Yazar "Boran, Filiz" seçeneğine göre listele

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    Aloe vera-based antibacterial porous sponges for wound dressing applications
    (Springer, 2021) Tamahkar, Emel; Özkahraman, Bengi; Özbaş, Zehra; İzbudak, Burçin; Yarimcan, Filiz; Boran, Filiz; Bal Öztürk, Ayça
    The antibacterial sponges with high macroporosity, high interconnectivity and high biocompatibility is a significant concern for wound healing applications. In this work, novel Aloe vera (AV) based sponges were developed via subsequent lyophilization with further chemical crosslinking throughout the double network sponges. Single network was composed of gelatin-sodium alginate (G-SA) while the double network using gelatin-sodium alginate- sodium hyaluronate (G-SA-HA) was produced with the addition of hyaluronic acid solution into the gelatin-sodium alginate matrix. Lastly, Aloe vera as the bioactive agent was fabricated throughout the gelatin-sodium alginate-sodium hyaluronate matrix. The AV-based sponges demonstrated large pores with high interconnectivity. The swelling degree of the AV-based sponges were higher than that of G-SA and G-SA-HA sponges. The release of AV from the sponges reached an equilibrium value after 24 h showing a more controlled release at pH 5.5 than at pH 7.4. AV-based sponges showed antibacterial activity against Staphylococcus aureus, Enterococcus faecalis, Streptococcus pneumoniae and Bacillus cereus and displayed any cytotoxicity against Mesenchymal stem cells.
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    Effect of surfactant types on the size of tin oxide nanoparticles
    (Polish Academy of Sciences, 2017) Boran, Filiz; Çetinkaya, Sevil; Şahin, Melike Ekin
    In this study, tin oxide (SnO2) nanoparticles were synthesized by hydrothermal method in the presence of hydrazine and ammonia by adding surfactant for 12 h in a Teflon autoclave at 100°C reaction temperature. Tin(II) chloride hydrate as an inorganic precursor, hexadecyl trimethyl ammonium bromide (CTAB), and tetrapropyl ammonium bromide (TPAB) as cationic, and sodium dodecyl sulfonate (SDS) as anionic surfactants were used. The results showed that the size and shape of nanoparticles depended on the surfactant types. The nanoparticles sizes between 17.5 and 19.7 nm were obtained by changing types of surfactants. Synthesized tin oxide nanoparticles were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and the Fourier transform infrared spectroscopy.
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    Encapsulation of CuO nanoparticles inside the channels of the multi-walled carbon nanotubes functionalized with thermal stress
    (Elsevier Science Sa, 2021) Boran, Filiz
    Commercially available multi-walled carbon nanotubes (MWCNTs), which are generally naturally intertwined, were cut by sudden, repeated exposure to oxidizing conditions in the air. This process has been proved to be an effective handle of producing open ended and medium level functionalization. Results showed that the typical closed graphite end caps for carbon nanotubes via functionalized with thermal stress (CNT-M) can be shorten long MWCNTs, while improving average graphite quality. These results were supported by the increase of Brunauer-Emmett-Teller (BET) surface area from 284.772 m(2)g(-1) to 463.890 m(2)g(-1). Copper oxide nanoparticles (CuO-PEGx) which were synthesized using polyethylene glycol (PEG) nonionic surfactants with different derivative (polyethylene glycol methyl ether methacrylate) and molecular weights (Mw: 200, 2000 and 5000), were encapsulated into CNT-Ms by simple wet impregnation technique. The filling capacity depended on the preparation conditions and particle size of CuO nanostructures. While other samples showed a multiple particle size distribution, only CNT-M-CuO-PEG950 sample indicated uniform particle size distribution with the smallest particles (3.6 nm) inside CNT-M channels. The BET surface areas of the nanocomposites (274.865-304.859 m(2)g(-1)) were lower than the surface area (463.890 m(2)g(-1)) of CNT-Ms while they were close and large to the surface area of MWCNTs (284.772 m(2)g(-1)).
