Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Conference Object X-Ray Fluorescence Spectroscopic Determination of Heavy Metal and Trace Element Concentrations of Origanum Sipyleum From Turkey(Georg Thieme Verlag, 2015) Erdoğan, T. F.; Gönenç, T. M.; Kayalar, H.; Durmuşkahya, Cenk; Hortooğlu, Zehra Sinem; Toktaş, Ümit; Boyalı, F.[No abstract available]Article Citation - WoS: 4Citation - Scopus: 4Color-Tunable All-Inorganic Cspbbr3 Perovskites Nanoplatelet Films for Photovoltaic Devices(American Chemical Society, 2019) Özcan, Mehmet; Özen, Sercan; Topçu, Gökhan; Demir, Mustafa Muammer; Şahin, HasanHerein, we demonstrate a novel coating approach to fabricate CsPbBr3 perovskite nanoplatelet film with heat-free process via electrospraying from precursor solution. A detailed study is carried out to determine the effect of various parameters such as ligand concentration, electric field, flow rate, etc. on the optical properties. By controlling the volume ratios of the oleylamine (OAm) and oleic acid (OA), the coalescing and thickness of the resulting nanoplatelets can be readily tuned that results in control over emission in the range of 100 nm without any antisolvent crystallization or heating processes. The varying electrical field and flow rate was found as inefficient on the emission characteristics of the films. In addition, the crystal films were obtained under ambient conditions on the ITO coated glass surfaces as in the desired pattern. As a result, we demonstrated a facile and reproducible way of synthesizing and coating of CsPbBr3 perovskite nanoplatelets which is suitable for large-scale production. In this method, the ability of tuning the degree of quantum confinement for perovskite nanoplatelets is promising approach for the one-step fabrication of crystal films that may enable the use in optoelectronics.Article Citation - WoS: 85Citation - Scopus: 91Ballistic Thermoelectric Properties of Monolayer Semiconducting Transition Metal Dichalcogenides and Oxides(American Physical Society, 2019) Özbal, Gözde; Senger, Ramazan Tuğrul; Sevik, Cem; Sevinçli, HaldunCombining first-principles calculations with Landauer-Mittiker formalism, ballistic thermoelectric transport properties of semiconducting two-dimensional transition metal dichalcogenides (TMDs) and oxides (TMOs) (namely MX2 with M = Cr, Mo, W, Ti, Zr, Hf; X = O, S, Se, Te) are investigated in their 2H and 1T phases. Having computed structural, as well as ballistic electronic and phononic transport properties for all structures, we report the thermoelectric properties of the semiconducting ones. We find that 2H phases of four of the studied structures have very promising thermoelectric properties, unlike their 1T phases. The maximum room temperature p-type thermoelectric figure of merit (ZT) of 1.57 is obtained for 2H-HfSe2, which can be as high as 3.30 at T = 800 K. Additionally, 2H-ZrSe2, 2H-ZrTe2, and 2H-HfS2 have considerable ZT values (both nand p-type), that are above 1 at room temperature. The 1T phases of Zr and Hf-based oxides possess relatively high power factors, however their high lattice thermal conductance values limit their ZT values to below 1 at room temperature.Article Citation - WoS: 89Citation - Scopus: 85Cspbbr3 Perovskites: Theoretical and Experimental Investigation on Water-Assisted Transition From Nanowire Formation To Degradation(American Physical Society, 2018) Akbalı, Barış; Topçu, Gökhan; Güner, Tuğrul; Özcan, Mehmet; Demir, Mustafa Muammer; Şahin, HasanRecent advances in colloidal synthesis methods have led to an increased research focus on halide perovskites. Due to the highly ionic crystal structure of perovskite materials, a stability issue pops up, especially against polar solvents such as water. In this study, we investigate water-driven structural evolution of CsPbBr3 by performing experiments and state-of-the-art first-principles calculations. It is seen that while an optical image shows the gradual degradation of the yellowish CsPbBr3 structure under daylight, UV illumination reveals that the degradation of crystals takes place in two steps: transition from a blue-emitting to green-emitting structure and and then a transition from a green-emitting phase to complete degradation. We found that as-synthesized CsPbBr3 nanowires (NWs) emit blue light under a 254 nm UV source. Before the degradation, first, CsPbBr3 NWs undergo a water-driven structural transition to form large bundles. It is also seen that formation of such bundles provides longer-term environmental stability. In addition theoretical calculations revealed the strength of the interaction of water molecules with ligands and surfaces of CsPbBr3 and provide an atomistic-level explanation to a transition from ligand-covered NWs to bundle formation. Further interaction of green-light-emitting bundles with water causes complete degradation