Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 6Citation - Scopus: 6Inverse Effects of Lanthanide Co-Doping on the Photocatalytic Hydrogen Production and Dye Degradation Activities of Cu Doped Sol-Gel Tio<sub>2</Sub>(Elsevier, 2023) Yurtsever, Husnu Arda; Erzin, Kubilay; Ciftcioglu, Muhsin; Yurtsever, Hüsnü Arda; Erzin, Kubilay; Çiftçioğlu, MuhsinCopper doped and lanthanide-copper co-doped titania powders were prepared by sol-gel technique and the effects of co-doping on the photocatalytic reduction and oxidation activities of titania were investigated in this work. Characterization studies indicated that a reduced structure was formed due to the presence of Ti3+ species in copper doped titania powder and a more stable structure was formed when lanthanides were used as co-dopants. Copper doped powder had a significantly higher activity in photocatalytic hydrogen production (1037 mu mol/g/h) than the co-doped powders (similar to 400 mu mol/g/h). The oxidation activities of co-doped powders however were determined to be about 2 times higher than that of the copper doped powder. The decrease in the reduction activity was attributed to the decrease in the number of Ti3+ sites, whereas the increase in oxidation activity was probably a result of the increase in the surface area and dye adsorption due to lanthanide co-doping.Article Citation - WoS: 10Citation - Scopus: 12Enhanced Model Protein Adsorption of Nanoparticulate Hydroxyapatite Thin Films on Silk Sericin and Fibroin Surfaces(Springer, 2022) Özcan, Selçuk; Çiftçioğlu, MuhsinHydroxyapatite coated metallic implants favorably combine the required biocompatibility with the mechanical properties. As an alternative to the industrial coating method of plasma spraying with inherently potential deleterious effects, sol-gel methods have attracted much attention. In this study, the effects of intermediate silk fibroin and silk sericin layers on the protein adsorption capacity of hydroxyapatite films formed by a particulate sol-gel method were determined experimentally. The preparation of the layered silk protein/hydroxyapatite structures on glass substrates, and the effects of the underlying silk proteins on the topography of the hydroxyapatite coatings were described. The topography of the hydroxyapatite layer fabricated on the silk sericin was such that the hydroxyapatite particles were oriented forming an oriented crystalline surface. The model protein (bovine serum albumin) adsorption increased to 2.62 µg/cm2 on the latter surface as compared to 1.37 µg/cm2 of hydroxyapatite on glass without an intermediate silk sericin layer. [Figure not available: see fulltext.].Article Citation - WoS: 7Citation - Scopus: 8Compositional, Microstructural and Mechanical Effects of Nacl Porogens in Brushite Cement Scaffolds(Elsevier, 2021) Şahin, Erdem; Çiftçioğlu, MuhsinModification of the setting process of brushite cements by varying the concentration of ions that alter calcium phosphate crystallization kinetics, is known to enable control on the monetite conversion extent and the accompanying microporosity. This is useful because monetite serves as a suitable matrix in macroporous scaffolds due to its higher phase stability and finer crystal morphology compared to its hydrous counterpart brushite. In this study the synergistic effect of NaCl and citric acid on the microstructural evolution of brushite cement was demonstrated and microporosity of macroporous monetite-rich cement blocks was minimized by a variable NaCl porogen size distribution approach. Initially, maximum packing ratio of various combinations of NaCl size groups in PEG were determined by their rheological analysis in a range between 57% and 69%. Statistical analysis revealed a positive correlation between the amounts of NaCl particles under 38 mu m and 212 mu m and the maximum packing ratio. Further broadening the size distributions of NaCl porogens with fine cement precursors was effective in increasing the solids packing ratio of cement blocks more than the maximum packing ratio for the porogens. This improvement in packing was accompanied by a reduction in microporosity despite the increase in micropore volume with ion induced monetite formation. The detrimental effect of the microporosity introduced to the structure during monetite formation was balanced for some size distributions and not so much for others, thereby resulting in a wide range of porosities and mechanical properties. Thus, the exponential dependence of mechanical properties on porosity and the mechanical properties of monetite-rich macroporous blocks at the theoretical zero-porosity were determined