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Öğe Eco-friendly chitosan/?-carrageenan membranes reinforced with activated bentonite for adsorption of methylene blue(Elsevier Science Sa, 2022) Ulu, Ahmet; Alpaslan, Musa; Gultek, Ahmet; Ates, BurhanIn this work, the chitosan/kappa-carrageenan/acid-activated bentonite composite membranes were prepared through blending method and used to adsorb methylene blue dye. The prepared composite membranes were characterized with several spectroscopic and microscopic techniques. The results revealed that the bentonite was homogeneously distributed in the membrane matrix, which means extensive porous structure was formed on the surface. The effects of initial concentration of methylene blue, adsorbent dosage, pH value, contact time, ionic strength, and temperature on methylene blue removal percentage the prepared membrane was investigated in detail. Adsorption kinetics and equilibrium adsorption isotherm fitted pseudo-second-order kinetic model and Freundlich isotherm model well, respectively. The thermodynamics analysis suggested that the adsorption process of methylene blue onto the chitosan/kappa-carrageenan/acid-activated bentonite composite membrane was spontaneous and endothermic. The highest removal rate (98%) was achieved under the following conditions: adsorbent dose, 0.05 g; solution pH, 4; temperature, 50 degrees C; and time, 200 min. The maximum adsorption capacity for methylene blue was 18.80 mg/g at 50 degrees C. Moreover, the prepared composite membrane demonstrated the high reusability and adsorption rate (similar to 77%) without significant loss after sixth adsorption-desorption cycles. Considering of the above results, the prepared composite membrane can be a promising adsorbent candidate having low cost and high recyclability to remove methylene blue.Öğe Effects of coating with different ceromers on the impact strength, transverse strength and elastic modulus of polymethyl methacrylate(Japanese Soc Dental Materials Devices, 2015) Gul, Esma Basak; Atala, Mustafa Hayati; Eser, Bekir; Polat, Nilufer Tulin; Asilturk, Meltem; Gultek, AhmetThe aim of this study was to evaluate the mechanical properties of polymethyl methacrylate (PMMA) after coating with different ceromers. For transverse strength and modulus of elasticity tests, specimens of 65x10x2.5 mm dimensions were prepared (5 groups, n=10). For impact strength test, specimens of 60x7.5x4 mm dimensions were prepared (5 groups, n=10). Test group specimens were coated with one of four different types of ceromers, and specimens in the control group were not coated. After specimens were tested for transverse and impact strengths, the data were analyzed with Kruskal-Wallis and Conover post hoc tests (p<0.05). GLYMOTEOS-TiO2 and A174-TEOS significantly increased the transverse strength of PMMA. All ceromers caused a statistically significant increase in the elastic modulus of PMMA. While GLYMO-TEOS-ZrO2 significantly decreased the impact strength, the other ceromers did not cause any statistically significant difference in impact strength. Coating with ceromers substantially improved the mechanical properties of PMMA.Öğe Electrical characterization of ZnO/NiO p-n junction prepared by the sol-gel method(Springer Heidelberg, 2017) Akyuzlu, A. Merih; Dagdelen, Fethi; Gultek, Ahmet; Hendi, A. A.; Yakuphanoglu, FahrettinZnO and NiO films were synthesized on fluourine-doped tin oxide (FTO) glass substrate by the sol-gel method. The surface morphology of the films was investigated by atomic force microscopy. The optical band gaps of the ZnO and NiO films were found to be 3.198 and 3.827eV, respectively. A ZnO/NiO p-n junction diode was prepared and electrical charge transport mechanism of the diode was analyzed using thermionic emission and Norde functions. The ideality factor, barrier height and series resistance of the diode were determined to be 6.46, 1.036eV and 39.1 M , respectively. The obtained results indicate that ZnO/NiO p-n junction can be used as transparent diode for optic communications.Öğe Investigation of long-term water absorption behavior of carbon fabric reinforced epoxy composites containing hydrophobic nanosilica(Tubitak Scientific & Technological Research Council Turkey, 2016) Ekin, Nurten; Icduygu, Mehmet Galip; Gultek, AhmetThe effect of water absorption on the chemical and mechanical properties of hydrophobic filler containing epoxy matrix composites was investigated by keeping them in distilled water for 9 months. Aerosil R812 (8 nm) and Aerosil R972 (12 nm) were utilized at 3% and 5% w/w filler to resin ratio and the resin/filler mixture was combined with 12-ply carbon fabric to get 15 x 15 cm samples. Samples were molded under a hot press and for each sample 50 test samples obtained by cutting them with a water jet. The obtained samples were characterized by TG, FTIR, and SEM. The effect of water absorption was evaluated by measuring percentage water absorption and flexural strength of samples over 9 months. The results revealed that filler addition lowers the damage created by distilled water a considerable amount and addition of hydrophobic fillers to epoxy matrix composites can be especially beneficial for applications where long-term water exposure is desired.