Browsing by Author "Uyar, Tamer"
Now showing 1 - 20 of 205
Results Per Page
Sort Options
Item Open Access Amidoxime functionalized Polymers of Intrinsic Microporosity (PIM-1) electrospun ultrafine fibers for rapid removal of uranyl ions from water(Elsevier, 2018) Satılmış, Berk; Işık, T.; Demir, M. M.; Uyar, TamerThe Polymers of Intrinsic Microporosity (PIM-1) is considered as one of the most promising polymer candidates for adsorption applications owing to its high surface area and the ability to tailor the functionality for the targeted species. This study reports a facile method for the preparation of amidoxime functionalized PIM-1 fibrous membrane (AF-PIM-FM) by electrospinning technique and its practical use for the extraction of U(VI) ions from aqueous systems via column sorption under continuous flow. Fibrous membrane form of amidoxime functionalized PIM-1 (AF-PIM-FM) was prepared by electrospinning method owing to its excellent processability in dimethylformamide. Bead-free and uniform fibers were obtained as confirmed by SEM imaging and average fiber diameter was 1.69 ± 0.34 μm for AF-PIM-FM. In addition, electrospun PIM-1 fibrous membrane (PIM-FM) was prepared as a control group. Structural and thermal characterization of powder and membrane forms of the materials were performed using FT-IR, 1 H NMR, XPS, Elemental analyses, TGA, and DSC. The porosity of the samples was measured by N2 sorption isotherms confirming amidoxime PIM-1 still maintain their porosity after functionalization. Amidoxime functionality along with membrane structure makes AF-PIM-FM a promising material for uranyl adsorption. First, a comparison between powder and membrane form of amidoxime functionalized PIM-1 was investigated using batch adsorption process. Although membrane form has shown slightly lower adsorption performance in the batch adsorption process, the advantage of using the membrane in column adsorption processes makes membrane form more feasible for real applications. In addition, amidoxime modification enhanced the uranium adsorption ability of PIM-FM up to 20 times. The effect of initial concentration and pH were investigated along with regeneration of the adsorbents. AF-PIM-FM was successfully used for five adsorption-desorption cycles without having any damage on the fibrous structure.Item Open Access Amine modified electrospun PIM-1 ultrafine fibers for an efficient removal of methyl orange from an aqueous system(Elsevier, 2018) Satılmış, B.; Uyar, TamerPolymers of Intrinsic Microporosity (PIM-1) is a promising material for adsorption and separation applications. While PIM-1 displays high affinity for neutral species, it shows lack of interaction with charged molecules in an aqueous system due to non-polar nature of it. Functionalization of PIM-1 provides an advantage of tailoring the interaction ability as well as the adsorption performance of PIM-1 towards target pollutants. In this study, electrospun Polymer of Intrinsic Microporosity (PIM-1) fibrous membrane (PIM-FM) was reacted with borane dimethyl sulfide complex to obtain amine modified PIM-1 fibrous membrane (AM-PIM-FM). Furthermore, PIM-1 film, which is referred as PIM-1 dense membrane (PIM-DM), was also modified under the same conditions as a control material. Structural analyses have confirmed that nitrile groups of PIM-1 have been fully converted to amine group as a result of the reduction reaction. Average fiber diameter of parent PIM-1 fibers was found 2.3 ± 0.3 μm, and it remained almost the same after the amine modification. In addition, no physical damage has been observed on fiber structure based on the SEM analysis. Both amine modified PIM-1 dense and fibrous membranes became insoluble in common organic solvents. Before the modification, water contact angle of PIM-FM was 138 ± 2° which also remained almost the same after the modification, showing