Browsing by Subject "Durability"

Now showing 1 - 5 of 5

Open Access
Enhanced photocatalytic activity of homoassembled ZnO nanostructures on electrospun polymeric nanofibers: a combination of atomic layer deposition and hydrothermal growth
(Elsevier, 2014) Kayaci, F.; Vempati S.; Ozgit Akgun, C.; Bıyıklı, Necmi; Uyar, Tamer
We report on the synthesis and photocatalytic activity (PCA) of electrospun poly(acrylonitrile) (PAN) nanofibrous mat decorated with nanoneedles of zinc oxide (ZnO). Apart from a detailed morphological and structural characterization, the PCA has been carefully monitored and the results are discussed elaborately when juxtaposed with the photoluminescence. The present hierarchal homoassembled nanostructures are a combination of two types of ZnO with diverse optical qualities, i.e. (a) controlled deposition of ZnO coating on nanofibers with dominant oxygen vacancies and significant grain boundaries by atomic layer deposition (ALD), and (b) growth of single crystalline ZnO nanoneedles with high optical quality on the ALD seeds via hydrothermal process. The needle structure (~25. nm in diameter with an aspect ratio of ~24) also supports the vectorial transport of photo-charge carriers, which is crucial for high catalytic activity. Furthermore, it is shown that enhanced PCA is because of the catalytic activity at surface defects (on ALD seed), valence band, and conduction band (of ZnO nanoneedles). PCA and durability of the PAN/ZnO nanofibrous mat have also been tested with aqueous solution of methylene blue and the results showed almost no decay in the catalytic activity of this material when reused.
Open Access
Functional electrospun polymeric nanofibers incorporating geraniol-cyclodextrin inclusion complexes: high thermal stability and enhanced durability of geraniol
(Elsevier Ltd, 2014) Kayaci, F.; Sen, H. S.; Durgun, Engin; Uyar, Tamer
In this study, solid geraniol/cyclodextrin inclusion complexes (geraniol/CD-IC) were successfully prepared by using three types of native CD (α-CD, β-CD and γ-CD). The modeling studies for inclusion complexation between CD and geraniol were performed by using ab initio techniques. Both experimentally and theoretically, the complexation efficiency between geraniol and γ-CD was higher; therefore, geraniol/γ-CD-IC was chosen and then incorporated into polyvinyl alcohol (PVA) nanofibers (NF) via electrospinning. The scanning electron microscopy imaging elucidated that the aggregates of geraniol/γ-CD-IC crystals were distributed in the PVA NF, whereas bead-free and uniform PVA and PVA/geraniol NF without CD-IC were obtained. Higher thermal stability of geraniol was observed in the electrospun PVA/geraniol/γ-CD-IC NF. However, geraniol molecules having volatile nature could not be preserved without CD-IC during electrospinning or during storage; therefore, the complete evaporation of geraniol in PVA/geraniol NF was unavoidable even after one day of its production. On the contrary, the loss of geraniol was minimal (~. 10%) for PVA/geraniol/γ-CD-IC NF even after storage of these NF for two years owing to inclusion complexation. Our study demonstrated that electrospun NF incorporating CD-IC may be quite applicable in food industry, e.g.: active food packaging or functional foods, due to very high surface area and nanoporous structure of NF; high thermal stability and enhanced durability of active agents and functional food ingredients.
Open Access
Graphene nanoplatelet integrated thermally drawn PVDF triboelectric nanocomposite fibers for extreme environmental conditions
(Wiley-VCH Verlag GmbH & Co. KGaA, 2024-01-03) Sadeque, Md Sazid Bin; Rahman, Mahmudur; Hasan, Md Mehdi; Ordu, Mustafa
Triboelectric nanogenerators (TENGs) utilize the synergetic eﬀect of triboelectriﬁcation and electrostatic induction to guide electrons through an external circuit, enabling low-frequency mechanical and biomechanical energy harvesting and self-powered sensing. Integrating 2D material with a high speciﬁc surface area into ﬂexible ferroelectric polymers such as polyvinylidene diﬂuoride (PVDF) has proven to be an eﬃcient strategy to improve the performance of TENG devices. Scalable fabrication of graphene-integrated PVDF nanocomposite ﬁber using thermal drawing process is demonstrated for the ﬁrst time in this study. The open-circuit voltage and short-circuit current show 1.41 times and 1.48 times improvement with the integration of 5% graphene in the PVDF ﬁbers, respectively. The TENG fabric shows a maximum power output of 32.14 μW at a matching load of 7 M𝛀 and a power density of 53.57 mW m$^{−2}$. The ﬁbers exhibit excellent stability in harsh environmental conditions such as alkaline medium, high/low temperature, multi-washing cycle, and long-time usage.
Open Access
One-step codoping of reduced graphene oxide using boric and nitric acid mixture and its use in metal-free electrocatalyst
(Elsevier, 2015) Tien H.N.; Kocabas, C.; Hur, S.H.
In this study, the preparation of a highly efficient metal-free electrocatalyst, boron and nitrogen codoped reduced graphene oxide (BN-rGO), with an excellent durability is reported. The BN-rGO were prepared in one step using boric and nitric acid mixture, exhibiting highly improved oxygen reduction reaction (ORR) activity than those of the pristine GO and single doped rGOs. The electrocatalyst also showed the excellent long-term durability and CO tolerance than those of the commercial Pt/C catalysts. © 2014 Elsevier B.V.All rights reserved.
Embargo
Spatial variation of physical, mechanical, and thermophysical properties of 3D printed concrete across a full-scale wall
(Elsevier BV, 2024-07-14) Bayrak, A.T.; Shaban, N.; Choubi, S.S.; Tuncer, E.; Yang, S.H.; Yılmaz, H.D.; Alkilani, Abdallah Zaid; Dal, H.; Unluer, C.; Dino, İ.G.; Örtemiz, E.; Sarıtaş, A.; Akgül, C.M.
3D-printed concrete (3DPC) is a layered anisotropic material whose properties are significantly impacted by the production parameters. To design and analyze large-scale printed structures, it is vital to understand the spatial variation of material properties throughout full-scale printed components. Presented study addresses this need by presenting a comprehensive experimental investigation that explores the variation of physical, mechanical, and thermophysical properties across a full-scale 3DPC wall with an approximate height of 2.36 m. The cores extracted from the wall were categorized in terms of the extraction location along the wall height (upper (U) and lower (L)) and the alignment of the specimen’s longitudinal axis with respect to the printing space (printing (P), translation (T), and deposition (D) direction). Additionally, direct shear and four-point bending tests were carried out on printed beams. Control samples, mold-cast from the same concrete mix, were used for comparison. Obtained results indicated a pronounced anisotropy and property variation along the 3DPC wall height. These were linked not only to the frequency and orientation but also to the porosity of the interfaces which was significantly influenced by the self-weight compaction of the layers and the progressively increasing concrete viscosity caused by pump system heating over time. CT investigations, rate of water absorption, and water penetration tests revealed sparse and less connected interstrip and interlayer porosity in the L samples. Depending on the sample orientation and loading direction, compressive strength, elastic modulus and splitting tensile strength increased by up to 108 %, 53 %, and 100 %, respectively, in the L samples when compared to the U samples. The same trend was observed in the Poisson’s ratio, albeit to a lesser extent. The triaxial thermal conductivities of the L samples calculated from the transient plane source measurements were up to 26 % higher than those for the U samples. Given the limited number of studies on real-scale applications, the presented research can serve as a benchmark, offering valuable insights to explore and validate the 3DPC behavior on a large scale.