Browsing by Subject "Core-shell nanofibers"

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Open Access
Electrospinning of cyclodextrin functionalized nanofibers and their applications
(2016-08) Aytaç, Zeynep
Electrospinning is a widely used versatile method to produce nanofibers with high surface to volume ratio and porous structure. Owing to the unique properties, electrospun nanofibers are of great importance as a carrier matrix for drugs; antioxidant, and antibacterial agents, flavour/fragrances. Though polymers are material of choice for producing electrospun nanofibers, it is likely to obtain nanofibers from low molecular weight molecules. Cyclodextrin (CDs) are intriguing molecules having the capability of forming inclusion complex (IC) with numerous guest molecules such as drugs, food additives, flavour/fragrances, antioxidant and antibacterial agents. Therefore, CD-ICs enhance solubility, reduce volatility, and provide controlled release of the guest molecules. Integrating CD-ICs with electrospinning opens a new door to produce remarkable materials. In this thesis, nanofibers containing CD-ICs of bioactive agents including antioxidant/antibacterial and flavour/fragrance molecules were produced via electrospinning technique. Firstly, CD-ICs of antioxidant/antibacterial compounds (gallic acid, α-tocopherol, quercetin, and thymol) were synthesized and then, added into polylactic acid or zein solutions to produce CD-IC incorporated electrospun polymeric nanofibers. Afterwards, the release behavior, antioxidant and antibacterial activity of these nanofibers were investigated. In addition, the potential use of these nanofibers as active food packaging and delivery material was revealed by packing meat samples by these nanofibers. Secondly, electrospun nanofibers were developed as a releasing material from CD-ICs of volatile flavour/fragrance molecules (geraniol, limonene, and linalool) without using polymeric matrix. The preservation of volatile compounds is shown to be possible to a great extent with antibacterial CD-IC nanofibers. Furthermore, the shelf life of flavour/fragrance molecules has been enhanced at least 50 days by CD-IC nanofibers. Finally, for the first time in the literature core-shell nanofibers were designed by using CD-IC of curcumin, an antioxidant molecule and polylactic acid solutions as core and shell, respectively. The ability of core-shell nanofibers as a drug delivery carrier was suggested by release and antioxidant activity tests. To conclude, CD-IC incorporated electrospun nanofibers produced by three different approach is shown to be used as efficient material for various applications particularly for food packaging and drug delivery.
Open Access
Low-temperature hollow cathode plasma-assisted atomic layer deposition of crystalline III-nitride thin films and nanostructures
(Wiley - V C H Verlag GmbH & Co. KGaA, 2015) Ozgit Akgun, C.; Goldenberg, E.; Bolat, S.; Tekcan, B.; Kayaci, F.; Uyar, Tamer; Okyay, Ali Kemal; Bıyıklı, Necmi
Hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD) is a promising technique for obtaining III-nitride thin films with low impurity concentrations at low temperatures. Here we report our previous and current efforts on the development of HCPA-ALD processes for III-nitrides together with the properties of resulting thin films and nanostructures. The content further includes nylon 6,6-GaN core-shell nanofibers, proof-of-concept thin film transistors and UV photodetectors fabricated using HCPA-ALD-grown GaN layers, as well as InN thin films deposited by HCPA-ALD using cyclopentadienyl indium and trimethylindium precursors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Transformation of polymer-ZnO core-shell nanofibers into ZnO hollow nanofibers: Intrinsic defect reorganization in ZnO and its influence on the photocatalysis
(Elsevier, 2015) Kayaci, F.; Vempati S.; Ozgit Akgun, C.; Donmez, I.; Bıyıklı, Necmi; Uyar, Tamer
Photocatalytic activity (PCA) on semiconductors is known to be majorly influenced by specific surface area and intrinsic lattice defects of the catalyst. In this report, we tested the efficiencies of 1D ZnO catalysts of varying fiber diameter (80. nm and 650. nm of inner diameter) in two formats, viz. core-shell and hollow nanofibers, where the former is calcined to yield the latter. These nanofibrous catalysts were produced by combining electrospinning and atomic layer deposition processes which were then subjected to thorough characterization including photoluminescence (PL) unveiling the details of intrinsic defects/densities. During the thermal treatment, intrinsic defects are reorganized and as a result a new PL band is observed apart from some significant changes in the intensities of other emissions. The densities of various intrinsic defects from PL are compared for all samples and juxtaposed with the PCA. Careful scrutiny of the various results suggested an anti-correlation between surface area and PCA; i.e., higher surface area does not necessarily imply better PCA. Beyond a limit, the most deterministic factor would be the density of surface defects rather than the specific surface area. The results of this study enable the researchers to fabricate 1D semiconductor photocatalysts while striking the balance between surface area and density of defects.