water contact angle of 131 ± 8°. The insolubility along with amine functionality make membranes promising materials for adsorption of anionic dyes from wastewater. Here, dye (i.e. Methyl Orange) removal ability of AM-PIM-FM from an aqueous system was investigated and compared with parent PIM-1 (PIM-FM) as well as dense membrane form (AM-PIM-DM). AM-PIM-FM shows extremely higher adsorption capacity than that of PIM-FM and AM-PIM-DM. The maximum adsorption capacity of AM-PIM-FM was found 312.5 mg g−1 for Methyl Orange. Langmuir isotherm model was found more favorable for the adsorption. AM-PIM-FM was employed effectively in continuous adsorption/desorption studies for several times without having any damage on fiber morphology using batch adsorption process. Furthermore, AM-PIM-FM was successfully used as a molecular filter for the removal of methyl orange from an aqueous system. The results indicate that AM-PIM-FM could be a promising adsorbent for removal of anionic molecules from an aqueous system.Item Open Access Amorphous to tetragonal zirconia anostructures and evolution of valence and core regions(American Chemical Society, 2015) Vempati S.; Kayaci-Senirmak, F.; Ozgit-Akgun, C.; Bıyıklı, Necmi; Uyar, TamerIn this report, we study the evolution of valence band (VB) structure during a controlled amorphous to tetragonal transformation of ZrO2 core-shell nanostructures fabricated from electrospun nanofiber template (at 130, 200, and 250 °C). Shell-ZrO2 was formed with atomic layer deposition. X-ray diffraction and transmission electron microscopy are employed to unveil the transformation of amorphous to crystalline structure of ZrO2. O 1s core-level spectra indicated chemisorbed oxygen (OCh) of almost invariant fraction for the three samples. Zr 3s level suggested that the sample deposited at 130 °C has depicted a peak at relatively higher binding energy. Analyses on Zr 3d spectra indicated the presence of metallic-Zr (Zr+ζ, 0 ≤ |ζ| < 4), the fraction of which decreases with increasing template temperature. VB region is analyzed until ∼64 eV below the Fermi level (EF). The region close to EF depicted features that are dissimilar to the literature. This discrepancy is explained on the basis of the analyses from O 1s, Zr 3d, and Zr 4p levels including hybridization of orbitals from chemisorbed species. These levels were analyzed in terms of peak characteristics such as spectral position, area under the peak, etc. The results of this study would enhance the understanding of the evolution of various bands in the presence of OCh and changes to the crystallinity enabling the functionalities that are not available in the single-phase ZrO2.Item Open Access Antibacterial electrospun nanofibers from triclosan/cyclodextrin inclusion complexes(Elsevier, 2014) Celebioglu A.; Umu, O. C. O.; Tekinay, T.; Uyar, TamerThe electrospinning of nanofibers (NF) from cyclodextrin inclusion complexes (CD-IC) with an antibacterial agent (triclosan) was achieved without using any carrier polymeric matrix. Polymer-free triclosan/CD-IC NF were electrospun from highly concentrated (160% CD, w/w) aqueous triclosan/CD-IC suspension by using two types of chemically modified CD; hydroxypropyl-beta-cyclodextrin (HPβCD) and hydroxypropyl-gamma-cyclodextrin (HPγCD). The morphological characterization of the electrospun triclosan/CD-IC NF by SEM elucidated that the triclosan/HPβCD-IC NF and triclosan/HPγCD-IC NF were bead-free having average fiber diameter of 520±250nm and 1100±660nm, respectively. The presence of triclosan and the formation of triclosan/CD-IC within the fiber structure were confirmed by 1H-NMR, FTIR, XRD, DSC, and TGA studies. The initial 1:1molar ratio of the triclosan:CD was kept for triclosan/HPβCD-IC NF after the electrospinning and whereas 0.7:1molar ratio was observed for triclosan/HPγCD-IC NF and some uncomplexed