Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Article Citation - WoS: 1Citation - Scopus: 1Investigating Triple Superphosphate for Lead Removal From Aqueous Solutions(Taylor & Francis, 2022) Souley Garba, Mahamane Chapiou; Kaya, Erol; Gökelma, Mertol; Seyrankaya, AbdullahThe aim of this research is to investigate monocalcium phosphate monohydrate [Ca(H2PO4)2. H2O] also called triple superphosphate (TSP) for the removal of lead (Pb) from aqueous solutions. In this study, TSP was selected amongst various phosphate-based materials and fertilizers to act as the source of orthophosphate (PO43-) which is a powerful tool for metal fixation in soil and water. Thermodynamic equilibrium dissolution-precipitation relationships for the systems of Pb-H2O and Pb-PO43--H2O were drawn with the aid of Eh-pH stability diagrams to determine the predominance areas of different species. The lead phosphate compounds, identified through the stability area diagrams, were verified with the batch precipitation tests performed with standard solutions of lead and TSP at different conditions. It was observed that, depending upon solution conditions, TSP can precipitate 99.9% of the lead from the solution. Lead precipitates, analyzed by x-ray diffraction, showed the formation of lead phosphate compounds. The mechanism of TSP for the removal of lead from aqueous solutions is discussed.Article Citation - WoS: 11Citation - Scopus: 13Effect of Cnt Incorporation on Pan/Ppy Nanofibers Synthesized by Electrospinning Method(TÜBİTAK, 2020) İnce Yardımcı, Atike; Tanoğlu, Metin; Yılmaz, Selahattin; Selamet, YusufIn this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H2SO4/HNO3/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.Article Citation - WoS: 3Citation - Scopus: 3Green Fabrication of Lanthanide-Doped Hydroxide-Based Phosphors: Y(oh)(3):eu3+ Nanoparticles for White Light Generation(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2019) Güner, Tuğrul; Kuş, Anılcan; Özcan, Mehmet; Genç, Aziz; Şahin, Hasan; Demir, Mustafa MuammerPhosphors can serve as color conversion layers to generate white light with varying optical features, including color rendering index (CRI), high correlated color temperature (CCT), and luminous efficacy. However, they are typically produced under harsh synthesis conditions such as high temperature, high pressure, and/or by employing a large amount of solvent. In this work, a facile, water-based, rapid method has been proposed to fabricate lanthanide-doped hydroxide-based phosphors. In this sense, sub-micrometer-sized Y(OH)(3):Eu3+ particles (as red phosphor) were synthesized in water at ambient conditions in <= 60 min reaction time. The doping ratio was controlled from 2.5-20 mol %. Additionally, first principle calculations were performed on Y(OH)(3):Eu3+ to understand the preferable doping scenario and its optoelectronic properties. As an application, these fabricated red phosphors were integrated into a PDMS/YAG:Ce3+ composite and used to generate white light. The resulting white light showed a remarkable improvement (approximate to 24%) in terms of luminous efficiency, a slight reduction of CCT (from 3900 to 3600 K), and an unchanged CRI (approximate to 60) as the amount of Y(OH)(3):Eu3+ was increased.Article Citation - WoS: 25Citation - Scopus: 27Osteogenic Differentiation of Mesenchymal Stem Cells on Random and Aligned Pan/Ppy Nanofibrous Scaffolds(SAGE Publications, 2019) Selamet, Yusuf; İnce Yardımcı, Atike; Baskan, Öznur; Yılmaz, Selahattin; Meşe, Gülistan; Özçivici, EnginThe aim of this study was to develop random and aligned polyacrilonitrile (PAN)/polypyrrole (PPy) nanofibrous scaffolds by electrospinning technique for osteogenic differentiation of mesenchymal stem cells. Nanofibers were fabricated successfully as straight, smooth, and free from bead formation. The average diameter of random and aligned nanofibers was 268(+/- 49) nm and 225(+/- 72) nm, respectively. Alignment process increased the tensile strength of nanofibers 3.9-fold, while the tensile strain of nanofibers decreased by 78%. PAN/PPy nanofibers were hydrophilic with the contact angle value of about 32 degrees and alignment did not affect the contact angle value. Random and