueous solutions by a new consecutive process consisting of supported liquid membrane and electrodialysis

Altın, Süreyya | Altın, Ahmet

Article | 2019 | Journal of Electrochemical Science and Technology10 ( 1 ) , pp.14 - 21

Supported liquid membrane process usually is used for recovering or enrichment of valuable metals in the industrial wastewater. But, even if the metals in the wastewater was separated with high chemical selectivity, it cannot be enough concentrated since separation performance of supported liquid membrane (SLM) process is limited by concentration gradient between feed solution and stripping solution. If metal concentration in the stripping solution to be enough low, transport of metal through membrane can be accomplishment constantly. Therefore, Electrodialysis (ED) has been placed after SLM process and the stripping solution of SLM . . . was used as the feed solution for the ED process. Transport of ions in the solutions is successfully performed by ED process. Thus, the metal concentration in the stripping solution does not rise as to stop ion transport. Besides, valuable metals easily are concentrated by ED process for re-use. In this study, effects of operation parameters like initial Cd(II) concentration, HCl concentration in the feed solution of SLM and applied voltage are investigated on separation efficiency, flux and permeability of the both processes. As the feed solution concentration increased, all performance values has increased. When initial concentration of 100 mg/L is used, separation performances (SP) are 55% and 70%, for SLM and consecutive process, respectively. The best HCl concentration in the feed solution of SLM has determined as 2 M, in this conditions SP are 64% and 72%, for SLM and consecutive process, respectively. With increased of applied voltage on ED process, SP of the consecutive process has been raised from 72% to 83%. According to the obtained experimental data, consecutive process has better separation performance than SLM. When the separation performances of both processes were compared for the same operating conditions, it was determined higher the separation efficiency, permeability and flux values of the consecutive process, 8%, 9% and %10.6, respectively. Consequently, the use of the consecutive process increases the performance efficiency of both processes. The consecutive process studied has quite a good chemical separation efficiency, and enrichment capability. Moreover, this process requires few water and energy. © 2019, Korean Electrochemical Society. All rights reserved Daha fazlası Daha az

Electroflotation of oily wastewater using stainless steel sponge electrodes

Genç, Ayten | Göç, Sercan

Article | 2018 | Water Science and Technology78 ( 7 ) , pp.1481 - 1488

In this study, emulsified oil removals have been studied electrochemically by using stainless steel sponge electrode beds. A first-order electroflotation model was developed and the model estimation were consistent with the experimental results. It was found out that the mean electroflotation rate constant was mainly a function of the voltage applied to the electrode beds. In addition, the properties of intermediate materials (electrical conductivity) placed between the anode and cathode electrode beds strongly affected removal yields. For the initial concentration of 57,150 mg/L, the chemical oxygen demand (COD) removal was obtaine . . .d as 85% under the conditions of voltage gradient 15 V. The experiments were also performed by varying the electrode bed lengths. Even though higher oil yields were obtained at 27 cm bed length, similar oil yields were also obtained at 18 cm bed length, especially after 60 min, with less energy consumption. Therefore, the optimum electrode bed length was concluded to be 18 cm. © IWA Publishing 2018 Water Science & Technology Daha fazlası Daha az

Transport of silver ions through a flat-sheet supported liquid membrane

Altın, Süreyya | Yıldırım, Yılmaz | Altın, Ahmet

Article | 2010 | HYDROMETALLURGY103 ( 01.Apr ) , pp.144 - 149

Toxic metals from industrial wastewaters are an important environmental issue. The use of supported liquid membrane processes has gained momentum in recent years, as it allows the reuse of water and toxic metals. The aim of this study is to investigate the active transport of silver ion through a supported liquid membrane (micro-porous Fluoropore PTFE) of DC18C6 (Dicyclohexano18crown6) in toluene under various experimental conditions. For this purpose, the effects of various parameters including binary carriers, carrier concentration, feed phase concentration, the nature and concentration of stripping agents in the stripping phase a . . .nd flow rates of feed and stripping phases on transport efficiency were also investigated. The maximum transport efficiency was observed at the following conditions: flow rates of 50 mL/min in both phases, 0.05 M DC18C6 in toluene as carrier solution. 50 ppm Ag(+) dissolved in 0.015 M HNO(3) as feed solution and 0.08 M Na(2)S(2)O(3) as stripping solution Optimum operation time was determined as 240 min. Under these conditions, 94% of the silver ions were transported from the feed phase to the membrane phase. However, the transport rate from the membrane phase to the stripping phase remained at approximately 81%. (C) 2010 Elsevier B.V. All rights reserved Daha fazlası Daha az

Power improvement of enzymatic fuel cells used for sustainable energy generation

Korkut, Şeyda | Kılıç, Muhammet Samet

Article | 2016 | Environmental Progress and Sustainable Energy35 ( 3 ) , pp.859 - 866

Poly(3-thiopheneacetic acid-co-3-methylthiophene) conductive polymer was electrosynthesized with ferrocene and used for an enzymatic fuel cell including glucose oxidase and bilirubin oxidase enzymes. The system was operated in a single-compartment and membrane-less cell by using glucose as fuel. Detailed optimization ensured to achieve considerable power output to generate sustainable energy from municipal wastewater as a renewable fuel source. Maximum power density of 1 µW/cm2was generated at a cell voltage of +0.56 V in 100 mM, pH 7.4 phosphate buffer with the addition of 10 mM synthetic glucose. The working electrodes could harve . . .st glucose readily found in the municipal wastewater of Zonguldak City in Turkey by generating a power density of 4 µW/cm2for the municipal wastewater sample. In this way, the organic pollutants in wastewater could be evaluated by converting them into the electrical energy using an enzymatic fuel cell for the first time. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 859–866, 2016. © 2015 American Institute of Chemical Engineers Environ Pro Daha fazlası Daha az

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