Doktora Tezleri

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Adsorption of reformer off-gas on NaX zeolite and metal organic framework (mil53(AI)): Equilibria and kinetics
(Izmir Institute of Technology, 2013) Güneş Yerkesikli, Alev; Çakicioğlu Özkan, Seher Fehime
Synthetic gas produced from steam methane reforming (SMR off -gas) is a mixture of H2, CO, CO2, and CH4 can be used in fuel cell after purification. In this study adsorption as a purification tool was used to obtain high H2 content of gas mixture from SMR off gas. Zeolites and metal organic framework were used as an adsorbent. CO2 equilibrium studies on K rich NaX zeolites, prepared with ultrasonic and traditional methods, and metal organic framework MIL53 (Al) shows high adsorption on zeolites than MIL53(Al) up to 1 atm. K rich zeolites give lower adsorption than NaX zeolite. Adsorption isotherms obtained for MIL53 (Al) is linear ( favorable for zeolites). This makes MIL53(Al) is an promising adsorbent for high pressure application. Adsorption equilibrium at 5 atm shows that NaX zeolite is good adsorbent for the SMR off gas with the following orders: CO2>CH4>CO> H2. Kinetics of SMR off gas in MIL 53 (Al) were studied by using Zero Length Column (ZLC) method. The results show that the calculated diffusivities are strongly dependent on temperature but weakly dependent on purge flow rate. The study reveals that transport is controlled by intracrystalline diffusion. The activation energy on diffusion are nearly same (about 41 kJ/mol) and not change with respect to kinetic diameter of SMR off gases. Heat of SMR off gas adsorption on MIL53(Al) obtained from Henry’s constant shows that adsorption is exothermic. The study shows that the ZLC method is an effective tool to investigate the diffusion kinetics of SMR off-gas gases in MIL53(Al).
Adsorptive characteristics of aflatoxin B1 in the presence of purified clinoptilolite rich mineral and lactobacillus plantarum S2
(Izmir Institute of Technology, 2012) Bulut Albayrak, Çisem; Ülkü, Semra
The human diet contains a wide variety of natural carcinogens. Aflatoxin B1 (afB1) is the most toxic and most prevalent compound. Both probiotic lactic acid bacteria and clinoptilolite rich zeolite mineral have potential to eliminate this toxin. This study was planned in order to investigate adsorptive characteristics of afB1 by local purified clinoptilolite rich mineral (PNZ) and probiotic strains which were isolated from different natural sources (fermented cabbage, boza ) in the present work. PNZ and isolated strains were characterized by using several physical, chemical and biological techniques. Adsorption characteristics of both probiotic lactobacilli and PNZ were investigated in simulated gastrointestinal solutions. The chosen probiotic strain was identified as L. plantarum .The studies indicated that, both L. plantarum S2 and PNZ can eliminate afB1 in the phosphate buffer solution. They are more effective when they were used together (45% for L. plantarum S2, 32% for PNZ, 86%for L. plantarum S2 and PNZ together). AfB1 adsorption equilibrium data were best represented by Sips isotherm model for PNZ, whereas by Langmuir isotherm model for L. plantarum S2. Thermodynamic studies implied that afB1 adsorption by mineral and L. plantarum S2 was physical adsorption. Experiments with different temperatures showed that afB1 adsorption by PNZ was exothermic but afB1 adsorption by lactobacilli was endothermic. Adsorption kinetics were analysed by diffusional models and reaction models for afB1 adsorption by PNZ mineral. Both film diffusion and /or intra particle diffusion were effective on adsorption kinetics depending on the experimental conditions (Temperature, pH, agitation speed, etc).