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    Enhancement of dispersion stability of inorganic additives via poly(sodium-4- styrenesulfonate) treatment geared to hydrogel applications
    (TUBITAK, 2021) Boran, Filiz; Okutan, Merve
    This study reports the preparation of poly(sodium-4-styrene sulfonate) (PSS) treated bentonite and clinoptilolite to prevent the agglomeration and sedimentation of these inorganic fillers during the preparation of hydrogel. For this purpose PSS treated fillers were prepared by using various techniques (dip and dry, hydrothermal, one-step ball milling and ultrasonication methods). The most suitable technique for preparing these PSS treated inorganic fillers (abbreviated as BP-dip and CP-dip) was the dip and dry method. BP-dip and CP-dip based polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP) composite hydrogels were prepared using the freeze/ thawing method after the addition of one of BP-dip and CP-dip inorganic fillers in various amounts. The swelling properties, stability behaviors and Rhodamine B (RhB) adsorption of the composite hydrogels were studied. It was found that the swelling degrees of CP-dip and BP-dip based composite hydrogels with 25 mg of filler were higher than that of all other samples. The kinetic mechanism of RhB adsorption process and the related characteristic kinetic parameters were investigated by Pseudo kinetic models. The adsorption kinetics results for RhB adsorption were found best fitted with pseudo-second-order kinetics model. The maximum RhB adsorption capacity was determined to be for PVA/PVP-CP-dip25, which was 3.3 times higher than that of the unfilled PVA/PVP hydrogel. © 2021 TUBITAK. All rights reserved.
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    Geliştirilmiş elektrik iletkenliğine sahip POT/Na-Feldispat iletken kompozitlerinin sentezlenmesi ve karakterizasyonu
    (Dicle Üniversitesi, 2017) Boran, Filiz; Çetinkaya, Sevil; Anaklı, Duygu; Karakışla, Meral; Saçak, Mehmet
    Bu çalışmada iletken POT/Sodyum Feldispat kompoziti in-situ kimyasal polimerizasyon yöntemi ile hazırlandı. Sodyum Feldispat partikülleri varlığında asidik sulu ortamda hazırlanan kompozitin iletkenliği ve %POT verimi üzerine sodyum feldispatın tanecik boyutunun ve polimerizasyon koşullarının etkisi araştırıldı. En yüksek elektriksel iletkenlik ve verim için en uygun reaksiyon koşulları 45µm altı partikül boyutundaki Na-Feldispat, 1 M HCl, 0.3 M o-toluidin, 0.0375 M K2Cr2O7 ve 0°C sıcaklık olarak belirlendi. En yüksek POT verimi ve elektriksel iletkenlik değerleri sırasıyla %24.51 ve 22×10-5 Scm-1 bulundu. Hazırlanan kompozitin karakterizasyonu, kompozitin bileşenlerinin saf halleri ile karşılaştırılmalı olarak Fourier dönüşümlü kızılötesi spektroskopisi (FTIR), X-ışınları kırınımı (XRD), termal gravimetrik analiz (TGA) ve taramalı elektron mikroskop (SEM) teknikleri kullanılarak yapıldı.
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    Green Reduction Of Graphene Oxide By Using Kombucha Tea
    (2019) Kütük, Nurşah; Boran, Filiz; Çetinkaya Gürer, Sevil
    In this study, a simple and efficient method of reduction for the preparation of reduced graphene oxide (RGO) from graphene oxide (GO) using Kombucha Tea (KT) is reported. The graphene oxides (GOs) were produced from natural graphite (Gr) powders based on Hummers’ method. KT was used as natural reductants to reduction of GO. Polyphenol content of KT was determined by using Folin-Cioceltau method. KT and GO were mixed in certain ratios to reduce graphene oxide (RGO) at room temperature. RGO was characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourer Transform Infrared (FTIR). It was clearly observed that the functional groups containing oxygen were reduced as a result of the analyzes.
