Person: GENÇ, SEVAL
Loading...
Email Address
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
GENÇ
First Name
SEVAL
Name
17 results
Search Results
Now showing 1 - 10 of 17
Publication Metadata only Rheological characteristics of exopolysaccharides (EPSs) produced by Brevibacillus thermoruber(ELSEVIER SCIENCE BV, 2012) TOKSOY ÖNER, EBRU; Yildiz, Songul Yasar; Ozer, Tugba; Radchenkova, Nadia; Genc, Seval; Oner, Ebru Toksoy; Kambourova, MargaritaPublication Open Access Evaluation of the Potential Use of Levan Polysaccharide in Paper Conservation(WILEY-HINDAWI, 2020-08-10) TOKSOY ÖNER, EBRU; Saglam, Rumeysa Ozen; Genc, Seval; Oner, Ebru ToksoyConservation of paper-based materials, namely, manuscripts, includes repair of tears, gap filling, consolidation, and fixation, which requires the use of adhesives. The adhesive in use for these purposes should be compatible with the chemical and physical properties of paper and should present good aging characteristics. In this study, we conducted a set of experiments with paper samples on which fructan-based biopolymer Halomonas levan (Hlevan) was applied for the first time and compared with glucan-based adhesive starch. Adhesive-applied samples were initially prepared by the application of different historical recipes of sizing and ink. Then, they underwent accelerated thermal aging. Chemical and physical changes of paper samples (crystallinity, pH, and color) were analyzed. Finally, Principal Component Analysis was performed to identify dominating factors affecting sample behavior with applied adhesives. This study demonstrates the aging characteristics of Hlevan on cellulose-based materials. The results showed that there is a color shift from blue to yellow for all samples after aging, but it is more pronounced for some samples with Hlevan. In addition, Hlevan is slightly less acidic than starch in all cases and acted as a plasticizer for a specific kind of sizing material. The methodology of this research is also efficacious in terms of understanding the interaction of paper media with the adhesives and their effects on aging.Publication Open Access Synthesis and characterization of interpenetrating network (IPN) based levan-polyacrylamide hydrogels and their application in conservation of cultural heritage(2023-11-01) ÜNAL YILDIRIM, SEMRA; OKTAR, FAİK NÜZHET; GENÇ, SEVAL; TOKSOY ÖNER, EBRU; Özen Sağlam R., Ünal Yıldırım S., Oktar F. N., Genç S., Erdem G., Toksoy Öner E.In this study, an IPN based enzymatic levan-polyacrylamide hydrogel (EL-PA) was developed and characterized for its structural, morphological, rheological properties and swelling kinetics to underline hydrogel properties and its potential use in paper conservation. The addition of levan also led to changes in the viscoelastic behavior of the hydrogels, with the complex viscosity of EL-PA samples showing pronounced dependence on shear rate. The swelling and the overall surface area of the hydrogels were increased with the addition of levan into the polymer network. Source associated structural differences were found to be negligible such that both microbially produced linear and enzymatically produced branched forms of levan performed equally well. Solvent loaded hydrogels were then applied on an artifact, a 19th century book of Namık Kemal, and investigated using FTIR, SEM, XRD and colorimetric analysis. Old adhesive layers were successfully removed, and hydrogels showed good compatibility and ease of application. This study has shown that levan has improved hydrogel properties and levan based systems bear high potential in conservation science.Publication Metadata only Laser-induced tunable white light emission in Yb3+/Er3+/Tm3+ Ion-doped La2Ti2O7(2023-07-01) GENÇ, SEVAL; Cantürk S. B., Tabanlı S., Örücü H., Genç S., Erdem M., Eryürek G.Publication Open Access Experimental Studies on Magnetorheological Fluids(Elsevier, 2022-01-01) GENÇ, SEVAL; GENÇ S.Smart materials are defined as the materials having properties that can be tuned or altered under externally applied fields. These materials are usually polycrystalline or single crystal in their solid state. These smart materials exhibit properties such as ferroelectricity, pyroelectricity, piezoelectricity, and magnetostriction. Another class of smart materials is known as the “field responsive fluids”. Magnetorheological (MR) fluids, electrorheological (ER) fluids, ferrofluids, and some gels belong to this group. A common property of these fluids is that they are all dispersions of particles in a carrier liquid and their properties are controlled by externally applied magnetic or electrical field. MR fluid can be defined as ferromagnetic or ferrimagnetic particles dispersed in an organic or aqueous carrier liquid. MR fluid has reversible and tunable ability to transform from liquid to viscoelastic solid in fractions of a millisecond when subjected to a magnetic field. MR fluid has a consistency like paints in the “off-state” (B ¼ 0T) regime. In the “on-state” (B a 0T) regime the magnetic