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Öğe Adsorption kinetics of malachite green onto activated carbon prepared from Tuncbilek lignite(Elsevier, 2006) Önal, Y; Akmil-Basar, C; Eren, D; Sarici-Özdemir, Ç; Depci, TAdsorbent (T(3)K618) has been prepared from Tuncbilek lignite by chemical activation with KOH. Pore properties of the activated carbon such as BET surface area, pore volume, pore size distribution, and pore diameter were characterized by t-plot based on N-2 adsorption isotherm. The N-2 adsorption isotherm of malachite green on T(3)K618 is type I. The BET surface area of the adsorbent which was primarily contributed by micropores was determined 1000 m(2)/g. T(3)K618 was used to adsorb malachite green (MG) from an aqueous solution in a batch reactor. The effects of initial dye concentration, agitation time, initial pH and adsorption temperature have been studied. It was also found that the adsorption isotherm followed both Freundlich and Dubinin-Radushkevich models. However, the Freundlich gave a better fit to all adsorption isotherms than the Dubinin-Radushkevich. The kinetics of adsorption of MG has been tested using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. Results show that the adsorption of MG from aqueous solution onto micropores T(3)K618 proceeds according to the pseudo-second-order model. The intraparticle diffusion of MG molecules within the carbon particles was identified to be the rate-limiting step. The adsorption of the MG was endothermic (Delta H degrees = 6.55-62.37 kJ/mol) and was accompanied by an increase in entropy (Delta S degrees = 74-223 J/mol K) and a decrease in mean value of Gibbs energy (Delta G degrees = -6.48 to -10.32 kJ/mol) in the temperature range of 20-50 degrees C. (c) 2005 Elsevier B.V. All rights reserved.Öğe Adsorptions of high concentration malachite green by two activated carbons having different porous structures(Elsevier, 2005) Akmil-Basar, C; Önal, Y; Kiliçer, T; Eren, DThe adsorption of malachite green (MG) from aqueous solution by two different adsorbents (CZn5, PETNa8) were studied. Adsorbents were prepared from pine sawdust and polyethyleneterephatalate (PET) by chemical activation with ZnCl2 and NaOH, respectively. The adsorption was carried out in a batch system as a function of dye concentration, pH and contact time. Both adsorbents were found to be very effective in removing the dye at high concentration with adsorption percentage in the order of CZn5 > PETNa8. The pH of dye solution in the range of 6-10, was found favorable for the removal of malachite green by using the two adsorbents at high concentrations. Equilibrium times were 120 and 90 min for CZN5 and PETNa8, respectively. Kinetics of removal MG was studied using Lagergren equation and diffusion phenomena was analyzed using Weber and Morris intraparticle diffusion plots. It was also showed that the adsorption isotherm followed Langmuir model. (c) 2005 Elsevier B.V. All rights reserved.Öğe Characterization of TiO2 synthesized in alcohol by a sol-gel process: The effects of annealing temperature and acid catalyst(Tubitak Scientific & Technological Research Council Turkey, 2005) Sayilkan, F; Asiltürk, M; Sayilkan, H; Önal, Y; Akarsu, M; Arpaç, EThe effects of annealing temperature and hydrolysis catalyst on the crystalline form and crystallite size of TiO2 prepared by a sol-gel process were investigated. Three types of TiO2 were synthesized by hydrolysis of titanium(IV)-iso-propoxide with water in n-propanol without catalyst (Type-A) and with HCl as catalyst, where the H+/Ti4+ mol ratio was 0.54 for Type-B and 0.2 for Type-C. Hydrolysis products were thermally treated at 100, 200, 300, 400 and 500 degrees C for 1 h after drying at room temperature. Characterization of the particles was carried out using XRD, BET, TG/DTA and SEM analysis. The pore size distributions were computed by the DFT plus method. The results showed that the acid catalyst and catalyst/alkoxide ratio have a large effect on the formation of anatase TiO2. In particular, it was found that anatase phase TiO2 particles occur at 400 and 500 degrees C for Type-A TiO2, while they do so at nearly 100 degrees C for Type-B and Type-C TiO2. The crystallile size of Type-A, Type-B and Type-C increased from 17.96 to 19.24 nm, from 12.38 to 15.12 nm and from 10.60 to 12.20 nm, respectively, when the thermal treatment temperature was raised from 400 to 500 degrees C.Öğe Demineralisation of lignites by single and successive pretreatment(Elsevier Sci Ltd, 2003) Karaca, H; Önal, YIn this study, two Turkish lignites (Bolu-Mengen, Kutahya-Tuncbilek) were treated under atmospheric and reflux conditions with 10-30% NaOH, 10% HCl and 10% H2SO4 solutions, singly and/or successive treatments to determine the effects of this treatment on the mineral matter and acidic functional groups. Characterisation of the treated and untreated samples was by Fourier transform infrared spectroscopy. The process of successive pretreatment was found to be more effective than single steps in terms of demineralisation and removal of carboxylate structures. During NaOH treatment, the first of successive steps, salts soluble in acid but not in water were determined. In successive demineralisation steps with 30% NaOH and 10% HCl, a low level of 3.3% ash was obtained for the Tuncbilek lignite. In addition, during the pretreatment, most of the Ca and K were exchanged with Na. (C) 2003 Elsevier Science Ltd. All rights reserved.