triclosan was detected suggesting that the complexation efficiency of triclosan with HPγCD was lower than that of HPβCD. The antibacterial properties of triclosan/CD-IC NF were tested against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. It was observed that triclosan/HPβCD-IC NF and triclosan/HPγCD-IC NF showed better antibacterial activity against both bacteria compared to uncomplexed pure triclosan.Item Open Access Antibacterial electrospun zein nanofibrous web encapsulating thymol/cyclodextrin-inclusion complex for food packaging(Elsevier, 2017-10) Aytac Z.; Ipek, S.; Durgun, Engin; Tekinay, T.; Uyar, TamerThymol (THY)/γ-Cyclodextrin(γ-CD) inclusion complex (IC) encapsulated electrospun zein nanofibrous webs (zein-THY/γ-CD-IC-NF) were fabricated as a food packaging material. The formation of THY/γ-CD-IC (1:1 and 2:1) was proved by experimental (X-ray diffraction (XRD), thermal gravimetric analysis (TGA), 1H NMR) and computational techniques. THY/γ-CD-IC (2:1) exhibited higher preservation rate and stability than THY/γ-CD-IC (1:1). It is worth mentioning that zein-THY/γ-CD-IC-NF (2:1) preserved much more THY as observed in TGA and stability of THY/γ-CD-IC (2:1) was higher, as shown by a modelling study. Therefore, much more THY was released from zein-THY/γ-CD-IC-NF (2:1) than zein-THY-NF and zein-THY/γ-CD-IC-NF (1:1). Similarly, antibacterial activity of zein-THY/γ-CD-IC-NF (2:1) was higher than zein-THY-NF and zein-THY/γ-CD-IC-NF (1:1). It was demonstrated that zein-THY/γ-CD-IC-NF (2:1) was most effective in inhibiting the growth of bacteria on meat samples. These webs show potential application as an antibacterial food packaging material.Item Open Access Antioxidant activity and photostability of α-tocopherol/β-cyclodextrin inclusion complex encapsulated electrospun polycaprolactone nanofibers(Elsevier, 2016-06) Aytaç, Zeynep; Uyar, TamerCyclodextrin inclusion complexes (CD-ICs) can be encapsulated into electrospun nanofibers in order to achieve delivery systems having high surface area and highly porous nanofibrous structures. In this study, a well-known antioxidant molecule, α-tocopherol (α-TC) (vitamin E) was chosen as an active agent for inclusion complexation with β-cyclodextrin. Polycaprolactone (PCL) nanofibers encapsulating α-tocopherol/β-cyclodextrin inclusion complex (α-TC/β-CD-IC) which has high antioxidant activity and photostability was produced via electrospinning (PCL/α-TC/β-CD-IC-NF). The formation of α-TC/β-CD-IC was confirmed by XRD. Phase solubility studies showed An-type complex formation between α-TC and β-CD. SEM revealed that bead-free nanofibers were successfully produced from PCL/α-TC/β-CD-IC system. PCL nanofibers encapsulating α-TC without CD-IC was also produced for comparison (PCL/α-TC-NF). Antioxidant test results showed that PCL/α-TC/β-CD-IC-NF had higher antioxidant activity as compared to PCL/α-TC-NF in methanol:water (1:1) system due to the stabilization and solubility increment of α-TC in the cavity of β-CD. PCL/α-TC/β-CD-IC-NF was more stable against UV-light when compared to PCL/α-TC-NF due to the presence of inclusion complexation. In brief, PCL/α-TC/β-CD-IC-NF with the advantages of having nanofibrous structure and encapsulating CD-ICs, may serve as a novel route for administration of α-TC due to its higher antioxidant activity and better UV-light stability.Item Open Access Antioxidant electrospun zein nanofibrous web encapsulating quercetin/cyclodextrin inclusion complex(Springer, 2018) Aytaç, Zeynep; İpek, S.; Durgun, Engin; Uyar, TamerQuercetin/gamma-cyclodextrin inclusion complex (quercetin/γ-CD-IC)-encapsulated electrospun zein nanofibers were designed as a quick and an efficient antioxidant nanofibrous material via electrospinning. Structural and thermal analyses along with the solubility enhancement as observed in phase-solubility diagram support