particles line up, forming chain-like structure in the direction of the applied magnetic field in order to minimize the magnetic dipole interactions between the particles. This chain alignment causes a considerable increase in the yield stress. This increase is non-linear since the particles are ferro or ferrimagnetic. Depending on the composition, particle size, volume fraction, magnetic saturation, and flux density, the yield stress can go up to 100 kPa (Genç and Phulé, 2002). The ferromagnetic or ferrimagnetic magnetic phase is multi-domain with low coercivity and high saturation magnetization. The diameters of the particles range from 0.01 to 20 mm. Due to its high saturation magnetization (Ms ¼ 203.7 emu/gr), carbonyl iron (CI) produced by decomposition iron penta-carbonyl (Fe(CO)5), is the most commonly used magnetic material (Cullity and Graham, 2010). Besides iron, cobalt, nickel, iron oxides (Fe3O4, Fe2O3), ferrites, and transition metal alloys are also used in the synthesis of the MR fluid. Silicone oils, synthetic or semi-synthetic oils, lubricating oils and mineral oils, many other polar organic liquid and water have all been reported to be used as carrier liquid (Genc and Derin, 2012). Due to their field dependent rheology, MR fluid is used in automobile dampers, (Abu-Ein et al., 2010; Zeinali et al., 2016; Attia et al., 2017), clutches (Hema Latha et al., 2017), and brakes (Kumbhar et al., 2015). They are also utilized in polishing devices (Jha and Jain, 2009), loud speakers, vacuum sealing, cancer therapy (Liu et al., 2001). Although iron having high saturation magnetization could be a good candidate for magnetic phase, its high density could be a disadvantage. Mismatch between the density of the magnetic particles and carrier liquid causes sedimentation which deteriorates the MR effect. To improve the sedimentation stability without sacrificing the MR effect is a challenge. One way to make a stable suspension is to coat the magnetic particles with a surfactant in order to create steric stabilization (Phulé et al., 1999). The stability could also be improved by using nanoparticles such as magnetite (Fe3O4), because thermodynamic forces can overcome the gravitation settling when the particle size decreases to a critical value (Rosensweig, 2014). Microcrystalline cellulose, carbon nanotubes, silica, and graphene oxide, nano-hollow Fe3O4 spheres are other additives that are investigated by various scientists (Ashtiani et al., 2015). After the brief introduction of MR fluids, in the rest of the paper, the recent experimental studies of the MR fluids will be discussed. These studies will include the improvement of MR effect and sedimentation stability, as well as the experimental findings of the rheological and stability measurements.Publication Open Access Phosphate recovery from sewage sludge supernatants using magnetic nanoparticles(ELSEVIER, 2021-04) SEMERCİ, NESLİHAN; Gulyas, Anett; Genc, Seval; Can, Zehra Semra; Semerci, NeslihanPhosphorus removal and recovery from synthetic solutions and sewage sludge supernatants by using magnetic nanoparticles (MNP) were investigated through batch adsorption experiments. The adsorption kinetics and isotherms on the removal of phosphate have been studied using different MNP doses, contact time, pH, and initial P concentrations. Reusability of the MNP and the enrichment of phosphate in desorption solution from dewatering supernatants were tested in a series of adsorption-desorption cycles. The removal efficiency was between 29 and 97 % after 24 h depending on the P concentrations and adsorbent concentrations. This efficiency was detectable in pH similar to 3-5 but decreased in case of increased pH levels. Intra particle (IP) diffusion model kinetic tests demonstrated that the adsorption process was controlled by a multi-step mechanism and the reaction equilibrium was reached after 120 min. Besides phosphate, ammonium, magnesium and calcium ions were adsorbed on MNP to a lesser extent. Surface characterization and adsorption mechanism were discussed based on XRD, SEM and FTIR analyses. MNP can be very effective for both ammonia and phosphate removal and recovery from dewatering supernatant solutions.Publication Metadata only Adsorptive removal of bisphenol A from aqueous solutions using phosphonated levan(ELSEVIER, 2019) HACIOSMANOĞLU, GÜL GÜLENAY; Haciosmanoglu, Gul Gulenay; Dogruel, Tugce; Genc, Seval; Oner, Ebru Toksoy; Can, Zehra SemraIn this study, the potential use of phosphonated Halomonas Levan (PhHL) as a natural and cost effective adsorbent for Bisphenol A (BPA), was systematically investigated via the study of the adsorption equilibrium, kinetics, and reuse potential as well as the interpretation of adsorption mechanism. The effects of pH and temperature on the adsorption were also evaluated. The maximum amount of BPA adsorbed on the unit weight of PhHL was determined as 104.8 (-/+ 5.02) mg/g (at 298 K) and the maximum adsorption capacity was calculated as 126.6 mg/g by Sips model. FTIR and XPS