Biofuels and biochemicals production from microalgae over solid catalysts
(Izmir Institute of Technology, 2020-07) Deliismail, Özgün; Şeker, Erol
The target of this study was the investigation of biofuel and/or biochemical production from microalgae in growth medium or its lipids over heterogenous catalyst. The primary aim was to study the conversion of 6 wt. % N. Oculata into biofuels without harvesting and dewatering over Ni-Al2O3-SiO2 catalyst at 80oC and 1 atm for 24 h. Solgel method was used to synthesize the catalyst by using the acids of H2SO4, HCl, and HNO3 to investigate the effect of acid type on catalytic activity. The catalyst prepared with H2SO4 yielded the highest conversion. The treatment of the catalyst prepared by H2SO4, with NaCl increased the conversion from 74 % to 91.5 % under same reaction conditions. The products included poly- or monosaccharides, esters and fatty acids. To achieve this conversion, Ni presence was significant beside total acidity of 25 µmol per gram of catalyst, and acidic strength ranging between 130-380oC. A new industrial application was proposed for direct conversion of 6 wt. % N. Oculata into biofuels at 80oC and 1 atm. The capacity of the plant was 1669 liters biofuel per year from 1064 liters microalgae solution per hour. The catalyst prepared with H2SO4 was used to coat either inner surface of tubes or 1-meter pluggable monoliths in tubular reactor having 20 m length and 1000 tubes each of which had 4 cm diameter. The microalgae solution was heated with Therminol®66 heated via parabolic troughs. For operation continuity, ~46000 kg of oil was stored in the tank at 120 o C for 12 h. The production of ethyl ester biodiesel from Spirulina sp. and N. Oculata lipids over 60 % CaO/Al2O3 was studied at 50oC and 1 atm. Ethanol: lipid molar ratio, catalyst amount and reaction time were investigated parameters to identify their effects on catalytic activity. The study showed that ~59 % biodiesel yield was obtained in the presence of the catalyst which was 6 wt. % of lipids, in 30 min. at ethanol: lipid molar ratio of 12 while 90 %-99 % yield was acquired at ethanol: lipid molar ratios of 24 and 48. To achieve these yields, weak basic strength in the form of bicarbonate was necessary while high basicity was not essential. Pure alumina and CaO did not yield any lipid conversion. Glycerolysis of triacylglycerol took place in series with reverse transesterification of triacylglycerol at catalyst amount which was 6 wt. % of lipids, ethanol: lipid molar ratio of 24 and 48, and 60 min. reaction time.
Catalytic conversion of glucose to alkyl glucosides
(Izmir Institute of Technology, 2020-06) Mutlu, Vahide Nuran; Yılmaz, Selahattin
In this study, it was pursued to develop acidic mesoporous catalysts for the synthesis of octyl glucosides. Butyl glucoside synthesis was used for catalyst screening. Tungstophosphoric acid (TPA) incorporated mesoporous silica (TPA-SBA-15), sulfated La incorporated titania-silica (SO4/La-TiO2-SiO2), organosulfonic acid functionalized mesoporous silica (Propyl-SO3-SBA-15), and sulfated mesoporous carbon (SO4/CMK-3) catalysts were prepared for this purpose. The effects of the active species (sulfates, tungstophosphoric acid and organosulfonic acid) and promoter (La) on the catalyst properties and activity were investigated. All the catalysts had mesoporous structure and high surface area. The acidity and acid site character varied depending on the catalyst type and amount of the active sites. La promoter was found effective to enhance the sulfation performance and to improve the stability of sulfates. The TPA-SBA-15 catalysts provided high glucose conversions (over 99%) and butyl glucoside yields (over 95%) due to their acidity, Keggin ion structure and pore size. The SO4/La-TiO2-SiO2 catalysts and SO4/CMK-3 catalysts were also active with glucose conversions of 74.4 % and 70 % respectively. The reaction parameters such as the reaction temperature (117 and 100 oC) and catalyst amount (20 and 30 wt% wrt. glucose) were studied in butyl glucoside synthesis over TPA-SBA-15 and SO4/La-TiO2-SiO2 which were the most active catalysts. These catalysts were found to be reusable in glycosidation with 1-butanol. Octyl glucoside synthesis was carried out via direct glycosidation. The octyl glucoside yields obtained over TPA-SBA-15 and SO4/La-TiO2-SiO2 catalysts were above 55 % and 43 % respectively. The catalysts were found promising for further investigations.
Cr (VI) removal with natural, surfactant modified and bacteria loaded zeolites
(Izmir Institute of Technology, 2011) Cansever Erdoğan, Beyhan; Ülkü, Ayşe Semra
The objective of the study is to determine the bacteria removal performances of the local clinoptilolite rich mineral and its surfactant modified forms and to investigate potential applications of clinoptilolite rich mineral, surfactant modified clinoptilolite rich mineral and bacteria loaded forms in Cr (VI) sorption. Characterizations of clinoptilolite rich mineral and its modified forms were studied. Batch sorption experiments were performed and the effects of the parameters such as pH, initial concentration, agitation speed, particle size and temperature were investigated. Sorption kinetic data were analysed by external mass transfer, intraparticle diffusion, pseudo first and second order models. Intraparticle diffusion model results indicated that sorption of Cr (VI) on the sorbents was a multi-step process, involving external and intraparticle diffusion. Effective diffusion coefficient results implied that Cr (VI) sorption process was not solely intraparticle diffusion controlled and external film diffusion was also effective. Biot number (100-3000) results indicated that Cr (VI) sorption process was mainly controlled by intraparticle diffusion. The sorption reaction model results revealed that sorption of Cr (VI) onto sorbents was well represented by the pseudo-second order kinetic model. Sorption isotherm model results indicated that the Langmuir isotherm fitted well with the experimental data. Thermodynamic analysis, Gibbs energy change (<-20 kJ/mol), entropy change of sorption (<-0.2 kJ/mol K), enthalpy change (<-100kJ/mol) and activation energy (<40 kJ/mol) showed that sorption process was exothermic, spontaneous and physical sorption.
