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Article Citation - WoS: 42Citation - Scopus: 53Preparation and Photocatalytic Activity of G-c3n4< Heterojunctions Under Solar Light Illumination(Elsevier Sci Ltd, 2020) Gundogmus, Pelin; Park, Jongee; Ozturk, AbdullahThe solar light sensitive g-C3N4/TiO2 heterojunction photocatalysts containing 20, 50, 80, and 90 wt% graphitic carbon nitride (g-C3N4) were prepared by growing Titania (TiO2) nanoparticles on the surfaces of g-C3N4 particles via one step hydrothermal process. The hydrothermal reactions were allowed to take place at 110 degrees C at autogenous pressure for 1 h. Raman spectroscopy analyses confirmed that an interface developed between the surfaces of TiO2 and g-C3N4 nanoparticles. The photocatalyst containing 80 wt% g-C3N4 was subsequently heat treated 1 h at temperatures between 350 and 500 degrees C to improve the photocatalytic efficiency. Structural and optical properties of the prepared g-C3N4/TiO2 heterojunction nanocomposites were compared with those of the pristine TiO2 and pristine g-C(3)N(4 )powders. Photocatalytic activity of all the nanocomposites and the pristine TiO2 andg-C3N4 powders were assessed by the Methylene Blue (MB) degradation test under solar light illumination. g-C3N4/TiO2 heterojunction photocatalysts exhibited better photocatalytic activity for the degradation of MB than both pristine TiO2 and g-C3N4. The photocatalytic efficiency of the g-C3N4/TiO2 heterojunction photocatalyst heat treated at 400 degrees C for 1 his 1.45 times better than that of the pristine TiO2 powder, 2.20 times better than that of the pristine g-C3N4 powder, and 1.24 times better than that of the commercially available TiO2 powder (Degussa P25). The improvement in photocatalytic efficiency was related to i) the generation of reactive oxidation species induced by photogenerated electrons, ii) the reduced recombination rate for electron-hole pairs, and iii) large specific surface area.Article Citation - WoS: 12Citation - Scopus: 11Enhanced Bioactivity and Low Temperature Degradation Resistance of Yttria Stabilized Zirconia/Clay Composites for Dental Applications(Elsevier Sci Ltd, 2022) Tufan, Yigithan; Park, Jongee; Ozturk, Abdullah; Ercan, BaturYttria stabilized zirconia (YSZ)/clay composites were produced to improve osseointegration and undesired tetragonal-to-monoclinic phase transformation (low temperature degradation, LTD) of YSZ ceramics so that long-term clinical success of YSZ implants is achieved. Various amounts (0.5,1,2, and 4 wt%) of clay was incorporated to YSZ. Predetermined amounts of clay and YSZ were mixed and pressed uniaxially at 15 MPa into compacts that were subsequently pressureless sintered at 1450 degrees C. Density, compressive strength, hardness and indentation crack resistance of 4 wt% clay incorporated YSZ/clay composite were 5.77 +/- 0.01 g/cm3, 1188 +/- 121 MPa, 1223 +/- 9 HV, and 4.4 +/- 0.1 MPa root m, respectively. Additionally, biological properties of YSZ/clay composites were assessed in vitro using bone cells. Incorporation of 4 wt% clay significantly enhanced bone cell prolifer-ation, spreading, and functions. Moreover, a significant increase in the LTD resistance of YSZ was achieved upon 4 wt% clay incorporation. The findings collectively suggest that YSZ/clay composites have a potential to be used as an alternative material for dental applications.Article Citation - WoS: 25Citation - Scopus: 26Production and Properties of Tooth-Colored Yttria Stabilized Zirconia Ceramics for Dental Applications(Elsevier Sci Ltd, 2018) Kaplan, Melis; Park, Jongee; Kim, Soo Young; Ozturk, AbdullahDense zirconia stabilized with 3 mol% yttria ceramics were produced in disc shape by first cold isostatically pressing at 100 MPa and then sintering at 1450 degrees C at ambient laboratory conditions. Coloring was accomplished by immersion the discs in NiCl2, MoCl3, and NiCl2 + MoCl3 solutions for 5, 30, and 60 s. Different concentrations (0.1, 0.25, and 0.5 wt%) were applied to get the color of natural tooth. The density, color, microhardness, fracture toughness, compressive strength, and wear rate of the discs were measured to evaluate the suitability of the colored discs for dental applications. Color assessments were made by measuring CIE Lab L*, a*, b, and Delta E* values. Low temperature degradation of the samples was evaluated by aging sensitivity tests in autoclave for 2, 4, and 6 h. Results have shown that color produced depends on the kind and concentration of the colorant solution while time of immersion has no significant effect on coloring process. Coloring solutions containing 0.1 and 0.25 wt% MoCl3 provided clinically acceptable color with the Delta E* value ranging from 5.16 to 6.42 for dental applications.Article Citation - WoS: 22Citation - Scopus: 24Mechanical