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    Impact of titania phase structure and surface reactivity on the photocatalytic degradation of various dyes and textile wastewater
    (Natl Inst Science Communication-Niscair, 2023) Yurtsever, Husnu Arda; Iloglu, Onur; ciftcioglu, Muhsin
    Titania (TiO2) powders have been prepared by precipitation method in different precipitation media which contain sulfate, nitrate or organic species. Photocatalytic degradation of different dyes and a real textile wastewater have been conducted with these powders along with commercial powder Degussa P25 for comparison. Ethyl alcohol (organic medium), sulfuric acid (sulfate medium) and nitric acid (nitrate medium) have been used to dissolve titanium precursor for the precipitation of TiO2 in ammonia solution. UV-Vis DRS and XPS results indicate that S doping in sulfate medium precipitated powder and N doping in nitrate medium precipitated powder has been occurred and the presence of S or N containing impurities on the grain boundaries have been improved light absorption of TiO2 significantly. However, these powders have exhibited low surface reactivities. The highest surface reactivity has been obtained with the powder precipitated in organic medium which also has the highest crystallite sizes (76 nm rutile and 34 nm anatase crystallites) with relatively low rutile weight percentage (10.0%). The surface-normalized rate constants of this powder are 0.02038 min-1.m-2 in real textile wastewater degradation and 0.0161 min-1.m-2 in methyl orange degradation, which are 0.01563 and 0.0091 min-1.m-2, respectively, for Degussa P25. Results have shown that this powder show 30-70% higher surface reactivities compared to Degussa P25. The main structural difference of organic medium precipitated powder and Degussa P25 has been found to be the anatase-rutile weight ratio and crystallite size of rutile phase whereas band gap energy of Degussa P25 is lower and other properties are not significantly different.
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    Öğe
    Structural, magnetic and optical properties of Au/YIG, YIG/Au and Au/YIG/Au multilayer thin film stacks
    (Elsevier, 2020) Akyol, Mustafa; Demiryurek, Nazan; Iloglu, Onur; Tumen, Kutluhan Utku; Karadag, Faruk; Ekicibil, Ahmet
    Y3Fe5O12 shortly named YIG thin film and various form of Au and YIG thin film stacks have been grown on quartz substrate using both spin-coating and sputtering methods. The films are crystallized in cubic phase after heat treatments process that is optimized to avoid cracks on the surface. The thickness of the YIG layer measured by cross-section electron microscope imaging technique are found as about 80 nm for all samples. While the root-mean-square surface roughness of the YIG film is in sub-nanometer scale, it increases up to 2.86 nm by adding Au layer in the film structure. All films exhibit in-plane easy axis and low coercive field at room temperature. But, the saturation magnetization values of films decrease with Au layer. Whereas the optical transmission value is around 80% for YIG samples above 400 nm, it decreases dramatically with Au in the film stacks. The highest absorption coefficient value is found as similar to 20 x 10(4) cm(-1) in Q/Au/YIG structure. This strong absorption might come from the localized surface plasmon polaritons of Au noble metals in YIG structure because it enhances the electronic transition from crystal field splitting. As a result of these measurements, it is seen that the Au layer reduces the magnetization of the films, while increases the absorption rate significantly. Due to considerably low production cost of YIG in this work, it might open to commonly use of them in the magneto-optical devices.
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    Öğe
    The effects of annealing temperature on the thickness, morphology, band gap energy, and photocatalytic performance of ZIF-8-derived ZnO/TiO2 thin films
    (Springer, 2024) Iloglu, Onur; Yurtsever, Husnu Arda
    Multi-oxide photocatalytic materials derived from metal organic frameworks (MOFs) are attracting widespread attention in recent years. The heterostructure originating from oxide-oxide junctions and nonmetal doping due to the combustion of organics from MOFs provide desirable properties to the photocatalytic material. In this study, the effects of annealing temperature on the material properties and photocatalytic activity of ZIF-8-derived ZnO/TiO2 thin films were investigated. XRD, XPS, and FTIR analyses confirmed the oxidation of ZIF-8 to ZnO and SEM analysis revealed the formation of a porous structure at the annealing temperature of 500 degrees C. UV-Vis analysis indicated that the band gap energy decreased from 3.23 to 2.04 eV with increasing annealing temperature. Photocatalytic methylene blue degradation experiments showed that the thin film annealed at 500 degrees C had higher activity than the films annealed at lower temperatures. The thin film annealed at 500 degrees C had more than two times the dye degradation efficiency of the film annealed at 400 degrees C (72% and 33%, respectively). This film was also active in the photocatalytic degradation of caffeic acid which is a colorless pollutant. The high photocatalytic activity of the thin film annealed at higher temperature was attributed to its narrower band gap energy, higher porosity, and more efficient electron-hole separation, which are due to the presence of heterostructure, nonmetal doping, and deficient zones formed by the oxidation of imidazole rings.