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    Hydrophobic surface modification and characterization of melamine foam
    (TUBİTAK, 2023) Okutan, Merve; Boran, Filiz; Ergün, Ayça; Kanca, Yusuf; Özkahraman, Bengi; Deligöz, Hüseyin
    Abstract: Superhydrophobic and oleophilic modification of commercial acoustic melamine foam (MF) was made in this study. The modification was carried out with chitosan (CHI) and silica particles (SiO2 ), by using both a layer-by-layer-like approach (LbL) and dip coating technique. Subsequently, 1-octadecanethiol was used as a secondary modification agent. QCM-D, SEM, and FTIR analyses confirmed that the coating was successfully performed. After the modification, the column wall thicknesses increased than that of MF and they ranged from 25% to 48% for modified MF with an LbL-like approach (MMF) and modified MF via dip coating technique (MMFd), respectively. The sorption experiments showed that modified MFs, which had a water contact angle (WCA) above 160°, could sorb several model pollutants (vegetable oil, chloroform, ethanol, and toluene) up to 76–130 times their original weight. It had been determined that MMF protects its open-pore structure better than that of MMFd, which indicated that MF has a more uniform pore structure after modification. Furthermore, after 10 cycles of the sorption and release process, there was no significant change in sorption capacity, and they preserved their mechanical stability and flexibility
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    Mor lahana özütü kullanarak grafen oksitin indirgenmesi ve oksidasyon ile fotokatalitik aktivitesinin incelenmesi
    (GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2023) Kütük, Nurşah; Boran, Filiz; Çetinkaya Gürer, Sevil
    Grafen ve türevleri pek çok eşsiz sayılabilecek özelliğe sahip, fotokatalitik bozunum ve adsorpsiyon uygulamalarında potansiyeli olan önemli bir malzemelerdir. Grafen oksitin (GO) indirgenerek oksijen içeren fonksiyonel grupların giderilmesi son yıllarda sıkça kullanılan ilgi çekici bir yöntemdir. Bu çalışmanın amacı, kolay ve etkili bir yöntem olan, yeşil sentez yöntemi ile mor lahana sulu özütü kullanarak GO indirgenmesi ve fotokatalitik giderim uygulamalarında kullanımının incelenmesidir. Sentezleme koşullarını optimize etmek için reaksiyon sıcaklığı 25, 50 ve 100?’de ve reaksiyon süresinin etkisi ise 1, 2, 4 ve 6 h için incelendi. XRD, FTIR, UV/vis ve SEM sonuçlarına göre 100? reaksiyon sıcaklığı ve 6 h reaksiyon süresi GO’nun indirgenmesi için uygun deneysel şartlar olarak bulundu. Elde edilen indirgenmiş grafen oksit (IGO) organik ve katyonik bir boya olan metilen mavisinin (MM) sulu çözeltisinde UV lamba altında ve H2O2 varlığında fotokatalitik bozunum deneylerinde kullanıldı. Sonuçlar 120 min sonunda IGO’nun sulu çözeltiden MM’yi %85 oranında giderdiğini gösterdi. Sentezlenen IGO kullanarak MM’nin fotokatalitik bozunum tepkime kinetiğinin sözde ikinci dereceden reaksiyon kinetiğine uyduğu belirlendi.
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    Poli(sodyum 4-stiren sülfonat) Kaplı SnO2 Nanoparçacıklarının Sentezi, Karakterizasyonu ve Gaz Algılama Özelliklerinin İncelenmesi
    (2019) Boran, Filiz; Taşkıran, İmren; Çetinkaya Gürer, Sevil
    Bu çalışmada, poli(etilen glikol)(PEG)-Kalay Oksit/poli(sodyum 4-stiren sülfonat) PEG-SnO2/PSS nanokompozitleri, 2 saat boyuncadimetil formamid (DMF) varlığında hidrotermal işlemle hazırlandı. Bunun için yüzey aktif madde PEG ile birlikte daha öncedensentezlenmiş olan 16,4 nm büyüklüğündeki SnO2 nanoparçacıkları kullanıldı. PEG-SnO2/PSS nanokompoziti, PSS ve PEG-SnO2 ilebirlikte DMF varlığında 0°C reaksiyon sıcaklığında 2 saat sürede sentezlendi. Hazırlanan PEG-SnO2/PSS nanokompozitinin yapısal veelementel analizi, taramalı elektron mikrokopisi (SEM), Enerji Dağılım X-Işınları Spektrometresi (EDS), X-ışını difraksiyonu (XRD)ve Fourier transform infrared (FTIR) spektroskopisi teknikleri ile yapıldı. FTIR ve XRD analizleri SnO2 nanoparçacıklarının PSSpolimer yapısına katıldığını gösterirken, SEM ve EDS analizleriSnO2nanoparçacıklarının morfolojik yapısının, PSS ile kompozitlerihazırlandığında PSS polimeri ile kapsüllenerek nanoyapıdan mikroküre yapılara dönüştüğünü gösterdi. Ayrıca, sonuçlar, PEG-SnO2yüzeyinin, güçlü ?-? etkileşimleri altında PSS ile % 39,53'lük bir kapsülleme oranı ile kaplandığını gösterdi. Bu örneklerin amonyak,etanol, aseton, formaldehit ve kloroform gibi uçucu organik bileşen (VOC) buharlarına karşı gaz duyarlılıkları, oda sıcaklığında, ikiprobe tekniği ile elektrometre kullanılarak incelendi. PEG-SnO2 nanoparçacıklarının etanol gazı için yüksek algılama performansısergilediği görüldü. Saf olarak kullanılan PSS, VOC gazlarının hepsine karşı yüksek oranda duyarlılık gösterdi. Deney sonuçlarına göre,PSS ile kapsüllenen PEG-SnO2 nanokompozitinin gaz sensörü malzemesi olarak kullanım potansiyelinin arttırılabildiği söylenebilir.
