Yazar "Demir, Halil" seçeneğine göre listele

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    Determination of Nucleation Kinetics of Ammonium Biborate Tetrahydrate
    (2014) Demir, Halil
    The ammonium biborate tetrahydrate was synthesized by stoichiometric incorporation of boric acid and ammonium hydroxide in aqueous solution and the effects of supersaturation, temperature, pH of solution, cooling rate and presence of impurities upon the metastable zone width (MZW) were investigated. The MZW of ammonium biborate tetrahydrate aqueous solution was increased with increasing concentration of impurities. The saturation temperature was increased in the presence of Ca (II) ion and decreased in the presence of Pb (II) and Mg (II) ions.
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    Hydrogen Generation from Sodium Borohydride Hydrolysis with a Cu–Co-Based Catalyst: A Kinetic Study
    (Taylor and francis, 2015) Demir, Halil
    In the present work, Cu–Co-supported catalysts were tested for hydrogen generation from the hydrolysis reaction of an alkaline sodium borohydride solution. Cu–Co catalysts were prepared by the chemical reduction with NaBH4 and characterized with scanning electron microscope. The effect of Cu–Co ratio was investigated. The results suggested that the optimal mixture percentage of Cu–Co catalyst was 60:40; excessive Cu resulted in poor catalytic activity. The reactions were carried out at temperatures of 20, 30, 40, and 50°C. The experimental data was fitted to the nth-order kinetic models. The results indicate that the nth-order model gives a reasonable description of the hydrogen generation rate over all of the temperature range. The activation energy and pre-exponential factor of the nth-order reaction model were obtained as 42.66 kJ mol−1 and 1.21 × 104, respectively.
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    Hydrogen production from sodium borohydride for fuel cells in presence of electrical field
    (Wiley, 2010) Sahin, Oemer; Dolas, Hacer; Kayal, Mustafa; Lzgi, Mehmet Sait; Demir, Halil
    Sodium borohydride (NaBH4) reacts with water to produce 4 mol of hydrogen per mol of compound at room temperature. Under certain conditions, it was found that 6 mol of hydrogen per mol of sodium borohydride was produced in the presence of electrical field created by DC voltages, whereas 4 mol of hydrogen was produced in the presence or catalyst per mole of sodium borohydride. Electrical field created by alternative current with three different waves (sin, square and triangle type) increases the hydrolysis of sodium borohydride. It was found that hydrogen produced from sodium borohydride by applying, an electrical field can be effectively used for both increasing the electrolysis of water and hydrolysis of sodium borohydride. The hydrolysis reaction was carried out at temperature of 20, 30, 40 and 60 degrees C in the presence of electrical field created by AC voltages square wave. The experimental data were fitted to the kinetic models of zero-order, first-order and nth-order. The results indicate that the first-order and nth-order model give a reasonable description of the hydrogen generation rate at the temperature higher than 30 degrees C. Reaction rate constant at different temperatures were determined from experimental data, and activation energy was found to be 50.20 and 52.28 kJ mol(-1) for first-order and nth-order, respectively. Copyright (C) 2009 John Wiley & Sons, Ltd.
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    Investigation of the properties of photocatalytically active Cu-doped Bi2S3 nanocomposite catalysts
    (Springer, 2020) Demir, Halil; Sahin, Omer; Baytar, Orhan; Horoz, Sabit
    In the current study, pure Bi2S3 and Cu-doped Bi2S3 nanocomposite catalysts with different Cu concentrations (0.33, 1, and 3%) were synthesized by the hydrothermal method and photocatalytic degradation experiments of methylene blue were carried out in the presence of these catalysts for the first time. The samples were labeled as Bi2S3, Cu(0.33%):Bi2S3, Cu(1%):Bi2S3 and Cu(3%):Bi2S3, respectively. Cu(0.33%):Bi2S3 nanocomposite catalyst was found to have higher photocatalytic degradation efficiency compared to other catalysts. Moreover, the crystalline size and bandgap value of pure Bi2S3 and Cu(0.33%):Bi2S3 nanocomposite catalysts were determined by X-ray diffraction and ultraviolet-visible spectrophotometry (UV-Vis) measurements, respectively. Consequently, it was observed for the first time in this study that the Cu-doped metal effectively affects the photocatalytic degradation efficiency of Bi2S3 nanocomposite catalyst.
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    A new method on producing high surface area activated carbon: The effect of salt on the surface area and the pore size distribution of activated carbon prepared from pistachio shell
    (Elsevier, 2011) Dolaş, Hacer; Şahin, Ömer; Saka, Cafer; Demir, Halil
    Activated carbons having high surface area were produced from pistachio shells that were chemically activated using zinc chloride at room temperature and then activated in carbon dioxide gas that was saturated in water vapor. The surface area and pore structure of activated carbon produced from pistachio shells were investigated depending on the amount of chemical activating reagent, activation temperature, duration time in the reagent solution and the kinds of activation reagent. In this study, a method, which provides activated carbons having the highest surface area was developed. As a result, the activated carbon produced from pistachio shells treating with 40% ZnCl2 then with 40% HCl in room temperature and then activated at 900 °C for 90 min has 3256 m2/g of BET surface area and 3822 m2/g of DR surface area and 1.36 cc/g of DR micropore volume. It was found that the activated carbon produced from pistachio shells treated 40% of sodium chloride and activated at 900 °C for 90 min has 3895 m2/g of BET surface area and 5235 m2/g of DR surface area and 1.86 cc/g of DR micropore volume.