Öğe Magnetite Flotation from Sanidine with Environmental Benign Collector Poly(Amidoamine)(Springer Heidelberg, 2023) Sener, Muhammed; Gultek, AhmetThe flotation chemicals are important in mineral processing, and new progress is made in this area day by day. For sanidine purification, some commercial collectors, which can be harmful to the environment, are used. In that respect, the poly(amidoamine) (PAMAM) dendrimers, which are non-toxic for the environment, are good candidates for flotation applications. In this study, the second-generation PAMAM dendrimer was used as a collector to remove magnetite from sanidine by microflotation method, and obtained results were compared with commercial collectors. The results showed that the PAMAM dendrimer is an efficient and selective collector for magnetite. PAMAM adsorption mechanism was determined by zeta potential and FTIR spectra. According to the microflotation results, 87.76% of magnetite recovered at pH 8 by using PAMAM as a collector. It was found that the flotation recovery with the PAMAM dendrimers is similar to the Aero 704 between pH 2 and 6 but less between pH 6 and 9 and more between pH 9 and 12. All experiments were carried out five times and the standard deviation of all results was evaluated with p = 0.05 confidence interval. The second-generation PAMAM dendrimers can be an alternative flotation chemical to the commercial ones concerning usability at a wide pH range, recovery potential, and environmentally benign.Öğe Metallo-supramolecular materials based on terpyridine-functionalized polyhedral silsesquioxane(Wiley, 2014) Koytepe, Sueleyman; Demirel, Maruf Hursit; Gultek, Ahmet; Seckin, TurgayIn this study, novel metallo-supramolecular materials based on terpyridine-functionalized polyhedral silsesquioxane were synthesized from 4 '-chloro-2,2 ':6 ',2 ''-terpyridine and amino-group-functionalized polyhedral oligomeric silsesquioxane. The obtained terpyridine-functionalized polyhedral silsesquioxanes were converted to metallo-supramolecular hybrid materials by coordination polycondensation reaction with Co(II) or Cu(II) ions. The supramolecular polymers created were characterized by means of structure, morphology and stimuli-responsive performance employing scanning electron microscopy, amperometric techniques and UV-visible and Fourier transform IR spectroscopy. UV-visible and cyclic voltammetry studies showed that both the optical and electrochemical properties of metallo-supramolecular materials are affected by the substituent at the pyridine periphery. The supramolecular polymers obtained exhibited electrochromism during the oxidation processes of cyclic voltammogram studies. As a result, these terpyridine-functionalized polyhedral silsesquioxanes are good candidates for electronic, opto-electronic and photovoltaic applications as smart stimuli-responsive materials. (c) 2013 Society of Chemical IndustryÖğe Preparation of sumac extract loaded microemulsion-alg microcomposites(2020) Kıvılcım, Fadime Nulufer; Gultek, Ahmet; Cing Yildirim, SevalAbstract: Our skin is the largest organ that covers our body against the external environment and it is in constant contact with microorganisms compared to our other organs. The bacterial infection does not develop easily on our skin due to many protective factors. However, bacterial infections occur when there is a deterioration in any of these protective mechanisms. Therapeutic plants and spices are widely used as antibacterial agents for dermatological use. In this study, it is aimed to prepare a microemulsion loaded with bioactive sumac extract and to test bioactivity of microalgae (Chlorella sp.) commonly used in cosmetic formulations by using an innovative approach. The microcomposites prepared by this method are expected to have a better effect on fat, bacteria and toxins on the surface of skin. Sumac fruit (Rhus coriaria), which is used as a spice, was extracted by using ethanol in Soxhlet apparatus. Algae-microcomposites were prepared with different amounts of sumac extract (1%, 2% and 3% (w/v). Excess of ethanolic extract of sumac fruit was mixed in 3 ml oleic acid for 72 hours at 37°C and and the insoluble fraction was removed by centrifugation. Tween 80 was added to the solution as a surfactant and PEG-400 was added as a co-surfactant at 2: 1 ratio into the solution. While the mixture was stirred at the medium intensity on the magnetic stirrer, pure water was added dropwise over solution until a homogenous clear solution was obtained. The bioactivity tests of the microcomposites were carried out using gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacteria which are generally found on the skin surface. Microcomposites containing 2 % and 3 % sumac extract showed bioactive properties by inhibiting the growth of S. aureus and E. coli bacteria.