and Biological Properties of Al2o3< and Tio2 Co-Doped Zirconia Ceramics(Elsevier Sci Ltd, 2017) Agac, Ozlem; Gozutok, Melike; Sasmazel, Hilal Turkoglu; Ozturk, Abdullah; Park, JongeeVarious amounts (ranging from 0 to 2 wt%) of TiO2 and Al2O3 were mono and co-doped to tetragonal zirconia ceramic containing 3 mol% yttria (3Y-TZP) by mechanical ball milling. Powders were compacted by uniaxial pressing at a pressure of 23 MPa. The compacts were pressureless sintered at 1450 degrees C for 2 h. Density, hardness, fracture toughness, and cell attachment of the co-doped 3Y-TZP ceramics were measured with respect to dopant addition to determine the effects of the kind and amount of dopants on the properties. The results show that density decreased gradually as the amount of dopant was increased. The mechanical properties showed the maximum value when 0.5 wt% TiO2 and 1.0 wt% Al2O3 were co-doped to 3Y-TZP. Crystalline phase formation and microstructural morphology were investigated by XRD and SEM analyses to explain the variations in the properties. Co-doping of TiO2 and Al2O3 to 3Y-TZP did not have an influence on the phases present, but decreased the grain size. The co-doping also affected the cell attachment and the growth on the surface of the zirconia ceramics.Article Citation - WoS: 31Citation - Scopus: 37Effect of Initial Water Content and Calcination Temperature on Photocatalytic Properties of Tio2 Nanopowders Synthesized by the Sol-Gel Process(Elsevier Sci Ltd, 2015) Agartan, Lutfi; Kapusuz, Derya; Park, Jongee; Ozturk, AbdullahThe effects of initial water content and calcination temperature on sol gel synthesized TiO2 powders were studied. Mother solutions had water/Ti-precursor mole ratios (R ratio) of 1, 5, 10, and 50. Dried aerogels were calcined for 3 h at temperatures of 300, 400, and 500 degrees C to obtain crystallized TiO2 nanopowders in the range of 15-30 nm. PE-scanning electron microscopy and X-ray diffraction techniques were employed to investigate the morphological and structural properties of the nanopowders synthesized. Profound effect of gel viscosity was observed on the formation mechanism and extent of crystallinity in the powders. Methylene blue degradation test results suggest, photocatalytic performance is enhanced as initial water content and calcination temperature increased. Band-gap energy of the powders ranged from 3.09 to 3.27 eV. Overall, this study shows that initial water content and calcination regime have a profound effect on the phase assembly, crystallite size, band-gap energy, and photocatalytic performance of sol gel synthesized TiO2 nanopowders. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Article Citation - WoS: 22Citation - Scopus: 25Facile synthesis of CsPbBr3/PbSe composite clusters(Taylor & Francis Ltd, 2018) Thang Phan Nguyen; Ozturk, Abdullah; Park, Jongee; Sohn, Woonbae; Tae Hyung Lee; Jang, Ho Won; Kim, Soo YoungIn this work, CsPbBr3 and PbSe nanocomposites were synthesized to protect perovskite material from self-enlargement during reaction. UV absorption and photoluminescence (PL) spectra indicate that the addition of Se into CsPbBr3 quantum dots modified the electronic structure of CsPbBr3, increasing the band gap from 2.38 to 2.48 eV as the Cs:Se ratio increased to 1:3. Thus, the emission color of CsPbBr3 perovskite quantum dots was modified from green to blue by increasing the Se ratio in composites. According to X-ray diffraction patterns, the structure of CsPbBr3 quantum dots changed from cubic to orthorhombic due to the introduction of PbSe at the surface. Transmission electron microscopy and X-ray photoemission spectroscopy confirmed that the atomic distribution in CsPbBr3/PbSe composite clusters is uniform and the composite materials were well formed. The PL intensity of a CsPbBr3/PbSe sample with a 1:1 Cs: Se ratio maintained 50% of its initial intensity after keeping the sample for 81 h in air, while the PL intensity of CsPbBr3 reduced to 20% of its initial intensity. Therefore, it is considered that low amounts of Se could improve the stability of CsPbBr3 quantum dots.Article Citation - WoS: 4Citation - Scopus: 6A Study on Microstructural Characterization of the Interface Between Apatite-Wollastonite Based Glass Ceramic and Feldspathic Dental Porcelain(Elsevier Sci Ltd, 2016) Pekkan, Gurel; Pekkan, Keriman; Park, Jongee; Ozturk, AbdullahIn this study, the contact area between the glass ceramic containing apatite [Ca-10(PO4)6(O,F-2)] and wollastonite [CaO center dot SiO2] crystals (A-W glass ceramic) and feldspathic dental porcelain was characterized using scanning electron microscope and energy dispersive spectroscopy. Alumina-added A W glass ceramics were prepared by sintering glass compacts in the MgO-CaO-SiO2-P2O5-Al2O3 system at 1100 degrees C. Commercially available dental