Development of a novel hybrid process for the conversion of cellulose into high-value chemicals by applying voltage in hot compressed water
(Izmir Institute of Technology, 2017-07) Akın, Okan; Yüksel Özşen, Aslı
In this study, a novel hybrid method of hydrothermal electrolysis implemented for the decomposition of microcrystalline cellulose (MCC) into high value added chemicals such as levulinic acid, 5-hydroxymethylfurfural (5-HMF), and furfural. The hypothesis of the study was that, when direct current (DC) is applied the formation of ionic and radical species can alter the hydrolysis of cellulose. Based on this hypothesis, the purpose of the study was to build an integrated method of hydrothermal electrolysis that can lower energy requirement of cellulose hydrolysis by altering the selectivity. In order to investigate the individual and coupled effect of operating parameters such as reaction temperature (170-200 ℃), time (30-120 min.), electrolyte concentration (1-50 mM H2SO4), constant current (0-2 A), statistical analysis was conducted by a fractional factorial design. Analysis of variance (ANOVA) test was applied to the main hydrolysis products yields of MCC, total organic carbon (TOC) and cellulose conversion. Based on the response surface plots, 1A of current at 200 ºC maximized TOC yield and cellulose conversions to 62% and 81%, respectively. In order to enhance the selectivity, constant voltage (2.5, 4.0 and 8.0 V) was applied at 200℃. Application of 2.5 V increased TOC (54%) and alter the selectivity of 5-HMF (30%) and levulinic acid (21%). The structural changes in solid residues were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and found that MCC particles functionalized by carboxylic acid and sulfonated groups by application of 2.5 V. Therefore, change in the selectivity values were conducted with the functionalization of MCC particles due to applied voltage under sub-critical conditions.
Development of a plasmonic biosensor for detection of exosomes
(Izmir Institute of Technology, 2020-07) Taykoz, Damla; Bulmuş Zareie, Esma Volga; Tekin, Hüseyin Cumhur
The aim of this work was to develop Localized Surface Plasmon Resonance (LSPR) surfaces for quantitative detection of exosomes from different sources. For this aim, gold nanorods (AuNRs) with a mean diameter of 40 nm with an aspect ratio of 2.9 were first synthesized and characterized. The self-assembly of AuNRs on glass wafers were optimized through several experiments. In parallel, PEGylation of cetrimonium bromide (CTAB) stabilized AuNRs was investigated using PEGs with three different molecular weights via LSPR, zeta potential and XPS techniques. PEGylated AuNRs were further self-assembled on silanized microscope slides as confirmed. Surface functionalization of AuNR patterned slides was performed using alkane thiol molecules having carboxylic acid and hydroxyl functional groups and confirmed via XPS, FTIR and zeta potential. Specific antibodies (Ab) were conjugated to the surface following two different methods, i.e. click and NHS/EDC chemistry. To perform click chemistry strategy, ImmuneLink® molecules were conjugated with Abs and the final conjugate was used to functionalize surfaces prepared beforehand using azide bearing molecules. The functionalization procedure was confirmed via XPS FTIR and LSPR spectroscopy. The orientation of the antibodies on the AuNRs patterned surfaces was investigated with LSPR in comparison with conventional EDC/NHS chemistry. The click-chemistry strategy proved to provide conjugation of antibodies through their Fc regions exposing Fab regions better for antigen recognition. Finally, surfaces functionalized with a variety of antibodies were used to detect first a pregnancy-associated protein, PLAP, and then exosomes obtained from human semen samples with pre-determined exosome concentrations. The LoD of the biosensor surfaces was found to be between 103-104 exosomes/mL and 5 ng/mL (0.3 pM) PLAP. Human breast cancer cell culture samples having an unknown concentration of exosomes were further analyzed using the newly developed LSPR biochips and the exosome concentration was determined as 108 exosomes/mL for MCF-7 cell line and 107 exosomes/mL for MDA-MB-231 cell line.