the successful formation of the inclusion complexation between quercetin and γ-CD. The molar ratio of quercetin and γ-CD was found 1:1 in quercetin/γ-CD-IC which was confirmed with experimental (phase solubility and 1H-NMR) and computational modeling studies. Computational modeling was also useful to indicate that B orientation is more favorable when quercetin is forming host-guest inclusion complexation with γ-CD from the narrow rim. This result was also consistent with the calculations of the experimental studies performed by 1H-NMR. The successful electrospinning of zein nanofiber encapsulating quercetin/γ-CD-IC (zein-quercetin/γ-CD-IC-NF) yielded bead-free nanofiber morphology having 750 ± 255 nm fiber diameter. For comparative studies, pristine zein nanofibers (zein-NF, 695 ± 290 nm) and zein nanofibers encapsulating quercetin only (zein-quercetin-NF, 750 ± 310 nm) were also electrospun. The antioxidant (AO) characteristics of zein-quercetin/γ-CD-IC-NF were studied by the concentration-dependent AO activity tests.Item Open Access Antioxidant vitamin E/cyclodextrin inclusion complex electrospun nanofibers: enhanced water solubility, prolonged shelf life, and photostability of vitamin E(American Chemical Society, 2017) Çelebioğlu, Aslı; Uyar, TamerHere, we demonstrated the electrospinning of polymer-free nanofibrous webs from inclusion complex (IC) between hydroxypropyl-β-cyclodextrin (HPβCD) and Vitamin E (Vitamin E/HPβCD-IC NF). The inclusion complexation between HPβCD and Vitamin E was prepared by using two different molar ratios (Vitamin E/HPβCD; 1:2 and 1:1), which correspond to theoretical value of ∼13% (w/w) and 26% (w/w) loading of Vitamin E in the nanofiber (NF) matrix. After electrospinning and storage, a very high loading of Vitamin E (up to ∼11% w/w, with respect to fiber matrix) was preserved in Vitamin E/HPβCD-IC NF. Because of the cyclodextrin inclusion complexation, only a minimal weight loss (only ∼2% w/w) was observed. While pure Vitamin E is insoluble in water, Vitamin E/HPβCD-IC NF web has displayed fast-dissolving behavior. Because of the greatly enhanced water-solubility of Vitamin E, Vitamin E/HPβCD-IC NF web has shown effective antioxidant activity. Additionally, Vitamin E/HPβCD-IC NF web has provided enhanced photostability for the sensitive Vitamin E by the inclusion complexation in which Vitamin E/HPβCD-IC NF still kept its antioxidant activity even after exposure to UV-light. Moreover, a 3 year-old Vitamin E/HPβCD-IC NF sample has shown very similar antioxidant efficiency when compared with freshly prepared Vitamin E/HPβCD-IC NF indicating that long-term stability was achieved for Vitamin E in the CD-IC fiber matrix. In brief, our results suggested that polymer-free electrospun Vitamin E/HPβCD-IC nanofibrous webs could have potential applications in food, pharmaceuticals, and healthcare thanks to its efficient antioxidant activity along with enhanced water-solubility, prolonged shelf life, and high photostability of Vitamin E.Item Open Access Antioxidant α-tocopherol/γ-cyclodextrin–inclusion complex encapsulated poly(lactic acid) electrospun nanofibrous web for food packaging(John Wiley and Sons Inc., 2017-01) Aytac, Z.; Keskin, N. O. S.; Tekinay, T.; Uyar, Tamerα-Tocopherol (α-TC) and α-TC/cyclodextrin (CD)–inclusion complex (IC) incorporated electrospun poly(lactic acid) (PLA) nanofibers (NF) were developed via electrospinning (PLA/α-TC–NF and PLA/α-TC/γ-CD–IC–NF). The release of α-TC into 95% ethanol (fatty food simulant) was much greater from PLA/α-TC/γ-CD–IC–NF than from PLA/α-TC–NF because of the solubility increase in α-TC; this was confirmed by a phase-solubility diagram. 