Department of Chemical Engineering

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    DEVELOPMENT OF PLATINUM CONTAINING ELECTROCATALYSTS SUPPORTED ON HYBRID MATERIAL OF PEM FUEL CELL
    ( 2023-01-27) ALJANABI, Ahmed ; YAMAN, Şeniz Özalp ; DEVRİM, Yılser
    Increasing energy demand in the world has increased the need for alternative energy technologies. Fuel cells using hydrogen, an important alternative energy source, have attracted great interest in recent years. Among the fuel cell types, proton exchange membrane fuel cells (PEMFC) are the most interesting fuel cell type due to their modular structure, high efficiency and low operating temperatures. Particularly, component development studies attract attention to increase the performance of PEMFCs. In this thesis multiwalled carbon nanotube-graphene MWCNT-supported Pt catalysts are synthesized using the microwave-assisted approach to examine the method to investigate the PEMFC performance. MWCNT-supported platinum catalysts were prepared for PEMFC application by using [(NH4)2[Pt2(HPO4)4(H2O)2] (Ptcomplex-1) & [(NH4)2[Pt2(SO4)4(H2O)2] (Ptcomplex-2) complexes as starting materials. TGA, XRD, HR-TEM and XPS analyzes were applied to examine the microstructure and morphology of the catalysts. Among the prepared catalysts Ptcomplex-1/MWCNT-3 and Ptcomplex-2/MWCNT-3 catalysts were tested in PEMFC with H2/air at the range of 60- 80 °C. The maximum power density values were determined for a membrane electrode assembly (MEA) prepared using Ptcomplex-1/MWCNT-3 catalyst as 0.36, 0.39, 0.41, and 0.26 W/cm2 and 0.38, 0.423, 0.44 and 0.28 W/cm2 for Ptcomplex-2/MWCNT-3 catalyst at 60, 65, 70 and 80 ⁰C, respectively. It was determined that the prepared Ptcomplex/MWCNT catalysts showed a better PEMFC performance than that of the Pt/C catalyst. The performance of the catalysts can be further improved with MEA optimization studies to be carried out with the catalysts prepared in the future.
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    INVESTIGATION OF THE EFFECT OF SENESCENCE ON ANTIOXIDANT RESPONSES FOR MG-63 (HUMAN OSTEOSARCOMA) AND MC3T3-E1 (MOUSE PRE-OSTEOBLAST) CELL LINES
    ( 2023-02-01) AYAN, Fırat ; İŞGÖR, Sultan Belgin
    Aging and its effects have been revealed by many researchers, the effects of aging on living systems are still being investigated today. In this study, antioxidant enzyme responses of mouse osteosarcoma (MG-63) and mouse preosteoblast cells (MC3T3- E1) against aging, which are used in many scientific studies; Superoxide Dismutase Glutathione-S-Transferase (GST), Glutathione Peroxidase (GPx) and DPPH activities were investigated. In this study before performing the enzyme assays, the protein contents of the cells were found, and they were determined as 0.05 mg/mL for MG-63 young, 0.05 mg/mL for MG-63 young, 0.05 mg/mL for MC3T3-E1 young and 0.03 mg/mL for MC3T3-E1 young were found, respectively. Enzyme activities were analyzed comparatively for passages 10, 15, 20, 25, 30, 35, 40 and 45. As can be seen, GST, GPX activities are higher in senescent cancer cells. However, SOD activity was found to be higher in aging progenitor bone cells. In DPPH activity, senescent cancer cells were found to have the highest oxidant scavenging effect with 71.2%. On the other hand, both cell lines were stained with S-A-β-Galactosidase, and β-Galactosidase accumulations due to senescence were qualitatively investigated, and blue stain accumulation was found to be higher in aged osteosarcoma cells. Finally, cell kinetics were examined, and doubling times and specific growth rates were found for the old and young passages of both cell lines used. Doubling times of cells were found to be as respectively, 4.45 hours for MG-63 young, 2.48 hours for MG-63 young, 3.04 hours for MC3T3-E1 old and 3.30 hours for MC3T3-E1 young.
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    INFLUENCE OF SURFACE TREATMENTS OF FELDSPAR AND QUARTZ MINERALS TO ELASTOMERIC POLYURETHANE BASED COMPOSITES
    ( 2022-06-20) BOUZMANE, Hajar ; TİRKEŞ, Seha ; TAYFUN, Ümit
    In this thesis study, surface treatment routes including silane modifications were applied to quartz and feldspar minerals (purchased from Eczacıbaşı Esan, Istanbul, Türkiye) to achieve a compatible mineral surface with the polymer matrix. Surface characteristics of minerals were examined using chemical analysis and surface functionality by Fourier transformed infrared spectroscopy (FTIR) method. Thermoplastic polyurethane-TPU (supplied by Ravago Petrochemicals, Izmir, Türkiye) was compounded with pristine and modified minerals by melt-blending technique. TPU-based composites were fabricated at a constant adding amount of 10% by weight for each additive. The dogbone-shaped test samples were prepared using an injection molding process. Mechanical, thermo-mechanical, melt-flow, and morphological characterizations of TPU and composites were performed by tensile and Shore hardness tests, dynamic mechanical analysis (DMA), melt flow index (MFI) measurements, and scanning electron microscopy (SEM), respectively. Effects of surface treatments were discussed comparing the findings of composites filled with pristine and modified minerals with the help of test data.
