Browsing by Subject "Sodium"

Now showing 1 - 6 of 6

Open Access
Changes in the resistance to corrosion of thermally passivated titanium aluminide during exposure to sodium chloride solution
(Kluwer Academic Publishers, 2015) Saebnoori, E.; Shahrabi, T.; Jafarian H.; Ghaffari, M.
In this study the surface of Ti-47Al-2Cr (at. %) was modified by heating and exposure to nitrogen gas flow to form a predominantly oxide layer on the surface. Samples were then immersed in Ringer's solution and 3.5 wt. % sodium chloride solution and electrochemical impedance spectroscopy tests were performed at regular intervals. The results showed that the layer is highly resistant to corrosion. The equivalent circuit proposed for the impedance curves includes a Warburg element, because diffusion is controlling charge transfer through the passive surface layer. The resistance of the layer was not significantly reduced even after 300 h exposure to solutions and scanning electron micrographs showed the surface was not damaged. © 2013 Springer Science+Business Media Dordrecht.
Open Access
In situ synthesis of biomolecule encapsulated gold-cross-linked poly(ethylene glycol) nanocomposite as biosensing platform: A model study
(Elsevier BV, 2010) Odaci, D.; Kahveci, M.U.; Sahkulubey, E.L.; Ozdemir, C.; Uyar, Tamer; Timur, S.; Yagci Y.
In situ synthesis of poly(ethylene glycol) (PEG) hydrogels containing gold nanoparticles(AuNPs) and glucose oxidase (GOx) enzyme by photo-induced electron transfer process was reported here and applied in electrochemical glucose biosensing as the model system. Newly designed bionanocomposite matrix by simple one-step fabrication offered a good contact between the active site of the enzyme and AuNPs inside the network that caused the promotion in the electron transfer properties that was evidenced by cyclic voltammetryas well as higher amperometric biosensing responses in comparing with response signals obtained from the matrix without AuNPs. As well as some parameters important in the optimization studies such as optimum pH, enzyme loading and AuNP amount, the analytical characteristics of the biosensor (AuNP/GOx) were examined by the monitoring of chronoamperometric response due to the oxygen consumption through the enzymatic reaction at − 0.7 V under optimized conditions at sodium acetate buffer (50 mM, pH 4.0) and the linear graph was obtained in the range of 0.1–1.0 mM glucose. The detection limit (LOD) of the biosensor was calculated as 0.06 mM by using the signal to noise ratio of 3. Moreover, the presence of AuNPs was visualized by TEM. Finally, the biosensor was applied for glucose analysis for some beverages and obtained data were compared with HPLC as the reference method to test the possible matrix effect due to the nature of the samples.
Open Access
Nickel nanoparticles decorated on electrospun polycaprolactone/chitosan nanofibers as flexible, highly active and reusable nanocatalyst in the reduction of nitrophenols under mild conditions
(Elsevier, 2017-04) Karakas, K.; Celebioglu A.; Celebi, M.; Uyar, Tamer; Zahmakiran, M.
Today, the reduction of nitro aromatics stands a major challenge because of the pollutant and detrimental nature of these compounds. In the present study, we show that nickel(0) nanoparticles (Ni-NP) decorated on electrospun polymeric (polycaprolactone(PCL)/chitosan) nanofibers (Ni-NP/ENF) effectively catalyze the reduction of various nitrophenols (2-nitrophenol, 2,4-dinitrophenol, 2,4,6-trinitrophenol) under mild conditions. Ni-NP/ENF nanocatalyst was reproducibly prepared by deposition-reduction technique. The detailed characterization of these Ni-NP/ENF based nanocatalyst have been performed by using various spectroscopic tools including ICP-OES, P-XRD, XPS, SEM, BFTEM, HRTEM and BFTEM-EDX techniques. The results revealed the formation of well-dispersed nickel(0) NP (dmean = 2.71–2.93 nm) on the surface of electrospun polymeric nanofibers. The catalytic activity of the resulting Ni-NP/ENF was evaluated in the catalytic reduction of nitrophenols in aqueous solution in the presence of sodium borohydride (NaBH4) as reducing agent, in which Ni-NP/ENF nanocatalyst has shown high activity (TOF = 46.2 mol 2-nitrophenol/mol Ni min; 48.2 mol 2,4-dinitrophenol/mol Ni min; 65.6 mol 2,4,6-trinitrophenol/mol Ni min). More importantly, due to the nanofibrous polymeric support, Ni-NP/ENF has shown a flexible characteristics along with reusability property. Testing the catalytic stability of Ni-NP/ENF revealed that this new catalytic material provides high reusability performance (at 3rd reuse 86% for 2-nitrophenol, 83% 2,4-dinitrophenol and 82% 2,4,6-trinitrophenol) for the reduction of nitrophenols even at room temperature and under air. The present study reported here also includes the compilation of wealthy kinetic data for Ni-NP/ENF catalyzed the reduction of nitrophenols in aqueous sodium borohydride solution depending on temperature and type of support material (Al2O3, C, SiO2) to understand the effect of the support material and determine the activation parameters.
