Yazar "Tabak, Ahmet" seçeneğine göre listele
Listeleniyor 1 - 14 / 14
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Activated carbon derived from tea waste: A promising supporting material for metal nanoparticles used as catalysts in hydrolysis of ammonia borane(Pergamon-Elsevier Science Ltd, 2020) Akbayrak, Serdar; Ozcifci, Zehra; Tabak, AhmetActivated carbons with high porosity and high surface area are promising materials to be used in wide-range applications. They can easily be prepared from various biomass source following by simple and reproducible activation and carbonization steps. In this study, the woody part of tea which is highly available tea waste after the harvesting of tea leaves is considered as the precursor of highly porous activated carbon. In fact, activated carbon with well-ordered porous structure (micropore area = 1614.3 m(2) g(-1), micropore volume = 1.13 cm(3) g(-1)) and high surface area (2559 m(2) g(-1)) was achieved using this tea waste. The obtained activated carbon was used to support cobalt, nickel and copper nanoparticles which were used as catalysts in H-2 generation from aqueous ammonia borane. The results reveal that Co nanoparticles with an average particle size of 3.18 nm on activated carbon provide higher activity (TOF = 7.5 min(-1)) as compared to nickel (TOF = 4.8 min(-1)) and copper nanoparticles in this reaction. Herein, we report also the kinetic studies including the effect of temperature, metal concentration and metal loading on the catalytic activity in hydrolysis of ammonia borane.Öğe Artifacts in cranial MRI caused by extracranial foreign bodies and analysis of these foreign bodies(Wolters Kluwer Medknow Publications, 2019) Kayaci, Selim; Tabak, Ahmet; Durur-Subasi, Irmak; Eldes, Tugba; Koksal, Vaner; Sirin, Murat; Arslan, Yusuf KemalPurpose: The purpose of our study was to conduct a chemical analysis of extracranial foreign bodies (FBs) causing artifacts in cranial magnetic resonance imaging (MRI) and to investigate the association between chemical composition, magnetic susceptibility, and artifact size. Materials and Methods: A total of 12 patients were included in the study. The FBs responsible for the artifacts were visualized using cranial computed tomography (CT). Artifact-causing FBs were removed from the scalps of 10 patients and analyzed using scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction spectroscopy (X-RD), and Fourier-transform infrared spectroscopy (FT-IR). The magnetic susceptibility of the samples was determined using the reference standard material MnCl2.6H(2)O. The volume of the MRI artifacts was measured in cubic centimeters (cm(3)). Results: EDS results demonstrated that the mean Fe ratio was 5.82% in the stone samples and 0.08% in the glass samples. Although no phase peaks were detected in the X-RD spectra of the glass samples, peaks of Fe2O3, Al2Ca (SiO4) were detected in the X-RD spectra of the stone samples. The FT-IR spectra revealed metal oxide peaks corresponding to Fe, Al, in the stone samples and peaks confirming Al2SiO5 and Na2SiO3 structures in the glass samples. The mean volumes of the MRI artifacts produced by the stone and glass samples were 5.9 cm(3) and 2.5 cm(3), respectively. Conclusions: Artifacts caused by extracranial FBs containing metal/metal oxide components are directly associated with their chemical composition and the artifact size are also related to element composition and magnetic susceptibility.