according to Rice's model. Zero-porosity extrapolations were much higher than those predicted for brushite cement, contrary to the common assumption that brushite is mechanically stronger than monetite.Article Citation - WoS: 13Citation - Scopus: 14Monetite Promoting Effect of Citric Acid on Brushite Cement Setting Kinetics(Maney Publishing, 2014) Şahin, Erdem; Çiftçioğlu, MuhsinBrushite forming calcium phosphate cements receive growing interest in hard tissue scaffold applications due to their high surface area and high bioresorbability. The finer microstructure of monetite, the dehydrated form of brushite, has attracted attention for bone tissue engineering applications. The reduction in brushite content of the b-tricalcium phosphate-monocalcium phosphate monohydrate cement system by selective inhibition of growth upon addition of citric acid to excess setting liquid was investigated. The relaxation period during cement setting was monitored by pH stat titration and free drift runs. Spectrometric analysis revealed that the change in solubility of calcium phosphates upon addition of citric acid caused the inhibition of brushite formation and promotion of monetite precipitation. Dissolution of monetite crystals was insensitive to citrate adsorption despite their lower surface area compared to brushite. Overall brushite/ monetite ratio decreased consistently with increasing citric acid concentration in the of 0?1-0?5M range.Article Citation - WoS: 17Citation - Scopus: 19Effect of Compaction Pressure on Structural and Superconducting Properties of Bi-2223 Superconductors(Springer Verlag, 2010) Kocabaş, Kemal; Gökçe, Melis; Çiftçioğlu, Muhsin; Bilgili, ÖzlemIn this work, effects of compaction pressure on the structural and superconducting properties of BSCCO ceramic superconductors were investigated. The study was carried out on two systems which were, System I: Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O y and System II: Bi 1.6Pb 0.3Ag 0.1Sr 2Ca 2Cu 3O y, respectively. Ceramic powders were prepared by conventional solid-state reaction method and sintered at 850°C after compaction at five different pressures in the 150-750 MPa range. Critical temperatures of samples were determined by resistivity-temperature determinations made by four-point probe method in liquid nitrogen conditions. XRD analysis was conducted by powder X-ray diffraction method. Morphology of the grains present in the samples were determined by using scanning electron microscope (SEM) photographs at 2 K× and 2.5 K× magnifications for System I and System II, respectively. Sintered densities of the superconducting ceramics were measured by Archimedes water displacement method and unit cell parameters were additionally obtained from XRD data. T c values for System I was determined to be in the 109-115 K with sample D having the highest T c of 115 K while T c varied in the 104-109 K range and sample B had the highest T c value of 109 K for System II. The transition width, which is a sign of the purity of the samples, was determined to be narrow for both systems. The data obtained from X-ray diffraction measurements have shown that 2223 high-T c phase was dominant in both systems. The determination of the optimum pellet compaction pressure for BSCCO ceramic superconductors was the main purpose of this work. The results of this work indicated that compaction at around 450 MPa improves the superconducting and structural properties of the BSCCO ceramic superconductors. © 2009 Springer Science+Business Media, LLC.Article Citation - WoS: 12Citation - Scopus: 12The Effect of Zn Substitution of Ca in Bipbsrcacuo Superconductors Sintered at 830°c(Springer Verlag, 2009) Kocabaş, Kemal; Şakiroğlu, Serpil; Çiftçioğlu, Muhsin; Ercan, İsmail; Epik, Hakan; Bilgili, ÖzlemThe effect of partial substitution of Ca by Zn in Bi 1.7Pb 0.3Sr 2Ca 2-x Zn x Cu 3O y at x=0.00, 0.05, 0.10, 0.15 and 0.20 levels on the electrical and structural properties was investigated in this work. The characterization of the ceramics prepared by the conventional solid-state reaction method were done by resistance-temperature measurements, XRD, SEM and density analysis. Low levels of Zn substitution of Ca caused significant changes in the properties of the ceramics. The low-T c superconducting properties were enhanced and the fraction of the low-T c (2212) phase were found to increase at x=0.15 level of Zn substitution at 830°C sintering temperature. Zero resistance was observed only in sample D with x=0.15 and the T c was determined as 92 K. The SEM micrographs and the density analysis have shown that this was the densest packed ceramic.