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    SYNTHESIS, CHARACTERIZATION AND INVESTIGATIONS OF THERMAL BEHAVIOR OF THE NITRO-IMIDAZOLE-BASED ENERGETIC COORDINATION COMPOUNDS
    ( 2022-06-16) YAMAN, Vahide Selen ; ÖZALP YAMAN, Şeniz ; EKİNCİ MACHIN, Nesrin
    Energetic materials produced in various structures have different applications both in the military as explosives and in the civilian field as propellant and pyrotechnics. However, due to the adverse effects of these materials on the environment and health as well as their high sensitivity to light and friction, it is desired to replace them with environmentally friendly, toxic metal-free and easy-handling alternatives. The main aim of this study is to synthesize and explore the performance of novel energetic organic and coordination compounds. In this scope, 5-(chloro(nitro)methyl)-4-nitro 1H-imizadole (HL) and its sodium (NaL) and ammonium (NH4L) salts were designed and synthesized as a first time. Next, totally 34 cobalt(II/III), copper(II), iron(II/III) and zinc(II) complexes containing 5-(chloro(nitro)methyl)-4-nitro-1H-imizadole were designed in octahedral and tetrahedral structures, [M(NH3)x(L)y] n [x:0, 2-4; y:1, 2, 4 or 6; n:(+1)-(-4)]. However, only 26 of these complexes could be synthesized successfully and characterized via various spectroscopic techniques (HRMS, NMR, FTIR). Especially, 6 L coordinated cobalt(II)/III) and iron(II)/III) complexes were found to be unstable due to the steric effect as it was also indicated by their optimized geometry calculations carried out as a part of the TUBITAK Project 117Z391 [1]. Thermo-gravimetric and differential thermal analyses (TGA-DSC) of these newly generated energetic coordination compounds were achieved and their thermal stability, thermal decomposition characteristics and kinetic parameters were determined to explore their potential to be used as an energetic material. The simultaneous TGA-DSC curves pointed out the similar decomposition processes with the high thermal stability within the range of 25-1200 oC for all the studied complexes. Among all these compounds; HL, NaL, NH4L and only five of the metal complexes showed exothermic behavior at around 800-1100 oC. It was observed that the exothermic decomposition temperature of the HL and its salts moved from 800 oC to 1100 oC upon coordination to the metal ions. It was very suprising that solely Co(II), Fe(II) and Cu(II) complexes including one or two L showed an exothermic character. Impact and friction sensitivity tests applied to the most promising two energetic compounds, [Co(NH3)4(L)2] and [Fe(NH3)4(L)2], revealed that these complexes were very resistant to impact and insensitive to friction. The agreement between the desired energy and sensitivity results indicated that our complexes can be applied as propellants in rocket systems and as additives in small amounts to modify the ballistic properties of propellants.
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    SYNTHESIS OF CHEMILUMINESCENT COMPOUNDS AND THEIR USAGE IN METAL ION RECOGNITION AND BLOOD DETECTION
    ( 2022-06-13) BALCI, BURCU ; Cihaner, Atilla
    Luminescent compounds have gained great importance recently due to their wide application areas. In addition, chemiluminescent compounds have been used for many studies in analytical chemistry due to their high luminescence sensitivity. In this thesis, a new series of chemiluminescent compounds, namely 5,8-di(furan-2-yl)-2,3- dihydrophthalazine-1,4-dione (F2B-Lum), 5,8-di(selenophene-2-yl)-2,3- dihydrophthalazine-1,4-dione (S2B-Lum) and 5,7-di(selenophen-2-yl)-2,3- dihydrothieno[3,4-d] pyridazine-1,4-dione (S2T-Lum), was synthesized via electron donor-acceptor-donor approach. Their structures were confirmed by using NMR, FTIR and HRMS techniques. Then, the chemiluminescence reactions of compounds with hydrogen peroxide in an alkaline solution (0.1 M NaOH(aq)) in the presence of different metal ions, hemin and blood samples were investigated and the results were compared with luminol. As expected, the compounds were sensitive to copper(II), iron(III) ions and blood. It can be easily concluded that the corresponding compounds as new derivatives of luminol are potential candidates for the detection of blood findings in forensic science. In addition, the sensitivity of the compounds to copper(II) ion makes them usable for copper ion recognition in analytical applications. Furthermore, cyclic voltammetry technique was used to investigate the redox behaviors of the compounds and they exhibited irreversible oxidation peaks. Also, reactive oxygen species can be detected by using these compounds via square wave potential method by applying an external potential of -1.05 V. Finally, among the compounds, S2T-Lum was successfully polymerized electrochemically. The corresponding polymer PS2T-Lum can be a precious member of luminol type polymers since it is electroactive and bears chemiluminescent active appendages in its polymeric structure.