Öğe Çeşitli Katyon Değiştirilmiş ve Sütunlanmış Artvin Bentonitlerinin Karakterizasyonu ve Seçilmiş Bir Organik Reaksiyonda Katalizör Olarak Kullanılmaları(2020) Tabak, Ahmet; Caglar, Bulent; Kaya, MehmetBu çalışmada Artvin ham bentonitinin, bazı metal katyonları (Fe3+ ve Cu2+) değiştirilmiş ve Fe- ve Alsütunlanmış türevlerinin benzaldehitin 2,3-bütandiol ile asetalleşme reaksiyonundaki katalitik aktiviteleri araştırıldı. Bu katalizörlerin yapısal ve fizikokimyasal özellikleri X–ışınları toz kırınım (XRD), taramalı elektron mikroskobu (SEM), Fourier transform infrared (FTIR), ve yüzey alanı ölçüm teknikleri yardımıyla aydınlatılmıştır. Cu-bentonit ve Al sütunlu-bentonit katalizörlü reaksiyonlarda verimin çok az olduğu buna karşın Fe-bentonit ve Fe-sütunlu bentonit katalizörlerinin kullanıldığı tepkimelerde ise sırasıyla % 60 ve % 63 verimle asetalleşme reaksiyonu gerçekleştiği tespit edilmiştir. Bu çalışma ülkemizin önemli yerli kaynaklarından birini teşkil eden Artvin bentonitinin modifiye edilmesiyle organik reaksiyonları katalizleyebildiğini ve bu ürünlerin küçük ölçekte ve endüstriyel proseslerdeki reaksiyonlar için kullanılabileceğini ortaya koymuştur.Öğe Determination of the superior quality properties of randomly selected chestnut honey samples from the Sinop region(Taylor & Francis Inc, 2023) Avsar, Cumhur; Aslan, Hakan; Yumak, Tugrul; Tabak, Ahmet; Deniz, Nuray TurkIn this study, a total of 43 chestnut honey samples were randomly selected and collected from the Erfelek, Ayancik, and Turkeli districts of Sinop. The pollen content of all honey samples was determined, revealing that chestnut pollen accounted for over 90% in most cases. The chestnut honey from the Sinop region is considered of high quality compared to other chestnut honeys, primarily due to its low HMF (Hydroxymethylfurfural) levels, low moisture content, high proline content, and significant pollen content. The antibacterial activities of these honey samples were assessed using the agar well diffusion method, Minimal Inhibitory Concentrations (MIC), and Minimal Bactericidal Concentrations (MBC) methods. It is worth mentioning that certain samples exhibited significant activity against Staphylococcus aureus, with inhibition zones ranging from 15 to 20 mm, which is comparable to standard antibiotics. The antioxidant activities of all honey samples were evaluated using a 1,1-Diphenyl-2-picrylhydrazine assay. The results obtained indicate that the chestnut honey produced from the chestnut forests in the Sinop province meets the criteria outlined in the Turkish Food Codex Honey Communique. The high proline content exceeding 1000 mg/kg and very low hydroxymethyl furfural values below 1 mg/kg observed in certain chestnut honey samples contribute to their high quality and safety. Additionally, the average pH of 4.81 and free acidity values below 50 meq/kg recorded for the analyzed honeys further reinforce these findings.Öğe Dimethyl sulfoxide Species Entrapped by Raw and Acid-Activated Sepiolite Framework(Sinop Üniversitesi, 2016) Tabak, Ahmet; Afsin, Beytullah; Çaglar, Bülent; Çaglar, SemaNovel hybridorganic-clay materials were prepared by interaction of dimethyl sulfoxidemolecules in the interlayer space of raw and acid activated sepiolitecomposites. The structural and thermal properties of the hybrid materials, raw andacid activated sepiolite were examined by using Fourier transform infrared, thermalanalysis, X-ray powder diffraction and surface area measurement techniques. Thermalanalysis data prove the remarkable effects of acid activation on the frameworkof sepiolite which are reflected by the intercalation mechanism proceedingthrough the replacement partly of the interstitial water by dimethyl sulfoxidespecies. The protons are directly involved in the actual structure and thusenhances the thermal stability of the complex between dimethyl sulfoxide andthe sepiolite. The noticeable surface area increase of activated sepiolite thanthat of the raw one is connected to the micropore formation. The data presentedin this study may also provide further insight into catalysis studies and theapplication of clays in the growing field of environmental management.