porcelains for alumina frameworks were applied on the A-W glass ceramic specimen by brushing and carving, and then fired at 960 degrees C using an electrically heated vacuum-furnace. Results revealed that veneering of feldspathic dental porcelain on alumina-added A-W glass ceramic is possible by an interaction between them, with which a diffusion process involving i) seperation of the phases forming the alumina-added A-W glass ceramic, ii) chemical diffusion of elements between alumina-added A-W glass ceramic and feldspathic dental porcelain, and iii) formation of an interface layer, is taking place. The system studied has interfacial characteristics similar to the commercially available dental materials currently used in restorative dentistry. Hence, it may be further processed for potential clinical applications.Article Citation - WoS: 44Citation - Scopus: 43Silver-Loaded Tio2 Powders Prepared Through Mechanical Ball Milling(Elsevier Sci Ltd, 2013) Aysin, Basak; Ozturk, Abdullah; Park, JongeeSilver (Ag) was loaded on TiO2 powders through mechanical ball milling. Ag-loading was accomplished by adding 4.6, 9.2, and 13.8 ml of AgNO3 solution to the TiO2 powders during the milling process. The resulting powder was characterized by XRD, XPS, SEM, and EDS. The photocatalytic activity of the silver-loaded powder was evaluated in terms of the degradation of methyl orange (MO) solution under ultraviolet (UV) illumination. XRD patterns were refined using the Rietveld analysis to determine the lattice parameters. XRD analysis suggested that Ag was loaded on TiO2 powders in the form of AgO. X-ray photoelectron spectroscopy and Rietveld analysis revealed that silver did not dope into the crystal structure of TiO2. SEM investigations confirmed that ball milling caused a decrease in the average particle size of the powders. Silver-loading improved the photocatalytic activity of the TiO2 powders. The TiO2 powder ball milled without Ag-loading degraded 46% of the MO solution whereas the ball milled with 13.8 ml AgNO3 solution degraded 96% of the MO solution under 1 h UV irradiation. Moreover, TiO2 powders gained antibacterial property after Ag-loading. (c) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Article Citation - WoS: 28Citation - Scopus: 27Hydrothermal Synthesis of 3d Tio2 Nanostructures Using Nitric Acid: Characterization and Evolution Mechanism(Elsevier Sci Ltd, 2016) Erdogan, Nursev; Ozturk, Abdullah; Park, JongeeVarious morphologies of TiO2 nanostructures were synthesized by HNO3 assisted hydrothermal treatment with respect to the acid molarity (1 M, 3 M, and 8 M), temperature (110, 140, and 180 degrees C), and time (1, 3, and 6 h). An additional sample was synthesized inside the protonated titanate nanoribbon coated vessel with the acid molarity of 8M at 140 degrees C for 3 h. The crystal structure and morphology of the nanostructures synthesized were investigated using X-Ray diffractometer, scanning electron microscope, and transmission electron microscope. The results revealed that lower acid concentrations, longer synthesis durations and higher temperatures favored anatase phase formation. Meanwhile, a phase pure 3D lotus structure ruffle TiO2 could be obtained by hydrothermal synthesis at 8M HNO3 concentration at 140 degrees C for 3 h using protonated Htitanate nanoribbons. A probable mechanism for the evolution of 3D ruffle lotus structure was highlighted. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Article Citation - WoS: 30Citation - Scopus: 33Boron and zirconium co-doped TiO2 powders prepared through mechanical ball milling(Elsevier Sci Ltd, 2013) Tokmakci, Tolga; Ozturk, Abdullah; Park, JongeeA titania photocatalyst co-doped with boron and zirconium was prepared by mechanical ball milling. The resulting powder was characterized by XRD, XPS, SEM, and EDS. The photocatalytic performance of the powder was evaluated by degradation of methylene blue (MB) solution under UV illumination. XRD patterns were refined by Rietveld analysis to obtain accurate lattice parameters and positions of the atoms in the crystal structure of the photocatalyst. XRD, XPS, and Rietveld analysis results indicated that mechanical ball milling successfully weaved the dopant elements into the crystal structure and distorted the lattice of TiO2. Also, SEM micrographs confirmed that mechanical ball milling led to a decrease in average particle size of the photocatalyst. Boron and zirconium co-doped TiO2 particles exhibited a better visible light response and photocatalytic activity than those of the mono-element doped TiO2 (i.e. B-TiO2 and Zr-TiO2) and undoped TiO2 particles. The enhanced photocatalytic activity is attributed to the synergistic effects of boron zirconium co-doping and particle size reduction. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
