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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: 57Citation - Scopus: 68Mechanical Properties of B4c-sic Composites Fabricated by Hot-Press Sintering(Elsevier Sci Ltd, 2020) So, Sung Min; Choi, Woo Hyuk; Kim, Kyoung Hun; Park, Joo Seok; Kim, Min Suk; Park, Jongee; Kim, Hyung SunWe fabricated boron carbide-silicon carbide (B4C-SiC) composites by hot-press sintering without additives and evaluated the crystal phase, relative density, microstructure, and mechanical properties of the sintered body. When B4C and SiC were uniformly dispersed in the composite, crystal growth was inhibited, and a sintered body with a fine and uniform microstructure, with improved mechanical properties, was fabricated. The relative density of B4C-SiC composites sintered at temperatures lower than 2000 degrees C and 40 MPa of pressure exceeded 99.8%, and the bending strength and Vickers hardness at B4C 50 wt% were 645 MPa and 30.6 GPa, respectively.Article Citation - WoS: 44Citation - Scopus: 54Preparation 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: 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: 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: 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: 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: 21Citation - Scopus: 25Inorganic Hole Transport Materials in Perovskite Solar Cells Are Catching Up(Elsevier Sci Ltd, 2023) Sajid, Sajid; Alzahmi, Salem; Ben Salem, Imen; Park, Jongee; Obaidat, Ihab M.More research is required to further optimize device efficiency, stability, and reduce the materials cost as perovskite solar cells (PSCs) approach to industrialization. Modulating the optoelectronic features and chemical coupling of the hole transport materials (HTMs) remains a prominent field of study in PSCs due to the significant impact these materials have on the device performance and stability. In order to speed up the commercialization of these cells, it is also important to use cost-effective HTMs in PSCs. InorganicHTMs are superior to other types of HTMs in terms of their advantages in boosting device performance and producing PSCs at a reasonable cost, in addition to their superior charge transport capabilities, desired energy levels, and intrinsic thermal and chemical stability. A detailed overview of inorganicHTMs, including metal oxides, cyanates, phthalocyanines, chalcogenides, nitrides, and carbides, is presented in this review. After briefly discussing the primary physical and optoelectronic characteristics of inorganic-HTMs, the critical functions of the above-mentioned materials as HTMs in PSCs are addressed. This review concludes by offering suggestions for future research that could considerably boost the performance of the PSCs with cost-effective inorganic-HTMs.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.