Öğe Investigation of molecular structure and solvent/temperature effect on tautomerism in (E)-4,6-dibromo-3-methoxy-2-[(p-tolylimino)methyl] phenol, a new thermochromic Schiff base, by using XRD, FT-IR, UV-vis, NMR and DFT methods(Pergamon-Elsevier Science Ltd, 2019) Kastas, Gokhan; Kastas, Cigdem Albayrak; Tabak, AhmetThe molecular structure and the solvent temperature effect on the tautomerism in a new Schiff base, (E)-4,6-clibromo-3-methoxy-2-[(p-tolylimino)methyllphenol, were investigated using spectroscopic (NMR, UV-vis, FT-1R), crystallographic (XRD), computational (DFT and TD-DET) methods and harmonic oscillator model of aromaticity (HOMA). The XRD, DFT and MIR results show that the compound exists in the phenol-imine form in the solid state. HOMA indices support the aromatic structure of the compound. DFT calculations were performed to understand proton transfer process and relatively close values were obtained for the energies of tautomers. UV-vis studies prove the solvent dependence of the tautomerism in the compound by revealing the existence of both phenol-imine and keto-amine forms in polar solvents and only the phenol-imine form in apolar solvent. The TD-DFT results for the electronic transitions lead to the same conclusion as the absorption spectra. H-1 NMR and C-13 NMR studies at room and low (-60 degrees C) temperatures indicate that the tautomeric equilibrium occurs rapidly in the compound. Therefore, it is difficult to observe two tautomers. However, the presence of tautomeric structures is clearly seen in acetone d(6), alternatively underlying the solvent and temperature dependence of tautomerism in the title compound. (C) 2019 Elsevier B.V. All lights reserved.Öğe Microplastic Contamination of the Seawater in the Hamsilos Bay of the Southern Black Sea(Springer Int Publ Ag, 2024) Oztekin, Aysah; Ustun, Funda; Bat, Levent; Tabak, AhmetThe marine ecosystem is severely threatened by microplastics. The entire marine environment of the Black Sea is contaminated with both macro- and microplastics but the contamination of the water column with this pollutant has received less attention. This study aims to obtain data on the microplastic abundance, and vertical and temporal distribution of the microplastics in the water column of Hamsilos Bay which is a natural protected area, and an important area for fishery and tourism on the Sinop coast in the Black Sea. This study was carried out for 12 months in 7 stations. Microplastic abundance varied among 5.58 +/- 6.12-8.12 +/- 9.17 pieces/m3 in and 1.74 +/- 0.80-21.07 +/- 3.84 pieces/m3 in stations. The dominant microplastics were fibre by shape (73.92%), 1-2 mm (28.35%) by size class, and blue (37.98%) by colour. The synthetic polymers in the examined microplastic samples of this study were PET (47%), PE (34%), HDPE (10%), PVC (7%) and PS (2%). The results of this study show that the coastal area is widely contaminated with microplastics. Microplastic pollution is an increasingly significant environmental issue that poses a threat to the Black Sea which is particularly vulnerable to microplastic pollution. The region is an important ecological hotspot in the Black Sea and this study can provide valuable insights into the extent of microplastic pollution and will contribute to the literature on the evaluation of microplastic pollution in marine ecosystems. These types of investigations; efforts to address the environmental challenges facing the Black Sea, including the development of programs to reduce pollution, increase sustainability, and support the protection of the region's natural resources, are crucial to its continuity.Öğe New metal complexes with diclofenac containing 2-pyridineethanol or 2-pyridinepropanol: synthesis, structural, spectroscopic, thermal properties, catechol oxidase and carbonic anhydrase activities(Taylor & Francis Ltd, 2016) Caglar, Sema; Dilek, Esra; Caglar, Bulent; Adiguzel, Ekrem; Temel, Ersin; Buyukgungor, Orhan; Tabak, AhmetFour new neutral diclofenac-based complexes, [Co(dicl)2(2-pyet)2] 1, [Ni(dicl)2(2-pyet)2] 2, [Cu2(dicl)2(2-pyet)2] 3, and [Cu2(dicl)2(2-pypr)2] 4 have been synthesized and characterized by elemental analysis, FT-IR, thermal analysis. Complexes 1, 3, and 4 have also been characterized by X-ray single-crystal structural analysis. The compounds of Co(II) and Ni(II) have octahedral geometry with two diclofenac and two 2-pyridineethanol ligands in