of CsPbBr3 and the photoluminescence signal is entirely quenched. Moreover, Raman and x-ray-diffraction measurements revealed that completely degraded regions are decomposed to PbBr2 and CsBr precursors. We believe that the findings of this study may provide further insight into the degradation mechanism of CsPbBr3 perovskite by water.Article Citation - WoS: 14Citation - Scopus: 15Medical Waste Treatment Via Waste Electrospinning of Ps(Korean Fiber Society, 2018) Isık, Tuğba; Demir, Mustafa MuammerBody fluid medical wastes are infectious clinical wastes (blood, saliva, urine) due to their high pathogenic content. Incineration is the most commonly used method in waste management that possess high water content along with molecularly dissolved species such as proteins. The process is costly; so that the removal of solid content dissolved in aqueous part by preliminary filtration can reduce the volume of the waste material. In this study, fibrous mats were prepared by electrospinning of PS wastes from DMF and THF solutions. Then they are employed in the removal of protein-based solid contents of body fluid medical wastes before their disposal. Two sources of PS waste (CD cover and Styrofoam) were employed along with virgin PS for comparison. The adsorption capacity of as-prepared electrospun fibers was examined for three model proteins: Bovine Serum Albumin (BSA), Myoglobin (MYO), and Trypsin (TRY). The fibers obtained from PS CD wastes have remarkably larger protein sorption capacities (particularly BSA) than the fibers obtained from virgin PS. XPS reveals the presence of CaCO3 domains in CD covers added into PS during their production steps probably to increase mechanical properties. There may be an electrostatic interaction between Ca2+ and the negatively charged groups of the protein. In this way, PS wastes could be converted to a beneficial secondary product by electrospinning and also resulting materials promises for the disposal of body fluid medical wastes. This may be one of the frontiers study on the removal of medical wastes by adsorbents produced via electrospinning of waste polymers.Article Citation - WoS: 1Citation - Scopus: 1Directed Growth of Hydrogen Lines on Graphene: High-Throughput Simulations Powered by Evolutionary Algorithm(American Physical Society, 2018) Özbal, Gözde; Falkenberg, J. T.; Brandbyge, M.; Senger, Ramazan Tuğrul; Sevinçli, HaldunWe set up an evolutionary algorithm combined with density functional tight-binding calculations to investigate hydrogen adsorption on flat graphene and graphene monolayers curved over substrate steps. During the evolution, candidates for the new generations are created by adsorption of an additional hydrogen atom to the stable configurations of the previous generation, where a mutation mechanism is also incorporated. Afterwards a two-stage selection procedure is employed. Selected candidates act as the parents of the next generation. The evolutionary algorithm predicts formation of lines of hydrogen atoms on flat graphene. In curved graphene, the evolution follows a similar path except for a new mechanism, which aligns hydrogen atoms on the line of minimum curvature. The mechanism is due to the increased chemical reactivity of graphene along the minimum radius of curvature line (MRCL) and to sp(3) bond angles being commensurate with the kinked geometry of hydrogenated graphene at the substrate edge. As a result, the reaction barrier is reduced considerably along the MRCL and hydrogenation continues like a mechanical chain reaction. This growth mechanism enables lines of hydrogen atoms along the MRCL, which has the potential to overcome substrate or rippling effects and could make it possible to define edges or nanoribbons without actually cutting the material.Article Citation - WoS: 31Citation - Scopus: 32Evaluating the Critical Roles of Precursor Nature and Water Content When Tailoring Magnetic Nanoparticles for Specific Applications(American Chemical Society, 2018) Cotin, Geoffrey; Kiefer, Celine; Perton, Francis; Boero, Mauro; Özdamar, Burak; Bouzid, Assil; Begin-Colin, SylvieBecause of the broad range of application of iron oxide nanoparticles (NPs), the control of their size and shape on demand remains a great challenge, as these parameters are of upmost importance to provide NPs with magnetic properties tailored to the targeted application. One promising synthesis process to tune their size and shape is the thermal decomposition one, for which a lot of parameters were investigated. But two crucial issues were scarcely addressed: the precursors nature and water content. Two in house iron stearates with two or three stearate chains were synthesized, dehydrated, and then tested in standard synthesis conditions of spherical and cubic NPs. Investigations combined with modeling showed that the precursors nature and hydration rate