2,2-Diphenyl-1-picrylhydrazyl radical-scavenging assay shows that PLA/α-TC–NF and PLA/α-TC/γ-CD–IC–NF had 97% antioxidant activities; this value was expected to be high enough to inhibit lipid oxidation. PLA/α-TC–NF and PLA/α-TC/γ-CD–IC–NF were tested directly on beef with the thiobarbituric acid reactive substance (TBARS) method, and the nanofibers displayed a lower TBARS content than the unpackaged meat sample. Thus, active packaging significantly enhanced the oxidative stability of the meat samples at 4 °C. In conclusion, PLA/α-TC/γ-CD–IC–NF was shown to be promising as an active food-packaging material for prolonging the shelf life of foods.Item Open Access Applications of core-shell nanofibers: Drug and biomolecules release and gene therapy(Elsevier, 2018) Aytaç, Zeynep; Uyar, Tamer; Focarete, M. L.; Tampieri, A.Item Open Access Associative behaviour and effect of functional groups on the fluorescence of graphene oxide(Royal Society of Chemistry, 2018) Özcan, Şefika; Vempati, Sesha; Çırpan, A.; Uyar, TamerWe have juxtaposed the structural, vibrational and emission properties of graphene oxide (GO) with various degrees of reduction with and without a model dispersant, unveiling a strong associative behavior between GO sheets and the influence of H-bonds. The interlayer spacings are ∼0.84 and 0.78 nm for the as prepared and reduced samples. -OH groups are predominantly effected by the photo-thermal reduction. Also we note some regeneration of CO and -COOH groups in reduced samples. Clear changes to the phonon density of states indicated the doping effects due to H-bonds via the oxygeneous groups. Importantly, the defect related Raman bands are rather prone to the effect of dispersant, unveiling their intrinsic nature. In the context of fluorescence, internal vibration relaxation mediated by CC stretch vibrations emphasized the localized nature of sp2 domains of relatively smaller size. Fluorescence consists of 6 components, where the higher energy components are more influenced due to H-bonds than those of the lower energy regime, attributed to their associative behavior and chemical functionality, respectively. Excitation dependent fluorescence measurements indicated a range of optical gaps from ∼3.5 to 2 eV. The associative behavior of GO and rGO with and without a dispersant provides crucial insights into the fundamental understanding of various molecular processes.Item Open Access Atomic layer deposition of Co3O4 nanocrystals on N-doped electrospun carbon nanofibers for oxygen reduction and oxygen evolution reactions(Royal Society of Chemistry, 2019) Khalily, Mohammad Aref; Patil, Bhushan; Yılmaz, Eda; Uyar, TamerThe oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are considered as the two crucial reactions in key renewable-energy technologies including fuel cells and water splitting. Despite promising research progress in the preparation of various non-noble metal based electrocatalysts, it is still highly challenging but desirable to develop novel fabrication strategies to synthesize highly active and cost-effective ORR/OER bifunctional electrocatalysts in a precisely controlled manner. Herein, we report atomic layer deposition (ALD) of highly monodisperse Co3O4 nanocrystals of different sizes on N-doped electrospun carbon nanofibers (nCNFs) as high performance bifunctional catalysts (Co@nCNFs) for the ORR and OER. Co@nCNFs (with an average Co3O4 particle size of ∼3 nm) show high ORR performance exhibiting an onset potential of 0.87 V with a low Tafel slope of 119 mV dec−1 approaching that of commercial Pt/C. Similarly, the Co@nCNF electrocatalyst showed remarkable catalytic activity in the OER. The turnover frequency (TOF) value determined at an overpotential of 550 mV for the Co@nCNFs is ∼0.14 s−1 which is ca. 3 and ca. 15-fold higher than those of bulk Co (∼0.05 s−1) and the standard state-of-the-art IrOx (0.0089 s−1) catalyst, respectively. This work will open new possibilities for fabrication of inexpensive non-noble metal materials in highly controlled manner for applications as bifunctional