aligned PAN/PPy nanofibers were investigated as a scaffold material for osteogenic differentiation of D1 ORL UVA mouse bone marrow mesenchymal stem cells. Cells were able to attach and grow on nanofibers confirmed by cell viability results. Stem cells that were cultured with osteogenic induction were able to mineralize on electrospun nanofibers based on alizarin red and Von Kossa dye staining. For aligned PPy nanofibers, mineralization occurred in the fiber alignment direction. Consequently, PAN/PPy nanofibrous mats in both random and aligned forms would be potential candidates for bone tissue engineering.Article Citation - WoS: 21Citation - Scopus: 22Green Function, Quasi-Classical Langevin and Kubo-Greenwood Methods in Quantum Thermal Transport(IOP Publishing, 2019) Sevinçli, Haldun; Roche, S.; Cuniberti, G.; Brandbyge, M.; Gutierrez, R.; Sandonas, L. MedranoWith the advances in fabrication of materials with feature sizes at the order of nanometers, it has been possible to alter their thermal transport properties dramatically. Miniaturization of device size increases the power density in general, hence faster electronics require better thermal transport, whereas better thermoelectric applications require the opposite. Such diverse needs bring new challenges for material design. Shrinkage of length scales has also changed the experimental and theoretical methods to study thermal transport. Unsurprisingly, novel approaches have emerged to control phonon flow. Besides, ever increasing computational power is another driving force for developing new computational methods. In this review, we discuss three methods developed for computing vibrational thermal transport properties of nano-structured systems, namely Green function, quasi-classical Langevin, and Kubo-Green methods. The Green function methods are explained using both nonequilibrium expressions and the Landauer-type formula. The partitioning scheme, decimation techniques and surface Green functions are reviewed, and a simple model for reservoir Green functions is shown. The expressions for the Kubo-Greenwood method are derived, and Lanczos tridiagonalization, continued fraction and Chebyshev polynomial expansion methods are discussed. Additionally, the quasi-classical Langevin approach, which is useful for incorporating phonon-phonon and other scatterings is summarized.Article Citation - WoS: 18Citation - Scopus: 14Optimization and Performance of Nitrogen-Doped Carbon Dots as a Color Conversion Layer for White-Led Applications(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2019) Güner, Tuğrul; Yüce, Hürriyet; Taşçıoğlu, Didem; Şimşek, Eren; Savacı, Umut; Genç, Aziz; Demir, Mustafa MuammerIn this study, green-emitting nitrogen-doped carbon dots (N-CDots) were synthesized and incorporated into drop-cast composite films for use as color conversion layers in a white-LED configuration to generate white light. In order to resolve the red deficiency of this configuration, a commercial red phosphor was integrated into the system. Moreover, the N-CDots were also processed into polymer/N-CDot composite fibers, for which we determined the amount of N-CDots that yielded adequate white-light properties. Finally, we showed that white light with excellent properties could be generated by employing both of the fabricated N-CDot composites either as drop-cast films or composite fibers. Hence, N-CDots provide a promising alternative to inorganic phosphors that are commonly employed in white-LED configurations.Article Citation - WoS: 3Citation - Scopus: 3Monolayer Aste2: Stable Robust Metal in 2d, 1d and 0d(Wiley, 2018) Badalov, S. V.; Kandemir, Ali; Şahin, HasanThe structural, phononic, and electronic properties of the monolayer structures of AsTe2 are characterized by performing density functional theory (DFT) calculations. Total energy optimization and phonon calculations reveal that single layers of the 2H-AsTe2 and 1T-AsTe2 phases form dynamically stable crystal structures. Electronic structure analysis also shows that both 2H and 1T phases have nonmagnetic metallic character. It is also predicted that the metallic nature of the ultra-thin both 2H-AsTe2 and 1T-AsTe2 structures remain unchanged even under high