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    Poly(vinyl alcohol)/(hyaluronic acid-g-kappa-carrageenan) hydrogel as antibiotic-releasing wound dressing
    (Springer Int Publ Ag, 2021) Özbaş, Zehra; Özkahraman, Bengi; Bayrak, Gülşen; Kılıç Süloğlu, Aysun; Perçin, Işık; Boran, Filiz; Tamahkar, Emel; Boran, Filiz
    The aim of this research was to investigate the potential of ampicillin-loaded hydrogels based on polyvinyl alcohol (PVA), hyaluronic acid (HA) and kappa-carrageenan ((K)-Carr) as an antibiotic-releasing wound dressing. Firstly, the novel polymers (HA-g-(K)-Carr) were synthesized by grafting of HA onto (K)-Carr using 4-dimethylaminopyridine/1-(3-dimethylaminopyl)-3-ethyl-carbodiimide hydrochloride as catalyst system via esterification reaction. The characterization of the polymer structure was performed by Fourier transform infrared spectrum (FTIR), proton nuclear magnetic resonance and thermogravimetric analysis. Secondly, PVA/(HA-g-(K)-Carr) hydrogel with/without loading of ampicillin molecules was formed via freeze-thawing method since PVA/K-Carr and PVA/HA hydrogels were also fabricated as control groups. The hydrogels were subjected to characterizations with FTIR and X-ray diffractometer. PVA/(HA-g-(K)-Carr) hydrogel demonstrated the highest swelling amount and highest ampicillin release amount reaching an equilibrium value after 480 min rather than the other hydrogels. Also, PVA/(HA-g-(K)-Carr) hydrogel exhibited inhibition zone against Escherichia coli and Staphylococcus aureus and no cytotoxic effect for L929 cells. All the results showed that PVA/(HA-g-(K)-Carr) hydrogels are good candidates for wound dressing applications.
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    Polyvinyl alcohol/CuO nanocomposite hydrogels: facile synthesis and long-term stability
    (2019) Boran, Filiz; Karakaya, Çiğdem
    Within this study, Polyvinyl alcohol/CuO nanocomposite hydrogels were synthesized through dispersing CuO nanoparticles in a PVA solution, using the freeze-thawing procedure in order for physically crosslinking. The average particle size of CuO nanoparticles which was added to the hydrogel was determined as 3.51 nm according to the XRD analysis after the ball milling process. The presence of CuO nanoparticles in nanocomposite hydrogels was determined by UV-vis spectroscopy, FESEM, EDS, and FTIR analysis. Also, the rheological properties of neat hydrogel and PVA/CuO nanocomposite hydrogels were examined. The addition of CuO nanoparticles to the polymer structure develops rheological features of PVA hydrogels. The Effect of CuO content of nanocomposite hydrogels on the swelling behavior and long term stability was investigated. These nanocomposite hydrogels demonstrated unique properties for biomedical applications due to their high swellability at pH 2.1 as the pH values of the stomach and long term stability. According to these results, the addition of CuO to the hydrogel structure improved the swelling characteristics of neat PVA hydrogel.
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    Preparation and swelling properties of zeolite-poly(2-hydroxyethyl methacrylate-co-acrylic acid) hydrogel composites
    (Polish Academy of Sciences, 2016) Aktı, Filiz; Boran, Filiz
    Zeolite-Poly(2-hydroxyethyl methacrylate (HEMA)-co-acrylic acid (AA)) hydrogel composite materials were synthesized by in situ free radical addition polymerization technique. The swelling values obtained highly for the hydrogel are synthesized at HEMA/AA monomer ratio value of 80/20. The hydrogel composites synthesized with zeolite having-90 ?m particle size and 20 wt% amount showed the highest swelling degree. Zeolite adding to the hydrogel structure increased the swelling values of hydrogel. Synthesized samples were characterized using a Fourier transform infrared spectrometer technique.