the coordination sphere. The compounds of Cu(II) have square-pyramidal geometry and Cu(II) ions are linked via oxygens to the bridging 2-pyridineethanol or 2-pyridinepropanol ligands. The values acquired by FT-IR are in agreement with the single XRD data. Studies on the thermal properties are reported and the complexes are stable to 196, 216, 215, and 201 degrees C in air, respectively. Two dinuclear Cu(II) complexes have demonstrated catalytic activity on oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone showing saturation kinetics at high substrate concentrations. The diclofenac complexes are investigated as inhibitors of the human cytosolic isoforms hCA I and II. The complexes are good as hCA I inhibitors (Kis of 1.52-55.06M) but only moderately efficient as hCA II inhibitors (Kis of 0.23-5.61M). [GRAPHICS] .Öğe Noble metal nanoparticles supported on activated carbon: Highly recyclable catalysts in hydrogen generation from the hydrolysis of ammonia borane(Academic Press Inc Elsevier Science, 2019) Akbayrak, Serdar; Ozcifci, Zehra; Tabak, AhmetNoble metal nanoparticles including rhodium, ruthenium and palladium have been extensively used in catalysis field. Since their limited abundance and high cost, many methods have been developed to obtain highly active and recyclable catalysts. In this work, Rh3+, Ru3+, Pd2+ ions were impregnated on activated carbon derived from pumpkin stalk in distilled water and then reduced with sodium borohydride to form Rh-0, Ru-0, Pd-0 nanoparticles on the surface of carbon. The analyses show that these nanoparticles were successfully dispersed on the activated carbon. Rh-0, Ru-0, Pd-0 nanoparticles on activated carbon provide a turnover frequency value of 188 min(-1), 235 min(-1) and 40 min(-1), respectively, at 25.0 +/- 0.1 degrees C. They preserve their activity even after multiple use in H-2 generation from the hydrolysis of ammonia borane. (C) 2019 Elsevier Inc. All rights reserved.Öğe Preparation and characterization of a novel activated carbon component via chemical activation of tea woody stem(Springer, 2019) Tabak, Ahmet; Sevimli, Kadir; Kaya, Mehmet; Caglar, BuelentThe novel activated carbon materials were synthesized by the carbonization and chemical activation of agricultural bio-waste from tea woody stems (TWS), and these materials were characterized by using FTIR, SEM, TG/DTA and surface analysis (BET surface area; pore distribution; pore size, area and volume) techniques. The higher carbonization times and amount of chemical reagent generally produce the higher surface area at 400 and 500 degrees C. The experimental data demonstrated that the highest BET surface area was 789 m(2) g(-1) at 500 degrees C, 75 mu m particle size, TWS/KOH ratio of 1:2 and carbonization time of 3 h. The activated carbon IR spectrum showed the increases in intense of aromatic C-H out-of-plane bending and C=C vibrations and the disappearance of olefinic C=C functional groups. Thermal analysis curves of TWS are ascribed to decomposition of organic derivate corresponding to lignin, cellulose and hemicelluloses components up to 700 degrees C from 200 degrees C. The SEM images and textural analysis data signified that the pore development of carbon skeleton structure during carbonization and activation process formed and type of micropores in these pore structures was dominant.Öğe Recycling of an Agricultural Bio-waste as a Novel Cellulose Aerogel: A Green Chemistry Study(Springer, 2020) Kaya, Mehmet; Tabak, AhmetCellulose aerogel (CA) isolated from tea stem wastes (TSW) is a good fire retardant and heat insulator, environmentally friendly, thermally stable and highly porous material with a network structure. These outstanding properties have attracted a huge interest in the materials world. In this study, firstly, following delignification and removing hemicellulose, pure raw cellulose was isolated using TSW, hydrogel form of cellulose was prepared by regeneration of cellulose solution, and then, the final product (CA) was produced via freeze-drying. The data results showed that the aerogel had a three dimensionally network structure. Moreover, it can be deduced that thermal durability of the studied CA could be effective because of its fire retardant and heat insulating property. In addition, the production process of CA is easily available at low cost and sustainable.