Öğe Synthesis and Characterization of Novel Sulfonated Hybrid Congo Red Membranes from Chlorofunctionalized Silsesquioxanes for Fuel Cell Application(Wiley-V C H Verlag Gmbh, 2010) Gultek, Ahmet; Gokcen, Yusuf; Koytepe, Suleyman; Seckin, TurgayA new sulfonated copolymers containing congo red groups were synthesized as a potential electrolyte for high temperature PEFCs. The resulting cross-linked sulfonated hybrid congo red membranes showed greatly improved water stability in comparison with the uncrosslinked ones while high proton conductivity was maintained. sulfonated membranes have been tested with respect to fuel cell performance. Short term fuel cell test for 100 hr gave a stable performance. These membranes are less expensive compared to Nafion. New sulfonated proton exchange composites membranes were used biological fuel cells. Molasses which is the waste of sugar factory, was used in anode as fuel and different bacteria species was sowing. Potential change was reported in biological fuel cells.Öğe Synthesis and Stimuli-Responsive Properties of Metallo-Supramolecular Phosphazene Polymers Based on Terpyridine Metal Complexes(Springer, 2021) Sezer, Selda; Koytepe, Suleyman; Gultek, Ahmet; Seckin, TurgayIn this study, terpyridine functionalized phosphazene based metallo-supramolecular polymers were synthesized by three step reaction method. In the first step, 4 '-(4-aminophenyl)-2,2 ':6 ',2 ''-terpyridine was synthesized with p-nitro benzaldehyde and 2-acetylpyridine. Then, the monomer containing six terpyridine (TPY) units attached to the phosphazene was prepared from 4 '-(4-aminophenyl)-2,2 ':6 ',2 ''-terpyridine and hexachlorocyclotriphosphazene by a condensation reaction. Finally, metallo-supramolecular phosphazene polymers were synthesised with these TPY functional phosphazenes and different transition metal ions (Cu, Co, Ni, and Zn ions). Prepared metallo-supramolecular polymers containing phosphazene unit were investigated by elemental analysis, different spectroscopic methods, energy dispersive X-ray spectrometry (EDX) and thermal analysis techniques. The stimuli-responsive, optoelectronic and spectroscopic properties of the synthesised metallo-supramolecular phosphazene polymers were investigated for external effects with UV-Vis spectroscopy and electro-analytic techniques. In addition, competitive ligand effect on these metallo-supramolecular polymers was examined with ethylenediaminetetraacetic acid (EDTA). The resulting metallo-supramolecular polymers containing phosphazene unit show very fast stimuli-responsive properties, such as 3 s. they also showed a single reversible redox structure resulting from the bonding of homometallic segments to polymer chain. In addition, they showed d-pi transition (in the range of lambda = 330-550 nm) depending on the metal (Co, Ni and Zn) ion forming the supramolecular structure. The addition of competing EDTA ligands caused the degradation of metallo-supramolecular polymer structures. These metallo-supramolecular phosphazene polymers are a good alternative smart material for opto-electronic, electrochromic, photochromic and intelligent material applications.Öğe Synthesis and stimuli-responsive properties of the phenanthroline based metallo-supramolecular polymers(Springer, 2014) Demirel, Maruf Hursit; Koytepe, Suleyman; Gultek, Ahmet; Seckin, TurgayA series of functional metallo-supramolecular materials based on polyhedral oligomeric silsesquioxane (POSS) and phenanthroline ligand were prepared using a two-step approach. Firstly, using a phenanthroline ligand, an amino-functionalized transition metal complex was prepared by tin(II) chloride. In the second step, this metal complex was subsequently reacted with the octakis(3-chloropropyl)octasilsesquioxane, resulting for the metallosupramolecular polymers bearing POSS structure. All the synthesized compounds were fully characterized by spectroscopic analysis, thermal and electron microscopy techniques. Stimuli responsible properties of metallo-supramolecular materials were also investigated the reversibility upon external factors, such as electrochemical or the addition of competitive complexing ligands by electroanalytic techniques and UV-Vis spectroscopy. The electro- and chemo-responsive properties of the metallo-supramolecular materials were also improved. As a result, prepared phenanthroline-functionalized polyhedral silsesquioxane are good candidates for electronic, opto-electronic, and photovoltaic applications as a smart stimuli-responsive material.