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Now showing items 1 - 16 of 17337

  • Functionalized sepiolite for heavy metal ions adsorption

    Mehmet Do?an   Yasemin Turhan   Mahir Alkan   Hilmi Namli   P?nar Turan   ?zkan Demirba?  

    Surface modification of clays has become increasingly important due to the practical applications of clays such as fillers and adsorbents. The surface modification of sepiolite with [3-(2-aminoethylamino)propyl]trimethoxysilane has been employed. The modified sepiolite surface was investigated by FTIR, XRD and DTA/TG analysis. It was found that the chemical bonding takes place between the hydroxyl groups and/or oxygen atoms within the structure of sepiolite and methoxy groups of [3-(2-aminoethylamino)propyl]trimethoxysilane. The changes on electrokinetic properties of modified sepiolite particles were studied by measuring the zeta potential of particle as a function of metal concentration and equilibrium pH of solution. It was found that the zeta potential of the clay particles was always negative independent of the metal concentration in solution. This study also provides some evidence for the adsorption of metal ions on modified sepiolite. The adsorption of metal ions onto modified sepiolite has varied with the type of metal cations. The available basic nitrogen centers covalently bonded to the sepiolite skeleton were studied for Co(II), Cu(II), Mn(II), Zn(II), Fe(III) and Cd(II) adsorption from aqueous solutions. It was found that the amount of metal ion adsorbed onto modified sepiolite increases with increase in solution equilibrium pH and temperature, whereas it generally decreases with the ionic strength. The experimental data were correlated reasonably well by the Langmuir adsorption isotherm and the isotherm parameters (qm and K) were calculated. The ability to adsorb the cations gave a capacity order of Zn(II) > Cu(II) ~ Co(II) > Fe(III) > Mn(II) > Cd(II) with affinities of 2.167×10-4, 1.870×10-4, 1.865×10-4, 1.193×10-4, 0.979×10-4 and 0.445×10-4 mol g-1, respectively.
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  • Adsorption of copper (II) ions onto sepiolite and electrokinetic properties

    Mehmet Do?an   Ayd?n Türkyilmaz   Mahir Alkan   ?zkan Demirba?  

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  • Adsorption kinetics of maxilon yellow 4GL and maxilon red GRL dyes on kaolinite

    Mehmet Do?an   M. Hamdi Karao?lu   Mahir Alkan  

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  • Adsorption kinetics of maxilon blue GRL onto sepiolite from aqueous solutions

    Mehmet Do?an   Mahir Alkan   ?zkan Demirba?   Yasemin ?zdemir   Cengiz ?zmetin  

    Adsorption isotherm of maxilon blue GRL on sepiolite was determined and correlated with common isotherm equations such as Langmuir and Freundlich models. It was found that the Langmuir model appears to fit the isotherm data better than the Freundlich model. Furthermore, adsorption kinetics experiments were carried out to remove the maxilon blue GRL from its aqueous solutions using sepiolite as an adsorbent. The remove rate of maxilon blue GRL by sepiolite was studied by varying parameters such as the contact time, stirring speed, initial dye concentration, ionic strength, pH and temperature. The kinetics experiments indicated that initial dye concentration, ionic strength, pH and temperature could affect the adsorption rate of maxilon blue GRL. Sorption data were fitted to pseudo-first-order, the Elvoich equation, pseudo-second-order, mass transfer and intra-particle diffusion models, and found that adsorption kinetics can be described according to the pseudo-second-order model, from which the rate constant and the adsorption capacity were determined. Rate constants under different conditions were also estimated. In addition, we found that the rate-limiting step was intra-particle diffusion. According to the change of intra-particle diffusion parameter, the adsorption processes could be divided into different stages. Thermodynamic activation parameters such as activation energy Ea, enthalpy Delta H*, entropy Delta S* and free energy Delta G* were determined. These parameters indicate that the adsorption has a low potential barrier corresponding to a physisorption; the adsorption reaction is not a spontaneous one; and the adsorption is physical in nature involving weak forces of attraction and is also endothermic. [All rights reserved Elsevier]
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  • Adsorption kinetics of methyl violet onto perlite

    Mehmet Do?an   Mahir Alkan  

    This study examines adsorption kinetics and activation parameters of methyl violet on perlite. The effect of process parameters like contact time, concentration of dye, temperature and pH on the extent of methyl violet adsorption from solution has been investigated. Results of the kinetic studies show that the adsorption reaction is first order with respect to dye solution concentration with activation energy of 13.2 kJ mol-1. This low activation energy value indicates that the adsorption reaction is diffusion controlled. The activation parameters using Arrhenius and Eyring equations have been calculated. Adsorption increases with increase of variables such as contact time, initial dye concentration, temperature and pH.
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  • Kinetics and mechanism of removal of methylene blue by adsorption onto perlite

    Mehmet Do?an   Mahir Alkan   Ayd?n Türkyilmaz   Yasemin ?zdemir  

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  • Removal of methyl violet from aqueous solution by perlite

    Mehmet Do?an   Mahir Alkan  

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  • Adsorption of Methylene Blue from Aqueous Solution onto Perlite

    Mehmet Do?an   Mahir Alkan   Yavuz Onganer  

    Adsorption of methylene blue from aqueous solutions onto unexpanded and expanded perlite samples activated by H2SO4 and NaCl solutions has been investigated, to assess the possibility of using perlite for removing cationic dyes from aqueous solutions. The effects of pH and temperature of dye solution on the adsorption capacities have been evaluated. The experimental data were correlated reasonably well by the Langmuir adsorption isotherm and the isotherm parameters (Qm and K) have been calculated. The removal efficiency (P) and dimensionless separation factor (R) have shown that perlite can be used for removal of methylene blue from aqueous solutions, but unexpanded perlite is more effective.
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  • Adsorption of methylene blue onto hazelnut shell: Kinetics, mechanism and activation parameters

