Browsing by Author "Erim, F. Bedia"

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Citation Count: 16
Cation Effect on Slow Release from Alginate Beads: A Fluorescence Study
(Springer/Plenum Publishers, 2014) Kaygusuz, Hakan; Erim, F. Bedia; Pekcan, Önder; Evingür, Gülşen Akin
In this study spherical alginate beads containing pyranine (P-y) as a fluorescence probe were prepared by ionotropic gelation of a sodium alginate solution. The steady state fluorescence technique was used to study pyranine release from the alginate beads crosslinked with calcium barium and aluminum ions respectively. The slow release of P-y was observed with the time drive mode of the spectrophotometer at 512 nm. Fluorescence emission intensity (I-p) from P-y was monitored during the release process and the encapsulation efficiency (EE) of pyranine from the alginate beads was calculated. The Fickian Diffusion model was used to measure the release coefficients D-sl. It was seen that the slow release coefficients of pyranine from the alginate beads crosslinked with Ca2+ Ba2+ and Al3+ ions increased in the following order: D-sl (Al3+)> D-sl (Ca2+)> D-sl (Ba2+). In contrast the initial amount of pyranine and EE into the beads showed the reverse behavior.
Citation Count: 6
Effect of Calcium Ion Concentration on Small Molecule Desorption from Alginate Beads
(Taylor & Francis Inc, 2014) Evingür, Gülşen Akin; Kaygusuz, Hakan; Erim, F. Bedia; Pekcan, Önder
Spherical alginate beads were prepared by ionotropic gelation of sodium alginate through the use of calcium ions. Pyranine (Py) was added to the alginate solution as a small molecule probe for fluorescence studies. Desorption of Py in water from the alginate beads cross-linked with calcium ions was studied by using the steady state fluorescence technique. The fluorescence emission intensity (I) from Py was monitored during the desorption process at 512 nm using the time drive mode of the spectrofluorometer. The increase in I was attributed to Py release from the beads. The Fickian diffusion model was used to calculate the desorption coefficients D which were found to be increased up to 3% (w/v) CaCl2 concentration in the beads and then decreased with a further increase of CaCl2 content. On the other hand the encapsulation efficiency of Py in the calcium alginate beads presented the reverse behavior compared to D. It was observed that when the content of CaCl2 was increased the incubation time t(0) for the start of desorption increased.
Citation Count: 29
Efficient Photocatalytic Degradation of Methylene Blue Dye from Aqueous Solution with Cerium Oxide Nanoparticles and Graphene Oxide-Doped Polyacrylamide
(Amer Chemical Soc, 2023) Kalaycioglu, Zeynep; Uysal, Bengu Ozugur; Pekcan, Onder; Erim, F. Bedia
A cerium oxide nanoparticles (CeO2-NPs)/graphene oxide (GO)/polyacrylamide (PAM) ternary composite was synthesized through free-radical polymerization of acrylamide in the presence of CeO2 nanoparticles and GO in an aqueous system. The synthesized composite material was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy techniques and applied for the photocatalytic degradation of methylene blue (MB) dye from an aqueous solution. Tauc's model for direct transition was used to model for the optical band gap. The key operating parameters such as the amounts of CeO2-NPs and GO, pH, initial MB concentration, type of light irradiation, and contact time have been optimized to achieve the highest MB degradation percentage. The photocatalysis process was pH-dependent, and the optimum pH value was found to be 12.0. Under UV-A light, 90% dye degradation occurred in 90 min. The degradation of MB was also specified in terms of total organic carbon (TOC) and chemical oxygen demand (COD). Free-radical capture experiments were also performed to determine the role of radical species during the photocatalytic oxidation process. The photocatalytic process showed that the equilibrium data is in good agreement with the Langmuir-Hinshelwood kinetic model. A rate constant of 0.0259 min-1 was obtained. The hydrogel was also tested to assess its reusability, which is an important key factor in practical wastewater treatment. The photocatalytic activity only decreased to 75% after nine uses.