Open Access
Rational synthesis of Na and S co-catalyst TiO2-based nanofibers: presence of surface-layered TiS3 shell grains and sulfur-induced defects for efficient visible-light driven photocatalysis
(Royal Society of Chemistry, 2017) Ranjith, K. S.; Uyar, Tamer
Surface-modified TiO2 nanofibers (NFs) with tunable visible-light photoactive catalysts were synthesised through electrospinning, followed by a sulfidation process. The utilization of sodium-based sulfidation precursors effectively led to the diffusion and integration of sulfur impurities into TiO2, modifying its band function. The optical band function of the sulfur-modified TiO2 NFs can be easily manipulated from 3.17 eV to 2.28 eV through surface modification, due to the creation of oxygen vacancies through the sulfidation process. Sulfidating TiO2 NFs introduces Ti-S-based nanograins and oxygen vacancies on the surface that favor the TiO2-TiS3 core-shell interface. These defect states extend the photocatalytic activity of the TiO2 NFs under visible irradiation and improve effective carrier separation and the production of reactive oxygen species. The surface oxygen vacancies and the Ti-S-based surface nanograins serve as charge traps and act as adsorption sites, improving the carrier mobility and avoiding charge recombination. The diffused S-modified TiO2 NFs exhibit a degradation rate of 0.0365 cm-1 for RhB dye solution, which is 4.8 times higher than that of pristine TiO2 NFs under visible irradiation. By benefiting from the sulfur states and oxygen vacancies, with a narrowed band gap of 2.3 eV, these nanofibers serve as suitable localized states for effective carrier separation.
Open Access
Sorption studies of Cs+, Ba2+, and Co2+ ions on bentonite using radiotracer, ToF-SIMS, and XRD techniques
(De Gruyter Oldenbourg, 2001) Shahwan, T.; Erten H. N.
The sorption behaviour of Cs+, Ba2+, and Co2+ ions on bentonite were investigated using the radiotracer method, Time of Flight-Secondary Ion Mass Spectroscopy (ToF-SIMS), and X-Ray Diffraction (XRD). The sorption of Cs+ and Ba2+ were exothermic while sorption of Co2+ was endothermic. The sorption data were well described by Freundlich and Dubinin-Radushkevich isotherms. According to ToF-SIMS results Na+ and Mg2+ were the primary exchanging ions in bentonite. The XRD spectra showed that no structural changes were associated with the sorption of Cs+ and Co2+, and BaCO3 precipitate was formed upon the sorption of Ba2+ on bentonite.
Open Access
Structural, microstructural and thermal properties of lead-free bismuth-sodium-barium-titanate piezoceramics synthesized by mechanical alloying
(2013) Amini, R.; Ghazanfari, M.R.; Alizadeh, M.; Ardakani H.A.; Ghaffari, M.
Bismuth-sodium-barium-titanate piezoceramics with a composition of (Bi 0.5Na0.5)0.94Ba0.06TiO3 (BNBT) were prepared by mechanical alloying (MA). Structural analysis and phase identification were performed by X-ray diffraction (XRD). Microstructural studies and chemical composition homogeneity were performed by scanning electron microscope (SEM) coupled with energy dispersive X-ray analysis (EDX). Furthermore, thermal properties of the as-milled powders were evaluated by thermogravimetry/differential thermal analysis (TG/DTA). During the initial milling, the constituents were transformed to the perovskite, pyrochlore, and BNT phases; in addition, partial amorphization of the structure appeared during the milling cycle. As MA progressed, transformation of pyrochlore-to-perovskite and crystallization of the amorphous phase occurred and also, the BNBT phase was significantly developed. It was found that the MA process has the ability to synthesize the BNBT powders with a submicron particle size, regular morphology, and uniform elemental distribution. © 2012 Elsevier Ltd.