    Mehmet Do?an   Harun Abak   Mahir Alkan  

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  • Application of Total Reflection X-Ray Fluorescence Spectrometry in the Textile Industry

    Mehmet Do?an   Mustafa Soylak   Latif El?i   Alex von Bohlen  

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  • Adsorption kinetics and mechanism of cationic methyl violet and methylene blue dyes onto sepiolite

    Mehmet Do?an   Yasemin ?zdemir   Mahir Alkan  

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  • American Missionaries and the Middle East: Foundational Encountersby Mehmet Ali Do?an; Heather J. Sharkey

    Review by: Hans-Lukas Kieser  

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  • Effect of polymer additives and process temperature on the physical properties of bitumen-based composites

    Mehmet Do?an   Erdal Bayramli  

    Polymer modified bitumen (PMB) is a binder obtained by the incorporation of polymer into the bitumen by mechanical mixing or chemical reaction. This study deals with the modification of bitumen with three types of polymers (LDPE, EVA, and SBS) in the presence of filler (CaCO 3). The morphological, mechanical, rheological properties, and thermal conductivity of the PMBs have been analyzed by scanning electron microscopy, tensile testing, melt flow index (MFI) measurements and hot wire method, respectively. The results indicate that the above-mentioned properties of PMBs are influenced by polymer and bitumen nature and its composition. The mechanical properties of composites prepared at different temperatures exhibit small differences. In general, the inclusion of polymer increases tensile strength and Young's modulus and reduces percentage strain and MFI values, also, polymer inclusion reduces the thermal conductivity values of the composites. copy 2009 Wiley Periodicals, Inc.
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  • Biosorption of Methylene Blue from Aqueous Solutions by Hazelnut Shells: Equilibrium, Parameters and Isotherms

    Mehmet Do?an   Harun Abak   Mahir Alkan  

    This paper presents a study on the batch adsorption of a basic dye, methylene blue (MB), from aqueous solution onto ground hazelnut shell in order to explore its potential use as a low-cost adsorbent for wastewater dye removal. A contact time of 24 h was required to reach equilibrium. Batch adsorption studies were carried out by varying initial dye concentration, initial pH value (3-9), ionic strength (0.0-0.1 mol L-1), particle size (0-200 mu m) and temperature (25-55 degrees C). The extent of the MB removal increased with increasing in the solution pH, ionic strength and temperature but decreased with increase in the particle size. The equilibrium data were analysed using the Langmuir and Freundlich isotherms. The characteristic parameters for each isotherm were determined. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by Langmuir isotherm equation. The maximum adsorption capacities for MB were 2.14x10(-4), 2.17x10(-4), 2.20x10(-4) and 2.31x10(-4) mol g(-1) at temperature of 25, 35, 45 and 55 degrees C, respectively. Adsorption heat revealed that the adsorption of MB is endothermic in nature. The results indicated that the MB strongly interacts with the hazelnut shell powder.
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  • Physical properties and cure characteristics of natural rubber/nanoclay composites with two different compatibilizers

    Mehmet Do?an   Demet Dengiz Oral   Betül Y?lmaz   Melih Savu   Sel?uk Karahan   Erdal Bayraml?  

    The effects of epoxidized natural rubber (ENR) and maleic anhydride-grafted polybutadiene (PB- g-MA) as compatibilizers to rubber formulations with and without organo-modified layered silicates are investigated. The physical properties and curing characteristics of composites are studied by moving die rheometer, rubber process analyzer, tensile, tear, and hardness testing. The state of organoclay intercalation was determined by X-ray diffraction method. The addition of compatibilizers, especially ENR 50, results in further intercalation or exfoliation of the organoclay that increased the clay dispersion in the rubber matrix. ENR 50 with organo-modified clay improves the physical properties and changes the curing profile. The addition of PB- g-MA without organoclay increases the tensile strength (sigma max) by increasing the stock viscosity of the rubber compound. Interestingly, simultaneous increase in hardness and sigma max is achieved in the presence of both compatibilizers, a characteristic that is difficult to achieve and sometimes required in rubber processing. copy 2011 Wiley Periodicals, Inc.
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  • Effect of boron-containing materials on the flammability and thermal degradation of polyamide 6 composites containing melamine

    Mehmet Do?an   Erdal Bayraml?  

    Three different boron-containing substances-zinc borate (ZnB), borophosphate (BPO 4), and a boron- and silicon-containing oligomer (BSi)-were used to improve the flame retardancy of melamine in a polyamide 6 (PA-6) matrix. The combustion and thermal degradation characteristics of PA-6 composites were investigated with the limiting oxygen index (LOI), the UL-94 standard, thermogravimetric analysis (TGA)/Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). A slight increase was seen in the LOI values of a sample containing BSi (1 wt %). BPO 4 at high loadings showed a V0 rating (indicating the best flame retardancy) and slightly lower LOI values in comparison with samples with only melamine. For ZnB and BSi, glassy film and char formation decreased the dripping rate and sublimation of melamine, and this led to low LOIs. According to the TGA-FTIR results, the addition of boron compounds did not change the decomposition product distribution of melamine and PA-6. The addition of boron compounds affected the flame retardancy by physical means. The TGA data showed that boron compounds and melamine reduced the decomposition temperature of PA-6. According to the DSC data, the inclusion of boron compounds increased the onset temperature of sublimation of melamine and also affected the flame retardancy negatively. copy 2010 Wiley Periodicals, Inc.
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