Development of antifouling nanofiltration and antibiofouling ultrafiltration polymeric membranes using facile protocols
(Izmir Institute of Technology, 2021-07) Cihanoğlu, Aydın; Altınkaya, Sacide; Şeker, Erol; Izmir Institute of Technology
One of the major goals in membrane separation technology is to develop fouling-resistant membranes that can provide a long operating time and low operation costs. This thesis aims to manufacture fouling and biofouling-resistant polymeric nanofiltration (NF) and ultrafiltration (UF) membranes using unique approaches. The first approach was to change coagulation bath composition in the phase inversion technique for manufacturing fouling-resistant polyamide-imide (PAI) based NF and biofouling-resistant polysulfone (PSF)/sulfonated polyethersulfone (PSF-SPES) based UF membranes. To this end, hydrophilic branched polyethyleneimine (PEI) dissolved in the coagulation bath allowed the preparation of a positively charged PAI based NF membrane by forming a covalent bond with the imide group in the PAI. To manufacture antibacterial UF membranes, a strong antibacterial surfactant, cetyltrimethylammonium bromide (CTAB), was dissolved in the coagulation bath and made an electrostatic interaction with SPES at the polymer/bath interface during phase inversion. Both membranes were prepared in a one-step process without using any pore formers in the casting solution. The second approach used in the thesis focused on modification of commercial polyethersulfone (PES) UF membranes with co-deposition of dopamine and CTAB molecules to impart antibiofouling behavior without compromising the pore size and pure water flux of the support. To achieve this task, during modification, an inert physical barrier was created inside the membrane pores by continuously feeding nitrogen gas (N2) from the backside of the support to prevent pore penetration. In the last approach, ultrasound as a green, controllable trigger was used for modifying PSF and PSF-SPES UF membranes with dopamine. The main purpose of using ultrasound was to accelerate the polymerization kinetics of dopamine, hence shortening the modification time.
Development of chitosan based biofoams
(Izmir Institute of Technology, 2020-07) Olcay Kurt, Aybike Nil; Polat, Mehmet; Polat, Hürriyet
Chitosan is a preferred bio-foam material used in many research fields such as tissue engineering and drug delivery due to its unique structural features (wide pH stability, nontoxic-biocompatible-biodegradable, anti-inflammatory, antimicrobial). However, chitosan foams are mechanically too weak to maintain the desired shape until newly formed tissue natures. A wound infection and serious tissue necrosis, endanger human's lives. So, a dressing is required to protect loss of fluids and proteins from the wound area and prevents any bacterial invasion replacing the function of skin temporarily. Therefore controlled drug release from a wound dressing is necessary with a biocompatibility and enough mechanical strength. The aim of this study was the synthesis of mechanically durable - dual porosity chitosan bio-foams to provide a controlled drug release. For this purpose, oil droplets formed in a chitosan solution were used as templates to produce micropores that also contain vancomycin (a model antibiotic-hydrophylic) and curcumin (a model anti-inflammatory-hydrophobic) in the walls of the chitosan matrix with large structural voids. An anionic surfactant, sodium dodecyl sulfate (SDS) alone, was used as a crosslinking agent which was a new approach. Then the structures were characterized by SEM, FTIR, mechanical tests and BET analysis. The chitosan foams have dual pore structures. 1) The intrinsic micro pores that the walls of chitosan matrix have with different morphology that depends on the oil phase. 2) The structural voids that the chitosan matrix have, present even in the absence of an oil phase that depends on the experimental conditions. The mechanical strength of the foams were found to be much higher (up to 250 kPa) compare to the foams produced in literature and suggested to be suitable to use for wound dressing applications. The drug release mechanism of foams were found to depend on the conditions used for foam development and the released kinetics were presented with a mathematical model.