strongly affect the thermal decomposition kinetics and yields, which, in turn, influence the NP size. The cubic shape depends on the decomposition kinetics but also crucially on the water content. A microscopic insight was provided by first-principles simulation showing an iron reduction along the reaction pathway and a participation of water molecules to the building unit formation.Article Citation - WoS: 104Citation - Scopus: 107Poly(dopamine) Grafted Bio-Silica Composite With Tetraethylenepentamine Ligands for Enhanced Adsorption of Pollutants(Institution of Chemical Engineers, 2019) Arıca, Tuğçe Aybüke; Kuman, Merve; Gerçel, Özgül; Ayas, ErhanIn this study, diatomite fossil particles (i.e., bio-silica) was treated with strong acid solution and coated with polydopamine (bio-silica-PDA) using aqueous-based bioinspired coating method. The bio-silica-PDA was grafted with tetraethylenepentamine (TEPA) ligand to increase binding sites on the material surfaces. The biosilica-PDA-TEPA particles was characterized using Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), X-Ray Diffraction (XRD) and Brunauer-Emmett-Teller (BET) method. The adsorption performance of the biosilica-PDA-TEPA particles was studied using a model dye (i.e., Direct Blue 74; DB-74) from aqueous solutions using biosilica-PDA as a control system. Batch system was used to optimize experimental conditions for the removal of DB-74 dye on the sorbents. The adsorption of DB-74 on the biosilica-PDA-TEPA particles was studied in the pH range of 2.0-8.0. The amount adsorbed DB-74 dye on the biosilica-PDA-TEPA was 363.3 mg g(-1) (using initial dye concentration 1200 mg L-1, pH 3.0 and temperature 25 degrees C). Adsorption of DB-74 dye on biosilica-PDA-TEPA particles fitted well Langmuir model. The equilibrium adsorption time was completed within 10 min and the experimental data was defined well by the pseudo-second-order model. In addition, the biosilica-PDA-TEPA particles presented a good performance after regeneration. This result show that the presented low-cost porous biosilica-PDA-TEPA particles can be a good candidate as a novel sorbent system for removal of micro-pollutants from wastewaters. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.Article Citation - WoS: 18Citation - Scopus: 46Phosphor-Based White Led by Various Glassy Particles:control Over Luminous Efficiency(The Optical Society, 2019) Yüce, Hürriyet; Güner, Tuğrul; Balcı, Sinan; Demir, Mustafa MuammerGenerating white light through a mainstream remote phosphor design suffers from phosphor conversion efficiency loss due to a backscattering of light. Such a loss also reduces luminous efficiency of the resulting white light. To overcome this issue, various glassy scatterers with different morphologies such as glass bubbles, glass beads, and nanosized silica particles were employed as scatterers, together with a fixed amount of yellow phosphor (YAG:Ce3+) and a poly(dimethylsiloxane) (PDMS) matrix. In addition, the simulation of the system validates the rigorous multiple scattering of the incoming light most probably due to refractive index mismatch between the glass bubbles and surrounding PDMS matrix along with the internal reflections. (C) 2019 Optical Society of AmericaArticle Citation - WoS: 7Citation - Scopus: 7Increasing Spontaneous Wet Adhesion of Dopa With Gelation Characterized by Epr Spectroscopy(Elsevier Ltd., 2019) Göksel, Yaman; Akdoğan, YaşarThe presence of water molecules around both adhesive materials and surface results in the hydration barriers that weaken adhesion. In nature, mussels attach to various types of surfaces by using 3,4-dihydroxyphenylalanine (DOPA) containing mussel foot proteins. DOPA shows wet adhesive properties before and after contribution in the hydrogel formation. Here, the wet adhesive properties of DOPA modified four armed poly (ethylene glycol) polymer (PEG-(DOPA)(4)) and its hydrogels induced by (IO4)(-) or (Cr2O7)(2-) ions are compared by using electron paramagnetic resonance (EPR) spectroscopy in terms of their surface coverages. In water, spin labeled hydrophobic polystyrene (SL-PS) and hydrophilic silica (SL-SiO2) nanoparticles are prepared, and the percentages of their covered surface values are obtained. Without applying force, the adhesion to SL-PS increases in the order of PEG-(DOPA)(4) < PEG-(DOPA)(4) + (IO4)(-) hydrogel < PEG-(DOPA)(4) + (Cr2O7)(2-) hydrogel with the percentages of surface coverages 65%, 76% and 93%, respectively. Although, neither of PEG-(DOPA)(4) polymer and (IO4)(-) induced PEG-(DOPA)(4) hydrogel adhere to SL-SiO2 nanoparticle spontaneously, (Cr2O7)(2-) induced PEG-(DOPA)(4) hydrogel adhere to SL-SiO2 with a 59% of surface coverage. These results show that gelation mechanisms of DOPA have effect on the spontaneous adhesion of DOPA to the wet surfaces even for the hydrophilic silica surface.