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    Size controllable synthesis and characterization of cuO nanostructure
    (Trans Tech Publications Ltd, 2018) Candemir, Duygu; Boran, Filiz
    In this study, copper oxide (CuO) nanostructures were successfully prepared by adding EG (ethylene glycol) and PEG (4000, 8000) (polyethylene glycol) via an in-situ chemical precipitation method. EG and PEG (4000, 8000) were effective for changing the particular size of CuO and we examined the effects of drying type such as freeze drying, muffle and horizontal furnace on the size of CuO nanostructure. The structure, morphology and elemental analysis of CuO nanostructure were analyzed by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Also, the CuO nanostructures showed excellent electrical conductivity by the changing of PEG’s molecular weight and drying processes. © 2018 Trans Tech Publications, Switzerland.
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    Sno2/graphene nanocomposites with enhanced gas sensing performance
    (Trans Tech Publications Ltd, 2018) Boran, Filiz; Çetinkaya, Sevil
    Graphene-Tin Oxide (G-SnO2) nanocomposites in different morphology were synthesized using tin (II) chloride (SnCl2) and graphene Oxide (GO) via hydrothermal process in the presence of hydrazine and ammonia by adding surfactant for 12 hours in a teflon autoclave at 100ºC reaction temperature. Poly(vinyl prolidon) (PVP) and poly(ethylene glycol) (PEG) were used as nonionic surfactants while hexadecyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfonate (SDS) were utilized as cationic and anionic surfactants, respectively. The synthesized nanocomposites were characterized by XRD, FESEM, C-TEM and FT-IR. The gas sensing properties of the obtained samples to the vapors of various Volatile Organic Compounds (VOC), such as Ethanol, Methanol, Chloroform, Toluene and Acetone were also investigated at room temperature. The prepared G-SnO2 nanocomposites exhibited high detection performances for ethanol, chloroform and methanol. The nanocomposites could be used as sensor material for VOC gases. © 2018 Trans Tech Publications, Switzerland.
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    Synthesis and characterization of modified diatomite-leaf-like cuO nanosheet composites
    (Trans Tech Publications Ltd, 2018) Boran, Filiz
    In this work, firstly we described the effect of freeze drying on modification of raw diatomite. And then, modified diatomite-leaf-like copper oxide (CuO) nanosheet composite was successfully prepared by surfactant-free in-situ chemical precipitation method. The structure, morphology and elemental analysis of CuO nanosheets and its composite were analyzed by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), fourier transform infrared (FTIR) spectroscopy and energy dispersive X-ray spectroscopy (EDAX). Dimensions of leaf-like CuO nanosheets were approximately determined as 160 nm in width, 320 nm in length and 20 nm in thickness. According to the EDAX spectrum, leaf-like CuO nanosheets composed of Cu and O atoms without any impurity and also uniformly covered the entire surface of modified diatomite. © 2018 Trans Tech Publications, Switzerland.
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    Synthesis and characterization of poly(o-toluidine)/kaolinite conductive composites for humidity and temperature sensing
    (2018) Boran, Filiz; Çetinkaya Gürer, Sevil; Karakışla, Meral; Saçak, Mehmet
    Conductive poly(o-toluidine)/kaolinite composite was synthesized via chemical polymerization of o-toluidine in the availability of kaolinite using ammonium persulfate as oxidizing agent. To investigate the use of the prepared conductive composite as humidity and temperature sensor, the effect of polymerization conditions such as HCl, o-toluidine and oxidant concentrations on the amount of conductive POT contained in the composite and the conductivity values of composites were investigated. It was found that the composites with the highest poly (o- toluidine) content (29.4%) and conductivity (8.3×10-4 Scm -1 ) were obtained by 0.2 M ammonium persulfate, 0.4 M o-toluidine and 1 M hydrochloric acid for 2 hours of continuous polymerization at 20 °C. The resistivity values of pure poly(o-toluidine) and poly (o-toluidine)/kaolinite composite were monitored during heating- cooling cycles in the range of 0-100 °C. Changes in resistivity for pure poly(o-toluidine) and poly(o-toluidine)/kaolinite composite with humidity 30-90% were examined and humidity sensor behavior was determined. Characterization of the prepared composite was performed by Fourier transform ınfrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy techniques (SEM).
