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    Efficient removal of methylene blue by photocatalytic degradation with TiO2 nanorod array thin films
    (Springer, 2013) Kerkez, Ozge; Boz, Ismail
    TiO2 nanorod array thin films were synthesized on fluorine doped tin oxide (FTO) glass substrate by the hydrothermal method. The prepared TiO2 nanorod arrays were characterized by X-ray diffraction, scanning electron microscopy and UV-Vis diffuse reflectance spectroscopy. The effect of different synthesis conditions was investigated on the growth and photocatalytic activity of the samples. X-ray diffraction results show that the main phase of TiO2 is rutile and nanorod growth significantly depends on the synthesis conditions. TiO2 nanorod array thin films were used for the photocatalytic degradation of methylene blue in aqueous solution under UV irradiation (254 and 365 nm). The hydrothermal synthesis conditions of TiO2/FTO sample were determined for maximum photodegradation efficiency. Total degradation of 94 % was achieved under 254 nm and 69 % degradation was achieved under 365 nm with TiO2/FTO sample prepared with initial HCl:H2O = 1:1 ratio, 1.0 ml TiCl4 at 180 A degrees C for 2 h hydrothermal growth. The apparent reaction rate constant was calculated to be 0.0108 min(-1) under 254 nm and 0.0044 min(-1) under 365 nm.
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    La, Mn and Zn promoted microporous iron catalysts with high productivity and stability for Fischer-Tropsch synthesis
    (Springer, 2016) Gul, Omer F.; Atac, Ozlem; Boz, Ismail; Ozkara-Aydinoglu, Seyma
    Fischer-Tropsch synthesis is studied over precipitated Fe catalysts promoted with Mn, Zn and La metals. The results showed that there was a large increase in surface area and pore volume, and a sharp decrease in average pore size upon the addition of promoters. Catalyst productivity and rate of syngas converted as well as hydrocarbon yield increased with addition of promoters to Fe structure during precipitation step. Addition of metal promoters led catalyst samples of microporous structures with relatively high surface areas. This effect probably yielded catalysts with enhanced long-term activity and stability. Samples containing 10 % Zn and 5 % Mn exhibited the highest catalytic activity and stability. Increasing the loading of Zn from 5 to 10 wt% led to a noteworthy increase on yield and productivity as well as rate of syngas converted. The highest productivity was obtained for the sample containing 10 % Zn, highest yield was attained over the sample containing 5 % Mn. The results indicate that the selectivity to C-12-C-18 range was more pronounced for the catalyst promoted with Mn metal whereas alpha-olefins and higher molecular weight products were increased with the addition of 5 % Zn over Fe based catalysts. The decrease in temperature from 523 to 493 K resulted in an increase in heavy hydrocarbons and a significant decrease in gaseous and light hydrocarbons for Fe4Si5Mn catalyst.
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    ?-olefin selectivity of Fe-Cu-K catalysts in Fischer-Tropsch synthesis: Effects of catalyst composition and process conditions
    (Elsevier Science Sa, 2012) Ozkara-Aydinoglu, Seyma; Atac, Ozlem; Gul, Omer F.; Kinayyigit, Solen; Sal, Sinan; Baranak, Murat; Boz, Ismail
    Fischer-Tropsch (FT) synthesis has been studied over a series of precipitated Fe catalysts promoted to investigate the effect of K and Cu promoters on the carbon number distribution of FT product. The main intention is to maximize the alpha-olefin selectivity by controlling the secondary reactions of alpha-olefin as a function of potassium and copper loadings. The results showed that impregnation of different loadings of Cu and K promoters to precipitated iron-based catalyst was found to have significant influences on the crystallographic structure, morphological and physical properties of iron-based catalysts, as well as catalytic activity, stability and selectivity performances during FT synthesis. 100Fe7Cu3K sample exhibited the highest catalytic activity and stability in TOS tests. The catalyst is capable of working under a variety of temperatures and space velocities at a same activity level with no significant activity loss. Proper control of Cu and K contents is essential to obtain maximum C-5+ yield since the changes in the relative loadings of both Cu and K promoters affect hydrocarbon product distribution. 100Fe7Cu3K sample has high secondary alpha-olefin hydrogenation activity as olefin/paraffin ratio decreases with increasing carbon number while C-19+ selectivity is relatively low compared to other samples. The effects of space velocity and temperature on alpha-olefin selectivity are strongly dependent on the amounts of Cu and K promoters and chain length. The maximum alpha-olefin/n-paraffin ratio has been obtained over 100Fe3Cu1K sample at 543 K with a space velocity of 3 NL/h/g-cat. (C) 2011 Elsevier B.V. All rights reserved.