Development of innovative polymeric membranes using green approaches for water and energy sustainability
(01. Izmir Institute of Technology, 2022-12) Güngörmüş Deliismail, Elif; Altınkaya, Sacide
In this thesis, innovative polymeric membranes with fast, simple, and easily scalable manufacturing procedures were developed to demonstrate the potential of membrane technology in making chemical processes more sustainable. In this scope, firstly, it was focused on minimizing the adverse chemical, environmental, and economic effects of conventional drying processes by integrating membrane technology into the production of nano/microparticles. Acid-resistant polyaniline based ultrafiltration (UF) membrane and solvent-resistant poly (ether imide sulfone) based UF membrane were developed to produce aluminum sulfate powder and silica powder, respectively. The developed high-performance and antifouling membranes made the production of powders more sustainable and environmentally friendly by enabling the recovery of the acid/solvent used in the synthesis and the reduction of energy consumption for drying. The third part of the thesis focused on biodiesel production with a high-performance, antifouling, alumina-calcium oxide catalyst-modified polyethersulfone UF membrane. Combining membrane technology with reaction engineering allowed for the elimination of the catalyst recovery step, shortened the reaction time to reach a desirable yield, and reduced energy consumption, resulting in more sustainable biodiesel production than existing production techniques. In the last part of the thesis, a high-performance, antibiofouling/antibacterial citric acid doped polyaniline based UF membrane was developed. Ensuring sustainability improvement in membrane production in all applications was the main objective of this thesis. By reducing the number of steps in membrane production, the amount of wastewater generated, and toxic waste released during membrane production was minimized, and energy consumption was significantly reduced.
DNA adsorption on silica, alumina and hydroxyapatite and imaging of dna by atomic force microscopy
(Izmir Institute of Technology, 2013) Yetgin, Senem; Balköse, Devrim
The scope of the study is to investigate calf thymus DNA adsorption process on solid powders such as silica, alumina and hydroxyapatite (HAP) to improve DNA solid phase extraction efficiency and to visiulize DNA adsorption by atomic force microscopy (AFM). The equilibrium and kinetics of the DNA adsorption were investigated in batch adsorption on a commercial silica gel and a synthesized silica aerogel, commercial alumina and HAP powders from aqueous DNA solution. Commercial DNA extraction kit adsorbents were also characterized and used for adsorption. Adsorbed DNA was imaged in ambient air on flat surfaces of mica, silica and alumina wafers and HAP particles coated glass surfaces and a HAP pellet surface by AFM. Effects of ambient air, nitrogen flow and freeze drying methods on DNA morphology on the releted surfaces were also investigated. Adsorption of DNA on silica, alumina and HAP increased with the decrease of pH from 9.0 to 2.0. Enhancements of the adsorption capacities of adsorbents were obtained with the addition of MgCl2. It was found that the Van der Waals and the hydrogen bonds rather than the surface charge were the cause of the adsorption. The adsorption isotherms of DNA on silica, alumina and HAP were fitted to Langmuir model in pH range 2-9. The adsorption kinetics obeyed pseudo second order model. The sharpest image of DNA by AFM was obtained by freeze drying method on alumina surface. Dispersed DNA in water was adsorbed on the surfaces not as single molecules but as supercoils consisting of many molecules.
Effect of colloidal interactions in the forming of lead magnesium niobate ceramics
(Izmir Institute of Technology, 2007) Deliormanlı, Aylin Müyesser; Polat, Mehmet
Electrokinetic properties of lead magnesium niobate (PMN) powders in liquid medium are investigated in this thesis. Isoelectric point of aqueous PMN suspensions was determined as a function of solids concentration. Dissolution character of both Pb+2 and Mg+2 cations in PMN structure were examined as a function of pH. Poly(acrylic acid)-poly(ethylene) oxide PAA/PEO comb polymers were tested as the novel dispersant in this system and their effect on the stability and flow behavior of aqueous PMN suspensions was investigated. Stability and flow behavior were mainly studied by rheological measurements and sedimentation experiments as a function of pH and polyelectrolyte concentration. Adsorption of comb polymers onto PMN surface and their effect on the powder dissolution were also investigated. Results indicated that the PAA/PEO comb polymers impart stability to PMN suspensions over a wide pH range and ionic strength where pure PAA fails. In the course of this study PMN powders were consolidated using two different wet shaping methods. First, PMN films were produced using aqueous tape casting method which is widely used in the manufacture of multilayer ceramic capacitors. Secondly, three-dimensional PMN lattices were produced using robocasting method. In the former case, the goal was to provide alternative recipes for the aqueous tape casting process to be utilized in industrial applications since the current technology is based on the organic solvent based techniques. Results showed that it was possible to produce high quality PMN films with thicknesses in the range of 10 to 250 .m using aqueous based tape casting process. In the latter case, the results showed that robocasting is a suitable technique for the preparation of three dimensional PMN ceramics. Based on these results overall conclusion and the contribution of this study can be summarized as follows: The work carried out gives new insights into the manufacturing of PMN based ceramics using aqueous based techniques. Such improvements may bring benefits in the manufacturing of smaller electronic components employed in the personal computers and mobile phones and other consumer products in the near future.
