Yazar "Sengel, Sultan B." seçeneğine göre listele

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    Highly regenerable ionic liquid microgels as inherently metal-free green catalyst for H2 generation
    (Wiley, 2018) Ozturk, Omer F.; Demirci, Şahin; Sengel, Sultan B.; Şahiner, Nurettin
    Polymeric ionic liquid (PIL) microgel of poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) (p(MTMA)) was synthesized by using an inverse suspension polymerization technique. The anion-exchanged PIL microgels via chloride replacement from p(MTMA) were prepared as p(MTMA)-potassium thiocyanate (p(MTMA)-KSCN), p(MTMA)-sodium tetrafluoroborate (p(MTMA)-NaBF4), and p(MTMA)-sodium dicyanamide (p(MTMA)-NaN(CN)(2)) microgels by treatment with corresponding salts of potassium thiocyanate (KSCN), sodium tetrafluoroborate NaBF4, and sodium dicyanamide NaN(CN)(2) in aqueous media. The prepared microgels were found to be efficient metal-free catalysts, and their catalytic activity in H-2 production from the methanolysis of NaBH4 was investigated. Moreover, various parameters affecting H-2 production such as the effect of microgel size, the concentration of NaBH4, the effect of the anion in the microgel, the reusability of the microgel, and temperature were investigated. The Ea value calculated for the methanolysis reaction of NaBH4 catalyzed by p(MTMA) microgels was found as 24.1 +/- 0.7kJmol(-1) ranging from -15 to 45 degrees C, and this Ea value is lower than some Ea values for the same reaction. Interestingly, 10-time successive use of p(MTMA) microgel as catalyst in NaBH4 methanolysis reduced its catalytic activity to 49%, whereas the anion-exchanged forms of p(MTMA) microgel, p(MTMA)-KSCN, p(MTMA)-NaBF4, and p(MTMA)-NaN(CN)(2) only reduced their catalytic activity to 89, 86, and 79%, respectively, after 10 consecutive uses. Therefore, these anion-exchanged microgel catalysts are highly efficient in comparison with virgin p(MTMA) microgels for regenerable H-2 generation from the methanolysis of NaBH4.
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    Removal of arsenate and dichromate ions from different aqueous media by amine based p(TAEA-co-GDE) microgels
    (Academic Press Ltd- Elsevier Science Ltd, 2017) Rehman, Saif Ur; Khan, Abdur Rahman; Şahiner, Mehtap; Sengel, Sultan B.; Aktas, Nahit; Siddiq, Muhammad; Şahiner, Nurettin
    In this work, microgels based on tris(2-aminoethyl) amine (TAEA) and glycerol diglycidyl ether (GDE) via simple microemulsion polymerization was prepared as p(TAEA-co-GDE) microgels were used as adsorbent for removal of dichromate (Cr (VI)) and arsenate (As (V)) ions from different aqueous environments. The p(TAEA-co-GDE) microgels were demonstrated very efficient adsorption capacity for Cr (VI), and As (V) that are 164.98 mg/g, and 123.64 mg/g from distilled (DI) water, respectively. The effect of the medium pH on the adsorption capacity of p(TAEA-co-GDE) microgels for Cr (VI) and As (V) ions were investigated. The maximum adsorption capacity was obtained at pH 4.0 for both ions with maximum adsorbed amounts of 160.62, and 98.72 mg/g, respectively. In addition, the microgels were also shown moderate adsorption capacity for Cr (VI) and As (V) from other water sources; tap water with 115.18 mg/g and 82.86 mg/g, sea water with 64.24 mg/g and 46.88 mg/g and creek water with 73.52 mg/g and 59.33 mg/g, respectively. Moreover, the increase in adsorbent dose from 0.025 to 0.125 g enhanced % adsorption of Cr (VI) from 54.13 to 98.03, and As (V) from % 26.72-98.70, respectively. For the adsorption process Langmuir and Freundlich adsorption isotherms were applied and found that Langmuir adsorption isotherm with R-2 value of 0.99 for both the metal ions are suitable. Moreover, the experimental adsorption capacities of Cr (VI) and As (V) were found very close to the theoretical values calculated from Langmuir adsorption isotherm. More importantly, the microgels were made magnetic responsive to recover them easily from adsorption medium for reuse studies by applying external magnetic field with little decrease in adsorption capacity. Additionally, reusability of p(TAEA-co-GDE) microgels was also evaluated for adsorption of Cr (VI) and As (V) from DI water. (C) 2017 Elsevier Ltd. All rights reserved.