ORR/OER electrocatalysis.Item Open Access Atomic layer deposition of functional III-Nitride thin films & nano-structures(2012) Bıyıklı, N.; Ozgit-Akgun, C.; Dönmez, İ.; Kayacı, F.; Uyar, TamerItem Open Access Atomic layer deposition of NiOOH/Ni(OH) 2 on PIM-1-based N-Doped carbon nanofibers for electrochemical water splitting in alkaline medium(Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Patil, Bhushan; Satılmış, Bekir; Khalily, Mohammad Aref; Uyar, TamerPortable and flexible energy devices demand lightweight and highly efficient catalytic materials for use in energy devices. An efficient water splitting electrocatalyst is considered an ideal future energy source. Well‐aligned high‐surface‐area electrospun polymers of intrinsic microporosity (PIM‐1)‐based nitrogen‐doped carbon nanofibers were prepared as a free‐standing flexible electrode. A non‐noble‐metal catalyst NiOOH/Ni(OH)2 was precisely deposited over flexible free‐standing carbon nanofibers by using atomic layer deposition (ALD). The morphology, high surface area, nitrogen doping, and Ni states synergistically showed a low onset potential (ηHER=−40 and ηOER=290 mV vs. reversible hydrogen electrode), small overpotential at η10 [oxygen evolution reaction (OER)=390.5 mV and hydrogen evolution reaction (HER)=−147 mV], excellent kinetics (Tafel slopes for OER=50 mV dec−1 and HER=41 mV dec−1), and high stability (>16 h) towards water splitting in an alkaline medium (0.1 m KOH). The performance was comparable with that of state‐of‐the‐art noble‐metal catalysts (e.g., Ir/C, Ru/C for OER, and Pt/C for HER). Post‐catalytic characterization with X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy further proved the durability of the electrode. This study provides insight into the design of 1D‐aligned N‐doped PIM‐1 electrospun carbon nanofibers as a flexible and free‐standing NiOOH/Ni(OH)2 decorated electrode as a highly stable nanocatalyst for water splitting in an alkaline medium.Item Open Access Atomic layer deposition of palladium nanoparticles on a functional electrospun poly-cyclodextrin nanoweb as a flexible and reusable heterogeneous nanocatalyst for the reduction of nitroaromatic compounds(Royal Society of Chemistry, 2019-09) Topuz, Fuat; Uyar, TamerWe here show a rational approach for the fabrication of a flexible, insoluble catalytic electrospun nanoweb of cross-linked cyclodextrin (CD) for the reduction of nitroaromatics. CD nanofibers were produced by electrospinning an aqueous HP-β-CD solution containing a multifunctional cross-linker (i.e., 1,2,3,4-butanetetracarboxylic acid, BTCA) and were subsequently cross-linked by heat treatment, which led to an insoluble electrospun poly-CD nanoweb. The poly-CD nanoweb was decorated with Pd nanoparticles (Pd-NPs) by atomic layer deposition (ALD) technique over 20 cycles to give rise to a catalytic electrospun nanoweb (i.e., Pd@poly-CD). The formation of the Pd-NPs on the poly-CD nanofiber surface was clearly evidenced by TEM and STEM imaging, which displayed the homogeneously distributed Pd-NPs with a mean size of 4.34 nm. ICP-MS analysis revealed that the Pd content on the Pd@poly-CD nanoweb was 0.039 mg per mg of nanoweb. The catalytic performance of the Pd@poly-CD nanoweb was tested for the reduction of a nitroaromatic compound (i.e., 4-nitrophenol (4-NP)), and high catalytic performance of the Pd@poly-CD nanoweb was observed with a corresponding TOF value of 0.0316 min−1. XPS was used to explore the oxidation state of Pd atoms before and after the catalytic reduction of 4-NP, and no significant change was observed after catalytic reactions. In brief, the Pd@poly-CD nanoweb having handy, flexible, structural stability and reusability can be effectively used in environmental applications as a heterogeneous nanocatalyst for the reduction of toxic nitroaromatics.Item Open Access Atomic