Öğe Some physicochemical properties of pure and pollution-free Sinop chestnut honey(Taylor & Francis Inc, 2024) Tabak, Ahmet; Deniz, Nuray Turk; Avsar, Cumhur; Aslan, Hakan; Yumak, TugrulThis study was designed to investigate some physicochemical properties (color, electrical conductivity, ash, water-insoluble and mineral matter contents) of chestnut honey produced in the Ayanc & imath;k, T & uuml;rkeli and Erfelek regions of Sinop province, where chestnut forests are dense. The experimental data showed that most of the honey samples had different amber color tones. The electrical conductivity values and the amounts of water-insoluble matter for all chestnut honeys were determined above 0.8 mS/cm and below 0.1 g per 100 g, respectively. In addition, honey samples contained mainly potassium and calcium and other minerals such as magnesium, sodium, aluminum and iron. It has been demonstrated that these chestnut honeys are registered with Geographical Indication and meet the criteria required in the Turkish Food Codex Honey Communiqu & eacute; of the Ministry of Agriculture and Forestry. These honeys have not been exposed to any external processing (heat treatment, etc.), have not been adulterated, do not contain impurities, and are pure and high quality.Öğe Structural, thermal and morphological properties of a novel poly(acrylamide-co-methacrylic acid)/organoclay nanocomposite(Taylor & Francis Inc, 2017) Caglar, Bulent; Coldur, Fatih; Caglar, Sema; Cubuk, Osman; Tabak, Ahmet; Topcu, CihanA novel poly(acrylamide-co-methacrylic acid)/organoclay nanocomposite was prepared and its structural, thermal, and morphological properties were investigated by various techniques. The absence of diffraction peaks for the organomodified-smectite nanocomposite showed that dispersion of the clay nanolayers within the polymer matrix was in the form of an exfoliated nanostructure. Morphological studies confirmed that organomodified-clay dispersed homogeneously in the polymer matrix. Infrared spectroscopy results indicated that the organosmectite is physically dispersed in the polymer network without forming any chemical bonds. The thermal analysis data revealed that there are significant increases in temperatures of decomposition and softening points of polymer with addition of organoclay.Öğe Synthesis, crystal structure, spectroscopy, thermal properties and carbonic anhydrase activities of new metal(II) complexes with mefenamic acid and picoline derivatives(Taylor & Francis Ltd, 2017) Dilek, Esra; Caglar, Sema; Dogancay, Nesrin; Caglar, Bulent; Sahin, Onur; Tabak, AhmetThe mononuclear six metal(II) complexes ([Co(mef)(2)(3-pic)(2)(CH3OH)(2)] (1), [Ni(mef)(2)(3-pic)(2)(CH3OH)(2)] (2), [Cu(mef)(2)(3-pic)(2)] (3), [Co(mef)(2)(4-pic)(2)] (4), [Ni(mef)(2)(4-pic)(2)] (5), and [Cu(mef)(2)(4-pic)(2)] (6) with mefenamic acid and picoline ligands were synthesized, characterized, and their carbonic anhydrase inhibitory activities were evaluated. The six complexes were characterized by elemental analysis, FT-IR spectroscopy, and thermal analyses. The crystal structures of 1, 3, and 6 were determined by X-ray crystallography. The complexes have octahedral geometry. In 1, the mefenamato ligand behaved as monodentate whereas in 3 and 6, the mefenamato ligand acted as a bidentate ligand. Complexes 3 and 6 consist of the mefenamate and 4-picoline ligands. In 1, unlike the other complexes, methanol acted as a ligand and was involved in the coordination. Carbonic anhydrase I and II isoenzymes were purified from human erythrocytes. The in vitro effects of mefenamic acid, 3-picoline, 4-picoline, and the six metal(II) complexes on these isoenzymes were evaluated. [GRAPHICS]
