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    Anode performance of hydrothermally grown carbon nanostructures and their molybdenum chalcogenides for Li-ion batteries
    (Cambridge Univ Press, 2018) Simsir, Hamza; Eltugral, Nurettin; Frohnhoven, Robert; Ludwig, Tim; Gonullu, Yakup; Karagoz, Selhan; Mathur, Sanjay
    Three different hydrothermally grown carbonaceous materials and their molybdenum chalcogenides derived from glucose (HTC, HTC-MoO2, HTC-MoS2) were investigated to evaluate their potential as Li-ion battery anodes. All tested materials exhibited good cycling performance at a current density of 100 mA/g and showed high coulombic efficiency, >98%, after the 50th cycle. Reversible charge capacities of HTC, HTC-MoO2, and HTC-MoS2 were 296, 266, and 484 mAh/g, respectively, after 50 successive cycles. This study demonstrated that the HTC-MoS2 showed the highest reversible charge capacity which promises to be a good candidate for an environmentally friendly anode material for Li-ion batteries.
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    Assessment of uv protection factor of flax, polyester and nylon fabrics treated with zinc oxide nanoparticles
    (2021) Eltugral, Nurettin
    In this study, influence of nano-zinc oxide treatment on the UV protection properties of the widely used apparel fabrics including flax, polyester, and nylon, were investigated by means of ultraviolet protection factor (UPF) assessment. Nanoparticle content of the flax, polyester, and nylon fabrics were determined to be 1.2, 0.9, and 1.5 wt%, respectively. The UPFs of non-treated fabrics were in the range of 1.5 to 2.2 in the entire UV region. An improvement in UPF was obtained after introducing the nanoparticles into the fabrics. Approximately a sixfoldincrease in UPF (11.02 ± 1.57) against UV-B was recorded for nylon. Flax and polyester fabrics had nearly the same UPF values around 2.8 against UV-B, while they were close to each other (2.71 ± 0.22 and 2.61 ± 0.28 for flax and polyester, respectively) against UV-A. SEM micrographs showed that nanoparticles agglomerated on flax and polyester in high extent, whereas they existed as dispersed particles at micro scale together with some slight agglomeration inside nylon.
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    Effects of Acidic and Alkaline Metal Triflates on the Hydrothermal Carbonization of Glucose and Cellulose
    (Amer Chemical Soc, 2019) Simsir, Hamza; Eltugral, Nurettin; Karagoz, Selhan
    The transformation of glucose and cellulose into carbon-rich solid materials was carried out in hydrothermal media at 200 degrees C for 48 h with and without the use of acidic (Al(OTf)(3)) and alkaline (NaOTf) catalysts. The effects of the catalyst type on the yield of hydrothermal carbons (HTCs) and their properties were investigated. The use of Al(OTf)(3) led to a decrease in the yields of HTCs for both feedstocks. This result was reversed for the runs with NaOTf. Glucose-derived solid product without the use of a catalyst produced carbon spheres of a diameter between 500 and 600 nm. The use of a catalyst (regardless of whether Al(OTf)(3) or NaOTf) produced larger particles. Scanning electron microscopy images of HTC from cellulose exhibited irregular morphology. Carbon spheres produced from cellulose without the use of a catalyst ranged between 200 nm and 2 mu m. HTC products from cellulose with Al(OTf)(3) yielded aggregated carbon spheres with a diameter ranging between 300 and 600 nm. The use of NaOTf inhibited the secondary char formation. Although a small number of carbon spheres were observed on the surface, the surface was mostly smooth, like raw cellulose. The final chemical structures of HTC products were further investigated using advanced C-13 solid-state nuclear magnetic resonance (NMR). NMR spectra demonstrated that glucose was completely transformed into HTCs with and without a catalyst, because there were no peaks identified with carbon atoms of glucose. However, the peaks identified with carbon atoms of cellulose were observed in the non catalytic and catalytic runs with NaOTf. Cellulose was completely transformed into HTCs with only Al(OTf)(3).
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    Efficiency Assessment of an Evacuated U-Tube Solar Collector Using Silver Nanofluid
    (Asme, 2019) Kaya, Huseyin; Eltugral, Nurettin; Kurukavak, Ali; Arslan, Kamil
    A water-based silver nanofluid (Ag/PW) was prepared from gelatin-stabilized silver nanoparticles (Ag NPs) of about 15 nm and further used as a working fluid in an evacuated U-tube solar collector (EUSC) to investigate the variation in the collector efficiency. An Ag/PW nanofluid having 0.035 wt% was prepared and demonstrated a good promise of colloidal stability when dispersed in pure water. Collector efficiency measurements were carried out at outdoor conditions with four different mass flow rate values (0.063, 0.051, 0.033, and 0.02 kg/s). Results showed that Ag/PW have superior heat transfer properties than that of pure water as the base fluid. It was found that the efficiency of the collector was directly proportional to the mass flow rate of the working fluid until an optimum value was attained. Experimental results show that the highest collector efficiency was 72.2% at 0.051 kg/s mass flow rate, which is 21.3% higher than that of the pure water.