layer deposition of Pd nanoparticles on N-Doped electrospun carbon nanofibers: optimization of ORR activity of Pd-Based nanocatalysts by tuning their nanoparticle size and loading(Wiley-VCHVerlagGmbH& Co. KGaA,Weinheim, 2019) Khalily, Mohammad Aref; Patil, Bhushan; Yılmaz, Eda; Uyar, TamerOptimization of size, loading and chemical composition of catalytic nanoparticles is a crucial step to achieve cost‐effective and efficient (electro) catalysts. This report elaborates optimization of palladium (Pd) nanoparticle size and loading on the electrospun based N‐doped carbon nanofibers (nCNF) towards oxygen reduction reaction (ORR) for the energy devices like fuel cell, metal air batteries. Electrospinning was utilized to produce one‐dimensional (1D) polyacrylonitrile nanofibers followed by a two‐step carbonization process obtaining well‐defined conductive nCNF having diameters in the range of 200–350 nm. As‐synthesized nCNF was decorated with discrete Pd nanoparticles ranging from 2.6±0.4 nm to 4.7±0.5 nm via thermal atomic layer deposition (ALD) technique. We found that nCNF deposited Pd nanoparticles having 3.9±0.6 nm size (Pd20/nCNF) showed the best ORR activity with the smallest Tafel slope of 58 mV dec−1 along with four electrons involved in the ORR. In addition, high value at half wave potential (E1/2=806 mV vs. RHE) and exchange current densities (i0=6.998 mA cm−2) at Pd20/nCNF makes it efficient catalyst among other Pd decorated nCNF. Moreover, we found that electrocatalyst with lower loading/density of Pd nanoparticles showed enhanced ORR activity.Item Open Access Atomic layer deposition of ruthenium nanoparticles on electrospun carbon nanofibers: a highly efficient nanocatalyst for the hydrolytic dehydrogenation of methylamine borane(American Chemical Society, 2018) Khalily, Mohammad Aref; Yurderi, M.; Haider, Ali; Bulut, A.; Patil, Bhushan; Zahmakiran, M.; Uyar, TamerWe report the fabrication of a novel and highly active nanocatalyst system comprising electrospun carbon nanofiber (CNF)-supported ruthenium nanoparticles (NPs) (Ru@CNF), which can reproducibly be prepared by the ozone-assisted atomic layer deposition (ALD) of Ru NPs on electrospun CNFs. Polyacrylonitrile (PAN) was electropsun into bead-free one-dimensional (1D) nanofibers by electrospinning. The electrospun PAN nanofibers were converted into well-defined 1D CNFs by a two-step carbonization process. We took advantage of an ozone-assisted ALD technique to uniformly decorate the CNF support by highly monodisperse Ru NPs of 3.4 ± 0.4 nm size. The Ru@CNF nanocatalyst system catalyzes the hydrolytic dehydrogenation of methylamine borane (CH3NH2BH3), which has been considered as one of the attractive materials for the efficient chemical hydrogen storage, with a record turnover frequency of 563 mol H2/mol Ru × min and an excellent conversion (>99%) under air at room temperature with the activation energy (Ea) of 30.1 kJ/mol. Moreover, Ru@CNF demonstrated remarkable reusability performance and conserved 72% of its inherent catalytic activity even at the fifth recycle.Item Open Access Bacteria encapsulated electrospun nanofibrous webs for remediation of methylene blue dye in water(Elsevier, 2017-04) Sarioglu O.F.; Keskin, N. O. S.; Celebioglu A.; Tekinay, T.; Uyar, TamerIn this study, preparation and application of novel biocomposite materials that were produced by encapsulation of bacterial cells within electrospun nanofibrous webs are described. A commercial strain of Pseudomonas aeruginosa which has methylene blue (MB) dye remediation capability was selected for encapsulation, and polyvinyl alcohol (PVA) and polyethylene oxide (PEO) were selected as the polymer matrices for the electrospinning of bacteria encapsulated nanofibrous webs. Encapsulation of bacterial cells was monitored by scanning electron microscopy (SEM) and fluorescence microscopy, and