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    A comparative study for lipase immobilization onto alginate based composite electrospun nanofibers with effective and enhanced stability
    (Elsevier, 2017) Dogac, Yasemin Ispirli; Deveci, Ilyas; Mercimek, Bedrettin; Teke, Mustafa
    In this study, lipase was successfully immobilized on polyvinyl alcohol/alginate and polyethylene oxide/alginate nanofibers that were prepared by electrospinning. Results showed that nanofibers (especially polyvinyl alcohol/alginate) enhanced the stability properties of lipase. When the free lipase lost its all activity after 40-60 min at high temperatures, both lipase immobilized nanofibers kept almost 65-70% activity at the same time. The lipase immobilized poly vinyl alcohol/alginate and polyethylene oxide/alginate nanofibers protected approximately all of their activities until pH 9. Lipase immobilized polyvinyl alcohol/alginate and polyethylene oxide/alginate nanofibers maintained 60% of their activities after 14 and 7 reuses, respectively. The morphology of nanofibers was characterized by Scanning Electron Microscope, Fourier Transform Infrared Spectroscopy and Thermal Gravimetric Analyzer. As a result, this nanofiber production method, electrospinning, is simple, versatile and economical for preparing appropriate carrier to immobilize the enzymes. (C) 2016 Elsevier B.V. All rights reserved.
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    Performance of SiO2/Ag Core/Shell particles in sonocatalalytic degradation of Rhodamine B
    (Elsevier Science Bv, 2019) Deveci, Ilyas; Mercimek, Bedrettin
    In this study, SiO2/Ag Core/Shell nanoparticles was prepared and sonocatalytic activity of prepared catalyst was investigated by using Rhodamine B as model contaminant, at 35 kHz using ultrasonic power of 160 W within 90 min. The change in efficiency in the sonocatalytic degradation of Rhodamine B catalyzed by SiO2/Ag Core/Shell nanoparticles with respect to the initial concentration of dye, catalyst amount and temperature were firstly investigated. Optimal conditions were found as follows: catalyst amount = 15 mg/L, Temperature = 25 degrees C and initial concentration of dye = 10 ppm. Influence factors such as pH of solution, O-2 saturation of solution and the concentration of H2O2 added to the solution, on degradation efficiency in presence of catalyst, were investigated. SiO2/Ag Core/Shell nanoparticles showed higher sonocatalytic activity at pH = 7 with respect to acidic and alkaline conditions. Degradation efficiency was reached up to 67% in experiments which air pumped (0.6 L/min) through the solution with in 90 min. It was observed that the dye removal increased via increase while H2O2 concentration lower than 10 mM. Higher concentration of H2O2 than the optimal concentration had adverse effect on degradation efficiency. Our results showed that the SiO2/Ag Core/Shell nanoparticles were active catalyst for sonocatalytic degradation of dyes. Reusability of the catalyst was investigated.
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    Refractory-Metal-Based Chalcogenides for Energy
    (Wiley-V C H Verlag Gmbh, 2022) Ozel, Faruk; Arkan, Emre; Coskun, Halime; Deveci, Ilyas; Yildirim, Murat; Yildirim, Mehmet; Orak, Ikram
    When it is asked, where can refractory metals be used?, the possible shortest answer is, where cannot they be used? The uses of refractory-metal-based compounds in research and industry are too many to be enumerated; nevertheless, some outstanding examples are briefly mentioned here. Essentially, chalcogenide forms of refractory metals are preferred in the fabrication of high-performance structures. Therefore, expanding the current studies that usually focus on tungsten- and molybdenum-based structures to other materials may open new opportunities. Moreover, research on ternary and quaternary structures can also be a keystone in creating high-performance products. The rationale of the present review is to give a brief overview of the recent history of refractory-metal-based chalcogenides (RMCs). Initially, the framework is confined to the general design and approaches for the synthesis of refractory metal chalcogenides. The assay is continued by extending with characteristic features of materials from crystalline properties to thermoelectric attributes and examining device fabrication processes. Taken together, the device fabrication part where RMCs are mainly used is extensively focused upon. Finally, outlook and future perspectives are given on the design and construction of RMCs to enable future inspiration and innovation.
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    Synthesis and Characterization of Chitosan/TiO2 Composite Beads for Improving Stability of Porcine Pancreatic Lipase
    (Humana Press Inc, 2015) Deveci, Ilyas; Dogac, Yasemin Ispirli; Teke, Mustafa; Mercimek, Bedrettin
    The purpose of the present work is improving stability properties of porcine pancreatic lipase (triacylglycerol lipase, E.C.3.1.1.3) by immobilization on chitosan/TiO2 composite beads. The immobilization parameters were initial enzyme concentration (0.5-2 mg/ml), adsorption time (5-25 min), and glutaraldehyde concentration (1-4 % v/v). The optimum temperature (20-60 A degrees C), optimum pH (3.0-10.0), kinetic parameters, thermal stability (4-70 A degrees C), pH stability (4.0-9.0), and reusability (9 times) were investigated for characterization of immobilized lipase system. The optimum temperatures of free and immobilized lipase were 30 A degrees C. The temperature profile of the immobilized lipase was spread over a large area. The optimum pH values for the free lipase and immobilized lipase were found to be 6.5 and 7.5, respectively. The thermal stability of immobilized lipase was evaluated, and it maintained 45 % activity at 70 A degrees C. But, at this temperature, soluble lipase protected only 15 % activity. Also, the structural characterization of chitosan/TiO2 composite beads was analyzed with scanning electron microscope (SEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and attenuated total reflection Fourier transform infrared spectroscopy analysis (ATR-FTIR). The significance of this study is improving of stability properties of lipase for the industrial usage especially production of biodiesel and dairy products.