Browsing by Author "Aktas, PS"

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    Metal-chelated cryogels for amyloglucosidase adsorption: application for continuous starch hydrolysis
    Evli, S; Orhan, H; Aktas, PS; Uygun, M; Uygun, DA
    In the present work, a new metal-chelating platform was designed by using IDA as a chelating agent and Cu(II) as an affinity component for amyloglucosidase adsorption. Poly(AAm-GMA) cryogels were used as structural elements, while GMA monomer served reactive epoxy groups for IDA immobilization. Synthesized cryogels were characterized by FTIR, SEM and EDX studies. Pore diameter of the whole polymeric structure was 3-10 Effects of medium pH, temperature, ionic strength along with amyloglucosidase concentration were also investigated for more effective amyloglucosidase adsorption and maximum adsorbed amount of amyloglucosidase was cryogel by the optimum conditions. Reusability profile of the poly(AAm-GMA)-IDA-cryogels was also studied and it was found that the synthesized cryogels could be used repeatedly for many times without any significant decrease on their adsorption capacity. Also continuous hydrolysis of starch by using immobilized form of amyloglucosidase in a column system was studied.
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    Influence of synthesis procedures on the preparation of strontium titanate nanoparticles and photocatalytic application for methylene blue degradation
    Ay, E; Aktas, PS
    SrTiO3 is a well-known photocatalyst with various applications, such as antibacterial agents, self-cleaning surfaces, and water and air conditioning. With the increased environmental pollution, SrTiO3 is one of the most studied perovskite photocatalysts, exhibiting pronounced photocatalytic activity for removing chemical pollutants and water splitting. In the present work, pure Strontium titanate (ST) nanoparticles were successfully prepared using high-energy ball milling and Pechini techniques and characterized by X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier Transform Infrared spectroscopy (FTIR), scanning and transmission electron microscopy, respectively. Structural parameters were evaluated by Rietveld refinement analysis from XRD data, which confirmed the cubic system of SrTiO3 with Pm-3 m space group. Scanning electron microscope results showed that ST1 samples consisted of agglomerated and irregular-shaped structures between 20 and 40 nm, and in ST2, the particles were round-shaped and had an average size of 150 nm. The obtained nanoparticles were used for photocatalytic methylene blue (MB) degradation, and synthesis methods' influence on catalytic activity was investigated. The photocatalytic studies examining the decoloration of MB dye reveal the function of smaller particles in increasing the rate of reactions. The degradation rate constant of MB on the ST1 (Pechini-synthesized sample) and ST2 (high energy ball milled sample) is 0.0145 and 0.0112 min(-1), respectively. The better photocatalytic activity of the ST1 demonstrated 93% degradation of dye under the solar light simulator. The photocatalytic reaction data provided well a first-order kinetic model. [GRAPHICS]
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    Synthesis of BaTi5O11 by an aqueous co-precipitation method via a stable organic titanate precursor
    Aktas, PS
    BaTi5O11 has been widely researched due to its unique microwave properties. Conventionally, it is challenging to obtain this compound as a single phase. The BaTi5O11 was synthesized via a co-precipitation technique using an aqueous solution of titanium(IV)(triethanolaminato) isopropoxide, barium nitrate and ammonia as precursors, which are stable in aqueous media. The phase evolution, purity, and structure were identified by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy analysis. The desired BaTi5O11 structure was obtained by calcination at 900 degrees C. Furthermore, the structure was characterized by TGA, FT-IR and Raman studies. The study showed that the particles were between 80 and 120 nm in size and the average crystallite size was determined from the Scherrer formula as 68.1 nm at 900 degrees C.
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    Structural investigation of barium zirconium titanate Ba(Zr0.5Ti0.5)O3 particles synthesized by high energy ball milling process
    Aktas, PS
    In this study, pure barium zirconium titanate Ba(Zr0.5Ti0.5)O-3 (BZT) powders were successfully synthesized via the mechanochemical route using barium carbonate and titanium oxide as precursors. Structural properties of BZT are characterized by X-ray diffraction (XRD), Rietveld refinement, scanning electron microscope, energy dispersive X-ray spectrometry, thermogravimetric analysis, and FT-IR spectroscopy. It was observed that the ball milling operation has a significant influence on sintering temperature. Single-phase BZT was obtained under sintering conditions at 1350 degrees C. XRD and Rietveld refinement studies revealed that BZT composition has a cubic structure with a space group of Pm-3m(#221). As estimated by the Scherrer formula, the average crystallite size was determined as 79.2 nm for sintering temperature at 1350 degrees C.
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    Structural and morphological investigations of barium zirconium titanate particles synthesized by the Pechini method
    Aktas, PS
    Barium zirconium titanate systems are lead-free, environmentally friendly materials exhibiting relaxor behavior with increasing Zr content. Therefore, the study proposed preparing and characterization of an ecologically favorable Pb-free relaxor from Ba(Zr0.5Ti0.5)O-3 (BZT). The results reported here are based on the research of BZT micrometric powders prepared by the Pechini method. The phase evolution was monitored by X-ray diffraction from 800 degrees C to 1300 degrees C, and results show that the formation of BZT starts around 1050 degrees C and continues until 1300 degrees C. The Rietveld refinement of data at 1300 degrees C confirms that BZT has a cubic structure. The thermal and structural properties of BZT samples were identified by thermogravimetric analysis and Fourier-transform infrared spectroscopy. Scanning electron microscopy results reveal that the synthesized particles are micron-sized (2-2.8 mu m), rounded, polygonal-shaped, and agglomerated.
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    Synthesis, structure, electrochemical and antimicrobial properties of N,N′-bis(ferrocenylmethyl)imidazolinium salts
    Özbek, HA; Aktas, PS; Daran, JC; Oskay, M; Demirhan, F; Çetinkaya, B
    The N, N'-bis(ferrocenylmethyl)imidazolinium chloride (3) and bromide (4) were prepared by reaction of N,N'-bis(ferrocenylmethyl)ethylenediamine (2) with NH4X (X = Cl, Br). The N,N'-bis(ferrocenylmethyl)imidazolinium tetrafluoroborate (6) was obtained in two steps from compound (2). The first step involves the synthesis of N,N'-bis(ferrocenylmethyl)imidazolidine (5) by condensation of (2) with aqueous formaldehyde. Compound (5) was successfully converted to the N,N'-bis(ferrocenylmethyl)imidazolinium tetrafluoroborate (6) by treatment with tritylium tetrafluoroborate. The new compounds were characterized by H-1 and C-13 NMR, IR and elemental analysis techniques which support the proposed structures. The X-ray crystal structure of the N,N'-bis(ferrocenylmethyl)imidazolidine (5) shows two ferrocenyl moieties bridged by an imidazolidine ring. The electrochemical properties were determined by cyclic voltammetry for all compounds. The compounds were screened for their in vitro antimicrobial activities against the Gram-positive, Gram-negative bacteria and antifungal activity against a Candida albicans. (3), (4), (6) show significant antimicrobial activity and theirs MIC values ranged from 169 to 520 mu g/mL. (C) 2014 Elsevier B.V. All rights reserved.