The effect of microwaves on ion exchange in zeolites
(Izmir Institute of Technology, 2009) Akdeniz, Yelda; Ülkü, Semra
Recent innovations of microwave field lead many scientists to focus on this phenomenon and it has been begun to be applied in different fields of zeolite applications. The purpose of this study is to determine the effect of microwave irradiation on ion exchange degree and on the structure of natural zeolite. The clinoptilolite rich mineral from Western Anatolia was used throughout the experiments. The ion exchange experiments were performed using AgNO3, Co.(NO3)26H2O and Cu (NO3)25/2H2O within 0.01M - 1M and 40 oC - 80 oC concentration and temperature range in conventional waterbath and microwave. Different solid and solution conditions on ion exchange degree were determined, as well. Metal exchanged minerals were characterized by using instrumental techniques. Antibacterial activity of the Agexchanged clinoptilolite against E. coli was determined by Kirby.Bauer method. The Ag +, Co2+ and Cu2+ amounts within the mineral increased with decreasing S/L while increased with increasing temperature and time. For some utilized parameters microwave treatment was effective however on the whole it did not significantly improved the degree of ion exchange compared to waterbath treatment. The inspection of XRD patterns and FTIR spectra of metal exchanged minerals confirmed that no transition of clinoptilolite phase and no shifts in peak positions occurred with exchange methods applied. The sorption processes are controlled mainly by external-phase mass transfer. Ag+, Co2+ and Cu2+ sorptions on NaCLI exhibited a good fit to Freundlich model and Langmuir models. All metal exchanged minerals showed considerable superiority against E.Coli.
Electrochemical and oxygen/water permeation behavior of fluorinated siloxane copolymers synthesized via initiated chemical vapor deposition
(Izmir Institute of Technology, 2021-12) Cihanoğlu, Gizem; Ebil, Özgenç; Izmir Institute of Technology
Metal-air batteries are considered as one of the best alternatives to current Li-ion batteries with their high energy densities (1000-13000 Wh/kg) also, they are lightweight, cheap, and safe. However, secondary alkaline metal-air batteries suffer from catalyst corrosion, anode passivation and corrosion, electrolyte loss, and pore-clogging leading to performance loss and reduced cycle life. This thesis aims to evaluate the feasibility of highly cross-linked, hydrophobic, and oxygen selective thin homopolymers and copolymers films as potential candidates for Gas Diffusion Layer (GDL) materials in Gas Diffusion Electrodes (GDEs) for alkaline metal-air batteries. Homopolymers of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2-(perfluorohexyl)ethyl acrylate (PFHEA) and 2-(perfluoroalkyl)ethylmethacrylate (PFEMA) and their copolymers were synthesized via initiated chemical vapor deposition (iCVD). iCVD deposited fluoropolymer thin films exhibited low water transmission rates and excellent oxygen diffusion with a high oxygen/water selectivity up to 13.6. GDEs with iCVD GDLs exhibited higher oxygen reduction current density (228.2 mA cm-2) when compared to commercial counterparts (132.7 mA cm-2). In addition, the chemical stability, durability and corrosion protection aspects of these films were investigated by substrate adhesion and immersion tests in organic solvents and NaCl solution. The results of the corrosion test together with chemical stability and durability evaluation indicate that iCVD deposited copolymers exhibit excellent adhesion, good solvent resistance and offer effective physical and chemical protection without the need for surface pretreatment. iCVD copolymer films provide better anti-corrosion barriers with lower corrosion efficiency (85-99 %) for metal surfaces compared to homopolymer counterparts. By combining siloxane and fluorinated matrix, the copolymer films provide enhanced oxygen transport and reduce moisture entrance significantly as a GDLs and also improve physical, chemical, corrosion protection.