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    Synthesis optimization of ZrO2 nanostructures for photocatalytic applications
    (Scientific and Technological Research Council Turkey, 2023) Boran, Filiz; Okutan, Merve
    Abstract: This study aims to optimize the synthesis of semiconductor zirconia (ZrO2 ) nanoparticles for future photocatalytic applications in degradation of pollutants in wastewater under ultraviolet (UV) light. The synthesis procedure of ZrO2 nanoparticles was optimized by examining the effects of synthesis methods (ultrasound-assisted, hydrothermal method in an autoclave and conventional precipitation), reaction time (2, 6, 10, and 18 h), ambient pH (3, 7, 10, 13), and surfactant type (anionic, cationic, and non-ionic), on the particle size and crystal phase of the nanomaterial. The characterization of the synthesized samples was performed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), high-contrast transmission electron microscopy (HR-TEM), and transmission electron microscope (TEM) analysis. Consequently, to synthesize ZrO2 nanoparticles with the smallest particle size and monoclinic/tetragonal phase, the experimental conditions were optimized as ultrasound-assisted synthesis method, pH 10, and 6 h reaction time without surfactant. Moreover, percentage yield, particle size, crystallinity, monoclinic and tetragonal volumes of ZrO2 nanostructures synthesized under optimized conditions were determined as 39.40%, approximately 9 nm, 46.77, 79%, and 21%, respectively. It has been determined that the particle sizes can be kept under control by controlling the phase composition of ZrO2 nanostructures by optimizing the synthesis parameters. Structural and morphological characterization results can be correlated to the photocatalytic application, showing the potential of this material for the photodegradation of organic dye pollutants.
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    Synthesis, characterization and sensing behavior of WO3 nanocrystalline powder for toluene vapor
    (Polish Academy of Sciences, 2017) Boran, Filiz; Çetinkaya, Sevil
    Tungsten oxide (WO3) nanocrystalline powder was successfully synthesized by direct precipitation technique starting from sodium tungstate dehydrate (Na2WO4•2H2O) as precursor at 80°C for 48 h. The morphological characteristics, distribution, and crystallite size of WO3 nanocrystalline powder were analysed by transmission electron microscopy, X-ray diffraction, and the Fourier transform infrared spectroscopy. According to transmission electron microscopy results, the mean particle size of WO3 nanocrystalline powder was approximately determined as 41.7 nm. The gas sensing performance of WO3 nanocrystalline powder for saturated toluene vapor was measured by two probe resistivity unit in a closed vessel at room temperature. In addition, WO3 nanocrystalline powder was able to respond the lowest concentration of 500 ppm. The results showed that the sample exhibited high sensitivity (93%) and good response reproducibility (0.93 + 5.5%) for toluene vapor.
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    The effect of starting material types on the structure of graphene oxide and graphene
    (2019) Boran, Filiz; Çetinkaya Gürer, Sevil
    In this study, the effects of starting material types on graphene oxide (GO) are reported with the aim of developing graphene (GR) synthesis. The GOs were prepared from natural graphite (NG) powder and graphite nanoplate (GNp) based on the Hummers method. Two kinds of GR were successfully synthesized using GOs, which were prepared from NG and GNp in the presence of hydrazine and ammonia for 24 h at a 100 ? C reaction temperature. The synthesized GOs and GRs were characterized by X-ray diffraction (XRD) techniques, Fourier transform infrared, highcontrast transmission electron microscopy (HCTEM), dispersive Raman spectroscopic analyses, and elemental analyses. HCTEM analyses of GOs and GRs exhibited largely folded, convoluted, and entwined GO and GR structures. The XRD and Raman analyses showed that the number of layers of GO1, GO2, GR1, and GR2 were 9.27, 13.53, 4.11, and 5.26, respectively. On the other hand, GR1, prepared from NG powder, showed much higher quality (peak intensities (I D /I G) = 1.53, C/O = 3.64) than GR2, which was prepared from GNp (I D /I G = 1.64, C/O = 3.17). Thus, this study provides a way to produce higher quality GOs and GRs.
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    The influence of freeze-thawing conditions on swelling and long-term stability properties of poly(vinyl alcohol) hydrogels for controlled drug release
    (Springer, 2021) Boran, Filiz
    The preparation of poly(vinyl alcohol) (PVA) hydrogels was succeeded via the freeze-thawing (F/T) method by varying the synthesis parameter conditions. The swelling capacity and long-term stability of the hydrogels were determined as a function of time at pH 2.1, 5.5 and 7.4 and found to be mainly affected by the synthesis parameter conditions. These studies showed that the swelling ratio generally increased with a low number of F/T cycles (2 and 3), high freezing temperature (- 5 and - 16 degrees C) and freeze-dried of drying type for all three pH mediums. The dried hydrogels at room temperature were found to be more stable hydrogels. In addition, the drug release studies of salicylic acid as a drug model were investigated at pH 7.4 and displayed controlled release for 120 h. The release kinetic studies obtained from drug release data demonstrated that the PVA hydrogel fits well into the Higuchi model. The release mechanism of PVA hydrogel was also determined as super case II type.