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    Experimental investigation of thermal performance of an evacuated U-Tube solar collector with ZnO/Etylene glycol-pure water nanofluids
    (Pergamon-Elsevier Science Ltd, 2018) Kaya, Huseyin; ArsIan, Kamil; Eltugral, Nurettin
    In this paper, the efficiency of an evacuated U-tube solar collector (EUSC) with ZnO/Etylene Glycol-Pure Water (ZnO/EG-PW) as a working fluid was experimentally investigated. 50%-50% EG-PW was used as a base fluid. To prepare the nanofluids ZnO nanoparticles were added to the EG-PW base fluid at different volume concentrations (1.0%, 2.0%, 3.0% and 4.0%). The maximum collector efficiency was obtained at equal working fluid inlet temperature and ambient temperature in all experiments. Moreover, the highest collector efficiency was determined 62.87% for 3.0 vol.% and mass flow rate of 0.045 kg/s that it was 26.42% higher than EG-PW as a working fluid. Also, this value is 5.2% and 6.88% higher than the base fluid for the mass flow rates of 0.03 and 0.02 kg/s, respectively. It was determined also that the thermal conductivity of ZnO/EG-PW nanofluid increases with increasing nanoparticle volume concentration. (C) 2018 Elsevier Ltd. All rights reserved.
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    Hydrothermal carbonization for the preparation of hydrochars from glucose, cellulose, chitin, chitosan and wood chips via low-temperature and their characterization
    (Elsevier Sci Ltd, 2017) Simsir, Hamza; Eltugral, Nurettin; Karagoz, Selhan
    In this work, the hydrothermal carbonization of glucose, cellulose, chitin, chitosan and wood chips at 200 degrees C at processing times between 6 and 48 h was studied. The carbonization degree of wood chips, cellulose and chitosan obviously increases as function of time. The heating value of glucose increases to 88% upon carbonization for 48 h, while it is only 5% for chitin. It is calculated to be between 44 and 73% for wood chips, chitosan and cellulose. Glucose yielded complete formation of spherical hydrochar structures at a shorter processing time, as low as 12 h. However, carbon spheres with narrow size (similar to 560 nm) distribution were obtained upon 48 h of residence time. Cellulose and wood chips yielded a similar morphology with an irregular size distribution. Chitin seemed not to undergo hydrothermal carbonization, whereas densely aggregated spheres of a uniform size around 42 nm were obtained from chitosan after 18 h. (C) 2017 Elsevier Ltd. All rights reserved.
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    Preparation of nano-silver-supported activated carbon using different ligands
    (Springer, 2016) Eltugral, Nurettin; Simsir, Hamza; Karagoz, Selhan
    In this study, we investigated the effect of water soluble ligands [i.e., sodium borohydride (NaBH4), polyvinyl alcohol, glucose and galactose] on the preparation of nano-silver-supported activated carbon (AC). Ligand-stabilized Ag nanoparticle dispersion characteristics were also compared with those of ligand-free Ag nanoparticles. The nanoparticle distribution was investigated using a scanning electron microscope (SEM) which enabled a qualitative analysis of ligand-dependent nanoparticle adsorption onto AC. Silver nanoparticles with average sizes ranging from 7 to 20 nm were synthesized with different coatings. In particular, silver nanoparticles reduced and stabilized by NaBH4 were found to have a dense and homogenous dispersion of sizes in the range of 100-400 nm on the AC surface. These particles also seemed to remain on the AC surface after rinsing with water. The distribution of silver nanoparticles prepared in the presence of NaBH4/PVA was not as good as the one prepared with NaBH4. Their aggregate size varied from 300 to 600 nm on the AC surface and particles greater than 500 nm were eliminated from the AC surface upon rinsing with water. Glucose- and galactose-stabilized silver nanoparticles did not display an extensive adsorption and their adsorption seemed to be poor. However, glucose-stabilized silver nanoparticles could still be detectable to some extent after rinsing, while galactose-stabilized ones could not. Antimicrobial studies showed that all silver-containing carbons studied in this study inhibit bacterial growth and act as bacteriostatic agents.
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    The role of capping agents in the fabrication of nano-silver-decorated hydrothermal carbons
    (Elsevier Sci Ltd, 2019) Simsir, Hamza; Eltugral, Nurettin; Karagoz, Selhan
    In this work, silver-decorated hydrothermally grown carbons were fabricated by introducing either silver nitrate, or silver nanoparticles (Ag NPs) which were coated differently with polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), gelatin, and glucose. Hybrid nanostructures were prepared by methods which involve either in situ formation under hydrothermal conditions or mixing of as-prepared hydrothermal carbons (HTCs) with Ag NPs. With these approaches, hybrid nanostructures could be fabricated with some differences in their morphologies. Interestingly, a dense silver core at the center of the HTCs was observed after hydrothermal processing of glucose with gelatin-stabilized Ag NPs while particles were observed to attach to the HTCs surface under mixing conditions. PVP-stabilized Ag NPs were shown to form hybrid products where particles were attached to the surface rather than encapsulated at the center. On the other hand, PVA-stabilized ones were hardly observed on the HTCs upon mixing for 48 h, and they seemed not to produce any hybrid HTC-Ag under hydrothermal processing. Besides, glucose-stabilized Ag NPs were also subjected to the hydrothermal process and HTCs produced with interesting surface characteristics revealed that Ag NPs induce their morphology.