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    Responsive biopolymer-based microgels/nanogels for drug delivery applications
    (Woodhead Publ Ltd, 2018) Suner, Selin S.; Şahiner, Mehtap; Sengel, Sultan B.; Rees, Daniel J.; Reed, Wayne F.; Şahiner, Nurettin
    [Anstract Not Available]
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    Surfactant free synthesis and characterization of poly(vinyl carbazole) microgel and its chemical modifications
    (Elsevier, 2017) Şahiner, Nurettin; Sengel, Sultan B.
    Here, for the first time poly( vinyl carbazole) (p(VC)) particles were prepared via surfactant free emulsion polymerization using 9-vinylcarbazole (VC) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linker and ammonium persulfate (APS) as initiator. The prepared p(VC) particles were readily separated by decantation and centrifugation into micro- and nano-sized p(VC) particles, respectively. Almost monodispersed bimodal particles of p(VC) with particle diameters of about 1500 nm and 250 nm were measured with DLS measurements. The characterization of p(VC) microgel was done by optic microscope, SEM, FT-IR spectroscopy and TGA measurement. Micrometer-sized p(VC) particles were further used for chemical modification e.g., quaternization by using modifying agents such as 4-bromonitrile and 1,6-bromohexane on nitrogen atoms of p(VC), and by nitro addition to the benzene ring of p(VC). Additionally, UV absorption properties of the p(VC) microparticles were evaluated by using UV-vis Spectrometer. (C) 2016 Elsevier B.V. All rights reserved.
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    Synthesis and characterization of poly(N-(2-mercaptoethyl) acrylamide) microgel for biomedical applications
    (Wiley, 2019) Sengel, Sultan B.; Şahiner, Nurettin
    N-(2-mercaptoethyl) acrylamide (MEAM) monomer was synthesized by acrylation of cysteamine and was cross-linked with ethylene glycol dimethacrylate (EGDMA) via dispersion polymerization forming poly(N-(2-mercaptoethyl) acrylamide) (p(MEAM)) microgel. Then, the prepared microgels were tested for potential biomedical use, eg, antioxidant capacity and blood compatibility, cytotoxicity, apoptotic, and necrotic cell death; drug delivery properties were determined. Antioxidant studies of p(MEAM) microgels revealed a super antioxidant capability with total phenol content and trolox equivalent antioxidant capacity as 6.05 +/- 1.15 mg/L gallic acid equivalency and 40.96 +/- 2.40 mM trolox/g, respectively. Moreover, the blood compatibility of p(MEAM) microgels on fresh blood was resulted in lower than 1.0% hemolysis ratios for all the studied concentration range, and the blood clotting index was determined as 60.66% at 2.0 mg/mL at microgel concentration. The biocompatibility studies employing WST-1 test on L929 fibroblast cells and DLD-1 colon cancer cells have shown that p(MEAM) microgel was biocompatible up to 200 mu g/mL concentration with the cell viability values of 84.54% and 86.15% on L929 fibroblast and DLD-1 colon cancer cells, respectively. Using Captopril was used as model drug to test p(MEAM) microgel as drug delivery device for in vitro release studies at different pHs. Release profile of Captopril was found linear up to 5 hours with the released amounts of 9.81, 12.24, and 13.78 mg g(-1)microgel at the pH 1.5, 7.4, and 9.0, respectively.
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    Tunable Friction Through Stimuli Responsive Hybrid Carbon Microspheres
    (Amer Chemical Soc, 2019) Oak, Shreyas; Pashazanusi, Leila; Sengel, Sultan B.; Omarova, Marzhana; Hemstock, Jamie L.; He, Wei; He, Jibao
    We explore the use of poly(N-isopropylacrylamide) (PNIPAm)-grafted carbon microspheres (CM) dispersed in water as a stimulus-responsive lubricant. A critical concentration between 3 and 5 mg/mL of PNIPAm-grafted CM is needed to achieve low friction (coefficient of friction similar to 0.04) at room temperature between borosilicate and silicon surfaces. An increase in the temperature of the system above the lower critical solution temperature (LCST) causes the aggregation of PNIPAm-grafted CM which leads to an increase in friction forces. The process is not immediately reversible unless the lubricant is sonicated so as to redisperse the aggregates. This work provides insight into the rolling friction mechanism and demonstrates the importance of particle singlets in achieving effective lubrication through a rolling mechanism.