Enhancement of thermal, electrical and optical properties of zinc oxide filled polymer matrix nano composites
(Izmir Institute of Technology, 2009) Özmıhçı, Filiz; Balköse, Devrim
The purpose of this study is to enhance the electrical, thermal and optical properties of polyethylene and polypropylene by the addition of zinc oxide (ZnO) filler.Embedding ZnO in a polymeric matrix could make an economic, weight saving, chemically resistive, optical, flexible and conductive materials which possesses the properties of zinc oxide.Composites with higher electrical and thermal conductivity having luminescence properties were prepared using commercial and hydrothermally synthesized ZnO powders with different particle size and conductivity. Effect of ZnO loading and surface treatment on composite properties was investigated. Luminescence effects in green and blue regions were detected in all powders due to the defects on the structure of ZnO.The powders were found to be moderately conductive materials, as well. Un-homogenously dispersed composites were prepared using rheomixer since especially nano powders tended to be agglomerated in the composite. On the other hand, different surface properties of powder and polymer caused adhesion and wetting problems. Microvoids were detected in the interphase, as well.Composites can be used as an electrostatic dissipation and moderate electrical conductive applications in the field of electrical conductivity, as a heat sink in the field of thermal conductivity and as a solid state lamp due to luminescence properties. Stiffness of the composites was very high compared to neat polymer and can be properly used as an engineering material.
Enhancement of tribological properties of mineral oil by addition of sorbitan monostearate and borate
(Izmir Institute of Technology, 2010) Atakul Savrık, Sevdiye; Çiftçioğlu, Muhsin
The development of modern automobile and engine industries requires lubricants that can withstand high temperatures and pressures. Recent advances made in the chemistry provide the use of inorganic particles as lubricant additives. Therefore inorganic boron-based additives have been the focus of much attention, as they posses a good combination of properties, such as wear resistance, friction-reducing ability. In this study, the state of art in the field of inorganic particle, zinc borate synthesis and its employment in tribology were investigated. The synthesis of zinc borate was achieved not just by precipitation, but also production methods such as inverse emulsions. The products were characterized by SEM, FTIR, TGA, DSC, EDX. In lubrication part, the friction reducing and antiwear ability of the particles as an additive in the mineral oil was focused. Sorbitan monostearate was used to cover the surfaces of inorganic particles in order to provide better dispersion of additives in the oil. Friction and wear behavior of the lubricants were measured by four-ball wear test machine. The effects of dispersing agent, zinc borate type as well as surfactant concentration on the tribological properties of the lubricants were investigated. Sorbitan monostearate not only outperformed as a dispersing agent of inorganic particles, but also it proved to be an efficient antiwear agent. The lowest wear scar diameter was obtained by the lubricant containing zinc borate synthesized via coordination precipitation method. The addition of this sample with the surfactant in the oil reduced the wear scar diameter from 1.402 mm to 0.550 mm.
Enzymatic degradation of phthalic acid esters
(Izmir Institute of Technology, 2013) Baytak, Derya; Sofuoğlu, Sait Cemil
Endocrine disrupting compounds (EDCs) are environmental pollutants which interfere with the hormone system even at low concentrations resulting in adverse health effects on both human and wildlife. In this study, we aimed to investigate enzymatic degradation of diethylhexyl phthalate (DEHP) and diethyl phthalate (DEP) using both commercial porcine pancreas lipase and lipase from recombinant E.Coli strains that contain lipase genes from thermophilic Bacillus sp. isolated from Balçova Geotermal region in İzmir. Incubation of 20 mg/L DEHP with 20,000 U/L PPL enzyme for 7 days resulted in formation of monoethyl phthalate (MEHP), phthalic acid (PA), and dimethyl phthalate (DMP) which are the possible metabolites of DEHP. The percent decrease in DEHP (20 mg/L) was found to be 92% compared to positive control samples. In the case of DEP, about 53% decrease was obtained after incubation with 20.000 U/L for 7 days. Hydrolysis constants for DEHP ranged between 0.13 and 0.22 d-1, whereas those for DEP ranged 0.43 and 0.54 d-1. As a result of enzymatic hydrolysis of DEHP (1-20 mg/L) with 4000 U PPL enzyme, DEP was produced as hydrolysis product of DEHP after 44 h. In the case of DEP (1-20 mg/L) incubated with 4000 U crude lipase solution for 140 h, DMP was obtained as a possible product of transesterification reaction. The maximum rate (Vmax) of enzymatic hydrolysis reaction for DEHP and DEP was calculated as 0.79 mg/L.h and 1.83 mg/L.h, respectively. The Michealis-Menten constants (Km) for enzymatic hydrolysis of DEHP and DEP were calculated as 2.45 and 2.12 mg/L, respectively.