Öğe Influence of pretreatment on solvent-swelling and extraction of some Turkish lignites(Elsevier Sci Ltd, 2003) Önal, Y; Akol, SIn this study, three Turkish lignites (Beypazan (LGN-1), Golbasi (LGN-2) and Kangal (LGN-3)) have been pretreated with the solutions of 0.1N HCl, 10% HCl, HCl-HF or with air oxidation at 200 degreesC. Swelling ratios of original and pretreated lignites have been determined by using 11 different solvents. Original and pretreated samples have been subjected to preswollen by using THF at room temperature. Toluene Soxhlet extraction experiments of these and unswollen samples have been also carried out. The effect of solvent swelling ratio on the extraction yields of the original and pretreated lignites have been examined. The results showed that the swelling ratios were high in hydrogen bonding solvents but low in non-hydrogen bonding solvents. It is found that the best solvent is 2-ethanolamine and-second is pyridine for these lignites. The pretreatment increased the swelling values of the lignites by all solvents. Comparing with original lignites in all solvents except pyridine and 2-ethanolamine, the swelling values were not changed by oxidation. The results have indicated that both swelling and extraction yields generally increased after the pretreatments and the increments are higher with hydrogen bonding solvents. (C) 2003 Elsevier Science Ltd. All rights reserved.Öğe Optimization of nickel adsorption from aqueous solution by using activated carbon prepared from waste apricot by chemical activation(Elsevier, 2005) Erdogan, S; Önal, Y; Akmil-Basar, C; Bilmez-Erdemoglu, S; Sarici-Özdemir, Ç; Köseoglu, E; Içduygu, GWaste apricot supplied by Malatya apricot plant (Turkey) was activated by using chemical activation method and K2CO3 was chosen for this purpose. Activation temperature was varied over the temperature range of 400-900 degrees C and N-2 atmosphere was used with 10 degrees C/min heat rate. The maximum surface area (1214 m(2)/g) and micropore volume (0.355 cm(3)/g) were obtained at 900 degrees C, but activated carbon was predominantly microporous at 700 degrees C. The resulting activated carbons were used for removal of Ni(H) ions from aqueous solution and adsorption properties have been investigated under various conditions such as pH, activation temperature, adsorbent dosage and nickel concentration. Adsorption parameters were determined by using Langmuir model. Optimal condition was determined as; pH 5, 0.7 g/10 ml adsorbent dosage, 10 mg/l Ni(H) concentration and 60 min contact time. The results indicate that the effective uptake of Ni(II) ions was obtained by activating the carbon at 900 degrees C. (c) 2005 Elsevier B.V. All rights reserved.Öğe Poly(methacrylic) acid and ?-methacryloxypropyltrimethoxy silane/clay nanocomposites prepared by in-situ polymerization(Tubitak Scientific & Technological Research Council Turkey, 2002) Gültek, A; Seçkin, T; Önal, Y; Içduygu, MGPoly(methacrylic acid) and poly(acrylic acid) nanocomposites were prepared by in-situ polymerization of gamma-methacryloxypropyltrimethoxysilane (A174)/clay nanocomposites in which the macromonomer was generated by grafting A-174 onto activated clay samples via hydroxyl groups or via intercalation. In- situ polymerization was carried out in the presence of an initiator. It was found that the structural affinity between the methacrylic or acrylic acid monomers and the amount of clay played an important role in the hybrid structure. The nanocomposites were quantified by both X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), and differential thermal analysis (DTA).Öğe Polymerization and characterization of acrylonitrile with ?-methacryloxypropyltrimethoxy-silane grafted bentonite clay(Wiley, 2002) Seçkin, T; Gültek, A; Içduygu, MG; Önal, YNovel natural clay-polymer hybrid materials are prepared from natural bentonite that was modified with silane-coupling agent, gamma-methacryloxypropyltrimethoxysilane (A-174), and acrylonitrile. By changing the molar ratio of acrylonitrile in the initial monomer feed, several clay-hybrid materials were prepared. The structure and thermal stability of hybrid materials were investigated by various methods. The A-174-modified bentonite was dispersed in a solution of acrylonitrile in toluene. In this system, radical polymerization in the presence of AIBN was carried out. Product formed at the particle surface was either physically bound by entanglement or chemically bound by covalent bonding to the silane. In this way, core-shell morphology was obtained with an inorganic core and a polymer shell. The results showed that bonding at the surface of bentonite took place by hydrolytic cleavage of methoxy groups of A-174 with hydroxy groups of bentonite. (C) 2002 John Wiley Sons, Inc.Öğe Thermogravimetric analysis of pretreated Turkish lignites(Elsevier Sci Ltd, 1999) Ceylan, K; Karaca, H; Önal, YThe kinetics of nonisothermal pyrolysis of raw, demineralized or oxidized Turkish lignites have been investigated by thermogravimetry, differential thermal analysis and differential scanning calorimetry. The analyses were carried out in an inert atmosphere or in air atmosphere. The weight loss data indicate that pyrolysis characteristics of the lignites and the prevailing kinetic mechanism vary depending on temperature. The weight loss rates show essentially two regimes, and the major weight loss occurs in the range of 300 degrees C-650 degrees C. The results for the low temperature region (T < 200 degrees C) suggest that the weight loss may be represented by 1.2-1.4-th order of reaction with an activation energy of approximately 15-35 kJ mol(-1). The differential thermal analysis and the differential scanning calorimetry data gave similar values for the overall reaction order and activation energies for this temperature region. At the higher temperature region (T > 300 degrees C), 1.2-1.8-th order of reaction shows a good fit with the weight loss data. The values of the estimated activation energies for this region vary from approximately 40 to 85 kJ mol(-1) depending on the type of sample. However, the differential thermal analysis data suggest that the overall reaction order is around 1.0-1.2 and the effective activation energies vary approximately from 170 to 250 kJ mol(-1). (C) 1999 Elsevier Science Ltd. All rights reserved.