biaxial strain values. For further examination of the dimensionality effect in the robust metallicity in 2D AsTe2 phases, electronic characteristics of 1D nanoribbons and 0D quantum dots are also investigated. It is found that independent from the dimension and crystallographic orientations 0D and 1D structures of 2H- and 1T-AsTe2 structures have metallic behavior. It is found that single layers of AsTe2 are quite promising materials for nanodevice applications owing to the robust metallic character.Article Citation - WoS: 12Citation - Scopus: 12Ordering of Air-Oxidized Decanethiols on Au(111)(American Chemical Society, 2018) Sotthewes, Kai; Kap, Özlem; Wu, Hairong; Thompson, Damien; Huskens, Jurriaan; Zandvliet, Harold J. W.Self-assembled monolayers (SAMs) of alkanethiols on gold are a commonly used platform for nanotechnology owing to their ease of preparation and high surface coverage. Unfortunately, the gold-sulfur bond is oxidized at ambient conditions which alters the stability and structure of the monolayer. We show using scanning tunneling microscopy and X-ray photoelectron spectroscopy that decanethiolate molecules oxidize into decanesulfonates that organize into a hitherto unknown striped phase. Air-exposed SAMs oxidize, as can be determined by a shift of the S 2p peak and the appearance of O 1s photoelectrons as part of the decanethiol monolayer transforms into a lamellae-like decanesulfonate structure when exposed to air. The herringbone structure of the Au(111) surface is preserved, indicating that the interaction between the molecules and the surface is rather weak as these findings are substantiated by density functional theory calculations.Article Citation - WoS: 8Citation - Scopus: 10Stability, Electronic and Phononic Properties of Ss and 1t Structures of Sitex (x = 1, 2) and Their Vertical Heterostructures(IOP Publishing Ltd., 2017) Kandemir, Ali; İyikanat, Fadıl; Şahin, HasanBy performing first-principles calculations, we predict a novel, stable single layer phase of silicon ditelluride, 1T-SiTe2, and its possible vertical heterostructures with single layer β-SiTe. Structural optimization and phonon calculations reveal that 1T-SiTe2 structure has a dynamically stable ground state. Further analysis of the vibrational spectrum at the - point shows that single layer 1T-SiTe2 has characteristic phonon modes at 80, 149, 191 and 294 cm-1. Electronic-band structure demonstrates that 1T-SiTe2 phase exhibits a nonmagnetic metallic ground state with a negligible intrinsic spinorbit splitting. Moreover, it is shown that similar structural parameters of 1T-SiTe2 and existing β-SiTe phases allows construction of 1T-β heterostructures with a negligible lattice mismatch. In this regard, it is found that two energetically favorable stacking orders, namely AA and ATB, have distinctive shear and layer breathing phonon modes. It is important to note that the combination of semiconducting β-SiTe and metallic 1T-SiTe2 building blocks forms ultra-thin Schottky barriers that can be used in nanoscale optoelectronic device technologies.Article Citation - WoS: 3Citation - Scopus: 2?-Silicene as Oxidation-Resistant Ultra-Thin Coating Material(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2017) Kandemir, Ali; İyikanat, Fadıl; Bacaksız, Cihan; Şahin, HasanBy performing density functional theory (DFT)-based calculations, the performance of a-silicene as oxidation-resistant coating on Ag(111) surface is investigated. First of all, it is shown that the Ag(111) surface is quite reactive against O atoms and O2 molecules. It is known that when single-layer silicene is formed on the Ag(111) surface, the 3 × 3-reconstructed phase, a-silicene, is the ground state. Our investigation reveals that as a coating layer, a-silicene (i) strongly absorbs single O atoms and (ii) absorbs O2 molecules by breaking the strong O-O bond. (iii) Even the hollow sites, which are found to be most favorable penetration path for oxygens, serves as high-energy oxidation barrier, and (iv) α-silicene becomes more protective and less permeable in the presence of absorbed O atom. It appears that single-layer silicene is a quite promising material for ultra-thin oxidation-protective coating applications.