studies were conducted to elucidate the adsorption mechanism. Based on the obtained results OH-pi and CH-pi interactions were found to be effective in the adsorption mechanism. The reuse ability was studied with three cycles of adsorption-desorption, and the results showed that the BPA adsorbed per gram of the PhHL decreased 28.6% after the third cycle. This study has shown that PhHL can be used as an effective adsorbent for the removal of BPA from aqueous solutions. The obtained results may be useful in the development of PhHL based adsorption systems for the removal of EDCs with similar chemical properties to BPA.Publication Metadata only Synthesis and characterization of levan hydrogels and their use for resveratrol release(SAGE PUBLICATIONS LTD, 2021) TOKSOY ÖNER, EBRU; Selvi, Sinem Selvin; Haskoylu, Merve Erginer; Genc, Seval; Toksoy Oner, EbruConsidering the need for systematic studies on levan based hydrogels to widen their use in drug delivery systems and biomedical applications, this study is mainly focused on the synthesis and comprehensive characterization as well as drug release properties of hydrogels based on Halomonas levan (HL) and its chemical derivatives. For this, hydrolyzed and phosphonated HL derivatives were chemically synthesized and then cross-linked with 1,4-Butanediol diglycidyl ether (BDDE) and the obtained hydrogels were characterized in terms of their swelling, adhesivity, and rheological properties. Both native and phosphonated HL hydrogels retained their rigid gel like structure with increasing shear stress levels and tack test analysis showed superior adhesive properties of the phosphonated HL hydrogels. Moreover, hydrogels were loaded with resveratrol and entrapment and release studies as well as cell culture studies with human keratinocytes were performed. Biocompatible and adhesive features of the hydrogels confirmed their suitability for tissue engineering and drug delivery applications.Publication Metadata only Mechanical and electrical properties of Bi1.5-xLaxZn0.92Nb1.5O6.92 pyrochlore ceramics(SPRINGER, 2016) GENÇ, SEVAL; Qasrawi, A. F.; Kmail, Renal R. N.; Mergen, A.; Genc, SevalThe physical properties of Bi1.5-xLaxZn0.92Nb1.5O6.92 solid solutions are investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS), and temperature dependent relative permittivity and electrical resistivity measurements. The La content which was varied from 0.10 to 0.60 is found to be solvable up to 0.21. Further increase in the amount of the La content caused the appearance of Bi0.4La0.6O1.5, LaNbO4, and ZnO minor phases in the pyrochlore matrix. While the lattice parameter and the theoretical, bulk and relative density are hardly affected by the increase in the La content, the strain, the dislocation density and the crystallite size are remarkably varied. The relative permittivity and temperature coefficient of relative permittivity are found to be sensitive to the La-Content. The electrical resistivity is observed to be temperature invariant below 390 K. It exhibits an insulator-semiconductor transition property at a critical temperature that increases with the increasing La content. Such observation is assigned to the increase in the dislocation density, which arises from the increment in the La content. The activation energies of the doped ceramics, which are determined from the electrical resistivity analysis are found to be similar to 1.12-1.00 eV.Publication Metadata only Production and microwave electromagnetic shielding effectiveness of polyaniline-La2Ti2O7:Er,Yb composites(KOREAN ASSOC CRYSTAL GROWTH, INC, 2021) GENÇ, SEVAL; Sahin, Ethem Ilhan; Canturk, Selim Burak; Emek, Mehriban; Genc, Seval; Kartal, MesutIn this research, La2Ti2O7 doped with erbium-ytterbium was produced by using solid state technique. A series of compounds with the chemical equation (La1-x-yREx-y)(2)Ti2O7 were doped with (Er3+, x = 0.025, 0.050) and (Yb3+ y = 0.02) rare earth ions prepared by conventional solid state reaction method at 1350 degrees C for 24 h. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were carried out for the structural analysis, which showed that second phase did not form in (La1-x-yREx-y)(2)Ti2O7. Additionally, the polyaniline- erbium, ytterbium doped La2Ti2O7 composites were fabricated via hot pressing using the compositions of (La0.955Yb0.02Er0.025)(2)Ti2O7, (La0.93Yb0.02Er0.05)(2)Ti2O7 and aniline. The weight ratios of erbium-ytterbium doped lanthanum titanate and aniline were 1:1 and 1:3 respectively, and epoxy resin was utilized to develop microwave shielding effectiveness composites. The microwave shielding effectiveness performances of polyaniline- La2Ti2O7: erbium-ytterbium composites were examined by shielding effect in 0-8 GHz using two-port vector network analyzer. A minimum of - 34.37 dB shielding effect performance was obtained in 6.27 GHz at the thickness of 2.0 mm. This shielding effect performance can be adjusted easily by managing the content of polyaniline in the composites for the needed frequency bands.