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    Optimizing hydrogen production from alkali hydrides using supported metal catalysts
    (Springer Heidelberg, 2023) Karabulut, Abdurrahman; Izgi, M. Sait; Demir, Halil; Sahin, Oemer; Horoz, Sabit
    The present study aimed to investigate the effect of different parameters on the hydrogen production rate (HPR) during KBH4 hydrolysis using Co-B (pure) and Co-B@GO (supported) catalysts. The results showed that the HPR value for Co-B@GO catalyst was 2299.81 mL*gcat-1 min-1, which was approximately 2.3 times higher than that of the Co-B catalyst (1012.71 mLgcat-1 *min-1). The activation energy of Co-B@GO was also calculated to be 21.62 kJ/mol, lower than some reported values in the literature. This demonstrates the potential of Co-B@GO as a cost-effective and efficient catalyst for hydrogen production from alkali hydrides. The results of this study provide novel insights into the optimization of hydrogen production processes using supported metal catalysts.
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    Removal of Lead(II) from Aqueous Solutions using Pre-boiled and Formaldehyde-Treated Onion Skins as a New Adsorbent
    (Taylor Francis, 2011) Cafer, Saka; Şahin, Ömer; Demir, Halil; Kahyaoğlu, Mustafa
    The adsorption characteristics of Pb2+ on pre-boiled treated onion skins (PTOS) and formaldehyde-treated onion skins (FTOS) were evaluated. The effects of Pb2+ initial concentration, agitation rate, solution pH, and temperature on Pb2+ adsorption were investigated in batch systems. Pb2+ adsorption was found to increase with increase in initial concentration. The point of zero net charge (PZC) was 6.53. The optimum pH for the maximum removal of Pb2+ was 6.0. The adsorption equilibrium data was best represented by the Langmuir isotherm model for FTOS and the Freundlich isotherm model for PTOS. The maximum amounts of Pb2+ adsorbed (qm), as evaluated by the Langmuir isotherm, was 200 mgg-1 for FTOS. The efficiencies of PTOS and FTOS for Pb2+ removal were 84,8.0% and 93.5% at 0.15 g/200 mL-1 adsorbent dose, respectively. (C 0 = 50 mg L-1). Study concluded that onion skins, a waste material, have good potential as an adsorbent to remove toxic metals like Pb2+ from water. Boehm titration analysis was conducted to determine the surface groups. It was found that the adsorption kinetics of Pb2+ obeyed pseudo-first-order kinetic model as based on ?q (%) values. FTIR and SEM images before and after adsorption was recorded to explore changes in adsorbent-surface morphology. Activation energy (Ea) was obtained as 25.596 kJ/mol.
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    SODYUM BOR HİDRÜRÜN HİDROLİZİNDE KARBON NANOTÜP DESTEKLİ Co-Cr-B KATALİZÖRÜN KULLANILMASI
    (2021) Baytar, Orhan; Ağrak, Selman; Demir, Halil; Şahin, Ömer
    Artan teknoloji ile birlikte hem enerji ihtiyacı artmakta hem de mevcut fosil yakıtların miktarı gün geçtikçe azalmaktadır. Fosil yakıtların azalması ve enerji ihtiyacının artması araştırmacıları yenilenebilir enerji kaynakları için araştırmaya yönlendirmiştir. Hidrojen enerjisi bu yenilenebilir enerji kaynaklardan bir tanesidir. Sodyum borhidrür(NaBH4) hidrojen taşıyıcısıdır. Sodyum borhidrür hidrolizinde açığa çıkan hidrojenin yarısının sudan gelmesi büyük bir avantajdır. Bu çalışmada, NaBH4 hidrolizinde kullanılmak üzere karbon nanotüp destekli(KNT) Co-Cr-B katalizörü sentezlenmiştir. Sentezlenen katalizörün karakterizasyonu SEM, EDX, XRD ve BET ile gerçekleştirilmiştir. NaBH4 hidrolizinde NaOH konsantrasyonu, NaBH4 konsantrasyonu, katalizör miktarı ve sıcaklık parametrelerin etkisi incelenmiştir. Desteksiz Co-Cr-B katalizörün hidrojen üretim hızı 3560 ml.g-1 .dk-1 . iken KNT destekli Co-Cr-B katalizörün hidrojen üretim hızı 6600 ml.g-1 .dk-1 . olarak belirlenmiştir. NaBH4 hidroliz aktivasyon enerjisi ve kinetiği tespit edilmiş ve sırasıyla 55,88 kj/mol ve 0,2 olduğu tespit edilmiştir.
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    Thermal decomposition kinetics of sodium perborate tetrahydrate to sodium metaborate by using model-fitting and model-free methods
    (Springer, 2011) Demir, Halil
    Model-free and model-fitting methods have been applied to data for nonisothermal and isothermal decomposition of sodium perborate tetrahydrate to sodium metaborate. The kinetic triplet (f(a), A and E) of sodium perborate tetrahydrate was found by model fitting method defined with a single step reaction, which has an excellent fit for nonisothermal data and obeys different kinetic models and yields highly uncertain values of Arrhenius parameters. The isothermal and nonisothermal data for thermal decomposition of sodium perborate tetrahydrate to sodium perborate monohydrate and sodium metaborate were evaluated by model-free isoconversional method. The complex nature of multi-step process of sodium perborate tetrahydrate to sodium metaborate was more easily indicated by using wide temperature range in nonisothermal isoconversional method.