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Öğe Acidity of silica-alumina catalysts by amine titration using Hammett indicators and FT-IR study of pyridine adsorption(Scientific Technical Research Council Turkey, 1999) Yurdakoç, M; Akçay, M; Tonbul, Y; Yurdakoç, KIn this study, characterization and surface acidity of Siral (SiO2-Al2O3) compounds were investigated with Hammett acidity functions, the n-butylamine titration method and FTIR analysis of the spectra of pyridine adsorption. All the samples had an acid strength of H-0 less than or equal to +2.8. The calculated total amount of acid of the samples increased with the increase in SiO2 content up to Siral 40 and then decreased sharply in the case of Siral 80. Maximum amount of acidity was observed in the case of Siral 40 as 1.37mmole/g. No evidence was found for a band at 1540 cm(-1) on Pural indicating that there were no Bronsted sites on the surface strong enough to react with pyridine. As a result, we can say that the Lewis sites predominate in all the silica-aluminas.Öğe The characterization of prepared organomontmorillonite (DEDMAM) and sorption of phenoxyalkanoic acid herbicides from aqueous solution(Academic Press Inc Elsevier Science, 2006) Akçay, G; Akçay, M; Yurdakoç, KThe montmorillonite has been subjected to modification through ion-exchange reaction by N,N'-didodecyl-N,N'-tetramethylethanediammoniumdiiodide (DEDMAI). The modified sample was studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The basal spacing of modified montmorillonite was determined as 28.72 angstrom. The IR spectra of organomontmorillonite showed changes in C-H vibrations. The characterization of N,N'-didodecyl-N,N'-tetramethylethanediammonium montmorillonite (DEDMAM) and the adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenoxybutyric acid (2,4-DB), 4-chloro-2-methylphenoxyacetic acid (MCPA), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) on organomontmorillonite was studied as a function of the solution concentration. The adsorption energy (E) and adsorption capacity (q(m)) for phenoxyalkanoic acid herbicides adsorbing on organomontmorillonite (DEDMAM) were estimated using the Dubinin-Radushkevic (D-R) equation. These isotherms were modeled according to Freundlich and Dubinin-Radushkevic adsorption isotherms. The sorption of the herbicides on DEDMAM increased in order of MCPA < 2,4-D < 2,4-DB < 2,4,5-T. (c) 2005 Elsevier Inc. All rights reserved.Öğe FTIR study of the adsorption of ammonia and pyridine on V2O5/MgO catalysts(Marcel Dekker Inc, 1998) Akçay, M; Yurdakoç, M; Tonbul, Y; Yurdakoç, K; Hönicke, DThe adsorption of ammonia and pyridine on the surface of the V2O5/MgO catalysts has been studied for the determination of the Bronsted and Lewis acid sites. The data showed that the catalysts have medium Lewis acidity, but are also weak Bronsted acids, having active hydroxy groups able to interact with pyridine by H-bonding and by protonation. Pyridine is a suitable basic probe for the quantification of the catalysts. 32% V2O5/MgO catalyst is the most acidic catalyst.Öğe Removal of 2,4-dichlorophenoxy acetic acid from aqueous solutions by partially characterized organophilic sepiolite(Academic Press Inc Elsevier Science, 2005) Akçay, G; Akçay, M; Yurdakoç, KThe adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) on organophilic sepiolite (dodecylammonium sepiolite, DAS) was Studied as a function of solution concentration and temperature. The observed adsorption rates were found to be equal to the first-order kinetics. The rate constants were calculated for temperatures ranging between 25 and 40 degreesC at constant concentration. The adsorption energies, E. and adsorption capacity, q(m), for 2,4-D adsorption on organophilic sepiolite was estimated using the Dubinin-Radushkevic equation. Thermodynamic parameters (Deltag(a), Deltah(a), Deltas(a)) were determined by a new approximation from the isotherm of 2,4-D adsorption on DAS. Also, DeltaS(0) and DeltaH(0) values were calculated from the van't Hoff equation. These isotherms were modeled according to the Freundlich and Dubinin-Radushkevic adsorption equations. The amount of adsorption of this herbicide on organophilic sepiolite was found to be dependent on the relative energies of adsorbent-adsorbate, ad sorbate-sol vent, and adsorbate-adsorbate interaction. (C) 2004 Elsevier Inc. All rights reserved.Öğe Removal of various phenoxyalkanoic acid herbicides from water by organo-clays(Wiley-V C H Verlag Gmbh, 2000) Akçay, G; Yurdakoç, KDodecylammonium bentonite (DB) and dodecylammonium sepiolite (DS) were used as sorbents for phenoxyalkanoic acid herbicides 2,4-D ((2,4-dichlorophenoxy)acetic acid), 2,4-DP ((RS)-2-(2,4-dichlorophenoxy)propionic acid), 2,4-DB (4-(2,4-dichlorophenoxy)butyric acid), 2,4,5-T ((2,4,5-trichlorophenoxy)acetic acid), and MCPA ((4-chloro-2-methylphenoxy)acetic acid). Langmuir, Freundlich, and the linear Henry's Law isotherm adsorption parameters were calculated from the adsorption isotherms. Langmuir equation showed poor fit for both adsorbents. According to the evaluation using the Freundlich equation, the DS sample showed much higher and stronger sorption capacity than DB. Similar behaviour was also observed in the case of the linear Henry's Law isotherm. The adsorption of the herbicides on both DB and DS decreased in the order of 2,4-DB > 2,4,5-T > 2,4-DP > 2,4-D > MCPA.Öğe Thermogravimetric investigation of the dehydration kinetics of KSF, K10 and Turkish bentonite(Scientific Technical Research Council Turkey, 2001) Tonbul, Y; Yurdakoç, KThe kinetic parameters for the dehydration of bentonite from Turkey, KSF and K10 were determined by using dynamic TG techniques. The Ozawa method is better for the dehydration of the clay samples than the first order equation of Coats and Redfern. The former function calculates consistently higher activation energies than the latter. The mean values of the activation energies in the alpha range 0.1-0.7, are 56-66 kJ mol(-1) in the Ozawa method.