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    Photo(electro)catalytic Activity of Cu2+-Modified TiO2 Nanorod Array Thin Films under Visible Light Irradiation
    (Pergamon-Elsevier Science Ltd, 2014) Kerkez, Ozge; Boz, Ismail
    In the present study, a two-step method was applied to synthesise Cu2+-modified TiO2 nanorod array thin films for photocatalytic processes. TiO2 nanorod array thin films were synthesised by a hydrothermal method and then modified with an ultrasonic-assisted sequential cation adsorption method. The samples were characterised by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and inductively coupled plasma mass spectroscopy (ICP-MS) analysis. The photoelectrochemical properties of the samples were evaluated by linear sweep voltammetry and Mott-Schottky analysis; photocatalytic activities were tested by methylene blue degradation under visible light. The photocurrent density of the TiO2/FTO sample modified with 50 mM Cu2+ solution was 26 times higher than that of the unmodified TiO2/FTO sample. Additionally, methylene blue degradation efficiency under visible light was increased 40% with respect to the efficiency of the unmodified sample. The mechanism of the photocatalytic activity enhancement of Cu2+-modified TiO2 nanorod films was discussed. (C) 2013 Elsevier Ltd. All rights reserved.
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    Photodegradation of Methylene Blue with Ag2O/TiO2 under Visible Light: Operational Parameters
    (Taylor & Francis Inc, 2015) Kerkez, Ozge; Boz, Ismail
    Ag2O modified TiO2 nanoparticles were synthesized by precipitation and wet impregnation method. They were characterized by X-ray diffraction technique, UV-vis diffuse reflectance spectrophotometry and Fourier transform infrared spectroscopy. Inductively coupled plasma mass spectrometry was performed to quantify Ag amount in the photocatalysts. The photocatalysts occurred in the concentration range of 0.05%-2% in the Ag/Ti molar ratio. The photocatalytic activity was investigated for the degradation of methylene blue as a model organic dye. Optimum reaction conditions were determined to provide maximum dye degradation efficiencies under visible light. Under visible light illumination, C2-Ag2O/TiO2 (Ag/Ti=0.1/100) showed the highest activity. Reaction rate constants were calculated and compared for various reaction conditions.
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    Synergistic effect of Pt0 and M2+ (Cu2+, Ni2+, Co2+) on photo(electro) catalytic activity of TiO2 nanorod array thin films
    (Elsevier Science Sa, 2015) Kerkez-Kuyumcu, Ozge; Boz, Ismail
    M2+ (Cu2+, Ni2+, Co2+) and Pt-0-M2+ loaded TiO2 nanorod film samples were prepared on transparent conducting oxide glass (FTO/F:SnO2). Two step method was used consisting a hydrothermal method to grow TiO2 nanorods on the surface and an ultrasonic-assisted sequential cation adsorption method to modify the nanorods. The samples were characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy. The photoelectrochemical properties of the samples were evaluated by linear sweep voltammetry, photocatalytic activities were tested by methylene blue degradation under visible light. M2+-TiO2/FTO samples were compared with Pt-0-M2+-TiO2/FTO samples; the synergistic effect of Pt-0 and M2+ was discussed. Pt-0-Ni2+-TiO2/FTO showed superior photoelectrocatalytic activity with 1.358 mA cm(-2) and 78.3% methylene blue degradation under visible light. Quantum yields were calculated separately as a sign for H-2 generation rate and as a conversion of methylene blue molecule per absorbed light. (C) 2015 Elsevier B.V. All rights reserved.