the viability of encapsulated bacteria was checked by live/dead staining and viable cell counting assay. Both bacteria/PVA and bacteria/PEO webs have shown a great potential for remediation of MB, yet bacteria/PEO web has shown higher removal performances than bacteria/PVA web, which was probably due to the differences in the initial viable bacterial cells for those two samples. The bacteria encapsulated electrospun nanofibrous webs were stored at 4 °C for three months and they were found as potentially storable for keeping encapsulated bacterial cells alive. Overall, the results suggest that electrospun nanofibrous webs are suitable platforms for preservation of living bacterial cells and they can be used directly as a starting inoculum for bioremediation of water systems.Item Open Access Bacteria immobilized electrospun polycaprolactone and polylactic acid fibrous webs for remediation of textile dyes in water(Elsevier, 2017-10) Sarioglu O.F.; S. Keskin, N. O.; Celebioglu A.; Tekinay, T.; Uyar, TamerIn this study, preparation and application of novel biocomposite materials for textile dye removal which are produced by immobilization of specific bacteria onto electrospun nanofibrous webs are presented. A textile dye remediating bacterial isolate, Clavibacter michiganensis, was selected for bacterial immobilization, a commercial reactive textile dye, Setazol Blue BRF-X, was selected as the target contaminant, and electrospun polycaprolactone (PCL) and polylactic acid (PLA) nanofibrous polymeric webs were selected for bacterial integration. Bacterial adhesion onto nanofibrous webs was monitored by scanning electron microscopy (SEM) imaging and optical density (OD) measurements were performed for the detached bacteria. After achieving sufficient amounts of immobilized bacteria on electrospun nanofibrous webs, equivalent web samples were utilized for testing the dye removal capabilities. Both bacteria/PCL and bacteria/PLA webs have shown efficient remediation of Setazol Blue BRF-X dye within 48 h at each tested concentration (50, 100 and 200 mg/L), and their removal performances were very similar to the free-bacteria cells. The bacteria immobilized webs were then tested for five times of reuse at an initial dye concentration of 100 mg/L, and found as potentially reusable with higher bacterial immobilization and faster dye removal capacities at the end of the test. Overall, these findings suggest that electrospun nanofibrous webs are available platforms for bacterial integration and the bacteria immobilized webs can be used as starting inocula for use in remediation of textile dyes in wastewater systems.Item Open Access Bacteria-immobilized electrospun fibrous polymeric webs for hexavalent chromium remediation in water(Springer Berlin Heidelberg, 2016) Sarioglu, O.F.; Celebioglu A.; Tekinay, T.; Uyar, TamerThe development of hexavalent chromium remediating fibrous biocomposite mats through the immobilization of a hexavalent chromium reducing bacterial strain, Morganella morganiiSTB5, on the surfaces of electrospun polystyrene and polysulfone webs is described. The bacteria-immobilized biocomposite webs have shown removal yields of 93.60 and 93.79 % for 10 mg/L, 99.47 and 90.78 % for 15 mg/L and 70.41 and 68.27 % for 25 mg/L of initial hexavalent chromium within 72 h, respectively, and could be reused for at least five cycles. Storage test results indicate that the biocomposite mats can be stored without losing their bioremoval capacities. Scanning electron microscopy images of the biocomposite webs demonstrate that biofilms of M. morganii STB5 adhere strongly to the fibrous polymeric surfaces and are retained after repeated cycles of use. Overall, the results suggest that reusable bacteria-immobilized fibrous biocomposite webs might be applicable for continuous hexavalent chromium remediation in water systems.