Estimation of the surface charge distribution of solids in liquids by using atomic force microscopy
(Izmir Institute of Technology, 2011) Yelken Özek, Gülnihal; Polat, Mehmet
Colloidal systems are widely encountered in minerals, ceramics, environment, biology, pharmaceuticals and cosmetics industries. These systems consist of micronsized particulates dispersed in a solvent. Homogeneity, dispersibility, stability of colloidal systems determines the economy and success of the final product in these applications. Control and manipulation of these properties depend on detailed analysis of the interactions among the particles. Electrophoretic potential measurements or colloidal titration methods are widely employed to characterize the charging of colloidal systems. However these methods only yield average charging information, not the charge distribution on the surface. Atomic Force Microscope (AFM) allows topographic surface analysis at nanometer level resolutions. Though it is widely used to obtain derived information AFM directly measures the forces between the tip and the surface atoms. The objective of the present work is to assess the applicability of AFM to surface charge mapping, i.e., the detection of positive or negative charged regions on metal oxide surfaces. Hence, well defined tips were prepared and allowed to interact with well defined oxide surfaces under different pH conditions. The influence of solution ion concentration and pH on the forces measured was also investigated. These measured force-distance curves were analyzed using a new solution of the one dimensional Poisson-Boltzmann equation to isolate the electrical double layer force, hence the surface charge on each measurement point. The new solution in question provides analytical expressions for all charging conditions which are amenable to such analysis.Repetitive force measurements on a predefined grid on the solid surface ultimately yield the charge distribution of the surface. Such an analysis procedure is new and advances the charge measurements on solids in solution to a new level.
Experimental and computational investigation of transport phenomena in initiated chemical vapor deposition (iCVD) process
(Izmir Institute of Technology, 2017-12) Ateş, Selcan; Ebil, Özgenç
As a polymer thin-film deposition technique, initiated CVD (iCVD) is a heterogeneous process involving gas phase precursors and solid film formation on a solid/liquid substrates at different temperature regions. Obtaining fine-tuned film properties over different substrate geometries at different process conditions is a challenging tasks and requires experimental trials. The major goal of this study is to develop a computational model which describes all relevant transport phenomena occurring in iCVD process, and which is capable to predict the polymer film thickness at different deposition conditions for flat and/or non-flat substrates in a 3D reactor geometry. A Finite Element Analysis (FEA)-based 3D computational model, which can be applied to a variety number of iCVD reactor and substrate geometries, has been developed in the study. To validate the model, reported experimental conditions of 1H,1H,2H,2Hperfluorodecyl acrylate (PFDA) deposition with t-butyl peroxide (TBPO) initiator, and butyl acrylate (BA) deposition with t-amyl peroxide (TAPO) initiator, are applied to the model, respectively. The simulation results of both deposition processes show good agreement with experimental results reported in literature. Presented model successfully describes the relevant transport phenomena, and provides a priori predictions on polymerization rate, and film thickness on complex substrate geometries for a polymerization reaction with known kinetic data. For further studies, presented model can be modified or used as an approach for modeling of other types of CVD systems as well as facilitating process scale-up. The model can also extract valuable polymerization kinetics data provided that a sufficient number of experiments are performed at a specified substrate temperature, and process parameters and measured final film thicknesses are entered to the model.
An experimental and theoretical study on the improvement of adsorption heat pump performance
(Izmir Institute of Technology, 2008) Demir, Hasan; Ülkü, Semra
Adsorption heat pumps, which have considerably sparked attentions in recent years, have the advantage of being environmentally friendly and operating with heat sources such as waste heat, solar and geothermal energies as well as storing the energy.The present investigation covers working principle of adsorption heat pumps, a detailed literature survey on the performed studies, information about adsorption phenomena, experimental results of two differently designed and constructed systems, numerical simulation of heat and mass transfer in an annular adsorbent bed, and microcalorimetric study for obtaining isosteric heat of adsorption for water vapor-silica gel pair. The two intermittent adsorption heat pumps can operate without any leakage. The silica gelwater was employed as the adsorbent-adsorbate pair in both of the systems. The temperature and pressure in the evaporator, condenser and adsorbent bed were measured and the coefficients of performance, total entropy generation, the second law efficiency, specific heating and cooling power values were calculated based on these measured values for all of the representative cycles. The heat transfer area of the second designed adsorption heat pump is 550% greater than the first designed adsorption heat pump and this increase resulted in 170% and 200% of improvements in specific heating power (SHP) and specific cooling power (SCP) values respectively. The silica gel granules were mixed with small size metal pieces in order to accelerate heat transfer in the bed. Experiments were performed to measure the thermal diffusivity through the adsorbent bed in which adsorbent is mixed with metal pieces. It was observed that the mixing of silica gel grains with 10wt% of small size aluminum pieces increases the SHP and SCP values of the second heat pump by 250%.

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