Citation Count: 3
Electric-field induced phase transitions in capillary electrophoretic systems
(Aip Publishing, 2021) Kaygusuz, Hakan; Erim, F. Bedia; Berker, A. Nihat
The movement of particles in a capillary electrophoretic system under electroosmotic flow was modeled using Monte Carlo simulation with the Metropolis algorithm. Two different cases with repulsive and attractive interactions between molecules were taken into consideration. Simulation was done using a spin-like system, where the interactions between the nearest and second closest neighbors were considered in two separate steps of the modeling study. A total of 20 different cases with different rates of interactions for both repulsive and attractive interactions were modeled. The movement of the particles through the capillary is defined as current. At a low interaction level between molecules, a regular electroosmotic flow is obtained; on the other hand, with increasing interactions between molecules, the current shows a phase transition behavior. The results also show that a modular electroosmotic flow can be obtained for separations by tuning the ratio between molecular interactions and electric field strength.
Citation Count: 2
Gelation of PAAm-PVP composites: A fluorescence study
(World Scientific, 2014) Evingür, Gülşen Akin; Kaygusuz, Hakan; Erim, F. Bedia; Pekcan, Önder
Hybrid hydrogels are a new class of composite materials. Polyacrylamide (PAAm) hydrogels are mainly produced by free radical crosslinking copolymerization (FCC) of AAm in the presence of N N'-methylene bis (acrylamide) (BIS) as the crosslinker. Pyranine doped PAAm-poly (N-vinyl pyrrolidone) (PVP) composite were prepared with different amounts of PVP varying in the range between 0.0015 and 0.1 gr. It was observed that pyranine molecules as a fluoroprobe bind to AAm and PVP chains upon the initiation of the polymerization causing the fluorescence spectra of the bonded pyranines shift to the shorter wavelengths. The sol-gel phase transition and its universality were monitored and tested as a function of PVP contents. Observations around the critical point show that the gel fraction exponent beta agreed with the percolation result for below 0.025 gr PVP contents. However classical result was observed above 0.0125 gr PVP content.
Citation Count: 16
Monitoring the gelation of polyacrylamide-sodium alginate composite by fluorescence technique
(Taylor & Francis Ltd, 2012) Evingür, Gülşen Akin; Tezcan, Filiz; Erim, F. Bedia; Pekcan, Önder
Polyacrylamide (PAAm)-sodium alginate (SA) composite was prepared with different amounts of SA varying in the range between 0.06% and 2% (w/v). The PAAm-SA composite was characterized by the steady-state fluorescence technique. Pyranine was added as a fluoroprobe for monitoring the polymerization. It was observed that pyranine molecules bind to AAm and SA chains upon the initiation of the polymerization. Thus the fluorescence spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allowed us to monitor the sol-gel phase transition and to test the universality of the sol-gel transition as a function of SA contents. Observations around the critical point show that the gel fraction exponent beta and the weight average degree of polymerization exponent gamma agreed with the percolation result for (<0.25% (w/v)) SA contents. However classical results were produced at (<2% (w/v)) SA contents.
Citation Count: 44
Surfactant and Metal Ion Effects on the Mechanical Properties of Alginate Hydrogels
(Elsevier Science Bv, 2016) Kaygusuz, Hakan; Evingür, Gülşen Akin; Pekcan, Önder; von Klitzing, Regine; Erim, F. Bedia
This paper addresses the controlled variation of the mechanical properties of alginate gel beads by changing the alginate concentration or by adding different surfactants or cross-linking cations. Alginate beads containing nonionic Brij 35 or anionic sodium dodecyl sulfate (SDS) surfactants were prepared with two different types of cations (Ca2+ Ba2+) as crosslinkers. Compression measurements were performed to investigate the effect of the surfactant and cation types and their concentrations on the Young's modulus of alginate beads. The Young's modulus was determined by using Hertz theory. For all types of alginate gel beads the Young's modulus showed an increasing value for increasing alginate contents. Addition of the anionic surfactant SDS increases the Young's modulus of the alginate beads while the addition of non-ionic surfactant Brij 35 leads to a decrease in Young's modulus. This opposite behavior is related to the contrary effect of both surfactants on the charge of the alginate beads. When Ba2+ ions were used as crosslinker cation the Young's modulus of the beads with the surfactant SDS was found to be approximately two times higher than the modulus of beads with the surfactant Brij 35. An ion specific effect was found for the crosslinking ability of divalent cations. (C) 2016 Elsevier B.V. All rights reserved.